446 research outputs found
Strong-coupling branching of FQHL edges
We have developed a theory of quasiparticle backscattering in a system of
point contacts formed between single-mode edges of several Fractional Quantum
Hall Liquids (FQHLs) with in general different filling factors and one
common single-mode edge of another FQHL. In the strong-tunneling limit,
the model of quasiparticle backscattering is obtained by the duality
transformation of the electron tunneling model. The new physics introduced by
the multi-point-contact geometry of the system is coherent splitting of
backscattered quasiparticles at the point contacts in the course of propagation
along the common edge . The ``branching ratios'' characterizing the
splitting determine the charge and exchange statistics of the edge
quasiparticles that can be different from those of Laughlin's quasiparticles in
the bulk of FQHLs. Accounting for the edge statistics is essential for the
system of more than one point contact and requires the proper description of
the flux attachement to tunneling electrons.Comment: 12 pages, 2 figure
Study of the heating effect contribution to the nonlinear dielectric response of a supercooled liquid
We present a detailed study of the heating effects in dielectric measurements
carried out on a liquid. Such effects come from the dissipation of the electric
power in the liquid and give a contribution to the nonlinear third harmonics
susceptibility chi_3 which depends on the frequency and temperature. This study
is used to evaluate a possible `spurious' contribution to the recently measured
nonlinear susceptibility of an archetypical glassforming liquid (Glycerol).
Those measurements have been shown to give a direct evaluation of the number of
dynamically correlated molecules temperature dependence close to the glass
transition temperature T_g~190K (Crauste-Thibierge et al., Phys. Rev. Lett
104,165703(2010)). We show that the heating contribution is totally negligible
(i) below 204K at any frequency; (ii) for any temperature at the frequency
where the third harmonics response chi_3 is maximum. Besides, this heating
contribution does not scale as a function of f/f_{\alpha}, with f_{\alpha}(T)
the relaxation frequency of the liquid. In the high frequency range, when
f/f_{\alpha} >= 1, we find that the heating contribution is damped because the
dipoles cannot follow instantaneously the temperature modulation due to the
heating phenomenon. An estimate of the magnitude of this damping is given.Comment: 25 pages, 10 figures, Accepted for publication in Journal of Chemical
Physic
Comparison of the Meat Quality of Turopolje, German Landrace x Turopolje and German Landrace x Pietrain Pigs
Aim of the study was to evaluate, if the mixed breed German Landrace x Turopolje (L x T) was suitable for conventional fattening and the production of high quality palatable meat. Hence, we chose to study the carcass characteristics of three different breeds: true bred Turopolje (T x T) (n=15), an autochthonous Croatian breed, German Landrace x Pietrain (L x P) (n=19), a typical German pig hybrid and German Landrace x Turopolje (L x T) (n=23) as mixed breed. All three breeds were kept in a conventional fattening indoor system. The data consisted of the chemical and physical values of the carcass and the difference between breeds during breeding and fattening. All pigs were fattened with a conventional ad libidum feeding system. The feed consisted of an optimal mixture for the fattening of L x P. The daily feed intake and the weight from birth until the end of the fattening was recorded every 14 days. The quality of the carcass was evaluated at the age of 20 and 25 weeks. The measurement of the carcass was based on the “Richtlinie für die Stationsprüfung auf Mastleistung, Schlachtkörperwert und Fleischbeschaffenheit beim Schwein” published by the national German control office. L x T showed the lowest feed intake per kg carcass compared to the other breeds. The quality of meat was characterized by pH, conductance, intramuscular fat and water holding capacity. L x T showed a trend for a lower conductance in week 25. The value of pH and water holding capacity was not significant between the breeds. Surprisingly, the intramuscular fat of L x T was by trend higher compared to L x P and significantly lower than T x T (p < 0.05). L x T had by trend a higher carcass weight and a larger carcass length compared to L x P, which was significantly higher than T x T (p < 0.05). In conclusion, the new breed L x T seems to be suitable for an indoor fattening system and produces a high quality palatable meat. The energy and protein intake should be slightly reduced, which would reduce the cost of meat production
Flow equations for QED in the light front dynamics
The method of flow equations is applied to QED on the light front. Requiring
that the partical number conserving terms in the Hamiltonian are considered to
be diagonal and the other terms off-diagonal an effective Hamiltonian is
obtained which reduces the positronium problem to a two-particle problem, since
the particle number violating contributions are eliminated. No infrared
divergencies appear. The ultraviolet renormalization can be performed
simultaneously.Comment: 15 pages, Latex, 3 pictures, Submitted to Phys.Rev.
