ShantanuT01/DACTYL-Pretraining huggingface dataset:
We report first-principles density-functional study of electron-phonon interactions and thermoelectric transport properties of full-Heusler compounds Sr$_{2}$BiAu and Sr$_{2}$SbAu. Our results show that ultrahigh intrinsic bulk thermoelectric performance across a wide range of temperatures is physically possible and point to the presence of multiply degenerate and highly dispersive carrier pockets as the key factor for achieving it. Sr$_{2}$BiAu, which features ten energy-aligned low effective mass pockets (six along $\Gamma-X$ and four at $L$), is predicted to deliver $n$-type $zT=0.4-4.9$ at $T=100-700$~K. Comparison with the previously investigated Ba$_{2}$BiAu compound shows that the additional $L$-pockets in Sr$_{2}$BiAu significantly increase its low-temperature power factor to a maximum value of $12$~mW~m$^{-1}$~K$^{-2}$ near $T=300$~K. However, at high temperatures the power factor of Sr$_{2}$BiAu drops below that of Ba$_{2}$BiAu because the $L$ states are heavier and subject to strong scattering by phonon deformation as opposed to the lighter $\Gamma-X$ states that are limited by polar-optical scattering. Sr$_{2}$SbAu is predicted to deliver lower $n$-type of $zT=3.4$ at $T=750$~K due to appreciable misalignment between the $L$ and $\Gamma-X$ carrier pockets, generally heavier scattering, and slightly higher lattice thermal conductivity. Soft acoustic modes, responsible for low lattice thermal conductivity, also increase vibrational entropies and high-temperature stability of the Heusler compounds, suggesting that their experimental synthesis may be feasible. The dominant intrinsic defects are found to be Au vacancies, which drive the Fermi level towards the conduction band and work in favor of $n$-doping.
Full-disk spectroheliograms have been taken in Coimbra on a daily basis since 1926 in the Ca II K-line (K1 and K3). Later, in 1989, with the upgrade of the equipment it was possible to start the observations in the H-alpha line. The spectroheliograms of Coimbra constitutes a huge dataset of solar images, which requires an efficient automatic tool to detect and analyse solar activity features. This work presents a mathematical morphology approach applied to the CaII K3 series. The objective is to create a tool based on the segmentation by watershed transform combined with other morphological operators to detect automatically and analyse chromospheric plages during the solar cycle 24. The tool is validated by comparing its results for cycle 23 with those presented by Dorotovic et al. (2007, 2010). The results obtained are in very good agreement with those, including on images obtained in non-ideal meteorological conditions (eg. some clouds in sky). The results were also qualitatively compared with the results obtained through the application of ASSA model to SDO HMI magnetograms.
The determination of solar wind outflow velocity is fundamental in order to probe the mechanisms of wind acceleration in the corona. We aim to study, via the Doppler dimming technique, the effects that the chromospheric Ly{\alpha} line profile shape causes on the determination of the outflow speed of coronal HI atoms. The Doppler dimming technique takes into account the decrease of coronal Ly{\alpha} radiation in regions where HI atoms flow out in the solar wind. Starting from UV observations (UVCS/SOHO) of the coronal Ly{\alpha} line and simultaneous measurements of pB (LASCO/SOHO and Mk3/MLSO), we studied the effect of the pumping chromospheric Ly{\alpha} line profile through measurements from SOHO/SUMER, UVSP/SMM and LPSP/OSO-8, taken from representative on-disk regions and as a function of time during the solar activity cycle. In particular, we considered the effect of four chromospheric line parameters: line width, depth of the central reversal, asymmetry and distance of the peaks. We find that the range of variability of these parameters is of about 50% for the width, 69% for the depth of the central reversal, 35% for the asymmetry, and 50% for the distance of the peaks. Then, we find that the variability of the pumping Ly{\alpha} profile affects the estimates of the coronal HI velocity by about 9-12%. Therefore, this uncertainty is smaller than other physical quantities uncertainties, and a constant in time and unique shape of the Ly{\alpha} profile over the solar disk can be adopted in order to estimate the solar wind outflow velocity.
It is shown that in the absence of free abelian gauge fields, the conserved currents of (classical) Yang-Mills gauge models coupled to matter fields can be always redefined so as to be gauge invariant. This is a direct consequence of the general analysis of the Wess-Zumino consistency condition for Yang-Mills theory that we have provided recently.
