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  • 1
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 1966-1968 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Ultrafast absorption studies on free-standing porous silicon films have been carried out at room temperature to investigate the carrier dynamics and the luminescence mechanism. Ultraviolet and visible excitations were used on an as-prepared sample and two annealed samples. Transient absorption curves of UV pumped, as-prepared samples contain a fast decay (τf) of 0.8±0.2 ps and a slower decay of (approximately-greater-than)30 ps. τf is found to be shorter for both the 500 °C annealed sample with UV excitation and for the as-prepared sample with visible excitation. The faster decay rates suggest that the subpicosecond component of the transient absorption may be due to carrier thermalization rather than core-to-surface state excitation transfer. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 2475-2477 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Low energy electron-enhanced etching of Si(100) has been achieved by placing the sample on the anode of a dc discharge in hydrogen/helium mixtures. Over a broad range of gas composition, gas pressure, and discharge current, nonpatterned samples gave etch yields of 0.01–0.02 atoms/electron, and average etch rates of 2000–3000 A(ring)/min. Postetch examination by atomic force microscopy revealed surface roughness of 2–3 nm. These results are related to incident flux of H atoms and electrons through a simple model of the anode sheath layer above the sample. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Zoomorphology 32 (1937), S. 276-288 
    ISSN: 1432-234X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Materialart: Digitale Medien
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  • 4
    ISSN: 1432-1084
    Schlagwort(e): Key words: Thyroid ; Biopsy ; Interventional MR ; MR guidance ; Stereotaxis ; Ultrasound
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract. The aim of this study was to demonstrate the clinical feasibility and utility of an interactive MR-guidance system to target and biopsy thyroid lesions, and to compare resolution between ultrasound and interventional MR imaging in the evaluation of thyroid lesions. Twenty thyroid lesions of 18 patients were interactively biopsied using a 0.5-T superconducting open magnet system. Stereotactic localization of the needle and imaging was accomplished using T1-weighted gradient-recalled-echo (GRE) images. Representative cytological material was retrieved in 16 of 20 lesions (benign cystic or colloid goiter: n = 14; one de Quervain's thyroiditis and one follicular neoplasia). Lesions smaller than 1.5 cm detected by ultrasound could not be visualized adequately on GRE images. Lesions smaller than 1.5 cm were successfully biopsied by ultrasound (three colloid and haemorrhagic goiters and one adenoma). Magnetic-resonance-guided interactive biopsies and positioning of non-ferromagnetic needles in the thyroid gland are technically feasible and safe. Compared with high-resolution ultrasound, lesions larger than 1.5 cm can be adequately visualized and biopsied. Magnetic-resonance-guided placement of non-ferromagnetic needles is no substitute for high-resolution ultrasound in clinical work-up of thyroid lesions.
    Materialart: Digitale Medien
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  • 5
    ISSN: 1432-1084
    Schlagwort(e): Key words: Spine ; Intervertebral disks ; Lasers ; MR imaging guidance ; MR imaging temperature monitoring
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract. The purpose of this study was to perform percutaneous laser disc decompression (PLDD) under MR guidance in an open configuration 0.5-T MR system. Following failed conservative treatment for 6 months, eight patients with contained disc herniations were enrolled in the study. Following MR guided introduction of the laser fiber into the targeted disc space, the laser-induced temperature distribution was visualized using a color-coded subtraction technique based on a T1-weighted GRE sequence. In seven patients PLDD could be performed. In all cases laser effects were depicted by MR. In this regard the color-coded technique was found to be superior to conventional magnitude images. Whereas no apparent decrease in the extent of herniation was discovered immediately following PLDD, T2-weighted FSE images showed signal intensity alterations in two of the seven patients. Clinical evaluation, obtained 3–4 months after PLDD, revealed a fair (n = 2) or good (n = 4) response to the treatment. One patient showed no change in symptoms. MR guidance and monitoring of PLDD is feasible within an open 0.5-T system and seems to render PLDD more safe and controllable.
