bluuebunny/crossref_metadata_2025 huggingface dataset:
On Kolmogorov- and Kraichnan-type spectra due to the reflection Alfvén waves
Authors: Campos L. M. B. C. , Isaeva N. L , Gil P. J. S.
Published: July 2002

Alfvén waves are considered in a radially inhomogeneous medium under a radial background magnetic field: In order for the latter to be divergence free, the magnetic field strength must decay like the inverse square of the distance; for the radial dependence of the mass density an arbitrary inverse power of the distance is assumed. The Alfvén wave equation is solved exactly in terms of Bessel functions, and the properties of the solutions are examined: (i) for small radial distances, when the reflection of waves by the inhomogeneity of the medium depends on frequency, thereby changing their spectrum; (ii) for large radial distances, when the ray approximation holds, the spectrum no longer changes and the equipartition of kinetic and magnetic energies is true; (iii) for intermediate radial distances the evolution between the limits (i) and (ii) is illustrated by plotting (Figs. 1 to 4) the wave forms of the velocity and magnetic field perturbations, for a variety of wave periods. The present problem involves some features of Alfvén wave propagation in the solar wind (monopole background magnetic field and radially decaying density), but omits others (the presence of background flow, nonradial or spiral components of the background magnetic field and multiple ion species) and thus applies only near to the sun, viz. when the mean flow velocity is still small relative to the Alfvén speed. The present model does account for the effects of nonuniform mass density for all wavelengths, whether short, long, or comparable to the length scales of variation of the mass density. It shows that the process of wave reflection can lead to Kolmogorov, Kraichnan, or similar types of spectra observed in the solar wind; thus wave reflection remains a linear theory alternative to the nonlinear turbulent cascade as a model for Alfvénic disturbances in the solar wind. Moreover, the growth of Alfvén waves with distance could lead to nonlinear effects which drive the energy cascade of hydromagnetic turbulence by the interaction of direct and reflected Alfvén waves; this would establish a relation between “wave” and “turbulent” models of Alfvénic disturbances in the solar wind. Some of the literature on Alfvén waves and magnetohydrodynamic turbulence in the solar wind uses the Elsasser equations in original form for incompressible disturbances, overlooking the fact that there are additional terms in the case of an inhomogeneous medium, as shown in Appendix A.
Radial dependence of magnetohydrodynamic continuum modes in axisymmetric toroidal geometry
Authors: Salat A. , Tataronis J. A.
Published: July 2002

A characteristic feature of modes in the continua (“Alfvén” and “slow”) of magnetohydrodynamics (MHD) is their singularity at a magnetic surface ψ=ψ0. For axisymmetric toroidal configurations the dependence of continuum modes on the distance ψ−ψ0 is reexamined. It is found that, in general, the normal component ξψ of the plasma displacement has an oscillatory type of singularity: ξψ∼(ψ−ψ0)σ∼sin(|σ|ln|ψ−ψ0|+const), where σ is an imaginary constant. For special classes of MHD configurations σ vanishes. In this case the previously derived law ξψ∼ln|ψ−ψ0|, [Y. Pao, Nucl. Fusion 15, 631 (1975)] remains valid. Configurations with up/down symmetry pertain to these classes.
Temporal behavior of backscattering instabilities in a three-dimensional cylindrical hot spot: I. Standard decay regime
Authors: Divol Laurent , Mounaix Philippe
Published: July 2002

The space and time behavior of backscattering instabilities in a three-dimensional cylindrical hot spot of finite lifetime is computed analytically in the so-called standard decay (or weak coupling) regime. A uniform expression for the instantaneous backscattered power, valid for any time and any hot spot intensity in the standard decay regime, is proposed. It is shown that the finite transverse size of the hot spot leads to important diffraction effects that can significantly reduce the hot spot backscattered energy. The plasma is assumed to be homogeneous and the hot spot depletion is ignored. The coupled mode equations are solved in terms of fluctuating source terms corresponding to the noise from which the instability grows. Diffraction effects on the growth of the absolute instability inside a long lifetime hot spot is investigated.
Strong variation of average ion energy in oscillation frequency of sheath potential
Authors: Lee Young D. , Kim S. S. , Ku S. H. , Chang C. S.
Published: July 2002

In a modern plasma etching device, the plasma sheath potential is usually superposed by an externally driven oscillating voltage to enhance and control the bombarding ion energy. A collisionless particle simulation is used to study the variation of average kinetic energy 〈K〉(νrf) of bombarding ions as a function of a wide range of sheath oscillation frequency νrf (0.1νpi⩽νrf⩽10νpi, where νpi is the ion plasma frequency). It is found that a resonance phenomenon between the ion transit motion and the sheath oscillation can yield a strongly peaked enhancement of 〈K〉(νrf) near νrf≃0.5νpi. Ion species with different mass show the peaks at different νrf. The relative importance of different ion molecules in an ion-enhanced etching process will be sensitive to νrf. This phenomenon may allow a reduction of the undesirable capacitive coupling by optimizing νrf to yield an enhanced 〈K〉 of desired ion species at low applied voltages.
Eikonal scattering cross section for elastic electron–ion collisions in nonideal plasmas
Authors: Jung Young-Dae , Yoon Jung-Sik
Published: July 2002

