bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Diffusion Factor of Neon from Column Measurements
Authors: Raman S. , Dave S. M. , Narayanan T. K. S.
Published: December 2004

Thermal diffusion factor of neon at 300.5 °K has been determined to be 0.0205 ± 0.002, by means of separation studies, with and without the introduction of spacers, in a hot-wire thermal diffusion column of 1.42 m length. The theory propounded earlier by the authors for evaluation of parasitic remixing is used. Within the experimental error the above value agrees fairly well with the calculated value on the basis of exp −6 potential model.
Thomson Scattering Measurements of Magnetic Annular Shock Tube Plasmas
Authors: Patrick Richard M.
Published: December 2004

Measurements of Thomson scattering from the plasma electrons created by high speed shock waves in a magnetic annular shock tube have been used to determine the electron density behind shock waves and some preliminary measurements of the electron velocity distribution. A Q-switched ruby laser furnished the light beam which was scattered by the plasma electrons. A rotating quartz prism furnished the Q-switching of the optical cavity for the ruby laser, and rather long Q-switched pulses were obtained (between 10−7 and 10−6 sec duration). The power level during the Q-switched pulse was between 30 and 100 mW. Rayleigh scattering from an air sample at various pressures was used to calibrate the power output of the laser and gave for all of the tests a simultaneous measure of the laser output power, while the Thomson scattering was being measured. The measurements of the electron density using the Thomson scattering and the plasma continuum intensities agreed within the scatter of the data. The electron temperature measurements obtained with the Thomson scattering showed that the electron temperature increased with increasing shock speed for a given initial condition.
Adiabatic Containment of Charged Particles in Combined Mirror-Multipole Cusp Magnetic Fields
Authors: Siambis J. G. , Trivelpiece A. W.
Published: December 2004

Properties of combined mirror-multiple cusp magnetic fields and the motion of charged particles in such fields are presented for the cases of mirror-quadrupole and mirror-hexapole fields. The two methods used to study the motion numerically are: the adiabatic motion in terms of the magnetic moment and longitudinal invariant of the particle; and the guiding center motion. The regions of stable containment in these field configurations are determined by means of the adiabatic motion. The guiding center motion is used to determine when the simpler method of the adiabatic motion is valid. For weakly stabilized field configurations, the adiabatic motion is valid; however, for strongly stabilized field configurations, the guiding center motion shows that the adiabatic dsecription has a very limited range of validity. In addition, the effects of shear and torsion of the field on the guiding center motion are shown.
Small Amplitude Wave Propagation in Hot Ionized Gases
Authors: Khosla P. K. , Murgai M. P.
Published: December 2004

Radiative transfer effects on both the forced and the free small-amplitude wave propagation problem in an ordinary as well as an ionized gas have been investigated. The results predict an additional radiation induced mode. For an ionized medium, in the presence of a magnetic field, we have the Alfvén wave, adiabatic and isothermal magnetosonic, fast and slow waves. These investigations also show that the skin depth for the waves is proportional to the mean free path of the radiation and the lifetime to the time taken by a sound wave to travel a distance equal to the wavelength or radiation mean free path. The magnetic field seems to support the propagation of some modes, but oppose that of the radiation induced wave in an ionized medium.
Approximate Solution of the Shear Flow Boundary Layer on a Flat Plate
Authors: Devan Leroy
Published: December 2004

A nonsimilar solution of the incompressible boundary layer over a flat plate in the presence of shear flow is considered. The Dorodnitzyn method of approximate solution, utilizing integral relations, is applied to Crocco forms of the boundary layer equations. Agreement is obtained with the similar solutions of Ting. The computations provide numerical results for the transition between the cases of Li and Murray and of Ting.
Hall Effect in the Two-Dimensional Flow along an Insulating Plane
Authors: Hasimoto H. , Janowitz G. S.
Published: December 2004

Two-dimensional flow of a conducting gas interacting weakly with an external inhomogeneous magnetic field is considered. It is proved that for flow over an insulating wall, the total drag force is reduced by the Hall effect, and the total transverse force is zero. General expressions for the Hall current and the induced transversal flow are obtained for the case of flow with small Hall parameter over an infinite insulating plane. Examples are given for the dipole magnetic field. An inversion of the transversal flow, varying with the dipole orientation, is found. This situation also suggests a transversal deflection of the flow behind a magnetized body in the flow of a plasma.
Transverse Wave Motion on a Thin Capillary Jet of a Viscous Liquid
Authors: Middleman S. , Gavis J.
Published: December 2004

An analysis for the transverse wave patterns observed on jets of viscous Newtonian liquids upon ejection from sinusoidally, transversely vibrating capillary nozzles into air is presented. Propagation is controlled by fluid density and surface tension, and is affected by viscosity. The analysis is a linearized one, which ignores internal motion of the jet fluid, but accounts satisfactorily for viscous dissipation. The analysis is compared with experimental data. Discrepancies are accounted for by the linearization processes in the analysis.
Thermodynamic Properties of 3He and 4He Solutions. III. A Refinement in Excess Functions Above the Superfluid Transition in Solution
Authors: Nanda V. S. , Chandra R.
Published: December 2004

