bluuebunny/crossref_metadata_2025 huggingface dataset:
Stress and field dependence of critical current in Ba2YCu3O7−δ superconductors
Authors: Jin S. , Sherwood R. C. , Tiefel T. H. , van Dover R. B. , Johnson D. W. , Grader G. S.
Published: July 2002

Superconductors in practical applications are subjected to large stresses such as caused by coil winding, thermal contraction, and the Lorentz force generated by magnetic field. In this letter, the stress and field dependence of the critical current density ( JC) of the high-temperature superconductor (Ba2YCu3O7−δ) has been investigated. It has been found that the JC value is essentially independent of the applied stress, tensile or compressive, up to the level of fracture stress. This observation suggests that the grain boundary stress concentration is not likely to be one of the major causes of the ‘‘weak links’’ responsible for the relatively poor JC values in polycrystalline Ba2YCu3O7−δ. The rapid deterioration of JC in applied magnetic field does not seem to be affected by the co-presence of applied stress.
Scattering in low-loss GaAs/AlGaAs rib waveguides
Authors: Deri R. J. , Kapon E. , Schiavone L. M.
Published: July 2002

Single-mode rib waveguides with low propagation loss (0.2 dB/cm) were fabricated on GaAs/AlGaAs single heterostructures by dry etching. The attenuation of these guides was measured to study the effect of rib structure on propagation loss at 1.52 μm. An increase in loss with increased rib height and decreased rib width was associated with scattering due to a rib surface roughness of approximately 50 nm for ion milled waveguides. Fabrication with reactive ion etching reduced the rib roughness and its associated scattering loss by a factor of 3 or more in waveguides with strong optical confinement (effective index difference of 0.012) of the fundamental guided mode.
Structural and compositional integrity of lattice-matched ZnSe0.95S0.05 on (100) orientated GaAs
Authors: Yates Heather M. , Williams John O.
Published: July 2002

Lattice-matched ZnSe0.95S0.05 epitaxial layers have been grown on (100) oriented GaAs substrates by atmospheric pressure metalorganic vapor phase epitaxy. Blue room-temperature photoluminescence is observed and the interface is both compositionally and structurally abrupt as shown by secondary ion mass spectrometry and high-resolution transmission electron microscopy.
Atomic arsenic detection by ArF laser-induced fluorescence
Authors: Selwyn Gary S.
Published: July 2002

Arsenic atoms sputtered from gallium arsenide wafers or arsenic-doped n-type silicon wafers have been detected in argon plasmas using the laser-induced fluorescence technique (LIF). Two methods of LIF detection were employed. One used a tunable, frequency-doubled dye laser to pump a metastable transition of atomic arsenic at 228.81 nm. The second technique used the broadband output of an ArF excimer laser to pump a ground-state transition of As at 193.76 nm.
One-step two-level etching technique for monolithic integrated optics
Authors: Grande W. J. , Braddock W. D. , Shealy J. R. , Tang C. L.
Published: July 2002

We describe a one-step two-level etching technique for the batch fabrication of monolithically integrated optical circuits. The ability to fabricate high-quality laser devices with this process is demonstrated.
Interaction between radiation-induced defects and the Pt-related center in silicon
Authors: Weng Y. M. , Ohta E. , Sakata M.
Published: July 2002

The interaction of Pt with electron irradiation induced defects has been observed. Platinum in silicon increases irradiation-induced defects remarkably, especially of the A center, and lowers the annealing temperature to 220–140 °C for the A and E centers, respectively. The level Ea (0.23) in the Pt-doped silicon is the Pt(−/0) level, an acceptor like the A center.
Photodegradation in hydrogenated amorphous silicon films at a high level of illumination
Authors: Eser E. , Urbanski E.
Published: July 2002

The rate of photodegradation of glow discharge deposited hydrogenated amorphous silicon films was measured at temperatures between 150 and 283 K at an illumination intensity of 16AM1. Down to a certain degradation level, the experimental data fit quite well to a model where the recombination of the photogenerated carriers via a single level situated between two quasi-Fermi levels is assumed to be responsible in generating the metastable defects. In this regime, the degradation rate constant is found to be thermally activated with an activation energy of 0.15 eV. As the degradation proceeds beyond that level, a different mechanism which is not fully analyzed here, is found to be operational.
Thermal stressing of bipolar transistors with metal-insulator-semiconductor heterojunction emitters
Authors: Szeto N. , Pulfrey D. L. , Tarr N. G.
Published: July 2002

Silicon bipolar junction transistors employing metal-thin insulator-semiconductor tunnel junction emitters are capable of realizing extremely high common-emitter current gains. The experimental evidence presented here indicates a possible limitation of these devices as regards their inability to withstand moderate temperature stressing.
Lattice relaxation due to hydrogen passivation in boron-doped silicon
Authors: Stutzmann M. , Harsanyi J. , Breitschwerdt A. , Herrero C. P.
Published: July 2002

The influence of hydrogen on the lattice constant of boron-doped crystalline silicon is studied by x-ray diffraction. It is found that hydrogen passivation of the boron acceptors is accompanied by a noticeable expansion of the passivated layer. A value of +(2.5±0.5)×10−24 cm3/atom is obtained for the expansion coefficient due to B-H complexes.
Liquid phase epitaxy of Pb1−xEuxTe thin films
Authors: Hacham A. , El-Hanany U. , Rotter S. , Shapira Yoram
Published: July 2002

