bluuebunny/crossref_metadata_2025 huggingface dataset:
Rate of infraposition of reimplanted ankylosed incisors related to age and growth in children and adolescents
Authors: Malmgren Barbro , Malmgren Olle
Published: July 2002

Abstract – In growing individuals, infraposition of a reimplanted, ankylosed tooth may disrupt normal alveolar development and compromise prosthetic treatment. The aims of this study were to analyze the rate of infraposition of ankylosed incisors in growing subjects and to provide guidelines for the timing of extraction. The subjects comprised 30 boys and 12 girls, selected consecutively from patients on annual post‐trauma follow‐up, and observed for periods ranging from 1 to 10 years. Only patients with one replanted ankylosed maxillary central incisor were included, the homologous teeth with healthy periodontal ligaments serving as controls. Growth intensity was evaluated from analyses of annual body height measurements. The following four periods were established: before the growth spurt, from initial to maximal growth spurt, from maximal growth spurt to the end and after the growth spurt. In 11 patients, cephalograms were taken at diagnosis and at extraction. Progression of infraposition varied individually. Diagnosis before the age of 10 or before the growth spurt was associated with very high risk of severe infraposition. In these cases the ankylosed tooth should be removed within 2–3 years. If ankylosis develops during the growth spurt, the tooth should be monitored regularly, but no intervention is indicated provided the adjacent teeth do not tilt and infraposition is minor or stable. Annual body height measurements, indicating the intensity of skeletal growth, are an aid to assessment. Cephalometric radiographs are important for evaluating the direction of growth of the jaws since there is a difference between horizontal and vertical growers.
Activation of mouse Pi-class glutathione S-transferase gene by Nrf2(NF-E2-related factor 2) and androgen
Authors: IKEDA Hiromi , SERRIA Mohamed S. , KAKIZAKI Ikuko , HATAYAMA Ichiro , SATOH Kimihiko , TSUCHIDA Shigeki , MURAMATSU Masami , NISHI Shinzo , SAKAI Masaharu
Published: July 2002

The Pi-class glutathione S-transferases (GSTs) play pivotal roles in the detoxification of xenobiotics, carcinogenesis and drug resistance. The mechanisms of regulation of these genes during drug induction and carcinogenesis are yet to be elucidated. Recently, Nrf2 (NF-E2-related factor 2; a bZip-type transcription factor) knockout mice were shown to display impaired induction of Pi-class GST genes by drugs. It is known that the mouse Pi-class GST gene GST-P1 is expressed predominantly in the male liver, and is regulated by androgen. To determine whether Nrf2 and the androgen receptor regulate GST-P1 directly, we analysed the molecular mechanism of activation of this gene by these factors. The promoter of the GST-P1 gene was activated markedly by Nrf2 in transient transfection analyses. Gel mobility shift assay and footprinting analyses revealed three Nrf2 binding sites: one at the proximal and two at distal elements, located at positions −59, −915 and −937 from the cap site. The fifth intron of the GST-P1 gene contains the androgen-responsive region. Multiple androgen receptor binding sites are clustered within a 500bp region of this intron. The whole fragment contains a minimum of seven androgen receptor binding sites, which collectively display strong androgen-dependent enhancer activity. However, on division into small fragments containing two or three elements each, individual enhancer activities were dramatically decreased. This suggests that multiple elements work synergistically as a strong androgen-responsive enhancer. Our findings indicate that Nrf2 and the androgen receptor directly bind to and activate the mouse GST-P1 gene.
Membrane‐bound iron contributes to oxidative damage of β‐thalassaemia intermedia erythrocytes
Authors: Tavazzi Dario , Duca Lorena , Graziadei Giovanna , Comino Alessia , Fiorelli Gemino , Cappellini Maria Domenica
Published: July 2002

Iron‐dependent oxidative reactions in β‐thalassaemic erythrocyte membranes are involved in premature cell removal and anaemia. We studied 22 β‐thalassaemia intermedia patients (i) to assess if membrane iron accumulation influences the oxidative damage to thalassaemic cells, and (ii) to see whether the mechanisms of haemoglobin destabilization described in vitro have indicators in circulating erythrocytes. Serum non‐transferrin‐bound iron as potentially toxic iron for erythrocytes was also evaluated. Membrane‐bound free iron significantly correlated to bound haemichromes, suggesting a causal relation, but was poorly related to serum non‐transferrin iron, which seems to contribute little to damage from outside the cells. The spleen played an important role in the removal of cells with more membrane iron.
Mutation analysis of C‐KIT in patients with myelodysplastic syndromes without mastocytosis and cases of systemic mastocytosis
Authors: Fritsche‐Polanz Robert , Jordan John‐Hendrik , Feix Alexandra , Sperr Wolfgang R. , Sunder‐Plassmann Gere , Valent Peter , Födinger Manuela
Published: July 2002

