64,908 research outputs found
Pump power reduction by photodarkening in Yb-doped fibres
The influence of the photodarkening at a pump wavelength to envisage the direct impact of the photodarkening in the YDF based devices is reported. Results suggest that the photodarkening does not only induce excess background loss as commonly interpreted, but also influences pump efficiency
Effective Hamiltonian Approach to the Master Equation
A method of exactly solving the master equation is presented in this letter.
The explicit form of the solution is determined by the time evolution of a
composite system including an auxiliary system and the open system in question.
The effective Hamiltonian governing the time evolution of the composed system
are derived from the master equation. Two examples, the dissipative two-level
system and the damped harmonic oscillator, are presented to illustrate the
solving procedure.
PACS number(s): 05.30.-d, 05.40.+j, 42.50.CtComment: 4 pages, no figure
Interactions between a massless tensor field with the mixed symmetry of the Riemann tensor and a massless vector field
Consistent couplings between a massless tensor field with the mixed symmetry
of the Riemann tensor and a massless vector field are analyzed in the framework
of Lagrangian BRST cohomology. Under the assumptions on smoothness, locality,
Lorentz covariance, and Poincare invariance of the deformations, combined with
the requirement that the interacting Lagrangian is at most second-order
derivative, it is proved that there are no consistent cross-interactions
between a single massless tensor field with the mixed symmetry of the Riemann
tensor and one massless vector field.Comment: LaTeX, 24 page
Ground-state properties of the two-site Hubbard-Holstein model: an exact solution
We revisit the two-site Hubbard-Holstein model by using extended phonon
coherent states. The nontrivial singlet bipolaron is studied exactly in the
whole coupling regime. The ground-state (GS) energy and the double occupancy
probability are calculated. The linear entropy is exploited successfully to
quantify bipartite entanglement between electrons and their environment
phonons, displaying a maximum entanglement of the singlet-bipolaron in strong
coupling regime. A dramatic drop in the crossover regime is observed in the GS
fidelity and its susceptibility. The bipolaron properties is also characterized
classically by correlation functions. It is found that the crossover from a
two-site to single-site bipolaron is more abrupt and shifts to a larger
electron-phonon coupling strength as electron-electron Coulomb repulsion
increases.Comment: 6 pages, 6 figure
Dihadron fragmentation functions and high Pt hadron-hadron correlations
We propose the formulation of a dihadron fragmentation function in terms of
parton matrix elements. Under the collinear factorization approximation and
facilitated by the cut-vertex technique, the two hadron inclusive cross section
at leading order (LO) in e+ e- annihilation is shown to factorize into a short
distance parton cross section and the long distance dihadron fragmentation
function. We also derive the DGLAP evolution equation of this function at
leading log. The evolution equation for the non-singlet quark fragmentation
function is solved numerically with a simple ansatz for the initial condition
and results are presented for cases of physical interest.Comment: Latex, 4 pages, 4 figures, talk given at Quark Matter 2004, To appear
in J. Phys.
High Pt hadron-hadron correlations
We propose the formulation of a dihadron fragmentation function in terms of
parton matrix elements. Under the collinear factorization approximation and
facilitated by the cut-vertex technique, the two hadron inclusive cross section
at leading order (LO) in e+ e- annihilation is shown to factorize into a short
distance parton cross section and the long distance dihadron fragmentation
function. We also derive the DGLAP evolution equation of this function at
leading log. The evolution equation for the non-singlet and singlet quark
fragmentation function and the gluon fragmentation function are solved
numerically with the initial condition taken from event generators.
Modifications to the dihadron fragmentation function from higher twist
corrections in DIS off nuclei are computed. Results are presented for cases of
physical interest.Comment: 7 pages, 8 figures, Latex, Proceedings of Hot Quarks 2004, July
18-24, Taos, New Mexic
Mitochondrial function assessed by 31P MRS and BOLD MRI in non-obese type 2 diabetic rats
The study aims to characterize ageâassociated changes in skeletal muscle bioenergetics by evaluating the response to ischemiaâreperfusion in the skeletal muscle of the GotoâKakizaki (GK) rats, a rat model of nonâobese type 2 diabetes (T2D). 31P magnetic resonance spectroscopy (MRS) and blood oxygen levelâdependent (BOLD) MRI was performed on the hindlimb of young (12 weeks) and adult (20 weeks) GK and Wistar (control) rats. 31PâMRS and BOLDâMRI data were acquired continuously during an ischemia and reperfusion protocol to quantify changes in phosphate metabolites and muscle oxygenation. The time constant of phosphocreatine recovery, an index of mitochondrial oxidative capacity, was not statistically different between GK rats (60.8 ± 13.9 sec in young group, 83.7 ± 13.0 sec in adult group) and their ageâmatched controls (62.4 ± 11.6 sec in young group, 77.5 ± 7.1 sec in adult group). During ischemia, baselineânormalized BOLDâMRI signal was significantly lower in GK rats than in their ageâmatched controls. These results suggest that insulin resistance leads to alterations in tissue metabolism without impaired mitochondrial oxidative capacity in GK rats
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