From statistical mechanics to machine learning: effective models for neural activity

In the retina, the activity of ganglion cells, which feed information through the optic nerve to the rest of the brain, is all that our brain will ever know about the visual world. The interactions between many neurons are essential to processing visual information and a growing body of evidence suggests that the activity of populations of retinal ganglion cells cannot be understood from knowledge of the individual cells alone. Modelling the probability of which cells in a population will fire or remain silent at any moment in time is a difficult problem because of the exponentially many possible states that can arise, many of which we will never even observe in finite recordings of retinal activity. To model this activity, maximum entropy models have been proposed which provide probabilistic descriptions over all possible states but can be fitted using relatively few well-sampled statistics. Maximum entropy models have the appealing property of being the least biased explanation of the available information, in the sense that they maximise the information theoretic entropy. We investigate this use of maximum entropy models and examine the population sizes and constraints that they require in order to learn nontrivial insights from finite data. Going beyond maximum entropy models, we investigate autoencoders, which provide computationally efficient means of simplifying the activity of retinal ganglion cells

“Fish, chicken, lean meat and eggs can be eaten daily”: A food-based dietary guideline for South Africa

Food products from animals provide a variety of macro- and  micronutrients. Animal sources of food, such as fish, chicken, meat and eggs, constitute high-quantity and high-quality protein, as they contain essential amino acids in the right proportions. In South Africa, eight micronutrients, namely vitamin A, vitamin B1, vitamin B2, vitamin B6, vitamin B12, niacin, iron and zinc, have been identified as lacking in the population’s diet. Animal-sourced food is a particularly rich source of these nutrients. Relatively small amounts of these foods, added to a mixed diet, make a substantial contribution to nutrient adequacy. Generally, animal sources of food are associated with nutrients that are less desirable in the diet, such as saturated fat and cholesterol. However, by choosing lean prudent portions of these foods, the intake of such macronutrients can be controlled. Animal sources of food add variety and nutrients to the diet. Adding a small amount of these food products to a plant-based diet can yield considerable improvements in human health. For a variety of reasons, some people choose not to eat meat, but as there is no evidence that a moderate intake of fish, chicken, lean meat and eggs has a negative effect on health, there is no scientific justification to exclude them from the diet. As recommended in global food-based dietary guidelines, when consumed in moderation, fish, chicken, lean meat and eggs can be part of a healthy, South African diet

Attitudes and acceptance of South African urban consumers towards genetically modified white maize

The introduction of genetically modified (GM) food products to food markets around the world, has led to considerable controversy. In many cases consumer attitudes and perceptions of GM food products were revealed as fears, concern for, and avoidance of the new technology. The importance of GM foods in South Africa is increasing, even though the GM Food debate lags behind many other (often more developed) parts of the world. This paper investigates the knowledge, attitudes and acceptance of urban South African white-grain maize consumers regarding GM maize. Conjoint- and cluster analysis were used to develop clusters/market segments among the urban consumers of white maize. A range of additional questions was used to develop profiles of the identified market segments. These aspects covered demographics, GM knowledge aspects as well as GM attitude aspects. Four distinct clusters/market segments were identified with specific characteristics: "Anti-GM, Brand aware" cluster (35% of valid responses), "Brand unaware, Farmer sympathetic" cluster (20%), "GM consumer benefit, Brand aware" cluster (25%) and the "Brand aware, Pro-GM" cluster (20%). The most significant differences between the clusters were based on the consumers' attitudes towards GM food products.Consumer/Household Economics,

