bluuebunny/crossref_metadata_2025 huggingface dataset:
Field-reversed configuration translation into a compression coil
Authors: Chrien Robert E.
Published: July 2002

Field-reversed configuration translation into a conducting cylinder that does not conserve flux is analyzed and compared to translation into a flux conserver. The differences are found to be important for the design of an adiabatic compressional heating experiment.
Stability of compact-torus ion-ring hybrid systems to magnetohydrodynamic tilt and shift modes
Authors: Turnbull A. D. , Sudan R. N.
Published: July 2002

The low-frequency stability of a compact-torus ion-ring hybrid configuration, in which part of the toroidal current is carried by a ring of high-energy ions, is studied. In particular, the magnetohydrodynamic (MHD) tilt and radial shift instabilities in spheromak-like hybrid systems are considered. The ion ring has a stabilizing effect on the tilt mode, through its modification of the magnetic geometry. For the shift mode, the stabilization is dynamic for moderate elongation, but is again geometrical in the limit of large elongation. For moderate elongation, it is found that a high-energy ion component substantially enhances stability against the MHD shift mode.
Verification of the Taylor (minimum energy) state in a spheromak
Authors: Hart G. W. , Janos A. , Meyerhofer D. D. , Yamada M.
Published: July 2002

Experimental measurements of the equilibrium in the S-1 spheromak [M. Yamada, J. Sinnis, H. P. Furth, M. Okabayashi, G. Sheffield, T. H. Stix, and A. M. M. Todd, in Proceedings of the US-Japan Symposium on Compact Toruses and Energetic Particle Injection (Princeton Plasma Physics Laboratory, Princeton, NJ, 1979), p. 171] by use of magnetic probes inside the plasma show that the final magnetic equilibrium is one that has relaxed close to the Taylor (minimum-energy) state, even though the plasma is far from that state during formation. The comparison is made by calculating the two-dimensional μ profile of the plasma from the probe data, where μ is defined as μ0 j∥/B. Measurements using a triple Langmuir probe proved evidence to support the conclusion that the pressure gradients in the relaxed state are confined to the edge region of the plasma.
Collisional effects on kinetic electromagnetic modes and associated quasilinear transport
Authors: Rewoldt G. , Tang W. M. , Hastie R. J.
Published: July 2002

The general procedure for the analysis of low-frequency electrostatic and electromagnetic modes in toroidal geometry is now well known. In the collisionless limit, the relevant dynamics (e.g., trapped particles, resonances, etc.) can be treated appropriately. However, with the introduction of collisional effects it is customary, for tractability, to employ model collision operators of varying degrees of complexity. Guided by results of earlier studies of alternative collision operators in unsheared slab geometry and in toroidal geometry, an improved model collision operator is introduced here for calculating toroidal eigenmodes. Analytic and numerical results are presented to support its relevance and to demonstrate its improvement over earlier models. The associated quasilinear particle and energy transport coefficients for each species are also calculated, and compared with the usual Dj≂κj≂γ/k2⊥ estimate.
Control of low-frequency plasma instabilities by a nonuniform radial electric field
Authors: Komori Akio , Watanabe Kowashi , Kawai Yoshinobu
Published: July 2002

Flute instability of a magnetoplasma is generated and controlled experimentally by a nonuniform weak radial electric field. Six concentric electrodes, biased separately, are used to change the radial electric field. The instability, which is different from the velocity shear flute instability, is observed in a plasma with well-type potential and hill-type density profiles.
The origin of the rotation in field-reversed configurations
Authors: Tuszewski M. , Barnes G. A. , Chrien R. E. , Hugrass W. N. , Rej D. J. , Siemon R. E. , Wright B.
Published: July 2002

A review of experimental data suggests that particle loss and end shorting contribute together to the rotation of field-reversed configurations. Neither process can account for all available data by itself. An empirical scaling law based on both mechanisms is proposed that is consistent with all data.
Spheromak tilt stabilization with an energetic particle component
Authors: Mehanian C. , Lovelace R. V. E.
Published: July 2002

The tilt and shift stability of a spheromak plasma in the presence of a large orbit ion-ring component is determined by evaluating the magnetic interaction of the plasma with the ion ring and the external coils. Neither the ion-ring toroidal current nor the ring inverse aspect ratio is required to be small. The influence of conducting walls is considered to be negligible, as is appropriate for compression experiments. The plasma tilt and shift stability has been evaluated for a comprehensive set of numerically generated, self-consistent, hybrid spheromak/ion-ring equilibria. Stable equilibria are found over a considerable range of the parameters. The tilt stabilization of the plasma typically requires that more than about 25% of the total toroidal current be carried by the ion ring.
Interactions between two electrified liquid columns pinned on a dielectric solid surface
Authors: Feng James Q. , Basaran Osman A.
Published: July 2002