A semiclassical approach to the problem of 3He and 4He solutions for temperatures above the superfluid transition in solution was presented earlier by Chandra and Nanda. The question of a proper choice of the nonideality parameter is now considered. A satisfactory representation of the excess chemical potentials, excess enthalpy, and excess entropy is thus obtained. The contributions of the like and unlike pairs to the cohesion in the solution are also compared.
Experiment on the Intrusion of Plasma into a Simulated Magnetic Cavity
Authors: Kawashima Nobuki , Mori Sigeru
Published: December 2004

The interaction of a plasma stream with a three-dimensional dipole has been experimentally investigated. The time-resolved photographs, magnetic probe and Rogowski coil measurement, and double probe measurement showed the intrusion of plasma in the magnetic cavity. Plasma and current distribution is found to be asymmetric with respect to the plasma gun-dipole line and the direction of the current in the magnetic cavity corresponds to the westward one around the earth.
Completeness Property of Solutions of the Relaxation Problem in Kinetic Theory
Authors: Ferziger J. H.
Published: December 2004

It is shown that the separation of variables solution of the kinetic theory relaxation problem yields a complete set of eigenfunctions provided generalized functions are admitted as solutions. The presence of a continuum of eigenfunctions is explicitly exhibited and it is shown how the theory of singular integral equations can be utilized to give a solution of the initial value problem.
Microscopic Fluctuations and Diffusion Coefficients of a Nonequilibrium Plasma in a Magnetic Field
Authors: Weinstock Jerome
Published: December 2004

A relationship is deduced between the electron density correlation function and the ``parallel'' and ``perpendicular'' diffusion coefficient of a partially ionized nonequilibrium (but homogeneous) plasma in an external magnetic field. This relationship is derived in a particularly simple and direct way from within the rigorous framework of microscopic theory by expanding the Fourier transform of the microscopic electron density in terms of semi-invariants. The previous result derived by Ichimaru—by means of hydrodynamic arguments—is seen to be a special case of the present result.
Explosions in Rarefied Atmospheres
Authors: Stuart G. W.
Published: December 2004

Explosions in cold, homogeneous atmospheres are considered; initially the mean free path of an explosive-product atom through the atmosphere is much longer than the dimension of the expanding material. On the basis that a uniform expansion persists for all time, a snowplow model is derived from the virial theorem and is used to describe the expansion. To illustrate the method, a chemical explosion in the earth's atmosphere at 150-km altitude is analyzed.
Definition of Temperature in Nonequilibrium Processes
Authors: Mates Robert E. , Weatherston Roger C.
Published: December 2004

The validity of using a multiple-temperature heat bath model for the description of nonequilibrium processes is examined. Several models have been proposed which utilize temperatures defined by statistical distribution functions or chemical mass action laws. Since, however, the heat bath model is described by classical thermodynamic temperatures which are defined in terms of heat exchange between a reversible engine and energy reservoirs, the validity of such models requires justification. It is shown that the classical thermodynamic temperature can sometimes be used to characterize a particular degree of freedom, such as vibration, even if it is not in equilibrium with the other degrees of freedom. However, it does not appear to be possible in general to associate a thermodynamic temperature with a nonequilibrium chemical composition. To demonstrate this, the entropy rise in vibrational and chemical nonequilibrium processes is computed using the concept of multiple temperatures and compared to the classical result. The results agree for vibrational nonequilibrium. For chemical nonequilibrium the results do not agree except for chemical systems in which the reactants and products have equal constant volume mass specific heats. An example of such a system is the ideal dissociating gas of Lighthill.
Continuous Radiation from Regions not in Local Thermodynamic Equilibrium
Authors: Stuart G. W. , Vulliet W. G.
Published: December 2004

It is known that at sufficiently low density an optically thin medium cannot be in local thermodynamic equilibrium. For this regime, we employ a model to calculate the maximum deviation of the continuous radiation rate (free—bound and free—free) from this quantity obtained assuming local thermodynamic equilibrium, the usual procedure. The comparison is on the basis of constant energy density (erg/cm3), a quantity independent of local thermodynamic equilibrium. Attention is restricted to local thermodynamic equilibrium temperatures between 1 and 10 eV. It is found that the continuous radiation rate is fairly insensitive to the local thermodynamic equilibrium condition.
Calculation of the Singularities of a Magnetic Field
Authors: Greene John M.
Published: December 2004

This work is concerned with one problem which arises when finding the external magnetic field necessary to support a hydromagnetic configuration. If the hydromagnetic configuration is given without regard to the vacuum field that contains it, then that external vacuum field will in general have singularities at a finite distance from the fluid-vacuum boundary. The location of these singularities is considered. This is a good thing to know since it provides the essential limitation to the position of the external current system that ultimately contains the fluid.
Magnetic-Dipole-Induced Plasma Motions
Authors: Yoshihara H. , Thommen H.
Published: December 2004

