bluuebunny/crossref_metadata_2025 huggingface dataset:
The protein composition of Friend cell nuclear matrix stabilized by various treatments. Different recovery of nucleolar proteins B23 and C23 and nuclear lamins
Authors: Martelli Alberto M. , Manzoli Lucia , Rubbini Silvia , Billi Anna Maria , Bareggi Renato , Cocco Lucio
Published: July 2002

Summary— Using two‐dimensional polyacrylamide gels stained with Coomassie blue we have studied the protein composition of the nuclear matrix obtained from mouse erythroleukemic nuclei kept at O°C throughout the isolation procedure to prepare the high ionic strength resistant fraction (control matrix) or stabilized in vitro or in vivo by different procedures prior to subfractionation (ie 37°C incubation of isolated nuclei; sodium tetrathionate exposure of purified nuclei; heat shock of intact cells). When the matrix obtained from 37°C incubated nuclei was compared with the control matrix, striking differences in the polypeptide pattern were seen if the protein was obtained in both cases from an equivalent number of nuclei. On the other hand, if the same amount of protein for both the samples was applied to the gels the differences were less evident. Sodium tetrathionate stabilization of isolated nuclei and heat shock of intact cells produced a matrix protein pattern that was very similar and differed from that of the in vitro heat‐exposed matrix. Using specific polyclonal antisera, we demonstrate that nucleolar proteins B23/numatrin and C23/nucleolin were very abundant in the matrix obtained from chemically‐treated nuclei or in vivo heat‐stabilized nuclei but were recovered in very small amounts (B23) or completely absent (C23) in the matrix prepared from nuclei heated to 37°C in vitro. Differences were seen also in the recovery of nuclear lamins, and especially lamin B, that was poorly represented in the sodium tetrathionate‐stabilized matrix. The results demonstrate that in mouse erythroleukemia cells the increased recovery of nuclear matrix protein that is seen after in vitro heating of isolated nuclei is predominantly due to an additional recovery of the same types of polypeptides that are detected also in the absence of such a treatment. The data also indicate that in vivo heat shock of intact cells produces a nuclear matrix protein pattern that is more similar to the pattern seen after stabilization of purified nuclei with sodium tetrathionate and differs significantly from that obtained by exposing nuclei to 37°C in vitro, unlike to that what previous reports have indicated.
Identification and characterization of GSTT3, a third murine Theta class glutathione transferase
Authors: COGGAN Marjorie , FLANAGAN Jack U. , PARKER Michael W. , VICHAI Vanicha , PEARSON William R. , BOARD Philip G.
Published: July 2002

A novel Theta class glutathione transferase (GST) isoenzyme from mouse termed mGSTT3 has been identified by analysis of the expressed sequence tag database. The gene encoding mGSTT3 is clustered with the mGSTT1 and mGSTT2 genes on chromosome 10 and has an exon/intron structure that is similar to that of the other Theta class genes. mGSTT3 is expressed strongly in the liver and to a decreasing extent in the kidney and testis. Recombinant mGSTT3-3 expressed in Escherichia coli had a substrate-specificity profile that differed significantly from that of GSTT1-1 and GSTT2-2 isoenzymes. A molecular model of mGSTT3 suggested that, in comparison with GSTT2, a decrease in volume of the hydrophobic substrate-binding site and the loss of the sulphate-binding pocket prevents its use of the GSTT2 substrate 1-menaphthyl sulphate.
Functional analysis of basic transcription element (BTE)-binding protein (BTEB) 3 and BTEB4, a novel Sp1-like protein, reveals a subfamily of transcriptional repressors for the BTE site of the cytochrome P4501A1 gene promoter
Authors: KACZYNSKI Joanna A. , CONLEY Abigail A. , ZAPICO Martin FERNANDEZ , DELGADO Sharon M. , ZHANG Jin-San , URRUTIA Raul
Published: July 2002

The Sp1-like family of transcription factors is emerging as an integral part of the cellular machinery involved in the control of gene expression. Members of this family of proteins contain three highly homologous C-terminal zinc-finger motifs that bind GC-rich sequences found in the promoters of a diverse number of genes, such as the basic transcription element (BTE) in the promoter of the carcinogen-metabolizing cytochrome P4501A1 (CYP1A1) gene. In the present study, we report the molecular and functional characterization of BTE-binding protein (BTEB) 4, a novel ubiquitously expressed member of the Sp1-like proteins family. This protein represents a new homologue of BTEB1, originally described as a regulator of the BTE site in the CYP1A1 gene promoter. Similarly to the recently described BTEB3, we demonstrate that the N-terminal region of BTEB4 directly represses transcription and binds the co-repressor mSin3A. In addition, we show that the C-terminal zinc-finger domain of BTEB4 binds specifically the BTE site of the CYP1A1 promoter, similar to BTEB1 and BTEB3. Also, we show that both BTEB3 and BTEB4 repress the CYP1A1 gene promoter via the BTE site in HepG2 and BxPC3 cells. Thus the identification of this protein expands the repertoire of BTEB-like members of the Sp1-like protein family involved in transcriptional repression. Furthermore, our results demonstrate that the BTEB subfamily can repress the CYP1A1 gene promoter via the BTE site.
Anti‐(Raf‐1) RNA aptamers that inhibit Ras‐induced Raf‐1 activation
Authors: Kimoto Michiko , Shirouzu Mikako , Mizutani Shin , Koide Hiroshi , Kaziro Yoshito , Hirao Ichiro , Yokoyama Shigeyuki
Published: July 2002

