Showing papers by "Cardiff University published in 1970"

Connectance of large dynamic (cybernetic) systems: critical values for stability.

Abstract: MANY systems being studied today are dynamic, large and complex: traffic at an airport with 100 planes, slum areas with 104 persons or the human brain with 1010 neurones. In such systems, stability is of central importance, for instability usually appears as a self-generating catastrophe. Unfortunately, present theoretical knowledge of stability in large systems is meagre: the work described here was intended to add to it.

Non-repetitive sequences

Abstract: This note is concerned with infinite sequences whose terms are chosen from a finite set of symbols. A segment of such a sequence is a set of one or more consecutive terms, and a repetition is a pair of finite segments that are adjacent and identical. A non-repetitive sequence is one that contains no repetitions.

Hemolysis near a transversely oscillating wire.

Abstract: Erythrocyte suspensions were subjected to hydrodynamic forces generated by a partially submerged tungsten wire set into transverse oscillation at 20 kilohertz. Free hemoglobin appears in solution when the oscillation amplitude exceeds a critical threshold value. The hemolysis probably results from stresses exerted on cell by a microstreaming field established near the wire.

The Structure and Function of a Connective Chordotonal Organ in the Cockroach Leg

Abstract: The micromorphology of the tibio-tarsal joint of Periplaneta is described, based on the mesothoracic limb. There are two muscles acting on the joint, numbered 144 and 145. There is a connective chordotonal organ, which branches off from the trunk of N5 proximally and inserts on the intersegmental membrane distally. In addition, a previously undescribed group of campaniform sensilla is reported from the tibiotarsal joint. The tibio-tarsal chordotonal organ subdivides into a main branch and two side branches. It contains 26 bipolar sensory neurons, whose dendrites are associated distally with 14 scolopales. These scolopidia are arranged in three groups which differ in position, fine structure and number of cells per scolopale. There is one group I scolopidium in each of the side branches and two proximally in the main branch. Group 2 scolopidia are spread out along the main branch and group 3 scolopidia occur distally in the main branch. Group 1 scolopidia consist of two bipolar neurons, 15 to 20 $\mu m$ in diameter, whose dendrites, heavily sheathed, insert in a single scolopale. Group 2 scolopidia consist of two bipolar neurons, 8 to 15 $\mu m$ in diameter, whose dendrites are less well sheathed and insert in a single scolopale. Group 3 scolopidia consist of a single bipolar neuron, about 10 $\mu m$ in diameter, with a short, poorly sheathed dendrite inserting in a single scolopale. The scolopales of groups 1 and 2 are identical, consisting of the usual pattern of a ring of scolopale rods inserting into a distal cap and enclosing the cilia on the dendrite terminations. In this case, the cap is particularly long and pointed and both the cilia and the scolopale rods penetrate a long way into it. The cilia of the two members of a pair of dendrites are identical but the ciliary roots differ between the two members of a pair. Electrophysiological recordings show that the organ responds to downward and backward deflexion of the tarsus. The response comprises at least two classes of sensory fibre distinguishable both by their size and by their behaviour. The larger fibres show a unidirectional phasic and tonic response to extreme deflexion of the tarsus and are identified with the group 1 scolopidia. The smaller fibres show a unidirectional tonic response to the full range of deflexion of the tarsus and are identified with the group 2 scolopidia. On structural evidence, it is suggested that the differences in adaptation between these two groups of scolopidia is not likely to be caused by differences in mechanical attachment. The combination of electrophysiological and fine structural evidence indicates that in this chordotonal organ the adequate stimulus of the scolopidia is an increase in their longitudinal tension but it is not possible to say which fine structural component responds to strain.

Postoperative pancreatitis: A study of seventy cases*****

Abstract: Summary It is not difficult to appreciate that trauma to the pancreatic tissue and ducts or to the surrounding structures could cause edema, obstruction of the ducts, impairment of the blood supply, and subsequent autodigestion. Secondly, there is some evidence that hypovolemic shock may precipitate pancreatitis. The formation of microthrombi is possibly a common factor in instances in which local trauma is absent. Thirdly, depressed trypsin inhibitor activity after operations reduces tissue immunity to autodigestion. The following factors are important in the prevention and treatment of postoperative pancreatitis: o 1. Meticulous attention to general operative technics is a self-evident requirement in gastric and biliary surgery. 2. Bakes' dilators greater than 3 mm should not be used. If stenosis of the ampulla of Vater is suspected, transduodenal sphincterotomy should be carried out. One should avoid high pressure injections when doing syringe cholangiograms. 3. In cases in which there is a question of possible obstruction to the pancreatic duct, external drainage by cannulating the duct will provide free passage of pancreatic secretions to the outside until local edema has disappeared. 4. Long-arm T tubes should not be used; if found to be the basis of an attack of acute pancreatitis, they should be removed and replaced with a short-arm tube.

