bluuebunny/crossref_metadata_2025 huggingface dataset:
Antiproliferative actions of inhalational anesthetics: comparisons to the valproate teratogen
Authors: O'Leary Geraldine , Bacon Christopher L. , Odumeru Oladapo , Fagan Carl , Fitzpatrick Therese , Gallagher Helen C. , Moriarty Denis C. , Regan Ciaran M.
Published: July 2002

The antiproliferative potential of the volatile anesthetics isoflurane, enflurane and sevoflurane was determined and compared to the valproate teratogen. The in vitro system employed, a G1 phase proliferative arrest endpoint in C6 glioma, has served previously to discriminate agents with known teratogenic potential in vivo. Based on estimated IC50 values that were within twice the estimated minimum aveolar concentration value, the rank antiproliferative potency of the inhalational anesthetics employed was isoflurane=enflurane≫sevoflurane. Flow cytometric analysis of growth‐arrested cell populations failed to reveal specific accumulation in any cell cycle phase and the lack of a G1 phase‐specific effect was confirmed by the absence of a transient, time‐dependent sialylation event in synchronized cells. The antiproliferative mechanism of volatile anesthetics, and valproate, was mediated at hydrophobic binding sites, as increasing the hydration sphere of the drug‐micelle complex, using the hygroscopic qualities of the dimethylsulfoxide vehicle, completely reversed this effect. Our findings suggest inhalational anesthetics lack the specific in vitro characteristics of the valproate teratogen.
Manifestations of Delegative Democracy in Russian Local Politics: What Does It Mean for the Future of Russia?
Authors: Tsygankov Andrei
Published: July 2002

In attempts to describe post-communist politics adequately, this paper employs the concept of delegative democracy for analyzing Russia's local politics. It argues that the election rather than appointment by the President of local governors in Russia has facilitated the establishment of a system which can be generally described as delegative democracy. This regime inherits free and contested elections from the democratic system and non-democratic methods of power consolidation from the authoritarian system. As a mixture of those two hardly reconcilable types of political system, delegative democracy in Russia has gained a shape and reached a certain degree of stability during 1993–95. This gain may delay the consolidation of representative democracy in Russia for an indefinite time and eventually lead to a new level of economic stagnation and a return to authoritarianism.
Diurnal pattern of acetaldehyde emission by flooded poplar trees
Authors: Kreuzwieser Jürgen , Kühnemann Frank , Martis Albert , Rennenberg Heinz , Urban Wolfgang
Published: July 2002

The emission of the tropospheric trace gas acetaldehyde was determined in leaves of 4‐month‐old poplar trees (Populus tremula×P. alba) grown under controlled environmental conditions in a greenhouse. Using a dynamic cuvette system together with a high sensitivity laser‐based photoacoustic detection unit, rates of acetaldehyde emission were measured with the high time resolution of about 15 min. Submergence of the roots resulted in the emission of acetaldehyde by the leaves. The emission increased linearly before reaching more or less steady‐state values (ca 350 nmol m−2 min−1; ca 470 ng g−1 dry weight min−1) after approximately 6 h. Prolonged flooding of poplar trees resulted in a clear diurnal rhythm of acetaldehyde emission. The emission rates decreased when the light was switched off in the evening and peaked in the morning after the light was turned on again. This pattern significantly correlated with diurnal rhythms of stomatal conductance, photosynthesis, transpiration and with the concentrations of ethanol, the assumed precursor of acetaldehyde, in the xylem sap of flooded poplar trees. It may be concluded that under conditions of diminished stomatal conductance, acetaldehyde emission declines because its diffusive flux is reduced. Alternatively, reduced transpiration may decrease ethanol transport from the roots to the shoots and appreciable amounts of the acetaldehyde precursor ethanol are lacking in the leaves. The present results support the view that acetaldehyde emitted by the leaves of plants is derived from ethanol produced by alcoholic fermentation in submerged roots and transported to the leaves with the transpiration stream.
Reaction of protein chloramines with DNA and nucleosides: evidence for the formation of radicals, protein–DNA cross-links and DNA fragmentation
Authors: HAWKINS Clare L. , PATTISON David I. , DAVIES Michael J.
Published: July 2002

Stimulated phagocyte cells produce the oxidant HOCl, via the release of the enzyme myeloperoxidase and hydrogen peroxide. HOCl is important in bacterial cell killing, but excessive or misplaced generation can damage the host tissue and may lead to the development of certain diseases such as cancer. The role of HOCl in the oxidation of isolated proteins, DNA and their components has been investigated extensively, but little work has been performed on the protein—DNA (nucleosome) complexes present in eukaryotic cell nuclei. Neither the selectivity of damage in such complexes nor the possibility of transfer of damage from the protein to DNA or vice versa, has been studied. In the present study, kinetic modelling has been employed to predict that reaction occurs predominantly with the protein and not with the DNA in the nucleosome, using molar HOCl excesses of up to 200-fold. With 50–200-fold excesses, 50–80% of the HOCl is predicted to react with histone lysine and histidine residues to yield chloramines. The yield and stability of such chloramines predicted by these modelling studies agrees well with experimental data. Decomposition of these species gives protein-derived, nitrogen-centred radicals, probably on the lysine side chains, as characterized by the EPR and spin-trapping experi ments. It is shown that isolated lysine, histidine, peptide and protein chloramines can react with plasmid DNA to cause strand breaks. The protection against such damage afforded by the radical scavengers Trolox (a water-soluble α-tocopherol derivative) and 5,5-dimethyl-1-pyrroline-N-oxide suggests a radical-mediated process. The EPR experiments and product analyses have also provided evidence for the rapid addition of protein radicals, formed on chloramine decomposition, to pyrimidine nucleosides to give nucleobase radicals. Further evidence for the formation of such covalent cross-links has been obtained from experiments performed using 3H-lysine and 14C-histidine chloramines. These results are consistent with the predictions of the kinetic model and suggest that histones are major targets for HOCl in the nucleosome. Furthermore, the resulting protein chloramines and the radicals derived from them may act as contributing agents in HOCl-mediated DNA oxidation.
A model of information systems development project performance
Authors: Yetton Philip , Martin Andrew , Sharma Rajeev , Johnston Kim
Published: July 2002

