Miracle-dz/UniFAR-FTUs huggingface dataset:
Asymmetries of the emission lines of QSOs, Seyfert galaxies, and Novae

The permitted emission-line profiles of Seyfert galaxies and QSOs often contain more light in the red wing than in the violet wing. Such an asymmetry can arise as a consequence of self-absorption of the line radiation in an expanding system of optically thick clouds. Calculations are presented of the anisotropy of line emission from photoionized clouds, and the resulting asymmetry in the line profiles is discussed. This process is shown to have operated in Nova Cygni 1975. For Seyfert galaxies, considerations of Balmer decrements, ionization equilibrium, and the O I lambda8446 emission indicate that the Balmer line optical depths are large enough to give strongly asymmetric line profiles for pure expansion. However, the observed lack of strong asymmetry in the Balmer lines of most Seyfert galaxies suggests that the broad-line widths may result primarily from random motions, or that the clouds radiate isotropically for some reason, perhaps because they are immersed in an extended source of ionizing continuum. In this case, the frequently observed absorption of the violet wing of L.cap alpha. must occur in a surrounding region undergoing systematic outflow. Alternatively, the weakness of the Balmer line asymmetries can be understood if most of the Balmer line emission resultsmore » from collisional excitation from n=2. « less
Attenuation Measurements in Cement-Based Materials Using Laser Ultrasonics

This research uses laser ultrasonic techniques to quantify the frequency-dependent attenuation losses of Rayleigh waves in cement-based materials; these materials are heterogeneous in nature, and this heterogeneity is seen at multiple length scales. As a result, ultrasonic waves that propagate in cement-based materials exhibit a high degree of (material) attenuation losses. Physically, these attenuation losses are a combination of internal friction, such as the work done at material interfaces (ultrasonic absorption) and the scattering losses due to material heterogeneity. The high fidelity, large frequency bandwidth, and absolute, noncontact nature of laser ultrasonics makes this an ideal methodology to measure attenuation in these materials. This research uses a dual-probe, heterodyne interferometer to experimentally measure these attenuation losses (as a function of frequency) in three different materials: (1) aluminum; (2) mortar; and (3) granite. The aluminum results (aluminum is homogeneous at the wavelengths used here) are used to demonstrate the fidelity of the laser ultrasonic measurement technique, while the mortar and granite results (both are heterogeneous at these wavelengths) are used to quantify the attenuation losses present in each material.
Equilibrium layers and wall turbulence

In turbulent flow past rigid boundaries, there can be distinguished regions close to the wall in which the local rates of energy production and dissipation are so large that aspects of the turbulent motion concerned with these processes are determined almost solely by the distribution of shear stress within the region and are independent of conditions outside it. These regions are here called equilibrium layers because of the equilibrium existing between local rates of energy production and dissipation. Three kinds of equilibrium layer have been studied experimentally, the constant-stress layer, the transpiration layer and the zero-stress layer, but there are other possible forms. One that is of importance in the theory of self-preserving flow in boundary layers and in diffusers is the ‘linear-stress’ layer in which the stress increases linearly with distance from the wall. The properties of these various equilibrium layers are considered and the distributions of mean velocity are derived from the equation for the turbulent kinetic energy and certain assumptions of flow similarity. The theory of self-preserving wall flow, usually expressed as a combination of the law of the wall and the defect law, assumes compatibility between the outer flow and the equilibrium layer, and the course of development depends on the kind of equilibrium layer. Earlier work by the author, which assumed the defect law, is only valid if the whole of the equilibrium layer is a constant-stress layer and this is not true in strong adverse pressure gradients. A consistent theory is developed for these flows by assuming a ‘linear-stress’ layer, and the solutions show the relation between flows of finite stress and of zero stress and provide a plausible explanation of the phenomenon of downstream instability observed by Clauser. Self-preserving flow in wedges is treated on similar lines.
The Sobolev-P method: a generalization of the Sobolev method for the treatment of the polarization state of radiation and the polarizing effect of resonance line scattering

La methode de Sobolev est generalisee pour l'etude de l'etat de polarisation du rayonnement et les effets polarisants de la diffusion des raies resonnantes. Une application de la methode pour le transfert radiatif, avec ou sans opacite de continuum, est realisee pour les modeles axisymetriques de systemes de supernova
Discovery of the Orbit of the X-Ray Pulsar OAO 1657-415

