bluuebunny/crossref_metadata_2025 huggingface dataset:
Caries Risk Assessment and Detection of Streptococcus Mutans Count in Plaque and Saliva Using Mutans-Sanguis Agar
Authors: Tyagi Vineet , Ramalingam Karthikeyan , Tyagi Ridhima , Kumar Manish , Tanwar Mamta , Bose Suddhasatva , Kakkar Amisha
Published: March 2022

Assessment of the caries risk of individual patients is a critical component in determining an appropriate management strategy.

A total of 160 samples were taken from the outpatients of dental clinics in Surendera Dental College, Sriganganagar, Rajasthan. The age group of the participants ranged from 16-60 years.

We have used the ADA caries risk assessment form among our study samples to ascertain their caries risk and compared it with their Streptococcus mutans levels in saliva and plaque using mutans-sanguis agar. The colonies were counted after 18 hours of incubation at 37oC. The S.mutans colonies were greyish-yellow in colour and those of S.sanguis were colourless. The colonies were counted with a digital colony counter.

The tabulated data were subjected to statistical analysis using ANOVA and t-test with SPSS.

The findings of the present study indicated the Streptococcus mutans counts among high risk and moderate risk group were statistically insignificant when compared to low risk and control group even though the mean value showed an increase. We observed that the CFU yield was higher in unstimulated saliva than the plaque samples in contrast to reported literature.

Moreover, Dental caries risk assessment should become a routine component in dental practice. Estimation of the caries risk will help to establish the periodicity and intensity of caries management protocol.

Our data suggest that the MS count in oral microflora are influenced by age and various other factors such as diet, time and host response. As dental caries is multifactorial disease further clinical studies are needed to identify the actual pathogenesis.
A Comprehensive Review of a New Nanosuspension for Improving the Oral Bioavailability of Poorly Soluble Drugs
Authors: Karthick G. , Akiladevi D. , Ahamed M. Irfan
Published: March 2022

Nanosuspension is a novel drug formulation for the delivery of hydrophobic drugs. The problem of medications that are poorly water-soluble and have low bioavailability is countered by nanosuspension technology. Solubility is a significant physiochemical element that influences drug absorption and therapeutic effectiveness. Poor aqueous solubility has the potential to impair formulation development. Nanosuspension technology can improve the drug's stability and bioavailability. Nanosuspensions can be formulated for various routes of administration such as oral, parenteral, ocular, topical, and pulmonary routes. Nanosuspension can be used for targeted drug delivery also by mucoadhesive gels and ocular inserts. Recent studies were approached to develop nanosuspension on site-specific drug delivery.
Study of Some Herbal Formulations Available for Rheumatoid Arthritis Treatment in Indian Market
Authors: Somani Vaishali , Jain Ashish
Published: March 2022

Rheumatoid arthritis is an immune mediated inflammatory disease (IMID) of the joints, characterized by destruction of bones and joints. Genetic, hormonal, environmental and nutritional, and socio-economic, age and sex, ethnicity, smoking, infections are some risk factors of rheumatoid arthritis. The treatments which are available including steroidal and non-steroidal allopathic therapies cannot cure or prevent the disease and having severe side effects. These treatments can only provide temporary relief by suppressing and reducing the pain in the joints. Traditional medicines are prevalent in the treatment of rheumatoid arthritis due to severe side effect of allopathic medicines in many countries. Many native medicinal plant of India have effective properties on rheumatoid arthritis. In this review, marketed herbal products available in Indian market are studied. In this study, a search was done to compile marketed herbal formulation and we complied ten herbal products which are sold in Indian market by companies like Himalaya, Dabur, Patanjali, Charak etc for the treatment of rheumatoid arthritis.
Covid-19 Pandemic and the Degree of Informality of Sole Proprietor Entrepreneurship (SPE)
Authors: Eho Olong Christopher , Mfondo Merlin , Tabeko Gilbert
Published: March 2022

This study reports a survey conducted July and August 2021 in the cities of Bamenda and Buea respectively capital cities of North West and South West regions of Cameroon amongst 255 sole proprietor entrepreneurs (SPE). The study seeks to examine the personal and Structural factor driving SPE in whole or in part to operate informal and their degree of informality during the Covid-19 pandemic. The study adopted a survey research design. The finding showed that 38.4% of SPE operate wholly informal, 17.3% largely informal, 14.9% largely formal and 29.4% wholly formal since the outbreak of covid-19 pandemic in the cities.  Using ordinary logistic regression model, the study revealed that the structural factors of tax avoidance and tax fraud are high in the cities of Bamenda and Buea. Revealing that there is a high significant likelihood that as tax avoidance and tax fraud increase by one unit, more sole proprietor entrepreneur chose to remain wholly informal within the period of covid-19 pandemic. This suggests SPE have adopted tax avoidance and tax fraud as resilience strategies to overcome the challenges posed by Covid-19.
Angus McEachen's house
Authors: White Ross , O'Connell Chris , Oliver Fay , Anderson Sue
Published: March 2022

This report presents the results of an excavation and historical study of an early 19th-century settlement at Brunary Burn near Arisaig, Highlands (NGR: NM 6770 8578). CFA Archaeology Ltd carried out the excavation during October 2005 in advance of the realignment and upgrading works of the A830 between Fort William and Arisaig. Two rectangular drystone buildings were excavated, along with a yard area between them. Artefacts recovered included pottery, iron tools, cauldron fragments, slate roofing and clay pipe fragments. The project provided an opportunity to bring together social historical research with archaeological evidence for a somewhat archaeologically under-studied period, and also identified the former inhabitants of the settlement as Angus McEachen and his extended family. The buildings appear to have been occupied for perhaps a single generation before the family was evicted and moved to new accommodation within the area.
Severe Terrain Archaeological Campaign
Authors: McHardy Ian , Barrowman Chris , MacLeod Mary , MacSween Ann , McKenzie Jo , Ramsay Susan , Smith Catherine , Ballin Smith Beverley
Published: March 2022