Epitaxial layers of Pb1−xEuxTe with x<0.06 have been grown for the first time using liquid phase epitaxy. The epitaxy was done from Te-rich solutions since the commonly used Pb solutions, which exothermally form Pb-Eu intermetallics, cannot be used to grow this compound. The basic growth parameters and conditions were investigated. The results show that the incorporation of Eu into PbTe lattice is an endothermal process, with an activation energy of 1.0 eV. The reported technique yields device quality layers showing flat surfaces and sharp interfaces.
Visible free-electron-laser oscillator (constant and tapered wiggler)
Authors: Edighoffer J. A. , Neil G. R. , Fornaca S. , Thompson H. R. , Smith T. I. , Schwettman H. A. , Hess C. E. , Frisch J. , Rohatgi R.
Published: July 2002

The first linac-based visible free-electron-laser oscillator was operated in February 1987 at a wavelength of 525 nm with and without a wiggler taper. Peak output power of 29 kW with a macropulse average power of 1.1 W was observed. The cavity dielectric mirrors were damaged at approximately 21 kW/cm2 of average intracavity power.
Effect of boron incorporation on the light-induced effect in amorphous silicon solar cells
Authors: Jang Jin , Lee Yi Sang
Published: July 2002

The effect of light illumination on the photovoltaic performances of hydrogenated amorphous silicon (a-Si:H) n+-p-p+ solar cells has been investigated. The degradation increases as the doping concentration of p-type a-Si:H increases, and it decreases with increasing the substrate (or annealing) temperature. These results indicate that the light-induced degradation increases with the microvoid density in the material. The increase of conversion efficiency has been observed for a-Si:H n+-p-p+ cells after light exposure, and this is due to the increase of doping efficiency for p-type a-Si:H during light illumination.
Fabrication of gatable submicron channels in AlxGa1−xAs-GaAs heterostructures
Authors: Owusu-Sekyere K. , Chang A. M. , Chang T. Y.
Published: July 2002

A new, simplified process has been developed for fabricating submicron AlxGa1−xAs-GaAs heterostructure devices for low-temperature transport studies, with the advantage of gatability. This process utilizes electron beam lithography, photolithography, and wet etching techniques to laterally confine the two-dimensional electron gas, and possesses the unique feature that the metal etch mask for the electron beam defined narrow section is deposited directly on top of the heterostructure surface, allowing for use as a gate. Devices of lithographic widths from 0.4 to 2.0 μm have been successfully fabricated, where the 0.4 μm devices of both enhancement and depletion modes have been demonstrated to function down to 0.35 K in temperature.
CdS/p-Si solar cells made by serigraphy
Authors: García F. J. , Ortíz-Conde A. , Sa-Neto A.
Published: July 2002

CdS/p-Si solar cells have been fabricated depositing the CdS layer by serigraphy. Open circuit voltages of 538 mV, short circuit current densities of 32 mA cm−2, fill factors of 0.52, and conversion efficiencies of 8.1% have been measured under 100 mW cm−2 (AM1) simulated solar illumination.
Effects of hot sources on residual doping in GaAs grown by molecular beam epitaxy
Authors: Sacks R. N. , Pastorello R. A.
Published: July 2002

A study of the effects of impurities evolving from a hot (1350–1500 °C) empty effusion cell on the residual doping concentrations in GaAs grown by molecular beam epitaxy (MBE) has been made. The influence of these impurities on electron concentrations in highly doped GaAs:Si has also been investigated. p-type residual doping was seen in all cases, with 1×1016/cm3 being the highest level observed. More typical were concentrations in the mid-to-high 1014 range after the empty cell had been properly degassed. While most of the acceptors appear to be C, there is some evidence that N may be involved at the higher concentrations. No effect from the hot source on the doping level of GaAs:Si with n=4×1018/cm3 was seen, showing that effusion cell evolved impurities are not responsible for limiting high electron concentrations in MBE-grown GaAs:Si.
High conductivity polycrystalline silicon obtained by molecular beam deposition
Authors: Delage S. L. , Jeng S.-J. , Jousse D. , Iyer S. S.
Published: July 2002

The structural and electrical properties have been investigated of antimony doped polycrystalline silicon films obtained by molecular beam deposition on oxidized silicon substrates. We show that low-resistivity films with smooth morphology are obtained by solid phase crystallization of antimony doped amorphous silicon layers deposited at 250 °C. A resistivity of 4.3 mΩ cm is obtained by crystallizing the films at temperatures as low as 650 °C for 15 min. In situ crystallization of the amorphous silicon is absolutely necessary to achieve low resistivities. We also show that direct deposition above 650 °C gives rise to polycrystalline silicon with much higher resistivities.
Excitonic trapping from atomic layer epitaxial ZnTe within ZnSe/(Zn,Mn)Se heterostructures
Authors: Kolodziejski L. A. , Gunshor R. L. , Fu Q. , Lee D. , Nurmikko A. V. , Gonsalves J. M. , Otsuka N.
Published: July 2002

ZnSe-based structures have been fabricated, consisting of monolayers of ZnTe grown by atomic layer epitaxy spaced by appropriate dimensions to approximate a Zn(Se,Te) mixed crystal; this method has been used to overcome the difficulties encountered in the molecular beam epitaxy (MBE) of the alloy with a low Te concentration. Reported work has shown that blue-blue/green luminescence, originating from exciton self-trapping at Te sites in Zn(Se,Te) bulk crystal alloys, is significantly more intense than the light emitted from ZnSe. Luminescence originating from ZnTe-containing ZnSe/ZnTe superlattice and ZnSe/(Zn,Mn)Se multiple quantum well structures was used to illustrate how the presence of ZnTe acts to trap excitons. Optical signatures of the MBE-grown structures were similar to those of the random alloy, indicating that the exciton self-trapping mechanism is important to the interpretation of recombination processes in structures containing ZnSe/ZnTe heterointerfaces.
Solidification mechanisms of laser-annealed thin copper films: Dual phase formation
Authors: Bloch J. , Zeiri Y. , Venkert A.
Published: July 2002

