Spatial gene drives and pushed genetic waves

Gene drives have the potential to rapidly replace a harmful wild-type allele with a gene drive allele engineered to have desired functionalities. However, an accidental or premature release of a gene drive construct to the natural environment could damage an ecosystem irreversibly. Thus, it is important to understand the spatiotemporal consequences of the super-Mendelian population genetics prior to potential applications. Here, we employ a reaction-diffusion model for sexually reproducing diploid organisms to study how a locally introduced gene drive allele spreads to replace the wild-type allele, even though it possesses a selective disadvantage $s>0$. Using methods developed by N. Barton and collaborators, we show that socially responsible gene drives require $0.5<s<0.697$, a rather narrow range. In this "pushed wave" regime, the spatial spreading of gene drives will be initiated only when the initial frequency distribution is above a threshold profile called "critical propagule", which acts as a safeguard against accidental release. We also study how the spatial spread of the pushed wave can be stopped by making gene drives uniquely vulnerable ("sensitizing drive") in a way that is harmless for a wild-type allele. Finally, we show that appropriately sensitized drives in two dimensions can be stopped even by imperfect barriers perforated by a series of gaps

Helping Mothers and Children Bond: Sharing Children’s Literature After Domestic Violence Experiences

This qualitative study explores how mothers attempt to bond with their children after the trauma of family domestic violence. This study was based on the use of two psychoeducational focus groups with women who are mothers and victims of domestic violence. Focus groups based on a semi-structured interview guide were held before and after a shared book experience with the group participants. Women from two Minnesota domestic violence agencies (Group A=five and Group B =eight) comprised the study sample. Findings indicated that mothers are working to create bonds with their children but have a number of roadblocks. Participants were empowered to try the practice of reading with their children to repair the damaged mother/child dyad through the process of spending time reading with their children

Constraints on resonant-trapping for two planets embedded in a protoplanetary disc

We investigate the evolution of two-planet systems embedded in a protoplanetary disc, which are composed of a Jupiter-mass planet plus another body located further out in the disc. We consider outermost planets with masses ranging from 10 earth masses to 1 M_J. We also examine the case of outermost bodies with masses < 10 earth masses (M_E). Differential migration of the planets due to disc torques leads to different evolution outcomes depending on the mass of the outer protoplanet. For planets with mass < 3.5 M_E the type II migration rate of the giant exceeds the type I migration rate of the outer body, resulting in divergent migration. Outer bodies with masses in the range 3.5 < m_o < 20 M_E become trapped at the edge of the gap formed by the giant planet, because of corotation torques. Higher mass planets are captured into resonance with the inner planet. If 30 < m_o < 40 M_E or m_o=1 M_J, then the 2:1 resonance is established. If 80 < m_o < 100 M_E, the 3:2 resonance is favoured. Simulations of gas-accreting protoplanets of mass m_o > 20 M_E, trapped initially at the edge of the gap, or in the 2:1 resonance, also result in eventual capture in the 3:2 resonance as the planet mass grows to become close to the mass of Saturn. Our results suggest that there is a theoretical lower limit to the mass of an outer planet that can be captured into resonance with an inner Jovian planet, which is relevant to observations of extrasolar multiplanet systems. Furthermore, capture of a Saturn-like planet into the 3:2 resonance with a Jupiter-like planet is a very robust outcome of simulations. This result is relevant to recent scenarios of early Solar System evolution which require Saturn to have existed interior to the 2:1 resonance with Jupiter prior to the onset of the Late Heavy Bombardment.Comment: 10 pages, 9 figures, Accepted for publication in A&

Global MHD simulations of stratified and turbulent protoplanetary discs. I. Model properties

We present the results of global 3-D MHD simulations of stratified and turbulent protoplanetary disc models. The aim of this work is to develop thin disc models capable of sustaining turbulence for long run times, which can be used for on-going studies of planet formation in turbulent discs. The results are obtained using two codes written in spherical coordinates: GLOBAL and NIRVANA. Both are time--explicit and use finite differences along with the Constrained Transport algorithm to evolve the equations of MHD. In the presence of a weak toroidal magnetic field, a thin protoplanetary disc in hydrostatic equilibrium is destabilised by the magnetorotational instability (MRI). When the resolution is large enough (25 vertical grid cells per scale height), the entire disc settles into a turbulent quasi steady-state after about 300 orbits. Angular momentum is transported outward such that the standard alpha parameter is roughly 4-6*10^{-3}. We find that the initial toroidal flux is expelled from the disc midplane and that the disc behaves essentially as a quasi-zero net flux disc for the remainder of the simulation. As in previous studies, the disc develops a dual structure composed of an MRI--driven turbulent core around its midplane, and a magnetised corona stable to the MRI near its surface. By varying disc parameters and boundary conditions, we show that these basic properties of the models are robust. The high resolution disc models we present in this paper achieve a quasi--steady state and sustain turbulence for hundreds of orbits. As such, they are ideally suited to the study of outstanding problems in planet formation such as disc--planet interactions and dust dynamics.Comment: 19 pages, 29 figures, accepted in Astronomy & Astrophysic

