11,787 research outputs found
Remarks on the Theory of Cosmological Perturbation
It is shown that the power spectrum defined in the Synchronous Gauge can not
be directly used to calculate the predictions of cosmological models on the
large-scale structure of universe, which should be calculated directly by a
suitable gauge-invariant power spectrum or the power spectrum defined in the
Newtonian Gauge.Comment: 13 pages, 1 figure, minor changes, to be published in Chinese Physics
Letter
Quark-gluon vertex with an off-shell O(a)-improved chiral fermion action
We perform a study the quark-gluon vertex function with a quenched Wilson
gauge action and a variety of fermion actions. These include the domain wall
fermion action (with exponentially accurate chiral symmetry) and the Wilson
clover action both with the non-perturbatively improved clover coefficient as
well as with a number of different values for this coefficient. We find that
the domain wall vertex function behaves very well in the large momentum
transfer region. The off-shell vertex function for the on-shell improved clover
class of actions does not behave as well as the domain wall case and,
surprisingly, shows only a weak dependence on the clover coefficient
for all components of its Dirac decomposition and across all momenta. Including
off-shell improvement rotations for the clover fields can make this action
yield results consistent with those from the domain wall approach, as well as
helping to determine the off-shell improved coefficient .Comment: 11 pages, 13 figures, REVTeX
Evaluation of Formal posterior distributions via Markov chain arguments
We consider evaluation of proper posterior distributions obtained from
improper prior distributions. Our context is estimating a bounded function
of a parameter when the loss is quadratic. If the posterior mean of
is admissible for all bounded , the posterior is strongly
admissible. We give sufficient conditions for strong admissibility. These
conditions involve the recurrence of a Markov chain associated with the
estimation problem. We develop general sufficient conditions for recurrence of
general state space Markov chains that are also of independent interest. Our
main example concerns the -dimensional multivariate normal distribution with
mean vector when the prior distribution has the form on the parameter space . Conditions on for strong
admissibility of the posterior are provided.Comment: Published in at http://dx.doi.org/10.1214/07-AOS542 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
A Fringe Center Detection Technique Based on a Sub-Pixel Resolution, and Its Applications Using Sinusoidal Gratings
A common problem in optical profilometry is the accuracy in locating fringe centers. This paper presents an accurate fringe center detection technique based on sub-pixel resolution using the fringe projection method. An optimum reconstruction filter is developed which has low sensitivity to noise. In fringe center detection, computer simulation results of using one-pixel and sub-pixel resolutions are compared. The detection technique is then applied to radius measurement of cylindrical objects and surface profile measurement of diffuse objects. The experimental results thus obtained through the proposed optimum reconstruction filter show significant improvement in measurement accuracy
A Fringe Center Detection Technique Based on a Sub-Pixel Resolution, and Its Applications Using Sinusoidal Gratings
A common problem in optical profilometry is the accuracy in locating fringe centers. This paper presents an accurate fringe center detection technique based on sub-pixel resolution using the fringe projection method. An optimum reconstruction filter is developed which has low sensitivity to noise. In fringe center detection, computer simulation results of using one-pixel and sub-pixel resolutions are compared. The detection technique is then applied to radius measurement of cylindrical objects and surface profile measurement of diffuse objects. The experimental results thus obtained through the proposed optimum reconstruction filter show significant improvement in measurement accuracy
Realization of random-field dipolar Ising ferromagnetism in a molecular magnet
The longitudinal magnetic susceptibility of single crystals of the molecular
magnet Mn-acetate obeys a Curie-Weiss law, indicating a transition to a
ferromagnetic phase due to dipolar interactions. With increasing magnetic field
applied transverse to the easy axis, the transition temperature decreases
considerably more rapidly than predicted by mean field theory to a T=0 quantum
critical point. Our results are consistent with an effective Hamiltonian for a
random-field Ising ferromagnet in a transverse field, where the randomness is
induced by an external field applied to Mn-acetate crystals that are
known to have an intrinsic distribution of locally tilted magnetic easy axes.Comment: 4 pages, 4 figure
Electrical coupling between ventricular myocytes and myofibroblasts in the infarcted mouse heart
Aims:
Recent studies have demonstrated electrotonic coupling between scar tissue and the surrounding myocardium in cryoinjured hearts. However, the electrical dynamics occurring at the myocyte-nonmyocyte interface in the fibrotic heart remain undefined. Here, we sought to develop an assay to interrogate the nonmyocyte cell type contributing to heterocellular coupling and to characterize, on a cellular scale, its voltage response in the infarct border zone of living hearts.
Methods and results:
We used two-photon laser scanning microscopy in conjunction with a voltage-sensitive dye to record transmembrane voltage changes simultaneously from cardiomyocytes and adjoined nonmyocytes in Langendorff-perfused mouse hearts with healing myocardial infarction. Transgenic mice with cardiomyocyte-restricted expression of a green fluorescent reporter protein underwent permanent coronary artery ligation and their hearts were subjected to voltage imaging 7-10 days later. Reporter-negative cells, i.e. nonmyocytes, in the infarct border zone exhibited depolarizing transients at a 1:1 coupling ratio with action potentials recorded simultaneously from adjacent, reporter-positive ventricular myocytes. The electrotonic responses in the nonmyocytes exhibited slower rates of de- and repolarization compared to the action potential waveform of juxtaposed myocytes. Voltage imaging in infarcted hearts expressing a fluorescent reporter specifically in myofibroblasts revealed that the latter were electrically coupled to border zone myocytes. Their voltage transient properties were indistinguishable from those of nonmyocytes in hearts with cardiomyocyte-restricted reporter expression. The density of connexin43 expression at myofibroblast-cardiomyocyte junctions was ∼5% of that in the intercalated disc regions of paired ventricular myocytes in the remote, uninjured myocardium, whereas the ratio of connexin45 to connexin43 expression levels at heterocellular contacts was ∼1%.
Conclusion:
Myofibroblasts contribute to the population of electrically coupled nonmyocytes in the infarct border zone. The slower kinetics of myofibroblast voltage responses may reflect low electrical conductivity across heterocellular junctions, in accordance with the paucity of connexin expression at myofibroblast-cardiomyocyte contacts
Fidelity, dynamic structure factor, and susceptibility in critical phenomena
Motivated by the growing importance of fidelity in quantum critical
phenomena, we establish a general relation between fidelity and structure
factor of the driving term in a Hamiltonian through a newly introduced concept:
fidelity susceptibility. Our discovery, as shown by some examples, facilitates
the evaluation of fidelity in terms of susceptibility using well developed
techniques such as density matrix renormalization group for the ground state,
or Monte Carlo simulations for the states in thermal equilibrium.Comment: 4 pages, 2 figures, final version accepted by PR
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