Showing papers by "University of St Andrews published in 1989"

Noise in solid-state microstructures: A new perspective on individual defects, interface states and low-frequency (1/ƒ) noise

Abstract: In very small electronic devices the alternate capture and emission of carriers at an individual defect site generates discrete switching in the device resistance—referred to as a random telegraph signal (RTS) The study of RTSs has provided a powerful means of investigating the capture and emission kinetics of single defects, has demonstrated the defect origins of low-frequency (1/ƒ) noise in these devices, and has provided new insight into the nature of defects at the Si/SiO2 interface

Frameworks of analysis for the neural representation of animate objects and actions.

Abstract: A variety of cell types exist in the temporal cortex providing high-level visual descriptions of bodies and their movements. We have investigated the sensitivity of such cells to different viewing conditions to determine the frame(s) of reference utilized in processing. The responses of the majority of cells in the upper bank of the superior temporal sulcus (areas TPO and PGa) found to be sensitive to static and dynamic information about the body were selective for one perspective view (e.g. right profile, reaching right or walking left). These cells can be considered to provide viewer-centred descriptions because they depend on the observer's vantage point. Viewer-centred descriptions could be used in guiding behaviour. They could also be used as an intermediate step for establishing view-independent responses of other cell types which responded to many or all perspective views selectively of the same object (e.g. head) or movement. These cells have the properties of object-centred descriptions, where the object viewed provides the frame of reference for describing the disposition of object parts and movements (e.g. head on top of shoulders, reaching across the body, walking forward 'following the nose'). For some cells in the lower bank of the superior temporal sulcus (area TEa) the responses to body movements were related to the object or goal of the movements (e.g. reaching for or walking towards a specific place). This goal-centred sensitivity to interaction allowed the cells to be selectively activated in situations where human subjects would attribute causal and intentional relationships.

Dynamic light scattering by non-ergodic media

Abstract: We consider dynamic light scattering (DLS) by non-ergodic media, such as glasses or gels, in which the scattering elements are able only to make limited Brownian excursions about fixed average positions. We point out that, for such media, the time-averaged correlation function of the intensity of scattered light, the quantity obtained from a single DLS measurement, is different from the ensemble-averaged function. An expression for this time-averaged intensity correlation function is derived and its properties and experimental analysis are discussed. Some of the literature on DLS by polymer gels is re-evaluated in the light of these new theoretical predictions.

An approach to persistent programming

Abstract: This paper presents the identification of a new programming language concept and reports our initial investigations of its utility. The concept is to identify persistence as an orthogonal property of data, independent of data type and the way in which data is manipulated. This is expressed by the principle that all data objects, independent of their data type, should have the same rights to persistence or transience. We expect to achieve persistent independent programming, so that the same code is applicable to data of any persistence. We have designed a language PS-algol by using these ideas and constructed a number of implementations. The experience gained is reported here, as a step in the task of achieving languages with proper accommodation for persistent programming.

Population genetic structure and outcrossing rate of Arabidopsis thaliana (L.) Heynh.

Abstract: The population genetic structure of Arabidopsis thaliana was investigated in and among 16 British populations by means of an electrophoretic survey of nine enzyme systems. Seven out of 17 allozyme loci examined were polymorphic. One polymorphic locus was used as a marker locus for estimating outcrossing rates. No outcrossing was observed within any of seven populations surveyed and a joint estimate of the upper limit of outcrossing, tu, indicated that average outcrossing in the wild does not exceed 0·3 per cent. The genetic structure of A. thaliana as measured by Nei's gene diversity statistics, gene correlation F statistics, and estimates of multilocus genotypic diversity is concordant with that which is expected for a plant species which shows almost complete uniparental reproduction. Despite considerable genetic differentiation between populations, there was no evidence of a division between English and Scottish populations based on genetic distance.

