ShantanuT01/DACTYL-Pretraining huggingface dataset:
It is shown that the interplay of a confining potential with a periodic potential leads for free particles to states spatially confined on a fraction of the total extension of the system. A more complex `slicing' of the system can be achieved by increasing the period of the lattice potential. These results are especially relevant for fermionic systems, where interaction effects are in general strongly reduced for a single species at low temperatures.
We propose DoubleFusion, a new real-time system that combines volumetric dynamic reconstruction with data-driven template fitting to simultaneously reconstruct detailed geometry, non-rigid motion and the inner human body shape from a single depth camera. One of the key contributions of this method is a double layer representation consisting of a complete parametric body shape inside, and a gradually fused outer surface layer. A pre-defined node graph on the body surface parameterizes the non-rigid deformations near the body, and a free-form dynamically changing graph parameterizes the outer surface layer far from the body, which allows more general reconstruction. We further propose a joint motion tracking method based on the double layer representation to enable robust and fast motion tracking performance. Moreover, the inner body shape is optimized online and forced to fit inside the outer surface layer. Overall, our method enables increasingly denoised, detailed and complete surface reconstructions, fast motion tracking performance and plausible inner body shape reconstruction in real-time. In particular, experiments show improved fast motion tracking and loop closure performance on more challenging scenarios.
Deep neural networks have exhibited promising performance in image super-resolution (SR) due to the power in learning the non-linear mapping from low-resolution (LR) images to high-resolution (HR) images. However, most deep learning methods employ feed-forward architectures, and thus the dependencies between LR and HR images are not fully exploited, leading to limited learning performance. Moreover, most deep learning based SR methods apply the pixel-wise reconstruction error as the loss, which, however, may fail to capture high-frequency information and produce perceptually unsatisfying results, whilst the recent perceptual loss relies on some pre-trained deep model and they may not generalize well. In this paper, we introduce a mask to separate the image into low- and high-frequency parts based on image gradient magnitude, and then devise a gradient sensitive loss to well capture the structures in the image without sacrificing the recovery of low-frequency content. Moreover, by investigating the duality in SR, we develop a dual reconstruction network (DRN) to improve the SR performance. We provide theoretical analysis on the generalization performance of our method and demonstrate its effectiveness and superiority with thorough experiments.
Using dark matter only N-body cosmological simulations, we measure the pericentre distance of dark matter halos on their first infall into group and cluster halos. We find that the pericentre distance (R$_{\rm{peri}}$) is an important parameter as it significantly affects the strength of tidal mass loss in dense environments, and likely other environmental mechanisms as well. We examine what determines the R$_{\rm{peri}}$ value and find that, for most infallers, the dominant parameter is V$_{\rm{\perp}}$, the tangential component of the orbital velocity as the halo enters the group/cluster halo for the first time. This means that the strength of tidal stripping acting near the cores of groups/clusters are strongly influenced by the external peculiar velocity field of the large scale structure surrounding them, which differs between clusters, and is sensitive to the mass ratio of infaller to host. We find that filament feeding also partially contributes to feeding in low V$_{\rm{\perp}}$ halos. Dynamical friction can also play a role in reducing R$_{\rm{peri}}$ but this is only significant for those few relatively massive infallers ($>$10\% of the mass of their host). These results highlight how the response of galaxies to dense environments will sensitively depend on dynamics inherited from far outside those dense environments.
The dynamical consistency of the non-projectable version of Horava gravity is investigated by focusing on the asymptotically flat case. It is argued that for generic solutions of the constraint equations the lapse must vanish asymptotically. We then consider particular values of the coupling constants for which the equations are tractable and in that case we prove that the lapse must vanish everywhere -- and not only at infinity. Put differently, the Hamiltonian constraints are generically all second-class. We then argue that the same feature holds for generic values of the couplings, thus revealing a physical inconsistency of the theory. In order to cure this pathology, one might want to introduce further constraints but the resulting theory would then lose much of the appeal of the original proposal by Horava. We also show that there is no contradiction with the time reparametrization invariance of the action, as this invariance is shown to be a so-called "trivial gauge symmetry" in Horava gravity, hence with no associated first-class constraints.
