bluuebunny/crossref_metadata_2025 huggingface dataset:
1H NMR study of the interaction ofN,N′,N″‐triacetyl chitotriose with Ac‐AMP2, a sugar binding antimicrobial protein isolated fromAmaranthus caudatus
Authors: Verheyden Patricia , Pletinckx Jurgen , Maes Dominique , Pepermans Henri A.M. , Wyns Lode , Willem Rudolph , Martins JoséC.
Published: July 2002

The interaction between Ac‐AMP2, a lectin‐like small protein with antimicrobial and antifungal activity isolated fromAmaranthus caudatus, andN,N′,N″‐triacetyl chitotriose was studied using1H NMR spectroscopy. Changes in chemical shift and line width upon increasing concentration ofN,N′,N″‐triacetylchitotrioseto Ac‐AMP2 solutions at pH 6.9 and 2.4 were used to determine the interaction site and the association constantKa. The most pronounced shifts occur mainly in the C‐terminal half of the sequence. They involve the aromatic residues Phe18, Tyr20and Tyr27together with their surrounding residues, as well as the N‐terminal Val‐Gly‐Glu segment. Several NOEs between Ac‐AMP2 and theN,N′,N″‐triacetyl chitotriose resonances are reported.
Distinct carboxy‐termini confer divergent characteristics to the mitogen‐activated protein kinase p38α and its splice isoform Mxi2
Authors: Sanz Victoria , Arozarena Imanol , Crespo Piero
Published: July 2002

The p38 family of mitogen‐activated protein kinases is composed of several isoforms. Mxi2 is a splicing variant of p38α that harbors a unique carboxy‐terminus. Here we show that this sole divergence results in remarkable differences between Mxi2 and p38α. Mxi2 is distinctively activated by stress stimuli and potently activated by mitogens. Mxi2 affinity for bona fide p38 substrates is remarkably diminished and Mxi2 activity is largely unaffected by the phosphatase CL100. Also, Mxi2 sensitivity to inhibition by SB203580 is greatly reduced. Interestingly, we show that the p38 C‐terminus is involved in conferring sensitivity to this compound. Overall, our results point to the p38 carboxy‐terminus as a key determinant of the biochemical properties of this family of kinases.
Characterization and Catalytic Property of Surfactant‐Laccase Complex in Organic Media
Authors: Okazaki Shin‐ya , Goto Masahiro , Wariishi Hiroyuki , Tanaka Hiroo , Furusaki Shintaro
Published: July 2002

The oxidation of o‐phenylenediamine catalyzed in anhydrous organic solvents by surfactant‐laccase complex was investigated. The complex was prepared by utilizing a novel preparation technique in water‐in‐oil (W/O) emulsions. The surfactant‐laccase complex effectively catalyzed the oxidation reaction in various dry organic solvents, while laccase, lyophilized from an aqueous buffer solution in which its activity was optimized, exhibited no catalytic activity in nonaqueous media. To optimize the preparation and reaction conditions for the surfactant‐enzyme complexes, we examined the effects of pH in the water pool of W/O emulsions, the concentration of enzyme and surfactant at the preparation stage, and the nature of organic solvents at the reaction stage on the laccase activity in organic media. Surfactant‐laccase complex showed a strong pH‐dependent catalytic activity in organic media. Its optimum activity was obtained when the complex was prepared at a pH of about 3. Interestingly, native laccase in an aqueous buffer solution exhibited an optimum activity at the same pH of 3. The optimum preparation conditions of surfactant‐laccase complex were [laccase] = 0.8 mg/mL and [surfactant] = 10 mM, and the complex showed the highest catalytic activity in toluene among nine anhydrous organic solvents. The effect of a cosolubilized mediator (1‐hydroxybenzotriazole (HBT)) on the reaction was also investigated. The addition of HBT at the preparation stage of the enzyme complex did not accelerate the catalytic reaction because HBT was converted to an inactive benzotriazole (BT) by laccase. However, the addition of HBT at the reaction stage enhanced the catalytic performance by a factor of five compared to that without HBT.
Synthesis Rates of Cellular Proteins Involved in Translation and Protein Folding Are Strongly Altered in Response to Overproduction of Basic Fibroblast Growth Factor by Recombinant Escherichia coli
Authors: Rinas Ursula
Published: July 2002

The cellular response to temperature‐induced production of human basic fibroblast growth (bFGF) factor by recombinant E. coli (bacteriophage λ PRPL promoter/cI857 repressor expression system) was studied by one‐ and two‐dimensional gel electrophoresis. Temperature shift from 30 to 42 °C caused the induction of heat‐shock protein synthesis and the repression of synthesis of ribosomal proteins and the protein folding catalyst trigger factor. Compared to control cells, carrying the expression vector without structural bFGF gene cells, producing the heterologous protein exhibited a stronger increase in the synthesis rate of heat‐shock proteins ClpB (HtpM), DnaK, HtpG, GroEL, GrpE, and IbpB (HtpE) in response to temperature upshift. Unexpectedly, formation of the chaperone heat‐shock protein GroES was not detected after temperature shift to 42 °C in cells producing bFGF. In addition to amplified heat‐shock protein formation, the syntheses of ribosomal proteins and of the protein folding catalyst trigger factor were more severely repressed after temperature upshift in cells producing bFGF. In conclusion, the normal cellular stress response caused by the high inducing temperature was strongly amplified by heterologous protein synthesis. In particular, syntheses of proteins involved in translation and protein folding were affected by the overproduction of the heterologous protein.
Effects of Long‐Term Passaging of BTI‐Tn5B1–4 Insect Cells on Growth and Recombinant Protein Production
Authors: Donaldson Michael S. , Shuler Michael L.
Published: July 2002

