Miracle-dz/UniFAR-FTUs huggingface dataset:
Interpretation of Lorentz microscopy observations of vortices in high-temperature superconductors with columnar defects

In order to interpret recent experimental observations of superconducting vortices interacting with tilted columnar defects in high-temperature superconducting materials, we have extended to the case of anisotropic materials our Fourier space approach for the calculation of the electron optical phase shift experienced by the high-energy electrons in a transmission electron microscope. The case of a London vortex having its core not perpendicular to the specimen surfaces is considered. The same configuration is also analyzed in the framework of a simplified pancake model and the influence of the number of stacks on the phase shift and images is investigated. The results obtained by the two models are compared between them and with the experimental results. The agreement between theory and experiment confirms that anisotropy plays a major role in affecting the electron microscopy images.
A comparative study on different scattering techniques and data evaluation methods for sizing of colloidal systems using light scattering

Quasi-elastic light scattering, elastic light scattering and Fraunhofer diffraction can be used for optical particle sizing. Simulated data were used to compare the different scattering techniques in terms of resolution and range of applicability. Elastic scattering techniques have a ten times higher resolution but cover a smaller size range than quasi-elastic light scattering. The most important inversion techniques for data evaluation for such experiments were also compared. Regularization techniques with positivity constraints and interpolating cubic B-splines proved to be superior to truncated singular value decomposition and maximum entropy methods.
The effect of data analysis techniques on the interpretation of wide-angle longwave radiation measurements

Abstract Three different data analysis techniques—shape factor, parameter estimation, and deconvolution—have been applied to the same set of satellite radiation measurements to determine their effect on the estimated radiation field. The measurements are from a wide-angle, horizon-to-horizon, nadir-pointing sensor. The shape factor technique reduces each measurement to a radiant exitance at the top of the atmosphere by simple division by a constant. The parameter estimation technique processes all measurements together as a batch and defines the radiant exitance as a least-squares fit to the data. The deconvolution technique takes advantage of the fact that spherical harmonies are the eigenfunctions of the measurement operator. All three techniques are derived, and their assumptions, advantages and disadvantages are discussed. Their results are compared globally, zonally, regionally and on a spatial spectrum basis. All three techniques give comparable results for global parameters. However, results on a r.
An improved algebraic Reynolds stress model and corresponding nonlinear stress model

An improved algebraic Reynolds stress model is developed from the modeled dynamic equations for the Reynolds stress. The improved model more closely represents the original Reynolds stress model equation than the standard algebraic Reynolds stress model over the range of time scales for the turbulence and mean flow strain field. Quasi‐non‐local convective effects are also included in the formulation. Explicit solutions to the algebraic Reynolds stress model equation set, in the form of nonlinear stress‐strain models, are presented for two and three dimensions.
Sensitivity computations of eddy viscosity models with an application in drag computation

This paper presents a numerical study of the sensitivity of an eddy viscosity model with respect to the variation of the eddy viscosity parameter for the two‐dimensional driven cavity problem and flow around a cylinder. The main objective is to provide a comparison between computing the sensitivity using sensitivity equation and computing the sensitivity using finite difference methods and also numerically illustrate the application of the sensitivity computations in improving drag flow functional. Copyright © 2006 John Wiley & Sons, Ltd.
Lucas' theorem refined ∗

We prove a refined version of the classical Lucas' theorem: if p is a polynomial with zeros a 1,…,a n+1 all having modulus one and φis the Blaschke product whose zeros are those of the derivative p 1, then the compression of the shift S(φ) has its numerical range circumscribed about by the (n+ l)-gon a 1…a n+1 with tangent points the midpoints of then+ l sides of the polygon. This is proved via a special matrix representation of S(φ) and is a generalization of the known case for n= 2.
The effective transverse thermal conductivity of amorphous Si3N4 thin films

The effective transverse thermal conductivity of Si3N4 thin films is determined as a function of film thickness. Results indicate that the effective thermal conductivity behavior of Si3N4 thin films is similar to that exhibited by amorphous SiO2 films; that is, there is no significant difference between the thermal conductivity of amorphous Si3N4 and amorphous SiO2 thin films as a function of thickness or temperature. The average effective transverse thermal conductivity decreases drastically as the film thickness is reduced. This strong thickness dependence is ascribed to a thermal resistance that is localized at the amorphous film/Si‐substrate interface. Within the narrow temperature range studied, the interfacial thermal resistance and the intrinsic conductivity of amorphous films increase with temperature; however, the interfacial resistance dominates as the film thickness is reduced. In light of the observed similarities between the Si3N4 results and those previously obtained on SiO2, the reduction i.
Evaluation of dynamic absorber to suppress subharmonic nonlinear vibration in car powertrain

