14,147 research outputs found
Tripropellant engine study
The potential for converting the space shuttle main engine (SSME) to a dual-fuel, dual-mode engine using LOX/hydrocarbon propellants in mode 1 and LOX/H2 in mode 2 was examined. Various engine system concepts were formulated that included staged combustion and gas generator turbine power cycles, and LOX/RP-1, LOX/CH4, and LOX/C3H8 mode 1 propellants. Both oxidizer and fuel regenerative cooling were considered. All of the SSME major components were examined to determine their adaptability to the candidate dual-fuel engines
High-pressure LOX/CH4 injector program
Two injector types, either coaxial or impinging elements, for high pressure LOX/CH4 operation with an existing 40K chamber are examined. A comparison is presented. The detailed fabrication drawings and supporting analysis are presented
Yang-Mills gravity in biconformal space
We write a gravity theory with Yang-Mills type action using the biconformal
gauging of the conformal group. We show that the resulting biconformal
Yang-Mills gravity theories describe 4-dim, scale-invariant general relativity
in the case of slowly changing fields. In addition, we systematically extend
arbitrary 4-dim Yang-Mills theories to biconformal space, providing a new arena
for studying flat space Yang-Mills theories. By applying the biconformal
extension to a 4-dim pure Yang-Mills theory with conformal symmetry, we
establish a 1-1, onto mapping between a set of gravitational gauge theories and
4-dim, flat space gauge theories.Comment: 27 pages; paper emphasis shifted to focus on gravity; references
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The reduced cost of providing a nationally recognised service for familial hypercholesterolaemia
OBJECTIVE: Familial hypercholesterolaemia (FH) affects 1 in 500 people in the UK population and is associated with premature morbidity and mortality from coronary heart disease. In 2008, National Institute for Health and Care Excellence (NICE) recommended genetic testing of potential FH index cases and cascade testing of their relatives. Commissioners have been slow to respond although there is strong evidence of cost and clinical effectiveness. Our study quantifies the recent reduced cost of providing a FH service using generic atorvastatin and compares NICE costing estimates with three suggested alternative models of care (a specialist-led service, a dual model service where general practitioners (GPs) can access specialist advice, and a GP-led service).METHODS: Revision of existing 3?year costing template provided by NICE for FH services, and prediction of costs for running a programme over 10?years. Costs were modelled for the first population-based FH service in England which covers Southampton, Hampshire, Isle of Wight and Portsmouth (SHIP). Population 1.95 million.RESULTS: With expiry of the Lipitor (Pfizer atorvastatin) patent the cost of providing a 10-year FH service in SHIP reduces by 42.5% (£4.88 million on patent vs £2.80 million off patent). Further cost reductions are possible as a result of the reduced cost of DNA testing, more management in general practice, and lower referral rates to specialists. For instance a dual-care model with GP management of patients supported by specialist advice when required, costs £1.89 million.CONCLUSIONS: The three alternative models of care are now <50% of the cost of the original estimates undertaken by NICE
Economic Efficiency of Short-Term Versus Long-Term Water Rights Buyouts
Because of the decline of the Ogallala Aquifer, water districts, regional water managers, and state water officers are becoming increasingly interested in conservation policies. This study evaluates both short-term and long-term water rights buyout policies. This research develops dynamic production functions for the major crops in the Texas Panhandle. The production functions are incorporated into optimal temporal allocation models that project annual producer behavior, crop choices, water use, and aquifer declines over 60 years. Results suggest that long-term buyouts may be more economically efficient than short-term buyouts.dynamic production function, nonlinear optimization, Ogallala Aquifer, water rights buyout, Agribusiness, Environmental Economics and Policy, Q30, Q32, Q38,
Attosecond pulse shaping around a Cooper minimum
High harmonic generation (HHG) is used to measure the spectral phase of the
recombination dipole matrix element (RDM) in argon over a broad frequency range
that includes the 3p Cooper minimum (CM). The measured RDM phase agrees well
with predictions based on the scattering phases and amplitudes of the
interfering s- and d-channel contributions to the complementary photoionization
process. The reconstructed attosecond bursts that underlie the HHG process show
