354 research outputs found
The pulsar contribution to the diffuse galactic gamma-ray emission
Here we investigate to what extent unresolved \gr pulsars contribute to the
galactic diffuse emission, and further whether unresolved \gr pulsars can be
made responsible for the excess of diffuse galactic emission above 1 GeV which
has been observed by EGRET. Our analysis is based only on the properties of the
six pulsars which have been identified in the EGRET data, and is independent of
choice of a pulsar emission model. We find that pulsars contribute very little
to the diffuse emission at lower energies, whereas above 1 GeV they can account
for 25% of the observed intensity in selected regions for a reasonable number
of directly observable \gr pulsars (12). While the excess above 1 GeV \gr
energy is observed at least up to six or eight degrees off the plane, the
pulsar contribution would be negligible there. Thus pulsars do significantly
contribute to the diffuse galactic -ray emission above 1 GeV, but they
can not be made responsible for all the discrepancy between observed intensity
and model predictions in this energy range.Comment: 5 pages, Proceedings of the 4th Compton Symposiu
Multifactorial evaluation of atenolol, caffeine, carbamazepine and ibuprofen on raphidocelis subcapitata and chlorella vulgaris
Micropollutants in aquatic resources have raised global concerns regarding the conservation of ecosystems. Although they are usually found in the environment at trace concentrations to a maximum of several µg/L, it is still necessary to address the potential risks these pollutants may represent to organisms. A multifactor analysis was conducted using two algae as bioindicators. Four different pharmaceuticals were chosen based on their occurrence in domestic wastewaters and persistency after biological treatment processes ranging from 1/8th to four-fold representative environmental concentrations over 96 h exposure. The present multifactor analysis evaluated cell size, photosynthetic capacity and growth rate. These data were later combined into a simplified single entity: “the index effect”. The results obtained showed that, even at concentrations below the environmentally relevant concentrations (ERC), the pharmaceuticals’ residues (PRs), caused a cellular behavioural variation in both organisms. In addition, the algae cultures’ response to exposure to these stressors was generally dependent on the concentration over time. By examining four different PR over three different characteristics of two types of algal bioindicators, this work covers significant and specific responses on the algae exposure cycle. This is unique research since most studies do not consider multiple parameters in the assessment of the environment risk for bioindicators
Regulating in vivo calcification of alginate microbeads
Alginate calcification has been previously reported clinically and during animal implantation; however no study has investigated the mechanism, extensively characterized the mineral, or evaluated multiple methods to regulate or eliminate mineralization. In the present study, alginate calcification was first studied in vitro: calcium-crosslinked alginate beads sequestered surrounding phosphate while forming traces of hydroxyapatite. Calcification in vivo was then examined in nude mice using alginate microbeads with and without adipose stem cells (ASCs). Variables included the delivery method, site of delivery, sex of the animal, time in vivo, crosslinking solution, and method of storage prior to delivery. Calciumcrosslinked alginate microbeads mineralized when injected subcutaneously or implanted intramuscularly after 1e6 months. More extensive analysis with histology, microCT, FTIR, XRD, and EDS showed calcium phosphate deposits throughout the microbeads with surface mineralization that closely matched hydroxyapatite found in bone. Incorporating 25 mM bisphosphonate reduced alginate calcification whereas using barium chloride eliminated mineralization. Buffering the crosslinking solution with HEPES at pH 7.3 while washing and storing samples in basal media prior to implantation also eliminated calcification in vivo. This study shows that alginate processing prior to implantation can significantly influence bulk hydroxyapatite formation and presents a method to regulate alginate calcificationAlginate calcification has been previously reported clinically and during animal implantation; however no study has investigated the mechanism, extensively characterized the mineral, or evaluated multiple methods to regulate or eliminate mineralization. In the present study, alginate calcification was first studied in vitro: calcium-crosslinked alginate beads sequestered surrounding phosphate while forming traces of hydroxyapatite. Calcification in vivo was then examined in nude mice using alginate microbeads with and without adipose stem cells (ASCs). Variables included the delivery method, site of delivery, sex of the animal, time in vivo, crosslinking solution, and method of storage prior to delivery. Calciumcrosslinked alginate microbeads mineralized when injected subcutaneously or implanted intramuscularly after 1e6 months. More extensive analysis with histology, microCT, FTIR, XRD, and EDS showed calcium phosphate deposits throughout the microbeads with surface mineralization that closely matched hydroxyapatite found in bone. Incorporating 25 mM bisphosphonate reduced alginate calcification whereas using barium chloride eliminated mineralization. Buffering the crosslinking solution with HEPES at pH 7.3 while washing and storing samples in basal media prior to implantation also eliminated calcification in vivo. This study shows that alginate processing prior to implantation can significantly influence bulk hydroxyapatite formation and presents a method to regulate alginate calcificatio
Unidentified EGRET Sources and the Extragalactic Gamma-Ray Background
The large majority of EGRET point sources remain to this day without an
identified low-energy counterpart. Whatever the nature of the EGRET
unidentified sources, faint unresolved objects of the same class must have a
contribution to the diffuse gamma-ray background: if most unidentified objects
are extragalactic, faint unresolved sources of the same class contribute to the
background, as a distinct extragalactic population; on the other hand, if most
unidentified sources are Galactic, their counterparts in external galaxies will
contribute to the unresolved emission from these systems. Understanding this
component of the gamma-ray background, along with other guaranteed
contributions from known sources, is essential in any attempt to use gamma-ray
observations to constrain exotic high-energy physics. Here, we follow an
empirical approach to estimate whether a potential contribution of unidentified
sources to the extragalactic gamma-ray background is likely to be important,
