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In this work, we systematically study the strong decay behaviors of the charmed mesons $D_{1}^{*}(2680)$, $D_{3}^{*}(2760)$ and $D_{2}^{*}(3000)$ reported by the LHCb collaboration. By comparing the masses and the decay properties with the results of the experiment, we assigned these newly observed mesons as the $2S\frac{1}{2}1^{-}$, $1D\frac{5}{2}3^{-}$ and $1F\frac{5}{2}2^{+}$ states respectively. As a byproduct, we also study the strong decays of the unobserved $2P\frac{3}{2}2^{+}$ and $2F\frac{5}{2}2^{+}$ charmed mesons, which is helpful to the future experiments in searching for these charmed mesons. | Analysis of the charmed mesons $D_{1}^{*}(2680)$, $D_{3}^{*}(2760)$ and $D_{2}^{*}(3000)$ |
For studying how dynamical responses to external stimuli depend on the synaptic-coupling type, we consider two types of excitatory and inhibitory synchronization (i.e., synchronization via synaptic excitation and inhibition) in complex small-world networks of excitatory regular spiking (RS) pyramidal neurons and inhibitory fast spiking (FS) interneurons. For both cases of excitatory and inhibitory synchronization, effects of synaptic couplings on dynamical responses to external time-periodic stimuli $S(t)$ (applied to a fraction of neurons) are investigated by varying the driving amplitude $A$ of $S(t)$. Stimulated neurons are phase-locked to external stimuli for both cases of excitatory and inhibitory couplings. On the other hand, the stimulation effect on non-stimulated neurons depends on the type of synaptic coupling. The external stimulus $S(t)$ makes a constructive effect on excitatory non-stimulated RS neurons (i.e., it causes external phase lockings in the non-stimulated sub-population), while $S(t)$ makes a destructive effect on inhibitory non-stimulated FS interneurons (i.e., it breaks up original inhibitory synchronization in the non-stimulated sub-population). As results of these different effects of $S(t)$, the type and degree of dynamical response (e.g., synchronization enhancement or suppression), characterized by the dynamical response factor $D_f$ (given by the ratio of synchronization degree in the presence and absence of stimulus), are found to vary in a distinctly different way, depending on the synaptic-coupling type. Furthermore, we also measure the matching degree between the dynamics of the two sub-populations of stimulated and non-stimulated neurons in terms of a "cross-correlation" measure $M_c$. With increasing $A$, based on $M_c$, we discuss the cross-correlations between the two sub-populations, affecting the dynamical responses to $S(t)$. | Dynamical Responses to External Stimuli for Both Cases of Excitatory and Inhibitory Synchronization in A Complex Neuronal Network |
Let F be a totally real field and p a rational prime unramified in F. We prove a partial classicality theorem for overconvergent Hilbert modular forms: when the slope is small compared to certain but not all weights, an overconvergent form is partially classical. We use the method of analytic continuation. | Partial Classicality of Hilbert Modular Forms |
The retrieval approach is currently a standard method for deriving atmospheric properties from observed spectra of exoplanets. However, the approach ignores disequilibrium chemistry in most current retrieval codes, which can lead to misinterpretation of the metallicity or elemental abundance ratios of the atmosphere. We have implemented the disequilibrium effect of vertical mixing or quenching for the major species in hydrogen/helium-dominated atmospheres, namely $\mathrm{CH_4}$, $\mathrm{CO}$, $\mathrm{H_2O}$, $\mathrm{NH_3}$, $\mathrm{N_2}$, and $\mathrm{CO_2}$, for the spectral retrieval code ARCiS with a physical basis using the chemical relaxation method. Then, using ARCiS updated with this module, we have performed retrievals of the observed transmission spectra of 16 exoplanets with sizes ranging from Jupiter to mini-Neptune. As a result, we find indications of disequilibrium chemistry for HD 209458b ($\geq 4.1\sigma$) and WASP-39b ($\geq 2.7\sigma$). The retrieved spectrum of HD 209458b exhibits a strong $\mathrm{NH_3}$ absorption feature at 10.5 $\mu$m accessible by JWST owing to an enhanced abundance of $\mathrm{NH_3}$ due to the quenching effect. This feature is absent in the spectrum retrieved assuming equilibrium chemistry, which makes HD 209458b an ideal target for studying disequilibrium chemistry in exoplanet atmospheres. Moreover, for HAT-P-11b and GJ 436b, we obtain relatively different results than for the retrieval with the equilibrium assumption, such as a $2.9\sigma$ difference for the C/O ratio. We have also examined the retrieved eddy diffusion coefficient, but could not identify a trend over the equilibrium temperature, possibly due to the limits of the current observational precision. | Implementation of disequilibrium chemistry to spectral retrieval code ARCiS and application to sixteen exoplanet transmission spectra: Indication of disequilibrium chemistry for HD 209458b and WASP-39b |
We show that lower bounds on the border rank of matrix multiplication can be used to non-trivially derandomize polynomial identity testing for small algebraic circuits. Letting $\underline{R}(n)$ denote the border rank of $n \times n \times n$ matrix multiplication, we construct a hitting set generator with seed length $O(\sqrt{n} \cdot \underline{R}^{-1}(s))$ that hits $n$-variate circuits of multiplicative complexity $s$. If the matrix multiplication exponent $\omega$ is not 2, our generator has seed length $O(n^{1 - \varepsilon})$ and hits circuits of size $O(n^{1 + \delta})$ for sufficiently small $\varepsilon, \delta > 0$. Surprisingly, the fact that $\underline{R}(n) \ge n^2$ already yields new, non-trivial hitting set generators for circuits of sublinear multiplicative complexity. | On Matrix Multiplication and Polynomial Identity Testing |
The time dependent Schroedinger equation for two identical and charged pions is solved using wavepacket states. It is shown that the expected Coulomb distortion in the momentum correlation function is obliterated by the dispersion of the localized states, and therefore becomes unobservable. | The role of the quantum dispersion in the Coulomb correction of Bose-Einstein correlations |
Finding the entropy rate of Hidden Markov Processes is an active research topic, of both theoretical and practical importance. A recently used approach is studying the asymptotic behavior of the entropy rate in various regimes. In this paper we generalize and prove a previous conjecture relating the entropy rate to entropies of finite systems. Building on our new theorems, we establish series expansions for the entropy rate in two different regimes. We also study the radius of convergence of the two series expansions. | Taylor series expansions for the entropy rate of Hidden Markov Processes |
The impurity incorporation in host high-spin orbit coupling materials like platinum has shown improved charge-to-spin conversion by modifying the up-spin and down-spin electron trajectories by bending or skewing them in opposite directions. This enables efficient generation, manipulation, and transport of spin currents. In this study, we irradiate the platinum with non-focus dense plasma to incorporate the oxygen ion species. We systematically analyze the spin Hall angle of the oxygen plasma irradiated Pt films using spin torque ferromagnetic resonance. Our results demonstrate a 2.4 times enhancement in the spin Hall effect after plasma treatment of Pt as compared to pristine Pt. This improvement is attributed to the introduction of disorder and defects in the Pt lattice, which enhances the spin-orbit coupling and leads to more efficient charge-to-spin conversion without breaking the spin-orbit torque symmetries. Our findings offer a new method of dense plasma-based modification of material for the development of advanced spintronic devices based on Pt and other heavy metals. | Dense plasma irradiated platinum with improved spin Hall effect |
The unknown $\gamma$-ray excess in the northwest region of Arp 220 was revisited by analyzing $\sim$11.8 years of the \textit{Fermi} Large Area Telescope (\textit{Fermi}-LAT) data in this study. We found that its photon flux was approximately three times higher than that of the previous study in the 0.2-100 GeV band, and the corresponding significance level$\sim8.15\sigma$ was approximately four times higher than before. The light curves of 15 and 45 time bins from the whole time all showed two active periods, and the variability of the second period was more significant than that of the first period. The spectral indices from the two active periods were not statistically different and were close to the range of $\gamma$-ray flat-spectrum radio quasars observed by \textit{Fermi}-LAT. Because the position of CRATES J153246+234400 was consistent with the best-fit position of our analysis, we suggest that CRATES J153246+234400 is more likely a $\gamma$-ray counterpart for the variational region. For Arp 220, there was no significant variability in the $\gamma$-ray emission. | The Likely Counterpart to $\gamma$-Ray Excess from The Northwest Region of Arp 220 |
In 1948 Tellegen suggested that an assembly of the lined up electric-magnetic dipole twins can construct a new type of an electromagnetic material. Till now, however, the problem of creation of the Tellegen medium is a subject of strong discussions. An elementary symmetry analysis makes questionable an idea of a simple combination of two (electric and magnetic) dipoles to realize local materials with the Tellegen particles as structural elements. In this paper we show that in his search of sources with local junctions of the electrical and magnetic properties one cannot rely on the induced parameters of small electromagnetic scatterers. No near-field electromagnetic structures and classical motion equations for point charges give a physical basis to realize sources with the local junction of the electrical and magnetic properties. We advance a hypothesis that local magnetoelectric (ME) particles should be the physical objects with eigenmode oscillation spectra and non-classical symmetry breaking effects. Our studies convincingly prove this assumption. We show that a quasi-2D ferrite disk with magnetic-dipolar-mode oscillations is characterized by unique symmetry features with topological phases resulting in appearance of the ME properties. The entire ferrite disk can be characterized as a combined system with eigen electric and magnetic moments. The fields near such a particle are distinguished by special symmetry properties. | Do the Tellegen particles really exist in electromagnetics? |
Thuiller et al. analyzed the consequences of anticipated climate change on plant, bird, and mammal phylogenetic diversity (PD) across Europe. They concluded that species loss will not be clade specific across the Tree of Life, and that there will not be an overall decline in PD across the whole of Europe. We applaud their attempt to integrate phylogenetic knowledge into scenarios of future extinction but their analyses raise a series of concerns. We focus here on their analyses of plants. | Climates and clades: biased methods, biased results |
We time-resolve the spin-transfer-torque-induced switching in perpendicularly magnetized tunnel junctions of diameters from 50 to 250 nm in the thermally activated regime. When the field and the spin-torque concur to favor the P to AP transition, the reversal yields monotonic resistance ramps that can be interpreted as a domain wall propagation through the device at velocities of 17 to 30 nm/ns; smaller cells switch hence faster. When the field hinders the P to AP transition, the switching is preceded by repetitive switching attempts, during which the resistance transiently increases until successful reversal occurs. At 50 nm, the P to AP switching proceeds reproducibly in 3 ns, with a monotonic increase of the device resistance. In the reverse transition (AP to P), several reversal paths are possible even in the smallest junctions. Besides, the non uniform nature of the response seems still present at nanoscale, with sometimes electrical signatures of strong disorder during the reversal. The AP to P transition is preceded by a strong instability of the AP state in devices above 100 nm. The resistance becomes extremely agitated before switching to P in a path yielding a slow (20-50 ns) irregular increase of the conductance with variability. Unreversed bubbles of 60 nm can persist a few microseconds in the largest junctions. The complexity of the AP to P switching is reduced but not suppressed when the junctions are downsized below 60 nm. The instability of the initial AP state is no longer detected but the other features remain. In the smallest junctions (50 nm) we occasionally observe much faster (sub-1 ns) switching events. We discuss the origin of the switching asymmetry and its size dependence, with an emphasis on the role of the non uniformities of the stray field emanating from the reference layers, which affects the zones in which nucleation is favored. | Size-dependence of nanosecond-scale spin-torque switching in perpendicularly magnetized tunnel junctions |
