A scaling analysis of ozone photochemistry

International audienceA scaling analysis has been used to capture the integrated behaviour of several photochemical mechanisms for a wide range of precursor concentrations and a variety of environmental conditions. The Buckingham Pi method of dimensional analysis was used to express the relevant variables in terms of dimensionless groups. These grouping show maximum ozone, initial NOx and initial VOC concentrations are made non-dimensional by the average NO2 photolysis rate (jav) and the rate constant for the NO?O3 titration reaction (kNO); temperature by the NO?O3 activation energy (ENO) and Boltzmann constant (k) and total irradiation time by the cumulative jav?t photolysis rate. The analysis shows dimensionless maximum ozone concentration can be described by a product of powers of dimensionless initial NOx concentration, dimensionless temperature, and a similarity curve directly dependent on the ratio of initial VOC to NOx concentration and implicitly dependent on the cumulative NO2 photolysis rate. When Weibull transformed, the similarity relationship shows a scaling break with dimensionless model output clustering onto two straight line segments, parameterized using four variables: two describing the slopes of the line segments and two giving the location of their intersection. A fifth parameter is used to normalize the model output. The scaling analysis, similarity curve and parameterization appear to be independent of the details of the chemical mechanism, hold for a variety of VOC species and mixtures and a wide range of temperatures and actinic fluxes

A scaling analysis of ozone photochemistry: I Model development

International audienceA scaling analysis has been used to capture the integrated behaviour of several photochemical mechanisms for a wide range of precursor concentrations and a variety of environmental conditions. The Buckingham Pi method of dimensional analysis was used to express the relevant variables in terms of dimensionless groups. These grouping show maximum ozone, initial NOx and initial VOC concentrations are made non-dimensional by the average NO2 photolysis rate (jav) and the rate constant for the NO-O3 titration reaction (kNO); temperature by the NO-O3 activation energy (ENO) and Boltzmann constant (k) and total irradiation time by the cumulative jav?t photolysis rate (?3). The analysis shows dimensionless maximum ozone concentration can be described by a product of powers of dimensionless initial NOx concentration, dimensionless temperature, and a similarity curve directly dependent on the ratio of initial VOC to NOx concentration and implicitly dependent on the cumulative NO2 photolysis rate. When Weibull transformed, the similarity relationship shows a scaling break with dimensionless model output clustering onto two straight line segments, parameterized using four variables: two describing the slopes of the line segments and two giving the location of their intersection. A fifth parameter is used to normalize the model output. The scaling analysis, similarity curve and parameterization appear to be independent of the details of the chemical mechanism, hold for a variety of VOC species and mixtures and a wide range of temperatures and actinic fluxes

A scaling analysis of ozone photochemistry: II Investigation of the similarity relationship

International audienceThe similarity relationship for maximum ozone concentration as a function of initial precursor concentrations developed in the first article of this 2-part series exhibits a scale break, most easily seen after a Weibull transformation, which identifies a characteristic scale for ozone photochemistry. In this paper, we investigate the similarity relationship using simple semi-quantitative models and model output. From this investigation, we develop a set of properties characterizing ozone-precursor relationships. We find the scaling break is associated with a change in the temporal variability of ozone production. Finally, we examine a series of smog chamber experiments for evidence of a scaling break. We find the data support a slight break after suitable transformation. It is difficult to tell if the lack of distinct break is due to smog chamber experimental limitations, a bias in the test conditions or if the processes leading to the scaling break are overly enhanced by chemical mechanisms

The value-added statement: An appeal for standardisation

Owing to the absence of accounting standards for the preparation of a value-added statement (VAS), a large variety of methods are used in financial statements. In this study the published value-added statements (PVAS) of companies listed on the JSE Securities Exchange during the period 1976-2005 have been standardised by the Graduate School of Business of the University of Stellenbosch (USB) in order to quantify the differences between the standardised VAS (SVAS) and the PVAS. These differences consist of the inclusion of items that do not belong in the VAS, items that are erroneously allocated among the distribution to stakeholders, and interpretation differences in whether a certain item forms part of the calculation of value added or the distribution thereof. The greatest difference quantified was the overstatement of the distribution to government that amounted to 54.4% of total differences. For users, including government, to properly calculate and compare the value added of different business entities, a standard for the preparation and presentation of VAS ought to be published. In the South African context the need of a precise measurement of each business entity's contribution to the growth of the national economy is relevant, and this need should also be addressed.Value added, Gross Domestic Product, South Africa, financial statements

