4,619 research outputs found
Ecological notes on the East Gippsland burrowing crayfish Engaeus orientalis, including burrow structure and associated fauna
Despite Australia having a high diversity of freshwater crayfish species, the ecology of many of these species remains poorly known, particularly burrowing crayfish of the genus Engaeus. Biological information on colour, behaviour, burrow structure, associated burrow fauna and habitat of the East Gippsland Burrowing Crayfish Engaeus orientalis obtained during incidental observations in 2007 and 2008 is provided. The burrow structure took the form of radiating runways under a rock slab, while the burrow location was in a semi-disturbed site away from water. Both are atypical for this species
A high altitude observation of the beautiful firetail Stagonopleura bella from East Gippsland, Victoria
There has been little research on the ecological requirements of the Beautiful Firetail Stagonopleura bella, and its habitat preferences are poorly understood. On mainland Australia, the Beautiful Firetail is generally considered to be a bird of coastal regions and the lowlands. This note reports an observation of Beautiful Firetails on the Great Dividing Range at a height of more than 1100 metres above sea level from an atypical habitat for mainland Australia. It appears that the observation may be the highest altitude at which this species has been recorded on the mainland
Simulations of the dynamic switching of vortex chirality in magnetic nanodisks by a uniform field pulse
We present a possibility to switch the chirality of a spin vortex occurring
in a magnetic nanodisk by applying a uniform in-plane field pulse, based on
optimizing its strength and duration. The related spin-dynamical process,
investigated by micromagnetic simulations, consists of several stages. After
applying the field, the original vortex is expelled from the disk, after which
two C-shaped states oscillate between each other. The essence of the method is
based on turning the field off at a suitably chosen moment for which the
orientation of the C-state will evolve into the nucleation of a vortex with the
desirable chirality. This idea simply uses the information about the original
chirality present inside the nanodisk during the dynamic process before losing
it in saturation, and can thus be regarded as analogous to the recent studies
on the polarity switching.Comment: In this version only small formal changes are mad
Local Policy Search in a Convex Space and Conservative Policy Iteration as Boosted Policy Search
International audienceLocal Policy Search is a popular reinforcement learning approach for handling large state spaces. Formally, it searches locally in a parameterized policy space in order to maximize the associated value function averaged over some pre-defined distribution. The best one can hope in general from such an approach is to get a local optimum of this criterion. The first contribution of this article is the following surprising result: if the policy space is convex, any (approximate) local optimum enjoys a global performance guarantee. Unfortunately, the convexity assumption is strong: it is not satisfied by commonly used parameterizations and designing a parameterization that induces this property seems hard. A natural so-lution to alleviate this issue consists in deriving an algorithm that solves the local policy search problem using a boosting approach (constrained to the convex hull of the policy space). The resulting algorithm turns out to be a slight generalization of conservative policy iteration; thus, our second contribution is to highlight an original connection between local policy search and approximate dynamic pro-gramming
Upper-Confidence-Bound Algorithms for Active Learning in Multi-Armed Bandits
International audienceIn this paper, we study the problem of estimating the mean values of all the arms uniformly well in the multi-armed bandit setting. If the variances of the arms were known, one could design an optimal sampling strategy by pulling the arms proportionally to their variances. However, since the distributions are not known in advance, we need to design adaptive sampling strategies to select an arm at each round based on the previous observed samples. We describe two strategies based on pulling the arms proportionally to an upper-bound on their variances and derive regret bounds for these strategies. %on the excess estimation error compared to the optimal allocation. We show that the performance of these allocation strategies depends not only on the variances of the arms but also on the full shape of their distributions
On Convergence Properties of Shannon Entropy
Convergence properties of Shannon Entropy are studied. In the differential
setting, it is shown that weak convergence of probability measures, or
convergence in distribution, is not enough for convergence of the associated
differential entropies. A general result for the desired differential entropy
convergence is provided, taking into account both compactly and uncompactly
supported densities. Convergence of differential entropy is also characterized
in terms of the Kullback-Liebler discriminant for densities with fairly general
supports, and it is shown that convergence in variation of probability measures
guarantees such convergence under an appropriate boundedness condition on the
densities involved. Results for the discrete setting are also provided,
allowing for infinitely supported probability measures, by taking advantage of
the equivalence between weak convergence and convergence in variation in this
setting.Comment: Submitted to IEEE Transactions on Information Theor
Data production models for the CDF experiment
The data production for the CDF experiment is conducted on a large Linux PC
farm designed to meet the needs of data collection at a maximum rate of 40
MByte/sec. We present two data production models that exploits advances in
computing and communication technology. The first production farm is a
centralized system that has achieved a stable data processing rate of
approximately 2 TByte per day. The recently upgraded farm is migrated to the
SAM (Sequential Access to data via Metadata) data handling system. The software
and hardware of the CDF production farms has been successful in providing large
computing and data throughput capacity to the experiment.Comment: 8 pages, 9 figures; presented at HPC Asia2005, Beijing, China, Nov 30
- Dec 3, 200
Factors influencing awareness of community-based shorebird conservation projects in Australia
We examine the awareness of potential volunteers (n = 360) living near nine community-based shorebird conservation projects. About half of the people sampled (54%) were unaware of the nearest project. Awareness of interviewees varied substantially among projects (28-78%). Apart from gaining awareness of projects through membership of natural history groups (43%), many respondents heard of projects through friends and relatives (20%), rather than through media such as newspapers (14%) and television (2.3%). We demonstrate that community-based projects can be quantitatively and critically assessed for awareness. The use of rapid, cost-effective assessments of awareness levels has application in many conservation projects. <br /
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