The STAC (Severe Terrain Archaeological Campaign) project conducted topographic and archaeological surveys of sea stacks and other cliff-bound coastal sites around the Isle of Lewis over three annual field seasons from 2003–2005. The project made use of a specialised access system called 'Industrial Rope Access', which proved to be both a safe and a practical way of achieving archaeological research in such places. The first part of this report details the formation and methods of the STAC project, and discusses some relevant geographical issues. The second part presents the results of the eleven site surveys. One of these sites, Dunasbroc, was thought to be particularly vulnerable to erosion and was subject to small-scale excavation, the results of which form the third part of the report.
The analysis of modified peroxisome proliferator responsive elements of the peroxisomal bifunctional enzyme in transfected HepG2 cells reveals two regulatory motifs
Authors: Bardot Olivier , Clemencet Marie Claude , Passilly Patricia , Latruffe Norbert
Published: July 2002

Peroxisome proliferators (PPs) are non‐genotoxic carcinogens in rodents. They can induce the expression of numerous genes via the heterodimerization of two members of the steroid hormone receptor superfamily, called the peroxisome proliferator‐activated receptor (PPAR) and the 9‐cis retinoic acid receptor (RXR). Many of the PP responsive genes possess a peroxisome proliferator response element (PPRE) formed by two TGACCT‐related motifs. The bifunctional enzyme (HD) PPRE contains 3 such motifs, creating DR1 and DR2 sequences. PPAR and RXR regulate transcription via the DR1 element while DR2 modulates the expression of the gene via auxiliary factors in HepG2 cells.
Synthesis of chloramphenicol acetyltransferase in a coupled transcription‐translation in vitro system lacking the chaperones DnaK and DnaJ
Authors: Vysokanov Alexander V
Published: July 2002

A trimeric enzyme chloramphenicol acetyltransferase (CAT1) has been synthesized in the Zubay system genetically depleted from DnaK and DnaJ. Most of CAT formed in the system fail to assemble into an active trimer. Instead CAT is accumulated in either a GroEL‐bound complex or as an inactive monomer. Addition of purified DnaK and DnaJ to the system prior to the start of protein synthesis leads to the increase of the specific activity of formed CAT. A portion of exogenous DnaK and DnaJ added to the system associate with nascent polypeptide chains in the ribosomes. DnaK also comigrates with 50S‐ribosomal subunits.
Use of double-stranded RNA-mediated interference to determine the substrates of protein tyrosine kinases and phosphatases
Authors: MUDA Marco , WORBY Carolyn A. , SIMONSON-LEFF Nancy , CLEMENS James C. , DIXON Jack E.
Published: July 2002

Despite the wealth of information generated by genome-sequencing projects, the identification of in vivo substrates of specific protein kinases and phosphatases is hampered by the large number of candidate enzymes, overlapping enzyme specificity and sequence similarity. In the present study, we demonstrate the power of RNA interference (RNAi) to dissect signal transduction cascades involving specific kinases and phosphatases. RNAi is used to identify the cellular tyrosine kinases upstream of the phosphorylation of Down-Syndrome cell-adhesion molecule (Dscam), a novel cell-surface molecule of the immunoglobulin—fibronectin super family, which has been shown to be important for axonal path-finding in Drosophila. Tyrosine phosphorylation of Dscam recruits the Src homology 2 domain of the adaptor protein Dock to the receptor. Dock, the ortho- logue of mammalian Nck, is also essential for correct axonal path-finding in Drosophila. We further determined that Dock is tyrosine-phosphorylated in vivo and identified DPTP61F as the protein tyrosine phosphatase responsible for maintaining Dock in its non-phosphorylated state. The present study illustrates the versatility of RNAi in the identification of the physiological substrates for protein kinases and phosphatases.
Pharmacological basis for cladribine resistance in a human acute T lymphoblastic leukaemia cell line selected for resistance to etoposide
Authors: Lotfi Kourosh , Månsson Emma , Chandra Joya , Wang Yuying , Xu Dawei , Knaust Eva , Spasokoukotskaja Tatjana , Liliemark Eva , Eriksson Staffan , Albertioni Freidoun
Published: July 2002

Cross‐resistance between different classes of anti‐neoplastic agents can jeopardize successful combination cancer chemotherapy. In this study, we observed an unexpected cross‐resistance between the podophyllotoxine derivative etoposide (VP) and the nucleoside analogue cladribine (CdA) in CCRF‐CEM cells developed for resistance to VP. The resistant cells also displayed 14‐ and twofold resistance to cytarabine (ara‐C) and gemcitabine respectively. Closer analysis of these cells showed that they contained lower amounts of topoisomerase (topo) IIα (P < 0·001) and β protein (P < 0·026), formed substantially lower amounts of the topo II–DNA complex, and had a markedly decreased level of Fas (CD95/APO‐1)‐ligand mRNA expression. Interestingly, Fas expression in the resistant cells did not differ from that in the parental cell line. No differences were observed in the accumulation/efflux of daunorubicin or in the gene expressions of P‐glycoprotein, multidrug resistance‐associated protein and the lung resistance‐related protein. The activity of deoxycytidine kinase (dCK), responsible for activation of CdA and ara‐C, was the same for resistant and wild‐type cells. However, there was an increase in the activity of the cytosolic 5′‐nucleotidases (5′‐NT), responsible for deactivation of nucleotides, amounting to 206% (P < 0·001) for the high Km and 134% (P < 0·331) for the low Km 5′‐NT in resistant cells. The high Km 5′‐NT is probably responsible for the decreased amount of the active metabolite CdA 5′‐triphosphate [40% decreased (P < 0·045)], as well as for other purine ribonucleosides and deoxyribonucleosides triphosphates in the resistant cells. In contrast, a significantly higher deoxycytidine triphosphate (dCTP) level (167%, P < 0·001) was observed in the resistant cells. Thus, this study suggests that the major cause of resistance to the nucleoside analogues CdA and ara‐C in cells selected for resistance to VP is a result of metabolic alterations producing increased activity of 5′‐NT and higher dCTP levels. Furthermore, these results indicate that there is a common factor in the regulation of nucleotide‐degrading enzymes and DNA topoisomerases, which may be altered in cross‐resistant cells.
Increased IL-12 release by monocytes in nephrotic patients
Authors: Matsumoto K , Kanmatsuse K
Published: July 2002

