Invariant manifolds and the geometry of front propagation in fluid flows

Recent theoretical and experimental work has demonstrated the existence of one-sided, invariant barriers to the propagation of reaction-diffusion fronts in quasi-two-dimensional periodically-driven fluid flows. These barriers were called burning invariant manifolds (BIMs). We provide a detailed theoretical analysis of BIMs, providing criteria for their existence, a classification of their stability, a formalization of their barrier property, and mechanisms by which the barriers can be circumvented. This analysis assumes the sharp front limit and negligible feedback of the front on the fluid velocity. A low-dimensional dynamical systems analysis provides the core of our results.Comment: 14 pages, 11 figures. To appear in Chaos Focus Issue: Chemo-Hydrodynamic Patterns and Instabilities (2012

A protected area influences genotype-specific survival and the structure of a Canis hybrid zone

It is widely recognized that protected areas can strongly influence ecological systems and that hybridization is an important conservation issue. However, previous studies have not explicitly considered the influence of protected areas on hybridization dynamics. Eastern wolves are a species of special concern and their distribution is largely restricted to a protected population in Algonquin Provincial Park (APP), Ontario, Canada, where they are the numerically dominant canid. We studied intrinsic and extrinsic factors influencing survival and cause-specific mortality of hybrid and parental canids in the three-species hybrid zone between eastern wolves, eastern coyotes, and gray wolves in and adjacent to APP. Mortality risk for eastern wolves in areas adjacent to APP was significantly higher than for other sympatric Canis types outside of APP, and for eastern wolves and other canids within APP. Outside of APP, the annual mortality rate of all canids by harvest (24%) was higher than for other causes of death (4–7%). Furthermore, eastern wolves (hazard ratio ¼ 3.5) and nonresidents (transients and dispersing animals, hazard ratio ¼ 2.7) were more likely to die from harvest relative to other Canis types and residents, respectively. Thus, eastern wolves dispersing from APP were especially vulnerable to harvest mortality. For residents, eastern wolf survival was more negatively influenced by increased road density than for other Canis types, further highlighting the sensitivity of eastern wolves to human disturbance. A cycle of dispersal from APP followed by high rates of mortality and hybridization appears to maintain eastern wolves at low density adjacent to APP, limiting the potential for expansion beyond the protected area. However, high survival and numerical dominance of eastern wolves within APP suggest that protected areas can allow rare hybridizing species to persist even if their demographic performance is compromised and barriers to hybridization are largely absent in the adjacent matrix

Extinction vortex dynamics of top predators isolated by urbanization

Extinction risk is elevated in small, isolated populations due to demographic and genetic interactions. Therefore, it is critical to model these processes realistically in population viability analyses (PVA) to inform local management and contribute to a greater understanding of mechanisms within the extinction vortex. We conducted PVA’s for two small mountain lion populations isolated by urbanization in southern California to predict population growth, extinction probability, and loss of genetic diversity with empirical data. Specifically, we (1) provide the first PVA for isolated mountain lions in the Santa Ana Mountains (SAM) that considers both demographic and genetic risk factors and (2) test the hypothesis that variation in abundance and mortality between the SAM and Santa Monica Mountains (SMM) result in differences in population growth, loss of heterozygosity, and extinction probability. Our models predicted 16–21% probability of local extinction in the SAM due purely to demographic processes over 50 yr with current low levels or no immigration. Our models also predicted that genetic diversity will further erode in the SAM such that concern regarding inbreeding depression is warranted unless gene flow is increased, and that if inbreeding depression occurs, rapid local extinction will be highly likely. Dynamics of the two populations were broadly similar, but they also exhibited differences driven by larger population size and higher mortality in the SAM. Density-independent scenarios predicted a rapidly increasing population in the SMM, whereas growth potential did not differ from a stable trend in the SAM. Demographic extinction probability and loss of heterozygosity were greater in the SMM for density-dependent scenarios without immigration. However, higher levels of immigration had stronger, positive influences on both demographic viability and retention of genetic diversity in the SMM driven by lower abundance and higher adult survival. Our results elucidate demographic and genetic threats to small populations within the extinction vortex, and how these vary relative to demographic structure. Importantly, simulating seemingly attainable increases in connectivity was sufficient to greatly reduce extinction probability. Our work highlights that conservation of large carnivores is achievable within urbanized landscapes, but requires land protection, connectivity, and strategies to promote coexistence with humans

