bluuebunny/crossref_metadata_2025 huggingface dataset:
The structure of procaspase 6 is similar to that of active mature caspase 6
Authors: KANG Byoung Heon , KO Eunsil , KWON Oh-Keun , CHOI Kwan Yong
Published: July 2002

To investigate the structural characteristics and activation mechanism of the precursor caspase, genes encoding the inactive pro-form and the active mature form of caspase 6 were expressed in Escherichia coli and the proteins of both forms were purified to homogeneity. The structure of each protein was characterized by chemical cross-linking, size-exclusion chromatography, CD and fluorescence spectroscopies. The pro-form caspase 6 exhibits a dimeric structure and its overall secondary structure was found to be similar to that of the mature caspase 6. Upon the maturation of procaspase 6, the maximum fluorescence wavelength λmax was red-shifted from 330 to 337nm and the fluorescence intensity of λmax was increased. This fluorescence spectral change indicates that the environment of a tryptophan residue in the substrate-binding site can be changed to a more polar one when the procaspase 6 is processed. Taken together, our results strongly demonstrate that precursor caspase 6 exists as a dimer and its overall structure is similar to that of the active caspase 6. Our results also suggest that the local conformational change at the substrate-binding site, with no drastic change in the overall structure, seems to enable precursor caspase 6 to become the active mature enzyme.
Nitric oxide regulates oestrogen-activated signalling pathways at multiple levels through cyclic GMP-dependent recruitment of insulin receptor substrate 1
Authors: FALCONE Sestina , MAURO Loredana , de ROSE Giacinta , PAOLUCCI Clara , SCIORATI Clara , ANDO Sebastiano , CLEMENTI Emilio
Published: July 2002

The gaseous messenger nitric oxide (NO) contributes to biological effects of oestrogen in target tissues, including reproductive organs, bone, cardiovascular and central nervous systems. Vasodilation and anti-atherosclerotic properties of NO have been shown to play a role in these effects. The possibility that NO acts also through regulation of the signal transduction cascade triggered by oestrogen, instead, has never been investigated. To study this we have used the MCF-7 human breast cancer cell line, an established model for oestrogen signalling. Exposure of these cells to 17-β-oestradiol (E2) in the presence of NO gave rise to activation of signalling events additional to those triggered by E2 alone, namely tyrosine phosphorylation of specific proteins, including the insulin receptor substrate-1, with recruitment to this adapter of the phosphatidylinositol 3′-kinase and persistent activation of Akt (protein kinase B). Active Akt, in turn, prevented E2 from activating p42/44 extracellular signal-regulated kinases (ERK 1/2). These effects of NO, which were mediated through generation of cyclic GMP and activation of the cGMP-dependent protein kinase I, initiated in the first minutes after administration of oestrogen. The consequences, however, were long lasting, as modulation of Akt and ERK 1/2 activities by NO was responsible for inhibition of E2-triggered cell growth and regulation of oestrogen responsive-element dependent gene transcription. Generation of NO is stimulated by both E2 and growth factors known to contribute to the complex network of intracellular events regulating the biological actions of oestrogen. It is conceivable, therefore, that modulation by NO of E2 early signalling, here described for the first time, has broad significance in regulating cellular responses to the hormone.
Limnanthes douglasii lysophosphatidic acid acyltransferases: immunological quantification, acyl selectivity and functional replacement of the Escherichia coli plsC gene
Authors: BROWN Adrian P. , CARNABY Simon , BROUGH Clare , BRAZIER Melissa , SLABAS Antoni R.
Published: July 2002

Antibodies were raised against the two membrane-bound lysophosphatidic acid acyltransferase (LPAAT) enzymes from Limnanthes douglasii (meadowfoam), LAT1 and LAT2, using the predicted soluble portion of each protein as recombinant protein antigens. The antibodies can distinguish between the two acyltransferase proteins and demonstrate that both migrate in an anomalous fashion on SDS/PAGE gels. The antibodies were used to determine that LAT1 is present in both leaf and developing seeds, whereas LAT2 is only detectable in developing seeds later than 22daf (days after flowering). Both proteins were found exclusively in microsomal fractions and their amount was determined using the recombinant antigens as quantification standards. LAT1 is present at a level of 27pg/μg of membrane protein in leaf tissue and ≤ 12.5pg/μg of membrane protein in developing embryos. The amount of LAT2 reaches a peak at 305pg/μg of membrane protein 25daf and is not expressed 20daf or before. This is the first study to quantify these membrane-bound proteins in a plant tissue. The maximal level of LAT2 protein coincides with the maximal level of erucic acid synthesis in the seeds. Both full-length proteins were expressed in the Escherichia coli LPAAT mutant JC201, and membranes from these strains were used to investigate the substrate selectivity of these two enzymes, demonstrating that they are different. Finally, we report that LAT2 and a maize LPAAT enzyme (MAT1) can functionally replace the E. coli plsC gene after its deletion in the chromosome, whereas LAT1 and a coconut LPAAT (Coco1) cannot. This is probably due to differences in substrate utilization.
Effects of mutations at the two processing sites of the precursor for the small subunit of ribulose-bisphosphate carboxylase in Chlamydomonas reinhardtii
Authors: INVERNIZZI Cédric , IMHOF Jonathan , BURKARD Gabriela , SCHMID Katharina , BOSCHETTI Arminio
Published: July 2002

