bluuebunny/crossref_metadata_2025 huggingface dataset:
Scaling of spectral anisotropy with magnetic field strength in decaying magnetohydrodynamic turbulence
Authors: Oughton Sean , Matthaeus William H. , Ghosh Sanjoy
Published: July 2002

Space plasma measurements, laboratory experiments, and simulations have shown that magnetohydrodynamic (MHD) turbulence exhibits a dynamical tendency towards spectral anisotropy given a sufficiently strong background magnetic field. Here the undriven decaying initial-value problem for homogeneous MHD turbulence is examined with the purpose of characterizing the variation of spectral anisotropy of the turbulent fluctuations with magnetic field strength. Numerical results for both incompressible and compressible MHD are presented. A simple model for the scaling of this spectral anisotropy as a function of the fluctuating magnetic field over total magnetic field is offered. The arguments are based on ideas from reduced MHD (RMHD) dynamics and resonant driving of certain non-RMHD modes. The results suggest physical bases for explaining variations of the anisotropy with compressibility, Reynolds numbers, and spectral width of the (isotropic) initial conditions.
Paraxial Gaussian wave beam propagation in an anisotropic inhomogeneous plasma
Authors: Poli E. , Pereverzev G. V. , Peeters A. G.
Published: July 2002

The beam tracing technique describes electromagnetic wave beam propagation in the short wavelength limit, including diffraction effects, not described by the usual geometric optics. It involves a set of ordinary differential equations: a central or reference ray is determined and around this the beam profile and the shape of the phase front are calculated. Here, these equations are obtained for a Gaussian wave beam. Analytic solutions in an inhomogeneous magnetized plasma are given for perpendicular propagation in a slab geometry. The beam is found to show a strong deformation of its cross section due to the anisotropy of the medium. The rotation of the cross section and that of the curvature of the phase front are discussed.
Gyrokinetic theory of slab ion temperature gradient mode in negative shear tokamaks
Authors: Idomura Y. , Tokuda S. , Wakatani M.
Published: July 2002

In a slab configuration modeling the negative shear tokamak, a linear analysis of the ion temperature gradient (ITG) mode is performed based on a gyrokinetic integral eigenvalue equation with retaining the full finite Larmor radius (FLR) effect. Numerical results show that characteristics of the slab ITG mode are greatly changed in the negative shear configuration. When a single mode-rational surface exists at the qmin-surface, the steep ion temperature gradient and the associated FLR effect produce an asymmetric mode structure with respect to the mode-rational surface. In the weak magnetic shear region near the qmin-surface, an unstable region of the ITG mode is divided into two separate regions, which are located in both sides of the mode-rational surface. Since the ion Larmor radius varies significantly between these regions, low-ky (high-ky) modes appear in the high-Ti (low-Ti) side due to the asymmetric FLR effect, where ky corresponds to the wavenumber in the poloidal direction. When double mode-rational surfaces exist near the qmin-surface, it is found that the ITG mode becomes unstable in the interior region between the two mode-rational surfaces. Since the shear stabilization disappears in this region, the unstable ky region spreads up to an extremely short wavelength region or kyρti⩽10, where ρti is the ion Larmor radius.
On the theory of low-pressure magnetron glow discharge
Authors: Pekker L. , Krasheninnikov S. I.
Published: July 2002

An analytical model of a magnetron glow discharge is considered, assuming classical electron and ion transport across the magnetic field lines. The theoretical volt-ampere characteristic of the discharge is obtained. The shape of this characteristic is similar to that found in experiments. However, the experimental current densities exceed the theoretical ones calculated with the present model. Possible reasons for this discrepancy between theoretical calculations and experimental results are discussed.
Kinetic model of three-component, weakly ionized, collisional plasma with a beam of neutral particles
Authors: Tsiklauri David
Published: July 2002

Kinetic model of three component, weakly ionized, collisional plasma with a beam of neutral particles is developed. New dispersion relations for linear perturbations are derived and analyzed in various limiting cases.
Electromagnetic effects on toroidal-ion-temperature-gradient modes and associated nonthermal cross-field transports
Authors: Farid Tahir , Shukla P. K.
Published: July 2002

The electromagnetic effects are incorporated in the study of toroidal ion-temperature-gradient (ITG) modes in a nonuniform magnetoplasma. For this purpose, dispersion relations have been derived by employing the fluid and gyrokinetic responses for the ions, as well as the fluid electron response along with Ampère’s law. The dispersion relations are numerically analyzed and results for the real and imaginary parts of the ITG wave frequencies are displayed for different values of εn=2Ln/LB (where Ln and LB are the characteristic scale lengths of the density and magnetic field gradients, respectively) and λi∥=k∥λi, where k∥ is the parallel component of the wave vector and λi is the collisionless ion skin depth. It is found that electromagnetic effects are stabilizing. Furthermore, also presented are brief calculations of particle as well as ion thermal transports in the presence of nonthermal electromagnetic fluctuations. The relevance of this investigation to the plasma confinement in tokamaks is discussed.
Impurity toroidal rotation and transport in Alcator C-Mod ohmic high confinement mode plasmas
Authors: Rice J. E. , Goetz J. A. , Granetz R. S. , Greenwald M. J. , Hubbard A. E. , Hutchinson I. H. , Marmar E. S. , Mossessian D. , Pedersen T. Sunn , Snipes J. A. , Terry J. L. , Wolfe S. M.
Published: July 2002

