bluuebunny/crossref_metadata_2025 huggingface dataset:
3′‐Hydroxymethyl 2′‐deoxynucleoside 5′‐triphosphates are inhibitors highly specific for reverse transcriptase
Authors: Kutateladze Tamara V. , Kritzyn Anatoli M. , Florentjev Vladimir L. , Kavsan Vadim M. , Chidgeavadze Zurab G. , Beabealashvilli Robert Sh.
Published: July 2002

dNTP(3′‐OCH3), a 3′‐O‐methyl derivative of dNTP, is a chain terminator substrate for DNA synthesis catalyzed by AMV reverse transriptase. The enzyme seems to be the only DNA polymerase susceptible to the inhibitor while all the other DNA polymerases tested are fully resistant to the nucleotide analog. The resistant polymerases are: E. coli DNA polymerase I, Klenow's fragment of DNA polymerase I, phage T4 DNA polymerase, calf thymus DNA polymerase α, rat liver DNA polymerase β and calf thymus terminal deoxyribonucleotidyl transferase.
Inactivation of the galactose transport system in Saccharomyces cerevisiae
Authors: DeJuan Carmen , Lagunas Rosario
Published: July 2002

The galactose transport system of Saccharomyces cerevisiae consists of one component which shows a K
m value of approx. 4 mM in growing cells. A rapid and irreversible inactivation of this transport is detected on impairment of protein synthesis. This inactivation shows the following characteristics: (i) it is due to changes in the K
m and V
max of the transport system; (ii) it follows first‐order kinetics; (iii) it is an energy‐dependent process and is stimulated by the presence of an exogenous carbon source; (iv) fermentable substrates stimulate inactivation more efficiently than non‐fermentable substrates.
A catalytic subunit of calpain possesses full proteolytic activity
Authors: Yoshizawa Toshio , Sorimachi Hiroyuki , Tomioka Shigeo , Ishiura Shoichi , Suzuki Koichi
Published: July 2002

Previous studies on the refolding of calpain, a heterodimer comprising a catalytic 80 kDa subunit and a regulatory 30 kDa subunit, indicate that both subunits are required for the expression of full protease activity. We reexamined the conditions for refolding of calpain and found that under optimized conditions the renatured 80 kDa subunit has full enzyme activity even in the absence of the 30 kDa subunit. The 30 kDa subunit stabilizes the 80 kDa subunit rather than enhancing its activity. The theory that calpain functions as a dimer requires reexamination.
A quantitative secondary structure analysis of the 33 kDa extrinsic polypeptide of photosystem II by FTIR spectroscopy
Authors: Ahmed A. , Tajmir-Riahi H.A. , Carpentier R.
Published: July 2002

In chloroplast photosystem II, the extrinsic polypeptide of 33 kDa is involved in the stabilization the Mn cluster in charge of water splitting and in the fulfillment of the Ca2+‐cofactor requirement for oxygen evolution. The conformational analysis of the purified 33 kDa extrinsic polypeptide was carried out using FTIR spectroscopy with its self‐deconvolution and second derivative resolution enhancement as well as curve‐fitting procedures. The FTIR spectroscopic results showed that the isolated polypeptide is characterized by a major proportion β‐sheet conformation (36%) with 27% α‐helix, 24% turn, and 13% β‐antiparallel structures.
l‐Arginine depletion by arginase reduces nitric oxide production in endotoxic shock: an electron paramagnetic resonance study
Authors: Bune A.J. , Shergill J.K. , Cammack R. , Cook H.T.
Published: July 2002

Nitric oxide (NO) synthesis was measured in the liver, lung, spleen and kidney of lipopolysaccharide‐treated male rats using the nitric oxide spin trap, iron (II)‐diethyldithiocarbamate (FeDETC2). Nitric oxide formation in vivo was determined by the increase in intensity of the characteristic triplet hyperfine EPR spectrum of [NO‐FeDETC2]. Intravenous bovine liver arginase, at a dose which completely depleted circulating arginine, significantly reduced the formation of nitric oxide in these tissues. The general decrease in NO levels was confirmed by the decrease in plasma nitrite levels. These results directly demonstrate that NO formation in endotoxic shock depends on extracellular arginine; depletion of plasma arginine may be a useful therapeutic strategy.
The Optimal Allocation of Pension Fund Assets
Authors: Potts Tom L. , Reichenstein William
Published: July 2002

This study asks which assets in individual should hold indirectly in a pension in order to maximize total portfolio return, where the totaI portfolio consists of assets held directly outside of pensions pIus the pro rata share of pension assets. The answer depends upon whether the individual actively or passively manages the nonpension portion of the total portfolio. Most individuals should place high-yield stocks in the pension fund. But active investors should place low-yield growth stocks in the pension, while very passive investors should place bonds in the pension fund. Rei~tatement of capital gains excbon would usually make corporate bonds the optimal pension asset.
Life Insurance Companies as Investment Managers
Authors: Kleiman Robert T. , Sahu Anandi P.
Published: July 2002

This paper examines the attractiveness of the equity portfolios of life insurance companies as an alternative investment to mutual funds. In particular, this study analyzes the risk- adjusted investment performance of the stock portfolios of ltfe insurance companies, attributable to their stock selection and market timing abilities. Using conventional measures of risk-adjusted portfolio performance, we find that ltfe insurance companies exhibit performance similar to mutualfunds. The evidence suggests that the ltfe insurance companies, like their mutual fund counterparts, fail to exhibit differential stock selection or market timing abilities that are statistically significant. While the risk-adjusted investment performance of the two investment vehicles is similar, the variable annuity contracts of life insurance companies may offer an edge over mutualfunds due to their ability to defer taxes.
Determinants of Household Check Writing
Authors: Murphy Neil B.
Published: July 2002