that the derivative of the RDM spectral phase, the group delay, does not have a
straight-forward interpretation as an emission time, in contrast to the usual
attochirp group delay. Instead, the rapid RDM phase variation caused by the CM
reshapes the attosecond bursts.Comment: 5 pages, 5 figure
Headwaters are critical reservoirs of microbial diversity for fluvial networks
Streams and rivers form conspicuous networks on the Earth and are among nature's most effective integrators. Their dendritic structure reaches into the terrestrial landscape and accumulates water and sediment en route from abundant headwater streams to a single river mouth. The prevailing view over the last decades has been that biological diversity also accumulates downstream. Here, we show that this pattern does not hold for fluvial biofilms, which are the dominant mode of microbial life in streams and rivers and which fulfil critical ecosystem functions therein. Using 454 pyrosequencing on benthic biofilms from 114 streams, we found that microbial diversity decreased from headwaters downstream and especially at confluences. We suggest that the local environment and biotic interactions may modify the influence of metacommunity connectivity on local biofilm biodiversity throughout the network. In addition, there was a high degree of variability in species composition among headwater streams that could not be explained by geographical distance between catchments. This suggests that the dendritic nature of fluvial networks constrains the distributional patterns of microbial diversity similar to that of animals. Our observations highlight the contributions that headwaters make in the maintenance of microbial biodiversity in fluvial networks
Phase field modeling of electrochemistry II: Kinetics
The kinetic behavior of a phase field model of electrochemistry is explored
for advancing (electrodeposition) and receding (electrodissolution) conditions
in one dimension. We described the equilibrium behavior of this model in [J. E.
Guyer, W. J. Boettinger, J.A. Warren, and G. B. McFadden, ``Phase field
modeling of electrochemistry I: Equilibrium'', cond-mat/0308173]. We examine
the relationship between the parameters of the phase field method and the more
typical parameters of electrochemistry. We demonstrate ohmic conduction in the
electrode and ionic conduction in the electrolyte. We find that, despite making
simple, linear dynamic postulates, we obtain the nonlinear relationship between
current and overpotential predicted by the classical ``Butler-Volmer'' equation
and observed in electrochemical experiments. The charge distribution in the
interfacial double layer changes with the passage of current and, at
sufficiently high currents, we find that the diffusion limited deposition of a
more noble cation leads to alloy deposition with less noble species.Comment: v3: To be published in Phys. Rev. E v2: Attempt to work around
turnpage bug. Replaced color Fig. 4a with grayscale 13 pages, 7 figures in 10
files, REVTeX 4, SIunits.sty, follows cond-mat/030817
Wigner-Yanase skew information as tests for quantum entanglement
A Bell-type inequality is proposed in terms of Wigner-Yanase skew
information, which is quadratic and involves only one local spin observable at
each site. This inequality presents a hierarchic classification of all states
of multipartite quantum systems from separable to fully entangled states, which
is more powerful than the one presented by quadratic Bell inequalities from
two-entangled to fully entangled states. In particular, it is proved that the
inequality provides an exact test to distinguish entangled from nonentangled
pure states of two qubits. Our inequality sheds considerable light on
relationships between quantum entanglement and information theory.Comment: 5 page
Temporal Ordering in Quantum Mechanics
We examine the measurability of the temporal ordering of two events, as well
as event coincidences. In classical mechanics, a measurement of the
order-of-arrival of two particles is shown to be equivalent to a measurement
involving only one particle (in higher dimensions). In quantum mechanics, we
find that diffraction effects introduce a minimum inaccuracy to which the
temporal order-of-arrival can be determined unambiguously. The minimum
inaccuracy of the measurement is given by dt=1/E where E is the total kinetic
energy of the two particles. Similar restrictions apply to the case of
coincidence measurements. We show that these limitations are much weaker than
limitations on measuring the time-of-arrival of a particle to a fixed location.Comment: New section added, arguing that order-of-arrival can be measured more
accurately than time-of-arrival. To appear in Journal of Physics
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