Central toroidal rotation and impurity transport coefficients have been determined in Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] Ohmic high confinement mode (H-mode) plasmas from observations of x-ray emission following impurity injection. Rotation velocities up to 3×104 m/sec in the co-current direction have been observed in the center of the best Ohmic H-mode plasmas. Purely ohmic H-mode plasmas display many characteristics similar to ion cyclotron range of frequencies (ICRF) heated H-mode plasmas, including the scaling of the rotation velocity with plasma parameters and the formation of edge pedestals in the electron density and temperature profiles. Very long impurity confinement times (∼1 sec) are seen in edge localized mode-free (ELM-free) Ohmic H-modes and the inward impurity convection velocity profile has been determined to be close to the calculated neoclassical profile.
Measurement of radial neutral pressure and plasma density profiles in various plasma conditions in large-area high-density plasma sources
Authors: Yun Seokmin , Taylor Kurt , Tynan George R.
Published: July 2002

Hollow neutral pressure profiles, with significant on-axis reductions in neutral pressure (up to 40%), are observed across the face of an inert wafer in discharges with uniform plasma density. These results show that significant neutral depletion, which may cause the nonuniform plasma process results, can occur in large-area high-density plasma sources with a wafer present. The neutral depletion is explained by the ion pumping effect, wherein electron impact ionization of neutral particles is followed by their rapid movement from the plasma to the chamber wall by the presheath electric field. Cooling of plasma electrons via inelastic neutral collisions is also observed at elevated fill pressure, and results in a reduction of the magnitude of neutral depletion, thus demonstrating the linkage between plasma equilibrium and neutral equilibrium conditions. Initial experiments have also been performed in O2 discharges. Similar hollow neutral pressure profiles are observed, suggesting that similar effects occur in chemically reactive discharges.
Raman scattering in GaSb-AlSb strained layer superlattices
Authors: Jusserand B. , Voisin P. , Voos M. , Chang L. L. , Mendez E. E. , Esaki L.
Published: July 2002

We observe that the energy of the GaSb longitudinal optical phonons in GaSb-AlSb superlattices is about 2 cm−1 lower than in bulk GaSb. We show that this effect is fully explained by the consideration of the misfit strains which are known to exist in these superlattices. This shift of the Raman frequency allows a direct optical determination of the strains in heterostructures.
Diffusion and precipitation in amorphous Si
Authors: Elliman R. G. , Gibson J. M. , Jacobson D. C. , Poate J. M. , Williams J. S.
Published: July 2002

The diffusion and precipitation of several ion implanted impurities in amorphous Si have been observed at temperatures of 300–600 °C. Typical slow diffusers in crystalline Si, such as As, In, Sb, and Bi, show little or no diffusion at low concentrations. At high concentrations (>1 at. %), they diffuse rapidly with D≳10−15 cm2/s in the temperature range 500–600 °C. Typical fast diffusers in crystalline Si, such as Cu and Au, diffuse in amorphous Si with D>10−12 cm2/s at 400–600 °C. Precipitation has been observed for both the fast and slow diffusers in amorphous Si.
Injection locking of coupled-stripe diode laser arrays
Authors: Goldberg L. , Taylor H. F. , Weller J. F. , Scifres D. R.
Published: July 2002

The control of the far-field beam pattern and the spectrum of 10-element laser diode array by injection locking to a single-mode master laser are described. With less than 3 mW of injected power an array output of 105 mW at a single frequency with a 0.5° wide far-field lobe is obtained. Similar results are observed when the entire array is illuminated by the master laser beam, or when only one of the stripes is illuminated. The narrow lobe contains 60–70% of the total power and is centered at an angle of about 4° relative to the normal of the array facet.
Gain measurements in InGaAsP multiquantum well lasers
Authors: Dutta N. K. , Craft D. C. , Napholtz S. G.
Published: July 2002

This letter reports the polarization dependence and temperature dependence of gain spectrum in InGaAsP multiquantum well (MQW) lasers emitting at 13 μm. The gain of the TE mode is larger (by ∼40 cm−1) than that of the TM mode. The peak gain for the TM mode is shifted towards shorter wavelengths from that of the TE mode. This is because both light hole and heavy hole transitions contribute to TE emission whereas the TM emission is principally due to light hole transitions. The large gain difference between the TE and TM mode suggests that the occurrence of stress induced effects (e.g., light-current kinks) may be reduced in MQW active layer lasers. The net gain G is found to vary linearly with the injection current I. The slope dG/dI of the gain-current curve for these MQW lasers decreases with increasing temperature. However, the decrease is considerably smaller than that for conventional InGaAsP double heterostructure lasers. The smaller decrease is consistent with the observed lower temperature dependence of threshold (high T0) of the MQW lasers.
KrF laser with longitudinal discharge excitation
Authors: Eichler H. J. , Hamisch J. , Nagel B. , Schmid W.
Published: July 2002

Lasing in KrF was obtained with a longitudinal, self-sustained, high-voltage discharge. The output powers and energies at 248 nm have been measured for some tube geometries as a function of different He, Kr, and F2 partial pressures and mirror reflectivities. A maximum laser energy of 50 μJ has been obtained by discharging a capacitor of 360 pF and 60 kV across a segmented discharge tube with a total length of 70 cm and 6.5 mm inner diameter.
Formation of hydroxyl due to reaction of hydrogen with silica optical fiber preforms
Authors: Stone J. , Wiesenfeld J. M. , Marcuse D. , Burrus C. A. , Yang S.
Published: July 2002