The BTI‐Tn‐5B1–4 insect cell line from Trichopulsi ni has enabled better secretion and higher productivity of recombinant proteins in the baculovirus expression system. An early passage stock of this cell line is compared here to the commercially available “High Five” cell line stock. The early passage Tn5B1–4 cells grew to over 11 × 106 cells/mL and expressed 2.5‐fold more recombinant secreted alkaline phosphatase (SEAP) than the High Five cells. While the specific productivity on a cell number basis was only slightly higher, the early passage Tn5B1–4 cells maintained this productivity at higher cell densities, increasing their volumetric productivity to 50 μg/mL under elevated oxygen conditions. We propose that the difference in these two stocks of cells is the length of time they have been cultured, 130 total passages for the early passage versus 360 passages for the High Five cells. This conclusion is supported by the facts that the early passage Tn5B1–4 cells are smaller in diameter by 4 μm, smaller in cellular protein content (206 versus 270 μg of protein/106 cells), have an increased propensity to clump in suspension culture, and are less susceptible to dispersion of these clumps by dextran sulfate compared to the High Five cells.
Zinc‐promoted simple synthesis of oligomer‐freeNα‐Fmoc‐amino acids using Fmoc‐Cl as an acylating agent under neutral conditions
Authors: Gopi Hosahudya N. , Suresh Babu Vommina V.
Published: July 2002

Abstract:A range of Nα‐Fmoc‐protected amino acids, including those that contain t‐butyl moiety, have been synthesized by employing Fmoc‐Cl utilizing the activated, commercial zinc dust‐promoted synthesis of carbamates under neutral conditions.A general procedure is described that circumvents the oligomerization side reaction normally noticed in Schotten–Baumann conditions. It is a simple, convenient and clean method. Thus, Fmoc‐amino acids are obtained in high yield (85–92%) and purity as checked by thin‐layer chromatography, high‐performance liquid chromatography and other physical methods.
Optimized aminolysis conditions for cleavage of N‐protected hydrophobic peptides from solid‐phase resins
Authors: Greathouse D.V. , Goforth R.L. , Crawford T. , Van Der Wel P. C. A. , Killian J.A.
Published: July 2002

Abstract:Solid‐phase synthesis and aminolysis cleavage conditions were optimized to obtain N‐ and C‐terminally protected hydrophobic peptides with both high quality and yield. Uncharged ‘WALP’ peptides, consisting of a central (Leu‐Ala)nrepeating unit (wheren = 5, 10.5 or 11.5) flanked on both sides by Trp ‘anchors’, and gramicidin A (gA) were synthesized using 9‐fluorenylmethoxycarbonyl chemistry from either Wang or Merrifield resins. For WALP peptides, the N‐terminal amino acid was capped by couplingN‐acetyl‐ orN‐formyl‐Ala or ‐Gly to the peptide/resin or by formylation of the completed peptide/resin withpara‐nitrophenylformate (p‐NPF). N‐Terminal acetyl‐ or formyl‐Ala racemized when coupled as an HOBt‐ester to the resin‐bound peptide, but not when the peptide was formylated withp‐NPF. Racemization was avoided at the last step by completing the peptide with acetyl‐ or formyl‐Gly. For both WALP peptides and gA, cleavage conditions using ethanolamine or ethylenediamine were optimized as functions of solvent, time, temperature and resin type. For WALP peptides, maximum yields of highly pure peptide were obtained by cleavage with 20% ethanolamine or ethylenediamine in 80% dichloromethane for 48 h at 24°C.N‐Acetyl‐protected WALP peptides consistently gave higher yields than those protected withN‐formyl. For gA, cleavage with 20% ethanolamine or ethylenediamine in 80% dimethylformamide for 48 h at 24°C gave excellent results. For both WALP peptides and gA, decreasing the cleavage time to 4 h and increasing the temperature to 40–55°C resulted in significantly lower yields. The inclusion of hexafluoroisopropanol in the cleavage solvent mixture did not improve yields for either gA or WALP peptides.
A light microscopic and immunohistochemical evaluation of scars
Authors: Kamath Nandan V. , Ormsby Adrian , Bergfeld Wilma F. , House Nancy S.
Published: July 2002

Background: Scars are commonly encountered by dermatopathologists and usually do not present a diagnostic challenge. However, in some cases, the pathologist may need to consider a broad differential diagnosis including fibrohistiocytic tumors, smooth muscle tumors, myofibroblastic proliferations and desmoplastic malignant melanoma. Although specific histologic aspects of scars have been well studied, a complete histochemical profile of scars, especially at various stages of evolution, has not been described.

Methods: Twenty‐five cases of scars including 8 normal scars, 5 hypertrophic scars and 12 keloids were studied. Sections were examined with Verhoeff van Giesson, colloidal iron, Giemsa, smooth muscle actin (SMA), CD34, Factor XIIIa and S‐100.

Results: All scars were negative for CD34 expression. Factor XIIIa immunostaining identified only rare dermal dendrocytes. S‐100 was absent in 23 of 25 cases and stained scattered cells (less than 10%) in the other 2 cases. SMA was positive in 14 of 25 cases with 6 of these showing staining of up to 50% of spindled cells. Elastic fibers were markedly reduced or absent in all cases, mucin showed moderate or marked staining in three‐fourths of the cases and dermal mast cells showed a moderate increase in 5 cases.