An unusual solidification pattern was found to occur in thin coper films following pulsed laser irradiation, under limited conditions of pulse length and beam power. Two phases of different crystal size and orientation are obtained. Simulations of the temperature distribution during and after the laser pulse together with a morphological analysis suggest that the two phases result from two different solidification mechanisms.
Fabrication of free-standing single-crystal silicon wires
Authors: Potts A. , Hasko D. G. , Cleaver J. R. A. , Ahmed H.
Published: July 2002

A fabrication process for free-standing single-crystal silicon wires of submicrometer cross-sectional dimensions and lengths in excess of 40 μm is reported. The starting material is silicon-on-insulator that has been recrystallized using a dual electron beam recrystallizing system. The wires are then fabrictaed in the recrystallized layer by a combination of electron beam lithography and plasma etching. Electrical measurements have been performed and the fabrication limits of the process are discussed.
Quench rate enhancement in pulsed laser melting of Si by processing under water
Authors: Polman A. , Sinke W. , Saris F. W. , Uttormark M. J. , Thompson Michael O.
Published: July 2002

The thermal quench rate during pulsed laser heating of Si can be enhanced by immersing the sample in a liquid (e.g., water) during irradiation. The liquid in contact with the irradiated surface acts as an additional heat sink increasing the thermal quench rate. The heat transfer processes and phase transformations were studied in real time using transient optical reflectance and electrical conductance techniques. Measurements of the melting and solidification dynamics of the Si reveal that the quench rate may be enhanced by 30% for deep melts. The measurements also indicate that a steam or superheated water phase is formed near the Si surface during the laser pulse. The observed phenomena are analyzed in terms of standard heat flow.
Pulse compression effect in a laser-driven flash x-ray tube
Authors: Krehl P.
Published: July 2002

The performance characteristics of a high-vacuum discharge flash x-ray tube, such as dose, maximum dose rate, discharge delay time, and pulse width, can be improved by triggering the tube with a laser-produced plasma at the cathode. The system consists of an open flash x-ray diode of classical coaxial electrode geometry, driven at 50 kV by a 10 Ω, 69 ns transmission line and a neodymium:yttrium aluminum garnet laser of 10 ns pulse width, which is focused onto the cathode rim. It could be demonstrated that already at small incident laser energy a significant x-ray pulse compression could be achieved, which also goes in parallel with an increase in dose output. Experiments with laser energies at 110 mJ indicate a saturation in optimum tube performance.
Measurement of soft x-ray multilayer mirror reflectance at normal incidence using laser-produced plasmas
Authors: Trail J. A. , Byer R. L. , Barbee T. W.
Published: July 2002

We have used laser-produced plasmas as a broadband source of soft x rays to measure the normal incidence reflectance of multilayer mirrors in the 10–25 nm spectral region. The measurements have a spectral resolution of 0.03 nm and a reflectance resolution of 10%. Measurements made on a Mo/Si multilayer show excellent agreement with results obtained using a synchrotron and indicate a normal incidence peak reflectance of over 50% at 15 nm. By repeating the reflectance measurement at different positions across a single 7.5 cm mirror we determined multilayer uniformity as a function of position and we relate this dependence to the geometry of the deposition process.
InGaAsP multiple quantum well lasers with planar buried heterostructure prepared by metalorganic chemical vapor deposition
Authors: Ishiguro H. , Kawabata T. , Koike S.
Published: July 2002

Planar buried heterostructure InGaAsP multiple quantum well (MQW) lasers consisting of six InGaAsP (λg =1.34 μm at room temperature) wells and five InP barriers were prepared by low-pressure metalorganic chemical vapor deposition. The threshold current was 35 mA, and the differential quantum efficiency was 45% at an emission wavelength of 1.3 μm. In the temperature range from −35 to 30 °C, the characteristic temperature was T0=57 K. No significant improvement in T0 was observed in these MQW lasers. However, stable single longitudinal mode operation could be obtained in a wide range of injection current without any mode changes. This effect was considered to be a result of gain narrowing of the MQW lasers.
Discharge interruption induced by an ArF laser in a C2H3Cl/CF4/CH4 mixture
Authors: Sasagawa Teruo , Kawahara Akihiro , Obara Minoru
Published: July 2002

We have successfully demonstrated discharge interruption induced by ArF laser irradiation in a discharge medium of C2H3Cl/CF4/CH4, using a hollow cathode type discharge tube. With a mixture of C2H3Cl/CF4/CH4 (1.8 Torr of CH4 with 0.7% of C2H3Cl and 10% of CF4), a discharge current of 1 mA (0.14 mA/cm2), and after laser irradiation of 27 mJ/cm2 (10 ns full width at half-maximum), first a discharge current peak appeared and then the discharge current was decreased rapidly with a current decay time constant of 1.0 μs. A corresponding discharge current decay rate (dI/dt) of 1 kA/s was obtained. The discharge interruption condition was limited by the gas mixture and the total pressure. Moreover, dependences of dI/dt and the time constant (τ) on both laser fluence and discharge current were observed.
Effect of low-frequency intensity noise on high-frequency direct modulation of semiconductor injection lasers
Authors: Lau K. Y. , Blauvelt H.
Published: July 2002

