170 research outputs found
dS/CFT at uniform energy density and a de Sitter "bluewall"
We describe a class of spacetimes that are asymptotically de Sitter in the
Poincare slicing. Assuming that a dS/CFT correspondence exists, we argue that
these are gravity duals to a CFT on a circle leading to uniform energy-momentum
density, and are equivalent to an analytic continuation of the Euclidean AdS
black brane. These are solutions with a complex parameter which then gives a
real energy-momentum density. We also discuss a related solution with the
parameter continued to a real number, which we refer to as a de Sitter
"bluewall". This spacetime has two asymptotic de Sitter universes and Cauchy
horizons cloaking timelike singularities. We argue that the Cauchy horizons
give rise to a blue-shift instability.Comment: Latex, 13pgs, 2 figs. v2: 14pgs, published version, some rephrasing
of language in terms of Euclidean CFT on a circle, more elaborate discussion
on blueshif
Evaluation of incorporation of bone allograft at the site of implantation in various clinical conditions along with its complications
Background: Bone transplants have been used routinely in the present century for diverse purposes to unite fractures, fuse joints, and repair skeletal defects.Methods: Twelve patients with fracture, bone defect, deformity, difficulty in the fusion of bone, etc. were taken in the study for elective surgery with fresh frozen allograft in the orthopedics department with the incorporation of inclusion and exclusion criteria.Results: Out of 12 cases in this study, 7 cases were related to spinal fusion, 3 cases were of fractures with bone defects, 1 case of non-union neck femur fracture and 1 case was of revision hip arthroplasty with the acetabular bone defect. Seventy-five percent (9 patients) and 25% (3 patients) were graded fair and poor respectively in the preoperative phase. At 6 months, excellent results were obtained in 50% (6 patients), good in 25% (3 patients), fair in 25% (3 patients), while none were graded as poor in terms of clinical evaluation.Conclusions: Fresh frozen bone, a good source of abundant bone allograft, can be stored in -70° freezer for use in orthopedic surgery to fill any filling defect in the bone. Also, proper storage, better surgical technique, hospital infection control policy, antibiotic policy, preoperative use of antibiotics before surgery has a good clinical outcome
\u3cem\u3edS/CFT\u3c/em\u3e at uniform energy density and a de Sitter “bluewall”
We describe a class of spacetimes that are asymptotically de Sitter in the Poincare slicing. Assuming that a dS/CFT correspondence exists, we argue that these are gravity duals to a CFT on a circle leading to uniform energy-momentum density, and are equivalent to an analytic continuation of the Euclidean AdS black brane. These are solutions with a complex parameter which then gives a real energy-momentum density. We also discuss a related solution with the parameter continued to a real number, which we refer to as a de Sitter “bluewall”. This spacetime has two asymptotic de Sitter universes and Cauchy horizons cloaking timelike singularities. We argue that the Cauchy horizons give rise to a blue-shift instability
Time Dependent Cosmologies and Their Duals
We construct a family of solutions in IIB supergravity theory. These are time
dependent or depend on a light-like coordinate and can be thought of as
deformations of AdS_5 x S^5. Several of the solutions have singularities. The
light-like solutions preserve 8 supersymmetries. We argue that these solutions
are dual to the N=4 gauge theory in a 3+1 dimensional spacetime with a metric
and a gauge coupling that is varying with time or the light-like direction
respectively. This identification allows us to map the question of singularity
resolution to the dual gauge theory.Comment: 13 pages REVTeX and AMSLaTeX. v2: corrected typos and made some
clarifications; reference added; v3: more clarifications, references adde
Gauge theory duals of cosmological backgrounds and their energy momentum tensors
We revisit type IIB supergravity backgrounds with null and spacelike singularities with natural gauge theory duals proposed in [S.R. Das, J. Michelson, K. Narayan, and S.P. Trivedi, Phys. Rev. D 74, 026002 (2006)] and [S.R. Das, J. Michelson, K. Narayan, and S.P. Trivedi, Phys. Rev. D 75, 026002 (2007)]. We show that for these backgrounds there are always choices of the boundaries of these deformed AdS5×S5 space-times, such that the dual gauge theories live on flat metrics and have space-time dependent couplings. We present a new time dependent solution of this kind where the effective string coupling is always bounded and vanishes at a spacelike singularity in the bulk, and the space-time becomes AdS5×S5 at early and late times. The holographic energy momentum tensor calculated with a choice of flat boundary is shown to vanish for null backgrounds and to be generically nonzero for time dependent backgrounds
