Showing papers by "University of the Witwatersrand published in 1974"

New fast method for generating discrete random numbers with arbitrary frequency distributions

Abstract: A new method for generating discrete random numbers with arbitrary amplitude/frequency distributions is presented. It consists essentially of amplitude manipulation of uniformly distributed, statistically independent sequential numbers. A digital-hardware implementation of the system features fast single-clock operation, with good statistical properties, and is well suited to software implementation.

Optimization of stochastic linear systems with additive measurement and process noise using exponential performance criteria

Abstract: The expected value of a multiplicative performance criterion, represented by the exponential of a quadratic function of the state and control variables, is minimized subject to a discrete stochastic linear system with additive Gaussian measurement and process noise. This cost function, which is a generalization of the mean quadratic cost criterion, allows a degree of shaping of the probability density function of the quadratic cost criterion. In general, the control law depends upon a gain matrix which operates linearly on the smoothed history of the state vector from the initial to the current time. This gain matrix explicitly includes the covariance of the estimation errors of the entire state history. The separation theorem holds although the certainty equivalence principle does not. Two special cases are of importance. The first occurs when only the terminal state is costed. A feedback control law, linear in the current estimate of the state, results where the feedback gains are functionally dependent upon the error covariance of the current state estimate. The second occurs if all the intermediate states are costed but there is no process noise except for an initial condition uncertainty. A feedback law results which depends not only upon the current dynamical state estimate but also on an additional vector which is path dependent.

On a Distribution Representing Sentence-Length in Written Prose

Abstract: SUMMARY A new model for representing sentence-length distributions is suggested in equation (8) which is a special case of equation (2), with parameter y = -2 known a priori Eight known sentence-length frequency counts taken from English, Greek and Latin prose were all satisfactorily described by distribution (8) For these eight fits, the average probability P(X2) was 0 50 A ninth observed distribution, taken from a Latin text of unknown authorship failed the x2 test applied to the fit of the data to the model in equation (8) This corroborates Yule's (1939) conclusion that it is highly unlikely that de Gerson could have written De Imitatione Christi It is further conjectured that the last-mentioned observed frequency distribution could be well represented by the more general model in equation (2), with a parameter y much smaller than -2 THE first substantial investigation on sentence-length as a statistical tool to be used in deciding disputed authorship was published by Yule in 1939 Simple statistical indices such as the average number of words per sentence and the standard deviation of sentence-lengths were employed Yule did not suggest a particular mathematical distribution model Later (Yule, 1944) he explored word-frequency of an author in addition to sentence-length Although Yule mentions in that book the negative binomial, he discards this distribution model as totally inadequate for representation of word frequencies and sentence-lengths Williams (1940, 1970) suggests and uses the lognormal distribution as a model for sentence-length To verify lognormality, Williams plots the observed cumulative percentage frequencies of sentence-lengths on log-probability paper in the hope that these plots will approach a straight line No x2 tests are given for any of Williams's examples Wake (1957), who discusses sentence-lengths in works of Greek authors, also makes use of the lognormal distribution by superimposing the observed histograms of the logarithms of sentence-lengths over the "expected" normal distributions No x2 tests are given The authorship of Greek prose is again investigated by Morton (1965) who works with distribution-free statistics such as the mean, the median, the quartiles and the deciles Mosteller and Wallace (1963), in their study of the authorship of the Federalist papers, came to the conclusion that the mean and standard deviation of sentence- length was of no help in solving disputed authorship In their particular research Mosteller and Wallace found the mean and standard deviations of sentence-length to be virtually identical for Madison and Hamilton It can be shown, however, that two

Further evidence that enterochromaffin cells are not derived from the neural crest.

Abstract: Recently, a previous finding that the enterochromaffin cells of chick embryos are not derived from the neural crest has been contested, and so further evidence has been sought. Presumptive gut, i.e. endoderm and adherent mesoderm, of embryos between the short head-process stage and the 25-somite stage was grown on the chorio-allantoic membranes of host embryos. Whether the presumptive gut was excised before or after the probable time of arrival of neural crest cells in the gut, enterochromaffin cells occurred in the intestine in the grafts. The presence or absence of enteric ganglia indicated the presence or absence, respectively, of neural crest cells. Enterochromaffin cells were plentiful even if the donor had been at a stage preceding that at which cells of the neural crest start to migrate, or preceding that at which the crests themselves first appear. In a second experiment, presumptive gut of embryos at 10- to 21-somite stages was excised so as to exclude the portion underlying the somites. Enteric ganglia were lacking in the intestine of these grafts, but enterochromaffin cells were invariably present. These experiments show that the precursors of enterochromaffin cells are present in the more lateral part of the presumptive gut before the neural crest precursors of enteric ganglia reach the region; and that they are present in the presumptive gut long before any crest cells could have arrived there. This evidence supports the view that enterochromaffin cells are not derived from the neural crest in chick embryos.

