bluuebunny/crossref_metadata_2025 huggingface dataset:
Linking genotypic and phenotypic changes in the E. coli long-term evolution experiment using metabolomics
Authors: Favate John S , Skalenko Kyle S , Chiles Eric , Su Xiaoyang , Yadavalli Srujana Samhita , Shah Premal
Published: April 2023

Changes in an organism’s environment, genome, or gene expression patterns can lead to changes in its metabolism. The metabolic phenotype can be under selection and contributes to adaptation. However, the networked and convoluted nature of an organism’s metabolism makes relating mutations, metabolic changes, and effects on fitness challenging. To overcome this challenge, we use the long-term evolution experiment (LTEE) with E. coli as a model to understand how mutations can eventually affect metabolism and perhaps fitness. We used mass spectrometry to broadly survey the metabolomes of the ancestral strains and all 12 evolved lines. We combined this metabolic data with mutation and expression data to suggest how mutations that alter specific reaction pathways, such as the biosynthesis of nicotinamide adenine dinucleotide, might increase fitness in the system. Our work provides a better understanding of how mutations might affect fitness through the metabolic changes in the LTEE and thus provides a major step in developing a complete genotype–phenotype map for this experimental system.
Alterations of the gut microbiota in type 2 diabetics with or without subclinical hypothyroidism
Authors: Lv Yanrong , Liu Rong , Jia Huaijie , Sun Xiaolan , Gong Yuhan , Ma Li , Qiu Wei , Wang Xiaoxia
Published: April 2023

Background

Diabetes and thyroid dysfunction are two closely related endocrine diseases. Increasing evidences show that gut microbiota plays an important role in both glucose metabolism and thyroid homeostasis. Meanwhile, copy number variation (CNV) of host salivary α-amylase gene (AMY1) has been shown to correlate with glucose homeostasis. Hence, we aim to characterize the gut microbiota and CNV of AMY1 in type 2 diabetes (T2D) patients with or without subclinical hypothyroidism (SCH).

Methods

High-throughput sequencing was used to analyze the gut microbiota of euthyroid T2D patients, T2D patients with SCH and healthy controls. Highly sensitive droplet digital PCR was used to measure AMY1 CN.

Results

Our results revealed that T2D patients have lower gut microbial diversity, no matter with or without SCH. The characteristic taxa of T2D patients were Coriobacteriales, Coriobacteriaceae, Peptostreptococcaceae, Pseudomonadaceae, Collinsella, Pseudomonas and Romboutsia. Meanwhile, Escherichia/Shigella, Lactobacillus_Oris, Parabacteroides Distasonis_ATCC_8503, Acetanaerobacterium, Lactonifactor, uncultured bacterium of Acetanaerobacterium were enriched in T2D patients with SCH. Moreover, serum levels of free triiodothyronine (FT3) and free thyroxine (FT4) in T2D patients were both negatively correlated with richness of gut microbiota. A number of specific taxa were also associated with clinical parameters at the phylum and genus level. In contrast, no correlation was found between AMY1 CN and T2D or T2D_SCH.

Conclusion

This study identified characteristic bacterial taxa in gut microbiota of T2D patients with or without SCH, as well as the taxa associated with clinical indices in T2D patients. These results might be exploited in the prevention, diagnosis and treatment of endocrine disorders in the future.
Clinico-epidemiological Profile of Incidentally Detected Gastrointestinal Neuroendocrine Tumours on Gastrointestinal Endoscopy: A Retrospective Study
Authors: Koushik AK , Reddy J Sai Harish , Ganesh P , Shanmuganathan S
Published: April 2023

Introduction: Neuroendocrine tumours (NETs) are rare tumours, with the Gastrointestinal (GI) tract and the lung as the most common sites with indolent course. Endoscopists play a pivotal role in the diagnosis of GI-NETS because the majority of patients with NETs are asymptomatic and NETs are discovered during screening examinations. Since GI-NETs are less common than other cancers, their natural history, diagnosis, and treatment may not be completely understood. Aim: To estimate the prevalence and to characterize the clinical, endoscopic, and histological features of incidentally detected GI NETs in nodular/polypoidal/ulcerated lesions on GI endoscopy. Materials and Methods: This record-based retrospective study was conducted at the Department of Medical Gastroenterology of a tertiary care facility. The data belonged to the period between January 2018 to December 2020. Data belonged to the patients that underwent Oesophago- gastro duodenoscopy (OGD)/ Colonoscopy and were found to have nodular/ polypoidal lesions. Records on serum chromogranin, serum gastrin and radiological tests such as Ultrasonography(USG) or Computed Tomography (CT) scan were recorded. The histopathological with immunohistochemistry staining report was used to diagnose NETs. Continuous variables were analysed for normality by the Kolmogorov Smirnov test. Results: A total of 59 eligible patients were studied. The prevalence of GI NET tumours in 2018 was 17 (0. 32%), 19 (0. 33%) in 2019, and 23 (0. 41%) in 2020 with an overall rate of 59 (0. 36%) for all the three years. Total male participants were 35 (59.32%), and the mean age of the patients was 56.13 ±12.44 years. Majority had abdominal pain (32, 54.24%) and 35(59.32%) had tumours in the duodenum, 15 (25.42 %) in the stomach. The most common site was duodenum 35 (59.32%). As per World Health Organisation (WHO) NET, most tumours were Grade I (50, 45.76%). Majority of tumours had Synaptophysin (57, 96.61%), Chromogranin (49, 83.05%), and a Ki67 (Kiel-clone no.67) index≤ 2 (49, 83.05%), while 27 (84. 75 %) tumours were of size of <1 cm. Conclusion: GI-NETs are uncommon, and their biology, histopathology, and clinical behavior are distinct. Typically, they are slow-growing tumours, but their growth rate can fluctuate depending on the location, size, and grade of the tumour
Composition and Nutrition of Wild Bees in Solanum melongena L. Agroecosystems in Pune, Maharashtra, India
Authors: Andhale Ramnath , Pathare Vishal , Pai Kalpana , Pandit R. S. , Skeels Matthew , Pai Aswini
Published: April 2023

