bluuebunny/crossref_metadata_2025 huggingface dataset:
Scalar field measurements of a laminar starting plume cap using digital processing of interferograms
Authors: Chay Avraham , Shlien D. J.
Published: July 2002

The scalar field (heat or species concentration) of a small-source laminar starting plume was measured at a single dimensionless buoyancy injection rate for two values of the ratio of momentum diffusivity to scalar diffusivity, Pr=7 and 300. Digital image processing was used to extract concentration contours from the interferograms, which considerably reduced the data reduction time and permitted an improved resolution. The effect of Pr was clearly visible in the scalar contours, especially in terms of the entrained fluid that is found to be undiluted far inside the cap of the higher Pr. The scalar contours were not self-similar when a single length scale was used, but the data collapsed well using a two-length scale normalization. The convective velocity of the cap was also measured for the two cases, suggesting a possible logarithmic effect of Pr. An analysis confirms the speculation. It was also found that about 37% of the total injection rate into the starting plume is convected into the cap. This work is the first experimental investigation demonstrating the effect of change in Pr on the motion of small buoyancy-source laminar gravitational convection phenomena.
Analysis and simulation of virtual cathode oscillations
Authors: Kadish Abraham , Faehl Rickey J. , Snell Charles M.
Published: July 2002

A nonlinear mechanism for virtual cathode oscillations is derived from an analysis of a cold plasma fluid model. Frequency scalings and field wave shapes are predicted. These are compared with extensive numerical simulation studies of non-neutral electron beams using both one- and two-dimensional particle-in-cell codes.
A comparison of the structure of the wake behind a circular cylinder in a steady flow with that in a perturbed flow
Authors: Armstrong B. J. , Barnes F. H. , Grant I.
Published: July 2002

A description is given of the structure of the turbulent wake behind a circular cylinder that was determined using a conditional averaging technique. The structure was found for a steady flow and also for a flow in which an in-line velocity perturbation was superimposed on the steady component. The perturbation frequency was chosen so that the frequency of vortex shedding locked-in to the perturbation frequency. The structures of the two wakes are compared and it is found that large changes occur with lock-in, with the strength of the vortices increasing and their lateral separation decreasing. It is estimated that the increase in the vortex strength results from an increase in the amount of vorticity shed from the cylinder and also a small change in the amount of vorticity surviving the vortex formation process. The model, which Davies [J. Fluid Mech. 75, 209 (1976)] found gave a good representation of the average wake flow, was used to provide comparisons with the experimental results. In general, the agreement between the theoretical and experimental results was very satisfactory.
Statistical modeling of a transport equation for the kinetic energy dissipation rate
Authors: Yoshizawa Akira
Published: July 2002

A transport equation for the kinetic energy dissipation rate ε is investigated using the results from a two-scale direct-interaction approximation. A model equation for ε is constructed from the equation for kinetic energy k with the aid of a differential transformation. A comparison between the present equation and the counterpart in the k-ε model is performed.
The equation of bubble dynamics in a compressible liquid
Authors: Prosperetti Andrea
Published: July 2002

An equation accounting to lowest order for the effects of liquid compressibility on the radial motion of a spherical bubble is deduced from the statement of energy conservation for the liquid.
The mechanics of spin coating of polymer films
Authors: Lawrence C. J.
Published: July 2002

The process of spin coating is described, with particular attention to applications in microelectronics. The physical mechanisms involved in the process are discussed and those mechanisms that affect the final state are identified, viz., centrifugal and viscous forces, solute diffusion, and solvent evaporation: A model is proposed that incorporates only the latter mechanisms, with viscosity and diffusivity depending on solute concentration. The evaporation of solvent during spinning causes the solution viscosity to increase and the flow is reduced. The thickness of the final solid film is related to the thickness of a diffusion boundary layer near the free surface. The model predicts the final dry film thickness in terms of the primary process variables, spin speed, and initial polymer concentration. A similarity boundary-layer analysis leads to a simple approximate result for the final film thickness that is consistent with limited experimental data, hf ∼KC0(ν0D0)1/4/Ω1/2, where K is a number of order unity and the other quantities are, respectively, the initial polymer concentration, the kinematic viscosity, the solute diffusivity, and the spin speed. The dependence on diffusivity has not previously been described theoretically. The total spin time is shown to be proportional to Ω−1, in agreement with experiment. The rate of solvent evaporation is shown to be proportional to Ω, which contradicts previous assumptions.
Bluff-body propulsion produced by combined rotary and translational oscillation
Authors: Blackburn H. M. , Elston J. R. , Sheridan J.
Published: July 2002

Flows produced by combined oscillatory translation and rotation of a circular cylinder in quiescent fluid have been studied using a two-dimensional direct numerical simulation technique. Results are presented for one set of the five dimensionless groups which characterize these flows, for which it is found that a streaming flow normal to the axis of translation is generated. The consequent reaction force is then used to propel the cylinder in the direction opposite to the jet, thus demonstrating a novel propulsion mechanism for bluff bodies.
Computer studies on the fast reconnection mechanism under an externally driven boundary condition
Authors: Ugai M.
Published: July 2002

