1,981 research outputs found
School Vouchers in Practice: Competition Won't Hurt You!
An important issue in the debate on voucher systems and school choice is what effects competition from independent schools will have on public schools. Sweden has made a radical reform of its system for financing schools. Independent and public schools operate on close to equal terms under a voucher system covering all children. Sample selection models are estimated, using a data set of about 28 000 individuals. In addition, panel data models are estimated on 288 Swedish municipalities. The findings support the hypothesis that school results in public schools improve due to competition.Public Education; Independent Schools; Student Achievement; School Vouchers; School Choice; Sample Selection Model; Panel Data Model; Instrumental Variable Estimation
Search for Supersymmetric Dark Matter with Superfluid He3 (MACHe3)
MACHe3 (MAtrix of Cells of superfluid He3) is a project of a new detector for
direct Dark Matter search, using superfluid He3 as a sensitive medium. This
paper presents a phenomenological study done with the DarkSUSY code, in order
to investigate the discovery potential of this project of detector, as well as
its complementarity with existing and planned devices.Comment: 15 pages, 5 figures, submitted to Phys. Letters B, minor changes in
the tex
Human resources for control of tuberculosis and HIV-associated tuberculosis.
The global targets for tuberculosis (TB) control were postponed from 2000 to 2005, but on current evidence a further postponement may be necessary. Of the constraints preventing these targets being met, the primary one appears to be the lack of adequately trained and qualified staff. This paper outlines: 1) the human resources and skills for global TB and human immunodeficiency virus (HIV) TB control, including the human resources for implementing the DOTS strategy, the additional human resources for implementing joint HIV-TB control strategies and what is known about human resource gaps at global level; 2) the attempts to quantify human resource gaps by focusing on a small country in sub-Saharan Africa, Malawi; and 3) the main constraints to human resources and their possible solutions, under six main headings: human resource planning; production of human resources; distribution of the work-force; motivation and staff retention; quality of existing staff; and the effect of HIV/AIDS. We recommend an urgent shift in thinking about the human resource paradigm, and exhort international policy makers and the donor community to make a concerted effort to bridge the current gaps by investing for real change
Significant Gamma Lines from Inert Higgs Dark Matter
One way to unambiguously confirm the existence of particle dark matter and
determine its mass would be to detect its annihilation into monochromatic
gamma-rays in upcoming telescopes. One of the most minimal models for dark
matter is the inert doublet model, obtained by adding another Higgs doublet
with no direct coupling to fermions. For a mass between 40 and 80 GeV, the
lightest of the new inert Higgs particles can give the correct cosmic abundance
of cold dark matter in agreement with current observations. We show that for
this scalar dark matter candidate, the annihilation signal of monochromatic
\gamma\gamma and Z\gamma final states would be exceptionally strong. The energy
range and rates for these gamma-ray line signals make them ideal to search for
with the soon upcoming GLAST satellite.Comment: 4 pages, 3 figures; minor changes and text improvements; references
updated; published versio
Dark matter annihilation at the galactic center
If cold dark matter is present at the galactic center, as in current models
of the dark halo, it is accreted by the central black hole into a dense spike.
Particle dark matter then annihilates strongly inside the spike, making it a
compact source of photons, electrons, positrons, protons, antiprotons, and
neutrinos. The spike luminosity depends on the density profile of the inner
halo: halos with finite cores have unnoticeable spikes, while halos with inner
cusps may have spikes so bright that the absence of a detected neutrino signal
from the galactic center already places interesting upper limits on the density
slope of the inner halo. Future neutrino telescopes observing the galactic
center could probe the inner structure of the dark halo, or indirectly find the
nature of dark matter.Comment: 4 pages, 5 figure
Dark matter as a dynamic effect due to a non-minimal gravitational coupling with matter
In this work the phenomenology of models possessing a non-minimal coupling
between matter and geometry is discussed, with a particular focus on the
possibility of describing the flattening of the galactic rotation curves as a
dynamically generated effect derived from this modification to General
Relativity. Two possibilities are discussed: firstly, that the observed
discrepancy between the measured rotation velocity and the classical prediction
is due to a deviation from geodesic motion, due to a non-(covariant)
conservation of the energy-momentum tensor; secondly, that even if the
principle of energy conservation holds, the dynamical effects arising due to
the non-trivial terms in the Einstein equations of motion can give rise to an
extra density contribution that may be interpreted as dark matter. The
mechanism of the latter alternative is detailed, and a numerical session
