bluuebunny/crossref_metadata_2025 huggingface dataset:
The voltage‐gated Ca2+ release channel in the vacuolar membrane of sugar beet resides in two activity states
Authors: Johannes Eva , Sanders Dale
Published: July 2002

The voltage‐gated Ca2+ release channel in the vacuolar membrane of sugar beet tap roots resides in two states which show similar reversal potentials in biionic conditions but differ dramatically in their single channel current and open frequency. State I has a unitary Ca2+ conductance of 3.9 ± 0.5 pS and channel openings are rare at vacuolar resting potentials. After spontaneous and reversible transition into State II the unitary Ca2+ conductance increases three‐fold, accompanied by a concomitant rise in channel activity over the physiological voltage range. The 15‐ to 19‐fold increase in total Ca2+ current after the State I to State II transition could play an essential role in channel activation during signal transduction.
Synthesis and characterization of Respiratory Syncytial Virus protein G related peptides containing two disulfide bridges
Authors: Beck A. , Bussat M.C. , Haeuw J.F. , Corvaïa N. , Nguyen T.N. , Bonnefoy J.Y. , Zorn N. , Van Doersselaer A.
Published: July 2002

Abstract: Respiratory Syncytial Virus (RSV) is the most important cause of bronchiolitis and viral pneumonia in infants and young children. Approximately 100 000 children are hospitalized in the USA each year as a result of RSV infections. During the research and development of subunit human Respiratory Syncytial Virus vaccines (hRSV), we have produced numerous synthetic peptides and recombinant proteins containing the four cysteines of the highly conserved central region of the G attachment protein. For several of these disulfide‐containing peptides, all possible oxidized isomers were synthesized using various oxidation conditions and resulting in different ratios of isomers. Each isolated isomer was fully characterized by RP‐HPLC, FZCE and ES‐MS after purification by preparative RP‐HPLC. The different cysteine pairings were unambiguously established after enzymatic digestion, LC‐MS analysis and peptide microsequencing. These synthesis and analytical methods were developed for the characterization on one hand, of recombinant fusion protein BBG2Na which is currently being investigated in advanced clinical phases as a very promising vaccine candidate, and on the other hand, for peptides which were synthesized to be evaluated as conjugate vaccines or as immunochemical tools, after covalent coupling to carrier proteins. Furthermore, these studies allowed us to determine which of the different possible isomers was the most stable and probably the preferred form in native conditions. Finally, the different oxidation and analysis conditions, should be useful for disulfide pairing studies of other peptides and proteins having the same ‘xCxxCxxxxxCxxxCx’ framework, such as G proteins of non‐human RSV strains, developed by other groups as veterinary vaccine candidates for example.
Analysis of binding sites and efficacy of a species‐specific peptide at rat and human neurotensin receptors
Authors: Cusack B. , Chou T. , Jansen K. , McCormick D.J. , Richelson E.
Published: July 2002

Abstract: We have developed a neurotensin analog, l‐[3,1′‐naphthylalanine11]NT(8–13), NT34, that can distinguish between rat and human neurotensin receptors, and exhibits more than a 100‐fold difference in binding affinities and a 60‐fold difference in functional coupling to phosphatidylinositol turnover. Using cells transfected with different numbers of the appropriate receptors, we measured the changes in phosphatidylinositol production, and then evaluated the efficiency of receptor–effector coupling based on Furchgott’s design. The binding of NT34 at both rat and human neurotensin receptors stably expressed in CHO‐K1 cells was to two sites, while the binding of NT was to one site. At the rat receptor the equilibrium dissociation constant (Kd) for NT34 at the high‐affinity site was 0.058 nM, while that at the low‐affinity site was 3.1 nM. For the human receptor at the high‐affinity site, the Kd for NT34 was 18 nM, while that at the low‐affinity site was 180 nM. For both species the percentage of receptors representing the high‐affinity site was ≈ 60–70% with 30–40% at the low‐affinity site. We derived agonist dissociation constants (Ka) for NT and NT34, which suggest that for NT34, the low‐affinity site is functionally coupled to phosphatidylinositol turnover. Finally, we compared the relative efficacies of both compounds and found that NT34 was about 2‐fold and 4‐fold more efficacious than NT in stimulating phosphatidylinositol turnover in rat and human NT receptors, respectively.
Design and evaluation of benzophenone‐containing conformationally constrained ligands as tools for photoaffinity scanning of the integrin αVβ3–ligand bimolecular interaction
Authors: Bitan G. , Scheibler L. , Teng H. , Rosenblatt M. , Chorev M.
Published: July 2002

Abstract: Integrins are cell‐surface adhesion molecules involved in mediating cell–extracellular matrix interactions. High‐resolution structural data are not available for these heterodimeric receptors. In order to generate tools for photoaffinity scanning of the RGD‐binding site of human integrin αVβ3, new conformationally constrained ligands were designed. The ligands were based on five different cyclic peptidic or peptidomimetic scaffolds with high affinity for αVβ3. A single photoreactive group (a benzophenone moiety) was introduced at different positions relative to the RGD triad. In addition, an 125I or a biotin group was introduced as a reporting tag. Twenty‐four cyclic ligands were prepared and their binding affinity for αVβ3 was determined. In most cases, the modifications resulted in a 5‐ to 500‐fold decrease in affinity relative to the unmodified scaffold. Analogs representing three of the five families were screened for their cross‐linking efficiency. Ligands with submicromolar affinities cross‐linked efficiently and specifically to the integrin receptor, whereas ligands with weaker affinities gave specific cross‐linking, but with lower efficiency. Almost all of the screened ligands cross‐linked predominantly to the β3 subunit.
(1H‐Benzotriazol‐1‐yloxy)‐N,N‐dimethylmethaniminium hexachloroantimonate (BOMI), a novel coupling reagent for solution and solid‐phase peptide synthesis
Authors: Li P. , Xu J.C.
Published: July 2002