Conclusions: These findings confirm prior reports that negative staining with CD34, Factor XIIIa and S‐100 can help differentiate scars from dermatofibrosarcoma protuberans, dermatofibroma and desmoplastic malignant melanoma, respectively. SMA staining is much more variable and requires careful interpretation.
Biosynthesis of riboflavin
Authors: Fischer Markus , Haase Ilka , Feicht Richard , Richter Gerald , Gerhardt Stefan , Changeux Jean‐Pierre , Huber Robert , Bacher Adelbert
Published: July 2002

A cDNA sequence from Schizosaccharomyces pombe with similarity to 6,7‐dimethyl‐8‐ribityllumazine synthase was expressed in a recombinant Escherichia coli strain. The recombinant protein is a homopentamer of 17‐kDa subunits with an apparent molecular mass of 87 kDa as determined by sedimentation equilibrium centrifugation (it sediments at an apparent velocity of 5.0 S at 20 °C). The protein has been␣crystallized in space group C2221. The crystals diffract to a resolution of 2.4 Å. The enzyme catalyses the formation of 6,7‐dimethyl‐8‐ribityllumazine from 5‐amino‐6‐ribitylamino‐2,4(1H,3H)‐pyrimidinedione and 3,4‐dihydroxy‐ 2‐butanone 4‐phosphate. Steady‐state kinetic analysis afforded a vmax value of 13 000 nmol·mg−1·h−1 and Km values of 5 and 67 µm for 5‐amino‐6‐ribitylamino‐2,4(1H,3H)‐pyrimidinedione and 3,4‐dihydroxy‐2‐butanone 4‐phosphate, respectively. The enzyme binds riboflavin with a Kd of 1.2 µm. The fluorescence quantum yield of enzyme‐bound riboflavin is < 2% as compared with that of free riboflavin. The protein/riboflavin complex displays an optical transition centered around 530 nm as shown by absorbance and CD spectrometry which may indicate a charge transfer complex. Replacement of tryptophan 27 by tyrosine or phenylalanine had only minor effects on the kinetic properties, but complexes of the mutant proteins did not show the anomalous long wavelength absorbance of the wild‐type protein. The replacement of tryptophan 27 by aliphatic amino acids substantially reduced the affinity of the enzyme for riboflavin and for the substrate, 5‐amino‐6‐ribitylamino‐2,4(1H,3H)‐pyrimidinedione.
Spectral karyotyping and fluorescence in situ hybridization detect novel chromosomal aberrations, a recurring involvement of chromosome 21 and amplification of the MYC oncogene in acute myeloid leukaemia M2
Authors: Hilgenfeld E. , Padilla‐Nash H. , McNeil N. , Knutsen T. , Montagna C. , Tchinda J. , Horst J. , Ludwig W.‐D. , Serve H. , Büchner T. , Berdel W. E. , Schröck E. , Ried T.
Published: July 2002

Recurring chromosomal aberrations are of aetiological, diagnostic, prognostic and therapeutic importance in acute myeloid leukaemia (AML). However, aberrations are detected in only two thirds of AML cases at diagnosis and recurrent balanced translocations in only 50%. Spectral karyotyping (SKY) enables simultaneous visualization of all human chromosomes in different colours, facilitating the comprehensive evaluation of chromosomal abnormalities. Therefore, SKY was used to characterize 37 cases of newly diagnosed AML‐M2, previously analysed using G‐banding. In 15/23 patients it was possible to obtain metaphases from viably frozen cells; in 22 additional cases, fixed‐cell suspensions were used. Of the 70 chromosomal aberrations identified by SKY, 30 aberrations were detected for the first time, 18 aberrations were redefined and 22 were confirmed. SKY detected two reciprocal translocations, t(X;3) and t(11;19). In five cases, eight structural aberrations resulted in partial gains of chromosome 21, six of which were undetected by G‐banding. In 4/5 cases, these resulted in copy number increases for AML1. Amplification of MYC was detected in three cases. Using SKY and FISH, clonal aberrations were identified in 5/18 cases with a presumed normal karyotype; 3/5 aberrations were of known unfavourable prognostic significance. Karyotypes were entered into a custom‐designed SKY database, which will be integrated with other cytogenetic and genomic databases.
Population dynamics of a tree‐dwelling aphid: regulation and density‐independent processes
Authors: Jarošiacute;K V. , Dixon A. F. G.
Published: July 2002

1. A population of the Turkey‐oak aphid (Myzocallis boerneri Stroyan) was sampled at approximately weekly intervals on two Turkey‐oak trees for 19 years.

2. On one tree (A), the aphids exhibited a distinct seasonal pattern with a spring increase, summer decrease, early autumn increase, and late autumn decline. On the other tree (B) the aphids remained at low densities after the decrease in summer.

3. On tree A, significant undercompensating density dependence occurred during all periods of the seasonal population development, and their strength varied little during the course of the season. On tree B, significant density dependence compensated exactly for increase, but appeared only after the decrease in summer when the population remained at very low densities for the rest of the season.

4. Density‐independent weather variables affected the population dynamics very little. Their influence was marginally significant only at very low densities when the aphids were regulated exactly by compensating density‐dependent factors.

5. The results suggest a curvilinear density dependence, with strong regulation at low densities, and weak at high densities. That is, this aphid was most regulated not at the peak but at the trough densities.
Do habitat characteristics influence predation on red grouse?
Authors: Thirgood Simon J. , Redpath Stephen M. , Campbell Steve , Smith Adam
Published: July 2002

Predation is not only an important ecological process in the population dynamics of red grouseLagopuslagopusscoticus, but also has conservation implications for their predators such as hen harrierCircus cyaneusand peregrine falconFalcoperegrinus. It has been suggested that habitat management might reduce the susceptibility of grouse to predation and thus reduce conflicts between grouse management and raptor conservation.

We investigated whether habitat characteristics influenced predation on red grouse on a managed moor near Langholm in southern Scotland during 1992–96. We combined demographic studies of the grouse population with radio‐telemetry of individual grouse to assess the influence of habitat on mortality rates. Systematic observations of hen harriers were also used to assess the effect of habitat characteristics on their encounter rates and strike success with grouse and other prey.

There was no evidence that habitat characteristics directly influenced grouse mortality rates at the scale of the grouse population. However, grouse densities were higher and overwinter losses of grouse were lower on areas with greater cover of heatherCallunavulgaris. The most likely explanation for the observed pattern of winter loss was that grouse dispersed into areas with more heather, to some extent locally compensating for losses to predators.