A supersonic flow of an electron plasma past a weak magnetic dipole is examined using a linearized set of two-species continuum plasma equations. The resulting perturbations were found to exhibit both a hyperbolic as well as an elliptic behavior. The results as found are not directly applicable to the solar wind interaction with the geomagnetic dipole, but they strongly suggest the necessity of re-examining the validity of magnetospheric models of the interaction, starting from the full two-species plasma equations.
Relationship for Plasma Sheaths about Langmuir Probes
Authors: Bettinger Richard T. , Walker Evan Harris
Published: December 2004

In order to arrive at ion and electron concentrations, temperatures, etc., from Langmuir probe data, one uses the Mott-Smith-Langmuir equations and, in most cases, a rather arbitrary assumption of a fixed value of sheath thickness. This approach has obvious limitations since the sheath's properties are not fixed but must depend on the potential and size of the probe; sheath thickness is clearly zero at zero potential. Walker has treated the nonlinear screening problem for the case of spherical bodies in collisionless monoenergetic and Maxwellian plasmas. The calculations are elaborate, but results can be displayed graphically or given by approximate analytic expressions. We have extracted from these a relationship for the sheath thickness s in terms of the probe's radius ρ and potential ψ, for use in the Mott-Smith-Langmuir equations: s = 0.83 ψ½ ρ⅓; where s, ρ are measured in Debye lengths ψ in terms of kT. For the case of cylindrical symmetry, s = 1.66 ψ¾, and depends only weakly on ρ.
Kinetic-Theory Approach to the Problem of Shock-Wave Structure in a Binary Mixture
Authors: Oberai Madan Mohan
Published: December 2004

The method of Mott-Smith is extended to the study of the shock-wave structure in a mixture of two monatomic inert gases. Given the steady state ahead of the shock and assuming a bimodal velocity distribution function for each component gas, the steady state behind the shock is obtained with the help of the conservation equations. One additional transfer equation is needed to obtain differential equations giving number-density distribution within the shock; the collision integral for this equation is calculated on the assumption that the molecules obey Maxwellian law of force. The case where the initial mixture contains only a small fraction (α) of the second gas is studied in detail: expanding various characteristics in power series of α, analytical expression for the first approximation is obtained. The solution is, for all values of the shock strength and for all values of the mass ratio of the two gases, free from the anomaly found by Sherman who solved this problem in the frame-work of Navier-Stokes equations. For two specific cases, the velocity profiles calculated from this approximation are explicitly given.
Experiments with Magnetohydrodynamically Supported Shock Layers
Authors: Locke E. , Petschek H. E. , Rose P. H.
Published: December 2004

Shock tube experiments have been performed to quantitatively determine the interaction of a hypersonic flow with the magnetic field of a straight current-carrying wire oriented perpendicular to the flow direction. The interaction which takes place in a thin layer behind a detached shock wave is subject to the following restrictions: (1) Negligible conductivity upstream of the shock, (2) low magnetic Reynolds number, and (3) scalar conductivity in the shock layer. The straight wire geometry under these restrictions has been analyzed theoretically by Levy and Petschek. The analysis, which is briefly reviewed, predicts the location of a thin shock layer which is concentric with the wire. Most of the experimental work was performed in a 50–50 mixture of argon and oxygen, at an initial pressure of 1 mm Hg, and in a range of shock velocities between 4.3 and 6 mm/μsec. Data have been obtained by observing the flow luminosity, using an image converter and mirror camera looking both perpendicular to and along the wire. A circular shock front was observed to stand up to 5½ cm in front of a 1-cm-radius cylinder producing the magnetic field. The data on shock position versus current were in surprisingly good agreement with theory in view of the fact that at a density ratio across the shock of 0.25 the theory was not expected to predict the shock position to accuracies better than a factor of two.
Nonlinear Stability of the Extraordinary Wave in a Plasma
Authors: Engel Robert D.
Published: December 2004

The linear theory predicts that certain anisotropic velocity distributions will produce unstable extraordinary waves. The development of these unstable waves in the nonlinear regime is investigated and their final amplitudes are estimated. The analysis is restricted to infinite homogeneous plasmas where the background distribution and the wave energy density may be considered as slowly varying functions of time. A set of nonlinear integro-differential equations, which describe the evolution of the system, are derived and discussed. For the physically interesting case where the wave frequency is much less than the cyclotron frequency, the basic behavior of the system and the characteristics of the equilibrium solutions may be estimated without computing the transient behavior of the system. For this case, it is shown that the main diffusion of the background distribution occurs along the v = const lines, in which v is the magnitude of the velocity. Since these lines are also constant energy lines, very little energy is transferred to the waves during the diffusion process. A Maxwellian plasma which has been disturbed by injecting a stream of electrons into it is considered as an example.
General Criterion for Mirror Instability of a Plasma
Authors: Rose D. J.
Published: December 2004

