Miracle-dz/UniFAR-FTUs huggingface dataset:
Flow due to an oscillating sphere and an expression for unsteady drag on the sphere at finite Reynolds number

Unsteady flow due to an oscillating sphere with a velocity U0cosωt’, in which U0 and ω are the amplitude and frequency of the oscillation and t’ is time, is investigated at finite Reynolds number. The methods used are: (i) Fourier mode expansion in the frequency domain; (ii) a time-dependent finite difference technique in the time domain; and (iii) a matched asymptotic expansion for high-frequency oscillation. The flow fields of the steady streaming component, the second and third harmonic components are obtained with the fundamental component. The dependence of the unsteady drag on ω is examined at small and finite Reynolds numbers. For large Stokes number, ε = (ωa2/2v)½ [Gt ] 1, in which a is the radius of the sphere and v is the kinematic viscosity, the numerical result for the unsteady drag agrees well with the high-frequency asymptotic solution; and the Stokes (1851) solution is valid for finite Re at ε [Gt ] 1. For small Strouhal number, St = ωa/U0 [Lt ] 1, the imaginary component of the unsteady drag (Scaled by 6πU0pfva, in which Pf is the fluid density) behaves as Dml ∼ (h0Stlog St–h1St), m = 1,3,5… This is in direct contrast to an earlier result obtained for an unsteady flow over a stationary sphere with a small-amplitude oscillation in the free-stream velocity (hereinafter referred to as the SA case) in which D1∼ –h1 St (Mei, Lawrence & Adrian 1991). Computations for flow over a sphere with a free-stream velocity U0(1–α1+α1cosωt’) at Re = U02a/v = 0.2 and St [Lt ] 1 show that h0 for the first mode varies from 0 (at α1 = 0) to around 0.5 (at α1 = 1) and that the SA case is a degenerated case in which the logarithmic dependence of the drag in St is suppressed by the strong mean uniform flow. The numerical results for the unsteady drag are used to examine an approximate particle dynamic equation proposed for spherical particles with finite Reynolds number. The equation includes a quasi-steady drag, an added-mass force, and a modified history force. The approximate expression for the history force in the time domain compares very well with the numerical results of the SA case for all frequencies; it compares favourably for the PO case for moderate and high frequencies; it underestimates slightly the history force for the PO case at low frequency. For a solid sphere settling in a stagnant liquid with zero initial velocity, the velocity history is computed using the proposed particle dynamic equation. The results compare very well with experimental data of Moorman (1955) over a large range of Reynolds numbers. The present particle dynamic equation at finite Re performs consistently better than that proposed by Odar & Hamilton (1964) both qualitatively and quantitatively for three different types of spatially uniform unsteady flows.
Greedy Algorithms andM-Term Approximation with Regard to Redundant Dictionaries

We study the efficiency of greedy type algorithms with regard to redundant dictionaries in Hilbert space and we prove a general result which gives a sufficient condition on a dictionary to guarantee that the pure greedy algorithm is near best in the sense of power decay of error of approximation. We discuss also some important examples. It is already known (see DeVore and Temlyakov,Adv. Comput. Math.5(1996), 173? 187) that the Pure Greedy Algorithm for some dictionaries has a saturation property. We construct an example which shows that a natural generalization of the Pure Greedy Algorithm also has a saturation property. Next we discuss some new phenomena which occur in approximation by a greedy type algorithm with regards to a highly redundant dictionary.
Preliminary study of radiation damage in liquid scintillators

An initial examination of radiation-damage phenomenology in selected liquid scintillators was made. Standard liquid scintillators exhibited substantial radiation damage after dosage levels of several megarads. Unlike the case with plastic scintillators, no significant changes in transmission were detected, implying that no strong absorption of the secondary fluor should occur in long samples. The observed substantial drop in scintillation pulse height after exposures of several megarad from a /sup 60/Co gamma source is attributed to radiation-induced absorption of the primary fluor's emission by the damaged solvent. Some new formulations have shown significantly greater radiation resistance. >
Multiple hypothesis track confirmation for infrared surveillance systems

An overall methodology is described for the application of a multiple hypothesis tracking (MHT) algorithm to the infrared (IR) surveillance system problem of establishing tracks on dim targets in a heavy clutter or false alarm background. The authors discuss the manner in which the detection and tracking systems are jointly designed to optimize performance. They present approximate methods that can conveniently be used for preliminary system design and performance prediction. They discuss the use of a detailed Monte Carlo simulation for final system evaluation and present results illustrating the proposed methods and comparing predicted and simulation performance. >
On the band structure lineup of ZnO heterostructures

