bluuebunny/crossref_metadata_2025 huggingface dataset:
Protein kinases — structure and function
Authors: Bossemeyer Dirk
Published: July 2002

The solution of crystal structures from half a dozen protein kinases during the last four years in different laboratories has deepened our understanding of the catalysis and regulation of this enzyme class, and given a vigorous impetus to the whole field. Due to the great degree of sequence conservation among protein kinases the informational yield with every new structure is high, as each is a representative of the enzyme family in general and most often of a subclass in particular. This review will focus on the active site structure of cAMP‐dependent protein kinase (cAPK) with special regard to two new crystal structures; one of an active protein kinase CK1∗, which may represent an as yet unsolved step in the kinetic pathway, and the other of the insulin receptor kinase domain, the first structure of a tyrosine kinase.
Anti‐apoptotic role of phospholipase D in spontaneous and delayed apoptosis of human neutrophils
Authors: Park Myung-Ae , Lee Min-Jung , Lee Sang-Hwa , Jung Dong-Keun , Kwak Jong-Young
Published: July 2002

Neutrophil apoptosis is a constitutive process that can be enhanced or delayed by signals induced by various stimuli. We investigated the role of phospholipase D (PLD) in neutrophil apoptosis. The apoptotic rate of neutrophils was found to be increased by 1‐butanol and decreased by the exogenous addition of PLD. Moreover, the delay of apoptosis by apoptosis‐delaying stimuli such as granulocyte/macrophage colony‐stimulating factor or lipopolysaccharide (LPS) was also blocked by 1‐butanol. Unstimulated PLD activity in cultured cells for 20 h was higher than that in freshly isolated cells and further increased in cultured cells with LPS. These results suggest that PLD is involved in the up‐regulation of neutrophil survival.
Lexical decision tasks in depressive patients: semantic priming before and after clinical improvement
Authors: Besche-Richard C. , Passerieux C. , Hardy-Baylé M.-C.
Published: July 2002

This study was designed to evaluate the effect of semantic priming with a lexical decision task in 22 depressed patients (DSM-III-R, 1987) and 30 control subjects. These patients were evaluated twice: first when they arrived at the hospital, and secondly, after clinical improvement. Clinical improvement was evaluated using standard depression rating scales. A lexical decision task involving semantic relations (related vs. unrelated, e.g., apple-pear) was used to evaluate the processing of semantic information. The results showed that, for the first evaluation, the depressives presented similar semantic priming to control subjects. When we compared semantic priming in the first and the second passes, we observed that its amplitude was identical. The sole difference between the two passes concerns the global reaction time in the depressive group. This last result suggested that, with clinical improvement, the characteristic psychomotor retardation declines. One of the major results concerns the fact that severe depressive patients (first pass) exhibit normal semantic priming in a lexical decision task. These results indicate, in this clinical population, the preservation of controlled processes implicated in this lexical decision task.
Influence of Water‐Miscible Aprotic Solvents on α‐Chymotrypsin Stability
Authors: Lozano Pedro , de Diego Teresa , Iborra José L.
Published: July 2002

The influence of five different water‐miscible aprotic solvents (dimethyl sulfoxide, dimethylformamide, acetonitrile, acetone, and tetrahydrofuran) on the stability of immobilized α‐chymotrypsin adsorbed onto Celite, has been studied. In all cases, α‐chymotrypsin exhibited non‐first‐order deactivation kinetics, which were adequately analyzed by a two‐step series‐type deactivation model. The main effects of solvents were observed in the first‐step of the kinetic mechanism. The most hydrophilic solvent (DMSO) enhanced greatly the enzyme stability, while the increase in solvent hydrophobicity determines a loss in their protective effect. For the most assayed hydrophobic solvent (THF) a denaturative effect was always showed. These facts were also observed from the analysis of the evolution of the half‐live of the enzyme, as a function of the solvent concentrations and the water distribution between both the macro‐ and microenvironment of the enzyme.
Effect of Cell Morphology on Dead‐End Filtration of the Dimorphic Yeast Kluyveromycesmarxianus Var. marxianus NRRLy2415
Authors: McCarthy Anthony A. , O'Shea Donal G. , Murray Niamh T. , Walsh Padraig K. , Foley Greg
Published: July 2002

The dead‐end filtration characteristics of the dimorphic yeast Kluyveromyces marxianus var. marxianus (formerly fragilis) NRRLy2415 were investigated for a range of mean cell morphologies, ranging from predominantly yeast‐like to predominantly filamentous. Semiautomated image analysis was used to measure the mean cell specific surface area, Sv, and the mean ratio of cell length to equivalent cylindrical diameter, Ldm, in each broth. The method of Ju and Ho (Biotechnol. Bioeng. 1988, 32, 95–99) was used to show that for broths with Ldm values between 1.72 and 10.03, the voidage of cell pellets formed by centrifugation increased with increasing Ldm. In the pressure range 30–180 kPa, the specific filter cake resistance, α, was found to be related to pressure, ΔP, through the equation α = α0(1 + kcΔP) . The dependence of α0/Sv2 on Ldm was found to be qualitatively consistent with the pellet voidage data and the Carman−Kozeny equation. Considerably better agreement with the experimental data was obtained when the Kozeny constant, K, was treated as variable and related to Ldm through the equation K = 4.83 + 7.08 log10 Ldm. The cake compressibility constant, kc, was found to increase with increasing Ldm, a phenomenon consistent with the wide range of voidages that can be displayed by beds of long cylinders.
Detection of Fel d 1–immunoglobulin G immune complexes in cord blood and sera from allergic and non‐allergic mothers
Authors: Casas Rosaura , Björkstén Bengt
Published: July 2002