In recent years, there has been a simultaneous deregulation of interest ceilings on household deposits and a dramatic deployment of automatic teller machines (ATM) by the banking industry. At one time, there was a belief that the U.S. would evolve into a “checkless society” because of the development of electronic funds transfer systems such as the ATM. That has clearly not happened. The purpose of this paper is to estimate the impacts of both the use of A TM and the change in pricing due to deregulation on household check writing. The source of the data is a survey of households conducted by the Board of Governors of the Federal Reserve System. The results of the tests indicate that use of electronic banking services had no discernible impact on check writing while different methods of pricing checking account services did have a substantial impact on check writing.
The presence and subcellular localization of caspase 3‐like proteinases in plant cells
Authors: Korthout Henrie A.A.J. , Berecki Géza , Bruin Wouter , van Duijn Bert , Wang Mei
Published: July 2002

Caspases play a very important role in initiating and executing apoptotic processes in animal cells. In this study we show that plant mitochondria were able to initiate the activation of caspase 3 in a Xenopus cell free system. Caspase 3‐like activity was found to be present in plant cells and could only be inhibited by the specific caspase 3 inhibitor N‐acetyl‐Asp‐Glu‐Val‐Asp‐fluoromethylketone (Ac‐DEVD‐fmk) and not by cysteine protease inhibitors. By micro‐injection of the caspase 3 substrate in living Chara cells we showed that caspase 3‐like activity was mainly present in the cytosol rather than in the vacuole. This is the first time that in vivo caspase 3‐like activity has been demonstrated in plants.
CHILDBEARING EXPERIENCES OF ABUSED HISPANIC WOMEN
Authors: Records Kathie , Rice Michael
Published: July 2002

Previous research has documented that abused childbearing women have longer and more difficult labors than non‐abused women. Prevalence of abuse differs depending on the ethnic group involved. Hispanic women experience higher rates of abuse and endure higher rates before reporting abuse than do Caucasian women. The purpose of this study was to explore the experience of childbearing for abused Hispanic women to provide guidance for clinical practice and further research. Cognitive dissonance theory guided the study. A sample of seven abused Hispanic women was recruited from a rural prenatal clinic. Criteria for selection of subjects included self‐identification as Hispanic, less than 24 months postpartum, disclosure of abuse status, and willingness to be interviewed in English or Spanish. An acculturation scale and demographic form were completed. Interviews were conducted individually, and data were analyzed by using Van Kaam's 12‐step psycho‐phenomenologic technique. Findings indicated that subjects experienced the normal responses associated with having a baby. However, the women also demonstrated a kindled neuroendocrine trauma response that was based on, and often similar to, their prior abuse experiences. The kindled emotional response was triggered by the normative events of childbearing. Understanding of the childbearing experiences of abused Hispanic women will facilitate the development of cultural‐specific interventions that may ease the difficulties associated with birth for these women.
Selective Flocculation and Precipitation for the Improvement of Virus‐Like Particle Recovery from Yeast Homogenate
Authors: Tsoka Sophia , Ciniawskyj Ohla C. , Thomas Owen R. T. , Titchener‐Hooker Nigel J. , Hoare Michael
Published: July 2002

The purification of an intracellular product from a complex mixture of contaminants after cell disruption is a common problem in processes downstream of fermentation systems. This is particularly challenging for the recovery of particulate (80 nm in diameter) multimeric protein products, named virus‐like particles (VLPs), from cell debris and other intracellular components. Selective flocculation for debris removal followed by selective precipitation of the target protein can be used as a preclarification step to aid purification. In this paper, selective borax flocculation of cell debris in yeast homogenate, followed by selective poly(ethylene glycol) precipitation of VLPs are defined with a view to demonstrating their potential in aiding the initial clarification stages of the purification sequence. The translation from laboratory scale to pilot scale operation is addressed, demonstrating the challenge of scale‐up of solid‐liquid separation stages for biological particle processing.
Model Process for Removal of Caseins from Milk of Transgenic Animals
Authors: Morçöl Tülin , He Qing , Bell Steve J. D.
Published: July 2002

We describe a method for selective removal of caseins from milk. The method was developed as a model for transgenic milk processing. Raw cow milk spiked with nonmilk proteins was chosen as the model to resemble transgenic animal milk containing recombinant proteins. The most important elements of the process are (1) “deconstruction” of casein micelles in milk by destroying their Ca2+ core using a chelating agent (EDTA), thus freeing any protein that might be entrapped in casein aggregates, and (2) “reconstruction” of micelles by providing them with a new Ca2+ core, thus precipitating them away from the whey proteins, and the protein of interest. Calcium phosphate particles (CAP) were used to reform the disrupted casein micelles. The crystal clear supernatant fraction generated by this method provided >90% recovery and 6‐ to 13‐fold concentration of the desired protein. Product‐rich supernatant contained no detectable casein residues, as silver‐stained SDS‐PAGE and Western blot analyses demonstrated.
High‐Yield Recovery of Xanthan by Precipitation with Isopropyl Alcohol in a Stirred Tank
Authors: Galindo Enrique , Albiter Verónica
Published: July 2002

