792 research outputs found
Exact low temperature results for transport properties of the interacting resonant level model
Using conformal field theory and integrability ideas, we give a full
characterization of the low temperature regime of the anisotropic interacting
resonant level (IRLM) model. We determine the low temperature corrections to
the linear conductance exactly up to the 6th order. We show that the structure
displays 'Coulomb deblocking' at resonance, i.e., a strong impurity-wire
capacitive coupling enhances the conductance at low temperature.Comment: 4 pages, 2 figure
Gauging of Geometric Actions and Integrable Hierarchies of KP Type
This work consist of two interrelated parts. First, we derive massive
gauge-invariant generalizations of geometric actions on coadjoint orbits of
arbitrary (infinite-dimensional) groups with central extensions, with gauge
group being certain (infinite-dimensional) subgroup of . We show that
there exist generalized ``zero-curvature'' representation of the pertinent
equations of motion on the coadjoint orbit. Second, in the special case of
being Kac-Moody group the equations of motion of the underlying gauged WZNW
geometric action are identified as additional-symmetry flows of generalized
Drinfeld-Sokolov integrable hierarchies based on the loop algebra {\hat \cG}.
For {\hat \cG} = {\hat {SL}}(M+R) the latter hiearchies are equivalent to a
class of constrained (reduced) KP hierarchies called {\sl cKP}_{R,M}, which
contain as special cases a series of well-known integrable systems (mKdV, AKNS,
Fordy-Kulish, Yajima-Oikawa etc.). We describe in some detail the loop algebras
of additional (non-isospectral) symmetries of {\sl cKP}_{R,M} hierarchies.
Apart from gauged WZNW models, certain higher-dimensional nonlinear systems
such as Davey-Stewartson and -wave resonant systems are also identified as
additional symmetry flows of {\sl cKP}_{R,M} hierarchies. Along the way we
exhibit explicitly the interrelation between the Sato pseudo-differential
operator formulation and the algebraic (generalized) Drinfeld-Sokolov
formulation of {\sl cKP}_{R,M} hierarchies. Also we present the explicit
derivation of the general Darboux-B\"acklund solutions of {\sl cKP}_{R,M}
preserving their additional (non-isospectral) symmetries, which for R=1 contain
among themselves solutions to the gauged WZNW field
equations.Comment: LaTeX209, 47 page
Impurity Quantum Phase Transitions
We review recent work on continuous quantum phase transitions in impurity
models, both with fermionic and bosonic baths - these transitions are
interesting realizations of boundary critical phenomena at zero temperature.
The models with fermion bath are generalizations of the standard Kondo model,
with the common feature that Kondo screening of the localized spin can be
suppressed due to competing processes. The models with boson bath are related
to the spin-boson model of dissipative two-level systems, where the interplay
between tunneling and friction results in multiple phases. The competition
inherent to all models can generate unstable fixed points associated with
quantum phase transitions, where the impurity properties undergo qualitative
changes. Interestingly, certain impurity transitions feature both
lower-critical and upper-critical "dimensions" and allow for epsilon-type
expansions. We present results for a number of observables, obtained by both
analytical and numerical renormalization group techniques, and make connections
to experiments.Comment: 22 pages, 11 figs, review article to be published in Phil. Ma
Hofstadter butterfly as Quantum phase diagram
The Hofstadter butterfly is viewed as a quantum phase diagram with infinitely
many phases, labelled by their (integer) Hall conductance, and a fractal
structure. We describe various properties of this phase diagram: We establish
Gibbs phase rules; count the number of components of each phase, and
characterize the set of multiple phase coexistence.Comment: 4 prl pages 1 colored figure typos corrected, reference [26] added,
"Ten Martini" assumption adde
Tunneling and orthogonality catastrophe in the topological mechanism of superconductivity
We compute the angular dependence of the order parameter and tunneling
amplitude in a model exhibiting topological superconductivity and sketch its
derivation as a model of a doped Mott insulator. We show that ground states
differing by an odd number of particles are orthogonal and the order parameter
is in the d-representation, although the gap in the electronic spectrum has no
nodes. We also develop an operator algebra, that allowes one to compute
off-diagonal correlation functions.Comment: 4 pages, Revtex, psfig; some references are correcte
Comparison of costs of service and self-service methods in retail meat departments
The objectives of this study were to compare the costs of service and self-service methods of selling meat and to show the relationship of cost to volume of sales.
Cost data were obtained from 23 self-service and 26 service stores for the period October 6 to 11, 1952. The cost items compared were labor, equipment, market floor space and paper supplies. These costs constitute about 85 percent of the total costs of operating the meat department. The volume of meat sales of the stores in this study ranged from 7,000 per week. Thus, the following results are applicable only to stores in this range.
Physical hours of labor per dollar of sales averaged lower under. self-service than service methods up to a sales volume of about $2,000 per week. Beyond that point the self-service method required more physical hours of labor
Chiral non-linear sigma-models as models for topological superconductivity
We study the mechanism of topological superconductivity in a hierarchical
chain of chiral non-linear sigma-models (models of current algebra) in one,
two, and three spatial dimensions. The models have roots in the 1D
Peierls-Frohlich model and illustrate how the 1D Frohlich's ideal conductivity
extends to a genuine superconductivity in dimensions higher than one. The
mechanism is based on the fact that a point-like topological soliton carries an
electric charge. We discuss a flux quantization mechanism and show that it is
essentially a generalization of the persistent current phenomenon, known in
quantum wires. We also discuss why the superconducting state is stable in the
presence of a weak disorder.Comment: 5 pages, revtex, no figure
Self-Service or Salesman-Service Meat Retailing?
Farmers get about 60 cents of the consumer\u27s meat dollar. Processing and distribution take the other 40 cents. And about half of the latter goes to retailing- by far the largest single cost item in meat distribution
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