340,780 research outputs found
Continuous-wave operation of extremely low-threshold GaAs/AlGaAs broad-area injection lasers on (100)Si substrates at room temperature
Room-temperature continuous-wave operation of large-area (120 μm X 980 μm) GaAs/AlGaAs graded-refractive-index separate-confinement heterostructure lasers on (100) Si substrates has been obtained. Minimum threshold-current densities of 214 A/cm2 (1900-μm cavity length), maximum slope efficiencies of about 0.8 W/A (600-μm cavity length), and optical power in excess of 270 mW/facet (900-μm cavity length) have been observed under pulsed conditions
Detecting and diagnosing faults in dynamic stochastic distributions using a rational b-splines approximation to output PDFs
Describes the process of detecting and diagnosing faults in dynamic stochastic distributions using a rational b-splines approximation to output PDFs
Figure of Merit for Dark Energy Constraints from Current Observational Data
Choosing the appropriate figure of merit (FoM) for dark energy (DE)
constraints is key in comparing different DE experiments. Here we show that for
a set of DE parameters {f_i}, it is most intuitive to define FoM =
1/\sqrt{Cov(f1,f2,f3,...)}, where Cov(f1,f2,f3,...) is the covariance matrix of
{f_i}. The {f_i} should be minimally correlated. We demonstrate two useful
choices of {f_i} using 182 SNe Ia (compiled by Riess et al. 2007), [R(z_*),
l_a(z_*), \Omega_b h^2] from the five year Wilkinson Microwave Anisotropy Probe
(WMAP) observations, and SDSS measurement of the baryon acoustic oscillation
(BAO) scale, assuming the HST prior of H_0=72+/-8 km/s Mpc^{-1} and without
assuming spatial flatness. We find that the correlation of (w_0,w_{0.5})
[w_0=w_X(z=0), w_{0.5}=w_X(z=0.5), w_X(a) = 3w_{0.5}-2w_0+3(w_0-w_{0.5})a] is
significantly smaller than that of (w_0,w_a) [w_X(a)=w_0+(1-a)w_a]. In order to
obtain model-independent constraints on DE, we parametrize the DE density
function X(z)=\rho_X(z)/\rho_X(0) as a free function with X_{0.5}, X_{1.0}, and
X_{1.5} [values of X(z) at z=0.5, 1.0, and 1.5] as free parameters estimated
from data. If one assumes a linear DE equation of state, current data are
consistent with a cosmological constant at 68% C.L. If one assumes X(z) to be a
free function parametrized by (X_{0.5}, X_{1.0}, X_{1.5}), current data deviate
from a cosmological constant at z=1 at 68% C.L., but are consistent with a
cosmological constant at 95% C.L.. Future DE experiments will allow us to
dramatically increase the FoM of constraints on (w_0,w_{0.5}) and of (X_{0.5},
X_{1.0}, X_{1.5}). This will significantly shrink the DE parameter space to
enable the discovery of DE evolution, or the conclusive evidence for a
cosmological constant.Comment: 7 pages, 3 color figures. Submitte
Giant Magneto-optical Kerr Effect and Universal Faraday Effect in Thin-film Topological Insulators
Topological insulators can exhibit strong magnetoelectric effects when their
time-reversal symmetry is broken. In this Letter we consider the
magneto-optical Kerr and Faraday effects of a topological insulator thin film
weakly exchange-coupled to a ferromagnet. We find that its Faraday rotation has
a universal value at low-frequencies, where is the vacuum fine structure
constant, and that it has a giant Kerr rotation .
These properties follow from a delicate interplay between thin-film cavity
confinement and the surface Hall conductivity of a topological insulator's
helical quasiparticles.Comment: 5 pages, 4 figure
Quantum vortex dynamics in two-dimensional neutral superfluids
We derive an effective action for the vortex position degree-of-freedom in a
superfluid by integrating out condensate phase and density fluctuation
environmental modes. When the quantum dynamics of environmental fluctuations is
neglected, we confirm the occurrence of the vortex Magnus force and obtain an
expression for the vortex mass. We find that this adiabatic approximation is
valid only when the superfluid droplet radius , or the typical distance
between vortices, is very much larger than the coherence length . We go
beyond the adiabatic approximation numerically, accounting for the quantum
dynamics of environmental modes and capturing their dissipative coupling to
condensate dynamics. For the case of an optical-lattice superfluid we
demonstrate that vortex motion damping can be adjusted by tuning the ratio
between the tunneling energy and the on-site interaction energy . We
comment on the possibility of realizing vortex Landau level physics.Comment: 14 pages, 10 figures, accepted by PRA with corrected references and
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