It was experimentally observed that low-frequency intensity noise in 1.3 μm semiconductor lasers can be translated to high frequencies through beating with a high-frequency modulation signal, thus imposing a maximum achievable signal/noise ratio. An analysis of this effect using a formalism developed for treating intermodulation distortion yields good agreement with the experimental results.
Oxides grown on textured single-crystal silicon for enhanced conduction
Authors: Fong Y. , Wu A. T. , Ko P. K. , Hu C.
Published: July 2002

The electrical properties and integrity of oxides grown on textured single-crystal silicon (TSC oxides) are investigated and are compared to oxides grown on untextured single-crystal silicon (normal oxides) and oxides grown on polycrystalline silicon (polyoxides). The 230 Å TSC oxide exhibited enhanced electron injection in both polarities, reducing the voltage necessary for JG=+1 mA/cm2 from 21 V for normal 230 Å oxides to 5 V. This made the 230 Å TSC oxide approximately equivalent to a 60 Å normal oxide. The electron trapping rate for the TSC oxide was similar to that of 230 Å normal oxides but is much smaller than that of polyoxides. Charge-to-breakdown (QBD) measurements showed a much better QBD histogram (large area capacitors) for the TSC oxide than for 230 Å and 60 Å normal oxides.
Interaction of a polycrystalline silicon/SiO2/silicon substrate under thermal/electrical fields
Authors: Chou T. C. , Tu K. N.
Published: July 2002

Electric current induced breakdown phenomenon of silicon dioxide film was studied by annealing the sandwich samples of polycrystalline Si/SiO2 /Si substrate at 700 °C under electric currents. Cross-sectional transmission electron microscopy revealed two interesting results: (1) the aggregation of voids into large holes at the interface of polycrystalline Si/SiO2 , and (2) the nucleation and growth of crystalline Si in the silicon dioxide layer. The crystalline Si was either of single crystalline or polycrystalline forms, depending on the nucleating interfaces. Local melting as a result of Joule heating was observed. The breakdown of the oxide is mainly attributed to the loss of oxide integrity as a result of heterogeneous Joule heating. The nucleation and growth of crystalline Si in the amorphous oxide layer suggest the direct decomposition of SiO2 during the oxide breakdown process.
Low-temperature x-ray diffraction of the Y1Ba2Cu3O9−x oxide ceramic superconductor
Authors: Yin Hua-qing , Gao Yi-mei , Du Jia-ju , Chen Ben-pei , Jiang Jian-yi , Wang Xiang
Published: July 2002

The change of the lattice parameter with temperature (82–320 K) of the single phase Y1Ba2Cu3O9−x superconductor has been investigated by x-ray diffractometer. The experimental result shows that there exist two abrupt changes of lattice parameter at about 250 and 125 K separately in the curve of the lattice parameter versus temperature. But no change of structure symmetry was observed as shown by x-ray diffraction. The abrupt change of lattice parameter at about 250 and 125 K may be associated to the position adjusting of oxygen atoms in oxide ceramic.
Native oxides on etched Zn3P2 surfaces studied by x-ray photoelectron spectroscopy
Authors: Kato Yoshimine , Kurita Shoichi
Published: July 2002

The native oxides formed on air exposed, etched bulk polycrystalline Zn3P2 were investigated in the as-etched condition, using x-ray photoemission spectroscopy. The sputter-etched surfaces appeared to be composed primarily of ZnO with a small concentration of P2O3 or phosphate underneath. The bromine-methanol etched surfaces were less oxidized, and the native oxides appeared to become predominantly of phosphorus compound oxides. P2O5 was not observed in either case.
Interface traps at midgap during defect transformation in (100) Si/SiO2
Authors: Nishioka Yasushiro , Ma T. P.
Published: July 2002

The interface traps generated by ionizing radiation or hot-electron injection undergo continuous changes with time after the damaging source is turned off. This letter focuses on the interfacial defect transformation process in (100) Si/SiO2, in which a large portion of the interface trap peak in the upper half of the Si band gap gradually converts into a second peak in the lower half of the band gap. It will be shown that, when the interfacial defect transformation process dominates, the interface trap density at midgap does not change with time, despite the fact that other portions of the interface traps undergo drastic changes. The time-dependent behavior of the midgap density provides a convenient indicator to determine whether the dominant process is defect transformation, annealing (the midgap density decreases with time), or latent generation (the midgap density increases with time).
Two-dimensional electron gas at a Ga0.47In0.53As/ (AlxGa1−x)0.48In0.52As interface
Authors: Ben Amor S. , Dmowski L. , Portal J. C. , Praseuth J. P. , Goldstein L.
Published: July 2002

We report the first observation of a two-dimensional electron gas in (AlGa) InAs/GaInAs heterostructures. Angular-dependent Shubnikov–de Haas oscillations and quantum Hall effect prove the two dimensionality of the system. We discuss the effect of the barrier composition on the electronic structure of the system. A significant number of electrons remain confined even for the smallest confinement barrier. Persistent photoconductivity was observed at low temperature.
Free-electron laser based on the effect of channeling in an intense standing light wave
Authors: Fedorov M. V. , Oganesyan K. B. , Prokhorov A. M.
Published: July 2002

Channeling of electrons moving across an intense standing light wave is described. This effect is proposed to be used for the creation of a free-electron laser. Its linear gain is found and estimated.
Ordering of Al0.5Ga0.5P by high-energy electron irradiation
Authors: Wada Takao , Maeda Yoshinobu
Published: July 2002