The proto‐oncogene C‐KIT encodes a tyrosine kinase receptor that is expressed on mast cells and haematopoietic stem cells and can show somatic mutations in patients with mastocytosis. Only scattered information is available about mutations in C‐KIT in patients with other myeloid neoplasms. Moreover, the prevalence of mutations in C‐KIT in bone marrow specimens of individuals with systemic mastocytosis is largely unknown. Using sequence analysis, we have screened cDNAs of the C‐KIT domain encompassing codon 510–626 and codon 763–858 in bone marrow (BM) mononuclear cells (MNCs) of patients with myelodysplastic syndromes (n = 28) and patients with systemic mastocytosis (n = 12) for the presence of mutations. Furthermore, restriction fragment length polymorphism analysis was applied for identification of the C‐KIT 2468A→T and the C‐KIT 1700T→G mutation, as well as the C‐KIT 1642A→C polymorphism. All 11 patients with systemic indolent mastocytosis tested positive for C‐KIT 2468A→T. In contrast, no mutation was identified in the case of aggressive mastocytosis. Among patients with myelodysplastic syndromes, no patient showed a somatic mutation in C‐KIT. The allele frequency for C‐KIT 1642A→C among the entire patient population was 0·038 and was 0·125 among age‐ and sex‐matched healthy controls. Our data demonstrate that myelodysplastic syndromes without histological or cytological evidence of mastocytosis do not exhibit somatic mutations in exons 10, 11, 12, 16, 17 and 18 of C‐KIT. In contrast, BM MNCs of patients with systemic indolent mastocytosis were all positive for C‐KIT 2468A→T and negative for additional mutations in these exons. The C‐KIT 1642A→C polymorphism is not associated with myelodysplastic syndrome or systemic mastocytosis.
Differences in the pathogenesis of bacteria isolated from contact‐lens‐induced infiltrative conditions
Authors: Willcox Mark D P , Hume Emma B H
Published: July 2002

Purpose:The purpose of this study was to examine the ability of Gram‐negative bacteria isolated from the non‐infectious condition contact‐lens‐induced acute red eye (CLARE) and infectious microbial keratitis (MK) to infect the eyes of mice.

Methods:One cornea of BALB/c mice was scratched with a needle and 5 × 106bacteria applied. Bacterial types used werePseudomonas aeruginosa, Haemophilus influenzae, Serratia marcescens, Stenotrophomonas maltophiliaandAeromonas hydrophilia. The mice were killed after 1, 4 and 24 h and examined by slit lamp, histology and microbiology.

Results:CLARE strains were unable to infect the mouse corneas. The eyes inoculated with the CLARE strains had low levels of polymorphonuclear leucocytes (PMN) in the stroma. All eyes that had MK contained bacteria and large numbers of PMN after 24 h.

Conclusions:The development of CLARE or MK is dependent on the type of bacteria with specific bacterial types being responsible for CLARE or MK.
SURGICAL ADHESIONS: EVIDENCE FOR ADSORPTION OF SURFACTANT TO PERITONEAL MESOTHELIUM
Authors: Chen Y. , Hills B. A.
Published: July 2002

Background: It has been speculated that the formation of surgical adhesions must be preceded by physical adhesion of the two surfaces, a process normally prevented by a lining of adsorbed surface‐active phospholipid (surfactant) acting as both a superb boundary (solid‐to‐solid) lubricant and a release (antistick) agent. Animal trials administering exogenous surfactant as a dry powder (ALEC™) have previously demonstrated a reduction of 80% in abdominal adhesions.

Methods: Incubation of rat peritoneum (both live and excised) with radiolabelled dipalmitoyl phosphatidylcholine (DPPC) has been used to demonstrate adsorption; while the normal lining of surfactant in the human abdominal cavity has been confirmed by epifluorescence microscopy using Phosphin E as the hydrophobic probe.

Aims: The overall aim is to confirm that peritoneal mesothelium has a lining of surfactant known for its lubricating and release properties, and that this lining can be enhanced by the adsorption of exogenous material.

Results: Adsorption of DPPC to peritoneal mesothelium was 470 ng/cm
2 (n = 8) ex vivo and 598 ng/cm
2 (n = 18) in vivo, these rates being enhanced by EggPG by 62%ex vivo and 47%in vivo to reach the equivalent of almost three close‐packed monolayers.

Conclusions: These results can explain the reduction in surgical adhesions previously reported in animals by administering ALEC™ (7:3 DPPC:EggPG) as a highly surface‐active dry powder, although it is now used in saline suspension to treat respiratory distress syndrome in newborns, in whom it has no side‐effects. These findings would appear to justify clinical trials for dry ALEC™ in suppressing surgical adhesions with minimal risk of an adverse reaction. The results of these trials are also discussed and found to be compatible with the known ability of surfactant to resist physical adhesion by fibronectin, the tacky ‘glue’ by which fibroblasts attach to surfaces as the first step in formation of fibrinous adhesions.
Effect of ageing and diabetes on glucose‐dependent insulinotropic polypeptide and dipeptidyl peptidase IV responses to oral glucose
Authors: Meneilly G. S. , Demuth H. ‐U. , McIntosh C. H. S. , Pederson R. A.
Published: July 2002

Aims Glucose‐dependent insulinotropic polypeptide (GIP) acts on the pancreas to potentiate glucose‐induced insulin secretion (enteroinsular axis). GIP is rapidly inactivated in vivo by the enzyme dipeptidyl dipeptidase IV (DPP‐IV). The current studies were designed to examine the effect of ageing, obesity and diabetes on GIP and DPP‐IV responses to oral glucose.

Methods Healthy controls (nine middle‐aged, age 42 ± 2 years, body mass index (BMI) 33 ± 1 kg/m2; nine elderly, age 71 ± 1 years, BMI 30 ± 1 kg/m2) and patients with Type 2 diabetes (12 middle‐aged, age 44 ± 2 years, BMI 34 ± 2 kg/m2; 19 elderly, age 74 ± 1 years, BMI 31 ± 1 kg/m2) underwent a 3‐h oral glucose tolerance test (OGTT) (glucose dose 40 g/m2).

