ShantanuT01/DACTYL-Pretraining huggingface dataset:
In this comprehensive and detailed study, vacancy-mediated self-diffusion of A- and B-elements in 'triple-defect' B2-ordered ASB(1-S) binaries is simulated by means of a kinetic Monte Carlo (KMC) algorithm involving atomic jumps to nearest-neighbour (nn) and next-nearest-neighbour (nnn) vacancies. The systems are modelled with an Ising-type Hamiltonian with nn and nnn pair interactions complete with migration barriers dependent on local configurations. Self-diffusion is simulated at equilibrium and temperature-dependent vacancy concentrations are generated by means of a Semi Grand Canonical MC (SGCMC) code. The KMC simulations reproduced the phenomena observed experimentally in Ni-Al intermetallics being typical representatives of the 'triple-defect' binaries. In particular, they yielded the characteristic 'V'-shapes of the isothermal concentration dependencies of A- and B-atom diffusivities, as well as the strong enhancement of the B-atom diffusivity in B-rich systems. The atomistic origins of the phenomenon, as well as other features of the simulated self-diffusion such as temperature and composition dependences of tracer correlation factors and activation energies are analyzed in depth in terms of a number of nanoscopic parameters that are able to be tuned and monitored exclusively with atomistic simulations. The roles of equilibrium and kinetic factors in the generation of the observed features are clearly distinguished and elucidated.
We present a novel dark matter candidate, an Elastically Decoupling Relic (ELDER), which is a cold thermal relic whose present abundance is determined by the cross-section of its elastic scattering on Standard Model particles. The dark matter candidate is predicted to have a mass ranging from a few to a few hundred MeV, and an elastic scattering cross-section with electrons, photons and/or neutrinos in the $10^{-3}-1$ fb range.
Before cosmic reionization, hydrogen atoms acquire a spin polarization quadrupole through interaction with the anisotropic 21-cm radiation field. The interaction of this quadrupole with anisotropies in the cosmic microwave background (CMB) radiation field gives a net spin orientation to the hydrogen atoms. The 21-cm radiation emitted by these spin-oriented hydrogen atoms is circularly polarized. Here, we reformulate succinctly the derivation of the expression for this circular polarization in terms of Cartesian (rather than spherical) tensors. We then compute the angular power spectrum of the observed Stokes-$V$ parameter in the standard $\Lambda$CDM cosmological model and show how it depends on redshift, or equivalently, the observed frequency.
Gravitational lensing time delays are well known to depend on cosmological parameters, but they also depend on the details of the mass distribution of the lens. It is usual to model the mass distribution and use time-delay observations to infer cosmological parameters, but it is naturally also possible to take the cosmological parameters as given and use time delays as constraints on the mass distribution. This paper develops a method to isolate what exactly those constraints are, using a principal-components analysis of ensembles of free-form mass models. We find that time delays provide tighter constraints on the distribution of matter in the very high dense regions of the lensing clusters. We apply it to the cluster lens SDSS J1004+4112, whose rich lensing data includes two time delays. We find, assuming a concordance cosmology, that the time delays constrain the central region of the cluster to be rounder and less lopsided than would be allowed by lensed images alone. This detailed information about the distribution of the matter is very useful for studying the dense regions of the galaxy clusters which are very difficult to study with direct measurements. A further time-delay measurement, which is expected, will make this system even more interesting.
The origin of early superhumps, which are double-wave periodic modulations seen only during the earliest stage of WZ Sge-type outburst, has not been well understood. Based on recent discovery of two-armed arch-like patterns on Doppler tomograms in conjunction with early superhumps, we propose a new interpretation on the origin of early superhumps, following the new interpretation by Smak (2001) and Ogilvie (2001) of the two-armed pattern seen in IP Peg. If we consider irradiation of the elevated surface of the accretion disk caused by vertical tidal deformation, we can consistently explain the observed features on Doppler tomograms and photometric waves at the same time. We interpret that a combination of low mass-ratios (q) and low mass-transfer rates, necessary to give rise to these tidal effects, discriminate WZ Sge-type stars from other SU UMa-type dwarf novae. Based on recent fluid calculations, such an effect would be observable in higher q systems. We interpret that RZ Leo is an example of such objects.
Chern-Simons theory can be defined on a cell complex, such as a network of bubbles, which is not a (Hausdorff) manifold. Requiring gauge invariance determines the action, including interaction terms at the intersections, and imposes a relation between the coupling constants of the CS terms on adjacent cell walls. We also find simple conservation laws for charges at the intersections.
Uniform Harnack inequalities for harmonic functions on the pre- and graphical Sierpinski carpets are proved using a probabilistic coupling argument. Various results follow from this, including the construction of Brownian motion on Sierpinski carpets embedded in $\R^d$, $d\geq 3$, estimates on the fundamental solution of the heat equation, and Sobolev and Poincar\'e inequalities.
