ShantanuT01/DACTYL-Pretraining huggingface dataset:
The quantum criticality of an Ising-like screw chain antiferromagnet SrCo$_2$V$_2$O$_8$, with a transverse magnetic field applied along the crystalline $a$-axis, is investigated by ultra-low temperature NMR measurements. The N\'{e}el temperature is rapidly and continuously suppressed by the field, giving rise to a quantum critical point (QCP) at $H_{C{_1}}$$\approx$~7.0~T. Surprisingly, a second QCP at $H_{C{_2}}\approx$~7.7~T featured with gapless excitations is resolved from both the double-peak structure of the field dependent spin-lattice relaxation rate $1/^{51}T_1$ at low temperatures and the weakly temperature-dependent $1/^{51}T_1$ at this field. Our data, combined with numerical calculations, suggest that the induced effective staggered transverse field significantly lowers the critical fields, and leads to an exposed QCP at $H_{C{_2}}$, which belongs to the one-dimensional transverse-field Ising universality.
We establish a variational formula for the exponential decay rate of the Green function of Brownian motion evolving in a random stationary and ergodic nonnegative potential. Such a variational formula is established by Schroeder in 'Green's Functions for the Schr\"odinger Operator with Periodic Potential', J. Funct. Anal. 77 (1988), for potentials on compact spaces and is generalised in the present article to a non-compact setting. We show exponential decay of the Green function implicitly. This formula for the Lyapunov exponent has several direct implications. It allows to compare the influence of a random potential to the influence of the averaged potential. It also leads to a variational expression for the quenched free energy.
Dwarf novae are white dwarfs accreting matter from a nearby red dwarf companion. Their regular outbursts are explained by a thermal-viscous instability in the accretion disc, described by the disc instability model that has since been successfully extended to other accreting systems. However, the prototypical dwarf nova, SS Cygni, presents a major challenge to our understanding of accretion disc theory. At the distance of 159 +/- 12 pc measured by the Hubble Space Telescope, it is too luminous to be undergoing the observed regular outbursts. Using very long baseline interferometric radio observations, we report an accurate, model-independent distance to SS Cygni that places the source significantly closer at 114 +/- 2 pc. This reconciles the source behavior with our understanding of accretion disc theory in accreting compact objects.
We outline the phenomenon of deep crustal heating in transiently accreting neutron stars. It is produced by nuclear transformations (mostly, by pycnonuclear reactions) in accreted matter while this matter sinks to densities rho > 10^{10} g/cc under the weight of freshly accreted material. We consider then thermal states of transiently accreting neutron stars (with mean mass accretion rates \dot{M}=(10^{-14}-10^{-9}) M_\odot/yr) determined by deep crustal heating. In a simplified fashion we study how the thermal flux emergent from such stars depends on the properties of superdense matter in stellar interiors. We analyze the most important regulators of the thermal flux: strong superfluidity in the cores of low-mass stars and fast neutrino emission (in nucleon, pion-condensed, kaon-condensed, or quark phases of dense matter) in the cores of high-mass stars. We compare the results with observations of soft X-ray transients in quiescent states.
We present the evolution of dust and molecular gas properties in a sample of 11 $z\sim0.03$ starburst to post-starburst (PSB) galaxies selected to span an age sequence from ongoing starburst to 1 Gyr after the starburst ended. All PSBs harbour significant molecular gas and dust reservoirs and residual star formation, indicating that complete quenching of the starburst due to exhaustion or expulsion of gas has not occurred during this timespan. As the starburst ages, we observe a clear decrease in the star-formation efficiency, molecular gas and SFR surface density, and effective dust temperature, from levels coincident with starburst galaxies to those of normal star-forming galaxies. These trends are consistent with a natural decrease in the SFR following consumption of molecular gas by the starburst, and corresponding decrease in the interstellar radiation field strength as the starburst ages. The gas and dust contents of the PSBs are coincident with those of star-forming galaxies and molecular gas-rich early-type galaxies, and are not consistent with galaxies on the red-sequence. We find no evidence that the global gas reservoir is expelled by stellar winds or AGN feedback. Our results show that although a strong starburst in a low-redshift galaxy may cause the galaxy to ultimately have a lower specific SFR and be of an earlier morphological type, the galaxy will remain in the "green valley" for an extended time. Multiple such episodes may be needed to complete migration of the galaxy from the blue- to red-sequence.
