bluuebunny/crossref_metadata_2025 huggingface dataset:
Histopathological Spectrum of Cardiac Lesions in Sudden Cardiac DeathAn Autopsy Study
Authors: Mahapatra Rashmi Rekha , Gouda Kalyani Prava , Das Rupa , Mohanty Punyanshu , Prusty Gouranga Charan
Published: March 2023

Introduction: Sudden Cardiac Death (SCD) is a serious health concern, and the incidence of SCD is rising globally. A number of causes can result in SCD in apparently healthy individuals and in people with undiagnosed cardiac disease. The study was done to evaluate the probable cause of death by observing various histomorphological changes in cardiac autopsies. Aim: To establish the cause of SCD and study the histopathology, age and sex distribution, frequency, and location of different types of cardiac lesions. Materials and Methods: The study was a descriptive, crosssectional, observational study carried out in the Department of Pathology and Forensic Medicine and Toxicology (FMT) at PRM Medical College and Hospital, Baripada, Odisha, over a period of three years. Gross and microscopic findings on Haematoxylin & Eosin (H&E)-stained cardiac sections were studied. The final diagnosis was made on the basis of clinical, autopsy, and histopathological findings. The study was compared with other relevant studies. The data was analysed using Microsoft Excel 2019 software. Results: A total of 164 cases of SCD were included in this study. The maximum number of deaths occurred in the age group of 51-60 years (42 cases). The male to female ratio was 2.6:1, indicating an overall male preponderance. Out of 164 autopsied hearts, 85 cases of Ischemic Heart Disease (IHD), including new, old, and mixed lesions were found, followed by Hypertrophic Cardiomyopathy (HCM) in 25 cases, multiple lesions in 12 cases, dilated cardiomyopathy in four cases, tubercular pericarditis with myocarditis in one case, infective endocarditis in three cases, atherosclerosis in one case, coronary insufficiency in one case, cardiac myxoma in one case. Conclusion: Many factors can lead to SCD in apparently healthy individuals or in people with cardiac disease. In the present study, the most common cause contributing to SCD was IHD. The cause of SCD can be identified by a thorough post-mortem examination and histological analysis.
Influence of Tillage Systems on the Productivity of Wheat Varieties in the Conditions of Balkh Afghanistan
Authors: Ansari Mohammad Akbar , Osmani Khuwaja Safiullah , Payenda Poya , Yonusi Mohammad Mobin
Published: March 2023

In Afghanistan, the greatest challenges in agriculture system are major soil erosion, high soil moisture loss, and farming of the same crop every year leads to drop in fertility level of the soil. Conservation Agriculture defined by three principles namely minimum soil disturbance, crop rotation and permanent soil cover. A field experiment was conducted during winter and summer season of 2018 at research farm of Dehdadi, Balkh, Afghanistan. The experiment was laid out in a split plot design, comprising ten treatment combinations. The main factor was conservation agriculture and conventional agriculture with sub factor by five varieties of wheat (Moqawium, Baghlan, Chunt, Darlaman and local).The main objective of this study is to compare and determine the performance of new wheat varieties under conservation and conventional agriculture, for improving and identifying it’s effect on wheat yield and wheat varieties under conservation agriculture.

The result indicated that different soil conservation practice could cause significant changes in term of wheat growth and yield attributes like bundle weight and yield of wheat and among wheat varieties Chunte variety significantly difference on number of tillers, bundle weight, straw yield, yield and thousand wheat kernel as compare to local wheat variety. In short time there was not any difference in soil chemical and physical of soil in term of pH, OC, N, P and K, but in long term there will be minor changes occur, so we do recommend conserving to improve the soil fertility and cultivate the chunte variety for more yield.
Characterization of a highly toxic, large molecular size heat‐stable enterotoxin produced by a clinical isolate of Yersinia enterocolitica
Authors: Yoshino Ken-ichi , Takao Toshifumi , Huang Xiaozhe , Murata Hiroshi , Nakao Hiroshi , Takeda Tae , Shimonishi Yasutsugu
Published: July 2002

A novel heat‐stable enterotoxin (ST) designated as Y‐STc was purified to homogeneity from the culture supernatant of a pathogenic strain of Yersinia enterocolitica serotype O3 and its amino acid sequence was determined. The mature Y‐STc was found to consist of 53 amino acid residues, which includes the putative pro‐sequence. The molecular weight of Y‐STc was 5683 and constituted the largest molecular size in the family of currently known STs. The minimum effective dose of purified Y‐STc in the suckling mouse assay was 0.6 ng (0.1 pmol), indicating that, despite the long sequence, Y‐STc is the most toxic in the ST family.
Isozyme hybrids within the protruding third loop domain of the barley α‐amylase (β/α)8‐barrel implication for BASI sensitivity and substrate affinity
Authors: Juge Nathalie , Rodenburg Kees W. , Guo Xiao-Jun , Chaix Jean-Claude , Svensson Birte
Published: July 2002

Barley α‐amylase isozymes AMY1 and AMY2 contain three structural domains: a catalytic (β/α)8‐barrel (domain A) with a protruding loop (domain B; residues 89–152) that binds Ca2+, and a small C‐terminal domain. Different parts of domain B secure isozyme specific properties as identified for three AMY1–AMY2 hybrids, obtained by homeologous recombination in yeast, with crossing‐over at residues 112, 116, and 144. The AMY1 regions Val90‐Thr112 and Ala145‐Leu161 thus confer high affinities for the substrates p‐nitrophenyl α‐d‐maltoheptaoside and amylose, respectively. Leu117‐Phe144, and to a lesser degree Ala145‐Leu161, are critical for the stability at low pH characteristic of AMY1 and for the sensitivity to barley α‐amylase/subtilisin inhibitor specific to AMY2.
Alteration in relative activities of phenylalanine dehydrogenase towards different substrates by site‐directed mutagenesis
Authors: Seah Stephen Y.K. , Linda Britton K. , Baker Patrick J. , Rice David W. , Asano Yasuhisa , Engel Paul C.
Published: July 2002

