566 research outputs found
An evaluation of a two year cognitive intervention programme in technology education for Key Stage 4
We reported (in Vol. 1 No 2 1996) an interim evaluation of the effects of a small-scale cognitive intervention programme in technology. The subjects in this study were 120 Year 10 students (15+) attending a girls comprehensive school in an inner London. Education Authority. The students were randomly placed in eight all ability classes according to the normal school practice and policy. Three experimental classes (45 students) and five control classes (75 students) were identified. The new head of design and technology had targeted this year group in order to try to raise achievement of a group of students in a domain which had not previously performed as effectively as had been expected. The teacher would be taking the three experimental groups designated 10.1, 10.2, 10.5. Two other teachers would have the responsibility of teaching the five control classes. Unfortunately we were unable to establish a control group being taught by the teacher of the experimental groups.The model that was adopted for the study utilised principles from Cognitive Acceleration through Science Education (CASE) (the five pillars), from Instrumental Enrichment and from the Somerset Thinking Skills project. The essential feature of the study was to concentrate on enhancing the students' thinking, reasoning and problem solving capability with the teacher acting as a mediator and director of the activities and of the discussion that occurred. (For details see pp 121-124 Vol. 1 No 21996). The results suggested that the intenention was having a positive but modest effect in technology achievement on the experimental classes, but that there was little or no effect in other areas of the curriculum that we were investigating. This article is a follow-up to the original paper and presents further data showing the effects of the inteNention after the full two years of the programme. The subjects, design and methodology adopted throughout this project are described in the original paper (Hamaker et al 1996).The established groups with their corresponding teachers are summarised in Table 1. Each of the experimental classes had one core technology lesson replaced by an inteNention lesson each fortnight. Class 10.2 had a further graphical communication option replaced by an intervention lesson each fortnight. The five control classes received a normal allocation of technology core and option lessons. The tests and measures used for analyses are similar to that already described (Hamaker et al 1996). Further clarification on the nature of these tests and measures can be obtained from the authors of this article
Radio astronomical polarimetry and phase-coherent matrix convolution
A new phase-coherent technique for the calibration of polarimetric data is
presented. Similar to the one-dimensional form of convolution, data are
multiplied by the response function in the frequency domain. Therefore, the
system response may be corrected with arbitrarily high spectral resolution,
effectively treating the problem of bandwidth depolarization. As well, the
original temporal resolution of the data is retained. The method is therefore
particularly useful in the study of radio pulsars, where high time resolution
and polarization purity are essential requirements of high-precision timing. As
a demonstration of the technique, it is applied to full-polarization baseband
recordings of the nearby millisecond pulsar, PSR J0437-4715.Comment: 8 pages, 4 figures, accepted for publication in Ap
Radio Astronomical Polarimetry and Point-Source Calibration
A mathematical framework is presented for use in the experimental
determination of the polarimetric response of observatory instrumentation.
Elementary principles of linear algebra are applied to model the full matrix
description of the polarization measurement equation by least-squares
estimation of non-linear, scalar parameters. The formalism is applied to
calibrate the center element of the Parkes Multibeam receiver using
observations of the millisecond pulsar, PSR J0437-4715, and the radio galaxy,
3C 218 (Hydra A).Comment: 8 pages, 4 figures, to be published in ApJ
Bootstrap resampling as a tool for radio-interferometric imaging fidelity assessment
We report on a numerical evaluation of the statistical bootstrap as a
technique for radio-interferometric imaging fidelity assessment. The
development of a fidelity assessment technique is an important scientific
prerequisite for automated pipeline reduction of data from modern radio
interferometers. We evaluate the statistical performance of two bootstrap
methods, the model-based bootstrap and subsample bootstrap, against a Monte
Carlo parametric simulation, using interferometric polarization calibration and
imaging as the representative problem under study. We find both statistical
resampling techniques to be viable approaches to radio-interferometric imaging
fidelity assessment which merit further investigation. We also report on the
development and implementation of a new self-calibration algorithm for
radio-interferometric polarimetry which makes no approximations for the
polarization source model.Comment: Accepted by AJ; 41 pages, 13 figure
Capillary pressure of van der Waals liquid nanodrops
The dependence of the surface tension on a nanodrop radius is important for
the new-phase formation process. It is demonstrated that the famous Tolman
formula is not unique and the size-dependence of the surface tension can
distinct for different systems. The analysis is based on a relationship between
the surface tension and disjoining pressure in nanodrops. It is shown that the
van der Waals interactions do not affect the new-phase formation thermodynamics
since the effect of the disjoining pressure and size-dependent component of the
surface tension cancel each other.Comment: The paper is dedicated to the 80th anniversary of A.I. Rusano
Effect of hydrodynamic interactions on the distribution of adhering Brownian particles
Brownian dynamics simulations were used to study the adhesion of hard spheres on a solid surface by taking the hydrodynamic interactions into account. Special attention was paid to analyze the configuration of the assembly of adsorbed particles. These results were compared to configurations generated by the extensively studied random sequential adsorption (RSA) model. In our case the adsorption probability for a particle is almost uniform over the entire available surfae. This surprising result shows that RSA provides a good approximation to generate adsorbed particle configurations
Instrumental and Analytic Methods for Bolometric Polarimetry
We discuss instrumental and analytic methods that have been developed for the
first generation of bolometric cosmic microwave background (CMB) polarimeters.
