Miracle-dz/UniFAR-FTUs huggingface dataset:
Eigenmodes of a Counter-Rotating Vortex Dipole

Highly resolved solutions of the two-dimensional incompressible Navier-Stokes and continuity equations describing the evolution of a counter-rotating pair of vortices have been obtained accurately and efficiently by spectral-collocation methods and an eigenvalue decomposition algorithm. Such solutions have formed the basic state for subsequent three-dimensional biglobal-eigenvalue-problem linear-instability analyses, which monitor the modal response of these vortical systems to small-amplitude perturbations, periodic along the homogeneous axial spatial direction, without the need to invoke an assumption of azimuthal spatial homogeneity. A finite element methodology (Gonzalez, L. M., Theofilis, V., and Gomez-Blanco, R., "Finite Element Numerical Methods for Viscous Incompressible Biglobal Linear Instability Analysis on Unstructured Meshes," AIAA Journal, Vol. 45, No. 4,2007, pp. 840-855) has been adapted to study the instability of vortical flows and has been validated on the Batchelor vortex (Mayer, E. W., and Powell, K. G., "Viscous and Inviscid Instabilities of a Trailing Vortex," Journal of Fluid Mechanics, Vol. 245, 1992, pp. 91-114). Subsequently, the instability of the counter-rotating dipole has been analyzed; aspects monitored have been the dependence of the results on the Reynolds number, the value of the (nonzero) axial velocity considered, and the time at which the quasi-steady basic flow has been monitored. Essential to the success of the analysis has been the appropriate design of a calculation mesh, as well as exploitation of the symmetries of the basic state. The spatial structure of the amplitude functions of all unstable eigenmodes reflects the inhomogeneity of the basic state in the azimuthal spatial direction, thus providing a posteriori justification for the use of the biglobal-eigenvalue-problem concept.
Dynamical consequences of a constraint on the Langevin thermostat in molecular cluster simulation

We investigate some unusual behaviour observed while performing molecular dynamics simulations of small molecular clusters using a constrained Langevin thermostat. Atoms appear to be thermalised to different temperatures that depend on their mass and on the total number of particles in the system. The deviation from the zeroth law of thermodynamics can be considerable for small systems of heavy and light particles. We trace this behaviour to the absence of thermal noise acting on the centre of mass of the system. This is demonstrated by solving the stochastic dynamics for the constrained thermostat and comparing the results with simulation data. By removing the constraint, the Langevin thermostat may be restored to its intended behaviour. We also investigate a Langevin thermostat constrained to have zero total force acting on its centre of mass, and find similar deficiencies.
Fiber specklegram sensing by means of an adaptive joint transform correlator

An adaptive joint transform correlator is used to process the speckle fields derived from a multimode optical fiber. The system is applied to evaluate changes in the speckle field when the fiber is used as a sensor element. We experimentally demonstrate that the sensitivity for temperature measurement and for submicrometer displacement measurement can be as high as 0.1°C and 0.2 μm, respectively. The duty cycle of the proposed fiber sensing system is about 2.5 s, which is limited by the microcomputer that we have used. To extend the dynamic range of sensing measurement, an updated algorithm can be used, by which the dynamic range of sensing capability can be further extended.
Potential of the ITER electron cyclotron equatorial launcher for heating and current drive at nominal and reduced fields

Electron cyclotron (EC) heating and current drive (HCD), at 170 GHz, 20 MW, is one of the heating systems foreseen to assist and sustain the development of various ITER scenarios since the early phase of ITER. It is usually assumed that EC is efficient only at magnetic fields operating around full field (5.3 T) and half field (2.65 T), and most of the analyses presented so far have focused on the ECRH&CD performances at flat-top. Here, the EC capabilities are investigated for different plasma parameters corresponding to different phases of the ITER plasma discharge, from current ramp-up up to burn, and for a wide range of magnetic fields, focusing in particular on the EC potential for heating and for L- to H-mode assist. It is found that the EC system can contribute to a wide range of heating scenarios during the ramp-up of the magnetic field, significantly increasing the applicable range as a function of magnetic field as compared with traditional views.
A probability measure for FLRW models