We present a detailed study of a single vortex in a holographic symmetry breaking phase. At low energies the system flows to an nontrivial conformal fixed point. Novel vortex physics arises from the interaction of these gapless degrees of freedom with the vortex: at low energies the vortex may be understood as a conformal defect in this low energy theory. Defect conformal symmetry allows the construction of a simple infrared geometry describing a new kind of extremal horizon: a Poincare horizon with a small bubble of magnetic Reissner-Nordstrom horizon inside it that carries a single unit of magnetic flux and a finite amount of entropy even at zero temperature. We also construct the full geometry describing the vortex at finite temperature in a UV complete theory. We study both superfluid and superconducting boundary conditions and calculate thermodynamic properties of the vortex. A study of vortex stability reveals that the dual superconductor can be Type I or Type II, depending on the charge of the condensed scalar. Finally, we study forces on a moving vortex at finite temperature from the point of view of defect conformal symmetry and show that these forces can be expressed in terms of Kubo formulas of defect CFT operators. | Vortices in holographic superfluids and superconductors as conformal defects |
We consider the general case of a type IIA string compactified on a Calabi-Yau manifold which has a heterotic dual description. It is shown that the nonabelian gauge symmetries which can appear nonperturbatively in the type II string but which are understood perturbatively in the heterotic string are purely a result of string-string duality in six dimensions. We illustrate this with some examples. | Enhanced Gauge Symmetries and Calabi-Yau Threefolds |
It has been suggested that a Random Tree Puzzle (RTP) process leads to a Yule-Harding (YH) distribution, when the number of taxa becomes large. In this study, we formalize this conjecture, and we prove that the two tree distributions converge for two particular properties, which suggests that the conjecture may be true. However, we present evidence that, while the two distributions are close, the RTP appears to converge on a different distribution than does the YH. | Is the Random Tree Puzzle process the same as the Yule-Harding process? |
Recently resonant inelastic x-ray scattering experiments reported fine details of the charge excitations around the in-plane momentum ${\bf q}_{\parallel}=(0,0)$ for various doping rates in electron-doped cuprates ${\rm La_{2-x}Ce_xCuO_4}$. We find that those new experimental data are well captured by acoustic-like plasmon excitations in a microscopic study of the layered $t$-$J$ model with the long-range Coulomb interaction. The acoustic-like plasmon is not a usual plasmon typical to the two-dimensional system, but has a small gap proportional to the interlayer hopping $t_z$. | Close inspection of plasmon excitations in cuprate superconductors |
We address the question of whether the primal-dual approach for the design and analysis of online algorithms can be applied to nonmonotone problems. We provide a positive answer by presenting a primal-dual analysis to the online algorithm of Awerbuch et al.[AAPW01] for routing virtual circuits with unknown durations. | A Nonmonotone Analysis with the Primal-Dual Approach: online routing of virtual circuits with unknown durations |
We investigate some types of composition operators, linear and not, and conditions for some spaces to be mapped into themselves and for the operators to satisfy some good properties. | A survey on composition operators on some function spaces |
We study the crackling noise emerging during single crack propagation in a specimen under three-point bending conditions. Computer simulations are carried out in the framework of a discrete element model where the specimen is discretized in terms of convex polygons and cohesive elements are represented by beams. Computer simulations revealed that fracture proceeds in bursts whose size and waiting time distributions have a power law functional form with an exponential cutoff. Controlling the degree of brittleness of the sample by the amount of disorder, we obtain a scaling form for the characteristic quantities of crackling noise of quasi-brittle materials. Analyzing the spatial structure of damage we show that ahead of the crack tip a process zone is formed as a random sequence of broken and intact mesoscopic elements. We characterize the statistics of the shrinking and expanding steps of the process zone and determine the damage profile in the vicinity of the crack tip. | Crackling noise in three-point bending of heterogeneous materials |
Based on the recent development of Jacobian-free Lax-Wendroff (LW) approaches for solving hyperbolic conservation laws [Zorio, Baeza and Mulet, Journal of Scientific Computing 71:246-273, 2017], [Carrillo and Par\'es, Journal of Scientific Computing 80:1832-1866, 2019], a novel collection of explicit Jacobian-free multistage multiderivative solvers for hyperbolic conservation laws is presented in this work. In contrast to Taylor time-integration methods, multiderivative RungeKutta (MDRK) techniques achieve higher-order of consistency not only through the excessive addition of higher temporal derivatives, but also through the addition of Runge-Kutta-type stages. This adds more flexibility to the time integration in such a way that more stable and more efficient schemes could be identified. The novel method permits the practical application of MDRK schemes. In their original form, they are difficult to utilize as higher-order flux derivatives have to be computed analytically. Here we overcome this by adopting a Jacobian-free approximation of those derivatives. In this paper, we analyze the novel method with respect to order of consistency and stability. We show that the linear CFL number varies significantly with the number of derivatives used. Results are verified numerically on several representative testcases. | Jacobian-free explicit multiderivative Runge-Kutta methods for hyperbolic conservation laws |
We use cosmological simulations to study the effects of supernova (SN) feedback on the dark matter distribution in galaxies. We simulate the formation of a Milky-Way type galaxy using a version of the SPH code GADGET2 which includes chemical enrichment and energy feedback by SN, a multiphase model for the gas component and metal-dependent cooling. We analyse the impact of the main three input SN feedback parameters on the amplitude and shape of the dark matter density profiles, focusing on the inner regions of the halo. In order to test the dependence of the results on the halo mass, we simulated a scale-down version of this system. First results of this ongoing work show that the dark matter distribution is affected by the feedback, through the redistribution of the baryons. Our findings suggest that the response of the dark matter halo could be the result of a combination of several physical parameters such as the amount of stellar mass formed at the centre, its shape, and probably the bursty characteristics of the star formation rate. As expected, we find that the dark matter haloes of small galaxies are more sensitive to SN feedback. Higher resolution simulations are being performed to test for numerical effects. | Effects of SN Feedback on the Dark Matter Distribution |
We develop two different solar dynamo models to verify the hypothesis that a deep meridional flow can restrict the apperance of sunspots below 45 degrees, proposed by Nandy & Choudhuri (2002). In the first one, a single polytropic approximation for the density profile was taken, for both radiative and convective zones. In the second one, two polytropes were used to distinguish between both zones Pinzon & Calvo-Mozo (2001). The magnetic buoyancy mechanism proposed by Dikpati & Charbonneau (1999) was chosen in both models. We, actually, have obtained that a deep meridional flow pushes the maxima of toroidal magnetic field toward the solar equator, but in contrast to Nandy & Choudhuri (2002) a second zone of maximal fields remains at the poles. The second model, although closely resembling the solar standard model of Bahcall, Pinsonneault & Wasserbug (1995); Bahcall, Pinsonneault & Basu (2001), gives solar cyles three times longer than observed. | Kinematic solar dynamo models with a deep meridional flow |
Internet of things (IoT) has significantly altered the traditional lifestyle to a highly technologically advanced society. Some of the significant transformations that have been achieved through IoT are smart homes, smart transportation, smart city, and control of pollution. A considerable number of studies have been conducted and continue to be done to increase the use of technology through IoT. Furthermore, the research about IoT has not been done fully in improving the application of technology through IoT. Besides, IoT experiences several problems that need to be considered in order to get the full capability of IoT in changing society. This research paper addresses the key applications of IoT, the architecture of IoT, and the key issues affecting IoT. In addition, the paper highlights how big data analytics is essential in improving the effectiveness of IoT in various applications within society. | Different Applications and Technologies of Internet of Things (IoT) |
This work proposes a windowed least-squares (WLS) approach for model-reduction of dynamical systems. The proposed approach sequentially minimizes the time-continuous full-order-model residual within a low-dimensional space-time trial subspace over time windows. The approach comprises a generalization of existing model reduction approaches, as particular instances of the methodology recover Galerkin, least-squares Petrov-Galerkin (LSPG), and space-time LSPG projection. In addition, the approach addresses key deficiencies in existing model-reduction techniques, e.g., the dependence of LSPG and space-time LSPG projection on the time discretization and the exponential growth in time exhibited by a posteriori error bounds for both Galerkin and LSPG projection. We consider two types of space-time trial subspaces within the proposed approach: one that reduces only the spatial dimension of the full-order model, and one that reduces both the spatial and temporal dimensions of the full-order model. For each type of trial subspace, we consider two different solution techniques: direct (i.e., discretize then optimize) and indirect (i.e., optimize then discretize). Numerical experiments conducted using trial subspaces characterized by spatial dimension reduction demonstrate that the WLS approach can yield more accurate solutions with lower space-time residuals than Galerkin and LSPG projection. | Windowed least-squares model reduction for dynamical systems |
Using elementary geometric tools, we apply essentially the same methods to derive expressions for the rotation angle of the swing plane of Foucault's pendulum and the rotation angle of the spin of a relativistic particle moving in a circular orbit (Thomas precession effect). | Rotation of the swing plane of Foucault's pendulum and Thomas spin precession: Two faces of one coin |
It is shown that the entropic force formula $F_e=-\lambda\partial S/\partial A$ leads to a Newtonian $r^{-2}$ dependence. Here we employ the universal property of the information entropy $S=a+b\ln N$ ($N$ is the number of particles of a quantum system and $A$ is the area containing the system). This property was previously obtained for fermionic systems (atoms, atomic clusters, nuclei and infinite Fermi systems i.e. electron gas, liquid $^3$He and nuclear matter) and bosonic ones (correlated boson-atoms in a trap). A similar dependence of the entropic force has been derived very recently by Plastino et al with a Bose or Fermi gas entropy, inspired by Verlinde's conjecture~\cite{Verlide-11} that gravity is an emergent entropic force. Finally, we point out that our simple argument holds for classical systems as well. | A simple link of information entropy of quantum and classical systems with Newtonian $r^{-2}$ dependence of Verlinde's entropic force |