Microbial polysaccharides (xanthan being the most successful example) are important commercial products having a wide range of applications in a variety of industries. Production processes of xanthan typically involve aseptic fermentation and a number of downstream operations. A key issue in the economics of the production of biopolymers such as xanthan is its recovery. This operation is commonly performed by precipitation with low molecular weight aliphatic alcohols. In this work, three particular aspects were evaluated: the effect of the electrolyte concentration (KCl), the amount of alcohol, and the heat treatment of the fermentation broths on the precipitation yield and on the quality of the final product. A Rushton turbine and a marine propeller were used as mixing devices. Dehydrated−reconstituted fermentation broths to which the ionic strength was adjusted (with NaCl) to a value close to that exhibited by an actual broth, behaved&—;from the precipitation point of view&—;as fresh broths. The Rushton turbine gave slightly higher yields as stirring speed was higher. On the other hand, the marine propeller showed a pronounced drop in yield as stirring speed was increased. In both cases, composition analysis (xanthan as equivalent sugars, nitrogen, and ash) revealed that lower yields were associated with higher precipitate purities. This means that mixing conditions importantly determine the quality of the product and can be fixed to meet a given specification. However, it is clear that a compromise has to be established between quantity and quality. The heat treatment applied to the broths substantially improved the precipitation yields, compared with nontreated broths. On the basis of precipitable solids, using 2% (w/wgum) KCl as a electrolyte and two volumes of alcohol per volume of broth, a recovery of 80% was achieved in the heat‐treated broths (as compared with 65% in the nontreated broths). When 2 volumes of alcohol per volume of broth were used, the increase of electrolyte (KCl) concentration from 2% (w/wgum) to 3% increased precipitation yield (on the basis of precipitable solids) from 70 to 80%. Increasing further the electrolyte concentration (up to 5%, w/wgum) improved the yield only slightly. In general, the effect of KCl concentration on the precipitation y ield was very similar in heat‐treated broths than in nontreated broths. When 3% (w/wgum) KCl was used as electrolyte and 1:1.4 volumes of alcohol per volume of broth were employed in order to precipitate xanthan from heat‐treated, reconstituted broths (containing 25 kg m−3of xanthan), yields up to 99% (based on xanthan) were achieved.
Thermodynamics of Metabolic Pathways for Penicillin Production: Analysis of Thermodynamic Feasibility and Free Energy Changes During Fed‐Batch Cultivation
Authors: De Noronha Pissarra Pedro , Nielsen Jens
Published: July 2002

This paper describes the thermodynamic analysis of pathways related to penicillin production in Penicillium chrysogenum. First a thermodynamic feasibility analysis is performed of the l‐lysine pathway of which one of the precursors for penicillin biosynthesis (α‐aminoadipic acid) is an intermediate. It is found that the l‐lysine pathway in P. chrysogenum is thermodynamically feasible and that the calculated standard Gibbs free energy values of the two enzymes controlling the pathway flux indicate that they operate far from equilibrium. It is therefore proposed that the regulation of α‐aminoadipate reductase by lysine is important to maintain a high concentration of α‐aminoadipate in order to direct the carbon flux to penicillin production. Secondly the changes in Gibbs free energy in the penicillin biosynthetic pathway during fed‐batch cultivation were studied. The analysis showed that all reactions in the pathway were thermodynamically irreversible at physiological conditions during fed‐batch cultivations. Furthermore it was observed that the higher thermodynamic driving force of IAT could explain why penicillin is mainly formed from isopenicillin N in a one‐step reaction, as it has been previously proposed.
Improved Erythromycin Production in a Genetically Engineered Industrial Strain of Saccharopolyspora erythraea
Authors: Minas Wolfgang , Brünker Peter , Kallio Pauli T. , Bailey James E.
Published: July 2002

An industrial erythromycin production strain of Saccharopolyspora erythraea spp. was used to demonstrate that careful genetic engineering can significantly improve productivity. The chromosomally integrated Vitreoscilla hemoglobin gene (vhb) was shown to enhance the final titer of erythromycin by some 70% compared to the original S. erythraea spp. Overall, specific erythromycin yields were about 2.5 g of erythromycin/g of total protein for S. erythraea::vhb but <1 for the S. erythraea spp. The maximum rates of biosynthesis were 57.5 mg of erythromycin/(L/h) and 24.3 mg/(L/h) for the recombinant strain S. erythraea::vhb and S. erythraea spp., respectively. Overall space−time yield was 100% higher for the S. erythraea::vhb fermentation (1.1 g of erythromycin/(L/day)) than for the S. erythraea spp. fermentation (0.56 g of erythromycin/(L/day)). The genetic stability of the recombinant strain was high, and no selective pressure was needed throughout the cultivations. Expression of functional Vitreoscilla hemoglobin throughout the cultivations was verified by CO difference spectrum assays.
Structured Model‐Based Analysis and Control of the Hyaluronic Acid Fermentation by Streptococcuszooepidemicus: Physiological Implications of Glucose and Complex‐Nitrogen‐Limited Growth
Authors: Cooney M. J. , Goh L.‐T. , Lee P. L. , Johns M. R.
Published: July 2002

