925 research outputs found
Symmetry breaking from confined water wave fields propels an oscillating robot
We discover a new phenomenon in which a symmetrically oscillating,
free-floating robot can be attracted to or repelled from a horizontal boundary.
The device generates radially expanding gravity-capillary (GC) waves at the
fluid surface. Visualization of the wave field dynamics reveals that when near
a boundary, the complex interference of generated and reflected waves induces a
wave amplitude asymmetry that generates a net radiation force that drives robot
motion. Direct force measurements reveal that attraction increases as wave
frequency increases or robot-boundary separation decreases. Theory on confined
GC wave radiation dynamics developed by Hocking in the 1980s captures the
observed parameter dependence due to these ``Hocking fields".Comment: 11 pages, 5 figures, 8 supplementary figure
yourSky: rapid desktop access to custom astronomical image mosaics
The yourSky custom astronomical image mosaicking software has a Web portal architecture that allows access via ordinary desktop computers with low bandwidth network connections to high performance and highly customizable mosaicking software deployed in a high performance computing and communications environment. The emphasis is on custom access to image mosaics constructed from terabytes of raw image data stored in remote archives. In this context, custom access refers to new technology that enables on the fly mosaicking to meet user-specified criteria for region of the sky to be mosaicked, datasets to be used, resolution, coordinate system, projection, data type and image format. The yourSky server is a fully automated end-to-end system that handles all aspects of the mosaic construction. This includes management of mosaic requests, determining which input images are required to fulfill each request, management of a data cache for both input image plates and output mosaics, retrieval of input image plates from massive remote archives, image mosaic construction on a multiprocessor system, and making the result accessible to the user on the desktop. The URL for yourSky is http://yourSky.jpl.nasa.gov
Interplay of signal recognition particle and trigger factor at L23 near the nascent chain exit site on the Escherichia coli ribosome
As newly synthesized polypeptides emerge from the ribosome, they interact with chaperones and targeting factors that assist in folding and targeting to the proper location in the cell. In Escherichia coli, the chaperone trigger factor (TF) binds to nascent polypeptides early in biosynthesis facilitated by its affinity for the ribosomal proteins L23 and L29 that are situated around the nascent chain exit site on the ribosome. The targeting factor signal recognition particle (SRP) interacts specifically with the signal anchor (SA) sequence in nascent inner membrane proteins (IMPs). Here, we have used photocross-linking to map interactions of the SA sequence in a short, in vitro–synthesized, nascent IMP. Both TF and SRP were found to interact with the SA with partially overlapping binding specificity. In addition, extensive contacts with L23 and L29 were detected. Both purified TF and SRP could be cross-linked to L23 on nontranslating ribosomes with a competitive advantage for SRP. The results suggest a role for L23 in the targeting of IMPs as an attachment site for TF and SRP that is close to the emerging nascent chain
Binary Quasars in the Sloan Digital Sky Survey: Evidence for Excess Clustering on Small Scales
We present a sample of 218 new quasar pairs with proper transverse
separations R_prop < 1 Mpc/h over the redshift range 0.5 < z < 3.0, discovered
from an extensive follow up campaign to find companions around the Sloan
Digital Sky Survey and 2dF Quasar Redshift Survey quasars. This sample includes
26 new binary quasars with separations R_prop < 50 kpc/h (theta < 10
arcseconds), more than doubling the number of such systems known. We define a
statistical sample of binaries selected with homogeneous criteria and compute
its selection function, taking into account sources of incompleteness. The
first measurement of the quasar correlation function on scales 10 kpc/h <
R_prop < 400 kpc/h is presented. For R_prop < 40 kpc/h, we detect an order of
magnitude excess clustering over the expectation from the large scale R_prop >
3 Mpc/h quasar correlation function, extrapolated down as a power law to the
separations probed by our binaries. The excess grows to ~ 30 at R_prop ~ 10
kpc/h, and provides compelling evidence that the quasar autocorrelation
function gets progressively steeper on sub-Mpc scales. This small scale excess
can likely be attributed to dissipative interaction events which trigger quasar
activity in rich environments. Recent small scale measurements of galaxy
clustering and quasar-galaxy clustering are reviewed and discussed in relation
to our measurement of small scale quasar clustering.Comment: 25 pages, 12 figures, 9 tables. Submitted to the Astronomical Journa
Type IIA Orientifolds on General Supersymmetric Z_N Orbifolds
We construct Type IIA orientifolds for general supersymmetric Z_N orbifolds.
