Miracle-dz/UniFAR-FTUs huggingface dataset:
A kinetic model for dust acoustic waves applied to planetary rings

We have derived a kinetic model for the propagation of low-frequency waves in a dusty plasma containing dust particles and drifting plasma particles. The model includes Landau damping or growth and damping from charge variation on the dust particles, and is applied to dust-acoustic waves in planetary rings. Analytic expressions for the dispersion function are used to examine the stability of this wave mode. The dispersion properties are also found numerically for dense dust clouds or large drift velocities, where the analytical expressions are not applicable. We show how the stability condition depends on the density of dust particles and the wavelength, for plasma and dust parameters which may apply to Saturn's F ring, G ring, and E ring, and to Jupiter's ring.
Delta‐doped Schottky diode nonlinear transmission lines for 480‐fs, 3.5‐V transients

Waveforms having 480‐fs, 3.5‐V transients were generated with a delta‐doped GaAs Schottky diode nonlinear transmission line and measured with an on‐chip diode sampling bridge at room temperature. Integration of delta‐doped diodes with high C(V) nonlinearity and uniform‐doped diodes with high speed made possible a transient waveform two times shorter than any previously measured.
The VLF complex permittivity of deep Antarctic ice measured in situ

The results of the first in-situ measurement at VLF of the complex permittivities of deep Antarctic ice are presented as functions of depth, projected along the vertical. Measurements made with an electrically short dipole probe at five frequencies to a depth of 1500 m below the ice surface are reported. Temperature is identified as a dominant factor affecting the ice permittivity. This fact, coupled with the measurements of complex permittivity to 1500 m depth, is used to estimate ice permittivities from 1500 m to the bottom of the ice sheet at 2164 m. Comparison of the in-situ measurements with those of surface measurements is made; it is concluded that for the purpose of VLF antenna and propagation studies the Antarctic ice sheet cannot be considered to be an isotropic homogeneous material, but must be treated at least as a horizontally stratified medium whose dielectric and loss properties vary in the vertical direction with temperature.
The Influence of the Inclusion of Soil Freezing on Simulations by a Soil–Vegetation–Atmosphere Transfer Scheme

The interactions between the soil, biosphere, and atmosphere (ISBA) land surface parameterization scheme has been modified to include soil ice. The liquid water equivalent volumetric ice content is modeled using two reservoirs within the soil: a thin surface layer that directly affects the surface energy balance, and a deep soil layer. The freezing/drying, wetting/thawing analogy is used, and a description of the modifications to the ISBA force‐restore scheme, in particular to the hydrological and thermal transfer coefficients, is presented. In addition, the ISBA surface/vegetation scheme is coupled to a multilayer explicit diffusion soil heat and mass transfer model in order to investigate the accuracy of the force‐restore formalism soil freezing parameterization as compared with a higher-order scheme. An example of the influence of the inclusion of soil freezing in ISBA on predicted surface and soil temperatures and surface fluxes is examined using prescribed atmospheric forcing from a micrometeorological case study that includes freeze‐thaw cycles. Surface temperature prediction is improved in comparison with the observed values, especially at night, primarily from the release of latent heat as the soil freezes. There is an improvement in the overall surface flux prediction, although for some specific periods there is increased error in the prediction of various components of the surface energy budget. Last, the simplified force‐restore approach is found to produce surface flux and temperature predictions consistent with the higher-resolution model on typical numerical weather prediction model timescales (on the order of several days to two weeks) for this particular site.
Volume Changes Accompanying the Extension of Rubber

The volume changes accompanying extension of peroxide vulcanizates of natural gum rubber were measured using a dilatometer technique. Measurements of the force‐extension behavior and compressibilities were made on the same samples for the range of extension and volume change covered in the volume experiments. A constant compressibility was found; however, the volume changes accompanying extension were not proportional to the isotropic part of the stress. Thus, the strain energy cannot be separated into a sum of two parts, one due to the shear and one due to the dilatation.
The viscosity-volume fraction relation for suspensions of rod-like particles by falling-ball rheometry

