Improvements to MLE Algorithm for Localizing Radiation Sources with a Distributed Detector Network

Maximum Likelihood Estimation (MLE) is a widely used method for the localization of radiation sources using distributed detector networks. While robust, MLE is computationally intensive, requiring an exhaustive search over parameter space. To mitigate the computational load of MLE, many techniques have been presented, including iterative and multi-resolution methods. In this work, we present two ways to improve the MLE localization of radiation sources. First, we present a method to mitigate the pitfalls of a standard multi-resolution algorithm. Our method expands the search region of each layer before performing the MLE search. Doing so allows the multi-resolution algorithm to correct an incorrect selection made in a prior layer. We test our proposed method against single-resolution MLE and standard multi-resolution MLE algorithms, and find that the use of grid expansion incurs a general decrease in localization error and a negligible increase in computation time over the standard multi-resolution algorithm. Second, we present a method to perform the MLE localization without prior knowledge of the background radiation intensity. We estimate the source and background intensities using linear regression (LR) and then use these estimates to initialize the intensity parameter search for MLE. We test this method using single-resolution, multi-resolution, and multi-resolution with grid expansion MLE algorithms and compare performance to MLE algorithms that don\u27t use the LR initialization method. We found that using the LR estimates to initialize the intensity parameter search caused a marginal increase in both localization error and computation time for the tested algorithms. The technique is only beneficial in the case of an unknown background intensity

Lake Victoria Stock Assessment: Status Report

This report will bring you up-to-date on the status of our Stock assessment activities. It will also fulfill the request made by D. W. Kelley in his 30th January, 1970 letter for our "approach to stock assessment" for use at the Assessment Seminar this May. It is also a timely exercise since we have just completed bottom trawling and will soon begin another phase of the lakewide survey

Past trends, present stocks and possible future state of the fisheries of the Tanzania part of the Lake Victoria

The Tanzania part of Lake Victoria is the most important single fishery resource for the country. Past fishing practice caused disparity between the relative abundance in the catches and in the available stocks by overfishing some species while under-fishing others. Preliminary studies of distribution pattern, biomass estimates, etc, as derived from bollom trawl exploratory data, and the trend of the commercial catch statistics from 1958 to 1970, suggest that many of the commercially preferred species may not have the biotic potential 10 sustain higher yields under present ecological and fishing regimes. Haplochromis and a few other fish might be the only hope. Geographic extension of fishing to deeper waters may not be very promising as species diversificarion and fish density decline with depth. To develop and manage the fisheries, make full use of the resource and ensure economic and biological perpetuation of thc fishery, the appropriate fishing strategy cannot be properly developcd overnight

Batho-spatial distribution pattern and biomass estimate of the major demersal fishes in Lake Victoria

A generalized bottom trawl exploratory survey was carried out on Lake Victoria to: (i) define the distributional pattern and magnitude of the lakewide demersal stocks, (ii) determine the commercial potential of Haplochromis spp. and (iii) evaluate trawling as a commercial fishing technique for Lake Victoria fisheries. Preliminary results suggest that: (i) bottom trawl catches are more representative of the stocks, (ii) species diversification and fish density decrease with increasing mean depth and (iii) at least 80%of the catchable demersal ichthyomass is Haplochromis. Though bottom trawling is a much more efficient fishing technique for the Lake Victoria fisheries, bio-socio-economic consideration impose that mechanization of the fishery should better proceed in graded steps. Besides demographic and nutritional considerations indicate the necessity for rational management and increased direct human utilization of the fishery resource

A bi-objective model for the single-machine scheduling problem with rejection cost and total tardiness minimization

We study the problem of scheduling jobs on a single machine with a rejection possibility, concurrently minimizing the total tardiness of the scheduled jobs and the total cost of the rejected ones. The model we consider is fully bi-objective, i.e. its aim is to enumerate the Pareto front. We tackle the problem both with and without the presence of hard deadlines. For the case without deadlines, we provide a pseudo-polynomial time algorithm, based on the dynamic program of Steiner and Zhang (2011), thereby proving that the problem is weakly NP-hard. For the case with deadlines, we propose a branch-and-bound algorithm and prove its efficiency by comparing it to an \u3b5-constrained approach on benchmark instances based on those proposed in the literature on similar problems

Past trends, present stocks and possible future state of the fisheries of the Tanzania part of the lake Victoria

The fisheries resources of mainland Tanzania are comprised of both marine and freshwater sources. The freshwater fisheries, however, are the more important and depend upon Lakes Victoria, Tanganyika, Rukwa, Kitangiri, and other smaller 1akes, rivers, swamps, dams and domestic fishponds. Of these, the Tanzania portion of Lake Victoria, which is about 51% of the whole lake area, is the most important single fishery. Its to

Progress report on identification of "organisms" in Lake Victoria responsible for echosounder traces

Exploratory fishing with midwater trawls in the pelagic zone of Lake Victoria generally yielded low quantities of fish even where dense traces appeared on the echosounder. Efforts to identify the "organisms" met with limited success. Types of gear were tested the midwater trawl, high-speed beam trawl, Lampara net, zooplankton net and SCUBA. This information plus that of earlier investigators indicate that the bulk of the traces are not caused by fish. The evidence however is not conclusive and further studies are warranted. Some recommendations for study are presented

Insights from human sleep research on neural mechanisms of Alzheimer’s disease

The current research in the field of sleep and AD is increasing in importance, denoting a possible innovative future in terms of non-invasive and early interventions and prevention strategies. The above-mentioned results on sleep electroencephalogram in relation with AD have to be considered as preliminary reports, because other confirmations are needed. Future researches should propose complex and integrated experimental protocols, in order to provide concurrent electrophysiological, behavioral, anatomical and neuropsychological data. At this purpose, longitudinal studies that follow the entire course of the pathology, since the preclinical stage of the disease are needed. Further investigations on the role of specific NREM sleep components are also required, with the aim of confirming the original and promising existing evidence

The multimode covering location problem

In this paper we introduce the Multimode Covering Location Problem. This is a generalization of the Maximal Covering Location Problem that consists in locating a given number of facilities of different types with a limitation on the number of facilities sharing the same site. The problem is challenging and intrinsically much harder than its basic version. Nevertheless, it admits a constant factor approximation guarantee, which can be achieved combining two greedy algorithms. To improve the greedy solutions, we have developed a Variable Neighborhood Search approach, based on an exponential-size neighborhood. This algorithm computes good quality solutions in short computational time. The viability of the approach here proposed is also corroborated by a comparison with a Heuristic Concentration algorithm, which is presently the most effective approach to solve large instances of the Maximal Covering Location Problem