bluuebunny/crossref_metadata_2025 huggingface dataset:
Cobalt‐substituted Fe‐type nitrile hydratase of Rhodococcus sp. N‐771
Authors: Nojiri Masaki , Nakayama Hiroshi , Odaka Masafumi , Yohda Masafumi , Takio Koji , Endo Isao
Published: July 2002

When the genes encoding α and β subunits of Fe‐type nitrile hydratase (NHase) from Rhodococcus sp. N‐771 were expressed in Escherichia coli in Co‐supplemented medium without co‐expression of the NHase activator, the NHase specifically incorporated not Fe but Co ion into the catalytic center. The produced Co‐substituted enzyme exhibited rather weak NHase activity, initially. However, the activity gradually increased by the incubation with an oxidizing agent, potassium hexacyanoferrate. The oxidizing agent is likely to activate the Co‐substituent by oxidizing the Co atom to a low‐spin Co3+ state and/or modification of αCys‐112 to a cysteine‐sulfinic acid. It is suggested that the NHase activator not only supports the insertion of an Fe ion into the NHase protein but also activates the enzyme via the oxidation of its iron center.
Serotonergic innervation of the hypothalamic suprachiasmatic nucleus and photic regulation of circadian rhythms
Authors: Pickard Gary E. , Rea Michael A.
Published: July 2002

Converging lines of evidence have firmly established that the hypothalamic suprachiasmatic nucleus (SCN) is a light‐entrainable circadian oscillator in mammals, critically important for the expression of behavioral and physiological circadian rhythms. Photic information essential for the daily phase resetting of the SCN circadian clock is conveyed directly to the SCN from retinal ganglion cells via the retinohypothalamic tract. The SCN also receives a dense serotonergic innervation arising from the mesencephalic raphe. The terminal fields of retinal and serotonergic afferents within the SCN are co‐extensive, and serotonergic agonists can modify the response of the SCN circadian oscillator to light. However, the functional organization and subcellular localization of 5HT receptor subtypes in the SCN are just beginning to be clarified. This information is necessary to understand the role 5HT afferents play in modulating photic input to the SCN. In this paper, we review evidence suggesting that the serotonergic modulation of retinohypothalamic neurotransmission may be achieved via at least two different cellular mechanisms: 1) a postsynaptic mechanism mediated via 5HT1A or 5ht7 receptors located on SCN neurons; and 2) a presynaptic mechanism mediated via 5HT1B receptors located on retinal axon terminals in the SCN. Activation of either of these 5HT receptor mechanisms in the SCN by specific 5HT agonists inhibits the effects of light on circadian function. We hypothesize that 5HT modulation of photic input to the SCN may serve to set the gain of the SCN circadian system to light.
High content of cytosolic glutamine synthetase does not accompany a high activity of the enzyme in rice (Oryza sativa) leaves of indica cultivars
Authors: Obara Mitsuhiro , Sato Tadashi , Yamaya Tomoyuki
Published: July 2002

Reproductive stages of 5 japonica, 9 indica, and 2 javanica cultivars of rice (Oryza sativa L.) were provided to compare the contents of protein for cytosolic glutamine synthetase (GS1; EC 6.3.1.2) in the lowest position of the attached leaf blade (position 6 from the primary leaf) and those for NADH‐glutamate synthase (NADH‐GOGAT; EC 1.4.1.14) in non‐green portion of the expanding 10th leaf blade. Some of the indica cultivars, including Kasalath, contained GS1 protein twice as high as other japonica and javanica cultivars based on total leaf nitrogen. Most of the indica cultivars, on the other hand, contained less NADH‐GOGAT protein than japonica and javanica cultivars. Immunostaining proved that GS1 protein was located in vascular tissues of the leaf blades of Kasalath, which was identical to our previous results with a japonica cultivar [Sakurai et al. (1996) Planta 200: 306–311]. Although relative contents of GS1 protein in the leaf blade of Kasalath increased as a function of leaf age, GS1 activity remained relatively constant. In addition, Kasalath showed lower activity than other japonica and javanica cultivars, especially during leaf expansion. GS1 activity, based on GS1 protein amount, changed during the life span of the leaf blade and we thus assume that GS1 activity was modulated post‐translationally in rice leaves.
Simultaneous inhibition of B7 and LFA‐1 signaling prevents rejection of discordant neural xenografts in mice lacking CD40L
Authors: Larsson Lena C. , Corbascio Matthias , Widner Håkan , Pearson Thomas C. , Larsen Christian P. , Ekberg Henrik
Published: July 2002

Abstract: Transplantation of embryonic human neural tissue can restore dopamine neurotransmission and improve neurological function in patients with Parkinson's disease. Logistical and ethical factors limit the availability of human embryonic allogeneic tissue. Embryonic xenogeneic neural tissue from porcine donors is an alternative form of donor tissue, but effective immunomodulatory techniques are warranted for neural xenotransplantation to become clinically feasible. We transplanted embryonic porcine ventral mesencephalic tissue into the brains of adult untreated C57BL/6 mice, untreated CD40L‐/–mice and CD40L‐/–mice that received injections of anti‐LFA‐1, CTLA4Ig or both compounds. Double‐treated CD40L‐/–mice had large grafts with high numbers of dopaminergic neurons 4 wk after transplantation. The grafts were completely devoid of lymphocytes, macrophages and activated microglia. Untreated C57BL/6 mice had rejected their grafts. Untreated CD40L‐/–mice and CD40L‐/–mice treated with monotherapy of anti‐LFA‐1 or CTLA4Ig had smaller grafts and more microglial and lymphocytic infiltration than double‐treated CD40L‐/–mice. We conclude that immunomodulation with concomitant inhibition of LFA‐1 and B7 signaling in the perioperative period in CD40L‐/–mice prevented the rejection of discordant neural xenografts. The treatment most likely reduced antigen presenting capacity and interfered with the costimulatory signaling needed for T cell activation to occur.
G-protein-coupled receptors for neurotransmitter amino acids: C-terminal tails, crowded signalosomes
Authors: EL FAR Oussama , BETZ Heinrich
Published: July 2002