The relative viscosities of suspensions of randomly oriented rods in a Newtonian fluid were measured using falling-ball rheometry. The rods were monodisperse and sufficiently large to render colloidal and Brownian forces negligible. Steel and brass ball bearings were dropped along the centreline of cylindrical columns containing the suspensions. The terminal velocities of the falling balls were measured and used to determine the average viscosities of the suspensions. The suspensions behaved as Newtonian fluids in that they were characterized by a constant viscosity. They exhibited a linear relative viscosity-volume fraction relationship for volume fractions less than 0.125, and, for volume fractions between 0.125 and 0.2315, the specific viscosity increased with the cube of the volume fraction. The relative viscosity was found to be independent of falling-ball size for a ratio of falling ball to fibre length greater than 0.3. It was found to be independent of the diameter of the containing cylindrical column for a ratio of column diameter to fibre length greater than 3.2. The value determined for the intrinsic viscosity is in good agreement with theoretical predictions for suspensions of randomly oriented rods.
Perturbation Theory for the Fock-Dirac Density Matrix

In Hartree-Fock theory and its various generalizations, it is customary to solve an eigenvalue problem involving an effective one-body Hamiltonian. The eigenvectors determine the Fock-Dirac density matrix, which also appears in the effective Hamiltonian, and solution proceeds iteratively until self-consistency is achieved.An alternative (necessary and sufficient) condition for a solution is that the density matrix ($\ensuremath{\rho}$) is idempotent and commutes with the Hamiltonian (h). The change in $\ensuremath{\rho}$, accompanying a change $\ensuremath{\Delta}$ in h, can then be expressed as a perturbation series. Formulas for the perturbation, to all orders, are obtained in terms of the unperturbed Hamiltonian and density matrix. It is also shown that the whole perturbation may be obtained directly, without separating the orders, and that the approach is related to earlier steepest-descent methods.
Investigation of Fluid Structures in a Smooth Open-Channel Flow Using Proper Orthogonal Decomposition

This paper reports particle image velocimetry (PIV) measurements of the instantaneous velocity fields in a smooth open-channel flow. The Reynolds number of the flow based on the water depth was 21,000. The instantaneous velocity fields were analyzed using proper orthogonal decomposition (POD) to expose the vortical structures. The velocity fields were reconstructed using different combination of modes; the first 12 modes to expose the energetic structures, and from Modes 13 to 100 to expose the less energetic structures. The first set recovered about 50% of the turbulent kinetic energy while the second group of modes recovered about 33% of the energy. The POD results were further combined with the results from the momentum analysis as well as with the conditional quadrant analysis performed at three different threshold levels. The POD results revealed the existence of hairpin vortices of different sizes and energy levels. Most of the large eddies are elongated and inclined toward the boundaries in the str.
Cataclysmic variable production in globular clusters

We consider the production of cataclysmic variables (CVs) in globular clusters. We investigate whether the binaries that would produce CVs in the field are likely to contribute to the CV population in globular clusters. We find that such potential CVs (PCVs) are unlikely to survive if they reside in the core of a cluster. However, in a number of globular clusters, the relaxation time is sufficiently long that a fraction of the binaries will not have time to sink into the core. Further, for binaries only marginally heavier than 1 Mo' the relaxed distribution will be such that a fraction of the systems will remain outside of the core and thus survive to produce a CV. We therefore conclude that the contribution of PCVs to CV production in globulars may be significant. Such systems will be found in the cluster halo while those produced via tidal capture and from interactions between binaries and single stars are more likely to be found in the core. Observations of the distribution of CV s within a particular globular cluster will therefore indicate the relative efficiency of these different pathways to CV production.
Tailoring of magnetic properties of patterned cobalt antidots by simple manipulation of lattice symmetry

