bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies on the expression, induction and mutation of connexin genes in human gastric cancer
Authors: Shourong Shen , Fue Li , Yang Liu , Zhengzhuan Shi , Yiyou Zou , Xichun Zhang , Huihuan Tang
Published: July 2002

OBJECTIVE: To study: (i) the expression of connexin (Cx) genes; (ii) the effects of inducers on Cx expression; and (iii) the effects of mutations in Cx coding sequences in human gastric cancer.

METHODS: Northern blots, reverse transcription– polymerase chain reaction and polymerase chain reaction–single strand conformational polymorphism were the techniques used.

RESULTS: There were regular expression patterns of the Cx genes in normal human gastric epithelium, paracancerous tissues and gastric cancers. Retinoic acid (RA) and dimethyl sulfoxide induced the expression of Cx43 in gastric cancer but Cx46 expression was reduced when induced by RA and 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA). There were no mutations found in the Cx43 coding region.

CONCLUSIONS: The Cx32 gene might specifically maintain intercellular communication via gap junctions in the gastric epithelium. Cx43 is an inducible gene in gastric cancer cells. The reduced expression of Cx43 is not caused by mutation of the Cx coding region. A hypothesis explaining the variation in Cx gene expression in human gastric cancer is proposed.
Optimizing symptom control across the patient spectrum
Authors: Scadding G. K.
Published: July 2002

Allergic seasonal and perennial rhinitis are common diseases that have a considerable adverse impact on the quality of life of the sufferer. Despite the excellent available treatment, the morbidity of allergic rhinitis remains high, because patients often do not seek medical advice and also because physicians tend to underestimate the disruptive problems caused by the disease. In order to improve patient compliance with medication, the diagnosis of allergic rhinitis should be confirmed and the treatment prescribed should be effective with a simple dosage regimen.
Clinical nasal decongestant activity with oral antihistamines
Authors: Howarth P.
Published: July 2002

Allergic rhinitis is an inflammatory condition with increasing prevalence in many developed countries. Although first‐generation antihistamines have shown efficacy in the treatment of this disease, they are relatively ineffective for the treatment of nasal blockage. By contrast, studies with newer antihistamines, such as fexofenadine, cetrizine, mizolastine, desloratadine, and azelastine, have shown efficacy in reducing all symptoms of allergic rhinitis, including nasal congestion. This paper focuses on the clinical studies that have been carried out with some of the newer antihistamines and discusses the mechanisms by which they may exert their additional anti‐allergic effects.
Numerical study of the influence of the shell structure of the crystalline lens on the refractive properties of the human eye
Authors: Masajada A. Popiolek
Published: July 2002

In this paper, the numerical model of the refractive properties of the human eye is given. A special account is given of the laminated structure of the crystalline lens. The crystalline lens is presented in the form of hundreds of shells with rotational symmetry, and with the refractive index constant within each shell. The shells have the form of two semi‐ellipsoids joined along the equator. The refractive index increases from the cortical shell to the inner one, according to the exponential dependency. The cornea, approximated by two ellipsoidal surfaces, is added in front of the crystalline lens. A ray‐tracing procedure is applied to study the refractive properties of such a system: refractive power, spherical aberration and energy distribution. The optical properties of the given model are analysed by changing some parameters such as refractive index profile and number of shells. Calculations show that the gradient of the refractive index inside the crystalline lens results in the generation of many focal planes in such an optical system.
Timber Certification: Where Is the Voice of the Biologist?
Authors: Bennett Elizabeth L.
Published: July 2002

Editor's note: This Conservation Forum begins with a reprinted editorial by Elizabeth Bennett from the August 2000 issue of Conservation Biology. Several papers were submitted in repsonse to that piece, and it is reprinted here to start this forum.
Developing a Geriatric Business Plan for an Academic Medical Center
Authors: Goodwin James S.
Published: July 2002

Leaders of geriatric programs at academic health centers (AHCs) face several challenges in seeking support for clinical program development. These challenges relate to how revenues from Medicare activities flow within AHCs. Typically, clinical departments such as the Department of Medicine see a very small proportion of total AHC Medicare revenue and frequently experience losses on their Medicare activities. In contrast, hospitals in AHCs see the bulk of the revenues and typically experience substantial profits. This article examines this situation in some detail, with specific examples from AHCs with which the author has consulted.
Detecting Nucleotide Additivity from Direct Sequences is a SNAP: An Example from Sidalcea (Malvaceae)
Authors: Whittall J. , Liston A. , Gisler S. , Meinke R. J.
Published: July 2002

Abstract: Superimposed nucleotide additivity patterns (SNAPs) were detected from direct sequences of the nuclear ribosomal DNA internal transcribed spacers in a complex of perennial Sidalcea species (Malvaceae) from the Pacific Northwest of the United States. Although only 2.8 % sequence variation exists among the eight ITS accessions, parsimony analysis identified two distinct lineages within this complex consistent with known ploidy levels. Six SNAPs were identified in a known tetraploid S. virgata, suggesting allopolyploid origins from diploid S. virgata and one of two hexaploid Sidalcea species. A dosage effect detected at all six SNAP sites is consistent with the unequal sized parental genomes of allopolyploid S. virgata.
Deep states in silicon-on-insulator substrates prepared by oxygen implantation using current deep level transient spectroscopy
Authors: McLarty P. K. , Ioannou D. E. , Hughes H. L.
Published: July 2002

