Showing papers by "University of Aberdeen published in 1984"

The extraction of ionic conductivities and hopping rates from a.c. conductivity data

Abstract: Over a wide range of frequencies, the a.c. conductivity of ionic materials shows two regions of frequency-dependent conductivity. These are each characterized by a term Kω p 1− ω n where K, n are constants, ω p is a fundamental frequency identified with the hopping rate and ω is the measuring frequency. This behaviour is an example of Jonscher's Law of Dielectric Response for ionic conductors. In many cases, the region of low-frequency dispersion approximates to a frequency-independent plateau which may be taken as the d.c. conductivity. In others, a significant low-frequency dispersion is present and cannot be ignored in determining the effective d.c. conductivity. A method for the extraction of d.c. conductivities, hopping rates and for estimating carrier concentration effects is described. Data for three different types of material, single-crystal LiGaO2, β″-alumina and Na/Ag β-alumina are used to illustrate the method.

The effects of pressure on the molecular structure and physiological functions of cell membranes

Abstract: The effects of high pressure on the phase state and molecular structure of pure lipid bilayers are discussed. The relations of $\Delta$ H, $\Delta$ S and $\Delta$ V in phase transitions are straightforward and are discernible in heterogeneous bilayers in natural membranes. The effects of pressure on the dynamic properties of bilayer constituents are less clearly understood, but order parameters obtained at pressure by different techniques show agreement. The extent and significance of hydration is poorly understood. Four physiological functions are discussed: passive permeability, active transport, membrane excitability and synaptic transmission. It is shown that a full interpretation of the kinetic effects of pressure on these processes requires much more detailed molecular information than is available at present.

Selectivities of opioid peptide analogues as agonists and antagonists at the δ‐receptor

Abstract: The endogenous opioid ligands interact with more than one of the mu-, delta- and kappa-binding sites. By the use of binding assays and bioassays, enkephalin analogues have been assessed for their selectivity for binding at the delta-binding site and for their agonist and antagonist activities at the delta-receptor. The electrically-induced contractions of myenteric plexus-longitudinal muscle preparations of the guinea-pig ileum were inhibited by mu- and kappa-receptor ligands. Inhibitions were seen with mu-, delta- and kappa-receptor ligands in the mouse vas deferens, mainly with mu-receptor ligands in the rat vas deferens and only with kappa-receptor ligands in the rabbit vas deferens. From observations on a considerable number of [Leu5] enkephalin analogues, it has been concluded that [D-Pen2, D-Pen5] enkephalin and [D-Pen2, L-Pen5] enkephalin are the most selective delta-agonists and that N,N-diallyl-Tyr-Aib-Aib-Phe-Leu-OH is the most selective antagonist (Aib = alpha-aminoisobutyric acid). The binding of these peptides at the delta-site is 99% of the total binding. As to potency, the agonists are superior to the antagonists.

Distortions in the Memory of Children

Abstract: One does not have far to go to find expressions of the belief in the extreme suggestibility of children. But are children more suggestible than adults? The memory of adults is readily contaminated; by comparison, children appear to be more easily influenced in only some instances. If an event is not encoded well, or if a delay weakens the child's memory relative to an adult's, then differences in memory may emerge. On the other hand, if an event is understandable and interesting to both children and adults, and if their memory for it is still equally strong, there may be no differences in suggestibility. If a suggestion is accomplished through the subtle use of language, or if well-developed knowledge structures are required to comprehend the suggestion, then children may actually be less easily influenced. In short, whether children are more or less suggestible than adults probably depends on the interaction of age with other factors.

New infrared band assignments for the arsenate ion adsorbed on synthetic goethite (α-FeOOH)

Abstract: SUMMARY Infrared spectroscopy was used to show that arsenate is adsorbed on the surface of synthetic goethite (α-FeOOH) as the acidic HAsO42- ion, replacing singly coordinated surface OH groups. In this respect, arsenate is analogous to phosphate, but its larger size apparently causes it to interact more strongly with some of the OH groups that remain on the surface. This has suggested an alternative assignment for the absorption bands of these OH groups.

