Role Of Compression Research Articles

Density functional theory of simple polymers in a slit pore. II. The role of compressibility and field type

Simple tangent, hard site chains near a hard wall are modeled with a density functional (DF) theory that uses the direct correlation function, c(r), as its “input.” Two aspects of this DF theory are focused upon: (1) the consequences of variations in c(r)’s detailed form; and (2) the correct way to introduce c(r) into the DF formalism. The most important aspect of c(r) is found to be its integrated value, ĉ(0). Indeed, it appears that, for fixed ĉ(0), all reasonable guesses of the detailed shape of c(r) result in surprisingly similar density distributions, ρ(r). Of course, the more accurate the c(r), the better the ρ(r). As long as the length scale introduced by c(r) is roughly the hard site diameter and as long as the solution remains liquid-like, the ρ(r) is found to be in good agreement with simulation results. The c(r) is used in DF theory to calculate the medium-induced potential, UM(r), from the density distribution, ρ(r). The form of UM(r) can be chosen to be one of a number of different forms. It is found that the forms for UM(r)which yield the most accurate results for the wall problem are also those which were suggested as accurate in previous, related studies.

Stellar Turbulent Convection. I. Theory

The description of stellar turbulent convection requires a minimum of five coupled, time-dependent, nonlocal, differential equations for the five variables: turbulent kinetic energy, turbulent potential energy, turbulent pressure, convective flux, and energy dissipation. Any fewer number of equations makes the model local. In this paper, we present the following results: 1. We derive the five coupled equations using a new turbulence model. The physical foundations and the turbulence statistics on which the model was tested are discussed. The model is able to reproduce the high Rayleigh number laboratory and direct numerical simulation data corresponding to medium-to-high values of the Peclet number (a measure of the efficiency of convection). 2. One of the major difficulties for any stellar convective model is the description of the low-efficiency, low Pe number region in which the physical timescale is no longer the turbulent timescale but the radiative one. No previous turbulence model has been able to incorporate these multiple timescales within the same framework properly. The present model does. 3. Overshooting is an unsolved problem in stellar structure. Its solution requires not only the above ingredients, but an additional one, a nonlocal model. This is because in the stably stratified region where ? - ?ad < 0, the only source of energy is diffusion, a nonlocal process. We discuss why the expressions used thus far to describe diffusion terms are inadequate. We then present a model that was successfully tested against LES data on the convective planetary boundary layer. 4. We analyze the nonlocal models of Gough and Xiong and discuss the approximations that are required to derive them from the full set of equations. 5. We discuss a model that relates the up/down drafts filling factors found by DNS/LES to the skewness of the velocity field which can be computed from the turbulence model. The results from DNS/LES and this model can thus be cross-checked. 6. We show that the stationary, local limit of the model reproduces recent local models (independently derived) which have been successfully tested against a variety of astrophysical data. 7. We discuss the fact that if the dissipation is described by a local model with a mixing length l (as done by all authors thus far), the remaining nonlocal equations exhibit divergences which preclude a physical solution to be found. OV results based on this method may be a coincidence since they are arrived at by fine tuning a coefficient. 8. The role of compressibility is discussed.

SALT MIGRATION AND SUBTLE STRUCTURES: MODELLING OF THE PETREL SUB-BASIN, NORTHWEST AUSTRALIA.

Salt diapirs have been well documented in the Petrel Sub-basin of the Bonaparte Basin, offshore northwestern Australia, indicating that mobile salt exists at depth. G raphi- cal manipulation of geometric shapes on paper and analogue sandbox modelling were used to investigate the nature of structures produced in the sub-basin. The models rely on assumptions about the shapes developed by the moving salt, the timing of the movement and use the principle of vertical shear to adjust the accommodation space created by simple subsidence. The slug-like shape of the mobile salt wedges was adapted from the shapes imaged in the Gulf of Mexico by recent 3D seismic surveys.A simple graphic model of lateral salt migration replicates structures seen on a seismic panel from the Petrel Sub-basin in which wedges of sediment prograde from the basin centre to the basin margin. A more complex graphical model accounts for simple basin subsidence and salt migration shows many of the unusual features seen along the AGSO regional seismic Line 100/03. A sandbox model replicated the same features, including the broad dome of the Petrel structure, the sharper anticline around Tern, the depocentre northeast of Petrel, the smaller depocentre to the southeast and a number of small step-like structures. All these features are unusual as the amplitude diminishes upwards and downwards with no apparent basement control.The striking similarity of the models to the structures imaged by seismic suggests that salt has moved laterally, largely confined within the original evaporite stratigraphic level, taking on a slug-like shape, with an enlarged head and thin tail.This work gives an alternative explanation to the development of structures previously ascribed to compression, although the role of compression is not entirely discounted. The involvement of salt in the formation of large, but subtle structures such as the Petrel gas field, implies a longer history for the structures with influence on hydrocarbon migration, entrapment and the distribution of reservoir facies.

