801 research outputs found
An inverse approach to Einstein's equations for non-conducting fluids
We show that a flow (timelike congruence) in any type warped product
spacetime is uniquely and algorithmically determined by the condition of zero
flux. (Though restricted, these spaces include many cases of interest.) The
flow is written out explicitly for canonical representations of the spacetimes.
With the flow determined, we explore an inverse approach to Einstein's
equations where a phenomenological fluid interpretation of a spacetime follows
directly from the metric irrespective of the choice of coordinates. This
approach is pursued for fluids with anisotropic pressure and shear viscosity.
In certain degenerate cases this interpretation is shown to be generically not
unique. The framework developed allows the study of exact solutions in any
frame without transformations. We provide a number of examples, in various
coordinates, including spacetimes with and without unique interpretations. The
results and algorithmic procedure developed are implemented as a computer
algebra program called GRSource.Comment: 9 pages revtex4. Final form to appear in Phys Rev
The Creative Hawker Center for Small - Family - Business in Traditional Food of Surabaya
The Traditional Food Seller were mostly managed by the family, so they could be categorized as Family Businesses (FB). Furthermore, The FB in traditional food needed integrated business development strategy (related to marketing, business information system as well as architectural design). It was found during the research supported by UBCHEA in Surabaya. One of the strategies needed was to create the legal family food hawker center place quality. The strategy was in line with the Surabaya Municipality Government, The Cooperative and SME's Business (Dinas Koperasi dan UMKM). A mini hawker center (consisting of 5 hawkers) was proposed in the roadside of the neighborhood collector. Additional to the center, a culinary park was provided onsite for catering the social interactions of Indonesian. The center was designed with creativity, but with low-cost local material such as brick, wood and bamboo. The design was also equipped with clean water, sanitations as well as food storages. All these would create positive branding and ensure sustainability of the hawker center
Epithelioid hemangioendothelioma of the temporal artery presenting as temporal arteritis: case report and literature review
<span style="font-size: small; font-family: ArialUnicodeMS;"><span style="font-size: small; font-family: ArialUnicodeMS;"><p align="left">Hemangioendotheliomas are classified as epithelioid hemangioendothelioma</p><p align="left">(EHE), retiform hemangioendothelioma, composite hemanioendothelioma, Kaposiform hemangioendothelioma (with or without Kasabach-Merritt syndrome), and Spindle cell hemangioendothelioma. The latter two types of hemangioendotheliomas usually follow a benign course, in contrast to the other types of hemangioendotheliomas, which are considered as a low grade malignant sarcoma with unpredictable prognosis. EHE's are rare tumors, mostly described in organs particularly the lungs and liver. Though endothelial in origin, EHE's reported to originate from small sized arteries are extremely rare. We report a very rare case of EHE arising from the temporal artery showing a peculiar presentation.</p></span></span
Preparation and characterization of in situ polymerized cyclic butylene terephthalate/graphene nanocomposites
Graphene reinforced cyclic butylene terephthalate (CBT) matrix nanocomposites were prepared and characterized by mechanical and thermal methods. These nanocomposites containing different amounts of graphene (up to 5 wt%) were prepared by melt mixing with CBT that was polymerized in situ during a subsequent hot pressing. The nanocomposites and the neat polymerized CBT (pCBT) as reference material were subjected to differential scanning calorimetry (DSC), dynamical mechanical analysis (DMA), thermogravimetrical analysis (TGA) and heat conductivity measurements. The dispersion of the grapheme nanoplatelets was characterized by transmission electron microscopy (TEM). It was established that the partly exfoliated graphene worked as nucleating agent for crystallization, acted as very efficient reinforcing agent (the storage modulus at room temperature was increased by 39 and 89% by incorporating 1 and 5 wt.% graphene, respectively). Graphene incorporation markedly enhanced the heat conductivity but did not influence the TGA behaviour due to the not proper exfoliation except the ash content
On perfect fluid models in non-comoving observational spherical coordinates
We use null spherical (observational) coordinates to describe a class of
inhomogeneous cosmological models. The proposed cosmological construction is
based on the observer past null cone. A known difficulty in using inhomogeneous
models is that the null geodesic equation is not integrable in general. Our
choice of null coordinates solves the radial ingoing null geodesic by
construction. Furthermore, we use an approach where the velocity field is
uniquely calculated from the metric rather than put in by hand. Conveniently,
this allows us to explore models in a non-comoving frame of reference. In this
frame, we find that the velocity field has shear, acceleration and expansion
rate in general. We show that a comoving frame is not compatible with expanding
perfect fluid models in the coordinates proposed and dust models are simply not
possible. We describe the models in a non-comoving frame. We use the dust
models in a non-comoving frame to outline a fitting procedure.Comment: 8 pages, 1 figure. To appear in Phys.Rev.
