bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential degradation of calpastatin by μ‐ and m‐calpain in Ca2+‐enriched human neuroblastoma LAN‐5 cells
Authors: De Tullio Roberta , Averna Monica , Salamino Franca , Pontremoli Sandro , Melloni Edon
Published: July 2002

In neuroblastoma LAN‐5 cells during calpain activation, in addition to the two expressed 70 kDa and 30 kDa calpastatin forms, other inhibitory species are produced, having molecular masses of 50 kDa and 15 kDa. At longer times of incubation, both native and new calpastatin species disappear. The formation of these new calpastatins as well as the decrease in intracellular total calpastatin activity are mediated by calpain itself, as indicated by the effect of the synthetic calpain inhibitor I, which prevents both degradative processes. Analysis of the calcium concentrations required for the two processes indicates that the first conservative proteolytic event is mediated by μ‐calpain, whereas the second one is preferentially carried out by m‐calpain. The appearance of the 15 kDa form, containing only the calpastatin repetitive inhibitory domain and identified also in red cells of hypertensive rats as the major inhibitor form, can be considered a marker of intracellular calpain activation, and it can be used for the monitoring of the involvement of calpain in pathological situations.
High‐Pressure Refolding of Disulfide‐Cross‐Linked Lysozyme Aggregates: Thermodynamics and Optimization
Authors: John Richard J. St. , Carpenter John F. , Randolph Theodore W.
Published: July 2002

Previous exploratory work revealed that high pressure (200 MPa), in combination with oxido‐shuffling agents such as glutathione, effectively refolds covalently cross‐linked aggregates of lysozyme into catalytically active native molecules, at concentrations up to 2 mg/mL ( 1). To understand further and optimize this process, in the current study we varied the redox conditions and levels of guanidine hydrochloride (GdnHCl) in the refolding buffer. Maximum refolding yields of 80% were seen at 1 M GdnHCl; higher concentrations did not increase refolding yields further. A maximum in refolding yield was observed at redox conditions with a 1:1 ratio of oxidized to reduced glutathione (GSSG:GSH). Yields decreased dramatically at more oxidizing conditions ([GSSG] > [GSH]). Kinetics of dissolution and refolding of covalently cross‐linked aggregates of lysozyme depended strongly on redox conditions. At GSSG:GSH ratios of 4:1, 1:1, and 1:16, lysozyme dissolved and refolded with time constants of 62, 20, and 8 h, respectively. Estimates of the free energy of unfolding of lysozyme in GdnHCl solutions at 200 MPa suggested that the native state of lysozyme is strongly favored (ca.18.6 kJ/mol) under the conditions used for dissolution and refolding.
Reverse Micellar Extraction of Antibiotics from Aqueous Solutions
Authors: Fadnavis Nitin W. , Satyavathi B. , Deshpande Ashlesha A.
Published: July 2002

Several antibiotics such as erythromycin, oxytetracyclin, benzylpenicillin, and actidione were extracted from aqueous buffers into reverse micellar solution of bis(2‐ethylhexyl) sulfosuccinate sodium salt (AOT) in isooctane and recovered with high efficiency under mild conditions. Preliminary experiments with oxytetracycline dissolved in a fermentation broth indicate that the antibiotic can be selectively extracted from the broth and recovered efficiently without serious loss of potency.
Model for Inactivation of α‐Amylase in the Presence of Salts: Theoretical and Experimental Studies
Authors: Lecker Douglas N. , Khan Arshad
Published: July 2002

According to a previous report, only the smaller anions, like chlorides, that readily fit into the anion binding site of α‐amylase can cause an increased stability (relative to enzymes in aqueous solution), and the anions that are too large to fit into the binding site should have no effect on the enzyme. Even though the results on large benzoate ions are consistent with the above postulate, much larger citrate ions from sodium and potassium citrate show stabilization at moderate salt concentrations and follow an expected trend of low stability only at large salt concentrations. The citrate ions from ammonium citrate exhibit very little to almost no stabilization. In addition, low to moderate concentrations of NaCl that provide a large stability to the enzyme show almost no stability in the presence of EDTA. We put forward an inactivation model that involves a reversible dissociation of the anion bound to the protein, followed by a reversible inactivation step of calcium ion dissociation and an irreversible denaturation step of apoenzyme.
Modeling Conductive Heat Transfer and Process Uniformity during Batch High‐Pressure Processing of Foods
Authors: Denys Siegfried , Ludikhuyze Linda R. , Van Loey Ann M. , Hendrickx Marc E.
Published: July 2002

A numerical model for predicting conductive heat transfer during batch high hydrostatic pressure (HHP) processing of foods was developed and tested for a food simulator (agar gel). For a comprehensive evaluation of the proposed method, both “conventional” HHP processes, HHP processes with gradual, step‐by‐step pressure buildup and pressure release, and pressure cycling HHP processes were included. In all cases, good agreement between experimental and predicted temperature profiles was observed. The model provides a very useful tool to evaluate batch HHP processes in terms of uniformity of any heat‐ and/or pressure‐related effect. This is illustrated for inactivation of Bacillus subtilis α‐amylase, an enzymatic model system with known pressure‐temperature degradation kinetics.
Plant food allergens homologous to pathogenesis‐related proteins
Authors: Ebner Christof , Hoffmann‐Sommergruber Karin , Breiteneder Heimo
Published: July 2002

