853 research outputs found
A possible cooling effect in high temperature superconductors
We show that an adiabatic increase of the supercurrent along a superconductor
with lines of nodes of the order parameter on the Fermi surface can result in a
cooling effect. The maximum cooling occurs if the supercurrent increases up to
its critical value. The effect can also be observed in a mixed state of a bulk
sample. An estimate of the energy dissipation shows that substantial cooling
can be performed during a reasonable time even in the microkelvin regime.Comment: 5 pages, to appear in Phys. Rev.
Combined Paramagnetic and Diamagnetic Response of YBCO
It has been predicted that the zero frequency density of states of YBCO in
the superconducting phase can display interesting anisotropy effects when a
magnetic field is applied parallel to the copper-oxide planes, due to the
diamagnetic response of the quasi-particles. In this paper we incorporate
paramagnetism into the theory and show that it lessens the anisotropy and can
even eliminate it altogether. At the same time paramagnetism also changes the
scaling with the square root of the magnetic field first deduced by Volovik
leading to an experimentally testable prediction. We also map out the analytic
structure of the zero frequency density of states as a function of the
diamagnetic and paramagnetic energies. At certain critical magnetic field
values we predict kinks as we vary the magnetic field. However these probably
lie beyond currently accessible field strengths
A General Approach to Casimir Force Problems Based on Local Reflection Amplitudes and Huygen's Principle
In this paper we describe an approach to Casimir Force problems that is
ultimately generalizable to all fields, boundary conditions, and cavity
geometries. This approach utilizes locally defined reflection amplitudes to
express the energy per unit area of any Casimir interaction. To demonstrate
this approach we solve a number of Casimir Force problems including the case of
uniaxial boundary conditions in a parallel-plate cavity.Comment: 9 pages, 5 figures, Equation 18 has been corrected, [v1] contained a
typ
On the torque on birefringent plates induced by quantum fluctuations
We present detailed numerical calculations of the mechanical torque induced
by quantum fluctuations on two parallel birefringent plates with in plane
optical anisotropy, separated by either vacuum or a liquid (ethanol). The
torque is found to vary as , where represents the angle
between the two optical axes, and its magnitude rapidly increases with
decreasing plate separation . For a 40 m diameter disk, made out of
either quartz or calcite, kept parallel to a Barium Titanate plate at nm, the maximum torque (at ) is of the order of
Nm. We propose an experiment to observe this torque
when the Barium Titanate plate is immersed in ethanol and the other
birefringent disk is placed on top of it. In this case the retarded van der
Waals (or Casimir-Lifshitz) force between the two birefringent slabs is
repulsive. The disk would float parallel to the plate at a distance where its
net weight is counterbalanced by the retarded van der Waals repulsion, free to
rotate in response to very small driving torques.Comment: 7 figures, submitted to Phys. Rev.
Applying dissipative dynamical systems to pseudorandom number generation: Equidistribution property and statistical independence of bits at distances up to logarithm of mesh size
The behavior of a family of dissipative dynamical systems representing
transformations of two-dimensional torus is studied on a discrete lattice and
compared with that of conservative hyperbolic automorphisms of the torus.
Applying dissipative dynamical systems to generation of pseudorandom numbers is
shown to be advantageous and equidistribution of probabilities for the
sequences of bits can be achieved. A new algorithm for generating uniform
pseudorandom numbers is proposed. The theory of the generator, which includes
proofs of periodic properties and of statistical independence of bits at
distances up to logarithm of mesh size, is presented. Extensive statistical
testing using available test packages demonstrates excellent results, while the
speed of the generator is comparable to other modern generators.Comment: 6 pages, 3 figures, 3 table
Dispersion Interactions between Optically Anisotropic Cylinders at all Separations: Retardation Effects for Insulating and Semiconducting Single Wall Carbon Nanotubes
We derive the complete form of the van der Waals dispersion interaction
between two infinitely long anisotropic semiconducting/insulating thin
cylinders at all separations. The derivation is based on the general theory of
dispersion interactions between anisotropic media as formulated in [J. N.
Munday, D. Iannuzzi, Yu. S. Barash and F. Capasso, {\sl Phys. Rev. A} {\bf 71},
042102 (2005)]. This formulation is then used to calculate the dispersion
interactions between a pair of single walled carbon nanotubes at all
separations and all angles. Non-retarded and retarded forms of the interactions
are developed separately. The possibility of repulsive dispersion interactions
and non-monotonic dispersion interactions is discussed within the framework of
the new formulation
Retarded Casimir-Polder force on an atom near reflecting microstructures
We derive the fully retarded energy shift of a neutral atom in two different
geometries useful for modelling etched microstructures. First we calculate the
energy shift due to a reflecting cylindrical wire, and then we work out the
energy shift due to a semi-infinite reflecting half-plane. We analyze the
results for the wire in various limits of the wire radius and the distance of
the atom from the wire, and obtain simple asymptotic expressions useful for
estimates. For the half-plane we find an exact representation of the
Casimir-Polder interaction in terms of a single, fast converging integral,
which is easy to evaluate numerically.Comment: 12 pages, 8 figure
Electromagnetic Force in Dispersive and Transparent Media
A hydrodynamic-type, macroscopic theory was set up recently to simultaneously
account for dissipation and dispersion of electromagnetic field, in
nonstationary condensed systems of nonlinear constitutive relations~\cite{JL}.
Since it was published in the letter format, some algebra and the more subtle
reasonings had to be left out. Two of the missing parts are presented in this
paper: How algebraically the new results reduce to the known old ones; and more
thoughts on the range of validity of the new theory, especially concerning the
treatment of dissipation.Comment: 10 pages, 0 figur
Electromagnetic force density in dissipative isotropic media
We derive an expression for the macroscopic force density that a narrow-band
electromagnetic field imposes on a dissipative isotropic medium. The result is
obtained by averaging the microscopic form for Lorentz force density. The
derived expression allows us to calculate realistic electromagnetic forces in a
wide range of materials that are described by complex-valued electric
permittivity and magnetic permeability. The three-dimensional energy-momentum
tensor in our expression reduces for lossless media to the so-called Helmholtz
tensor that has not been contradicted in any experiment so far. The momentum
density of the field does not coincide with any well-known expression, but for
non-magnetic materials it matches the Abraham expression
Van der Waals interaction between microparticle and uniaxial crystal with application to hydrogen atoms and multiwall carbon nanotubes
The Lifshitz theory of the van der Waals force is extended for the case of an
atom (molecule) interacting with a plane surface of an uniaxial crystal or with
a long solid cylinder or cylindrical shell made of isotropic material or
uniaxial crystal. For a microparticle near a semispace or flat plate made of an
uniaxial crystal the exact expressions for the free energy of the van der Waals
and Casimir-Polder interaction are presented. An approximate expression for the
free energy of microparticle- cylinder interaction is obtained which becomes
precise for microparticle-cylinder separations much smaller than cylinder
radius. The obtained expressions are used to investigate the van der Waals
interaction between hydrogen atoms (molecules) and graphite plates or multiwall
carbon nanotubes. To accomplish this the behavior of graphite dielectric
permittivities along the imaginary frequency axis is found using the optical
data for the complex refractive index of graphite for the ordinary and
extraordinary rays. It is shown that the position of hydrogen atoms inside
multiwall carbon nanotubes is energetically preferable compared with outside.Comment: 23 pages, 8 figures, 2 tables. Minor corrections are made and new
references added. Accepted for publication in Phys. Rev.
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