As a preliminary to understanding the complicated interactions between two electrified drops, this paper analyzes the simpler but instructive problem of the electrohydrostatic interactions between two parallel, translationally symmetric supported liquid columns. The columns are taken to be electrically conducting, surrounded by an insulating fluid, and pinned at their contact lines on the surface of an insulating solid support. The issue of the shapes and stability of the columns is mathematically a two-dimensional, nonlinear free boundary problem, which is solved here by means of the Galerkin/finite element method. Despite the generality of the formulation of the problem and that of the numerical scheme used to solve it, attention is focused here on situations in which the two columns have the same volume per unit length and their undeformed cross sections correspond to semicircles bounded by a straight line that represents the solid plane on which the columns are pinned. Computational results are reported that show different behaviors of electrified columns obtained by varying the direction in which the external field is applied or connecting/disconnecting the columns from power supplies that maintain them at fixed electric potentials. When the potentials of the columns are held fixed, an externally applied field always tends to pull them apart. For isolated columns, however, an externally applied field within a large range of oblique angles tends to pull the columns together. In the absence of an externally applied field, electrostatic interactions can also arise when the columns bear net electrical charges. Whether the interaction forces are attractive or repulsive then depends on the relative amounts of charge on the columns. An attractive force can result even when the two columns bear net charges of the same sign, provided that the relative difference in the amounts of charge is large enough.
Linear nonaxisymmetric oscillations of nearly inviscid liquid bridges
Authors: Higuera Marı́a , Nicolás José A.
Published: July 2002

Linear nonaxisymmetric oscillations of liquid bridges are analyzed in the limit of large capillary Reynolds number C−1. A boundary layer analysis is used that yields a second approximation of the damping rate and frequency in terms of the capillary Reynolds number, the slenderness of the bridge and the axial and azimuthal wave numbers of the mode being excited. Very good agreement with previous numerical results is obtained for C≲0.01, while the first correction of the damping rate gives a poor approximation, except for unrealistically small values of C (C≲10−5).
Vortex dynamics in jets from inclined nozzles
Authors: Webster D. R. , Longmire E. K.
Published: July 2002

Experimental tests were performed on round jets exiting inclined nozzles at a Reynolds number of 9000. Both natural jets and jets forced with single frequencies corresponding to StD=0.25, 0.5, 0.75, and 1.0 were examined. In the natural case, the nozzle incline caused a mild increase in the radial spreading in the plane of azimuthal symmetry. The forcing amplified the asymmetric radial spreading by altering the vortex structure. In general, the inclined vortex rings rolled up at an angle slightly smaller than the nozzle incline angle. As the rings moved downstream, they migrated away from the jet centerline and their incline angle increased. Vortex rings generated at StD=0.5 did not pair because that Strouhal number was near the “preferred” mode. For nozzles with slight inclines, forcing at larger Strouhal numbers led to pairing near x/D=2 in order to achieve the “preferred” mode. For nozzles with larger inclines, the vortex cores broke down before pairing could occur. Forcing at a lower Strouhal number (StD=0.25) yielded ring formation at StD=0.5 and subsequent pairing. Increasing the incline angle moved the pairing location closer to the nozzle lip. Also, the pairing process was found to depend on the nozzle incline angle.
Scalar dissipation rate modelling in variable density turbulent axisymmetric jets and diffusion flames
Authors: Sanders J. P. H. , Gökalp I.
Published: July 2002

In recent years several transport equation models for the scalar dissipation rate have been proposed to replace the well known algebraic expression based on equality of mechanical and scalar turbulent time scales. In this study various transport equation models are compared with each other and the model equation of Yoshizawa [J. Fluid Mech. 195, 541 (1988)] is given special attention. The latter is shown to allow an algebraic solution that is different from the classical “equal-scales” algebraic model. The constants that appear in this equation are assigned values based on similarity behavior in turbulent jets and based on studies of homogeneous isotropic turbulence. Both algebraic models and the transport equation models are compared and applied to isothermal variable density jets and jet diffusion flames. It is found that general features, such as the behavior of scalar fluctuation intensities of variable density turbulent jets are relatively well predicted by all the models. Differences between the models exist regarding the predicted time scale ratios.
A model of heavy particle dispersion by organized vortex structures wrapped around a columnar vortex core
Authors: Marshall J. S.
Published: July 2002

Dispersion of heavy particles from the core of a turbulent vortex with nonzero axial flow is investigated using an axisymmetric computational model, in which the coherent turbulent structures are modeled as periodic vortex rings wrapped around a columnar vortex. Two regimes of particle dispersion are distinguished, which are mapped in the space of two dimensionless parameters; the ratio L/R of vortex ring spacing to ring radius and the ratio ΓR/ΓC of ring strength to columnar vortex strength. In one regime, the outward particle drift is arrested by the ring vortices and the particles become trapped on a single wavy surface enclosing the columnar vortex core. In the other regime, the particles continue to move radially past the vortex rings and the particle dispersion is enhanced by the ring-induced velocity.
An analysis of flow, temperature, and chemical composition distortion in gas sampling through an orifice during chemical vapor deposition
Authors: Swihart Mark T. , Girshick Steven L.
Published: July 2002

Measurement of the chemical composition of gases sampled through a small hole in the substrate can be a useful diagnostic for investigations of the chemistry of chemical vapor deposition (CVD) processes. Ideally, one would measure the composition of the gas at the growth surface. However, the flow disturbance due to sampling causes the conditions at the mouth of the orifice to be different from those at the growth surface. Unless the orifice diameter is sufficiently small, relative to the thickness of chemical and thermal boundary layers above the growth surface, the sampled composition will differ from the composition at the growth surface. In this work, we present results of two-dimensional simulations of the flow, heat transfer, and chemical reactions in an axisymmetric stagnation point flow with gas sampling through a small orifice in the substrate on the symmetry axis of the flow field. Detailed results are given for atmospheric-pressure radio-frequency plasma CVD of diamond, corresponding to experiments performed in our laboratory. We also present more general results, approximate analytical representations of the flow field, and scaling rules for the size of the disturbance due to the sampling orifice.
The late-time development of the Richtmyer–Meshkov instability
Authors: Prasad J. K. , Rasheed A. , Kumar S. , Sturtevant B.
Published: July 2002

