A Simple Fluid Model for the Analysis of SQUIRREL

Peer-to-peer (P2P) systems are complex to analyze, due to their large number of users who connect intermittently, and to the frequency of requests for files or Web objects.In this paper we propose a mathematical model where request streams are represented as fluid flows and apply it to analyze Squirrel, a recent P2P cooperative Web cache. Our fluid model provides a low-complexity means to estimate the performance of Squirrel (hit probability, latency) and exhibits some key qualitative properties of this system. A comparison with discrete-event simulation validates the accuracy of our model

Transient analysis of induction motor using different simulation models

Squirrel cage induction motors have wide range of applications in many industrial drive systems due to their simple construction, robust design and low operational costs. Their application becomes even wider as a result of implementation of voltage inverters providing very good speed-torque control characteristics. In this paper a dynamic behaviour of a squirrel cage induction motor type 2AZ 155-4, produced by Rade Koncar, is analysed. The motor has the following rated data: voltage (Δ/Y) 220/380 V, number of poles 2p=4, rated current 8,7/5 A, power factor cosϕ=0,81, rated speed nn=1410 rpm, frequency 50 Hz. The first simulation motor model, supplied from a symmetrical power supply, is developed in MATLAB/Simulink [1]. The following dynamic motor characteristics, such as: speed characteristic, electromagnetic torque characteristic and current were obtained from this model. Than the analysis is extended with a simulation model of the motor fed by a voltage inverter. In this case the motor transient speed, current and electromagnetic torque characteristics are obtained, for rated frequency as well as for frequencies lower and higher than the rated one. The results obtained from the simulation in MATLAB/Simulink are compared and verified with the results from the second simulation model developed in the software program PSIM. Distribution of magnetic flux density inside the motor cross section is gained by application of the Finite Elements Method (FEM) for all motor operation regimes. Simulatio

Combining a Dispersal Model with Network Theory to Assess Habitat Connectivity

Assessing the potential for threatened species to persist and spread within fragmented landscapes requires the identification of core areas that can sustain resident populations and dispersal corridors that can link these core areas with isolated patches of remnant habitat. We developed a set of GIS tools, simulation methods, and network analysis procedures to assess potential landscape connectivity for the Delmarva fox squirrel (DFS; Sciurus niger cinereus), an endangered species inhabiting forested areas on the Delmarva Peninsula, USA. Information on the DFS’s life history and dispersal characteristics, together with data on the composition and configuration of land cover on the peninsula, were used as input data for an individual-based model to simulate dispersal patterns of millions of squirrels. Simulation results were then assessed using methods from graph theory, which quantifies habitat attributes associated with local and global connectivity. Several bottlenecks to dispersal were identified that were not apparent from simple distance-based metrics, highlighting specific locations for landscape conservation, restoration, and/or squirrel translocations. Our approach links simulation models, network analysis, and available field data in an efficient and general manner, making these methods useful and appropriate for assessing the movement dynamics of threatened species within landscapes being altered by human and natural disturbances

Comparing the cost-effectiveness of methods for estimating population density for primates in the Amazon rainforest Peru

