A multi-sensor system for robotics proximity operations

Robots without sensors can perform only simple repetitive tasks and cannot cope with unplanned events. A multi-sensor system is needed for a robot to locate a target, move into its neighborhood and perform operations in contact with the object. Systems that can be used for such tasks are described

MARIE Measurements and Model Predictions of Solar Modulation of Galactic Cosmic Rays at Mars

Recent data from the MARIE (Martian Radiation Environment Experiment) instrument on board the 2001 Mars Odyssey spacecraft currently in Mars orbit are presented. It is shown that the short-term modulations of galactic cosmic rays (GCR) are well described by correlating the so lar modulation parameter, , with Earth-based neutron monitor counts using a 85-day time lag and the NASA Models - HZETRN (High Z and Energy Transport) and QMSFRG (Quantum Multiple Scattering theory of nuclear Fragmentation). The dose rates observed by the MARIE instrument are within 10% of the model calculations

Discovery of a Novel Class of Orally Active Trypanocidal N-Myristoyltransferase Inhibitors

N-Myristoyltransferase (NMT) represents a promising drug target for human African trypanosomiasis (HAT), which is caused by the parasitic protozoa Trypanosoma brucei. We report the optimization of a high throughput screening hit (1) to give a lead molecule DDD85646 (63), which has potent activity against the enzyme (IC50 = 2 nM) and T. brucei (EC50 = 2 nM) in culture. The compound has good oral pharmacokinetics and cures rodent models of peripheral HAT infection. This compound provides an excellent tool for validation of T. brucei NMT as a drug target for HAT as well as a valuable lead for further optimization.</p

Mechanical Response of Fuel Cell Membranes Subjected to a Hygro-Thermal Cycle

The mechanical response of fuel cell proton exchange membranes subjected to a single hygro-thermal duty cycle in a fuel cell assembly is investigated through numerical means. To this end, the behavior of the membrane with temperature and humidity dependent material properties is simulated under temperature and humidity loading and unloading conditions. The stress-evolution during a simplified operating cycle is determined using finite element analysis for two clamping methods and two alignments of the bipolar plates. It is shown that compressive, plastic deformation occurs during the hygro-thermal loading, resulting in tensile residual stresses after unloading. These residual in-plane stresses in the membrane may explain the occurrence of cracks and pinholes in the membrane under cyclic loading

Mechanical Behavior of Fuel Cell Membranes under Humidity Cycles and Effect of Swelling Anisotropy on the Fatigue Stresses

The mechanical response of proton exchange membranes in a fuel cell assembly is investigated under humidity cycles at a constant temperature (85°C). The behavior of the membrane under hydration–dehydration cycles is simulated by imposing a humidity gradient from the cathode to the anode. Linear elastic, plastic constitutive behavior with isotropic hardening and temperature and humidity dependent material properties are utilized in the simulations for the membrane. The evolution of the stresses and plastic deformation during the humidity cycles are determined using finite element analysis for two clamping methods and various levels of swelling anisotropy. The membrane response strongly depends on the swelling anisotropy where the stress amplitude decreases with increasing anisotropy. These results suggest that it may be possible to optimize a membrane with respect to swelling anisotropy to achieve better fatigue resistance, potentially enhancing the durability of fuel cell membranes

Mechanical Response of Fuel Cell Membranes Subjected to a Hygro-Thermal Cycle

The mechanical response of fuel cell proton exchange membranes subjected to a single hygro-thermal duty cycle in a fuel cell assembly is investigated through numerical means. To this end, the behavior of the membrane with temperature and humidity dependent material properties is simulated under temperature and humidity loading and unloading conditions. The stress-evolution during a simplified operating cycle is determined using finite element analysis for two clamping methods and two alignments of the bipolar plates. It is shown that compressive, plastic deformation occurs during the hygro-thermal loading, resulting in tensile residual stresses after unloading. These residual in-plane stresses in the membrane may explain the occurrence of cracks and pinholes in the membrane under cyclic loading

Numerical Investigation of Mechanical Durability in Polymer Electrolyte Membrane Fuel Cells

