24,875 research outputs found
A planned program of study and guidance for parents of acoustically handicapped children
Thesis (Ed.M.)--Boston Universit
Orbital Dependence of Quasiparticle Lifetimes in Sr2RuO4
Using a phenomenological Hamiltonian, we investigate the quasiparticle
lifetimes and dispersions in the three low energy bands, gamma, beta, and alpha
of Sr2RuO4. Couplings in the Hamiltonian are fixed so as to produce the mass
renormalization as measured in magneto-oscillation experiments. We thus find
reasonable agreement in all bands between our computed lifetimes and those
measured in ARPES experiments by Kidd et al. [1] and Ingle et al. [2]. In
comparing computed to measured quasiparticle dispersions, we however find good
agreement in the alpha-band alone.Comment: 7 pages, 5 figure
Fresnel concentrating collector
An advanced point focusing solar technology demonstrated potential for near term commercialization as a renewable energy technology. The design features combine to produce a highly efficient, low cost, safe, adaptable, durable system which is simple to manufacture, install and maintain
Vortices in self-gravitating disks
Vortices are believed to greatly help the formation of km sized planetesimals
by collecting dust particles in their centers. However, vortex dynamics is
commonly studied in non-self-gravitating disks. The main goal here is to
examine the effects of disk self-gravity on the vortex dynamics via numerical
simulations. In the self-gravitating case, when quasi-steady gravitoturbulent
state is reached, vortices appear as transient structures undergoing recurring
phases of formation, growth to sizes comparable to a local Jeans scale, and
eventual shearing and destruction due to gravitational instability. Each phase
lasts over 2-3 orbital periods. Vortices and density waves appear to be coupled
implying that, in general, one should consider both vortex and density wave
modes for a proper understanding of self-gravitating disk dynamics. Our results
imply that given such an irregular and rapidly changing, transient character of
vortex evolution in self-gravitating disks it may be difficult for such
vortices to effectively trap dust particles in their centers that is a
necessary process towards planet formation.Comment: to appear in the proceedings of Cool Stars, Stellar Systems and The
Sun, 15th Cambridge Workshop, St. Andrews, Scotland, July 21-25, 200
Kaolinite-catalyzed air oxidation of hydrazine: Consideration of several compositional, structural and energetic factors in surface activation
Clay minerals have been shown to have numerous, curious, energetic properties by virtue of ultra-violet light release which can be triggered by gentle environmental changes such as wetting and dewetting by a variety of liquids, unique among them water and hydrazine. Since both water and hydrazine play multiple key roles in the air-oxidation of hydrazine on kaolinite surfaces, this reaction would seem to have prime potential for studying interrelationships of energy storage, release and chemical reactivity of clay surfaces, capacities basic to either the Bernal or Cairns-Smith roles of minerals in the origin of life. Establishment of the capacity for stored electronic energy to significantly alter surface chemistry is important, regardless of the reaction chosen to demonstrate it. Hydrazine air oxidation is overawingly complex, given the possibilities for step-wise control and monitoring of parameters. In the light of recently extended characterization of the kaolinite and model sheet catalysts we used to study hydrazine oxidation and gamma-irradiated silica, previous studies of hydrazine air-oxidation on aluminosilicate surfaces have been reevaluated. Our former conclusion remains intact that, whereas trace structural and surface contaminants do play some role in the catalysis of oxidation, they are not the only, nor even the dominant, catalytic centers. Initial intermediates in the oxidation can now be proposed which are consistent with production via O(-)-centers as well as ferric iron centers. The greater than square dependence of the initial reaction rate on the weight of the clay is discussed in the light of these various mechanistic possibilities
Fiscal Paradise: Foreign Tax Havens and American Business
The offshore tax haven affiliates of American corporations account for more than a quarter of US foreign investment, an nearly a third of the foreign profits of US firms. This paper analyzes the origins of this tax haven activity and its implications for the US and foreign governments. Based on the behavior of US fins in 1982, it appears that American companies report extraordinarily high profit rates on both their real and their financial investments in tax havens. We calculate from this behavior that the tax rate that maximizes tax revenue for a typical haven is around 6%. The revenue implications for the US are more complicated, since tax havens may ultimately enhance the ability of the US government to tax the foreign earnings of American companies.
Strong Coupling Expansions for Antiferromagnetic Heisenberg S=1/2 Ladders
The properties of antiferromagnetic Heisenberg ladders with
2, 3, and 4 chains are expanded in the ratio of the intra- and interchain
coupling constants. A simple mapping procedure is introduced to relate the 4
and 2-chain ladders which holds down to moderate values of the expansion
parameters. A second order calculation of the spin gap to the lowest triplet
excitation in the 2- and 4-chain ladders is found to be quite accurate even at
the isotropic point where the couplings are equal. Similar expansions and
mapping procedures are presented for the 3-chain ladders which are in the same
universality class as single chains.Comment: 10 physical pages, uuencoded compressed PostScript file including 12
figures, ETH-TH/942
The Doped Two Chain Hubbard Model
The properties of the two-chain Hubbard Model doped away from half-filling
are investigated. The charge gap is found to vanish, but a finite spin gap
exists over a range of interchain hopping strength . In this range,
there are modified --like pairing correlations whose strength is
correlated with the size of the spin gap. It is found that the pair field
correlations are enhanced by the onsite Coulomb interaction U.Comment: 10 pages and 5 postscript figures, RevTeX 3.0, UCI-CMTHE-94-0
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