Modified eikonal approximation is applied to investigate the elastic electron–ion collisions in nonideal plasmas. An effective pseudopotential model, taking into account the plasma screening and collective effects, is applied to describe the electron–ion interaction potential in a classical nonideal plasma. The semiclassical straight-line trajectory approximation is applied to the motion of the projectile electron in order to investigate the variation of the total elastic scattering cross section as a function of the projectile energy, nonideal plasma parameter, and Debye length. The results show that the scaled total cross section in ideal plasmas described by the Debye–Hückel potential model is found to be greater than that in nonideal plasmas described by the pseudopotential model. It is also found that the scaled cross section is decreased with increasing the nonideal plasma parameter (γ), i.e., the nonideality of plasmas reduces the electron–ion collision cross section.
A kinetic magnetohydrodynamic energy integral in three dimensional geometry
Authors: Könies Axel
Published: July 2002

Recent observations of Alfvén wave excitations in stellarator geometry and their successful description by the global magnetohydrodynamic (MHD) stability code CAS3D (Code for the Analysis of the MHD Stability of 3D Equilibria) [C. Nührenberg, Phys. Plasmas 6, 137 (1998)] have raised the question of to what extent a fast particle population may destabilize such modes. In answering this question a theoretical basis must be developed through which the influence of fast particles upon global MHD modes in realistic three-dimensional geometries can be investigated. As a first step towards this goal, a linearized drift-kinetic equation for electro-magnetic perturbations is derived and solved. It is furthermore shown that a generalized kinetic MHD energy integral exists which is nonlinear with respect to the mode frequencies. This energy integral agrees with previous less general results in their limits.
Nonlinear stability limit in high β tokamaks
Authors: Kleva Robert G. , Guzdar Parvez N.
Published: July 2002

Linearly unstable high β tokamak equilibria are shown to be nonlinearly stabilized by an axisymmetric flow containing both toroidal and poloidal components. As fingers of hot plasma produced by pressure driven ballooning instabilities start to convect out towards the bounding wall, an axisymmetric flow is self-consistently generated and opposes the growth of the fingers, maintaining confinement. However, as β increases the growth rate of the fingers increases until there is insufficient time for the developing axisymmetric flow to halt their rapid progress to the wall, and confinement is lost. The ultimate stability of a tokamak plasma is determined by a nonlinear stability limit in β.
Breakdown in silicon oxides (II)—correlation with Fe precipitates
Authors: Honda Kouichirou , Ohsawa Akira , Toyokura Nobuo
Published: July 2002

Thin silicon oxides of metal-oxide-semiconductor (MOS) capacitors were studied by transmission electron microscopy. The MOS capacitors were fabricated on silicon wafers which had been intentionally contaminated by Fe+ ion implantation. It was found that Fe precipitates crossing the SiO2/Si interface penetrated into the silicon oxide from the silicon substrate. They reduced the breakdown strength by inducing singularity points in the silicon oxide.
Picosecond pulse amplification using a copper vapor laser
Authors: Hopkins J. B. , Rentzepis P. M.
Published: July 2002

A high repetition amplification scheme for picosecond pulses has been developed using a copper vapor laser. Pulses of <5 ps full width at half-maximum duration and ∼0.7 nJ energy from a synchronously pumped mode-locked dye laser have been amplified up to ∼50 μJ. This technique offers an attractive means for the generation of stable, high repetition 5 kHz picosecond pulses which can be used advantageously for spectroscopic and Raman studies.
Dry, laser-assisted rapid HBr etching of GaAs
Authors: Brewer P. D. , McClure D. , Osgood R. M.
Published: July 2002

Dry, rapid etching of GaAs has been accomplished using an excimer laser (ArF, 193 nm) with HBr etching gas by photochemical initiation. Spatially uniform etch rates of up to 8 μm/min have been achieved on large-area, masked substrates. Selective crystallographic etching is observed and controlled in the process.
Direct imaging of Au and Ag clusters by scanning tunneling microscopy
Authors: Abraham David W. , Sattler Klaus , Ganz Eric , Mamin H. Jonathon , Thomson Ruth Ellen , Clarke John
Published: July 2002

Clusters of Au and Ag deposited on the surface of highly oriented pyrolitic graphite have been imaged in air using a scanning tunneling microscope. An image is shown of a 350-Å silver cluster obtained in the constant-current (topographic) mode. In the variable-current mode, clusters of 6–20 atoms have been observed with atomic resolution. The motion and growth of clusters on the support are observed.
Energy-gap spectroscopy of superconductors using a tunneling microscope
Authors: Le Duc H. G. , Kaiser W. J. , Stern J. A.
Published: July 2002

A unique scanning tunneling microscope (STM) system has been developed for spectroscopy of the superconducting energy gap. High-resolution control of tunnel current and voltage allows for measurement of superconducting properties at tunnel resistance levels 102–103 greater than that achieved in prior work. The previously used STM methods for superconductor spectroscopy are compared to those developed for the work reported here. Superconducting energy-gap spectra are reported for three superconductors, Pb, PbBi, and NbN, over a range of tunnel resistance. The measured spectra are compared directly to theory.
Temporal measurements of photofragment attenuation at 248 nm in the laser ablation of polyimide in air
Authors: Koren G.
Published: July 2002