The origins of utilization behaviour

Abstract: Utilization behaviour has previously been described clinically by Lhermitte (1983). An experimental investigation is reported of utilization behaviour in a patient with a localized inferior medial bifrontal lesion. The patient picked up and used irrelevant objects not only when placed directly in front of him—the procedure developed by Lhermitte—but also when he had been instructed to carry out other tasks and his attention had not been directed to the objects. The behaviour occurred most frequently in the brief intervals between tasks, and more often when auditory-verbal rather than visuomotor tasks were being performed. The results are interpreted within an information-processing model of frontal lobe function. A differentiation is made between two forms of utilization behaviour—an ‘incidental’ form, as exhibited by the patient, and an ‘induced’ form where it occurs only when Lhermitte's procedure is adopted.

Oxygen toxicity and superoxide dismutase as an antioxidant in physiological stress

Abstract: Although oxygen is vital for all aerobic life forms, excessive levels of oxygen free radical production can lead to potentially lethal oxidative reactions. The role of superoxide dismutase is examined as an integral part of the defence against oxidative injury resulting from various physiological stresses.

Toxicity of pyrethroid insecticides to fish

Abstract: A selected review of the biological, chemical and environmental factors that affect the acute and chronic, lethal and sublethal toxicity of pyrethroid insecticides to fish is presented. Pyrethroid insecticides are extremely toxic to fish; for example, 96—h LC50 values are in the nmol/L range. The symptoms associated with acute lethality suggest that effects on the nervous system, respiratory surfaces and renal ion regulation are associated with the mechanism of lethal action in fish. Qualitative structure—activity relationships indicate that the structural features required for good insecticidal activity and for lethality to fish are the same. Lethality also varies with biological (species, size) and environmental (temperature, sediment) factors. Some of these effects may be related to bioavailability and rates of pyrethroid biotransformation. Chronic exposure studies indicate that newly hatched larvae or early juveniles are the life stages most sensitive to pyrethroids. Exposures of fish to sublethal concentrations of pyrethroids have resulted in decreased growth and impaired swimming performance. The effects on bioenergetics and energy metabolism are variable.

Bird song learning: causes and consequences

Abstract: This article starts with a brief description of the phenomenon of song learning in birds, and then outlines various consequences that it has for the individuals that show it and the groups to which they belong. Among these are the following features, each of which has been described in at least some species: the sharing of song between kin and between neighbours; changes in song with time; changes with distance, including the phenomenon of dialects. The final section is a discussion of which of these consequences may have functional significance and so be likely to be an advantage of song learning. It is suggested that cultural evolution, geographical variation and dialect boundaries, being features of populations rather than individuals, are epiphenomena without functional significance in themselves. However, song learning may confer advantages stemming from the copying process itself, in interactions with neighbours and in matching song to habitat. The evidence that learnt dialects have a role in assort...

Enhanced mode locking of color-center lasers.

Abstract: A significant enhancement in the mode locking of a KCl:Tl color-center laser has been observed when a length of optical fiber having positive group-velocity dispersion was incorporated within an external control cavity. Pulse durations of ~260 fsec were obtained by this method, representing a compression factor ~60× that with the color-center laser alone. Similar results have also been observed with an InGaAsP semiconductor diode amplifier as the nonlinear element within the control cavity.

Modulation of event-related potentials by word repetition: the effects of inter-item lag.

Abstract: The modulation of event-related potentials by word repetition was investigated in two experiments. In both experiments, subjects responded to occasional nonwords interspersed among a series of words. A proportion of the words were repetitions of previously presented items. Words were repeated after 0 or 6 intervening items in Experiment 1 and after 6 or 19 items in Experiment 2. Event-related potentials to repeated words were characterised by a sustained, widespread positive-going shift with an onset of approximately 300 ms. This effect did not vary significantly as a function of lag in either experiment. When words were repeated immediately, this repetition-evoked positive shift was preceded by a transient negative deflection (onset ca. 200 ms) which was absent in event-related potentials to words repeated at longer lags. These results suggest that the modulation of event-related potentials by word repetition is influenced by at least two processes. One of these processes acts relatively early during the processing of a repeated word, but subsides rapidly as inter-item lag between first and second presentations increases. The second process occurs later in time, but is considerably more robust over variations in inter-item lag.