In general, pathogenesis‐related (PR) proteins are expressed by plants in response to stress conditions like infection, exposure to certain chemicals, wounding and environmental conditions. In some plant tissues, however, PR proteins are constitutively expressed, e.g. in pollens or fruits, tissues that are more likely to be attacked (by insects or fungi) or exposed to atmospheric conditions (e.g. UV irradiation). PR proteins display multiple effects within the plant and possess antimicrobial activity, and can thus be regarded as a part of the plant's defense system. Analyzing known amino acid sequences and functions of characterized (cloned) food allergens, it is remarkable that many of these molecules can be classified as PR proteins. Many PR proteins are stable at low pH, and display considerable resistance to proteases, requirements to act as food allergens. According to sequence characteristics and their enzymatic or biologic activity, PR proteins can be divided into 14 groups. Seven of these 14 groups contain proteins with allergenic properties, six groups contain food allergens.
Hepatocyte growth factor activates phosphoinositide 3-kinase C2β in renal brush-border plasma membranes
Authors: CRLJEN Vladiana , VOLINIA Stefano , BANFIC Hrvoje
Published: July 2002

Upon stimulation of renal cortical slices with hepatocyte growth factor (HGF), inositol lipid metabolism was studied in basal-lateral plasma membranes (BLM) and brush-border plasma membranes (BBM). Whereas in BLM rapid increases in 1,2-diacylglycerol, PtdIns(3,4,5)P3 and PtdIns(3,4)P2 were observed, suggesting that in BLM HGF activates both phospholipase C (PLC) and phosphoinositide 3-kinase (PI3K), in BBM only HGF-induced transient accumulation of PtdIns3P was seen, which was temporarily delayed from signalling events in BLM and could be blocked by the PtdIns-specific-PLC inhibitor ET-18-OCH3 and the calpain inhibitor calpeptin, suggesting that 3-kinase activation in BBM lies downstream of PLC activation in BLM and is a calpain-mediated event. Moreover, the increase in immunoprecipitable PI3K-C2β activity, which is sensitive to wortmannin (10nM) and shows strong preference for PtdIns over PtdIns4P as a substrate, was observed only in BBM upon stimulation of renal cortical slices with HGF and could be mimicked by the Ca2+ ionophore A23187 and blocked by the cell-penetrant Ca2+ chelator BAPTA-AM [1,2-bis-(2-aminophenoxy)ethane-N,N,N′,N′-tetra-acetic acid tetrakis(acetoxymethyl ester)]. On Western blots PI3K-C2β revealed a single immunoreactive band of 180kDa in BLM and BBM, while after stimulation with HGF a gel shift of 18kDa was noticed only in BBM, suggesting that the observed enzyme activation is achieved by proteolysis. When BBM were subjected to short-term (15min) exposure toμ-calpain, a similar gel shift together with an increase in PI3K-C2β activity was observed, when compared with the BBM harvested after HGF stimulation. The above-mentioned gel shift and increase in PI3K-C2β activity could be prevented by the calpain inhibitor calpeptin. The data presented in this report show that in renal cells there is a spatial separation of the inositol lipid signalling system between BLM and BBM, and that HGF causes activation of PLC and PI3K primarily in BLM, which leads to calpain-mediated activation of PI3K-C2β in BBM with a concomitant increase in PtdIns3P.
Expression of the Pycnoporus cinnabarinus laccase gene in Aspergillus niger and characterization of the recombinant enzyme
Authors: Record Eric , Punt Peter J. , Chamkha Mohamed , Labat Marc , van den Hondel Cees A. M. J. J. , Asther Marcel
Published: July 2002

Pycnoporus cinnabarinus laccase lac1 gene was overexpressed in Aspergillus niger, a well‐known fungal host producing a large amount of homologous or heterologous enzymes for industrial applications. The corresponding cDNA was placed under the control of the glyceraldehyde‐3‐phosphate dehydrogenase promoter as a strong and constitutive promoter. The laccase signal peptide or the glucoamylase preprosequence of A. niger was used to target the secretion. Both signal peptides directed the secretion of laccase into the culture medium as an active protein, but the A. niger preprosequence allowed an 80‐fold increase in laccase production. The identity of the recombinant protein was further confirmed by immunodetection using Western blot analysis and N‐terminal sequencing. The molecular mass of the mature laccase was 70 kDa as expected, similar to that of the native form, suggesting no hyperglycosylation. The recombinant laccase was purified in a three‐step procedure including a fractionated precipitation using ammonium sulfate, and a concentration by ultrafiltration followed by a Mono Q column. All the characteristics of the recombinant laccase are in agreement with those of the native laccase. This is the first report of the production of a white‐rot laccase in A. niger.
Pilot study of the cyclic fatigue characteristics of five endodontic posts with four core materials
Authors: Cohen B. I. , Pagnillo M. K. , Newman I. , Musikant B. L. , Deutsch A. S.
Published: July 2002

This pilot study concerned the cyclic fatigue of five different endodontic post systems (AccessPost®, Flexi‐Flange®, Flexi‐Post®, ParaPost®, and Vlock®) with four different core materials (Tytin® Silver amalgam, Ti‐Core®, Ketac‐Silver® and G‐C Miracle Mix®). In vitro cyclic fatigue was performed using a fatigue machine that simulates masticatory fatigue forces. An instantaneous force of 5 lb was applied to each post and core combination for a test configuration of 4 000 000 repetitions or until failure occurred. The type of failure and number of repetitions at failure was recorded for each sample tested. Two‐way anova was used to compare groups. All posts/core samples with Ti‐Core and Tytin Silver amalgam completed the test configuration of 4 000 000 cycles without failures. All posts/core samples with Ketac‐Silver failed before the 4 000 000 test cycle configuration, all as a result of core failures. All posts/core samples with G‐C Miracle Mix failed in a similar way. The Newman–Keuls multiple comparison test illustrated that Ti‐Core and Tytin Silver amalgam were similar to each other and were superior to both G‐C Miracle Mix and Ketac‐Silver. Similar fatigue test results are found in the literature.
Photodynamic Alteration of the Surface Receptor Expression Pattern of Murine Splenic Dendritic Cells
Authors: KING D. E. , JIANG H. , SIMKIN G. O. , OBOCHI M. O. K. , LEVY J. G. , HUNT D. W. C.
Published: July 2002