This paper analyzed the suppression method of the nonlinear vibration called subharmonic vibration of order 1/2 in the car powertrain by using a dynamic absorber. In the car powertrain, the torsional forced vibration caused by engine explosions leads to inhibition of the ride quality. Thus, in the torque converter of an automatic transmission car, a piecewise-linear spring called damper is used to reduce the transmission of the forced vibration. However, the subharmonic vibration occurred in the actual vehicle, when the spring restoring characteristics is around the switching point. The fundamental vibration frequency of the subharmonic vibration is half to the engine forced vibration frequency. Although the design of the dynamic absorber to suppress the forced vibration has been established for the linear systems, the optimum design to suppress the subharmonic vibration of order 1/2 has not yet been investigated. The powertrain is modeled by multi degree-of-freedom system as an actual vehicle, including engine, torque converter, transmission gears and wheels. Equation of motion is developed with also considering spring restoring force of piecewise-linear spring. The numerical result shows subharmonic vibration occurs when the engine excitation frequency is almost twice of the second mode of natural frequency, and the result shows a good agreement with the experimental data. Then, the dynamic absorber is introduced to suppress the occurrence of subharmonic vibration theoretically. In this paper, the optimum design of the dynamic absorber to suppress the subharmonic vibration is discussed. The numerical result shows the optimally designed dynamic absorber in the natural frequency and the damping ratio is capable of suppressing the occurrence of the subharmonic vibration.
Characterization and efficient computation of the structured singular value

The concept of structured singular value was recently introduced by Doyle [1] as a tool for the analysis and synthesis of feedback systems with structured uncertainties. It is a key to the design of control systems under joint robustness and performance specifications and it very nicely complements the H^{\infty} approach to control system design. in this paper, it is shown that the structured singular value can be obtained as the solution of several smooth optimization problems. Properties of these optimization problems are exhibited, leading to a fast algorithm that always yields the structured singular value for block structures of size no larger than 3, and often does for block structures of larger size.
A Novel Method to Calculate the Phase Center of Antennas

A new numerical method — the Method of Moving Reference Point (MMRP) is proposed to calculate the phase center of antenna in this paper. This method is based on the optimized theory. Using the new method the phase centre of any kind of antennas can be obtained as long as its far field radiation expression is determined, for example the horn antenna and the log-periodic dipole antenna (LPDA). The relationship between the phase center and the phase deviation, as well as the relationship between the angle width of equiphase surface and the phase deviation can also be obtained by this method, so we can determine the fitting phase deviation as the request of engineering to choose the prefect phase center position and angle width of equiphase surface. The results obtained by this method are credible.
Plasma turbulence enhanced current collection: Results from the plasma motor generator electrodynamic tether flight

The plasma motor generator (PMG) experiment, launched June 26, 1993, was a tethered system of two identical plasma contactors connected via a 500-m conducting tether. The experiment was designed to demonstrate the ability of plasma contactors to provide a low-impedance connection between a spacecraft and the ionosphere for both the electron emission and collection. The flight data indicate that plasma contactors enhance electron collection and emission by both neutralizing the electron space charge and scattering electrons across the geomagnetic field lines. Up to a 0.3 A steady current flowed along the tether in a circuit completed through the ionosphere. An analytical model for plasma contactor interaction with a background plasma which incorporates electron scattering by plasma waves is compared with the flight data. Good agreement between the model and the data is achieved for an effective scattering frequency equal to one twentieth of the local plasma contactor plasma frequency.
Temperature independence of the spin-injection efficiency of a MgO-based tunnel spin injector

The spin polarization of electrons injected into GaAs from a CoFe∕MgO(100) tunnel spin injector is inferred from the circular polarization of light emitted from a GaAs-based quantum well (QW) detector. The circular polarization strongly depends on the spin and electron hole recombination lifetimes in the QW. Using time-resolved optical techniques, we show that these lifetimes are highly temperature dependent. A peak in the charge lifetime versus temperature is likely responsible for the previously observed dip in the electroluminescence polarization. Evidence for a temperature-independent spin injection efficiency of ∼70% from 10 K to room temperature is found.
Microwave Pulse Compression Using a Periodically Dielectric Loaded Dispersive Waveguide Section

The study of pulse compression phenomena in periodically dielectric-slab-loaded TE 10 waveguide structures of conductive walls and finite length is carried out using wave analysis techniques when the structure is excited by a stepping frequency input signal waveform. The periodically loaded waveguide shows highly dispersive phenomena and keeps losses to a minimum. The aim is to find a properly frequency modulated wave that propagates through this waveguide, so that pulse compression phenomena can take place. An exact Fourier analysis is carried out to compute the compressed wave field intensities.
Gravitational lenses: odd or even images?

