359 research outputs found
Synthesis and control of crosslinked poly(acrylic acid) based viscosity modifiers using dense phase carbon dioxide as a solvent
We investigate the clean synthesis of a cross-linked poly(acrylic acid) viscosity modifier using supercritical CO2 to replace more hazardous volatile organic solvents that are typically used for this process. The polymers were analysed by aqueous swell ratio studies to demonstrate the effect of process conditions such as pressure and temperature on the cross-link density of the materials. The reactions were optimised to yield high swelling polymers of up to 134âŻg water/g polymer. Dynamic mechanical analysis (DMA) was also applied to investigate the mechanical properties of the synthesised cross-linked poly(acrylic acid) materials and these data were directly correlated with swell ratio. In addition, rheological studies demonstrate that the hydrated gels are comparable with commercially available equivalents
Short Gamma Ray Bursts as possible electromagnetic counterpart of coalescing binary systems
Coalescing binary systems, consisting of two collapsed objects, are among the
most promising sources of high frequency gravitational waves signals
detectable, in principle, by ground-based interferometers. Binary systems of
Neutron Star or Black Hole/Neutron Star mergers should also give rise to short
Gamma Ray Bursts, a subclass of Gamma Ray Bursts. Short-hard-Gamma Ray Bursts
might thus provide a powerful way to infer the merger rate of two-collapsed
object binaries. Under the hypothesis that most short Gamma Ray Bursts
originate from binaries of Neutron Star or Black Hole/Neutron Star mergers, we
outline here the possibility to associate short Gamma Ray Bursts as
electromagnetic counterpart of coalescing binary systems.Comment: 4 pages, 1 figur
Quantum phase transitions from topology in momentum space
Many quantum condensed matter systems are strongly correlated and strongly
interacting fermionic systems, which cannot be treated perturbatively. However,
physics which emerges in the low-energy corner does not depend on the
complicated details of the system and is relatively simple. It is determined by
the nodes in the fermionic spectrum, which are protected by topology in
momentum space (in some cases, in combination with the vacuum symmetry). Close
to the nodes the behavior of the system becomes universal; and the universality
classes are determined by the toplogical invariants in momentum space. When one
changes the parameters of the system, the transitions are expected to occur
between the vacua with the same symmetry but which belong to different
universality classes. Different types of quantum phase transitions governed by
topology in momentum space are discussed in this Chapter. They involve Fermi
surfaces, Fermi points, Fermi lines, and also the topological transitions
between the fully gapped states. The consideration based on the momentum space
topology of the Green's function is general and is applicable to the vacua of
relativistic quantum fields. This is illustrated by the possible quantum phase
transition governed by topology of nodes in the spectrum of elementary
particles of Standard Model.Comment: 45 pages, 17 figures, 83 references, Chapter for the book "Quantum
Simulations via Analogues: From Phase Transitions to Black Holes", to appear
in Springer lecture notes in physics (LNP
Measurement of the scintillation time spectra and pulse-shape discrimination of low-energy beta and nuclear recoils in liquid argon with DEAP-1
The DEAP-1 low-background liquid argon detector was used to measure
scintillation pulse shapes of electron and nuclear recoil events and to
demonstrate the feasibility of pulse-shape discrimination (PSD) down to an
electron-equivalent energy of 20 keV.
In the surface dataset using a triple-coincidence tag we found the fraction
of beta events that are misidentified as nuclear recoils to be (90% C.L.) for energies between 43-86 keVee and for a nuclear recoil
acceptance of at least 90%, with 4% systematic uncertainty on the absolute
energy scale. The discrimination measurement on surface was limited by nuclear
recoils induced by cosmic-ray generated neutrons. This was improved by moving
the detector to the SNOLAB underground laboratory, where the reduced background
rate allowed the same measurement with only a double-coincidence tag.
The combined data set contains events. One of those, in the
underground data set, is in the nuclear-recoil region of interest. Taking into
account the expected background of 0.48 events coming from random pileup, the
resulting upper limit on the electronic recoil contamination is
(90% C.L.) between 44-89 keVee and for a nuclear recoil
acceptance of at least 90%, with 6% systematic uncertainty on the absolute
energy scale.
We developed a general mathematical framework to describe PSD parameter
distributions and used it to build an analytical model of the distributions
observed in DEAP-1. Using this model, we project a misidentification fraction
of approx. for an electron-equivalent energy threshold of 15 keV for
a detector with 8 PE/keVee light yield. This reduction enables a search for
spin-independent scattering of WIMPs from 1000 kg of liquid argon with a
WIMP-nucleon cross-section sensitivity of cm, assuming
negligible contribution from nuclear recoil backgrounds.Comment: Accepted for publication in Astroparticle Physic
Origin and Evolution of Saturn's Ring System
The origin and long-term evolution of Saturn's rings is still an unsolved
problem in modern planetary science. In this chapter we review the current
state of our knowledge on this long-standing question for the main rings (A,
Cassini Division, B, C), the F Ring, and the diffuse rings (E and G). During
the Voyager era, models of evolutionary processes affecting the rings on long
time scales (erosion, viscous spreading, accretion, ballistic transport, etc.)