It is an established fact that T‐cell responses of fetal origin to inhalant allergens are present in most cord blood samples. These immune responses could be explained by trans‐placental passage of peptides, either as free antigens or in complexes with immunoglobulin G (IgG), providing the fetus with a trigger for priming the T‐cell system already present in utero. The aim of this study was to investigate the presence of the major cat allergen, Fel d 1, in complexes with IgG in cord blood and maternal sera. Serum samples from 75 mothers (38 allergic, 37 non‐allergic), and cord blood from their infants, were investigated for the presence of Fel d 1–IgG immune complexes (ICs) by using an amplified enzyme‐linked immunosorbent assay (ELISA). Three monoclonal antibodies to Fel d 1 were used for coating. The specificity of the method was confirmed by inhibition experiments. ICs of Fel d 1–IgG were detected in the sera of 45% allergic and 49% non‐allergic mothers, and in, respectively, 34% and 41% of their infants. Therefore, neither the prevalence nor the level of ICs were affected by maternal allergy. Low levels of trans‐placentally transferred ICs can provide the fetus with a signal for the priming of T‐cell responses to inhalant allergens. However, this is not necessarily related to allergic disease.
Hypoxia/reoxygenation induction of monocyte chemoattractant protein-1 in melanoma cells: involvement of nuclear factor-κB, stimulatory protein-1 transcription factors and mitogen-activated protein kinase pathways
Authors: KUNZ Manfred , BLOSS Gisela , GILLITZER Reinhard , GROSS Gerd , GOEBELER Matthias , RAPP Ulf. R. , LUDWIG Stephan
Published: July 2002

Monocyte chemoattractant protein-1 (MCP-1) expression is found in malignant melanoma and melanoma metastases. Since areas of hypoxia/reoxygenation (H/R) are a common feature of malignant tumours and metastases, we addressed the question whether melanoma cells produce MCP-1 upon exposure to H/R. In the present study, we show that melanoma cells up-regulate MCP-1 mRNA and protein under H/R. By means of reporter gene analysis, we further demonstrate that H/R induces transcriptional activation of the MCP-1 promoter carrying a stimulatory protein-1 (SP1) and two nuclear factor-κB (NF-κB) binding motifs. Accordingly, H/R-stimulated melanoma cells showed enhanced binding activity of both transcription factors NF-κB and SP1 in electrophoretic mobility-shift assay. A common upstream activator of NF-κB, inhibitory κBα kinase, was not significantly activated under H/R conditions. Further analysis of upstream signalling events revealed that members of the mitogen-activated protein kinases family, namely extracellular signal-regulated protein kinase, c-Jun N-terminal kinase/ stress-activated protein kinase and p38 stress kinase, may be involved in MCP-1 transcriptional regulation under H/R. In summary, we conclude that H/R induces MCP-1 production in melanoma cells via the co-operative action of both transcription factors NF-κB and SP1, and involves mitogen-activated protein kinase signalling pathways. Functionally, H/R-induced MCP-1 production may contribute to tumour progression by committing selective pressure on tumour cells via chemoattraction and activation of tumour-infiltrating monocytes/macrophages.
Changing expectations: the impact of ‘child protection’ on Irish social work
Authors: Walsh T.
Published: July 2002

In this paper, the author (who has worked as a social worker in both Ireland and the UK) contends that there has been an uncritical importation of expectations and responsibilities from the British system into Irish state social work. In the area of child and family social work this has been most marked by the introduction and construction of ‘child protection’ as the dominant discourse. Yet fundamental differences exist between Irish and British social policy, differences that are reflected in the structure, nature and culture of social work services. Some of the historical differences between the two welfare systems are explored and three core features of modern Irish social work with children and families are identified. Possibilities for recreating Irish social work in discourse and in practice are suggested, particularly around the notions of certainty/uncertainty and the potential for linguistically based frameworks for practice.
Four‐dimensional factor analysis of confocal image sequences (4D‐FAMIS) to detect and characterize low copy numbers of human papillomavirus DNA by FISH in HeLa and SiHa cells
Authors: KAHN E. , LIZARD G. , PÉLÉGRINI M. , FROUIN F. , ROIGNOT P. , CHARDONNET Y. , DI PAOLA R.
Published: July 2002

Visualization and localization of specific DNA sequences were performed by fluorescence in situ hybridization, confocal laser scanning microscopy (CLSM), and four‐dimensional factor analysis of biomedical image sequences (4D‐FAMIS). HeLa and SiHa cells containing, respectively 20–50 and 1–2 copies per cell of human papillomavirus (HPV) DNA type 18 and 16 integrated in cellular DNA were used as models. HPV‐DNA was identified using DNA probes containing the whole genome of HPV‐DNA type 18 or 16, and DNA–DNA hybrids were revealed by alkaline phosphatase and Fast Red. Cell nuclei were counterstained with thiazole orange (TO) or TOTO‐iodide. 4D image sequences were obtained using successive dynamic or spectral sequences of images on different optical sections from CLSM. The location of fluorescent signals within the preparations was determined by FAMIS. This original method summarizes image sequences into a reduced number of images called factor images, and curves called factors. Factors estimate different individual physical behaviours in the sequence such as extinction velocity, spectral patterns and depth emission profiles. Factor images correspond to spatial distributions of the different factors. We distinguished between Fast Red and nucleus stainings in HPV‐DNA hybridization signals by taking into account differences in their extinction velocities (fluorescence decay rate) or spectral patterns, and in their focus (depth emission profiles). In HeLa cells, factor images showed that Fast‐Red‐stained targets could be distinguished from nucleus stainings, and were located on different focal planes of the nuclei. In SiHa cells, 4D‐FAMIS determined as few as 1–2 copies per cell of HPV‐DNA type 16 located in continuous focal planes. Therefore, 4D‐FAMIS, together with CLSM, made the detection and characterization of low copy numbers of genes in whole cells possible.
Chagasic patients develop a type 1 immune response to Trypanosoma cruzi trans‐sialidase
Authors: Ribeirao Marcelo , Lücia Vera , Ferguson Pereira‐Chioccola , Rénia Laurent , Fragata Filho Abílio Augusto , Schenkman Sergio , M,Rodrigues Mauricio
Published: July 2002

