Improved Determination of Bimodal Size Distributions from Measurements with Diffusional Size Classification

The size distribution of the unattached fraction of the short-lived radon progeny is reported in the literature to have a bimodal structure. Due to the weak size resolution of diffusional size classification, a wide variety of bimodal size distributions yields similar measurement results, obstructing the reconstruction of size distribution parameters from measured data. For example, it could be shown that although 2 of the commonly used nonlinear approximation algorithms per formed well for the reconstruction of a monomodal size distribution, the reproduc tion of parameters of a bimodal size distribution was unsatisfactory. In conse quence, a "random walk" approach is presented. The basic idea for this approach consists of probing the complete parameter space as an ideal method for locating the best set of parameters. Additionally, 2 steps are introduced for the reduction of computation time to render the ideal approach to an applicable method. The range of geometric standard deviations for the calculation was restricted to values between 1 and 5. The range of median diameters was limited according to the penetration functions of the diffusional samplers. This restricted volume of param eter space was subdivided into 10⁴ cells. During the calculation, cells with exceptionally large values of the minimization functional were eliminated from further computation. Compared to the results of EM and Simplex algorithms, this ''random walk'' method was able to retrieve parameters of both monomodal and bimodal size distributions with improved accuracy.     

The impact of sulfur on the performance of a solid oxide fuel cell (SOFC) system operated with hydrocarboneous fuel gas

The impact of thiophene in the fuel gas of a commercial solid oxide fuel cell (SOFC) system is investigated for concentrations up to 400 ppmV. Based on the measured voltage–current curves, an empiric correlation for the estimation of the expectable power output of the investigated SOFC system when operated with sulfur containing fuel gases is derived. An interrelation between the open circuit voltage (OCV) and the sulfur concentration of the investigated hydrocarboneous fuel gas is presented and discussed based on corresponding model simulations. The reduction of the steam reforming (STR) activity of the anode cermet material and of the catalytic partial oxidation catalyst used for the fuel gas processing in the investigated SOFC system are found important factors regarding the power output reduction induced by sulfur traces in the fuel gas of SOFCs.     

Comparative analysis of 8-oxo-2' -deoxyguanosine in DNA by 32P- and 33P-postlabeling and electrochemical detection

8-Oxo-2'-deoxyguanosine (8-oxo-dG) is emerging as a useful marker for oxidative DNA damage. Reported basal levels determined by 32P-postlabeling (PPL) method were 10-fold or more higher than those obtained with HPLC/electrochemical detection (ECD). This discrepancy was investigated. In commercial calf thymus DNA, levels of 4 +/- 1 and 64 +/- 14 8-oxo-dG per 10(6) 2'-deoxynucleosides (dN) were measured by the standard HPLC/ECD and PPL methods, respectively. DNA digestion by micrococcal nuclease/spleen phosphodiesterase and nuclease P1 (as used in the standard PPL method), followed by ECD analysis resulted in a level of 8 +/- 3. In calf thymus DNA spiked with chemically synthesized 8-oxo-dGp to give an increment of 9 8-oxo-dG/10(6) dN, the added standard produced a significant increase with HPLC/ECD but not PPL. After spiking the DNA with 90 8-oxo-dG/10(6) dN, the added 8-oxo-dGp was detectable also with PPL, with a labeling efficiency of 65%. In order to investigate the role of ionizing radiation from 32P for the higher 8-oxo-dG levels in PPL, incubation times and amounts of radioactivity in the phosphorylation reaction with commercial dGp were increased, and external irradiation of commercial dG with 32P was investigated. All modifications resulted in higher values of 8-oxo-dG measured, but the effect was not large enough to fully explain the discrepancy between PPL and HPLC/ECD. Using [gamma-33P]ATP instead of [gamma-32P]ATP or adding [33P]phosphate to a 32P-PPL assay resulted in even higher levels of 8-oxo-dG measured. The increase in 8-oxo-dG levels during the PPL workup is attributed to the presence and oxidation of unmodified dGp in the reaction mixture. For a determination of true basal levels, the PPL method will have to be modified, including the removal of dGp prior to the phosphorylation reaction.     