Measurements have been made of the growth by the Richtmyer–Meshkov instability of nominally single-scale perturbations on an air/sulfur hexafluoride (SF6) interface in a large shock tube. An approximately sinusoidal shape is given to the interface by a wire mesh which supports a polymeric membrane separating the air from the SF6. A single shock wave incident on the interface induces motion by the baroclinic mechanism of vorticity generation. The visual thickness δ of the interface is measured from schlieren photographs obtained singly in each run and in high-speed motion pictures. Data are presented for δ at times considerably larger than previously reported, and they are tested for self-similarity including independence of initial conditions. Four different initial amplitude/wavelength combinations at one incident shock strength are used to determine the scaling of the data. It is found that the growth rate decreases rapidly with time, dδ/dt∝t−p (i.e., δ∝t1−p), where 0.67≲p≲0.74 and that a small dependence on the initial wavelength λ0 persists to large time. The larger value of the power law exponent agrees with the result of the late-time-decay similarity law of Huang and Leonard [Phys. Fluids 6, 3765–3775 (1994)]. The influence of the wire mesh and membrane on the mixing process is assessed.
Kinetic modeling of a two-dimensional, collisionless bounded plasma
Authors: Pedit H. , Kuhn S.
Published: July 2002

A (2d,3v), electrostatic, collisionless kinetic slab model for a wide class of negative-bias dc states of the single-ended Q machine is developed. The self-consistent plasma state is found by means of an iterative scheme in which the charge-density and potential distributions are alternately advanced. The electron and ion velocity distribution functions are calculated via trajectory integration, which ensures high accuracy and resolution in both configuration and velocity spaces. As compared to similar previous schemes, this ‘‘trajectory-simulation’’ method exhibits some modifications, significantly reducing computing time and enhancing numerical stability, so that it is also applicable to ‘‘long’’ systems (≥102 Debye lengths). Macroscopic quantities as well as velocity distribution functions for two exemplary special cases are systematically presented. To the authors’ knowledge, these results represent the most comprehensive and detailed kinetic analysis of any bounded plasma system given so far.
Isotopic scaling of confinement in deuterium–tritium plasmas
Authors: Scott S. D. , Zarnstorff M. C. , Barnes Cris W. , Bell R. , Bretz N. L. , Bush C. , Chang Z. , Ernst D. , Fonck R. J. , Johnson L. , Mazzucato E. , Nazikian R. , Paul S. , Schivell J. , Synakowski E. J. , Adler H. , Bell M. , Budny R. , Fredrickson E. , Grek B. , Janos A. , Johnson D. , McCune D. , Park H. , Ramsey A. , Redi M. H. , Taylor G. , Thompson M. , Wieland R.
Published: July 2002

The confinement and heating of supershot plasmas are significantly enhanced with tritium beam injection relative to deuterium injection in the Tokamak Fusion Test Reactor [Plasma Phys. Controlled Fusion 26, 11 (1984)]. The global energy confinement and local thermal transport are analyzed for deuterium and tritium fueled plasmas to quantify their dependence on the average mass of the hydrogenic ions. Radial profiles of the deuterium and tritium densities are determined from the D–T fusion neutron emission profile. The inferred scalings with average isotopic mass are quite strong, with τE∝〈A〉0.85±0.20, τEthermal∝〈A〉0.89±0.20, χitot∝〈A〉−2.6±0.5, and De∝〈A〉−1.4±0.2 at fixed Pinj. For fixed local plasma parameters χitot∝〈A〉−1.8±0.4 is obtained. The quoted 2σ uncertainties include contributions from both diagnostic errors and shot irreproducibility, and are conservatively constructed to attribute the entire scatter in the regressed parameters to uncertainties in the exponent on plasma mass.
Alpha power channeling using ion-Bernstein waves
Authors: Fisch N. J.
Published: July 2002

An economically superior development path to a tokamak reactor may be possible, if α-particle power can first be extracted by plasma waves and then channeled to heat fuel ions. In principle, both increased reactivity and current drive could be accomplished at once. The most complete channeling is likely to be realized only through the excitation of a variety of waves, since α-particles at different velocities or at different locations within the tokamak interact most effectively with different waves. The necessary characteristics for these waves have been identified, but no specific implementation is yet at hand. The mode converted ion Bernstein wave, however, has a certain number of the required wave features, and is likely to play a useful role in helping to realize the channeling effect.
Electrodynamics as a problem of eigenvalues. I. Maxwell operator and its properties. Momentum-energy tensor
Authors: Yudin Lev A. , Efimov Sergey P. , Kapchinsky Michael I. , Korenev Igor L.
Published: July 2002

A new method of formulation of problems in macroscopic electrodynamics is proposed. Maxwell equations are written in the abstract-operator form. A solution to the formal problem of eigenvalues and eigenfunctions of the introduced Maxwell operator allows us to use the well-developed mathematical technique of linear operator theory for various electrodynamical problems. In particular, calculation of the momentum-energy tensor, wave generation, perturbation theory, and variational approach can be applied for electrodynamical systems (cavities, waveguides, free space) filled with media of arbitrary dispersion. In the first part of the paper we deal with a formal foundation of the method and calculation of the momentum-energy tensor.
Electrodynamics as a problem of eigenvalues. III. Maxwell operator and perturbation theory
Authors: Yudin Lev A. , Kapchinsky Michael I. , Korenev Igor L. , Efimov Sergey P.
Published: July 2002