We derive a theory that describes homogeneous nucleation of grain boundary (GB) phases. Our analysis takes account of the energy resulting from the GB phase junction, the line defect separating two different GB structures, which is necessarily a dislocation as well as an elastic line force due to the jump in GB stresses. The theory provides analytic forms for the elastic interactions and the core energy of the GB phase junction that, along with the change in GB energy, determine the nucleation barrier. We apply the resulting nucleation model to simulations of GB phase transformations in tungsten. Our theory explains why under certain conditions GBs cannot spontaneously change their structure even to a lower energy state.
Using extensions of the Newman-Penrose and Geroch-Held-Penrose formalisms to five dimensions, we invariantly classify all Petrov type $D$ vacuum solutions for which the Riemann tensor is isotropic in a plane orthogonal to a pair of Weyl alligned null directions
Numerical simulations of minor mergers, typically having mass ratios greater than 3:1, predict little enhancement in the global star formation activity. However, these models also predict that the satellite galaxy is more susceptible to the effects of the interaction than the primary. We use optical integral field spectroscopy and deep optical imaging to study the NGC7771+NGC7770 interacting system (~10:1 stellar mass ratio) to test these predictions. We find that the satellite galaxy NGC7770 is currently experiencing a galaxy-wide starburst with most of the optical light being from young and post-starburst stellar populations(<1Gyr). This galaxy lies off of the local star-forming sequence for composite galaxies with an enhanced integrated specific star formation rate. We also detect in the outskirts of NGC7770 Halpha emitting gas filaments. This gas appears to have been stripped from one of the two galaxies and is being excited by shocks. All these results are consistent with a minor-merger induced episode(s) of star formation in NGC7770 after the first close passage. Such effects are not observed on the primary galaxy NGC7771.
In order to better understand a complex theory like quantum mechanics, it is sometimes useful to take a step back and create alternative theories, with more intuitive foundations, and examine which features of quantum mechanics can be reproduced by such a foil theory. A prominent example is Spekkens' toy theory, which is based off a simple premise: "What if we took a common classical theory and added the uncertainty principle as a postulate?" In other words, the theory imposes an epistemic restriction on our knowledge about a physical system: only half of the variables can ever be known to an observer. Like good science fiction, from this simple principle a rich behaviour emerges, most notoriously when we compose several systems. The toy theory emulates some aspects of quantum non-locality, although crucially it is still a non-contextual model. In this pedagogical review we consolidate different approaches to Spekkens' toy theory, including the stabilizer formalism and the generalization to arbitrary dimensions, completing them with new results where necessary. In particular, we introduce a general characterization of measurements, superpositions and entanglement in the toy theory.
Radiative shock waves in the Cygnus Loop and other supernova remnants show different morphologies in [O III] and H{\alpha} emission. We use HST spectra and narrowband images to study the development of turbulence in the cooling region behind a shock on the west limb of the Cygnus Loop. We refine our earlier estimates of shock parameters that were based upon ground-based spectra, including ram pressure, vorticity and magnetic field strength. We apply several techniques, including Fourier power spectra and the Rolling Hough Transform, to quantify the shape of the rippled shock front as viewed in different emission lines. We assess the relative importance of thermal instabilities, the thin shell instability, upstream density variations, and upstream magnetic field variations in producing the observed structure.
