Base exchange in soils : a study of the reproducibility of base exchange values for some South African soils, as indicated by leaching with normal ammonium acetate solution

A very reliable method for the total analysis of the ammonium acetate leachate has been outlined. This is both simple and straight forward and is more rapid than any which have been seen in the literature. It is particularly applicable where a worker must perform a large number of routine analyses in the minimum of time. Shirley (29) and other workers have shown that 1000 ml. of leaching solution is generally necessary to extract all the exchangeable gases. The present investigation has shown that the time of leaching makes no appreciable difference to the amounts of bases replaced, as long as this exceeds four hours. Two alternative methods have been introduced for the rapid determination of the total exchangeable bases in a soil and there are considered to be more reliable than that of Bray and White. It is suggested that the two new methods might yield a still greater degree of accuracy if larger aliquots were to be used for each determination. It is further pointed out that the values obtained by the chloride methods are more likely to represent correct values than the sum totals of the bases as determined individually, since these are arrived at by summing the results of four different estimations, each of which is liable to experimental error, whereas in the chloride methods there is only one perfectly straightforward determination. The values for the total exchangeable bases in the soils examined were found to vary over the range 2.50 to 14.28 m.e. per 100 g. soil, with a variance of up to ± 0.2sm.e. per 100 g., corresponding to a percentage error of up to ± 4.7%. These figures are based on the analysis of 12 separate leachings of each soil with normal ammonium acetate solution of pH 7.00. This rather wide variance can be attributed to the fact that the exchangeable bases in some soils are more easily replaceable than in other soils. It is regretted that the shortage of time and the non-availability of a complete range of samples of all typical South African soils has prevented the attainment of an original objective, namely, a statistical evaluation of the base exchange figures for all South African soil types. It would also have been of great interest to have been able to establish exactly the composition of the double salt of calcium and magnesium, whose existence has been postulated to explain the effect of the Ca/Mg ratio on the results yielded by the first chloride method. Summary, p. 67-68

Open timelike curves violate Heisenberg's uncertainty principle

Toy models for quantum evolution in the presence of closed timelike curves (CTCs) have gained attention in the recent literature due to the strange effects they predict. The circuits that give rise to these effects appear quite abstract and contrived, as they require non-trivial interactions between the future and past which lead to infinitely recursive equations. We consider the special case in which there is no interaction inside the CTC, referred to as an open timelike curve (OTC), for which the only local effect is to increase the time elapsed by a clock carried by the system. Remarkably, circuits with access to OTCs are shown to violate Heisenberg's uncertainty principle, allowing perfect state discrimination and perfect cloning of coherent states. The model is extended to wave-packets and smoothly recovers standard quantum mechanics in an appropriate physical limit. The analogy with general relativistic time-dilation suggests that OTCs provide a novel alternative to existing proposals for the behaviour of quantum systems under gravity

Teacher burnout: Construct equivalence and the role of union membership

The objective in this study was to investigate its structure and validate the Maslach Burnout Inventory for educators in the Goldfields region of the northern Free State province of South Africa. A cross-sectional survey design was used, where a sample of educators was drawn from the total population (N=468). An adapted version of the Maslach Burnout Inventory and a biographical questionnaire were administered. Exploratory factor analysis with target rotations confirmed construct equivalence of burnout dimensions for an Afrikaans and English subgroup and an African Languages subgroup. Burnout is described as consisting of exhaustion, cynicism, depersonalisation, and professional efficacy. However, the depersonalisation construct showed better fit across language groups than the cynicism construct. Item bias analysis was carried out for the cynicism items. For biographical differences, it was found that union membership presented an important distinction in educators ' experience of burn out.South African Journal of Education Vol. 26 (4) 2006: pp. 541-55

Mid-trimester termination ofpregnancy - a randomised controlled trial of two prostaglandin regitnens

Objective. To detennine the more applicable of two ways of prostaglandin induction currently in use in second trimester induced abortions for congenital or chromosomal abnormalities.Design. A prospective randomised controlled trial.Setting. Department of Obstetrics and Gynaecology, Tygerberg Hospital, CP.Study population. Twenty consecutive patients admitted for tennination of pregnancy for congenital or chromosomal abnormalities between 14 and 26 weeks' pregnancy duration. Management. Patients were randomly selected to receive either 1,5 mg prostaglandin E, (PGE,) gel extra-amniotically or 25 mg prostaglandin F,a (PGF,a) intra-amniotically. Patients in both groups received oxytocin to a maximum dosage of 120 IllU per minute if they had not aborted 18 hours after the original administration of either prostaglandin regimen. If abortion had not taken place 36 hours after cotnmencement of treatment, management was considered unsuccessful.Main outcome measurements. Proportion of successful inductions and complications.Results. Complications of management were rare and did not differ between the two management groups. However, there were significantly more failures in the group who receh'ed intraamniotic PGF,a (7 v. 2 patients) as well as a significantly higher need for oxytocin in this group (10 v. 4 patients).Conclusions. With· proIllising drugs such as prostaglandin analogues and anti-progesterones not universally available, methods of induction suitable to the local situation should be sought. Extra-atnniotic PGE, seems more suitable than intra-amniotic PGF,a because of a shorter induction- to-delivery time without increased morbidity