We have studied the formation of hydroxyl in silica glass made by the modified chemical vapor deposition process and exposed to hydrogen at 900 °C. The spatial hydroxyl concentration profiles have been measured as a function of exposure time. The observations are explained by a theoretical model involving diffusion of hydrogen in the silica, and reaction with sites to form hydroxyl. The model assumes local equilibrium between hydrogen and hydroxyl, and the existence of a finite number of reaction sites which are consumed in the reaction.
Ion beam and temperature annealing during high dose implants
Authors: Cannavò S. , Grimaldi M. G. , Rimini E. , Ferla G. , Gandolfi L.
Published: July 2002

The regrowth of a Si amorphous layer under a masked region during an implant of 120 keV–7.5×1015 P+/cm2 at an average dose rate of 9.0 μA/cm2 has been measured by the channeling technique. The amorphous layer reorders epitaxially over ∼20 nm after the implant, in agreement with calculations based on the temperature dose rise and regrowth velocity. A single implant of 7.5×1015 P+/cm2 produces a nearly damage-free region implying a regrowth rate enhanced by the large amount of mobile point defects generated in the collision cascade of the impinging ions.
Investigation of transient diffusion effects in rapid thermally processed ion implanted arsenic in silicon
Authors: Sedgwick T. O. , Michel A. E. , Cohen S. A. , Deline V. R. , Oehrlein G. S.
Published: July 2002

Arsenic dopant profile motion in ion implanted Si samples annealed for a few seconds at 1100 °C is adequately described by a model involving concentration enhanced diffusion. There is no evidence of an initial rapid diffusive transient. Diffusion in samples preannealed at 550 °C is consistent with this result.
High-field-induced voltage-dependent oxide charge
Authors: Olivo P. , Riccò B. , Sangiorgi E.
Published: July 2002

In this work, we investigate the effects of nondisruptive high-field stress on the tunneling characteristics of thin SiO2 films (<100 Å) and show that after the stress the charge trapped within the oxide reversibly depends on the applied voltage. This is explained with a model where electrons tunnel in and out of trap states located near the injecting interface. Consequently, the trap occupation, hence oxide charge, is determined by transmission coefficients that strongly depend on the actual oxide potential.
Effect of pulse sharpening on imploding neon Z-pinch plasmas
Authors: Stephanakis S. J. , Apruzese J. P. , Burkhalter P. G. , Davis J. , Meger R. A. , McDonald S. W. , Mehlman G. , Ottinger P. F. , Young F. C.
Published: July 2002

The radial implosion of hollow, cylindrical neon gas columns, driven by currents of up to 1.45 MA, produces a linear Z pinch with over 70% of the radiation in neon K lines. A plasma erosion opening switch (PEOS) is used to eliminate prepulse and to reduce the current rise time from ∼60 to ∼20 ns. Incorporation of the PEOS improves the uniformity of the Z pinch and increases the radiation yield.
Ambient and dopant effects on boron diffusion in oxides
Authors: Wong C. Y. , Lai F. S.
Published: July 2002

Diffusion of boron from ion implanted polycrystalline silicon source through 12.5 nm oxides was measured as a function of annealing ambience and doping concentrations of phosphorus or arsenic in the polycrystalline silicon. For comparison, boron ion implanted into 500 nm oxides was also investigated. In both cases, annealing in forming gas (90% N2, 10% H2) increases the diffusion rate of boron over that in nitrogen and the rate increase is the result of a large increase in the pre-exponential term. Diffusion of ion implanted boron in oxides is much slower than that from an ion implanted polycrystalline silicon source. The lowering of the rate is the result of the five orders of magnitude decrease in the pre-exponential term, even though concurrently there is also a decrease in the activation energy. Co-doping of polycrystalline silicon with either phosphorus or arsenic lowers the pre-exponential term by approximately 10%. Therefore, we conclude that boron diffusion through oxides is entropy dominated.
Novel attenuated total internal reflectance spectroscopic cell using infrared fibers for aqueous solutions
Authors: Simhony S. , Kosower E. M. , Katzir A.
Published: July 2002

Silver halide (AgCl:AgBr) fibers were used as the light conductor for total internal reflection measurements in a Fourier transform infrared (FTIR) spectrometer, to obtain spectra of aqueous solutions. The use of optical fibers in an attenuated total reflectance type cell with an FTIR spectrometer was demonstrated for the first time. Spectra of acetone in water and of glycine in water were acquired with the cell.
Temperature-dependent optical spectra of single quantum wells fabricated using interrupted molecular beam epitaxial growth
Authors: Koteles Emil S. , Elman B. S. , Jagannath C. , Chen Y. J.
Published: July 2002

Photoluminescence excitation (PLE) and temperature-dependent photoluminescence (PL) spectroscopies have been employed to interpret fine structure observed in the low-temperature PL spectra of GaAs/AlGaAs single quantum wells grown by molecular beam epitaxy under conditions of interrupted growth. Multiple peaks observed in the low-temperature PL spectra of similar samples grown by others have been held to be proof of monolayer steps in exceptionally smooth interfaces. We show that similar structure in the low-temperature PL spectra of our samples is not intrinsic. However, PLE or higher temperature PL spectroscopy yields unambiguous evidence for the model of interface smoothing due to growth interruption.
Rayleigh wave diffraction from surface-breaking discontinuities
Authors: Tittmann B. R. , Ahlberg L. A. , Mal A. K.
Published: July 2002

