1,016 research outputs found
Shuttle TPS thermal performance and analysis methodology
Thermal performance of the thermal protection system was approximately as predicted. The only extensive anomalies were filler bar scorching and over-predictions in the high Delta p gap heating regions of the orbiter. A technique to predict filler bar scorching has been developed that can aid in defining a solution. Improvement in high Delta p gap heating methodology is still under study. Minor anomalies were also examined for improvements in modeling techniques and prediction capabilities. These include improved definition of low Delta p gap heating, an analytical model for inner mode line convection heat transfer, better modeling of structure, and inclusion of sneak heating. The limited number of problems related to penetration items that presented themselves during orbital flight tests were resolved expeditiously, and designs were changed and proved successful within the time frame of that program
Unified chiral analysis of the vector meson spectrum from lattice QCD
The chiral extrapolation of the vector meson mass calculated in
partially-quenched lattice simulations is investigated. The leading one-loop
corrections to the vector meson mass are derived for partially-quenched QCD. A
large sample of lattice results from the CP-PACS Collaboration is analysed,
with explicit corrections for finite lattice spacing artifacts. To incorporate
the effect of the opening decay channel as the chiral limit is approached, the
extrapolation is studied using a necessary phenomenological extension of chiral
effective field theory. This chiral analysis also provides a quantitative
estimate of the leading finite volume corrections. It is found that the
discretisation, finite-volume and partial quenching effects can all be very
well described in this framework, producing an extrapolated value of M_\rho in
excellent agreement with experiment. This procedure is also compared with
extrapolations based on polynomial forms, where the results are much less
enlightening.Comment: 30 pages, 13 fig
Chiral and Continuum Extrapolation of Partially-Quenched Lattice Results
The vector meson mass is extracted from a large sample of partially quenched,
two-flavor lattice QCD simulations. For the first time, discretisation,
finite-volume and partial quenching artefacts are treated in a unified
framework which is consistent with the low-energy behaviour of QCD. This
analysis incorporates the leading infrared behaviour dictated by chiral
effective field theory. As the two-pion decay channel cannot be described by a
low-energy expansion alone, a highly-constrained model for the decay channel of
the rho-meson is introduced. The latter is essential for extrapolating lattice
results from the quark-mass regime where the rho is observed to be a physical
bound state.Comment: 9 pages, 3 figures; revised version appearing in PL
Chiral and Continuum Extrapolation of Partially-Quenched Hadron Masses
Using the finite-range regularisation (FRR) of chiral effective field theory,
the chiral extrapolation formula for the vector meson mass is derived for the
case of partially-quenched QCD. We re-analyse the dynamical fermion QCD data
for the vector meson mass from the CP-PACS collaboration. A global fit,
including finite lattice spacing effects, of all 16 of their ensembles is
performed. We study the FRR method together with a naive polynomial approach
and find excellent agreement ~1% with the experimental value of M_rho from the
former approach. These results are extended to the case of the nucleon mass.Comment: 6 pages, Contribution to Lattice2005, PoS styl
Observations of transients and pulsars with LOFAR international stations
The LOw FRequency ARray - LOFAR is a new radio telescope that is moving the
science of radio pulsars and transients into a new phase. Its design places
emphasis on digital hardware and flexible software instead of mechanical
solutions. LOFAR observes at radio frequencies between 10 and 240 MHz where
radio pulsars and many transients are expected to be brightest. Radio frequency
signals emitted from these objects allow us to study the intrinsic pulsar
emission and phenomena such as propagation effects through the interstellar
medium. The design of LOFAR allows independent use of its stations to conduct
observations of known bright objects, or wide field monitoring of transient
events. One such combined software/hardware solution is called the Advanced
Radio Transient Event Monitor and Identification System (ARTEMIS). It is a
backend for both targeted observations and real-time searches for millisecond
radio transients which uses Graphical Processing Unit (GPU) technology to
remove interstellar dispersion and detect millisecond radio bursts from
astronomical sources in real-time using a single LOFAR station.Comment: To appear in the proceedings of the Electromagnetic Radiation from
Pulsars and Magnetars conference, Zielona Gora, 2012. 4 pages, 1 figur
Proof that the Hydrogen-antihydrogen Molecule is Unstable
In the framework of nonrelativistic quantum mechanics we derive a necessary
condition for four Coulomb charges ,
where all masses are assumed finite, to form the stable system. The obtained
stability condition is physical and is expressed through the required minimal
ratio of Jacobi masses. In particular this provides the rigorous proof that the
hydrogen-antihydrogen molecule is unstable. This is the first result of this
sort for four particles.Comment: Submitted to Phys.Rev.Let
Quantum master equation descriptions of a nanomechanical resonator coupled to a single-electron transistor
We analyse the quantum dynamics of a nanomechanical resonator coupled to a
normal-state single-electron transistor (SET). Starting from a microscopic
description of the system, we derive a master equation for the SET island
charge and resonator which is valid in the limit of weak electro-mechanical
coupling. Using this master equation we show that, apart from brief transients,
the resonator always behaves like a damped harmonic oscillator with a shifted
frequency and relaxes into a thermal-like steady state. Although the behaviour
remains qualitatively the same, we find that the magnitude of the resonator
damping rate and frequency shift depend very sensitively on the relative
magnitudes of the resonator period and the electron tunnelling time. Maximum
damping occurs when the electrical and mechanical time-scales are the same, but
the frequency shift is greatest when the resonator moves much more slowly than
the island charge. We then derive reduced master equations which describe just
the resonator dynamics. By making slightly different approximations, we obtain
two different reduced master equations for the resonator. Apart from minor
differences, the two reduced master equations give rise to a consistent picture
of the resonator dynamics which matches that obtained from the master equation
including the SET island charge.Comment: 22 pages, 4 figure
Entanglement and decoherence of a micromechanical resonator via coupling to a Cooper box
We analyse the quantum dynamics of a micromechanical resonator capacitively
coupled to a Cooper box. With appropriate quantum state control of the Cooper
box, the resonator can be driven into a superposition of spatially separated
states. The Cooper box can also be used to probe the environmentally-induced
decoherence of the resonator superposition state.Comment: 4 pages, 3 figure
Beyond shareholder primacy? Reflections on the trajectory of UK corporate governance.
Core institutions of UK corporate governance, in particular the City Code on Takeovers and Mergers, the Combined Code on Corporate Governance and the law on directors’ duties, are strongly orientated towards the norm of shareholder primacy. Beyond the core, however, stakeholder interests are better represented, in particular at the intersection of insolvency and employment law. This reflects the influence of European Community laws on information and consultation of employees. In addition, there are signs that some institutional shareholders are redirecting their investment strategies, under government encouragement, away from a focus on short-term returns, in such a way as to favour stakeholder-inclusive practices by firms. On this basis we suggest that the UK system is currently in a state of flux and that the debate over shareholder primacy has not been concluded
Fermi point in graphene as a monopole in momentum space
We consider the effective field theory of graphene monolayer with the Coulomb
interaction between fermions taken into account. The gauge field in momentum
space is introduced. The position of the Fermi point coincides with the
position of the corresponding monopole. The procedure of extracting such
monopoles during lattice simulations is suggested.Comment: Latex, 12 page
- …