ShantanuT01/DACTYL-Pretraining huggingface dataset:
The detection of X-ray emission from Ap stars can be an indicator for the presence of magnetic activity and dynamo action, provided different origins for the emission, such as wind shocks and close late-type companions, can be excluded. Here we report on results for gamma Equu, the only roAp star for which an X-ray detection is reported in ROSAT catalogs. We use high resolution imaging in X-rays with Chandra and in the near-infrared with NACO/VLT that allow us to spatially resolve companions down to ~1" and ~0.06" separations, respectively. The bulk of the X-ray emission is associated with a companion of gamma Equu identified in our NACO image. Assuming coevality with the primary roAp star (~900 Myr), the available photometry for the companion points at a K-type star with ~0.6 M_sun. Its X-ray properties are in agreement with the predictions for its age and mass. An excess of photons with respect to the expected background and contribution from the nearby companion is observed near the optical position of gamma Equu. We estimate an X-ray luminosity of log L_x [erg/s] = 26.6 and log(L_x/L_bol) = -7.9 for this emission. A small offset between the optical and the X-ray image leaves some doubt on its association with the roAp star. The faint X-ray emission that we tentatively ascribe to the roAp star is difficult to explain as a solar-like stellar corona due to its very low L_x/L_bol level and the very long rotation period of gamma Equu. It could be produced in magnetically confined wind shocks implying a mass loss rate of ~10^(-14) M_sun/yr or from an additional unknown late-type companion at separation ~0.4". If confirmed by future deeper X-ray observations this emission could point at the origin for the presence of radioactive elements on some roAp stars.
Conduction electrons coupled to a mesoscopic superconducting island hosting Majorana bound states have been shown to display a topological Kondo effect with robust non-Fermi liquid correlations. With $M$ bound states coupled to $M$ leads, this is an SO($M$) Kondo problem, with the asymptotic high and low energy theories known from bosonization and conformal field theory studies. Here we complement these approaches by analyzing the Bethe ansatz equations describing the exact solution of these models at all energy scales. We apply our findings to obtain nonperturbative results on the thermodynamics of $M\rightarrow M-2$ crossovers induced by tunnel couplings between adjacent Majorana bound states.
Physical conditions inside a supernova remnant can vary significantly between different positions. However, typical observational data are integrated data or contemplate specific portions of the remnant. We study the spatial variation in the physical properties of the N\,49 supernova remnant based on a spectroscopic mapping of the whole nebula. Long-slit spectra were obtained with the slit ($\sim4\arcmin \times 1.03\arcsec$) aligned along the east-west direction from 29 different positions spaced by $2\arcsec$ in declination. A total of 3248 1D spectra were extracted from sections of $2\arcsec$ of the 2D spectra. More than 60 emission lines in the range 3550\,\AA{} to 8920\,\AA{} were measured in these spectra. Maps of the fluxes and of intensity ratios of these emission lines were built with a spatial resolution of $2\arcsec \times 2\arcsec$. An electron density map has been obtained using the [S\,{\sc ii}]\,$\lambda6716/\lambda6731$ line ratio. Values vary from $\sim$500\,cm$^{-3}$ at the northeast region to more than 3500 cm$^{-3}$ at the southeast border. We calculated electron temperature using line ratio sensors for the ions S$^{+}$, O$^{++}$, O$^{+}$, and N$^{+}$. Values are about 3.6$\times10^{4}$\,K for the O$^{++}$ sensor and about 1.1$\times10^{4}$\,K for other sensors. The H$\alpha$/H$\beta$ ratio map presents a ring structure with higher values that may result from collisional excitation of hydrogen. We detected an area with high values of [N\,{\sc ii}]\,$\lambda6583$/H$\alpha$ extending from the remnant center to its northeastern border, that can be indicating an overabundance of nitrogen in the area due to contamination by the progenitor star. We found a radial dependence in many line intensity ratio maps. We observed an increase toward the remnant borders of the intensity ratio of any two lines in which the numerator comes before in a sequence of lines.
We consider two dimensional string backgrounds. We discuss the physics of long strings that come from infinity. These are related to non-singlets in the dual matrix model description.
