bluuebunny/crossref_metadata_2025 huggingface dataset:
Human platelets respond differentially to lysophosphatidic acids having a highly unsaturated fatty acyl group and alkyl ether-linked lysophosphatidic acids
Authors: TOKUMURA Akira , SINOMIYA Junya , KISHIMOTO Seishi , TANAKA Tamotsu , KOGURE Kentaro , SUGIURA Takayuki , SATOUCHI Kiyoshi , WAKU Keizo , FUKUZAWA Kenji
Published: July 2002

Lysophosphatidic acid (LPA) is a physiological agonist that is produced by lysophospholipase D, phospholipase A1 and phospholipase A2 in the blood of animals. It exerts diverse biological actions on a broad range of animal cells. Specific receptors for this important agonist have been characterized. In this investigation, for the first time we prepared LPAs having a highly unsaturated fatty acyl group, such as the eicosapentaenoyl or docosahexaenoyl residue, and their acetylated derivatives. Human platelets aggregated more potently in response to the highly unsaturated acyl-LPAs than to LPAs with a C18 fatty acyl group, such as an oleoyl group, while alkyl ether-linked LPAs (alkyl-LPA) had much stronger aggregating activity. Two positional isomers of LPAs with an arachidonoyl, eicosapentaenoyl or docosahexaenoyl group had equipotent aggregatory activity as well as the positional isomers of their acetylated analogues, indicating that putative LPA receptors could not distinguish the difference between the positional isomers. We found that platelet preparations from two individuals showed no aggregatory response to alkyl-LPAs, although they contained mRNAs for known LPA receptors in the following order of expression level: endothelial differentiation gene (Edg)-4>Edg-7>Edg-2. We also obtained evidence that 2-(p-amylcinnamoyl)amino-4-chlorobenzoic acid (ONO-RS-082), a phospholipase A2 inhibitor, potentiated alkyl-LPA-induced platelet aggregation, but inhibited highly unsaturated acyl-LPA-induced platelet aggregation. These results indicated that human platelets express acyl-LPA-selective and alkyl-LPA-selective receptors on their plasma membrane.
Binding, degradation and apoptotic activity of stearoylethanolamide in rat C6 glioma cells
Authors: MACCARRONE Mauro , PAUSELLI Riccardo , di RIENZO Marianna , FINAZZI-AGRÒ Alessandro
Published: July 2002

Stearoylethanolamide (SEA) is present in human, rat and mouse brain in amounts comparable with those of the endocannabinoid anandamide (arachidonoylethanolamide; AEA). Yet, the biological activity of SEA has never been investigated. We synthesized unlabelled and radiolabelled SEA to investigate its binding, degradation and biological activity in rat C6 glioma cells. We report that SEA binds to a specific site distinct from known cannabinoid or vanilloid receptors, and that AEA and capsazepine partly (approx. 50%) antagonized this binding. Treatment of C6 cells with SEA inhibits cellular nitric oxide synthase and does not affect adenylate cyclase, whereas treatment with cannabinoid type 1 agonist 2-arachidonoylglycerol activates the former enzyme and inhibits the latter. C6 cells also have a specific SEA membrane transporter, which is inhibited by NO, and a fatty acid amide hydrolase capable of cleaving SEA. In these cells, SEA shows pro-apoptotic activity, due to elevation of intracellular calcium, activation of the arachidonate cascade and mitochondrial uncoupling. NO further enhances SEA-induced apoptosis. Moreover, the cannabinoid type 1 receptor-mediated decrease in cAMP induced by AEA in C6 cells is potentiated by SEA, suggesting that this compound also has an ‘entourage’ effect. Taken together, this study shows that SEA is an endocannabinoid-like compound which binds to and is transported by new components of the endocannabinoid system. It seems noteworthy that degradation and pro-apoptotic activity of SEA are regulated by NO in a way opposite to that reported for AEA.
Substrate recognition by three family 13 yeast α‐glucosidases
Authors: Frandsen Torben P. , Palcic Monica M. , Svensson Birte
Published: July 2002

Important hydrogen bonding interactions between substrate OH‐groups in yeast α‐glucosidases and oligo‐1,6‐glucosidase from glycoside hydrolase family 13 have been identified by measuring the rates of hydrolysis of methyl α‐isomaltoside and its seven monodeoxygenated analogs. The transition‐state stabilization energy, ΔΔG‡, contributed by the individual OH‐groups was calculated from the activities for the parent and the deoxy analogs, respectively, according to ΔΔG‡ = –RT ln[(Vmax/Km)analog/(Vmax/Km)parent]. This analysis of the energetics gave ΔΔG‡ values for all three enzymes ranging from 16.1 to 24.0 kJ·mol−1 for OH‐2′, ‐3′, ‐4′, and ‐6′, i.e. the OH‐groups of the nonreducing sugar ring. These OH‐groups interact with enzyme via charged hydrogen bonds. In contrast, OH‐2 and ‐3 of the reducing sugar contribute to transition‐state stabilization, by 5.8 and 4.1 kJ·mol−1, respectively, suggesting that these groups participate in neutral hydrogen bonds. The OH‐4 group is found to be unimportant in this respect and very little or no contribution is indicated for all OH‐groups of the reducing‐end ring of the two α‐glucosidases, probably reflecting their exposure to bulk solvent. The stereochemical course of hydrolysis by these three members of the retaining family 13 was confirmed by directly monitoring isomaltose hydrolysis using 1H NMR spectroscopy. Kinetic analysis of the hydrolysis of methyl 6‐S‐ethyl‐α‐isomaltoside and its 6‐R‐diastereoisomer indicates that α‐glucosidase has 200‐fold higher specificity for the S‐isomer. Substrate molecular recognition by these α‐glucosidases are compared to earlier findings for the inverting, exo‐acting glucoamylase from Aspergillus niger and a retaining α‐glucosidase of glycoside hydrolase family 31, respectively.
HRT and its effect on normal ageing of the brain and dementia
Authors: Compton Jacqueline , Van Amelsvoort Therese , Murphy Declan
Published: July 2002