The photosensitizer benzoporphyrin‐derivative monoacid ring A (BPD‐MA, verteporfin), in combination with visible light irradiation, a clinical procedure termed photodynamic therapy (PDT), has immunomodulatory activity in various mouse models. We studied the impact of BPD‐MA and light upon DBA/2 mouse splenic dendritic cells (DC), a potent antigen‐presenting cell (APC) type. DC treated with nanomolar amounts of BPD‐MA and 690 nm wavelength light had a reduced capacity to stimulate the proliferation of alloreactive T cells. Treatment with BPD‐MA and light reduced DC levels of major histocompatibility (MHC) Class I and II antigens, intercellular adhesion molecule‐1 (ICAM‐1, CD54), the costimulatory B7‐1 (CD80) and B7‐2 (CD86) molecules, leucocyte common antigen CD45, the apoptosis‐regulating Fas (CD95) receptor and the integrin CD11c. In contrast, DC expression of leucocyte function‐associated‐1 (LFA‐1, CD11a), Mac‐1 (CD11b), integrin β2 chain (CD18) and the DEC‐205 receptor increased, while CD40 levels were relatively unchanged 24 h after the treatment. MHC Class I and ICAM‐1 levels decreased to 40% of control levels within 2 h following the photodynamic treatment. In the absence of light, BPD‐MA did not affect DC receptor levels. Changes in DC receptor levels produced by BPD‐MA and red light were similar to those produced by ultraviolet B light irradiation. The photodynamic treatment of activated splenic B cells, a separate APC class, had little effect upon receptor expression, except that MHC Class II levels were moderately decreased 24 h later. Changes in DC receptor expression may contribute to the immunomodulatory action of PDT.
Developmental stability and adaptive radiation in the Spalax ehrenbergi superspecies in the Near-East
Authors: Auffray J.-C. , Renaud S. , Alibert P. , Nevo E.
Published: July 2002

Chromosomal species of the mole rat, Spalax ehrenbergi, in Israel have been shown to display distinct adaptive strategies to increasing aridity. This adaptive radiation appeared to be associated with an increase in allozymic heterozygosity. In the present study, the developmental stability (DS) estimated by fluctuating asymmetry (FA) of dental traits was used to assess the suitability of habitat and the efficiency of adaptation to local environmental conditions among populations and chromosomal species. Although FA levels were highly heterogeneous among populations, they were not found to differ between species. DS of populations appeared, however, to be impaired at higher altitudes and in indurate soils. Since these environmental features were largely covariant, the effect of each one could not be precisely determined. Interestingly, while aridity is considered as the major selective force acting on populations southwards, DS was not altered under arid conditions, suggesting that mole rat populations were adapted to their local conditions of aridity. However, the cline of aridity is matched to several environmental and genetic clines among which are the increasing heterozygosity and recombination rate among species southwards. In studies of natural populations, the potential complementary effects of environmental and genetics on DS have to be considered and hamper the interpretation of habitat suitability expressed by DS in terms of adaptive strategies.
Cystic lumbar nerve sheath tumours: MRI features in five patients
Authors: Parmar Hemant , Patkar Deepak , Gadani Sameer , Shah Jeshil
Published: July 2002

Intraspinal cystic lumbar nerve sheath tumours constitute an uncommon subset of tumours with distinct clinico‐biological behaviour. The MRI findings in five such cases are presented. Four of these were cystic schwannomas and one was a cystic neurofibroma. The pathology, MRI findings and the differential diagnosis of these rare tumours are analysed.
Free radicals, antioxidants and international nutrition*
Authors: PhD Okezie I Aruoma
Published: July 2002

The oxidative degradation of polyunsaturated fatty acids is the primary factor in limiting the shelf‐life of most manufactured foods. Free radical mechanisms are implicated in the pathogenesis of human diseases and in the process of ageing. This has led to the suggestion that antioxidants, and plant diet‐derived antioxidants in particular, might have health benefits as prophylactic agents. Delineating the in vivo contribution of plant extracts and/or plant‐derived antioxidants (the pure active principles in plant extracts with antioxidant indications) to the modulation of the pathological consequences of oxidative stress in the human body is complicated by the fact that antioxidant actions may be achieved through more than one mechanism. The interest in the health promoting qualities of plant foods may be ascribed to the observation that various compounds present in these foods possess antioxidant properties in vitro. From a food stability perspective, one would be interested in the integrity of the food and the effects of storage on the molecular components of the food. For humans, the emphasis is on the importance of nutritional antioxidants in health and disease management.
Experience of nevirapine use in a London cohort of HIV‐infected pregnant women
Authors: Edwards Sg , Larbalestier N , Hay P , De Ruiter A , Welch J , Taylor Gp , Easterbrook P
Published: July 2002

1
King's College Hospital,

2
St Thomas' Hospital,

3
St George's Hospital and

4
St Mary's Hospital, London, UK

Objective  To describe the experience of four London HIV centres prescribing nevirapine (NVP) to HIV‐1 infected pregnant women with respect to immunological and virological response, tolerability and pregnancy outcome.