Abstract: A HOBt‐based immonium‐type compound,(1H‐benzotriazol‐1‐yloxy)‐N,N‐dimethyl methaniminium hexachloro‐antimonate (BOMI), was synthesized and successfully applied to the synthesis of various oligopeptides with good yields. The estimation of racemization and the influence of several reaction parameters such as solvents, bases and temperature were studied by HPLC using a model reaction. It was found that the reactivity of BOMI was much higher than that of HOBt‐based phosphonium‐ and uronium‐type coupling reagents. Moreover, its racemization was lower than that of other HOBt‐derived coupling reagents. The effectiveness of BOMI was also demonstrated by the synthesis of Leu‐enkephalin both in solution and in the solid‐phase.
Synthesis and anti‐aggregatory activity of linear retro‐inverso RGD peptides
Authors: Dal Pozzo A. , Fagnoni M. , Bergonzi R. , Vanini L. , De Castiglione R. , Aglio C. , Colli S.
Published: July 2002

Abstract: Six retro‐inverso tri‐ and tetrapeptide analogues of RGD were prepared and their anti‐aggregatory activity was determined by platelet aggregation tests in comparison with the corresponding parent peptides. An efficient method for the introduction of a malonyl‐aspartic residue into a peptide chain is described for the first time. A 2–3‐fold decrease in potency or total loss of bioactivity was observed with the new peptides; structure–activity relationships are discussed.
Role of phosphoenolpyruvate carboxylase in organic acid accumulation during peach fruit development
Authors: Moing Annick , Rothan Christophe , Svanella Laurence , Just Daniel , Diakou Paraskevi , Raymond Philippe , Gaudillère Jean‐Pierre , Monet René
Published: July 2002

The synthesis of organic acids was studied during fruit development of two peach (Prunus persica L. Batsch) cultivars, Fantasia and Jalousia, having fruits with high and low organic acid content, respectively. The malate content was higher in cv. Fantasia than in cv. Jalousia at the end of the first rapid growth stage (50 days after bloom [DAB]). Malate and citrate contents were higher in Fantasia than in Jalousia during the second rapid growth stage (from 100 DAB to maturity). The expression of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31), which is involved in organic acid synthesis, was studied during peach fruit development. PEPC mRNA levels, and protein levels on a total soluble protein basis, peaked at 23 and 108 DAB in Fantasia. In Jalousia, they were very low at 23 DAB and reached levels similar to Fantasia at 108 DAB. For both cultivars, in vitro PEPC activity expressed on a dry weight basis was maximal at 24 DAB, decreased from 24 to 60 DAB, and then remained constant. The activity of peach fruit PEPC appeared extremely sensitive to malate (I0.5 of 100 μM for Fantasia and 65 μM for Jalousia at pH 7.3) and low pH. PEPC may participate in the control of organic acid accumulation during fruit development in the normal‐acid fruit of Fantasia. However, mechanisms other than organic acid synthesis might account for the differences in acidity between normal‐acid and non‐acid peach fruit.
Expression of two gibberellin‐regulated cDNAs during early flower development in tomato (Solanum lycopersicon). Effect of grafting and paclobutrazol
Authors: Van Den Heuvel K. J. P. T. , Heijnen P. H. F. , Barendse G. W. M. , Wullems G. J.
Published: July 2002

To study the role of translocation of gibberellin (GA) intermediates or bioactive GAs from other plant parts to buds during early flower development in tomato (Solanum lycopersicon), the effect of grafting and paclobutrazol (PAC) treatment on the expression of tgas100 and tgas118, two GA‐regulated mRNAs, was analysed. Both mRNAs accumulated in a dose‐dependent fashion. Application of 0.5 ng GA3 per bud to developmentally arrested flower buds of a GA‐deficient mutant of tomato (gib‐1) induced tgas100 expression, while the tgas118 abundance increased. For obtaining normal flower development through anthesis in the mutant, a single GA3 treatment was required of at least 5 ng GA3 per bud. In wild‐type flower buds, PAC decreased the abundance of tgas100 and tgas118 mRNAs either when PAC was sprayed on whole plants or directly applied to buds. When only the wild‐type buds were treated with PAC, the expression profiles characteristic for untreated buds were not restored by translocation of endogenous GAs. Grafting of gib‐1 scions onto wild‐type donor plants did not result in normal flower development or expression profiles like in wild‐type buds. We conclude that the role of GA transport in early flower development of tomato is negligible and that the GAs required for development have to be synthesized in the flower bud itself.
Detection of xenoantibodies using a simple flow cytometric assay
Authors: Al‐Hussein Khaled , Al‐Mukhalafi Zuhah , Pyle Haywood Robert , Parhar Ranjit S. , Al‐Mohanna Futwan , Lee Jennifer
Published: July 2002

