6,930 research outputs found
Random Acts of STEM: A systematic review of local k-12 school division STEM experiences in Virginia
The initial purpose of the study was to determine whether the school divisions in Virginia have definitions of STEM education. For the divisions that have described STEM education, the following valuation was based on the precise STEM education definition each has implemented. The population for the study included all 132 school divisions in This mixed-methods study investigated the implementation of STEM programs in Virginia K-12 schools. Data were collected through two avenues: publicly available online resources from school divisions and interviews with STEM leaders in the Virginia educational system. Data analysis on these two sources yielded five themes: (a) existence of sense-making definition of STEM; (b) differentiated STEM programs; (c) scaling embedded STEM integration; (d) interest in STEM drives successful inclusion of gender, minority, and students with disabilities; and (e) standardized testing is a barrier to STEM participation
Modeling good research practices - overview: a report of the ISPOR-SMDM modeling good research practices task force - 1.
Models—mathematical frameworks that facilitate estimation of the consequences of health care decisions—have become essential tools for health technology assessment. Evolution of the methods since the first ISPOR modeling task force reported in 2003 has led to a new task force, jointly convened with the Society for Medical Decision Making, and this series of seven papers presents the updated recommendations for best practices in conceptualizing models; implementing state–transition approaches, discrete event simulations, or dynamic transmission models; dealing with uncertainty; and validating and reporting models transparently. This overview introduces the work of the task force, provides all the recommendations, and discusses some quandaries that require further elucidation. The audience for these papers includes those who build models, stakeholders who utilize their results, and, indeed, anyone concerned with the use of models to support decision making
Research Notes : Evaluation of chlorophyll-retention near-isogenic lines of soybeans
The phenomenon of chlorophyll retention in soybeans [Glycine max (L.) Merrill] is worthy of investigation for several different reasons: 1) it may have a physiological impact upon yield, 2) it may be useful in helping to explain the process of senescence, and 3) it causes production of green seeds, which may differ from normal yellow seeds in chemical composition, size, germination, nutritional qualities, and/or potential usefulness as vegetable types. Different genetic systems control the retention of chlorophyll, which results in green seed color (1). Ten near-isogenic lines in both \u27Clark\u27 and \u27Harosoy\u27 backgrounds are currently being studied to characterize and compare the different chlorophyll-retention types with their normal counter-parts
Phasing diffuse scattering. Application of the SIR2002 algorithm to the non-crystallographic phase problem
A new phasing algorithm has been used to determine the phases of diffuse
elastic X-ray scattering from a non-periodic array of gold balls of 50 nm
diameter. Two-dimensional real-space images, showing the charge-density
distribution of the balls, have been reconstructed at 50 nm resolution from
transmission diffraction patterns recorded at 550 eV energy. The reconstructed
image fits well with scanning electron microscope (SEM) image of the same
sample. The algorithm, which uses only the density modification portion of the
SIR2002 program, is compared with the results obtained via the
Gerchberg-Saxton-Fienup HIO algorithm. In this way the relationship between
density modification in crystallography and the HiO algorithm used in signal
and image processing is elucidated.Comment: 7 pages, 12 figure
Stable Determination of the Electromagnetic Coefficients by Boundary Measurements
The goal of this paper is to prove a stable determination of the coefficients
for the time-harmonic Maxwell equations, in a Lipschitz domain, by boundary
measurements
Short-range order and precipitation in Fe-rich Fe-Cr alloys: Atomistic off-lattice Monte Carlo simulations
Short-range order (SRO) in Fe-rich Fe-Cr alloys is investigated by means of
atomistic off-lattice Monte Carlo simulations in the semi-grand canonical
ensemble using classical interatomic potentials. The SRO parameter defined by
Cowley [Phys. Rev. B 77, 669 (1950)] is used to quantify the degree of
ordering. In agreement with experiments a strong ordering tendency in the Cr
distribution at low Cr concentrations (~< 5%) is observed, as manifested in
negative values of the SRO parameters. For intermediate Cr concentrations (5%
~< c_Cr ~< 15%) the SRO parameter for the alpha-phase goes through a minimum,
but at the solubility limit the alpha-phase still displays a rather strong SRO.
In thermodynamic equilibrium for concentrations within the two-phase region the
SRO parameter measured over the entire sample therefore comprises the
contributions from both the alpha and alpha-prime phases. If both of these
contributions are taken into account, it is possible to quantitatively
reproduce the experimental results and interpret their physical implications.
It is thereby shown that the inversion of the SRO observed experimentally is
due to the formation of stable (supercritical) alpha-prime precipitates. It is
not related to the loss of SRO in the alpha-phase or to the presence of
unstable (subcritical) Cr precipitates in the alpha-phase.Comment: 9 pages, 8 figure
Photo-desorption of H2O:CO:NH3 circumstellar ice analogs: Gas-phase enrichment
We study the photo-desorption occurring in HO:CO:NH ice mixtures
irradiated with monochromatic (550 and 900 eV) and broad band (250--1250 eV)
soft X-rays generated at the National Synchrotron Radiation Research Center
(Hsinchu, Taiwan). We detect many masses photo-desorbing, from atomic hydrogen
(m/z = 1) to complex species with m/z = 69 (e.g., CHNO, CHO,
CHN), supporting the enrichment of the gas phase.
At low number of absorbed photons, substrate-mediated exciton-promoted
desorption dominates the photo-desorption yield inducing the release of weakly
bound (to the surface of the ice) species; as the number of weakly bound
species declines, the photo-desorption yield decrease about one order of
magnitude, until porosity effects, reducing the surface/volume ratio, produce a
further drop of the yield.
We derive an upper limit to the CO photo-desorption yield, that in our
experiments varies from 1.4 to 0.007 molecule photon in the range ~absorbed photons cm. We apply these findings to a
protoplanetary disk model irradiated by a central T~Tauri star
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