Results Insulin responses were similar in elderly controls and patients with diabetes, but were lower in middle‐aged patients with diabetes than in controls (308 ± 65 vs. 640 ± 109 p
M, P < 0.05). GIP responses were similar in controls and patients with diabetes in each age group, but were higher in elderly controls (middle‐aged 45 ± 13; elderly 112 ± 13 p
M, P < 0.01) and patients with diabetes (middle‐aged 55 ± 10; elderly 99 ± 10 p
M, P < 0.01). DPP‐IV levels were lower in patients with diabetes in both middle‐aged (control 0.241 ± 0.015; diabetes 0.179 ± 0.017 ΔOD/20 min, P < 0.05) and elderly groups (control 0.223 ± 0.019; diabetes 0.173 ± 0.010 ΔOD/20 min, P < 0.05).

Conclusions It was concluded that ageing in obese subjects is associated with enhanced GIP responses to oral glucose. In addition, DPP‐IV activity is reduced in middle‐aged and elderly obese patients with diabetes.
Plasma lipids and urinary albumin excretion rate in Type 1 diabetes mellitus: the EURODIAB IDDM Complications Study
Authors: Mattock M. B. , Cronin N. , Cavallo‐Perin P. , Idzior‐Walus B. , Penno G. , Bandinelli S. , Standl E. , Kofinis A. , Fuller J. H. , The Eurodiab Iddm Complications Study Group
Published: July 2002

SUMMARY

Aims  To examine the relationship between increased urinary albumin excretion rate and fasting plasma lipids among male and female respondents to the EURODIAB IDDM Complications Study, and attempt to explain inconsistencies in previous reports.

Methods  A cross‐sectional study of 3250 randomly selected Type 1 diabetic patients from 31 diabetes clinics in 16 European countries was carried out between 1989 and 1990. Plasma lipids and urinary albumin were measured centrally. The present analysis was confined to the subgroup of 2205 patients attending after a 10–12 h overnight fast. Mean age was 33 years (sd 10) and mean duration of Type 1 diabetes mellitus was 15 years (sd 9).

Results  The prevalence of microalbuminuria (24‐h urinary albumin excretion rate 20–200 μg/min) was 21.7% (95% confidence interval 19.9–23.5) and macroalbuminuria (24‐h urinary albumin excretion rate > 200 μg/min) 7.8% (6.6–9.0). In comparison to patients with normal urinary albumin excretion rate (< 20 μg/min), and after controlling for age, sex, glycaemic control, duration of diabetes and current smoking, macroalbuminuria was associated with significantly (P < 0.01) increased fasting plasma triglycerides, cholesterol, LDL‐cholesterol, cholesterol:HDL‐cholesterol ratio and, in women, reduced HDL‐cholesterol. In men and women with microalbuminuria, the only significant association was with increased plasma triglycerides.

Conclusions  These data confirm that there is an association between fasting plasma lipids and increasing urinary albumin excretion rate in European Type 1 diabetic patients. In microalbuminuric patients, however, the association was weaker than previously reported and partly explained by confounding factors.
Characteristic patterns of circadian variation in plasma catecholamine levels, blood pressure and heart rate variability in Type 2 diabetic patients
Authors: Kondo K. , Matsubara T. , Nakamura J. , Hotta N.
Published: July 2002

Aims To investigate whether Type 2 diabetic patients exhibit characteristic patterns of circadian variation in plasma levels of catecholamines, blood pressure (BP) and heart rate variability (HRV).

Methods Ten Type 2 diabetic and eight control in‐patients were studied. Blood for catecholamine measurement was collected every 4 h, and non‐invasive ambulatory BP and heart rate were monitored throughout the day. HRV was determined using frequency domain methods.

Results Diabetic patients showed a different pattern of circadian variation in BP and HRV from that of controls, the diurnal‐nocturnal differences (D‐N) being significantly smaller. The mean 24‐h HRV levels were reduced in diabetic subjects. The mean 24‐h plasma noradrenaline level of 1.36 ± 0.12 nmol/l in diabetic patients was significantly lower than the 2.03 ± 0.20 nmol/l in controls (P < 0.01). In contrast, no significant difference in adrenaline levels was observed. The mean 24‐h plasma noradrenaline level demonstrated a significant positive correlation with D‐N in systolic BP (r = 0.49, P = 0.0153).

Conclusions The present study demonstrated distinctive patterns of circadian variation in plasma noradrenaline level, BP and HRV in Type 2 diabetic patients, associated with an abnormal circadian pattern of sympathovagal modulation.
A brief neuropsychological assessment for the differential diagnosis between frontotemporal dementia and Alzheimer's disease
Authors: Siri S. , Benaglio I. , Frigerio A. , Binetti G. , Cappa S. F.
Published: July 2002

The neuropsychological performance (including measures of language, semantic memory, visual and spatial perception and executive functions) of a group of 14 patients with the clinical diagnosis of probable frontotemporal dementia was compared with that of a group of 14 patients with a clinical diagnosis of probable Alzheimer's disease. The aim was to identify a specific cognitive profile of frontotemporal dementia, which could be used to select a sensitive, short evaluation for the differential diagnosis with Alzheimer's disease. Both groups were severely impaired in most tasks, including those ‘frontal lobe’ tests which have been suggested to play an important role in differential diagnosis. Significant differences were found only for a minority of tests (oral praxis, visual–spatial perception, and verbal fluency). A logistic regression showed that a shortened testing procedure based on four tests (Rey–Osterreith complex figure test recall, phonemic fluency, oral apraxia, and cube analysis) achieved a 70% sensitivity and 80% specificity for the correct classification of patients in the frontotemporal dementia or Alzheimer's disease group. In conclusion, a brief neuropsychological evaluation including these four tests, as well as other measures sensitive to the frontal impairment, can be useful in the differential diagnosis between the two pathologies, along with the clinical data.
Occupational exposure to optical radiation and the ocular health status of glassblowers*
Authors: Oriowo Olanrewaju M. , Chou B. Ralph , Cullen Anthony P. , Robinson Barbara E.
Published: July 2002

