bluuebunny/crossref_metadata_2025 huggingface dataset:
Steady compressible flow of cohesionless granular materials through a wedge-shaped bunker
Authors: Prakash J. Ravi , Rao K. Kesava
Published: April 2006

A continuum model based on the critical-state theory of soil mechanics is used to generate stress, density, and velocity profiles, and to compute discharge rates for the flow of granular material in a mass flow bunker. The bin–hopper transition region is idealized as a shock across which all the variables change discontinuously. Comparison with the work of Michalowski (1987) shows that his experimentally determined rupture layer lies between his prediction and that of the present theory. However, it resembles the former more closely. The conventional condition involving a traction-free surface at the hopper exit is abandoned in favour of an exit shock below which the material falls vertically with zero frictional stress. The basic equations, which are not classifiable under any of the standard types, require excessive computational time. This problem is alleviated by the introduction of the Mohr–Coulomb approximation (MCA). The stress, density, and velocity profiles obtained by integration of the MCA converge to asymptotic fields on moving down the hopper. Expressions for these fields are derived by a perturbation method. Computational difficulties are encountered for bunkers with wall angles θw[ges ] 15° these are overcome by altering the initial conditions. Predicted discharge rates lie significantly below the measured values of Nguyenet al.(1980), ranging from 38% at θw= 15° to 59% at θw= 32°. The poor prediction appears to be largely due to the exit condition used here. Paradoxically, incompressible discharge rates lie closer to the measured values. An approximate semi-analytical expression for the discharge rate is obtained, which predicts values within 9% of the exact (numerical) ones in the compressible case, and 11% in the incompressible case. The approximate analysis also suggests that inclusion of density variation decreases the discharge rate. This is borne out by the exact (numerical) results – for the parameter values investigated, the compressible discharge rate is about 10% lower than the incompressible value. A preliminary comparison of the predicted density profiles with the measurements of Fickieet al.(1989) shows that the material within the hopper dilates more strongly than predicted. Surprisingly, just below the exit slot, there is good agreement between theory and experiment.
Square patterns and secondary instabilities in driven capillary waves
Authors: Milner S. T.
Published: April 2006

Amplitude equations (including nonlinear damping terms) are derived which describe the evolution of patterns in large-aspect-ratio driven capillary wave experiments. For drive strength just above threshold, a reduction of the number of marginal modes (from travelling capillary waves to standing waves) leads to simpler amplitude equations, which have a Lyapunov functional. This functional determines the wavenumber and symmetry (square) of the most stable uniform state. The original amplitude equations, however, have a secondary instability to transverse amplitude modulation (TAM), which is not present in the standing-wave equations. The TAM instability announces the restoration of the full set of marginal modes.
Laboratory experiments on the tripolar vortex in a rotating fluid
Authors: van Heijst G. J. F. , Kloosterziel R. C. , Williams C. W. M.
Published: April 2006

Within the framework of the study of coherent vortex structures as emerging in rotating, quasi-two-dimensional flows, the tripolar vortex is a relatively novel feature. It consists of a symmetric, linear arrangement of three patches of distributed vorticity of alternate signs, and the axis of this configuration rotates about the centre of the core vortex. This paper describes an experimental study of the formation of a tripole from an unstable axisymmetric vortex in a solidly rotating, homogeneous fluid. The flow is visualized by addition of dye, and is measured by streak photography of tracer particles. After digitization, the spatial distributions of the vorticity ω and the stream function ψ are calculated numerically, and 'scatter plots’ of ω versus ψ are presented for the various stages in the tripole formation process. Owing to viscous effects (spin-down by the bottom Ekman layer and lateral entrainment of ambient fluid) the tripole shows an exponential decay, both in its rotation speed and its internal, relative flow. The comparison of the observed flow characteristics with a simple point-vortex model shows reasonable quantitative agreement.
The hydrodynamical alpha-effect in a compressible medium
Authors: Khomenko G. A. , Moiseev S. S. , Tur A. V.
Published: April 2006

The problem of the interaction of large-scale vortices with small-scale homogeneous isotropic helical turbulence in a compressible medium is considered. Averaged equations are derived using a closure procedure which is based on the functional technique. It is shown that the averaged vorticity equation has solutions that grow exponentially in time and which describe the effect of amplification of large-scale helical vortices by turbulence (hydrodynamical α-effect). The dependence of the growth rate on the compressibility is analysed, the limiting cases of incompressible fluid and turbulence δ-correlated in time being considered. The applications of the hydrodynamical α-effect discussed include the Earth's atmosphere and interstellar gas of spiral galaxies.
Steady incompressible flow past a row of circular cylinders
Authors: Fornberg Bengt
Published: April 2006

Numerical solutions are presented for steady two-dimensional incompressible flow past an infinite row of cylinders (of unit radii, with distances W between their centres). The calculations cover R [les ] 700 for 5 [les ] W [les ] ∞ and also R = 800 for 5 [les ] W [les ] 100 (where R denotes the Reynolds number based on the cylinder diameters). The recirculation regions (wake bubbles) are found to grow in length approximately linearly with R in all cases. For high values of R, a major change occurs in their character when W is increased past Wcrit ≈ 16. While they have remained slender up to this point (essentially only stretching in length in proportion to R), their centres of circulation have moved towards their ends. As W is further increased, the wake bubbles widen rapidly, beginning from the rear of the wakes. In the limit of W→∞, the present results agree with the previous ones for a single cylinder as reported by Fornberg (1985).
Moving loads on ice plates of finite thickness
Authors: Strathdee J. , Robinson W. H. , Haines E. M.
Published: April 2006