abstract. Performance in information systems development (ISD) projects can be critical to business success. But, while project performance has been the subject of much debate, there has been little empirical research into its determinants. A survey of IS projects in the UK and New Zealand is analysed to test hypotheses concerning performance in terms of both project completion and budget (time‐cost) variances. Subsequently, a secondary analysis of the findings is used to build a more complete empirical model of project performance. The paper helps to develop the theory of IS development project performance and also has significant implications for practice. Discussion of the findings highlights the importance of project team dynamics, risk management, senior management support for strategic projects and user participation in ensuring successful IS project performance.
Unemployment and under‐employment in adults with vision impairment: The RVIB Employment Survey
Authors: McCarty Cathy A , Burgess Mary , Keeffe Jill E
Published: July 2002

Purpose: The purpose of this study was to describe the labour force status in Victorian adults with vision impairment and any factors associated with unemployment and under‐employment.

Methods: Participants were recruited in 1997. A telephone interview was conducted by trained interviewers.

Results: A total of 250 people participated. They ranged in age from 19 to 59 years (mean 40.7 years) and 119 (48%) were male. Thirty‐nine (16%) people regarded themselves to be totally blind. Nearly everyone (n = 241, 96%) had been employed at some time during their lifetime; however, only 149 (60%) were currently employed. The current rate of participation in the labour force was 73.3% (95% CL, 67.8%, 78.8%) and the current unemployment rate was 18.2% (95% CL, 12.6%, 23.9%). The current rate of under‐employment was 16.0% (95% CL, 10.7%, 21.4%). A total of 126 (50%) people had used services that help with employment at some stage; this was not significantly associated with current employment status (P > 0.10). The factors significantly associated with unemployment in multivariate analyses were a self‐report of eyesight limiting time available for work or other activities (OR = 3.02; 95% CL, 1.56, 5.85) and currently looking for work (OR = 5.92; 95% CL, 2.94, 11.9); never having worked was of borderline significance (OR = 5.26; 95% CL, 0.85, 32.7) as a result of the small numbers of people surveyed. The only factor significantly associated with under‐employment was self‐employment (OR = 5.46; 95% CL, 1.95, 15.3).

Discussion: Results from this study reveal that visual function is not a predictor of labour force status. The relatively low use of specialty employment services and the rather high rate of discouraged job seekers suggest that the employment outcomes of people who use these services should be investigated further, and that attention should be directed at improving retention of employment in people with vision impairment.
Evaluating the outcomes of low vision rehabilitation
Authors: Harper Robert , Doorduyn Kate , Reeves Barney , Slater Linda
Published: July 2002

The requirement for those providing healthcare to measure outcomes raises the fundamental question of how these should be measured. Both the scale of the low vision population and the different models of care proposed make it a pressing need to determine outcomes using valid and reliable measures. In this study we describe the development and piloting of a questionnaire designed to meet this requirement. The questionnaire was piloted on 56 subjects with age‐related macular degeneration (ARMD). Test‐retest reliability of the questionnaire was estimated using a further sample of 28 subjects with ARMD. Pilot testing confirmed the feasibility of administering the questionnaire to an elderly population with ARMD. A total of 87% of the sample reported using an LVA (65% on a daily basis), predominantly for a reading task. The number of tasks an LVA was used for, its frequency of use, length of continuous use and ease of use are significantly associated with the rating of an LVA as important/less important (P<0.0001), but the acuity achieved with the device is not significantly associated with rated importance (P=0.11), reinforcing doubt about the validity of visual function outcomes. The limitations of this pilot study and earlier case series in describing the outcomes of low vision care are discussed and a randomised controlled trial using a broad range of outcomes is proposed in order to fully describe the effectiveness of low vision rehabilitation and inform the debate about models of care.
Guar Gum Reduces Postprandial Hypotension in Older People
Authors: Jones Karen L. , MacIntosh Caroline , Su Yu‐Chung , Wells Fiona , Chapman Ian M. , Tonkin Anne , Horowitz Michael
Published: July 2002

OBJECTIVE: To determine whether slowing of gastric emptying and glucose absorption with guar gum would reduce the fall in blood pressure after an oral glucose load in older subjects.

DESIGN: A randomized, experimental, cross‐over study.

SETTING: Department of Nuclear Medicine, Royal Adelaide Hospital, Adelaide, SA, Australia.

PARTICIPANTS: Ten healthy subjects, age 67 to 78.

MEASUREMENTS: Simultaneous measurements of gastric emptying, blood pressure, blood glucose, serum insulin, and oral glucose absorption (3‐O‐methyl‐D‐glucose [3‐OMG]) on two occasions after ingestion of 300 mL water containing 50 g glucose and 30 mL lemon juice, 3 g 3‐OMG labeled with 99mTc‐sulphur colloid; with or without 9 g guar gum. Blood pressure and gastric emptying were monitored for 180 minutes.

