ShantanuT01/DACTYL-Pretraining huggingface dataset:
We study the two-dimensional (2D) Hubbard model using exact diagonalization for spin-1/2 fermions on the triangular and honeycomb lattices decorated with a single hexagon per site. In certain parameter ranges, the Hubbard model maps to a quantum compass model on those lattices. On the triangular lattice, the compass model exhibits collinear stripe antiferromagnetism, implying $d$-density wave charge order in the original Hubbard model. On the honeycomb lattice, the compass model has a unique, quantum disordered ground state that transforms nontrivially under lattice reflection. The ground state of the Hubbard model on the decorated honeycomb lattice is thus a 2D fermionic symmetry-protected topological phase. This state -- protected by time-reversal and reflection symmetries -- cannot be connected adiabatically to a free-fermion topological phase.
Grain boundary wetting as a preliminary stage for zinc induced grain boundary weakening and embrittlement in a Zn coated press hardened 20MnB8 steel was analyzed by means of electron backscatter diffraction, Auger electron spectroscopy, energy dispersive X-ray analysis, atom probe tomography and transmission electron microscopy on the nanometer scale. Microcracks at prior austenite grain boundaries were observed and structures that developed after microcrack formation were identified. Zn/Fe intermetallic phases with grain sizes smaller than 100 nm in diameter are present at the crack surfaces and at the wedge-shaped crack tips. In order to get a complete picture, including the microstructure before cracking, an undeformed, electrolytically coated reference sample which underwent the same heat treatment as the press hardened material was investigated. Here, Zn, in the order of one atomic layer or less, could be found along prior austenite grain boundaries several micrometers away from the actual Zn/Fe phases in the coating. Such a grain boundary weakening by Zn wetting of prior austenitic grain boundaries during austenitization and/or hot forming is a necessary condition for microcrack formation.
Observational evidence has been accumulating that thermonuclear X-ray bursts ignited on the surface of neutron stars influence the surrounding accretion flow. Here, we exploit the excellent sensitivity of NuSTAR up to 79 keV to analyze the impact of an X-ray burst on the accretion emission of the neutron star LMXB 4U 1608-52. The ~200 s long X-ray burst occurred during a hard X-ray spectral state, and had a peak intensity of ~30-50 per cent of the Eddington limit with no signs of photospheric radius expansion. Spectral analysis suggests that the accretion emission was enhanced up to a factor of ~5 during the X-ray burst. We also applied a linear unsupervised decomposition method, namely non-negative matrix factorization (NMF), to study this X-ray burst. We find that the NMF performs well in characterizing the evolution of the burst emission and is a promising technique to study changes in the underlying accretion emission in more detail than is possible through conventional spectral fitting. For the burst of 4U 1608-52, the NMF suggests a possible softening of the accretion spectrum during the X-ray burst, which could potentially be ascribed to cooling of a corona. Finally, we report a small (~3 per cent) but significant rise in the accretion emission ~0.5 h before the X-ray burst, although it is unclear whether this was related to the X-ray burst ignition.
Coronal mass ejections (CMEs) are tightly related to filament eruptions and usually are their continuation in the upper solar corona. It is common practice to divide all observed CMEs into fast and slow ones. Fast CMEs usually follow eruptive events in active regions near big sunspot groups and associated with major solar flares. Slow CMEs are more related to eruptions of quiescent prominences located far from active regions. We analyze ten eruptive events with particular attention to the events on 2013 September 29 and on 2016 January 26, one of which was associated with a fast CME, while another was followed by a slow CME. We estimated the initial store of free magnetic energy in the two regions and show the resemblance of pre-eruptive situations. The difference of late behaviour of the two eruptive prominences is a consequence of the different structure of magnetic field above the filaments. We estimated this structure on the basis of potential magnetic field calculations. Analysis of other eight events confirmed that all fast CMEs originate in regions with rapidly changing with height value and direction of coronal magnetic field.
