20 research outputs found
Holographic Equilibration under External Dynamical Electric Field
The holographic equilibration of a far-from-equilibrium strongly coupled
gauge theory is investigated. The dynamics of a probe D7-brane in an AdS-Vaidya
background is studied in the presence of an external time-dependent electric
field. Defining the equilibration times and , at which
condensation and current relax to their final equilibrated values, receptively,
the smallness of transition time or is enough to observe a
universal behaviour for re-scaled equilibration times
and . Moreover, regardless of the values for and
, also behaves universally for large enough value of
the ratio of the final electric field to final temperature. Then a simple
discussion of the static case reveals that . For an
out-of-equilibrium process, our numerical results show that, apart from the
cases for which is small, the static time ordering persists.Comment: 6 pages, 8 figure
A Classical String in Lifshitz-Vaidya Geometry
We study the time evolution of the expectation value of a rectangular Wilson
loop in strongly anisotropic time-dependent plasma using gauge-gravity duality.
The corresponding gravity theory is given by describing time evolution of a
classical string in the Lifshitz-Vaidya background. We show that the
expectation value of the Wilson loop oscillates about the value of the static
potential with the same parameters after the energy injection is over. We
discuss how the amplitude and frequency of the oscillation depend on the
parameters of the theory. In particular, by raising the anisotropy parameter,
we observe that the amplitude and frequency of the oscillation increase.Comment: 19 pages, 5 figure
Far-from-equilibrium initial conditions probed by a nonlocal observable
Using the gauge/gravity duality, we investigate the evolution of an
out-of-equilibrium strongly-coupled plasma from the viewpoint of the two-point
function of scalar gauge-invariant operators with large conformal dimension.
This system is out of equilibrium due to the presence of anisotropy and/or a
massive scalar field. Considering various functions for the initial anisotropy
and scalar field, we conclude that the effect of the anisotropy on the
evolution of the two-point function is considerably more than the effect of the
scalar field. We also show that the ordering of the equilibration time of the
one-point function for the non-probe scalar field and the correlation function
between two points with a fixed separation can be reversed by changing the
initial configuration of the plasma, when the system is out of the equilibrium
due to the presence of at least two different sources like our problem. In
addition, we find the equilibration time of the two-point function to be
linearly increasing with respect to the separation of the two points with a
fixed slope, regardless of the initial configuration that we start with.
Finally we observe that, for larger separations the geodesic connecting two
points on the boundary crosses the event horizon after it has reached its final
equilibrium value, meaning that the two-point function can probe behind the
event horizon
The Radiative Corrections to the Mass of the Kink Using an Alternative Renormalization Program
In this paper we compute the radiative correction to the mass of the kink in
theory in 1+1 dimensions, using an alternative renormalization
program. In this newly proposed renormalization program the breaking of the
translational invariance and the topological nature of the problem, due to the
presence of the kink, is automatically taken into account. This will naturally
lead to uniquely defined position dependent counterterms. We use the mode
number cutoff in conjunction with the above program to compute the mass of the
kink up to and including the next to the leading order quantum correction. We
discuss the differences between the results of this procedure and the
previously reported ones.Comment: 8 pages, 2 figures. arXiv admin note: substantial text overlap with
arXiv:0806.036
Optimum design of microchannel heat sinks
Analyses have been performed to obtain momentum and thermal characteristics in microchannel heat sinks. The applicability of existing correlations for friction factor and Nusselt number is investigated. The study revealed that existing correlations based on the analytical results can predict the heat sink performance to within the accuracy limits acceptable for use in design. A user friendly computer code has been developed as an aid in the optimum design of microchannel heat sinks. The program, using thermal resistance models, operates in two modes, In mode one, the performance capabilities, power requirements and efficiencies of an existing heat sink design are evaluated. Mode two is used as a design tool for heat sink optimization. In this mode, given the overall heat sink geometry, fluid and substrate properties, and inlet and outlet boundary conditions, the program determines the optimum channel spacing and fin thickness. Implementation of the optimization scheme is presented and its effectiveness is evaluated. Improvements of up to 45% in heat transfer rates are observed by analyzing thermal resistance surface plots for wide ranges of fin thickness and channel spacing. In addition, the idea of designing heat sinks for turbulent conditions rather than laminar are examined. The results show that significant reductions in the total thermal resistance are not achieved by designing for turbulent flow. In contrast, significantly higher pumping power requirements are realized when designing for turbulent flow with only slight improvement in overall thermal performance