A 248-nm laser pulse of 35 ns duration was split spatially into two beams: a strong beam used to completely ablate in a single pulse 1000- and 5000-Å-thick polyimide films on fused silica substrates, and a weak, time-delayed probe beam directed almost perpendicularly onto the sample through the ablated fragments in order to measure their transmission versus time. When ablating the 1000-Å-thick film at 1.1 J/cm2, a weak attenuation of the probe beam with a maximum value of 10–12% was observed during the laser pulse. Ablation of the 5000-Å-thick film at 4.2 J/cm2 showed a strong attenuation of 83% which lasted for 90 ns from the beginning of the ablating laser pulse and then dropped to 50% at 130 ns. These results indicate increased attenuation of the laser beam as the laser fluence increases, thus explaining the reduced ablation efficiency at high fluences.
Optical and electronic properties of reactively sputtered amorphous GeNx:H
Authors: Honma I. , Kawai K. , Komiyama H. , Tanaka K.
Published: July 2002

Basic photoelectronic properties of hydrogenated amorphous germanium nitride (a-GeNx:H) are presented for the first time. Amorphous-GeNx:H films were prepared by an rf reactive sputtering of a Ge target using Ar+N2+H2 mixed gases and their optical band gaps were controlled continuously in the range from 1.0 to 3.3 eV by varying the compositional ratio of nitrogen to germanium. In contrast to H-free a-GeNx, the temperature dependence of the dark conductivity of a-GeNx:H shows that thermally activated band conduction prevails in the carrier transport over a wide temperature range at least down to 180 K. The photo-to-dark conductivity ratio under AM1 light of unoptimized a-GeNx:H amounts to 40.
Model for defect-impurity pair diffusion in silicon
Authors: Mulvaney B. J. , Richardson W. B.
Published: July 2002

A new model for impurity diffusion in silicon by a point defect-impurity pair mechanism is described. A pair of coupled, nonlinear, partial differential equations for the silicon self-interstitial and the impurity is derived and solved numerically. The familiar kink and tail of phosphorus and, to a lesser extent, boron diffused profiles arise naturally from the solution. The coupling between defect and impurity becomes smaller at high temperatures and at low impurity concentrations, in agreement with experimental observations. The transient buildup of the defect concentration may have implications for models of rapid thermal processes.
Lifetime measurements in semiconductors by infrared absorption due to pulsed optical excitation
Authors: Ling Z. G. , Ajmera P. K. , Anselment M. , DiMauro L. F.
Published: July 2002

A new contactless technique for determination of excess carrier lifetime in semiconductors is demonstrated. The technique involves measuring the change in the transmitted intensity of a continuous probe beam (hνEg). The technique has been applied to silicon samples having different doping densities. The measured lifetime values in the range of 0.5–200 μs on both n-type and p-type silicon samples by this new technique agree well with the values obtained by the traditional photoconductive decay method.
Reactive ion etch process with highly controllable GaAs-to-AlGaAs selectivity using SF6 and SiCl4
Authors: Salimian S. , Cooper C. B. , Norton R. , Bacon J.
Published: July 2002

The use of a reactive ion etch process with high selectivity for etching GaAs layers and stopping on underlying AlGaAs layers is reported. A key feature is the high degree of control that can be maintained over the GaAs-to-AlGaAs selectivity by changing the SF6/SiCl4 ratio while keeping other etch parameters such as pressure, dc bias, or power constant. Values of the GaAs-to-AlGaAs selectivity can be varied from 1 to 500. Diluent gases such as helium can be added to reduce the etch rate, which is important to avoid damage to sensitive device structures and to the overhang profile of resist materials used for liftoff metallization. The application of this etch process for high electron mobility transistor fabrication is discussed.
High-speed GaAs p-i-n photodiodes grown on Si substrates by molecular beam epitaxy
Authors: Paslaski J. , Chen H. Z. , Morkoç H. , Yariv A.
Published: July 2002

We present results on high-speed GaAs p-i-n photodiodes grown on Si substrates by molecular beam epitaxy. In addition to the dc operating characteristics, we also report the first impulse response and microwave frequency response measurements of GaAs-on-Si photodiodes. Results include an impulse response pulse width of 45 ps and a modulation corner frequency >4 GHz at a reverse bias of −3 V.
Model study of the local vibration center related to EL2 levels in GaAs
Authors: Zhong Xuefu , Jiang Desheng , Ge Weikun , Song Chunying
Published: July 2002

A tentative explanation is given for a recently reported local vibrational mode induced infrared absorption which is related to EL2 centers in GaAs. Interstitial (or off-center substitutional) oxygen is suggested to be responsible for these vibration modes. Taking lattice relaxation into account, a simple model based on the two-center bond theory is proposed and evaluated. The adequacy of this model strongly implies a relationship of EL2 centers in the measured samples with oxygen.
Observation of p
n junctions on implanted silicon using a scanning tunneling microscope
Authors: Hosaka Sumio , Hosoki Shigeyuki , Takata Keiji , Horiuchi Katsutada , Natsuaki Nobuyoshi
Published: July 2002

Si pn junctions fabricated by photoresist masked As+ implantation were observed using current imaging tunneling spectroscopy (CITS) in a scanning tunneling microscope (STM). Using the CITS, a specific bias was chosen to define n-type or p-type areas according to whether or not current flowed. The pn junctions could be easily identified from the current image at this bias and in the STM topographic image. It also proved possible to find processing faults related to implantation. The STM images also identified the structure (corrugations) near the junctions, associated with volume expansion caused by implantation and annealing.
Resonant tunneling and intrinsic bistability in asymmetric double-barrier heterostructures
Authors: Zaslavsky A. , Goldman V. J. , Tsui D. C. , Cunningham J. E.
Published: July 2002