Let $G=(V,E)$ be an undirected graph without loops and multiple edges. A subset $C\subseteq V$ is called \emph{identifying} if for every vertex $x\in V$ the intersection of $C$ and the closed neighbourhood of $x$ is nonempty, and these intersections are different for different vertices $x$.   Let $k$ be a positive integer. We will consider graphs where \emph{every} $k$-subset is identifying. We prove that for every $k>1$ the maximal order of such a graph is at most $2k-2.$ Constructions attaining the maximal order are given for infinitely many values of $k.$   The corresponding problem of $k$-subsets identifying any at most $\ell$ vertices is considered as well.
Self-supervised learning has recently shown great potential in vision tasks through contrastive learning, which aims to discriminate each image, or instance, in the dataset. However, such instance-level learning ignores the semantic relationship among instances and sometimes undesirably repels the anchor from the semantically similar samples, termed as "false negatives". In this work, we show that the unfavorable effect from false negatives is more significant for the large-scale datasets with more semantic concepts. To address the issue, we propose a novel self-supervised contrastive learning framework that incrementally detects and explicitly removes the false negative samples. Specifically, following the training process, our method dynamically detects increasing high-quality false negatives considering that the encoder gradually improves and the embedding space becomes more semantically structural. Next, we discuss two strategies to explicitly remove the detected false negatives during contrastive learning. Extensive experiments show that our framework outperforms other self-supervised contrastive learning methods on multiple benchmarks in a limited resource setup.
Historically, finding two-dimensional (2D) magnets is well known to be a difficult task due to instability against thermal spin fluctuations. Metals are also normally considered poor thermoelectric (TE) materials. Combining intrinsic magnetism in two dimensions with conducting properties, one may expect to get the worst for thermoelectrics. However, we will show this is not always the case. Here, we investigate spin-dependent TE properties of monolayer chromium pnictides (CrX, where X = P, As, Sb, and Bi) using first-principles calculations of electrons and phonons, along with Boltzmann transport formalism under energy-dependent relaxation time approximation. All the CrX monolayers are dynamically stable and they also exhibit half metallicity with ferromagnetic ordering. Using the spin-valve setup with antiparallel spin configuration, the half metallicity and ferromagnetism in monolayer CrX enable manipulation of spin degrees of freedom to tune the TE figure of merit (ZT). At optimized chemical potential and operating temperature of 500 K, the maximum ZT values (= 0.22, 0.12, and 0.09) with the antiparallel spin-valve setup in CrAs, CrSb, and CrBi improve up to almost twice the original values (ZT = 0.12, 0.08, and 0.05) without the spin-valve configuration. Only in CrP, which is the lightest species and less spin-polarized among CrX, the maximum ZT (= 0.34) without the spin-valve configuration is larger than that (= 0.19) with the spin-valve one. We also find that, at 500 K, all the CrX monolayers possess exceptional TE power factors of about 0.02-0.08 W/m.K2, which could be one of the best values among 2D conductors.
The content of matter in the Universe is estimated to be the 27% of its critical density. It is almost universally accepted that most ot this matter is non-baryonic. Constraints from primordial nucleosynthesis and cosmic background radiation measurements impose that the baryonic content of the Universe cannot exceed the 4% of the critical density, so the nature of the remaining 23% has yet to be identi ed. In this sense, one of the most promising candidates is represented by supersymmetric neutralinos. If they exist, they give rise to relic densities in the required range, and are very well motivated in the framework of theoretical extensions of the Standard Model of particle physics. In addition to direct neutralino searches and collider experiments, neutralino annihilation into gamma rays, neutrinos and synchrotron emission from the charged products represents a reliable way of detecting these intriguing particles. The strongest signals are expected to come from the Galactic Center and from the nearest dwarf spheroidals. Clumps of dark matter in galactic haloes are well predicted by high resolution cold dark matter numerical simulations. In this work we present our studies on the gamma-ray emission from the Galactic Center and from the Draco dwarf spheroidal. We investigate the e ect of clumpiness on the detection of signals from neutalinos for di erent mass density pro les. One of the scienti c goals of the MAGIC telescope are just searches for the stable lightest supersymmetric particle in the di erent physical scenarios in which they are produed. Assuming MAGIC speci cations, we draw some conclusions about the potentialities of this telescope in such a kind of investigation.
