A Numerical Perspective on Hartree-Fock-Bogoliubov Theory

The method of choice for describing attractive quantum systems is Hartree-Fock-Bogoliubov (HFB) theory. This is a nonlinear model which allows for the description of pairing effects, the main explanation for the superconductivity of certain materials at very low temperature. This paper is the first study of Hartree-Fock-Bogoliubov theory from the point of view of numerical analysis. We start by discussing its proper discretization and then analyze the convergence of the simple fixed point (Roothaan) algorithm. Following works by Canc\`es, Le Bris and Levitt for electrons in atoms and molecules, we show that this algorithm either converges to a solution of the equation, or oscillates between two states, none of them being a solution to the HFB equations. We also adapt the Optimal Damping Algorithm of Canc\`es and Le Bris to the HFB setting and we analyze it. The last part of the paper is devoted to numerical experiments. We consider a purely gravitational system and numerically discover that pairing always occurs. We then examine a simplified model for nucleons, with an effective interaction similar to what is often used in nuclear physics. In both cases we discuss the importance of using a damping algorithm

Participation and Performance in Education in Sub-Saharan Africa with special reference to Kenya: Improving Policy and Practice

This paper explores aspects of exclusion from education and how patterns of participation have been changing using national data sets. The first part of the analysis uses administrative data from countries in Sub Saharan Africa to chart enrolments by grade over the last decade and explore how enrolment has been changing in terms of grade, gender, and age. After establishing key issues that are raised by the data across eight countries the paper develops a detailed case study of changes in participation and performance in Kenya using data from the Kenya National Examinations Council. The study shows that the aspirations of Education for All remain far from being met in many countries and many of those who enrol in Grade 1 fail to complete primary or lower secondary school. Progress has been patchy and it remains the case that over enrolment in the lower Grades is common (with more enrolled than there are children in the relevant age group as a result of over-aged entry and progression), and less than half the age group progressing through lower secondary school. Gender equity in enrolments is being approached in the eight countries included in the analysis but patterns differ and are contextually located. In all the countries many of those enrolled remain seriously over-age, and urban rural differences persist in enrolment status. The detailed case study of data from Kenya complements the cross national analysis. It shows how uneven growth in participation has been after the announcement of free primary education, and how strongly patterns vary by county. Strikingly it confirms that older children score on average much lower on the Kenya Certificate of Primary Education (KCPE) than younger children, and that this is likely to exclude older candidates from the best secondary schools. This is a source of considerable inequity since over-age status is associated with poverty

Dealing with the coffee crisis in Central America - impacts and strategies

Current coffee prices are at record lows and below the cost of production for many producers in Central America. Moreover, the coffee crisis is structural, and changes in supply and demand do not indicate a quick recovery of prices. So, coffee producers in Central America are facing new challenges-as are coffee laborers, coffee exporters, and others linked to the coffee sector. Coffee plays a major economic role in Costa Rica, El Salvador, Guatemala, Honduras, and Nicaragua. The coffee crisis is actually part of a broader rural crisis caused by weather shocks (such as Hurricane Mitch and droughts), low international agricultural commodity prices, and the global recession. These challenges call for new strategies for Central American countries aimed at broad-based sustainable development of their rural economies. The authors deal with the impact of the coffee crisis and strategies to deal with it. They include an analysis of the international coffee situation and country-specific analyses. The authors explore options and constraints for increased competitiveness and diversification, and discuss social, environmental, and institutional dimensions of the crisis. The authors conclude that there are specific solutions that can be pursued for the coffee sector. Some are already being applied, but more can be done in a more systematic way. Also, there is a need for safety nets to deal with the short-term impact of the crisis. Longer-term solutions are to be found in increased competitiveness and diversification in the context of broad-based sustainable rural economic development.Crops&Crop Management Systems,Environmental Economics&Policies,Labor Policies,Economic Theory&Research,Markets and Market Access,Crops&Crop Management Systems,Environmental Economics&Policies,Economic Theory&Research,Access to Markets,Markets and Market Access

Preliminary Investigation into Modeling The Damage to Carbon Fibre Composites Due to the Thermo-electric Effects of a Lightning Strikes

