37,777 research outputs found
Imidazopyrrolone/imide copolymers Patent
Synthesis and chemical properties of imidazopyrrolone/imide copolymer
Dosimeter for high levels of absorbed radiation Patent
Development of dosimeter for measuring absorbed dose of high energy ionizing radiatio
A Bayesian Classifier for Photometric Redshifts: Identification of high redshift clusters
Photometric redshift classifiers provide a means of estimating galaxy
redshifts from observations using a small number of broad-band filters.
However, the accuracy with which redshifts can be determined is sensitive to
the star formation history of the galaxy, for example the effects of age,
metallicity and on-going star formation. We present a photometric classifier
that explicitly takes into account the degeneracies implied by these
variations, based on the flexible stellar population synthesis code of Kodama &
Arimoto. The situation is encouraging since many of the variations in stellar
populations introduce colour changes that are degenerate. We use a Bayesian
inversion scheme to estimate the likely range of redshifts compatible with the
observed colours. When applied to existing multi-band photometry for Abell 370,
most of the cluster members are correctly recovered with little field
contamination. The inverter is focussed on the recovery of a wide variety of
galaxy populations in distant (z~1) clusters from broad band colours covering
the 4000 angstrom break. It is found that this can be achieved with impressive
accuracy (), allowing detailed investigation into the
evolution of cluster galaxies with little selection bias.Comment: 18 pages, including 15 figures, Accepted for publication in MNRA
The bimodal spiral galaxy surface brightness distribution
We have assessed the significance of Tully and Verheijen's (1997) bimodal
Ursa Major Cluster spiral galaxy near-infrared surface brightness distribution,
focussing on whether this bimodality is simply an artifact of small number
statistics. A Kolmogorov-Smirnov style of significance test shows that the
total distribution is fairly represented by a single-peaked distribution, but
that their isolated galaxy subsample (with no significant neighbours within a
projected distance of around 80 kpc) is bimodal at the 96 per cent level. We
have also investigated the assumptions underlying the isolated galaxy surface
brightness distribution, finding that the (often large) inclination corrections
used in the construction of this distribution reduce the significance of the
bimodality. We conclude that the Ursa Major Cluster dataset is insufficient to
establish the presence of a bimodal near-infrared surface brightness
distribution: an independent sample of around 100 isolated, low inclination
galaxies is required to establish bimodality at the 99 per cent level.Comment: 5 pages LaTeX; 2 embedded figures; re-submitted to MNRAS after
replying to referee's comment
Condensation transition in DNA-polyaminoamide dendrimer fibers studied using optical tweezers
When mixed together, DNA and polyaminoamide (PAMAM) dendrimers form fibers
that condense into a compact structure. We use optical tweezers to pull
condensed fibers and investigate the decondensation transition by measuring
force-extension curves (FECs). A characteristic plateau force (around 10 pN)
and hysteresis between the pulling and relaxation cycles are observed for
different dendrimer sizes, indicating the existence of a first-order transition
between two phases (condensed and extended) of the fiber. The fact that we can
reproduce the same FECs in the absence of additional dendrimers in the buffer
medium indicates that dendrimers remain irreversibly bound to the DNA backbone.
Upon salt variation FECs change noticeably confirming that electrostatic forces
drive the condensation transition. Finally, we propose a simple model for the
decondensing transition that qualitatively reproduces the FECs and which is
confirmed by AFM images.Comment: Latex version, 4 pages+3 color figure
Galaxy bulges and their black holes: a requirement for the quenching of star formation
One of the central features of the last 8 to 10 billion years of cosmic
history has been the emergence of a well-populated red sequence of
non-star-forming galaxies. A number of models of galaxy formation and evolution
have been devised to attempt to explain this behavior. Most current models
require feedback from supermassive black holes (AGN feedback) to quench star
formation in galaxies in the centers of their dark matter halos (central
galaxies). Such models make the strong prediction that all quenched central
galaxies must have a large supermassive black hole (and, by association, a
prominent bulge component). I show using data from the Sloan Digital Sky Survey
that the observations are consistent with this prediction. Over 99.5% of red
sequence galaxies with stellar masses in excess of 10^{10} M_{\sun} have a
prominent bulge component (as defined by having a Sersic index n above 1.5).
Those very rare red sequence central galaxies with little or no bulge (n<1.5)
usually have detectable star formation or AGN activity; the fraction of truly
quenched bulgeless central galaxies is <0.1% of the total red sequence
population. I conclude that a bulge, and by implication a supermassive black
hole, is an absolute requirement for full quenching of star formation in
central galaxies. This is in agreement with the most basic prediction of the
AGN feedback paradigm.Comment: 6 pages, 4 color figures (figure 1 is of slightly degraded quality).
To appear in August 1 edition of the Astrophysical Journa
Local Hidden Variable Theories for Quantum States
While all bipartite pure entangled states violate some Bell inequality, the
relationship between entanglement and non-locality for mixed quantum states is
not well understood. We introduce a simple and efficient algorithmic approach
for the problem of constructing local hidden variable theories for quantum
states. The method is based on constructing a so-called symmetric
quasi-extension of the quantum state that gives rise to a local hidden variable
model with a certain number of settings for the observers Alice and Bob.Comment: 8 pages Revtex; v2 contains substantial changes, a strengthened main
theorem and more reference
Multiphoton path entanglement by non-local bunching
Multiphoton path entanglement is created without applying post-selection, by
manipulating the state of stimulated parametric down-conversion. A specific
measurement on one of the two output spatial modes leads to the non-local
bunching of the photons of the other mode, forming the desired multiphoton path
entangled state. We present experimental results for the case of a heralded
two-photon path entangled state and show how to extend this scheme to higher
photon numbers.Comment: 4 pages, 5 figures, published versio
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