RNA aptamers with affinity for the Ras‐binding domain (RBD) of Raf‐1 were isolated from a degenerate pool by in␣vitro selection. These aptamers efficiently inhibited the Ras interaction with the Raf‐1 RBD, and also inhibited Ras‐induced Raf‐1 activation in a cell‐free system. The RNA aptamer with the most potent inhibitory effect specifically inhibited the Ras·Raf‐1 interaction and had no affinity for the RBD of the RGL protein, a homolog of the Ral GDP dissociation stimulator. Although the aptamer was capable of binding to the B‐Raf RBD, the RNA did not inhibit the interaction between Ras and the B‐Raf RBD. Enzymatic and chemical probing experiments indicated that the aptamer was folded into a pseudoknot structure, and some loop regions of the pseudoknot were located at the binding interface for the Raf‐1 RBD.
Prognostic and immunohistochemical validation of the Capella classification of pancreatic neuroendocrine tumours: an analysis of 82 sporadic cases
Authors: Heymann M F , Joubert M , Nemeth J , Ranc B , Visset J , Hamy A , Le Borgne J , Le Neel J C , Murat A , Cordel S , Le Bodic M F
Published: July 2002

Aims

To study the clinical outcome of 82 cases of pancreatic neuroendocrine tumours classified according to the recent histological and prognostic classification of Capella.

Methods and results

Eighty‐two surgical cases of pancreatic neuroendocrine tumours were examined histologically with immunohistochemical staining of paraffin sections using streptavidin–biotin complex and application of antibodies against chromogranin A and 10 hormonal peptides. Classification in four groups correlated with long follow‐up and outcome of these cases. Histological examination showed 30 group I, four group II, 41 group III and seven group IV tumours. Twenty‐one (70%) of group I tumours were insulinomas, whereas 25% of group III tumours were glucagonomas and 25% were unclassified. Most group IV tumours were unclassified, showing no immunohistochemical staining with any of the 10 hormonal peptides tested. Outcome was clearly correlated with tumour group. Among the 14 patients who died of the disease, four had group IV and 10 group III tumours. Thus, unclassified asymptomatic tumours without immunohistochemical staining had a poorer prognosis than asymptomatic tumours with staining.

Conclusion

This study validates the Capella classification as easy to apply and useful in predicting clinical outcome.
Changes in nutritional status in adults over Christmas 1998
Authors: Reid R. , Hackett A.F.
Published: July 2002

Background: Anecdotal evidence suggests that Christmas often leads to positive energy balance and a deterioration in nutritional status but there have been few studies.

Methods: Twenty‐six adults completed anthropometric, blood pressure and total blood cholesterol measurements before and after the Christmas holiday.

Results: An increase in mean weight occurred (0.93 kg) despite five subjects being ill. Diastolic blood pressure increased most (8%) with six subjects being classified as mildly hypertensive after Christmas, but only two before. This might be explained by alcohol intake and/or changes in insulin secretion/resistance.

Conclusion: Changes consequent upon Christmas and their correction deserve further attention.
Freezing method affects the concentration and variability of urine proteins and the interpretation of data on microalbuminuria
Authors: Schultz C. J. , Dalton R. N. , Turner C. , Neil H. A. W. , Dunger D. B. , Group For The Oxford Regional Prospective Study
Published: July 2002

Aims Microalbuminuria and, to a lesser extent, renal tubular proteins are widely used in the early detection of incipient nephropathy in diabetes mellitus. Recent reports have indicated detrimental effects of storage at −20°C on urine proteins. This study investigated the effects of storage on the measurement of urine proteins and discusses implications for the interpretation of data.

Methods Two‐hundred and sixty‐eight specimens, collected from children with Type 1 diabetes, split into duplicate aliquots and stored at −20°C and −70°C, respectively, for 6–8 months, were analysed for albumin, retinol binding protein, N‐acetyl glucosaminidase and creatinine, in the same assays to eliminate inter‐assay variability. Two independent non‐diabetic cohorts of children provided urine specimens, which were stored at −20°C for one cohort and −70°C for the other, to determine normal ranges for urine proteins.

Results Storage at −20°C led to a variable underestimation of all three urine proteins in 20% of specimens. Creatinine was unaffected. This underestimation was greater in more concentrated urine (r2 = 0.38, P < 0.001, n = 262). Consequently storage at −20°C increased the variance of the albumin/creatinine ratio more than the variance of albumin concentration. Temperature of storage affected the normal range, which was 0.1–2.1 mg/mmol at −20°C compared to 0.3–3.1 mg/mmol at −70°C. The prevalence of microalbuminuria (> 2
sd above the geometric mean in non‐diabetic specimens stored at −20°C) was 27% after storage at −70°C vs. 24% after − 20°C. The prevalence of microalbuminuria (> 2
sd above the geometric mean in non‐diabetic specimens stored at −70°C) was 21% after storage at −70°C vs. 17% after −20°C.

Conclusions Urine proteins are significantly but variably underestimated after storage at − 20 °C. These effects account for increased variance and differences in the normal range, but have less effect on the detection of microalbuminuria than might be predicted.
Oculomotor functions and late‐onset myopia
Authors: Jiang Bai‐chuan , Morse Stephen E.
Published: July 2002