In 2016, a star KIC 8462852 caught the world's attention due to a paper by citizen scientists who noticed its seemingly unexplainable brightness variations. The forward theory was offered - KIC 8462852 is surrounded by a Dyson sphere, a megastructure made by an alien civilization to collect all energy output from their star. Finally, in 2018, its light curve showed chromaticity more characteristic of the dust (from comets or asteroids) rather than of something made from solid material, but the world was woken up to the idea of megastructures. But, in Dyson's time, only Solar System planets were known; it took more than 20 years to realize that nature has no problem making planets and does it with a flair -- the total number of planets in the Galaxy is estimated to be in billions. With such abundance of planets, there would be no need to destroy the entire planetary system to make one sphere. Instead, a civilization can expand to a system that has planet(s) in the habitable zone (HZ), or a planet can be moved into it. Alternatively, a free-floating planet (FFP) can be captured and moved into the HZ. These shifts can be performed at a constant low-thrust acceleration using high power directional lasers, resulting in a gradual spiral transfer from one orbit to another. We propose here to search for ETI by looking for high-power laser technosignatures and consider merits of such signatures. We suggest to specifically pay attention to the multiple planetary systems that have Strange Exoplanetary Architectures (SEA) - unusual planetary arrangements that cannot be explained by current planetary formation theories, because these could be the result of ETI moving planets intentionally to suit their needs. | Making Habitable Worlds: Planets Versus Megastructures |
Deep learning frameworks leverage GPUs to perform massively-parallel computations over batches of many training examples efficiently. However, for certain tasks, one may be interested in performing per-example computations, for instance using per-example gradients to evaluate a quantity of interest unique to each example. One notable application comes from the field of differential privacy, where per-example gradients must be norm-bounded in order to limit the impact of each example on the aggregated batch gradient. In this work, we discuss how per-example gradients can be efficiently computed in convolutional neural networks (CNNs). We compare existing strategies by performing a few steps of differentially-private training on CNNs of varying sizes. We also introduce a new strategy for per-example gradient calculation, which is shown to be advantageous depending on the model architecture and how the model is trained. This is a first step in making differentially-private training of CNNs practical. | Efficient Per-Example Gradient Computations in Convolutional Neural Networks |
Elastic scattering of pions from finite nuclei is investigated utilizing a contemporary, momentum--space first--order optical potential combined with microscopic estimates of second--order corrections. The calculation of the first--order potential includes:\ \ (1)~full Fermi--averaging integration including both the delta propagation and the intrinsic nonlocalities in the $\pi$-$N$ amplitude, (2)~fully covariant kinematics, (3)~use of invariant amplitudes which do not contain kinematic singularities, and (4)~a finite--range off--shell pion--nucleon model which contains the nucleon pole term. The effect of the delta--nucleus interaction is included via the mean spectral--energy approximation. It is demonstrated that this produces a convergent perturbation theory in which the Pauli corrections (here treated as a second--order term) cancel remarkably against the pion true absorption terms. Parameter--free results, including the delta--nucleus shell--model potential, Pauli corrections, pion true absorption, and short--range correlations are presented. (2 figures available from authors) | Microscopic approach to pion-nucleus dynamics |
We present efficient theoretical tools for describing the optical pumping of atoms by light propagating at arbitrary directions with respect to an external magnetic field, at buffer-gas pressures that are small enough for velocity-selective optical pumping (VSOP) but large enough to cause substantial collisional relaxation of the velocities and the spin. These are the conditions for the sodium atoms at an altitude of about 100 km that are used as guidestars for adaptive optics in modern ground-based telescopes to correct for aberrations due to atmospheric turbulence. We use spin and velocity relaxation modes to describe the distribution of atoms in spin space (including both populations and coherences) and velocity space. Cusp kernels are used to describe velocity-changing collisions. Optical pumping operators are represented as a sum of poles in the complex velocity plane. Signals simulated with these methods are in excellent agreement with previous experiments and with preliminary experiments in our laboratory. | Spin-velocity correlations of optically pumped atoms |
We study theoretically an influence of the near-interfacial insulator traps and electron-hole puddles on the small-signal capacitance and conductance characteristics of the gated graphene structures. Based on the self-consistent electrostatic consideration and taking into account the interface trap capacitance the explicit analytic expressions for charge carrier density and the quantum capacitance as functions of the gate voltage were obtained. This allows to extract the interface trap capacitance and density of interface states from the gate capacitance measurements. It has shown that self-consistent account of the interface trap capacitance enables to reconcile discrepancies in universal quantum capacitance vs the Fermi energy extracted for different samples. The electron-hole puddles and the interface traps impact on transfer I-V characteristics and conductivity has been investigated. It has been shown that variety of widths of resistivity peaks in various samples could be explained by different interface trap capacitance values. | Influence of Interface Traps and Electron-Hole Puddles on Quantum Capacitance and Conductivity in Graphene Field-Effect Transistors |
In many environmental applications involving spatially-referenced data, limitations on the number and locations of observations motivate the need for practical and efficient models for spatial interpolation, or kriging. A key component of models for continuously-indexed spatial data is the covariance function, which is traditionally assumed to belong to a parametric class of stationary models. While convenient, the assumption of stationarity is rarely realistic; as a result, there is a rich literature on alternative methodologies which capture and model the nonstationarity present in most environmental processes. This review document provides a rigorous and concise description of the existing literature on nonstationary methods, paying particular attention to process convolution (also called kernel smoothing or moving average) approaches. A summary is also provided of more recent methods which leverage covariate information and yield both interpretational and computational benefits. Note: the article is borrowed from Chapters 1 and 2 of the author's Ph.D. dissertation, joint with Catherine A. Calder. | Review: Nonstationary Spatial Modeling, with Emphasis on Process Convolution and Covariate-Driven Approaches |
With the advancements of various autonomous car projects aiming to achieve SAE Level 5, real-time detection of traffic signs in real-life scenarios has become a highly relevant problem for the industry. Even though a great progress has been achieved in this field, there is still no clear consensus on what the state-of-the-art in this field is. Moreover, it is important to develop and test systems in various regions and conditions. This is why the "Ice Vision" competition has focused on the detection of Russian traffic signs in winter conditions. The IceVisionSet dataset used for this competition features real-world collection of lossless frame sequences with traffic sign annotations. The sequences were collected in varying conditions, including: different weather, camera exposure, illumination and moving speeds. In this work we describe the competition and present the solutions of the 3 top teams. | Recognition of Russian traffic signs in winter conditions. Solutions of the "Ice Vision" competition winners |
We report on the theory of a Luneburg lens for forward-volume magnetostatic spin waves, and verify its operation via micromagnetic modelling. The lens converts a plane wave to a point source (and vice versa) by a designed graded index, realised here by either modulating the thickness or the saturation magnetization in a circular region. We find that the lens enhances the wave amplitude by 5 times at the lens focus, and 47% of the incident energy arrives in the focus region. Furthermore, small deviations in the profile can still result in good focusing, if the lens index is graded smoothly. | A Luneburg lens for spin waves |
Using the 135-second cadence of the photospheric vector data provided by the Helioseismic and Magnetic Imager telescope on board the Solar Dynamic Observatory, we examined the time-evolution of magnetic helicity fluxes across the photosphere during 16 flares with the energy class lower than M5.0. During the flare in 4 out of 16 events, we found impulsive changes in the helicity fluxes. This indicates that even the flare with less energy could be associated with anomalistic transportation of the magnetic helicity across the photosphere. Accompanying the impulsive helicity fluxes, the poynting fluxes across the photosphere evolved from positive to negative. As such, the transportations of magnetic energy across the photosphere were toward solar interior during these flares. In each of the 4 events, the impulsive change in the helicity flux was always mainly contributed by abrupt change in horizontal velocity field on a sunspot located near the flaring polarity inversion line. The velocity field on each sunspot shows either an obvious vortex patten or an shearing patten relative to the another magnetic polarity, which tended to relax the magnetic twist or shear in the corona. During these flares, abrupt change in the Lorentz force acting on these sunspots were found. The rotational motions and shearing motions of these sunspots always had the same directions with the resultant Lorentz forces. These results support the view that the impulsive helicity transportation during the flare could be driven by the change in the Lorentz force applied on the photosphere. | A Survey of Changes in Magnetic Helicity Flux on the Photosphere During Relatively Low Class Flares |
Detachment of neutral cations/anions from solid alkali halides can in principle be provoked by donating/subtracting electrons to the surface of alkali halide crystals, but generally constitutes a very endothermic process. However, the amount of energy required for emission is smaller for atoms located in less favorable positions, such as surface steps and kinks. For a corner ion in an alkali halide cube the binding is the weakest, so it should be easier to remove that atom, once it is neutralized. We carried out first principles density functional calculations and simulations of neutral and charged NaCl nanocubes, to establish the energetics of extraction of neutralized corner ions. Following hole donation (electron removal) we find that detachment of neutral Cl corner atoms will require a limited energy of about 0.8 eV. Conversely, following the donation of an excess electron to the cube, a neutral Na atom is extractable from the corner at the lower cost of about 0.6 eV. Since the cube electron affinity level (close to that a NaCl(100) surface state, which we also determine) is estimated to lie about 1.8 eV below vacuum, the overall energy balance upon donation to the nanocube of a zero energy electron from vacuum will be exothermic. The atomic and electronic structure of the NaCl(100) surface, and of the nanocube Na and Cl corner vacancies are obtained and analyzed as a byproduct. | Charging Induced Emission of Neutral Atoms from NaCl Nanocube Corners |
