Navigational efficiency in a biased and correlated random walk model of individual animal movement

Understanding how an individual animal is able to navigate through its environment is a key question in movement ecology that can give insight into observed movement patterns and the mechanisms behind them. Efficiency of navigation is important for behavioral processes at a range of different spatio-temporal scales, including foraging and migration. Random walk models provide a standard framework for modeling individual animal movement and navigation. Here we consider a vector-weighted biased and correlated random walk (BCRW) model for directed movement (taxis), where external navigation cues are balanced with forward persistence. We derive a mathematical approximation of the expected navigational efficiency for any BCRW of this form and confirm the model predictions using simulations. We demonstrate how the navigational efficiency is related to the weighting given to forward persistence and external navigation cues, and highlight the counter-intuitive result that for low (but realistic) levels of error on forward persistence, a higher navigational efficiency is achieved by giving more weighting to this indirect navigation cue rather than direct navigational cues. We discuss and interpret the relevance of these results for understanding animal movement and navigation strategies

Delirium screening and mortality in patients with dementia admitted to acute hospitals

Objectives: Delirium is associated with increased mortality in older adults. National guidance recommends that all people with dementia who are admitted to hospital are screened for delirium. However, the impact of screening for delirium among inpatients with dementia has not been examined. This study aims to examine this relationship.Methods: Secondary analysis of data from 10,047 patients admitted to 199 hospitals in England and Wales that took part in the third round of the National Audit of Dementia. Data on patients with dementia who died during their admission were compared with those who survived. We calculated odds of mortality among those who were screened for delirium, received cognitive testing, and, in those with delirium, an expert clinical review.Results: The mean age of study patients was 84 years (SD = 7.9), 40.1% were male and 82.1% white British. 1,285 patients (12.8%) died during their admission to hospital. Overall, 4,466 (44.5%) patients were screened for delirium, of whom 2,603 (58.6%) screened positive. The odds of mortality were lower in patients who underwent delirium screening (OR: 0.79, 95% confidence interval (CI): 0.69-0.90) and in those receiving cognitive testing (OR: 0.71, 95%CI: 0.61-0.82).Conclusion: These results demonstrate that, among people with dementia who are admitted to hospital, screening for delirium and assessment of cognitive functioning are associated with lower mortality. While we cannot be certain that these associations are causal, the findings support efforts that are being made to increase levels of screening for delirium among people with dementia who are admitted to hospital

Health surveillance for occupational asthma in the UK

Background Periodic health surveillance (HS) of workers can identify early cases of occupational asthma. Information about its uptake and its content in the UK is lacking. Aims To identify the overall levels of uptake and quality of HS for occupational asthma within three high risk industry sectors in the UK. Methods A telephone survey of employers, and their occupational health (OH) professionals, carried out in three sectors with exposures potentially capable of causing occupational asthma (bakeries, wood working and motor vehicle repair). Results A total of 457 organizations participated (31% response rate). About 77% employed <10 people, 17% between 10 and 50 and 6% >50. Risk assessments were common (67%) and 14% carried out some form of HS for occupational asthma, rising to 19% if only organizations reporting asthma hazards and risks were considered. HS was carried out both by in-house (31%) and external providers (69%). Organizational policies were often used to define HS approaches (80%), but infrequently shared with the OH provider. OH providers described considerable variation in practice. Record keeping was universal, but worker-held records were not reported. HS tools were generally developed in-house. Lung function was commonly measured, but only limited interpretation evident. Referral of workers to local specialist respiratory services was variable. Conclusions This study provided new insights into the real world of HS for occupational asthma. We consider that future work could and should define simpler, more practical and evidence-based approaches to HS to ensure maximal consistency and use of high-quality approaches

21st century fisheries management: a spatio-temporally explicit tariff-based approach combining multiple drivers and incentivising responsible fishing

Abstract Kraak, S. B. M., Reid, D. G., Gerritsen, H. D., Kelly, C. J., Fitzpatrick, M., Codling, E. A., and Rogan, E. 2012. 21st century fisheries management: a spatio-temporally explicit tariff-based approach combining multiple drivers and incentivising responsible fishing. – ICES Journal of Marine Science, 69: 590–601. Traditionally fisheries management has focused on biomass and mortality, expressed annually and across large management units. However, because fish abundance varies at much smaller spatio-temporal scales, fishing mortality can potentially be controlled more effectively if managed at finer scale. The ecosystem approach requires more indicators at finer scales as well. Incorporating ecosystem targets would need additional management tools with potentially conflicting results. We present a simple, integrated, management approach that provides incentives for “good behaviour”. Fishers would be given a number of fishing-impact credits, called real-time incentives (RTIs), to spend according to spatio-temporally varying tariffs per fishing day. RTI quotas and tariffs could be based on commercial stocks and ecosystem targets. Fishers could choose how to spend their RTIs, e.g. by limited fishing in high-catch or sensitive areas or by fishing longer in lower-catch or less sensitive areas. The RTI system does not prescribe and forbid, but instead allows fishers to fish wherever and whenever they want; ecosystem costs are internalized and fishers have to take them into account in their business decisions. We envisage no need for traditional landings or catch quotas for the fleets while operating under the scheme. The approach could facilitate further devolution of responsibility to industry.</jats:p

Role of infochemical mediated zooplankton grazing in a phytoplankton competition model