In order to elucidate the role of optical defocus in the development of late‐onset myopia (LOM), we employed both theoretical and experimental approaches. In the theoretical study, which has been reported previously, we suggested a model in which an accommodative sensory operator was added to simulate the sensory part of the accommodation system. Results derived from the model showed that the sensory part might increase the system’s threshold to the accommodative error (or defocus) signal. In this study, we measured the perceptual depth‐of‐focus and the system’s threshold to the defocus signal for three refractive error groups: emmetropic (Emm), stable myopic (S.M.), and progressing myopic (P.M.). Results show that there are no significant differences in the perceptual depth‐of‐focus among the three groups. However, the defocus threshold values of the P.M. group are significantly higher than the values of the other two groups. This result in combination with our previous findings, leads us to suggest that individuals susceptible of developing myopia from sustained near‐work have a specific oculomotor risk profile. Although we are still trying to determine the specific sequence of changes among dark‐focus, AC/A ratio, the accommodative system’s defocus threshold, and refractive error, we are convinced that the changes of oculomotor parameters underlie the type of myopia associated with near‐work.
The Role of Vigabatrin in Childhood Seizure Disorders: Results from a Clinical Audit
Authors: Prasad Asuri N. , Penney S. , Buckley David J.
Published: July 2002

Summary:  Purpose: The emergence of visual field defects attributed to vigabatrin (VGB) treatment and intramyelinic edema in animal experiments has raised concerns about its future role in the treatment of childhood seizures.

Methods: We evaluated our experience with this antiepileptic agent with retrospective analysis of database and chart audit.

Results: Of 73 patients, 43 girls and 33 boys were treated with VGB over a 7‐year period. The mean age of patients at the introduction of VGB was 87 months (range, 5–257 months). In 12 of 73 cases, VGB was used as monotherapy; in 61 of 73 cases, it was used as an add‐on drug. Seizure types included secondarily generalized seizures (21), mixed seizures (21), partial seizures (18), and generalized seizures (13). Seizure etiology was idiopathic/cryptogenic in 22 patients, symptomatic in 50, and undetermined in a single patient. The mean duration of therapy was 16 months (median, 10 months; range, 1–144 months). VGB was effective in 30 (seven seizure free, 23 with >90% reduction in seizures), partially effective in four (50–90% reduction in seizures), and ineffective in 38 (<50% reduction in seizures). Nearly 50% of patients with infantile spasms responded to VGB. All patients underwent ophthalmic evaluation; two (16%) of 12 patients who could undergo static threshold perimetry were demonstrated to have the characteristic visual field constriction.

Conclusions: VGB is effective in producing a significant reduction in seizure frequency in nearly half the patients with childhood seizures, including refractory epilepsy. Despite emerging concerns regarding visual side effects, this drug retains an important role in the medical management of childhood epilepsy.
A Self‐Paced Step Test to Predict Aerobic Fitness in Older Adults in the Primary Care Clinic
Authors: Petrella Robert J. , Koval John J. , Cunningham David A. , Paterson Donald H.
Published: July 2002

OBJECTIVES: To study the potential usefulness of a submaximal self‐paced step test as a prediction of maximal aerobic capacity (VO2max) in older adults in the primary care setting.

DESIGN: Data were collected during a prospective randomized study of an exercise program.

SETTING: Four university family medical clinics in London, Ontario, Canada.

PARTICIPANTS: A random sample of 240 healthy older (≥65) men (n = 118) and women (n = 122) from four family medical clinics underwent self‐paced step testing in the clinic with a family physician (n = 16), and step testing and a maximal exercise treadmill test with measurement of respired gases in an exercise laboratory. Testing was done in random order (clinic/laboratory) separated by 2 weeks and then repeated at 52 weeks, following introduction of an exercise program. Relationships between outcome variables were examined by Pearson correlation coefficients while prediction of VO2max was examined using multivariate regression analysis. Cross‐validation with 30 age‐matched hypertensive and 40 age‐matched post‐hip arthroplasty patients was used to test the accuracy of the predictive models.

MEASUREMENTS: Measured VO2max, predicted VO2max, step test time, step test heart rate, body mass index (BMI), and O2 pulse.

RESULTS: Two hundred women (n = 108) and men (n = 92) completed both the initial and 52‐week assessments. Stepping time, heart rate, age, BMI, and O2 pulse were strongly associated with VO2max for both a normal and a fast step pace and were chosen to develop the predictive model. Normal step‐pace correlation with VO2max (ml/kg/min) was no different (female 0.93: male 0.91) from fast pace (0.95:0.90) with no difference between clinic and laboratory measurement at baseline or 52 weeks. Cross‐validation showed no significant difference from the main group using the predictive model.

CONCLUSIONS: The self‐paced step test is a safe and simple clinical instrument that strongly and reliably predicts VO2max, is sensitive to change, and is generalizable in the family practice setting among community‐dwelling older adults differing in fitness and health status.
Prescription Duration After Drug Copay Changes in Older People: Methodological Aspects
Authors: Schneeweiss Sebastian , Maclure Malcolm , Soumerai Stephen B.
Published: July 2002

OBJECTIVES:

Impact assessment of drug benefits policies is a growing field of research that is increasingly relevant to healthcare planning for older people. Some cost‐containment policies are thought to increase noncompliance. This paper examines mechanisms that can produce spurious reductions in drug utilization measures after drug policy changes when relying on pharmacy dispensing data. Reference pricing, a copayment for expensive medications above a fixed limit, for angiotensin‐converting enzyme (ACE) inhibitors in older British Columbia residents, is used as a case example.

DESIGN:

Time series of 36 months of individual claims data. Longitudinal data analysis, adjusting for autoregressive data.

SETTING:

Pharmacare, the drug benefits program covering all patients aged 65 and older in the province of British Columbia, Canada.

PARTICIPANTS:

All noninstitutionalized Pharmacare beneficiaries aged 65 and older who used ACE inhibitors between 1995 and 1997 (N = 119,074).

INTERVENTION:

The introduction of reference drug pricing for ACE inhibitors for patients aged 65 and older.

MEASUREMENTS:

Timing and quantity of drug use from a claims database.

