ShantanuT01/DACTYL-Pretraining huggingface dataset:
We report the discovery of an L dwarf companion to the A3V star \beta{} Circini. VVV J151721.49-585131.5, or \beta{} Cir B, was identified in a proper motion and parallax catalogue of the Vista Variables in the V\'{i}a L\'{a}ctea survey as having near infrared luminosity and colour indicative of an early L dwarf, and a proper motion and parallax consistent with that of \beta{} Cir. The projected separation of $\sim$3.6' corresponds to $6656$ au, which is unusually wide. The most recent published estimate of the age of the primary combined with our own estimate based on newer isochrones yields an age of $370-500$ Myr. The system therefore serves as a useful benchmark at an age greater than that of the Pleiades brown dwarfs and most other young L dwarf benchmarks. We have obtained a medium resolution echelle spectrum of the companion which indicates a spectral type of L1.0$\pm$0.5 and lacks the typical signatures of low surface gravity seen in younger brown dwarfs. This suggests that signs of low surface gravity disappear from the spectra of early L dwarfs by an age of $\sim370-500$ Myr, as expected from theoretical isochrones. The mass of \beta{} Cir B is estimated from the BHAC15 isochrones as $0.056\pm0.007$ M$_{\odot}$.
A vision system that can assess its own performance and take appropriate actions online to maximize its effectiveness would be a step towards achieving the long-cherished goal of imitating humans. This paper proposes a method for performing an online performance analysis of local feature detectors, the primary stage of many practical vision systems. It advocates the spatial distribution of local image features as a good performance indicator and presents a metric that can be calculated rapidly, concurs with human visual assessments and is complementary to existing offline measures such as repeatability. The metric is shown to provide a measure of complementarity for combinations of detectors, correctly reflecting the underlying principles of individual detectors. Qualitative results on well-established datasets for several state-of-the-art detectors are presented based on the proposed measure. Using a hypothesis testing approach and a newly-acquired, larger image database, statistically-significant performance differences are identified. Different detector pairs and triplets are examined quantitatively and the results provide a useful guideline for combining detectors in applications that require a reasonable spatial distribution of image features. A principled framework for combining feature detectors in these applications is also presented. Timing results reveal the potential of the metric for online applications.
In recent years two sets of planar (2D) shape attributes, provided with an intuitive physical meaning, were proposed to the remote sensing community by, respectively, Nagao & Matsuyama and Shackelford & Davis in their seminal works on the increasingly popular geographic object based image analysis (GEOBIA) paradigm. These two published sets of intuitive geometric features were selected as initial conditions by the present R&D software project, whose multi-objective goal was to accomplish: (i) a minimally dependent and maximally informative design (knowledge/information representation) of a general purpose, user and application independent dictionary of 2D shape terms provided with a physical meaning intuitive to understand by human end users and (ii) an effective (accurate, scale invariant, easy to use) and efficient implementation of 2D shape descriptors. To comply with the Quality Assurance Framework for Earth Observation guidelines, the proposed suite of geometric functions is validated by means of a novel quantitative quality assurance policy, centered on inter feature dependence (causality) assessment. This innovative multivariate feature validation strategy is alternative to traditional feature selection procedures based on either inductive data learning classification accuracy estimation, which is inherently case specific, or cross correlation estimation, because statistical cross correlation does not imply causation. The project deliverable is an original general purpose software suite of seven validated off the shelf 2D shape descriptors intuitive to use. Alternative to existing commercial or open source software libraries of tens of planar shape functions whose informativeness remains unknown, it is eligible for use in (GE)OBIA systems in operating mode, expected to mimic human reasoning based on a convergence of evidence approach.
Implementation of an optically active material on silicon has been a persistent technological challenge. For tandem photovoltaics using a Si bottom cell, as well as for other optoelectronic applications, there has been a longstanding need for optically active, wide band gap materials that can be integrated with Si. ZnSiP$_2$ is a stable, wide band gap (2.1 eV) material that is lattice matched with silicon and comprised of inexpensive elements. As we show in this paper, it is also a defect-tolerant material. Here, we report the first ZnSiP$_2$ photovoltaic device. We show that ZnSiP$_2$ has excellent photoresponse and high open circuit voltage of 1.3 V, as measured in a photoelectrochemical configuration. The high voltage and low band gap-voltage offset are on par with much more mature wide band gap III-V materials. Photoluminescence data combined with theoretical defect calculations illuminate the defect physics underlying this high voltage, showing that the intrinsic defects in ZnSiP$_2$ are shallow and the minority carrier lifetime is 7 ns. These favorable results encourage the development of ZnSiP$_2$ and related materials as photovoltaic absorber materials.