We perform a series of simplified numerical experiments to explore how rotation impacts on the three-dimensional (3D) hydrodynamics of core-collapse supernovae. For the sake of our systematic study, we employ a light-bulb scheme to trigger explosions and a three-flavor neutrino leakage scheme to treat deleptonization effects and neutrino losses from proto-neutron star interior. Using a 15 solar mass progenitor, we compute thirty models in 3D with a wide variety of initial angular momentum and light-bulb neutrino luminosity. We find that the rotation can help onset of neutrino-driven explosions for the models in which the initial angular momentum is matched to that obtained in recent stellar evolutionary calculations (0.3-3 rad/s at the center). For the models with larger initial angular momentum, the shock surface deforms to be more oblate due to larger centrifugal force. This makes not only a gain region more concentrated around the equatorial plane, but also the mass in the gain region bigger. As a result, buoyant bubbles tend to be coherently formed and rise in the equatorial region, which pushes the revived shock ever larger radii until a global explosion is triggered. We find that these are the main reasons that the preferred direction of explosion in 3D rotating models is often perpendicular to the spin axis, which is in sharp contrast to the polar explosions around the axis that was obtained in previous 2D simulations.
We study the nonlinear stochastic heat equation in the spatial domain $\mathbb {R}$, driven by space-time white noise. A central special case is the parabolic Anderson model. The initial condition is taken to be a measure on $\mathbb {R}$, such as the Dirac delta function, but this measure may also have noncompact support and even be nontempered (e.g., with exponentially growing tails). Existence and uniqueness of a random field solution is proved without appealing to Gronwall's lemma, by keeping tight control over moments in the Picard iteration scheme. Upper bounds on all $p$th moments $(p\ge2)$ are obtained as well as a lower bound on second moments. These bounds become equalities for the parabolic Anderson model when $p=2$. We determine the growth indices introduced by Conus and Khoshnevisan [Probab. Theory Related Fields 152 (2012) 681-701].
Using very long molecular dynamics simulation runs, temperature protocols spanning up to five orders of magnitude in time-scales are performed to investigate thermally activated structural relaxation in a model amorphous solid. The simulations demonstrate significant local structural excitations as a function of increasing temperature and show that enthalpy rather than energy is primarily responsible for relaxation. The observed enthalpy changes are of the order seen in experiment, and can be correlated with the level of internal hydrostatic stress homogenization and icosahedral content within the solid.
Stability with respect to neutron emission is studied for highly neutron-excessive Oxygen isotopes in the framework of Hartree-Fock-Bogoliubov approach with Skyrme forces Sly4 and Ska. Our calculations show increase of stability around 40O.
We explore some of the constraints imposed by positivity of the QCD measure (Weingarten's inequalities) on the parameters defining chiral perturbation theory. We find, in particular, that $2 m_q (\mu)\leq B_0(\mu) Z(\mu)$. The use of further properties of the exact fermion propagator yields information on some higher order parameters.
This paper is concerned with the existence of globally smooth solutions for the second boundary value problem for Monge-Ampere equations and the application to regularity of potentials in optimal transportation. The cost functions satisfy a weak form of our condition A3, under which we proved interior regularity in a recent paper with Xi-nan Ma. Consequently they include the quadratic cost function case of Caffarelli and Urbas as well as the various examples in the earlier work. The approach is through the derivation of global estimates for second derivatives of solutions.
Suppose $G$ is a simple graph with $n$ vertices, $m$ edges, and rank $r$. Let $\chi_G(t)=a_0t^n-a_1t^{n-1}+\cdots +(-1)^ra_rt^{n-r}$ be the chromatic polynomial of $G$. For $q,k\in \Bbb{Z}$ and $0\le k\le q+r+1$, we obtain a sharp two-side bound for the partial binomial sum of the coefficient sequence, that is, \[ {r+q\choose k}\le \sum_{i=0}^{k}{q\choose k-i}a_{i}\le {m+q\choose k}. \] Indeed, this bound holds for the characteristic polynomial of hyperplane arrangements and matroids, and its weak version can be generalized to the characteristic polynomial of toric arrangements and arithmetic matroids. We also propose a problem on the geometric interpretation of the above bound.
