bluuebunny/crossref_metadata_2025 huggingface dataset:
Radiative instability in a diverted plasma
Authors: Capes H. , Ghendrih Ph. , Samain A.
Published: July 2002

Bifurcations between thermal equilibria are studied in a slab radiating plasma at constant pressure. The thermal stability is discussed in connection with the behavior of the equilibrium solutions when the input power flux in the radiating layer is varied. A general necessary and sufficient stability criterion is demonstrated. In the case of a constant impurity concentration it leads to a simple stability condition in terms of the edge temperature only.
Two-dimensional aspects of toroidal drift waves in the ballooning representation
Authors: Zhang Y. Z. , Mahajan S. M. , Zhang X. D.
Published: July 2002

By systematically doing the higher-order theory, the predictions of the conventional ballooning theory (CBT) are examined for nonideal systems. For the complex solvability condition to be satisfied, radial variation of the lowest-order mode amplitude needs to be invoked. It turns out, however, that even this procedure with its concomitant modifications of eigenvalues and eigenstructures, is not sufficient to justify the predictions of many CBT solutions; only a small set of the CBT solutions could be put on firm footing. To demonstrate this work’s general conclusions, theoretical and numerical results are presented for a system of fluid drift waves with nonadiabatic electron response.
Probing the magnetosphere using chemical releases from the Combined Release and Radiation Effects Satellite
Authors: Bernhardt P. A.
Published: July 2002

During the recent Combined Release and Radiation Effects Satellite (CRRES) mission, a series of chemical releases occurred in the magnetosphere and ionosphere to study a wide range of plasma processes. The experiments were designed to investigate (1) stimulated electron and ion precipitation, (2) ion transport in the magnetotail, (3) critical ionization velocity (CIV), (4) field line tracing and parallel acceleration, (5) diamagnetic cavity formation and collapse, and (6) plasma instabilities. The satellite orbit was highly elliptical having an apogee of 33 600 km and a perigee of 350 km. The range of altitudes permitted variations in background magnetic field strength and injection velocity. The release materials included barium, lithium, strontium, calcium, and europium. In situ diagnostics on board CRRES and ground-based optical instruments recorded the effects of the chemical releases. The CRRES experiments either (1) verified theoretical predictions, (2) showed new, unanticipated effects, or (3) presented none of the predicted phenomena. Examples of each category are illustrated by one of more of the CRRES chemical releases.
Investigation of global Alfvén instabilities in the Tokamak Fusion Test Reactor
Authors: Wong K. L. , Durst R. , Fonck R. J. , Paul S. F. , Roberts D. R. , Fredrickson E. D. , Nazikian R. , Park H. K. , Bell M. , Bretz N. L. , Budny R. , Cheng C. Z. , Cohen S. , Hammett G. W. , Jobes F. C. , Johnson L. , Meade D. M. , Medley S. S. , Mueller D. , Nagayama Y. , Owens D. K. , Sabbagh S. , Synakowski E. J.
Published: July 2002

Toroidal Alfvén eigenmodes (TAE) were excited by the energetic neutral beam ions tangentially injected into plasmas at low magnetic field in the Tokamak Fusion Test Reactor (TFTR) [Proceedings of the 11th International Conference on Plasma Physics and Controlled Fusion Research (IAEA, Vienna, 1987), Vol. 1, p. 51]. The injection velocities were comparable to the Alfvén speed. The modes were identified by measurements from Mirnov coils and beam emission spectroscopy (BES). TAE modes appear in bursts whose repetition rate increases with beam power. The neutron emission rate exhibits sawtoothlike behavior and the crashes always coincide with TAE bursts. This indicates ejection of fast ions from the plasma until these modes are stabilized. The dynamics of growth and stabilization were investigated at various plasma currents and magnetic fields. The results indicate that the instability can effectively clamp the number of energetic ions in the plasmas. The observed instability threshold is discussed in light of recent theories. In addition to these TAE modes, intermittent oscillations at three times the fundamental TAE frequency were observed by Mirnov coils, but no corresponding signal was found in BES. It appears that these high-frequency oscillations do not have a direct effect on the plasma neutron source strength.
Sub-Alfvénic plasma expansion
Authors: Ripin B. H. , Huba J. D. , McLean E. A. , Manka C. K. , Peyser T. , Burris H. R. , Grun J.
Published: July 2002

A large ion Larmor radius plasma undergoes a particularly robust form of Rayleigh–Taylor instability when sub-Alfvénically expanding into a magnetic field. Results from an experimental study of this instability are reported and compared with theory, notably a magnetohydrodynamic (MHD) treatment that includes the Hall term, a generalized kinetic lower-hybrid drift theory, and with computer simulations. Many theoretical predictions are confirmed while several features remain unexplained. New and unusual features appear in the development of this instability. In the linear stage there is an onset criterion insensitive to the magnetic field, initial density clumping (versus interchange), linear growth rate much higher than in the ‘‘classic’’ MHD regime, and dominant instability wavelength of order of the plasma density scale length. In the nonlinear limit free-streaming flutes, apparent splitting (bifurcation) of flutes, curling of flutes in the electron cyclotron sense, and a highly asymmetric expansion are found. Also examined is the effect on the instability of the following: an ambient background plasma (that adds collisionality and raises the expansion speed/Alfvén speed ratio), magnetic-field line tying, and expansion asymmetries (that promotes plasma cross-field jetting).
Kinetic quasitoroidal ion temperature gradient instability in the presence of sheared flows
Authors: Dong J. Q. , Horton W.
Published: July 2002