Individual radio‐tagged grouse that survived the winter had more blaeberryVacciniummyrtillusin their home ranges than grouse that were killed in winter by predators. There was, however, no effect of heather cover, vegetation height or vegetation density on the likelihood of individual grouse survival.

Hen harriers were more likely to encounter grouse broods in a mixture of heather and grass than expected from the observed distributions of grouse broods on moorland. However, having encountered a grouse brood, there was no effect of habitat type or vegetation height on the strike success of the harriers.

We conclude that the direct effects of habitat on the susceptibility of red grouse to predation are limited under current predator control regimes on managed moorland. Habitat management aimed at mitigating conflicts between raptor conservation and grouse management should focus on reducing the availability of passerine and small mammal prey for hen harriers and thus reducing harrier abundance on grouse moors. Further research is required, however, to assess the consequences of such management for biodiversity.
Epidemiology of transitional cell carcinoma of the bladder: profile of an urban population in the south‐west of England
Authors: Probert  , Persad  , Greenwood  , Gillatt  , Smith
Published: July 2002

Objectives

 To produce an epidemiological profile of patients with transitional cell carcinoma (TCC) of the bladder living in the city of Bristol (south‐west England), to determine if TCC tumorigenesis is linked to possible risk factors (occupational exposure, cigarette smoking, alcohol consumption and coffee consumption) and to assess phenotypic acetylation status and thus determine whether there may be a genetic component to tumour development.

Patients and methods

 This cross‐sectional observational epidemiological study recruited both cases and controls from one‐stop haematuria clinics, providing two groups with a similar age and sex distribution. Before diagnosis, all patients were interviewed by the same researcher and results recorded on a specially designed database questionnaire, to eliminate both recall and investigator bias. Metabolic studies were also performed before diagnosis.

Results

 There were significant associations for occupational exposure, cigarette smoking, and beer consumption (but not wine or spirits), but no significant association with coffee consumption. Slow acetylation status also conferred an increased risk. There were linear trends in terms of dose–response for both beer and cigarette consumption, although this was significant only for cigarettes. There was no difference in risk between the use of filtered or unfiltered cigarettes.

Conclusion

 Occupational exposure and cigarette smoking have been well documented as risk factors in the development of TCC of the bladder, as has slow acetylation status. There are very few studies linking bladder cancer with alcohol consumption. It is important to subdivide types of alcohol consumed when considering this factor in an epidemiological study. In the case of beer, methods used by different brewing processes may also contribute to differences found, were such a study to be performed on a national scale.
Postictal Diffusion‐Weighted Imaging for the Localization of Focal Epileptic Areas in Temporal Lobe Epilepsy
Authors: Diehl Beate , Najm Imad , Ruggieri Paul , Tkach Jean , Mohamed Armin , Morris Harold , Wyllie Elaine , Fisher Elizabeth , Duda Jeffrey , Lieber Michael , Bingaman William , Lüders Hans O.
Published: July 2002

Summary:  Purpose: Diffusion‐weighted MR imaging (DWI) is a novel technique to delineate focal areas of cytotoxic edema of various etiologies. We hypothesized that DWI may also detect the epileptogenic region and adjacent areas during the ictal and early postictal periods in patients with temporal lobe epilepsy (TLE).

Methods: We studied patients with intractable TLE (n = 9), due to hippocampal sclerosis (HS, n = 7), left mesial temporal lobe tumor (n = 1), and of unknown etiology (n = 1). Informed consent was obtained before inclusion in the study. All patients with single short seizures were scanned immediately after EEG‐documented seizures (between 45 and 150 min); one of two patients in status was scanned 14 h after cessation of seizures. DWI results were analyzed visually and by calculating apparent diffusion coefficient (ADC) maps.

Results: We found significant decreases in ADC postictally in one of six patients with TLE due to HS and single short seizures. One patient with an incompletely resected temporal lobe tumor also exhibited ADC abnormalities. One patient in focal status epilepticus revealed a decrease in ADC, and one patient with a continuous aura had no DWI abnormality.

Conclusions: Postictal DWI technique may occasionally help delineate epileptic areas in some patients with TLE. Yield is low in patients with HS and single short seizures: it may be higher in patients with tumor or status epilepticus.
Mycoparasitism by Three Species ofDiplococcium(Hyphomycetes)
Authors: Kirschner R. , Oberwinkler F.
Published: July 2002

Abstract:The interactions between three species ofDiplococciumand their respective host fungi were investigated using light and transmission electron microscopy. Two types of interactions were detected:D. clarkiiandD. clavariarum,colonizing fruit bodies of basidiomycetes, produce appressoria with protrusions into the cell walls of the host fungi. The host reacts by apposition of secondary wall‐like material at the site of the interaction. Hyphae ofD. parcum,a species reported from wood and bark, were encircled by hyphae of another fungus, probably belonging to a species ofTulasnella.SinceD. parcumcould not be cultivated in pure culture, this association between both fungi indicates thatD. parcumwas parasitic on hyphae of the presumedTulasnellaspecies.
Optical sensing of in-plane ultrasonic transients
Authors: McKie A. D. W. , Wagner J. W.
Published: July 2002

An optical sensor has been developed, based on the differential laser Doppler anemometer, for the detection of in-plane ultrasonic transients. Ultrasonic pulse propagation around a 90° corner has been investigated in an aluminum block. By generating ultrasonic pulses on diametrically opposite sides of the detector a polarity inversion of the ultrasonic pulses detected is demonstrated. The results obtained are as expected for the case of in-plane displacement measurements.
Miniband dispersion in GaAs/AlxGa1−xAs superlattices with wide wells and very thin barriers
Authors: Peterson M. W. , Turner J. A. , Parsons C. A. , Nozik A. J. , Arent D. J. , Van Hoof C. , Borghs G. , Houdré R. , Morkoç H.
Published: July 2002