Recently, low light level charge coupled devices (L3CCDs) capable of on-chip gain have been developed, leading to sub-electron effective readout noise, allowing for the detection of single photon events. Optical interferometry usually requires the detection of faint signals at high speed and so L3CCDs are an obvious choice for these applications. Here we analyse the effect that using an L3CCD has on visibility parameter estimation (amplitude and triple product phase), including situations where the L3CCD raw output is processed in an attempt to reduce the effect of stochastic multiplication noise introduced by the on-chip gain process. We establish that under most conditions, fringe parameters are estimated accurately, whilst at low light levels, a bias correction which we determine here, may need to be applied to the estimate of fringe visibility amplitude. These results show that L3CCDs are potentially excellent detectors for astronomical interferometry at optical wavelengths.
Halide perovskites are strongly influenced by large amplitude anharmonic lattice fluctuations at room temperature. We develop a tight binding model for dynamically disordered MAPbI$_3$ based on density functional theory (DFT) calculations to calculate electronic structure for finite temperature crystal structures at the length scale of thermal disorder and carrier localization. The model predicts individual Hamiltonian matrix elements and band structures with high accuracy, owing to the inclusion of additional matrix elements and descriptors for non-Coulombic interactions. We apply this model to electronic structure at length and time scales inaccessible to first principles methods, finding an increase in band gap, carrier mass, and the sub-picosecond fluctuations in these quantities with increasing temperature as well as the onset of carrier localization in large supercells induced by thermal disorder at 300 K. We identify the length scale $L^*= 5$ nm as the onset of localization in the electronic structure, associated with associated with decreasing band edge fluctuations, increasing carrier mass, and Rashba splitting approaching zero.
We apply the bottom-up reconstruction technique in the context of bouncing cosmology in F(R) gravity, where the starting point is a suitable ansatz of observable quantity (like spectral index or tensor to scalar ratio) rather than a priori form of Hubble parameter. In inflationary scenario, the slow roll conditions are assumed to hold true, and thus the observational indices have general expressions in terms of the slow-roll parameters, as for example the tensor to scalar ratio in F(R) inflation can be expressed as $r = 48\epsilon_F^2$ with $\epsilon_F = -\frac{1}{H_F^2}\frac{dH_F}{dt_F}$ and $H_F$, $t_F$ are the Hubble parameter, cosmic time respectively. However, in the bouncing cosmology (say in F(R) gravity theory), the slow-roll conditions are not satisfied, in general, and thus the observable quantities do not have any general expressions that will hold true irrespective of the form of F(R). Thus, in order to apply the bottom-up reconstruction procedure in F(R) bouncing model, we use the conformal correspondence between F(R) and scalar-tensor model where the conformal factor in the present context is chosen in a way such that it leads to an inflationary scenario in the scalar-tensor frame. Due to the reason that the scalar and tensor perturbations remain invariant under conformal transformation, the observable viability of the scalar-tensor inflationary model confirms the viability of the conformally connected F(R) bouncing model. Motivated by these arguments, here we construct a viable non-singular bounce in F(R) gravity directly from the observable indices of the corresponding scalar-tensor inflationary model.
We report trigonometric parallaxes for 134 low mass stars and brown dwarfs, of which 38 have no previously published measurement and 79 more have improved uncertainties. Our survey targeted nearby targets, so 119 are closer than 30 pc. Of the 38 stars with new parallaxes, 14 are within 20 pc and seven are likely brown dwarfs (spectral types later than L0). These parallaxes are useful for studies of kinematics, multiplicity, and spectrophotometric calibration. Two objects with new parallaxes are confirmed as young stars with membership in nearby young moving groups: LP 870-65 in AB Doradus and G 161-71 in Argus. We also report the first parallax for the planet-hosting star GJ 3470; this allows us to refine the density of its Neptune-mass planet. One T-dwarf, 2MASS J12590470-4336243, previously thought to lie within 4 pc, is found to be at 7.8 pc, and the M-type star 2MASS J01392170-3936088 joins the ranks of nearby stars as it is found to be within 10 pc. Five stars that are over-luminous and/or too red for their spectral types are identified and deserve further study as possible young stars.
