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  • 1
    ISSN: 1432-1106
    Keywords: Long-term potentiation (LTP) ; Ventral posterior medial ; Thalamus ; Somatosensory cortex ; Bicuculline ; in vivo
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Extracellular single-unit techniques were employed to record unitary activity simultaneously from the thalamic ventral posterior medial (VPM) nucleus and the ipsilateral primary somatosensory cortex of adult rats. Cross-correlation analysis triggered by the spontaneous firing of thalamocortical relay neurons in VPM and the discharge of layer IV neurons in the corresponding ipsilateral cortical barrel indicated that the paired-units included in this study were strongly correlated in their activity. The baseline responses of highly correlated cortical/thalamic pairs to a 10 ms deflection of a vibrissa on the contralateral side were measured using poststimulus time histograms. After establishing the baseline response, high frequency activity in VPM was induced in one of two ways: i) direct electrical stimulation of thalamic neurons or ii) whisker stimulation in the presence of bicuculline methiodide (BIC) released near the thalamic neurons. Both methods resulted in a conditioning stimulus (CS) paradigm consisting of “bursts” of high-frequency activity (50–100 Hz) with an inter-burst interval of 150 ms (∼7 Hz). Almost immediately following the presentation of the CS, the response of layer IV cortical neurons to vibrissa stimulation increased by 37–62% over baseline values, which was maintained after the effects of BIC had worn off in VPM. This enhancement in the response of the cortical neurons was not accompanied by a concomitant increase in the thalamic responses. Thus, these results strongly suggest that the potentiation first occurred at the thalamocortical synapse.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-601X
    Keywords: 25.85.Ge ; 25.70.Jj ; 25.70.Gh
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We examine what information can be obtained from fission angular distributions through precise measurements and an analysis in terms of the simple statistical model of Ericson. We report on the systematics of the decoupling angle and present the role of the angular momentum coupling between the entrance and the exit channel. The results indicate that the directional coupling of the angular momentum in the entrance and the exit channel is always strong for heavy-ion induced fission, and the angular momentum coupling plays a decisive role on the angular distribution of fission fragments. The average channel spins of fission fragments 〈If〉 are deduced through the decoupling angles determined experimentally. They agree well with γ-multiplicity measurements.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1434-601X
    Keywords: 25.70.Jj ; 25.70.Lm ; 25.85.Ge
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The binary decay properties of the47V nucleus, produced in the35Cl +12C reaction, have been investigated at the35Cl bombarding energiesE lab = 180 and 200 MeV by means of a kinematical coincidence technique. Binary reaction products show full energy equilibration and a characteristic 1/sin(θ cm) angular distribution. The elemental distribution of the fully-damped products is asymmetric, similar to what has previously been observed in the decay of the56Ni nucleus. Comparison with theoretical model predictions suggests the occurrence of a fusion-fission rather than orbiting process. Moreover the calculations performed using the Extended Hauser-Feshbach Method reproduce well the experimental fission yields. A general discussion of orbiting and fusionfission experimental data of light heavy-ion systems is presented in the framework of the calculated number of available open channels for these systems.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 853-855 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A quantum mechanical formalism for the excitonic photoluminescence linewidth in semiconductor alloys due to band gap fluctuations caused by the random distributions of alloy components is presented. Using a quantum mechanical description for the excitonic system, the mean deviation of its transition energy due to the statistical potential fluctuations is calculated using a first-order perturbation theory. We then apply this formalism to calculate the linewidth of the ground state excitonic transition as a function of composition. Specifically, the excitonic linewidth in AlxGa1−xAs alloy as a function of Al concentration is calculated and compared with earlier models and available low-temperature photoluminescence data.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A variety of resist systems have been studied that owe their sensitivity to the occurrence of catalyzed electrophilic rearrangements or substitution processes. In most designs, polyfunctional or polymer-bound benzylic ethers, esters, or alcohols are used in the key step of the reaction, which is initiated by protonation of the latent electrophilic moiety, resulting in formation of a carbocationic center. Thermal activation of the electrophilic process leads to the formation of new C-C bonds with liberation of a proton; therefore the overall process is catalytic and amounts to chemical amplification. A variety of polymers and active small molecules that provide access to both negative and positive tone images have been tested, and sensitivities as high as 0.1 mJ/cm2 have been measured. In addition, several image reversal schemes involving either selective silylation of non-exposed areas or the in situ photogeneration of base have been tested and are presented.