The response of a floating ice plate to a moving load is given in terms of a pair of Green's functions. General expressions for these Green's functions are derived for the case of an infinite isotropic plate of uniform thickness supported on a fluid base of uniform depth. The distributions of stress and strain in the vicinity of a concentrated load receive significant contributions from waves of length comparable with the plate thickness and their description necessitates an exact description of thickness effects. Circumstances in which the classical thin-plate theory can be recovered are discussed. The steady-state response to a uniformly moving load displays a so-called ‘critical’ behaviour for load velocities in the neighbourhood of a threshold value at which radiation commences. At the critical speed the amplitude is limited by dissipative forces in the ice plate. To describe this a simple viscoelastic term is included in our model. Calculations indicate that thin-plate theory is accurate to within 5% for distances greater than twenty times the ice thickness.
Turbulence in a separated boundary layer
Authors: Dianat M. , Castro Ian P.
Published: April 2006

This paper presents and discusses the results of an extensive experimental investigation of a flat-plate turbulent boundary subjected to an adverse pressure gradient sufficiently strong to lead to the formation of a large separated region. The pressure gradient was produced by applying strong suction through a porous cylinder fitted with a rear flap and mounted above the boundary layer and with its axis in the spanwise direction. Attention is concentrated on the structure of the turbulent flow within the separated region and it is shown that many features are similar to those that occur in separated regions produced in a very dissimilar manner. These include the fact that structure parameters, like Reynolds stress ratios, respond markedly to the re-entrainment of turbulent fluid transported upstream from the reattachment region, the absence of any logarithmic region in the thin wall boundary layer beneath the recirculation zone and the lack of any effective viscous scaling in this wall region, and the presence of a significant low-frequency motion having timescales much longer than those of the large-eddy structures around reattachment.

Similarities with boundary layers separating under the action of much weaker pressure gradients are also found, despite the fact that the nature of the flow around separation is quite different. These similarities and also some noticeable differences are discussed in the paper, which concludes with some inferences concerning the application of turbulence models to separated flows.
Thermal hydraulic jump: theory and experiment
Authors: Baddour R. E.
Published: April 2006

A thermally stratified internal hydraulic jump in a fresh water ambient, which has a temperature equal to or greater than 4 °C, is investigated theoretically and experimentally. The thermal jump solutions obtained using a nonlinear buoyancy function are compared with the density jump solutions obtained using a linear buoyancy function. The study reveals considerable difference between thermal and density jump behaviour in a range of temperature above 4 °C. The error of treating a thermal jump as a density jump is found to increase with Froude number and temperature difference and decrease with ambient temperature. Thermal jump-experiments are conducted at ambient water temperatures of 4 °C and 16 °C. The two sets of experiments have identical Froude number, Reynolds number and temperature difference. Experimental observations compare favourably with the thermal jump theory. The analysis of temperature fluctuations suggests that ambient temperature is also modifying the internal mixing characteristics of thermal jumps.
The stability of an air film in a liquid flow
Authors: Lezzi A. M. , Prosperetti A.
Published: April 2006

A number of processes in which air is entrained in a flow appear to involve the formation of a thin air film between a relatively fast liquid stream and a region of slow recirculation. Eventually, the film breaks into bubbles. This study addresses a possible mechanism causing this process. The linear stability of a vertical film of a viscous gas bounded by liquid in uniform motion on one side, and by liquid at rest on the other side, is studied. Instabilities are found that, depending on the parameter values of the undisturbed flow, are controlled by two basic mechanisms. One is due to the velocity jump across the film and can be related to the usual Kelvin–Helmholtz instability. The second one is controlled by the viscosity jump across the air liquid interfaces. The relation between the remainder of the discrete spectrum and the spectrum of other parallel shear flows bounded by solid or free surfaces is also discussed.
Convection and particle entrainment driven by differential sedimentation
Authors: Huppert Herbert E. , Kerr Ross C. , Lister John R. , Turner J. Stewart
Published: April 2006

When a suspension of small particles is overlain by a clear fluid whose density is greater than that of the interstitial fluid, but less than that of the bulk suspension, the settling of the dense suspended particles can lead to vigorous convection in the overlying fluid. This novel situation is investigated experimentally and theoretically. A sharp interface is observed between the convecting upper region and a stagnant lower region in which there is unimpeded sedimentation at low Reynolds number. There is no transport of fluid from the upper region into the lower, though there is mixing of both buoyant fluid and entrained particles from the lower region into the upper. The interface between the two regions is found to descend at a constant velocity. Systematic laboratory measurements have determined how this velocity depends on the densities of the layers and the distributions of settling velocities of the particles. A theoretical description is developed which calculates the evolution of the density of the lower region due to differential sedimentation of polydisperse particles. Buoyancy arguments based on the calculated density profile are used to place upper and lower bounds on the amount of particle entrainment into the upper layer and on the rate of fall of the interface between the convecting and sedimenting regions. The theoretical predictions are in good agreement with the experimental observations. The analysis of the interaction between convection and sedimentation in the system considered here may be particularly relevant to the description of evolving crystal-rich layers in magma chambers and of silt-laden outflow from rivers, and has a wide range of other industrial, environmental and geological applications.
Unsteady entrance flow in a 90° curved tube
Authors: Rindt C. C. M. , van Steenhoven A. A. , Janssen J. D. , Vossers G.
Published: April 2006