The role of the two processing sites in the precursor of the small subunit (SS) of ribulose-1,5-bisphosphate carboxylase/oxygenase (pSS) of Chlamydomonas reinhardtii was studied by introducing mutations at the cleavage sites for the stromal processing peptidases SPP-1 and SPP-2, which hydrolyse wild-type pSS (20.6kDa) to an intermediate-sized product iSS (18.3kDa) and to the mature SS (16.3kDa), respectively. The mutations introduced into cDNA resulted in exchange of (a) two amino acids flanking processing site 1, or (b) one or (c) both amino acids flanking processing site 2. Mutation (a) prevented pSS from being processed at site 1 but not from cleavage at site 2. Mutation (c) abolished the action of SPP-2 but not SPP-1. When pSS with mutation (c) was imported into isolated chloroplasts, iSS accumulated while SS formation was abolished. However, mature SS was produced even in the absence of iSS synthesis (mutation a). Import of pSS bearing mutation (b), which only partially inhibited processing at the SPP-2 site, slowed the rate of SS formation down whereas iSS and some slightly smaller derivatives accumulated. These experiments suggested that in Chlamydomonas processing of pSS can occur in two steps, whereby the first step is facultative. The same three mutations were studied in vivo after transformation of SS-deficient C. reinhardtii T60-3 with mutated genomic DNA. Growth and photosynthesis was as in control transformants, except for the slower-growing transformants (mutation c) where no mature SS was immuno-detected. However, pSS fragments with molecular masses between those of iSS and SS were present even in the ribulose-1,5-bisphosphate carboxylase/oxygenase holoenzyme.
Changes in the registration of stillbirths < 500 g in Canada, 1985–95
Authors: Joseph  , Allen  , Kramer  , Cyr  , Fair  , For The Fetal‐Infant Mortality Study Group of the Canadian P
Published: July 2002

We assessed recent temporal trends in the registration of stillbirths in Canada, with particular regard to stillbirths < 500 g. Data from the Statistics Canada live birth and stillbirth databases for the period 1985‐95 were used for the study. The primary analysis was restricted to data from 10 of the 12 provinces and territories of Canada. Data from Newfoundland were excluded because birthweight distributions were not available prior to 1990, and data from Ontario were excluded because of concerns about data quality. The proportion of stillbirths < 500 g increased by 47%[95% confidence interval (CI) 32, 63%], from 12.7% of stillbirths with known birthweight in 1985–7 to 18.7% in 1993‐5. Similarly, the rate of stillbirths < 500 g increased by 36%[95% CI 21, 53%], from 7.2 to 9.8 per 10 000 total births from 1985–7 to 1993–5. Similar increases in stillbirth rates were not observed in other low birthweight categories. Live births < 500 g increased 53%[95% CI 33, 77%], from 4.6 to 7.0 per 10 000 live births. Some provinces and territories had low rates of stillbirths < 500 g and no increasing trend, whereas other provinces showed higher rates and increases over time. These regional differences were consistent with differences in stillbirth definitions across the provinces and territories of Canada. Spatio‐temporal comparisons of crude stillbirth rates are likely to be compromised unless differences and changes in birth registration practices are addressed.
INS VNTR allelic variation and dynamic insulin secretion in healthy adult non‐diabetic Caucasian subjects
Authors: Ahmed S. , Bennett S. T. , Huxtable S. J. , Todd J. A. , Matthews D. R. , Gough S. C. L.
Published: July 2002

Aims To elucidate the relationship between the human insulin gene INS VNTR regulatory polymorphism and insulin secretion. The polymorphism arises from tandem repetition of 14–15 bp oligonucleotides. In Caucasians, repeat number varies from 26 to over 200, with two main and discrete allele size classes: class I (26–63 repeats) and class III (141–209 repeats). Class I allele homozygosity is associated with elevated risk of developing Type 1 diabetes, while the class III allele has been associated with increased risk of Type 2 diabetes, polycystic ovary syndrome (PCOS) and with larger size at birth, which may influence development of adult disease.

Methods Thirty‐one healthy adult subjects with normal glucose tolerance, underwent an intravenous glucose tolerance test with one minute sampling. Seventeen subjects were homozygous for class I alleles (14 excluding individuals carrying alleles associated with parent‐of‐origin effects and heterogeneity in allele transmission) and 14 homozygous for class III alleles. The groups were well matched.

Results No significant differences in amount or rate of insulin secretion, or beta cell function were detected between the two groups. There was a difference in pattern of pulsatile insulin secretion with more 9‐minute oscillations in class I homozygotes (P < 0.026). The after‐load glucose concentration was also higher in subjects with class I alleles (P < 0.03).

Conclusions These results warrant further analysis of possible association between allelic variation of the INS VNTR and the pulsatility of insulin secretion.
Erbium luminescence in doped amorphous silicon
Authors: Oestereich T. , Swiatkowski C. , Broser I.
Published: July 2002

For the first time the observation of a sharp peak in the broad luminescence spectrum of hydrogenated amorphous silicon (a-Si:H) has been achieved, using erbium as a dopant. Thus, a method of investigating the structure of solid-state systems which previously has only been used with crystals can now be applied to a-Si:H. The idea is to measure the splitting of the luminescence of ‘‘spy’’ atoms, or ions, by the crystal field of the host substance subject of investigation into which they are incorporated. Finding a suitable substance for use with a-Si:H has proven to be a difficult task, which we now have accomplished as a first step in establishing this method for the investigation of amorphous substances.
X-ray streak camera with 2 ps response
Authors: Murnane M. M. , Kapteyn H. C. , Falcone R. W.
Published: July 2002

