No description available.

No description available.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1981. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 220-227).

ATP synthase (F_1 F_O-ATPase) is an essential enzyme for life. Powered by an electrochemical proton gradient, it catalyzes ADP and phosphate into ATP. The F_1-subunit of ATP synthase is called F_1-ATPase as it also independently catalyzes the reverse reaction in absence of F_O-part. The nearly 100% energy conversion efficiency of the molecular motor has attracted the attention of many physicists and biologists to explore the underlying thermodynamics. Recently, a new nonequilibrium equality derived by Harada and Sasa (Harada & Sasa, 2005) was applied to the experimental time series data on F_1-ATPase to extract heat flow to the environment. A phenomenological model for rotary motion was proposed and shown to reproduce key experimental features. Interested in the high efficiency of F_1-ATPase and the good performance of the corresponding model, we carried out a detailed computational study of the model to understand its behavior in a broader range of parameter values. We solved the model using a modified Gillespie algorithm for stochastic simulation and by integrating the Fokker-Planck equation. Various physical properties of the model, such as the relation between rotational velocity and parameters characterizing angular dependence (q) and ATP switching rates (W), the relation between two kinds of dissipation and rotational velocity, the negative heat flow from environment to system through ATP binding etc. are analyzed in detail. Importantly, we modified the driving potential to investigate the factors affecting the efficiency. Additionally, we found some inconsistences between properties of this model and previous studies and we could unify them by some adjustments, which may be useful for constructing more precise models in the future.

The induced potential difference across a standing shock front can be used to drive electric current through external loads. Such a "standing shock generator" presents an alternative scheme to the MHD generator for direct conversion of energy from high temperature supersonic flows. We make use of the supersonic flow behind a free running shock in a shock tube and let the flow impinge onto a conical obstacle mounted in the middle of the tube to create a standing shock. This cone has a conducting surface which acts as the anode. The cathode is mounted flush with the shock tube wall at a position upstream of the standing shock. By varying the load resistance, we have obtained current-voltage characteristics for the standing shock generator. These characteristics are families of parallel straight lines similar to the characteristics of a battery. The open-circuit voltage is found to depend on the standing shock potential and the work functions of the electrodes. The internal resistance (equivalent to the slope of the characteristic) is found to be dominated by the plasma-wall interaction at the surface boundary layers. The maximum current collected by the electrode is therefore limited to its ion saturation current. A typical result of the standing shock generator in our experiment gives 1 volt with 0.5.amp for the. 30X10⁻⁶ sec test time duration. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

No description available.

Thesis (Ph. D.)--University of Illinois, 1967. / Includes bibliographical references (leaves 161-164).

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During operation of the solid polymer fuel cell (SPFC). its performance is limited by the concentrations of hydrogen and oxygen at the reaction interfaces and in most SPFC designs, the hydration state of the membrane. Since in general, the concentrations of water and the gaseous species vary along the flow channel, the performance is also likely to change along the flow channel. In order to study this phenomenon, a measurement system was developed to map the current distribution across the electrode surface. The current distribution has been measured by dividing one of the current collectors into a number of electrically isolated segments. The current flowing through each of the segments was measured while maintaining a constant potential across the surface of the gas diffusion layer. Two separate segmented current collectors were developed. The first was used to measure the current distribution for an 80 cm2 single cell, and the second was used to investigate the local current densities around a single flow channel. The effects of the feed gas humidities on the spatial current density in the 80 cm2 fuel cell were investigated for two different membrane-electrode configurations. With Nafion 117 as electrolyte and at a cell temperature of 80°C. the membrane was found to dehydrate in the initial portion of the gas flow channel when the relative humidity of both the hydrogen and oxygen feed gases was less than 50%. With a Gore-Select membrane electrode assembly (hydrogen and air. temperature- 60°C). the membrane was sufficiently hydrated at all feed gas humidification conditions. The performance of the cell was found to deteriorate at higher feed gas humidities as a result of the lower partial pressures of the reactant gases. Measurements of the effects of gas pressures, stoichiometries and humidities on the length-wise and width-wise perfonnance around a single flow channel (Gore-Select membrane electrode assembly) are discussed in relation to a gas flow model.