Very high energy gamma-ray observations offer indirect methods for studying the highest energy cosmic rays in our Universe. The origin of cosmic rays at energies greater than $10^{18}$ eV remains a mystery, and many questions in particle astrophysics exist. The VERITAS observatory in southern Arizona, USA, carries out an extensive observation program of the gamma-ray sky at energies above 85 GeV. Observations of Galactic and extragalactic sources in the TeV band provide clues to the highly energetic processes occurring in these objects, and could provide indirect evidence for the origin of cosmic rays and the sites of particle acceleration in the Universe. VERITAS has now been operational for ten years with the complete array of four atmospheric Cherenkov telescopes. In this review, we present the status of VERITAS, and give few results from three of its key scientific programs: extragalactic science, Galactic physics, and study of fundamental physics and cosmology.
The X-ray afterglow plateau emission observed in many Gamma-ray Bursts (GRBs) has been interpreted as either being fueled by fallback onto a newly formed black hole, or by the spin-down luminosity of an ultra-magnetized millisecond neutron star. If the latter model is assumed, GRB X-ray afterglow light curves can be analytically reproduced. We fit a sample of GRB X-ray plateaus, interestingly yielding a distribution in the magnetic field versus spin period (B-P) diagram consistent with $B\propto P^{7/6}$. This is expected from the well-established physics of the spin-up line minimum period for Galactic millisecond pulsars. The normalisation of the relation we obtain perfectly matches spin-up line predictions for the expected masses ($\sim 1 M_{\odot}$) and radii ($\sim 10 {\rm ~km}$) of newly born magnetars, and mass accretion rates consistent with GRB expectations of $10^{-4} M_{\odot}/{\rm s} <\dot{M}< 10^{-1} M_{\odot}/{\rm s}$. Short GRBs with extended emission (SEE) appear towards the high period end of the distribution, while the long GRBs (LGRBs) towards the short period end. This result is consistent with spin-up limit expectations where the total accreted mass determines the position of the neutron star in the B-P diagram. The P-B distribution for LGRBs and SEE are statistically different, further supporting the idea that the fundamental plane relation \citep{dainotti16c,Dainotti2017} is a powerful discriminant among those populations. Our conclusions are robust against suppositions regarding the GRB collimation angle and magnetar breaking index, which shifts the resulting magnetar properties parallel to the spin-up line, and strongly support a magnetar origin for GRBs presenting X-ray plateaus.
In this paper we confirm a conjecture of F\"uredi, Jiang, and Seiver, and determine an exact formula for the Tur\'an number $ex_3(n; P_3^3)$ of the 3-uniform linear path $P^3_3$ of length 3, valid for all $n$. It coincides with the analogous formula for the 3-uniform triangle $C^3_3$, obtained earlier by Frankl and F\"uredi for $n\ge 75$ and Cs\'ak\'any and Kahn for all $n$. In view of this coincidence, we also determine a `conditional' Tur\'an number, defined as the maximum number of edges in a $P^3_3$-free 3-uniform hypergraph on $n$ vertices which is \emph{not} $C^3_3$-free.
Let $ \{W(t), t\ge 0\}$ be a standard Brownian motion. If $I$ is a bounded interval on which $W $ has no zero, an almost sure lower bound to $\inf\{|W(t)|, t\in I\}$ can be provided, when $I$ is taken from a given countable family of intervals covering the positive half-line.
