Adiabatic reduction near a bifurcation in stochastically modulated systems

We re-examine the procedure of adiabatic elimination of fast relaxing variables near a bifurcation point when some of the parameters of the system are stochastically modulated. Approximate stationary solutions of the Fokker-Planck equation are obtained near threshold for the pitchfork and transcritical bifurcations. Stochastic resonance between fast variables and random modulation may shift the effective bifurcation point by an amount proportional to the intensity of the fluctuations. We also find that fluctuations of the fast variables above threshold are not always Gaussian and centered around the (deterministic) center manifold as was previously believed. Numerical solutions obtained for a few illustrative examples support these conclusions.Comment: RevTeX, 19 pages and 16 figure

Women rebuilding lives post-disaster: innovative community practices for building resilience and promoting sustainable development

Disasters result in devastating human, economic, and environmental effects. The paper highlights women's active participation in community-based disaster recovery efforts drawing from the results of the ‘Rebuilding Lives Post-disaster: Innovative Community Practices for Sustainable Development’ by an international research partnership. Two case studies are presented from Pakistan and the USA to demonstrate how women contribute to building resilience and promoting sustainable development in diverse post-disaster contexts. The policy and practice implications are relevant for discussions regarding the post-2015 Sustainable Development Goals and framework

Les enjeux éthiques de l’enseignement en ergothérapie : des pistes de solutions

Cet article consiste en la 2e partie des résultats d’une étude que notre équipe a menée sur les enjeux éthiques de l’enseignement en ergothérapie et leurs pistes de solutions. Tandis que le premier article de 2020 a mis en lumière ces enjeux, le présent article porte sur les moyens de les résoudre. L’ergothérapeute qui enseigne à des étudiants en ergothérapie est tôt ou tard confronté à des enjeux éthiques. Or, ces enjeux sont peu documentés dans les écrits, de même que les pistes de solutions que les ergothérapeutes qui enseignent utilisent ou envisagent. Cette étude qualitative a permis à onze ergothérapeutes-enseignantes des quatre universités francophones du Québec qui préparent la relève ergothérapique de partager leurs bons coups. Dix unités de sens relatives à ces pistes de solutions émergent des résultats, lesquelles ont été regroupées suivant les trois domaines de l’éthique (micro, méso et macro) de Glaser. Les quatre pistes de solutions micro-environnementales sont : a) développer ses compétences éthiques; b) se soutenir entre pairs; c) développer ses compétences en lien avec sa tâche; et d) prendre soin de soi. Les quatre pistes de solutions méso-environnementales sont : a) créer des espaces de parole; b) offrir de la formation en éthique; c) faire de l’advocacy méso; et d) changer la culture académique. Les deux pistes de solutions macro-environnementales sont : a) faire de l’advocacy macro et b) travailler en partenariat avec les milieux cliniques. Bien que des pistes de solutions documentées dans les écrits n’aient pas été discutées par les participantes, celles que ces dernières discutent rejoignent les pistes de solutions abordées dans les écrits. Il ressort des résultats que l’éthique occupe une place limitée dans la préparation et la formation continue des enseignants en ergothérapie et que le contexte organisationnel, c’est-à-dire la culture du monde académique en général et de la recherche en particulier, est susceptible d’occasionner des enjeux éthiques préoccupants. This article presents the second part of the results of a study our team conducted on the ethical issues in occupational therapy education and their solutions. While the first article in 2020 highlighted these issues, this article focuses on ways to address them. The occupational therapist who teaches occupational therapy students is sooner or later confronted with ethical issues. However, these issues are not well documented in the literature, nor are the solutions used or considered by occupational therapists educators. In this qualitative study, eleven occupational therapist educators from four francophone universities in Quebec who are preparing the next generation of occupational therapists shared their success stories. Ten units of meaning related to these solutions emerge from the results, which have been grouped according to Glaser’s three domains of ethics (micro, meso and macro). The four micro-environmental solutions include: a) developing ethical skills; b) peer support; c) developing task-related skills; and d) self-care. The four meso-environmental solutions are: a) creating spaces for discussion; b) providing ethics training; c) doing meso advocacy; and d) changing the academic culture. The two macro-environmental solutions are: a) macro-level advocacy; and b) working in partnership with clinical settings. Although some of the solutions documented in the literature were not discussed by the participants, those discussed by the participants were consistent with the solutions discussed in the literature. The results indicate that ethics has a limited place in the preparation and continuing education of occupational therapy educators and that the organizational context, i.e., the culture of academia in general and research in particular, is likely to create ethical issues of concern

A highly reproducible rotenone model of Parkinson's disease

Producción CientíficaThe systemic rotenone model of Parkinson's disease (PD) accurately replicates many aspects of the pathology of human PD and has provided insights into the pathogenesis of PD. The major limitation of the rotenone model has been its variability, both in terms of the percentage of animals that develop a clear-cut nigrostriatal lesion and the extent of that lesion. The goal here was to develop an improved and highly reproducible rotenone model of PD. In these studies, male Lewis rats in three age groups (3, 7 or 12-14 months) were administered rotenone (2.75 or 3.0 mg/kg/day) in a specialized vehicle by daily intraperitoneal injection. All rotenone-treated animals developed bradykinesia, postural instability, and/or rigidity, which were reversed by apomorphine, consistent with a lesion of the nigrostriatal dopamine system. Animals were sacrificed when the PD phenotype became debilitating. Rotenone treatment caused a 45% loss of tyrosine hydroxylase-positive substantia nigra neurons and a commensurate loss of striatal dopamine. Additionally, in rotenone-treated animals, alpha-synuclein and poly-ubiquitin positive aggregates were observed in dopamine neurons of the substantia nigra. In summary, this version of the rotenone model is highly reproducible and may provide an excellent tool to test new neuroprotective strategies

