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Canberra, Australia

Du L.,Macquarie University | Buntine W.,Canberra Research Laboratory | Jin H.,CSIRO
EMNLP-CoNLL 2012 - 2012 Joint Conference on Empirical Methods in Natural Language Processing and Computational Natural Language Learning, Proceedings of the Conference | Year: 2012

Topic models are increasingly being used for text analysis tasks, often times replacing earlier semantic techniques such as latent semantic analysis. In this paper, we develop a novel adaptive topic model with the ability to adapt topics from both the previous segment and the parent document. For this proposed model, a Gibbs sampler is developed for doing posterior inference. Experimental results show that with topic adaptation, our model significantly improves over existing approaches in terms of perplexity, and is able to uncover clear sequential structure on, for example, Herman Melville's book "Moby Dick". © 2012 Association for Computational Linguistics.

Shah A.,Canberra Research Laboratory | Shah A.,Australian National University
Journal of Signal Processing Systems | Year: 2015

A model-free method for efficiently capturing drifts in functional magnetic resonance imaging (fMRI) data is presented. The proposed algorithm applies a first order differencing to the fMRI time series samples in order to remove the drift effect. Initially, a consistent hemodynamic response function (HRF) of the fMRI voxel is estimated using linear least-squares. An optimal estimate of the drift is then obtained based on a wavelet thresholding technique applied to the generated residuals after eliminating the induced activation response. Finally, the de-drifted fMRI voxel response is acquired by removing the estimated drift from the fMRI time-series. Its performance is assessed using simulated and motor-task real fMRI data sets obtained from both block and event-related designs. The application results reveal that the proposed method, which avoids the selection of a model to remove the drift component unlike traditional methods, is efficient in de-drifting the fMRI time-series and offers blood oxygen level-dependent (BOLD)-fMRI signal improvement and enhanced activation detection. © 2014, Springer Science+Business Media New York.

Engerer N.A.,Australian National University | Engerer N.A.,Canberra Research Laboratory | Mills F.P.,Australian National University | Mills F.P.,Space Science Institute
Solar Energy | Year: 2014

The rapidly growing installed base of distributed solar photovoltaic (PV) systems is causing increased interest in forecasting their power output. A key step towards this is accurately estimating the output from a PV system based on the known output from a nearby PV system. However, each PV system is unique with its own hardware configuration, orientation, shading, etc. Thus, the process of using the power output from one system to estimate the power output of another nearby system is not necessarily straightforward. In order to address these challenges, a modified clear-sky index for photovoltaics is proposed. This index is the ratio of the instantaneous PV power output to the instantaneous theoretical clear-sky power output derived from a clear-sky radiation model and PV system simulation routine. This definition performs better than previous clear-sky indices when both PV systems' characteristics are known and the two PV systems have similar orientations. Through this index, the performance of a nearby PV system can be predicted quite accurately. This is demonstrated through the analysis of power output data from five residential PV systems in Canberra, Australia. © 2014 Elsevier Ltd.

Engerer N.A.,Australian National University | Engerer N.A.,Canberra Research Laboratory | Mills F.P.,Australian National University | Mills F.P.,Space Science Institute
Solar Energy | Year: 2015

There have been many validation studies of clear sky solar radiation models, however, to date, no such analysis has been completed for Australia. Clear sky models are essential for estimating the generation potential of various solar energy technologies, the basic calibration of radiation measuring equipment, quality control of solar radiation datasets, engineering design (e.g. heating and cooling of buildings) and in agricultural and biological sciences (e.g. forestry). All of these areas are of considerable interest to the Australian economy and will benefit from an assessment of clear sky radiation models. With the recent provision of one-minute interval radiation data by the Australian Bureau of Meteorology for 20 sites across Australia, such a study can now be undertaken at a level not previously possible. Using up to ten years of data from each of 14 of these sites, clear sky periods are extracted through an automated detection algorithm. With these clear sky periods identified, nine of the most prominent beam and global clear sky radiation models are assessed using the relative Mean Bias Error, relative Root Mean Square Error and Coefficient of Determination as metrics. Further testing assessed model performance as a function of solar zenith angle and apparent solar time. Results show that for global clear sky simulations, the Solis, Esra and REST2 approaches perform best, while the Iqbal, Esra and REST2 methods are the most proficient clear sky beam models. © 2015 Elsevier Ltd.

Wang H.,Australian National University | Wang H.,Canberra Research Laboratory | Zhou X.,University of New South Wales | Reed M.C.,Australian National University
IEEE Transactions on Wireless Communications | Year: 2013

This paper studies the information-theoretic secrecy performance in large-scale cellular networks based on a stochastic geometry framework. The locations of both base stations and mobile users are modeled as independent two-dimensional Poisson point processes. We consider two important features of cellular networks, namely, information exchange between base stations and cell association, to characterize their impact on the achievable secrecy rate of an arbitrary downlink transmission with a certain portion of the mobile users acting as potential eavesdroppers. In particular, tractable results are presented under diverse assumptions on the availability of eavesdroppers' location information at the serving base station, which captures the benefit from the exchange of the location information between base stations. © 2002-2012 IEEE.

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