Current deep level transient spectroscopy was applied using enhancement n-channel metal-oxide-semiconductor field-effect transistors fabricated in silicon-on-insulator substrates (prepared by oxygen implantation) to study the deep levels existing in the substrates. The current transients are not affected by the large series resistances which affect the measurement of capacitance transients on thin films. For the transistors used in this work a hole trap was found with energy ET=0.63 eV above the valence-band edge. The concentration and capture cross section of this state were estimated to be 1014 cm−3 and 10−16 cm2, respectively.
Carrier-activated light modulation
Authors: Johnson N. F. , Ehrenreich H. , Jones R. V.
Published: July 2002

A variety of superlattices is predicted to exhibit high-speed carrier-activated light modulation. The proposal is based on the large, tunable, and very narrow absorption peak for transitions between the two lowest conduction subbands. The theory, which is demonstrated to be predictive, also suggests correspondingly large variations of the refractive index.
Beam breakup instabilities in linear accelerators: Transition, phase mixing, and nonlinear focusing
Authors: Colombant D. G. , Lau Y. Y.
Published: July 2002

The temporal and spatial evolution of the cumulative beam breakup instability (BBU) is analyzed numerically using a continuum model. It is found that neither phase mixing nor linear transverse focusing is sufficient to render BBU stable in a long pulse machine, when external damping is absent. A sufficiently strong nonlinear octupole focusing field may limit the BBU growth, however.
AlGaAs/GaAs heterojunction bipolar transistors with heavily C-doped base layers grown by flow-rate modulation epitaxy
Authors: Makimoto Toshiki , Kobayashi Naoki , Ito Hiroshi , Ishibashi Tadao
Published: July 2002

AlGaAs/GaAs heterojunction bipolar transistors are fabricated using carbon-doped p-type GaAs base regions grown for the first time by flow-rate modulation epitaxy. Because of the much smaller diffusion coefficient of carbon atoms in GaAs than that of beryllium and other p-type impurities, sharp impurity profiles are achieved. The heterojunction bipolar transistors exhibited high current gains up to 40 for a base layer width of 150 nm and base doping of 2.4×1019 cm−3 . The electron lifetime in heavily carbon-doped GaAs layers is considerably long, indicating favorable quality of heavily carbon-doped layers.
Room-temperature continuous-wave vertical-cavity surface-emitting GaAs injection lasers
Authors: Tai K. , Fischer R. J. , Seabury C. W. , Olsson N. A. , Huo T-C. D. , Ota Y. , Cho A. Y.
Published: July 2002

Room-temperature continuous-wave oscillation with an emission power in excess of 1 mW was achieved in vertical-cavity surface-emitting lasers containing a 0.5-μm-thick GaAs active layer sandwiched between a distributed Bragg reflector (DBR) and a hybrid metal DBR. The devices have a cw threshold current of 40 mA in 15-μm-diam size and a T0 of 115 K. Fiber butt coupling and pseudorandom data modulation of these lasers with open eyes up to 500 Mbit/s were demonstrated.
Reduced-confinement antennas for GaAlAs integrated optical waveguides
Authors: Bossi D. E. , Goodhue W. D. , Finn M. C. , Rauschenbach K. , Bales J. W. , Rediker R. H.
Published: July 2002

Monolithically integrated reduced-confinement antennas are shown to produce reductions of >35% in the far-field beam divergence for radiation emitted from single-mode GaAlAs slab waveguides, yielding far-field beams as narrow as 8.2° FWHM along the direction perpendicular to the wafer surface. Reduced confinement of the guided mode near the output endface is achieved using a novel molecular beam epitaxy growth technique to produce a longitudinal variation in the refractive index and thickness of the waveguide film. Unlike present horn antennas, the reduced-confinement geometry has the distinct advantage of being compatible with two-dimensional antenna development.
Large Stark shifts of the local to global state intersubband transitions in step quantum wells
Authors: Mii Y. J. , Karunasiri R. P. G. , Wang K. L. , Chen M. , Yuh P. F.
Published: July 2002

Large Stark shifts of intersubband transitions in a step quantum well are observed for the first time. The Stark shifts are ∼8 and 7 meV at ∼18 kV/cm for the 1→2 and 1→3 intersubband transitions, respectively, while the Stark shift of a similar transition in a square quantum well is only about 0.5 meV under the same bias condition. The intersubband transitions in step quantum wells can be either red or blue Stark shifted depending on the direction of the applied electric field. The large Stark shifts of intersubband transitions in the step quantum wells can be exploited for the fabrication of optical modulators operating in the range from mid to far infrared.
Dielectric breakdown in thin Si oxynitride films produced by rapid thermal processing
Authors: Novkovski N. , Dutoit M. , Solo de Zaldivar J.
Published: July 2002

Thin films of silicon oxide and oxynitride were prepared by rapid thermal processing. Under optimum conditions (e.g., nitridation at 1100 °C for 4 s followed by reoxidation at 1150 °C for 60 s), their electrical properties (charge trapping, low-field leakage, and charge to breakdown) were significantly improved over those of the starting oxide. Values of Qbd as high as 260 C/cm2 for a positive current density of 200 mA/cm2 were obtained. Yet, the improvement was much smaller for negative than positive stress. This difference is ascribed to the asymmetrical role of nitridation on the prevention of interface trap generation at high fields and is consistent with models of the generation of interface traps described in the literature.
Interband resonant tunneling diode in δ-doped GaAs
Authors: Wang Y. H.
Published: July 2002