Cobalt (Co) antidot arrays with different lattice geometries, square and rhomboid structures were fabricated and their magnetic reversal properties were studied by scanning-electron microscopy (SEM), magneto-optic Kerr effect, and magnetic force microscopy (MFM). Different lattice symmetries induced the corresponding anisotropies with changing easy and hard axes. The nearest-neighbor rule is not applicable in case of the rhomboid antidot lattice, while the inclusion theory is. These results are different from those of the previous investigations. The differences are due to different sizes and spacing’s between the antidots. The MFM images in the remanent state showed well-defined domain structures, periodic in nature according to the lattice geometry.
Condensation Pressure Drop in Circular Microchannels

Abstract This paper presents a multiple flow-regime model for pressure drop during the condensation of refrigerant R134a in horizontal microchannels. Two-phase pressure drops were measured in five circular channels ranging in hydraulic diameter from 0.5 mm to 4.91 mm. For each tube under consideration, pressure drop measurements were first taken over the entire range of qualities from 100% vapor to 100% liquid for five different refrigerant mass fluxes between 150 kg/m2-s and 750 kg/m2-s. Results from the previous work by the authors on condensation flow mechanisms in microchannel geometries were used to assign the applicable flow regime to the data points. Pressure drop models for intermittent [1] and annular [2] flow reported earlier by the authors were modified and combined to develop a comprehensive model that addresses the entire progression of the condensation process from the vapor phase to the liquid phase. This combined model accurately predicts condensation pressure drops in the annular, disperse wave, mist, discrete wave, and intermittent flow regimes. Overlap and transition regions between the respective regimes are also addressed using an appropriate interpolation technique that results in relatively smooth transitions between the predicted pressure drops. The resulting model predicts 82% of the data within ± 20%.
A comparison of numerical solutions to the Eady frontogenesis problem

The semi‐geostrophic solution to the Eady frontogenesis problem is believed to represent an asymptotic limit of the full Euler equations as the Rossby number tends to zero. This is investigated using numerical solutions. The exercise is non‐trivial because the semi‐geostrophic solution is discontinuous, and so may not be found as the limit of the Eulerian form of the equations. It is shown that solutions of the two‐dimensional compressible Euler equations converge to a singular limit with geostrophic balance in the cross‐front direction. The convergence is at the expected second‐order rate in Rossby number up to the formation of the discontinuity and at a first‐order rate for some time afterwards. Numerical robustness can be assured and the degree of convergence improved if a quasi‐monotone form of interpolation is used in the semi‐Lagrangian advection. Direct integrations of a semi‐geostrophic model using standard numerical methods require significant computational compromises, and give a somewhat smoothed version of this limit. © Crown Copyright 2008. Reproduced with the permission of HMSO. Published by John Wiley & Sons, Ltd.
Analytical Model of Two-Dimensional Dispersion in Laterally Nonuniform Axial Velocity Distributions

An analytical model of the advection-dispersion phenomenon in rivers with a laterally nonuniform axial velocity distribution is presented. The dispersion phenomenon is assumed to be governed by the two-dimensional advection-diffusion equation with constant but anisotropic turbulent diffusion coefficients. An infinitely long river with a prismatic cross section bounded laterally by parallel nondispersive banks is assumed. The velocity distribution is allowed to vary in an arbitrary functional form, but was restricted in this work to a family of power-law velocity distributions. The method of moments is used to derive the important statistical parameters of the concentration distribution. The concentration moment equations are solved analytically using the method of Greens function coupled with the method of images. The moments are then used to construct an approximate model of two-dimensional dispersion for an arbitrary velocity function, an initial distribution, and source injection scenarios. A one-dimensional simplification of the two-dimensional dispersion model with a time-dependent dispersion coefficient is also outlined. The dependence of the concentration moments on the velocity distribution and the shape of the source distribution is analyzed, and numerical results for a plane source and vertical line sources at the centerline and at the side are compared. The effect of the asymmetry of the velocity profile on the mixing length and time and on the skewness of the concentration distribution is shown to be significant, which might partly explain the persistence of the skewness observed in the field. However, the effect of the source injection scenario was not significant at large times. The analytical results can be used to model the fate and movement of pollutants and to better assess the effect of discharge siting on the dispersion of a contaminant. The model can be also used as a simple practical tool in simulating transport in a nearly prismatic river system.
Flux pinning properties of Gd–Ba–Cu–O trapped field magnets grown by a modified top-seeded melt growth