There are significant gender differences in human brain disease. For example, females are significantly more likely to suffer from Alzheimer's disease (AD) than men (even after correcting for differences in life expectancy), and females on hormone replacement therapy (HRT) are significantly less likely to suffer from Alzheimer's disease than women who do not take HRT. However the neurobiological basis to these differences in clinical brain disease were unknown until relatively recently. In this review we will discuss results of studies that show; (i) gender differences in human brain disease are most likely to be explained by gender differences in brain development and ageing; (ii) sex steroids have a significant effect on the brain; (iii) sex steroids are crucial to the development and ageing of brain regions affected in age‐related brain diseases (for example AD); (iv) sex steroids interact with neuronal networks and chemical systems at many different levels; (v) sex steroids affect cognitive function in elderly women. Thus, the current literature supports the hypothesis that sex steroids can modulate brain ageing, and this provides a neurobiological explanation for the significantly higher prevalence of AD in females who do not take HRT, and may lead to new treatment approaches for age‐related brain disease including AD.
Reduction of the pituitary GH releasable pool in short children with GH neurosecretory dysfunction
Authors: Aimaretti G. , Bellone S. , Bellone J. , Chiabotto P. , Baffoni C. , Corneli G. , Origlia C. , de Sanctis C. , Camanni F. , Ghigo E.
Published: July 2002

OBJECTIVES The classical ‘GH neurosecretory dysfunction’ (GHNSD) refers to slowly growing children with normal GH responses to classical provocative tests but impaired spontaneous GH secretion over 24 h frequently leading to low IGF‐I levels. Thus it has been assumed that these subjects have insufficiency of spontaneous GH secretion due to neuroendocrine abnormalities in spite of a normal releasable pool of GH. However, classical provocative tests do not reliably assess the maximal somatotroph capacity; thus it is still unclear if the GH pool is really preserved or not. GHRH + arginine test is more potent than the classical tests and evaluates the maximal secretory capacity of somatotroph cells. The GH response to this stimulus is reproducible and also independent of age and puberty.

DESIGN AND PATIENTS We studied the GH response to GHRH (1 μg/kg iv) + arginine (ARG, 0·5 g/kg iv) in 19 short children with GHNSD (14 boys and 5 girls, age: 12·1 ± 0·7 years, pubertal stages I‐III, HV‐SDS between 1·6 and −4·9; GH peak > 10 μg/l after classical stimuli but mean GH concentration (mGHc) < 3 μg/l). The results in GHNSD were compared with those in 38 short children with idiopathic or organic severe GHD (GHD, 29 boys and 9 girls, age: 11·2 ± 0·6 years., pubertal stages I‐III, HV‐SDS between −1·8 and −4·4; GH peak < 10 μg/l after 2 classical provocative tests) and in 83 children with normal or familial short stature (NC, 59 boys and 24 girls, age: 11·5 ± 0·3 years., pubertal stages I‐III; HV‐SDS > 25th centile, normal IGF‐I levels).

RESULTS Mean IGF‐I levels in GHNSD (121·9 ± 20·3 μg/l) were lower (P < 0·001) than those in NC (270·3 ± 13·8 μg/l) but higher (P < 0·001) than those in GHD (72·0 ± 4·0 μg/l). The mean GH concentration (mGHc) in GHNSD (2·1 ± 0·1 μg/l) was lower (P < 0·01) than that in NC (4·9 ± 0·5 μg/l) but higher (P < 0·01) than that in GHD (1·5 ± 0·2 μg/l). On the other hand, the mean peak GH response to GHRH +ARG in GHNSD (43·7 ± 3·7μg/l) was markedly higher (P < 0·001) than that in GHD (8·2 ± 0·9 μg/l) but significantly lower (P < 0·01) than that in NC (60·4 ± 2·7 μg/l). All GHD patients had peak GH responses to GHRH +ARG below the 3rd centile limit of normality (20 μg/l), while all GHNSD patients had peak GH responses within the normal range. No significant correlation was found between GH peak after GHRH +ARG, mGHc and IGF‐I levels in each group.

CONCLUSION Our study demonstrates that short children with ‘GH neurosecretory dysfunction’ show reduction in the GH releasable pool evaluated by the provocative and potent GHRH + arginine test. However, the peak GH response to a single GHRH + arginine test in GH neurosecretory dysfunction is always within the normal range indicating that this test as well as classical stimuli does not distinguish normal subjects from GH neurosecretory dysfunction.
Comparing global models of terrestrial net primary productivity (NPP): comparison of NPP to climate and the Normalized Difference Vegetation Index (NDVI)
Authors: Schloss A. L. , Kicklighter D. W. , Kaduk J. , Wittenberg U. , Intercomparison ThE. Participants OF. ThE. Potsdam NpP. Model
Published: July 2002

