Population studies of the Cabbage aphid Brevicoryne brassicae (L.) and its parasites, with special reference to synchronisation

Imperial Users onl

Polynomial Linear Programming with Gaussian Belief Propagation

Interior-point methods are state-of-the-art algorithms for solving linear programming (LP) problems with polynomial complexity. Specifically, the Karmarkar algorithm typically solves LP problems in time O(n^{3.5}), where $n$ is the number of unknown variables. Karmarkar's celebrated algorithm is known to be an instance of the log-barrier method using the Newton iteration. The main computational overhead of this method is in inverting the Hessian matrix of the Newton iteration. In this contribution, we propose the application of the Gaussian belief propagation (GaBP) algorithm as part of an efficient and distributed LP solver that exploits the sparse and symmetric structure of the Hessian matrix and avoids the need for direct matrix inversion. This approach shifts the computation from realm of linear algebra to that of probabilistic inference on graphical models, thus applying GaBP as an efficient inference engine. Our construction is general and can be used for any interior-point algorithm which uses the Newton method, including non-linear program solvers.Comment: 7 pages, 1 figure, appeared in the 46th Annual Allerton Conference on Communication, Control and Computing, Allerton House, Illinois, Sept. 200

Indirect observation of phase conjugate magnons from non-degenerate four-wave mixing

A phase conjugate mirror utilising four-wave mixing in a magnetic system is experimentally realised for the first time. Indirect evidence of continuous-wave phase conjugation has been observed experimentally and is supported by simulations. The experiment utilizes a pump-probe method to excite a four-wave mixing process. Two antennae are used to pump a region of a thin-film yttrium iron garnet waveguide with magnons of frequency $f_{1}$ to create a spatio-temporally periodic potential. As the probe magnons of $f_{\mathrm{p}}$ impinge on the pumped region, a signal with frequency $f_{\mathrm{c}} = 2f_{1}-f_{\mathrm{p}}$ is observed. The amplitude of the nonlinear signal was highly dependent on the applied magnetic field $H$. Width modes of the probe magnons and standing wave modes of the pump magnons were shown to affect the amplitude of the signal at $f_{\mathrm{c}}$. Experimental data is compared with simulations and theory to suggest that $f_{\mathrm{c}}$ is a phase conjugate of $f_{\mathrm{p}}$.Comment: 6 pages, 6 figure

A Hybrid Multicast-Unicast Infrastructure for Efficient Publish-Subscribe in Enterprise Networks

One of the main challenges in building a large scale publish-subscribe infrastructure in an enterprise network, is to provide the subscribers with the required information, while minimizing the consumed host and network resources. Typically, previous approaches utilize either IP multicast or point-to-point unicast for efficient dissemination of the information. In this work, we propose a novel hybrid framework, which is a combination of both multicast and unicast data dissemination. Our hybrid framework allows us to take the advantages of both multicast and unicast, while avoiding their drawbacks. We investigate several algorithms for computing the best mapping of publishers' transmissions into multicast and unicast transport. Using extensive simulations, we show that our hybrid framework reduces consumed host and network resources, outperforming traditional solutions. To insure the subscribers interests closely resemble those of real-world settings, our simulations are based on stock market data and on recorded IBM WebShpere subscriptions

Recruiting and Using Children as Soldiers: The Case for Defining the Offence as a Crime Against Humanity

The increasing number of domestic conflicts around the world has put civilian populations in general, and children specifically, in harmʼs way. Due to their vulnerability and the lack of social support that is likely to result as a consequence of combat, children are often recruited and put to use as soldiers and participants in these wars. The international community has only recently begun to address this egregious practice, and much remains to be done to halt the recruitment and use of child soldiers. This paper surveys the current humanitarian and human rights laws applicable to this issue, and examines the likely effect the new International Criminal Court will have on the prosecution of those who forcibly conscript children. The definitions of War Crimes and Crimes Against Humanity will be considered, and it will be recommended that the latter concept extended to include the offence of using and recruiting children as soldiers. Such an extension will facilitate the prosecution and punishment of offenders, while increasing the likelihood that proceedings are brought in domestic courts