We report measurements of the current-voltage characteristics of an asymmetric GaAs/AlGaAs double-barrier resonant tunneling device. The structure was designed to increase the space charge in the well under forward bias and consequently enhance the electrostatic feedback that leads to intrinsic bistability. The magnetotunneling data demonstrate unambiguously that the observed bistability is the property of the device, rather than the biasing circuit.
Eukaryotic-type elongator tRNA
Met
of
Trypanosoma brucei
becomes formylated after import into mitochondria
Authors: Tan Timothy H. P. , Bochud-Allemann Natacha , Horn Elke K. , Schneider André
Published: July 2002

The mitochondrion of
Trypanosoma brucei
lacks tRNA genes. Its translation system therefore depends on the import of cytosolic, nucleus-encoded tRNAs. Thus, most trypanosomal tRNAs function in both the cytosol and the mitochondrion, and all are of the eukaryotic type. This is also the case for the elongator tRNA
Met
, whereas the only other trypanosomal tRNA
Met
, the eukaryotic initiator, is found exclusively in the cytosol. Unlike their cytosolic counterparts, organellar initiator tRNAs
Met
carry a formylated methionine. This raises the question of how initiation of translation works in trypanosomal mitochondria, where only elongator tRNA
Met
is found. Using
in organello
charging and formylation assays, we show that unexpectedly a fraction of elongator tRNA
Met
becomes formylated after import into mitochondria. Furthermore,
in vitro
experiments with mitochondrial extracts demonstrate that only the trypanosomal elongator and not the initiator tRNA
Met
is recognized by the formylation activity. Finally, RNA interference assays identify the gene encoding the trypanosomal formylase activity. Whereas the predicted protein is homologous to prokaryotic and mitochondrial methionyl-tRNA
Met
formyltransferases, it has about twice the mass of any of these proteins.
BimD/SPO76
is at the interface of cell cycle progression, chromosome morphogenesis, and recombination
Authors: van Heemst Diana , Käfer Etta , John Tricia , Heyting Christa , van Aalderen Mirjam , Zickler Denise
Published: July 2002

BIMD of
Aspergillus nidulans
belongs to a
highly conserved protein family implicated, in filamentous fungi, in
sister-chromatid cohesion and DNA repair. We show here that BIMD is
chromosome associated at all stages, except from late prophase through
anaphase, during mitosis and meiosis, and is involved in several
aspects of both programs. First,
bimD
+
function must be executed during S through M. Second, in
bimD6
germlings, mitotic nuclear divisions and overall
cellular program occur more rapidly than in wild type. Thus, BIMD, an
abundant chromosomal protein, is a negative regulator of normal cell
cycle progression. Third,
bimD6
reduces the level of
mitotic interhomolog recombination but does not alter the ratio between
crossover and noncrossover outcomes. Moreover,
bimD6
is
normal for intrachromosomal recombination. Therefore, BIMD is probably
not involved in the enzymology of recombinational repair
per
se
. Finally, during meiosis, staining of the
Sordaria
ortholog Spo76p delineates robust chromosomal
axes, whereas BIMD stains all chromatin.
SPO76
and
bimD
are functional homologs with respect to their roles
in mitotic chromosome metabolism but not in meiosis. We propose that
BIMD exerts its diverse influences on cell cycle progression as well as
chromosome morphogenesis and recombination by modulating chromosome
structure.
Structure of Hjc, a Holliday junction resolvase, from
Sulfolobus solfataricus
Authors: Bond Charles S. , Kvaratskhelia Mamuka , Richard Derek , White Malcolm F. , Hunter William N.
Published: July 2002

The 2.15-Å structure of Hjc, a Holliday junction-resolving enzyme
from the archaeon
Sulfolobus solfataricus
, reveals
extensive structural homology with a superfamily of nucleases that
includes type II restriction enzymes. Hjc is a dimer with a large
DNA-binding surface consisting of numerous basic residues surrounding
the metal-binding residues of the active sites. Residues critical for
catalysis, identified on the basis of sequence comparisons and
site-directed mutagenesis studies, are clustered to produce two active
sites in the dimer, about 29 Å apart, consistent with the requirement
for the introduction of paired nicks in opposing strands of the
four-way DNA junction substrate. Hjc displays similarity to the
restriction endonucleases in the way its specific DNA-cutting pattern
is determined but uses a different arrangement of nuclease subunits.
Further structural similarity to a broad group of
metal/phosphate-binding proteins, including conservation of
active-site location, is observed. A high degree of conservation of
surface electrostatic character is observed between Hjc and T4-phage
endonuclease VII despite a complete lack of structural homology. A
model of the Hjc–Holliday junction complex is proposed, based on the
available functional and structural data.
DNA containing CpG motifs induces angiogenesis
Authors: Zheng Mei , Klinman Dennis M. , Gierynska Malgorzata , Rouse Barry T.
Published: July 2002

New blood vessel formation in the cornea is an essential step in the pathogenesis of a blinding immunoinflammatory reaction caused by ocular infection with herpes simplex virus (HSV). By using a murine corneal micropocket assay, we found that HSV DNA (which contains a significant excess of potentially bioactive “CpG” motifs when compared with mammalian DNA) induces angiogenesis. Moreover, synthetic oligodeoxynucleotides containing CpG motifs attract inflammatory cells and stimulate the release of vascular endothelial growth factor (VEGF), which in turn triggers new blood vessel formation.In vitro, CpG DNA induces the J774A.1 murine macrophage cell line to produce VEGF.In vivoCpG-induced angiogenesis was blocked by the administration of anti-mVEGF Ab or the inclusion of “neutralizing” oligodeoxynucleotides that specifically oppose the stimulatory activity of CpG DNA. These findings establish that DNA containing bioactive CpG motifs induces angiogenesis, and suggest that CpG motifs in HSV DNA may contribute to the blinding lesions of stromal keratitis.
Differential gene expression in p53-mediated apoptosis-resistant vs. apoptosis-sensitive tumor cell lines
Authors: Maxwell Steve A. , Davis George E.
Published: July 2002

