592 research outputs found
Thermal Relics in Modified Cosmologies: Bounds on Evolution Histories of the Early Universe and Cosmological Boosts for PAMELA
Alternative cosmologies, based on extensions of General Relativity, predict
modified thermal histories in the Early Universe during the pre Big Bang
Nucleosynthesis (BBN) era, epoch which is not directly constrained by
cosmological observations. When the expansion rate is enhanced with respect to
the standard case, thermal relics typically decouple with larger relic
abundances. The correct value of the relic abundance is therefore obtained for
larger annihilation cross--sections, as compared to standard cosmology. A
direct consequence is that indirect detection rates are enhanced. Extending
previous analyses of ours, we derive updated astrophysical bounds on the dark
matter annihilation cross sections and use them to constrain alternative
cosmologies in the pre--BBN era. We also determine the characteristics of these
alternative cosmologies in order to provide the correct value of relic
abundance for a thermal relic for the (large) annihilation cross--section
required to explain the PAMELA results on the positron fraction, therefore
providing a "cosmological boost" solution to the dark matter interpretation of
the PAMELA data.Comment: 19 pages, 27 figures, matches published versio
Systematic uncertainties in the determination of the local dark matter density
A precise determination of the local dark matter density and an accurate
control over the corresponding uncertainties are of paramount importance for
Dark Matter (DM) searches. Using very recent high-resolution numerical
simulations of a Milky Way like object, we study the systematic uncertainties
that affect the determination of the local dark matter density based on
dynamical measurements in the Galaxy. In particular, extracting from the
simulation with baryons the orientation of the Galactic stellar disk with
respect to the DM distribution, we study the DM density for an observer located
at 8 kpc from the Galactic center {\it on the stellar disk}, .
This quantity is found to be always larger than the average density in a
spherical shell of same radius , which is the quantity inferred
from dynamical measurements in the Galaxy, and to vary in the range
. This suggests that the actual dark matter
density in the solar neighbourhood is on average 21\% larger than the value
inferred from most dynamical measurements, and that the associated systematic
errors are larger than the statistical errors recently discussed in the
literature.Comment: 6 pages, 3 figures, matches published versio
Penerimaan Panelis Serta Analisis Usaha Mi Instan Berbasis Jagung Lokal Pelalawan dan Tapioka
The purposes of this study were to analyze the level of acceptance by the panelists and to analyze the business feasibility of instant noodles made from Pelalawan local corn flour and tapioca. The research was conducted experimentally by making instant noodles from local corn flour and tapioca and then tested for panelists acceptance and business analysis. Data of panelists acceptance were analysis by Cochran's Q test at the level of 5%. Test results show that Cochran's Q indicates the number of 5.455 which means H0 accepted with the understanding that the instant noodles made from local corn flour and tapioca were accepted by the panelists. Business analysis of instant noodles made from Pelalawan local corn flour and tapioca show that HPP values obtained by the total cost were Rp. 1,268.05 and HPP from main total variable cost were Rp. 1,206.69. Profit obtained was Rp 221,048.37/20 kg of main raw materials. Business efficiency with RCR of 1.58. BEP based on the amount of production value were 191.48 and the BEP based on production price were Rp. 1,268.05 with economic value were Rp. 239,580
Coupling biochemistry and mechanics in cell adhesion: a model for inhomogeneous stress fiber contraction
Biochemistry and mechanics are closely coupled in cell adhesion. At sites of
cell-matrix adhesion, mechanical force triggers signaling through the
Rho-pathway, which leads to structural reinforcement and increased
contractility in the actin cytoskeleton. The resulting force acts back to the
sites of adhesion, resulting in a positive feedback loop for mature adhesion.
