bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth and Induction Kinetics of Inducible and Autoinducible Expression of Heterologous Protein in Suspension Cultures of Recombinant Mouse L Cell Lines
Authors: Gu Man Bock , Todd Paul , Kompala Dhinakar S.
Published: July 2002

Mouse Ltk− cells were transfected with four different plasmids for autoinducible and highly‐inducible expression of the bacterial lacZ gene and cultivated in suspension. Two selection genes, thymidine kinase (tk) and neomycin resistance (neor), were used to select the clones in both cell lines. The resulting two cell lines, designated M4 and R2, differ in that the inducible MMTV promoter from mouse mammary tumor virus (MMTV) controls glucocorticoid receptor (gr) gene and lacZ gene expression in the M4 cell line (“autoinducible”), while the constitutive rous sarcoma virus (RSV) promoter controls gr gene expression and the MMTV promoter controls lacZ gene expression in the R2 cell line (“highly‐inducible”). Both cell lines were stable with respect to reproducibility of growth rate in spinner flasks and inducibility of β‐galactosidase expression. The exponential growth rate of R2 cells was slower than that of M4 cells before induction because the R2 cell line continuously expressed gr genes under the constitutive RSV promoter, and the percent reduction of exponential growth rate mainly caused by gr gene expression was about 20%. The inducibility of the M4 cell line was greater than that of the R2 cell line because in the M4 cell line MMTV promoter controlled gr and lacZ gene expression autoinducibly. Maximum induction of the M4 cell line occurred after induction with the hormone dexamethasone (Dex) at 10−7 M, and the final β‐galactosidase content increased 400‐fold after induction. The optimum conditions for inducer concentration and induction time were determined, and the highest production of β‐galactosidase occurred when Dex was added after the cell concentration had reached its maximum in batch culture. Dex (10−9 M) is a critical inducer concentration in view of inducibility between M4 and R2 cell lines. The inducibility of R2 cell line is higher than that of the M4 cell line from 0 to 10−9 M Dex, but the inducibility of M4 was higher than that of the R2 cell line at Dex concentrations of more than 10−9 M.
Biosynthetic Burden and Plasmid Burden Limit Expression of Chromosomally Integrated Heterologous Genes (pdc,adhB) in Escherichiacoli
Authors: Martinez Alfredo , York Sean W. , Yomano Lorraine P. , Pineda Van L. , Davis Francis C. , Shelton John C. , Ingram Lonnie O.
Published: July 2002

Previous studies have shown an unexpectedly high nutrient requirement for efficient ethanol production by ethanologenic recombinants of Escherichia coli B such as LY01 which contain chromosomally integrated Zymomonas mobilis genes (pdc,adhB) encoding the ethanol pathway. The basis for this requirement has been identified as a media‐dependent effect on the expression of theZ. mobilis genes rather than a nutritional limitation. Ethanol production was substantially increased without additional nutrients simply by increasing the level of pyruvate decarboxylase activity. This was accomplished by adding a multicopy plasmid containing pdc alone (but not adhB alone) to strain LY01, and by adding multicopy plasmids which express pdc and adhB from strong promoters. New strong promoters were isolated from random fragments of Z. mobilis DNA and characterized but were not used to construct integrated biocatalysts. These promoters contained regions resembling recognition sites for 3 different E. coli sigma factors: σ70, σ38, and σ28. The most effective plasmid‐based promoters for fermentation were recognized by multiple sigma factors, expressed both pdc and adhB at high levels, and produced ethanol efficiently while allowing up to 80% reduction in complex nutrients as compared to LY01. The ability to utilize multiple sigma factors may be advantageous to maintain the high levels of PDC and ADH needed for efficient ethanol production throughout batch fermentation. From this work, we propose that the activation of biosynthetic genes in nutrient‐poor media creates a biosynthetic burden that reduces the expression of chromosomal pdc and adhB by competing for transcriptional and translational machinery. This reduced expression can be viewed as analogous to the effect of plasmids (plasmid burden) on the expression of native chromosomal genes.
Structural aspects of cross‐reactivity and its relation to antibody affinity
Authors: Aalberse Rob C. , Kleine Budde Ilona , Stapel Steven O. , Van Ree Ronald
Published: July 2002

In the context of IgE/allergen interactions, affinity is largely determined by the stability of the allergen‐IgE complex: a low affinity is usually equated with a rapid dissociation of the complex. Regular solid‐phase assays are not well suited for affinity estimates because of multivalency effects, “unstirred layer” effects and “invisible” antibodies. Elution of IgE bound to solid‐phase coupled allergen might be a good measure of intrinsic affinity, provided that reassociation of antibodies is prevented by a high concentration of soluble allergen. Allergen‐mediated IgE‐dependent triggering of a mast cell is presumably a two‐step process. During the first step, the allergen is bound to a cell‐bound IgE antibody and dragged over the cell surface. The second step is the interaction between this cell‐bound allergen and another IgE antibody. The hypothesis is that the affinity requirements for the first step are higher than for the second. The implication is that a mast cell can be triggered by a single high‐affinity antibody in combination with one or more low‐affinity antibodies.
Nonallergic anaphylaxis to pantoprazole
Authors: Kaatz M. , Bauer A. , Hipler C. , Elsner P.
Published: July 2002

Consider reactions to proton pump blockers in suspected food hypersensitivity
Influence of hydrophobic interactions on the conformational adaptability of the β‐Ala residue
Authors: Thakur A.K. , Kishore R.
Published: July 2002