Computer simulations study the temporal dynamics of magnetic reconnection in a current sheet system under a continuous local plasma injection imposed on the inflow boundary. The basic reconnection process is strongly influenced by the resistivity model. For a uniform resistivity model, the field lines become flattened with time so that the resulting quasisteady configuration involves a long diffusion region and the reconnection rate strongly depends on the resistivity, in good agreement with the Sweet–Parker mechanism. For an anomalous resistivity model, magnetic reconnection drastically occurs, leading to development of a large-scale plasmoid. Once an effective resistivity is triggered, a quasisteady fast reconnection mechanism spontaneously develops even in the absence of the specified boundary condition, in good agreement with the spontaneous fast reconnection model. When the imposed plasma injection is larger than the one inherent to the spontaneous fast reconnection mechanism, the fast reconnection mechanism can no longer proceed steadily and multiple X points and plasmoids result. It is concluded that it is not the boundary condition that drives the fast reconnection mechanism; the boundary condition may simply initiate the onset of magnetic reconnection (or effective resistivity) but has no essential effect on the fast reconnection development.
Pulsed currents carried by whistlers. V. Detailed new results of magnetic antenna excitation
Authors: Rousculp C. L. , Stenzel R. L. , Urrutia J. M.
Published: July 2002

A low frequency, oblique whistler wave packet is excited from a single current pulse applied to a magnetic loop antenna. The magnetic field is mapped in three dimensions. The dominant angle of radiation is determined by the antenna dimensions, not by the resonance cone. Topological properties of the inductive and space charge electric fields and space charge density confirm an earlier physical model. Transverse currents are dominated by Hall currents, while no net current flows in the parallel direction. Electron-ion collisions damp both the energy and the helicity of the wave packet. Landau damping is negligible. The radiation resistance of the loop is a few tenths of an Ohm for the observed frequency range. The loop injects zero net helicity. Rather, oppositely traveling wave packets carry equal amounts of opposite signed helicity.
Macro-particle simulations of collisionless magnetic reconnection
Authors: Tanaka Motohiko
Published: July 2002

The basic process of collisionless reconnection is studied in terms of coalescence of two flux bundles using an implicit particle simulation of two-dimensions. As the toroidal electric field is generated by magnetic induction, an elongated current sheet whose width is a few electron skin depths is formed. Sub-Alfvénic plasma outflow off the reconnection region is generated in the poloidal plane which spreads within the dual fans originating at the X-point. Significant toroidal acceleration and streaming of the electrons without direct thermalization is observed in the current sheet. The electron parallel transport is proved to enhance the reconnection rate by comparing the implicit and hybrid-particle simulations; in the latter the electrons are spatially frozen to the ions. The reconnection rate is insensitive to finite Larmor radii of the ions in the regime where the magnetic flux merges constantly in time. The simulation results support that the collisionless reconnection is mediated by the electron inertia.
Experimental studies of charged dust particles
Authors: Robertson Scott
Published: July 2002

Measurements of the charge on individual dust grains of glass and copper have been made in a double plasma device with monoenergetic primary electrons and a tenuous plasma. In conditions where the current collected by grains is dominated by the primary electrons, the grains charge to the potential which repels the primary electrons. The charging potential is reduced from this value when the fast electrons are sufficiently energetic to release a comparable current of secondary electrons. In addition, confinement of charged dust has been investigated in evacuated electrostatic traps consisting of a center electrode at high potential within a grounded enclosure. The confinement time of particles orbiting the center conductor may be an hour or ∼105 orbits. The orbits are visible and the effects of perturbations have been videotaped.
Electrostatic ion cyclotron instabilities in negative ion plasmas
Authors: Chow V. W. , Rosenberg M.
Published: July 2002

The effect of negative ions on the collisionless electrostatic ion cyclotron instability (EICI) is investigated analytically and numerically. The singly ionized negative ion species has mass greater than or equal to the mass of the singly ionized positive ion species. Standard linear Vlasov theory is used to estimate the critical electron drift velocity. It is shown that the critical drifts for the excitation of both the light and heavy ion EIC modes decrease as the relative density of negative ions increases. Our results are compared with available negative ion plasma experiments concerning the EICI, and possible applications to experiments in the ionosphere are briefly discussed.
Theoretical analysis of driven magnetic reconnection experiments
Authors: Uzdensky Dmitri A. , Kulsrud Russell M. , Yamada Masaaki
Published: July 2002

In this paper we present a theoretical framework for the Magnetic Reconnection Experiment (MRX) [M. Yamada et al., Bull. Am. Phys. Soc. 40, 1877 (1995)] in order to understand the basic physics of the experiment, including the effect of the external driving force, and the difference between co- and counterhelicity cases of the experiment. The problem is reduced to a one-dimensional (1-D) resistive magnetohydrodynamic (MHD) model. A special class of holonomic boundary conditions is defined, under which a unique sequence of global equilibria can be obtained, independent of the rate of reconnection. This enables one to break the whole problem into two parts: a global problem for the ideal region, and a local problem for the resistive reconnection layer. The calculations are then carried out and the global solution for the ideal region is obtained in one particular case of holonomic constraints, the so called ‘‘constant force’’ regime, for both the co- and counterhelicity cases. After the sequence of equilibria in the ideal region is found, the problem of the rate of reconnection in the resistive reconnection region is considered. This rate tells how fast the plasma proceeds through the sequence of global equilibria but does not affect the sequence itself. Based on a modified Sweet–Parker model for the reconnection layer, the reconnection rate is calculated, and the difference between the co- and counterhelicity cases, as well as the role of the external forces is demonstrated. The results from the present analysis are qualitatively consistent with the experimental data, predicting faster reconnection rate for the counterhelicity merging and yielding a positive correlation with external forcing.
Quasi-two-dimensional fast kinematic dynamo instabilities of chaotic fluid flows
Authors: Reyl Charles , Antonsen Thomas M. , Ott Edward
Published: July 2002