We show analytically that the ability of Dirac materials to localize an electron in both a barrier and a well can be utilized to open a pseudo-gap in graphene's spectrum. By using narrow top-gates as guiding potentials, we demonstrate that graphene bipolar waveguides can create a non-monotonous one-dimensional dispersion along the electron waveguide, whose electrostatically controllable pseudo-band-gap is associated with strong terahertz transitions in a narrow frequency range.
The surface states of a topological insulator in a fine-tuned magnetic field are ideal candidates for realizing a topological metal which is protected against disorder. Its signatures are (1) a conductance plateau in long wires in a finely tuned longitudinal magnetic field and (2) a conductivity which always increases with sample size, and both are independent of disorder strength. We numerically study how these experimental transport signatures are affected by bulk physics in the interior of the topological insulator sample. We show that both signatures of the topological metal are robust against bulk effects. However the bulk does substantially accelerate the metal's decay in a magnetic field and alter its response to surface disorder. When the disorder strength is tuned to resonance with the bulk band the conductivity follows the predictions of scaling theory, indicating that conduction is diffusive. At other disorder strengths the bulk reduces the effects of surface disorder and scaling theory is systematically violated, signaling that conduction is not fully diffusive. These effects will change the magnitude of the surface conductivity and the magnetoconductivity.
We have studied the Devonshire-Landau potential underlying the phase transition sequence of BaTiO3 using the first-principles effective Hamiltonian of Zhong, Vanderbilt, and Rabe [Phys. Rev. Lett. 73, 1861 (1994)], which has been very successful in reproducing the phase transitions and the dielectric and piezoelectric properties of this compound. The configuration space (determined by the polarization P as order parameter) was explored with the help of auxiliary electric fields. We show that the typically assumed form of the potential, a sixth-order expansion in P around the paraelectric cubic phase, properly accounts for the behavior of the system, but we find a non-trivial temperature dependence for all the coefficients in the expansion, including the quadratic one, which is shown to behave non-linearly. Our results also prove that the sixth-order terms in the free-energy expansion (needed to account for the first-order character of the transitions and the occurrence of an orthorhombic phase) emerge from an interaction model that only includes terms up to fourth order.
We examine isotropic and anisotropic random walks which begin on the surface of linear ($N$), square ($N \times N$), or cubic ($N \times N \times N$) lattices and end upon encountering the surface again. The mean length of walks is equal to $N$ and the distribution of lengths $n$ generally scales as $n^{-1.5}$ for large $n$. Our results are interesting in the context of an old formula due to Cauchy that the mean length of a chord though a convex body of volume $V$ and surface $S$ is proportional to $V/S$. It has been realized in recent years that Cauchy's formula holds surprisingly even if chords are replaced by irregular insect paths or trajectories of colliding gas molecules. The random walk on a lattice offers a simple and transparent understanding of this result in comparison to other formulations based on Boltzmann's transport equation in continuum.
We investigate the relationship between two properties of quantum transformations often studied in popular subtheories of quantum theory: covariance of the Wigner representation of the theory and the existence of a transformation noncontextual ontological model of the theory. We consider subtheories of quantum theory specified by a set of states, measurements and transformations, defined specifying a group of unitaries, that map between states (and measurements) within the subtheory. We show that if there exists a Wigner representation of the subtheory which is covariant under the group of unitaries defining the set of transformations then the subtheory admits of a transformation noncontextual ontological model. We provide some concrete arguments to conjecture that the converse statement also holds provided that the underlying ontological model is the one given by the Wigner representation. In addition, we investigate the relationships of covariance and transformation noncontextuality with the existence of a quasiprobability distribution for the theory that represents the transformations as positivity preserving maps. We conclude that covariance implies transformation noncontextuality, which implies positivity preservation.
