1,685 research outputs found
Declines in student achievement in science-- implications for public education
During the 1960s and 1970s, major innovative science curricula were introduced into public schools in the United States, and federal funds were used to improve the quality of science teachers. Nevertheless, student achievement in science has generally declined since 1963. This research focused on changes in four of the key variables related to science achievement--teachers, students, curricula, and school goals. The research examined (a) meta-analyses of the effectiveness of the innovative science curricula on student achievement, (b) research on changes in teacher and student characteristics during the last 30 years, (c) educational literature on changes in the goals of public education during this same period, and (d) changes in student achievement. The results of this research suggest that the recent declines in science achievement are related to changes in student motivation, school goals, and school autonomy. The data indicate that contrary to the claims of some recent education commission reports, teachers and curricula have improved steadily over the last three decades. The conclusions developed from this research suggest that a number of the current educational reforms such as teacher competency testing, merit pay, curricular reform, student competency testing, and year-round schools should have little positive effect on student achievement. The research also suggests that parental involvement in education could have a negative influence on science achievement. The findings do suggest that schools of choice, corporate educational partnerships, and teacher empowerment could significantly improve student science achievement
Knowledge-based variable selection for learning rules from proteomic data
<p>Abstract</p> <p>Background</p> <p>The incorporation of biological knowledge can enhance the analysis of biomedical data. We present a novel method that uses a proteomic knowledge base to enhance the performance of a rule-learning algorithm in identifying putative biomarkers of disease from high-dimensional proteomic mass spectral data. In particular, we use the Empirical Proteomics Ontology Knowledge Base (EPO-KB) that contains previously identified and validated proteomic biomarkers to select <it>m/z</it>s in a proteomic dataset prior to analysis to increase performance.</p> <p>Results</p> <p>We show that using EPO-KB as a pre-processing method, specifically selecting all biomarkers found only in the biofluid of the proteomic dataset, reduces the dimensionality by 95% and provides a statistically significantly greater increase in performance over no variable selection and random variable selection.</p> <p>Conclusion</p> <p>Knowledge-based variable selection even with a sparsely-populated resource such as the EPO-KB increases overall performance of rule-learning for disease classification from high-dimensional proteomic mass spectra.</p
Evolution of FLRW spacetime after the birth of a cosmic string
We consider the evolution of an initially FLRW universe after the formation
of a long, straight, cosmic string with arbitrary tension and mass per unit
length. The birth of the string sources scalar and tensor-type perturbations in
the background metric and both density and velocity perturbations in the
background fluid, which compensate for the string mass and maintain energy
conservation. The former generate the deficit angle within the light cone of
the string and a gravitational shock front at the cosmological horizon, whereas
the latter are confined within the sound cone. We study the properties of the
metric within each region of the resulting spacetime and give the explicit
coordinate transformations which demonstrate non-violation of causality. This
paper generalizes the work of previous studies for the Nambu-Goto string.Comment: 16 pages, 2 figures, published versio
Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant
We present observations of 10 type Ia supernovae (SNe Ia) between 0.16 < z <
0.62. With previous data from our High-Z Supernova Search Team, this expanded
set of 16 high-redshift supernovae and 34 nearby supernovae are used to place
constraints on the Hubble constant (H_0), the mass density (Omega_M), the
cosmological constant (Omega_Lambda), the deceleration parameter (q_0), and the
dynamical age of the Universe (t_0). The distances of the high-redshift SNe Ia
are, on average, 10% to 15% farther than expected in a low mass density
(Omega_M=0.2) Universe without a cosmological constant. Different light curve
fitting methods, SN Ia subsamples, and prior constraints unanimously favor
eternally expanding models with positive cosmological constant (i.e.,
Omega_Lambda > 0) and a current acceleration of the expansion (i.e., q_0 < 0).
With no prior constraint on mass density other than Omega_M > 0, the
spectroscopically confirmed SNe Ia are consistent with q_0 <0 at the 2.8 sigma
and 3.9 sigma confidence levels, and with Omega_Lambda >0 at the 3.0 sigma and
4.0 sigma confidence levels, for two fitting methods respectively. Fixing a
``minimal'' mass density, Omega_M=0.2, results in the weakest detection,
Omega_Lambda>0 at the 3.0 sigma confidence level. For a flat-Universe prior
(Omega_M+Omega_Lambda=1), the spectroscopically confirmed SNe Ia require
Omega_Lambda >0 at 7 sigma and 9 sigma level for the two fitting methods. A
Universe closed by ordinary matter (i.e., Omega_M=1) is ruled out at the 7
sigma to 8 sigma level. We estimate the size of systematic errors, including
evolution, extinction, sample selection bias, local flows, gravitational
lensing, and sample contamination. Presently, none of these effects reconciles
the data with Omega_Lambda=0 and q_0 > 0.Comment: 36 pages, 13 figures, 3 table files Accepted to the Astronomical
Journa
Grid Pricing of Fed Cattle
4 pp., 2 tablesThere are several value-based fed cattle pricing systems, including formula pricing, price grids and alliances. This publication describes the different cattle pricing methods and helps you decide which is best for you
Cosmological Results from High-z Supernovae
The High-z Supernova Search Team has discovered and observed 8 new supernovae
in the redshift interval z=0.3-1.2. These independent observations, confirm the
result of Riess et al. (1998a) and Perlmutter et al. (1999) that supernova
luminosity distances imply an accelerating universe. More importantly, they
extend the redshift range of consistently observed SN Ia to z~1, where the
signature of cosmological effects has the opposite sign of some plausible
systematic effects. Consequently, these measurements not only provide another
quantitative confirmation of the importance of dark energy, but also constitute
a powerful qualitative test for the cosmological origin of cosmic acceleration.
