ShantanuT01/DACTYL-Pretraining huggingface dataset:
The Lithium Depletion Boundary (LDB) is a robust method for accurately determining the ages of young clusters, but most pre-main-sequence models used to derive LDB ages do not include the effects of magnetic activity on stellar properties. In light of this, we present results from our spectroscopic study of the very low-mass members of the southern open cluster Blanco 1 using the Gemini-North telescope, program IDs: GN-2009B-Q-53 and GN-2010B-Q-96. We obtained GMOS spectra at intermediate resolution for cluster candidate members with $I$$\approx$13--20 mag. From our sample of 43 spectra, we find 14 probable cluster members by considering proximity to the cluster sequence in an $I/I-K\rm_s$ color-magnitude diagram, agreement with the cluster's systemic radial velocity, and magnetic activity as a youth indicator. We systematically analyze the H$\alpha$ and Li features and update the LDB age of Blanco 1 to be $126^{+13}_{-14}$ Myr. Our new LDB age for Blanco 1 shows remarkable coevality with the benchmark Pleiades open cluster. Using available empirical activity corrections, we investigate the effects of magnetic activity on the LDB age of Blanco 1. Accounting for activity, we infer a corrected LDB age of $114^{+9}_{-10}$ Myr. This work demonstrates the importance of accounting for magnetic activity on LDB inferred stellar ages, suggesting the need to re-investigate previous LDB age determinations.
Materials with an allotropic phase transformation can result in the formation of microstructures where grains have orientation relationships (ORs) determined by the transformation history. These microstructures influence the final material properties. In zirconium alloys, there is a solid-state body centred cubic (BCC) to hexagonal close packed (HCP) phase transformation, where the crystal orientations of the HCP phase can be related to the parent BCC structure via the Burgers orientation relationship (BOR). In the present work, we adapt a reconstruction code developed for steels which uses a Markov Chain clustering algorithm to analyse electron backscatter diffraction (EBSD) maps and apply this to the HCP and BCC BOR. This algorithm is released as open-source code (via github, as ParentBOR). The algorithm enables new post processing of the original and reconstructed data set to analyse the variants of the HCP alpha-phase that are present and understand shared crystal planes and shared lattice directions within each parent beta grain, and we anticipate that this assists in understanding the transformation related deformation properties of the final microstructure. Finally, we compare the ParentBOR code with recently released reconstruction codes implemented in MTEX to reveal differences and similarities in how the microstructure is described.
Using the outer gap model, we investigate the emission region for the multi-wavelength light curve from energetic pulsars. We assume that gamma-ray and non-thermal X-ray photons are emitted from a particle acceleration region in the outer magnetosphere, and UV/optical photons originate above that region. We assume that gamma-rays are radiated only by outwardly moving particles, whereas the other photons are produced by particles moving inward and outward. We parameterize the altitude of the emission region as the deviation from the rotating dipole in vacuum and determine it from the observed multi-wavelength pulse profile using the observationally constrained magnetic dipole inclination angle and viewing angle of the pulsars. We find that the outer gap model can explain the multi-wavelength pulse behavior by a simple distribution of emissivity, and discuss the possibility of further improvement. From observational fitting, we also find a general tendency for the altitude of the gamma-ray emission region to depend on the inclination angle. In particular, the emission region for low inclination angle is required to be located in very low altitude, which corresponds to the inner region within the last-open field line of rotating dipole in vacuum. This model suggests a modification of statistics about observed gamma-ray pulsars. Number of the sources with low inclination and viewing angles increases compared with previous estimate.
Quantum fluctuations are of central importance in itinerant ferromagnets; in the case of the Stoner Hamiltonian, with contact interactions, they deliver a rich phase diagram featuring a first order ferromagnetic transition preempted by a spin spiral and a paired density wave. However, to date all analyses of fluctuation corrections neglect the finite ranged nature of the Coulomb interaction. We develop the formalism to consider the effects of fluctuations with a realistic screened Coulomb potential. The finite ranged interaction suppresses the tricritical point temperature of the first order ferromagnetic transition, bringing theory into line with experiment, whilst retaining the exotic spin spiral and paired density wave. In an ultracold atomic gas a finite ranged interaction damps the competing molecular instability, permitting the observation of ferromagnetic correlations.
