Miracle-dz/UniFAR-FTUs huggingface dataset:
The Steady Motion and Stability of a Helical Vortex

1. Introductory . —This is the third of a series of papers dealing with the stability or instability of certain forms of vortex motion associated with the wake of a body moving in a fluid. In the earlier papers we examined the case of a system of equal vortex rings in parallel planes, as they might form in the rear of a sphere in steady motion. Nisi and Porter have shown that the lowest speed at which the vortex ring forms is 8·14 v / d where v is the kinematic viscosity of the fluid and d is the diameter of the sphere. Such a system of vortices has been proved to be only partially stable, and it is therefore to be inferred that their production occurs at a transition stage to a more stable type of flow. Now it is well known that in the case of two dimensional flow past a cylinder of any cross-sectional shape, eddies are formed in symmetrical pairs at low values of Reynolds' number, whereas at higher values asymmetry sets in and the eddying is formed alternately at one side of the cylinder and then at the other with regular periodicity. This latter stage occurs over a range of values of Reynolds’ number extending from about 70 to 105. Detailed explorations of the field for some distance behind the cylinder have established that the centres of eddying approximately assume the stable formation which has come to be known as the “Karman vortex street. "
Tremendous outburst amplitude dwarf novae

For many years, observers have noted the existence of a number of tremendous outburst amplitude dwarf novae. We present a summary of the known observational parameters for these exceptional systems. They show outburst amplitudes of 6-10 mag, have rare outbursts (interoutburst times being months to decades), and only seem to exist in dwarf novae with short orbital periods. We calculate new accretion disk models which can reproduce their outburst behavior very well. It appears that these dwarf novae have low mass transfer rates at minimum, and the viscosity during quiescence is about 10 times smaller than for other dwarf novae. Their relation to SU UMa stars is discussed.
On the probability of making Type I errors.

A statistical test leads to a Type I error whenever it leads to the rejection of a null hypothesis that is in fact true. The probability of making a Type I error can be characterized in the following three ways: the conditional prior probability (the probability of making a Type I error whenever a true null hypothesis is tested), the overall prior probability (the probability of making a Type I error across all experiments), and the conditional posterior probability (the probability of having made a Type I error in situations in which the null hypothesis is rejected). In this article, we show (a) that the alpha level can be equated with the first of these and (b) that it provides an upper bound for the second but (c) that it does not provide an estimate of the third, although it is commonly assumed to do so. We trace the source of this erroneous assumption first to statistical texts used by psychologists, which are generally ambiguous about which of the three interpretations is intended at any point in their discussions of Type I errors and which typically confound the conditional prior and posterior probabilities. Underlying this, however, is a more general fallacy in reasoning about probabilities, and we suggest that this may be the result of erroneous inferences about probabilistic conditional statements. Finally, we consider the possibility of estimating the (posterior) probability of a Type I error in situations in which the null hypothesis is rejected and, hence, the proportion of statistically significant results that may be Type I errors. Â© 1987 American Psychological Association.
Adiabatic propagation in potential structures

In this work the adiabatic approximation is applied to the propagation of matter waves in confined geometries like those experimentally realized in recent atom optical experiments. Adiabatic propagation along a channel is assumed not to mix the various transverse modes. Nonadiabatic corrections arise from the potential squeezing and bending. Here we investigate the effect of the former. Detailed calculations of two-dimensional propagation are carried out both exactly and in an adiabatic approximation. This offers the possibility to analyze the validity of adiabaticity criteria. A semiclassical (sc) approach, based on the sc Massey parameter is shown to be inadequate, and the diffraction due to wave effects must be included separately. This brings in the Fresnel parameter well known from optical systems. Using these two parameters, we have an adequate understanding of adiabaticity on the system analyzed. Thus quantum adiabaticity must also take cognizance of the intrinsic diffraction of matter waves.
Synthesis of Circular Antenna Array Using Crossed Particle Swarm Optimization Algorithm

