2,882 research outputs found
Hausdorff dimension of repellors in low sensitive systems
Methods to estimate the Hausdorff dimension of invariant sets of scattering
systems are presented. Based on the levels' hierarchical structure of the time
delay function, these techniques can be used in systems whose
future-invariant-set codimensions are approximately equal to or greater than
one. The discussion is illustrated by a numerical example of a scatterer built
with four hard spheres located at the vertices of a regular tetrahedron.Comment: 9 pages, 5 figures, accepted in Physics Letters
Corrections to the apparent value of the cosmological constant due to local inhomogeneities
Supernovae observations strongly support the presence of a cosmological
constant, but its value, which we will call apparent, is normally determined
assuming that the Universe can be accurately described by a homogeneous model.
Even in the presence of a cosmological constant we cannot exclude nevertheless
the presence of a small local inhomogeneity which could affect the apparent
value of the cosmological constant. Neglecting the presence of the
inhomogeneity can in fact introduce a systematic misinterpretation of
cosmological data, leading to the distinction between an apparent and true
value of the cosmological constant. We establish the theoretical framework to
calculate the corrections to the apparent value of the cosmological constant by
modeling the local inhomogeneity with a solution. Our assumption
to be at the center of a spherically symmetric inhomogeneous matter
distribution correspond to effectively calculate the monopole contribution of
the large scale inhomogeneities surrounding us, which we expect to be the
dominant one, because of other observations supporting a high level of isotropy
of the Universe around us.
By performing a local Taylor expansion we analyze the number of independent
degrees of freedom which determine the local shape of the inhomogeneity, and
consider the issue of central smoothness, showing how the same correction can
correspond to different inhomogeneity profiles. Contrary to previous attempts
to fit data using large void models our approach is quite general. The
correction to the apparent value of the cosmological constant is in fact
present for local inhomogeneities of any size, and should always be taken
appropriately into account both theoretically and observationally.Comment: 16 pages,new sections added analyzing central smoothness and accuracy
of the Taylor expansion approach, Accepted for publication by JCAP. An essay
based on this paper received honorable mention in the 2011 Essay Context of
the Gravity Research Foundatio
Spherically symmetric analysis on open FLRW solution in non-linear massive gravity
We study non-linear massive gravity in the spherically symmetric context. Our
main motivation is to investigate the effect of helicity-0 mode which remains
elusive after analysis of cosmological perturbation around an open
Friedmann-Lemaitre-Robertson-Walker (FLRW) universe. The non-linear form of the
effective energy-momentum tensor stemming from the mass term is derived for the
spherically symmetric case. Only in the special case where the area of the two
sphere is not deviated away from the FLRW universe, the effective energy
momentum tensor becomes completely the same as that of cosmological constant.
This opens a window for discriminating the non-linear massive gravity from
general relativity (GR). Indeed, by further solving these spherically symmetric
gravitational equations of motion in vacuum to the linear order, we obtain a
solution which has an arbitrary time-dependent parameter. In GR, this parameter
is a constant and corresponds to the mass of a star. Our result means that
Birkhoff's theorem no longer holds in the non-linear massive gravity and
suggests that energy can probably be emitted superluminously (with infinite
speed) on the self-accelerating background by the helicity-0 mode, which could
be a potential plague of this theory.Comment: 16 pages, references added; minor modification to match version
published in JCA
Exact soliton solution and inelastic two-soliton collision in spin chain driven by a time-dependent magnetic field
We investigate dynamics of exact N-soliton trains in spin chain driven by a
time-dependent magnetic field by means of an inverse scattering transformation.