We use Jaynes' principle to find new probability measures for ensembles of open and closed dust-FLRW models and generalize the results to a γ-equation of state. For big-bang solutions the measures are non-integrable at Ω0 = 1 and Ω0 = ∞. Together with additional restrictions on the possible values of the cosmological constant Λ, these measures can solve the flatness problem.
Energetic particle measurements during the Earth swing‐by of the Cassini spacecraft in August 1999

We report on energetic particle measurements from the Low-Energy Magnetospheric Measurement System (LEMMS) aboard the Cassini spacecraft during the Earth swing-by maneuver in August 1999. LEMMS is capable of identifying the energy and incidence direction of energetic ions and electrons with energies of a few tens of keV to several tens of MeV. Cassini flew by Earth with a velocity of 16 kms−1 or 9 Earth radii (RE) per hour, which means that the entire day side magnetosphere was passed within 1 hour. This fast flyby trajectory of the spacecraft provided a snapshot of the Earth's magnetosphere where key regions were passed within a few hours instead of typically tens of hours or days for orbiting spacecraft. The measurements provide a means to show the performance of the instrument's capabilities as well as to test models of energetic particle distributions within the Earth's magnetosphere [e.g. Sibeck et al., 1987]. Particle pitch angle distributions (PADs) on the inbound pass along the 1300 magnetic local time (MLT) meridian gradually changed from normal distributions (maximum at 90° pitch angle) to butterfly pitch angle distributions (maximum at intermediate pitch angles). Close to the plasmapause, LEMMS observed field-aligned bidirectional distributions. During the outbound pass through the inner magnetosphere at 0130 MLT, pitch angle distributions are generally close to isotropic. Shortly after a substorm onset, identified by ground-based observations and aboard the Polar spacecraft [Khan et al., this issue], LEMMS observed an energy-time dispersed enhancement in the differential flux of low-energy electrons. We further address the question of whether signatures of the Earth magnetotail were observed at distances beyond 5000 RE when Cassini passed through the Earth's downstream region. LEMMS measured a series of particle increases during that time. The angular distributions during these enhancements show that most of these particles did indeed arrive from the Earth's direction. Nevertheless, the lack of singly charged heavy ions does not allow for a definite identification of this event as a deep-tail encounter.
Simulation study of an electrogasdynamic power converter using CFD

An electrogasdynamic (EGD) power converter, a device that converts mechanical energy into electric energy without moving parts, is described. A mathematical model that describes the complex two-phase fluid flow and electric field interaction was developed using a commercial CFD program. The axi-symmetric Navier-Stokes equations were solved for the carrying gas stream. Compressible flow was considered because of the high velocity (Ma > 1) inside the converter. The aerosol particles were tracked using a Lagrangian approach. Discrete particle motion and the electric field were coupled through the Poisson equation. The results indicated that because of the high velocities, particle motion is governed by the drag forces, the Coulomb forces having a minor effect. It was found that particle diameter and charge to mass ratio were the most important factors in the conversion efficiency. Copyright , Manchester University Press.
S-Processing in Massive Stars as a Function of Metallicity and Interpretation of Observational Trends

The s-process in massive stars is analyzed as a function of metallicity. The nucleosynthesis occurring in both core helium and shell carbon burning is investigated by numerically modeling nuclear reaction networks, subject to the conditions provided by stellar models. The efficiency of the neutron-capture mechanism depends on the amount of enhancement that is assumed for the α-rich nuclei, that are observed to be overabundant with respect to iron in stars of metallicity lower than solar
Dual-core photonic crystal fibers for dispersion compensation

