14,886 research outputs found
Correlation between electric-field-induced phase transition and piezoelectricity in lead zirconate titanate films
We observed that electric field induces phase transition from tetragonal to
rhombohedral in polycrystalline morphotropic lead zirconate titanate (PZT)
films, as reported in 2011 for bulk PZT. Moreover, we evidenced that this
field-induced phase transition is strongly correlated with PZT film
piezoelectric properties, that is to say the larger the phase transition, the
larger the longitudinal piezoelectric coefficient d 33,eff . Although d 33,eff
is already comprised between as 150 to 170 pm/V, our observation suggests that
one could obtain larger d 33,eff values, namely 250 pm/V, by optimizing the
field-induced phase transition thanks to composition fine tuning
Design of small Stirling dynamic isotope power system for robotic space missions
Design of a multihundred-watt Dynamic Isotope Power System (DIPS) based on the U.S. Department of Energy (DOE) General Purpose Heat Source (GPHS) and small (multihundred-watt) free-piston Stirling engine (FPSE) technology is being pursued as a potential lower cost alternative to radioisotope thermoelectric generators (RTG's). The design is targeted at the power needs of future unmanned deep space and planetary surface exploration missions ranging from scientific probes to Space Exploration Initiative precursor missions. Power level for these missions is less than a kilowatt. Unlike previous DIPS designs which were based on turbomachinery conversion (e.g. Brayton), this small Stirling DIPS can be advantageously scaled down to multihundred-watt unit size while preserving size and mass competitiveness with RTG's. Preliminary characterization of units in the output power ranges 200-600 We indicate that on an electrical watt basis the GPHS/small Stirling DIPS will be roughly equivalent to an advanced RTG in size and mass but require less than a third of the isotope inventory
Nanoscale surface relaxation of a membrane stack
Recent measurements of the short-wavelength (~ 1--100 nm) fluctuations in
stacks of lipid membranes have revealed two distinct relaxations: a fast one
(decay rate of ~ 0.1 ns^{-1}), which fits the known baroclinic mode of bulk
lamellar phases, and a slower one (~ 1--10 \mu s^{-1}) of unknown origin. We
show that the latter is accounted for by an overdamped capillary mode,
depending on the surface tension of the stack and its anisotropic viscosity. We
thereby demonstrate how the dynamic surface tension of membrane stacks could be
extracted from such measurements.Comment: 4 page
The Parametric Ordinal-Recursive Complexity of Post Embedding Problems
Post Embedding Problems are a family of decision problems based on the
interaction of a rational relation with the subword embedding ordering, and are
used in the literature to prove non multiply-recursive complexity lower bounds.
We refine the construction of Chambart and Schnoebelen (LICS 2008) and prove
parametric lower bounds depending on the size of the alphabet.Comment: 16 + vii page
Barriers That Influence Adoption of ACL Injury Prevention Programs Among High School Girls’ Soccer Coaches
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Design of multihundredwatt DIPS for robotic space missions
Design of a dynamic isotope power system (DIPS) general purpose heat source (GPHS) and small free piston Stirling engine (FPSE) is being pursued as a potential lower cost alternative to radioisotope thermoelectric generators (RTG's). The design is targeted at the power needs of future unmanned deep space and planetary surface exploration missions ranging from scientific probes to SEI precursor missions. These are multihundredwatt missions. The incentive for any dynamic system is that it can save fuel which reduces cost and radiological hazard. However, unlike a conventional DIPS based on turbomachinery converions, the small Stirling DIPS can be advantageously scaled to multihundred watt unit size while preserving size and weight competitiveness with RTG's. Stirling conversion extends the range where dynamic systems are competitive to hundreds of watts (a power range not previously considered for dynamic systems). The challenge of course is to demonstrate reliability similar to RTG experience. Since the competative potential of FPSE as an isotope converter was first identified, work has focused on the feasibility of directly integrating GPHS with the Stirling heater head. Extensive thermal modeling of various radiatively coupled heat source/heater head geometries were performed using data furnished by the developers of FPSE and GPHS. The analysis indicates that, for the 1050 K heater head configurations considered, GPHS fuel clad temperatures remain within safe operating limits under all conditions including shutdown of one engine. Based on these results, preliminary characterizations of multihundred watt units were established
The NASA CSTI high capacity power project
The SP-100 Space Nuclear Power Program was established in 1983 by DOD, DOE, and NASA as a joint program to develop technology for military and civil applications. Starting in 1986, NASA has funded a technology program to maintain the momentum of promising aerospace technology advancement started during Phase 1 of SP-100 and to strengthen, in key areas, the chances for successful development and growth capability of space nuclear reactor power systems for a wide range of future space applications. The elements of the Civilian Space Technology Initiative (CSTI) High Capacity Power Project include Systems Analysis, Stirling Power Conversion, Thermoelectric Power Conversion, Thermal Management, Power Management, Systems Diagnostics, Environmental Interactions, and Material/Structural Development. Technology advancement in all elements is required to provide the growth capability, high reliability and 7 to 10 year lifetime demanded for future space nuclear power systems. The overall project will develop and demonstrate the technology base required to provide a wide range of modular power systems compatible with the SP-100 reactor which facilitates operation during lunar and planetary day/night cycles as well as allowing spacecraft operation at any attitude or distance from the sun. Significant accomplishments in all of the project elements will be presented, along with revised goals and project timelines recently developed
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