In this paper we report the numerical design and experimental validation of a pentamode cloak for scattering reduction of elliptical targets in underwater acoustics. Despite being a well-known theoretical concept, experimental validations of transformation-based acoustic cloaking for non-axisymmetric targets have been hindered due to the difficulties related to the complexity of the required material distribution. We overcome these by adopting a linear quasi-symmetric map defined in elliptic coordinates that allows for the design of a pentamode cloak with constant anisotropic elasticity and a scalar inhomogeneous density. We then perform the long-wavelength homogenization based optimization of unit cells that implement the computed material distribution. Numerical validations allow to assess the working range of the designed microstructure, which depends solely on the ratio between the wavelength and the size of the microstructure, and is thus expressed in terms of the maximum normalized wavenumber \kappa L_c, being L_c the characteristic length of the considered unit cell. The influence on the scattering performance of the cloak of a pentamode bandgap common to all the cells in the microstructure is also discussed, finding that it is actually detrimental for the scattering reduction. Finally, the specimen is fabricated and experimentally tested over the range 0.45<\kappa L_c<1.34.
We introduce an algorithm for treating growth on surfaces which combines important features of continuum methods (such as the level-set method) and Kinetic Monte Carlo (KMC) simulations. We treat the motion of adatoms in continuum theory, but attach them to islands one atom at a time. The technique is borrowed from the Dielectric Breakdown Model. Our method allows us to give a realistic account of fluctuations in island shape, which is lacking in deterministic continuum treatments and which is an important physical effect. Our method should be most important for problems close to equilibrium where KMC becomes impractically slow.
Deep residual networks have recently emerged as the state-of-the-art architecture in image segmentation and object detection. In this paper, we propose new image features (called ResFeats) extracted from the last convolutional layer of deep residual networks pre-trained on ImageNet. We propose to use ResFeats for diverse image classification tasks namely, object classification, scene classification and coral classification and show that ResFeats consistently perform better than their CNN counterparts on these classification tasks. Since the ResFeats are large feature vectors, we propose to use PCA for dimensionality reduction. Experimental results are provided to show the effectiveness of ResFeats with state-of-the-art classification accuracies on Caltech-101, Caltech-256 and MLC datasets and a significant performance improvement on MIT-67 dataset compared to the widely used CNN features.
We explore the S-wave and P-wave amplitudes for $NNK$ and $\Lambda\Lambda K$ interactions using chiral perturbation theory to ${\cal O}(m_s\log m_s)$. In contrast to the large corrections found in P-wave amplitudes in the nonleptonic decay of octet baryons, the $NNK$ amplitudes receive only small corrections to their tree-level values. The uncertainty in the $\Lambda\Lambda K$ amplitudes is found to be large.
Context. The mass-loss mechanism of cool massive evolved stars is poorly understood. The proximity of Betelgeuse makes it an appealing target to study its atmosphere, map the shape of its envelope, and follow the structure of its wind from the photosphere out to the interstellar medium. Aims. A link is suspected between the powerful convective motions in Betelgeuse and its mass loss. We aim to constrain the spatial structure and temporal evolution of the convective pattern on the photosphere and to search for evidence of this link. Methods. We report new interferometric observations in the infrared H band using the VLTI/PIONIER instrument. We monitored the photosphere of Betelgeuse between 2012 January and 2014 November to look for evolutions that may trigger the outflow. Results. Our interferometric observations at low spatial frequencies are compatible with the presence of a hot spot on the photosphere that has a characteristic width of one stellar radius. It appears to be superposed on the smaller scale convective pattern. In the higher spatial frequency domain, we observe a significant difference between the observations and the predictions of 3D hydrodynamical simulations. Conclusions. We bring new evidence for the presence of a convective pattern in the photosphere of red supergiants. The inferred hot spot is probably the top of a giant convection cell although an asymmetric extension of the star cannot be excluded by these interferometric observations alone. The properties of the observed surface features show a stronger contrast and inhomogeneity as predicted by 3D radiative hydrodynamical simulations. We propose that the large observed feature is modifying the signature of the convective pattern at the surface of the star in a way that simulations cannot reproduce.
Asymptotics of solutions to Schroedinger equations with singular magnetic and electric potentials is investigated. By using a Almgren type monotonicity formula, separation of variables, and an iterative Brezis-Kato type procedure, we describe the exact behavior near the singularity of solutions to linear and semilinear (critical and subcritical) elliptic equations with an inverse square electric potential and a singular magnetic potential with a homogeneity of order -1.
