Reaching large lengths and long times in polymer dynamics simulations

A lattice model is presented for the simulation of dynamics in polymeric systems. Each polymer is represented as a chain of monomers, residing on a sequence of nearest-neighbor sites of a face-centered-cubic lattice. The polymers are self- and mutually avoiding walks: no lattice site is visited by more than one polymer, nor revisited by the same polymer after leaving it. The dynamics occurs through single-monomer displacements over one lattice spacing. To demonstrate the high computational efficiency of the model, we simulate a dense binary polymer mixture with repelling nearest-neighbor interactions between the two types of polymers, and observe the phase separation over a long period of time. The simulations consist of a total of 46,080 polymers, 100 monomers each, on a lattice with 13,824,000 sites, and an interaction strength of 0.1 kT. In the final two decades of time, the domain-growth is found to be d(t) ~ t^1/3, as expected for a so-called "Model B" system.Comment: 6 pages, 4 eps figure

Electrophoresis simulated with the cage model for reptation

The cage model for polymer reptation is extended to simulate DC electrophoresis. The drift velocity v of a polymer with length L in an electric field with strength E shows three different regions: if the strength of field is small, the drift velocity scales as E/L; for slightly larger strengths, it scales as E^2, independent of length; for high fields, but still E much smaller than 1, the drift velocity decreases exponentially to zero. The behaviour of the first two regions are in agreement with earlier reports on simulations of the Duke-Rubinstein model and with experimental work on DNA polymers in agarose gel.Comment: 14 pages, 9 pictures, 2 table

Transformative self-discoveries for a preschool child : from a passive to an agentic lifeposition

This explorative case study was undertaken to uncover how transformative self-discoveries were facilitated through Gestalt playtherapy, enabling agency of a single pre-school participant. Data were captured around the participant's baseline agentic status; emerging agency, facilitated trough the intervention and post-intervention agentic status. A content analysis aided thematic coding. Theme 1 identified inherent agency trends and the agency blocks "what is that". Theme 2 dealt with patterns of active resistance "I don't want to feel / I don't want to know". Theme 3 captured enhanced agentic behaviour "I can and I understand". Through the intervention the participant's entrapped agency was unleashed, leading to an awareness of her `being', enabling her `doing' and thereby allowing her to `become'. Enabled agency increased the participant's active involvement in her life and her engagement in developmental tasks was increased. Implications of the findings support further investigation and application of this intervention.Educational StudiesM. Diac (Play Therapy

DNA electrophoresis studied with the cage model

The cage model for polymer reptation, proposed by Evans and Edwards, and its recent extension to model DNA electrophoresis, are studied by numerically exact computation of the drift velocities for polymers with a length L of up to 15 monomers. The computations show the Nernst-Einstein regime (v ~ E) followed by a regime where the velocity decreases exponentially with the applied electric field strength. In agreement with de Gennes' reptation arguments, we find that asymptotically for large polymers the diffusion coefficient D decreases quadratically with polymer length; for the cage model, the proportionality coefficient is DL^2=0.175(2). Additionally we find that the leading correction term for finite polymer lengths scales as N^{-1/2}, where N=L-1 is the number of bonds.Comment: LaTeX (cjour.cls), 15 pages, 6 figures, added correctness proof of kink representation approac

Simulation of Polymer Dynamics in Gels and Melts

I have worked on computer simulations of lattice polymer models. Those models describe a polymer as a long chain of segments, connecting neighboring lattice sites. Polymers show interesting behavior if their freedom of movement is restricted, for example if the polymers move through a gel. The gel forms a three-dimensional structure that blocks sideways movements of the polymers. The polymer can only move by diffusion of "stored length" from one end of the chain to the other end. This is called reptation. We have extended an existing model for a polymer in a gel to simulate a DNA fragment in a gel under the influence of an applied electric field. In weak fields, long fragments move slower than short ones. In this way, fragments of different length can be separated. If the field strength is increased, the fragments orientate themselves parallel to the field, and shorter and longer fragments move with the same velocity. In strong fields, fragments can get trapped in a U-shape, in which the applied field pulls on both ends of the fragment, while the middle cannot move in the direction of the field because of the gel. We also introduce a new lattice polymer model for polymer solutions (melts). In this model, we simulate many polymers, mutually restricting their freedom of motion. We have investigated a mixture of two mutually repelling polymer types. At high temperatures the polymers are homogeneously distributed but if the temperature is lowered, phase separation sets in. The polymer model turns out to be highly efficient, and is the first where the growth of the phase domains can be directly observed. We have also investigated the composition of the two phases after full phase separation. Each phase consists mostly of one type of polymer, but there is always a small contamination with the other polymer type. If the polymers of one type are not all of equal length, then the shorter polymers will occur more often in the rare phase than the long ones. This is called fractionation

Intercultural communicative competence is essential for students of international business - but can it be taught? The case of third-year BCom students