RESULTS:

We observed a transitional sharp decline of 11%± a standard error of 3% (P = .02) in the overall utilization rate of all ACE inhibitors after the policy implementation; five months later, utilization rates had increased, but remained under the predicted prepolicy trend. Coinciding with the sharp decrease, we observed a reduction in prescription duration by 31% in patients switching to no‐cost drugs. This reduction may be attributed to increased monitoring for intolerance or treatment failure in switchers, which in turn led to a spurious reduction in total drug utilization. We ruled out the extension of medication use over the prescribed duration through reduced daily doses (prescription stretching) by a quantity‐adjusted analysis of prescription duration.

CONCLUSION:

The analysis of prescription duration after drug policy interventions may provide alternative explanations to apparent short‐term reductions in drug utilization and adds important insights to time trend analyses of drug utilization data in the evaluation of drug benefit policy changes. J Am Geriatr Soc 50:521–525, 2002.
HIV Infection: Treatment Outcomes in Older and Younger Adults
Authors: Wellons Melissa Fair , Sanders Linda , Edwards Lloyd J. , Bartlett John A. , Heald Alison E. , Schmader Kenneth E.
Published: July 2002

OBJECTIVES:

To determine the effect of antiretroviral therapy (ART) on the immunological and virological outcomes of older human immunodeficiency virus (HIV)‐infected patients compared with younger HIV‐infected patients.

DESIGN:

Matched (1:2) retrospective case‐control study (1993–1999).

SETTING:

Duke University Infectious Diseases Clinic.

PARTICIPANTS:

One hundred one older patients, mean age 56.7 (range 50–79) and 202 younger patients, mean age 32.8 (range 21–39). Patients were matched on baseline CD4+ cell count and date of clinic entry.

MEASUREMENTS:

The virological and immunological outcomes were viral suppression (HIV ribonucleic acid (RNA) level ≤400 copies/ml) and change in CD4+ cell count. To estimate differences in antiretroviral drug exposure, the percentage of patients on ART overall and by drug class was compared. To assess antiretroviral drug exposure further, the percentage of patients having interruptions in ART was compared.

RESULTS:

The older and younger groups had similar baseline CD4+ cell counts (332 vs 306 cells/mm3; P = .31) and similar increases in CD4+ cell counts (+3.47 vs +4.60 cells/mm3/month; P = .37) over a mean ± standard deviation of 2.4 ± 1.7 years of follow‐up. The older group had a higher percentage of patients with current plasma HIV RNA levels less than 400 (46% vs 34%; P = .05). The groups had similar rates of non‐nucleoside reverse transcriptase, nucleoside reverse transcriptase, and protease inhibitor use. The older group had fewer interruptions in ART than the younger group (11% vs 26%; P = .01).

CONCLUSIONS:

Older HIV‐infected patients responded well to ART, with a significantly greater percentage achieving a current plasma HIV RNA below detectable limits. Older patients experienced similar increases in CD4+ cell count as younger matched controls. Older patients were less likely to interrupt ART, which suggests better adherence and/or tolerance and may explain the higher rate of HIV RNA suppression. J Am Geriatr Soc 50:603–607, 2002.
Molecular Phylogeny of Caryophyllidae s.l. Based on MatK Sequences with Special Emphasis on Carnivorous Taxa
Authors: Meimberg H. , Dittrich P. , Bringmann G. , Schlauer J. , Heubl G.
Published: July 2002

Abstract: Despite intensive morphological, chemical and cladistic studies on Caryophyllidae, the circumscription of this subclass and the interfamilial relationships are still under discussion. Using comparative sequencing of the chloroplast matK gene, hypotheses of relationships between the carnivorous Droseraceae, Nepenthaceae and Dioncophyllaceae and ten other families of the Caryophyllidae s.l. were tested and compared with previously published cladograms based on rbcL, 18S rDNA and ORF2280 sequences. Parsimony analyses indicate two well‐differentiated clades. One strongly supported clade comprises the carnivorous families Droseraceae and Nepenthaceae, along with its close relatives Dioncophyllaceae and Ancistrocladaceae. The second clade is restricted to the Polygonaceae, Plumbaginaceae, Tamaricaceae and Frankeniaceae. The Simmondsiaceae are more closely related to Caryophyllales and are at the base of the remaining taxa. Results of this analysis suggest that carnivory within Caryophyllidae s.l. has a monophyletic origin and, with the exception of Triphyophyllum, this syndrome was lost in the taxa of Dioncophyllaceae and Ancistrocladaceae. The exclusion of Drosophyllum from Droseraceae suggests no close relationship with this family. Finally, the data support a sister group relationship between the Plumbaginaceae and Polygonaceae and the Frankeniaceae and Tamaricaceae. An extensive survey of the rpl2 intron via PCR amplification indicates that the intron is absent from chloroplast genomes of Droseraceae and all taxa of Caryophyllales, but is present in Drosophyllum. Consequently, there is evidence for a multiple loss of the intron and strong support that Drosophyllum has affinities outside the Droseraceae. Our sequence data corroborate many aspects of recent cladistic analyses based predominantly on rbcL sequences. This study shows that matK sequences are useful for'phylogenetic inference among closely related members of Caryophyllidae.
Intrinsic strain at lattice-matched Ga0.47In0.53As/InP interfaces as studied with high-resolution x-ray diffraction
Authors: Vandenberg J. M. , Panish M. B. , Temkin H. , Hamm R. A.
Published: July 2002

High-resolution x-ray studies of Ga0.47In0.53As/InP superlattices reveal, for the first time, the presence of an intrinsic interfacial strain at heteroepitaxial interfaces. This strain is produced by an asymmetric ordering of the atomic layers in the leading and trailing interfaces of each quantum well as the result of the normal growth sequence during gas source molecular beam epitaxy.
Dopant distribution for maximum carrier mobility in selectively doped Al0.30Ga0.70As/GaAs heterostructures
Authors: Schubert E. F. , Pfeiffer Loren , West K. W. , Izabelle A.
Published: July 2002