To analyse the broad‐scale behaviour of 15 global models of the terrestrial biosphere, we evaluated the sensitivity of simulated net primary productivity (NPP) to spatial and seasonal variations in precipitation, temperature and solar radiation, and to the Normalized Difference Vegetation Index (NDVI). For annual NPP estimates, the models’ sensitivities to climate were the most similar in regions where NPP was not limited by precipitation. The largest differences in sensitivities occurred in regions where NPP was limited by both temperature and precipitation. Water use efficiencies within the models were relatively constant across latitudes so that higher correlations occurred between the latitudinal distribution of NPP and precipitation than with the other climate variables. The sensitivities of NPP estimates to solar radiation varied considerably with latitude. The largest differences in temperature sensitivity among NPP estimates occurred in the northern latitudes (50°N–70°N), i.e. the zone with the shortest active growing seasons. The sensitivity of NPP estimates to climate also varied seasonally. At the beginning and end of the active growing season in the boreal zone, monthly NPP estimates of all models were the most sensitive to temperature. In the tropics, sensitivities to climate varied widely among and within models. Seasonal changes in water balance and the structure of the vegetation canopy, as reflected by seasonal changes in NDVI, modified the sensitivity of NPP to climate in both boreal and tropical zones. Because these are both highly productive regions sensitive to climate change, continued investigations and better validation of models are necessary before we can fully understand and predict changes in ecosystem structure and function under various climatic conditions.
Subcortical neural circuits for ocular accommodation and vergence in primates
Authors: Gamlin Paul D.R.
Published: July 2002

Our current knowledge of the neural bases of vergence and accommodation has increased significantly over the past few years. The behavior of medial rectus motoneurons during vergence, which has been reported by a number of investigators, is described. The behavior of Edinger–Westphal neurons during accommodation is also described, as are the characteristics of midbrain near‐response neurons in the supraoculomotor area. Evidence that some of these near‐response neurons provide the vergence input to medial rectus motoneurons and possibly the accommodation input to Edinger–Westphal neurons is reviewed.

Anatomical studies have shown that the midbrain near‐response region receives input from two deep cerebellar nuclei, the posterior interposed and the fastigial nucleus. Single‐unit recording in the posterior interposed nucleus has revealed cells that increase their activity during the far‐response, and the behavior of these neurons is reviewed. In addition, studies of a precerebellar nucleus, the nucleus reticularis tegmenti pontis, have revealed some cells that increase their activity during the near‐response and others that do so during the far‐response. The behavior of these neurons is reviewed.

This review documents the great strides that are occurring in our understanding of the anatomy and physiology of the neural pathways controlling vergence and accommodation in the primate.
Quantitative defect etching of GaAs on Si: Is it possible?
Authors: Stirland D. J.
Published: July 2002

The Wright etch [M. W. Jenkins, J. Electrochem. Soc. 124, 757 (1977)], hitherto used to reveal defects in silicon, has been examined as a defect etchant for GaAs epitaxial layers on silicon. Various calibration techniques, including transmission electron microscopy of etched epitaxial layers, have been used to establish that etch features correspond with dislocations. Problems involved in direct comparisons of defect densities measured by different methods are discussed.
Improvement of YBa2Cu3O7−x thick films by doping with silver
Authors: Miller J. H. , Holder S. L. , Hunn J. D. , Holder G. N.
Published: July 2002

Composite thick films of YBa2Cu3O7−x and silver have been prepared on alumina substrates using a paint-on method. It is found that thick films containing greater than about 10% silver by weight have greatly reduced normal resistivities for T>Tc (onset) and significantly enhanced Tc (R=0) as compared with undoped films processed under identical conditions. These results are interpreted in terms of enhanced grain growth and an improved coupling between grain boundaries because of proximity-induced electron pairing in the silver regions.
Lateral dopant profiling with 200 nm resolution by scanning capacitance microscopy
Authors: Williams C. C. , Slinkman J. , Hough W. P. , Wickramasinghe H. K.
Published: July 2002

Measurement of dopant density in silicon with lateral resolution on the 200 nm scale has been demonstrated with a near-field capacitance technique. The technique is based upon the measurement of local capacitance between a 100 nm tip and a semiconducting surface. Lateral dopant imaging is achieved by the measurement of the voltage-dependent capacitance between tip and sample due to the depletion of carriers in the semiconductor, as the tip is scanned laterally over the surface. Measurements of dopant density have been demonstrated over a dopant range of 1015–1020 cm−3. Capacitance-voltage measurements have been made on a submicrometer scale.
Noninductive detection of single-proton magnetic resonance
Authors: Sidles J. A.
Published: July 2002

The presence of nuclear magnetic resonance can be detected noninductively by coupling the nuclear spin to the motion of a mechanical oscillator. The coupling is obtained by applying a large-gradient magnetic field, which exerts a mechanical force on the particle by virtue of its magnetic moment. The coupling increases in strength as the oscillator mass is decreased and the gradient length scale is made shorter. Oscillator-based detection is thus only marginally effective for macroscopic samples, but can be quite effective for single protons interacting with a micron-scale oscillator. This letter describes the physics of devices in which single-nucleon magnetic resonance is detected by monitoring the excitation of a mechanical oscillator.
Low-temperature growth of Ge on Si(100)
Authors: Eaglesham D. J. , Cerullo M.
Published: July 2002

Heteroepitaxial MBE growth of Ge on Si(100) is studied at temperatures down to room temperature. We show that, as for Si and GaAs homoepitaxy, the low-temperature limit to growth is an epitaxial thickness, hepi, before the amorphous phase is nucleated. hepi increases with increasing temperature with an apparent activation energy of 0.5±0.1 eV at 0.2 Å/s. Above 170 °C hepi increases discontinuously and becomes effectively infinite, possibly as solid phase begins to occur. We show that growth is planar for all temperatures below 300 °C, so that low-temperature growth can be used near 200 °C to suppress island formation without encountering the limited thickness effect. In contrast with planar growth at high temperatures with an As ‘‘surfactant’’, strain relaxation of these planar epilayers occurs by normal dislocation introduction to give an array of predominantly edge misfit dislocations.
High-speed InGaAs/GaAs strained multiple quantum well lasers with low damping
Authors: Nagarajan Radhakrishnan , Fukushima Toru , Bowers John E. , Geels Randall S. , Coldren Larry A.
Published: July 2002