Methods  We identified all HIV‐1‐infected women who received NVP as part of a triple antiretroviral regimen during pregnancy between January 1997 and September 1999. Laboratory results, clinical events, side‐effects and pregnancy outcome were abstracted using a standardized proforma from the medical records.

Results  Forty‐six women were identified, 85% of whom were black African. At initiation of NVP, the median age was 29 years and the median baseline CD4 cell count and viral load were 242 cells/μL and 4.15 log10 copies/mL, respectively. Thirty‐two out of 36 women who had a plasma sample obtained at, or just prior to, delivery had an undetectable viral load (< 50 to < 400 copies/mL). Adverse events that were definitely attributed to NVP included a generalized rash (n = 2) and hepatitis (n = 2). Obstetric complications occurred in nine women (19.5%), which was not statistically different (P = 0.36) from that found in a historical (1990–96) control group 7/51 (14%). The rate of preterm delivery (13%) was similar to that previously reported in HIV‐1 infected pregnant women (18%).

Conclusions  NVP (as part of highly active antiretroviral therapy) reduced plasma viraemia to below the limit of detection in 89% of women. It was generally well tolerated and clinical and laboratory adverse events were infrequent. There was no evidence of an increase in obstetric complications including preterm delivery during the second and third trimesters of pregnancy.
Tolerability and efficacy of hydrocolloid dressings in the treatment of venous leg ulcers under tropical conditions: an open prospective study
Authors: Zeegelaar JE , Langenberg W , Hu R , Lai A Fat RFM , Faber WR
Published: July 2002

In the Western world, hydrocolloid dressings are widely used in wound treatment. However, little is known about their tolerability and efficacy under tropical conditions. The purpose of this study was to assess the tolerability and efficacy of a hydrocolloid dressing in combination with short stretch compressive bandages under tropical conditions. Seventeen patients with venous leg ulcers attending an outpatient clinic in Surinam were enrolled in the study for a period of 6 weeks. Swabs for bacterial cultures were taken at the beginning and end of the study. All ulcers showed a good healing tendency. Percentage of granulation tissue in the ulcers improved from mean 27% at start to 92% at the end. Mean circumference at start was 9.9 cm, at the end 4.9 cm. Exudation diminished from moderate in six and severe in eight ulcers, to moderate in 10 and almost none in two ulcers. In general, the dressing was very well accepted, pain was never reported. Leakage was noticed 39 times in the 164 dressing changes. This study revealed no differences in the rate of bacterial infections or colonization of wounds compared with studies performed in temperate regions. Our data indicate that hydrocolloid dressings can be used under tropical conditions.
The ideal nasal corticosteroid: balancing efficacy, safety and patient preference
Authors: Durham S. R.
Published: July 2002

Topical corticosteroids represent first‐line treatment in patients with moderate–severe persistent allergic rhinitis. Topical steroids have a wide range of anti‐inflammatory properties, particularly suppression of the release of Th2‐type cytokines from T cells and also from mast cells and basophils. Topical corticosteroids are effective against all nasal symptoms including nasal blockage. They are more potent than oral antihistamines and topical cromones. They may also improve seasonal asthma. Potential disadvantages include a slightly slower onset of effect (days), the need for regular treatment and occasional local irritation/bleeding. The properties of an ideal intranasal corticosteroid include high efficacy against all nasal symptoms, a rapid onset of action and a proven once‐daily dosing schedule. Local corticosteroid preparations should be acceptable to patients with low or absent local/systemic side‐effects. There should be no long‐term adverse effects on the nasal mucosa. Triamcinolone acetonide (TAA) aqueous nasal spray meets these criteria and a particular advantage is its lack of taste and smell, which may improve acceptability and compliance in some patients.
Implications of Genotypic Diversity and Phenotypic Plasticity in the Ecophysiological Success of CAM Plants, Examined by Studies on the Vegetation of Madagascar1
Authors: Kluge M. , Razanoelisoa B. , Brulfert J.
Published: July 2002

Abstract: On the basis of δ13C‐values, genotypic diversity and phenotypic plasticity of CAM behaviour in plants of the Malagasy vegetation is surveyed. The study compares CAM patterns performed in the wild on the levels of genera (Kalanchoë [Crassulaceae], Angraecum [Orchidaceae], Lissochilus [Orchidaceae] and Rhipsalis [Cactaceae]), on the level of a family (Didiereaceae) and finally on the level of a common growth form, namely in leafless orchids. For Rhipsalis, also non‐Malagasy species were included in the comparison. The genus Kalanchoë was found to be dominated by species representing the CAM‐physiotype with CO2 fixation taking place only during the night, whereas the CAM/C3‐ and the C3‐physiotypes (with limited intrinsic CAM potential) were less frequent. The opposite holds true for Angraecum. In the genus Rhipsalis, in the Didiereacean family and in the leafless orchids only the CAM‐physiotype is represented. The photosynthetic physiotypes of CAM plants were found to be related to the environmental conditions of the habitat. That is, strong CAM performers are typically abundant in the dry climatic zones or at otherwise dry niches, species of the C3‐physiotype (possibly with weak intrinsic capability of CAM performance) are distributed at humid sites and those of the CAM/C3‐physiotype occupy sites with medium and changing exposure to stress. Phenotypic plasticity of CAM, as indicated by the intraspecific variability of the δ13C‐values, was lower in the CAM‐physiotype compared with the CAM/C3‐physiotype.

