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We propose a splitting method for solving an equilibrium problem involving the sum of two bifunctions satisfying standard conditions. We prove that this problem is equivalent to find a zero of two appropriate maximally monotone operators. Our algorithm is a consequence of the Douglas--Rachford splitting applied to this auxiliary monotone inclusion. Connections between monotone inclusions and equilibrium problems are studied. | A Douglas-Rachford Splitting Method for Solving Equilibrium Problems |
We explore correlations between visual extinction and polarization along the western side of the IRAS Vela Shell using a published polarimetric catalog of several hundreds of objects. Our extinction maps along this ionization front (I-front) find evidence of clumpy structure with typical masses between 1.5 and 6 solar masses and a mean length scale L ~ 0.47pc. The polarimetric data allowed us to investigate the distribution of the local magnetic field in small (~pc) scales across the I-front. Using the dispersion of polarization position angles, we find variations in the kinetic-to-magnetic energy density ratio of, at least, one order of magnitude along the I-front, with the magnetic pressure generally dominating over the turbulent motions. These findings suggest that the magnetic component has a significant contribution to the dynamical balance of this region. Along the I-front, the mean magnetic field projected on the sky is [0.018 +/- 0.013]mG. The polarization efficiency seems to change along the I-front. We attribute high polarization efficiencies in regions of relatively low extinction to an optimum degree of grain alignment. Analysis of the mass-to-magnetic flux ratio shows that this quantity is consistent with the subcritical regime (lambda < 1), showing that magnetic support is indeed important in the region. Our data extend the overall lambda-N(H2) relation toward lower density values and show that such trend continues smoothly toward low N(H2) values. This provides general support for the evolution of initially subcritical clouds to an eventual supercritical stage. | Polarimetry toward the IRAS Vela Shell. II. Extinction and Magnetic Fields |
In this paper, we explore techniques centered around periodic sampling of model weights that provide convergence improvements on gradient update methods (vanilla \acs{SGD}, Momentum, Adam) for a variety of vision problems (classification, detection, segmentation). Importantly, our algorithms provide better, faster and more robust convergence and training performance with only a slight increase in computation time. Our techniques are independent of the neural network model, gradient optimization methods or existing optimal training policies and converge in a less volatile fashion with performance improvements that are approximately monotonic. We conduct a variety of experiments to quantify these improvements and identify scenarios where these techniques could be more useful. | Improving Model Training by Periodic Sampling over Weight Distributions |
We study both function theoretic and spectral properties of the weighted Laplacian $\Delta_f$ on complete smooth metric measure space $(M,g,e^{-f}dv)$ with its Bakry-\'{E}mery curvature $Ric_f$ bounded from below by a constant. In particular, we establish a gradient estimate for positive $f-$harmonic functions and a sharp upper bound of the bottom spectrum of $\Delta_f$ in terms of the lower bound of $Ric_{f}$ and the linear growth rate of $f.$ We also address the rigidity issue when the bottom spectrum achieves its optimal upper bound under a slightly stronger assumption that the gradient of $f$ is bounded. Applications to the study of the geometry and topology of gradient Ricci solitons are also considered. Among other things, it is shown that the volume of a noncompact shrinking Ricci soliton must be of at least linear growth. It is also shown that a nontrivial expanding Ricci soliton must be connected at infinity provided its scalar curvature satisfies a suitable lower bound. | Analysis of weighted Laplacian and applications to Ricci solitons |
We report the discovery of the ``mm fundamental plane of black-hole accretion'', which is a tight correlation between the nuclear 1 mm luminosity ($L_{\rm \nu, mm}$), the $2$ -- $10$~keV X-ray luminosity ($L_{\rm X,2-10}$) and the supermassive black hole (SMBH) mass ($M_{\rm BH}$) with an intrinsic scatter ($\sigma_{\rm int}$) of $0.40$ dex. The plane is found for a sample of 48 nearby galaxies, most of which are radiatively-inefficient, low-luminosity active galactic nuclei (LLAGN). Combining these sources with a sample of high-luminosity (quasar-like) nearby AGN, we find that the plane still holds. We also find that $M_{\rm BH}$ correlates with $L_{\rm \nu, mm}$ at a highly significant level, although such correlation is less tight than the mm fundamental plane ($\sigma_{\rm int}=0.51$ dex). Crucially, we show that spectral energy distribution (SED) models for both advection-dominated accretion flows (ADAFs) and compact jets can explain the existence of these relations, which are not reproduced by the standard torus-thin accretion disc models usually associated to quasar-like AGN. The ADAF models reproduces the observed relations somewhat better than those for compact jets, although neither provides a perfect prediction. Our findings thus suggest that radiatively-inefficient accretion processes such as those in ADAFs or compact (and thus likely young) jets may play a key role in both low- and high-luminosity AGN. This mm fundamental plane also offers a new, rapid method to (indirectly) estimate SMBH masses. | A fundamental plane of black hole accretion at millimetre wavelengths |
In present-day quantum communications, one of the main problems is the lack of a quantum repeater design that can simultaneously secure high rates and long distances. Recent literature has established the end-to-end capacities that are achievable by the most general protocols for quantum and private communication within a quantum network, encompassing the case of a quantum repeater chain. However, whether or not a physical design exists to approach such capacities remains a challenging objective. Driven by this motivation, in this work, we put forward a design for continuous-variable quantum repeaters and show that it can actually achieve the feat. We also show that even in a noisy regime our rates surpass the Pirandola-Laurenza-Ottaviani-Banchi (PLOB) bound. Our repeater setup is developed upon using noiseless linear amplifiers, quantum memories, and continuous-variable Bell measurements. We, furthermore, propose a non-ideal model for continuous-variable quantum memories that we make use of in our design. We then show that potential quantum communications rates would deviate from the theoretical capacities, as one would expect, if the quantum link is too noisy and/or low-quality quantum memories and amplifiers are employed. | Capacity-approaching quantum repeaters for quantum communications |
The paper studies a dynamic blocking problem, motivated by a model of optimal fire confinement. While the fire can expand with unit speed in all directions, barriers are constructed in real time. An optimal strategy is sought, minimizing the total value of the burned region, plus a construction cost. It is well known that optimal barriers exists. In general, they are a countable union of compact, connected, rectifiable sets. The main result of the present paper shows that optimal barriers are nowhere dense. The proof relies on new estimates on the reachable sets and on optimal trajectories for the fire, solving a minimum time problem in the presence of obstacles. | On the Regularity of Optimal Dynamic Blocking Strategies |
For a spin-carrying particle moving in a spatially varying magnetic field, effective electromagnetic forces can arise due to the geometric phase associated with adiabatic spin rotation of the particle. We report the observation of a geometric Hall effect in a spinor Bose-Einstein condensate with a skyrmion spin texture. Under translational oscillations of the spin texture, the condensate resonantly develops a circular motion in a harmonic trap, demonstrating the existence of an effective Lorentz force. When the condensate circulates, quantized vortices are nucleated in the boundary region of the condensate and the vortex number increases over 100 without significant heating. We attribute the vortex nucleation to the shearing effect of the effective Lorentz force from the inhomogeneous effective magnetic field. | Observation of a Geometric Hall Effect in a Spinor Bose-Einstein Condensate with a Skyrmion Spin Texture |
We extend the cascade-exciton model (CEM), and the Los Alamos version of the quark-gluon string model (LAQGSM), event generators of the Monte-Carlo N-particle transport code version 6 (MCNP6), to describe production of energetic light fragments (LF) heavier than 4He from various nuclear reactions induced by particles and nuclei at energies up to about 1 TeV/nucleon. In these models, energetic LF can be produced via Fermi break-up, preequilibrium emission, and coalescence of cascade particles. Initially, we study several variations of the Fermi break-up model and choose the best option for these models. Then, we extend the modified exciton model (MEM) used by these codes to account for a possibility of multiple emission of up to 66 types of particles and LF (up to 28Mg) at the preequilibrium stage of reactions. Then, we expand the coalescence model to allow coalescence of LF from nucleons emitted at the intranuclear cascade stage of reactions and from lighter clusters, up to fragments with mass numbers A < 8, in the case of CEM, and A < 13, in the case of LAQGSM. Next, we modify MCNP6 to allow calculating and outputting spectra of LF and heavier products with arbitrary mass and charge numbers. The improved version of CEM is implemented into MCNP6. Finally, we test the improved versions of CEM, LAQGSM, and MCNP6 on a variety of measured nuclear reactions. The modified codes give an improved description of energetic LF from particle- and nucleus-induced reactions; showing a good agreement with a variety of available experimental data. They have an improved predictive power compared to the previous versions and can be used as reliable tools in simulating applications involving such types of reactions. | Production of Energetic Light Fragments in CEM, LAQGSM, and MCNP6 |
Performing Data Assimilation (DA) at a low cost is of prime concern in Earth system modeling, particularly at the time of big data where huge quantities of observations are available. Capitalizing on the ability of Neural Networks techniques for approximating the solution of PDE's, we incorporate Deep Learning (DL) methods into a DA framework. More precisely, we exploit the latent structure provided by autoencoders (AEs) to design an Ensemble Transform Kalman Filter with model error (ETKF-Q) in the latent space. Model dynamics are also propagated within the latent space via a surrogate neural network. This novel ETKF-Q-Latent (thereafter referred to as ETKF-Q-L) algorithm is tested on a tailored instructional version of Lorenz 96 equations, named the augmented Lorenz 96 system: it possesses a latent structure that accurately represents the observed dynamics. Numerical experiments based on this particular system evidence that the ETKF-Q-L approach both reduces the computational cost and provides better accuracy than state of the art algorithms, such as the ETKF-Q. | Latent Space Data Assimilation by using Deep Learning |