G-protein-coupled receptors (GPCRs) represent a superfamily of highly diverse integral membrane proteins that transduce external signals to different subcellular compartments, including nuclei, via trimeric G-proteins. By differential activation of diffusible Gα and membrane-bound Gβγ subunits, GPCRs might act on both cytoplasmic/intracellular and plasma-membrane-bound effector systems. The coupling efficiency and the plasma membrane localization of GPCRs are regulated by a variety of interacting proteins. In this review, we discuss recently disclosed protein interactions found with the cytoplasmic C-terminal tail regions of two types of presynaptic neurotransmitter receptors, the group III metabotropic glutamate receptors and the γ-aminobutyric acid type-B receptors (GABABRs). Calmodulin binding to mGluR7 and other group III mGluRs may provide a Ca2+-dependent switch for unidirectional (Gα) versus bidirectional (Gα and Gβγ) signalling to downstream effector proteins. In addition, clustering of mGluR7 by PICK1 (protein interacting with C-kinase 1), a polyspecific PDZ (PSD-95/Dlg1/ZO-1) domain containing synaptic organizer protein, sheds light on how higher-order receptor complexes with regulatory enzymes (or ‘signalosomes') could be formed. The interaction of GABABRs with the adaptor protein 14-3-3 and the transcription factor ATF4 (activating transcription factor 4) suggests novel regulatory pathways for G-protein signalling, cytoskeletal reorganization and nuclear gene expression: processes that may all contribute to synaptic plasticity.
Hydroxyurea versus busulphan for chronic myeloid leukaemia: an individual patient data meta‐analysis of three randomized trials
Authors:   Chronic Myeloid Leukaemia Trialists' Collaborative Group
Published: July 2002

Although interferon alpha (IFN) has been shown to prolong survival in chronic myeloid leukaemia (CML), it cannot be used in all patients. Reliable evidence on the relative benefits of busulphan and hydroxyurea is of value in treating those patients who will not receive interferon. Data for each individual patient was sought from trials which randomized patients with CML to hydroxyurea vs. busulphan. Intention‐to‐treat stratified log rank survival analyses were performed, reporting two‐sided P‐values. Data were collected on 812 patients in the three trials identified. In the group of 690 patients with confirmed Philadelphia chromosome (Ph)‐positive CML, survival at 4 years was 45·1% with busulphan and 53·6% with hydroxyurea, an absolute benefit of 8·5% (95% confidence interval 0·1–16·9; logrank P = 0·01 over 4 years). There seemed to be no further benefit for hydroxyurea in later years, but there was no apparent delayed adverse effect either. The difference between hydroxyurea and busulphan was not statistically significantly different from the overall result in any subgroup. Survival of patients with Ph‐positive CML is better with hydroxyurea treatment than with busulphan.
Platelet tests in the prediction of myocardial infarction and ischaemic stroke: evidence from the Caerphilly Prospective Study
Authors: Elwood P. C. , Beswick A. , Pickering Janet , McCarron P. , O'Brien J. R. , Renaud S. R. , Flower R. J.
Published: July 2002

A platelet test that is predictive of myocardial infarction (MI) and/or stroke would enable the targeting of anti‐platelet drugs towards high‐risk patients. The predictive power of several platelet tests for MI and for stroke was examined in 2000 older men in the Caerphilly Cohort Study of Heart Disease, Stroke and Cognitive Decline. The tests were: aggregation to adenosine diphosphate (ADP) in platelet‐rich plasma (PRP); aggregation to ADP in whole blood measured using an impedance method and a test of platelet aggregation induced in whole blood by high‐shear flow. Around 200 MIs and 100 ischaemic strokes occurred during a 10‐year follow‐up. Neither primary nor secondary aggregation in PRP was predictive of MI. However, the fifth of men in whom the primary response to ADP was least, showed the highest risk of a subsequent stroke [relative odds (RO) 1·64; 95% confidence interval (CI) 1·12–2·43]. Aggregation in whole blood was not predictive of MI but, again, the fifth of men with the least platelet response showed the highest stroke incidence (RO 1·79; 95% CI 1·06–3·00). Retention of platelets in the high‐shear test was not predictive of either event.
Human agency and the process of healing: lessons learned from women living with a chronic illness — ‘re‐writing the expert’
Authors: Tang Sannie Y S , Anderson Joan M
Published: July 2002

In this paper we examine the notion of human agency in the context of women experiencing a chronic illness. Based on two qualitative studies conducted with Canadian women of Chinese‐ and Anglo‐descent living with diabetes, we unmask the complex power relations inherent in patient–practitioner interactions, and problematize the privileging of healthcare providers as knowers and experts on the patient’s body. Specifically, we analyse the meanings that women ascribe to their illness experience. We discuss how women experience the loss of agency in healthcare encounters, how they resist patienthood by reclaiming agency, and how healthcare providers foster agency in their interactions with women. Rather than suggesting that biomedical experts should be ‘written out’, we propose to rewrite healthcare providers as ‘reflexive practitioners’ through the construction of transformative knowledge. We argue that praxis‐oriented practice, which is based on transformative knowledge, will provide the space for women and healthcare providers to enter into a new dialogue and a relation in which women can sustain a sense of self, and begin the journey of healing.
Incidence of Guillain—Barré Syndrome in Sweden 1996
Authors: Cheng Q. , Jiang G.‐X. , Fredrikson S. , Link H. , de Pedro‐Cuesta J. ,   Network Members of the Swedish GBS Epidemiology Study Group
Published: July 2002