Abstract: Higher primates, including humans, have high levels of pre‐existing naturally circulating antibodies that predominantly recognize the epitope Gal (1,3‐Gal), which is highly expressed on the surface of xenogenic cells. Deposition of these antibodies on the endothelial cell surface of vascularized xenografts leads to an activation of the classical pathway of the complement system, resulting in tissue ischemia and necrosis with rapid demise of the xenograft. This hyperacute rejection (HAR) is always a major barrier in xenograft transplantation and should be minimized by accurately monitoring the naturally occurring antibodies. In the present study, we utilized a simple and rapid flow cytometric (FCM) assay to monitor the presence of these naturally occurring antibodies. We found that the FCM assay is very effective in measuring human antibodies bound to the xenogenic cells, which cause cytotoxicity. This assay could be useful in the pre‐ and post‐xenotransplantation monitoring of xenoantibodies, thus, helping in the development of strategies to block the binding of preformed human antibodies to the xenograft in order to overcome the problem of HAR.
Differential changes in corticospinal and Ia input to tibialis anterior and soleus motor neurones during voluntary contraction in man
Authors: Morita H. , Olivier E. , Baumgarten J. , Petersen N.T. , Christensen L.O.D. , Nielsen J.B.
Published: July 2002

Motor‐evoked potentials (MEPs) were recorded in the tibialis anterior and soleus muscles following transcranial magnetic stimulation (TMS) of the motor cortex. In the soleus, the H‐reflex amplitude increased with the contraction level to the same extent as that of MEPs, whereas in the tibialis anterior, the H‐reflex amplitude increased significantly less than that of MEPs. The latency of the MEPs decreased with contraction, whereas this was not the case of the H‐reflexes. In the tibialis anterior, the response probability of single‐motor units (SMU) to TMS increased more substantially during voluntary contraction than following stimulation of the peroneal nerve. In the tibialis anterior, the response probability of SMU increased more substantially during voluntary contraction than following stimulation of the peroneal nerve. The short‐latency facilitation, presumably monosynaptic of origin, of the soleus H‐reflex evoked by subthreshold TMS increased as a function of the plantarflexion force. This was not the case for the heteronymous Ia facilitation of the soleus H‐reflex following stimulation of the femoral nerve. It is concluded that the corticospinal input to lower limb motor neurones generated by TMS increases with the level of voluntary contraction, whereas this is true only to a limited extent for the synaptic input from Ia afferents. It is suggested that this reflects changes in the susceptibility of corticospinal cells to TMS during voluntary contraction.
Environmental factors influencing bird species diversity in Kenya
Authors: Oindo Boniface O. , De By Rolf A. , Skidmore Andrew K.
Published: July 2002

Sustainable resource management requires understanding the factors that increase or decrease species richness. Regional species richness patterns may be predicted by analysing patterns of variation in the environment. A number of studies have shown that bird species richness at a regional scale is influenced by climatic variables. We examined environmental correlates of bird species richness at a quarter degree square scale (55 × 55 km). Mean annual potential evapotranspiration accounts for 46% of the observed variation in species richness, while mean annual temperature and range annual potential evapotranspiration are significantly correlated with species richness and together account for a further 5% of the observed variation. The results are consistent with the hypothesis that environmentally available energy limits regional species richness.
Sauropus androgynus‐constrictive obliterative bronchitis/bronchiolitis — histopathological study of pneumonectomy and biopsy specimens with emphasis on the inflammatory process and disease progression
Authors: Wang J‐S , Tseng H‐H , Lai R‐S , Hsu H‐K , Ger L‐P
Published: July 2002

Aims: 

The histopathology of the Sauropus androgynus (SA)‐constrictive bronchiolitis obliterans (BO) is still controversial. A recent report using pneumonectomy specimens showed that the major histopathology was obliterative arteriopathy with segmental necrosis of small bronchi instead of constrictive BO as previously described.

Methods and results: 

We analysed semiquantitatively and immunohistochemically the histopathology of one pneumonectomy and four biopsies specimens of SA‐associated lung disease. We found a significant number of constrictive and obliterative bronchioles 1 mm or less in diameter and segmental inflammatory destruction with complete luminal obliteration of the bronchi less than 3 mm in diameter in the pneumonectomy specimen (37% and 25%, respectively). Fibromuscular intimal sclerosis of the bronchial arteries was identified in 15% of the bronchi 4 mm or less in diameter. The inflammation in these airways was composed predominantly of T‐lymphocytes, macrophages, mast cells and eosinophils. They were present throughout the evolutionary stages of the bronchiolitis ranging from early oedematous to the late fibrotic obliterative stage. Double immunohistochemical stains revealed negative proliferative cell nuclear antigen for most of the T‐lymphocytes and macrophages but positive for fibroblasts.

Conclusions: 

A more accurate histopathological designation of the SA‐associated lung disease should be constrictive obliterative bronchitis/bronchiolitis, with the participation of T‐lymphocytes, macrophages, mast cells, eosinophils and fibroblasts in its morphogenesis. The persistent accumulation of inflammatory cells was mediated predominantly by continued recruitment to the site of injury from the bloodstream, resulting eventually in the irreversible fibrosis of the bronchioles and the bronchi less than 3 mm in diameter. Obliterative arteriopathy is suspected of being only an indirect contributing factor.
Influence of alteration of occlusal relationship on activity of jaw closing muscles and mandibular movement during submaximal clenching
Authors: Baba K. , Akishige S. , Yaka T. , Ai M.
Published: July 2002