This part of the work deals with perturbation theory. The standard technique permits us to solve problems of volume disturbances in free space, waveguides, and cavities, of disturbances of boundary conditions caused by finite conductivity of walls, and of disturbances of the boundary shape. Expressions for frequency and wave number shifts caused by the perturbation are obtained by the unified method. Several examples are presented: wave amplification in the waveguide filled with a resonant medium like an electron beam in a longitudinal magnetic field, the frequency shift (and increment/decrement) of a cavity loaded by an electron beam, and the field disturbance in the waveguide caused by finite conductivity of the walls.
On the sideband structure of free electron laser emission spectra
Authors: Spindler G. , Renz G.
Published: July 2002

Assuming the magnetic field in a planar undulator of a typical infrared free electron laser, in the paper we address specific effects on the spontaneous emission and the small-signal gain imposed by the electron dynamics. It is analytically demonstrated that weak misalignment (order of 1 mrad) of the undulator axis with respect to the optical axis of the resonator leads to a spectrum being rich in side maxima (sidebands). These sidebands appear as a consequence of a phase modulation of the radiation of the electrons caused by the betatron oscillation, their spectral spacing roughly given by the Doppler up-shifted betatron frequency.
Chaotic behavior and strange attractor in time-dependent solutions of the magnetohydrodynamic equations for the Faraday disc
Authors: Ingraham R. L. , Vulcan T.
Published: July 2002

Chaos and a strange attractor were found in time-dependent solutions of the full magnetohydrodynamic equations for a Faraday disc in an applied magnetic “seed” field. These were treated by the Galerkin method, truncated at five modes. The seed field is amplified several hundredfold. There are also aperiodic “partial pole reversals.”
Brillouin enhanced four-wave mixing and phase conjugation in weakly collisional plasmas
Authors: Shukla P. K.
Published: July 2002

Brillouin enhanced four-wave mixing and phase conjugation of electromagnetic waves in weakly collisional fully ionized plasmas are considered. It is found that the nonlinearity associated with the nonlocal electron heat transport may dominate over the ponderomotive force and consequently there might appear an enhanced degenerate four-wave mixing and phase conjugation reflectivity.
E×B
flow shear and enhanced confinement in the Madison Symmetric Torus reversed-field pinch
Authors: Chapman B. E. , Almagri A. F. , Anderson J. K. , Chiang C.-S. , Craig D. , Fiksel G. , Lanier N. E. , Prager S. C. , Sarff J. S. , Stoneking M. R. , Terry P. W.
Published: July 2002

Strong E×B flow shear occurs in the edge of three types of enhanced confinement discharge in the Madison Symmetric Torus [Dexter et al., Fusion Technol. 19, 131 (1991)] reversed-field pinch. Measurements in standard (low confinement) discharges indicate that global magnetic fluctuations drive particle and energy transport in the plasma core, while electrostatic fluctuations drive particle transport in the plasma edge. This paper explores possible contributions of E×B flow shear to the reduction of both the magnetic and electrostatic fluctuations and, thus, the improved confinement. In one case, shear in the E×B flow occurs when the edge plasma is biased. Biased discharges exhibit changes in the edge electrostatic fluctuations and improved particle confinement. In two other cases, the flow shear emerges (1) when auxiliary current is driven in the edge and (2) spontaneously, following sawtooth crashes. Both edge electrostatic and global magnetic fluctuations are reduced in these discharges, and both particle and energy confinement improve.
Dynamics of seed magnetic island formation due to geometrically coupled perturbations
Authors: Hegna C. C. , Callen J. D. , LaHaye R. J.
Published: July 2002

Seed magnetic island formation due to a dynamically growing external source in toroidal confinement devices is modeled as an initial value, forced reconnection problem. For an external source whose amplitude grows on a time scale quickly compared to the Sweet–Parker time of resistive magnetohydrodynamics, the induced reconnection is characterized by a current sheet and a reconnected flux amplitude that lags in time the source amplitude. This suggests that neoclassical tearing modes, whose excitation requires a seed magnetic island, are more difficult to cause in high Lundquist number plasmas.
Dispersion of ideal particles in a two-dimensional model of electrostatic turbulence
Authors: Naulin V. , Nielsen A. H. , Rasmussen J. Juul
Published: July 2002

The dispersion of ideal test particles in electrostatic drift-wave turbulence is investigated numerically. A self-consistent model with an internal instability drive is used to obtain the turbulent two-dimensional (2D) flow-field. It is shown that nonlinear couplings lead to the formation of coherent vortical structures in the flow. The dispersion of the particles is found to be anisotropic, with the weakest dispersion in the direction of the density gradient. By distinguishing between particles trapped in structures and free particles, it is demonstrated that the trapping and subsequent displacement of particles by nonlinear vortex structures enhances the particle diffusion in the direction of the background density gradient. Conditional diffusion coefficients are obtained showing that particles trapped by the vortex structures are convected by the structures. The time a particle on the average stays trapped in the structure is closely related to the lifetime of the vortical structures. The relation between the diffusion coefficient obtained from the test particle dispersion and an effective diffusion coefficient obtained from the cross-field turbulent flux is discussed.
Energy distribution of ionized electrons from He atoms in strong laser fields
Authors: Baozhen Chen
Published: July 2002