Strained In0.2Ga0.8As/GaAs multiple quantum well polyimide buried ridge waveguide lasers with 3 dB bandwidths of 20 GHz and K factors as low as 0.17 ns have been fabricated. This is the highest bandwidth and the lowest K factor reported to date for quantum well lasers in any material system or for lasers of the ridge waveguide geometry.
Estimates of infrared intersubband emission and its angular dependence in GaAs/AlGaAs multiquantum well structures
Authors: Choe J.-W. , Perera A. G. U. , Francombe M. H. , Coon D. D.
Published: July 2002

This letter describes results of a modeling analysis of IR radiative efficiency for cascade-type quantum well emitter structures, and the angular dependence of spontaneous emission. The radiative decay rates are calculated for different IR wavelength ranges. Estimates of radiative efficiency indicate that the performance of these cascade mode devices in the long- and midwavelength infrared range can be comparable to or superior to that reported at far-infrared range. Based upon calculations of the angular dependence of IR emission, an etched surface grating structure is proposed which should lead to high effective coupling efficiencies.
In situ x-ray investigation of the melting of Bi-Sr-Ca-Cu-O phases
Authors: Polonka J. , Xu Ming , Li Qiang , Goldman A. I. , Finnemore D. K.
Published: July 2002

High-temperature x-ray studies of the melting of Bi2Sr2Ca1Cu2O8−δ/Ag composites have been undertaken in order to determine the factors that control the melting temperature and the various phases that form during the melt-processing part of the fabrication of these conductors. During the melting process, three distinct phases form and then dissolve in the Bi-rich liquid: first (Sr,Ca)1Cu1O2, then (Sr,Ca)2Cu1O3, and finally (Sr,Ca)O. Ag suppresses the melting point about 30 °C and as much as 10% Ag can dissolve in the Bi-rich liquid. A slight Bi excess also decreases the temperature where the Bi2Sr2Ca1Cu2O8−δ structure disappears and liquid forms.
Novel infrared detector based on a tunneling displacement transducer
Authors: Kenny T. W. , Kaiser W. J. , Waltman S. B. , Reynolds J. K.
Published: July 2002

The pneumatic infrared detector [M. J. E. Golay, Rev. Sci. Instrum. 18, 347 (1947)] uses thermal expansion of a gas to detect infrared radiation. We have designed a detector based on this principle, but which is constructed entirely from micromachined silicon, and uses an electron tunneling displacement transducer to detect the expansion of the gas. The design, fabrication, and characterization of the first prototype sensor are described. Its sensitivity is competitive with the best available uncooled infrared detectors.
Logarithmic relaxation in the levitation force in a magnet-high T
c superconductor system
Authors: Riise A. B. , Johansen T. H. , Bratsberg H. , Yang Z. J.
Published: July 2002

The dynamic response of the levitation force between a permanent magnet and a bulk YBCO superconductor when subjected to a sudden motion-induced step in the magnetic field has been measured. It is found that the levitation force relaxes logarithmically with time. Assuming that force and magnetization behave similarly, the rate of decay can be interpreted in terms of a thermally activated flux creep with a depinning activation energy of U0=0.20 eV. A replot of previously published results for melt-quenched YBCO also demonstrates that also in this material the force relaxation is characterized by a logarithmic decay.
Minority carrier lifetimes in ideal InGaSb/InAs superlattices
Authors: Grein C. H. , Young P. M. , Ehrenreich H.
Published: July 2002

Calculations of band-to-band Auger and radiative recombination lifetimes of the recently proposed InxGa1−xSb/InAs superlattices (SL) show them to be promising infrared detectors. Several superlattices with energy gaps in the 5–11 μm range exhibit suppressed p-type Auger recombination rates due to a large light hole–heavy hole splitting. The p-type Auger lifetime at 77 K of an 11 μm InxGa1−xSb/InAs SL is found to be, respectively, three and five orders of magnitude longer than those of bulk and superlattice HgCdTe with the same energy gap. The n-type lifetimes are comparable.
High critical current densities in ultrathin YBa2Cu3O7−δ films sandwiched between (PrxY1−x)Ba2Cu3O7−δ layers
Authors: Kwon C. , Li Qi , Xi X. X. , Bhattacharya S. , Doughty C. , Venkatesan T. , Zhang H. , Lynn J. W. , Peng J. L. , Li Z. Y. , Spencer N. D. , Feldman K.
Published: July 2002

YBa2Cu3O7−δ (YBCO) films with nominal thicknesses of 1–4 unit cells were grown by pulsed laser deposition using (PrxY1−x)Ba2Cu3O7−δ [(PrxY1−x)BCO] (1≥x≥0) as buffer layers and cap layers. The films of 1 unit cell thick were superconducting for all the x values while Tc increased when x was reduced. For adjacent layers of (Pr0.6Y0.4)BCO which is semiconducting, a Tc of 43 K and Jc of 2×106 A/cm2 for B∥ab and 4×105 A/cm2 for B⊥ab at B=7 T and 4.2 K were obtained in a one-unit cell thick YBCO layer. The Jc values of a few unit cell thick YBCO layers nearly approached that of thick YBCO films. The results suggest the absence of significant weak-link effects in these films.
Photovoltaic and photoconductive dual-mode operation GaAs quantum well infrared photodetector for two-band detection
Authors: Wang Y. H. , Li Sheng S. , Ho Pin
Published: July 2002