We have developed an x-ray streak camera system with a temporal response of 2 ps (full width at half maximum). The response of the camera was measured using soft x rays in the 30 eV to 1 keV energy range which were emitted from a plasma created by a high-intensity, subpicosecond laser pulse. A single shot, resolution-limited, relative timing precision of 0.2 ps was demonstrated for x-ray emission events.
Modulation of quantized levels of GaAs/AlGaAs quantum wells by InAs monomolecular plane insertion
Authors: Sato Michio , Horikoshi Yoshiji
Published: July 2002

GaAs/AlGaAs quantum well structures with InAs monomolecular planes are fabricated by flow-rate modulation epitaxy. Photocurrent spectra of these structures are measured to investigate the effect of the InAs planes on the quantized levels. The InAs monomolecular plane inserted at the center of the well shifts the transition peak between the lowest levels (n=1 heavy hole and electron), but does not shift the transition peak between n=2 levels. The amplitude of the wave function for the electrons and holes on the n=2 levels is zero at the center of the well. Therefore, an InAs plane at the center does not modify the distribution of the n=2 carriers. When two InAs planes are inserted in a well and the distance between the two planes is varied, both n=1 and n=2 transition peaks are shifted. Measured spectra are well explained by a finite square well model calculation using the band parameters of GaAs and strained InAs.
Nonlinear optical properties of 2-adamantylamino-5-nitropyridine crystals
Authors: Tomaru S. , Matsumoto S. , Kurihara T. , Suzuki H. , Ooba N. , Kaino T.
Published: July 2002

Several organic materials with a bulky donor group have been developed for second-order nonlinear optics. Among these materials, 2-adamantylamino-5-nitropyridine (AANP) crystal has the largest second-order nonlinear optical coefficient. By second-harmonics measurement at 1.064 μm, coefficients of d31 and d33 were determined to be 80 and 60 pm/V, respectively. Angle-tuned phase-matched second-harmonic generation with a conversion efficiency=2×10−3 W−1 has been demonstrated using a 1 mm AANP bulk crystal at 1.064 μm.
Cobalt thin films prepared by chemical vapor deposition from cobaltous acetate
Authors: Maruyama Toshiro , Nakai Tsuyoshi
Published: July 2002

Cobalt thin films were prepared by a low-temperature atmospheric-pressure chemical vapor deposition method. The raw material was cobaltous acetate which is nontoxic and easy to handle. At a reaction temperature of 300 °C, [111]-oriented polycrystalline films can be obtained on amorphous substrates. Increasing the H2 partial pressure over the requirement for both the highest deposition rate and lowest resistivity promotes the crystallization with [111] preferential orientation of the film without affecting the crystallite size. Cobaltous acetate appears to offer a viable alternative to cobalt acetylacetonate for low-temperature cobalt film production.
Multibeam laser manipulation and fixation of microparticles
Authors: Misawa Hiroaki , Sasaki Keiji , Koshioka Masanori , Kitamura Noboru , Masuhara Hiroshi
Published: July 2002

A multibeam laser trapping–reaction system was developed to demonstrate independent manipulation of plural microparticles as well as to induce photochemical reaction in a laser-trapped particle(s). Photopolymerization of vinyl monomers dissolved in a sample solution was employed to fix polystyrene latex particles regularly aligned by laser trapping. Integrated latex structures created by the successive manipulation/polymerization procedures were also shown to be freely manipulated by laser beams.
35% efficient nonconcentrating novel silicon solar cell
Authors: Li Jianming , Chong Ming , Zhu Jiancheng , Li Yuanjing , Xu Jiadong , Wang Peida , Shang Zuoqi , Yang Zhankun , Zhu Ronghua , Cao Xiolan
Published: July 2002

An energy conversion efficiency of 35% was obtained at 1-sun, air mass 1.5 for a novel silicon cell. The critical feature of the cell structure is the inclusion of local defect layers near a p-n junction. The local defect layers were proven to hold the key to achieving the exceptionally high efficiency of the novel cell fabricated via noncomplex processing.
Superconducting terahertz mixer using a transition-edge microbolometer
Authors: Prober D. E.
Published: July 2002

We present a new device concept for a mixer element for THz frequencies. This uses a superconducting transition-edge microbridge biased at the center of its superconducting transition near 4.2 K. It is fed from an antenna or waveguide structure. Power from a local oscillator and a rf signal produce a temperature and resulting resistance variation at the difference frequency. The new aspect is the use of a very short bridge in which rapid (<0.1 ns) outdiffusion of hot electrons occurs. This gives large intermediate frequency (if) response. The mixer offers ≊4 GHz if bandwidth, ≊80 Ω rf resistive impedance, good match to the if amplifier, and requires only 1–20 nW of local oscillator power. The upper rf frequency is determined by antenna or waveguide properties. Predicted mixer conversion efficiency is 1/8, and predicted double-sideband receiver noise temperatures are 260 and 90 K for transition widths of 0.1 and 0.5 Tc, respectively.
Tribological improvements of polished chemically vapor deposited diamond films by fluorination
Authors: Miyake S.
Published: July 2002

In an effort to realize wear resistant and lubricating surfaces, polished chemically vapor deposited (CVD) diamond films are fluorinated. The effect of these films on improving frictional properties is then investigated. On fluorinated diamond surfaces, C—F bonds are formed and carbon and oxygen contents decrease. Fluorination can reduce the surface energy, as evaluated by contact angle to the water. The relationship between friction coefficient and initial Hertzian stress of polished diamond film can be expressed as one curve designated as the ‘‘master curve’’ independent of tip radius and material. Fluorination decreases friction coefficient and change of friction coefficient of polished CVD diamond with increasing load and opposing tip radius.
Comparison of short range and asymptotic measurements of the kinetic energy distributions of laser ablated aluminum atoms
Authors: Macler Michel , Fajardo Mario E.
Published: July 2002