The career orientation of final year teacher training students

The research was prompted by the assumption that the many problems in South African education (e.g. continuous curiculum changes, insufficient in-service training and support, classroom overcrowding, discipline problems,administrative paperwork, low teacher morale, high teacher attrition rate, low societal status of the teaching profession) must have an adverse effect on the career orientation of teacher training students. Our research was embedded in the theoretical framework of eco-systemic theory (Bronfenbrenner 1990), through which we indicated how the teacher is surrounded and influenced by various societal systems in four levels of proximity: the micro, meso, exo and macro levels. From these systems we established the conceptual framework, in which we discussed negative forces on the teacher as these are eminent in societal expectations about the teacher, the professional identity of the teacher and the retention rate in the teaching profession. The discussion of these negative forces and their impact affirmed our initial assumption and led to our research question: To what extent are teaching training students positively inclined towards a career in teaching? This question implied attention to a) the career motivation, and b) the moral values of the modern South African teaching training student. The empirical study was conceptualised as a pilot project. We involved the full number of final year teaching training students at one of the largest education faculties in South Africa, namely at the University of Pretoria. The students (n = 403) were asked to complete a questionnaire which focused inter alia on respondents’ exposure to daily news, reasons for choosing the education career path, attitudes towards the teaching profession and medium to long term prospects in the profession. Moral inclinations were also probed, e.g. with items on religion, discipline, language of instruction, multicultural teaching and being a role model. The questionnaire findings were verified in a focus group interview with five purposively selected respondents in the questionnaire survey. Our findings nullified our initial assumptions. Not only were the students strongly committed to their chosen career, notwithstanding the questionable societal status of the teaching profession and the formidable teaching challenges (of which they were apparently keenly aware), but they also conveyed a strong message about moral values and the teacher’s role in modelling those in and beyond the school. Our findings are prospective and certainly need verification on a broader scale. We are also planning a follow-up study with the same respondents, once they have completed two years of full time teaching. The findings could serve as impetus for education management measures to ensure that aspiring teachers’ level of commitment is sustainable. One of these measures could be an online advice and counselling service for beginner teachers.Die navorsing het ontstaan uit die aanname dat die onderwysproblematiek in Suid-Afrika (voortdurende kurrikulumwysigings, gebrekkige indiensopleiding, dissiplineprobleme, lae beroepsmotivering onder onderwysers en gebrekkige aansien van die onderwysberoep) ’n negatiewe uitwerking op die beroepsinstelling van onderwysstudente het. Vanuit die teoretiese raamwerk wat gebruik is, naamlik Bronfenbrenner (1990) se ekosistemiese samelewingsmodel, is die negatiewe kragte wat op die onderwys inwerk, nader toegelig. In die lig van die intensiteit van hierdie kragte het die volgende as navorsingsvraag gedien: In welke mate het die huidige onderwysstudent ’n positiewe beroepsingesteldheid? In ’n vraelysopname onder 403 finalejaar onderwysstudente, is die aanvanklike aanname verkeerd bewys. Die vraelysrespondente was nie alleen positief ingestel teenoor hul toekomstige loopbaan in die onderwys nie, maar hulle was ook uitgesproke oor hul taak daarin as morele rolmodelle. Die positiewe aard van ons voorlopige bevindings onderstreep alreeds die absolute noodsaaklikheid van onderwysbestuursmaatreëls om die volhoubaarheid van beginneronderwysers se positiewe beroepsingesteldheid te verseker. ’n Elektroniese advies- en motiveringsdiens vir beginneronderwysers kan heel moontlik as eerste en uitvoerbare projek hiertoe dien.http://www.journals.co.za/ej/ejour_akgees.htmlgv201

Isotopic Production Cross Sections in Proton-Nucleus Collisions at 200 MeV

Intermediate mass fragments (IMF) from the interaction of $^{27}$Al, $^{59}$Co and $^{197}$Au with 200 MeV protons were measured in an angular range from 20 degree to 120 degree in the laboratory system. The fragments, ranging from isotopes of helium up to isotopes of carbon, were isotopically resolved. Double differential cross sections, energy differential cross sections and total cross sections were extracted.Comment: accepted by Phys. Rev.

Improving cost-effectiveness of hypertension management at a community health centre

Objectives. To describe the pattern of prescribing for hypertension at a community health centre (CHC) and to evaluate the impact of introducing treatment guidelines and restricting availability of less cost-effective antihypertensive drugs on prescribing patterns, costs of drug treatment and blood pressure (BP) control.Design. Before/after intervention study.Setting. Medium-sized CHC in the Cape Flats area of Cape Town.Subjects. 1 084 hypertensive patients attending the CHC, who had at least two prescriptions for antihypertensive drugs during a 1-year period starting on 1 January 1992. Interventions. 1. Implementation of stepped-care guidelines for hypertension, specifying treatment with more cost-effective drugs and minimising drug treatment. 2. Reducing availability for routine prescribing by CHC doctors of 10 less cost-effective antihypertensive drugs or drug combinations.Outcome measures. 1. Mean number of drugs prescribed per patient. 2. Proportion of prescriptions for: each major class of antihypertensive drug; restricted availability and freely prescribable drugs; and more and less cost-effective drugs. 3. Mean monthly cost of drugs prescribed per patient. 4. Mean blood pressure and proportion of BP readings controlled (<160/95 mmHg) or uncontrolled (≥160/95 mmHg).Results. A mean of 1.7 active drugs was prescribed per patient per visit. The most frequently prescribed drugs were thiazide-like diuretics (44.8%), centrally acting agents (28.4%) and b-blockers (13.2%). Mean monthly drug costs per patient decreased significantly by R1.99 (24.2%) from R8.24 to R6.25 between the first and last prescription for each patient (exclusive of any reduction due to withdrawal of treatment). This was attributable to reduced prescribing of more expensive drugs withdrawn from routine use and a 51.1% increase in prescribing of the most cost-effective drugs. The overall annual cost-saving of the changes in prescribing for this CHC are estimated at R75 150. Blood pressure control did not change significantly.Conclusion. The pattern of changes in prescribing and drug costs was consistent with a causal effect of the interventions. The study demonstrates the potential forimproving cost-effectiveness of hypertension care in primary care in South Africa and the potential for research in this setting