Infective forms of Trypanosoma cruzi, the parasite that causes Chagas’ disease, express on their surface an enzyme denominated trans‐sialidase (TS). The present study was designed to evaluate the naturally acquired immune responses to a bacterial recombinant protein representing the catalytic domain of TS in chronically infected chagasic individuals. The cellular immune response was measured by in‐vitro T‐cell proliferation and by interferon (INF)‐g, interleukin (IL)‐4 and IL‐10 production in response to a whole‐parasite homogenate and the recombinant protein. The peripheral blood mononuclear cells of 78·6% of 28 chagasic patients responded to the recombinant protein as estimated by T‐cell proliferation. With respect to cytokine production, 88% of the cells of the chagasic individuals produced IFN‐g on stimulation with the recombinant protein. In contrast, IL‐4 or IL‐10 were minimally produced in response to TS. The cellular immune response was specific because most healthy individuals never exposed to T. cruzi failed to react with this recombinant protein. The plasma of 71·4% or 100% of chagasic patients had IgG antibodies as determined by ELISA or by the presence of TS inhibitory antibodies, respectively. We conclude that the catalytic domain of TS is recognized by IFN‐g producing type 1 cells and antibodies in a large proportion of patients infected with T. cruzi.
JOINT‐PRESERVING OPERATION FOR OSTEOARTHROSIS OF THE HIP IN ADULT CEREBRAL PALSY
Authors: Nishioka Eiji , Momota Kou , Shiba Naoto , Higuchi Fujio , Inoue Akio
Published: July 2002

Background: A joint‐preserving operation was performed on 15 hips with osteoarthrosis, involving 12 patients who had adult cerebral palsy.

Methods: Eleven hips underwent Chiari pelvic osteotomy only; three hips underwent Chiari pelvic osteotomy with femoral osteotomy and the other one hip underwent femoral varus osteotomy only. The mean follow‐up period after surgery was 6 years and 2 months (with follow‐up range of 2 years and 3 months to 10 years and 6 months).

Results: Good results were achieved in 13 of the 15 hips (86.6%). Two patients with athetotic tetraplegia treated with Chiari pelvic osteotomy had pelvic obliquity. Progressive osteoarthrotic change continued in bilateral hips in one case treated with Chiari pelvic osteotomy.

Conclusion: We confirm that usual treatment for osteoarthrosis of the hip was also applicable for osteoarthrosis of the hip in cases of adult cerebral palsy, provided sufficient attention is given to the complications accompanying spastic paralysis.
Are babies of normal birth weight who fail to reach their growth potential as diagnosed by ultrasound at increased risk?
Authors: Stratton J. F. , Ni Scanaill S. , Stuart B. , Turner M. J.
Published: July 2002

The objectives of this study were to identify, by means of two third‐ trimester scans, fetuses with ultrasound evidence of inadequate growth but who were born with birth weights above the 10th centile for gestational age; and to determine if these infants constitute a high‐risk group by comparing the incidence of obstetric intervention, of intrapartum complications and of neonatal morbidity between this group and the group of infants who showed no ultrasound evidence of intrauterine growth restraint.

A total of 285 women with singleton pregnancies who were referred for a third‐trimester ultrasound examination were included in this prospective study. Fetal weight was estimated by ultrasound twice in the third trimester and at each examination was assigned a centile score. A fall of > 20 centiles was taken as evidence of inadequate growth. The outcomes measured were the incidence of abnormal umbilical artery Doppler, induction of labor, meconium‐staining of the liquor, intrapartum fetal blood sampling, operative vaginal delivery, Cesarean section, Apgar score of < 7 at 5 min and admission to the neonatal intensive care unit.

Seventy‐five patients showed a drop of > 20 centiles between the first and second scans. The incidence of admission to the neonatal intensive care unit was greater in those infants who had ultrasound evidence of growth restraint.

We conclude that infants of normal birth weight with inadequate growth diagnosed on ultrasound are not at increased risk, they have an increased incidence of admission to the neonatal intensive care unit, and they are more commonly found in mothers with diabetes mellitus. Copyright © 1995 International Society of Ultrasound in Obstetrics and Gynecology
Repeatability of measurements of interpupillary distance
Authors: Holland Belinda J. , Siderov John
Published: July 2002

The purpose of this study was to determine inter‐ and intra‐examiner repeatability of measurements of interpupillary distance (IPD). Three methods were used: Viktorin’s, corneal reflection, and pupillometer. In Experiment 1, an experienced optometrist measured IPD on forty‐nine subjects, on two occasions, using each method. In Experiment 2, thirty‐five optometrists measured the IPD of one subject, on one occasion only, using the same three methods. The results of Experiment 1 showed that measurements of IPD differed depending on the method used, although the differences were small. The 95% limits of agreement were largest with Viktorin’s method and least with the pupillometer. The results of Experiment 2 also revealed a small difference in IPD between the three methods of measurement. As in Experiment 1, the 95% limits of agreement were greatest with Viktorin’s method and least with the pupillometer. Small differences in IPD were found between Viktorin’s, corneal reflection and pupillometer methods of measurement. Not surprisingly, inter‐examiner repeatability was slightly poorer than intra‐examiner repeatability. However, the differences were small enough not to be clinically significant for the majority of patients.
Environmental and Evolutionary Preconditionsfor the Origin and Diversification of the C4 PhotosyntheticSyndrome
Authors: Sage R. F.
Published: July 2002