A theoretical model is proposed to describe energy distributions of electrons ionized from helium atoms in a circularly polarized laser light with short pulse and high intensity, especially, the high resolution energy distributions given by Mohideen group experimental measurements [V. Mohideen et al. Phys. Rev. Lett. 71, 509 (1993)]. It is found that the serious peak intensity discrepancy between the experimental and previous theoretical distributions can be considerably eliminated.
Mercury cadmium telluride solar cell with 10.6% efficiency
Authors: Basol Bulent M. , Tseng Eric S.
Published: July 2002

Cd-rich mercury cadmium telluride (MCT) is a promising material for thin-film solar cell applications. In this letter we present data on the deposition of MCT films by a simple electroplating technique and report on the highest efficiency polycrystalline MCT thin-film solar cell to date, which has an efficiency of 10.6% under AM1.5 illumination.
Visible, room-temperature, surface-emitting laser using an epitaxial Fabry–Perot resonator with AlGaAs/AlAs quarter-wave high reflectors and AlGaAs/GaAs multiple quantum wells
Authors: Gourley P. L. , Drummond T. J.
Published: July 2002

We report operation of a new surface-emitting laser. This epitaxial laser is fabricated with molecular beam epitaxy by the growth of quarter-wave high reflectors of AlAs/Al0.4Ga0.6As (710 Å/630 Å) which surround a 4.5-μm-thick multiple quantum well of GaAs/Al0.4Ga0.6As (100 Å/200 Å). We characterize the structure with cw spectroscopy (absorption, reflection, and luminescence) and investigate stimulated emission spectra under pulsed photopumping. When photopumped, the structure lases in its as-grown condition without need of substrate removal, cleaving, or heatsinking. The lasing wavelength is as short as 7400 Å and can be tuned to as long as 8400 Å by positioning the pump spot to different regions across the wafer. The pulsed threshold irradiance has a very weak temperature dependence varying from 6×105 W/cm2 at 4.2 K to 1.6×106 W/cm2 at 295 K.
Identification in traditional herbal medications and confirmation by synthesis of factors that inhibit cholera toxin-induced fluid accumulation
Authors: Oi Hiroshi , Matsuura Daisuke , Miyake Masami , Ueno Masamiti , Takai Izumi , Yamamoto Takeshi , Kubo Masayoshi , Moss Joel , Noda Masatoshi
Published: July 2002

Kampo formulations are traditional herbal medications used in China and Japan for many centuries to treat diarrheal diseases such as cholera. Our studies were undertaken to identify and verify by chemical synthesis the active components that inhibited cholera toxin (CT), the virulence factor secreted by
Vibrio cholerae
, the causative agent of cholera. The Kampo formulation, Daio-kanzo-to, inhibited CT activities (i.e., ADP-ribosylation, Chinese hamster ovary cell elongation); in Daio-kanzo-to, Daio (
Rhei rhizoma
) was responsible for this effect. Among several components purified from Daio extract, rhubarb galloyl-tannin, a compound characterized by a polygallate structure, was the most effective. To define the active component, gallate analogues similar to rhubarb galloyl-tannin were synthesized. These gallate compounds inhibited all CT activities including ADP-ribosylation, elongation of Chinese hamster ovary cells, and importantly, fluid accumulation in ileal loops. Thus, Kampo formulations or their gallate components might be effective adjunctive therapy with oral rehydration solution for the severe diarrhea of cholera.
Linkage disequilibrium between the beta frequency of the human EEG and a GABA
A
receptor gene locus
Authors: Porjesz Bernice , Almasy Laura , Edenberg Howard J. , Wang Kongming , Chorlian David B. , Foroud Tatiana , Goate Alison , Rice John P. , O'Connor Sean J. , Rohrbaugh John , Kuperman Samuel , Bauer Lance O. , Crowe Raymond R. , Schuckit Marc A. , Hesselbrock Victor , Conneally P. Michael , Tischfield Jay A. , Li Ting-Kai , Reich Theodore , Begleiter Henri
Published: July 2002

Human brain oscillations represent important features of information processing and are highly heritable. A common feature of beta oscillations (13–28 Hz) is the critical involvement of networks of inhibitory interneurons as pacemakers, gated by γ-aminobutyric acid type A (GABA
A
) action. Advances in molecular and statistical genetics permit examination of quantitative traits such as the beta frequency of the human electroencephalogram in conjunction with DNA markers. We report a significant linkage and linkage disequilibrium between beta frequency and a set of GABA
A
receptor genes. Uncovering the genes influencing brain oscillations provides a better understanding of the neural function involved in information processing.
PIP
3
inhibition of RGS protein and its reversal by Ca
2+
/calmodulin mediate voltage-dependent control of the G protein cycle in a cardiac K
+
channel
Authors: Ishii Masaru , Inanobe Atsushi , Kurachi Yoshihisa
Published: July 2002