We describe a period map for those simply connected Enriques surfaces in characteristic 2 whose canonical double cover is K3. The moduli stack for these surfaces has a Deligne-Mumford quotient that is an open substack of a $\mathbb P^1$-bundle over the period space. We also give some general results relating local and global moduli for algebraic varieties and describe the difference in their dimensions in terms of the failure of the automorphism group scheme to be reduced.
We use a 24 micron selected sample containing more than 8,000 sources to study the evolution of star-forming galaxies in the redshift range from z=0 to z~3. We obtain photometric redshifts for most of the sources in our survey using a method based on empirically-built templates spanning from ultraviolet to mid-infrared wavelengths. The accuracy of these redshifts is better than 10% for 80% of the sample. The derived redshift distribution of the sources detected by our survey peaks at around z=0.6-1.0 (the location of the peak being affected by cosmic variance), and decays monotonically from z~1 to z~3. We have fitted infrared luminosity functions in several redshift bins in the range 0<z<~3. Our results constrain the density and/or luminosity evolution of infrared-bright star-forming galaxies. The typical infrared luminosity (L*) decreases by an order of magnitude from z~2 to the present. The cosmic star formation rate (SFR) density goes as (1+z)^{4.0\pm0.2} from z=0 to z=0.8. From z=0.8 to z~1.2, the SFR density continues rising with a smaller slope. At 1.2<z<3, the cosmic SFR density remains roughly constant. The SFR density is dominated at low redshift (z<0.5) by galaxies which are not very luminous in the infrared (L_TIR<1.e11 L_sun, where L_TIR is the total infrared luminosity, integrated from 8 to 1000 micron). The contribution from luminous and ultraluminous infrared galaxies (L_TIR>1.e11 L_sun) to the total SFR density increases steadily from z~0 up to z~2.5, forming at least half of the newly-born stars by z~1.5. Ultraluminous infrared galaxies (L_TIR>1.e12 L_sun) play a rapidly increasing role for z>~1.3.
We calculate the polarization of Lambda and Anti-Lambda particles produced in deep inelastic polarized lepton scattering. We use two models: the naive quark model and a model in which SU(3)$_F$ symmetry is used to deduce the spin structure of SU(3) octet hyperons from that of the proton. We perform the calculations for Lambda and Anti-Lambda produced directly or as decay products of $\Sigma^0$ and $\Sigma^*$.
We report the systematic studies of spin current transport and relaxation mechanism in highly doped organic polymer film. In this study, we have determined spin diffusion length (SDL), spin lifetime, and spin diffusion constant by using different experimental techniques. The spin lifetime estimated from the electron paramagnetic resonance experiment is much shorter than the previous expectation beyond the experimental ambiguity. This suggests that significantly large spin diffusion constant, which is reasonably explained by the hopping transport mechanism in degenerate semiconductors, exists in highly doped organic semiconductors. The calculated SDL using the spin lifetime and spin diffusion constant estimated from our experiment is comparable to the experimentally obtained SDL of the order of one hundred nanometers. Moreover, the present study revealed that the spin angular momentum is almost preserved in the hopping events. In other words, the spin relaxation mainly occurs due to the spin-orbit coupling at the nanoscale crystalline grains.
The aim of this paper is to employ a strategy known from fluid dynamics in order to provide results for the linear heat equation $u_{t}-\Delta u-V(x)u=0$ in $\mathbb{R}^{n}$ with singular potentials. We show well-posedness of solutions, without using Hardy inequality, in a framework based in the Fourier transform, namely $PM^{k}$-spaces. For arbitrary data $u_{0}\in PM^{k}$, the approach allows to compute an explicit smallness condition on $V$ for global existence in the case of $V$ with finitely many inverse square singularities. As a consequence, well-posedness of solutions is obtained for the case of the monopolar potential $V(x)=\frac{\lambda}{\left|x\right|^{2}}$ with $\left|\lambda\right|<\lambda_{\ast}=\frac{(n-2)^{2}}{4}$. This threshold value is the same one obtained for the global well-posedness of $L^{2}$-solutions by means of Hardy inequalities and energy estimates. Since there is no any inclusion relation between $L^{2}$ and $PM^{k}$, our results indicate that $\lambda_{\ast}$ is intrinsic of the PDE and independent of a particular approach. We also analyze the long time behavior of solutions and show there are infinitely many possible asymptotics characterized by the cells of a disjoint partition of the initial data class $PM^{k}$.