The aim of this study was to investigate the relationships between occlusal contacts, responses of muscles, and jaw movements during simulated clenching. Seven healthy human males who possessed complete natural dental arches with normal occlusion, ranging from 24 to 29 years of age, volunteered for this study. Acrylic occlusal stops were fabricated for the lower jaw to simulate various occlusal conditions. Vertical movements of the lower jaw were measured by four sets of linear variable differential transformers. Simultaneously, electromyographic (EMG) activity from the bilateral masseter and anterior temporal muscles was measured. Under experimentally altered occlusal conditions, the subjects performed clenching tasks at 50% of their maximal voluntary contraction level. Analysis of EMG responses revealed clenching on the unilateral occlusal support tended to cause a unilateral activity of the ipsilateral anterior temporalis. Analysis of the movement amplitude revealed a significant difference between the experimental occlusal conditions (P<0·05). Clenching on unilateral occlusal stops caused a larger upward movement on the contralateral side. Bilateral first premolar clenching without molar support caused a larger upward movement of the mandible in the posterior region, whereas bilateral second molar clenching did not cause a significant upward movement.
Epidemiology and predictors of infant morbidity in rural Malawi
Authors: Vaahtera M. , Kulmala T. , Maleta K. , Cullinan T. , Salin M.‐L. , Ashorn P.
Published: July 2002

In rural Malawi, 703 newborns were visited monthly for 1 year to describe the epidemiology and health‐seeking behaviour during acute episodes of diarrhoea, respiratory infections (ARI) and malaria. On average, the infants suffered from 1.3 annual episodes (11.0 illness days) of diarrhoea, 1.1 episodes (9.4 days) of ARI and 0.7 episodes (4.8 days) of malaria. Multivariate analysis with polychotomous logistic regression indicated that the amount of morbidity was associated with the child’s area of residence, weight in early life, number of siblings, father’s marital status and the source of drinking water. Diarrhoea and malaria were most common at 6–12 months of age and during the rainy months whereas respiratory infections peaked at 1–3 months of age and in the cold season. Ten per cent of diarrhoea, 9% of ARI and 7% of malaria episodes lasted for more than 14 days. Fifty‐eight infants died, giving case fatality rates of 1% for diarrhoea, 2% for ARI and 4% for malaria. One‐third (37%) of the illness episodes were managed at home without external advice. A traditional healer was consulted in 16% of episodes and a medical professional in 55% of episodes. If consulted, traditional healers were seen earlier than medical professionals (median duration after the onset of symptoms 0.7 vs. 1.8 days, P < 0.001). Traditional healers were significantly more commonly used by those families whose infants died than by those whose infants did not die (odds ratio 1.8, 95% CI 1.1, 3.0). Our results emphasise the influence of seasonality, care and living conditions on the morbidity of infants in rural Malawi. Case fatality for diarrhoea, ARI and malaria was high and associated with health‐seeking behaviour among the guardians. Future interventions must aim at early and appropriate management of common childhood illnesses during infancy.
Adaptation of Reptilian Paramyxovirus to Mammalian Cells (Vero Cells)
Authors: Mayr A. , Franke J. , Ahne W.
Published: July 2002

The reptilian paramyxovirus GOV was successfully adapted to Vero cells in 80 passages at 30°C. The virus replicated with HA titres of 1 : 64 and 107.5 TCID50/ml in the heterologous host cells forming syncytia, giant cells and cytoplasmic inclusion bodies. After 80 passages GOV was identified by immuno‐fluorescence, by immune electron microscopy and by PCR. Sequencing of RT‐PCR products of GOV after 80 passages did not reveal changes in the nucleotide sequence of the partial l‐gene of GOV.
Moon phase and other factors affecting light‐trap catches of Culicoides brevitarsis Kieffer (Diptera: Ceratopogonidae)
Authors: Bishop Al , McKenzie Hj , Barchia Im , Spohr Lj
Published: July 2002

Light‐trap catches of Culicoides brevitarsis were affected by the phase of the moon with least being caught at the full moon. Seasonal catches were also influenced by temperature and windspeed. Conversely, changes in moonlight overnight at the full moon had no obvious effect on the species capture in light traps. Nightly catches were mainly influenced by temperature when the effect of windspeed was negated. Differences related to moon phase were most likely the result of alterations to the effective limit of attraction of traps induced by competition with moonlight. This and the other factors would make it difficult to interpret and compare numbers of C. brevitarsis caught in light traps at different times and locations.
Placental size and large‐for‐gestational‐age infants in women with abnormal glucose tolerance in pregnancy
Authors: Leung T. W. , Lao T. T.
Published: July 2002

Aims To determine if the placental size is disproportionately increased in the large‐for‐gestational age infants in pregnancies complicated by impaired glucose tolerance.

Methods A retrospective study was performed on 568 consecutive singleton pregnancies complicated by gestational impaired glucose tolerance controlled with diet and who delivered within a 15‐month period. The cases were categorized by the infant birthweight percentile into three groups, i.e. small‐for‐gestational age (< 10th percentile), appropriate‐for‐gestational age (10th to 90th percentile) and large‐for‐gestational age (> 90th percentile). Maternal and infant anthropometric data, glycaemic status, and placental weight‐to‐birthweight ratio were compared among the three groups.

Results The infant body mass index and placental weight showed a significantly increasing trend from the small‐for‐gestational age to the large‐for‐gestational age groups, but there was no significant difference in the placental weight‐to‐birthweight ratio, values of the oral glucose tolerance test, or haemoglobin A1c among the three groups. On the other hand, the maternal body mass index before pregnancy and at delivery were significantly higher in the large‐for‐gestational age group. The placental weight, but not the ratio, was significantly correlated with the maternal body mass index before pregnancy and at delivery (P < 0.001).

