3,701 research outputs found
The Isoelectric Focusing of Creatine Kinase Variants: I. The Heterogeneity of Creatine Kinase in Human Heart Cytosol and Mitochondria
Peer Reviewe
Shear modulus of the hadron-quark mixed phase
Robust arguments predict that a hadron-quark mixed phase may exist in the
cores of some "neutron" stars. Such a phase forms a crystalline lattice with a
shear modulus higher than that of the crust due to the high density and charge
separation, even allowing for the effects of charge screening. This may lead to
strong continuous gravitational-wave emission from rapidly rotating neutron
stars and gravitational-wave bursts associated with magnetar flares and pulsar
glitches. We present the first detailed calculation of the shear modulus of the
mixed phase. We describe the quark phase using the bag model plus first-order
quantum chromodynamics corrections and the hadronic phase using relativistic
mean-field models with parameters allowed by the most massive pulsar. Most of
the calculation involves treating the "pasta phases" of the lattice via
dimensional continuation, and we give a general method for computing
dimensionally continued lattice sums including the Debye model of charge
screening. We compute all the shear components of the elastic modulus tensor
and angle average them to obtain the effective (scalar) shear modulus for the
case where the mixed phase is a polycrystal. We include the contributions from
changing the cell size, which are necessary for the stability of the
lower-dimensional portions of the lattice. Stability also requires a minimum
surface tension, generally tens of MeV/fm^2 depending on the equation of state.
We find that the shear modulus can be a few times 10^33 erg/cm^3, two orders of
magnitude higher than the first estimate, over a significant fraction of the
maximum mass stable star for certain parameter choices.Comment: 22 pages, 12 figures, version accepted by Phys. Rev. D, with the
corrections to the shear modulus computation and Table I given in the erratu
Approximations to seismic AVA responses: Validity and potential in glaciological applications
Amplitude-variation-with-angle (AVA) methods establish the seismic properties of material either side of a reflective interface, and their use is growing in glaciology. The AVA response of an interface is defined by the complex Knott-Zoeppritz (K-Z) equations, numerous approximations to which we typically assume weak interface contrasts and isotropic propagation, inconsistent with the strong contrasts at glacier beds and the vertically transverse isotropic (VTI) fabrics were associated with englacial reflectivity. We considered the validity of a suite of approximate K-Z equations for the exact P-wave reflectivity RP of ice overlying bedrock, sediment and water, and englacial interfaces between isotropic and VTI ice.We found that the approximations of Aki-Richards, Shuey, and Fatti match exact glacier bed reflectivity to within RP ± 0.05, smaller than the uncertainty in typical glaciological AVA analyses, but only for maximum incident angle θi limited to 30°. A stricter limit of θi ≤ 20° offered comparable accuracy to a hydrocarbon benchmark case of shale overlying gas-charged sand. The VTI-compliant Rüger approximation accurately described englacial reflectivity, to within RP ± 0.01, and it can be modified to give a quadratic expression in sin2 (θi)suitable for curve-matching operations. Having shown the circumstances under which AVA approximations were valid for glaciological applications, we have suggested that their interpretative advantages can be exploited in the future AVA interpretations
Spin-Peierls instability in a quantum spin chain with Dzyaloshinskii-Moriya interaction
We analysed the ground state energy of some dimerized spin-1/2 transverse XX
and Heisenberg chains with Dzyaloshinskii-Moriya (DM) interaction to study the
influence of the latter interaction on the spin-Peierls instability. We found
that DM interaction may act either in favour of the dimerization or against it.
The actual result depends on the dependence of DM interaction on the distortion
amplitude in comparison with such dependence for the isotropic exchange
interaction.Comment: 12 pages, latex, 3 figure
Valley degeneracy in biaxially strained aluminum arsenide quantum wells
This paper details a complete formalism for calculating electron subband
energy and degeneracy in strained multi-valley quantum wells grown along any
orientation with explicit results for the AlAs quantum well case. A
standardized rotation matrix is defined to transform from the conventional-
cubic-cell basis to the quantum-well-transport basis whereby effective mass
tensors, valley vectors, strain matrices, anisotropic strain ratios, and
scattering vectors are all defined in their respective bases. The specific
cases of (001)-, (110)-, and (111)-oriented aluminum arsenide (AlAs) quantum
wells are examined, as is the unconventional (411) facet, which is of
particular importance in AlAs literature. Calculations of electron confinement
and strain in the (001), (110), and (411) facets determine the critical well
width for crossover from double- to single-valley degeneracy in each system.