The impact of a lightning strike causes a short high electrical current burst through Carbon Fibre Composites (CFC). Due to the electrical properties of CFC the large current leads to a rapid heating of the surrounding impact area which degrades and damages the CFC. It is therefore necessary to study in detail the thermal response and possible degradation processes caused to CFC. The degradation takes place in two ways, firstly via direct mechanical fracture due to the thermal expansion of the CFC and secondly via thermo-chemical processes (phase change and pyrolysis) at high temperatures. The main objective of this work is to construct a numerical model of the major physical processes involved, and to understand the correlation between the damage mechanisms and the damage witnessed in modern CFC. For this work we are only considering the thermo-chemical degradation of CFC. Bespoke numerical models have been constructed to predict the extent of the damage caused by the two thermo-chemical processes separately (e.g. a model for phase change and a model for pyrolysis). The numerical model predictions have then been verified experimental by decoupling of the damage mechanisms, e.g. the real Joule heating from a lightning strike is replaced by a high power laser beam acting on composite surface. This was done to simplify the physical processes which occur when a sample is damaged. The experimentally damaged samples were then investigated using X-ray tomography to determine the physical extent of the damage. The experimental results are then compared with the numerical predictions by considering the physical extent of the polymer removal. The extent of polymer removal predicted by the numerical model, solving for pyrolysis, gave a reasonable agreement with the damage seen in the experimental sample. Furthermore the numerical model predicts that the damage caused by polymer phase change has a minimal contribution to the overall extent of the damage

Modeling of the Partial Discharge Process in a Liquid Dielectric: Effect of Applied Voltage, Gap Distance, and Electrode Type

The partial discharge (PD) process in liquid dielectrics is influenced by several factors. Although the PD current contains the information representing the discharge process during the PD event, it is difficult to determine the detailed dynamics of what is happening in the bulk of the liquid. In this paper, a microscopic model describing the dynamics of the charge carriers is implemented. The model consists of drift-diffusion equations of electrons, positive and negative ions coupled with Poisson’s equation. The stochastic feature of PD events is included in the equation. First the model is validated through comparison between the calculated PD current and experimental data. Then experiments are conducted to study the effects of the amplitude of the applied voltage, gap distance and electrode type on the PD process. The PD currents under each condition are recorded. Simulations based on the model have been conducted to analyze the dynamics of the PD events under each condition, and thus explain the mechanism of how these factors influence the PD events. The space charge generated in the PD process is revealed as the main reason affecting the microscopic process of the PD events

Efectos de la Política de Estado Hondureña sobre la Seguridad Alimentaria

Honduras, Seguridad Aliemntaria, Política Pública, Agricultura

Affect of photo-oxidation products on electroluminescence emission and conduction current of LDPE

There is great interest in understanding the effects of long term ageing and degradation of high voltage insulation in an effort to improve its lifetime and efficiency. One area of interest regards the movement and interaction of charge within the polymeric insulation. Under ac electric stress polymers give out a faint light known as electroluminescence (EL), this emission is thought to relate to the charge injection, trapping and recombination near the electrode-polymer interface. The ultraviolet (UV) ageing of low density polyethylene (LDPE) films has shown an increase in oxidation products (carbonyl and hydroxyl groups) which may act as extra charge trapping sites. Samples have been masked during ageing such that a direct comparison in EL intensity can be made between both the aged and virgin condition. Initial EL measurements on aged materials have shown an increasing intensity and shift in phase angle for short ageing times but reduced emission in heavily aged samples. This change in EL is thought to relate to the easier injection of charge carriers and extra availability of charge trapping sites after short ageing times but then increased conduction through the material after heavy ageing reducing the availability of charge for recombination. The full paper will compare increases in oxidation products due to UV ageing with EL emission and conduction current in LDPE samples

The Dollar Game Curriculum: Inspiring Wealth Creation in Rural Communities

Rural wealth creation and local entrepreneurship are emerging economic development approaches that bring back a sense of self-determination to rural communities. However, their potential is often greatly diminished by preconceived and opposing notions within the community on what drives economic growth. The Dollar Game is an innovative curriculum where participants collectively build an understanding of how innovation, income distribution and export affect their communities. Teams play different scenarios, starting with an island economy isolated from grants, subsidies, and trading opportunities and builds to a connected economy where they eventually lose ownership of the local value-chain