ShantanuT01/DACTYL-Pretraining huggingface dataset:
Time-resolved polarisation measurements of pulsars offer an unique insight into the geometry of their emission regions. Such measure\ ments provide observational constraints on the different models proposed for the pulsar emission mechanisms. Optical polarisation data of the Crab Nebula was obtained from the HST archive. The data set consists of a series of observations of the nebula taken with the HST/ACS. We produced polarisation vector maps of the inner nebula and measured, for the first time, the degree of linear polarisation (P.D.) and the position angle (P.A.) of the pulsar's integrated pulse beam, and of its nearby synchrotron knot. This yielded $\rm P.D.=5.2\pm0.3%$ and $\rm P.A.=105.1\pm1.6\degr$ for the pulsar, and $\rm P.D.=59.0\pm1.9%$ and $\rm P.A.=124.7\pm1.0\degr$ for the synchrotron knot. This is the first high-spatial resolution multi-epoch study of the polarisation of the inner nebula and pulsar. None of the main features in the nebula show evidence of significant polarisation evolution in the period covered by these observations. The results for the pulsar are consistent with those obtained by S{\l}owikowska et al (2009) using the high-time resolution photo-polarimeter OPTIMA, once the DC component has been subtracted. Our results clearly prove that the knot is the main source of the DC component.
We give a new combinatorial proof of the well known result that the dinv of an $(m,n)$-Dyck path is equal to the area of its sweep map image. The first proof of this remarkable identity for co-prime $(m,n)$ is due to Loehr and Warrington. There is also a second proof (in the co-prime case) due to Gorsky and Mazin and a third proof due to Mazin.
A topological insulator Bi2Se3 which shows superconducting property due to Cu doping has been studied using high resolution transmission electron microscopy which provides for the first time, the direct evidence of intercalation sites. A careful study exhibits the presence of two intercalation sites in this material when projected along the [-1-1 2 0] direction. Stoichiometry of the intercalated unit cell was also calculated from the projected potential.
Supra-arcade downflows (SADs) and supra-arcade downflowing loops (SADLs) descending from reconnection regions toward solar post-flare arcades seem to be two different observational signatures of retracting, isolated reconnected flux tubes with irreducible three-dimensional geometries. This dissertation describes work in refining and improving a novel model of patchy reconnection, where only a small bundle of field lines is reconnected across a current sheet and forms a reconnected thin flux tube. Traditional models have not been able to explain why some of the observed SADs appear to be hot and relatively devoid of plasma. The present work shows that plasma depletion naturally occurs in flux tubes that are reconnected across nonuniform current sheets and slide trough regions of decreasing magnetic field magnitude. Moreover, through a detailed theoretical analysis of generalized thin flux tube equations, we show that the addition to the model of pressure-driven parallel dynamics, as well as temperature-dependent, anisotropic viscosity and thermal conductivity is essential for self-consistently producing gas-dynamic shocks inside reconnected tubes that heat and compress plasma to observed temperatures and densities. The shock thickness can be as long as the entire tube and heat can be conducted along tube's legs, possibly driving chromospheric evaporation. We developed a computer program that solves numerically the thin flux tube equations that govern the retraction of reconnected tubes. Simulations carried out with this program corroborate our theoretical predictions. A comparison of these simulations with fully three-dimensional magnetohydrodynamic simulations is presented to assess the validity of the thin flux tube model. We also present an observational method based on total emission measure and mean temperature to determine where in the current sheet a tube was reconnected.