Aiming at objective early detection of neuromotor disorders such as cerebral palsy, we proposed an innovative non-intrusive approach using a pressure sensing device to classify infant general movements (GMs). Here, we tested the feasibility of using pressure data to differentiate typical GM patterns of the ''fidgety period'' (i.e., fidgety movements) vs. the ''pre-fidgety period'' (i.e., writhing movements). Participants (N = 45) were sampled from a typically-developing infant cohort. Multi-modal sensor data, including pressure data from a 32x32-grid pressure sensing mat with 1024 sensors, were prospectively recorded for each infant in seven succeeding laboratory sessions in biweekly intervals from 4-16 weeks of post-term age. For proof-of-concept, 1776 pressure data snippets, each 5s long, from the two targeted age periods were taken for movement classification. Each snippet was pre-annotated based on corresponding synchronised video data by human assessors as either fidgety present (FM+) or absent (FM-). Multiple neural network architectures were tested to distinguish the FM+ vs. FM- classes, including support vector machines (SVM), feed-forward networks (FFNs), convolutional neural networks (CNNs), and long short-term memory (LSTM) networks. The CNN achieved the highest average classification accuracy (81.4%) for classes FM+ vs. FM-. Comparing the pros and cons of other methods aiming at automated GMA to the pressure sensing approach, we concluded that the pressure sensing approach has great potential for efficient large-scale motion data acquisition and sharing. This will in return enable improvement of the approach that may prove scalable for daily clinical application for evaluating infant neuromotor functions. | Infant movement classification through pressure distribution analysis |
We present a Monte Carlo study of the high-temperature phase of the two-dimensional driven lattice gas at infinite driving field. We define a finite-volume correlation length, verify that this definition has a good infinite-volume limit independent of the lattice geometry, and study its finite-size-scaling behavior. The results for the correlation length are in good agreement with the predictions based on the field theory proposed by Janssen, Schmittmann, Leung, and Cardy. The theoretical predictions for the susceptibility and the magnetization are also well verified. We show that the transverse Binder parameter vanishes at the critical point in all dimensions $d\ge 2$ and discuss how such result should be expected in the theory of Janssen et al. in spite of the existence of a dangerously irrelevant operator. Our results confirm the Gaussian nature of the transverse excitations. | Finite-Size Scaling in the Driven Lattice Gas |
We have investigated the problem of traversability of wormholes in the framework of quantum improvement of gravity theory arising from functional renormalization group methods to describe the asymptotic safe quantum gravity. We have shown that improved pseudospherical wormholes could be traversable with non--exotic matter, while spherical ones could not. This is done within a specific model of improvement. | Traversability of quantum improved wormhole solution |
Cross sections for neutron capture in the range of unresolved resonances are predicted simultaneously to level distances at the neutron threshold for more than 100 spin-0 target nuclei with A >70. Assuming triaxiality in nearly all these nuclei a combined parameterization for both, level density and photon strength is presented. The strength functions used are based on a global fit to IVGDR shapes by the sum of three Lorentzians adding up to the TRK sum rule and theory-based predictions for the A-dependence of pole energies and spreading widths. For the small spins reached by capture level densities are well described by only one free global parameter; a significant collective enhancement due to the deviation from axial symmetry is observed. Reliable predictions for compound nuclear reactions also outside the valley of stability as expected from the derived global parameterization are important for nuclear astrophysics and for the transmutation of nuclear waste. | Importance of nuclear triaxiality for electromagnetic strength, level density and neutron capture cross sections in heavy nuclei |
The frequencies of kHz QPOs are widely interpreted as being indicative of the values of characteristic frequencies related to orbital motion around neutron stars, e.g., the radial epicyclic frequency. In regions directly exposed to the radiation from the luminous neutron star these frequencies change with the luminosity. Including radiative corrections will change the neutron star mass value inferred from the QPO frequencies. Radiative forces may also be behind the puzzling phenomenon of parallel tracks. | Radiative corrections to the neutron star mass inferred from QPO frequencies |
The comparison of two universities in terms of bibliometric indicators frequently faces the problem of assessing the differences as meaningful or not. This Letter to the Editor proposes some benchmarks which can be used for supporting the interpretation of institutional differences. | Which differences can be expected when two universities in the Leiden Ranking are compared? Some benchmarks for institutional research evaluations |
The physics of the solar chromosphere is complex from both theoretical and modeling perspectives. The plasma temperature from the photosphere to corona increases from ~5,000 K to ~1 million K over a distance of only ~10,000 km from the chromosphere and the transition region. Certain regions of the solar atmosphere have sufficiently low temperature and ionization rates to be considered as weakly-ionized. In particular, this is true at the lower chromosphere. As a result, the Cowling resistivity is orders of magnitude greater than the Coulomb resistivity. Ohm's law therefore includes anisotropic dissipation. To evaluate the Cowling resistivity, we need to know the external magnetic field strength and to estimate the neutral fraction as a function of the bulk plasma density and temperature. In this study, we determine the magnetic field topology using the non-force-free field (NFFF) extrapolation technique based on SDO/HMI SHARP vector magnetogram data, and the stratified density and temperature profiles from the Maltby-M umbral core model for sunspots. We investigate the variation and effects of Cowling resistivity on heating and magnetic reconnection in the chromosphere as the flare-producing active region (AR) 11166 evolves. In particular, we analyze a C2.0 flare emerging from AR11166 and find a normalized reconnection rate of 0.051. | Effects of Cowling Resistivity in the Weakly-Ionized Chromosphere |
We investigate the stability and robustness properties of a continuification-based strategy for the control of large-scale multiagent systems. Within continuation-based strategy, one transforms the microscopic, agent-level description of the system dynamics into a macroscopic continuum-level, for which a control action can be synthesized to steer the macroscopic dynamics towards a desired distribution. Such an action is ultimately discretized to obtain a set of deployable control inputs for the agents to achieve the goal. The mathematical proof of convergence toward the desired distribution typically relies on the assumptions that no disturbance is present and that each agent possesses global knowledge of all the others' positions. Here, we analytically and numerically address the possibility of relaxing these assumptions for the case of a one-dimensional system of agents moving in a ring. We offer compelling evidence in favor of the use of a continuification-based strategy when agents only possess a finite sensing capability and spatio-temporal perturbations affect the macroscopic dynamics of the ensemble. We also discuss some preliminary results about the role of an integral action in the macroscopic control solution. | Continuification control of large-scale multiagent systems under limited sensing and structural perturbations |
We review how experimental data collected at the HERA lepton-hadron collider have improved our theoretical and phenomenological understanding of the standard model, and specifically of its QCD sector. | Tests of the Standard Model at HERA |
D4-D8 and D3-D7 systems are studied and a possible holographic dual of large N QCD (SU(N) gauge fields and fundamental quarks) is sought. A candidate system is found, for which however no explicit solution is available. Susy is broken by having a $D7-\bar{D7}$ condensing to a D5. The mechanism for supersymmetry breaking is then used to try to construct a Standard Model embedding. One can either obtain too few low energy fields or too many. The construction requires TeV scale string theory. | On Dp-Dp+4 systems, QCD dual and phenomenology |
We study tunneling of charge carriers in single- and bilayer graphene. We propose an explanation for non-zero "magic angles" with 100% transmission for the case of symmetric potential barrier, as well as for their almost-survival for slightly asymmetric barrier in the bilayer graphene known previously from numerical simulations. Most importantly, we demonstrate that these magic angles are not protected in the case of bilayer and give an explicit example of a barrier with very small electron transmission probability for any angles. This means that one can lock charge carriers by a p-n-p (or n-p-n) junction without opening energy gap. This creates new opportunities for the construction of graphene transistors. | Chiral tunneling through generic one-dimensional potential barriers in bilayer graphene |
Scattering on a resonance state coupled to a complicated background is a typical problem for mesoscopic quantum many-body systems as well as for wave propagation in the presence of a complex environment. On average, such a simple mode acquires an effective damping, the so-called "spreading" width, due to mixing with the background states. Modeling the latter by random matrix theory and employing the strength function formalism, we derive the joint distribution of the reflection and total transmission at arbitrary absorption in the background. The distribution is found to possess a remarkable symmetry between its reflection and transmission sectors, which is controlled by the ratio of the spreading to escape width. This in turn results in a symmetry relation between the marginal densities, despite the absence of the flux conservation at finite absorption. As an application, we study the statistics of total losses in the system at arbitrary coupling to the background. | Statistics of a simple transmission mode on a lossy chaotic background |
Event temporal reasoning aims at identifying the temporal relations between two or more events. However, knowledge conflicts arise when there is a mismatch between the actual temporal relations of events in the context and the prior knowledge or biases learned by the model. We first systematically define distinct kinds of bias in event temporal reasoning, which include event relation prior bias, tense bias, narrative bias, and dependency bias, as indicators to study knowledge conflicts. To mitigate such event-related knowledge conflict, we introduce a Counterfactual Data Augmentation based method that can be applied to both Pre-trained Language Models (PLMs) and Large Language Models (LLMs) either as additional training data or demonstrations for In-Context Learning. Experiments suggest the importance of mitigating knowledge conflicts in event temporal reasoning tasks for reducing hallucination and highlight the potential of counterfactual data augmentation for improving model performance. | Getting Sick After Seeing a Doctor? Diagnosing and Mitigating Knowledge Conflicts in Event Temporal Reasoning |
Background: Spectroscopic factors, overlaps, and isospin symmetry are often used in conjunction with single-particle wave functions for the phenomenological analysis of nuclear structure and reactions. Many differing prescriptions for connecting these quantities to physically relevant asymptotic normalization constants or widths are available in the literature, but their relationship and degree of validity are not always clear. Purpose: This paper derives relationships among the above quantities of interest using well-defined methodology and starting assumptions. Method: $R$-matrix theory is used as the primary tool to interoperate between the quantities of interest to this work. Particular attention is paid to effects arising from beyond the nuclear surface, where isospin symmetry is strongly violated. Results: Relationships among the quantities of interest are derived. Example applications of these methods to mirror levels in nucleon+${}^{12}{\rm C}$, nucleon+${}^{16}{\rm O}$, and nucleon+${}^{26}{\rm Al}$ are presented. A new approach to multi-level mirror symmetry is derived and applied to the first three $2^+$ states of ${}^{18}{\rm O}$ and ${}^{18}{\rm Ne}$. Conclusions: The relationship between the quantities of interest is clarified and certain procedures are recommended. It is found that the asymptotic normalization constant of the second $2^+$ state in ${}^{18}{\rm Ne}$ deduced from the mirror state in ${}^{18}{\rm O}$ is significantly larger than found in previous work. This finding has the effect of increasing the ${}^{17}{\rm F}(p,\gamma){}^{18}{\rm Ne}$ reaction rate in novae. | Spectroscopic factors, overlaps, and isospin symmetry from an $R$-matrix point of view |
