10,059 research outputs found
Radio and X-ray observations of an exceptional radio flare in the extreme z=4.72 blazar GB B1428+4217
We report on the extreme behaviour of the high redshift blazar GB B1428+4217
at z=4.72. A continued programme of radio measurements has revealed an
exceptional flare in the lightcurve, with the 15.2 GHz flux density rising by a
factor ~3 from ~140 mJy to ~430 mJy in a rest-frame timescale of only ~4 months
-- much larger than any previous flares observed in this source. In addition to
new measurements of the 1.4-43 GHz radio spectrum we also present the analysis
and results of a target-of-opportunity X-ray observation using XMM-Newton, made
close to the peak in radio flux. Although the X-ray data do not show a flare in
the high energy lightcurve, we are able to confirm the X-ray spectral
variability hinted at in previous observations. GB B1428+4217 is one of several
high-redshift radio-loud quasars that display a low energy break in the X-ray
spectrum, probably due to the presence of excess absorption in the source.
X-ray spectral analysis of the latest XMM-Newton data is shown to be consistent
with the warm absorption scenario which we have hypothesized previously. Warm
absorption is also consistent with the observed X-ray spectral variability of
the source, in which the spectral changes can be successfully accounted-for
with a fixed column density of material in which the ionization state is
correlated with hardness of the underlying power-law emission.Comment: 8 pages, 5 figures, MNRAS accepte
Water exchange at a hydrated platinum electrode is rare and collective
We use molecular dynamics simulations to study the exchange kinetics of water
molecules at a model metal electrode surface -- exchange between water
molecules in the bulk liquid and water molecules bound to the metal. This
process is a rare event, with a mean residence time of a bound water of about
40 ns for the model we consider. With analysis borrowed from the techniques of
rare-event sampling, we show how this exchange or desorption is controlled by
(1) reorganization of the hydrogen bond network within the adlayer of bound
water molecules, and by (2) interfacial density fluctuations of the bulk liquid
adjacent to the adlayer. We define collective coordinates that describe the
desorption mechanism. Spatial and temporal correlations associated with a
single event extend over nanometers and tens of picoseconds.Comment: 10 pages, 9 figure
Stratigraphic Strips: Variable Dimensions
The two projects created for the exhibition discuss two forms of reality: ‘the constructed and the revealed’. The installation oscillates between the scientific reality of Howard’s painstaking conservationbased stratigraphy and a fictionalised representation of that knowledge through the use of historic colour windows placed at key locations within the East Wing. The actual layering of the decoration within each space is both real and speculative - the distinction between the two often blurred, providing the viewer with an insight into the life of the spaces they use.
Alan Chandler is a Specialist Conservation Architect with the London based practice Arts Lettres Techniques and a Reader in Architecture at the University of East London. Helen Howard is a Scientific Officer [Microscopist] at the National Gallery in London, an expert in non-invasive investigations of wall painting using optical coherence tomography and hyperspectral imaging. Architect Gilles Retsin works as senior designer at Kokkugia and directs computational architecture at the University of East London. Retsin’s computer coding explores the hidden structural details and materiality of buildings
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The use of the Continuously Regenerating Trap (CRT<sup>TM</sup>) and SCRT<sup>TM</sup> Systems to meet future emissions legislation
The progressive tightening of particulate matter (PM) legislation presents challenges to the engine development and aftertreatment communities. The Continuously Regenerating Trap (CRTTM) has been developed to enable diesel engines to meet the proposed future legislation. This passive filter system combines an oxidation catalyst with a Diesel Particulate Filter (DPF); the filter traps the PM and the oxidation catalyst generates NO2 which combusts the trapped PM at substantially lower temperatures than is possible using oxygen.
This paper outlines the operating principle of the CRTTM, and describes the performance of the system. It has been shown that the very high PM conversions obtained with the CRTTM can enable even Euro 1 engines to meet the PM limits proposed for introduction in Europe in 2005. In addition, the system removes PM across the whole particle size range, including ultrafine particulates. These results will be discussed, as will in-field durability studies which have shown that the system is still capable of converting 90% of PM after very high mileage operation (up to 600,000 km).