The interface-induced gap states (IFIGS) are the fundamental mechanism which determines the band structure lineup at semiconductor interfaces. The valence-band offsets of semiconductor heterostructures are given by the difference of the respective IFIGS branch-point energies and electric-dipole terms which may be omitted for elemental group-IV semiconductors, SiC, as well as the III–V, II–VI, and I–III–VI2 compounds and alloys. The branch-point energy of ZnO is determined as 3.04±0.21eV from an analysis of experimental valence-band offsets reported for various ZnO heterostructures.
A multisignal automatic calibration methodology for hydrochemical models: A case study of the Birkenes Model

Most hydrochemical models employ immeasurable or “artificial” parameters that need to be estimated from calibration data. A methodology is presented here for the automatic calibration of artificial parameters, which improves parameter identifiability through increasing the information available for determining the parameter values. Instead of calibrating the model using only one signal (e.g., the hydrograph), multiple signals (e.g., chemical signals as well as the hydrograph) are considered simultaneously. Either a simple least squares or a weighted least squares objective function may be used. The methodology is applied to the hydrologic module of the Birkenes hydrochemical model using artificial data. From a wide range of starting points, a gradient search optimization technique is able to consistently locate the correct parameter values uniformly better when using two signals (the hydrograph and a conservative tracer) than when only one signal (the hydrograph) is used.
Optimal fault signal estimation

We consider here both fault identification and fault signal estimation. Regarding fault identification, we seek either exact or almost fault identification. On the other hand, regarding fault signal estimation, we seek either ℋ︁2 optimal, ℋ︁2 suboptimal or ℋ︁∞ suboptimal estimation. By appropriate combination of these two aspects, we formulate five different fault identification and fault signal estimation problems. We analyse and synthesize appropriate residual generators for fault identification and estimators which generate fault signal estimates for all these problems. Solvability conditions for all these problems are given. Also, for each of these problems, the architecture of integrating the residual generator that isolates the fault and estimators that estimate the fault signals is developed. Copyright © 2002 John Wiley & Sons, Ltd.
Stabilized wave segments in an excitable medium with a phase wave at the wave back

The propagation velocity and the shape of a stationary propagating wave segment are determined analytically for excitable media supporting excitation waves with trigger fronts and phase backs. The general relationships between the mediumʼs excitability and the wave segment parameters are obtained in the framework of the free boundary approach under quite usual assumptions. Two universal limits restricting the region of existence of stabilized wave segments are found. The comparison of the analytical results with numerical simulations of the well-known Kessler–Levine model demonstrates their good quantitative agreement. The findings should be applicable to a wide class of systems, such as the propagation of electrical waves in the cardiac muscle or wave propagation in autocatalytic chemical reactions, due to the generality of the free-boundary approach used.
Nonlinear dynamics of forced transitional jets: periodic and chaotic attractors

Conclusive experimental evidence is presented for the existence of a low-dimensional temporal dynamical system in an open flow, namely the near field of an axisymmetric, subsonic free jet. An initially laminar jet (4 cm air jet in the Reynolds number range 1.1 × 104 [Lt ] ReD × 9.1 × 104) with a top-hat profile was studied using single-frequency, longitudinal, bulk excitation. Two non-dimensional control parameters – forcing frequency StD (≡fexD/Ue, where fez is the excitation frequency, D is the jet exit diameter and Ue is the exit velocity) and forcing amplitude af (≡ u’f/Ue, where u’f is the jet exit r.m.s. longitudinal velocity fluctuation at the excitation frequency) – were varied over the ranges 10-4 < af < 0.3 and 0.3 < StD < 3.0 in order to construct a phase diagram. Periodic and chaotic states were found over large domains of the parameter space. The periodic attractors correspond to stable pairing (SP) and stable double pairing (SDP) of rolled-up vortices. One chaotic attractor, near SP in the parameter space, results from nearly periodic modulations of pairing (NPMP) of vortices. At large scales (i.e. approximately the size of the attractor) in phase space, NPMP exhibits approximately quasi-periodic behaviour, including modulation sidebands around ½fex in u-spectra, large closed loops in its Poincaré sections, correlation dimension v ∼ 2 and largest Lyapunov exponent λ1 ∼ 0. But investigations at smaller scales (i.e. distances greater than, but of the order of, trajectory separation) in phase space reveal chaos, as shown by v > 2 and λ1 > 0. The other chaotic attractor, near SDP, results from nearly periodic modulations of the first vortex pairing but chaotic modulations of the second pairing and has a broadband spectrum, a dimension 2.5 [Lt ] v [Lt ] 3 and the largest Lyapunov exponent 0.2 [Lt ] λ1 [Lt ] 0.7 bits per orbit (depending on measurement locations in physical and parameter spaces). A definition that distinguishes between physically and dynamically open flows is proposed and justified by our experimental results. The most important conclusion of this study is that a physically open flow, even one that is apparently dynamically open due to convective instability, can exhibit dynamically closed behaviour as a result of feedback. A conceptual model for transitional jets is proposed based on twodimensional instabilities, subharmonic resonance and feedback from downstream vortical structures to the nozzle lip. Feedback was quantified and shown to affect the exit fundamental–subharmonic phase difference ϕ – a crucial variable in subharmonic resonance and, hence, vortex pairing. The effect of feedback, the sensitivity of pairings to ϕ, the phase diagram, and the documented periodic and chaotic attractors demonstrate the validity of the proposed conceptual model.
On the physics of dusty atmospheres