Timing observations of the 38 s accreting X-ray pulsar OAO 1657-415 made with the BATSE large-area detectors on the Compton Gamma Ray Observatory have revealed a binary orbit with an X-ray eclipse by the stellar companion. Arrival time analysis of 20-60 keV data yielded the following best-fit orbital elements: P_(orb) = 10^d.4436 ± 0^d.0038, a_x sin i = 106.0 ± 0.5 lt-sec, e = 0.104 ± 0.005, ω = 93° ± 5°, T_(π/2) = JD 2,448,516.49 ± 0.05 TDB. From the pulsar mass function f_x(M) = 11.7 ± 0.2 M_⊙ and the measured eclipse half-angle θ_e = 29.7 ± 1.3 deg, we infer that the stellar companion is a supergiant of spectral class B0-B6. If the companion can be identified and its orbital velocity measured, the neutron star mass can be constrained. Both intrinsic spin-up and spin-down of the pulsar were measured during our observation.
Continuous monitoring of tissue growth inside a perfusion bioreactor by optical coherence tomography

Tissue engineering aims to create in vitro functional tissues that could ultimately be used as autologous implants. Considering the large number of parameters that have to be tested to optimize the tissue growth and to achieve a better understanding of tissue formation, relevant biological in vitro models are needed which can be monitored and characterized all along the different stages of tissue engineering: cell seeding, cell growth, extra-cellular matrix (ECM) deposition, matrix turn-over and tissue organization. We developed porous chitosan scaffolds (&fgr;1.5mm) that enclose a 300&mgr;m microchannel to encourage fluid shear-stress stimulation and more specifically to support bundle formation for the specific case of tendon tissue engineering. These scaffolds were loaded in perfusion bioreactors and monitored during several days by optical coherence tomography (OCT). The fiber based time domain OCT employed a 1300nm superluminescent diode with a bandwith of 52 nm and a xyz resolution of 16*16*14 in free space. This set up allowed us to assess the volume fraction of cell seeded in the microchannels, and thus to optimize the seeding procedure. The cell growth and ECM deposition were successfully monitored at different time point as the channels were filled by newly formed material. Different scattering behaviors have been observed during cell growth and ECM production. The possibility to monitor continuously the scaffolds under perfusion will allow an easy discrimination of the parameters affecting the pre-tissue formation rate growth.
Star formation in protogalactic clouds

The physical processes determining the rate of star formation in protogalactic clouds and the resulting effects on the structure of the galaxies are examined with reference to analytical results and numerical simulations. For spheroidal systems, it is found that rapid star formation cannot be prevented once the density exceeds a typical value. The corresponding length scale is comparable to the length scales of spheroidal systems. The gas is converted into stars at a time scale of 2 Gyr or less, during which the total luminosity of the protogalaxy in ionizing photons is 10 exp 43-44 ergs/s, and the gas is enriched to solar abundance with a steep gradient. A simplistic analysis of the resulting stellar distribution finds that de Vaucouleurs profiles may naturally result. The Faber-Jackson relation is also found to follow naturally. The Fischer-Tully relation follows by an analysis similar to that used to derive the Faber-Jackson relation, provided that the peak rotational velocity is determined by the bulge mass.
N-stream approximations to radiative transfer

Abstract Schuster's two-stream approximation is first derived from Chandrasekhar's radiative transfer equation, and then generalized to an arbitrary number of streams. The resulting technique for solving the transfer equation that is similar to the discrete ordinate and spherical harmonic methods, is found to be especially useful for modeling atmospheres with complicated phase functions and moderate optical depths. To illustrate the method, a four-stream approximation is evaluated for a Henyey-Greenstein phase function with asymmetry factor g = 0.5.
Evaluation of an Approximate Method for Synthesizing Covariance Matrices for Use in Meta-Analytic SEM

Meta-analytic structural equation modeling (MA-SEM) is increasingly being used to assess model-fit for variables' interrelations synthesized across studies. MA-SEM researchers have analyzed synthesized correlation matrices using structural equation modeling (SEM) estimation that is designed for covariance matrices. This can produce incorrect model-fit chi-square statistics, standard error estimates (Cudeck, 1989), or both for parameters that are not scale free or that describe a scale-noninvariant model unless corrected SEM estimation is used to analyze the correlations. This study introduced univariate and multivariate approximate methods for synthesizing covariance matrices for use in MA-SEM. A simulation study assessed the approximate methods by estimating parameters in a scale-noninvariant model using synthesized covariances versus synthesized correlations with and without the appropriate corrections. Standard error bias was noted only for uncorrected analyses of pooled correlations. Chi-square model-fit statistics were overly conservative except when covariance matrices were analyzed. Benefits and limitations of this approximate method are presented and discussed.
Temperature dependence of the gain and of the lasing cross section of a ~1.06μ transition in gadolinium scandium gallium garnet crystals doped with chromium and neodymium

A study was made of a lasing transition at ~1. 06μ in a gadolinium scandium gallium garnet crystal doped with chromium and neodymium (GSGG:Cr:Nd) in a wide range of temperatures. The temperature dependences of the position and half-width of the luminescence line, gain, resonance losses, and transition cross sections were determined. The results obtained made it possible to analyze various situations encountered in laser systems with GSGG:Cr:Nd crystals and to determine the permissible heating of the active medium at which the required energy characteristics could be achieved in laser sources.
High-order harmonic generation in alkanes