We study the electron self--energy in a strong magnetic field when the parameter \eta\equiv (\alpha/2\pi) \ln^2 (eB/m^2_0) \sim 1 and explore the transition between the perturbative regime \eta<<1 and the nonperturbative massless QED regime \eta>>1 where chiral symmetry is broken spontaneously and electrons acquire the dynamically induced mass.
It is proposed that to the usual probability theory, three definitions and a new theorem are added, the resulting theory allows one to displace the central role usually given to the notion of conditional probability. When a mapping $\phi$ is defined between two measurable spaces, to each measure $\mu$ introduced on the first space, there corresponds an image $\phi[\mu]$ on the second space, and, reciprocally, to each measure $\nu$ defined on the second space the corresponds a reciprocal image $\phi^{-1}[\nu]$ on the first space. As the intersection $\cap$ of two measures is easy to introduce, a relation like $ \phi[ \mu \cap \phi^{-1} [\nu] ] = \phi[\mu] \cap \nu $ makes sense. It is, indeed, a theorem of the theory. This theorem gives mathematical consistency to inferences drawn from physical measurements.
Understanding the physics of how stars form is a highly-prioritized goal of modern Astrophysics, in part because star formation is linked to both galactic dynamics on large scales and to the formation of planets on small scales. It is well-known that stars form from the gravitational collapse of molecular clouds, which are in turn formed out of the turbulent interstellar medium. Star formation is highly inefficient, with one of the likely culprits being the regulation against gravitational collapse provided by magnetic fields. Measurement of the polarized emission from interstellar dust grains, which are partially aligned with the magnetic field, provides a key tool for understanding the role these fields play in the star formation process. Over the past decade, much progress has been made by the most recent generation of polarimeters operating over a range of wavelengths (from the far-infrared through the millimeter part of the spectrum) and over a range of angular resolutions (from less than an arcsecond through fractions of a degree). Future developments in instrument sensitivity for ground-based, airborne, and space-borne polarimeters operating over range of spatial scales are critical for enabling revolutionary steps forward in our understanding of the magnetized turbulence from which stars are formed.
We generalize the construction of Raynaud of smooth projective surfaces of general type in positive characteristic that violate the Kodaira vanishing theorem. This corrects an earlier paper of the same purpose. These examples are smooth surfaces fibered over a smooth curve whose direct images of the relative dualizing sheaves are not nef, and they violate Koll\'ar's vanishing theorem. Further pathologies on these examples include the existence of non-trivial vector fields and that of non-closed global differential 1-forms.
We investigate arrangements of hyperplanes whose normal vectors are given by connected subgraphs of a fixed graph. These include the resonance arrangement and certain ideal subarrangements of Weyl arrangements. We characterize those which are free, simplicial, factored, or supersolvable. In particular, such an arrangement is free if and only if the graph is a cycle, a path, an almost path, or a path with a triangle attached to it.