A numerical model enabling the prediction of the axial and secondary velocity fields in three-dimensional configurations at moderate Reynolds numbers and Womersley parameters is presented. Steady and unsteady entrance flows in a 90° curve tube (δ = ⅙) under various flow conditions are analysed. The good quality agreement between axial and secondary velocities for a sinusoidally varying flow rate at a Womersley parameter of α = 7.8, obtained from a finite-element calculation, and those obtained from laser-Doppler measurements justify the use of the numerical model.

Halfway into the deceleration phase for a sinusoidally varying flow rate (200 < Re < 800, α = 7.8) a strong resemblance is found to the steady flow case (Re = 700). In contrast with steady flow, near the inner wall reversed axial flow regions are found halfway into and at the end of the deceleration phase. Throughout the flow cycle the Dean-type secondary flow field highly influences axial flow resulting in a shift of the maximal axial velocity towards the outer wall, C-shaped axial isovelocity lines and an axial velocity plateau near the inner wall. Further downstream in the curved tube the Dean-type secondary vortex near the plane of symmetry is deflected towards the sidewall (’tail’–formation), as is also found for steady flow. An increase of the Womersley parameter (α = 24.7) results in a constant secondary flow field which is probably mainly determined by the steady component of the flow rate. A study on the flow phenomena occurring for a physiologically varying flow rate suggests that the diastolic phase is only of minor importance for the flow phenomena occurring in the systolic phase. Elimination of the steady flow component (− 300 < Re < 300) results in a pure Dean-type secondary flow field (no ‘tail’-formation) for α = 7.8 and in a Lyne-type secondary flow field for α = 24.7. The magnitude of the secondary velocities for α = 24.7 are of O(10−2) as compared to the secondary velocities for α = 7.8.
Twist vortices and their instabilities in the Taylor–Couette system
Authors: Weisshaar E. , Busse F. H. , Nagata M.
Published: April 2006

The problem of three-dimensional flows arising from the twist instability of Taylor vortices is investigated numerically in the narrow gap limit of the Taylor–Couette system with nearly corotating cylinders. There are two types of twist vortices: those that do not deform the in– and outflow boundaries of the Taylor vortices and those that do. The latter type are called wavy twist vortices and correspond to class II of Nagata (1986). The stability of the twist vortices with respect to arbitrary infinitesimal disturbances is analysed with the result that the twist solutions are unstable within a large part of the parameter space with respect to Eckhaus and skewed-varicose-type instabilities. An analytical model is described which fits the numerical results on the transition from axisymmetric vortices to unstable twist solutions. The theoretical findings are compared with experimental observations.
A steady separated viscous corner flow
Authors: McLachlan Robert
Published: April 2006

An example is presented of a separated flow in an unbounded domain in which, as the Reynolds number becomes large, the separated region remains of size 0(1) and tends to a non-trivial Prandtl-Batchelor flow. The multigrid method is used to obtain rapid convergence to the solution of the discretized Navier-Stokes equations at Reynolds numbers of up to 5000. Extremely fine grids and tests of an integral property of the flow ensure accuracy. The flow exhibits the separation of a boundary layer with ensuing formation of a downstream eddy and reattachment of a free shear layer. The asymptotic (’triple deck’) theory of laminar separation from a leading edge, due to Sychev (1979), is clarified and compared to the numerical solutions. Much better qualitative agreement is obtained than has been reported previously. Together with a plausible choice of two free parameters, the data can be extrapolated to infinite Reynolds number, giving quantitative agreement with triple-deck theory with errors of 20% or less. The development of a region of constant vorticity is observed in the downstream eddy, and the global infinite-Reynolds-number limit is a Prandtl-Batchelor flow; however, when the plate is stationary, the occurrence of secondary separation suggests that the limiting flow contains an infinite sequence of eddies behind the separation point. Secondary separation can be averted by driving the plate, and in this case the limit is a single-vortex Prandtl-Batchelor flow of the type found by Moore, Saffman & Tanveer (1988); detailed, encouraging comparisons are made to the vortex-sheet strength and position. Altering the boundary condition on the plate gives viscous eddies that approximate different members of the family of inviscid solutions.
A bifurcation study of mixed-convection heat transfer in horizontal ducts
Authors: Nandakumar K. , Weinitschke H. J.
Published: April 2006