The gyrokinetic integral equations for the study of the ion temperature gradient driven mode (ηi mode) in toroidal geometry, at low plasma pressure, are extended to include equilibrium ion parallel v0∥(r) and perpendicular vE(r) sheared flows, where r is the minor radius of the flux surface. Magnetic gradient and curvature drifts of the ions, as well as finite ion Larmor radius effects, are included. The parallel sheared flow is shown to be destabilizing. The perpendicular sheared flow is a stabilizing mechanism. Mixing length estimates show that the ηi-mode induced ion thermal transport increases with increasing parallel flow shear, and decreases with perpendicular flow shear. The decrease of the ion transport is due not only to the decrease of the mode growth rate, but also to the shrinking of the mode width. Using the mixing length formulas for the thermal transport associated with the unstable modes, it is shown that the results are consistent with the experimental observations concerning the improvement of confinement in H-mode discharges coincident with the increase of cross-field sheared flows.
A proposal for a redefinition of the turbulent stresses in the filtered Navier–Stokes equations
Authors: Germano M.
Published: July 2002

A redefinition of the Leonard term, the subgrid scale cross term, and the subgrid scale Reynolds stress is proposed, consistent with a general statement concerning turbulent stresses. The main advantage of the new redefined stresses consists of their term by term Galilean invariance.
High-energy components and collective modes in thermonuclear plasmas
Authors: Coppi B. , Cowley S. , Kulsrud R. , Detragiache P. , Pegoraro F.
Published: July 2002

The theory of a class of collective modes of a thermonuclear magnetically confined plasma, with frequencies in the range of the ion-cyclotron frequency and of its harmonics, is presented. These modes can be excited by their resonant cyclotron interaction with a plasma component of relatively high-energy particles characterized by a strongly anisotropic distribution in velocity space. Normal modes that are spatially localized by the inhomogeneity of the plasma density are found. This ensures that the energy gained by their resonant interaction is not convected away. The mode spatial localization can be significantly altered by the magnetic field inhomogeneity for a given class of plasma density profiles. Special attention is devoted to the case of a spin polarized plasma, where the charged products of fusion reactions are anisotropically distributed. It is shown that for the mode of polarization that enhances nuclear reaction rates the tritium will be rapidly depolarized for toroidal configurations with relatively mild gradients of the confining magnetic field.
Large amplitude ion-acoustic double layers in a double Maxwellian electron plasma
Authors: Bharuthram R. , Shukla P. K.
Published: July 2002

A finite amplitude theory for an ion-acoustic double layer (DL) in a plasma with cold ions and two distinct groups of Boltzmann–Maxwellian distributed hot electrons is presented. Conditions are obtained under which large amplitude stationary double layers can exist. For physical parameters of interest, the DL profiles and the relationship between the maximum DL amplitude and the Mach number are found. A perturbation technique is introduced to derive a modified Korteweg–de Vries (MKdV) equation which governs the dynamics of a weak double layer. It is found that the parameter regimes for the existence of small and finite amplitude DL are not complementary to each other. The relevance of this investigation to space and laboratory plasmas is pointed out.
Momentum and thermal transport in neutral-beam-heated tokamaks
Authors: Mattor N. , Diamond P. H.
Published: July 2002

The relation between momentum and thermal transport in neutral-beam-heated tokamaks with subsonic toroidal rotation velocity has been investigated. A theory of diffusive momentum transport driven by ion-temperature-gradient-driven turbulence (ηi turbulence) is presented. In addition, the level of ηi turbulence is enhanced by radially sheared toroidal rotation. The resulting ion shear viscosity is χφ=1.3{(1+ηi)/τ+[(Ln/2cs) (dV0/dr)]2}2(ρ2scs/ Ls). The associated ion thermal diffusivity, χi, is identical to χφ. Thus a scenario based on velocity-shear-enhanced ηi turbulence is consistent with the experimentally observed relationship between thermal and momentum confinement.
Small-scale structures in Boussinesq convection
Authors: E Weinan , Shu Chi-Wang
Published: July 2002

Two-dimensional Boussinesq convection is studied numerically using two different methods: a filtered pseudospectral method and a high-order accurate eno scheme. The issue whether finite time singularity occurs for initially smooth flows is investigated. In contrast to the findings of Pumir and Siggia who reported finite time collapse of the bubble cap, the present numerical results suggest that the strain rate corresponding to the intensification of the density gradient across the front saturates at the bubble cap. Consequently, the thickness of the bubble decreases exponentially. On the other hand, the bubble experiences much stronger straining and intensification of gradients at its side. As the bubble rises, a secondary front also forms from its tail. Together with the primary front, they constitute a pair of tightly bound plus and minus double vortex sheet structure which is highly unstable and vulnerable to viscous dissipation.
The instability of a liquid layer heated from the side when the upper surface is open to air
Authors: De Saedeleer C. , Garcimartin A. , Chavepeyer G. , Platten J. K. , Lebon G.
Published: July 2002

