27,762 research outputs found
Lattice QCD at non-vanishing density: phase diagram, equation of state
We propose a method to study lattice QCD at non-vanishing temperature (T) and
chemical potential (\mu). We use n_f=2+1 dynamical staggered quarks with
semi-realistic masses on L_t=4 lattices. The critical endpoint (E) of QCD on
the Re(\mu)-T plane is located. We calculate the pressure (p), the energy
density (\epsilon) and the baryon density (n_B) of QCD at non-vanishing T and
\mu.Comment: Contributed to Workshop on Strong and Electroweak Matter (SEWM 2002),
Heidelberg, Germany, 2-5 Oct 200
The QCD equation of state at finite T/\mu on the lattice
We present N_t=4 lattice results for the equation of state of 2+1 flavour
staggered, dynamical QCD at finite temperature and chemical potential. We use
the overlap improving multi-parameter reweighting technique to extend the
equation of state for non-vanishing chemical potentials. The results are
obtained along the line of constant physics. Our physical parameters extend in
temperature and baryon chemical potential upto \approx 500-600 MeV.Comment: 13 pages 9 figures, talk given at Finite Density QCD at Nara, Nara,
Japan, 10-12 July 200
Symmetry-surfing the moduli space of Kummer K3s.
A maximal subgroup of the Mathieu group M24 arises as the combined
holomorphic symplectic automorphism group of all Kummer surfaces whose Kaehler
class is induced from the underlying complex torus. As a subgroup of M24, this
group is the stabilizer group of an octad in the Golay code. To meaningfully
combine the symmetry groups of distinct Kummer surfaces, we introduce the
concepts of Niemeier markings and overarching maps between pairs of Kummer
surfaces. The latter induce a prescription for symmetry-surfing the moduli
space, while the former can be seen as a first step towards constructing a
vertex algebra that governs the elliptic genus of K3 in an M24-compatible
fashion. We thus argue that a geometric approach from K3 to Mathieu Moonshine
may bear fruit.Comment: 20 pages; minor changes; accepted for publication in the Proceedings
Volume of String-Math 201
Towards the QCD phase diagram from analytical continuation
We calculate the QCD cross-over temperature, the equation of state and
fluctuations of conserved charges at finite density by analytical continuation
from imaginary to real chemical potentials. Our calculations are based on new
continuum extrapolated lattice simulations using the 4stout staggered actions
with a lattice resolution up to . The simulation parameters are tuned
such that the strangeness neutrality is maintained, as it is in heavy ion
collisions.Comment: 4 pages, 2 figures, Proceedings of the Quark Matter 2015 conference,
Kobe, Japa
Robo-line storage: Low latency, high capacity storage systems over geographically distributed networks
Rapid advances in high performance computing are making possible more complete and accurate computer-based modeling of complex physical phenomena, such as weather front interactions, dynamics of chemical reactions, numerical aerodynamic analysis of airframes, and ocean-land-atmosphere interactions. Many of these 'grand challenge' applications are as demanding of the underlying storage system, in terms of their capacity and bandwidth requirements, as they are on the computational power of the processor. A global view of the Earth's ocean chlorophyll and land vegetation requires over 2 terabytes of raw satellite image data. In this paper, we describe our planned research program in high capacity, high bandwidth storage systems. The project has four overall goals. First, we will examine new methods for high capacity storage systems, made possible by low cost, small form factor magnetic and optical tape systems. Second, access to the storage system will be low latency and high bandwidth. To achieve this, we must interleave data transfer at all levels of the storage system, including devices, controllers, servers, and communications links. Latency will be reduced by extensive caching throughout the storage hierarchy. Third, we will provide effective management of a storage hierarchy, extending the techniques already developed for the Log Structured File System. Finally, we will construct a protototype high capacity file server, suitable for use on the National Research and Education Network (NREN). Such research must be a Cornerstone of any coherent program in high performance computing and communications
Effective grain surface area in the formation of molecular hydrogen in interstellar clouds
In the interstellar clouds, molecular hydrogens are formed from atomic
hydrogen on grain surfaces. An atomic hydrogen hops around till it finds
another one with which it combines. This necessarily implies that the average
recombination time, or equivalently, the effective grain surface area depends
on the relative numbers of atomic hydrogen influx rate and the number of sites
on the grain. Our aim is to discover this dependency. We perform a numerical
simulation to study the recombination of hydrogen on grain surfaces in a
variety of cloud conditions. We use a square lattice (with a periodic boundary
condition) of various sizes on two types of grains, namely, amorphous carbon
and olivine. We find that the steady state results of our simulation match very
well with those obtained from a simpler analytical consideration provided the
`effective' grain surface area is written as , where, is
the actual physical grain area and is a function of the flux of atomic
hydrogen which is determined from our simulation. We carry out the simulation
for various astrophysically relevant accretion rates. For high accretion rates,
small grains tend to become partly saturated with and and the
subsequent accretion will be partly inhibited. For very low accretion rates,
the number of sites to be swept before a molecular hydrogen can form is too
large compared to the actual number of sites on the grain, implying that
is greater than unity.Comment: 8 pages, 5 figures in eps forma
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