The hyaluronic acid (HA) fermentation by Streptococcus zooepidemicus under anaerobic and aerated conditions in glucose‐complex media was well described by a structured, two‐compartment model. The two‐compartment model framework was found to be robust, easily adaptable, and able to predict the transient consumption of substrates and formation of products. Aerobic culture produced a substantially higher concentration of HA than an equivalent anaerobic culture; however biomass‐specific growth rate and yield were lower due to partial inhibition by hydrogen peroxide. The model was then used to investigate the physiological implications of glucose and complex‐nitrogen‐limited growth on the anaerobic production of hyaluronic acid (HA). Glucose‐limited growth agreed well with model predictions, although the HA molecular weight was lower than expected even though the absolute HA concentration remained unaffected. Heterofermentative growth was also observed for growth rates below 0.1 h−1. Despite a comparatively lower specific growth rate, the biomass yield was higher; however the metabolic shift did not significantly affect HA production. For complex‐nitrogen‐limited growth, diauxic growth on complex‐nitrogen (yeast extract) was observed and explained by partitioning the array of nitrogen components into two distinct but homogeneous pools. While nitrogen‐limited growth was found to increase the HA to biomass yield, like that observed under glucose‐limited growth, the resulting HA molecular weight was reduced.
Studies on the relevance of the glycan at Asn-52 of the α-subunit of human chorionic gonadotropin in the αβ dimer
Authors: ERBEL Paul J.A. , HASELEY Simon R. , KAMERLING Johannis P. , VLIEGENTHART Johannes F.G.
Published: July 2002

Glycosylation of Asn-52 of the α-subunit (αAsn-52) is required for bioactivity of the αβ-dimeric human chorionic gonadotropin (hCG), although at a molecular level the effect of the glycan at αAsn-52 is not yet understood. To study the role of this glycan for heterodimer stability, the β-subunit was recombined in solution with either the α-subunit or the α-subunit enzymically deglycosylated at αAsn-52. Enzymic deglycosylation avoids modification of the glycans at αAsn-78 and disturbing the protein folding. The efficiency of recombination after 16h is 80%, independent of whether αAsn-52 is glycosylated or not. The dissociation constant of the hCG complex, with or without the glycan at αAsn-52, is less than 1×10−5s−1, indicating that the glycan at αAsn-52 does not contribute significantly to the stability of the dimer. CD and NMR spectra indicate a local conformational difference between both αβ-dimeric hCG variants, most probably involving amino acids of the hCG β-subunit close to the glycan at αAsn-52. These data explain the native-like receptor-binding abilities of hCG lacking the glycan at αAsn-52. It is proposed that for bioactivity the glycan at αAsn-52 is necessary for inducing and stabilizing a conformational change in hCG upon binding to the receptor, resulting in activation of the signal-transduction pathway.
Extreme prematurity and school outcomes
Authors: Buck G.M. , Msall M.E. , Schisterman E.F. , Lyon N.R. , Rogers B.T.
Published: July 2002

The purpose of this study was to assess the impact of extreme prematurity on three global measures of school outcomes. Using a matched cohort design, exposed infants comprised all surviving singleton infants 28 weeks gestation born at one regional neonatal intensive care hospital between 1983 and 1986 (n = 132). Unexposed infants comprised randomly selected full‐term infants ( 37 weeks gestation) frequency matched on date of birth, zip code and health insurance. All children were selected from a regional tertiary children’s centre serving western New York population. Standardised telephone interviews elicited information on grade repetition, special education placement and use of school‐based services. Unconditional logistic regression was used to estimate odds ratios (OR) and corresponding 95% confidence intervals (CI) adjusted for potential confounders for children without major handicaps. Extreme prematurity was associated with a significant increase in risk of grade repetition (OR = 3.22; 95% CI = 1.63, 6.34), special education placement (OR = 3.16; 95% CI = 1.14, 8.76) and use of school‐based services (OR = 4.56; 95% CI = 1.82, 11.42) in comparison with children born at term, even after controlling for age, race, maternal education, foster care placement and the matching factors. These findings suggest that survivors of extreme prematurity remain at risk of educational underachievement.
GENETIC AND PHYSIOLOGICAL VARIATION IN PIGMENT COMPOSITION OF EMILIANIA HUXLEYI (PRYMNESIOPHYCEAE) AND THE POTENTIAL USE OF ITS PIGMENT RATIOS AS A QUANTITATIVE PHYSIOLOGICAL MARKER
Authors: Stolte Willem , Kraay Gijsbert W. , Noordeloos Anna A. M. , Riegman Roel
Published: July 2002

Genetic variation of pigment composition was studied in 16 different strains of Emiliania huxleyi (Lohm.) Hay et Mohler in batch culture. Distinct strain‐dependent differences were found in the ratios of fucoxanthin, 19′‐hexanoyloxyfucoxanthin, and 19′‐butanoyloxyfucoxanthin, hampering the use of these individual pigments as a taxonomic marker at the species level. The molar ratio of total carotenoids to chl a, however, was constant for all strains tested. In addition, the pigment composition of one axenic strain (L) of E. huxleyi at different growth rates in light‐, nitrate‐, and phosphate‐limited continuous cultures was analyzed quantitatively. The pigments fucoxanthin and 19′‐hexanoyloxyfucoxanthin correlated closely under all conditions. From steady‐state rate calculations, it is hypothesized that 19′‐hexanoyloxyfucoxanthin is synthesized from fucoxanthin, with light as a modulating factor. The net rate of synthesis of diatoxanthin depended both on the concentration of diadinoxanthin (its partner in the xanthophyll cycle) and on light, illustrating its photoprotective function in the xanthophyll cycle. In axenic strain L, the ratio of total fucoxanthins to chl a correlated strongly with photon flux density and can potentially be used to assess the physiological status with respect to irradiance in field populations. In multispecific bloom situations, the ratio of diadinoxanthin plus diatoxanthin to total fucoxanthins could be used as an alternative indicator for the light‐dependent physiological state of E. huxleyi, provided that no other chromophytes are present. Application of these correlations to mesocosm data from the literature has so far provided no evidence that E. huxleyi blooms form only at inhibiting light levels, as previously suggested.
Evolution of Chlorophyll Degradation: The Significance of RCC Reductase
Authors: Hörtensteiner S. , Rodoni S. , Schellenberg M. , Vicentini F. , Nandi O. I. , Qui Y‐L. , Matile Ph.
Published: July 2002