Novel negative differential resistance (NDR) diodes, suggesting interband resonant tunneling diodes, in δ-doped GaAs prepared by molecular beam epitaxy are demonstrated. Two Si and one Be δ-doped planes were inserted in the GaAs layer, i.e., n+-δn+-i-δp+-i-δn+-n+, to form the required band structure. Electrons are then transported from the conduction band of the n+ layer and resonantly tunnel through the valence band of the δp+ induced quantum well. Symmetric NDR characteristics with a peak-to-valley current ratio of 1.7 and a peak current density of 5 kA/cm2 under forward and reverse biases operating at room temperature are observed.
Surface-stabilized ferroelectric liquid-crystal electro-optic waveguide switch
Authors: Clark Noel A. , Handschy Mark A.
Published: July 2002

We demonstrate control of the optical coupling between a pair of planar waveguides by application of voltage to surface-stabilized ferroelectric liquid-crystal films between them. A prototype switch exhibited a response time of 200 μs and a 40:1 switching ratio.
YBa2Cu3O7−δ superconducting films with low microwave surface resistance over large areas
Authors: Newman N. , Char K. , Garrison S. M. , Barton R. W. , Taber R. C. , Eom C. B. , Geballe T. H. , Wilkens B.
Published: July 2002

We demonstrate that in situ off-axis sputtering from a composite target can reproducibly fabricate very high quality YBa2Cu3O7−δ films over large areas of deposition. A significant reduction in the microwave surface resistance, Rs, compared to many previously reported values is found. Rs values at 10 GHz were found to be as low as 20 μΩ at 4.2 K and 450 μΩ at 77 K. A systematic variation of several properties including the transition temperature, critical current density at high magnetic fields, and the c-axis lattice parameter across the 3.8 cm×3.8 cm (14.5 cm2) deposition area was found.
Novel cavity design for high reflectivity changes in a normally off electroabsorption modulator
Authors: Pezeshki B. , Thomas D. , Harris J. S.
Published: July 2002

We demonstrate both theoretically and experimentally a novel Fabry–Perot electroabsorption modulator. Both a normally off reflectivity characteristic and negative differential conductivity were obtained by increasing the optical absorption coefficient with voltage. Using the large absorption change of the quantum confined Stark effect, we obtain excellent modulation characteristics with a change in absolute reflectivity of 47% and a contrast ratio greater than 15.
Electro-optic AlGaAs spatial light deflector/modulator based on a grating phased array
Authors: Vasey F. , Reinhart F. K. , Houdré R. , Stauffer J. M.
Published: July 2002

A novel beam steering device using gratings integrated on rib waveguides as input and output couplers is proposed. Phasing is achieved electro-optically by applying an electric field on an indium-tin-oxide/AlGaAs Schottky junction. A two elements device is first used to characterize the phase modulation characteristics of the structure. A 43 elements device with sawtooth electrodes is then presented, that permits spatial three-point digital beam steering or amplitude modulation. The outcoupled beams have an angular width of 1.8 mrad full width at half maximum. The switched beam angular separation is 9 mrad, the switching voltage is −21 V.
Low-temperature growth of GexSi1−x/Si heterostructures on Si(100) by remote plasma-enhanced chemical vapor deposition
Authors: Kinosky D. , Qian R. , Irby J. , Hsu T. , Anthony B. , Banerjee S. , Tasch A. , Magee C. , Grove C. L.
Published: July 2002

Low-temperature growth processes are needed in order to fully exploit the potential of GexSi1−x/Si heterostructures. Remote plasma-enhanced chemical vapor deposition has been successful for silicon homoepitaxy at substrate temperatures as low as 150 °C. We report the growth of GexSi1−x/Si heterostructures with values of x between 0.07 and 0.73, and at substrate temperatures of 305 and 450 °C. The films grown at 450 °C have excellent crystallinity, low defect densities, and very abrupt interfaces, while films grown at 305 °C have degraded crystallinity.
In situ study of the growth of hydrogenated amorphous silicon by infrared ellipsometry
Authors: Blayo N. , Drévillon B.
Published: July 2002

The early stage of the growth of plasma deposited amorphous silicon (a-Si:H) on glass substrates is investigated by in situ infrared phase modulated ellipsometry in the silicon–hydrogen stretching mode region. Analysis of the spectra provides unprecedented sensitivity and quantitative information on the film evolution. In particular SiH, SiH2, and SiH3 bonds are identified in 5–20 Å thick samples. The bond densities of SiH and SiH2 in thin films are estimated. After the interaction with the substrate, a-Si:H films grow beneath a hydrogen rich overlayer containing SiH2 and SiH3 bonds. At 250 °C the thickness of this overlayer is compatible with one monolayer. The hydrogen-passivated surface of a-Si:H is then weakly reactive.
Novel annealing scheme for fabricating high-quality Ti-silicided shallow n+p junction by P+ implantation into thin Ti films on Si substrate
Authors: Juang M. H. , Cheng H. C.
Published: July 2002

A TiSi2 silicided shallow n+p junction with a leakage current density of about 3 nA/cm2, a forward ideality factor of 1.00, and a junction depth of about 0.11 μm has been fabricated by implanting P+ ions into thin amorphous-Si/Ti bilayer films on silicon substrate and subsequently processed by a rapid thermal annealing (RTA) at 800 °C/60 s with a post-conventional furnace annealing (CFA) at 600 °C/30 m. RTA not only minimizes the diffusion of knock-on Ti into the junction region, but also facilitates the silicidation and damage annihilation. The low-temperature CFA treatment following the high-temperature RTA process greatly increases the diffusion of dopants into the junction region and thus improves the junction characteristics significantly. The increased diffusion of dopants from the silicide layer into the junction region by the post-CFA process is attributed to the crystallization of the titanium silicide.
Transient behavior of organic thin film electroluminescence
Authors: Hosokawa Chishio , Tokailin Hiroshi , Higashi Hisahiro , Kusumoto Tadashi
Published: July 2002

