Regular maps of high density

A regular map is a surface together with an embedded graph, having properties similar to those of the surface and graph of a platonic solid. We analyze regular maps with reflection symmetry and a graph of density strictly exceeding 1/2, and we conclude that all regular maps of this type belong to a family of maps naturally defined on the Fermat curves x^n+y^n+z^n=0, excepting the one corresponding to the tetrahedron.Comment: 13 pages, 4 figure

Approximate solution to a hybrid model with stochastic volatility: a singular-perturbation strategy

We study a hybrid model of Schobel-Zhu-Hull-White-type from a singular-perturbation-analysis perspective. The merit of the paper is twofold: On one hand, we find boundary conditions for the deterministic non-linear degenerate parabolic partial differential equation for the evolution of the stock price. On the other hand, we combine two-scales regular- and singular-perturbation techniques to find an approximate solution to the pricing PDE. The aim is to produce an expression that can be evaluated numerically very fast

Contextualising theological education in Africa by doing theology in a missional hermeneutic

This article originated at curriculum development workshops for seminaries at different venues in sub-Saharan Africa. Its goal was to provide guidelines towards finding a hermeneutic key to practising theology contextually as a response to a process of spiritual discernment which would lead to a contextualised, missional theological curriculum and training. It briefly described elements of the history and context of theological training in the Christendom paradigm. It has little faith in the future of this paradigm, and argued that the southern shift of the heartland of Christianity points us in a new direction. The article said: look at the changing context, the influence of globalisation and the information revolution and revisit key theological parameters in Scripture. Observe what is happening in missional congregations and let all of these developments guide us on a journey to discover a new hermeneutic to do and teach theology in Africa

Missional theology and social development

The article describes a theological paradigm shift taking place in congregations in South Africa that empower them to become  involved in development work as a way of serving their neighbor. It also opens the possibility of working interdisciplinary without compromising theological and faith values. The perspectives and assumptions of the new paradigm are outlined and the basic  methodology of doing theology is described. The new paradigm is a missional one, taking the focus on God as its point of    departure and describing the identity and purpose of the church by looking at God’s identity and plan or mission with creation and humankind. Social development is seen as being in line with God’s mission and as such the church should not have difficulty in working with those who pursue the same goals

Aspect and assertion in Mandarin Chinese

Chinese has a number of particles such as le, guo, zai and zhe that add a particular aspectual value to the verb to which they are attached. There have been many characterisations of this value in the literature. In this paper, we review several existing influential accounts of these particles, including those in Li and Thompson (1981), Smith (1991), and Mangione and Li (1993). We argue that all these characterisations are intuitively plausible, but none of them is precise.We propose that these particles serve to mark which part of the sentence''s descriptive content is asserted, and that their aspectual value is a consequence of this function. We provide a simple and precise definition of the meanings of le, guo, zai and zhe in terms of the relationship between topic time and time of situation, and show the consequences of their interaction with different verb expressions within thisnew framework of interpretation

Koinonia in die stad: Verhoudinge in die groter stadsgemeentes van die Gereformeerde kerke

Koinonia in the city: Relations in the larger urban congregations of the Reformed churchesKoinonia is of vital importance for the church. It is not only a Biblical injunction, but also, sociologically speaking, a prerequisite for the preservation of faith in theChristian community. Therefore it is imperative that the church’s ministry encourages koinonia. This is especially true for the church in an urban context, where relational networks have been severely impaired. The traditional pattern of ministry of churches in the Reformed tradition, the shepherd-flock model, does not succeed in stimulating koinonia under these circumstances. Therefore, the choice is rather made for the body of Christ-model, with complementary koinonia-groupings as theory of practice

Enhancing magneto-optic effects in two-dimensional magnets by thin-film interference