An oriented graph $G^\sigma$ is a digraph without loops or multiple arcs whose underlying graph is $G$. Let $S\left(G^\sigma\right)$ be the skew-adjacency matrix of $G^\sigma$ and $\alpha(G)$ be the independence number of $G$. The rank of $S(G^\sigma)$ is called the skew-rank of $G^\sigma$, denoted by $sr(G^\sigma)$. Wong et al. [European J. Combin. 54 (2016) 76-86] studied the relationship between the skew-rank of an oriented graph and the rank of its underlying graph. In this paper, the correlation involving the skew-rank, the independence number, and some other parameters are considered. First we show that $sr(G^\sigma)+2\alpha(G)\geqslant 2|V_G|-2d(G)$, where $|V_G|$ is the order of $G$ and $d(G)$ is the dimension of cycle space of $G$. We also obtain sharp lower bounds for $sr(G^\sigma)+\alpha(G),\, sr(G^\sigma)-\alpha(G)$, $sr(G^\sigma)/\alpha(G)$ and characterize all corresponding extremal graphs.
Observed galaxy clustering exhibits local transverse statistical isotropy around the line-of-sight (LOS). The variation of the LOS across a galaxy survey complicates the measurement of the observed clustering as a function of the angle to the LOS, as fast Fourier transforms (FFTs) based on Cartesian grids, cannot individually allow for this. Recent advances in methodology for calculating LOS-dependent clustering in Fourier space include the realization that power spectrum LOS-dependent moments can be constructed from sums over galaxies, based on approximating the LOS to each pair of galaxies by the LOS to one of them. We show that we can implement this method using multiple FFTs, each measuring the LOS-weighted clustering along different axes. The N log(N) nature of FFTs means that the computational speed-up is a factor of >1000 compared with summing over galaxies. This development should be beneficial for future projects such as DESI and Euclid which will provide an order of magnitude more galaxies than current surveys.
Nonlocal metric dimension ${\rm dim}_{\rm n\ell}(G)$ of a graph $G$ is introduced as the cardinality of a smallest nonlocal resolving set, that is, a set of vertices which resolves each pair of non-adjacent vertices of $G$. Graphs $G$ with ${\rm dim}_{\rm n\ell}(G) = 1$ or with ${\rm dim}_{\rm n\ell}(G) = n(G)-2$ are characterized. The nonlocal metric dimension is determined for block graphs, for corona products, and for wheels. Two upper bounds on the nonlocal metric dimension are proved. An embedding of an arbitrary graph into a supergraph with a small nonlocal metric dimension and small diameter is presented.
Although current deep learning-based face forgery detectors achieve impressive performance in constrained scenarios, they are vulnerable to samples created by unseen manipulation methods. Some recent works show improvements in generalisation but rely on cues that are easily corrupted by common post-processing operations such as compression. In this paper, we propose LipForensics, a detection approach capable of both generalising to novel manipulations and withstanding various distortions. LipForensics targets high-level semantic irregularities in mouth movements, which are common in many generated videos. It consists in first pretraining a spatio-temporal network to perform visual speech recognition (lipreading), thus learning rich internal representations related to natural mouth motion. A temporal network is subsequently finetuned on fixed mouth embeddings of real and forged data in order to detect fake videos based on mouth movements without overfitting to low-level, manipulation-specific artefacts. Extensive experiments show that this simple approach significantly surpasses the state-of-the-art in terms of generalisation to unseen manipulations and robustness to perturbations, as well as shed light on the factors responsible for its performance. Code is available on GitHub.
We consider a hierarchy of many particle systems on the line with polynomial potentials separable in parabolic coordinates. Using the Lax representation, written in terms of $2\times 2$ matrices for the whole hierarchy, we construct the associated linear $r$-matrix algebra with the $r$-matrix dependent on the dynamical variables. A dynamical Yang-Baxter equation is discussed.
Let $F$ be a quadratic form in four variables, let $m\in\mathbb{N}$ and let $\mathbf{k}\in \mathbb{Z}^4$. We count integer solutions to $F(\mathbf{x})=0$ with $\mathbf{x}\equiv \mathbf{k}\:\mathrm{mod}(m)$. One can compare this to the similar problem of counting solutions to $F(\mathbf{x})=0$ without the congruence condition. It turns out that adding the congruence condition sometimes gives a very different main term than the homogeneous case. In particular, there are examples where the number of primitive solutions to the problem is $0$, while the number of unrestricted solutions is nonzero.