Generalized Swiss-cheese cosmologies: Mass scales
We generalize the Swiss-cheese cosmologies so as to include nonzero linear
momenta of the associated boundary surfaces. The evolution of mass scales in
these generalized cosmologies is studied for a variety of models for the
background without having to specify any details within the local
inhomogeneities. We find that the final effective gravitational mass and size
of the evolving inhomogeneities depends on their linear momenta but these
properties are essentially unaffected by the details of the background model.Comment: 10 pages, 14 figures, 1 table, revtex4, Published form (with minor
corrections
Dark energy constraints from cosmic shear power spectra: impact of intrinsic alignments on photometric redshift requirements
Cosmic shear constrains cosmology by exploiting the apparent alignments of
pairs of galaxies due to gravitational lensing by intervening mass clumps.
However galaxies may become (intrinsically) aligned with each other, and with
nearby mass clumps, during their formation. This effect needs to be
disentangled from the cosmic shear signal to place constraints on cosmology. We
use the linear intrinsic alignment model as a base and compare it to an
alternative model and data. If intrinsic alignments are ignored then the dark
energy equation of state is biased by ~50 per cent. We examine how the number
of tomographic redshift bins affects uncertainties on cosmological parameters
and find that when intrinsic alignments are included two or more times as many
bins are required to obtain 80 per cent of the available information. We
investigate how the degradation in the dark energy figure of merit depends on
the photometric redshift scatter. Previous studies have shown that lensing does
not place stringent requirements on the photometric redshift uncertainty, so
long as the uncertainty is well known. However, if intrinsic alignments are
included the requirements become a factor of three tighter. These results are
quite insensitive to the fraction of catastrophic outliers, assuming that this
fraction is well known. We show the effect of uncertainties in photometric
redshift bias and scatter. Finally we quantify how priors on the intrinsic
alignment model would improve dark energy constraints.Comment: 14 pages and 9 figures. Replaced with final version accepted in
"Gravitational Lensing" Focus Issue of the New Journal of Physics at
http://www.iop.org/EJ/abstract/1367-2630/9/12/E0
Perturbations of Self-Accelerated Universe
We discuss small perturbations on the self-accelerated solution of the DGP
model, and argue that claims of instability of the solution that are based on
linearized calculations are unwarranted because of the following: (1) Small
perturbations of an empty self-accelerated background can be quantized
consistently without yielding ghosts. (2) Conformal sources, such as radiation,
do not give rise to instabilities either. (3) A typical non-conformal source
could introduce ghosts in the linearized approximation and become unstable,
however, it also invalidates the approximation itself. Such a source creates a
halo of variable curvature that locally dominates over the self-accelerated
background and extends over a domain in which the linearization breaks down.
Perturbations that are valid outside the halo may not continue inside, as it is
suggested by some non-perturbative solutions. (4) In the Euclidean continuation
of the theory, with arbitrary sources, we derive certain constraints imposed by
the second order equations on first order perturbations, thus restricting the
linearized solutions that could be continued into the full nonlinear theory.
Naive linearized solutions fail to satisfy the above constraints. (5) Finally,
we clarify in detail subtleties associated with the boundary conditions and
analytic properties of the Green's functions.Comment: 39 LaTex page
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