Glycine‐124 and leucine‐307 of phenylalanine dehydrogenase from Bacillus sphaericus were altered by site‐specific mutagenesis to the corresponding residues in leucine dehydrogenase: alanine and valine, respectively. These two residues have previously been implicated from molecular modelling as important in determining the substrate discrimination of the two enzymes. Single and double mutants displayed lower activities towards l‐phenylalanine and enhanced activity towards almost all aliphatic amino acid substrates tested compared to the wild‐type, thus confirming the predictions made from molecular modelling.
Long‐chain fatty acid‐promoted swelling of mitochondria: further evidence for the protonophoric effect of fatty acids in the inner mitochondrial membrane
Authors: Schönfeld Peter , Więckowski Mariusz R. , Wojtczak Lech
Published: July 2002

Swelling of non‐respiring rat liver mitochondria suspended in isotonic potassium acetate at pH 6.5–7.4 in the presence of valinomycin was promoted by long‐chain fatty acids, such as myristate, indicating a protonophoric mechanism. This swelling was partly inhibited by inhibitors or substrates of mitochondrial anion carriers. The results show that the fatty acid cycling mechanism responsible for uncoupling of oxidative phosphorylation can also operate in the direction opposite to that originally proposed [Skulachev, V.P. (1991) FEBS Lett. 294, 158–162], i.e. the inwardly directed transfer of the fatty acid anion accompanied by outwardly directed free passage of undissociated fatty acid. They also extend the list of mitochondrial anion carriers, that are involved in this process, over the mono‐ and tricarboxylate transporters. At pH 8, myristate, but not the synthetic protonophore, p‐trifluoromethoxycarbonyl‐cyanide phenylhydrazone, induced mitochondrial swelling in both potassium acetate and KCl media, that did not require the presence of valinomycin. This indicates that, at alkaline pH, myristate facilitates permeation of the inner mitochondrial membrane to monovalent cations and, possibly, activates the inner membrane anion channel.
Scorpine, an anti‐malaria and anti‐bacterial agent purified from scorpion venom
Authors: Conde Renaud , Zamudio Fernando Z. , Rodrı́guez Mario H. , Possani Lourival D.
Published: July 2002

A novel peptide, scorpine, was isolated from the venom of the scorpion Pandinus imperator, with anti‐bacterial activity and a potent inhibitory effect on the ookinete (ED50 0.7 μM) and gamete (ED50 10 μM) stages of Plasmodium berghei development. It has 75 amino acids, three disulfide bridges with a molecular mass of 8350 Da. Scorpine has a unique amino acid sequence, similar only to some cecropins in its N‐terminal segment and to some defensins in its C‐terminal region. Its gene was cloned from a cDNA library.
Novel intracellular effects of human connective tissue growth factor expressed in Cos‐7 cells
Authors: Kubota Satoshi , Hattori Takako , Shimo Tsuyoshi , Nakanishi Tohru , Takigawa Masaharu
Published: July 2002

To clarify the multiple functionality of connective tissue growth factor (CTGF), we examined the effects of nascent CTGF within the cell by transient expression. In Cos‐7 cells, expression of human CTGF induced an altered cell morphology. It was associated with an increased cellular DNA content and loose attachment, indicating the cells were in G2/M phase. Overexpression of CTGF did not induce cell growth, whereas recombinant CTGF efficiently stimulated the proliferation extracellularly. These results indicate that intracellular CTGF may act as an antimitotic agent, thus it should also be noted that nascent CTGF was found to accumulate around the central mitotic machinery.
Metabolic engineering of xanthophyll content in tomato fruits
Authors: Dharmapuri Sridhar , Rosati Carlo , Pallara Patrizia , Aquilani Riccardo , Bouvier Florence , Camara Bilal , Giuliano Giovanni
Published: July 2002

Ripe tomato fruits accumulate significant amounts of the linear carotene lycopene, but only trace amounts of xanthophylls (oxygenated carotenoids). We overexpressed the lycopene β‐cyclase (b‐Lcy) and β‐carotene hydroxylase (b‐Chy) genes under the control of the fruit‐specific Pds promoter. Transgene and protein expression was followed through semi‐quantitative reverse transcription‐PCR, Western blotting, and enzyme assays. Fruits of the transformants showed a significant increase of β‐carotene, β‐cryptoxanthin and zeaxanthin. The carotenoid composition of leaves remained unaltered. The transgenes and the phenotype are inherited in a dominant Mendelian fashion. This is the first example of successful metabolic engineering of xanthophyll content in tomato fruits.
The immunoreactivity of glial fibrillary acidic protein in mesangial cells and podocytes of the glomeruli of rat kidney in vivo and in culture
Authors: Buniatian Gayane , Traub Peter , Albinus Margitta , Beckers Gerhard , Buchmann Albrecht , Gebhardt Rolf , Osswald Hartmut
Published: July 2002