Infochemicals released by marine phytoplankton play important roles in food web interactions by influencing the feeding behavior and selectivity of zooplanktonic predators. Recent modeling efforts have focused on the role of such chemicals as toxic grazing deterrents in phytoplankton competition. However, infochemicals may also be utilized as grazing cues, leading predators to profitable foraging patches. Here we investigate the role of infochemical mediated zooplankton grazing in a standard 3-species phytoplankton competition model, with the aim of further elucidating the ecological role of phytoplankton derived infochemicals. We then extend this to consider a more realistic 4-species model. The models produce a range of solutions depending on the strength of competition and microzooplankton grazing selectivity. Our key result is that infochemical chemoattractants, which increase the susceptibility of the producer to grazing, can provide a refuge for both competing phytoplankton species by attracting carnivorous copepods to consume microzooplankton grazers in a multi-trophic interaction. Our results indicate that infochemicals potentially have important consequences for the dynamics of marine food webs. © 2012 Elsevier B.V

Emergence of the wrapped Cauchy distribution in mixed directional data

Inferring the most appropriate distribution (or distributions) to describe observed directional data is important in many applications of circular statistics. In particular, animal movement paths are typically analysed and modelled by considering the distribution of step lengths and turning (or absolute) angles. Here we demonstrate that a single-wrapped Cauchy distribution can appear to fit directional data mixed from two different underlying wrapped normal distributions. We derive mathematical expressions to calculate the parameter space for which this occurs and illustrate the result by analysing an example data set of the movements of African bull elephants (Loxodonta Africana). We conclude that the presence of a wrapped Cauchy distribution in observed directional data can, in certain cases, be explained by data coming from two distinct underlying distributions. We discuss how this may relate to the presence of multiple movement modes within an observed path when analysing animal movement data

Dissociation spectrum of H2+_2^+ from a short, intense infrared laser pulse: vibration structure and focal volume effects

The dissociation spectrum of the hydrogen molecular ion by short intense pulses of infrared light is calculated. The time-dependent Schr\"odinger equation is discretized and integrated in position and momentum space. For few-cycle pulses one can resolve vibrational structure that commonly arises in the experimental preparation of the molecular ion from the neutral molecule. We calculate the corresponding energy spectrum and analyze the dependence on the pulse time-delay, pulse length, and intensity of the laser for $\lambda \sim 790$nm. We conclude that the proton spectrum is a both a sensitive probe of the vibrational dynamics and the laser pulse. Finally we compare our results with recent measurements of the proton spectrum for 55 fs pulses using a Ti:Sapphire laser ($\lambda \sim 790$nm). Integrating over the laser focal volume, for the intensity $I \sim 3 \times 10^{15}$W cm$^{-2}$, we find our results are in excellent agreement with these experiments.Comment: 17 pages, 8 figures, preprin

Correlation dynamics between electrons and ions in the fragmentation of D2_2 molecules by short laser pulses

We studied the recollision dynamics between the electrons and D$_2^+$ ions following the tunneling ionization of D$_2$ molecules in an intense short pulse laser field. The returning electron collisionally excites the D$_2^+$ ion to excited electronic states from there D$_2^+$ can dissociate or be further ionized by the laser field, resulting in D$^+$ + D or D$^+$ + D$^+$, respectively. We modeled the fragmentation dynamics and calculated the resulting kinetic energy spectrum of D$^+$ to compare with recent experiments. Since the recollision time is locked to the tunneling ionization time which occurs only within fraction of an optical cycle, the peaks in the D$^+$ kinetic energy spectra provides a measure of the time when the recollision occurs. This collision dynamics forms the basis of the molecular clock where the clock can be read with attosecond precision, as first proposed by Corkum and coworkers. By analyzing each of the elementary processes leading to the fragmentation quantitatively, we identified how the molecular clock is to be read from the measured kinetic energy spectra of D$^+$ and what laser parameters be used in order to measure the clock more accurately.Comment: 13 pages with 14 figure

“Micropersonality” traits and their implications for behavioral and movement ecology research

Many animal personality traits have implicit movement‐based definitions and can directly or indirectly influence ecological and evolutionary processes. It has therefore been proposed that animal movement studies could benefit from acknowledging and studying consistent interindividual differences (personality), and, conversely, animal personality studies could adopt a more quantitative representation of movement patterns. Using high‐resolution tracking data of three‐spined stickleback fish (Gasterosteus aculeatus), we examined the repeatability of four movement parameters commonly used in the analysis of discrete time series movement data (time stationary, step length, turning angle, burst frequency) and four behavioral parameters commonly used in animal personality studies (distance travelled, space use, time in free water, and time near objects). Fish showed repeatable interindividual differences in both movement and behavioral parameters when observed in a simple environment with two, three, or five shelters present. Moreover, individuals that spent less time stationary, took more direct paths, and less commonly burst travelled (movement parameters), were found to travel farther, explored more of the tank, and spent more time in open water (behavioral parameters). Our case study indicates that the two approaches—quantifying movement and behavioral parameters—are broadly equivalent, and we suggest that movement parameters can be viewed as “micropersonality” traits that give rise to broad‐scale consistent interindividual differences in behavior. This finding has implications for both personality and movement ecology research areas. For example, the study of movement parameters may provide a robust way to analyze individual personalities in species that are difficult or impossible to study using standardized behavioral assays

The Riemann Hypothesis

This literature review provides a brief discussion of the Riemann Hypothesis, a conjecture regarding the location of the zeros on the Riemann zeta function. We also look at the implications of solving the hypothesis, and investigate historical attempts to solve the conjecture