The role of compression in document databases

The extensive use of compression means that the MG retrieval system is capable of managing multi-gigabyte document collections in an effective and efficient manner. This article reviews the main features of MG and notes its relevance to large hypermedia collections.

On the role of compression in distributed systems

Compression has been used in numerous ways for many years, but recently two factors have combined in a way to push compression to the forefront of distributed systems. First, the disparity between processor speeds and I/O rates is ever-increasing, making it possible to perform compression in software to a much greater extent than was previously feasible. Second, the growth of new applications demanding enormous data rates, such as digital video and audio, makes hardware compression increasingly desirable: I discuss the importance of compression in various environments and describe how compression may be used not only to reduce the demand for disk space, disk bandwidth, and network bandwidth, but also to appear to extend physical memory.

Two-phase displacement of compressible fluids from stratified reservoirs

Mutual displacement equations are derived within the framework of the modified phase permeability model, taking the compressibility of one of the phases into account. A self-similar solution of one-dimensional displacement problems is obtained. The role of compressibility in displacement from nonuniform stratified reservoirs is analyzed.

Role of compressibility on driven magnetic reconnection

Whether it is induced by an ideal (current driven) instability or by an external force, plasma flow causes a change in the magnetic field configuration and often gives rise to a current intensification locally, thereby a fast driven reconnection being driven there. Many dramatic phenomena in magnetically confined plasmas such as magnetospheric substorms, solar flares, magnetohydrodynamic (MHD) self-organization, and tokamak sawtooth crash, may be attributed to this fast driven reconnection. Using a fourth-order MHD simulation code it is confirmed that compressibility of the plasma plays a crucial role in leading to a fast (MHD time scale) driven reconnection. This indicates that the incompressible representation is not always applicable to the study of a global dynamical behavior of a magnetically confined plasma.

Energetics of compressible models of fast steady-state magnetic reconnection

An understanding of the energy transfer that takes place during magnetic reconnection is crucial to the study of this fundamental process. It depends on two factors: the type of reconnection regime (which is determined by the boundary conditions) and the degree of compressibility. Here we examine the role of compressibility in the energetics of a family of reconnection models. When the inflow Mach number (or reconnection rate) Me is small the effects of compressibility may be more important than the differences between regimes. We find that for a slow-compression regime with Me = 0·005 compressibility decreases by 39% the efficiency of the shocks in converting magnetic energy and increases by 14% the ratio of thermal to kinetic energy in the outflow jet. This compares with a 13% decrease in the shock efficiency and a 7% decrease in the jet ratio obtained by choosing instead a flux-pile-up regime. As Me is increased, however, the differences between regimes become larger and may be comparable to or greater than the effects of compressibility. Thus when the above Mach number is doubled we find that a change of regime now has 1–6 times the effect on the jet energy ratio as the introduction of compressibility. For those regimes, therefore, which only exist at low inflow Mach numbers, compressibility will always be important. At higher values of Me the type of regime may be the dominant factor governing the energetics.

Compressible Rayleigh–Taylor instability

The role of compressibility in modifying the growth rate of Rayleigh–Taylor instability is discussed. Compressibility can either enhance or decrease the growth rate. If the sound speeds in the two media are the same, compressibility can still have an effect, in contrast to ‘‘first-order’’ theory. Compressibility becomes less important as the density ratio between the fluids increases. Experimental results have shown that compressibility can enhance growth rates compared to the incompressible value.

