ShantanuT01/DACTYL-Pretraining huggingface dataset:
In this letter, we have demonstrated the possibility to efficiently relay the radiative heat flux between two nanoparticles by opening a smooth channel for heat transfer. By coating the nanoparticles with a silica shell and modifying the substrate with multilayered graphene sheets respectively, the localized phonon polaritons excited near the nanoparticles can couple with the multiple surface plasmon polaritons near the substrate to realize the heat relay in the long distance. The heat transfer can be enhanced by more than six orders of magnitude and the relay distance can be as high as 35 times in the far-field regime. The work may provide a way to realize the energy modulation or thermal communications especially in long distance.
In quantum electrodynamics, photon-photon scattering can be the result of the exchange of virtual electron-positron pairs. This gives rise to a non-trivial dispersion relation for a single photon moving on a background of electromagnetic fields. Knowledge of the dispersion relation can be transferred, using standard methods, into new insights in the dynamical equations for the photons. Effectively, those equations will contain different types of self-interaction terms, depending on whether the photons are coherent or not. It is shown that coherent photons are governed by a nonlinear Schroedinger type equation, such that the self-interaction terms vanish in the limit of parallel propagating waves. For incoherent photons, a set of fluid equations can determine the evolution of the corresponding radiation gas. In the case of a self-interacting radiation fluid, it is shown that Landau damping can occur.
We construct large velocity vector solutions to the three dimensional inhomogeneous Navier-Stokes system. The result is proved via the stability of two dimensional solutions with constant density, under the assumption that initial density is point-wisely close to a constant. Key elements of our approach are estimates in the maximal regularity regime and the Lagrangian coordinates. Considerations are done in the whole $\R^3$.
We show that the orbital variation in the UV P Cygni lines of the X-ray binary LMC X-4 results when X-rays photoionize nearly the entire region outside of the X-ray shadow of the normal star. We fit models to HST GHRS observations of N V and C IV P Cygni line profiles. Analytic methods assuming a spherically symmetric wind show that the wind velocity law is well-fit by v~(1-1/r)^beta, where beta is likely 1.4-1.6 and definitely <2.5. Escape probability models can fit the observed P Cygni profiles, and provide measurements of the stellar wind parameters. The fits determine Lx/Mdot=2.6+/-0.1 x10^43 erg/s/Msun yr, where Lx is the X-ray luminosity and Mdot is the mass-loss rate of the star. Allowing an inhomogeneous wind improves the fits. IUE spectra show greater P Cygni absorption during the second half of the orbit than during the first. We discuss possible causes of this effect.
This discussion examines recent developments in the theory of a Weyl-like, Cartan geometry with natural Schr\"odinger field behavior proposed previously. In that model, very nearly exactly a coupled Einstein-Maxwell- Schr\"odinger, classical field theory emerges from a gauge invariant, purely geometric action based solely on variations of the electromagnetic potentials and the metric. In spite of this, only slight differences appear between the resulting Schr\"odinger part, and the conventional theory of the Schr\"odinger field. Close examination of the differences reveals that most are general relativistic effects which are unobservable in flat spacetime, and which are estimated to interact significantly only via their gravitational fields, or on scales comparable with neutrino interaction cross sections. The only remaining difference is that the wavefunction obeying the conjugate wave equation is not always restricted to be exactly the complex conjugate of the primary wavefunction. Generalizations of the model lead naturally to spinlike phenomena, a possible new mechanism for a theory of rest mass, and spinor connections containing the form of an SU(2) potential.
We provide accurate assessments of the consequences of violations of self-consistency in Hartree-Fock (HF) based random phase approximation (RPA) calculations of the centroid energy $E_{cen}$ of isoscalar and isovector giant resonances of multi-polarities $L=0-3$ in a wide range of nuclei. This is done by carrying out highly accurate HF-RPA calculations neglecting the particle-hole (ph) spin-orbit or Coulomb interaction in the RPA and comparing with the fully self-consistent HF-RPA results. We find that the shifts in the value of $E_{cen}$ due to self-consistency violation associated with the spin-orbit and Coulomb interactions are comparable or larger than the current experimental errors in $E_{cen}$.
