Showing papers by "University of Leeds published in 1968"

Is the Troodos Massif of Cyprus a Fragment of Mesozoic Ocean Floor

Abstract: Available geological and geophysical data indicate that the Troodos massif is a Mesozoic volcanic complex the structure of which is comparable with that, deduced from geophysical data, for present day mid-ocean rises. It is suggested that the massif evolved beneath an oceanic Tethys and may represent a fragment of a mid-Tethyan rise.

Factors Influencing Shell Shape in the Mussel Mytilus Edulis

Abstract: An attempt is made to explain the great variations in gross shell morphology noted in field populations of Mytilus edulis.In any one mussel population, variation in shell form can be attributed to differences in age, old mussels having proportionately heavier shells where width often exceeds shell height. This is invariably accompanied by down-turned, divergent umbones and varying degrees of incurvature of the ventral shell margin.Variations in the age structure of mussel populations from different habitats can also account for local variability in shell morphology. Localities where the life expectancy of mussels is increased due to absence of predators (especially in the upper shore) reveal a high incidence of old ‘ungulate’ individuals, whereas populations in which the mussel turnover is more rapid show a preponderance of relatively young mussels.Shell morphology is greatly influenced by growth rate and density. These probably exert their effect through physical compression which is maximum in localities of fast growth and high density and least in areas of slow growth and low density. High compression leads to an elongate form whereas low compression results in higher, more triangular shaped shells. Growth rates and densities, even within the same habitat, are, however, exceedingly variable.Since all environmental conditions vary in both time and space, wide variation in shell morphology is to be expected, even in animals from the same locality.Transplantation experiments indicate that variation in shell morphology is essentially phenotypic, older animals being more likely to exhibit a form which is characteristic of their particular habitat. Smaller mussels from widely different habitats show remarkable similarity in shell morphology.

Measurement of High Gas Temperatures with Fine Wire Thermocouples

Abstract: The recent advent of reliable thermocouple pairs of high melting point has provided new capabilities for high temperature gas measurement. The errors involved in such measurements using fine wire t...

Synthesis of Symmetrical Branch-Guide Directional Couplers

Abstract: A synthesis procedure is described for the design of branch-guide directional couplers which gives results showing a significant improvement over previous approximate methods. The synthesis technique adopted gives exact Butterworth characteristics and almost exact Chebyshev equal-ripple characteristics, the deviations in the latter case being so small that in most practical cases they may be neglected. The design of branch-guide couplers for bandwidths of greater than one octave is demonstrated. The design information for a large number of cases of practical interest is presented in tabular form, and experimental results for several branch-guide couplers constructed in waveguide and in stripline are in good agreement with the theory. The technique could prove valuable in the design of microminiature stripline hybrids and couplers.

Flame structure and flame reaction kinetics II. Transport phenomena in multicomponent systems

Abstract: The transport fluxes in multicomponent flame systems due to diffusion and thermal conduc­tion, and to thermal diffusion and its reciprocal effect, are considered from the standpoint of the extension of the Chapman–Enskog kinetic theory to polyatomic gases by Wang Chang, Uhlenbeck & de Boer (1951, 1964) and the subsequent development by Mason, Monchick and coworkers (1961-66). Equations are given for the various diffusional, thermal diffusional and thermal fluxes which it is necessary to derive in order to obtain reaction rates from experimental temperature and composition profiles in flames; and the organization of com­puter programs for calculation of the multicomponent diffusion and thermal diffusion coefficients and the thermal conductivity is described. The use of matrix partitioning tech­niques in suitable circumstances to reduce the amount of computation is also discussed. The expressions for the transport fluxes are next used to derive equations for the mole fraction and temperature gradients in flowing reaction systems such as flames where trans­port processes and reaction occur side by side. From the mole fraction and temperature at one point in the system it is then possible by a numerical integration method such as the Runge–Kutta procedure to compute the complete composition and temperature profiles. Two methods of obtaining the mole fraction and temperature gradients are described, one of which, the Stefan–Maxwell formulation, leads to the more economical computation. A hydrogen–oxygen–nitrogen–steam mixture was chosen under conditions which simu­lated the pre-reaction region of a hydrogen–oxygen–nitrogen flame that had been studied experimentally, and the detailed composition profiles due to diffusion were computed. The experimental method of measurement involved continuous sampling from the flame and mass spectrometric analysis, a technique which had not previously been checked on a flame system itself. Good agreement between theory and experiment was found when thermal diffusion was considered in the calculation, although the computed hydrogen profile was slightly displaced with respect to the experimental one. This last observation is possibly due to diffusion effects in the pressure gradient at the probe tip. Otherwise the experimental technique seemed to be satisfactory. The computed profiles also showed a number of interesting features such as a maximum in the nitrogen concentration profile caused by thermal diffusion effects.