Regulators of G protein signaling (RGS) accelerate intrinsic GTP hydrolysis on α subunits of trimeric G proteins and play crucial roles in the physiological regulation of G protein-mediated cell signaling. The control mechanisms of the action of RGS proteins
per se
are poorly clarified, however. We recently showed a physiological mode of action of a RGS protein in cardiac myocytes. The voltage-dependent formation of Ca
2+
/calmodulin facilitated the GTPase activity of RGS by an unidentified mechanism, which underlay the “relaxation” behavior of G protein-gated K
+
(K
G
) channels. Here we report the mechanism which is the reversal by Ca
2+
/calmodulin of phosphatidylinositol-3,4,5,-trisphosphate (PIP
3
)-mediated inhibition of RGS. Purified RGS4 protein alone inhibited GTP-induced K
G
channel activity in inside-out patches from atrial myocytes. The inhibitory effect of RGS4 was reduced by PIP
3
and restored by addition of Ca
2+
/calmodulin. The intracellular application of anti-PIP
3
antibody abolished the RGS-dependent relaxation behavior of K
G
current in atrial myocytes. This study, therefore, reveals a general physiological control mechanism of RGS proteins by lipid–protein interaction.
Structural basis for recruitment of CBP/p300 by hypoxia-inducible factor-1α
Authors: Freedman Steven J. , Sun Zhen-Yu J. , Poy Florence , Kung Andrew L. , Livingston David M. , Wagner Gerhard , Eck Michael J.
Published: July 2002

Adaptation to hypoxia is mediated by transactivation of hypoxia-responsive genes by hypoxia-inducible factor-1 (HIF-1) in complex with the CBP and p300 transcriptional coactivators. We report the solution structure of the cysteine/histidine-rich 1 (CH1) domain of p300 bound to the C-terminal transactivation domain of HIF-1α. CH1 has a triangular geometry composed of four α-helices with three intervening Zn
2+
-coordinating centers. CH1 serves as a scaffold for folding of the HIF-1α C-terminal transactivation domain, which forms a vise-like clamp on the CH1 domain that is stabilized by extensive hydrophobic and polar interactions. The structure reveals the mechanism of specific recognition of p300 by HIF-1α, and shows how HIF-1α transactivation is regulated by asparagine hydroxylation.
Anatomical and ecological constraints on Phanerozoic animal diversity in the marine realm
Authors: Bambach Richard K. , Knoll Andrew H. , Sepkoski J. John
Published: July 2002

We grouped the fossil records of marine animal genera into suites defined by function and physiology. The stratigraphic coherence of the resulting diversity history indicates the importance of ecological structure in constraining taxonomic richness through time. The proportional representation of major functional groups was stably maintained for intervals as long as 200 million years, despite evolutionary turnover and changes in total diversity. Early Paleozoic radiations established stable ecosystem relationships, and thereafter only the great era-bounding mass extinctions were able to break patterns of incumbency, permitting the emergence of new community structures with distinct proportional diversity relationships.
The endopolyphosphatase gene: Essential in
Saccharomyces cerevisiae
Authors: Sethuraman Anand , Rao Narayana N. , Kornberg Arthur
Published: July 2002

Endopolyphosphatases (Ppn1) from yeast and animal cells hydrolyze inorganic polyphosphate (poly P) chains of many hundreds of phosphate residues into shorter lengths. The limit digest consists predominantly of chains of 60 (P
60
) and 3 (P
3
) P
i
residues. Ppn1 of
Saccharomyces cerevisiae
, a homodimer of 35-kDa subunits (about 352-aa) is of vacuolar origin and requires the protease activation of a 75-kDa (674-aa) precursor polypeptide. The Ppn1 gene (
PPN1
) now has been cloned, sequenced, overexpressed, and deleted. That
PPN1
encodes Ppn1 was verified by a 25-fold increase in Ppn1 when overexpressed under a
GAL
promoter and also by several peptide sequences that match exactly with sequences in a yeast genome ORF, the mutation of which abolishes Ppn1 activity. Null mutants in Ppn1 accumulate long-chain poly P and are defective in growth in minimal media. A double mutant of
PPN1
and
PPX1
(the gene encoding a potent exopolyphosphatase) loses viability rapidly in stationary phase. Whether this loss is a result of the excess of long-chain poly P or to the lack of shorter chains (i.e., poly P
60
and P
3
) is unknown. Overexpression of the processed form of Ppn1 should provide a unique and powerful reagent to analyze poly P when the chain termini are unavailable to the actions of polyPase and poly P kinase.
Preservation of light signaling to the suprachiasmatic nucleus in vitamin A-deficient mice
Authors: Thompson Carol L. , Blaner William S. , Van Gelder Russell N. , Lai Katherine , Quadro Loredana , Colantuoni Vittorio , Gottesman Max E. , Sancar Aziz
Published: July 2002

To investigate the role of retinal-based pigments (opsins) in
circadian photoreception in mice, animals mutated in plasma retinol
binding protein were placed on a vitamin A-free diet and tested for
photic induction of gene expression in the suprachiasmatic nucleus.
After 10 months on the vitamin A-free diet, the majority of mice
contained no detectable retinal in their eyes. These mice demonstrated
fully intact photic signaling to the suprachiasmatic nucleus as
measured by acute
mPer
mRNA induction in the
suprachiasmatic nucleus in response to bright or dim light. The data
suggest that a non-opsin pigment is the primary circadian photoreceptor
in the mouse.
The function of herpes simplex virus genes: a primer for genetic engineering of novel vectors.
Authors: Roizman B
Published: July 2002

