bluuebunny/crossref_metadata_2025 huggingface dataset:
Protein disulfide isomerase mediates integrin‐dependent adhesion
Authors: Lahav J. , Gofer-Dadosh N. , Luboshitz J. , Hess O. , Shaklai M.
Published: July 2002

Cell adhesion is mediated by the integrin adhesion receptors. Receptor–ligand interaction involves conformational changes in the receptor, but the underlying mechanism remains unclear. Our earlier work implied a role for sulfhydryls in integrin response to ligand binding in the intact blood platelet. We now show that non‐penetrating blockers of free sulfhydryls inhibit β1 and β3 integrin‐mediated platelet adhesion regardless of the affinity state of the integrin. Removal of the inhibitors prior to adhesion fully restores adhesion despite the irreversible nature of inhibitor–thiol interaction, indicating sulfhydryl exposure in response to adhesion. We further show that blocking protein disulfide isomerase (PDI) inhibits adhesion. These data indicate that: (a) ecto‐sulfhydryls are necessary for integrin‐mediated platelet adhesion; (b) disulfide exchange takes place during this process; (c) surface PDI is involved in integrin‐mediated adhesion.
Involvement of decreased myo‐inositol transport in lipopolysaccharide‐induced depression of phosphoinositide hydrolysis in vascular smooth muscle
Authors: Sotoda Yoko , Negoro Munetaka , Wakabayashi Ichiro
Published: July 2002

The mechanism underlying lipopolysaccharide (LPS)‐induced depression of phosphoinositide (PI) hydrolysis was investigated using rat aortas. In LPS‐pretreated aortas, the 5‐hydroxytryptamine‐stimulated accumulation of inositol monophosphate and incorporation of exogenous myo‐inositol into PIs were significantly less than those in control aortas. Both sodium‐myo‐inositol cotransporter (SMIT) and phosphatidylinositol transfer protein (PITP) genes were constituently expressed in rat aortas. The mRNA level of SMIT was remarkably lower in LPS‐pretreated aortas, while that of PITP mRNA was not affected by LPS. These results suggest that LPS‐induced depression of SMIT expression is involved in inhibition of agonist‐stimulated PI hydrolysis by LPS.
In vivo microdialysis studies of age‐related alterations in potassium‐evoked overflow of dopamine in the dorsal striatum of Fischer 344 rats
Authors: Stanford John A. , Giardina Karen , Gerhardt Greg A.
Published: July 2002

Intracerebral microdialysis was used to measure basal levels and potassium (K+)‐stimulated overflow of dopamine (DA), homovanillic acid (HVA) and dihydroxyphenylacetic acid (DOPAC), in the dorsal striatum of young (6 months) and aged (24 months) Fischer 344 (F344) rats. Basal levels of HVA were lower in aged rats whereas basal DA and DOPAC did not differ significantly between the two groups. The administration of three low to moderate doses of K+ (10, 25, and 50 mM) through the microdialysis probe for one collection period revealed differences between the two age groups of F344 rats. DA overflow increased in a dose‐dependent manner in the young but not aged rats. Extracellular levels of DOPAC and HVA decreased during the K+ stimulation and there was a significant difference in the changes in HVA produced by K+ stimulation in the young vs aged animals. These data support the hypothesis that low to moderate doses of K+ may be necessary to demonstrate age‐related differences in K+‐evoked DA overflow, since previous microdialysis studies using higher doses have not reported age‐related differences in DA overflow.
PSA‐NCAM: an important regulator of hippocampal plasticity
Authors: Cremer H. , Chazal G. , Lledo P.M. , Rougon G. , Montaron M.F. , Mayo W. , Le Moal M. , Abrous D.N.
Published: July 2002

The Neural Cell Adhesion Molecule (NCAM) serves as a temporally and spatially regulated modulator of a variety of cell‐cell interactions. This review summarizes recent results of studies aimed at understanding its regulation of expression and biological function, thereby focussing on its polysialylated isoforms (PSA‐NCAM). The detailed analysis of the expression of PSA and NCAM in the hippocampal mossy fiber system and the morphological consequences of PSA‐NCAM deficiency in mice support the notion that the levels of expression of NCAM are important not only for the regulation and maintenance of structural changes, such as migration, axonal growth and fasciculation, but also for activity‐induced plasticity. There is evidence that PSA‐NCAM can specifically contribute to a presynaptic form of plasticity, namely long‐term potentiation at hippocampal mossy fiber synapses. This is consistent with previous observations that NCAM‐deficient mice show deficits in spatial learning and exploratory behavior. Furthermore, our data points to an important role of the hypothalamic–pituitary–adrenal axis, which is the principle adaptive response of the organism to environmental challenges, in the control of PSA‐NCAM expression in the hippocampal formation. In particular, we evidence an inhibitory influence of corticosterone on PSA‐NCAM expression.
Remarkable Antiagglomeration Effect of a Yeast Biosurfactant, Diacylmannosylerythritol, on Ice‐Water Slurry for Cold Thermal Storage
Authors: Kitamoto Dai , Yanagishita Hiroshi , Endo Akira , Nakaiwa Masaru , Nakane Takashi , Akiya Takaji
Published: July 2002

