ShantanuT01/DACTYL-Pretraining huggingface dataset:
A model of an electron and a Dirac monopole interacting through an axially symmetric non-hermitian but \mathcal{PT}-symmetric potential is discussed in detail. The intriguing localization of the wave-packet as a result of the anomalous breaking of the scale symmetry is shown to provide a scale for the system. The symmetry algebra for the system, which is the conformal algebra SO(2,1), is discussed and is shown to belong to the enveloping algebra of the combined algebra, composed of the Virosoro algebra, \{L_n, n\in \mathbb{N}\} and an abelian algebra, \{P_n,n\in \mathbb{N}\}.
We use an all-electron implementation of the GW approximation to analyze several possible sources of error in the theory and its implementation. Among these are convergence in the polarization and Green's functions, the dependence of QP levels on choice of basis sets, and differing approximations for dealing with core levels. In all GW calculations presented here, G and W are generated from the local-density approximation (LDA), which we denote as the \GLDA\WLDA approximation. To test its range of validity, the \GLDA\WLDA approximation is applied to a variety of materials systems. We show that for simple sp semiconductors, \GLDA\WLDA always underestimates bandgaps; however, better agreement with experiment is obtained when the self-energy is not renormalized, and we propose a justification for it. Some calculations for Si are compared to pseudopotential-based \GLDA\WLDA calculations, and some aspects of the suitability of pseudopotentials for GW calculations are discussed.
The scaling properties of post-mortem fracture surfaces of brittle (silica glass), ductile (aluminum alloy) and quasi-brittle (mortar and wood) materials have been investigated. These surfaces, studied far from the initiation, were shown to be self-affine. However, the Hurst exponent measured along the crack direction is found to be different from the one measured along the propagation direction. More generally, a complete description of the scaling properties of these surfaces call for the use of the 2D height-height correlation function that involves three exponents zeta = 0.75, beta = 0.6 and z = 1.25 independent of the material considered as well as of the crack growth velocity. These exponents are shown to correspond to the roughness, growth and dynamic exponents respectively, as introduced in interface growth models. They are conjectured to be universal.
The Blanco DECam Bulge Survey (BDBS) imaged more than 200 square degrees of the Southern Galactic bulge using the ugrizY filters of the Dark Energy Camera, and produced point spread function photometry of approximately 250 million unique sources. In this paper, we present details regarding the construction and collation of survey catalogs, and also discuss the adopted calibration and dereddening procedures. Early science results are presented with a particular emphasis on the bulge metallicity distribution function and globular clusters. A key result is the strong correlation (sigma ~ 0.2 dex) between (u-i)o and [Fe/H] for bulge red clump giants. We utilized this relation to find that interior bulge fields may be well described by simple closed box enrichment models, but fields exterior to b ~ -6 degrees seem to require a secondary metal-poor component. Applying scaled versions of the closed box model to the outer bulge fields is shown to significantly reduce the strengths of any additional metal-poor components when compared to Gaussian mixture models. Additional results include: a confirmation that the u-band splits the sub-giant branch in M 22 as a function of metallicity, the detection of possible extra-tidal stars along the orbits of M 22 and FSR 1758, and additional evidence that NGC 6569 may have a small but discrete He spread, as evidenced by red clump luminosity variations in the reddest bands. We do not confirm previous claims that FSR 1758 is part of a larger extended structure.
We report on the detection of two Halpha-emitting extreme compact objects from deep images of the Abell 634 and Abell 539 clusters of galaxies at z ~ 0.03. Follow up long slit spectroscopy of these two unresolved sources revealed that they are members of their respective clusters showing HII type spectra. The luminosity and the extreme equivalent width of Halpha+[NII] measured for these sources, together with their very compact appearance, has raised the question about the origin of these intense starbursts in the cluster environment. We propose the compact starburst in Abell 539 resulted from the compression of the interstellar gas of a dwarf galaxy when entering the cluster core; while the starburst galaxy in Abell 634 is likely to be the result of a galaxy-galaxy interaction, illustrating the preprocessing of galaxies during their infall towards the central regions of clusters. The contribution of these compact star-forming dwarf galaxies to the star formation history of galaxy clusters is discussed, as well as a possible link with the recently discovered early-type ultra-compact dwarf galaxies. We note that these extreme objects will be rarely detected in normal magnitude-limited optical or NIR surveys, mainly due to their low stellar masses (of the order of 10^6 solar masses), whereas they will easily show up in dedicated Halpha surveys given the high equivalent width of their emission lines.