Religious Identity, Religious Attendance, and Parental Control

Using a national sample of adolescents aged 10–18 years and their parents (N = 5,117), this article examines whether parental religious identity and religious participation are associated with the ways in which parents control their children. We hypothesize that both religious orthodoxy and weekly religious attendance are related to heightened levels of three elements of parental control: monitoring activities, normative regulations, and network closure. Results indicate that an orthodox religious identity for Catholic and Protestant parents and higher levels of religious attendance for parents as a whole are associated with increases in monitoring activities and normative regulations of American adolescents

Comprehensive Geriatric Assessment on an Acute Medical Unit: a Qualitative Study of Older People’s and Informal Carer’s Perspectives of the Care and Treatment Received

Objective: This qualitative study was imbedded in a randomized controlled trial evaluating the addition of geriatricians to usual care to enable the comprehensive geriatric assessment process with older patients on acute medical units. The qualitative study explored the perspectives of intervention participants on their care and treatment.Design: A constructivist study incorporating semi-structured interviews that were conducted in patients’ homes within six weeks of discharge from the acute medical unit. These interviews were recorded, transcribed, and analysed using thematic analysis.Setting: An acute medical unit in the United Kingdom.Participants: Older patients (n = 18) and their informal carers (n = 6) discharged directly home from an acute medical unit, who had been in the intervention group of the randomized controlled trial.Results: Three core themes were constructed: (1) perceived lack of treatment on the acute medical unit; (2) nebulous grasp of the role of the geriatrician; and (3) on-going health and activities of daily living needs postdischarge. These needs impacted upon the informal carers, who either took over, or helped the patients to complete their activities of daily living. Despite the help received with activities of daily living, a lot of the patients voiced a desire to complete these activities themselves.Conclusions:The participants perceived they were just monitored and observed on the acute medical unit, rather than receiving active treatment, and spoke of on-going unresolved health and activity of daily living needs following discharge, despite receiving the additional intervention of a geriatrician

The effect of prior androgen synthesis inhibition on outcomes of subsequent therapy with docetaxel in patients with metastatic castrate-resistant prostate cancer: results from a retrospective analysis of a randomized phase 3 clinical trial (CALGB 90401) (Alliance).

BACKGROUND: Preliminary data suggest a potential decreased benefit of docetaxel in patients with metastatic, castration-resistant prostate cancer (mCRPC) who previously received abiraterone acetate, a novel androgen synthesis inhibitor (ASI). Cancer and Leukemia Group B (CALGB) trial 90401 (Alliance), a phase 3 trial in patients with mCRPC who received docetaxel-based chemotherapy, offered the opportunity to evaluate effect of prior ketoconazole, an earlier generation ASI, on clinical outcomes after docetaxel. METHODS: In CALGB trial 90401, 1050 men with chemotherapy-naive mCRPC were randomized to receive treatment with docetaxel and prednisone that included either bevacizumab or placebo. In total, 1005 men (96%) had data available regarding prior ketoconazole therapy. The observed effects of prior ketoconazole on overall survival (OS), progression-free survival (PFS), prostate-specific antigen (PSA) decline, and the objective response rate (ORR) were assessed using proportional hazards and Poisson regression methods adjusted for validated prognostic factors and treatment arm. RESULTS: Baseline characteristics between patients who did (N=277) and did not (N=728) receive prior ketoconazole therapy were similar. There were no statistically significant differences between patients who did and those who did not receive prior ketoconazole therapy with respect to OS (median OS, 21.1 months vs 22.3 months, respectively; stratified log-rank P=.635), PFS (median PFS, 8.1 months vs 8.6 months, respectively; stratified log-rank P=.342), the proportion achieving a decline ≥ 50% in PSA (61% vs 66%, respectively; relative risk, 1.09; adjusted P=.129), or ORR (39% vs 43%, respectively; relative risk, 1.11; adjusted P=.366). CONCLUSIONS: As measured by OS, PFS, PSA, and the ORR, there was no evidence that prior treatment with ketoconazole had an impact on the clinical outcomes of patients with mCRPC who received subsequent docetaxel-based therapy. The current results highlight the need for prospective studies to assess for potential cross-resistance with novel ASIs and to define the optimal sequence of therapy in mCRPC