In two-view geometry, the essential matrix describes the relative position and orientation of two calibrated images. In three views, a similar role is assigned to the calibrated trifocal tensor. It is a particular case of the (uncalibrated) trifocal tensor and thus it inherits all its properties but, due to the smaller degrees of freedom, satisfies a number of additional algebraic constraints. Some of them are described in this paper. More specifically, we define a new notion --- the trifocal essential matrix. On the one hand, it is a generalization of the ordinary (bifocal) essential matrix, and, on the other hand, it is closely related to the calibrated trifocal tensor. We prove the two necessary and sufficient conditions that characterize the set of trifocal essential matrices. Based on these characterizations, we propose three necessary conditions on a calibrated trifocal tensor. They have a form of 15 quartic and 99 quintic polynomial equations. We show that in the practically significant real case the 15 quartic constraints are also sufficient.
The IceCube Neutrino Observatory opened the window on high-energy neutrino astronomy by confirming the existence of PeV astrophysical neutrinos and identifying the first compelling astrophysical neutrino source in the blazar TXS0506+056. Planning is underway to build an enlarged detector, IceCube-Gen2, which will extend measurements to higher energies, increase the rate of observed cosmic neutrinos and provide improved prospects for detecting fainter sources. IceCube-Gen2 is planned to have an extended in-ice optical array, a radio array at shallower depths for detecting ultra-high-energy (>100 PeV) neutrinos, and a surface component studying cosmic rays. In this contribution, we will discuss the simulation of the in-ice optical component of the baseline design of the IceCube-Gen2 detector, which foresees the deployment of an additional ~120 new detection strings to the existing 86 in IceCube over ~7 Antarctic summer seasons. Motivated by the phased construction plan for IceCube-Gen2, we discuss how the reconstruction capabilities and sensitivities of the instrument are expected to progress throughout its deployment.
(Abridged) AVOCADO aims at establishing firm conclusions on the formation and evolution of dwarf galaxies by constructing and analysing a homogeneous, multiwavelength dataset for a statistically significant sample of approximately 6500 nearby dwarfs (M_i > -18 mag). We present the sample selection criteria and describe the suite of analysis tools, some of them developed in the framework of the Virtual Observatory. We make use of optical spectra and UV-to-NIR imaging of the dwarf sample to derive SFRs, stellar masses, ages and metallicities - which are further supplemented with structural parameters that are used to classify them morphologically. This dataset, coupled with a detailed characterisation of each dwarf's environment, allows for a fully comprehensive investigation of their origins and to track the potential evolutionary paths between the different dwarf types. We characterise the local environment of all dwarfs in our sample, paying special attention to trends with current star formation activity. We find that virtually all quiescent dwarfs are located in the vicinity (projected distances < 1.5 Mpc) of L* companions, consistent with recent results. While star-forming dwarfs are preferentially found at separations of the order of 1 Mpc, there appears to be a tail towards low separations (<100 kpc) in the distribution of projected distances. We speculate that, modulo projection effects, this probably represents a genuine population of late-type dwarfs caught upon first infall about their host and before environmental quenching has fully operated. In this context, these results suggest that internal mechanisms -such as gas exhaustion via star formation or feedback effects- are not sufficient to completely cease the star formation activity in dwarf galaxies, and that becoming the satellite of a massive central galaxy appears to be a necessary condition to create a quiescent dwarf.
A comparison of impulse approximation calculations for the (e,e'p) reaction, based on the Dirac equation and the Schrodinger one is presented. Trivial (kinematics) differences are indicated, as well as how to remove them from the standard nonrelativistic formalism. Signatures of the relativistic approach are found where the enhancement of the lower components (spinor distortion or negative energy contributions) modifies TL observables with respect to the nonrelativistic predictions, what seems to be confirmed by the experiment. Finally, the relativistic approach is used to analyze several experiments for the reaction 16O(e,e'p)15N taken at values of Q^2 from 0.2 to 0.8 (GeV/c)^2, not finding a significant Q^2 dependence of the scale factors over this range.
