Miracle-dz/UniFAR-FTUs huggingface dataset:
Structure and luminosity of strong shock waves in air

A set of numerical computations of the thermal structure and optical luminosity of strong shock waves in air is described. The model includes radiation transport coupled with hydrodynamics under assumed conditions of steady flow. With shock velocities above 10 km/sec a thermal precursor develops ahead of the shock front, and increases in prominence with increasing shock strength. For velocities above 50 km/sec the precursor is partially opaque to visible light and the computed brightness is smaller than that of a blackbody at the shock temperature. At higher velocities the brightness decreases with increasing shock strength. Steady solutions could not be found for velocities above 80 km/sec.
Shellings of Spheres and Polytopes.

Abstract : Bruggesser and Mani proved the boundary complex B(P) of a polytope P always admits a shelling. By constructing appropriate linear functionals on certain polytopes dual to P, shellings are here produced that satisfy strong conditions on the order of appearance of P's facets. Also included are some results on shellings of more general complexes. The results on shellings contained here play a role in a current attack on the d-step conjecture of linear programming. (Author)
The Effects of High-Performing, High-Turnover Teachers on Long-Run Student Achievement: Evidence From Teach For America

An increasing share of new teachers participate in alternative preparation programs. A fundamental question is what effect these programs have on long-run student achievement. To address this question, I study Teach For America (TFA) teachers working in New York City (NYC). I first estimate within-teacher returns to experience and find that TFA alumni teachers improve at double the rate of the average NYC teacher over their first 5 years in the classroom. I then model the joint relationship between turnover and performance over time. The results suggest that the net effect of TFA hiring on long-run student achievement is positive, despite the regular churn within the TFA workforce.
Global attractor for a class of Kirchhoff models

The paper studies the longtime behavior of solutions to the initial boundary value problem (IBVP) for a class of Kirchhoff models arising in elastoplastic flow utt−div{|∇u|m−1∇u}−Δut+Δ2u+h(ut)+g(u)=f(x). By combining the decomposition idea with the operate technique, it proves that under rather mild conditions, the dynamical system associated with above-mentioned IBVP possesses in different phase spaces a global attractor which is connected, respectively. For application, the fact shows that for the concerned elastoplastic flow the permanent regime (global attractor) can be observed when the excitation starts from any bounded set in phase space.
Representation and description of curved objects

Abstract : Three dimensional images, similar to depth maps, are obtained with a triangulation system using a television camera, and a deflectable laser beam diverged into a plane by a cylindrical lens. Complex objects are represented as structures joining parts called generalized cylinders. These primitives are formalized in a volume representation by an arbitrary cross section varying along a space curve axis. Several types of joint structures are discussed. Experimental results are shown for the description (building of internal computer models) of a handful of complex objects, beginning with laser range data from actual objects. Our programs have generated complete descriptions of rings, cones, and snake-like objects, all of which may be described by a single primitive. Complex objects, such as dolls, have been segmented into parts, most of which are well described by programs which implement generalized cylinder descriptions.
Airglow and Aurorae at Dome A, Antarctica

Despite the absence of artificial light pollution at Antarctic plateau sites such as Dome A, other factors such as airglow, aurorae, and extended periods of twilight have the potential to adversely affect optical observations. We present a statistical analysis of the airglow and aurorae at Dome A using spectroscopic data from Nigel, an optical/near-IR spectrometer operating in the 300–850 nm range. These data complement photometric images from Gattini, a wide-field (90°) CCD camera with B, V, and R filters, allowing the background sky brightness to be disentangled from the various airglow and auroral emission lines. The median auroral contribution to the B, V, and R photometric bands is found to be 22.9, 23.4, and 23.0 mag arcsec-2, respectively. Auroral emissions most frequently occur between 10–23 hr local time, when up to 50% of observations are above airglow-level intensities. While infrequent, the strongest emissions detected occurred in the hours just prior to magnetic midnight. We are also able to quantify the amount of annual dark time available as a function of wavelength, as well as in the standard BVR photometric bands. On average, twilight ends when the Sun reaches a zenith distance of 102.6°.
Statistical Analysis of ‘Probabilities of Causation’ Using Co‐variate Information

