Miracle-dz/UniFAR-FTUs huggingface dataset:
Compton Thick AGN

Abstract Compton thick active galactic nuclei (AGN), which are obscured by column density NH > 1.5 × 104 cm−2, can be difficult to identify. They are certainly cosmically significant, both in producing the observed cosmic X-ray background, and in providing a location where black hole growth is hidden from view. Here I review some recent results from surveys that provide indications of Compton thick AGN, considering X-ray, radio, and infrared selection techniques. I also offer a caution against using mid-infrared silicate features to measure line-of-sight obscuration to active galactic nuclei. Instead, these features better indicate the geometric distribution of dust that the central engine heats. I conclude that the outstanding problem of Compton thick AGN is not the cases where the obscuration is directly associated with the environment of the active nucleus itself, even in the most obscured examples. Instead, we still risk missing the completely buried AGN, which are obscured by large amounts of gas and dust over large solid angles. The solution to finding Compton thick AGN may be to begin the search based on infrared emission and star formation, and then select for nuclear activity.
A model for spatio‐temporal clustering using multinomial probit regression: application to avalanche counts

Although modeling complex environmental spatio‐temporal processes, separability between time and space effects is often assumed as a first approach, even though it may be unrealistic. Hence, the development of adapted non‐separable spatio‐temporal models is a challenging issue. In this work, we are interested in modeling avalanche counts over the whole French Alps, a large area that exhibits zones characterized by distinct climatic behaviors. We have at our disposal a data set of 405, 63‐year series of avalanche counts, one series for one township. We assume the series can be divided into several spatial clusters presenting specific temporal trends. On the latent layer of a hierarchical negative binomial‐lognormal structure, the clusters are characterized by independent temporal evolutions, modeled using smoothing splines. The clusters arise as the result of a multinomial probit regression, with spatial coordinates used as covariates. Inference is performed within the Bayesian hierarchical framework. The number of clusters is assessed using cross validation. The best score is obtained for a three‐cluster model, but other configurations also share some evidence. The first cluster is located in the east of the French Alps, whereas the others are located together in the west part of the French Alps. The three contrasted temporal trends corresponding to the three clusters result from regional climate change effects, interacting with a strong altitudinal control and data limitation. The proposed model could be used for analyzing various other climatic and environmental data sets. Copyright © 2012 John Wiley & Sons, Ltd.
Commissioning of the diamond light source storage ring vacuum system

The Diamond storage ring has been operating with a 3 GeV electron beam since September 2006 and 190 A.h of beam dose have been accumulated. The pressure in the storage ring is 4.2 10-10 mbar without beam, rising to 7.9 10-10 mbar with 125 mA of stored beam. Data on the storage ring vacuum performance and experience from commissioning and beam conditioning are presented.
Detecting misspecifications in autoregressive conditional duration models and non‐negative time‐series processes

We develop a general theory to test correct specification of multiplicative error models of non‐negative time‐series processes, which include the popular autoregressive conditional duration (ACD) models. Both linear and nonlinear conditional expectation models are covered, and standardized innovations can have time‐varying conditional dispersion and higher‐order conditional moments of unknown form. No specific estimation method is required, and the tests have a convenient null asymptotic N(0,1) distribution. To reduce the impact of parameter estimation uncertainty in finite samples, we adopt Wooldridge's (1990a) device to our context and justify its validity. Simulation studies show that in the context of testing ACD models, finite sample correction gives better sizes in finite samples and are robust to parameter estimation uncertainty. And, it is important to take into account time‐varying conditional dispersion and higher‐order conditional moments in standardized innovations; failure to do so can cause strong overrejection of a correctly specified ACD model. The proposed tests have reasonable power against a variety of popular linear and nonlinear ACD alternatives.
Multivariable identification of continuous-time fractional system

This paper presents two subspace-based methods, from the MOESP (MIMO output-error state space) family, for state-space identification of continuous-time fractional commensurate models from sampled input-output data. The methodology used in this paper involves a continuous-time fractional operator allowing to reformulate the problem so that the state-space matrices can be estimated with conventional discrete-time subspace techniques based on QR and singular value decompositions. The first method is a deterministic one whereas the second approach takes place in a stochastic context. The performance of both methods is demonstrated using Monte Carlo simulations at various signal-to-noise ratios. The deterministic method leads, as expected, to biased estimates. This bias is removed in the stochastic method by the use of an instrumental variable. As compared to rational systems, the commensurate differentiation order must be estimated besides the state-space matrices which is done using nonlinear programming. This is the first work developed for multi-input multi-output system identification using fractional models.
Boron and Polytetrafluoroethylene as a Fuel Composition for Hybrid Rocket Applications