RESULTS: The magnitude of the falls in systolic (P = .02), diastolic (P < .05), and mean arterial (P = .05) blood pressure were less, and gastric emptying slower (P < .05), after guar. Blood glucose, insulin, and 3‐OMG concentrations were reduced (P < .001 for all) by guar. 3‐OMG concentrations were inversely related to the intragastric retention of glucose (r = −0.72, P = .02) and blood pressure was inversely related to 3‐OMG (r = −0.64, P < .05) after the drink without guar. The blood glucose concentration was related to 3‐OMG (r > 0.64, P < .05).

CONCLUSION: Guar gum reduces the magnitude of the fall in blood pressure after oral glucose. Slowing of gastric emptying and glucose absorption may represent a novel approach to the treatment of postprandial hypotension.
Are Aggressive Treatment Strategies Less Cost‐Effective for Older Patients? The Case of Ventilator Support and Aggressive Care for Patients with Acute Respiratory Failure
Authors: Hamel Mary Beth , Phillips Russell S. , Davis Roger B. , Teno Joan , Desbiens Norman , Lynn Joanne , Tsevat Joel
Published: July 2002

OBJECTIVES:A common assumption is that life‐sustaining treatments are much less cost‐effective for older patients than for younger patients. We estimated the incremental cost‐effectiveness of providing mechanical ventilation and intensive care for patients of various ages who had acute respiratory failure.

DESIGN:Retrospective analysis of data on acute respiratory failure from Study to Understand Prognoses and Preferences for Outcomes and Risks of Treatments (SUPPORT).

SETTING:Acute hospital.

PARTICIPANTS:1,005 with acute respiratory failure; 963 received ventilator support and 42 had ventilator support withheld.

MEASUREMENTS:We studied 1,005 patients enrolled in a five‐center study of seriously ill patients (SUPPORT) with acute respiratory failure (pneumonia or acute respiratory distress syndrome and an Acute Physiology Score ≥10) requiring ventilator support. For cost‐effectiveness analyses, we estimated life expectancy based on long‐term follow‐up of SUPPORT patients and estimated utilities (quality‐of‐life weights) using time‐tradeoff questions. We used hospital fiscal data and Medicare data to estimate healthcare costs. We divided patients into three age groups (<65, 65–74, and ≥75 years); for each age group, we performed separate analyses for patients with a ≤50% probability of surviving at least 2 months (high‐risk group) and those with a> 50% probability of surviving at least 2 months (low‐risk group).

RESULTS:Of the 963 patients who received ventilator support, 44% were female; 48% survived 6 months; and the median (25th, 75th percentile) age was 63 (46, 75) years. For the 42 patients for whom ventilator support was withheld, the median survival was 3 days. For low‐risk patients (>50% estimated 2‐month survival), the incremental cost (1998 dollars) per quality‐adjusted life‐year (QALY) saved by providing ventilator support and aggressive care increased across the three age groups ($32,000 for patients age <65, $44,000 for those age 65–74, and $46,000 for those age ≥75). For high‐risk patients, the incremental cost‐effectiveness was much less favorable and was least favorable for younger patients ($130,000 for patients age <65, $100,000 for those age 65–74, and $96,000 for those age ≥75). When we varied our assumptions from 50% to 200% of our baseline estimates in sensitivity analyses, results were most sensitive to the costs of the index hospitalization.

CONCLUSIONS:For patients with relatively good short‐term prognoses, we found that ventilator support and aggressive care were economically worthwhile, even for patients 75 years and older. For patients with poor short‐term prognoses, ventilator support and aggressive care were much less cost‐effective for adults of all ages.
Evaluation of Different Methods for Assessing Intracellular Fluid in Healthy Older People: A Cross‐Validation Study
Authors: Dittmar Manuela , Reber Helmut
Published: July 2002

OBJECTIVES: To cross‐validate existing anthropometric and bioimpedance equations to establish their validity and accuracy for estimating intracellular water (ICW) in healthy older Germans and to develop a new equation with improved accuracy and precision for predicting ICW from multifrequency bioimpedance analysis (MFBIA).

DESIGN: Cross‐validation study.

SETTING: University of Mainz.

PARTICIPANTS: One hundred fifty‐five healthy volunteers aged 60 to 80 years (77 men, 78 women; mean ages ± standard deviation 67.7 ± 4.8 and 68.6 ± 5.5 years, respectively).

MEASUREMENTS: ICW was measured by whole‐body counting of 40potassium (40K) (40K method) as the reference method and compared by cross‐validation techniques against five existing bioimpedance and three anthropometric prediction equations. A new equation for estimating ICW from MFBIA was developed using the 40K method as criterion method.

RESULTS: Compared with the 40K method, the existing bioimpedance and anthropometric equations showed large prediction errors in ICW estimates for older men (−32.3% to +37.7%) and women (−34.2% to +26.6%), depending significantly and positively on ICW volume and inversely on weight. A new equation for estimating ICW from MFBIA was developed (R2 = 0.933, standard error of the estimate (SEE) = 0.92 L) involving phase angle at 5 kHz, impedance, height, and gender, with data from 100 subjects chosen at random. Cross‐validation on an independent group (n = 55, R2 = 0.958, SEE = 0.68 L) showed no significant bias (0.013 ± 1.52 L).

