Asymmetric Expansion Research Articles

Sub-Alfvénic plasma expansion

A large ion Larmor radius plasma undergoes a particularly robust form of Rayleigh–Taylor instability when sub-Alfvénically expanding into a magnetic field. Results from an experimental study of this instability are reported and compared with theory, notably a magnetohydrodynamic (MHD) treatment that includes the Hall term, a generalized kinetic lower-hybrid drift theory, and with computer simulations. Many theoretical predictions are confirmed while several features remain unexplained. New and unusual features appear in the development of this instability. In the linear stage there is an onset criterion insensitive to the magnetic field, initial density clumping (versus interchange), linear growth rate much higher than in the ‘‘classic’’ MHD regime, and dominant instability wavelength of order of the plasma density scale length. In the nonlinear limit free-streaming flutes, apparent splitting (bifurcation) of flutes, curling of flutes in the electron cyclotron sense, and a highly asymmetric expansion are found. Also examined is the effect on the instability of the following: an ambient background plasma (that adds collisionality and raises the expansion speed/Alfvén speed ratio), magnetic-field line tying, and expansion asymmetries (that promotes plasma cross-field jetting).

Asymmetric Maxillary Expansion Appliance (ABHE)

Asymmetric Maxillary Expansion Appliance (ABHE)

Asymmetric Maxillary Expansion Appliance (ABHE)

Asymmetric Maxillary Expansion Appliance (ABHE)

Glaciation and tectonics in an active intracratonic basin: the Late Palaeozoic Itararé Group, Paraná Basin, Brazil

ABSTRACTThe Paraná Basin (1 600 000 km2) is the largest intracratonic basin in southern South America and contains a thick (1300 m) Permo‐Carboniferous glacial succession (the Itararé Group). This paper describes over 1700 m of drill core recovered during recent exploration for oil and gas. Itararé Group sediments consist of massive and stratified diamictites interbedded with massive and graded sandstones, and massive and laminated mudstones. Facies are interpreted as the product of sediment gravity flows in a glacially influenced marine basin.Three stratigraphic formations can be defined across the basin, each consisting of a lowermost sandstone‐rich member overlain by a diamictite‐rich member. Examination of Itararé Group rocks both in core and outcrop shows that depositional processes were influenced by active faulting and downslope resedimentation on relatively steep and unstable substrate slopes. Primary glacial deposits such as tillites and associated striated pavements occur along the present eastern outcrop belt which probably coincided with the eastern basin margin during deposition of the Itararé Group. Ice masses fringing the eastern (southern African) and western (Bolivian) basin margins supplied sediment to the basin in the form of fluvio‐glacial deltas, fans and floating ice tongues. This sediment was then resedimented downslope as debris flows and turbidites.Both stratigraphic relationships and the regional distribution of facies types identify a clear pattern of basin subsidence and step‐wise expansion by outward faulting within Late Proterozoic mobile belts. The position of successive basin margins can be related to specific lineament structures in the underlying basement. Asymmetric expansion of the Paraná Basin occurred along the northern and southern basin margins during deposition of the Itararé Group; this expansion probably reflects shallow crustal adjustments activated by collisional movements along the Andean margin of South America during the Hercynian Orogeny.

Laminar coupled flow downstream of an asymmetric sudden expansion

The effect of the expansion ratio and temperature varying viscosity on the hydrodynamic and heat transfer characteristics of the laminar flowfield over a backward facing step is studied numerically. Both walls are maintained at uniform but different temperatures, while the flow at the step is assumed to be hydrodynamically and thermally fully developed. Calculations are carried out for different Reynolds numbers in the laminar flow regime and for a Prandtl number of 5.3. It is shown that an increase in the expansion ratio results in the augmentation of the heat transfer coefficient along both walls, the augmentation becoming substantial at high expansion ratios. Empirical correlations are obtained for the average Stanton number in the recirculating zone as a function of the Reynolds number and the expansion ratio. The variation of viscosity with temperature is shown to have a substantial effect on both the reattachment length and the local Nusselt number distribution along both the step and flat walls, the effect becoming stronger as the Reynolds number increases.