Interstellar dust is a key element in our understanding of the interstellar medium and star formation. The manner in which dust populations evolve with the excitation and the physical conditions is a first step in the comprehension of the evolution of inter- stellar dust. Within the framework of the Evolution of interstellar dust Herschel key program, we have acquired PACS and SPIRE spec- trophotometric observations of various photodissociation regions, to characterise this evolution. The aim of this paper is to trace the evolution of dust grains in the Orion Bar photodissociation region. We use Herschel/PACS (70 and 160 mic) and SPIRE (250, 350 and 500 mic) together with Spitzer/IRAC observations to map the spatial distribution of the dust populations across the Bar. Brightness profiles are modelled using the DustEM model coupled with a radiative transfer code. Thanks to Herschel, we are able to probe finely the dust emission of the densest parts of the Orion Bar with a resolution from 5.6" to 35.1". These new observations allow us to infer the temperature of the biggest grains at different positions in the Bar, which reveals a gradient from \sim 80 K to 40 K coupled with an increase of the spectral emissivity index from the ionization front to the densest regions. Combining Spitzer/IRAC observations, which are sensitive to the dust emission from the surface, with Herschel maps, we have been able to measure the Orion Bar emission from 3.6 to 500 mic. We find a stratification in the different dust components which can be re- produced quantitatively by a simple radiative transfer model without dust evolution. However including dust evolution is needed to explain the brightness in each band. PAH abundance variations, or a combination of PAH abundance variations with an emissivity enhancement of the biggest grains due to coagulation give good results.
We propose a new type of hybrid systems formed by conventional semiconductor nanostructures with the addition of remote insulating layers, where the electron-hole interaction is enhanced by combining quantum and dielectric confinement over different length scales. Due to the polarization charges induced by the dielectric mismatch at the semiconductor/insulator interfaces, we show that the exciton binding energy can be more than doubled. For conventional III-V quantum wires such remote dielectric confinement allows exciton binding at room temperature.
Ce3+ is known to show broad optical emission peaking in the green spectral range. For the stabilization of 3-valent cerium in ceramic phosphors such as calcium scandate CaSc2O4, often co-doping with sodium for charge compensation is performed (Na+, Ce3+ = 2 Ca2+). At the melting point of CaSc2O4 (ca. 2110 deg C), however, alkaline oxides evaporate completely and co-doping is thus no option for crystal growth from the melt. It is shown that even without co-doping Ce3+:CaSc2O4 crystal fibers can be grown from the melt by laser-heated pedestal growth (LHPG) in a suitable reactive atmosphere. Reactive means here that the oxygen partial pressure is a function of temperature and pO2(T) rises for this atmosphere in such a way that Ce3+ is kept stable for all T. Crystal fibers with ca. 1 mm diameter and up to 50 mm length were grown and characterized. Differential thermal analysis (DTA) was performed in the pseudo-binary system CaO-Sc2O3, and the specific heat capacity cp(T) of CaSc2O4 was measured up to 1240 K by differential scanning calorimetry (DSC). Near and beyond the melting point of calcium scandate significant evaporation of calcium tends to shift the melt composition towards the Sc2O3 side. Measurements and thermodynamic calculations reveal quantitative data on the fugacities of evaporating species.
The Dirac Equation is solved approximately for relativistic generalized Woods-Saxon potential including Coulomb-like tensor potential in exact pseudospin and spin symmetry limits. The bound states energy eigenvalues are found by using wavefunction boundary conditions, and corresponding radial wavefunctions are obtained in terms of hypergeometric function. Some numerical examples are given for the dependence of bound states energy eigenvalues on quantum numbers and potential parameters.
The energy spectrum of the quantum Klein-Gordon lattice is computed numerically for different nonlinear contributions to the Hamiltonian. In agreement with the studies on the effective Hubbard Hamiltonian for boson quasi-particles (see for instance Refs.\onlinecite{AGRANOVICH,Eilbeck}) a pairing of the phonon states is found when the nonlinearity of the lattice is significant. On the opposite, when the nonlinear contribution is weak or moderate, which is common in materials the effective Hamiltonian is not appropriate because it neglects all the energy terms that do not conserve the boson number. Then for a realistic modelling of the hybridization between the free phonon and the phonon bound pairs, the Klein-Gordon Hamiltonian is required since it is derived from the potential energy of the atoms and thus it does not involve any arbitrary quanta conservation. Actually, when the nonlinearity is weak we prove that the binding energy of the phonon bound pairs vanishes at the center of the lattice Brillouin zone whereas at the edge, it may be comparable to the phonon band width.Consequently, the signature of a weak nonlinearity is found to be a pseudogap that opens in the spectrum region of the two phonon energy, at the edge of the lattice Brillouin zone. Our results are shown to be valid for all the lattice dimensions and for some model parameters that are relevant for the optical phonon spectra.