Osteoporosis and the effects of ageing on bone mass in elderly men and women.

Abstract: Summary A longitudinal study of the effects of ageing on bone mass, height, and body weight was made in random samples of a defined population of elderly men and women. The observations were made twice with an interval of 11 years between them. At initial survey ages ranged from 55 to 64 years. Bone mass was assessed from measurements of the second metacarpal cortex made directly from radiographs. Loss of bone occurred in both sexes but this was not a universal phenomenon; some men and women lost little or no bone over the period of study. In those persons in whom bone loss did take place this happened at different rates; and the women tended to lose more bone than the men.Change in bone mass in the metacarpal was not related to loss of heigh, change in body weight, the occurence of fracture, or the presence of back pains. A separate population of persons with the clinical syndrome of senile osteoporosis was not identified.

Prediction of operator performance during learning of repetitive tasks

Abstract: SUMMARY Learning effects in the execution of repetitive tasks may often be adequately described by an exponential law commonly found in physical systems. This law is characterised by the rise time and the final value of output rate. An iterative method is developed for the determination of rise time and final value using only performance data recorded during early stages of learning, and is shown to predict these parameters sufficiently accurately for use in costing and in continuously updating lime standards. Further uses of the predictive technique include highlighting the need for increased supervision, or the replacement of particular operatives. When experimental data is oscillatory in nature, prediction errors are greatly reduced by three-point averaging tuned to the period of oscillation. Much of the experimental data has been recorded in industrial environments, frequently for long production runs.

Effect of Gross Pollution by Kerosine Hydrocarbons on the Microflora of a Moorland Soil

Abstract: THE microbiology of the degradation of hydrocarbons in soil has been studied in some detail1–4; as well as the many bacteria able to oxidize alkanes, certain fungi are thought to be involved to a significant degree in moorland soil5.

A Study of the Cross Flow Fan

Abstract: The cross flow fan has developed from the ideas of Mortier in the late 19th century and recently has been used with conspicuous success in small domestic appliances. No satisfactory theory is known, improvements having come from experimental development.The present work is also experimental. A closed-circuit fan test rig was constructed to obtain pressure, volume flow rate and efficiency for fans of various designs. Detailed measurements within the rotors were also obtained by hot-wire traverses. These tests were supplemented by visualization studies in a water test rig.It is found that improved pressure–flow characteristics are obtained by constructing the casing so that the vortex which forms in the fan is allowed to move circumferentially round the rotor as the output is throttled. This preserves a strong vortex and keeps the total pressure approximately constant as the flow is throttled. In many previous designs, which do not allow this kind of displacement, the vortex tends to move towards the centre...

Scanning electron microscopy of intact colonies of microorganisms.

Abstract: Colonies of S. mutans OMZ61, Streptococcus sp. D182, Staphylococcus aureus Oxford NCTC 6571, and Candida albicans type A, MRL 3153 were grown on various media. Cubes of agar bearing two to three colonies were excised and processed for scanning electron microscopy. The characteristic shape of the colonies was seen when examined at low magnifications. At a magnification of 2,000 diameters, the arrangement of individual organisms within the colonies was observed. Plano-convex colonies consisted of uniformly distributed organisms, whereas S. mutans colonies presented a more complex arrangement possibly associated with the production of extracellular polysaccharides. Certain colonies were totally or partially covered by an adherent film through which the outline of the organisms could be distinguished.

Partial purification and properties of an enzyme from rat liver that catalyses the sulphation of L-tyrosyl derivatives.