A long-range order of Al0.5Ga0.5P layers grown by electron beam epitaxy on a (100) GaP substrate has been detected. Surfaces of Al layers deposited by vacuum evaporation on GaP wafers were irradiated with a fluence of (1–5)×1017 electrons cm−2 at 7 MeV and 50 °C. It is speculated that since a great number of electron-hole pairs are created, the strong enhancement of the diffusion of Al atoms may be caused by the energy release mechanism and an Al interstitial may preferably occupy a Ga site by the ‘‘kick-out’’ mechanism and for the formation of much stabler bonds between group III and V atoms.
Broad-area tandem semiconductor laser
Authors: Chen T. R. , Mehuys D. , Zhuang Y. H. , Mittelstein M. , Wang H. , Derry P. L. , Kajanto M. , Yariv A.
Published: July 2002

A tandem combination of a uniform gain broad-area semiconductor laser and a (lateral) periodic gain section displays a stable, near-diffraction-limited single-lobed far-field pattern. The GaAs/GaAlAs quantum well lasers display a high degree of coherence across 60-μm-wide apertures provided that the broad-area section is sufficiently long.
Rib profile effects on scattering in semiconductor optical waveguides
Authors: Deri R. J. , Hawkins R. J. , Kapon E.
Published: July 2002

A novel method for studying the dependence of scattering loss on guide structure in integrated-optic semiconductor rib waveguides is presented. The results provide a simple experimental test for determining the nature of the scattering loss. Differences in scattering due to changes in epilayer structure and ribwall slope are also investigated.
Complexity of the erythroid transcription factor NF-E2 as revealed by gene targeting of the mouse p18 NF-E2 locus.
Authors: Kotkow K J , Orkin S H
Published: July 2002

High-level globin expression in erythroid precursor cells depends on the integrity of NF-E2 recognition sites, transcription factor AP-1-like protein-binding motifs, located in the upstream regulatory regions of the alpha- and beta-globin loci. The NF-E2 transcription factor, which recognizes these sites, is a heterodimer consisting of (i) p45 NF-E2 (the larger subunit), a hematopoietic-restricted basic leucine zipper protein, and (ii) a widely expressed basic leucine zipper factor, p18 NF-E2, the smaller subunit. p18 NF-E2 protein shares extensive homology with the maf protooncogene family. To determine an in vivo role for p18 NF-E2 protein we disrupted the p18 NF-E2-encoding gene by homologous recombination in murine embryonic stem cells and generated p18 NF-E2-/- mice. These mice are indistinguishable from littermates throughout all phases of development and remain healthy in adulthood. Despite the absence of expressed p18 NF-E2, DNA-binding activity with the properties of the NF-E2 heterodimer is present in fetal liver erythroid cells of p18 NF-E2-/- mice. We speculate that another member of the maf basic leucine zipper family substitutes for the p18 subunit in a complex with p45 NF-E2. Thus, p18 NF-E2 per se appears to be dispensable in vivo.
Kinetics of cytokine expression during primary human immunodeficiency virus type 1 infection.
Authors: Graziosi C , Gantt K R , Vaccarezza M , Demarest J F , Daucher M , Saag M S , Shaw G M , Quinn T C , Cohen O J , Welbon C C , Pantaleo G , Fauci A S
Published: July 2002

In the present study, we have determined the kinetics of constitutive expression of a panel of cytokines [interleukin (IL) 2, IL-4, IL-6, IL-10, interferon gamma (IFN-gamma), and tumor necrosis factor alpha (TNF-alpha)] in sequential peripheral blood mononuclear cell samples from nine individuals with primary human immunodeficiency virus infection. Expression of IL-2 and IL-4 was barely detected in peripheral blood mononuclear cells. However, substantial levels of IL-2 expression were found in mononuclear cells isolated from lymph node. Expression of IL-6 was detected in only three of nine patients, and IL-6 expression was observed when transition from the acute to the chronic phase had already occurred. Expression of IL-10 and TNF-alpha was consistently observed in all patients tested, and levels of both cytokines were either stable or progressively increased over time. Similar to IL-10 and TNF-alpha, IFN-gamma expression was detected in all patients; however, in five of nine patients, IFN-gamma expression peaked very early during primary infection. The early peak in IFN-gamma expression coincided with oligoclonal expansions of CD8+ T cells in five of six patients, and CD8+ T cells mostly accounted for the expression of this cytokine. These results indicate that high levels of expression of proinflammatory cytokines are associated with primary infection and that the cytokine response during this phase of infection is strongly influenced by oligoclonal expansions of CD8+ T cells.
Targeted expression of a multifunctional chimeric neurotrophin in the lesioned sciatic nerve accelerates regeneration of sensory and motor axons
Authors: Funakoshi Hiroshi , Risling Mårten , Carlstedt Thomas , Lendahl Urban , Timmusk Tõnis , Metsis Madis , Yamamoto Yuji , Ibáñez Carlos F.
Published: July 2002