Hypertension care at a Cape Town community health centre

Objectives. To describe the demographic profile of hypertensive patients and the quality of care for hypertension at a Cape Town community health centre (CHC).Design. Prospective, descriptive study.Setting and subjects. Medium-sized CHC, attended by 1098 hypertensive patients during a 1-year period from 1 January 1992.Outcome measures. Default rate - proportion of due visits not attended. Loss to follow-up - proportion of patients persistently defaulting or not responding to recall. Frequency of blood pressure measurement - per 12 due visits. Compliance - proportion of patients collecting ≥ 75% of antihypertensive drugs. Blood pressure control - mean blood pressure of aggregated readings; and proportion controlled (<160/95 mmHg) on the basis of all blood pressure readings and mean blood pressures of individual patients with two or more readings during the study period.Results. More than half (51.6%) of the hypertensive patients were aged ≥ 65 years; 81.7% were female. The default rate was between 11.9% and 19.4%. Compliance was high (76.9%). Loss to follow-up was 8.1 %. Blood pressure was recorded a mean of 4.0 times per 12 due visits. There were no significant gender differences with regard to these measures. Mean blood pressure was 158.3/89.6 mmHg. Over half (56.7%) of all individual readings over the year were uncontrolled and 51.4% of patients were found to be uncontrolled when categorised by their mean blood pressure. Control was significantly poorer among women ≥ 65 years.Conclusion. We found better compliance, more frequent blood pressure measurement, and lower defaulting and loss to follow-up compared with previous South African studies in similar settings. Despite this, blood pressure control was mediocre. Possible explanations for this are discussed. The low proportion of male hypertensives attending the CHC suggests that the accessibility or acceptability of care is poor for this group. The study illustrates the potential for research in this setting and for the use of computers to monitor the quality of primary care.

The National Food Consumption Survey (NFCS): South Africa, 1999

Objective: The aim of the National Food Consumption Survey (NFCS) in South Africa was to determine the nutrient intakes and anthropometric status of children (1-9 years old), as well as factors that influence their dietary intake. Design: This was a cross-sectional survey of a nationally representative sample of all children aged 1-9 years in South Africa. A nationally representative sample with provincial representation was selected using 1996 Census information. Subjects: Of the 3120 children who were originally sampled data were obtained from 2894, a response rate of 93%. Methods: The sociodemographic status of each household was assessed by a questionnaire. Dietary intake was assessed by means of a 24-hour recall and a food-frequency questionnaire from the caregivers of the children. Food purchasing practices were determined by means of a food procurement questionnaire. Hunger was assessed by a modified hunger scale questionnaire. Nutritional status was determined by means of anthropometric measurements: height, weight, head circumference and arm circumference. Results: At the national level, stunting (height-for-age below minus two standard deviations (< -2SD) from the reference median) was by far the most common nutritional disorder, affecting nearly one in five children. The children least affected (17%) were those living in urban areas. Even with regard to the latter, however, children living in informal urban areas were more severely affected (20%) compared with those living in formal urban areas (16%). A similar pattern emerged for the prevalence of underweight (weight-for-age < -2SD), with one in 10 children being affected at the national level. Furthermore, one in 10 (13%) and one in four (26%) children aged 1-3 years had an energy intake less than half and less than two-thirds of their daily energy needs, respectively. For South African children as a whole, the intakes of energy, calcium, iron, zinc, selenium, vitamins A, D, C and E, riboflavin, niacin, vitamin B6 and folic acid were below two-thirds of the Recommended Dietary Allowances. At the national level, data from the 24-hour recalls indicated that the most commonly consumed food items were maize, sugar, tea, whole milk and brown bread. For South African children overall, one in two households (52%) experienced hunger, one in four (23%) were at risk of hunger and only one in four households (25%) appeared food-secure. Conclusion: The NFCS indicated that a large majority of households were food-insecure and that energy deficit and micronutrient deficiencies were common, resulting in a high prevalence of stunting. These results were used as motivation for the introduction of mandatory fortification in South Africa. © The Authors 2005.Conference Pape