This letter presents theoretical and experimental results treating the interaction between Rayleigh waves and surface-breaking discontinuities, such as cracks and grooves, in the regime where crack depth is large compared to the Rayleigh wavelength. Particular emphasis is placed on the mode conversion to bulk waves at the crack tip. Radiation patterns are presented for both the longitudinal and shear wave contributions. The experimental data agree well with theory and show that the generation of shear waves polarized perpendicular to the crack face is particularly efficient.
High gain InGaAs/InP heterostructure bipolar transistors grown by gas source molecular beam epitaxy
Authors: Nottenburg R. N. , Temkin H. , Panish M. B. , Hamm R. A.
Published: July 2002

The capability for high quality heterostructure bipolar transistors with structures in the InGaAs/InP system has been demonstrated by gas source molecular beam epitaxy. These devices are characterized by high current gain, β∼1100, only weakly dependent on the collector current. The current-voltage characteristics of the emitter base junction exhibit an ideality factor n=1.2 over a wide bias range.
Lattice constant changes and electro-optic effects in proton-exchanged LiNbO3 optical waveguides
Authors: Minakata Makoto , Kumagai Kouichi , Kawakami Shojiro
Published: July 2002

Lattice constants and electro-optic constants have been measured on proton-exchanged LiNbO3 single crystals by means of the x-ray rocking curve method and the phase modulation technique to examine the relationship between the refractive index and the strain, and the degradation of the electro-optic effect.
Growth of Cd1−xZnxTe by molecular beam epitaxy
Authors: Feldman R. D. , Austin R. F. , Dayem A. H. , Westerwick E. H.
Published: July 2002

Cd1−xZnxTe has been grown on GaAs substrates for compositions from x=0 to x=1. Binaries are shown to be of high quality, but x-ray rocking curve half-widths are extremely broad for most ternary compositions. Attempts to modify the interface yield only modest and uneven improvement in rocking curve half-widths. The poor quality appears to be due to a phase separation.
Lorentz microscopy of micron-sized laser-written magnetic domains in TbFe
Authors: Suits J. C. , Geiss R. H. , Lin C. J. , Rugar D. , Bell A. E.
Published: July 2002

High resolution images of laser-written magnetic domains in thin sputtered films of terbium iron have been obtained using Lorentz microscopy. The domains, written with a GaAs diode laser, are generally circular in shape with diameters in the range 0.9–2.2 μm. Conditions necessary for the observation of highly detailed images are described. It was found that with certain values of laser power and applied magnetic field, smaller irregular domains appear within the principal domains.
Nondestructive analysis of silicon-on-insulator wafers
Authors: Bunker S. N. , Sioshansi P. , Sanfacon M. M. , Tobin S. P.
Published: July 2002

Silicon-on-insulator structures have been fabricated using implantation of 160 keV oxygen ions at a dose of 1.9×1018 atoms/cm2 with a wafer temperature of 500 °C and no oxide cap. Both the as-implanted and annealed wafers were examined with optical reflectometry to determine the resultant interference pattern produced by the presence of the buried layer of SiO2. The optical data are compared to the predictions of a calculation which simulated the geometry using a detailed multilayer optical model. Parameters of the model were adjusted to provide a best fit to the data. The optical prediction closely matches data from destructive measurements. It is demonstrated that the redistribution of oxygen due to annealing can be monitored with this technique.
Damage assessment in low-dose Si-implanted GaAs by Raman spectroscopy
Authors: Wagner Joachim
Published: July 2002

Allowed and forbidden first-order as well as resonant second-order Raman scattering has been used to study implantation damage in low-dose (5×1011–1×1013 cm−2) 29Si+-implanted GaAs. Symmetry forbidden scattering by longitudinal optical (LO) phonons and allowed 2LO scattering were found to be most sensitive to lattice damage for the range of implantation doses given above. The intensity ratio of the 2LO peak to the forbidden LO phonon line measures variations in the implantation dose with an accuracy better than ±7% for an average dose of 2×1012 cm−2. The potential of spatially resolved Raman spectroscopy for the assessment of homogeneity in as-implanted GaAs wafers has been demonstrated.
Stability and epitaxy of NiAl and related intermetallic films on III-V compound semiconductors
Authors: Sands T.
Published: July 2002

The cubic transition metal-gallium and transition metal-aluminum intermetallic compounds with the CsCl structure (e.g., NiGa and CoAl) have been identified as candidate materials for stable and epitaxical contacts to III-V semiconductors. Fabrication of these stable and epitaxical contacts using only conventional vacuum deposition (e.g., electron gun evaporation) has been demonstrated for the NiAl/GaAs system. It is expected that this unique class of contact materials will find application in III-V-based field-effect transistors as well as novel electronic and photonic devices based on multiple semiconductor/metal heterojunctions.
Room-temperature copper metallization for ultralarge-scale integrated circuits by a low kinetic-energy particle process
Authors: Ohmi T. , Saito T. , Shibata T. , Nitta T.
Published: July 2002

Copper films were epitaxially grown on (100)Si substrates at room temperatures utilizing low kinetic-energy particle bombardment of growing copper film surfaces. The crystallographic structure of the film, such as (100) or (111) orientation, was selected by controlling the energy of incident particles. Low-temperature, damage-free substrate surface cleaning has also been realized by the low kinetic-energy particle process, which has made it possible to form ideal metal-semiconductor contacts without employing any alloying heat cycles.
Direct dissociation of F2 in electron beam pumped excimer lasers: The effect on electron density
Authors: Kushner Mark J. , Moratz Thomas J.
Published: July 2002