Cosmologies with Null Singularities and their Gauge Theory Duals
We investigate backgrounds of Type IIB string theory with null singularities
and their duals proposed in hep-th/0602107. The dual theory is a deformed N=4
Yang-Mills theory in 3+1 dimensions with couplings dependent on a light-like
direction. We concentrate on backgrounds which become AdS_5 x S^5 at early and
late times and where the string coupling is bounded, vanishing at the
singularity. Our main conclusion is that in these cases the dual gauge theory
is nonsingular. We show this by arguing that there exists a complete set of
gauge invariant observables in the dual gauge theory whose correlation
functions are nonsingular at all times. The two-point correlator for some
operators calculated in the gauge theory does not agree with the result from
the bulk supergravity solution. However, the bulk calculation is invalid near
the singularity where corrections to the supergravity approximation become
important. We also obtain pp-waves which are suitable Penrose limits of this
general class of solutions, and construct the Matrix Membrane theory which
describes these pp-wave backgrounds.Comment: 43 pages REVTeX and AMSLaTeX. v2: references adde
Transcending Grids: Point Clouds and Surface Representations Powering Neurological Processing
In healthcare, accurately classifying medical images is vital, but
conventional methods often hinge on medical data with a consistent grid
structure, which may restrict their overall performance. Recent medical
research has been focused on tweaking the architectures to attain better
performance without giving due consideration to the representation of data. In
this paper, we present a novel approach for transforming grid based data into
its higher dimensional representations, leveraging unstructured point cloud
data structures. We first generate a sparse point cloud from an image by
integrating pixel color information as spatial coordinates. Next, we construct
a hypersurface composed of points based on the image dimensions, with each
smooth section within this hypersurface symbolizing a specific pixel location.
Polygonal face construction is achieved using an adjacency tensor. Finally, a
dense point cloud is generated by densely sampling the constructed
hypersurface, with a focus on regions of higher detail. The effectiveness of
our approach is demonstrated on a publicly accessible brain tumor dataset,
achieving significant improvements over existing classification techniques.
This methodology allows the extraction of intricate details from the original
image, opening up new possibilities for advanced image analysis and processing
tasks
Gauge Theories with Time Dependent Couplings and their Cosmological Duals
We consider the N=4 SYM theory in flat 3+1 dimensional spacetime with a time
dependent coupling constant which vanishes at , like . In an
analogous quantum mechanics toy model we find that the response is singular.
The energy diverges at , for a generic state. In addition, if the
phase of the wave function has a wildly oscillating behavior, which does not
allow it to be continued past . A similar effect would make the gauge
theory singular as well, though nontrivial effects of renormalization could
tame this singularity and allow a smooth continuation beyond . The gravity
dual in some cases is known to be a time dependent cosmology which exhibits a
space-like singularity at . Our results, if applicable in the gauge theory
for the case of the vanishing coupling, imply that the singularity is a genuine
sickness and does not admit a meaningful continuation. When the coupling
remains non-zero and becomes small at , the curvature in the bulk becomes
of order the string scale. The gauge theory now admits a time evolution beyond
this point. In this case, a finite amount of energy is produced which possibly
thermalizes and leads to a black hole in the bulk.Comment: 45 pages, 1 figure; v2. minor modifications; v3: PRD version,
conclusions in the field theory case significantly revised to include
possible renormalization effects, quantum mechanics toy model unchanged,
abstract and introduction revised, additional subsection 4.1 adde
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