Antiagglomeration effects of different surfactants on ice slurry formation were examined to improve the efficiency of an ice‐water slurry system to be used for cold thermal storage. Among the chemical surfactants tested, a nonionic surfactant, poly(oxyethylene) sorbitan dioleate, was found to show a greater antiagglomeration effect on the slurry than anionic, cationic, or amphoteric surfactants. More interestingly, diacylmannosylerythritol, a glycolipid biosurfactant produced by a yeast strain of Candida antarctica, exhibited a remarkable effect on the slurry, attaining a high ice packing factor (35%) for 8 h at a biosurfactant concentration of 10 mg/L. These nonionic glycolipid surfactants are likely to effectively adsorb on the ice surface in a highly regulated manner to suppress the agglomeration or growth of the ice particles. This is the first report on the utilization of biosurfactant for thermal energy storage, which may significantly expand the commercial applications of the highly environmentally friendly slurry system.
Aconitase activity and expression during the development of lemon fruit
Authors: Sadka Avi , Dahan Esther , Cohen Lidya , Marsh Kenneth B.
Published: July 2002

Citrus fruits are characterized by the accumulation of high levels of citric acid in the juice sac cells and a decline in acid level toward maturation. It has been suggested that changes in mitochondrial aconitase (EC 4.2.1.3) activity affect fruit acidity. Recently, a cytosolic aconitase (cyt‐Aco) homologous to mammalian iron‐regulated proteins was identified in plants, leading us to re‐evaluate the role of aconitase in acid accumulation. Aconitase activity was studied in 2 contrasting citrus varieties, sweet lime (Citrus limettioides Tan., low acid) and sour lemon (Citrus limon var. Eureka, high acid). Two aconitase isozymes were detected. One declined early in sour lemon fruit development, but was constant throughout sweet lime fruit development. Its reduction in sour lemon was associated with a decrease in aconitase activity in the mitochondrial fraction. Another isozyme was detected in sour lemon toward maturation, and was associated with an increase in aconitase activity in the soluble fraction, suggesting a cytosolic localization. The cyt‐Aco was cloned from lemon juice sac cells, but in contrast to the changes in isozyme activity, its expression was constant during fruit development. We present a model, which suggests that reduction of the mitochondrial aconitase activity plays a role in acid accumulation, while an increase in the cyt‐Aco activity reduces acid level toward fruit maturation.
Sucrose metabolism in spring and winter wheat in response to high irradiance, cold stress and cold acclimation
Authors: Savitch Leonid V. , Harney Tracy , Huner Norman P. A.
Published: July 2002

Effects of low‐temperature stress, cold acclimation and growth at high irradiance in a spring (Triticum aestivum L. cv. Katepwa) and a winter wheat (Triticum aestivum L. cv. Monopol) were examined in leaves and crowns with respect to the sucrose utilisation and carbon allocation. Light‐saturated and carbon dioxide (CO2)‐saturated rates of CO2 assimilation were decreased by 50% in cold‐stressed spring and winter wheat cultivars. Cold‐ or high light‐acclimated Katepwa spring wheat maintained light‐saturated rates of CO2 assimilation comparable to those of control spring wheat. In contrast, cold‐ or high light‐acclimated winter wheat maintained higher light and CO2‐saturated rates of CO2 assimilation than non‐acclimated controls. In leaves, during either cold stress, cold acclimation or acclimation to high irradiance, the sucrose/starch ratio increased by 5‐ to 10‐fold and neutral invertase activity increased by 2‐ to 2.5‐fold in both the spring and the winter wheat. In contrast, Monopol winter wheat, but not Katepwa spring wheat, exhibited a 3‐fold increase in leaf sucrose phosphate synthase (SPS) activity, a 4‐fold increase in sucrose:sucrose fructosyl transferase activity and a 6.6‐fold increase in acid invertase upon cold acclimation. Although leaves of cold‐stressed and high light‐grown spring and winter wheat showed 2.3‐ to 7‐fold higher sucrose levels than controls, these plants exhibited a limited capacity to adjust either sucrose phosphate synthase or sucrose synthase activity (SS[s]). In addition, the acclimation to high light resulted in a 23–31% lower starch abundance and no changes at the level of fructan accumulation in leaves of either winter or spring wheat when compared with controls. However, high light‐acclimated winter wheat exhibited a 1.8‐fold higher neutral invertase activity and high light‐acclimated spring wheat exhibited an induction of SS(d) activity when compared with controls. Crowns of Monopol showed higher fructan accumulation than Katepwa upon cold and high light acclimation. We suggest that the differential adjustment of CO2‐saturated rates of CO2 assimilation upon cold acclimation in Monopol winter wheat, as compared with Katepwa spring wheat, is associated with the increased capacity of Monopol for sucrose utilisation through the biosynthesis of fructans in the leaves and subsequent export to the crowns. In contrast, the differential adjustment of CO2‐saturated rates of CO2 assimilation upon high light acclimation of Monopol appears to be associated with both increased fructan and starch accumulation in the crowns.
Oxygen cycle in a hippo pool, Serengeti National Park, Tanzania
Authors: Wolanski Eric , Gereta Emmanuel
Published: July 2002

The vertical distribution of temperature and dissolved oxygen was sampled over 24 h in a pond of the Seronera River inhabited by hippos. The waters were very turbid (visibility < 2 cm) because of the high turbidity from animals trampling sediment and a permanent surface algal bloom sustained by faecal matter. Direct solar heating was restricted to the top few centimetres. This resulted in a strong thermal and density stratification inhibiting aeration of the water column. Waters at mid‐depth were aerated only when hippos stirred the water. Anoxic conditions were common in bottom water, these were occasionally ventilated in daytime by mixing due to bottom heating from decaying organic matter and at night by convective cooling. Poor water quality in hippo pools may affect wildlife.
Antibiotic resistance in Streptococcus pneumoniae isolated from children
Authors: Nasrin D , Collignon PJ , Wilson EJ , Pilotto LS , Douglas RM
Published: July 2002

Objective: To determine the level of antibiotic resistance in pneumoniae (S. pneumoniae) isolated from nasal swabs of healthy children.

