1,165 research outputs found
Geometric scalar theory of gravity
We present a geometric scalar theory of gravity. Our proposal will be
described using the "background field method" introduced by Gupta, Feynman and
others as a field theory formulation of general relativity. We analyze previous
criticisms against scalar gravity and show how the present proposal avoids
these difficulties. This concerns not only the theoretical complaints but also
those related to observations. In particular, we show that the widespread
belief of the conjecture that the source of scalar gravity must be the trace of
the energy-momentum tensor - which is one of the main difficulties to couple
gravity with electromagnetic phenomenon in previous models - does not apply to
our geometric scalar theory. Some consequences of the new scalar theory are
explored.Comment: We did some modifications which do not change the content of the tex
Cosmology in GSG
We describe what cosmology looks like in the context of the geometric theory
of gravity (GSG) based on a single scalar field. There are two distinct classes
of cosmological solutions. An interesting feature is the possibility of having
a bounce without invoking exotic equations of state for the cosmic fluid. We
also discuss cosmological perturbation and present the basis of structure
formation by gravitational instability in the framework of the geometric scalar
gravity.Comment: 12 pages, 5 figures, accepted for publication in Phys. Rev.
More about scalar gravity
We discuss a class of models for gravity based on a scalar field. The models
include and generalize the old approach by Nordstr\"om which predated and in
some way inspired General Relativity. The class include also a model that we
have recently introduced and discussed in its cosmological aspects (GSG). We
present here a complete characterisation of the Schwarschild geometry as a
vacuum solution of GSG and sketch a discussion of the first Post-Newtonian
approximation.Comment: 11 pages, 1 figure, accepted for publication in PR
State-Relevant Maxwell's Equation from Kaluza-Klein Theory
We study a five-dimensional perfect fluid coupled with Kaluza-Klein (KK)
gravity. By dimensional reduction, a modified form of Maxwell's equation is
obtained, which is relevant to the equation of state of the source. Since the
relativistic magnetohydrodynamics (MHD) and the 3-dimensional formulation are
widely used to study space matter, we derive the modified Maxwell's equations
and relativistic MHD in 3+1 form. We then take an ideal Fermi gas as an example
to study the modified effect, which can be visible under high density or high
energy condition, while the traditional Maxwell's equation can be regarded as a
result in the low density and low temperature limit. We also indicate the
possibility to test the state-relevant effect of KK theory in a telluric
laboratory.Comment: 11 pages, 3 figures; version published in PR
Piriform spider silk sequences reveal unique repetitive elements.
Orb-weaving spider silk fibers are assembled from very large, highly repetitive proteins. The repeated segments contain, in turn, short, simple, and repetitive amino acid motifs that account for the physical and mechanical properties of the assembled fiber. Of the six orb-weaver silk fibroins, the piriform silk that makes the attachment discs, which lashes the joints of the web and attaches dragline silk to surfaces, has not been previously characterized. Piriform silk protein cDNAs were isolated from phage libraries of three species: A. trifasciata, N. claVipes, and N. cruentata. The deduced amino acid sequences from these genes revealed two new repetitive motifs: an alternating proline motif, where every other amino acid is proline, and a glutamine-rich motif of 6-8 amino acids. Similar to other spider silk proteins, the repeated segments are large (>200 amino acids) and highly homogenized within a species. There is also substantial sequence similarity across the genes from the three species, with particular conservation of the repetitive motifs. Northern blot analysis revealed that the mRNA is larger than 11 kb and is expressed exclusively in the piriform glands of the spider. Phylogenetic analysis of the C-terminal regions of the new proteins with published spidroins robustly shows that the piriform sequences form an ortholog group
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