Renal blood flow: measurement in vivo with rapid spiral MR imaging

PURPOSE: To evaluate the use of stent-grafts for the percutaneous closure of arteriovenous fistulas that develop after cardiac catheterization. MATERIALS AND METHODS: From January 1994 to November 1997, 14 arteriovenous fistulas in 13 patients (eight men, five women; age range, 46-65 years; mean age, 53.5 years) were treated. Eleven fistulas were situated between the deep femoral artery and the common femoral vein, and three fistulas were between the superficial femoral artery and the common femoral vein. All fistulas were closed with stent-grafts positioned in the artery at the level of the fistula. RESULTS: The percutaneous treatment of arteriovenous fistulas was successful in all cases. The findings at angiography performed after the procedure demonstrated the closure of the fistulas and the correct positioning of the prostheses; veins were no longer visible. One complication occurred--a partial thrombosis of the common femoral vein at the puncture site after manual compression. CONCLUSION: On the basis of the preliminary data, the authors believe that the percutaneous closure of arteriovenous fistulas with stent-grafts is a safe and effective alternative to conventional surgery.     

Simulation of the forming of mash seam welded sheets

The paper presents results on the optimization of the process of mash seam welding for improving the formability of the joined sheet metal semi-products. An integrated concept including the welding, smoothing and heat treatment of mash welded sheets has been developed. As an example, fatigue tests and the simulation of the forming behaviour of a mash seam welded tensile specimen simulated by the finite element method (FEM) is discussed. The determination of the material properties of the seam which, so far, have been determined experimentally is thus considerably simplified.     

Quantitative Determination of Brönsted Acid Sites on Zeolites: A New Approach Towards the Chemical Composition of Zeolites

An original quantitative method based on H/D exchange between H₂O/D₂O molecules and the OH groups of different zeolites has been developed for the titration of the Brönsted acid sites present on the solid surface. The measured Brönsted acid sites density appears to be in good agreement with the theoretical amount estimated by the Si/Al ratio. In contrary to classical methods, this non-destructive anhydride method titrates the whole quantity of Brönsted acid sites of zeolites.     

Postperceptual effects and P300 latency

BACKGROUND: Structural and functional brain changes have been described in elderly patients with unipolar affective disorder. Changes appear to be more marked in patients with late-onset depression, but the reversibility of such changes after clinical recovery is not known. METHODS: Magnetic resonance imaging, electroencephalography (EEG), and cognitive tests were performed in 23 elderly patients (mean age 66.5 years) clinically recovered from major depression. Twelve had late-onset depression (first episode over 55 years of age); 11 had early onset (first episode before 50 years). EEG and cognitive testing were also performed on 15 control subjects. RESULTS: Patients with late-onset depression had larger third and lateral ventricles, increased ventricular-brain ratio, and greater frequency and severity of subcortical white matter lesions than those with early onset. There was no difference between early- and late-onset patients in EEG and cognitive measures, but compared with controls patients showed significant changes in EEG evoked potentials and increased slow-wave activity, slowed reaction times, and global impairments in cognitive function. CONCLUSIONS: These results suggest that structural changes are greater in patients with late-onset depression, and that EEG and cognitive impairments persist after recovery, regardless of age of onset of depression, and are independent of structural changes.     

Esophageal scintigraphy of Zenker''s diverticula before and after diverticulotomy]

To assess the role of insulin in the development of obesity induced by antipsychotic drugs, a glucose tolerance test was conducted in 40 female rats during the peak of sulpiride-induced weight gain and in 40 vehicle-treated animals. The glucose area under the curve did not differ between the groups (P = 0.24), however, the area under the insulin curve was significantly decreased by sulpiride (55.2 +/- 2.8 versus 115.6 +/- 18.9, P = 0.007). The results suggest that insulin resistance and hyperinsulinaemia are not involved in the excessive weight gain observed in this animal model of drug-induced obesity. Alternatively, the insulin-dampened response observed in the sulpiride-treated rats may be related to increased insulin sensitivity, which may promote weight gain as proposed by Ravussin (1995).     

A method for the determination of N-nitrosoalkanolamines in cosmetics

Summary A method für the determination of N-nitrosoalkanolamines in cosmetics and toiletries is described. The ingredients used in their manufacture N-nitroso-bis-(2-hydroxyethyl)amine (N-nitrosodiethanolamine, NDELA) and N-nitroso-bis-(2-hydroxypropyl)amine (NBHPA) are almost exclusively the contaminants. The method has therefore been modified for their determination. N-Nitroso-(2-hydroxyethyl)-(2-hydroxypropyl)amine is used as the internal standard. After dilution with water, the cosmetic is adsorbed onto a kieselguhr column and extracted with n-butanol. The extract is brought to dryness, re-dissolved in chloroform/acetone (5 + 1) and transferred to a silica gel column. The column is washed and eluted with acetone. The eluate is dried and the residue is treated with N-methyl-N-trimethylsilyl-heptafluorobutyramide. Trimethylsilyl (TMS)derivatives of N-nitrosoalkanolamines are determined by gas-chromatography with a thermal energy analyzer (TEA). Recovery of the internal standard is 95% and the determination limit is 5 g/kg, Repeated analyses of a foam bath, spiked with 30 g/kg NDELA, gave an average content of 32 g/kg NDELA (variation coefficient 8.8%;n=10). In order to avoid artefact formation during the clean-up process, kieselguhr containing 50% sodium ascorbate has to be used when cosmetics containing free dialkanolamines are analyzed.