We describe the incidence of Guillain‐Barré syndrome (GBS) in Sweden in 1996. Information of incident GBS patients was mainly collected by a multicentre network of 18 neurologists prospectively monitoring a general population with 4.48 million inhabitants across the country and complemented with data from the national hospital in‐patient registry. GBS diagnoses for all patients were validated by neurologists. While 53 patients with GBS were identified by the network neurologists from the study population, the other 20 GBS patients were recognized after carefully reviewing the registered data. There were 44 (60%) male patients and 29 (40%) female patients and the mean age at onset for all patients was 48.6 (SD 24.3) years. The GBS incidence, age‐adjusted to the European standard population, was 1.51 (95% CI 1.18–1.90) per 100 000 person‐years in 1996, higher in males and increased with age. When compared with selected studies, the GBS incidence in Sweden is moderately high, and the variation of GBS incidence in Europe seems to be small.
Closed‐ and open‐loop handwriting performance in patients with multiple sclerosis
Authors: Schenk T. , Walther E. U. , Mai N.
Published: July 2002

Normal subjects use an open‐loop motor control strategy in handwriting, but they are able to switch to closed‐loop motor control when the demands on accuracy increase. These closed‐loop handwriting movements of normal subjects resemble the inefficient movements found in writing‐impaired patients. The hypothesis that such movement deficits may in fact reflect the use of a closed‐loop strategy was tested in a group of writing‐impaired patients with multiple sclerosis (MS). The handwriting movements of 10 MS patients and 20 control subjects were examined with a digitizing tablet. Three conditions were used: a standard writing task (expt 1), a closed‐loop condition (expt 2), and an open‐loop condition (expt 3). Individual stroke movements were analysed. Stroke duration and segmentation were increased for MS patients in the standard writing task. The same was found for control subjects when they wrote under closed‐loop conditions. However, under open‐loop conditions, the handwriting movements of the MS patients were as fast and fluent as that of control subjects. The results support the hypothesis that the movement characteristics of the writing‐impaired MS patients reflect an inadequate use of a closed‐loop motor control strategy.
The prevalence of optometric anomalies and symptoms in children receiving special tuition
Authors: Baraas Rigmor C. , Demberg Anneli
Published: July 2002

A case‐control study was performed where 9 pupils receiving special tuition (ST‐group) were compared with 36 controls. Six (66,7%) of the pupils in the ST‐group were diagnosed as dyslexic. No significant correlation was revealed between receiving special tuition and having reduced visual function, nor between reduced visual function and number of visually related symptoms. Although the number of symptoms was not significantly greater in the ST‐group, some of the symptoms were significantly more common in the ST‐group, and none were significantly more common in the control group.
Leaf Epidermal Hydathodes and the Ecophysiological Consequences of Foliar Water Uptake in Species of Crassula from the Namib Desert in Southern Africa
Authors: Martin C. E. , von Willert D. J.
Published: July 2002

Abstract: Epidermal hydathodes were found on leaves of 46 of 48 species of Crassula collected from the Namib Desert in southern Africa. The possibility that these structures might allow the absorption of surface water was investigated in 27 species (including subspecies). The presence of hydathodes on leaf epidermi correlated, in most cases, with increases in leaf thickness and enhanced rates of nocturnal, and sometimes diurnal, CO2 uptake following wetting of the leaves during the night. The precise nature of these responses varied depending on the species. In addition, wetting only the older leaves on the lower portion of the shoot of C. tetragona ssp. acutifolia not only resulted in increased thickness of these leaves, but also effected an increase in leaf thickness and stimulation of CO2 uptake rates in the distal, younger portion of the shoot that was not wetted. Overall, foliar hydathodes were implicated in the absorption of surface water in many species of Crassula such that the ecophysiology of these desert succulents was positively affected. Although rainfall in the Namib Desert is infrequent, surface wetting of the leaves is a more common occurrence as a result of nighttime dew or fog deposition. Presumably, species with hydathodes benefit directly from this source of moisture. These findings have important implications in understanding a relatively unexplored adaptation of some xerophytes to an extremely arid environment.
Fabrication of YBa2Cu3O7−y superconducting coatings by electrophoretic deposition
Authors: Chu C. T. , Dunn B.
Published: July 2002

Coatings of YBa2Cu3O7−y were deposited by electrophoresis on Cu, Ag, polycrystalline Al2O3, and single-crystal MgO and YSZ substrates. Acetone was used as the electrophoretic vehicle and a field of 500 V/cm was applied in the deposition process. The deposited coatings were fired in air at or above 900 °C. For coatings on Ag, MgO(Ag), and YSZ(Ag) substrates, sharp superconducting transitions at ∼90 K were obtained. Intermediate layers were formed on Cu, Al2O3(Al), and YSZ(Ag) substrates as a result of interfacial reactions during firing. The interfacial reactions affected the superconducting transition and also led to the development of a preferred orientation in the coating.
Ruderman–Kittel coupling between ferromagnets separated by a nonmagnetic layer
Authors: Baltensperger W. , Helman J. S.
Published: July 2002