Simulating planet migration in globally evolving disks

Numerical simulations of planet-disk interactions are usually performed with hydro-codes that -- because they consider only an annulus of the disk, over a 2D grid -- can not take into account the global evolution of the disk. However, the latter governs planetary migration of type II, so that the accuracy of the planetary evolution can be questioned. To develop an algorithm that models the local planet-disk interactions together with the global viscous evolution of the disk, we surround the usual 2D grid with a 1D grid ranging over the real extension of the disk. The 1D and 2D grids are coupled at their common boundaries via ghost rings, paying particular attention to the fluxes at the interface, especially the flux of angular momentum carried by waves. The computation is done in the frame centered on the center of mass to ensure angular momentum conservation. The global evolution of the disk and the local planet-disk interactions are both well described and the feedback of one on the other can be studied with this algorithm, for a negligible additional computing cost with respect to usual algorithms.Comment: 12 pages, 11 figures, accepted for publication in A&

Path integrals for spinning particles, stationary phase and the Duistermaat-Heckman theorem

We examine the problem of the evaluation of both the propagator and of the partition function of a spinning particle in an external field at the classical as well as the quantum level, in connection with the asserted exactness of the saddle point approximation (SPA) for this problem. At the classical level we argue that exactness of the SPA stems from the fact that the dynamics (on the two--sphere $S^2$) of a classical spinning particle in a magnetic field is the reduction from \br^4 to $S^2$ of a linear dynamical system on \br^4. At the quantum level, however, and within the path integral approach, the restriction, inherent to the use of the SPA, to regular paths clashes with the fact that no regulators are present in the action that enters the path integral. This is shown to lead to a prefactor for the path integral that is strictly divergent except in the classical limit. A critical comparison is made with the various approaches to the same problem that have been presented in the literature. The validity of a formula given in literature for the spin propagator is extended to the case of motion in an arbitrary magnetic field.Comment: 29 pages, Late

Relativistic Kinetics of Phonon Gas in Superfluids

The relativistic kinetic theory of the phonon gas in superfluids is developed. The technique of the derivation of macroscopic balance equations from microscopic equations of motion for individual particles is applied to an ensemble of quasi-particles. The necessary expressions are constructed in terms of a Hamilton function of a (quasi-)particle. A phonon contribution into superfluid dynamic parameters is obtained from energy-momentum balance equations for the phonon gas together with the conservation law for superfluids as a whole. Relations between dynamic flows being in agreement with results of relativistic hydrodynamic consideration are found. Based on the kinetic approach a problem of relativistic variation of the speed of sound under phonon influence at low temperature is solved.Comment: 23 pages, Revtex fil

Narrative, identity and mental health: How men with serious mental illness re-story their lives through sport and exercise

Objectives: It has been suggested that mental illness threatens identity and sense of self when one's personal story is displaced by dominant illness narratives focussing on deficit and dysfunction. One role of therapy, therefore, is to allow individuals to re-story their life in a more positive way which facilitates the reconstruction of a meaningful identity and sense of self. This research explores the ways in which involvement in sport and exercise may play a part in this process. Design: Qualitative analysis of narrative. Method: We used an interpretive approach which included semi-structured interviews and participant observation with 11 men with serious mental illness to gather stories of participants' sport and exercise experiences. We conducted an analysis of narrative to explore the more general narrative types which were evident in participants' accounts. Findings: We identified three narrative types underlying participants' talk about sport and exercise: (a) an action narrative about "going places and doing stuff"; (b) an achievement narrative about accomplishment through effort, skill or courage; (c) a relationship narrative of shared experiences to talk about combined with opportunities to talk about those experiences. We note that these narrative types differ significantly from-and may be considered alternatives to-dominant illness narratives. Conclusion: This study provides an alternative perspective on how sport and exercise can help men with serious mental illness by providing the narrative resources which enabled participants to re-story aspects of their lives through creating and sharing personal stories through which they rebuilt or maintained a positive sense of self and identity. © 2007 Elsevier Ltd. All rights reserved

Turbulent transport and its effect on the dead zone in protoplanetary discs

Protostellar accretion discs have cool, dense midplanes where externally originating ionisation sources such as X-rays or cosmic rays are unable to penetrate. This suggests that for a wide range of radii, MHD turbulence can only be sustained in the surface layers where the ionisation fraction is sufficiently high. A dead zone is expected to exist near the midplane, such that active accretion only occurs near the upper and lower disc surfaces. Recent work, however, suggests that under suitable conditions the dead zone may be enlivened by turbulent transport of ions from the surface layers into the dense interior. In this paper we present a suite of simulations that examine where, and under which conditions, a dead zone can be enlivened by turbulent mixing. We use three-dimensional, multifluid shearing box MHD simulations, which include vertical stratification, ionisation chemistry, ohmic resistivity, and ionisation due to X-rays from the central protostar. We compare the results of the MHD simulations with a simple reaction-diffusion model. The simulations show that in the absence of gas-phase heavy metals, such as magnesium, turbulent mixing has essentially no effect on the dead zone. The addition of a relatively low abundance of magnesium, however, increases the recombination time and allows turbulent mixing of ions to enliven the dead zone completely beyond a distance of 5 AU from the central star, for our particular disc model. During the late stages of protoplanetary disc evolution, when small grains have been depleted and the disc surface density has decreased below its high initial value, the structure of the dead zone may be significantly altered by the action of turbulent transport.Comment: 20 pages, 11 figures, accepted for publication in A&A, high resolution pdf available at http://www.maths.qmul.ac.uk/~rpn/preprints/index.htm