6,824 research outputs found
Recommended from our members
The "Common Core" Standards Initiative: An Effective Reform Tool?
Very little evidence supports the contention that establishing national academic standards for K-12 schools will improve the quality of American public education, and the standards push may distract attention from other vital school reforms, concludes a new policy brief, The "Common Core" Standards Initiative: An Effective Reform Tool? The brief, authored by William J. Mathis, was released today by the Great Lakes Center for Education Research and Practice. "Without addressing both the in-school and out-of-school influences on test scores, common core standards are not likely to improve the quality and equity of America's public schools," Mathis explains. The Obama administration has embraced "common core" standards and has pressured states to adopt them by stating that federal Title I aid will be withheld from states that do not adopt standards such as those being developed by the National Governors Association and the Council of Chief State School Officers. In addition, states that adopt the standards have a major advantage on their Race to the Top applications. Standards advocates argue that common standards are necessary for keeping the nation competitive in a global economy. But Mathis points out that research does not support this oft-expressed rationale. No studies support a true causal relationship between national standards and economic competitiveness, and at the most superficial level we know that nations with centralized standards generally tend to perform no better (or worse) on international tests than those without. Further, research shows that national economic competitiveness is influenced far more by economic decisions than by test scores. Mathis also raises questions about the rapid development of the common-core standards, the lack of field testing, and the overarching need for any high-stakes consequences to be "valid," pursuant to established professional guidelines. Given these concerns, he says that the prospect of positive effects on educational quality or equality "seems improbable.
Grain alignment by ferromagnetic impurities
The observed wavelength dependence of linear polarization, and its variation from region to region can be explained by the following assumptions. Interstellar grains resemble interplanetary grains, in that they are composed of collections of small particles coagulated together into elongated masses. A fraction of the small particles are ferromagnetic. Presumably these are either metallic Fe or magnetite, Fe3O4. If and only if a large grain contains one or more magnetic particles is the grain aligned in the galactic magnetic field. The magnetic particles stick only to silicate grains because of chemical similarities, or (equivalently) any pure carbon grains in the diffuse interstellar medium (ISM) are too spherical to produce polarization. Grains in dense regions, such as the outer parts of molecular clouds, are larger than those in the diffuse ISM because of coagulation of the grains rather than accretion of icy mantles. These regions are known to have larger than normal values of lambda (max), the wavelength of the maximum of linear polarization. The above assumptions are sufficient to allow the calculation of the wavelength dependence of the polarization
Transport and mixing in the radiation zones of rotating stars: I-Hydrodynamical processes
The purpose of this paper is to improve the modelization of the rotational
mixing which occurs in stellar radiation zones, through the combined action of
the thermally driven meridional circulation and of the turbulence generated by
the shear of differential rotation. The turbulence is assumed to be
anisotropic, due to the stratification, with stronger transport in the
horizontal directions than in the vertical. The main difference with the former
treatments by Zahn (1992) and Maeder & Zahn (1998) is that we expand here the
departures from spherical symmetry to higher order, and include explicitly the
differential rotation in latitude, to first order. This allows us to treat
simultaneously the bulk of a radiation zone and its tachocline(s). Moreover, we
take fully into account the non-stationarity of the problem, which will enable
us to tackle the rapid phases of evolution. The system of partial differential
equations, which govern the transport of angular momentum, heat and chemical
elements, is written in a form which makes it ready to implement in a stellar
evolution code. Here the effect of a magnetic field is deliberately ignored; it
will be included in forthcoming papers.Comment: 16 pages, no figures, accepted for publication in A&
A comparison of recently introduced instruments for measuring rice flour viscosity
The Rapid Visco-Analyser (RVA) and the Micro Visco-Amylograph (MVA) were compared in measuring the viscosity properties of rice flours. A total of 72 rice samples were procured from three cultivars harvested at two locations and three moisture contents and separated into thin, medium, and thick kernel-thickness fractions. A fast and a slow heating rate was used in the procedure for both instruments. Cultivar, kernel thickness, and harvest location affected rice viscosity. The RVA viscosity profiles using a fast heating rate were best correlated with those of the MVA using a slow heating rate. The RVA slow heating rate resulted in lower final viscosities than those using the MVA because of the spindle structure of the RVA. For both the RVA and the MVA, greater rice flour peak viscosities and less trough and final viscosities were obtained with a slow rather than a fast heating rat
Dependence of Gas Phase Abundances in the ISM on Column Density
Sightlines through high- and intermediate-velocity clouds allow measurements
of ionic gas phase abundances, A, at very low values of HI column density,
N(HI). Present observations cover over 4 orders of magnitude in N(HI).
Remarkably, for several ions we find that the A vs N(HI) relation is the same
at high and low column density and that the abundances have a relatively low
dispersion (factors of 2-3) at any particular N(HI). Halo gas tends to have
slightly higher values of A than disk gas at the same N(HI), suggesting that
part of the dispersion may be attributed to the environment. We note that the
dispersion is largest for NaI; using NaI as a predictor of N(HI) can lead to
large errors. Important implications of the low dispersions regarding the
physical nature of the ISM are: (a) because of clumping, over sufficiently long
pathlengths N(HI) is a reasonable measure of the_local_ density of_most_ of the
H atoms along the sight line; (b) the destruction of grains does not mainly
take place in catastrophic events such as strong shocks, but is a continuous
function of the mean density; (c) the cycling of the ions becoming attached to
grains and being detached must be rapid, and the two rates must be roughly
equal under a wide variety of conditions; (d) in gas that has a low average
density the attachment should occur within denser concentrations
Development of low cost ablative nozzles for solid propellant rocket motors, volume 1 Final report
Evaluating low cost ablative materials for use in large solid propellant rocket motor
- …