Object detection and recognition is an important task in many computer vision applications. In this paper an Android application was developed using Eclipse IDE and OpenCV3 Library. This application is able to detect objects in an image that is loaded from the mobile gallery, based on its color, shape, or local features. The image is processed in the HSV color domain for better color detection. Circular shapes are detected using Circular Hough Transform and other shapes are detected using Douglas-Peucker algorithm. BRISK (binary robust invariant scalable keypoints) local features were applied in the developed Android application for matching an object image in another scene image. The steps of the proposed detection algorithms are described, and the interfaces of the application are illustrated. The application is ported and tested on Galaxy S3, S6, and Note1 Smartphones. Based on the experimental results, the application is capable of detecting eleven different colors, detecting two dimensional geometrical shapes including circles, rectangles, triangles, and squares, and correctly match local features of object and scene images for different conditions. The application could be used as a standalone application, or as a part of another application such as Robot systems, traffic systems, e-learning applications, information retrieval and many others.
Density functional theory (DFT) has become a standard tool for the study of point defects in materials. However, finding the most stable defective structures remains a very challenging task as it involves the solution of a multimodal optimization problem with a high-dimensional objective function. Hitherto, the approaches most commonly used to tackle this problem have been mostly empirical, heuristic and/or based on domain knowledge. In this contribution, we describe an approach for exploring the potential energy surface based on the covariance matrix adaption evolution strategy (CMA-ES) and supervised and unsupervised machine learning models. We show how the original CMA-ES can be modified to suit the specific problem of DFT studies of point defects in the dilute limit. The resulting algorithm depends only on a limited set of physically interpretable hyperparameters. The approach offers a robust and systematic way for finding low-energy configurations of point defects in solids. We demonstrate the applicability and moderate computational cost on the intrinsic defects in silicon. We also apply the methodology to the neutral oxygen vacancy oxygen vacancy in TiO$_2$ anatase and reproduce the known defect structures. Furthermore, a new defect structure, stable at the level of hybrid density functional theory and characterized by a delocalized electronic structure, is found for this system.
Submillimetre observations reveal a cosmologically significant population of high-redshift dust-enshrouded galaxies. The form of evolution inferred for this population can be reconciled easily with COBE FIRAS and DIRBE measurements of the cosmic background radiation (CBR) at wavelengths >100 microns. At shorter wavelengths, however, the 60-micron CBR intensity reported by Finkbeiner et al. is less easily accounted for. Lagache et al. have proposed that this excess CBR emission is a warm Galactic component, and the detection of the highest-energy gamma-rays from blazars limits the CBR intensity at these wavelengths, but here we investigate sources of this excess CBR emission, assuming that it has a genuine extragalactic origin. We propose and test three explanations, each involving additional populations not readily detected in existing submm-wave surveys. First, dust-enshrouded galaxies with hot dust temperatures, perhaps dust-enshrouded, Compton-thick AGN as suggested by recent deep Chandra surveys. Secondly, a population of relatively low-redshift dusty galaxies with SEDs more typical of the existing submm-selected galaxies, which could plausibly be associated with the assembly of groups and clusters of galaxies. Thirdly, a population of low-luminosity, cool, quiescent spiral galaxies. Hot AGN and the assembly of groups can account for the excess 60-micron background. There are significant problems with the cluster assembly scenario, in which too many bright IRAS sources are predicted. Spiral galaxies have the wrong SEDs to account for the excess. Future wide-field far-IR surveys using SIRTF and Herschel will sample representative volumes of the distant Universe, allowing any hot population of dusty AGNs and forming groups to be detected.