For the coupling of two ferromagnets separated by a nonmagnetic layer, the Ruderman–Kittel [C. Kittel, Quantum Theory of Solids (Wiley, New York, 1963)] theory gives an expression which oscillates as a function of the thickness of the laser and asymptotically decreases as the reciprocal square of the thickness. The prefactor is independent of the electron density.
Preparation and characterization of nanocrystalline cubic boron nitride by microwave plasma-enhanced chemical vapor deposition
Authors: Saitoh Hidetoshi , Yarbrough Walter A.
Published: July 2002

Polycrystalline boron nitride films have been deposited using microwave plasma-enhanced chemical vapor deposition. IR absorption spectra of films deposited using NaBH4 as the boron source in NH3 and H2 gases showed absorptions which are nearly the same as the characteristic vibrational modes seen in cubic and pyrolytic boron nitrides. Films deposited at 5 Torr also showed electron diffraction patterns for pyrolytic boron nitride, turbostratic boron nitride and cubic boron nitride. At higher gas pressures, only rings consistent with the formation of amorphous and cubic boron nitride were observed. Although the Raman spectra from a film deposited at 60 Torr showed broad peaks at ∼1080 and ∼1310 cm−1, the positions of the Raman lines for cubic boron nitride, no x-ray diffraction lines could be observed except that of the silicon substrate.
Molecular beam epitaxy growth of epitaxial barium silicide, barium oxide, and barium titanate on silicon
Authors: McKee R. A. , Walker F. J. , Conner J. R. , Specht E. D. , Zelmon D. E.
Published: July 2002

Thin-film epitaxial structures of BaSi2, BaO, and BaTiO3, have been grown on the (001) face of silicon using ultrahigh vacuum, molecular beam epitaxy (MBE) methods. Source shuttering for the metal species coordinated with a pulsed, or cyclic, oxygen arrival at the growing oxide surfaces significantly improves film quality. The epitaxial growth of BaO is accomplished without silica formation at the BaO/Si interface by stabilizing BaSi2 as a submonolayer template structure. In situ ellipsometric measurements of the indices of refraction for BaO and for BaTiO3 in a BaTiO3/BaO/Si multilayer gave n=1.96 for BaO and n=2.2 for the BaTiO3, within 10% of their bulk values. These values suggest that this structure can be developed as an optical waveguide. BaO is impermeable to silicon for films as thin as 10 nm at temperatures as high as 800 °C, and good epitaxy can be obtained from room temperature to 800 °C. The epitaxy is such that BaTiO3(001)∥BaO(001)∥Si(001) and BaTiO 3〈110〉∥BaO〈100〉∥Si〈100〉.
Blue continuously pumped upconversion lasing in Tm:YLiF4
Authors: Hebert T. , Wannemacher R. , Macfarlane R. M. , Lenth W.
Published: July 2002

Blue upconversion laser operation in Tm:YLiF4 at 450.2 nm on the 1D2→3F4 transition, and at 483.0 nm on the 1G4→3H6 transition has been achieved using cw pumping with Ti Sapphire and DCM dye lasers. The 450.2-nm laser was excited by sequential two-photon absorption with 784.5-nm and 648-nm laser sources and was operated at temperatures up to 70 K. The 483.0-nm laser was pumped with a single red-dye laser using a wavelength resonant only with absorption from a metastable intermediate state but not with absorption from the ground state. With this avalanche absorption pumping scheme, 483.0-nm laser emission was observed up to 160 K.
Electro-optic and all-optical phase modulator on an indium tin oxide single-mode waveguide
Authors: Chen R. T. , Robinson D.
Published: July 2002

We have successfully demonstrated an In2O3:Sn semiconductor thin-film waveguide. The energy gap of the film can be manipulated from 3.1 eV (0.4 μm) to 3.7 eV (0.335 μm) by changing the ratio of In2O3 and SnO2. Waveguide propagation losses of 3 dB/cm for transverse magnetic (TM) and 8 dB/cm for transverse electric (TE) guided waves were experimentally confirmed at the wavelength of 632.8 nm. A phase modulator containing an indium tin oxide waveguide, two holographic mirrors, two microprisms, and two ohmic contacts were fabricated. Electro-optic (current injection) and all-optical modulations were conducted. A modulation depth of 18% was experimentally confirmed for the current injection device, using 15-V applied voltage, and a modulation depth of 15% using 250 mW 355 nm UV light as the activation sources. An In2O3:Sn waveguide device working at the cutoff boundary was made. A modulation depth of 26 dB was measured with an applied voltage of 30 V. An array of applications, including use in current sensors, ozone UV sensors, attenuated total reflection (ATR) modulators, delay lines for phased array antennae, and multiquantum wells are highly feasible.
Cubic boron nitride films synthesized by low-energy ion-beam-enhanced vapor deposition
Authors: Ikeda Tsutomu
Published: July 2002

Single phase-cubic boron nitride (cBN) films have been synthesized by means of the low-energy ion-beam-enhanced vapor deposition method. Cubic BN films were deposited at 4 nm min−1 by electron-beam evaporation of boron with N2+Ar ion beam bombardment under the energy range of 500–600 eV, at ion beam current density around 0.4 mA cm−2, and also, could be obtained in both cases with external rf or dc substrate biasing. The infrared spectra showed strong absorption at 1090 cm−1, which was shifted significantly towards a higher wave number due to the residual internal stress in the cBN films. High-resolution transmission electron microscopy of cBN films deposited showed that the microstructure consists of polycrystalline particles with a size of 10 nm.
Relative intensity noise of vertical cavity surface emitting lasers
Authors: Kuchta Daniel M. , Gamelin J. , Walker J. D. , Lin J. , Lau K. Y. , Smith J. S. , Hong M. , Mannaerts J. P.
Published: July 2002