Transient behavior for an organic thin film electroluminescence (EL) cell with ITO/triphenylamine derivative/tris (8-hydroxyquinolino) aluminum (Alq)/Mg:Ag structure was observed by short voltage pulse measurements. The EL response was of the order of 10−7 s, and faster than that previously measured by Tang et al. [J. Appl. Phys. 65, 3610 (1989)]. In these measurements, we could observe carrier transit time. Then we concluded this carrier transit time should be attributed to that of electrons in Alq layer and the electron mobility of (5±2)×10−5 cm2/V s was obtained above the electric field of 1 MV/cm.
Electro-optic modulation by electron transfer in multiple InGaAsP/InP barrier, reservoir, and quantum well structures
Authors: Agrawal N. , Hoffmann D. , Franke D. , Li K. C. , Clemens U. , Witt A. , Wegener M.
Published: July 2002

Recently, a novel optical modulator heterostructure has been introduced based on voltage controlled electron transfer from a reservoir to a closely spaced quantum well. It has proven to exhibit large absorptive and refractive modulation at high speed and low power dissipation. In order to achieve monolithic integration with the existing high quality InGaAsP/InP lasers for high bit-rate systems, it is crucial to implement such devices within the same material system. In this letter, we demonstrate for the first time, InGaAsP/InP electron-transfer modulators grown using metalorganic vapor phase epitaxy.
Identification of an interface defect generated by hot electrons in SiO2
Authors: Stathis J. H. , DiMaria D. J.
Published: July 2002

Hot electrons in the gate dielectric (SiO2) of field effect transistors create defects at the Si/SiO2 interface. Using electrically detected magnetic resonance, we have identified a major component of these interface defects as the well-known Pb0 center. We show that the generation rate of the Pb0 centers increases when the oxide field is sufficient to cause electron heating, thus establishing the correlation with hot-electron generated interface states. Hot-electron induced defect generation is shown to be fundamentally different from another interface degradation mechanism, electron-hole recombination near the interface, which produces interface defects but does not produce Pb0 centers.
Nondestructive detection of titanium disilicide phase transformation by picosecond ultrasonics
Authors: Lin H.-N. , Stoner R. J. , Maris H. J. , Harper J. M. E. , Cabral C. , Halbout J.-M. , Rubloff G. W.
Published: July 2002

We demonstrate that picosecond ultrasonics is a sensitive nondestructive probe of the formation of TiSi2 from the reaction of titanium films on silicon annealed at temperatures of 300–800 °C. From the measured change in optical reflectivity, the responses due to electronic excitation, acoustic echoes, and thermal coupling to the underlying Si are resolved. The results show significant differences in the electronic response and the ultrasonic echo pattern before and after the structural phases C49 and C54 TiSi2 are formed. The longitudinal sound velocity is measured to be (8.3±0.2)×105 cm/s for C49 TiSi2, and about 5% lower for the C54 phase.
Passive mode locking in erbium fiber lasers with negative group delay
Authors: Fermann M. E. , Andrejco M. J. , Stock M. L. , Silberberg Y. , Weiner A. M.
Published: July 2002

100 fs pulses are generated in passively mode-locked erbium fiber lasers with small negative group-velocity dispersion. The pulses are obtained at a pump power significantly higher than the mode-locking threshold. An optimization of fiber lengths leads to the elimination of pedestal formation and the generation of stable pulse trains with high contrast ratios.
GaN grown on hydrogen plasma cleaned 6H-SiC substrates
Authors: Lin M. E. , Strite S. , Agarwal A. , Salvador A. , Zhou G. L. , Teraguchi N. , Rockett A. , Morkoç H.
Published: July 2002

We report epitaxial GaN layers grown on 6H-SiC (0001) substrates. A two stage substrate preparation procedure is described which effectively removes oxygen from the SiC substrate surface without the need of elaborate high temperature processing. In the first step, dangling Si bonds on the substrate surface are hydrogen passivated using a HF dip before introduction into vacuum. Second, the substrate is treated with a hydrogen plasma reducing the amount of oxygen-carbon bonding to below the x-ray photoemission detection limit. Upon heating in the molecular beam epitaxy (MBE) growth chamber, the SiC substrates are observed to have a sharp (1×1) reconstruction with Kikuchi lines readily visible. GaN epilayers deposited on AlN buffer layers by plasma enhanced MBE show sharp x-ray diffraction and photoluminescence peaks.
Low resistance wavelength-reproducible p-type (Al,Ga)As distributed Bragg reflectors grown by molecular beam epitaxy
Authors: Chalmers S. A. , Lear K. L. , Killeen K. P.
Published: July 2002

We report the reproducible molecular beam epitaxial growth of Be-doped piecewise linearly graded (Al,Ga)As distributed Bragg reflectors that have vertical series resistivities near bulk values. For mirrors with three linear segments per interface, the center wavelength reproducibility is 0.1% and the series resistivity is as low as 1.8×10−5 Ω cm2 for hole concentrations of 5×1018 cm−3. Measured reflectivities of 6.0% per interface are comparable to conventional single-linear-grade mirrors. Vertical-cavity surface-emitting lasers incorporating these mirrors exhibit record-low voltage thresholds of less than 1.5 V.
Structure of pentacene/tetracene superlattices deposited on glass substrate
Authors: Akimichi H. , Inoshita T. , Hotta S. , Noge H. , Sakaki H.
Published: July 2002

