Linear and non-linear theory of a parametric instability of hydrodynamic warps in Keplerian discs

We consider the stability of warping modes in Keplerian discs. We find them to be parametrically unstable using two lines of attack, one based on three-mode couplings and the other on Floquet theory. We confirm the existence of the instability, and investigate its nonlinear development in three dimensions, via numerical experiment. The most rapidly growing non-axisymmetric disturbances are the most nearly axisymmetric (low m) ones. Finally, we offer a simple, somewhat speculative model for the interaction of the parametric instability with the warp. We apply this model to the masing disc in NGC 4258 and show that, provided the warp is not forced too strongly, parametric instability can fix the amplitude of the warp.Comment: 14 pages, 6 figures, revised version with appendix added, to be published in MNRA

modCHIMERA: A novel murine closed-head model of moderate traumatic brain injury

AbstractTraumatic brain injury is a major source of global disability and mortality. Preclinical TBI models are a crucial component of therapeutic investigation. We report a tunable, monitored model of murine non-surgical, diffuse closed-head injury—modCHIMERA—characterized by impact as well as linear and rotational acceleration. modCHIMERA is based on the Closed-Head Impact Model of Engineered Rotational Acceleration (CHIMERA) platform. We tested this model at 2 energy levels: 1.7 and 2.1 Joules—substantially higher than previously reported for this system. Kinematic analysis demonstrated linear acceleration exceeding injury thresholds in humans, although outcome metrics tracked impact energy more closely than kinematic parameters. Acute severity metrics were consistent with a complicated-mild or moderate TBI, a clinical population characterized by high morbidity but potentially reversible pathology. Axonal injury was multifocal and bilateral, neuronal death was detected in the hippocampus, and microglial neuroinflammation was prominent. Acute functional analysis revealed prolonged post-injury unconsciousness, and decreased spontaneous behavior and stimulated neurological scores. Neurobehavioral deficits were demonstrated in spatial learning/memory and socialization at 1-month. The overall injury profile of modCHIMERA corresponds with the range responsible for a substantial portion of TBI-related disability in humans. modCHIMERA should provide a reliable platform for efficient analysis of TBI pathophysiology and testing of treatment modalities.</jats:p

Integrated knowledge translation strategies that enhance the lives of persons with dementia and their family caregivers

Purpose: To understand the lived experience of persons with dementia and their family caregivers who receive home care in northern Alberta, Canada, and to reveal how integrated knowledge translation (iKT) strategies influence the uptake of best available dementia care evidence over time. Sample: Three persons living with dementia and thirteen family caregivers were interviewed at the beginning of the study, nine months after implementation of the knowledge broker (KB), and six months after termination of the KB role (total interviews = 41). Method: The PARiHS framework guided our longitudinal case study that included two rural home care centres. A qualitative interpretive descriptive approach was used. A KB was hired for 12 months to facilitate the development of different iKT strategies with staff. Site A developed two strategies: 1) a planning meeting to discuss local needs and suggestions for improving access to dementia care information and community supports; and 2) the development of an information package. Site B focused on working through modules of the U-First program that entailed dementia education and training for the home care providers (HCPs). They then used the U-First wheels with clients during their home visits. Findings: Persons living with dementia spoke of both positive and negative aspects of their dementia journey and how they attempted to manage their lives. Family caregivers struggled to find the best approaches and supports to use to enable their family member with dementia to remain at home for as long as possible. iKT strategies such as a KB, the information resource package developed by the HCPs, use of the U-First modules and wheels, and a support group were examples of effective iKT. Conclusion: iKT strategies and projects increased access to dementia care information and supports. These assisted caregivers to better care for their family member for longer periods at home. Keywords: Persons living with dementia, family caregivers, integrated knowledge translation strategies, rural, and home car

The New Realities of Voting by Mail in 2016

The vote-by-mail process can be more convenient for voters who are unable or unwilling to contend with lines at polling places on Election Day. However, voting by mail is not a voting option without risk. Outdated laws, new administrative policies, and the realities of the political process today introduce obstacles voters may not be aware of. Without recognizing that voting by mail in 2016 is very different than in years past, voters are more likely to unwittingly disenfranchise themselves

Bounding biomass in the Fisher equation

The FKPP equation with a variable growth rate and advection by an incompressible velocity field is considered as a model for plankton dispersed by ocean currents. If the average growth rate is negative then the model has a survival-extinction transition; the location of this transition in the parameter space is constrained using variational arguments and delimited by simulations. The statistical steady state reached when the system is in the survival region of parameter space is characterized by integral constraints and upper and lower bounds on the biomass and productivity that follow from variational arguments and direct inequalities. In the limit of zero-decorrelation time the velocity field is shown to act as Fickian diffusion with an eddy diffusivity much larger than the molecular diffusivity and this allows a one-dimensional model to predict the biomass, productivity and extinction transitions. All results are illustrated with a simple growth and stirring model.Comment: 32 Pages, 13 Figure

Evidence of strong small-scale population structure in the Antarctic freshwater copepod Boeckella poppei in lakes on Signy Island, South Orkney Islands