A study of the relative intensity noise (RIN) of two all semiconductor vertical cavity surface emitting lasers is presented. We find that the slope of the low frequency RIN agrees with theory for the fundamental mode only and that transverse modes introduce sharp changes in the RIN and put a limit on the minimum attainable RIN. For the fundamental mode, both devices achieve a RIN of less than −140 dB/Hz for optical powers less than 1 mW. This good performance is attributed to the high reflectivity of the cavity mirrors.
Observation of boron-related photoluminescence in GaAs layers grown by molecular beam epitaxy
Authors: Brierley Steven K. , Hendriks Henry T. , Hoke William E. , Lemonias Peter J. , Weir David G.
Published: July 2002

Boron-doped GaAs films grown by molecular beam epitaxy have been studied by photoluminescence. Two boron-related peaks have been observed in the spectra. The temperature dependence of these peaks is characteristic of acceptor levels, and a quantitative analysis yields activation energies of 71–72 and 188 meV. While the peak with the lower activation energy can be assigned with some confidence to the BAs0/− level, the second peak may be due to a BAs-SiGa complex rather than the BAs−/−− level.
Effect of Cr doping on the magnetoresistance and saturation field of epitaxial Fe1−xCrx(001)/Cr(001) multilayers
Authors: Daniels B. J. , Clemens B. M.
Published: July 2002

The effect of Cr doping of the Fe layer on the magnetoresistance and saturation field of epitaxial, sputter-deposited Fe1−xCrx(001)/Cr(001) multilayers was examined. Films with a composition of 100 Å Cr/[14 Å Fe1−xCrx/8 Å Cr]50, where x was varied from 0 to 0.5, were deposited onto single crystal MgO(001). The room temperature magnetoresistance was constant at approximately 31% for x≤0.2 and decreased with higher Cr concentrations. The saturation field decreased linearly with increasing Cr concentration over the entire range. Doping the Fe layer with Cr results in an increase of the spin-dependent scattering (Δρ) for 0.1≤x≤0.2 and an increase in the sensitivity of these films for all Cr concentrations.
Optimization of soft x-ray monochromators (invited)
Authors: Padmore H. A.
Published: July 2002

The development of high-resolution, grazing-incidence soft x-ray monochromators is discussed, and the performance of competing designs is reviewed in terms of efficiency, ultimate resolution, and order sorting. In particular, the characteristics of astigmatically corrected spherical grating monochromator systems (SGM) is examined. A new design is presented in which a variable angle premirror is used to eliminate the wavelength dependent image distance of the SGM and allows the use of order sorting ranges. The properties of a competing design using a plane variable angle premirror, plane grating, and spherical mirror combination are presented, and similarities between this and the corrected SGM are discussed. Flux and resolution data are presented for an undulator monochromator of this latter design.
A low noise highly integrated bolometer array for absolute measurement of VUV and soft x radiation
Authors: Mast K. F. , Vallet J. C. , Andelfinger C. , Betzler P. , Kraus H. , Schramm G.
Published: July 2002

A new low noise miniaturized multichannel bolometer module for absolute measurements in the VUV and soft x spectral ranges is described. Highly integrated four-channel modules (2×3.3×1.5 cm3) each comprising four independent ac-excited (50 kHz) metal resistor bolometer bridges were successfully tested on a large tokamak (Tore Supra in Cadarache) and on an electron synchrotron (BESSY in Berlin). The bolometer system features a linear response to the absorbed radiation power, a low detection limit (≤1.0×10−6 W cm−2 on Tore Supra with an integration time of τint=10×10−3 s) and a low NEP (≤10×10−9 W on BESSY). The thermal cross-talk between adjacent detectors is negligible (<0.003) and a low thermal drift ΔUBr/ΔT < 10−4 V °C−1 is achieved. It can be operated at a maximum temperature of 150 °C, at high magnetic fields (tested up to B=4.5 T in the laboratory) and survives high nuclear radiation doses. The system offers the possibility of detecting low-power VUV and soft x-radiation with sampling rates of up to 10 kHz on plasma machines and of absolutely calibrating VUV and soft x instruments. Effective suppression of electric, thermal and nuclear radiation interferences is characteristic of the bolometer system.Strain gauge effects, which could affect the behavior of the bolometers at high magnetic fields, are suppressed by the ac-excitation technique.
Recent advances in photoacoustic calorimetry: Theoretical basis and improvements in experimental design
Authors: Arnaut Luís G. , Caldwell Richard A. , Elbert Jeffrey E. , Melton Lynn A.
Published: July 2002

Recent developments in time-resolved photoacoustic calorimetry (PAC) are discussed. An equation is derived relating the amplitude of the maximum photoacoustic signal to parameters of a photoacoustic cell, to physical properties of the solvents, and to the energy deposited as heat. The equation is validated by a series of scaling experiments: it correctly correlates the dependence of the PAC signal on cell thickness, on energy deposition, and on solvent properties. The dominant sources of background signal have been determined and the background signal reduced substantially relative to previous work. It is now possible to measure energies and lifetimes of transients in solutions with optical densities as low as ∼5×10−4. Data are presented for the energy of 2-cyclopentenone triplet, a transient for which interpretable PAC measurements were previously not possible. Its triplet energy is 73.1±1.1 kcal/mole. With reduced background and a faster digital storage oscilloscope, a quite short transient lifetime, 7.53±0.2 ns, and a triplet energy of 51.0±2.1 kcal/mol have been measured for 1,1-bis-(p-bromophenyl)ethene. The lifetime agrees very well with that determined by kinetic absorption spectroscopy and the triplet energy agrees with expectation based on the unsubstituted 1,1-diphenylethene.
Optical diagnostic to measure ion temperature and parallel velocity fluctuations on the Tokamak Fusion Test Reactor
Authors: Evensen H. T. , Durst R. , Fonck R. J. , Paul S. F.
Published: July 2002