A plasma column in an axial magnetic induction B exhibits the well-recognized ``mirror'' instability if the pressure p⊥ perpendicular to B becomes too high, as follows. A small azimuthally symmetric bulge in the field may trap additional plasma via the usual mirror effect. The increased diamagnetism further weakens the field in the bulge, thus trapping more plasma, and so forth. The criterion for stability against this mode for an azimuthally symmetric velocity distribution function f(v, θ) is ∫ 0∞dv ∫ 0π/2 dθ πmv4sin3θtanθ∂f∂θ<Be22μ0[1−β+κρK0(κρ)2K1(κρ)]. Here, v is speed, m is mass, θ is colatitude angle, and Be is the uniform induction outside the plasma; β=2μ0p⊥/Be2 is (plasma perpendicular pressure/total pressure), κ is axial wavenumber of the unstable mode, and ρ is plasma column radius; K0 and K1 are modified Bessel functions of the second kind. The integral is a measure of changing p⊥ if an incipient bulge forms in the plasma column; the κρ term represents stabilizing effect of a finite wavelength perturbation. This criterion is more general than the two-temperature criteria obtained hitherto.
Collision Integrals for the Exponential Attractive Potential
Authors: Munn R. J. , Mason E. A. , Smith Francis J.
Published: December 2004

Collision integrals for the exponential attractive potential are calculated by accurate numerical integration. There are some unexpected differences from what had been expected by analogy with inverse power attractive potentials. Some implications of these results for the calculation of high-temperature gas transport properties are discussed.
High-Frequency Conductivity of a Plasma
Authors: Thourson T. L. , Lewis M. B.
Published: December 2004

The high-frequency conductivity of a fully ionized plasma is calculated from the Bogoliubov—Born—Green—Kirkwood—Yvon equations for a plasma subjected to an applied field. These equations are used in the plasma limit but with the further approximation that those terms which lead to a screened Coulomb potential are replaced by a Coulomb potential with a range of the Debye length. This leads to a generalized Fokker—Planck equation, i.e., the collisional term has a more general space and time dependence than the usual Fokker—Planck equation. The equation is linearized about equilibrium and is solved by assuming that the effect of the field dominates the effect of the collisions. The effects of electron—electron as well as electron—ion collisions are considered and the results are calculated to second order in the wavenumber.
Effects of Low-Frequency Instabilities on Plasma Surface Waves
Authors: Napoli L. S. , Swartz G. A. , Wexler H. T.
Published: December 2004

Surface wave propagation experiments have been performed on a fluctuating-density plasma column. The wave is a highly attenuated backward wave in which the energy is being transferred to sideband frequencies. The amplitude of the sideband increases as the wave progresses down the plasma column. The total energy of the composite wave is conserved except for a loss due to electron—neutral collisions.
Microwave Emission from a Fully Ionized Plasma
Authors: Kuckes A. F. , Wong A. Y.
Published: December 2004

The microwave radiation from a fully ionized thermal plasma was observed as a function of magnetic confining field and plasma density. The plasma generated radiation was found to be in substantial agreement with a theory based on the high frequency resistivity computed by Dawson and Oberman in the range of plasma density 0.01 < ωp2/ω2 < 0.1 and magnetic field 0.7 < ωc/ω < 1.25 (ω/2π = 35 Gc/sec).
Stability of a Homogeneous Fluid Cooled Uniformly from Above
Authors: Foster Theodore D.
Published: December 2004

The stability of an initially homogeneous layer of fluid which is cooled uniformly from above is examined. A simplified mathematical model in which the velocity and temperature perturbations vanish at the top and bottom boundaries but which takes into account nonlinear, time-dependent temperature profiles is developed. Solution of the stability equation is achieved by expanding the velocity perturbation in a Fourier sine series with time dependent coefficients and solving the resulting system of coupled differential equations numerically. The initial behavior of the system is found to depend upon the Rayleigh and Prandtl numbers. For large Rayleigh numbers the time needed for the system to manifest convective behavior is independent of the depth of the fluid layer but depends on the rate and manner of cooling and on the properties of the fluid. For large Rayleigh numbers, the horizontal wavenumber of disturbances which are amplified the most when convective behavior is manifest in the system also is independent of the depth of the fluid layer but depends on the rate and manner of cooling and on the properties of the fluid.
Motion of a Test Particle in a Plasma
Authors: Perkins Francis
Published: December 2004

The motion of a charged test particle in a completely ionized gas without a magnetic field is investigated. The possible trajectories of this test particle are described by a distribution function that spreads out in phase space as time increases. A convergent kinetic equation which accounts for long-range collective effects and short-range collisions in a consistent manner is derived to describe the time evolution of the distribution function. Expressions for the energy loss rate and dynamical friction are calculated from appropriate moments of the kinetic equation, and they show how the Coulomb logarithm, ln Λ, varies with the velocity of the test particle. The errors introduced by the use of a convergent kinetic equation are estimated, and these indicate that the kinetic equation method gives the test particle's diffusion in phase space only on coarse grained time and spatial scales. For the case of a fast electron, the time scale must be larger than the electron plasma period and the spatial scale larger than e2/KT.
Instabilities of ``Top-Hat'' Jets and Wakes in Compressible Fluids
Authors: Gill A. E.
Published: December 2004