Pentacene/tetracene organic superlattices were formed by deposition on a glass substrate, and their structure was investigated by x-ray diffraction and photoluminescence. For samples in which the number (n) of constituent pentacene (or tetracene) molecular layers within a period is such that n≥3, the first-order x-ray diffraction peak was found to consist of several equally spaced subpeaks. Comparison of the spectra with calculated structure factors established that a well-defined superlattice structure was achieved in these samples. In contrast, samples with n<3 showed no evidence of superlattice formation. Photoluminescence spectra show clear correlation with the x-ray results.
Relationship between growth conditions, nitrogen profile, and charge to breakdown of gate oxynitrides grown from pure N2O
Authors: Okada Yoshio , Tobin Philip J. , Lakhotia Vikas , Feil William A. , Ajuria Sergio A. , Hegde Rama I.
Published: July 2002

We studied the relationship between the growth conditions, the nitrogen profile, and the charge to breakdown of N2O oxynitrides grown in a RTP and in a conventional furnace. RTP oxynitride shows nitrogen accumulation at the Si/SiO2 interface. On the other hand, furnace oxynitride shows almost uniform nitrogen distribution in the bulk, resulting in poor charge to breakdown characteristics. We find that two-step oxynitridation processes provide nitrogen accumulation at the Si/SiO2 interface and result in better electrical properties than those of one-step oxynitrides.
Epitaxial growth of p-type ZnMgSSe
Authors: Okuyama Hiroyuki , Kishita Yuko , Miyajima Takao , Ishibashi Akira , Akimoto Katsuhiro
Published: July 2002

N-doped p-type ZnMgSSe was grown by molecular beam epitaxy. Nitrogen was induced by electron cyclotron resonance plasma. The maximum net acceptor concentration (NA−ND) and the activation energy of the nitrogen acceptor (EN) depend on the band-gap energy of ZnMgSSe. With increasing band-gap energy, the maximum NA-ND is decreased and EN is increased. The maximum NA-ND and the EN of ZnMgSSe with a band-gap energy of 3.05 eV at 77 K are 2.5×1016 cm−3 and 140 meV, respectively.
Relation between hole density and impurity density in ZnMgSSe semiconductors
Authors: Kondo K. , Okuyama H. , Ishibashi A.
Published: July 2002

Using amphoteric native defect model [Walukiewicz, Phys. Rev. B 37, 4760 (1988)], we have considered the energy-gap Eg dependence of nitrogen doping in ZnMgSSe semiconductors. We have explained the energy-gap Eg dependence of saturated hole concentration in ZnMgSSe semiconductors based on the amphoteric native defect model and available effective hole masses in ZnSe using the valence band discontinuity ΔEv as a fitting parameter. The Fermi-level stabilization energy EFS and the pinned Fermi-level energy ESI are, to a good approximation, universal for II-VI materials as well as for III-V materials. We have estimated the ESI is located at 1.895 eV below EFS. It is indicated that the band-gap discontinuity between ZnSe and ZnMgSSe is ΔEc: ΔEv=0.55:0.45 if effective hole mass is 1.4 m0 for ZnMgSSe and ΔEc:ΔEv=0.67:0.33 if effective hole mass is 0.6 m0.
Optical properties near the band gap on hexagonal and cubic GaN
Authors: Okumura H. , Yoshida S. , Okahisa T.
Published: July 2002

We have measured the photoluminescence and optical reflection spectra of cubic and hexagonal GaN films epitaxially grown on GaAs and 3C-SiC substrates by gas-source molecular beam epitaxy using microwave-activated NH3 source. The crystalline quality of the epilayers was improved by using an activated NH3 beam and 3C-SiC substrates, which enabled us to obtain intense optical signals. The measured spectra suggest that the band gap of cubic GaN is around 190 meV smaller than that of hexagonal GaN.
Double-heterostructure diode lasers emitting at 3 μm with a metastable GaInAsSb active layer and AlGaAsSb cladding layers
Authors: Choi H. K. , Eglash S. J. , Turner G. W.
Published: July 2002

Double-heterostructure diode lasers emitting at 3 μm have exhibited pulsed operation at temperatures up to 255 K and cw operation up to 170 K, with cw output power of 45 mW/facet at 100 K. The laser structure, grown on GaSb substrates by molecular beam epitaxy, has a metastable GaInAsSb active layer and AlGaAsSb cladding layers. The lowest pulsed threshold current density is 9 A/cm2 obtained at 40 K. The characteristic temperature is 35 K at low temperatures and 28 K above 120 K.
Change in crystalline morphologies of polycrystalline silicon films prepared by radio-frequency plasma-enhanced chemical vapor deposition using SiF4+H2 gas mixture at 350 °C
Authors: Kaneko Toshiki , Wakagi Masatoshi , Onisawa Ken-ichi , Minemura Tetsuroh
Published: July 2002

Polycrystalline silicon films have been deposited on glass substrates at 350 °C by radio-frequency plasma-enhanced chemical vapor deposition using a SiF4+H2 gas mixture. Crystalline fraction decreased abruptly with increasing gas flow ratio. Film structure drastically changed by increasing gas pressure from 0.4 to 2.0 Torr. At lower gas pressure, columnar crystals 30 nm in diameter grew from the glass substrates, while at higher gas pressure larger columnar crystals with a maximum diameter of approximately 100 nm grew on an amorphous Si layer approximately 170 nm thick.
Calibration of grazing incidence spectrometers using charge transfer excitation (abstract)
Authors: Isler R. C. , Langley R. A.
Published: July 2002