The bifurcation structure of two-dimensional, pressure-driven flows through a horizontal, rectangular duet that is heated with a uniform flux in the axial direction and a uniform temperature around the periphery is examined. The solution structure of the flow in a square duct is determined for Grashof numbers (Gr) in the range of 0 to 106using an arclength continuation scheme. The structure is much more complicated than reported earlier by Nandakumar, Masliyah & Law (1985). The primary branch with two limit points and a hysteresis behaviour between the two-and four-cell flow structure that was computed by Nandakumaret al.is confirmed. An additional symmetric solution branch, which is disconnected from the primary branch (or rather connected via an asymmetric solution branch), is found. This has a two-cell flow structure at one end, a four-cell flow structure at the other, and three limit points are located on the path. Two asymmetric solution branches emanating from symmetry-breaking bifurcation points are also found for a square duct. Thus a much richer solution structure is found with up to five solutions over certain ranges of Or. A determination of linear stability indicates that all two-dimensional solutions develop some form of unstable mode by the time Gr is increased to about 220000. In particular, the four-cell becomes unstable to asymmetric perturbations. The paths of the singular points are tracked with respect to variation in the aspect ratio using the fold-following algorithm. Transcritical points are found at aspect ratios of 1.408 and 1.456 respectively for Prandtl numbersPr= 0.73 and 5. Above these aspect ratios the four-cell solution is no longer on the primary branch. Some of the fold curves are connected in such a way as to form a tilted cusp. When the channel cross-section is tilted even slightly (1°) with respect to the gravity vector, the bifurcation points unfold and the two-cell solution evolves smoothly as the Grashof number is increased. The four-cell solutions then become genuinely disconnected from the primary branch. The uniqueness range in Grashof number increases with increasing tilt, decreasing aspect ratio and decreasing Prandtl number.
Mass transport in two-dimensional water waves
Authors: Iskandarani Mohamed , Liu Philip L.-F.
Published: April 2006

Mass transport in various kind of two-dimensional water waves is studied. The characteristics of the governing equations for the mass transport depend on the ratio of viscous lengthscale to the amplitude of the free-surface displacement. When this ratio is small, the nonlinearity is important and the mass transport flow acquires a boundary-layer character. Numerical schemes are developed to investigate mass transport in a partially reflected wave and above a hump in the seabed. When the mass transport is periodic in the horizontal direction, a spectral scheme based on a Fourier–Chebyshev expansion, is presented for the solution of the equations. For the ease of a hump on the seabed, the flow domain is divided into three regions. Using the spectral scheme, the mass transport in the uniform-depth regions is calculated first. and the results are used to compute the steady flow in the inhomogeneous flow region which encloses the hump on the seabed.
Viscous motion of disk-shaped particles through parallel-sided channels with near-minimal widths
Authors: Halpern1 D. , Secomb T. W.
Published: April 2006

The motion of a rigid disk-shaped particle with rounded edges, which fits closely in the space between two parallel flat plates, and which is suspended in a viscous fluid subject to an imposed pressure gradient, is analysed. This problem is relevant to the squeezing of red blood cells through narrow slot-like channels which are found in certain tissues. Mammalian red cells, although highly flexible, conserve volume and surface area as they deform. Consequently, a red cell cannot pass intact through a channel which is narrower than some minimum width. In channels that are just wide enough to permit cell passage, the cell is deformed into its ‘critical’ shape: a disk with rounded edges. In this paper, the fluid mechanical aspects of such motions are considered, and the particle is assumed to be rigid with the critical shape. The channel cross-section is assumed to be rectangular. The flow of the suspending fluid is described using lubrication theory. Use of lubrication theory is justified by considering the motion of a circular cylinder between parallel plates. For disk-shaped particles, approximate solutions are obtained by applying lubrication equations throughout the flow domain. In the region beyond the particle, this is equivalent to assuming a Hele-Shaw flow. More accurate solutions are obtained by including effects of boundary layers around the particle and at the sides of the channel. Pressure distributions and particle velocities are computed as functions of geometrical parameters, and it is shown that the particle may move faster or slower than the mean velocity of the surrounding fluid, depending on the channel dimensions.
Home range and habitat use of the Vulnerable Virginia northern flying squirrel Glaucomys sabrinus fuscus in the Central Appalachian Mountains, USA
Authors: Menzel Jennifer M. , Ford W. Mark , Edwards John W. , Terry Tamara M.
Published: April 2006

The Virginia northern flying squirrel Glaucomys sabrinus fuscus is a Vulnerable sciurid that has experienced a 90% reduction of suitable high elevation boreal montane forest habitat over the last century in the central Appalachians of West Virginia and Virginia, USA. Using radiotelemetry and GIS analyses we examined the species' home range size and habitat use in the Monongahela National Forest, Kumbrabow State Forest and the MeadWestvaco Ecosystem Research Forest in West Virginia during the summers of 2000–2003. The mean home range sizes of male and female squirrels were 54.2 and 15.3 ha, respectively, based on the adaptive kernel method. Euclidean distance analysis indicated the squirrels used spruce, mixed spruce-northern hardwood, and open habitats more than was available across the landscape. Selection of spruce and mixed spruce-northern hardwood habitats indicates that forest management activities designed to restore and increase these types in the central Appalachian landscape are required to conserve and increase this Vulnerable species.
User Outcomes and Children's Services Reform: Ambiguity and Conflict in the Policy Implementation Process
Authors: Hudson Bob
Published: April 2006