A new photoconductive (PC) and photovoltaic (PV) dual-mode operation quantum well infrared photodetection (DM-QWIP) using an enlarged GaAs (110 Å) quantum well and enlarged Al0.25Ga0.75As (875 Å) barrier layer has been developed for two-color intersubband detection. The detection scheme uses transitions from the ground-state and the first excited-state inside the enlarged GaAs quantum well to the continuum states slightly above the AlGaAs barrier layers. The detectivity Dλ* for the PV mode was found to be 1.5×109√Hz/ W at the peak response wavelength λp=7.7 μm and T=77 K, while the values of Dλ* for the PC mode were found to be 2×1010, 1×1010 cm√Hz/W for Vb=1,2 V at λp=12 μm and T=77 K, respectively.
Laser surface photovoltage spectroscopy: A new tool for the determination of surface state distributions
Authors: Kronik L. , Burstein L. , Shapira Yoram , Oron M.
Published: July 2002

A new experimental technique, which utilizes a tunable laser as the illumination source for surface photovoltage spectroscopy measurements, is presented. The data obtained by this technique make it possible to determine the distribution function of gap states observed at semiconductor interfaces. An outline of the approach together with experimental results obtained using a Ti:sapphire laser on InAlAs and CdTe crystals is given.
Oxidation enhanced diffusion in Si B-doping superlattices and Si self-interstitial diffusivities
Authors: Gossmann H.-J. , Rafferty C. S. , Luftman H. S. , Unterwald F. C. , Boone T. , Poate J. M.
Published: July 2002

A special thin film structure has been grown by low temperature molecular beam epitaxy for an investigation of the properties of self-interstitials in Si. It consists of a doping superlattice made from B spikes separated from each other by 100 nm of Si. After dry oxidation, the width of each spike is directly proportional to the interstitial concentration at that depth. The superlattice as a whole thus gives a depth profile of the time-averaged interstitial concentration, allowing the direct determination of the diffusion coefficient of interstitials. The abrupt dopant concentration transitions possible in low-temperature molecular-beam-epitaxy-grown films allow this investigation in the temperature range 750–900 °C. At 800 °C we find a value of DI=(1.4±0.4)10−13 cm2/s. Performing the experiments as a function of temperature yields DI = D0eEa/kT with D0=102±2 cm2/s and Ea=(3.1±0.4) eV.
Photoelectron spectroscopy measurements of the band gap in porous silicon
Authors: van Buuren T. , Tiedje T. , Dahn J. R. , Way B. M.
Published: July 2002

Photoemission and x-ray absorption spectroscopy show that both the conduction and valence bands of porous silicon are shifted relative to the bands for bulk silicon, as expected in the quantum confinement model for the optical properties of porous silicon. The shift in the valence band is larger than the shift in the conduction band and proportional to it, with a proportionality constant that is consistent with effective mass theory. No oxygen is detected in the as-prepared porous silicon.
Ultra-low-temperature growth of high-integrity gate oxide films by low-energy ion-assisted oxidation
Authors: Kawai Y. , Konishi N. , Watanabe J. , Ohmi T.
Published: July 2002

The gate oxide films have been grown at a temperature as low as 450 °C by direct oxidation of silicon. Such a low-temperature oxidation has been realized by employing a precision controlled ion bombardment in an Ar/O2 mixed plasma for the surface activation. Perfectly controlled Ar ions give the bombardment energy for the oxide film growth. Dielectric breakdown fields of 10 MV/cm are achieved. Integration in a total low-temperature device process has been demonstrated by fabricating self-aligned Al-gate metal-oxide-silicon field effect transistor (MOSFET) formed without any heat processing over 450 °C. The precise control of the ion bombardment is quite essential for the low-temperature process.
Anisotropic high-field diffusion of holes in silicon
Authors: Hinckley J. M. , Singh J.
Published: July 2002

Anisotropy of the silicon valence band leads to a strong dependence of charge carrier transport properties, upon the orientation of the electric field. A detailed anisotropic Monte Carlo method has been applied to the calculation of the hole diffusion coefficient in silicon, studying its dependence on field magnitude and orientation. The longitudinal diffusion coefficient is found to have a dependence on the field orientation which is similar in degree to the more familiar dependence of the drift velocity on field orientation. However, it is found that the transverse diffusion coefficient has a substantially stronger dependence on field orientation. At the highest field which has been studied, 50 kV/cm, the transverse diffusion coefficient almost doubles as one shifts from a field oriented in the [100] direction to one in the [101] direction and considers the [101̄] transverse direction.
Design and performance of compact vacuum-compatible submillimeter viewing dumps
Authors: Kato K. , Hutchinson I. H.
Published: July 2002

Compact, vacuum-compatible submillimeter viewing dumps, whose design parameters were based on the results of simple ray calculations, have been fabricated from Pyrex, Macor, and alumina. The measured performance of the dumps agrees qualitatively with calculated results. The absorption is somewhat lower than expected, but still acceptable (≥99% absorption for Pyrex and Macor). In an electron cyclotron plasma emission experiment on Alcator C tokamak, comparison of the emission spectra with and without the dump shows that the dump in this configuration is effective in suppressing the unwanted radiation by approximately 90%. The additional reflection is believed to be due to a portion of the antenna pattern missing the dump.
Alcator C vertical viewing electron cyclotron emission diagnostic
Authors: Kato K. , Hutchinson I. H.
Published: July 2002