Nonstoichiometric Sr$_{1-y}$Mn$_{1-z}$Sb$_{2}$ (y, z~$<$0.1) is known to exhibit a coexistence of magnetic order and the nontrivial semimetallic behavior related to Dirac or Weyl fermions. Here, we report inelastic neutron scattering analyses of the spin dynamics and density functional theory studies on the electronic properties of Sr$_{1-y}$Mn$_{1-z}$Sb$_{2}$. We observe a relatively large spin excitation gap $\approx$ 8.5 meV at 5 K, and the interlayer magnetic exchange constant only 2.8 \% of the dominant intralayer magnetic interaction, providing evidence that Sr$_{1-y}$Mn$_{1-z}$Sb$_{2}$ exhibits a quasi-2D magnetism. Using density functional theory, we find a strong influence of magnetic orders on the electronic band structure and the Dirac dispersions near the Fermi level along the Y-S direction in the presence of a ferromagnetic ordering. Our study unveils novel interplay between the magnetic order, magnetic transition, and electronic property in Sr$_{1-y}$Mn$_{1-z}$Sb$_{2}$, and opens new pathways to control the relativistic band structure through magnetism in ternary compounds.
Core-collapse supernovae are found in galaxies with ongoing star-formation. In a starburst galaxy hosting an active galactic nucleus with a relativistic jet, supernovae can take place inside the jet. The collision of the supernova ejecta with the jet flow is expected to lead to the formation of an interaction region, in which particles can be accelerated and produce high-energy emission. We study the non-thermal radiation produced by electrons accelerated as a result of a supernova explosion inside the jet of an active galactic nucleus within a star-forming galaxy. We first analyzed the dynamical evolution of the supernova ejecta impacted by the jet. Then, we explored the parameter space using simple prescriptions for the observed gamma-ray lightcurve. Finally, the synchrotron and the inverse Compton spectral energy distributions for two types of sources, a radio galaxy and a powerful blazar, are computed. For a radio galaxy, the interaction between a supernova and a jet of power $\sim 10^{43}-10^{44}$~erg~s$^{-1}$ can produce apparent gamma-ray luminosities of $\sim 10^{42}-10^{43}$~erg~s$^{-1}$, with an event duty cycle of supernova remnant (SNR) interacting with the jet close to one for one galaxy. For a blazar with a powerful jet of $\sim 10^{46}$~erg~s$^{-1}$, the jet-supernova ejecta interaction could produce apparent gamma-ray luminosities of $\sim 10^{43}-10^{44}$~erg~s$^{-1}$, but with a much lower duty cycle. The interaction of supernovae with misaligned jets of moderate power can be relatively frequent, and can result in steady gamma-ray emission potentially detectable for sources in the local universe. For powerful blazars much farther away, the emission would be steady as well, and it might be detectable under very efficient acceleration, but the events would be rather infrequent.
This paper deals with different characterizations of sets of nonlinear parabolic capacity zero, with respect to the parabolic p-Laplace equation. Specifically we prove that certain interior polar sets can be characterized by sets of zero nonlinear parabolic capacity. Furthermore we prove that zero capacity sets are removable for bounded supersolutions and that sets of zero capacity have a relation to a certain parabolic Hausdorff measure.
In this paper, we establish the global regularity for the 3D tropical climate model with fractional dissipation.
Using the extremely high S/N quasar absorption-line sample described in the first paper of the series, we investigate which intergalactic CIV absorption line systems could be directly associated with galactic outflows at z = 2 - 3.5 from an analysis of the velocity widths of the CIV absorption line systems. Only about half the systems with a peak tau(CIV) above 0.4 in the 1548 Angstrom line (roughly a column density of CIV above about 2 x 10^13 cm^-2) have velocity widths large enough to originate in this way, and very few of the weaker systems do. The median velocity full width at a tenth max is found to be 50 km/s for systems with peak tau(CIV) in the range 0.1--0.4 and 160 km/s for systems with a peak tau(CIV) in the range 0.4--3. We show that this critical value of tau(CIV) also separates systems that could be ionized by galaxy-like spectra from those in which the ionization is clearly AGN-dominated. Together the results are consistent with a picture in which almost all the lower column density, and at least half the higher column density, systems lie in the more general IGM whereas about half of the higher column density systems could be produced directly by the outflows and possibly be ionized by their parent galaxies.