In this paper we first recall the Morse relations for light rays in vacuum. They can be obtained, under quite general assumptions, by the relativistic Fermat principle stated by Kovner and correctly proved by Perlick. They can be used for a global mathematical description of the gravitational lens effect. Afterwards we consider the well known thin lens model and we observe that the light rays having a geometrical index equal to 2 have a strong constraint about the surface density where they pass the deflector. Finally, we note that in situations similar, for example, to the Einstein cross (whose models predict the existence of one light ray having its geometrical index equal to 2), the constraint on the surface density suggests that the absorption may be so high that the related image is quite difficult to detect.
Posterior probabilities for choosing a regression model

SUMMARY A simple Bayesian formula for the posterior probability of one of several regression models is shown to be systematically misleading unless all models have the same number of para- meters. Even in this case the use of improper priors leads to arbitrary inferences, as it does more generally. An alternative weighting for choosing a model is suggested and the relation- ship between significance tests and data-dependent priors mentioned. An alternative to the analysis of variance and related significance tests for choosing regression models is the calculation of the posterior probabilities of the competing models. These two methods can lead to sharply opposed inferences, both asymptotically and for a finite number of observations. It is the purpose of the present paper to examine in detail the potentially misleading behaviour of the apparent posterior probabilities of the models, particularly as a function of the number of observations. In passing, some errors in the literature are identified and some anomalies explained. The calculation of posterior probabilities after each observation arises in a natural way in the analysis of designed experiments for discriminating between regression models. In such experiments sequential procedures are desirable. A formula for updating the posterior probabilities of the models after each observation is given by Box & Hill (1967). In ? 2 the nonsequential form for these posterior probabilities is derived and related to posterior probabilities calculated in the customary way by integration over the parameter space of each model. This relationship makes clear the prior assumptions underlying the sequential procedure. The difficulties which arise from the use of improper priors are also mentioned in ? 2. The design of experiments is peripheral to the main discussion of the present paper. But since the numerical investigation of the behaviour of the posterior probabilities requires sequential experiments, design is discussed briefly in ? 3. The behaviour of the posterior probabilities is investigated in ? 4 for models with the same and with differing numbers of parameters when none, some or all of the models are true. Empirical weights for model plausibilities are derived in ? 5 and related to data-dependent prior probabilities for the models. The argument of the paper is almost entirely conducted in terms of two models with additive independent normal errors of constant known variance. The restriction to two models is purely for convenience, the extension to any number of models being straight- forward as is the extension to linearized nonlinear models. If the variance of the errors is unknown, the expressions for the posterior probabilities of the models become more com- plicated while the properties of the probabilities remain similar to those described here.
Soliton solutions of the dispersive sine-Gordon and the dispersive sinh-Gordon equations with fourth spatial or spatio-temporal derivatives

In this work, the dispersive sine-Gordon equation and the dispersive sinh-Gordon equations with fourth spatial or spatio-temporal derivatives are examined. The conditions for the creation of soliton complex dynamics in a strongly dispersive medium are obtained. The simplified form of Hirota's method will be employed to conduct the analytic study.
Flapping motions of the magnetotail current sheet excited by nonadiabatic ions

Observations by the Cluster spacecraft on 3 August 2004 are presented as an example of flapping motions of the magnetotail current sheet excited by nonadiabatic ions. It is found that the current sheet up‐down motions are exactly corresponding to alternating hemispherical asymmetries of the bouncing ion population. We show that those hemisphere‐asymmetric nonadiabatic ion populations are present in the magnetic field configuration with an effective finite guiding component due to the local current sheet inclination. These results demonstrate that the current sheet flapping motion is a self‐organized circulation process between the alternating hemispherical asymmetries of the nonadiabatic ion population inside the plasma sheet and the current sheet equilibrium itself.
How Eventful are Event Studies?