A composition consisting of 80% polytetrafluoroethylene and 20% boron (by weight) was considered as a potential high-density solid fuel mixture for mixed hybrid rocket propulsive applications. Constant-pressure strand burner experiments for the given formulation indicated a low-pressure self-deflagration limit of approximately 2.2 MPa (319 psia), and a burning rate correlation rb[cm/s]=0.042(P[MPa])0.531 was determined. Pressurized counterflow burner experiments conducted using pure oxygen revealed formation of surface char, which prevented measurement of solid fuel regression rates below 2 MPa, indicating an additional resistance for heat and mass transfer. Static-fired rocket motor experiments, conducted to determine the pressure and flow dependencies of the system, exhibited characteristic exhaust velocity efficiencies ranging from approximately 86 to 96%. Whereas classical hybrids do not have a strong dependence of fuel regression rate on pressure, a pressure dependence was observed in this system bel.
Variation in Ferroelectric Characteristics of Lead Zirconate Titanate Ceramics Due to Minor Chemical Modifications

Lead zirconate titanate ceramics with certain 3‐ or 5‐valent additions (lanthanum, neodynium, tantalum, and niobium) are found to be characterized by low aging of electrical and mechanical properties, a well‐defined hysteresis loop, and by high electrical and mechanical losses. Experimental investigations are reported on plain lead zirconate titanate and on a low‐aging niobium modification.The experiments included an electron microscope study of the ceramics and a number of electrical measurements. As a result of the study, the changed properties of the substituted material have been explained as being due to domain wall motion under low electric field. The results of electrical measurements supporting this conclusion, and a hypothesis accounting for the effects in terms of lattice vacancies, are presented.The 3‐ or 5‐valent additives described in the foregoing also cause greatly increased volume resistivity in the ceramic. This has not been satisfactorily explained.
Lucas's theorem and some related results for extended pascal triangles

RICHARD BOLLINGER received his Ph.D. in 1961 from the University of Pittsburgh, with a thesis in Summability Theory under the direction of George Laush; he has since also worked in other areas of analysis, statistics, reliability theory, and, more recently, combinatorics. He has been at Penn State since 1962, most of that time at Penn State, Erie, The Behrend College, where he is currently Professor of Mathematics.
Exploring the Mechanisms of Ice Nucleation on Kaolinite: From Deposition Nucleation to Condensation Freezing

AbstractTo identify the temperature and humidity conditions at which different ice nucleation mechanisms are active, the authors conducted experiments on 200-, 400-, and 800-nm size-selected kaolinite particles, exposing them to temperatures between 218 and 258 K and relative humidities with respect to ice (RHi) between 100% and 180%, including the typical conditions for cirrus and mixed-phase-cloud formation. Measurements of the ice active particle fraction as a function of temperature and relative humidity with respect to ice are reported. The authors find enhanced activated fractions when water saturation is reached at mixed-phase-cloud temperatures between 235 and 241 K and a distinct increase in the activated fraction below 235 K at conditions below water saturation. To provide a functional description of the observed ice nucleation mechanisms, the experimental results are analyzed by two different particle-surface models within the framework of classical nucleation theory. Describing the ice nucleat.
Iterative solvers for hierarchal vector finite element analysis of microwave problems

The finite element analysis of microwave devices reduces to the solution of a large, sparse matrix equation. Several iterative solution methods were tested on the matrices arising when high-order, hierarchical edge elements are used. The best algorithm tested was the conjugate gradient method, with a preconditioner based on symmetric successive overrelaxation. The number of iterations needed was found to increase only slowly with element order for the first three orders, despite the corresponding large increase in the matrix dimension. In all cases there was a rapid deterioration in performance when the element size exceeded about a tenth of a wavelength.
A novel framework in complex network analysis: Considering both structure of relations and individual characteristics in closeness centrality computation

A B S T R A C T In this paper, we develop a novel framework for defining radial measures of centrality in complex networks. This framework is based on the combination of two approaches: social network analysis and traditional social science approach by considering both structure of relations and individual characteristics. It is always an important issue to detect communities in complex networks as efficiently as possible to understand both the structure and function of the networks and to interpret radial centrality measures. Therefore, we propose spectral clustering by determining the best number of communities as a prerequisite stage before finding radial measures. Based on the proposed framework, an algorithm to compute the closeness centrality in complex networks is developed. We test the proposed algorithm on Zachary's karate club network, which is considerably used as a benchmark for community detection in a network. The preliminary results indicate that the new method is efficient at detecting both good inter-cluster closeness centrality and the appropriate number of clusters.
Algorithm for random close packing of spheres with periodic boundary conditions