This paper tests previous heuristically derived general theoretical results for the fast kinematic dynamo instability of a smooth, chaotic flow by comparison of the theoretical results with numerical computations on a particular class of model flows. The class of chaotic flows studied allows very efficient high resolution computation. It is shown that an initial spatially uniform magnetic field undergoes two phases of growth, one before and one after the diffusion scale has been reached. Fast dynamo action is obtained for large magnetic Reynolds number Rm. The initial exponential growth rate of moments of the magnetic field, the long time dynamo growth rate, and multifractal dimension spectra of the magnetic fields are calculated from theory using the numerically determined finite time Lyapunov exponent probability distribution of the flow and the cancellation exponent. All these results are numerically tested by generating a quasi-two-dimensional dynamo at magnetic Reynolds number Rm of order up to 105.
Recent progress in the design of stellarator experiments
Authors: Garabedian P. R.
Published: July 2002

To evaluate stellarators as power plants, a helias configuration was developed by running high performance computer codes written at New York University. A modular coil set was found that had ample spacing for a reactor and took advantage of the concept of quasihelical symmetry. Since that time, the design has been further optimized and a similar stellarator has been discovered that has just two field periods and a plasma with the low aspect ratio 3.5. Its principal advantage is that in a flux coordinate system its magnetic-field structure comes close to having axial symmetry, so transport is predicted to be almost as good as that in a tokamak at high temperatures. Only 16 moderately twisted coils are required to produce the external magnetic field, and the configuration might well be viewed as a steady-state tokamak rather than an alternate concept.
Compressible magnetohydrodynamic Kelvin–Helmholtz instability with vortex pairing in the two-dimensional transverse configuration
Authors: Miura Akira
Published: July 2002

For a two-dimensional (2-D) transverse configuration, where the plasma motion occurs in a 2-D plane transverse to the magnetic field, the nonlinear evolution of the magnetohydrodynamic (MHD) Kelvin–Helmholtz (K–H) instability is investigated by means of a 2-D MHD simulation for a convective fast magnetosonic Mach number 0.35, which is defined for the total jump of the flow velocity. The compressibility and the nonzero baroclinic vector are shown to violate the conservation of the enstrophy for the 2-D MHD transverse configuration and for the 2-D fluid motion. After the nonlinear saturation of the linearly fastest growing vortices, the vortices continue to coalesce until no more vortex pairing is allowed, owing to a finite length of the simulation system. The plasma inside the vortex is rarefied strongly by the fast magnetosonic rarefaction and each vortex is associated with an eddy current, which is inertia current in nature. The plasma flow velocity is enhanced at the periphery of the vortex and the net momentum transport and shear relaxation by the instability occur as long as the vortex pairing continues. Anomalous viscosity by the K–H instability increases with the vortex pairing and its increase is due to the growth of subharmonic modes.
Direct-drive hydrodynamic instability experiments on the GEKKO XII laser
Authors: Azechi H. , Nakai M. , Shigemori K. , Miyanaga N. , Shiraga H. , Nishimura H. , Honda M. , Ishizaki R. , Wouchuk J. G. , Takabe H. , Nishihara K. , Mima K. , Nishiguchi A. , Endo T.
Published: July 2002

Hydrodynamic instabilities, such as the Rayleigh–Taylor (R–T) instability, play a critical role in inertial confinement fusion as they finally cause fuel-pusher mixing that potentially quenches thermonuclear ignition. Good understanding of the instabilities is necessary to limit the mixing within a tolerable level. A series of experiments has been conducted on the GEKKO XII laser facility [C. Yamanaka et al., IEEE J. Quantum Electron. QE-17, 1639 (1981)] to measure hydrodynamic instabilities in planar foils directly irradiated by 0.53 μm laser light. It has been found that (1) the imprint is reasonably explained by an imprint model based on the equation of motion with the pressure perturbation smoothed by the cloudy-day effect, and (2) the experimental R–T growth rate is significantly reduced from the classical growth rate due probably to ablative stabilization enhanced by nonlocal heat transport.
Two-dimensional magneto-hydrodynamic modeling of carbon fiber Z-pinch experiments
Authors: Chittenden J. P. , Aliaga Rossel R. , Lebedev S. V. , Mitchell I. H. , Tatarakis M. , Bell A. R. , Haines M. G.
Published: July 2002

A two-dimensional magneto-hydrodynamic simulation incorporating cold start conditions is used to explain the early phase of carbon fiber Z-pinch experiments. The rapid development of large scale, nonlinear m=0 perturbations in the plasma corona is reproduced. X-ray bright spot formation in the necks of the instability is followed by bright spot bifurcation and fast axial motion. Bright spot bifurcation is found to be due to axial components of the j×B force and occurs off-axis due to the presence of a residual core of unionized carbon. Artificial diagnostic images are generated from the simulations data to allow direct comparison with experimental x-ray imaging and laser probing diagnostics. The accurate reproduction of the experimental images provides confirmation that the experimentally observed features are a repercussion of the non-linear development of the m=0 instability in an ionizing medium.
Geometrical influences on neoclassical magnetohydrodynamic tearing modes
Authors: Kruger S. E. , Hegna C. C. , Callen J. D.
Published: July 2002

