Experimental Steep, Braided Flow: Application to Flooding Risk on Fans

Flooding processes occurring on alluvial fans are considerably different from those occurring along single thread rivers with well defined floodplains. Active erosion, rapid sedimentation, and the uncertainty in flow path make the prediction of flood evolution and extent difficult. Based on a large scale experiment, this study investigates the long term evolution of the flow on a steep, noncohesive sediment surface resembling a complex of merged alluvial fans. The results are pertinent to the assessment of flooding hazard on alluvial fans. At any given time, the average flow occupancy was 21% of the surface. However, the flow was characterized by active channel switching and overflow processes. The percentage of the surface remaining dry was found to decay harmonically with time. A reworking time was defined as the time at which half of the surface that was initially dry remained dry, whereas the other half was inundated at least once. An empirical expression was developed in which reworking time is proportional to the average cross sectional area of flow and inversely proportional to the sediment supply.     

Parallelization of deduction strategies: An analytical study

In this paper we present a general analysis of the parallelization of deduction strategies. We classify strategies assubgoal-reduction strategies, expansion-oriented strategies, andcontraction-based strategies. For each class we analyze how and what types of parallelism can be utilized. Since the operational semantics of deduction-based programming languages can be construed as subgoal-reduction strategies, our analysis encompasses, at the abstract level, both strategies for deduction-based programming and those for theorem proving. We distinguish different types of parallel deduction based on the granularity of parallelism. These two criteria — the classification of strategies and of types of parallelism — provide us with a framework to treat problems and with a grid to classify approaches to parallel deduction. Within this framework, we analyze many issues, including the dynamicity and size of the database of clauses during the derivation, the possibility of conflicts between parallel inferences, and duplication versus sharing of clauses. We also suggest the type of architectures that may be suitable for each class of strategies. We substantiate our analysis by describing existing methods, emphasizing parallel expansion-oriented strategies and parallel contraction-based strategies for theorem proving. The most interesting and least explored by existing approaches are the contraction-based strategies. The presence of contraction rules — rules that delete clauses — and especially the application ofbackward contraction, emerges as a key issue for parallelization of these strategies. Backward contraction is the main reason for the impressive experimental success of contraction-based strategies. Our analysis shows that backward contraction makes efficient parallelization much more difficult. In our analysis, coarse-grain parallelism appears to be the best choice for parallelizing contraction-based reasoning. Accordingly, we propose a notion ofparallelism at the search level as coarse-grain parallelism for deduction.Supported by the GE Foundation Faculty Fellowship to the University of Iowa and by the National Science Foundation with grant CCR-94-08667.Supported by grant NSC 83-0408-E-002-012T of the National Science Council of the Republic of China.     

Hyperosmolar nonketotic coma at the onset of type I diabetes in a child

The expression of multidrug resistance-associated protein (MRP) mRNA was examined in ten samples of Ewing's sarcoma of bone (ES) and in one nude mice transplantable ES and two malignant peripheral neuroectodermal tumor (MPNT) cell lines using an RT-PCR assay. MRP mRNA expression was recognized in eight of the ten clinical specimen and in all three cell lines. On the other hand, the expression of multidrug resistance gene (MDR1) was demonstrated in three of the ten clinical samples and all three cell lines. Our results may contribute to elucidation of the mechanism of anti-cancer-drug resistance in this tumor.     

Plasma endothelin-1 levels during transient acute myocardial ischaemia in men: effects of coronary revascularization

The endothelium-derived peptide endothelin-1 (ET-1) was evaluated in 14 male patients [mean age 52.74 years (SEM 1.10)] affected by coronary artery disease during a bicycle electrocardiographic stress test and dipyridamole echocardiogram. Both tests were performed before and after coronary revascularization. Fourteen healthy male subjects served as controls [mean age 53.21 years (SEM 1.63)]. Baseline plasma endothelin-1 levels were higher (P < 0.0001) in ischaemic patients [1.81 pg mL-1 (0.15, n = 14)] than in control subjects [0.61 pg mL-1 (0.03, n = 14)], but did not increase with exercise in both groups. Similar results were obtained with dipyridamole infusion. Endothelin-1 levels significantly decreased after coronary revascularization [before: mean 1.81 pg mL-1 (SEM 0.15, n = 14); after: mean 1.16 pg mL-1 (SEM 0.11), P < 0.002], without changes in the peptide response to both tests. In conclusion, elevated plasma endothelin-1 concentrations were found in patients with stable angina compared with non-ischaemic subjects. No changes were observed during exercise or dipyridamole infusion in both groups. Coronary revascularization was followed by a significant decrease in plasma endothelin-1 levels.     