Abstract: C4 photosynthesis is an evolutionary solution to high rates of photorespiration and low kinetic efficiency of Rubisco in CO2‐depleted atmospheres of recent geologic time. About 7500 plant species are C4, in contrast to 30 000 CAM and 250 000 C3 species. All C4 plants occur in approximately 90 genera from 18 angiosperm families. In all of these families, the C4 pathway evolved independently. In many, multiple independent origins have occurred, such that over 30 distinct evolutionary origins of the C4 pathway are recognized. Fossil and carbon isotope evidence show that the C4 syndrome is at least 12 to 15 million years old, although estimates based on molecular sequence comparisons indicate it is over 20 million years old. The evolutionary radiation of herbaceous angiosperms may have been required for C4 plant evolution. All C4 species occur in advanced angiosperm families that appeared in the fossil record in the past 70 million years. Most of these families diversified in terms of genera and species numbers between 20 to 40 million years ago, during a period of global cooling, atmospheric CO2 reduction and aridification. During the period of diversification, numerous traits arose in the C3 flora that enhanced their performance in arid environments and atmospheres of reduced CO2. Some of these traits may have predisposed certain taxa to develop the C4 pathway once atmospheric CO2 levels declined to a point where the ability to concentrate CO2 had a selective advantage. Leading traits in C3 plants that may have facilitated the initial transition to C4 photosynthesis include close vein spacing and an enlargement of the bundle sheath cell layer to form a Kranz‐like anatomy. Ecological factors not directly connected with photosynthesis probably also played a role. For example, extensive ecological disturbance may have been needed to convert C3‐dominated woodlands into open, high‐light habitats where herbaceous C4 plants could succeed. Disturbances in the form of fire, and browsing by large mammals, increase during the time of C4 plant evolution and diversification. Fire increased because of the drying climate, while browsing increased with the evolutionary diversification of the mammalian megafauna in the Oligocene and Miocene epochs. In summary, the origin of C4 plants is hypothesized to have resulted from a novel combination of environmental and phylogenetic developments that, for the first time, established the preconditions required for C4 plant evolution.
Optical nonlinearities induced by thermal effects in polymer dispersed liquid crystals
Authors: Simoni F. , Cipparrone G. , Umeton C. , Arabia G. , Chidichimo G.
Published: July 2002

The first experimental observation of strong optical nonlinearities induced by a laser field in polymer dispersed liquid crystals is reported. The measured rise time of the effect agrees with the interpretation of a thermal origin of the phenomenon.
Quantum wires in InGaAs/InP fabricated by holographic photolithography
Authors: Miller B. I. , Shahar A. , Koren U. , Corvini P. J.
Published: July 2002

Quantum wires ≊300–400 Å wide were fabricated by holographic photolithography from a wafer having a single 100 Å InGaAs quantum well. The wires were then recoated with InP using atmospheric pressure organometallic vapor phase epitaxy, which resulted in a planar surface. A high-resolution scanning electron microscope showed little deterioration of the wires due to recoating. At moderate intensities ≊10 W/cm2, photoluminescence (PL) studies showed a small shift in energy (≊6 meV) and a slight line narrowing consistent with a one-dimensional structure. The quantum efficiency of the wires was comparable to the control wafer—above that expected from the fill factor of 17%. Some evidence of states below the energy gap is seen at low PL excitation, but these appear to saturate at higher excitations.
A 27.3% efficient Ga0.5In0.5P/GaAs tandem solar cell
Authors: Olson J. M. , Kurtz S. R. , Kibbler A. E. , Faine P.
Published: July 2002

A two-terminal, monolithic cascade solar cell with an efficiency of 27.3% is reported. The device structure consists of a Ga0.5In0.5P homojunction grown epitaxially upon a GaAs homojunction, with a GaAs tunnel diode interconnect. The tandem combination of these two materials is lattice matched, and has a theoretical efficiency of 34%. The device was grown by metalorganic chemical vapor deposition at 700 °C, using trimethylgallium, trimethylindium, arsine, and phosphine as sources. The minority-carrier transport properties of the Ga0.5In0.5P are shown to be relatively insensitive to variations of the growth temperature and phosphine overpressure. Other factors that affect the efficiency of the device are presented and discussed.
Large room-temperature magneto-optical Kerr effect in CuCr2Se4
Authors: Brändle H. , Schoenes J. , Wachter P. , Hulliger F. , Reim W.
Published: July 2002

The magneto-optical polar Kerr effect has been measured on CuCr2Se4 single crystals between 0.55 and 5.0 eV. The single Kerr ellipticity εK reaches −1.19° at 0.96 eV which is (besides PtMnSb with θK=−1.27° at 1.72 eV) the highest value ever observed at room temperature. The figure of merit R1/2(θ2K + ε2K)1/2 has a maximum value of 0.84° at 0.88 eV which is as high as in PtMnSb (0.83° at 1.57 eV). This large magneto-optical Kerr effect is due to the steep plasma edge observed in the reflectivity R. First experiments show that the photon energy at which the plasma edge occurs can be shifted by suitable substitutions in CuCr2Se4.
Self-propagating explosive reactions in Al/Ni multilayer thin films
Authors: Ma E. , Thompson C. V. , Clevenger L. A. , Tu K. N.
Published: July 2002