The Detection of Errors in Multivariate Data Using Principal Components

Abstract: Serious problems arise in the maintenance of reliability in large data bases, since it becomes difficult to verify incoming data manually. This article considers the case in which the base consists of data vectors following a multivariate normal distribution. Five screening procedures are proposed—a “one-at-a-time” test, the standard χ2 test, and three statistics derived from principal component analysis. From analysis of a practical example, it emerges that the statistics derived from principal component analysis have superior performance.

Iron absorption from rice meals cooked with fortified salt containing ferrous sulphate and ascorbic acid

Abstract: 1. Iron absorption from rice-containing meals was measured by red cell utilization of radioactive Fe in sixty-six volunteer multiparous Indian women.2. In all the studies salt added during the cooking process was used as the carrier for supplemental inorganic Fe and ascorbic acid.3. Intrinsic Fe in the rice and supplementary inorganic Fe were absorbed to the same extent, with a wide range of absorption values.4. There was a striking difference between the mean absorption of a 3 mg dose of ferrous Fe given to fasting subjects in a solution containing 30 mg ascorbic acid and that of Fe in a rice meal (48.7 and 3.5% respectively).5. When ascorbic acid was added during cooking there was a threefold increase in the absorption of both intrinsic Fe and supplementary Fe when a sufficient quantity (60 mg) was present.6. It is concluded that the Fe nutrition of rice-eating communities could be improved significantly by the addition of ascorbic acid to the diet.

Pulpal response to phosphoric acid.

Abstract: . The chemical treatment of tooth surfaces to improve bonding of dental materials to enamel and dentin is one of the approaches in overcoming the lack of adhesion of the available restorative materials to tooth structure. The acid etch technique is now an accepted procedure in restorative and preventive dentistry and for the direct bonding of orthodontic attachments. The pulpal response elicited by one of the conditioning agents, 50 % H3PO4 applied for 1 minute, was investigated in the teeth of the vervet monkey. The differences between most of the criteria used to evaluate the pulpal responses in acid-treated and control teeth at three time intervals, namely 4, 14 and 42 days, were statistically significant. These results suggest that a protective lining should be used to cover exposed dentin before etching adjacent enamel surfaces with 50 % H3PO4.

A histological comparison of the giant cells in the central giant cell granuloma of the jaws and the giant cell tumor of long bone.

Abstract: A histological comparison has been made of the giant cells in 10 cases which had been diagnosed as central giant cell granuloma of the jaws and 10 cases diagnosed as giant cell tumor of long bone. The numbers of nuclei in each of 50 giant cells were counted in the 20 lesions. The giant cells were measured in order to compare their sizes in the respective lesions. It was found that the giant cells of the jaw lesions contained significantly fewer nuclei than those of the lesions in other bones. Secondly it was found that cells in the lesions of long bone have significantly larger dimensions than those in the jaw lesions. There was, however, an area of overlap. It was concluded that these data supported the view that giant cell tumor and giant cell granuloma are distinct entities. Some giant cell lesions of long bones are, however, morphologically indistinguishable from lesions of the jaws; and conversely giant cell lesions of the jaws are indistinguishable from some giant cell lesions of the long bones. It seems possible, therefore, that some jaw lesions are giant cell tumors and that some giant cell lesions outside the jaws are giant cell granulomas.

Behavior of Prosimians

Abstract: Publisher Summary This chapter discusses behavior of prosimians. Fossil evidence implies an evolutionary link between prosimian and monkey. Prosimians occupy a diversity of habitats within the tropical and semitropical regions of the Old World. In the wild, primates restrict their activities to a measurable, circumscribed geographic area called a home range. With the exception of the tupaiids and the possible exception of exclusively solitary species like Daubentonia madagascariensis, probably only female prosimians build nests. The lemurines and indriids are predominantly herbivorous and frugivorous. Together with a well-developed visual sense, one tends to think of a high degree of manual dexterity as one of the most important and obvious characteristics of the order Primates. Olfactory information may be expected to play a more important role in prosimians than in other primates. Dolhinow and Bishop regard play as a major category of primate behavior, as a preparation for adult life. Primates show intelligence both in relations with inanimate objects and in relations with social fellows.