Reaktorstabilität und sichere Reaktionsführung

Reactor stability and safe reaction engineering . Stable operating behaviour of chemical reactors and stability in the sense of stability theory of chemical processes are by no means synonymous concepts. Thus, appropriate control can permit reliable operation at a unstable operating point, while even global stability will not necessarily rule out a runaway reaction. The latter is the case when strongly exothermal reactions are characterized by a pronounced parametric sensitivity. In order to delineate the concepts, ?stability”? and ?parametric sensitivity”? are explained first for stirred tank and tubular reactors with strongly exothermal reaction. Both the conventional view of reaction engineering and the theory of heat explosion commonly used in reaction engineering are considered in detail. Practical problems of safe reaction engineering are subsequently discussed for the control of batch reactors, the control of semibatch reactors, and the behaviour of bundled-tube reactors.     

Simulatoren zur Unterstützung der Prozeß- und Betriebsführung

Simulators for support of process and plant management. Process simulators are increasingly used for plant and process operation purposes. These simulators differ from those used in process design in the user interface, which is identical to the usual operator interface of distributed control systems. The progress of the numerical solution parallels the dynamic behaviour of the real process, and not that of the numerical procedure. The simulation-supported tasks of plant and process operation are: education of operators, training and instruction of operators, support of plant operation by interpretion of plant states and transitions and by helping to formulate operating instructions. These tasks, the available simulation concepts and examples are discussed in detail.     

Effect of boundary conditions and workpiece geometry on residual stresses and microstructure in quenching process

In this study, the internal and residual stress states in quenched C60 steel cylinders are analyzed both numerically and experimentally in order to investigate the effects of boundary conditions (such as quench severity and temperature of quench bath) and specimen geometry. Specimen geometry has been analyzed by introducing a hole in a cylinder and varying hole diameter and its eccentricity. In the numerical analysis, the finite element method is applied and both temperature gradients and phase transformations are considered. Experiments include microstructural examination and X-ray measurements of residual stresses of the first kind. It has been found that the value of the convective heat transfer coefficient is very critical to obtain simulation results close to real ones. For instance, when a constant value obtained as the mean of a temperature dependent distribution is used for this parameter, residual stresses are seriously underestimated (up to 40%). The temperature of the quench bath affects directly the convective heat transfer coefficient. The lower the bath temperature, the higher are the resulting residual stresses. Under the same quenching conditions, if the diameter of the hole is greater than a critical value, a transition occurs from the shallow hardening case to the through hardening case, i.e., the residual stress distribution is reversed. On the other hand, for a constant hole diameter, if the eccentricity ratio reaches a critial value, a complex residual stress state results, i.e., compressive/tensile stress transition regions along the circumference are observed.     

Dermatology and the Internet--uses for the clinic and research

Improvement brought to iodinated molecules aims to obtain an optimal enhancement effect together with a lower toxicity. However, benign adverse events remain a common risk, and anaphylactoid reactions from the intravascular administration of iodinated contrast media may occur at random and are unpredictable. Although most contrast reactions are mild and self-limited, severe and even life-threatening reactions can occur at any time and for any kind of agent. Physicians must be aware of possible complications related to administration of this kind of agents and must be able to identify patients at risk, to care for prevention and prescribe an appropriate premedication regimen.     

Determination of free and conjugated oestrogens in peripheral blood plasma, feces and urine of cattle throughout pregnancy

