Miracle-dz/UniFAR-FTUs huggingface dataset:
Theoretical Considerations on the Properties of Accreting Millisecond Pulsars

We examine a number of evolutionary scenarios for the recently discovered class of accretion-powered millisecond X-ray pulsars in ultracompact binaries, including XTE J0929-314 and XTE J1751-305. These systems have very short orbital periods of Porb = 43.6 and 42.4 minutes, respectively, and extremely small mass functions. We focus on a particular scenario that can naturally explain the present-day properties of these systems. This model invokes a donor star that was either very close to the main-sequence turnoff at the onset of mass transfer or had sufficient time to evolve during the mass-transfer phase. We have run a systematic set of binary evolution calculations with a wide range of initial conditions. We find that these two ultracompact binaries can best be fitted by models wherein the donors start to lose mass at orbital periods of ~15 hr. The orbital periods then decrease to a minimum value of ≲40 minutes and finally evolve back up to about 43 minutes. We present the results of our binary evolution calculations for these systems, including interior profiles for the donor stars. We find that the initial properties of the donor star and the exact mode of orbital angular momentum losses do not have to be individually fine-tuned in order to reproduce the observed properties. We also carry out an analysis based on the measured mass functions of XTE J0929-314 and XTE J1751-305 to establish formal probability distributions for the current donor masses, chemical compositions, and thermal bloating factors of these systems. These distributions are evaluated in the context of our binary evolution models. We conclude that the donor masses are likely to be in the range ~0.012-0.025 M☉ and have radii of ~0.042-0.055 R☉. These radii are factors of ~1.1-1.3 times larger than the corresponding radii of zero-temperature stars of the same mass and chemical composition. According to the evolutionary scenario proposed in this paper, the interiors of the donors are largely composed of He, and the surface H abundances are almost certainly less than 10% (by mass). The orbital period derivative of these systems is very likely to be positive, i.e., orb/Porb > 0, with typical values in the range ~3 × 10-10 to 2 × 10-8 yr-1. Long-term average values of the mass-transfer rate could be as high as ~10-11 to 3 × 10-10 M☉ yr-1 but is more likely to be ~10-11 M☉ yr-1. Our study supports the hypothesis that X-ray irradiation has had a minimal effect on enhancing the radius of the low-mass donor. We also show how, in the context of this same basic evolutionary scenario, we can model the properties of the SAX 1808.4-3658 binary millisecond X-ray pulsar (Porb = 2 hr). Finally, we point out that if the proposed scenario to explain the ultracompact systems is correct, then these binaries truly link (as evolutionary cousins) systems that (1) evolve to become wide binary millisecond pulsars containing low-mass He dwarfs and (2) those ordinary low-mass X-ray binaries in which the H-rich donors are slowly reduced to planetary masses.
An innovation approach to non-Gaussian time series analysis

The paper shows that the use of both types of random noise, white noise and Poisson noise, can be justified when using an innovations approach. The historical background for this is sketched, and then several methods of whitening dependent time series are outlined, including a mixture of Gaussian white noise and a compound Poisson process: this appears as a natural extension of the Gaussian white noise model for the prediction errors of a non-Gaussian time series. A statistical method for the identification of non-linear time series models with noise made up of a mixture of Gaussian white noise and a compound Poisson noise is presented. The method is applied to financial time series data (dollar-yen exchange rate data), and illustrated via six models.
Estimation of Planetary Photometric Emissions for Extremely Close-in Exoplanets.

The fine precision of photometric data available from missions like Kepler provide researchers with the ability to measure changes in light on the order of tens of parts per million (ppm). This level of precision allows researchers to measure the loss of light due to exoplanet transits as well as the light emitted by an exoplanet, or planetary photometric emissions. The planetary photometric emissions are due to the thermal emissions of the exoplanet, and reflected stellar light. In many cases it is assumed that the incident stellar light may be modeled as plane parallel rays. For extremely close-in exoplanets the finite angular size of the host star must be taken into account and the plane parallel ray model breaks down. One consequence of modeling the incident stellar radiation in this manner is the creation of three distinct zones as opposed to the two zones present in the plane parallel ray model. The three zones are the fully illuminated, penumbral, and un-illuminated zones. The existence of the penumbral zone means that more than half of the exoplanet will be at least partially illuminated by the host star. In this work we will present a complete derivation of the reflective luminosity of the fully illuminated zone. In addition, we will present an outline for the derivation of the reflected intensity distribution of the penumbral zone. Within this work we will also derive a new expression for the thermal luminosity of an exoplanet by treating each of the three zones as a blackbody emitting at a constant temperature. Finally, it will be shown that an estimation of the radius of the exoplanet requires proper accounting of light from the penumbral zone during the primary transit. Not doing so risks underestimating the radius of the exoplanet and an overestimation of its geometric albedo and nightside temperature.
Formation Rate, Evolving Luminosity Function, Jet Structure, and Progenitors for Long Gamma-Ray Bursts