In this work we prove a prime number type theorem involving the normalised Fourier coefficients of holomorphic and Maass cusp forms, using the classical circle method. A key point is in a recent paper of Fouvry and Ganguly, based on Hoffstein-Ramakrishnan's result about the non-existence of the Siegel zeros for $GL(2)$ $L$-functions, which allows us to improve preceding estimates. | Quadratic forms connected with Fourier coefficients of holomorphic and Maass cusp forms |
From social networks to Internet applications, a wide variety of electronic communication tools are producing streams of graph data; where the nodes represent users and the edges represent the contacts between them over time. This has led to an increased interest in mechanisms to model the dynamic structure of time-varying graphs. In this work, we develop a framework for learning the latent state space of a time-varying email graph. We show how the framework can be used to find subsequences that correspond to global real-time events in the Email graph (e.g. vacations, breaks, ...etc.). These events impact the underlying graph process to make its characteristics non-stationary. Within the framework, we compare two different representations of the temporal relationships; discrete vs. probabilistic. We use the two representations as inputs to a mixture model to learn the latent state transitions that correspond to important changes in the Email graph structure over time. | Learning the Latent State Space of Time-Varying Graphs |
The counting rate of single muon tracks from the Project GRAND proportional wire chamber array is examined during the Ground Level Event (GLE) of April 15, 2001. The GLE was seen by neutron monitor stations shortly after the time of the solar X-ray flare. GRAND's single muon data are presented and compared with neutron monitor data from Climax, Newark, and Oulu. The single muon data have mean primary hadron energies higher than those of these neutron monitor stations and so contain information about higher energy hadrons. For the single muon data for Project GRAND, the GLE is detected at a statistical significance of 6.1-sigma. | Ground level muons in coincidence with the solar flare of April 15, 2001 |
The interplay of interactions and disorder is studied using the Anderson-Hubbard model within the typical medium dynamical cluster approximation. Treating the interacting, non-local cluster self-energy ($\Sigma_c[{\cal \tilde{G}}](i,j\neq i)$) up to second order in the perturbation expansion of interactions, $U^2$, with a systematic incorporation of non-local spatial correlations and diagonal disorder, we explore the initial effects of electron interactions ($U$) in three dimensions. We find that the critical disorder strength ($W_c^U$), required to localize all states, increases with increasing $U$; implying that the metallic phase is stabilized by interactions. Using our results, we predict a soft pseudogap at the intermediate $W$ close to $W_c^U$ and demonstrate that the mobility edge ($\omega_\epsilon$) is preserved as long as the chemical potential, $\mu$, is at or beyond the mobility edge energy. | Metal-Insulator-Transition in a Weakly interacting Disordered Electron System |
We study theoretically the deformation of the Fermi surface (FS) of a three-dimensional gas of Rydberg-dressed $^6$Li atoms. The laser dressing to high-lying Rydberg $D$ states results in angle-dependent soft-core-shaped interactions whose anisotropy is described by multiple spherical harmonics. We show that this can drastically modify the shape of the FS and that its deformation depends on the interplay between the Fermi momentum $k_F$ and the reciprocal momentum $\bar{k}$ corresponding to the characteristic soft-core radius of the dressing-induced potential. When $k_F< \bar{k}$, the dressed interaction stretches a spherical FS into an ellipsoid. When $k_F\gtrsim \bar{k}$, complex deformations are encountered which exhibit multipolar characteristics. We analyze the formation of Cooper pairs around the deformed FS and show that they occupy large orbital angular momentum states ($p$, $f$, and $h$ wave) coherently. Our study demonstrates that Rydberg dressing to high angular momentum states may pave a route toward the investigation of unconventional Fermi gases and multiwave superconductivity. | Multipolar Fermi-surface deformation in a Rydberg-dressed Fermi gas with long-range anisotropic interactions |
We calculate the gravitational radiation from a cusp of the chiral cosmic strings as a function of the current on the string in the limit of small values of the current. The smoothing of the cosmic string cusp due to the presence of the superconducting current on the string leads to the different behavior of the gravitational radiation from the cusp as compared with the non-superconducting (ordinary) string. The difference between the gravitational energy radiation from the chiral cusp and the ordinary one is proportional to the value of the current on the string. It is shown that there is a high-frequency cutoff in the spectrum of the gravitational radiation from the chiral string. The frequency cutoff depends on the value of the string current. This effect is crucial for the detection of gravitation wave bursts from cosmic strings: the rather large current on the string would lower the amplitude of the incoming signal. | Gravitational radiation from chiral string cusps |
We present high spatial resolution ($\approx$ 60--90 milliarcseconds) images of the molecular hydrogen emission in the Planetary Nebula (PN) NGC 2346. The data were acquired during the System Verification of the Gemini Multi-Conjugate Adaptive Optics System + Gemini South Adaptive Optics Imager. At the distance of NGC 2346, 700 pc, the physical resolution corresponds to $\approx$ 56 AU, which is slightly higher than that an [N II] image of NGC 2346 obtained with HST/WFPC2. With this unprecedented resolution we were able to study in detail the structure of the H$_2$ gas within the nebula for the first time. We found it to be composed of knots and filaments, which at lower resolution had appeared to be a uniform torus of material. We explain how the formation of the clumps and filaments in this PN is consistent with a mechanism in which a central hot bubble of nebular gas surrounding the central star has been depressurized, and the thermal pressure of the photoionized region drives the fragmentation of the swept-up shell. | High resolution imaging of NGC 2346 with GSAOI/GeMS: disentangling the planetary nebula molecular structure to understand its origin and evolution |
Fractal Hofstadter bands have become widely accessible with the advent of moir\'e superlattices, opening the door to studies of the effect of interactions in these systems. In this work we employ a renormalization group (RG) analysis to demonstrate that the combination of repulsive interactions with the presence of a tunable manifold of Van Hove singularities provides a new mechanism for driving unconventional superconductivity in Hofstadter bands. Specifically, the number of Van Hove singularities at the Fermi energy can be controlled by varying the flux per unit cell and the electronic filling, leading to instabilities toward nodal superconductivity and chiral topological superconductivity with Chern number $\mathcal{C} = \pm 6$. The latter is characterized by a self-similar fixed trajectory of the RG flow and an emerging self-similarity symmetry of the order parameter. Our results establish Hofstadter quantum materials such as moir\'e heterostructures as promising platforms for realizing novel reentrant Hofstadter superconductors. | Unconventional Self-Similar Hofstadter Superconductivity from Repulsive Interactions |
In the SACY (Search for Associations Containing Young-stars) project we try to identify associations of stars younger than the Local Association among HIPPARCOS and/or TYCHO-2 stars later than G0 which are counterparts of the ROSAT X-ray bright sources. High-resolution spectra for the possible optical counterparts were obtained in order to assess both the youth and the spatial motion of each target. More than 1000 ROSAT sources were observed, covering a large area in the Southern Hemisphere. Associations are characterized mainly by the similarity in UVW velocity space of their proposed member, but other parameters, as evolutionary age, Li abundance and distribution in space must also be taken into account. We proposed a method to identify associations when proper motions and radial velocities are available, but no parallaxes. Using the method we found eleven associations in the SACY data. | A Method to Search for Associations of Young Stars |
This paper sets out the results of a range of searches for linear and cyclic graph colourings with specific Ramsey properties. The new graphs comprise mainly 'template graphs' which can be used in a construction described by the current author in 2021 to build linear or cyclic compound graphs with inherited Ramsey properties. These graphs result in improved lower bounds for a wide range of multicolour Ramsey numbers. Searches were carried out using relatively simple programs (written in the language `C') to generate clauses for input to the PeneLoPe and Plingeling parallel SAT-solvers. When solutions were found, the output from the solvers specified the desired graph colourings. The majority of the graphs produced by this work are `template graphs' with parameters in the form $(k,k,3)$ or $(k,l,3)$ with $k \ne l$. Using these template graphs in familiar constructions, it has been possible to demonstrate significant improvements for lower bounds for most $R_r(k)$ for $5 \le k \le 9$ and $r \ge 4$. These improvements provide correspondingly increased lower bounds on $\Gamma(k) = \lim_{\substack{r \rightarrow \infty}} R{_r}(k)^{1/r}$. We also show that $R_3(8) \ge 7174$ and $R_3(9) \ge 15041$. Other new lower bounds include $R(3,6,6) \ge 338$ and $R(3,8,8) \ge 941$, based on non-template cyclic graphs, and the interesting particular cases $R(3,4,5,5) \ge 729$ and $R(3,5,5,5) \ge 1429$. A spreadsheet containing specimens of many of the graphs mentioned here will be attached as an ArXiv ancillary file. | Improved Lower Bounds for Multicolour Ramsey Numbers using SAT-Solvers |
A classical and widely used lemma of Erdos and Szekeres asserts that for every n there exists N such that every N-term sequence a of real numbers contains an n-term increasing subsequence or an n-term nondecreasing subsequence; quantitatively, the smallest N with this property equals (n-1)^2+1. In the setting of the present paper, we express this lemma by saying that the set of predicates Phi={x_1<x_2,x_1\ge x_2}$ is Erdos-Szekeres with Ramsey function ES_Phi(n)=(n-1)^2+1. In general, we consider an arbitrary finite set Phi={Phi_1,...,Phi_m} of semialgebraic predicates, meaning that each Phi_j=Phi_j(x_1,...,x_k) is a Boolean combination of polynomial equations and inequalities in some number k of real variables. We define Phi to be Erdos-Szekeres if for every n there exists N such that each N-term sequence a of real numbers has an n-term subsequence b such that at least one of the Phi_j holds everywhere on b, which means that Phi_j(b_{i_1},...,b_{i_k}) holds for every choice of indices i_1,i_2,...,i_k, 1<=i_1<i_2<... <i_k<= n. We write ES_Phi(n) for the smallest N with the above property. We prove two main results. First, the Ramsey functions in this setting are at most doubly exponential (and sometimes they are indeed doubly exponential): for every Phi that is Erd\H{o}s--Szekeres, there is a constant C such that ES_Phi(n) < exp(exp(Cn)). Second, there is an algorithm that, given Phi, decides whether it is Erdos-Szekeres; thus, one-dimensional Erdos-Szekeres-style theorems can in principle be proved automatically. | Erdos-Szekeres-type statements: Ramsey function and decidability in dimension 1 |