In steels and single-crystal superalloys the control of the formation of topologically close-packed (TCP) phases is critical for the performance of the material. The structural stability of TCP phases in multi-component transition-metal alloys may be rationalised in terms of the average valence-electron count $\bar{N}$ and the composition-dependent relative volume-difference $\overline{\Delta V/V}$. We elucidate the interplay of these factors by comparing density-functional theory calculations to an empirical structure map based on experimental data. In particular, we calculate the heat of formation for the TCP phases A15, C14, C15, C36, $\chi$, $\mu$, and $\sigma$ for all possible binary occupations of the Wyckoff positions. We discuss the isovalent systems V/Nb-Ta to highlight the role of atomic-size difference and observe the expected stabilisation of C14/C15/C36/$\mu$ by $\overline{\Delta V/V}$ at $\Delta N=0$ in V-Ta. In the systems V/Nb-Re, we focus on the well-known trend of A15$- \sigma - \chi$ stability with increasing $\bar{N}$ and show that the influence of $\overline{\Delta V/V}$ is too weak to stabilise C14/C15/C36/$\mu$ in Nb-Re. As an example for a significant influence of both $\bar{N}$ and $\overline{\Delta V/V}$, we also consider the systems Cr/Mo-Co. Here the sequence A15$- \sigma - \chi$ is observed in both systems but in Mo-Co the large size-mismatch stabilises C14/C15/C36/$\mu$. We also include V/Nb-Co that cover the entire valence range of TCP stability and also show the stabilisation of C14/C15/C36/$\mu$. Moreover, the combination of a large volume difference with a large mismatch in valence-electron count reduces the stability of the A15/$\sigma$/$\chi$ phases in Nb-Co as compared to V-Co. By comparison to non-magnetic calculations we also find that magnetism is of minor importance for the structural stability of TCP phases in Cr/Mo-Co and in V/Nb-Co.
We are concerned with the discretization of a solution of a Forward-Backward stochastic differential equation (FBSDE) with a jump process depending on the Brownian motion. In this paper, we study the cases of Lipschitz generators and the generators with a quadratic growth w.r.t. the variable z. We propose a recursive scheme based on a general existence result given in a companion paper and we study the error induced by the time discretization. We prove the convergence of the scheme when the number of time steps n goes to infinity. Our approach allows to get a convergence rate similar to that of schemes of Brownian FBSDEs.
Globular clusters are an excellent laboratory for stellar population and dynamical research. Recent studies have shown that these stellar systems are not as simple as previously assumed. With multiple stellar populations as well as outer rotation and mass segregation they turn out to exhibit high complexity. This includes intermediate-mass black holes which are proposed to sit at the centers of some massive globular clusters. Today's high angular resolution ground based spectrographs allow velocity-dispersion measurements at a spatial resolution comparable to the radius of influence for plausible IMBH masses, and to detect changes in the inner velocity-dispersion profile. Together with high quality photometric data from HST, it is possible to constrain black-hole masses by their kinematic signatures. We determine the central velocity-dispersion profile of the globular cluster NGC 2808 using VLT/FLAMES spectroscopy. In combination with HST/ACS data our goal is to probe whether this massive cluster hosts an intermediate-mass black hole at its center and constrain the cluster mass to light ratio as well as its total mass. We derive a velocity-dispersion profile from integral field spectroscopy in the center and Fabry Perot data for larger radii. High resolution HST data are used to obtain the surface brightness profile. Together, these data sets are compared to dynamical models with varying parameters such as mass to light ratio profiles and black-hole masses. Using analytical Jeans models in combination with variable M/L profiles from N-body simulations we find that the best fit model is a no black hole solution. After applying various Monte Carlo simulations to estimate the uncertainties, we derive an upper limit of the back hole mass of M_BH < 1 x 10^4 M_SUN (with 95 % confidence limits) and a global mass-to-light ratio of M/L_V = (2.1 +- 0.2) M_SUN/L_SUN.
The time-convolutionless master equation for the electronic populations is derived for a generic electron-phonon Hamiltonian. The equation can be used in the regimes where the golden rule approach is not applicable. The equation is applied to study the electronic relaxation in several models with the finite number normal modes. For such mesoscopic systems the relaxation behavior differs substantially from the simple exponential relaxation. In particular, the equation shows the appearance of the recurrence phenomena on a time-scale determined by the slowest mode of the system. The formal results are quite general and can be used for a wide range of physical systems. Numerical results are presented for a two level system coupled to Ohmic and super-Ohmic baths, as well as for a model of charge-transfer dynamics between semiconducting organic polymers.
Electron spin-momentum locking together with background magnetic textures can significantly alter the electron transport properties. We theoretically investigate the electron transport at the interface between a topological insulator and a magnetic insulator with magnetic skyrmions on the top. In contrast to the conventional topological Hall effect in normal metals, the skyrmions yield an additional contribution to the anomalous Hall conductivity even in the absence of in-plane magnetic texture, arising from the phase factor characteristic to Dirac electrons acquired at skyrmion boundary.