We compare the kinetic energy distributions of ultraviolet excimer laser ablated A1 atoms measured within 1 cm of the metal surface by optical transient absorption, to those measured over 20 cm from the surface by pulsed photoionization time-of-flight mass spectrometry. For the mild ablation conditions used the distributions are the same. This result demands the existence of a good one-to-one correspondence of atomic velocity to distance traveled from the ablated surface on the ∼1 μs timescale of the short range measurement, suggesting that the duration of the A1 atom production period is ≤100 ns. This study establishes the viability of a novel concept for a compact velocity selection scheme for faster laser ablated neutral species.
Optoelectronic generation and detection of single-flux-quantum pulses
Authors: Wang Chia-Chi , Currie Marc , Jacobs-Perkins Douglas , Feldman Marc J. , Sobolewski Roman , Hsiang Thomas Y.
Published: July 2002

We report on the direct observation of a single-flux-quantum (SFQ) pulse. The response of a metal–semiconductor–metal photodiode to a femtosecond laser pulse was used to switch Josephson junctions and to generate an SFQ voltage pulse on a superconducting microstrip line. The detailed shape of the pulse was measured optoelectronically, using a cryogenic electro-optic sampling system. The measured SFQ pulse had a width of 3.2 ps, an amplitude of 0.67 mV, and a total pulse content of 2.1±0.2 mV×ps, corresponding to the quantum of magnetic flux h/2e. With larger excitation, multiple SFQ pulses were observed. Numerical simulations are shown to be qualitatively similar to our experimental results.
Performance characteristics of a high-repetition rate, multichannel rail-gap switch
Authors: Sandstrom R. L. , Shields H. , Levatter J. I.
Published: July 2002

A multichannel rail-gap switch, triggered by ultraviolet radiation sources and capable of high repetition rate, long-life operation is described. The device will switch 30-kV, 30-kA, 80-ns pulses at pulse rates up to 100 Hz. Gas consumption is low (1-SLPM air), and under optimum conditions, switch inductance and jitter are 14 nH and ±5 ns, respectively. Prefire statistics and erosion rates have been studied.
Low-temperature atomic force microscopy
Authors: Kirk M. D. , Albrecht T. R. , Quate C. F.
Published: July 2002

A low-temperature atomic force microscope (LTAFM) has been constructed which is capable of resolving atomic scale features both in air at room temperature and immersed in liquid helium at 4.2 K. The instrument is of a rigid compact design, using microfabricated force-sensing cantilevers, and can easily be adapted for operation as a scanning tunneling microscope. Initial results have demonstrated that the LTAFM can image the atomic surface structure of 2H–MoS2 at 4.2 K and room temperature. Design criteria and applications of the LTAFM are discussed.
Noncontact laminar-flow polishing for GaAs
Authors: Ives N. A. , Leung M. S.
Published: July 2002

Laminar-flow polishing is a noncontact polishing technique capable of producing a highly polished surface with no subsurface mechanical damage. The method utilizes the hydrodynamic condition of laminar flow to provide the transport mechanisms responsible for the removal of the GaAs surface. The method is well suited to the preparation of semiconductor wafers for experiments where high-quality damage-free substrates are required. In addition, the ease of controlling the polishing conditions makes this method a useful technique in production where a high throughput of wafers with uniform and damage-free surfaces are essential.
A new type of multiparticle imaging detector
Authors: Belkacem A. , Faibis A. , Kanter E. P. , Koenig W. , Mitchell R. E. , Vager Z. , Zabransky B. J.
Published: July 2002

The foil-induced dissociation of molecular ions can provide a direct image of the stereochemical structures of small molecules. Such experiments require high-resolution measurements of the relative momenta of all dissociation fragments. In order to improve and extend previous studies of this type to a larger variety of molecules and clusters, we have developed a new type of low-pressure multiwire proportional counter. The novel feature of this large-area (25×50 cm2 ) multiparticle detector is that all the signals are recorded from a single two-level printed circuit board which serves as the anode. This segmented anode consists of three families of nonintersecting ‘‘wires’’ which are interwoven on the rear surface of the board. By redundantly determining positions and arrival times, the new segmented anode multiparticle detector provides good time resolution (100–200 ps) and high spatial resolution (0.2 mm) for detecting as many as six simultaneous particles.
A new combined ultrahigh vacuum and electrochemical apparatus
Authors: Leung Lam-Wing H. , Gregg Thomas W. , Goodman D. Wayne
Published: July 2002

A new combined ultrahigh vacuum (UHV) and electrochemical apparatus is described which allows easy and rapid controlled transfer of a well-characterized single-crystal surface between UHV and atmospheric liquid electrochemical environments.
Strain gauge manometer with pressure up to 0.5 GPa acting inside and on the ends of a free cylinder
Authors: Wisniewski R. , Molinar GF.
Published: July 2002

A free deforming-cylinder pressure transducer with bonded strain gauges is presented for pressure measurements in liquid media up to 0.5 GPa. Description is given of its operating principle and of its main metrological properties; the overall accuracy of this prototype pressure transducer is inside ±0.25 MPa.
Isolation of test masses in the advanced laser interferometric gravitational-wave antennae
Authors: Braginsky V. B. , Mitrofanov V. P. , Vyatchanin S. P.
Published: July 2002