Method: Cross‐sectional community survey.

Setting: Survey was undertaken in general practice settings in Canberra during March and April 1998.

Subjects: Four hundred and sixty‐one children under 3 years of age enrolled in a general practice trial of clinical practice guidelines for antibiotic use.

Outcome measures: Resistance to penicillin, erythromycin, co‐trimoxazole, tetracycline, chloramphenicol and cefotaxime among the isolates of S. pneumoniae.

Results: A total of 461 nasal swabs were collected and S. pneumoniae was isolated from 171 (37.1%). Penicillin resistance was found in 12.3% of these isolates, with high level resistance in 0.6%. Resistance rates were higher for cotrimoxazole (44.4%) and erythromycin (18.1%) than for penicillin. Multidrug resistance was found in 19% of these isolates. There was a significant association between the attendance at a day care centre and carriage of pneumococcus (53%vs 32%, odds ratio (OR) 2.4, 95% confidence interval (CI)1.5–3.7, P < 0.001). Children who attended day care centres and had received antibiotics during the 4 months prior to swab collection were three times more likely to carry an antibiotic‐resistant isolate than children who had neither attended a day care centre nor received antibiotics (68%vs 40%, OR 3.1, 95% CI 1.2–8.4, P = 0.02).

Conclusion: The level of antibiotic resistance in pneumococci from healthy children was of concern. Carriage of pneumococcus was significantly higher in children who attended a day care centre. Resistance was significantly correlated with antibiotic use in combination with day‐care attendance. These findings warrant more judicious use of antibiotics in children.
Naratriptan as Short‐Term Prophylaxis of Menstrually Associated Migraine: A Randomized, Double‐Blind, Placebo‐Controlled Study
Authors: Newman L. , Mannix L.K. , Landy S. , Silberstein S. , Lipton R.B. , Putnam D.G. Pait , Watson C. , Jöbsis M. , Batenhorst A. , O'Quinn S.
Published: July 2002

Objective.—To determine the efficacy of naratriptan 1‐mg and 2.5‐mg tablets twice daily compared with placebo as short‐term prophylaxis of menstrually associated migraine.

Background.—Approximately 60% of women with migraine report headaches associated with their menstrual cycles. Results from an open‐label study suggest that short‐term administration of sumatriptan is useful in the prophylaxis of menstrually associated migraine.

Methods.—A randomized, double‐blind, three‐arm, parallel‐group, placebo‐controlled study was conducted in women aged 18 years or older with a history of migraine with or without aura, as defined by the International Headache Society, of at least 6 months. Two dose strengths of naratriptan (1 mg, 2.5 mg) or identical‐appearing placebo tablets (1:1:1) were administered twice daily for 5 days starting 2 days prior to the expected onset of menses across four perimenstrual periods. End points included the number of menstrually associated migraines, total migraine days, peak headache severity, lost work/activity time, migraine‐related quality of life, and incidence of adverse events.

Results.—Overall, the intent‐to‐treat population comprised 206 women (naratriptan 1 mg, n = 70; naratriptan 2.5 mg, n = 70, and placebo, n = 66); 171 women treated four perimenstrual periods. Significantly more perimenstrual periods per subject treated with naratriptan, 1 mg, were headache‐free compared with placebo (50% versus 25%, P = .003). Naratriptan, 1 mg, significantly reduced the number of menstrually associated migraines (2.0 versus 4.0, P < .05) and menstrually associated migraine days (4.2 versus 7.0, P  <  .01) compared with placebo. More patients treated with naratriptan, 1 mg, were headache‐free across all treated perimenstrual periods compared with placebo (23% versus 8%). No difference in headache severity was observed in breakthrough headaches. The incidence and severity of adverse events was similar across treatment groups. Naratriptan, 2.5 mg, was not statistically superior to placebo for any measure.

Conclusions.—Naratriptan, 1 mg, with tolerability similar to placebo, is an effective, short‐term, prophylactic treatment for menstrually associated migraine.
Variation of Apigenin Quantity in Diploid and Tetraploid Chamomilla recutita (L.) Rauschert
Authors: Švehlíková V. , Repčák M.
Published: July 2002

Abstract: Apigenin, a pharmacologically important flavonoid of the chamomile plant, was analyzed at two ploidy levels during a three‐year period. This flavonoid accumulates in the ligulate florets of the anthodium. Higher percentages of apigenin were found in the ligulate florets of a diploid cultivar, in comparison with tetraploid plants. However, when the total apigenin (mg of compound) in the anthodium was evaluated, tetraploid individuals accumulated significantly more flavonoid. Moreover, in contrast to morphological quantitative characteristics of the anthodium, which varied significantly in different years, apigenin percentage in the ligulate florets was constant and not influenced by environmental conditions. Apigenin content was also found to change during inflorescence ontogeny. It represents the highest percentage of dry mass in young developing florets and anthodia of both cultivars. The total apigenin content of the anthodium, however, increases during flowering, although at later stages apigenin forms only a minor part of ligulate floret and anthodium dry mass.
Investigations on Net CO2 Assimilation, Transpiration and Root Growth of Fagus sylvatica Infested with Four Different Phytophthora Species
Authors: Fleischmann F. , Schneider D. , Matyssek R. , Oβwald W. F.
Published: July 2002