The motion of sound waves propagating in the perfect fluid with inhomogeneous background flow is effectively described as a massless scalar field on a curved space-time. This effective geometry is characterized by the acoustic metric, which depends on the background flow, and null geodesics on the geometry express the acoustic causal structure. Therefore by the effective geometry we can easily study the causality on the flows. In this paper, we consider a spherically symmetric, relativistic outflow and present the maximal causally connected region for a super-sonic flow. When Lorentz factor of the radial velocity of the flow is constant or obeys power-law with respect to the radial coordinate r, we can solve it analytically. As a result we show that in the constant case the maximum angle is proportional to inverse of Lorentz factor and logarithmically increases with respect to r, in contrast, accelerative expansions in power-law case make this angle bounded.
We present a complete theoretical scenario for classical Cepheids in the most commonly used HST/WFC3 filters, going from optical (F555W, F606W and F814W) to near-infrared (F160W) bands. The importance of such a study is related to the recent release of new classical Cepheids observed with HST/WFC3 in 8 distant galaxies where SNIa are hosted. These observations have posed sound constraints to the current distance scale with uncertainties on the Hubble constant Ho smaller than 3%. Our models explore a large range of metallicity and Helium content, thus providing a robust and unique theoretical tool for describing these new and future HST/WFC3 observations. As expected, the Period-Luminosity (PL) relation in F160W filter is linear and slightly dependent on the metallicity when compared with optical bands, thus it seems the most accurate tool to constrain extragalactic distances with Cepheids. We compare the pulsation properties of Cepheids observed with HST/WFC3-IR with our theoretical scenario and we discuss the agreement with the predicted Instability Strip for all the investigated galaxy samples including the case of NGC4258. Finally, adopting our theoretical F160W PL relation for Z=0.02 and log P>1.0, we derive new distance moduli. In particular, for NGC 4258, we derive a distance modulus mu0 = 29.345 +- 0.004 mag with a sigma = 0.34 mag, which is in very good agreement with the geometrical maser value. Moreover, using the obtained distance moduli, we estimate the Hubble constant value, Ho=76.0 +- 1.9 km s-1 Mpc-1 in excellent agreement with the most recent literature values.
Evidence was presented recently suggesting that the Fundamental Plane (FP) clusters studied in the Hubble Key Project may contain quantized intrinsic redshift components that are related to those reported by Tifft. Here we report the results of a similar analysis using 55 spiral (Sc and Sb) galaxies, and 36 Type Ia supernovae (SnIa) galaxies. We find that even when many more objects are included in the sample there is still clear evidence that the same quantized intrinsic redshifts are present and superimposed on the Hubble flow. We find Hubble constants of Ho = 60.0 and 57.5 km s^(-1) Mpc^(-1) for the Sc and Sb galaxies respectively. For the SnIa galaxies we find Ho = 58. These values are considerably lower than the value of Ho = 72 reported by the Hubble Key Project, but are good in agreement with the value Ho = 60 found for intermediate redshifts using the Sunyaev-Zel'dovich (SZ) effect. Evidence is also presented that suggests that the presence of unaccounted for intrinsic redshifts may have led us incorrectly to the conclusion that a "great attractor" is needed to explain the velocity data. The 91 galaxies examined here also offer new, independent confirmations of the importance of the redshift increment zf = 0.62.
The increasing sensitivity of current experiments, which nowadays routinely measure the thermal SZ effect within galaxy clusters, provide the hope that peculiar velocities of individual clusters of galaxies will be measured rather soon using the kinematic SZ effect. Also next generation of X-ray telescopes with microcalorimeters, promise first detections of the motion of the intra cluster medium (ICM) within clusters. We used a large set of cosmological, hydrodynamical simulations, which cover very large cosmological volume, hosting a large number of rich clusters of galaxies, as well as moderate volumes where the internal structures of individual galaxy clusters can be resolved with very high resolution to investigate, how the presence of baryons and their associated physical processes like cooling and star-formation are affecting the systematic difference between mass averaged velocities of dark matter and the ICM inside a cluster. We, for the first time, quantify the peculiar motion of galaxy clusters as function of the large scale environment. We also demonstrate that especially in very massive systems, the relative velocity of the ICM compared to the cluster peculiar velocity add significant scatter onto the inferred peculiar velocity, especially when measurements are limited to the central regions of the cluster. Depending on the aperture used, this scatter varies between 50% and 20%, when going from the core (e.g. ten percent of the virial radius) to the full cluster (e.g. the virial radius).
