1 kWe sodium borohydride hydrogen generation system: Part I: Experimental study

A 1 kW_e hydrogen generation system using hydrolysis of sodium borohydride (NaBH₄) has been designed and built. The effects of flow rate, fuel concentration, inlet temperature and operating pressure on chemical conversion have been systematically investigated. A 10-point thermocouple profile probe was used to measure the temperature distribution inside the catalyst bed. Chemical conversion was also qualitatively evaluated via the temperature profile. For the present adiabatic reactor, a large temperature gradient at the outlet implies low conversion, while a small temperature gradient at the outlet implies high conversion. In order to obtain accurate measurements of hydrogen flow rate, water vapor carried in the product stream was removed by a custom hydrogen conditioning station. Using 15% concentration NaBH₄ aqueous solution, this system generated hydrogen up to 20 SLPM with a reasonably high chemical conversion (95%). Discharge products from using NaBH₄ concentrations above 15% crystallized upon cooling to room temperature. Such products would be difficult to remove from the discharge tank in a practical setting. Considering the practical difficulties in heating the discharge product to prevent crystallization, the highest usable concentrations would likely fall in the range of 10–15%. The resulting maximum material gravimetric density is 3.1 wt% of hydrogen and falls short of the DOE on-board hydrogen storage system target of 6 wt% for year 2010.     

Improved Transmission Representations in Oligopolistic Market Models: Quadratic Losses, Phase Shifters, and DC Lines

Practical models of competition among power generators who possess market power have generally had to use simplified models of transmission costs and constraints in order to be tractable. In particular, the linearized dc load flow model has been popular in complementarity and other types of oligopoly models. In this paper, we show how such models can be generalized to include quadratic losses, controllable DC lines, and phase shifting transformers. These generalizations preserve convexity of the feasible region, a property that facilitates computation and proof of solution uniqueness and existence. Piecewise and successive linearization formulations are also provided that allow consideration of nonlinear losses in models that require linear constraints. A simple six-bus example illustrates the application of these generalizations. In that example, the impact of losses on prices is much greater under strategic behavior than under competition. Large-scale applications of these approaches to markets in western North America and the European Union illustrate how inclusion of nonlinear losses and controllable DC lines can affect estimates of prices, flows, and economic efficiency indices resulting from oligopoly models.      

Comparative wear under four different tribological conditions of acetylene enhanced cross-linked ultra high molecular weight polyethylene

In this study, the wear of ultra high molecular weight polyethylene (UHMWPE) (Grade RCH 1000) crosslinked by gamma irradiation in acetylene was compared to virgin (non-irradiated) UHMWPE using four different wear configurations: (i) unidirectional motion with a smooth counterface, (ii) multidirectional motion with a smooth counterface, (iii) unidirectional motion with a rough counterface and (iv) multidirectional motion with a rough counterface. ©©1999©Kluwer Academic Publishers     

A hip joint simulator study using simplified loading and motion cycles generating physiological wear paths and rates

In some designs of hip joint simulator the cost of building a highly complex machine has been offset with the requirement for a large number of test stations. The application of the wear results generated by these machines depends on their ability to reproduce physiological wear rates and processes. In this study a hip joint simulator has been shown to reproduce physiological wear using only one load vector and two degrees of motion with simplified input cycles. The actual path of points on the femoral head relative to the acetabular cup were calculated and compared for physiological and simplified input cycles. The in vitro wear rates were found to be highly dependent on the shape of these paths and similarities could be drawn between the shape of the physiological paths and the simplified elliptical paths.     