Our data support the view that strong stress leads to the dominance of highly adapted specialists among the CAM plants, with low phenotypic plasticity of the photosynthetic behaviour, whereas medium stress advances the unfolding of plastic CAM behaviour. Moreover, the data suggest that genera comprising all three physiotypes (Kalanchoë, Angraecum) are dispersed all over Madagascar, whilst groups comprising only strong CAM performers are restricted to limited areas or special types of habitats. This suggests that both genotypic diversity and phenotypic plasticity are important factors for the ecophysiological success of CAM.
Electrically controlled surface bistability in nematic liquid crystals
Authors: Barberi R. , Boix M. , Durand G.
Published: July 2002

The use of obliquely SiO evaporated glass plates at grazing incidence and controlled thickness gives a surface twofold degenerate oblique orientation for the nematic liquid-crystal MBBA (p-methoxy-benzylidine-p-n-butyl-aniline). Using a horizontal electric field and the linear flexoelectric coupling, one can switch the surface state from the first orientation to the other one, above a threshold value for the electric field. This represents the first example of an electrically controlled surface bistability in nematic liquid crystals.
Theory of magnetic force microscope images
Authors: Abraham David W. , McDonald F. Alan
Published: July 2002

A model is presented for magnetic force microscope (MFM) images obtained with a ferromagnetic tip and a ferromagnetic sample. Results of calculations are compared to recent MFM experiments and show good agreement using known values for magnetic parameters characterizing tip and sample. The model describes a limit in resolution determined by the demagnetizing effect of tip and sample, predicts the appearance of a novel image artifact which is particularly observable in images of narrow domains of reversed magnetization, and suggests an explanation for the observed contrast between regions of opposite magnetization.
Optical nonlinearity of CdSe microcrystallites in a sputtered SiO2 film
Authors: Yumoto J. , Shinojima H. , Uesugi N. , Tsunetomo K. , Nasu H. , Osaka Y.
Published: July 2002

Optical nonlinearity of a sputtered SiO2 film containing CdSe microcrystallites with an average diameter of 15 Å is measured by degenerate four-wave mixing (DFWM) experiments. An effective nonlinear cross section σeff of 1.4×10−16 cm2 is obtained. The DFWM signal as a function of the probe delay time shows biexponential behavior with a fast decay time of 10 ps and a slow decay time of 60 ps, which give fast and slow carrier recombination times as 20 ps and 120 ps. The third-order susceptibility ‖χ(3)‖ is estimated to be 1.3×10−8 esu. The photodarkening and laser annealing effects which are serious problems for device applications are not observed.
Influence of substrate temperature on the orientation of YBa2Cu3O7 films
Authors: Shi W. , Shi J. , Sun J. , Yao W. , Qi Zh.
Published: July 2002

The structural characteristics of YBa2Cu3O7 (YBCO) thin films were investigated by x-ray diffractometry. Films with good preferred orientation (001) and high Tc0 (86–90 K) can be prepared in situ using the dc magnetron sputtering method. For the films prepared on the ZrO2 (stabilized with Y2O3) substrate at a substrate temperature (Ts) less than 700 °C, there are different orientations and the degree of random orientation will decrease with increasing Ts. YBCO films with (001) can be obtained on ZrO2 with different crystal planes, such as (100), (110), and (111) at suitable temperature (760–850 °C). From the results it could be concluded that the YBCO film growth with c-axis orientation mainly depends on the substrate temperature Ts.
Photoreflectance study of surface photovoltage effects at (100)GaAs surfaces/interfaces
Authors: Yin X. , Chen H-M. , Pollak F. H. , Chan Y. , Montano P. A. , Kirchner P. D. , Pettit G. D. , Woodall J. M.
Published: July 2002

We report a photoreflectance study of surface photovoltage (VS) effects on the determination of Fermi level pinning (VF) on (100) n-GaAs in air and with W-metal coverage (in situ) as a function of temperature (77 K<T<450 K) and light intensity (I). The dependence of VS on T and I can be explained by a modification the theory of M. Hecht [Phys. Rev. B 41, 7918 (1990)] yielding a value of VF=0.73±0.02 V. The effect of metal coverage is to reduce the influence of VS.
GaAs p-n junction formed in quantum wire crystals
Authors: Haraguchi Keiichi , Katsuyama Toshio , Hiruma Kenji , Ogawa Kensuke
Published: July 2002

A p-n junction is formed for the first time in a cross-sectional area of a GaAs wire crystal with a diameter of about 100 nm. Ultrafine cylindrical growth by metalorganic vapor phase epitaxy is employed for the fabrication. Current-voltage and capacitance-voltage characteristics confirm the formation of the p-n junction in a narrow area at the midpoint of a wire crystal. Intensive light emission by current injection is observed at 77 K and even at room temperature. These results suggest that ultrafine optoelectronic devices with quantum-size p-n junction are possible.
Sputtering of YBa2Cu3O7−δ/NdAlO3/YBa2Cu3O7−δ trilayers
Authors: Rauch W. , Behner H. , Gieres G. , Sipos B. , Seeböck R. J. , Eibl O. , Kerner R. , Sölkner G. , Gornik E.
Published: July 2002