Predicting high temperature superconductors has long been a great challenge. The difficulty lies in how to predict the transition temperature (Tc) of superconductors. Although recent progress in material informatics has led to a number of machine learning models predicting Tc, prevailing models have not shown adequate generalization ability and physical rationality to find new high temperature superconductors, yet. In this work, a bond sensitive graph neural network (BSGNN) was developed to predict the Tc of various superconductors. In BSGNN, communicative message passing and graph attention methods were utilized to enhance the model's ability to process bonding and interaction information in the crystal lattice, which is crucial for the superconductivity. Consequently, our results revealed the relevance between chemical bond attributes and Tc. It indicates that shorter bond length is favored by high Tc. Meanwhile, some specific chemical elements that have relatively large van der Waals radius is favored by high Tc. It gives a convenient guidance for searching high temperature superconductors in materials database, by ruling out the materials that could never have high Tc. | Predicting Transition Temperature of Superconductors with Graph Neural Networks |
We disprove the conjecture that every sufficiently large natural number $n$ is the sum of three palindromic natural numbers where one of them can be chosen to be the largest or second largest palindromic natural number smaller than or equal to $n$. | On a conjecture of John Hoffman regarding sums of palindromic numbers |
We report highly sensitive specific heat measurement on mesoscopic superconducting loops at low temperature. These mesoscopic systems exhibit thermal properties significantly different from that of the bulk materials. The measurement is performed on a silicon membrane sensor where 450 000 superconducting aluminium loops are deposited through electron beam lithography under an applied magnetic field. Each entry of a vortex is associated to a jump in the specific heat of few thousands of Boltzmann constant kB indicating the existence of phase transitions. The periodicity of this sequential phase transitions is a nontrivial behaviour and varies strongly as the temperature is decreased. The successive phase transitions are well described by the Ginzburg-Landau theory of superconductivity. The presence of metastable states is responsible for the n-0 (n=1, 2, 3...) periodicity of the discontinuities of the measured specific heat. | Specific heat measurement of mesoscopic loops |
The purpose of this paper is twofold; (1) to develop several identities for the Generalized $k$-Pell sequence (including those of Binet, Catalan, Cassini, and d'Ocagne), and (2) to study applications of tridiagonal generating matrices for the $k$-Pell and Generalized $k$-Pell sequences. | Some properties of generalized $k$-Pell sequences |
Quantifying the flow of energy within and through fluctuating nanoscale systems poses a significant challenge to understanding microscopic biological machines. A common approach involves coarse-graining, which allows a simplified description of such systems. This has the side effect of inducing so-called hidden contributions (due to sub-resolution dynamics) that complicate the resulting thermodynamics. Here we develop a thermodynamically consistent theory describing the nonequilibrium excess power internal to autonomous systems, and introduce a phenomenological framework to quantify the hidden excess power associated with their operation. We confirm our theoretical predictions in numerical simulations of a minimal model for both a molecular transport motor and a rotary motor. | Hidden energy flows in strongly coupled nonequilibrium systems |
Rare decays of light mesons may be a discovery window for a new weakly coupled forces hidden at low energy QCD scale. BES-III Collaboration reported the observation of the rare decay $\eta'\rightarrow\pi^0\gamma\gamma$. The observed decay width disagrees with the preliminary theoretical estimations. We show that this tension may be attributed to the New Physics, presumably Dark Photon. For completeness, we consider the possible influence of the New Physics on a similar well-measured decay $\eta\rightarrow\pi^0\gamma\gamma$ and a recently measured one $\eta' \rightarrow \eta\gamma\gamma$ and show that the impact of the hypothetical Dark Photon may be also present in these decays also. | The problems of $\eta'\rightarrow\pi^0\gamma\gamma$ decay and the New Physics |
In this article, we study localizations of hearts of cotorsion pairs (U,V) where U is rigid on an extriangulated category B. The hearts of such cotorsion pairs are equivalent to the functor categories over the stable category of U. Inspired by Marsh and Palu, we consider the mutation of U that induces a cotorsion pair (U',V'). Generally speaking, the hearts of (U,V) and (U',V') are not equivalent to each other, but we will give a generalized pseudo-Morita equivalence between certain localizations of their hearts. | Localizations of the hearts of cotorsion pairs associated with mutations |
We study the real-time behavior of classical Yang-Mills theory under initial conditions with nonperturbatively large, infrared field amplitudes. Our lattice study confirms the cascade of energy towards higher momenta and lower occupancy, which occurs via a scaling solution $f[p,t_1] = (t_0/t_1)^{4/7}\, f[p (t_0/t_1)^{1/7},t_0]$. Above a characteristic scale p_{max}, f falls exponentially; below p_{max}, $f[p] \propto p^{-4/3}$. We find no evidence for different infrared exponents or for infrared occupancies in excess of those described by this scaling solution. We also investigate what the fate of large occupancies would be, both in the electric and the magnetic sector. | UV Cascade in Classical Yang-Mills Theory |
We present a database of the latest stellar models of the $Y^2$ (Yonsei-Yale) collaboration. This database contains the stellar evolutionary tracks from the pre-main-sequence birthline to the helium core flash that were used to construct the $Y^2$ isochrones. We also provide a simple interpolation routine that generates stellar tracks for given sets of parameters (metallicity, mass, and $\alpha$-enhancement). | The Y^2 Stellar Evolutionary Tracks |
The MAGIC Collaboration has provided new observational data pertaining to the TeV J2032+4130 gamma-ray source (within the Cygnus OB2 region), for energies E_gamma >400 GeV. It is then appropriate to update the impact of these data on gamma-ray production mechanisms in stellar associations. We consider two mechanisms of gamma-ray emission, pion production and decay (PION) and photo-excitation of high-energy nuclei followed by prompt photo-emission from the daughter nuclei (A*). We find that while the data can be accommodated with either scenario, the A* features a spectral bump, corresponding to the threshold for exciting the Giant Dipole Resonance, which can serve to discriminate between them. We comment on neutrino emission and detection from the region if the PION and/or A* processes are operative. We also touch on the implications for this analysis of future Fermi and Cerenkov Telescope Array data. | Present and Future Gamma-Ray Probes of the Cygnus OB2 Environment |
We analyze the effect of small changes in the underlying probabilistic model on the value of multi-period stochastic optimization problems and optimal stopping problems. We work in finite discrete time and measure these changes with the adapted Wasserstein distance. We prove explicit first-order approximations for both problems. Expected utility maximization is discussed as a special case. | Sensitivity of multiperiod optimization problems in adapted Wasserstein distance |
Two recent publications have reported intriguing analyses, tentatively suggesting that some aspects of IceCube data might be manifestations of quantum-gravity-modified laws of propagation for neutrinos. We here propose a strategy of data analysis which has the advantage of being applicable to several alternative possibilities for the laws of propagation of neutrinos in a quantum spacetime. In all scenarios here of interest one should find a correlation between the energy of an observed neutrino and the difference between the time of observation of that neutrino and the trigger time of a GRB. We select accordingly some GRB-neutrino candidates among IceCube events, and our data analysis finds a rather strong such correlation. This sort of studies naturally lends itself to the introduction of a "false alarm probability", which for our analysis we estimate conservatively to be of 1%. We therefore argue that our findings should motivate a vigorous program of investigation following the strategy here advocated. | IceCube and GRB neutrinos propagating in quantum spacetime |
Given a non-associative unital ring $R$, a monoid $G$ and a set $\pi$ of additive maps $R \rightarrow R$, we introduce the Ore monoid ring $R[\pi ; G]$, and, in a special case, the differential monoid ring. We show that these structures generalize, in a natural way, not only the classical Ore extensions and differential polynomial rings, but also the constructions, introduced by Cojuhari, defined by so-called $D$-structures $\pi$. Moreover, for commutative monoids, we give necessary and sufficient conditions for differential monoid rings to be simple. We use this in a special case to obtain new and shorter proofs of classical simplicity results for differential polynomial rings in several variables previously obtained by Voskoglou and Malm by other means. We also give examples of new Ore-like structures defined by finite commutative monoids. | Simplicity of Ore monoid rings |
This analysis quantitatively compares the evolution in summer and winter peak demands in the Electric Reliability Council of Texas (ERCOT) service area from 1997 through 2021. Weather data for the days in which peak demand occurred were also compiled to investigate the relationship between peak heating and cooling loads and ambient temperature. This relationship was then applied along with population projections and a climate scenario with medium to high radiative forcing to create winter and summer peak demand growth scenarios for 2025 through 2050. This analysis informs resource planners about how ERCOT peak demand might change in the future and provides new insight into how electric load growth and non-flexible electrified heating demand could have contributed to the February 2021 ERCOT blackouts. We found that historically, summer peak demand growth has been generally stable and approximately linear with time. The stable summer peak load is likely a consequence of fairly constant temperatures observed on summer peak demand days. Conversely, the winter peak demand growth has been less consistent, varying much more around the broader trend. This phenomenon is likely a consequence of high residential electrical heating load on winter peak demand days, which saw temperatures that varied widely from the mean value. Future peak winter and summer electricity demand scenarios indicated that while average temperatures on winter peak demand days will remain fairly constant, they will be more erratic than temperatures on summer peak demand days. As a result, winter peak demand will remain more erratic and will sporadically surpass summer peak demand between 2025 and 2050. Thus, resource planners in ERCOT should place less certainty on winter peak demand projections and an increased level of winter preparedness on both the supply and demand sectors appears warranted. | Observations of peak electric load growth in ERCOT with the rise of electrified heating and its implications for future resource planning |
Advancements in conversational systems have revolutionized information access, surpassing the limitations of single queries. However, developing dialogue systems requires a large amount of training data, which is a challenge in low-resource domains and languages. Traditional data collection methods like crowd-sourcing are labor-intensive and time-consuming, making them ineffective in this context. Data augmentation (DA) is an affective approach to alleviate the data scarcity problem in conversational systems. This tutorial provides a comprehensive and up-to-date overview of DA approaches in the context of conversational systems. It highlights recent advances in conversation augmentation, open domain and task-oriented conversation generation, and different paradigms of evaluating these models. We also discuss current challenges and future directions in order to help researchers and practitioners to further advance the field in this area. | Data Augmentation for Conversational AI |
HH 30 is an edge-on disk around a young stellar object. Previous imaging with the Hubble Space Telescope has show morphological variability that is possibly related to the rotation of the star or the disk. We report the results of two terrestrial observing campaigns to monitor the integrated magnitude of HH 30. We use the Lomb-Scargle periodogram to look for periodic modulation with periods between 2 days and almost 90 days in these two data sets and in a third, previously published, data set. We develop a method to deal with short-term correlations in the data. Our results indicate that none of the data sets shows evidence for significant periodic photometric modulation. | The Photometric Variability of HH 30 |