When a liquid layer is heated from the side, a monocellular flow develops immediately, no matter how small the temperature difference is. If the temperature gradient between the side walls is increased, this flow becomes unstable. Laser Doppler velocimetry measurements are reported here in an attempt to describe the main features of both the basic flow and the instability modes. It is found that before the appearance of traveling waves (the most dangerous mode as predicted by the theory), stable rolls with their axes perpendicular to the temperature gradient, span over the whole liquid layer, starting from the hot side, even if the aspect ratio (the length of the layer divided by its thickness) is very high. This unexpected situation modifies the basic flow. A further increase of the temperature gradient leads to the appearance of a time periodic motion.
Pattern recognition analysis of the turbulent flow past a backward facing step
Authors: Scarano F. , Benocci C. , Riethmuller M. L.
Published: July 2002

A pattern recognition technique for the investigation of large-scale coherent structures, is applied to analyze the turbulent separated flow over a backward facing step (BFS) at a Reynolds number Reh=5.0×103. The instantaneous two-dimensional velocity distribution is obtained by means of digital particle image velocimetry (D-PIV) measurements. High spatial resolution (Δr/h=1/25) is achieved with the application of an iterative window refinement image processing algorithm. The measurement plane is oriented in order to investigate spanwise aligned vortices footprints. The detection algorithm is based on velocity pattern spatial cross correlation. An additional isotropy condition is imposed to improve the detection of vortices and shear layer. The structure of the shear layer emanating from the step edge is examined emphasizing the role of coherent fluctuations with a length scale d ranging from 0.12 h to 0.44 h. A characteristic statistical spatial occurrence is found for the educed spanwise-aligned rollers: a quasi-linear spreading region extends from x/h=0.8 up to x/h=3.5. Within the same region the production of turbulent kinetic energy exhibits a maximum. At smaller scale, the vortices show a significant presence of counter-rotating structures inside the free shear layer suggesting that the spanwise rollers undergo early three dimensional instability and breakdown within a few step units. Conditional data averaging is also applied to the results and structural properties (coherent velocity, vorticity and turbulence production) are highlighted: close to the step edge the coherent vorticity distribution is strongly distorted showing an intense interaction between the rollers and the shear layer. A roughly circular pattern is recovered downstream x/h=4.
A review of the ablative stabilization of the Rayleigh–Taylor instability in regimes relevant to inertial confinement fusion
Authors: Kilkenny J. D. , Glendinning S. G. , Haan S. W. , Hammel B. A. , Lindl J. D. , Munro D. , Remington B. A. , Weber S. V. , Knauer J. P. , Verdon C. P.
Published: July 2002

It has been recognized for many years that the most significant limitation of inertial confinement fusion (ICF) is the Rayleigh–Taylor (RT) instability. It limits the distance an ablatively driven shell can be moved to several times its initial thickness. Fortunately material flow through the unstable region at velocity vA reduces the growth rate to √kg/1+kL−βkvA with β from 2–3. In recent years experiments using both x-ray drive and smoothed laser drive to accelerate foils have confirmed the community’s understanding of the ablative RT instability in planar geometry. The growth of small initial modulations on the foils is measured for growth factors up to 60 for direct drive and 80 for indirect drive. For x-ray drive large stabilization is evident. After some growth, the instability enters the nonlinear phase when mode coupling and saturation are also seen and compare well with modeling. Normalized growth rates for direct drive are measured to be higher, but strategies for reduction by raising the isentrope are being investigated. For direct drive, high spatial frequencies are imprinted from the laser beam and amplified by the RT instability. Modeling shows an understanding of this ‘‘laser imprinting.’’
Calculations of energy losses due to atomic processes in tokamaks with applications to the International Thermonuclear Experimental Reactor divertor
Authors: Post D. , Abdallah J. , Clark R. E. H. , Putvinskaya N.
Published: July 2002

Reduction of the peak heat loads on the plasma facing components is essential for the success of the next generation of high fusion power tokamaks such as the International Thermonuclear Experimental Reactor (ITER) [Rebut et al., Plasma Physics and Controlled Nuclear Fusion Research (International Atomic Energy Agency, Vienna, in press)]. Many present concepts for accomplishing this involve the use of atomic processes to transfer the heat from the plasma to the main chamber and divertor chamber walls and much of the experimental and theoretical physics research in the fusion program is directed toward this issue. The results of these experiments and calculations depend upon a complex interplay of many processes. In order to identify the key features of these experiments and calculations and the relative role of the primary atomic processes, simple quasianalytic models and the latest atomic physics rate coefficients and cross sections have been used to assess the relative roles of central radiation losses through bremsstrahlung, impurity radiation losses from the plasma edge, charge exchange and hydrogen radiation losses from the scrape-off layer, and divertor plasma and impurity radiation losses from the divertor plasma. This analysis indicates that bremsstrahlung from the plasma center and impurity radiation from the plasma edge and divertor plasma can each play a significant role in reducing the power to the divertor plates, and identifies many of the factors which determine the relative role of each process. For instance, for radiation losses in the divertor to be large enough to radiate the power in the divertor for high power experiments, a neutral fraction of 10−3 to 10−2 and an impurity recycling rate of neτrecycle of ∼1016 s m−3 will be required in the divertor.
Upper and lower bounds of the effective trapped particle fraction in general tokamak equilibria
Authors: Lin-Liu Y. R. , Miller R. L.
Published: July 2002

An upper bound and a lower bound of the effective trapped particle fraction, ft, in general tokamak equilibria are constructed by invoking the Schwartz inequality. A weighted average of these bounds that is easily evaluated is shown to give an accurate estimate of ft over a wide range of equilibrium parameters.
An evaluation of different antenna designs for helicon wave excitation in a cylindrical plasma source
Authors: Kamenski I. V. , Borg G. G.
Published: July 2002