We analyze the experimental conditions required for the action of thermal, seismic, and excess noises on the test mass in the advanced LIGO experiment to be smaller than the uncertainty of the coordinate corresponding to the standard quantum limit. It is shown that the contribution of thermal noise can be made small enough if existing low-dissipation materials are used for the suspension. On the other hand, the contribution of excess noise can be large and has to be examined thoroughly.
Precise magnetization measurements under high pressures in the diamond-anvil cell
Authors: Ishizuka Mamoru , Amaya Kiichi , Endo Shoich
Published: July 2002

A precise magnetization measurement system for extremely small samples in the diamond-anvil cell has been developed. The system is based on position differentiating detection (PDD) combined with the use of a SQUID magnetometer. The PDD is a kind of vibrating coil magnetometer and is suitable for the case where high sensitivity detection is required for a sample around which there is little space for the detection coil. The present system enables one to make magnetization measurements at pressures up to about 12 GPa in the temperature range from 1.4 to 30 K. The sensitivity is about 10−9–10−10 emu. Three piezoelectric actuators of a bimorph type are used at liquid–helium temperature for stable vibration of the detection coil with an amplitude of 90 μm around the tips of the diamond anvils. The design and construction of the system is described in detail. The performance of the system is illustrated by magnetization measurements of EuTe under high pressures.
Design of the anomalous scattering beamline at the European Synchrotron Radiation Facility
Authors: Lequien S. , Goirand L. , Lesimple F.
Published: July 2002

The European Synchroton Radiation Facility will construct a public beamline which will combine anomalous dispersion and mainly diffuse scattering. The two original features of this beamline are that small- and wide-angle x-ray scattering experiments might be carried out on the same spectrometer without moving the sample. The whole beamline will run under vacuum.
Instrumentation developments in scanning soft x-ray microscopy at the NSLS (invited)
Authors: Williams Shawn , Jacobsen Chris , Kirz Janos , Maser Jörg , Wirick Sue , Zhang Xiaodong , Ade Harald , Rivers Mark
Published: July 2002

The Scanning Transmission Soft X-ray Microscope at the NSLS has been instrumented for the following new forms of imaging: (1) XANES microscopy for the mapping of chemical constituents and for absorption spectroscopy of small specimen areas; (2) luminescence microscopy for locating visible light emitting labels at the resolution determined by the size of the x-ray microprobe; and (3) dichroism microscopy for mapping the alignment of molecules whose absorption spectra are polarization dependent. Since the instrument is used mostly for the imaging of biological and other radiation sensitive materials, a cryostage is being planned to accommodate frozen hydrated specimens.
Fast-ion-beam photoelectron spectrometer
Authors: Hanold K. A. , Sherwood C. R. , Garner M. C. , Continetti R. E.
Published: July 2002

A high-collection-efficiency fast-ion-beam photoelectron spectrometer is described. In a straight time-of-flight mode, the spectrometer collects ∼1% of the photoelectrons and achieves an energy resolution of ΔE/E of ∼5%. For coincidence experiments requiring greater collection efficiency, a paraboloidal electrostatic mirror is used. The mirror collects ∼40% of the photoelectrons while maintaining ΔE/E≤35%. In both modes of operation, a time- and position-sensitive electron detector allows conversion of the photoelectron laboratory energy to center-of-mass energy. The fast-ion-beam photoelectron spectrometer is used to prepare mass- and energy-selected neutral molecules which are used in molecular dissociation studies.
Role of space charge in SrS:Ce thin-film electroluminescent devices studied by the photoirradiation effect
Authors: Ohmi Koutoku , Ishitani Katsuaki , Tanaka Shosaku , Kobayashi Hiroshi
Published: July 2002

The role of space charge in SrS:Ce thin-film electroluminescent devices was studied by photoirradiation effects on capacitance–voltage and charge–voltage curves. Unique electrical and optical characteristics, such as relaxation of phosphor field and leading and trailing edge emission, are well interpreted by the model based on the formation of uniform space charge. The density of ionized traps, which cause positive space charge, was estimated to be 5.6×1016 cm−3. The polarization charge of 0.94 μC/cm2 due to the space charge is more than half of the total polarization charge.
Effects of frequency and magnetic field scaling on the superconducting electron cyclotron resonance ion source at MSU-NSCL
Authors: Gammino S. , Ciavola G. , Harkewicz R. , Harrison K. , Srivastava A. , Briand P.
Published: July 2002

A series of systematic tests have been carried out on the superconducting electron cyclotron resonance ion source SCECRIS at the Michigan State University National Superconducting Cyclotron Laboratory in order to better understand the role of different parameters which determine the performance of these sources. A relevant part of these tests has been focused on the role of magnetic field and microwave frequency, with the goal of demonstrating the capability of low frequency electron cyclotron resonance ion sources to produce high ion charge states, in spite of their relative low plasma density. This goal can be achieved using a very high magnetic confining field, according to the concept of a high B mode. A comparison of the source performance at 2.45 and 6.4 GHz for different levels of magnetic field is described in this article.
Fabrication of a hard x-ray sputtered-sliced Fresnel phase zone plate
Authors: Kamijo N. , Tamura S. , Suzuki Y. , Handa K. , Takeuchi A. , Yamamoto S. , Ando M. , Ohsumi K. , Kihara H.
Published: July 2002

