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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 6394-6397 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A method is proposed according to which critical current density Jc at various temperatures T and dc fields B is estimated on (Tl0.5Pb0.5)(Ba0.2Sr0.8)2Ca2Cu3Oy based upon the flux diffusion barrier heights U(J,B,T) determined by means of ac susceptibility measurement at different ac field amplitudes, frequencies, T, and B. Jc is also estimated by the dc hysteresis measurement and compared with the former. The high Jc(B,T) and Tc show that this Tl-based superconductor is one of the more promising high-Tc materials from a practical standpoint. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 1766-1770 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report here measurements of 1/f noise in vacuum photodiodes. The theoretical expression for the Hooge parameter αH is formally equivalent to the one for secondary emission 1/f noise. There is also 1/fγ noise due to fluctuations in the cathode work function; here γ∼3/2 is expected. The spectrum SIa( f ) for the latter varies as I2aV0a and for the former it varies as IaV3/2a, where Va is the anode voltage, and Ia the anode current. Enhanced shot noise was observed at higher frequencies; at lower frequencies the noise spectrum was of the 1/f type. The latter could be separated into a V0a component and a V3/2a component by measuring SIa( f ) vs Va. The V3/2a component of the 1/f spectrum could also be deduced from the current dependence of SIa( f ); both measurements mutually agreed well. The measured V3/2a component also agreed well with Handel's predictions; by proper choice of the anode-cathode distance dca (dca=0.6 cm) almost exact agreement could be obtained. In view of the fact that the overall accuracy of the data is not better than 25%–30%, any value of dca between 0.4 cm〈dca〈0.8 cm should be considered as giving good agreement; this is a very plausible range of values. We observed some poisoning effects in older devices. They are attributed to the decomposition of the dynode material under electron bombardment and give rise to long-term instability of the device noise.
    Materialart: Digitale Medien
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  • 3
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A systematic study of the 1/f noise dependence on the channel length in p- and n-channel silicon MOSFETs (metal-oxide-semiconductor field-effect transistors) is presented. Devices made by the same procedure on the same chip were used. In this way, the nonuniformity of noise sources, which strongly depend on the fabrication procedure (like 1/f noise produced by surface trapping), was avoided. Hooge's parameter αH was used as a measure of the magnitude of the 1/f noise in the device. The αH was found to vary as the square of the channel length in p MOSFETs and in the most of the n MOSFETs. Existing theories and known noise mechanisms do not explain this dependence. The incorporation of a recent theory involving the acceleration 1/f noise in semiconductors, developed by van der Ziel, explains the experimental data very well. The αH was found to be independent upon the electric field and the extraction of an effective time constant was used for comparison between theory and experiment.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 1182-1188 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The generation rates and annealing behavior of the irradiation defects in n- and p-type hydrogen-grown float-zoned silicon (irradiated with γ rays from 60Co) have been studied by the deep-level transient spectroscopy technique and compared with those of irradiated argon-grown float-zoned silicon. Assuming the generation rate of the irradiation defects created by γ rays in argon-grown float-zoned silicon is 1, then the generation rates of the A center, divacancy, and phosphorus vacancy in n-type hydrogen-grown float-zoned silicon are 0.23, 0.78, and 0.19, respectively, while the generation rates of the divacancy and H(0.37 eV) in p-type hydrogen-grown silicon are 0.79 and 0.10, respectively. Due to the existence of hydrogen, the generation rate reduction of the major irradiation defects in γ-ray irradiated silicon is more pronounced than that in 1-MeV electron irradiated silicon. Three hydrogen-related defects, H(0.10 eV), H(0.29 eV), and H(0.56 eV), were seen in γ-ray irradiated hydrogen-grown float-zoned silicon, among which H(0.10 eV) and H(0.56 eV) were reported by us to exist in electron irradiated hydrogen-grown float-zoned silicon, while H(0.29 eV) is reported for the first time. The convergence effect of annealing temperatures for the irradiation defects was observed. That is, the annealing temperatures at which the irradiation defects diminish are almost the same for most irradiation defects, similar to that in the case of electron irradiation, was observed, showing that this effect is characteristic of the hydrogen behavior in silicon, and irrelevent to the type of irradiation.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 3277-3280 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A 12-processor Linux PC cluster has been installed to perform between-pulse magnetic equilibrium reconstructions during tokamak operations using the EFIT code written in FORTRAN. The MPICH package implementing message passing interface is employed by EFIT for data distribution and communication. The new system calculates equilibria eight times faster than the previous system yielding a complete equilibrium time history on a 25 ms time scale 4 min after the pulse ends. A graphical interface is provided for users to control the time resolution and the type of EFITs. The next analysis to benefit from the cluster is CERQUICK written in IDL for ion temperature profile analysis. The plan is to expand the cluster so that a full profile analysis (Te, Ti, ne, Vr, Zeff) can be made available between pulses, which lays the ground work for Kinetic EFIT and/or ONETWO power balance analyses. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