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 51 (1994), S. 1765-1770 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The effect of the molecular weight and acrylonitrile (AN) content of the styrene-acrylonitrile copolymer (SAN) on the morphology, mechanical properties, and rheological properties of acrylonitrile-butadiene-styrene terpolymer/poly(methyl methacrylate) (ABS)/PMMA (60/40 by weight) blends were studied. When the AN content of matrix SAN (32%) was close to that of graft SAN (30%) AN, rubber particles existed separately. However, with matrix SAN having 35% AN, rubber particles showed tendency to agglomerate each other. With increasing molecular weight of matrix SAN, impact strength, ultimate elongation, and abrasion resistance of the blend generally increased. Yield strength increased with molecular weight at a constant AN content of matrix SAN, and it decreased with the decrease of AN content in spite of the increasing molecular weight of SAN. Melt properties, rather than the morphological and mechanical properties, were more sensitive to the AN content, rather than the molecular weight of matrix SAN. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 2848-2853 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have developed a variational formalism to calculate the effects of electric and magnetic fields on confined hydrogenic donor states in asymmetric coupled double quantum well structures. It is demonstrated that an electric field applied along the growth axis can easily shift the electron wave function from one quantum well across the center barrier into the neighboring well, without ejecting the electron from a confined donor state. Depending on donor location in the structure, binding energy can either increase or decrease under the applied electric field, as had been found in the case of single quantum wells, but with significantly greater rates of change in response to the external field. The magnetic field applied along the growth axis of the quantum well structure leads to additional quantum confinement, increasing both the donor binding energies and the transition energy between the 1s and 2p+ donor states. Effect of the relative size of the two coupled quantum wells on the donor binding energy is also discussed. Dipole moment and polarizability of the confined donor states are obtained simultaneously as well.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 1788-1796 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A quantum statistical formalism has been developed for the excitonic luminescence linewidths and line shapes in semiconductor binary alloys due to band-gap fluctuations caused by the random distributions of the alloy components in an applied magnetic field. The virtual crystal approximation is used to estimate the local band-gap variations. The shifts of the excitonic transition energy due to the band-gap fluctuations are obtained using the first-order perturbation theory. A Gaussian line shape is obtained for the excitonic transition using standard statistical techniques. This formalism is applied to calculate the linewidths and line shapes associated with the ground-state excitonic transition as a function of alloy composition and magnetic-field strength in AlxGa1−xAs and InxGa1−xP alloys. The resulting linewidths and line shapes are in good agreement with the available low-temperature photoluminescence data; however, the calculated linewidths are consistently smaller than the measured values. The possible mechanisms responsible for this discrepancy are discussed. A comparison of excitonic linewidths obtained from the present theory with those calculated earlier is also presented.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4211-4215 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Three amorphous alloy powders in the Ti-Fe system with the ratios of Ti:Fe at 1:2, 1:1, and 2:1 were prepared by mechanical alloying of the elemental powders in a high-energy ball mill. The amorphous powders were characterized by x-ray diffraction and high-resolution transmission electron microscopy. A complete amorphization of Ti1Fe1 was achieved, whereas a remaining crystalline portion besides the amorphous phase was present in Ti2Fe1 and Ti1Fe2. The crystallization temperatures for these alloys detected by differential scanning calorimetry varied from 714 to 791 K, which were corresponding to half of their melting points.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 2513-2520 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The optical transmission loss in dielectric waveguide bends is investigated using the finite-difference time-domain approach. An absorbing boundary condition, applied to reduce the size of the mesh, is proven to work very well for the waveguide structure. The desired modes are excited using the solution of a one-dimensional waveguide structure. The bending loss is then obtained using the methods of overlap integral and least-square fit. The structures of multiple-bend waveguides are analyzed. It is shown that the coupling between neighboring bends leads to direct transmission to the waveguide section on the aligned plane in addition to the transmission through the zigzag path. The bending loss in nonplanar laser arrays is investigated in detail. The possibility of having a shallow groove depth laser array is then discussed. Lateral lasing is prohibited by the radiation loss due to the bend. It is observed that the optical coupling between neighboring emitters is enhanced by the shallow groove depth, implying that phase-locked array modes can be obtained.
    Type of Medium: Electronic Resource
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