Intercultural communicative competence is essential for graduates wishing to work in the business sector. Such competence has become desirable for graduates who see themselves working in “demanding and highly-challenging international environments” (Sain, Kužnin and Roje 2017, 55‒56). In spite of the need for well-developed intercultural competence in the workplace, students of Economic and Business Science are rarely deliberately equipped with an understanding of what language, culture and communication entail. Against this background, we investigated if an intervention, in the form of a 28-lecture undergraduate course, can develop third-year BCom students’ intercultural competence so as to prepare them to deal with the heterogeneity that they will encounter in the workplace (and elsewhere), both in multilingual and multi-cultural South Africa and abroad.Based on eight of the skills and attributes identified by Deardorff (2004) as being markers of interculturally competent individuals (such as knowledge of self and others, respect, critical thinking skills, and an awareness of the importance of being interculturally competent), students (n=18) were assessed prior to the commencement of the course and again upon completion thereof. Pre- and post-course questionnaires were analysed qualitatively and quantitatively, and data were coded according to the eight Deardorff (2004) markers of intercultural competence. Additionally, a focus group discussion (n = 5) was held at the end of the course. The data showed that development took place in the students’ attitudes, knowledge and skills related to intercultural communicative competence. Certain markers of intercultural communicative competence, however, showed more substantial development than others, the notable marker showing such development being critical thinking skills.The finding is that skills indicative of intercultural competence can indeed be developed by means of a curriculum in such a way that students think more critically about (i) cultural and linguistic diversity and (ii) their responsibility as future leaders to communicate optimally in diverse cultural settings. Deliberately including courses on intercultural communication in programmes for students (not only students in Humanities and Social Sciences) could contribute to personal and professional development of students and lead to graduates who are better prepared for a career in multicultural national and international business sectors. Likewise, the introduction of in-service training in intercultural communicative competence can be considered for those who are no longer students, thereby contributing to improved intercultural communication in the workplace

Predictive variables in lifelong bilingualism: An exploratory study probing the effects of L2 English on L1 Afrikaans syntax

General Linguistic

Financial burden of orthopaedic gunshot-related injury management at a major trauma centre

Background. Violence and injuries are a significant global public health concern, and have a substantial emotional, physical and economic impact on society. In South Africa (SA), the Western Cape Injury Mortality Profile shows that homicides increased from 38 deaths per 100 000 in 2010 to 52 deaths per 100 000 in 2016. This increase is directly related to an increase in firearm-related homicides, which doubled from 2010 to 2016. Previous research estimated the average cost per gunshot wound (GSW)-related orthopaedic patient at USD2 940. GSW-related patient numbers as well as treatment costs have escalated exponentially over the past few years.Objectives. To calculate the financial costs involved in managing gunshot-related orthopaedic injuries both surgically and non-surgically at a tertiary centre in SA.Methods. After ethics approval, a retrospective review of all GSW patients seen in the emergency unit at Tygerberg Hospital in 2017 was undertaken. Patient records yielded data on the following parameters: injury site and characteristics, imaging modalities, orthopaedic management, hospital admission and duration of hospitalisation, theatre episodes, orthopaedic implants and blood products administered. Cost analysis was performed using this information.Results. A total of 389 patients (360 male and 29 female), average age (range, standard deviation) 28 (3 - 69, 9.50) years, were treated during the study period. Patient records identified a total of 449 orthopaedic injuries. A total of 187 patients were admitted, with 175 requiring surgical fixation. The conservatively calculated cost of managing this patient group was ZAR10 227 503. The average management cost per patient was ZAR26 292, with an average of ZAR46 670 per case requiring surgical management and ZAR8 810 for non-surgical cases (the average USD-ZAR exchange rate in 2017 was USD1-ZAR13.30).Conclusions. The total cost of managing 389 patients with gunshot-related orthopaedic injuries at a tertiary hospital was ZAR10 227 503. Improved understanding of these costs will help the healthcare system better prioritise orthopaedic trauma funding and training and highlights the urgent need for cost-saving measures, specifically primary prevention initiatives

‘Ja-nee. No, I'm fine’ : a note on YES and NO in South Africa

CITATION: Biberauer, T., et al. 2017. ‘Ja-nee. No, I'm fine’ : a note on YES and NO in South Africa. Stellenbosch Papers in Linguistics, 48:67-86 doi:10.5774/48-0-281.The original publication is available at http://spil.journals.ac.zaThis paper considers some unusual uses of NO and YES observed in South African English (SAE) and other languages spoken in South Africa. Our objective is to highlight the fundamentally speaker-hearer-oriented nature of many of these elements, and to offer a formal perspective on their use. We also aim to highlight the value of pursuing more detailed investigations of these and other perspectival elements employed in SAE and other languages spoken in South Africa.http://spil.journals.ac.za/pub/article/view/281Publisher’s versio

Variatie in biodiversiteit in sloten binnen een polder

Met meer dan 300.000 kilometer aan poldersloten en weteringen vormen de Nederlandse polders een uitgebreid potentieel leefgebied voor onder andere water- en oeverplanten, vissen, amfibieën en insecten. Toch ziet men poldersloten nog vaak slechts als uniforme transportwegen van eutroof water en kreeg de natuurfunctie binnen polders pas recentelijk meer aandacht. In het kader van een afstudeeropdracht van Wageningen Universiteit is onderzoek verricht naar de ruimtelijke verspreiding van de biodiversiteit in één polder. Verschillen in slootdimensies, landgebruik en onderhoud en beheer hebben invloed op het watermilieu en daarmee op de waterfauna. Dit maakt dat een polderdrainagesysteem een hogere ecologische diversiteit heeft dan wellicht gedacht wordt. Juist de kleine poldersloten tonen een hoge ecologische potentie, mits het waterbeheer daarop weet te anticiperen. Dit artikel laat zien hoe en waar ecologische zones binnen de polder ontstaan die verschillen in rijkdom en variabiliteit