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  • 1
    Digitale Medien
    Digitale Medien
    High precision soft x-ray reflectometer : Proceedings of the 5th international conference on synchrotron radiation instrumentation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 2248-2250 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: At the radiometry laboratory of the Physikalisch-Technische Bundesanstalt (PTB) a reflectometer for the soft x-ray spectral region has been operated for several years utilizing monochromatic radiation of a toroidal grating monochromator or a high-resolution plane grating monochromator. The monochromators cover the photon energy region from 35 to 1500 eV. New challenges due to the development of soft x-ray optical components led to the design of a second reflectometer with advanced capabilities. Samples with a diameter of up to 250 mm can be accommodated. The time required for sample exchange is reduced by using a lock chamber. The feasibility of sample positioning with high precision has been improved. Typical uncertainties of about 1%–2%, e.g., for the reflectance of multilayer mirrors, can be achieved. A detailed description of the reflectometer as well as some typical results showing the performance are presented. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1145720
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  • 2
    Digitale Medien
    Digitale Medien
    The soft x-ray transmission properties of thin polyimide windows and their application to future detectors (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 2570-2573 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The x-ray transmission properties of a very thin polyimide window in the range 7–310 A(ring) have been investigated. The window is nominally 0.24 μm thick and is supported by a hexagonal polyimide grid. Transmission of over 60% and 80% at the oxygen Kα and carbon Kα lines, respectively, have been achieved. The use of such windows as the entrance window of a gas scintillation counter (GSPC) operating as a broadband spectrometer at XUV wavelengths is discussed. Overall detector efficiencies of greater than 10% for wavelengths less than 150 A(ring) are possible to achieve. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1145659
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  • 3
    Digitale Medien
    Digitale Medien
    Fabrication and properties of intrinsic Josephson junctions in thin films of Tl-Ba-Ca-Cu-O (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 3396-3400 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have observed intrinsic Josephson effects for current flow perpendicular to the CuO2 planes in HTSC thin films. Tl-Ba-Ca-Cu-O thin films were deposited on step edges in LaAlO3 substrates. Due to the special preparation process, microbridges across such steps act as stacks of intrinsic Josephson junctions with current flow perpendicular to the CuO2 planes (STEP STACK junctions). Up to 130 individual junctions could be observed exhibiting high IcRN products up to 26 mV per junction. We observed ac-Josephson effects as Shapiro steps and in microwave emission experiments. At low temperatures sharp emission peaks were detected at frequencies of 11.3 and 24.2 GHz. Broad emission peaks from the whole stack were observed at temperatures close to Tc. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.363205
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  • 4
    Digitale Medien
    Digitale Medien
    Schottky-barrier fluctuations in Pb1−xSnxSe infrared sensors (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 7138-7143 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Epitaxial Pb1−xSnxSe layers have been grown on Si substrates, and Schottky-barrier infrared sensors were fabricated in the layers using Pb blocking contacts. The observed current–voltage characteristics (saturation currents j0 and ideality factors n) as a function of temperature are quantitatively explained with a fluctuation model of the barrier heights [J. H. Werner, W. Güttler, J. Appl. Phys. 69, 1991 (1522)]. The amount of the mean barrier fluctuation σ, which is typically 10–30 meV, depends on the layer quality and fabrication procedure. Higher σ causes higher j0 with increasing saturation values at low temperatures. In addition, the fluctuations cause high n(〉2) values at low temperatures. Layers with improved structural quality (higher mobilities and lower threading dislocation densities) lead to lower barrier fluctuations and, therefore, to increased sensitivities. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.363735
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  • 5
    Digitale Medien
    Digitale Medien
    Structure of epitaxial PbSe grown on Si(111) and Si(100) without a fluoride buffer layer (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 1911-1916 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Epitaxial growth of PbSe on (111)- and (100)-oriented Si substrates without an intermediate buffer layer is studied. It is found that on Si(111) the orientation of the IV-VI layer can by varied from (100) at 200 °C to (111) at 400 °C substrate temperature. On Si(100), only (100)-oriented layers were obtained for the whole temperature range. (100)-oriented layers with thicknesses above 0.5 μm were cracked due to thermally induced mechanical strain on cooldown to room temperature. This strain cannot be relaxed by dislocation glide in the first glide systems as it is the case for (111)-oriented layers. The structural quality of (100)-oriented PbSe layers on Si(100) and Si(111) is inferior compared to layers grown with an intermediate BaF2/CaF2 or CaF2 buffer layer. This implies that the covalent/ionic PbSe/Si interface seems to impede high-quality epitaxy, contrary to the well known ionic/ionic IV-VI/IIa-fluoride interface. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.361076
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  • 6
    Digitale Medien
    Digitale Medien
    Current carrying capability of multifilamentary (BiPb)2Sr2Ca2Cu3Ox tapes determined from transport and magnetization measurements (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 3287-3289 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The magnetic field dependence of the critical current IC(B) and the remanent magnetization of several multifilamentary (BiPb)2Sr2Ca2Cu3Ox tapes were measured. The low field behavior of IC(B) is interpreted by the self-field effect, whereas at higher fields, the field dependence for all tapes was found to be identical except for a constant factor. Although self-field transport critical current densities jC0 differed widely for the tapes, the intergranular critical current densities determined from remanent magnetization were found to be equal. The results indicate that the reduction of jC0 by macroscopic defects is an important factor, whereas locally the filaments are of high quality. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.120314