Role of compressibility in the high-speed interaction of solids

Role of compressibility in the high-speed interaction of solids

The Intramedullary Compression Rod

The Kaessmann compression device was employed in 26 patients with fractures of the long bones. In 15 fractures of the tibia, prompt healing occurred, even in fractures in the distal one-fourth of the tibia. Most of these cases were treated without external plaster support, and were permitted early ambulation, with partial weight-bearing. The technique for immobilizing these fractures involves a sliding a Kuntscher nail over a tension rod, and then fixing the clevis of the tension rod to the distal bone fragments by a transverse screw. The Kuntscher nail is fixed to the proximal bone fragment by a metal lip, and after compression is achieved, a locking sleeve fixed by a screw to the tension rod, prevents loss of compression. In 11 cases of pseudarthrosis of the tibia, the medullary canal was enlarged by passing graduated drills down the bony canal, over a guide wire. The compression rod was then inserted across the pseudarthrosis, and seventy to 80 kg/cm2 pressure was applied to the bone ends. No bone grafting procedure was performed. In all 11 cases, prompt union occurred. Postoperative management was similar to that employed in the treatment of fresh fractures. Three success fusions of the ankle also attest to the effectiveness of this immobilization. Although controversy exists regarding the role of compression in the healing of fractures, the axial compression rod does overcome distraction, compresses the bony surfaces, immobilizing them securely to produce union with an economy of callus.

The regional structure of the turanian platform and its development

The major features of regional structure and development of the Turanian platform are the result of the interaction of basement block movements with surrounding mobile belts. Some specific features, typical of the geosynclinal stage, can also be observed in the intermediate and platform stages. These features include subdivision of region by linear and smooth brachyform structures and the more pronounced irregularity in development of the former compared with the latter. The position of the most mobile elements of the Turanian platform are observed to migrate. As the intensity of movements in South Tien Shan—Kysylkum Hercynian branch (in the basement) decreased and activity of the Alpine geosyncline and postplatform orogene increased, the most mobile zone moved from the central and southeastern parts of the platform towards the southern and eastern periphery. Changes in the rates of sedimentation and growth of the majority of regional structures of the Turanian platform have a tendency to occur in opposite senses. The time of general subsidence in the Cretaceous corresponds to a decrease of growth rate of many structures. General platform upheaval during the recent phase coincides with an increase of structural growth. In peripheral and central aulocogen parts of the platform, stabilized or activated during the Jurassic, similar variations of sedimentation and growth rates are observed. The minor mobility of the biggest uplifts in comparison with the downwarps (except for the recent phase) indicates the predominance of continuous, general extension of the Turanian platform with an increase in the role of compression in Oligocene—Quaternary time. An almost equal number of regional structures of the Turanian platform occur with respectively conformable and unconformable relationship between the tectonics of the basin floor and that of the Moho. Beneath the structures developed in the southwestern mobile part of the platform deep crustal tectonics is a result of a long period of deformation during platform and intermediate stages. In the stable northeastern part of the platform crustal deformation during the platform stage was insignificant. The crustal tectonics here is probably a relic of Paleozoic pre-platform development.

Hydromagnetic stability of a compressible jet

This paper studies the hydromagnetic stability of a cylindrical jet of a perfectly-conducting, inviscid and compressible fluid. The fluid velocities and magnetic fields, inside and outside the jet, are uniform and in the axial direction, with possible discontinuities in their values across the jet surface. For large wavelength disturbances, the jet behaves as though it were incompressible. Numerical evaluation of the roots of the dispersion relation for a number of different magnetic-field strengths and jet velocities, but for disturbances of finite ranges of wavenumbers, indicates that the jet is stable against axisymmetric disturbances, but instability is present for asymmetric disturbances when the magnetic fields are sufficiently small. The magnetic field is found to have a stabilizinginfluence when compressibility is not very large; for high compressibility, it may have even a destabilizing effect. The paper explains physically the roles of compressibility and the magnetic field in bringing about the stability of the jet. When the wavelengths of disturbances are small, the dispersion relation reduces to that for a two-dimensional jet and a vortex sheet; and the results for these cases are known from earlier studies.

Role of Compressibility in the Magnetohydrodynamical Stability of the Diffuse Pinch Discharge

Role of Compressibility in the Magnetohydrodynamical Stability of the Diffuse Pinch Discharge

R OLE OF COMPRESSION IN THE AETIOLOGY OF BELL'S PALSY. AN EXPERIMENTAL STUDY.

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