The occupational radiation exposure levels and the ocular health status of a sample of glass‐blowers in southern Ontario were evaluated. The form of ocular protection was also assessed. Measurements of radiant emissions from different molten glass materials were carried out. A total of six glassblowing installations, 15 glassblowers and 42 non‐glassblowers participated in the study. The spectral transmittances of samples of the protective lenses were obtained. Tonometry, biomicroscopy, ophthalmoscopy, pachometry. Schirmer tear test, endothelial photography were completed on all the volunteering subjects. The glassblowers' ocular findings were compared to those of non‐glassblowers. No indication of cataract was observed among this group of glassblowers. Although, a preponderance of grade 2 polymegethism among the glass‐blowers (47% compared to 11% in non‐glassblowers) was found, there was no significant difference in their ocular health. Variation in the corneal irradiance from occupational exposure was obtained, and in addition, the use of protective lenses was found to be inappropriate. In order to prevent against any long‐term chronic pathologic effect, the use of appropriate ocular protection is advised.
Citalopram in patients with fibromyalgia— a randomized, double‐blind, placebo‐controlled study
Authors: Anderberg Ulla Maria , Marteinsdottir Ina , von Knorring Lars
Published: July 2002

The effect of the selective serotonin reuptake inhibitor citalopram was studied in a randomized, double‐blind, placebo‐controlled, 4‐month trial in patients with the fibromyalgia syndrome (FMS) who all fulfilled the American College of Rheumatology criteria. The citalopram doses varied between 20–40 mg daily. Forty female patients, 21 patients in the citalopram and 19 in the placebo group, participated. Assessment of pain, depressive symptoms and physical functioning were made using Visual Analogue Scales (VAS), the Montgomery Åsberg Depression Rating Scale (MADRS) and the Fibrositis Impact Questionnaire (FIQ).

In the global judgement of improvement, no significant changes were found between the citalopram and placebo groups as concerns pain or well‐being, either in the Intention to Treat (ITT) analysis or in the completer analysis. However, among the completers, it was a tendency that more patients in the citalopram group (52.9%) were improved as compared to the placebo group (22.2%) concerning well‐being.

Furthermore, the results indicated that treatment with citalopram had a significant effect on pain on the VAS after 2 months of treatment compared to baseline. After 4 months, however, the effect had diminished. Measured with the FIQ, significant differences in the pain ratings were seen at the end of the trial.

Significant effects on the depressive symptomatology measured by means of the MADRS were seen already after 1 month of treatment and were increasing further at the end of the trial, when a significant difference between the groups was also found. Copyright 2000 European Federation of Chapters of the International Association for the Study of Pain
Phenylalanine Ammonia‐Lyase Activity in Soybean Roots Extract Measured by Reverse‐Phase High Performance Liquid Chromatography
Authors: Ferrarese M. L. L. , Rodrigues J. D. , Ferrarese‐Filho O.
Published: July 2002

Abstract: The high performance liquid chromatography (HPLC) technique was applied to measure phenylalanine ammonia‐lyase (PAL, EC 4.3.1.5) activity in soybean (Glycine max L. Merril cv. BR16) roots. t‐Cinnamate, the catalytic product of the PAL reaction was quantified at 275nm by isocratic elution with methanol: water through an ODS(M) column. Comparative experiments were carried out with 1.0 mM ferulic acid, an inducer of PAL activity. The results suggest that liquid chromatography is a rapid and sensitive method to analyze PAL activity in non‐purified extract.
Semiconductor waveguide phase comparator
Authors: Lin S. C. , Chin M. K. , Jing X. L. , Walpita L. M. , Yu P. K. L. , Chang W. S. C. , Wang S. C.
Published: July 2002

A phase comparator based on two cascaded semiconductor electroabsorption waveguide modulators is demonstrated for the first time. The operation principle of this device is derived and experimentally confirmed.
Improved photoluminescence of GaAs in ZnSe/GaAs heterojunctions grown by organometallic epitaxy
Authors: Ghandhi S. K. , Tyagi S. , Venkatasubramanian R.
Published: July 2002

Zinc selenide layers, grown by organometallic vapor phase epitaxy on gallium arsenide, are shown to improve the photoluminescence intensity of the gallium arsenide. The improvement in the room-temperature photoluminescence intensity is found to be as high as 190, for n-type GaAs covered with an 1100 Å ZnSe layer. An improvement of 145 was observed for p-type GaAs covered by a ZnSe layer of the same thickness. No such improvement is seen for ZnSe thicknesses exceeding 1500 Å, the calculated critical thickness for this heterojunction. The effective recombination velocity is estimated to be approximately 1×103 cm/s for the GaAs-ZnSe interface, with thin ZnSe layers. Different epitaxial structures were used to check the consistency of the calculations, and the results match reasonably well. Our findings suggest that the behavior of the ZnSe/GaAs heterojunction is similar to the AlGaAs/GaAs heterojunction. This presents the possibility of its use in GaAs device, where it should offer some advantages over the existing structures using AlGaAs.
Reduction of degradation in vapor phase transported InP/InGaAsP mushroom stripe lasers
Authors: Jung H. , Burkhardt E. G. , Pfister W.
Published: July 2002

The rapid degradation rate generally observed in InP/InGaAsP mushroom stripe lasers can be considerably decreased by regrowing the open sidewalls of the active stripe with low-doped InP in a second epitaxial step using the hydride vapor phase transport technique. This technique does not change the fundamental laser parameters like light-current and current-voltage characteristics. Because of this drastic reduction in degradation, the vapor phase epitaxy regrown InP/InGaAsP mushroom laser seems to be an interesting candidate for application in optical communication.
Realistic modeling of the electronic properties of doped amorphous silicon
Authors: Hack M. , Street R. A.
Published: July 2002