Abstract: In angiosperms the key process of chlorophyll breakdown in senescing leaves is catalyzed by pheophorbide a oxygenase and RCC reductase which, in a metabolically channeled reaction, cleave the porphyrin macrocycle and produce a colourless primary catabolite, pFCC. RCC reductase is responsible for the reduction of the C20/C1 double bond of the intermediary catabolite, RCC. Depending on plant species, RCC reductase produces one of the two C1 stereoisomers, pFCC‐1 or pFCC‐2. Screening of a large number of taxa for the type of RCCR revealed that the isomer produced is uniform within families. It also revealed that type RCCR‐2 is predominant; RCCR‐1 seems to represent a recent derivation which in unrelated lineages has evolved independently from RCCR‐2. A third type of pFCC was produced by RCCR from basal pteridophytes and some gymnosperms; its structure is unknown. Collectively, the data suggest that the pathway of chlorophyll breakdown is very conserved in vascular plants. RCCR appears to represent a decisive addition to the catabolic pathway: it allows terrestrial plants to metabolize the porphyrin part of the chlorophyll molecule to photodynamically inactive final products that are stored in the vacuoles of senescing mesophyll cells.
Phenolic Compounds in the Embryo Development of Several Northern Hemisphere Fucoids
Authors: Schoenwaelder Monica E. A. , Wiencke C.
Published: July 2002

Abstract: Light and electron microscopy were used to study the involvement of phenolic compounds in the early development of the Northern Hemisphere fucoids, Fucus serratus (L.), Fucus spiralis (L.) and Himanthalia elongata (L.) S. F. Gray. Phenolic compounds, packaged within physodes are a major cytoplasmic component of brown algae. Physodes accumulate at the zygote periphery early in development and are secreted into the primary zygote wall. At germination, physodes accumulate at the rhizoid tip. Physodes, together with other wall components, contribute to the development of the cell plate. Good evidence already exists for the involvement of phenolic compounds in the development of Southern Hemisphere fucoids, and this study shows that phenolics play a similar role in the Northern Hemisphere. Consequently, their perceived role as herbivore deterrents in Northern Hemisphere species may be a consequence of their role in wall construction.
Suppression of acoustic phonon scattering in two-dimensional electron gas on (InAs)1(GaAs)1/InP heterointerfaces
Authors: Kodaira Yutaka , Kuwano Hiroshi , Tsubaki Kotaro
Published: July 2002

Acoustic phonon scattering of two-dimensional electron gas on (InAs)1(GaAs)1/InP heterointerfaces is observed by measuring electron energy loss rate, and is compared with that on GaInAs/InP heterointerfaces. The energy loss rate and effective mass of (InAs)1(GaAs)1/InP are obtained by analyzing Shubnikov–de Haas oscillation amplitude as a parameter of the electron temperature and lattice temperature. The resulting suppression of acoustic phonon scattering is due to the smaller deformation potential.
Pressure dependence of D
X center mobility in highly doped GaAs
Authors: O’Reilly E. P.
Published: July 2002

The electron mobility of heavily n-doped GaAs increases rapidly with applied hydrostatic pressure, as carriers are trapped at DX centers. This has been taken as evidence against the negative charge state model of the DX center (2d++2e−→d++DX−). However, here we use a modified Born approximation to analyze the pressure dependence of the mobility. It is energetically very favorable in highly doped samples for DX− centers to be formed close to d+ centers and we find that the experimental data are in fact fully consistent with the negative charge state model when such correlations are taken into account.
Role of two-photon absorption in ultrafast semiconductor optical switching devices
Authors: Aitchison J. S. , Oliver M. K. , Kapon E. , Colas E. , Smith P. W. E.
Published: July 2002

We report measurements of the two-photon absorption coefficient of GaAs optical waveguide structures at 1.06 μm. We show that for pulse lengths longer than ∼1 ps, light-induced index changes sufficient to induce all-optical switching will be predominantly due to carriers generated by two-photon absorption. These results allow us to predict limitations for ultrafast all-optical GaAs devices.
Antiparallel crystal orientation in CoSi2 epitaxial bilayers formed by ion implantation
Authors: Wu M. F. , Vantomme A. , Langouche G. , Maex K. , Vanderstraeten H. , Bruynseraede Y.
Published: July 2002

Orientation and strain in buried CoSi2 layers have been studied in a Si/CoSi2/Si/CoSi2/Si(111) structure. Using a well defined implantation and annealing procedure, a unique combination of CoSi2 epitaxial layers was obtained having the same strain but an opposite orientation. These novel structures are interesting for epitaxial growth studies and may have important device applications.
Optical switching in a resonant tunneling structure
Authors: England P. , Golub J. E. , Florez L. T. , Harbison J. P.
Published: July 2002

We describe the interaction of light pulses with a GaAs/AlAs resonant tunneling structure. We demonstrate that light with an average power of less than 10 μW can induce switching, and show that switching is accompanied by a change in the optical absorption. These results suggest a number of new applications for the resonant tunneling structure, including light-by-light switching.
Effects of crystallite size in PbTiO3 thin films
Authors: de Keijser M. , Dormans G. J. M. , van Veldhoven P. J. , de Leeuw D. M.
Published: July 2002

The lattice constants of tetragonal PbTiO3 grown by organometallic chemical vapor deposition, vary with average crystallite size in the thin film as determined from line broadening in x-ray diffraction patterns. The a- and c-lattice constants become equal when the average crystallite size decreases to below ∼5 nm. These data agree with the change in lattice constants as a function of average crystallite size found recently for submicron PbTiO3 powder.
Electrical resistivity of ultrathin, epitaxial CoGa on GaAs
Authors: Kuo T. C. , Wang K. L.
Published: July 2002