FW propagation and absorption in reactor plasmas in the ICR frequency range at the quasiperpendicular propagation

On the base of the numerical model, taking into account the strong transverse and longitudinal dispersion of plasma, the absorption and dispersion of the Fast Mode of fast magnetosonic wave (FW) near ICR harmonics ω=nωci at the quasiperpendicular propagation regime were investigated. It was shown that in the region of small longitudinal refractive index values NII there appears the additional absorption that provides the value of optical thickness τ being constant in the entire region of additional absorption. At first and second harmonics the additional absorption can be interesting for FW plasma heating in the reactor-size devices. For higher harmonics it can be important for HF diagnostic purposes and for investigation of astrophysical plasmas.Дисперсия и поглощение быстрой моды быстрой магнитозвуковой волны (БВ) в области ионных циклотронных гармоник ω=nωci исследованы на основе численной модели, учитывающей сильную продольную и поперечную дисперсии плазмы. Показано, что в области малых продольных замедлений появляется дополнительное поглощение, которое обеспечивает постоянное значение оптической толщи во всей области проявления дополнительного поглощения. На первой и второй гармониках такое поглощение может быть интересно для нагрева реакторной плазмы. Для более высоких гармоник оно может быть важным для ВЧ-диагностики, а также для исследования астрофизической плазмы.Дисперсія і поглинання швидкої моди швидкої магнітозвукової хвилі (ШХ) в області іонних циклотронних гармонік ω=nωci досліджені на основі чисельної моделі, що враховує сильну поздовжню і поперечну дисперсії плазми. Показано, що в області малих поздовжніх уповільнень з'являється додаткове поглинання, яке забезпечує постійне значення оптичної товщі у всій області прояви додаткового поглинання. На першій і другій гармоніках таке поглинання може бути цікавим для нагріву реакторної плазми. Для більш високих гармонік воно може бути важливим для ВЧ-діагностики, а також для дослідження астрофізичної плазми

Grain boundary pinning and glassy dynamics in stripe phases

We study numerically and analytically the coarsening of stripe phases in two spatial dimensions, and show that transient configurations do not achieve long ranged orientational order but rather evolve into glassy configurations with very slow dynamics. In the absence of thermal fluctuations, defects such as grain boundaries become pinned in an effective periodic potential that is induced by the underlying periodicity of the stripe pattern itself. Pinning arises without quenched disorder from the non-adiabatic coupling between the slowly varying envelope of the order parameter around a defect, and its fast variation over the stripe wavelength. The characteristic size of ordered domains asymptotes to a finite value $R_g \sim \lambda_0\ \epsilon^{-1/2}\exp(|a|/\sqrt{\epsilon})$, where$\epsilon\ll 1$is the dimensionless distance away from threshold,$\lambda_0$the stripe wavelength, and$a$ a constant of order unity. Random fluctuations allow defect motion to resume until a new characteristic scale is reached, function of the intensity of the fluctuations. We finally discuss the relationship between defect pinning and the coarsening laws obtained in the intermediate time regime.Comment: 17 pages, 8 figures. Corrected version with one new figur

Phase diagram for diblock copolymer melts under cylindrical confinement

We extensively study the phase diagram of a diblock copolymer melt confined in a cylindrical nanopore using real-space self-consistent mean-field theory. We discover a rich variety of new two-dimensional equilibrium structures that have no analog in the unconfined system. These include non-hexagonally coordinated cylinder phases and structures intermediate between lamellae and cylinders. We map the stability regions and phase boundaries for all the structures we find. As the pore radius is decreased, the pore accommodates fewer cylindrical domains and structural transitions occur as cylinders are eliminated. Our results are consistent with experiments, but we also predict phases yet to be observed.Comment: 12 pages, 3 figures. submitted to Physical Review Letter

Sharp interface limits of phase-field models

The use of continuum phase-field models to describe the motion of well-defined interfaces is discussed for a class of phenomena, that includes order/disorder transitions, spinodal decomposition and Ostwald ripening, dendritic growth, and the solidification of eutectic alloys. The projection operator method is used to extract the ``sharp interface limit'' from phase field models which have interfaces that are diffuse on a length scale $\xi$. In particular,phase-field equations are mapped onto sharp interface equations in the limits $\xi \kappa \ll 1$ and $\xi v/D \ll 1$, where $\kappa$ and $v$ are respectively the interface curvature and velocity and $D$ is the diffusion constant in the bulk. The calculations provide one general set of sharp interface equations that incorporate the Gibbs-Thomson condition, the Allen-Cahn equation and the Kardar-Parisi-Zhang equation.Comment: 17 pages, 9 figure

New Method for Phase transitions in diblock copolymers: The Lamellar case

A new mean-field type theory is proposed to study order-disorder transitions (ODT) in block copolymers. The theory applies to both the weak segregation (WS) and the strong segregation (SS) regimes. A new energy functional is proposed without appealing to the random phase approximation (RPA). We find new terms unaccounted for within RPA. We work out in detail transitions to the lamellar state and compare the method to other existing theories of ODT and numerical simulations. We find good agreements with recent experimental results and predict that the intermediate segregation regime may have more than one scaling behavior.Comment: 23 pages, 8 figure