The strength of unsaturated mixtures of sand and kaolin and the concept of effective stress

Abstract: SUMMARY Pastes containing sand and 0, 5, 20 and 80 g kaolin kg−1 mixture were equilibrated at matric potentials of – 2, – 10, – 100 and – 1000 kN m−2 or allowed to air-dry. The strength of cylindrical samples was determined in unconfined compression and by the indirect tensile strength test. Measured strengths are explained using the Coulomb-Mohr theory and the concept of effective stress. At pore water tensions greater than 10 kN m−2 effective stress was the dominant factor in determining compressive and tensile strength. The contrast between this behaviour and that of friable topsoils is discussed.

Studies on fire in Scottish heathland communities. II: Post-fire vegetation development

Abstract: (1) Post-fire regeneration was studied in experimentally burned stands of species-rich and species-poor heath whose age since burning varied from 6 to 39 years, and also in stands burned in earlier fires. (2) Regrowth of Calluna vulgaris and Erica cinerea declined with preburn stand age, with a switch from mostly vegetative growth in young stands to regrowth mainly from seed in older stands. (3) Where Vaccinium myrtillus was present before the fire it reappeared in abundance after the fire and attained dominance where Calluna vulgaris regrowth was slow. In the absence of rapid regrowth of Calluna vulgaris, Deschampsia flexuosa also spread quickly, both vegetatively and by seed produced after the fire. (4) In species-rich heath the numbers and abundances of grass, forb, and lichen species reappearing declined with preburn stand age; there was little grass or forb regrowth in older stands. (5) These trends were still evident 8 years after a fire, and it was concluded that the floristic composition set up immediately after the fire is the main determinant of post-fire development. (6) The result of burning very old stands is extremely slow regrowth, reduction in species diversity and persistence of bare ground for many years after the fire.

The response of prey to Stoat (Mustela erminea) scent

Abstract: Microtus agrestis and Orcadian Microtus arvalis avoid stoat scent and show a reduction in activity when surrounded by it. Such responses probably are adaptive and decrease the chances of an individual suffering predation. Since M. arvalis has been isolated from stoats on Orkney for several millenia the response is innate. For reasons unknown Apodemus sylvaticus does not respond to stoat scent.

Scent marking strategies in hyaenas (Mammalia)

Abstract: Brown hyaenas scent mark by making latrines and depositing onto grass stalks two distinct secretions produced in their anal pouch. The latter behaviour is called pasting. Pastings are found spaced throughout a territory but mainly in the interior where the hyaenas spend most of their time. Latrines are clumped near to, but not along, the border. Computer analyses show that intruders encounter scent marks very soon after entering a territory. Comparison with other species indicates that the length of border to be marked by each individual in a group is the important factor in determining whether they mark throughout the territory or just along the border.

Feldspars and the Thermal History of Igneous Rocks

Abstract: Development of alkali feldspars in igneous rocks can be considered in three stages: magmatic, involving crystal growth from the melt; subsolidus or postmagmatic, involving coherent exsolution and development of regular, strain-controlled crypto or microperthites; and deuteric or hydrothermal involving feldspar-fluid interactions which give rise to irregular coarse microperthites. The interplay of crystallization temperature, cooling rate, deformation, bulk composition and deuteric interactions leads to the variety in alkali feldspar textures.

Thessaly and the Grain Supply of Rome during the Second Century B.C.