We investigate extremely luminous dusty galaxies in the environments around WISE-selected hot dust obscured galaxies (Hot DOGs) and WISE/radio-selected active galactic nuclei (AGNs) at average redshifts of z = 2.7 and z = 1.7, respectively. Previous observations have detected overdensities of companion submillimetre-selected sources around 10 Hot DOGs and 30 WISE/radio AGNs, with overdensities of ~ 2 - 3 and ~ 5 - 6 , respectively. We find that the space densities in both samples to be overdense compared to normal star-forming galaxies and submillimetre galaxies (SMGs) in the SCUBA-2 Cosmology Legacy Survey (S2CLS). Both samples of companion sources have consistent mid-IR colours and mid-IR to submm ratios as SMGs. The brighter population around WISE/radio AGNs could be responsible for the higher overdensity reported. We also find the star formation rate density (SFRDs) are higher than the field, but consistent with clusters of dusty galaxies. WISE-selected AGNs appear to be good signposts for protoclusters at high redshift on arcmin scales. The results reported here provide an upper limit to the strength of angular clustering using the two-point correlation function. Monte Carlo simulations show no angular correlation, which could indicate protoclusters on scales larger than the SCUBA-2 1.5arcmin scale maps.
M74 (NGC 628) is a famous face-on spiral galaxy, hosting three core-collapse supernovae (SNe):SN Ic 2002ap, SN II-P 2003gd, and SN II-P 2013ej. However its distance is not well known. We present a distance estimation for this galaxy based on the Tip of the Red Giant Branch (TRGB) method. We obtain photometry of the resolved stars in the arm-free region of M74 from F555W and F814W images in the Hubble Space Telescope archive. The color-magnitude diagram of the resolved stars shows a dominant red giant branch (RGB) as well as blue main sequence stars, red helium burning stars, and asymptotic giant branch stars. The I-band luminosity function of the RGB stars shows the TRGB to be at I_TRGB = 26.13 pm 0.03 mag, and T_RGB = 25.97 pm 0.03. From this we derive the distance modulus to M74 to be 30.04 pm 0.04 (random) pm 0.12 (systematic) (corresponding to a linear distance, 10.19 pm 0.14 pm 0.56 Mpc). With this distance estimate, we calibrate the standardized candle method for SNe II-P. From the absolute magnitudes of SN 2003gd, we derive a value of the Hubble constant, H_0 = 72 pm 6 (random) pm 7 (systematic) km s^-1 Mpc^-1. It is similar to recent estimates based on the luminosity calibration of Type Ia supernovae.
The standard probability law on the set $S(x,y)$ of $y$-friable integers not exceeding $x$ assigns to each friable integer $n$ a probability proportional to $1/n^\alpha$ where $\alpha=\alpha(x,y)$ is the saddle-point of the inverse Laplace integral for $\Psi(x,y):=|S(x,y)|$. This law presents a structural bias inasmuch it weights integers $>x$. We propose a quantitative measure of this bias and exhibit a related Gaussian distribution.
RGBT tracking receives a surge of interest in the computer vision community, but this research field lacks a large-scale and high-diversity benchmark dataset, which is essential for both the training of deep RGBT trackers and the comprehensive evaluation of RGBT tracking methods. To this end, we present a Large-scale High-diversity benchmark for RGBT tracking (LasHeR) in this work. LasHeR consists of 1224 visible and thermal infrared video pairs with more than 730K frame pairs in total. Each frame pair is spatially aligned and manually annotated with a bounding box, making the dataset well and densely annotated. LasHeR is highly diverse capturing from a broad range of object categories, camera viewpoints, scene complexities and environmental factors across seasons, weathers, day and night. We conduct a comprehensive performance evaluation of 12 RGBT tracking algorithms on the LasHeR dataset and present detailed analysis to clarify the research room in RGBT tracking. In addition, we release the unaligned version of LasHeR to attract the research interest for alignment-free RGBT tracking, which is a more practical task in real-world applications. The datasets and evaluation protocols are available at: https://github.com/BUGPLEASEOUT/LasHeR.