In this paper we describe the geometry of the 2m-dimensional Fano manifold G parametrizing (m-1)-planes in a smooth complete intersection Z of two quadric hypersurfaces in the complex projective space P^{2m+2}, for m>0. We show that there are exactly 2^{2m+2} distinct isomorphisms in codimension one between G and the blow-up of P^{2m} at 2m+3 general points, parametrized by the 2^{2m+2} distinct m-planes contained in Z, and describe these rational maps explicitly. We also describe the cones of nef, movable and effective divisors of G, as well as their dual cones of curves. Finally, we determine the automorphism group of G. These results generalize to arbitrary even dimension the classical description of quartic del Pezzo surfaces (m=1).
This paper has been withdrawn by the author due to some mistakes
In classical and quantum spin ice, rod-like features appear in the neutron scattering structure factor when the pinchpoints characteristic of classical spin ice get washed out. We show that these features do not indicate the absence of spin correlations between planes perpendicular to the rods. Rather, they arise because unpolarised neutron scattering is largely insensitive to the three-dimensional correlations which are present throughout. We present two very simple models which exhibit a pristine incarnation of such scattering rods. This provides a physical picture for their appearance, elucidates the role played by monopole excitations and identifies conditions conducive to their observation.
In this paper we construct the moduli of semistable principal bundles with structure group a semisimple group, over nonsingular curves in positive characteristic, with good bounds on the prime.
Let $G$ be a finite abelian group. Let $g(G)$ be the smallest positive integer $t$ such that every subset of cardinality $t$ of the group $G$ contains a subset of cardinality $\mathrm{exp}(G)$ whose sum is zero. In this paper, we show that if X is a subset of $\mathbb{Z}^2_{2n}$ with cardinality $4n+1$ and $2n$ or $2n-1$ elements of $X$ have the same first coordintes, then $X$ contains a zero sum subset. As an application of our results we prove that $g(\mathbb{Z}^2_6) = 13.$ This settles Gao-Thangaduri's conjecture for the case $n=6.$ We also prove some results towards the general even $n$ cases of the conjecture.
We present a high density disc reflection spectral analysis of a sample of 17 Seyfert 1 galaxies to study the inner disc densities at different black hole mass scales and accretion rates. All the available XMM-Newton observations in the archive are used. OM observations in the optical/UV band are used to estimate their accretion rates. We find that 65% of sources in our sample show a disc density significantly higher than 1e15 cm^{-3}, which was assumed in previous reflection-based spectral analyses. The best-fit disc densities show an anti-correlation with black hole mass and mass accretion rate. High density disc reflection model can successfully explain the soft excess emission and significantly reduce inferred iron abundances. We also compare our black hole spin and disc inclination angle measurements with previous analyses.
Asteroseismology has undergone a profound transformation as a scientific field following the CoRoT and Kepler space missions. The latter is now yielding the first measurements of latitudinal differential rotation obtained directly from oscillation frequencies. Differential rotation is a fundamental mechanism of the stellar dynamo effect. Our goal is to measure the amount of differential rotation in the solar analogues 16 Cyg A and B, which are the components of a binary system. These stars are the brightest observed by Kepler and have therefore been extensively observed, with exquisite precision on their oscillation frequencies. We modelled the acoustic power spectrum of 16 Cyg A and B using a model that takes into account the contribution of differential rotation to the rotational frequency splitting. The estimation was carried out in a Bayesian setting. We then inverted these results to obtain the rotation profile of both stars under the assumption of a solar-like functional form. We observe that the magnitude of latitudinal differential rotation has a strong chance of being solar-like for both stars, their rotation rates being higher at the equator than at the pole. The measured latitudinal differential rotation, defined as the difference of rotation rate between the equator and the pole, is $320\pm269$ nHz and $440^{+363}_{-383}$ nHz for 16 Cyg A and B, respectively, confirming that the rotation rates of these stars are almost solar-like. Their equatorial rotation rates are $535\pm75$ nHz and $565_{-129}^{+150}$ nHz. Our results are in good agreement with measurements obtained from spectropolarimetry, spectroscopy, and photometry. We present the first conclusive measurement of latitudinal differential rotation for solar analogues. Their rotational profiles are very close to those of the Sun. These results depend weakly on the uncertainties of the stellar parameters.