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  • 7
    Digitale Medien
    Digitale Medien
    Wide bandwidth (100) GaAs/fluorides quarter-wavelength Bragg reflectors grown by molecular beam epitaxy (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 3474-3476 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Broadband quarter-wavelength Bragg reflectors that consist of periodic stacks of fluorides (CaF2–BaF2–CaF2) and GaAs, centered at 1.4 μm, were grown by molecular beam epitaxy. Despite a total fluoride thickness as high as 720 nm, crack-free surface morphology was obtained. In this letter, we report a crack-free standard quarter-wavelength III–V semiconductor-fluoride Bragg reflector. With only three stacks, the bandwidth with reflectance above 95% is about 650 nm (1.15–1.80 μm), while, near the center wavelength, the reflectivity is as high as 99%. Both important wavelengths of 1.3 and 1.55 μm for optical communication are included in the very wide high reflectance plateau. These mirrors are expected to have wide applications for optical and optoelectronic devices. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.117256
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  • 8
    Digitale Medien
    Digitale Medien
    Anthropogenic CO2 in Southern Ocean surface waters: evidence from stable organic carbon isotopes (1997)
    Oxford, UK : Blackwell Science Ltd
    Terra nova 9 (1997), S. 0 
    Details
    ISSN: 1365-3121
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: We present an approach for tracing the fate of anthropogenic CO2, compiling a large data set of stable organic carbon isotope ratios from surface sediments, plankton, and sinking matter in the Atlantic Ocean. The δ13C values of sinking matter are generally lower by 0.5–4.6‰ compared to the surface sediments. This difference increases with increasing latitude, which is explained by a stronger modern increase in surface water [CO2 (aq)] in the Southern Ocean relative to the Tropical/Subtropical Ocean. Preindustrial dissolved CO2 concentrations in Atlantic surface waters, estimated from the δ13Corg of surface sediments, are compared to recently measured surface water [CO2 (aq)] values taken from literature. We obtain only a slight increase in [CO2 (aq)] at lower latitudes but a significant change of about 7 ± 2 μm in high latitudinal surface waters which we attribute to anthropogenic perturbation. Our results suggest that CO2 released by human activities has been stored in Southern Ocean surface waters.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-3121.1997.d01-29.x
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  • 9
    Digitale Medien
    Digitale Medien
    Growth of coniferous trees exposed to SO2 and O3 using an open-air fumigation system (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 18 (1995), S. 0 
    Details
    ISSN: 1365-3040
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.) and Sitka spruce (Picea sitchensis Bong. Carr.) were planted as 2-year-old seedlings in an open-air fumigation facility at Liphook in southern England in March 1985. The soil was a humoferric podzol of pH 4. SO2 fumigation began in May 1987 and continued until December 1990. Long-term mean SO2 concentrations were 4,13 and 22 nmol mo−1. Three plots, one at each SO2 level, were also exposed to O3 at an average of 1–3.times the ambient level. O3 fumigation ran from March to December 1988, May to December 1989 and February to December 1990. Each species reacted differently to treatment. Scots pine showed no growth response to either pollutant, although other work on the site demonstrated a number of deleterious effects of SO2 on this species, including increased leaf loss and foliar injury. Stem basal diameter growth of Norway spruce was depressed in SO2-treated plots. In contrast, extension growth of shoots of Sitka spruce increased in SO2-treated plots, in apparent response to codeposition of NH3-N. However, diameter growth of Sitka spruce main stems did not increase. No effects of O3 on growth were recorded for any species.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-3040.1995.tb00358.x
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  • 10
    Digitale Medien
    Digitale Medien
    A TnphoA insertion within the Bradyrhizobium japonicum sipS gene, homologous to prokaryotic signal peptidases, results in extensive changes in the expression of PBM-specific nodulins of infected soybean (Glycine max) cells (1995)
    Osney Mead, Oxford OX2 0EL, UK : Blackwell Science Ltd
    Molecular microbiology 18 (1995), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: Bradyrhizobium japonicum mutant 132 was obtained by random TnphoA mutagenesis of strain 110spc4. A 6.5 kb BamHI kanamycin-resistance-coding DNA fragment of mutant 132 was used as a hybridization probe to clone the corresponding wild-type fragment. DNA sequence analysis of a 3213 bp BamHI—ClaI fragment revealed that three open reading frames (ORFs) were encoded in the same orientation. Based on sequence similarities to other proteins in the database, the second ORF was called sipS (signal peptidase). The TnphoA insertion in mutant 132 was found to be in frame near the 3′ end of sipS. The resulting SipS—PhoA hybrid polypeptide was shown to be expressed in free-living B. japonicum and in Escherichia coli cultures. An immunoblot analysis with a polyclonal antibody directed against the alkaline phosphatase revealed the appearance of a weak signal of a 70 kDa polypeptide both in B. Japonicum and in E. coli, in agreement with the calculated size of the hybrid polypeptide. A much stronger 52 kDa band was also detected. Mutant 132 was specifically disturbed in the interaction with soybean (Glycine max) when the bacteria were released from the infection threads. The bacteroids were not stably maintained within the symbiosome. Numerous vesicles were found in the plant cytosol, which finally resulted in the formation of large vacuoles within the infected nodule cells. Immunohistochemical analyses with antibodies directed against nodulins of the peribacteroid membrane indicated a lower expression of these proteins. The mutant phenotype was genetically complemented by 4.4 kb BamHI fragment including sipS. Subfragments thereof also complemented a temperature-sensitive E. coli lepB mutant, demonstrating that the B. japonicum fragment was functionally replacing Lepts in E. coli. Genetic studies suggested that the three genes are organized in one common operon which is expressed from a promoter upstream of the sequenced region. Inactivation of the gene downstream of sipS did not result in a detectable phenotype.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2958.1995.18050831.x
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