Abstract: In this contribution, we compare the influence of four different Phytophthora species on root development, net CO2 assimilation and transpiration of beech seedlings and saplings. Some few days after inoculation, photosynthesis and transpiration of seedlings infected with either P. citricola or P. cambivora were strongly reduced. In parallel, about 60 % of their root systems was destroyed compared to control plants. Three weeks after infection, all seedlings were dead, showing severe wilt symptoms on leaves. Remarkably, P. syringae and P. undulata infected seedlings and older beech plants did not differ from controls regarding photosynthesis and transpiration, although the root systems were damaged. However, a significant influence on net CO2 assimilation and transpiration of P. citricola infected beech saplings was visible after bud break in the following year. Some days before plants started to wilt, photosynthesis and transpiration were reduced to almost zero. Water use efficiency data (WUE) clearly indicated that infected plants suffered from severe drought.
Modulatable narrow-linewidth semiconductor lasers
Authors: Hollberg L. , Ohtsu M.
Published: July 2002

We find that using the technique of optical feedback locking, to narrow semiconductor linewidths, does not sacrifice the ability to modulate the laser’s frequency via the injection current. The frequency of a laser is stabilized to a separate Fabry–Perot reference cavity using resonant optical feedback and can be modulated efficiently at frequencies related by rational fractions to the free-spectral range of the reference cavity. This system can provide an array of narrow-linewidth, frequency-stable laser lines and shows promise for applications in frequency-division-multiplexed coherent communications, as well as laser frequency control and precision measurement systems.
Deposition and imaging of localized charge on insulator surfaces using a force microscope
Authors: Stern J. E. , Terris B. D. , Mamin H. J. , Rugar D.
Published: July 2002

A force microscope has been used in a new application to deposit and image localized surface charge on insulators. The lateral resolution for imaging surpasses that of currently available techniques. By applying voltage pulses to an etched nickel microscope tip, micron-sized regions of approximately 2×10−16 C were created on polymethylmethacrylate and single-crystal sapphire surfaces. After depositing the charge, high-contrast images of the charged region were obtained as contours of constant force gradient. The contrast was observed to decay over approximately 1 h, providing evidence for surface charge mobility. The minimum detectable surface charge was estimated to be on the order of 100 electrons.
Plateau and kink in P profiles diffused into Si: A result of strong bimolecular recombination?
Authors: Richardson W. B. , Mulvaney B. J.
Published: July 2002

A simplified five-species nonequilibrium kinetic model for phosphorus diffusion in silicon is presented. The resulting system of evolution equations is of a simple reaction-diffusion form with constant diffusivities. Using first-order thermodynamic estimates for reaction rates, the phosphorus profile after a 10 min predeposition shows the expected tail. However, only when the bimolecular generation-recombination rate is significantly increased does a kink-plateau result. This suggests that recombination may be the dominant factor in producing the known nonlinearity.
Low-temperature selective epitaxial growth of silicon at atmospheric pressure
Authors: Sedgwick T. O. , Berkenblit M. , Kuan T. S.
Published: July 2002

Epitaxial Si has been grown selectively on oxide-patterned substrates from 850 down to 600 °C for the first time in the Si-Cl-H system at atmospheric pressure. Si deposition was achieved by hydrogen reduction of dichlorosilane in an ultraclean system using a load lock. Epitaxy was achieved at low temperatures only when the hydrogen was purified to remove traces of H2O and O2 implying that an oxygen-free environment is the most important factor controlling epitaxy at low temperatures. Cross-sectional transmission electron micrographs reveal perfect crystallinity in the epitaxial layer and a totally clean and featureless interface between epitaxy and substrate.
Vertical cavity single quantum well laser
Authors: Jewell J. L. , Huang K. F. , Tai K. , Lee Y. H. , Fischer R. J. , McCall S. L. , Cho A. Y.
Published: July 2002

We have achieved room-temperature pulsed and cw lasing at 980 nm in an optically pumped vertical cavity structure grown by molecular beam epitaxy containing only a single quantum well (SQW) of In0.2Ga0.8As. Limited gain due to the extremely short active material length of 80 Å implies that losses due to absorption, scattering, and mirror transmission are extremely low. Using 10 ps pump pulses at 860 or 880 nm, the estimated energy density absorbed in the spacer was ∼12 fJ/μm2 at threshold, indicating a carrier density approximately four times that required for transparency. Continuous wave pumping yielded an estimated threshold absorbed intensity of ∼7 μW/μm2.
Single quantum wire semiconductor lasers
Authors: Kapon E. , Simhony S. , Bhat R. , Hwang D. M.
Published: July 2002

Single quantum wire GaAs/AlGaAs injection lasers were fabricated using organometallic chemical vapor deposition on V-grooved GaAs substrates. The quantum wire active region has a crescent-shaped cross section ∼100 Å thick and less than 1000 Å wide. Amplified spontaneous emission and lasing spectra of the quantum wire lasers exhibit effects due to transitions between quasi-one-dimensional subbands separated by ∼10 meV. Single quantum wire laser structures with tight optical confinement exhibited threshold currents as low as 3.5 mA for uncoated devices at room temperature.
Crack formation and thermal stress relaxation of GaAs on Si growth by metalorganic vapor phase epitaxy
Authors: Ackaert A. , Buydens L. , Lootens D. , Van Daele P. , Demeester P.
Published: July 2002