Electron cyclotron emission measured vertically through the center of a tokamak plasma yields detailed information about the electron velocity distribution. A diagnostic developed for this purpose on Alcator C tokamak uses specialized focusing optics to obtain a well-collimated viewing chord, a compact viewing dump made of Pyrex or Macor to reduce the effects of wall reflection and depolarization, and a rapid-scan polarizing Michelson interferometer InSb detector system for the spectrum measurement; all constrained by the limited access and the compact size of Alcator C. Results of diffraction analysis are used to evaluate the theoretical performance of the optical system.
H− beam extraction experiments on the Culham small multipole source
Authors: McAdams R. , Holmes A. J. T. , Nightingale M. P. S.
Published: July 2002

Beam extraction experiments have been carried out on a multicusp volume H− ion source operated in a dc mode. With an extraction aperture of 16-mm diameter, negative ion beams of up to 15 mA cm−2 have been extracted. Some experiments have been performed to investigate the physics of beam extraction from the plasma that indicate a fixed plasma boundary. The beam emittance has been measured as a function of various arc and accelerator parameters. The negative ion temperatures inferred from the emittance measurements cannot at present be explained.
A fiber-optic light-scattering spectrometer
Authors: Dhadwal H. S. , Chu Benjamin
Published: July 2002

A new fiber-optic light-scattering spectrometer, which uses fiber-optic detector probes each comprising of an optical fiber and a graded index microlens is described. The fiber-optic detectors form an integral part of the scattering cell, which no longer requires transparent windows for the exit (or entrance) light beam. This feature eliminates the need for a goniometer which is one of the most bulky and expensive components of a conventional light-scattering spectrometer. Thus, the spectrometer, unlike all of its predecessors, has no moving parts. Our fiber-optic light-scattering spectrometer can utilize a reaction vessel of whichever shape or composition as the scattering cell for light-scattering measurements because the fiber-optic detector probes are directly immersed in the scattering medium. Furthermore, with the miniaturization using the optical fiber/microlens combination, the light-scattering spectrometer can be held in the palm of one hand and the signals processed by standard optical fiber remote sensing techniques.
Study of photoluminescence in nanocrystalline silicon/amorphous silicon multilayers
Authors: Tong Song , Liu Xiang-na , Bao Xi-mao
Published: July 2002

We report in this letter the observation of visible photoluminescence (PL) at room temperature from hydrogenated nanocrystalline silicon (nc-Si:H)/amorphous silicon (a-Si:H) multilayers (MLs) prepared in a plasma enhanced chemical vapor deposition system without any postprocessing. The PL peak wavelength can be controlled, blueshifting from 750 to 708 nm, through reducing the width of the nc-Si:H sublayers from 4.0 to 2.1 nm. Quantum size effect in nc-Si:H sublayers of the ML is responsible for the emission above the band gap of bulk crystal Si.
Imaging plate for time-resolved x-ray measurements (invited)
Authors: Amemiya Yoshiyuki , Kishimoto Shunji , Matsushita Tadashi , Satow Yoshinori , Ando Masami
Published: July 2002

Two apparatus have been developed for time-resolved measurements of x-ray diffraction patterns using an imaging plate detector. The first one is based on a cinema method which permits up to 40 exposures of a two-dimensional x-ray pattern (100×108 mm2) with a 0.3-s time resolution. The second one works as a 200-mm-long linear detector which enables a time resolution of 23 μs for a duration of up to 46 ms, based on a streak-camera method. These apparatus have no count rate limitation, a high detective quantum efficiency (more than 80% for 8–20 keV), a 1:105 dynamic range in x-ray intensity and a spatial resolution of 150 μm (FWHM) due to the performance of the imaging plate.
Control of long-term output frequency drift in commercial dye lasers
Authors: Lindsay B. G. , Smith K. A. , Dunning F. B.
Published: July 2002

A simple technique using a scanning confocal Fabry-Perot etalon and a stabilized helium-neon laser is described that can be used to correct the long-term drift in output frequency of actively stabilized commercial dye lasers. Using this technique the long-term drift in the ultraviolet output frequency of an intracavity-doubled Coherent Inc. CR699-21 ring dye laser has been reduced to ≲±2 MHz.
Novel switching phenomena in ferroelectric Langmuir–Blodgett films
Authors: Bune A. , Ducharme Stephen , Fridkin V. , Blinov L. , Palto S. , Petukhova N. , Yudin S.
Published: July 2002

We have established ferroelectric switching and observed a novel conductance switching phenomenon in ferroelectric polymer films fabricated by the Langmuir–Blodgett technique. The films consist of 10–30 monolayers (ML) of a copolymer of vinylidene fluoride (70%) and trifluoroethylene (30%), exhibiting a first-order ferroelectric phase transition at 70 °C and nearly rectangular ferroelectric and conductance hysteresis at 24 °C. Ferroelectric switching is accompanied by switching of the conductance by three orders of magnitude. A model describing this switching phenomenon is proposed.
Measurements of isobaric heat capacities of gases from 323.15 to 573.15 K up to 30 MPa
Authors: Dordain L. , Coxam J.-Y. , Grolier J.-P. E.
Published: July 2002

A Setaram C-80 calorimeter has been modified in order to measure heat capacities at constant pressure of gases from ambient temperature to 573 K and at pressures up to 30 MPa. Special cells have been designed and an additional device has been incorporated into the calorimeter to better control the temperature. The calorimetric technique and the calibration method are described. Experimental heat capacities of CO2 in the temperature range 323.15–423.15 K at pressures up to 25 MPa are reported and compared with the best literature data.
Calibration and correction of distortions in two-dimensional detector systemsa)
Authors: Hammersley A. P. , Svensson S. O. , Thompson A. , Graafsma H. , Kvick Å. , Moy J. P.
Published: July 2002

