21,776 research outputs found
Accountability , Ability and Disability: Gaming the System
The past several years have been marked by a general trend towards increased high-stakes testing for students and schools and test-based school accountability systems. There are many potential school responses to testing programs. This paper investigates the potential that schools respond by gaming the system through reshaping the test pool. Using student-level panel data from six large counties in Florida, we study whether the introduction of the Florida Comprehensive Assessment Test in 1996 led schools to reclassify students as disabled and therefore ineligible to contribute to the school's aggregate test scores. Employing student-level fixed effect models and a series of secular trends as controls, we find that schools tend to reclassify low income and previously low performing students as disabled at significantly higher rates following the introduction of the testing regime. Moreover, these behaviors are concentrated among the low income schools most likely to be on the margin of failing the state's accountability system.
Origin of the fast magnetization tunneling in the single-molecule magnet [Ni(hmp)(tBuEtOH)Cl]4
We present high-frequency angle-dependent EPR data for crystals of
[NixZn1-x(hmp)(t-BuEtOH)Cl]4 (x = 1 and 0.02). The x = 1 complex behaves as a
single-molecule magnet at low temperatures, displaying hysteresis and
exceptionally fast magnetization tunneling. We show that this behavior is
related to a 4th-order transverse crystal-field interaction, which produces a
significant tunnel-splitting (~10 MHz) of the ground state of this S = 4
system. The magnitude of the 4th-order anisotropy, and the dominant axial term
(D), can be related to the single-ion interactions (Di and Ei) at the
individual NiII sites, as determined for the x = 0.02 crystals.Comment: 11 pages including 2 figure
Exploratory ASCA Observations of Broad Absorption Line Quasi-Stellar Objects
We present the analysis and interpretation of a sample of eight ASCA
observations of Broad Absorption Line Quasi-Stellar Objects (BALQSOs). This is
the first moderate-sized sample of sensitive BALQSO observations above 2 keV,
and the BALQSOs in our sample are among the optically brightest known
(B=14.5-18.5). Despite the ability of 2-10 keV X-rays to penetrate large column
densities, we find BALQSOs to be extremely weak sources above 2 keV, and we are
only able to add two new 2-10 keV detections (0226-104 and IRAS 07598+6508) to
those previously reported. By comparison with non-BALQSOs of similar optical
continuum magnitudes, we derive the column densities needed to suppress the
expected X-ray fluxes of our BALQSOs. In several cases we derive column
densities > 5x10^{23} cm^{-2} for a neutral absorber with solar abundances.
These are the largest X-ray column densities yet inferred for BALQSOs, and they
exceed ROSAT lower limits by about an order of magnitude. Optical brightness
does not appear to be a good predictor of 2-10 keV brightness for BALQSOs, but
our data do suggest that the BALQSOs with high optical continuum polarizations
may be the X-ray brighter members of the class. For example, the highly
polarized object PHL 5200 appears to be unusually X-ray bright for a BALQSO
given its optical magnitude. We discuss the implications of our results for
future observations with AXAF and XMM. If the objects in our sample are
representative of the BALQSO population, precision X-ray spectroscopy of most
BALQSOs will unfortunately prove difficult in the near future.Comment: 19 pages, ApJ in press, also available from
http://www.astro.psu.edu/users/niel/papers/papers.htm
A mathematical model for the sequestering of chemical contaminants by magnetic particles
A mathematical model is developed and implemented to characterize the pickup of various liquid chemical contaminants by
polyethylene-coated magnetic particles. The model and its associated experimental and analytical protocols were applied to a wide range
of liquid chemicals in order to gain insights into the physical basis for the pickup phenomenon. The characteristics of the pickup isotherms
range between “ideal” and “nonideal” behaviors that are reflected in the mathematical model by a single parameter, �0, where �0=1
corresponds to ideal behavior and �0�1 corresponds to a departure from idealized behavior that is directly quantified by the magnitude
of �0. The parameter �0 is also related to the efficiency of pickup, and since most isotherms observed in the study deviate from ideality,
the high efficiency of pickup observed in these systems has been attributed in part to this deviation. The proposed model and its associated
experimental and analytical protocols demonstrate great potential for the systematic evaluation of the uptake of chemical contaminants
using magnetic particle technology
A proposal for the coherent propagation studies portion of the 10.6-micrometer laser communications experiment Advanced Technology Satellite-F technical proposal
Coherent propagation study proposal for ATS-F 10.6 micrometer laser communications experimen
Intrinsic Josephson Effect and Violation of the Josephson Relation in Layered Superconductors
Equations describing the resistive state of a layered superconductor with
anisotropic pairing are derived. The similarity with a stack of Josephson
junctions is found at small voltages only, when current density in the
direction perpendicular to the layers can be interpreted as a sum of the
Josephson superconducting, the Ohmic dissipative and the interference currents.
In the spatially uniform state differential conductivity at higher voltages
becomes negative. Nonuniformity of the current distribution generates the
branch imbalance and violates the Josephson relation between frequency and
voltage.Comment: 11 pages, no figures, revtex, to be published in Phys. Rev. Let
The shock process and light element production in supernovae envelopes
Detailed hydrodynamic modeling of the passage of supernova shocks through the hydrogen envelopes of blue and red progenitor stars was carried out to explore the sensitivity to model conditions of light element production (specifically Li-7 and B-11) which was noted by Dearborn, Schramm, Steigman and Truran (1989) (DSST). It is found that, for stellar models with M is less than or approximately 100 M solar mass, current state of the art supernova shocks do not produce significant light element yields by hydrodynamic processes alone. The dependence of this conclusion on stellar models and on shock strengths is explored. Preliminary implications for Galactic evolution of lithium are discussed, and it is suspected that intermediate mass red giant stars may be the most consistent production site for lithium
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