33,078 research outputs found
Constitutive response of Rene 80 under thermal mechanical loads
The applicability of a classical constitutive model for stress-strain analysis of a nickel base superalloy, Rene' 80, in the gas turbine thermomechanical fatigue (TMF) environment is examined. A variety of tests were conducted to generate basic material data and to investigate the material response under cyclic thermomechanical loading. Isothermal stress-strain data were acquired at a variety of strain rates over the TMF temperature range. Creep curves were examined at 2 temperature ranges, 871 to 982 C and 760 to 871 C. The results provide optimism on the ability of the classical constitutive model for high temperature applications
Contribution of integrated farm management (IFM) to Defra objectives
A farming system comprises a complex of interrelated and interacting factors. Any study of an isolated part of the system will not provide adequate understanding of the behaviour of the entire system and interactions may be equally or more important than individual components. There is therefore a requirement for the development of integrated approaches and practices to help farming systems adapt to, eliminate or reduce the negative impacts of production on the environment. This must be achieved whilst maintaining the economic viability of the farm enterprise. Our analysis has confirmed that IFM techniques generally have far more beneficial than adverse effects on current Defra policy objectives. However, there are some notable ‘conflicts’ where a technique that has a large beneficial effect in one policy area has a large negative effect in another. Carbon footprinting is used to quantify the impact of some integrated farming practices
Mobilising communities to address alcohol harm : an Alcohol Health Champion approach
In this article, Cathy Ure et al. look at engaging communities in order to reduce alcohol harms. By training Alcohol Health Champions, individuals can support vulnerable friends and family, and work within their communities to influence policy and promote change
Testing a Simplified Version of Einstein's Equations for Numerical Relativity
Solving dynamical problems in general relativity requires the full machinery
of numerical relativity. Wilson has proposed a simpler but approximate scheme
for systems near equilibrium, like binary neutron stars. We test the scheme on
isolated, rapidly rotating, relativistic stars. Since these objects are in
equilibrium, it is crucial that the approximation work well if we are to
believe its predictions for more complicated systems like binaries. Our results
are very encouraging.Comment: 9 pages (RevTeX 3.0 with 6 uuencoded figures), CRSR-107
Implementing an apparent-horizon finder in three dimensions
Locating apparent horizons is not only important for a complete understanding
of numerically generated spacetimes, but it may also be a crucial component of
the technique for evolving black-hole spacetimes accurately. A scheme proposed
by Libson et al., based on expanding the location of the apparent horizon in
terms of symmetric trace-free tensors, seems very promising for use with
three-dimensional numerical data sets. In this paper, we generalize this scheme
and perform a number of code tests to fully calibrate its behavior in
black-hole spacetimes similar to those we expect to encounter in solving the
binary black-hole coalescence problem. An important aspect of the
generalization is that we can compute the symmetric trace-free tensor expansion
to any order. This enables us to determine how far we must carry the expansion
to achieve results of a desired accuracy. To accomplish this generalization, we
describe a new and very convenient set of recurrence relations which apply to
symmetric trace-free tensors.Comment: 14 pages (RevTeX 3.0 with 3 figures
Computing the Similarity Between Moving Curves
In this paper we study similarity measures for moving curves which can, for
example, model changing coastlines or retreating glacier termini. Points on a
moving curve have two parameters, namely the position along the curve as well
as time. We therefore focus on similarity measures for surfaces, specifically
the Fr\'echet distance between surfaces. While the Fr\'echet distance between
surfaces is not even known to be computable, we show for variants arising in
the context of moving curves that they are polynomial-time solvable or
NP-complete depending on the restrictions imposed on how the moving curves are
matched. We achieve the polynomial-time solutions by a novel approach for
computing a surface in the so-called free-space diagram based on max-flow
min-cut duality
Gravitational waves from black hole-neutron star binaries I: Classification of waveforms
Using our new numerical-relativity code SACRA, long-term simulations for
inspiral and merger of black hole (BH)-neutron star (NS) binaries are
performed, focusing particularly on gravitational waveforms. As the initial
conditions, BH-NS binaries in a quasiequilibrium state are prepared in a
modified version of the moving-puncture approach. The BH is modeled by a
nonspinning moving puncture and for the NS, a polytropic equation of state with
and the irrotational velocity field are employed. The mass ratio of
the BH to the NS, , is chosen in the range between 1.5
and 5. The compactness of the NS, defined by , is chosen to be between 0.145 and 0.178. For a large value of for
which the NS is not tidally disrupted and is simply swallowed by the BH,
gravitational waves are characterized by inspiral, merger, and ringdown
waveforms. In this case, the waveforms are qualitatively the same as that from
BH-BH binaries. For a sufficiently small value of Q \alt 2, the NS may be
tidally disrupted before it is swallowed by the BH. In this case, the amplitude
of the merger and ringdown waveforms is very low, and thus, gravitational waves
are characterized by the inspiral waveform and subsequent quick damping. The
difference in the merger and ringdown waveforms is clearly reflected in the
spectrum shape and in the "cut-off" frequency above which the spectrum
amplitude steeply decreases. When an NS is not tidally disrupted (e.g., for
Q=5), kick velocity, induced by asymmetric gravitational wave emission, agrees
approximately with that derived for the merger of BH-BH binaries, whereas for
the case that the tidal disruption occurs, the kick velocity is significantly
suppressed.Comment: 25 pages, 3 jpg figures, accepted for publication in PRD; erratum is
added on Jul 23. 201
- …