808 research outputs found
Fermion Density Induced Instability of the W-Boson Pair Condensate in Strong Magnetic Field
The electroweak vacuum structure in an external magnetic field close to the
lower critical value is considered at finite fermion density. It is shown that
the leading effect of the fermions is to reduce the symmetry of the W-pair
condensate in the direction of the magnetic field. The energy is minimized by
the appearance of a helicoidal structure of the condensate along the magnetic
field.Comment: 9 pages, LaTex, JHU-TIPAC-93000
Effect of the Casimir-Polder force on the collective oscillations of a trapped Bose-Einstein condensate
We calculate the effect of the interaction between an optically active
material and a Bose-Einstein condensate on the collective oscillations of the
condensate. We provide explicit expressions for the frequency shift of the
center of mass oscillation in terms of the potential generated by the substrate
and of the density profile of the gas. The form of the potential is discussed
in details and various regimes (van der Waals-London, Casimir-Polder and
thermal regimes) are identified as a function of the distance of atoms from the
surface. Numerical results for the frequency shifts are given for the case of a
sapphire dielectric substrate interacting with a harmonically trapped
condensate of Rb atoms. We find that at distances of , where
thermal effects become visible, the relative frequency shifts produced by the
substrate are of the order and hence accessible experimentally. The
effects of non linearities due to the finite amplitude of the oscillation are
explicitly discussed. Predictions are also given for the radial breathing mode.Comment: 28 pages, 10 figures. Submitted to PR
On finite-density QCD at large Nc
Deryagin, Grigoriev, and Rubakov (DGR) have shown that in finite-density QCD
at infinite Nc the Fermi surface is unstable with respect to the formation of
chiral waves with wavenumber twice the Fermi momentum, while the BCS
instability is suppressed. We show here that at large, but finite Nc, the DGR
instability only occurs in a finite window of chemical potentials from above
Lambda_QCD to mu_critical = exp(gamma ln^2 Nc + O(ln Nc ln ln Nc))Lambda_QCD,
where gamma = 0.02173. Our analysis shows that, at least in the perturbative
regime, the instability occurs only at extremely large Nc, Nc > 1000 Nf, where
Nf is the number of flavors. We conclude that the DGR instability is not likely
to occur in QCD with three colors, where the ground state is expected to be a
color superconductor. We speculate on possible structure of the ground state of
finite-density QCD with very large Nc.Comment: 13 pages, 5 figures, 3 figures drawn using PicTe
Coexistence of pion condensation and color superconductivity in two flavor quark matter
We show that the superconducting 2SC phase at high density and normal chiraly
broken quark phase at low density is separated by the mixed non-uniform phase
along the baryon density line.Comment: Change of the title. Journal-ref adda
Implement a laboratory workshop in physics and electrotechnical disciplines in the face of COVID-19 pandemic
Studying physics and many related disciplines at all education levels includes not only learning the theoretical material, but also the formation of skills and abilities to apply the knowledge gained in practice. This occurs mainly during laboratory work when students directly contact with specific laboratory equipment. With the forced transition to distance learning due to the development of the COVID-19 pandemic, the main difficulties in many universities arose precisely during the implementation of laboratory workshops. This study analyzed the possibilities of modern digital teaching aids for the effective remote implementation of a laboratory workshop in physics and related disciplines. The study was carried out on the basis of the Elabuga Institute of the Kazan Federal University. There were 79 students took part in the experiment (second and third-year students). The results showed that a well-arranged combination of various digital tools and technologies makes it possible to effectively implement laboratory works in physics and electrotechnical disciplines in a distance learning format. The research results are useful for university teachers using distance learning technologies in laboratory work in natural science disciplines
A mesoscopic model for microscale hydrodynamics and interfacial phenomena: Slip, films, and contact angle hysteresis
We present a model based on the lattice Boltzmann equation that is suitable
for the simulation of dynamic wetting. The model is capable of exhibiting
fundamental interfacial phenomena such as weak adsorption of fluid on the solid
substrate and the presence of a thin surface film within which a disjoining
pressure acts. Dynamics in this surface film, tightly coupled with
hydrodynamics in the fluid bulk, determine macroscopic properties of primary
interest: the hydrodynamic slip; the equilibrium contact angle; and the static
and dynamic hysteresis of the contact angles. The pseudo- potentials employed
for fluid-solid interactions are composed of a repulsive core and an attractive
tail that can be independently adjusted. This enables effective modification of
the functional form of the disjoining pressure so that one can vary the static
and dynamic hysteresis on surfaces that exhibit the same equilibrium contact
angle. The modeled solid-fluid interface is diffuse, represented by a wall
probability function which ultimately controls the momentum exchange between
solid and fluid phases. This approach allows us to effectively vary the slip
length for a given wettability (i.e. the static contact angle) of the solid
substrate
The effect of substrate roughness on air entrainment in dip coating
YesDynamic wetting failure was observed in the simple dip coating flow with a series of substrates, which had a rough side and a comparatively smoother side. When we compared the air entrainment speeds on both sides, we found a switch in behaviour at a critical viscosity. At viscosity lower than a critical value, the rough side entrained air at lower speeds than the smooth side. Above the critical viscosity the reverse was observed, the smooth side entraining air at lower speed than the rough side. Only substrates with significant roughness showed this behaviour. Below a critical roughness, the rough side always entrained air at lower speeds than the smooth side. These results have both fundamental and practical merits. They support the hydrodynamic theory of dynamic wetting failure and imply that one can coat viscous fluids at higher speeds than normal by roughening substrates. A mechanism and a model are presented to explain dynamic wetting failure on rough surfaces
Patterns of Symmetry Breaking in QCD at High Baryon Density
We study the structure of QCD at very large baryon density for an arbitrary
number of flavors . We provide evidence that for any number of flavors
larger than chiral symmetry remains broken at asymptotically large
chemical potential. For , chiral symmetry breaking follows the
standard pattern , but for unusual
patterns emerge. We study the case in more detail and calculate the
magnitude of the chiral order parameters in perturbative QCD. We show that, asymptotically,
is much smaller than . The
result can be understood in terms of an approximate discrete symmetry.Comment: 23 pages, revtex, erratum adde
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