For the positive integer $n$, let $f(n)$ denote the number of positive integer solutions $(n_1,\,n_2,\,n_3)$ of the Diophantine equation $$ {4\over n}={1\over n_1}+{1\over n_2}+{1\over n_3}. $$ For the prime number $p$, $f(p)$ can be split into $f_1(p)+f_2(p),$ where $f_i(p)(i=1,\,2)$ counts those solutions with exactly $i$ of denominators$n_1,\,n_2,\,n_3$ divisible by $p.$   Recently Terence Tao proved that $$ \sum_{p< x}f_2(p)\ll x\log^2x\log\log x $$ with other results. But actually only the upper bound $x\log^2x\log\log^2x$ can be obtained in his discussion. In this note we shall use an elementary method to save a factor $\log\log x$ and recover the above estimate.
Results from optical photometric observations of the pre-main sequence star GM Cep are reported in the paper. The star is located in the field of the young open cluster Trumpler 37 - a region of active star formation. GM Cep shows a large amplitude rapid variability interpreted as a possible outburst from EXor type in previous studies. Our data from BVRI CCD photometric observations of the star are collected from June 2008 to February 2011 in Rozhen observatory (Bulgaria) and Skinakas observatory (Crete, Greece). A sequence of sixteen comparison stars in the field of GM Cep was calibrated in the BVRI bands. Our photometric data for a 2.5 years period show a high amplitude variations (Delta V ~ 2.3m) and two deep minimums in brightness are observed. The analysis of collected multicolor photometric data shows the typical of UX Ori variables a color reversal during the minimums in brightness. On the other hand, high amplitude rapid variations in brightness typical for the Classical T Tauri stars also present on the light curve of GM Cep. Comparing our results with results published in the literature, we conclude that changes in brightness are caused by superposition of both: (1) magnetically channeled accretion from the circumstellar disk, and (2) occultation from circumstellar clouds of dust or from features of a circumstellar disk.
We present a Gupta-Bleuler quantization scheme for the electromagnetic field in time-dependent dielectric media. Starting from the Maxwell equations, a generalization of the Lorentz gauge condition adapted to time varying dielectrics is derived. Using this gauge, a Gupta-Bleuler approach to quantize all polarizations of the radiation field and the corresponding constraint condition are introduced. This new approach is different from the quantized electromagnetic field in vacuum in the sense that here the contributions of unphysical photons cannot be thoroughly eliminated, which further lead to a surface charge density. Finally, a discussion of potential experimental tests and possible implication is also made.
The electronic properties of pentavalent-ion (Nb$^{5+}$, Ta$^{5+}$, and I$^{5+}$) doped anatase and rutile TiO$_2$ are studied using spin-polarized GGA+\emph{U} calculations. Our calculated results indicate that these two phases of TiO$_2$ exhibit different conductive behavior upon doping. For doped anatase TiO$_2$, some up-spin-polarized Ti 3\emph{d} states lie near the conduction band bottom and cross the Fermi level, showing an \emph{n}-type half-metallic character. For doped rutile TiO$_2$, the Fermi level is pinned between two up-spin-polarized Ti 3\emph{d} gap states, showing an insulating character. These results can account well for the experimental different electronic transport properties in Nb (Ta)-doped anatase and rutile TiO$_2$.
