Passive and active spectroscopy on flowing plasmas

The equil. departures of two types of flowing plasmas were studied exptl. The combination of abs. emission spectroscopy with the non-intrusive active tool of Thomson/Rayleigh scattering made it possible to compare the at. state distribution function (ASDF) with its equil. form. The electron excitation kinetics (EEK) of a highly recombinative Cascaded Arc Created Magnetized Expanding Plasma was studied using time resolved laser induced fluorescence. The recombination process was found to be largely affected by heavy particle excitation kinetics (HEK). A comparable study of an inductively coupled plasma revealed that the deviations from partial local Saha equil. (pLSE) were much less pronounced. To get insight in this plasma, global active spectroscopy was performed by following the response to the power interruption

Application of a hybrid collisional radiative model to recombining argon plasmas

A collisional radiative model, in which a hybrid cut-off technique is used, is applied to recombining plasmas to study the atomic state distribution function (ASDF) and the recombination coefficient. Computations of the ASDF using semi-empirical rate coefficients of Vriens and Smeets (V-S) and Drawin (D) are compared with experimental values measured at various positions in a free expanding argon arc jet. Apart from the shock position, where the calculated results are too low, the model calculations are higher than the experimental results. The volumetric recombination coefficient has a T/sub e//sup -4.2/ and a T/sub e//sup -4.8/ dependence when semi-empirical rate coefficients of, respectively, V-S and D are used. The differences between the models based on the rate coefficients of V-S and D indicate that the recombination flow is sensitive to the low temperature behavior of the rate coefficient

Measurements of shock waves using Thomson- and Rayleigh scattering on an expanding plasma

A new combined Thomson and Rayleigh scattering setup is presented. A key problem in developing a Thomson-Rayleigh scattering setup is the level of the unwanted stray light. The level in the new setup is decreased to 10-2 torr Ar, making possible the measurement of neutral densities down to 1020 m-3. The setup is used to measure ne, n0, and Te in an expanding magnetized cascaded arc plasma, which, depending on the operating mode, has electron densities in the range 5 * 1017-1021 m-3, neutral densities in the range 1020-1023 m-3, and electron temps. of 1000-25,000 K. [on SciFinder (R)

In vivo (31)P magnetic resonance spectroscopy and morphometric analysis of the perfused vascular architecture of human glioma xenografts in nude mice.

The relationship between the bioenergetic status of human glioma xenografts in nude mice and morphometric parameters of the perfused vascular architecture was studied using (31)P magnetic resonance spectroscopy (MRS), fluorescence microscopy and two-dimensional digital image analysis. Two tumour lines with a different vascular architecture were used for this study. Intervascular distances and non-perfused area fractions varied greatly between tumours of the same line and tumours of different lines. The inorganic phosphate-nucleoside triphosphate (P(i)/NTP) ratio increased rapidly as mean intervascular distances increased from 100 microm to 300 microm. Two morphometric parameters - the percentage of intervascular distances larger than 200 microm (ivd200) and the non-perfused area fraction at a distance larger than 100 microm from a nearest perfused vessel (area100), - were deduced from these experiments and related to the P(i)/NTP ratio of the whole tumour. It is assumed that an aerobic to anaerobic transition influences the bioenergetic status, i.e. the P(i)/NTP ratio increased linearly with the percentage of ivd200 and the area100

Pimonidazole binding in C6 rat brain glioma: relation with lipid droplet detection

Item does not contain fulltextIn C6 rat brain glioma, we have investigated the relation between hypoxia and the presence of lipid droplets in the cytoplasm of viable cells adjacent to necrosis. For this purpose, rats were stereotaxically implanted with C6 cells. Experiments were carried out by the end of the tumour development. A multifluorescence staining protocol combined with digital image analysis was used to quantitatively study the spatial distribution of hypoxic cells (pimonidazole), blood perfusion (Hoechst 33342), total vascular bed (collagen type IV) and lipid droplets (Red Oil) in single frozen sections. All tumours (n=6) showed necrosis, pimonidazole binding and lipid droplets. Pimonidazole binding occurred at a mean distance of 114 microm from perfused vessels mainly around necrosis. Lipid droplets were principally located in the necrotic tissue. Some smaller droplets were also observed in part of the pimonidazole-binding cells surrounding necrosis. Hence, lipid droplets appeared only in hypoxic cells adjacent to necrosis, at an approximate distance of 181 microm from perfused vessels. In conclusion, our results show that severe hypoxic cells accumulated small lipid droplets. However, a 100% colocalisation of hypoxia and lipid droplets does not exist. Thus, lipid droplets cannot be considered as a surrogate marker of hypoxia, but rather of severe, prenecrotic hypoxia

Towards a knowledge-rich learning environment in preparatory secondary education

In this case study a novel educational programme for students in preparatory vocational education was studied. The research questions were: (1) Which teaching/learning processes occur in a simulated workplace using the concept of a knowledge-rich workplace? (2) What is the role of models and modelling in the teaching/learning processes? The curriculum project consisted of design and construction tasks. The students were collaboratively involved in the process of designing a tricycle for a real customer. This real-life activity creates opportunities for students to develop and use models, which can be used in more than in one context. The case study explored how the teachers deal with the students' explicit and implicit need for knowledge and skills. The main findings are that teachers more often provide this knowledge, rather than guide the students in reconstructing it, and towards the end of the project, knowledge tended to remain situated