We report a modified top-seeded melt-growth technology for processing high performance Gd–Ba–Cu–O trapped field magnets (TFMs) by providing an additional liquid source during the melt-textured growth. The enriched liquid source allows sufficient growth in the a−b plane with an increased growth rate, and depresses the accumulation of Gd2BaCuO5 (Gd211) particles, which largely suppresses the formation of sub-grain boundaries in the a-growth sectors. An average trapped magnet field of 1.2 T is achieved for the 32 mm Gd–Ba–Cu–O TFMs at 77 K. These Gd–Bd–Cu–O TFMs exhibit superior in-field flux trapping performance, thanks to the significant second peak effect of the critical current density (Jc). The additional liquid source intensifies the Gd–Ba substitution, and therefore increases the in-field Jc, especially at the temperature range of 30–70 K, which is meaningful for practical applications.
Algebraic properties of evolution partial differential equations modelling prices of commodities

Schwartz (J. Finance 1997; 52:923–973) presented three models for the pricing of a commodity. The simplest was a variation on the Black–Scholes equation. The second allowed for a stochastic convenience yield on the commodity and the third added a stochastic variation in the underlying interest rate. We apply the techniques of Lie group analysis to resolve these equations, discuss their peculiar algebraic properties and indicate the route to the addition of other stochastic influences. Copyright © 2007 John Wiley & Sons, Ltd.
Coupling strategies for biomedical fluid–structure interaction problems

The coupling of lightweight and often thin‐walled structures to fluids in an incompressible regime is a recurring theme in biomechanics. There are many fluid–structure interaction (FSI) solution schemes to address these kinds of problem, each one with its costs and benefits. Here, we attempt a comparison of the most important FSI schemes in the context of biomechanical problems, that is a comparison of different fixed‐point schemes and a block preconditioned monolithic scheme. The emphasis of this study is on the numerical behavior of these FSI schemes to gain an understanding of their effectiveness in comparison with each other. To this end a simplified benchmark problem is studied to show its applicability for more involved biomechanical problems. Two such examples with patient‐specific geometries are also discussed. The monolithic scheme proved to be much more efficient than the partitioned schemes in biomechanical problems. Copyright © 2009 John Wiley & Sons, Ltd.
Non-axisymmetric subcritical bifurcations in viscoelastic Taylor–Couette flow

Recently, an account of the linear and nonlinear analysis of the viscoelastic Taylor–Couette flow between independently rotating cylinders against axisymmetric disturbances was presented (Avgousti & Beris 1993a). However, more recent linear stability analysis has shown that for the range of geometric and kinematic parameters studied and for high enough values of flow elasticity, the critical instabilities are caused by non-axisymmetric, time-dependent disturbances (Avgousti & Beris 1993b). In this work, we calculate the bifurcating families corresponding to each one of the two possible non-axisymmetric patterns emerging at the point of criticality, namely the spirals and ribbons and determine their stability. It is shown that for a narrow gap size, for upper convected Maxwell and Oldroyd-B fluids, at least one of the non-axisymmetric families bifurcates subcritically. This result, in conjunction with the theoretical analysis of Hopf bifurcation in presence of symmetries (Golubitsky et al. 1988), implies that neither of the bifurcating families is stable. Consequently, there is a finite transition corresponding to infinitesimal changes of the flow parameters in the vicinity of the Hopf bifurcation point. Although a change in the ratio of the Deborah and Reynolds numbers has not been found to qualitatively affect this behaviour, calculations with a wider gap size have shown that both bifurcating families become supercritical. There, a Ginzburg–Landau analysis shows that the ribbons are the stable pattern. This behaviour is qualitatively similar to that seen for the newtonian fluid, but for counterrotating cylinders, albeit there, spirals have been found to be stable (Golubitsky & Langford 1988).
Simulations of edge and scrape off layer turbulence in mega ampere spherical tokamak plasmas