Classical XY Model in 1.99 Dimensions
We consider the classical XY model (O(2) nonlinear sigma-model) on a class of
lattices with the (fractal) dimensions 1<D<2. The Berezinskii's harmonic
approximation suggests that the model undergoes a phase transition in which the
low temperature phase is characterized by stretched exponential decay of
correlations. We prove an exponentially decaying upper bound for the two-point
correlation functions at non-zero temperatures, thus excluding the possibility
of such a phase transition.Comment: LaTeX 8 pages, no figure
Oblique Confinement and Phase Transitions in Chern-Simons Gauge Theories
We investigate non-perturbative features of a planar Chern-Simons gauge
theory modeling the long distance physics of quantum Hall systems, including a
finite gap M for excitations. By formulating the model on a lattice, we
identify the relevant topological configurations and their interactions. For M
bigger than a critical value, the model exhibits an oblique confinement phase,
which we identify with Lauglin's incompressible quantum fluid. For M smaller
than the critical value, we obtain a phase transition to a Coulomb phase or a
confinement phase, depending on the value of the electromagnetic coupling.Comment: 8 pages, harvmac, DFUPG 91/94 and MPI-PhT/94-9
p-Type semiconducting properties in lithium-doped MgO single crystals
The phenomenally large enhancement in conductivity observed when Li-doped MgO
crystals are oxidized at elevated temperatures was investigated by dc and ac
electrical measurements in the temperature interval 250-673 K. The
concentration of ([Li]^{0}) centers (Li^{+} ions each with a trapped hole)
resulting from oxidation was monitored by optical absorption measurements.
Both dc and ac experiments provide consistent values for the bulk resistance.
The electricalconductivity of oxidized MgO:Li crystals increases linearly with
the concentration of ([Li]^{0}) centers. The conductivity is thermally
activated with an activation energy of (0.70 +/- 0.01) eV, which is independent
of the ([Li]^{0}) content. The \textit{standard semiconducting} mechanism
satisfactorily explains these results. Free holes are the main contribution to
band conduction as they are trapped at or released from the ([Li]^{0})-acceptor
centers.
In as-grown MgO:Li crystals, electrical current increases dramatically with
time due to the formation of ([Li]^{0}) centers. The activation energy values
between 1.3 and 0.7 eV are likely a combination of the activation energy for
the creation of ([Li]^{0}) centers and the activation energy of ionization of
these centers. Destruction of ([Li]^{0}) centers can be induced in oxidized
crystals by application of an electric field due to Joule heating up to
temperatures at which ([Li]^{0}) centers are not stable.Comment: LaTeX, 20 pages, 9 Encapsulated Postscript Format Figures, use the
version 4.0 of REVTEX 4 macro packag
The Critical Behaviour of Potts models with symmetry breaking fields
The -state Potts model in two dimensions in the presence of external
magnetic fields is studied. For general special choices of these
magnetic fields produce effective models with smaller symmetry . The phase diagram of these models and their critical behaviour are
explored by conventional finite-size scaling and conformal invariance. The
possibility of multicritical behavior, for finite values of the symmetry
breaking fields, in the cases where is also analysed. Our results
indicate that for effective models with symmetry the
multicritical point occurs at zero field. This last result is also corroborated
by Monte Carlo simulations.Comment: 15 pages (standart LaTex), 2 figure (PostScript) available by request
to [email protected]
Poincare Semigroup Symmetry as an Emergent Property of Unstable Systems
The notion that elementary systems correspond to irreducible representations
of the Poincare group is the starting point for this paper, which then goes on
to discuss how a semigroup for the time evolution of unstable states and
resonances could emerge from the underlying Poincare symmetry. Important tools
in this analysis are the Clebsch-Gordan coefficients for the Poincare group.Comment: 17 pages, 1 figur
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