More than three hundred years ago, Ole Romer measured the speed of light only by observing the periodic shifting of the observed eclipse arrival times of Jupiter's moons arising from the varying Earth-Jupiter distance. The same method of measuring the periodic modulation of delays is still used in astrophysics. The ideal laboratories for this effect are eclipsing binaries. The unique system V994 Her consists of two eclipsing binaries orbiting each other. However, until now it was not certain whether these are gravitationally bound and what their orbital period is. We show that the system is in fact quintuple and the two eclipsing binaries are orbiting each other with period about 6.3 years. This analysis was made only from studying the periodic modulation of the two periods, when during the periastron passage one binary has an apparently shorter period, while the other one longer, exactly as required by a theory. Additionally, it was found that both inner eclipsing pairs orbit with slightly eccentric orbits undergoing a slow apsidal motions with a period of the order of centuries.
We provide a combined theoretical and experimental study of the electronic structure and the optical absorption edge of the orthorhombic perovskite LaInO$_{3}$. Employing density-functional theory and many-body perturbation theory, we predict a direct electronic quasiparticle band gap of about 5 eV and an effective electron (hole) mass of 0.31 (0.48) m$_{0}$. We find the lowest-energy excitation at 0.2 eV below the fundamental gap, reflecting a sizeable electron-hole attraction. Since the transition from the valence band maximum (VBM, $\Gamma$ point) is, however, dipole forbidden the onset is characterized by weak excitations from transitions around it. The first intense excitation appears about 0.32 eV above. Interestingly, this value coincides with an experimental value obtained by ellipsometry (4.80 eV) which is higher than the onset from optical absorption spectroscopy (4.35 eV). The latter discrepancy is attributed to the fact that the weak transitions that define the optical gap are not resolved by the ellipsometry measurement. The absorption edge shows a strong dependency on the light polarization, reflecting the character of the involved valence states. Temperature-dependent measurements show a redshift of the optical gap by about 120 meV by increasing the temperature from 5 to 300 K. Renormalization due to zero-point vibrations is extrapolated from the latter measurement to amount to 150 meV. By adding the excitonic binding energy of 0.2 eV obtained theoretically to the experimental optical absorption onset, we determine the fundamental band gap at room temperature to be 4.55 eV.
Very recently, the gravitational-wave (GW) event GW170817 was discovered to be associated with the short gamma-ray burst (GRB) 170817A. Multi-wavelength follow-up observations were carried out, and X-ray, optical, and radio counterparts to GW170817 were detected. The observations undoubtedly indicate that GRB 170817A originates from a binary neutron star merger. However, the GRB falls into the low-luminosity class that could have a higher statistical occurrence rate and detection probability than the normal (high-luminosity) class. This implies the possibility that GRB 170817A is intrinsically powerful, but we are off-axis and only observe its side emission. In this Letter, we provide a timely modeling of the multi-wavelength afterglow emission from this GRB and the associated kilonova signal from the merger ejecta, under the assumption of a structured jet, a two-component jet, and an intrinsically less-energetic quasi-isotropic fireball, respectively. Comparing the afterglow properties with the multi-wavelength follow-up observations, we can distinguish between these three models. Furthermore, a few model parameters (e.g., the ejecta mass and velocity) can be constrained.
We study the effect of electron doping on the bonding character and stability of two-dimensional (2D) structures of elemental boron, called borophene, which is known to form many stable allotropes. Our {\em ab initio} calculations for the neutral system reveal previously unknown stable 2D $\epsilon$-B and $\omega$-B structures. We find that the chemical bonding characteristic in this and other boron structures is strongly affected by extra charge. Beyond a critical degree of electron doping, the most stable allotrope changes from $\epsilon$-B to a buckled honeycomb structure. Additional electron doping, mimicking a transformation of boron to carbon, causes a gradual decrease in the degree of buckling of the honeycomb lattice that can be interpreted as piezoelectric response. Net electron doping can be achieved by placing borophene in direct contact with layered electrides such as Ca$_{2}$N. We find that electron doping can be doubled by changing from the B/Ca$_{2}$N bilayer to the Ca$_{2}$N/B/Ca$_{2}$N sandwich geometry.