Eggplant, (Solanum melongena L.), also called aubergine or Guinea squash, in the nightshade family (Solanaceae) is an economically important crop in India. We investigated the significance of Solanum melongena pollen in the diet of wild bees found in agroecosystems by examining pollen on the bees using a pollen load analysis and a nutritive analysis. We selected five agricultural sites that cultivate S. melongena near Pune, Maharashtra, India. At each site, over a two-year period, we sampled the wild bees that visited mature flowers. We sampled pollen from mature flowers and also from the bodies of the bee specimens. The pollen grains from the bees were observed under a light microscope and a scanning electron microscope. They were counted using a Neubauer chamber and the pollen probability index for each bee species was calculated. The nutritive value of S. melongena pollen was estimated by extracting and characterising their proteins using liquid chromatography mass-spectrometry. Protein peptides sequences were extracted from the NCBI protein database to examine their essential amino acids. We collected 324 bees representing 11 species in three families involved in S. melongena pollination. Apis florea and A. cerana were the most abundant bees that visited S. melongena flowers. Pollen load size is highly variable ranging between few thousand to 134146 pollen grains per bee. However, the pollen probability index indicated a high degree of specificity to S. melongena pollen. S. melongena has high pollen protein content and a total of 10 different proteins were identified that are important for plant cell activities as well as the nourishment of pollinators. Further proteomic characterization of the indicated that nearly half the essential amino acids played and nutrient role in the bees. This study highlights that nutrititive composition of S. melongena pollen and highlights its potential to play a significant role in wild bee diets.
Effects of Light on the Growth and β-carotene Accumulation in the Green Algae Dunaliella salina
Authors: Tran-Nguyen Quynh Anh , Tran Thi Tuong Vy , Trinh-Dang Mau
Published: April 2023

The marine microalgae Dunaliella salina holds significant economic value due to its rich content of β-carotene, a natural pigment with high antioxidant capacity, immune-stimulating properties, and a crucial role in antioxidant reactions with vitamins C and E. This study evaluated the effects of light factors on the growth and biosynthesis of β-carotene in the Dunaliella salina strain isolated from coastal waters in Central Vietnam. The microalgae strain was cultured in the static f/2 medium at 25°C, under different light spectra (blue, red, and white) and light intensities (13.5, 27.0, and 40.5 µmol photon/m2/s), with a similar light/dark cycle of 16/8. The results indicated that the microalgae strain showed the highest growth rate and production yield of β-carotene under the red LED light, whereas the highest β-carotene accumulation in each microalgal cell was obtained under the blue LED light. Regarding light intensity, the best growth and β-carotene production yield was observed under the highest experimental light intensity of 40.5 µmol photon/m2/s, but the highest β-carotene content per algal cell was reached under the lowest intensity (13.5 µmol photon/m2/s). These findings provide important scientific data for further research to identify the optimal conditions for increasing biomass and stimulating the accumulation of valuable secondary compounds of the microalgae Dunaliella salina in Vietnam.
Evaluation of Bacteria Composition in Smoked Fish Processed in Yeji-Pru East District, Ghana
Authors: Bardoe Dennis , Gyabeng Jones , Hayford Daniel , Ibrahim Ilyas
Published: April 2023

Background: Fish safety and quality have been a major area of public health concern. This situation was heavily influenced by several factors ranging from the harvesting environment to the dining table.

Aim: This study aimed at assessing the bacteriological quality of smoked fish in three (3) major fish processing communities in the Yeji-Pru East District, Ghana.

Study design: The study was a comparative cross-sectional design to explore bacteria species occurrence and abundance (loads) of smoked fish in Yeji-Pru East District, Ghana. It also was directed towards determining the characteristics of the situation as it existed during the period of the study, from June to December 2017.

Method: A closed-ended structured questionnaire was used to collect sociodemographic data from 20 owners of the fish processing site. Forty-eight smoked fish samples including; Oncorhynchus sp., Clupea harengus, Chrysichthys auratus and Oreochromis niloticus were surface sterilised, rinsed and dried at 45°C for 24 hours. Ten grams of each fish sample were diluted with 10 ml of Buffered Peptone Water.  Further dilution was prepared using 5 ml of the same diluent. The prepared samples were made to settle for isolations and later inoculated on MacConkey Agar, Shigella-Salmonella Agar, and Salt Mannitol Agar. Microbial colonies were then enumerated using the pour plate method. Data collected were analysed using Microsoft Excel, SPSS and Interactive Chi-square Test at a test significance of 5%.

Results: The results showed absence of Salmonella and Shigella in all fish samples studied. However, it revealed the presence of Escherichia coli and Staphylococcus species at a rate of 79.2 (n= 38) and 89.6% (n= 43), respectively. The microbial load for E. coli and Staphylococcus species were community specific. Statistical analysis showed a significant difference (p < 0.05) between the microbial loads in fish samples obtained at each study site. However, there was no spatial variation in the mean microbial abundances of each selected sample (p > 0.05). The bacteria load observed were lower than the permissible level for human consumption authorised by both the Ghana Standards Authority and the International Commission on Microbiological Specifications for Foods.