In this letter we describe a fundamental approach to calculating the electronic properties of doped amorphous silicon which takes into account the thermal history of the material. Above the equilibrium temperature, the material is in a thermodynamically stable state, and this is derived by minimizing the free energy using a simple density of states model. The calculations are based on the defect compensation model of doping, introducing distributions of formation energies for neutral dangling bonds and fourfold dopant atoms while preserving charge neutrality. Our results are in good agreement with experimental data providing a realistic model for use in device simulation programs.
GaInAs/GaInAsP/InP heterostructure bipolar transistors with very thin base (150 Å) grown by chemical beam epitaxy
Authors: Tsang W. T. , Levi A. F. J. , Burkhardt E. G.
Published: July 2002

It is demonstrated that chemical beam epitaxy (CBE) is suitable for growing high quality GaInAs(P)/InP heterostructure bipolar transistors. Step-graded double-heterostructure bipolar transistors with very thin base (150 Å) and very high p doping (∼5×1019 cm−3), and with an added ‘‘grading layer’’ of 200 Å GaInAsP (Eg =0.94 eV) between the GaInAs/InP base-collector junction, have shown good current drive capability and excellent current gain ( β=2500). In addition, CBE-grown standard single-heterostructure bipolar transistors with a 1000 Å base and 2×1018 cm−3 p doping are characterized by high gain, β∼3500, which is only weakly dependent on the collector current.
Ultrasonic imaging with a fixed instrument configuration
Authors: Witten Alan , Tuggle Joe , Waag Robert C.
Published: July 2002

Diffraction tomography is a technique based on an inversion of the wave equation which has been proposed for high-resolution ultrasonic imaging. While this approach has been considered for diagnostic medical applications, it has, until recently, been limited by practical limitations on the speed of data acquisition associated with instrument motions. This letter presents the results of an experimental study directed towards demonstrating tomography utilizing a fixed instrument configuration.
Inhomogeneous gain saturation in a mode-locked semiconductor laser
Authors: Serenyi M. , Göbel E. O. , Kuhl J.
Published: July 2002

The saturation of the light-dc prebias current characteristic of an actively mode-locked GaAs/AlGaAs semiconductor laser with external resonator reveals a pronounced dependence on lasing wavelength and peak intensity of the mode-locked pulses. The latter effect is attributed to inhomogeneous gain saturation.
Fiber optic distributed thermal sensor
Authors: Zur A. , Katzir A.
Published: July 2002

A novel concept of a fiber optic distributed sensor is presented. In particular, we describe a distributed thermal sensor formed by inducing a deliberated absorption in an infrared optical fiber. The increased absorption coefficient αab of this modified fiber determines the linear sensing length of the distributed thermal sensor. When part of the modified fiber is heated, infrared radiation is generated in the fiber and transmitted through it to its distal face. Measuring this radiation power with a radiometer, we are able to determine the average spatial temperature distribution along the fiber sensing length.
Spectral and picosecond temporal properties of flared guide Y-coupled phase-locked laser arrays
Authors: DeFreez R. K. , Bossert D. J. , Yu N. , Hartnett K. , Elliott R. A. , Winful H. G.
Published: July 2002

Spatio-spectral and spatio-temporal properties of flared waveguide ‘‘Y’’-coupled laser arrays are investigated in both cw and pulsed operation. In each case, regular sustained self-pulsations are exhibited. Destabilization of phase locking, caused by amplitude phase coupling, is thought to be the origin of the pulsations.
Effect of the sign of misfit strain on the dislocation structure at interfaces of heteroepitaxial GaAsxP1−x films
Authors: Petruzzello J. , Leys M. R.
Published: July 2002

It was shown, with the use of transmission electron microscopy, that the dislocation structure at interfaces of heteroepitaxial GaAsxP1−x films is dependent on the sign of the misfit strain. Under tensile strain the interface contains a square grid network of both perfect and partial misfit dislocations. The dislocations are straight and exist predominantly along 〈110〉 directions. This configuration of misfit dislocations is consistent with the nucleation of partial dislocations in tensile strained films. The compressive interface also contains a network of misfit dislocations many of which have curved segments. This indicates that a cross slip mechanism has occurred that is only possible with a perfect dislocation movement. This result supports the nucleation of perfect dislocations in films under a compressive strain. The different structural characteristics of the tensile and compressive systems can play a significant role in subsequent processing or devices made from them.
Optical observation of subbands in amorphous silicon ultrathin single layers
Authors: Hattori K. , Mori T. , Okamoto H. , Hamakawa Y.
Published: July 2002

Wavelength-differential absorption spectroscopy has been applied to amorphous silicon ultrathin single layers. The derivative spectra clearly show a step-like behavior for the layer of the thickness below 40 Å, indicating a splitting of the valence and conduction bands into a series of the subbands. Analysis of the observed energy shifts of subband transitions in terms of a one-dimensional quantum well model leads to the conclusion that the electron effective mass is less than 0.48m0, where m0 denotes free-electron mass.
Solution processes in photoelectrochemical cells
Authors: Winnick J. , Lessner P. M. , McLarnon F. , Cairns E. J.
Published: July 2002