A high-throughput, high-frequency charge exchange recombination spectroscopy diagnostic (HF-CHERS) has been developed to give localized measurements of ion temperature and parallel velocity microturbulence (T̃i,ṽ∥) in the plasma core of the Tokamak Fusion Test Reactor (TFTR). HF-CHERS uses an interference filter spectrometer to measure intensity fluctuations simultaneously over several wavelength intervals of the line shape of the n=8–7 transition of C+5 (529 nm). T̃i and ṽ∥ are deduced from the moments of the emitted line shape. Using the beam emission spectroscopy optics on TFTR, measurements are made with 1–2 μs time resolution and ≊2 cm spatial resolution. The initial implementation of the diagnostic is expected to be sensitive to temperature fluctuations of T̃/T≥1%.
Installation of an on-line Lamb shift spin-filter polarimeter in the Triangle Universities Nuclear Laboratory atomic beam polarized ion sourcea)
Authors: Mendez A. J. , Roper C. D. , Dunham J. D. , Clegg T. B.
Published: July 2002

An atomic beam polarized ion source, used heavily since 1989 for producing polarized H± and D± beams for experiments between 25 keV and 20 MeV, has been modified to accept a Lamb shift, spin-filter polarimeter. In this source, polarized ground-state H or D atoms enter an electron cyclotron resonance ionizer where they are stripped to produce an outgoing positive polarized ion beam. When negative ions are desired, cesium vapor is introduced into a downstream charge-exchange canal. The polarimeter, based on an atomic physics concept first developed to produce nuclear-spin-polarized beams at Los Alamos, is designed to monitor the polarization of 2S1/2 metastable H or D atoms emerging from the cesium canal. Metastable 2S1/2 atoms created by electron pickup in a collision with cesium are ‘‘filtered’’ by the polarimeter according to magnetic substate, as the magnetic field imposed on the polarimeter cavity is tuned between 53 and 61 mT. Photons produced by subsequent quenching of these filtered atoms to their ground state are monitored downstream by a phototube to reveal the magnetic substate population of the incident positive beam. To install the polarimeter cavity and phototube assembly, the existing polarized ion source was lengthened by 30 cm. Installation is complete, and comparisons with calibrated nuclear polarimeters have shown agreement to better than 0.023. Principles of operation, a description of the hardware, measurements for cross calibration, and impressions gained from its use are all presented.
A new type of electrostatic ion trap for storage of fast ion beams
Authors: Dahan M. , Fishman R. , Heber O. , Rappaport M. , Altstein N. , Zajfman D. , van der Zande W. J.
Published: July 2002

A new technique for trapping of fast (keV) ion beams is presented. The trap, which is electrostatic, works on a principle similar to that of optical resonators. The main advantages of the trap are the possibility to trap fast beams without need of deceleration, the well-defined beam direction, the easy access to the trapped beam by various probes, and the simple requirement in terms of external beam injection. Results of preliminary experiments related to the radiative cooling of molecular ions are also reported.
Far infrared laser interferometer system on the Large Helical Device
Authors: Kawahata K. , Tanaka K. , Ito Y. , Ejiri A. , Okajima S.
Published: July 2002

A multichannel far-infrared laser interferometer system has been developed for the measurement of the spatial and temporal behaviors of the electron density on the Large Helical Device (LHD) at the National Institute for Fusion Science. Of several candidates for high power laser sources a 119 μm CH3OH laser was taken as a probing light. The optical configuration is of the Michelson interferometer type with 13 channels. The optical system of the interferometer is mounted on a massive stainless frame floated on three vibration isolating mounts. The resolution of the fringe counters is 1/100 fringes, and it corresponds to a line averaged density of 5.6×1016 m−3 at the central chord. Preliminary results have been obtained in the initial experiments on the LHD.
A mechanical shutter for light using piezoelectric actuators
Authors: Adams C. S.
Published: July 2002

The design and performance of a mechanical shutter for laser light based on low voltage piezoelectric transducers is described. By focusing the beam through a pair of piezo-mounted slits, a transmission of 80%, a switching time of 10 μs, and an extinction ratio of 300:1 are obtained.
A fast and compact quantum random number generator
Authors: Jennewein Thomas , Achleitner Ulrich , Weihs Gregor , Weinfurter Harald , Zeilinger Anton
Published: July 2002

We present the realization of a physical quantum random number generator based on the process of splitting a beam of photons on a beam splitter, a quantum mechanical source of true randomness. By utilizing either a beam splitter or a polarizing beam splitter, single photon detectors and high speed electronics the presented devices are capable of generating a binary random signal with an autocorrelation time of 11.8 ns and a continuous stream of random numbers at a rate of 1 Mbit/s. The randomness of the generated signals and numbers is shown by running a series of tests upon data samples. The devices described in this paper are built into compact housings and are simple to operate.
Large exchange bias and its connection to interface structure in FeF2–Fe bilayers
Authors: Nogués J. , Lederman D. , Moran T. J. , Schuller Ivan K. , Rao K. V.
Published: July 2002