and we find that it is. Additionally, we comment on how the anticipated GLAST
measurement of the diffuse gamma-ray background will change, depending on the
nature of the majority of these sources.Comment: 6 pages, 3 figures, to appear in proceedings of "The Multi-Messenger
Approach to High Energy Gamma-Ray Sources", Barcelona, 4-7 July 2006;
comments welcom
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Application of the risk-based strategy to the Hanford tank waste organic-nitrate safety issue
This report describes the results from application of the Risk-Based Decision Management Approach for Justifying Characterization of Hanford Tank Waste to the organic-nitrate safety issue in Hanford single-shell tanks (SSTs). Existing chemical and physical models were used, taking advantage of the most current (mid-1997) sampling and analysis data. The purpose of this study is to make specific recommendations for planning characterization to help ensure the safety of each SST as it relates to the organic-nitrate safety issue. An additional objective is to demonstrate the viability of the Risk-Based Strategy for addressing Hanford tank waste safety issues
Gamma rays from the annihilation of singlet scalar dark matter
We consider an extension of the Standard Model by a singlet scalar that
accounts for the dark matter of the Universe. Within this model we compute the
expected gamma ray flux from the annihilation of dark matter particles in a
consistent way. To do so, an updated analysis of the parameter space of the
model is first presented. By enforcing the relic density constraint from the
very beginning, the viable parameter space gets reduced to just two variables:
the singlet mass and the higgs mass. Current direct detection constraints are
then found to require a singlet mass larger than 50 GeV. Finally, we compute
the gamma ray flux and annihilation cross section and show that a large
fraction of the viable parameter space lies within the sensitivity of
Fermi-GLAST.Comment: 13 pages, 5 figures. v2: minor modifications to text and figures;
main results unchanged. v3: some references adde
Determining the WIMP mass using the complementarity between direct and indirect searches and the ILC
We study the possibility of identifying dark matter properties from
XENON-like 100 kg experiments and the GLAST satellite mission. We show that
whereas direct detection experiments will probe efficiently light WIMPs, given
a positive detection (at the 10% level for GeV), GLAST
will be able to confirm and even increase the precision in the case of a NFW
profile, for a WIMP-nucleon cross-section
pb. We also predict the rate of production of a WIMP in the next generation of
colliders (ILC), and compare their sensitivity to the WIMP mass with the XENON
and GLAST projects.Comment: 32 pages, new figures and a more detailed statistical analysis. Final
version to appear in JCA
A New Approach to Searching for Dark Matter Signals in Fermi-LAT Gamma Rays
Several cosmic ray experiments have measured excesses in electrons and
positrons, relative to standard backgrounds, for energies from ~ 10 GeV - 1
TeV. These excesses could be due to new astrophysical sources, but an
explanation in which the electrons and positrons are dark matter annihilation
or decay products is also consistent. Fortunately, the Fermi-LAT diffuse gamma
ray measurements can further test these models, since the electrons and
positrons produce gamma rays in their interactions in the interstellar medium.
Although the dark matter gamma ray signal consistent with the local electron
and positron measurements should be quite large, as we review, there are
substantial uncertainties in the modeling of diffuse backgrounds and,
additionally, experimental uncertainties that make it difficult to claim a dark
matter discovery. In this paper, we introduce an alternative method for
understanding the diffuse gamma ray spectrum in which we take the intensity
ratio in each energy bin of two different regions of the sky, thereby canceling
common systematic uncertainties. For many spectra, this ratio fits well to a
power law with a single break in energy. The two measured exponent indices are
a robust discriminant between candidate models, and we demonstrate that dark
matter annihilation scenarios can predict index values that require "extreme"
parameters for background-only explanations.Comment: v1: 11 pages, 7 figures, 1 table, revtex4; v2: 13 pages, 8 figures, 1
table, revtex4, Figure 4 added, minor additions made to text, references
added, conclusions unchanged, published versio
Dark Matter Direct Detection Signals inferred from a Cosmological N-body Simulation with Baryons
We extract at redshift z=0 a Milky Way sized object including gas, stars and
dark matter (DM) from a recent, high-resolution cosmological N-body simulation
with baryons. Its resolution is sufficient to witness the formation of a
rotating disk and bulge at the center of the halo potential. The phase-space
structure of the central galactic halo reveals the presence of a dark disk
component, that is co-rotating with the stellar disk. At the Earth's location,
it contributes to around 25% of the total DM local density, whose value is
rho_DM ~ 0.37 GeV/cm^3. The velocity distributions also show strong deviations
from pure Gaussian and Maxwellian distributions, with a sharper drop of the
high velocity tail.
We give a detailed study of the impact of these features on the predictions
for DM signals in direct detection experiments. In particular, the question of
whether the modulation signal observed by DAMA is or is not excluded by limits
set by other experiments (CDMS, XENON and CRESST...) is re-analyzed and
compared to the case of a standard Maxwellian halo, in both the elastic and the
inelastic scattering scenarios. We find that the compatibility between DAMA and
the other experiments is improved. In the elastic scenario, the DAMA modulation
signal is slightly enhanced in the so-called channeling region, as a result of
several effects. For the inelastic scenario, the improvement of the fit is
mainly attributable to the departure from a Maxwellian distribution at high
velocity.Comment: 39 page
Lighthouse Schools and Crop Museums in the Philippines
In The Philippines, Lighthouse Schools (LSs) and school-based Crop Museums (CMs) serve as repositories of crop biodiversity. Specifically, LSs are research sites where the integration of school feeding, nutrition education and school gardens, is demonstrated and evidence is established; while CMs are located within the large network of LS and act as seed banks that enable the multiplication and exchange of crop types and varieties across schools. Together they have helped conserve and promote multiple varieties of traditional and indigenous vegetables (IVs)and fruits
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