In this letter we report on the use of selective metalorganic vapor phase epitaxy growth as an original tool to alleviate the problem of random formation of microcracks in thick GaAs-on-Si heteroepitaxial layers. Through the use of a special mask design including the definition of sharp wedges in the SiO2 mask material, the thermally induced stress in the GaAs-on-Si layers preferentially relaxes at precisely located sites on the substrate. The influence of mask configuration, wedge shape, wedge orientation, and layer thickness on microcrack formation has been investigated. Results obtained show that small-area SiO2 wedges are useful for the definition of microcrack location, and thus eventually for optoelectronic device processing.
Conduction- and valence-band offsets in GaAs/Ga0.51In0.49P single quantum wells grown by metalorganic chemical vapor deposition
Authors: Biswas D. , Debbar N. , Bhattacharya P. , Razeghi M. , Defour M. , Omnes F.
Published: July 2002

We have independently estimated the conduction- and valence-band offsets ΔEc and ΔEv in GaAs/Ga0.51In0.49P quantum wells by measuring the capacitance transient resulting from thermal emission of carriers from the respective wells. The heterostructure samples were grown by low-pressure metalorganic chemical vapor deposition. The band offsets are extrapolated from the emission activation energies with appropriate corrections. The estimated values of ΔEc and ΔEv are 0.198 and 0.285 eV, respectively.
Spatial distribution of CH3 and CH2 radicals in a methane rf discharge
Authors: Sugai H. , Kojima H. , Ishida A. , Toyoda H.
Published: July 2002

Spatial distributions of neutral radicals CH3 and CH2 in a capacitively coupled rf glow discharge of methane were measured by threshold ionization mass spectrometry. A strong asymmetry of the density profile was found for the CH2 radical in the high-pressure (∼100 mTorr) discharge. In addition, comprehensive measurements of electron energy distribution, ionic composition, and radical sticking coefficient were made to use as inputs to theoretical modeling of radicals in the methane plasma. The model predictions agree substantially with the measured radical distributions.
First observation of the 29Si hyperfine spectra of silicon dangling bond centers in silicon nitride
Authors: Lenahan P. M. , Curry Sean E.
Published: July 2002

We report the first observation of 29Si hyperfine spectra of the deep trapping center which dominates the electronic properties of silicon nitride films. Our results provide the first conclusive evidence that the center is a silicon ‘‘dangling bond’’ defect. Our results also demonstrate that the unpaired electron is highly localized (about 75%) on the central silicon and that the wave function is primarily p type.
Effect of ozone annealing on the dielectric properties of tantalum oxide thin films grown by chemical vapor deposition
Authors: Isobe Chiharu , Saitoh Masaki
Published: July 2002

Effects of the heat treatment in flowing oxygen containing ozone of 0.5–1 vol % (O3 annealing) on the dielectric properties of the Ta2O5 thin film (100–200 Å) grown on the Si substrate by the chemical vapor deposition method were investigated. The leakage current was drastically reduced from more than 10−3 to 10−9 A/cm2 in an electric field of 3 MV/cm by the O3 annealing at 400 °C. It was also found that the leakage current was decreased and increased reversibly between alternate O3 annealing and O2 annealing (without ozone). These two states of the leakage current can be attributed to the reproducible change of the oxygen vacancies in the Ta2O5 film.
Efficient continuous wave operation of vertical-cavity semiconductor lasers using buried-compensation layers to optimize current flow
Authors: Orenstein M. , Stoffel N. G. , Von Lehmen A. C. , Harbison J. P. , Florez L. T.
Published: July 2002

The lateral definition of vertical-cavity surface-emitting lasers (VCSELs) using buried ion implantation and the optimization of this process are described. A VCSEL structure was grown, and lasers were laterally defined using deep proton implantation process. The buried implantation process created a funnel shape current path into the laser active region. By optimizing this process, a serial resistance of 50 Ω, 2.1 mW continuous wave output power and a 1 V lower ‘‘turn on’’ voltage were achieved for an optimum dose of 1×1013 ions/cm2 for 10×10 μm2 lasers. These improvements were achieved, while retaining the same low threshold current level of fully confined VCSELs.
Column V acceptors in ZnSe: Theory and experiment
Authors: Chadi D. J.
Published: July 2002

First-principles pseudopotential calculations are used in conjunction with extensive experimental data on P and As-derived acceptor states in ZnSe to develop a microscopic theory of their atomic and electronic properties. A structural model that explains the presence of both shallow and deep acceptor states, the thermal and optical quenching of photoluminescence lines, and the strong C3v symmetry of the electron-spin-resonance (ESR) active state is derived. The primary result of the calculations is that a neutral acceptor possesses two atomic configurations: a metastable effective-mass state with a small lattice relaxation labeled a0, and a deep A0 state with a large lattice distortion which is responsible for most of the observed properties of acceptors in ZnSe. Nitrogen impurities are proposed to give rise to a shallow acceptor state in either the small or large-lattice-relaxed limits. Extension of the results to ZnTe is discussed.
Development of high-strength, high-conductivity Cu–Ag alloys for high-field pulsed magnet use
Authors: Sakai Y. , Inoue K. , Asano T. , Wada H. , Maeda H.
Published: July 2002