ascertaining the order of magnitude of the relevant parameters is undertaken,
with possible cosmological implications discussed.Comment: Talk given at First Mediterranean Conference on Classical and Quantum
Gravity, Kolymbari, Greece, 14-18 September 2009
Diffuse inverse Compton and synchrotron emission from dark matter annihilations in galactic satellites
Annihilating dark matter particles produce roughly as much power in electrons
and positrons as in gamma ray photons. The charged particles lose essentially
all of their energy to inverse Compton and synchrotron processes in the
galactic environment. We discuss the diffuse signature of dark matter
annihilations in satellites of the Milky Way (which may be optically dark with
few or no stars), providing a tail of emission trailing the satellite in its
orbit. Inverse Compton processes provide X-rays and gamma rays, and synchrotron
emission at radio wavelengths might be seen. We discuss the possibility of
detecting these signals with current and future observations, in particular
EGRET and GLAST for the gamma rays.Comment: 13 pages, 5 figure
Two photon annihilation of Kaluza-Klein dark matter
We investigate the fermionic one-loop cross section for the two photon
annihilation of Kaluza-Klein (KK) dark matter particles in a model of universal
extra dimensions (UED). This process gives a nearly mono-energetic gamma-ray
line with energy equal to the KK dark matter particle mass. We find that the
cross section is large enough that if a continuum signature is detected, the
energy distribution of gamma-rays should end at the particle mass with a peak
that is visible for an energy resolution of the detector at the percent level.
This would give an unmistakable signature of a dark matter origin of the
gamma-rays, and a unique determination of the dark matter particle mass, which
in the case studied should be around 800 GeV. Unlike the situation for
supersymmetric models where the two-gamma peak may or may not be visible
depending on parameters, this feature seems to be quite robust in UED models,
and should be similar in other models where annihilation into fermions is not
helicity suppressed. The observability of the signal still depends on largely
unknown astrophysical parameters related to the structure of the dark matter
halo. If the dark matter near the galactic center is adiabatically contracted
by the central star cluster, or if the dark matter halo has substructure
surviving tidal effects, prospects for detection look promising.Comment: 17 pages, 3 figures; slightly revised versio
Compact stars in the standard model - and beyond
In the context of the standard model of particle physics, there is a definite
upper limit to the density of stable compact stars. However, if there is a
deeper layer of constituents, below that of quarks and leptons, stability may
be re-established far beyond this limiting density and a new class of compact
stars could exist. These objects would cause gravitational lensing of white
dwarfs and gamma-ray bursts, which might be observable as a diffraction pattern
in the spectrum. Such observations could provide means for obtaining new clues
about the fundamental particles and the origin of cold dark matter.Comment: 16 pages, 6 figures, contribution to the 42nd course of the
international school of subnuclear physics, 'How and where to go beyond the
standard model', Erice, Aug. 29 - Sep. 7, 200
Genome-wide analysis of chimpanzee genes with premature termination codons
<p>Abstract</p> <p>Background</p> <p>Premature termination codons (PTCs) cause mRNA degradation or a truncated protein and thereby contribute to the transcriptome and proteome divergence between species. Here we present the first genome-wide study of PTCs in the chimpanzee. By comparing the human and chimpanzee genome sequences we identify and characterize genes with PTCs, in order to understand the contribution of these mutations to the transcriptome diversity between the species.</p> <p>Results</p> <p>We have studied a total of 13,487 human-chimpanzee gene pairs and found that ~8% were affected by PTCs in the chimpanzee. A majority (764/1,109) of PTCs were caused by insertions or deletions and the remaining part was caused by substitutions. The distribution of PTC genes varied between chromosomes, with Y having the highest proportion. Furthermore, the density of PTC genes varied on a megabasepair scale within chromosomes and we found the density to be correlated both with indel divergence and proximity to the telomere. Within genes, PTCs were more common close to the 5' and 3' ends of the amino acid sequence. Gene Ontology classification revealed that olfactory receptor genes were over represented among the PTC genes.</p> <p>Conclusion</p> <p>Our results showed that the density of PTC genes fluctuated across the genome depending on the local genomic context. PTCs were preferentially located in the terminal parts of the transcript, which generally have a lower frequency of functional domains, indicating that selection was operating against PTCs at sites central to protein function. The enrichment of GO terms associated with olfaction suggests that PTCs may have influenced the difference in the repertoire of olfactory genes between humans and chimpanzees. In summary, 8% of the chimpanzee genes were affected by PTCs and this type of variation is likely to have an important effect on the transcript and proteomic divergence between humans and chimpanzees.</p
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