The stability of unbounded two- and three-dimensional flows subject to body forces: some exact solutions

Abstract: A formulation, previously employed to find exact Navier-Stokes solutions for planar disturbances in two- and three-dimensional flows with spatially uniform rates of strain, is here adapted to incorporate the contribution of various types of body force. In the absence of body forces, it is known that unbounded flows with constant vorticity and elliptical streamlines are unstable to certain planar disturbances, which are amplified by a Floquet mechanism. The influence of a Coriolis force upon this instability mechanism is here described in detail, as an illustration of the general formulation. The results are likely to be of geophysical interest and may also have relevance to the breakdown of closed-eddy structures in turbulence. The final section of the paper reviews other systems for which analogous exact solutions may be obtained.

The course of the superior gluteal nerve in the lateral approach to the hip

Abstract: The superior gluteal nerve and its branches were dissected bilaterally in ten cadavera. The patterns of branching and the distribution of the branches were identified. The reference point for measurements was the mid-point of the superior border of the greater trochanter. Two patterns of neural branching were thus established. The points of termination of all branches formed an arcuate pattern along the middle one-third of the deep surface of the gluteus medius muscle. The so-called safe area of the gluteus medius muscle was found to be as much as five centimeters adjacent to the greater trochanter. If this distance is not exceeded by the intramuscular incision, the risk to the superior gluteal nerve and its branches will be minimum.

Improved transformation efficiency of Aspergillus niger using the homologous niaD gene for nitrate reductase.

Abstract: Aspergillus niger transformation frequencies of up to 1,176 transformants per μg DNA were achieved using the plasmid vector pSTA10 containing the A niger nitrate reductase structural gene Analysis of genomic endonuclease cleaved DNA from nitrate utilising transformants by DNA hybridisation, showed that most integration events are as a result of homologous recombination The niaD transformation system was used successfully for the introduction of the unselected Escherichia coli fusion genes lacZ, encoding β-galactosidase, and uidA, for β-glucuronidase, as well as the Neurospora crassa tub-2 gene, for β-tubulin pSTA10 was also capable of transforming niaD mutants of other filamentous fungi such as A nidulans, A oryzae and Penicillium chrysogenum

The development of a homologous transformation system for Aspergillus oryzae based on the nitrate assimilation pathway: A convenient and general selection system for filamentous fungal transformation

Abstract: The development of an efficient and homologous transformation system for Aspergillus oryzae is described. This is based on nitrate reductase (niaD) of the nitrate assimilation pathway. The niaD system offers a number of inherent advantages over many other systems and may be of general use for nitrate-utilising filamentous fungi. Transformation frequencies of up to 800 transformants per microgram DNA are observed with A. oryzae. The preponderance of integration events take place at the resident niaD locus either by gene conversion (41%), single integration (23%) or multiple tandem integration (36%). Heterologous expression of the A. oryzae niaD gene in the filamentous fungi A. nidulans, A. niger and Penicillum chrysogenum is observed. That heterologous putative niaD hybridisation signals are seen with other fungal DNAs affords the oppotunity to isolate the corresponding niaD from various fungi in order to develop homolgous transformation. Co-transformation with the introduction of the non-selected markers pyrG, tub-2, and uidA has been achieved.

Characterization of the adenovirus proteinase: substrate specificity.