    Materialart: Digitale Medien
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  • 6
    ISSN: 1432-2102
    Schlagwort(e): Schlüsselwörter Endometriose ; Biopsie ; Nadel ; Magnetresonanztomographie ; Interventionelle Radiologie ; Key words Endometriosis ; Biopsy ; needle ; Magnetic resonance imaging ; Interventional radiology
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Summary Introduction and Methods: A 0.5 T open-configuration MR system allows free access to the patient via a 58-cm-wide opening on both sides of the machine. A newly developed system for needle guidance enables the examiner to perform biopsies in combination with real-time imaging and to position laser fibers in the human body. For imaging, a 2D gradient echo sequence is used (TR 19 ms, TE 9 ms, flip angle 30 °, FOV 24 × 24 cm, slice thickness 10 mm matrix 256 × 128). The acquired images are displayed on two LCD screens localized within the MR system, thus allowing an interactive needle guidance. This procedure is illustrated by a case report. Discussion: The handling of the system for needle guidance was simple, mainly due to a real-time adaption of the scan plane to the needle direction. The possibility of multi-angulated approaches makes biopsies of hardly accessible anatomic regions feasible. Conclusion: We think that MR-guided needle positioning will play an important role in combination with thermosensitive therapies. Thermosensitivity of MR imaging allows extensive monitoring of such interventions.
    Notizen: Zusammenfassung Ein offenes, interventionelles MR-Gerät (0,5 Tesla) erlaubt durch eine 58 cm breite Öffnung den Zugang zum im Gerät liegenden Patienten. Ein spezielles Punktionssystem ermöglicht es, unter Echtzeitbildgebung Punktionen vorzunehmen sowie auch Laserfasern im menschlichen Körper zu plazieren. Zur Bildgebung wird eine 2d-Gradientenechosequenz verwendet (TR 19 ms, TE 9 ms, Flipwinkel 30 °, FOV 24 × 24 cm, Schichtdicke 10 mm, Matrix 256 × 128). Die akquirierten Bilder werden dem punktierenden Radiologen auf 2 im Gerät angebrachten LCD-Monitoren angezeigt, wodurch eine interaktive Nadelführung ermöglicht wird. Es wurden bereits zahlreiche Punktionen an Patienten durchgeführt. Wichtig wird die MR-gesteuerte Punktion von Läsionen in Kombination mit der Durchführung thermosensitiver Therapien. Die der MR-Bildgebung inhärente Temperatursensitivität ermöglicht ein umfassendes Monitoring solcher Eingriffe in Echtzeit.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    The European physical journal 30 (1978), S. 129-143 
    ISSN: 1434-6036
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The theory for the photoemission process is inspected taking into account many body effects. Simple equations for the analysis of experimental spectra are deduced which allow to determine the relative importance of the many body effects to the observed spectrum. The core level spectra for Be, Na, Mg and Al metal are analysed quantitatively yielding the magnitude of the intrinsic and extrinsic contribution to the plasmon creation.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    The European physical journal 97 (1995), S. 25-34 
    ISSN: 1434-6036
    Schlagwort(e): 79.60 ; 71.28
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The electronic structure of the layered compounds LaI2 and CeI2 was investigated by photoemission and electron energy loss spectroscopy. From the experimental results we are able to confirm the metallic nature of these compounds, and by using photon energy dependent measurements of the valence band we can identify the orbital character of the conduction band as essentially 5d1-like. A detailed analysis of the Ce 3d and 4f spectra yields a remarkably small 4f-5d hybridization strength, almost completely decoupling the f-electron from the conduction band, which makes CeI2 a somewhat unusual system compared to other metallic Ce compounds. Band structure calculations by Jepsen and Andersen [1] confirm these experimental results.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    The European physical journal 97 (1995), S. 83-93 
    ISSN: 1434-6036
    Schlagwort(e): 79.60 ; 71.20 ; 71.28
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We have investigated hole doped (by lithium) and electron-doped (by nickel metal) NiO with photoemission (PES), inverse photoemission (IPES) and low and high energy electron energy loss spectroscopy (EELS). Both types of doping create empty states approximately in the middle of the charge transfer gap of undoped NiO.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Journal of low temperature physics 26 (1977), S. 83-100 
    ISSN: 1573-7357
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract From Mössbauer experiments on dilute sources of57Co in Mo the local moment behavior of the Kondo system Fe in Mo is obtained. In addition, impurity-impurity interactions are clearly seen from line broadening of the Mössbauer spectra, which depend on the preparation of the samples. The local magnetization deduced from the splitting of the Mössbauer spectra in external fields is identical for samples with differing impurity concentrations, indicating that it is characteristic of isolated Fe in Mo. The initial local susceptibility is in good agreement with earlier bulk magnetization data. The low-temperature susceptibility yields a Kondo temperature of about 0.2 K. On the other hand, the overall temperature dependence of the susceptibility is more complex than the simple Curie-Weiss law with saturation to a constant value at low temperatures known for typical Kondo systems such asCuFe.
    Materialart: Digitale Medien
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