Salt Weathering in Deserts

Abstract: WEATHERING of rocks as the result of pressures exerted by the crystallization of salts from solutions in confined spaces has been recognized for many years. Studies of crystal growth pressures have been summarized by Buckley1. The roles of such pressures in rock weathering have been described by Birot2, and analysed by Wellman and Wilson3, who stated that for rocks of equal mechanical strength those with large pores separated from each other by microporous regions are most liable to salt weathering. The process is pronounced in desert and coastal areas. It is likely to be most effective (i) in the humid deserts of western littorals where the supply of salts from fogs and chemical weathering is accompanied by frequent wetting and drying of the surface, and (ii) around the margins of playas and along channels in desert areas where salts tend to be concentrated and wetting and drying is most frequent. We accept the effectiveness of salt crystallization pressures, the Salzsprengung of German authors, but we suggest that there are two additional factors associated with salts which may lead to the disintegration of rock: (i) stresses exerted by the expansion of many salts in confined spaces as they are heated, and (ii) stresses caused by hydration of certain salts in confined spaces.

Halophytes, succulence and sodium in plants—a unified theory

Abstract: Summary Reference to the relevant literature shows that sodium ions can bring about increased succulence and, with regard to their response to sodium, halophytes differ from mesophytes only in degree, not in kind. Attention is drawn to the fact that the effect of sodium parallels the effect of increased light and aridity. It is proposed that these three factors exert the same effect on plant cells, namely to bring about an increased ATP synthesis. The mechanism whereby sodium ions bring this about is thought to be due to the reversal of a membrane-bound ATPase which can otherwise act as a sodium pump. Aridity brings about increased concentration of sodium ions in the xylem sap and light brings about increased ATP synthesis via photophosphorylation. It is pointed out that the cell membranes must possess certain other physiological properties, if sodium is to act in the manner described. Attention is drawn to the fact that such an action of sodium ions would provide a homeostatic mechanism whereby the plant cell could avoid the detrimental effect of high concentrations of toxic ions.

The effect of pollen grains on infections caused by Botrytis cinerea Fr.

Abstract: SUMMARY The addition of pollen to spores of Botrytis cinerea Fr. in droplets of distilled water stimulates spore germination, growth of germ tubes and lesion development. Aqueous diffusate from pollen is as effective as pollen grains, and frozen pollen is more stimulatory than freshly collected pollen. The presence of pollen grains reduces considerably the number of spores needed to allow infection to occur. The lost germination ability and infectivity of old spores is restored by pollen. The stimulatory effect of the presence of pollen has been demonstrated both in vitro and on the surfaces of strawberry petals, strawberry fruits and broad bean leaves. Complete removal of the source of pollen, the anthers from strawberry fruits, markedly affected the speed and severity of infections of strawberry fruits. On broad bean leaves the addition of pollen grains to spores induced the development of spreading aggressive lesions. Preliminary work indicates that the effective principle in pollen is water-soluble, dialysable and heat-stable. Although glucose and fructose are important components of diffusate, neither glucose solution nor fructose solution nor a mixture of the two showed as marked effects as did pollen. Orange juice produces similar effects.

Acetate-nonutilizing Mutants of Neurospora crassa II. Biochemical Deficiencies and the Roles of Certain Enzymes

Abstract: The levels of Krebs cycle, glyoxylate cycle, and certain other enzymes were measured in a wild-type strain and in seven groups of acetate-nonutilizing (acu) mutants of Neurospora crassa, both after growth on a medium containing sucrose and after a subsequent 6-hr incubation in a similar medium, containing acetate as the sole source of carbon. In the wild strain, incubation in acetate medium caused a rise in the levels of isocitrate lyase, malate synthase, phosphoenolpyruvate carboxykinase, acetyl-coenzyme A synthetase, nicotinamide adenine dinucleotide phosphate-linked isocitrate dehydrogenase, citrate synthase, and fumarate hydratase. Isocitrate lyase activity was absent in acu-3 mutants; acu-5 mutants lacked acetyl-coenzyme A synthetase activity; and no oxoglutarate dehydrogenase activity (or only low levels) could be detected in acu-2 and acu-7 mutants. In acu-6 mutants, phosphoenolpyruvate carboxykinase activity was either very low or absent. No specific biochemical deficiencies could be attributed to the acu-1 and acu-4 mutations. The role of several of these enzymes during growth on acetate is discussed.