In this study the presence of glial fibrillary acidic protein (GFAP) in kidney is for the first time demonstrated in cryostat sections and cultures of isolated glomerular explants derived from rat kidneys. In double immunolabelling analysis of adult rat kidney sections using antiserum against GFAP and monoclonal antibody (mAb) against vimentin or desmin, the presence of immunoreactivity for GFAP could be observed in the glomerulus of the kidney and vascular cells situated in the peritubular space which expressed vimentin and desmin. Labelling of the sections with absorbed antiserum against GFAP completely abolished the staining in all these cells. The mAb against GFAP, clone GF12.24 which is known to label GFAP both in neural and non‐neural cells, recognised its antigen only in the cells located in glomeruli. The investigations performed on early 2‐ or 3‐day‐old cultures from glomerular explants revealed different patterns of staining for GFAP in mesangial cells and podocytes: weak filamentous in mesangial cells and a strong non‐filamentous perinuclear pattern in podocytes. Due to prominent perinuclear expression in podocytes GFAP may be considered as a marker of these cells. A different pattern of distribution of immunoreactivity for GFAP in podocytes and mesangial cells might be due to function‐related posttranslational modifications of GFAP resulting in assembly or disassembly of GFAP filaments. The different pattern of staining for GFAP in the podocytes and mesangial cells, cells which exert a different influence on the capillaries of the glomeruli, suggests a role for GFAP in regulation of the tension and permeability of vascular walls. Previous investigations and present studies hint at GFAP as being a general marker of perivascular cells.
Modeling of Growth, Lactate Consumption, and Volatile Fatty Acid Production by Megasphaera elsdenii Cultivated in Minimal and Complex Media
Authors: Soto‐Cruz Oscar , Favela‐Torres Ernesto , Saucedo‐Castañeda Gerardo
Published: July 2002

Use of the Pirt and Luedeking–Piret equations permits the determination of the effect of medium composition on the metabolic patterns of Megasphaera elsdenii grown in minimal and complex media with lactate as the major carbon source. To establish the significance of the parameters involved in the Pirt and Luedeking–Piret equations, a quantitative statistical criterion was proposed. In the complex medium, lactate was completely used for growth and product formation, whereas in the minimal medium a fraction of the energy obtained from lactate was used for maintenance purposes. Modeling of VFA production by the Luedeking–Piret equation showed that, independent of the type of medium, acetate and propionate are growth‐associated products, while butyrate and valerate are only partially growth‐associated. The growth‐associated products are related to energy‐yielding metabolism and the non‐growth‐associated products are related to the consumption of reducing equivalents.
Growth Kinetics, Nutrient Uptake, and Expression of the Alcaligenes eutrophus Poly(β‐hydroxybutyrate) Synthesis Pathway in Transgenic Maize Cell Suspension Cultures
Authors: Hahn J. J. , Eschenlauer Arthur C. , Narrol Matt H. , Somers David A. , Srienc Friedrich
Published: July 2002

Transgenic suspension cultures of Black Mexican Sweet maize (Zea mays L.) expressing the Alcaligenes eutrophus genes encoding enzymes of the pathway for biosynthesis of the biodegradable polymer poly(β‐hydroxybutyrate) (PHB) were established as a tool for investigating metabolic regulation of the PHB pathway in plant cells. Cultures were grown in a 2 L modified mammalian cell bioreactor and in shake flasks. Biomass doubling times for transgenic bioreactor cultures (3.42 ± 0.76 days) were significantly higher than those for untransformed cultures (2.01 ± 0.33 days) . Transgenic expression of the bacterial enzymes β‐ketothiolase (0.140 units/mg protein) and acetoacetyl‐CoA reductase (0.636 units/mg protein) was detected by enzyme assays and immunoblots. However, over the first 2 years of cultivation, reductase activity decreased to 0.120 units/mg protein. Furthermore, the PHB synthase gene, although initially present, was not detectable after 1.5 years of cultivation in suspension culture. These facts suggest that transgenic expression of PHB pathway genes in plant cells may not be stable. A hydroxybutyrate derivative was detected via gas chromatography even after 4 years of cultivation. Although the method used to prepare samples for gas chromatography cannot directly distinguish among PHB polymer, hydroxybutyryl‐CoA (HB‐CoA), and hydroxybutyric acid, solvent washing experiments indicated that most or all of the signal was non‐polymeric, presumably HB‐CoA. The synthesis of HB‐CoA appeared to be linked to substrate growth limitation, with HB‐CoA accumulation increasing dramatically and cell growth ceasing upon depletion of ammonium. This suggests that the PHB synthesis pathway in plants is subject to regulatory mechanisms similar to those in prokaryotic cells.
Plasminogen activator inhibitor‐1 fused with erythropoietin (EPO) mimetic peptide (EMP) enhances the EPO activity of EMP
Authors: Kuai Le‐tian , Wu Chun‐lei , Qiu Qi‐feng , Zhang Jing , Zhou Ai‐wu , Wang Shi‐quan , Zhang He‐yun , Song Qian , Liao Shu‐ning , Han Yu ,   Jian‐ning Liu, Zhong Ma
Published: July 2002

Abstract: Erythropoietin (EPO) mimetic peptide (EMP) encoding sequence was inserted into the gene of plasminogen activator inhibitor‐1 (PAI‐1) between Ala348 and Pro349 (P2′–P3′), generating a novel gene, PAI‐1/EMP (PMP). This was cloned into pET32a expression vector, fused with TrxA peptide in the vector, and a 63‐kDa protein was expressed in inclusion bodies with an expression level > 50%. The TrxA/PMP protein was purified by Ni‐NTA‐agarose metal–ligand affinity chromatography to a purity > 90%, showing a single, silver‐stained band on SDS–PAGE. Using a reticulocyte counting assay, the EPO activity of PMP was determined to be 5000 IU/mg, 2500‐fold that of EMP.
Neonatal porcine pancreatic cell clusters as a potential source for transplantation in humans: Characterization of proliferation, apoptosis, xenoantigen expression and gene delivery with recombinant AAV
Authors: Vizzardelli* Caterina , Molano R. Damaris , Pileggi Antonello , Berney Thierry , Cattan† Pierre , Fenjves Elizabeth S. , Peel Alyson , Fraker Chris , Ricordi Camillo , Inverardi Luca
Published: July 2002

