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  • Digitale Medien  (8)
  • 1995-1999  (8)
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Materialart
  • Digitale Medien  (8)
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  • 1
    Digitale Medien
    Digitale Medien
    Radiation damage induced by MeV alpha particles in polycrystalline diamond films (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 5006-5013 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Radiation damage induced by 2 MeV alpha particles in polycrystalline diamond films has been studied as a function of the irradiation dose D (1012≤D≤1017 cm−2). The films were characterized using Raman/photoluminescence spectroscopy and I(V,T) measurements. The results can be summarized as follows. In undoped samples the H3 luminescent center (N–V–N) is observed for D≥1014 cm−2. The Raman diamond peak is broadened and shifted to lower frequencies for D(approximately-greater-than)1015 cm−2. No new graphitic component is detected after irradiation. On the contrary graphitic sp2 defects are annealed by irradiation. For D=3×1016 cm−2 new Raman defect peaks are detected at 1496 and 1635 cm−1. I(V,T) characteristics remain unaffected for D≤1016 cm−2. An increase in the conductivity is observed for D=3×1016 cm−2. At this dose we observe an activation energy of 0.4 eV and thermally stimulated currents related to defect levels at about 0.3 eV. A boron-doped sample (100 Ω cm) has been irradiated at 1017 cm−2 for comparison. After irradiation the conductivity of this sample is reduced and the activation energy of the conductivity is also reduced. Less damage is detected by Raman spectroscopy in the B-doped material. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.363545
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  • 2
    Digitale Medien
    Digitale Medien
    Poole–Frenkel conduction in polycrystalline diamond (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 3778-3780 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: High-field electrical conduction has been studied in undoped polycrystalline diamond over a wide temperature range. The current increases exponentially with the electric field with an exponential factor which increases linearly with the inverse of temperature. The activation energy of the conductivity is found to be strongly field dependent and to decrease linearly with the electric field. The experimental data support a Poole–Frenkel conduction with overlapping centers. The centers are found to be located at around 1.1 eV from the band edge with a density of about 2×1017 cm−3. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.361212
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  • 3
    Digitale Medien
    Digitale Medien
    Formation of buried p-type conducting layers in diamond (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 1492-1494 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Deeply buried boron doped layers are realized in single crystal diamond using MeV ion implantation. Contact to the buried layers is accomplished using pulsed focused laser irradiation which is selectively absorbed in the implanted layer to form a graphite column up to the surface. The contacts are ohmic over a wide range of applied voltage. Implantation induced defects that are responsible for compensation of the acceptors are identified. It is found that removal of these defects requires annealing temperatures of about 1450 °C, but once these defects are removed the buried B doped layer displays excellent activation of the acceptors with an activation energy of 0.372 eV. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.119946
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  • 4
    Digitale Medien
    Digitale Medien
    Photoinduced conductivity changes in polycrystalline diamond films (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 1238-1240 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report that the dark electrical properties of polycrystalline chemical vapor deposition diamond films are modified after exposure to UV light. UV illumination gives rise to an increase in the dark conductivity and to a change in the I–V characteristic from Iα exp (aV) for the as-grown material to IαV2 following UV irradiation. Thermally stimulated currents corresponding to an activation energy of about 1.9 eV are observed after UV illumination. The effects of UV irradiation can be totally reversed by thermal annealing and partially reversed by exposing the samples to white light. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.115938
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  • 5
    Digitale Medien
    Digitale Medien