Abstract: In a speech attributed by Xenophon to Jason of Pherae, Thessaly is described as an exporter of grain, in contrast with Athens which was obliged to supplement its own foodstocks with the surplus of others. The ancient sources record the dispatch of Thessalian grain to a few Greek cities; but Thessaly must have been a resource for other Greeks in peacetime, as it was in wartime to Roman armies operating in the region in the middle and late Republic. A newly published inscription from Larisa indicates that on one occasion in the middle of the second century B.C. the Thessalians actually provided grain for the Roman populace itself, in response to a request delivered to the Thessalian koinon by a Roman magistrate. Our main objective in this paper is to place this inscription in a suitable historical context and explain its significance for Rome and Thessaly.

The growth and gravitropic responses of wild‐type and auxinresistant mutants of Arabidopsis thaliana

Abstract: Growth and gravitropism have been studied in three mutant strains of Arabidopsis thaliana L, that are resistant to auxin-herbicide. Two of the mutations are allelic and recessive (aux-1 and aux-2) and are unlinked to a dominant mutation, Dwf, which confers a very high level of auxin-resistance and is apparently lethal when homozygous. The aux-1 and Dwf strains have altered response to gravity whereas aux-2 appears to be gravitropically normal. After 96 h in the normal, vertical position only minor differences in elongation were observed between roots of wild-type, aux-1 and aux-2, but the hypocotyls of aux-1 were significantly retarded compared with the gravitropically normal aux-2 and wild-type. In the progeny of selfed Dwf plants, where both normal (dwf) and agravitropic (Dwf) seedlings are present, the Dwf seedlings had much longer roots and shorter hypocotyls than dwf+. During 22 h of continuous stimulation the optimum angle for gravitropism in wild-type roots and hypocotyls was 135° (i.e. the organ points obliquely upwards), with decreasing responses in the order 90° and 45°. The agravitropic nature of the roots of aux-1 was confirmed as no significant response was obtained at any of the stimulation angles. In marked contrast, the negative gravitropic response of aux-1 hypocotyls was greater than the wild-type response in terms of the final angle attained at 22 h, but between 6 and 22 h the elongation rate was lower in aux-1. After varying stimulation periods in the horizontal position, the curvature which had developed, decreased rapidly and almost disappeared during ensuing rotation on clinostats (2 and 4 rpm). Rotation on the clinostats had no effect on the agravitropic behaviour of aux-1.

Coding morphometric characters for constructing distance wagner networks.

Abstract: Distance Wagner networks are unrooted trees which can be used to indicate the relationships between taxa. They are converted into trees or cladograms by being given a root and thus provide one of the techniques of numerical cladistics (Farris, 1972). These networks not only enable one to hypothesize the branching sequence but also the relative extent of anagenesis. These networks can be constructed from continuous and meristic morphometric characters. When morphometric data are used there is disagreement as to the appropriate coding procedure. There has been insufficient analysis of the influence of character coding on these networks and Colless (1980) considers "This whole area has been poorly investigated." Johnson and Mickevich (1977) used gap-coding on their six morphometric characters to convert them to ordinal multistate characters. These were then transformed to binary variables by additive coding. Riska (1979) points out some potential difficulties in comparing evolutionary rates of gap-coded characters, while Colless (1980) regards gapcoding as arbitrary and suggests range coding as an alternative. In reply, Mickevich and Farris (1981) have criticized range coding because it treats all characters as if they have evolved the same amount. However, some overt decision about coding is necessary if the characters have been recorded in different or arbitrary units. This paper attempts to indicate the influence of different coding methods on Distance Wagner networks. The data set is based on a large number of morphometric variables recorded from populations of the western grass snake, Natrix natrix helvetica (Lacepede). This is one of the four semispecies of the grass snake species complex. The systematics of this species complex have been the subject to a series of investigations based on multivariate morphometry (references in Thorpe, 1980). The causative factor for the main phenetic pattern of geographical variation is thought to be historical (microphylogenesis) rather than adaptation to current ecological conditions (Thorpe, 1979) and subsequently Distance Wagner networks have proved extremely useful in understanding the phylogeny and range expansion of the species complex (Thorpe, 1982, 1983, 1984). This has enabled a decision to be made between a primary or secondary origin for the transition (hybrid) zones within the species. Numerical cladistics have also proved useful for investigating variation in other species where the OTUs may be smaller units, i.e., demes (Johnson and Mickevich, 1977) or larger units, i.e., subspecies (Loudenslager and Gall, 1980) than the compound localities used in this study. It is not only the network configuration that is of interest at this level but also the relative extent of anagenesis (Thorpe, 1982, 1983, 1984). The ability ofthe coding procedure to differentiate between the populations is also pertinent because if one cannot differentiate between populations some critical phylogenetic information can be lost, as for example, in the study of range expansion in the eastern grass snake (Thorpe, 1984).

