Showing papers by "Wolfgang Wagner published in 1997"

On the extrapolation behavior of empirical equations of state

Abstract: Generally, the extrapolation behavior of empirical equations of state is regarded as poor, but it can be shown that state-of-the-art equations of state yield reliable results well beyond the range where they were fitted to experimental data. During the past years a new generation of highly accurate equations of state which yield reasonable results even up to the limits of chemical stability of the considered substances has been developed. In this paper, the positive influence of recent methods for the development of equations of state on their extrapolation behavior is discussed. The influence of the mathematical structure on the extrapolation characteristics is analyzed and requirements for a reasonable behavior up to extreme temperatures and pressures are formulated. As possible ways for assessment of the extrapolation behavior of an equation of state, comparisons with experimental data at very high pressures and temperatures and with theoretically predicted features of the so-called “ideal curves” of a fluid are discussed. Finally, the current status of our knowledge of the extrapolation behavior of empirical equations of state is summarized and its shortcomings are pointed out.

Combined modality treatment with accelerated radiotherapy and chemotherapy in patients with locally advanced inoperable carcinoma of the pancreas: results of a feasibility study.

Abstract: Between July 1990 and September 1993, 32 patients with locally advanced irresectable adenocarcinoma of the pancreas, histologically proven by laparotomy, were involved in our study. Patients were treated with hyperfractionated, accelerated radiotherapy and simultaneous application of 5-fluorouracil and folinic acid. Chemotherapy was given on days 1,2 and 3. Determination of the target volume for radiotherapy was carried out by computerized axial tomography. The total tumour dose of 44.8 Gy was applied relative to the 90% isodose in two daily fractions of 1.6 Gy, resulting in ten fractions per week. On the first three days of radiotherapy, 600 mg m-3 of 5-fluorouracil and 300 mg m-3 of folinic acid were given i.v. According to response, chemotherapy was repeated in 4-week intervals. The median survival time for all patients was 12.7 months, compared with 3-7 months after palliative surgery (historical control). The median progression-free interval was 6.6 months. Toxicity and therapy-induced morbidity were recorded according to WHO criteria. Nausea and vomiting of WHO grade I and II occurred in 72.1% and of grade III and IV in 27.9% of the patients. WHO grade I and II diarrhoea was seen in 11 patients. The overall incidence of leucopenia and thrombocytopenia was 37.4%; severe side-effects (WHO III-IV) occurred in 9.3% of all patients. One patient experienced a severe mucositis (WHO III). This combined modality treatment consisting of accelerated hyperfractionated radiotherapy and chemotherapy turned out to be feasible for patients with locally advanced, irresectable pancreatic cancer. The therapy could be applied in a short period of time, approximately half the time used in conventional therapy schemes.

Convergence of a Nanbu type method for the Smoluchowski equation

Abstract: This paper studies a stochastic particle method for the numerical treatment of Smoluchowski's coagulation equation. Convergence in probability is established for the Monte Carlo estimators, when the number of particles tends to infinity. The deterministic limit is characterized as the solution of a discrete in time version of the Smoluchowski equation. The results are illustrated by numerical examples.

Grazing incidence X-ray diffraction analysis of surface modified SiC layers

Abstract: Thin films of silicon carbide with codeposited elemental silicon were prepared by chemical vapor deposition (CVD). In a second CVD-process a thin titanium layer was deposited on the SiC(Si) basic layer. The solid state reaction between titanium and the codeposited silicon can be observed by X-ray diffractometry. A helpful analytical method for the observation of the growth of the reaction products is grazing incidence X-ray diffractometry. Various diffraction patterns of titanium silicides can be obtained by decreasing incidence angles.

Intraoperative Radiotherapy of Malignant Brain Tumors

Abstract: Purpose: Feasibility and morbidity of intraoperative radiotherapy (IORT) for malignant brain tumors as well as value of innovative imaging for diagnosis of rest tumors and recurrences were examined. Patients and Methods: Between May 1992 and October 1995 40 patients suffering from malignant brain tumors were treated with IORT at the University of Munster. The patient group was heterogenous, negative selection had been applied, which – besides patients receiving primary treatment – included patients with relapses and metastases with whom all treatment efforts had been exhausted. Therapy consisted of radical surgical resection and intraoperative electron beam therapy using total doses of 15-25 Gy, normalized to the 90% isodose. Thereafter, patients without prior treatment underwent percutaneous irradiation to a dose of 60 Gy of the residual tumor tissue or the area supporting the tumor, including a safety margin of 2 cm. Results: No increase of perioperative morbidity and of late sequelae was observed; however, the follow-up period was short. The 1-year survival rate was 42.9% for patients with grade III gliomas (WHO), and 51.5% for patients with glioblastomas. Considering the selection criteria according to Matsutani (initial therapy of supratentorial, peripherally located astrocytoma grade III or glioblastoma with less than 5 cm in diameter and a Karnofsky index of > 60% possibility of wide resection), the 1-year survival rate amounted to 71.4%. Imaging with 123I-α-methyltyrosine SPECT proved to be a valuable method for diagnosing not resected tumor tissue as well as relapse. Conclusions: The practicability of IORT for malignant brain tumors is shown in this study. Neither perioperative morbidity nor subacute sequelae were increased.

Production and characterization of nitrided CVD-SiC films

Abstract: Silicon Carbide (SiC) and SiC with free silicon [SiC(Si)] thin films were prepared by chemical vapor deposition (CVD) using a CH3SiCl3-H2-Ar gas mixture at a temperature of 1223 K. Afterwards these layers were gas nitrided in an ammonia-hydrogen-argon mixture at 1273 K. The solid product is an extremely thin film of silicon nitride on SiC or SiC(Si)-basic layers. These ultra thin silicon nitride films were investigated by glow discharge optical spectroscopy (GDOS) and x-ray photoelectron spectroscopy (XPS). The thickness of the layers was determined to a maximum value of 30 nm.

Individuals and States as Democratic Subjects

Abstract: Meaningful politics has been transferred increasingly from the national to the international arena. Substantively, more national control over public policy making cannot be regained, short of impairing certain desired outcomes—if it can be regained at all. Day‐to‐day activities within nations increasingly bear the mark of events occurring across the world and they generate their own global reverberations as well. The scope of national (democratic) decision making seems like it will diminish in the future. Yet in the long run, international policy making will require democratic legitimacy. This claim stems from two arguments. First, a causal relation exists between legitimacy and effectiveness. The legitimacy of international institutions must be enhanced because those that lack legitimacy seldom act effectively over the long run. Second, since democracy has become a universal value, any institution making substantive decisions faces demands for democratic procedures. As the role of international instituti...