In particular, we provide the methods to deal with the non-factorisable
six-dimensional tori for the cases Z7, Z8, Z8', Z12 and Z12'. As an application
of these methods we explicitly construct many new orientifold models.Comment: 48 pages, LaTeX, 14 figures, refs. added, closed string spectra
slightly change
The Sloan Digital Sky Survey Quasar Lens Search. II. Statistical lens sample from the third data release
We report the first results of our systematic search for strongly lensed quasars using the spectroscopically confirmed quasars in the Sloan Digital Sky Survey (SDSS). Among 46,420 quasars from the SDSS Data Release 3 (~4188 deg^2), we select a subsample of 22,683 quasars that are located at redshifts between 0.6 and 2.2 and are brighter than the Galactic extinction-corrected i-band magnitude of 19.1. We identify 220 lens candidates from the quasar subsample, for which we conduct extensive and systematic follow-up observations in optical and near-infrared wavebands, in order to construct a complete lensed quasar sample at image separations between 1" and 20" and flux ratios of faint to bright lensed images larger than 10^(−0.5). We construct a statistical sample of 11 lensed quasars. Ten of these are galaxy-scale lenses with small image separations (~ 1"-2") and one is a large separation (15") system which is produced by a massive cluster of galaxies, representing the first statistical sample of lensed quasars including both galaxy- and cluster-scale lenses. The Data Release 3 spectroscopic quasars contain an additional 11 lensed quasars outside the statistical sample
yourSky: rapid desktop access to custom astronomical image mosaics
The yourSky custom astronomical image mosaicking software has a Web portal architecture that allows access via ordinary desktop computers with low bandwidth network connections to high performance and highly customizable mosaicking software deployed in a high performance computing and communications environment. The emphasis is on custom access to image mosaics constructed from terabytes of raw image data stored in remote archives. In this context, custom access refers to new technology that enables on the fly mosaicking to meet user-specified criteria for region of the sky to be mosaicked, datasets to be used, resolution, coordinate system, projection, data type and image format. The yourSky server is a fully automated end-to-end system that handles all aspects of the mosaic construction. This includes management of mosaic requests, determining which input images are required to fulfill each request, management of a data cache for both input image plates and output mosaics, retrieval of input image plates from massive remote archives, image mosaic construction on a multiprocessor system, and making the result accessible to the user on the desktop. The URL for yourSky is http://yourSky.jpl.nasa.gov
The Sloan Digital Sky Survey Quasar Lens Search. III. Constraints on Dark Energy from the Third Data Release Quasar Lens Catalog
We present cosmological results from the statistics of lensed quasars in the
Sloan Digital Sky Survey (SDSS) Quasar Lens Search. By taking proper account of
the selection function, we compute the expected number of quasars lensed by
early-type galaxies and their image separation distribution assuming a flat
universe, which is then compared with 7 lenses found in the SDSS Data Release 3
to derive constraints on dark energy under strictly controlled criteria. For a
cosmological constant model (w=-1) we obtain
\Omega_\Lambda=0.74^{+0.11}_{-0.15}(stat.)^{+0.13}_{-0.06}(syst.). Allowing w
to be a free parameter we find
\Omega_M=0.26^{+0.07}_{-0.06}(stat.)^{+0.03}_{-0.05}(syst.) and
w=-1.1\pm0.6(stat.)^{+0.3}_{-0.5}(syst.) when combined with the constraint from
the measurement of baryon acoustic oscillations in the SDSS luminous red galaxy
sample. Our results are in good agreement with earlier lensing constraints
obtained using radio lenses, and provide additional confirmation of the
presence of dark energy consistent with a cosmological constant, derived
independently of type Ia supernovae.Comment: 9 pages, 3 figures, 2 tables, accepted for publication in A
Intestine-Specific, Oral Delivery of Captopril/Montmorillonite: Formulation and Release Kinetics
The intercalation of captopril (CP) into the interlayers of montmorillonite (MMT) affords an intestine-selective drug delivery system that has a captopril-loading capacity of up to ca. 14 %w/w and which exhibits near-zero-order release kinetics
LSST Science Book, Version 2.0
A survey that can cover the sky in optical bands over wide fields to faint
magnitudes with a fast cadence will enable many of the exciting science
opportunities of the next decade. The Large Synoptic Survey Telescope (LSST)
will have an effective aperture of 6.7 meters and an imaging camera with field
of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over
20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with
fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a
total point-source depth of r~27.5. The LSST Science Book describes the basic
parameters of the LSST hardware, software, and observing plans. The book
discusses educational and outreach opportunities, then goes on to describe a
broad range of science that LSST will revolutionize: mapping the inner and
outer Solar System, stellar populations in the Milky Way and nearby galaxies,
the structure of the Milky Way disk and halo and other objects in the Local
Volume, transient and variable objects both at low and high redshift, and the
properties of normal and active galaxies at low and high redshift. It then
turns to far-field cosmological topics, exploring properties of supernovae to
z~1, strong and weak lensing, the large-scale distribution of galaxies and
baryon oscillations, and how these different probes may be combined to
constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at
http://www.lsst.org/lsst/sciboo
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