8,151 research outputs found
A wave driver theory for vortical waves propagating across junctions with application to those between rigid and compliant walls
A theory is described for propagation of vortical waves across alternate rigid and compliant panels. The structure in the fluid side at the junction of panels is a highly vortical narrow viscous structure which is idealized as a wave driver. The wave driver is modelled as a ‘half source cum half sink’. The incoming wave terminates into this structure and the outgoing wave emanates from it. The model is described by half Fourier–Laplace transforms respectively for the upstream and downstream sides of the junction. The cases below cutoff and above cutoff frequencies are studied. The theory completely reproduces the direct numerical simulation results of Davies & Carpenter (J. Fluid Mech., vol. 335, 1997, p. 361). Particularly, the jumps across the junction in the kinetic energy integral, the vorticity integral and other related quantities as obtained in the work of Davies & Carpenter are completely reproduced. Also, some important new concepts emerge, notable amongst which is the concept of the pseudo group velocity
A Conscientious Study of Blended Learning and Cardinal Tools
Evaluating the contexts, activities and relationships of participants in education is a complicated structure
that necessitates numerous ideologies and levels of assessment, specifically when it comes to
technological developments. Blended learning is a method of instruction that integrates offline and
virtual-based education. This article highlights the characteristics of technology and features in blended
learning, which enhances the learner engagement in higher education. It showcases some of the digital
technologies including video encapsulation and online learning systems that may assist in learning and
teaching. This paper delineates the consequences faced by the teachers of higher education while
explaining the conceptualization of blended learning. It also suggests the implications that can be
practiced for the optimization of blended learning evaluating the learner engagement. It also identifies
methods to improve the effectiveness of the teachers in evolving demands in blended learning for higher
education
Radiative Models of Sagittarius A* and M87 from Relativistic MHD Simulations
Ongoing millimeter VLBI observations with the Event Horizon Telescope allow
unprecedented study of the innermost portion of black hole accretion flows.
Interpreting the observations requires relativistic, time-dependent physical
modeling. We discuss the comparison of radiative transfer calculations from
general relativistic MHD simulations of Sagittarius A* and M87 with current and
future mm-VLBI observations. This comparison allows estimates of the viewing
geometry and physical conditions of the Sgr A* accretion flow. The viewing
geometry for M87 is already constrained from observations of its large-scale
jet, but, unlike Sgr A*, there is no consensus for its millimeter emission
geometry or electron population. Despite this uncertainty, as long as the
emission region is compact, robust predictions for the size of its jet
launching region can be made. For both sources, the black hole shadow may be
detected with future observations including ALMA and/or the LMT, which would
constitute the first direct evidence for a black hole event horizon.Comment: 8 pages, 2 figures, submitted to the proceedings of AHAR 2011: The
Central Kiloparse
If you can't be with the one you love, love the one you're with: How individual habituation of agent interactions improves global utility
Simple distributed strategies that modify the behaviour of selfish individuals in a manner that enhances cooperation or global efficiency have proved difficult to identify. We consider a network of selfish agents who each optimise their individual utilities by coordinating (or anti-coordinating) with their neighbours, to maximise the pay-offs from randomly weighted pair-wise games. In general, agents will opt for the behaviour that is the best compromise (for them) of the many conflicting constraints created by their neighbours, but the attractors of the system as a whole will not maximise total utility. We then consider agents that act as 'creatures of habit' by increasing their preference to coordinate (anti-coordinate) with whichever neighbours they are coordinated (anti-coordinated) with at the present moment. These preferences change slowly while the system is repeatedly perturbed such that it settles to many different local attractors. We find that under these conditions, with each perturbation there is a progressively higher chance of the system settling to a configuration with high total utility. Eventually, only one attractor remains, and that attractor is very likely to maximise (or almost maximise) global utility. This counterintutitve result can be understood using theory from computational neuroscience; we show that this simple form of habituation is equivalent to Hebbian learning, and the improved optimisation of global utility that is observed results from wellknown generalisation capabilities of associative memory acting at the network scale. This causes the system of selfish agents, each acting individually but habitually, to collectively identify configurations that maximise total utility
Note: estimating the charge size in explosive forming of sheet metal
Note: Estimating the charge size in explosive forming of sheet metal
In the explosive forming of sheet metal some relatively easy method
of estimating the size of the charge is needed. This short note describes
a method in which the size of the charge is found by equating the work done
in forming the component to that part of the explosive energy available
for doing work on the component … [cont]
A four-element end-fire microphone array for acoustic measurements in wind tunnels
A prototype four-element end-fire microphone array was designed and built for evaluation as a directional acoustic receiver for use in large wind tunnels. The microphone signals were digitized, time delayed, summed, and reconverted to analog form in such a way as to create a directional response with the main lobe along the array axis. The measured array directivity agrees with theoretical predictions confirming the circuit design of the electronic control module. The array with 0.15 m (0.5 ft) microphone spacing rejected reverberations and background noise in the Ames 40- by 80-foot wind tunnel by 5 to 12 db for frequencies above 400 Hz
Video Self-Monitoring as an Alternative to Traditional Methods of Pronunciation Instruction
Japanese students of English have difficulty pronouncing /f/, Ir/, /1/, /v/ and th , sounds that are either not present in their language, or as in the case of /r/, articulated in Japanese more like an English /di. Their difficulty with these sounds seems to affect their comprehensibility in English to native-speakers of English.