The reforms to children's services in the UK brought in by the Every Child Matters Green Paper and the subsequent Children Act 2004 represent the most significant change in this area of social policy since 1948. The policy approach has two distinguishing features – an ‘outcomes led’ approach rooted in the views of children and young people about what constitutes ‘wellbeing’ in their lives, and a partnership approach that recognises these outcomes can only be achieved through high levels of inter-agency and inter-professional working. This article suggests that the two features may be in tension, and that during the process of implementation there is a danger that user defined outcomes will be re-interpreted to fit in with other organisational and professional agendas. The analysis draws upon Rick Matland's framework for exploring the impact of conflict and ambiguity respectively upon the implementation process.
Psychotherapie der Aufmerksamkeitsdefizit-/Hyperaktivitätsstörung (ADHS) im Erwachsenenalter
Authors: Nyberg Elisabeth , Stieglitz Rolf-Dieter
Published: April 2006

Zusammenfassung: Wenngleich in der Behandlung der Aufmerksamkeitsdefizit-/Hyperaktivitätsstörung (ADHS) im Erwachsenenalter die medikamentöse Behandlung mit Stimulanzien die Grundlage darstellt, können psychosoziale Interventionen in Kombination mit der Pharmakotherapie einen wichtigen Beitrag zur lebenslangen Bewältigung der Störung leisten. Ein multimodales Programm sollte daher Medikation und Psychotherapie umfassen. Im Beitrag soll ein Überblick zu den verschiedenen psychosozialen Behandlungsansätzen der ADHS im Erwachsenenalter und deren Wirksamkeit gegeben werden. Die Ergebnisse von Studien unterstreichen, dass in Kombination mit einer Medikation Verbesserungen der Kernsymptomatik zu erreichen sind. Aufgrund zum Teil großer methodischer Probleme der meisten Studien sind jedoch weitere kontrollierte Studien notwendig.
Collisional-radiative model in air for earth re-entry problems
Authors: Bultel Arnaud , Chéron Bruno G. , Bourdon Anne , Motapon Ousmanou , Schneider Ioan F.
Published: April 2006

A nonlinear time-dependent two-temperature collisional-radiative model for air plasma has been developed for pressures between 1kPa and atmospheric pressure to be applied to the flow conditions of space vehicle re-entry into the Earth’s atmosphere. The model consists of 13 species: N2, O2, N, O, NO, N2+, O2+, N+, O+, NO+, O2−, O− in their ground state and major electronic excited states and of electrons. Many elementary processes are considered given the temperatures involved (up to 10 000K). Time scales to reach the final nonequilibrium or equilibrium steady states are derived. Then we apply our model to two typical re-entry situations and show that O2− and O− play an important role during the ionization phase. Finally, a comparison with existing reduced kinetic mechanisms puts forward significant discrepancies for high velocity flows when the flow is in chemical nonequilibrium and smaller discrepancies when the flow is close to chemical equilibrium. This comparison illustrates the interest of using a time-dependent collisional-radiative model to validate reduced kinetic schemes for the relevant time scales of the flows studied.
Slow magnetohydrodynamic waves in stratified and viscous plasmas
Authors: Ballai Istvan , Erdélyi Robert , Hargreaves James
Published: April 2006

The propagation of slow magnetohydrodynamic waves in vertical thin flux tubes embedded in a vertically stratified plasma in the presence of viscosity is shown here to be governed by the Klein-Gordon-Burgers (KGB) equation, which is solved in two limiting cases assuming an isothermal medium in hydrostatic equilibrium surrounded by a quiescent environment. The results presented here can be applied to, e.g., study the propagation of slow magnetohydrodynamic waves generated by the granular buffeting motion in thin magnetic photospheric tubes. When the variation in the reduced velocity occurs over typical lengths much larger than the gravitational scale height, the KGB equation can be reduced to a Klein-Gordon equation describing the propagation of an impulse followed by a wake oscillating with the frequency reduced by viscosity and the solution has no spatial or temporal decay. However, in the other limiting case, i.e., typical variations in the reduced velocity occur over characteristic lengths much smaller than the gravitational scale height, waves have a temporal and spatial decay.
Spherical tokamak with a plasma center column
Authors: Tang X. Z. , Boozer A. H.
Published: April 2006

Low aspect ratio toroidal pinches such as the standard (q>1) and the ultralow q (q<1) spherical tori or tokamaks (ST), would have a far more robust reactor engineering design if a plasma center column (PCC) can be used in place of a material center post. Biased electrodes across the plasma center column would drive a plasma current to produce the toroidal magnetic field in lieu of the toroidal field (TF) coils. The operation of such a device is naturally divided into two distinct phases: formation by driven relaxation under magnetic helicity injection and sustainment by auxiliary current drive and heating such as rf and neutral beam injection (NBI). The initial design constraints of a ST-PCC experiment are primarily motivated by the formation rather than the sustainment physics. With a Taylor-relaxed plasma as the baseline case, it is shown that three essential factors guide the design. First, the flux amplification factor determines the aspect ratio of the ST-PCC. Second, the plasma shaping in general and plasma elongation in particular gives the most freedom in shaping the q profile of the relaxed plasma. Two examples are the standard spherical tokamak with q>1 throughout the plasma and the ultralow q (ULQ) spherical tokamak with q much less than unity for the bulk of the plasma. Third, the vacuum bias magnetic flux plays the second most important role in modifying the q profile. As an example, it is shown how the bias flux can be designed to delineate a standard spheromak experiment from that of an ULQ ST-PCC. These physics understandings help define the design space of the ST-PCC experiments and directions for optimization.
Formation of laser plasma channels in a stationary gas
Authors: Dunaevsky A. , Goltsov A. , Greenberg J. , Valeo E. , Fisch N. J.
Published: April 2006