The electron impact dissociation of molecular fluorine in XeF and KrF excimer lasers is examined. Two methods of dissociation are discussed: dissociative attachment and direct neutral dissociation by excitation to the dissociative electronic states a3Πu and A1Πu. Computer models for the kinetics of the lasers are parameterized, and predictions of electron density are compared to experimental results for electron beam pumped Ne/Xe/F2 gas mixtures [W. D. Kimura, D. R. Guyer, S. E. Moody, J. F. Seamans, and D. H. Ford, Appl. Phys. Lett. 50, 60 (1987)]. To obtain agreement with experiment, the ratio of direct dissociation to dissociative attachment must be ≥2. The implications of these results with respect to electron quenching and the validation of computer models are discussed.
Growth of highly oriented CdS thin films by laser-evaporation deposition
Authors: Kwok H. S. , Zheng J. P. , Witanachchi S. , Mattocks P. , Shi L. , Ying Q. Y. , Wang X. W. , Shaw D. T.
Published: July 2002

CdS films have been grown by laser-evaporation deposition in a clean vacuum environment. The films are highly oriented with a c axis perpendicular to the surface, and are optically smooth and homogeneous. These high quality films should be useful in nonlinear integrated optics applications.
Waveguiding in spun films of soluble polydiacetylenes
Authors: Townsend P. D. , Baker G. L. , Schlotter N. E. , Klausner C. F. , Etemad S.
Published: July 2002

In prism coupling experiments, the guiding of 1.06 μm light over 3 cm pathlengths was demonstrated in thin spun films of soluble polydiacetylenes. From measurements of the intensity of scattered light, we estimate the transmission losses in the films were as low as 1 dB/cm. Although spun films appeared isotropic when examined under polarized light, the coupling angle observed for the TM waveguide mode was ∼6° higher than that of the TE mode, implying that the films were istropic in the plane of the film, but the refractive index normal to the plane of the film was lower.
Amplification of high repetition rate picosecond pulses using an InGaAsP traveling-wave optical amplifier
Authors: Eisenstein G. , Hansen P. B. , Wiesenfeld J. M. , Tucker R. S. , Raybon G.
Published: July 2002

We report amplification of picosecond pulses at high repetition rates in a 1.3 μm traveling-wave optical amplifier. At 4 GHz repetition rate, the small-signal chip gain is 20 dB, the amplified peak output power at the facet is 400 mW (corresponding to a pulse energy of 3 pJ/pulse), and there is no measurable pulse shape distortion of 12 ps pulses for gain compression up to 1.5 dB. We also directly measure the time constant of the gain recovery to be 100 ps.
Reversibly locking a protein fold in an active conformation with a disulfide bond: Integrin αL I domains with high affinity and antagonist activityin vivo
Authors: Shimaoka Motomu , Lu Chafen , Palframan Roger T. , von Andrian Ulrich H. , McCormack Alison , Takagi Junichi , Springer Timothy A.
Published: July 2002

The integrin αLβ2 has three different domains in its headpiece that have been suggested to either bind ligand or to regulate ligand binding. One of these, the inserted or I domain, has a fold similar to that of small G proteins. The I domain of the αM and α2 subunits has been crystallized in both open and closed conformations; however, the αL I domain has been crystallized in only the closed conformation. We hypothesized that the αL domain also would have an open conformation, and that this would be the ligand binding conformation. Therefore, we introduced pairs of cysteine residues to form disulfides that would lock the αL I domain in either the open or closed conformation. Locking the I domain open resulted in a 9,000-fold increase in affinity to intercellular adhesion molecule-1 (ICAM-1), which was reversed by disulfide reduction. By contrast, the affinity of the locked closed conformer was similar to wild type. Binding completely depended on Mg2+. Orders of affinity were ICAM-1 > ICAM-2 > ICAM-3. Thekon,koff, andKDvalues for the locked open I domain were within 1.5-fold of values previously determined for the αLβ2 complex, showing that the I domain is sufficient for full affinity binding to ICAM-1. The locked open I domain antagonized αLβ2-dependent adhesionin vitro, lymphocyte homingin vivo, and firm adhesion but not rolling on high endothelial venules. The ability to reversibly lock a protein fold in an active conformation with dramatically increased affinity opens vistas in therapeutics and proteomics.
Molecular kinesis in cellular function and plasticity
Authors: Tiedge Henri , Bloom Floyd E. , Richter Dietmar
Published: July 2002

Intracellular transport and localization of cellular components are
essential for the functional organization and plasticity of eukaryotic
cells. Although the elucidation of protein transport mechanisms has
made impressive progress in recent years, intracellular transport of
RNA remains less well understood. The National Academy of Sciences
Colloquium on Molecular Kinesis in Cellular Function and Plasticity
therefore was devised as an interdisciplinary platform for participants
to discuss intracellular molecular transport from a variety of
different perspectives. Topics covered at the meeting included RNA
metabolism and transport, mechanisms of protein synthesis and
localization, the formation of complex interactive protein ensembles,
and the relevance of such mechanisms for activity-dependent regulation
and synaptic plasticity in neurons. It was the overall objective of the
colloquium to generate momentum and cohesion for the emerging research
field of molecular kinesis.
Folliculostellate cell network: A route for long-distance communication in the anterior pituitary
Authors: Fauquier Teddy , Guérineau Nathalie C. , McKinney R. Anne , Bauer Karl , Mollard Patrice
Published: July 2002