Abstract: 1. An enzyme that catalyses the transfer of sulphate from adenosine 3'-phosphate 5'[(35)S]-sulphatophosphate to l-tyrosine methyl ester and tyramine was purified approx. 70-fold from female rat livers. 2. The partially purified preparation is still contaminated with adenosine 3'-phosphate 5'-sulphatophosphate-phenol sulphotransferase (EC 2.8.2.1), but a partial separation of the two enzymes can be achieved by chromatography on columns of Sephadex G-200 and DEAE-Sephadex. 3. The enzyme responsible for the sulphation of l-tyrosine methyl ester and tyramine is activated by dithiothreitol, 2-mercaptoethanol and GSH, the degree of activation being more marked with preparations previously stored at 0 or -10 degrees C. In contrast, the enzymic sulphation of p-nitrophenol is inhibited by all three thiols. Again, there is a quantitative difference in the degree of inhibition of the two enzymes by o-iodosobenzoate, p-chloromercuribenzoate, N-ethylmaleimide and iodoacetate. 4. Mixed-substrate experiments support the hypothesis that the enzyme responsible for the sulphation of l-tyrosine methyl ester and tyramine is separate from that responsible for the sulphation of p-nitrophenol. However, p-nitrophenol is a potent inhibitor of the sulphation of both tyrosyl derivatives whereas these latter compounds have no effect on the sulphation of p-nitrophenol.

Albumin metabolism in chronic renal failure

Abstract: SUMMARY 1. Plasma albumin concentration was measured in fifty-eight patients with chronic renal failure. The mean value was 3-27 g/100 ml (SD 0.44 g/lOO ml; range 2.4-4-3 g/ 100 ml) which is significantly lower (P

An improved technique for transfer function synthesis from frequency response data

Abstract: An improved curve fitting technique, based on modification of work by Levy and Sanathanan and Koerner, incorporating known physical constraints is described. A comparison with experimental results on high-order systems shows that there is a much better guarantee of obtaining stable transfer functions and of predicting responses in other domains.

The burrowing of Priapulus caudatus

Abstract: An account is given of the way in which Priapulus caudatus burrows in the muddy sea-bed in which it lives. Three phases are distinguishable in the muscular activity which is responsible for locomotion. During the first phase the animal is able to feed and defaecate, during the second the proboscis becomes invaginated, and during the third the animal moves forward. The power for locomotion is provided by contraction of the longitudinal and circular muscles of the body wall, not, as has been suggested previously, by the retractor muscles of the praesoma. Invagination of the proboscis is apparently stimulated by the arrival of a wave of contraction in the body wall musculature, propagated from the trunk. In general the animal burrows in a way common for soft-bodied animals; the anterior and posterior extremities acting in turn as “terminal” and “penetration” anchors in the substratum. The muscular activities of the larva are limited by the presence of a lorica which encases the trunk, and the animal's powers of movement at this stage are very restricted.

A morphological and histochemical study of Trichuris suis (Schrank, 1788) with special reference to the host-parasite relationship

Abstract: Adult forms of the pig whipworm, T. suis, are able to establish intimate contact with the host's tissues by the formation of a tunnel-like construction which covers a section of the thread-like oesophageal region. The extreme anterior oral end and the stouter posterior region are not covered and lie free in the lumen of the caecum. The attachment tunnel is composed of host mucosal cells and goblet cell secretion and its possible mode of construction is discussed. Host tissue not directly involved in tunnel formation appears unharmed by the presence of the parasite. T. suis is therefore not a serious pathogen under natural conditions.It has been demonstrated that characteristic structures of the trichuroid oesophageal region, e.g. bacillary band and stichosome are metabolically active. The former penetrates the layered cuticle in the form of columnar protrusions originating in the hypodermis. Each hypodermal column represents a gland cell or bacifiary cell, which displays enzymic activity, e.g. acid phosphatase, non-specific esterase, glucose-6-phosphatase, succinate dehydrogenase, cytochrome oxidase and β-d-glucosidase. Its possible function at the host-parasite interface and in the metabolism of the whipworm is discussed. The layered cuticle is proteinaceous and enzymically inert.Glandular activity is also displayed by the stichosome surrounding the capillary-like oesophagus. This evidence confirms earlier suggestions that the stichosome is a series of oesophageal glands.Although the bacillary band may be involved in nutrient uptake the evidence obtained indicates that this is via the mouth which is favourably placed for the ingestion of mucoid material which was detected in the oesophagus. This may be subjected to preliminary hydrolysis by the enzymes present in the oesophagus and stichosome.

The misuse of taste names by untrained observers.

Abstract: Many subjects cannot identify sour and bitter solutions which they can clearly taste. Subjects show a great deal of agreement on the taste of predominantly sweet and predominantly salt substances, but much less agreement on predominantly bitter and predominantly sour substances. The argument is put forward that we do not easily learn the sour/bitter distinction because few food substances taste strongly bitter. Because bitter has an unpleasant connotation a large minority tends to use it wrongly for substances that are unpleasantly sour.