Abstract: Summary Peptides were synthesized based on the cleavage sites in the adenovirus type 2 proteins pVI and pVII. The synthetic peptides were incubated with disrupted, purified adenovirus as a source of proteinase and specific cleavages were monitored by fast protein liquid chromatography and amino acid analysis. Using this approach it was established that all the peptides cleaved were of the form M(L)XGX↓G or M(L)XGG↓X. Thus we have shown that the adenoviral proteinase recognizes a specific secondary structure formed by a sequence of at least five amino acids, the main determinants of specificity being two and four residues to the N-terminal side of the bond cleaved. We were able to examine the relevant structural features of the peptide substrates by utilizing the CHEM-X molecular modelling package. Using our consensus sequence we were able to predict the cleavage sites in the viral proteins pVIII, pre-terminal protein (pTP), 11K and IIIa. Octapeptides containing the predicted sites in pVIII and the pTP were synthesized and shown to be cleaved by the proteinase.

Persistent object management system

Abstract: This is a description of the integrated Persistent Object Management System (POMS) for the language PS-algol. The objective of POMS is to provide an implementation of the PS-algol persistent heap1 entirely by means of procedures written in PS-algol.

Influence of salinity on the energetics of gill and kidney of Atlantic salmon (Salmo salar).

Abstract: The effect of seawater acclimation and adaptation to various salinities on the energetics of gill and kidney of Atlantic salmon (Salmo salar) was examined. Smolts and non-smolts previously reared in fresh water were exposed to a rapid increase in salinity to 30 ppt. Plasma osmolarity, [Na(+)], [Cl(-)], [K(+)] and [Mg(++)] increased in both groups but were significantly lower in smolts than non-smolts. Gill Na(+), K(+)-ATPase specific activity, initially higher in smolts, increased in both groups after 18 days in seawater. Kidney Na(+), K(+)-ATPase specific activity was not affected by salinity in either group. Gill and kidney citrate synthase specific activity was not affected by seawater exposure in smolts but decreased in non-smolts. In a second experiment, Atlantic salmon smolts reared in fresh water were acclimated to 0, 10 or 30 ppt seawater for 3 months at a temperature of 13-14°C. Gill Na(+), K(+)-ATPase was positively correlated with salinity, displaying 2.5- and 5-fold higher specific activity at 10 and 30 ppt, respectively, than at 0 ppt. Kidney Na(+), K(+)-ATPase specific activity was not significantly affected by environmental salinity. Citrate synthase and cytochrome c oxidase specific activities in gill were slightly (6-13%) lower at 10 ppt than at 0 and 30 ppt, whereas kidney activities were lowest at 30 ppt. Oxygen consumption of isolated gill filaments was significantly higher when incubated in isosmotic saline and at 30 ppt than at 0 ppt, but was not affected by the prior acclimation salinity. The results indicate that although high salinity induces increased gill Na(+), K(+)-ATPase activity, it does not induce substantial increases in metabolic capacity of gill or kidney.

Oxygen Transport and Acid-Base Balance in the Haemolymph of the Lobster, Homarus Gammarus, During Aerial Exposure and Resubmersion

Abstract: Submerged lobsters at 15°C were normoxaemic (CaOO2 = 0.52 mmol l−1 at a PaOO2 of 6.53 kPa) and normocapnic (PaCOCO2 = 0.44kPa; [HCO3−] = 9.3mequiv l−1 and pHa = 7.78). After 3h in air the haemolymph was markedly hypoxic and hypercapnic (PaOO2 = 1.6 kPa; CaOO2 0.2 mmol l−1; PaCOCO2 = 0.7kPa and pHa = 7.64). Disturbance after 3h in air caused a greater increase in PaCOCO2 to 1.28 kPa and a fourfold increase in lactate levels to 3.6 mmol 1−1. The combined respiratory and metabolic acidosis reduced pHa to 7.39. After 14 h in air, undisturbed lobsters remained hypoxic and hypercapnic (PaOO2 = 1.2kPa; PaCOCO2 = 1.2kPa). Lactate levels had increased to 6.2 mmol l−1. Despite this clear limit on respiratory gas exchange in air, oxygen transport by the haemolymph was restored. A rise in buffer base ([HCO3−] = l5.8 mequiv l−1) compensated for the potential respiratory and metabolic acidosis and pH was unchanged at 7.63. The combined effects of the increase in lactate (ΔlogP50/Δlog[lactate] = −0.175) and calcium (ΔlogP50/Δlog[Ca2+] = −0.20 at pH7.63) levels contributed to an increase in oxygen affinity of haemocyanin at constant pH. Consequently, mean CaOO2 increased from 0.2 to 0.38 mmol l−1 between 3h and 14h in air. Resubmergence after 14 h in air resulted in a transient alkalosis due to retention of bicarbonate; oxygen and CO2 were rapidly restored to submerged levels. The lobster possesses the appropriate respiratory adaptations for survival during the relatively long periods of exposure in air encountered during commercial shipment.