The interaction between electrons and lattice vibrations determines key physical properties of materials, including their electrical and heat transport, excited electron dynamics, phase transitions, and superconductivity. We present a new ab initio method that employs atomic orbital (AO) wavefunctions to compute the electron-phonon (e-ph) interactions in materials and interpolate the e-ph coupling matrix elements to fine Brillouin zone grids. We detail the numerical implementation of such AO-based e-ph calculations, and benchmark them against direct density functional theory calculations and Wannier function (WF) interpolation. The key advantages of AOs over WFs for e-ph calculations are outlined. Since AOs are fixed basis functions associated with the atoms, they circumvent the need to generate a material-specific localized basis set with a trial-and-error approach, as is needed in WFs. Therefore, AOs are ideal to compute e-ph interactions in chemically and structurally complex materials for which WFs are challenging to generate, and are also promising for high-throughput materials discovery. While our results focus on AOs, the formalism we present generalizes e-ph calculations to arbitrary localized basis sets, with WFs recovered as a special case.
QSO B0218+357 is a blazar located at a cosmological redshift of z=0.944. It is gravitationally lensed by a spiral galaxy at a redshift of z=0.68. The blazar and its lens are well studied in the radio through X-ray bands, and several blazar outbursts were detected by Fermi-LAT at energies above 100 MeV. Strong gravitational lensing was invoked to explain the two components appar- ent in the radio and GeV light curves, separated by 10-12 days. In July 2014 another outburst was observed by Fermi-LAT, triggering follow-up observations with the MAGIC telescopes at energies above 100 GeV. The observations were scheduled at the expected time of arrival of the component delayed by the strong gravitational field of the lens, resulting in a firm detection of QSO B0218+357. Using the combined Fermi-LAT and MAGIC data sets, we report on variability of this unique blazar, the most distant among all currently known very high energy sources.
We present period measurements of a large sample of field stars in the solar neighbourhood, observed by CoRoT in two different directions of the Galaxy. The presence of a period was detected using the Scargle Lomb Normalized Periodogram technique and the autocorrelation analysis. The assessment of the results has been performed through a consistency verification supported by the folded light curve analysis. The data analysis procedure has discarded a non-negligible fraction of light curves due to instrumental artifacts, however it has allowed us to identify pulsators and binaries among a large number of field stars. We measure a wide range of periods, from 0.25 to 100 days, most of which are rotation periods. The final catalogue includes 1978 periods, with 1727 of them identified as rotational periods, 169 are classified as pulsations and 82 as orbital periods of binary systems. Our sample suffers from selection biases not easily corrected for, thus we do not use the distribution of rotation periods to derive the age distribution of the main-sequence population. Nevertheless, using rotation as a proxy for age, we can identify a sample of young stars (< 600 Myr), that will constitute a valuable sample, supported by further spectroscopic observations, to study the recent star formation history in the solar neighborhood.
Since the first investigation of the Hubbard model in the limit of infinite dimensions by Metzner and Vollhardt, dynamical mean-field theory (DMFT) has become a very powerful tool for the investigation of lattice models of correlated electrons. In DMFT the lattice model is mapped on an effective quantum impurity model in a bath which has to be determined self-consistently. This approach lead to a significant progress in our understanding of typical correlation problems such as the Mott transition; furthermore, the combination of DMFT with ab-initio methods now allows for a realistic treatment of correlated materials. The focus of these lecture notes is on the relation between quantum impurity physics and the physics of lattice models within DMFT. Issues such as the observability of impurity quantum phase transitions in the corresponding lattice models are discussed in detail.
We study theoretically the linear conductance of a quantum dot connected to ferromagnetic leads. The dot level is split due to a non-collinear magnetic field or intrinsic magnetization. The system is studied in the non-interacting approximation, where an exact solution is given, and, furthermore, with Coulomb correlations in the weak tunneling limit. For the non-interacting case, we find an anti-resonance for a particular direction of the applied field, non-collinear to the parallel magnetization directions of the leads. The anti-resonance is destroyed by the correlations, giving rise to an interaction induced enhancement of the conductance. The angular dependence of the conductance is thus distinctly different for the interacting and non-interacting cases when the magnetizations of the leads are parallel. However, for anti-parallel lead magnetizations the interactions do not alter the angle dependence significantly.
Lidar based 3D object detection and classification tasks are essential for autonomous driving(AD). A lidar sensor can provide the 3D point cloud data reconstruction of the surrounding environment. However, real time detection in 3D point clouds still needs a strong algorithmic. This paper proposes a 3D object detection method based on point cloud and image which consists of there parts.(1)Lidar-camera calibration and undistorted image transformation. (2)YOLO-based detection and PointCloud extraction, (3)K-means based point cloud segmentation and detection experiment test and evaluation in depth image. In our research, camera can capture the image to make the Real-time 2D object detection by using YOLO, we transfer the bounding box to node whose function is making 3d object detection on point cloud data from Lidar. By comparing whether 2D coordinate transferred from the 3D point is in the object bounding box or not can achieve High-speed 3D object recognition function in GPU. The accuracy and precision get imporved after k-means clustering in point cloud. The speed of our detection method is a advantage faster than PointNet.