The design, characterization, and analysis of data obtained using Polarization
Sensitive Bolometers (PSBs) are described in detail. This is followed by a
brief study of the effect of various polarization modulation techniques on the
recovery of sky polarization from scanning polarimeter data. Having been
successfully implemented on the sub-orbital Boomerang experiment, PSBs are
currently operational in two terrestrial CMB polarization experiments (QUaD and
the Robinson Telescope). We investigate two approaches to the analysis of data
from these experiments, using realistic simulations of time ordered data to
illustrate the impact of instrumental effects on the fidelity of the recovered
polarization signal. We find that the analysis of difference time streams takes
full advantage of the high degree of common mode rejection afforded by the PSB
design. In addition to the observational efforts currently underway, this
discussion is directly applicable to the PSBs that constitute the polarized
capability of the Planck HFI instrument.Comment: 23 pages, 11 figures. for submission to A&
A very brief description of LOFAR - the Low Frequency Array
LOFAR (Low Frequency Array) is an innovative radio telescope optimized for
the frequency range 30-240 MHz. The telescope is realized as a phased aperture
array without any moving parts. Digital beam forming allows the telescope to
point to any part of the sky within a second. Transient buffering makes
retrospective imaging of explosive short-term events possible. The scientific
focus of LOFAR will initially be on four key science projects (KSPs): 1)
detection of the formation of the very first stars and galaxies in the universe
during the so-called epoch of reionization by measuring the power spectrum of
the neutral hydrogen 21-cm line (Shaver et al. 1999) on the ~5' scale; 2)
low-frequency surveys of the sky with of order expected new sources; 3)
all-sky monitoring and detection of transient radio sources such as gamma-ray
bursts, x-ray binaries, and exo-planets (Farrell et al. 2004); and 4) radio
detection of ultra-high energy cosmic rays and neutrinos (Falcke & Gorham 2003)
allowing for the first time access to particles beyond 10^21 eV (Scholten et
al. 2006). Apart from the KSPs open access for smaller projects is also
planned. Here we give a brief description of the telescope.Comment: 2 pages, IAU GA 2006, Highlights of Astronomy, Volume 14, K.A. van
der Hucht, e
Benchmark Parameters for CMB Polarization Experiments
The recently detected polarization of the cosmic microwave background (CMB)
holds the potential for revealing the physics of inflation and gravitationally
mapping the large-scale structure of the universe, if so called B-mode signals
below 10^{-7}, or tenths of a uK, can be reliably detected. We provide a
language for describing systematic effects which distort the observed CMB
temperature and polarization fields and so contaminate the B-modes. We identify
7 types of effects, described by 11 distortion fields, and show their
association with known instrumental systematics such as common mode and
differential gain fluctuations, line cross-coupling, pointing errors, and
differential polarized beam effects. Because of aliasing from the small-scale
structure in the CMB, even uncorrelated fluctuations in these effects can
affect the large-scale B modes relevant to gravitational waves. Many of these
problems are greatly reduced by having an instrumental beam that resolves the
primary anisotropies (FWHM << 10'). To reach the ultimate goal of an
inflationary energy scale of 3 \times 10^{15} GeV, polarization distortion
fluctuations must be controlled at the 10^{-2}-10^{-3} level and temperature
leakage to the 10^{-4}-10^{-3} level depending on effect. For example pointing
errors must be controlled to 1.5'' rms for arcminute scale beams or a percent
of the Gaussian beam width for larger beams; low spatial frequency differential
gain fluctuations or line cross-coupling must be eliminated at the level of
10^{-4} rms.Comment: 11 pages, 5 figures, submitted to PR
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