The influence of geometry on the pressure drives of nonideal magnetohydrodynamic tearing modes is presented. In order to study the effects of elongation, triangularity, and aspect ratio, three different machines are considered to provide a range of tokamak configurations: Tokamak Fusion Test Reactor (circular) [Fusion Technol. 21, 1324 (1992)], DIII-D (D-shaped) [Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159], and Pegasus (extremely low aspect ratio) [Fonck et al., Bull. Am. Phys. Soc. 41, 1400 (1996)]. For large aspect ratio tokamaks, shaping does very little to influence the pressure gradient drives, while at low aspect ratios, a very strong sensitivity to the profiles is found. In particular, this sensitivity is connected to the strong dependence on the magnetic shear. This suggests that at low aspect ratio it may be possible to stabilize neoclassical tearing modes by a flattening the q profile near low order rational surfaces (e.g., q=2/1) using a combination of shaping and localized current drive, whereas at large aspect ratio it is more difficult.
Saturation of perturbation growth in ablatively driven planar laser targets
Authors: Velikovich Alexander L. , Dahlburg Jill P. , Gardner John H. , Taylor Robert J.
Published: July 2002

Saturation of the mass variation growth during the shock transit time, theoretically predicted for the surface roughness case by Ishizaki and Nishihara [Phys. Rev. Lett. 78, 1920 (1997)] and for the laser imprint case by Taylor et al. [Phys. Rev. Lett. 79, 1861 (1997)], is studied analytically and numerically. The saturation is demonstrated to be essentially the same effect in both cases, caused by the stabilizing action of mass ablation. Scalings of saturation time and saturation level for the two cases are related. For lower-density foam targets, the peak level of mass variation is proportional approximately to ρ01/2 and exactly to ρ0 for the cases of laser imprint and surface roughness, respectively.
Modern computational techniques in plasma physics
Authors: Karney Charles F. F.
Published: July 2002

This paper offers practical suggestions for how to make the best use of computers to model plasma behavior. This includes advice for ensuring the correctness of a computer code, how to manage a large code project, and how to take advantage of parallel computers.
The physics of neoclassical magnetohydrodynamic tearing modes
Authors: Hegna C. C.
Published: July 2002

Neoclassical effects alter the nonlinear evolution properties of magnetic islands in toroidal plasmas. While the perturbed bootstrap current effects tend to dominate the nonlinear evolution and mode saturation properties in tokamak plasmas, a number of additional effects complicate the picture. A novel aspect of the mode evolution properties is the appearance of a nonlinear threshold width, below which island formation is suppressed. The structure and strength of various closure relations for the ion viscosity and heat fluxes impact the size and scaling of the threshold width. The potential impact of this physics on low aspect ratio tokamaks and stellarator configurations is also discussed.
Coronal plasma behavior of the Z pinch produced from carbon and cryogenic deuterium fibers
Authors: Lebedev S. V. , Aliaga-Rossel R. , Chittenden J. P. , Mitchell I. H. , Dangor A. E. , Haines M. G. , Worley J. F.
Published: July 2002

A series of fiber pinch experiments has been carried out on the MAGPIE (mega-ampere generator for plasma implosion experiments) generator (1.8 MA, 150 ns) [Mithell et al., Rev. Sci. Instrum. 67, 1533 (1996)] to study the temporal evolution of the coronal plasma. Analysis of schlieren photographs, axial streak images and gated x-ray photographs gives the radial and axial motion of the coronal plasma. The influence of a current pulse (prepulse) of 30 kA applied 200 ns before the main discharge was also studied. Radial expansion velocities of 5.5×106 cm/s for carbon fiber shots without prepulse and 3.6×106 cm/s for carbon fibers with prepulse were measured. Axial wavelengths (λz) of dominant instabilities in the corona were between 0.05 and 0.2 cm corresponding to ka∼10–20. Comparison of the results obtained with carbon fibers with and without current prepulse and cryogenic deuterium fibers are presented.
Computer simulations of asymmetric spontaneous fast reconnection
Authors: Ugai M.
Published: July 2002

The spontaneous fast reconnection model is extended to the general asymmetric situations, where magnetic reconnection may take place between the field lines that are anchored in different magnetic dipole sources. It is demonstrated for a wide variety of parameters that the asymmetric fast reconnection mechanism can evolve as a nonlinear instability, so that an asymmetric plasmoid swells predominantly in the region of a weaker magnetic field and propagates along the field lines. In the central diffusion region, the secondary tearing is likely to take place and significant erosion of the stronger magnetic field occurs; accordingly, the X neutral point moves with time, where the (current-driven) anomalous resistivity is found to be always locally enhanced, allowing the fast reconnection mechanism to be sustained quasisteadily and extended outwards further. The associated shock structure standing at the boundary of the stronger magnetic field is identified with the ordinary slow shock, in general, combined with an intermediate wave in the presence of sheared field. On the other hand, the shock standing at the boundary of the weaker magnetic field has an intermediate shock-like structure near the diffusion region, which propagates along the shock layer to finally become the ordinary combination of a slow shock and a finite-amplitude rotational intermediate wave at the plasmoid boundary.
Schottky barrier height measurements of epitaxial NiSi2 on Si
Authors: Hauenstein R. J. , Schlesinger T. E. , McGill T. C. , Hunt B. D. , Schowalter L. J.
Published: July 2002

Photoresponse measurements of the Schottky barrier heights of epitaxial NiSi2 layers on nondegenerate n-(111) Si, for type-A and type-B orientations, have been performed. The type-A and type-B cases are consistently observed to differ in barrier height by greater than 0.1 eV. We obtain measured values for φB0 (at T=300 K) of 0.62±0.01 eV and 0.77±0.05 eV for type A and B, respectively.
Role of tip structure in scanning tunneling microscopy
Authors: Kuk Y. , Silverman P. J.
Published: July 2002

