75,121 research outputs found
QCD Critical Point in a Quasiparticle Model
Recent theoretical investigations have unveiled a rich structure in the
quantum chromodynamics (QCD) phase diagram which consists of quark gluon plasma
(QGP) and the hadronic phases but also supports the existence of a cross-over
transition ending at a critical end point (CEP). We find a too large variation
in determination of the coordinates of the CEP in the temperature (T), baryon
chemical potential () plane and, therefore, its identification in the
current heavy-ion experiments becomes debatable. Here we use an equation of
state (EOS) for a deconfined QGP using a thermodynamically consistent
quasiparticle model involving quarks and gluons having thermal masses. We
further use a thermodynamically consistent excluded volume model for the hadron
gas (HG) which was recently proposed by us. Using these equations of state, a
first order deconfining phase transition is constructed using Gibbs' criteria.
This leads to an interesting finding that the phase transition line ends at a
critical point (CEP) beyond which a cross-over region exists. Using our thermal
HG model, we obtain a chemical freeze out curve and we find that the CEP lies
in close proximity to this curve as proposed by some authors. The coordinates
of CEP are found to lie within the reach of RHIC experiment.Comment: 15 pages, 3 figures, 1 table; minor corrections, to be appeared in
Phys. Rev.
Consideration of the relationship between Kepler and cyclotron dynamics leading to prediction of a non-MHD gravity-driven Hamiltonian dynamo
Conservation of canonical angular momentum shows that charged particles are
typically constrained to stay within a poloidal Larmor radius of a poloidal
magnetic flux surface. However, more detailed consideration shows that
particles with a critical charge to mass ratio can have zero canonical angular
momentum and so be both immune from centrifugal force and not constrained to
stay in the vicinity of a specific flux surface. Suitably charged dust grains
can have zero canonical angular momentum and in the presence of a gravitational
field will spiral inwards across poloidal magnetic surfaces toward the central
object and accumulate. This accumulation results in a gravitationally-driven
dynamo, i.e., a mechanism for converting gravitational potential energy into a
battery-like electric power source.Comment: 14 pages, 1 figur
Transient and steady-state shear banding in a lamellar phase as studied by Rheo-NMR
Flow fields and shear-induced structures in the lamellar (L-alpha) phase of the system triethylene glycol mono n-decyl ether (C10E3)/water were investigated by NMR velocimetry, diffusometry, and H-2 NMR spectroscopy. The transformation from multilamellar vesicles (MLVs) to aligned planar lamellae is accompanied by a transient gradient shear banding. A high-shear-rate band of aligned lamellae forms next to the moving inner wall of the cylindrical Couette shear cell while a low-shear-rate band of the initial MLV structure remains close to the outer stationary wall. The band of layers grows at the expense of the band of MLVs until the transformation is completed. This process scales with the applied strain. Wall slip is a characteristic of the MLV state, while aligned layers show no deviation from Newtonian flow. The homogeneous nature of the opposite transformation from well aligned layers to MLVs via an intermediate structure resembling undulated multilamellar cylinders is confirmed. The strain dependence of this transformation appears to be independent of temperature. The shear diagram, which represents the shear-induced structures as a function of temperature and shear rate, contains a transition region between stable layers and stable MLVs. The steady-state structures in the transition region show a continuous change from layer-like at high temperature to MLV-like at lower temperature. These structures are homogeneous on a length scale above a few micrometers
Conjugate gradient solvers on Intel Xeon Phi and NVIDIA GPUs
Lattice Quantum Chromodynamics simulations typically spend most of the
runtime in inversions of the Fermion Matrix. This part is therefore frequently
optimized for various HPC architectures. Here we compare the performance of the
Intel Xeon Phi to current Kepler-based NVIDIA Tesla GPUs running a conjugate
gradient solver. By exposing more parallelism to the accelerator through
inverting multiple vectors at the same time, we obtain a performance greater
than 300 GFlop/s on both architectures. This more than doubles the performance
of the inversions. We also give a short overview of the Knights Corner
architecture, discuss some details of the implementation and the effort
required to obtain the achieved performance.Comment: 7 pages, proceedings, presented at 'GPU Computing in High Energy
Physics', September 10-12, 2014, Pisa, Ital
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