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  • 1
    Electronic Resource
    Electronic Resource
    Does beryllium doping suppress the formation of Ga vacancies in nonstoichiometric GaAs layers grown at low temperatures? (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 4313-4315 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigate native defects in nonstoichiometric GaAs layers grown at low temperatures by molecular-beam epitaxy (LT-GaAs) doped with Be. Ga vacancies (VGa) are found by positron annihilation in all layers. The concentration of VGa is independent of the Be doping in contrast to the previous belief that it decreases. Simultaneously, the concentration of As antisite defects (AsGa) was measured by optical absorption. We find the same relationship between VGa and AsGa concentrations as reported earlier for undoped LT-GaAs. Thus, Be doping has no significant influence on the incorporation of native point defects in LT-GaAs. The thermal stability of such material must therefore be explained otherwise. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1427150
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  • 2
    Electronic Resource
    Electronic Resource
    Compression of the dc drain current by electron trapping in AlGaN/GaN modulation doped field-effect transistors (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 2896-2898 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The frequently observed dc drain current compression of AlGaN/GaN modulation doped field-effect transistors is associated with partial loss of the two-dimensional electron gas caused by electron trapping. The behavior of the temperature-dependent electron concentration and persistent photoconductivity at low temperature in the AlGaN/GaN modulation doped heterostructure are indicative of the presence of DX centers in the AlGaN layer. Deep-level transient spectroscopy of the drain current reveals carrier trapping with activation energy of 0.28 eV. However, this value appears to be too small to explain the compression of the dc drain current or to attribute these traps to DX centers in AlGaN. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1367274
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  • 3
    Electronic Resource
    Electronic Resource
    Recombination activity of copper in silicon (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 2937-2939 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The carrier recombination activity of copper in n-type and p-type silicon has been investigated. The minority carrier diffusion length has been found to decrease monotonically with increasing copper concentration in n Si and to exhibit a step-like behavior in p-type silicon at Cu concentrations above a certain critical level. It is suggested that the impact of copper on the minority carrier diffusion length is determined by the formation of copper precipitates. This process is retarded in perfect silicon due to the large lattice mismatch between Cu3Si and the silicon lattice and even more retarded in p Si, due to electrostatic repulsion effects between the positively charged copper precipitates and interstitial copper ions. Comparison of the impact of Cu on minority carrier diffusion length obtained with p-Si samples of different resistivity confirmed the electrostatic model. Studies of the impact of copper on minority carrier diffusion length in samples with internal gettering sites indicated that they provide heterogeneous nucleation sites for Cu precipitation at subcritical Cu concentration. Above a certain threshold of Cu concentration, the bulk recombination activity is dominated by quasihomogeneous formation of Cu precipitates, a process that is not detectably affected by the presence of oxide precipitates. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1415350
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  • 4
    Electronic Resource
    Electronic Resource
    Temperature dependence of the iron donor level in silicon at device processing temperatures (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 2734-2736 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Iron depth profiles in a p-type silicon epitaxial layer on a p+-type silicon substrate have been examined by deep-level transient spectroscopy and computer simulations. By comparing the experimental results with the simulations, we revealed the position of the iron deep donor level to be 0.42±0.04 eV from the valence-band edge at 412–580 °C, which is in a device processing temperature range. The iron donor level was nearly temperature independent within error. Knowing the temperature dependence of the iron donor level at the device processing temperatures, we can design iron gettering in silicon more precisely. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126459
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  • 5
    Electronic Resource
    Electronic Resource
    The incidence of transient neurological symptoms after spinal anaesthesia with lidocaine compared to prilocaine (2000)
    Oxford, UK : Blackwell Science Ltd
    Anaesthesia 55 (2000), S. 0 
    Details
    ISSN: 1365-2044
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The purpose of this double-blind study was to investigate the incidence of transient neurological symptoms after the use of isobaric lidocaine and isobaric prilocaine for spinal anaesthesia. Seventy patients (ASA 1–2, age between 18 and 70 years) were randomly assigned to two groups of 35 patients each, to receive either isobaric 2% lidocaine 4 ml or isobaric 2% prilocaine 4 ml intrathecally, at the L3−4 interspace. One patient in the prilocaine group could not be included because data were incomplete. On the first postoperative day, patients were evaluated for transient neurological symptoms. Pain was scored on a 10-point scale. Seven patients (20%) in the lidocaine group had transient neurological symptoms with a mean pain score of 5.3, whereas no patient in the prilocaine group had these complaints (p = 0.006). Symptoms disappeared within 4 days. Prilocaine results in a lower incidence of transient neurological symptoms than lidocaine intrathecally and therefore it is more suitable for short surgical procedures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2044.2000.01618-4.x
