2,033 research outputs found
Public health lessons from a pilot programme to reduce mother-to-child transmission of HIV-1 in Khayelitsha
Objective. Short-course antiretroviral therapy (ART) has been shown to be effective in reducing mother-to-child transmission (MTCT) of HIV-1. This article details the public health lessons learnt from a district-based pilot programme where a short-murse zidovudine (ZDV) regimen has been used in a typical South African peri-urban setting.Methods. The pilot programme was initiated at two midwife obstetric units in January 1999. Lay counsellors conducted pre- and post-test counselling and nurses took blood for HIV enzyme-linked imrnunosorbent assay (EUSA) testing. Shortcourse ZDV was administered antenatally (from 36 weeks gestation) and during labour. Mother-infant pairs were followed up at eight child health clinics where free formula feed was dispensed weekly. Infants received co-trimoxazole prophylaxis and were EUSA tested for HIV at 9 and 18 months. After 17 months protocol changes aimed at eliminating weaknesses included initiation of ZDV at 34 weeks, self-administration of the first dose of ZDV with the onset of labour, and rapid HIV testing for both mothers and infants.Results. Voluntary counselling and testing was shown to be highly acceptable, with individual counselling more effective than group counselling. Based on less than optimal availability of records, ZDV utilisation was encouraging with up to 59% of subjects initiating treatment, 3 weeks' median duration of ZDV use, and up to 88% receiving at least one intrapartum ZDV dose. Self-administration of the intrapartum dose reached 41%.Conclusions. Short-course antenatal and intrapartum ART to prevent MTCT of HIV1 was shown to be feasible
Massive Gravity Theories and limits of Ghost-free Bigravity models
We construct a class of theories which extend New Massive Gravity to higher
orders in curvature in any dimension. The lagrangians arise as limits of a new
class of bimetric theories of Lovelock gravity, which are unitary theories free
from the Boulware-Deser ghost. These Lovelock bigravity models represent the
most general non-chiral ghost-free theories of an interacting massless and
massive spin-two field in any dimension. The scaling limit is taken in such a
way that unitarity is explicitly broken, but the Boulware-Deser ghost remains
absent. This automatically implies the existence of a holographic -theorem
for these theories. We also show that the Born-Infeld extension of New Massive
Gravity falls into our class of models demonstrating that this theory is also
free of the Boulware-Deser ghost. These results extend existing connections
between New Massive Gravity, bigravity theories, Galileon theories and
holographic -theorems.Comment: 11+5 page
Comments on Holographic Entanglement Entropy and RG Flows
Using holographic entanglement entropy for strip geometry, we construct a
candidate for a c-function in arbitrary dimensions. For holographic theories
dual to Einstein gravity, this c-function is shown to decrease monotonically
along RG flows. A sufficient condition required for this monotonic flow is that
the stress tensor of the matter fields driving the holographic RG flow must
satisfy the null energy condition over the holographic surface used to
calculate the entanglement entropy. In the case where the bulk theory is
described by Gauss-Bonnet gravity, the latter condition alone is not sufficient
to establish the monotonic flow of the c-function. We also observe that for
certain holographic RG flows, the entanglement entropy undergoes a 'phase
transition' as the size of the system grows and as a result, evolution of the
c-function may exhibit a discontinuous drop.Comment: References adde
Holographic GB gravity in arbitrary dimensions
We study the properties of the holographic CFT dual to Gauss-Bonnet gravity
in general dimensions. We establish the AdS/CFT dictionary and in
particular relate the couplings of the gravitational theory to the universal
couplings arising in correlators of the stress tensor of the dual CFT. This
allows us to examine constraints on the gravitational couplings by demanding
consistency of the CFT. In particular, one can demand positive energy fluxes in
scattering processes or the causal propagation of fluctuations. We also examine
the holographic hydrodynamics, commenting on the shear viscosity as well as the
relaxation time. The latter allows us to consider causality constraints arising
from the second-order truncated theory of hydrodynamics.Comment: 48 pages, 9 figures. v2: New discussion on free fields in subsection
3.3 and new appendix B on conformal tensor fields. Added comments on the
relation between the central charge appearing in the two-point function and
the "central charge" characterizing the entropy density in the discussion.
References adde
The Dawning Era of Personalized Medicine Exposes a Gap in Medical Education
Medical student Keyan Salari argues that it is crucial that medical students be trained to use and interpret patients' genetic information appropriately and responsibly
Holographic studies of quasi-topological gravity
Quasi-topological gravity is a new gravitational theory including
curvature-cubed interactions and for which exact black hole solutions were
constructed. In a holographic framework, classical quasi-topological gravity
can be thought to be dual to the large limit of some non-supersymmetric
but conformal gauge theory. We establish various elements of the AdS/CFT
dictionary for this duality. This allows us to infer physical constraints on
the couplings in the gravitational theory. Further we use holography to
investigate hydrodynamic aspects of the dual gauge theory. In particular, we
find that the minimum value of the shear-viscosity-to-entropy-density ratio for
this model is .Comment: 45 pages, 6 figures. v2: References adde
Wilsonian Approach to Fluid/Gravity Duality
The problem of gravitational fluctuations confined inside a finite cutoff at
radius outside the horizon in a general class of black hole geometries
is considered. Consistent boundary conditions at both the cutoff surface and
the horizon are found and the resulting modes analyzed. For general cutoff
the dispersion relation is shown at long wavelengths to be that of a
linearized Navier-Stokes fluid living on the cutoff surface. A cutoff-dependent
line-integral formula for the diffusion constant is derived. The
dependence on is interpreted as renormalization group (RG) flow in the
fluid. Taking the cutoff to infinity in an asymptotically AdS context, the
formula for reproduces as a special case well-known results derived
using AdS/CFT. Taking the cutoff to the horizon, the effective speed of sound
goes to infinity, the fluid becomes incompressible and the Navier-Stokes
dispersion relation becomes exact. The resulting universal formula for the
diffusion constant reproduces old results from the membrane
paradigm. Hence the old membrane paradigm results and new AdS/CFT results are
related by RG flow. RG flow-invariance of the viscosity to entropy ratio is shown to follow from the first law of thermodynamics together with
isentropy of radial evolution in classical gravity. The ratio is expected to
run when quantum gravitational corrections are included.Comment: 34 pages, harvmac, clarified boundary conditio
Holographic current correlators at finite coupling and scattering off a supersymmetric plasma
By studying the effect of the order(\alpha'^3) string theory corrections to
type IIB supergravity, including those corrections involving the Ramond-Ramond
five-form field strength, we obtain the corrected equations of motion of an
Abelian perturbation of the AdS_5-Schwarzschild black hole. We then use the
gauge theory/string theory duality to examine the coupling-constant dependence
of vector current correlators associated to a gauged U(1) sub-group of the
global R-symmetry group of strongly-coupled N=4 supersymmetric Yang-Mills
theory at finite temperature. The corrections induce a set of higher-derivative
operators for the U(1) gauge field, but their effect is highly suppressed. We
thus find that the order(\alpha'^3) corrections affect the vector correlators
only indirectly, through the corrected metric. We apply our results to
investigate scattering off a supersymmetric Yang-Mills plasma at low and high
energy. In the latter regime, where Deep Inelastic Scattering is expected to
occur, we find an enhancement of the plasma structure functions in comparison
with the infinite 't Hooft coupling result.Comment: 38 pages, 6 figures, minor clarifications added, typos corrected,
references adde
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