A spectroelectrochemical and chemical study on oxidation of hydroxycinnamic acids in aprotic medium

Electrochemical and chemical oxidation of hydroxycinnamic acids (HCAs) was studied to investigate the mechanisms occurring in their antioxidant activities in a protons poor medium. Electrolyses and chemical reactions were followed on-line by monitoring the UV-spectral changes with time; final solutions were analysed by HPLC-MS. Anodic oxidation of mono- and di-HCAs, studied by cyclic voltammetry and controlled potential electrolyses, occurs via a reversible one-step two-electrons process, yielding the corresponding stable phenoxonium cation. A cyclization product was also proposed, as supported by ESR studies. Chemical oxidation with lead dioxide leads to different oxidation products according to the starting substrate. Di-HCAs like chlorogenic and rosmarinic acids and the ethyl ester of caffeic acid gave the corresponding neutral o-quinones, while mono-HCAs like cumaric, ferulic and sinapinic acids yielded the corresponding unstable neutral phenoxyl radical, as supported by the formation of dimerization products evidenced by HPLC-MS. In the case of caffeic acid, traces of the dimerization product suggest that the neutral phenoxyl radical may competitively undergo dimerization or decomposition of the neutral quinone.Chemical oxidation of HCAs was also followed by ESR spectroscopy: the di-HCAs radical anions were generated and detected, whereas among the mono-HCAs only the phenoxyl radical of the sinapinic acid was recorded.     

Photocatalytic transformations of aminopyrimidines on TiO2 in aqueous solution

In this paper, the effect of the presence of humidity and molecular oxygen on the low temperature oxidation of carbon monoxide on a Co₃O₄ powder surface was studied. The interaction between the probe molecules and the Co₃O₄ surface was investigated by means of diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and quadrupolar mass spectrometry (QMS).

Carbon monoxide interacts with the Co₃O₄ surface and is converted to carbon dioxide at rather low temperature (T≥323 K); the formation of carbonate species is also evident. The reactivity of Co₃O₄ is strongly depressed by humidity: as a matter of fact, in steam conditions carbon monoxide oxidation is significant at temperatures higher than 523 K. Moreover, the formation of carbonate species is more evident than in dry conditions. The Co₃O₄ powder surface interacts with oxygen molecules at T≥323 K to originate several activated surface oxygen species. The activation with oxygen does not appear to facilitate significantly the formation of carbon dioxide.     

Influence of recycling and contamination on structure and transport properties of polypropylene

In this work the effect of three processing cycles on the physical properties of polypropylene (PP) was studied and related to the changes in the structure (molecular weight, molecular weight distribution, morphology) occurring during recycling. In order to simulate both the use and the recycling process of PP in the laboratory, PP pellets were contaminated with three model substances and submitted to three cycles of processing by injection molding. The bars for testing were produced from virgin and recycled polymers. The amount of degradation occurring during the reprocessing was estimated by means of viscosity and gel permeation chromatography measurements. Differential scanning calorimetry and scanning electron microscopy analyses were performed to investigate the crystallization behavior and the morphology of virgin and recycled PP. In order to obtain information on the structural organization and mobility of the amorphous phase, a dynamic mechanical thermal analysis and measurements of the transport properties were carried out. The results obtained were attributed to the different structural organization of the bars in relation to the number of processing cycles and contamination. Part of the work was focused on the recyclability of PP for food packaging applications, considering the residual contamination and migrational behavior after repeated processing cycles. In particular, the relationships existing between reprocessing, the residual amounts of contaminants, and the migrational behavior were investigated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1768–1778, 2003     

A new approach for closed-form transient analysis of multiconductor transmission lines

A novel closed-form model for multiconductor transmission lines is presented. The proposed model is derived from the analytical characterization of half-T ladder networks, which using closed-form polynomials (named DFF and DFFz), allow one to exactly extract poles and residues of the two-port representation of multiconductor transmission lines, thus, generating a time domain macromodel that can be incorporated in a circuit simulator. Since the model is derived from a stable and passive equivalent network, its stability and passivity are strictly preserved. Simulation results for one, two, and three-conductor transmission lines with linear and nonlinear terminations are presented, confirming the validity of the proposed model.