11,788 research outputs found
The Stabilizing Effectiveness of Conical Flares on Bodies with Conical Noses
An analysis is presented of published results of force tests on 80 cone-cylinder-flare configurations at Mach numbers of 2.18, 2.81, and 4.04. The contributions, excluding interference effects, of the cone-cylinder bodies to the over-all normal force derivatives have been removed by means of the second-order shock-expansion method, and the normal force derivatives at zero angle of attack due to the flares alone are shown. The results from a wide variety of configurations are correlated by plotting ratios of the normal force derivatives of the flares to the normal force derivatives of cones having the same included angle. Comparisons are made of the experimental normal force results with the normal force derivatives obtained by assuming conical flow over the flares and with those obtained by use of the second-order shock-expansion method. The comparisons show that use of the second-order shock-expansion method is generally the superior of the two, and in most cases gives values of the normal force derivatives of the flares which agree very well with the experimental results. Centers of pressure of the flares are presented and comparisons are made with results obtained from the theories mentioned. In general, the comparisons show that the assumption of conical flow over the flares is comparable to use of the second-order shock-expansion method in determining the centers of pressure, and in many cases both methods give values which agree closely with the experimental results
Experimental archeology and serious games: challenges of inhabiting virtual heritage
Experimental archaeology has long yielded valuable insights into the tools and techniques that featured in past peoplesâ relationship with the material world around them. However, experimental archaeology has, hitherto, confined itself to rigid, empirical and quantitative questions. This paper applies principles of experimental archaeology and serious gaming tools in the reconstructions of a British Iron Age Roundhouse. The paper explains a number of experiments conducted to look for quantitative differences in movement in virtual vs material environments using both âvirtualâ studio reconstruction as well as material reconstruction. The data from these experiments was then analysed to look for differences in movement which could be attributed to artefacts and/or environments. The paper explains the structure of the experiments, how the data was generated, what theories may make sense of the data, what conclusions have been drawn and how serious gaming tools can support the creation of new experimental heritage environments
Locally Optimally Emitting Clouds and the Origin of Quasar Emission Lines
The similarity of quasar line spectra has been taken as an indication that
the emission line clouds have preferred parameters, suggesting that the
environment is subject to a fine tuning process. We show here that the observed
spectrum is a natural consequence of powerful selection effects. We computed a
large grid of photoionization models covering the widest possible range of
cloud gas density and distance from the central continuum source. For each line
only a narrow range of density and distance from the continuum source results
in maximum reprocessing efficiency, corresponding to ``locally
optimally-emitting clouds'' (LOC). These parameters depend on the ionization
and excitation potentials of the line, and its thermalization density. The mean
QSO line spectrum can be reproduced by simply adding together the full family
of clouds, with an appropriate covering fraction distribution. The observed
quasar spectrum is a natural consequence of the ability of various clouds to
reprocess the underlying continuum, and can arise in a chaotic environment with
no preferred pressure, gas density, or ionization parameter.Comment: 9 pages including 1 ps figure. LaTeX format using aaspp4.st
Targeting Mr Average: Participation, gender equity and school sport partnerships
The School Sport Partnership Programme (SSPP) is one strand of the national strategy for physical education and school sport in England, the physical education and school sport Club Links Strategy (PESSCL). The SSPP aims to make links between school physical education (PE) and out of school sports participation, and has a particular remit to raise the participation levels of several identified under-represented groups, of which girls and young women are one. National evaluations of the SSPP show that it is beginning to have positive impacts on young people's activity levels by increasing the range and provision of extra curricular activities (Office for Standards in Education (OFSTED), 2003, 2004, 2005; Loughborough Partnership, 2005, 2006). This paper contributes to the developing picture of the phased implementation of the programme by providing qualitative insights into the work of one school sport partnership with a particular focus on gender equity. The paper explores the ways in which gender equity issues have been explicitly addressed within the 'official texts' of the SSPP; how these have shifted over time and how teachers are responding to and making sense of these in their daily practice. Using participation observation, interview and questionnaire data, the paper explores how the coordinators are addressing the challenge of increasing the participation of girls and young women. The paper draws on Walby's (2000) conceptualisation of different kinds of feminist praxis to highlight the limitations of the coordinators' work. Two key themes from the data and their implications are addressed: the dominance of competitive sport practices and the PE professionals' views of targeting as a strategy for increasing the participation of under-represented groups. The paper concludes that coordinators work within an equality or difference discourse with little evidence of the transformative praxis needed for the programme to be truly inclusive. Š 2008 Taylor & Francis
Squeezing in the audio gravitational wave detection band
We demonstrate the generation of broad-band continuous-wave optical squeezing
down to 200Hz using a below threshold optical parametric oscillator (OPO). The
squeezed state phase was controlled using a noise locking technique. We show