Abstract: Neonatal porcine islets are characterized by reproducible isolation success and high yields, sizable advantages over adult islets. In this work we have analyzed selected phenotypic and functional characteristics of porcine neonatal islets relevant to their possible use for transplant in humans. We show that porcine islet cells proliferate in culture, and synthesize and store islet‐specific hormones. Proliferating beta cells can be easily identified. Implant of cultured neonatal islets in immunodeficient rodents results in the reversal of diabetes, albeit with delay. We also show that measurable apoptosis occurs in cultured neonatal porcine islets. Further, antigens recognized by human natural antibodies are expressed in a dynamic fashion over the culture period analyzed and are not limited to the alpha‐Gal epitope. Lastly, we demonstrate that a recombinant Adeno‐Associated virus can be used to efficiently deliver a reporter gene in porcine islets. This characterization might be helpful in the definition of the potential use of neonatal porcine islets for human transplantation.
‘But what about the really ill, poorly people?’ (An ethnographic study into what it means to nurses on medical admissions units to have people who have harmed themselves as their patients)
Authors: Hopkins Clare
Published: July 2002

In the UK, someone dies by suicide every 2 hours. An increasing number are also harming themselves. Many of these people are admitted to Medical Admissions Units of General Hospitals. Department of Health guidelines now recommend that anyone who harms him or herself should have a psychosocial and risk assessment. This means that they have to stay in hospital until they are assessed and this renders them ‘different’ from other patients. This study uses an ethnographic approach to search for the meaning to nurses of having this group of patients on the ward, using participant observation and semistructured interviews with four nurses. Three themes were isolated through analysis of the data: the busy quality of such wards (busyness) how this group of clients impede the busy quality and the strategies which nurses use to cope with the difficulties. Analysis of the data revealed that the research participants found difficulty in understanding why people harm themselves and that they felt that they did not have the requisite skills to deal with this group of people. This appears to leave them with a sense of frustration and helplessness which perhaps mirrors that of this client group.
Cumulative impact of early maternal marital age during the childbearing period
Authors: Shawky  , Milaat
Published: July 2002

Early marriage of girls, close to age of menarche, is a widespread practice in Arab countries. Knowledge on the cumulative effect of early maternal marriage on maternal and infant health during the childbearing period is insufficient. The objectives of this study were to estimate the prevalence of early maternal marriage in Jeddah, identify its relation with other maternal risk factors, and investigate the cumulative impact of early maternal marriage on subsequent maternal health and pregnancy outcomes throughout the reproductive period. Data were collected from six randomly selected primary health care units in Jeddah City. Married women with an infant 12 completed months of age were interviewed and information on sociodemographic characteristics, maternal health and previous pregnancy outcomes were collected. Early marriage of girls before the age of 16 years accounted for 26.5% of the study population and was reported by a third of mothers currently below the age of 20 years. Illiterate mothers, housewives, multiparae, smokers and those married to a relative reported the highest proportion of marriages before their sixteenth birthday. Those who married before the age of 16 were at about double the risk of developing chronic diseases and experiencing miscarriage, stillbirths and infant deaths. These results suggest that early maternal marriage still exists in our community and is intimately related to other maternal risk factors. Maternal marriage < 16 years appears to be fraught with insecurities for the mother and infant throughout the whole length of the childbearing period and not merely the first pregnancy. Thus, even if culture norms claim early marriage of girls, it should be discouraged before the age of 16 years. Moreover, it is recommended that future research on maternal and infant health considers the cumulative effect of the various risk factors during the whole reproductive period and not only a single pregnancy outcome.
Early onset of hypernatraemic dehydration and fever in exclusively breast‐fed infants
Authors: Ng PC , Chan HB , Fok TF , Lee CH , Chan KM , Wong W , Cheung KL
Published: July 2002

Abstract: Five cases of moderately severe hypernatraemic dehydration were identified within a 5‐month period between two regional hospitals in Hong Kong. Unlike previous reported cases, these exclusively breast‐fed infants presented with the unusual triad of fever, absence of overt signs of dehydration and within the first week of life. Three of the cases also had high serum bilirubin concentrations at presentation. The fever subsided quickly and the serum bilirubin concentration fell rapidly within a few hours of rehydration. All infants made an uneventful recovery without permanent neurological sequelae. Fever, presumably secondary to dehydration, is an useful early warning sign. These cases emphasize the importance of early and regular measurement of bodyweight in exclusively breast‐fed infants so that prompt identification of affected cases may prevent potentially detrimental complications.
Increased incidence of Acanthamoeba keratitis associated with contact lens wear: the need to prevent this waterborne infection
Authors: Seal D. , Hay J. , Kirkness O. M. ,   West of Scotland Keratitis Study Group
Published: July 2002

The incidence of Acanthamoeba keratitis has been assessed in the 1995 West of Scotland Keratitis Study. All patients with microbial keratitis in the 3 million population were reported to us prospectively by optometrists, ophthalmologists and microbiologists. Contact lens (CL) wearing patients completed detailed questionnaires; 50 healthy CL wearers were visited at home as controls and similarly investigated. Additionally all 340 optician practices were polled for their annual turnover of CL types and disinfectant solutions.

Acanthamoeba keratitis occurred with an incidence of 1/10000 CL wearers based on this large, reliable community study of 164 000 CL wearers. This is 25 times more frequent than the previous American estimate (i.e. 1:250 000). The relationship to CL material type, ineffective cold chemicals solutions and hygiene compliance is complex, but is directly related to use of contaminated tap water as part of CL care, this vehicle being the source of the amoebae.

