12,280 research outputs found
Electromagnetic Energy, Absorption, and Casimir Forces. Inhomogeneous Dielectric Media
A general, exact formula is derived for the expectation value of the
electromagnetic energy density of an inhomogeneous absorbing and dispersive
dielectric medium in thermal equilibrium, assuming that the medium is well
approximated as a continuum. From this formula we obtain the formal expression
for the Casimir force density. Unlike most previous approaches to Casimir
effects in which absorption is either ignored or admitted implicitly through
the required analytic properties of the permittivity, we include dissipation
explicitly via the coupling of each dipole oscillator of the medium to a
reservoir of harmonic oscillators. We obtain the energy density and the Casimir
force density as a consequence of the van der Waals interactions of the
oscillators and also from Poynting's theorem.Comment: 13 pages, no figures. Updated version with generalization to finite
temperature and added example
On the Dichotomy between the Nodal and Antinodal Excitations in High-temperature Superconductors
Angle-resolved photoemission data on optimally- and under-doped high
temperature superconductors reveal a dichotomy between the nodal and antinodal
electronic excitations. In this paper we propose an explanation of this unusual
phenomenon by employing the coupling between the quasiparticle and the
commensurate/incommensurate magnetic excitations.Comment: 11 pages, 9 figure
Structural anisotropy and orientation-induced Casimir repulsion in fluids
In this work we theoretically consider the Casimir force between two periodic
arrays of nanowires (both in vacuum, and on a substrate separated by a fluid)
at separations comparable to the period. Specifically, we compute the
dependence of the exact Casimir force between the arrays under both lateral
translations and rotations. Although typically the force between such
structures is well-characterized by the Proximity Force Approximation (PFA), we
find that in the present case the microstructure modulates the force in a way
qualitatively inconsistent with PFA. We find instead that effective-medium
theory, in which the slabs are treated as homogeneous, anisotropic dielectrics,
gives a surprisingly accurate picture of the force, down to separations of half
the period. This includes a situation for identical, fluid-separated slabs in
which the exact force changes sign with the orientation of the wire arrays,
whereas PFA predicts attraction. We discuss the possibility of detecting these
effects in experiments, concluding that this effect is strong enough to make
detection possible in the near future.Comment: 12 pages, 9, figure. Published version with expanded discussio
Structural anisotropy and orientation-induced Casimir repulsion in fluids
In this work we theoretically consider the Casimir force between two periodic
arrays of nanowires (both in vacuum, and on a substrate separated by a fluid)
at separations comparable to the period. Specifically, we compute the
dependence of the exact Casimir force between the arrays under both lateral
translations and rotations. Although typically the force between such
structures is well-characterized by the Proximity Force Approximation (PFA), we
find that in the present case the microstructure modulates the force in a way
qualitatively inconsistent with PFA. We find instead that effective-medium
theory, in which the slabs are treated as homogeneous, anisotropic dielectrics,
gives a surprisingly accurate picture of the force, down to separations of half
the period. This includes a situation for identical, fluid-separated slabs in
which the exact force changes sign with the orientation of the wire arrays,
whereas PFA predicts attraction. We discuss the possibility of detecting these
effects in experiments, concluding that this effect is strong enough to make
detection possible in the near future.Comment: 12 pages, 9, figure. Published version with expanded discussio
Monensin and brefeldin A differentially affect the phosphorylation and sulfation of secretory proteins.
Chromogranin B and secretogranin II, two members of the granin family, are known to be post-translationally modified by the addition of O-linked carbohydrates to serine and/or threonine, phosphate to serine and threonine, and sulfate to carbohydrate and tyrosine residues. In the present study, chromogranin B and secretogranin II were used as model proteins to investigate in which subcompartment of the Golgi complex secretory proteins become phosphorylated. Monensin, a drug known to block the transport from the medial to the trans cisternae of the Golgi stack, inhibited the phosphorylation of the granins, indicating that this modification occurred distal to the medial Golgi. Monensin also blocked the addition of galactose to O-linked carbohydrates and the sulfation of the granins, confirming previous data that these modifications take place in the trans Golgi. To distinguish, within the trans Golgi, between the trans cisternae of the Golgi stack and the trans Golgi network, we made use of the previous observation that brefeldin A results in the redistribution to the endoplasmic reticulum of membrane-bound enzymes of the trans cisternae of the Golgi stack, but not of the trans Golgi network. Brefeldin A treatment abolished granin sulfation but resulted in the accumulation of phosphorylated and galactosylated granins. Differential effects of brefeldin A on membranes of the Golgi stack versus the trans Golgi network were also observed by immunofluorescence analysis of marker proteins specific for either compartment. Our results suggest that the phosphorylation of secretory proteins, like their galactosylation, largely occurs in the trans cisternae of the Golgi stack, whereas the sulfation of secretory proteins on both carbohydrate and tyrosine residues takes place selectively in the trans Golgi network
Rapid Syphilis Tests as Catalysts for Health Systems Strengthening: A Case Study from Peru.