that low frequency noise sources, such as seed noise, pump noise and detuning
fluctuations, present in optical parametric amplifiers have negligible effect
on squeezing produced by a below threshold OPO. This low frequency squeezing is
ideal for improving the sensitivity of audio frequency measuring devices such
as gravitational wave detectors.Comment: 5 pages, 6 figure
Connected component identification and cluster update on GPU
Cluster identification tasks occur in a multitude of contexts in physics and
engineering such as, for instance, cluster algorithms for simulating spin
models, percolation simulations, segmentation problems in image processing, or
network analysis. While it has been shown that graphics processing units (GPUs)
can result in speedups of two to three orders of magnitude as compared to
serial codes on CPUs for the case of local and thus naturally parallelized
problems such as single-spin flip update simulations of spin models, the
situation is considerably more complicated for the non-local problem of cluster
or connected component identification. I discuss the suitability of different
approaches of parallelization of cluster labeling and cluster update algorithms
for calculations on GPU and compare to the performance of serial
implementations.Comment: 15 pages, 14 figures, one table, submitted to PR
Electronic and optical properties of beryllium chalcogenides/silicon heterostructures
We have calculated electronic and optical properties of
Si/BeSeTe heterostructures by a semiempirical
tight-binding method. Tight-binding parameters and band bowing of
BeSeTe are considered through a recent model for highly
mismatched semiconductor alloys. The band bowing and the measurements of
conduction band offset lead to a type II heterostucture for
Si/BeSeTe with conduction band minimum in the Si layer and
valence band maximum in the BeSeTe layer. The electronic
structure and optical properties of various (Si/(BeSeTe [001] superlattices have been considered. Two
bands of interface states were found within the bandgap of bulk Si. Our
calculations indicate that the optical edges are below the fundamental bandgap
of bulk Si and the transitions are optically allowed.Comment: 16 pager, 7 figure
The Large and Small Scale Structures of Dust in the Star-Forming Perseus Molecular Cloud
We present an analysis of ~3.5 square degrees of submillimetre continuum and
extinction data of the Perseus molecular cloud. We identify 58 clumps in the
submillimetre map and we identify 39 structures (`cores') and 11 associations
of structures (`super cores') in the extinction map. The cumulative mass
distributions of the submillimetre clumps and extinction cores have steep
slopes (alpha ~ 2 and 1.5 - 2 respectively), steeper than the Salpeter IMF
(alpha = 1.35), while the distribution of extinction super cores has a shallow
slope (alpha ~ 1). Most of the submillimetre clumps are well fit by stable
Bonnor-Ebert spheres with 10K < T < 19K and 5.5 < log_10(P_ext/k) < 6.0. The
clumps are found only in the highest column density regions (A_V > 5 - 7 mag),
although Bonnor-Ebert models suggest that we should have been able to detect
them at lower column densities if they exist. These observations provide a
stronger case for an extinction threshold than that found in analysis of less
sensitive observations of the Ophiuchus molecular cloud. The relationship
between submillimetre clumps and their parent extinction core has been
analyzed. The submillimetre clumps tend to lie offset from the larger
extinction peaks, suggesting the clumps formed via an external triggering
event, consistent with previous observations.Comment: 38 pages, 12 figures, accepted by Astrophysical Journal slight
changes to original due to a slight 3" error in the coordinates of the SCUBA
ma
The impact of elbow and knee joint lesions on abnormal gait and posture of sows
<p>Abstract</p> <p>Background</p> <p>Joint lesions occur widespread in the Danish sow population and they are the most frequent cause for euthanasia. Clinically, it is generally impossible to differentiate between various types of non-inflammatory joint lesions. Consequently, it is often necessary to perform a post mortem examination in order to diagnose these lesions. A study was performed in order to examine the relation of abnormal gait and posture in sows with specific joint lesions, and thereby obtaining a clinical diagnostic tool, to be used by farmers and veterinarians for the evaluation of sows with joint problems.</p> <p>Methods</p> <p>The gait, posture and lesions in elbow- and knee joints of 60 randomly selected sows from one herd were scored clinically and pathologically. Associations between the scorings were estimated.</p> <p>Results</p> <p>The variables 'fore- and hind legs turned out' and 'stiff in front and rear' were associated with lesions in the elbow joint, and the variables 'hind legs turned out' and 'stiff in rear' were associated with lesions in the knee joint.</p> <p>Conclusion</p> <p>It was shown that specified gait and posture variables reflected certain joint lesions. However, further studies are needed to strengthen and optimize the diagnostic tool.</p
An Atlas of Computed Equivalent Widths of Quasar Broad Emission Lines
We present graphically the results of several thousand photoionization
calculations of broad emission line clouds in quasars, spanning seven orders of
magnitude in hydrogen ionizing flux and particle density. The equivalent widths
of 42 quasar emission lines are presented as contours in the particle density -
ionizing flux plane for a typical incident continuum shape, solar chemical
abundances, and cloud column density of . Results are
similarly given for a small subset of emission lines for two other column
densities ( and ), five other incident
continuum shapes, and a gas metallicity of 5 \Zsun. These graphs should prove
useful in the analysis of quasar emission line data and in the detailed
modeling of quasar broad emission line regions. The digital results of these
emission line grids and many more are available over the Internet.Comment: 16 pages, LaTeX (AASTeX aaspp4.sty); to appear in the 1997 ApJS: full
contents of the 9 photoionization grids presented in this paper may be found
at http://www.pa.uky.edu/~korista/grids/grids.htm
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