NASA's K2 mission began observing fields along the ecliptic plane in 2014. Each observing campaign lasts approximately 80 days, during which high-precision optical photometry of select astrophysical targets is collected by the Kepler spacecraft. Due to the 4 arcsec pixel scale of the Kepler photometer, significant blending between the observed targets can occur (especially in dense fields close to the Galactic plane). We undertook a program to use the Wide Field Camera (WFCAM) on the 3.8 m United Kingdom InfraRed Telescope (UKIRT) to collect high-spatial-resolution near-infrared images of targets in select K2 campaign fields, which we report here. These 0.4 arcsec resolution K-band images offer the opportunity to perform a variety of science, including vetting exoplanet candidates by identifying nearby stars blended with the target star and estimating the size, color, and type of galaxies observed by K2. | High-Spatial-Resolution K-Band Imaging of Select K2 Campaign Fields |
A generalized Euler parameterization of a compact Lie group is a way for parameterizing the group starting from a maximal Lie subgroup, which allows a simple characterization of the range of parameters. In the present paper we consider the class of all compact connected Lie groups. We present a general method for realizing their generalized Euler parameterization starting from any symmetrically embedded Lie group. Our construction is based on a detailed analysis of the geometry of these groups. As a byproduct this gives rise to an interesting connection with certain Dyson integrals. In particular, we obtain a geometry based proof of a Macdonald conjecture regarding the Dyson integrals correspondent to the root systems associated to all irreducible symmetric spaces. As an application of our general method we explicitly parameterize all groups of the class of simple, simply connected compact Lie groups. We provide a table giving all necessary ingredients for all such Euler parameterizations. | Compact Lie groups: Euler constructions and generalized Dyson conjecture |
W51 is a giant radio complex lying along the tangent to the Sagitarius arm at a distance of about 7kpc from Sun, with an extension of about 1deg in the sky. It is divided into three components A,B,C where W51A and W51B consist of many compact HII regions while W51C is a supernova remnant. We have made continuum radio observations of these HII regions of the W51 complex at 240,610,1060,1400 MHz using GMRT with lower resolution 20''x15'' at the lowest frequency. The observed spectra of the prominent thermal subcomponents of W51 have been fitted to a free-free emission spectrum and their physical properties like electron temperatures and emission measures have been estimated. The electron temperatures from continuum spectra are found to be lower than the temperatures reported from radio recombination line (RRL) studies of these HII regions indicating the need for a filling factor even at this resolution. Also, the observed brightness at 240MHz is found to be higher than expected from the best fits suggesting the need for a multicomponent model for the region. | Electron Temperatures in W51 Complex from High Resolution, Low Frequency Radio Observations |
I consider magnetic Schr\"odinger operator in dimension $d=2$ assuming that coefficients are smooth and magnetic field is non-degenerating. Then I extend the remainder estimate $O(\mu^{-1}h^{-1}+1)$ derived in \cite{Ivr1} for the case when $V/F$ has no stationary points to the case when it has non-degenerating stationary points. If some of them are saddles and $\mu^3h\ge 2$ then asymptotics contains correction terms of magnitude $\mu^{-1}h^{-1}|\log \mu^3 h|$. | Sharp Spectral Asymptotics for 2-dimensional Schr\"odinger operator with a strong magnetic field. Note about forgotten generic case |
We investigate the parametric electron pumping of a double barrier structure in the presence of a superconducting lead. The parametric pumping is facilitated by cyclic variation of the barrier heights $x_1$ and $x_2$ of the barriers. In the weak coupling regime, there exists a resonance line in the parameter space $(x_1,x_2)$ so that the energy of the quasi-bound state is in line with the incoming Fermi energy. Levinson et al found recently that the pumped charge for each pumping cycle is quantized with $Q=2e$ for normal structure when the pumping contour encircles the resonance line. In the presence of a superconducting lead, we find that the pumped charge is quantized with the value $2e$. | Quantization of adiabatic pumped charge in the presence of superconducting lead |
We present a catalogue of 22755 objects with slitless, optical, Hubble Space Telescope (HST) spectroscopy from the Grism Lens-Amplified Survey from Space (GLASS). The data cover $\sim$220 sq. arcmin to 7-orbit ($\sim$10 ks) depth in 20 parallel pointings of the Advanced Camera for Survey's G800L grism. The fields are located 6' away from 10 massive galaxy clusters in the HFF and CLASH footprints. Thirteen of the fields have ancillary HST imaging from these or other programs to facilitate a large number of applications, from studying metal distributions at $z\sim0.5$, to quasars at $z\sim4$, to the star formation histories of hundreds of galaxies in between. The spectroscopic catalogue has a median redshift of $\langle z\rangle=0.6$ with a median uncertainty of $\Delta z / (1+z)\lesssim2\%$ at $\rm F814W\lesssim23$ AB. Robust continuum detections reach a magnitude fainter. The 5 $\sigma$ limiting line flux is $f_{\rm lim}\approx5\times10^{-17}\rm~erg~s^{-1}~cm^{-2}$ and half of all sources have 50% of pixels contaminated at $\lesssim$1%. All sources have 1- and 2-D spectra, line fluxes/uncertainties and identifications, redshift probability distributions, spectral models, and derived narrow-band emission line maps from the Grism Redshift and Line Analysis tool (GRIZLI). We provide other basic sample characterisations, show data examples, and describe sources and potential investigations of interest. All data and products will be available online along with software to facilitate their use. | The Grism Lens-Amplified Survey from Space (GLASS). XIII. G800L optical spectra from the parallel fields |
As a main result of this paper we give conditions under which the generalized $X$-join of Cayley graphs is a Cayley graph. In particular, we show that $X$-join of isomorphic Cayley graphs is a Cayley grpah. To do this, new properties for a generalized wreath product of permutation groups are given in the case where the base group acts regularly. These are used to give conditions for the generalized wreath product to contain a regular subgroup, which are then applied to generalized $X$-joins of Cayley graphs. Along the way, it is shown that the generalized $X$-join of isomorphic Cayley graphs will always be a vertex transitive graph. | The generalized X-join of Cayley graphs |
The Local arm of the Milky Way, a short spiral feature near the Sun whose existence is known for decades, was recently observed in detail with different tracers. Many efforts have been dedicated to elaborate plausible hypotheses concerning the origin of the main spiral arms of the Galaxy; however, up to now, no specific mechanism for the origin of the Local arm was proposed. Here we explain, for the first time, the Local arm as an outcome of the spiral corotation resonance, which traps arm tracers and the Sun inside it. We show that the majority of maser sources belonging to the Local arm, together with the Sun, evolve inside the corotation resonance, never crossing the main spiral arms but instead oscillating in the region between them. This peculiar behavior of the Sun could have numerous consequences to our understanding of the local kinematics of stars, the Galactic Habitable Zone, and the Solar System evolution. | The dynamical origin of the Local arm and the Sun's trapped orbit |
It is known that under microwave irradiation, in 2D electron systems with high filling factors oscillations of longitudinal magnetoresistance appear in the range of magnetic fields where ordinary SdH oscillations are suppressed. In the present paper we propose a simple quasiclassical model of these new oscillations based on the Boltzmann kinetic equation. Our model also predicts similar oscillations in diffusion component of thermoelectric coefficients, which should be observable at low temperatures. | Oscillations of 2DEG thermoelectric coefficients in magnetic field under microwave irradiation |
Recently Allahverdyan and Nieuwenhuizen (cond-mat/0006404) argued that the second law of thermodynamics may be violated in a quantum system as a "consequence of quantum coherence in the presence of the slightly off-equilibrium nature of the bath." By using a standard result about relative entropy, we prove rigorously that the second law is never violated (and, in particular, a perpetual motion of the second kind can never be realized) in quantum systems no matter how strong ``quantum coherence'' is or no matter how far one goes from equilibrium. | Comment on "Extraction of work from a single thermal bath in the quantum regime" |
Modern high performance computing clusters heavily rely on accelerators to overcome the limited compute power of CPUs. These supercomputers run various applications from different domains such as simulations, numerical applications or artificial intelligence (AI). As a result, vendors need to be able to efficiently run a wide variety of workloads on their hardware. In the AI domain this is in particular exacerbated by the existence of a number of popular frameworks (e.g, PyTorch, TensorFlow, etc.) that have no common code base, and can vary in functionality. The code of these frameworks evolves quickly, making it expensive to keep up with all changes and potentially forcing developers to go through constant rounds of upstreaming. In this paper we explore how to provide hardware support in AI frameworks without changing the framework's source code in order to minimize maintenance overhead. We introduce SOL, an AI acceleration middleware that provides a hardware abstraction layer that allows us to transparently support heterogeneous hardware. As a proof of concept, we implemented SOL for PyTorch with three backends: CPUs, GPUs and vector processors. | SOL: Effortless Device Support for AI Frameworks without Source Code Changes |
We present the results of CO(1-0) and CO(4-3) observations of the host galaxy of a long-duration gamma-ray burst GRB080207 at z = 2.0858 by using the Karl G. Jansky Very Large Array and the Atacama Large Millimeter/submillimeter Array. The host is detected in CO(1-0) and CO(4-3), becoming the first case for a GRB host with more than two CO transitions detected combined with CO(2-1) and CO(3-2) in the literature. Adopting a metallicity-dependent CO-to-H2 conversion factor, we derive a molecular gas mass of Mgas = 8.7 x 10^10 Modot, which places the host in a sequence of normal star-forming galaxies in a Mgas-star-formation rate (SFR) plane. A modified blackbody fit to the far-infrared--millimeter photometry results in a dust temperature of 37 K and a dust mass of Mdust = 1.5 x 10^8 Modot. The spatially-resolving CO(4-3) observations allow us to examine the kinematics of the host. The CO velocity field shows a clear rotation and is reproduced by a rotation-dominated disk model with a rotation velocity of 350 km/s and a half-light radius of 2.4 kpc. The CO spectral line energy distribution derived from the four CO transitions is similar to that of starburst galaxies, suggesting a high excitation condition. Comparison of molecular gas properties between the host and normal (main-sequence) galaxies at similar redshifts shows that they share common properties such as gas mass fraction, gas depletion timescale, gas-to-dust ratio, location in the Mgas-SFR (or surface density) relation, and kinematics, suggesting that long-duration GRBs can occur in normal star-forming environments at z ~ 2. | Molecular Gas Properties in the Host Galaxy of GRB080207 |
The compositeness is defined as the weight of the hadronic molecule in the hadron wave function. We can determine the internal structure of the weak-binding system without any specific models from the compositeness. In order to estimate the compositeness of the system with a large effective range, we introduce the range correction to Weinberg's weak-binding relation by modifying the correction terms. We study the applicability of the weak-binding relations by the numerical calculation and show that the improved relation can be applied to a larger parameter region compared with the previous one. | Range correction in the weak-binding relation for unstable states |