Peripheral nerve injury markedly regulates expression of neurotrophins and their receptors in the lesioned nerve. However, the role of endogenously produced neurotrophins in the process of nerve regeneration is unclear. Expression of a multifunctional neurotrophin, pan-neurotrophin-1 (PNT-1), was targeted to the peripheral nerves of transgenic mice by using a gene promoter that is specifically activated after nerve lesion but that is otherwise silent in all other tissues and during development. PNT-1 is a chimeric neurotrophin that combines the active sites of the neurotrophins nerve growth factor, brain-derived neurotrophic factor, and neurotrophin-3 and binds and activates all known neurotrophin receptors. In adult transgenic mice, PNT-1 was highly expressed in transected but not in intact sciatic nerve. Morphometric analyses at the electron microscopy level showed increased and accelerated recovery of axon diameter of myelinated fibers in crushed peripheral nerves of transgenic mice compared with wild type. Examination of nerve bundles in target tissues indicated accelerated reinnervation of foot pad dermis and flexor plantaris muscle in transgenic mice. Moreover, transected sensory and motor axons of transgenic mice showed faster and increased return of neurophysiological responses, suggesting an accelerated rate of axonal elongation. Importantly, transgenic mice also showed a markedly ameliorated loss of skeletal muscle weight, indicating functional regeneration of motor axons. Together, these data provide evidence, at both the anatomical and functional levels, that neurotrophins endogenously produced by the lesioned nerve are capable of significantly accelerating the regeneration of both sensory and motor axons after peripheral nerve damage. In addition, our results indicate that exogenous PNT-1 administration may be an effective therapeutic treatment of peripheral nerve injuries.
The role of the D
2
dopamine receptor (D
2
R) in A
2A
adenosine receptor (A
2A
R)-mediated behavioral and cellular responses as revealed by A
2A
and D
2
receptor knockout mice
Authors: Chen Jiang-Fan , Moratalla Rosario , Impagnatiello Francesco , Grandy David K. , Cuellar Beatriz , Rubinstein Marcelo , Beilstein Mark A. , Hackett Elizabeth , Fink J. Stephen , Low Malcolm J. , Ongini Ennio , Schwarzschild Michael A.
Published: July 2002

The A
2A
R is largely coexpressed with
D
2
Rs and enkephalin mRNA in the striatum where it modulates
dopaminergic activity. Activation of the A
2A
R antagonizes
D
2
R-mediated behavioral and neurochemical effects in the
basal ganglia through a mechanism that may involve direct
A
2A
R–D
2
R interaction. However, whether the
D
2
R is required for the A
2A
R to exert its
neural function is an open question. In this study, we examined the
role of D
2
Rs in A
2A
R-induced behavioral and
cellular responses, by using genetic knockout (KO) models (mice
deficient in A
2A
Rs or D
2
Rs or both). Behavioral
analysis shows that the A
2A
R agonist
2–4-(2-carboxyethyl)phenethylamino-5′-
N
-ethylcarboxamidoadenosine
reduced spontaneous as well as amphetamine-induced locomotion in
both D
2
KO and wild-type mice. Conversely, the nonselective
adenosine antagonist caffeine and the A
2A
R antagonist
8-(3-chlorostyryl)caffeine produced motor stimulation in mice lacking
the D
2
R, although the stimulation was significantly
attentuated. At the cellular level, A
2A
R inactivation
counteracted the increase in enkephalin expression in striatopallidal
neurons caused by D
2
R deficiency. Consistent with the
D
2
KO phenotype, A
2A
R inactivation partially
reversed both acute D
2
R antagonist (haloperidol)-induced
catalepsy and chronic haloperidol-induced enkephalin mRNA expression.
Together, these results demonstrate that A
2A
Rs elicit
behavioral and cellular responses despite either the genetic deficiency
or pharmacological blockade of D
2
Rs. Thus,
A
2A
R-mediated neural functions are partially independent of
D
2
Rs. Moreover, endogenous adenosine acting at
striatal A
2A
Rs may be most accurately viewed as a
facilitative modulator of striatal neuronal activity rather than simply
as an inhibitory modulator of D
2
R neurotransmission.
The Theory Arsenal: The Cambridge Circus and the Origins of the Keynesian Revolution
Authors: Aslanbeigui Nahid , Oakes Guy
Published: July 2002

In the winter of 1934–35, when John Maynard Keynes was beginning to circulate proofs ofThe General Theory of Employment, Interest, and Money, he indulged in a playful exchange of letters with George Bernard Shaw devoted mainly to the merits of Karl Marx as an economist. At the end of his letter of January 1, 1935, Keynes's observations took a more serious turn, documenting fundamental changes in his theoretical ambitions following the publication of hisTreatise on Moneyin 1930: “To understandmystate of mind, however, you have to know that I believe myself to be writing a book on economic theory which will largely revolutionize—not, I suppose, at once but in the course of the next ten years—the way the world thinks about economic problems” (Keynes 1973a, p. 492).
Oral but Not Parenteral Interleukin (IL)-12 Redirects T Helper 2 (Th2)-type Responses to an Oral Vaccine Without Altering Mucosal IgA Responses
Authors: Marinaro Mariarosaria , Boyaka Prosper N. , Finkelman Fred D. , Kiyono Hiroshi , Jackson Raymond J. , Jirillo Emilio , McGhee Jerry R.
Published: July 2002

Our past studies have shown that the mucosal adjuvant cholera toxin (CT) induces T helper type 2 (Th2) responses with systemic IgG1, IgE and mucosal secretory IgA (S-IgA) antibodies (Abs). In this study, recombinant murine IL-12 (rmIL-12) was given either parenterally or orally to mice orally immunized with tetanus toxoid (TT) and CT to determine whether this cytokine could redirect the CT-induced Th2-type responses and what effect this shift would have on S-IgA Ab responses. Intraperitoneal administration of rmIL-12 shifted TT-specific responses toward Th1-type and resulted in CD4+ T cells producing IFN-γ and IL-2 with markedly reduced levels of Th2-type cytokines. This cytokine profile was accompanied by increased delayed-type hypersensitivity (DTH) and shifts in serum IgG1 to IgG2a and IgG3 anti-TT Ab responses. Further, serum IgE and S-IgA Ab responses were markedly reduced by parenteral IL-12. When IL-12 complexed to liposomes was given orally both shifts to IgG2a and IgG3 and low IgE Abs again occurred concomitant with enhanced serum IFN-γ and DTH responses. Interestingly, oral rmIL-12 did not result in significant levels of serum IL-12 nor altered S-IgA Ab responses and resulted in higher levels of some Th2-type cytokines both in vitro and in vivo when compared with parenteral IL-12. Our results show that the shifts in systemic immune responses with intact S-IgA Abs which occur after oral delivery of IL-12-liposomes are due to cytokine effects in the Peyer's patches and suggest new strategies for the targeted manipulation of Th1- and Th2-type responses to mucosal vaccines.
CD45RC Isoforms Define Two Types of CD4 Memory T Cells, One of which Depends on Persisting Antigen
Authors: Bunce Campbell , Bell Eric B.
Published: July 2002