Mass number dependence of the nuclear radii is closely related to the nuclear matter properties. It is known that the most of nuclei exhibit some deformation. We discuss how the nuclear density profile is modified by the nuclear deformation to elucidate the enhancement mechanism of the nuclear radii through a systematic investigation of neutron-rich Ne, Mg, Si, S, Ar, Ti, Cr, and Fe isotopes. Skyrme-Hartree-Fock calculations are performed in a three-dimensional Cartesian grid to describe the nuclear deformation in a non-empirical way. The role of the nuclear deformation on the nuclear density profiles is explored in comparison to calculations with spherical limit. We find correlations between the nuclear deformation and the internal nuclear density. The evolution of the nuclear radii appears to follow the core swelling mechanism recently proposed in spherical nuclei [Phys. Rev. C 101, 061301(R) (2020)], and the radius is further enhanced by the nuclear deformation. This study demands further theoretical and experimental investigations for the internal density.
We study the magnetic structure of the "stuffed" (Tb-rich) pyrochlore iridate Tb$_{2+x}$Ir$_{2-x}$O$_{7-y}$, using resonant elastic x-ray scattering (REXS). In order to disentangle contributions from Tb and Ir magnetic sublattices, experiments were performed at the Ir $L_3$ and Tb $M_5$ edges, which provide selective sensitivity to Ir $5d$ and Tb $4f$ magnetic moments, respectively. At the Ir $L_3$ edge, we found the onset of long-range ${\bf k}={\bf 0}$ magnetic order below $T_{N}^\text{Ir}\sim$ 71 K, consistent with the expected signal of all-in all-out (AIAO) magnetic order. Using a single-ion model to calculate REXS cross-sections, we estimate an ordered magnetic moment of $\mu_{5d}^{\text{Ir}} \approx 0.34(3)\,\mu_B$ at 5 K. At the Tb $M_5$ edge, long-range ${\bf k}={\bf 0}$ magnetic order appeared below $\sim40$ K, also consistent with an AIAO magnetic structure on the Tb site. Additional insight into the magnetism of the Tb sublattice is gleaned from measurements at the $M_5$ edge in applied magnetic fields up to 6 T, which is found to completely suppress the Tb AIAO magnetic order. In zero applied field, the observed gradual onset of the Tb sublattice magnetisation with temperature suggests that it is induced by the magnetic order on the Ir site. The persistence of AIAO magnetic order, despite the greatly reduced ordering temperature and moment size compared to stoichiometric Tb$_{2}$Ir$_{2}$O$_{7}$, for which $T_{N}^{\text{Ir}} =130$ K and $\mu_{5d}^{\text{Ir}}=0.56\,\mu_B$, indicates that stuffing could be a viable means of tuning the strength of electronic correlations, thereby potentially offering a new strategy to achieve topologically non-trivial band crossings in pyrochlore iridates.
Sheaves on non-reduced curves can appear in moduli space of 1-dimensional semistable sheaves over a surface, and moduli space of Higgs bundles as well. We estimate the dimension of the stack $\mathbf{M}_{X}(nC,\chi)$ of pure sheaves supported at the non-reduced curve $nC~(n\geq 2)$ with $C$ an integral curve on $X$. We prove that the Hilbert-Chow morphism $h_{L,\chi}:\mathcal{M}^H_X(L,\chi)\rightarrow |L|$ sending each semistable 1-dimensional sheaf to its support have all its fibers of the same dimension for $X$ Fano or with trivial canonical line bundle and $|L|$ contains integral curves.