Self-propagating explosive reactions, with a reaction front speed of about 4 m/s, have been observed in free-standing polycrystalline Al/Ni multilayer thin films. The resultant phases and microstructures are compared with those obtained by conventional thermal annealing. We show evidence which indicates that melting occurred in the explosive reactions of films with an atomic concentration ratio of 3Al:1Ni. It is also observed that the propensity of multilayer films to undergo explosive reactions is dependent on the modulation length of the film as well as on the ambient temperature. These observations are interpreted with a simple model based on the rate balance between the rates of heat generation and heat dissipation.
Observation of avalanche propagation by multiplication assisted diffusion in p-n junctions
Authors: Lacaita A. , Mastrapasqua M. , Ghioni M. , Vanoli S.
Published: July 2002

We have investigated for the first time the propagation of the avalanche multiplication over the area of p-n junctions reverse biased above the breakdown voltage. The multiplication process spreads from the point where the avalanche is triggered to the whole junction area with a speed proportional to the final steady-state value of the avalanche current. The values of the propagation speed suggest that the phenomenon is due to diffusion of carriers assisted by avalanche multiplication. This effect strongly affects the rise of the avalanche current and turns out to limit the performance of single photon avalanche diodes.
Novel all-optical 10 μm waveguide modulator based on intersubband absorption in GaAs/AlGaAs quantum wells
Authors: Julien F. H. , Vagos P. , Lourtioz J.-M. , Yang D. D. , Planel R.
Published: July 2002

Efficient all-optical modulation of mid-infrared radiations based on photoinduced intersubband absorption of a GaAs/AlGaAs multiquantum well structure is demonstrated at room temperature. The sample designed for mid-infrared waveguiding was grown by molecular beam epitaxy. A double-resonance spectroscopy of both interband and intersubband transitions of the quantum wells is presented. The intersubband resonance is found at 9.56 μm. An AlGaAs laser diode is used to optically pump the quantum wells. On/off modulation ratios as high as 150:1 are obtained with only 45 mW pump power and for mid-infrared input powers up to 0.5 W. The frequency bandwidth of the device is presently comparable to that of acousto-optic modulators available at mid-infrared wavelengths.
Photoluminescence of InGaN films grown at high temperature by metalorganic vapor phase epitaxy
Authors: Yoshimoto N. , Matsuoka T. , Sasaki T. , Katsui A.
Published: July 2002

InGaN single-crystal films were grown on (0001) plane sapphire substrates at 800 °C by metalorganic vapor phase epitaxy. By using such a high temperature for growth, the crystalline quality has been greatly improved. But a high nitrogen over pressure and high indium source flow rate were necessary to achieve significant indium incorporation during growth. For the first time, photoluminescence has been observed in InGaN, and near-band edge emission is seen in the photoluminescence at 77 K. From this photoluminescence, the dependence of a near-band edge emission on the indium mole fraction of InGaN has been investigated.
Creation of 45° grain-boundary junctions by lattice engineering
Authors: Wu X. D. , Luo L. , Muenchausen R. E. , Springer K. N. , Foltyn S.
Published: July 2002

The in-plane, orientational relationships between LaAlO3, SrTiO3, yttria-stabilized zirconia, MgO, CeO2, BaZrO3, and YBa2Cu3O7−δ(YBCO) are studied. Using a idea of continuous lattice match and photolithographic technique, a 45° YBCO grain-boundary junction can be created on most substrates. The key element of the process is the utilization of a bridge layer. In addition to MgO bridge material, BaZrO3 was found to work functionally well. The crystallinity of the bridge layer is critical to obtain a clean boundary junction.
Laser performance of Cr4+:Y2SiO5
Authors: Deka C. , Chai B. H. T. , Shimony Y. , Zhang X. X. , Munin E. , Bass M.
Published: July 2002

Laser action in Cr4+ doped yttrium-orthosilicate Cr4+:Y2SiO5 cooled to 77 K was demonstrated for the first time with 1064 and 532 nm pumping from a pulsed Nd:YAG laser and broad band (@ 840 nm) pumping from a Q-switched Cr:LiSAF laser.
New oxide phase with wide band gap and high electroconductivity, MgIn2O4
Authors: Ueda Naoyuki , Omata Takahisa , Hikuma Naoko , Ueda Kazushige , Mizoguchi Hiroshi , Hashimoto Takuya , Kawazoe Hiroshi
Published: July 2002

It was demonstrated that the MgIn2O4 spinel is a very promising material as a transparent electronic conductor. By the measurements of diffuse reflectance spectra, the optical band gap of MgIn2O4 (∼3.4 eV) was found to be wider than that of ITO (indium tin oxide). Electrical conductivity of the sintered sample of MgIn2O4 at room temperature has reached almost 102 S cm−1 with no intentional doping. The conduction was found to be due to electrons introduced from oxygen vacancies.
Large electric field effects in YBa2Cu3O7−δ films containing weak links
Authors: Mannhart J. , Ströbel J. , Bednorz J. G. , Gerber Ch.
Published: July 2002

The influence of applied electric fields on the transport properties of weak links in YBa2Cu3O7−δ films has been investigated. It is found that the critical temperature Tc0 of epitaxial films containing weak links can be reduced by 10 K with applied electric fields of 6 MV/cm. In one case, Tc0 shifts of up to 25–30 K were observed. These are by far the largest Tc shifts reported for any superconducting system.
Filament formation in a tapered GaAlAs optical amplifier
Authors: Goldberg Lew , Surette Marc R. , Mehuys David
Published: July 2002