The ultrastructure, based on stereoscan observations, of the oral sucker of the cercaria of Schistosoma mansoni with special reference to penetration.

Abstract: The ultrastructure of the oral sucker of the cercaria of Schistosoma mansoni was investigated using stereoscan and transmission electron microscopy. Secretions of the penetration glands are released through ducts which open at the bases of a series of raised tegumentary folds on the anterior tip of the oral sucker and not through hollow spines. These tegumentary folds may serve to protect the duct apertures during the free swimming period of the cercaria. During penetration into the final host the folds may act as a “rasp” to break down the host skin and in addition help to confine the enzymatic activity of the glandular secretions to a particular area. A series of sensory structures, in close proximity to the duct openings, probably enable the cercaria to test the host surface which results in the selection and penetration of a suitable site.

Ultrasonic Dispersal of Activated Sludge Floes

Abstract: Summary A novel device which could be used for the disruption of activated sludge flocs, using a transversely oscillating wire, is discussed The acoustic microstreaming generated around the wire produced hydrodynamic shear forces sufficiently strong to break up sludge flocs, without causing a loss in viability of the component cells A 20-fold increase in total heterotrophs and Thiobacillus-type organisms was observed Electron micrographs provided visual evidence for the disruption of flocs

An Evaluation of the Possible use of Prostaglandin E1, E2 and F2α for Induction of Labour

Abstract: The stimulatory effect on uterine contractility of prostaglandin E1, E2 and F2α was studied in 29 term pregnant women and 4 midpregnant volunteers admitted for therapeutic abortion. The substances were administered intravenously and uterine contractility recorded by measuring the amniotic pressure. In a careful analysis of the quantitative tracings it was found that suitable doses of the prostaglandins induce efficient uterine contractions. However, these contractions are characterized by a comparatively low intensity in relation to frequency and also occurrence of incoordinated contraction complexes. The results do not support the opinion that the prostaglandins are superior to oxytocin for induction of labour at term pregnancy.

The host-parasite interface of strigeoid trematodes. IX. A probe and transmission electron microscope study of the tegument of Diplostomum phoxini Faust, 1918.

Abstract: A combined study using electron probe (Stereoscan) and transmission electron microscopy has revealed the existance of surface specialisation of the adhesive organ of adult Diplostomum phoxini Faust, 1918. The lateral walls of the adhesive organ bear stout spines, whereas the surface which comes into contact with the host tissues consists of numerous small chambers approximately 2 μ high and 0.5–1 μ in diameter. Within the chambers are slender microvilli. This surface is cytoplasmic and is in continuity with unicellular gland cells, lying within the body of the adhesive organ, via cytoplasmic processes. The chambered adhesive organ surface and the processes contain mitochondria, granular material and membrane bounded secretion bodies 0.18 μ in diameter containing densely staining granular contents. A fibrous basement layer is poorly developed and the basal plasma membrane of this surface is in close contact with adjacent parenchymal cells and the lacuna excretory system. Histochemistry has demonstrated the presence of non-specific acid phosphatase activity in the walls of the chambers, in the microvilli and in the cisternae of the gland cell endoplasmic reticulum. The gland cells contain extensive granular endoplasmic reticulum and numerous golgi complexes. The concept of surface specialisation in relation to function is discussed.

The reactions of CF3 radicals with cyclanes and the determination of C?H bond dissociation energies in cyclanes

Abstract: The reactions of CF3 radicals with the C3 to C7 cyclanes and spiropentane were studied and the following Arrhenius parameters were obtained for the reaction CF3 + c-RH CF3H + c-R: Text Table Text. c-RH log A (cm3mole−1sec−1) E (kcal/mole) D(c-R—H) (kcal/mole) Cyclopropane 11.54 8.73 100.7 Cyclobutane 11.66 6.48 95.7 Cyclopentane 12.30 6.18 94.3 Cyclohexane 12.12 6.26 94.9 Cycloheptane 12.43 5.89 94.0 Spiropentane 11.91 8.12 98.8 The CF3 radicals were generated by photolysis of hexafluoroacetone or CF3I and a comparison is made of the utility of the two compounds as radical sources. The Arrhenius parameters are compared with those for corresponding reactions of CH3 radicals with cyclanes, and the general reactivity of cyclic compounds toward free radicals is discussed. An Evans-Polanyi treatment is used to derive CH bond dissociation energies in cyclanes; and these results, based on the reactions of CF3 with cyclanes, agree well with those previously obtained using CH3 plus cyclanes. The final mean values are shown above.