For a graph $G = (V, E)$ embedded in the Klein bottle, let $\mathcal{F}(G)$ denote the set of faces of $G$. Then, $G$ is called a $C_k$-face-magic Klein bottle graph if there exists a bijection $f: V(G) \to \{1, 2, \dots, |V(G)|\}$ such that for any $F \in \mathcal{F}(G)$ with $F \cong C_k$, the sum of all the vertex labelings along $C_k$ is a constant $S$. Let $x_v =f(v)$ for all $v\in V(G)$. We call $\{x_v : v\in V(G)\}$ a $C_k$-face-magic Klein bottle labeling on $G$. We consider the $m \times n$ grid graph, denoted by $\mathcal{K}_{m,n}$, embedded in the Klein bottle in the natural way. We show that for $m,n\ge 2$, $\mathcal{K}_{m,n}$ admits a $C_4$-face-magic Klein bottle labeling if and only if $n$ is even. We say that a $C_4$-face-magic Klein bottle labeling $\{x_{i,j}: (i,j) \in V(\mathcal{K}_{m,n}) \}$ on $\mathcal{K}_{m,n}$ is equatorially balanced if $x_{i,j} + x_{i,n+1-j} = \tfrac{1}{2} S$ for all $(i,j) \in V(\mathcal{K}_{m,n})$. We show that when $m$ is odd, a $C_4$-face-magic Klein bottle labeling on $\mathcal{K}_{m,n}$ must be equatorially balanced. Also when $m$ is odd, we show that (up to symmetries on the Klein bottle) the number of $C_4$-face-magic Klein bottle labelings on the $m \times 4$ Klein bottle grid graph is $2^m \, (m-1)! \, \tau(m)$, where $\tau(m)$ is the number of positive divisors of $m$. Furthermore, let $m\ge 3$ be an odd integer and $n \ge 6$ be an even integer. Then, the minimum number of distinct $C_4$-face-magic Klein bottle labelings $X$ on $\mathcal{K}_{m,n}$ (up to symmetries on a Klein bottle) is either $(5\cdot 2^m)(m-1)!$ if $n \equiv 0\pmod{4}$, or $(6\cdot 2^m)(m-1)!$ if $n \equiv 2\pmod{4}$. | Equatorially balanced C4-face-magic labelings on Klein bottle grid graphs |
We present a discussion of the design issues and trade-offs that have been considered in putting together a new concept for MOSAIC, the multi-object spectrograph for the E-ELT. MOSAIC aims to address the combined science cases for E-ELT MOS that arose from the earlier studies of the multi-object and multi-adaptive optics instruments. MOSAIC combines the advantages of a highly-multiplexed instrument targeting single-point objects with one which has a more modest multiplex but can spatially resolve a source with high resolution (IFU). These will span across two wavebands: visible and near-infrared. | Developing an integrated concept for the E-ELT Multi-Object Spectrograph (MOSAIC): design issues and trade-offs |
In the top-down holographic model of QCD based on D4/D8-branes in type IIA string theory and some of the bottom up models, the low energy effective theory of mesons is described by a 5 dimensional Yang-Mills-Chern-Simons theory in a certain curved background with two boundaries. The 5 dimensional Chern-Simons term plays a crucial role to reproduce the correct chiral anomaly in 4 dimensional massless QCD. However, there are some subtle ambiguities in the definition of the Chern-Simons term for the cases with topologically non-trivial gauge bundles, which include the configurations with baryons. In particular, for the cases with three flavors, it was pointed out by Hata and Murata that the naive Chern-Simons term does not lead to an important constraint on the baryon spectrum, which is needed to pick out the correct baryon spectrum observed in nature. In this paper, we propose a formulation of well-defined Chern-Simons term which can be used for the cases with baryons, and show that it recovers the correct baryon constraint as well as the chiral anomaly in QCD. | Chern-Simons 5-form and Holographic Baryons |
Two rectangular models described by the one-dimensional Schroedinger equation with sharply localized potentials are suggested. The potentials have a multi-layer thin structure being composed from adjacent barriers and wells. Their peculiar tunneling properties are studied in considerable detail. Particularly, in the zero-range limit when the potentials are squeezed to a single point, sharp peaks with total transmission are observed at certain (positive and negative) quantized values of the potential strength constant forming infinite discrete sets. Beyond these sets, the barrier-well structures behave as a perfectly reflecting wall. The transcendental equations with respect to potential strengths, the solutions of which determine transmission (resonance) sets, are derived. In this regard, both the models are exactly solvable. The energy dependence of an incident particle is shown to reveal a resonance behavior, being completely different from that observed in a typical double barrier structure. | Single point potentials with total resonant tunneling |
We report late-time spectroscopic observations of the Type IIn SN 1998S, taken 14 years after explosion using the Large Binocular Telescope. The optical spectrum exhibits broad emission features of [O I], [O II], [O III], H-alpha, H-beta, and [Fe II]. The last decade of evolution has exhibited a strengthening of the oxygen transitions, evidence that the late-time emission is powered by increasingly metal-rich SN ejecta crossing the reverse shock. The H-alpha luminosity requires that SN 1998S is still interacting with dense circumstellar material (CSM), probably produced by the strong wind of a red supergiant progenitor at least ~1000 years before explosion. The emission lines exhibit asymmetric blueshifted profiles, which implies that the receding hemisphere of the SN is obscured by dust. The [O III] line, in particular, exhibits a complete suppression of its red wing. This could be the result of the expected wavelength dependence for dust extinction or a smaller radial distribution for [O III]. In the latter case, the red wing of [O III] could be absorbed by core dust, while both the blue and red wings are absorbed by dust within the cool dense shell between the forward and reverse shocks; this interpretation could explain why late-time [O III] emission from SNe is often weaker than models predict. The [O I] line exhibits double-peaked structure on top of the broader underlying profile, possibly due to emission from individual clumps of ejecta or ring-like structures of metal-rich debris. The centroids of the peaks are blueshifted and lack a red counterpart. However, an archival spectrum obtained on day 1093 exhibits a third, redshifted peak, which we suspect has become extinguished by dust that formed over the last decade. This implies that the "missing" red components of multi-peaked oxygen profiles observed in other SNe might be obscured by varying degrees of dust extinction. | Supernova 1998S at 14 years Postmortem: Continuing Circumstellar Interaction and Dust Formation |
We propose a novel self-supervised method, referred to as Video Cloze Procedure (VCP), to learn rich spatial-temporal representations. VCP first generates "blanks" by withholding video clips and then creates "options" by applying spatio-temporal operations on the withheld clips. Finally, it fills the blanks with "options" and learns representations by predicting the categories of operations applied on the clips. VCP can act as either a proxy task or a target task in self-supervised learning. As a proxy task, it converts rich self-supervised representations into video clip operations (options), which enhances the flexibility and reduces the complexity of representation learning. As a target task, it can assess learned representation models in a uniform and interpretable manner. With VCP, we train spatial-temporal representation models (3D-CNNs) and apply such models on action recognition and video retrieval tasks. Experiments on commonly used benchmarks show that the trained models outperform the state-of-the-art self-supervised models with significant margins. | Video Cloze Procedure for Self-Supervised Spatio-Temporal Learning |
A virtual element method (VEM) with the first order optimal convergence order is developed for solving two-dimensional Maxwell interface problems on a special class of polygonal meshes that are cut by the interface from a background unfitted mesh. A novel virtual space is introduced on a virtual triangulation of the polygonal mesh satisfying a maximum angle condition, which shares exactly the same degrees of freedom as the usual H(curl)-conforming virtual space. This new virtual space serves as the key to prove that the optimal error bounds of the VEM are independent of high aspect ratio of the possible anisotropic polygonal mesh near the interface. | A Virtual Finite Element Method for Two Dimensional Maxwell Interface Problems with a Background Unfitted Mesh |
Combinatorial network optimization algorithms that compute optimal structures taking into account edge weights form the foundation for many network protocols. Examples include shortest path routing, minimal spanning tree computation, maximum weighted matching on bipartite graphs, etc. We present CLRMR, the first online learning algorithm that efficiently solves the stochastic version of these problems where the underlying edge weights vary as independent Markov chains with unknown dynamics. The performance of an online learning algorithm is characterized in terms of regret, defined as the cumulative difference in rewards between a suitably-defined genie, and that obtained by the given algorithm. We prove that, compared to a genie that knows the Markov transition matrices and uses the single-best structure at all times, CLRMR yields regret that is polynomial in the number of edges and nearly-logarithmic in time. | Online Learning for Combinatorial Network Optimization with Restless Markovian Rewards |
In their study of local models of Shimura varieties for totally ramified extensions, Pappas and Rapoport posed a conjecture about the reducedness of a certain subscheme of $n \times n$ matrices. We give a positive answer to their conjecture in full generality. Our main ideas follow naturally from two of our previous works. The first is our proof of a conjecture of Kreiman, Lakshmibai, Magyar, and Weyman on the equations defining type A affine Grassmannians. The second is the work of the first two authors and Kamnitzer on affine Grassmannian slices and their reduced scheme structure. We also present a version of our argument that is almost completely elementary: the only non-elementary ingredient is the Frobenius splitting of Schubert varieties. | On a conjecture of Pappas and Rapoport about the standard local model for $GL_d$ |
We propose a simple two-dimensional acoustic crystal to realize topologically protected edge states for acoustic waves. The acoustic crystal is composed of a triangular array of core-shell cylinders embedded in a water host. By utilizing the point group symmetry of two doubly degenerate eigenstates at the \Gamma point, we can construct pseudo-time-reversal symmetry as well as pseudo-spin states in this classical system. We develop an effective Hamiltonian model for the associated dispersion bands around the Brillouin zone center, and find the inherent link between the band inversion and the topological phase transition. With numerical simulations, we unambiguously demonstrate the unidirectional propagation of acoustic edge states along the interface between a topologically nontrivial acoustic crystal and a trivial one, and the robustness of the edge states against defects with sharp bends. Our work provides a new design paradigm for manipulating and transporting acoustic waves in a topologically protected manner. Technological applications and devices based on our design are expected in various frequency ranges of interest, spanning from infrasound to ultrasound. | Pseudo-time-reversal symmetry and topological edge states in two-dimensional acoustic crystals |
