Surfactant-induced gradients in the three-dimensional Belousov-Zhabotinsky reaction

Scroll waves are prominent patterns formed in three-dimensional excitable media, and they are frequently considered highly relevant for some types of cardiac arrhythmias. Experimentally, scroll wave dynamics is often studied by optical tomography in the Belousov-Zhabotinsky reaction, which produces CO2 as an undesired product. Addition of small concentrations of a surfactant to the reaction medium is a popular method to suppress or retard CO2 bubble formation. We show that in closed reactors even these low concentrations of surfactants are sufficient to generate vertical gradients of excitability which are due to gradients in CO2 concentration. In reactors open to the atmosphere such gradients can be avoided. The gradients induce a twist on vertically oriented scroll waves, while a twist is absent in scroll waves in a gradient-free medium. The effects of the CO2 gradients are reproduced by a numerical study, where we extend the Oregonator model to account for the production of CO2 and for its advection against the direction of gravity. The numerical simulations confirm the role of solubilized CO2 as the source of the vertical gradient of excitability in reactors closed to the atmosphere.Peer ReviewedPostprint (published version

The Engineers' Bookshelf

Our perception of an object’s size arises from the integration of multiple sources of visual information including retinal size, perceived distance and its size relative to other objects in the visual field. This constructive process is revealed through a number of classic size illusions such as the Delboeuf Illusion, the Ebbinghaus Illusion and others illustrating size constancy. Here we present a novel variant of the Delbouef and Ebbinghaus size illusions that we have named the Binding Ring Illusion. The illusion is such that the perceived size of a circular array of elements is underestimated when superimposed by a circular contour – a binding ring – and overestimated when the binding ring slightly exceeds the overall size of the array. Here we characterize the stimulus conditions that lead to the illusion, and the perceptual principles that underlie it. Our findings indicate that the perceived size of an array is susceptible to the assimilation of an explicitly defined superimposed contour. Our results also indicate that the assimilation process takes place at a relatively high level in the visual processing stream, after different spatial frequencies have been integrated and global shape has been constructed. We hypothesize that the Binding Ring Illusion arises due to the fact that the size of an array of elements is not explicitly defined and therefore can be influenced (through a process of assimilation) by the presence of a superimposed object that does have an explicit size

Understanding Misperceived Size through Assimilation in a Novel Illusion: The Binding Ring

How do we perceive the size of objects? This research attempts answer a small part of that question by describing and quantifying the binding ring illusion, a novel (and previously uncharacterized) illusion of misperceived size. Following the establishment of the binding ring as a legitimate size illusion, experiments were performed in an attempt to identify what visual processing stream mechanisms were responsible for the illusion and further, to obtain any information as to the relative whereabouts of said mechanism(s) in the visual processing stream. These experiments were performed because many processing mechanisms of the visual stream (and their relative location therein), especially those in the relatively ‘high’ portion of the visual stream, are very poorly understood. The results of the study gave three primary results: first, the binding ring illusion occurs primarily through a process of assimilation; second, this assimilation process is heavily influenced by a process of perceptual unification; and third, the mechanisms of assimilation and unification are likely located relatively high in the visual processing stream, very likely occurring after spatial frequency integration and either after or during the creation of global shape representations

Der Einfluss der erfolgreichen Kataraktoperation auf Lebensqualität, Haushaltseinkommen und sozialen Status in Süd-Indien

Hintergrund: Die Studie untersuchte die Hypothese, dass die sehverbessernde Katarakt-Operation in armen ländlichen Populationen nicht nur positive Auswirkungen auf den Visus und die sehbezogene Lebensqualität, sondern auch auf die Armut und den gesellschaftlichen Status der Patienten hat. Methoden: Die Teilnehmer wurden in Outreach-Camps in Tamil Nadu (Süd-Indien) rekrutiert, erhielten eine kostenlose Katarakt-Operation (manual small incision cataract surgery, SICS) mit Implantation einer intraokularen Linse (IOL), und wurden im Abstand von einem Jahr nachkontrolliert. Die Armut wurde über das Monatseinkommen, die Erwerbstätigkeit und die Anzahl der arbeitenden Haushaltsmitglieder erfragt. Der gesellschaftliche Status wurde über die Wiederverheiratungsraten verwitweter Teilnehmer erfragt. Die sehbezogene Lebensqualität wurde mittels des IND-VFQ-33-Fragebogens gemessen. Assoziationen wurden mittels logistischer Regression untersucht (SPSS 19). Ergebnisse: Von den 294 Teilnehmern (mittleres Alter ± Standardabweichung: 60 ± 68 Jahre; 54 % männlich) waren nach einem Jahr von ursprünglich 67 % nur noch 11 % sehbehindert (p Schlussfolgerung: Unsere Ergebnisse zeigen den breiten positiven Einfluss einer sehverbessernden Katarakt-Operation auf das Leben der Patienten und ihrer Familien auf. Die Verfügbarkeit qualitativ hochwertiger Kataraktchirurgie in marginalisierten ländlichen Populationen trägt nicht nur zur Verringerung vermeidbarer Blindheit bei, sondern ist langfristig auch - zu einem gewissen Anteil - ein Beitrag zur Armutsbekämpfung.The impact of successful cataract surgery on quality of life, household income and social status in South India Background: To explore the hypothesis that sight-restoring cataract surgery provided to impoverished rural communities will improve not only visual acuity and vision-related quality of life (VRQoL) but also poverty and social status. Methods: Participants were recruited at outreach camps in Tamil Nadu, South India, and underwent free routine manual small incision cataract surgery (SICS) with intra-ocular lens (IOL) implantation, and were followed up one year later. Poverty was measured as monthly household income, being engaged in income-generating activities and number of working household members. Social status was measured as rates of re-marriage amongst widowed participants. VRQoL was measured using the IND-VFQ-33. Associations were explored using logistic regression (SPSS 19). Results: Of the 294 participants, mean age ± standard deviation (SD) 60±8 years, 54% men, only 11% remained vision impaired at follow-up (67% at baseline; p Conclusion: These findings indicate the broad positive impact of sight-restoring cataract surgery on the recipients’ as well as their families’ lives. Providing free high-quality cataract surgery to marginalized rural communities will not only alleviate avoidable blindness but also - to some extent - poverty in the long run