Plasma channels with nonuniformity of about ±3.5% have been produced by a 0.3J, 100ps laser pulses in a nonflowing gas, contained in a cylindrical chamber. The laser beam passed through the chamber along its axis via pinholes in the chamber walls. Plasma channels with an electron density in the range of 1018–1019cm−3 were formed in pure He, N2, Ar, and Xe. A uniform channel forms in an optimal pressure range at a certain time delay, depending on the gas molecular weight. The interaction of the laser beam with the gas leaking out of the chamber through the pinholes was not significant. However, the formation of the ablative plasma on the walls of pinholes by the wings of radial profile of the laser beam plays an important role in the plasma channel formation and its uniformity. A low-current glow discharge initiated in the chamber improves the uniformity of the plasma channel slightly, while a high-current arc discharge leads to overdense plasma near the front pinhole and further refraction of the laser beam. These results indicate the potential for using nonflowing gas targets to create uniform plasma channels.
Effective dielectric constant of nanostructured Si layers
Authors: Delerue C. , Allan G.
Published: April 2006

We calculate the dielectric response of single layers of cubic and spherical Si nanocrystals using a self-consistent tight binding approach. We show that the effective dielectric constant is strongly influenced by the nanostructuring, leading to a strong reduction with respect to the bulk dielectric constant and to the value for the perfectly crystalline layer. These results are explained by the effect of the local fields and by the reduction of the dielectric response near the surface of the nanocrystals. We provide analytical expressions for the effective dielectric constant versus size.
Influence of contact geometry on the magnetoresistance of elliptical rings
Authors: Morecroft D. , Castaño F. J. , Jung W. , Feuchtwanger J. , Ross C. A.
Published: April 2006

Room temperature magnetotransport measurements have been carried out on NiFe single layer and NiFe∕Cu∕Co∕Au multilayer elliptical rings. The shape of the magnetoresistance response is strongly dependent on the contact configuration and the direction of the applied field with respect to the easy axis of the ellipse. The magnetization states and magnetoresistance can be quantitatively modeled.
Discharging, enhancement, and control of electron emission of hydrogen free diamond film surfaces by subband gap light illumination
Authors: Hoffman A. , Lafosse A. , Azria R.
Published: April 2006

We report on the surface charge elimination, enhancement, and control of secondary electron emission from hydrogen free polycrystalline diamond film surfaces subjected to continuous low energy electron irradiation. Hydrogen free diamond surfaces severely charge under electron irradiation by nonresonance charge trapping in surface π bonds associated with surface reconstruction. Concurrent electron irradiation and illumination of the diamond surface with subband gap photons enhance the secondary electron emission yield and discharge the surface accumulated charge. These effects are suggested to be associated to direct photoexcitation of trapped charge in midgap surface states which result in neutralization and unpinning of the surface bands.
Application of zero-temperature-gradient zero-bias thermally stimulated current spectroscopy to ultrathin high-dielectric-constant insulator film characterization
Authors: Lau W. S. , Wong K. F. , Han Taejoon , Sandler Nathan P.
Published: April 2006

Previously, we have reported our application of the zero-bias thermally stimulated current (ZBTSC) spectroscopy technique to study defect states in high-dielectric-constant insulator films such as tantalum oxide with much less parasitic current which can be a serious limitation for the conventional thermally stimulated current method. However, a parasitic current can still be observed for ZBTSC because of a small parasitic temperature gradient across the sample. The thermal design of the ZBTSC system can be improved, resulting in zero-temperature-gradient ZBTSC which can be used to detect deeper traps than those by ZBTSC.
Magnetoresistive anisotropy and strain relaxation in oxygen deficient La0.65Ca0.35MnO3−δ films near the metal-insulator transition
Authors: Patterson R. , Ozeroff C. , Chow K. H. , Jung J.
Published: April 2006

The magnetoresistance (MR) and the “out-of-plane” magnetoresitive anisotropy (AMRout) peaks were measured in vacuum annealed La0.65Ca0.35MnO3−δ films across the metal-insulator transition. The measurements were performed for a very small increase in oxygen deficiency δ, which leads not only to an increase of resistivity but also to a decrease of the magnitude of both the AMRout and MR peaks. The decrease of the MR and AMRout peaks is attributed to the epitaxial strain relaxation resulting from thermal treatment. These properties could originate from the lattice strain in agreement with a recent model of strain-induced metal-insulator phase coexistence in manganites.
Reversal of Alzheimer's-like pathology and behavior in human APP transgenic mice by mutation of Asp664
Authors: Galvan Veronica , Gorostiza Olivia F. , Banwait Surita , Ataie Marina , Logvinova Anna V. , Sitaraman Sandhya , Carlson Elaine , Sagi Sarah A. , Chevallier Nathalie , Jin Kunlin , Greenberg David A. , Bredesen Dale E.
Published: April 2006

