2,029 research outputs found
Diffraction-contrast imaging of cold atoms
We consider the inverse problem of in-line holography, applied to
minimally-destructive imaging of cold atom clouds. Absorption imaging
near-resonance provides a simple, but destructive measurement of atom column
density. Imaging off resonance greatly reduces heating, and sequential images
may be taken. Under the conditions required for off-resonant imaging, the
generally-intractable inverse problem may be linearized. A
minimally-destructive, quantitative and high-resolution image of the atom cloud
column density is then retrieved from a single diffraction pattern.Comment: 4 pages, 3 figures v2: minor changes in response to referee reports,
mostly additional experimental detail v3: revisions to figure 3: added trace
and changed image. Minor text and referencing changes. Accepted by Phys Rev A
(Rapid Commun
Relative intensity squeezing by four-wave mixing with loss: an analytic model and experimental diagnostic
Four-wave mixing near resonance in an atomic vapor can produce relative
intensity squeezed light suitable for precision measurements beyond the
shot-noise limit. We develop an analytic distributed gain/loss model to
describe the competition of mixing and absorption through the non-linear
medium. Using a novel matrix calculus, we present closed-form expressions for
the degree of relative intensity squeezing produced by this system. We use
these theoretical results to analyze experimentally measured squeezing from a
Rb vapor and demonstrate the analytic model's utility as an experimental
diagnostic.Comment: 10 pages, 5 figure
Consequences of wall stiffness for a beta-soft potential
Modifications of the infinite square well E(5) and X(5) descriptions of
transitional nuclear structure are considered. The eigenproblem for a potential
with linear sloped walls is solved. The consequences of the introduction of
sloped walls and of a quadratic transition operator are investigated.Comment: RevTeX 4, 8 pages, as published in Phys. Rev.
Alternative Interpretation of Sharply Rising E0 Strengths in Transitional Regions
It is shown that strong 0+2 -> 0+1 E0 transitions provide a clear signature
of phase transitional behavior in finite nuclei. Calculations using the IBA
show that these transition strengths exhibit a dramatic and robust increase in
spherical-deformed shape transition regions, that this rise matches well the
existing data, that the predictions of these E0 transitions remain large in
deformed nuclei, and that these properties are intrinsic to the way that
collectivity and deformation develop through the phase transitional region in
the model, arising from the specific d-boson coherence in the wave functions,
and that they do not necessarily require the explicit mixing of normal and
intruder configurations from different IBA spaces.Comment: 6 pages, 3 figure
The study of bronze statuettes with the help of neutron-imaging techniques
Until recently fabrication techniques of Renaissance bronzes have been studied only with the naked eye, microscopically, videoscopically and with X-radiography. These techniques provide information on production techniques, yet much important detail remains unclear. As part of an interdisciplinary study of Renaissance bronzes undertaken by the Rijksmuseum Amsterdam, neutron-imaging techniques have been applied with the aim of obtaining a better understanding of bronze workmanship during the Renaissance period. Therefore, an explanation of the fabrication techniques is given to better understand the data collected by these neutron-imaging techniques. The data was used for tomography studies, which reveal hidden aspects that could not at all or scarcely be seen using X-radiography. For this specific study, the representative bronze ‘Hercules Pomarius’ of Willem van Tetrode (ca 1520–1588) has been examined, along with 20 other Renaissance bronzes from the Rijksmuseum collection
Host use of the elkhorn coral crab <i>Domecia acanthophora</i> (Brachyura : Domeciidae), with a phylogeny of the genus
Coral-dwelling crabs form a diverse community on coral reefs, and various families independently colonised scleractinian corals. Species of Domecia have a circumtropical distribution, with two known species in the Indo-Pacific, one in the West Atlantic and one in the East Atlantic. New host records for the West Atlantic species D. acanthophora are recorded from Guadeloupe, as well as the first dwellings in Acropora prolifera from Curaçao. Here we provide an overview of all known hosts of Domecia species and, based on COI mtDNA, the first phylogeny of the genus. The coral Orbicella faveolata and the sponge Callyspongia sp. are recorded as new hosts for D. acanthophora. Host records for this species now include eight scleractinian hosts, Millepora fire corals and records on sponges. Our phylogenetic reconstruction shows that D. acanthophora is closest to the wide-ranging Indo-Pacific species D. hispida, and more distantly related to D. glabra. Domecia acanthophora appears to be less host specific than its congeners D. hispida and D. glabra that predominantly associate with Pocillopora and Acropora corals, respectively. Differences in host-specificity between Indo-Pacific and Atlantic species are briefly discussed in the light of similar observations on other coral-dwelling crab species
