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  • 1
    ISSN: 0942-0940
    Keywords: Post-traumatic subdural hygroma ; chronic subdural haematoma ; pathogenesis ; evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Thirteen of 145 patients with post-traumatic subdural hygroma (SDHy) developed chronic subdural haematoma (CSDH) at the involved site over a period of 6 years. CSDHs were found at the site of SDHys with no history of further head injury at a mean interval of 56 days. It appeared that these 13 patients did not have any distinguishing clinical features early on. Old age and brain atrophy on CT scans do not seem to be reasonable causative factors in the evolution of SDHy into CSDH. Initial enlargement of subdural accumulations at an early stage of SDHy and a subsequent increase in density at a later stage may point to the development of CSDH from SDHy in some instances. Ten of these 13 CSDH cases underwent surgical drainage, and the remaining 3 cases received no specific management. All resolved completely. The prognosis was good in all patients. The possible mechanism for the evolution of SDHy into CSDH is discussed.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0630
    Keywords: 72.20 ; 85.30 ; 81.10
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract p +/n + In0.53Ga0.47As tunnel diodes were prepared by liquid phase epitaxy and their electrical properties were characterized. These devices exhibit large forward conductances (2.59×103 Ω−1 cm−2), high peak current densities (793 A/cm2) and large peak to valley current ratios (16.2). These devices offer great promise as intercell ohmic contacts (IOCs) for InP-based, onolithic multijunction solar cells.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The ratio of the hydrogen and manganese neutron absorption cross sections, σH/σMn, is a most important parameter in the determination of radioactive neutron source strength by the manganese bath technique. The ratio is well measured by observing the change in56Mn activity induced in the manganese bath by a fixed neutron source as the manganese concentration of the bath is changed. In the present study, the neutron source was a Maxwellian beam from252Cf. Concentrations were determined by the two methods: volumetric and gravimetric. The cross section ratio has turned out to be σH/σMn=0.02506.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 1268-1270 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A voltage tunable three-color quantum well infrared photodetector (QWIP) consisting of asymmetric GaAs/AlGaAs double quantum wells has been demonstrated. The detector uses electron intersubband transitions in a coupled asymmetric double quantum well superlattice. The infrared photocurrent spectrum characterized using a blackbody monochromator source shows three prominent peaks appearing at 8.4 μm, 9.6 μm, and 10.3 μm under different biases. The three detection peaks are well resolved and can be independently selected by tuning the applied voltage. The responsivity and the detectivity of the detector at different biases and operating temperatures are characterized and found to be sufficient for detector operation at temperatures ∼60 K.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the optical properties of single strained InxGa1−xAs/GaAs quantum wells (QWs) grown on GaAs substrates oriented off the (100) surface. Photoluminescence measurements indicate that QW structures grown on GaAs(100)5° toward (111)A possess superior interfaces as evidenced by the linewidth. There appears to be a decrease in the density of optically inactive traps as the angle of misorientation is increased, resulting in an enhanced optical efficiency at 77 K. However, these traps freeze out at 2 K and consequently, the optical efficiency of the various layers become independent of substrate orientation.
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 1348-1350 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new hot-electron transistor for 10 μm infrared radiation detection is presented and discussed. The device utilizes an infrared sensitive GaAs/AlGaAs multiple quantum well structure as emitter, a wide quantum well as base, and a thick quantum barrier placed in front of the collector as an electron energy high pass filter. The energy filter selectively permits the higher energy photocurrent to pass to the collector; the lower energy dark current is rejected by the filter, and is drained through the base. The device detectivity, as noted by the collector photocurrent measurements, is much enhanced in comparison with companion infrared photoconductive devices.
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 76-78 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We introduce and utilize a novel method to characterize the energy levels of quantum well structures. In this method, thermal stimulation is utilized to excite conduction electrons from the lowest subband to the higher subbands of the structure while the structure is subjected to an applied voltage. The energy distribution of the electrons injected from this structure is then analyzed by a quantum barrier placed adjacent to the structure. This spectroscopic method results in the identification of the energy levels and the electron transport mechanisms of the structure in question. In this letter, excitation spectra from three different quantum well structures are presented to demonstrate the utility of this technique.
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 592-594 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have conducted a detailed study on the properties of a multiple quantum well infrared photodetector (QWIP) with a single bound state. From the optical absorption experiment, we found that the peak absorption energy is determined by the resonant states associated with each individual well and not by the global miniband structure. From the transport experiment, we observed that the photoelectron distribution over the QWIP is extremely narrow and close to the top of the quantum well barriers, indicative of the diffusive nature of the hot-electron transport in this structure. At large bias, the photoelectron distribution begins to shift up in energy, and is found strongly correlated to the observed photoconductive gain of the detector.
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  • 9
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present the first report of a strained-layer asymmetric triangular In0.15Ga0.85As/GaAs multiple quantum well structure realized by molecular beam epitaxy. Low-temperature photoluminescence experiments showed that the optical efficiency of such a structure is more than five times higher than an equivalent rectangular In0.15Ga0.85As/GaAs multiple quantum well structure grown under the same conditions. This is due to an increased collection of photoexcited carriers that are being swept by the well as a result of the field formed by compositional grading and a reduction of nonradiative recombination centers.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A long-wavelength λc=18 μm infrared hot-electron transistor (IHET) with low dark current is demonstrated. In order to achieve long-wavelength absorption, a low barrier height is required, which in turn results in a large dark current. Therefore, operation of a normal long-wavelength quantum-well infrared photodetector (QWIP) structure is limited to very low temperatures and biases due to the thermally activated dark current. In the IHET, a high-energy pass filter placed after 30 periods of GaAs/AlGaAs quantum wells blocks the temperature-activated dark current while allowing high-energy photoexcited electrons to pass and be collected as photocurrent. A comparison of the dark current to the 300 K background photocurrent shows that the QWIP structure without the high-energy pass filter demonstrates background-limited infrared photodetection (BLIP) only at T≤35 K. Furthermore, in order to avoid saturating a typical readout circuit, detector operation of the QWIP is restricted to biases less than 0.08 V at 35 K. In contrast, the filtered dark current in the IHET is reduced by two to four orders of magnitude such that BLIP performance can be achieved for temperatures up to T=55 K without saturating the readout circuit. Because of the preferential current filtering effect, the noise equivalent temperature difference of the IHET can be improved by a factor of 100 at T=55 K. The dark-current-limited detectivity was found to be D*=1×1010 cm Hz1/2/W at λp=15 μm, Ve=−0.2 V, and T=55 K.
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