10,393 research outputs found
Improving Rural Educational Attainment
More often than not, policymakers focus on school-based strategies to spur improvements in the educational progress of students. The 2002 No Child Left Behind Act, which demands greater school accountability for student performance, is a case in point. Yet, what happens in the classroom is only part of the story.In fact, as Lionel J. Beaulieu, Glenn D. Israel and Ronald C. Wimberley show in their chapter in "Challenges for Rural America in the Twenty-First Century", family characteristics have from 5 to 10 times as much impact as school characteristics on reading and math scores of rural U.S. eighth graders.In addition, community characteristics have as much impact as school characteristics on test scores, although both community and chool characteristics tend to be more important in geographically isolated rural areas than those adjacent to metropolitan areas. Clearly, helping rural youth succeed academically is the collective responsibility of families, schools, and communities.This issue brief is a joint product of the Rural Sociological Society and the National Coalition for Rural Entrepreneurship, a collaboration of four Regional Rural Development Centers: The Northeast Regional Center for Rural Development, the Southern Rural Development Center, the North Central Regional Center for Rural Development, and the Western Rural Development Center. Funding was also made available from the Ford Foundation.This brief is part of a policy brief series by the Rural Sociological Society and the Regional Rural Development Centers that stresses the importance of community collective action and developing the capacity of people and organizations to meet the community's needsThe Rural Sociological Society and the Regional Rural Development Centers creates new Public Policy Issue Brief series based on its recent book, "Challenges for Rural America in the Twenty-First Century".The briefs synthesize the context and substance of important issues raised in the book and address alternative policy options, with the goal of bringing important research to the policy community
Bearings use dry self-lubricating cage materials
Rolling element bearings in spacecraft mechanical systems use solid lubricant composites of polytetrafluoroethylene in the bearing cage which functions as the lubricant reservoir. The cage spaces the rolling elements equally and provides the lubricant at the bearing load-carrying surface
NICMOS Observations of the Pre-Main-Sequence Planetary Debris System HD 98800
Spectral energy distributions (SEDs) from 0.4 to 4.7 microns are presented
for the two principal stellar components of HD~98800, A and B. The third major
component, an extensive planetary debris system (PDS), emits > 20% of the
luminosity of star B in a blackbody SED at 164 +/- 5K extending from mid-IR to
millimeter-wavelengths. At 0.95 microns a preliminary upper limit of < 0.06 is
obtained for the ratio of reflected light to the total from star B. This result
limits the albedo of the PDS to < 0.3. Values are presented for the
temperature, luminosity, and radius of each major systemic component.
Remarkable similarities are found between the PDS and the interplanetary debris
system around the Sun as it could have appeared a few million years after its
formation.Comment: LaTeX, 9 pages with 1 encapsulated postscript figure and one
specially formatted Table which is rendered as a postscript file and included
as a figure. Accepted for publication in Astrophysical Journal Letter
Analytical description of spin-Rabi oscillation controlled electronic transitions rates between weakly coupled pairs of paramagnetic states with S=1/2
We report on an analytical description of spin-dependent electronic
transition rates which are controlled by a radiation induced spin-Rabi
oscillation of weakly spin-exchange and spin-dipolar coupled paramagnetic
states (S=1/2). The oscillation components (the Fourier content) of the net
transition rates within spin-pair ensembles are derived for randomly
distributed spin resonances with account of a possible correlation between the
two distributions that correspond to the two individual pair partners. The
results presented here show that when electrically or optically detected Rabi
spectroscopy is conducted under an increasing driving field B_ 1, the Rabi
spectrum evolves from a single resonance peak at s=\Omega_R, where
\Omega_R=\gamma B_1 is the Rabi frequency (\gamma is the gyromagnetic ratio),
to three peaks at s= \Omega_R, s=2\Omega_R, and at low s<< \Omega_R. The
crossover between the two regimes takes place when \Omega_R exceeds the
expectation value \delta_0 of the difference of the Zeeman energies within the
pairs, which corresponds to the broadening of the magnetic resonance lines in
the presence of disorder caused by hyperfine field or distributions of Lande
g-factors. We capture this crossover by analytically calculating the shapes of
all three peaks at arbitrary relation between \Omega_R and \delta_0. When the
peaks are well-developed their widths are \Delta s ~ \delta_0^2/\Omega_R.Comment: 10 page, 5 figure
Towards a Molecular Inventory of Protostellar Discs
The chemical environment in circumstellar discs is a unique diagnostic of the
thermal, physical and chemical environment. In this paper we examine the
structure of star formation regions giving rise to low mass stars, and the
chemical environment inside them, and the circumstellar discs around the
developing stars.Comment: 9 page PDF, 550 kbyte
VLBA Polarization Observations of Markarian 421 After a Gamma-Ray High State
We present four high dynamic range, dual-circular polarization, Very Long
Baseline Array (VLBA) observations at 22 GHz of Markarian 421, taken throughout
the year following the source's unprecedented gamma-ray high state in early
2001. These four new VLBA observations are combined with data from our earlier
1999 paper and archival VLBA data-sets that have become available since 1999 to
produce a combined 28 epoch VLBA data-set on Mrk 421 spanning the years 1994 to
2002. No new component associated with the 2001 flares was seen on the total
intensity images, but the combined data-set allowed precise measurements of the
apparent speeds of the existing components. The peak measured apparent speed
was for component C5, which has an apparent speed of 0.1 +/- 0.02 c (H_0=71 km
s^{-1} Mpc^{-1}, Omega_m=0.27, and Omega_Lambda=0.73). No counterjet is seen
with a limit on the jet to counterjet brightness ratio J >~ 100. These observed
VLBI properties of Markarian 421 are consistent with a jet with a bulk Lorentz
factor of about 2 and an angle to the line-of-sight of about 1 degree,
suggesting a jet that decelerates between the gamma-ray producing region and
the parsec scale. The VLBI core and inner jet (component C7) have fractional
polarizations of about 5%, and an electric vector position angle (EVPA) aligned
with the jet axis. Component C5 (at 1.5 mas from the core) has a higher
fractional polarization of about 15%, and an EVPA nearly orthogonal to the jet
axis. Significant variability is detected in the EVPA of component C6, which at
two of the four epochs shows an EVPA aligned with the jet axis, possibly a sign
of propagating disturbances that are only visible on the polarization images.
If these propagating disturbances are linked to the 2001 gamma-ray high state,
then their inferred apparent speed is between 1 and 3 c.Comment: 11 pages, accepted to Ap
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