Conclusion: The study showed that the pre-smoking and post-smoking activities along the fish processing chain could affect the microbial load and diversity. Therefore, the adoption of a good processing practice was highly advocated.
Guanine nucleotide activation of adenylate cyclase in saponin permeabilized glioma cells
Authors: Rasenick Mark M. , Kaplan Randi S.
Published: July 2002

We have compared the regulation of adenylate cyclase activity in membrane fractions from C6 glioma cells and in monolayer cultures of C6 cells that had been permeabilized with saponin. Guanine nucleotides (GTP and GTPγS) and isoproterenol increase adenylate cyclase activity in C6 membranes and in permeabilized C6 cells. In C6 membranes, guanine nucleotides activate adenylate cyclase in the presence or absence of isoproterenol; in permeabilized cells, however, guanine nucleotides increase adenylate cyclase activity only in the presence of isoproterenol. We suggest that the properties of the permeabilized cells more closely resemble those of intact cells, and that some component which is present in permeabilized cells but is lost following cell disruption may be important for the normal regulation of adenylate cyclase activity.
Phospholipid membrane permeability of peptide nucleic acid
Authors: Wittung Pernilla , Kajanus Johan , Edwards Katarina , Nielsen Peter , Nordén Bengt , Malmström Bo G.
Published: July 2002

Phospholipid vesicles (liposomes) as membrane models have been used to study the penetration properties of peptide nucleic acid (PNA), a new DNA analog in which the nucleobases are attached to a pseudo‐peptide backbone. The liposomes were characterised by carboxyfluorescein efflux, light‐scattering and cryogenic transmission electron microscopy. The liposome structure was found not to be affected by the incorporation of PNA or an oligonucleotide. Two 10‐mer fluorescein‐labelled PNAs were found to have low efflux rates (half‐times of 5.5 and 11 days), comparable to a 10‐mer oligonucleotide (half‐time of 7 days). We conclude that passive diffusion of unmodified PNA is not an effective way of transport into biological cells.
Low‐molecular‐weight heparin for thrombophilia in pregnant women
Authors: Bar J , Cohen‐Sacher B , Hod M , Blickstein D , Lahav J , Merlob P
Published: July 2002

Objective: Low‐molecular‐weight heparin (LMWH) is the anticoagulant of choice during pregnancy because it is associated with a low incidence of osteoporosis and thrombocytopenia. Antithrombotic therapy has recently been used to prevent pregnancy loss in high‐risk patients with evidence of acquired or congenital thrombophilia. The aim of the present study was to gain further information on the teratogenic potential of LMWH in this patient group. Methods: The study population included 46 patients with a history of recurrent abortions, intrauterine fetal death or intrauterine growth restriction (IUGR) and severe early‐onset preeclampsia. Patients with a history of thromboembolism or positive findings for thrombophilia were prescribed LMWH (enoxaparin sodium, 40 mg daily) in combination with low‐dose aspirin (100 mg daily) in the first trimester (group 1, n=14) or the second trimester (group 2, n=17); the remaining 15 patients received low‐dose aspirin alone (group 3). Results: No significant differences were noted between the groups in the incidence of congenital malformations or abortions, IUGR or preterm deliveries. One infant in group 1 had familial bilateral postaxial polydactyly of the hands and one in group 3 had patent ductus arteriosus. Conclusion: Despite the small size of the study groups, our results support the assumption that the use of LMWH is safe, at least as a teratogenic agent, in patients with thrombophilia throughout pregnancy.
The prevalence of subclinical hypothyroidism at different total plasma cholesterol levels in middle aged men and women: a need for case‐finding?
Authors: Bindels Alexander J. G. H. , Westendorp Rudi G. J. , Frölich Marijke , Seidell Jacob C. , Blokstra Anneke , Smelt Augustinus H. M.
Published: July 2002

OBJECTIVE

In order to determine whether screening of thyroid function is justified in patients with hypercholesterolaemia, we determined the prevalence of subclinical hypothyroidism at different levels of total plasma cholesterol in middle‐aged men and women.

DESIGN AND METHODS

1200 participants were selected from a population based cross sectional study on risk factors for cardiovascular diseases. The participants were divided into three groups: total plasma cholesterol <5 mmol/l, total plasma cholesterol 5–8 mmol/l, total plasma cholesterol >8 mmol/l. Each group was comparable in size and sex distribution. Subclinical hypothyroidism was defined as plasma TSH levels higher than 4 mU/l, in the presence of normal free thyroxine (FT44) concentration.

RESULTS

Plasma samples of a total of 1191 participants were analyzed. The overall prevalence of subclinical hypothyroidism was 1.9% in men and 7.6% in women of middle age. In women the prevalence of subclinical hypothyroidism increased from 4.0 percent in the lowest, to 10.3 percent in the highest cholesterol stratum (P = 0.02). In men, the mean prevalence was 1.8 percent and roughly similar in the various strata. After age correction, an increase of 1 mU/l TSH in women was associated with an increase of 0.09 mmol/l total plasma cholesterol (95% confidence interval (CI) 0.02–0.16 mmol/l). A similar trend was found in men (0.16 mmol/l, 95% CI −0.02–0.34 mmol/l).