Photoreflectance spectra have been used to characterize miniband formation in GaAs/ Alx Ga1−x As superlattices with wide wells (275–255 Å) and withb arriers as thin as 17 Å. Thirty-two optical transitions are resolved in the photoreflectance spectra of the 17 Å barrier sample. These experimental transitions match all those theoretically predicted from the selection rule Δn=0, including Γ- and Π-type transitions arising from miniband dispersion; these results imply sample perfection. A sample with a 40 Å barrier exhibits forbidden transitions with Δn≠0; these additional transitions, together with the narrow width of the minibands for 40 Å barriers, create difficulty in resolving the miniband structure.
Electronic beam steering in monolithic grating-surface-emitting diode laser arrays
Authors: Carlson N. W. , Evans G. A. , Amantea R. , Palfrey S. L. , Hammer J. M. , Lurie M. , Carr L. A. , Hawrylo F. Z. , James E. A. , Kaiser C. J. , Kirk J. B. , Reichert W. F.
Published: July 2002

Electronic beam steering has been demonstrated in both one- and two-dimensional injection-coupled grating-surface-emitting diode laser arrays. By appropriately varying the drive current to the electrically independent gain sections of an injection-coupled grating-surface-emitting laser array, the angular position of the far-field output can be steered. Experimental results for two-dimensional surface-emitting arrays are presented, as well as a theoretical model which shows that beam steering is a general property of injection-coupled surface-emitting arrays.
Sidewall growth by atomic layer epitaxy
Authors: Ide Y. , McDermott B. T. , Hashemi M. , Bedair S. M. , Goodhue W. D.
Published: July 2002

Atomic layer epitaxy (ALE) has successfully been used to grow epitaxial layers over chemically etched grooves and dry etched sidewalls formed on GaAs(100) substrates. GaAs/InGaAs multilayers were deposited on V-shaped and inverted trapezoid-shaped grooves that were 4–5 μm deep and 8–20 μm wide. Growth conforming to the original sidewall surfaces was accomplished both on the chemically etched and on ion beam assisted etched surfaces. These features show distinct improvement over similar attempts by metalorganic chemical vapor deposition or molecular beam epitaxy. The ability of ALE to proceed in a self-limiting fashion on such structures is expected to lead to the realization of novel device concepts.
Reduction of defects and inhomogeneous strain in heteroepitaxial ZnSe
Authors: Skromme B. J. , Tamargo M. C. , de Miguel J. L. , Nahory R. E.
Published: July 2002

We present low-temperature ZnSe photoluminescence spectra having very narrow bound exciton linewidths (0.55 meV), which demonstrate for the first time that thin, pseudomorphic ZnSe layers with minimal inhomogeneous strain can be grown directly on GaAs by molecular beam epitaxy. Similar characterization of ZnSe/AlAs/GaAs heterostructures shows that AlAs layers up to 4 μm thick exhibit only kinetically limited, partial lattice relaxation, which prevents the overgrowth of uniform, coherently strained ZnSe layers. However, pseudomorphic ZnSe/AlAs/GaAs structures with thin (≲0.5 μm) AlAs layers exhibit the narrowest bound exciton peaks (≲0.37 meV full width at half maximum) ever reported for heteroepitaxial ZnSe, indicating a high degree of structural perfection.
Electron irradiation induced amorphization in YBa2Cu3O7 and GdBa2Cu3O7 superconductors
Authors: Nastasi M. , Parkin Don M. , Zocco T. G. , Koike J. , Okamoto P. R.
Published: July 2002

Transmission electron microscope specimens of the oxide superconductors YBa2Cu3O7 and GdBa2Cu3O7 have been irradiated at 35 K with 1 MeV electrons and doses up to 1.5×1023 e/cm2. Electron diffraction data show the two different superconductors do not respond similarly with GdBa2Cu3O7 being more resistant to amorphization than YBa2Cu3O7. Amorphization appears to be dependent on displacements occurring at the Y/Gd lattice site. In addition, it appears that within each material, the electron dose required to initiate amorphization is lower for grain boundary irradiations relative to large single grain irradiations.
High T
c Y-Ba-Cu-O thin films by ion beam sputtering
Authors: Gao J. , Zhang Y. Z. , Zhao B. R. , Out P. , Yuan C. W. , Li L.
Published: July 2002

High quality Y-Ba-Cu-O thin films were successfully prepared by using ion beam sputtering. Zero resistance was reached at 90 K. The critical current density at 77 K was 4–5×104 A/cm2. The surface morphology of the films was observed by scanning electron microscopy.
Absorption edges of mixed silver-halide crystals and polycrystalline optical fibers
Authors: Barkay N. , Moser F. , Kowal D. , Katzir A.
Published: July 2002

Optical absorption edges of mixed AgClxBr1−x (0≤x≤1) crystals and polycrystalline fibers were investigated as a function of composition. Both visible edge, resulting from electronic transitions, and infrared edge due to multiphonon processes behave as the one-mode (amalgamation) type of mixed crystals, shifting continuously with composition. Quantitative expressions were used to discuss the results. Polycrystalline extruded fibers preserve this spectral window of silver-halide crystals, except for slight deviations which are explained by the small-grain structure of the fibers.
Temperature dependence of the mercury telluride-cadmium telluride band offset
Authors: Malloy K. J. , Van Vechten J. A.
Published: July 2002

After reviewing the experimental data on the valence-band offset for HgTe-CdTe heterojunctions, we support previous suggestions of an extreme temperature dependence for this offset with a calculation based on a bond charge model. The model predicts the T dependence of the valence-band offset to be 77% of the difference in the band-gap temperature dependence of the heterojunction constituents. In the HgTe-CdTe system, the opposite signs of the band gap T variations yield an anomalously large increase in the offset of 213 meV between 0 and 300 K.
Ultrafast carrier dynamics in modified semiconductor-doped glass
Authors: Zheng J. P. , Kwok H. S.
Published: July 2002