The formation of flare loops by magnetic reconnection and chromospheric ablation

Abstract: Slow-mode shocks produced by reconnection in the corona can provide the thermal energy necessary to sustain flare loops for many hours. These slow shocks have a complex structure because strong thermal conduction along field lines dissociates the shocks into conduction fronts and isothermal subshocks. Heat conducted along field lines mapping from the subshocks to the chromosphere ablates chromospheric plasma and thereby creates the hot flare loops and associated flare ribbons. Here we combine a non-coplanar compressible reconnection theory with simple scaling arguments for ablation and radiative cooling, and predict average properties of hot and cool flare loops as a function of the coronal vector magnetic field. For a coronal field strength of 100 G the temperature of the hot flare loops decreases from 1.2 × 107 K to 4.0 × 106 K as the component of the coronal magnetic field perpendicular to the plane of the loops increases from 0% to 86% of the total field. When the perpendicular component exceeds 86% of the total field or when the altitude of the reconnection site exceeds 106km, flare loops no longer occur. Shock enhanced radiative cooling triggers the formation of cool Hα flare loops with predicted densities of ≈ 1013 cm−3, and a small gap of ≈ 103 km is predicted to exist between the footpoints of the cool flare loops and the inner edges of the flare ribbons.

Microtubule polarities indicate that nucleation and capture of microtubules occurs at cell surfaces in Drosophila.

Abstract: Hook decoration with pig brain tubulin was used to assess the polarity of microtubules which mainly have 15 protofilaments in the transcellular bundles of late pupal Drosophila wing epidermal cells. The microtubules make end-on contact with cell surfaces. Most microtubules in each bundle exhibited a uniform polarity. They were oriented with their minus ends associated with their hemidesmosomal anchorage points at the apical cuticle-secreting surfaces of the cells. Plus ends were directed towards, and were sometimes connected to, basal attachment desmosomes at the opposite ends of the cells. The orientation of microtubules at cell apices, with minus ends directed towards the cell surface, is opposite to the polarity anticipated for microtubules which have elongated centrifugally from centrosomes. It is consistent, however, with evidence that microtubule assembly is nucleated by plasma membrane-associated sites at the apical surfaces of the cells (Mogensen, M. M., and J. B. Tucker. 1987. J. Cell Sci. 88:95-107) after these cells have lost their centriole-containing, centrosomal, microtubule-organizing centers (Tucker, J. B., M. J. Milner, D. A. Currie, J. W. Muir, D. A. Forrest, and M.-J. Spencer. 1986. Eur. J. Cell Biol. 41:279-289). Our findings indicate that the plus ends of many of these apically nucleated microtubules are captured by the basal desmosomes. Hence, the situation may be analogous to the polar-nucleation/chromosomal-capture scheme for kinetochore microtubule assembly in mitotic and meiotic spindles. The cell surface-associated nucleation-elongation-capture mechanism proposed here may also apply during assembly of transcellular microtubule arrays in certain other animal tissue cell types.

Distribution of carbonic anhydrase in British marine macroalgae.

