356 research outputs found
Asymptotic perfect fluid dynamics as a consequence of AdS/CFT
We study the dynamics of strongly interacting gauge-theory matter (modelling
quark-gluon plasma) in a boost-invariant setting using the AdS/CFT
correspondence. Using Fefferman-Graham coordinates and with the help of
holographic renormalization, we show that perfect fluid hydrodynamics emerges
at large times as the unique nonsingular asymptotic solution of the nonlinear
Einstein equations in the bulk. The gravity dual can be interpreted as a black
hole moving off in the fifth dimension. Asymptotic solutions different from
perfect fluid behaviour can be ruled out by the appearance of curvature
singularities in the dual bulk geometry. Subasymptotic deviations from perfect
fluid behaviour remain possible within the same framework.Comment: 19 pages, 1 figure; v2: free streaming example changed to s=1;
conclusions unchange
A numerical relativity approach to the initial value problem in asymptotically Anti-de Sitter spacetime for plasma thermalization - an ADM formulation
This article studies a numerical relativity approach to the initial value
problem in Anti-de Sitter spacetime relevant for dual non-equilibrium evolution
of strongly coupled non-Abelian plasma undergoing Bjorken expansion. In order
to use initial conditions for the metric obtained in arXiv:0906.4423 we
introduce new, ADM formalism-based scheme for numerical integration of
Einstein's equations with negative cosmological constant. The key novel element
of this approach is the choice of lapse function vanishing at fixed radial
position, enabling, if needed, efficient horizon excision. Various physical
aspects of the gauge theory thermalization process in this setup have been
outlined in our companion article arXiv:1103.3452. In this work we focus on the
gravitational side of the problem and present full technical details of our
setup. We discuss in particular the ADM formalism, the explicit form of initial
states, the boundary conditions for the metric on the inner and outer edges of
the simulation domain, the relation between boundary and bulk notions of time,
the procedure to extract the gauge theory energy-momentum tensor and
non-equilibrium apparent horizon entropy, as well as the choice of point for
freezing the lapse. Finally, we comment on various features of the initial
profiles we consider.Comment: 25 pages, 9 figures, 1 table; see also the companion article
arXiv:1103.3452; v2: typos fixed; v3: references added and updated, publishe
Viscous hydrodynamics relaxation time from AdS/CFT
We consider an expanding boost-invariant plasma at strong coupling using the
AdS/CFT correspondence for N=4 SYM. We determine the relaxation time in second
order viscous hydrodynamics and find that it is around thirty times shorter
than weak coupling expectations. We find that the nonsingularity of the dual
geometry in the string frame necessitates turning on the dilaton which leads to
a nonvanishing expectation value for tr F^2 behaving like tau^(-10/3).Comment: 10 pages, Mathematica script included in the source; v2: typo in (28)
fixed, statement about electric/magnetic modes correcte
Multiplying unitary random matrices - universality and spectral properties
In this paper we calculate, in the large N limit, the eigenvalue density of
an infinite product of random unitary matrices, each of them generated by a
random hermitian matrix. This is equivalent to solving unitary diffusion
generated by a hamiltonian random in time. We find that the result is universal
and depends only on the second moment of the generator of the stochastic
evolution. We find indications of critical behavior (eigenvalue spacing scaling
like ) close to for a specific critical evolution time
.Comment: 12 pages, 2 figure
Scaling Up Magnetic Nanobead Synthesis with Improved Stability for Biomedical Applications
The growing interest in multifunctional nano-objects based on polymers and magnetic nanoparticles for biomedical applications motivated us to develop a scale-up protocol to increase the yield of polymeric magnetic nanobeads while aiming at keeping the structural features at optimal conditions. The protocol was applied to two different types of magnetic ferrite nanoparticles: the Mn-ferrite selected for their properties as contrast agents in magnetic resonance imaging and iron oxide nanostar shaped nanoparticles chosen for their heat performance in magnetic hyperthermia. At the same time, some experiments on surface functionalization of nanobeads with amino modified polyethyelene glycol (PEG) molecules have provided further insight into the formation mechanism of magnetic nanobeads and the need to cross-link the polymer shell to improve the stability of the beads, making them more suitable for further manipulation and use. The present work summarizes the most important parameters required to be controlled for the upscaling of nanobead synthesis in a bench protocol and proposes an alternative cross-linking strategy based on prefunctionalization of the polymer prior to the nanobead formation as a key parameter to improve the nanobead structural stability in solutions at different pHs and during surface functionalization
