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991.
The electroluminescence and stimulated emission of lasers with one layer of InAs quantum dots (QD’s) grown in a single molecular-beam epitaxial process on vicinal GaAs(001) surfaces misoriented in the direction [010] by 2, 4 and 6° are investigated. It is discovered that an increase in the misorientation angle leads to a blue shift and a decrease in the full width at half maximum (FWHM) of the electroluminescence spectrum. This effect is attributed to a decrease in the size of the quantum dots and improvement in their size uniformity. A strong dependence of the threshold current density on the width of the spontaneous luminescence spectrum is discovered. The room-temperature threshold current density of the lasers with one layer of quantum dots and the spontaneous luminescence spectrum having the smallest FWHM (54 meV) equals 210 A/cm2. Fiz. Tekh. Poluprovodn. 32, 1482–1486 (December 1998)  相似文献   
992.
For discontinuity analysis more and more sophisticated methods are used in the nuclear industry. The rapid development of computer technology offers the possibility to use imaging techniques. Instead of specialized focusing transducers the more flexible synthetic focusing techniques can be used. Presupposing that the material is ultrasonically isotropic and homogeneous, imaging techniques make it possible to visualize the reflectivity of the volume to be tested.Siemens developed the high speed holographic instrument Holo 3000 in cooperation with the University of Bochum. In this paper the method of Broad Band Holography is presented in the context of other imaging techniques.Different filtering methods have been investigated in order to achieve highest resolution and best signal to noise ratio with a given dataset. Different transducers respective wave modes have been applied to austenitic welds and claddings. The reconstructed image was evaluated using image processing techniques in order to investigate the possibilities to produce results easier to be quantifed than the original reconstruction.The results presented show a reliable expert tool for analysis measurements which also can be used for flaw detection.  相似文献   
993.
The newly described slow cortical rhythm (approximately 0.3 Hz), whose depolarizing-hyperpolarizing components are analyzed in the preceding article, is now investigated from the standpoint of its relations with delta (1-4 Hz) and spindle (7-14 Hz) rhythmicity. Regular-spiking and intrinsically bursting cortical neurons were mostly recorded from association suprasylvian areas 5 and 7; fewer neurons were also recorded from pericruciate motor and posterolateral visual areas. Although most cells were investigated under various anesthetics, a similar slow cortical rhythm was found in animals with brainstem transection at the low- or high-collicular levels. These cerveau isolé (isolated forebrain) preparations display the major sleep rhythms of the EEG in the absence of general anesthetics. In 38% of recorded cortical neurons (n = 105), the slow rhythm was combined with delta oscillation. Both cellular rhythms were phase locked to the slow and delta oscillations in the surface- and depth-recorded EEG. In a group of this cell sample (n = 47), delta activity occurred as stereotyped, clock-like action potentials during the interdepolarization lulls of the slow rhythm. In another neuronal subsample (n = 58), delta events were grouped in sequences superimposed upon the depolarizing envelope of the slow rhythm, with such sequences recurring rhythmically at approximately 0.3-0.4 Hz. The associations between the two cellular and EEG rhythms (1-4 Hz and 0.3-0.4 Hz) were quantified by means of autocorrelograms, cross-correlograms, and spike-triggered averages. In 26% of recorded neurons (n = 72), the slow rhythm was combined with spindle oscillations. Regular-spiking cortical neurons fully reflected the whole frequency range of thalamically generated spindles (7-14 Hz). However, during similar patterns of EEG spindling, intrinsically bursting cells fired grouped action potentials (with intraburst frequencies of 100-200 Hz) at only 2-4 Hz. The dependence of the slow cortical oscillation upon the thalamus was studied by lesions and stimulation. The slow rhythm survived extensive ipsilateral thalamic destruction by means of electrolytic lesions or kainate-induced loss of perikarya in thalamic nuclei that were input sources to the recorded cortical neurons. To further prevent the possibility of a thalamic role in the genesis of the slow rhythm, through the contralateral thalamocortical systems and callosal projections, we also transected the corpus callosum in thalamically lesioned animals, and still recorded the slow rhythm in cortical neurons. These data indicate that the thalamus is not essentially implicated in the genesis of the slow rhythm.(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   
994.
The specific surface areas (A) of different clay mineral powders were measured by both the BET method and by thin layer wicking. The values of A for the BET and the wicking experiments coincided within a few percent. Thus, the simple and inexpensive thin layer wicking approach may well suffice to obtain reliable specific surface area values for most powders. From the wicking data it is also possible to obtain a rough estimate of the average particle size.  相似文献   
995.
996.
It is shown that the electrical breakdown voltages of polycarbonate film/metal foil capacitors can be increased. This can be achieved by briefly exposing the metal foil in these spirally wound film foil sections to a low-pressure, low-temperature gas plasma. Exposure of tin/lead foil to a 96% CF4/4% O2 gas plasma for four min, for example, produced >500% increase in breakdown voltage of sealed polycarbonate capacitors  相似文献   
997.
998.
In right middle cerebral territory infarction a new sign, excessive closure of the right eye ipsilateral to the lesion and mild closure of the left eye on command, was noted. The excessive ipsilateral eye closure was not observed on spontaneous eye closure.  相似文献   
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