The relationship between the mechanical behavior and water transport in the membrane electrode assembly (MEA) is numerically investigated. Swelling plays a key role in the mechanical response of the MEA during fuel cell operation because swelling can be directly linked to the development of stresses. Thus, in the model introduced here, the stresses and the water distribution are coupled. Two membranes are studied: unreinforced perfluorosulfonic acid (PFSA) and an experimental reinforced composite membrane. The results suggest that open-circuit voltage operations lead to a uniform distribution of stresses and plastic deformation, whereas under current-load operation, the stresses and the plastic deformation are generally lower and localized at the cathode side of the MEA. For the experimental reinforced membrane investigated, the in-plane swelling and, consequently, the stresses and plastic deformation are lower than in an unreinforced PFSA membrane. This reduction is a favorable outcome for improving durability. The model also suggests that the mechanical constraints due to the clamping of the cell may limit the swelling of the membrane and consequently change the water distribution

Stresses in Proton Exchange Membranes Due to Hygro-Thermal Loading

Durability of the proton exchange membrane (PEM) is a major technical barrier to the commercial viability of polymer electrolyte membrane fuel cells (PEMFC) for stationary and transportation applications. In order to reach Department of Energy objectives for automotive PEMFCs, an operating design lifetime of at least 5000 h over a broad temperature range is required. Reaching these lifetimes is an extremely difficult technical challenge. Though good progress has been made in recent years, there are still issues that need to be addressed to assure successful, economically viable, long-term operation of PEM fuel cells. Fuel cell lifetime is currently limited by gradual degradation of both the chemical and hygro-thermomechanical properties of the membranes.Eventually the system fails due to a critical reduction of the voltage or mechanical damage. However, the hygro-thermomechanical loading of the membranes and how this effects the lifetime of thefuel cell is not understood. The long-term objective of the research is to establish a fundamental understanding of the mechanical processes in degradation and how they influence the lifetime of PEMFCs based on perfluorosulfuric acid membrane. In this paper, we discuss the finite element models developed to investigate the in situ stresses in polymer membranes

Mechanical Behavior of Fuel Cell Membranes under Humidity Cycles and Effect of Swelling Anisotropy on the Fatigue Stresses

The mechanical response of proton exchange membranes in a fuel cell assembly is investigated under humidity cycles at a constant temperature (85°C). The behavior of the membrane under hydration–dehydration cycles is simulated by imposing a humidity gradient from the cathode to the anode. Linear elastic, plastic constitutive behavior with isotropic hardening and temperature and humidity dependent material properties are utilized in the simulations for the membrane. The evolution of the stresses and plastic deformation during the humidity cycles are determined using finite element analysis for two clamping methods and various levels of swelling anisotropy. The membrane response strongly depends on the swelling anisotropy where the stress amplitude decreases with increasing anisotropy. These results suggest that it may be possible to optimize a membrane with respect to swelling anisotropy to achieve better fatigue resistance, potentially enhancing the durability of fuel cell membranes

Stresses in Proton Exchange Membranes Due to Hygro-Thermal Loading

Durability of the proton exchange membrane (PEM) is a major technical barrier to the commercial viability of polymer electrolyte membrane fuel cells (PEMFC) for stationary and transportation applications. In order to reach Department of Energy objectives for automotive PEMFCs, an operating design lifetime of at least 5000 h over a broad temperature range is required. Reaching these lifetimes is an extremely difficult technical challenge. Though good progress has been made in recent years, there are still issues that need to be addressed to assure successful, economically viable, long-term operation of PEM fuel cells. Fuel cell lifetime is currently limited by gradual degradation of both the chemical and hygro-thermomechanical properties of the membranes.Eventually the system fails due to a critical reduction of the voltage or mechanical damage. However, the hygro-thermomechanical loading of the membranes and how this effects the lifetime of thefuel cell is not understood. The long-term objective of the research is to establish a fundamental understanding of the mechanical processes in degradation and how they influence the lifetime of PEMFCs based on perfluorosulfuric acid membrane. In this paper, we discuss the finite element models developed to investigate the in situ stresses in polymer membranes