We study biased, diffusive transport of Brownian particles through narrow, spatially periodic structures in which the motion is constrained in lateral directions. The problem is analyzed under the perspective of the Fick-Jacobs equation which accounts for the effect of the lateral confinement by introducing an entropic barrier in a one dimensional diffusion. The validity of this approximation, being based on the assumption of an instantaneous equilibration of the particle distribution in the cross-section of the structure, is analyzed by comparing the different time scales that characterize the problem. A validity criterion is established in terms of the shape of the structure and of the applied force. It is analytically corroborated and verified by numerical simulations that the critical value of the force up to which this description holds true scales as the square of the periodicity of the structure. The criterion can be visualized by means of a diagram representing the regions where the Fick-Jacobs description becomes inaccurate in terms of the scaled force versus the periodicity of the structure.
Many gamma ray bursts (GRBs) have been observed with the Burst-Alert and X-Ray telescopes of the Swift satellite. The successive `pulses' of these GRBs end with a fast decline and a fast spectral softening, until they are overtaken by another pulse, or the last pulse's decline is overtaken by a less rapidly-varying `afterglow'. The fast decline-phase has been attributed, in the currently-explored standard fireball model of GRBs, to `high-latitude' synchrotron emission from a collision of two conical shells. This high latitude emission does not explain the observed spectral softening. In contrast, the temporal behaviour and the spectral evolution during the fast-decline phase agree with the predictions of the cannonball model of GRBs.
The high dimensionality of hyperspectral images consisting of several bands often imposes a big computational challenge for image processing. Therefore, spectral band selection is an essential step for removing the irrelevant, noisy and redundant bands. Consequently increasing the classification accuracy. However, identification of useful bands from hundreds or even thousands of related bands is a nontrivial task. This paper aims at identifying a small set of highly discriminative bands, for improving computational speed and prediction accuracy. Hence, we proposed a new strategy based on joint mutual information to measure the statistical dependence and correlation between the selected bands and evaluate the relative utility of each one to classification. The proposed filter approach is compared to an effective reproduced filters based on mutual information. Simulations results on the hyperpectral image HSI AVIRIS 92AV3C using the SVM classifier have shown that the effective proposed algorithm outperforms the reproduced filters strategy performance.   Keywords-Hyperspectral images, Classification, band Selection, Joint Mutual Information, dimensionality reduction ,correlation, SVM.
Context. Global MHD simulations show Kelvin-Helmholtz (KH) instabilities at the contact surface of two merging neutron stars. That region has been identified as the site of efficient amplification of magnetic fields. However, these global simulations, due to numerical limitations, were unable to determine the saturation level of the field strength, and thus the possible back-reaction of the magnetic field onto the flow. Aims. We investigate the amplification of initially weak fields in KH unstable shear flows, and the back-reaction of the field onto the flow. Methods. We use a high-resolution ideal MHD code to perform 2D and 3D local simulations of shear flows. Results. In 2D, the magnetic field is amplified in less than 0.01ms until it reaches locally equipartition with the kinetic energy. Subsequently, it saturates due to resistive instabilities that disrupt the KH vortex and decelerate the shear flow on a secular time scale. We determine scaling laws of the field amplification with the initial field strength and the grid resolution. In 3D, this hydromagnetic mechanism may be dominated by purely hydrodynamic instabilities limiting the amplification. We find maximum magnetic fields of 10^16 G locally, and r.m.s. maxima within the box of 10^15 G. However, such strong fields exist only for a short period. In the saturated state, the magnetic field is mainly oriented parallel to the shear flow for strong initial fields, while weaker initial fields tend to lead to a more balanced distribution of the field energy. In all models the flow shows small-scale features. The magnetic field is at most in equipartition with the decaying shear flow. (abridged)
Energy band structure of the bilayer graphene superlattices with $\delta$-function magnetic barriers and zero average magnetic flux is studied within the four-band continuum model, using the transfer matrix method. The periodic magnetic potential effects on the zero-energy Dirac point of pristine bilayer graphene are exactly analyzed. Magnetic potential is shown also to generate finite-energy Dirac points at the edges of Brillouin zone the positions of which and the related dispersions are determined in the case of symmetric potentials.