Measurements of particle size and concentration of atmospheric dust have been made at Alexandria in various degrees of turbidity. Except for ‘dust haze,’ reasonable agreement is obtained between the measurements and Koschmieder's equation for visibility in terms of optical attenuation. In ‘duststorms’ the required attenuation implies a scatter coefficient per particle 8/3 times the cross-sectional area of the particles, while in occasions of ‘dust’ the scatter coefficient implied per particle is 4 times the cross-sectional area of the particles. The results are as follows: tbl1 Table tbl1. Dusty atmosphere Visibility (m) Average concentration (cm−3) Average particle diameter (μ) 90% of particles have diameter ≤ (μ) Scatter coefficient per particle/cross-sectional area of particles Dust haze 5,000–6,000 200 0.5 1.3 Dust 2,000–2,500 330 1.3 2.0 4 Duststorm 750–1,000 550 2.0 3.5 8/3
Which functions preserve Cauchy laws

A real random variable X has a Cauchy law C(a, b) if its density is bv~l[(x — af + b2]~l, with b > 0 and a real. Let / be a measurable function such that f(X) also has a Cauchy law for any a and b. We prove that there exist o real, k > 0, e = ± 1 and a singular positive bounded measure /i on R such that for almost all x of R
Meteor showers of cometary origin in the Solar System: Revised predictions

For meteor shower forecasting on the other planets of the Solar System, we have identified a list of periodic comets having close enough encounters with planetary orbits to produce regular showers. We revisit a previous study, done with an analytical approximation of the problem that proves to be unsuitable for the present purpose. By applying an accurate numerical method, we found significant differences in the results and identified more cometary candidates from the same initial sample. We give approximate dates for the potential meteor showers, highlighting the ones expected to occur during future planetary missions.
Finite element method for moving boundary problems in river flow

This paper presents the two-step explicit finite element method, which has been successfully applied to solve the shallow water equation of river flow. The linear interpolation functions for both discharge and water elevation have been used based on the three node triangular finite element. In the analysis of this paper, the treatment of the boundary configuration, which moves according to whether the water elevation increases or decreases, is considered. Distinctive features of the analysis are summarised.
Jones transfer matrix for polarization mode dispersion fibers

With the advent of long distance high bit rate optical systems, polarization mode dispersion (PMD) has become an important source of limitation for the system performance. In a first order approximation, PMD, that is described by a differential group delay (DGD) between two orthogonal states of polarization (PSPs), causes an undesired output pulse broadening; the frequency dependence of DGD and PSPs produces other distorting effects, considered as higher order PMD effects. A useful theoretical means of predicting the overall distortion of the transmitted signal is the evaluation of the Jones transfer matrix of the fiber but, unfortunately, the statistics of its coefficients are not available up to now. On the other hand, the statistical behavior of the three-dimensional dispersion vector, that characterizes the PMD of the fiber in the Stokes space and can be measured, is known up to a second order PMD approximation. Consequently, finding the analytical relationship between the PMD vector and the coefficients of the Jones matrix is mandatory. In the work, the tight methodology of calculating the Jones matrix, starting from the knowledge of the PMD vector, is shown. This new method is used to determine the output temporal pulse expression in a second order PMD approximation and it is applied to evaluate the performance of a system affected by PMD. The results obtained with the present model are compared to the performance evaluated by numerical simulations, where all order PMD effects are taken into account; our model gives a performance curve that is more accurate in the approximation of all order PMD effects.
Time asymptotic behaviour for linear transport equations with abstract boundary conditions in slab geometry

Abstract This paper is concerned with the large-time asymptotic behaviour of the solution to transport Cauchy problems in slab geometry with general boundary operators H relating the incoming and outgoing fluxes. It is composed of two parts. First, we consider the transport Cauchy problems with a general class of dissipative or conservative boundary conditions (∥H∥ ≤ 1). In the second part, we treat the case of an arbitrary compact boundary operator H with no restriction on its norm. Our approach relies on the inverse Laplace transform and applies to dissipative as well as multiplying boundary conditions.
H emission in pre-main sequence stars. I. An atlas of line profiles

