Showing papers by "University of St Andrews published in 1982"

Place navigation impaired in rats with hippocampal lesions.

Abstract: Electrophysiological studies have shown that single cells in the hippocampus respond during spatial learning and exploration1–4, some firing only when animals enter specific and restricted areas of a familiar environment. Deficits in spatial learning and memory are found after lesions of the hippocampus and its extrinsic fibre connections5,6 following damage to the medial septal nucleus which successfully disrupts the hippocampal theta rhythm7, and in senescent rats which also show a correlated reduction in synaptic enhancement on the perforant path input to the hippocampus8. We now report, using a novel behavioural procedure requiring search for a hidden goal, that, in addition to a spatial discrimination impairment, total hippocampal lesions also cause a profound and lasting placenavigational impairment that can be dissociated from correlated motor, motivational and reinforcement aspects of the procedure.

Which Factors Determine the Reactivity and Regioselectivity of Free Radical Substitution and Addition Reactions

Abstract: The relative importance of bond strength, steric effects, and polarity in determining the rate and orientation of free radical subsitution and free radical addition reaction is considered. The factors which control substitution reaction (radical transfer reaction) are gathered together as five “rules”, and a similar five “rules” are proposed for addition rections. These “rules” are shown to be special cases of two “laws” which govern all free radical reactions.

The Duhem-Quine Thesis, Lakatos and the Appraisal of Theories in Macroeconomics

Abstract: The point of this paper is to outline the implications of the Duhem-Quine thesis for the task of appraising theories in economics. The Duhem-Quine thesis (DQfrom now on) states that it is not possible to falsify single hypotheses because it is invariably conjunctions of hypotheses which are being tested. Thus if a particular hypothesis is found to be in conflict with some piece of empirical evidence all that we can say is that the conjunction of the particular hypothesis with a set of auxiliary hypotheses is false. We can never be sure that it is not one or more of the auxiliary hypotheses which is responsible for the anomalous empirical evidence, rather than the particular hypothesis in which we are most interested. Expressed in symbols, this means that arguments of the form [Ho -* 0. 0] --* Ho are not justified, where Ho is a particular hypothesis, O is the observational evidence and the symbols -*, . and mean 'imply', 'conjoined with', and 'not'. Instead our arguments can only justifiably be phrased in the form [G1 -* 0. 0] -* G1, where G1 is a conjunction of hypotheses which contains Ho: there could well be some different conjunction of hypotheses GN which contains Ho which is consistent with the empirical evidence. The contention of this paper is that many of the debates in macroeconomics have been misguided in that the jointness of hypothesis testing has been ignored by participants in the debates. Instead the focus of attention has been on the appraisal of single target hypotheses considered in isolation from supportive auxiliary hypotheses, the implicit assumption being that it is possible to falsify single target hypotheses. The latter assumption is wrong. Following the logic of the DQ thesis we are obliged to conduct our appraisal at the level of groupings of hypotheses, that is to appraise any target hypothesis in conjunction with its supportive auxiliary hypotheses. The implications of this line of reasoning are perhaps best unravelled in the context of concrete examples from debates in macroeconomics over the last two decades. Before moving to this task we will, in Section I, provide a brief outline of the history of the DQ thesis. Section II will then illustrate the misguidedness of appraising target hypotheses in isolation from their supportive auxiliary hypotheses with reference to the often heated and continuing debate regarding the stability of the demand for money function. The question of how to appraise groupings of hypotheses is considered in Section III. Here we will centre the

The dynamics of a river bend: a study in flow and sedimentary processes

Abstract: Comprehensive field measurements of flow and sedimentary processes have been made with the aid of stable scaffolding bridges spaced along the length of a bend of the River South Esk, Scotland. At river stages between about two-thirds full and bankfull, channel width, mean depth and mean flow velocity at a cross-section vary little in the streamwise direction. Flow resistance reaches a maximum at these stages, and the bed topography is stable and in equilibrium with flow and bedload transport. Stable flow geometry is thus related in some way to energy conservation, and to maximization of flow resistance. Detailed observations over a large range of river stages of mean velocity distributions, secondary circulation, water surface configuration, bed shear stress and resistance to flow, bed configurations and bed load transport rates agree with much (but not all) of the comparable published experimental studies and selected theoretical work. Generalized physical models of flow and sediment transport in natural curved channels (Engelund, 1974; Bridge, 1977) are demonstrated to be sound in basis and can simulate the bend studied very well. Although there is a pressing need for further development of these models, the results lend confidence to their use in simulating ancient river sedimentation. Sediment deposited on point bars is the result mainly of bedload transport over a range of near-bankfull stages. The areal distribution of grain-size characteristics and bed configurations at these stages give rise, with lateral deposition, to vertical facies sequences that vary substantially in the streamwise direction.

