35,754 research outputs found
On the role of ground state correlations in hypernuclear non-mesonic weak decay
The contribution of ground state correlations (GSC) to the non--mesonic weak
decay of C and other medium to heavy hypernuclei is studied
within a nuclear matter formalism implemented in a local density approximation.
We adopt a weak transition potential including the exchange of the complete
octets of pseudoscalar and vector mesons as well as a residual strong
interaction modeled on the Bonn potential. Leading GSC contributions, at first
order in the residual strong interaction, are introduced on the same footing
for all isospin channels of one-- and two--nucleon induced decays. Together
with fermion antisymmetrization, GSC turn out to be important for an accurate
determination of the decay widths. Besides opening the two--nucleon stimulated
decay channels, for C GSC are responsible for 14% of the rate
while increasing the ratio by 4%. Our final
results for C are: ,
and . The
saturation property of with increasing hypernuclear mass
number is clearly observed. The agreement with data of our predictions for
, and is rather good.Comment: 32 pages, 9 figure
Studies of specific nuclear light bulb and open-cycle vortex stabilized gaseous nuclear rocket engines
Specific nuclear light bulb and open-cycle vortex stabilized gaseous nuclear rocket engine design
Interaction Effects in Conductivity of Si Inversion Layers at Intermediate Temperatures
We compare the temperature dependence of resistivity \rho(T) of Si MOSFETs
with the recent theory by Zala et al. This comparison does not involve any
fitting parameters: the effective mass m* and g*-factor for mobile electrons
have been found independently. An anomalous increase of \rho with temperature,
which has been considered a signature of the "metallic" state, can be described
quantitatively by the interaction effects in the ballistic regime. The in-plane
magnetoresistance \rho(B) is qualitatively consistent with the theory; however,
the lack of quantitative agreement indicates that the magnetoresistance is more
susceptible to the sample-specific effects than \rho(T).Comment: 4 pages, 5 figures. References update
Phase Transitions in a Two-Component Site-Bond Percolation Model
A method to treat a N-component percolation model as effective one component
model is presented by introducing a scaled control variable . In Monte
Carlo simulations on , , and simple cubic
lattices the percolation threshold in terms of is determined for N=2.
Phase transitions are reported in two limits for the bond existence
probabilities and . In the same limits, empirical formulas
for the percolation threshold as function of one
component-concentration, , are proposed. In the limit a new
site percolation threshold, , is reported.Comment: RevTeX, 5 pages, 5 eps-figure
Modal Interface Automata
De Alfaro and Henzinger's Interface Automata (IA) and Nyman et al.'s recent
combination IOMTS of IA and Larsen's Modal Transition Systems (MTS) are
established frameworks for specifying interfaces of system components. However,
neither IA nor IOMTS consider conjunction that is needed in practice when a
component shall satisfy multiple interfaces, while Larsen's MTS-conjunction is
not closed and Bene\v{s} et al.'s conjunction on disjunctive MTS does not treat
internal transitions. In addition, IOMTS-parallel composition exhibits a
compositionality defect. This article defines conjunction (and also
disjunction) on IA and disjunctive MTS and proves the operators to be
'correct', i.e., the greatest lower bounds (least upper bounds) wrt. IA- and
resp. MTS-refinement. As its main contribution, a novel interface theory called
Modal Interface Automata (MIA) is introduced: MIA is a rich subset of IOMTS
featuring explicit output-must-transitions while input-transitions are always
allowed implicitly, is equipped with compositional parallel, conjunction and
disjunction operators, and allows a simpler embedding of IA than Nyman's. Thus,
it fixes the shortcomings of related work, without restricting designers to
deterministic interfaces as Raclet et al.'s modal interface theory does.Comment: 28 page
Factorization of e+e- Event Shape Distributions with Hadronic Final States in Soft Collinear Effective Theory
We present a new analysis of two-jet event shape distributions in soft
collinear effective theory. Extending previous results, we observe that a large
class of such distributions can be expressed in terms of vacuum matrix elements
of operators in the effective theory. We match these matrix elements to the
full theory in the two-jet limit without assuming factorization of the complete
set of hadronic final states into independent sums over partonic collinear and
soft states. We also briefly discuss the relationship of this approach to
diagrammatic factorization in the full theory.Comment: 21 pages. Journal version. Defined an explicit thrust axis operator;
clarified meaning of a delta function operato
Spin relaxation and spin Hall transport in 5d transition-metal ultrathin films
The spin relaxation induced by the Elliott-Yafet mechanism and the extrinsic
spin Hall conductivity due to the skew-scattering are investigated in 5d
transition-metal ultrathin films with self-adatom impurities as scatterers. The
values of the Elliott-Yafet parameter and of the spin-flip relaxation rate
reveal a correlation with each other that is in agreement with the Elliott
approximation. At 10-layer thickness, the spin-flip relaxation time in 5d
transition-metal films is quantitatively reported about few hundred nanoseconds
at atomic percent which is one and two orders of magnitude shorter than that in
Au and Cu thin films, respectively. The anisotropy effect of the Elliott-Yafet
parameter and of the spin-flip relaxation rate with respect to the direction of
the spin-quantization axis in relation to the crystallographic axes is also
analyzed. We find that the anisotropy of the spin-flip relaxation rate is
enhanced due to the Rashba surface states on the Fermi surface, reaching values
as high as 97% in 10-layer Hf(0001) film or 71% in 10-layer W(110) film.
Finally, the spin Hall conductivity as well as the spin Hall angle due to the
skew-scattering off self-adatom impurities are calculated using the Boltzmann
approach. Our calculations employ a relativistic version of the
first-principles full-potential Korringa-Kohn-Rostoker Green function method
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