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  • Springer  (5)
  • German Medical Science GMS Publishing House; Düsseldorf
  • 1990-1994  (5)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 50 (1990), S. 151-156 
    ISSN: 1432-0630
    Keywords: 61.70 ; 17.55
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Electrically active deep levels related to zinc in silicon are investigated in n- and p-type silicon using Deep-Level Transient Fourier Spectroscopy (DLTFS) measurements. While in n-type silicon a level at E C−0.49 eV is observed, the main zinc-related levels in p-type silicon are determined to be E V+0.27 eV and E V+0.60 eV. The latter are associated with zinc situated on regular silicon lattice sites. The emission rate of these centers exhibits a field dependence which cannot be quantitatively explained with the Poole-Frenkel model. On the other hand, a shallow level at E V+0.09 eV is observed only in boron-doped silicon which may be related to a zinc-boron complex. Other zinc-related levels are found at E V+0.23 eV and E V+0.33 eV, their concentration depending on that of zinc on substitutional sites. In addition, the evaluation of depth profiles and the analysis of the field dependence of the emission rate based on the DLTFS method is presented.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1351
    Keywords: Eye growth ; Diurnal rhythms ; Myopia ; Dopamine ; Retina ; Chicken
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract 1. If the eyes of young chickens are deprived of clear vision by translucent occluders, they develop considerable amounts of axial myopia within days. At the same time, the day time retinal dopamine levels drop by about 30%. Because the retinal dopamine levels of normally sighted chicks also differ diurnally and are low at night, we expected that the rate of axial eye growth might also differ during this time. 2. Unexpectedly, eyes grew in length only during the day (about 0.13 mm/day) and even shrank during the night (about -0.04 mm/night, average net growth + 0.09 mm in 24 h). 3. If the eyes were occluded, they grew both during the day and also at night (average net growth: + 0.16 mm in 24 h). Therefore, development of deprivation myopia was a result of the lack of growth inhibition at night rather than of excessive growth during the day when the actual deprivation occurred. 4. Suppression of dopaminergic retinal pathways by intravitreal injections of the neurotoxin 6-hydroxy-dopamine (6-OHDA) also suppressed development of deprivation myopia and it restored the growth inhibition at night. With normal visual experience, the drug had no effect on axial eye growth and refractive state. 5. Diurnal growth rhythms of the eyes disappeared under continuous light. 6. Our results show that: (a) normal diurnal eye growth rhythms require a “normal” (12/12 h) light cycle and normal visual experience; with a degraded retinal image during the day, growth rates at night change so that they relate to retinal dopamine levels in the opposite way as with normal visual experience, (b) intact retinal dopaminergic pathways are necessary to mediate the deprivation-induced alterations in diurnal growth rhythms and myopia, (c) deprivation myopia is not simply a result of the lack of visual feedback control of eye growth during deprivation but rather of an active process related to abnormal diurnal dopamine rhythms.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2072
    Keywords: Conflict schedule ; FG 7142 ; Inverse agonist ; Punishment ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Previous work (Thomas et al. 1990) showed that an anxiolytic benzodiazepine increased the time allocated to responding in a conflict situation (where responses were both food-reinforced and shock-punished) versus a nonpunishment situation. The present experiment tested whether a benzodiazepine-receptor inverse agonist (FG 7142, 1–30 mg/kg) would have the opposite effect (i.e., decrease time spent responding in a punishment situation). Chain pulls determined whether a rat's lever presses were reinforced on 1) a lean variable-interval schedule, or 2) a richer variable-interval schedule in which responding also produced shock intermittently. FG 7142 dose-dependently decreased nonpunished lever responding, but did not affect punished responding. The drug nonselectively decreased chain pulling (the schedule-switching response). Like chlordiazepoxide, FG 7142 increased the time spent in the punishment component, showing that not all effects of benzodiazepine-receptor agonists and inverse agonists are opposite. These results are inconsistent with expectations that anxiogenic actions of FG 7142 should 1) decrease punished responding; 2) increase the rate of responses that terminate the punishment condition; and 3) decrease time spent in the punishment component. Rather, nonsuppressed responding seems most sensitive to decreases by FG 7142.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-2072
    Keywords: Chlordiazepoxide ; Flumazenil ; Preference ; Multiple schedule ; Conflict ; Rats
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Male food-restricted hooded rats were trained to respond on a two-component multiple schedule. Reinforcement density was several times higher in one component than in the other. However, responses were intermittently punished with shock in the richer reinforcement component (conflict situation). Shock intensities were adjusted to produce mild and strong suppression of responding in two separate phases. Half of the rats controlled which component was operating (Preference group) and half did not (Yoked group). The effect of chlordiazepoxide (CDZ; 0, 1, 3, and 10 mg/kg; IP) was measured on component preference and response rate. Chlordiazepoxide increased both time spent in the conflict situation and response rate in that component. This is the first study employing a schedule that permitted these two behavioral indices to be measured independently in a conflict paradigm. Response rates were also increased in the unpunished response alternative, but to a lesser degree than in the conflict situation. The effects of CDZ were at least partially mediated by the benzodiazepine receptor because CDZ's effects were diminished by flumanezil (10 mg/kg; IP), a benzodiazepine antagonist.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The gain recovery dynamics of multiple quantum well semiconductor optical amplifiers, following gain compression caused by ultrashort optical pulse excitation, have been studied for several devices of different structures. Fast, slow, and intermediate time constants are identified. The fast component (0.6 to 0.9 ps) corresponds to cooling of the dense, inverted electron-hole plasma. The slow component (150 to 300 ps) corresponds to replenishment of carriers from the external bias supply, with the dynamics dominated by spontaneous recombination (primarily Auger) of the electron-hole plasma. The intermediate time constant (2 to 14 ps) is caused by carrier capture by the quantum wells and is structure-dependent. For most of the devices, the capture process is dominated by diffusion-limited transport in the cladding/barrier region. The variation of carrier density and temperature also affects the refractive index profile of the devices and, hence, affects the waveguiding properties. Dynamical variation of the mode confinement factor is observed on the fast and slow timescales defined above.
    Type of Medium: Electronic Resource
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