Herpes simplex virus vectors are being developed for delivery and expression of human genes to the central nervous system, selective destruction of cancer cells, and as carriers for genes encoding antigens that induce protective immunity against infectious agents. Vectors constructed to meet these objectives must differ from wild-type virus with respect to host range, reactivation from latency, and expression of viral genes. The vectors currently being developed are (i) helper free amplicons, (ii) replication defective viruses, and (iii) genetically engineered replication competent viruses with restricted host range. Whereas the former two types of vectors require stable, continuous cell lines expressing viral genes for their replication, the replication competent viruses will replicate on approved primary human cell strains.
Discovery of an algal mitochondrial carbonic anhydrase: molecular cloning and characterization of a low-CO2-induced polypeptide in Chlamydomonas reinhardtii.
Authors: Eriksson M , Karlsson J , Ramazanov Z , Gardeström P , Samuelsson G
Published: July 2002

In green unicellular algae, several polypeptides are induced upon exposure to limiting CO2. We report here on the localization and characterization of one of these, a 22-kDa polypeptide in Chlamydomonas reinhardtii. This nuclear-encoded polypeptide is induced in the mitochondria by a lowering of the partial pressure of CO2 in the growth medium from 5% to air CO2 levels. Sequencing of two different cDNA clones coding for the polypeptide identified it as a 20.7-kDa beta-type carbonic anhydrase (CA; carbonate dehydratase, carbonate hydro-lyase, EC 4.2.1.1). The two clones differ in their nucleotide sequences but code for identical proteins, showing that this CA is encoded by at least two genes. Northern blot hybridization reveals that mRNA transcripts are only present in cells transferred to air CO2 levels. A comparison of the deduced amino acid sequence with those of other beta-CAs shows the largest degree of similarity with CA from the cyanobacterium Synechocystis (50% identity and 66% similarity). To our knowledge, this is the first identification and characterization of a mitochondrial CA from a photosynthetic organism.
Microtubule reorganization is obligatory for growth cone turning
Authors: Williamson Toni , Gordon-Weeks Phillip R. , Schachner Melitta , Taylor Joanne
Published: July 2002

To examine the role of microtubules in growth cone turning, we have
compared the microtubule organization in growth cones advancing on
uniform laminin substrates with their organization in growth cones
turning at a laminin–tenascin border. The majority (82%) of growth
cones on laminin had a symmetrical microtubule organization, in which
the microtubules entering the growth cone splay out toward the
periphery of the growth cone. Growth cones at tenascin borders had
symmetrically arranged microtubules in only 34% of cases, whereas in
the majority of cases the microtubules were displaced toward one-half
of the growth cone, presumably stabilizing in the direction of the turn
along the tenascin border. These results suggest that reorganization of
microtubules could underlie growth cone turning. Further evidence for
the involvement of microtubule rearrangement in growth cone turning was
provided by experiments in which growth cones approached tenascin
borders in the presence of nanomolar concentrations of the microtubule
stabilizing compound, Taxol. Taxol altered the organization of
microtubules in growth cones growing on laminin by restricting their
distribution to the proximal regions of the growth cone and increasing
their bundling. Taxol did not stop growth cone advance on laminin. When
growing in the presence of Taxol, growth cones at tenascin borders were
not able to turn and grow along the laminin–tenascin border, and
consequently stopped at the border. Growth cones were arrested at
borders for as long as Taxol was present (up to 6 h) without
showing any signs of drug toxicity. These effects of Taxol were
reversible. Together, these results suggest that microtubule
reorganization in growth cones is a necessary event in growth cone
turning.
Production of transgenic dwarf surfclams, Mulinia lateralis, with pantropic retroviral vectors.
Authors: Lu J K , Chen T T , Allen S K , Matsubara T , Burns J C
Published: July 2002

A pantropic pseudotyped retroviral vector containing the envelope protein of vesicular stomatitis virus was used as a gene transfer vector in the dwarf surfclam, Mulinia lateralis. These pantropic retroviral vectors have an extremely broad host cell range and can infect many nonmammalian species. Newly fertilized dwarf surfclam eggs were electroporated at 700 V in the presence of 1 x 10(4) colony-forming units of pantropic pseudotyped retroviral particles. Infection was well tolerated and did not affect the survival rate of the embryos. Gametes collected from P1 presumptive transgenic animals were analyzed for the presence of provirus by PCR, and in different experiments 13-33% of the gamete pools were positive for the transgene. Dot blot hybridization of DNA samples from the F1 offspring of two different crosses between infected P1 and wild-type individuals revealed that 28% and 31% of F1 offspring were transgenic, respectively. Southern blot analysis of DNA isolated from PCR-positive F1 animals confirmed integration of a single copy of the provirus into the host genome. Thus, the germ lines of these two P1 transgenic animals were mosaic for the transgene. Expression of beta-galactosidase encoded by the provirus was detected in transgenic but not control surfclam embryos. Pantropic pseudotyped retroviral vectors provide a useful method for the stable introduction of foreign genetic information into surfclams and may facilitate the introduction of desirable genetic traits into commercially important shellfish and crustaceans.
P2X4: an ATP-activated ionotropic receptor cloned from rat brain.
Authors: Soto F , Garcia-Guzman M , Gomez-Hernandez J M , Hollmann M , Karschin C , Stühmer W
Published: July 2002