CONCLUSIONS

In the population, the prevalence of subclinical hypothyroidism is up to 10 percent in middle aged women with high levels of total plasma cholesterol and may justify case‐finding. In these women approximately 0.5 mmol/l of total plasma cholesterol can be attributed to the subclinical thyroid dysfunction. In men a similar correlation between thyroid dysfunction and total plasma cholesterol is seen, but the prevalence of thyroid dysfunction is considerably lower.
Equivalence of the Huygens–Fresnel and Debye approach for the calculation of high aperture point‐spread functions in the presence of refractive index mismatch
Authors: EGNER A.. , HELL S. W.
Published: July 2002

As discussed in recent work (Sheppard, C. J. R. & Török, P., J. Microsc., 185, 366–384; Török et al., J. Microsc., 188, 158–172), two approaches have been used extensively for vectorial computations of high aperture confocal point‐spread functions when focusing through a dielectric interface. Whereas the equation by Hell, Reiner, Cremer & Stelzer (J. Microsc., 169, 391–405) is based on the Huygens–Fresnel principle, the more recent approach by Török, Varga & Booker (J. Opt. Soc. Am. A, 12, 325–332; J. Opt. Soc. Am. A, 12, 2136–2144) is based on the Debye approximation. While the earlier theory considers a large but finite focal length the second theory is derived for an infinitely high Fresnel number. In a high aperture microscope, a high Fresnel number is equivalent to assuming that the focal length be infinitely large with respect to the wavelength. So far, the two theories are regarded as different, with the one by Török et al. being rigorous. In this paper, we demonstrate that, if the same conditions are applied, the equation by Török et al. can be analytically derived from that by Hell et al. Producing the same results, the benefit brought about by the equation by Török et al. is improved flexibility and computational speed for cases with azimuthal symmetry.
The far interpupillary distance. A gender‐specific variation with advancing age
Authors: Pointer Jonathan S.
Published: July 2002

A knowledge of the magnitude of the far interpupillary distance (FIPD) in relation to a specific population is of clinical, practical and theoretical interest. A FIPD database is presented here, comprising material collated from the spectacle dispensing records of n=1800 subjects seen in routine optometric practice. All measurements were taken by the author on healthy Caucasian (white, Northern European) males and females. The data were equi‐partitioned either across three age bands (16–25, 26–40, 41–65 years: mixed refractive types, total n=900) or between the three distance refractive types (emmetropia, hypermetropia, myopia: all subjects aged between 41–65 years, total n=900).

A consistent gender difference (male>female) was confirmed throughout this material, irrespective of age group; refractive type, however, had no influence on the magnitude of this facial parameter. Summary results of this anthropometric survey are presented in tabular form, facilitating reference by ophthalmic and dental clinicians and by the designers of binocular optical instruments.

There was also revealed evidence of a gender‐specific pattern of change in the FIPD variable with advancing age. An approximately 3% increase in the magnitude of the human FIPD from the mid‐teens to later middle age was attained in males by early middle age, being little altered thereafter: in contrast females continued to record an increase in this facial parameter into later middle age. An explanation for this hitherto unremarked feature of human facial anthropometry might be sought in the gender‐specific changes post‐puberty of the cranial skeletal anatomy and in the soft tissues of the orbital region.
Sensitivity and Specificity of Cognitive and Functional Screening Instruments for Dementia: The Indo‐U.S. Dementia Epidemiology Study
Authors: Pandav Rajesh , Fillenbaum Gerda , Ratcliff Graham , Dodge Hiroko , Ganguli Mary
Published: July 2002

There is a shortage of adequate screening instruments for dementia in poorly educated populations and non–English‐speaking groups. An epidemiological survey was conducted in a population‐based, largely illiterate, sample of 5,126 individuals aged 55 and older in 28 villages in the rural community of Ballabgarh in northern India. All participants were administered a general mental status test, the Hindi Mental State Examination (HMSE), and a brief battery of neuropsychological tests. Their informants answered a questionnaire assessing functional ability, the Everyday Abilities Scale for India (EASI). Six hundred thirty‐two participants underwent clinical diagnostic evaluation for dementia. We investigated whether the sensitivity, specificity, and predictive value for dementia of the mental status test could be improved by the addition of the brief neuropsychological test battery or the functional questionnaire, comparing the instruments alone and in combination. In participants who could be tested cognitively, the HMSE, the neuropsychological battery, and EASI had sensitivities of 81.3%, 81.3%, and 62.5%, respectively, with specificities of 60.2%, 74.5%, and 89.7%, respectively. The combination of all three was 93.8% sensitive and 41.8% specific. The sensitivity of the HMSE alone was nonsignificantly improved by the addition of either the EASI or the neuropsychological battery, whereas its specificity was significantly decreased by either addition. An advantage of the EASI was that it could also be administered to informants of subjects who were cognitively untestable. In this largely illiterate community, with a low prevalence of dementia, the combination of cognitive tests and a functional ability questionnaire had substantial value for population screening.
Effects of two-dimensional confinement on the optical properties of InGaAs/InP quantum wire structures
Authors: Gershoni D. , Temkin H. , Dolan G. J. , Dunsmuir J. , Chu S. N. G. , Panish M. B.
Published: July 2002

We describe fabrication and photoluminescence excitation of InGaAs/InP quantum wires with a lateral dimension of ∼350 Å. Transverse confinement results in the splitting of the n=1 heavy hole-electron transition. Three of these levels are observed in the excitation spectrum. The exciton energies agree with the theoretical predictions based on a new method of solving the two-dimensional effective mass Schrödinger equation.
Transmission of molecular fluorescence through a thin metal film by surface plasmons
Authors: Gruhlke R. W. , Hall D. G.
Published: July 2002

We examine the use of surface plasmons to mediate the transport of molecular fluorescence across a corrugated thin metal film deposited onto a luminescent material. We find that for a given wavelength component, the amount of fluorescence reradiated by the long-range surface plasmon into a narrow angular range can be as large as ∼30% of that emitted isotropically into the medium above the sample in the absence of the metal layer.
Schottky barrier height of InxAl1−xAs epitaxial and strained layers
Authors: Chu P. , Lin C. L. , Wieder H. H.
Published: July 2002