Abstract: The chemical synthesis and X‐ray crystal structure analysis of a model peptide incorporating a conformationally flexible β‐Ala residue: Boc‐β‐Ala‐Pda, 1 (C23H46N2O3: molecular weight = 398.62) have been described. The peptide crystallized in the crystal system triclinic with space group P21: a = 5.116(3) Å, b = 5.6770(10) Å, c = 21.744(5) Å; α = 87.45°, β = 86.87°, γ = 90.0°; Z = 1. An attractive feature of the crystal molecular structure of 1 is the induction of a reasonably extended backbone conformation of the β‐Ala moiety, i.e. the torsion angles φ ≈ −115°, µ ≈ 173° and ψ ≈ 122°, correspond to skew−, trans and skew+ conformation, respectively, by an unbranched hydrophobic alkyl chain, Pda, which prefers an all‐anti orientation (θ1 ≈ −153°, θ2 ≈ … θ14 ≈ ±178°). The observation is remarkable because, systematic conformational investigations of short linear β‐Ala peptides of the type Boc‐β‐Ala‐Xaa‐OCH3 (Xaa = Aib or Acc6) have shown that the chemical and stereochemical characters of the neighboring moieties may be critical in dictating the overall folded and/or unfolded conformational features of the β‐Ala residue. The overall conformation of 1 is typical of a ‘bar’. It appears convincing that, in addition to a number of hydrophobic contacts between the parallel arranged molecules, an array of conventional N‐H…O=C intermolecular H‐bonding interactions stabilize the crystal molecular structure. Moreover, the resulting 14‐membered pseudo‐ring motif, generated by the amide–amide interactions between the adjacent molecules, is completely devoid of nonconventional C−H…O interaction. The potentials of the conformational adaptation of the β‐Ala residue, to influence and stabilize different structural characteristics have been highlighted.
Distinctive anti-influenza properties of recombinant collectin 43
Authors: HARTSHORN Kevan L. , HOLMSKOV Uffe , HANSEN Soren , ZHANG Pengnian , MESCHI Joseph , MOGUES Tirsit , WHITE Mitchell R. , CROUCH Erika C.
Published: July 2002

Collectins play important roles in innate defence against viral, fungal and bacterial pathogens. CL-43, a bovine serum collectin, which appears to have evolutionarily evolved from surfactant protein D (SP-D), shows unique structural and functional properties. In the present study, we describe the initial characterization of a recombinant CL-43 expressed in mammalian cells. Like natural CL-43, the recombinant is secreted as trimeric forms that show a preference for mannose and N-acetyl mannosamine. The natural and recombinant proteins have significantly higher haemagglutination-inhibiting activity against influenza A virus (IAV) than recombinant trimeric forms of SP-D. In contrast with the more highly multimerized forms of SP-D, namely conglutinin or mannose-binding lectin, CL-43 did not induce viral or bacterial aggregation and did not enhance IAV-induced neutrophil H2O2 generation. Like SP-D, CL-43 also strongly enhanced neutrophil uptake of IAV. However, the mechanism of this enhanced internalization is different from that of SP-D in that it did not require viral aggregation. These studies establish that the trimeric structure of CL-43 is specified by its primary sequence and indicate that this naturally occurring trimeric collectin has unique antiviral activities. These findings could facilitate the development of recombinant collectins with novel antimicrobial properties.
Epitope mapping of the O‐chain polysaccharide of Legionella pneumophila serogroup 1 lipopolysaccharide  by saturation‐transfer‐difference NMR spectroscopy
Authors: Kooistra Oliver , Herfurth Lars , Lüneberg Edeltraud , Frosch Matthias , Peters Thomas , Zähringer Ulrich
Published: July 2002

Two modifications of 5‐acetimidoylamino‐7‐acetamido‐3,5,7,9‐tetradeoxy‐d‐glycero‐d‐galacto‐non‐2‐ulosonic acid (5‐N‐acetimidoyl‐7‐N‐acetyllegionaminic acid) in the O‐chain polysaccharide (OPS) of the Legionella pneumophila serogroup 1 lipopolysaccharide (LPS) concern N‐methylation of the 5‐N‐acetimidoyl group in legionaminic acid. Both N‐methylated substituents, the (N,N‐dimethylacetimidoyl) amino and acetimidoyl(N‐methyl)amino group, could be allocated to one single legionaminic acid residue in the long‐ and middle‐chain OPS, respectively. Using mutants devoid of N‐methylated legionaminic acid derivatives, it could be shown that N‐methylation of legionaminic acid correlated with the expression of the mAb 2625 epitope. In the present study we investigated the binding of the LPS‐specific monoclonal antibody mAb 2625 to isolated OPS with surface‐plasmon‐resonance biomolecular interaction analysis and saturation‐transfer‐difference (STD) NMR spectroscopy in order to map the mAb 2625 epitope on a molecular level. It could be demonstrated that the binding affinity of the N‐methylated legionaminic acid derivatives was independent from the size of the isolated OPS molecular species. In addition, STD NMR spectroscopic studies with polysaccharide ligands with an average molecular mass of up to 14 kDa revealed that binding was mainly mediated via the N‐methylated acetimidoylamino group and via the closely located 7‐N‐acetyl group of the respective legionaminic acid residue, thus indicating these derivatives to represent the major epitope of mAb 2625.
Anthropogenic change in subtropical dry forest during a century of settlement in Jaiquí Picado, Santiago Province, Dominican Republic
Authors: Roth Linda C.
Published: July 2002

AimThe dry forests of the tropics have received little scholarly attention relative to their significance and their rate of disappearance. This study aimed to characterize the structure and composition of two intermingled Antillean subtropical dry forest types and shed light upon their origins, development, and possible future conditions.

