3,122 research outputs found
Strongly Localized State of a Photon at the Intersection of the Phase Slips in 2D Photonic Crystal with Low Contrast of Dielectric Constant
Two-dimensional photonic crystal with a rectangular symmetry and low contrast
(< 1) of the dielectric constant is considered. We demonstrate that, despite
the {\em absence} of a bandgap, strong localization of a photon can be achieved
for certain ``magic'' geometries of a unit cell by introducing two
phase slips along the major axes. Long-living photon mode is bound to the
intersection of the phase slips. We calculate analytically the lifetime of this
mode for the simplest geometry -- a square lattice of cylinders of a radius,
. We find the magic radius, , of a cylinder to be 43.10 percent of the
lattice constant. For this value of , the quality factor of the bound mode
exceeds . Small () deviation of from results in a
drastic damping of the bound mode.Comment: 6 pages, 2 figure
Adaption of the ex vivo mycobacterial growth inhibition assay for use with murine lung cells.
In the absence of a correlate(s) of protection against human tuberculosis and a validated animal model of the disease, tools to facilitate vaccine development must be identified. We present an optimised ex vivo mycobacterial growth inhibition assay (MGIA) to assess the ability of host cells within the lung to inhibit mycobacterial growth, including Bacille Calmette-Guérin (BCG) and Mycobacterium tuberculosis (MTB) Erdman. Growth of BCG was reduced by 0.39, 0.96 and 0.73 log10 CFU following subcutaneous (s.c.) BCG, intranasal (i.n.) BCG, or BCG s.c. + mucosal boost, respectively, versus naïve mice. Comparatively, a 0.49 (s.c.), 0.60 (i.n.) and 0.81 (s.c. + mucosal boost) log10 reduction in MTB CFU was found. A BCG growth inhibitor, 2-thiophenecarboxylic acid hydrazide (TCH), was used to prevent quantification of residual BCG from i.n. immunisation and allow accurate MTB quantification. Using TCH, a further 0.58 log10 reduction in MTB CFU was revealed in the i.n. group. In combination with existing methods, the ex vivo lung MGIA may represent an important tool for analysis of vaccine efficacy and the immune mechanisms associated with vaccination in the organ primarily affected by MTB disease
Superradiance for atoms trapped along a photonic crystal waveguide
We report observations of superradiance for atoms trapped in the near field
of a photonic crystal waveguide (PCW). By fabricating the PCW with a band edge
near the D transition of atomic cesium, strong interaction is achieved
between trapped atoms and guided-mode photons. Following short-pulse
excitation, we record the decay of guided-mode emission and find a superradiant
emission rate scaling as for average atom number atoms, where
is the peak single-atom radiative decay
rate into the PCW guided mode and is the Einstein- coefficient
for free space. These advances provide new tools for investigations of
photon-mediated atom-atom interactions in the many-body regime.Comment: 11 pages, 10 figure
Velocity correlations in dense granular gases
We report the statistical properties of spherical steel particles rolling on
an inclined surface being driven by an oscillating wall. Strong dissipation
occurs due to collisions between the particles and rolling and can be tuned by
changing the number density. The velocities of the particles are observed to be
correlated over large distances comparable to the system size. The distribution
of velocities deviates strongly from a Gaussian. The degree of the deviation,
as measured by the kurtosis of the distribution, is observed to be as much as
four times the value corresponding to a Gaussian, signaling a significant
breakdown of the assumption of negligible velocity correlations in a granular
system.Comment: 4 pages, 4 Figure
Trapped Atoms in One-Dimensional Photonic Crystals
We describe one-dimensional (1D) photonic crystals that support a guided mode suitable for atom trapping within a unit cell, as well as a second probe mode with strong atom–photon interactions. A new hybrid trap is analyzed that combines optical and Casimir–Polder forces to form stable traps for neutral atoms in dielectric nanostructures. By suitable design of the band structure, the atomic spontaneous emission rate into the probe mode can exceed the rate into all other modes by more than tenfold. The unprecedented single-atom reflectivity r_0 ≳ 0.9 for the guided probe field should enable diverse investigations of photon-mediated interactions for 1D atom chains and cavity quantum electrodynamics
Feasibility of detecting single atoms using photonic bandgap cavities
We propose an atom-cavity chip that combines laser cooling and trapping of
neutral atoms with magnetic microtraps and waveguides to deliver a cold atom to
the mode of a fiber taper coupled photonic bandgap (PBG) cavity. The
feasibility of this device for detecting single atoms is analyzed using both a
semi-classical treatment and an unconditional master equation approach.
Single-atom detection seems achievable in an initial experiment involving the
non-deterministic delivery of weakly trapped atoms into the mode of the PBG
cavity.Comment: 11 pages, 5 figure
Hepatitis C prevalences in the psychiatric setting: Cost-effectiveness of scaling-up screening and direct-acting antiviral therapy.
Patients hospitalised because of mental illness often have risk factors for contracting HCV. Scaling-up HCV screening for all psychiatric inpatients as a case-detection strategy for viral elimination is underexplored. This study aimed to evaluate the cost-effectiveness of scaling-up HCV screening and treatment for psychiatry hospital admissions in Switzerland vs. the current standard-of-care risk-based approach, where only those with a history of substance misuse disorder are offered testing.
HCV prevalence by history of substance misuse disorder was analysed in medical records from inpatient admissions to a Swiss psychiatry department. Cost-effectiveness was analysed from a healthcare provider perspective through a decision-tree screening model, using these HCV prevalence data. Model and parameter uncertainty were assessed using deterministic and probabilistic sensitivity analyses.
Prevalence of HCV in psychiatry inpatients with a history of substance misuse disorder (n = 1,013) was 25.7%, compared with 3.5% among the remaining inpatients (n = 3,535). Scaling up HCV screening and treatment for all psychiatry admissions was cost-effective vs. the risk-based approach, with an incremental cost-effectiveness ratio of US435,156,348, with 917 additional patients per year detected and treated at a cost of US2,122 under risk-based screening).
Scaling up HCV screening and treatment at diagnosis with all-oral, interferon-free regimens as a generalised approach for psychiatric admissions was cost-effective and could support reaching World Health Organization targets for HCV elimination by 2030.
Patients hospitalised because of mental illness often have risk factors for HCV. We found that testing all psychiatry patients in hospital for HCV was cost-effective compared with testing only patients who have a history of substance misuse. Scaling up HCV testing and treatment could help to wipe out HCV
Electron scattering in multi-wall carbon-nanotubes
We analyze two scattering mechanisms that might cause intrinsic electronic
resistivity in multi-wall carbon nanotubes: scattering by dopant impurities,
and scattering by inter-tube electron-electron interaction. We find that for
typically doped multi-wall tubes backward scattering at dopants is by far the
dominating effect.Comment: 6 pages, 2 figures, to appear in Phys. Rev.
Mutator Dynamics on a Smooth Evolutionary Landscape
We investigate a model of evolutionary dynamics on a smooth landscape which
features a ``mutator'' allele whose effect is to increase the mutation rate. We
show that the expected proportion of mutators far from equilibrium, when the
fitness is steadily increasing in time, is governed solely by the transition
rates into and out of the mutator state. This results is a much faster rate of
fitness increase than would be the case without the mutator allele. Near the
fitness equilibrium, however, the mutators are severely suppressed, due to the
detrimental effects of a large mutation rate near the fitness maximum. We
discuss the results of a recent experiment on natural selection of E. coli in
the light of our model.Comment: 4 pages, 3 figure
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