The Schottky barrier height of n-type semiconducting and semi-insulating InxAl1−xAs grown by molecular beam epitaxy has been determined on the lattice-matched composition, x=0.523, in tension and in compression relative to their (110) oriented InP substrates. For the semiconducting material in the composition range 0.43<x<0.62, the barrier height is φbn=0.62±0.05 eV while the anomalous rise and saturation of φbn at 1.2 eV of the semi-insulating material, within the same composition range, is attributed to the presence of AlAs clusters within an InxAl1−xAs matrix.
Intensity-dependent photoluminescence spectra of semiconductor-doped glasses
Authors: Zheng J. P. , Shi L. , Choa F. S. , Liu P. L. , Kwok H. S.
Published: July 2002

The photoluminescence spectra of CdSx Se1−x doped glasses were found to be strongly dependent on the pumping laser intensity. Two spectral features corresponding to two different recombination mechanisms were identified. The dynamic behavior can be explained by the competition between tunneling-mediated recombination of deeply trapped charges and direct recombination of excitons, free and shallowly trapped carriers, and nonradiative recombination. Large (>30 nm) blue shifts of both peaks were also observed as a function of the laser intensity.
Real-time monitoring of laser ablation deposition of superconductors by fluorescence and secondary-ion spectra
Authors: Chen C. H. , McCann M. P. , Phillips R. C.
Published: July 2002

Fluorescence spectra and secondary-ion spectra for laser ablation of high-temperature metal-oxide superconductors are reported. These processes can be used to monitor a thin-film deposition process. The fluorescence spectra are more suitable for Y, Ba, and Ca ions. However, ion spectra can be used to monitor and identify Tl and Ca ions easier than by fluorescence spectra.
Analysis of the H2 vibrational distribution in a hydrogen discharge
Authors: Hiskes J. R. , Karo A. M.
Published: July 2002

The H2(v″) vibrational distribution observed in a medium-density hydrogen discharge is analyzed in terms of standard collisional processes. All processes in the model are specified independently of adjustable parameters. The calculated distribution is found to be a sensitive function of the wall relaxation process. The warm-gas-temperature discharge analyzed here leads to a substantially more rapid H2(v″) wall relaxation than is inferred from cold-gas systems.
High-temperature kinetics in He and Ne buffered XeF lasers: The effect on absorption
Authors: Moratz Thomas J. , Saunders Todd D. , Kushner Mark J.
Published: July 2002

Excimer lasers excited by electron or ion beams having energy deposition of 100’s J/ℓ over many microseconds experience a temperature rise of hundreds of degrees (K). The increase in gas temperature may greatly impact both the kinetics and spectroscopic parameters. In this letter we discuss the high-temperature (≤900 K) plasma kinetics and absorption in He and Ne buffered gas mixtures for particle beam pumped XeF lasers. We find both gain and absorption depend differently on gas temperature in these mixtures (absorption decreasing in He mixtures, increasing in Ne mixtures). The differences are attributed to a reduction in diatomic absorbing species with increasing temperature and differences in the temperature dependence of the optical absorption cross sections for NeXe+ and Xe+2.
Molecular beam epitaxy growth of CoSi2 at room temperature
Authors: Tung R. T. , Schrey F.
Published: July 2002

Single-crystal type B CoSi2 thin layers have been grown on Si(111) by codeposition at room temperature. The existence of a good quality CoSi2 template layer on the surface prior to the codeposition is essential. This requirement can be satisfied by either an annealed CoSi2 thin layer or by a small amount of cobalt deposited at room temperature. The topography of the original substrate surface has a predominant effect on the structure of line defects at the CoSi2 interface formed at room temperature. Results obtained from transmission electron microscopy and Rutherford backscattering are presented.
Electronic passivation of GaAs surfaces through the formation of arsenic—sulfur bonds
Authors: Sandroff C. J. , Hegde M. S. , Farrow L. A. , Chang C. C. , Harbison J. P.
Published: July 2002

X-ray photoelectron spectroscopy reveals that the remarkable electronic quality of GaAs/sulfide interfaces can be ascribed to the formation of AsxSy phases which grow on an oxide-free GaAs surface. While one of these phases is akin to As2S3, another shows significant in-plane S—S bonding. Raman experiments indicate that the band bending on this disulfide- terminated surface has been reduced to 0.12 eV.
High critical currents in epitaxial YBa2Cu3O7−x thin films on silicon with buffer layers
Authors: Wu X. D. , Inam A. , Hegde M. S. , Wilkens B. , Chang C. C. , Hwang D. M. , Nazar L. , Venkatesan T. , Miura S. , Matsubara S. , Miyasaka Y. , Shohata N.
Published: July 2002

As-deposited superconducting thin films (∼0.1 μm) of YBa2Cu3O7−x have been prepared by pulsed laser deposition on (100) Si with buffer layers of BaTiO3/MgAl2O4. X-ray diffraction studies reveal that the films grow epitaxially with the c axis preferentially oriented normal to the substrate surface. This is confirmed by ion channeling measurements along the (100) (normal to the surface) and (110) directions of the Si substrate showing a minimum yield of 54% along the (100), and 78% along the (110) axes using 2.8 MeV He++. Preliminary transmission electron microscopy study also supports these results. The as-deposited films have zero resistance temperatures of 86–87 K, and critical current densities of 6×104 A/cm2 at 77 K and 1.2×105 A/cm2 at 73 K. Our results indicate that the superconducting properties of the films are limited primarily by the quality and degree of epitaxal growth of the buffer layers on the silicon substrate.
Role of atomic oxygen in the low-temperature growth of YBa2Cu3O7−δ thin films by laser ablation deposition
Authors: Koren G. , Gupta A. , Baseman R. J.
Published: July 2002