The isotropic algorithm is constructed for random close packing of equisized spheres with triply periodic boundary conditions. All previously published packing methods with periodic boundaries were kinetics-determined; i.e., they contained a densification rate as an arbitrary parameter. In contrast, the present algorithm is kinetic-independent and demonstrates an unambiguous convergence to the experimental results. To suppress crystallization, the main principles of our algorithm are (1) to form a contact network at an early stage and (2) retain contacts throughout the densification, as far as possible. The particles are allowed to swell by the numerical solution of the differential equations of densification. The RHS of these equations is calculated efficiently from a linear system by a combination of conjugate gradient iterations and exact sparse matrix technology. When an excessive contact occurs and one of the existing bonds should be broken to continue the densification, an efficient criterion based on multidimensional simplex geometry is used for searching the separating bond. The algorithm has a well-defined termination point resulting in a perfect contact network with the average coordination number six (for particle number N>1) and a system of normal reactions between the spheres maintaining the structure. These forces are the counterpart of the algorithm and can be used to calculate small elastic particle deformations in a granular medium. Extensive calculations are presented for 50 @? N 5 400 and demonstrate very good agreement with the experimental packing density (about 0.637 ) and structure.
A simplex-based approach to seek ambiguous scattering points in the scene for bistatic SAR

Ambiguous area of bistatic SAR will vary with the change of bistatic geometrical configuration and is difficult to be predetermined. Ambiguous scattering points in the scene can be found through observing the momentary image grid formed by iso-range contours and iso-Doppler contours, but it is an attended method which is invalid in many unattended occasions. In the paper the problem has been converted into an unconstrained nonlinear optimization, the idea of random search is combined with Nelder-Mead method and a simplex-based approach to seek ambiguous scattering points has been presented. Simulation results demonstrate the validity of simplex-based approach. (4 pages)
The microwave absorbing phenomena of ferrite microwave absorbers

The complex permeability dispersions and the microwave absorbing phenomena are investigated in ferrite microwave absorbers. The complex permeability of hexagonal (Y- and Z-type) and spinel (NiZn ferrite and NiZnCo ferrite) ferrite microwave absorbers were measured in 200 MHz-16 GHz range. The theoretical matching frequencies are determined by plotting the measured complex permeability loci on the impedance matching solution map. One or two impedance matching phenomena are observed in the ferrite absorbers according to their complex permeability loci on the impedance matching solution map. It was discovered that the first matching frequency (f/sub m1/) of the ferrite absorber strongly depends on its spin resonance frequency (f/sub r2/) and the second matching frequency (f/sub m2/) is independent of the resonance frequency. >
THE RADIO SOURCE AROUND ETA CARINAE

We present high spatial resolution radio observations of the peculiar southern star Eta Carinae, made with the Australian Telescope. The images, at 8 and 9 GHz with a resolution of 1.0 arcsec show a source of dimension 10 arcsec and total flux of 0.7 Jy dominated by a strong central peak. The radio emission is unpolarized and offers no support to models which invoke degenerate stars or more exotic objects within the core of Eta Car. In these data we find no evidence for more than one energy source in the core with arcsecond separations as some infrared observations have suggested. Several levels of structure are evident in the radio image, which shows symmetry on the larger scales. Conventional formulae for stellar wind radio sources give a mass loss rate of order 3 x 10(exp -4) Solar Mass/yr based on the radio flux in the central peak, which yields a wind momentum flux of order 20% of the momentum flux available from the star's radiation field. The radio emission at these frequencies is consistent with thermal emission from gas flowing away from a 'luminous blue variable' star (LBV) Eta Car is probably the brightest thermal stellar wind radio source in the sky.
Photoluminescence investigation of the carrier confining properties of multiquantum barriers

A comparative luminescence study of two Ga/sub 0.52/In/sub 0.48/P-(Al/sub 0.5/Ga/sub 0.5/)/sub 0.52/In/sub 0.48/P single-quantum-well (SQW) samples with bulk and multiquantum barrier (MQB) barriers is presented. When excess carriers are only created in the quantum wells (QW's) of the samples by resonant excitation using a dye laser, the luminescence efficiency of both samples as a function of temperature is found to be essentially identical. We find, therefore, no evidence for any enhancement in the confining potential of the MQB sample over the bulk barrier sample. From Arrhenius plots of the integrated luminescence intensity, it is found that carrier loss from the QW is dominated by a nonradiative loss mechanism with an activation energy considerably smaller than that expected from direct thermal loss of electrons and holes into the barriers. We suggest that the improved device characteristics reported for lasers containing MQB's is due to effects other than the quantum interference of electrons.
Flexibility in flapping foil suppresses meandering of induced jet in absence of free stream