These findings are of considerable concern. They suggest that many new cases of painful, distressing and potentially blinding infection will be seen in Asia as CL wear becomes more widely available. Local expertise for recognition of Acanthamoeba keratitis will be required plus treatment with a combination of 0.02% chlorhexidine and 0.1% propamidine. Tap water must be avoided in CL care, and rigorous attention paid to CL hygiene.
Carbon doping in molecular beam epitaxy of GaAs from a heated graphite filament
Authors: Malik R. J. , Nottenberg R. N. , Schubert E. F. , Walker J. F. , Ryan R. W.
Published: July 2002

Carbon doping of GaAs grown by molecular beam epitaxy has been obtained for the first time by use of a heated graphite filament. Controlled carbon acceptor concentrations over the range of 1017–1020 cm−3 were achieved by resistively heating a graphite filament with a direct current power supply. Capacitance-voltage, p/n junction, and secondary-ion mass spectrometry measurements indicate that there is negligible diffusion of carbon during growth and with post-growth rapid thermal annealing. Carbon was used for p-type doping in the base of Npn AlGaAs/GaAs heterojunction bipolar transistors. Current gains greater than 100 and near-ideal emitter heterojunctions were obtained in transistors with a carbon base doping of 1×1019 cm−3. These preliminary results indicate that carbon doping from a solid graphite source may be an attractive substitute for beryllium which is known to have a relatively high diffusion coefficient in GaAs.
Heavy carbon doping of metalorganic chemical vapor deposition grown GaAs using carbon tetrachloride
Authors: Cunningham B. T. , Haase M. A. , McCollum M. J. , Baker J. E. , Stillman G. E.
Published: July 2002

A mixture of 500 ppm CCl4 in H2 has been used to grow heavily doped p-type GaAs by low-pressure metalorganic chemical vapor deposition with TMGa and AsH3 as the group III and V sources, respectively. Carbon acceptor concentrations between 1×1016 and 1×1019 cm−3 were obtained. In addition, abrupt carbon-doping profiles were achieved with no noticeable memory effects. Carrier concentration was studied as a function of CCl4 flow, V/III ratio, growth temperature, and growth rate using electrochemical capacitance-voltage profiling. Carbon incorporation was found to depend on CCl4 flow, V/III ratio, and growth temperature. Carbon incorporation had no dependence on the growth rate.
Evaluation of the feasibility of a far-infrared laser based on intersubband transitions in GaAs quantum wells
Authors: Borenstain Shmuel I. , Katz Joseph
Published: July 2002

The threshold current and quantum efficiency are calculated for a far-infrared injection laser, based on intersubband transitions in GaAs single quantum wells. By considering the balance of gain against the free carrier and transverse optical (TO) phonon absorption, and the intersubband transition time in the intermediate to the far infrared, the wavelength dependence of the threshold current is calculated. We find that for the wavelength range 50–120 μm, the required threshold currents are the lowest and have reasonable values of 103–104 A/cm2. The threshold quantum efficiency in that range is expected to be ∼10−4.
Highly oriented Bi(Pb)-Sr-Ca-Cu-O superconducting thin films by magnetron sputtering of a single target
Authors: Hakuraku Y. , Higo S. , Ogushi T.
Published: July 2002

Superconducting Bi(Pb)-Sr-Ca-Cu-O thin films have been prepared onto (100) MgO substrates by dc magnetron sputtering using a single sintered target. The targets used were Bi2.7 ,Pbx Sr2 Ca2.25 Cu3.75 Oy (x=1.5, 1.75, 2.0, 2.25 and 2.5) in nominal composition. All the films were deposited at 400 °C and annealed at 850 °C for 3 h in air. Although the superconducting properties of the thin films were very sensitive to the Pb content of the target, reproducible results were obtained. After deposition from the target with x=2.0 and subsequent high-temperature annealing, we have succeeded in obtaining highly c-axis oriented thin films which have shown zero resistivity at 115 K. This may be due to the optimum substitution of Pb for Bi in addition to the conditions during the high-temperature process. The average cationic ratio of the film was shown to be Bi:Pb:Sr:Ca:Cu=1.75:0.17:2:2.1:3.2 by electron-probe x-ray microanalysis.
Nondestructive multiple breakdown events in very thin SiO2 films
Authors: Suñé J. , Farrés E. , Placencia I. , Barniol N. , Martín F. , Aymerich X.
Published: July 2002

Several breakdown events and multilevel current fluctuations have been observed when ultrathin SiO2 films are subjected to constant-voltage stresses. These breakdown events are sometimes reversible, and consist in a local change of conduction mechanism. This reversibility shows that no catastrophic thermal effects occur, and that the breakdown is only a local switching between two oxide conduction states of very different conductivities.
Mapping of local temperatures on mirrors of GaAs/AlGaAs laser diodes
Authors: Brugger Hans , Epperlein Peter W.
Published: July 2002

Spatially resolved Raman scattering measurements (<1 μm) have been performed to determine the surface temperature distribution on coated and uncoated facets of ridge-waveguided GaAs/AlGaAs single quantum well graded-index separate-confinement heterostructure lasers. A strong nonlinear temperature versus output-power dependence is observed for cleaved, uncoated mirrors (ΔT>100 K for P>1 MW/cm2). Raman line scans show hot spot regions at the facets. Degradation strength correlates with facet heating. Disorder-activated Raman phonon modes indicate strong crystal damage. Laser mirrors with λ/2-Al2O3 coatings withstand up to 4–5 times the power density without significant heating and degradation. Local electroluminescence measurements along the cavity confirm increasing temperatures when approaching the facets and show that the resonator bulk material remains cold (ΔT<5 K).
Quasi-epitaxial growth of organic multiple quantum well structures by organic molecular beam deposition
Authors: So F. F. , Forrest S. R. , Shi Y. Q. , Steier W. H.
Published: July 2002