Thin films of YBa2Cu3O7−δ were deposited on (100) SrTiO3 substrates held at 600 and 700 °C in N2O and O2 ambients using 355 nm Nd-YAG laser pulses for ablation of the target. The experiments were done either in the presence or absence of 193 nm excimer laser irradiation of the ambient gas between the target and the substrate. Results without the excimer irradiation show that in 0.2 Torr of both N2O and O2, at 700 °C substrate surface temperature, excellent smooth films with Tc (R=0) of 93 K and Jc (88 K) of 1.3×106 A/cm2 were obtained. At 600 °C, semiconducting films with no superconducting transition were obtained in O2 ambient, whereas in N2O, semiconducting normal state behavior with broad superconducting transition was found. With the 193 nm irradiation, no change was observed in the electrical properties of the films deposited in O2 at 600 °C, whereas in N2O reasonably good superconducting films with normal metallic behavior and Tc (R=0) of 84 K were found. Since the 193 nm photons hardly dissociate O2 molecules, but very efficiently photodissociate the N2O molecules to form N2 and O(1D), it is concluded that the atomic oxygen produced by photodissociation of N2O is responsible for the superconducting film deposition at 600 °C.
Generation of high-energy atomic beams in laser-superconducting target interactions
Authors: Zheng J. P. , Huang Z. Q. , Shaw D. T. , Kwok H. S.
Published: July 2002

High-energy atomic beams with Mach numbers as high as 5 were observed in excimer laser-superconducting target interactions. The velocity distributions of the Y, Ba, Cu, and O atoms and ions could be described very well by a supersonic expansion-type mechanism similar to a molecule beam. The physics of the atomic beam formation process is discussed.
Adjustable four-electrode electron mirror as an aberration corrector
Authors: Shao Zhifeng , Wu Xiao Dong
Published: July 2002

A numerical analysis of a four-electrode electrostatic mirror is presented. The results indicate that this mirror provides correct aberrations as a corrector for electron optical systems and unlike all other mirror configurations known to date, this new system shows for the first time that an adjustable mirror, both in magnitude of the aberration coefficients and in the ratio of CS/Cc, can indeed be found in a practical system.
Electronic transport properties of epitaxial erbium silicide/silicon heterostructures
Authors: Duboz J. Y. , Badoz P. A. , d’Avitaya F. Arnaud , Chroboczek J. A.
Published: July 2002

We studied electrical parallel and perpendicular transport in thin epitaxial erbium silicide films obtained by solid phase reaction and by codeposition of Er and Si on (111) Si. Resistivity measurements show that the silicide is metallic with a room-temperature resistivity of 34 μΩ cm; the dependence of the Hall coefficient on temperature can be explained by a two-band conduction model. Magnetic effects are shown to affect the low-temperature resistivity and the Hall coefficient. Perpendicular transport properties are studied by electrical [current-voltage I(V) and capacitance-voltage C(V) characteristics] and internal photoemission methods on erbium silicide/n- or p-type Si diodes. The p-type diodes have a perfect rectifying behavior with a Schottky barrier height of about 0.74 eV measured by I(V) and photoemission methods. The n-type junction is ohmic at room temperature and rectifying at low temperatures; C(V) and optical measurements yield a Schottky barrier height of about 0.28 eV. Some potential applications of erbium silicide/Si heterostructures are presented.
Evidence for local composition variations within YBa2Cu3O7−δ grain boundaries
Authors: Babcock S. E. , Larbalestier D. C.
Published: July 2002

The composition variations associated with grain boundaries in bulk sintered YBa2Cu3O7−δ have been investigated by means of energy-dispersive x-ray microanalysis in a high spatial resolution scanning transmission electron microscope. A series of composition profiles indicates that considerable variations in composition occur on a very local scale both parallel and perpendicular to these grain boundaries. The regular, oscillatory (period ∼25 nm) nature of the composition variations observed along a grain boundary suggests that these heterogeneities may be an intrinsic feature of the boundary. Some possible implications of these observations for percolative conduction mechanisms are discussed briefly.
Ferrimagnetic rare-earth orthoferrites: A new, magnetic substrate for the growth of epitaxial Y-Ba-Cu-O thin films
Authors: Ramesh R. , Inam A. , Bonner W. A. , England P. , Wilkens B. J. , Meagher B. J. , Nazar L. , Wu X. D. , Hegde M. S. , Chang C. C. , Venkatesan T. , Padamsee H.
Published: July 2002

We report, for the first time, growth of thin films of Y-Ba-Cu-O by pulsed laser deposition onto [001] YbFeO3 single-crystal substrates. A Tc,0 of 88 K was obtained along with a critical current greater than 105 A/cm2 at 77 K. X-ray diffraction shows epitaxial growth of the 1-2-3 phase with the c axis oriented normal to the substrate plane. Rocking curve measurements show a 0.5° full width at half maximum, indicating good alignment of the layered structure. The composition was verified by Rutherford backscattering, while channeling results reveal a 17% yield, consistent with the rocking curve measurements. Growth of thin films of 1-2-3 on a magnetic substrate may open the way for potentially new applications.
Luminescence spectra of an n-channel metal-oxide-semiconductor field-effect transistor at breakdown
Authors: Das N. C. , Arora B. M.
Published: July 2002