HD4539 (alias PG0044+097 or EPIC220641886) is a bright (V=10.2) long-period V1093 Her-type subdwarf B (sdB) pulsating star that was observed by the Kepler spacecraft in its secondary (K2) mission. We use the K2 light curve (78.7 days) to extract 169 pulsation frequencies, 124 with a robust detection. Most of these frequencies are found in the low-frequency region typical of gravity (g-)modes, but some higher frequencies corresponding to pressure (p-)modes are also detected. Therefore HD4539 is a hybrid pulsator and both the deep and surface layers of the star can potentially be probed through asteroseismology. The lack of any frequency splitting in its amplitude spectrum suggests that HD4539 has a rotation period longer than the K2 run and/or that it is seen pole-on. From asymptotic period spacing we see many high-degree modes, up to l=12, in the spectrum of HD4539, with amplitudes as low as a few ppm. A large fraction of these modes can be identified and for ~29% of them we obtain a unique and robust identification corresponding to l<=8. Our study includes also a new determination of the atmospheric parameters of the star. From low-resolution spectroscopy we obtain Teff=22,800+-160 K, logg=5.20+-0.02 and log(N(He)/N(H))=-2.34+-0.05. By fitting the SED we obtain Teff=23,470+650-210 K, R_star=0.26+-0.01 Rsun and M_star=0.40+-0.08 Msun. Moreover, from 11 high-resolution spectra we see the radial velocity variations caused by the stellar pulsations, with amplitudes of ~150~m/s for the main modes, and we can exclude the presence of a companion with a minimum mass higher than a few Jupiter masses for orbital periods below ~300 days.
Let $\cX$ be a family of subsets of a finite set $E$. A matroid on $E$ is called an $\cX$-matroid if each set in $\cX$ is a circuit. We consider the problem of determining when there exists a unique maximal $\cX$-matroid in the weak order poset of all $\cX$-matroids on $E$, and characterizing its rank function when it exists.
Cosmic-ray and X-ray heating are derived from the electron energy loss calculations of Dalgarno, Yan and Liu for hydrogen-helium gas mixtures. These authors treated the heating from elastic scattering and collisional de-excitation of rotationally excited hydrogen molecules. Here we consider the heating that can arise from all ionization and excitation processes, with particular emphasis on the reactions of cosmic-ray and X-ray generated ions with the heavy neutral species, which we refer to as chemical heating. In molecular regions, chemical heating dominates and can account for 50 per cent of the energy expended in the creation of an ion pair. The heating per ion pair ranges in the limit of negligible electron fraction from about 4.3 eV for diffuse atomic gas, to about 13 eV for the moderately dense regions of molecular clouds and to about 18 eV for the very dense regions of protoplanetary disks. An important general conclusion of this study is that cosmic-ray and X-ray heating depends on the physical properties of the medium, i.e., on the molecular and electron fractions, the total density of hydrogen nuclei, and to a lesser extent on the temperature. It is also noted that chemical heating, the dominant process for cosmic-ray and X-ray heating, plays a role in UV irradiated molecular gas.
The pion scalar radius is given by $<r^2_S>=(6/\pi)\int_{4M^2_\pi}^\infty{\rm d}s \delta_S(s)/s^2$, with $\delta_S$ the phase of the scalar form factor. Below $\bar{K}K$ threshold, $\delta_S=\delta_\pi$, $\delta_\pi$ being the isoscalar, S-wave $\pi\pi$ phase shift. At high energy, $s>2 {\rm GeV}^2$, $\delta_S$ is given by perturbative QCD. In between I argued, in a previous letter, that one can interpolate $\delta_S\sim\delta_\pi$, because inelasticity is small, compared with the errors. This gives $<r^2_S>=0.75\pm0.07 {\rm fm}^2$. Recently, Ananthanarayan, Caprini, Colangelo, Gasser and Leutwyler (ACCGL) have claimed that this is incorrect and one should have instead $\delta_S\simeq\delta_\pi-\pi$; then $<r^2_S>=0.61\pm0.04 {\rm fm}^2$. Here I show that the ACCGL phase $\delta_S$ is pathological in that it is discontinuous for small inelasticity, does not coincide with what perturbative QCD suggests at high energy, and only occurs because these authors take a value for $\delta_\pi(4m^2_K)$ different from what experiment indicates. If one uses the value for $\delta_\pi(4m^2_K)$ favoured by experiment, the ensuing phase $\delta_S$ is continuous, agrees with perturbative QCD expectations, and satisfies $\delta_S\simeq\delta_\pi$, thus confirming the correctness of my previous estimate,   $<r^2_S>=0.75\pm0.07 {\rm fm}^2$.