TECTONIC CONTROL OF WORLD OIL RESERVES: AUSTRALIA'S POSITION

Although simple extensional clay models may be representative of grabens tens of kilometres in length, rotational divergence of continents on a sphere produces very different structures. Repeated periods of compression during separation result in wrench faults and compressional anticlines developing along major crustal fractures as a consequence of changes in momentum between a continent and adjacent smaller continental blocks along its rifted margin.The global distribution of rotationally divergent continental margins can be accounted for by asymmetric expansion of the earth. The southern bulge caused by expansion has emphasised non-marine deposition on southern continents with marine deposition more common in the northern hemisphere.Phanerozoic source rocks of the northern hemisphere account for 97 per cent of the world's produced and current reserves of oil. Australia's share of this extreme distribution asymmetry is less than one half of one per cent, yet the country covers five per cent of the Earth's continental crust.The proportion of undiscovered oil reserves outside OPEC and the former USSR is approximately 30 per cent, or some 12 per cent of the world's estimated ultimately recoverable reserve of 2 trillion (Tera) barrels. The majority of Australia's undiscovered reserves lie on the North West Shelf where about 12 per cent of the country's estimated ultimately recoverable reserve could be found.Although Australia is politically stable, lower petroleum taxes would attract exploration for smaller, structurally complex oil fields. While such taxes may be considered politically difficult at present, a by-product of concerted oil exploration would be an enormous increase in Australia's gas reserves to feed the national pipeline grid for the 21st century. Industry can assist increased success rates by greater attention to current technical deficiencies, such as the structural interpretation of seismic lines.

Asymmetric envelope expansion of supernova 1987A

Analytic models for the spherically symmetric expansion of SN 1987 A are discussed. The SN model includes a bend in the expanded density profiles at a velocity of about 4000 km/s and employs an asymmetric initial density distribution or energy deposition on the assumption of radial flow. The calculations show that there is a tendency for the flow to become more spherical during the expansion phase, and that the sense of density asymmetry changes across the bend in the density profile.

EFFECTS OF OPEN BOUNDARY ON INCOMPRESSIBLE NAVIER-STOKES FLOW COMPUTATION: NUMERICAL EXPERIMENTS

The issue of the acceptable numerical treatment along downstream open boundaries for incompressible flow calculations is investigated. The conventional viewpoint holds that the flow problem is not well posed when both inflow and outflow appear on open boundaries. To test this point, a series of Navier-Stokes flow calculations have been conducted for both a planar channel with a one-sided asymmetric expansion and a planar channel with a two-sided symmetric expansion with varying Reynolds numbers and grid densities. Several interesting results have been observed that are not consistent with the conventional viewpoint. The numerical experiments indicate that even with inflow across some portions of an open boundary, the numerical procedure can be well posed by adopting the straightforward extrapolation formula on the open boundary. Overall, it appears that the numerical stability of the computation is related to the Reynolds number, especially for flows with multiple recirculating eddies across the open boun...

Observation of helical sawtooth oscillations in a tokamak

In the Tokapole II tokamak [Nucl. Fusion 19, 1509 (1979)] the three-dimensional structure of the rapid sawtooth crash that accompanies internal disruptions has been observed. The sawtooth crash is helical, i.e., the decrease in soft x-ray intensity occurs along a q=1 helical contour, in accord with the standard reconnection model. The poloidally asymmetric radial expansion of the crash inward from the q=1 surface provides a measure of the reconnection time consistent with single helicity reconnection from a growing, nonrotating magnetic island.

Arc expansion in xenon flashlamps

Plasma arcs in large diameter (d>1 cm) xenon flashlamps often do not completely fill the bore of the discharge tube. The arc is usually initiated on one side of the discharge tube, adjacent to the ground plane, and the fraction of the discharge tube filled with plasma varies as a function of axial location. A model is presented that describes, from first principles, arc expansion in xenon flashlamps. The model simultaneously solves a coupled set of one-dimensional transport equations in different regions of the discharge tube to simulate two-dimensional effects in hydrodynamics, electron kinetics, and radiation transport. Using this method, expansion of arcs initiated at arbitrary locations within the discharge tube can be studied. Arc filling fractions are found to decrease with increasing filling pressure of xenon, increasing diameter of the discharge tube, and decreasing stored energy in the discharge circuit. The arc filling fraction also decreases as the breakdown filament moves away from the axis of the discharge tube and towards the wall. Arc expansion is slowed and ultimately halted by a lowered E/N (electric field/gas density) in the gas exterior to the arc, rapid conversion of atomic ions to molecular ions and their subsequent recombination, and by the efficient manner in which radiation dissipates energy which might otherwise be available for thermodynamic expansion of the arc. The asymmetric expansion of the plasma arc results in asymmetric heating of the inside wall of the discharge tube, also calculated in the model. The growth of the plasma arc is also found to be in part responsible for changes in the spectrum of radiation emitted from the arc for various angles of observation. This effect results from wavelength-dependent absorption coefficients in the plasma.