Photon emission occurs from the drain gate boundary of a metal-oxide-semiconductor field-effect transistor when drain bias exceeds the drain-to-source breakdown value. Spectral measurement of luminescence has been carried out over a wide range 0.7–3.1 eV in order to understand the origin of the emission. Three different types of detectors are used to measure the luminescence spectrum. A continuous broad spectrum is observed with a peak near 1.0 eV. The emission intensity decreases almost exponentially in the higher energy range.
Growth of high quality AlGaAs by metalorganic molecular beam epitaxy using trimethylamine alane
Authors: Abernathy C. R. , Jordan A. S. , Pearton S. J. , Hobson W. S. , Bohling D. A. , Muhr G. T.
Published: July 2002

AlGaAs grown by metalorganic molecular beam epitaxy (MOMBE) has been problematic due to oxygen and carbon contamination, particularly when triethylaluminum (TEAl) has been used as the aluminum source. Consequently, we have investigated trimethylamine alane (TMAAl) as a potential replacement for the conventional metalorganic Al sources. AlGaAs films with excellent structural and optical properties have been grown with this source. Photoluminescence intensities from AlGaAs grown by MOMBE at 500 °C using TMAAl are comparable to those from material grown by metalorganic chemical vapor deposition at 675 °C using triethylaluminum (TMAl). Carbon and oxygen levels in MOMBE-grown AlGaAs are drastically reduced in comparison to similar films grown with TEAl.
Subpicosecond photoresponse of carriers in low-temperature molecular beam epitaxial In0.52Al0.48As/InP
Authors: Gupta S. , Bhattacharya P. K. , Pamulapati J. , Mourou G.
Published: July 2002

Femtosecond time-resolved reflectivity and photoconductive switching measurements have been made of In0.52Al0.48As grown by molecular beam epitaxy on (100) InP substrates at growth temperatures ranging from 150 to 480 °C. A response/switching time of ∼400 fs is measured in the sample grown at 150 °C. Temperature-dependent measurements shed light on the nature of the material producing the ultrafast response.
Infrared optical characterization of InAs/Ga1−xInxSb superlattices
Authors: Miles R. H. , Chow D. H. , Schulman J. N. , McGill T. C.
Published: July 2002

InAs/Ga1−xInxSb superlattices have been examined by photoluminescence, photoconductivity, and infrared optical transmission. Samples display clear photoconductive thresholds at energies in agreement with band gaps derived from photoluminescence. Far-infrared energy gaps (8–14 μm and beyond) are obtained for InAs/Ga0.75In0.25Sb superlattices with periods <75 Å, in good agreement with gaps calculated from a simple two-band model. An absorption coefficient of ∼2000 cm−1 at 10 μm is measured in a superlattice with an energy gap of 11.4 μm. The magnitude and shape of this absorption edge is comparable to that of bulk Hg1−xCdxTe, suggesting that infrared detectors based on InAs/Ga1−xInxSb superlattices may be competitive in the 8–14 μm range and beyond.
Forbidden Auger process in strained InGaSb/AlGaSb quantum wells
Authors: Jiang Y. , Teich M. C. , Wang W. I.
Published: July 2002

Carrier loss due to Auger recombination has been known to be the major factor limiting the performance of long-wavelength semiconductor lasers. We show for the first time that the dominant Auger process in InGaSb/AlGaSb and InGaAs/InP strained quantum well structures can be suppressed because of the conversation of energy and crystal momentum with the sufficient reduction of the in-plane heavy hole masses. As a result, low-threshold currents and good temperature performance can be achieved in strained quantum well semiconductor lasers. An analytic expression for the in-plane effective hole masses in a strained quantum well is derived and used to calculate the hole masses of InGaSb/AlGaSb strained quantum wells.
Charge non-neutrality in the quantum well region of a GaAs-AlGaAs intersubband 9 μm detector
Authors: Liu H. C. , Buchanan M. , Wasilewski Z. R. , Chu H.
Published: July 2002

Infrared transmission is employed to study intersubband transitions in a GaAs-AlGaAs quantum well detector with spectral response peaked at about 9 μm. Under dc bias, our experiments show directly that the density of electrons in the doped quantum wells changes significantly, i.e., a charge non-neutrality occurs in the multiquantum well region of the detector. This degrades the detector internal quantum efficiency. Theoretical calculations compared with our experiments show that under a dc bias, the intersubband transition energy shifts are dominated by many-particle effects when the electron density in the well is changed; while the Stark shift is expected to dominate when the electron density remains constant.
Selective area deposition of boron on Si(111) induced by synchrotron radiation
Authors: Rosenberg R. A. , Perkins F. K. , Mancini D. C. , Harp G. R. , Tonner B. P. , Lee S. , Dowben P. A.
Published: July 2002

We have performed the first deposition of boron on Si(111) induced by broadband synchrotron radiation (SR). Contamination-free thin films were grown at room temperature using decaborane (B10H14) as the source gas. After deposition the films were examined using photoelectron microscopy, which showed that film growth was limited to the region illuminated by SR. The temperature of the substrate rose less than 10 K. These results indicate that gas-phase excitations are not important and that the films are deposited by a nonthermal, photoinduced mechanism. Masked exposures demonstrate the potential of this technique for patterned deposition.
Proposal for III-V ordered alloys with infrared band gaps
Authors: Wei Su-Huai , Zunger Alex
Published: July 2002

It is shown theoretically that the recently observed spontaneous ordering of III-V alloys that yields alternate monolayer (111) superlattices provides the opportunity for achieving infrared band gaps in systems such as (InAs)1(InSb)1 and (GaSb)1(InSb)1. A substantial reduction in the direct band gap is predicted to result from the L-point folding that repel the Γ band-edge states.
Epitaxial MgO on Si(001) for Y-Ba-Cu-O thin-film growth by pulsed laser deposition
Authors: Fork D. K. , Ponce F. A. , Tramontana J. C. , Geballe T. H.
Published: July 2002