The authors designed a new class of dual-core photonic crystal fibers (PCF) composed of several rings of air holes and two concentric cores. The central inner core is circular and made of material with a higher refractive index in comparison to the background material. The outer core is formed by replacing air holes in one or more intermediate rings with a material that possesses a higher refractive index. The dispersion characteristics, effective index, fiber V-parameters, and modal fields of the fundamental mode were investigated using the finite difference time domain method. The dual-core PCFs exhibit large negative dispersion over a wide wavelength rangewhose largest value is as high as −9000 ps ⋅ nm −1 ⋅ km −1 . The dispersion profile of the fibers can be controlled by controlling the diameter of the higher index region in the intermediate rings and diameter of the inner core. © 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). (DOI: 10.1117/1.JNP.6.063520)
Spontaneous generation of vortex crystals from forced two-dimensional homogeneous turbulence

The long-term limit of statistically stationary two-dimensional turbulence is shown to depend on the form of the large-scale forcing, in agreement with previous results. That effect is studied systematically by continuously varying the forcing from deterministic to Brownian in direct numerical simulations in doubly periodic boxes. As expected, this switches on or off the enstrophy cascade and the presence of strong coherent structures, but the transition is not monotonic. Under intermediate forcing conditions, the flow evolves to a stationary vortex crystal with triangular lattice, which appears to be stable and to last indefinitely. Deterministic forcings frustrate crystallization through the formation of fast-moving dipoles, and very random ones melt the crystal. The dispersion properties of the different regimes are studied, and it is shown that efficient particle dispersion depends on the presence of multiscale turbulence. The relation with other two-dimensional systems is discussed.
Growth kinetics of a single InP 1-x As x nanowire

Semiconductor nanowires offer additional properties and more flexibility for many potential applications. However the precise control of their growth is very challenging and much more complex than for two-dimensional layers. Here, we present a method which provides detailed information on their formation. The method is implemented with In(P,As) nanowires grown by Au-catalyzed molecular beam epitaxy. Controlled and periodic modulations of the incident vapor phase are generated. Due to these modulations, the nanowires show small and short oscillations of composition along their growth axis. These oscillations furnish a time scale which is recorded in the nanowire solid phase. The instantaneous growth rate and the total length of the nanowire at any time of the growth are accessible. The experimental data are fitted with models. The adatom diffusion lengths on the different surfaces and the chemical potentials in the adsorbed and liquid phases are extracted. It appears that the vapor flux intercepted by the nanowire sidewalls is the dominant contribution to their elongation. We discuss which contribution allows one initiating their growth from the catalyst drop.
Experimental Identification of a Self-Sensing Magnetorheological Damper Using Soft Computing

AbstractThis paper presents the development and application of a soft-computing technique in identification of forward and inverse dynamics of a self-sensing magnetorheological (MR) damper based on experimental measurements. This technique is developed by the synthesis of an NARX (nonlinear autoregressive with exogenous inputs) model structure and neural network within a Bayesian inference framework. The Bayesian inference procedures essentially eschew overfitting that could occur in network learning and improve generalization (prediction) capability by regularizing the complexity of learning. In applying the developed technique to the self-sensing MR damper, the present and past information of its input and output quantities, which contain the physical knowledge of the damper, is used to formulate its nonlinear dynamics. The NARX network architecture is then optimized to enhance modeling effectiveness, efficiency, and robustness. Experimental data of the damper subjected to both harmonic and random excit.
Bootstrap unconditional P-Values for the Sign Test with Ties and the 2 × 2 Matched-Pairs Trial

The use of approximate unconditional P-values is examined in the sign test with ties and the 2 × 2 matched-pairs trial. These P-values are calculated using a simple bootstrap plug-in rule, which requires no Monte Carlo and can be iterated an arbitrary number of times. Certain of these P-values yield corresponding tests of hypotheses which are very nearly exact and have considerably higher unconditional power than the usual exact conditional test. They can also be expected to have higher power than competing exact unconditional tests and are easier to compute.
Internal flow numerical simulation of a cross‐flow fan in refrigerant operating condition using user‐defined functions