A modular system of techniques and software has been developed for the calibration and correction of intensity linearity, uniformity of response, spatial distortion, and image plate decay. With calibration the Molecular DynamicsTM Imaging Plate scanner system has been shown to give comparable results to the MarResearchTM scanner. The ESRF x-ray image intensifier/charge-coupled device detectors inherently cause large spatial and uniformity of response distortions, and successful data analysis depends on calibration and correction. Results of synchrotron radiation experiments are presented.
The Bragg resonance picture of one-dimensional fluctuation reflectometry beyond the Born approximationa)
Authors: Chou Albert E. , Afeyan B. B. , Cohen B. I.
Published: July 2002

By using HELM1D, a numerical, one-dimensional Helmholtz equation solver, we have studied the scattering phase shift of S-polarized O modes in fluctuation reflectometry both within and beyond the Born approximation. Comparisons are made between these numerical results and analytical expressions obtained through the use of the Born approximation. As the fluctuation amplitude increases, various peaks of the phase response evolve with distinct growth rates. This leads to steepening and distortion of the scattering phase shift due to a single wave-number fluctuation. The simultaneous coexistence of large amplitude fluctuations with nearby wave numbers complicates the task of resolving the response at each wave number.
Inexpensive, reliable control electronics for stick–slip motion in air and ultrahigh vacuum
Authors: Eng L. M. , Eng F. , Seuret Ch. , Kündig A. , Günter P.
Published: July 2002

In this paper we report on an inexpensive (under $100) and reliable electronic device that is used for stick–slip motion control in air and ultrahigh vacuum (UHV) devices. Though the high-voltage amplifier provides driving potentials of up to ±800 V, only a ±15 V power supply is needed. The versatile concept of stick–slip motion is based on variations of duration, slope, and repetition rate of a sawtooth pulse that drives the amplifiers. Our electronic device provides control of all these parameters. Thus the sawtooth output can easily be adapted to drive different devices. Application of this electronic will be demonstrated with four examples: (a) an x–y translation table; (b) a z-approach device working against gravity; (c) a φ rotation device; and (d) a ϑ–φ rotatory mirror device. All the devices are designed to run properly in both air and UHV.
Measurements of the neutron source strength at DIII-D
Authors: Heidbrink W. W. , Taylor P. L. , Phillips J. A.
Published: July 2002

A set of neutron counters and a pair of scintillators measure the 2.5 MeV neutron emission produced by the DIII-D tokamak. The neutron counter set provides a large dynamic range (∼7 orders of magnitude) while the scintillators provide the very fast resolution needed for studying transient events. The counters are absolutely calibrated in situ with a 252Cf source and the scintillators are cross calibrated to the counters. The historic variations in the emission measured by the various detectors have been compared and are consistent within the estimated accuracy of the absolute calibration (15%). In the discharges with the highest emission levels (2.4×1016 n/s), the signals from the neutron counters and the scintillators agree well. Comparisons with other diagnostics also corroborate the neutron measurements.
Cross-polarization scattering from low-frequency electromagnetic waves in the GAMMA10 tandem mirror
Authors: Kogi Y. , Mase A. , Bruskin L. G. , Oyama N. , Tokuzawa T. , Kubota S. , Itakura A. , Ichimura M. , Hojo H. , Tamano T. , Yatsu K.
Published: July 2002

A cross-polarization scattering (CPS) diagnostic method was applied to the GAMMA10 tandem mirror in order to study electromagnetic plasma waves with frequency less than 10 MHz. In the CPS process, an incident ordinary (extraordinary) wave is converted to an extraordinary (ordinary) wave by magnetic fluctuations in a plasma. The frequency spectra, and the density and magnetic fluctuations of the waves can be evaluated from both the CPS and reflectometry. The converted wave propagates through the cutoff layer and reaches a different diagnostic port with a receiver horn. The observed waves are identified as the electromagnetic drift wave assuming the wave number matching condition. The low frequency waves nonlinearly coupled with the Alfven ion cyclotron waves are also observed with increase in the plasma pressure.
Determination of fluorine atom density in reactive plasmas by vacuum ultraviolet absorption spectroscopy at 95.85 nm
Authors: Sasaki K. , Kawai Y. , Kadota K.
Published: July 2002

Vacuum ultraviolet absorption spectroscopy was developed for the measurement of absolute fluorine (F) atom density in reactive plasmas. In order to minimize the influence of radiation trapping (self-absorption) in the light source, fluorescence at a wavelength of 95.85 nm from the F atoms in an electron–cyclotron resonance (ECR) CF4 plasma, which was operated with a low microwave power (0.1 kW) and a low gas pressure (1 mTorr), was employed as the probe emission. A windowless transmission system for the probe emission was constructed by connecting the ECR light source with the target plasma and the detection system using vacuum tubes having small slits. The connection tubes were differentially evacuated with turbomolecular pumps to prevent neutral particles from passing through between the ECR and target plasmas. The present method was applied to high-density CF4 and C4F8 plasmas produced by helicon-wave discharges. The accuracy of the measurement was examined carefully by evaluating various sources of error. In the present article, we have emphasized the evaluation of the radiation trapping effect in the light source plasma.
Multichannel time-resolved optical tomographic imaging system
Authors: Eda Hideo , Oda Ichiro , Ito Yasunobu , Wada Yukihisa , Oikawa Yukio , Tsunazawa Yoshio , Takada Michinosuke , Tsuchiya Yutaka , Yamashita Yutaka , Oda Motoki , Sassaroli Angelo , Yamada Yukio , Tamura Mamoru
Published: July 2002