A magnetohydrodynamic numerical model, based on the finite element method, is employed to analyze the antenna radiation resistance in a cylindrical helicon wave driven plasma source. The antenna radiation resistances of four commonly used antennas are compared. The effects on antenna radiation resistance of frequency, plasma density, density profile and the system dimensions are investigated. It is confirmed that m=+1 is the most strongly excited mode. It is shown that the plasma density gradient tends to suppress the excitation of negative m-modes. Some wave field patterns are also presented which demonstrate commonly observed features in the experiments such as the beat patterns of copropagating radial modes. The findings highlight the importance of antenna radiation resistance modelling as a first step to a self consistent model of the discharge physics of cool dense helicon wave driven sources.
Transport processes and entropy production in toroidally rotating plasmas with electrostatic turbulence
Authors: Sugama H. , Horton W.
Published: July 2002

A new gyrokinetic equation is derived for rotating plasmas with large flow velocities on the order of the ion thermal speed. Neoclassical and anomalous transport of particles, energy, and toroidal momentum are systematically formulated from the ensemble-averaged kinetic equation with the gyrokinetic equation. As a conjugate pair of the thermodynamic force and the transport flux, the shear of the toroidal flow, which is caused by the radial electric field shear, and the toroidal viscosity enter both the neoclassical and anomalous entropy production. The interaction between the fluctuations and the sheared toroidal flow is self-consistently described by the gyrokinetic equation containing the flow shear as the thermodynamic force and by the toroidal momentum balance equation including the anomalous viscosity. Effects of the toroidal flow shear on the toroidal ion temperature gradient driven modes are investigated. Linear and quasilinear analyses of the modes show that the toroidal flow shear decreases the growth rates and reduces the anomalous toroidal viscosity.
Determination of local tokamak parameters by magnetohydrodynamic spectroscopy
Authors: Holties H. A. , Fasoli A. , Goedbloed J. P. , Huysmans G. T. A. , Kerner W.
Published: July 2002

The influence of local equilibrium parameters on the Alfvén spectrum is studied. The aim is to solve the inverse problem: identification of the plasma profiles, and especially the safety factor profile, using measurements of magnetohydrodynamic (MHD) waves. A study case is presented to determine what the possible uses of MHD spectroscopy are. The dependence of the TAE (Toroidicity induced Alfvén Eigenmode) frequency on the safety factor at the edge is shown. The possible use of Alfvén continuum modes near the edge is investigated. A very accurate determination of the safety factor on axis will be presented for plasmas where core-localized TAE’s are present. It will be shown how measurements of mode structures can provide information on plasma parameters at particular points in the plasma. The numerical findings will be compared to experimental results from the Joint European Torus (JET) [P. H. Rebut and the JET Team, Plasma Physics and Controlled Nuclear Fusion Research 1984 (International Atomic Energy Agency, Vienna, 1985), Vol. 1, p. 11] active Alfvén wave diagnostic.
Dynamics and control of internal transport barriers in reversed shear discharges
Authors: Newman D. E. , Carreras B. A. , Lopez-Bruna D. , Diamond P. H. , Lebedev V. B.
Published: July 2002

Transitions to an enhanced confinement regime in tokamak plasmas with negative central magnetic shear have been observed in a number of devices. A simple model incorporating the nonlinear coupling between the turbulent fluctuations and the sheared radial electric field is added to a transport model in order to investigate the dynamics of the transition to this enhanced confinement mode. In this model, by incorporating both the instability growth rate profiles and particle and/or power deposition profiles, a rich variety of transition dynamics is uncovered. Transition dynamics and their concomitant thresholds are examined within the context of these models. In the course of investigating these transitions, potential methods for triggering and controlling these enhanced confinement regimes have been discovered and are discussed.
Optical absorption characteristics in semi-insulating GaAs crystals
Authors: Mita Yoh
Published: July 2002

Bleaching and related optical characteristics investigations have been carried out on near-infrared absorption bands in undoped, semi-insulating GaAs to examine the nature of As-rich defects relevant to the absorption. The results obtained for preferential bleaching characteristics have led to the conclusion that the defects responsible for the absorption are not likely to be isolated defects or a single species of simple associated defects.
Dependence of the photoreflectance of semi-insulating GaAs on temperature and pump chopping frequency
Authors: Shen H. , Hang Z. , Pan S. H. , Pollak Fred H. , Woodall J. M.
Published: July 2002

The amplitude of the photoreflectance (PR) spectra of the direct gap of semi-insulating GaAs has been studied as a function of pump chopping frequency (2–4000 Hz) and temperature (25–198 °C). We have been able to deduce a temperature-dependent trap time and hence trap activation energy of 0.70±0.05 eV. Our experiment demonstrates that PR can be used as a contactless method to study deep traps in semiconductors, analogous to deep level transient spectroscopy.
Force microscopy of magnetization patterns in longitudinal recording media
Authors: Mamin H. J. , Rugar D. , Stern J. E. , Terris B. D. , Lambert S. E.
Published: July 2002

