Showing papers by "University of St Andrews published in 1976"

A rational model for Langmuir circulations

Abstract: A realistic theoretical model of steady Langmuir circulations is constructed. Vorticity in the wind direction is generated by the Stokes drift of the gravity-wave field acting upon spanwise vorticity deriving from the wind-driven current. We believe that the steady Langmuir circulations represent a balance between this generating mechanism and turbulent dissipation.Nonlinear equations governing the motion are derived under fairly general conditions. Analytical and numerical solutions are sought for the case of a directional wave spectrum consisting of a single pair of gravity waves propagating at equal and opposite angles to the wind direction. Also, a statistical analysis, based on linearized equations, is developed for more general directional wave spectra. This yields an estimate of the average spacing of windrows associated with Langmuir circulations. The latter analysis is applied to a particular example with simple properties, and produces an expected windrow spacing of rather more than twice the length of the dominant gravity waves.The relevance of our model is assessed with reference to known observational features, and the evidence supporting its applicability is promising.

Acid-Base Properties of Electronically Excited States of Organic Molecules

Abstract: Publisher Summary This chapter discusses acid–base properties of electronically excited states of organic molecules. Excited state pK-values are most easily accessible through the use of the Forster cycle. To perform this calculation for a particular molecule, it is necessary to know the ground state equilibrium constant for the reaction in question and to have some measure of the energy difference between the lowest vibrational level of the ground and the excited state in both the B and BH + forms. The effects of solvation on 0–0 energies are discussed. The changes in molecular fluorescence with acidity give information about the protolytic behavior of the excited singlet state of a compound. Two techniques, phase and pulse fluorometry, are used for the direct measurement of fluorescence decay rates. The excited state acid-base behavior of molecules has direct implications in the field of analytical fluorimetry and phosphorimetry.

An experimental investigation of olivine morphology

Abstract: Olivine crystals can adopt ten types of shape. Experimental crystallization of eight rock melts shows that there is a systematic change from polyhedral or granular olivines → hopper olivines → branching olivines → randomly oriented chain olivines → parallel-growth chain olivines → chain+lattice olivines → plate or feather olivines, with increase in cooling rate and with increase in degree of supercooling. This sequence involves changes from complete to progressively less complete crystals and from equant habit to elongate bladed habit (c>a≫b) to tabular habit (a≃c ≫ b). The sequence is not affected by the phase relations of the melt. The larger the olivine content of a melt the slower the cooling rate at which a particular olivine shape grows, whereas the lower the melt viscosity, the greater the cooling rate. Irrespective of the melt composition, comparable crystal shapes grow at the same degrees of supercooling. By comparison of the shapes of olivine crystals in experiments with those in rocks of similar composition, it is possible to deduce the cooling rate through the olivine crystallization interval and the approximate degree of supercooling at which the olivine crystals nucleated and grew in the rocks. The various shapes of skeletal olivines in many picrites, olivine-rich basalts and the Archaean “spinifex” rocks are not due to rapid cooling, but to rapid olivine growth caused by the high normative olivine content of the magma.

The mechanism of chill‐ and drought‐hardening of phaseolus vulgaris leaves

Abstract: SUMMARY Drought-hardening at 25° C, 40% R.H. by witholding water from the roots for 4 days is as effective in preventing chilling-injury to the leaves of Phaseolus vulgaris as 4 days chill-hardening at 12° C, 85% R.H. During chill-hardening the degree of unsaturation of the fatty acids associated with the phospholipids increased and this was considered to prevent water loss and electrolyte leakage by lowering the temperature at which phase changes occur in the membrane lipids to below 5° C (Wilson and Crawford, 1974b). However, drought-hardening at 25° C, 40% R.H. resulted in no increase in the degree of unsaturation of the phospholipids or glycolipids suggesting that lipid phase changes are not the primary cause of chilling-injury. Furthermore, a re-examination of the conditions under which water and electrolytes leak from the leaves of P. vulgaris indicates that phase changes in the membrane lipids of the plasmalemma and other organelles at 5° C are only of minor importance in determining the extent and speed of chilling-injury. The primary cause of chilling-injury to P. vulgaris leaves on transfer from 25° C, 85% R.H. to 5° C, 85% R.H. is leaf dehydration due to the opening of the stomata at a time when the permeability of the roots to water is low. The primary factor inducing hardening against chilling-injury in P. vulgaris is a water stress and not low temperature per se.

Evidence for involvement of nuclear envelope nucleoside triphosphatase in nucleocytoplasmic translocation of ribonucleoprotein

Abstract: A NUCLEOSIDE triphosphatase activity showing broad substrate specificity has been found in nuclear envelope isolated from rat and pig liver, Tetrahymena macronucleus, and cultured SV-3T3 fibroblasts using the method of Harris and Milne1, and has been extensively characterised in this laboratory. There is evidence that in purified nuclear envelopes there is only one enzyme which catalyses nucleoside triphosphate hydrolysis: the activities observed with different substrates and metal ions are not additive, and they show a single pH optimum, the value of which varies with the source of the envelopes2. This enzyme seems to be localised in the nuclear pore complexes3. Several reports4–13 have indicated that ATP markedly stimulates the release of mRNA from isolated nuclei, but no evidence has been presented to suggest that this stimulation necessarily requires hydrolysis of the ATP. In this paper, however, we present evidence that the nucleoside triphosphatase is an essential component of the mechanism of nucleocytoplasmic translocation of ribonucleoprotein.

