107,808 research outputs found
The role of active galactic nuclei in galaxy formation
We use Monte-Carlo Markov chain techniques to constrain acceptable parameter
regions for the Munich L-Galaxies semi-analytic galaxy formation model.
Feedback from active galactic nuclei (AGN) is required to limit star-formation
in the most massive galaxies. However, we show that the introduction of tidal
stripping of dwarf galaxies as they fall into and merge with their host systems
can lead to a reduction in the required degree of AGN feedback. In addition,
the new model correctly reproduces both the metallicity of large galaxies and
the fraction of intracluster light.Comment: Monster's Fiery Breath Conference Proceedings, 4 page
The First Moments of Nucleon Generalized Parton Distributions
We extrapolate the first moments of the generalized parton distributions
using heavy baryon chiral perturbation theory. The calculation is based on the
one loop level with the finite range regularization. The description of the
lattice data is satisfactory and the extrapolated moments at physical pion mass
are consistent with the results obtained with dimensional regularization,
although the extrapolation in the momentum transfer to does show
sensitivity to form factor effects which lie outside the realm of chiral
perturbation theory. We discuss the significance of the results in the light of
modern experiments as well as QCD inspired models.Comment: 14 pages, 9 figure
Studies of noble-metal thermocouple stability at high temperatures
Two investigatory studies on performance characteristics of noble-metal thermocouples are described. (1) thermoelectric stability as affected by preferential oxidation of iridium in the system iridium-40% rhodium versus iridium, and (2) the effects of temperature gradients on the emf stability of the systems platinum-13% rhodium versus platinum and iridium-40% rhodium versus iridium, operating in air. The stability investigation was carried out at three temperatures - 1700, 1850, and 2000 C - by comparing the output of the test thermocouple in air with the output of an identically constructed reference thermocouple in nitrogen. The results show that no calibration shift was observed producing a change in output greater than that corresponding to a 2.0% change in the indicated temperature for all samples tested. The investigation of gradient effects was carried out by subjecting test thermocouples to both severe and mild gradients for periods up to 200 hours. For the platinum system, the operating temperature was 1500 C with gradients of 1475 and 700 C/cm; for the iridium system, 2000 C with gradients of 700, 1500, and 1975 C/cm. Exposure to temperature gradients was found to introduce significant changes in calibration for both systems. In both investigations, the thermoelements were examined by means of electron-probe analysis and by metallographic methods to detect chemical and structural changes. Data and micrographs are presented
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The Law Commission presumption concerning the dependability of computer evidence
We consider the condition set out in section 69(1)(b) of the Police and Criminal Evidence Act 1984 (PACE 1984) that reliance on computer evidence should be subject to proof of its correctness, and compare it to the 1997 Law Commission recommendation that acommon law presumption be used that a computer operated correctly unless there is explicit evidence to the contrary (LC Presumption). We understand the LC Presumption prevails in current legal proceedings. We demonstrate that neither section 69(1)(b) of PACE 1984 nor the LC presumption reflects the reality of general software-based system behaviour
Pure sea-quark contributions to the magnetic form factors of baryons
We propose the pure sea-quark contributions to the magnetic form factors of
baryons, and , as priority
observables for the examination of sea-quark contributions to baryon structure,
both in present lattice QCD simulations and possible future experimental
measurement. , the -quark contribution to the magnetic form
factor of , and , the -quark contribution to the
magnetic form factor of , are similar to the strange quark
contribution to the magnetic form factor of the nucleon, but promise to be
larger by an order of magnitude. We explore the size of this quantity within
chiral effective field theory, including both octet and decuplet intermediate
states. The finite range regularization approach is applied to deal with
ultraviolet divergences. Drawing on an established connection between quenched
and full QCD, this approach makes it possible to predict the sea quark
contribution to the magnetic form factor purely from the meson loop. In the
familiar convention where the quark charge is set to unity . We find a value of , which is
about seven times larger than the strange magnetic moment of the nucleon found
in the same approach. Including quark charge factors, the -quark
contribution to the magnetic moment exceeds the strange quark
contribution to the nucleon magnetic moment by a factor of 14.Comment: 5 pages, 3 figures. arXiv admin note: text overlap with
arXiv:1312.337
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