Epitaxial YBa2Cu3O7−δ/NdAlO3/YBa2Cu3O7−δ-trilayers were grown by sputtering from stoichiometric targets. The YBa2Cu3O7−δ (YBCO) films were deposited by dc-magnetron sputtering. For the NdAlO3 films, rf-magnetron sputtering was used. The individual YBCO films revealed critical-current densities up to 3×106 A/cm2 at 77 K. The bilayer and trilayer structures were characterized by x-ray diffraction, Rutherford backscattering spectroscopy, and transmission electron microscopy (TEM). The channel yield χmin of the YBCO film on top was 15% for an in situ deposited trilayer. The epitaxial growth of the subsequent layers was proved by cross-sectional TEM. Although the NdAlO3 layer contained misoriented grains, the top YBCO layer grows in single orientation over these areas. Preliminary electrical measurements show that NdAlO3 is a useful insulating dielectric for microelectronic applications.
Nanobridges of optimized YBa2Cu3O7 thin films for superconducting flux-flow type devices
Authors: Schneider J. , Kohlstedt H. , Wördenweber R.
Published: July 2002

Superconducting nanobridges of YBa2Cu3O7 thin films with widths down to w=200 nm and lengths from 0.2 to 10 μm are patterned using metal masks fabricated by electron-beam lithography and reactive ion etching. The YBa2Cu3O7 films were dry etched by ion beam milling at minimal energies of 250 eV on a liquid-nitrogen-cooled sample holder. Long bridges (l=10 μm) showed superconducting features similar to those of unstructured YBa2Cu3O7 films. Short nanobridges exhibited phase-slip center behavior up to the transition temperature of 87–89 K. Shapiro steps were observed in the current-voltage characteristics in applied microwave fields and the critical current decreased linearly with the amplitude of the microwave field.
Oxygen exchange between CO2 adsorbate and TiO2 surfaces
Authors: Yanagisawa Y. , Sumimoto T.
Published: July 2002

Using temperature-programmed desorption gas analysis, thermal desorptions of C18O2 and C16O18O with a small amount of C16O2 were observed in the temperature range 350–500 K after C18O2 was adsorbed on vacuum-annealed TiO2 powders at room temperature. This indicates that oxygen isotope exchange takes place between C18O2 gas and TiO2 surfaces. After 16O2 exposure of the C18O2-preadsorbed powders, the amount of C16O2 desorption increased, suggesting that isotope mixing may occur through a CO2-O2 intermediate complex.
Oriented ferroelectric La-Sr-Co-O/Pb-La-Zr-Ti-O/La-Sr-Co-O heterostructures on [001] Pt/SiO2 Si substrates using a bismuth titanate template layer
Authors: Ramesh R. , Lee J. , Sands T. , Keramidas V. G. , Auciello O.
Published: July 2002

We demonstrate the growth of c-axis oriented La-Sr-Co-O/Pb-La-Zr-Ti-O/La-Sr-Co-O ferroelectric capacitor heterostructures on a highly [001] oriented Pt film which was grown on a thermally oxidized Si (SiO2/Si) substrate. The [001] growth orientation in the Pt film is induced by depositing it on a thin c-axis oriented bismuth titanate template layer which is previously grown on the SiO2/Si substrate. The test capacitors show saturation and remnant polarization values comparable with that obtained on single-crystal LaAlO3 substrates. The use of a Pt layer reduces the sheet resistance of the bottom electrode stack by at least 3–5 times. Since the Pt layer is strongly [001] oriented, it favors the growth of [001] La-Sr-Co-O (LSCO) and lead zirconate titanate layers. The use of the LSCO top and bottom electrodes in contact with the ferroelectric thin film provides the resistance to bipolar fatigue, consistent with our earlier results.
Deposition of high quality cubic boron nitride films on nickel substrates
Authors: Zhang Fangqing , Guo Yongping , Song Zhizhong , Chen Guanghua
Published: July 2002

The well-crystallized cubic boron nitride (c-BN) films have been prepared on polycrystalline Ni substrates using a hot filament assisted rf plasma chemical vapor deposition method. X-ray diffraction showed that high quality c-BN films had been deposited without hexagonal BN (h-BN) or amorphous BN codeposition. Both (111) and (100) faces were observed in scanning electron microscopy images. These results suggested that Ni had catalyst effects on the nucleation and the growth of c-BN phase and inhibited the formation of h-BN.
Misfit dislocation propagation kinetics in GexSi1−x/Ge(100) heterostructures
Authors: Hull R. , Bean J. C. , Peticolas L. J. , Weir B. E. , Prabhakaran K. , Ogino T.
Published: July 2002

We report measurements of misfit dislocation propagation velocities in GexSi1−x epilayers grown upon Ge(100) substrates, as opposed to the more usual Si(100) substrates. This geometry allows us to study structures with high Ge concentration (x≥0.8), and to compare with previous extensive measurements for lower Ge concentration layers (x≤0.35) grown upon Si(100). It is found that all data are well described by a misfit dislocation velocity which is linear with excess stress, and which incorporates a compositionally dependent activation energy with linear interpolation between bulk values for Si and Ge. The combined data sets from structures grown on Si(100) and Ge(100) substrates is analyzed in the framework of the diffusive double kink model for dislocation motion.
Sub-band-gap laser micromachining of lithium niobate
Authors: Christensen F. K. , Müllenborn M.
Published: July 2002

Laser processing of insulators and semiconductors is usually realized using photon energies exceeding the band-gap energy. This makes laser processing of insulators difficult since high photon energies typically require either a pulsed laser or a frequency-doubled continuous-wave laser. A new method is reported which enables us to do laser processing of lithium niobate using sub-band-gap photons. Using high scan speeds, moderate power densities, and sub-band-gap photon energies results in volume removal rates in excess of 106μm3/s. This enables fast micromachining of small piezoelectric structures, or simple etching of grooves for precision positioning of optical fibers.
Multichordal charge exchange recombination spectroscopy on the Doublet III tokamak
Authors: Seraydarian R. P. , Burrell K. H. , Brooks N. H. , Groebner R. J. , Kahn C.
Published: July 2002