All higher life forms critically depend on hormones being rhythmically released by the anterior pituitary. The proper functioning of this master gland is dynamically controlled by a complex set of regulatory mechanisms that ultimately determine the fine tuning of the excitable endocrine cells, all of them heterogeneously distributed throughout the gland. Here, we provide evidence for an intrapituitary communication system by which information is transferred via the network of nonendocrine folliculostellate (FS) cells. Local electrical stimulation of FS cells in acute pituitary slices triggered cytosolic calcium waves, which propagated to other FS cells by signaling through gap junctions. Calcium wave initiation was because of the membrane excitability of FS cells, hitherto classified as silent cells. FS cell coupling could relay information between opposite regions of the gland. Because FS cells respond to central and peripheral stimuli and dialogue with endocrine cells, the form of large-scale intrapituitary communication described here may provide an efficient mechanism that orchestrates anterior pituitary functioning in response to physiological needs.
Sequential repression and activation of the CCAAT enhancer-binding protein-α (C/EBPα) gene during adipogenesis
Authors: Jiang Man-Shiow , Lane M. Daniel
Published: July 2002

CCAAT enhancer-binding protein-α (C/EBPα) functions as a
pleiotropic transcriptional activator of adipocyte genes during
adipogenesis. Nuclear factor C/EBP undifferentiated protein (CUP), an
isoform of activator protein-2α (AP-2α), binds to repressive
elements in the C/EBPα gene promoter, silencing the gene until late
in the differentiation program. The CUP regulatory element overlaps a
Sp (GT-box) element in the promoter to which Sp3 (or Sp1) can bind.
Binding by Sp3 or Sp1 and CUP/AP2-α is mutually exclusive. Sp3 is a
strong transcriptional activator of the C/EBPα gene promoter in
3T3-L1 preadipocytes and Schneider cells, this activation being
repressed by CUP/AP-2α. Sp3 is expressed throughout
differentiation, whereas CUP/AP-2α, which is expressed only by
preadipocytes, is down-regulated during differentiation coincident with
transcription of the C/EBPα gene. Thus, CUP/AP-2α delays access
of Sp3 to the Sp regulatory element, preventing premature expression of
C/EBPα and thereby interference by C/EBPα (which is
antimitotic) with mitotic clonal expansion, an essential early event in
the differentiation program.
Adeno-associated virus (AAV) site-specific recombination does not require a Rep-dependent origin of replication within the AAV terminal repeat
Authors: Young Samuel M. , Samulski Richard Jude
Published: July 2002

Adeno-associated virus (AAV) is the only known eukaryotic virus capable of targeted integration in human cells. An AAV Rep binding element (RBE) and terminal resolution site (
trs
) identical to the viral terminal repeats required for AAV DNA replication are located on chromosome (ch) 19. Both ch-19 RBE and
trs
elements have been shown to be essential for viral targeting to this locus. To characterize the role of the AAV inverted terminal repeat (ITR) cis-acting sequences in targeted integration an AAV
trs
mutant incapable of supporting viral replication was tested. Wild-type and mutant substrates were assayed for targeted integration after cotransfection in the presence or absence of Rep. Our results demonstrated that, in the presence of Rep78, both ITR substrates targeted to ch-19 with similar frequency. Molecular characterization of the mutant ITR integrants confirmed the presence of the
trs
mutation in the majority of samples tested. Complementation analysis confirmed that the mutant targeted viral genomes were unable to rescue and replicate. In addition, Rep78 induced extensive rearrangement and amplification of ch-19 sequences independent of wild-type or mutant targeting substrate. These studies demonstrate that Rep-dependent nicking of the viral cis-acting
trs
sequence is not a prerequisite for site-specific recombination and suggests AAV targeting is mediated by Rep78/68-dependent replication from the ch-19 origin of replication (
ori
). These studies have significant impact toward the understanding of AAV site-specific recombination and the development of targeting vectors.
Molecular cloning of the first metazoan beta-1,3 glucanase from eggs of the sea urchin Strongylocentrotus purpuratus.
Authors: Bachman E S , McClay D R
Published: July 2002

We report the molecular cloning of the first beta-1,3 glucanase from animal tissue. Three peptide sequences were obtained from beta-1,3 glucanase that had been purified from eggs of the sea urchin Strongylocentrotus purpuratus and the gene was cloned by PCR using oligonucleotides deduced from the peptide sequences. The full-length cDNA shows a predicted enzyme structure of 499 aa with a hydrophobic signal sequence. A 3.2-kb message is present in eggs, during early embryogenesis, and in adult gut tissue. A polyclonal antibody to the native 68-kDa enzyme recognizes a single band during early embryogenesis that reappears in the adult gut, and recognizes a 57-kDa fusion protein made from a full-length cDNA clone for beta-1,3 glucanase. The identity of this molecule as beta-1,3 glucanase is confirmed by sequence homology, by the presence of all three peptide sequences in the deduced amino acid sequence, and by the recognition of the bacterial fusion protein by the antibody directed against the native enzyme. Data base searches show significant homology at the amino acid level to beta-1,3 glucanases from two species of bacteria and a clotting factor from the horseshoe crab. The homology with the bacteria is centered in a 304-aa region in which there are seven scattered regions of high homology between the four divergent species. These four species were also found to have two homologous regions in common with more distantly related plant, fungal, and bacterial proteins. A global phylogeny based on these regions strongly suggests that the glucanases are a very ancient family of genes. In particular, there is an especially deep split within genes taken from the bacterial genus Bacillus.
Oxygen causes fetal pulmonary vasodilation through activation of a calcium-dependent potassium channel.
Authors: Cornfield D N , Reeve H L , Tolarova S , Weir E K , Archer S
Published: July 2002

