322 research outputs found
Thermodiffusion in binary liquids: the role of irreversibility
We study thermal diffusion in binary mixtures in the framework of
non-equilibrium thermodynamics. Our formal result displays the role of partial
enthalpies and Onsager's generalized mobilities. The mobility ratio provides a
measure for the irreversible character of thermal diffusion. Comparison with
experimental data on benzene, cyclohexane, toluene and alkanes shows that
irreversibility is essential for thermal diffusion, and in particular for the
isotope effect.Comment: 7 pages, 2 figure
Polarization of active Janus particles
We study the collective motion of Janus particles in a temperature or
concentration gradient. Because of the torque exerted by an external or
self-generated field, the particles align their axis on this gradient. In a
swarm of self-driven particles, this polarization enhances the
interactiondriven confinement. Self-polarization in a non-uniform laser beam
could be used for guiding hot particles along a given trajectory.Comment: 5 pages, 2 figure
Paramagnetic tunneling state concept of the low-temperature magnetic anomalies of multicomponent insulating glasses
A generalized tunneling model of multicomponent insulating glasses is
formulated, considering tunneling states to be paramagnetic centers of the
electronic hole type. The expression for magnetic field dependent contribution
into the free energy is obtained. The derivation is made of the expression for
the nonmonotonic magnetic field dependence of dielectric susceptibility,
recently observed in amorphous BaO-Al_2O_3-SiO_2 in sub-Kelvin temperature
range.Comment: submitted to Physica
On the thermopower of ionic conductor and ionic capacitors
We theoretically study the thermoelectric response of ionic conductors to an
applied temperaturegradient. As a main result we find that open and closed
systems with respect to charge exchange,result in different expressions for the
thermopower which may even take opposite signs. For theexperimentally most
relevant zero-current steady state, we show that the thermopower of ionic
conductorsdoes not depend on the mobilities, contrary to what is known for
metals and semiconductors.The different behavior of ionic and electronic
conductors is traced back to the unlike conservationlaws for ionic carriers and
electron-hole pairs
Dielectric Susceptibility and Heat Capacity of Ultra-Cold Glasses in Magnetic Field
Recent experiments demonstrated unexpected, even intriguing properties of
certain glassy materials in magnetic field at low temperatures. We have studied
the magnetic field dependence of the static dielectric susceptibility and the
heat capacity of glasses at low temperatures. We present a theory in which we
consider the coupling of the tunnelling motion to nuclear quadrupoles in order
to evaluate the static dielectric susceptibility. In the limit of weak magnetic
field we find the resonant part of the susceptibility increasing like
while for the large magnetic field it behaves as 1/B. In the same manner we
consider the coupling of the tunnelling motion to nuclear quadrupoles and
angular momentum of tunnelling particles in order to find the heat capacity.
Our results show the Schotky peak for the angular momentum part, and
dependence for nuclear quadrupoles part of heat capacity, respectively. We
discuss whether or not this approach can provide a suitable explanation for
such magnetic properties.Comment: 10 pages, 1 figur
Elastic response of [111]-tunneling impurities
We study the dynamic response of a [111] quantum impurity, such as lithium or
cyanide in alkali halides, with respect to an external field coupling to the
elastic quadrupole moment. Because of the particular level structure of a
eight-state system on a cubic site, the elastic response function shows a
biexponential relaxation feature and a van Vleck type contribution with a
resonance frequency that is twice the tunnel frequency . This
basically differs from the dielectric response that does not show relaxation.
Moreover, we show that the elastic response of a [111] impurity cannot be
reduced to that of a two-level system. In the experimental part, we report on
recent sound velocity and internal friction measurements on KCl doped with
cyanide at various concentrations. At low doping (45 ppm) we find the dynamics
of a single [111] impurity, whereas at higher concentrations (4700 ppm) the
elastic response rather indicates strongly correlated defects. Our theoretical
model provides a good description of the temperature dependence of
and at low doping, in particular the relaxation peaks, the absolute
values of the amplitude, and the resonant contributions. From our fits we
obtain the value of the elastic deformation potential eV.Comment: 19 pages, 5 figure
Influence of Random Internal Fields on the Tunneling of OH Defects in NaCl Crystals
Alkali halide crystals doped with certain impurity ions show a low
temperature behaviour, which differs significantly from that of pure crystals.
The origin of these characteristic differences are tunneling centers formed by
atomic or molecular impurity ions. We have investigated the dielectric
susceptibility of hydroxyl ions in NaCl crystals at very low concentrations
(below 30 ppm), where interactions are believed to be negligible. We find that
the temperature dependence of the susceptibility is noticeably different from
what one would expect for isolated defects in a symmetric environment. We
propose that the origin of these deviations are random internal strains arising
from imperfections of the host crystal. We will present the experimental data
and a theoretical model which allows a quantitative understanding on a
microscopic basis.Comment: 3 pages 3 figures, REVTeX, submitted to the proceedings of the
PHONONS 2001 conferenc
On the theory of resonant susceptibility of dielectric glasses in magnetic field
The anomalous magnetic field dependence of dielectric properties of
insulating glasses in the temperature interval is considered. In
this temperature range, the dielectric permittivity is defined by the resonant
contribution of tunneling systems. The external magnetic field regulates
nuclear spins of tunneling atoms. This regulation suppresses a nuclear
quadrupole interaction of these spins with lattice and, thus, affects the
dielectric response of tunneling systems. It is demonstrated that in the
absence of an external magnetic field the nuclear quadrupole interaction
results in the correction to the permittivity in the
temperature range of interest. An application of a magnetic field results in a
sharp increase of this correction approximately by a factor of two when the
Zeeman splitting approaches the order of . Further increase of the
magnetic field results in a relatively smooth decrease in the correction until
the Zeeman splitting approaches the temperature. This smooth dependence results
from tunneling accompanied by a change of the nuclear spin projection. As the
magnetic field surpasses the temperature, the correction vanishes. The results
obtained in this paper are compared with experiment. A new mechanism of the low
temperature nuclear spin-lattice relaxation in glasses is considered.Comment: 9 Pages, 5 Figures, To be submitted to the Physical Review B, please
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Electric-field induced capillary interaction of charged particles at a polar interface
We study the electric-field induced capillary interaction of charged
particles at a polar interface. The algebraic tails of the electrostatic
pressure of each charge results in a deformation of the interface . The resulting capillary interaction is repulsive and varies as with the particle distance. As a consequence, electric-field induced
capillary forces cannot be at the origin of the secondary minimum observed
recently for charged PMMA particles at on oil-water interface.Comment: June 200
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