Before the 1970s, precision tests for gravity theories were constrained to the weak gravitational fields of the Solar system. Hence, only the weak-field slow-motion aspects of relativistic celestial mechanics could be investigated. Testing gravity beyond the first post-Newtonian contributions was for a long time out of reach.   The discovery of the first binary pulsar by Russell Hulse and Joseph Taylor in the summer of 1974 initiated a completely new field for testing the relativistic dynamics of gravitationally interacting bodies. For the first time the back reaction of gravitational wave emission on the binary motion could be studied. Furthermore, the Hulse-Taylor pulsar provided the first test bed for the orbital dynamics of strongly self-gravitating bodies.   To date there are a number of pulsars known, which can be utilized for precision test of gravity. Depending on their orbital properties and their companion, these pulsars provide tests for various different aspects of relativistic dynamics. Besides tests of specific gravity theories, like general relativity or scalar-tensor gravity, there are pulsars that allow for generic constraints on potential deviations of gravity from general relativity in the quasi-stationary strong-field and the radiative regime.   This article presents a brief overview of this modern field of relativistic celestial mechanics, reviews some of the highlights of gravity tests with radio pulsars, and discusses their implications for gravitational physics and astronomy, including the upcoming gravitational wave astronomy.
There is a theorem known as a Virial theorem that restricts the possible existence of non-trivial static solitary waves with scalar fields in a flat space-time with 3 or more spatial dimensions. This raises the following question: Does the analogous curved space-time version hold?. We investigate the possibility of solitons in a 4-D curved space-time with a simple model using numerical analysis. We found that there exists a static solution of the proposed non linear wave equation. This proves that in curved space-time the possibilities of solitonic solutions is enhanced relative to the flat space-time case.
In this paper, we propose a new redundant wavelet transform applicable to scalar functions defined on high dimensional coordinates, weighted graphs and networks. The proposed transform utilizes the distances between the given data points. We modify the filter-bank decomposition scheme of the redundant wavelet transform by adding in each decomposition level linear operators that reorder the approximation coefficients. These reordering operators are derived by organizing the tree-node features so as to shorten the path that passes through these points. We explore the use of the proposed transform to image denoising, and show that it achieves denoising results that are close to those obtained with the BM3D algorithm.
Given a graph $G$, we let $s^+(G)$ denote the sum of the squares of the positive eigenvalues of the adjacency matrix of $G$, and we similarly define $s^-(G)$. We prove that   \[\chi_f(G)\ge 1+\max\left\{\frac{s^+(G)}{s^-(G)},\frac{s^-(G)}{s^+(G)}\right\}\] and thus strengthen a result of Ando and Lin, who showed the same lower bound for the chromatic number $\chi(G)$.   We in fact show a stronger result wherein we give a bound using the eigenvalues of $G$ and $H$ whenever $G$ has a homomorphism to an edge-transitive graph $H$. Our proof utilizes ideas motivated by association schemes.
Currently, detecting 3D objects in Bird's-Eye-View (BEV) is superior to other 3D detectors for autonomous driving and robotics. However, transforming image features into BEV necessitates special operators to conduct feature sampling. These operators are not supported on many edge devices, bringing extra obstacles when deploying detectors. To address this problem, we revisit the generation of BEV representation and propose detecting objects in perspective BEV -- a new BEV representation that does not require feature sampling. We demonstrate that perspective BEV features can likewise enjoy the benefits of the BEV paradigm. Moreover, the perspective BEV improves detection performance by addressing issues caused by feature sampling. We propose PersDet for high-performance object detection in perspective BEV space based on this discovery. While implementing a simple and memory-efficient structure, PersDet outperforms existing state-of-the-art monocular methods on the nuScenes benchmark, reaching 34.6% mAP and 40.8% NDS when using ResNet-50 as the backbone.
Collisions and mergers of gas-rich galaxies trigger bursts of star and cluster formation. Of the thousands of clusters typically formed during a major merger, only the most massive and compact survive for Gigayears as globular clusters (GCs). In <~1 Gyr old merger remnants, these `second-generation' GCs appear by the hundreds as young halo clusters of about solar metallicity. Their likely descendants, metal-rich GCs of intermediate age (2 - 5 Gyr), have recently been found in ~10 elliptical galaxies, where they appear as slightly overluminous red GCs with a still power-law-like luminosity function. Their color and radial distributions suggest that they evolve into the red metal-rich GCs observed in old ellipticals. There is good evidence that second-generation GCs form from giant molecular clouds shocked by the rapid pressure increase in merger-induced starbursts. This mechanism supports the view that the universal pressure increase during cosmological reionization may have triggered the formation of the metal-poor globulars observed in galaxies of all types.