A Fresnel phase zone plate for hard x ray was fabricated by physical vapor deposition alternating transparent and opaque layers onto a fine gold wire core 47 μm in diameter. The zone plate, which is comprised of 25 pairs of alternating Ag and C layers, is designed to operate with a focal length of 124 mm for a parallel beam at 8.1 keV. The thickness of the zone plate is less than 10 μm and is capable of operating as a phase zone plate. Using the brilliant monochromatized x-ray beam from the TRISTAN Main Ring, with an undulator, the minimum focal spot size attained for the first order focal beam was 0.5 μmφ. The light collecting efficiency was determined to be near 11%.
Temperature dependence of the fluorescence lifetime in Pr3+:ZBLAN glass for fiber optic thermometry
Authors: Sun T. , Zhang Z. Y. , Grattan K. T. V. , Palmer A. W. , Collins S. F.
Published: July 2002

An analysis of the fluorescence decay behavior of Pr 3+ in ZBLAN glass, at different concentrations, has been undertaken, for applications of the material to fiber optic thermometry. The study has shown that with the temperature increase, the measured lifetimes of the fluorescence emission from the Pr 3+ doped glass are also seen to increase slowly. The results obtained are found not to support a simple two-level model based on the thermalization of the states involved but a new three-level model that has been introduced can explain the observed results in a very satisfactory way. The application of the work in optical thermometry is discussed and comparisons with other systems are made.
Optomechanical Q-switch shutter with resonant piezoelectric element
Authors: Georgiou Efstratios , Papadakis Antonios
Published: July 2002

A new type of low cost optomechanical laser-beam shutter without any wearing parts, consisting of a resonantly oscillating piezoelectric element and an optical telescope, is described. In intracavity operation, the 2.5 μs optical switching time is suitable for Q-switching lasers having long buildup times.
High voltage fast ramp pulse generation using avalanche transistor
Authors: Jinyuan Liu , Bing Shan , Zenghu Chang
Published: July 2002

The authors have developed an avalanche transistor based pulser for use as a pockel cells driver and for gating a microchannel plate. The output voltage ranges from 1–4 kV to 50 Ω, with fall times of 200–300 ps. The repetition rate is less than 1 kHz. The trig jitter is less than 100 ps. Trig delay is about 8 ns.
Diagnostic characterization of a prepulsed carbon fiber Z pinch using spectral line intensity analyses
Authors: Lorenz A. , Peacock N. J. , O’Mullane M. G. , Neely David
Published: July 2002

Plasma formation and x-ray generation efficiency of a carbon fiber Z pinch are dramatically improved by means of an optimized current prepulse. In this article results are presented of time-integrated and also time-resolved electron temperature measurements using the optical line emission of the coronal plasma surrounding a still, cold fiber. Two phases of discharges with current prepulse are studied: the preionization phase only in which time-integrated spectra of C II–C IV emission are recorded and time resolution of the heating phase after onset of the main current pulse using C III and C IV line emission. Experimentally obtained, n=3–4, 3–3, line ratios are fitted with collisional radiative, ADAS computations of line intensity ratios as a function of electron temperature, density, ne and variable confinement, τ. All levels up to n=5 are included with the influence of higher levels also accounted for. Deviations from coronal balance give an effective value for the product 〈neτ〉. As a result, the electron temperature of the preionized coronal plasma is estimated at Te=5 eV at a density of ne≈1017 cm−3. The temperature rises to about 12 eV at the same density after the start of the main current with prepulse. Similar analytic techniques are applied to time-integrated C V and C VI XUV resonance lines from the main pinch and give plasma parameters in accord with the x-ray continuum diagnostics.
Acoustically adjustable LiNbO3 double-crystal monochromator for synchrotron radiation
Authors: Polikarpov Igor , de Oliveira Ricardo Toledo , Zolotoyabko Emil
Published: July 2002

First experiments with the acoustically controlled LiNbO3 double-crystal monochromator for synchrotron radiation have been performed on the diffraction beamline of the Brazilian National Synchrotron Light Laboratory. In order to modify x-ray optical properties of LiNbO3 crystals, 290 MHz surface acoustic waves were generated with the aid of interdigital transducers, fabricated on the polished crystal surfaces by using microelectronics technology. It was shown that by the appropriate choice of diffraction planes, the LiNbO3 double-crystal monochromator can be used for both high-flux and high-resolution applications. Surface acoustic waves allow adjustment of an angular width of diffraction profile to a divergence of the incident synchrotron radiation, optimizing matching conditions for x rays of different wavelengths. Diffraction measurements under surface acoustic wave excitation demonstrated that the parameters of the x-ray beam issuing from the monochromatization system are indeed acoustically controlled, providing a 2–2.5-fold broadening of the diffraction profile and a 1.5-fold gain in the maximum diffraction intensity.
Evaluation of laser-irradiated Ar clusters as a source for time-resolved x-ray studies
Authors: Larsson J. , Sjögren A.
Published: July 2002

We have measured the absolute average photon flux, the spectral characteristics, and the time structure of x rays emitted from Ar clusters which were irradiated by a 100 fs laser with an intensity of 1017 W/cm2. The measured photon flux was 107 photons per shot in the Kα (at 3 keV) line in a 4π sr solid angle. The temporal structure was measured using a streak camera with a 10 ps time resolution. It was found that less than 1% of the photons were emitted within the 10 ps time-response function of the streak camera. The emission profile is roughly exponential with a time constant of 3 ns.
ac ohm meter for low-temperature thermometry
Authors: Feng X. G. , Zelakiewicz S. , Gramila T. J.
Published: July 2002