Conclusions The results indicate that the placenta is not disproportionately bigger, and therefore unlikely to be the cause, in large‐for‐gestational age infants. Maternal size appeared to be the major determinant of birthweight percentile ranking in pregnancies with gestational impaired glucose tolerance.
rbcL Plastid Pseudogene as a Tool for Orobanche (Subsection Minores) Identification
Authors: Benharrat H. , Delavault P. , Theodet Catherine , Figureau C. , Thalouarn P.
Published: July 2002

Abstract: Among members of the Orobanchaceae, parasitism has led to a drastic reduction in the morphological characters useful in identification. This is especially the case of species belonging to the subsection Minores (section Orobanche), which is a real tangle for agronomists and botanists. In this study, more than 120 specimens collected in the west of France were studied for their morphological characters and molecular markers. Their rbcL plastid gene was analyzed by RFLP and nucleotide sequencing. Because of several substitutions, insertions and deletions in the coding sequence, leading to stop codons and frameshift, this rbcL gene could be considered as a pseudogene. Variations in both 5′ upstream and coding regions allowed us to distinguish among specimens inside the Minores subsection. It was then possible to point out morphological characters, not used in floras, that fit with molecular analysis and confirm the existence of four taxa. Consequently, a new key to species determination using molecular analysis or morphological characters or a combination of both is proposed for O. hederae, O. amethystea, O. minor and O. loricata. Finally, the value of plastid pseudogenes in taxonomy is discussed.
Crystal structure analysis of epitaxial silicon films formed by a low kinetic energy particle process
Authors: Ohmi T. , Ichikawa T. , Shibata T. , Iwabuchi H.
Published: July 2002

Formation of high quality epitaxial silicon films at 350 °C by a low kinetic energy particle process has been verified by a series of crystal structure analyses performed on these films. It was found that the crystallinity of a grown film is drastically changed by the energy of Ar ions concurrently bombarding the growing silicon film surface. The epitaxially grown film with an optimum ion bombardment energy is defect-free both at the interface and in the bulk of the film as revealed by high-resolution transmission electron microscopy.
Efficient fiber coupling to low-loss diluted multiple quantum well optical waveguides
Authors: Deri R. J. , Yasuoka N. , Makiuchi M. , Kuramata A. , Wada O.
Published: July 2002

We demonstrate the use of diluted multiple quantum wells to achieve low-loss fiber-matched optical waveguides. A fiber mismatch loss of 0.2 dB/interface and propagation loss of 0.4 dB/cm are achieved at 1.54 μm wavelength using InGaAsP/InP materials.
Incorporation of Si in δ-doped GaAs studied by local vibrational mode spectroscopy
Authors: Wagner J. , Ramsteiner M. , Stolz W. , Hauser M. , Ploog K.
Published: July 2002

Raman scattering by local vibrational modes has been used to study the incorporation of Si in single δ-doped GaAs layers. Placing the doping spike at different depths underneath the surface, a depth profile of the dopant concentration incorporated on lattice sites has been obtained. For samples grown by molecular beam epitaxy under conditions which are known to lead to a significant broadening of the doping spike, the applied Raman technique reveals the incorporation of Si on Ga sites with a broadening of the Si distribution in excess of 20 nm.
Contrast phenomena of band-band and deep level photoluminescence topographs in annealed semi-insulating GaAs
Authors: Alt H. Ch. , Neef M. , von Philipsborn H.
Published: July 2002

The effect of wafer annealing on radiative recombination is studied by high-resolution photoluminescence imaging at room temperature. After long-time annealing (920 °C for 7 h) remarkable changes of photoluminescence contrast are observed for the EL2-related as well as for the band-band emission. The EL2-related emission at 0.68 eV becomes spatially homogeneous whereas the band-band recombination shows a complete contrast reversal as compared to the as-grown condition. It is concluded that after annealing the carrier lifetime is determined by recombination at the EL2 level. In as-grown material the existence of an additional trap is postulated which is spatially anticorrelated with EL2 and leads to a dominating nonradiative recombination path.
Can barriers with inverted tunneling rates lead to subband population inversion?
Authors: Helm M. , Allen S. J.
Published: July 2002

When the conduction-band edge of the quantum wells in a superlattice is close to the valence-band edge of the barriers, the tunneling probabilities out of the quantum well states can be inverted. We examine if this feature can be exploited to achieve intersubband population inversion. If correct matching of the wave function at the interfaces is included, we find that the inversion of the tunneling rates does not persist for low-energy electrons, relevant for intersubband emission.
Self-electro-optic device based on a superlattice asymmetric Fabry–Perot modulator with an on/off ratio ≳100:1
Authors: Law K-K. , Yan R. H. , Coldren L. A. , Merz J. L.
Published: July 2002

A self-electro-optic effect device based on a Fabry–Perot reflection modulator has been demonstrated for the first time. This modulator is a normally-off high-contrast asymmetric Fabry–Perot modulator using Wannier–Stark localization in a superlattice. Optical bistability has been achieved with a record-high on/off ratio of 130:1 at the operating wavelength of 7620 Å. The modulator with an appropriate reverse-bias voltage supply was connected in series to a silicon photodiode which when illuminated with an appropriate light source acted as a current source load for the modulator.
Defect-free epitaxial lateral overgrowth of oxidized (111) Si by liquid phase epitaxy
Authors: Bergmann R. , Bauser E. , Werner J. H.
Published: July 2002

We report on epitaxial lateral overgrowth of Si on oxidized (111) Si wafers by liquid phase epitaxy. The growth starts in oxide-free seeding windows and proceeds laterally over the SiO2. Growth effectively ceases when (111) sidewalls form. This observation allows the development of a geometrical model that, for the first time, explains the observed dependence of the overgrowth width on the orientation of the seeding windows. We obtain a maximum overgrowth width of 120–130 μm and a maximum aspect ratio of 40:1. Transmission electron microscopy reveals no crystallographic defects in the overgrown lamellae.
Inducing normally forbidden transitions within the conduction band of GaAs quantum wells
Authors: Pan Janet L. , West Lawrence C. , Walker Susan J. , Malik Roger J. , Walker John F.
Published: July 2002