The notation is generalized to include miscut angles, and can be adapted to
other multi-valley systems. To help classify anisotropic inter-valley
scattering events, a new primitive unit cell is defined in momentum space which
allows one to distinguish purely in-plane inter-valley scattering events from
those that requires an out-of-plane momentum scattering component.Comment: 17 pages, 4 figures, 2 table
Blattduftstoffe und Spinnmilbenresistenz bei Erdbeere - Signalstoffanalytik in der Pflanzenzüchtung
Proof firm downsizing and diagnosis-specific disability pensioning in Norway
<br>Background: We wanted to investigate if firm downsizing is related to an increased rate of disability pensions among the former employed, especially for those with musculoskeletal and psychiatric diagnoses, and for those having to leave the firm.</br>
<br>Methods: Statistics Norway provided a linked file with demographic information and all social security grants from the National Insurance Administration for 1992–2004 for all inhabitants in Norway. Our sample was aged 30–55 years in 1995, being alive, employed and not having a disability pension at the end of 2000. Downsizing was defined as percent change in number of employed per firm from 1995 to end 2000. Employment data were missing for 25.6% of the sample.</br>
<br>Results: Disability pension rates in the next four years were 25% higher for those experiencing a 30-59% downsizing than for those not experiencing a reduction of the workforce. 1-29% and 60-100% downsizing did not have this effect. Stayers following down-sizing had higher disability pension rates than leavers. What we have called complex musculoskeletal and psychiatric diagnoses were relatively most common.</br>
<br>Conclusion: Moderate downsizing is followed by a significant increase in disability pension rates in the following four years, often with complex musculoskeletal and psychiatric diagnoses.</br>
Epidemic analysis of the second-order transition in the Ziff-Gulari-Barshad surface-reaction model
We study the dynamic behavior of the Ziff-Gulari-Barshad (ZGB) irreversible
surface-reaction model around its kinetic second-order phase transition, using
both epidemic and poisoning-time analyses. We find that the critical point is
given by p_1 = 0.3873682 \pm 0.0000015, which is lower than the previous value.
We also obtain precise values of the dynamical critical exponents z, \delta,
and \eta which provide further numerical evidence that this transition is in
the same universality class as directed percolation.Comment: REVTEX, 4 pages, 5 figures, Submitted to Physical Review
Magnetic Field Effects on the Structure and Evolution of Overdense Radiatively Cooling Jets
We investigate the effect of magnetic fields on the propagation dynamics and
morphology of overdense, radiatively cooling, supermagnetosonic jets, with the
help of fully three-dimensional SPMHD simulations. Evaluated for a set of
parameters which are mainly suitable for protostellar jets (with density ratios
between the jet and the ambient medium 3-10, and ambient Mach number ~ 24),
these simulations are also compared with baseline non-magnetic and adiabatic
calculations. We find that, after amplification by compression and
re-orientation in nonparallel shocks at the working surface, the magnetic field
that is carried backward with the shocked gas into the cocoon improves the jet
collimation relative to the purely hydrodynamic (HD) systems. Low-amplitude,
approximately equally spaced internal shocks (which are absent in the HD
systems) are produced by MHD K-H reflection pinch modes. The longitudinal field
geometry also excites non-axisymmetric helical modes which cause some beam
wiggling. The strength and amount of these modes are, however, reduced (by ~
twice) in the presence of radiative cooling relative to the adiabatic cases.
Besides, a large density ratio between the jet and the ambient medium also
reduces, in general, the number of the internal shocks. As a consequence, the
weakness of the induced internal shocks makes it doubtful that the magnetic
pinches could produce by themselves the bright knots observed in the overdense,
radiatively cooling protostellar jets.Comment: To appear in ApJ; 36 pages + 16 (gif) figures. PostScript files of
figures are available at http://www.iagusp.usp.br/preprints/preprint.htm
Rotational modes in molecular magnets with antiferromagnetic Heisenberg exchange
In an effort to understand the low temperature behavior of recently
synthesized molecular magnets we present numerical evidence for the existence
of a rotational band in systems of quantum spins interacting with
nearest-neighbor antiferromagnetic Heisenberg exchange. While this result has
previously been noted for ring arrays with an even number of spin sites, we
find that it also applies for rings with an odd number of sites as well as for
all of the polytope configurations we have investigated (tetrahedron, cube,
octahedron, icosahedron, triangular prism, and axially truncated icosahedron).
It is demonstrated how the rotational band levels can in many cases be
accurately predicted using the underlying sublattice structure of the spin
array. We illustrate how the characteristics of the rotational band can provide
valuable estimates for the low temperature magnetic susceptibility.Comment: 14 pages, 7 figures, to be published in Phys. Rev.
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