Filament formation in a tapered GaAlAs amplifier with an output width of 320 μm is characterized by injecting an input beam with a superimposed sinusoidal intensity modulation (30 μm period, 30% peak-to-peak modulation). Strong seeded filamentation of the output near field, and large far field side lobes are observed for powers above approximately 1 W. Time dependent decay of the main far field lobe, characterized by a time constant of several microseconds, is used to separate the effects of localized carrier density variations from the thermal contribution to intensity and phase distortion of the output beam.
Reactive ion etching of gallium nitride in silicon tetrachloride plasmasa)
Authors: Adesida I. , Mahajan A. , Andideh E. , Khan M. Asif , Olsen D. T. , Kuznia J. N.
Published: July 2002

The reactive ion etching characteristics of gallium nitride (GaN) in silicon tetrachloride plasmas (SiCl4, 1:1/SiCl4:Ar, and 1:1/SiCl4:SiF4) in the pressure range between 20 and 80 mTorr have been investigated. For the pressure range investigated, etch rates are found to be essentially identical for the different gas mixtures and also invariant with pressure. However for all gas mixtures, etch rates increased monotonically with increasing plasma self-bias voltage exceeding 50 nm/min at 400 V. This is one of the highest etch rate ever reported for GaN. Smooth and anisotropic etch profiles are demonstrated for structures of submicrometer dimensions. The slight overcut observed in the etch profiles is attributed to the significant role of physical ion bombardment in the etching mechanism. Auger electron spectroscopy show that a wet etch in dilute HF is needed to clear the Si (in the form of SiOx) embedded in the near surface of GaN during etching thereby restoring etched surfaces to their virgin state.
Nonlinear optical and electro-optical properties of single crystal CsTiOAsO4
Authors: Cheng L. T. , Cheng L. K. , Bierlein J. D. , Zumsteg F. C.
Published: July 2002

We report the development of a new nonlinear optical crystal CsTiOAsO4 (CTA). The relatively large cesium ion leads to a structural instability in the orthorhombic structure, which significantly affects its crystal growth properties. Modification of the crystal growth process, however, allows the growth of large inclusion-free single crystals measuring up to 30×20×25 mm3. The refractive indices, nonlinear optical coefficients, electro-optic coefficients, and dielectric properties of these crystals were measured using standard techniques. Compared to KTiOPO4, CTA has a smaller birefringence which makes it particularly suitable for frequency doubling Nd:YAG lasers operating near 1.32 μm. We also report the ferroelectric poling of multidomain CTA crystals and discuss possible extension of this poling process to other KTP isomorphs.
p-type gallium nitride by reactive ion-beam molecular beam epitaxy with ion implantation, diffusion, or coevaporation of Mg
Authors: Rubin M. , Newman N. , Chan J. S. , Fu T. C. , Ross J. T.
Published: July 2002

Gallium nitride is one of the most promising materials for ultraviolet and blue light-emitting diodes and lasers. The principal technical problem that limits device applications has been achieving controllable p-type doping. Molecular beam epitaxy assisted by a nitrogen ion beam produced p-type GaN when doped via ion implantation, diffusion, or coevaporation of Mg. Nearly intrinsic p-type material was also produced without intentional doping, exhibiting hole carrier concentrations of 5×1011 cm−3 and hole mobilities of over 400 cm2/V/s at 250 K. This value for the hole mobility is an order of magnitude greater than previously reported.
Fabrication of single-crystal diamond microcomponents
Authors: Hunn John D. , Withrow S. P. , White C. W. , Clausing R. E. , Heatherly L. , Christensen C. Paul
Published: July 2002

We have combined a technique for the lift-off of thin diamond films from a bulk diamond with a technique for engraving diamond with a focused excimer laser to produce free-standing single-crystal diamond microstructures. One microcomponent that has been produced is a 12 tooth gear ∼400 μm in diameter and ∼13 μm thick. Other microstructures have also been demonstrated, showing the versatility of this method. This process should be applicable to producing diamond microcomponents down to spatial dimensions (width and thickness) of a few micrometers.
Langmuir probe technique for plasma parameter measurement in a medium density discharge
Authors: Hopkins M. B. , Graham W. G.
Published: July 2002

The development of a microcomputer-controlled electrostatic probe as a diagnostic technique is described. The technique uses cylindrical probes and the definitive theory of Laframboise to give rapid measurements of the plasma parameters in a medium density (1010 to 1012 cm−3) plasma including the fast electron density and temperature. The iterative technique described overcomes many of the problems associated with established methods of Langmuir probe analysis.
Effects of a magnetic field on hot electron transport in quantum wires
Authors: Telang N. , Bandyopadhyay S.
Published: July 2002

We have performed Monte Carlo simulation of electron magnetotransport in a GaAs quantum wire at 77 and 300 K. At sufficiently high electric fields, a magnetic field was found to enhance the electron drift velocity significantly by preferentially suppressing backscattering events. Moreover, the field also decreases the electron temperature (suppressing it well below the lattice temperature at 300 K over a wide range of electric field) which reduces Johnson noise. Surprisingly, the electron temperature is lower at a lattice temperature of 300 K than at a lattice temperature of 77 K when a magnetic field is present. All of these have important implications for the transconductance, unity gain frequency and noise margin of quasi-one-dimensional electronic devices such as quantum wire field effect transistors.
Ultrasmall scanning tunneling microscope for use in a liquid-helium storage Dewar
Authors: Smith Douglas P. E. , Binnig Gerd
Published: July 2002