The L-mode interchange turbulence in the edge and scrape-off-layer (SOL) of the tight aspect ratio tokamak MAST is investigated numerically. The dynamics of the boundary plasma are studied using the 2D drift-fluid code ESEL, which has previously shown good agreement with large aspect ratio machines. In this context, a MAST-TCV comparison is presented in order to link the present analysis to well documented references. Next, scans of various edge parameters, such as density, temperature and current, are performed in the simulations with the aim of characterizing the profiles, fluctuation level and statistics of the edge/SOL density and temperature. In addition, we also discuss how the system changes when the length of the divertor leg is modified. This allows one to better understand the regime of operation of the Super-X divertor which will be implemented on MAST-Upgrade. The results obtained qualitatively agree with experimental observations. In particular, a universal behaviour of the fluctuation statistics is found for disparate edge conditions. Furthermore, the density and temperature decay lengths are inversely proportional to the plasma current and the edge temperature, while they are rather insensitive to the edge density (not to be confused with the line-averaged density).
A quantum mechanical model of the Bloch NMR flow equations for electron dynamics in fluids at the molecular level

Understanding of processes such as carrier mobility, electron transfer reactions, chemical reactions in fluids, electron solvation in fluids and electron attachment and localization in clusters relies crucially on the understanding of electron dynamics in fluids at the molecular level. Because of its very small mass, an electron is a quantum object and some of its properties such as diffusion coefficient of a solvated electron in water can be explained only by resorting to quantum mechanical formulation. In this study, we have solved the Bloch NMR flow equations to describe the evolution of the wavelike properties and find the wave functions which can be useful to solve a particular fluid flow problem quantum mechanically. Based on the uncertainty principle, a wave packet is assumed to initially describe the fluid particle (electron) under study. Then, when the particle encounters a force (so its potential energy is no longer zero), the force modifies the wave packet. Finding such propagation techniques, and applying them appropriately can provide useful techniques to find solutions to biological, medical and physical problems which otherwise could not be easily solved.
A magnetospheric energy principle for hydromagnetic stability problems

[1] A magnetospheric energy principle is formulated to study hydromagnetic stability of a magnetospheric plasma. The magnetospheric plasma is either in a two-dimensional or three-dimensional static equilibrium. It is surrounded by lateral perfectly conducting walls and ideal ionospheres in both cases and also by dawn-dusk periodic boundaries in the two-dimensional case. The two-dimensional case has a translational symmetry and has no unperturbed magnetic field component in the dawn-dusk direction. Unlike the conventional energy principle for a plasma surrounded by a perfectly conducting wall, field lines are assumed to vertically thread the ionospheric boundary, which is not a perfectly conducting rigid wall. Ideal ionospheric boundary conditions are obtained, so that the force operator becomes self-adjoint and the magnetospheric energy principle is valid. There are four ideal ionospheric boundary conditions to satisfy these requirements: horizontally free, conducting, free, and rigid. A change in the potential energy becomes equal to the sum of the change in the fluid energy and an ionospheric surface contribution, which is negative and thus destabilizing for horizontally free and free ionospheric boundary conditions. A minimization condition for the change in the potential energy is obtained. When an unperturbed field-aligned current vanishes, the horizontally free, conducting, free, and rigid boundary conditions allow interchange, incompressible ballooning, incompressible ballooning, and compressible ballooning modes, respectively. Different characteristics of those three pressure-driven modes are clarified. Existing interchange stability criteria are compared and results of several different numerical stability analyses of ballooning instabilities for different magnetospheric equilibria are discussed systematically in light of the present magnetospheric energy principle.