At birth, pulmonary vasodilation occurs as air-breathing life begins. The mechanism of O2-induced pulmonary vasodilation is unknown. We proposed that O2 causes fetal pulmonary vasodilation through activation of a calcium-dependent potassium channel (KCa) via a cyclic nucleotide-dependent kinase. We tested this hypothesis in hemodynamic studies in acutely prepared fetal lambs and in patch-clamp studies on resistance fetal pulmonary artery smooth muscle cells. Fetal O2 tension (PaO2) was increased by ventilating the ewe with 100% O2, causing fetal total pulmonary resistance to decrease from 1.18 +/- 0.14 to 0.41 +/- 0.03 mmHg per ml per min. Tetraethylammonium and iberiotoxin, preferential KCa-channel inhibitors, attenuated O2-induced fetal pulmonary vasodilation, while glibenclamide, an ATP-sensitive K+-channel antagonist, had no effect. Treatment with either a guanylate cyclase antagonist (LY83583) or cyclic nucleotide-dependent kinase inhibitors (H-89 and KT 5823) significantly attenuated O2-induced fetal pulmonary vasodilation. Under hypoxic conditions (PaO2 = 25 mmHg), whole-cell K+-channel currents (Ik) were small and were inhibited by 1 mM tetraethylammonium or 100 nM charybdotoxin (CTX; a specific KCa-channel blocker). Normoxia (PaO2 = 120 mmHg) increased Ik by more than 300%, and this was reversed by 100 nM CTX. Nitric oxide also increased Ik. Resting membrane potential was -37.2 +/- 1.9 mV and cells depolarized on exposure to CTX, while hyperpolarizing in normoxia. We conclude that O2 causes fetal pulmonary vasodilation by stimulating a cyclic nucleotide-dependent kinase, resulting in KCa-channel activation, membrane hyperpolarization, and vasodilation.
Lambert-Eaton sera reduce low-voltage and high-voltage activated Ca2+ currents in murine dorsal root ganglion neurons.
Authors: García K D , Mynlieff M , Sanders D B , Beam K G , Walrond J P
Published: July 2002

Voltage-gated Ca2+ channels are categorized as either high-voltage activated (HVA) or low-voltage activated (LVA), and a subtype (or subtypes) of HVA Ca2+ channels link the presynaptic depolarization to rapid neuro-transmitter release. Reductions in transmitter release are characteristic of the autoimmune disorder, Lambert-Eaton syndrome (LES). Because antibodies from LES patients reduce Ca2+ influx in a variety of cell types and disrupt the intramembrane organization of active zones at neuromuscular synapses, specificity of LES antibodies for the Ca2+ channels that control transmitter release has been suggested as the mechanism for disease. We tested sera from four patients with LES. Serum samples from three of the four patients reduced both the maximal LVA and HVA Ca2+ conductances in murine dorsal root ganglion neurons. Thus, even though LES is expressed as a neuromuscular and autonomic disorder, our studies suggest that Ca2+ channels may be broadly affected in LES patients. To account for the specificity of disease expression, we suggest that incapacitation of only a fraction of the Ca2+ channels clustered at active zones would severely depress transmitter release. In particular, if several Ca2+ channels in a cluster are normally required to open simultaneously before transmitter release becomes likely, the loss of a few active zone Ca2+ channels would exponentially reduce the probability of transmitter release. This model may explain why LES is expressed as a neuromuscular disorder and can account for a clinical hallmark of LES, facilitation of neuromuscular transmission produced by vigorous voluntary effort.
Cloning and characterization of myr 6, an unconventional myosin of the dilute/myosin-V family.
Authors: Zhao L P , Koslovsky J S , Reinhard J , Bähler M , Witt A E , Provance D W , Mercer J A
Published: July 2002

We have isolated cDNAs encoding a second member of the dilute (myosin-V) unconventional myosin family in vertebrates, myr 6 (myosin from rat 6). Expression of myr 6 transcripts in the brain is much more limited than is the expression of dilute, with highest levels observed in choroid plexus and components of the limbic system. We have mapped the myr 6 locus to mouse chromosome 18 using an interspecific backcross. The 3' portion of the myr 6 cDNA sequence from rat is nearly identical to that of a previously published putative glutamic acid decarboxylase from mouse [Huang, W.M., Reed-Fourquet, L., Wu, E. & Wu, J.Y. (1990) Proc. Natl. Acad. Sci. USA 87, 8491-8495].
Expression in yeast of binding regions of karyopherins α and β inhibits nuclear import and cell growth
Authors: Enenkel Cordula , Schülke Norbert , Blobel Günter
Published: July 2002

Using truncated forms of recombinant yeast karyopherins α and β
in
in vitro
binding assays, we mapped the regions of
karyopherin α that bind to karyopherin β and the regions of
karyopherin β that interact with karyopherin α and with Ran-GTP.
Karyopherin α’s binding region for karyopherin β was localized to
its N-terminal domain, which contains several clusters of basic
residues, whereas karyopherin β’s binding region for karyopherin α
was localized to an internal region containing two clusters of acidic
residues. Karyopherin β’s binding region for Ran-GTP overlaps with
that for karyopherin α and comprises at least one of the two acidic
clusters required for karyopherin α binding in addition to further
downstream determinants not required for karyopherin α binding.
Overexpression in yeast of fragments containing either karyopherin
β’s binding region for α and Ran-GTP or karyopherin α’s binding
region for β resulted in sequestration of most of the cytosolic
karyopherin α or karyopherin β, respectively, in complexes
containing the truncated proteins. As these binding region-containing
fragments lack other domains required for function of the corresponding
protein, the overexpression of either fragment also inhibited
in
vivo
nuclear import of a model reporter protein as well as cell
growth.
Growth hormone-releasing hormone antagonist MZ-4-71 inhibits
in vivo
proliferation of Caki-I renal adenocarcinoma
Authors: Jungwirth Andreas , Schally Andrew V. , Pinski Jacek , Groot Kate , Armatis Patricia , Halmos Gabor
Published: July 2002