We describe a scanning tunneling microscope which is extremely compact and rigid. Neither springs nor stacks of metal plates and rubber are necessary for vibration isolation. It can resolve the atomic structure of graphite at room and liquid-helium temperatures. Its small size permits it to be dipped into a standard liquid-helium storage Dewar.
Mössbauer study of the (Fe1−xNix)4N compounds (0≤x≤0.6)
Authors: Li Fashen , Yang Jinbo , Xue Desheng , Zhou Rongjie
Published: July 2002

Single phase γ′-Fe4N type (Fe1−xNix)4N compounds (0≤x≤0.6) have been synthesized by heating iron-nickel oxalates under a mixture stream of NH3 and H2. The compounds were investigated by x-ray diffraction and Mössbauer spectroscopy. The results confirm that the lattice constants decrease with increasing content of nickel. Compared with the same compositional Fe1−xNix alloys, the average expansion of the unit cell (δV/V) is 16.7% for γ-Fe-Ni alloys. The Mössbauer study shows that the substitution of nickel atoms for iron atoms has a tendency to locate at the corner sites. When x=0.5, all of the corner sites are completely occupied by nickel atoms.
Miniaturization techniques for obtaining static pressures comparable to the pressure at the center of the earth: X-ray diffraction at 416 GPa
Authors: Ruoff Arthur L. , Xia Hui , Luo Huan , Vohra Yogesh K.
Published: July 2002

X-ray diffraction studies on tungsten and molybdenum were performed, using a 4-μm-diam x-ray beam, to very high pressures, with the pressures being obtained from the measured lattice parameters and isothermal equations of state of tungsten and molybdenum deduced from shock data. The bcc structure persists to the highest pressure, 378 GPa in tungsten, and 416 GPa in molybdenum. The static pressures generated and measured here exceed the pressure of 361 GPa at the center of the earth, the first time that this has been achieved and measured with a calibrated pressure scale. The details of the pressure profile at 335 GPa are shown and are of great use in designing anvils for future research. It is noted that the maximum pressures attained by x-ray diffraction with beveled anvils varies linearly with D−1/2 where D is the diameter of the flat suggesting that, perhaps, even higher pressures are possible with further miniaturization. A scaling law is used to calculate the minimum correction due to the presence of nonhydrostatic stress.
Scanning x-ray microscopy using a laser-plasma source
Authors: Michette A. G. , Turcu I. C. E. , Schulz M. S. , Browne M. T. , Morrison G. R. , Fluck P. , Buckley C. J. , Foster G. F.
Published: July 2002

Previously high-resolution soft x-ray microscopy has only been possible with synchrotron sources. Here, the first successful attempts at using a scanning transmission x-ray microscope with a laser-plasma source are reported. Spatial resolutions were limited to about 650 nm by electrical noise in the detector, but single shot per pixel images were obtained of test and real specimens. The microscope was not optimized to the source since it was designed for use on the undulator beam line of a synchrotron. With an improved system, it is demonstrated that single shot per pixel imaging at high resolution (better than 50 nm) will routinely be possible.
Comparison of enthalpy probe and laser light scattering measurement of thermal plasma temperatures and velocities
Authors: Fincke J. R. , Snyder S. C. , Swank W. D.
Published: July 2002

Gas temperature and velocity profiles in argon thermal plasmas, measured by an enthalpy probe and high spectral resolution laser light scattering, are compared. In the laser scattering measurement the plasma temperature and velocity are determined directly from high-resolution Doppler-shifted line-shape analysis of light scattered by the plasma. The technique yields an unambiguous determination of gas or kinetic temperature without the assumption of local thermodynamic equilibrium. Velocity is determined directly from the measured Doppler shift. The enthalpy probe is a combination Pitot tube and flowing calorimeter. The assumption of thermodynamic equilibrium is required to obtain velocity and temperature from measured enthalpy and stagnation pressure. Peak temperature and velocity values observed were ∼13 000 K and 1300 m s−1. The results from both the intrusive enthalpy probe and nonintrusive laser light scattering technique compare favorably. The limitations of both techniques are discussed.
New technique for compact discharge electrodes design
Authors: Flora F. , Mezi L.
Published: July 2002

An analytical technique, based on a generalization of the Stappaerts method which takes into account asymmetry elements, is proposed for discharge electrodes designing. In particular, compact electrode profiles are proposed for laser cells with current return bars and for double-head lasers.
Crossatron-based modulator for high repetition rate operation with arbitrary pulse widths
Authors: Mathew J.
Published: July 2002

This article describes a Crossatron-based modulator for driving 10–1000 μs duration plasma discharges. The modulator has demonstrated burst mode operation at pulse repetition rates of 50 kHz. Insulated gate bipolar transistors (IGBTs) are used to trigger the Crossatron. The pulse width of each individual pulse in a burst can be varied over a large range. A Jorway 221 timing and sequencing module command triggers the modulator, and a Labview-based program is used to control the timing module via a GPIB bus. The modulator can output 25 kV pulses at 100 A. It can also operate at 10% duty cycle with peak currents of 10–20 A.
Development of a centrifuge ball viscometer for polymer melts
Authors: Linliu Kung , Yeh Fengji , Shook Jeffrey W. , Tuminello William H. , Chu Benjamin
Published: July 2002