The simplicity of construction of a photoelectrochemical cell (PEC) as compared with solid-state devices, combined with thin-film deposition technology, offers the potential for low-cost direct energy conversion. PEC’s utilizing cadmium chalcogenide photoanodes in alkali polysulfide solutions have shown sustained efficiency of solar-to-electric conversion over 12%. While the composition of the solution has been known for several years to have a remarkable effect on performance, the chemical and electrochemical processes involved remained obscure. We report here the result of a series of quantitative electrochemical experiments which show the species controlling the rate of hole-induced oxidation is disulfide, S2−2, whereas that controlling the reduction at the counterelectrode is the supersulfide ion, S−2, the product of the disulfide oxidation.
Interaction of focused light beams with multilayer films: Optimization of magneto-optic recording media
Authors: Li Z.-M. , Parsons R. R.
Published: July 2002

Reflectance and transmittance of a light beam strongly focused on multilayer thin films are derived at far field. Using the Fourier transfer technique, the reflectance (transmittance) can be expressed in terms of the reflection (transmission) matrix for plane waves. The readout from magneto-optic multilayer films is optimized for a strongly focused beam. It is found that when the focal spot size w0 is less than three wavelengths, the readout is significantly different from that calculated for plane waves.
Infrared fiber optics for thermometry in microwave
Authors: Katzir A. , Bowman F. , Asfour Y. , Zur A. , Valery C. R.
Published: July 2002

Electromagnetic (microwave or radio frequency) field-induced heating is used in industrial, medical, and domestic applications. In most cases, efficient, rapid, and controllable heating is needed. A problem with this heating modality is the difficulty in gaining an accurate measurement of temperature in the presence of a strong electromagnetic field. A simple infrared fiber-radiometer system has been developed for thermometry in the presence of these strong electromagnetic fields. The radiometer was used to measure temperatures in the range 0–70 °C, with an accuracy of ±0.5 °C. The signal obtained varied almost linearly with temperature.
Metallic behavior of lanthanum disilicide
Authors: Long Robert G. , Bost M. C. , Mahan John E.
Published: July 2002

Polycrystalline thin films of LaSi2 were prepared by reaction of sputter-deposited lanthanum layers with silicon wafers. Samples of the low-temperature tetragonal and the high-temperature orthorhombic phases were separately obtained. The room-temperature intrinsic resistivities were 24 and 57 μΩ cm for the low- and high-temperature structures, respectively. Although lanthanum disilicide had been previously reported to be a semiconductor, we find classical metallic behavior for both phases.
Spin-dependent pair generation at Si/SiO2 interfaces
Authors: Vranch R. L. , Henderson B. , Pepper M.
Published: July 2002

We report spin-dependent generation of electron-hole pairs at the Si/SiO2 interface detected via microwave-induced changes in the recombination current through a gate-controlled diode.
High-pressure phases of SiO2 made in air by Fedoseev–Derjaguin laser process
Authors: Alam M. , DebRoy T. , Roy R. , Breval E.
Published: July 2002

Exposure of a falling stream of 1 μm average size α-quartz particles to a continuous wave or pulsed CO2 laser beam in air resulted in the formation of a complete series of high-pressure phases of silica: coesite, stishovite, and apparently even denser forms with α-PbO2 and Fe2N structures. Since the laser exposure technique works with the carbon black to diamond transition, the technique is confirmed as a simple and generally applicable means to achieve the same effects as exposure to several hundred kilobars pressure.
Intrinsically resonant traveling-wave Y-fed directional couplers at high frequency
Authors: Bourbin Y. , Papuchon M. , Enard A. , Werner M. , Moronvalle C.
Published: July 2002

Traveling-wave Y-fed directional couplers are shown to have a high-frequency bandpass response because of the inherent velocity mismatch between the optical and electrical waves. Furthermore, if their characteristic parameters are suitably chosen, it is possible to achieve an intrinsic resonance by using uniform electrodes. These principles are theoretically investigated and experimentally demonstrated at center frequencies up to 8.5 GHz for titanium indiffused in lithium niobate (Ti:LiNbO3 ) waveguides at 1.3 μm wavelength.
Aluminum cladding of high T
c superconductor by thermocompression bonding
Authors: Richardson T. J. , DeJonghe L. C.
Published: July 2002

Thermocompression bonding of aluminum to YBa2Cu3O7−x (YBCO) has been demonstrated. The superconductor is protected by a thin barrier layer of silver. The specific resistivity of the Al/Ag/YBCO interface was measured at 77 K as a function of current density and is below 3.2×10−5 Ω cm2 for electrode current densities of at least 400 A cm−2 . This technique provides a convenient means of cladding bulk superconducting ceramics with a strong, inexpensive, and highly conductive metal.
Bistable spatial light modulator using liquid crystal and Bi12SiO20 crystal layers
Authors: Takizawa Kuniharu , Okada Masakatsu , Kikuchi Hiroshi , Aida Tahito
Published: July 2002

A compact spatial light modulator having optical bistability has been constructed with a twisted nematic liquid-crystal layer, a polarizing film, and a Bi12SiO20 crystal layer. The optical bistability is produced by combining the nonlinear optical transmittance property of the liquid-crystal electro-optic light modulator with the photoconductive property of the Bi12SiO20 crystal layer. The device performs optically bistable operations in a controllable manner, and parallel processing of intensity-level image thresholding is also demonstrated for several threshold levels.
Spatially selective photochemical vapor deposition of GaAs on synthetic fused silica
Authors: Norton D. P. , Ajmera P. K.
Published: July 2002

Photochemical vapor deposition of polycrystalline GaAs on synthetic fused silica is reported here. A Hg-Xe arc lamp is used as the light source with triethylgallium and arsine serving as the reactants. We report, for the first time, on a GaAs deposition process using the above-mentioned light source and reactants which is completely controlled by the light source with no deposition occurring in the absence of light. GaAs thin films of thicknesses up to 1.6 μm have been deposited. X-ray diffraction, energy-dispersive spectrometry, and optical transmittance are used to analyze these films.
Rheological study of a gel-forming precursor for superconducting YBa2Cu3O7−x
Authors: Khan Saad A. , Barboux P. , Bagley B. G. , Tarascon J. M.
Published: July 2002