An ultrahigh vacuum scanning tunneling microscope (STM) equipped with a field ion microscope (FIM) has been built. By using the FIM image, a tungsten tip was tailored for high STM resolution in a scan of the Au(001) surface. The measured corrugation depth of the (1×5) rows was found to be a function of the size of the atomic cluster on the first plane of the tungsten tip.
Optical properties of InGaAs-InP single quantum wells grown by atmospheric pressure metalorganic chemical vapor deposition
Authors: Skolnick M. S. , Tapster P. R. , Bass S. J. , Apsley N. , Pitt A. D. , Chew N. G. , Cullis A. G. , Aldred S. P. , Warwick C. A.
Published: July 2002

Low-temperature photoluminescence and photoconductivity studies of high quality InGaAs-InP quantum wells grown by metalorganic chemical vapor deposition at atmospheric pressure are reported. The best luminescence linewidth obtained for a 100-Å well is found to be 7.9 meV. The residual line broadening is discussed in terms of interface fluctuations, and is compared directly with structural properties as determined by high resolution lattice imaging transmission electron microscopy.
Investigation of surface passivation of amorphous silicon using photothermal deflection spectroscopy
Authors: Frye R. C. , Kumler J. J. , Wong C. C.
Published: July 2002

We have used photothermal deflection spectroscopy to examine optical absorption in amorphous silicon films using a variety of surface passivation techniques. Absorption coefficients well below the band gap in these films are strongly influenced by surface state densities. Surfaces oxidized by either chemical treatment or in oxygen-containing plasmas show lower interface state densities than do those passivated with deposited dielectrics.
Preparation of single crystals of superconducting YBa2Cu3O7−x from CuO melts
Authors: Damento M. A. , Gschneidner K. A. , McCallum R. W.
Published: July 2002

Millimeter size single crystals of superconducting YBa2Cu3O7−x (Tc ∼90 K) were grown by melting a mixture of stoichiometric YBa2Cu3O7−x plus excess CuO at 1150 °C followed by holding at 900 °C for four days. Crystals were in the form of plates with c axis normal to the plate face. Growth of the crystals is believed to be aided by a liquid phase which is present at the holding temperature.
Demonstration of an InAsSb strained-layer superlattice photodiode
Authors: Kurtz S. R. , Dawson L. R. , Zipperian T. E. , Lee S. R.
Published: July 2002

A photodiode consisting of a p-n junction embedded in an InAs0.09Sb0.91/InSb strained-layer superlattice with equal 130-Å-thick layers was grown using molecular beam epitaxy. This nonoptimized device exhibited photoresponse out to a wavelength of 8.7 μm at 77 K. The resistance and the minority-carrier diffusion length of the photodiode result in a detectivity (3×109 cm Hz1/2/W) at 7 μm that is within one order of magnitude of the detectivity of the best HgCdTe detectors at that wavelength.
Similarities between the initial phase of a transient nonuniform glow discharge in nitrogen and the negative corona Trichel pulse formation in an electronegative gas
Authors: Černák Mirko , Hosokawa Tatsuzo
Published: July 2002

Measurements have been made of the initial stage of breakdown in a short negative point-to-plane gap in nitrogen at pressures of 50–750 Torr and at various overvoltages. The transient glow discharge regime was found to be preceded by a peaked current signal of conspicuous similarity to the Trichel pulse rise and its initial decay in an electronegative gas.
Linear electro-optic effect in β-BaB2O4
Authors: Ebbers Chris A.
Published: July 2002

The linear electro-optic (EO) coefficients of beta-barium borate (β-BaB2O4) have been measured. The clamped and unclamped values of ryyy and rc are ‖rTyyy‖ =2.5 pm/V, ‖rTc‖ =0.17 pm/V, ‖rSyyy‖=0.24rSxyz (KDP), and ‖rSc‖=0.013rSxyz (KDP). The magnitude of the EO coefficient is due mainly to the electronic nonlinearity.
The single-channel properties of human acetylcholine α7 receptors are altered by fusing α7 to the green fluorescent protein
Authors: Fucile Sergio , Palma Eleonora , Martínez-Torres Ataúlfo , Miledi Ricardo , Eusebi Fabrizio
Published: July 2002

Neuronal nicotinic acetylcholine (AcCho) receptors composed of α7-subunits (α7-AcChoRs) are involved in many physiological activities. Nevertheless, very little is known about their single-channel characteristics. By using outside-out patch-clamp recordings from
Xenopus
oocytes expressing wild-type (
wt
) α7-AcChoRs, we identified two classes of channel conductance: a low conductance (γ
L
) of 72 pS and a high one (γ
H
) of 87 pS, with mean open-times (τ
op
) of 0.6 ms. The same classes of conductances, but longer τ
op
(3 ms), were seen in experiments with chimeric α7 receptors in which the wtα7 extracellular C terminus was fused to the green fluorescent protein (
wt
α7-GFP AcChoRs). In contrast, channels with three different conductances were gated by AcCho in oocytes expressing α7 receptors carrying a Leu-to-Thr 248 mutation (
mut
α7) or oocytes expressing chimeric
mut
α7-GFP receptors. These conductance levels were significantly smaller, and their mean open-times were larger, than those of
wt
α7-AcChoRs. Interestingly, in the absence of AcCho, these oocytes showed single-channel openings of the same conductances, but shorter τ
op
, than those activated by AcCho. Accordingly, human homomeric
wt
α7 receptors open channels of high conductance and brief lifetime, and fusion to GFP lengthens their lifetime. In contrast,
mut
α7 receptors open channels of lower conductance and longer lifetime than those gated by
wt
α7-AcChoRs, and these parameters are not greatly altered by fusing the
mut
α7 to GFP. All this evidence shows that GFP-tagging can alter importantly receptor kinetics, a fact that has to be taken into account whenever tagged proteins are used to study their function.
Polarized cytokinesis in vacuolate cells of
Arabidopsis
Authors: Cutler Sean R. , Ehrhardt David W.
Published: July 2002