The stability of jets or wakes in a compressible fluid is examined for the case of ``top-hat'' velocity profiles, where the jet or wake is a region of uniform velocity separated on either side from the external uniform flow by a vortex sheet. In both the two-dimensional and axisymmetric cases, these jets or wakes are unstable at all Mach numbers to disturbances of all nonzero wavenumbers. For subsonic flows and for disturbances to supersonic flows of sufficiently small wavenumbers, there are only a few unstable modes (one for each symmetry in the two-dimensional case and one for each azimuthal Fourier component in the axisymmetric case), but for sufficiently rapid flows and for disturbances whose wavenumber is not too small, there are a large number of unstable modes. These are made possible by the transfer of energy across the jet or wake by sound waves, and the different modes correspond to the different numbers of waves that it is possible to ``fit in.'' There is an enhanced instability when the sound waves within a top-hat jet or wake reflect at certain resonant angles.
Convergence of the Chapman-Enskog Expansion for the Linearized Boltzmann Equation
Authors: McLennan James A.
Published: December 2004

The convergence of the Chapman-Enskog expansion for the linearized Boltzmann equation is discussed, using methods of perturbation theory. It is shown that, under suitable conditions, a normal solution exists, and has a convergent perturbation expansion, for processes which vary sufficiently slowly; furthermore, the normal solution dominates all other solutions with the passage of time. The necessary conditions are such as to make the total scattering cross section nonvanishing at high energy. This is the case in classical theory for any cutoff potential and in quantum theory for hardcore potentials. In contrast, if the cross section vanishes at high energy, then there is no normal solution with similar properties.
Resistive Instability of Shearing Magnetic Fields in an Incompressible Plasma
Authors: Lessen Martin , Deshpande Narayan
Published: December 2004

The stability of a shearing magnetic field in an incompressible plasma is examined, and it is found that the existence of a ``resistive'' mode of instability is questionable.
Hydromagnetically Stable Periodic Magnetic Field
Authors: BenDaniel D. J.
Published: December 2004

Results of the analysis of a class of periodic magnetic fields which have the property that the flux tube volume can decrease in the θ = 0 plane and increase in the θ = ½π plane. By symmetrizing the system with connecting regions between semistable units, closed surfaces of flux tube volume with negative gradient are obtained. Quadrupole and quadrupole-octupole stabilization is considered. Realizable current configurations are proposed for stabilizing a periodic mirror system.
Time-Dependent Ambipolar Diffusion Waves
Authors: Shimony Z. , Cahn J. H.
Published: December 2004

A theory for the propagation of a plasma into an ambient gas is proposed. It is an extension of the usual ambipolar diffusion which takes into account the inertia of the particles and predicts a finite velocity for the propagation of the plasma. The equation ∇2ne=(1/u2)(∂2ne/∂t2)+(1/Da)(∂ne/∂t)is obtained for the electron density in the expanding plasma, where u = (Daνa)½, Da is the ambipolar diffusion coefficient and νa is an ``ambipolar collision frequency.'' u gives the speed of propagation of the plasma interface and is equal to the velocity (kTe/Mi)½, if the electron temperature Te is much higher than the ion temperature. This equation is solved in one-dimensional geometry and some characteristics of the solution discussed. It is shown that the maximum density of the plasma propagates with speed u in the case of low pressure of the gas but with much lower speed in the case of higher pressure.
A Haptic Face-Inversion Effect
Authors: Kilgour Andrea R , Lederman Susan J
Published: December 2004

We examined whether a face-inversion effect occurs when participants explore faces by touch. We used a haptic version of the inversion paradigm with 3-D clay facemasks and non-face control objects (teapots) moulded from real objects. Young, neurologically intact, blindfolded participants performed a temporally unconstrained haptic same/different task in each of four stimulus conditions: upright facemasks, inverted facemasks, upright teapots, and inverted teapots. There was a significant inversion effect for faces in terms of accuracy, but none for teapots. The results are considered in terms of the consequences of sequential manual exploration for haptic face processing.
Regional Variation in the Inversion Effect for Faces: Differential Effects for Feature Shape, Feature Configuration, and External Contour
Authors: Malcolm George L , Leung Connie , Barton Jason J S
Published: December 2004

Faces are perceived via an orientation-dependent expert mechanism. We previously showed that inversion impaired perception of the spatial relations of features more in the lower face than in the (more salient) upper face, suggests a failure to rapidly process this type of structural data from the entire face. In this study we wished to determine if this interaction between inversion and regional salience, which we consider a marker for efficient whole-face processing, was specific to second-order (coordinate) spatial relations or also affected other types of structural information in faces. We used an oddity paradigm to test the ability of seventeen subjects to discriminate changes in feature size, feature spatial relations, and external contour in both the upper and lower face. We also tested fourteen subjects on perception of two different types of spatial relations: second-order changes that create plausible alternative faces, and illegal spatial changes that transgress normal rules of facial geometry. In both experiments we examined for asymmetries between upper-face and lower-face perceptual accuracy with brief stimulus presentations. While all structural changes were less easily discerned in inverted faces, only changes to spatial relations showed a marked asymmetry between the upper and lower face, with far worse performance in the mouth region. Furthermore, this asymmetry was found only for second-order spatial relations and not illegal spatial changes. These results suggest that the orientation-dependent face mechanism has a rapid whole-face processing capacity specific to the internal second-order (coordinate) spatial relations of facial features.
Taxonomy of Castroviejoa, a new genus of Gnaphalieae (Asteraceae), endemic to the Mediterranean Islands Corsica and Sardinia
Authors: Galbany-Casals M. , Sáez L. , Benedí Carles
Published: December 2004

