659 research outputs found
Microscopic Realization of the Kerr/CFT Correspondence
Supersymmetric M/string compactifications to five dimensions contain BPS
black string solutions with magnetic graviphoton charge P and near-horizon
geometries which are quotients of AdS_3 x S^2. The holographic duals are
typically known 2D CFTs with central charges c_L=c_R=6P^3 for large P. These
same 5D compactifications also contain non-BPS but extreme Kerr-Newman black
hole solutions with SU(2)_L spin J_L and electric graviphoton charge Q obeying
Q^3 \leq J_L^2. It is shown that in the maximally charged limit Q^3 -> J_L^2,
the near-horizon geometry coincides precisely with the right-moving temperature
T_R=0 limit of the black string with magnetic charge P=J_L^{1/3}. The known
dual of the latter is identified as the c_L=c_R=6J_L CFT predicted by the
Kerr/CFT correspondence. Moreover, at linear order away from maximality, one
finds a T_R \neq 0 quotient of the AdS_3 factor of the black string solution
and the associated thermal CFT entropy reproduces the linearly sub-maximal
Kerr-Newman entropy. Beyond linear order, for general Q^3<J_L^2, one has a
finite-temperature quotient of a warped deformation of the magnetic string
geometry. The corresponding dual deformation of the magnetic string CFT
potentially supplies, for the general case, the c_L=c_R=6J_L CFT predicted by
Kerr/CFT.Comment: 18 pages, no figure
Brick Walls and AdS/CFT
We discuss the relationship between the bulk-boundary correspondence in
Rehren's algebraic holography (and in other 'fixed-background' approaches to
holography) and in mainstream 'Maldacena AdS/CFT'. Especially, we contrast the
understanding of black-hole entropy from the viewpoint of QFT in curved
spacetime -- in the framework of 't Hooft's 'brick wall' model -- with the
understanding based on Maldacena AdS/CFT. We show that the brick-wall
modification of a Klein Gordon field in the Hartle-Hawking-Israel state on
1+2-Schwarzschild AdS (BTZ) has a well-defined boundary limit with the same
temperature and entropy as the brick-wall-modified bulk theory. One of our main
purposes is to point out a close connection, for general AdS/CFT situations,
between the puzzle raised by Arnsdorf and Smolin regarding the relationship
between Rehren's algebraic holography and mainstream AdS/CFT and the puzzle
embodied in the 'correspondence principle' proposed by Mukohyama and Israel in
their work on the brick-wall approach to black hole entropy. Working on the
assumption that similar results will hold for bulk QFT other than the Klein
Gordon field and for Schwarzschild AdS in other dimensions, and recalling the
first author's proposed resolution to the Mukohyama-Israel puzzle based on his
'matter-gravity entanglement hypothesis', we argue that, in Maldacena AdS/CFT,
the algebra of the boundary CFT is isomorphic only to a proper subalgebra of
the bulk algebra, albeit (at non-zero temperature) the (GNS) Hilbert spaces of
bulk and boundary theories are still the 'same' -- the total bulk state being
pure, while the boundary state is mixed (thermal). We also argue from the
finiteness of its boundary (and hence, on our assumptions, also bulk) entropy
at finite temperature, that the Rehren dual of the Maldacena boundary CFT
cannot itself be a QFT and must, instead, presumably be something like a string
theory.Comment: 54 pages, 3 figures. Arguments strengthened in the light of B.S. Kay
`Instability of Enclosed Horizons' arXiv:1310.739
Virtual Reality Simulator for Medical Auscultation Training
© Springer Nature Switzerland AG 2019. According to the Oxford English dictionary, auscultation is “the action of listening to sounds from the heart, lungs, or other organs, typically with a stethoscope, as a part of medical diagnosis.” In this work, we describe a medical simulator that includes audio, visual, pseudo-haptic, and spatial elements for training medical students in auscultation. In our training simulator, the user is fully immersed in a virtual reality (VR) environment. A typical hospital bedside scenario was recreated, and the users can see their own body and the patient increase immersion. External tracking devices are used to acquire the user’s movements and map them into the VR environment. The main idea behind this work is for the user to associate the heart and lung sounds, as heard through the stethoscope with the corresponding health-related problems. Several sound parameters including the volume, give information about the type and severity of the disease. Our simulator can reproduce sounds belonging to the heart and lungs. Through the proposed VR-based training, the medical student ideally will learn to relate sounds to illnesses in a realistic setting, accelerating the learning process
Schr\"odinger Deformations of AdS_3 x S^3
We study Schr\"odinger invariant deformations of the AdS_3 x S^3 x T^4 (or
K3) solution of IIB supergravity and find a large class of solutions with
integer and half-integer dynamical exponents. We analyze the supersymmetries
preserved by our solutions and find an infinite number of solutions with four
supersymmetries. We study the solutions holographically and find that the dual
D1-D5 (or F1-NS5) CFT is deformed by irrelevant operators of spin one and two.Comment: 23 page
Transport in holographic superfluids
We construct a slowly varying space-time dependent holographic superfluid and
compute its transport coefficients. Our solution is presented as a series
expansion in inverse powers of the charge of the order parameter. We find that
the shear viscosity associated with the motion of the condensate vanishes. The
diffusion coefficient of the superfluid is continuous across the phase
transition while its third bulk viscosity is found to diverge at the critical
temperature. As was previously shown, the ratio of the shear viscosity of the
normal component to the entropy density is 1/(4 pi). As a consequence of our
analysis we obtain an analytic expression for the backreacted metric near the