The cellular basis of immunological memory remains a controversial area with respect to the identity of memory T cells and the role of persisting antigen. CD4 T cells are phenotypically divided by the expression of high and low molecular weight isoforms of CD45, surface markers that are frequently used to identify “naive” (CD45Rhigh) and “memory” (CD45Rlow) subsets. The latter subset responds rapidly in antigen recall assays but paradoxically has a short life span, a property that is difficult to reconcile with long-term memory. The present study examines these issues using a DTH (delayed-type hypersensitivity) model in which contact sensitivity to dinitrochlorobenzene (DNCB) was transferred to athymic nude rats by recirculating CD4 T cell subsets defined in the rat by the anti-CD45RC mAb OX22. As expected, CD45RC+ (but not RC−) CD4 T cells from normal unprimed rats transferred a DNCB-specific DTH response, whereas, 4 d after sensitization the CD45RC− (memory) subset alone contained the DNCB reactivity. However, when donor cells were collected from thymectomized rats sensitized two mo earlier, DNCB-specific responses were transferred by both CD45RC− and RC+ subsets suggesting that many of the latter had developed from cells with a memory phenotype. This was confirmed when CD45RC− CD4 T cells from 4-d primed rats were parked in intermediate nude recipients and recovered 2 mo later. DNCB-specific activity was now found wholly within the CD45RC+ “revertant” subset; the CD45RC− CD4 T cell population was devoid of activity. Importantly, we found that the total switch-back from CD45RC− to RC+ could be prevented, apparently by persisting antigen. The results indicate that there are two functionally distinct categories of memory T cells: one, a short-lived CD45Rlow type which orchestrates the rapid kinetics, the other, a longer-lived CD45Rhigh revertant which ensures that immunological memory endures.
Hidden Markov Model Analysis of Intermediate Gating Steps Associated with the Pore Gate of Shaker Potassium Channels
Authors: Zheng Jie , Vankataramanan Lalitha , Sigworth Fred J.
Published: July 2002

Cooperativity among the four subunits helps give rise to the remarkable voltage sensitivity of Shaker potassium channels, whose open probability changes tenfold for a 5-mV change in membrane potential. The cooperativity in these channels is thought to arise from a concerted structural transition as the final step in opening the channel. Recordings of single-channel ionic currents from certain other channel types, as well as our previous recordings from T442S mutant Shaker channels, however, display intermediate conductance levels in addition to the fully open and closed states. These sublevels might represent stepwise, rather than concerted, transitions in the final steps of channel activation. Here, we report a similar fine structure in the closing transitions of Shaker channels lacking the mutation. Describing the deactivation time course with hidden Markov models, we find that two subconductance levels are rapidly traversed during most closing transitions of chimeric, high conductance Shaker channels. The lifetimes of these levels are voltage-dependent, with maximal values of 52 and 22 μs at −100 mV, and the voltage dependences of transitions among these states suggest that they arise from equivalent conformational changes occurring in individual subunits. At least one subconductance level is found to be traversed in normal conductance Shaker channels. We speculate that voltage-dependent conformational changes in the subunits give rise to changes in a “pore gate” associated with the selectivity filter region of the channel, producing the subconductance states. As a control for the hidden Markov analysis, we applied the same procedures to recordings of the recovery from N-type inactivation in Shaker channels. These transitions are found to be instantaneous in comparison.
Author's editors: facilitators of science information transfer
Authors: Shashok Karen
Published: July 2002

I set out to describe the multifaceted role of author's editors in scientific‐technical‐medical (STM) information transfer. Help with manuscript preparation is only part of the picture; author's editors deal with many other formats for information transfer in addition to manuscripts that report original research. They may advise authors on publication ethics, peer review, and the publication process. They may work individually with authors, or as part of a writing and documentation team. They may act as the author's mentor and advocate when circumstances threaten authors' rights or dilute their responsibilities as communicators of science. Up to now author's editors have generally remained anonymous, but I conclude that recent developments in authorship policy may give more credit and public acknowledgement to the valuable part they play in the process of communicating scientific research. I also suggest that their close interaction with the producers, distributors, and consumers of STM information puts them in a prime position to contribute to research aimed at identifying and correcting deficiencies in current publication processes.
Soluble recombinant influenza vaccines
Authors: Fiers Walter> , Neirynck Sabine , Deroo Tom , Saelens Xavier , Jou Willy Min
Published: July 2002