Abstract: Thirty-four species of marine macroalgae from around St. Andrews, Scotland, have been assayed for their external activity and thirty-three species for their total activity of carbonic anhydrase. Activity was detected in all the Rhodophyta tested apart from Chondrus crispus, but was absent in Codium fragile, Enteromorpha sp. and Monostroma fuscum (Chlorophyta), and Alaria esculenta, Laminaria digitata, L. saccharina and L. hyperborea (Phaeophyta). Total activity of carbonic anhydrase per unit fresh weight tended to be higher in the Rhodophyta than in the Chlorophyta or Phaeophyta. External activity was present in two of the six Chlorophyta, four of the twelve Phaeophyta and four of the sixteen Rhodophyta tested. On average, when present, external carbonic anhydrase activity represented 2.7% of the total activity. A relationship was found between total carbonic anhydrase activity and habitat. Species from the high intertidal and the low-light subtidal habitats had significantly higher activity than species from the mid and low intertidal, rockpools, or high-light region of the subtidal. External carbonic anhydrase activity did not vary significantly with habitat. There appeared to be no strong relationship between carbonic anhydrase activity and the ability of a species to use HCO -3 in photosynthesis under water.

Social relationships of mountain baboons: Leadership and affiliation in a non-female-bonded monkey

Abstract: Instead of close and differentiated relationships among adult females, the accepted norm for savanna baboons, groups of Drakensberg mountain baboons (Papio ursinus) showed strong affiliation of females towards a single male. The same male was usually the decision-making animal in controlling group movements. Lactating or pregnant females focused their grooming on this "leader" male, producing a radially patterned sociogram, as in the desert baboon (P. hamadryas); the leader male supported young animals in the group against aggression and protected them against external threats. Unlike typical savanna baboons, these mountain baboons rarely displayed approach-retreat or triadic interactions, and entirely lacked coalitions among adult females. Both groups studied were reproductively one-male; male-female relationships in one were like those in a unit of a hamadryas male at his peak, while the other group resembled the unit of an old hamadryas male, who still leads the group, with a male follower starting to build up a new unit and already monopolizing mating. In their mountain environment, where the low population density suggests conditions as harsh for baboons as in deserts, adults in these groups kept unusually large distances apart during ranging; kin tended to range apart, and spacing of adults was greatest at the end of the dry, winter season. These facts support the hypothesis that sparse food is responsible for convergence with hamadryas social organization. It is suggested that all baboons, though matrilocal, are better categorized as "cross-sex-bonded" than "female bonded".

The adenovirus type 40 hexon: sequence, predicted structure and relationship to other adenovirus hexons.

Abstract: Summary The gene encoding the major capsid protein (hexon) of human adenovirus type 40 (Ad40) has been isolated and sequenced. Comparison of the predicted amino acid sequence of the Ad40 hexon with the corresponding polypeptide of the human enteric adenovirus, Ad41, reveals an overall identity of 88%. The majority of the changes in sequence are located in two areas, amino acids 131 to 287 and 390 to 425. Regions in the hexon protein that vary between Ad40 and Ad41 (subgroup F) were the same regions that varied between Ad2 and Ad5 (subgroup C) suggesting that these areas of the protein represent type-specific antigenic determinants. Other areas were conserved within members of a subgroup but varied between subgroups. Fitting of the Ad40 hexon sequence to the known three-dimensional structure of the Ad2 hexon demonstrates that the variable regions are located in the l1, l2 and l4 loops that form the surface of the virion. Of major significance is the absence in Ad40 of the highly acidic region present in both Ad2 and Ad5. In Ad2 this region stretches down into the D-strand of the β-barrel forming the P1 domain. Molecular modelling indicates that the amino acids in Ad40 which correspond to the acidic region of Ad2 can also be accommodated in the eight-stranded β-barrel, thereby maintaining the integrity of the barrel. Since the acidic region is also absent from the hexon of Ad41, the sequence of amino acids that replaces the acidic residues may be responsible for some of the distinctive biological properties of the subgroup F adenoviruses.