The deficits characteristic of Alzheimer's disease (AD) are believed to result, at least in part, from the neurotoxic effects of β-amyloid peptides, a set of 39–43 amino acid fragments derived proteolytically from β-amyloid precursor protein (APP). APP also is cleaved intracytoplasmically at Asp-664 to generate a second cytotoxic peptide, APP-C31, but whether this C-terminal processing of APP plays a role in the pathogenesis of AD is unknown. Therefore, we compared elements of the Alzheimer's phenotype in transgenic mice modeling AD with vs. without a functional Asp-664 caspase cleavage site. Surprisingly, whereas β-amyloid production and plaque formation were unaltered, synaptic loss, astrogliosis, dentate gyral atrophy, increased neuronal precursor proliferation, and behavioral abnormalities were completely prevented by a mutation at Asp-664. These results suggest that Asp-664 plays a critical role in the generation of Alzheimer-related pathophysiological and behavioral changes in human APP transgenic mice, possibly as a cleavage site or via protein–protein interactions.
Wild rhesus monkeys generate causal inferences about possible and impossible physical transformations in the absence of experience
Authors: Hauser Marc , Spaulding Bailey
Published: April 2006

Human infants and adults generate causal inferences about the physical world from observations of single, novel events, thereby violating Hume's thesis that spatiotemporal cooccurrence from prior experience drives causal perception in our species. Is this capacity unique or shared with other animals? We address this question by presenting the results of three experiments on free-ranging rhesus monkeys (
Macaca mulatta
), focusing specifically on their capacity to generate expectations about the nature of completely unfamiliar physical transformations. By using an expectancy violation looking-time method, each experiment presented subjects with either physically possible or impossible transformations of objects (e.g., a knife, as opposed to a glass of water, appears to cut an apple in half). In both experiments, subjects looked longer when the transformation was impossible than when it was possible. Follow up experiments ruled out that these patterns could be explained by association. These results show that in the absence of training or direct prior experience, rhesus monkeys generate causal inferences from single, novel events, using their knowledge of the physical world to guide such expectations.
Treatment of Oesophageal Bile Reflux in Children
Authors: Orel Rok , Brecelj Jernej , Homan Matjaž , Heuschkel Robert
Published: April 2006

Objectives:

Reflux of duodenal juice into the oesophagus has a role in the pathogenesis of both oesophageal and laryngopharyngeal inflammatory and neoplastic lesions. As little is known about effective therapy, we studied the effect of proton pump inhibitor therapy on oesophageal bile reflux in children.

Methods:

Twenty‐nine children with moderate to severe erosive oesophagitis and abnormal oesophageal bile reflux were studied before and after treatment with omeprazole 1 mg/kg per day. Outcomes included a clinical symptom score, oesophageal acid and bile reflux (simultaneous 24‐hour pH and Bilitec 2000 monitoring), and mucosal healing.

Results:

After 8 weeks of therapy, 17 (59%) of the patients were symptom‐free, and 5 (17%) had minimal symptoms. Mucosal healing or reduction to low‐grade oesophagitis was achieved in 25 children (86%; P < 0.0005). Mean percentages of total, upright, and supine time with oesophageal pH less than 4 were reduced from 17.0%, 16.8%, and 19.2% before treatment, to 2.83%, 3.17%, and 2.07%, respectively, after treatment (all P < 0.00001). Similarly, mean percentages of total, upright, and supine time with bile reflux were reduced from 16.96%, 12.67%, and 22.0%, to 2.27%, 1.91%, and 2.23%, respectively (P < 0.000001, P < 0.0001, and P < 0.000001, respectively).

Conclusions:

Omeprazole 1 mg/kg per day is an effective therapy for the majority of children with severe erosive oesophagitis due to abnormal isolated bile reflux or combined acid and bile reflux. It remains unclear how patients with treatment‐resistant bile reflux should be managed.
Tunnel plasticity and quaternary structural integrity of a pentameric protein ring
Authors: Woycechowsky Kenneth J. , Seebeck Florian P. , Hilvert Donald
Published: April 2006

Cyclic protein oligomers are common in cells. However, the importance of the residues that line the central tunnel of protein rings for overall architectural integrity is not well understood. To investigate the role of tunnel positions in protein assembly and stability, we prepared variants of the homo‐pentameric lumazine synthase (LS) from Saccharomyces cerevisiae in which the three residues that line the middle of the tunnel were simultaneously changed. As a consequence of symmetry, these mutations cause a total of 15 changes in the structure of the pentameric complex. Detailed characterization of the variants indicates that they retain quaternary structural integrity, even in cases where the mutations induce considerable secondary structure alterations. The tunnels of symmetric ring‐shaped proteins, such as LS, may consequently represent an overlooked site for protein engineering.
Crystal structure of human peptidoglycan recognition protein Iα bound to a muramyl pentapeptide from Gram‐positive bacteria
Authors: Guan Rongjin , Brown Patrick H. , Swaminathan Chittoor P. , Roychowdhury Abhijit , Boons Geert‐Jan , Mariuzza Roy A.
Published: April 2006

