Miracle-dz/UniFAR-FTUs huggingface dataset:
Stability analysis of stratified shear flows with a monotonic velocity profile without inflection points

The two-layer model of a stably stratified medium has been used to investigate the stability of flows without inflection points on the profile of the velocity $V_x\,{=}\,u(y)$, which is monotonically increasing from zero at the bottom ($y\,{=}\,0$) to its maximum value $U_0$ (when $y\,{\to}\,\infty$). It is shown that in the case of flows of a general form (in which $u''(y)\,{<}\,0$ everywhere) an instability sets in for an arbitrarily small density difference; furthermore, perturbations of all scales build up simultaneously. With an enhancement of stratification, the real part $c_r$ of the phase velocity of unstable perturbations increases. The upper boundary of the instability domain is determined by the fact that at a certain stratification level (a particular one for perturbations of each scale), $c_r$ reaches $U_0$, the perturbation is no longer in phase resonance with the flow and turns into a neutral oscillation of the medium. For flows of a special kind, having points of zero curvature (where $u''=0$) on the velocity profile (but having no inflection points as before), the influence of neutral modes, associated with these points, on the formation of the instability domain configuration is analysed, and an interpretation of this influence is given in terms of the resonance and non-resonance contributions to shear flow instability.
Growth rate control and solid–gas modeling of TFA-YBa2Cu3O7 thin film processing

The trifluoroacetate metal-organic decomposition route to YBa2Cu3O7 film growth was investigated in order to bring new insights in the growth mechanism and its dependence on processing conditions and critical current density. Precursor films were processed on LaAlO3 substrates at different total pressure, oxygen partial pressure, water vapor partial pressure, and volume gas flow rate keeping the growth temperature at 740 °C. The influence of these various experimental parameters on the film growth rate, which was evaluated by in situ electrical resistance measurements, was studied thoroughly. It was found that the growth rate is nearly independent of the oxygen pressure and proportional to the square root of the water pressure. Additionally, the growth rate increases with a decrease of the total pressure or an increase of the gas flow rate. An empirical multi-exponential model simulates the experimental data, however, a better understanding was achieved using a theoretical solid–gas reaction–diffusion model, including both the diffusion of the product HF gas from the surface and the chemical reaction kinetics at the YBCO/precursor interface. A complex cross-linked relationship between the film growth rate and the processing parameters has been properly verified from the experimental data. Finally we showed that the growth rate is an important parameter influencing the critical current densities of YBCO films because it controls the nucleation of non-c-axis oriented grains.
The Mesoscale Structure of Some Regions of Clear-Air Turbulence

Abstract The structure of the atmosphere in regions of clear-air turbulence is investigated by means of aircraft observations of wind and temperature in combination with objective and subjective turbulence records. The nature of the aircraft data and the assumptions inherent in the analyses are described. The detailed fields of vertical and horizontal wind shear, stability and Richardson number are presented for turbulence encountered in three different patterns of flow, viz., a sharp trough, an anticyclonic jet stream, and an intense straight jet. Severe turbulence (equivalent in intensity to that measured by the same aircraft in a mature thunderstorm) was found in certain portions of the trough and ridge, and moderate turbulence existed in the straight jet. Comparison of these cases and of twenty other flights indicates certain similarities and certain differences of the flow conditions in the turbulent regions. The necessary and sufficient conditions for the existence of clear-air turbulence have not b.
Estimation of Finite Population Mean Using Optional RRT Models in the Presence of Nonsensitive Auxiliary Information

SYNOPTIC ABSTRACT Sousa, Shabbir, Corte-Real, and Gupta (2010) and Gupta, Shabbir, Sousa, and Corte-Real (2012) have presented ratio and regression estimators for the finite population mean of a sensitive study variable utilizing nonsensitive auxiliary information. We improve the results further by using optional scrambling. In the process, we also estimate the sensitivity level of the underlying sensitive question. We compare the proposed method with Sousa et al. (2010) and Gupta et al. (2012) estimators.
Influence of strut cross-section of stents on local hemodynamics in stented arteries