Source-area environments of late Jurassic and early Cretaceous sediments in Southeast England

Abstract: Source-area environments of Late Jurassic and Early Cretaceous sediments in Southeast England. Proc. Geol. Ass. 95 (2), 149-163. Clay mineralogical and palynofacies data indicate that the Jurassic-Cretaceous transition in Southeast England was marked by a change in climate from semi-arid with less than 500 mm of rain per annum, to humid temperate with more than 1000 mm. Soils and weathering profiles on the Anglo-Brabant Massif, the main source of the sediments deposited in the Weald Basin, changed from alkaline and poorly-leached (pedocals) to acidic and well-leached (podzols), and the vegetation became significantly more diverse. Temperatures remained warm throughout, averaging 20-25°C and dropping to about 10°C in cool spells. The climatic change was essentially local due to uplift of various massifs in Northwest Europe and not linked to global shifts in climatic zones. During the Early Cretaceous, faulting caused fluctuations in the elevation of the Anglo-Brabant Massif that were sufficient to continue to affect the climate locally. When the Massif was relatively high, rainfall was also high, ferns and lycopods were widespread, chemical weathering and acid leaching in the soils and weathering profiles were intense, and there was considerable run-off into the basin leading to rapid dumping of sandy sediments. When it was low, there was less rain and hence not as much leaching of the soils, the ferns and lycopods were more restricted in their distribution, and run-off into the basin was reduced. This led to the deposition of mostly fine silt and clay. Evaporation during these periods often raised salinities within the basin.

Primary and secondary transition zones in speciation and population differentiation: a phylogenetic analysis of range expansion.

Abstract: Transition (hybrid, tension, intergradation and contact) zones are the focus of attention of many evolutionary studies. Concepts of speciation and population evolution are dependent on whether the zone is thought to be due to the differentiation of the populations in situ (i.e., primary zones) as in area effect, clinal and stasipatric speciation (Endler, 1977; White, 1978) or due to secondary contact of populations (i.e., secondary zones) as in allopatric speciation or differentiation. It has been pointed out (Endler, 1977) that a major logical flaw in many such studies is that one cannot distinguish between a primary and secondary original event by the nature of the zone. Irrespective of the truth of this it is obviously logically desirable to hypothesize the origin of a zone independent of its nature. Using grass snake populations as an example, this paper describes some ideas

Peritoneal inflammatory cells in plaice, Pleuronectes platessa L.: effects of stress and endotoxin

Abstract: When plaice were injected intraperitoneally with either oyster glycogen or live Vibrio alginolyticus an acute cellular inflammatory response was observed. The duration of these responses, 7 and 15 days respectively, exceeded the time course of the mammalian cellular inflammatory reaction. Peak leucocyte numbers were found at 2–3 days and neutrophils, which were phagocytic, were more numerous than macrophages. Although the increase in macrophage numbers was less marked, these cells appeared more actively phagocytic than neutrophils. Cortisol injections and environmentally-induced stress caused a significant reduction in the extent of inflammatory cell infiltrates, while endotoxin significantly enhanced the response.