An instrument has been developed to spectroscopically measure ion temperature and rotation speed spatial profiles in neutral-beam-heated tokamak plasmas. Up to eight spatial chords of data can be obtained for 32 time slices during a single discharge with selectable resolution times as short as 2 ms. A special arrangement of fiber optics allows simultaneous data acquisition from all chords without the use of scanning mirrors or other moving parts. Techniques used to analyze the data from the system are discussed.
Use of simultaneous reflections for precise absolute energy calibration of x rays
Authors: Arthur J.
Published: July 2002

An experimental study of intensity variations in a synchrotron x-ray beam caused by the presence of simultaneous reflections in the silicon monochromator crystals has been compared with calculations based on dynamical diffraction theory in an effort to determine the practical limits to the use of such intensity variations for energy calibration. It has been found that relative misalignments of the monochromator crystals can lead to errors of approximately 0.01% (1 eV at 10 keV), but that with some care energy calibration to within 0.002% (0.2 eV at 10 keV) can be achieved in a short measurement.
Time domain reflectometry to study the dielectric properties of liquids: Some problems and solutions
Authors: Bertolini D. , Cassettari M. , Salvetti G. , Tombari E. , Veronesi S.
Published: July 2002

After a brief introduction we review the fundamental mathematical relations necessary to discuss the main aspects of the time domain dielectrometry performed with total reflection from an open cell. Experimental problems due to the presence of resonances in the sample cell, spurious reflections, and fringing fields are considered and possible solutions are suggested. An experimental apparatus realized to study liquids with dielectric constant values up to those of water and water solutions from 10 MHz up to 10 GHz in the temperatures range −45 °C+70 °C is also presented. The performances of some different experimental cells for liquids are compared and representative results obtained with different procedures are reported. The use of the numerical solution of a transcendental equation that takes into account for wave propagation allows us to measure the complex dielectric constant without the use of reference liquids, once the electrical parameters of the sample cell are known. In this case an accuracy better than 2% both in the real and in the imaginary parts of the dielectric constant can be obtained up to 7 GHz, as tested with chloroform. Calibration procedures using liquids of known permittivity can remove the contributions of spurious effects, so allowing us to perform measurements with the same accuracy up to 10 GHz and more on highly polar liquids too.
Fiber-optic high-temperature sensor based on the fluorescence lifetime of alexandrite
Authors: Zhang Zhiyi , Grattan K. T. V. , Palmer A. W.
Published: July 2002

A fiber-optic sensor for continuous temperature measurement from room temperature to ≳700 °C is presented. The device is based upon the excitation of the synthetic crystal alexandrite with light from a diode laser operating at 670 nm and the measurement of its fluorescence lifetime. A simple low cost optical configuration is described together with the introduction of a new effective signal processing scheme for fluorescence lifetime measurement, and a high sensitivity and repeatability are observed, at best ±1 °C.
Low coherence fiber optic system for remote sensors illuminated by a 1.3 μm multimode laser diode
Authors: Ribeiro A. B. L. , Jackson D. A.
Published: July 2002

A fiber optic sensor probe, with two low-finesse Fabry–Perot cavities enabling the determination of displacement (in the range of a typical diaphragm pressure sensor) and temperature, is described. The sensors are connected in a reflective array network and their status is read using coherence tuned sensing based upon a multimode laser diode at 1.3 μm wavelength. Data are presented which show the resolution and linearity of the sensors for the measurement of displacement and temperature.
Manganese doped zinc sulphide nanoparticles by aqueous method
Authors: Khosravi Ali Azam , Kundu Manisha , Kuruvilla Beena Annie , Shekhawat G. S. , Gupta R. P. , Sharma A. K. , Vyas P. D. , Kulkarni S. K.
Published: July 2002

Zinc sulphide nanoparticles in the size range ∼10–40 Å diameter have been synthesized using the aqueous chemical method. Scanning tunneling microscopy showed that particles are indeed nanosize particles. The size dependent band gap could be varied from a bulk value of 3.68 to 4.5 eV. X-ray diffraction indicated that nanoparticles are crystalline except for those with band gap ∼4.5±0.1 eV. Nanoparticles with particle size ∼21×2 Å diameter or energy gap 4.1×0.1 eV were doped with manganese. The photoluminescence peak at ∼600 nm corresponding to yellow light emission was observed. Atomic absorption studies show that maximum luminescence intensity is achievable with 0.12 at. wt % of Mn doping.
A rheometer for the measurement of a high shear modulus covering more than seven decades of frequency below 50 kHz
Authors: Christensen T. , Olsen N. B.
Published: July 2002

A new rheometer is described. It consists of a transducer unit supplied with an electric impedance analyzing unit. The transducer unit converts a mechanical impedance into an electrical impedance by the piezoelectric effect. A detailed quantitative analysis of the interaction between the sample and the transducer is given. The real and imaginary parts of the shear modulus of a viscoelastic sample can be found in the frequency range of 1 mHz–50 kHz, modulus range of 0.1 MPa–10 GPa, and the temperature range of 150–300 K. The sample volume is 0.3 cm3 and the strain amplitude is exceedingly small. The small size of the transducer allows for good temperature control and equilibration. It has a simple construction based on inexpensive components. Results on the supercooled liquid 2-metyl-2,4-pentandiol at the glass transition obtained by the method are included.
Focusing characteristics of diamond crystal x-ray monochromators. An experimental and theoretical comparisona)
Authors: Sánchez del Río M. , Grübel G. , Als-Nielsen J. , Nielsen M.
Published: July 2002