We have investigated the process of high-order harmonic generation in light alkanes by using femtosecond laser pulses. We show the experimental results cannot be matched by a model that assumes a single active electron only in a hydrogenic $s$ orbital. Clear evidences are shown of the important role played by the $p$-like character originating from the covalent $\mathrm{C}\text{\ensuremath{-}}\mathrm{H}$ bond. By constructing a suitable mixture of $s$-type and $p$-type atomic wave functions, an excellent agreement between measurements in methane and simulations is found, thus confirming the validity of the developed method as a general tool for the analysis of high-order harmonic generation in complex molecules.
Variability of the equatorial oscillations induced by gravity wave filtering

Large variations are observed in the Semi‐Annual Oscillation (SAO) and Quasi‐Biennial Oscillation (QBO) near the equator that are not well understood. We had shown earlier that small scale gravity waves (GW) can generate these oscillations. Here we demonstrate that GW filtering can also produce the variability. Our model incorporates Hines' Doppler Spread Parameterization (DSP) for GW. In the present version, we employ a larger GW flux and a more realistic description of Newtonian cooling. This model produces a QBO with amplitudes close to 15 m/s at 25 km and periods around 33 months. At higher altitudes, the model produces a SAO with amplitudes varying between 5 and 30 m/s. We interpret these variations in terms of GW filtering by the QBO that produces beat periods between 4 and 8.5 years. To provide better understanding, we present also a case in which the QBO period is virtually locked at 18 months. The SAO amplitude then varies with a regular pattern having a period of 18 months, and the Annual Oscillation (AO) amplitude varies with a period of 36 months. For QBO's with periods of 18 (or 30) months, the phase relationship with the seasonal cycle of solar forcing would tend to synchronize and stabilize the oscillations.
Relativistic generalization of the Einstein-Milne relations

The Einstein-Milne relations for the continuum are generalized to a nondegenerate relativistic gas in thermodynamic equilibrium, using the relativistic ionization equation which has been recently established by us [J. Phys. A 16, 2347 (1983)] and which must replace the Saha equation at temperatures above ${10}^{8}$ K. The macroscopic continuum opacity and emissivity of this gas are also derived.
Theory of Hyperfine Structure

Considering the classical electric and magnetic interactions between atomic electrons and the nucleus, we arrive at a representation of the hyperfine interactions in terms of a multipole expansion of the field potentials. Treating these noncentral interactions in first order perturbation theory we can give the form of the general interval structure and analyze for the multipole interaction constants using Racah coefficients. Pertinent matrix elements for a single valence electron are calculated relativistically. Some second order terms of the dipole and quadrupole interactions are calculated as they affect the interpretation of the first order octupole interaction. In this work we also take into account quantitatively the effect of some electronic configuration interaction. Finally the values of nuclear magnetic octupole moments expected according to different models are calculated and compared with the experimental data thus far collected. Generally the measured octupole moments are in as good agreement with the values predicted by the single-particle shell model as are the corresponding dipole moments.
Soret and Dufour effects in three-dimensional flow of Maxwell fluid with chemical reaction and convective condition

Purpose – The purpose of this paper is to address the heat and mass transfer effects in three-dimensional flow of Maxwell fluid over a stretching surface with convective boundary conditions. Mass transfer is considered in the presence of first order chemical reaction. Conservation laws of energy and concentration are based upon the Soret and Dufour effects. Convergent series solutions to the resulting non-linear problems are developed. Effects of Biot and Deborah numbers on the Sherwood number are decreasing. Local Nusselt reduces with an increase in Eckert numbers. It is also interesting to note further that variations of Prandtl and Biot numbers on the Nusselt number are increasing while Sherwood number decreases with an increase in Prandtl number. Design/methodology/approach – The involved partial differential systems are reduced to the ordinary differential systems using appropriate transformations. Series solutions by homotopy analysis method are constructed and analyzed. Graphical results are presen.
Left K‐Completeness in Quasi‐Metric Spaces

Regular left K-sequentially complete quasi-metric spaces are characterized. We deduce that these spaces are complete Aronszajn and that every metrizable space admitting a left K-sequentially complete quasi-metric is completely metrizable. We also characterize quasi-metric spaces having a quasi-metric left K-sequential completion in terms of certain bases of countable order.
INTRODUCTION TO NESTED MARKOV MODELS