The sequence of radiative cascades following charge transfer between energetic neutral atoms and C6+, N7+, and O8+ are readily observed in high-temperature plasma devices where the field of view of a vacuum spectrometer includes a neutral heating beam. These charge exchange excited (CXE) lines have well defined relative intensities that are not strongly dependent on the theory used to compute the primary excitation.1 They have been exploited in the ISX-B tokamak as an in situ method of measuring the relative response of a grazing incidence spectrometer from 102 to 1164 Å. Mixing of energy levels by external fields or by collisions are shown to have little effect on treating l as a good quantum number when computing the ratios of effective emission cross sections.
Highly sensitive Faraday balance for magnetic susceptibility studies of dilute protein solutions
Authors: Petersson L. , Ehrenberg A.
Published: July 2002

A highly sensitive Faraday balance has been constructed. It has been designed for accurate measurement of paramagnetic susceptibility of dilute protein solutions. Particular attention has been paid to sample handling. Measurements can at present be made within the temperature range 10–200 K. The reproducibility in measured volume susceptibility, for a 0.1-ml sample volume, is 2×10−10 emu/cm3 above 45 K and 4×10−10 emu/cm3 in the temperature range 10–45 K. The instrument has so far been applied to studies of antiferromagnetic interaction in some Fe- or Cu-containing proteins and of electronic zero-field separations in a high-spin Fe(II)-containing protein.
Rotor electrometer: New instrument for bulk matter quark search experiments
Authors: Price John C. , Innes Walter , Klein Spencer , Perl Martin
Published: July 2002

The rotor electrometer is a new instrument which we hope will make possible searches for rare fractionally charged impurities in very large quantities of matter. The ultimate goal of the project is to be able to measure the net charge of 10 mg samples of any material to an accuracy of 0.05 qe in a few minutes (qe is the electron’s charge). This paper reports the achievement of subelectron (0.3 qe) charge resolution with the new device. We discuss effects which limit the resolution and consider prospects for improving the performance to the point where a fractional charge search may be attempted.
Review of Japanese compact electron storage rings and their applications (invited)
Authors: Tomimasu T.
Published: July 2002

Key technologies needed to realize compact synchrotron radiation (SR) facilities used for industrial and medical uses are discussed, and the recent status of nine Japanese small rings used in SR lithography is reported. The majority of their applications is focused on SR lithography: that is, wide and uniform exposure of SR by the electron undulating method using short beamlines.
Image-intensified photodiode array as a fluorescence detector in cw-laser experiments
Authors: Hiller Bernhard , Paul Phillip H. , Hanson Ronald K.
Published: July 2002

Imaging systems based on image-intensified photodiode-array cameras are excellent detectors for laser-induced fluorescence experiments in fluid mechanics and combustion science. The principles of operation of such a system are described. Special attention is given to the use of an image intensifier in conjunction with cw-laser experiments. In that mode, ghost images caused by the finite phosphor decay time can contribute major systematic errors. Measurements of the phosphor decay times for exposure times between 0.1 and 100 ms (a typical range for cw-laser experiments) were conducted and show that the decay time increases with exposure time. Methods for circumventing the ghosting problem are suggested. The signal and noise analysis points to analog-to-digital converter noise (ADC) or quantization error of the camera and to photon shot noise as the dominating noise sources. The image intensifier improves time resolution and signal-to-noise ratio (SNR) by moving the system from the camera noise limit to the shot-noise limit. Once the shot-noise limit is reached, the SNR can only be improved by increasing the quantum efficiency of the intensifier, not by increasing the intensifier gain. The spatial resolution of such a system is generally limited by the photodiode array, but can be dominated by focusing errors, if lenses with low f numbers are used. Within a certain range of imaging magnifications, the use of a fiber-optic minifier between intensifier and array in lieu of a 1:1 fiber bundle can improve the collection efficiency, and thereby both signal and camera-limited SNR. Use of a minifier will always improve the shot-noise-limited SNR.
Focusing x-ray spectrograph for laser fusion studies
Authors: Yaakobi B. , Boehly T. , Audebert P.
Published: July 2002

A modified Rowland-circle x-ray spectrograph for laser fusion experiments is described and analyzed. It can be used either as a high-spectral-resolution device or as a monochromatic imaging device (including a backlighting option). The relative merits in each configuration are discussed in detail, and an actual design is worked out numerically.
A split high-Q superconducting cavity
Authors: Hughey Barbara J. , Gentile Thomas R. , Kleppner Daniel , Ducas Theodore W.
Published: July 2002

We describe the construction of a 35-GHz split high-Q superconducting cavity operating in the TM010 mode. The cavity is tuned by varying the spacing between the halves. Radiation loss from this gap is suppressed by a choke groove. Q=4×107 has been achieved in both lead-plated copper and niobium cavities at a temperature of 2 K. Q>107 can be maintained over a 300-MHz tuning range, corresponding to a gap between the halves of 85 μm.
A variable inductor circuit design for inductive energy storage systems
Authors: Andrianov V. V. , Baev V. P. , Kazantsev N. A. , Ostashev V. E. , Parizh M. B. , Sheinkman V. S.
Published: July 2002

A circuit design for matching an inductive energy storage to a utility grid and a complex load (railgun accelerator) is discussed. A circuit design is suggested for control of the discharge current to provide effective transfer of the energy stored in the inductive storage. It is shown that this circuit design, with a variable winding inductance, provides energy transmission control and allows both a higher efficiency of energy transfer and arrangement of a quick response reserve power source to maintain high-current energy transmission. The arrangement discussed may be used to provide matching of the energy user’s load current to the energy storage’s initial current which is determined either by the possibility of energy accumulation in the system or by the power supply source’s current.
An rf excited circular waveguide CO2 laser
Authors: Walsh C. J.
Published: July 2002