A high accuracy, low excitation ohm meter optimized for cryogenic thermometry is described. While the instrument simply measures the ac voltage induced across a resistance thermometer for a fixed applied current, a number of design innovations were necessary in order to maintain a high signal-to-noise ratio and absolute accuracy of greater than 10−4 with excitation voltages as low as 50 μV. Among these are a very high stability ac oscillator, a precision current source both stable and accurate with large capacitance loads, and an amplitude locked feedback loop to permit effective filtering of low level 60 Hz pickup.
Initial results from ground-based testing of an atomic oxygen sensor designed for use in earth orbit
Authors: Osborne J. J. , Roberts G. T. , Chambers A. R. , Gabriel S. B.
Published: July 2002

Many sensors have been applied to the problem of measuring neutral atomic oxygen fluxes in low Earth orbit. The techniques used to date tend to suffer from several key disadvantages, variously: large mass and power budgets, large size, high cost, the ability to make only one measurement and poor time resolution. In this article preliminary results from ground-based testing of a novel atomic oxygen sensor based on a semiconducting metal oxide are reported. Such sensors are simple and relatively cheap while also requiring small power and mass budgets and, most importantly, are reusable. The sensors have been used in laboratory experiments to investigate the axial variation of atomic oxygen flux in a pulsed laser atomic oxygen source; the results compare well with readings taken with a carbon-coated quartz crystal microbalance. A small instrument based on these sensors has been designed and built for application on the UK’s STRV-1c microsatellite.
Design of electron cyclotron resonance ion source using liquid-helium-free superconducting solenoid coils
Authors: Kurita Tetsuro , Nakagawa Takahide , Kawaguchi Takeo , Lee Sang-Moo
Published: July 2002

In 1998, we started to design the superconducting electron cyclotron resonance (ECR) ion source. One of the main features of this source is to use Gifford–McMahon refrigerators for cooling the solenoid coils instead of liquid He. This feature allows us to avoid the higher cost for liquid He, operation complexity, and less compactness of ordinary superconducting magnets using liquid He. A maximum axial magnetic field of 3 T and a radial magnetic field of 1 T on plasma chamber wall are provided with this magnetic system. The microwave of 14.5 GHz (maximum power of 2 KW) will be used for plasma heating. The source is designed for the production of highly charged heavy ions to be provided for atomic cluster experiments. In this contribution, we present the structure of the superconducting ECR ion source, and especially the unbalanced magnetic force between the coils and the yokes.
Characterization of surface imperfections of silicon-on-insulator wafers by means of extremely asymmetric x-ray reflection topography
Authors: Kimura Shigeru , Ogura Atsushi , Ishikawa Tetsuya
Published: July 2002

Surface imperfections of silicon-on-insulator (SOI) wafers are investigated by means of extremely asymmetric x-ray reflection topography, in which the glancing angle of the incident x rays is near the critical angle of total reflection; this geometry is achieved by using tunable wavelength synchrotron radiation. Two kinds of SOI wafers: bonded and two oxygen implanted silicon wafers are used as samples. The experimental topographs reveal a characteristic contrast for each sample, which cannot be observed by conventional x-ray topography. The observed contrasts strongly depend on the fabrication techniques of the SOI wafers.
Normal-incidence epitaxial SiGeC photodetector near 1.3 μm wavelength grown on Si substrate
Authors: Huang F. Y. , Wang Kang L.
Published: July 2002

We report on the fabrication of photodetectors with a response near 1.3 μm wavelength using an epitaxial SiGeC alloy grown on a Si substrate. The active absorption layer of the SiGeC/Si pin photodiode consists of a strained SiGeC alloy with a Ge content of 60% and a thickness of 800 Å. The device exhibits a peak response at 0.85 μm with the response extending to 1.3 μm and a cutoff wavelength at around 1.55 μm. The photocurrent response of the device versus reverse bias voltage saturates at 0.5 V. The leakage current density at the saturation voltage is 70 pA/μm2. These results may shed some light on Si-based SiGeC alloys for photodetector applications in the 1.3–1.55 μm wavelength range.
Transport of argon ions in an inductively coupled high-density plasma reactor
Authors: Sadeghi N. , van de Grift M. , Vender D. , Kroesen G. M. W. , de Hoog F. J.
Published: July 2002

The first direct observation of the velocity distribution of the metastable Ar+*(2G9/2) ions in the presheath of an inductively coupled plasma has been achieved by using the Doppler shifted laser induced fluorescence technique. Drift of the ions along the electric field in the presheath is observed and distribution functions of the velocity in both parallel and perpendicular directions, relative to the E field, are deduced at 5 and 40 mTorr. Present results show that in high density plasmas the velocity distribution of the metastable ions is directly related to that of the ground state argon ions. Neutral gas temperature of around 600 K is also measured from the absorption profile of a diode laser beam, set on one of the 772.4 nm argon lines.
Time-resolved observation of thermal oscillations by transmission electron microscopy
Authors: Osakabe N. , Harada K. , Lutwyche M. I. , Kasai H. , Tonomura A.
Published: July 2002

Time-dependent acoustic oscillations driven by stochastic thermal force have been observed by means of transmission electron microscopy. An electron-beam current passing in the vicinity of the edge of the vibrating sample, and thereby modulated, was led through an aperture at the image plane and measured with the electron counting technique as the power spectral density function, allowing the resonant frequency and the Q factor to be found. This enables estimation of the Young’s modulus and the internal friction. The method can be extended to the investigation of the elastic properties of nanoscaled samples.
X-ray yields from Xe clusters heated by short pulse high intensity lasers
Authors: Ditmire T. , Smith R. A. , Marjoribanks R. S. , Kulcsár G. , Hutchinson M. H. R.
Published: July 2002