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  • 6
    Electronic Resource
    Electronic Resource
    Cephalexin tolerated despite delayed aminopenicillin reactions (2001)
    Copenhagen : Munksgaard International Publishers
    Allergy 56 (2001), S. 0 
    Details
    ISSN: 1398-9995
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1398-9995.2001.056008790.x
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  • 7
    Electronic Resource
    Electronic Resource
    Assessing radiographically occult upper extremity fractures with dedicated extremity MRI (2000)
    Springer
    Emergency radiology 7 (2000), S. 339-348 
    Details
    ISSN: 1438-1435
    Keywords: Key words Magnetic resonance imaging, low-field-strength imaging – Extremities, MR – Fractures, MR – Trauma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Purpose: To examine the utility of low-field, dedicated extremity MRI for assessing acute upper extremity trauma in patients with radiographs that are negative for fracture. Secondly, to determine which sequences are most useful when screening for fractures. Methods: Forty-four of 46 patients with acute upper extremity trauma and initial radiographs negative for fracture were imaged with a 0.2-T MRI system. Findings were verified with follow-up clinical assessment and plain radiography. Results: In 21 patients, dedicated extremity MRI demonstrated 26 ultimately proven occult fractures, none of which were seen on the initial conventional radiographs. True fractures demonstrated marrow edema and a linear fracture line on low-field MRI. One bone contusion showed edema with no fracture line and was misdiagnosed as a fracture. Low-field MRI correctly identified 23 remaining patients with no fracture. Sensitivity and specificity for fracture in the 44 patients successfully imaged were 100 % and 96 %, respectively. Additionally, 21 soft-tissue injuries were found incidentally by MRI. However, these may not merely be incidental findings of an acute nature, but may very well be chronic, and therefore merit no specific treatment. T1-weighted gradient-echo and short-tau inversion recovery sequences demonstrated the fracture line and marrow edema to best advantage, and were thus the most useful sequences to assess fractures on low-field MRI. Conclusion: Extremity MRI is highly sensitive and specific for radiographically occult fractures of the upper extremity and can also identify associated soft-tissue injuries. In our study, the management was altered in 45 % of the patients following MRI. When adequate sequences are used this modality can direct appropriate therapy while obviating the added expense and morbidity of unnecessary immobilization and follow-up imaging of patients without fracture.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00011854
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  • 8
    Electronic Resource
    Electronic Resource
    Influence of age and duration of symptoms on fibre type distribution and size of the back muscles in chronic low back pain patients (2000)
    Springer
    European spine journal 9 (2000), S. 273-281 
    Details
    ISSN: 1432-0932
    Keywords: Key words Chronic low back pain ; Erector spinae muscle ; MRI ; Muscle biopsy ; Fibre type ; distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Many studies have documented an association between chronic low back pain (LBP) and deficits in back muscle strength and endurance. The sub-optimal performance is believed to be the result of alterations in the size and structure of the muscle, although the long-standing issue of whether the observed changes precede or are a consequence of the pain remains unresolved. If consequent to the problem, and predominantly related to disuse of the muscles, then it may be expected that a relationship between muscle structure and symptom duration would exist. Lumbar paraspinal muscle samples were obtained from 59 chronic LBP patients using the percutaneous biopsy technique. The samples were subject to routine histochemical analysis for the examination of muscle fibre type characteristics and cytochemical architectural changes. In 55 of the patients, the gross cross-sectional areas of magnetic resonance images of the trunk muscles were also measured. Multivariate analysis showed that symptom duration was the strongest predictor of the individual proportions of the fast-fatigable type IIX fibres; with age and gender included in the model, nearly 30% of the variance in fibre type distribution could be accounted for. Duration of pain had no influence on fibre size. Gross muscle cross-sectional area correlated directly with lean body mass and inversely with age, but showed no relationship with symptom duration. Pathological changes in the internal fibre structure were more frequently encountered in older patients, and were independent of symptom duration. The results suggest that, over the long term, fibre type transformations rather than alterations in fibre size are the predominant changes to be found in the muscles of chronic LBP patients. The direction of change supports the results of many previous studies that have demonstrated corresponding differences in the fatigability of the muscles. There is a strong case for the early implementation of active measures to attempt to offset the development of these changes in back pain patients.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s005860000189
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