The spatial propagation of many livestock infectious diseases critically depends on the animal movements among premises; so the knowledge of movement data may help us to detect, manage and control an outbreak. The identification of robust spreading features of the system is however hampered by the temporal dimension characterizing population interactions through movements. Traditional centrality measures do not provide relevant information as results strongly fluctuate in time and outbreak properties heavily depend on geotemporal initial conditions. By focusing on the case study of cattle displacements in Italy, we aim at characterizing livestock epidemics in terms of robust features useful for planning and control, to deal with temporal fluctuations, sensitivity to initial conditions and missing information during an outbreak. Through spatial disease simulations, we detect spreading paths that are stable across different initial conditions, allowing the clustering of the seeds and reducing the epidemic variability. Paths also allow us to identify premises, called sentinels, having a large probability of being infected and providing critical information on the outbreak origin, as encoded in the clusters. This novel procedure provides a general framework that can be applied to specific diseases, for aiding risk assessment analysis and informing the design of optimal surveillance systems. | Optimizing surveillance for livestock disease spreading through animal movements |
Author developed a method in the paper, which, unlike the circle method of Hardy and Littlewood (CM), allows you to perform a lower estimate for the number of natural (integer) solutions of algebraic Diophantine equation with integer coefficients. It was found the lower estimate of the number of natural solutions to various types of homogeneous algebraic Diophantine equations with integer coefficients diagonal form with any number of variables using this method. Author obtained upper bound of the number of the natural solutions (using CM) of one type of homogeneous Diophantine equation for values $k \geq \log_2 s$, where $k$ is the degree of the equation and $s$ is the number of variables. It was also found the upper bound of the number of the natural solutions of the homogeneous algebraic Diophantine equation with integer coefficients with a small number of variables. Author investigated the relations of upper and lower estimates of the number of natural solutions of homogeneous Diophantine equation with integer coefficients diagonal form in the paper. | Estimating of the number of natural solutions of homogeneous algebraic Diophantine diagonal equations with integer coefficients |
We present a unified framework for designing deterministic monotone polynomial time approximation schemes (PTAS's) for a wide class of scheduling problems on uniformly related machines. This class includes (among others) minimizing the makespan, maximizing the minimum load, and minimizing the l_p norm of the machine loads vector. Previously, this kind of result was only known for the makespan objective. Monotone algorithms have the property that an increase in the speed of a machine cannot decrease the amount of work assigned to it. The key idea of our novel method is to show that for goal functions that are sufficiently well-behaved functions of the machine loads, it is possible to compute in polynomial time a highly structured nearly optimal schedule. Monotone approximation schemes have an important role in the emerging area of algorithmic mechanism design. In the game-theoretical setting of these scheduling problems there is a social goal, which is one of the objective functions that we study. Each machine is controlled by a selfish single-parameter agent, where its private information is its cost of processing a unit sized job, which is also the inverse of the speed of its machine. Each agent wishes to maximize its own profit, defined as the payment it receives from the mechanism minus its cost for processing all jobs assigned to it, and places a bid which corresponds to its private information. For each one of the problems, we show that we can calculate payments that guarantee truthfulness in an efficient manner. Thus, there exists a dominant strategy where agents report their true speeds, and we show the existence of a truthful mechanism which can be implemented in polynomial time, where the social goal is approximated within a factor of 1+epsilon for every epsilon>0. | A unified approach to truthful scheduling on related machines |
We study the fractional Schr\"odinger equation with quasilocal perturbations. These are a family of nonlocal perturbations vanishing at infinity, which include e.g. convolutions against Schwartz functions. We show that the qualitative unique continuation and Runge approximation properties hold in the assumption of sufficient decay. Quantitative versions of both results are also obtained via a propagation of smallness analysis for the Caffarelli-Silvestre extension. The results are then used to show uniqueness in the inverse problem of retrieving a quasilocal perturbation from DN data under suitable geometric assumptions. Our work generalizes recent results regarding the locally perturbed fractional Calder\'on problem. | Uniqueness for the fractional Calder\'on problem with quasilocal perturbations |
Computational methods to compute similarities between floor plans can help architects explore floor plans in large datasets to avoid duplication of designs and to search for existing plans that satisfy their needs. Recently, LayoutGMN delivered state-of-the-art performance for computing similarity scores between floor plans. However, the high computational costs of LayoutGMN make it unsuitable for the aforementioned applications. In this paper, we significantly reduced the times needed to query results computed by LayoutGMN by projecting the floor plans into a common low-dimensional (e.g., three) data space. The projection is done by optimizing for coordinates of floor plans with Euclidean distances mimicking their similarity scores originally calculated by LayoutGMN. Quantitative and qualitative evaluations show that our results match the distributions of the original LayoutGMN similarity scores. User study shows that our similarity results largely match human expectations. | Floor Plan Exploration Framework Based on Similarity Distances |
Motivated by the successful application of MCRG in momentum space to $\lambda \phi^4_3$ we determine the critical exponents at the crumpling transition in fixed triangulated surfaces. The results are still tentative, but suggest that $-1.0\ge \eta \ge -1.3$, pointing at a value for the fractal Hausdorff dimension at the crumpling transistion fixed point somewhere between 3 and 4. | Determination of the Crumpling Fractal Dimension Via k-Space MCRG |
For a much-studied model of random copolymer at a selective interface we prove that the slope of the critical curve in the weak-disorder limit is strictly smaller than 1, which is the value given by the annealed inequality. The proof is based on a coarse-graining procedure, combined with upper bounds on the fractional moments of the partition function. | Coarse graining, fractional moments and the critical slope of random copolymers |
We report the detection of carbon monoxide (CO) emission from the young supernova remnant Cassiopeia A (Cas A) at wavelengths corresponding to the fundamental vibrational mode at 4.65 micron. We obtained AKARI Infrared Camera spectra towards 4 positions which unambiguously reveal the broad characteristic CO ro-vibrational band profile. The observed positions include unshocked ejecta at the center, indicating that CO molecules form in the ejecta at an early phase. We extracted a dozen spectra across Cas A along the long 1 arcmin slits, and compared these to simple CO emission models in Local Thermodynamic Equilibrium to obtain first-order estimates of the excitation temperatures and CO masses involved. Our observations suggest that significant amounts of carbon may have been locked up in CO since the explosion 330 years ago. Surprisingly, CO has not been efficiently destroyed by reactions with ionized He or the energetic electrons created by the decay of the radiative nuclei. Our CO detection thus implies that less carbon is available to form carbonaceous dust in supernovae than is currently thought and that molecular gas could lock up a significant amount of heavy elements in supernova ejecta. | Spectroscopic detection of Carbon Monoxide in the Young Supernova Remnant Cassiopeia A |
A (simple) hypergraph is a family H of pairwise incomparable sets of a finite set. We say that a hypergraph H is a domination hypergraph if there is at least a graph G such that the collection of minimal dominating sets of G is equal to H. Given a hypergraph, we are interested in determining if it is a domination hypergraph and, if this is not the case, we want to find domination hypergraphs in some sense close to it, the domination completions. Here we will focus on the family of hypergraphs containing all the subsets with the same cardinality, the uniform hypergraphs of maximum size. Specifically, we characterize those hypergraphs H in this family that are domination hypergraphs and, in any other case, we prove that the hypergraph H is uniquely determined by some of its domination completions and that H can be recovered from them by using a suitable hypergraph operation. | Uniform hypergraphs and dominating sets of graphs |
Refactoring is widely recognized as one of the efficient techniques to manage technical debt and maintain a healthy software project through enforcing best design practices or coping with design defects. Previous refactoring surveys have shown that code refactoring activities are mainly executed by developers who have sufficient knowledge of the system's design and disposing of leadership roles in their development teams. However, these surveys were mainly limited to specific projects and companies. In this paper, we explore the generalizability of the previous results by analyzing 800 open-source projects. We mine their refactoring activities, and we identify their corresponding contributors. Then, we associate an experience score to each contributor in order to test various hypotheses related to whether developers with higher scores tend to 1) perform a higher number of refactoring operations 2) exhibit different motivations behind their refactoring, and 3) better document their refactoring activity. We found that (1) although refactoring is not restricted to a subset of developers, those with higher contribution scores tend to perform more refactorings than others; (2) while there is no correlation between experience and motivation behind refactoring, top contributed developers are found to perform a wider variety of refactoring operations, regardless of their complexity; and (3) top contributed developer tend to document less their refactoring activity. Our qualitative analysis of three randomly sampled projects shows that the developers who are responsible for the majority of refactoring activities are typically in advanced positions in their development teams, demonstrating their extensive knowledge of the design of the systems they contribute to. | Behind the Scenes: On the Relationship Between Developer Experience and Refactoring |
We apply the solution to the recursion relation for the double-off-shell quark current to the problem of computing one loop amplitudes with an arbitrary number of gluons. We are able to compute amplitudes for photon-gluon scattering, electron-positron annihilation to gluons, and gluon-gluon scattering via a quark loop in the case of like-helicity gluons. In addition, we present the result for the one-loop gluon-gluon scattering amplitude when one of the gluons has opposite helicity from the others. | Multigluon Helicity Amplitudes Involving a Quark Loop |