Abstract. This article deals with two problems concering the probabilities of causation defined by Pearl (Causality: models, reasoning, and inference, 2nd edn, 2009, Cambridge University Press, New York) namely, the probability that one observed event was a necessary (or sufficient, or both) cause of another; one is to derive new bounds, and the other is to provide the covariate selection criteria. Tian & Pearl (Ann. Math. Artif. Intell., 28, 2000, 287–313) showed how to bound the probabilities of causation using information from experimental and observational studies, with minimal assumptions about the data‐generating process, and identifiable conditions for these probabilities. In this article, we derive narrower bounds using covariate information that is available from those studies. In addition, we propose the conditional monotonicity assumption so as to further narrow the bounds. Moreover, we discuss the covariate selection problem from the viewpoint of the estimation accuracy, and show that selecting a covariate that has a direct effect on an outcome variable cannot always improve the estimation accuracy, which is contrary to the situation in linear regression models. These results provide more accurate information for public policy, legal determination of responsibility and personal decision making.
Laplacian Electrocardiograms Simulated Using Realistically Shaped Heart-Torso Model During Normal and Abnormal Ventricular Depolarization

This paper presents simulation studies of Laplacian electrocardiograms using a realistically shaped heart-torso model. Body surface Laplacian maps (BSLMs) during normal excitation and abnormal excitation with the Wolff-ParkinsonWhite syndrome are examined in comparison with the body surface potential maps (BSPMs). It shows that the BSLM can distinguish the left ventricular breakthrough with a special pattern, which is not distinguished with BSPM. It also shows that the BSLM has better specificity in discriminating multiple accessory pathways than the BSPM. These simulations theatrically suggest the advantages of Laplacian electrocardiogram as a non-invasive method in exploring the excitation processes of the heart.
A MERLIN neutral hydrogen absorption study of the luminous infrared merger NGC 6240

We present neutral hydrogen absorption observations of the luminous infrared merger NGC 6240 using MERLIN with a resolution of 0.2 arcsec. Broad absorption (a few hundred km s) has been found against two compact radio sources within the central kpc providing dynamical information about the neutral gas components in front of these sources. A narrow absorption component is also detected superimposed upon this broad absorption and additionally against some of the extended L-band continuum. From these results we deduce that the broad component is a result of absorption by a highly disturbed disc-like structure of neutral gas aligned along the position angle of the two compact radio sources, similar to the model previously proposed by Tacconi et al. at the end of the last century based on spectral CO emission data. The narrow component is likely to arise from absorption by less disturbed neutral gas at much larger scales within the system. Continuum observations presented here at 1.4 and 5 GHz support the view that NGC 6240 contains a double nucleus resulting from a galactic merger event and show these as two compact radio sources separated by 1.52 arcsec. We have also applied luminosity and morphological considerations to the continuum results to determine the most feasible source of radio emission for this luminous merger galaxy. We conclude that the most likely source of the radio flux found in NGC 6240 is a combination of starburst emission from radio luminous supernova remnants, similar to those found in Arp 220, and emission from a weak AGN probably triggered by a merger event.
Self‐similar evolutionary solutions for an accreting magneto‐fluid around a compact object with finite electrical conductivity