The pathogenesis of minimal-change nephrotic syndrome (MCNS) is obscure. It has been postulated that this glomerular disease may be a systemic disorder of cell-mediated immunity. IL-12 is a heterodimeric cytokine that is produced primarily by antigen-presenting cells and plays a primary role in the induction of cell-mediated immunity. To gain insight into the involvement of this cytokine, in vitro IL-12 levels were assessed in patients with MCNS and IgA nephropathy (IgAN) who were in either a stable or active clinical condition. The levels were compared with values in healthy controls. Significantly increased spontaneous and lipopolysaccharide (LPS)-stimulated release of IL-12 was detected in peripheral blood monocyte (PBM) cultures of MCNS and IgAN patients with the nephrotic syndrome (NS) compared with those of normal controls. Moreover, when individual MCNS patients were followed through their clinical illness, IL-12 levels were increased during the active phase and normalized as the patients went into remission. The amounts of IL-12 are significantly correlated with the levels of vascular permeability factor (VPF) in MCNS patients. This study describes a correlation between in vitro IL-12 release by PBM from two types of nephrotic patients and their disease activity, as well as a correlation with release of VPF by the same cultures. The study contributes to the understanding of this class of diseases and the observations may have a prognostic/diagnostic value.
Pilocytic astrocytomas do not show most of the genetic changes commonly seen in diffuse astrocytomas
Authors: Cheng Y , Pang J C‐S , Ng H‐K , Ding M , Zhang S‐F , Zheng J , Liu D‐G , Poon W‐S
Published: July 2002

Aims: While it is well known that pilocytic astrocytomas are clinically distinct from diffuse astrocytomas, few comprehensive studies have focused on their genetic differences. The aim of this study was to examine pilocytic astrocytomas for genetic alterations that are commonly seen in diffuse astrocytomas.

Methods and results:

By using molecular genetic and immunohistochemical techniques, we evaluated p16, p53, CDK4 and PTEN genes in 29 pilocytic astrocytomas. Mutation screening of p53 and PTEN was performed by single strand conformation polymorphism analysis followed by direct sequencing. Loss of heterozygosity (LOH) of p53, p16 and 10q23–25 loci was performed with microsatellite markers and genomic microsatellite instability (MSI) was also screened. Protein expression of p16, p53, CDK4 and PTEN was examined by immunohistochemistry. Five tumours were found to have single genetic alterations, which included a p53 mutation, a PTEN mutation, MSI at a single microsatellite marker of the p16 locus, and one single LOH at each p16 and 10q23 loci. Protein expressions of p16, CDK4 and PTEN were detected in 73%, 61% and 38% of tumours, respectively. Significantly and in sharp contrast to diffuse astrocytomas, no pilocytic astrocytoma in our series stained for p53 protein.

Conclusion:

Pilocytic astrocytomas have neither MSI phenotype nor recurrent alterations of the p53 and p16 genes. However, altered expression of PTEN may be important in the genesis of pilocytic astrocytomas. We conclude that pilocytic astrocytomas are genetically distinct from diffuse astrocytomas. Lack of p53 mutation/immunostaining may serve as a diagnostic adjunct for differentiating pilocytic astrocytomas from diffuse astrocytomas in small neurosurgical biopsies.
Report of a nutritional screening audit
Authors: Wheatley P.
Published: July 2002

Background: Malnutrition in hospitals has been widely documented and nutritional screening forms part of the National Professional Standards for Dietitians. As a result of this concern, a nutrition screening tool has been incorporated into the nursing care plan documentation.

Aims: To audit the use of the screening tool in nursing care plans for elderly patients and examine the communication methods concerning the need for individual nutritional care.

Methods: A standard chart was used to audit patient notes. In addition, a short informal interview was conducted with nursing staff.

Results: Use of the screening tool was variable and fewer than half of those identified by this tool as in need of nutritional care were referred to the dietitian.

Conclusion: Ward staff are prioritizing patients referred for dietetic care, even when they have been identified by the screening tool, but this is not always done systematically. Improvements could be made in the relevant documentation. Further training of ward staff and a follow‐up audit should be undertaken.
An extended role for the hospital optometrist
Authors: Oster J. , Culham L.E. , Daniel R.
Published: July 2002

The management of patients within shared care programmes would seem to have significant benefits in terms of individuals' convenience, addressing resource needs and expanding professional horizons. To date, these schemes have typically concentrated on the monitoring of patients with diabetes and glaucoma. At Moorfields Eye Hospital, we attempted to develop the role of the hospital optometrist by establishing a study to evaluate the clinical appraisal of new referrals in a busy out‐patient clinic. The results showed a high level of diagnostic accuracy which suggests that the role of hospital optometrists may be successfully extended to include some aspects of patient evaluation not typically undertaken.
Restraint Use, Restraint Orders, and the Risk of Falls in Hospitalized Patients
Authors: Shorr Ronald I. , Guillen M. Katherine , Rosenblatt Linda C. , Walker Kathryn , Caudle Cynthia E. , Kritchevsky Stephen B.
Published: July 2002

OBJECTIVES:

TTo determine the relationship between physical restraints and falls in the acute hospital setting.

