Response of Dark-Adapted Retinal Rod Photoreceptors

The process of phototransduction, whereby light is converted into an electrical response, in rod and cone photoreceptors in the retina, involves as a key setp, the diffusion of the cytoplasmic, signaling molecules cGMP (cyclic guanosime monophosphate) and Ca2+ diffuse in the cytoplasm (the fluid surrounding the discs). the complex geometry of the rod creates computational difficulties. We present spatio-temporal compuational models for interacctions and diffusion of cGMP and Ca2+ in the cytoplasm of vertebrate rod photoreceptors, as well as numerical simulations fo the response to light of dark-adapted Salamander rods

The quasi-stationary approximation for the Stefan problem with a convective boundary condition

We show that the solution to the Stefan problem with a convective boundary condition tends to the quasi-stationary approximation as the specific heat tends to zero. Additional properties of the approximation are given, and some examples are presented

Monolithic simulation of convection-coupled phase-change - verification and reproducibility

Phase interfaces in melting and solidification processes are strongly affected by the presence of convection in the liquid. One way of modeling their transient evolution is to couple an incompressible flow model to an energy balance in enthalpy formulation. Two strong nonlinearities arise, which account for the viscosity variation between phases and the latent heat of fusion at the phase interface. The resulting coupled system of PDE's can be solved by a single-domain semi-phase-field, variable viscosity, finite element method with monolithic system coupling and global Newton linearization. A robust computational model for realistic phase-change regimes furthermore requires a flexible implementation based on sophisticated mesh adaptivity. In this article, we present first steps towards implementing such a computational model into a simulation tool which we call Phaseflow. Phaseflow utilizes the finite element software FEniCS, which includes a dual-weighted residual method for goal-oriented adaptive mesh refinement. Phaseflow is an open-source, dimension-independent implementation that, upon an appropriate parameter choice, reduces to classical benchmark situations including the lid-driven cavity and the Stefan problem. We present and discuss numerical results for these, an octadecane PCM convection-coupled melting benchmark, and a preliminary 3D convection-coupled melting example, demonstrating the flexible implementation. Though being preliminary, the latter is, to our knowledge, the first published 3D result for this method. In our work, we especially emphasize reproducibility and provide an easy-to-use portable software container using Docker.Comment: 20 pages, 8 figure

A mathematical model of melt lake development on an ice shelf

The accumulation of surface meltwater on ice shelves can lead to the formation of melt lakes. Melt lakes have been implicated in ice shelf collapse; Antarctica's Larsen B Ice Shelf was observed to have a large amount of surface melt lakes present preceding its collapse in 2002. Such collapse can affect ocean circulation and temperature, cause habitat loss and contribute to sea level rise through the acceleration of tributary glaciers. We present a mathematical model of a surface melt lake on an idealised ice shelf. The model incorporates a calculation of the ice shelf surface energy balance, heat transfer through the firn, the production and percolation of meltwater into the firn, the formation of ice lenses and the development and refreezing of surface melt lakes. The model is applied to the Larsen C Ice Shelf, where melt lakes have been observed. This region has warmed several times the global average over the last century and the Larsen C firn layer could become saturated with meltwater by the end of the century. When forced with weather station data, our model produces surface melting, meltwater accumulation, and melt lake development consistent with observations. We examine the sensitivity of lake formation to uncertain parameters, and provide evidence of the importance of processes such as lateral meltwater transport. We conclude that melt lakes impact surface melt and firn density and warrant inclusion in dynamic-thermodynamic models of ice shelf evolution within climate models, of which our model could form the basis for the thermodynamic component

Traversing the margins of corruption amidst informal economies in Amazonia

This article focuses on local idioms of extra-legal economic activity among indigenous Amazonians in eastern Peru, and its overall argument is that these idioms are part of a broader context in which indigenous people are compelled by a variety of factors to act in a seemingly corrupt manner. I further suggest that within such a context these idioms are not confined to the informal economy but are also used to refer to activities that fall within the formal economy, supporting Hart’s (2009) claim that the informal economy is a way of imagining the orthodox economy. I argue that corruption within Amazonian economies is commonly perceived by non-indigenous people as contrasting with the workings of the orthodox economy without proper consideration of the economic conditions and bureaucratic structures that give rise to it. Lastly, I argue that, here, corruption can contravene bureaucracy by restoring the humanity that Herzfeld (1993) claims bureaucracy rejects through its acts of indifference toward individuals

A gradient approach to localization of deformation. I. Hyperelastic materials

By utilizing methods recently developed in the theory of fluid interfaces, we provide a new framework for considering the localization of deformation and illustrate it for the case of hyperelastic materials. The approach overcomes one of the major shortcomings in constitutive equations for solids admitting localization of deformation at finite strains, i.e. their inability to provide physically acceptable solutions to boundary value problems in the post-localization range due to loss of ellipticity of the governing equations. Specifically, strain-induced localized deformation patterns are accounted for by adding a second deformation gradient-dependent term to the expression for the strain energy density. The modified strain energy function leads to equilibrium equations which remain always elliptic. Explicit solutions of these equations can be found for certain classes of deformations. They suggest not only the direction but also the width of the deformation bands providing for the first time a predictive unifying method for the study of pre- and post-localization behavior. The results derived here are a three-dimensional extension of certain one-dimensional findings reported earlier by the second author for the problem of simple shear.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42674/1/10659_2004_Article_BF00040814.pd

Ethnobotanical study of medicinal plants used by people in Zegie Peninsula, Northwestern Ethiopia

An ethnobotanical study was conducted from October 2005 to June 2006 to investigate the uses of medicinal plants by people in Zegie Peninsula, northwestern Ethiopia. Information was gathered from 200 people: 70 female and 130 males, using semistructured questionnaire. Of which, six were male local healers. The informants, except the healers, were selected randomly and no appointment was made prior to the visits. Informant consensus factor (ICF) for category of aliments and the fidelity level (FL) of the medicinal plants were determined. Sixty-seven medicinal plants used as a cure for 52 aliments were documented. They are distributed across 42 families and 64 genera. The most frequently utilized plant part was the underground part (root/rhizome/bulb) (42%). The largest number of remedies was used to treat gastrointestinal disorder and parasites infections (22.8%) followed by external injuries and parasites infections (22.1%). The administration routes are oral (51.4%), external (38.6%), nasal (7.9%), and ear (2.1%). The medicinal plants that were presumed to be effective in treating a certain category of disease, such as 'mich' and febrile diseases (0.80) had higher ICF values. This probably indicates a high incidence of these types of diseases in the region, possibly due to the poor socio-economic and sanitary conditions of this people. The medicinal plants that are widely used by the local people or used as a remedy for a specific aliment have higher FL values (Carissa spinarum, Clausena anisata, Acokanthera schimperi, Calpurnia aurea, Ficus thonningii, and Cyphostemma junceum) than those that are less popular or used to treat more than one type of aliments (Plumbago zeylanicum, Dorstenia barnimiana)