Bibliothek

Notizen: Electrical characteristics associated with radiation detection were measured on single-crystal natural type-IIa diamond using two techniques: charged particle-induced conductivity and time-resolved transient photoinduced conductivity. The two techniques complement each other: The charged particle-induced conductivity technique measures the product of the carrier mobility μ and lifetime τ throughout the bulk of the material while the transient photoconductivity technique measures the carrier mobility and lifetime independently at the first few micrometers of the material surface. For each technique, the μτ product was determined by integration of the respective signals. The collection distance that a free carrier drifts in an electric field was extracted by each technique. As a result, a direct comparison of bulk and surface electrical properties was performed. The data from these two techniques are in agreement, indicating no difference in the electrical properties between the bulk and the surface of the material. The collection distance continues to increase with field up to 25 kV/cm without saturation. Using the transient photoconductivity technique the carrier mobility was measured separately and compared with a simple electron-phonon scattering model. The general characteristics of carrier mobility, lifetime, and collection distance at low electric field appear to be adequately described by the model.

Notizen: The impact of metal–oxide–semiconductor processing on strained Si/SiGe device structures has been examined. Material was grown by gas-source molecular beam epitaxy and ultra low pressure chemical vapor deposition, with different as-grown surface roughness. The effects of RCA cleaning, gate oxidation and rapid thermal annealing on this material were studied by atomic force microscopy (AFM) and optical profilometry. Certain processes caused reactions common to both material types, whereas others yielded dissimilar responses. Filtering AFM roughness data of specific wavelengths enabled the effects of processing on large-scale surface roughness dominated by the cross-hatching morphology and smaller scale microroughness to be investigated. The results suggest that as-grown Si/SiGe material quality is not a good indicator of processed device performance, rather morphological changes which occur during processing must be considered. © 2002 American Institute of Physics.

Notizen: Abstract Natural, pure CO2 inclusions in quartz and olivine (c. Fo90) were exposed to controlled fH2 conditions at T= 718–728°C and Ptotal= 2 kbar; their compositions were monitored (before and after exposures) by microsampling Raman spectroscopy (MRS) and microthermometry. In both minerals exposed at the graphite–methane buffer (fH2= 73 bar), fluid speciations record the diffusion of hydrogen into the inclusions. In quartz, room-temperature products in euhedral isolated (EI type) inclusions are carbonic phases with molar compositions of c. CO2(60) + CH4(40) plus graphite (Gr) and H2O, whereas anhedral inclusions along secondary fractures (AS type) are Gr-free and contain H2O plus carbonic phases with compositions in the range c. CO2(60) + CH4(40) to CO2(10) + CH4(90). EI type inclusions in olivine evolved to c. CO2(90–95) + CH4(5–10) without Gr, whereas AS type inclusions have a range of compositions from CO2(90) + CH4(10) ± Gr to CH4(50) + H2(50) ± Gr; neither H2O nor any hydrous species was detected by optical microscopy or MRS in the olivine-hosted products. Differences in composition between and among the texturally distinct populations of inclusions in both minerals probably arise from variations in initial fluid densities, as all inclusions apparently equilibrated with the ambient fH2. These relations suggest that compositional variability among inclusions in a given natural sample does not require the entrapment of multiple generations of fluids. In addition, the absence of H2O in the olivine-hosted inclusions would require the extraction of oxygen from the fluids, in which case re-equilibration mechanisms may be dependent on the composition and structure of the host mineral.Many of the same samples were re-exposed to identical P–T conditions using Ar as the pressure medium, yielding ambient fH2= 0.06 bar. In most inclusions, the carbonic fluids returned to pure CO2 and graphite persisted in the products. Reversal of the mechanisms from the prior exposure at fH2= 73 bar did not occur in any inclusions but the AS types in olivine, in which minor CO2 was produced at the expense of CH4 and/or graphite. The observed non-reversibility of previous mechanisms may be attributed to: (1) slower fluid–solid reactions compared to reactions in the homogeneous fluid phase; (2) depressed activities of graphite due to poor ordering; and/or (3) low ambient fO2 at the conditions of the second run.