had suggested that Saturn's rings are not older than 100 My. In addition,
Saturn's large system of diffuse rings has been thought to be the result of
material loss from one or more of Saturn's satellites. In the Cassini era, high
spatial and spectral resolution data have allowed progress to be made on some
of these questions. Discoveries such as the ''propellers'' in the A ring, the
shape of ring-embedded moonlets, the clumps in the F Ring, and Enceladus' plume
provide new constraints on evolutionary processes in Saturn's rings. At the
same time, advances in numerical simulations over the last 20 years have opened
the way to realistic models of the rings's fine scale structure, and progress
in our understanding of the formation of the Solar System provides a
better-defined historical context in which to understand ring formation. All
these elements have important implications for the origin and long-term
evolution of Saturn's rings. They strengthen the idea that Saturn's rings are
very dynamical and rapidly evolving, while new arguments suggest that the rings
could be older than previously believed, provided that they are regularly
renewed. Key evolutionary processes, timescales and possible scenarios for the
rings's origin are reviewed in the light of tComment: Chapter 17 of the book ''Saturn After Cassini-Huygens'' Saturn from
Cassini-Huygens, Dougherty, M.K.; Esposito, L.W.; Krimigis, S.M. (Ed.) (2009)
537-57
Evolution of the Toarcian (Early Jurassic) carbon-cycle and global climatic controls on local sedimentary processes (Cardigan Bay Basin, UK)
The late Early Jurassic Toarcian Stage represents the warmest interval of the Jurassic Period, with an abrupt rise in global temperatures of up to âŒ7â°C in mid-latitudes at the onset of the early Toarcian Oceanic Anoxic Event (T-OAE; âŒ183 Ma). The T-OAE, which has been extensively studied in marine and continental successions from both hemispheres, was marked by the widespread expansion of anoxic and euxinic waters, geographically extensive deposition of organic-rich black shales, and climatic and environmental perturbations. Climatic and environmental processes following the T-OAE are, however, poorly known, largely due to a lack of study of stratigraphically well-constrained and complete sedimentary archives. Here, we present integrated geochemical and physical proxy data (high-resolution carbon-isotope data (ÎŽ13C), bulk and molecular organic geochemistry, inorganic petrology, mineral characterisation, and major- and trace-element concentrations) from the biostratigraphically complete and expanded entire Toarcian succession in the Llanbedr (Mochras Farm) Borehole, Cardigan Bay Basin, Wales, UK. With these data, we (1) construct the first high-resolution biostratigraphically calibrated chemostratigraphic reference record for nearly the complete Toarcian Stage, (2) establish palaeoceanographic and depositional conditions in the Cardigan Bay Basin, (3) show that the T-OAE in the hemipelagic Cardigan Bay Basin was marked by the occurrence of gravity-flow deposits that were likely linked to globally enhanced sediment fluxes to continental margins and deeper marine (shelf) basins, and (4) explore how early Toarcian (tenuicostatum and serpentinum zones) siderite formation in the Cardigan Bay Basin may have been linked to low global oceanic sulphate concentrations and elevated supply of iron (Fe) from the hinterland, in response to climatically induced changes in hydrological cycling, global weathering rates and large-scale sulphide and evaporite deposition
Does congenital deafness affect the structural and functional architecture of primary visual cortex?
Deafness results in greater reliance on the remaining senses. It is unknown whether the cortical architecture of the intact senses is optimized to compensate for lost input. Here we performed widefield population receptive field (pRF) mapping of primary visual cortex (V1) with functional magnetic resonance imaging (fMRI) in hearing and congenitally deaf participants, all of whom had learnt sign language after the age of 10 years. We found larger pRFs encoding the peripheral visual field of deaf compared to hearing participants. This was likely driven by larger facilitatory center zones of the pRF profile concentrated in the near and far periphery in the deaf group. pRF density was comparable between groups, indicating pRFs overlapped more in the deaf group. This could suggest that a coarse coding strategy underlies enhanced peripheral visual skills in deaf people. Cortical thickness was also decreased in V1 in the deaf group. These findings suggest deafness causes structural and functional plasticity at the earliest stages of visual cortex
The role of sulfoglucuronosyl glycosphingolipids in the pathogenesis of monoclonal IgM paraproteinemia and peripheral neuropathy
In IgM paraproteinemia and peripheral neuropathy, IgM M-protein secretion by B cells leads to a T helper cell response, suggesting that it is antibody-mediated autoimmune disease involving carbohydrate epitopes in myelin sheaths. An immune response against sulfoglucuronosyl glycosphingolipids (SGGLs) is presumed to participate in demyelination or axonal degeneration in the peripheral nervous system (PNS). SGGLs contain a 3-sulfoglucuronic acid residue that interacts with anti-myelin-associated glycoprotein (MAG) and the monoclonal antibody anti-HNK-1. Immunization of animals with sulfoglucuronosyl paragloboside (SGPG) induced anti-SGPG antibodies and sensory neuropathy, which closely resembles the human disease. These animal models might help to understand the disease mechanism and lead to more specific therapeutic strategies. In an in vitro study, destruction or malfunction of the blood-nerve barrier (BNB) was found, resulting in the leakage of circulating antibodies into the PNS parenchyma, which may be considered as the initial key step for development of disease
Measurement of the cross section for isolated-photon plus jet production in pp collisions at âs=13 TeV using the ATLAS detector
The dynamics of isolated-photon production in association with a jet in protonâproton collisions at a centre-of-mass energy of 13 TeV are studied with the ATLAS detector at the LHC using a dataset with an integrated luminosity of 3.2 fbâ1. Photons are required to have transverse energies above 125 GeV. Jets are identified using the anti- algorithm with radius parameter and required to have transverse momenta above 100 GeV. Measurements of isolated-photon plus jet cross sections are presented as functions of the leading-photon transverse energy, the leading-jet transverse momentum, the azimuthal angular separation between the photon and the jet, the photonâjet invariant mass and the scattering angle in the photonâjet centre-of-mass system. Tree-level plus parton-shower predictions from Sherpa and Pythia as well as next-to-leading-order QCD predictions from Jetphox and Sherpa are compared to the measurements
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