39,698 research outputs found
Streamlined life cycle assessment of transparent silica aerogel made by supercritical drying
This is the post-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2011 ElsevierWhen developing sustainable building fabric technologies, it is essential that the energy use and CO2 burden arising from manufacture does not outweigh the respective in-use savings. This study investigates this paradigm by carrying out a streamlined life cycle assessment (LCA) of silica aerogel. This unique, nanoporous translucent insulation material has the lowest thermal conductivity of any solid, retaining up to four times as much heat as conventional insulation, whilst being highly transparent to light and solar radiation. Monolithic silica aerogel has been cited as the âholy grailâ of future glazing technology. Alternatively, translucent granular aerogel is now being produced on a commercial scale. In each case, many solvents are used in production, often accompanied by intensive drying processes, which may consume large amounts of energy and CO2. To date, there has been no peer-reviewed LCA of this material conducted to the ISO 14000 standard. Primary data for this âcradle-to-factory gateâ LCA is collected for silica aerogel made by low and high temperature supercritical drying. In both cases, the mass of raw materials and electricity usage for each process is monitored to determine the total energy use and CO2 burden. Findings are compared against the predicted operational savings arising from retrofitting translucent silica aerogel to a single glazed window to upgrade its thermal performance. Results should be treated as a conservative estimate as the aerogel is produced in a laboratory, which has not been developed for mass manufacture or refined to reduce its environmental impact. Furthermore, the samples are small and assumptions to upscale the manufacturing volume occur without major changes to production steps or equipment used. Despite this, parity between the CO2 burden and CO2 savings is achieved in less than 2 years, indicating that silica aerogel can provide a measurable environmental benefit.This work is funded by the EPSRC, Brunel University and Buro Happold Ltd, the University of Bath is funded by the EPSRC grant EP/F018622/1
Use of the painDETECT tool in rheumatoid arthritis suggests neuropathic and sensitization components in pain reporting.
Rheumatoid arthritis (RA) is an inflammatory autoimmune condition typified by systemic inflammation targeted toward synovial joints. Inhibition of proinflammatory networks by disease-modifying antirheumatic drugs, eg, methotrexate and biologic therapies, including tumor necrosis factor-α inhibitors, often leads to suppression of disease activity observed at the clinical level. However, despite the era of widespread use of disease-modifying treatments, there remain significant groups of patients who continue to experience pain. Our study formulated a pain assessment tool in the arthritis clinic to assess feasibility of measurements including the visual analog scale (VAS) and painDETECT to assess multimodal features of pain in people with established RA (n=100). Clinical measures of disease activity (Disease Activity Score in 28 Joints [DAS28]) were also recorded. Our data showed that despite the majority of subjects on at least one disease-modifying agent, the majority of patients reported severe pain (54%) by VAS, despite well-controlled clinical disease, with mean DAS28 2.07±0.9. Using the painDETECT questionnaire, 67% of patients had unlikely neuropathic pain. A significant proportion of subjects (28%) had possible neuropathic pain and 5% had features of likely neuropathic pain by painDETECT scoring. We found a positive correlation between VAS and painDETECT (R (2)=0.757). Of note, the group who had likely or probable neuropathic pain also showed significantly increased pain reporting by VAS (P30) also had statistically higher proportions of pain reporting (VAS 89.0±0.7 mm) compared with subjects who had a normal body mass index (VAS 45.2±21.8 mm), P<0.05. Our findings suggest that multimodal features of pain perception exist in RA, including neuropathic and sensitization elements, perhaps explaining why a subgroup of people with RA continue to experience ongoing pain, despite their apparent suppression of inflammation
Cooperative orbital ordering and Peierls instability in the checkerboard lattice with doubly degenerate orbitals
It has been suggested that the metal-insulator transitions in a number of
spinel materials with partially-filled t_2g d-orbitals can be explained as
orbitally-driven Peierls instabilities. Motivated by these suggestions, we
examine theoretically the possibility of formation of such orbitally-driven
states within a simplified theoretical model, a two-dimensional checkerboard
lattice with two directional metal orbitals per atomic site. We include orbital
ordering and inter-atom electron-phonon interactions self-consistently within a
semi-classical approximation, and onsite intra- and inter-orbital
electron-electron interactions at the Hartree-Fock level. We find a stable,
orbitally-induced Peierls bond-dimerized state for carrier concentration of one
electron per atom. The Peierls bond distortion pattern continues to be period 2
bond-dimerization even when the charge density in the orbitals forming the
one-dimensional band is significantly smaller than 1. In contrast, for carrier
density of half an electron per atom the Peierls instability is absent within
one-electron theory as well as mean-field theory of electron-electron
interactions, even for nearly complete orbital ordering. We discuss the
implications of our results in relation to complex charge, bond, and
orbital-ordering found in spinels.Comment: 8 pages, 5 figures; revised versio
Expected characteristics of the subclass of Supernova Gamma-ray Bursts (S-GRBs)
The spatial and temporal coincidence between the gamma-ray burst (GRB) 980425
