71,635 research outputs found
Efficient data augmentation techniques for some classes of state space models
Data augmentation improves the convergence of iterative algorithms, such as
the EM algorithm and Gibbs sampler by introducing carefully designed latent
variables. In this article, we first propose a data augmentation scheme for the
first-order autoregression plus noise model, where optimal values of working
parameters introduced for recentering and rescaling of the latent states, can
be derived analytically by minimizing the fraction of missing information in
the EM algorithm. The proposed data augmentation scheme is then utilized to
design efficient Markov chain Monte Carlo (MCMC) algorithms for Bayesian
inference of some non-Gaussian and nonlinear state space models, via a mixture
of normals approximation coupled with a block-specific reparametrization
strategy. Applications on simulated and benchmark real datasets indicate that
the proposed MCMC sampler can yield improvements in simulation efficiency
compared with centering, noncentering and even the ancillarity-sufficiency
interweaving strategy.Comment: Keywords: Data augmentation, State space model, Stochastic volatility
model, EM algorithm, Reparametrization, Markov chain Monte Carlo,
Ancillarity-sufficiency interweaving strateg
Talk your way round: a speech interface to a virtual museum
Purpose: To explore the development of a speech interface to a Virtual World and to consider its relevance for disabled users. Method: The system was developed using mainly software that is available at minimal cost. How well the system functioned was assessed by measuring the number of times a group of users with a range of voices had to repeat commands in order for them to be successfully recognised. During an initial session, these users were asked to use the system with no instruction to see how easy this was. Results: Most of the spoken commands had to be repeated less than twice on average for successful recognition. For a set of ‘teleportation’ commands this figure was higher (2.4), but it was clear why this was so and could easily be rectified. The system was easy to use without instruction. Comments on the system were generally positive. Conclusions: While the system has some limitations, a Virtual World with a reasonably reliable speech interface has been developed almost entirely from software which is available at minimal cost. Improvements and further testing are considered. Such a system would clearly improve access to Virtual Reality technologies for those without the skills or physical ability to use a standard keyboard and mouse. It is an example of both Assistive Technology and Universal Design
Parametrized energy spectrum of cosmic-ray protons with kinetic energies down to 1 GeV
A new estimation of the interstellar proton spectrum is made in which the source term of primary protons is taken from shock acceleration theory and the cosmic ray propagation calculation is based on a proposed nonuniform galactic disk model
Spectral shape variation of interstellar electrons at high energies
The high energy electron spectrum analysis has shown that the electron intensity inside the H2 cloud region, or in a spiral arm, should be much lower than that outside it and the observed electron energy spectrum should flatten again at about 1 TeV. In the framework of the leady box model the recently established rigidity dependence of the escape pathlength of cosmic rays would predict a high energy electron spectrum which is flatter than the observed one. This divergence is explained by assuming that the leaky box model can only apply to cosmic ray heavy nuclei, and light nuclei and electrons in cosmic rays may have different behaviors in the interstellar propagation. Therefore, the measured data on high energy electrons should be analyzed based on the proposed nonuniform galactic disk (NUGD) mode
Analysis of experimental data on interstellar antiprotons in the light of measurements of high-energy electrons and He-3 nuclei
The interstellar antiproton calculations were reexamined in view of the recent progress in measurements of interstellar electrons and He(3) nuclei. It was found that the divergence between the predicted antiproton flux and the existing datum at very low energies is increased. The proposed nonuniform galactic disk (NUGD) model qualitatively explains the unexpectedly large flux of interstellar antiprotons. Some ambiguities existed in the prototype of the model. It was unclear what fraction of observed antiprotons is of local origin. Previously the value of cosmic ray escape pathlength was suggested with quite a large arbitrariness
Interpretation of cosmic-ray anisotropy below 10(14) eV
It is found that the measured data on the degree of anisotropy of cosmic rays are consistent with our proposed nonuniform galactic disk model. Moreover, it is pointed out that the abrupt increase of the anisotropy of cosmic rays beyond 10 to the 14th power eV should imply a change of their mass composition
Management accounting education: is there a gap between academia and practitioner perceptions?
A mail survey was conducted of all Institute of Chartered Accountants of New Zealand accredited Tertiary Education Institutions and 300 randomly selected New Zealand companies to ascertain the views of management accounting academics and practitioners on the contents of management accounting courses and the skills and competencies of recent graduates.
The results show that practitioners placed an emphasis on traditional management accounting techniques, while academics placed an emphasis on contemporary techniques. Both groups were in agreement on the skills and characteristics required of recent graduates. An interesting finding was the emergence of negative comments on the arrogance of new graduates and an increased need for graduates to be work ready. These two aspects were not a feature of previous studies.
The implications of the results are that academics cannot ignore the teaching of traditional management accounting techniques and may need to increase the coverage of the issues involved in implementing contemporary management accounting techniques
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