Induction of wild-type p53 in the ECV-304 bladder carcinoma cell
line by infection with a p53 recombinant adenovirus (Ad5CMV-p53)
resulted in extensive apoptosis and eventual death of nearly
all of the cells. As a strategy to determine the molecular events
important to p53-mediated apoptosis in these transformed cells,
ECV-304 cells were selected for resistance to p53 by repeated
infections with Ad5CMV-p53. We compared the expression of 5,730 genes
in p53-resistant (DECV) and p53-sensitive ECV-304 cells by reverse
transcription–PCR, Northern blotting, and DNA microarray analysis. The
expression of 480 genes differed by 2-fold or more between the two
p53-infected cell lines. A number of potential targets for p53 were
identified that play roles in cell cycle regulation, DNA repair, redox
control, cell adhesion, apoptosis, and differentiation. Proline
oxidase, a mitochondrial enzyme involved in the
proline/pyrroline-5-carboxylate redox cycle, was up-regulated by p53
in ECV but not in DECV cells. Pyrroline-5-carboxylate (P5C), a
proline-derived metabolite generated by proline oxidase, inhibited the
proliferation and survival of ECV-304 and DECV cells and induced
apoptosis in both cell lines. A recombinant proline oxidase
protein tagged with a green fluorescent protein at the amino terminus
localized to mitochondria and induced apoptosis in p53-null
H1299 non-small cell lung carcinoma cells. The results directly
implicate proline oxidase and the proline/P5C pathway in p53-induced
growth suppression and apoptosis.
cAMP-response element modulator tau is a positive regulator of testis angiotensin converting enzyme transcription.
Authors: Zhou Y , Sun Z , Means A R , Sassone-Corsi P , Bernstein K E
Published: July 2002

Testis angiotensin-converting enzyme (ACE) is a unique form of ACE, only produced by male germ cells, and results from a testis-specific promoter found within the ACE gene. We have investigated the role of cAMP-response element modulator (CREM)tau in testis ACE transcription. In gel shift experiments, testes nuclear proteins retard an oligonucleotide containing the cAMP-response element (CRE) found at position -55 in the testis ACE promoter. Anti-CREM antibody supershifts this complex. Competitive gel shift shows that recombinant CREM tau protein and testis nuclear proteins have a similar specificity of binding to the tests ACE CRE. Functional analysis using in vitro transcription and transfection studies also demonstrate that CREM tau protein is a transcriptional activator of the testis ACE promoter. Western blot analysis identifies CREM tau protein in the protein-DNA complex formed between nuclear proteins and the testis ACE CRE motif. This analysis also identified other CREM isoforms in the gel-shifted complex, which are thought to be CREM tau 1/2, CREM alpha/beta, and S-CREM. These data indicate that CREM tau isoforms play an important role as a positive regulator in the tissue-specific expression of testis ACE.
Evidence for the existence of a sulfonylurea-receptor-like protein in plants: Modulation of stomatal movements and guard cell potassium channels by sulfonylureas and potassium channel openers
Authors: Leonhardt Nathalie , Marin Elena , Vavasseur Alain , Forestier Cyrille
Published: July 2002

Limitation of water loss and control of gas exchange is accomplished in plant leaves via stomatal guard cells. Stomata open in response to light when an increase in guard cell turgor is triggered by ions and water influx across the plasma membrane. Recent evidence demonstrating the existence of ATP-binding cassette proteins in plants led us to analyze the effect of compounds known for their ability to modulate ATP-sensitive potassium channels (K-ATP) in animal cells. By using epidermal strip bioassays and whole-cell patch-clamp experiments with
Vicia faba
guard cell protoplasts, we describe a pharmacological profile that is specific for the outward K
+
channel and very similar to the one described for ATP-sensitive potassium channels in mammalian cells. Tolbutamide and glibenclamide induced stomatal opening in bioassays and in patch-clamp experiments, a specific inhibition of the outward K
+
channel by these compounds was observed. Conversely, application of potassium channel openers such as cromakalim or RP49356 triggered stomatal closure. An apparent competition between sulfonylureas and potassium channel openers occurred in bioassays, and outward potassium currents, previously inhibited by glibenclamide, were partially recovered after application of cromakalim. By using an expressed sequence tag clone from an
Arabidopsis thaliana
homologue of the sulfonylurea receptor, a 7-kb transcript was detected by Northern blot analysis in guard cells and other tissues. Beside the molecular evidence recently obtained for the expression of ATP-binding cassette protein transcripts in plants, these results give pharmacological support to the presence of a sulfonylurea-receptor-like protein in the guard-cell plasma membrane tightly involved in the outward potassium channel regulation during stomatal movements.
Existence of distinct tyrosylprotein sulfotransferase genes: Molecular characterization of tyrosylprotein sulfotransferase-2
Authors: Beisswanger Roland , Corbeil Denis , Vannier Christian , Thiele Christoph , Dohrmann Ulrike , Kellner Roland , Ashman Keith , Niehrs Christof , Huttner Wieland B.
Published: July 2002