In view of evidence that growth hormone (GH) and insulin-like growth factors (IGF) may play a role in the development of renal cell carcinoma (RCC), we investigated the effects of growth hormone-releasing hormone (GH-RH) antagonist MZ-4-71 on the proliferation of the human renal adenocarcinoma cell line Caki-I
in vitro
and
in vivo.
Male nude mice bearing xenografts of human Caki-I RCC were treated for 4 weeks with MZ-4-71 injected s.c. twice daily at a dose of 20 μg per animal. Tumor growth, serum, liver, and tumor IGF levels and IGF-I receptor concentrations in Caki-I cell membranes were measured. After 4 weeks of therapy, the final volume of Caki-I tumors in nude mice treated with MZ-4-71 was significantly (
P
< 0.01) decreased to 52.6 ± 12.3 mm
3
as compared with controls that measured 504.2 ± 104.1 mm
3
. Treatment with GH-RH antagonist also significantly reduced tumor weight, serum levels of GH and IGF-I, liver concentrations of IGF-I, and tumor levels of IGF-I and IGF-II. High-affinity binding sites for IGF-I were detected in the cell membranes of Caki-I tumors. IGF-I and IGF-II stimulated the proliferation of Caki-I cells in tissue cultures. Antagonist MZ-4-71 could inhibit
in vitro
growth of Caki-I cells, but only at high concentrations. Our findings demonstrate that GH-RH antagonist MZ-4-71 can significantly inhibit the growth of Caki-I RCC. MZ-4-71 may exert its suppressive effect on tumor growth through a reduction in GH release from the pituitary and the subsequent decrease in the production of IGF-I in the liver and IGF-I and II by the tumors. The efficacy of MZ-4-71 suggests that this compound could be considered for the therapy of recurrent or metastatic RCC.
Selective enhancement of emotional, but not motor, learning in monoamine oxidase A-deficient mice
Authors: Kim Jeansok J. , Shih Jean C. , Chen Kevin , Chen Lu , Bao Shaowen , Maren Stephen , Anagnostaras Stephan G. , Fanselow Michael S. , De Maeyer Edward , Seif Isabelle , Thompson Richard F.
Published: July 2002

Mice deficient in monoamine oxidase A (MAOA), an enzyme that metabolizes monoamines such as norepinephrine and serotonin, have elevated norepinephrine and serotonin levels in the frontal cortex, hippocampus, and cerebellum, compared with normal wild-type mice. Since monoamines in these areas are critically involved in a variety of behaviors, we examined learning and memory (using emotional and motor tasks) in MAOA mutant mice. The MAOA-deficient mice exhibited significantly enhanced classical fear conditioning (freezing to both tone and contextual stimuli) and step-down inhibitory avoidance learning. In contrast, eyeblink conditioning was normal in these mutant mice. The female MAOA-deficient mice also displayed normal species-typical maternal behaviors (nesting, nursing, and pup retrieval). These results suggest that chronic elevations of monoamines, due to a deletion of the gene encoding MAOA, lead to selective alterations in emotional behavior.
Site-specific, photochemical proteolysis applied to ion channels
in vivo
Authors: England Pamela M. , Lester Henry A. , Davidson Norman , Dougherty Dennis A.
Published: July 2002

A method for site-specific, nitrobenzyl-induced photochemical proteolysis of diverse proteins expressed in living cells has been developed based on the chemistry of the unnatural amino acid (2-nitrophenyl)glycine (Npg). Using the
in vivo
nonsense codon suppression method for incorporating unnatural amino acids into proteins expressed in
Xenopus
oocytes, Npg has been incorporated into two ion channels: the
Drosophila
Shaker B K
+
channel and the nicotinic acetylcholine receptor. Functional studies
in vivo
show that irradiation of proteins containing an Npg residue does lead to peptide backbone cleavage at the site of the novel residue. Using this method, evidence is obtained for an essential functional role of the “signature” Cys128–Cys142 disulfide loop of the nAChR α subunit.
Design of fast enzymes by optimizing interaction potential in active site
Authors: Zhou Huan-Xiang , Wong Kwan-Yin , Vijayakumar M.
Published: July 2002

The diffusional encounter between substrate and enzyme, and hence catalytic efficiency, can be enhanced by mutating charged residues on the surface of the enzyme. In this paper we present a simple method for screening such mutations. This is based on our earlier result that electrostatic enhancement of the enzyme-substrate binding rate constant can be accounted for just by the interaction potential within the active site. Assuming that catalytic and structural integrity is maintained, the catalytic efficiency can be optimized by surface charge mutations which lead to stronger interaction potential within the active site. Application of the screening method on superoxide dismutase shows that only charge mutations close to the active site will have practical effect on the catalytic efficiency. This rationalizes a large number of findings obtained in previous simulation and experimental studies.
A gene–culture coevolutionary model for brother–sister mating
Authors: Aoki Kenichi , Feldman Marcus W.
Published: July 2002

We present a gene–culture coevolutionary model for brother–sister
mating in the human. It is shown that cultural—as opposed to
innate—determination of mate preference may evolve, provided the
inbreeding depression is sufficiently high. At this coevolutionary
equilibrium, sib mating is avoided because of cultural pressures.