DESIGN:

Matched case‐control study.

SETTING:

Inpatients at a 528‐bed, urban, community‐based, acute care hospital.

PARTICIPANTS:

Two hundred twenty‐eight patients who fell during hospitalization and 228 controls matched to cases by nursing unit and length of stay.

MEASUREMENTS:

Persons who fell were systematically evaluated at the time of fall by trained fall evaluators. For the cases, we sought to validate “orders for restraints” using “observed restraint use,” defined as the use of restraints at the time of fall as determined through direct observation or interviews with nursing staff.

RESULTS:

Patients with orders for restraints were more likely to fall than patients without orders for restraints (multivariate relative risk = 6.3, 95% confidence interval (CI) = 1.8–22.3). However, in the cases, there was poor correlation between “orders for restraints” and “observed restraint use” at the time of fall (kappa = 0.15, 95% CI = −0.4–0.34).

CONCLUSION:

Because orders for restraint use may not reflect actual restraint use at the time of a fall, observational studies relating use of restraints to the risk of falls should be interpreted with caution. Despite this caveat, we could find no evidence that restraints protect hospitalized patients from falling. J Am Geriatr Soc 50:526–529, 2002.
Measurement of opaque coating thickness using photothermal radiometry
Authors: Sheard S. J. , Somekh M. G.
Published: July 2002

We describe a method for determination of film thickness using the photothermal radiometric microscope. The method is noncontacting and nondestructive, and is applicable to coatings covering the entire surface of the material. The frequency variation of both the amplitude and phase of the thermal wave response is used to determine the film thickness. This gives two independent measures. The technique is valid regardless of the properties of the substrate material, but is more accurate when these differ substantially from those of the coating.
Consequence of layer thickness fluctuations on superlattice miniband structures
Authors: Davies R. A. , Kelly M. J. , Kerr T. M.
Published: July 2002

The miniband structure of a perfect superlattice depends on the thicknesses and compositions of the constituent layers. We describe simple modeling of the consequences of fluctuations in the layer thickness. Experimental results from an asymmetric superlattice tunnel diode, where the presence of negative differential conductance reflects the existence of a miniband gap, are used to show how the sensitivity of the miniband structure to such fluctuations depends on the choice of layer thicknesses.
Line spectrum of the interstitial iron donor in silicon
Authors: Olajos J. , Nielsen B. Bech , Kleverman M. , Omling P. , Emanuelsson P. , Grimmeiss H. G.
Published: July 2002

Photothermal ionization spectroscopy and infrared transmission measurements have been carried out on iron-doped silicon. A series of sharp lines in the range from 6100 to 6400 cm−1 was observed with both techniques. Photoionization cross-section spectra were determined by photothermal ionization spectroscopy and photoelectron paramagnetic resonance, and it is concluded that the lines originate from electronic transitions to excited shallow donor states at the interstitial iron impurity in the neutral charge state Fe0i. The lines and the Fe0i -related electron paramagnetic resonance signal annealed out together at approximately 170 °C. The line spectra are analyzed in terms of three overlapping donor series and the origins of these are discussed.
Lanthanum gallate substrates for epitaxial high-temperature superconducting thin films
Authors: Sandstrom R. L. , Giess E. A. , Gallagher W. J. , Segmüller A. , Cooper E. I. , Chisholm M. F. , Gupta A. , Shinde S. , Laibowitz R. B.
Published: July 2002

We demonstrate that lanthanum gallate (LaGaO3) has considerable potential as an electronic substrate material for high-temperature superconducting films. It provides a good lattice and thermal expansion match to YBa2Cu3O7−x, can be grown in large crystal sizes, is compatible with high-temperature film processing, and has a reasonably low dielectric constant (ε≂25) and low dielectric losses. Epitaxial YBa2Cu3O7−x films grown on LaGaO3 single-crystal substrates by three techniques have zero resistance between 87 and 91 K.
Special grain boundaries in YBa2Cu3O7
Authors: Smith D. A. , Chisholm M. F. , Clabes J.
Published: July 2002

The orientation distribution produced in strings of YBa2Cu3O7−x often referred to as 123, crystals produced from a melt is not random. The individual crystals are kinematically free to rotate during the coalescence process and it is found that coincidence site lattice misorientations are selected. This observation suggests that grain boundaries in 123 have structures related to those in other crystalline materials.
Structural and optical properties of GaAlInAs lattice matched to InP grown by low-pressure metalorganic vapor phase epitaxy
Authors: Davies J. I. , Marshall A. C. , Scott M. D. , Griffiths R. J. M.
Published: July 2002

We report for the first time, the metalorganic vapor phase epitaxy (MOVPE) growth of the quaternary alloy GaxAlyIn1−x−yAs, lattice matched to InP. Single epitaxial layers were prepared showing specular morphologies and lattice matching within Δa/a=10−3. Epilayers showed a high degree of crystallinity with routine x-ray linewidths of 20–40 seconds of arc. The lowest linewidth achieved was 22 seconds of arc. Room temperature and 4 K photoluminescence (PL) studies demonstrated very narrow excitonic transitions with ΔE at 4 K down to 5.4 meV. Band-gap energies, obtained from the absorption edge and PL peak energies, plotted against Al composition showed that the alloy was best described by a straight line relationship between the ternary end points, Ga0.47In0.53As and Al0.48In0.52As with no bowing observed.
Growth, patterning, and weak-link fabrication of superconducting YBa2Cu3O7−x thin films
Authors: Hilton G. C. , Harris E. B. , Van Harlingen D. J.
Published: July 2002