Stenting is a very effective treatment for stenotic vascular diseases, but vascular geometries altered by stent implantation may lead to flow disturbances which play an important role in the initiation and progression of restenosis, especially in the near wall in stented arterial regions. So stent designs have become one of the indispensable factors needed to be considered for reducing the flow disturbances. In this paper, the structural designs of strut cross-section are considered as an aspect of stent designs to be studied in details. Six virtual stents with different strut cross-section are designed for deployments in the same ideal arterial model. Computational fluid dynamics (CFD) methods are performed to study how the shape and the aspect ratio (AR) of strut cross-section modified the local hemodynamics in the stented segments. The results indicate that stents with different strut cross-sections have different influence on the hemodynamics. Stents with streamlined cross-sectional struts for circular arc or elliptical arc can significantly enhance wall shear stress (WSS) in the stented segments, and reduce the flow disturbances around stent struts. The performances of stents with streamlined cross-sectional struts are better than that of stents with non-streamlined cross-sectional struts for rectangle. The results also show that stents with a larger AR cross-section are more conductive to improve the blood flow. The present study provides an understanding of the flow physics in the vicinity of stent struts and indicates that the shape and AR of strut cross-section ought to be considered as important factors to minimize flow disturbance in stent designs.
Accelerating Implicit Finite Difference Schemes Using a Hardware Optimized Tridiagonal Solver for FPGAs

We present a design and implementation of the Thomas algorithm optimized for hardware acceleration on an FPGA, the Thomas Core. The hardware-based algorithm combined with the custom data flow and low level parallelism available in an FPGA reduces the overall complexity from 8N down to 5N serial arithmetic operations, and almost halves the overall latency by parallelizing the two costly divisions. Combining this with a data streaming interface, we reduce memory overheads to 2 N-length vectors per N-tridiagonal system to be solved. The Thomas Core allows for multiple independent tridiagonal systems to be continuously solved in parallel, providing an efficient and scalable accelerator for many numerical computations. Finally we present applications for derivatives pricing problems using implicit finite difference schemes on an FPGA accelerated system and we investigate the use and limitations of fixed-point arithmetic in our algorithm.
Overview of the Shanghai EBIT

EBIT (Electron Beam Ion Trap) is an excellent instrument both as light source and ion source, and is widely used in atomic physics research. In principle EBITs can produce ions of any charge state and of any element. In this report, a general introduction to the Shangai EBIT and short discussions of the spectroscopy platform are presented. Due to the repetitious running of the Shanghai EBIT over the past 5 years, it became necessary for the Shanghai EBIT to be disassem- bled for some maintenances and further modifications/improvements. The new design contains two major improvements. Furthermore, some experimental results on studies of dielectronic recombi- nation processes for highly charged Xe ions will be discussed.
The strain energy density distribution of the capping layer surface for InAs/GaAs quantum dot along different growth directions

In this paper, we calculated the strain distribution of low dimension structure using the elastic continuum model. The strain energy density distribution on the different thickness of capping layer surface for the self-organized InAs/GaAs quantum dots system is investigated by the numerical finite element method. The influence of the different growth directions on the strain energy density distributions can be found from the calculated results. The results can explain some experiment results, such as the ordering array of the quantum dots supper-lattices. So the growth direction and spacing thickness can be regarded as another control parameters for strain engineering self-organized semiconductor quantum materials. As a comparison, the strain distributions of other low-dimension self-organized materials are also calculated.
Latent Class Models for Stage-Sequential Dynamic Latent Variables

Stage-sequential dynamic latent variables are of interest in many longitudinal studies. Measurement theory for these latent variables, called Latent Transition Analysis (LTA), can be found in recent generalizations of latent class theory. LTA expands the latent Markov model to allow applications to more complex latent variables and the use of multiple indicators. Because complex latent class models result in sparse contingency tables, that may lead to poor parameter estimation, a simulation study was conducted in order to determine whether model parameters are recovered adequately by LTA, and whether additional indicators result in better measurement or in impossibly sparse tables. The results indicated that parameter recovery was satisfactory overall, although as expected the standard errors were large in some conditions with few subjects. The simulation also indicated that at least within the conditions examined here, the benefits of adding indicators outweigh the costs. Additional indicators improved s.
On the determination of absolute magnitude zero-points from Hipparcos parallaxes

The period–luminosity (PL) relation zero-point determination from Hipparcos trigonometric parallaxes of Cepheids is contentious. It is shown that the method used by Feast &38; Catchpole is equivalent to a standard minimization of sum of squares, and that it is free of Lutz–Kelker bias. The same technique is applied to RR Lyrae and field HB star data, the PL relation being replaced by a luminosity–metallicity relation.
Time-frequency transfer function calculus (symbolic calculus) of linear time-varying systems (linear operators) based on a generalized underspread theory

We introduce a generalized concept of underspread linear time-varying systems (linear operators) which contains a previous definition as a special case. We show that an existing approximate transfer function calculus (symbolic calculus) can be extended to this wider and practically more relevant class of underspread operators. As a mathematical underpinning of this calculus, we establish explicit bounds on various error quantities associated with it. The transfer function calculus provides a theoretical basis for various methods recently proposed for nonstationary signal processing, and it has important implications in the theory of time-varying power spectra.
Stress Energy tensor in LCFT and the Logarithmic Sugawara construction