Perfect crystals in transmission (Laue) geometry can be used effectively for x-ray monochromators, and moreover, perfect Laue crystals show an interesting focusing effect when the incident beam is white and divergent. This focusing is directly dependent on the incident beam divergence and on the diffraction profile width of the crystal. The aim of this work is to study whether this property can be used for focusing a synchrotron x-ray beam, and to obtain quantitatively the dimensions of the resulting monochromatic beam. We have experimentally measured the size of an undulator beam after diffraction from a diamond crystal in Laue geometry, and we analyze and explain the results by comparison with ray-tracing simulations.
Scintillating-fiber 14 MeV neutron detector on TFTR during DT operation
Authors: Wurden G. A. , Chrien R. E. , Barnes Cris W. , Sailor W. C. , Roquemore A. L. , Lavelle M. J. , O’Gara P. M. , Jordan R. J.
Published: July 2002

A compact 14 MeV neutron detector using an array of scintillating fibers has been tested on the TFTR tokamak under conditions of a high gamma background. This detector uses a fiber-matrix geometry, a magnetic field-insensitive phototube with an active HV base and pulse-height discrimination to reject low-level pulses from 2.5 MeV neutrons and intense gammas. Laboratory calibrations have been performed at EG&G Las Vegas using a pulsed DT neutron generator and a 30 kCi 60Co source as background, at PPPL using DT neutron sources, and at LANL using an energetic deuterium beam and target at a tandem Van de Graaff accelerator. During the first high-power DT shots on TFTR in December 1993, the detector was 15.5 m from the torus in a large collimator. For a rate of 1×1018 n/s from the tokamak, it operated in an equivalent background of 1×1010 gammas/cm2/s (∼4 mA current drain) at a DT count rate of 200 kHz.
Complete high-frequency measurement of Mueller matrices based on a new coupled-phase modulator
Authors: Compain Eric , Drevillon Bernard
Published: July 2002

A new polarization modulator is presented. It uses two phase-locked identical electro-optic phase modulators at 50 kHz. Thanks to a coupling object introduced between the two phase modulators, the four Stokes parameters of the light beam are independently modulated on the basis of the first and second complex harmonics of the modulation signal. A Mueller matrix ellipsometer (MME) using this new modulation and a multichannel polarimeter are also described. The data processing and the feedback control of Pockels cells is based on a numerical Fourier transform system. It allows one to measure simultaneously, in one modulation period (20 μs), the 16 coefficients of any Mueller matrix. This MME takes advantage of an easy-to-operate calibration method. The high-frequency modulation of the four parameters of the polarization enables low-light-level measurements (without any chopper and lock-in) and presents spectroscopic capabilities. It provides a promising tool for the study of many subjects of growing interest like, for example, rough surfaces treatment or particle characterization.
New diesel injection nozzle flow measuring device
Authors: Marčič Milan
Published: July 2002

A new measuring device has been developed for diesel injection nozzle testing, allowing measuring of the steady flow through injection nozzle and the injection rate. It can be best applied for measuring the low and high injection rates of the pintle and single hole nozzle. In steady flow measuring the fuel pressure at the inlet of the injection nozzle is 400 bar. The sensor of the measuring device measures the fuel charge, resulting from fuel rubbing in the fuel injection system, as well as from the temperature gradient in the sensor electrode. The electric charge is led to the charge amplifier, where it is converted into electric current and amplified. The amplifier can be used also to measure the mean injection rate value.
Thermal lens determination of end-pumped solid-state lasers with transverse beat frequencies
Authors: Ozygus B. , Erhard J.
Published: July 2002

By measuring the beat frequency of adjacent transverse modes it is possible to determine the thermal lensing of end-pumped laser crystals. Because frequencies are used the method is very precise. Even for very weak thermal lensing the technique can be applied.
The energetics of {113} stacking fault formation in Si from supersaturated interstitials
Authors: Cuendet Nicolas , Halicioglu Timur , Tiller William A.
Published: July 2002

Using a Tersoff-type empirical potential energy function, the free energy of formation for {113}-type stacking faults in silicon has been calculated both as a function of stacking fault rod length and width at a variety of temperatures. A particular tetrahedral-tetrahedral dimer has the lowest free energy of formation at 0 K and this type of stacking fault forms an assemblage of such dimers. The free energy of formation per interstitial in a ribbon fault decreases with ribbon width, ribbon length, and increase of temperature.
High resolution Fowler-Nordheim field emission maps of thin silicon oxide layers
Authors: Ruskell Todd G. , Workman Richard K. , Chen Dong , Sarid Dror , Dahl Sarah , Gilbert Stephen
Published: July 2002

An improved method for characterizing thin oxide films using Fowler-Nordheim field emission is reported. The method uses a conducting-tip atomic force microscope with dual feedback systems, one for the topography and a second for the field emission bias voltage. Images of the voltage required to maintain a 10 pA emission current through a 3 nm oxide film thermally grown on p-type Si(100) demonstrate a spatial resolution of 8 nm.
Thin film light emitting devices from an electroluminescent ruthenium complex
Authors: Lee J.-K. , Yoo D. S. , Handy E. S. , Rubner M. F.
Published: July 2002

A ruthenium polypyridyl complex has been synthesized and examined as an emitter material in thin film electroluminescent devices. This material exhibits photoluminescent and electroluminescent effects as well as several reversible one-electron oxidation and reduction processes. Electroluminescent devices fabricated from this ruthenium complex either via spin coating methods or self-assembly techniques exhibit relatively high electroluminescent efficiencies and luminance levels in some cases as high as 100 cd/m2.