The magnitude of potential fluctuations due to remote ionized dopants is calculated for selectively doped heterostructures using unscreened and screened Coulomb potentials. Potential fluctuations are found to be minimized (corresponding to maximum carrier mobility) if the dopant distribution is δ-function-like. Our experimental study of electron mobilities in selectively doped heterostructures grown by molecular beam epitaxy reveals that carrier mobility indeed increases as the thickness of the doped layer is reduced, in agreement with the calculation. A peak electron mobility of 5.5×106 cm2 /V s is obtained at low temperatures in a selectively δ-doped heterostructure.
Hyperabrupt-doped GaAs nonlinear transmission line for picosecond shock-wave generation
Authors: Madden C. J. , Marsland R. A. , Rodwell M. J. W. , Bloom D. M. , Pao Y. C.
Published: July 2002

Voltage waveforms with 6 V amplitude and 1.6 ps fall time were generated by voltage shock-wave formation on a hyperabrupt-doped Schottky diode monolithic GaAs nonlinear transmission line.
Variation in misfit dislocation behavior as a function of strain in the GeSi/Si system
Authors: Hull R. , Bean J. C.
Published: July 2002

We show how strained-layer relaxation via misfit dislocation introduction varies significantly in GexSi1−x/Si (100) epitaxy as a function of the strain in this system. It is found that for samples grown by molecular beam epitaxy at a substrate temperature of 550 °C, structures with lower strain (x=0.15) are highly metastable, relaxing most of their excess stress on annealing to temperatures ∼650–750 °C. Structures with higher strain (x=0.25) are observed to relax far more gradually over the temperature range 550–900 °C. In situ electron microscope observations explain this behavior in terms of misfit dislocation interactions in the relaxing material.
Kinetics and mechanism of oxidation of SiGe: dry versus wet oxidation
Authors: LeGoues F. K. , Rosenberg R. , Meyerson B. S.
Published: July 2002

The rates of oxidation of SiGe and of Si covered with a thin ‘‘marker’’ of Ge have been measured, and compared with rates of oxidation for pure Si, both for wet and dry ambient. It is shown that the presence of Ge at the SiO2/Si interface increases the rate of wet oxidation by a factor of about 2.5, while it does not affect the rate of dry oxidation. By decreasing the partial pressure of H2O sufficiently, the rate of wet oxidation can be decreased to match that of dry oxidation. In this case again, Ge has no effect on the rate. Contrary to what has been proposed before, Ge is being piled up at the interface both for fast and slow oxidation. We demonstrate that the role of Ge is to suppress the formation of Si interstitials and that this is the rate limiting step in cases of rapid oxidation. For slower oxidation, interstitials have considerably more time to diffuse away and thus their formation and/or diffusion is not rate limiting.
In-plane hole effective masses in InxGa1−xAs/Al0.15Ga0.85As modulation-doped heterostructures
Authors: Jaffe M. , Oh J. E. , Pamulapati J. , Singh J. , Bhattacharya P.
Published: July 2002

We have determined the strain dependence of the in-plane hole effective mass in pseudomorphic Inx Ga1−x As/Al0.15 Ga0.85As modulation-doped heterostructures by low-temperature Shubnikov–de Haas measurements. An effective mass equal to 0.18m0 is measured for x=0.2. The measured values are in good agreement with theoretical calculations.
Photocapacitance spectroscopy of GaAs/AlGaAs multiquantum wells
Authors: Rosencher R. , Vodjdani N. , Nagle J. , Bois P. , Costard E. , Delaitre S.
Published: July 2002

Electron-hole generation in GaAs/AlGaAs quantum wells by illumination is shown to induce variations in the dynamical capacitance of multiquantum well capacitors. These variations monitored as a function of photon wavelength give a sensitive and unambiguous way to study excitonic resonances. It is shown that this photocapacitance spectroscopy technique leads to quantitative information on the product of the electron-hole pair density and their electrical polarizability. Assuming a simple theoretical model for electron-hole electrical polarizability, this method is applied to study the enhancement of exciton lifetime by a perpendicular electric field.
Composition of phosphorus-nitride film deposited on InP surfaces by a photochemical vapor deposition technique and electrical properties of the interface
Authors: Jeong Yoon-Ha , Lee Jae-Hak , Bae Young-Ho , Hong Young-Tae
Published: July 2002

Low-temperature (100–200 °C) growth of phosphorus nitride (P3N5) on InP surfaces has been successfully developed using a mixture of PCl3 and NH3 gases by a direct photochemical vapor deposition. The films have a resistivity of 1×1014 Ω cm and a breakdown voltage of 1×107 V/cm. The minimum density of interface trap states for the aluminum (Al)-P3N5-InP metal-insulator-semiconductor structure after the in situ processes is about 3.6×1010 cm−2 eV−1 near the midgap of InP. Auger electron spectroscopy and x-ray photoelectron spectroscopy measurements were used to evaluate the film and the film/InP interface.
Disappearance of grain boundaries in sintering
Authors: Berry R. Stephen , Bernholc J. , Salamon Peter
Published: July 2002

An exactly solvable model of grain boundary annealing in sinters is introduced and studied for a range of particle sizes. The model explains well the cluster fusion events observed by high-resolution transmission electron microscopy.
Nonleaky optical waveguides in KNbO3 by ultralow dose MeV He ion implantation
Authors: Strohkendl F. P. , Fluck D. , Günter P. , Irmscher R. , Buchal Ch.
Published: July 2002