Rheological measurements are used to monitor the sol-gel behavior of a superconducting precursor. A precursor made with an aged yttrium component [Y(OH)3] has a much higher elastic modulus (G′) and complex viscosity (η*) but the same loss modulus (G″) compared to that made with a fresher yttrium solution. The G″/G′ ratio is less than unity for the older solution but greater than 1 for the fresher sample, indicating that the former solution has a more gel-like character. The high viscosity sample gives better fired thick-film superconducting properties but has a shorter shelf life. Measurements on yttrium components of different age show differences in viscosity and G″/G′ which correlate with the behavior of the oxide precursors. Reshearing the precursor solution at any stage during its gelation process can cause irreversible changes in the gel structure.
Electro-optic switching using total internal reflection by a ferroelectric liquid crystal
Authors: Meadows M. R. , Handschy M. A. , Clark N. A.
Published: July 2002

An electro-optic switch using total internal reflection by a ferroelectric liquid crystal is reported. The device has rise and fall times of about 150 μs, and causes the optical power in the output beam to be attenuated by a factor of 500 000 in the off state. It does not employ polarizers, and its operation is nearly independent of wavelength. The measurements here cover the 400–1600 nm band.
Space-charge-limited current analysis of the leakage current and interface states of GaAs p/n diode solar cells
Authors: Partain L. D. , Liu D. D.
Published: July 2002

GaAs p/n junction solar cells, grown by vapor transport, frequently show a change in efficiency with light concentration that exceeds the predictions of the standard model based on diffusion limited and generation/recombination current-voltage mechanisms. A cell was selected where the efficiency changed from 12 to 22% between 1 and 600 suns concentration or about four times that predicted by the standard model. The dark and light, current-voltage characteristics of this cell were modeled with a trap controlled, space-charge-limited current diode model for the device leakage current. A good fit to the experimental data required a distribution density of electron traps, in the high-resistance p/n junction interface region, on the order of 1018 cm−3  eV−1 with a minimum at 0.4 eV below the conduction-band edge. Since the measured thickness of the high resistance region is 0.1 μm, the equivalent interface state density is on the order of 1013 cm−2  eV−1 .
Characteristics of electron spin resonance in hydrogenated amorphous silicon-carbon/hydrogenated amorphous silicon heterojunctions
Authors: Chen Guanghua , Sun Guosheng , Zhang Fangqing
Published: July 2002

The characteristics of light soaking and equilibrium electron spin resonance (ESR) in p-hydrogenated amorphous silicon-carbon/i-hydrogenated amorphous silicon heterojunction are investigated. The influence of the carbon content in the p layer on ESR is also studied in this letter. We find that the light-induced silicon dangling bond defects mainly originate from the i layer and the increased spin density can be decayed by annealing at a low temperature (160 °C). Possible microscopic mechanisms of the light-induced defects observed in the p/i heterojunction are discussed as well.
Photorefractive waveguides and nonlinear mode coupling effects
Authors: Fischer Baruch , Segev Mordechai
Published: July 2002

Nonlinear photorefractive wave mixing in waveguides provides unusual intermode coupling effects which are independent of the overall light intensities. We present and demonstrate processes in which high-order modes of a guided beam are converted into the low modes (funnel-like) and vice versa (antifunnel-like). We also show capabilities of launching and amplifying a guided beam by pumping the waveguide laterally. Another use of polarization state conversion is discussed.
High repetition rate femtosecond dye amplifier using a laser diode pumped neodymium:YAG laser
Authors: Zysset B. , LaGasse M. J. , Fujimoto J. G. , Kafka J. D.
Published: July 2002

A high repetition rate femtosecond dye amplifier is demonstrated using a laser diode pumped Q-switched Nd:YAG laser. Amplification of wavelength tunable 300 fs pulses from a synchronously mode-locked rhodamine dye laser is achieved with a saturated gain of 70 and a small gain of 200 at a repetition rate of 800 Hz. Maximum pulse energies of 40 nJ are obtained, and pulse compression to as short as 30 fs is demonstrated.
Light-induced changes of gap-state profile in phosphorus-doped hydrogenated amorphous silicon
Authors: Okushi Hideyo , Furui Tatsuya , Banerjee Ratnabali , Tanaka Kazunobu
Published: July 2002

We have determined the gap-state profiles of phosphorus-doped hydrogenated amorphous silicon before and after light soaking in a broader energy range [0.25–1.50 eV below the conduction-band edge (Ec) ] by using several variations of isothermal capacitance transient spectroscopy. It is found that gap states are created in the range of 0.25–0.35 eV below Ec, which are attributed to 31P-related hyperfine electron-spin-resonance centers.
Monolithic integration of GaAs/GaAlAs buried-heterostructure orthogonal facet laser and optical waveguide
Authors: Ribot H. , Sansonetti P. , Brandon J. , Carre M. , Menigaux L. , Azoulay R. , Bouadma N.
Published: July 2002

Monolithic integration of a quarter-circle laser evanescently coupled to an optical waveguide located below the active layer is demonstrated on GaAs. The curved resonator consists of a 45-μm-long straight part and a quarter circle with a curvature radius of 150 μm. The component exhibits a threshold current of 50 mA in a pulsed regime. A 10 mW emission is measured from a 415-μm-long tangential straight waveguide for an injection current of 140 mA.
Sensitivity of direct electro-optic sampling to adjacent signal lines
Authors: Freeman J. L. , Bloom D. M. , Jefferies S. R. , Auld B. A.
Published: July 2002