Tyrosylprotein sulfotransferase (TPST) is a 54- to 50-kDa integral membrane glycoprotein of the trans-Golgi network found in essentially all tissues investigated, catalyzing the tyrosine O-sulfation of soluble and membrane proteins passing through this compartment. Here we describe (
i
) an approach to identify the TPST protein, referred to as MSC (
m
odification after
s
ubstrate
c
rosslinking) labeling, which is based on the crosslinking of a substrate peptide to TPST followed by intramolecular [
35
S]sulfate transfer from the cosubstrate 3′-phosphoadenosine 5′-phosphosulfate (PAPS); and (
ii
) the molecular characterization of a human TPST, referred to as TPST-2, whose sequence is distinct from that reported [TPST-1; Ouyang, Y.-B., Lane, W. S. & Moore, K. L. (1998)
Proc. Natl. Acad. Sci. USA
95, 2896–2901] while this study was in progress. Human TPST-2 is a type II transmembrane protein of 377 aa residues that is encoded by a ubiquitously expressed 1.9-kb mRNA originating from seven exons of a gene located on chromosome 22 (22q12.1). A 304-residue segment in the luminal domain of TPST-2 shows 75% amino acid identity to the corresponding segment of TPST-1, including conservation of the residues implicated in the binding of PAPS. Expression of the TPST-2 cDNA in CHO cells resulted in an ≈13-fold increase in both TPST protein, as determined by MSC labeling, and TPST activity. A predicted 359-residue type II transmembrane protein in
Caenorhabditis elegans
with 45% amino acid identity to TPST-2 in a 257-residue segment of the luminal domain points to the evolutionary conservation of the TPST protein family.
Multiple left-right asymmetry defects in
Shh
−/−
mutant mice unveil a convergence of the Shh and retinoic acid pathways in the control of
Lefty-1
Authors: Tsukui Tohru , Capdevila Javier , Tamura Koji , Ruiz-Lozano Pilar , Rodriguez-Esteban Concepción , Yonei-Tamura Sayuri , Magallón Jorge , Chandraratna Roshantha A. S. , Chien Kenneth , Blumberg Bruce , Evans Ronald M. , Belmonte Juan Carlos Izpisúa
Published: July 2002

Asymmetric expression of
Sonic hedgehog
(
Shh
) in Hensen’s node of the chicken embryo plays a key role in the genetic cascade that controls left-right asymmetry, but its involvement in left-right specification in other vertebrates remains unclear. We show that mouse embryos lacking
Shh
display a variety of laterality defects, including pulmonary left isomerism, alterations of heart looping, and randomization of axial turning. Expression of the left-specific gene
Lefty-1
is absent in
Shh
−/−
embryos, suggesting that the observed laterality defects could be the result of the lack of
Lefty-1
. We also demonstrate that retinoic acid (RA) controls
Lefty-1
expression in a pathway downstream or parallel to
Shh
. Further, we provide evidence that RA controls left-right development across vertebrate species. Thus, the roles of
Shh
and RA in left-right specification indeed are conserved among vertebrates, and the
Shh
and RA pathways converge in the control of
Lefty-1
.
Toward elimination of discrepancies between theory and experiment: The rate constant of the atmospheric conversion of SO
3
to H
2
SO
4
Authors: Loerting Thomas , Liedl Klaus R.
Published: July 2002

The hydration rate constant of sulfur trioxide to sulfuric acid is shown to depend sensitively on water vapor pressure. In the 1:1 SO
3
-H
2
O complex, the rate is predicted to be slower by about 25 orders of magnitude compared with laboratory results [Lovejoy, E. R., Hanson, D. R. & Huey, L. G. (1996)
J. Phys. Chem.
100, 19911–19916; Jayne, J. T., Pöschl, U., Chen, Y.-m., Dai, D., Molina, L. T., Worsnop, D. R., Kolb, C. E. & Molina, M. J. (1997)
J. Phys. Chem. A
101, 10000–10011]. This discrepancy is removed mostly by allowing a second and third water molecule to participate. An asynchronous water-mediated double proton transfer concerted with the nucleophilic attack and a double proton transfer accompanied by a transient H
3
O
+
rotation are predicted to be the fastest reaction mechanisms. Comparison of the predicted negative apparent “activation” energies with the experimental finding indicates that in our atmosphere, different reaction paths involving two and three water molecules are taken in the process of forming sulfate aerosols and consequently acid rain.
Psychiatric Symptoms in Problem Gambling and Non‐Problem Gambling Substance Abusers
Authors: Petry Nancy M.
Published: July 2002

This study compared demographic characteristics, Addiction Severity Index (ASI) ratings, and psychiatric symptoms in 103 substance abusers with and without gambling problems. Thirty‐one of the substance abusers were identified as probable pathological gamblers on the South Oaks Gambling Screen. Although no differences in demographic characteristics or ASI ratings were noted between the groups, subjects with a gambling problem consistently reported more psychiatric distress than substance abusers without a gambling problem. Specifically, they had increased ratings on somatization, obsessive‐compulsive, interpersonal sensitivity, hostility, and paranoia scales. These results are discussed in terms of the need to identify and treat gambling problems among substance abusers.
The Specificity of Family History of Alcohol and Drug Abuse in Cocaine Abusers
Authors: Compton Wilson M. , Cottler Linda B. , Ridenour Ty , Ben‐Abdallah Arbi , Spitznagel Edward L.
Published: July 2002

