6,843 research outputs found
AN ANALYSIS OF HOUSEHOLD CONSUMPTION OF FRESH POTATOES IN DELAWARE
Food Consumption/Nutrition/Food Safety,
Evolution of the Dark Matter Distribution with 3-D Weak Lensing
We present a direct detection of the growth of large-scale structure, using
weak gravitational lensing and photometric redshift data from the COMBO-17
survey. We use deep R-band imaging of two 0.25 square degree fields, affording
shear estimates for over 52000 galaxies; we combine these with photometric
redshift estimates from our 17 band survey, in order to obtain a 3-D shear
field. We find theoretical models for evolving matter power spectra and
correlation functions, and fit the corresponding shear correlation functions to
the data as a function of redshift. We detect the evolution of the power at the
7.7 sigma level given minimal priors, and measure the rate of evolution for
0<z<1. We also fit correlation functions to our 3-D data as a function of
cosmological parameters sigma_8 and Omega_Lambda. We find joint constraints on
Omega_Lambda and sigma_8, demonstrating an improvement in accuracy by a factor
of 2 over that available from 2D weak lensing for the same area.Comment: 11 pages, 4 figures; submitted to MNRA
Previous attentional set can induce an attentional blink with task-irrelevant initial targets
Identification of a second target is often impaired by the requirement to process a prior target in a rapid serial visual presentation (RSVP). This is termed the attentional blink. Even when the first target is task-irrelevant an attentional blink may occur providing this first target shares similar features with the second target (contingent capture). An RSVP experiment was undertaken to assess whether this first target can still cause an attentional blink when it did not require a response and did not share any features with the following target. The results revealed that such task-irrelevant targets can induce an attentional blink providing that they were task-relevant on a previous block of trials. This suggests that irrelevant focal stimuli can distract attention on the basis of a previous attentional set
Decoherence-Free Subspaces for Multiple-Qubit Errors: (I) Characterization
Coherence in an open quantum system is degraded through its interaction with
a bath. This decoherence can be avoided by restricting the dynamics of the
system to special decoherence-free subspaces. These subspaces are usually
constructed under the assumption of spatially symmetric system-bath coupling.
Here we show that decoherence-free subspaces may appear without spatial
symmetry. Instead, we consider a model of system-bath interactions in which to
first order only multiple-qubit coupling to the bath is present, with
single-qubit system-bath coupling absent. We derive necessary and sufficient
conditions for the appearance of decoherence-free states in this model, and
give a number of examples. In a sequel paper we show how to perform universal
and fault tolerant quantum computation on the decoherence-free subspaces
considered in this paper.Comment: 18 pages, no figures. Major changes. Section on universal fault
tolerant computation removed. This section contained a crucial error. A new
paper [quant-ph/0007013] presents the correct analysi
Cosmic Shear of the Microwave Background: The Curl Diagnostic
Weak-lensing distortions of the cosmic-microwave-background (CMB) temperature
and polarization patterns can reveal important clues to the intervening
large-scale structure. The effect of lensing is to deflect the primary
temperature and polarization signal to slightly different locations on the sky.
Deflections due to density fluctuations, gradient-type for the gradient of the
projected gravitational potential, give a direct measure of the mass
distribution. Curl-type deflections can be induced by, for example, a
primordial background of gravitational waves from inflation or by second-order
effects related to lensing by density perturbations. Whereas gradient-type
deflections are expected to dominate, we show that curl-type deflections can
provide a useful test of systematics and serve to indicate the presence of
confusing secondary and foreground non-Gaussian signals.Comment: 8 pages, 3 figures; PRD submitte
The Planetary Nebulae Population in the Nuclear Regions of M31: the SAURON view
Following a first study of the central regions of M32 that illustrated the
power of integral-field spectroscopy (IFS) in detecting and measuring the [O
III]{\lambda}5007 emission of PNe against a strong stellar background, we turn
to the very nuclear PN population of M31, within 80 pc of its centre. We show
that PNe can also be found in the presence of emission from diffuse gas and
further illustrate the excellent sensitivity of IFS in detecting extragalactic
PNe through a comparison with narrowband images obtained with the Hubble Space
Telescope. We find the nuclear PNe population of M31 is only marginally
consistent with the generally adopted form of the PNe luminosity function
(PNLF). In particular, this is due to a lack of PNe with absolute magnitude
M5007 brighter than -3, which would only result from a rather unfortunate draw
from such a model PNLF. We suggest that the observed lack of bright PNe in the
nuclear regions of M31 is due to a horizontal-branch population that is more
tilted toward less massive and hotter He-burning stars, so that its progeny
consists mostly of UV-bright stars that fail to climb back up the asymptotic
giant branch (AGB) and only of few, if any, bright PNe powered by central
post-AGB stars. These results are also consistent with recent reports on a
dearth of bright post-AGB stars towards the nucleus of M31, and lend further
support to the idea that the metallicity of a stellar population has an impact
on the way the horizontal branch is populated and to the loose anticorrelation
between the strength of the UV-upturn and the specific number of PNe that is
observed in early-type galaxies. Finally, our investigation also serves to
stress the importance of considering the same spatial scales when comparing the
PNe population of galaxies with the properties of their stellar populations.Comment: 11 pages, 10 figures, accepted for publication on Monthly Notices of
the Royal Astronomical Societ
Reconstitution of T cell receptor signaling in ZAP-70-deficient cells by retroviral transduction of the ZAP-70 gene.
A variant of severe combined immunodeficiency syndrome (SCID) with a selective inability to produce CD8 single positive T cells and a signal transduction defect in peripheral CD4+ cells has recently been shown to be the result of mutations in the ZAP-70 gene. T cell receptor (TCR) signaling requires the association of the ZAP-70 protein tyrosine kinase with the TCR complex. Human T cell leukemia virus type I-transformed CD4+ T cell lines were established from ZAP-70-deficient patients and normal controls. ZAP-70 was expressed and appropriately phosphorylated in normal T cell lines after TCR engagement, but was not detected in T cell lines from ZAP-70-deficient patients. To determine whether signaling could be reconstituted, wild-type ZAP-70 was introduced into deficient cells with a ZAP-70 retroviral vector. High titer producer clones expressing ZAP-70 were generated in the Gibbon ape leukemia virus packaging line PG13. After transduction, ZAP-70 was detected at levels equivalent to those observed in normal cells, and was appropriately phosphorylated on tyrosine after receptor engagement. The kinase activity of ZAP-70 in the reconstituted cells was also appropriately upregulated by receptor aggregation. Moreover, normal and transduced cells, but not ZAP-70-deficient cells, were able to mobilize calcium after receptor ligation, indicating that proximal TCR signaling was reconstituted. These results indicate that this form of SCID may be corrected by gene therapy
Symmetric coupling of four spin-1/2 systems
We address the non-binary coupling of identical angular momenta based upon
the representation theory for the symmetric group. A correspondence is pointed
out between the complete set of commuting operators and the
reference-frame-free subsystems. We provide a detailed analysis of the coupling
of three and four spin-1/2 systems and discuss a symmetric coupling of four
spin-1/2 systems.Comment: 20 pages, no figure
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