5,598 research outputs found
A Sunyaev-Zel'dovich Effect Survey for High Redshift Clusters
Interferometric observations of the Sunyaev-Zel'dovich Effect (SZE) toward
clusters of galaxies provide sensitive cosmological probes. We present results
from 1 cm observations (at BIMA and OVRO) of a large, intermediate redshift
cluster sample. In addition, we describe a proposed, higher sensitivity array
which will enable us to survey large portions of the sky. Simulated
observations indicate that we will be able to survey one square degree of sky
per month to sufficient depth that we will detect all galaxy clusters more
massive than 2x10^{14} h^{-1}_{50}M_\odot, regardless of their redshift. We
describe the cluster yield and resulting cosmological constraints from such a
survey.Comment: 7 pages, 6 figures, latex, contribution to VLT Opening Symposiu
Theory of Dynamic Stripe Induced Superconductivity
Since the recently reported giant isotope effect on T* [1] could be
consistently explained within an anharmonic spin-charge-phonon interaction
model, we consider here the role played by stripe formation on the
superconducting properties within the same model. This is a two-component
scenario and we recast its basic elements into a BCS effective Hamiltonian. We
find that the stripe formation is vital to high-Tc superconductivity since it
provides the glue between the two components to enhance Tc to the unexpectedly
large values observed experimentally.Comment: 7 pages, 2 figure
The polymerisation of oligo(ethylene glycol methyl ether) methacrylate from a multifunctional poly(ethylene imine) derived amide: a stabiliser for the synthesis and dispersion of magnetite nanoparticles
A facile synthetic route to poly(ethylene imine)-graft-poly(oligo(ethylene glycol methyl ether)) (PEI-graft-POEGMA) functionalised superparamagnetic magnetite nanoparticles is described. The polymerisation of OEGMA from a model molecular amide demonstrated the feasibility of POEGMA synthesis under mild ATRP conditions (20 °C in ethanol) albeit with low initiator efficiencies. DFT studies suggest that the amide functionality is intrinsically of lower activity than ester functional monomers and initiators for atom transfer polymerisation (ATRP) as a consequence of higher bond dissociation energies and bond dissociation free energies (BDFE). However these studies further highlighted that use of an appropriate solvent could reduce the free energy of dissociation thereby reducing the relative difference in BDFE between the ester and amide groups. A commercial branched PEI sample was functionalised by reaction with 2-bromo-2-methylpropanoyl bromide giving an amide macroinitiator suitable for the atom transfer radical polymerisation (ATRP) of oligo(ethylene glycol methyl ether) methacrylate. The resulting PEI-graft-POEGMA copolymers were characterised by SEC, FT-IR and 1H and 13C NMR spectroscopy. PEI-graft-POEGMA coated magnetite nanoparticles were synthesised by a basic aqueous co-precipitation method and were characterised by transmission electron microscopy, thermogravimetric analysis and vibrating sample magnetometry and dynamic light scattering. These copolymer coated magnetite nanoparticles were demonstrated to be effectively stabilised in an aqueous medium. Overall the particle sizes and magnetic and physical properties of the coated samples were similar to those of uncoated samples
Intrinsic and structural isotope effects in Fe-based superconductors
The currently available results of the isotope effect on the superconducting
transition temperature T_c in Fe-based high-temperature superconductors (HTS)
are highly controversial. The values of the Fe isotope effect (Fe-IE) exponent
\alpha_Fe for various families of Fe-based HTS were found to be as well
positive, as negative, or even be exceedingly larger than the BCS value
\alpha_BCS=0.5. Here we demonstrate that the Fe isotope substitution causes
small structural modifications which, in turn, affect T_c. Upon correcting the
isotope effect exponent for these structural effects, an almost unique value of
\alpha~0.35-0.4 is observed for at least three different families of Fe-based
HTS.Comment: 4 pages, 2 figure
External Shear in Quadruply Imaged Lens Systems
We use publicly available N-body simulations and semi-analytic models of
galaxy formation to estimate the levels of external shear due to structure near
the lens in gravitational lens systems. We also describe two selection effects,
specific to four-image systems, that enhance the probability of observing
systems to have higher external shear. Ignoring additional contributions from
"cosmic shear" and assuming that lens galaxies are not significantly flattened,
we find that the mean shear at the position of a quadruple lens galaxy is 0.11,
the rms shear is roughly 0.15, and there is roughly a 45% likelihood of
external shear greater than 0.1. This is much larger than previous estimates
and in good agreement with typical measured external shear. The higher shear
primarily stems from the tendency of early-type galaxies, which are the
majority of lenses, to reside in overdense regions.Comment: 5 pages, 2 figures, ApJ in press, minor revision
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