This study addresses the issue of whether the increased rates of substance‐related problems for family members of cocaine abusers are specific for each substance. The present analysis examined the prevalence of problems due to alcohol or drug use separately for mothers, fathers, sisters, and brothers using the Family History Assessment Module. The probands were 343 out‐of‐treatment subjects with DSM‐III‐R cocaine disorders who did or did not have additional alcohol and opiate disorders. After accounting for age, race, gender, and antisocial personality, family history of alcohol‐related problems had an odds ratio of 1.6 (p < .05) if a participant was alcoholic in addition to abusing cocaine. Specifically, a significantly greater proportion of participants' sisters (p < .001) and brothers (p < .05) had alcohol‐related problems if the participant had a history of alcoholism. Among probands who reported opiate abuse or dependence, 38% had relatives with drug‐related problems, while participants without opiate abuse or dependence had less than 31% of relatives with drug‐related problems (p < .05). However, this association with opiate abuse or dependence and family history of drug‐related problems was non‐significant after controlling for participants' age, race, gender, treatment status, and antisocial personality diagnosis (odds ratio = 1.4, 95% C.I. = 0.8–2.4). Associations between participants' alcoholism and first‐degree relatives' drug‐related problems (and vice versa) showed that participants' history of opiate addiction did improve prediction of first‐degree relatives' alcohol‐related problems, except for participants' brothers. Additional familial risks for alcoholism were seen among siblings of drug abusers who also reported abuse of or dependence on alcohol even after controlling for relatives' ages. Furthermore, parental prevalence of alcohol‐related problems were greater when participants had opiate addiction in addition to cocaine addiction. This seems to indicate that opiate addiction in addition to cocaine addiction has particularly strong inheritance patterns. In contrast, parental prevalence of drug‐related problems was not greater when participants had alcohol addiction in addition to cocaine addiction. Thus, the cross‐substance parent‐child familial risk is limited to the dually diagnosed illicit drug.
Distinct Families of Z-Line Targeting Modules in the Cooh-Terminal Region of Nebulin
Authors: Ojima K. , Lin Z.X. , Bang M.-L. , Holtzer S. , Matsuda R. , Labeit S. , Sweeney H.L. , Holtzer H.
Published: July 2002

To learn how nebulin functions in the assembly and maintenance of I-Z-I bands, MYC- and GFP- tagged nebulin fragments were expressed in primary cultured skeletal myotubes. Their sites of incorporation were visualized by double staining with anti-MYC, antibodies to myofibrillar proteins, and FITC- or rhodamine phalloidin. Contrary to expectations based on in vitro binding studies, none of the nebulin fragments expressed in maturing myotubes were incorporated selectively into I-band ∼1.0-μm F-α-actin–containing thin filaments. Four of the MYC/COOH-terminal nebulin fragments were incorporated exclusively into periodic ∼0.1-μm Z-bands. Whereas both anti-MYC and Rho-phalloidin stained intra-Z-band F-α-actin oligomers, only the latter stained the pointed ends of the polarized ∼1.0-μm thin filaments. Z-band incorporation was independent of the nebulin COOH-terminal Ser or SH3 domains. In vitro cosedimentation studies also demonstrated that nebulin SH3 fragments did not bind to F-α-actin or α-actinin. The remaining six fragments were not incorporated into Z-bands, but were incorporated (a) diffusely throughout the sarcoplasm and into (b) fibrils/patches of varying lengths and widths nested among normal striated myofibrils. Over time, presumably in response to the mediation of muscle-specific homeostatic controls, many of the ectopic MYC-positive structures were resorbed. None of the tagged nebulin fragments behaved as dominant negatives; they neither blocked the assembly nor induced the disassembly of mature striated myofibrils. Moreover, they were not cytotoxic in myotubes, as they were in the fibroblasts and presumptive myoblasts in the same cultures.
On the class number of certain imaginary quadratic fields
Authors: Cohn J.
Published: July 2002

Theorem. Let

n
>
2

n>2

denote an integer,

D
D

the square-free part of

2
n

−
1

2^n-1

and

h
h

the class number of the field

Q
[

−
D

]

Q[\sqrt {-D}]

. Then except for the case

n
=
6

n=6

,

n
−
2

n-2

divides

h
h

.
Every complete doubling metric space carries a doubling measure
Authors: Luukkainen Jouni , Saksman Eero
Published: July 2002

We prove that a complete metric space 

X
X

carries a doubling measure if and only if

X
X

is doubling and that more precisely the infima of the homogeneity exponents of the doubling measures on 

X
X

and of the homogeneity exponents of 

X
X

are equal. We also show that a closed subset 

X
X

of 

R

n

\mathbf {R}^{n}

carries a measure of homogeneity exponent 

n
n

. These results are based on the case of compact 

X
X

due to Vol

′

^{\prime }

berg and Konyagin.
The spaces of index one minimal surfaces and stable constant mean curvature surfaces embedded in flat three manifolds
Authors: Ritoré Manuel , Ros Antonio
Published: July 2002

It is proved that the spaces of index one minimal surfaces and stable constant mean curvature surfaces with genus greater than one in (non fixed) flat three manifolds are compact in a strong sense: given a sequence of any of the above surfaces we can extract a convergent subsequence of both the surfaces and the ambient manifolds in the

C
k

C^k

topology. These limits preserve the topological type of the surfaces and the affine diffeomorphism class of the ambient manifolds. Some applications to the isoperimetric problem are given.
Coloring graphs with fixed genus and girth
Authors: Gimbel John , Thomassen Carsten
Published: July 2002