We present a calculation of the NLO QCD corrections to heavy flavor photoproduction with longitudinally polarized beams. We apply our results to study the spin asymmetry for total charm quark production which will be used for a first direct determination of Delta g by the COMPASS experiment. We also briefly discuss the main theoretical uncertainties inherent in this calculation.
In the standard paradigm, astrophysical black holes can be described solely by their mass and angular momentum - commonly referred to as `spin' - resulting from the process of their birth and subsequent growth via accretion. Whilst the mass has a standard Newtonian interpretation, the spin does not, with the effect of non-zero spin leaving an indelible imprint on the space-time closest to the black hole. As a consequence of relativistic frame-dragging, particle orbits are affected both in terms of stability and precession, which impacts on the emission characteristics of accreting black holes both stellar mass in black hole binaries (BHBs) and supermassive in active galactic nuclei (AGN). Over the last 30 years, techniques have been developed that take into account these changes to estimate the spin which can then be used to understand the birth and growth of black holes and potentially the powering of powerful jets. In this chapter we provide a broad overview of both the theoretical effects of spin, the means by which it can be estimated and the results of ongoing campaigns.
Context: Hydrogenation reactions are expected to be among the most important surface reactions on interstellar ices. However, solid state astrochemical laboratory data on reactions of H-atoms with common interstellar ice constituents are largely lacking. Aims: The goal of our laboratory work is to determine whether and how carbon dioxide (CO2), formic acid (HCOOH) and acetaldehyde (CH3CHO) react with H-atoms in the solid state at low temperatures and to derive reaction rates and production yields. Methods: Pure CO2, HCOOH and CH3CHO interstellar ice analogues are bombarded by H-atoms in an ultra-high vacuum experiment. The ices are monitored by reflection absorption infrared spectroscopy and the reaction products are detected in the gas phase through temperature programmed desorption to determine the destruction and formation yields as well as the corresponding reaction rates. Results: Within the sensitivity of our set-up we conclude that H-atom bombardment of pure CO2 and HCOOH ice does not result in detectable reaction products. The upper limits on the reaction rates are less or equal to 7e(-17) cm^2/s which make it unlikely that these species play a major role in the formation of more complex organics in interstellar ices due to reactions with H-atoms. In contrast, CH3CHO does react with H-atoms. At most 20% is hydrogenated to ethanol (C2H5OH) and a second reaction route leads to the break-up of the C-C bond to form solid state CH4 (~20%) as well as H2CO and CH3OH (15-50%). The methane production yield is expected to be equal to the summed yield of H2CO and CH3OH and therefore CH4 most likely evaporates partly after formation due to the high exothermicity of the reaction. The reaction rates for CH3CHO destruction depend on ice temperature and not on ice thickness.
Density functional study of strain effects on the electronic band structure and transport prop- erties of the graphene nanoribbons (GNR) is presented. We apply a uniaxial strain in the x (nearest-neighbor) and y (second nearest-neighbor) directions, related to the deformation of zigzag and armchair edge GNRs (AGNR and ZGNR), respectively. We calculate the quantum conduc- tance and band structures of the GNR using the Wannier function in a strain range from -8% to +8% (minus and plus signs show compression and tensile strain). As strain increases, depending on the AGNR family type, the electrical conductivity changes from an insulator to a conductor. This is accompanied by a variation in the electron and hole effective masses. The compression x direction strain in ZGNR shifts some bands to below the Fermi level (Ef ) and the quantum conductance does not change, but the tensile x direction strain causes an increase in the quantum conductance to 10e2/h near the Ef . For transverse direction, it is very sensitive to strain and the tensile y direction strain causes an increase in the conductance while the compressive y direction strain decreases the conductance at first but increases later.