Multiple quantum well structures consisting of alternating layers of two crystalline organic semiconductors, namely, 3,4,9,10 perylenetetracarboxylic dianhydride (PTCDA) and 3,4,7,8 naphthalenetetracarboxylic dianhydride (NTCDA), have been grown by organic molecular beam deposition. The individual layer thicknesses in the multilayer samples were varied from 10 to 200 Å. X-ray diffraction and birefringence data show that there is a strong structural ordering in all layers, as well as across large spatial distances along the sample surface. Thus, the growth is ‘‘quasi-epitaxial’’ even though the PTCDA and NTCDA crystal structures are incommensurate. From the optical absorption spectra, it was found that the lowest energy PTCDA singlet exciton line shifts to higher energy with decreasing layer thickness. Comparison of these results with a quantum mechanical model based on exciton confinement in the PTCDA layers is proposed to describe the energy shift.
Resonant interband tunneling through a 110 nm InAs quantum well
Authors: Beresford R. , Luo L. F. , Longenbach K. F. , Wang W. I.
Published: July 2002

The mechanism of resonant interband tunneling in polytype heterostructures of GaSb/AlSb/InAs gives excellent peak-to-valley current ratios due to the band-gap blocking of the nonresonant current components. Using InAs as the base in a double-barrier polytype heterostructure, it is possible to demonstrate resonant tunneling at room temperature through a quantum well as wide as 110 nm. At this width, which is about 20 times larger than that typically used in resonant tunneling diodes in the GaAs/AlGaAs system, the peak-to-valley ratio is 44:1 (77 K). Significant negative differential resistance is observed even for 240 nm wells. The projected device response time for a resonant tunneling transistor with a wide InAs quantum base is more than five times faster than for a GaAs device, due to the reduced base resistance.
A 970 nm strained-layer InGaAs/GaAlAs quantum well laser for pumping an erbium-doped optical fiber amplifier
Authors: Wu Ming C. , Olsson N. A. , Sivco D. , Cho A. Y.
Published: July 2002

We report the performance of a 970 nm strained-layer InGaAs/GaAlAs quantum well laser and its application for pumping Er-doped optical fiber amplifiers. The laser was grown by molecular beam epitaxy and has three In0.2Ga0.8As/GaAs quantum wells. For a 5-μm-wide and 400-μm-long ridge-waveguide laser, a cw threshold current of 20 mA and an external quantum efficiency of 0.28 mW/mA per facet were obtained. Maximum output power exceeds 32 mW/facet. With antireflection coating, even higher external quantum efficiency (0.40 mW/mA) was achieved, and more than 20 mW of power was coupled into a single mode fiber. Preliminary experiments of pumping the Er-doped fiber amplifier gave 15 dB of gain at 1.555 μm for a pump power of 14 mW into the Er fiber.
Growth of diamond films on silicon from an oxygen-acetylene flame
Authors: Tzeng Y. , Cutshaw C. , Phillips R. , Srivinyunon T. , Ibrahim A. , Loo B. H.
Published: July 2002

Clear diamond films have been deposited on silicon substrates by a tilted oxygen-acetylene flame operating at one atmosphere pressure in air. High quality diamond films are formed by well-defined diamond crystallites in the octahedral and cubooctahedral shapes as well as of intermediate forms. Raman spectra of the flame deposited diamond display a peak very close to that for natural diamond with little or no broad band corresponding to graphitic bonding as well as a peak corresponding to the underlying silicon substrate. This shows that the diamond is transparent to visible light and that there are little or no interfacial materials other than silicon and diamond. Using an O2 :C2 H2 volume ratio around 0.98 high quality diamond films thicker than 10 μm have been grown on silicon in less than 30 min by an oxygen-acetylene flame that is aimed at the silicon substrate at about 70° with respect to the direction normal to the silicon surface.
Improved design of AlAs/GaAs resonant tunneling diodes
Authors: Cheng Peng , Harris James S.
Published: July 2002

We have investigated the effect of complex barrier structures in double-barrier resonant tunneling diodes (DBRTDs). The largest room-temperature peak-to-valley current ratios (PVCRs) to date have been observed for AlGaAs/GaAs DBRTDs. PVCRs as high as 5.1 were observed in AlAs/GaAs DBRTDs with an Al0.14Ga0.86As chair barrier in the cathode. We attribute the improvement in the PVCRs to the chair barrier in the cathode which significantly reduces the valley current.
Quasi-phase-matched second-harmonic generation of blue light in periodically poled LiNbO3
Authors: Magel G. A. , Fejer M. M. , Byer R. L.
Published: July 2002

LiNbO3 crystals with periodically alternating ferroelectric domains have been produced using laser-heated pedestal growth. Domain thicknesses as small as 1 μm have been achieved. This material was applied to room-temperature, quasi-phase-matched frequency doubling to generate light at wavelengths as short as 407 nm, using the d33 and d22 nonlinear coefficients. The measured conversion efficiencies and wavelength and temperature tuning bandwidths are consistent with an effective interaction length of ≊320 μm (>230 domains). An initial test with high-intensity focused blue beams showed that the periodically poled material exhibits no discernible photorefractive damage effect.
Electrical characteristics of ultrathin oxynitride gate dielectric prepared by rapid thermal oxidation of Si in N2O
Authors: Hwang Hyunsang , Ting Wenchi , Maiti Bikas , Kwong Dim-Lee , Lee Jack
Published: July 2002