Polymorphism for outcrossing frequency at the ray floret locus in senecio vulgaris L. I. Evidence

Abstract: Polymorphism for outcrossing frequency at the ray floret locus in senecio vulgaris L. III. causes

A glacio-isostatic facies model and amino acid stratigraphy for late Quaternary events in Spitsbergen and the Arctic

Abstract: Strong early Holocene crustal uplift over the Spitsbergen archipelago reflects disappearance of an ice mass centred just north-east of the archipelago and which decayed rapidly just after 10,000 BP after a maximum extension between 12,600 and 10,000 BP. From the lithofacies distributions associated with these events a glacio-isostatic facies model can be defined which, combined with analyses of amino acid racemization, provides a valuable stratigraphic method for correlating pre-Holocene glacio-isostatic events. These are correlated with events in Greenland, and both are contrasted with Weichselian glacial events at the southern margins of the two great Northern Hemisphere ice sheets and with contemporary water mass changes in the North Atlantic and Norwegian Sea. The geographical variation in glacier response through time is explained by three principal climatic circulation patterns.

FMRFamide neuropeptides simultaneously increase and decrease K+ currents in an identified neurone

Abstract: Phe-Met-Arg-Phe-NH2, or FMRFamide, discovered in ganglia of the clam Macrocallista nimbosa1 has potent cardio-stimulatory activity in some molluscan species, but is cardio-inhibitory in others, and produces contractions of certain non-cardiac muscles2. A peptide with similar properties is present in the ganglia of the snail Helix3, and is thought to differ from the Macrocallista peptide in having one or more additional amino acids combined with the terminal free amino nitrogen. An homologous opiate peptide, Tyr-Gly-GIy-Phe-Met-Arg-Phe (or YGGFMRF, using single letter abbreviations4), was identified in adrenal medullary granules and the striatum5. YGGFMRFamide has chromatographic properties more similar, though not identical, to the Helix peptide than FMRFamide itself (D. A. Price, M. J. Greenberg and G.A.C., unpublished). FMRFamide has potent and complex effects on Helix neurones. One neurone in each cerebral ganglion, the C1 or giant serotonin neurone (GSN), is hyperpolarized by FMRFamide at the resting membrane level, but depolarized at less negative potentials6.I show here that YGGFMRFamide has similar effects to FMRFamide and examine further the ionic mechanisms underlying the two responses of the GSN. The results indicate that the hyperpolarizing, outward current response results from an increase in conductance to K+ whereas the depolarizing response, which was recorded as a reduction in net outward current, is due to the suppression of a Ca2+ activated K+current.

Laser diffraction studies of sarcomere dynamics during ‘isometric’ relaxation in isolated muscle fibres of the frog