Designs for sealed-off, air-cooled rf excited waveguide lasers with a circular bore are discussed. The devices are straightforward to manufacture and show good performance with respect to lifetime, efficiency, and mode purity. The design can be easily adopted to accommodate PZT and grating tuning.
Dual laser acousto-optical diffraction technique for the calibration of a CO2 laser scattering apparatus
Authors: Chang Li-Yan , Zeng Lei , Cao Jin-Xiang , Yu Chang-Xuan , Zu Qing-Xin
Published: July 2002

In this paper a dual laser acousto-optical diffraction technique is described that provides an absolute calibration of a CO2 laser coherent scattering apparatus and other heterodyne receivers. Rather than directly detecting the sound pressure of the acoustic field or the power diffracted from the CO2 laser beam, the sound pressure is measured with the heterodyne detection of acousto-optical diffraction from a He-Ne laser beam. Noise equivalent power (NEP) measurement of the heterodyne receiver for the CO2 laser scattering apparatus and the studies of the detector bias and local oscillator power dependence of NEP values are performed by this technique. The measured minimum NEP value (6.8×10−20 W/Hz) is very close to the quantum noise limit.
Inexpensive, automatic range-switching electrometer
Authors: Vanderschmidt G. F.
Published: July 2002

A simple circuit is described which implements automatic range switching for an electrometer. The circuit may be expanded to any number of ranges and provides dead-time delay following a range switch. The operator may override automatic operation and use the circuit in conventional manual mode.
Fast-switching, high-temperature propellant source for multistage pneumatic acceleration of hydrogen fuel pellets
Authors: Andersen S. A. , Baekmark L.
Published: July 2002

A fast, arc-driven hydrogen gas source and its application as a module in a scheme for multiple downstream propellant supply to a light-gas gun is described. The potential of this scheme for high-speed acceleration of hydrogen fuel-pellets for fusion plasma fueling is considered. In experiments with a single module in which 200 J of electrical energy were dissipated with a power level approaching 5 MW within 30 μs, the velocity of a 23-mg plastic dummy pellet was increased from 1.7 to 2.4 km/s. Barrel pressure transients and arc characteristics are described.
Scattering device for the determination of turbulent fluctuations of aerosol
Authors: de Leeuw G. , Boden J. A. , Cohen L. H. , Deutekom M. , de Krijger A. J. T. , Kunz G. J. , Moerman M. M. , Lamberts C. W.
Published: July 2002

A small optical device has been constructed to determine aerosol total area concentrations from angular scattering. Particles in the open sample volume are irradiated by a pulsed laser diode. Radiation scattered at angles between 15° and 35° is detected by a photodiode. The amplified signals are processed with a sample/hold circuit. This instrument has been applied for measurements on sea spray aerosol near the air-sea interface. Wave-induced fluctuations were clearly demonstrated. Other applications are indicated.
A fibre optic interferometric system for surface profiling
Authors: Farahi F. , Jackson D. A.
Published: July 2002

An optical interferometric sensor for the measurement of surface roughness is described, which incorporates optical fiber links to achieve a passive remote sensing head. Signal recovery is achieved via a pseudo heterodyne technique. It is demonstrated that the system is capable of both differential and absolute measurements, a resolution of ∼0.1 nm/√Hz was achieved.
A UHV-compatible thin-film stress-measuring apparatus based on the cantilever beam principle
Authors: Koch R. , Leonhard H. , Thurner G. , Abermann R.
Published: July 2002

A stress-measuring apparatus based on the cantilever beam principle is described that can be used to determine the internal stress of thin films continuously during and after their deposition. The displacement of the free end of the cantilever beam−which is proportional to the film stress−is determined with high sensitivity and long time stability using a differential capacitance method in combination with phase-sensitive detection. The entire apparatus is fully compatible with UHV requirements and includes provisions for heating and cooling the substrate. The reproducible performance of the stress-measuring apparatus is demonstrated with silver films deposited onto MgF2-coated substrates.
Polystyrene latex particles as a size calibration for the atomic force microscope
Authors: Li Y. , Lindsay S. M.
Published: July 2002

A simple method for spreading polystyrene-latex spheres onto mica substrates to form highly crystalline layers is described. These layers can be used as a simple calibration standard for the atomic force microscope in the nanometer to micron size range. In particular, they provide simultaneous x, y, and z calibration. The concentration of particles of about 0.01% is found to be good for forming ordered structures. Two-dimensional polycrystalline structures of polytstyrene spheres with different packing orders (cubic and hexagonal close-pack) and some defects (vacancies, dislocations, and grain boundaries) were observed.
Vacuum chamber for sample attachment in atomic force microscopy
Authors: Putman Constant A. J. , van der Werf Kees O. , van Oort Geeske , de Grooth Bart G. , van Hulst Niek F. , Greve Jan
Published: July 2002

A small ring-shaped vacuum chamber has been constructed and connected to the piezotube used for scanning samples in the atomic force microscope (AFM). Samples made up of any material, up to 50 mm in diameter, can be firmly attached onto the piezotube without causing damage to the sample. A 50-ℓ beer container forms a buffer between vacuum pump and chamber. With this supply of vacuum, the AFM can be operated for a 4–8 h period without turning on the vacuum pump again. Samples can be changed within 30 s. The scan frequency when using microscope slides is limited to 40 Hz due to resonance effects of the microscope slides.
Isotherms of natural sea surface films: A novel device for sampling and properties studies
Authors: Pogorzelski Stanislaw J.
Published: July 2002