Soluble, recombinant forms of influenza A virus haemagglutinin and neuraminidase have been produced in cells of lower eukaryotes, and shown in a mouse model to induce complete protective immunity against a lethal virus challenge. Soluble neuraminidase, produced in a baculovirus system, consisted of tetramers, dimers and monomers. Only the tetramers were enzymatically active. The immunogenicity decreased very considerably in the order tetra > di > mono. Therefore, we fused the head part of the neuraminidase gene to a tetramerizing leucine zipper sequence; the resulting product was enzymatically active, tetrameric neuraminidase. The protective immunity induced by this engineered neuraminidase, however, remained fairly strain–specific. A third influenza A virus protein, the M2 protein, has only 23 amino acids exposed on the outer membrane surface. This extracellular part, M2e, has been remarkably conserved in all human influenza A strains since 1933. By fusing the M2e sequence to hepatitis B virus core protein, we could obtain highly immunogenic particles that induced complete, strain–independent, long–lasting protection in mice against a lethal viral challenge. Native M2 is a tetrameric protein and this conformation of the M2e part can also be mimicked by fusing this sequence to a tetramerizing leucine zipper. The potential of the resulting protein as a vaccine candidate remains to be evaluated.
Thermal physics in the introductory physics course: Why and how to teach it from a unified atomic perspective
Authors: Reif Frederick
Published: July 2002

Heat and thermodynamics are traditionally taught in the introductory physics course from a predominantly macroscopic point of view. However, it is advantageous to adopt a more modern approach that systematically builds on students’ knowledge of the atomic structure of matter and of elementary mechanics. By focusing on the essential physics without requiring more than elementary classical mechanics, this approach can be made sufficiently simple to be readily teachable during five or six weeks of an ordinary calculus-based introductory physics course. This approach can be highly unified, using atomic considerations to infer the properties of macroscopic systems while also enabling thermodynamic analyses independent of specific atomic models. Furthermore, this integrated point of view provides a deeper physical understanding of basic concepts (such as internal energy, heat, entropy, and absolute temperature) and of important phenomena (such as equilibrium, fluctuations, and irreversibility).
Laser ultrasonic studies of solid–liquid interfaces
Authors: Queheillalt Douglas T. , Lu Yichi , Wadley Haydn N. G.
Published: July 2002

A laser ultrasonic approach has been developed and used to measure the time-of-flight (TOF) for rays penetrating model cylindrical solid–liquid interfaces. Since the longitudinal acoustic wave speed in the solid is 45% higher than the liquid, TOF measurements for ultrasonic rays that propagate through the interface are found to be sensitive to the instantaneous position and shape of the interface. A ray tracing code (incorporating both interface refracted and creeping rays) has predicted the ray paths and their time-of-flights as a function of axial position for opposingly aligned source/receiver points on the diametral plane. When used in conjunction with a nonlinear least-squares method, the ray propagation model enabled reconstruction of the interface position, its convexity, and the velocities of both the liquid and solid phases from a few parallel beam TOF measurements collected on the diametral plane.
Anomalous attenuation effect on reflectivity of an ultrasonic wave from a thin layer between dissimilar materials
Authors: Lavrentyev A. I. , Rokhlin S. I.
Published: July 2002

Distinctive features of ultrasonic spectroscopy of adhesive joints of dissimilar materials (including anisotropic) are addressed both in theory and experiment. It is found that for dissimilar joining materials the depth of the reflection spectrum minimum depends nonmonotonically on attenuation in the layer and differs for measurements from opposite sides of the joint. It depends on both the attenuation in the adhesive and on adhesive/substrate impedance mismatches, resulting sometimes in zero reflectivity at nonzero attenuation in the adhesive. The effect is observed at normal and oblique incidence. A technique for measurement of the layer attenuation from amplitude and phase spectra is proposed. Experimental results show good agreement with theoretical predictions.
Solid–liquid interface reconstructions from ultrasonic time-of-flight projection data
Authors: Queheillalt Douglas T. , Wadley Haydn N. G.
Published: July 2002

The large difference in the ultrasonic velocity of solid and liquid semiconducting materials results in significant ray refraction and pulse time delays during propagation through solid–liquid interfaces. This has led to an interest in the use of ultrasonic time-of-flight (TOF) measurements for deducing the interfacial geometry. A ray-tracing analysis has been used to analyze two-dimensional wave propagation in the diametral plane of model cylindrical solid–liquid interfaces. Ray paths, wavefronts, and TOFs for rays that travel from a source to an arbitrarily positioned receiver on the diametral plane have been calculated and compared to experimentally measured TOF data obtained using a laser generated/optically detected ultrasonic system. Examinations of both the simulations and the experimental results reveals that the interfacial region can be identified from transmission TOF data. When the TOF data collected in the diametral plane were used in conjunction with a nonlinear least-squares reconstruction algorithm, the interface geometry (i.e., axial location and shape) were precisely recovered and the ultrasonic velocities of both solid and liquid phases were obtained with error of less than ∼3%.
Acoustic analysis of the effects of alcohol on the human voice
Authors: Cooney Orla M. , McGuigan Kevin G. , Murphy Peter J. P. , Conroy Ronan M.
Published: July 2002

Experiments to determine the physical effects of alcohol on the human voice are reported. Recordings of sustained phonations and prescribed texts were taken from 12 volunteers at various stages of alcohol consumption, to determine whether a significant change in voice frequencies occurs when alcohol has been consumed. No association between the fundamental frequency of a sustained phonation and level of alcohol consumption is observed (regression coefficient=0.146, t ratio=0.28, df=71, p=0.781). Similar results for the higher formant frequencies are also observed. The effect of alcohol on duration of speech is also investigated. Prescribed-text, sentence duration is found to increase at the rate of 6.4% (standard error =0.5%, p<0.0001) per ml of alcohol consumed per kilogram of body weight. There is no evidence that the sex of the speaker is related to the effect of alcohol on sentence duration. Acoustic analysis of fixed-text voice recordings is therefore not a suitable method of determining whether a person is alcoholically intoxicated. [This research was supported by the Research Committee of the Royal College of Surgeons in Ireland.]