Abstract: 1. A study has been made of changes in sarcomere length and tension which occur during relaxation from isometric (‘fixed ends’) tetani in isolated muscle fibres of the frog. Sarcomere lengths were calculated from measurements of the separation of the zero-to-first-order intensity maxima in diffraction patterns generated by illuminating small segments of fibre with a He—Ne laser. Diffraction spectra were recorded continuously on cine-film using the method of ‘streak’ photography. 2. Many sarcomeres in a muscle fibre are found to undergo active shortening during relaxation, at the expense of others located elsewhere which become passively extended. The time of onset of changes in sarcomere length coincides with the well known ‘shoulder’ on the tension record, and their amplitude is maximal at the time when isometric force approaches zero. The original pattern of sarcomere lengths is only re-established after tension has disappeared. 3. The variability in the pattern of sarcomere length changes during relaxation was studied in a sample of twenty fibres, by making ‘streak’ recordings from successive 1 mm segments along the entire length of each fibre. This survey showed that segments which elongate are located predominantly, though not exclusively, close to the fibre ends. The fractional length of the fibre which underwent shortening was found to vary considerably in different preparations. In many ‘streak’ recordings the first order line fragmented into several distinct intensity maxima. 4. The effects of varying the initial fibre length on the time course of the tension decay and on the accompanying changes in sarcomere length were studied. The range of fibre lengths investigated corresponded with sarcomere spacings of 1·9-3·2 μm. The rate constant, R, for the exponential (later) component of the tension decay decreased with increasing fibre length and this was accompanied by a reduction in the mean amplitude of sarcomere shortening [Formula: see text] and lengthening [Formula: see text]. However, the time interval during which sarcomeres shortened or elongated increased, and so the mean velocities of sarcomere length changes ([Formula: see text] and [Formula: see text]) also displayed an inverse dependence upon fibre length. 5. The effects of altering temperature (0-20 °C) on the time course of the changes in sarcomere length and tension were investigated. The time to onset of the length changes, t1, the time to maximum amplitude, t2, and the time to full recovery, t3, all decreased exponentially with increasing temperature, but to differing extents. Temperature co-efficients for the velocity of sarcomere length changes during the interval t2 — t1 and for the fast tension decay were 2·47 ([Formula: see text]), 2·54 ([Formula: see text]) and 2·45 (R). The rate of the slow tension decay (before the tension ‘shoulder’) also increased with temperature, with a Q10 of 2·43. 6. The complex patterns of sarcomere length changes seen during relaxation appear to be due to variations in the duration of mechanical activity in different fibre segments. A model is presented which shows that the characteristic form of the tension decay can be accounted for by the progressive emergence of local inequalities in the relative strengths of adjacent sarcomeres, as relaxation proceeds.

Capillarisation, oxygen diffusion distances and mitochondrial content of carp muscles following acclimation to summer and winter temperatures.

Abstract: Many species of fish show a partial or complete thermal compensation of metabolic rate on acclimation from summer to winter temperatures. In the present study Crucian carp (Carassius carassius L.) were acclimated for two months to either 2° C or 28° C and the effects of temperature acclimation on mitochondrial content and capillary supply to myotomal muscles determined.

The drift velocity of water waves

Abstract: The important role of viscosity in producing second-order Eulerian drift currents in the presence of small-amplitude water waves was first recognized by Longuet-Higgins (1953).The theoretical and experimental background is first reviewed. It is then shown that, contrary to previous belief, the presence of surface contamination must greatly enhance the drift velocity of short waves. We then solve an initial-value problem for the drift current associated with temporally decaying waves, thereby resolving questions raised by the work of Liu & Davis (1977), whose solution exhibits anomalous singularities. Next, the steady drift velocity of spatially decaying waves is calculated and shown to bear a close resemblance to Longuet-Higgins’ ‘conduction solution’ for unattenuated waves.Finally, we establish that unidirectional drift currents of both surface and inter-facial waves are sure to be unstable to spanwise-periodic disturbances; the instability mechanism being identical to that first proposed by Craik (1977), and recently developed by Leibovich & Paolucci (1981), to explain the generation of Langmuir circulations.

Regular semigroups with a multiplicative inverse transversal

Abstract: By an inverse transversal of a regular semigroup S we mean an inverse subsemigroup that contains a single inverse of every element of S. A certain multiplicative property (which in the case of a band is equivalent to normality) is imposed on an inverse transversal and a complete description of the structure of S is obtained.

Simultaneous and successive contrast effects in the perception of depth from motion-parallax and stereoscopic information.

Abstract: Prolonged inspection of a three-dimensional corrugated surface resulted in a successive contrast effect, or aftereffect, of depth, whereby a subsequently-viewed physically-flat test surface appeared to be corrugated in depth with the opposite phase to the adapting surface. The aftereffect occurred both when the depth was specified by motion parallax, in the absence of all other sources of depth information, and when it was specified solely by stereoscopic information. The depth aftereffect was measured by 'nulling' the apparent depth in the test surface with physical relative motion or binocular disparity until the test surface appeared flat. Up to 70% of the depth in the adapting surface was necessary to null the aftereffect. Simultaneous contrast effects in the perception of three-dimensional surfaces were used to investigate the spatial interactions that exist in the processing of motion-parallax and stereoscopic information. A physically vertical surface appeared to slope in depth in the opposite direction to the slope of a surrounding surface. In this case up to 50% of the slope of the inducing surface was necessary to null the contrast effect. Similar results were again obtained for motion-parallax and stereoscopic depth.