Castroviejoa Galbany, L. S�ez & Bened� has been recently described as a new genus of Gnaphalieae, and comprises the two Mediterranean species Castroviejoa frigida (Labill.) Galbany, L. S�ez & Bened� and C. montelinasana (Schmid) Galbany, L. S�ez & Bened�, formerly known as Helichrysum frigidum (Labill.) Willd. and H. montelinasanum Schmid. In the present paper their morphology is accurately described and compared with that of Helichrysum and related genera. These two species present three morphological characters that are not found together in other Helichrysum species, and which characterise the genus Castroviejoa: the multicellular, biseriate, glandular hairs present on the corolla tube; the undivided stereome; and the apical sweeping hairs that also extend dorsally along the style branches. The full taxonomic treatment of the new genus is provided.
Variation in Australian populations of Halfordia kendack s.l. (Rutaceae): evidence from leaf essential oils
Authors: Forster Paul I. , Brophy Joseph J. , Goldsack Robert J.
Published: December 2004

The leaf oils of Halfordia kendack (Montrouz.) Guillaumin s.l. from locations throughout its range in Australia were investigated to ascertain if the disjunct nature of the species' distribution affected their composition and whether any variation detected supported the recognition of a second species (H. scleroxyla F.Muell.). While three groups of populations could be classified on the basis of leaf oil composition, these groups were not associated with geographic locality or altitudinal range and habitat. It was found that plants from low altitude sites in north Queensland all produced leaf oils that contained the aromatic ethers methyl eugenol and elemicin in variable amounts, included in an otherwise terpenoid oil. Plants from the other three areas examined; north Queensland montane sites, south-east Queensland low altitude and south-east Queensland montane sites, all produced leaf oils which were terpenoid in nature and contained no aromatic ethers. This lack of correlation in leaf oil composition with locality or habitat would lend support to the proposition that Halfordia exists in only one variable species in Australia.
Patch use by the greater glider (Petauroides volans) in a fragmented forest ecosystem. III. Night-time use of trees
Authors: Cunningham R. B. , Pope M. L. , Lindenmayer D. B.
Published: December 2004

Night-time use of feed trees by 40 radio-collared individuals of the greater glider (Petauroides volans) was recorded within five remnant patches of eucalypt forest near Tumut in south-eastern Australia. Radio-collared animals were observed making 663 night-time visits to 433 trees. For these observations, we recorded the number of visits by an animal to each tree, the number of different animals using each tree, the characteristics of trees that animals used, and the category of activity or behaviour displayed by animals (classified as feeding, perching, and moving).
We found no evidence of a significant difference in patterns of behaviour between male and female P. volans in their night-time use of trees within remnant patches, regardless of patch size or population density. There were few records of animals (4%) from the radiata pine (Pinus radiata) plantation that surrounded the eucalypt remnants, although 20 observations were made of P. volans feeding on the young male cones and buds of this introduced tree species. There was evidence of preference for feeding in ribbon gum (Eucalyptus viminalis), mountain gum (E. dalrympleana) and narrow-leaved peppermint (E. radiata), with 72% of feeding observations of P. volans coming from these three tree species. Animals were generally solitary and spent most of the night feeding and perching in the upper canopy. Most trees were used by a single individual, with 96% of observations being of a single animal in a tree. The limited number of cases of sharing and co-use of trees were generally between an adult male and adult female (assumed mates), and females and their young. The probability that a tree was used increased with the average size of a tree (a composite measure of diameter, height and crown features) until approaching an asymptote of 1.0, i.e. all large trees were used. The number of visits a tree received from P. volans also was positively related to the measure of its size.
Can farm-management practices reduce the impact of house mouse populations on crops in an irrigated farming system?
Authors: Brown Peter R. , Davies Micah J. , Singleton Grant R. , Croft J. David
Published: December 2004

The impacts of a range of farm-management practices on house mouse (Mus domesticus) populations were tested in a large replicated field study in a complex irrigated farming system in southern New South Wales, Australia. An advisory panel, made up of farmers, extension officers, industry representatives and scientists developed a series of best-practice farm-management actions to minimise the impact of mice. Twelve experimental sites were split into six treated sites, where farmers were encouraged to conduct the recommended practices, and six untreated sites, where farmers conducted their normal farming practices. Mouse abundance was generally low to moderate for the 4-year project (5–60% adjusted trap success). We found significant reductions in population abundance of mice on treated sites when densities were moderate, but no differences when densities were low. Biomass of weeds and grasses around the perimeter of crops were significantly lower on treated sites because of applications of herbicide sprays and grazing by sheep. We could not detect any significant difference in mouse damage to crops between treated and untreated sites; however, levels of damage were low (<5%). Yields of winter cereals and rice crops were significantly higher on treated sites by up to 40%. An analysis of benefits and costs of conducting farming practices on treated sites compared with untreated sites showed a 2 : 1 benefit to cost ratio for winter cereals, 9 : 1 for rice and 4 : 1 for soybeans.
Microtubule-binding drugs offset tau sequestration by stabilizing microtubules and reversing fast axonal transport deficits in a tauopathy model
Authors: Zhang Bin , Maiti Arpita , Shively Sharon , Lakhani Fara , McDonald-Jones Gaye , Bruce Jennifer , Lee Edward B. , Xie Sharon X. , Joyce Sonali , Li Chi , Toleikis Philip M. , Lee Virginia M.-Y. , Trojanowski John Q.
Published: December 2004