We analyze the set of two-qubit states from which a secret key can be extracted by single-copy measurements plus classical processing of the outcomes. We introduce a key distillation protocol and give the corresponding necessary and sufficient condition for positive key extraction. Our results imply that the critical error rate derived by Chau, Phys. Rev. A {\bf 66}, 060302 (2002), for a secure key distribution using the six-state scheme is tight. Remarkably, an optimal eavesdropping attack against this protocol does not require any coherent quantum operation.
The most energetic flares start with a filament rise followed by magnetic reconnection below this filament. The start of the reconnection corresponds to the beginning of the flare impulsive phase. In this paper we study processes before this phase. During the filament rise we recognize an unusual radio continuum with a starting boundary drifting toward lower frequencies. The estimated velocity of the agent generating this continuum boundary is about 400 km/s, similar to that of the rising filament. In association with this filament rise, transient X-ray sources and extreme ultaviolet (EUV) brightenings are found near the filament footpoint and outside the locations where later two parallel flare ribbons appear. Moreover, oscillations with a ~30 s period are found simultaneously in radio, EUV, and X-ray observations. Around the end of these oscillations the flare impulsive phase starts as seen in observations of the drifting pulsation structure and X-ray source located at the upper part of the rising filament. We interpret the unusual radio continuum and transient X-ray sources, which are located outside the two parallel flare ribbons, as those generated during an interaction of the rising filament with the above-lying magnetic loops. The EUV brightening at the filament footpoint could be a signature of the magnetic reconnection inside the magnetic rope carrying the filament. Possible scenarios of the ~30 s period oscillations in radio, X-ray, and EUV are discussed.
Line intensity mapping (LIM) is an emerging observational method to study the large-scale structure of the Universe and its evolution. LIM does not resolve individual sources but probes the fluctuations of integrated line emissions. A serious limitation with LIM is that contributions of different emission lines from sources at different redshifts are all confused at an observed wavelength. We propose a deep learning application to solve this problem. We use conditional generative adversarial networks to extract designated information from LIM. We consider a simple case with two populations of emission line galaxies; H$\rm\alpha$ emitting galaxies at $z = 1.3$ are confused with [OIII] emitters at $z = 2.0$ in a single observed waveband at 1.5 $\rm\mu$m. Our networks trained with 30,000 mock observation maps are able to extract the total intensity and the spatial distribution of H$\rm\alpha$ emitting galaxies at $z = 1.3$. The intensity peaks are successfully located with 74% precision. The precision increases to 91% when we combine the results of 5 networks. The mean intensity and the power spectrum are reconstructed with an accuracy of $\sim$10%. The extracted galaxy distributions at a wider range of redshift can be used for studies on cosmology and on galaxy formation and evolution.
We report measurements of the bias dependence of the Fano factor in ensembles of atomic-scale Au junctions at 77 K. Previous measurements of shot noise at room temperature and low biases have found good agreement of the Fano factor with the expectations of the Landauer- B\"uttiker formalism, while enhanced Fano factors have been observed at biases of hundreds of mV [R. Chen et al., Sci. Rep. 4, 4221 (2014)]. We find even stronger enhancement of shot noise at 77 K with an "excess" Fano factor up to ten times the low bias value. We discuss the observed ensemble Fano factor bias dependence in terms of candidate models. The results are most consistent with either a bias-dependent channel mixing picture or a model incorporating noise enhancement due to current-driven, nonequilibrium phonon populations, though a complete theoretical treatment of the latter in the ensemble average limit is needed.
We count the number of walks of length n on a k-node circular digraph that cover all k nodes in two ways. The first way illustrates the transfer-matrix method. The second involves counting various classes of height-restricted lattice paths. We observe that the results also count so-called k-balanced strings of length n, generalizing a 1996 Putnam problem.
