3,690 research outputs found
The Evaluation of the Effectiveness of Mastery Learning, Whole Group Pacing for Reading Instruction in the Clarkson Elementary School
The teaching of reading to elementary students is a very important task for teachers. Children enter school with a wide range of abilities and potentials. The child\u27s experience in language building activities can play a significant role in that child\u27s success in reading. Schools are challenged to receive all children as they are and develop reading skills through an articulated K-6 curriculum so as to provide all children with the ability to perform successfully in the academic areas of the secondary school
Semiclassical spin liquid state of easy axis Kagome antiferromagnets
Motivated by recent experiments on Nd-langasite, we consider the effect of
strong easy axis single-ion anisotropy on spins interacting with
antiferromagnetic exchange on the Kagome lattice. When , the
collinear low energy states selected by the anisotropy map on to configurations
of the classical Kagome lattice Ising antiferromagnet. However, the low
temperature limit is quite different from the cooperative Ising paramagnet that
obtains classically for . We find that sub-leading multi-spin interactions arising from the transverse quantum
dynamics result in a crossover from an intermediate temperature classical
cooperative Ising paramagnet to a semiclassical spin liquid with distinct
short-ranged correlations for .Comment: 4 pages, 3 eps figure
No Indications of Axion-Like Particles From Fermi
As very high energy (~100 GeV) gamma rays travel over cosmological distances,
their flux is attenuated through interactions with the extragalactic background
light. Observations of distant gamma ray sources at energies between ~200 GeV
and a few TeV by ground-based gamma ray telescopes such as HESS, however,
suggest that the universe is more transparent to very high energy photons than
had been anticipated. One possible explanation for this is the existence of
axion-like-particles (ALPs) which gamma rays can efficiently oscillate into,
enabling them to travel cosmological distances without attenuation. In this
article, we use data from the Fermi Gamma Ray Space Telescope to calculate the
spectra at 1-100 GeV of two gamma ray sources, 1ES1101-232 at redshift z=0.186
and H2356-309 at z=0.165, and use this in conjunction with the measurements of
ground-based telescopes to test the ALP hypothesis. We find that the
observations can be well-fit by an intrinsic power-law source spectrum with
indices of -1.72 and -2.1 for 1ES1101-232 and H2356-309, respectively, and that
no ALPs or other exotic physics is necessary to explain the observed degree of
attenuation.Comment: 7 pages, 4 figures. v3: Matches published version, the analysis of
H2356-309 is revised, no change in conclusion
Consistent Scenarios for Cosmic-Ray Excesses from Sommerfeld-Enhanced Dark Matter Annihilation
Anomalies in direct and indirect detection have motivated models of dark
matter consisting of a multiplet of nearly-degenerate states, coupled by a new
GeV-scale interaction. We perform a careful analysis of the thermal freezeout
of dark matter annihilation in such a scenario. We compute the range of "boost
factors" arising from Sommerfeld enhancement in the local halo for models which
produce the correct relic density, and show the effect of including constraints
on the saturated enhancement from the cosmic microwave background (CMB). We
find that boost factors from Sommerfeld enhancement of up to ~800 are possible
in the local halo. When the CMB bounds on the saturated enhancement are
applied, the maximal boost factor is reduced to ~400 for 1-2 TeV dark matter
and sub-GeV force carriers, but remains large enough to explain the observed
Fermi and PAMELA electronic signals. We describe regions in the DM mass-boost
factor plane where the cosmic ray data is well fit for a range of final states,
and show that Sommerfeld enhancement alone is enough to provide the large
annihilation cross sections required to fit the data, although for light
mediator masses (less than ~200 MeV) there is tension with the CMB constraints
in the absence of astrophysical boost factors from substructure. Additionally,
we consider the circumstances under which WIMPonium formation is relevant and
find for heavy WIMPs (greater than ~2 TeV) and soft-spectrum annihilation
channels it can be an important consideration; we find regions with dark matter
mass greater than 2.8 TeV that are consistent with the CMB bounds and have
~600-700 present-day boost factors.Comment: Related web application at
http://astrometry.fas.harvard.edu/mvogelsb/sommerfeld . v2: added brief
clarification regarding propagation parameters, plots now show effect of
relaxing CMB bounds. 35 pages in JCAP format, 4 figures. Accepted for
publication in JCA
Exchange parameters from approximate self-interaction correction scheme
The approximate atomic self-interaction corrections (ASIC) method to density
functional theory is put to the test by calculating the exchange interaction
for a number of prototypical materials, critical to local exchange and
correlation functionals. ASIC total energy calculations are mapped onto an
Heisenberg pair-wise interaction and the exchange constants J are compared to
those obtained with other methods. In general the ASIC scheme drastically
improves the bandstructure, which for almost all the cases investigated
resemble closely available photo-emission data. In contrast the results for the
exchange parameters are less satisfactory. Although ASIC performs reasonably
well for systems where the magnetism originates from half-filled bands, it
suffers from similar problems than those of LDA for other situations. In
particular the exchange constants are still overestimated. This reflects a
subtle interplay between exchange and correlation energy, not captured by the
ASIC.Comment: 10 page
The State of State Science Standards 2012
American science performance is lagging as the economy becomes increasingly high tech, but our current science standards are doing little to solve the problem. Reviewers evaluated science standards for every state for this report and their findings were deeply troubling: The majority of states earned Ds or Fs for their standards in this crucial subject, with only six jurisdictions receiving As. Explore all the state report cards and see how your state performed
- …