Six heretofore unobserved envelope state transitions within the conduction band of an AlAs/GaAs quantum well are reported, two of which are forbidden in a symmetric quantum well. The highest energy transition is resonant with 2.86 μm wavelength light. These resonant energies and absorption strengths agree with predictions based on a many-body theory of electrons in nonparabolic energy bands. A new type of infrared modulator is possible via absorption changes in the ‘‘forbidden’’ transition between the first and the third conduction subbands.
Relaxation of strained InGaAs during molecular beam epitaxy
Authors: Whaley G. J. , Cohen P. I.
Published: July 2002

Relaxation of strained InxGa1−xAs films grown on GaAs substrates has been measured in situ during molecular beam epitaxy growth by reflection high-energy electron diffraction (RHEED). Growth is found to be layer by layer up to a strain-dependent ‘‘critical’’ thickness where three-dimensional clusters with {114} facets form. The onset of cluster growth is simultaneous with lattice relaxation as measured by RHEED. The relaxation during growth is compared with the Dodson–Tsao model for strained-layer relaxation [Appl. Phys. Lett. 53, 1325 (1987)]. Two distinct mechanisms for relaxation were found depending on film strain. An activation energy for relaxation was measured to be 4.4 eV for a film strain of 2.3%. The relaxation deviated from the Dodson–Tsao model for nongrowth conditions.
Growth velocity variations during metalorganic vapor phase epitaxy through an epitaxial shadow mask
Authors: Demeester P. , Buydens L. , Van Daele P.
Published: July 2002

A novel shadow masking technique is proposed for the local variation of growth velocity in GaAs/AlGaAs structures grown on GaAs by metalorganic vapor phase epitaxy. This mask makes use of epitaxially grown spacer and mask layers and windows in the mask are lithographically defined. This results in a highly accurate and reproducible shadow mask which can be removed by lift-off. Growth velocity variations up to 50% have been observed. The application of this technique to the coupling of passive and active waveguide structures is proposed.
High contrast, submilliwatt power InGaAs/GaAs strained-layer multiple-quantum-well asymmetric reflection modulator
Authors: Jin R. , Khitrova G. , Gibbs H. M. , Lowry C. , Peyghambarian N.
Published: July 2002

A high contrast, low power optical reflection modulator with an InGaAs/GaAs strained-layer multiple quantum well (MQW) nonlinear spacer is demonstrated. Taking advantage of large absorptive and dispersive nonlinearities near the exciton peak, on/off contrast ratios exceeding 29 dB are achieved with submilliwatt pump powers at room temperature.
High-voltage 6H-SiC p-n junction diodes
Authors: Matus L. G. , Powell J. A. , Salupo C. S.
Published: July 2002

A chemical vapor deposition (CVD) process has been used to produce device structures of n-and p-type 6H-SiC epitaxial layers on commercially produced single-crystal 6H-SiC wafers. Mesa-style p-n junction diodes were successfully fabricated from these device structures using reactive ion etching, oxide passivation, and electrical contact metallization techniques. When tested in air, the 6H-SiC diodes displayed excellent rectification characteristics up to the highest temperature tested, 600 °C. To observe avalanche breakdown of the p-n junction diodes, testing under a high-electrical-strength liquid was necessary. The avalanche breakdown voltage was 1000 V representing the highest reverse breakdown voltage to be reported for any CVD-grown SiC diode.
Undoped semi-insulating InP by high-pressure annealing
Authors: Kainosho K. , Shimakura H. , Yamamoto H. , Oda O.
Published: July 2002

Undoped semi-insulating (SI) InP wafers were obtained by high-temperature annealing under high phosphorus over pressure. These wafers show resistivities higher than 107 Ω cm, with mobilities greater than 4000 cm2 V−1 s−1. The SI properties could be held even after cap annealing with SiNx films at 700 °C for 15 min. The activation energy of deep levels causing the semi-insulation was estimated as 0.64 eV. Photoluminescence measurements made on undoped SI InP show hitherto unknown peaks in the long wavelength region between 1000 and 1400 nm.
Interface disorder in AlAs/(Al)GaAs Bragg reflectors
Authors: Asom M. T. , Geva M. , Leibenguth R. E. , Chu S. N. G.
Published: July 2002

We have investigated the structural properties of Bragg reflectors grown by molecular beam epitaxy. The reflectors consist of quarter-wavelength stacks of AlAs/ AlxGa1−xAs. We find a strong dependence of the interface quality on the substrate growth temperature, the Al composition in the ternary alloy, and the presence of impurities in AlAs. We have classified the interface disorder into two categories: interface roughness and structural waviness. We ascribe interface roughness to the segregation of oxygen during AlAs growth. The structural waviness originates from differing surface migration kinetics of Al and Ga which results in phase separation during growth of AlGaAs.
InAs/GaAs short-period strained-layer superlattices grown on GaAs as quantum confined Stark effect modulators
Authors: Jupina Michael , Garmire Elsa , Hasenberg Tom C. , Kost Alan
Published: July 2002

We report here the first use of InAs/GaAs short-period strained-layer superlattices as Stark effect modulators. We have observed differential transmission changes as large as 38% with a corresponding change in quantum-well absorption of 0.28 μm−1 at an applied field of 43 kV/cm. The Kramers–Kronig relation predicts a maximum change in the quantum-well index of refraction of 0.019 for a field of 43 kV/cm. There is a unique light-hole feature in the absorption and electroabsorption spectra that is attributed to resonant tunneling in the presence of high internal strain in the InAs layers.
Lattice-matched InGaAsP/InP long-wavelength quantum well infrared photodetectors
Authors: Gunapala S. D. , Levine B. F. , Ritter D. , Hamm R. A. , Panish M. B.
Published: July 2002

