484 research outputs found
Comment on "unique translation between Hamiltonian operators and functional integrals"
A comment on the letter by Tim Gollisch and Christof Wetterich, Phys. Rev. Lett. 86, 1 (2001).Michael Weyrauch, and Andreas W. Schreibe
The large system asymptotics of persistent currents in mesoscopic quantum rings
We consider a one-dimensional mesoscopic quantum ring filled with spinless
electrons and threaded by a magnetic flux, which carries a persistent current
at zero temperature. The interplay of Coulomb interactions and a single on-site
impurity yields a non-trivial dependence of the persistent current on the size
of the ring. We determine numerically the asymptotic power law for systems up
to 32000 sites for various impurity strengths and compare with predictions from
Bethe Ansatz solutions combined with Bosonization. The numerical results are
obtained using an improved functional renormalization group (fRG) method. We
apply the density matrix renormalization group (DMRG) and exact diagonalization
methods to benchmark the fRG calculations. We use DMRG to study the persistent
current at low electron concentrations in order to extend the validity of our
results to quasi-continuous systems. We briefly comment on the quality of
calculated fRG ground state energies by comparison with exact DMRG data.Comment: REVTex, 12 pages, 12 figs, accepted in Phys. Rev.
External review of the Rimisp Rural Territorial Dynamics (RTD) project : synthesis of science/policy influence and organizational evaluations
An impressive and regionally unique combination of scientific output, policy influence and organizational structure has emerged at Rimisp over the past four years (2011). This document synthesizes the results of both evaluation components, the first focusing on scientific contributions and policy influence, and the second focusing on organizational issues. The Rimisp-RTD program integrates and synthesizes policy, practice and intellectual debate at a subnational geographic scale in a way that links disciplines. It contributes to the design and implementation of more effective public policies that will stimulate and support rural territorial dynamics in Latin America and the Caribbean (LAC)
Reduction of quantum noise in optical interferometers using squeezed light
We study the photon counting noise in optical interferometers used for
gravitational wave detection. In order to reduce quantum noise a squeezed
vacuum state is injected into the usually unused input port. Here, we
specifically investigate the so called `dark port case', when the beam splitter
is oriented close to 90{\deg} to the incoming laser beam, such that nearly all
photons go to one output port of the interferometer, and only a small fraction
of photons is seen in the other port (`dark port'). For this case it had been
suggested that signal amplification is possible without concurrent noise
amplification [R.Barak and Y.Ben-Aryeh, J.Opt.Soc.Am.B25(361)2008]. We show
that by injection of a squeezed vacuum state into the second input port,
counting noise is reduced for large values of the squeezing factor, however the
signal is not amplified. Signal strength only depends on the intensity of the
laser beam.Comment: 8 pages, 1 figur
Flow Equation for Supersymmetric Quantum Mechanics
We study supersymmetric quantum mechanics with the functional RG formulated
in terms of an exact and manifestly off-shell supersymmetric flow equation for
the effective action. We solve the flow equation nonperturbatively in a
systematic super-covariant derivative expansion and concentrate on systems with
unbroken supersymmetry. Already at next-to-leading order, the energy of the
first excited state for convex potentials is accurately determined within a 1%
error for a wide range of couplings including deeply nonperturbative regimes.Comment: 24 pages, 8 figures, references added, typos correcte
External review of the Rimisp Territorial Cohesion for Development (CTD) Program : scientific contributions, policy influence and organizational development
The Rimisp – Centro Latinamericano para el Desarrollo Rural (Latin American Center for Rural Development) project contributes to the design and implementation of more comprehensive, cross-cutting and effective public policies to stimulate and support rural territorial dynamics in Latin America. The report documents findings that focus on scientific contributions, policy influence, and organizational development. The scope of this in-depth review is the overall program, consisting of the IDRC grant, along with several others in support of policy engagement activities. Annex 2 tables “Policy Influence Achievements” in terms of: Main results; Related policy influence projects; Examples of related research/technical assistance documents; Relevant governmental counterparts
Insulin Resistance Does Not Impair Mechanical Overload-Stimulated Glucose Uptake, but Does Alter the Metabolic Fate of Glucose in Mouse Muscle
Skeletal muscle glucose uptake and glucose metabolism are impaired in insulin resistance. Mechanical overload stimulates glucose uptake into insulin-resistant muscle; yet the mechanisms underlying this beneficial effect remain poorly understood. This study examined whether a differential partitioning of glucose metabolism is part of the mechanosensitive mechanism underlying overload-stimulated glucose uptake in insulin-resistant muscle. Mice were fed a high-fat diet to induce insulin resistance. Plantaris muscle overload was induced by unilateral synergist ablation. After 5 days, muscles were excised for the following measurements: (1) [3H]-2-deoxyglucose uptake; (2) glycogen; 3) [5-3H]-glucose flux through glycolysis; (4) lactate secretion; (5) metabolites; and (6) immunoblots. Overload increased glucose uptake ~80% in both insulin-sensitive and insulin-resistant muscles. Overload increased glycogen content ~20% and this was enhanced to ~40% in the insulin-resistant muscle. Overload did not alter glycolytic flux, but did increase muscle lactate secretion 40–50%. In both insulin-sensitive and insulin-resistant muscles, overload increased 6-phosphogluconate levels ~150% and decreased NADP:NADPH ~60%, indicating pentose phosphate pathway activation. Overload increased protein O-GlcNAcylation ~45% and this was enhanced to ~55% in the insulin-resistant muscle, indicating hexosamine pathway activation. In conclusion, insulin resistance does not impair mechanical overload-stimulated glucose uptake but does alter the metabolic fate of glucose in muscle
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