266,285 research outputs found
Monitoring What Matters About Context and Instruction in Science Education: A NAEP Data Analysis Report
This report explores background variables in the National Assessment of Educational Progress (NAEP) to examine key context and instructional factors behind science learning for eighth grade students. Science education is examined from five perspectives: student engagement in science, science teachers' credentials and professional development, availability and use of science resources, approaches to science instruction, and methods and uses of science assessment
Modelling the brightness increase signature due to asteroid collisions
We have developed a model to predict the post-collision brightness increase
of sub-catastrophic collisions between asteroids and to evaluate the likelihood
of a survey detecting these events. It is based on the cratering scaling laws
of Holsapple and Housen (2007) and models the ejecta expansion following an
impact as occurring in discrete shells each with their own velocity. We
estimate the magnitude change between a series of target/impactor pairs,
assuming it is given by the increase in reflecting surface area within a
photometric aperture due to the resulting ejecta. As expected the photometric
signal increases with impactor size, but we find also that the photometric
signature decreases rapidly as the target asteroid diameter increases, due to
gravitational fallback. We have used the model results to make an estimate of
the impactor diameter for the (596) Scheila collision of D=49-65m depending on
the impactor taxonomy, which is broadly consistent with previous estimates. We
varied both the strength regime (highly porous and sand/cohesive soil) and the
taxonomic type (S-, C- and D-type) to examine the effect on the magnitude
change, finding that it is significant at early stages but has only a small
effect on the overall lifetime of the photometric signal. Combining the results
of this model with the collision frequency estimates of Bottke et al. (2005),
we find that low-cadence surveys of approximately one visit per lunation will
be insensitive to impacts on asteroids with D<20km if relying on photometric
detections
Objective Bayes and Conditional Frequentist Inference
Objective Bayesian methods have garnered considerable interest and support among statisticians,
particularly over the past two decades. It has often been ignored, however, that in
some cases the appropriate frequentist inference to match is a conditional one. We present
various methods for extending the probability matching prior (PMP) methods to conditional
settings. A method based on saddlepoint approximations is found to be the most
tractable and we demonstrate its use in the most common exact ancillary statistic models.
As part of this analysis, we give a proof of an exactness property of a particular PMP in
location-scale models. We use the proposed matching methods to investigate the relationships
between conditional and unconditional PMPs. A key component of our analysis is a
numerical study of the performance of probability matching priors from both a conditional
and unconditional perspective in exact ancillary models. In concluding remarks we propose
many routes for future research
TRECVID: benchmarking the effectiveness of information retrieval tasks on digital video
Many research groups worldwide are now investigating techniques which can support information retrieval on archives of digital video and as groups move on to implement these techniques they inevitably try to evaluate the performance of their techniques in practical situations. The difficulty with doing this is that there is no test collection or any environment in which the effectiveness of video IR or video IR sub-tasks, can be evaluated and compared. The annual series of TREC exercises has, for over a decade, been benchmarking the effectiveness of systems in carrying out various information retrieval tasks on text and audio and has contributed to a huge improvement in many of these. Two years ago, a track was introduced which covers shot boundary detection, feature extraction and searching through archives of digital video. In this paper we present a summary of the activities in the TREC Video track in 2002 where 17 teams from across the world took part
Looking for vertex number one
Given an instance of the preferential attachment graph , we
would like to find vertex 1, using only 'local' information about the graph;
that is, by exploring the neighborhoods of small sets of vertices. Borgs et. al
gave an an algorithm which runs in time , which is local in the
sense that at each step, it needs only to search the neighborhood of a set of
vertices of size . We give an algorithm to find vertex 1, which
w.h.p. runs in time and which is local in the strongest sense
of operating only on neighborhoods of single vertices. Here
is any function that goes to infinity with .Comment: As accepted for AA
What Does the Public Know about Economic Policy, and How Does It Know It?
opinion, policy, influence, politicians
A kiss is just...
This paper proposes that a survey of representations of men not-kissing men in recent television drama series makes clear a particularly hysterical fascination. While the Australian program GP has managed to produce a banal representation of two men kissing, American equivalents have resorted to a series of strategies which make insistently clear that not only can men not kiss-but that the act of not-kissing must be repeatedly displayed. By refusing to have lovers kiss; by having lovers kiss but refusing to show the act; by having gay lovers, but having one played by a woman; by having men kiss but rendering the act ridiculous; in these ways, American television programs make clear the importance of this act by consistently pointing towards it and declaring its impossibility. This paper calls for the justice of equal access to public images of kissing
Illumination by Taylor Polynomials
Let f(x) be a differentiable function on the real line R, and let P be a
point not on the graph of f(x). Define the illumination index of P to be the
number of distinct tangents to the graph of f which pass thru P. We prove that
if f '' is continuous and nonnegative on R, f '' > m >0 outside a closed
interval of R, and f '' has finitely many zeroes on R, then every point below
the graph of f has illumination index 2. This result fails in general if f ''
is not bounded away from 0 on R. Also, if f '' has finitely many zeroes and f
'' is not nonnnegative on R, then some point below the graph has illumination
index not equal to 2. Finally, we generalize our results to illumination by odd
order Taylor polynomials.Comment: Minor modifications and correction
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