We have grown thin films of the high-temperature superconducting ceramic oxides and investigated techniques for fabricating weak-link structures. Films of YBa2Cu3O7−x grown on SrTiO3 by a combination of dc magnetron sputtering and thermal evaporation from the three sources have been patterned into microbridges with widths down to 2 μm. We find evidence that the bridges behave as arrays of Josephson-coupled superconducting islands. Further weak-link behavior is induced by in situ modification of the coupling by ion milling through the bridge.
Unidirectional ring resonator in photorefractive bismuth silicon oxide with two pump beams
Authors: Erbschloe D. R. , Solymar L.
Published: July 2002

Experiments using a new photorefractive gain mechanism involving two pump beams are described. A ring resonator is used to provide a frequency-shifted signal beam. The gain with two pumps of equal intensity is found to exceed that with a single pump by about a factor of 4.
Low-frequency, multigigawatt microwave pulses generated by a virtual cathode oscillator
Authors: Platt R. , Anderson B. , Christofferson J. , Enns J. , Haworth M. , Metz J. , Pelletier P. , Rupp R. , Voss D.
Published: July 2002

An axially extracted virtual cathode oscillator driven by a 4 MV, 80 kA elecron beam has been used to generate microwave pulses with an average peak power of 7.5 GW at a frequency of 1.17 GHz. Peak power efficiency was 5.3% and energy efficiency was 2.3%.
Generation of high-power, high repetition rate, subpicosecond pulses by intracavity chirped pulse regenerative amplification
Authors: Yan Li , Ho P.-T. , Lee Chi H. , Burdge G. L.
Published: July 2002

A neodymium phosphate glass regenerative amplifier is used for both pulse energy amplification and spectral broadening. After compression by a grating pair, 0.55 ps pulses of 11 μJ energy are generated at a 370 Hz repetition rate.
Radiative recombination in PbTe quantum wells
Authors: Heyen E. T. , Hagerott M. , Nurmikko A. V. , Partin D. L.
Published: July 2002

Recombination of quasi-two-dimensional (2D) free-electron-hole pairs in PbTe/(Pb,Eu)Te multiple quantum wells has been studied in time-resolved photoluminescence experiments in the 4–5 μm region on subnanosecond scale by an infrared upconversion method. Over a finite temperature range, the recombination rate is seen to vary approximately as 1/T, as expected for a radiative process in a nondegenerate 2D carrier gas. A model is presented where the recombination is enhanced by the presence of a substantial background hole density in the PbTe wells, generated in a manner analogous to modulation doping.
Application of the Williams–Watts decay law to D
X center capture and emission kinetics
Authors: Campbell A. C. , Streetman B. G.
Published: July 2002

The Williams–Watts or stretched exponential decay of the form A(t)=exp[−(t/τ)β] and variations of this form are compared to the capture and emission kinetics of the DX center observed by a number of authors. It is found that the time and temperature behavior of the DX center capture and emission characteristics can be reproduced with a thermally activated time constant τ and a linear dependence of β on temperature. Activation energies, lattice vibration frequencies, and models of implicit distributions of activation energies are compared to values previously found in the literature. Consistency is found between parameters for both capture and emission, and implications of this model are discussed.
Room-temperature pseudomorphic InxGa1−xAs/GaAs quantum well surface-emitting lasers at 0.94–1.0 μm wavelengths
Authors: Huang K. F. , Tai K. , Jewell J. L. , Fischer R. J. , McCall S. L. , Cho A. Y.
Published: July 2002

We report room-temperature lasing at 0.94–1.002 μm in high-finesse Fabry– Perot resonators with Inx Ga1−x As/GaAs multiple quantum well active layers (x=0.18–0.2). The quantum wells and AlAs/GaAs quarter-wave stack mirrors were epitaxially grown on GaAs substrates. Optically pumping with 0.875 μm, 10 ps pulses yielded a threshold of 15 pJ incident pulse energy. The equivalent threshold current density is about 26 μA/μm2 (2.6 kA/cm2 ), suggesting ultralow thresholds in micrometer-size devices. At the lasing wavelengths the GaAs substrates are essentially transparent allowing the possibility of integrating micro-optic lenslets on the substrate backsides for light collection. Nonlinear optical gating of 1.064 μm light was also achieved in these structures.
Nonlinear behavior of the field-induced molecular tilt near the smectic A–C* transition
Authors: Lee Sin-Doo , Patel J. S.
Published: July 2002

A deviation from the linear relationship between induced molecular tilt and applied electric field has been observed in the vicinity of the transition from the smectic A to the chiral smectic C* phase. Near the transition temperature Tc, the induced tilt angle θ initially grows linearly with the strength of an applied electric field E, and clearly exhibits a crossover to Eα (1/3 <α<1) above a certain field strength. As temperature increases, however, the exponent α approaches 1 in a wide range of the electric field we studied. A simple mean field model is presented to explain the observed nonlinear behavior.
Preparation of Bi-Sr-Ca-Cu-O thin film by coevaporation and its thermal stability
Authors: Yoshitake T. , Fujita J. , Kubo Y. , Igarashi H. , Satoh T.
Published: July 2002