LocationJaiquí Picado, Santiago Province, Dominican Republic (19° 26′ N, 70° 54′ W).

MethodsBiophysical data from quadrat sampling of vegetation, soils, and site characteristics were subjected to cluster analysis, means comparisons, discriminant analysis, and linear regression. Extensive interviews with local land users provided information on early forests as well as present and historical land use practices.

ResultsSpatial patterning of the area's two main forest types relates closely to past land use but not to any observed differences in the physical characteristics of their sites. ‘Old‐growth’ stands found on land never placed in cultivation resemble the forests encountered by late‐nineteenth‐century settlers of the area in their wealth of woody plant taxa and relative abundance of endemic and other native species. In the ‘scrub’ stands growing on land abandoned from grazing, fully 70% of stems belong to one native (Acacia macracantha Willd.) and two exotic (Haematoxylon campechianum L. and Prosopis juliflora (Sw.) DC.) woody legumes that contribute to the markedly greater representation of deciduous and thorn‐bearing individuals in this type. The two forest types do not differ significantly in average bole dimensions, but the canopies of scrub stands are concentrated in a narrower layer, their understories are more open, and they contain more multiple stems of apparent sprout origin. A chronosequence of scrub stands covering a range in age of three decades indicates a moderate increment in species diversity over time and gradual disappearance of some of the more abundant invasive shrubs; but such stands continue to be dominated throughout this period by the same three scrub trees, while most species characteristic of old‐growth forests, including many of the least abundant, fail to appear among the regeneration in their understories.

Main conclusionsAntillean forests classified as thorn scrub may include a form of ‘disclimax’ created through past land use activities in areas once bearing more diverse tropical dry forest. Whether they will ever develop into stands similar to the previous forests is uncertain, given the present state of fragmentation and other processes taking place within these ecosystems.
THE PATTERN OF NODAL RECURRENCE FOLLOWING DEFINITIVE RADIOTHERAPY FOR NASOPHARYNGEAL CARCINOMA
Authors: Khoo Mark L. C. , Soo Khee‐Chee , Lim Dennis T. H. , Fong KAM‐WENG , Sethi Christopher H. K. Goh§** and Dharambir S.
Published: July 2002

Background: The pattern of nodal metastasis in previously untreated nasopharyngeal carcinoma (NPC) has been studied and reported. In order to analyse the pattern of recurrent nodal disease in previously treated NPC, a retrospective study on 68 patients who underwent radical neck dissection for regionally recurrent NPC was conducted.

Methods: Seventy‐four neck dissections were performed on 68 patients who developed nodal recurrence after a mean disease‐free interval of 39.2 months. None of the patients had evidence of local or systemic disease at the time of surgery. Histopathological reports of the 74 neck dissections were analysed with regard to the number of positive nodes as well as the number of involved nodal levels.

Results: Of the 65 neck dissection specimens with analysable data, 31 showed metastatic disease at a single nodal level with a mean number of positive nodes of 1.2, while 34 showed metastatic disease at multiple levels with a mean number of positive nodes of 6.6. Nodal recurrence occurred at level II with the greatest frequency (78.5%). Of the 31 specimens with single level nodal involvement, 21 (67.7%) occurred at level II. Isolated involvement at the other levels did occur, but was uncommon (range 3–16%). Of the 34 specimens with multiple level nodal involvement, 30 (88.2%) showed involvement at level II. Once more than one level was involved, the frequency of involvement at any given level was at least 30%.

Conclusion: The predominant involvement at level II and the high frequencies of involvement at all levels support the use of a classical radical neck dissection in treating recurrent nodal disease in NPC.
IMPLANTATION CARCINOMA DEVELOPING LATE AFTER LAPAROSCOPIC CHOLECYSTECTOMY FOR SUPERFICIAL CARCINOMA OF THE GALL‐BLADDER
Authors: Wettstein A. R. , Field A. S. , Hugh T. B. , Vickers C. R.
Published: July 2002

Key words: laparoscopic cholecystectomy, tumour implantation.
EARLY EXPERIENCE WITH CLINICAL INDICATORS IN SURGERY
Authors: Collopy B. T. , Rodgers L. , Woodruff P. , Williams J.
Published: July 2002

Background: In 1997 a set of 53 clinical indicators developed by the Royal Australasian College of Surgeons (RACS) and the Australian Council on Healthcare Standards (ACHS) Care Evaluation Programme (CEP), was introduced into the ACHS Evaluation and Quality Improvement Programme (EQuIP). The clinical indicators covered 20 different conditions or procedures for eight specialty groups and were designed to act as flags to possible problems in surgical care.

Methods: The development process took several years and included a literature review, field testing, and revision of the indicators prior to approval by the College council. In their first year 155 health‐care organizations (HCO) addressed the indicators and this rose to 210 in 1998. Data were received from all states and both public and private facilities.

Results: The collected data for 1997 and 1998 for some of the indicators revealed rates which were comparable with those reported in the international literature. For example, the rates of bile duct injury in laparoscopic cholecystectomy were 0.7 and 0.53%, respectively; the mortality rates for coronary artery graft surgery were 2.5 and 2.1%, respectively; the mortality rates after elective abdominal aortic aneurysm repair were 2.5 and 3.7%, respectively; and the post‐tonsillectomy reactionary haemorrhage rates were 0.9 and 1.3%, respectively. Results for some indicators differed appreciably from other reports, flagging the need for further investigation; for example, the negative histology rates for appendectomy in children were 18.6 and 21.2%, respectively, and the rates for completeness of excision of malignant skin tumours were 90.7 and 90%, respectively. The significance of these figures, however, depends upon validation of the data and their reliability and reproducibility. Because reliability can be finally determined only at the hospital level they are of limited value for broader comparison.