A centrifuge ball viscometer was developed for fluids with a wide viscosity range. The viscosity η could be obtained from an empirically derived relationship ac=b(ηV∞)c, where ac is the applied acceleration, b and c are empirically determined parameters, and V∞ is the terminal velocity. The key features of this viscometer are as follows. (1) A wide range of viscosities can be accommodated: about 10−1 to 105 Pa s with 1010 Pa s achievable, in principle, for about a one-data point per day measurement. (2) A computer controlled motion controller allows rotation speed of the motor varying over a speed of 1 to 5000 (±0.01) RPM (revolutions per minute). Thus, measurements at different low shear rates can be accomplished. (3) About 0.5 ml of sample volume is needed for the present setup. (4) The temperature can be maintained from ambient to over 400 °C (±0.05 °C). (5) The samples are isolated by sealing them in glass tubes, a potential advantage when dealing with polymer solutions, polymer melts, and/or those systems subject to oxidative degradation.
A blow-down combustion bomb for engine in-cylinder kinetics research
Authors: Linne M. A. , Mackay R. K. , Bahn W. L.
Published: July 2002

In order to conduct chemical kinetic investigations under piston engine like conditions, a combustion bomb which emulates the pressure rise and decay within a piston engine cylinder has been designed and built. This allows one to investigate chemical kinetics in a realistic pressure-time burst, without the complication of turbulent mixing. While phenomena like flame speed and heat release depend much more strongly upon fluid mechanics, emissions formation and removal depend strongly upon chemical kinetics. Typical problems of interest include soot oxidation during the pressure decay, coupling of emissions-related chemical kinetic pathways for various components of reformulated fuel mixtures, investigation of toxics formation, and development of reduced kinetic mechanisms for engine codes which include chemical submodels. Here, the device and the processes by which it works, experimental data and a modified two-zone thermodynamic model by which one can infer temperatures, volumes, and mass fractions are described. Combined results from experiments and the model indicate that the BDCB produces an excellent imitation of an internal combustion (IC) engine pressure-time burst. Moreover, this device exhibits better cycle-to-cycle reproducibility than research engines, and it allows for unimpeded optical access and rapid sampling.
Piezoresistive cantilevers utilized for scanning tunneling and scanning force microscope in ultrahigh vacuum
Authors: Giessibl F. J. , Trafas B. M.
Published: July 2002

Piezoresistive cantilevers have been utilized in a novel ultrahigh vacuum scanning probe microscope which allows in situ scanning tunneling microscopy (STM), contact atomic force microscopy (AFM), and noncontact atomic force microscopy. The instrument uses interchangeable tungsten tips (for STM imaging) and piezoresistive cantilevers (for AFM or STM imaging) and is capable of atomic resolution in both STM and AFM modes of operation. In situ tip exchange under vacuum conditions is performed quickly and reliably using a high precision rotary/linear feedthrough and a tip/cantilever storage system. Piezoresistive force-sensing cantilevers provide a new detection scheme for AFM, using an all-electronic detector that requires no alignment or optical detection system. The microscope features a high-resolution, dual-axis, inertial-drive translation stage with an open access sample mount designed to optimize vibration isolation.
Performance optimization of active quenching circuits for picosecond timing with single photon avalanche diodes
Authors: Lacaita A. , Cova S. , Samori C. , Ghioni M.
Published: July 2002

The front-end electronic circuitry plays a fundamental role in determining the performance obtained from ultrafast and highly sensitive photodetectors. In this paper we deal with electronic problems met working with single photon avalanche diodes for detecting single optical photons and measuring their arrival time with picosecond resolution. We describe an active quenching circuit capable of driving the detector in a remote position, connected with a coaxial cable. By minimizing the noise of the input stage we succeeded in reducing the contribution of the detector circuitry to the measured time resolution to less than 10 ps full width at half-maximum.
Multilayer-coated echelle gratings for soft x rays and extreme ultraviolet
Authors: Underwood J. H. , Malek C. Khan , Gullikson E. M. , Krumrey M.
Published: July 2002

Mechanically ruled or ion-etched blazed diffraction gratings can be coated with multilayer reflectors to increase their on-blaze efficiency in the soft x-ray and extreme ultraviolet (EUV) spectral regions. The quality of the groove facets produced by these conventional manufacturing techniques precludes their use in high spectral orders to achieve high resolving power, i.e., as echelles. However, coarse gratings fabricated in crystalline silicon by orientation-dependent etching have excellent groove profile and extremely smooth facets, which make them ideal for coating with multilayers for use as echelles at short wavelengths. Such a grating was coated with tungsten-carbon multilayers for use at soft x-ray wavelengths near the carbon K edge. It was evaluated using both a reflectometer based on a laser-produced plasma source and with synchrotron radiation. In the 50–220 Å wavelength region, diffraction orders up to the 61st were observed, allowing the grating performance to be compared with theoretical predictions. Such multilayer-coated echelles offer the possibility of extremely high spectral resolving power in the EUV and soft x-ray region.
Current status of the 6 m low-energy spherical grating monochromator beamline at SRRC
Authors: Tseng P.-C. , Lin H.-J. , Chung S.-C. , Chen C.-I. , Lin H.-F. , Dann T.-E. , Song Y.-F. , Hsieh T.-F. , Tsang K.-L. , Chang C.-N.
Published: July 2002

The 6 m low-energy spherical grating monochromator (6 m-LSGM) beamline at SRRC is at its commission stage. The 6 m-LSGM beamline, which covers photon energies from 15 to 200 eV, is based on Dragon concept with spherical gratings and movable exit slit. Some of the commission data will be presented in this paper. The photoabsorption spectra of Ar, He, and Kr have been recorded with resolution so far unattained in the vacuum ultraviolet region.