How well does man thermoregulate during sleep

Abstract: Eine Versuchsperson, im Calorimeter fur Menschen einer warmen Umgebung ausgesetzt, zeigte auffallend grosse Unterschiede in der Schweissrate im Schlaf gegenuber dem Wach-Zustand. Perioden mit unterdrucktem Schwitzen waren mit aktiven (REM) Schlaf verbunden

Hepatitis-B antigen and cirrhosis in Bantu patients with primary liver cancer.

Abstract: Hepatitis-B antigen (HBAg) was found in the serum of 30 of 75 (40%) Bantu patients with primary liver cancer (PLC), but in only 7% of 18,377 apparently healthy rural Bantu, confirming an association between this tumor and persistence of the hepatitis-B virus. No relationship could be demonstrated between hepatitis-B antigenemia and alpha-fetoprotein, which was present in 77% of the patients. HBAg was not more common in the younger patients. In 60% of the patients, PLC coexisted with „posthepatitic” or postnecrotic cirrhosis. HBAg was found in 45.6% of the patients with cirrhosis, but also in 31% of those without, an insignificant difference. Our findings may be interpreted as meaning that persistence of the hepatitis-B virus is the cause or result of PLC, or that some immunologic defect is responsible for both. If the former, the virus must be directly oncogenic, in addition to having the potential to induce neoplasia indirectly via chronic parenchymal liver disease.

Radiocarbon and tritium evidence for direct rain recharge to ground waters in the northern Kalahari

Abstract: THE Kalahari, a flat and sand-covered region of more than 600,000 km2 (Fig. 1), has long been classified as a desert because of the virtual absence of surface waters in the form of springs or perennial rivers. The only exception is the inland drainage system in the north, the Okavango delta and Makgadigadi salt pan, which are fed successively by rainwater which drains from the remote highlands of Angola through the Okavango river.

The development of ion-bombardment surface structures on stainless steel

Abstract: A brief review is given of the formation and characteristics of conical surface structures resulting from ion etching. The effect of low-energy ion bombardment of 18-8 stainless steel surfaces has been studied. The topography generated has been related to microstructural detail. The conical protrusions are found to arise from slag silicate particles while the pillar type structures result from fibrous manganese sulphide inclusions. Scanning electron microscopy has shown the development of both of these structure types to be in accord with previously published ion-etching models.

Background to the Transvaal Iron Age - new discoveries at Olifantspoort and Broederstroom

Abstract: The work being done on Iron Age sites in the Transvaal is descriptionbed, with particular reference to the finds at Olifantspoort and Broederstroom. The material so far found provides evidence for the production of iron and copper, the farming of cattle and sheep, and the construction of large villages by people who were probably ancestral to the present Bantu population. The material dates from as early as A.D. 270, but clear indications occur from A.D. 460 onwards.

A modified horton equation for infiltration during intermittent rainfall

Abstract: A simple infiltration concept based on Horton's infiltration equation has been developed for use in mathematical rainfall-runoff modelling. Horton's infiltration formula is valid only where rainfall intensity at all times exceeds infiltration and, moreover, it does not provide adequately for the handling of a variety of initial soil moisture conditions. In contrast to Horton's concept where infiltration rate is expressed as a decay function of time, the procedure advocated in this paper expresses the infiltration rate as a function of soil moisture storage state. The procedure permits infiltration losses during intermittent rainfall sequences to be evaluated and accommodates a range of initial soil moisture conditions.

Tidal flat associations from a Lower Proterozoic carbonate sequence in South Africa

Abstract: An association of structures is documented from a Lower Proterozoic carbonate sequence in South Africa: this is dominated by finely laminated material which may display flat (smooth), small domical (blister), crinkled (tufted) and pustular (mamillate) surface. The lamination may display overfolded structures and contain flat encapsulated features. Lens-like flat-pebble breccias are common, while edgewise breccias were seen less frequently. Small-scale features suggestive of vertical algal moulds were also recorded. This facies is considered to be analogous to contemporary tidal flat sedimentation developed in specific settings at Shark Bay in Western Australia, and at Abu Dhabi where it is the dominant growth form. This analogy is most notably clear in relation to the protected embayments at Shark Bay, and as a result, an inner intertidal to marginal supratidal environment is suggested for the specific horizons under consideration from the Transvaal Dolomite. Other structures are associated with this facies. These include larger domes, coarser bedding, oolites, ripple-marks and, in one case, columnar stromatolites. Using the basic facies as an environmental datum, a model is developed in which these latter structures extend into the outer intertidal zone. They are also considered to be associated with varying states of turbulence in the intertidal regime.