Abstract Thrust-generating flapping foils are known to produce jets inclined to the free stream at high Strouhal numbers $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\mathit{St} = fA/U_{\infty }$ , where $f$ is the frequency and $A$ is the amplitude of flapping and $U_{\infty }$ is the free-stream velocity. Our experiments, in the limiting case of $\mathit{St} \rightarrow \infty $ (zero free-stream speed), show that a purely oscillatory pitching motion of a chordwise flexible foil produces a coherent jet composed of a reverse Bénard–Kármán vortex street along the centreline, albeit over a specific range of effective flap stiffnesses. We obtain flexibility by attaching a thin flap to the trailing edge of a rigid NACA0015 foil; length of flap is $0.79\, c$ where $c$ is rigid foil chord length. It is the time-varying deflections of the flexible flap that suppress the meandering found in the jets produced by a pitching rigid foil for zero free-stream condition. Recent experiments (Marais et al., J. Fluid Mech., vol. 710, 2012, p. 659) have also shown that the flexibility increases the $\mathit{St}$ at which non-deflected jets are obtained. Analysing the near-wake vortex dynamics from flow visualization and particle image velocimetry (PIV) measurements, we identify the mechanisms by which flexibility suppresses jet deflection and meandering. A convenient characterization of flap deformation, caused by fluid–flap interaction, is through a non-dimensional ‘effective stiffness’, $EI^{*} = 8 \, EI/(\rho \, V_{{{TE_{{max}}}}}^2 \, s_{{{f}}} \, c_{{{f}}}^3/2)$ , representing the inverse of the flap deflection due to the fluid-dynamic loading; here, $EI$ is the bending stiffness of flap, $\rho $ is fluid density, $V_{{{TE_{{max}}}}}$ is the maximum velocity of rigid foil trailing edge, $s_{{{f}}}$ is span and $c_{{{f}}}$ is chord length of the flexible flap. By varying the amplitude and frequency of pitching, we obtain a variation in $EI^{*}$ over nearly two orders of magnitude and show that only moderate $EI^{*}\ (0.1 \lesssim EI^{*} \lesssim 1)$ generates a sustained, coherent, orderly jet. Relatively ‘stiff’ flaps ( $EI^{*} \gtrsim 1$ ), including the extreme case of no flap, produce meandering jets, whereas highly ‘flexible’ flaps ( $EI^{*} \lesssim 0.1$ ) produce spread-out jets. Obtained from the measured mean velocity fields, we present values of thrust coefficients for the cases for which orderly jets are observed.
Partial recovery of potentials in generalized nonlinear Schrödinger equations on the line

The inverse Born approximation method is applied to inverse scattering problems for two one-dimensional nonlinear Schrodinger equations. We prove that all jumps and singularities of the unknown function are recovered from the Born function sequence. In particular, one can locate any bounded interval on the line. The result is based on the accurate determination of the first nonlinear term of the Born sequence.
Hybrid model of quench propagation in coated conductors for fault current limiters

We developed a hybrid model of the quench propagation in coated conductors in the current limitation condition. This model combines the finite element method, to study the thermal behaviour of the coated conductors, and analytical calculation of the heat dissipation. We demonstrate that the evaluation of the heat dissipation can be conducted on a larger mesh than the FEM thermal problem. The results obtained with this model are in very good agreement with experiments, without the need of using free parameters for adjustment. Parametric studies are then conducted to evaluate the influence of both the substrate thickness and the layer interface thermal properties on the transition propagation behaviour. 3D simulations of a thin superconducting line placed on a wider substrate are also presented. Significant transverse heat propagation is observed in spite of the low thermal conductivity of the substrate, though this has little to no influence on the transition propagation along the line. These results are discussed in the context of FCL design.
Mixing in ejecta of supernovae. I. General properties of two-dimensional Rayleigh-Taylor instabilities and mixing width in ejecta of supernovae

Nonlinear growth of two-dimensional Rayleigh-Taylor (R-T) instabilities are numerically studied to apply to the mixing in the supernova ejecta. First, much refined calculations of mixing in the realistic model of SN 1987A ar epresented with a better code and various mesh resolutions. The results show that the mixing width (or the extent of mixing) due to Rayleigh-Taylor instabilities is still too small to account for the observations even with relatively large initial perturbation. The mixing width is found to depend only slightly on the mesh resolution when the initial amplitude is larger than ∼5% of the expansion speed
Large Deformation Triangular Plate Elements for Multibody Problems

In this paper, triangular finite elements based on the absolute nodal coordinate formulation are introduced. Triangular elements employ the Kirchhoff plate theory and can, accordingly, be used in thin plate bending problems. These elements can exactly describe arbitrary rigid body motion while their mass matrices are constant. Previous plate developments in the absolute nodal coordinate formulation have focused on rectangular elements that are difficult to use when arbitrary meshes need to be described. The elements introduced in this study have overcome this problem and represent an important addition to the absolute nodal coordinate formulation. The two elements introduced are based on Specht’s and Morley’s shape functions. The numerical solutions of these elements are compared with results obtained using the previously proposed rectangular finite element and analytical results.Copyright © 2007 by ASME