A force microscope with a magnetic tip has been used to examine magnetization patterns in a thin-film cobalt-alloy sample similar to that used in magnetic disk recording. Longitudinal magnetic bits were written on discrete tracks with a recording head flown over the surface of the sample. After minimal sample preparation, images were obtained showing strong magnetic contrast. Model calculations for the expected image contrast were found to be in excellent qualitative agreement with experimental results. By using a constant height imaging mode, enhanced contrast for fine detail was obtained.
A liposome-based therapeutic vaccine against β-amyloid plaques on the pancreas of transgenic NORBA mice
Authors: Nicolau Claude , Greferath Ruth , Balaban Teodor Silviu , Lazarte Jaime E. , Hopkins Robert J.
Published: July 2002

Immune tolerance to β-amyloid (Aβ) was broken in NORBA transgenic mice presenting Aβ plaques on their pancreases. Vaccination of Black C57, BALB/c, and NORBA mice with the synthetic Aβ
1–16
sequence modified by covalently attaching two palmitoyl residues at each end of the peptide, subsequently reconstituted in liposomes–Lipid A elicited titers of 1:5,000 of anti-Aβ
1–16
antibodies within 10 weeks after the first inoculation. On direct interaction, sera with antibody titers of 1:5,000 solubilized
in vitro
up to 80% of preformed Aβ
1–42
aggregates. Cryosections of pancreases of unvaccinated NORBA mice show, on staining with Thioflavin T, extensive areas of high-intensity fluorescence in the acinar cell fields. Quantitation of the average fluorescence intensity in each section indicated that: (
i
) whereas nonvaccinated NORBA mice develop plaques within 45–60 days after birth, vaccinated 8-week-old NORBA mice did not develop amyloid plaques on their pancreases over a period of 7 months; (
ii
) cryosections from pancreases of 9- and 15-month-old vaccinated NORBA mice showed less than 50% of the fluorescence shown by cryosections from unvaccinated animals of the same age. The results indicate that palmitoylated Aβ peptides, reconstituted in liposomes–lipid A, are highly immunogenic, eliciting “therapeutic” antibody titers within 3 months of the first inoculation and preventing amyloid plaque formation in young animals or significantly reducing existing plaques in older transgenic mice. Possible implications for the therapy of Alzheimer's disease are discussed.
Visualization of gas flow and diffusion in porous media
Authors: Kaiser Lana G. , Meersmann Thomas , Logan John W. , Pines Alexander
Published: July 2002

The transport of gases in porous materials is a crucial component of many important processes in science and technology. In the present work, we demonstrate how magnetic resonance microscopy with continuous flow laser-polarized noble gases makes it possible to “light up” and thereby visualize, with unprecedented sensitivity and resolution, the dynamics of gases in samples of silica aerogels and zeolite molecular sieve particles. The “polarization-weighted” images of gas transport in aerogel fragments are correlated to the diffusion coefficient of xenon obtained from NMR pulsed-field gradient experiments. The technique provides a unique means of studying the combined effects of flow and diffusion in systems with macroscopic dimensions and microscopic internal pore structure.
Adeno-associated viral vector-mediated gene transfer results in long-term enzymatic and functional correction in multiple organs of Fabry mice
Authors: Jung Sung-Chul , Han Ina P. , Limaye Advait , Xu Ruian , Gelderman Monique P. , Zerfas Patricia , Tirumalai Kamala , Murray Gary J. , During Matthew J. , Brady Roscoe O. , Qasba Pankaj
Published: July 2002

Fabry disease is a lysosomal storage disorder caused by a
deficiency of the lysosomal enzyme α-galactosidase A (α-gal A).
This enzyme deficiency leads to impaired catabolism of
α-galactosyl-terminal lipids such as globotriaosylceramide (Gb3).
Patients develop painful neuropathy and vascular occlusions that
progressively lead to cardiovascular, cerebrovascular, and renal
dysfunction and early death. Although enzyme replacement therapy and
bone marrow transplantation have shown promise in the murine analog of
Fabry disease, gene therapy holds a strong potential for treating this
disease in humans. Delivery of the normal α-gal A gene (cDNA) into a
depot organ such as liver may be sufficient to elicit corrective
circulating levels of the deficient enzyme. To investigate this
possibility, a recombinant adeno-associated viral vector encoding human
α-gal A (rAAV-AGA) was constructed and injected into the hepatic
portal vein of Fabry mice. Two weeks postinjection, α-gal A
activity in the livers of rAAV-AGA-injected Fabry mice was 20–35% of
that of the normal mice. The transduced animals continued to show
higher α-gal A levels in liver and other tissues compared with the
untouched Fabry controls as long as 6 months after treatment. In
parallel to the elevated enzyme levels, we see significant reductions
in Gb3 levels to near normal at 2 and 5 weeks posttreatment. The lower
Gb3 levels continued in liver, spleen, and heart, up to 25 weeks with
no significant immune response to the virus or α-gal A. Also, no
signs of liver toxicity occurred after the rAAV-AGA administration.
These findings suggest that an AAV-mediated gene transfer may be useful
for the treatment of Fabry disease and possibly other metabolic
disorders.
A psychophysical dissection of the brain sites involved in color-generating comparisons
Authors: Moutoussis K. , Zeki S.
Published: July 2002