We study the finite-temperature effective potential of the Minimal Supersymmetric Standard Model, in the limit of only one light Higgs boson. Because of the large top Yukawa coupling, there can be significant differences with respect to the Standard Model case: for given values of the Higgs and top masses, little supersymmetry breaking in the stop sector can make the phase transition more strongly first-order. After including the full structure of the stop mass matrix, the most important experimental constraints and the leading plasma effects, we find that the present limits on Higgs and squark masses are still compatible with the scenario of electroweak baryogenesis, in a small region of parameter space corresponding to $m_h \simlt 70 \gev$ and $\msba \simlt 105 \gev$.
Eutectic high entropy alloys (EHEAs) are emerging as an exciting new class of structural alloys as they have shown very promising mechanical properties. However, how to design these alloys has been a challenge. In this work, a simple approach is presented for designing EHEAs. The introduced approach uses the composition of binary and ternary eutectic alloys for finding the composition of EHEAs. The approach is based on the assumption that EHEAs are originated from binary and ternary eutectic alloys. The approach is applied for alloy systems Al-Co-Cr-Fe-Ni, Co-Cr-Fe-Ni, Co-Cr-Fe-Ni-Ti, and Co-Cr-Fe-Ni-Ta and several EHEAs are predicted for these alloy systems. The predicted results are verified with thermodynamic simulations and experimental data. The results show that the introduced approach can be considered as a feasible and easy-to-use method for designing EHEAs. Based on the developed approach, any binary eutectic alloy can be used for designing multicomponent eutectic alloys.
Assisted hopping effects in magnetic impurities and quantum dots are analyzed. The magnitude of the assisted hopping term in a quantum dot in the limit of large level spacing is comparable to other corrections induced by the electron-electron interactions. Assisted hopping leads to differences between conductance peaks associated to the same level, and, when the effect is sufficiently strong, to local pairing correlations.
Recently, the elephant random walk has attracted a lot of attentions. A wide range of literature is available for the asymptotic behavior of the process, such as the central limit theorems, functional limit theorems and the law of iterated logarithm. However, there is not result concerning Wassertein-1 distance for the normal approximations.In this paper, we show that the Wassertein-1 distance in the central limit theorem is totally different when a memory parameter $p$ belongs to one of the three cases $0< p < 1/2,$ $1/2< p<3/4$ and $p=3/4.$
Markarian 421 is the nearest high-energy peaked blazar and also is the first extragalactic source to be detected in multi-TeV $\gamma$-rays. It has been observed in multiwavelength for exceptionally long period of time with dense monitoring and several major outbursts have been detected from this source. In March 2010, the source was in a high state of activity and was observed in multiwavelength by various telescopes for 13 consecutive days. During this period the position of the synchrotron peak was found to be above $10^{17}$ Hz and also the position of the second peak was shifted towards higher energy, a signature of extreme HBL-like behavior. We observed that the standard photohadronic model is inadequate to explain the observed spectra. However, a recently proposed two-zone photohadronic model explains very well the GeV-TeV flaring events observed by both MAGIC and VERITAS telescopes. From the observation of the highest energy $\gamma$-ray event on MJD 55266 we also estimated the minimum bulk Lorentz factor.
Due to medical data privacy regulations, it is often infeasible to collect and share patient data in a centralised data lake. This poses challenges for training machine learning algorithms, such as deep convolutional networks, which often require large numbers of diverse training examples. Federated learning sidesteps this difficulty by bringing code to the patient data owners and only sharing intermediate model training updates among them. Although a high-accuracy model could be achieved by appropriately aggregating these model updates, the model shared could indirectly leak the local training examples. In this paper, we investigate the feasibility of applying differential-privacy techniques to protect the patient data in a federated learning setup. We implement and evaluate practical federated learning systems for brain tumour segmentation on the BraTS dataset. The experimental results show that there is a trade-off between model performance and privacy protection costs.
A complete characterization of Wishart distributions on the cones of positive semi-definite matrices is provided in terms of a description of their maximal parameter domain. This result is new in that also degenerate scale parameters are included. For such cases, the standard constraints on the range of the shape parameter may be relaxed. Furthermore, the infinitely divisible Wishart distributions are revealed as suitable transformations and embeddings of one dimensional gamma distributions. This note completes the findings of L\'evy (1937) concerning infinite divisibility and Gindikin (1975) regarding the existence issue.