The Fortification of Common Salt with Ascorbic Acid and Iron

Abstract: Summary. Common salt fortified with ascorbic acid or iron compounds became discoloured on storage, the reaction being accelerated by heat and humidity. Soluble iron compounds such as FeSO4 caused discoloration more readily than insoluble compounds such as ferric orthophosphate (FePO4). Fortification with both ascorbic acid and iron led to more rapid discoloration than fortification with either alone. Colour developed more rapidly in coarse salt than in refined commercial salt, while chemical NaCk developed a faint discoloration only under very hot and humid conditions. Discoloration was inhibited if starch was mixed with the salt: coarse salt mixed with 2.5% starch, 1.25% ascorbic acid and 0.1% iron as FePOI retained an acceptable appearance during storage under subtropical conditions (Durban) for more than I yr. A double isotope red cell utilization method was employed to assess the absorption of iron from maize porridge and from a standard rice meal cooked with fortified salt. The absorption of both the intrinsic food iron and the iron in the fortified salt was increased threefold if the salt contained 50 mg ascorbic acid as well as FePO4. The amount of iron absorbed was similar whether the salt contained 50 mg ascorbic acid and 4 mg iron as FePO4 or 50 mg ascorbic acid and 4 mg iron as FeSO4. It was concluded that crude common salt could be fortified with 0.1% iron as FePO, and 1.25% ascorbic acid and stored under all but the most extreme tropical conditions, provided that 2.5% starch was added to prevent the development of discoloration, and that such fortification would significantly improve the iron nutrition in countries where the staple food is rice or maize.

Prediction of the apex angle of surface cones on ion-bombarded crystalline materials

Abstract: Different methods of calculation based on ion channelling in a target matrix have been applied to the computation of the apex angle of surface conical shapes derived from ion bombardment. Comparison with values obtained experimentally by electron microscopy and deduced from sputter yield curves in the energy range 0.2 to 27.0 keV indicate that reasonable agreement can be achieved using a smeared Thomas Fermi atomic plane potential.

Measurements of K, Rb, U, Sr, and Pb in diamonds containing inclusions

Abstract: KNOWLEDGE of the Pb and Sr isotopic compositions of syngenetic inclusions in diamonds is important for several reasons. As diamonds probably crystallised at depths of more than 100 km, the isotopic data may provide constraints on the mode of the geochemical evolution of the Earth. It may also be possible to test assumed U/Pb ratios (U/Pb=μ) for the mantle and to estimate the age of particular diamonds. Diamonds are particularly appropriate for these studies because, in contrast to kimberlites and their associated nodules, any contamination by crustal material can be overcome by washing in acid.

Relationship between pica and iron nutrition in Johannesburg Black adults.

Abstract: On direct questioning by a Black staff nurse, 23% of 348 consecutive unselected adult outpatients attending the Johannesburg Non-European Hospital said that they regularly are earth or ash. The prevalence was higher in the women (33%) than in the men (11 %), and in 50 women with minor gynaecological complaints who were interviewed by a Black psychologist, it was 72%. The quantity eaten varied from an occasional tablespoonful to several handfuls a day. In an attempt to define the reasons for the habit a thematic apperception test was used. A strong association with pregnancy was identified, but the explanation for this was not established. Some subjects claimed that the material was eaten for medicinal purposes, while others merely liked the taste. The effect on iron nutrition appeared to be variable, depending on the ironbinding capacity of the soluble iron content of the material consumed. S. Afr. Med. J ., 48. 1655 (1974)

Improved Correlation of Film Condensation Data Based on a More Rigorous Application of Similarity Parameters

Abstract: It is shown that a most consistent application of similarity parameters reduces the “random error” of experimental results in film condensation by 90%, in extreme situations even more. On the basis of physical considerations a correlation of data is presented which shows the Nusselt number as a function not only of the Reynolds number but also in certain ranges of the Prandtl and Weber number. Although the latter parameters varied only moderately in the experiments presented here the general idea is supported clearly. Further experiments will have to provide for quantitatively more reliable results.