We discuss the multiband energy release in a model of a collapsing galactic nucleus, and we try to interpret the unique super-long cosmic gamma-ray event Swift J164449.3+573451 (GRB 110328A by early classification) in this scenario. Neutron stars and stellar-mass black holes can form evolutionary a compact self-gravitating subsystem in the galactic center. Collisions and merges of these stellar remnants during an avalanche contraction and collapse of the cluster core can produce powerful events in different bands due to several mechanisms. Collisions of neutron stars and stellar-mass black holes can generate gamma-ray bursts (GRBs) similar to the ordinary models of short GRB origin. The bright peaks during the first two days may also be a consequence of multiple matter supply (due to matter release in the collisions) and accretion onto the forming supermassive black hole. Numerous smaller peaks and later quasi-steady radiation can arise from gravitational lensing, late accretion of gas onto the supermassive black hole, and from particle acceleration by shock waves. Even if this model will not reproduce exactly all the Swift J164449.3+573451 properties in future observations, such collapses of galactic nuclei can be available for detection in other events. | Swift J164449.3+573451 event: generation in the collapsing star cluster? |
The detection of quasars at $z>6$ unveils the presence of supermassive black holes (BHs) of a few billion solar masses. The rapid formation process of these extreme objects remains a fascinating and open issue. Such discovery implies that seed black holes must have formed early on, and grown via either rapid accretion or BH/galaxy mergers. In this theoretical review, we discuss in detail various BH seed formation mechanisms and the physical processes at play during their assembly. We discuss the three most popular BH formation scenarios, involving the (i) core-collapse of massive stars, (ii) dynamical evolution of dense nuclear star clusters, (iii) collapse of a protogalactic metal free gas cloud. This article aims at giving a broad introduction and an overview of the most advanced research in the field. | Formation of supermassive black hole seeds |
We present a new approach for generation of solutions in the four-dimensional heterotic string theory with one vector field and in the five-dimensional bosonic string theory starting from the static Einstein-Maxwell fields. Our approach allows one to construct the solution classes invariant with respect to the total subgroup of the three-dimensional charging symmetries of these string theories. The new generation procedure leads to the extremal Israel-Wilson-Perjes subclass of string theory solutions in a special case and provides its natural continuous extension to the realm of non-extremal solutions. We explicitly calculate all string theory solutions related to three-dimensional gravity coupled to an effective dilaton field which arises after an appropriate charging symmetry invariant reduction of the static Einstein-Maxwell system. | String theory extensions of Einstein-Maxwell fields: the static case |
We propose a trajectory-based method for simulating nonadiabatic dynamics in molecular systems with two coupled electronic states. Employing a quantum-mechanically exact mapping of the two-level problem to a spin-1/2 coherent state, we construct a classical phase space of a spin vector constrained to a spherical surface with a radius consistent with the quantum magnitude of the spin. In contrast with the singly-excited harmonic oscillator basis used in Meyer-Miller-Stock-Thoss (MMST) mapping, the theory requires no additional projection operators onto the space of physical states. When treated under a quasiclassical approximation, we show that the resulting dynamics is equivalent to that generated by the MMST Hamiltonian. What differs is the value of the zero-point energy parameter as well as the initial distribution and the measurement operators. For various spin-boson models the results of our method are seen to be a significant improvement compared to both standard Ehrenfest dynamics and linearized semiclassical MMST mapping, without adding any computational complexity. | Spin-mapping approach for nonadiabatic molecular dynamics |
We determine the elastic moduli of two-dimensional assemblies of disks by computer simulations. The disks interact through elastic contact forces, that oppose the relative displacement at the contact points by means of a normal and a tangential stiffness, both taken constant. Our simulations confirm that the uniform strain assumption results in inaccurate predictions of the elastic moduli, since large fluctuations in particle displacements and rotations occur. We phrase their contribution in terms of the relative displacement they induce at the contact points. We show that the fluctuations that determine the equivalent continuum behavior depend on the average geometry of the assembly. We further separate the contributions from the center displacement and the particle rotation. The fluctuations result in a relaxation of the system, but along the tangential direction the relaxation is generally entirely due to rotations. We consider two theoretical formulations for predicting the elastic moduli that include the fluctuations, namely the ``pair-fluctuation'' and the ``particle-fluctuation'' method. They are both based on the equilibrium of a small subassembly, which is considered representative of the average structure. We investigate the corresponding predictions of the elastic moduli over a range of coordination numbers and of ratios between tangential and normal stiffness. We find a significant improvement with respect to the uniform strain theory. Furthermore, the dependence of the fluctuations on coordination number and ratio of tangential to normal stiffness is qualitatively captured. | On the elastic moduli of two-dimensional assemblies of disks: relevance and modeling of fluctuations in particle displacements and rotations |
We have analyzed high velocity resolution HI synthesis observations of the nearly face-on Sc galaxy NGC 1232. The neutral gas distribution extends well beyond the optical extent of the galaxy. As expected, local peaks in the HI column density are associated with the spiral arms. Further, the HI column density drops precipitously near the center of the galaxy. Closed contours in the velocity field suggest either that the system is warped, or that the rotation curve declines. The velocity dispersion is approximately constant throughout the system, with a median value of 9.9 +/- 1.8 km/s. When corrected for rotational broadening, there is no indication of a radial trend in the neutral gas velocity dispersion in this galaxy. | Neutral Gas Distribution and Kinematics of the Nearly Face-on Spiral Galaxy NGC 1232 |
The direct collapse black hole (DCBH) scenario describes the isothermal collapse of a pristine gas cloud directly into a massive, M_BH=10^4-10^6 M_sun black hole. In this paper we show that large HI column densities of primordial gas at T~10^4 K with low molecular abundance - which represent key aspects of the DCBH scenario - provide optimal conditions for pumping of the 2p-level of atomic hydrogen by trapped Lyman alpha (Lya) photons. This Lya pumping mechanism gives rise to inverted level population of the 2s_1/2-2p_3/2 transition, and therefore to stimulated fine structure emission at 3.04 cm (rest-frame). We show that simplified models of the DCBH scenario amplify the CMB by up to a factor of 10^5, above which the maser saturates. Hyperfine splitting of the 3-cm transition gives rise to a characteristic broad (FWHM ~ tens of MHz in the observers frame) asymmetric line profile. This signal subtends an angular scale of ~ 1-10 mas, which translates to a flux of ~ 0.3-3 microJy, which is detectable with ultra-deep surveys being planned with SKA1-MID. While challenging, as the signal is visible for a fraction of the collapse time of the cloud, the matching required physical conditions imply that a detection of the redshifted 3-cm emission line would provide direct evidence for the DCBH scenario. | 3-cm Fine Structure Masers: A Unique Signature of Supermassive Black Hole Formation via Direct Collapse in the Early Universe |
For a prime $p>2$ and a smooth proper $p$-adic formal scheme $X$ over $\mathcal{O}_K$ where $K$ is a $p$-adic field, we study a series of conditions ($\mathrm{Cr}_s$), $s\geq 0$ that partially control the $G_K$-action on the image of the associated Breuil-Kisin prismatic cohomology $\mathrm{R}\Gamma_{\Delta}(X/\mathfrak{S})$ inside the $A_{\mathrm{inf}}$-prismatic cohomology $\mathrm{R}\Gamma_{\Delta}(X_{A_{\mathrm{inf}}}/A_{\mathrm{inf}})$. The condition ($\mathrm{Cr}_0$) is a criterion for a Breuil-Kisin-Fargues $G_K$-module to induce a crystalline representation used by Gee and Liu, and thus leads to a proof of crystallinity of $\mathrm{H}^i_{\text{\'{e}t}}(X_{\overline{\eta}}, \mathbb{Q}_p)$ that avoids the crystalline comparison. The higher conditions ($\mathrm{Cr}_s$) are used to adapt the strategy of Caruso and Liu in order to establish ramification bounds for the mod $p$ representations $\mathrm{H}^{i}_{\text{\'{e}t}}(X_{\overline{\eta}}, \mathbb{Z}/p\mathbb{Z}),$ for arbitrary $e$ and $i$, which extend or improve existing bounds in various situations. | Crystalline condition for $A_{\mathrm{inf}}$-cohomology and ramification bounds |
Dual use, the intentional, harmful reuse of technology and scientific artefacts, is a problem yet to be well-defined within the context of Natural Language Processing (NLP). However, as NLP technologies continue to advance and become increasingly widespread in society, their inner workings have become increasingly opaque. Therefore, understanding dual use concerns and potential ways of limiting them is critical to minimising the potential harms of research and development. In this paper, we conduct a survey of NLP researchers and practitioners to understand the depth and their perspective of the problem as well as to assess existing available support. Based on the results of our survey, we offer a definition of dual use that is tailored to the needs of the NLP community. The survey revealed that a majority of researchers are concerned about the potential dual use of their research but only take limited action toward it. In light of the survey results, we discuss the current state and potential means for mitigating dual use in NLP and propose a checklist that can be integrated into existing conference ethics-frameworks, e.g., the ACL ethics checklist. | Thorny Roses: Investigating the Dual Use Dilemma in Natural Language Processing |
Hacks are one of the most damaging types of cryptocurrency related crime, accounting for billions of dollars in stolen funds since 2009. Professional investigators at Chainalysis have traced these stolen funds from the initial breach on an exchange to off-ramps, i.e. services where criminals are able to convert the stolen funds into fiat or other cryptocurrencies. We analyzed six hack subnetworks of bitcoin transactions known to belong to two prominent hacking groups. We analyze each hack according to eight network features, both static and temporal, and successfully classify each hack to its respective hacking group through our newly proposed method. We find that the static features, such as node balance, in degree, and out degree are not as useful in classifying the hacks into hacking groups as temporal features related to how quickly the criminals cash out. We validate our operating hypothesis that the key distinction between the two hacking groups is the acceleration with which the funds exit through terminal nodes in the subnetworks. | Analyzing Hack Subnetworks in the Bitcoin Transaction Graph |
We report on the X-ray spectral (using XMM-Newton data) and timing behavior (using XMM-Newton and Rossi X-ray Timing Explorer [RXTE] data) of the very faint X-ray transient and black hole system Swift J1357.2-0933 during its 2011 outburst. The XMM-Newton X-ray spectrum of this source can be adequately fitted with a soft thermal component with a temperature of ~0.22 keV (using a disc model) and a hard, non-thermal component with a photon index of ~1.6 when using a simple power-law model. In addition, an edge at ~ 0.73 keV is needed likely due to interstellar absorption. During the first RXTE observation we find a 6 mHz quasi-periodic oscillation (QPO) which is not present during any of the later RXTE observations or during the XMM-Newton observation which was taken 3 days after the first RXTE observation. The nature of this QPO is not clear but it could be related to a similar QPO seen in the black hole system H 1743-322 and to the so-called 1 Hz QPO seen in the dipping neutron-star X-ray binaries (although this later identification is quite speculative). The observed QPO has similar frequencies as the optical dips seen previously in this source during its 2011 outburst but we cannot conclusively determine that they are due to the same underlying physical mechanism. Besides the QPO, we detect strong band-limited noise in the power-density spectra of the source (as calculated from both the RXTE and the XMM-Newton data) with characteristic frequencies and strengths very similar to other black hole X-ray transients when they are at low X-ray luminosities. We discuss the spectral and timing properties of the source in the context of the proposed very high inclination of this source. We conclude that all the phenomena seen from the source cannot, as yet, be straightforwardly explained neither by an edge-on configuration nor by any other inclination configuration of the orbit. | An X-ray view of the very faint black hole X-ray transient Swift J1357.2-0933 during its 2011 outburst |