A wire-conductor fabrication method has been developed for Cu–Ag alloys containing 2–60 at. % Ag where high strength and high conductivity conductors are obtained by cold working combined with intermediate heat treatment. The intermediate heat treatment is repeated 3–4 times at 350–450 °C for 1–2 h at appropriate stages of reduction of area. The optimized Cu-16 at. % Ag alloy wire with 99% reduction of area showed a tensile strength of 1000 MPa and an electrical conductivity of 80% IACS at room temperature. This suggests that the wires fabricated may be very promising for high-field pulsed magnet use.
Sub-μm, planarized, Nb-AlOx-Nb Josephson process for 125 mm wafers developed in partnership with Si technology
Authors: Ketchen M. B. , Pearson D. , Kleinsasser A. W. , Hu C.-K. , Smyth M. , Logan J. , Stawiasz K. , Baran E. , Jaso M. , Ross T. , Petrillo K. , Manny M. , Basavaiah S. , Brodsky S. , Kaplan S. B. , Gallagher W. J. , Bhushan M.
Published: July 2002

We have demonstrated a new planarized all-refractory technology for low Tc superconductivity (PARTS). With the exception of the Nb-AlOx-Nb trilayer preparation, the processing is done almost exclusively within an advanced Si technology fabrication facility. This approach has allowed us to leverage highly off of existing state-of-the-art lithography, metal etching, materials deposition, and planarization capabilities. Using chemical-mechanical polish as the planarization technique we have fabricated Josephson junctions ranging in size from 0.5–100 μm2. Junction quality is excellent with the figure of merit Vm typically exceeding 70 mV. PARTS has yielded fully functional integrated Josephson devices including magnetometers, gradiometers, and soliton oscillators.
Evaporated CoPt alloy films with strong perpendicular magnetic anisotropy
Authors: Lin C.-J. , Gorman G. L.
Published: July 2002

CoPt alloy films with large perpendicular magnetic anisotropy, perpendicular coercivity, and saturated perpendicular remanence are reported. These films were fabricated by e-beam evaporation at substrate temperatures near 200 °C and above. Well-(111)-textured Pt underlayers are shown to dramatically increase the perpendicular magnetic anisotropy of CoPt alloy films. The large perpendicular magnetic anisotropy is shown to be strongly related to good CoPt(111) texture, and not to the ordered tetragonal Co50Pt50 phase.
Neodymium-doped glass channel waveguide laser containing an integrated distributed Bragg reflector
Authors: Roman J. E. , Winick K. A.
Published: July 2002

An integrated, distributed Bragg reflector laser in a Nd-doped, glass, channel waveguide is reported for the first time. The waveguide is fabricated using Ag+ thermal ion exchange in a soda-lime-silicate-glass containing 2% Nd2O3 by weight. The distributed Bragg reflector grating is produced holographically in photoresist and then etched into the waveguide using argon ion milling. The device lases in a single longitudinal mode with a pump threshold of 50 mW and a slope efficiency of 1%.
Observation of magnetic focusing in two-dimensional hole systems
Authors: Heremans J. J. , Santos M. B. , Shayegan M.
Published: July 2002

We report the first observation of transverse magnetic hole focusing in high quality two-dimensional hole systems confined in square and triangular quantum wells grown on (311)A GaAs substrates. The results demonstrate ballistic hole transport over distances up to 11 μm and allow us to probe the constant energy contours in k-space for these two types of confinement.
Low-threshold InGaAs/GaAs/AlGaAs quantum-well laser with an intracavity optical modulator by impurity-induced disordering
Authors: Zou W. X. , Young D. B. , Law K-K. , Merz J. L.
Published: July 2002

A novel InGaAs/GaAs/AlGaAs QW laser with an intracavity optical modulator has been fabricated by impurity-induced disordering. Both the active and the passive sections of the device were built along an identical waveguide created by Si diffusion. The electrical isolation between the emitter and the modulator was increased by an order of magnitude by making the Zn diffusion selective in the longitudinal direction while self-aligned in the lateral direction. The typical device has a pulsed threshold of Ith=23 mA with zero bias on the modulator and an on–off ratio of 32:1 with a biasing swing of 1.8 V for normally-on operation.
Cholesteric/polymer dispersed light shutters
Authors: West J. L. , Akins R. B. , Francl J. , Doane J. W.
Published: July 2002

We report cholesteric/polymer dispersed (CPD) materials that switch from a reflecting, planar state to a relatively transparent, focal conic state. The reflective wavelength of the CPD materials can be continuously adjusted by varying the cholesteric pitch length. The electro-optic properties of these materials are similar to the recently reported polymer stabilized cholesteric materials; however, the polymer concentration is sufficient to provide a self-sustaining and self-adhering film, offering the potential of large area devices fabricated on flexible substrates.
Tapered active stripe for 1.5-μm InGaAsP/InP strained multiple quantum well lasers with reduced beam divergence
Authors: Doussiere P. , Garabedian P. , Graver C. , Derouin E. , Gaumont-Goarin E. , Michaud G. , Meilleur R.
Published: July 2002

We propose and demonstrate the application of an intracavity horizontally tapered (in width) active stripe to adiabatically reduce the output beam divergence of a 1.48-μm InGaAsP/InP strained quantum well laser. We achieve far-field full width at half-maximum divergences as low as 13° together with 100 mW emitted power into stable single transverse mode and 400 mA driving current. Maximum coupling efficiency to lensed single mode fiber of 73% is obtained.
Mobility enhancement in double δ-doped GaAs/InxGa1−xAs/GaAs pseudomorphic structures by grading the heterointerfaces
Authors: Wu C. L. , Hsu W. C. , Shieh H. M. , Liu W. C.
Published: July 2002