The view of plant-cell cytokinesis commonly depicted in textbooks is of a symmetrical process, with the phragmoplast initiating in the center of the cell and growing outward to the parental cell membrane. In contrast to this picture, we observe that cell-plate development in
Arabidopsis
shoot cells is highly polarized along the plane of division. Three-dimensional live-cell imaging reveals that the mitotic spindle and phragmoplast are laterally displaced, and that the growing cell plate anchors on one side of the cell at an early stage of cytokinesis. Growth of phragmoplast across the cell creates a new partition in its wake, giving the visual effect of a curtain being pulled across the cell. Throughout this process, the advancing front of the phragmoplast is in intimate contact with the parental wall, suggesting that short-range interactions between the phragmoplast and plasma membrane may play important roles in guiding the cell plate throughout much of its development. Polarized cytokinesis was observed in a wide variety of vacuolate shoot cells and in some small root cells, implying that it is not solely a function of cell size. This mode of cytokinesis may provide a mechanically robust mechanism for cell-plate formation in large cells and suggests a simple explanation for the occurrence of cell wall stubs observed upon drug treatment or in cytokinetic mutants.
Quantitative measurement of translesion replication in human cells: Evidence for bypass of abasic sites by a replicative DNA polymerase
Authors: Avkin Sharon , Adar Sheera , Blander Gil , Livneh Zvi
Published: July 2002

Mutations in oncogenes and tumor suppressor genes are critical in the development of cancer. A major pathway for the formation of mutations is the replication of unrepaired DNA lesions. To better understand the mechanism of translesion replication (TLR) in mammals, a quantitative assay for TLR in cultured cells was developed. The assay is based on the transient transfection of cultured cells with a gapped plasmid, carrying a site-specific lesion in the gap region. Filling in of the gap by TLR is assayed in a subsequent bioassay, by the ability of the plasmid extracted from the cells, to transform an
Escherichia coli
indicator strain. Using this method it was found that TLR through a synthetic abasic site in the adenocarcinoma H1299, the osteogenic sarcoma Saos-2, the prostate carcinoma PC3, and the hepatoma Hep3B cell lines occurred with efficiencies of 92 ± 6%, 32 ± 2%, 72 ± 4%, and 26 ± 3%, respectively. DNA sequence analysis showed that 85% of the bypass events in H1299 cells involved insertion of dAMP opposite the synthetic abasic site. Addition of aphidicolin, an inhibitor of DNA polymerases α, δ, and ɛ, caused a 4.4-fold inhibition of bypass. Analysis of two XP-V cell lines, defective in DNA polymerase η, showed bypass of 89%, indicating that polymerase η is not essential for bypass of abasic sites. These results suggest that in human cells bypass of abasic sites does not require the bypass-specific DNA polymerase η, but it does require at least one of the replicative DNA polymerases, α, δ, or ɛ. The quantitative TLR assay is expected to be useful in the molecular analysis of lesion bypass in a large variety of cultured mammalian cells.
A multipotential β-1,6-N-acetylglucosaminyl-transferase is encoded by bovine herpesvirus type 4
Authors: Vanderplasschen Alain , Markine-Goriaynoff Nicolas , Lomonte Patrick , Suzuki Masami , Hiraoka Nobuyoshi , Yeh Jiunn-Chern , Bureau Fabrice , Willems Luc , Thiry Etienne , Fukuda Minoru , Pastoret Paul-Pierre
Published: July 2002

The β-1,6-N-acetylglucosaminyltransferase (β1,6GnT) gene family encodes enzymes playing crucial roles in glycan synthesis. Important changes in β1,6GnT expression are observed during development, oncogenesis, and immunodeficiency. The most characterized β1,6GnTs in this gene family are the human (h) C2GnT-L and h-IGnT, which have core 2 [Galβ1→3(GlcNAcβ1→6)GalNAc] and I branching [GlcNAcβ1→3(GlcNAcβ1→6)Gal] activities, respectively. Recently, h-C2GnT-M was shown to be unique in forming core 2, core 4 [GlcNAcβ1→3(GlcNAcβ1→6)GalNAc], and I structures. To date, the β1,6GnT gene family has been characterized only in mammals. Here, we describe that bovine herpesvirus type 4 (BHV-4) encodes a β1,6GnT expressed during viral replication and exhibiting all of the core 2, core 4, and I branching activities. Sequencing of the BHV-4 genome revealed an ORF, hereafter called BORFF3–4, encoding a protein (pBORFF3–4) exhibiting 81.1%, 50.7%, and 36.6% amino acid identity with h-C2GnT-M, h-C2GnT-L, and h-IGnT, respectively. Reverse transcriptase-PCR analysis revealed that BORFF3–4 is expressed during BHV-4 replication. Expression of BORFF3–4 in Chinese hamster ovary cells directed the expression of core 2 branched oligosaccharides and I antigenic structures on the cell surface. Moreover, a soluble form of pBORFF3–4 had core 4 branching activity in addition to core 2 and I branching activities. Finally, infection of a C2GnT-negative cell line with BHV-4 induced expression of core 2 branched oligosaccharides. This study extends the β1,6GnT gene family to a viral gene and provides a model to study the biological functions of a β1,6GnT in the context of viral infection.
Electroretinogram analysis of relative spectral sensitivity in genetically identified dichromatic macaques
Authors: Hanazawa Akitoshi , Mikami Akichika , Angelika Puti Sulistyo , Takenaka Osamu , Goto Shunji , Onishi Akishi , Koike Satoshi , Yamamori Tetsuo , Kato Keichiro , Kondo Aya , Suryobroto Bambang , Farajallah Achmad , Komatsu Hidehiko
Published: July 2002