The recombination lifetime in CdSx Se1−x semiconductor-doped glass was measured by time-resolved photoluminescence. It was found that long-term exposure of the glass to high-intensity laser pulses produced a permanent reduction of the free-carrier lifetime from 80 ps to less than 10 ps. This change could be reversed by thermal annealing and should have applications to ultrafast optical signal processing.
Photoemission investigation of the room-temperature adsorption of trimethylgallium on GaAs surface
Authors: Claverie Pierre , Ueyama Kosuke , Maeda Shigeru , Namba Hidetoshi , Kuroda Haruo
Published: July 2002

The adsorption of trimethylgallium (TMG) on GaAs (110) surface at room temperature was studied with ultraviolet photoemission spectroscopy by use of synchrotron radiation. The adsorption was found to saturate for TMG exposure as low as 3 langmuirs (L) resulting in a coverage of less than 0.1 monolayer. It is concluded that TMG molecules are adsorbed on the GaAs surface without decomposition.
Gain recovery time of traveling-wave semiconductor optical amplifiers
Authors: Eisenstein G. , Tucker R. S. , Wiesenfeld J. M. , Hansen P. B. , Raybon G. , Johnson B. C. , Bridges T. J. , Storz F. G. , Burrus C. A.
Published: July 2002

We propose a mechanism which may shorten the gain recovery time in semiconductor optical amplifiers. The mechanism is carrier diffusion from nearby carrier storage regions (carrier reservoirs), which enhances the carrier recovery process in the active region and consequently reduces the gain recovery time. Bias-independent recovery times as short at 100 ps are demonstrated in a 1.3-μm traveling-wave amplifier.
Excess carrier lifetimes in the silicon doping superlattice
Authors: Leith G. A. , Zukotynski S. , Landheer D. , Denhoff M. W. , Buchanan M.
Published: July 2002

The excess carrier lifetimes in a silicon doping superlattice were investigated by measuring the decay of both the photovoltage and the photoconductance. The photovoltage decayed exponentially with a time constant of 1 s at liquid-nitrogen temperature. In addition, persistent photoconductivity extending over many hours was observed in the n-type layers.
Quantum size effects and observation of microcrystallites in colored filter glasses
Authors: Yanagawa T. , Sasaki Y. , Nakano H.
Published: July 2002

The CdSxSe1−x microcrystallites contained in colored filter glasses have been considered to be spherical. This letter demonstrates that in fact they are hexagonal columns, implying a wurtzite structure. Microcrystallite grain growth is observed in real time using an electron beam annealing method. Each grain is confirmed by energy dispersive spectrometry to be CdSxSe1−x. The grain size difference produces different optical transmission spectra due to quantum size effects. On the optical transmission spectrum of a sample with grains of 30 Å, a new absorption band appears. This band can be explained by size quantization of the valence band.
Radiation to coherent light converter
Authors: Wang C. L. , Bar-Chaim N. , Lau K. Y. , Marshall B. R. , Thomas M. C. , Zagarino P. A.
Published: July 2002

We have developed a radiation to coherent light converter with a monolithically integrated semiconductor chip that consists of a chromium-doped GaAs photoconductor detector and a GaAlAs laser diode. When irradiated, the electric pulse generated by the photoconductor detector modulates the laser diode, which has been biased above the lasing threshold, thus converting a radiation pulse to an electric pulse and then to a light pulse. The laser pulse is then transmitted to a fast recorder through a high bandwidth optical fiber. In the absence of a single-step x-ray pumped laser, our converter appears to be the first integrated device that can efficiently convert x-ray flux into coherent light. This device has been tested successfully with the 50 ps electron beams of 17 MeV linear accelerator and with 50 ns x-ray pulses from a Z-pinch plasma source.
Ion channeling analysis of a Si1−xGex(As)/Si strained layer
Authors: Moore J. A. , Lennard W. N. , Massoumi G. R. , Jackman T. E. , Baribeau J-M. , Jackman J. A.
Published: July 2002

A strained layer of Si1−x Gex (As)/Si has been grown by molecular beam epitaxy (MBE) with the As dopant introduced by 1 keV ion implantation during growth. Analysis of the layer was made using secondary-ion mass spectrometry (SIMS), Rutherford backscattering (RBS), and proton-induced x-ray emission (PIXE)/channeling, using 2 MeV H+ ions. The layer thickness (∼1.4 μm) and composition (x∼0.015; nAs ∼6×1018 cm−3) measurements by SIMS, RBS, and PIXE were in agreement. RBS, PIXE/channeling showed that the crystalline quality of the strained layer was equivalent to that of the Si substrate. The substitutional fraction (∼0.75) of the As dopant was determined by PIXE/channeling.
Sidewall damage in n+-GaAs quantum wires from reactive ion etching
Authors: Cheung R. , Lee Y. H. , Knoedler C. M. , Lee K. Y. , Smith T. P. , Kern D. P.
Published: July 2002

Electron cyclotron resonance and radio frequency reactive ion etching have been used to fabricate narrow n+-GaAs wires employing CCl2F2/He as the etch gas. A comparison of the induced sidewall damage is made using room-temperature conductivity measurements of the etched structures and the effect of overetching is investigated. In addition, preliminary analysis of low-temperature transport reveals that the amplitude of universal conductance fluctuations is extremely sensitive to sidewall damage.
Detection of surface (∼1 μm) impurity phases in high T
c superconductors
Authors: Cooke D. W. , Jahan M. S. , Smith J. L. , Maez M. A. , Hults W. L. , Raistrick I. D. , Peterson D. E. , O’Rourke J. A. , Richardson S. A. , Doss J. D. , Gray E. R. , Rusnak B. , Lawrence G. P. , Fortgang C.
Published: July 2002

