Bibliothek

Notizen: Optical absorption of nanocrystalline thin films can be influenced by the presence of both porosity and grain size effects. If both are present simultaneously, their effects are difficult to separate. In this study it is shown that the combination of uv-vis transmittance and reflectance measurements on porous CeO2 films provides enough data to make this separation. The CeO2 films were prepared by deposition of nanosized (∼5 nm) particles from a water colloidal suspension onto sapphire and subjecting these films to sintering temperatures sufficiently high to provide a series of films with a typical thickness of 0.6 μm with a wide range of grain sizes and porosity. X-ray diffraction, scanning electron microscopy, ellipsometry, and profilometry were used to characterize the films and to compare the observed grain sizes and porosity with that obtained from optical measurements. All of the techniques used gave results on porosity and grain size which were in good agreement, from 15% to 50% and 5 to 65 nm, respectively. For these porous films it was found that the changes in absorption which are normally explained by quantum confinement effects due to the small crystallite size can be attributed primarily to changes in porosity rather than in grain size. © 2001 American Institute of Physics.

Notizen: A multiline visible emission spectrum, yielding "white" light, has been observed from a low-pressure Ba discharge. A five atomic level numerical model reproduces the observations qualitatively, suggesting that a low-pressure Ba discharge light source is capable of a significantly better color rendering than previously thought. © 2000 American Institute of Physics.

Notizen: The final hardware modifications for tritium operation have been completed for the Tokamak Fusion Test Reactor (TFTR) [Fusion Technol. 21, 1324 (1992)]. These activities include preparation of the tritium gas handling system, installation of additional neutron shielding, conversion of the toroidal field coil cooling system from water to a FluorinertTM system, modification of the vacuum system to handle tritium, preparation, and testing of the neutral beam system for tritium operation and a final deuterium–deuterium (D–D) run to simulate expected deuterium–tritium (D–T) operation. Testing of the tritium system with low concentration tritium has successfully begun. Simulation of trace and high power D–T experiments using D–D have been performed. The physics objectives of D–T operation are production of ≈10 MW of fusion power, evaluation of confinement, and heating in deuterium–tritium plasmas, evaluation of α-particle heating of electrons, and collective effects driven by alpha particles and testing of diagnostics for confined α particles. Experimental results and theoretical modeling in support of the D–T experiments are reviewed.

Notizen: After many years of fusion research, the conditions needed for a D–T fusion reactor have been approached on the Tokamak Fusion Test Reactor (TFTR) [Fusion Technol. 21, 1324 (1992)]. For the first time the unique phenomena present in a D–T plasma are now being studied in a laboratory plasma.The first magnetic fusion experiments to study plasmas using nearly equal concentrations of deuterium and tritium have been carried out on TFTR. At present the maximum fusion power of 10.7 MW, using 39.5 MW of neutral-beam heating, in a supershot discharge and 6.7 MW in a high-βp discharge following a current rampdown. The fusion power density in a core of the plasma is ≈2.8 MW m−3, exceeding that expected in the International Thermonuclear Experimental Reactor (ITER) [Plasma Physics and Controlled Nuclear Fusion Research (International Atomic Energy Agency, Vienna, 1991), Vol. 3, p. 239] at 1500 MW total fusion power. The energy confinement time, τE, is observed to increase in D–T, relative to D plasmas, by 20% and the ni(0) Ti(0) τE product by 55%. The improvement in thermal confinement is caused primarily by a decrease in ion heat conductivity in both supershot and limiter-H-mode discharges. Extensive lithium pellet injection increased the confinement time to 0.27 s and enabled higher current operation in both supershot and high-βp discharges. Ion cyclotron range of frequencies (ICRF) heating of a D–T plasma, using the second harmonic of tritium, has been demonstrated. First measurements of the confined alpha particles have been performed and found to be in good agreement with TRANSP [Nucl. Fusion 34, 1247 (1994)] simulations. Initial measurements of the alpha ash profile have been compared with simulations using particle transport coefficients from He gas puffing experiments. The loss of alpha particles to a detector at the bottom of the vessel is well described by the first-orbit loss mechanism. No loss due to alpha-particle-driven instabilities has yet been observed. D–T experiments on TFTR will continue to explore the assumptions of the ITER design and to examine some of the physics issues associated with an advanced tokamak reactor. © 1995 American Institute of Physics.

Notizen: A large, consecutive series of 562 patients with endometrial adenocarcinomas was investigated with respect to prognostic factors. In the histopathologic evaluation the World Health Organization (WHO) classification system was used. In addition to that, in moderately differentiated (MD) tumors small areas of solid growth were identified and the proportions of these out of the whole areas of tumor (in the predominant number of cases this being less than 5%) were later determined by morphometry, showing a good accordance with the subjective estimations. Differentiated tumors with small solid areas (MD + S tumors) implied a significantly worse prognosis compared to tumors without a solid component (P 〈 0.001), which was also confirmed in a multivariate analysis. In the multivariate analysis MD+S differentiation had an independent prognostic impact, as strong as age, clinical stage and myometrial invasion. It is suggested that the occurrence of even a very small solid component is an ominous sign, the presence (or absence) of which might be an important parameter to take into consideration in the discrimination between high- and low-risk endometrial carcinomas.

Notizen: Objective To investigate the effects of anxiety and depression during pregnancy on obstetric complications using the data collected from the St George's Birthweight Study.Design Prospective population study.Setting District general hospital in inner London.Subjects A consecutive series of 1860 white women booking for delivery were approached. Of these, 136 refused and 209 failed to complete the study for other reasons, leaving a sample of 1515.Main outcome measure Data were obtained by research interviewers at booking, 17, 28, and 36 weeks gestation and from the structured antenatal and obstetric record. The predictor variables were the anxiety and depression scores measured using the General Health Questionnaire. The outcome variables were five obstetric complications: preterm delivery; nonspontaneous onset of labour; major analgesia in the first and second stages of labour; and nonspontaneous vaginal deliveries. The possible confounding effects of 35 socio-economic, psychological and personal variables were investigated using logistic regression.Results The factors that had the strongest relation with the outcomes were parity and maternal age. Depression during pregnancy was unrelated to the obstetric complications. Anxiety was weakly related to analgesia/anaesthesia in the second stage of labour (P= 0.04). However, anxiety accounted for only 0.1 % of the variance in use of major analgesia/anaesthesia. The most effective model, that for analgesia/anaesthesia in the first stage of labour, accounted for only 7.3% of the variance.Conclusions In the general population of pregnant women, anxiety and depression during pregnancy, while undesirable in themselves, are of little importance in the evolution of obstetric complications.

Notizen: Forty-six patients with early (Stage I and II) ovarian cancer referred as free of residual disease after primary surgery, selected for high-risk features, were treated with adjuvant single-agent alkylating therapy comprising either intravenous cyclophosphamide (1 g/m2) in 36 patients, or oral melphalan (0·2 mg/kg daily for 5 days) in eight. Cyclophosphamide was repeated every 3 weeks for 10 cycles and melphalan every 6 weeks for 12 cycles. With a median follow-up of 36+ months, 18 patients have relapsed. The actuarial 5-year relapse-free survival was 48% and the overall 5-year survival was 54%; median survival was 84 months. Pretreatment FIGO stage was the single most important predictor of relapse-free and overall survival duration. For patients with Stage IA and IB tumours the 5-year actuarial relapse-free survival was 89%; for patients with stage 1C and II (all substages), the 5-year relapsefree survival was 24% (P=0·001). For this latter group adjuvant single alkylating agent therapy was not adequate and alternative therapeutic regimens are required. The problem of suboptimal primary surgical staging is also addressed.