Planar optical waveguides in single crystals of KNbO3 were produced by 1 and 2 MeV He ion implantation with doses between 5×1013 and 5×1014 cm−2. We observe nonleaky waveguiding due to an implantation induced increase of nc, the smallest of the three refractive indices of KNbO3. For 2 MeV He ions and a dose of 1014 cm−2 waveguides with typical propagation losses of ∼3 dB/cm have been fabricated. The possibility of producing nonleaky waveguides by ultralow dose implantation promises the creation of complicated channel waveguide structures within minutes.
High-power operation of strained InGaAs/AlGaAs single quantum well lasers
Authors: Moser A. , Oosenbrug A. , Latta E. E. , Forster Th. , Gasser M.
Published: July 2002

The high-power integrity of strained single quantum well InGaAs/AlGaAs lasers grown by molecular beam epitaxy is investigated. In the high-power regime, the lifetime of the Lz=7 nm strained quantum well laser emitting at ≂ 980 nm is found to be limited by the air-cleaved facets. However, a comparison with lattice-matched 7 nm quantum well GaAs/AlGaAs lasers, which otherwise have an almost identical vertical structure shows a substantial lifetime improvement. This indicates that lattice hardening due to the indium in the quantum well is effective in the facet region. The investigations demonstrate the feasibility of 150 mW single mode operation with sufficient lifetime for practical applications in the wavelength range of ≂1 μm.
Simple model for the study of period-doubling instabilities in the nonlinear ring cavity
Authors: Haelterman M.
Published: July 2002

In the good cavity limit, the two-dimensional Ikeda map [K. Ikeda, Opt. Commun. 30, 257 (1979)] representing the evolution of the field in a nonlinear ring cavity may be approximated by a set of two coupled-differential equations for the description of the dynamics of the period-2 regime of Ikeda instability. Our theory, which constitutes a generalization, to period doubling, of the single-mode mean-field theory of passive nonlinear cavities, provides a new insight of Ikeda instabilities in these devices.
Coherent measurement of THz optical rectification from electro-optic crystals
Authors: Zhang X.-C. , Jin Y. , Ma X. F.
Published: July 2002

We report the results of coherent measurement (phase and amplitude) of optical rectification from a variety of electro-optic crystals. We also present a comparison of the experimental data with a theoretical calculation.
Electro-optic microwave measurements in the frequency domain
Authors: Loualiche S. , Clerot F.
Published: July 2002

A new electro-optic system is developed to probe microwave signals on nonlinear crystals. The method uses two narrow linewidth solid state continuous wave (cw) lasers. The beat frequency between the two cw lasers is set equal to the microwave frequency plus a few MHz. The wave mixing between the beat frequency and the microwave signal is used to down convert the high frequency signal from the GHz to the MHz range where it is treated and displayed. The actual frequency bandwidth of the method is limited by the excursion between the two lasers (in our case, 50 GHz).
Enhanced spectral power density and reduced linewidth at 1.3 μm in an InGaAsP quantum well resonant-cavity light-emitting diode
Authors: Hunt N. E. J. , Schubert E. F. , Logan R. A. , Zydzik G. J.
Published: July 2002

The active region of an InGaAsP single-quantum well light-emitting diode (LED) emitting at 1.3 μm has been placed in the antinode of a resonant cavity consisting of a 32-period distributed Bragg reflector (DBR) and a top silver mirror, with reflectivities of 92% and 95%, respectively. The dominant feature of the 300 K electroluminescence emission at all current levels is a 3 nm (2.8 meV) wide spontaneous emission peak centered on the cavity resonance wavelength. The spectral power density of the structure is more than one order of magnitude higher as compared to a structure without cavity. The resonant-cavity LED operates without gain yet the extremely narrow spectrum indicates that the structure is suitable for wavelength division multiplexing applications.
Highly stabilized sputter deposition of YBa2Cu3O7
Authors: Krüger U. , Kutzner R. , Wördenweber R. , Mank G. , Kraemer-Flecken A.
Published: July 2002

A method of stabilizing and homogenizing the plasma during on-axis high-pressure dc sputter deposition of YBa2Cu3O7 is introduced, which leads to improved reproducibility and uniformity of the deposition process. The plasma is monitored and controlled via optical emission spectroscopy. Strong changes of the plasma intensity and intensity profile above the target are observed in the standard sputter process, which lead to unstable and inhomogeneous deposition of high Tc material. These changes are counteracted by adequate variation of the composition of the process gas (Ar/O2). The intensity of the plasma flicker is thus reduced by a factor of 4–5, long term drifts in the plasma intensity, and arcing of the plasma are eliminated.
Picosecond, narrow-band, widely tunable optical parametric oscillator using a temperature-tuned lithium borate crystal
Authors: Zhou H. , Zhang J. , Chen T. , Chen C. , Shen Y. R.
Published: July 2002

A highly efficient, picosecond, narrow-band, widely tunable optical parametric oscillator using a temperature-tuned LBO crystal synchronously pumped by cw, Q-switched, mode-locked pulses is described. A signal conversion efficiency of 30% with an output linewidth of 0.14 nm is obtained. The latter can be further reduced to 0.01 nm.
Processing dependence of the interfacial microstructure of Ag contacts to YBa2Cu3O7−δ thin films
Authors: Gong Z. H. , Vassenden F. , Fagerberg R. , Grepstad J. K. , Bardal A. , Ho/ier R.
Published: July 2002