It is well known that the maximum chromatic number of a graph on the orientable surface

S
g

S_g

is

θ
(

g

1

/

2

)

\theta (g^{1/2})

. We prove that there are positive constants

c
1

,

c
2

c_1,c_2

such that every triangle-free graph on

S
g

S_g

has chromatic number less than

c
2

(
g

/

log
⁡
(
g
)

)

1

/

3

c_2(g/\log (g))^{1/3}

and that some triangle-free graph on

S
g

S_g

has chromatic number at least

c
1

g

1

/

3

log
⁡
(
g
)

c_1\frac {g^{1/3}}{\log (g)}

. We obtain similar results for graphs with restricted clique number or girth on

S
g

S_g

or

N
k

N_k

. As an application, we prove that an

S
g

S_g

-polytope has chromatic number at most

O
(

g

3

/

7

)

O(g^{3/7})

. For specific surfaces we prove that every graph on the double torus and of girth at least six is 3-colorable and we characterize completely those triangle-free projective graphs that are not 3-colorable.
Inert actions on periodic points
Authors: Kim K. , Roush F. , Wagoner J.
Published: July 2002

The action of inert automorphisms on finite sets of periodic points of mixing subshifts of finite type is characterized in terms of the sign-gyration-compatibility condition. The main technique used is variable length coding combined with a “nonnegative algebraic K-theory" formulation of state splitting and merging. One application gives a counterexample to the Finite Order Generation Conjecture by producing examples of infinite order inert automorphisms of mixing subshifts of finite type which are not products of finite order automorphisms.
The art of pedigree drawing: algorithmic aspects
Authors: Tores Frédéric , Barillot Emmanuel
Published: July 2002

Motivation: Giving a meaningful representation of a pedigree is not obvious when it includes consanguinity loops, individuals with multiple mates or several related families.

Results: We show that finding a perfectly meaningful representation of a pedigree is equivalent to the interval graph sandwich problem and we propose an algorithm for drawing pedigrees.

Contact: Emmanuel.Barillot@infobiogen.fr

* To whom correspondence should be addressed.
REPUTATION IN BARGAINING: NATIONAL FOOTBALL LEAGUE CONTRACT NEGOTIATIONS
Authors: Conlin Michael
Published: July 2002

This article examines a sequence of two bargaining games where a single buyer participates in both. The bargaining games are modeled with two‐sided private information and are “linked” through the buyer's valuation, which is positively correlated across bargaining games. I empirically test the comparative static results obtained from the model's unique equilibrium outcome using National Football League (NFL) contract data. The empirical results suggest that an NFL team's contract negotiations are affected by not only the terms agreed to in the team's prior contract negotiations but also the length of time required to negotiate these prior contracts.
The influence of the molecular basis of resistance on insecticide discovery
Authors: Broadjurst M. D.
Published: July 2002

This paper focuses on the process of invention and development of new insecticides and the impact of current research in resistance mechanisms on that process. The topic is introduced in the context of (i) the critical need to develop new insect–control agents to ensure a continued supply of high–quality food and fibre; (ii) how resistance development will continue to influence the potential to ensure the supply of these essentials; and (iii) why new insect–control technology is welcomed by growers. The main section of the paper describes a generic agrochemical invention process and discusses the impact that an understanding of the molecular basis of resistance will have on the various stages of this process, using specific examples to illustrate these points. By focusing on insecticide invention, this paper provides a context in which other information more specific to insecticide resistance from this issue can be understood.
Therapeutic strategies in multiple sclerosis. II. Long–term repair
Authors: Scoldingf Neil
Published: July 2002

Spontaneous myelin repair in multiple sclerosis (MS) provides a striking example of the brain's inherent capacity for sustained and stable regenerative tissue repair—but also clearly emphasizes the limitations of this capacity; remyelination ultimately fails widely in many patients, and disability and handicap accumulate. The observation of endogenous partial myelin repair has raised the possibility that therapeutic interventions designed to supplement or promote remyelination might have a useful and significant impact both in the short term, in restoring conduction, and in the long term, in safeguarding axons. Therapeutic remyelination interventions must involve manipulations to either the molecular or the cellular environment within lesions; both depend crucially on a detailed understanding of the biology of the repair process and of those glia implicated in spontaneous repair, or capable of contributing to exogenous repair. Here we explore the biology of myelin repair in MS, examining the glia responsible for successful remyelination, oligodendrocytes and Schwann cells, their ‘target’ cells, neurons and the roles of astrocytes. Options for therapeutic remyelinating strategies are reviewed, including glial cell transplantation and treatment with growth factors or other soluble molecules. Clinical aspects of remyelination therapies are considered—which patients, which lesions, which stage of the disease, and how to monitor an int–ervention—and the remaining obstacles and hazards to these approaches are discussed.
Positive operator valued measure in quantum information processing
Authors: Brandt Howard E.
Published: July 2002

The positive operator valued measure (POVM), also known as the probability operator valued measure, is useful in quantum information processing. The POVM consists of a set of non-negative quantum-mechanical Hermitian operators that add up to the identity. The probability that a quantum system is in a particular state is given by the expectation value of the POVM operator corresponding to that state. Following a brief review of the mathematics and history of POVMs in quantum theory, and an expository discussion of the quantum mechanics of photonic qubits, a particular implementation of a POVM for use in the measurement of photonic qubits is reviewed.