Large exchange bias effects (ΔE∼1.1 erg/cm2) were observed in antiferromagnetic (FeF2)–ferromagnetic (Fe) bilayers grown on MgO. The FeF2 grows along the spin-compensated (110) direction. The FeF2–Fe interface roughness was characterized using specular and diffuse x-ray diffraction and atomic force microscopy. The magnitude of the exchange bias field HE increases as the interface roughness decreases. These results imply that magnetic domain creation in the antiferromagnet plays an important role.
First implementation of a superconducting integrated receiver at 450 GHz
Authors: Koshelets Valery P. , Shitov Sergey V. , Filippenko Lyudmila V. , Baryshev Andrey M. , Golstein Hans , de Graauw Thijs , Luinge Willem , Schaeffer Harry , van de Stadt Herman
Published: July 2002

An integrated quasioptical receiver consisting of a planar double dipole antenna, superconductor-insulator-superconductor mixer and a superconducting local oscillator (LO) with matching circuits has been designed, fabricated and tested in the frequency range 360–490 GHz. A flux-flow oscillator (FFO) based on unidirectional and viscous flow of magnetic vortexes in a long Josephson tunnel junction, is employed as a local oscillator. All components of the receiver are integrated on a 4 mm×4 mm×0.2 mm crystalline quartz substrate using a single Nb–AlOx–Nb trilayer. The lowest DSB noise temperature of 470–560 K has been achieved within a frequency range of 425–455 GHz.
Short-pulse wavelength shifting by four wave mixing in passive InGaAsP/InP waveguides
Authors: Darwish A. M. , Ippen E. P. , Le H. Q. , Donnelly J. P. , Groves S. H. , Swanson E. A.
Published: July 2002

We have demonstrated wavelength conversion in the 1.5 μm regime using the near band gap nonlinearity of semiconductor quantum wells. In a 7.5 mm long passive InGaAsP/InP single quantum well waveguide, a wavelength shift of 20 nm has been obtained with −11 dB conversion efficiency using picosecond pulses. We confirmed the ultrafast nature of the nonlinearity by measuring the conversion efficiency as a function of the frequency shift. An order of magnitude increase in the value of n2 close to the band gap is observed compared with the off-resonance value.
Electrical isolation in GaAs by light ion irradiation: The role of antisite defects
Authors: de Souza J. P. , Danilov I. , Boudinov H.
Published: July 2002

The evolution of the sheet resistance (Rs) in n-type GaAs layers during ion irradiation was studied using light mass projectiles like proton, deuterium, and helium ions at various energies. For all the cases, at the beginning of the irradiation, Rs increases with the accumulation of the dose. After reaching ≊109 Ω/⧠, Rs saturates, forming a plateau. This plateau is succeeded by a decreasing of Rs with the increase of the dose, denoting that conduction via damage-related mechanisms is taking place. The threshold dose to convert the conductive layer to a highly resistive one at room temperature or at 100 °C is found to scale with the inverse of the estimated number of displaced lattice atoms along the depth of the doped layer. Antisite defects formed by the replacement collisions are invoked to play the major role in isolation formation in GaAs by virtue of their lower sensitivity to dynamic annealing compared to other point defects.
The chemistry of the light rare-earth elements as determined by electron energy loss spectroscopy
Authors: Fortner J. A. , Buck E. C.
Published: July 2002

The energy loss spectra of the rare earths are characterized by sharp M4,5 edges, the relative intensities of which are characteristic of the 4f-shell occupancy of the excited ion. For the light rare earths, the dependence of these relative peak heights on 4f-shell occupancy is quite pronounced. Thus they may be used to determine the oxidation state of the multivalent elements Ce and Pr. The second derivative of the spectrum is shown to be extremely sensitive to the chemical environment. Modern instrumentation and detection techniques allow the oxidation state of Ce and Pr to be determined even when they are present as only minor constituents.
Grain boundary effects on carrier transport in undoped polycrystalline chemical-vapor-deposited diamond
Authors: Han S. , Wagner R. S.
Published: July 2002

A quantitative measure of grain-boundary effects on the carrier transport properties in polycrystalline chemical-vapor-deposited diamond has been obtained using a 10-ns hard x-ray excitation source. Two device geometries were used to gain insight into the extent of grain-boundary effects: one having the applied electric field normal and the other parallel to the grain orientation. The applied electric field intensity was varied to adjust the mean-free carrier drift distance. The degradation in the carrier transport properties at an electric field intensity of 10 kV/cm by the grain-boundary appears to be approximately a factor of two in comparison to the intragrain carrier transport.
Silicon micromachined ultrasonic immersion transducers
Authors: Soh H. T. , Ladabaum I. , Atalar A. , Quate C. F. , Khuri-Yakub B. T.
Published: July 2002

Broadband transmission of ultrasound in water using capacitive, micromachined transducers is reported. Transmission experiments using the same pair of devices at 4, 6, and 8 MHz with a signal-to-noise ratio greater than 48 dB are presented. Transmission is observed from 1 to 20 MHz. Better receiving electronics are necessary to demonstrate operation beyond this range. Furthermore, the same pair of transducers is operated at resonance to demonstrate ultrasound transmission in air at 6 MHz. The versatile transducers are made using silicon surface micromachining techniques. Computer simulations confirm the experimental results and are used to show that this technology promises to yield immersion transducers that are competitive with piezoelectric devices in terms of performance, enabling systems with 130 dB dynamic range. The advantage of the micromachined transducers is that they can be operated in high-temperature environments and that arrays can be fabricated at lower cost.
High p-type conductivity in cubic GaN/GaAs(113)A by using Be as the acceptor and O as the codopant
Authors: Brandt Oliver , Yang Hui , Kostial Helmar , Ploog Klaus H.
Published: July 2002