A generalization of the Emden-Fowler equation is presented and its solutions are investigated. This paper is devoted to asymptotic behavior of its solutions. The procedure is entirely based on a previous paper by the author.
An increase in the efficiency of sampling from Boltzmann distributions would have a significant impact on deep learning and other machine-learning applications. Recently, quantum annealers have been proposed as a potential candidate to speed up this task, but several limitations still bar these state-of-the-art technologies from being used effectively. One of the main limitations is that, while the device may indeed sample from a Boltzmann-like distribution, quantum dynamical arguments suggest it will do so with an {\it instance-dependent} effective temperature, different from its physical temperature. Unless this unknown temperature can be unveiled, it might not be possible to effectively use a quantum annealer for Boltzmann sampling. In this work, we propose a strategy to overcome this challenge with a simple effective-temperature estimation algorithm. We provide a systematic study assessing the impact of the effective temperatures in the learning of a special class of a restricted Boltzmann machine embedded on quantum hardware, which can serve as a building block for deep-learning architectures. We also provide a comparison to $k$-step contrastive divergence (CD-$k$) with $k$ up to 100. Although assuming a suitable fixed effective temperature also allows us to outperform one step contrastive divergence (CD-1), only when using an instance-dependent effective temperature do we find a performance close to that of CD-100 for the case studied here.
The Coulomb blockade in an open quantum dot connected to a bulk lead by a single mode point contact is studied numerically using the path-integral Monte Carlo method. The Coulomb oscillation of the average charge and capacitance of the dot is investigated, and is compared with the analytic expression for strong tunneling. At the degeneracy point, we observe logarithmic divergence of the capacitance for strong backscattering at the point contact. This observation supports the conjecture that the nature of the present system at the degeneracy point is described by the two-channel Kondo problem for an arbitrary strength of tunneling.
Fast cadence time resolved spectra taken at the CTIO-4m telescope with the RC-spectrograph during 2 consecutive nights revealed a long term modulation of the binary radial velocity. Chandra hard X-ray spectra taken with the HETGS instrument showed features typically observed in magnetic white dwarfs (WD). Here, we present the new data and suggest that CP Pup is possibly a long orbital period intermediate polar.
Recently, it has been shown that multi-terminal superconducting nanostructures may possess topological properties that involve Berry curvatures in the parametric space of the superconducting phases of the terminals, and associated Chern numbers that are manifested in quantized transconductances of the nanostructure. In this Article, we investigate how the continuous spectrum that is intrinsically present in superconductors, affects these properties. We model the nanostructure within scattering formalism deriving the action and the response function that permits a re-definition of Berry curvature for continuous spectrum.   We have found that the re-defined Berry curvature may have a non-topological phase-independent contribution that adds a non-quantized part to the transconductances. This contribution vanishes for a time-reversible scattering matrix. We have found compact expressions for the redefined Berry curvature for the cases of weak energy dependence of the scattering matrix and investigated the vicinity of Weyl singularities in the spectrum.
With 2D hydrodynamical simulations, we study the evolution of the hot gas flows in early-type galaxies, focussing on the effects of galaxy rotation on the thermal and dynamical status of the ISM. The galaxy is modelled as a two-component axisymmetric system (stars and dark matter), with a variable amount of azimuthal velocity dispersion and rotational support; the presence of a counter rotating stellar disk is also considered. It is found that the ISM of the rotationally supported (isotropic) model is more prone to thermal instabilities than the fully velocity dispersion counterpart, while its ISM temperature and X-ray luminosity are lower. The model with counter rotation shows an intermediate behaviour.