In this work we study the effect of the nuclear tensor force on properties related with deformation. We focus on isotopes in the Mg, Si, S, Ar, Sr and Zr chains within the Hartree-Fock-Bogoliubov theory using the D1ST2a Gogny interaction. Contributions to the tensor energy in terms of saturated and unsaturated subshells are analyzed. Like-particle and proton-neutron parts of the tensor term are independently examinated. We found that the tensor term may considerably modify the potential energy landscapes and change the ground state shape. We analyze too how the pairing characteristics of the ground state change when the tensor force is included.
We analyze the results of scanning near-field infrared spectroscopy performed on thin films of a-SiO2 on Si substrate. The measured near-field signal exhibits surface-phonon resonances whose strength has a strong thickness dependence in the range from 2 to 300 {nm}. These observations are compared with calculations in which the tip of the near-field infrared spectrometer is modeled either as a point dipole or an elongated spheroid. The latter model accounts for the antenna effect of the tip and gives a better agreement with the experiment. Possible applications of the near-field technique for depth profiling of layered nanostructures are discussed.
We study the ground-state properties of frustrated Heisenberg ferrimagnetic ladders with antiferromagnetic exchange interactions and two types of alternating sublattice spins. In the limit of strong rung couplings, we show that the mixed spin-1/2 and spin-1 ladders can be systematically mapped onto a spin-1/2 Heisenberg model with additional next-nearest-neighbor exchanges. The system is either in a ferrimagnetic state or in a critical spin-liquid state depending on the competition between the spin exchanges along the legs and the diagonal exchanges.
We construct for the first time, the sequences of stable neutron star (NS) models capable of explaining simultaneously, the glitch healing parameters, $Q$, of both the pulsars, the Crab ($Q \geq 0.7$) and the Vela ($Q \leq 0.2$), on the basis of starquake mechanism of glitch generation, whereas the conventional NS models cannot give such consistent explanation. Furthermore, our models also yield an upper bound on NS masses similar to those obtained in the literature for a variety of modern equations of state (EOSs) compatible with causality and dynamical stability. The results obtained in this paper set an upper and lower bound on the energy of a gravitationally redshifted electron-positron annihilation line in the range of about 0.309 - 0.315 MeV from the Crab and in the range of about 0.425 - 0.439 MeV from the Vela pulsar.
We use matrix model technology to study the N=2 U(N) gauge theory with N_f massive hypermultiplets in the fundamental representation. We perform a completely perturbative calculation of the periods a_i and the prepotential F(a) up to the first instanton level, finding agreement with previous results in the literature. We also derive the Seiberg-Witten curve and differential from the large-M solution of the matrix model. We show that the two cases N_f<N and N \le N_f < 2N can be treated simultaneously.
This talk gives a brief introduction to black hole horizons and their role in black hole thermodynamics. In particular a distinction is made between quasi-locally defined horizons and event horizons. Currently some new techniques have led to interesting developments and the field seems to be growing in two distinct directions. We will show how thermodynamics can equally well be applied to locally defined horizons and discuss some recent results. The emphasis is on giving simple intuitive pictures and mathematical details are largely omitted.
A family of diffusion-annihilation processes is introduced, which is exactly solvable. This family contains parameters that control the diffusion- and annihilation- rates. The solution is based on the Bethe ansatz and using special boundary conditions to represent the reaction. The processes are investigated, both on the lattice and on the continuum. Special cases of this family of processes are the simple exclusion process and the drop-push model.