An investigation into some of the underlying associative verbal processes of the stroop colour effect

Abstract: The Stroop test was examined to throw some light on the verbal basis of the test. When words are presented printed in the wrong colour it is found that the written word provides more interference with response to the colour of print than occurs the other way round (the Stroop effect). It was shown that, by allowing subjects to match the colour of the print with colour patches instead of words, the interference due to the written word can be considerably reduced. In a further experiment, associations were formed by the subjects between nonsense syllables and colours in the course of a paired-associate learning task. When nonsense syllables were presented printed in colours different from those associated with them, it was found that the interference effects depended upon the direction of the stimulus-response association in the paired-associate experiment. It is concluded that the underlying processes in the Stroop effect are primarily verbal and depend partly upon the directionality of previously establis...

Experiments on the resynthesis of symbiosis in Convoluta roscoffensis with different flagellate cultures

Abstract: The symbiotic condition of Convoluta roscoffensis has been resynthesized in vitro by feeding new-born colourless larvae with various clones of Platymonas convolutae Parke & Manton available in culture. Greening has also been brought about by feeding larvae with other species distinguishable from the natural symbiont by pyrenoid characters, but subsequent growth of the greened larvae was less and the length of time required for greening greater. The minimum presentation time effective in initiating greening with alien symbionts in 100% of tested larvae was also greater. Cell multiplication of successful symbionts is mitotic, division stages being demonstrated in sections of worms with different types of symbiont. When cultures of potential symbionts were made available competitively in pairs, greening normally involved only one member of a pair, success being apparently determined by the order of relative efficiency demonstrated in the single-culture infections. A chimaeral condition, with two different symbionts present together, was produced and is demonstrated—but only as a temporary phase in an experiment designed to give an alien symbiont a very long start before admitting the real one. In this experiment effective greening with Prasinocladus marinas did not impede prompt entry of Platymonas convolutae when it was supplied, and this was followed by rapid and complete elimination of the alien symbiont. An interpretation of these various findings is discussed in a preliminary way.

The distribution of monoamines in the hypothalamus of the Japanese quail, Coturnix coturnix japonica.

Abstract: The distribution of monoamines in the hypothalamus of the Japanese quail (Coturnix coturnix japonica) has been studied using a histochemical fluorescence technique. In the posterior hypothalamus catecholamine-containing nerve fibres are localised in the nucleus tuberis and nucleus hypothalamicus posterior medialis and are linked by fluorescent tracts running in the stratum cellulare internum. Further tracts may be traced from the nucleus tuberis around the base of the third ventricle to the sub-ependymal layer of the median eminence, where they then appear to pass through the hypothalamo-hypophysial neurosecretory tract to terminate in the palisade zone on the portal vascular bed. The innervation of the palisade layer by catecholamines is sparse. The fluorescent terminals are spread evenly throughout both the anterior and posterior divisions of the median eminence. There is no monoamine innervation of the pars nervosa. The paraventricular organ has both 5-hydroxytryptamine- and catecholamine-containing cell bodies and axons may be traced into the region of the nucleus hypothalamicus posterior medialis. In the anterior hypothalamus the neurosecretory paraventricular nucleus contains many catecholamine nerve fibres and terminals. These are linked by fibre tracts to the nucleus basalis and to the nucleus hypothalamicus posterior medialis. The supraoptic nucleus is less well innervated although a dense accumulation of fibres lies in the preoptic recess. The latter is thought to give rise to long axons which pass in association with the neurosecretory tract to end in the nucleus tuberis.

The Radiolysis of aqueous Solutions of Oxybromine Compounds; the Spectra and Reactions of BrO and BrO_2

