4,922,482 research outputs found
Enumeration of self avoiding trails on a square lattice using a transfer matrix technique
We describe a new algebraic technique, utilising transfer matrices, for
enumerating self-avoiding lattice trails on the square lattice. We have
enumerated trails to 31 steps, and find increased evidence that trails are in
the self-avoiding walk universality class. Assuming that trails behave like , we find and .Comment: To be published in J. Phys. A:Math Gen. Pages: 16 Format: RevTe
Coulomb potential from a particle in uniform ultrarelativistic motion
The Coulomb potential produced by an ultrarelativistic particle (such as a
heavy ion) in uniform motion is shown in the appropriate gauge to factorize
into a longitudinal Dirac delta function of (z - t) times the simple two
dimensional potential solution in the transverse direction. This form makes
manifest the source of the energy independence of the interaction.Comment: 5 pages, latex, revtex source, no figure
Hydrodynamic simulations of correlation and scatter in galaxy cluster maps
The two dimensional structure of hot gas in galaxy clusters contains
information about the hydrodynamical state of the cluster, which can be used to
understand the origin of scatter in the thermodynamical properties of the gas,
and to improve the use of clusters to probe cosmology. Using a set of
hydrodynamical simulations, we provide a comparison between various maps
currently employed in the X-ray analysis of merging clusters and those cluster
maps anticipated from forthcoming observations of the thermal
Sunyaev-Zel'dovich effect. We show the following: 1) an X-ray pseudo-pressure,
defined as square root of the soft band X-ray image times the temperature map
is a good proxy for the SZ map; 2) we find that clumpiness is the main reason
for deviation between X-ray pseudo-pressure and SZ maps; 3) the level of
clumpiness can be well characterized by X-ray pseudo-entropy maps. 4) We
describe the frequency of deviation in various maps of clusters as a function
of the amplitude of the deviation. This enables both a comparison to
observations and a comparison to effects of introduction of complex physical
processes into simulation.Comment: 7 pages, A&A in pres
Temperature effects on material characteristics
Some of the physical properties of the main elements of interest in
high temperature technology are reviewed. Some general trends emerge
when these properties are viewed as a function of melting point, but there
are a few notable exceptions. Titanium, zirconium, niobium and tantalum
all have disappointingly low moduli; chromium is excellent in many ways,
but has a limited ductility at lower temperatures; molybdenum oxidises
catastrophically above about 700° C, and niobium suffers from severe
oxygen embrittlement. Beryllium and carbon (in the graphitic form) both
stand out as exceptional materials, both have very low densities, beryllium
a very high modulus but an unfortunately low ductility, while graphite has
a relatively low strength at the lower temperatures, although at temperatures
of 2000° C and above it emerges as a quite exceptional (and probably as the
ultimate) high temperature material. Some of the fundamental factors
involved in high temperature material development are examined, in the
light, particularly, of past progress with the nickel alloys. If a similar
progress can be achieved with other base elements then a considerable
margin still remains to be exploited. Protection from oxidation at high
temperatures is evidently a factor of major concern, not only with metals,
but with graphite also. Successful coatings are therefore of high importance and the questions they raise, such as bonding, differential thermal expansion,
and so on, represent aspects of an even wider class covered by the term
“composite structures". Such structures appear to offer the only serious
solution to many high temperature requirements, and their design,
construction and utilization has created a whole series of new exercises
in materials assessment. Matters have become so complex, that a very
radical and fundamental reassessment is required if we are to change, in
any very significant way, the wasteful and ad hoc methods which characterise
so much of present-day materials engineering
The 2+2-Signature and the 1+1-Matrix-Brane
We discuss different aspects of the 2+2-signature from the point of view of
the quatl theory. In particular, we compare two alternative approaches to such
a spacetime signature, namely the 1+1-matrix-brane and the 2+2-target spacetime
of a string. This analysis also reveals hidden discrete symmetries of the
2+2-brane action associated with the 2+2-dimensional sector of a
2+10-dimensional target background.Comment: 12 pages, Latex, to appear in Mod. Phys. Lett.
Remarks on Weyl invariant p-branes and Dp-branes
A mechanism to find different Weyl invariant p-branes and Dp-branes actions
is explained. Our procedure clarifies the Weyl invariance for such systems.
Besides, by considering gravity-dilaton effective action in higher dimensions
we also derive a Weyl invariant action for p-branes. We argue that this
derivation provides a geometrical scenario for the Weyl invariance of p-branes.
Our considerations can be extended to the case of super-p-branes.Comment: 18 pages, Late
Meadow enriched ACP process algebras
We introduce the notion of an ACP process algebra. The models of the axiom
system ACP are the origin of this notion. ACP process algebras have to do with
processes in which no data are involved. We also introduce the notion of a
meadow enriched ACP process algebra, which is a simple generalization of the
notion of an ACP process algebra to processes in which data are involved. In
meadow enriched ACP process algebras, the mathematical structure for data is a
meadow.Comment: 8 pages; correction in Table
R^2 Dark Matter
There is a non-trivial four-derivative extension of the gravitational
spectrum that is free of ghosts and phenomenologically viable. It is the so
called -gravity since it is defined by the only addition of a term
proportional to the square of the scalar curvature. Just the presence of this
term does not improve the ultraviolet behaviour of Einstein gravity but
introduces one additional scalar degree of freedom that can account for the
dark matter of our Universe.Comment: 6 pages, 1 figure, to appear in the Proceedings of the sixth
International Workshop on the Dark Side of the Universe (DSU2010) Leon,
Guanajuato, Mexico 1-6 June 201
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