In the present study we employed density functional theory calculations to investigate the mechanical behavior, bonding nature and defect processes of the new ordered MAX phase Mo2ScAlC2. The mechanical stability of the compound is verified with its single crystal elastic constants. The new phase Mo2ScAlC2 is anticipated to be prone to shear along the crystallographic b and c axes, when a rational force is applied to the crystallographic a axis. The compressibility along the <001> direction under uniaxial stress is expected to be easier in Mo2ScAlC2. Additionally, the volume deformation should be easier in Mo2ScAlC2 than in the isostructural Mo2TiAlC2. Mo2ScAlC2 is predicted to behave in a brittle manner. Due to its higher Debye temperature, Mo2ScAlC2 is expected to be thermally more conductive than Mo2TiAlC2. The cross-slip pinning procedure should be significantly easier in Mo2ScAlC2 as compared to Mo2TiAlC2. The new ordered MAX phase Mo2ScAlC2 has a mixed character of strong covalent and metallic bonding with limited ionic nature. Both Mo-C and Mo-Al bonds are expected to be more covalent in Mo2ScAlC2 than those of Mo2TiAlC2. the level of covalency of Sc-C bond is somewhat low compared to a similar bond Ti-C in Mo2TiAlC2. Due to its reduced hardness, Mo2ScAlC2 should be softer and more easily machinable compared to Mo2TiAlC2. Fermi surface topology of the new compound is formed mainly due to the low-dispersive Mo 4d-like bands. The intrinsic defect processes reveal that the level of radiation tolerance in Mo2ScAlC2 is not as high as in other MAX phases such as Ti3AlC2.
We present infrared spectroscopy from the Spitzer Space Telescope at one disk position and two positions at a height of 1 kpc from the disk in the edge-on spiral NGC 891, with the primary goal of studying halo ionization. Our main result is that the [Ne III]/[Ne II] ratio, which provides a measure of the hardness of the ionizing spectrum free from the major problems plaguing optical line ratios, is enhanced in the extraplanar pointings relative to the disk pointing. Using a 2D Monte Carlo-based photo-ionization code which accounts for the effects of radiation field hardening, we find that this trend cannot be reproduced by any plausible photo-ionization model, and that a secondary source of ionization must therefore operate in gaseous halos. We also present the first spectroscopic detections of extraplanar PAH features in an external normal galaxy. If they are in an exponential layer, very rough emission scale-heights of 330-530 pc are implied for the various features. Extinction may be non-negligible in the midplane and reduce these scale-heights significantly. There is little significant variation in the relative emission from the various features between disk and extraplanar environment. Only the 17.4 micron feature is significantly enhanced in the extraplanar gas compared to the other features, possibly indicating a preference for larger PAHs in the halo.
Commissioning observations with the Apache Point Observatory Galactic Evolution Experiment (APOGEE), part of the Sloan Digital Sky Survey III, have produced radial velocities (RVs) for ~4700 K/M-giant stars in the Milky Way bulge. These high-resolution (R \sim 22,500), high-S/N (>100 per resolution element), near-infrared (1.51-1.70 um; NIR) spectra provide accurate RVs (epsilon_v~0.2 km/s) for the sample of stars in 18 Galactic bulge fields spanning -1<l<20 deg, |b|<20 deg, and dec>-32 deg. This represents the largest NIR high-resolution spectroscopic sample of giant stars ever assembled in this region of the Galaxy. A cold (sigma_v~30 km/s), high-velocity peak (V_GSR \sim +200 km/s) is found to comprise a significant fraction (~10%) of stars in many of these fields. These high RVs have not been detected in previous MW surveys and are not expected for a simple, circularly rotating disk. Preliminary distance estimates rule out an origin from the background Sagittarius tidal stream or a new stream in the MW disk. Comparison to various Galactic models suggests that these high RVs are best explained by stars in orbits of the Galactic bar potential, although some observational features remain unexplained.
Landau's theory of the Fermi liquid is adapted to analyze the impact of electron-electron ($e-e$) interactions on the deficit of the superfluid density $\rho_{s0}=\rho_s(T=0)$ in dirty superconducting electron systems in which the damping $\gamma$ of single-particle excitations exceeds the zero temperature BCS gap $\Delta_0$. In the dirty strong-coupling limit $\gamma/\Delta_0\gg 1,m^*/m_e\gg 1$, the formula derived for $\rho_{s0}$ is shown to coincide with the well-known empirical Uemura relation provided pair-breaking contributions are nonexistent. The roles of the crystal lattice and magnetic pair-breaking effects in the observed decline of the zero-temperature superfluid density $\rho_{s0}$ in overdoped LSCO compounds are also discussed. Our method is also applied to elucidation of results from the pioneering experimental studies performed recently by Bozovi\`c and collaborators in overdoped LSCO compounds.
