1,044 research outputs found
Photonic Crystal Vertical Cavity Lasers
Photonic crystal confinement in vertical cavity surface-emitting lasers (VCSELs) is a robust and reliable technology for achieving operation in the fundamental lateral mode and is potentially applicable to a variety of materials systems and operating wavelengths. We demonstrate photonic crystal VCSELs operating in a single transverse mode with over 30 dB side mode suppression and over 1 mW of output power. These lasers have been subjected to a post-process technique to introduce the etched holes making up the photonic crystals that surround a centralized defect in which lasing occurs. We also show that coupling between adjacent defects in a photonic lattice is possible, further increasing the power available in the devices
Liquid Crystal-Solid Interface Structure at the Antiferroelectric-Ferroelectric Phase Transition
Total Internal Reflection (TIR) is used to probe the molecular organization
at the surface of a tilted chiral smectic liquid crystal at temperatures in the
vicinity of the bulk antiferroelectric-ferroelectric phase transition. Data are
interpreted using an exact analytical solution of a real model for
ferroelectric order at the surface. In the mixture T3, ferroelectric surface
order is expelled with the bulk ferroelectric-antiferroelectric transition. The
conditions for ferroelectric order at the surface of an antiferroelectric bulk
are presented
HST Observations of SGR 0526-66: New Constraints on Accretion and Magnetar Models
Soft Gamma-ray Repeaters (SGRs) are among the most enigmatic sources known
today. Exhibiting huge X- and Gamma-ray bursts and flares, as well as soft
quiescent X-ray emission, their energy source remains a mystery. Just as
mysterious are the Anomalous X-ray pulsars (AXPs), which share many of the same
characteristics. Thanks to recent Chandra observations, SGR 0526-66, the first
SGR, now appears to be a transition object bridging the two classes, and
therefore observations of it have implications for both SGRs and AXPs. The two
most popular current models for their persistent emission are accretion of a
fossil disk or decay of an enormous (~10^15 G) magnetic field in a magnetar. We
show how deep optical observations of SGR 0526-66, the only SGR with small
enough optical extinction for meaningful observations, show no evidence of an
optical counterpart. These observation place strong new constraints on both
accretion disk and magnetar models, and suggest that the spectral energy
distribution may peak in the hard-UV. Almost all accretion disks are excluded
by the optical data, and a magnetar would require a ~10^15-10^16 G field.Comment: 23 pages, 5 figures. Accepted by Ap
Universal scaling behavior of coupled chains of interacting fermions
The single-particle hopping between two chains is investigated by
exact-diagonalizations techniques supplemented by finite-size scaling analysis.
In the case of two coupled strongly-correlated chains of spinless fermions, the
Taylor expansion of the expectation value of the single-particle interchain
hopping operator of an electron at momentum k_F in powers of the interchain
hopping t_perp is shown to become unstable in the thermodynamic limit. In the
regime alpha<alpha_{tp} (alpha_{tp} simeq 0.41) where transverse two-particle
hopping is less relevant than single-particle hopping, the finite-size effects
can be described in terms of a universal scaling function. From this analysis
it is found that the single-particle transverse hopping behaves as
t_perp^{alpha/(1-alpha)} in agreement with a RPA-like treatment of the
interchain coupling. For alpha>alpha_{tp}, the scaling law is proven to change
its functional form, thus signaling, for the first time numerically, the onset
of coherent transverse two-particle hopping.Comment: 12 pages, Late
Coherent vs incoherent interlayer transport in layered metals
The magnetic-field, temperature, and angular dependence of the interlayer
magnetoresistance of two different quasi-two-dimensional (2D) organic
superconductors is reported. For -(BEDT-TTF)I we find a
well-resolved peak in the angle-dependent magnetoresistance at (field parallel to the layers). This clear-cut proof for the coherent
nature of the interlayer transport is absent for
''-(BEDT-TTF)SFCHCFSO. This and the non-metallic
behavior of the magnetoresistance suggest an incoherent quasiparticle motion
for the latter 2D metal.Comment: 4 pages, 4 figures. Phys. Rev. B, in pres
AIDS in the Netherlands, clinical and microbiological data in 36 cases
Contains fulltext :
4450.pdf (publisher's version ) (Open Access
Energy loss of fast quarks in nuclei
We report an analysis of the nuclear dependence of the yield of Drell-Yan
dimuons from the 800 GeV/c proton bombardment of , C, Ca, Fe, and W
targets. Employing a new formulation of the Drell-Yan process in the rest frame
of the nucleus, this analysis examines the effect of initial-state energy loss
and shadowing on the nuclear-dependence ratios versus the incident proton's
momentum fraction and dimuon effective mass. The resulting energy loss per unit
path length is GeV/fm. This is the first
observation of a nonzero energy loss of partons traveling in nuclear
environment.Comment: 5 pages, including 4 figure
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