Single photon emitters (SPEs) in solids have emerged as promising candidates for quantum photonic sensing, communications, and computing. Defects in hexagonal boron nitride (hBN) exhibit high-brightness, room-temperature quantum emission, but their large spectral variability and unknown local structure significantly challenge their technological utility. Here, we directly correlate hBN quantum emission with the material's local strain using a combination of photoluminescence (PL), cathodoluminescence (CL) and nano-beam electron diffraction. Across 40 emitters and 15 samples, we observe zero phonon lines(ZPLs) in PL and CL ranging from 540-720 nm. CL mapping reveals that multiple defects and distinct defect species located within an optically-diffraction-limited region can each contribute to the observed PL spectra. Local strain maps indicate that strain is not required to activate the emitters and is not solely responsible for the observed ZPL spectral range. Instead, four distinct defect classes are responsible for the observed emission range. One defect class has ZPLs near 615 nm with predominantly matched CL-PL responses; it is not a strain-tuned version of another defect class with ZPL emission centered at 580 nm. A third defect class at 650 nm has low visible-frequency CL emission; and a fourth defect species centered at 705 nm has a small, ~10 nm shift between its CL and PL peaks. All studied defects are stable upon both electron and optical irradiation. Our results provide an important foundation for atomic-scale optical characterization of color centers, as well as a foundation for engineering defects with precise emission properties.
The existence of electric fields close to their critical value $E_c=\frac{m_e^2 c^3}{e \hbar}$ has been proved for massive cores of $10^7$ up to $10^{57}$ nucleons using a proton distribution of constant density and a sharp step function at its boundary. We explore the modifications of this effect by considering a smoother density profile with a proton distribution fulfilling a Woods--Saxon dependence. The occurrence of a critical field has been confirmed. We discuss how the location of the maximum of the electric field as well as its magnitude is modified by the smoother distribution.
We show, using the N-body code GADGET-2, that stellar scattering by massive clumps can produce exponential discs, and the effectiveness of the process depends on the mass of scattering centres, as well as the stability of the galactic disc. Heavy, dense scattering centres in a less stable disc generate an exponential profile quickly, with a timescale shorter than 1 Gyr. The profile evolution due to scattering can make a near-exponential disc under various initial stellar distributions. This result supports analytic theories that predict the scattering processes always favour the zero entropy gradient solution to the Jeans/Poisson equations, whose profile is a near-exponential. Profile changes are accompanied by disc thickening, and a power-law increase in stellar velocity dispersion in both vertical and radial directions is also observed through the evolution. Close encounters between stars and clumps can produce abrupt changes in stellar orbits and shift stars radially. These events can make trajectories more eccentric, but many leave eccentricities little changed. On average, orbital eccentricities of stars increase moderately with time.
The present work deals with an interacting dark energy model in the framework of f(T) cosmology. A cosmologically viable form of f(T) is chosen (T is the torsion scalar in teleparallelism) in the background of flat homogeneous and isotropic Friedmann-Robertson-Walker (FRW) space-time model of the universe. The matter content of the universe is chosen as dust interacting with minimally coupled scalar field. The evolution equations are reduced to an autonomous system of ordinary differential equations by suitable transformation of variables. The nature of critical points are analyzed by evaluating the eigenvalues of the linearized Jacobi matrix and stable attractors are examined from the point of view of cosmology. Finally, both classical and quantum stability of the model have been discussed.
Using the geodesic method and the perturbative approach, we study the deflection of light by time-periodic spherically symmetric gravitational fields. Assuming the weakness of the gravitational field, we derive general formulas that determine the deflection angle in the leading order approximation. The formulas are valid for both time-periodic and static metrics. Using these results, we calculate the deflection angle of a light ray passing through a spherically symmetric oscillating distribution of a self-gravitating scalar field with a logarithmic potential. It turned out that in this case the deflection angle does not depend on time in the leading order.
In this paper, we share our experience in designing a convolutional network-based face detector that could handle faces of an extremely wide range of scales. We show that faces with different scales can be modeled through a specialized set of deep convolutional networks with different structures. These detectors can be seamlessly integrated into a single unified network that can be trained end-to-end. In contrast to existing deep models that are designed for wide scale range, our network does not require an image pyramid input and the model is of modest complexity. Our network, dubbed ScaleFace, achieves promising performance on WIDER FACE and FDDB datasets with practical runtime speed. Specifically, our method achieves 76.4 average precision on the challenging WIDER FACE dataset and 96% recall rate on the FDDB dataset with 7 frames per second (fps) for 900 * 1300 input image.