350 research outputs found
On the nucleation of hadronic domains in the quark-hadron transition
We present numerical results on bubble profiles, nucleation rates and time
evolution for a weakly first-order quark-hadron phase transition in different
expansion scenarios. We confirm the standard picture of a cosmological
first-order phase transition, in which the phase transition is entirely
dominated by nucleation. We also show that, even for expansion rates much lower
than those expected in heavy-ion collisions nucleation is very unlikely,
indicating that the main phase conversion mechanism is spinodal decomposition.Comment: 4 pages, 2 images. To be published in the proceedings of SEWM 200
Modelling and analysis of asynchronous and synchronous torques in split-phase induction machines
In this thesis, the nature of asynchronous and synchronous torques in a split-phase induction machine is investigated and quantified.
The equivalent circuit for this type of machine is derived using the rotating field theory. It is extended to include harmonic effects. Using this model, winding harmonics and permeance harmonics may be calculated independently of each other so that the model can be used to analyse asynchronous torques from winding harmonics as well as synchronous torques from permeance harmonics. These are calculated separately. The asynchronous torques appear as perturbations in the steady-state torque-speed curve while the synchronous torques only appear at specific speeds. The synchronous torques are superimposed onto the torque-speed curves to model both effects together.
The model predictions are compared against test results using purpose-built experimental machines together with production machines. These have varying rotor bar number and skew. Different methods are used to assess the synchronous torques. It is found that measuring synchronous locking torque is not a straightforward matter; however, reasonable agreement is found between calculation and measurement.
The work highlights the need for the correct choice of stator and rotor slot numbers together with the effect skew has on reducing the synchronous and asynchronous locking torques
Density inhomogeneities in heavy ion collisions around the critical point
We study the hydrodynamical expansion of a hot and baryon-dense quark fluid
coupled to classical real-time evolution of the long wavelength modes of the
chiral field. Significant density inhomogeneities develop dynamically when the
transition to the symmetry-broken state occurs. We find that the amplitude of
the density inhomogeneities is larger for expansion trajectories crossing the
line of first-order transitions than for crossovers, which could provide some
information on the location of a critical point. A few possible experimental
signatures for inhomogeneous decoupling surfaces are mentioned briefly.Comment: 6 pages, 4 figures, accepted for publication in PL
Strange Fluctuations at RHIC
Robust statistical observables can be used to extract the novel isospin
fluctuations from background contributions in K-short K-plus measurements in
nuclear collisions. To illustrate how this can be done, we present new HIJING
and UrQMD computations of these observables.Comment: 4 pages, 2 figures, talk at Quark Matter 200
The role of noise and dissipation in the hadronization of the quark-gluon plasma
We discuss the role of noise and dissipation in the explosive spinodal
decomposition scenario of hadron production during the chiral transition after
a high-energy heavy ion collision. We use a Langevin description inspired by
nonequilibrium field theory to perform real-time lattice simulations of the
behavior of the chiral fields. Preliminary results for the interplay between
additive and multiplicative noise terms, as well as for non-Markovian
corrections, are also presented.Comment: 8 pages, invited talk at the Workshop on Quark Gluon Plasma
Thermalization, Vienna, August 10-12, 200
Study of the Fluctuations of Net-charge and Net-protons Using Higher Order Moments
We present the STAR preliminary results on mid-rapidity and low transverse
momentum mean, standard deviation, skewness, and kurtosis of net-charge and
net-proton distributions in Au+Au and Cu+Cu collisions at = 200
GeV for various collision centralities. All the measured high moments of these
distributions can be scaled by the number of participating nucleons, consistent
with the soft process emissions. The ratios of fourth to second order cumulants
of both the net-charge and net-proton distributions are consistent with models
without QCD critical point.Comment: 4 pages, 3 figures - To appear in the conference proceedings for
Quark Matter 2009, March 30 - April 4, Knoxville, Tennesse
Explosive Decomposition in Ultrarelativistic Heavy Ion Collision
Recent results from Au+Au collisions at BNL-RHIC energy hint at explosive hadron production at the QCD transition rather than soft hydrodynamic evolution. We speculate that this is due to a rapid variation of the effective potential for QCD close to Tc. Performing real-time lattice simulations of an effective theory we show that the fast evolution of the potential leads to ``explosive'' spinodal decomposition rather than bubble nucleation or critical slowing down
- …