In the paper, a cross‐flow fan in refrigerant operating condition is systematically simulated using user‐defined functions. Three‐dimensional simulations are acquired with Navier–Stokes equations coupled with k–ε turbulence model, and internal flow characteristics of an indoor split‐type air conditioner are obtained, which is mainly composed of cross‐flow fan and heat exchanger. It has systematically been simulated in the isothermal flow condition that the performance of cross‐flow fan may be reduced easily with dry or humid air, and in the refrigerant operating condition in which user‐defined functions are applied to the humid air, considered as a mixture of dry air and vapor. A density‐modulated function is adopted to deal with the condensation of the vapor at the heat‐transfer region approximately. The results show flow mechanism of the two gas‐phase flow, including phase‐vary process. The distribution of the parameters is not uniform at the inlet of the machine, the intensity and position of pressure and velocity vary along the axial direction of the fan, the distribution of vapor volume fraction and turbulent intensity in heat‐transfer region is obtained, and the external characteristic data of the indoor machine are obtained and analyzed. Compared with the experimental data, the calculated characteristic curves and designed parameters are on target. © British Crown Copyright 2010/MOD. Reproduced with permission. Published by John Wiley & Sons, Ltd.
Demonstration of a semipolar (101¯3¯) InGaN∕GaN green light emitting diode

We demonstrate the growth and fabrication of a semipolar (101¯3¯) InGaN∕GaN green (∼525nm) light emitting diode (LED). The fabricated devices demonstrated a low turn-on voltage of 3.2V and a series resistance of 14. 3Ω. Electroluminescence measurements on the semipolar LED yielded a reduced blueshifting of the peak emission wavelength with increasing drive current, compared to a reference commercial c-plane LED. On-wafer measurements yielded an approximately linear increase in output power with drive current, with measured values of 19.3 and 264μW at drive currents of 20 and 250mA, respectively. The external quantum efficiency did not decrease appreciably at high currents. Polarization anisotropy was also observed in the electroluminescence from the semipolar green LED, with the strongest emission intensity parallel to the [12¯10] direction. A polarization ratio of 0.32 was obtained at a drive current of 20mA.
The polarization of luminescence associated with the 4150 and 5032 Å centres in diamond

The polarization of luminescence of the 2.989 eV (4150 A) and 2.464 eV (5032 A) centres in diamond as a function of the energy of excitation is compared with the excitation spectra of these centres. The results are interpreted in terms of two electric dipole transitions in both types of centre. The 2.989 eV and 3.602 eV absorption lines are shown to be associated with a defect of trigonal symmetry, while the 2.464 eV and 3.368 eV absorption lines are associated with a defect of monoclinic I symmetry.
Linear Dissipation in Solids

In solid materials the properties of transient creep, internal friction and dispersion can be correlated on the basis of a linear theory, if the strains are small throughout. The theory, first given by Boltzmann, is developed in some detail. Dissipative properties of the material are shown to depend on a function of time called the ``creep function'' φ(t). The general condition 1/Q≅constant is examined. This condition is compatible with a creep function of logarithmic type. Velocity dispersion of plane or spherical waves is very small in such a medium. Graphs of 1/Q, phase and group velocities vs frequency are given, and a quantitative relationship between creep and internal friction constants is derived. The results are substantially applicable to the problem of losses in dielectrics, by carrying out the electromechanical analogy.
Polymorphic transitions in single crystals: A new molecular dynamics method

A new Lagrangian formulation is introduced. It can be used to make molecular dynamics (MD) calculations on systems under the most general, externally applied, conditions of stress. In this formulation the MD cell shape and size can change according to dynamical equations given by this Lagrangian. This new MD technique is well suited to the study of structural transformations in solids under external stress and at finite temperature. As an example of the use of this technique we show how a single crystal of Ni behaves under uniform uniaxial compressive and tensile loads. This work confirms some of the results of static (i.e., zero temperature) calculations reported in the literature. We also show that some results regarding the stress‐strain relation obtained by static calculations are invalid at finite temperature. We find that, under compressive loading, our model of Ni shows a bifurcation in its stress‐strain relation; this bifurcation provides a link in configuration space between cubic and hexagonal c.
On the Size of a Double Blocking Set inPG(2,q)