Laser frequency offset locking using electromagnetically induced transparency
The authors have used an electromagnetically induced transparency resonance in rubidium as a dispersive reference to lock the relative frequency of two lasers to the atomic ground-statehyperfine splitting. The beat frequency between the two lasers directly generates a microwave signal at 3.036GHz (⁸⁵Rb) or 6.835GHz (⁸⁷Rb). High bandwidth (600kHz) feedback was achieved with only low-frequency (10MHz)electronics using the frequency modulation sideband method. The spectral width of the microwave beat frequency was reduced to less than 1kHz. The technique offers a convenient and low-cost method suitable for many topical two-frequency experiments, including coherent population trapping, slow light, lasing without inversion, and Raman sideband cooling.This research was supported under the Discovery funding
scheme of the Australian Research Council Project No.
DP0557505
Mapping environmental injustices: pitfalls and potential of geographic information systems in assessing environmental health and equity.
Geographic Information Systems (GIS) have been used increasingly to map instances of environmental injustice, the disproportionate exposure of certain populations to environmental hazards. Some of the technical and analytic difficulties of mapping environmental injustice are outlined in this article, along with suggestions for using GIS to better assess and predict environmental health and equity. I examine 13 GIS-based environmental equity studies conducted within the past decade and use a study of noxious land use locations in the Bronx, New York, to illustrate and evaluate the differences in two common methods of determining exposure extent and the characteristics of proximate populations. Unresolved issues in mapping environmental equity and health include lack of comprehensive hazards databases; the inadequacy of current exposure indices; the need to develop realistic methodologies for determining the geographic extent of exposure and the characteristics of the affected populations; and the paucity and insufficiency of health assessment data. GIS have great potential to help us understand the spatial relationship between pollution and health. Refinements in exposure indices; the use of dispersion modeling and advanced proximity analysis; the application of neighborhood-scale analysis; and the consideration of other factors such as zoning and planning policies will enable more conclusive findings. The environmental equity studies reviewed in this article found a disproportionate environmental burden based on race and/or income. It is critical now to demonstrate correspondence between environmental burdens and adverse health impacts--to show the disproportionate effects of pollution rather than just the disproportionate distribution of pollution sources
Polarized radio emission from extensive air showers measured with LOFAR
We present LOFAR measurements of radio emission from extensive air showers.
We find that this emission is strongly polarized, with a median degree of
polarization of nearly , and that the angle between the polarization
direction of the electric field and the Lorentz force acting on the particles,
depends on the observer location in the shower plane. This can be understood as
a superposition of the radially polarized charge-excess emission mechanism,
first proposed by Askaryan and the geomagnetic emission mechanism proposed by
Kahn and Lerche. We calculate the relative strengths of both contributions, as
quantified by the charge-excess fraction, for individual air showers. We
find that the measured charge-excess fraction is higher for air showers
arriving from closer to the zenith. Furthermore, the measured charge-excess
fraction also increases with increasing observer distance from the air shower
symmetry axis. The measured values range from for very
inclined air showers at to for almost
vertical showers at . Both dependencies are in qualitative
agreement with theoretical predictions.Comment: 22 pages, 14 figures, accepted for publication in JCA
- …