We find a rate for SN Ia of 1.4+/-0.5E-04 h^3/Mpc^3/yr at a mean redshift of
0.5. We present distances and host extinctions for 230 SN Ia. These place the
following constraints on cosmological quantities: if the equation of state
parameter of the dark energy is w=-1, then H0 t0 = 0.96+/-0.04, and O_l - 1.4
O_m = 0.35+/-0.14. Including the constraint of a flat Universe, we find O_m =
0.28+/-0.05, independent of any large-scale structure measurements. Adopting a
prior based on the 2dF redshift survey constraint on O_m and assuming a flat
universe, we find that the equation of state parameter of the dark energy lies
in the range -1.48-1,
we obtain w<-0.73 at 95% confidence. These constraints are similar in precision
and in value to recent results reported using the WMAP satellite, also in
combination with the 2dF redshift survey.Comment: 50 pages, AAS LateX, 15 figures, 15 tables. Accepted for publication
by Astrophysical Journa
Tests of the Accelerating Universe with Near-Infrared Observations of a High-Redshift Type Ia Supernova
We have measured the rest-frame B,V, and I-band light curves of a
high-redshift type Ia supernova (SN Ia), SN 1999Q (z=0.46), using HST and
ground-based near-infrared detectors.
A goal of this study is the measurement of the color excess, E_{B-I}, which
is a sensitive indicator of interstellar or intergalactic dust which could
affect recent cosmological measurements from high-redshift SNe Ia. Our
observations disfavor a 30% opacity of SN Ia visual light by dust as an
alternative to an accelerating Universe. This statement applies to both
Galactic-type dust
(rejected at the 3.4 sigma confidence level) and greyer dust (grain size >
0.1 microns; rejected at the 2.3 to 2.6 sigma confidence level) as proposed by
Aguirre (1999). The rest-frame -band light cur ve shows the secondary
maximum a month after B maximum typical of nearby SNe Ia of normal luminosi ty,
providing no indication of evolution as a function of redshift out to z~0.5. A
n expanded set of similar observations could improve the constraints on any
contribution of extragalactic dust to the dimming of high-redshift SNe Ia.Comment: Accepted to the Astrophysical Journal, 12 pages, 2 figure
Changes in Gene Expression Foreshadow Diet-Induced Obesity in Genetically Identical Mice
High phenotypic variation in diet-induced obesity in male C57BL/6J inbred mice suggests a molecular model to investigate non-genetic mechanisms of obesity. Feeding mice a high-fat diet beginning at 8 wk of age resulted in a 4-fold difference in adiposity. The phenotypes of mice characteristic of high or low gainers were evident by 6 wk of age, when mice were still on a low-fat diet; they were amplified after being switched to the high-fat diet and persisted even after the obesogenic protocol was interrupted with a calorically restricted, low-fat chow diet. Accordingly, susceptibility to diet-induced obesity in genetically identical mice is a stable phenotype that can be detected in mice shortly after weaning. Chronologically, differences in adiposity preceded those of feeding efficiency and food intake, suggesting that observed difference in leptin secretion is a factor in determining phenotypes related to food intake. Gene expression analyses of adipose tissue and hypothalamus from mice with low and high weight gain, by microarray and qRT-PCR, showed major changes in the expression of genes of Wnt signaling and tissue re-modeling in adipose tissue. In particular, elevated expression of SFRP5, an inhibitor of Wnt signaling, the imprinted gene MEST and BMP3 may be causally linked to fat mass expansion, since differences in gene expression observed in biopsies of epididymal fat at 7 wk of age (before the high-fat diet) correlated with adiposity after 8 wk on a high-fat diet. We propose that C57BL/6J mice have the phenotypic characteristics suitable for a model to investigate epigenetic mechanisms within adipose tissue that underlie diet-induced obesity
Imaging and Demography of the Host Galaxies of High-Redshift Type Ia Supernovae
We present the results of a study of the host galaxies of high redshift Type
Ia supernovae (SNe Ia). We provide a catalog of 18 hosts of SNe Ia observed
with the Hubble Space Telescope (HST) by the High-z Supernova Search Team
(HZT), including images, scale-lengths, measurements of integrated (Hubble
equivalent) BVRIZ photometry in bands where the galaxies are brighter than m ~
25 mag, and galactocentric distances of the supernovae. We compare the
residuals of SN Ia distance measurements from cosmological fits to measurable
properties of the supernova host galaxies that might be expected to correlate
with variable properties of the progenitor population, such as host galaxy
color and position of the supernova. We find mostly null results; the current
data are generally consistent with no correlations of the distance residuals
with host galaxy properties in the redshift range 0.42 < z < 1.06. Although a
subsample of SN hosts shows a formally significant (3-sigma) correlation
between apparent V-R host color and distance residuals, the correlation is not
consistent with the null results from other host colors probed by our largest
samples. There is also evidence for the same correlations between SN Ia
properties and host type at low redshift and high redshift. These similarities
support the current practice of extrapolating properties of the nearby
population to high redshifts pending more robust detections of any correlations
between distance residuals from cosmological fits and host properties.Comment: 35 pages, 12 figures, 4 tables, accepted for publication in A
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