We obtain lower bounds for the size of a double blocking set in the Desarguesian projective planePG(2,q). These bounds are best possible forq< 11 and in the caseqis a square. With the same technique we also exclude certain values for the size of an ordinary minimal blocking set.
Mechanical properties of pillared-graphene nanostructures using molecular dynamics simulations

The deformation behaviour and mechanical properties of three-dimensional (3D) pillared graphene are investigated using molecular dynamics simulations. The Tersoff–Brenner many-body potential model is employed to evaluate the interactions between 3D pillared-graphene carbon atoms and nanotube carbons. The Lennard-Jones potential model is used to compute the interactions between a conical indenter and 3D pillared-graphene carbon atoms. The effects of the size and geometric structure of 3D pillared-graphene are evaluated in terms of the indentation force and contact stiffness. The simulation results for an armchair nanotube of 3D pillared graphene show that the contact stiffness increases with increasing chiral vector of the 3D-pillared graphene. However, the adhesive force sharply decreases with increasing chiral vector of the 3D-pillared graphene. A zigzag nanotube of 3D-pillared graphene exhibits better mechanical properties compared with those of the armchair nanotube.
Interaction of low-energy positrons with molecular nitrogen

Low energy collision and annihilation parameters for positrons scattered by molecular nitrogen have been calculated in the adiabatic (fixed nuclei) approximation. The interaction of the positron with the nitrogen molecule is represented as a superposition of static and polarization potentials. The elastic scattering cross section, the annihilation rate and the rotational excitation cross section are presented.
Control of jet breakup by a superposition of two Rayleigh–Plateau-unstable modes

Abstract We experimentally, numerically and theoretically demonstrate a novel method of producing a stream of widely spaced high-velocity droplets by imposing a superposition of two Rayleigh–Plateau-unstable modes on a liquid jet. The wavelengths of the two modes are chosen close to the wavelength of the most unstable mode. The interference pattern of the two superimposed modes causes local asymmetries in the capillary tension. The velocity of the initial droplets depends on these local asymmetries. Due to their different velocities, the droplets coalesce to produce a stream of larger droplets spaced at a much larger distance than the initial droplets. We analytically derive the perturbations that robustly induce this process and investigate the influence of the nonlinear interactions of the two Rayleigh–Plateau-unstable modes on the coalescence process. Experiments and numerical simulations demonstrate that the jet breakup and the subsequent droplet merging are fully governed by the selected modes.
Nonparametric Tests of Panel Conditioning and Attrition Bias in Panel Surveys

Over the past decades there has been an increasing use of panel surveys at the household or individual level. Panel data have important advantages compared to independent cross sections, but also two potential drawbacks: attrition bias and panel conditioning effects. Attrition bias arises if dropping out of the panel is correlated with a variable of interest. Panel conditioning arises if responses are influenced by participation in the previous wave(s); the experience of the previous interview(s) may affect the answers to questions on the same topic, such that these answers differ systematically from those of respondents interviewed for the first time. In this study the authors discuss how to disentangle attrition and panel conditioning effects and develop tests for panel conditioning allowing for nonrandom attrition. First, the authors consider a nonparametric approach with assumptions on the sample design only, leading to interval identification of the measures for the attrition and panel conditioning effects. Second, the authors introduce additional assumptions concerning the attrition process, which lead to point estimates and standard errors for both the attrition bias and the panel conditioning effect. The authors illustrate their method on a variety of repeated questions in two household panels. The authors find significant panel conditioning effects in knowledge questions, but not in other types of questions. The examples show that the bounds can be informative if the attrition rate is not too high. In most but not all of the examples, point estimates of the panel conditioning effect are similar for different additional assumptions on the attrition process.