We discuss the partners of the stress energy tensor and their structure in Logarithmic conformal field theories. In particular we draw attention to the fundamental differences between theories with zero and non-zero central charge. However they are both characterised by at least two independent parameters. We show how, by using a generalised Sugawara construction, one can calculate the logarithmic partner of T. We show that such a construction works in the c = ? 2 theory using the conformal dimension one primary currents which generate a logarithmic extension of the Kac-Moody algebra.
Three‐Dimensional Coupled Dynamics of a Buoy and Multiple Mooring Lines: Formulation and Algorithm

The equations of the coupled three-dimensional motion of a submerged buoy and multiple mooring lines are formulated using Kane's formalism. The lines are modelled using lumped masses and tension-only springs including structural damping. Surface waves are described by Stokes's second-order wave theory. The hydrodynamic loads due to viscous drag are applied via a Morison's equation approach using the instantaneous relative velocities between the fluid field and the bodies (buoy and lines). The detailed algorithm is presented and the equations are solved using a robust implementation of the Runge-Kutta method provided in MATLAB. The mathematical model and associated algorithm are validated by comparison with special cases of an elastic catenary mooring line and other published data.
Correlation Characteristics of a Wall Pressure Fluctuation Field in a Turbulent Boundary Layer Induced by a Longitudinal Flow along a Flexible Extended Cylinder

Results of an experimental research on correlation characteristics of the wall pressure fluctuations of a turbulent boundary layer, formed by a longitudinal flow along a flexible extended cylinder, are presented. It has been found out that the intensity of the wall pressure fluctuations of the turbulent boundary layer is higher at the flexible cylinder than at a flat plate or at a rigid cylinder. The pressure-inducing vortical structures are transported downstream along the longitudinal axis of the cylinder. The degeneration rate of maximum magnitudes of the space-time correlation factor for the flexible cylinder is higher than for the plate but lower than for the rigid cylinder. Large-scale vortical systems have a greater “lifetime” and are transported at larger distances than small-scale high-frequency vortical structures.
A Procedure for Using DNS Databases

A second moment closure (SMC) computation is compared in detail with the direct numerical simulation (DNS) data of Le et al. (1997) for the backstep flow at Re = 5100 in an attempt to understand why the intensity of the backflow and, consequently, the friction coefficient in the recirculation bubble are under-estimated. The data show that this recirculation bubble is far from being laminar except in the very near wall layer. A novel “differential a priori” procedure was used, in which the full transport equation for one isolated component of the Reynolds stress tensor was solved using DNS data as input. Conclusions are then different from what would have been deduced by comparing a full simulation to a DNS. In particular, the e-equation, usually blamed for faults in model predictions, has been found to give excellent results in this case. In fact, the main problem comes from the uv -equation which predicts a too high turbulent force. A modification, by including the gradients of mean flow in the transport model, has then been attempted and has cured 50 percent of the backflow discrepancy.
The Pacific–North American pattern associated diabatic heating and its relationship to ENSO

The Pacific–North American (PNA) pattern associated atmospheric diabatic heating is examined by linearly isolating the influence of El Niño‐Southern Oscillation (ENSO). Both the vertically integrated and three‐dimensional (3D) diabatic heating are calculated on the basis of NCEP/NCAR reanalysis. The PNA‐related heating is dominated by anomalies in the eastern Pacific, with a north–south dipole structure in mid‐latitudes and in the northern subtropics. The tropical heating anomalies are rather weak, remarkably different from those related to ENSO variability, and may be characterized by the heating nonlinearity with anomalies in the vicinity of the western Pacific. The results provide further evidence of the independence of the PNA on ENSO from the diabatic heating point of view. Copyright © 2007 Royal Meteorological Society
Long‐time Solutions of the Ostrovsky Equation

The Ostrovsky equation is a modification of the Korteweg‐de Vries equation which takes account of the effects of background rotation. It is well known that the usual Korteweg‐de Vries solitary wave decays and is replaced by radiating inertia gravity waves. Here we show through numerical simulations that after a long‐time a localized wave packet emerges as a persistent and dominant feature. The wavenumber of the carrier wave is associated with that critical wavenumber where the underlying group velocity is a minimum (in absolute value). Based on this feature, we construct a weakly nonlinear theory leading to a higher‐order nonlinear Schrödinger equations in an attempt to describe the numerically found wave packets.
Part II. finite periodic stationary gravity waves in a perfect liquid