Extracellular ATP exerts pronounced biological actions in virtually every organ or tissue that has been studied. In the central and peripheral nervous system, ATP acts as a fast excitatory transmitter in certain synaptic pathways [Evans, R.J., Derkach, V. & Surprenant, A. (1992) Nature (London) 357, 503-505; Edwards, F.A., Gigg, A.J. & Colquhoun, D. (1992) Nature (London) 359, 144-147]. Here, we report the cloning and characterization of complementary DNA from rat brain, encoding an additional member (P2X4) of the emerging multigenic family of ligand-gated ATP channels, the P2X receptors. Expression in Xenopus oocytes gives an ATP-activated cation-selective channel that is highly permeable to Ca2+ and whose sensitivity is modulated by extracellular Zn2+. Surprisingly, the current elicited by ATP is almost insensitive to the common P2X antagonist suramin. In situ hybridization reveals the expression of P2X4 mRNA in central nervous system neurons. Northern blot and reverse transcription-PCR (RT-PCR) analysis demonstrate a wide distribution of P2X4 transcripts in various tissues, including blood vessels and leukocytes. This suggests that the P2X4 receptor might mediate not only ATP-dependent synaptic transmission in the central nervous system but also a wide repertoire of biological responses in diverse tissues.
Fas ligand deficiency in HIV disease
Authors: Sieg Scott , Smith Dawn , Yildirim Zafer , Kaplan David
Published: July 2002

Apoptosis is postulated to be involved as an anti-viral immune mechanism by killing infected cells before viral replication has occurred. The Fas–Fas ligand interaction is a powerful regulator of T cell apoptosis and could potentially act as a potent anti-viral immune mechanism against T cell tropic virus such as human immunodeficiency virus (HIV). We investigated the status of Fas ligand in peripheral blood mononuclear cells (PBMCs) obtained from persons infected with HIV. We found that monocytes in freshly isolated PBMCs from healthy individuals possess cell surface Fas ligand. In contrast, monocytes in freshly isolated PBMCs from HIV-infected patients had no detectable Fas ligand on the cell surface. Consistent with these findings of surface expression, Fas ligand activity was deficient in the cells from HIV-infected persons. The effect of replacing Fas ligand activity on HIV production by patients’ cells was assessed in anin vitroassay. The addition of a functional anti-Fas antibody to PBMCs from HIV-infected individuals inhibited viral production by greater than 90% without affecting lymphocytic function. These findings suggest the possibility of a new therapeutic modality for the treatment of HIV-infected individuals based on the reconstitution of Fas ligand activity.
Long-term potentiation involves increases in the probability of neurotransmitter release
Authors: Schulz Paul E.
Published: July 2002

There is great interest in understanding the mechanisms of expression underlying long-term potentiation (LTP). They are agreed to involve an increase in synaptic efficacy, which is described by three multiplicative parameters:
p
, the probability of neurotransmitter release;
n
, the number of active release sites; and
q
, the postsynaptic unit response to transmitter release. We report three new lines of evidence suggesting that increases in
p
contribute to LTP expression. (
i
) When the contributions to LTP by
p
,
n
, and
q
are maximized, and
p
alone is decreased, another high-frequency stimulation elicits additional LTP. The additional potentiation is only associated with decreases in paired-pulse facilitation (PPF) suggesting an increase in
p
. (
ii
) There is an inverse relationship between baseline I
p
and the magnitude of LTP elicited, consistent with I
p
having more or less room to increase when
p
is smaller or greater. (
iii
) It has been shown that there is an inverse relationship between the magnitude of LTP induced and the associated changes in PPF. Now I find that decreasing
p
before inducing LTP moves the set-point for measuring those changes in PPF from before to after
p
is decreased, which would only occur if
p
contributes to LTP. Three lines of evidence, then, suggest that increases in
p
contribute to LTP expression, which is consistent with a presynaptic contribution to LTP. These experiments do not address potential postsynaptic contributions.
Isolation of a multispecific organic anion and cardiac glycoside transporter from rat brain
Authors: Noé Birgitta , Hagenbuch Bruno , Stieger Bruno , Meier Peter J.
Published: July 2002

A novel multispecific organic anion transporting polypeptide (oatp2) has been isolated from rat brain. The cloned cDNA contains 3,640 bp. The coding region extends over 1,983 nucleotides, thus encoding a polypeptide of 661 amino acids. Oatp2 is homologous to other members of the
oatp
gene family of membrane transporters with 12 predicted transmembrane domains, five potential glycosylation, and six potential protein kinase C phosphorylation sites. In functional expression studies in
Xenopus laevis
oocytes, oatp2 mediated uptake of the bile acids taurocholate (
K
m
≈ 35 μM) and cholate (
K
m
≈ 46 μM), the estrogen conjugates 17β-estradiol-glucuronide (
K
m
≈ 3 μM) and estrone-3-sulfate (
K
m
≈ 11 μM), and the cardiac gylcosides ouabain (
K
m
≈ 470 μM) and digoxin (
K
m
≈ 0.24 μM). Although most of the tested compounds are common substrates of several oatp-related transporters, high-affinity uptake of digoxin is a unique feature of the newly cloned oatp2. On the basis of Northern blot analysis under high-stringency conditions, oatp2 is highly expressed in brain, liver, and kidney but not in heart, spleen, lung, skeletal muscle, and testes. These results provide further support for the overall significance of oatps as a new family of multispecific organic anion transporters. They indicate that oatp2 may play an especially important role in the brain accumulation and toxicity of digoxin and in the hepatobiliary and renal excretion of cardiac glycosides from the body.