The successful growth of ultrathin CoGa on GaAs by MBE is demonstrated. The crystalline quality of the films is verified by in situ RHEED, RBS, and x-ray rocking curve. Transport studies are performed in the temperature range of 4 to 300 K for layer thickness from 10 to 730 Å, and all the films are found to be electrically continuous. The Markowitz’s model [Phys. Rev. B 15, 3617 (1977)] of the electrical resistivity is applied to analyze the measured data. Finally, the specularly scattering probability of these thin films is studied using Fuchs’ theory [Proc. Cambridge Philos. Soc. 34, 100 (1938)].
Transition from lateral to transverse phase separation during film co-deposition
Authors: Adams C. D. , Atzmon M. , Cheng Y.-T. , Srolovitz D. J.
Published: July 2002

We report observations of two distinct types of phase-separated microstructures in co-deposited Al-Ge films. In the initial stages of growth, lateral phase separation is observed, with a temperature dependence consistent with surface diffusion. As the film grows thicker, the Ge-rich phase becomes increasingly buried, and a transverse phase-separated microstructure results, consisting of an Al-rich layer covering a Ge-rich layer. This observation is explained in terms of the competition between surface and interfacial free energies. We discuss the kinetic aspects of the phase separation process, and the resulting behavior in the thick-film limit.
Electromechanical deflections of piezoelectric tubes with quartered electrodes
Authors: Chen C. Julian
Published: July 2002

The deflection of a piezoelectric tube, with the outer (or inner) metal coating sectioned into four quadrants, is analyzed. We show that by applying a voltage V on one of the quadrants, the electromechanical deflection is (√2d31VL2/πDh), where d31 is the piezoelectric coefficient, L is the length, D the diameter, and h the wall thickness of the tube. The deflections calculated with it agree well with the results of finite-element calculations and direct experimental measurements. The formula can be used in the design and application of tube scanners in scanning tunneling microscopes and scanning force microscopes.
Atomic layer epitaxy of GaN over sapphire using switched metalorganic chemical vapor deposition
Authors: Asif Khan M. , Skogman R. A. , Van Hove J. M. , Olson D. T. , Kuznia J. N.
Published: July 2002

In this letter we report the first switched atomic layer epitaxy (SALE) of single crystal GaN over basal plane sapphire substrates. A low pressure metalorganic chemical vapor deposition (LPMOCVD) system was used for the epilayer depositions. In contrast to conventional LPMOCVD requiring temperatures higher than 700 °C, the SALE process resulted in single crystal insulating GaN layers at growth temperatures ranging from 900 to 450 °C. The band-edge transmission and the photoluminescence of the films from the SALE process were comparable to the best LPMOCVD films. To the best of our knowledge this is the first report of insulating GaN films which show excellent band-edge photoluminescence.
Temperature dependence of the polar anchoring strength of weakly rubbed polyimide films for the nematic liquid crystal (5CB)
Authors: Seo Dai-Shik , Iimura Yasufumi , Kobayashi Shunsuke
Published: July 2002

We have succeeded in measuring the polar anchoring energy of a nematic liquid crystal (5CB) aligned on rubbed polyimide films. The polar anchoring energy gradually weakens with increasing temperature and tends to zero as the nematic-isotropic (NI) transition temperature (35.3 °C) is approached. This indicates a strong correlation between the polar anchoring energy and the surface order parameter. Under the weakest rubbing condition, a polar anchoring energy of 8×10−4 J/m2 is obtained at a cell temperature T=30 °C. This result indicates that, even with the weakest rubbing strength, the anchoring strength of the rubbed polyimide films is stronger than that of other alignment films.
On the origin of visible photoluminescence in nanometer-size Ge crystallites
Authors: Kanemitsu Yoshihiko , Uto Hiroshi , Masumoto Yasuaki , Maeda Yoshihito
Published: July 2002

We have studied the origin of visible photoluminescence of Ge nanocrystals in SiO2 glassy matrix. Spectroscopic analyses of Ge nanocrystals indicate that the room-temperature photoluminescence comes from Ge nanocrystals of diameter of 4 nm or less. High-resolution electron microscopic studies imply that the structure of Ge nanocrystals of diameter ≤4 nm differs from the diamond structure. These data suggest that new nanostructure crystalline Ge having a character of direct optical transition exhibits the visible photoluminescence.
Polarized Raman spectroscopy in ion irradiated graphite
Authors: Compagnini G. , Baratta G.
Published: July 2002

Polarized Raman spectra have been performed in keV ion irradiated highly oriented pyrolytic graphite in order to investigate the disorder induced by energetic ions in the carbon matrix at room temperature. Early stages of ion irradiation (1012–1015 He+/cm2 3 keV) induce a high depolarization ratio of the 1360 cm−1 D line, leaving the 1580 cm−1 line almost unchanged. This was interpreted by an anisotropic damage induced in the highly oriented pyrolytic graphite structure by an ion collision cascade.
Chemical, structural, and electronic properties of sulfur-passivated InP(001) (2×1) surfaces treated with (NH4)2Sx
Authors: Gallet D. , Hollinger G.
Published: July 2002