A cosmological gauge field with isotropic stress-energy introduces parity violation into the behavior of gravitational waves. We show that a primordial spectrum of inflationary gravitational waves develops a preferred handedness, left- or right-circularly polarized, depending on the abundance and coupling of the gauge field during the radiation era. A modest abundance of the gauge field would induce parity-violating correlations of the cosmic microwave background temperature and polarization patterns that could be detected by current and future experiments. | Chiral Imprint of a Cosmic Gauge Field on Primordial Gravitational Waves |
The paper is concerned with various types of noncommutative Positivstellens\"atze for the matrix algebra $M_n(\cA)$, where $\cA$ is an algebra of operators acting on a unitary space, a path algebra, a cyclic algebra or a formally real field. Some new types of Positivstellens\"atze are proposed and proved, it is shown by examples that they occur. There are a number of results stating that a type of Positivstellensatz is valid for $M_n(\cA)$ provided that it holds for $\cA$. | Positivstellens\"atze for Algebras of Matrices |
The quark-monopole potential is computed at finite temperature in the context of $AdS/CFT$ correspondence. It is found that the potential is invariant under $g \to 1/g$ and $U_T \to U_T / g$. As in the quark-quark case there exists a maximum separation between quark and monopole, and $L$-dependence of the potential exhibits a bifurcation behavior. We find a functional relation $dE_{QM}^{Reg} / dL = [(1/E_{(1,0)}^{Reg}(U_0))^2 + (1/E_{(0,1)}^{Reg}(U_0))^2]^{-1/2}$ which is responsible for the bifurcation. The remarkable property of this relation is that it makes a relation between physical quantities defined at the $AdS$ boundary through a quantity defined at the bulk. The physical implication of this relation for the existence of the extra dimension is speculated. | Hidden functional relation in Large-N Quark-Monopole system at finite temperature |
In this paper, our aim is to find the relations amongst the cohomology classes of Brill-Noether subvarieties of the moduli space of semistable bundles over an elliptic curve. We obtain results similar to the Poincar\'e relations on a Jacobian variety. | Tautological algebra of the moduli space of semistable bundles on an elliptic curve |
We treat hydrodynamic limits of the Vlasov-Maxwell-Boltzmann system for one and two species of particles in a viscous incompressible regime. | From the Vlasov-Maxwell-Boltzmann system to incompressible viscous electro-magneto-hydrodynamics |
It was shown recently, building on work of Alexakis, Balehowksy, and Nachman that the geometry of (some portion of) a manifold with boundary is uniquely fixed by the areas of a foliation of two-dimensional disk-shaped surfaces anchored to the boundary. In the context of AdS/CFT, this implies that (a portion of) a four-dimensional bulk geometry can be fixed uniquely from the entanglement entropies of disk-shaped boundary regions, subject to several constraints. In this Note, we loosen some of these constraints, in particular allowing for the bulk foliation of extremal surfaces to be local and removing the constraint of disk topology; these generalizations ensure uniqueness of more of the deep bulk geometry by allowing for e.g. surfaces anchored on disconnected asymptotic boundaries, or HRT surfaces past a phase transition. We also explore in more depth the generality of the local foliation requirement, showing that even in a highly dynamical geometry like AdS-Vaidya it is satisfied. | More of the Bulk from Extremal Area Variations |
We consider a gravitational field in steady state galaxy models of two kinds. Some of them are axisymmetrical and others are triaxial. Equipotentials and potential law are given separately in accordance to Kutuzov and Ossipkov (1980). The relatively simple potential law is based on Kuzmin-Malasidze model (1969). Two kinds of models contain four and five structural parameters respectively. One composite model is suggested as well. Some examples of trajectories are calculated in these models. The simplest method to describe orbits is drawing their projections on coordinate planes. However it needs a great amount of calculation and makes troubles in an interpretation of information. In the case of axisymmetrical models a motion in co-moving meridional plane (with cylindrical coordinates R, z) is considered as a common way. In the case of triaxial models one can use three different co-moving planes passing through moving star and corresponding coordinate axis. We describe models in sections 2-4, calculated orbits are discussed in section 5. | Some orbits in various models of galactic gravitational field |
We investigate the mid-infrared radiation of galaxies that are powered by a starburst or by an AGN. For this end, we compare the spectra obtained at different spatial scales in a sample of infrared bright galaxies. ISO observations which include emission of the nucleus as well as most of the host galaxy are compared with TIMMI2 spectra of the nuclear region. We find that ISO spectra are generally dominated by strong PAH bands. However, this is no longer true when inspecting the mid-infrared emission of the pure nucleus. Here PAH emission is detected in starbursts whereas it is significantly reduced or completely absent in AGNs. A physical explanation of these new observational results is presented by examining the temperature fluctuation of a PAH after interaction with a photon. It turns out that the hardness of the radiation field is a key parameter for quantifying the photo-destruction of small grains. Our theoretical study predicts PAH evaporation in soft X-ray environments. Radiative transfer calculations of clumpy starbursts and AGN corroborate the observational fact that PAH emission is connected to starburst activity whereas PAHs are destroyed near an AGN. The radiative transfer models predict for starbursts a much larger mid-infrared size than for AGN. This is confirmed by our TIMMI2 acquisition images: We find that the mid-infrared emission of Seyferts is dominated by a compact core while most of the starbursts are spatially resolved. | Mid-infrared emission of galactic nuclei: TIMMI2 versus ISO observations and models |
While attention mechanisms have been proven to be effective in many NLP tasks, majority of them are data-driven. We propose a novel knowledge-attention encoder which incorporates prior knowledge from external lexical resources into deep neural networks for relation extraction task. Furthermore, we present three effective ways of integrating knowledge-attention with self-attention to maximize the utilization of both knowledge and data. The proposed relation extraction system is end-to-end and fully attention-based. Experiment results show that the proposed knowledge-attention mechanism has complementary strengths with self-attention, and our integrated models outperform existing CNN, RNN, and self-attention based models. State-of-the-art performance is achieved on TACRED, a complex and large-scale relation extraction dataset. | Improving Relation Extraction with Knowledge-attention |
This paper focuses on the estimation of a driver's psychological characteristics using driving data for driving assistance systems. Driving assistance systems that support drivers by adapting individual psychological characteristics can provide appropriate feedback and prevent traffic accidents. As a first step toward implementing such adaptive assistance systems, this research aims to develop a model to estimate drivers' psychological characteristics, such as cognitive function, psychological driving style, and workload sensitivity, from on-road driving behavioral data using machine learning and deep learning techniques. We also investigated the relationship between driving behavior and various cognitive functions, including the Trail Making Test (TMT) and Useful Field of View (UFOV) test, through regression modeling. The proposed method focuses on road type information and captures various durations of time-series data observed from driving behaviors. First, we segment the driving time-series data into two road types, namely, arterial roads and intersections, to consider driving situations. Second, we further segment data into many sequences of various durations. Third, statistics are calculated from each sequence. Finally, these statistics are used as input features of machine learning models to estimate psychological characteristics. The experimental results show that our model can estimate a driver's cognitive function, namely, the TMT~(B) and UFOV test scores, with Pearson correlation coefficients $r$ of 0.579 and 0.708, respectively. Some characteristics, such as psychological driving style and workload sensitivity, are estimated with high accuracy, but whether various duration segmentation improves accuracy depends on the characteristics, and it is not effective for all characteristics. | Estimating Driver Personality Traits from On-Road Driving Data |
We investigate the notion of real form of complex Lie superalgebras and supergroups, both in the standard and graded version. Our functorial approach allows most naturally to go from the superalgebra to the supergroup and retrieve the real forms as fixed points, as in the ordinary setting. We also introduce a more general notion of compact real form for Lie superalgebras and supergroups, and we prove some existence results for Lie superalgebras that are simple contragredient and their associated connected simply connected supergroups. | Real forms of complex Lie superalgebras and supergroups |
Traffic forecasting is of great importance to transportation management and public safety, and very challenging due to the complicated spatial-temporal dependency and essential uncertainty brought about by the road network and traffic conditions. Latest studies mainly focus on modeling the spatial dependency by utilizing graph convolutional networks (GCNs) throughout a fixed weighted graph. However, edges, i.e., the correlations between pair-wise nodes, are much more complicated and interact with each other. In this paper, we propose the Multi-Range Attentive Bicomponent GCN (MRA-BGCN), a novel deep learning model for traffic forecasting. We first build the node-wise graph according to the road network distance and the edge-wise graph according to various edge interaction patterns. Then, we implement the interactions of both nodes and edges using bicomponent graph convolution. The multi-range attention mechanism is introduced to aggregate information in different neighborhood ranges and automatically learn the importance of different ranges. Extensive experiments on two real-world road network traffic datasets, METR-LA and PEMS-BAY, show that our MRA-BGCN achieves the state-of-the-art results. | Multi-Range Attentive Bicomponent Graph Convolutional Network for Traffic Forecasting |
We apply the Lindstedt-Poincar\'{e} method to the Lotka-Volterra model and discuss alternative implementations of the approach. By means of an efficient systematic algorithm we obtain an unprecedented number of perturbation corrections for the two dynamical variables and the frequency. They enable us to estimate the radius of convergence of the perturbation series for the frequency as a function of the only model parameter. The method is suitable for the treatment of systems with any number of dynamical variables. | On the application of the Lindstedt-Poincar\'{e} method to the Lotka-Volterra system |
Extensive Path Integral Monte Carlo simulations of condensed para-Hydrogen in two dimensions at low temperature have been carried out. In the zero temperature limit, the system is a crystal at equilibrium, with a triangular lattice structure. No metastable liquid phase is observed, as the system remains a solid down to the spinodal density, and breaks down into solid clusters at lower densities. The equilibrium crystal is found to melt at a temperature close to 7 K. | Low temperature phase diagram of condensed para-Hydrogen in two dimensions |