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Ein Bestimmungsverfahren für N-Nitrosoalkanolamine in kosmetischen Mitteln

Zusammenfassung Ein Verfahren zur Bestimmung von N-Nitrosoalkanolaminen in kosmetischen Mitteln wird beschrieben. Da die technisch eingesetzten Grundstoffe praktisch ausschließlich zu Kontamination mit N-Nitroso-bis-(2-hydroxyethyl)amin (N-Nitrosodiethanolamin, NDELA) und N-Nitroso-bis-(2-hydroxypropyl)amin (NBHPA) führen, ist das Verfahren auf die Erfassung dieser Nitrosamine optimiert. Die mit Wasser verdünnte Probe wird nach Aufgabe auf eine Kieselgursäule mit n-Butanol extrahiert. Das Lösungsmittel wird abgedampft, der Rückstand in Chloroform/Aceton (5 + 1) aufgenommen und auf eine Kieselgelsäule gegeben. Nach Waschen wird mit Aceton eluiert. Das Eluat wird von Aceton befreit, der Rückstand trimethylsilyliert. Trimethylsilyl (TMS)-Derivate der N-Nitrosoalkanolamine werden gaschromatographisch mit dem Thermal Energy Analyzer (TEA) erfaßt. Die Wiederfindung des internen Standards N-Nitroso-(2-hydroxyethyl)-(2-hydroxypropyl)amin (NBHPA) liegt bei 95%, die Bestimmungsgrenze für NDELA bei 5 g/kg. Wiederholte Analysen eines mit 30 g/kg dotierten Schaumbades ergaben einen mittleren Gehalt von 32 g/kg NDELA (Variationskoeffizient = 8,8%,n=10). Zur Vermeidung der Artefaktbildung während der Aufarbeitung muß bei Analysen von kosmetischen Mitteln mit Gehalt an freien Dialkanolaminen Kieselgur mit Zusatz von 50% Natriumascorbat zur Festphasenextraktion verwendet werden.

     

String Methods for Stochastic Image and Shape Matching

Matching of images and analysis of shape differences is traditionally pursued by energy minimization of paths of deformations acting to match the shape objects. In the large deformation diffeomorphic metric mapping (LDDMM) framework, iterative gradient descents on the matching functional lead to matching algorithms informally known as Beg algorithms. When stochasticity is introduced to model stochastic variability of shapes and to provide more realistic models of observed shape data, the corresponding matching problem can be solved with a stochastic Beg algorithm, similar to the finite-temperature string method used in rare event sampling. In this paper, we apply a stochastic model compatible with the geometry of the LDDMM framework to obtain a stochastic model of images and we derive the stochastic version of the Beg algorithm which we compare with the string method and an expectation-maximization optimization of posterior likelihoods. The algorithm and its use for statistical inference is tested on stochastic LDDMM landmarks and images.     

Linking card sorting to browsing performance – are congruent municipal websites more efficient to use?

Card sorting is a method for eliciting mental models and is frequently used for creating efficient website navigation structures. The present studies set out to validate card sorting by linking browsing performance to the degree of match between the mental model and the navigation structure. First, a card sorting study was conducted (n?=?27) to elicit users’ mental model of municipal websites. Second, performance was measured for a number of search tasks with varying degrees of congruence with users’ mental model (n?=?50). Analysis by linear mixed-effect models suggests that the match between mental model and website structure has no effect on browsing performance. We discuss possible reasons and consequences of the failure to validate card sorting for designing navigation structures of informational websites.     

Homocoupling Defects in a Conjugated Polymer Limit Exciton Diffusion

Copolymers such as PCDTBT (poly(N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole))) are commonly employed as donor material in bulk heterojunction solar cells. Recently, chemical defects such as homocouplings have been shown to form at the material synthesis stage, strongly reducing the short circuit current in organic photovoltaics. Here it is shown that both low molecular weight and homocoupling defects reduce the short circuit current of solar cells because of limited exciton diffusion. A model that unites and explains the influence of both chemical parameters with the distribution of conjugation lengths is proposed. The connection between limited exciton diffusion and short circuit current is revealed via kinetic Monte Carlo simulation of bulk heterojunctions. The findings are likely applicable for copolymers in general.     

Agglomeration and breakage of nanoparticles in stirred media mills—a comparison of different methods and models

The increasing industrial demand for nanoparticles challenges the application of stirred media mills to grind in the sub-micron size range. It was shown recently [Mende et al., 2003. Mechanical production and stabilization of submicron particles in stirred media mills. Powder Technology 132, 64-73] that the grinding behavior of particles in the sub-micron size range in stirred media mills and the minimum achievable particle size is strongly influenced by the suspension stability and thus the agglomeration behavior of the suspension. Therefore, an appropriate modeling of the process must include a superposition of the two opposing processes in the mill i.e., breakage and agglomeration which can be done by means of population balance models. Modeling must now include the influence of colloidal surface forces and hydrodynamic forces on particle aggregation and breakup. The superposition of the population balance models for agglomeration and grinding with the appropriate kernels leads to a system of partial differential equations, which can be solved in various ways numerically. Here a modified h-p Galerkin algorithm which is implemented in the commercially available software package PARSIVAL developed by CiT (CiT GmbH, Rastede, Germany) and the moment methodology according to [Diemer and Olsen, 2002a. A moment methodology for coagulation and breakage problems: Part I—analytical solution of the steady-state population balance. Chemical Engineering Science 57 (12), 2193-2209; Diemer and Olsen, 2002b. A moment methodology for coagulation and breakage problems: Part II—moment models and distribution reconstruction. Chemical Engineering Science 57 (12), 2211-2288] are used and compared to explicit data on alumina. This includes a comparison of the derived particle size distributions, moments and its accuracy depending on the starting particle size distribution and the used agglomeration and breakage kernels. Finally, the computational effort of both methods in comparison to the prior mentioned parameters is evaluated in terms of practical application.