The particle swarm optimization (PSO) algorithm presents a new way for finding an optimal solution of complex optimization problems. In this paper a modified particle swarm optimization algorithm is applied to the optimization of the antenna array. We modify the PSO algorithm in some aspects. Firstly, the dynamic parameter is introduced to update the position equation, and the particles are limited in the search region. A new strategy for updating the speed is then adopted, in which the speed is weakened linearly. Based on these strategies, we proposed a new PSO algorithm named the crossed PSO algorithm. Simulation results show that the optimal pattern of the antenna array is able to approach the desired pattern. The results also demonstrate that the modified algorithm is superior to the original algorithm and the nonlinear least-square method.
Influence of a Strong Electric Field on the Carrier Capture by Nonradiative Deep-Level Centers in GaAs

The techniques of capacitance spectroscopy are used to measure directly electron and hole capture cross-sections of deep levels in a neutral material at zero electric field and in the depletion layer with a strong electric field. The data show that if at zero electric field the electron capture cross-sections onto the centers are thermally activated and described by the theory of nonradiative multiphonon capture, then in a strong electric field (F ≈ 104 V/cm) the capture cross-sections increase to the limiting large value (σ ≈ 10−14 to 10−12 cm2) and are only little dependent on temperature. It is shown that an electric field causes a simultaneous increase of the electron and hole capture cross-sections of the level EL2 by five orders of magnitude at low temperatures (T ≈ 90 K). [Russian Text Ignored]
Estimation of Multivariate Observation-Error Statistics for AMSU-A Data

AbstractAdvanced Microwave Sounding Unit A (AMSU-A) observation-error covariances are objectively estimated by comparing satellite radiances with radiosonde data. Channels 6–8 are examined as being weakly dependent on the surface and on the stratosphere above the radiosonde top level. Significant horizontal, interchannel, temporal, and intersatellite correlations are found. Besides, cross correlations between satellite and forecast (background) errors (largely disregarded in practical data assimilation) proved to be far from zero. The directional isotropy hypothesis is found to be valid for satellite error correlations. Dependencies on the scan position, the season, and the satellite are also checked. Bootstrap simulations demonstrate that the estimated covariances are statistically significant. The estimated correlations are shown to be caused by the satellite errors in question and not by other (nonsatellite) factors.
Dynamics of a Repetitively Pump‐Pulsed Nd:YAG Laser

Laser pulse dynamics in a repetitively pump‐pulsed Nd:YAG laser are examined. Analytic expressions for the laser pulse height and pulse width for a pump‐pulsed laser are given, and the variation of the pulse height and width with pump power, cavity length, and cavity loss in the pump‐pulsed mode is compared to the variation in the Q‐switched mode. By pulsing a xenon pump lamp (with the lamp discharge maintained at a subthreshold value between pulses), 200 W, 200 nsec laser pulses were generated at repetition rates of several hundred per second. The predicted variation of the laser pulse height, width, and delay with pulsed pump power was verified. Using currently available YAG material and pump cavities, it is shown that 3600 W, 200 nsec laser pulses should be available at 50 kW pulsed pump powers.
Focus-free optical-resolution photoacoustic microscopy using an all-fiber Bessel beam generator

Optical-resolution photoacoustic microscopy (OR-PAM) becomes a premier microscopic imaging tool in biomedicine because it provides agent-free optical absorption information in tissues. By tightly focusing light to a spot, the fine lateral resolution can be achieved in OR-PAM. The focal spot size is typically determined by the numerical aperture of the used objective lens. Here, we demonstrate focus-free OR-PAM using a Bessel beam generator. In this approach, no objective lens is required. We have photoacoustically imaged a carbon fiber with a diameter of ~6 μm, and the measured lateral resolution was ~6-7 μm. Beneficially, the complexities of the existing OR-PAM systems can be greatly relieved.
Impurity transport during pulsed poloidal current drive experiment in the reversed field pinch experiment RFX