The pCa‐tension and force‐velocity characteristics of skinned fibres isolated from fish fast and slow muscles

Abstract: .1. Single fast fibres and small bundles of two to six slow fibres were dissected from the myotomal muscles of the cod, Gadus morhua, and the dogfish, Scyliorhinus canicula. Fibres were chemically skinned with the non-ionic detergent Brij 58. 2. The isometric tension properties were investigated. Maximal isometric tensions (mean:ts.E. of mean) were 18.65:t1.18 (n = 11) and 8.34:t0.98 (n = 13) N cm-2 for cod fast and slow fibres, and 18.34 :t0.88 (n = 28) and 8.24 :t0.39 (n = 12) N cm-2 for dogfish fast and slow fibres respectively. The values are comparable to those observed in mammalian and amphibian skinned fibres. The lower tensions generated by the slow fibres cannot be fully explained on the basis of their lower myofibrillar fractional volume. 3. In common with previous studies, a steep sigmoid relationship between pCa and tension was observed. The threshold for tension generation was around pCa 7.2. Half-maximal pCas were 6.08 and 6.42 for cod fast and slow muscle, and 6.41 and 6.50 for dogfish fast and slow fibres respectively. Cod fibres were maximally activated at around pCa 5.18, and dogfish fibres at pCa 5.62. 4. Contraction-induced residual tensions were observed in cod fast fibres after return to relaxing solution. This phenomenon is a feature common to many skinned fibre studies, but the mechanism behind it has yet to be resolved. 5. The force-velocity characteristics of fast and slow fibres have been investigated (at 8 °C). 6. Points below 0.6 Po on the p- V curves could be fitted to a linear form of the Hill equation. Extrapolated Vmaxs were calculated as follows: cod fast fibre V max = 1.01 muscle length sec-1 (Lsec-l) (a = 0.21 Po; b = 0.21 Lsec-l). Slow fibre = 0.53 Lsec-l (a = 0.28Po; b = 0.21 Lsec-l).Dogfishfastfibre V max = 2.34 Lsec-1 (a = 0.06 Po; b = 0.14 Lsec-l). Slow fibre = 0.67 Lsec-1 (a = 0.19 Po; b = 0.13 Lsec-l). 7. Contraction velocity in cod slow fibres decreased continuously to produce markedly non-linear velocity transients, similar to those reported for amphibian slow fibres.

Numerical study of line-tied magnetic reconnection

Abstract: A two-dimensional configuration, analogous to that at the start of the main phase in two-ribbon flares, is modelled numerically by self-consistently solving the time-dependent MHD equations. The initial state consists of a vertical current sheet with an external plasma beta value of 0.1 and a magnetic Reynolds number of 10−3. Although the model does not yet include gravity or a full energy equation, many of the principal dynamical features of the main phase in a flare are present. In particular, the numerical results confirm the earlier prediction of the kinematic Kopp-Pneuman (1976) model that a neutral line forms at the base of the corona and rises upwards as open, extended field lines close back down to form loops (i.e., ‘post’-flare loops). By the end of the computation a state of nonlinear reconnection containing slow shocks has developed, and the velocity of the plasma flowing into the neutral line region is approximately 0.06 times the corresponding inflow Alfven velocity - a value consistent with the steady-state nonlinear reconnection theory of Soward and Priest (1977). The speed at which the neutral line rises in the numerical simulation varies from an initial value of ≲ 0.02 to a final value of ∼- 0.12 times the inflow Alfven speed.

Asymmetry of Manual Preference and Performance

Abstract: Laterality assessments for 1,966 unselected psychology undergraduates are compared on three questionnaires of tested reliability. Performances of the right and left hands of 167 university students...

Slow-shock heating and the kopp-pneuman model for 'post'-flare loops

Abstract: The heating of ‘post’-flare loops in the Kopp-Pneuman (1976) model is here reconsidered. In that kinematic model the loops are heated by gas-dynamic shocks to at most 3–4 × 106 K. However, in a full dynamic model they would be replaced by slow magnetohydrodynamic shocks, which may provide more heating due to the additional release of magnetic energy. It is shown from a local compressible analysis that such shock waves can account for the observed temperatures of 5 × 106–107 K and also for the observed upward loop speeds of 1–50 km s-1. The above values are obtained when the ambient plasma beta is 0.01 and the shocks propagate at highly sub-Alfvenic velocities. However, if the velocity of shock propagation approaches the Alfven speed, then temperatures of 108 K are produced. This may explain the extremely high temperatures that have been observed with the Solar Maximum Mission, when it is realised that the ‘post’-flare loop phenomenon may well be occurring very early on in the flare.