We constrain the isotropic luminosity function (LF) and formation rate of long γ-ray bursts (GRBs) by fitting models jointly to both the observed differential peak-flux and redshift distributions. We find evidence supporting an evolving LF, where the luminosity scales as (1 + z)δ, with an optimal δ of 1.0 ± 0.2. For a single-power law LF, the best slope is approximately -1.57 with an upper luminosity of 1053.3 ergs s-1, while the best slopes for a double-power law LF are approximately -1.6 and -2.6, with a break luminosity of 1052.7 ergs s-1. Our finding implies a jet model intermediate between the universal structured ϵ(θ) ∝ θ-2 model and the quasi-universal Gaussian structured model. For the uniform-jet model our result is compatible with an angle distribution between 2° and 15°. Our best-constrained GRB formation rate histories increase from z = 0 to 2 by a factor of ~30 and then continue increasing slightly. We connect these histories to the cosmic star formation history and compare with observational inferences up to z ~ 6. GRBs could be tracing the cosmic rates of both the normal and obscured star formation regimes. We estimate a current GRB event rate in the Milky Way of ~5 × 10-5 yr-1 and compare it with the birthrate of massive close Wolf-Rayet + black hole binaries with orbital periods of hours. The agreement is rather good, suggesting that these systems could be the progenitors of the long GRBs.
de Sitter attractors in generalized gravity

We obtain conditions for the existence and stability of de Sitter attractors in the phase space of homogeneous and isotropic cosmology in generalized theories of gravity (including nonlinear and scalar-tensor theories). These conditions are valid for any form of the coupling functions of the theory. Stability with respect to inhomogeneous perturbations is analyzed using a covariant and gauge-invariant formalism. The relevance for inflationary scenarios of the early universe and for quintessence models of the present era is discussed.
Strings from Quivers, Membranes from Moose

We consider = 2 moose/quiver gauge theories corresponding to N1 D3-branes at a 2/N2 singularity in the ``large moose'' limit where N1 and N2 are scaled to infinity together. In the dual holographic description, this scaling gives rise to a maximally supersymmetric pp-wave background with a compact light-cone direction. We identify the gauge theory operators that describe the Discrete Light-Cone Quantization (DLCQ) of the string in this background. For each discrete light-cone momentum and winding sector there is a separate ground state and Fock space. The large moose/quiver diagram provides a useful graphical representation of the string and its excitations. This representation has a natural explanation in a T-dual language. The dual theory is a non-relativistic type-IIA string wound around the T-dual direction, and bound by a quadratic newtonian potential. We end with some comments on D-string/D-particle states, a possible lift to M-theory and the relation to deconstruction.
Influence of a non-Gaussian state model on the position estimation in the nonlinear filtration

In navigation systems with nonlinear filtration algorithms extended Kalman filter is being used to estimate position. In this filter, the state model distribution and all relevant noise destinies are approximated by Gaussian random variable. What is more, this approach can lead to poor precision of estimation. Unscented Kalman filter UKF approximates probability distribution instead of approximating nonlinear process. The state distribution is represented by a Gaussian random variable specified using weighted sigma points, which completely capture true mean and covariance of the distribution. Another solution for the general filtering problem is to use sequential Monte Carlo methods. It is particle filtering PF based on sequential importance sampling where the samples (particles) and their weights are drawn from the posterior distribution.
Collapse and Fragmentation in Finite Sheets

We present two-dimensional simulations of finite, self-gravitating gaseous sheets. Unlike the case of infinite sheets, such configurations do not constitute equilibrium states but instead are subject to global collapse unless countered by pressure forces or rotation. The initial effect of finite geometry is to promote concentrations of material at the edges of the sheet. If the sheet is not perfectly circular, gravitational focusing results in enhanced concentrations of mass. In the second-most simple geometry, that of an elliptical outer boundary, the general result is collapse to a filamentary structure with the densest concentrations of mass at the ends of the filament. We suggest that these simple calculations have interesting implications for the gravitational evolution of overall molecular cloud structure, envisioning that such clouds might originate as roughly sheetlike sections of gas accumulated as a result of large-scale flows in the local interstellar medium. We show some examples of local clouds with overall filamentary shape and denser concentrations of mass and star clusters near the ends of the overall extended structure, suggestive of our simple ellipse collapse calculations. We suggest that cluster-forming gas is often concentrated as a result of gravity acting on irregular boundaries; this mechanism can result in very rapid infall of gas, which may be of importance to the formation of massive stars. This picture suggests that much of the supersonic "turbulence" observed in molecular clouds might be gravitationally generated. Our results may provide impetus for further theoretical explorations of global gravitational effects in molecular clouds and their implications for generating the substructure needed for fragmentation into stars and clusters.
Nonlinear Force-free Coronal Magnetic Stereoscopy