The characteristics of the impurity transport in the RFX reversed field pinch experiment during enhanced confinement regimes, such as those obtained performing pulsed poloidal current drive and oscillating poloidal current drive, have been investigated. It is found that during the enhanced confinement period, the ratio between the Ly α line of C VI and the resonance line of C V increases systematically well beyond the expected enhancement due to the temperature improvement. Experimental data have been reproduced by means of a one-dimensional, time dependent, collisional–radiative impurity transport code, which simulates several C and O lines, continuum emission and radiated power. In standard RFX plasmas the typical diffusion coefficient is ~20 m2 s−1 at the plasma centre decreasing to ~1 m2 s−1 at the edge. Best simulations of the spectroscopic data during the enhancement confinement phases are obtained by expanding the low diffusion region at the edge from r/a = 0.9 to r/a = 0.8±0.05 and shrinking the neutral density profile at the edge.
Bayesian identification of non-linear state-space models: Part I- Input design

Abstract We propose an algorithm for designing optimal inputs for on-line Bayesian identification of stochastic non-linear state-space models. The proposed method relies on minimization of the posterior Cramer Rao lower bound derived for the model parameters, with respect to the input sequence. To render the optimization problem computationally tractable, the inputs are parametrized as a multi-dimensional Markov chain in the input space. The proposed approach is illustrated through a simulation example.
Kinetic simulation of steady states of ion temperature gradient driven turbulence with weak collisionality

Statistically steady states of the ion temperature gradient driven turbulence with weak collisionality, where the collision frequency is much lower than characteristic ones of the turbulence, are investigated by means of a Eulerian kinetic simulation with high resolution. In the saturated state of the entropy variable, the ion heat transport balances with the collisional dissipation that is indispensable to realizing a steady-turbulence state of perturbed distribution function δf. The kinetic simulation definitely confirms the conventional hypothesis that, in a low-collisionality limit, the low-order velocity-space moments of δf as well as the ion heat transport flux agree with those in the quasisteady state of the collisionless turbulence with the constant entropy production. A spectral analysis of δf in the velocity-space clarifies the transfer and dissipation processes of the entropy variable associated with fluctuations, where the phase mixing, the E×B nonlinearity, and the finite collisionality are t.
Ultrafast balanced-homodyne chronocyclic spectrometer

We describe an optical detection system for simultaneous time- and frequency-resolved measurements: the Balanced-Homodyne Chronocyclic Spectrometer (chrono equals time; cyclic equals frequency). This system uses balanced, optical homodyne detection, with a wavelength- tunable, pulsed local-oscillator (LO) field to time resolve the spectrum of weak light pulses. The LO field defines the time and frequency window in which the signal field is sampled. The method time resolves the photon statistics as well as the mean intensity. Measurement examples are given for: (1) Temporal oscillations of laser pulses transmitted through a semiconductor quantum well in an optical microcavity and (2) The time-frequency profile of a linearly chirped ultrashort laser pulse.
Deep hard X-ray survey of the Large Magellanic Cloud

Results of the deep survey of the Large Magellanic Cloud (LMC) obtained with theINTEGRAL observatory are presented. The long exposure (∼7 Ms) allowed us to detect 21 sources in this sky region: ten belonging to the LMC itself (7 HMXBs, 2 PSRs, 1 LMXB), six of extragalactic origin and three belonging to other galaxies in the Local Group – the Milky Way (2 sources) and Small Magellanic Cloud (1 source). Four of the 21 sources were newly discovered hard X-ray sources, in addition to IGR J05414-6858 reported earlier; two of them were identified with extragalactic objects. We report also for the first time the detection of hard X-ray emission from the Crab-like pulsar PSR J0537-6910 and the identification of the hard X-ray source IGR J05305-6559 with the high-mass X-ray binary EXO 053109-6609.
Modified Anderson orthogonality catastrophe power law in the presence of shell structure

