Structure and dynamics of round turbulent jets

Laser‐induced fluorescence and particle streak velocity measurements were conducted to investigate the structure and dynamics of round turbulent jets. The results suggest that the far‐field region of the jet is dominated by large‐scale vortical structures, which appear to be axisymmetric or helical a large part of the time. Entrainment and mixing of the reservoir fluid with the jet fluid is found to be intimately connected with the kinematics of these structures. Unmixed reservoir fluid is found to reach and cross the jet axis

Nesting Ecology, Management and Population Genetics of Bumblebees: An Integrated Approach to the Conservation of an Endangered Pollinator Taxon

Bumblebees have shown both long and short-term declines throughout their range. These declines may be attributed to a range of factors including changes in land use, alterations in climatic conditions and species introductions. However, management strategies for bumblebee conservation often focus on provision of summer forage resources and other factors are frequently overlooked. Provision of spring forage and nesting sites for bumblebee queens are rarely considered, though colony foundation and early colony growth are two of the most sensitive stages in bumblebee life history. Here, the efficacy of certain agri-environment prescriptions for providing spring forage and nest sites for bumblebees is assessed, highlighting a need for specific schemes targeted towards the provision of these vital resources in the rural environment. The nesting ecology of bumblebees is poorly understood because wild colonies are difficult to locate. However, a greater knowledge of the colony-level effects of environmental change is crucial to understanding bumblebee declines. Attracting bumblebee queens to nest in artificial domiciles could provide a valuable tool for studying colony-level responses. However, domicile trials and the findings of a literature review presented here demonstrate that this approach may be largely impractical for use in the UK. Conversely, a nationwide public bumblebee nest survey produced numerous data regarding nest site preferences among bumblebee species and also demonstrated that citizen science may also provide a sensitive method for detecting declines in currently common bumblebee species. An understanding of the ecology of species interactions and coexistence can provide valuable insights into factors that may influence declines. Data presented here suggest that coexistence between some bumblebee species may be maintained by resource partitioning based on diel activity patterns that are linked to species-specific environmental tolerances. If this is the case, the potential role of climate change in bumblebee declines may be severely underestimated. There is also increasing evidence that genetic factors may play a role in bumblebee losses, accelerating declines of small, fragmented populations as a result of reduction in genetic diversity and inbreeding depression. Here, the feasibility of reintroducing British B. subterraneus (now extinct in the UK) from New Zealand into England is assessed using population genetic techniques. The findings suggest that the population history of B. subterraneus in New Zealand has resulted in a dramatic loss of genetic diversity and high genetic divergence from the original UK population, suggesting that it may not be a suitable for use in the reintroduction attempt. This work draws together some understudied aspects of bumblebee ecology with a particular focus on nest site requirements, availability of spring forage, mechanisms of avoidance of inter-specific competition and population genetic processes. The potential role of these in bumblebee declines is considered and new data relevant to the conservation of these important species is presented. It is hoped that this work will inform future management strategies for bumblebee conservation, highlight areas in need of further study and provide a sound starting point for future research in these areas

Systematic Influences on Teaching Evaluations : The Case for Caution

The evaluation of teaching and learning has become an important activity in tertiary education institutions. Student surveys provide information about student perceptions and judgments of a particular subject. However, as is widely recognised, the appropriate interpretation of this data is problematic. There is a large literature, mainly for the US, on the use and usefulness of student subject evaluations. This literature has highlighted a number of ‘mitigating factors’ such as subject difficulty, discipline area, etc., that should be taken into account in interpreting the results of these questionnaires. In this paper we examine 8 years of QOT responses from an Economics Department in an Australian University which accounted for more than 79,000 student subject enrolments in 565 subjects. The purpose of this analysis is to establish how the information contained in these data can be used to interpret the responses. In particular, we determine to what extent other factors besides the instructor in charge of the subject have an impact on the raw average student evaluation scores. We find that the following characteristics of the students in these classes had an influence on the average QOT score: year level, enrolment size, the quantitative nature of the subject, the country of origin of the students, the proportion that are female, Honours status of the student, the differential in their mark from previous marks, quality of workbook, quality of textbook and the relative QOT score versus other subjects taught at the same time. However, a number of other factors proposed in the literature to be important influences were found not to be. These include the student’s fee paying status, whether they attended a public, private or catholic secondary school, which other faculty within the University they came from, and if the subject was taught in multiple sessions.