We present a calculation of the ground state energy of massive spinor fields and massive scalar fields in the background of an inhomogeneous magnetic string with potential given by a delta function. The zeta functional regularization is used and the lowest heat kernel coefficients are calculated. The rest of the analytical calculation adopts the Jost function formalism. In the numerical part of the work the renormalized vacuum energy as a function of the radius $R$ of the string is calculated and plotted for various values of the strength of the potential. The sign of the energy is found to change with the radius. For both scalar and spinor fields the renormalized energy shows no logarithmic behaviour in the limit $R\to 0$, as was expected from the vanishing of the heat kernel coefficient $A_2$, which is not zero for other types of profiles.
The phonon modes at finite temperature in graphene and single-walled carbon nanotubes (SWCNT) are investigated by the mode projection technique combined with molecular dynamics simulation. It is found that the quadratic phonon spectrum of the flexural mode in graphene is renormalized into linear at finite temperature by the phonon-phonon scattering. Possible influence of this renormalization on the electron-phonon interaction and phonon thermal transport is analyzed. For the SWCNT, however the quadratic property of the phonon spectrum for the flexural mode can survive at finite temperature under protection of the two-fold degeneracy of the flexural mode in SWCNT due to its quasi-one-dimensional structure. The frequency and life time of optical phonon modes are also studied at different temperatures. In particular, the life time of the in-plane optical phonons in graphene and the axial optical phonon in SWCNT can be described by an uniform formula $\tau (T)=560/T$, which coincides with the experimental results.
We consider a hypothesis testing problem for displacement parameters of n independent copies of an m-mode squeezed quantum Gaussian state whose mixture parameter is known. Given n>1, we construct a quantum measurement as a test using an observable which is invariant by n-fold tensor product of any m-mode squeezing operator. For a pure state case, we calculate the type II error probability of this test. We compare this test with a Hotelling's T-squared test which is based on heterodyne measurements.
We investigate the logarithmic bundles associated to arrangements of hypersurfaces with a fixed degree in a smooth projective variety. We then specialize to the case when the variety is a quadric hypersurface and a multiprojective space to prove a Torelli type theorem in some cases.
We calculate the ages, orbits and phase-space coordinates for a sample of $\sim$4 million LAMOST and Gaia stars. The ages are crossmatched and compared with values from two other popular age catalogs which derive the ages using different methods. Of these $\sim$4 million stars, we select a sample of 1.3 million stars and investigate their radial metallicity gradients (as determined by orbital radii) as a function of their ages. This analysis is performed on various subsets of the data split by chemistry and orbital parameters. We find that commonly used selections for ``thin disk'' stars (such as low-$\alpha$ chemistry or vertically thin orbits) yield radial metallicity gradients which generally grow shallower for the oldest stars. We interpret this as a hallmark feature of radial migration (churning). Constraining our sample to very small orbital Z$_{max}$ (the maximal height of a star's integrated orbit) makes this trend most pronounced. A chemistry-based ``thin disk'' selection of $\alpha$-poor stars displays the same trend, but to a lesser extent. Intruigingly, we find that ``thick disk'' selections in chemistry and Z$_{max}$ reveal a slightly positive radial metallicity gradients which seem similar in magnitude at all ages. This may imply that the thick disk population is well mixed in age, but not in radius. This finding could help constrain conditions during the early epochs of Milky Way formation, and shed light on processes such as the accretion and reaccretion of gasses of different metallicities.
We present a Fermi liquid approach to superconducting Kondo problems applicable when the Kondo temperature is large compared to the superconducting gap. To illustrate the theory, we study the current-phase relation and the Andreev level spectrum for an Anderson impurity between two $s$-wave superconductors. In the particle-hole symmetric Kondo limit, we find a $4\pi$ periodic Andreev spectrum. The $4\pi$ periodicity persists under a small voltage bias which however causes an asymmetric distortion of Andreev levels. The latter distinguishes the present $4\pi$ effect from the one in topological Majorana junctions.
In this paper we give a short, elementary proof of the following too extreme cases of the Leopoldt conjecture: the case when $\K/\Q$ is a solvable extension and the case when it is a totally real extension in which $p$ splits completely. The first proof uses Baker theory, the second class field theory. The methods used here are a sharpening of the ones presented at the SANT meeting in G\"ottingen, 2008 and exposed in \cite{Mi2}, \cite{Mi1}.