In addition to requiring very high PM conversion, the proposed future legislation requires substantial reductions in NOx emissions form heavy duty diesel vehicles. To meet these challenges the SCRTTM has been developed. This combines the CRTTM with SCR (Selective Catalytic Reduction) technology, and enables very high simultaneous conversions of CO, HC, PM and NOx to be achieved. The SCRTTM system is described, and its operating characteristics are discussed. It has been shown that the SCRTTM can potentially meet the legislative limits proposed for introduction in Europe in 2008
Perturbation theory of the mass enhancement for a polaron coupled to acoustic phonons
We use both a perturbative Green's function analysis and standard
perturbative quantum mechanics to calculate the decrease in energy and the
effective mass for an electron interacting with acoustic phonons. The
interaction is between the difference in lattice displacements for neighbouring
ions, and the hopping amplitude for an electron between those two sites. The
calculations are performed in one, two, and three dimensions, and comparisons
are made with results from other electron-phonon models. We also compute the
spectral function and quasiparticle residue, as a function of characteristic
phonon frequency. There are strong indications that this model is always
polaronic on one dimension, where an unusual relation between the effective
mass and the quasiparticle residue is also found.Comment: 9 pages, 5 figures, submitted to PR
Review of modern concepts in the engineering interpretation of earthquake response spectra
The design response spectrum is typically the starting point of most codified seismic design and assessment procedures and is used predominantly to prescribe the applied inertia forces induced by earthquake ground motions. This paper introduces and reviews modern concepts related to the effective development and application of earthquake design response spectra, including the conventional acceleration response spectrum, the velocity spectrum, and the displacement spectrum. It further briefly reviews the concepts of the inelastic response spectrum and the capacity spectrum. A number of the ideas presented are targeted particularly at assisting practising engineers working in low- and moderate-seismicity environments. The principal purpose is to enlighten engineers to modern concepts in response spectra development, in order to subsequently facilitate the effective use of the information contained in an earthquake response spectrum for both analysis and design applications.published_or_final_versio
Anisotropic spatially heterogeneous dynamics in a model glass-forming binary mixture
We calculated a four-point correlation function G_4(k,r;t) and the
corresponding structure factor S_4(k,q;t) for a model glass-forming binary
mixture. These functions measure the spatial correlations of the relaxation of
different particles. We found that these four-point functions are anisotropic
and depend on the angle between vectors k and r (or q). The anisotropy is the
strongest for times somewhat longer than the beta relaxation time but it is
quite pronounced even for times comparable to the alpha relaxation time,
tau_alpha. At the lowest temperatures S_4(k,q;tau_alpha) is strongly
anisotropic even for the smallest wavevector q accessible in our simulation
The E-3 Test Facility at Stennis Space Center: Research and Development Testing for Cryogenic and Storable Propellant Combustion Systems
This paper will provide the reader a broad overview of the current upgraded capabilities of NASA's John C. Stennis Space Center E-3 Test Facility to perform testing for rocket engine combustion systems and components using liquid and gaseous oxygen, gaseous and liquid methane, gaseous hydrogen, hydrocarbon based fuels, hydrogen peroxide, high pressure water and various inert fluids. Details of propellant system capabilities will be highlighted as well as their application to recent test programs and accomplishments. Data acquisition and control, test monitoring, systems engineering and test processes will be discussed as part of the total capability of E-3 to provide affordable alternatives for subscale to full scale testing for many different requirements in the propulsion community
Implementation of the Hierarchical Reference Theory for simple one-component fluids
Combining renormalization group theoretical ideas with the integral equation
approach to fluid structure and thermodynamics, the Hierarchical Reference
Theory is known to be successful even in the vicinity of the critical point and
for sub-critical temperatures. We here present a software package independent
of earlier programs for the application of this theory to simple fluids
composed of particles interacting via spherically symmetrical pair potentials,
restricting ourselves to hard sphere reference systems. Using the hard-core
Yukawa potential with z=1.8/sigma for illustration, we discuss our
implementation and the results it yields, paying special attention to the core
condition and emphasizing the decoupling assumption's role.Comment: RevTeX, 16 pages, 2 figures. Minor changes, published versio
Dynamics of Annihilation II: Fluctuations of Global Quantities
We develop a theory for fluctuations and correlations in a gas evolving under
ballistic annihilation dynamics. Starting from the hierarchy of equations
governing the evolution of microscopic densities in phase space, we
subsequently restrict to a regime of spatial homogeneity, and obtain explicit
predictions for the fluctuations and time correlation of the total number of
particles, total linear momentum and total kinetic energy. Cross-correlations
between these quantities are worked out as well. These predictions are
successfully tested against Molecular Dynamics and Monte-Carlo simulations.
This provides strong support for the theoretical approach developed, including
the hydrodynamic treatment of the spectrum of the linearized Boltzmann
operator. This article is a companion paper to arXiv:0801.2299 and makes use of
the spectral analysis reported there.Comment: 19 page
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