A nonzero potential at the backside of a GaAs substrate causes errors in direct electro-optic measurements. We examine how the backside potential depends on the arrangement of the frontside conductors for digital-like structures. Ground-to-ground spacing, or conductor pitch, most strongly determines the magnitude of this electro-optic error. A single driven line in a 30 μm pitch array of grounded parallel lines on 20 mil GaAs contributes a backside potential 3% of the applied signal.
Photopumped phonon-assisted laser operation (77 K) of In0.5(AlxGa1−x)0.5P quantum well heterostructures
Authors: Nam D. W. , Holonyak N. , Hsieh K. C. , Kuo C. P. , Fletcher R. M. , Osentowski T. D. , Craford M. G.
Published: July 2002

The photopumped phonon-assisted laser operation (612 nm, 77 K) of a high-gap In1−y(AlxGa1−x)yP quantum well heterostructure (QWH) lattice matched to GaAs (y≊0.5) is identified using a single rectangular sample that is shifted in its heat sinking from (a) low Q when clamped onto Au (bare edges) to (b) high Q when further compressed into Au with all four edges reflecting. For the low-Q QWH sample photopumped in a spot (partially photopumped), phonon-assisted laser operation (abrupt threshold, narrow spectrum) is observed on closely spaced end-to-end laser modes ΔE=ℏωLO≊45–47 meV below the lowest confined-particle transitions. For the same sample shifted to high Q, edge-to-edge laser operation across the sample on confined-particle transitions is ‘‘turned on’’ also, thus providing an unambiguous experimental reference (ℏωLO≊45–47 meV) for the phonon sideband.
Effect of growth conditions on the stability of α-Sn grown on CdTe by molecular beam epitaxy
Authors: Reno J. L. , Stephenson L. L.
Published: July 2002

The effect of growth conditions on the stability of α-Sn films grown by molecular beam epitaxy on CdTe is studied. The growth conditions considered are substrate orientation, thickness, growth rate, and substrate temperature. The transition temperature from α-Sn to β-Sn, as determined by optical microscopy, is used as the measure of stability. It is shown that CdTe(110) is a somewhat better orientation than CdTe(100), and CdTe(111)B is totally unacceptable for the growth by molecular beam epitaxy of α-Sn films. The transition temperature from α-Sn to β-Sn shows a dependence on the total film thickness, with thinner films having a somewhat higher transition temperature than thicker. The quality of the films is the best when the growth rate is about 0.5 Å/s and the growth temperature is about 75 °C. Since the transition from α-Sn to β-Sn starts at defects in the film, improving the quality of the film by lowering the growth rate and raising the growth temperature raises the transition temperature.
Ultralong minority-carrier lifetimes in GaAs grown by low-pressure organometallic vapor phase epitaxy
Authors: Molenkamp L. W. , Kampschöer G. L. M. , de Lange W. , Maes J. W. F. M. , Roksnoer P. J.
Published: July 2002

We have measured minority-carrier lifetimes of up to 4.9 μs in GaAs layers that have been grown by low-pressure organometallic vapor phase epitaxy. These lifetimes, representing a major improvement compared with previously obtained results, are governed by radiative recombination processes. Carbon incorporation during crystal growth at low arsine partial pressures is of prime importance in understanding the origin of these very long lifetimes.
Observation of light-induced defect formation in hydrogenated amorphous silicon by subgap illumination
Authors: Skumanich Andrew , Fathallah Mohamed , Amer Nabil M.
Published: July 2002

The effect of subgap illumination on the formation of light-induced defects in hydrogenated amorphous silicon was investigated using photothermal deflection spectroscopy. As with broadband illumination, an enhancement in the subgap absorption is observed and is related to the silicon dangling bonds. The magnitude of the enhancement varies with the photon energy and with the amount of doping. The results are consistent with the mechanism of recombination of photoexcited electrons with trapped holes producing metastable defects.
Double active region index-guided semiconductor laser
Authors: Chen T. R. , Kajanto M. , Zhuang Yuhua , Yariv A.
Published: July 2002

A buried crescent InGaAsP/InP laser with a double active layer was fabricated. The laser showed very high characteristic temperature T0 and highly nonlinear light versus current characteristics. A theoretical model using a rate equation approach showed good agreement with the experimental results.
Fully adjustable optical limiter for fiber optics using nonlinear silicon films
Authors: Normandin R. , Houghton D. C.
Published: July 2002

A fully adjustable self-limiter and optical clamp in a geometry suitable for use in a fiber optics context is demonstrated. Edge-coupled light into a silicon thin film on a doped silicon substrate lowers the refractive index of the guiding film and eventually brings it to the cutoff condition. Furthermore, by varying the amount of light incident on the nonlinear substrate and the nonlinear film waveguide, a fully adjustable limiting action is obtained. It is shown that absorption effects are not important at power levels compatible with fiber optics, making the limiter highly damage resistant.
Enhanced Schottky barriers produced by recoil implantation of Mg into n-GaAs
Authors: Eizenberg M. , Callegari A. C. , Sadana D. K. , Hovel H. J. , Jackson T. N.
Published: July 2002

Enhancement of Schottky barrier height of Ti-Pt-Au on n-type GaAs was obtained by heavily (2×1018 cm−3) counter doping the near-surface region of the substrate. The p-type region was produced by recoil implantation of Mg from a Mg thin film (300 Å) irradiated by a 60 keV As+ beam. The film was subsequently chemically etched. The recoil-implanted samples showed an enhancement of 140 meV in the Schottky barrier height following rapid thermal annealing in an AsH3 furnace at 850 °C for nominal zero second.