5,266 research outputs found
Nambu-Jona-Lasinio Model in Curved Spacetime with Magnetic Field
We discuss the phase structure of the NJL model in curved spacetime with
magnetic field using -expansion and linear curvature approximation. The
effective potential for composite fields is calculated using
the proper-time cut-off in the following cases: a) at non-zero curvature, b) at
non-zero curvature and non-zero magnetic field, and c) at non-zero curvature
and non-zero covariantly constant gauge field. Chiral symmetry breaking is
studied numerically. We show that the gravitational field may compensate the
effect of the magnetic field what leads to restoration of chiral symmetry.Comment: LaTex file, 11 pages, 5 figures (not included) avaliable by request
from first or third autho
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Vortex Shedding and Modal Behavior of a Circular Cylinder Equipped with Flexible Flaps
When a cylinder is subject to a flow, vortices will be shed that can lead to strong tonal noise. The modification of the cylinder with soft, flexible flaps made of silicone rubber has been shown to affect the vortex shedding cycle in a way that the Strouhal number associated with the vortex shedding suddenly jumps to a higher value at a certain Reynolds number. In the present study, the effect of the flexible flaps on the vortex shedding is further examined by subsequently reducing the number of flaps and additionally shortening their length. Acoustic measurements and camera recordings of the flap motion, performed in an aeroacoustic wind tunnel, suggest that the sudden jump of the Reynolds number is caused by the movement of the outer flaps. A comparison with the eigenfrequencies obtained from a numerical modal analysis of the different flap rings revealed that the cause of the Strouhal number jump is most likely a lock-in of the natural vortex shedding cycle with the next higher eigenfrequency of the outer flaps
Comment on "Thermal Lifshitz force between an atom and a conductor with a small density of carriers"
We demonstrate that the generalization of the Lifshitz theory proposed by L.
P. Pitaevskii arXiv:0801.0656 [Phys. Rev. Lett. v.101, 163202 (2008)] violates
the Nernst heat theorem for many dielectric materials and is experimentally
inconsistent.Comment: 2 pages, 1 figure; minor revisions are made in accordance with the
text accepted for publication in Phys. Rev. Let
Small-angle x-ray-scattering study of phase separation and crystallization in the bulk amorphous Mg62Cu25Y10Li3 alloy
We report on a small-angle x-ray-scattering (SAXS) and differential scanning calorimetry study of phase separation and crystallization in rapidly quenched amorphous Mg62Cu25Y10Li3 alloy samples. Differential scanning calorimetry demonstrates the occurrence of crystallization and grain growth upon isothermal annealing of these samples at 135 °C. The SAXS studies show the presence of large inhomogeneities even in the rapidly quenched as-prepared Mg62Cu25Y10Li3 alloy that is attributed to phase separation in the undercooled liquid during the cooling process. After isothermal annealing at 135 °C for longer than 30 min the samples exhibit a strong SAXS intensity that monotonically increases with increasing annealing time. During heat treatment, crystallization and growth of a nanocrystalline bcc-Mg7Li3 phase occurs in the Y-poor and MgLi-rich domains. The initially rough boundaries of the nanocrystals become sharper with increasing annealing time. Anomalous small-angle x-ray-scattering investigations near the Cu K edge indicate that while Cu is distributed homogeneously in the as-prepared sample, a Cu composition gradient develops between the matrix and the bcc-Mg7Li3 nanocrystals in the annealed sample
Oxidation and crystallization of an amorphous Zr60Al15Ni25 alloy
The amorphous ternary metallic alloy Zr60Al15Ni25 was oxidized in dry oxygen in the temperature range 310 ±C to 410 ±C. Rutherford backscattering (RBS) and cross-sectional transmission electron microscopy (TEM) studies suggest that during this treatment an amorphous layer of zirconium-aluminum-oxide is formed at the surface. Nickel was depleted in the oxide and enriched in the amorphous alloy near the interface. The oxide layer thickness grows parabolically with annealing duration, with a transport constant of 2.8 x 10^-5 m^2/s x exp(-1.7 eV/kT). The oxidation rate may be controlled by the diffusion of Ni in the amorphous alloy. At later stages of the oxidation process, precipitates of nanocrystalline ZrO2 appear in the oxide near the interface. Finally, two intermetallic phases nucleate and grow simultaneously in the alloy, one at the interface and one within the alloy. An explanation involving preferential oxidation is proposed
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