Logic, algebra, and databases

Abstract: Inevitably, reading is one of the requirements to be undergone. To improve the performance and quality, someone needs to have something new every day. It will suggest you to have more inspirations, then. However, the needs of inspirations will make you searching for some sources. Even from the other people experience, internet, and many books. Books and internet are the recommended media to help you improving your quality and performance.

The hydration of tricalcium silicate

Abstract: Evidence on the mechanism and products of tricalcium silicate hydration is summarized, and present-day interpretations of that evidence critically discussed, partly with a view to supplying a basis for mathematical modeling of the hydration process. There is general agreement on many, broad features of the reaction and its products, and it should be possible to express many of the proposed hypotheses in mathematical form. Uncertainties nevertheless remain about many questions that are of essential importance if kinetic equations based on an unequivocal understanding of the mechanism are to be formulated. The paper concludes with a list of these questions.

Effects of pre‐ and post‐prandial starvation on meal size and evacuation rate of juvenile Atlantic salmon, Salmo salar L.

Abstract: After a pre-prandial period of starvation or feeding with unlabelled food, 0+ salmon parr (0.8–11.7 g) were fed a test meal of iron particle labelled food and subsequently were again either starved or fed unlabelled food. The quantity of labelled food consumed and the evacuation rate was determined by serial radiographs. In fish of all sizes, pre-prandial starvation causes a larger test meal (as a percentage of body weight) to be consumed when compared to pre-prandially fed fish. In addition, pre-prandial starvation results in relatively larger meals as a percentage of body weight being taken by smaller compared to larger fish. This result was not evident for pre-prandially fed fish. Evacuation rate was unrelated to body size irrespective of feeding history. Post-prandial starvation decreased evacuation rate but this effect was inversely related to the quantity of food consumed. Larger meals were not evacuated differently from smaller meals if feeding occurred post-prandially, irrespective of pre-prandial starvation.

Flavobacterium heparinum 2-O-sulphatase for 2-O-sulphato-Δ4,5-glycuronate-terminated oligosaccharides from heparin

Abstract: The glycosulphatase which hydrolyses the 2-O-sulphate of the disaccharide, 4-deoxy-2-O-sulphato-α-l-threo-hex-4-enopyranosyl uronic acid-(1 4)-2-deoxy-2-sulphamido-6-O-sulphato-d-glucose (ΔUA-2S GlcNS6S), has been isolated from the soluble fraction of disrupted Flavobacterium heparinum. The activity was purified 3300-fold by chromatography on CM-Sepharose CL-6B, hydroxyapatite, taurine-Sepharose CL-4B and blue-Sepharose CL-6B. From sodium dodecylsulphate/polyacrylamide gel electrophoresis, the enzyme was homogeneous and of 62000 Mr. A novel assay was devised using the de-N-sulphonated [1-3H]alditol, 4-deoxy-2-O-sulphato-α-l-threo-hex-4-enopyranosyl uronic acid-(1 4)-2-amino-2-deoxy-6-O-sulphato-d-[1-3H]glucitol (ΔUA-2S [1-3H]GlcNH2-ol-6S). This alditol was shown by 13C-NMR to be desulphated in the analogous manner to the original reducing trisulphated disaccharide. The purified 2-O-sulphatase was completely free of heparinase I, heparinase II (heparitinase), chondroitinases AC, chondroitinase B, the Δ4,5-glycuronidase for heparin Δ4, 5-disaccharides, the 6-O-sulphatase and the 2-sulphamidase. It was optimally active over the range pH 5.5–6.5 and was practically unaffected by Na, K, Ca or Mg ions. Inorganic phosphate inhibited the activity. The Km value for the alditol substrate was 1.22 mmol dm−3. Using 13C-NMR, the 2-O-sulphatase was found to hydrolyse the analogous esters of higher Δ4, 5-oligosaccharides from heparin. This contrasts with the findings of other authors [Dietrich, C. P., Silva, M. E., and Michelacci, Y. M. (1973) J. Biol. Chem. 248, 6408–6415].