CONCLUSIONS: Published bioimpedance and anthropometric prediction equations are not applicable to older Germans because they might be population‐specific. The bioimpedance equation of the manufacturer of the bioimpedance analyzer used in this study provides accurate estimates of ICW for normal weight, but not overweight, older men. The newly developed equation improves accuracy and precision of ICW estimates by MFBIA.
Low frequency TENS is less effective than high frequency TENS at reducing inflammation‐induced hyperalgesia in morphine‐tolerant rats
Authors: Sluka Kathleen A. , Judge Mary A. , McColley Michele M. , Reveiz Pauley M. , Taylor Bethany M.
Published: July 2002

Both transcutaneous electrical nerve stimulation (TENS) and morphine are commonly used for relief of pain. Extensive research has been done on the effectiveness of each of these two methods for pain relief when given independently. However, very little literature exists examining the effectiveness of their combined use. Systemically administered morphine activates μ opioid receptors and when administered for prolonged periods results in analgesic tolerance. Low (4 Hz) and high (100 Hz) frequency TENS activate μ ‐ and δ ‐opioid receptors, respectively, It is thus possible that TENS would be less effective in morphine‐tolerant subjects. The current study investigated the effectiveness of high‐ and low‐frequency TENS in the reversal of hyperalgesia in inflamed rats that were morphine‐tolerant. Morphine tolerance was induced by subcutaneous implantation of morphine pellets over 10 days. Knee joint inflammation was induced by injection of kaolin and carrageenan into the knee joint cavity. Secondary heat hyperalgesia was tested by measuring the paw withdrawal latency to radiant heat (1) before pellet implantation (either morphine or placebo), (2) after pellet implantation and before inflammation, (3) after inflammation and (4) after TENS. Both high (100 Hz) and low (4 Hz) frequency TENS caused nearly 100% inhibition of secondary hyperalgesia in animals receiving placebo pellets. In contrast, the hyperalgesia in morphine‐tolerant animals with knee joint inflammation was unaffected by low frequency TENS but fully reversed by high frequency TENS. These results suggest that patients who are tolerant to morphine may respond better to high frequency TENS than to low frequency TENS.
Epiphytic Ferns for Sale: Influence of Commercial Plant Collection on the Frequency of Platycerium stemaria (Polypodiaceae) in Coconut Plantations on the Southeastern Ivory Coast
Authors: Porembski S. , Biedinger N.
Published: July 2002

Abstract: On the southeastern Ivory Coast, two coconut plantations were compared with regard to the frequency of the epiphytic fern Platycerium stemaria on coconut trees as influenced by plant collecting for commercial purposes. At each of the two sites, 250 coconut trees were investigated for the presence of P. stemaria and signs of collecting activity. General species richness of vascular epiphytes at the study sites was low, with only three other epiphytic ferns (Asplenium sp., Microgramma owariensis, Phymatodes scolopendria) being present. At study site no. 1, which was located directly behind several flower stalls offering P. stemaria for sale, the number of coconuts bearing living P. stemaria was significantly lower than at site no. 2 with no flower stalls in the immediate surroundings. At site no. 1, the frequency of P. stemaria was lowest in the neighbourhood of the flower stalls and increased with distance. Within a distance of less than 50 m from the flower stalls, ca. 70 % of the coconuts showed signs of P. stemaria collecting activity. Compared with site no. 1, the number of palm trees with living P. stemaria at site no. 2 was considerably higher (ca. 20 %) and only three coconut trees showed signs of Platycerium collection. Over much of the Ivorian rain forest region where the forest has been cut or converted into agricultural land, plantation trees are important phorophytes (in particular cocoa trees). In many West African regions plantation trees form the last remaining sites for vascular epiphytes, which often occur with considerable abundance. In the Ivory Coast, the collecting of P. stemaria in coconut plantations causes locally a drastic decline in the population size. However, much more threatening to the long‐term maintenance of epiphyte communities in plantations is their conversion into non‐tree plantations (e.g., pineapples, bananas) or their replacement by urban structures and tourist facilities.
Threshold pump power of a solar-pumped dye laser
Authors: Lee Ja H. , Kim Kyung C. , Kim Kyong H.
Published: July 2002

Threshold solar power for dye laser pumping has been determined by measuring the gain of a rhodamine 6G dye laser amplifier at various solar-simulated irradiances on an amplifier cell. The measured threshold was 20 000 solar constants (2.7 kW/cm2) for the dye volume of 2×5×40 mm3 and the optimum dye concentration of 1×10−3 M. The threshold is about one-third of that achievable with a high-intensity solar concentrator.
Epitaxial growth of YBa2Cu3O7−x thin films by a laser evaporation process
Authors: Roas B. , Schultz L. , Endres G.
Published: July 2002

Thin films of YBa2 Cu3 O7−x have been grown epitaxially in c-axis orientation on 〈100〉 SrTiO3 by pulsed excimer laser evaporation from a stoichiometric 1-2-3 target. The substrate temperature was adjusted between 720 and 780 °C, and the oxygen partial pressure during the deposition was chosen in the range 0.1–0.3 mbar. Cooled to ambient temperature in situ for 1 h in flowing oxygen gas, the films showed complete diamagnetism and zero resistance at 90 K with a transition width of 2 K. Critical current densities of 2.2×106 A/cm2 in zero magnetic field and 1.5×105 A/cm2 at 2 T were measured at 77 K. The resistivity at 100 K was about 60 μΩ cm.
Low-loss substrate for epitaxial growth of high-temperature superconductor thin films
Authors: Simon R. W. , Platt C. E. , Lee A. E. , Lee G. S. , Daly K. P. , Wire M. S. , Luine J. A. , Urbanik M.
Published: July 2002

