4,392 research outputs found
Best Practice for Deaf and Hard-of-hearing Student Success in Postsecondary Education
More deaf students graduated from college in the United States in 1987 than were enrolled altogether just 25 years ago (Walter 1989). Yet this number is only about 30% of those who attempt postsecondary studies. In light of this estimated 70% withdrawal rate, we must ask whether the special needs of deaf students are being met in a manner that provides them equal opportunity to succeed at the postsecondary level (Stinson and Walter, 1992, p 57)
Multitransitional observations of the CS core of L673
A multitransitional study with the BIMA interferometric array was carried out
toward the starless core found in the L673 region, in order to study the
small-size structure of the cores detected with previous single--dish
observations, which provides us with a test of the predictions of the chemical
model of Taylor et al. (1996; 1998). We detected emission in the CS (2-1), N2H+
(1-0), and HCO+ (1-0) lines. Several clumps of size ~0.08 pc were found for
each line distributed all over the region where previous single-dish emission
was found (Morata et al. 1997). Each molecular transition traces differently
the clump distribution, although in some cases the detected clumps are
coincident. The distribution of the N2H+ emission and the single-dish NH3
emission are coincident and compatible with an origin in the same gas. The
large fraction of missing flux measured for the CS (2-1) transition can be
explained if the cloud is formed by a clumpy and heterogeneous medium. Four
positions were selected to derive the abundance ratios [N2H+/CS] and [HCO+/CS]
from the molecular column density determinations, and to compare them with the
values predicted by the chemical model. The model was able to explain the
interferometric observations, and, in particular, the chemical differentiation
of the detected clumps and the coincidence of the NH3 and N2H+ emissions. The
lack of HCO+ towards the two selected positions that trace the more evolved
clumps cannot be accounted for by the model, but it is possibly due to strong
self-absorption. We propose a classification of the studied clumps according to
the stage of chemical evolution indicated by the molecular abundances.Comment: 10 pages, 9 figures, accepted for publication in A&
Do pollinators contribute to nutritional health?
Despite suggestions that animal pollinators are crucial for human nutritional health, no studies have actually tested this claim. Here, we combined data on crop pollination requirements, food nutrient densities, and actual human diets to predict the effects of pollinator losses on the risk of nutrient deficiency. In four developing countries and across five nutrients, we found that 0 to 56% of populations would become newly at risk if pollinators were removed. Increases in risk were most pronounced for vitamin A in populations with moderate levels of total nutrient intake. Overall, the effects of pollinator decline varied widely among populations and nutrients. We conclude that the importance of pollinators to human nutrition depends critically on the composition of local diets, and cannot be reliably predicted from global commodity analyses. We identify conditions under which severe health effects of pollinator loss are most likely to occur
On The Interaction Of D0-Brane Bound States And RR Photons
We consider the problem of the interaction between D0-brane bound state and
1-form RR photons by the world-line theory. Based on the fact that in the
world-line theory the RR gauge fields depend on the matrix coordinates of
D0-branes, the gauge fields also appear as matrices in the formulation. At the
classical level, we derive the Lorentz-like equations of motion for D0-branes,
and it is observed that the center-of-mass is colourless with respect to the
SU(N) sector of the background. Using the path integral method, the
perturbation theory for the interaction between the bound state and the RR
background is developed. We discuss what kind of field theory may be
corresponded to the amplitudes which are calculated by the perturbation
expansion in world-line theory. Qualitative considerations show that the
possibility of existence of a map between the world-line theory and the
non-Abelian gauge theory is very considerable.Comment: LaTeX, 28 pages, 4 eps figures. v2 and v3: eqs. (3.18) and (B.2) are
corrected, very small change
Fuzzy Rings in D6-Branes and Magnetic Field Background
We use the Myers T-dual nonabelin Born-Infeld action to find some new
nontrivial solutions for the branes in the background of D6-branes and Melvin
magnetic tube field. In the D6-Branes background we can find both of the fuzzy
sphere and fuzzy ring solutions, which are formed by the gravitational
dielectric effect. We see that the fuzzy ring solution has less energy then
that of the fuzzy sphere. Therefore the fuzzy sphere will decay to the fuzzy
ring configuration. In the Melvin magnetic tube field background there does not
exist fuzzy sphere while the fuzzy ring configuration may be formed by the
magnetic dielectric effect. The new solution shows that propagating in
the D6-branes and magnetic tube field background may expand into a rotating
fuzzy ring. We also use the Dirac-Born-Infeld action to construct the ring
configuration from the D-branes.Comment: Latex, 15 pages, detailed comments in section 2, typos correcte
Exact N=2 Supergravity Solutions With Polarized Branes
We construct several classes of exact supersymmetric supergravity solutions
describing D4 branes polarized into NS5 branes and F-strings polarized into D2
branes. These setups belong to the same universality class as the perturbative
solutions used by Polchinski and Strassler to describe the string dual of N=1*
theories. The D4-NS5 setup can be interpreted as a string dual to a confining
4+1 dimensional theory with 8 supercharges, whose properties we discuss. By
T-duality, our solutions give Type IIB supersymmetric backgrounds with
polarized branes.Comment: 22 pages. v2 - references added, details clarifie
Transverse Fivebranes in Matrix Theory
M-theory on the maximally supersymmetric plane wave background of
eleven-dimensional supergravity admits spherical BPS transverse M5-branes with
zero light-cone energy. We give direct evidence that the single M5-brane state
corresponds to the trivial (X=0) classical vacuum in the large N limit of the
plane wave matrix theory. In particular, we show that the linear fluctuation
spectrum of the spherical fivebrane matches exactly with the set of exactly
protected excited states about the X=0 vacuum in the matrix model. These states
include geometrical fluctuations of the sphere, excitations of the worldvolume
two-form field, and fermion excitations. In addition, we propose a description
of multiple fivebrane states in terms of matrix model vacua.
Finally, we discuss how to obtain the continuum D2/M2 and NS5/M5 theories on
spheres from the matrix model. The matrix model can be viewed as a
regularization for these theories.Comment: Latex file, 2 eps figures, 22 pages; v2: typo correcte
Towards a supersymmetric non-abelian Born-Infeld theory
We define an iterative procedure to obtain a non-abelian generalization of
the Born-Infeld action. This construction is made possible by the use of the
severe restrictions imposed by kappa-symmetry. We have calculated all bosonic
terms in the action up to terms quartic in the Yang-Mills field strength and
all fermion bilinear terms up to terms cubic in the field strength. Already at
this order the fermionic terms do not satisfy the symmetric trace-prescription.Comment: 9 pp. Latex, to appear in the proceedings of the Strings 2000
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