We study Anderson orthogonality catastrophe (AOC) for an parabolic quantum dot (PQD), one of the experimentally realizable few-electron systems. The finite number of electrons in PQD causes AOC to be incomplete, with a broad distribution of many-body overlaps. This is a signature of mesoscopic fluctuations and is in agreement with earlier results obtained for chaotic quantum dots. Here, we focus on the effects of degeneracies in PQDs, realized through their inherent shell structures, on AOC. We find rich and interesting behaviours as a function of the strength and position of the perturbation, the system size, and the applied magnetic field. In particular, even for weak perturbations, we observe a pronounced AOC which is related to the degeneracy of energy levels. Most importantly, the power law decay of the many-body overlap as a function of increasing number of particles is modified in comparison to the metallic case due to rearrangements of energy levels in different shells.
NIRCAM image simulations for NGST wavefront sensing

The Next Generation Space Telescope (NGST) will be a segmented, deployable, infrared-optimized 6.5m space telescope. Its active primary segments will be aligned, co-phased, and then fine-tuned in order to deliver image quality sufficient for the telescope's intended scientific goals. Wavefront sensing used to drive this tuning will come from the analysis of focussed and defocussed images taken with its near-IR science camera, NIRCAM. There is a pressing need to verify that this will be possible with the near-IR detectors that are still under development for NGST. We create simulated NIRCAM images to test the maintenance phase of this plan. Our simulations incorporate Poisson and electronics read noise, and are designed to be able to include various detector and electronics non-linearities. We present our first such simulation, using known or predicted properties of HAWAII HgCdTe focal plane array detectors. Detector effects characterized by the Independent Detector Testing Laboratory will be included as they become available. Simulating InSb detectors can also be done within this framework in future. We generate Point-Spread Functions (PSF's) for a segmented aperture geometry with various wavefront aberrations, and convolve this with typical galaxy backgrounds and stellar foregrounds. We then simulate up-the-ramp (MULTIACCUM in HST parlance) exposures with cosmic ray hits. We pass these images through the HST NICMOS `CALNICA' calibration task to filter out cosmic ray hits. The final images are to be fed to wavefront sensing software, in order to find the ranges of exposure times, filter bandpass, defocus, and calibration star magnitude required to keep the NGST image within its specifications.
Conduction band structure in wurtzite GaAs nanowires: A resonant Raman scattering study

We report on a room temperature Raman resonance at 1.56 eV in GaAs wurtzite nanowires together with the emergence of a strong forbidden longitudinal optical phonon line. We attribute this resonance, absent in zinc blende wires with similar diameters, to an additional excitonic transition due to conduction band folding in agreement with recent theoretical predictions.
A Planetesimal Accretion Zone in a Circumbinary Disk

We investigate the conditions for planetesimal accretion in a circumbinary disk. Until recently, it had been believed that only single solar-type stars might harbor planetary systems. On the other hand, circumbinary disks have been detected by infrared or radio observation. Planets may be formed in such disks. Binary systems give stronger gravitational perturbation against planetesimals orbiting nearer to the binary. Therefore, the relative velocities between planetesimals will be larger and when they exceed the escape velocity it is impossible for the planetesimals to accumulate into planets. We performed long-term numerical integrations of binary and planetesimal orbital motions in the framework of the coplanar elliptic restricted three-body problem and have found the upper limit of the orbital radius inside of which the relative velocity between the planetesimals exceeds the escape velocity. One of our results is that planetesimal accretion cannot occur in a zone within 13 AU from the barycenter of the binary system when the binary semimajor axis is 1 AU, the binary eccentricity 0.1, the total mass m1 + m2 = 1 M☉, and the mass ratio m2/(m1 + m2) = 0.2. In regions farther out than 13 AU, planetesimals can accrete. We also derive analytic expressions of the eccentricity of a planetesimal pumped up by the gravitational perturbation of the binary and the inner boundary radius of the planetesimal accretion zone according to the secular perturbation theory.
Generation of synthetic turbulent inflow data for large eddy simulation of spatially evolving wall-bounded flows