Epitaxial MgO thin films were grown on Si(001) by pulsed laser deposition. In spite of a large (−22.5%) lattice mismatch, epitaxy occurs with alignment of all crystallographic axes. Epitaxial quality and deposition rate are both sensitive to temperature and oxygen pressure. We believe this is the first demonstration of epitaxial MgO on Si. We employ MgO intermediate layers for superconducting epitaxial YBa2Cu3O7−δ/BaTiO3 thin films on Si with a critical current density of 6.7×105 A/cm2 at 77 K.
High-mobility InSb grown by organometallic vapor phase epitaxy
Authors: Gaskill D. K. , Stauf G. T. , Bottka N.
Published: July 2002

The highest mobility InSb epilayer grown to date by organometallic vapor phase epitaxy has been achieved by utilizing high-purity organometallic sources, choosing a reactor geometry to reproducibly control the source concentrations above the substrate, and using a high- integrity reactor system. On a p-type InSb substrate, an unintentionally doped layer had a 77 K n-type carrier concentration and mobility of 1.4×1015 cm−3 and 2.53×105 cm2/V s. Growths on GaAs substrates were greatly affected by the lattice mismatch and had 77 K carrier concentrations similar to the InSb case but with mobilities of (5.0–9.0)×104 cm2/V s. The crystal quality, morphology, and cyclotron resonance characteristics are reported and found to be comparable to state-of-the-art molecular beam epitaxy layers.
Low-temperature-grown GaAs quantum wells: Femtosecond nonlinear optical and parallel-field transport studies
Authors: Knox W. H. , Doran G. E. , Asom M. , Livescu G. , Leibenguth R. , Chu S. N. G.
Published: July 2002

We find that GaAs-AlGaAs quantum wells grown at low temperature (300 °C) by molecular beam epitaxy are nearly semi-insulating and exhibit a broadened excitonic resonance. Studies of the femtosecond time-resolved nonlinear optical saturation response and parallel-field transport properties indicate that a subpicosecond nonradiative decay dominates the carrier recombination of this material. Annealing of low-temperature-grown quantum wells causes the arsenic point defects to form arsenic metallic precipitates within the quantum wells and up-shifts the absorption edge.
Scanning tunneling microscopy of Pt/Co multilayers on Pt buffer layers
Authors: Tang S. L. , Carcia P. F. , Coulman D. , McGhie A. J.
Published: July 2002

We have obtained scanning tunneling microscope (STM) images of Pt/Co multilayers sputter-deposited on Pt buffer layers, as well as images of only the Pt buffer layer. The surface structure of both the Pt/Co multilayers and the Pt layers evolved toward nanometer-scale crystallites with distinct, mostly six-sided polygonal grain boundaries with increasing Pt buffer layer thickness. Near-atomic resolution images revealed monatomic steps and flat terraces for an ∼1000 Å thick Pt layer. From these images we concluded that the texture of the multilayer and the Pt buffer layer improved as the thickness of the Pt buffer layer increased. The correlation of the film structure of the Pt/Co multilayer to its magnetic coercivity is discussed.
Transit-time effects on photocurrent spectra of multiple quantum well diodes
Authors: Leavitt R. P. , Bradshaw J. L.
Published: July 2002

We consider the effects on photocurrent spectra of the finite transit times of carriers through the 2-μm-thick intrinsic region of a p-i-n diode containing multiple quantum wells. If the transit time is comparable to or greater than the carrier recombination time, the photocurrent spectra show severe distortion. We have observed an anomalously large decrease in the diode’s quantum efficiency, accompanied by a compression of the spectral features and eventually an apparent splitting of each photocurrent peak into two separate peaks, as the electric field is lowered. A carrier-transport model is presented that accurately describes the essential experimental features.
Molecular beam epitaxy of GaSb
Authors: Longenbach K. F. , Wang W. I.
Published: July 2002

The p-type nature of unintentionally doped GaSb molecular beam epitaxy grown layers has been attributed to native defects resulting from insufficient Sb incorporation. As a means to improve the quality of GaSb epilayers, growth on (311) B substrates was studied and shown to produce Te-doped GaSb layers with room-temperature mobilities of 6780 cm2/V s at carrier densities of 9×1015 cm−3 and AlGaSb/GaSb p-i-n diode structures with breakdown voltages as high as 20 V. These mobilities and breakdown voltages are the highest achieved for molecular beam epitaxy grown GaSb-based structures.
Residual losses in epitaxial thin films of YBa2Cu3O7 from microwave to submillimeter wave frequencies
Authors: Miller D. , Richards P. L. , Etemad S. , Inam A. , Venkatesan T. , Dutta B. , Wu X. D. , Eom C. B. , Geballe T. H. , Newman N. , Cole B. F.
Published: July 2002

We have measured the residual loss in five epitaxial a-b plane films of the high-Tc superconductor YBa2Cu3O7. Microwave measurements near 10 GHz were made by resonance techniques at 4 K. Submillimeter measurements from ∼1.5 to 21 THz were made at 2 K by a direct absorption technique. We use a model of weakly coupled superconducting grains and a homogeneous two-fluid model to fit the data for each film below the well-known absorption edge at 13.5 THz. When the penetration depth determined from muon spin rotation measurements is used to constrain each model, the weakly coupled grain model is able to fit the measured absorptivities for all films, but the two-fluid model is less successful.