Characterization of the Leaf Anatomy of Panicum Virgatum Germplasm

Both the yield and digestibility of C4 grasses have been related to anatomical characteristics. The objectives of the current work were to test switchgrass with varied yield and digestibility for variation in anatomical measurements and to develop a method of graphically representing the anatomy. Six accessions were established in replicated field plots and the lamina were sampled, dehydrated and embedded for anatomical study. Midrib dimensions were excluded from study but perimeters of primary and secondary vascular bundles in the lamina were measured. Lamina thickness was determined at the primary bundle, secondary bundle and at the minimum between the bundles. The distance between the primary and secondary bundles was also measured. The accessions differed in perimeter of primary vascular bundles, lamina thickness at the primary bundle and the distance from primary to secondary vascular bundle (P\u3c0.05). Variation in lamina thickness at the secondary vascular bundles approached significance (P\u3c0.10)

Randomised trials in the South African Medical Journal, 1948- 1997

Objective. To describe randomised controlled trials (RCTs) published in the South African Medical Journal (SAMJ) over a 50-year period from 1948 to 1997 with regard to number, topic and quality.Methods. We hand searched all issues of the SAMJ published during the study period to identify all published RCTs.Outcome measures. Number, topic and quality of RCTs published from 1948 to 1997.Results. Eight hundred and fifty-eight clinical trials were published during the period reviewed. Eighty-four per cent of RCTs were published as full articles. During the 1980s the number of RCTs published increased rapidly,  with a peak of 35 in 1985, but then declined to only 5 in 1997. The majority (92%) of RCTs were conducted in a hospital setting. A varied range of subjects was covered, with gastroenterology taking the lead and no trials in public health. The sample size in more than 50% of RCTs was smaller than 50 patients. Fifty-one per cent (435 trials) used random allocation and 49% (423) quasi-random methods of allocation. Concealment of treatment allocation was judged to be adequate in 46% of studies (N == 200), blinding of observers assessing outcomes was adequate in 28% (123), and all the allocated test subjects were included in the primary analysis in 28% (123). The follow-up period was more than 1 year in 4% (17) and less than 6 days in 16% (71).Conclusions. Compared with other international journals the SAMJ is highly regarded in terms of the number of trials published. There are, however, a number of deficiencies in the quality of the trials

Non-Linear diffusion processes and applications

Diffusion models are useful tools for quantifying the dynamics of continuously evolving processes. Using diffusion models it is possible to formulate compact descriptions for the dynamics of real-world processes in terms of stochastic differential equations. Despite the exibility of these models, they can often be extremely difficult to work with. This is especially true for non-linear and/or time-inhomogeneous diffusion models where even basic statistical properties of the process can be elusive. As such, we explore various techniques for analysing non-linear diffusion models in contexts ranging from conducting inference under discrete observation and solving first passage time problems, to the analysis of jump diffusion processes and highly non-linear diffusion processes. We apply the methodology to a number of real-world ecological and financial problems of interest and demonstrate how non-linear diffusion models can be used to better understand such phenomena. In conjunction with the methodology, we develop a series of software packages that can be used to accurately and efficiently analyse various classes of non-linear diffusion models

The lesson of causal discovery algorithms for quantum correlations: Causal explanations of Bell-inequality violations require fine-tuning

An active area of research in the fields of machine learning and statistics is the development of causal discovery algorithms, the purpose of which is to infer the causal relations that hold among a set of variables from the correlations that these exhibit. We apply some of these algorithms to the correlations that arise for entangled quantum systems. We show that they cannot distinguish correlations that satisfy Bell inequalities from correlations that violate Bell inequalities, and consequently that they cannot do justice to the challenges of explaining certain quantum correlations causally. Nonetheless, by adapting the conceptual tools of causal inference, we can show that any attempt to provide a causal explanation of nonsignalling correlations that violate a Bell inequality must contradict a core principle of these algorithms, namely, that an observed statistical independence between variables should not be explained by fine-tuning of the causal parameters. In particular, we demonstrate the need for such fine-tuning for most of the causal mechanisms that have been proposed to underlie Bell correlations, including superluminal causal influences, superdeterminism (that is, a denial of freedom of choice of settings), and retrocausal influences which do not introduce causal cycles.Comment: 29 pages, 28 figs. New in v2: a section presenting in detail our characterization of Bell's theorem as a contradiction arising from (i) the framework of causal models, (ii) the principle of no fine-tuning, and (iii) certain operational features of quantum theory; a section explaining why a denial of hidden variables affords even fewer opportunities for causal explanations of quantum correlation