A perovskite-like single-crystal substrate material has been investigated that simultaneously permits epitaxial growth of 1-2-3 superconductor films and possesses desirable rf properties of low dielectric constant and loss tangent. The lattice constant of 3.792 Å provides a lattice match to within 1% of the a axis of 1-2-3. Sputtered films of erbium-barium-copper-oxide have been produced on (100) LaAlO3 substrates that exhibit sharp resistive transitions at 90 K (ΔT=1K), bulk superconductivity as determined by ac susceptibility measurements, and nearly single-crystal growth as evidenced by x-ray diffraction and high-resolution scanning electron microscopy. The high-frequency dielectric properties of LaAlO3 were experimentally investigated at several temperatures. The low-frequency dielectric constant was measured to be 15 and the microwave loss tangent ranged from 6×10−4 at room temperature to 5×10−6 at 4 K.
Nanoindentation study of the mechanical properties of copper-nickel multilayered thin films
Authors: Cammarata R. C. , Schlesinger T. E. , Kim C. , Qadri S. B. , Edelstein A. S.
Published: July 2002

The mechanical properties of multilayered Cu-Ni thin films with bilayer thicknesses of 1.6–12 nm were investigated by a nanoindentation technique. Force-displacement curves generated during loading and unloading of a diamond tip indenter were used to determine the hardness and elastic properties of the films. No enhancement in the elastic properties (supermodulus effect) was seen, but an enhancement in the hardness was observed. It is suggested that the enhancement, which displayed a Hall–Petch-type behavior, can be understood as owing to dislocation pinning at the interfaces analogous to the mechanism of grain boundary hardening.
Impurity-induced 900 °C (2×2) surface reconstruction of SrTiO3(100)
Authors: Andersen Jens E. T. , Mo/ller Preben J.
Published: July 2002

A p(2×2)surface reconstruction is observed over the 800–900 °C range for SrTiO3 (100), the temperature range which is used in the oxygen anneal of Y, Ba, Cu layers on SrTiO3 (100) substrates in the synthesis of high Tc superconducting thin films. As observed by Auger electron spectroscopy, high-temperature annealing causes calcium to segregate to the surface. Initially, at a Ca content of 3% upon a SrO-terminated SrTiO3 (100) surface, the Ca atom is incorporated in a superstructure, which is attributed to multiple scattering across the two topmost interfaces. When the surface Ca content is below 1% the p(2×2) surface reconstruction is induced. The p(2×2) surface reconstruction disappears when the calcium content is removed.
Multilayer YBa2Cu3Ox-SrTiO3-YBa2Cu3Ox films for insulating crossovers
Authors: Kingston John J. , Wellstood Frederick C. , Lerch Philippe , Miklich Andrew H. , Clarke John
Published: July 2002

We describe our procedure for fabricating YBa2Cu3Ox-SrTiO3-YBa2Cu3Ox thin-film trilayer structures. Each film is grown in situ by excimer laser deposition onto a heated (100)MgO substrate. The geometrical configuration of each layer is defined by a metal mask; the vacuum chamber is opened between depositions to allow the targets and masks to be changed. The lower and upper YBa2Cu3Ox films in the best trilayer structure had transition widths of 1 and 3 K (10–90%), respectively, and transition temperatures (zero resistance) of 87 K. The resistance between the YBa2Cu3Ox films at 77 K was 108 Ω for an overlapping area of 0.2 mm2, corresponding to a SrTiO3 resistivity of 4×109 Ω cm.
Room-temperature operation of an InGaAsP double-heterostructure laser emitting at 1.55 μm on a Si substrate
Authors: Sugo Mitsuru , Mori Hidefumi , Tachikawa Masami , Itoh Yoshio , Yamamoto Mitsuo
Published: July 2002

The room-temperature operations of an InGaAsP double-heterostructure (DH) laser emitting at 1.55 μm on a Si substrate is reported. A pulsed threshold current as low as 46 mA has been measured for a ridge waveguide laser with a 4 μm strip width and a 200 μm cavity length. This successful laser operation is due to the high crystalline quality of the DH structure with full width at half maximum of x-ray rocking curves as low as 110 arcsec grown on a Si substrate by the organometallic vapor phase epitaxy/vapor mixing epitaxy hybrid method. A correlation between the optical property of an InGaAsP DH and its crystalline quality is also discussed.
Carrier density dependent photoconductivity in diamond
Authors: Pan L. S. , Kania D. R. , Pianetta P. , Landen O. L.
Published: July 2002

Single-crystal natural diamonds have been intrinsically photoexcited using 2 ps laser pulses. Electron and hole mobilities and decay times are examined as a function of induced carrier density. Two major density dependent effects are observed. First, at high induced carrier densities, a dramatic decrease in the carrier mobility is observed. This is attributed to carrier-carrier scattering between the electrons and the holes. A model describing carrier-carrier scattering in silicon and germanium has been scaled to diamond. Second, the decay time of the electrons decreases as the initially photoexcited density increases. A simple one-level recombination model successfully explains this density dependence. The combination of these two effects results in a minimum in the measured photoconductive decay times.
Properties of metal/diamond interfaces and effects of oxygen adsorbed onto diamond surface
Authors: Mori Yusuke , Kawarada Hiroshi , Hiraki Akio
Published: July 2002

