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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 768 (1995), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 774 (1995), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
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  • 3
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The results of spectral measurements in the D iii–D divertor region, carried out using a high-resolution spectrometer and a survey spectrograph developed at the TRINITI Laboratory, Russia are presented in this report. Observations were made along a vertical chord passing through the X point and intersecting the divertor floor at the major radius of the V1 ports. The high-resolution spectrometer is designed for simultaneous measurements along eight spatial chords with a time resolution of 7 ms. Each of the eight spectra is dispersed over 512 pixels on an intensified charge coupled device (CCD) detector. 768 frames of data are recorded directly to RAM memory of a PC computer during every discharge. High optical throughput is achieved simultaneously with high spectral resolution; the instrument has an f/number of 3 and a spectral resolution of 0.025 nm. The spectrometer can also operate in survey mode, recording a spectral region of 13 nm with 0.1-nm resolution. Using Doppler broadening of spectral lines, the temperature of deuterium atoms and of C ii and C iii was obtained for L, H, and ELMing H-mode regimes in D iii–D. Using the survey spectrograph, photographic exposures of divertor plasma radiation were obtained spanning the spectral ranges 340–424 and 486–848 nm, in second and first orders of the grating, respectively. The spectrograph is stigmatic and has an f/number of 3. © 1995 American Institute of Physics.
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the investigation of the effect of growth temperature on point defect density of unintentionally doped GaN grown by atmospheric pressure metalorganic chemical vapor deposition and hydride vapor phase epitaxy. A correlation between photoluminescence (PL) spectra and the concentration of donors and acceptors in unintentionally doped GaN is presented. The effects of oxygen and native acceptors on the electrical and optical properties of GaN epitaxial layers are discussed and a classification of PL data is presented. On this basis we show that oxygen creates a shallow donor in GaN with an activation energy of about 23.5±1 meV. We determine that the concentration of native acceptors in GaN increases with an increase in growth temperature. These native acceptors, probably gallium antisites (GaN) and/or gallium vacancies (VGa), are nonradiative defects. We show that a second donor level in GaN has an activation energy of about 52.5±2.5 meV and produces a PL peak with an energy of about 3.45 eV at low temperatures. From Hall investigations we show that a third donor in GaN has an activation energy of 110±10 meV. © 1999 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 2566-2568 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Band gap measurements have been carried out in strained and relaxed InxGa1−xN epilayers with x〈0.25. Values of x were determined from x-ray diffraction of relaxed films. The lowest energy absorption threshold, measured by transmittance, was found to occur at the same energy as the peak of the photoluminescence spectrum. Bowing parameters for both strained and relaxed films were determined to be 3.42 and 4.11 eV, respectively. The dependence of the band gap shift, ΔEg, on strain is presented. © 1999 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 2776-2778 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present an approach to determine the critical layer thickness in the InxGa1−xN/GaN heterostructure based on the observed change in the photoluminescence emission as the InxGa1−xN film thickness increases. From the photoluminescence data, we identify the critical layer thickness as the thickness where a transition occurs from the strained to unstrained condition, which is accompanied by the appearance of deep level emission and a drop in band edge photoluminescence intensity. The optical data that indicate the onset of critical layer thickness, was also confirmed by the changes in InxGa1−xN surface morphology with thickness, and is consistent with x-ray diffraction measurements. © 1999 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 2550-2552 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental results are presented for the phase noise of a relaxation oscillator consisting of a resonant-tunneling diode in series connection with a transmission line, one end of which is shorted. Unlike constant-wave negative-resistance oscillators, the resonant-tunneling relaxation oscillator (RTRO) emits a sequence of sharp current pulses that are mode locked to the fundamental mode of the cavity formed by the short-circuited transmission line. The phase noise in the RTRO was investigated with and without injection locking by a weak sinusoidal source. Injection-locking gain of 51 dB was measured for fundamental injection locking. Subharmonic injection locking was demonstrated out to the 12th subharmonic. Also, timing jitter as low as 200 fs was measured for an RTRO that emitted ∼ 30 ps pulses at a repetition rate of 1.1 GHz. © 1998 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 2742-2753 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Possible domain patterns are developed for (001) oriented (pseudocubic indexing) epitaxial rhombohedral perovskite ferroelectric (FR) films. We assume that the films are grown above their Curie temperature (TC) in a cubic paraelectric (PC) state. The rhombohedral distortion consists of a "stretch" along one of the four 〈111〉 crystallographic directions of the cubic perovskite unit cell. Domain pattern formation is concurrent with the PC→FR transformation on cooling from the growth temperature. The domain patterns form to minimize elastic energy in the film, at the energetic expense of both forming domain boundaries and developing local stresses in the substrate. Eight possible domains may form, half of which are related by inversion, thus leading to four mechanically distinct variants. The possible domain walls are determined by mechanical and charge compatibility and follow closely from the analysis of Fousek and Janovec [J. Appl. Phys. 40, 135 (1969)]. Domain patterns may develop with either {100} or {101} boundaries. In both cases, the individual domains in the patterns are energetically degenerate and thus equal width lamellar patterns are predicted. When polarization is included in the analysis, the {100} boundary patterns have no normal component of the net polarization, whereas the {101} boundary patterns correspond to the fully poled state. We report on experimental observation of {100} domain patterns in epitaxial PbZr0.80Ti0.20O3 and PbZr0.65Ti0.35O3 films. © 1998 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 2787-2789 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental and numerical results are presented for a high-frequency oscillator consisting of a resonant-tunneling diode (RTD) series-embedded in a transmission line, one end of which is short circuited and the other end terminated with a load resistor. Like relaxation oscillators, the ac voltage across the RTD is a square wave. However, the current wave form (and hence the load wave forms) consists of a sequence of sharp pulses that are essentially locked to the fundamental mode of the transmission line. © 1997 American Institute of Physics.
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  • 10
    ISSN: 1615-6102
    Keywords: Adenylate cyclase ; Cell cycle ; Chlamydomonas reinhardtii ; Cyclic AMP ; Cyclic nucleotide phosphodiesterase ; Mutant strains
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Three independent isolates ofChlamydomonas, selected for caffeine resistance, were found to arrest in G1 phase, as determined by quantitative fluorescence measurements of DNA, when grown at a non-permissive temperature. This cell cycle arrest correlated with lowered levels of cAMP and of adenylate cyclase activity. The arrested cells could be rescued by added cAMP but not AMP, hence the defect was not one of general purine metabolism. Back-crosses to wild type revealed that the phenotypes observed result from a combination of three separable mutations. It is clear that the mutations define functions that are more stringently required for cell division than for growth since the mutant strains are able to grow up to fifteen times normal size while blocked at the non-permissive temperature. The possible interaction of cAMP dependent events with division is discussed.
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