In order to further characterize oestrogen production and metabolism during bovine pregnancy, free (f) and conjugated (c) estrone (E1), total free and conjugated oestrogens (tfcOe) and total free oestrogens (tfOe) were determined as marker oestrogens in blood plasma respectively in urine and feces of 10 pregnant cows. For the determination of individual oestrogens blood, urine and feces samples of days 240, 200, 160, 100, 60, 30, 10 and 5 prior to parturition were pooled and the free, sulfo (sc)- and glucuconjugated (gc) forms of E1, 17 beta-estradiol (E2 beta) and 17 alpha-estradiol (E2 alpha) were obtained following differential enzyme hydrolysis and separation by HPLC; hormone assay was by established RIA-procedures. FE1 and cE1 concentration in blood plasma, tfOe in feces and tfcOe in urine showed a similar pattern. A first rise occurred between days 110 and 120 of pregnancy, an additional overproportional rise commenced at around days 230-250. Highest concentrations were measured in feces (tfOe ca. 500 ng/g 1 day a. p.), followed by urine (tfcOe ca. 3.5 ng/mosmol 2 days a. p.) and blood plasma (fE1 ca. 8 nmol/l and cE1 ca. 20 nmol/l 2 days a. p.). Determination of individual oestrogens in blood plasma revealed that fE2 beta and fE2 alpha could only be found 10 days a. p. while the conjugated forms could already be detected on days 100 and 160 a. p. With 62% E1 was the dominant oestrogen, followed by E2 alpha (37%) and E2 beta (1.0%); E1 occurred predominantly as sulfate, E2 alpha and E2 beta predominantly as glucuronide. Main metabloite in feces was fE2 alpha (56.7%), followed by fE2 beta (32%) and fE1 (11.3%); conjugated oestrogens were not detected. Main metabolite in urine was scE1 followed by gcE2 alpha and gcE2 beta. ScE2 alpha and scE2 beta were not detected or were present in small quantities only. Hormonal changes over time were highly significant. Main product of placental oestrogen synthesis is scE1, the concentrations of f and c E2 beta and E2 alpha in plasma largely result from oestrogen metabolism and enterohepatic circulation.     

Understanding the dendritic cell lineage through a study of cytokine receptors

Dendritic cells form a system of antigen presenting cells that are specialized to stimulate T lymphocytes, including quiescent T cells. The lineage of dendritic cells is not fully characterized, although prior studies have shown that growth and differentiation are controlled by cytokines, particularly granulocyte/macrophage colony-stimulating factor (GM-CSF). To further elucidate the nature and control of the dendritic cell lineage, we have studied the expression of specific cytokine receptors. Sufficient numbers of dendritic cells were purified from spleen and skin to do quantitative binding studies with radiolabeled M-CSF, GM-CSF, and interleukin 1 (IL-1). To verify the nonlymphoid nature of dendritic cells, we made an initial search for rearrangements in T cell receptor and immunoglobulin genes and none were found. M-CSF binding sites, a property of mononuclear phagocytes, also were absent. In contrast, GM-CSF receptors were abundant on mature dendritic cells, with approximately 3,000 binding sites/cell with a single Kd of 500-1,000 pM. Substantial numbers of high affinity (< 100 pM) IL-1 binding sites were identified as well; cultured epidermal dendritic cells (i.e., epidermal Langerhans cells) had 500/cell and spleen dendritic cells approximately 70/cell. Cross-linking approaches showed the 80-kD species that is expected of high-affinity type 1 IL-1 receptor. Anti-type 1 IL-1 receptor (R) mAbs also visualized these receptors by flow cytometry on freshly isolated epidermal dendritic cells. These results provide new evidence that dendritic cells represent a differentiation pathway distinct from lymphocytes and monocytes. Together with recent findings on the effects of IL-1 and GM-CSF on epidermal dendritic cells in situ (see Results and Discussion), the data lead to a proposal whereby IL-1 signals IL-1R to upregulate GM-CSF receptors and thereby, the observed responsiveness of dendritic cells to GM-CSF for growth, viability, and function.     

Simulation in der Prozeßleittechnik

Simulation in process control. Distributed control systems provide their users with many potential benefits which are exhaustively used only in a small number of applications. Distributed control systems supply process data in real time in a digital format. When processing these data together with process models, the advantages of distributed control systems can be considerably extended. Process models are understood as mathematical systems containing a-priori knowledge about processes in a numerical or logical form. In the context of distributed control systems, some new and exciting applications of modelling and simulation techniques become accessible. Basic concepts of these specific techniques are described in this contribution. A collection of potential and realized applications show that these methods allow for a more detailed observation and for advanced process control strategies.