We show that thermally stimulated luminescence is an important method for detecting insulating impurity phases that commonly occur in high Tc superconductors. The technique is sensitive to impurity phases at <1% level with a probe depth of ∼ 1 μm, which is the region of interest for many superconductor applications. Samples of Y2O3, Y2BaCuO5, YBa2Cu3O6.2, BaCO3, Ba3CuO4, BaCuO2, and YBa2Cu3Ox (x≊7) were investigated. All but the high quality sintered pellets of YBa2Cu3Ox exhibited relatively intense luminescence. The absence of luminescence, and thus of insulating phases, is correlated with low values of rf surface resistance.
Characteristics of quenched Y-Ba-Cu-O thin films on SrTiO3 (100),(110) grown by organometallic chemical vapor deposition
Authors: Tsuruoka T. , Takahashi H. , Kawasaki R. , Kanamori T.
Published: July 2002

A thin Y-Ba-Cu-O film was formed by the organometallic chemical vapor deposition (OMCVD) method. The substrates used were (100) and (110) SrTiO3. After forming Y-Ba-Cu-O at 800 °C, it was cooled at a rate of 100 °C/min in O2 under 1 atm. This film was c-axis oriented, with its (001) surface grown in parallel to the (100) surface of SrTiO3 and Tc =88 K. The (110) surface of Y-Ba-Cu-O was grown in parallel to the substrate crystal and Tc =84 K on the (110) surface of SrTiO3. After forming, these films were quenched in air from 800 °C to room temperature. The change in resistance of the quenched sample with temperature was metallic, Tonset =75 K, and Tc =60 K.
Analysis of dislocations in Y-Ba-Cu-O superconductors
Authors: Nakahara S. , Jin S. , Sherwood R. C. , Tiefel T. H.
Published: July 2002

Transmission electron microscopy was used to characterize dislocations in Y-Ba-Cu-O superconductors. Dislocations which are rarely seen in the sintered YBa2Cu3O7−δ superconductor are found to be abundant in grain-oriented samples fabricated by the melt-textured growth method. The density of dislocations is estimated to be about 109 –1010 lines/cm2, which is 2–3 orders of magnitude increased over that for the sintered sample. An analysis using the ḡ⋅b̄=0, 1, and 2 criteria unambiguously proves that the Burgers vectors of the dislocations are of [100] or [010] type with the slip occuring on the (010), (100), or (001) plane. These results imply the possibility of using slip deformation to increase the defect density and influence the flux pinning behavior.
Crystal structure of the high T
c (107 K) superconducting phase in Pb-Bi-Sr-Ca-Cu-O
Authors: Rong T. S. , Shi F. , Wu X. F. , Zhu T. J. , Shi Z. H. , Du J. , Zhou S. Z. , Shi N. C.
Published: July 2002

The crystal structure of the high Tc superconducting phase in a Pb-doped Bi-Sr-Ca-Cu-O system (nominal composition Pb0.3Bi1.7Sr2Ca3Cu4OY) with a zero-resistance temperature of 107 K was determined with transmission electron microscopy. The investigation shows that the crystal structure, which is different from the Pb-free one, is monocline with dimensions a=0.532 nm, b=0.383 nm, c=3.71 nm, α=β=90° and γ=134.8°. A distinct change of wave vector of incommensurate modulation was also observed.
Structure and stability of metastable α-Sn
Authors: Asom M. T. , Kortan A. R. , Kimerling L. C. , Farrow R. C.
Published: July 2002

We report for the first time the growth of high quality films of metastable α-Sn. The structural properties of the molecular beam epitaxy grown metastable α-Sn are investigated by means of in situ reflection high-energy electron diffraction (RHEED) analysis, scanning electron microscopy including electron channeling patterns, and high-resolution x-ray scattering techniques. Scanning electron microscopy reveals a growth morphology of smooth and uniform surfaces. RHEED patterns yield a highly streaked (2×1) surface reconstruction suggesting a layer-by-layer growth mechanism. Triple-axis x-ray diffractometry was employed to determine structural parameters and the strain distribution. In-plane rocking scans of the (400) reflection indicate a half width of 3 arcsec for the heterostructure α-Sn/InSb. Out-of-plane scans reveal a tetragonal distortion perpendicular to the film plane, contributing a net strain of ∼0.28%. These results are in quantitative agreement with values calculated using simple elastic theory.
Investigation of charge storage in InAs/AlAsSb quantum well capacitors
Authors: Lott J. A. , Dawson L. R. , Weaver H. T. , Zipperian T. E. , Caldwell R. B.
Published: July 2002

We report the electrical chracterization of an InAs/AlAsSb quantum well heterostructure capacitor fabricated on material grown by molecular beam epitaxy. Hysteresis associated with electron storage was observed in the capacitance-voltage data from which we derived exponential charge decay constants of 50 s at 77 K.
Electron capture processes in optically excited In0.53Ga0.47As/InP quantum wells
Authors: Cebulla U. , Bacher G. , Forchel A. , Schmitz D. , Jürgensen H. , Razeghi M.
Published: July 2002

We have performed picosecond time-resolved measurements on In0.53Ga0.47As/InP quantum wells with varying barrier thicknesses using 10 ps Nd:YAG excitation. For this excitation, holes and electrons are created in the In0.53Ga0.47As layers. Due to momentum conservation the Nd:YAG excitation accelerates the electrons above the InP barrier where they can diffuse but cannot recombine. By examining the rise time of the quantum well emission, we can show that for samples with thick barriers, the barrier geometry largely controls the dynamic properties of the carriers after Nd:YAG excitation.
Raman scattering determination of strain in CdTe/ZnTe superlattices
Authors: Jackson M. K. , Miles R. H. , McGill T. C. , Faurie J. P.
Published: July 2002

