647 research outputs found
Microscopic Calculation of Total Ordinary Muon Capture Rates for Medium - Weight and Heavy Nuclei
Total Ordinary Muon Capture (OMC) rates are calculated on the basis of the
Quasiparticle Random Phase Approximation for several spherical nuclei from
90^Zr to 208^Pb. It is shown that total OMC rates calculated with the free
value of the axial-vector coupling constant g_A agree well with the
experimental data for medium-size nuclei and exceed considerably the
experimental rates for heavy nuclei. The sensitivity of theoretical OMC rates
to the nuclear residual interactions is discussed.Comment: 27 pages and 3 figure
Working Group Report on the "TeV Particle Astrophysics and Physics Beyond the Standard Model"
This working group focused mainly on the complementarity among particle
physics and astrophysics. The analysis of data from both fields will better
constrain theoretical models. Much of the discussion focused on detecting dark
matter and susy particles, and on the potential of neutrino and gamma-ray
astrophysics for seeking or constraining new physics.Comment: Report on Working Group in the TeV Particle Astrophysics Workshop II
- Madison - Aug 200
Scintillation and charge extraction from the tracks of energetic electrons in superfluid helium-4
An energetic electron passing through liquid helium causes ionization along
its track. The ionized electrons quickly recombine with the resulting positive
ions, which leads to the production of prompt scintillation light. By applying
appropriate electric fields, some of the ionized electrons can be separated
from their parent ions. The fraction of the ionized electrons extracted in a
given applied field depends on the separation distance between the electrons
and the ions. We report the determination of the mean electron-ion separation
distance for charge pairs produced along the tracks of beta particles in
superfluid helium at 1.5 K by studying the quenching of the scintillation light
under applied electric fields. Knowledge of this mean separation parameter will
aid in the design of particle detectors that use superfluid helium as a target
material.Comment: 10 pages, 8 figure
Recommended from our members
Biochar and biochar with N-fertilizer affect soil N2O emission in Haplic Luvisol
The benefits of biochar application are well described in tropical soils, however there is a dearth of information on its effects in agricultural temperate soils. An interesting and little explored interaction may occur in an intensive agriculture setting; biochar addition may modify the effect of commonplace N-fertilization.We conducted a field experiment to study the effects of biochar application at the rate of 0, 10 and 20 t haâ1 (B0, B10 and B20) in combination with 0, 40 and 80 kg N haâ1 of N-fertilizer (N0, N40, N80).We followed nitrous oxide (N2O) emissions, analysed a series of soil physicochemical properties and measured barley yield in a Haplic Luvisol in Central Europe. Seasonal cumulative N2O emissions from B10N0 and B20N0 treatments decreased by 27 and 25% respectively, when compared to B0N0. Cumulative N2O emissions from N40 and N80 combined with B10 and B20 were also lower by 21, 19 and 25, 32%, respectively compared to controls B0N40 and B0N80. Average pH was significantly increased by biochar addition. Increased soil pH and reduces NOâ3 content seen in biochar treatments could be the two possible mechanisms responsible for reduced N2O emissions. There was a statistically significant increase of soil water content in B20N0 treatment compared to B0N0 control, possibly as a result of larger surface area and the presence of microspores having altered pore size distribution and water-holding capacity of the soil. Application of biochar at the rate of 10 t haâ1 had a positive effect on spring barley grain yield
Explaining the unobserved: why quantum mechanics is not only about information
A remarkable theorem by Clifton, Bub and Halvorson (2003)(CBH) characterizes
quantum theory in terms of information--theoretic principles. According to Bub
(2004, 2005) the philosophical significance of the theorem is that quantum
theory should be regarded as a ``principle'' theory about (quantum) information
rather than a ``constructive'' theory about the dynamics of quantum systems.