The current-voltage characteristics of Schottky diodes fabricated using as-grown diamond films depend on the electronegativities of metals. However for diamond films oxidized by boiling in a saturated solution of CrO in H2SO4 or by exposure to an oxygen plasma, this dependence vanishes. This is because of the adsorption of oxygen onto the surfaces of diamond synthesized by chemical vapor deposition. It has been shown by x-ray photoelectron spectroscopy that very little oxide is present on the as-grown surfaces, but that at least submonolayer oxygen coverage is present on the oxidized surfaces.
Atomic layer and unit cell layer growth of (Ca,Sr)CuO2 thin film by laser molecular beam epitaxy
Authors: Kanai Masaki , Kawai Tomoji , Kawai Shichio
Published: July 2002

Thin films of (Ca,Sr)CuO2, the parent material of high Tc cuprate superconductors, have been formed by the laser ablation method under molecular beam epitaxial condition, and the growth mechanism has been investigated with reflection high-energy electron diffraction (RHEED). Analyses of RHEED patterns and intensity oscillations show that this material grows with two-dimensional layer growth. When all the metal elements are supplied simultaneously in NO2 atmosphere, the layer growth occurs with the unit-cell layer of (Ca,Sr)CuO2. Furthermore, it has become evident that the growth unit can be separated into Ca (Sr) atomic layer and CuOx atomic layer by monitoring the RHEED intensity oscillation. The successive supply of each metal element leads to one atomic layer growth of this material.
Simulations of high-rate diamond synthesis: Methyl as growth species
Authors: Goodwin D. G.
Published: July 2002

The results of numerical simulations of two high-rate diamond growth environments (oxygen-acetylene torch and dc arcjet) are reported. The calculations account in detail for boundary-layer transport, gas-phase chemistry, and gas-surface chemistry. Diamond growth rates are calculated self-consistently with the gas-phase concentrations, using a recently proposed methyl growth mechanism. The calculated growth rates agree well with the measured values, indicating that this growth mechanism can account for both high- and low-rate diamond growth.
Beam target interaction during growth of YBa2Cu3O7−x by the laser ablation technique
Authors: Cohen A. , Allenspacher P. , Brieger M. M. , Jeuck I. , Opower H.
Published: July 2002

It was proven by powder x-ray diffractometry and by energy dispersive x-ray analysis (EDX) that after ablation of the ceramic YBa2Cu3O7−x target by the excimer laser pulses the original composition of the target remained unchanged. The depth of ablation was measured as a function of the energy density of the laser beam. The absorption coefficient for ablation, in case of ceramic material with a density of 5.4 g/cm3, was α=4.45×104 cm−1 and the minimum energy density was 2.5 J/cm2. The temperature that the ablated material was subjected to, in the energy range of 2.5–3.4 J/cm2, did not exceed 970 °C.
Temperature dependence of GaAs-AlGaAs vertical cavity surface emitting lasers
Authors: Tell B. , Brown-Goebeler K. F. , Leibenguth R. E. , Baez F. M. , Lee Y. H.
Published: July 2002

The temperature performance of GaAs-AlGaAs vertical cavity surface emitting lasers has been studied from 60 to −160 °C. A minimum threshold current occurs considerably below room-temperature where the wavelength of the Fabry–Perot resonance of the cavity matches the wavelength of the maximum gain of the active region. The laser quantum efficiency increases for decreasing temperature, exhibiting a change of slope near the temperature of the threshold minimum.
Doping in semiconductors with variable activation energy
Authors: Tsang W. T. , Schubert E. F. , Cunningham J. E.
Published: July 2002

A concept of doping that permits for the first time the freedom to design the desired activation energy of a dopant in a semiconductor is introduced and demonstrated. This doping engineering (DE) may also offer the possibility of achieving dopings in semiconductors in which a normally employed doping process is not successful, such as in wide band-gap II-VI semiconductors. Experimentally, we demonstrated that the normal activation energy, ∼19–25 meV of berrylium (Be) in GaAs was reduced to 4 meV in DE GaAs/δ-Al0.3Ga0.7As(Be) sample.
Polymer coated silver halide infrared fibers as sensing devices for chlorinated hydrocarbons in water
Authors: Krska R. , Rosenberg E. , Taga K. , Kellner R. , Messica A. , Katzir A.
Published: July 2002

Fiberoptic evanescent wave spectroscopy (FEWS) based on AgClBr fibers and a Fourier transform infrared (FTIR) spectrometer was used for the first time to measure chlorinated hydrocarbons (CH) in water. A minimum detection limit lower than 10 mg/l was achieved by coating the fiber with low density polyethylene (LDPE), which shows reversible enrichment of CH. The response of the sensor to CH diffusion through the polymer layer was analyzed theoretically and the results were found to be in good agreement with the experiments.
Identification of paramagnetic Pb+3 defects in lead zirconate titanate ceramics
Authors: Warren W. L. , Tuttle B. A. , McWhorter P. J. , Rong F. C. , Poindexter E. H.
Published: July 2002

We report the first observation of positively charged Pb+3 defect centers in lead zirconate titanate (PZT) ceramics using electron paramagnetic resonance. The charged traps were optically generated using ultraviolet light energies roughly corresponding to the band gap of PZT (3.4 eV). The interpretation of the 207Pb+3 hyperfine parameters indicates that the defect’s unpaired electron is approximately 48% localized on the Pb nucleus. These observations may be of considerable importance since they prove that charged carriers created by optical excitation become trapped and form charged paramagnetic defects.
Metal semiconductor field effect transistor based on single crystal GaN
Authors: Asif Khan M. , Kuznia J. N. , Bhattarai A. R. , Olson D. T.
Published: July 2002