A method for generating inflow conditions for large eddy simulations (LESs) of spatially developing turbulent boundary layers is presented. It is an adaptation of the synthetic eddy method (SEM) of Jarrin et al. [Int. J. Heat Fluid Flow 27, 585 (2006)], which uses the Cholesky decomposition of the Reynolds stress tensor to enforce second-order moments starting from a normalized stochastic velocity signal, the latter being constructed with a superimposition of turbulent structures with prescribed geometrical shape and random signs and position. The present method modifies the definition of the stochastic signal so that it can be split into several modes, with different time, length and velocity scales and also with different vorticity contents. The idea is to reproduce more realistically the distribution of scales in the wall-normal direction of a turbulent boundary layer flow. The novelty of the proposed modified SEM is that physical information concerning the coherent vortical structures of such flows ar.
Nonparametric estimation of the shape function in a Gamma process for degradation data

The author considers estimation under a Gamma process model for degradation data. The setting for degradation data is one in which n independent units, each with a Gamma process with a common shape function and scale parameter, are observed at several possibly different times. Covariates can be incorporated into the model by taking the scale parameter as a function of the covariates. The author proposes using the maximum pseudo‐likelihood method to estimate the unknown parameters. The method requires usage of the Pool Adjacent Violators Algorithm. Asymptotic properties, including consistency, convergence rate and asymptotic distribution, are established. Simulation studies are conducted to validate the method and its application is illustrated by using bridge beams data and carbon‐film resistors data. The Canadian Journal of Statistics 37: 102‐118; 2009 © 2009 Statistical Society of Canada
On the Discrete-Time Integral Sliding Mode Control

A new discrete-time integral sliding mode control (DISMC) scheme is proposed for sampled-data systems. The new control scheme is characterized by a discrete-time integral switching surface which inherits the desired properties of the continuous-time integral switching surface, such as full order sliding manifold with eigenvalue assignment, and elimination of the reaching phase. In particular, comparing with existing discrete-time sliding mode control, the new scheme is able to achieve more precise tracking performance. It is shown in this work that, the new control scheme achieves O(T2) steadystate error for state regulation with the widely adopted delay-based disturbance estimation. Another desirable feature is, the proposed DISMC prevents the generation of overlarge control actions, which are usually inevitable due to the deadbeat poles of a reduced order sliding manifold designed for sampled-data systems. Both the theoretical analysis and illustrative example demonstrate the validity of the proposed scheme
On neutral-beam injection counter to the plasma current

It is well known that when neutral beams inject ions into trapped orbits in a tokamak, the transfer of momentum between the beam and the plasma occurs through the torque exerted by a radial return current. It is shown that this implies that the angular momentum transferred to the plasma can be larger than the angular momentum of the beam, if the injection is in the opposite direction to the plasma current and the beam ions suffer orbit losses. On the Mega-Ampere Spherical Tokamak (MAST) [R. J. Akers, J. W. Ahn, G. Y. Antar, L. C. Appel, D. Applegate, C. Brickley et al., Plasma Phys. Controlled Fusion 45, A175 (2003)], this results in up to 30% larger momentum deposition with counterinjection than with co-injection, with substantially increased plasma rotation as a result. It is also shown that heating of the plasma (most probably of the ions) can occur even when the beam ions are lost before they have had time to slow down in the plasma. This is the dominant heating mechanism in the outer 40% of the MAST .
X‐Ray Diffractometry of Low‐Temperature Phase Transformations in Strontium Titanate

The lattice parameters of single‐crystal SrTiO3 were determined by x‐ray diffraction as a function of temperature from 4.2° to 300°K. In addition to the normal cubic structure three significant regions were found. From 65° to 100°K a tetragonal modification exists (c/a=1.00056), from 35° to 55°K line splitting consistent with orthorhombic symmetry was observed, and at 10°K an anomalous maximum in the lattice parameter vs temperature curve was found which suggested a third structure transformation. In the tetragonal region (at 78°K) various domain configurations were photographed with a polarizing microscope.