With increasingly extreme fluctuations in flood levels in the Amazon basin (Malhi et al. 2008, Marengo et al. 2012, Bodmer et al. 2014) the future of its' fauna is becoming more uncertain. It is essential therefore that effective monitoring is in place in order to detect drops in population before irreversible damage is done. In developing countries such as the ones situated in the Amazon basin funding for conservation is very limited (Danielsen et al. 2003), it is therefore vital that cost effective methods of monitoring the wildlife of the Amazon are found. Three surveying techniques for monitoring primates are compared in this thesis to find the most cost effective method of estimating population densities of primate species local to the Amazon basin; these are terrestrial transects, aquatic transects and audio-playback point counts. Data was collected in the Pacaya-Samiria National Reserve using these methods over a period of four months, from January to May 2014. For both terrestrial and aquatic transects, transect lines were traversed and data was recorded every time an individual or group of the 7 primates species were spotted. Audio-playback point counts were used to record data for red howler monkeys (Alouatta seniculus)and brown capuchin monkeys (Cebus apella). This was done by mimicking primate vocalisations at a point and recording any resultant responses or sightings of the species under observation. Each survey technique was compared with regards to three qualities; precision, ability to react to change and cost. On average over all 7 species of primate aquatic transects produced the most precise estimations of population density with a mean estimation CV% (percentage coefficient of variance) of 36.35% in comparison the 47.3% averaged by terrestrial transects. Both methods failed to produce precise results for the two rarest species present, the monk saki monkey (Pithecia monachus) and the white fronted capuchin monkey (Cebus albifrons). Aquatic transects were also shown to react to sudden change in population levels. For the two species Alouatta seniculus and Cebus apella aquatic transects once again on average gained the most precise results with a mean estimation CV% value of 20.05% in comparison to the 31.08% of terrestrial transects and 36.35% for audio-playback point counts. The estimates created using audio-playback point counts used considerably less time and resources than the other two methods for single species and was also shown to be the quickest to react to immediate changes in population densities. Thus it was concluded that audio-playback point counts can produce relatively precise estimates that react to population changes at low cost. However only one species can be observed at a time using audio-playback point counts; when observing multiple species at one time it was concluded that aquatic transects are by far the cheapest survey technique and the method that produces precise estimates more consistently. I would therefore recommend for a monitoring effort of several primate species at one given time in the Amazon basin, that aquatic transects be used as it is the most cost-effective overall. However if a single species is a monitoring target, perhaps to be used as an indicator species or because the primate is of most concern, then audio-playback point counts be used as it is possible to gain relatively precise results at a minimal cost. I would also like to suggest that the use of audio-playback point counts be tested on rarer primate species in future as neither terrestrial transects nor aquatic transects could produce a useful estimate in a combined effort of 104 half days. If audio-playback point counts could be used to get good estimates for rare primate species then monitoring strategies could be developed combining the use of audio- playback point counts and aquatic transects to gain precise density estimates for all primate species in an area whilst keeping costs low. A generic decision tree is presented at the end of this thesis as a guideline to cost-effective primate monitoring for any seasonally flooding rainforest study site

Functional evolution of the feeding system in rodents

The masticatory musculature of rodents has evolved to enable both gnawing at the incisors and chewing at the molars. In particular, the masseter muscle is highly specialised, having extended anteriorly to originate from the rostrum. All living rodents have achieved this masseteric expansion in one of three ways, known as the sciuromorph, hystricomorph and myomorph conditions. Here, we used finite element analysis (FEA) to investigate the biomechanical implications of these three morphologies, in a squirrel, guinea pig and rat. In particular, we wished to determine whether each of the three morphologies is better adapted for either gnawing or chewing. Results show that squirrels are more efficient at muscle-bite force transmission during incisor gnawing than guinea pigs, and that guinea pigs are more efficient at molar chewing than squirrels. This matches the known diet of nuts and seeds that squirrels gnaw, and of grasses that guinea pigs grind down with their molars. Surprisingly, results also indicate that rats are more efficient as well as more versatile feeders than both the squirrel and guinea pig. There seems to be no compromise in biting efficiency to accommodate the wider range of foodstuffs and the more general feeding behaviour adopted by rats. Our results show that the morphology of the skull and masticatory muscles have allowed squirrels to specialise as gnawers and guinea pigs as chewers, but that rats are high-performance generalists, which helps explain their overwhelming success as a group

Defining Landscape Resistance Values in Least-Cost Connectivity Models for the Invasive Grey Squirrel: A Comparison of Approaches Using Expert-Opinion and Habitat Suitability Modelling