Conclusion: The process of review established for the indicator set has led to refinement of some indicators through improvement of definitions, and to a considerable reduction in the number of indicators to 29 (covering 18 procedures), for the second version of the indicators (which was introduced for use from January 1999). The clinical indicator programme, as it has with other disciplines, hopefully will provide a stimulus to the modification and improvement of surgical practice. Clinician ownership should enhance the collection of reliable data and hence their usefulness.
In‐patient management of diabetes mellitus and patient satisfaction
Authors: Bhattacharyya A. , Christodoulides C. , Kaushal K. , New J. P. , Young R. J.
Published: July 2002

Aims To devise a system for assessing in‐patient glycaemic control and care satisfaction in diabetic patients admitted to hospital for reasons other than their diabetes.

Methods Consecutive January to March 2001 case‐notes were reviewed. Admissions with acute metabolic complications, acute myocardial infarction and pregestational or gestational diabetes were excluded. Glycaemic control, frequency of blood monitoring and management of hyperglycaemia were recorded. The diabetes treatment satisfaction questionnaire was used to assess preadmission satisfaction with care. Post‐admission a 12‐stem questionnaire was used to assess satisfaction with in‐patient diabetes management.

Results Hypoglycaemia was common. Although none developed a hyperglycaemic emergency, high blood glucose was prevalent and, frequently, persistent hyperglycaemia or recurrent hypoglycaemia was not acted on appropriately. The overall score for in‐patient satisfaction with treatment was fair (4.1 ± 1.8 on a six‐point scale; 6 = very satisfied and 1 = very dissatisfied). Scores were higher among patients on surgical wards than on medical wards (P = 0.008), but satisfaction did not vary when patients were stratified according to sex, age and mode of treatment.

Conclusion Current systems are not achieving satisfactory in‐patient glycaemic control and there is poor satisfaction with medical in‐patient diabetes care. Following changes intended to produce improvements, this assessment system can be used recurrently to monitor in‐patient care and satisfaction.
Cushing's syndrome secondary to inhaled corticosteroids mimicking HIV‐associated lipodystrophy
Authors: Le Roux CW , Beckles MA , Besser GM , Pinching AJ , Davison AG
Published: July 2002

We report the case of an asthmatic man with HIV infection who was initially diagnosed with HIV treatment‐associated lipodystrophy. Further investigations showed he had Cushing's syndrome secondary to 1600 μg of budesonide dry powder inhaler. Cushing's syndrome has not been reported previously on this normal dose of inhaled budesonide.
Fetal echocardiography during indomethacin treatment
Authors: Respondek M. , Weil S. R. , Huhta J. C.
Published: July 2002

Fetal echocardiograms were evaluated in 315 studies performed in 107 fetuses exposed to indomethacin. In the majority of cases, the results of the fetal echocardiography study were within normal limits (74%). The most common abnormal phenomena were tricuspid valve regurgitation (10%), ductal constriction (6%), tricuspid valve regurgitation and ductal constriction (5%), an increased ductal velocity (2%), and other (3%).

The difference between the prevalence of ductal constriction in the whole series of studies (11%) compared to the prevalence of ductal constriction per fetus (25%) (p < 0.001) suggests that this phenomenon was only temporary and disappeared when medication was discontinued. The mean gestational age for detection of tricuspid valve regurgitation was 27.7 ± 2.8 weeks and for ductal constriction, 30.9 ± 2.1 weeks (t‐test, p < 0.01). Trivial tricuspid valve regurgitation was detected at a mean of 26.7 ± 2.2 weeks and significant tricuspid valve regurgitation at 29.6 ± 2.3 weeks (t‐test, p < 0.01).

We conclude that indomethacin treatment is relatively safe for the fetal heart. The most common side‐effects are tricuspid valve regurgitation and ductal constriction. Tricuspid valve regurgitation may be detected before ductal constriction, but by itself it is not a contraindication for the continued use of indomethacin. Copyright © 1995 International Society of Ultrasound in Obstetrics and Gynecology
The effect of overstorey proteas on plant species richness in South African mountain fynbos
Authors: Vlok J. H. J. , Yeaton R. I.
Published: July 2002

Two South African mountain fynbos sites, similar in drainage, elevation, slope angle, slope aspect and soil type but with differing fire histories, were studied to measure how the effect of high densities of overstorey proteas in one fire cycle affects the α‐diversity levels of the plant community in the following fire‐cycle, how their repeated absence due to several short fire‐cycles affects their species richness and finally, at what spatial scale such patterns are most appropriately measured. High prefire canopy cover percentages and densities of overstorey proteas increase the postfire α‐diversity of understorey species. In addition, the increase in species richness observed occurred for all higher plant life history types present. At sites where one or more short fire cycles resulted in the repeated absence of overstorey proteas, the number of plant species present in the understorey was lower than at a site where overstorey proteas persisted. These results are dependent on the spatial scale at which the α‐diversity of understorey species is measured. At small quadrat sizes (< 5 m2), overstorey proteas decrease the number of understorey species present, while at larger quadrat sizes (100 m2) higher species richness is observed. The contradiction in conclusions when α‐diversity is measured at different spatial scales can be attributed to the patchiness of fynbos communities. Overstorey proteas play an important role in maintaining the patchiness component of fynbos communities by diminishing the effect of understorey resprouting species, making available regeneration niches for the maintenance of plant species richness. Where small quadrats are used, the effect of patchiness on the dynamics of the mountain fynbos community is lost. Thus, it is the fire history prior to the last fire and how it affects overstorey proteas that is important in the determination of α‐diversity levels in mountain fynbos plant communities.
Expression of the Tobacco Ext 1.4 Extensin Gene Upon Mechanical Constraint and Localization of Regulatory Regions
Authors: Salvá I. , Jamet É.
Published: July 2002