Some chemical, structural, and electronic properties of (NH4)2Sx-treated InP(001) surfaces have been studied using x-ray photelectron spectroscopy, x-ray photoelectron diffraction and reflection high-energy electron diffraction. A (2×1) surface reconstruction is observed for substrates heated in vacuum at a transition temperature of about 200–350 °C. Sulfur atoms are only bonded to indium atoms and the exchange between phosphorus and sulfur occurs in the first five atomic planes leading to the formation of an InP1−xSx pseudomorphic overlayer. The sulfur surface concentration varies from about 0.85±0.15 after annealing at 350 °C to 0.5±0.15 monolayer at 550 °C. The sulfidation treatment results in (2×1) reconstructed surfaces of high thermal stability up to 560 °C and of high chemical stability. Unpinned ultraclean surfaces, free of carbon and oxygen, are obtained after vacuum annealing at 550 °C.
Direct observation of the tip shape in scanning probe microscopy
Authors: Montelius L. , Tegenfeldt J. O.
Published: July 2002

In this study we report on the first direct observation of the real shape of the atomic force microscopy (AFM) tip using the AFM technique itself, utilizing a specially designed sample geometry. This is the first report of the so-called inverse AFM mode in which the tip is actually used as the sample and vice versa. We propose how this method can, with a very high accuracy, be used for studying objects, e.g., biomolecules, that are attached to the usual AFM cantilever tip. Finally, we discuss how this method can significantly increase the reliability of the obtained AFM images.
Polythienylenevinylene thin-film transistor with high carrier mobility
Authors: Fuchigami H. , Tsumura A. , Koezuka H.
Published: July 2002

A thin-film transistor (TFT) with high carrier mobility has been fabricated using precursor-route poly(2,5-thienylenevinylene) (PTV) as semiconductor. The carrier mobility has been determined to be 0.22 cm2/V s, which is in the same level of that of amorphous silicon TFT. It has also been made clear that the carrier mobility is linearly proportional to the conversion ratio from the insulated precursor polymer to π-conjugated PTV. The π-conjugation length is crucial to obtain high carrier mobility in π-conjugated polymer TFT.
Nanocrystalline barium titanate: Evidence for the absence of ferroelectricity in sol-gel derived thin-layer capacitors
Authors: Frey M. H. , Payne D. A.
Published: July 2002

Nanocrystalline BaTiO3 thin-layer capacitors were integrated onto silicon by sol-gel processing using alkoxide precursor solutions. 200-nm-thick layers were formed and found to be comprised of 25-nm grains in the cubic perovskite structure. Electrical measurements indicated a lack of polarization-reversal hysteresis characteristics and Curie–Weiss behavior. The dielectric constant was 230 at room temperature. Properties are discussed in terms of a crystallite size effect. Stable dielectric properties with respect to temperature and voltage suggest that nanocrystalline BaTiO3 could find possible use as an integrated capacitor in decoupling and dynamic random access memory applications.
Microstructure of epitaxial La0.5Sr0.5CoO3/ferroelectric Pb0.9La0.1 (Zr0.2Ti0.8)0.975O3/La0.5Sr0.5CoO3 heterostructures on LaAlO3
Authors: Ghonge Subodh G. , Goo Edward , Ramesh R. , Sands T. , Keramidas V. G.
Published: July 2002

The microstructure of epitaxial La0.5Sr0.5CoO3(LSCO)/ferroelectric Pb0.9La0.1(Zr0.2Ti0.8)0.975O3/ La0.5Sr0.5CoO3 (LSCO) heterostructures on [001] LaAlO3(LAO) has been investigated by x-ray diffraction and transmission electron microscopy (TEM). The ferroelectric film which is predominantly c-axis oriented, with a small degree of a-axis orientation, is epitaxial with the underlying LSCO and does not show any interfacial reaction. The LSCO film is epitaxial with the LAO substrate. LSCO films shows a doubling of lattice periodicity which is shown to be a TEM specimen preparation artifact.
Modeling of laser thermoelastic generation of ultrasound in an orthotropic medium
Authors: Dubois Marc , Enguehard Franck , Bertrand Lionel , Choquet Marc , Monchalin Jean-Pierre
Published: July 2002

We present a numerical model that calculates the surface displacements generated by the absorption of a laser pulse by an orthotropic medium. This model solves the heat and acoustic wave equations using temporal Laplace and spatial two-dimensional Fourier transformations. This model allows us to calculate the normal and in-plane displacements on the front or back surface of an orthotropic plate over a complete area and for virtually any time and beam profiles of the laser excitation. Numerical simulations are compared to experimental results obtained on an aluminum sample and on a graphite-epoxy plate. The experimental and numerical results are in good agreement.
Rare-earth garnet selective emitter
Authors: Lowe Roland A. , Chubb Donald L. , Farmer Serene C. , Good Brian S.
Published: July 2002

Thin film (Ho)-yttrium aluminum garnet (YAG) and Er-YAG emitters with a platinum substrate exhibit high spectral emittance in the emission band (ελ≊0.75, 4I15/2–4I13/2, for Er-YAG and ελ≊0.65, 5I7–5I8 for Ho-YAG) at 1500 K. In addition, low out-of-band spectral emittance, ελ<0.2, suggest these materials would be excellent candidates for high efficiency selective emitters in thermophotovoltaic (TPV) systems operating at moderate temperatures (1200–1500 K). Spectral emittance measurements of the thin films were made (1.2<λ<3.0 μm) and compared to the theoretical emittances calculated using measured values of the spectral extinction coefficient.
(Ba+Sr)/Ti ratio dependence of the dielectric properties for (Ba0.5Sr0.5)TiO3 thin films prepared by ion beam sputtering
Authors: Yamamichi Shintaro , Yabuta Hisato , Sakuma Toshiyuki , Miyasaka Yoichi
Published: July 2002