We present an atlas of very high resolution ( R ~ 50000) H α line profiles of 63 pre-main sequence stars, divided among 43 T Tauri stars, 18 Herbig Ae/Be stars, and 2 FU Orionis objects. H α emission is the most common and prominent spectroscopic feature of pre-main sequence stars, and although it is optically very thick it is still the most frequently modelled emission line in young stars. In T Tauri stars the principal models involve magnetically driven winds, and more recently the role of infalling magnetospheric material has been explored. For Herbig Ae/Be stars a variety of models have been proposed, current emphasis is directed towards obscuration by clumpy circumstellar disk structures. In order to provide constraints on such models, we have made a statistical analysis of the 63 high resolution profiles. We here ignore the considerable variability of the H α emission, which is discussed in detail in a second paper. Most of our observed lines show complex profiles due to an interplay between emission and absorption features, and we suggest a two-dimensional classification scheme to describe these line profiles, based on the relative height of a secondary peak to the primary peak, as well as whether the absorption is blue- or red-shifted. Among T Tauri stars, 25% have symmetric profiles, 49% have blueshifted absorption dips, and 5% have P Cygni profiles; the remaining 21% show a variety of redshifted absorptions. For Herbig Ae/Be stars symmetric lines are quite rare (11%), indeed almost all of these stars have deep and prominent central absorptions. We have measured the extent of the line wings for all of our stars at the I max /40 level, and find that almost all have very extended wings, with typical extents of ± 350 km/s, but in high spectra the wings can be traced to lower intensities, and velocities as high as ± 900 km/s have been observed. Pronounced asymmetries of these extended wings are found for many stars, suggesting the possibility that the highest velocity material could be non-uniformly distributed. The equivalent widths of the H α emission in our sample of stars span two orders of magnitude, with a distribution that increases with decreasing equivalent width.
Dual Grid Lattice Boltzmann method for multiphase flows

We present a new methodology for implementing multiphase flow solvers using the Lattice Boltzmann method. Two grids of different size are used to discretize the momentum and the order parameter so that derivatives of the latter (responsible for the forcing terms at the interfaces) are calculated with high accuracy while maintaining a moderate computational cost. We apply the technique to two recently proposed formulations of the multiphase Lattice Boltzmann method, and show that this technique produces significant improvements over a homogeneous mesh refinement in both cases. Copyright © 2010 John Wiley & Sons, Ltd.
Bonus–Malus systems with Weibull distributed claim severities

Abstract One of the pricing strategies for Bonus–Malus (BM) systems relies on the decomposition of the claims’ randomness into one part accounting for claims’ frequency and the other part for claims’ severity. By mixing an exponential with a Lévy distribution, we focus on modelling the claim severity component as a Weibull distribution. For a Negative Binomial number of claims, we employ the Bayesian approach to derive the BM premiums for Weibull severities. We then conclude by comparing our explicit formulas and numerical results with those for Pareto severities that were introduced by Frangos & Vrontos.
Quantum gravity and time reversibility

The meaning of time-reversal and CPT invariances of a theory is discussed both in the context of theories defined on flat space-time as well as in general relativity. It is argued that quantum gravity cannot be time-reversal or CPT invariant; that an ''arrow of time'' must be fundamentally built into the theory. However, a weaker form of CPT invariance could still hold, in which case the fundamental ''arrow of time'' would not show up in the measurements of observers who perform scattering experiments. Consequences of this weaker hypothesis are explored.
Fast Algorithms for Nearest Neighbour Search

The nearest neighbour problem is of practical significance in a number of fields. Often we are interested in finding an object near to a given query object. The problem is old, and a large number of solutions have been proposed for it in the literature. However, it remains the case that even the most popular of the techniques proposed for its solution have not been compared against each other. Also, many techniques, including the old and popular ones, can be implemented in a number of ways, and often the different implementations of a technique have not been thoroughly compared either. This research presents a detailed investigation of different implementations of two popular nearest neighbour search data structures, KDTrees and Metric Trees, and compares the different implementations of each of the two structures against each other. The best implementations of these structures are then compared against each other and against two other techniques, Annulus Method and Cover Trees. Annulus Method is an old technique that was rediscovered during the research for this thesis. Cover Trees are one of the most novel and promising data structures for nearest neighbour search that have been proposed in the literature.
Conceptual astronomy: A novel model for teaching postsecondary science courses

An innovative, conceptually based instructional model for teaching large undergraduate astronomy courses was designed, implemented, and evaluated in the Fall 1995 semester. This model was based on cognitive and educational theories of knowledge and, we believe, is applicable to other large postsecondary science courses. Major components were: (a) identification of the basic important concepts and their interrelationships that are necessary for connected understanding of astronomy in novice students; (b) use of these concepts and their interrelationships throughout the design, implementation, and evaluation stages of the model; (c) identification of students’ prior knowledge and misconceptions; and (d) implementation of varied instructional strategies targeted toward encouraging conceptual understanding in students (i.e., instructional concept maps, cooperative small group work, homework assignments stressing concept application, and a conceptually based student assessment system). Evaluation included the .