Notizen: Isocon analysis has been applied to five sets of leucosome, mafic selvages and immediately adjacent mesosome in the migmatites from a 15-m outcrop in the Colorado Front Range. The results show: (i) mafic selvages formed from the adjacent mesosome by loss of felsic components and therefore the mesosomes are indeed palaeosomes or protoliths; (ii) the leucosomes did not form in a closed system from the palaeosome (in which case the material lost from the palaeosome during selvage formation would become the leucosome). The observed volumes and compositions of leucosomes require that the present leucosome must contain some material in addition to the felsic components lost from the selvages. The materials that must be added are leucotonalitic to granitic in composition, varying greatly in K/(Na + Ca) ratio. The trend in leucosome composition can be reproduced by assuming that a metasomatic exchange, KNa + Ca, modified originally leucotonalitic leucosomes to more K-rich compositions. These leucosomes most likely formed by injection of silicate melts accompanied, or followed, by metasomatism. The trend of leucosome compositions in this study reflects the general trend in the leucosome compositions which have been published from other areas, indicating that the proposed mechanism can be applicable to other regional migmatites.

Notizen: Renal biopsies were performed in 30 psoriatics during long-term low-dose cyclosporin (CsA) therapy (range 2·5–6 mg/kg per day) of from 6 months to 8 years. The study included pretreatment biopsies in 25 of the patients. After 2 years all biopsies shared features consistent with CsA nephropathy despite completely normal pretreatment morphology in 17 of the 25 patients. The severity of the findings which consisted of arteriolar hyalinosis, focal interstitial fibrosis and sclerotic glomeruli increased with length of therapy. Mild renal lesions were seen durhig the first 2 years. After 4 years all but one had arteriolar hyalinosis. with interstitial fibrosis pronounced in live and moderate in six of 11 patients. At the same time glomerular sclerosis had become significant. A decrease in glomerular filtration rate (GFR) correlated with severity of structural lesions. The data from our study together with experiences from cardiac-transplanted patients treated with CsA indicate that patients with psoriasis after 2 years therapy with CsA should be rotated to other treatments or be followed carefully by GFR and sequential renal biopsies.

Notizen: (1) Age-associated loss of skeletal muscle mass and strength can partly be counteracted by resistance training, causing a net synthesis of muscular proteins. Protein synthesis is influenced synergistically by post-exercise amino acid supplementation, but the importance of the timing of protein intake remains unresolved. (2) The study investigated the importance of immediate (P0) or delayed (P2) intake of an oral protein supplement upon muscle hypertrophy and strength over a period of resistance training in elderly males. (3) Thirteen men (age 74 ± 1 years; body mass index (BMI), 25 ± 1 kg m− 2 (means ± SEM)) completed a 12-week resistance training program (three times per week) receiving oral protein in liquid form (10 g protein, 7 g carbohydrate, 3 g fat) immediately after (P0) or 2 h after (P2) each training session. Muscle hypertrophy was evaluated by magnetic resonance imaging (MRI) and from muscle biopsies and muscle strength was determined using dynamic and isokinetic strength measurements. Body composition was determined from dual-energy X-ray absorptiometry (DEXA) and food records were obtained over 4 days. The plasma insulin response to protein supplementation was also determined. (4) In response to training, the cross-sectional area of m. quadriceps femoris (54.6 ± 0.5–58.3 ± 0.5 cm2) and mean fiber area (4047 ± 320–5019 ± 615 μ m2) increased in the P0 group, whereas no significant increase was observed in P2. For P0 both dynamic and isokinetic strength increased, by 46 and 15%, respectively (P 〈 0.05), whereas P2 only improved in dynamic strength, by 36% (P 〈 0.05). No differences in glucose or insulin response were observed between protein intake at 0 and 2 h post-exercise. (5) We conclude that early intake of an oral protein supplement after resistance training is important for the development of hypertrophy in skeletal muscle of elderly men in response to resistance training.

Notizen: In this study we have investigated the effect of creatine supplementation on performance of repeated sprint runs in well-trained young male handball players. The subjects participated in a test before supplementation (T1) and then received creatine (15 g/d) or placebo for five days before a second test was carried out (T2). Following T2, a low dose of creatine (2 g/d) or placebo was maintained for an additional nine days before the third test was performed (T3). The tests consisted of eight 40 m maximal sprint runs with a 25-s rest period between each sprint. Run time was reduced on the last three sprint runs after five days with high doses of creatine supplementation compared to T1 (P〈0.05). Although the run time during the last three sprints was still significantly lower after supplementation of low doses of creatine compared to T1, analysis of variance showed only a tendency for an interaction between test day and random group (P = 0.14). No improvement was seen in the placebo group. Blood lactate was similar at T1 and T2 in the creatine and placebo groups. In conclusion, high doses of creatine supplementation improve performance during repeated sprint runs in well-trained handball players. Futher studies are needed to clarify whether low doses of creatine supplementation, after a period with supplementation of high doses, are able to maintain improved performance.