YY Gem is a short-period eclipsing binary system containing two nearly identical, rapidly rotating, very active early-M dwarfs. This binary represents an important benchmark system for calibrating empirical relations between fundamental properties of low-mass stars and for testing theories of interior structure and evolution of these objects. Both components of YY Gem exhibit inflated radii, which has been attributed to poorly understood magnetic activity effects. Despite a long history of magnetic activity studies of this system no direct magnetic field measurements have been made for it. Here we present a comprehensive characterisation of the surface magnetic field in both components of YY Gem. We reconstructed the global field topologies with the help of a tomographic inversion technique applied to high-resolution spectropolarimetric data. This analysis revealed moderately complex global fields with a typical strength of 200-300 G and anti-aligned dipolar components. A complementary Zeeman intensification analysis of the disentangled intensity spectra showed that the total mean field strength reaches 3.2-3.4 kG in both components of YY Gem. We used these results together with other recent magnetic field measurements of M dwarfs to investigate the relation between the global and small-scale fields in these stars. We also assessed predictions of competing magnetoconvection interior structure models developed for YY Gem, finding that only one of them anticipated the surface field strength compatible with our observations. Results of our star spot mapping of YY Gem do not support the alternative family of theoretical stellar models which attempts to explain the radii inflation by postulating a large spot filling factor.
We propose a theoretical scheme to show the possibility of generating motional nonlinear coherent states and their superposition for an undamped vibrating micromechanical membrane inside an optical cavity. The scheme is based on an intensity-dependent coupling of the membrane to the radiation pressure field. We show that if the cavity field is initially prepared in a Fock state, the motional state of the membrane may evolve from vacuum state to a special type of nonlinear coherent states. By examining the nonclassical properties of the generated state of the membrane, including the quadrature squeezing and the sub-Poissonian statistics, we find that by varying the Lamb-Dicke parameter and the membrane's reflectivity one can effectively control those properties. In addition, the scheme offers the possibility of generating various types of the so-called nonlinear multicomponent Schrodinger cat sates of the membrane. We also examine the effect of the damping of the cavity field on the motional state of the membrane.
The initial- and boundary-value problem for the Benjamin-Bona-Mahony (BBM) equation is studied in this paper. The goal is to understand the periodic behavior (termed as eventual periodicity) of its solutions corresponding to periodic boundary condition or periodic forcing. To this aim, we derive a new formula representing solutions of this initial- and boundary-value problem by inverting the operator $\partial_t +\alpha \partial_x -\gamma\partial_{xxt}$ defined in the space-time quarter plane. The eventual periodicity of the linearized BBM equation with periodic boundary data and forcing term is established by combining this new representation formula and the method of stationary phase.
The generic Bohmian trajectories are calculated for an isolated particle in an approximate energy eigenstate, for an arbitrary one-dimensional potential well. It is shown, that the necessary and sufficient condition for there to be a negligible probability of the trajectory deviating significantly from the classical trajectory at any stage in the motion is, that the state be a narrowly localised wave packet. The properties of the Bohmian trajectories are discussed in relationship to the theory of retrodictively optimal simultaneous measurements of position and momentum which was presented in several previous papers. It is shown that the Bohmian velocity at x is the expectation value of the velocity which would be observed at x, if one were to make a retrodictively optimal simultaneous measurement of x and p, in the limit as the error in the measurement of x tends to zero. This explains the tendency of the Bohmian particle to behave in a highly non-classical manner. It also explains why the trajectories in the interpretation recently proposed by Garcia de Polavieja tend to be much more nearly classical in the limit of large quantum number. The implications for other trajectory interpretations are considered.
We review some recent results on the Muskat problem modelling multiphase flow in porous media. Furthermore, we prove a new regularity criterion in terms of some norms of the initial data in critical spaces ($\dot{W}^{1,\infty}$ and $\dot{H}^{3/2}$).
The study of Gaussian measures on Banach spaces is of active interest both in pure and applied mathematics. In particular, the spectral theorem for self-adjoint compact operators on Hilbert spaces provides a canonical decomposition of Gaussian measures on Hilbert spaces, the so-called Karhunen-L{\`o} eve expansion. In this paper, we extend this result to Gaussian measures on Banach spaces in a very similar and constructive manner. In some sense, this can also be seen as a generalization of the spectral theorem for covariance operators associated to Gaussian measures on Banach spaces. In the special case of the standard Wiener measure, this decomposition matches with Paul L{\'e}vy's construction of Brownian motion.