Six and seven loop Konishi from Luscher corrections
In the present paper we derive six and seven loop formulas for the anomalous
dimension of the Konishi operator in N=4 SYM from string theory using the
technique of Luscher corrections. We derive analytically the integrand using
the worldsheet S-matrix and evaluate the resulting integral and infinite sum
using a combination of high precision numerical integration and asymptotic
expansion. We use this high precision numerical result to fit the integer
coefficients of zeta values in the final analytical answer. The presented six
and seven loop results can be used as a cross-check with FiNLIE on the string
theory side, or with direct gauge theory computations. The seven loop level is
the theoretical limit of this Luscher approach as at eight loops
double-wrapping corrections will appear.Comment: 18 pages, typos correcte
An fMRI study
Background Maternal sensitive behavior depends on recognizing one’s own
child’s affective states. The present study investigated distinct and
overlapping neural responses of mothers to sad and happy facial expressions of
their own child (in comparison to facial expressions of an unfamiliar child).
Methods We used functional MRI to measure dissociable and overlapping
activation patterns in 27 healthy mothers in response to happy, neutral and
sad facial expressions of their own school-aged child and a gender- and age-
matched unfamiliar child. To investigate differential activation to sad
compared to happy faces of one’s own child, we used interaction contrasts.
During the scan, mothers had to indicate the affect of the presented face.
After scanning, they were asked to rate the perceived emotional arousal and
valence levels for each face using a 7-point Likert-scale (adapted SAM
version). Results While viewing their own child’s sad faces, mothers showed
activation in the amygdala and anterior cingulate cortex whereas happy facial
expressions of the own child elicited activation in the hippocampus. Conjoint
activation in response to one’s own child happy and sad expressions was found
in the insula and the superior temporal gyrus. Conclusions Maternal brain
activations differed depending on the child’s affective state. Sad faces of
the own child activated areas commonly associated with a threat detection
network, whereas happy faces activated reward related brain areas. Overlapping
activation was found in empathy related networks. These distinct neural
activation patterns might facilitate sensitive maternal behavior
Wishart and Anti-Wishart random matrices
We provide a compact exact representation for the distribution of the matrix
elements of the Wishart-type random matrices , for any finite
number of rows and columns of , without any large N approximations. In
particular we treat the case when the Wishart-type random matrix contains
redundant, non-random information, which is a new result. This representation
is of interest for a procedure of reconstructing the redundant information
hidden in Wishart matrices, with potential applications to numerous models
based on biological, social and artificial intelligence networks.Comment: 11 pages; v2: references updated + some clarifications added; v3:
version to appear in J. Phys. A, Special Issue on Random Matrix Theor
Chiral Disorder in QCD
Using the Gell-Mann-Oakes-Renner (GOR) relation and semi-classical arguments,
we show that the bulk quark spectrum in QCD exhibits a variety of regimes
including the ergodic one described by random matrix theory. We analyze the
quark spectral form-factor in the diffusive and ballistic regime. We suggest
that a class of chiral transitions in QCD is possibly of the metal-insulator
type, with a universal spectral statistics at the mobility edge
Correlation functions of three heavy operators - the AdS contribution
We consider operators in N=4 SYM theory which are dual, at strong coupling,
to classical strings rotating in S^5. Three point correlation functions of such
operators factorize into a universal contribution coming from the AdS part of
the string sigma model and a state-dependent S^5 contribution. Consequently a
similar factorization arises for the OPE coefficients. In this paper we
evaluate the AdS universal factor of the OPE coefficients which is explicitly
expressed just in terms of the anomalous dimensions of the three operators.Comment: 49 pages, 3 figures; v.2 references corrected; v3: corrected
discussion in section 5, results unchange
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