Peptidoglycan recognition proteins (PGRPs) are pattern recognition receptors of the innate immune system that bind bacterial peptidoglycans (PGNs). We determined the crystal structure, to 2.1 Å resolution, of the C‐terminal PGN‐binding domain of human PGRP‐Iα in complex with a muramyl pentapeptide (MPP) from Gram‐positive bacteria containing a complete peptide stem (L‐Ala‐D‐isoGln‐L‐Lys‐D‐Ala‐D‐Ala). The structure reveals important features not observed previously in the complex between PGRP‐Iα and a muramyl tripeptide lacking D‐Ala at stem positions 4 and 5. Most notable are ligand‐induced structural rearrangements in the PGN‐binding site that are essential for entry of the C‐terminal portion of the peptide stem and for locking MPP in the binding groove. We propose that similar structural rearrangements to accommodate the PGN stem likely characterize many PGRPs, both mammalian and insect.
A comparison of the steady‐state pharmacokinetics of nevirapine in men, nonpregnant women and women in late pregnancy
Authors: Von Hentig Nils , Carlebach Amina , Gute Peter , Knecht Gaby , Klauke Stefan , Rohrbacher Maren , Stocker Hartmut , Kurowski Michael , Harder Sebastian , Staszewski Schlomo , Haberl Annette
Published: April 2006

Aims

To evaluate the pharmacokinetics of nevirapine and any possible influencing factors in pregnant women (n = 16), nonpregnant women (n = 13) and men (n = 14), who received nevirapine 200 mg twice daily together with nucleoside reverse transcriptase inhibitors.

Methods

Blood samples were taken for 12 h at steady state. Nevirapine concentrations were measured by liquid chromatography‐tandem mass spectrometry. The influence of gender, age, body weight and comedication on minimum and maximum concentrations (Cmin, Cmax), area under the concentration‐time curve (AUC), total clearance (CLtot), half‐life (t1/2) and volume of distribution (Vd) was analysed by multivariate techniques.

Results

Mean [95% confidence interval (CI)]Cmax, AUCss and clearance were 5221 ng ml−1 (4267, 6175), 50 789 ng −1h ml−1 (43 453, 58 125) and 69.9 ml min−1 for men, 5871 ng ml−1 (4848, 6895), 57 045 ng h−1 ml−1 (45 997, 68 093) and 65.6 ml min−1 for nonpregnant women and 4505 ng ml−1 (3644, 5366), 44 579 ng h−1 ml−1 (36 564, 52 594) and 82.1 ml min−1 for pregnant women. The differences between pregnant and nonpregnant women (% difference, 95% CI) in Cmax (−30.3; −28.5, −33.0), AUCss (−28.0; − 25.8, − 29.5) and clearance (20.2; 26.6, 15.6) reached statistical significance (P = 0.010, P = 0.028 and P = 0.028, respectively). The multivariate analysis underscored the influence of bodyweight on the plasma exposure to nevirapine.

Conclusions

Pregnant women exhibited an increased nevirapine clearance and comparably low plasma concentrations, whereas women with a low bodyweight achieved high plasma nevirapine concentrations. The large variability in nevirapine concentrations in women may lead to loss of efficacy and viral resistance, or drug toxicity, and therefore these patients should be monitored frequently.
Absence of HCV viral recombination following superinfection
Authors: Bernardin F. , Herring B. , Page‐Shafer K. , Kuiken C. , Delwart E.
Published: April 2006

Summary.  We sought evidence of viral recombination in five recently hepatitis C virus (HCV) infected young injection drug users who became superinfected with a distinguishable strain of HCV. The entire open reading frame of plasma HCV genomes was reverse transcribed, polymerase chain reaction amplified in two fragments, and directly sequenced. In two cases of same subtype (1a>1a) superinfections the initial and later strains were both sequenced and compared for evidence of recombination. In three cases of superinfection with strains of different genotype/subtype (3a>1a, 1a>3a, 1b>1a), the later time point HCV genomes were sequenced and compared with representative genomes of the initial genotype/subtype. No evidence of intra‐ or inter‐genotype/subtype recombination was detected using six different programs for detecting recombination. We conclude that the generation of viable recombinant HCV genomes able to dominate in the viral quasispecies is a rare event.
Cost‐effectiveness analysis in glaucoma: what drives utility? Results from a pilot study in Sweden
Authors: Kobelt Gisela , Jonsson Björn , Bergström Anders , Chen Enping , Lindén Christina , Alm Albert
Published: April 2006

Purpose:  To investigate the effect of different levels of visual field defect in glaucoma on utilities and to test if utilities could be assessed using a general questionnaire such as the EQ‐5D.

Methods:  A cross‐sectional study in 199 patients with ocular hypertension or open‐angle glaucoma grouped into 5 severity stages according to visual field defects was performed in 4 specialized ophthalmic centres. Descriptive analysis was performed for the sample and by stage, and the effect of vision loss on utility was investigated with multiple step‐wise regression analysis.

Results:  The mean age of the sample was 70 and the mean MD in the worse eye was −13.1 dB (SD 10.2). Visual acuity (VA) was 0.63 and 0.87 in the worse and better eye, respectively, and the mean utility was 0.80 (SD 0.23). Utility decreased with increasing glaucomatous damage, ranging from 0.84 for mild disease to 0.72 for severe damage (MD −2.5 to −28.1), but the difference between the groups was not statistically significant when controlling for co‐morbidity, except for the most severe stage (p < 0.01). In multiple regression analysis, visual field in the better eye was significantly correlated with utility, and there was an indirect correlation between visual field in the worse eye and utility: the effect of total VA on utility was significant, and MD in the worse eye was correlated with total VA.

Conclusions:  Utility is strongly correlated with overall vision. Our results suggest a relationship between glaucomatous damage and utility, and patients with severe damage have a significantly lower utility. However, this should be further investigated in larger samples that include more patients with moderate‐severe bilateral damage.