In this letter we report the fabrication and characterization of a metal semiconductor field effect transistor (MESFET) based on single crystal GaN. The GaN layer was deposited over sapphire substrate using low pressure metalorganic chemical vapor deposition. MESFET devices were fabricated on isolated mesas using TiAu for the source and drain ohmic contacts and silver for the gate Schottky. For devices with a gate length of 4 μm (channel opening, i.e., source to drain separation of 10 μm), a transconductance of 23 mS/mm was obtained at −1 V gate bias. Complete pinch-off was observed for a gate potential of −12 V.
New contacting technique for thin film resistance measurements perpendicular to the film plane
Authors: Gijs M. A. M. , Giesbers J. B. , Lenczowski S. K. J. , Janssen H. H. J. M.
Published: July 2002

Using microlithography, we have fabricated Au thin film structures for resistance measurements with current directed perpendicular to the film plane. We propose a novel contact geometry for accurate measurement of the very low metallic perpendicular resistance, which prevents any disturbing influence from the much larger resistance of the contact leads. Our experimental results are well explained by a classical model and our interpretation is independently confirmed by a three-dimensional electrostatic calculation based on the finite element method.
1.5 μm band efficient broadband wavelength conversion by difference frequency generation in a periodically domain-inverted LiNbO3 channel waveguide
Authors: Xu C. Q. , Okayama H. , Kawahara M.
Published: July 2002

Efficient 1.5 μm band wavelength conversion by difference frequency generation (DFG) in a periodically domain-inverted LiNbO3 channel waveguide is demonstrated, and DFG efficiency as high as 40% W−1 cm−2 is obtained. Nearly constant wavelength conversion efficiency has been confirmed over a broad wavelength range of 30 nm, which is the largest value ever reported.
Effect of diamond facet on the electrical properties of Pt/BF+2 ion implanted polycrystalline diamond contacts
Authors: Cheng Y. T. , Lin S. J. , Hwang J.
Published: July 2002

Very good quality of polycrystalline diamond films with different major facets were grown on the Si(100) substrates at different position of the plasma ball in a microwave plasma enhanced chemical vapor deposition chamber. Pt/BF+2 ion implanted polycrystalline diamond contacts were fabricated to examine the effect of diamond facets on their electrical properties. The Pt/diamond contact exhibited Schottky characteristics for the diamond film with major facet (100). In contrast, the Pt/diamond contact exhibited ohmic behavior for the diamond film with major facet (111). The I-V characteristics of the Pt/BF+2 ion implanted polycrystalline diamond contacts were not reliable if the diamond facet factor was not considered.
Magnetron sputter deposition with high levels of metal ionization
Authors: Rossnagel S. M. , Hopwood J.
Published: July 2002

A new deposition technique has been developed which combines conventional magnetron sputter deposition with a rf inductively coupled plasma (RFI). The RFI plasma is located in the region between the magnetron cathode and the sample position, and is set up by a metal coil immersed in the plasma. A large fraction of the metal atoms sputtered from the magnetron cathode are ionized in the RFI plasma. By placing a negative bias on the sample, metal ions are then accelerated across the sample sheath and deposited at normal incidence. Results from a gridded energy analyzer configured with a microbalance collector and located at the sample position indicate the level of ionization is low at a few mTorr and rises to ≳80% at pressures in the 25–35 mTorr range. Optical measurements of metal ion and neutral emission lines show scaling of the relative ionization to higher discharge powers. Significant cooling of the plasma electron temperature is observed when high concentrations of metal atoms were sputtered into the plasma.
Experimental evidence of different crystalline forms in chemical vapor deposited diamond films
Authors: Rossi M. , Vitali G. , Terranova M. L. , Sessa V.
Published: July 2002

Diamond films have been obtained on Ta polycrystalline substrates from mixtures of methane and hydrogen by the hot-filament chemical vapor deposition technique. The structural characteristics of the polycrystalline deposits have been investigated by reflection high energy electron diffraction (RHEED), while the surface morphologies have been observed by scanning electron microscopy or carbon replica transmission electron microscopy. For one of the films, the formation of thermal spikes during the deposition process yielded a structure giving a RHEED pattern with d spacings and intensities not corresponding to the already identified carbon and diamond phases. On the base of the RHEED pattern the observed phase has been identified as a face-centered-cubic lattice, belonging to the space group F4̄3m and ascribed to a so-called X-diamond polytype.
Visible electroluminescence from porous silicon diodes with an electropolymerized contact
Authors: Koshida Nobuyoshi , Koyama Hideki , Yamamoto Yuko , Collins George J.
Published: July 2002

An electrochemical technique is proposed to form a solid-state electrical contact of porous Si (PS) electroluminescence (EL) diodes. The PS layers were created by anodizing nondegenerate p-type single-crystal Si wafers in an HF solution, and then electrochemically polymerizing semitransparent conducting polypyrrole films into the PS layer. The current-voltage characteristics and the voltage and current dependence of the EL intensity were significantly improved in comparison with our experimental PS-EL diode with a thin Au film contact. Our result suggests that the electrode impregnation into PS is very useful for an efficient and stable EL operation.
Very high-efficiency semiconductor wafer-bonded transparent-substrate (AlxGa1−x)0.5In0.5P/GaP light-emitting diodes
Authors: Kish F. A. , Steranka F. M. , DeFevere D. C. , Vanderwater D. A. , Park K. G. , Kuo C. P. , Osentowski T. D. , Peanasky M. J. , Yu J. G. , Fletcher R. M. , Steigerwald D. A. , Craford M. G. , Robbins V. M.
Published: July 2002