Least-cost models are widely used to study the functional connectivity of habitat within a varied landscape matrix. A critical step in the process is identifying resistance values for each land cover based upon the facilitating or impeding impact on species movement. Ideally resistance values would be parameterised with empirical data, but due to a shortage of such information, expert-opinion is often used. However, the use of expert-opinion is seen as subjective, human-centric and unreliable. This study derived resistance values from grey squirrel habitat suitability models (HSM) in order to compare the utility and validity of this approach with more traditional, expert-led methods. Models were built and tested with MaxEnt, using squirrel presence records and a categorical land cover map for Cumbria, UK. Predictions on the likelihood of squirrel occurrence within each land cover type were inverted, providing resistance values which were used to parameterise a leastcost model. The resulting habitat networks were measured and compared to those derived from a least-cost model built with previously collated information from experts. The expert-derived and HSM-inferred least-cost networks differ in precision. The HSM-informed networks were smaller and more fragmented because of the higher resistance values attributed to most habitats. These results are discussed in relation to the applicability of both approaches for conservation and management objectives, providing guidance to researchers and practitioners attempting to apply and interpret a leastcost approach to mapping ecological networks.This project was funded by the Forestry Commission GB and the National School of Forestry at the University of Cumbria. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Experimental High-Frequency Parameter Identification of AC Electrical Motors

In order to predict conducted electromagnetic interference in inverter-motor drive systems, high-frequency (HF) motor models are requested and the involved parameters have to be available. In previous studies, the authors have presented an accurate HF model for induction motors and they have defined the procedures to identify the model parameters. In this paper, these results are extended to several types and sizes of industrial ac motors such as induction, synchronous reluctance (without interior permanent magnets), and brushless motors. The model parameter-identification procedure has been improved, and it is based on a least-squares data fitting applied to the measured magnitude and phase-frequency-response curves of the phase-to-ground and the phase-to-neutral impedances. The aim of this paper is to provide quick indications to select the suitable values of the HF model parameters, with reference to the size and type of the ac motor, to evaluate the HF voltage and current components in inverted-fed ac motor system

Mixture or mosaic? Genetic patterns in UK grey squirrels support a human-mediated ‘long-jump’ invasion mechanism

Aim Clarifying whether multiple introductions of a species remain relatively isolated or merge and interbreed is essential for understanding the dynamics of invasion processes. Multiple introductions from different sources can result in a mixture of genetically distinct populations, increasing the total genetic diversity. This mixing can resolve the ‘genetic paradox’, whereby in spite of the relatively small numbers of introduced individuals, the augmented diversity due to this mixing increases adaptability and the ability of the species to spread in new environments. Here, we aim to assess whether the expansion of a successful invader, the Eastern grey squirrel, was partly driven by the merger of multiple introductions and the effects of such a merger on diversity. Location UK, Ireland. Methods We analysed the genetic variation at 12 microsatellite loci of 381 individuals sampled from one historical and 14 modern populations of grey squirrels. Results Our data revealed that current UK population structure resembles a mosaic, with minimal interpopulation mixing and each element reflecting the genetic make-up of historic introductions. The genetic diversity of each examined population was lower than a US population or a historical UK population. Numbers of releases in a county did not correlate with county-level genetic diversity. Inbreeding coefficients remain high, and effective population sizes remain small. Main conclusions Our results support the conclusion that rapid and large-scale expansion in this species in the UK was not driven by a genetic mixing of multiple introduced populations with a single expansion front, but was promoted by repeated translocations of small propagules. Our results have implications for the management of grey squirrels and other invasive species and also demonstrate how invaders can overcome the genetic paradox, if spread is facilitated by human-mediated dispersal

An MPEG-7 scheme for semantic content modelling and filtering of digital video

Abstract Part 5 of the MPEG-7 standard specifies Multimedia Description Schemes (MDS); that is, the format multimedia content models should conform to in order to ensure interoperability across multiple platforms and applications. However, the standard does not specify how the content or the associated model may be filtered. This paper proposes an MPEG-7 scheme which can be deployed for digital video content modelling and filtering. The proposed scheme, COSMOS-7, produces rich and multi-faceted semantic content models and supports a content-based filtering approach that only analyses content relating directly to the preferred content requirements of the user. We present details of the scheme, front-end systems used for content modelling and filtering and experiences with a number of users