Carbon abundances in late-type stars are important in a variety of astrophysical contexts. However C i lines, one of the main abundance diagnostics, are sensitive to departures from local thermodynamic equilibrium (LTE). We present a model atom for non-LTE analyses of C i lines, that uses a new, physically-motivated recipe for the rates of neutral hydrogen impact excitation. We analyse C i lines in the solar spectrum, employing a three-dimensional (3D) hydrodynamic model solar atmosphere and 3D non-LTE radiative transfer. We find negative non-LTE abundance corrections for C i lines in the solar photosphere, in accordance with previous studies, reaching up to around 0.1 dex in the disk-integrated flux. We also present the first fully consistent 3D non-LTE solar carbon abundance determination: we infer log $\epsilon_{\text{C}}$ = $8.44\pm0.02$, in good agreement with the current standard value. Our models reproduce the observed solar centre-to-limb variations of various C i lines, without any adjustments to the rates of neutral hydrogen impact excitation, suggesting that the proposed recipe may be a solution to the long-standing problem of how to reliably model inelastic collisions with neutral hydrogen in late-type stellar atmospheres.
Suppose that $\Omega$ is a lattice in the complex plane and let $\sigma$ be the corresponding Weierstrass $\sigma$-function. Assume that the point $\tau$ associated to $\Omega$ in the standard fundamental domain has imaginary part at most 1.9. Assuming that $\Omega$ has algebraic invariants $g_2,g_3$ we show that a bound of the form $c d^m (\log H)^n$ holds for the number of algebraic points of height at most $H$ and degree at most $d$ lying on the graph of $\sigma$. To prove this we apply results by Masser and Besson. What is perhaps surprising is that we are able to establish such a bound for the whole graph, rather than some restriction. We prove a similar result when, instead of $g_2,g_3$, the lattice points are algebraic. For this we naturally exclude those $(z,\sigma(z))$ for which $z\in\Omega$.
We present high resolution echelle spectroscopy of a sample of H II galaxies. In all galaxies we identify different H(alpha) emitting knots along the slit crossing the nucleus. All of these have been isolated and separately analyzed through luminosity and size vs diagnosis plots. We find that in all cases, for a particular galaxy, the bulk of emission comes from their main knot and therefore, at least for the compact class galaxies we are dealing with, luminosity and sigma values measured using single aperture observations would provide similar results to what is obtained with spatially resolved spectroscopy. In the size vs plots as expected there is a shift in the correlations depending on whether we are including all emission in a single point or we split it in its different emitting knots. The problem of a proper determination of the size of the emitting region so that it can be used to determine the mass of the system remains open. From the data set gathered, using the highest surface brightness points as recently proposed by Fuentes-Masip et al. (2000), the best luminosity vs correlation turns out to be consistent with a Virial model.
Bandit problems model the trade-off between exploration and exploitation in various decision problems. We study two-armed bandit problems in continuous time, where the risky arm can have two types: High or Low; both types yield stochastic payoffs generated by a Levy process. We show that the optimal strategy is a cut-off strategy and we provide an explicit expression for the cut-off and for the optimal payoff.
Lymphocyte selection is a fundamental operation of adaptive immunity. In order to produce B-lymphocytes with a desired antigenic profile, a process of mutation-selection occurs in the germinal center, which is part of the lymph nodes. We introduce in this article a simplified mathematical model of this process, taking into account the main mechanisms of division, mutation and selection. This model is written as a non-linear, non-local, inhomogeneous second order partial differential equation, for which we develop a mathematical analysis in the case of piecewise-constant coefficients. We assess, mathematically and numerically, the performance of the biological function by evaluating the duration of this production process as a function of several parameters such as the mutation rate or the selection profile, in various asymptotic regimes.
We study various models of associative memories with sparse information, i.e. a pattern to be stored is a random string of $0$s and $1$s with about $\log N$ $1$s, only. We compare different synaptic weights, architectures and retrieval mechanisms to shed light on the influence of the various parameters on the storage capacity.
Finsler geometry is just riemannian geometry without the quadratic restriction[1]. In this paper, we study the motion of massive(non-zero rest mass) and massless particles for schwarzschild metric in finsler spacetime in the case of two dimensional Randers-Finsler space with unit positive flag curvature instead of two dimensional riemann sphere. We provide qualitative study of potential energy of particles at various distances near schwarzschild black hole and the results are then compared with schwarzschild metric in riemannian geometry. We will also describe the scattering of particles near schwarzschild black hole in finsler spacetime by finding capture cross section of absorption by the black hole.