A Comparison of Optimized Link State Routing with Traditional Ad-hoc Routing Protocols

The performance of mobile ad-hoc networks (MANET) is related to the efficiency of the routing protocols in adapting to frequently changing network topology and link status. This paper addresses the issue by comparing the relative performance of three key ad-hoc routing protocols: Destination-sequenced Distance Vector (DSDV), Ad-hoc Ondemand Distance Vector (AODV) and Optimized Link State Routing (OLSR). The protocols are tested based on two scenarios, namely, tactical networks for ships and sensor-based network nodes. Four performance metrics were measured by varying the maximum speed of mobile hosts, network size and traffic load, to assess the routing capability and protocol efficiency. The simulation results indicate that AODV performs better than OSLR and DSDV in the first scenario. Although OLSR also performed relatively well, the associated high routing overhead is the dominant reason for not choosing it. On the other hand, OLSR emerged as the protocol of choice for sensor networks, where the high routing overhead is counteracted by consistently better performance in all other metrics. Due to the slow evolution of the sensor network topology, OLSR performed satisfactorily for best effort traffic but needed subtle adjustments to balance between latency and bandwidth to meet the requirements of delay-sensitive applications

A Bose-Einstein condensate in a random potential

An optical speckle potential is used to investigate the static and dynamic properties of a Bose-Einstein condensate in the presence of disorder. For strong disorder the condensate is localized in the deep wells of the potential. With smaller levels of disorder, stripes are observed in the expanded density profile and strong damping of dipole and quadrupole oscillations is seen. Uncorrelated frequency shifts of the two modes are measured for a weak disorder and are explained using a sum-rules approach and by the numerical solution of the Gross-Pitaevskii equation

Classical noise and flux: the limits of multi-state atom lasers

By direct comparison between experiment and theory, we show how the classical noise on a multi-state atom laser beam increases with increasing flux. The trade off between classical noise and flux is an important consideration in precision interferometric measurement. We use periodic 10 microsecond radio-frequency pulses to couple atoms out of an F=2 87Rb Bose-Einstein condensate. The resulting atom laser beam has suprising structure which is explained using three dimensional simulations of the five state Gross-Pitaevskii equations.Comment: 4 pages, 3 figure

Observation of dynamical instability for a Bose-Einstein condensate in a moving 1D optical lattice

We have experimentally studied the unstable dynamics of a harmonically trapped Bose-Einstein condensate loaded into a 1D moving optical lattice. The lifetime of the condensate in such a potential exhibits a dramatic dependence on the quasimomentum state. This is unambiguously attributed to the onset of dynamical instability, after a comparison with the predictions of the Gross-Pitaevskii theory. Deeply in the unstable region we observe the rapid appearance of complex structures in the atomic density profile, as a consequence of the condensate phase uniformity breakdown

Effect of optical disorder and single defects on the expansion of a Bose-Einstein condensate in a one-dimensional waveguide

We investigate the one-dimensional expansion of a Bose-Einstein condensate in an optical guide in the presence of a random potential created with optical speckles. With the speckle the expansion of the condensate is strongly inhibited. A detailed investigation has been carried out varying the experimental conditions and checking the expansion when a single optical defect is present. The experimental results are in good agreement with numerical calculations based on the Gross-Pitaevskii equation.Comment: 5 pages, 5 figure

Unstable regimes for a Bose-Einstein condensate in an optical lattice

We report on the experimental characterization of energetic and dynamical instability, two mechanisms responsible for the breakdown of Bloch waves in a Bose-Einstein condensate interacting with a 1D optical lattice. A clear separation of these two regimes is obtained performing measurements at different temperatures of the atomic sample. The timescales of the two processes have been determined by measuring the losses induced in the condensate. A simple phenomenological model is introduced for energetic instability while a full comparison is made between the experiment and the 3D Gross-Pitaevskii theory that accounts for dynamical instability

Combination strategies for pandemic influenza response - a systematic review of mathematical modeling studies

<p>Abstract</p> <p>Background</p> <p>Individual strategies in pandemic preparedness plans may not reduce the impact of an influenza pandemic.</p> <p>Methods</p> <p>We searched modeling publications through PubMed and associated references from 1990 to 30 September 2009. Inclusion criteria were modeling papers quantifying the effectiveness of combination strategies, both pharmaceutical and non-pharmaceutical.</p> <p>Results</p> <p>Nineteen modeling papers on combination strategies were selected. Four studies examined combination strategies on a global scale, 14 on single countries, and one on a small community. Stochastic individual-based modeling was used in nine studies, stochastic meta-population modeling in five, and deterministic compartmental modeling in another five. As part of combination strategies, vaccination was explored in eight studies, antiviral prophylaxis and/or treatment in 16, area or household quarantine in eight, case isolation in six, social distancing measures in 10 and air travel restriction in six studies. Two studies suggested a high probability of successful influenza epicenter containment with combination strategies under favorable conditions. During a pandemic, combination strategies delayed spread, reduced overall number of cases, and delayed and reduced peak attack rate more than individual strategies. Combination strategies remained effective at high reproductive numbers compared with single strategy. Global cooperative strategies, including redistribution of antiviral drugs, were effective in reducing the global impact and attack rates of pandemic influenza.</p> <p>Conclusion</p> <p>Combination strategies increase the effectiveness of individual strategies. They include pharmaceutical (antiviral agents, antibiotics and vaccines) and non-pharmaceutical interventions (case isolation, quarantine, personal hygiene measures, social distancing and travel restriction). Local epidemiological and modeling studies are needed to validate efficacy and feasibility.</p