A double-walled submersible sea surface film sampler which ‘‘cuts out’’ an undisturbed film-covered area has been built for force-area isotherm studies of untreated water samples. Preliminary results on static and dynamic surface properties of naturally formed films present in coastal zones of the Baltic Sea are presented and discussed in reference to water samples collected in a bottle (depth of 20 cm) at the same site and time, which in turn significantly differ from each other. The new sampler also allows a few statements of oceanographic relevance on the film homogeneity (i.e., film filling factor) and the energy transfer through surface films from isotherm hysteresis measurements.
A flexible implementation of scanning tunneling spectroscopy utilizing C-language on the personal computer
Authors: Rong Z. Y. , Chang A. , Wolf E. L.
Published: July 2002

Scanning tunneling spectroscopy (STS) capable of measuring the local density of states dI/dV=G(V,x,y) correlated with the topography z(x,y) is implemented on a PC/AT computer system. An algorithm using dimensional decoupling and recursive linking is incorporated in a compact C-language code to achieve flexible and sophisticated STS control. Data acquisition and processing methods which provide the local density of states G(V,x,y,s) at different tip heights s in registry with z(x,y) are described. Examples of novel low-temperature experiments are given to show the capabilities of this implementation of STS.
Design of a compact uniaxial stress apparatus for optical measurements
Authors: Kircher J. , Böhringer W. , Dietrich W. , Hirt H. , Etchegoin P. , Cardona M.
Published: July 2002

The design and construction of an apparatus for the application of compressive uniaxial stress is described. In contrast to older machines a hydraulic force transmission is used allowing for a very compact and lightweight sample holder/stress unit. The less bulky machine allows more accurate alignment of the stressed sample in an optical experiment. The large force the machine can exert facilitates the use of samples with a large cross section such as those desirable for ellipsometric measurements. A low budget version of the machine, based on motorbike components, is suggested. The machine is used in conjuction with a rotating analyzer ellipsometer to measure the dielectric function under uniaxial stress. From these data we are able to extract the components of the piezo-optical tensor. We demonstrate this for the case of germanium.
An ultrahigh vacuum beam profile monitor
Authors: Stillman A. N. , Thern R. , Witkover R. L.
Published: July 2002

Ordinary gas ionization profile monitors, in common use at high-energy accelerators, are not useful in low density gases. Modern accelerators usually have high quality vacuum systems that maintain pressures below 10−8 Torr. We will describe a beam profile monitor that not only operates in the range of 10−11 Torr, but is noninvasive. Shaped electric fields sweep beam-generated ions out of a collection area onto the input face of a detector. The detector uses a dual microchannel plate to generate a gain of approximately 107 electrons per ion. An ultraviolet lamp provides a signal for monitoring the eventual degradation of the microchannel plate. The complete device contains a horizontal detector, a vertical detector, and a set of electrodes to nullify first-order electrostatic effects on the particle beam. Recent results from the initial use of the profile monitor are quite promising and demonstrate a new range of operation for this type of beam diagnostic device.
Automatic adjustment of bias current for direct current superconducting quantum interference device
Authors: Makie-Fukuda K. , Hotta M. , Okajima K. , Kado H.
Published: July 2002

A new method of adjusting the bias current of dc superconducting quantum interference device (SQUID) is described. It is shown that the signal-to-noise ratio of a SQUID magnetometer connected in a flux-locked loop configuration is proportional to the second harmonic of the output signal from the SQUID. A circuit configuration that can automatically optimize a SQUID’s bias current by measuring this second harmonic and adjusting the bias current accordingly is proposed.
Design of an electrostatic magnetic quadrupole accelerator
Authors: Mizuno M. , Ohara Y.
Published: July 2002

A new type of electrostatic acceleration system, electrostatic magnetic quadrupole (ESMQ) acceleration system, is proposed for efficient acceleration of negative ion beams. In this system, permanent magnets are buried in the acceleration electrodes so as to produce a quadrupole magnetic field in the electrode aperture region. Envelope simulation indicates that the quadrupole field can deflect electrons stripped from the negative ions. Beam envelope simulations for deuterium ions and electrons have been carried out using the beam envelope code trace. Electrons are largely divergent and most appear likely to hit downstream electrodes. Furthermore, maximum beam divergence of the deuterium ions is reduced to the focusing effect of the quadrupole magnetic field.
A phase-locked loop based analog simulator for a class of stochastic nonlinear dynamics
Authors: Hayashi Shigeo
Published: July 2002

An analog simulator has been built for such a class of second-order Langevin equations that the potential function is given by an integral of the phase angle of admittance for a piezoelectric resonator. It can be applied to the problem of noise induced escape from a potential well since the potential has a minimum at resonance frequency and a surmountable barrier at antiresonance frequency. The design is based on the phase-locked loop, and the system frequency plays a role of the random variable corresponding to the position of a particle performing a random walk. The modular design makes it possible to adapt the simulator to specific problems.
Soldered high-pressure high-temperature sapphire window
Authors: Gorbaty Yu. E. , Bondarenko G. V. , Mileiko S. T.
Published: July 2002

A technique for making reliable optical windows to be used in high-pressure high-temperature experiments is described. Gas-tight sealing of the cylindrical sapphire window is achieved by soldering it to a thin cylindrical shell with the eutectic silver–copper alloy.