We tested the hypothesis that microtubule (MT)-binding drugs could be therapeutically beneficial in tauopathies by functionally substituting for the MT-binding protein tau, which is sequestered into inclusions of human tauopathies and transgenic mouse models thereof. Transgenic mice were treated for 12 weeks with weekly i.p. injections of 10 or 25 mg/m
2
paclitaxel (Paxceed). Both doses restored fast axonal transport in spinal axons, wherein MT numbers and stable (detyrosinated) tubulins were increased, compared with sham treatment, and only Paxceed ameliorated motor impairments in tau transgenic mice. Thus, MT-stabilizing drugs could have therapeutic potential for treating neurodegenerative tauopathies by offsetting losses of tau function that result from the sequestration of this MT-stabilizing protein into filamentous inclusions.
Sequential multiple functions of the conserved sequence in sequence-specific termination by T7 RNA polymerase
Authors: Sohn Younghee , Kang Changwon
Published: December 2004

Escherichia coli rrn
B terminator t1 contains an RNA hairpin-dependent (class I) and a sequence-specific (class II) termination signal. The latter consists of an 8-bp conserved sequence (CS), TATCTGTT, immediately followed by an 8-bp T rich sequence. In this study, elongation complexes of T7 RNA polymerase at various positions of the class II signal and several mutant signals were obtained by stepwise walking on immobilized DNA templates free of the class I signal. Multiple CS-associated conformational changes were observed, starting at the beginning of the signal and occurring sequentially. When the complexes reach the first base pair of the CS–DNA duplex, which is downstream of the RNA–DNA heteroduplex, their stability, as measured by time-course retention of radiolabeled transcripts, markedly decreases. Further elongation leads to an abrupt change in polymerase–RNA interaction. Cross-linking of the polymerase to a 4-thio-UMP incorporated into RNA 8 nucleotides upstream of the 3′ end and just upstream of the heteroduplex is initially strong but diminishes when the polymerase reaches the fourth base pair of the CS. After a further 7-nt elongation, the exposed single-stranded region of nontemplate strand is contracted; RNA in the upstream half of the heteroduplex becomes dissociated, and the CS–DNA duplex is reformed. During the next 5-nt elongation before termination, the CS duplex is prevented from translocation, and the contracted transcription bubble expands only downstream. These findings suggest that the CS duplex plays essential roles by successively binding to polymerase both downstream and upstream of the heteroduplex.
On the capturing of low-energy electrons by DNA
Authors: Ray S. G. , Daube S. S. , Naaman R.
Published: December 2004

Many of the mutagenic or lethal effects of ionization radiation can be attributed to damage caused to the DNA by low-energy electrons. To gain insight on the parameters affecting this process, we measured the low-energy electron (<2 eV) transmission yield through self-assembled monolayers of short DNA oligomers. The electrons that are not transmitted are captured by the layer. Hence, the transmission reflects the capturing efficiency of the electrons by the layer. The dependence of the capturing probability on the base sequence was studied, as was the state of the captured electrons. It is found that the capturing probability scales with the number of G bases in the single-stranded oligomers and depends on their clustering level. Using two-photon photoelectron spectroscopy, we find that, once captured, the electrons do not reside on the bases. Rather, the state of the captured electrons is insensitive to the sequence of the oligomer. Double-stranded DNA does not capture electrons as efficiently as single-stranded oligomers; however, once captured, the electrons are bound more strongly than to the single strands.
Evidence for a p27 tumor suppressive function independent of its role regulating cell proliferation in the prostate
Authors: Shaffer David R. , Viale Agnes , Ishiwata Ryota , Leversha Margaret , Olgac Semra , Manova Katia , Satagopan Jaya , Scher Howard , Koff Andrew
Published: December 2004