In this paper, we investigate the time evolution of an accreting magneto-fluid with finite conductivity. For the case of a thin disk, the fluid equations along with Maxwell's equations are derived in a simplified, one-dimensional model that neglects the latitudinal dependence of the flow. The finite electrical conductivity of the plasma is taken into account by Ohm's law; however, the shear viscous stress is neglected, as well as the self-gravity of the disk. In order to solve the integrated equations that govern the dynamical behaviour of the magneto-fluid, we have used a self-similar solution. We introduce two dimensionless variables, S0 and eϱ, which represent the size of the electrical conductivity and the density behaviour with time, respectively. The effect of each of these on the structure of the disk is studied. While the pressure is obtained simply by solving an ordinary differential equation, the density, the magnetic field, the radial velocity, and the rotational velocity are presented analytically. The solutions show that the S0 and eϱ parameters affect the radial thickness of the disk. Also, radial velocity and gas pressure are more sensitive to the electrical conductivity in the inner regions of disk. Moreover, the parameter eϱ has a more significant effect on the physical quantities for small radii. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
A new method for obtaining stellar velocity distributions from absorption-line spectra: unresolved Gaussian decomposition

We have developed a new algorithm for extracting the line-of-sight velocity distributions (LOSVDs) of galaxies from the broadening of absorption lines in their spectra relative to those of a stellartemplate. This method models the LOSVD as the sum of a set of Gaussian distributions uniformly spaced in velocity. By choosing the dispersion, Δv, of these Gaussians so that the separate components are unresolved according to the Rayleigh criterion, such a sum can model any LOSVD that is smooth on scales smaller than Δv. The velocity scale on which the LOSVD is forced to be smooth is thus set explicitly by the user. The algorithm then involves solving for the amplitudes of the individual components to produce the LOSVD that, when convolved with the stellar template, best reproduces the observed galaxy spectrum in a least-squares sense
Self-similar secondary infall and accretion in an Einstein-de Sitter universe

Similarity solutions have been found for secondary infall and accretion onto an initially overdense perturbation in an Einstein--de Sitter (.cap omega. = 1) universe. After the initial collapse of a positive density perturbation, bound shells continue to turn around and fall in, with the radius of the shell currently turning around increasing as t/sup 8/9/ and the mass within this radius increasing as t/sup 2/3/. The secondary infall approaches a self-similar form, with the exact behavior depending on the kind of gas and on central boundary conditions. If there is a central black hole, it grows by accretion, with the density having the power-law form rhoproportionalr/sup 01.5/ near the center. If there is no central black hole, a rhoproportionalr/sup 02.25/ density profile results, with infalling matter added to successively larger radii.
Orthogonal Lie algebras with cone potential

We say that a Lie algebra g is orthogonal if it admits a non-degenerate invariant symmetric bilinear form. In this paper we give a complete decription of all orthogonal Lie algebras with cone potential, a property defined in terms of the root decomposition with respect to a compactly embedded Cartan subalgebra. The class of these Lie algebras arises naturally in the study of convexity properties of Hamiltonian torus actions which are related to decompositions of groups similar to Iwasawa decompositions G = KAN of real semisimple Lie groups. In [HiNe94] we have generalized Kostant’s nonlinear convexity theorem for the Iwasawa decomposition for a complex Lie group to the class of complex groups whose Lie algebras have a real form which is an orthogonal Lie algebra with cone potential. We even obtained a generalization to the class of real semisimple Lie algebras having a solvable minimal parabolic subalgebra. This work generalized results of Lu and Ratiu ([LR91]) and aims at a unified symplectic framework for the convexity theorem in [Ne94] and the linear convexity theorems for coadjoint orbits of convexity type in [HNP93]. The motivation for this paper is to clarify the scope of the convexity theorems proved in [HiNe94]. Our description gives a rather clear picture of the situation. Every orthognal Lie algebra with cone potential is the ideal direct sum of a solvable Lie algebra and a semisimple Lie algebra of the same type. A semisimple Lie algebras has cone potential if and only if has a compactly embedded Cartan subalgebra. The orthogonal solvable Lie algebras with cone potential also decompose into certain indecomposable pieces which can be described by a root decomposition.
Quasi-stationary laws for Markov processes: examples of an always proximate absorbing state