Palaeozoic and Mesozoic age trends for some ring complexes in Niger and Nigeria

Abstract: OVER 40 individual granitoid ring complexes exhibiting similar petrological and geochemical variations have been recognised in Nigeria1. They range in size from 1,500 km2 to < 2 km2. The ring complexes form part of a more extensive chain along the ninth meridian, extending from the north of the Air Massif through southern Niger and northern Nigeria to the northwestern margin of the Benue Trough in Nigeria (Fig. 1). In general the suite of Nigerian complexes are concentrated in a 200-km wide north-south zone and centred around the Jos Plateau. We have previously2 investigated the group of ring complexes forming the central zone of anorogenic magmatism in Nigeria, and found a southerly decreasing age trend from early Jurassic to mid-Jurassic times. We give here further evidence for this trend, and point out that its recognition may be useful in ascertaining the drifting motion of the African continent.

Garnet and pyroxene compositions in some diamondiferous eclogites

Abstract: Analyses are reported for garnet and pyroxene from 17 eclogites that contain diamond. The garnets contain small but significant contents of Na, Ti and P and the pyroxenes contain traces of K. The diamond-bearing eclogites do not constitute a unique compositional group but show a range of mineral compositions consistent with a very high P-T environment.

Vinamidine und Vinamidiniumsalze — Beispiele stabilisierter Push‐Pull‐Alkene

Abstract: Der Name Vinamidine wird fur 1,5-Diazapentadiene vorgeschlagen; diese Verbindungen lassen sich als vinyloge Amidine und zugleich als push-pull-substituierte (und damit stabilisierte) Alkene ansehen. Vinamidin- und Vinamidinium-Strukturelemente konnen auch Teile von Ringsystemen sein. Charakteristisch fur diese Verbindungsklasse sind ihre Reaktionsfahigkeit gegenuber Elektrophilen (an Cβ) und Nucleophilen (an Cα) sowie ihr regenerativer Charakter, d. h. ihre Tendenz zu Substitutions- anstelle von Additionsreaktionen. Besonders die Umsetzungen von Vinamidiniumsalzen mit Nucleophilen sind synthetisch wertvoll: Sie fuhren z.B. zu Pyrazolen, Oxazolen, Pyrimidinen, Diazepinen, Chinolinen und Chinolizinen.

Some physical properties of GeAsSe infrared optical glasses

Abstract: This paper presents measured data on glass transition temperature, thermal expansion, density, hardness, refractive index and electron microscopy of GeAsSe glasses and bring together some literature data on viscosity and mechanical properties Interpretation of this information to identify suitable compositions for bulk synthesis is discussed

13.—Some Integral Inequalities

Abstract: The theorems in this paper deal with the analogues for integrals of Hardy's Series Inequality and its generalisations.

The formation of current sheets during the emergence of new magnetic flux from below the photosphere

Abstract: Solar flares are frequently observed to occur where new magnetic flux is emerging and pressing up against strong active region magnetic fields. Since the solar plasma is highly conducting, current sheets develop at the boundary between the emergent and ambient flux, provided the two magnetic fields are inclined at a non-zero angle to one another. The present paper gives a simple two-dimensional model for the development of such sheets under the assumptions that no reconnection occurs and that the surrounding field remains a potential one. By using complex variable techniques, the position, orientation and shape of a current sheet may be determined, as well as the excess magnetic energy associated with it. Two examples are considered. The first, in which the ambient field is bipolar, may model new flux emergence near the edge of an active region, while the second example assumes a constant ambient field and may approximate the so-called ‘fibril crossings’ which occur prior to some flares. In each case, the current sheets are curved, and the magnetic energy which is stored in excess of potential is sufficient to supply a solar flare when the sheets are long enough.

Non-radiative transitions

Abstract: The problem of non-radiative transitions in solids is treated from two different points of view. One is a single configurational coordinate model, while the second is a suitable generalization of the one-dimensional molecular crystal model of Holstein in which the intermolecular coupling is explicitly taken into account. Results for the transition rate are obtained for three cases: arbitrary-coupling, zero temperature; weak-coupling, finite temperature; strong-coupling, high temperature. These are compared with the results of other workers, obtained by alternate methods.

Reactions of the spiny lobster,Palinunis vulgaris, to substrate tilt (I.)

Abstract: Movements of legs on a tilting footboard during fore-aft and side-side tilts elicit a number of different reactions in the spiny lobster,Palinurus vulgaris. Most prominent among these are the predominantly phasic equilibrium reactions of the antennae in the direction opposite to footboard tilt, and the compensatory phasic and tonic deviations of the eyestalks in the direction of footboard movement. Systematic movements of the abdomen and uropods also take place, and the legs display resistance reactions which oppose board movement. Stimulation of a single leg is sufficient to produce the major components of these responses. After stiffening of the C-B joints reactions fail to appear. Mechanism and functional significance of these reactions are discussed in the context of the relevant biological stimuli.