Reduced p27 levels correlate with poor prognosis in a wide spectrum of human tumors and can accelerate tumorigenesis in mouse tissues. To determine whether p27 deficiency can accelerate tumorigenesis in tissues with inactive Rb and p53 pathways, we examined the effect of p27 status on prostate tumorigenesis in mice expressing simian virus 40 large T antigen (LT). In p27-deficient mice expressing LT, tumors progressed from high-grade prostatic intraepithelial neoplasia to poorly differentiated carcinoma at a greatly accelerated rate. p27 deficiency could not collaborate with a mutant of LT that fails to inactivate the Rb pathway alone. Furthermore, p27 deficiency does not increase the proliferation index, reduce the apoptotic index, or affect the expression of E2F-dependent genes in cells expressing LT at any stage of the disease. Expression of LT alone leads to maximal proliferation, but p27 deficiency still increases the amount of cyclin A and cyclin-dependent kinase 2-associated kinase activity in tissues. Interestingly, this model recapitulates an important feature of the human disease, specifically a high frequency of allelic loss of chromosome 16q, which is syntenic to mouse chromosome 8. Loss of heterozygosity may accelerate the inactivation of other tumor suppressors, such as E-cadherin, which are located in this interval. These experiments provide direct physiological and causal evidence that p27 has tumor suppressive functions independent of its role regulating cell proliferation.
Phospholipase D Is Involved in Myogenic Differentiation through Remodeling of Actin Cytoskeleton
Authors: Komati Hiba , Naro Fabio , Mebarek Saida , De Arcangelis Vania , Adamo Sergio , Lagarde Michel , Prigent Annie-France , Némoz Georges
Published: December 2004

We investigated the role of phospholipase D (PLD) and its product phosphatidic acid (PA) in myogenic differentiation of cultured L6 rat skeletal myoblasts. Arginine-vasopressin (AVP), a differentiation inducer, rapidly activated PLD in a Rho-dependent way, as shown by almost total suppression of activation by C3 exotoxin pretreatment. Addition of 1-butanol, which selectively inhibits PA production by PLD, markedly decreased AVP-induced myogenesis. Conversely, myogenesis was potentiated by PLD1b isoform overexpression but not by PLD2 overexpression, establishing that PLD1 is involved in this process. The expression of the PLD isoforms was differentially regulated during differentiation. AVP stimulation of myoblasts induced the rapid formation of stress fiber-like actin structures (SFLSs). 1-Butanol selectively inhibited this response, whereas PLD1b overexpression induced SFLS formation, showing that it was PLD dependent. Endogenous PLD1 was located at the level of SFLSs, and by means of an intracellularly expressed fluorescent probe, PA was shown to be accumulated along these structures in response to AVP. In addition, AVP induced a PLD-dependent neosynthesis of phosphatidylinositol 4,5-bisphosphate (PIP2), which also was accumulated along actin fibers. These data support the hypothesis that PLD participates in myogenesis through PA- and PIP2-dependent actin fiber formation.
Confined developable elastic surfaces: cylinders, cones and the
Elastica
Authors: Cerda E. , Mahadevan L.
Published: December 2004

We consider two of the simplest problems associated with the packing of a naturally
flat thin elastic sheet. Both problems involve packing the sheet into a hollow cylinder;
the first considers the partial contact of a cylindrically curved sheet with a cylindrical
surface, while the second considers the partial contact of a conically curved sheet with
the edge of a cylindrical surface. In each case, we solve the free–boundary problems to
determine the shape, response and stability of the confined surfaces. In particular, we
show that an exact description of both the cylindrical and conical structures is given
by solutions of the Elastica equation, allowing us to present a unified description
of a large class of elastic developable surfaces. This includes what is possibly the
simplest example of strain localization, occurring at a point and forming one of the
constituent elements of a crumpled elastic sheet.
Exploring the temperature–pressure configurational landscape of biomolecules: from lipid membranes to proteins
Authors: Winter R. , Dzwolak W.
Published: December 2004

Hydrostatic pressure has been used as a physical parameter for studying the stability and energetics of biomolecular systems, such as lipid mesophases and proteins, but also because high pressure is an important feature of certain natural membrane environments and because the high–pressure phase behaviour of biomolecules is of biotechnological interest. By using spectroscopic and scattering techniques, the temperature– and pressure–dependent structure and phase behaviour of lipid systems, differing in chain configuration, headgroup structure and concentration, and proteins have been studied and are discussed. A thermodynamic approach is presented for studying the stability of proteins as a function of both temperature and pressure. The results demonstrate that combined temperature–pressure dependent studies can help delineate the free–energy landscape of proteins and hence help elucidate which features and thermodynamic parameters are essential in determining the stability of the native conformational state of proteins. We also introduce pressure as a kinetic variable. Applying the pressure jump relaxation technique in combination with time–resolved synchrotron X–ray diffraction and spectroscopic techniques, the kinetics of un/refolding of proteins has been studied. Finally, recent advances in using pressure for studying misfolding and aggregation of proteins will be discussed.
Tutors and Pupils: International Organizations, Central European Elites, and Western Models
Authors: Jacoby Wade
Published: December 2004

In the past decade, political elites in Central and Eastern Europe have often sought to imitate Western organizational and institutional models, while organizations like the EU and NATO have often acted as “institutional tutors” in the region. Using evidence from Hungary and the Czech Republic, this paper demonstrates why imitating Western structures has been both administratively expedient and useful in building political coalitions. It also stresses that the short‐term benefits of doing so are followed by longer‐term costs. The paper answers four questions: How have certain models been held up to CEE elites? Why might some such models be targets for elites to imitate? How does such imitation occur? And what results from imitation? Contrary to expectations that institutional modeling would be merely technocratic and used only yearly in the transformation, the paper's threefold heuristic of templates, thresholds, and adjustments shows that the process is both politically contentious and sustained.