The purpose of this partial replication of a 1994 study by MacDonald, Yule and Powers was to test three different methods of pronunciation instruction ( and a control) to determine which promoted the greatest improvement in the pronunciation of the five target sounds among Japanese speakers. The three types of pronunciation instruction included two traditional methods: a teacher-led lesson, listening to audiotapes in a language lab; and an experimental method, which consisted of a two phase video self-monitoring activity.
There were two hypotheses governing this study: 1) that the group participating in the video self-monitoring activity would score fewer errors in the target sounds than the subjects of the other three groups on Post-test 1, and 2) that this same group would score fewer errors two days later on Post-test 2.
The native-speaker\u27s evaluations of the results, which were registered as the number of inaccurate articulations of each of the five sounds, were subjected to a mixed-model ANOV A. Of the five phonemes, the hypotheses were supported for fl/ only, leading to the assumption that more time was necessary for the treatments to affect the subjects and that the native-speaker judges needed to be given an agreed upon level of acceptability for determining native-like pronunciation. However, results showed that for all five phonemes, the teacher-led classroom and language lab activity proved most consistent in fostering an improvement in pronunciation of those sounds, leading to the conclusion that the teacher can not be taken out of the equation in pronunciation teaching
The Submillimeter Bump in Sgr A* from Relativistic MHD Simulations
Recent high resolution observations of the Galactic center black hole allow
for direct comparison with accretion disk simulations. We compare
two-temperature synchrotron emission models from three dimensional, general
relativistic magnetohydrodynamic simulations to millimeter observations of Sgr
A*. Fits to very long baseline interferometry and spectral index measurements
disfavor the monochromatic face-on black hole shadow models from our previous
work. Inclination angles \le 20 degrees are ruled out to 3 \sigma. We estimate
the inclination and position angles of the black hole, as well as the electron
temperature of the accretion flow and the accretion rate, to be i=50+35-15
degrees, \xi=-23+97-22 degrees, T_e=(5.4 +/- 3.0)x10^10 K and
Mdot=(5+15-2)x10^-9 M_sun / yr respectively, with 90% confidence. The black
hole shadow is unobscured in all best fit models, and may be detected by
observations on baselines between Chile and California, Arizona or Mexico at
1.3mm or .87mm either through direct sampling of the visibility amplitude or
using closure phase information. Millimeter flaring behavior consistent with
the observations is present in all viable models, and is caused by magnetic
turbulence in the inner radii of the accretion flow. The variability at
optically thin frequencies is strongly correlated with that in the accretion
rate. The simulations provide a universal picture of the 1.3mm emission region
as a small region near the midplane in the inner radii of the accretion flow,
which is roughly isothermal and has \nu/\nu_c ~ 1-20, where \nu_c is the
critical frequency for thermal synchrotron emission.Comment: 14 pages, 17 figures, accepted by Ap
Estimating Small Area Income Deprivation: An Iterative Proportional Fitting Approach
Small area estimation and in particular the estimation of small area income deprivation has
potential value in the development of new or alternative components of multiple deprivation
indices. These new approaches enable the development of income distribution threshold based
as opposed to benefit count based measures of income deprivation and so enable the
alignment of regional and national measures such as the Households Below Average Income
with small area measures. This paper briefly reviews a number of approaches to small area
estimation before describing in some detail an iterative proportional fitting based spatial
microsimulation approach. This approach is then applied to the estimation of small area HBAI
rates at the small area level in Wales in 2003-5. The paper discusses the results of this
approach, contrasts them with contemporary ‘official’ income deprivation measures for the
same areas and describes a range of ways to assess the robustness of the results
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