The one-soliton solution indicates obviously the spin precession around the
magnetic field and periodic shape-variation induced by the time varying field
as well. In terms of the general soliton solutions N-soliton interaction and
particularly various two-soliton collisions are analyzed. The inelastic
collision by which we mean the soliton shape change before and after collision
appears generally due to the time varying field. We, moreover, show that
complete inelastic collisions can be achieved by adjusting spectrum and field
parameters. This may lead a potential technique of shape control of soliton.Comment: 5 pages, 5 figure
Identification of the active site of legumain links it to caspases, clostripain and gingipains in a new clan of cysteine endopeptidases
AbstractWe show by site-directed mutagenesis that the catalytic residues of mammalian legumain, a recently discovered lysosomal asparaginycysteine endopeptidase, form a catalytic dyad in the motif His-Gly-spacer-Ala-Cys. We note that the same motif is present in the caspases, aspartate-specific endopeptidases central to the process of apoptosis in animal cells, and also in the families of clostripain and gingipain which are arginyl/lysyl endopeptidases of pathogenic bacteria. We propose that the four families have similar protein folds, are evolutionarily related in clan CD, and have common characteristics including substrate specificities dominated by the interactions of the S1 subsite
Decaying Hidden Dark Matter in Warped Compactification
The recent PAMELA and ATIC/Fermi/HESS experiments have observed an excess of
electrons and positrons, but not anti-protons, in the high energy cosmic rays.
To explain this result, we construct a decaying hidden dark matter model in
string theory compactification that incorporates the following two ingredients,
the hidden dark matter scenario in warped compactification and the
phenomenological proposal of hidden light particles that decay to the Standard
Model. In this model, on higher dimensional warped branes, various warped
Kaluza-Klein particles and the zero-mode of gauge field play roles of the
hidden dark matter or mediators to the Standard Model.Comment: 15 pages; v4, several clarifications added, update on Fermi/HESS
result
Progress on Neutron-Target Multipoles above 1 GeV
We report a new extraction of nucleon resonance couplings using pi-
photoproduction cross sections on the neutron. The world database for the
process gn-->pi-p above 1 GeV has quadrupled with the addition of new
differential cross sections from the CEBAF Large Acceptance Spectrometer (CLAS)
at Jefferson Lab in Hall B. Differential cross sections from CLAS have been
improved with a new final-state interaction determination using a diagrammatic
technique taking into account the SAID phenomenological NN and piN final-state
interaction amplitudes. Resonance couplings have been extracted and compared to
previous determinations. With the addition of these new cross sections,
significant changes are seen in the high-energy behavior of the SAID cross
sections and amplitudes.Comment: 4 pages, 3 figures, 1 table; talk given at 12th International
Workshop on Meson Production, Properties and Interaction (MESON2012), 31 May
- 5 June 2012, Krakow, Poland; will be published online in European Journal
Web of Conference
Association of Insulin Resistance with Serum Interleukin-6 and TNF-α Levels During Normal Pregnancy
Overview The purpose of this study was to evaluate the role of Tumor Necrosis Factor-α (TNF-α) in insulin resistance (IR) during normal pregnancy. Approach This cross sectional study was carried out on 86 healthy pregnant women including 26, 23 and 37 individuals in the 1st, 2nd and 3rd trimesters, respectively, and in 21 healthy non pregnant women. Serum TNF-α concentration was measured by Enzyme Linked Immunosorbent Assay (ELISA) method. Results There were significant differences between serum TNF-α and IL-6 levels in pregnant women as compared with maternal healthy controls. There was significant correlation between gestational age and Body Mass Index (BMI) (r = 0.28, P = 0.01). There was no significant correlation between gestational age and insulin resistance (IR). We also did not find correlations between IR and TNF-α and IR and IL-6 in pregnant women. Conclusion In conclusion, our findings suggest that TNF-α and IL-6 are not greatly contributed to pregnancy induced insulin resistance in normal pregnancy
Microscopic Structure of the Calcium Isotopes
This research was sponsored by the National Science Foundation Grant NSF PHY-931478
Kinetics of coherent order-disorder transition in
Within a phase field approach which takes the strain-induced elasticity into
account, the kinetics of the coherent order-disorder transition is investigated
for the specific case of alloy. It is shown that a microstructure
with cubic precipitates appears as a transient state during the
decomposition of a homogeneous disordered solid solution into a microstructure
with tetragonal precipitates embedded into a disordered matrix. At
low enough temperature, favored by a weak internal stress, only
precipitates grow in the transient microstructure preceding nucleation of the
precipitates that occurs exclusively at the interface of the solid
solution with the precipitates. Analysis of microstructures at
nanoscopic scale shows a characteristic rod shape for the
precipitates due to the combination of their tetragonal symmetry and their
large internal stress.Comment: 2 postscript figures and 1 JPG pag
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