Insights into the 3D structure of the solar coronal magnetic field have been obtained in the past by two completely different approaches. The first approach are nonlinear force-free field (NLFFF) extrapolations, which use photospheric vector magnetograms as boundary condition. The second approach uses stereoscopy of coronal magnetic loops observed in EUV coronal images from different vantage points. Both approaches have their strengths and weaknesses. Extrapolation methods are sensitive to noise and inconsistencies in the boundary data, and the accuracy of stereoscopy is affected by the ability of identifying the same structure in different images and by the separation angle between the view directions. As a consequence, for the same observational data, the 3D coronal magnetic fields computed with the two methods do not necessarily coincide. In an earlier work (Paper I) we extended our NLFFF optimization code by including stereoscopic constrains. The method was successfully tested with synthetic data, and within this work, we apply the newly developed code to a combined data set from SDO/HMI, SDO/AIA, and the two STEREO spacecraft. The extended method (called S-NLFFF) contains an additional term that monitors and minimizes the angle between the local magnetic field direction and the orientation of the 3D coronal loops reconstructed by stereoscopy. We find that when we prescribe the shape of the 3D stereoscopically reconstructed loops, the S-NLFFF method leads to a much better agreement between the modeled field and the stereoscopically reconstructed loops. We also find an appreciable decrease by a factor of two in the angle between the current and the magnetic field. This indicates the improved quality of the force-free solution obtained by S-NLFFF.
Modeling dust emission in PN IC 418

We investigated the infrared (IR) dust emission from PN IC 418, using a detailed model controlled by a previous determination of the stellar properties and the characteristics of the photoionized nebula, keeping as free parameters the dust types, amounts, and distributions relative to the distance of the central star. The model includes the ionized region and the neutral region beyond the recombination front (photodissociation region, or PDR), where the [O I] and [C II] IR lines are formed. We succeeded in reproducing the observed infrared emission from 2 to 200 μm. The global energy budget is fitted by summing up contributions from big grains of amorphous carbon located in the neutral region and small graphite grains located in the ionized region (closer to the central star). Two emission features seen at 11.5 and 30 μm are also reproduced by assuming them to be due to silicon carbide (SiC) and magnesium and iron sulfides (MgxFe1−xS), respectively. For this, we needed to consider ellipsoidal shapes for the grains to reproduce the wavelength distribution of the features. Some elements are depleted in the gaseous phase: Mg, Si, and S have sub-solar abundances (−0.5 dex below solar by mass), while the abundance of C + N + O + Ne by mass is close to solar. Adding the abundances of the elements present in the dusty and gaseous forms leads to values closer to but not higher than solar, confirming that the identification of the feature carriers is plausible. Iron is strongly depleted (3 dex below solar) and the small amount present in dust in our model is far from being enough to recover the solar value. A remaining feature is found as a residue of the fitting process, between 12 and 25 μm, for which we do not have identification.
Retrieval of Cirrus Cloud Radiative and Backscattering Properties Using Combined Lidar and Infrared Radiometer (LIRAD) Measurements

Abstract A method for retrieval of cirrus macrophysical and radiative properties using combined ruby lidar and infrared radiometer measurements is explained in detail. The retrieval algorithm includes estimation of a variable backscatter-to-extinction ratio for each lidar profile, which accounts for changes in cloud microphysical properties with time. The technique also utilizes a correlated K distribution radiative transfer model, where absorption coefficients K have been tabulated specifically for the bandwidth and filter function of the infrared radiometer. The radiative transfer model allows for estimation of infrared emission due to atmospheric water vapor, ozone, and carbon dioxide, which is essential for deriving cirrus radiative properties. Also described is an improved technique for estimation of upwelling IR radiation that is emitted by the surface of the earth and reflected by the cloud into the radiometer field of view. Derived cirrus cloud properties include base and top height and temperatur.
J0815+4729: A Chemically Primitive Dwarf Star in the Galactic Halo Observed with Gran Telescopio Canarias

We report the discovery of the carbon-rich hyper metal-poor unevolved star J0815+4729. This dwarf star was selected from SDSS/BOSS as a metal-poor candidate and follow-up spectroscopic observations at medium resolution were obtained with the Intermediate dispersion Spectrograph and Imaging System (ISIS) at William Herschel Telescope and the Optical System for Imaging and low-intermediate-Resolution Integrated Spectroscopy (OSIRIS) at Gran Telescopio de Canarias. We use the FERRE code to derive the main stellar parameters, T eff = 6215 ± 82 K, and log g = 4.7 ± 0.5 , an upper limit to the metallicity of [Fe/H] ≤ −5.8, and a carbon abundance of [C/Fe] ≥ +5.0, while [ α / Fe ] = 0.4 is assumed. The metallicity upper limit is based on the Ca ii K line, which at the resolving power of the OSIRIS spectrograph cannot be resolved from possible interstellar calcium. The star could be the most iron-poor unevolved star known and also be among the ones with the largest overabundances of carbon. High-resolution spectroscopy of J0815+4729 will certainly help to derive other important elemental abundances, possibly providing new fundamental constraints on the early stages of the universe, the formation of the first stars, and the properties of the first supernovae.
Plasmon measurements with a seeded x-ray laser