phase transition for a particular type of holographic superfluid.Comment: 45 pages + appendice
Rhizobium strains competitiveness on bean nodulation in Cerrado soils
The objective of this work was to identify the most competitive and effective Rhizobium strains in order to increase common bean yield by nitrogen fixation as alternative or complementation to the nitrogen fertilization. Competitiveness tests were lead in axenic conditions, in Cerrado soil pots and in three field experiments, with native Rhizobium strains that were previously identified, according to their effectiveness and genetic variability. The identification of strains in nodules was performed using serological tests (axenic conditions) - agglutination and enzyme linked immunosorbent (Elisa) assays - and random amplified polymorfic DNA (RAPD) (Cerrado soil). Plant yield was determined using the dry weight (greenhouse conditions), total N and grain yield (field experiments). Among the analyzed Rhizobium strains, native strain SLA 2.2 and commercial strain CIAT 899 were the dominant nodules in plants of the most productive plots, presenting yield productivity similar or higher to those obtained in treatments where 20 kg ha-1 of N were applied.O objetivo deste trabalho foi identificar as estirpes de Rhizobium mais efetivas e competitivas, a fim de maximizar a produtividade do feijoeiro por meio da fixação de nitrogênio, como alternativa à adubação nitrogenada. Foram conduzidos testes de competitividade em condições axênicas, em vasos com solo do Cerrado e em três experimentos de campo, com estirpes de Rhizobium nativas, previamente selecionadas quanto à efetividade e à variabilidade genética. A identificação das estirpes nos nódulos foi efetuada por meio das técnicas de aglutinação e ensaio imunoabsorvente de ligação de enzimas (Elisa), em condições de casa de vegetação, e pela técnica de DNA polimórfico amplificado ao acaso (RAPD), em solo de Cerrado. A produtividade das plantas foi determinada pela produção de matéria seca, teor de N e produção de grãos (condições de campo). A estirpe nativa SLA 2.2 e a estirpe comercial CIAT 899 foram dominantes nos nódulos das plantas das parcelas mais produtivas, com índices de produtividade iguais ou superiores aos obtidos nos tratamentos em que foram aplicados 20 kg ha-1 de N
Charged, conformal non-relativistic hydrodynamics
We embed a holographic model of an U(1) charged fluid with Galilean
invariance in string theory and calculate its specific heat capacity and
Prandtl number. Such theories are generated by a R-symmetry twist along a null
direction of a N=1 superconformal theory. We study the hydrodynamic properties
of such systems employing ideas from the fluid-gravity correspondence.Comment: 31 pages, 1 figure, JHEP3 style, refs added, typos corrected, missing
terms in spatial charge current and field corrections added, to be published
in JHE
String Theory on Warped AdS_3 and Virasoro Resonances
We investigate aspects of holographic duals to time-like warped AdS_3
space-times--which include G\"odel's universe--in string theory. Using
worldsheet techniques similar to those that have been applied to AdS_3
backgrounds, we are able to identify space-time symmetry algebras that act on
the dual boundary theory. In particular, we always find at least one Virasoro
algebra with computable central charge. Interestingly, there exists a dense set
of points in the moduli space of these models in which there is actually a
second commuting Virasoro algebra, typically with different central charge than
the first. We analyze the supersymmetry of the backgrounds, finding related
enhancements, and comment on possible interpretations of these results. We also
perform an asymptotic symmetry analysis at the level of supergravity, providing
additional support for the worldsheet analysis.Comment: 24 pages + appendice
The Spectrum of Strings on Warped AdS_3 x S^3
String theory on NS-NS AdS_3 x S^3 admits an exactly marginal deformation
which breaks the SL(2,R)_R x SL(2,R)_L isometry of AdS_3 down to SL(2,R)_R x
U(1)_L. The holographic dual is an exotic and only partially understood type of
two-dimensional CFT with a reduced unbroken global conformal symmetry group. In
this paper we study the deformed theory on the string worldsheet. It is found
to be related by a spectral flow which is nonlocal in spacetime to the
undeformed worldsheet theory. An exact formula for the spectrum of massive
strings is presented.Comment: 26 pages, no figure
Nonlinear electrophoresis of dielectric and metal spheres in a nematic liquid crystal
Electrophoresis is a motion of charged dispersed particles relative to a
fluid in a uniform electric field. The effect is widely used to separate
macromolecules, to assemble colloidal structures, to transport particles in
nano- and micro-fluidic devices and displays. Typically, the fluid is isotropic
(for example, water) and the electrophoretic velocity is linearly proportional
to the electric field. In linear electrophoresis, only a direct current (DC)
field can drive the particles. An alternate current (AC) field is more
desirable because it allows one to overcome problems such as electrolysis and
absence of steady flows. Here we show that when the electrophoresis is
performed in a nematic fluid, the effect becomes strongly non-linear with a
velocity component that is quadratic in the applied voltage and has a direction
that generally differs from the direction of linear velocity. The new
phenomenon is caused by distortions of the LC orientation around the particle
that break the fore-aft (or left-right) symmetry. The effect allows one to
transport both charged and neutral particles, even when the particles
themselves are perfectly symmetric (spherical), thus enabling new approaches in
display technologies, colloidal assembly, separation, microfluidic and
micromotor applications.Comment: 15 pages, 4 figure
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