Environmental conditions were particularly severe during the Last Glacial Maximum, altering the distribution of the Southern Hemisphere biota, particularly at higher latitudes. The copepod Boeckella poppei is the only macroscopic continental invertebrate species known to be distributed today across the three main biogeographic regions in Antarctica as well as in southern South America. Signy Island (South Orkney Islands) is a unique location for the study of Antarctic freshwater ecosystems due to its location and geographic isolation; it contains 17 lakes in several low altitude catchments. We conducted phylogeographic and demographic analyses using the cox1 gene on 84 individuals of B. poppei from seven lakes across Signy Island. We recorded low levels of genetic diversity and a strong genetic differentiation signal between the eastern and western valleys within the island. Phylogeographic structure and demographic inference analyses suggested at least one asymmetrical dispersal event from west to east. Demographic inference detected a strong signal of population growth during the deglaciation process, which may have followed either (1) a strong genetic bottleneck due to a reduction in population size during the last glacial period, or (2) a founder effect associated with postglacial recolonization of Signy Island from elsewhere. The genetic architecture of this island's populations of B. poppei shows that historical events, rather than continuous dispersal events, likely played a major role in the species' current distribution. Finally, our study considers possible mechanisms for dispersal and colonization success of the most dominant species in the Antarctic freshwater community

Personal pack display and active smoking at outdoor café strips: assessing the impact of plain packaging 1 year postimplementation

Aims: We observed tobacco pack display and smoking at outdoor venues over three summers to assess changes in their prevalence following Australia's introduction of plain tobacco packaging with larger pictorial health warnings. Methods: Between January and April 2012 (preplain packaging (PP)), 2013 (early post-PP) and 2014 (1 year post-PP), we counted patrons, smokers and tobacco packs at cafés, restaurants and bars with outdoor seating. Pack type (branded, plain or unknown) and orientation were noted. Rates of active smoking, pack display and pack orientation were analysed using multilevel Poisson regression. Results: Prevalence of pack display among patrons declined from pre-PP (1 pack per 8.7 patrons) to early post-PP (1 pack per 10.4), and remained low 1 year post-PP (1 pack per 10.3). This appeared to be driven by a sustained decline in active smoking post-PP (pre-PP: 8.4% of patrons were smoking; early post-PP: 6.4%; 1 year post-PP: 6.8%). Notably, active smoking declined more in venues with children present than in those without. While early post-PP, plain packs were less often displayed face-up (74.0%) and more often concealed (8.9%) than branded packs pre-PP (face-up: 85.2%; concealed: 4.0%), this was not sustained 1 year post-PP (face-up: 85.7%; concealed: 4.4%). Also, external case use increased from pre-PP (1.2%) to early post-PP (3.5%), but returned to pre-PP levels 1 year post-PP (1.9%). Conclusions: This study demonstrated a sustained reduction in visibility of tobacco products and smoking in public, particularly in the presence of children, from pre-PP to 1 year post-PP. This effect is likely to reduce smoking-related social norms, thereby weakening an important influence on smoking uptake and better supporting quit attempts.Meghan Zacher, Megan Bayly, Emily Brennan, Joanne Dono, Caroline Miller, Sarah Durkin, Michelle Scollo, Melanie Wakefiel

Uncoupling of Genomic and Epigenetic Signals in the Maintenance and Inheritance of Heterochromatin Domains in Fission Yeast

Many essential aspects of genome function, including gene expression and chromosome segregation, are mediated throughout development and differentiation by changes in the chromatin state. Along with genomic signals encoded in the DNA, epigenetic processes regulate heritable gene expression patterns. Genomic signals such as enhancers, silencers, and repetitive DNA, while required for the establishment of alternative chromatin states, have an unclear role in epigenetic processes that underlie the persistence of chromatin states throughout development. Here, we demonstrate in fission yeast that the maintenance and inheritance of ectopic heterochromatin domains are independent of the genomic sequences necessary for their de novo establishment. We find that both structural heterochromatin and gene silencing can be stably maintained over an ∼10-kb domain for up to hundreds of cell divisions in the absence of genomic sequences required for heterochromatin establishment, demonstrating the long-term persistence and stability of this chromatin state. The de novo heterochromatin, despite the absence of nucleation sequences, is also stably inherited through meiosis. Together, these studies provide evidence for chromatin-dependent, epigenetic control of gene silencing that is heritable, stable, and self-sustaining, even in the absence of the originating genomic signals

Electromagnetic controlled cortical impact device for precise, graded experimental traumatic brain injury

Genetically modified mice represent useful tools for traumatic brain injury (TBI) research and attractive preclinical models for the development of novel therapeutics. Experimental methods that minimize the number of mice needed may increase the pace of discovery. With this in mind, we developed and characterized a prototype electromagnetic (EM) controlled cortical impact device along with refined surgical and behavioral testing techniques. By varying the depth of impact between 1.0 and 3.0 mm, we found that the EM device was capable of producing a broad range of injury severities. Histologically, 2.0-mm impact depth injuries produced by the EM device were similar to 1.0-mm impact depth injuries produced by a commercially available pneumatic device. Behaviorally, 2.0-, 2.5-, and 3.0-mm impacts impaired hidden platform and probe trial water maze performance, whereas 1.5-mm impacts did not. Rotorod and visible platform water maze deficits were also found following 2.5- and 3.0-mm impacts. No impairment of conditioned fear performance was detected. No differences were found between sexes of mice. Inter-operator reliability was very good. Behaviorally, we found that we could statistically distinguish between injury depths differing by 0.5 mm using 12 mice per group and between injury depths differing by 1.0 mm with 7-8 mice per group. Thus, the EM impactor and refined surgical and behavioral testing techniques may offer a reliable and convenient framework for preclinical TBI research involving mice

Size-Dependent Transition to High-Dimensional Chaotic Dynamics in a Two-Dimensional Excitable Medium

The spatiotemporal dynamics of an excitable medium with multiple spiral defects is shown to vary smoothly with system size from short-lived transients for small systems to extensive chaos for large systems. A comparison of the Lyapunov dimension density with the average spiral defect density suggests an average dimension per spiral defect varying between three and seven. We discuss some implications of these results for experimental studies of excitable media.Comment: 5 pages, Latex, 4 figure