We have examined the absolute yield of keV x-rays emitted from gaseous plasmas created by the intense irradiation of large Xe clusters. We find that >10 μJ of x rays with photon energies above 1 keV are produced from clustering Xe gas targets when heated by 250 mJ, 2 ps laser pulses at an intensity of ∼1017 W/cm2. The yields show strong laser intensity dependence and variation with Xe cluster size.
Organic light-emitting diodes using a gallium complex
Authors: Hamada Yuji , Kanno Hiroshi , Sano Takeshi , Fujii Hiroyuki , Nishio Yoshitaka , Takahashi Hisakazu , Usuki Tatsuro , Shibata Kenichi
Published: July 2002

A gallium complex (GaMq2Cl) consisting of two 2-methyl-8-hydroxyquinolines (Mq) and a chlorine was synthesized and used for the fabrication of organic light-emitting diodes (OLEDs). The photoluminescent peak of GaMq2Cl at 492 nm was as strong in intensity as that of tris(8-hydroxyquinolinato)aluminum (Alq3). The OLED using GaMq2Cl as an emitting material showed blue-green luminance of 10 490 cd/m2. When it was used as an electron transport material in a rubrene doped cell, an OLED with a high luminance of 27 700 cd/m2 was obtained. We found that GaMq2Cl also was useful as a host material.
Molecular dynamics-based ion-surface interaction models for ionized physical vapor deposition feature scale simulations
Authors: Coronell Daniel G. , Hansen David E. , Voter Arthur F. , Liu Chun-Li , Liu Xiang-Yang , Kress Joel D.
Published: July 2002

A procedure is presented for incorporating the results of atomistic simulations of ion–surface interactions into integrated circuit topographic simulations of ionized physical vapor deposition (PVD). Energy and angular dependent sticking probabilities for energetic Cu atoms impacting a {111} Cu surface, obtained from molecular dynamics simulations, were implemented in a simple Monte Carlo flux model. The resulting flux-averaged Cu sticking probability was found to vary significantly with position within submicron features and with the feature geometry. This illustrates the shortcomings of a constant (energy and angle independent) sticking probability model for ionized PVD.
On the optimal choice of monomer geometry in calculations of intermolecular interaction energies: Rovibrational spectrum of Ar–HF from two- and three-dimensional potentials
Authors: Jeziorska Malgorzata , Jankowski Piotr , Szalewicz Krzysztof , Jeziorski Bogumil
Published: July 2002

Alternatives to using a full-dimensional interaction-potential energy surface and performing a complete dynamics on that surface have been examined for the Ar–HF van der Waals complex. We have employed a symmetry-adapted perturbation theory potential including the dependence on the H–F internuclear distance r. This potential was used to obtain a reference rovibrational spectrum of Ar–HF from the complete three-dimensional dynamics calculations. From the three-dimensional surface we have generated several two-dimensional potentials: the vibrationally averaged potential and the potentials obtained by fixing r at its equilibrium value re and at the vibrationally averaged distances 〈r−2〉−1/2, 〈r〉, 〈r2〉1/2, and 〈r3〉1/3. For all two-dimensional potentials obtained in this way the rovibrational spectra have been computed and compared with the reference spectrum. We have found that the potential obtained by setting r=〈r〉 performs much better than that corresponding to r=re. The spectrum closest to the reference one is given by the vibrationally averaged potential. Of all potentials computed for a fixed r, the potential corresponding to r=〈r3〉1/3 performs best. The role of the so-called relaxation energy, computed often to assess the stabilizing effect of the monomer deformation upon dimer formation, has also been investigated. It has been found that this energy is of the order O(V2), where V is the interaction potential, and is expected to be negligible for molecules as rigid as HF. A simple formula estimating the relaxation energy with an error of the order of O(V3) has been given and numerically tested.
Calculated gas temperature profiles in argon glow discharges
Authors: Revel I. , Pitchford L. C. , Boeuf J. P.
Published: July 2002

We use a previously developed model for the electrical properties of glow discharges, coupled to a Monte Carlo simulation of the heavy particles (ions and fast neutrals) in the cathode sheath region, to calculate the gas heating source term in glow discharges in argon with planar electrodes. The gas temperature profile is calculated from the one-dimensional heat transport equation, and we report results for discharge current densities up to 4 mA/cm2 for a value of pd (product of the gas pressure and gap spacing) of 1.5 Torr cm. The gas temperature peaks at a position slightly inside the cathode sheath, and at the highest current density reported here the gas temperature reaches 354 K. A large fraction of the energy gained by the ions in the sheath is transported directly to the cathode (mostly through fast neutrals), and the fractional ion energy converted to thermal motion of the gas decreases with increasing current density. We report some results to show the dependence of the gas temperature on the thermal accommodation coefficient. For a constant current, the calculated discharge voltage is somewhat higher when gas heating is taken into account.
Quantized Hamilton dynamics
Authors: Prezhdo Oleg V. , Pereverzev Yu. V.
Published: July 2002

The Hamilton approach to classical dynamics is extended to incorporate quantum effects. Quantization of the Hamilton equations of motion results in a hierarchy of equations that are equivalent to quantum mechanics in the Heisenberg form. Closure of the hierarchy gives approximations to the exact quantum dynamics. A specific dynamics algorithm is presented and tested against model applications that exhibit tunneling and zero point motion effects. The quantized Hamilton approach is found accurate, consistent, flexible, and computationally very efficient.