This letter presents a unique process to grow high quality ultrathin (∼60 Å) gate dielectrics using N2O (nitrous oxide) gas. Compared with conventional rapid thermally grown oxide in the O2, the new oxynitride dielectrics show very large charge-to-breakdown (at +50 mA/cm2, 850 C/cm2 for oxynitride compared to 95 C/cm2 for the control thermal oxide) and less charge trapping under constant current stress. Significantly reduced interface state generation was also observed under constant current stress and x-ray radiation. A secondary-ion mass spectroscopy depth profile indicates a nitrogen-rich layer at the Si/SiO2 interface, which can explain the improved integrity of oxynitride dielectric.
Tunneling microscopy and spectroscopy of molecular beam epitaxy grown GaAs-AlGaAs interfaces
Authors: Albrektsen O. , Arent D. J. , Meier H. P. , Salemink H. W. M.
Published: July 2002

We report the first observation of GaAs/AlGaAs compound multilayers and interfaces at atomic scale resolution. Using a scanning tunneling microscope, the atomic registry in the epitaxial layers and their interfaces was observed. The semiconductor band gaps and valence-band offsets relative to the Fermi level are obtained via local spectroscopy in the GaAs and AlGaAs multilayers.
Experimental observation of negative differential resistance from an InAs/GaSb interface
Authors: Collins D. A. , Yu E. T. , Rajakarunanayake Y. , Söderström J. R. , Ting D. Z.-Y. , Chow D. H. , McGill T. C.
Published: July 2002

We have observed negative differential resistance at room temperature from devices consisting of a single interface between n-type InAs and p-type GaSb. InAs and GaSb have a type II staggered band alignment; hence, the negative differential resistance arises from the same mechanism as in a p+-n+ tunnel diode. Room-temperature peak current densities of 8.2×104 A/cm2 and 4.2×104 A/cm2 were measured for structures with and without undoped spacer layers at the heterointerface, respectively.
Electronic energy bands and optical nonlinearity of checker-board superlattices
Authors: Ram-Mohan L. R. , Shertzer J.
Published: July 2002

We investigate the structure of the conduction minibands in a two-dimensional periodic array of rectangular quantum wires. The finite barrier height in such a GaAs/Ga1−xAlxAs heterostructure gives rise to a ‘‘checker-board’’ pattern of wells and barriers, i.e., a checker-board superlattice (CBSL). The energy bands are obtained using the finite element method, in the effective mass approximation, with current continuity at interfaces. The free-carrier-induced optical nonlinear susceptibility χ(3) due to band nonparabolicity in the CBSL is obtained in both the rectangular directions. Our calculations predict an increase in χ(3) of about 1–2 orders of magnitude over bulk GaAs, for specific ranges of carrier concentrations.
One-dimensional lateral-field-effect transistor with trench gate-channel insulation
Authors: Nieder J. , Wieck A. D. , Grambow P. , Lage H. , Heitmann D. , Klitzing K. v. , Ploog K.
Published: July 2002

A novel unipolar transistor device has been realized starting from two-dimensional electron systems (2DES) in modulation-doped AlGaAs/GaAs heterostructures. A 600-nm-wide 1D channel is insulated laterally from 2DES regimes by 700-nm-wide deep mesa etched trenches. The conductivity in the quasi-one-dimensional channel can be tuned via the in-plane lateral field effect of the adjacent 2DES gates where the vacuum (or air) in the etched trenches serves as the dielectric. Room-temperature operation is demonstrated yielding a 17 μS transconductance corresponding to 170 mS/mm 2D transconductance.
Reaction between Cu and TiSi2 across different barrier layers
Authors: Chang Chin-An , Hu Chao-Kun
Published: July 2002

The reaction between Cu and TiSi2 is studied with and without barriers, Cu being used for interconnect and TiSi2 as the gate silicide for the metal-oxide-semiconductor devices. The barriers include Ta, TiN, and W. Without a barrier, Cu reacts with TiSi2 below 300 °C, forming Cu silicides. An improvement in thermal stability by 50–100 °C is obtained using the barriers, with TiN/Ti being the most effective. A combined use of these barriers, with a final structure of Ta/Cu/Ta/W/TiN/Ti/TiSi2 /Si, suppresses the Cu-TiSi2 reaction until above 600 °C. The reaction mechanisms involved, and their relation with the reactions between Cu and other silicides, are discussed.
Nature of the defects generated by electric field stress at the Si-SiO2 interface
Authors: Vuillaume Dominique , Goguenheim Didier , Bourgoin Jacques C.
Published: July 2002

We have characterized the density of states, the capture cross sections, and the annealing properties of the Si-SiO2 interface defects generated during electron injection under high electric field stress. These properties are compared to those of the interface states present in as-oxidized Si-SiO2 structures which are known to be due primarily to the trivalent silicon defects (Pb centers), the main intrinsic defects on thermally oxidized silicon. Although the energetic distribution of the state densities and the annealing properties are similar, we found that the capture cross sections are strongly different. This leads to the conclusion that the interface defects generated by high electric field stress are not strictly identical to Pb centers, but probably ‘‘Pb-like’’ defects. A possible model is discussed.
Electron wave interference device with fractional layer superlattices
Authors: Tsubaki Kotaro , Honda Takashi , Saito Hisao , Fukui Takashi
Published: July 2002