The magneto-optic Kerr effect is a powerful tool for measuring magnetism in thin films at microscopic scales, as was recently demonstrated by the major role it played in the discovery of two-dimensional (2D) ferromagnetism in monolayer CrI$_3$ and Cr$_2$Ge$_2$Te$_6$. These 2D magnets are often stacked with other 2D materials in van der Waals heterostructures on a SiO$_2$/Si substrate, giving rise to thin-film interference. This can strongly affect magneto-optical measurements, but is often not taken into account in experiments. Here, we show that thin-film interference can be used to engineer the magneto-optical signals of 2D magnetic materials and optimize them for a given experiment or setup. Using the transfer matrix method, we analyze the magneto-optical signals from realistic systems composed of van der Waals heterostructures on SiO$_2$/Si substrates, using CrI$_3$ as a prototypical 2D magnet, and hexagonal boron nitride (hBN) to encapsulate this air-sensitive layer. We observe a strong modulation of the Kerr rotation and ellipticity, reaching several tens to hundreds of milliradians, as a function of the illumination wavelength, and the thickness of the SiO$_2$ and layers composing the van der Waals heterostructure. Similar results are obtained in heterostructures composed by other 2D magnets, such as CrCl$_3$, CrBr$_3$ and Cr$_2$Ge$_2$Te$_6$. Designing samples for the optimal trade-off between magnitude of the magneto-optical signals and intensity of the reflected light should result in a higher sensitivity and shorter measurement times. Therefore, we expect that careful sample engineering, taking into account thin-film interference effects, will further the knowledge of magnetization in low-dimensional structures.Comment: manuscript: 12 pages, 4 figures. supplementary material: 22 pages, 20 figure

Cellijnen en Salmonella

In human gastrointestinal disease caused by Salmonella, transepithelial migration of neutrophils follows the attachment of bacteria to epithelial tissue. This migration of neutrophils is stimulated by the release of chemokines, including interleukin-8 (Il -8), from the epithelial cells. We have developed an in vitro model system (human epithelial monolayers, among which Caco-2 cells grown on microtiter multiwell plates) for studying host-pathogen interactions. After infection with different pathogens we measured Il-8 production during time. Results showed that Il-8 release was time related and varied with the pathogen. Salmonella enteritidis (Se) did induce the highest response. Subsequently, three doses of this Se strain were used and the Il-8 response was measured at different time points. Caco-2 cells remained intact over a period of 24h, the production of Il-8 increased in time and was found to be Se dose-dependent. Other tested epithelial monolayers, such as HT29 colon cancer cells, gave similar results.Infectie met Salmonella kan gepaard gaan met de invasie van darmepitheelcellen. De aan de invasie voorafgaande aanhechting leidt reeds tot de transmigratie van witte bloedcellen (neutrofielen) vanuit de bloedbaan naar het epitheelweefsel. De migratie wordt gestimuleerd door de productie van chemokines, waaronder interleukine-8 (Il-8) door epitheelcellen. Wij hebben een in vitro model systeem ontwikkeld (humaan epitheelweefsel gekweekt in microtiterplaten) waarin gastheer - pathogeen interacties kunnen worden bestudeerd. Epitheelcellen zijn gedurende een uur blootgesteld aan verschillende pathogene micro-organismen, waarna de Il-8 response is gemeten. Als controle zijn meegenomen een Escherichia coli stam zonder LPS en een probiotische Lactobacillus. De resultaten laten zien dat de IL-8 productie per pathogeen varieert, waarbij Salmonella enteritidis de hoogste respons geeft. In vervolgexperimenten zijn drie concentraties S. enteritidis gebruikt, waarna de respons gedurende 24 uur is gemeten. De gebruikte cellijn bleek na 24 uur nog intact, de Il-8 productie correleerde met de doses, en nam toe in de tijd. Hieruit kan geconcludeerd worden dat het door ons ontwikkelde model gebruikt kan worden voor het bestuderen van factoren die van invloed zijn op dosis-respons relaties. De respons betreft dan prikkeling van het immuunsysteem ten gevolge van adhesie en invasie van darmepitheelcellen door salmonellae. Tenslotte wordt een benaderingwijze voorgesteld om resultaten van in vitro dosis-respons experimenten te vertalen naar de mens