The possible existence, form and maximum height of strictly periodic finite stationary waves on the surface of a perfect liquid are discussed. A method of successive approximation to the solution of the hydrodynamical equations is formulated, and the solution is carried to the fifth order for the case of two-dimensional waves on a deep liquid. The convergence of the method has not been established, so that the existence of truly periodic stationary waves is not beyond doubt, but the calculations provide strong presumptive evidence for their existence, and for the existence of a finite stable wave of greatest height. The crest of this wave has a right-angled nodal form, in contrast with that of the greatest stable travelling wave for which the nodal angle is 120°. The maximum crest height is 0.141A, where A is the wave-length, and the maximum trough depth is 0.078 A. This means that the greatest stationary waves are greater than the maximum travelling waves, the ratio being 1.53. The motions of individual particles are studied and it is shown that particles in the surface, particularly those near the anti-nodes have large horizontal motions. For a given wave-length, the period increases with wave height. The wave pressure on a breakwater is examined, and the modification of the calculations to allow for the finite depth of water is considered. Doubly modulated oscillations in a deep rectangular tank are also briefly discussed.
Blow-Up Solutions and Global Existence for Quasilinear Parabolic Problems with Robin Boundary Conditions

We study the blow-up and global solutions for a class of quasilinear parabolic problems with Robin boundary conditions. By constructing auxiliary functions and using maximum principles, the sufficient conditions for the existence of blow-up solution, an upper bound for the “blow-up time,” an upper estimate of the “blow-up rate,” the sufficient conditions for the existence of global solution, and an upper estimate of the global solution are specified.
Full Coverage Shaped-Hole Film Cooling in an Accelerating Boundary Layer With High Freestream Turbulence

Full coverage shaped-hole film cooling and downstream heat transfer measurements have been acquired in the accelerating flows over a large cylindrical leading edge test surface. The shaped holes had an 8 deg lateral expansion angled at 30 deg to the surface with spanwise and streamwise spacings of 3 diameters. Measurements were conducted at four blowing ratios, two Reynolds numbers, and six well documented turbulence conditions. Film cooling measurements were acquired over a four to one range in blowing ratio at the lower Reynolds number and at the two lower blowing ratios for the higher Reynolds number. The film cooling measurements were acquired at a coolant to free-stream density ratio of approximately 1.04. The flows were subjected to a low turbulence (LT) condition (Tu = 0.7%), two levels of turbulence for a smaller sized grid (Tu = 3.5% and 7.9%), one turbulence level for a larger grid (8.1%), and two levels of turbulence generated using a mock aerocombustor (AC) (Tu = 9.3% and 13.7%). Turbulence level is shown to have a significant influence in mixing away film cooling coverage progressively as the flow develops in the streamwise direction. Effectiveness levels for the AC turbulence condition are reduced to as low as 20% of LT values by the furthest downstream region. The film cooling discharge is located close to the leading edge with very thin and accelerating upstream boundary layers. Film cooling data at the lower Reynolds number show that transitional flows have significantly improved effectiveness levels compared with turbulent flows. Downstream effectiveness levels are very similar to slot film cooling data taken at the same coolant flow rates over the same cylindrical test surface. However, slots perform significantly better in the near discharge region. These data are expected to be very useful in grounding computational predictions of full coverage shaped-hole film cooling with elevated turbulence levels and acceleration. Infrared (IR) measurements were performed for the two lowest turbulence levels to document the spanwise variation in film cooling effectiveness and heat transfer.
The Role of Katabatic Winds on the Antarctic Surface Wind Regime

Abstract Antarctica is known for its strong and persistent surface winds that are directed along topographic pathways. Surface winds are especially strong during the winter period. The high directional constancy of the wind and the close relationship of the wind direction to the underlying terrain can be interpreted as evidence of katabatic wind activity. Observations show that the directional constancy of the Antarctic surface wind displays little seasonal variation. Summertime winds cannot be expected to contain a significant katabatic component, owing to enhanced solar heating of the ice slopes. Observations also show that the coastal environs are subjected to wide variation in atmospheric pressure associated with frequent cyclone activity. The robust unidirectional nature of the Antarctic surface wind throughout the year implies that significant topographic influences other than those from katabatic forcing must be acting. Idealized numerical simulations have been performed to illustrate the potential.
Microscopic mechanisms of the growth of metastable silver icosahedra

The growth of free silver nanoclusters is investigated by molecular-dynamics simulations up to sizes close to $N=600$ atoms on realistic time scales, and in a temperature range from $400$ to 650 K. At low and intermediate temperatures, we grow mainly noncrystalline structures, as icosahedra and decahedra. In particular, at $Ng200,$ we obtain that perfectly ordered metastable icosahedra are very likely grown: either by a shell-by-shell mode on a small-size stable icosahedron, or by a complete structural transformation from a decahedron to a metastable icosahedron. The latter mechanism can explain why large silver icosahedra are more abundant than large decahedra in experiments. At high temperatures, crystalline fcc clusters are very frequently grown.