The strain configuration in CdTe/ZnTe strained-layer superlattices has been measured by Raman scattering near resonance. The ZnTe-like longitudinal optical phonon energy in the superlattice is significantly shifted from the bulk value to lower energies and the shift increases with increasing superlattice CdTe fraction. The observed shifts agree with calculations of strain shifts based on a free-standing strain distribution.
Effect of chopping on laser penetration of metal targets
Authors: Kim H. S. , Domankevitz Y. , Kwok H. S. , Copley J. A.
Published: July 2002

A new technique for increasing the laser penetration efficiency of metals has been developed. By amplitude modulating a free-running neodymium:yttrium aluminum garnet laser pulse, the depth of the crater was increased and the threshold energy for reliable hole drilling was decreased significantly. It was observed that the effect of chopping was optimal at 8–12 kHz with a 70% duty cycle. We believe that this improvement is due to an increase in the vapor recoil pressure and reduced plasma screening. Possible acoustic resonance effects have also been considered and will be discussed.
Solid phase epitaxy of a Ge-Si alloy on [111] Si through a Pd2Si layer
Authors: Hong Q. Z. , Zhu J. G. , Mayer J. W.
Published: July 2002

Solid phase epitaxy of a Ge70Si30 alloy on [111]Si substrates was achieved in the amorphous Ge/Pd2Si/[111]Si system. Upon annealing at temperatures above 600 °C,the Ge transported through the silicide layer and formed a Ge-rich, Si-Ge epitaxial layer on top of the Si substrate. At the same time the Pd silicide layer exchanged positions with the Ge, leading to the final configuration of Pd2Si/Si-Ge/[111]Si. The crystallinity of Pd2Si had a major effect on the epitaxy of the Ge-Si alloy. On [100]Si where the Pd2Si was polycrystalline, epitaxial Ge-Si growth was not observed.
Low-temperature annealing effect of as-grown Bi-Sr-Ca-Cu-O thin films on superconducting property and the c-axis lattice constant
Authors: Miura S. , Yoshitake T. , Manako T. , Miyasaka Y. , Shohata N. , Satoh T.
Published: July 2002

As-grown crystallized Bi2Sr2Ca1Cu2Ox phase films were prepared on MgO(100) substrates by rf magnetron sputtering. The as-grown film showed the Tc onset of 92 K and the Tc end of 82 K. By annealing in the furnace at 480 °C after deposition, superconducting property and the c-axis lattice constant varied with atmosphere during annealing. The film after annealing in air at 480 °C exhibited the highest superconducting transition with the Tc onset of 93 K and the Tc end of 85 K. The Tc onset increased when the c-axis lattice constant was increased, suggesting that the Tc onset increases with decreasing the oxygen content of the film.
Arsenic-induced step rearrangements on vicinal Si (111) substrates
Authors: Ohno T. R. , Williams Ellen D.
Published: July 2002

The orientational stability of stepped (vicinal) Si (111) surfaces during As exposure has been investigated using low-energy electron diffraction and Auger electron spectroscopy. When clean, Si (111) surfaces misoriented in the [2̄11] and [11̄0] directions are faceted, while those misoriented in the [21̄1̄] direction are step tripled. If these surfaces are equilibrated in an arsenic pressure, they all form orientationally stable step-doubled structures. However, exposure of the clean surfaces to As at temperatures<∼750 °C results in metastable structures with mixed step heights and/or facets.
Smooth, pseudosmooth, and rough GaAs/AlxGa1−xAs interfaces: Effect of substrate misorientation
Authors: Massies J. , Deparis C. , Neri C. , Neu G. , Chen Y. , Gil B. , Auvray P. , Regreny A.
Published: July 2002

GaAs/AlxGa1−xAs quantum well and superlattice structures have been grown at 600 °C by molecular beam epitaxy on GaAs (001) substrates exactly oriented or slightly misoriented towards (111) Ga and (111) As. It is shown that for the growth conditions used, the step orientation (nature) has a striking influence on the photoluminescence (PL) features of the grown structures: steps along [1̄10] (Ga-type steps) lead to sharp PL lines (pseudosmooth interfaces), while a considerable broadening of the PL (rough interfaces) is obtained when the steps are along [110] (As-type steps).
Sealed cw transversely excited CO2 laser operated with active catalysts
Authors: Wu Kaung-Hsiung
Published: July 2002

Two catalysts having the forms of tin-oxide-coated metal surfaces and platinum, palladium, and rhodium supported on cordierite (2MgO⋅2Al2O3⋅5SiO2) have been introduced for the first time in a cw transversely excited (TE) CO2 laser to perform a long-term sealed-off operation. Temporal variations of gas compositions and discharge conditions with and without these catalysts are analyzed. Sealed-off operation with an output level at 550 W for more than 110 h of discharge time was achieved.
Initial stages of growth of GaAs on silicon (211) substrates by migration-enhanced molecular beam epitaxy
Authors: Fotiadis L. , Kaplan R.
Published: July 2002

The nucleation of GaAs films grown by the alternate deposition of gallium and arsenic monolayers on Si(211) and (100) substrates has been studied in situ using Auger and energy-loss spectroscopies, and low-energy electron diffraction. Films were observed to become continuous at much smaller thicknesses when grown on (211), as compared to (100), substrates. This implies that the nucleation site density is much greater on the (211) surface, as expected from the very high step density for this orientation. The observed growth was consistent with a layer-by-layer growth mode.
Two-dimensional electron gas on etched GaAs sidewalls by liquid phase epitaxial regrowth
Authors: Frei M. R. , Tsui D. C.
Published: July 2002

A two-dimensional electron gas is created on the sidewalls of V grooves etched into a GaAs substrate, using the regrowth by liquid phase epitaxy of an n-AlGaAs modulation-doping layer. The two-dimensional electron gas is characterized by magnetotransport measurements. The dependence on the magnetic field orientation of the Shubnikov–de Haas oscillations shows unambiguously that the two-dimensional electron gas is on the sidewalls, not on the top of the mesas or the bottom of the grooves.