Transcription of genetic information in amphibian oocytes

Abstract: The lampbrush chromosomes of amphibian oocytes are highly active in RNA transcription. The extent of transcription and features of the transcriptional product have been studied both cytologically and by molecular hybridization. Each lampbrush loop is considered to be a unit of transcription which generates many primary transcript molecules. InTriturus the primary transcripts can be recovered as nuclear RNP particles which can be dispersed in the presence of formamide to give linear forms of up to 20 μm or more in length. Only part of the RNA extracted from nuclear RNP codes for protein, the remainder containing non-informational repetitive sequences. Although about 4% of the chromosomal DNA ofTriturus is transcribed during oogenesis, only 0.05–0.1% of the DNA is expressed as coding sequences. This informational sequence complexity is equivalent to approximately 104 different mRNA species. A model for the organization of genetic sequences in the lampbrush chromosomes is suggested.

Current sheet models of solar flares

Abstract: Current sheets have been suggested as the site for flare energy release because they can convert magnetic energy very rapidly into both heat and directed plasma energy. Also they contain electric fields with the potential of accelerating particles to high energies.

Variability of outcrossing frequency in Senecio vulgaris L.

Abstract: Using a marker gene controlling capitulum type, 30 lines derived from each of a dune and a garden population of Senecio vulgaris L. were tested for their tendency to outcross. Compared with previous estimates of outbreeding in the species a relatively high degree of outcrossing was found in both experimental populations (an overall average of 22·4 per cent). It was shown that the dune population had a slightly greater mean outcrossing frequency than the garden population but, more importantly, had significantly more heritable variation (between lines) for this trait. In discussion, some reasons are advanced to account for the unexpectedly high level of outcrossing in both populations. It is suggested that the presence of significant genetic variation for outcrossing within the dune population may provide for adaptive flexibility in the native dune habitat where there is much spatial and temporal variation of the environment.

Variation within common groundsel, senecio vulgaris l.

Abstract: SUMMARY Variation within and between four populations of the highly plastic and ephemeral plant Senecio vulgaris L. has been evaluated for several quantitative characters in three environments and at four stages of development. The populations were from soils of high and low nutrient levels and in habitats of different degrees of exposure. There are significant differences between the means and phenotypic variances of populations for most characters but the degree of difference tends to change both in level and direction between environments and throughout development. However, there are some consistent differences and these seem closely related to the differences between habitats. Of special interest was the variation within populations where it emerged that samples of the populations from sites that were highly heterogeneous for exposure showed much more heritable variation for height and several other characters which might influence the expression of stature than samples from apparently homogeneous sites. It is suggested that though S. vulgaris is capable of showing a wide measure of phenotypic plasticity which could be of adaptive significance in the field, many differences between and within populations may in part be attributed to gene differences that are likely to have resulted from the action of natural selection.

Effects of trauma on cell production in the subependymal layer of the rat neocortex

Abstract: The response of the subependymal layer (SEL) of the adult rat neocortex was studied after direct trauma, using X-rays, and indirect trauma, after placing a stab wound in the hemisphere close by, but without injuring, the SEL. The SEL in the injured hemisphere underwent marked hypertrophy and hyperplasia by ten days after injury, but the contralateral SEL was unaffected. It is proposed that hyperplasia of the SEL was brought about by the production of immature glial cells in response to the presence of a mitotic stimulant which had diffused into the SEL from the site of injury. X-irradiation caused 98% reduction in the numbers of dark subependymal cells within 24 hours but their numbers recovered within 10 days. In the experiment involving a combination of direct and indirect trauma, the recovery of dark cell number after irradiation was significantly enhanced in the injured, when compared to the uninjured hemisphere. This result supports the hypothesis that stimulation of mitosis by an anti-chalone-like substance, released after knife wounding, had occurred. This substance is likely to be a constituent of plasma, rather than a breakdown product of damaged brain parenchyma. Endogenous division and/or cellular importation may account for the recovery of the SEL observed in these experiments.

Ultrastructure of the terminals of an identified 5-hydroxytryptamine-containing neurone marked by intracellular injection of radioactive 5-hydroxytryptamine.

Abstract: The axons and terminal processes of an identified 5-hydroxytryptamine-containing neurone were located for study with the electron microscope. Tritiated 5-hydroxytryptamine was injected into the neurone's cell body, and after allowing time for the radioisotope to pass along the processes of the neurone, tissue was examined by electron microscope autoradiography. Terminal processes were observed at approximately 1 cm from the injected cell body, in areas of the nervous system where previous electrophysiological work had shown the presence of postsynaptic neurones. Dense-cored vesicles of mean diameter 100 nm were observed in the axons and terminal processes of the neurone. The terminal processes also contained aggregates of clear vesicles of mean diameter 65 nm. Structures resembling lysosomes, which were frequently labelled, were present in the axons of the neurone. No membrane specializations associated with typical synapses were observed.