Child factors associated with complementary feeding practices in Uganda

Objectives: The objective of the study was to identify child factors that influenced complementary feeding practices in 2006 and 2011 in Uganda.Design: Trend analysis of Uganda Demographic and Health Surveys (UDHS) from 2006 and 2011.Subjects and setting: Children aged 6 to 23 months, Uganda.Results: Between 2006 and 2011, the percentage of children in Uganda consuming an adequate complementary diet increased by 3.1%. Duration of breastfeeding increased in this time from 11 months to 12 months, with the percentage of mothers who were still breastfeeding their children at two years decreasing from 55.2% to 46.5%. Factors such as child’s age, deworming for intestinal parasites and receiving DPT3 and measles vaccines, increased the likelihood of caregivers providing children with a minimum acceptable diet. Children aged 6 to 8 months and 12 to 17 months tended to receive adequate complementary in both 2006 and 2011. Although bottle-feeding was highest among the children aged 6 to 11 months, amongst those reported with a fever, acute respiratory infection (ARI) or diarrhoea, it had no statistically significant effect in either 2006 or 2011.Conclusion: Caregivers who take their children for deworming and DPT3 and measles vaccinations are more likely to feed them adequate diets, especially those aged 6 to 17 months. This is probably due to the mothers’ interaction with healthcare practitioners who teach and support complementary feeding. Telling caregivers about complementary feeding practices during immunisation and deworming consultations is likely to encourage beneficial complementary feeding practices in Uganda.Keywords: child age, complementary feeding, deworming, immunisation, Uganda Demographic and Health Surve

The evaluation of a school-based substance abuse prevention programme

This research report presents the findings of an evaluation of a school-based substance abuse prevention programme presented as part of Project Awareness. The programme was presented as a one-day intervention for grade ten learners in eleven schools in Tshwane. The prevention program taught substance abuse refusal skills, anti-substance norms, personal self-management skills, and general social skills in an effort to provide students with skills and information for resisting substance offers, to decrease motivations to use substances, and decrease vulnerability to substance use social influences. The study evaluated this school-based substance abuse prevention intervention in a sample of learners (N=300) in six of the eleven schools. Measures were obtained on a behavioural survey to ascertain whether any knowledge, behaviour or attitude change occurred between the pre-intervention and post-intervention phases. In addition, focus group data and observational measures were implemented to determine how the learners experienced the programme and whether the programme was effective in capturing the attention of the learners. Results indicated that, from learners perceptions of the programme, the intervention seems to have had a positive impact on substance abuse prevention, but not on changing the behaviour of learners already engaging in substance abuse. The results from the behavioural survey indicated some change in learner attitudes to some degree, but not behavioural change. Suggestions for the improvement of the programme were made throughout the report, and the observational measures specifically indicated that the more practical oriented tasks were more efficient in capturing the attention of learners. It is concluded that although the programme certainly had room for improvement, that the programme did indeed address relevant issues. The program also had a direct positive effect on several cognitive, attitudinal, and personality variables believed to play a role in adolescent substance use.Dissertation (MA)--University of Pretoria, 2008.Psychologyunrestricte

