1,074 research outputs found
Nonabelian Fields in Exact String Solutions
Within the framework of "anomalously gauged" Wess-Zumino-Witten (WZW) models,
we construct solutions which include nonabelian fields. Both compact and
noncompact groups are discussed. In the case of compact groups, as an example
of background containing nonabelian fields, we discuss conformal theory on the
coset, which is the natural generalization of the 2D monopole
theory corresponding to the coset. In noncompact case, we
consider examples with and cosets.Comment: 15 pages, Late
Rapid Thermalization in Field Theory from Gravitational Collapse
Motivated by the duality with thermalization in field theory, we study
gravitational collapse of a minimally coupled massless scalar field in Einstein
gravity with a negative cosmological constant. We investigate the system
numerically and establish that for small values of the initial amplitude of the
scalar field there is no black hole formation, rather, the scalar field
performs an oscillatory motion typical of geodesics in AdS. For large enough
values of the amplitude of the scalar field we find black hole formation which
we detect numerically as the emergence of an apparent horizon. Using the time
of formation as an estimate for thermalization in the field theory we conclude
that thermalization occurs very rapidly, close to the causal bound for a very
wide range of black hole masses. We further study the thermalization time in
more detail as a function of the amplitude and the width of the initial
Gaussian scalar field profile and detect a rather mild structure.Comment: 5 pages, 4 figures. v2: References added, improved most grids by a
factor of 8, main results unchanged. v3 PRD versio
Low-Temperature Glassy Response of Ultrathin Manganite Films to Electric and Magnetic Fields
The glassy response of thin films of La0.8Ca0.2MnO3 to external magnetic and
gated electrostatic fields in a field-effect geometry has been studied at low
temperatures. A hierarchical response with irreversible memory effects,
non-ergodic time evolution, aging and annealing behavior of the resistance
suggest that the dynamics are governed by strain relaxation for both electronic
and magnetic perturbations. Cross-coupling of charge, spin, and strain have
been exploited to tune the coercivity of an ultrathin manganite film by
electrostatic gating.Comment: 4 pages, 5 figure
Tensions and Luscher Terms for (2+1)-dimensional k-strings from Holographic Models
The leading term for the energy of a bound state of k-quarks and k-antiquarks
is proportional to its separation L. These k-string configurations have a
Luscher term associated with their quantum fluctuations which is typically a
1/L correction to the energy. We review the status of tensions and Luscher
terms in the context of lattice gauge theory, Hamiltonian methods, and
gauge/gravity correspondence. Furthermore we explore how different
representations of the k-string manifest themselves in the gauge/gravity
duality. We calculate the Luscher term for a strongly coupled SU(N) gauge
theory in (2+1) dimensions using the gauge/gravity correspondence. Namely, we
compute one-loop corrections to a probe D4-brane embedded in the Cvetic,
Gibbons, Lu, and Pope supergravity background. We investigate quantum
fluctuations of both the bosonic and the fermionic sectors.Comment: 39 pages, reference added, same version to be published in JHE
Black Holes in Cascading Theories: Confinement/Deconfinement Transition and other Thermal Properties
We present numerical evidence for a transition between the Klebanov-Strassler
background and a solution describing a black hole in the class of cascading
solutions in the chirally restored phase. We also present a number of
properties of this solution, including the running of the coupling constant,
the viscosity to entropy ratio and the drag force on a quark moving in this
background.Comment: 34 pages, 7 figures. Version to be published by JHE
On Penrose Limits and Gauge Theories
We discuss various Penrose limits of conformal and nonconformal backgrounds.
In AdS_5 x T^{1,1}, for a particular choice of the angular coordinate in
T^{1,1} the resulting Penrose limit coincides with the similar limit for AdS_5
x S^5. In this case an identification of a subset of field theory operators
with the string zero modes creation operators is possible. For another limit we
obtain a light-cone string action that resembles a particle in a magnetic
field. We also consider three different types of backgrounds that are dual to
nonconformal field theories: The Schwarzschild black hole in AdS_5, D3-branes
on the small resolution of the conifold and the Klebanov-Tseytlin background.
We find that in all three cases the introduction of nonconformality renders a
theory that is no longer exactly solvable and that the form of the deformation
is universal. The corresponding world sheet theory in the light-cone gauge has
a \tau=x^+ dependent mass term.Comment: 17pp, late
Holographic Entanglement Entropy at Finite Temperature
Using a holographic proposal for the entanglement entropy we study its
behavior in various supergravity backgrounds. We are particularly interested in
the possibility of using the entanglement entropy as way to detect transitions
induced by the presence horizons. We consider several geometries with horizons:
the black hole in , nonextremal Dp-branes, dyonic black holes
asymptotically to and also Schwarzschild black holes in global
coordinates. Generically, we find that the entanglement entropy does not
exhibit a transition, that is, one of the two possible configurations always
dominates.Comment: v3: 31 pp, ten figures, modified to match version accepted by IJMP
Electrostatic Tuning of the Superconductor-Insulator Transition in Two Dimensions
Superconductivity has been induced in insulating ultra-thin films of
amorphous bismuth using the electric field effect. The screening of
electron-electron interaction was found to increase with electron concentration
in a manner correlated with the tendency towards superconductivity. This does
not preclude an increase in the density of states being important in the
development of superconductivity. The superconductor-insulator transition
appears to belong to the universality class of the three dimensional XY model.Comment: Four pages, three figures. Revised slightly to reflect referees'
comment
A new paradigm in respiratory hygiene: modulating respiratory secretions to contain cough bioaerosol without affecting mucus clearance
<p>Abstract</p> <p>Background</p> <p>Several strategies and devices have been designed to protect health care providers from acquiring transmissible respiratory diseases while providing care. In modulating the physical characteristics of the respiratory secretions to minimize the aerosolization that facilitates transmission of airborne diseases, a fundamental premise is that the prototype drugs have no adverse effect on the first line of respiratory defense, clearance of mucus by ciliary action.</p> <p>Methods</p> <p>To assess and demonstrate the primary mechanism of our mucomodulators (XLs), we have built our evidence moving from basic laboratory studies to an <it>ex-vivo </it>model and then to an <it>in-vivo </it>large animal model. We exposed anesthetized dogs without hypersecretion to different dose concentrations of aerosolized XL "B", XL "D" and XL "S". We assessed: cardio-respiratory pattern, tracheal mucus clearance, airway patency, and mucus viscoelastic changes.</p> <p>Results</p> <p>Exposure of frog palate mucus to XLs did not affect the clearance of mucus by ciliary action. Dogs maintained normal cardio-respiratory pattern with XL administration. Tracheal mucociliary clearance in anesthetized dogs indicated a sustained 40% mean increase. Tracheal mucus showed increased filance, and there was no mucus retention in the airways.</p> <p>Conclusion</p> <p>The <it>ex-vivo </it>frog palate and the <it>in-vivo </it>mammalian models used in this study, appear to be appropriate and complement each other to better assess the effects that our mucomodulators exert on the mucociliary clearance defence mechanism. The physiological function of the mucociliary apparatus was not negatively affected in any of the two epithelial models. Airway mucus crosslinked by mucomodulators is better cleared from an intact airway and normally functioning respiratory system, either due to enhanced interaction with cilia or airflow-dependent mechanisms. Data obtained in this study allow us to assure that we have complied with the fundamental requirement criteria established in the initial phase of developing the concept of mucomodulation: Can we modulate the physical characteristics of the respiratory secretions to reduce aerosolization without affecting normal mucociliary clearance function, or even better improving it?</p
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