Abstract: The regulation of the Ext 1.4 gene encoding a tobacco (Nicotiana tabacum L.) extensin was studied in response to mechanical constraints. Transgenic plants carrying chimeric Ext 1.4 promoter/GUS (β‐glucuronidase)/nos terminator or Ext 1.4 3′‐end constructs were obtained. Expression of gene fusions was found in tissues where mechanical stresses occur, e.g., during germination, as well as in root and stem tissues. Chimeric genes were successively and transiently expressed in different tissues during germination, i.e., at the tip of the root and then in the hypocotyl, during their growth through the seed coat. Moreover, they were expressed in cortical cells surrounding the emergence of adventitious and lateral roots and developmentally‐regulated in nodes. The expression of Ext 1.4 could be induced by imposing mechanical constraints due to curving of either the stems or roots. Expression then occurred in cells where it does not normally occur, i.e., in cortical cells of internodes and in the distal piliferous zone of roots. Accumulation of RNAs occurs several days after the start of the constraint. Promoter regions involved in regulation of expression of Ext 1.4 in stems, roots, and in seedlings upon mechanical constraint could be localized. Moreover, the 3′ non‐coding region was shown to modulate expression in roots. These results suggest that the regulation of Ext 1.4 following mechanical stress is dependent on both tissue‐specific and mechanical‐responsive elements.
Effect of Gibberellic Acid on Cell Division and Cell Elongation in Anthers of the Gibberellin Deficient gib‐1 Mutant of Tomato
Authors: van den Heuvel K. J. P. T. , Barendse G. W. M. , Wullems G. J.
Published: July 2002

Abstract: Analysis of flower development in the gibberellin (GA) deficient gib‐1 tomato mutant showed that while flower development is arrested the anther growth slowed down unless GA was applied. Northern blot analyses showed that treatment with GA3 enhanced the expression of genes which are correlated with DNA replication (histones h1 and h2b) and cell elongation (expansin and α‐tubulin). In anthers, at developmental arrest, cell elongation was affected in the tapetum, pollen mother cells and epidermal cells. Elongation was significantly less in the longitudinal direction, while in the transverse direction outer tapetum and pollen mother cells were also smaller. Except for the outer tapetum, the cell numbers were the same as in wild‐type tomato, indicating that cell division was less influenced. Scanning electron microscopy revealed that on the lateral surface of gib‐1 anthers the epidermal cells that were affected in their elongation due to GA deficiency did not differentiate into interlocking hairs. Induction of hair development, of which the timing was similar to wild type, occurred after treatment with GA3, GA1, GA4 and GA9, while GA20 was less effective. Analysis of the in situ localization of expansin and histone h2b transcripts in gib‐1 anthers after GA3 treatment revealed that the increased mRNA accumulation was predominantly localized in the cells that were less elongated compared to wild‐type cells. The consequence of reduced cell elongation due to GA deficiency on anther development is discussed.
Enhanced J
c properties in superconducting NbTi composites by introducing Nb artificial pins with a layered structure
Authors: Matsumoto Kaname , Takewaki Hirokazu , Tanaka Yasuzo , Miura Osuke , Yamafuji Kaoru , Funaki Kazuo , Iwakuma Masataka , Matsushita Teruo
Published: July 2002

High critical current densities (4250 A/mm2 at 5 T, 4.2 K, and 15 000 A/mm2 at 2 T, 4.2 K) were achieved by using an artificially designed pin structure composed of randomly oriented clusters of Nb/NbTi multilayer in a NbTi composite superconductor (with a round cross section). The maximum values were obtained when the Nb layer thickness was designed to be approximately twice the coherence length in NbTi, where the layer thickness is five to ten times thicker than that of the optimized α-Ti ribbon thickness in a conventional NbTi system.
Formation of new energy bands and minigap suppression by hybridization of barrier and well resonances in semiconductor superlattices
Authors: Sirtori Carlo , Capasso Federico , Sivco Deborah L. , Cho Alfred Y.
Published: July 2002

The first observation of band structure phenomena arising from the degeneracy of barrier and well resonances in suitably designed superlattices is reported. These effects are characterized by the formation of new minibands and the suppression of a minigap at a Brillouin zone boundary leading to striking modifications of the absorption spectrum. The interesting implications of this phenomenon for electronic transport are discussed.
A novel method to study single-particle dynamics by the resistive pulse technique
Authors: Berge L. I. , Feder J. , Jo/ssang T.
Published: July 2002