Dynamical mean-field approximation with explicit pairing is utilized to study the properties of a two-component Fermi gas at unitarity. The problem is approximated by the lattice Hubbard Hamiltonian, and the continuum limit is realized by diluting the lattice. We have found that at zero temperature the predictions of this theory for the energy and the pairing gap agree remarkably well with the results of full numerical Monte-Carlo simulations. Investigating the evolution of the system with temperature we identify the existence of a second order phase transition associated with a jump in the heat capacity and the collapse of the pairing gap.
Any permutation statistic $f:\sym\to\CC$ may be represented uniquely as a, possibly infinite, linear combination of (classical) permutation patterns: $f= \Sigma_\tau\lambda_f(\tau)\tau$. To provide explicit expansions for certain statistics, we introduce a new type of permutation patterns that we call mesh patterns. Intuitively, an occurrence of the mesh pattern $p=(\pi,R)$ is an occurrence of the permutation pattern $\pi$ with additional restrictions specified by $R$ on the relative position of the entries of the occurrence. We show that, for any mesh pattern $p=(\pi,R)$, we have $\lambda_p(\tau) = (-1)^{|\tau|-|\pi|}p^{\star}(\tau)$ where $p^{\star}=(\pi,R^c)$ is the mesh pattern with the same underlying permutation as $p$ but with complementary restrictions. We use this result to expand some well known permutation statistics, such as the number of left-to-right maxima, descents, excedances, fixed points, strong fixed points, and the major index. We also show that alternating permutations, Andr\'e permutations of the first kind and simsun permutations occur naturally as permutations avoiding certain mesh patterns. Finally, we provide new natural Mahonian statistics.
In this paper, we study the Cauchy problem of the 3-dimensional (3D) generalized incompressible Navier-Stokes equations (gNS) in Triebel-Lizorkin space $\dot{F}^{-\alpha,r}_{q_\alpha}(\mathbb{R}^3)$ with $(\alpha,r)\in(1,5/4)\times[2,\infty]$ and $q_\alpha=\frac{3}{\alpha-1}$. Our work establishes a {\it dichotomy} of well-posedness and ill-posedness depending on $r=2$ or $r>2$. Specifically, by combining the new endpoint bilinear estimates in $L^{q_\alpha}_x L^2_T$ with the characterization of Triebel-Lizorkin space via fractional semigroup, we prove the well-posedness of the gNS in $\dot{F}^{-\alpha,r}_{q_\alpha}(\mathbb{R}^3)$ for $r=2$. On the other hand, for any $r>2$, we show that the solution to the gNS can develop {\it norm inflation} in the sense that arbitrarily small initial data in the spaces $\dot{F}^{-\alpha,r}_{q_\alpha}(\mathbb{R}^3)$ can lead the corresponding solution to become arbitrarily large after an arbitrarily short time. In particular, such dichotomy of Triebel-Lizorkin spaces is also true for the classical N-S equations, i.e.\,\,$\alpha=1$. Thus the Triebel-Lizorkin space framework naturally provides better connection between the well-known Koch-Tataru's $BMO^{-1}$ well-posed work and Bourgain-Pavlovi\'c's $\dot{B}_\infty^{-1,\infty}$ ill-posed work.
We analyze observations from the Chandra X-ray Observatory of the southeast knot of the Cygnus Loop supernova remnant. In this region, the blast wave propagates through an inhomogeneous environment. Extrinsic differences and subsequent multiple projections along the line of sight rather than intrinsic shock variations, such as fluid instabilities, account for the apparent complexity of the images. Interactions between the supernova blast wave and density enhancements of a large interstellar cloud can produce the morphological and spectral characteristics. Most of the X-ray flux arises in such interactions, not in the diffuse interior of the supernova remnant. Additional observations at optical and radio wavelengths support this account of the existing interstellar medium and its role in shaping the Cygnus Loop, and they demonstrate that the southeast knot is not a small cloud that the blast wave has engulfed. These data are consistent with rapid equilibration of electron and ion temperatures behind the shock front, and the current blast wave velocity v_{bw} approx 330 km/s. Most of this area does not show strong evidence for non-equilibrium ionization conditions, which may be a consequence of the high densities of the bright emission regions.