Under consideration is a continuous-time Markov process with non-negative integer state space and a single absorbing state 0. Let T be the hitting time of zero and suppose P i (T < ∞) ≡ 1 and (*) lim i→∞ P i (T > t) = 1 for all t > 0. Most known cases satisfy (*). The Markov process has a quasi-stationary distribution iff E i (e ∊T ) < ∞ for some ∊ > 0. The published proof of this fact makes crucial use of (*). By means of examples it is shown that (*) can be violated in quite drastic ways without destroying the existence of a quasi-stationary distribution.
ASYMPTOTIC BEHAVIOR OF A VISCOUS FLUID WITH SLIP BOUNDARY CONDITIONS ON A SLIGHTLY ROUGH WALL

For an oscillating boundary of period and amplitude e, it is known that the asymptotic behavior when e tends to zero of a three-dimensional viscous fluid satisfying slip boundary conditions is the same as if we assume no-slip (adherence) boundary conditions. Here we consider the case where the period is still e but the amplitude is δe with δe/e converging to zero. We show that if tends to infinity, the equivalence between the slip and no-slip conditions still holds. If the limit of belongs to (0, +∞) (critical size), then we still have the slip boundary conditions in the limit but with a bigger friction coefficient. In the case where tends to zero the boundary behaves as a plane boundary. Besides the limit equation, we also obtain an approximation (corrector result) of the pressure and the velocity in the strong topology of L2 and H1 respectively.
Finite element approximations of singular parabolic problems

An efficient implementation of finite element methods for free boundary parabolic problems in general two dimensional space domains is presented. The Stefan problem, the Hele-Shaw problem and the porous medium equation are included. Backward differences or linearization techniques are used for the time discretization of the problem. The performances of these schemes are discussed with several numerical tests.
The Sensitivity of Gas-Phase Chemical Models of Interstellar Clouds to C and O Elemental Abundances and to a New Formation Mechanism for Ammonia

The effects of variations in the gas-phase carbon-to-oxygen elemental abundance ratio (0.42 ≤ C/O ≤ 1.2) and the absolute gas-phase carbon and oxygen elemental abundances on calculated molecular concentrations have been studied for three gas-phase chemical models of dense interstellar clouds. Both the C and O elemental abundances were varied from their "low metal" values, in which C/O = 0.42. The results were compared with observations of the dark interstellar clouds TMC-1 and L134N, the latter being chosen because TMC-1, with its singularly rich component of large hydrocarbons and cyanopolyynes, may not represent dense cores universally. In general, variations in the gas-phase C and O elemental abundances have a large and time-dependent effect on calculated molecular concentrations for all three models. For the "new standard" model, which does not contain many rapid neutral-neutral reactions, excellent "early-time" agreement with TMC-1 occurs for a variety of C/O ratios obtained by depleting the low metal O abundance, but the time of best agreement tends to increase with increasing C/O ratio. At these early times, ≈ 80% of the calculated abundances are within an order of magnitude of the observed values. Agreement at this level also occurs at steady state if the C and O abundances are first depleted by a factor of 5 and then O is additionally depleted so that C/O ≥ 0.80. In general, a factor of 5 depletion of both C and O increases the production efficiency of large molecules. When the new standard model is applied to L134N, the early-time agreement is not as good as for TMC-1 unless both C and O are first depleted by factors of 5 from their low metal values and the C/O ratio is then maintained at a value less than 0.80. Under these conditions, the steady state results are only slightly worse. The other two models, containing fast neutral-neutral reactions, have their best agreement with TMC-1 when C/O ≥ 1, although the level of agreement is typically worse than with the new standard model, and factor of 5 depletions have little effect. For L134N, on the other hand, the early-time agreement with these latter two models for a wide range of C/O values is almost as good as with the new standard model if factor of 5 depletions in C and O are utilized and is actually superior for most cases when C/O ≥ 1. In general, the negative conclusions concerning models with rapid neutral-neutral reactions may therefore be overly harsh. When the newly studied rapid reaction H+3+N→NH+2 + H is included in our model calculations, the abundances of some N-containing species are in better agreement with observed values, but this effect decreases as C/O is increased.
Weak and strong sources of gravity: An SO(1,3) -gauge theory of gravity

