21,064 research outputs found
Formulating a State Approach to Professional Development
When viewed from the perspective of an entire state\u27s needs, the challenges of designing professional development to meet the requirements of the federal No Child Left Behind legislation of 2001 are daunting. In Oklahoma, the concerns about delivering to rural and urban populations which contain a variety of underserved populations are further complicated by the differences in the way science and mathematics are structured as disciplines. We describe two model programs, one in science and one in mathematics, which take much different approaches. However, the programs have three common elements that make them highly successful. Each program engages teachers strongly, seeks to change learning by altering both teachers\u27 behavior and content knowledge, and is continuously reflective
Assessing the climate impacts of Chinese dietary choices using a telecoupled global food trade and local land use framework
Global emissions trajectories developed to meet the 2â°C temperature target are likely to rely on the widespread deployment of negative emissions technologies and/or the implementation of substantial terrestrial carbon sinks. Such technologies include afforestation, carbon capture and storage (CCS) and bioenergy with carbon capture and storage (BECCS), but mitigation options for agriculture appear limited. For example, using the Global Calculator tool (http://www.globalcalculator.org/), under a 2â°C pathway, the âforests and other land useâ sector is projected to become a major carbon sink, reaching -15 GtCO2e yr-1 by 2050, compared to fossil emissions of 21 GtCO2e yr-1. At the same time, rates of agricultural emissions remain static at about 6 GtCO2e yr-1, despite increasing demands for crop and livestock production to meet the forecast dietary demands of the growing and increasingly wealthy global population. Emissions in the Global Calculator are sensitive to the assumed global diet, and particularly to the level and type of meat consumption, which in turn drive global land use patterns and agricultural emissions. Here we assess the potential to use a modified down-scaled Global Calculator methodology embedded within the telecoupled global food trade framework, to estimate the agricultural emissions and terrestrial carbon stock impacts in China and Brazil, arising from a plausible range of dietary choices in China. These dietary choices are linked via telecoupling mechanisms to Brazilian crop production (e.g. Brazilian soy for Chinese animal feed provision) and drive land and global market dynamics. âSpill-overâ impacts will also be assessed using the EU and Malawi as case studies
Direct Investigation of Superparamagnetism in Co Nanoparticle Films
A direct probe of superparamagnetism was used to determine the complete
anisotropy energy distribution of Co nanoparticle films. The films were
composed of self-assembled lattices of uniform Co nanoparticles 3 nm or 5 nm in
diameter, and a variable temperature scanning-SQUID microscope was used to
measure temperature-induced spontaneous magnetic noise in the samples. Accurate
measurements of anisotropy energy distributions of small volume samples will be
critical to magnetic optimization of nanoparticle devices and media.Comment: 4 pages, 4 figures. Submitted to Physical Review Letter
On the Maximum Mass of Accreting Primordial Supermassive Stars
Supermassive primordial stars are suspected to be the progenitors of the most
massive quasars at z~6. Previous studies of such stars were either unable to
resolve hydrodynamical timescales or considered stars in isolation, not in the
extreme accretion flows in which they actually form. Therefore, they could not
self-consistently predict their final masses at collapse, or those of the
resulting supermassive black hole seeds, but rather invoked comparison to
simple polytropic models. Here, we systematically examine the birth, evolution
and collapse of accreting non-rotating supermassive stars under accretion rates
of 0.01-10 solar masses per year, using the stellar evolution code KEPLER. Our
approach includes post-Newtonian corrections to the stellar structure and an
adaptive nuclear network, and can transition to following the hydrodynamic
evolution of supermassive stars after they encounter the general relativistic
instability. We find that this instability triggers the collapse of the star at
masses of 150,000-330,000 solar masses for accretion rates of 0.1-10 solar
masses per year, and that the final mass of the star scales roughly
logarithmically with the rate. The structure of the star, and thus its
stability against collapse, is sensitive to the treatment of convection, and
the heat content of the outer accreted envelope. Comparison with other codes
suggests differences here may lead to small deviations in the evolutionary
state of the star as a function of time, that worsen with accretion rate. Since
the general relativistic instability leads to the immediate death of these
stars, our models place an upper limit on the masses of the first quasars at
birth.Comment: 5 pages, 4 figures. Accepted ApJ letter
The Evolution of Supermassive Population III Stars
Supermassive primordial stars forming in atomically-cooled halos at are currently thought to be the progenitors of the earliest quasars
in the Universe. In this picture, the star evolves under accretion rates of
yr until the general relativistic instability
triggers its collapse to a black hole at masses of .
However, the ability of the accretion flow to sustain such high rates depends
crucially on the photospheric properties of the accreting star, because its
ionising radiation could reduce or even halt accretion. Here we present new
models of supermassive Population III protostars accreting at rates yr, computed with the GENEVA stellar evolution code
including general relativistic corrections to the internal structure. We use
the polytropic stability criterion to estimate the mass at which the collapse
occurs, which has been shown to give a lower limit of the actual mass at
collapse in recent hydrodynamic simulations. We find that at accretion rates
higher than yr the stars evolve as red, cool
supergiants with surface temperatures below K towards masses
, and become blue and hot, with surface temperatures above K,
only for rates yr. Compared to previous
studies, our results extend the range of masses and accretion rates at which
the ionising feedback remains weak, reinforcing the case for direct collapse as
the origin of the first quasars
On the Rotation of Supermassive Stars
Supermassive stars born from pristine gas in atomically-cooled haloes are
thought to be the progenitors of supermassive black holes at high redshifts.
However, the way they accrete their mass is still an unsolved problem. In
particular, for accretion to proceed, a large amount of angular momentum has to
be extracted from the collapsing gas. Here, we investigate the constraints
stellar evolution imposes on this angular momentum problem. We present an
evolution model of a supermassive Population III star including simultaneously
accretion and rotation. We find that, for supermassive stars to form by
accretion, the accreted angular momentum has to be about 1% of the Keplerian
angular momentum. This tight constraint comes from the -limit, at
which the combination of radiation pressure and centrifugal force cancels
gravity. It implies that supermassive stars are slow rotators, with a surface
velocity less than 10-20% of their first critical velocity, at which the
centrifugal force alone cancels gravity. At such low velocities, the
deformation of the star due to rotation is negligible
Effects of the triaxial deformation and pairing correlation on the proton emitter 145Tm
The ground-state properties of the recent reported proton emitter 145Tm have
been studied within the axially or triaxially deformed relativistic mean field
(RMF) approaches, in which the pairing correlation is taken into account by the
BCS-method with a constant pairing gap. It is found that triaxiality and
pairing correlations play important roles in reproducing the experimental one
proton separation energy. The single-particle level, the proton emission orbit,
the deformation parameters beta = 0.22 and gamma = 28.98 and the corresponding
spectroscopic factor for 145Tm in the triaxial RMF calculation are given as
well.Comment: 17 pages, 7 figures and 1 table. accepted by Physical Review
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