We demonstrate the first long-wavelength quantum well infrared photodetector using the lattice-matched n-doped InGaAsP/InP materials system. A 45° prism coupled illumination responsivity of R=0.3 A/W and detectivity of D*λ=1.3×109 cm√Hz/W at T=50 K, for a cutoff wavelength λc=13.2 μm have been achieved.
Carrier capture and quantum confinement in GaAs/AlGaAs quantum wire lasers grown on V-grooved substrates
Authors: Walther M. , Kapon E. , Christen J. , Hwang D. M. , Bhat R.
Published: July 2002

Carrier capture mechanisms in semiconductor quantum wire (QWR) lasers grown by organometallic chemical vapor deposition on nonplanar substrates were investigated by cathodoluminescence and photoluminescence (PL) spectroscopy. Efficient carrier capture into the QWRs via adjacent quantum wells is manifested by a complete transfer of luminescence intensity from the well- to the wire-spectral lines at temperatures above ∼100 K. In addition, higher QWR subbands separated by 19 meV are observed in the PL spectra, in agreement with the calculated subband spacing. The quantum well assisted carrier capture in these wires is important for the efficient room temperature operation of lasers and other optoelectronic devices based on QWRs.
Luminescence decay in disordered low-dimensional semiconductors
Authors: Chen X. , Henderson B. , O’Donnell K. P.
Published: July 2002

The luminescence decay of excitons in disordered low-dimensional semiconductors with quantum confinement is shown experimentally to be characterized by a nonexponential profile and an absence of spectral diffusion. We are able to describe this luminescence as a hopping-assisted recombination using the correlation function approach to nondispersive transport developed by H. Scher, M. F. Shlesinger, and J. T. Bendler [Phys. Today 41, 26 (1991)]. We suggest a simple derivation of analytical functions which accurately describe the anomalous luminescence decays of disordered II-VI superlattices and of porous silicon, and show that this model includes exponential and Kohlrausch [Pogg. Ann. Phys. 119, 352 (1863)] (stretched-exponential) relaxations as special cases.
Circularly symmetric operation of a concentric-circle-grating, surface- emitting, AlGaAs/GaAs quantum-well semiconductor laser
Authors: Erdogan T. , King O. , Wicks G. W. , Hall D. G. , Anderson Erik H. , Rooks M. J.
Published: July 2002

A surface-emitting semiconductor laser that utilizes a concentric-circle grating defined by electron-beam lithography is observed to oscillate in a circularly symmetric fashion. The laser emits a circularly symmetric beam with a total beam divergence of less than 1°. Despite its broad-area geometry, the laser shows no evidence of filamentation. The laser maintains a relatively narrow wavelength spectrum approximately 1 Å in width.
Electroluminescence from bipolar resonant tunneling diodes
Authors: Van Hoof C. , Genoe J. , Mertens R. , Borghs G. , Goovaerts E.
Published: July 2002

The incorporation of an AlAs/GaAs resonant tunneling structure inside a GaAs p-n junction leads to strong quantum-well electroluminescence originating from electron and hole tunneling into the resonant tunneling structure. A large peak-to-valley ratio of 10:1 in the electroluminescence intensity is achieved at the electron resonance at 4.2 K, which decreases but persists (1.45:1) at room temperature. Resonant tunneling of holes is also apparent from the electroluminescence at low temperature.
Finite-element analysis of particle-particle forces in electrorheological fluids
Authors: Davis L. C.
Published: July 2002

The first finite-element analysis of the forces between particles in electrorheological fluids is presented. The shear modulus for chains of particles arrayed on a square lattice is calculated. Two limiting cases are considered: (1) dielectric particles in a dielectric fluid and (2) infinitely conducting particles in an insulating fluid. In (1), the modulus increases linearly with the ratio of dielectric constants Kp/Kf as the ratio becomes large, contrary to expectations from a simple dipole approximation where it would saturate. For case (2), the modulus depends sensitively on the interparticle spacing and diverges when the particles touch.
Investigation of In0.53Ga0.47As/AlAs resonant tunneling diodes for high speed switching
Authors: Chow D. H. , Schulman J. N. , Özbay E. , Bloom D. M.
Published: July 2002

We report an investigation of In0.53Ga0.47As/AlAs resonant tunneling diodes designed for high speed switching applications. Experimental peak current densities are observed to increase with decreasing AlAs barrier thicknesses, in good agreement with a two band tunneling calculation, which includes the effects of strain and band bending. Swing voltages over the range 0.5–1.0 V are demonstrated to be controllable via the thickness of a lightly doped depletion layer. Estimated RC time constants are compared with intrinsic tunneling times for the samples studied. A sample with 6 monolayer AlAs barriers yields devices with peak current densities of 3.1×105 A/cm2 and peak-to-valley current ratios of 6:1. The minimum rise time in this sample is calculated to be limited by RC switching delays to 1.6 ps.
Changes in electrical device characteristics during the in situ formation of dislocations
Authors: Ross F. M. , Hull R. , Bahnck D. , Bean J. C. , Peticolas L. J. , King C. A.
Published: July 2002