An accurate closed-form solution is obtained to the SIR Epidemic Model through the use of Asymptotic Approximants (Barlow et. al, 2017, Q. Jl Mech. Appl. Math, 70 (1), 21-48). The solution is created by analytically continuing the divergent power series solution such that it matches the long-time asymptotic behavior of the epidemic model. The utility of the analytical form is demonstrated through its application to the COVID-19 pandemic. | Accurate closed-form solution of the SIR epidemic model |
The theory about the brittle failures of multiple locked patches in a seismogenic fault system developed by us since 2010 is introduced in the present study. It is stated by the theory that the progressive failures of locked patch result in the occurrence of earthquakes due to fault movement, where the major earthquakes occurred at its volume expansion and peak strength points are referred to as characteristic ones. We analyze the seismogenic law of characteristic earthquakes in the Islamabad-Kathmandu seismic zone that extends along Himalayan seismic belt, and assess the seismicity trend of this zone by this theory. The results indicate that a MW 8.4 ~ 8.8 characteristic earthquake will strike the central Himalaya and the magnitude parameters of the 2015 Nepal earthquakes have a great impact on judging its occurrence time. When adopting the parameters by CEDC, the zone has almost reached the critical state and the expected characteristic one will take place in a short term (most likely within 10 years), probably with some less than or equal to MW 7.0 foreshocks. When adopting the parameters by NEIC, the occurrence time of the expected characteristic one cannot be judged at present until the critical state after the occurrence of some expected less than or equal to MW 8.1 preshocks is reached. Moreover, we reproduce the generation process of the 2015 Nepal earthquakes according to the self-similarity of seismogenic law for different-order locked patches. | Earthquake tendency of the Himalayan seismic belt |
We show that the transition matrix from the polytabloid basis to the web basis of the irreducible $\mathfrak{S}_{2n}$-representation of shape $(n,n)$ has nonnegative integer entries. This proves a conjecture of Russell and Tymoczko. | The polytabloid basis expands positively into the web basis |
In this paper we show a variant of colorful Tverberg's theorem which is valid in any matroid: Let $S$ be a sequence of non-loops in a matroid $M$ of finite rank $m$ with closure operator cl. Suppose that $S$ is colored in such a way that the first color does not appear more than $r$-times and each other color appears at most $(r-1)$-times. Then $S$ can be partitioned into $r$ rainbow subsequences $S_1,\ldots, S_r$ such that $cl\,\emptyset\subsetneq cl\,S_1\subseteq cl\, S_2\subseteq \ldots \subseteq cl\,S_r$. In particular, $\emptyset\neq \bigcap_{i=1}^r cl\,S_i$. A subsequence is called rainbow if it contains each color at most once. The conclusion of our theorem is weaker than the conclusion of the original Tverberg's theorem in $\mathbb R^d$, which states that $\bigcap conv\,S_i\neq \emptyset$, whereas we only claim that $\bigcap aff\,S_i\neq \emptyset$. On the other hand, our theorem strengthens the Tverberg's theorem in several other ways: 1) it is applicable to any matroid (whereas Tverberg's theorem can only be used in $\mathbb R^d$), 2) instead of $\bigcap cl\,S_i\neq \emptyset$ we have the stronger condition $cl\,\emptyset\subsetneq cl\,S_1\subseteq cl\,S_2\subseteq \ldots \subseteq cl\,S_r$, and 3) we add a color constraints that are even stronger than the color constraints in the colorful version of Tverberg's theorem. Recently, the author together with Goaoc, Mabillard, Pat\'akov\'a, Tancer and Wagner used the first property and applied the non-colorful version of this theorem to homology groups with $GF(p)$ coefficients to obtain several non-embeddability results, for details we refer to arXiv:1610.09063. | Tverberg type theorems for matroids |
We study the nontrivial topology of the parameter space of general $U(1)$-symmetric fermionic non-degenerately gapped system and its consequences on the transport properties in arbitrary dimensions. By a nonlinear parameter-gauge topological response theory, we find that such nontrivial topology can impose quantization constraints on the charge transport in the presence of background fluxes or, more generally, instantons in general dimensions and our result generalizes the Thouless pump and its higher dimensional generalizations. We also show that these nontrivial transport properties are related to an unconventional quantum anomaly, which generalizes $-1$-form anomalies. This anomaly imposes non-perturbative ingappabilities of various types of spatial interfaces or time-dependent system evolution. | Nonlinear parameter-gauge coupling approach to generalization of generalized Thouless pumps and $-1$-form anomaly |
We present the first calibrated CCD images of the faint supernova remnant G 114.3+0.3 in the emission lines of [OII], [OIII], Halpha+[NII] and [SII]. The deep low ionization CCD images reveal diffuse emission in the south and central areas of the remnant. These are correlated with areas of intense radio emission, while estimates of the [SII]/Halpha ratio suggest that the detected emission originates from shock heated gas. In the medium ionization image of [OIII] we discovered a thin filament in the south matching very well the outer radio contours. This filament is not continuous over its total extent but shows variations in the intensity, mainly in the south-west suggesting inhomogeneous interstellar clouds. Deep long-slit spectra were also taken along the [OIII] filament clearly identifying the observed emission as emission from shock heated gas. The Halpha emission is a few times 10^(-17) erg s^(-1) cm^(-2) arcsec^(-2), while the variations seen in the [OIII] flux suggest shock velocities into the interstellar clouds around or below 100 km/s. The sulfur line ratio approaches the low density limit implying electron densities less than ~500 cm^(-3). | Imaging and spectroscopy of the faint remnant G 114.3+0.3 |
In this paper we present a constructive method to control the bilinear Schr\"odinger equation via two controls. The method is based on adiabatic techniques and works if the spectrum of the Hamiltonian admits eigenvalue intersections, and if the latter are conical (as it happens generically). We provide sharp estimates of the relation between the error and the controllability time. | Adiabatic control of the Schr\"odinger equation via conical intersections of the eigenvalues |
The Bose-Einstein condensation (BEC) of magnons created by a strong pumping in ferromagnetic thin films of yttrium iron garnet used as systems of finite size is considered analytically. Such a peculiarity, typical for this magnetic material, as the presence of a minimum in the spectrum of spin waves at a finite value of the wave vector is taken into account. The definition of hightemperature BEC is introduced and its characteristics are discussed. A role of boundary conditions for spin variables is analyzed, and it is shown that in the case of free spins on the boundary the magnon lattice can form in the system. The factors responsible for its appearance are discussed. | On the theory of inhomogeneous Bose-Einstein condensation of magnons in yttrium garnet |
With the success of deep neural networks, Neural Architecture Search (NAS) as a way of automatic model design has attracted wide attention. As training every child model from scratch is very time-consuming, recent works leverage weight-sharing to speed up the model evaluation procedure. These approaches greatly reduce computation by maintaining a single copy of weights on the super-net and share the weights among every child model. However, weight-sharing has no theoretical guarantee and its impact has not been well studied before. In this paper, we conduct comprehensive experiments to reveal the impact of weight-sharing: (1) The best-performing models from different runs or even from consecutive epochs within the same run have significant variance; (2) Even with high variance, we can extract valuable information from training the super-net with shared weights; (3) The interference between child models is a main factor that induces high variance; (4) Properly reducing the degree of weight sharing could effectively reduce variance and improve performance. | Deeper Insights into Weight Sharing in Neural Architecture Search |
The Nuclear Spectroscopic Telescope Array (NuSTAR), launched in June 2012, flies two conical approximation Wolter-I mirrors at the end of a 10.15m mast. The optics are coated with multilayers of Pt/C and W/Si that operate from 3--80 keV. Since the optical path is not shrouded, aperture stops are used to limit the field of view from background and sources outside the field of view. However, there is still a sliver of sky (~1.0--4.0 degrees) where photons may bypass the optics altogether and fall directly on the detector array. We term these photons Stray-light. Additionally, there are also photons that do not undergo the focused double reflections in the optics and we term these Ghost Rays. We present detailed analysis and characterization of these two components and discuss how they impact observations. Finally, we discuss how they could have been prevented and should be in future observatories. | Observational Artifacts of NuSTAR: Ghost Rays and Stray Light |
Histopathology tissue analysis is considered the gold standard in cancer diagnosis and prognosis. Given the large size of these images and the increase in the number of potential cancer cases, an automated solution as an aid to histopathologists is highly desirable. In the recent past, deep learning-based techniques have provided state of the art results in a wide variety of image analysis tasks, including analysis of digitized slides. However, the size of images and variability in histopathology tasks makes it a challenge to develop an integrated framework for histopathology image analysis. We propose a deep learning-based framework for histopathology tissue analysis. We demonstrate the generalizability of our framework, including training and inference, on several open-source datasets, which include CAMELYON (breast cancer metastases), DigestPath (colon cancer), and PAIP (liver cancer) datasets. We discuss multiple types of uncertainties pertaining to data and model, namely aleatoric and epistemic, respectively. Simultaneously, we demonstrate our model generalization across different data distribution by evaluating some samples on TCGA data. On CAMELYON16 test data (n=139) for the task of lesion detection, the FROC score achieved was 0.86 and in the CAMELYON17 test-data (n=500) for the task of pN-staging the Cohen's kappa score achieved was 0.9090 (third in the open leaderboard). On DigestPath test data (n=212) for the task of tumor segmentation, a Dice score of 0.782 was achieved (fourth in the challenge). On PAIP test data (n=40) for the task of viable tumor segmentation, a Jaccard Index of 0.75 (third in the challenge) was achieved, and for viable tumor burden, a score of 0.633 was achieved (second in the challenge). Our entire framework and related documentation are freely available at GitHub and PyPi. | A Generalized Deep Learning Framework for Whole-Slide Image Segmentation and Analysis |
T cells use sophisticated shape dynamics (morphodynamics) to migrate towards and neutralise infected and cancerous cells. However, there is limited quantitative understanding of the migration process in 3D extracellular matrices (ECMs) and across timescales. Here, we leveraged recent advances in lattice light-sheet microscopy to quantitatively explore the 3D morphodynamics of migrating T cells at high spatiotemporal resolution. We first developed a new shape descriptor based on spherical harmonics, incorporating key polarisation information of the uropod. We found that the shape space of T cells is low-dimensional. At the behavioural level, run-and-stop migration modes emerge at ~150 s, and we mapped the morphodynamic composition of each mode using multiscale wavelet analysis, finding 'stereotyped' motifs. Focusing on the run mode, we found morphodynamics oscillating periodically (every ~100 s) that can be broken down into a biphasic process: front-widening with retraction of the uropod, followed by a rearward surface motion and forward extension, where intercalation with the ECM in both of these steps likely facilitates forward motion. Further application of these methods may enable the comparison of T cell migration across different conditions (e.g. differentiation, activation, tissues, and drug treatments), and improve the precision of immunotherapeutic development. | T cell morphodynamics reveal periodic shape oscillations in 3D migration |
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