In infinite-dimensional Hilbert spaces, the application of the concept of quasi-Hermiticity to the description of non-Hermitian Hamiltonians with real spectra may lead to problems related to the definition of the metric operator. We discuss these problems by examining some examples taken from the recent literature and propose a formulation that is free of these difficulties.
Using the theory of self-adjoint extensions, we construct all the possible hamiltonians describing the non relativistic Aharonov-Bohm effect. In general the resulting hamiltonians are not rotationally invariant so that the angular momentum is not a constant of motion. Using an explicit formula for the resolvent, we describe the spectrum and compute the generalized eigenfunctions and the scattering amplitude.
The ZrCo intermetallic was proposed as tritium storage material in the International Thermonuclear Experimental Reactors (ITER) project. The thermodynamic properties of ZrCo intermetallic were investigated both experimentally and theoretically to determine its applicability for the storage of hydrogen isotopes. The enthalpy increments of ZrCo were measured using a high temperature inverse drop calorimeter in the temperature range 645-1500 K. A set of thermodynamic functions such as entropy, Gibbs energy function, heat capacity, Gibbs energy and enthalpy values for ZrCo were calculated using the data obtained in this study. The polynomial expression of enthalpy increments and heat capacity obtained for ZrCo(s) in the temperature range 642-1497 K are given as: H(T) - H(298.15 K) (J/mol) = 25.682x(T/K) + 29.804x10e-4 (T/K)**2+ 2.1864x10e+5 (K/T) - 8655.5 Cp (J/K/mol) =25.682 + 5.916x10e-3 (T/K) - 2.1864x10e+5 (K/T)**2 The enthalpy of formation of ZrCo at 0 K was calculated as -55 kJ mol-1 using the ab-initio method. The entropy (S) and specific heat capacities (Cv and Cp) of ZrCo were also computed using Debye-Gr\"uneisen quasi-harmonic approximation. A good agreement between the experimental and theoretically calculated values of specific heat (CP) and entropy was obtained.
Graphene is a promising material for ultrafast and broadband photodetection. Earlier studies addressed the general operation of graphene-based photo-thermoelectric devices, and the switching speed, which is limited by the charge carrier cooling time, on the order of picoseconds. However, the generation of the photovoltage could occur at a much faster time scale, as it is associated with the carrier heating time. Here, we measure the photovoltage generation time and find it to be faster than 50 femtoseconds. As a proof-of-principle application of this ultrafast photodetector, we use graphene to directly measure, electrically, the pulse duration of a sub-50 femtosecond laser pulse. The observation that carrier heating is ultrafast suggests that energy from absorbed photons can be efficiently transferred to carrier heat. To study this, we examine the spectral response and find a constant spectral responsivity between 500 and 1500 nm. This is consistent with efficient electron heating. These results are promising for ultrafast femtosecond and broadband photodetector applications.
We present a method that accurately propagates residual uncertainties in photometric redshift distributions into the cosmological inference from weak lensing measurements. The redshift distributions of tomographic redshift bins are parameterised using a flexible modified Gaussian mixture model. We fit this model to pre-calibrated redshift distributions and implement an analytic marginalisation over the potentially several hundred redshift nuisance parameters in the weak lensing likelihood, which is demonstrated to accurately recover the cosmological posterior. By iteratively fitting cosmological and nuisance parameters arising from the redshift distribution model, we perform a self-calibration of the redshift distributions via the tomographic cosmic shear measurements. Our method is applied to the third data release of the Kilo-Degree Survey combined with the VISTA Kilo-Degree Infrared Galaxy Survey (KV450). We find constraints on cosmological parameters that are in very good agreement with the fiducial KV450 cosmic shear analysis and investigate the effects of the more flexible model on the self-calibrated redshift distributions. We observe posterior shifts of the medians of the five tomographic redshift distributions of up to $\Delta z \approx 0.02$, which are however degenerate with an observed decrease of the amplitude of intrinsic galaxy alignments by about $10\%$.