By adding electrical connections to a specimen heating holder for a transmission electron microscope (TEM), we have measured the characteristics of electronic devices, such as diodes, while they remain under observation. We have made TEM specimens from metastable GeSi/Si p-n junction diodes and introduced dislocations by heating in situ. We describe the changes in the electrical properties of these devices as dislocations form. We find that a generation-recombination process does not explain our results and instead, suggest a model based on the creation of point defects or the diffusion of metals during the formation of dislocations.
Effects of band mixing on hole tunneling times in GaAs/AlAs double-barrier heterostructures
Authors: Erdoğan M. U. , Kim K. W. , Stroscio M. A.
Published: July 2002

The tunneling time of holes in GaAs/AlAs double-barrier heterostructures is calculated within the envelope function approximation, including band-mixing effects. The phase delay time is obtained from the energy derivative of the total phase shift of the wave function upon tunneling. The results show clearly that mixing plays a very important role in hole tunneling. In particular, our study suggests that the conventional effective mass models (without band mixing) can significantly overestimate the heavy hole tunneling time and thus are not suitable for estimation of the hole tunneling time. It is also demonstrated that the effect of band mixing on hole tunneling times becomes more important for thicker barriers.
Cr-doped GaAs/AlGaAs semi-insulating multiple quantum well photorefractive devices
Authors: Partovi A. , Glass A. M. , Olson D. H. , Zydzik G. J. , O’Bryan H. M. , Chiu T. H. , Knox W. H.
Published: July 2002

Semi-insulating multiple quantum well photorefractive devices using GaAs/Al0.29Ga0.71As with an electric field applied perpendicular to the layers are demonstrated. Semi-insulating behavior is obtained by doping with Cr(1016/cm3) during epitaxial growth of the material. Diffraction efficiencies as high as 3% with an applied voltage of 20 V and microsecond response times are obtained in a 2 μm thick device. These devices are of importance for implementation of fast and sensitive two-dimensional optical information processing systems at wavelengths compatible with current diode lasers without the spatial-bandwidth limitations of thick photorefractive materials.
Nonresonant tunneling in InGaP/InAlP asymmetric double quantum wells
Authors: Buccafusca O. , Chilla J. L. A. , Menoni C. S. , Rocca J. J. , Hafich M. J. , Woods L. M. , Robinson G. Y.
Published: July 2002

Nonresonant tunneling rates have been measured in InGaP/InAlP asymmetric double quantum-well structures for which optical phonon assisted tunneling is energetically forbidden. For an initial photoexcited carrier density of 2.4×1011 cm−2, tunneling times of 220, 60, and less than 9 ps have been measured in samples with barrier thickness 4.5, 3.0, and 1.5 nm, respectively. The tunneling times were found to be strongly dependent on carrier density. The measured tunneling times and their dependence on carrier density are compatible with impurity scattering being the dominant mechanism assisting the tunneling.
Nitrogen incorporation in SiO2 by rapid thermal processing of silicon and SiO2 in N2O
Authors: Weidner G. , Krüger D.
Published: July 2002

The N2O-rapid thermal processing (RTP) of (100) silicon and of SiO2 at 1150 °C for 30, 100, and 300 s leads to a constant nitrogen maximum content in an interlayer between SiO2 and Si with the consequence of decreasing nitrogen content at surface and in bulk with process time. If 10–10 000 vpm H2 is added to N2O during RTP the nitrogen incorporation remains generally unchanged. The nitrogen should be incorporated from the NOx species dissociated at the interface with favoring the Si–O binding. The nitrogen compensates defective sites near the interface and in the bulk also in the presence of hydrogen.
High T
c superconductor-normal-superconductor Josephson junctions using CaRuO3 as the metallic barrier
Authors: Char K. , Colclough M. S. , Geballe T. H. , Myers K. E.
Published: July 2002

Josephson junctions of the SNS type have been fabricated in the edge and trilayer junction geometries using YBa2Cu3O7−δ/CaRuO3/YBa2Cu3O7−δ. The conducting oxide CaRuO3 was chosen because it grows epitaxially on YBa2Cu3O7−δ and its resistivity shows metallic behavior. Current-voltage characteristics display behavior with significant deviations from the resistivity shunted junction model. The dependence of critical currents and junction resistances on the CaRuO3 thickness suggest that the interface resistance between YBa2Cu3O7−δ and CaRuO3 plays an important role in determining the critical parameters of the junctions. A dc SQUID functioning at 77 K has been demonstrated with this type of junction.
Molecular beam epitaxy of strained PbTe/EuTe superlattices
Authors: Springholz G. , Bauer G.
Published: July 2002

Using reflection high energy electron diffraction (RHEED), the phase diagram of strained layer heteroepitaxy of EuTe by molecular beam epitaxy on PbTe(111) surfaces was determined. The EuTe(111) surface exhibits different surface reconstructions corresponding to a Te-stabilized or an Eu-stabilized surface state. For perfect two-dimensional layer-by-layer heteroepitaxial growth, only a narrow process window exists which can be determined by RHEED. Using such established growth conditions, we have fabricated strained PbTe/EuTe superlattices with superior structural perfection as shown by high resolution x-ray diffraction.
Generation mechanisms of crystal defects in arsenic and phosphorus implanted silicon devices
Authors: Tsai H. L. , Hemming S. M. , Eklund R. H. , Hosack H. H.
Published: July 2002

Arsenic and phosphorus are often implanted into silicon for localized doping during the processing of integrated circuits. The implant damages the silicon lattice, resulting in crystal defects during annealing. Crystal defects observed by transmission electron microscopy (TEM) appear at three different locations in patterned devices. The mechanisms underlying the generation of these defects are presented and discussed, based on an extensive study under various process conditions. These mechanisms form the basis for eliminating/reducing defects in arsenic or phosphorus implanted silicon devices.