2,799 research outputs found
Development of a static feed water electrolysis system
A one person level oxygen generation subsystem was developed and production of the one person oxygen metabolic requirements, 0.82 kg, per day was demonstrated without the need for condenser/separators or electrolyte pumps. During 650 hours of shakedown, design verification, and endurance testing, cell voltages averaged 1.62 V at 206 mA/sq cm and at average operating temperature as low as 326 K, virtually corresponding to the state of the art performance previously established for single cells. This high efficiency and low waste heat generation prevented maintenance of the 339 K design temperature without supplemental heating. Improved water electrolysis cell frames were designed, new injection molds were fabricated, and a series of frames was molded. A modified three fluid pressure controller was developed and a static feed water electrolysis that requires no electrolyte in the static feed compartment was developed and successfully evaluated
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Opportunities for and challenges to further reductions in the “specific power” rating of wind turbines installed in the United States
A wind turbine’s “specific power” rating relates its capacity to the swept area of its rotor in terms of Watt per square meter. For a given generator capacity, specific power declines as rotor size increases. In land-rich but capacity-constrained wind power markets, such as the United States, developers have an economic incentive to maximize megawatt-hours per constrained megawatt, and so have favored turbines with ever-lower specific power. To date, this trend toward lower specific power has pushed capacity factors higher while reducing the levelized cost of energy. We employ geospatial levelized cost of energy analysis across the United States to explore whether this trend is likely to continue. We find that under reasonable cost scenarios (i.e. presuming that logistical challenges from very large blades are surmountable), low-specific-power turbines could continue to be in demand going forward. Beyond levelized cost of energy, the boost in market value that low-specific-power turbines provide could become increasingly important as wind penetration grows
Small high-temperature nuclear reactors for space power
Criticality calculations for small, cylindrical, lithium cooled reactors for space power system
Josephson junction qubit network with current-controlled interaction
We design and evaluate a scalable charge qubit chain network with
controllable current-current coupling of neighbouring qubit loops via local
dc-current gates. The network allows construction of general N-qubit gates. The
proposed design is in line with current main stream experiments.Comment: 4 pages, 4 figure
The photoinduced transition in magnetoresistive manganites: a comprehensive view
We use femtosecond x-ray diffraction to study the structural response of
charge and orbitally ordered PrCaMnO thin films across a phase
transition induced by 800 nm laser pulses. By investigating the dynamics of
both superlattice reflections and regular Bragg peaks, we disentangle the
different structural contributions and analyze their relevant time-scales. The
dynamics of the structural and charge order response are qualitatively
different when excited above and below a critical fluence . For
excitations below the charge order and the superlattice is only partially
suppressed and the ground state recovers within a few tens of nanosecond via
diffusive cooling. When exciting above the critical fluence the superlattice
vanishes within approximately half a picosecond followed by a change of the
unit cell parameters on a 10 picoseconds time-scale. At this point all memory
from the symmetry breaking is lost and the recovery time increases by many
order of magnitudes due to the first order character of the structural phase
transition
Domain size effects on the dynamics of a charge density wave in 1T-TaS2
Recent experiments have shown that the high temperature incommensurate (I)
charge density wave (CDW) phase of 1T-TaS2 can be photoinduced from the lower
temperature, nearly commensurate (NC) CDW state. Here we report a time-resolved
x-ray diffraction study of the growth process of the photoinduced I-CDW
domains. The layered nature of the material results in a marked anisotropy in
the size of the photoinduced domains of the I-phase. These are found to grow
self-similarly, their shape remaining unchanged throughout the growth process.
The photoinduced dynamics of the newly formed I-CDW phase was probed at various
stages of the growth process using a double pump scheme, where a first pump
creates I-CDW domains and a second pump excites the newly formed I-CDW state.
We observe larger magnitudes of the coherently excited I-CDW amplitude mode in
smaller domains, which suggests that the incommensurate lattice distortion is
less stable for smaller domain sizes.Comment: 8 pages, 8 figure
Ultrafast relaxation dynamics of the antiferrodistortive phase in Ca doped SrTiO3
The ultrafast dynamics of the octahedral rotation in Ca:SrTiO3 is studied by
time resolved x-ray diffraction after photo excitation over the band gap. By
monitoring the diffraction intensity of a superlattice reflection that is
directly related to the structural order parameter of the soft-mode driven
antiferrodistortive phase in Ca:SrTiO3, we observe a ultrafast relaxation on a
0.2 ps timescale of the rotation of the oxygen octahedron, which is found to be
independent of the initial temperaure despite large changes in the
corresponding soft-mode frequency. A further, much smaller reduction on a
slower picosecond timescale is attributed to thermal effects. Time-dependent
density-functional-theory calculations show that the fast response can be
ascribed to an ultrafast displacive modification of the soft-mode potential
towards the normal state, induced by holes created in the oxygen 2p states
Examining the evidentiary basis of Congress\u27s commerce clause power to address individuals\u27 health insurance status
Chief among the issues that the United States Supreme Court considers in United States Department of Health and Human Services et al. v Florida et al. is the questionof whether Congress has the constitutional power to apply a “minimum essential coverage requirement” on most nonelderly Americans. Opponents of the provision (referred to under the Act as the “Individual Responsibility” requirement) argue that compelling individuals to buy affordable health insurance coverage exceeds Congressional powers. By contrast, the United States Department of Justice and supporters of the law assert that the minimum coverage requirement is consistent with a long line of Supreme Court decisions regarding the power of Congress to regulate individual conduct. The Administration, in a brief filed on January 9, 2012, argues that Congressional authority to act can be found under both its taxing powers as well as its power under the Commerce Clause and Necessary and Proper Clause to regulate interstate commerce. The Commerce Clause arguments are of special interest, because it is this basis of power that has received so much attention in the lower court decisions to date
Examining the evidentiary basis of Congress\u27s commerce clause power to address individuals\u27 health insurance status
Chief among the issues that the United States Supreme Court considers in United States Department of Health and Human Services et al. v Florida et al. is the questionof whether Congress has the constitutional power to apply a “minimum essential coverage requirement” on most nonelderly Americans. Opponents of the provision (referred to under the Act as the “Individual Responsibility” requirement) argue that compelling individuals to buy affordable health insurance coverage exceeds Congressional powers. By contrast, the United States Department of Justice and supporters of the law assert that the minimum coverage requirement is consistent with a long line of Supreme Court decisions regarding the power of Congress to regulate individual conduct. The Administration, in a brief filed on January 9, 2012, argues that Congressional authority to act can be found under both its taxing powers as well as its power under the Commerce Clause and Necessary and Proper Clause to regulate interstate commerce. The Commerce Clause arguments are of special interest, because it is this basis of power that has received so much attention in the lower court decisions to date
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