P-type room-temperature conductivities as high as 50/Ω cm are achieved in cubic GaN layers by the concept of reactive codoping. We use Be as the acceptor species and O as the reactive donor to render isolated Coulomb scatterers into dipole scatterers. This concept allows us to achieve high hole mobilities and thus p-type conductivities.
Transient terahertz reflection spectroscopy of undoped InSb from 0.1 to 1.1 THz
Authors: Howells S. C. , Schlie L. A.
Published: July 2002

Using transient terahertz reflection spectroscopy, the far-infrared (0.1–1.1 THz) reflection amplitude and associated phase change upon reflection from undoped InSb was measured between 80 and 260 K. Using the Drude model, the transient terahertz data were fit by adjusting the values for the electron mobility and carrier concentration. The close agreement between the data and model validates using the Drude model to describe the electronic and optical properties of InSb below 1 THz. These results suggest a possible application of transient terahertz reflection spectroscopy for measuring semiconductor properties of thick samples without surface contact.
Determination of lattice polarity for growth of GaN bulk single crystals and epitaxial layers
Authors: Ponce F. A. , Bour D. P. , Young W. T. , Saunders M. , Steeds J. W.
Published: July 2002

The polarity of the lattice of bulk single GaN crystals and the polarity of homoepitaxial and heteroepitaxial-on-sapphire GaN thin films has been studied using convergent beam electron diffraction. Diffraction patterns obtained at 200 kV for the 〈1–100〉 projection of GaN were matched with calculated patterns. The lattice orientations of two commonly observed bulk single-crystal facets were identified. It is shown that the smooth facets in single crystals correspond to the (0001), Ga-terminated, lattice planes, whereas the rough facets correspond to the (0001̄), N-terminated, planes. It is also shown that metalorganic chemical vapor deposition epitaxy retains the polarity of the substrate, i.e., no inversion boundaries were observed. Heteroepitaxy on sapphire is shown to grow in the (0001), Ga-terminated orientation.
Interfacial characteristics of N2O and NO nitrided SiO2 grown on SiC by rapid thermal processing
Authors: Li Hui-feng , Dimitrijev Sima , Harrison H. Barry , Sweatman Denis
Published: July 2002

Interfacial characteristics of Al/SiO2/n-type 6H–SiC metal–oxide–semiconductor capacitors fabricated by rapid thermal processing (RTP) with N2O and NO annealing are investigated. Interface state density was measured by a conductance technique at room temperature. RTP oxidation in pure O2 leads to an excellent SiO2/n-type 6H–SiC interface with interface state density in the order of 1010–1011 eV−1 cm−2. NO annealing improves the SiO2/n-type 6H–SiC interface, while N2O annealing increases the interface state density.
Hybrid Hall effect device
Authors: Johnson Mark , Bennett Brian R. , Yang M. J. , Miller M. M. , Shanabrook B. V.
Published: July 2002

A novel magnetoelectronic device incorporating a single microstructured ferromagnetic film and a micron scale Hall cross was fabricated and characterized at room temperature. Magnetic fringe fields from the edge of the ferromagnet generate a Hall voltage in a thin film semiconducting Hall bar. The sign of the fringe field, as well as the sign of the output Hall voltage, is switched by reversing the magnetization of the ferromagnet. This new device has excellent output characteristics and scaling properties, and may find application as a magnetic field sensor, nonvolatile storage cell, or logic gate.
Mixing at terahertz frequency band using YBa2Cu3O7−δ bicrystal Josephson junctions
Authors: Chen J. , Myoren H. , Nakajima K. , Yamashita T. , Wu P. H.
Published: July 2002

Using high-Tc Josephson junctions made of YBa2Cu3O7−δ deposited across MgO bicrystal boundary, at terahertz (THz) frequency band, we demonstrated both fundamental and harmonic mixing. Radiation from a far-infrared laser was coupled to the junction, which was integrated with a planar bow-tie antenna, via an extended hyperhemispherical silicon lens. Fundamental mixing manifested itself in the junction’s dc current–voltage (I–V) curve as a third Shapiro step in addition to those two induced by the THz laser lines from a slightly misaligned resonator. In harmonic mixing between a THz laser line and a microwave local oscillator, the highest harmonic number we could get was 490 with a signal-to-noise ratio of 9 dB at the intermediate frequency.
Stress-induced fragmentation of multiwall carbon nanotubes in a polymer matrix
Authors: Wagner H. D. , Lourie O. , Feldman Y. , Tenne R.
Published: July 2002

We report the observation of single nanotube fragmentation, under tensile stresses, using nanotube-containing thin polymeric films. Similar fragmentation tests with single fibers instead of nanotubes are routinely performed to study the fiber-matrix stress transfer ability in fiber composite materials, and thus the efficiency and quality of composite interfaces. The multiwall nanotube-matrix stress transfer efficiency is estimated to be at least one order of magnitude larger than in conventional fiber-based composites.
Lead-free high-strain single-crystal piezoelectrics in the alkaline–bismuth–titanate perovskite family
Authors: Chiang Yet-Ming , Farrey Gregory W. , Soukhojak Andrey N.
Published: July 2002

Doped alkaline–bismuth–titanate perovskite single crystals have been grown in ferroelectric phases with high piezoelectric actuation. Rhombohedral-phase Na1/2Bi1/2TiO3–BaTiO3 crystals exhibit up to 0.25% free strain with low hysteresis along the cubic 〈001〉 direction (d33∼450 pC/N). Tetragonal phase crystals exhibit free strains as high as 0.85% with greater hysteresis characteristic of domain switching; low field d33 exceeds 500 pC/N. Strain energy densities exceed those of optimized polycrystalline lead perovskites, and actuation capability is retained at compressive stresses >100 MPa.