Tensor decomposition and its applications

This dissertation reviews classical vector - tensor analysis, building up to the necessary techniques required to decompose a tensor into a tensor train and to reconstruct it back into the original tensor with minimal error. The tensor train decomposition decomposes a tensor of dimensionality d into a train of d third order tensors, whose sizes are dependent upon the rank and chosen error bound. I will be reviewing the required operations of matricization, tensor - matrix, vector and tensor multiplication to be able to compute this decomposition. I then move onto analysing the tensor train decomposition by ap-plying it to different types of tensor, of differing dimensionality with a variety of accuracy bounds to investigate their influence on the time taken to complete the decomposition and the final absolute error. Finally I explore a method to compute a d-dimensional integration from the tensor train, which will allow larger tensors to be integrated with the memory required dramatically reduced after the tensor is decomposed. I will be applying this technique to two tensors with different ranks and compare the efficiency and accuracy of integrating directly from the tensor to that of the tensor train decomposition

Distributed Large Scale Network Utility Maximization

Recent work by Zymnis et al. proposes an efficient primal-dual interior-point method, using a truncated Newton method, for solving the network utility maximization (NUM) problem. This method has shown superior performance relative to the traditional dual-decomposition approach. Other recent work by Bickson et al. shows how to compute efficiently and distributively the Newton step, which is the main computational bottleneck of the Newton method, utilizing the Gaussian belief propagation algorithm. In the current work, we combine both approaches to create an efficient distributed algorithm for solving the NUM problem. Unlike the work of Zymnis, which uses a centralized approach, our new algorithm is easily distributed. Using an empirical evaluation we show that our new method outperforms previous approaches, including the truncated Newton method and dual-decomposition methods. As an additional contribution, this is the first work that evaluates the performance of the Gaussian belief propagation algorithm vs. the preconditioned conjugate gradient method, for a large scale problem.Comment: In the International Symposium on Information Theory (ISIT) 200

Effects of Host Fruit and Larval Density on Development and Survival of Bactrocera sp. (Malaysian B). (Diptera: Tephritidae)

The effects of five fruits (guava, mango, papaya, starfruit and tomato) on the larval survival, adult eclosion and size of Bactrocera sp. (Malaysia B) were investigated. The percentage pupation and adult emergence from pupae were not affected by different hosts, except for guava which gave the lowest percentage of adult emergence. Papaya and mango yielded the largest adult (>2mm head width). Comparison of composition of fruits indicates that a high percentage of carbohydrate and high pH in fruits would produce larger adults. High larval density reduced the percentage of larval survival, adult emergence and adult size

Molecular diagnostic method for rapid and accurate identification of Malaria parasite species

Four of the five malaria parasite species infecting humans have been recorded in Malaysia (Plasmodium vivax, P. fa/ciparum, P. malariae and P. know/es,) with P. know/esi most prevalent in Sabah. Although the fifth species P. ovale is reported in Malaysia occasionally, it is only an imported species brought in by an infected visitor. Plasmodium species are identified mainly by microcopic examination of blood film on glass slides, using mainly the ring stage of the parasite within the red blood cells as a distinguishing feature. This can be done in most hospitals, but the accuracy of the method depends highly on the skill of the technician/ doctor and idetification errors have been recorded. A molecular method of species identification using DNA of Singh et al. (1999) has become popular. However this method involves two stages of PCR protocol and takes consderable time. Using this method, various investigators have shown that errors have been previously made in the identification of Plasmodium based on microscopic examination alone. For example, P. vivax and P. malariae had been misidentified as P. fa/ciparum by microscopy, almost all P. knowlesi misidentified as P. malariae or Plasmodium vivaxor P. falciparum (Singh et al., 1999) In our research, we also used a molecular method, but we used four different genes, and various DNA markers which could provide more accurate and faster identification, with lower error rates. Our approach was to examine the DNA sequences from GenBank website (www.ncbi.nlm.nih.gov/nucleotide) and determine which markers can be used as a species identification tool. We have designed new primers, tested in single as well as multiplex amplication of the four malaria species. Our results showed the multiplex PCR method is able to identify any of the five malaria species. Finally we compared our method with Singh's method and the traditional microscopic method to analyse over 100 blood samples. Our comparison indicated our multiplex method is faster, cheaper and as accurate