In this paper, we prove a function field-analogue of Poonen-Rains heuristics on the average size of $p$-Selmer group. Let $E$ be an elliptic curve defined over $\mathbb{Z}[t]$. Then $E$ is also defined over $\mathbb{F}_q$ for any $q$ of prime power. We show that for large enough $q$, the average size of the $p$-Selmer groups over the family of quadratic twists of $E$ over $\mathbb{F}_q[t]$ is equal to $p+1$ for all but finitely many primes $p$. Namely, if we twist the curve in $\mathbb{F}_q[t]$ by polynomials of fixed degree $n$ and let both $n$ and $q$ approach to infinity, then the average rank of $p$-Selmer group converges to $p+1$.
In this paper we study in detail the dynamics of flavor transformation for neutrinos propagating in the very dense environment of astrophysical compact objects as Type II supernova in post collapse phase and proto-neutron stars. The analysis is based on the formalism by Strack and Burrows, who introduced the generalized Boltzmann equation for Wigner phase space density. In appropriate limits the formalism reduces to the usual evolution equations for the wave functions or for density matrix elements of Liouville equation. We incorporate the most important aspects of neutrino propagation physics: the phenomenology of standard oscillations with MSW resonance induced by ordinary matter, collective behavior due to self-interaction, which can produce bipolar and synchronized flavor oscillations, whose relevance is recognized by recent literature, the combination of these effects with collisions including scattering, emission and absorption of neutrinos.
Facial expression recognition has been an active area in computer vision with application areas including animation, social robots, personalized banking, etc. In this study, we explore the problem of image classification for detecting facial expressions based on features extracted from pre-trained convolutional neural networks trained on ImageNet database. Features are extracted and transferred to a Linear Support Vector Machine for classification. All experiments are performed on two publicly available datasets such as JAFFE and CK+ database. The results show that representations learned from pre-trained networks for a task such as object recognition can be transferred, and used for facial expression recognition. Furthermore, for a small dataset, using features from earlier layers of the VGG19 network provides better classification accuracy. Accuracies of 92.26% and 92.86% were achieved for the CK+ and JAFFE datasets respectively.
The enhancon mechanism removes a family of time-like singularities from certain supergravity spacetimes by forming a shell of branes on which the exterior geometry terminates. The problematic interior geometry is replaced by a new spacetime, which in the prototype extremal case is simply flat. We show that this excision process, made inevitable by stringy phenomena such as enhanced gauge symmetry and the vanishing of certain D-branes' tension at the shell, is also consistent at the purely gravitational level. The source introduced at the excision surface between the interior and exterior geometries behaves exactly as a shell of wrapped D6-branes, and in particular, the tension vanishes at precisely the enhancon radius. These observations can be generalised, and we present the case for non-extremal generalisations of the geometry, showing that the procedure allows for the possibility that the interior geometry contains an horizon. Further knowledge of the dynamics of the enhancon shell itself is needed to determine the precise position of the horizon, and to uncover a complete physical interpretation of the solutions.
