7,901 research outputs found
Electroweak Sudakov at two loop level
We investigate the Sudakov double logarithmic corrections to the form factor
of fermion in the SU(2)XU(1) electroweak theory. We adopt the familiar Feynman
gauge and present explicit calculations at the two loop level. We show that the
leading logarithmic corrections coming from the infrared singularities are
consistent with the "postulated" exponentiated electroweak Sudakov form factor.
The similarities and differences in the "soft" physics between the electroweak
theory and the unbroken non-abelian gauge theory (QCD) will be clarified.Comment: 8 pages, 14 figure
Statistical mechanics and large-scale velocity fluctuations of turbulence
Turbulence exhibits significant velocity fluctuations even if the scale is
much larger than the scale of the energy supply. Since any spatial correlation
is negligible, these large-scale fluctuations have many degrees of freedom and
are thereby analogous to thermal fluctuations studied in the statistical
mechanics. By using this analogy, we describe the large-scale fluctuations of
turbulence in a formalism that has the same mathematical structure as used for
canonical ensembles in the statistical mechanics. The formalism yields a
universal law for the energy distribution of the fluctuations, which is
confirmed with experiments of a variety of turbulent flows. Thus, through the
large-scale fluctuations, turbulence is related to the statistical mechanics.Comment: 7 pages, accepted by Physics of Fluids (see http://pof.aip.org/
Non-equilibrium and non-linear stationary state in thermoelectric materials
Efficiency of thermoelectric materials is characterized by the figure of
merit Z. Z has been believed to be a peculiar material constant. However, the
accurate measurements in the present work reveal that Z has large size
dependence and a non-linear temperature distribution appears as stationary
state in the thermoelectric material. The observation of these phenomena is
achieved by the Harman method. This method is the most appropriate way to
investigate the thermoelectric properties because the dc and ac resistances are
measured by the same electrode configuration. We describe the anomalous
thermoelectric properties observed in mainly (Bi,Sb)2Te3 by the Harman method
and then insist that Z is not the peculiar material constant but must be
defined as the physical quantity dependent of the size and the position in the
material.Comment: 9 pages, 4 figures. submitted to Applied Physics Lette
Dual-camera system for high-speed imaging in particle image velocimetry
Particle image velocimetry is an important technique in experimental fluid
mechanics, for which it has been essential to use a specialized high-speed
camera. However, the high speed is at the expense of other performances of the
camera, i.e., sensitivity and image resolution. Here, we demonstrate that the
high-speed imaging is also possible with a pair of still cameras.Comment: 4 pages, accepted by Journal of Visualization (see
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Trends of mechanical consequences and modeling of a fibrous membrane around femoral hip prostheses
In the present study, the effects of a fibrous membrane between cement and bone in a femoral total hip replacement were investigated. The study involved the problem of modeling this fibrous membrane in finite-element analyses, and its global consequences for the load-transfer mechanism and its resulting stress patterns. A finite-element model was developed, suitable to describe nonlinear contact conditions in combination with nonlinear material properties of the fibrous membrane. The fibrous tissue layer was described as a highly compliant material with little resistance against tension and shear. The analysis showed that the load transfer mechanism from stem to bone changes drastically when such a membrane is present. These effects are predominantly caused by tensile loosening and slip at the interface, and are enhanced by the nonlinear membrane characteristics.\ud
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Using parametric analysis, it was shown that these effects on the load-transfer mechanism cannot be described satisfactorily with linear elastic models.\ud
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Most importantly, the fibrous tissue interposition causes excessive stress concentrations in bone and cement, and relatively high relative displacements between these materials
D-brane Categories for Orientifolds -- The Landau-Ginzburg Case
We construct and classify categories of D-branes in orientifolds based on
Landau-Ginzburg models and their orbifolds. Consistency of the worldsheet
parity action on the matrix factorizations plays the key role. This provides
all the requisite data for an orientifold construction after embedding in
string theory. One of our main results is a computation of topological field
theory correlators on unoriented worldsheets, generalizing the formulas of Vafa
and Kapustin-Li for oriented worldsheets, as well as the extension of these
results to orbifolds. We also find a doubling of Knoerrer periodicity in the
orientifold context.Comment: 45 pages, 6 figure
Diameter dependence of ferromagnetic spin moment in Au nanocrystals
Au nanoparticles exhibit ferromagnetic spin polarization and show diameter
dependence in magnetization. The magnetic moment per Au atom in the particle
attains its maximum value at a diameter of about 3 nanometer (nm) in the
Magnetization-Diameter curve. Because Au metal is a typical diamagnetic
material, its ferromagnetic polarization mechanism is thought to be quite
different from the ferromagnetism observed in transition metals. The size
effect strongly suggests the existence of some spin correlation effect at the
nanoscale. The so-called ``Fermi hole effect'' is the most probable one given
in the free electron gas system. Ferromagnetism in Au nanoparticles is
discussed using this model.Comment: 5 pages, 6 figures, to appear in Phys. Rev.
Vortex Tubes in Turbulence Velocity Fields at Reynolds Numbers 300-1300
The most elementary structures of turbulence, i.e., vortex tubes, are studied
using velocity data obtained in a laboratory experiment for boundary layers
with microscale Reynolds numbers 295-1258. We conduct conditional averaging for
enhancements of a small-scale velocity increment and obtain the typical
velocity profile for vortex tubes. Their radii are of the order of the
Kolmogorov length. Their circulation velocities are of the order of the
root-mean-square velocity fluctuation. We also obtain the distribution of the
interval between successive enhancements of the velocity increment as the
measure of the spatial distribution of vortex tubes. They tend to cluster
together below about the integral length and more significantly below about the
Taylor microscale. These properties are independent of the Reynolds number and
are hence expected to be universal.Comment: 8 pages, to appear in Physical Review
Diffusion and spectral dimension on Eden tree
We calculate the eigenspectrum of random walks on the Eden tree in two and
three dimensions. From this, we calculate the spectral dimension and the
walk dimension and test the scaling relation (
for an Eden tree). Finite-size induced crossovers are observed, whereby the
system crosses over from a short-time regime where this relation is violated
(particularly in two dimensions) to a long-time regime where the behavior
appears to be complicated and dependent on dimension even qualitatively.Comment: 11 pages, Plain TeX with J-Phys.sty style, HLRZ 93/9
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