We have used simple psychophysical methods to determine the sites of color-generating mechanisms in the brain. In our first experiment, subjects viewed an abstract multicolored “Mondrian” display through one eye and an isolated patch from the display through the other. With normal binocular/monocular viewing, the patch has a different color when viewed on its own (void mode) or as part of the Mondrian display (natural mode) [Land, E. H. (1974)
Proc. R. Inst. G. B.
49, 23–58]. When the two stimuli were viewed dichoptically, with the patch occupying the position that it would occupy in the Mondrian complex under normal viewing, the patch always appeared in its void color. In a second experiment, when subjects viewed multicolored displays through a different narrow-band filter placed over each eye, the information from the two eyes was combined to result in new colors, which were not seen through either of the two eyes alone. Taken together, these results dissect color-generating mechanisms into two stages, located at different sites of the brain: The first occurs before the appearance of binocular neurons in the cortex and compares wavelength information across space, whereas the second occurs after the convergence of the input from the two eyes and synthetically combines the results of the first.
Electrolytic actuators: Alternative, high-performance, material-based devices
Authors: Cameron Colin G. , Freund Michael S.
Published: July 2002

The emerging field of materials-based actuation continues to be the focus of considerable research because of its inherent scalability and its promise to drive micromechanical devices that cannot be realized with conventional mechanical actuator strategies. The electrolytic phase transformation actuator offers a new broad-spectrum solution to the problem of direct conversion of electrical to mechanical energy. Strains of 136,000% and unoptimized work cycle efficiencies near 50% are demonstrated in a prototype device. Conceivably capable of generating stress beyond 200 MPa, this new approach promises performance orders of magnitude beyond other novel actuation strategies.
A mouse model for adenovirus gene delivery
Authors: Tallone Tiziano , Malin Stephen , Samuelsson Annika , Wilbertz Johannes , Miyahara Mitsue , Okamoto Kensaku , Poellinger Lorenz , Philipson Lennart , Pettersson Sven
Published: July 2002

The cellular attachment receptor for adenovirus (Ad), Coxsackie adenovirus receptor (CAR), required for delivery of Ad into primary cells, is not present on all cell types, thus restricting Ad-gene delivery systems. To circumvent this constrain, a transgenic mouse has been generated that expresses a truncated human CAR in all tissues analyzed. These mice allowed efficient
in vitro
infections at low multiplicities into lymphoid, myeloid, and endothelial cells. Furthermore,
in vivo
administration of Ad-vectors results in infection of macrophages, lymphocytes, and endothelial cells. In addition, tail vein injection resulted in targeting of virus into previously inaccessible areas, such as the lung and the capillaries of the brain. The CAR transgenic mice will be useful for rapid functional genomic analysis
in vivo
, for testing the efficacy of gene therapy procedures or as a source of easily transducible cells.
Old yellow enzyme: Reduction of nitrate esters, glycerin trinitrate, and propylene 1,2-dinitrate
Authors: Meah Younus , Brown Bette Jo , Chakraborty Sumita , Massey Vincent
Published: July 2002

The reaction of the old yellow enzyme and reduced flavins with organic nitrate esters has been studied. Reduced flavins have been found to react readily with glycerin trinitrate (GTN ) (nitroglycerin) and propylene dinitrate, with rate constants at pH 7.0, 25°C of 145 M
−1
s
−1
and 5.8 M
−1
s
−1
, respectively. With GTN, the secondary nitrate was removed reductively 6 times faster than the primary nitrate, with liberation of nitrite. With propylene dinitrate, on the other hand, the primary nitrate residue was 3 times more reactive than the secondary residue. In the old yellow enzyme-catalyzed NADPH-dependent reduction of GTN and propylene dinitrate, ping-pong kinetics are displayed, as found for all other substrates of the enzyme. Rapid-reaction studies of mixing reduced enzyme with the nitrate esters show that a reduced enzyme–substrate complex is formed before oxidation of the reduced flavin. The rate constants for these reactions and the apparent
K
d
values of the enzyme–substrate complexes have been determined and reveal that the rate-limiting step in catalysis is reduction of the enzyme by NADPH. Analysis of the products reveal that with the enzyme-catalyzed reactions, reduction of the primary nitrate in both GTN and propylene dinitrate is favored by comparison with the free-flavin reactions. This preferential positional reactivity can be rationalized by modeling of the substrates into the known crystal structure of the enzyme. In contrast to the facile reaction of free reduced flavins with GTN, reduced 5-deazaflavins have been found to react some 4–5 orders of magnitude slower. This finding implies that the chemical mechanism of the reaction is one involving radical transfers.
Retinoic acid (RA) and As
2
O
3
treatment in transgenic models of acute promyelocytic leukemia (APL) unravel the distinct nature of the leukemogenic process induced by the PML-RARα and PLZF-RARα oncoproteins
Authors: Rego Eduardo M. , He Li-Zhen , Warrell Raymond P. , Wang Zhu-Gang , Pandolfi Pier Paolo
Published: July 2002