Graphical models provide a principled way to take advantage of independence constraints for probabilistic and causal modeling, while giving an intuitive graphical description of “qualitative features” useful for these tasks. A popular graphical model, known as a Bayesian network, represents joint distributions by means of a directed acyclic graph (DAG). DAGs provide a natural representation of conditional independence constraints, and also have a simple causal interpretation. When all variables are observed, the associated statistical models have many attractive properties. However, in many practical data analyses unobserved variables may be present. In general, the set of marginal distributions obtained from a DAG model with hidden variables is a much more complicated statistical model: the likelihood of the marginal is often intractable; the model may contain singularities. There are also an infinite number of such models to consider. It is possible to avoid these difficulties by modeling the observed marginal directly. One strategy is to define a model by means of conditional independence constraints induced on the observed marginal by the hidden variable DAG; we call this the ordinary Markov model. This model will be a supermodel that contains the set of marginal distributions obtained from the original DAG. Richardson and Spirtes (2002) and Evans and Richardson (2013a) gave parametrizations of this model in the Gaussian and discrete case, respectively. However, it has long been known that hidden variable DAG models also imply nonparametric constraints which generalize conditional independences; these are sometimes called “Verma Constraints”. In this paper we describe a natural extension of the ordinary Markov approach, whereby both conditional independences and these generalized constraints are used to define a nested Markov model. The binary nested Markov model may be parametrized via a simple extension of the binary parametrization of the ordinary Markov model of Evans and Richardson (2013a). We also give evidence for a characterization of nested Markov equivalence for models with four observed variables. A consequence of this characterization is that, in some instances, most structural features of hidden variable DAGs can be recovered exactly when a single generalized independence constraint holds under the distribution of the observed variables.
Towards efficient ab initio calculations of electron scattering by polyatomic molecules: I. Efficient numerical quadrature of the UGT term

The UGU term was used as a model of the UGT term, and its evaluation by numerical quadrature was examined systematically with a training set of eight molecules. Minimum numbers of points have been determined for radial Gauss–Legendre and angular Lebedev quadratures that preserve the accuracy needed for practical applications. These quadratures are recommended for efficient calculation of electron scattering by polyatomic molecules.
Allocation of interdependent resources for maximal throughput

A general queueing network model of computer and communication systems with interdependent resources is considered. The resources are modeled by a collection of servers that have to be allocated subject to certain constraints. Arrivals are Poisson, services are independent and identically distributed and service completions of different customers cannot be synchronized. A set of necessary conditions for the finiteness of long run average delays is obtained. An adaptive non-preemptive scheduling policy is presented and a set of sufficient conditions under which the policy achieves finite delays, is identified. The necessary and sufficient conditions differ only on the boundary region. The policy does not depend on the knowledge of the arrival rates and has polynomial time complexity for some applications
Gravity currents over fractured substrates in a porous medium

We consider the behaviour of a gravity current in a porous medium when the horizontal surface along which it spreads is punctuated either by narrow fractures or by permeable regions of limited extent. We derive steady-state solutions for the current, and show that these form part of a long-time asymptotic description which may also include a self-similar ‘leakage current’ propagating beyond the fractured region with a length proportional to t1/2. We discuss the conditions under which a current can be completely trapped by a permeable region or a series of fractures.
Leaves, flowers and garbage bags: Making waves

the world’s most durable mysteries. Some patterns—clouds, snowflakes— form in space. Others—the ebb and flow of tides, seasonal wet and dry spells—are patterns that form in time. Natural patterns are mysterious because they are complex, organized and interconnected, even though the laws of physics on which they rest—Newton’s classical laws of motion—are simple. The living world presents the ultimate examples of pattern formation. The patterns in biological systems are the most stunningly complex of any we encounter. Consider: In order to form a complex organism from an initial featureless collection of identical cells, a system must undergo myriad transitions that break its spatial symmetries and trigger the differentiation of cells at selected sites. How are these sites selected? How complex and controlled must a growth process be to direct that particular things happen in sequence and at the right sites? It is difficult to imagine how the impersonal interactions of atoms can lead to the growth of a plant or an animal from inanimate matter. Yet in fact this is what happens with the birth and development of every living thing. Some of the simplest features of biological shapes can be explained by basic physical laws. We will describe here an elegant example: the edges of flowers and leaves, where complex rippled shapes give the impressions of ruffles and frills. We suspected that very simple growth processes might provide the mechanism that shapes thin membranes and sheets into complex shapes in space, and indeed we have found that they do. By themselves, these processes do not break
Homologously collapsing stellar cores

We investigate the collapse of nonrotating gas spheres with a polytropic equation of state: n = 3, corresponding to y = 4/3. Such polytropes provide a reasonable approximation to collapsing stellar cores during the early phase before nuclear density is reached. We find a family of exact homologously collapsing configurations. Homologous collapse of the entire core is possible if the pressure at a given density is reduced by up to 3% from the value for a marginally stable static core. For a greater pressure reduction, an inner core can collapse homologously, the mass of which varies as the 3/2 power of the reduced pressure at the onset of collapse. Linear perturbations of these homologously collapsing solutions are separable in space and time. Low order radial and nonradial modes are calculated, and it is found that all modes are essentially stable.