(Ba0.5Sr0.5)TiO3 thin films were prepared by ion beam sputtering from powder targets with (Ba+Sr)/Ti ratios ranging from 0.80 to 1.50. All of the perovskite (Ba,Sr)TiO3 films were single phase except for the film with a (Ba+Sr)/Ti ratio of 1.41. The dielectric constant values notably depended on the (Ba+Sr)/Ti ratio for films thicker than 70 nm. The highest dielectric constant of 580 was achieved for the 5% (Ba+Sr) rich film. This (Ba+Sr)/Ti ratio dependence was diminished by the thickness dependence for thinner films. The grain sizes for the 9% (Ba+Sr) rich film and for the 6% (Ba+Sr) poor film ranged from 70 to 100 nm and from 30 to 60 nm, respectively. This grain size difference could explain why slightly A-site rich (Ba,Sr)TiO3 films have a larger dielectric constant than A-site poor films.
Continuous-wave, dual-cavity, doubly resonant, optical parametric oscillator
Authors: Colville F. G. , Padgett M. J. , Dunn M. H.
Published: July 2002

We have demonstrated a continuous-wave optical parametric oscillator that uses separate optical cavities to resonate independently the nondegenerate signal and idler frequencies. The three-mirror cavity utilizes the type II phase-matching geometry in lithium triborate, with the orthogonally polarized signal and idler fields separated by an intracavity, dichroic-coated, Brewster-angled beam splitter. This dual-cavity oscillator can overcome mode and cluster hopping effects, which are characteristic of doubly resonant, continuous-wave optical parametric oscillators. We measure a pump power threshold of ≊200 mW and smooth tuning over ≊0.4 GHz. The tuning range is limited by pump resonance effects within the idler cavity.
Production and characterization of smooth, hydrogen-terminated diamond C(100)
Authors: Thoms Brian D. , Owens Michael S. , Butler James E. , Spiro Clifford
Published: July 2002

We report the production of smooth and well-ordered C(100) surfaces by exposure to a pure hydrogen plasma. A two domain 2×1 surface reconstruction is observed by low energy electron diffraction with half-order spots visible using incident electrons with energies as low as 13 eV. High-resolution electron energy loss spectroscopy reveals a large enhancement in specular reflectivity of low energy electrons following plasma treatment. The hydrogenated surface is stable in air and free of adsorbed hydrocarbons upon insertion into ultrahigh vacuum.
Heavy ion beam probe energy analyzer for measurements of plasma potential fluctuations
Authors: Solensten L. , Connor K. A.
Published: July 2002

The operation of a Proca and Green type 30° parallel plate electrostatic energy analyzer is modeled in a new manner that permits high-resolution heavy ion beam probe measurements of fluctuating plasma potential. Systematic calibration procedures permit detection of potential changes smaller than 0.01% of the probing beam energy at frequencies up to a megahertz. Most recent applications of beam probes have made use of this new capability.
Electrical heating with polyimide-insulated magnet wire
Authors: Jewett Douglas M.
Published: July 2002

Polyimide-insulated copper magnet wire is capable of continuous service above 200 °C and can be used intermittently above 300 °C. For the construction of heaters where fast heating and cooling or novel geometries are required it offers a versatile alternative to resistance wire.
Instrumentation for glancing angle x-ray absorption spectroscopy on the Synchrotron Radiation Source
Authors: Pizzini S. , Roberts K. J. , Greaves G. N. , Harris N. , Moore P. , Pantos E. , Oldman R. J.
Published: July 2002

A versatile instrument for glancing-angle x-ray absorption spectroscopy (XAS) and x-ray reflectivity in routine use on the Daresbury Synchrotron Radiation Source is described. This facility can be used for XAS measurements in both reflectivity and fluorescence modes as well as for qualitative studies of angular dependent x-ray reflectivity. Reflectivity and XAS data obtained with this instrument on the oxidized surfaces of Cu thin films are presented.
Current sensing using Faraday rotation and a common path optical fiber heterodyne interferometer
Authors: Bartlett S. C. , Farahi F. , Jackson D. A.
Published: July 2002

An optical configuration for a current sensor utilizing the Faraday effect is described. A common path optical fiber heterodyne interferometer is used to greatly reduce noise produced by environmental effects. A miniature sensing element at the distal end of the fiber allows remote magnetic field or current measurements to be made. Solenoid generated magnetic fields over the range 0.7 to 10 μT, corresponding to solenoid currents from 10 to 150 mA, have been detected over a frequency range from 25 to 125 Hz with a linear response.
Absolute calibration of neutron detection systems on TFTR and accurate comparison of source strength measurements to transport simulations (invited)
Authors: Barnes Cris W. , Bell M. G. , Hendel H. W. , Jassby D. L. , Mikkelsen D. , Roquemore A. L. , Scott S. D. , Strachan J. D. , Zarnstorff M. C.
Published: July 2002

Accurate, absolutely calibrated measurements of the neutron source strength are needed for determining the quality of plasma performance, for constraining transport analysis, and for studying fast ion physics such as triton burnup. Obtaining an accurate calibration involves more than performing in situ source calibrations. Efforts on TFTR illustrate the additional need for careful detector characterization, periodic renormalization, and proper cross calibration of less sensitive detectors. Multiple detector systems have been developed on TFTR to provide redundancy and a range of energy sensitivity and time resolution. Three independently calibrated systems now agree in their determination of source strength within relative uncertainties of 15%–20%. These accurate neutron measurements can be effectively used to constrain transport simulations of neutral beam injection and test the modeling and simulation assumptions.