OBJECTIVES: Untreated maternal syphilis leads to adverse pregnancy outcomes. The use of point of care tests (POCT) offers an opportunity to improve screening coverage for syphilis and other aspects of health systems. Our objective is to present the experience of the introduction of POCT for syphilis in Peru and describe how new technology can catalyze health system strengthening. METHODS: The study was implemented from September 2009-November 2010 to assess the feasibility of the use of a POCT for syphilis for screening pregnant women in Lima, Peru. Outcomes measured included access to syphilis screening, treatment coverage, partner treatment, effect on patient flow and service efficiency, acceptability among providers and patients, and sustainability. RESULTS: Before the introduction of POCT, a pregnant woman needed 6 visits to the health center in 27 days before she received her syphilis result. We trained 604 health providers and implemented the POCT for syphilis as the "two for one strategy", offering with one finger stick both syphilis and HIV testing. Implementation of the POCT resulted in testing and treatment on the first visit. Screening and treatment coverages for syphilis improved significantly compared with the previous year. Implementation of POCT has been scaled up nationally since the study ended, and coverages for screening, treatment and partner treatment have remained over 92%. CONCLUSIONS: Implementation of POCT for syphilis proved feasible and acceptable, and led to improvement in several aspects of health services. For the process to be effective we highlight the importance of: (1) engaging the authorities; (2) dissipating tensions between providers and identifying champions; (3) training according to the needs; (4) providing monitoring, supervision, support and recognition; (5) sharing results and discussing actions together; (6) consulting and obtaining feedback from users; and (7) integrating with other services such as with rapid HIV testing
Effects of Gravity on the Acceleration and Pair Statistics of Inertial Particles in Homogeneous Isotropic Turbulence
Within the context of heavy particles suspended in a turbulent airflow, we study the effects of gravity on acceleration statistics and radial relative velocity (RRV) of inertial particles. The turbulent flow is simulated by direct numerical simulation (DNS) on a 2563 grid and the dynamics of O(106) inertial particles by the point-particle approach. For particles/droplets with radius from 10 to 60 µm, we found that the gravity plays an important role in particle acceleration statistics: (a) a peak value of particle acceleration variance appears in both the horizontal and vertical directions at a particle Stokes number of about 1.2, at which the particle horizontal acceleration clearly exceeds the fluid-element acceleration; (b) gravity constantly disrupts quasi-equilibrium of a droplet\u27s response to local turbulent motion and amplifies extreme acceleration events both in the vertical and horizontal directions and thus effectively reduces the inertial filtering mechanism. By decomposing the RRV of the particles into three parts: (1) differential sedimentation, (2) local flow shear, and (3) particle differential acceleration, we evaluate and compare their separate contributions. For monodisperse particles, we show that the presence of gravity does not have a significant effect on the shear term. On the other hand, gravity suppresses the probability distribution function (pdf) tails of the differential acceleration term due to a lower particle-eddy interaction time in presence of gravity. For bidisperse cases, we find that gravity can decrease the shear term slightly by dispersing particles into vortices where fluid shear is relatively low. The differential acceleration term is found to be positively correlated with the gravity term, and this correlation is stronger when the difference in colliding particle radii becomes smaller. Finally, a theory is developed to explain the effects of gravity and turbulence on the horizontal and vertical acceleration variances of inertial particles at small Stokes numbers, showing analytically that gravity affects particle acceleration variance both in horizontal and vertical directions, resulting in an increase in particle acceleration variance in both directions. Furthermore, the effect of gravity on the horizontal acceleration variance is predicted to be stronger than that in the vertical direction, in agreement with our DNS results. © 2015 AIP Publishing LLC
Experimental measurement of photothermal effect in Fabry-Perot cavities
We report the experimental observation of the photothermal effect. The
measurements are performed by modulating the laser power absorbed by the
mirrors of two high-finesse Fabry-Perot cavities. The results are very well
described by a recently proposed theoretical model [M. Cerdonio, L. Conti, A.
Heidmann and M. Pinard, Phys. Rev. D 63 (2001) 082003], confirming the
correctness of such calculations. Our observations and quantitative
characterization of the photothermal effect demonstrate its critical importance
for high sensitivity interferometric displacement measurements, as those
necessary for gravitational wave detection.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
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