The retinas of macaque monkeys usually contain three types of photopigment, providing them with trichromatic color vision homologous to that of humans. However, we recently used molecular genetic analysis to identify several macaques with a dichromatic genotype. The affected X chromosome of these animals contains a hybrid gene of long-wavelength-sensitive (L) and middle-wavelength-sensitive (M) photopigments instead of separate genes encoding L and M photopigments. The product of the hybrid gene exhibits a spectral sensitivity close to that of M photopigment; consequently, male monkeys carrying the hybrid gene are genetic protanopes, effectively lacking L photopigment. In the present study, we assessed retinal expression of L photopigment in monkeys carrying the hybrid gene. The relative sensitivities to middle-wavelength (green) and long-wavelength (red) light were measured by electroretinogram flicker photometry. We found the sensitivity to red light to be extremely low in protanopic male monkeys compared with monkeys with the normal genotype. In female heterozygotes, sensitivity to red light was intermediate between the genetic protanopes and normal monkeys. Decreased sensitivity to long wavelengths was thus consistent with genetic loss of L photopigment.
Interchain hydrogen-bonding interactions may facilitate translocation of K
+
ions across the potassium channel selectivity filter, as suggested by synthetic modeling chemistry
Authors: Mareque Rivas Juan C. , Schwalbe Harald , Lippard Stephen J.
Published: July 2002

A 4-fold symmetric arrangement of TVGYG polypeptides forms the
selectivity filter of the K
+
channel from
Streptomyces lividans
(KcsA). We report the synthesis
and properties of synthetic models for the filter,
p-tert
-butyl-calix[4]arene-(OCH
2
CO-XOBz)
4
(X = V, VG, VGY), 1–3. The first cation (Na
+
,
K
+
) binds to the four -{OCH
2
CO}- units, a
region devised to mimic the metal-binding site formed by the four T
residues in KcsA. NMR studies reveal that cations and valine amide
protons compete for the carbonyl oxygen atoms, converting
N—H
Val
⋅⋅⋅O⩵C hydrogen bonds to
M
+
⋅⋅⋅O⩵C bonds (M
+
=
Na
+
or K
+
). The strength of these interchain
N—H
Val
⋅⋅⋅O⩵C hydrogen bonds varies in
the order 3 > 2 > 1. We propose that such interchain
H-bonding may destabilize metal binding in the selectivity filter and
thus help create the low energy barrier needed for rapid cation
translocation.
An anti-angiogenic state in mice and humans with retinal photoreceptor cell degeneration
Authors: Lahdenranta Johanna , Pasqualini Renata , Schlingemann Reinier O. , Hagedorn Martin , Stallcup William B. , Bucana Corazon D. , Sidman Richard L. , Arap Wadih
Published: July 2002

Abnormal angiogenesis accompanies many pathological conditions including cancer, inflammation, and eye diseases. Proliferative retinopathy because of retinal neovascularization is a leading cause of blindness in developed countries. Another major cause of irreversible vision loss is retinitis pigmentosa, a group of diseases characterized by progressive photoreceptor cell degeneration. Interestingly, anecdotal evidence has long suggested that proliferative diabetic retinopathy is rarely associated clinically with retinitis pigmentosa. Here we show that neonatal mice with classic inherited retinal degeneration (
Pdeb

rd1

/Pdeb

rd1

) fail to mount reactive retinal neovascularization in a mouse model of oxygen-induced proliferative retinopathy. We also present a comparable human paradigm: spontaneous regression of retinal neovascularization associated with long-standing diabetes mellitus occurs when retinitis pigmentosa becomes clinically evident. Both mouse and human data indicate that reactive retinal neovascularization either fails to develop or regresses when the number of photoreceptor cells is markedly reduced. Our findings support the hypothesis that a functional mechanism underlying this anti-angiogenic state is failure of the predicted up-regulation of vascular endothelial growth factor, although other growth factors may also be involved. Preventive and therapeutic strategies against both proliferative and degenerative retinopathies may emerge from this work.
Black holes
Authors: Brügmann B. , Ghez A. M. , Greiner J.
Published: July 2002

Recent progress in black hole research is illustrated by three examples. We discuss the observational challenges that were met to show that a supermassive black hole exists at the center of our galaxy. Stellar-size black holes have been studied in x-ray binaries and microquasars. Finally, numerical simulations have become possible for the merger of black hole binaries.
J3-crystallin of the jellyfish lens: Similarity to saposins
Authors: Piatigorsky Joram , Norman Barbara , Dishaw Larry J. , Kos Lidia , Horwitz Joseph , Steinbach Peter J. , Kozmik Zbynek
Published: July 2002