Conventional Feedback-Linearization-based controller, applied to the tilt-rotor (eight inputs), results in the extensive changes in the tilting angles, which are not expected in practice. To solve this problem, we introduce the novel concept UAV gait to restrict the tilting angles. The gait plan was initially to solve the control problems for quadruped (four-legged) robots. Transplanting this approach, accompanied by feedback linearization, to the tiltrotor may cause the well-known non-invertible problem in the decoupling matrix. In this research, we explore the invertible gait for the tiltrotor and apply feedback linearization to stabilize the attitude and the altitude. The equivalent conditions to achieve a full-rank decoupling matrix are deduced and simplified to a near zero roll and zero pitch. This paper proposed several invertible gaits to conduct the attitude-altitude control test. The accepted gaits within the region of interest are visualized. The experiment is simulated in Simulink, MATLAB. The results show the promising response in attitude and altitude. | Gait Analysis for A Tilt-rotor: The Dynamic Invertible Gait |
We review the current status of spin-averaged and spin-dependent parton distribution functions (PDFs) of the nucleon. After presenting the formalism used to fit PDFs in modern global data analyses, we discuss constraints placed on the PDFs by specific data types. We give representative examples of unpolarized and polarized PDFs and their errors, and list open questions in global QCD fitting. Finally, we anticipate how future facilities, with fixed-target and collider experiments, may impact our knowledge of PDFs and reduce their uncertainties. | Parton momentum and helicity distributions in the nucleon |
Eigenstates and energy levels of a square quantum billiard in a magnetic field, or with an Aharonov-Bohm flux line, are found in quasiclassical approximation, that is, for high enough energy. Explicit formulas for the energy levels and wavefunctions are found. A number of interesting states are shown, together with their wavefunctions. Some states are diamagnetic, others paramagnetic, still others both dia- and paramagnetic. Some states are strongly localized. Related systems and possible experiments are briefly mentioned. | Square billiard with a magnetic flux |
The problem of detecting chirps is present in many applications of Signal Processing. Proper denoising, which involves filtering the signals after their acquisition, improves the efficacy of their detection. This manuscript describes how a recently-published method of Time-Frequency Analysis (TFA) with reassignment, namely the Newton Time-Extracting Wavelet Transform (NTEWT), can be employed as a highly-performing chirp filter. The proposed methodology has the advantage of denoising chirps without distorting their instantaneous phases, as linear convolutional filters do. Numerical experiments have proven the efficacy of the proposed filter. After NTEWT-based filtering, the resolution of chirp detection with matched filtering is notably improved, even when the signals contain white noise. The computation times of the proposed numerical implementation of the NTEWT are lower than those reported in its seminar paper. | Application of the Newton Time-Extracting Wavelet Transform as a chirp filter |
In this paper, we establish a simple criterion for two $L$-functions $L_1$ and $L_2$ satisfying a functional equation (and some natural assumptions) to have infinitely many distinct zeros. Some related questions have already been answered in the particular case of Automorphic forms using so-called Converse Theorems. Deeper results can also be stated for elements of the Selberg class. However, we shall give here a general answer that do not use any advanced topics in analytic number theory. Therefore, this paper should be accessible to anyone who has some basic notions in measure-theory and advanced complex analysis. | A Theorem for Distinct Zeros of L-Functions |
Photoluminescence (PL) spectra of zinc oxide (ZnO) samples with different hydrogen peroxide (H2O2) treatment durations were measured to examine several point defects on the surface of the films. These results suggest successful oxidation through the reaction between oxygen radicals dissociated from H2O2 and the ZnO surface. To further confirm the defect induced gain mechanism, we fabricate highly transparent Schottky diodes, and measure the key diode characteristics. Photocurrents are measured under different wavelengths, and possible explanations of the high optical gain within the ultraviolet (UV) region are provided. | Optical Properties of ITO/ZnO Schottky Diode with Enhanced UV Photoresponse |
The randomized technique of color coding is behind state-of-the-art algorithms for estimating graph motif counts. Those algorithms, however, are not yet capable of scaling well to very large graphs with billions of edges. In this paper we develop novel tools for the `motif counting via color coding' framework. As a result, our new algorithm, Motivo, is able to scale well to larger graphs while at the same time provide more accurate graphlet counts than ever before. This is achieved thanks to two types of improvements. First, we design new succinct data structures that support fast common color coding operations, and a biased coloring trick that trades accuracy versus running time and memory usage. These adaptations drastically reduce the time and memory requirements of color coding. Second, we develop an adaptive graphlet sampling strategy, based on a fractional set cover problem, that breaks the additive approximation barrier of standard sampling. This strategy gives multiplicative approximations for all graphlets at once, allowing us to count not only the most frequent graphlets but also extremely rare ones. To give an idea of the improvements, in $40$ minutes Motivo counts $7$-nodes motifs on a graph with $65$M nodes and $1.8$B edges; this is $30$ and $500$ times larger than the state of the art, respectively in terms of nodes and edges. On the accuracy side, in one hour Motivo produces accurate counts of $\approx \! 10.000$ distinct $8$-node motifs on graphs where state-of-the-art algorithms fail even to find the second most frequent motif. Our method requires just a high-end desktop machine. These results show how color coding can bring motif mining to the realm of truly massive graphs using only ordinary hardware. | Motivo: fast motif counting via succinct color coding and adaptive sampling |
We define the "localized index" of longitudinal elliptic operators on Lie groupoids associated to Lie algebroid cohomology classes. We derive a topological expression for these numbers using the algebraic index theorem for Poisson manifolds on the dual of the Lie algebroid. Underlying the definition and computation of the localized index, is an action of the Hopf algebroid of jets around the unit space, and the characteristic map it induces on Lie algebroid cohomology. This map can be globalized to differentiable groupoid cohomology, giving a definition as well as a computation of the "global index". The correspondence between the "global" and "localized" index is given by the van Est map for Lie groupoids. | The localized longitudinal index theorem for Lie groupoids and the van Est map |
The transformation of a system from one state to another is often mediated by a bottleneck in the system's phase space. In chemistry these bottlenecks are known as \emph{transition states} through which the system has to pass in order to evolve from reactants to products. The chemical reactions are usually associated with configurational changes where the reactants and products states correspond, e.g., to two different isomers or the undissociated and dissociated state of a molecule or cluster. In this letter we report on a new type of bottleneck which mediates \emph{kinetic} rather than configurational changes. The phase space structures associated with such \emph{kinetic transition states} and their dynamical implications are discussed for the rotational vibrational motion of a triatomic molecule. An outline of more general related phase space structures with important dynamical implications is given. | Reaction dynamics through kinetic transition states |
We consider self-affine arcs in $\mathbb R^2$ and prove that violation of "inner" weak separation property for such arcs implies that the arc is a parabolic segment. Therefore, if a self-affine Jordan arc is not a parabolic segment, then it is the attractor of some multizipper. | On weak separation property for self-affine Jordan arcs |
A universal method for the concatenation of a sequence of Markov right processes is established. It is then applied to the continued pasting of two Markov right processes, which can be used for pathwise constructions of locally defined processes like Brownian motions on compact intervals. | Concatenation and Pasting of Right Processes |
While low-dimensional organometal halide perovskites are expected to open up new opportunities for a diverse range of device applications, like in their bulk counterparts, the toxicity of Pb-based halide perovskite materials is a significant concern that hinders their practical use. We recently predicted that lead triiodide (PbI$_3$) columns de-rived from trimethylsulfonium (TMS) lead triiodide (CH$_3$)$_3$SPbI$_3$ (TMSPbI$_3$) by stripping off TMS ligands should be semimetallic, and additionally ultrahigh negative differential resistance (NDR) can arise from the heterojunction composed of a TMSPbI$_3$ channel sandwiched by PbI$_3$ electrodes. Herein, we computationally explore whether similar material and device characteristics can be obtained from other one-dimensional halide perovskites based on non-Pb metal elements, and in doing so deepen the understanding of their mechanistic origins. First, scanning through several candidate metal halide inorganic frameworks as well as their parental form halide perovskites, we find that the germanium triiodide (GeI$_3$) column also assumes a semimetallic character by avoiding the Peierls distortion. Next, adopting the bundled nanowire GeI$_3$-TMSGeI$_3$-GeI$_3$ junction configuration, we obtain a drastically high peak current density and ultrahigh NDR at room temperature. Furthermore, the robustness and controllability of NDR signals under strain are revealed, establishing its potential for flexible electronics applications. It will be emphasized that, despite the performance metrics notably enhanced over those from the PbI$_3$-TMSPbI$_3$-PbI$_3$ case, these device characteristics still arise from the identical quantum hybridization NDR mechanism. | Quantum hybridization negative differential resistance from non-toxic halide perovskite nanowire heterojunctions and its strain control |
Watermarking is a crucial tool for safeguarding copyrights and can serve as a more aesthetically pleasing alternative to QR codes. In recent years, watermarking methods based on deep learning have proved superior robustness against complex physical distortions than traditional watermarking methods. However, they have certain limitations that render them less effective in practice. For instance, current solutions necessitate physical photographs to be rectangular for accurate localization, cannot handle physical bending or folding, and require the hidden area to be completely captured at a close distance and small angle. To overcome these challenges, we propose a novel deep watermarking framework dubbed \textit{Aparecium}. Specifically, we preprocess secrets (i.e., watermarks) into a pattern and then embed it into the cover image, which is symmetrical to the final decoding-then-extracting process. To capture the watermarked region from complex physical scenarios, a locator is also introduced. Besides, we adopt a three-stage training strategy for training convergence. Extensive experiments demonstrate that \textit{Aparecium} is not only robust against different digital distortions, but also can resist various physical distortions, such as screen-shooting and printing-shooting, even in severe cases including different shapes, curvature, folding, incompleteness, long distances, and big angles while maintaining high visual quality. Furthermore, some ablation studies are also conducted to verify our design. | Aparecium: Revealing Secrets from Physical Photographs |