The interfacial microstructure of three differently prepared silver contacts on c-axis oriented YBa2Cu3O7−δ (YBCO) thin films was examined using high-resolution transmission electron microscopy (HRTEM). For contacts prepared in situ by Ag sputter deposition on films maintained at elevated temperature and ex situ by Ag vapor deposition on films annealed in ultrahigh vacuum prior to metallization, regions of atomically sharp YBCO(001)/Ag interfaces were observed. In contrast, the cross-section HRTEM images of contacts prepared by in situ Ag deposition at room temperature reveal an amorphous interfacial zone, typically 20 Å thick. Scattered Y2O3 precipitates are found at the YBCO surface of all three contacts. The data suggest that intrinsic reactions between Ag and YBCO(001) are negligible, and that the amorphous interface layer for in situ contacts to cold films must be ascribed to reactions with gaseous impurities in the sputter chamber ambient. In conclusion, we strongly emphasize the importance of using ultrahigh purity process gases in order to avoid formation of a resistive interfacial barrier.
Study of interface resistances in epitaxial YBa2Cu3O7−x/barrier/YBa2Cu3O7−x junctions
Authors: Char K. , Antognazza L. , Geballe T. H.
Published: July 2002

We have measured interface resistances in YBa2Cu3O7−x/barrier/YBa2Cu3O7−x junctions with different barrier materials in an edge junction geometry. CaRuO3, La0.5Sr0.5CoO3, Y0.7Ca0.3Ba2Cu3O7−x, YBa2Cu2.79Co0.21O7−x, and La1.4Sr0.6CuO4 have been employed as the epitaxial barrier materials. We observe interface resistances of the order of 1×10−8 Ω cm2 when we use CaRuO3 and La0.5Sr0.5CoO3 barriers. These two barrier materials are cubic perovskites. However, in the case of the layered barrier materials, the measured interface resistances are smaller than 1×10−10 Ω cm2. Our study suggests that the oxygen disorder at the YBa2Cu3O7−x surface, due to stress created by the thermal expansion mismatch between YBa2Cu3O7−x and the barrier, may be the origin of the interface resistances, and that the magnitude of this stress can change the resistance by orders of magnitude.
Double-crystal x-ray diffraction from periodically corrugated crystalline semiconductor surfaces
Authors: De Caro Liberato , Sciacovelli Pasquale , Tapfer Leander
Published: July 2002

In this work we present a diffraction model that allows us to calculate the double-crystal x-ray diffraction pattern of corrugated surfaces. The model is based on a semidynamical x-ray diffraction theory, where the dynamical theory is used in order to describe the diffraction of the substrate crystal, while the kinematical theory is used to describe the x-ray diffraction of the surface grating. The interface between different parts of the periodic surface array is described by using the multiple-slit Fraunhofer formalism. Our x-ray diffraction model is used to simulate the experimental (400) and (422) reflection patterns of corrugated (100) GaAs surfaces.
Large scale surface structure formed during GaAs (001) homoepitaxy
Authors: Orme C. , Johnson M. D. , Sudijono J. L. , Leung K. T. , Orr B. G.
Published: July 2002

Atomic force microscopy studies have been performed on GaAs (001) homoepitaxy films grown by molecular beam epitaxy. Multilayered features are seen to evolve when the growth conditions favor island nucleation. As the epilayer thickness is increased these features grow in all dimensions but the angle of inclination remains approximately constant at 1°. The mounding does not occur on surfaces grown in step flow. We propose that the multilayered features are an unstable growth mode which relies on island nucleation and the presence of a step edge barrier.
Nonlinear-transmission spectra of porous silicon: Manifestation of size quantization
Authors: Klimov V. I. , Dneprovskii V. S. , Karavanskii V. A.
Published: July 2002

Changes in the transmission of porous silicon layers induced by ultrashort laser pulses are studied by using picosecond pump and probe measurements. Bleaching bands attributed to the saturation of optical transitions in silicon wires or/and crystallites with nanometer dimensions are observed in time-resolved differential transmission spectra. The measured nonlinearity is characterized by a relatively high value of the third-order nonlinear susceptibility (≊10−8 esu) and by fast relaxation dynamics (transmission recovery time is 30–40 ps).
Integration of GaAs vertical-cavity surface emitting laser on Si by substrate removal
Authors: Yeh Hsi-Jen J. , Smith John S.
Published: July 2002

Substrate removal techniques are attractive for the integration of III-V compound semiconductor devices on Si for the integration of optical and electronic devices, and on thermally conducting substrates for heat sinking. Here we discuss the bonding of strained quantum well InGaAs vertical-cavity surface-emitting lasers on both Si and Cu substrates. The GaAs substrates are then removed by selective etching. Lasing was achieved with pulsed electrical pumping with Jth=2.5 kA/cm2. The performance characteristics of the Si and Cu bonded devices are compared.
Dynamic compaction of copper powder: Computation and experiment
Authors: Benson David J. , Nellis W. J.
Published: July 2002

A Monte Carlo/Eulerian computational code with 104 zones was used to simulate in two dimensions the dynamic compaction of 100 Cu particles 15–20 μm in diameter. The computational results are in good agreement with published shock velocity-mass velocity data for porous Cu compaction. The computed shapes of the consolidated particles are also in good agreement with those obtained by shock compaction at 2 GPa. The computational method may be generalized to other materials, particle size distributions, compaction rates, and higher pressures.
New high coercivity cobalt alloy thin film medium structure for longitudinal recording
Authors: Fang Leo Li Zen , Lambeth David N.
Published: July 2002