A novel double δ-doped heterostructure employing symmetric graded InGaAs quantum wells as the active channel grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) has been successfully fabricated. The proposed symmetrically graded InGaAs pseudomorphic structure manifests significantly improved electron mobility as high as 5300 (26 000) cm2/V s at 300 (77) K due to superior confinement and to the lower interface roughness scattering at GaAs/InGaAs heterointerfaces. We also carried out photoluminescence (PL) spectra and secondary-ion mass spectrometry (SIMS) profiles to confirm the quality of the proposed structures.
Effect of main chain length in the exciton spectra of helical-rod polysilanes as a model of a 5 Å wide quantum wire
Authors: Fujiki Michiya
Published: July 2002

Helical polysilane rods were regarded as a soluble, polymeric model of a quantum wire with a ∼5 Å width. Spectral characteristics of the lowest exciton band of the helix located at ∼4 eV in isooctane at 20 °C were first measured as a function of a wire length varying from ∼35 Å to ∼3000 Å. Both the extinction coefficient and the circular dichroism coefficient were found to tend to increase linearly as the logarithm of the wire length increases, whereas the exciton energy and the spectral band width approached limiting values.
High magnetic performance in mechanically alloyed Co-substituted Fe3O4
Authors: Ding J. , Reynolds T. , Miao W. F. , McCormick P. G. , Street R.
Published: July 2002

Nanocrystalline Co0.5Fe2.5O4 has been prepared by mechanical alloying and subsequent vacuum annealing. Significant increase of coercivity was observed after a postannealing at low temperatures in air. Magnetic annealing resulted in anisotropic sample with a coercivity of 2.8 kOe and a remanence of 81% of the saturation magnetization, providing a theoretical maximum energy product of 4 MG Oe.
Subharmonic Shapiro steps in high-T
c Josephson junctions
Authors: Terpstra D. , IJsselsteijn R. P. J. , Rogalla H.
Published: July 2002

We studied the response of high-Tc biepitaxial grain boundary junctions to 100 GHz radiation in the presence of a magnetic field. Integer as well as subharmonic constant voltage steps are observed, even at one-fifth of the voltage separation between integer (Shapiro) steps. Our results indicate that this behavior is due to the synchronized motion of Josephson vortices along the junction. We show that this effect is directly related to the width of the junction, and not to an array of weaker regions in the barrier.
Observations of dust trapping phenomena in the TRISTAN accumulation ring and a study of dust removal in a beam chamber
Authors: Saeki Hiroshi , Momose Takashi , Ishimaru Hajime
Published: July 2002

Using a gamma-ray detector and a television camera system for synchrotron light, high-energy bremsstrahlung and horizontal growth of the synchrotron light source were observed when sudden decrease in the electron-beam lifetime occurred due to dust trapping in the electron beam. Two types of beam current losses were found; one was a continuous beam current loss, and the other was a short-term beam current loss. High-energy bremsstrahlung at a location was observed in a short time and after that, the bremsstrahlung was not detected in spite of the occurrence of dust trapping phenomena. The fact suggests motions of the trapped dust particles in the longitudinal directions. Materials collected in the beam chamber are dust particles from ion pumps and dust particles made during the beam chamber processing for welding. Most of the collected dust particles were less than 2 mm in size and surfaces of some dust particles were melted with the electron beam. Simple analysis was carried out for the conditions necessary for a dust particle to be trapped, for motions of the trapped dust particle, and for interactions between the trapped dust particle and the electron beam. The analysis showed that a dust particle less than 3 mm in size, made of Al, can be trapped and that the trapped dust particle can move in the vertical and longitudinal directions.

The analysis also suggested that a dust particle in size of about 2 mm can be continuously trapped around the electron beam without being destroyed by the electron beam. Furthermore, the analysis explained the difference between the two types of beam current losses observed in the ring. Experiments which simulate the electron beam using a Cu wire in an evacuated beam chamber show that a dust particle (less than 70 μm) is trapped sufficiently. The experiments also coincide with theory for an attractive force acting to a conducting small particle. The calculated electric field of the electron beam and the calculated electric charge of dust particles given through the photoelectric effect in the TRISTAN accumulation ring are 100 times and 104–106 times higher than those of the simulated experiments, respectively. In the ring, the attractive force caused with the average electric field and with the expected charge is 10–103 times larger than that of the simulated experiments. Therefore, a dust particle (less than 2 mm) can be trapped sufficiently. An electrostatic dust collector using an electron beam and an electrostatic force are effective in removing all of the sample dust particles in the test chamber for the simulated experiments. A method to remove trapped dust particles using electrostatic electrodes is also discussed. It is expected that such electrodes can be useful for trapped dust particles moving in a longitudinal direction.
Piezoelectric inertial stepping motor with spherical rotor
Authors: Howald L. , Rudin H. , Güntherodt H.-J.
Published: July 2002

A piezoelectric inertial stepping motor for multiple rotations of small optical or mechanical components has been developed. The spherical rotor can be rotated about two or three orthogonal axes. Angular step resolution of 1 arcsec is achieved and the maximum speed lies in the range of degrees per second. The design is compact and eliminates mechanical backlash. Simple electronic control is achieved with only one wire per rotational axis. Low-voltage signals between 15 and 30 V are sufficient for driving the motor. No voltage is necessary for maintaining the rotor in a static position. A first application is described with laser optics as they are used in the detector of a scanning force microscope, offering the advantage of remote controlled adjustment.
Thin film position sensitive detector based on amorphous silicon p–i–n diode
Authors: Fortunato Elvira , Lavareda Guilherme , Vieira Manuela , Martins Rodrigo
Published: July 2002