Sagittarius A* (Sgr A*) is the supermassive black hole residing at the center of the Milky Way. It has been the main target of an extensive multiwavelength campaign we carried out in April 2007. Herein, we report the detection of a bright flare from the vicinity of the horizon, observed simultaneously in X-rays (XMM/EPIC) and near infrared (VLT/NACO) on April 4th for 1-2 h. For the first time, such an event also benefitted from a soft gamma-rays (INTEGRAL/ISGRI) and mid infrared (VLT/VISIR) coverage, which enabled us to derive upper limits at both ends of the flare spectral energy distribution (SED). We discuss the physical implications of the contemporaneous light curves as well as the SED, in terms of synchrotron, synchrotron self-Compton and external Compton emission processes. | Soft gamma-ray constraints on a bright flare from the Galactic Center supermassive black hole |
The spin filtering in storage rings is based on the multiple passage of a stored beam through a polarized internal gas target. Apart from the polarization by transmission, a unique geometrical feature of interaction with the target in such a filtering process, pointed out by H.O. Meyer \cite{Meyer}, is a scattering of stored particles within the beam. A rotation of the spin in the scattering process affects the polarization buildup. We derive here a quantum-mechanical evolution equation for the spin-density matrix of the stored beam which incorporates scattering within the beam. We show how the interplay of transmission and scattering with the beam changes from polarized electrons to polarized protons in the atomic target. After discussions of the FILTEX results on the filtering of stored protons \cite{FILTEX}, we comment on the strategy of spin filtering of antiprotons for the PAX experiment at GSI FAIR \cite{PAX-TP}. | Spin Filtering in Storage Rings |
We discuss Poincare three-brane solutions in D=5 M-Theory compactifications on Calabi-Yau (CY) threefolds with G-fluxes. We show that the vector moduli freeze at an attractor point. In the case with background flux only, the spacetime geometry contains a zero volume singularity with the three-brane and the CY space shrinking simultaneously to a point. This problem can be avoided by including explicit three-brane sources. We consider two cases in detail: a single brane and, when the transverse dimension is compactified on a circle, a pair of branes with opposite tensions. | Branes and Fluxes in D=5 Calabi-Yau Compactifications of M-Theory |
We derive a Khinchine-Pollaczek formula for random walks whose steps have a geometric left tail. The construction rests on the memory-less property of the geometric distribution. An example from a tandem queue modeling dynamic instability in microtubules is given. | Khintchine-Pollaczek formula for random walks whose steps have one geometric tail |
PAMELA and ATIC recently reported excesses in e+ e- cosmic rays. Since the interpretation in terms of DM annihilations was found to be not easily compatible with constraints from photon observations, we consider the DM decay hypothesis and find that it can explain the e+ e- excesses compatibly with all constraints, and can be tested by dedicated HESS observations of the Galactic Ridge. ATIC data indicate a DM mass of about 2 TeV: this mass naturally implies the observed DM abundance relative to ordinary matter if DM is a quasi-stable composite particle with a baryon-like matter asymmetry. Technicolor naturally yields these type of candidates. | Decaying Dark Matter can explain the electron/positron excesses |
Due to the enhancement of the couplings between Higgs boson and bottom quarks in the minimal sypersymmetric standard model (MSSM), the cross section of the process pp(p\bar{p}) \to h^0b(h^0\bar{b})+X at hadron colliders can be considerably enhanced. We investigated the production of Higgs boson associated with a single high-p_T bottom quark via subprocess bg(\bar{b}g) \to h^0b(h^0\bar{b}) at hadron colliders including the next-to-leading order (NLO) QCD corrections in MSSM. We find that the NLO QCD correction in the MSSM reaches 50%-70% at the LHC and 60%-85% at the Fermilab Tevatron in our chosen parameter space. | Higgs-Boson Production Associated with a Single Bottom Quark in Supersymmetric QCD |
Online social networks have increasing influence on our society, they may play decisive roles in politics and can be crucial for the fate of companies. Such services compete with each other and some may even break down rapidly. Using social network datasets we show the main factors leading to such a dramatic collapse. At early stage mostly the loosely bound users disappear, later collective effects play the main role leading to cascading failures. We present a theory based on a generalised threshold model to explain the findings and show how the collapse time can be estimated in advance using the dynamics of the churning users. Our results shed light to possible mechanisms of instabilities in other competing social processes. | Cascading collapse of online social networks |
We review the reduction of four-dimensional N=1 Seiberg duality to three dimensions focusing on the D brane engineering approach. We start with an overview of four-dimensional Seiberg duality for theories with various types of gauge groups and matter content both from a field-theoretic and a brane engineering point of view. Then we describe two families of N=2 three-dimensional dualities, namely Giveon-Kutasov-like and Aharony-like dualities. The last part of our discussion is devoted to the 4D/3D reduction of the dualities studied above. We discuss both the analysis at finite radius, crucial for preserving the duality in the dimensional reduction, and the zero-size limit that must be supported by a real mass flow and a Higgsing, which can differ case by case. We show that this mechanism is reproduced in the brane description by T-duality, supplying a unified picture for all the different cases. As a bonus we show that this analysis provides a brane description for Aharony-like dualities. | String theory and the 4D/3D reduction of Seiberg duality. A Review |
We consider the continuity equation for open chaotic quantum systems in the semiclassical limit. First we explicitly calculate a semiclassical expansion for the probability current density using an expression based on classical trajectories. The current density is related to the survival probability via the continuity equation, and we show that this relation is satisfied within the semiclassical approximation to all orders. For this we develop recursion relation arguments which connect the trajectory structures involved for the survival probability, which travel from one point in the bulk to another, to those structures involved for the current density, which travel from the bulk to the lead. The current density can also be linked, via another continuity equation, to a correlation function of the scattering matrix whose semiclassical approximation is expressed in terms of trajectories that start and end in the lead. We also show that this continuity equation holds to all orders. | The semiclassical continuity equation for open chaotic systems |
Electrical resistivity and magnetoresistance(MR) in polyaniline(PANI) with carbon nanotube(CNT) and functionalized carbon nanotube(fCNT) composites have been studied for different weight percentage down to the temperature 4.2K and up to magnetic field 5T. Resistivity increases significantly in composite at low temperature due to functionalization of CNT compare to only CNT. Interestingly transition from negative to positive magnetoresistance has been observed for 10wt% of composite as the effect of disorder is more in fCNT/PANI. This result depicts that the MR has strong dependency on disorder in the composite system. The transition of MR has been explained in the basis of polaron-bipolaron model. The long range Coulomb interaction between two polarons screened by disorder in the composite of fCNT/PANI, increases the effective on-site Coulomb repulsion energy to form bipolaron which leads to change the sign of MR from negative to positive. | Negative to Positive Magnetoresistance transition in Functionalization of Carbon nanotube and Polyaniline Composite |
We revisit the sharp-interface continuum thermodynamics of two-phase multicomponent fluid systems with interfacial mass. Since the published work is not fully consistent, we provide a rigorous derivation of the local balance equations and the entropy production rates, including all relevant steps and mathematical tools. Special emphasis is put on an axiomatic form of the entropy principle which, at the same time, allows for an efficient closure process. The latter builds on an appropriate representation of the entropy production rates, which is based on structural information being obtained from a more refined model which includes partial momenta and is given in an appendix. The closure relations obtained for the one-sided bulk-interface species transfer rates are further investigated, which leads to a novel model for mass transfer at fluid interfaces, influenced by the presence of adsorbed surface active agents. We finally compare our results in detail with the existing literature on continuum thermodynamics of two-phase multicomponent fluid systems with interfacial mass. | Sharp-Interface Continuum Thermodynamics of multicomponent fluid systems with interfacial mass |
We assess current experimental constraints on the bi-doublet + singlet model of top compositeness previously proposed in the literature. This model extends the standard model's spectrum by adding a custodially-embedded vector-like electroweak bi-doublet of quarks and a vector-like electroweak singlet quark. While either of those states alone would produce a model in tension with constraints from precision electroweak data, in combination they can produce a viable model. We show that current precision electroweak data, in the wake of the Higgs discovery, accommodate the model and we explore the impact of direct collider searches for the partners of the top quark. | Direct Search Implications for a Custodially-Embedded Composite Top |
How to account for the matter predominance of our Universe is a fundamental issue at the core of our existence. One condition is CP violation, but the Standard Model falls short by more than $10^{-10}$. Taking cue from a recent result from the $B$ factories, we find that a fourth quark generation can provide enhancement by a factor of $10^{13}$ or more. This could be the source of CP violation for the baryon asymmetry of the Universe. The main source of enhancement is the large Yukawa couplings of the heavy $t^\prime$ and $b^\prime$ quarks. With indications for a new, large CP violating phase $\sin2\Phi_{B_s}$ emerging at the Tevatron, our suggestion can be verified or refuted at the LHC in the next few years. | Source of CP Violation for the Baryon Asymmetry of the Universe |
We compare games under delayed control and delay games, two types of infinite games modelling asynchronicity in reactive synthesis. Our main result, the interreducibility of the existence of sure winning strategies for the protagonist, allows to transfer known complexity results and bounds on the delay from delay games to games under delayed control, for which no such results had been known. We furthermore analyze existence of randomized strategies that win almost surely, where this correspondence between the two types of games breaks down. | Strategies Resilient to Delay: Games under Delayed Control vs. Delay Games |
Vagueness and ambiguity in privacy policies threaten the ability of consumers to make informed choices about how businesses collect, use, and share their personal information. The California Consumer Privacy Act (CCPA) of 2018 was intended to provide Californian consumers with more control by mandating that businesses (1) clearly disclose their data practices and (2) provide choices for consumers to opt out of specific data practices. In this work, we explore to what extent CCPA's disclosure requirements, as implemented in actual privacy policies, can help consumers to answer questions about the data practices of businesses. First, we analyzed 95 privacy policies from popular websites; our findings showed that there is considerable variance in how businesses interpret CCPA's definitions. Then, our user survey of 364 Californian consumers showed that this variance affects the ability of users to understand the data practices of businesses. Our results suggest that CCPA's mandates for privacy disclosures, as currently implemented, have not yet yielded the level of clarity they were designed to deliver, due to both vagueness and ambiguity in CCPA itself as well as potential non-compliance by businesses in their privacy policies. | Fighting the Fog: Evaluating the Clarity of Privacy Disclosures in the Age of CCPA |