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  • 6
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The confinement and the stability properties of the DIII-D tokamak [Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159] high-performance discharges are evaluated in terms of rotational and magnetic shear, with an emphasis on the recent experimental results obtained from the negative central magnetic shear (NCS) experiments. In NCS discharges, a core transport barrier is often observed to form inside the NCS region accompanied by a reduction in core fluctuation amplitudes. Increasing negative magnetic shear contributes to the formation of this core transport barrier, but by itself is not sufficient to fully stabilize the toroidal drift mode (trapped-electron-ηi mode) to explain this formation. Comparison of the Doppler shift shear rate to the growth rate of the ηi mode suggests that the large core E×B flow shear can stabilize this mode and broaden the region of reduced core transport. Ideal and resistive stability analysis indicates the performance of NCS discharges with strongly peaked pressure profiles is limited by the resistive interchange mode to low βN≤2.3. This mode is insensitive to the details of the rotational and the magnetic shear profiles. A new class of discharges, which has a broad region of weak or slightly negative magnetic shear (WNS), is described. The WNS discharges have broader pressure profiles and higher β values than the NCS discharges, together with high confinement and high fusion reactivity. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 7
    ISSN: 1365-2222
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: Background 5-Lipoxygenase (5-LO) and 5-lipoxygenase-activating protein (FLAP) are essential for cysteinyl-leukotriene (cys-LT) production, critical mediators in asthma.Objective We sought to identify novel promoter polymorphisms within the FLAP (ALOX5AP) gene promoter and test the role of these and the previously identified 5-LO (ALOX5) Sp1 promoter polymorphism in asthma susceptibility.Methods To assess genetic association with asthma phenotypes, we genotyped 341 Caucasian families (containing two asthmatic siblings) and non-asthmatic control subjects (n=184). Genetic association was determined by case–control and transmission disequilibrium test (TDT) analyses. To determine the functional role of polymorphisms on basal transcription, we generated ALOX5AP-promoter-luciferase constructs and transiently transfected human HeLa cells.Results A novel G/A substitution at –336 bp and a poly(A) repeat (n=19 or 23) at position −169 to −146 bp were identified in the ALOX5AP promoter. Genotyping found the −336 A and poly(A19) alleles at frequencies of q=0.06 and 0.12, respectively. No ALOX5AP allele was associated with asthma or asthma-related phenotypes in case–control or TDT analyses. ALOX5AP-promoter-luciferase analyses did not support a functional role of the −336 or poly(A) polymorphism in determining basal transcription. The ALOX5 Sp1 polymorphism was predominantly homozygous wild-type 5/5 (frequency q=0.70) and heterozygous 4/5 (q=0.23) genotypes and no allele was associated with asthma or asthma-related phenotypes.Conclusion Taken together, these data do not support a significant role for these polymorphisms in genetic susceptibility to asthma in the Caucasian population.
    Materialart: Digitale Medien
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  • 8
    ISSN: 1365-2222
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: Background  IL-4 by binding to its receptor (IL-4R) is essential for the development of airway inflammation present in asthma, through the induction of IgE synthesis in B cells and differentiation of T cells to a Th2 phenotype.Objective  To investigate the role of four common polymorphisms in the IL-4 (IL4-34CT and IL4-589CT) and IL-4Rα chain (IL4RAI50V and IL4RAQ576R) genes in conferring susceptibility to the development of atopy and/or asthma.Methods  Two polymorphisms in the IL-4 gene promoter, IL4-34CT and IL4-589CT, and two polymorphisms in the IL-4Rα chain gene, IL4RAI50V and IL4RAQ576R, have been genotyped using PCR-based methods in 341 asthmatic families and in 184 non-asthmatic adults recruited from the south of England.Results  Case–control analysis did not reveal differences in the distribution of the four polymorphisms between asthmatics and controls. However, the transmission disequilibrium test showed that the IL4-589 T allele was preferentially transmitted to asthmatic children (P=0.036) and that the IL4RAQ576 was preferentially transmitted to children with atopic asthma (P=0.018). Haplotype analysis showed a strong association between the IL4-34T/-589T haplotype and asthma per se (P=0.041), and a strong association between the IL4RA I50/Q576 haplotype and atopic asthma (P=0.006).Conclusion  Our data suggest that polymorphisms in the IL-4 and IL-4Rα chain genes might play a role both conferring susceptibility to and modulating severity of atopy and asthma.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Amsterdam : Elsevier
    Electrochimica Acta 39 (1994), S. 2629-2632 
    ISSN: 0013-4686
    Schlagwort(e): electrocatalysis ; electropolymerization ; hydrazine. ; modified electrodes ; phthalocyanine
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Amsterdam : Elsevier
    Chinese Astronomy and Astrophysics 5 (1981), S. 103-110 
    ISSN: 0275-1062
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Physik
    Materialart: Digitale Medien
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