We have analyzed the spectral variations of the superluminal black-hole X-ray binary GRS 1915+105 by using data obtained with the PCA on the Rossi XTE. We find that, despite the marked differences in the structure and the time scale of variability, all spectral changes can be attributed to the rapid disappearing of the inner region of an accretion disk, followed by a slower re-filling of the emptied region. The time scale for each event is determined by the extent of the missing part of the disk. The observed relation between the duration of an event and the radius of the disappearing region matches remarkably well the expected radius dependence of the viscous time scale for the radiation-pressure dominated region of an accretion disk.
We present a method to derive macroscopic fluid-dynamic models from microscopic car-following models via a coarse-graining procedure. The method is first demonstrated for the optimal velocity model. The derived macroscopic model consists of a conservation equation and a momentum equation, and the latter contains a relaxation term, an anticipation term, and a diffusion term. Properties of the resulting macroscopic model are compared with those of the optimal velocity model through numerical simulations, and reasonable agreement is found although there are deviations in the quantitative level. The derivation is also extended to general car-following models.
The propagation of plane electromagnetic waves in the gravitational field inside a rotating cloud of dark matter is analyzed. Formulas for the deflection and absorption of light, and the rotation of the polarization plane are obtained in closed form in terms of the mass density and the angular velocity of the cloud. It is shown that the formulas can be considerably simplified for axisymmetric configurations. As an example, the formalism is applied to a rotating massive cloud described by a Plummer potential.
Using three hypergeometric identities, we evaluate the harmonic measure of a finite interval and of its complementary for a strictly stable real L{\'e}vy process. This gives a simple and unified proof of several results in the literature, old and recent. We also provide a full description of the corresponding Green functions. As a by-product, we compute the hitting probabilities of points and describe the non-negative harmonic functions for the stable process killed outside a finite interval.
The paper deals with the fabrication of nano-shells from pre-stressed nano-plates release. Due to geometrical and technological restrictions we have to cover a given surface with three-dimensional thin ribbons. We discuss the key role of the geodesic curvature in the design of such shell-ribbons. We show that including small-strains but large rotations we are able to control the metric tensor of both Lagrangian and Eulerian ribbons by an appropriate choice of the width and thickness of the ribbons. Moreover, the Green-Lagrange strain tensor is controlled by the distance between the curvature of the planar ribbon and the geodesic curvature of the supporting curve of the shell-ribbon. Under suitable constitutive assumptions, we deduce the field equations, the boundary conditions and the design equations. The former relate the pre-stress in the planar layer to the final geometry of the desired shell-ribbon. A fine tuning of the composition, geometry and of the pre-stress of the plate-ribon is necessary to design and fabricate the shell-ribbon. We design and fabricate a partial cover of the sphere with constant latitude ribbons starting from planar multi-layer semiconductor materials grown by molecular beam epitaxy. The details of fabrication method and its limitations are discussed.
B[e] supergiants (B[e]SGs) are emission-line objects, presumably in a short-lived phase in the post-main sequence evolution of massive stars. Their intense infrared excess emission indicates large amounts of warm circumstellar dust, and the stars were longtime assumed to possess an aspherical wind consisting of a classical line-driven wind in polar direction and a dense, slow equatorial wind dubbed outflowing disk. The general properties obtained for these disks are in line with this scenario, although current theories have considerable difficulties reproducing the observed quantities. Therefore, more sophisticated observational constraints are needed. These follow from combined optical and infrared spectroscopic studies, which delivered the surprising result that the circumstellar material of B[e]SGs is concentrated in multiple rings revolving the stars on stable Keplerian orbits. Such a scenario requires new ideas for the formation mechanism, in which pulsations might play an important role.
We establish the global existence of weak martingale solutions to the simplified stochastic Ericksen--Leslie system modeling the nematic liquid crystal flow driven by Wiener-type noises on the two-dimensional bounded domains. The construction of solutions is based on the convergence of Ginzburg--Landau approximations. To achieve such a convergence, we first utilize the concentration-cancellation method for the Ericksen stress tensor fields based on a Pohozaev type argument, and second the Skorokhod compactness theorem, which is built upon a uniform energy estimate.