Modulation-doped Al0.3Ga0.7As/GaAs heterostructure electron wave interference devices with fractional layer superlattices are fabricated. The periods of the fractional layer superlattice in the electron wave interference devices are 16, 12, and 8 nm, respectively. These devices show drain current oscillation due to electron wave interference at 4.2 K. The oscillation period is determined by the period of the fractional layer superlattice. From the analysis of the drain current oscillation, the peaks of the structure function agree with the multiples of the periods of the fractional layer superlattice.
Quantum efficiency enhancement of AlGaAs/GaAs quantum well infrared detectors using a waveguide with a grating coupler
Authors: Andersson J. Y. , Lundqvist L. , Paska Z. F.
Published: July 2002

Long wavelength quantum well detectors with very high quantum efficiency, based on the coupling of radiation into an optical resonant cavity or waveguide defined by a reflection grating coupler on one side of the infrared absorbing multiquantum well stack, and an aluminum arsenide cladding layer on the other, have been fabricated and the results compared with theory. Theory shows that quantum efficiencies up to 90% may be obtained (for polarized radiation). However, experimental results indicate that the response peak becomes broadened due to spread in the grating period and therefore the maximum quantum efficiency is in practice limited to 60%, corresponding to a current responsivity of 2.1 A/W. This is 2.7 times larger than for a 45° polished edge detector with the same quantum well characteristics.
Excellent uniformity and very low (<50 A/cm2) threshold current density strained InGaAs quantum well diode lasers on GaAs substrate
Authors: Chand Naresh , Becker E. E. , van der Ziel J. P. , Chu S. N. G. , Dutta N. K.
Published: July 2002

We report the growth and fabrication of InGaAs/GaAs strained quantum well (QW) lasers with a very low threshold current density, Jth, of <50 A cm−2 emitting at 0.98 μm. The lasers, 1350 μm long, had two InGaAs 80 Å quantum wells in the active region and Al0.6Ga0.4As in cladding layers, and were grown on 3° off (100) towards 〈111〉A GaAs substrate. Misorienting the substrate towards 〈111〉A improves the material quality and device performance substantially for x≊0.6 in the cladding layer, but degrades it somewhat for x≊0.35. The Jth increased about 25% with decreasing x from 0.6 to 0.35 due to decreased optical confinement. Single QW stripe lasers with x=0.35 tested on a 3.0 cm×1016 μm size bar, representative of the whole 5-cm-diam substrate, exhibited a yield of ≳90% and an excellent spatial uniformity of Jth and emission wavelengths which were 212±4 A cm−2 and 989±1 nm, respectively.
Tunneling assisted modulation of the intersubband absorption in double quantum wells
Authors: Vodjdani N. , Vinter B. , Berger V. , Böckenhoff E. , Costard E.
Published: July 2002

We present a new efficient modulator structure in which electron tunneling between asymmetric coupled quantum wells is used to populate or deplete the ground level for the infrared (IR) absorption, leading to externally controlled IR absorption at two different wavelengths (here 10.2 and 11.4 μm). The temperature dependence of the modulation depth is measured. We have used photoluminescence and photoluminescence excitation spectroscopies to analyze the space charge effects in the double quantum wells, and to estimate the carrier concentration in each well as a function of bias. The behavior of the device has been simulated using a self-consistent model.
Annealing effect on the electrical properties of heavily C-doped p+GaAs
Authors: Watanabe Kazuo , Yamazaki Hajime
Published: July 2002

The carrier concentration in heavily carbon-doped p+-GaAs epilayers (about 1.3×1020 cm−3) is decreased together with the mobility by annealing at temperatures of 700 °C or higher but not at temperatures of 600 °C or lower. In comparatively lightly C-doped p+ epilayers (about 3.5×1019 cm−3), the carrier concentration is not decreased by annealing at temperatures from 500 to 850 °C. The deep photoluminescence peak at a wavelength of around 1080 nm accompanied by a hump at around 1420 nm are found only in heavily C-doped epilayers; the wavelength of this peak is very close to that of the Ga vacancy −the C donor center. The photoluminescence intensity is increased by the annealing at 850 °C but not at 600 °C. The thermal behaviors of the deep photoluminescence levels can well explain those of carrier concentration and mobility if we consider the photoluminescence levels to be the index for the compensation centers.
Anisotropy in photoluminescence and absorption spectra of fractional layer superlattices
Authors: Kasu Makoto , Ando Hiroaki , Saito Hisao , Fukui Takashi
Published: July 2002

Polarization-dependent photoluminescence (PL) and optical absorption spectra of (AlAs)1/2(GaAs)1/2 and (Al0.5Ga0.5As)1/2(GaAs)1/2 fractional layer superlattices (FLSs) were measured at room temperature. For the first time, it was observed that the spectra are dependent on their polarizations. The anisotropies in the PL and absorption spectra show that quantum confinement unambiguously occurs in the direction parallel to the surface, i.e., lateral quantum carrier confinement effect appears. This finding proves that FLSs are promising for novel optical devices.
Investigation of tilted superlattices for quantum-wire laser applications
Authors: Yi Jong Chang , Dagli Nadir , Coldren Larry A.
Published: July 2002

A novel quantum-wire array, known as tilted superlattice, which is formed by direct molecular-beam epitaxial growth on vicinal surfaces, is analyzed, and its optical properties are assessed for quantum-wire laser applications.
Gate turn off capability of insulated gate metal/amorphous Si/crystalline Si (p-n) switching device
Authors: Fang Y. K. , Liu C. R. , Chen K. H. , Hwang S. B.
Published: July 2002

The gate turn off capability of a trench insulated gate metal/amorphous silicon (a-Si:H)/crystalline silicon (c-Si) (p-n) heterojunction switching device is studied. Using a negative gate voltage to modulate the depletion width in the a-Si:H region, and hence lowering the field for the multiplication of carriers, the heterojunction switching device can be gate turned off or even gate locked. Thus the device can be developed as a gate controllable light switch or light sensor.