J3-crystallin, one of the three major eye-lens proteins of the cubomedusan jellyfish (
Tripedalia cystophora
), shows similarity to vertebrate saposins, which are multifunctional proteins that bridge lysosomal hydrolases to lipids and activate enzyme activity. Sequence alignment of deduced J3-crystallin indicates two saposin-like motifs arranged in tandem, each containing six cysteines characteristic of this protein family. The J3-crystallin cDNA encodes a putative precursor analogous to vertebrate prosaposins. The J3-crystallin gene has seven exons, with exons 2–4 encoding the protein. Exon 3 encodes a circularly permutated saposin motif, called a swaposin, found in plant aspartic proteases. J3-crystallin RNA was found in the cubomedusan lens, statocyst, in bands radiating from the pigmented region of the ocellus, in the tentacle tip by
in situ
hybridization, and in the embryo and larva by reverse transcription–PCR. Our data suggest a crystallin role for the multifunctional saposin protein family in the jellyfish lens. This finding extends the gene sharing evolutionary strategy for lens crystallins to the cnidarians and indicates that the putative primordial saposin/swaposin J3-crystallin reflects both the chaperone and enzyme connections of the vertebrate crystallins.
Maternal germ-line transmission of mutant mtDNAs from embryonic stem cell-derived chimeric mice
Authors: Sligh James E. , Levy Shawn E. , Waymire Katrina G. , Allard Paulette , Dillehay Dirck L. , Nusinowitz Steven , Heckenlively John R. , MacGregor Grant R. , Wallace Douglas C.
Published: July 2002

We report a method for introducing mtDNA mutations into the
mouse female germ line by means of embryonic stem (ES) cell cybrids.
Mitochondria were recovered from the brain of a NZB mouse by fusion of
synaptosomes to a mtDNA-deficient (ρ°) cell line. These cybrids
were enucleated and the cytoplasts were electrofused to rhodamine-6G
(R-6G)-treated female ES cells. The resulting ES cell cybrids permitted
transmission of the NZB mtDNAs through the mouse maternal lineage for
three generations. Similarly, mtDNAs from a partially
respiratory-deficient chloramphenicol-resistant (CAP
R
) cell
line also were introduced into female chimeric mice and were
transmitted to the progeny. CAP
R
chimeric mice developed a
variety of ocular abnormalities, including congenital cataracts,
decreased retinal function, and hamaratomas of the optic nerve. The
germ-line transmission of the CAP
R
mutation resulted in
animals with growth retardation, myopathy, dilated cardiomyopathy, and
perinatal or
in utero
lethality. Skeletal and heart
muscle mitochondria of the CAP
R
mice were enlarged and
atypical with inclusions. This mouse ES cell-cybrid approach now
provides the means to generate a wide variety of mouse models of
mitochondrial disease.
The expression of human α-like globin genes in transgenic mice mediated by bacterial artificial chromosome
Authors: Feng Dong-Xiao , Liu De-Pei , Huang Yue , Wu Lin , Li Tie-Chang , Wu Min , Tang Xiao-Bin , Liang Chih-Chuan
Published: July 2002

After screening a bacterial artificial chromosome of human genomic
DNA library with human HS-40, ζ-, α-, and θ-globin probes, a
110-kb clone bearing the whole human α-globin gene cluster was
obtained and rare restriction endonuclease mapping was performed. The
bacterial artificial chromosome DNA was isolated, and transgenic
mice were generated. Three founders were detected from 35 newborn mice.
The copy numbers were 1, 2, and 2, and the expression of human
α-globin genes in various tissues at different developmental stages
in the transgenic mice was assayed. The human α-globin mRNA can be
detected in bone marrow, kidney, liver, brain, but not in muscle,
testis, or thymus. The human ζ-globin genes were switched off, and
the α-globin genes were switched at day 11.5 in mouse embryo,
indicating that developmental stage-specific expression of the α-like
globin genes was properly regulated. The human α-globin mRNA ranged
between 17–68% of the endogenous mouse α-globin,
suggesting that the expression of human α-globin genes is integration
site-dependent in transgenic mice. The ratio of human α
2
-
and α
1
-globin gene expression in adult transgenic mouse
is about 2.5:1 similar to the expression in human.
Evidence that the cell wall of
Bacillus subtilis
is protonated during respiration
Authors: Calamita H. G. , Ehringer W. D. , Koch A. L. , Doyle R. J.
Published: July 2002

Several independent experiments suggest that cell walls of
Bacillus subtilis
are protonated during growth.
When cells were grown in the presence of fluorescein-labeled dextran to
saturate the cell walls, centrifuged, and suspended in PBS,
fluorescence-activated cell sorter analyses revealed the
bacteria were only poorly fluorescent. In contrast, when the bacteria
were purged with N
2
to dissipate protonmotive force (pmf)
fluorescence became intense. Upon reconstitution of the pmf with
phenazine methosulfate, glucose, and oxygen, fluorescence declined.
Another approach used pH-dependent chemical modification of cell walls.
The walls of respiring
B. subtilis
cells were amenable
to carboxylate modification by [
14
C]ethanolamine and
1-ethyl-3-(3-dimethylaminopropyl) carbodiimide. The carbodiimide
activation of carboxylate groups occurs only in acidic conditions. Upon
dissipation of pmf the walls were refractory to chemical modification.
Ammonium groups can be condensed with FITC in alkaline medium, but the
condensation is very slow in acidic buffers. It was found that the
derivatization of the walls with FITC could occur in the absence of
pmf. The use of pH-dependent fluorophores and pH-dependent chemical
modification reactions suggest that cell walls of respiring
B.
subtilis
cells have a relatively low pH environment. This
study shows a bacterium has a protonated compartment.
Acidification of cell walls during growth may be one means of
regulating autolytic enzymes.