Here we criticize Bub's principle approach arguing that if the mathematical
formalism of quantum mechanics remains intact then there is no escape route
from solving the measurement problem by constructive theories. We further
propose a (Wigner--type) thought experiment that we argue demonstrates that
quantum mechanics on the information--theoretic approach is incomplete.Comment: 34 Page
Removal and Reconstitution of the Carotenoid Antenna of Xanthorhodopsin
Salinixanthin, a C40-carotenoid acyl glycoside, serves as a light-harvesting antenna in the retinal-based proton pump xanthorhodopsin of Salinibacter ruber. In the crystallographic structure of this protein, the conjugated chain of salinixanthin is located at the proteinâlipid boundary and interacts with residues of helices E and F. Its ring, with a 4-keto group, is rotated relative to the plane of the Ď-system of the carotenoid polyene chain and immobilized in a binding site near the β-ionone retinal ring. We show here that the carotenoid can be removed by oxidation with ammonium persulfate, with little effect on the other chromophore, retinal. The characteristic CD bands attributed to bound salinixanthin are now absent. The kinetics of the photocycle is only slightly perturbed, showing a 1.5-fold decrease in the overall turnover rate. The carotenoid-free protein can be reconstituted with salinixanthin extracted from the cell membrane of S. ruber. Reconstitution is accompanied by restoration of the characteristic vibronic structure of the absorption spectrum of the antenna carotenoid, its chirality, and the excited-state energy transfer to the retinal. Minor modification of salinixanthin, by reducing the carbonyl C=O double bond in the ring to a C-OH, suppresses its binding to the protein and eliminates the antenna function. This indicates that the presence of the 4-keto group is critical for carotenoid binding and efficient energy transfer
Microscopic nonequilibrium theory of double-barrier Josephson junctions
We study nonequilibrium charge transport in a double-barrier Josephson
junction, including nonstationary phenomena, using the time-dependent
quasiclassical Keldysh Green's function formalism. We supplement the kinetic
equations by appropriate time-dependent boundary conditions and solve the
time-dependent problem in a number of regimes. From the solutions,
current-voltage characteristics are derived. It is understood why the
quasiparticle current can show excess current as well as deficit current and
how the subgap conductance behaves as function of junction parameters. A
time-dependent nonequilibrium contribution to the distribution function is
found to cause a non-zero averaged supercurrent even in the presence of an
applied voltage. Energy relaxation due to inelastic scattering in the
interlayer has a prominent role in determining the transport properties of
double-barrier junctions. Actual inelastic scattering parameters are derived
from experiments. It is shown as an application of the microscopic model, how
the nature of the intrinsic shunt in double-barrier junctions can be explained
in terms of energy relaxation and the opening of Andreev channels.Comment: Accepted for Phys. Rev.
Microscopic self-consistent theory of Josephson junctions including dynamical electron correlations
We formulate a fully self-consistent, microscopic model to study the
retardation and correlation effects of the barrier within a Josephson junction.
The junction is described by a series of planes, with electronic correlation
included through a local self energy for each plane. We calculate current-phase
relationships for various junctions, which include non-magnetic impurities in
the barrier region, or an interfacial scattering potential. Our results
indicate that the linear response of the supercurrent to phase across the
barrier region is a good, but not exact indicator of the critical current. Our
calculations of the local density of states show the current-carrying Andreev
bound states and their energy evolution with the phase difference across the
junction.
We calculate the figure of merit for a Josephson junction, which is the
product of the critical current, Ic, and the normal state resistance, R(N), for
junctions with different barrier materials. The normal state resistance is
calculated using the Kubo formula, for a system with zero current flow and no
superconducting order. Semiclassical calculations would predict that these two
quantities are determined by the transmission probabilities of electrons in
such a way that the product is constant for a given superconductor at fixed
temperature. Our self-consistent solutions for different types of barrier
indicate that this is not the case. We suggest some forms of barrier which
could increase the Ic.R(N) product, and hence improve the frequency response of
a Josephson device.Comment: 46 pages, 21 figure
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