Thin film with a high Tc single phase was prepared on a (100)MgO substrate at a substrate temperature of about 620 °C by coevaporation of Bi2O3, Sr, Ca, and Cu metal. The resistive superconducting transition with onset Tc of 80 K was observed for this film. By post-deposition annealing at 850 °C, the high Tc phase was transformed into a low Tc phase, while films annealed at a higher temperature such as 890 °C maintained the high Tc phase. These results indicated that the high Tc phase can exist only at the high-temperature region (∼890 °C) while the stable phase existing at the low-temperature region (∼850 °C) is the low Tc phase.
Bi-Sr-Ca-Cu-O and Pb-Bi-Sr-Ca-Cu-O superconductor films via an electrodeposition process
Authors: Maxfield M. , Eckhardt H. , Iqbal Z. , Reidinger F. , Baughman R. H.
Published: July 2002

A novel electrochemical process has been developed for the formation of superconducting films. Using this process, superconducting films of Bi2Sr2Ca1Cu2O8 and (Pb,Bi)2Sr2Ca1Cu2O8 have been formed. The process consists of simultaneously depositing the metallic constituents of the superconductor from a single electrolyte, and thermally oxidizing the resulting precursor film to form the superconducting phase. Application of −4 to −5 V vs Ag/Ag+ to a conductive cathode substrate, immersed in an electrolyte containing salts of all of the metals, reduces the metal cations causing them to deposit on the cathode as a metallic film precursor. Precursor films having desired stoichiometries were obtained by regulating the electrolyte bath composition.
Multiple quantum well optical waveguides with large absorption edge blue shift produced by boron and fluorine impurity-induced disordering
Authors: O’Neill M. , Bryce A. C. , Marsh J. H. , De La Rue R. M. , Roberts J. S. , Jeynes C.
Published: July 2002

Impurity-induced disordering of GaAs/AlGaAs multiple quantum well waveguide structures has been carried out using the neutral impurities boron and fluorine, introduced by ion implantation and followed by thermal annealing. Substantial blue shifts (up to 100 meV) in the absorption edge have been obtained and, for similar conditions, fluorine-induced disordering produces larger shifts than boron-induced disordering. Optical transmission measurements performed in slab and rib waveguides indicate that the additional contribution to the absorption coefficient associated with boron disordering is 15 dB cm−1 and with fluorine disordering is only 6 dB cm−1.
Frequency modulation responses of two-electrode distributed feedback lasers
Authors: Kuo C. Y. , Twu Y. , Dutta N. K. , Wagner E. J. , Granlund S. W.
Published: July 2002

Frequency modulation (FM) response of a 1.3 μm two-electrode distributed feedback laser is studied in detail. We found that by adjusting the injection current applied to the modulated section, the FM bandwidth can be increased to a value as high as 900 MHz. However, as the bandwidth increases, the FM sensitivity decreases proportionally. This behavior is described satisfactorily by below-threshold carrier rate equation and shown to be closely related to the injected carrier lifetime.
Effect of stacking sequence on valence bands in Ga/As/Ge (001) monolayer superlattices
Authors: Saito T. , Ikoma T.
Published: July 2002

Valence bands of Ga/As/Ge (001) monolayer superlattices (MLSLs) are calculated by Harrison’s tight-binding method. The MLSLs have two possible types of growth cycles: a (Ga,As,Ge,Ga,As,Ge) cycle for an antiphase type (AP type) and a (Ga,As,Ge,As,Ga,Ge) cycle for a normal phase type (NP type). Cations and anions in the AP type occupy ‘‘antisites’’ of the zinc blende structure while those in the NP type occupy only ‘‘normal sites.’’ The two types have distinct features of the valence bands concerning degeneracy of the bands at the zone boundary, splitting of the valence-band maximum due to the tetragonal symmetry, and valence-band discontinuity in a (bulk Ge)/(the MLSL) junction.
Carbon and zinc delta doping for Schottky barrier enhancement on n-type GaAs
Authors: Pearton S. J. , Ren F. , Abernathy C. R. , Hobson W. S. , Chu S. N. G. , Kovalchick J.
Published: July 2002

The growth of thin (50–100 Å), C or Zn δ-doped layers on n-type GaAs is shown to yield large enhancements in the effective Schottky barrier height (ΦB) of TiPtAu contacts subsequently deposited on the material. The incorporation of a single C δ-doped layer (p=1.5×1020 cm−3, 50 Å wide) within 100 Å of the surface leads to a barrier height of 0.93 eV, a significant increase over the value for a control sample (0.76 eV). The use of two sequential δ-doped layers leads to an apparent barrier height in excess of the GaAs band gap (ΦB=1.67 eV). This appears to be consistent with the predictions of a unified defect model. Zinc δ doping (p∼3×1018 cm−3) in a similar fashion produces barrier heights of 0.81 eV for one spike and 0.95 eV for two spikes.
Electroabsorption spectroscopy of amorphous Si/SiC quantum well structures
Authors: Hattori K. , Tsujishita M. , Okamoto H. , Hamakawa Y.
Published: July 2002

The interband optical transition in quantum wells of hydrogenated amorphous silicon and silicon carbide has been studied by using electroabsorption (EA) spectroscopy. The observed EA spectrum exhibits a triangular line shape, identified as being due to a field-induced modification of the subband transition. The identification is confirmed by comparing with the experimental result of thermoabsorption spectroscopy.
Properties of ultrahigh vacuum self-implantation-induced amorphous germanium
Authors: Peto G. , Kanski J. , Holmen G.
Published: July 2002