The structural and dynamical elements of the Lorentz-Yang-Mills gauge theory of gravity are explained and analyzed. This theory is a generalized metric theory of gravity which no longer satisfies the principle of equivalence in any situation, but fits the very general framework of the Yang-Mills gauge theories used to describe the nongravitational interactions. It adds essentially gravitational self-interaction to general relativity in an amount which is not measurable in the solar system; the geometry contains stress-energy by itslef; this breaks the validity of the principle of equivalence for strong gravitational fields. Static and spherically symmetric space-time dispose, in addition to the mass M, of a second parameter . gamma. , which is a measure for the stress-energy content of the space-time geometry. We shown that for the weak limit . gamma. = 1 - epsilon with epsilon approx. = M/R; the Schwarzschild black hole (.gamma. = 1) is therefore no longer a candidate for the final state of collapsing matter.
A parametric Bayesian combination of local and regional information in flood frequency analysis

Because of their impact on hydraulic structure design as well as on floodplain management, flood quantiles must be estimated with the highest precision given available information. If the site of interest has been monitored for a sufficiently long period (more than 30–40 years), at‐site frequency analysis can be used to estimate flood quantiles with a fair precision. Otherwise, regional estimation may be used to mitigate the lack of data, but local information is then ignored. A commonly used approach to combine at‐site and regional information is the linear empirical Bayes estimation: Under the assumption that both local and regional flood quantile estimators have a normal distribution, the empirical Bayesian estimator of the true quantile is the weighted average of both estimations. The weighting factor for each estimator is conversely proportional to its variance. We propose in this paper an alternative Bayesian method for combining local and regional information which provides the full probability density of quantiles and parameters. The application of the method is made with the generalized extreme values (GEV) distribution, but it can be extended to other types of extreme value distributions. In this method the prior distributions are obtained using a regional log linear regression model, and then local observations are used within a Markov chain Monte Carlo algorithm to infer the posterior distributions of parameters and quantiles. Unlike the empirical Bayesian approach the proposed method works even with a single local observation. It also relaxes the hypothesis of normality of the local quantiles probability distribution. The performance of the proposed methodology is compared to that of local, regional, and empirical Bayes estimators on three generated regional data sets with different statistical characteristics. The results show that (1) when the regional log linear model is unbiased, the proposed method gives better estimations of the GEV quantiles and parameters than the local, regional, and empirical Bayes estimators; (2) even when the regional log linear model displays a severe relative bias when estimating the quantiles, the proposed method still gives the best estimation of the GEV shape parameter and outperforms the other approaches on higher quantiles provided the relative bias is the same for all quantiles; and (3) the gain in performance with the new approach is considerable for sites with very short records.
A comparative study of ultrasound and laser light diffraction techniques for particle size determination in dairy beverages

The particle size distribution (PSD) of milkfat droplets of raw and homogenized milk was determined by a diagnostic ultrasound technique that was initially calibrated with colloidal silica. The quality of the fit between ultrasound theory and experiment is discussed and provides a basis for comparison with the reference laser light scattering technique. The predicted ultrasonic attenuation was determined from the ECAH (Epstein P S and Carhart R R 1953 J. Acoust. Soc. Am. 25 553–65, Allegra J R and Hawley S A 1972 J. Acoust. Soc. Am. 51 1545–64) model using thermophysical data for milkfat and milk serum. New thermophysical properties of milkfat were established. The experimental data were obtained with the Ultrasizer spectrometer. Both techniques were affected by the milk proteins and could provide only qualitative milkfat PSD for the raw and the homogenized milk samples. Therefore, they showed their limitations to characterize multiple emulsions. However, preliminary results are shown for the ultrasound technique that account for the impact of the protein on the measured data and hence obtain quantitative results for the milkfat size distributions.