A time-resolved optical imaging system using near-infrared light has been developed. The system had three pulsed light sources and total 64 channels of detection, working simultaneously for acquisition of the time-resolved data of the pulsed light transmitted through scattering media like biological tissues. The light sources were provided by high power picosecond pulsed diode lasers, and optical switches directed one of the light sources to the object through an optical fiber. The light signals reemitted from the surface of the object were collected by optical fibers, and transmitted to a time-resolved detecting system. Each of the detecting channels consisted of an optical attenuator, a fast photomultiplier, and a time-correlated single photon counting circuit which contained a miniaturized constant fraction discriminator/time-to-amplitude converter module, and a signal acquisition unit with an A/D converter. The performance and potentiality of the imaging system have been examined by the image reconstruction from the measured data using solid phantoms.
Density-of-states effective mass and scattering parameter measurements by transport phenomena in thin films
Authors: Young D. L. , Coutts T. J. , Kaydanov V. I.
Published: July 2002

A novel machine has been developed to measure transport coefficients in the temperature range of 50–350 K of thin films deposited on electrically insulating substrates. The measured coefficients—resistivity, Hall, Seebeck, and Nernst—are applied to solutions of the Boltzmann transport equation to give information about the film’s density-of-states effective mass, the Fermi energy level, and an energy-dependent scattering parameter. The machine is designed to eliminate or compensate for simultaneously occurring transport phenomena that would interfere with the desired measured quantity, while allowing for all four coefficients to be measured on the same sample. An average density-of-states effective mass value of 0.29±0.04me was measured on the transparent conductive oxide, cadmium stannate (CTO), over a carrier concentration range of 2–7×1020 cm−3. This effective mass value matched previous results obtained by optical and thermoelectric modeling. The measured scattering parameter indicates that neutral impurities or a mixture of scattering mechanisms may inhibit the transport of carriers in CTO.
Reducing tilt errors in moiré linear encoders using phase-modulated grating
Authors: Song Ju-Ho , Kim Kyung-Chan , Kim Soo Hyun
Published: July 2002

A new hardware compensation method reducing displacement measurement errors, caused by tilt of the index scale in a moiré linear encoder, has been developed. In conventional moiré linear encoders, the detectors are aligned perpendicular to the line of the moiré fringes and this structure is very sensitive to an unwanted tilt of the gratings. In this article, a newly designed grating, called a phase-modulated grating, is developed to compensate for nonorthogonal errors. By using the phase-modulated grating instead of a conventional index, it is possible to reduce nonorthogonal errors of the moiré linear encoder.
Bonding characterization of BC2N thin films
Authors: Watanabe M. O. , Itoh S. , Mizushima K. , Sasaki T.
Published: July 2002

We have studied the bonding states of BC2N thin films prepared by chemical vapor deposition, one of the new layered BCN compounds. The chemical bonding states of boron, carbon, and nitrogen atoms in the BC2N thin films were investigated by using x-ray photoelectron spectroscopy to measure chemical shifts of 1s electrons, being compared with those in graphite and hexagonal (h-) BN. The results exhibited that the thin films had significant B–C and C–N bonds and were clearly different from graphite and h-BN, indicating that an atomic-level hybrid of the three elements was synthesized.
Dead space approximation for impact ionization in silicon
Authors: Spinelli A. , Pacelli A. , Lacaita A. L.
Published: July 2002

We demonstrate the validity of the dead space approximation for impact ionization in silicon. Monte Carlo simulations are used to obtain realistic ionization probabilities, and the corresponding avalanche gain in constant field structures is computed. We show that the hard-threshold dead space model is in good agreement with a more refined model taking into account soft-threshold effects, if an effective threshold energy of 3 eV is adopted for electrons. We also show that hole nonlocal effects do not significantly affect the result.
High-speed electrical sampling using optical second-harmonic generation
Authors: Nahata Ajay , Heinz Tony F. , Misewich James A.
Published: July 2002

We report the application of optical second-harmonic generation to the measurement of ultrafast electrical pulses. The technique relies on the sensitivity of the second-harmonic response to electric fields in centrosymmetric materials. Electrical pulses propagating on a silicon-based coplanar transmission line have been characterized with subpicosecond time resolution and 100 mV/√Hz sensitivity. We have measured the bias dependence of the second harmonic intensity over a 20 V range and have used this data to calibrate the transient response. The observed full-width at half maximum response time of the SHG waveform is ∼1 ps, which is consistent with the value obtained from an electronic cross-correlation measurement.
Electrode-induced degradation of Pb(ZrxTi1−x)O3 (PZT) polarization hysteresis characteristics in Pt/PZT/Pt ferroelectric thin-film capacitors
Authors: Kushida-Abdelghafar Keiko , Miki Hiroshi , Torii Kazuyoshi , Fujisaki Yoshihisa
Published: July 2002

One of the most serious forms of damage that occurs during the integration of Pt/PZT/Pt ferroelectric capacitors [where PZT is Pb(ZrxTi1−x)O3] is the disappearance of polarization hysteresis characteristics during the passivation process. The hydrogen content of the atmosphere during this process affects the ferroelectric capacitor characteristics. However, the PZT film itself is not damaged by annealing in a hydrogen-containing atmosphere even at 400 °C, whereas the Pt/PZT/Pt ferroelectric capacitor loses its polarization hysteresis characteristics at 300 °C. The top Pt electrode was found to induce this damage. Possible mechanisms such as stress and a chemical reaction with the Pt catalyst are discussed.