Plasmon measurements hold great promise for providing highly accurate data on the physical properties of plasmas in the high-energy density physics regime. To this end we demonstrate in recent experiments at the Linac Coherent Light Source the first spectrally-resolved measurements of plasmons using a seeded 8-keV x-ray laser beam. Forward x-ray Thomson scattering spectra from isochorically heated solid aluminum show a well-resolved plasmon feature that is down-shifted in energy by 19 eV from the incident 8 keV elastic scattering feature. In this spectral range, the simultaneously measured backscatter spectrum shows no spectral features indicating observation of collective plasmon oscillations on a scattering length comparable to the screening length. This technique is a prerequisite for Thomson scattering measurements in compressed matter where the plasmon shift is a sensitive function of the free electron density and where the plasmon intensity provides information on temperature.
On the Conservation and Impermeability Theorems for Potential Vorticity

Abstract If the partial analogy between the behavior of Rossby-Ertel potential vorticity (PV) and the behavior of chemical tracers is to be correctly used in the general case of diabatic, frictional motion, then certain fundamental differences, as well as similarities, between the behavior of PV and that of chemical tracers must be recognized. These differences stem from the well-known kinematical relationship between PV and isentropic circulation (via Stokes' theorem), which has no counterpart for chemical substances. One way of stating the analogy while recognizing the differences is to say first that PV behaves like the mixing ratio of a peculiar chemical “substance” that has zero source; i.e., is exactly conserved, away from boundaries (conserved not in the material or Lagrangian sense, but in the general sense associated with the idea of an indestructible chemical substance), and second that isentropic surfaces behave exactly as if they were impermeable to this “PV-substance” or “PVS,” even when diab.
Calculation of Gromov-Witten invariants for $ CP^{3},CP^{4}$,and $Gr(2,4)$

Using the associativity relations of the topological Sigma Models with target spaces, $CP^3, CP^4$ and $Gr(2,4)$ , we derive recursion relations of their correlation and evaluate them up to certain order in the expansion over the instantons. The expansion coeffieients are regarded as the number of rational curves in $CP^3, CP^4$ and $Gr(2,4)$ which intersect various types of submanifolds corresponding to the choice of BRST invariant operators in the correlation functions.
Phonon-Induced Decay of the Electron Spin in Quantum Dots

We study spin relaxation and decoherence in a GaAs quantum dot due to spin-orbit (SO) interaction. We derive an effective Hamiltonian which couples the electron spin to phonons or any other fluctuation of the dot potential. We show that the spin decoherence time T-2 is as large as the spin relaxation time T-1, under realistic conditions. For the Dresselhaus and Rashba SO couplings, we find that, in leading order, the effective B field can have only fluctuations transverse to the applied B field. As a result, T-2=2T(1) for arbitrarily large Zeeman splittings, in contrast to the naively expected case T-2
Return-Point Memory in an Amorphous Solid

A disordered material that cannot relax to equilibrium, such as an amorphous or glassy solid, responds to deformation in a way that depends on its past. In experiments we subject a 2D athermal amorphous solid to oscillatory shear that alternates between two amplitudes. We show that the system forms memories of both amplitudes, but only when the smaller one is applied last. This behavior, and the pattern of particle rearrangements as strain amplitude is varied, are consistent with the return-point memory seen in ferromagnets and many other systems. A simple model of a ferromagnet can reproduce the results of our experiments and of previous simulations. Unlike ferromagnets, amorphous solids' disorder is unquenched; they require "training" to develop this behavior.
Giant Planets Can Act as Stabilizing Agents on Debris Disks

We have explored the evolution of a cold debris disk under the gravitational influence of dwarf-planet-sized objects (DPs), both in the presence and absence of an interior giant planet. Through detailed long-term numerical simulations, we demonstrate that when the giant planet is not present, DPs can stir the eccentricities and inclinations of disk particles, in linear proportion to the total mass of the DPs; on the other hand, when the giant planet is included in the simulations, the stirring is approximately proportional to the mass squared. This creates two regimes: below a disk mass threshold (defined by the total mass of DPs), the giant planet acts as a stabilizing agent of the orbits of cometary nuclei, diminishing the effect of the scatterers; above the threshold, the giant contributes to the dispersion of the particles.