The Formation of Echinocytes by the Insertion of Oxygenated Sterol Compounds Into Red Cell Membranes

AbstractHuman red cells incubated with oxygenated sterol compounds (OSC) at a concentration of 2.5 × 10−5M in medium containing lipoprotein-depleted serum become echinocytic. The formation of echinocytes by OSC is impeded by low temperature, replacement of lipoprotein-depleted serum by bovine serum albumin, or lipoprotein-containing serum, but not by the presence of free cholesterol. Echinocyte formation is apparent within 2 min of exposure of red cells to OSC, reaches a peak at 5–150 min, and declines to a nadir at 2–8 hr. This reversal to normal shape is followed by a second phase of echinocyte formation, with the percentage of abnormally shaped red blood cells increasing progressively over the next 40 hr. Following a 24-hr incubation with OSC, the oxysterols can be detected in approximately equal amounts in extracts of whole red cells or red-cell stroma. The proportion of OSC in the incubation mixture inserted into erythrocyte membranes ranges from 2.4% in the case of 25-hydroxycholesterol to 36% for 7β-hydroxycholesterol. A non-echinocyte-forming OSC such as 20α-hydroxycholesterol enters red cell membranes with an efficiency equal to or greater than that of potent echinocyte-forming OSC. Virtually all OSC membrane insertion occurs within 1 hr of red cell exposure, and the amount of membrane-inserted OSC remains constant over the next 23 hr. OSC insertion into red cell membranes is impeded by the presence of lipoproteins, but not by the presence of free cholesterol. We postulate that the early formation of echinocytes by membrane-inserted OSC is a consequence of asymmetric expansion of the outer lamella of the red-cell membrane lipid bilayer due to the presence of bulky hydrophilic groups on sterol molecules inserted within the hydrophobic environment of the membrane hydrocarbon chains. Early disappearance of echinocytes may be a consequence of the “flip-flop” and equilibrium redistribution of membrane-inserted OSC between the outer and inner membrane halves. OSC may be involved in red cell echinocyte formation in certain human diseases.

両親媒性薬物によるヒト赤血球の変形と浸透圧抵抗性変化との関連

Many of the amphipathic drugs tested, which induced shape changes in intact human erythrocytes, produced biphasic effects on hypotonic hemolysis of cells in a similar concentration range, protection at low concentrations and stimulation at higher concentrations. Both the exvaginators and invaginators, which induced shape changes of the membrane exvagination and invagination type, respectively, showed the same type of effect on osmotic resistance. When two drugs of either the exvaginator or invaginator type are present together in a hemolyzing medium, their effects on osmotic resistance appeared to be additive, as was the case with their effects on cell shape. In contrast, when an exvaginator and an invaginator are present together, their effects, both on osmotic resistance and cell shape, seemed to be antagonistic. The present results suggest that these drug effects may be caused, at least partly, by an asymmetric expansion of the membrane lipid bilayer due to asymmetric distribution of the drugs incorporated into the membrane.

A differential pulse-height discriminator with full channel logic using two integrated circuits

A differential pulse height discriminator is described which is complete with full channel logic and which may be used with either symmetric or asymmetric expansion of the channel width, or operated as two independent discriminators sharing a common input terminal.

Hard wall sections in gradient-propagated magnetic bubble domains

Using high-speed photography to investigate the transient response of bubbles to a bias field pulse, a shift in the geometrical center has been related to the previous propagation history. For left (right) skew bubbles, a low-mobility section appeared at the left (right) side of the previous propagation direction. The location of the hard wall section in respect to the propagation direction agrees with Thiele’s vertical Bloch line theory. Applying this method to low-angle propagators, i.e., bubbles with few Bloch lines, an asymmetric expansion was found after propagation in a gradient drive field that was higher than a certain threshold. For these bubbles, hard wall sections of oppositely wound vertical Bloch lines pinned the two flanks of the bubble and reduced the mobility of the rear allowing the front to expand out asymmetrically. These vertical Bloch line bundles with opposite sense were generated in the front and rear, then clustered on the two flanks during the gradient propagation, consistent with a dynamic converion model.

Asymmetric Plasma Expansion from the ‘Starfish’ Explosion

Recent astronomical measurements of solar and celestial X-radiation have led to renewed interest in strong shock-wave phenomena arising from explosions which occur on an astrophysical scale as in solar flares, novae and in supernovae. Although on a much smaller scale, the ‘Starfish’ nuclear explosion at an altitude of 400 km over Johnson Island in 1962, provides a useful test of current understanding in this field.

Cardiac displacement in pectus excavatum.

Excerpt Displacement of the heart is most often encountered as the result of an asymmetric expansion or shrinkage of intrathoracic structures, most often in the presence of a large pleural effusion...