Chronology and Geochemistry of Lavas from the Nazca Ridge and Easter Seamount Chain: an ∼30 Myr Hotspot Record

The Easter Seamount Chain and Nazca Ridge are two of the most conspicuous volcanic features on the Nazca plate. Many questions about their nature and origin have remained unresolved because of a lack of geochronological and geochemical data for large portions of both chains. New ⁴⁰Ar⁻³⁹Ar incremental heating age determinations for dredged rocks from volcanoes east of Salas y Gomez Island show that, with very few exceptions, ages increase steadily to the east from 1·4 to 30 Ma, confirming that the two chains are parts of the same hotspot trail and indicating a hotspot location near Salas y Gomez rather than beneath Easter Island some 400 km farther west. Most of the volcanoes appear to have been erupted onto seafloor that was 5–13 Myr old, and no systematic variation in seafloor age at the time of seamount formation is apparent. At about 23 Ma, the formation of the Nazca Ridge ceased and that of the Easter Seamount Chain began, corresponding to a change in the direction of motion of the Nazca plate. Most of the studied rocks are moderately alkalic to transitional basalts. Their geochemical characteristics suggest that they represent relatively small mean amounts of partial melting initiating in garnet-bearing mantle and ending in the spinel facies. Nd–Sr–Pb isotopic compositions are within the range of values previously observed for volcanoes of the Easter Seamount Chain, west of Easter Island; moreover, most of our data cluster in a rather small part of this range [e.g. ε[subscript Nd](t) is between +6·0 and +4·0]. The results indicate that the mantle source has consisted of the same two principal components, a C/FOZO-type component and a high-ε[subscript Nd], incompatible-element-depleted Pacific mid-ocean ridge basalt-source-type component, since at least 30 Ma. The lack of any geochemical gradient along the chain east of Salas y Gomez implies that no systematic change over time has occurred in the proportions of these end-members.Keywords: Nazca Ridge, Pb-Nd-Sr isotopic ratios, Salas y Gomez Island, Easter Seamount Chain, ⁴⁰Ar⁻³⁹Ar geochronolog

The motivational antecedents of the development of mental toughness: a self-determination theory perspective

Mental toughness is a topic that has received growing attention in psychological literature over the past decade. Although some researchers have attempted to understand how mental toughness is developed, little effort has been made to integrate an understanding of mental toughness development with established psychological theory and research. The aim of our review is to demonstrate the utility of theory and research on motivation for understanding mental toughness and its development. In particular, we propose that self-determination theory provides a sound basis for understanding the motivational antecedents of mental toughness. To achieve our aim, we consider concepts that bridge mental toughness and self-determination theory literature, namely striving, surviving, and thriving. We conclude our review with suggestions for future lines of empirical enquiry that could be pursued to further test our propositions

Machine-learning of atomic-scale properties based on physical principles

We briefly summarize the kernel regression approach, as used recently in materials modelling, to fitting functions, particularly potential energy surfaces, and highlight how the linear algebra framework can be used to both predict and train from linear functionals of the potential energy, such as the total energy and atomic forces. We then give a detailed account of the Smooth Overlap of Atomic Positions (SOAP) representation and kernel, showing how it arises from an abstract representation of smooth atomic densities, and how it is related to several popular density-based representations of atomic structure. We also discuss recent generalisations that allow fine control of correlations between different atomic species, prediction and fitting of tensorial properties, and also how to construct structural kernels---applicable to comparing entire molecules or periodic systems---that go beyond an additive combination of local environments