The measurement of possible Higgs sector CP-violation in the tau decay channels at the LHC is investigated. A CP-violating effect would manifest itself in these decay modes in characteristic spin-spin correlations of the tau lepton pairs which can be accessed using the momenta and impact parameters of the charged tau decay particles. We examine a CP-sensitive observable for a 125 GeV Higgs boson resonance in the gluon fusion channel at the LHC. Furthermore, we consider the distribution of this observable for the irreducible Drell-Yan background. By splitting these events into two categories we obtain two different distributions which can be used for calibration purposes. Finally, we estimate the achievable precision of the scalar-pseudo-scalar mixing angle of the tau decay channel for Run II and the high luminosity run of the LHC. | Determination of the Higgs CP-mixing angle in the tau decay channels |
In this paper we present some results obtained in a previous paper about the Cartan's approach to Riemannian normal coordinates and our conformal transformations among pseudo-Riemannian manifolds. We also review the classical and the quantum angular momenta of a particle obtained as a consequence of geometry, without postulates. We present four classical principles, identifed as new results obtained from geometry. One of them has properties similar Heisemberg's uncertaintly principle and another has some properties similar to Bohr's principle. Our geometric result can be considered as a possible starting point toward a quantum theory without forces. | Physical Principles Based on Geometric Properties |
The coherent nonlinear dynamics of Abrikosov vortices in asymmetric pinning nanolandscapes is studied by theoretical modeling and combined microwave and dc electrical resistance measurements. The problem is considered on the basis of a single-vortex Langevin equation within the framework of a stochastic model of anisotropic pinning. When the distance over which Abrikosov vortices are driven during one half ac cycle coincides with one or a multiple of the nanostructure period, Shapiro steps appear in the current-voltage curves (CVCs) as a general feature of systems whose evolution in time can be described in terms of a particle moving in a periodic potential under combined dc and ac stimuli. While a dc voltage appears in response to the ac drive, the addition of a dc bias allows one to diminish the rectified voltage and eventually to change its sign when the extrinsic dc bias-induced asymmetry of the pinning potential starts to dominate the intrinsic one. This rectified negative voltage in the CVCs becomes apparent as \emph{zero-bias} Shapiro steps, which are theoretically predicted and experimentally observed for the first time. | Zero-bias Shapiro steps in asymmetric pinning nanolandscapes |
We show that the zeroth law of thermodynamics holds within an alternative version of nonextensive statistical mechanics based on {\it incomplete probability distribution}. The generalized zeroth law leads to a generalized definition of thermodynamic functions which are possible to be used for systems with important nonextensivity (nonadditivity) in energy, volume or other external variables. | Incomplete nonextensive statistics and zeroth law of thermodynamics |
In a wide class of paired comparisons, especially in the sports games, in which all subjects are divided into several groups, the intragroup comparisons are dense and the intergroup comparisons are sparse. Typical examples include the NFL regular season. Motivated by these situations, we propose group sparsity for paired comparisons and show the consistency and asymptotical normality of the maximum likelihood estimate in the Bradley-Terry model when the number of parameters goes to infinity in this paper. Simulations are carried out to illustrate the group sparsity and asymptotical results. | Grouped sparse paired comparisons in the Bradley-Terry model |
The use of simplified models of turbulent flows provides an appealing possibility to study the collision rate of turbulent suspensions, especially in conditions relevant to astrophysics, which require large time scale separations. To check the validity of such approaches, we used a direct numerical simulation (DNS) velocity field, which satisfies the Navier-Stokes equations (although it neglects the effect of the suspended particles on the flow field), and a kinematic simulation (KS) velocity field, which is a random field designed so that its statistics are in accord with the Kolmogorov theory for fully-developed turbulence. In the limit where the effects of particle inertia (characterised by the Stokes number) are negligible, the collision rates from the two approaches agree. As the Stokes number St increases, however, we show that the DNS collision rate exceeds the KS collision rate by orders of magnitude. We propose an explanation for this phenomenon and explore its consequences. We discuss the collision rate $R$ for particles in high Reynolds number flows at large Stokes number, and present evidence that $R\propto \sqrt{{\rm St}}$. | Collision rate for suspensions at large Stokes numbers - comparing Navier-Stokes and synthetic turbulence |
In this article the production of $K^+$ at energies close to the threshold is studied in detail. The production mechanisms, the influence of in-medium effects, cross sections, the nuclear equation of state and the dynamics of the nucleons on the kaon dynamics are discussed. A special regard will be taken on the collision of Au+Au at 1.5 GeV, a reaction that has recently been analyzed in detail by experiments performed by the KaoS and FOPI collaborations at the SIS accelerator at GSI. | Dynamics of $K^+$ Production in Heavy Ion Collisions close to Threshold |
Human Computer Interaction (HCI) is the biggest goal of computer vision researchers. Features form the different facial images are able to provide a very deep knowledge about the activities performed by the different facial movements. In this paper we presented a technique for feature extraction from various regions of interest with the help of Skin color segmentation technique, Thresholding, knowledge based technique for face recognition. | ROI Segmentation for Feature Extraction from Human Facial Images |
The variant of phenomenological theory of humankind future existence after time of demographic transition based on treating the time of demographic transition as a point of phase transition and taking into account an appearing of the new phase of mankind is proposed. The theory based on physical phenomenological theories of phase transitions and classical equations for system predatory-preys for two phases of mankind, take into account assumption about a multifractal nature of the set of number of people in temporal axis and contains control parameters. The theory includes scenario of destroying of existent now human population by new phase of humanity and scenario of old and new phases co-existence. In particular cases when the new phase of mankind is absent the equations of theory may be formulated as equations of Kapitza, Foerster, Hoerner, Kobelev and Nugaeva, Johansen and Sornette phenomenological theories of growth of mankind. | What Future Expects Humanity After the Demographic Transition Time? |
A recently introduced recurrence-relation ansatz applied to the Jaynes-Cummings-Hubbard model is here applied to the Bose-Hubbard model that reduced the model to an easily soluble model. The results obtained for the two-point density correlations resemble somewhat those obtained recently also but in a much more complicated fashion. Our ansatz may be of value for the solution of many-body quantum mechanical problems. | Nearest-Neighbor Tunneling Ansatz in the Bose-Hubbard Mode |
Light neutral mediators, with mass $\lesssim 1$ GeV, are common features of extensions to the Standard Model (SM). Current astrophysical and terrestrial experiments have constrained the model parameter space, and planned experiments around the world promise continued improvement in sensitivity. In this paper we study the prospects for probing light neutral mediators using terrestrial stopped pion and reactor sources in combination with ultra-low threshold nuclear and electron recoil detectors. We show that the coherent neutrino-nucleus and neutrino-electron scattering channels provide complementary sensitivity to light mediators. With low threshold detectors, we show that most stringent bounds on models arise from the nuclear scattering process, improving upon previous bounds from electron scattering of solar neutrinos by nearly an order of magnitude for mediator masses $\gtrsim 0.1$ GeV. | Probing light mediators at ultra-low threshold energies with coherent elastic neutrino-nucleus scattering |
We investigate the temperature distribution of CO-dark molecular hydrogen (H2) in a series of disk galaxies simulated using the AREPO moving-mesh code. In conditions similar to those in the Milky Way, we find that H2 has a flat temperature distribution ranging from 10 - 100 K. At $T < 30$ K the gas is almost fully molecular and has a high CO content, whereas at $T > 30$ K, the H2 fraction spans a broader range and the CO content is small, allowing us to classify gas in these two regimes as CO-bright and CO-dark, respectively. The mean sound speed in the CO-dark H2 is 0.64 km/s, significantly lower than the value in the cold atomic gas (1.15 km/s), implying that the CO-dark molecular phase is more susceptible to turbulent compression and gravitational collapse than its atomic counterpart. We further show that the temperature of the CO-dark H2 is highly sensitive to the strength of the interstellar radiation field, but that conditions in the CO-bright H2 remain largely unchanged. Finally, we examine the usefulness of the [CII] and [OI] fine structure lines as tracers of the CO-dark gas. We show that in Milky Way-like conditions, diffuse [CII] emission from this gas should be detectable. However, it is a problematic tracer of this gas, as there is only a weak correlation between the brightness of the emission and the H2 surface density. The situation is even worse for the [OI] line, which shows no correlation with the H2 surface density. | CO-dark gas and molecular filaments in Milky Way-type galaxies - II: The temperature distribution of the gas |
We investigate the dynamics of negative surface discharges in air through numerical simulations with a 2D fluid model. A geometry consisting of a flat dielectric embedded between parallel-plate electrodes is used. Compared to negative streamers in bulk gas, negative surface streamers are observed to have a higher electron density, a higher electric field and higher propagation velocity. On the other hand, their maximum electric field and velocity are lower than for positive surface streamers. In our simulations, negative surface streamers are slower for larger relative permittivity. Negative charge accumulates on a dielectric surface when a negative streamer propagates along it, which can lead to a high electric field inside the dielectric. If we initially put negative surface charge on the dielectric, the growth of negative surface discharges is delayed or inhibited. Positive surface charge has the opposite effect. | A Computational Study of Negative Surface Discharges: Characteristics of Surface Streamers and Surface Charges |
We report specific heat measurements of the heavy fermion superconductor CeCoIn5 in the vicinity of the superconducting critical field H_{c2}, with magnetic field in the [110], [100], and [001] directions, and at temperatures down to 50 mK. The superconducting phase transition changes from second to first order for field above 10 T for H || [110] and H || [100]. In the same range of magnetic field we observe a second specific heat anomaly within the superconducting state. We interpret this anomaly as a signature of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) inhomogeneous superconducting state. We obtain similar results for H || [001], with FFLO state occupying a smaller part of the phase diagram. | Fulde-Ferrell-Larkin-Ovchinnikov Superconducting State in CeCoIn5 |
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