We have developed a new method, a pressure-reversal technique, which extends the uses of the resistive pulse (Coulter counter) technique to single-particle dynamics. The resistive pulse technique measures the increase in resistance when particles suspended in an electrolyte are transported through a current-carrying aperture. By the new method, the pressure is reversed when a particle exits the pore. A trigger signal, derived from the particle pulses, is used to activate two miniature solenoid valves which serve as pressure switches. In this way, the particle reenters the pore. A single particle flowing back and forth may be studied over a long period of time. The time the particle spends outside the pore between reversals is variable from a few milliseconds to several seconds. We have so far used pore diameters in the range of 3–30 μm. The new technique enables us to study single-particle dissolution and single-particle flow dynamics. The experimental arrangement and the details of the new method are described together with some illustrative measurements.
High-speed image-acquisition system for energy subtraction angiography
Authors: Nishimura K. , Hyodo K. , Hosaka R. , Ando M. , Akisada M. , Hasegana S. , Takenaka E.
Published: July 2002

The aim of this study is to visualize the coronary artery with the intravenus injection of contrast media. We propose a method of rapid and successive acquisition of two-dimensional images in a digital processing system which uses a pair of video cameras, a shutter operation, and a beam-splitting apparatus. A prototype of the high-speed acquisition system was constructed. The two-monochromatic video-camera method was very suitable for quick acquisition. Electro-optical shutters (PLZT) were found practical with respect to the dynamic range and response time. The field blanking method was essential for the data acquisition.
Virtual phase CCD x-ray detectors
Authors: Clarke Roy , Rodricks Brian , Smither Robert
Published: July 2002

A two-dimensional charge-coupled device (CCD) detector, based on the Texas Instruments ‘‘virtual phase’’ CCD, has been developed at the University of Michigan for synchrotron radiation applications. A series of performance tests were carried out at the LURE synchrotron facility, and the results show that the detector is ideally suited to measurements in dispersive absorption spectroscopy, high-resolution diffuse scattering, and small-angle scattering. The characteristics of the detector also show great promise for time-resolved experiments.
Xenon ion sources for space applications (invited)
Authors: Beattie J. R. , Matossian J. N.
Published: July 2002

In this article, we describe the technology of xenon ion thrusters under development for space-propulsion and plasma-contactor applications. Emphasis is placed on the 1.4-kW Xenon Ion Propulsion Subsystem (XIPS) designed for satellite stationkeeping. The 25-cm-diam XIPS thruster produces 63.5 mN of thrust at a specific impulse of 2800 s, requiring only about one-tenth the propellant mass of conventional chemical-propulsion systems. Using a ring-cusp magnetic field to confine the discharge plasma, the XIPS thruster converts input power into thrust-beam power with an efficiency of over 82%. We also describe a XIPS ion source under development for more demanding propulsion applications such as orbit raising. A 30-cm-diam laboratory-model XIPS thruster scaled from the smaller unit produces over 340 mN of thrust with an input power in excess of 10 kW and a specific impulse of about 4900 s. Under these operating conditions, the XIPS thruster converts input power into thrust-beam power with an efficiency of 91%. With its ion-extraction electrodes and ion-beam neutralizer removed, the XIPS discharge chamber has been shown to be a highly efficient xenon plasma contactor for a variety of applications, ranging from space-science investigations to electrodynamic tethers. We will describe a 1991 flight application in which our 25-cm XIPS plasma contactor will be used to stabilize the electrical potential of the Shuttle Orbiter during firings of a 1.5-A electron beam from its payload bay.
Device for dispersal of micrometer- and submicrometer-sized particles in vacuum
Authors: Sheehan D. P. , Carillo M. , Heidbrink W.
Published: July 2002

A simple, versatile device for dispersing micrometer- and submicrometer-sized particles in vacuum is described. The source allows control of particle size (0.5 μm≤l≤200 μm) and particle flux density up to roughly 107 cm−2 s−1. Several types of microparticles were successfully dispersed.
Two-dimensional real-time imaging system for subtraction angiography using an iodine filter
Authors: Umetani Keiji , Ueda Ken , Takeda Tohoru , Anno Izumi , Itai Yuji , Akisada Masayoshi , Nakajima Teiichi
Published: July 2002

A new type of subtraction imaging system was developed using an iodine filter and a single-energy broad bandwidth monochromatized x ray. The x-ray images of coronary arteries made after intravenous injection of a contrast agent are enhanced by an energy-subtraction technique. Filter chopping of the x-ray beam switches energies rapidly, so that a nearly simultaneous pair of filtered and nonfiltered images can be made. By using a high-speed video camera, a pair of two 512 × 512 pixel images can be obtained within 9 ms. Three hundred eighty-four images (raw data) are stored in a 144-Mbyte frame memory. After phantom studies, in vivo subtracted images of coronary arteries in dogs were obtained at a rate of 15 images/s.
Electrometer preamplifier for scanning tunneling microscopy
Authors: Chen Y. P. , Cox A. J. , Hagmann M. J. , Smith H. D. A.
Published: July 2002

An optimized current preamplifier, consisting of a shunt resistor followed by a high speed field-effect transistor input instrumentation amplifier, appears suitable for use in scanning tunneling microscopy. The preamplifier has a transimpedance of 100 MΩ, a measured 3 dB bandwidth of 200 kHz, low phase distortion, and excellent noise performance.
Elastomeric binary phase gratings for measuring acceleration, displacement, strain, and stress
Authors: Rogers John A. , Qin Dong , Schueller Olivier J. A. , Whitesides George M.
Published: July 2002

This article describes the fabrication and operating principles of a device suitable for measuring displacements, stresses, strains, accelerations, and forces. The device consists of an elastomeric material with a surface relief diffraction grating embossed on its surface. Mechanical compression of this element changes the way that it diffracts light. This article also describes designs and performance characteristics of simple accelerometers and pressure sensors based on these devices.
Design of an imaging bolometer system for the large helical device
Authors: Wurden G. A. , Peterson B. J. , Sudo Shigeru
Published: July 2002

