136,835 research outputs found
Control of virtual environments for young people with learning difficulties
Purpose: The objective of this research is to identify the requirements for the selection or development of usable virtual environment (VE) interface devices for young people with learning disabilities. Method: a user-centred design methodology was employed, to produce a design specification for usable VE interface devices. Details of the users' cognitive, physical and perceptual abilities were obtained through observation and normative assessment tests. Conclusions : A review of computer interface technology, including virtual reality and assistive devices, was conducted. As there were no devices identified that met all the requirements of the design specification, it was concluded that there is a need for the design and development of new concepts. Future research will involve concept and prototype development and user-based evaluation of the prototypes
An autoregressive approach to house price modeling
A statistical model for predicting individual house prices and constructing a
house price index is proposed utilizing information regarding sale price, time
of sale and location (ZIP code). This model is composed of a fixed time effect
and a random ZIP (postal) code effect combined with an autoregressive
component. The former two components are applied to all home sales, while the
latter is applied only to homes sold repeatedly. The time effect can be
converted into a house price index. To evaluate the proposed model and the
resulting index, single-family home sales for twenty US metropolitan areas from
July 1985 through September 2004 are analyzed. The model is shown to have
better predictive abilities than the benchmark S&P/Case--Shiller model, which
is a repeat sales model, and a conventional mixed effects model. Finally, Los
Angeles, CA, is used to illustrate a historical housing market downturn.Comment: Published in at http://dx.doi.org/10.1214/10-AOAS380 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
The analysis of user behaviour of a network management training tool using a neural network
A novel method for the analysis and interpretation of data that describes the interaction between trainee network managers and a network management training tool is presented. A simulation based approach is currently being used to train network managers, through the use of a simulated network. The motivation is to provide a tool for exposing trainees to a life like situation without disrupting a live network. The data logged by this system describes the detailed interaction between trainee network manager and simulated network. The work presented here provides an analysis of this interaction data that enables an assessment of the capabilities of the trainee network manager as well as an understanding of how the network management tasks are being approached. A neural network architecture is implemented in order to perform an exploratory data analysis of the interaction data. The neural network employs a novel form of continuous self-organisation to discover key features in the data and thus provide new insights into the learning and teaching strategies employed
DSN advanced receiver: Breadboard description and test results
A breadboard Advanced Receiver for use in the Deep Space Network was designed, built, and tested in the laboratory. Field testing was also performed during Voyager Uranus encounter at DSS-13. The development of the breadboard is intended to lead towards implementation of the new receiver throughout the network. The receiver is described on a functional level and then in terms of more specific hardware and software architecture. The results of performance tests in the laboratory and in the field are given. Finally, there is a discussion of suggested improvements for the next phase of development
An Analysis of the Broadband (22-3900 MHz) Radio Spectrum of HB3 (G132.7+1.3): The Detection of Thermal Radio Emission from an Evolved Supernova Remnant?
We present an analysis of the broadband radio spectrum (from 22 to 3900 MHz)
of the Galactic supernova remnant (SNR) HB3 (G132.7+1.3). Published
observations have revealed that a curvature is present in the radio spectrum of
this SNR, indicating that a single synchrotron component appears is
insufficient to adequately fit the spectrum. We present here a fit to this
spectrum using a combination of a synchrotron component and a thermal
bremsstrahlung component. We discuss properties of this latter component and
estimate the ambient density implied by the presence of this component to be n
\~ 10 cm^-3. We have also analyzed extracted X-ray spectra from archived {\it
ASCA} GIS observations of different regions of HB3 to obtain independent
estimates of the density of the surrounding interstellar medium (ISM). From
this analysis, we have derived electron densities of 0.1-0.4 f^-1/2 cm^-3 for
the ISM for the three different regions of the SNR, where f is the volume
filling factor. By comparing these density estimates with the estimate derived
from the thermal bremsstrahlung component, we argue that the radio thermal
bremsstrahlung emission is emitted from a thin shell enclosing HB3. The
presence of this thermal bremsstrahlung component in the radio spectrum of HB3
suggests that this SNR is in fact interacting with an adjacent molecular cloud
associated with the HII region W3. By extension, we argue that the presence of
thermal emission at radio wavelengths may be a useful tool for identifying
interactions between SNRs and molecular clouds, and for estimating the ambient
density near SNRs using radio continuum data.Comment: 5 pages, 2 figures, accepted for ApJ
Energy Conversion Alternatives Study (ECAS), General Electric Phase 1. Volume 2: Advanced energy conversion systems. Part 1: Open-cycle gas turbines
Ten energy conversion systems are defined and analyzed in terms of efficiency. These include: open-cycle gas turbine recuperative; open-cycle gas turbine; closed-cycle gas turbine; supercritical CO2 cycle; advanced steam cycle; liquid metal topping cycle; open-cycle MHD; closed-cycle inert gas MHD; closed-cycle liquid metal MHD; and fuel cells. Results are presented
Limit cycles of a flexible shaft with hydrodynamic journal bearings in unstable regimes
A symmetric 3 mass rotor supported on hydrodynamic bearings is described. An approximate method of representing finite bearings is used to calculate bearing forces. As the method sums forces from a number of independent circular lobes lemon 3 and 4 lobe bearings are taken into account. The calculations are based on an axial groove bearing. Linear analysis precedes nonlinear simulation of some unstable conditions. The demonstration of small limit cycles suggests that necessarily flexible rotors e.g., helicopter tail rotors, may be practical without either tilt pad bearings or external dampers
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