Ge (111) was self-implanted in ultrahigh vacuum to prepare an impurity-free amorphous layer. The same extraordinary amorphous state of Ge was induced as that found earlier with 121Sb+ implantation in normal vacuum. This eliminates the possibility that this anomalous a-Ge is impurity stabilized.
Structural and electrical properties of epitaxial Si on insulating substrates
Authors: Rozgonyi G. A. , Radzimski Z. J. , Higuchi T. , Jiang B. L. , Lee D. M. , Zhou T. , Schmidt D. , Blake J.
Published: July 2002

In this work the role of extended defects on the electrical performance of epitaxial silicon on substrates containing an insulating SiO2 layer has been examined. The buried SiO2 layers in the substrates were obtained by two techniques: implantation of oxygen and zone melt recrystallization. In order to make a thorough structural and electrical evaluation of silicon on the insulator substrates, 5-μm-thick epitaxial capping layers have been simultaneously deposited via chemical vapor deposition on representative insulating substrates and reference wafers. The average minority-carrier lifetime was found to vary from 2.5 to 242 μs depending on the density and distribution of dislocations emerging from the capping epitaxial layer.
Numerical study of nonequilibrium electron transport in AlGaAs/GaAs heterojunction bipolar transistors
Authors: Beton P. H. , Levi A. F. J.
Published: July 2002

We have simulated numerically the dynamics of nonequilibrium electron transport in n-p-n AlGaAs/GaAs heterojunction bipolar transistors. We show that collector transit time is intimately related to base transport dynamics and high p-type carrier concentration in a thin base improves device performance. However, even for a very thin collector depletion region, the small Γ-X intervalley energy separation in GaAs places severe constraints on efficient collector transport.
Pumping wavelength dependence on gain factor of a 0.98 μm pumped Er3+ fiber amplifier
Authors: Suzuki Kazunori , Kimura Yasuo , Nakazawa Masataka
Published: July 2002

Gain characteristics of an Er3+-doped fiber are investigated with different pump wavelengths using a tunable Ti:sapphire laser in the 0.98 μm band. Maximum gain was obtained at a pump wavelength of 0.980 μm and the gain profile can be fully explained in terms of the pump absorption spectrum. The 3 dB gain bandwidth for the pump wavelength was 10–14 nm. A gain coefficient of 2.6 dB/mW was obtained for a 60 ppm Er3+-doped fiber with an absorbed pump power of 9 mW.
Resonant acousto-optical interaction in superlattices
Authors: He Jianjun , Sapriel Jacques
Published: July 2002

The remarkable acousto-optical properties of superlattices for light wavelength near the condition of the Bragg reflection at the interfaces are reported here for the first time. Because of the assistance of a reciprocal lattice vector in the phase-matching condition, the collinear coupling between the light and ultrasonic waves becomes possible in the superlattice. At the same time, the diffraction efficiency is strongly increased by an optical resonance effect in the superlattice. Acousto-optical devices based on semiconductor superlattice structures are proposed, which can be very efficient, rapid, and compact.
Investigation of the electrical degradation of silicon Schottky contacts due to mercury contamination
Authors: Jones P. L. , Corbett J. W.
Published: July 2002

A micrographic investigation of the effect of mercury exposure on silicon substrates was conducted. Mercury was found to leave a residue on the silicon surface. A further study was conducted to determine the extent of electrical degradation of Si Schottky contacts due to the presence of a contaminant mercury residue between the metal and the semiconductor. It was concluded that such a layer caused uncertainties in subsequent resistivity measurements, higher capacitance-voltage (C-V) barrier heights, and observable leakage currents in current-voltage (I-V) plots taken from mercury-contaminated Si Schottky diodes.
Below-band-gap photon recycling in AlxGa1−xAs
Authors: Bradshaw J. L. , Devaty R. P. , Choyke W. J. , Messham R. L.
Published: July 2002

A long minority-carrier diffusion length and the transmission of Alx Ga1−x As luminescence through Alx Ga1−x As layers are identified as two processes causing the excitation of GaAs spectra through thick Alx Ga1−x As layers, as well as contributing to enhancements in low-temperature photoluminescence intensity observed in Alx Ga1−x As layers without GaAs substrates. A simple model for intensity enhancement due to below-band-gap photon recycling is introduced to explain the observed enhancements. Some features that uniquely distinguish below-band-gap photon recycling from the better known room-temperature process are presented.
5:1 on-off contrast InGaAs/InP multiple quantum well Fabry–Perot étalon modulator
Authors: Tomita A. , Kohga Y. , Suzuki A. , Terakado T. , Ajisawa A.
Published: July 2002

We report the first demonstration of an InGaAs/InP multiple quantum well Fabry–Perot étalon modulator. The obtained on-off contrast is 5:1 at −16 V applied voltage for 1540 nm wavelength light. The absorption coefficient of the multiple quantum well around 1540 nm increases from 1000 to 6300 cm−1 as the applied voltage increases from 0 to −16 V, and the relative refractive index change is up to −0.9%.
Assessment of GaAs heteroepitaxial films grown on silicon-on-sapphire upgraded by double solid phase epitaxy
Authors: Posthill J. B. , Markunas R. J. , Humphreys T. P. , Nemanich R. J. , Das K. , Parikh N. R. , Ross P. L. , Miner C. J.
Published: July 2002

Characterization of heteroepitaxial GaAs grown on silicon-on-sapphire that had been microstructurally upgraded by the double solid phase epitaxy process reveals that microtwining and surface roughness are substantially reduced. Moreover, the thermally induced elastic strain in the GaAs film is found to be reduced by over a factor of 4 from the strain measured in GaAs-on-Si (100) grown in the same manner. The low-temperature photoluminescence characteristics are similar to GaAs homoepitaxial films grown by molecular beam epitaxy.
Quantum-switched heterojunction bipolar transistor
Authors: Wu Ming C. , Tsang W. T.
Published: July 2002