Data are presented demonstrating the operation of transparent-substrate (TS) (AlxGa1−x)0.5In0.5P/GaP light-emitting diodes (LEDs) whose efficiency exceeds that afforded by all other current LED technologies in the green to red (560–630 nm) spectral regime. A maximum luminous efficiency of 41.5 lm/W (93.2 lm/A) is realized at λ∼604 nm (20 mA, direct current). The TS (AlxGa1−x)0.5In0.5P/GaP LEDs are fabricated by selectively removing the absorbing n-type GaAs substrate of a p-n (AlxGa1−x)0.5In0.5P double heterostructure LED and wafer bonding a ‘‘transparent’’ n-GaP substrate in its place. The resulting TS (AlxGa1−x)0.5In0.5P/GaP LED lamps exhibit a twofold improvement in light output compared to absorbing-substrate (AS) (AlxGa1−x)0.5In0.5P/GaAs lamps.
Growth of cubic boron nitride on Si(100) by neutralized nitrogen ion bombardment
Authors: Lu Ming , Bousetta A. , Sukach R. , Bensaoula A. , Walters K. , Eipers-Smith K. , Schultz A.
Published: July 2002

Highly cubic phase and stoichiometric boron nitride films were deposited on Si(100) substrates using a neutralized nitrogen beam and electron beam evaporation of boron. High intensity, focused, and low-energy neutralized nitrogen beam was supplied using a newly developed neutralizer atomic beam ion source (NABS) adapted to a Kaufman-type ion source. The films were grown at substrate temperatures in the range 400–500 °C and a boron evaporation rate of 0.2 A/s. Infrared transmittance spectra of the films showed that a highly cubic phase (80%) was obtained in the area of the focused beam. These films were compared to those obtained using similar conditions but with the NABS disconnected from the ion source, and it was found that the cubic phase content decreases drastically (10%). The results show that the NABS was the determining factor in enhancing the formation of the cubic boron nitride films. Furthermore, the addition of Ar to N, which is reported to increase the momentum transfer and promote the formation of the cubic phase, did not play a significant role when the NABS was used.
Textured growth of cubic boron nitride film on nickel substrates
Authors: Song Zhizhong , Zhang Fangqing , Guo Yongping , Chen Guanghua
Published: July 2002

Textured cubic boron nitride (c-BN) films have been deposited on (220) oriented crystallized polycrystalline nickel substrate by a hot filament assisted rf plasma chemical vapor deposition method. X-ray diffraction shows that the films are (220) preferentially grown, the peak ratio of (220) to the main peak [i.e., the (111) peak] is about 5.2. The scanning electron microscopy images exhibit regular grain shapes. Most of the grains are rectangular, also indicating the (220) growth. The grain size is about 5 μm. The well-matched Ni lattice with c-BN, the catalytic effect of Ni, and the appropriate rf bias are considered to be the key factors in the textured growth.
Intense erbium-1.54-μm photoluminescence from 2 to 525 K in ion-implanted 4H, 6H, 15R, and 3C SiC
Authors: Choyke W. J. , Devaty R. P. , Clemen L. L. , Yoganathan M. , Pensl G. , Hässler Ch.
Published: July 2002

We have observed intense line spectra in the neighborhood of 1.54 μm from erbium-implanted samples of 4H, 6H, 15R, and 3C SiC. Samples were implanted to a fluence of about 1013 erbium ions/cm2 using four implant energies. An anneal at 1700 °C in a SiC cavity was used. The temperature dependence of the integrated luminescence intensity from 1.49 to 1.64 μm varies very little from 2 to 400 K. No major differences are found for the spectra of the hexagonal and rhombohedral polytypes but there is a difference for cubic SiC (3C SiC).
High dislocation densities in high efficiency GaN-based light-emitting diodes
Authors: Lester S. D. , Ponce F. A. , Craford M. G. , Steigerwald D. A.
Published: July 2002

The electrical, optical, and structural properties of light emitting diodes (LEDs) fabricated from the III–V nitride material system have been studied. LEDs with external quantum efficiencies as high as 4% were characterized by transmission electron microscopy and found to contain dislocation densities in excess of 2×1010 cm−2. A comparison to other III–V arsenide and phosphide LEDs shows that minority carries in GaN-based LEDs are remarkably insensitive to the presence of structural defects. Dislocations do not act as efficient nonradiative recombination sites in nitride materials. It is hypothesized that the benign character of dislocations arises from the ionic nature of bonding in the III–V nitrides.
Miniature liquid-3He refrigerator
Authors: Torre J. P. , Chanin G.
Published: July 2002

The use of a cryopump and high-pressure, internal storage of the cryogen makes it possible to miniaturize a one-shot recyclable 3He refrigerator while at the same time improving its performance. Because of their simplified interface requirements, such refrigerators are readily incorporated into existing 4He cryostats, allowing a convenient extension of their operating range down to 0.3 K. An analysis of the parameters describing refrigerator performance (condensation time, heat transfer to the 4He bath, lifetime, and refrigeration power) leads to the definition of an optimized refrigerator. Measured performance characteristics of a miniature [2-l standard temperature and pressure (STP) of 3He] refrigerator used in laboratory and stratospheric balloon-borne experiments are given.