Acute promyelocytic leukemia (APL) is associated with chromosomal translocations always involving the
RARα
gene, which variably fuses to one of several distinct loci, including
PML
or
PLZF
(X genes) in t(15;17) or t(11;17), respectively. APL in patients harboring t(15;17) responds well to retinoic acid (RA) treatment and chemotherapy, whereas t(11;17) APL responds poorly to both treatments, thus defining a distinct syndrome. Here, we show that RA, As
2
O
3
, and RA + As
2
O
3
prolonged survival in either leukemic PML-RARα transgenic mice or nude mice transplanted with PML-RARα leukemic cells. RA + As
2
O
3
prolonged survival compared with treatment with either drug alone. In contrast, neither in PLZF-RARα transgenic mice nor in nude mice transplanted with PLZF-RARα cells did any of the three regimens induce complete disease remission. Unexpectedly, therapeutic doses of RA and RA + As
2
O
3
can induce, both
in vivo
and
in vitro
, the degradation of either PML-RARα or PLZF-RARα proteins, suggesting that the maintenance of the leukemic phenotype depends on the continuous presence of the former, but not the latter. Our findings lead to three major conclusions with relevant therapeutic implications: (
i
) the X-RARα oncoprotein directly determines response to treatment and plays a distinct role in the maintenance of the malignant phenotype; (
ii
) As
2
O
3
and/or As
2
O
3
+ RA combination may be beneficial for the treatment of t(15;17) APL but not for t(11;17) APL; and (
iii
) therapeutic strategies aimed solely at degrading the X-RARα oncoprotein may not be effective in t(11;17) APL.
Altered transcription in yeast expressing expanded polyglutamine
Authors: Hughes Robert E. , Lo Russell S. , Davis Colleen , Strand Andrew D. , Neal Cassandra L. , Olson James M. , Fields Stanley
Published: July 2002

Expanded polyglutamine tracts are responsible for at least eight fatal neurodegenerative diseases. In mouse models, proteins with expanded polyglutamine cause transcriptional dysregulation before onset of symptoms, suggesting that this dysregulation may be an early event in polyglutamine pathogenesis. Transcriptional dysregulation and cellular toxicity may be due to interaction between expanded polyglutamine and the histone acetyltransferase CREB-binding protein. To determine whether polyglutamine-mediated transcriptional dysregulation occurs in yeast, we expressed polyglutamine tracts in
Saccharomyces cerevisiae
. Gene expression profiles were determined for strains expressing either a cytoplasmic or nuclear protein with 23 or 75 glutamines, and these profiles were compared to existing profiles of mutant yeast strains. Transcriptional induction of genes encoding chaperones and heat-shock factors was caused by expression of expanded polyglutamine in either the nucleus or cytoplasm. Transcriptional repression was most prominent in yeast expressing nuclear expanded polyglutamine and was similar to profiles of yeast strains deleted for components of the histone acetyltransferase complex Spt/Ada/Gcn5 acetyltransferase (SAGA). The promoter from one affected gene (
PHO84
) was repressed by expanded polyglutamine in a reporter gene assay, and this effect was mitigated by the histone deacetylase inhibitor, Trichostatin A. Consistent with an effect on SAGA, nuclear expanded polyglutamine enhanced the toxicity of a deletion in the SAGA component
SPT3
. Thus, an early component of polyglutamine toxicity, transcriptional dysregulation, is conserved in yeast and is pharmacologically antagonized by a histone deacetylase inhibitor. These results suggest a therapeutic approach for treatment of polyglutamine diseases and provide the potential for yeast-based screens for agents that reverse polyglutamine toxicity.
A viral member of the ERV1/ALR protein family participates in a cytoplasmic pathway of disulfide bond formation
Authors: Senkevich Tatiana G. , White Christine L. , Koonin Eugene V. , Moss Bernard
Published: July 2002

Proteins of the ERV1/ALR family are encoded by all
eukaryotes and cytoplasmic DNA viruses for which substantial sequence
information is available. Nevertheless, the roles of these proteins are
imprecisely known. Multiple alignments of ERV1/ALR proteins
indicated an invariant C-X-X-C motif, but no similarity to the
thioredoxin fold was revealed by secondary structure predictions. We
chose a virus model to investigate the role of these proteins as thiol
oxidoreductases. When cells were infected with a mutant vaccinia virus
in which the E10R gene encoding an ERV1/ALR family protein was
repressed, the disulfide bonds of three other viral proteins—namely,
the L1R and F9L proteins and the G4L glutaredoxin—were completely
reduced. The same outcome occurred when Cys-43 or Cys-46, the putative
redox cysteines of the E10R protein, was mutated to serine. These two
cysteines were disulfide bonded during a normal virus infection but not
if the synthesis of other viral late proteins was inhibited or the E10R
protein was expressed by itself in uninfected cells, suggesting a
requirement for an upstream viral thiol oxidoreductase. Remarkably, the
cysteine-containing domains of the E10R and L1R viral membrane proteins
and the glutaredoxin are in the cytoplasm, in which assembly of
vaccinia virions occurs, rather than in the oxidizing environment of
the endoplasmic reticulum. These data indicated a viral pathway of
disulfide bond formation in which the E10R protein has a central role.
By extension, the ERV1/ALR family may represent a ubiquitous
class of cellular thiol oxidoreductases that interact with
glutaredoxins or thioredoxins.
Meiotic lamin C2: The unique amino-terminal hexapeptide GNAEGR is essential for nuclear envelope association
Authors: Alsheimer Manfred , von Glasenapp Elisabeth , Schnölzer Martina , Heid Hans , Benavente Ricardo
Published: July 2002