We propose and demonstrate a negative differential resistance transistor—the quantum-switched heterojunction bipolar transistor (QSHBT). It has the highest current peak-to-valley ratio ever reported at room temperature (15 in an InGaAs/InP QSHBT). More important, the switching and peak-to-valley ratio can be controlled by a base current injected electronically or optically. For example, a peak current as high as 72 mA or 2.9 kA/cm2 can be controlled by either a few microamperes of base current or a few microwatts of optical signal. A gain of peak current of 8650 at room temperature is obtained. The present device is grown by chemical beam epitaxy.
Detection of Cl in rf plasmas by laser-excited stimulated emission
Authors: Sappey Andrew D. , Jeffries Jay B.
Published: July 2002

Laser-excited stimulated emission is used to detect chlorine atoms in a Cl2/Ar rf etching plasma. Two laser photons near 233.3 nm excite the 3p44p 4S0 electronic state of atomic chlorine in a spin-forbidden transition from the 3p5 2P0 ground state. At modest laser fluence stimulated emission is observed from the 3p44p 4S0→3p44s 4P transition. The stimulated emission signals are compared to simultaneously acquired laser-induced fluorescence from the same transition. The strong, collimated stimulated emission provides a means to detect atomic chlorine which only requires a single optical access window.
Homogeneous width of exciton absorption spectra in CuCl microcrystals
Authors: Masumoto Yasuaki , Wamura Tetsuro , Iwaki Atsushi
Published: July 2002

The homogeneous width of Z3 exciton absorption spectra in CuCl microcrystals was measured for the first time. It was determined to be 0.18+0.03−0.05 meV at 77 K by laser saturation spectroscopy. The temperature dependence of the Z3 exciton absorption linewidth also supported the result. The measurements of the saturation power density, the homogeneous linewidth, and the lifetime of Z3 excitons informed us of the transition dipole moment for a CuCl microcrystal. The obtained transition dipole moment for a CuCl microcrystal is about 13 times that for a unit cell in bulk CuCl.
Spatial imaging of the critical current density in epitaxial Y1Ba2Cu3O7 films
Authors: Gross R. , Hipler K. , Mannhart J. , Huebener R. P. , Chaudhari P. , Dimos D. , Tsuei C. C. , Schubert J. , Poppe U.
Published: July 2002

We report the first spatially resolved measurement of the critical transport current density of c-axis oriented epitaxial Y1Ba2Cu3O7 films on 〈100〉 SrTiO3 using low-temperature scanning electron microscopy (LTSEM). The local critical current density, imaged with a spatial resolution of ∼1 μm, has been found to vary considerably in these films. Possible reasons for the observed spatial inhomogeneities are surface imperfections of the substrate and precipitates in the film. The spatial inhomogeneity of the critical current density in epitaxial films might be a reason for differences in the temperature dependences of the critical current density obtained by magnetic and transport measurements.
Wet chemical etching of high-temperature superconducting Y-Ba-Cu-O films in ethylenediaminetetraacetic acid
Authors: Shokoohi F. K. , Schiavone L. M. , Rogers C. T. , Inam A. , Wu X. D. , Nazar L. , Venkatesan T.
Published: July 2002

A new wet chemical etchant for high-temperature superconducting films is reported, which leaves transition temperature unaffected within experimental accuracy (1 K) and does not require reoxygenation. The solution consists of ethylenediaminetetraacetic acid (EDTA) in water, and is suitable for micropatterning using standard photolithography. We have fabricated 3–50 μm patterns on laser-deposited Y-Ba-Cu-O films. The bulk of the films etches at 0.14 μm/min in a saturated solution at room temperature. Porous surface layers are removed three times faster than the dense portions of the films. Etch rate depends linearly on the solution concentration and exponentially on the solution temperature. These rates are reduced if etching is interrupted and the samples are exposed to atmosphere.
Superconducting properties of V3Ga prepared by rapid liquid quenching and solid-state precipitation
Authors: Habbal F. , Clemente G. B. , Turnbull D.
Published: July 2002

A modified solid-state precipitation process for the formation of stoichiometric A-15 V3Ga is presented which results in high values of Tc=15.0 K and Hc2(4.2)=22 T, excellent phase homogeneity, and a high critical current Jc(4.2 K)=3×105–6×104 A/cm2 over the field range 0–18 T. We find that grain boundary pinning is dominant, producing a very high specific pinning force Qmax=6.4×104 dyn/cm2. The nonparamagnetically limited Hc2 is needed to explain our high flux-pinning results.
Flux-creep-limited critical currents in YBa2Cu3O7−δ ceramics
Authors: Dai Uri , Hess Nir , Tessler Leandro R. , Deutscher Guy , Vetter Genevieve , Queyroux Francine , Bontemps Nicole , Mahoum Roger , Lagues Michel , Mocaer Philippe
Published: July 2002

Critical currents of YBa2Cu3O7−δ bulk-sintered samples were measured at and above 77 K in the presence of magnetic fields. In moderate magnetic fields a H−n dependence with n<1 was observed. Transport measurements give n≂0.5, indicating that critical currents are limited by flux creep rather than by field quenching of Josephson junctions.
Observation of a correlation between twin orientation and substrate step direction in thin GaAs films grown on intentionally misoriented Si (100)
Authors: Rajkumar K. C. , Madhukar A. , Liu J. K. , Grunthaner F. J.
Published: July 2002

A transmission electron microscope study of GaAs grown on Si tilted 4° off (100) has for the first time revealed that of the two twin variants propagating to the GaAs film surface, a substrate tilt about a 〈011〉-type direction favors one over the other.