In a recent survey of the stellar populations of LINERS and LINER/HII Transition Objects (TOs) we identified a numerous class of nuclei which stand out because of their conspicuous 10^8-9 yr populations. These objects were called ``Young-TOs'', since they all have TO-like emission line ratios. In this paper we investigate the radial variations of spectral properties in Low Luminosity AGN. Our analysis is based on high S/N, 3500-5500 A, long-slit spectra for 47 galaxies. The data probe distances of typically up to 850 pc from the nucleus with a resolution of ~ 100 pc and S/N ~ 30. Stellar population gradients are mapped by the radial profiles of absorption line equivalent widths and colours along the slit. These variations are further analyzed by means of a decomposition of each spectrum in terms of template galaxies representative of very young (<= 10^7 yr), intermediate age (10^8-9 yr) and old (10^10 yr) populations.   Our main findings are: (1) Significant stellar population gradients are found almost exclusively in Young-TOs. (2) The intermediate age population of Young-TOs, although heavily concentrated in the nucleus, reaches distances of up to a few hundred pc. (3) Objects with predominantly old populations present spatially homogeneous spectra, be they LINERs or TOs. (4) Young-TOs have much more dust in their central regions than other LLAGN. (5) The B-band luminosities of the central <~ 1 Gyr population in Young-TOs are within an order of magnitude of M_B = -15, implying masses of order ~ 10^7-10^8 Mo. This population was 10-100 times more luminous in its formation epoch, at which time young massive stars would have completely outshone any active nucleus, unless the AGN too was brighter in the past. (abridged)
The critical behavior of long straight rigid rods of length $k$ ($k$-mers) on square and triangular lattices at intermediate density has been studied. A nematic phase, characterized by a big domain of parallel $k$-mers, was found. This ordered phase is separated from the isotropic state by a continuous transition occurring at a intermediate density $\theta_c$. Two analytical techniques were combined with Monte Carlo simulations to predict the dependence of $\theta_c$ on $k$, being $\theta_c(k) \propto k^{-1}$. The first involves simple geometrical arguments, while the second is based on entropy considerations. Our analysis allowed us also to determine the minimum value of $k$ ($k_{min}=7$), which allows the formation of a nematic phase on a triangular lattice.
The Survey of HI in Extremely Low-mass Dwarfs (SHIELD) includes a volumetrically complete sample of 82 gas-rich dwarfs with M_HI~<10^7.2 Msun selected from the ALFALFA survey. We are obtaining extensive follow-up observations of the SHIELD galaxies to study their gas, stellar, and chemical content, and to better understand galaxy evolution at the faint end of the HI mass function. Here, we investigate the properties of 30 SHIELD galaxies using Hubble Space Telescope imaging of their resolved stars and Westerbork Synthesis Radio Telescope observations of their neutral hydrogen. We measure tip of the red giant branch (TRGB) distances, star formation activity, and gas properties. The TRGB distances are up to 4x greater than estimates from flow models, highlighting the importance of velocity-independent distance indicators in the nearby universe. The SHIELD galaxies are in under-dense regions, with 23% located in voids; one galaxy appears paired with a more massive dwarf. We quantify galaxy properties at low masses including stellar and HI masses, SFRs, sSFRs, SFEs, birthrate parameters, and gas fractions. The lowest mass systems lie below the mass thresholds where stellar mass assembly is predicted to be impacted by reionization. Even so, we find the star formation properties follow the same trends as higher mass gas-rich systems, albeit with a different normalization. The HI disks are small (<r><0.7 kpc) making it difficult to measure the HI rotation using standard techniques; we develop a new methodology and report the velocity extent, and its associated spatial extent, with robust uncertainties.
Galaxy interactions and mergers play a significant, but still debated and poorly understood role in the star formation history of galaxies. Numerical and theoretical models cannot yet explain the main properties of merger-induced starbursts, including their intensity and their spatial extent. Usually, the mechanism invoked in merger-induced starbursts is a global inflow of gas towards the central kpc, resulting in a nuclear starburst. We show here, using high-resolution AMR simulations and comparing to observations of the gas component in mergers, that the triggering of starbursts also results from increased ISM turbulence and velocity dispersions in interacting systems. This forms cold gas that are denser and more massive than in quiescent disk galaxies. The fraction of dense cold gas largely increases, modifying the global density distribution of these systems, and efficient star formation results. Because the starbursting activity is not just from a global compacting of the gas to higher average surface densities, but also from higher turbulence and fragmentation into massive and dense clouds, merging systems can enter a different regime of star formation compared to quiescent disk galaxies. This is in quantitative agreement with recent observations suggesting that disk galaxies and starbursting systems are not the low-activity end and high-activity end of a single regime, but actually follow different scaling relations for their star formation.
The present paper concerns the question of the violation of the r-th inequality for extremal curves in the projective r-space, posed by T. Kato and G. Martens. We show that the answer is negative in many cases. The result is obtained by a detailed analysis of the geometry of extremal curves and their canonical model. As a consequence, we show that particular curves on a Hirzebruch surface do not violate the slope inequalities in a certain range.