Meiotic lamin C2 is the only A-type lamin expressed during
mammalian spermatogenesis. Typical for this short lamin is the unique
hexapeptide GNAEGR, which substitutes the nonhelical amino terminus and
part of the α-helical rod domain present in somatic lamins. Meiotic
lamin C2 also lacks a carboxyl-terminal CaaX box, which is modified by
isoprenylation and involved in nuclear envelope (NE) association of
somatic isoforms. The mechanism by which lamin C2 becomes localized in
the NE is totally unknown. Here we demonstrate that the hexapeptide
GNAEGR is essential for this process: (
i
) Its deletion
resulted in a diffuse distribution of lamin C2 within nuclei of
transfected COS-7 cells; (
ii
) Mutated somatic lamin C,
containing the sequence GNAEGR at its amino terminus, was located at
the NE. The mass spectrometric analysis of the amino terminus of lamin
C2 revealed that it is modified by myristoylation. Correspondingly, the
substitution of the first glycine residue abolishes the NE association
of lamin C2. We conclude that NE association of lamin C2 is achieved by
a mechanism different from that of somatic lamins.
Algorithmic cooling and scalable NMR quantum computers
Authors: Boykin P. Oscar , Mor Tal , Roychowdhury Vwani , Vatan Farrokh , Vrijen Rutger
Published: July 2002

We present here algorithmic cooling (via polarization heat bath)—a powerful method for obtaining a large number of highly polarized spins in liquid nuclear-spin systems at finite temperature. Given that spin-half states represent (quantum) bits, algorithmic cooling cleans dirty bits beyond the Shannon's bound on data compression, by using a set of rapidly thermal-relaxing bits. Such auxiliary bits could be implemented by using spins that rapidly get into thermal equilibrium with the environment, e.g., electron spins. Interestingly, the interaction with the environment, usually a most undesired interaction, is used here to our benefit, allowing a cooling mechanism. Cooling spins to a very low temperature without cooling the environment could lead to a breakthrough in NMR experiments, and our “spin-refrigerating” method suggests that this is possible. The scaling of NMR ensemble computers is currently one of the main obstacles to building larger-scale quantum computing devices, and our spin-refrigerating method suggests that this problem can be resolved.
Dinosaurs, dragons, and dwarfs: The evolution of maximal body size
Authors: Burness Gary P. , Diamond Jared , Flannery Timothy
Published: July 2002

Among local faunas, the maximum body size and taxonomic affiliation of the top terrestrial vertebrate vary greatly. Does this variation reflect how food requirements differ between trophic levels (herbivores vs. carnivores) and with taxonomic affiliation (mammals and birds vs. reptiles)? We gathered data on the body size and food requirements of the top terrestrial herbivores and carnivores, over the past 65,000 years, from oceanic islands and continents. The body mass of the top species was found to increase with increasing land area, with a slope similar to that of the relation between body mass and home range area, suggesting that maximum body size is determined by the number of home ranges that can fit into a given land area. For a given land area, the body size of the top species decreased in the sequence: ectothermic herbivore > endothermic herbivore > ectothermic carnivore > endothermic carnivore. When we converted body mass to food requirements, the food consumption of a top herbivore was about 8 times that of a top carnivore, in accord with the factor expected from the trophic pyramid. Although top ectotherms were heavier than top endotherms at a given trophic level, lower metabolic rates per gram of body mass in ectotherms resulted in endotherms and ectotherms having the same food consumption. These patterns explain the size of the largest-ever extinct mammal, but the size of the largest dinosaurs exceeds that predicted from land areas and remains unexplained.
Stable transfer of intact high molecular weight DNA into plant chromosomes.
Authors: Hamilton C M , Frary A , Lewis C , Tanksley S D
Published: July 2002

In conjunction with an enhanced system for Agrobacterium-mediated plant transformation, a new binary bacterial artificial chromosome (BIBAC) vector has been developed that is capable of transferring at least 150 kb of foreign DNA into a plant nuclear genome. The transferred DNA appears to be intact in the majority of transformed tobacco plants analyzed and is faithfully inherited in the progeny. The ability to introduce high molecular weight DNA into plant chromosomes should accelerate gene identification and genetic engineering of plants and may lead to new approaches in studies of genome organization.
Distinct roles for two G protein α subunits in fungal virulence, morphology, and reproduction revealed by targeted gene disruption
Authors: Gao Shaojian , Nuss Donald L.
Published: July 2002

Reduced accumulation of the GTP-binding protein G
i
α
subunit CPG-1, due either to hypovirus infection or transgenic
cosuppression, correlates with virulence attenuation of the chestnut
blight fungus,
Cryphonectria parasitica
. The role of G
protein-mediated signal transduction in fungal virulence was further
examined by targeted disruption of the gene
cpg-1
,
encoding CPG-1, and a second Gα gene,
cpg-2
, encoding
the subunit CPG-2. Disruption of
cpg-1
resulted in a set
of phenotypic changes similar to, but more severe than, those
associated with hypovirus infection. Changes included a marked
reduction in fungal growth rate and loss of virulence, asexual
sporulation, female fertility, and transcriptional induction of the
gene
lac-1,
encoding the enzyme laccase. In contrast,
cpg-2
disruption resulted in only slight reductions in
growth rate and asexual sporulation and no significant reduction in
virulence, female fertility, or
lac-1
mRNA inducibility.
These results provide definitive confirmation of previous correlative
evidence that suggested a requirement of CPG-1-linked signaling for a
number of fungal processes, including virulence and reproduction, while
demonstrating that a second Gα, CPG-2, is dispensable for these
processes. They also significantly strengthen support for the apparent
linkage between hypovirus-mediated disruption of G protein signal
transduction and attenuation of fungal virulence.