The application of hydrogenated amorphous silicon (a–Si:H) to optoelectronic devices are now well established as a viable low cost technology and is presently receiving much interest. Taking advantage of the properties of a–Si:H based devices, single and dual axis large area (up to 80×80 mm2) thin film position sensitive detectors (TFPSD) based on a–Si:H p–i–n diodes have been developed, produced by plasma enhanced chemical vapor deposition. In this study, the main optoelectronic properties presented by the TFPSD as well as their behavior under operation conditions, concerning its linearity and signal to noise ratio, are reported.
The influence of strain energy on abnormal grain growth in copper thin films
Authors: Zielinski E. M. , Vinci R. P. , Bravman J. C.
Published: July 2002

Biaxial stress and strain in (100) and (111) oriented grains have been measured as a function of annealing temperature for a Cu film on an oxidized Si substrate which exhibits abnormal (100) grain growth. The observed behavior indicates isostrain averaging, which is consistent with grain growth that is controlled by strain energy density minimization. In contrast, two films which do not exhibit (100) abnormal grain growth appear to follow isostress averaging. Strain energy density minimization in this situation favors (111) grain growth.
Experimental investigation of a PtSi source and drain field emission transistor
Authors: Snyder John P. , Helms C. R. , Nishi Yoshio
Published: July 2002

A p-type PtSi source and drain, no ‘‘gap,’’ metal oxide semiconductor field effect transistor (MOSFET) has been successfully fabricated and experimentally investigated in detail down to 4.2 K. Gate curves (source current versus gate voltage) clearly show that, in the ‘‘on’’ state, the current flow mechanism from the source metal into the channel gradually changes from primarily thermal emission over the small ∼0.2 eV Schottky barrier to holes to completely field emission through the triangular Schottky barrier as the temperature is lowered below ∼100 K. Gate curves for different channel lengths also show minimal short channel effects down to 1.0 μm, in agreement with previous simulations. Drain curves (source current versus drain voltage) demonstrate that the drive current is comparable to that of a conventional MOSFET, and that the Schottky barrier is rendered transparent to the flow of holes when the device is strongly ‘‘on.’’
Instabilities and chaos in optically injected semiconductor lasers
Authors: Kovanis V. , Gavrielides A. , Simpson T. B. , Liu J. M.
Published: July 2002

We have experimentally obtained and theoretically analyzed a systematic map of the various instabilities induced in a semiconductor laser subject to strong optical injection as the amount of optical injection power and frequency detuning is varied. Two distinct islands of chaos have been identified in the injection-locked region. They are separated by regions of period one and period two solutions. Spontaneous emission noise obscures the observation of high periodic orbits.
Photoluminescence from wurtzite GaN under hydrostatic pressure
Authors: Kim Sangsig , Herman Irving P. , Tuchman J. A. , Doverspike K. , Rowland L. B. , Gaskill D. K.
Published: July 2002

The photoluminescence spectrum of undoped epitaxial wurtzite GaN layers on sapphire was measured for applied hydrostatic pressures up to 73 kbar at 9 K and up to 62 kbar at 300 K. The pressure dependences of the I2 exciton recombination line and the ‘‘yellow’’ band (2.2 eV band at ambient pressure) were examined at 9 and 300 K, and the series of donor-acceptor-pair emission lines was analyzed at 9 K. From the I2 lines, it was found that the band gap increases with pressure by 4.4±0.1 meV/kbar at 9 K and 4.7±0.1 meV/kbar at 300 K.
Radiative efficiency limit of terrestrial solar cells with internal carrier multiplication
Authors: Werner Jürgen H. , Brendel Rolf , Queisser Hans-Joachim
Published: July 2002

Charge multiplication by hot carriers in semiconductors opens a new perspective for improved photovoltaic energy conversion. Here, we estimate the theoretical limit for the efficiency of solar cells that make use of the best possible carrier multiplication and have the lowest possible recombination loss, i.e., radiative recombination only. For a terrestrial cell under 100 mW/cm2 air mass 1.5 global illumination, the uppermost efficiency amounts to 44.2%. Cells with internal carrier multiplication require a modified description of their saturation current density.
A new type of multiparticle three-dimensional imaging detector with subnanosecond time resolution
Authors: Amitay Z. , Zajfman D.
Published: July 2002

A new type of multiparticle three-dimensional imaging detector for the measurement of kinetic energy releases in molecular dissociation processes is presented. The detector makes use of the new generation of multianode photomultipliers to produce a timing signal for the simultaneous impact of several particles on the surface of a microchannel plate coupled to a phosphor screen. The detector is capable of subnanosecond time resolution (about 100 ps for the present setup) and position resolution (using a standard charge-coupled-device camera) of about 100 μm. The detector is suitable for ultrahigh-vacuum operation and can work with particles over a range of kinetic energies from keV to MeV.
Laser pulser for a time-of-flight laser radar
Authors: Kilpelä Ari , Kostamovaara Juha
Published: July 2002

A laser pulser for a pulsed time-of-flight laser radar is presented. The pulser is constructed using a single avalanche transistor in order to keep the schematic simple and to avoid the problems encountered when connecting several avalanche transistors in parallel. The schematic of the laser pulser was optimized and it was noticed that the optical peak pulse power of the laser can be increased significantly by adding a parallel capacitor to the laser. The measured increase of the optical power was up to 26%. The simulations show that the parallel capacitor and also the serial inductances of the components in the laser pulser play a significant role in adjusting the shape of the current pulse. In order to find the transistor, which gives the highest current, the properties of several transistor types were compared. It was noticed that there can be a great difference between the avalanche properties of a group of transistors even if they are of the same type.