Here we model this biochemical-mechanical feedback loop for the special case
when the actin cytoskeleton is organized in stress fibers, which are
contractile bundles of actin filaments. Activation of myosin II molecular
motors through the Rho-pathway is described by a system of reaction-diffusion
equations, which are coupled into a viscoelastic model for a contractile actin
bundle. We find strong spatial gradients in the activation of contractility and
in the corresponding deformation pattern of the stress fiber, in good agreement
with experimental findings.Comment: Revtex, 35 pages, 13 Postscript figures included, in press with New
Journal of Physics, Special Issue on The Physics of the Cytoskeleto
Deformed Gaussian Orthogonal Ensemble Analysis of the Interacting Boson Model
A Deformed Gaussian Orthogonal Ensemble (DGOE) which interpolates between the
Gaussian Orthogonal Ensemble and a Poissonian Ensemble is constructed. This new
ensemble is then applied to the analysis of the chaotic properties of the low
lying collective states of nuclei described by the Interacting Boson Model
(IBM). This model undergoes a transition order-chaos-order from the
limit to the limit. Our analysis shows that the quantum fluctuations of
the IBM Hamiltonian, both of the spectrum and the eigenvectors, follow the
expected behaviour predicted by the DGOE when one goes from one limit to the
other.Comment: 10 pages, 4 figures (avaiable upon request), IFUSP/P-1086 Replaced
version: in the previous version the name of one of the authors was omitte
New Constraints from PAMELA anti-proton data on Annihilating and Decaying Dark Matter
Recently the PAMELA experiment has released its updated anti-proton flux and
anti-proton to proton flux ratio data up to energies of ~200GeV. With no clear
excess of cosmic ray anti-protons at high energies, one can extend constraints
on the production of anti-protons from dark matter. In this letter, we consider
both the cases of dark matter annihilating and decaying into standard model
particles that produce significant numbers of anti-protons. We provide two sets
of constraints on the annihilation cross-sections/decay lifetimes. In the one
set of constraints we ignore any source of anti-protons other than dark matter,
which give the highest allowed cross-sections/inverse lifetimes. In the other
set we include also anti-protons produced in collisions of cosmic rays with
interstellar medium nuclei, getting tighter but more realistic constraints on
the annihilation cross-sections/decay lifetimes.Comment: 7 pages, 3 figures, 3 table
Genetic Studies of Sulfadiazine-resistant and Methionine-requiring \u3cem\u3eNeisseria\u3c/em\u3e Isolated From Clinical Material
Deoxyribonucleate (DNA) preparations were extracted from Neisseria meningitidis (four isolates from spinal fluid and blood) and N. gonorrhoeae strains, all of which were resistant to sulfadiazine upon primary isolation. These DNA preparations, together with others from in vitro mutants of N. meningitidis and N. perflava, were examined in transformation tests by using as recipient a drug-susceptible strain of N. meningitidis (Ne 15 Sul-s Met+) which was able to grow in a methionine-free defined medium. The sulfadiazine resistance typical of each donor was introduced into the uniform constitution of this recipient. Production of p-aminobenzoic acid was not significantly altered thereby. Transformants elicited by DNA from the N. meningitidis clinical isolates were resistant to at least 200 μg of sulfadiazine/ml, and did not show a requirement for methionine (Sul-r Met+). DNA from six strains of N. gonorrhoeae, which were isolated during the period of therapeutic use of sulfonamides, conveyed lower degrees of resistance and, invariably, a concurrent methionine requirement (Sul-r/Met−). The requirement of these transformants, and that of in vitro mutants selected on sulfadiazine-agar, was satisfied by methionine, but not by vitamin B12, homocysteine, cystathionine, homoserine, or cysteine. Sul-r Met+ and Sul-r/Met− loci could coexist in the same genome, but were segregated during transformation. On the other hand, the dual Sul-r/Met− properties were not separated by recombination, but were eliminated together. DNA from various Sul-r/Met− clones tested against recipients having nonidentical Sul-r/Met− mutant sites yielded Sul-s Met+ transformants. The met locus involved is genetically complex, and will be a valuable tool for studies of genetic fine structure of members of Neisseria, and of genetic homology between species
Can AMS-02 discriminate the origin of an anti-proton signal?
Indirect searches can be used to test dark matter models against expected signals in various channels, in particular antiprotons. With antiproton data available soon at higher and higher energies, it is important to test the dark matter hypothesis against alternative astrophysical sources, e.g. econdaries accelerated in supernova remnants. We investigate the two signals from different dark matter models and different supernova remnant parameters, as forecasted for the AMS-02, and show that they present a significant degeneracy
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