Rigid ball-polyhedra in Euclidean 3-space

A ball-polyhedron is the intersection with non-empty interior of finitely many (closed) unit balls in Euclidean 3-space. One can represent the boundary of a ball-polyhedron as the union of vertices, edges, and faces defined in a rather natural way. A ball-polyhedron is called a simple ball-polyhedron if at every vertex exactly three edges meet. Moreover, a ball-polyhedron is called a standard ball-polyhedron if its vertex-edge-face structure is a lattice (with respect to containment). To each edge of a ball-polyhedron one can assign an inner dihedral angle and say that the given ball-polyhedron is locally rigid with respect to its inner dihedral angles if the vertex-edge-face structure of the ball-polyhedron and its inner dihedral angles determine the ball-polyhedron up to congruence locally. The main result of this paper is a Cauchy-type rigidity theorem for ball-polyhedra stating that any simple and standard ball-polyhedron is locally rigid with respect to its inner dihedral angles.Comment: 11 pages, 2 figure

Overview of the INPRO Project

During the last fifty years remarkable results are achieved in the application of nuclear technology for the production of electricity. Looking ahead to the next fifty years it is clear that the demand for energy will grow considerably and also the requirements for the way the energy will be supplied. Within the International Project on Innovative Nuclear Reactors and Fuel Cycles (INPRO), the future of the energy demand and supply was explored and several scenario's identified. A leading requirement for energy supply is coming up and will play a crucial role: sustainability of the way the energy supply will be realized. Fulfilling the growing need for energy in developing countries is as well an important issue. Based on these scenario's for the next fifty years, an inventory of requirements for the future of nuclear energy systems has been collected as well a methodology developed by INPRO to assess innovative nuclear systems and fuel cycles. On the base of this assessment, the need for innovations and breakthroughs in existing technology can be defined. To facilitate the deployment of innovative nuclear systems also the infrastructure, technical as well as institutional has to be adjusted to the anticipated changes in the world such as the globalization. As a contribution to the conference the main messages of INPRO will be presented

The impact of successful cataract surgery on quality of life, household income and social status in South India.

BACKGROUND: To explore the hypothesis that sight restoring cataract surgery provided to impoverished rural communities will improve not only visual acuity and vision-related quality of life (VRQoL) but also poverty and social status. METHODS: Participants were recruited at outreach camps in Tamil Nadu, South India, and underwent free routine manual small incision cataract surgery (SICS) with intra-ocular lens (IOL) implantation, and were followed up one year later. Poverty was measured as monthly household income, being engaged in income generating activities and number of working household members. Social status was measured as rates of re-marriage amongst widowed participants. VRQoL was measured using the IND-VFQ-33. Associations were explored using logistic regression (SPSS 19). RESULTS: Of the 294 participants, mean age ± standard deviation (SD) 60 ± 8 years, 54% men, only 11% remained vision impaired at follow up (67% at baseline; p<0.001). At one year, more participants were engaged in income generating activities (44.7% to 77.7%; p<0.001) and the proportion of households with a monthly income <1000 Rps. decreased from 50.5% to 20.5% (p<0.05). Overall VRQoL improved (p<0.001). Participants who had successful cataract surgery were less likely to remain in the lower categories of monthly household income (OR 0.05-0.22; p<0.02) and more likely to be engaged in income earning activities one year after surgery (OR 3.28; p = 0.006). Participants widowed at baseline who had successful cataract surgery were less likely to remain widowed at one year (OR 0.02; p = 0.008). CONCLUSION: These findings indicate the broad positive impact of sight restoring cataract surgery on the recipients' as well as their families' lives. Providing free high quality cataract surgery to marginalized rural communities will not only alleviate avoidable blindness but also - to some extent - poverty in the long run

The Fermat-Torricelli problem in normed planes and spaces

We investigate the Fermat-Torricelli problem in d-dimensional real normed spaces or Minkowski spaces, mainly for d=2. Our approach is to study the Fermat-Torricelli locus in a geometric way. We present many new results, as well as give an exposition of known results that are scattered in various sources, with proofs for some of them. Together, these results can be considered to be a minitheory of the Fermat-Torricelli problem in Minkowski spaces and especially in Minkowski planes. This demonstrates that substantial results about locational problems valid for all norms can be found using a geometric approach