and supernova (SN) 1998bw has prompted speculation that there exists a class of
GRBs produced by SNe (``S-GRBs''). Robust arguments for the existence of a
relativistic shock have been presented on the basis of radio observations. A
physical model based on the radio observations lead us to propose the following
characteristics of supernovae GRBs (S-GRBs): 1) prompt radio emission and
implied brightness temperature near or below the inverse Compton limit, 2) high
expansion velocity of the optical photosphere as derived from lines widths and
energy release larger than usual, 3) no long-lived X-ray afterglow, and 4) a
single pulse (SP) GRB profile. Radio studies of previous SNe show that only
type Ib and Ic potentially satisfy the first condition. Accordingly we have
investigated proposed associations of GRBs and SNe finding no convincing
evidence (mainly to paucity of data) to confirm any single connection of a SN
with a GRB. If there is a more constraining physical basis for the burst
time-history of S-GRBs beyond that of the SP requirement, we suggest the 1% of
light curves in the BATSE catalogue similar to that of GRB 980425 may
constitute the subclass. Future optical follow-up of bursts with similar
profiles should confirm if such GRBs originate from some fraction of SN type
Ib/Ic.Comment: 11 pages of LaTeX with 1 figure. Submitted to the Astrophysical
Journal Letter
Determination of the Fermi Velocity by Angle-dependent Periodic Orbit Resonance Measurements in the Organic Conductor alpha-(BEDT-TTF)2KHg(SCN)4
We report detailed angle-dependent studies of the microwave (f=50 to 90 GHz)
interlayer magneto-electrodynamics of a single crystal sample of the organic
charge-density-wave (CDW) conductor alpha-(BEDT-TTF)2KHg(SCN)4. Recently
developed instrumentation enables both magnetic field (B) sweeps for a fixed
sample orientation and, for the first time, angle sweeps at fixed f/B. We
observe series' of resonant absorptions which we attribute to periodic orbit
resonances (POR) - a phenomenon closely related to cyclotron resonance. The
angle dependence of the POR indicate that they are associated with the low
temperature quasi-one-dimensional (Q1D) Fermi surface (FS) of the title
compound; indeed, all of the resonance peaks collapse beautifully onto a single
set of f/B versus angle curves, generated using a semiclassical
magneto-transport theory for a single Q1D FS. We show that Q1D POR measurements
provide one of the most direct methods for determining the Fermi velocity,
without any detailed assumptions concerning the bandstructure; our analysis
yields an average value of v_F=6.5x10^4 m/s. Quantitative analysis of the POR
harmonic content indicates that the Q1D FS is strongly corrugated. This is
consistent with the assumption that the low-temperature FS derives from a
reconstruction of the high temperature quasi-two-dimensional FS, caused by the
CDW instability. Detailed analysis of the angle dependence of the POR yields
parameters associated with the CDW superstructure which are consistent with
published results. Finally, we address the issue as to whether or not the
interlayer electrodynamics are coherent in the title compound.Comment: 28 pages, including 6 figures. Submitted to PR
Optical matrix elements in tight-binding models with overlap
We investigate the effect of orbital overlap on optical matrix elements in
empirical tight-binding models. Empirical tight-binding models assume an
orthogonal basis of (atomiclike) states and a diagonal coordinate operator
which neglects the intra-atomic part. It is shown that, starting with an atomic
basis which is not orthogonal, the orthogonalization process induces
intra-atomic matrix elements of the coordinate operator and extends the range
of the effective Hamiltonian. We analyze simple tight-binding models and show
that non-orthogonality plays an important role in optical matrix elements. In
addition, the procedure gives formal justification to the nearest-neighbor
spin-orbit interaction introduced by Boykin [Phys. Rev \textbf{B} 57, 1620
(1998)] in order to describe the Dresselahaus term which is neglected in
empirical tight-binding models.Comment: 16 pages 6 figures, to appear in Phys. Rev.
Absence of Hybridization Gap in Heavy Electron Systems and Analysis of YbAl3 in terms of Nearly Free Electron Conduction Band
In the analysis of the heavy electron systems, theoretical models with c-f
hybridization gap are often used. We point out that such a gap does not exist
and the simple picture with the hybridization gap is misleading in the metallic
systems, and present a correct picture by explicitly constructing an effective
band model of YbAl_3. Hamiltonian consists of a nearly free electron model for
conduction bands which hybridize with localized f-electrons, and includes only
a few parameters. Density of states, Sommerfeld coefficient, f-electron number
and optical conductivity are calculated and compared with the band calculations
and the experiments.Comment: 9 pages, 9 figures, submitted to J. Phys. Soc. Jp
Spitzer Space Telescope Observations of Circumbinary Dust Disks around Polars
We present Spitzer Space Telescope IRAC photometry of the magnetic cataclysmic variables EF Eri, MR Ser, VV Pup, V834 Cen, GG Leo and V347 Pav. When we combine our results with the 2MASS data, we find that at least five of the polars have flux densities in the mid-IR in excess of the emission expected from the stellar components alone. We are unable to model this mid-IR excess with cyclotron emission, but we can recreate the observed spectral energy distributions with the inclusion of a simple circumbinary dust disk model. Importantly, we find that the masses of our modelled disks are approximately 12 orders of magnitude lower than required to significantly affect CV evolution. The accretion disk-less polars are ideal places to search for these disks, since the luminous accretion disk in most CVs would drown out the faint IR signature of the cooler, dimmer circumbinary disks
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