We present results of new three-dimensional (3D) general-relativistic magnetohydrodynamic simulations of rapidly rotating strongly magnetized core collapse. These simulations are the first of their kind and include a microphysical finite-temperature equation of state and a leakage scheme that captures the overall energetics and lepton number exchange due to postbounce neutrino emission. Our results show that the 3D dynamics of magnetorotational core-collapse supernovae are fundamentally different from what was anticipated on the basis of previous simulations in axisymmetry (2D). A strong bipolar jet that develops in a simulation constrained to 2D is crippled by a spiral instability and fizzles in full 3D. While multiple (magneto-)hydrodynamic instabilities may be present, our analysis suggests that the jet is disrupted by an m=1 kink instability of the ultra-strong toroidal field near the rotation axis. Instead of an axially symmetric jet, a completely new, previously unreported flow structure develops. Highly magnetized spiral plasma funnels expelled from the core push out the shock in polar regions, creating wide secularly expanding lobes. We observe no runaway explosion by the end of the full 3D simulation at 185 ms after bounce. At this time, the lobes have reached maximum radii of 900 km.
We study non-linear optical effects in electron systems with and without inversion symmetry in a Fabry-Perot cavity. General photon up- and down-conversion processes are modeled by the coupling of a noninteracting lattice model to two modes of the quantized light field. Effective descriptions retaining the most relevant states are devised via downfolding and a generalized Householder transformation. These models are used to relate the transition amplitudes for even order photon-conversion processes to the shift vector, a topological quantity describing the difference in polarization between the valence and conduction band in non-centrosymmetric systems. We also demonstrate that the truncated models, despite their small Hilbert space, capture correlation effects induced by the photons in the electronic subsystem.
With fourth-order derivative theories leading to propagators of the generic ghost-like $1/(k^2-M_1^2)-1/(k^2-M_2^2)$ form, it would appear that such theories have negative norm ghost states and are not unitary. However on constructing the associated quantum Hilbert space for the free theory that would produce such a propagator, Bender and Mannheim found that the Hamiltonian of the free theory is not Hermitian but is instead $PT$ symmetric, and that there are in fact no negative norm ghost states, with all Hilbert space norms being both positive and preserved in time. Even though perturbative radiative corrections cannot change the signature of a Hilbert space inner product, nonetheless it is not immediately apparent how such a ghost-like propagator would not then lead to negative probability contributions in loop diagrams. Here we obtain the relevant Feynman rules and show that all states obtained in cutting intermediate lines in loop diagrams have positive norm. Also we show that due to the specific way that unitarity (conservation of probability) is implemented in the theory, negative signatured discontinuities across cuts in loop diagrams are cancelled by a novel and unanticipated contribution of the states in which tree approximation (no loop) graphs are calculated, an effect that is foreign to standard Hermitian theories. Perturbatively, the fourth-order derivative theory is thus viable. The theory associated with the pure massless $1/k^4$ propagator is equally shown to be perturbatively viable.
In matter, any spontaneous symmetry breaking induces a phase transition characterized by an order parameter, such as the magnetization vector in ferromagnets, or a macroscopic many-electron wave-function in superconductors. Phase transitions with unknown order parameter are rare but extremely appealing, as they may lead to novel physics. An emblematic, and still unsolved, example is the transition of the heavy fermion compound URu$_2$Si$_2$ (URS) into the so-called hidden-order (HO) phase when the temperature drops below $T_0 = 17.5$K. Here we show that the interaction between the heavy fermion and the conduction band states near the Fermi level has a key role in the emergence of the HO phase. Using angle resolved photoemission spectroscopy, we find that while the Fermi surfaces of the HO and of a neighboring antiferromagnetic (AFM) phase of well-defined order parameter have the same topography, they differ in the size of some, but not all, of their electron pockets. Such a non-rigid change of the electronic structure indicates that a change in the interaction strength between states near the Fermi level is a crucial ingredient for the HO-to-AFM phase transition.
We study a space-fractional Stefan problem, where the non-local diffusion flux is modeled by the Caputo derivative. We obtain the unique existence of classical solution to this problem.