497 research outputs found
The longer-term effects of human capital enrichment programs on poverty and inequality : Oportunidades in Mexico
Previous empirical research has shown that Mexicoâs Oportunidades program has succeeded in increasing schooling and improving health of disadvantaged children. This paper studies the programâs potential longer-term consequences for the poverty and inequality of these children. It adapts methods developed in DiNardo, Fortin and Lemieux (1996) and incorporates existing experimental estimates of the programâs effects on human capital to analyze how Oportunidades will affect future earnings of program participants. We nonparametrically simulate earnings distributions, with and without the program, and predict that Oportunidades will increase future mean earnings but have only modest effects on poverty rates and earnings inequality.Oportunidades, Human capital, Schooling, Health, Poverty, Inequality.
The leafage of a chordal graph
The leafage l(G) of a chordal graph G is the minimum number of leaves of a
tree in which G has an intersection representation by subtrees. We obtain upper
and lower bounds on l(G) and compute it on special classes. The maximum of l(G)
on n-vertex graphs is n - lg n - (1/2) lg lg n + O(1). The proper leafage l*(G)
is the minimum number of leaves when no subtree may contain another; we obtain
upper and lower bounds on l*(G). Leafage equals proper leafage on claw-free
chordal graphs. We use asteroidal sets and structural properties of chordal
graphs.Comment: 19 pages, 3 figure
Mitigating the risk of Zika virus contamination of raw materials and cell lines in the manufacture of biologicals
Ensuring the virological safety of biologicals is challenging due to the risk of viral contamination of raw materials and cell
banks, and exposure during in-process handling to known and/or emerging viral pathogens. Viruses may contaminate raw
materials and biologicals intended for human or veterinary use and remain undetected until appropriate testing measures
are employed. The outbreak and expansive spread of the mosquito-borne flavivirus Zika virus (ZIKV) poses challenges to
screening human- and animal -derived products used in the manufacture of biologicals. Here, we report the results of an in
vitro study where detector cell lines were challenged with African and Asian lineages of ZIKV. We demonstrate that this
pathogen is robustly detectable by in vitro assay, thereby providing assurance of detection of ZIKV, and in turn underpinning
the robustness of in vitro virology assays in safety testing of biologicals
Mitigating the wider health effects of covid-19 pandemic response
No abstract available
Tackling population health challenges as we build back from the pandemic
Gerry McCartney and colleagues argue for a new model of equitable, holistic, and sustainable public health should be central to recovery plan
Stellar Structure of Dark Stars: a first phase of Stellar Evolution due to Dark Matter Annihilation
Dark Stars are the very first phase of stellar evolution in the history of
the universe: the first stars to form (typically at redshifts )
are powered by heating from dark matter (DM) annihilation instead of fusion (if
the DM is made of particles which are their own antiparticles). We find
equilibrium polytropic configurations for these stars; we start from the time
DM heating becomes important () and build up the star via
accretion up to 1000 M. The dark stars, with an assumed particle mass
of 100 GeV, are found to have luminosities of a few times L,
surface temperatures of 4000--10,000 K, radii cm, lifetimes of
at least Myr, and are predicted to show lines of atomic and molecular
hydrogen. Dark stars look quite different from standard metal-free stars
without DM heating: they are far more massive (e.g. for 100
GeV WIMPs), cooler, and larger, and can be distinguished in future
observations, possibly even by JWST or TMT.Comment: 14 pages, 1 figure, 1 table, shortened manuscript for publication,
updated mansucript in accordance with referee's repor
The structure of HI in galactic disks: Simulations vs observations
We generate synthetic HI Galactic plane surveys from spiral galaxy
simulations which include stellar feedback processes. Compared to a model
without feedback we find an increased scale height of HI emission (in better
agreement with observations) and more realistic spatial structure (including
supernova blown bubbles). The synthetic data show HI self-absorption with a
morphology similar to that seen in observations. The density and temperature of
the material responsible for HI self-absorption is consistent with
observationally determined values, and is found to be only weakly dependent on
absorption strength and star formation efficiency.Comment: 12 pages, 7 figures. Accepted for publication in MNRA
Supermassive Dark Stars: Detectable in JWST
The first phase of stellar evolution in the history of the Universe may be
Dark Stars, powered by dark matter heating rather than by nuclear fusion.
Weakly Interacting Massive Particles, which may be their own antipartners,
collect inside the first stars and annihilate to produce a heat source that can
power the stars for millions to billions of years. In this paper we show that
these objects can grow to be supermassive dark stars (SMDS) with masses
\gtrsim (10^5-10^7) \msun. The growth continues as long as dark matter
heating persists, since dark stars are large and cool (surface temperature
K) and do not emit enough ionizing photons to prevent
further accretion of baryons onto the star. The dark matter may be provided by
two mechanisms: (1) gravitational attraction of dark matter particles on a
variety of orbits not previously considered, and (2) capture of WIMPs due to
elastic scattering. Once the dark matter fuel is exhausted, the SMDS becomes a
heavy main sequence star; these stars eventually collapse to form massive black
holes that may provide seeds for supermassive black holes in the Universe. SMDS
are very bright, with luminosities exceeding . We
demonstrate that for several reasonable parameters, these objects will be
detectable with JWST. Such an observational discovery would confirm the
existence of a new phase of stellar evolution powered by dark matter.Comment: 32 pages, 4 figure
Implications of primordial black holes on the first stars and the origin of the super--massive black holes
If the cosmological dark matter has a component made of small primordial
black holes, they may have a significant impact on the physics of the first
stars and on the subsequent formation of massive black holes. Primordial black
holes would be adiabatically contracted into these stars and then would sink to
the stellar center by dynamical friction, creating a larger black hole which
may quickly swallow the whole star. If these primordial black holes are heavier
than , the first stars would likely live only for a very
short time and would not contribute much to the reionization of the universe.
They would instead become black holes which (depending on
subsequent accretion) could serve as seeds for the super--massive black holes
seen at high redshifts as well as those inside galaxies today.Comment: 16 pages, 2 figures. v2: refereed versio
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