A combined underlayer of (110) textured Cr and a hexagonal close-packed (HCP) Co or CoCrTa intermediate layer yields an improved CoCrPt recording media. The addition of Pt greatly increases the coercivity of the cobalt films but also expands the lattice of Co alloys preventing a good lattice match to the Cr underlayer. However, HCP Co and CoCrTa lattice match reasonably well to Cr. It is shown that an intermediate HCP layer, as thin as 50 Å, provides a HCP template upon which (10.1) CoCrPt texture can develop, resulting in suppressed (00.2) texture. By adjusting the relative layer thicknesses, coercivities between 1700 and 4200 Oe are controllably obtained for an independent variety of Mrt values.
Independently contacted double quantum well structure fabricated by molecular beam epitaxial regrowth
Authors: Patel N. K. , Grimshaw M. P. , Burroughes J. H. , Leadbeater M. L. , Ritchie D. A. , Jones G. A. C.
Published: July 2002

Molecular beam epitaxial regrowth over a patterned substrate has been used to produce independent contacts to the two-dimensional electron gases in a double quantum well structure. Optimization of the growth conditions and incorporation of a buffer layer at the regrowth interface are critical to the success of these devices. This simple method provides a means of realizing full wafer production and increases the capability of producing mesoscopic devices in multiconducting layer systems.
Optimization of interface parameters and bulk properties in ZnSe-GaAs heterostructures
Authors: Bonanni A. , Vanzetti L. , Sorba L. , Franciosi A. , Lomascolo M. , Prete P. , Cingolani R.
Published: July 2002

The flux parameters employed during molecular beam epitaxy of ZnSe on GaAs control both the heterojunction band alignment and the optical quality of the II–VI wide-gap layer. Independent optimization of the band discontinuities and ZnSe optical properties was achieved by fabricating a 2-nm-thick interface layer in nonstoichiometric conditions to control the band alignment, followed by the optically active layer in near-stoichiometric conditions.
Measurement of the electron ionization coefficient at low electric fields in InGaAs-based heterojunction bipolar transistors
Authors: Canali C. , Forzan C. , Neviani A. , Vendrame L. , Zanoni E. , Hamm R. A. , Malik R. J. , Capasso F. , Chandrasekhar S.
Published: July 2002

The behavior of the electron impact-ionization coefficient αn in In0.53Ga0.47As is measured with unprecedented sensitivity down to very low electric fields. The data are derived from measurements of the multiplication coefficient M−1 in suitably designed heterojunction bipolar transistors. Previously available data are extended by two orders of magnitude in the low field domain, down to αn≊1 cm−1. The experimental behavior of αn at fields below 200 kV/cm is in agreement with the theoretical prediction of a weak field dependence of αn at low electric fields.
Low-noise YBa2Cu3O7−δ direct-current superconducting quantum interference device magnetometer with direct signal injection
Authors: Lee L. P. , Longo J. , Vinetskiy V. , Cantor R.
Published: July 2002

We have fabricated several low-noise direct-current superconducting quantum interference device (SQUID) magnetometers from single layers of YBa2Cu3O7−δ on 10 mm×10 mm bicrystal substrates. The magnetometer design consists of a single-turn pickup loop that is directly coupled to the SQUID inductance. At 77 K, these magnetometers exhibit large voltage modulation with applied flux of over 40 μV. The minimum flux noise, measured at 77 K using conventional flux-locked loop electronics with bias current reversal, is 3.5×10−6 Φ0/√Hz above 10 kHz and 6.5×10−6 Φ0/√Hz at 1 Hz. The field-to-flux conversion efficiency is measured to be 10 nT/Φ0, resulting in a white magnetic field noise of 35 fT/√Hz above 10 kHz, increasing to 65 fT/√Hz at 1 Hz.
Nanocomposite films of lead zirconate titanate and metallic nickel by sol-gel route
Authors: Kundu T. K. , Chakravorty D.
Published: July 2002

Films of composition 0.27 PbO, 0.24 ZrO2, 0.27 TiO2, 0.22 NiO, and containing micrometer sized lead zirconate titanate (PZT) crystallites and nanometer sized nickel particles have been synthesized by a sol-gel technique. Metal particles have diameters in the range 2.0–7.6 nm. The films exhibit values of dielectric constant in the range 220–410 at a frequency of 1 kHz at room temperature. The optical absorption coefficient of the films shows a peak at ∼400 nm. The peak position shifts to higher wavelengths as the metal particle size is increased. The Mie theory is used to explain the results.
Automated system for the characterization of liquid foam
Authors: Besio Gregory J. , Oyler George , Prud’homme Robert K.
Published: July 2002

A device is described which measures, on line, the bubble size distribution and volume fraction of gas in a liquid foam. There are four elements in the device: a flow channel, meniscus detection, velocity detection, and microcomputer data acquisition. The foam flows into a gently converging capillary to reorder the foam bubbles into alternating slugs of gas and liquid. The passage of the meniscus between a gas and liquid slug is detected by a matched light emitting diode/phototransistor pair. When gas is in the detection path, the detector signal is ‘‘low,’’ and when liquid is in the path, the signal is ‘‘high.’’ The volume fraction of gas is determined from the ratio of time the detector signal is low to the total elapsed time. A second detector pair is located a fixed distance further down the capillary. From the time shift between signals at the first detector and those at the second, the velocity of the foam in the capillary can be calculated. From the velocity, time that the detector signal is ‘‘low,’’ and known capillary geometry, the volume of a gas bubble can be determined. An IBM PC is used for rapid data acquisition and calculation. The device has been tested under a range of foam conditions to validate its performance.
Computerized system for photoelectrochemistry with application to solar-energy materials research
Authors: Carlsson Per , Holmström Bertil
Published: July 2002

Photoelectrochemistry (PEC) is the study of electrochemical processes induced by light. In addition to usual electrochemical quantities, two new parameters are of interest: the wavelength and the intensity of the illumination light.