1,474 research outputs found
Quasi-Homogeneous Thermodynamics and Black Holes
We propose a generalized thermodynamics in which quasi-homogeneity of the
thermodynamic potentials plays a fundamental role. This thermodynamic formalism
arises from a generalization of the approach presented in paper [1], and it is
based on the requirement that quasi-homogeneity is a non-trivial symmetry for
the Pfaffian form . It is shown that quasi-homogeneous
thermodynamics fits the thermodynamic features of at least some
self-gravitating systems. We analyze how quasi-homogeneous thermodynamics is
suggested by black hole thermodynamics. Then, some existing results involving
self-gravitating systems are also shortly discussed in the light of this
thermodynamic framework. The consequences of the lack of extensivity are also
recalled. We show that generalized Gibbs-Duhem equations arise as a consequence
of quasi-homogeneity of the thermodynamic potentials. An heuristic link between
this generalized thermodynamic formalism and the thermodynamic limit is also
discussed.Comment: 39 pages, uses RevteX. Published version (minor changes w.r.t. the
original one
Measurements of the effect of collisions on transverse beam halo diffusion in the Tevatron and in the LHC
Beam-beam forces and collision optics can strongly affect beam lifetime,
dynamic aperture, and halo formation in particle colliders. Extensive
analytical and numerical simulations are carried out in the design and
operational stage of a machine to quantify these effects, but experimental data
is scarce. The technique of small-step collimator scans was applied to the
Fermilab Tevatron collider and to the CERN Large Hadron Collider to study the
effect of collisions on transverse beam halo dynamics. We describe the
technique and present a summary of the first results on the dependence of the
halo diffusion coefficient on betatron amplitude in the Tevatron and in the
LHC.Comment: 4 pages, 2 figures. Submitted to the Proceedings of the ICFA
Mini-Workshop on Beam-beam Effects in Hadron Colliders (BB2013), Geneva,
Switzerland, 18-22 March 201
Petrological evidence in support of the death mask model for Ediacaran soft-bodied preservation in South Australia
Microbially mediated early diagenetic pyrite formation in the immediate vicinity of organic material has been the favoured mechanism by which to explain widespread preservation of soft-bodied organisms in late Ediacaran sedimentary successions, but an alternative rapid silicification model has been proposed for macrofossil preservation in sandstones of the Ediacara Member in South Australia. We here provide petrological evidence from Nilpena National Heritage Site and Ediacara Conservation Park to demonstrate the presence of grain-coating iron oxides, framboidal hematite, and clay minerals along Ediacara Member sandstone bedding planes, including fossil-bearing bed soles. SEM and petrographic data reveal that framboids and grain coatings, which we interpret as oxidized pyrite, formed before the precipitation of silica cements. In conjunction with geochemical and taphonomic considerations, our data suggest that anactualistically high concentrations of silica need not be invoked to explain Ediacara Member fossil preservation: we conclude that the pyritic âdeath maskâ model remains compelling.AGL is funded by the Natural Environment Research Council [grant number NE/L011409/2]. SM acknowledges support from the European Unionâs Horizon 2020 Research and Innovation Programme under Marie SkĆodowska-Curie grant agreement 747877 ... JJM recognises support from Mitacs ..
Evolutionary influences on the structure of red-giant acoustic oscillation spectra from 600d of Kepler observations
Context: The Kepler space mission is reaching continuous observing times long
enough to start studying the fine structure of the observed p-mode spectra.
Aims: In this paper, we aim to study the signature of stellar evolution on the
radial and p-dominated l=2 modes in an ensemble of red giants that show
solar-type oscillations. Results: We find that the phase shift of the central
radial mode (eps_c) is significantly different for red giants at a given large
frequency separation (Dnu_c) but which burn only H in a shell (RGB) than those
that have already ignited core He burning. Even though not directly probing the
stellar core the pair of local seismic observables (Dnu_c, eps_c) can be used
as an evolutionary stage discriminator that turned out to be as reliable as the
period spacing of the mixed dipole modes. We find a tight correlation between
eps_c and Dnu_c for RGB stars and no indication that eps_c depends on other
properties of these stars. It appears that the difference in eps_c between the
two populations becomes if we use an average of several radial orders, instead
of a local, i.e. only around the central radial mode, Dnu to determine the
phase shift. This indicates that the information on the evolutionary stage is
encoded locally, in the shape of the radial mode sequence. This shape turns out
to be approximately symmetric around the central radial mode for RGB stars but
asymmetric for core He burning stars. We computed radial modes for a sequence
of RG models and find them to qualitatively confirm our findings. We also find
that, at least in our models, the local Dnu is an at least as good and mostly
better proxy for both the asymptotic spacing and the large separation scaled
from the model density than the average Dnu. Finally, we investigate the
signature of the evolutionary stage on the small frequency separation and
quantify the mass dependency of this seismic parameter.Comment: 12 pages, 9 figures, accepted for publication in A&
Channeling and Volume Reflection Based Crystal Collimation of Tevatron Circulating Beam Halo (T-980)
The T980 crystal collimation experiment is underway at the Tevatron to
determine if this technique could increase 980 GeV beam-halo collimation
efficiency at high-energy hadron colliders such as the Tevatron and the LHC.
T980 also studies various crystal types and parameters. The setup has been
substantially enhanced during the Summer 2009 shutdown by installing a new
O-shaped crystal in the horizontal goniometer, as well as adding a vertical
goniometer with two alternating crystals (O-shaped and multi-strip) and
additional beam diagnostics. First measurements with the new system are quite
encouraging, with channeled and volume-reflected beams observed on the
secondary collimators as predicted. Investigation of crystal collimation
efficiencies with crystals in volume reflection and channeling modes are
described in comparison with an amorphous primary collimator. Results on the
system performance are presented for the end-of-store studies and for entire
collider stores. The first investigation of colliding beam collimation
simultaneously using crystals in both the vertical and horizontal plane has
been made in the regime with horizontally channeled and vertically
volume-reflected beams. Planning is underway for significant hardware
improvements during the FY10 summer shutdown and for dedicated studies during
the final year of Tevatron operation and also for a "post-collider beam physics
running" period.Comment: 3 pp. 1st International Particle Accelerator Conference: IPAC'10,
23-28 May 2010: Kyoto, Japa
Network information and connected correlations
Entropy and information provide natural measures of correlation among
elements in a network. We construct here the information theoretic analog of
connected correlation functions: irreducible --point correlation is measured
by a decrease in entropy for the joint distribution of variables relative
to the maximum entropy allowed by all the observed variable
distributions. We calculate the ``connected information'' terms for several
examples, and show that it also enables the decomposition of the information
that is carried by a population of elements about an outside source.Comment: 4 pages, 3 figure
Low-Temperature Fluorocarbonate Mineralization in Lower Devonian Rhynie Chert, UK
Funding: J.G.T.A was partially funded by the Natural Environment Research Council, grant number NE/T003677/1. Acknowledgments: We are grateful to W. Ritchie, J. Johnston, and J. Bowie for skilled technicalsupport. Samples were archived by N.H. Trewin, C.M. Rice and S. Fayers.Peer reviewedPublisher PD
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