Applications of the maximum entropy principle to time dependent processes

The maximum entropy principle, pioneered by Jaynes, provides a method for finding the least biased probability distribution for the description of a system or process, given as prior information the expectation values of a set (in general, a small number) of relevant quantities associated with the system. The maximum entropy method was originally advanced by Jaynes as the basis of an information theory inspired foundation for equilibrium statistical mechanics. It was soon realised that the method is very useful to tackle several problems in physics and other fields. In particular it constitutes a powerful tool for obtaining approximate and sometimes exact solutions to several important partial differential equations of theoretical physics. In Chapter 1 a brief review of Shannon’s information measure and Jaynes’ maximum entropy formalism is provided. As an illustration of the maximum entropy principle a brief explanation of how it can be used to derive the standard grand canonical formalism in statistical mechanics is given. The work leading up to this thesis has resulted in the following publications in peer-review research journals: • J.-H. Schönfeldt and A.R. Plastino, Maximum entropy approach to the collisional Vlasov equation: Exact solutions, Physica A, 369 (2006) 408-416, • J.-H. Schönfeldt, N. Jimenez, A.R. Plastino, A. Plastino and M. Casas, Maximum entropy principle and classical evolution equations with source terms, Physica A, 374 (2007) 573-584, • J.-H. Schönfeldt, G.B. Roston, A.R. Plastino and A. Plastino, Maximum entropy principle, evolution equations, and physics education, Rev. Mex. Fis. E, 52 (2)(2006) 151-159. Chapter 2 is based on Schönfeldt and Plastino (2006). Two different ways for obtaining exact maximum entropy solutions for a reduced collisional Vlasov equation endowed with a Fokker-Planck like collision term are investigated. Chapter 3 is based on Schönfeldt et al. (2007). Most applications of the maximum entropy principle to time dependent scenarios involved evolution equations exhibiting the form of a continuity equations and, consequently, preserving normalization in time. In Chapter 3 the maximum entropy principle is applied to evolution equations with source terms and, consequently, not preserving normalization. We explore in detail the structure and main properties of the dynamical equations connecting the time dependent relevant mean values , the associated Lagrange multipliers, the partition function, and the entropy of the maximum entropy scheme. In particular, we compare the H-theorems verified by the maximum entropy approximate solutions with the Htheorems verified by the exact solutions. Chapter 4 is based on Schönfeldt et al. (2006). In chapter 4 it is discussed how the maximum entropy principle can be incorporated into the teaching of aspects of theoretical physics related to, but not restricted to, statistical mechanics. We focus our attention on the study of maximum entropy solutions to evolution equations that exhibit the form of continuity equations (eg. Liouville equation, the diffusion equation the Fokker-Planck equation, etc.).Dissertation (MSc (Physics))--University of Pretoria, 2008.PhysicsMScunrestricte

Effect of different maize meal diets on growth and vitamin A : case-study on chickens

South Africa embarked on mandatory vitamin and mineral fortification of wheat flour and maize meal in 2003 as part of a multi-faceted approach to alleviate malnutrition. However, it was reported, in 2008, that vitamin A deficiency increased despite the mandatory fortification programme. This motivates an investigation into the absorption of vitamin A as fortificant in the maize meal. Relative absorption, in chickens as the biological model, was determined by evaluating growth and vitamin A status. The weight, cumulative feed intake and liver retinol stores of chickens on different diets were measured over a 6 week period. The fortified white maize meal diet was able to maintain the vitamin A status of the chickens. Poor absorption of the fortificant vitamin A is therefore not a constraint in combating vitamin A deficiency. It is in therefore also important to focus on the level of fortification delivered when consumed as a traditional prepared dish. In the traditional diet, maize porridge is often consumed with only a relish. The total fat content of the traditional meal is very low, lacking absorption enhancers.National Research Foundationhtt[p://www.elsevier.com/locate/foodchemhb201

Cholesterol, fatty acids profile and the indices of atherogenicity and thrombogenicity of raw lamb and mutton offal

Dietary fats may affect blood lipid levels and the development of cardiovascular diseases. Offal, may contribute to food security in marginalised communities and information on the contribution to dietary fat intake is needed to inform dietary guidelines and recommendations and consumers. This study aimed to describe the fatty acid profile, cholesterol content and indexes of lipid quality. The fatty acid profile and cholesterol were determined by gas chromatography coupled with flame ionisation detection (GC-FID). To evaluate lipid quality the indices of atherogenicity (IA) and thrombogenicity (IT) were calculated. Offal products can contribute beneficial fatty acids to the diet, not only in terms of essential fatty acids such as linoleic (C18:2n-6) and alpha linolenic (C18:3n-3) acids, but also the polyunsaturated fatty acids, arachidonic (C20:4n-6) and eicosapentaenoic (C20:5n3) acids. The offal studied in the present work showed a P/S ratio of 0.04–0.12 and the n-6/n-3 ratio varied between 3.9 and 12.5.The Department of Science and Technology (DST)/National Research Foundation (NRF) South African Research Chairs Initiative (SARChl) in the National Development Plan Priority Area of Nutrition and Food Security (Unique number: SARCI170808259212), the Research Technology Fund of the National Research Foundation and Red Meat Research and Development of South Africa.http://www.elsevier.com/locate/foodchem2021-12-13hj2021Animal and Wildlife Science