A new variational self-regular traction-BEM formulation for inter-element continuity of displacement derivatives

In this work, a non-symmetric variational approach is derived to enforce C ^1, continuity at inter-element nodes for the self-regular traction-BIE. This variational approach uses only Lagrangian C ⁰ elements. Two separate algorithms are derived. The first one enforces C ^1, continuity at smooth inter-element nodes, and the second enforces continuity of displacement derivatives in global coordinates at corner nodes, where C ^1, continuity cannot be enforced. The variational formulation for the traction-BIE is implemented in this work for two elastostatics problems with various discretizations and polynomial interpolants. Local and global measures of the discretization error are obtained by means of an error estimator recently derived by the authors. Comparisons are also made with the displacement-BIE, which does not require C ^1, continuity for the displacement. The lack of smoothness of the displacement derivatives at the inter-element nodes is shown to be an important source of both local and global error for the traction-BIE formulation, especially for quadratic elements. The accuracy of the boundary solution obtained from the traction-BIE improves significantly when C ^1, continuity is enforced where possible, i.e., at the smooth inter-element nodes only. The first author acknowledges the support received from CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico. The third author gratefully acknowledges support by the National Science Foundation (CTS-9983961). The fourth author acknowledges the support received from FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerais.     

Measuring the Decay of Vorticity in Superfluid 3He-B - A Progress Report

Recent measurements in superfluid ³ He-B have been interpreted as evidence in support of the Kibble-Zurek hypothesis for the formation of defects in the early Universe. The superfluid ³ He analogue to the cosmic string is the quantum vortex. We report here the preliminary attempts to detect the heat evolution from the decay of this vorticity in superfluid ³ He-B at temperatures down to 110 K. We produce vorticity by neutron irradiation of a small superfluid ³ He-B sample and attempt to measure the heat released as the vorticity decays. We detect a long time scale heat release and find that the lifetime of this decay varies inversely proportional to the quasiparticle excitation number density in the superfluid. However, we have yet to be convinced that this heat is from the decay of vorticity.     

Superfluid 3He Simulation of Cosmic String Creation in the Early Universe

We discuss the first experimental observations of a deficit in the thermal energy released after the exothermic neutron-³ He nuclear reaction in superfluid ³ He at temperatures approaching 100K. We propose that this deficit is associated with the creation of a vortex tangle as the liquid ³ He recrosses the superfluid transition. This process has many similarities with the theory of cosmic string creation during the GUT and electroweak transitions shortly after the Big Bang. Our measurements constitute the first quantitative test of defect creation via the cosmological Kibble mechanism for gauge symmetry breaking phase transitions and agree very well with the predictions of Zurek's scenario.     

The partitioned dynamic-priority scheduling of sporadic task systems

A polynomial-time algorithm is presented for partitioning a collection of sporadic tasks among the processors of an identical multiprocessor platform. Since the partitioning problem is NP-hard in the strong sense, this algorithm is unlikely to be optimal. A quantitative characterization of its worst-case performance is provided in terms of resource augmentation.

Pharmacokinetic and pharmacodynamic changes of furosemide after intravenous and oral administration to rats with alloxan-induced diabetes mellitus

We previously developed the "immunogene" approach toward cancer gene therapy using epidermal growth factor receptor (EGFR)-mediated endocytosis. Here, we describe an improved immunogene system, in which the antigen-binding (Fab) fragments of the monoclonal antibody (Ab) B4G7 against the human EGFR were conjugated with poly-L-lysine to form a gene delivery vehicle (designated Fab "immunoporter"). Within 12 hours, the beta-galactosidase beta-gal) gene was transferred via the Fab immunoporter to virtually all of the nuclei of human squamous carcinoma A431 cells that overproduce the EGFR, and the beta-gal enzyme activity was detected within 24 hours and retained for more than 3 days. The beta-gal gene was not transferred into human and mouse cells that were deficient in EGFRs, but it was delivered if those mouse cells were transformed with human EGFR genes. Beta-gal gene transfer via the Fab immunoporter was inhibited by pretreatment with excess amounts of the Fab fragment. The transfer efficiency of the beta-gal gene to A431 cells via the Fab immunoporter was approximately 2%, which is as high as the lipofection method and 20- to 100-fold higher than the whole Ab immunoporter. The transfer of the herpes simplex virus thymidine kinase gene into A431 tumor cells as a form of the thymidine kinase/Fab immunogene was successful, and subsequent treatment with ganciclovir induced remarkable suicide effects which conferred 1000-fold higher drug sensitivity. Thus, the Fab immunogene was substantially improved with regard to the whole Ab immunogene and could be used as a potent gene transfer vehicle for the in vivo targeting of EGFR-hyperproducing tumor cells.