Abstract: Pulse radiolysis supplemented by steady state radiolysis of aqueous solutions containing some of the following solutes: N 2 O, Br - , BrO - , BrO - 2 , BrO - 3 , CO 2- 3 , and OH - has been used to identify the absorption spectra of BrO ( λ max = 350 nm) and BrO 2 ( λ max = 475 nm) and to evaluate the following rate constants (units, M -1 s -1 ): e - aq. + BrO - → Br - + O - (2.3 ± 0.5 x 10 10 ); e - aq. + BrO - 2 → BrO + O 2- (1.8 ± 0.2 x 10 10 ); e - aq. + BrO - 3 → BrO 2 + O 2- (4.1 ± 0.2 x 10 9 ); OH + BrO - → OH - + BrO (4.5 x 10 9 ); O - + BrO - → BrO + O 2- (4.6 x 10 9 ); OH + BrO - 2 → OH - + BrO 2 (1.9 x 10 9 ); Br - 2 + BrO - → BrO + 2Br - (8.0 ± 0.7 x 10 7 ); Br - 2 + BrO - 2 → BrO + Br - + BrO - (8.0 ± 0.8 x 10 7 ); BrO + BrO - 2 → BrO - + BrO 2 (3.4 ± 0.7 x 10 8 ); 2BrO 2 ⇌ Br 2 O 4 ( k = 1.4 x 10 9 and K = 19 M -1 ); Br 2 O 4 + OH - → H + + BrO - 2 + BrO - 3 (7 x 10 8 ); 2BrO + H 2 O → BrO - + BrO - 2 + 2H + (4.9 ± 1.0 x10 9 ); CO - 3 + BrO - → CO 2- 3 + BrO (4.3 ± 0.4 x 10 7 ); CO - 3 + BrO - 2 → CO 2- 3 + BrO 2 (1.1 ± 0.1 x 10 8 ). In contrast to their chlorine analogues, little is known of the chemistry of the bromine oxides in aqueous solution. In this paper we describe the methods of formation and identification of the radicals BrO and BrO 2 , and their reactions with various oxybromine species, as elucidated by the techniques of pulse radiolysis and kinetic spectroscopy applied to aqueous solutions containing oxybromine anions.

The water intake of ewes.

Abstract: 1. Two experiments were carried out with non-pregnant ewes in which individual drymatter intake (DMI) and total water intake (TWI) were measured. TWI was closely correlated with DMI; TWI/unit DMI was higher for silage than for cubed dried grass and with both foods water intakes were higher than with long hay.2. Twelve ewes were fed on silage and twelve on hay from the 9th to the 19th week of pregnancy. TWI/unit DMI of each feed doubled during this period. Another twenty-four ewes were fed on silage from the 14th to the 20th week of pregnancy. TWI/unit DMI was positively related to litter size.3. Fifteen ewes were fed on hay from the 4th week of pregnancy until the 7th week of lactation. Milk yield was estimated weekly. Six non-pregnant ewes were controls. TWI/unit DMI for the seven twin-bearing and the nine single-bearing ewes in the last 4 and 3 weeks of pregnancy respectively was significantly higher than that of the six non-pregnant ewes. In the control group TWI/unit DMI was closely related to environmental temperature. In the first 4 weeks of lactation TWI/unit DMI was greater than the sum of TWI/unit DMI of the non-pregnant ewes plus the water in the milk.4. The results supplement those used by the Agricultural Research Council (1965) to assess the water requirements of sheep.

Water movements and their role in rocky shore ecology

Abstract: Water movement is considered in terms of water flow and wave crash, although differentation is not always possible. Ocean currents and residual drift mainly effect geographical distributio...

The electrical resistivity of nickel and its alloys

Abstract: The electrical resistivity has been measured over the temperature range 1 °K to 120 °K in dilute alloys of nickel with Pd, Cu, Co, Fe, Mn, Cr, V and Ti. The impurity (residual) resistivity is very small for alloys of nickel with its near neighbours in the periodic table, Pd, Cu, Co, Fe and Mn, but is an order of magnitude greater for alloys containing Cr, V and Ti. The ice-point values of the deviations from Matthiessen's rule are unusually large in the Ni-Co, Ni-Fe, Ni-Mn, and Ni-Cr alloys, somewhat smaller in the Ni-Cu, Ni-V and Ni-Ti alloys, and negligible in Ni-Pd. These results are interpreted on the assumption that the departures from Matthiessen's rule arise because of spin mixing between electrons in the spin downward arrow and spin upward arrow bands. On this basis it has proved possible to separate the two components of impurity resistivity for the two spin directions. The values obtained correlate well with the known band structure and impurity states of nickel and its alloys. In addition, the temperature dependence of the deviations in all the measured alloys can be explained on the basis of spin mixing, with the only adjustable parameter being capital Lambda, Greek(upward arrowdownward arrow), the mean free path between spin flips.

Acetate-nonutilizing Mutants of Neurospora crassa I. Mutant Isolation, Complementation Studies, and Linkage Relationships

Abstract: Sixty mutants of Neurospora crassa unable to grow on acetate as sole source of carbon, but able to utilize sucrose, were isolated. On the basis of complementation tests, they were divided into seven groups, each group representing a different gene. Six of the genes have been mapped; no two are closely linked. These loci have been designated acu-1 to acu-7. Mutations at four of these loci result in poor germination of ascospores.