By means of a model Hamiltonian approach we study the role of volume expansion, Hund's coupling and electron correlation in the standard hybridization mechanism for ferroelectricity in cubic CaMnO$_3$, a prototypical non-$d^0$ perovskite. Our results establish that the ferroelectric instability arises from a subtle balance between different energy contributions, explaining the origin of its enhancement under negative pressure. Expansion of volume is found to cause a strong reduction of the elastic energy, while leaving almost unchanged the tendency of Mn states to form covalent bonds with the surrounding oxygens. Hund's coupling with local spins of magnetic cations can reduce and even suppress the instability towards the ferroelectric state.
We continue our study on relationships between Bernoulli polynomials and balancing (Lucas-balancing) polynomials. From these polynomial relations, we deduce new combinatorial identities with Fibonacci (Lucas) and Bernoulli numbers. Moreover, we prove a special identity involving Bernoulli polynomials and Fibonacci numbers in arithmetic progression. Special cases and some corollaries will highlight interesting aspects of our findings. Our results complement and generalize these of Frontczak (2019).
Simultaneous simulation of HXR and MW emission with the same populations of electrons is still a great challenge for interpretation of observations in real events. In this paper we apply the FP kinetic model of precipitation of electron beam with energy range from 12 keV to 1.2 MeV to the interpretation of X-ray and microwave emissions observed in the flare of 10 March 2001. Methods. The theoretical HXR and MW emissions were calculated by using the distribution functions of electron beams found by solving time-dependent Fokker-Planck approach in a converging magnetic field (Zharkova at al., 2010; Kuznetsov and Zharkova, 2010) for anisotropic scattering of beam electrons on the ambient particles in Coloumb collisions and Ohmic losses. The simultaneous observed HXR photon spectra and frequency distribution of MW emission and polarization were fit by those simulated from FP models which include the effects of electric field induced by beam electrons and precipitation into a converging magnetic loop. Magnetic field strengths in the footpoints on the photosphere were updated with newly calibrated SOHO/MDI data. The observed HXR energy spectrum above 10 keV is shown to be a double power law which was fit precisely by the photon HXR spectrum simulated for the model including the self-induced electric field but without magnetic convergence. The MW emission simulated for different models of electron precipitation revealed a better fit to the observed distribution at higher frequencies for the models combining collisions and electric field effects with a moderate magnetic field convergence of 2. The MW simulations were able to reproduce closely the main features of the MW emission observed at higher frequencies.
We report the detection of a magnetic field in the helium-strong star CPD-57 3509 (B2 IV), a member of the Galactic open cluster NGC3293, and characterise the star's atmospheric and fundamental parameters. Spectropolarimetric observations with FORS2 and HARPSpol are analysed using two independent approaches to quantify the magnetic field strength. A high-S/N FLAMES/GIRAFFE spectrum is analysed using a hybrid non-LTE model atmosphere technique. Comparison with stellar evolution models constrains the fundamental parameters of the star. We obtain a firm detection of a surface averaged longitudinal magnetic field with a maximum amplitude of about 1 kG. Assuming a dipolar configuration of the magnetic field, this implies a dipolar field strength larger than 3.3 kG. Moreover, the large amplitude and fast variation (within about 1 day) of the longitudinal magnetic field implies that CPD-57 3509 is spinning very fast despite its apparently slow projected rotational velocity. The star should be able to support a centrifugal magnetosphere, yet the spectrum shows no sign of magnetically confined material; in particular, emission in H{\alpha} is not observed. Apparently, the wind is either not strong enough for enough material to accumulate in the magnetosphere to become observable or, alternatively, some leakage process leads to loss of material from the magnetosphere. The quantitative spectroscopic analysis of the star yields an effective temperature and a logarithmic surface gravity of 23750+-250 K and 4.05+-0.10, respectively, and a surface helium fraction of 0.28+-0.02 by number. The surface abundances of C, N, O, Ne, S, and Ar are compatible with the cosmic abundance standard, whereas Mg, Al, Si, and Fe are depleted by about a factor of 2. This abundance pattern can be understood as the consequence of a fractionated stellar wind. CPD-57 3509 is one of the most evolved He-strong stars known.