We describe a radical design for a bolometer system employing infrared (IR) imaging of a segmented-matrix absorber in a cooled-pinhole camera geometry, which we will prototype and demonstrate on the large helical device (LHD).1 LHD will be operational in early 1998, with an l=2 superconducting winding, a major radius of 3.9 m, a minor radius of 0.5–0.65 m, and input powers ranging from 3 MW (steady state) to 30 MW (pulsed). The bolometer design parameters are determined by modeling the temperature of the foils making up the detection matrix using a two-dimensional time-dependent solution of the heat conduction equation. This design will give a steady-state bolometry capability, with modest (60 Hz) time resolution, while simultaneously providing hundreds of channels of spatial information. No wiring harnesses will be required, as the temperature-rise data is measured via a 12-bit, ±0.025 °C resolution, 3–5 μm band, 256×256 pixel IR camera. The spatial data will be used to tomographically invert the profile of the highly shaped stellarator main plasma and divertor radiation, in conjunction with more conventional fanned arrays of traditional bolometers.
High-resolution high-speed synchronous epifluorescence imaging of cardiac activation
Authors: Lin Shien-Fong , Abbas Rashida A. , Wikswo John P.
Published: July 2002

An optical imaging technique with high spatial and temporal resolution was developed to record fractional changes in laser-induced epifluorescence associated with the cardiac transmembrane potential during and after the application of monophasic point stimuli. The technique takes advantage of the repeatability of the recorded events, and uses a synchronized laser strobing mechanism to overcome the speed limitation inherent to slow-scan charge-coupled device cameras, and achieves an effective frame rate of 500 frames/s at a spatial resolution of 100×100 pixels in a single frame with a pixel resolution of 75 μm. The signal-to-noise ratio can be improved with boxcar averaging. Patterns of virtual cathode and anode with distinctive regions of simultaneous depolarization and hyperpolarization during stimulation are demonstrated with stimuli applied to the resting myocardium of an isolated rabbit heart. The technique described in this article provides a powerful tool for investigating repeatable dynamics in the function of electrically active tissue.
Characterization of a low-energy constricted-plasma source
Authors: Anders André , Kühn Michael
Published: July 2002

The construction and principle of operation of the constricted-plasma source are described. A supersonic plasma stream is produced by a special form of a dc-glow discharge, the constricted glow discharge. The discharge current and gas flow pass through an orifice of small diameter (constriction) which causes a space charge double layer but also serves as a nozzle to gas-dynamically accelerate the plasma flow. Plasma parameters have been measured using Langmuir probes, optical emission spectroscopy, and a plasma monitor for mass-resolved energy measurements. Experiments have been done with nitrogen as the discharge gas. It was found that the energy distribution of both atomic and molecular ions have two peaks at about 5 and 15 eV, and the energy of almost all ions is less than 20 eV. The ionization efficiency decreases with increasing gas flow. The downstream plasma density is relatively low but activated species such as excited molecules and radicals contribute to film growth when the source is used for reactive film deposition.
Thulium-doped intrinsic fiber optic sensor for high temperature measurements (>1100 °C)
Authors: Zhang Zhi-Yi , Grattan K. T. V. , Palmer A. W. , Meggitt B. T.
Published: July 2002

The need to achieve higher temperature performance from fluorescence-based optical thermometers has prompted the investigation of a range of rare-earth doped materials. In this work, results are presented on the use of a thulium-doped fiber-based system. The performance of the thermometer is presented, and stable measurements at temperatures up to 1250 °C are reported using the fluorescence lifetime approach.
Hardness, elastic modulus, and structure of very hard carbon films produced by cathodic-arc deposition with substrate pulse biasing
Authors: Pharr George M. , Callahan Daniel L. , McAdams Shaun D. , Tsui Ting Y. , Anders Simone , Anders André , Ager Joel W. , Brown Ian G. , Bhatia C. Singh , Silva S. R. P. , Robertson John
Published: July 2002

The hardness, elastic modulus, and structure of several amorphous carbon films on silicon prepared by cathodic-arc deposition with substrate pulse biasing have been examined using nanoindentation, energy loss spectroscopy (EELS), and cross-sectional transmission electron microscopy. EELS analysis shows that the highest sp3 contents (85%) and densities (3.00 g/cm3) are achieved at incident ion energies of around 120 eV. The hardness and elastic modulus of the films with the highest sp3 contents are at least 59 and 400 GPa, respectively. These values are conservative lower estimates due to substrate influences on the nanoindentation measurements. The films are predominantly amorphous with a ∼20 nm surface layer which is structurally different and softer than the bulk.
Determination of surface polarity of c-axis oriented ZnO films by coaxial impact-collision ion scattering spectroscopy
Authors: Ohnishi T. , Ohtomo A. , Kawasaki M. , Takahashi K. , Yoshimoto M. , Koinuma H.
Published: July 2002

We have identified the surface polar structure of wurtzite-type ZnO films by coaxial impact-collision ion scattering spectroscopy. High-quality ZnO epitaxial films were prepared on sapphire (α-Al2O3) (0001) substrates by laser molecular beam epitaxy using a ZnO ceramic target. The (0001̄) crystallographic plane (the O face) was found to terminate the top surface of the ZnO film by comparing spectra of the films with those of well-defined (0001) and (0001̄) surfaces of bulk single crystals. The preferential [0001̄] growth direction of ZnO films is discussed from the viewpoints of the chemical interaction at the interface and surface stability against sublimation.
Near-equilibrium growth of micropipe-free 6H-SiC single crystals by physical vapor transport
Authors: Schulze N. , Barrett D. L. , Pensl G.
Published: July 2002

