48,905 research outputs found
High Density Mesoscopic Atom Clouds in a Holographic Atom Trap
We demonstrate the production of micron-sized high density atom clouds of
interest for meso- scopic quantum information processing. We evaporate atoms
from 60 microK, 3x10^14 atoms/cm^3 samples contained in a highly anisotropic
optical lattice formed by interfering di racted beams from a holographic phase
plate. After evaporating to 1 microK by lowering the con ning potential, in
less than a second the atom density reduces to 8x10^13 cm^- 3 at a phase space
density approaching unity. Adiabatic recompression of the atoms then increases
the density to levels in excess of 1x10^15 cm^-3. The resulting clouds are
typically 8 microns in the longest dimension. Such samples are small enough to
enable mesoscopic quantum manipulation using Rydberg blockade and have the high
densities required to investigate new collision phenomena.Comment: 4 pages, 4 figures, submitted to PR
Low-Threshold Electrically Pumps Vertical-Cavity Surface-Emitting Microlasers
Vertical-cavity electrically driven lasers with three GaInAs
quantum wells and diameters of several ÎŒm exhibit room-temperature pulsed current thresholds as low as 1.3mA with 958 nm output wavelength
Comparison of dimethyl sulfoxide treated highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) electrodes for use in indium tin oxide-free organic electronic photovoltaic devices
Indium tin oxide (ITO)-free organic photovoltaic (OPV) devices were fabricated using highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the transparent conductive electrode (TCE). The intrinsic conductivity of the PEDOT:PSS films was improved by two different dimethyl sulfoxide (DMSO) treatments â (i) DMSO was added directly to the PEDOT:PSS solution (PEDOT:PSSADD) and (ii) a pre-formed PEDOT:PSS film was immersed in DMSO (PEDOT:PSSIMM). X-ray photoelectron spectroscopy (XPS) and conductive atomic force microscopy (CAFM) studies showed a large amount of PSS was removed from the PEDOT:PSSIMM electrode surface. OPV devices based on a poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) bulk hetrojunction showed that the PEDOT:PSSIMM electrode out-performed the PEDOT:PSSADD electrode, primarily due to an increase in short circuit current density from 6.62 mA cmâ2 to 7.15 mA cmâ2. The results highlight the importance of optimising the treatment of PEDOT:PSS electrodes and demonstrate their potential as an alternative TCE for rapid processing and low-cost OPV and other organic electronic devices
Pattern formation and selection in quasi-static fracture
Fracture in quasi-statically driven systems is studied by means of a discrete
spring-block model. Developed from close comparison with desiccation
experiments, it describes crack formation induced by friction on a substrate.
The model produces cellular, hierarchical patterns of cracks, characterized by
a mean fragment size linear in the layer thickness, in agreement with
experiments. The selection of a stationary fragment size is explained by
exploiting the correlations prior to cracking. A scaling behavior associated
with the thickness and substrate coupling, derived and confirmed by
simulations, suggests why patterns have similar morphology despite their
disparity in scales.Comment: 4 pages, RevTeX, two-column, 5 PS figures include
Large parallel and perpendicular electric fields on electron spatial scales in the terrestrial bow shock
Large parallel ( 100 mV/m) and perpendicular ( 600 mV/m) electric
fields were measured in the Earth's bow shock by the vector electric field
experiment on the Polar satellite. These are the first reported direct
measurements of parallel electric fields in a collisionless shock. These fields
exist on spatial scales comparable to or less than the electron skin depth (a
few kilometers) and correspond to magnetic field-aligned potentials of tens of
volts and perpendicular potentials up to a kilovolt. The perpendicular fields
are amongst the largest ever measured in space, with energy densities of
of order 10%. The measured parallel electric field
implies that the electrons can be demagnetized, which may result in stochastic
(rather than coherent) electron heating
Zeros of Rydberg-Rydberg Foster Interactions
Rydberg states of atoms are of great current interest for quantum
manipulation of mesoscopic samples of atoms. Long-range Rydberg-Rydberg
interactions can inhibit multiple excitations of atoms under the appropriate
conditions. These interactions are strongest when resonant collisional
processes give rise to long-range C_3/R^3 interactions. We show in this paper
that even under resonant conditions C_3 often vanishes so that care is required
to realize full dipole blockade in micron-sized atom samples.Comment: 10 pages, 4 figures, submitted to J. Phys.
Cost studies for commercial fuselage crown designs
Studies were conducted to evaluate the cost and weight potential of advanced composite design concepts in the crown region of a commercial transport. Two designs from each of three design families were developed using an integrated design-build team. A range of design concepts and manufacturing processes were included to allow isolation and comparison of cost centers. Detailed manufacturing/assembly plans were developed as the basis for cost estimates. Each of the six designs was found to have advantages over the 1995 aluminum benchmark in cost and weight trade studies. Large quadrant panels and cobonded frames were found to save significant assembly labor costs. Comparisons of high- and intermediate-performance fiber systems were made for skin and stringer applications. Advanced tow placement was found to be an efficient process for skin lay up. Further analysis revealed attractive processes for stringers and frames. Optimized designs were informally developed for each design family, combining the most attractive concepts and processes within that family. A single optimized design was selected as the most promising, and the potential for further optimization was estimated. Technical issues and barriers were identified
Non-destructive spatial heterodyne imaging of cold atoms
We demonstrate a new method for non-destructive imaging of laser-cooled
atoms. This spatial heterodyne technique forms a phase image by interfering a
strong carrier laser beam with a weak probe beam that passes through the cold
atom cloud. The figure of merit equals or exceeds that of phase-contrast
imaging, and the technique can be used over a wider range of spatial scales. We
show images of a dark spot MOT taken with imaging fluences as low as 61 pJ/cm^2
at a detuning of 11 linewidths, resulting in 0.0004 photons scattered per atom.Comment: text+3 figures, submitted to Optics Letter
Thirty Meter Telescope Site Testing I: Overview
As part of the conceptual and preliminary design processes of the Thirty
Meter Telescope (TMT), the TMT site testing team has spent the last five years
measuring the atmospheric properties of five candidate mountains in North and
South America with an unprecedented array of instrumentation. The site testing
period was preceded by several years of analyses selecting the five candidates,
Cerros Tolar, Armazones and Tolonchar in northern Chile; San Pedro Martir in
Baja California, Mexico and the 13 North (13N) site on Mauna Kea, Hawaii. Site
testing was concluded by the selection of two remaining sites for further
consideration, Armazones and Mauna Kea 13N. It showed that all five candidates
are excellent sites for an extremely large astronomical observatory and that
none of the sites stands out as the obvious and only logical choice based on
its combined properties. This is the first article in a series discussing the
TMT site testing project.Comment: Accepted for publication in PASP, April 2009 issu
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