    Thermally stimulated currents in polycrystalline diamond films: Application to radiation dosimetry (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 2996-2998 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Thermally stimulated currents (TSC) were studied in polycrystalline diamond films to gain information about the trap levels in this material. The TSC glow curve is composed of a dominant peak at 555 K with smaller overlapping peaks in the 400–500 K range. The analysis of the TSC isothermal decay at high temperatures shows that the peak at 555 K is related to a trap level at 1.86 eV. The dose response and the room temperature fading rate of TSC were measured in order to evaluate the potential of these films for UV radiation dosimetry. The TSC are found to increase sublinearly with the dose over three decades and to decay with the logarithm of the storage time at room temperature. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.118768
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  • 6
    Digitale Medien
    Digitale Medien
    Imaging intracranial tuberculosis in childhood (1995)
    Springer
    Pediatric radiology 25 (1995), S. 165-170 
    Details
    ISSN: 1432-1998
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract A morphologically based imaging review of intracranial tuberculosis in childhood is presented. The computed tomography and magnetic resonance features of parenchymal tuberculoma, tuberculous meningitis and meningeal/meniningocerebral tuberculoma are illustrated. Recent insight into the nature of tuberculoma necrosis and its magnetic resonance correlation is reviewed. Pathogenesis, relevant clinical background and the role of modern imaging is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02021522
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  • 7
    Digitale Medien
    Digitale Medien
    Synaptic transmission in the pineal eye of young Xenopus laevis tadpoles: a role for NMDA and non-NMDA glutamate and non-glutaminergic receptors? (1997)
    Springer
    Journal of comparative physiology 181 (1997), S. 177-186 
    Details
    ISSN: 1432-1351
    Schlagwort(e): KeywordsXenopus tadpole ; Pineal ; Transmitter NMDA ; Photoreceptor
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract The pineal eye of Xenopus laevis tadpoles is directly photosensitive. A sudden reduction in light intensity produces a burst of activity in the pineal ganglion cells, which is closely followed by the onset of swimming. In this paper I present the results of experiments on the effects of agonists and antagonists of candidate pineal transmitters on ganglion cell activity. I found that NMDA and non-NMDA excitatory amino acid (EAA) agonists increased pineal activity, indicating the presence of both types of receptor. Kynurenic acid reduced activity, thus confirming that the photoreceptor transmitter is an EAA. Under physiological conditions, CNQX blocked activity almost completely whilst AP5 had little effect. In Mg2+-free saline CNQX had a considerably smaller effect, but joint application of CNQX and AP5 blocked almost all activity; therefore, the NMDA receptors are subject to blockage by Mg2+. Although GABAA and ACh receptors appear to be present, no evidence was found for GABA or ACh as pineal transmitters. In addition, 5-HT had no effect on pineal activity. The main pineal transmitter is an EAA acting on ganglion cells through both NMDA and non-NMDA receptors. Other receptors are present but appear to have no role in controlling pineal activity at this stage.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s003590050104
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  • 8
    Digitale Medien
    Digitale Medien
    Imaging gastrointestinal perforation in pediatric blunt abdominal trauma (1996)
    Springer
    Pediatric radiology 26 (1996), S. 188-194 
    Details
    ISSN: 1432-1998
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Objective. To assess the role of imaging, in particular CT, in the early detection of GI perforation. Subjects and methods. In a 10-year period, 43 patients with surgically confirmed GI perforation were identified from hospital records; 22 of these had preoperative CT evaluation. Medical records and radiology were retrospectively reviewed and CT studies were particularly assessed for extraluminal air, free intraperitoneal fluid, bowel wall thickening, bowel wall enhancement, and bowel dilatation. During the study period an additional 12 trauma patients were identified who had CT studies demonstrating the above findings, but who had hypovolemic shock bowel or nondisrupting bowel injury without perforation evident. Results. Extraluminal air was demonstrated in 47% of the imaged perforations. There was one false-positive extraluminal air. Perforation was confirmed in patients who had all five of the above CT findings, but this was the case for only 18% of patients with perforation. One or more of the five specified CT findings were present in all CT studies reviewed. No false-negative CT study was performed in the study period. Conclusion. Separating nondisrupting bowel injury from perforation is diagnostically difficult; however, CT remains a good modality for assessing GI perforation in pediatric blunt trauma, but it cannot replace diligent and repeated clinical evaluation of all potential perforation victims.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01405296
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