This paper reexamines the event study methodology in finance. We consider a formal specification of an event study in terms of a system of abnormal returns and, in particular, emphasise the possible limitations of using a methodology when misspecification may be present. In the first section of the paper, the theory of the event study is reviewed, with reference to the definition problems associated with the measurement of abnormal returns, the conditional information set embedded in return expectations, the determination of the event window, and the similarity across events. A major insight of our paper is to emphasise the importance of conditionality, learning and convergence in the theory of event studies and in the evolution of abnormal returns. In one section of the paper, we look at the question of recursive residuals, residuals formed when the information set is updated period by period, and implicitly question why they have not been used in event studies. In another section, the focus is on the specification of learning models, both across events and within the event period. Furthermore, we provide some conjectures about how to measure the information in events. Finally, we bring together the issues into a coherent methodology.
Versal deformations of linear optimal systems

System optimization over a parameter space produces optimal solutions which lie on the bifurcation set of the ambient space. As such, the optimality (quality) metric (as a function of the parameters) is highly sensitive to the parameters to the point of inducing instability for differential parameter variations. Singularities in this function diffeomorphically induce corresponding degenerate singularities in the optimal closed loop characteristic polynomials, which serves as a signature for potential catastrophic loss of quality that is most easily exhibited by the resulting dynamic instability. We examine the loss of quality in H/sup /spl infin// and related optimal systems via these diffeomorphic degenerate closed loop poles.
Supersonic and hypersonic flow with attached shock waves over delta wings

A unified theory is developed for supersonic and hypersonic flow with attached shock waves over the lower surface of a delta wing at an angle of attack. The flow field on the lower surface of a delta wing consists of uniform flow regions near the leading edges, where the cross flow is supersonic and a nonuniform flow region near the central part, where the cross flow is subsonic. In the nonuniform flow region, the theory is based on the assumption that the flow differs slightly from the corresponding two-dimensional flow over a flat plate. Thus a linearized perturbation on a nonlinear flow field is first calculated and then strained and corrected so that the flow is matched continuously to the uniform flow which is obtained exactly. When compared with available exact numerical solutions the theory gives, in all cases, almost identical results, except near the crossflow sonic line where existing numerical methods fail to produce a discontinuous slope in the pressure curve, whereas the present theory predicts such a discontinuity and shows that the slope has a square root singularity at the crossflow sonic line similar to that in the supersonic linear theory.
Experimental determination of the absolute value of the triple differential cross section for double photoionization in helium

The absolute triple differential cross section (TDCS) for double photoionization has been determined experimentally for the first time. The investigation was carried out for helium at a photon energy of 99 eV, for equal energy of the emitted electrons and in a plane perpendicular to the photon beam. Electron, ion and combined ion-electron spectrometry measurements were performed to put the data on an absolute scale. The result is compared with two recent calculations, and a parametrization is given which extends the TDCS obtained at one specific geometry to the whole space.
Decomposition of antenna signals into plane waves

A modification of Prony' method, in which an attempt is made to constrain the roots of the polynomial to the unit circle, is used to resolve a number of plane waves illuminating a uniformly spaced line array. A least squares method based on the eigenstructure of a certain correlation matrix is developed to handle the overdetermined case when there are excess numbers of antenna elements. Angle estimate variance is compared to the Cramer-Rao lower bound and with the forward-backward linear predictor method.
The Influence of Incipient Latent Heat Release on the Precipitation Distribution of the 24–25 January 2000 U.S. East Coast Cyclone

Abstract The role of a diabatically produced lower-tropospheric potential vorticity (PV) maximum in determining the precipitation distribution of the 24–25 January 2000 U.S. East Coast cyclone is investigated. Operational numerical weather prediction (NWP) models performed poorly with this storm, even within 24 h of the event, as they were unable to properly forecast the westward extent of heavy precipitation over the Carolinas and mid-Atlantic. The development of an area of incipient precipitation (IP) around 0600 UTC 24 January over the southeastern United States prior to rapid cyclogenesis was also poorly forecasted by the operational NWP models. It is hypothesized that the lower-tropospheric diabatic PV maximum initially produced by the IP was important to subsequent inland moisture transport over the Carolinas and mid-Atlantic. A PV budget confirms that latent heat release in the midtroposphere associated with the IP led to the initial formation of a PV maximum in the lower troposphere that propagate.
TESTING STATIONARITY IN THE MEAN OF AUTOREGRESSIVE PROCESSES WITH A NONPARAMETRIC REGRESSION TREND

In this paper, we suggest tests of stationarity in the mean of autoregressive time series versus arbitrary trend alternatives. As an intermediate, though essential, step local asymptotic normality of autoregressive models with a nonparametric regression trend is established. Moreover, a functional central limit theorem for the underlying likelihood ratio processes is derived. These results then offer a general construction principle by which every goodness of fit test (case 0), which is based on comparing the empirical distribution function and the hypothetical distribution function, corresponds to a test of stationarity in the mean of AR processes. The asymptotic power of these tests is derived. A small simulation study illustrates the performance of Kolmogorov-Smirnov and Cramer-von Mises type tests of stationarity in the mean at hand of a particular AR(2) process.