Two-loop electroweak corrections to the electron, muon, and tau lepton anomalous magnetic moments have been computed recently. Effects of hadronic contributions to the photon propagator in two-loop QED corrections have also been reanalysed. The common technique used in both calculations was asymptotic expansion of Feynman diagrams in the ratio of lepton mass to some heavy mass scale. In this talk we present some details of this method paying particular attention to the expansion of multi-scale diagrams.
We investigated properties of heavy rare-gases, Ne, Ar, Kr, Xe and Rn, adsorbed on graphene substrates using molecular dynamics. We gathered evidences of commensurate solids for Ne and Kr adlayers, one of them is given by a typical behavior of the nearest neighbor distance of the adatoms. The specific heat and the melting temperature were calculated and both indicate continuous melting for all heavy noble-gases studied. We also determined the distance between the adlayer and the substrate.
The nonequilibrium dynamics of molecular devices is studied in the framework of a generic model for single-molecule transistors: a resonant level coupled by displacement to a single vibrational mode. In the limit of a broad level and in the vicinity of the resonance, the model can be controllably reduced to a form quadratic in bosonic operators, which in turn is exactly solvable. The response of the system to a broad class of sudden quenches and ac drives is thus computed in a nonperturbative manner, providing an asymptotically exact solution in the limit of weak electron-phonon coupling. From the analytic solution we are able to (1) explicitly show that the system thermalizes following a local quantum quench, (2) analyze in detail the time scales involved, (3) show that the relaxation time in response to a quantum quench depends on the observable in question, and (4) reveal how the amplitude of long-time oscillations evolves as the frequency of an ac drive is tuned across the resonance frequency. Explicit analytical expressions are given for all physical quantities and all nonequilibrium scenarios under study.
Current results from the Lyman alpha forest assume that the primordial power spectrum of density perturbations follows a simple power law form, with running. We present the first analysis of Lyman alpha data to study the effect of relaxing this strong assumption on primordial and astrophysical constraints. We perform a large suite of numerical simulations, using them to calibrate a minimally parametric framework for describing the power spectrum. Combined with cross-validation, a statistical technique which prevents over-fitting of the data, this framework allows us to reconstruct the power spectrum shape without strong prior assumptions. We find no evidence for deviation from scale-invariance; our analysis also shows that current Lyman alpha data do not have sufficient statistical power to robustly probe the shape of the power spectrum at these scales. In contrast, the ongoing Baryon Oscillation Sky Survey (BOSS) will be able to do so with high precision. Furthermore, this near-future data will be able to break degeneracies between the power spectrum shape and astrophysical parameters.
We investigate the \textit{edge group irregularity strength} ($es_g(G)$) of graphs, i.e. the smallest value of $s$ such that taking any Abelian group $\mathcal{G}$ of order $s$, there exists a function $f:V(G)\rightarrow \mathcal{G}$ such that the sums of vertex labels at every edge are distinct. In this note we provide some upper bounds on $es_g(G)$ as well as for edge irregularity strength $es(G)$ and harmonious order $\rm{har}(G)$.
We propose a new approach to extract the wave functions of resonances by the bound state approximation which gives the mixed states of the resonance components and the continuum ones. In our approach, on the basis of the method of analytic continuation in the coupling constant (ACCC), we construct Pad\'e rational function by adopting the positive energies as well as the negative ones. We report the result of the application of this new method to the second $2^+$ state of $^{12}$C which was studied with the ACCC method in our previous work. It is found that the resonance parameters obtained by the ACCC method are well reproduced by the new method. Some advantages over the ACCC method are also shown.
We discuss a new method to compute the canonical height of an algebraic point on a hyperelliptic jacobian over a number field. The method does not require any geometrical models, neither $p$-adic nor complex analytic ones. In the case of genus 2 we also present a version that requires no factorisation at all. The method is based on a recurrence relation for the `division polynomials' associated to hyperelliptic jacobians, and a diophantine approximation result due to Faltings.