A process for growing micropipe-free single crystals has been developed by using the modified Lely method. The process parameters were kept close to thermal equilibrium. The maximum average thermal gradient inside the growth furnace leading to micropipe-free growth was 5 K/cm. A gradient of 7.5 K/cm already resulted in a strong defect formation and produced a high density of micropipes (>200 cm−2). The highest achieved growth rate providing micropipe-free growth was 0.27 mm/h. For the employed parameter range, 6H-SiC single boule crystals were grown on both the C face and the Si face of 6H-SiC Lely platelets. The grown crystals are electrically and optically characterized.
Tapping-mode atomic force microscopy and phase-imaging in higher eigenmodes
Authors: Stark Robert W. , Drobek Tanja , Heckl Wolfgang M.
Published: July 2002

Tapping-mode atomic force microscopy (TM-AFM) is a powerful tool to study soft biological samples. Higher eigenmodes of the vibrating cantilever offer enhanced signal and smaller time constants increasing the sensitivity of the tapping probe as compared to conventional TM-AFM. The first five eigenmodes of a v-shaped silicon cantilever were investigated with respect to their suitability for imaging. Stable imaging was possible in the first and third modes. Phase imaging in the third mode was extremely sensitive to surface inhomogeneities and surface contamination particles not visible in standard TM-AFM.
A method for fabricating large-area, patterned, carbon nanotube field emitters
Authors: Xu Xueping , Brandes G. R.
Published: July 2002

A method for fabricating large-area patterned carbon nanotube field emitters is reported. Carbon nanotube films were prepared by first depositing and patterning a transition metal catalyst film on a substrate and then by heating the substrate in a hydrocarbon atmosphere. The catalytically grown carbon nanotube films had a high emission current density of about 100–1000 mA cm−2 at a low macroscopic electric field of 10–15 V μm−1. Electron emission from the carbon nanotube films was observed at a macroscopic electric field of 1–5 V μm−1. The I–V curve obeyed the Fowler–Nordheim (FN) relationship at low emission current density, but at high electric field, the I–V curve deviated from the FN relationship due to defects on the tip of the catalytically grown carbon nanotubes. The catalytic growth of carbon nanotubes offers an inexpensive and controllable process to produce a uniform, high density of emitters on large substrate surfaces.
Electroluminescence of a cubic GaN/GaAs (001) p–n junction
Authors: As D. J. , Richter A. , Busch J. , Lübbers M. , Mimkes J. , Lischka K.
Published: July 2002

A cubic GaN p–n diode has been grown on n-type GaAs (001) substrates by plasma assisted molecular epitaxy. For p- and n-type doping, elemental Mg and Si beams have been used, respectively. The optical properties are characterized by photoluminescence at room temperature and 2 K. Current–voltage and capacitance–voltage measurements of the cubic GaN n+–p junction are performed at room temperature. The electroluminescence at 300 K is measured through a semitransparent Au contact. A peak emission at 3.2 eV with a full width at half maximum as narrow as 150 meV is observed, indicating that near-band edge transitions are the dominating recombination processes in our device. A linear increase of the electroluminescence intensity with increasing current density is measured.
Fabrication of n-type 4H–SiC/Ni junctions using electrochemical deposition
Authors: Oskam G. , Searson P. C. , Cole M. W.
Published: July 2002

We report on the electrochemical deposition of nickel films on n-type 4H–SiC. High quality nickel films were prepared by a double potential pulse method. The as-deposited n-SiC/Ni junctions were rectifying with a barrier height of about 1.8 eV. The contact was converted to an ohmic junction by annealing at 950 °C in a 10% H2/N2 atmosphere.
Probing deep interaction potentials with white-noise-driven atomic force microscope cantilevers
Authors: Koralek D. O. , Heinz W. F. , Antonik M. D. , Baik A. , Hoh J. H.
Published: July 2002

Perturbations to the thermally driven motion of an atomic force microscope (AFM) cantilever can be used to probe tip-sample interactions. One limitation of such thermal-noise-based measurements is that they fail for large attractive interactions with force gradients that exceed the stiffness of the cantilever. In such cases, the AFM tip jumps to the surface and is trapped there for long periods of time. Here, we describe an approach to overcome this limitation by driving the AFM cantilever with white noise, essentially simulating high temperatures. Effective temperatures of several thousand Kelvin are easily obtained. We show that this approach allows the AFM tip to “thermally” sample interactions that would otherwise capture the tip.
Formation of periodic steps with a unit-cell height on 6H–SiC (0001) surface by HCl etching
Authors: Nakamura Shun-ichi , Kimoto Tsunenobu , Matsunami Hiroyuki , Tanaka Satoru , Teraguchi Nobuaki , Suzuki Akira
Published: July 2002

Step bunching on 6H–SiC (0001)-vicinal face etched by HCl at 1300–1500 °C is investigated by atomic force microscopy. When the substrate has the inclination toward near 〈011̄0〉 or even 〈112̄0〉, continuous parallel and periodic microsteps with six-bilayer height are laid perpendicular to the off direction, although those perpendicular to 〈112̄0〉 are apt to decompose into three bilayer or less. Formation mechanism of unit-cell-height steps is discussed based on consideration of bond configuration at step edges.