Showing papers by "University of St Andrews published in 1991"

60-fsec pulse generation from a self-mode-locked Ti:sapphire laser.

Abstract: Pulses having durations as short as 60 fsec have been directly generated by a self-mode-locked, dispersion-compensated Ti:sapphire laser. By using an extracavity fiber-prism pulse compressor, pulse durations as short as 45 fsec have been obtained.

A neurological dissociation between perceiving objects and grasping them

Abstract: Studies of the visual capacity of neurological patients have provided evidence for a dissociation between the perceptual report of a visual stimulus and the ability to direct spatially accurate movements toward that stimulus. Some patients with damage to the parietal lobe, for example, are unable to reach accurately towards visual targets that they unequivocally report seeing. Conversely, some patients with extensive damage to primary visual cortex can make accurate pointing movements or saccades toward a stimulus presented in their 'blind' scotoma. But in investigations of visuomotor control in patients with visual disorders, little consideration has been given to complex acts such as manual prehension. Grasping a three-dimensional object requires knowledge not only of the object's spatial location, but also of its form, orientation and size. We have examined a patient with a profound disorder in the perception of such object qualities. Our quantitative analyses demonstrate strikingly accurate guidance of hand and finger movements directed at the very objects whose qualities she fails to perceive. These data suggest that the neural substrates for the visual perception of object qualities such as shape, orientation and size are distinct from those underlying the use of those qualities in the control of manual skills.

Viewer-centred and object-centred coding of heads in the macaque temporal cortex

Abstract: An investigation was made into the sensitivity of cells in the macaque superior temporal sulcus (STS) to the sight of different perspective views of the head. This allowed assessment of (a) whether coding was ‘viewer-centred’ (view specific) or ‘object-centred’ (view invariant) and (b) whether viewer-centred cells were preferentially tuned to ‘characteristic’ views of the head. The majority of cells (110) were found to be viewer-centred and exhibited unimodal tuning to one view. 5 cells displayed object-centred coding responding equally to all views of the head. A further 5 cells showed ‘mixed’ properties, responding to all views of the head but also discriminating between views. 6 out of 56 viewer and object-centred cells exhibited selectivity for face identity or species. Tuning to view varied in sharpness. For most (54/73) cells the angle of perspective rotation reducing response to half maximal was 45–70° but for 19/73 it was >90°. More cells were optimally tuned to characteristic views of the head (the full face or profile) than to other views. Some cells were, however, found tuned to intermediate views throughout the full 360 degree range. This coding of many distinct head views may have a role in the analysis of social signals based on the interpretation of the direction of other individuals' attention.

Dynamic light-scattering study of the glass transition in a colloidal suspension.

Abstract: This paper describes a light-scattering study of the glass transition in nonaqueous suspensions of sterically stabilized colloidal spheres. The observed phase behavior, fluid, crystal, and glass, is consistent with an essentially hard-sphere interaction between the particles. Metastable fluid states were obtained upon shear melting the crystalline phases by tumbling the samples. Their intermediate scattering functions, measured by dynamic light scattering, showed the emergence of a nondecaying component, implying structural arrest, at essentially the same concentration as that at which homogeneously nucleated crystallization was no longer observed. The overall forms of the intermediate scattering functions are consistent with the predictions of mode-coupling theories for the glass transition. Supplementary studies of the static structure factors indicated only short-ranged spatial order for particle concentrations ranging from the equilibrium fluid through the metastable fluid to the glass.

A comparison of phenoloxidase activity in the blood of marine invertebrates.

Abstract: A range of marine invertebrates were screened for prophenoloxidase (a marker protein of the prophenoloxidase activating system) in the coelomic fluid or hemolymph. The crustaceans and the ascidian, Ciona intestinalis, displayed strongest activity, with low levels found in the starfish, Asterias rubens, the sea urchin, D. antillarum, and the brachiopod, Liothyrella uva. The enzyme appeared to be absent from the isopod, Glyptonotus antarcticus. Further analyses of the blood cells of selected species revealed that prophenoloxidase tends to reside in the granular-type cells or their equivalent, and in the crustaceans and C. intestinalis is activated by lipopolysaccharides. In arthropods, prophenoloxidase is known to represent the terminal component of a complex cascade of enzymes that functions in non-self-recognition and host defence. The present study establishes that the enzyme is present in the blood cells of most, but not all, crustaceans and occurs in certain other invertebrate species, notably the urochordate, C. intestinalis.

Perception and recognition of photographic quality facial caricatures: Implications for the recognition of natural images

Abstract: The perception and recognition of photographic images of famous faces was compared with the same images transformed to produce caricatures of different degrees of exaggeration. Following Brennan (1982; 1985). caricatures were produced by first comparing the position of facial features in a frame-grabbed image with the average position for a series of faces; deviations from the average were then accentuated by a constant fraction (16, 32 or 48%). Photographic quality caricatures for seven famous faces were generated by distorting regions of the original images in accordance with the change in feature positions. Images reducing the distinctiveness of faces (anticaricatures) were produced by decreasing deviations from the norm. In Experiment 1, perceptual ratings of the degree to which images resembled the individuals depicted was found to vary with the degree of caricaturing (−32, −16, 0, +16, +32%). Interpolation from the data indicated that the best likeness occurred for images with a small degre...

crnA encodes a nitrate transporter in Aspergillus nidulans.

Abstract: The nucleotide sequence of the Aspergillus nidulans crnA gene for the transport of the anion nitrate has been determined. The crnA gene specifies a predicted polypeptide of 483 amino acids (molecular weight 51,769). A hydropathy plot suggests that this polypeptide has 10 membrane-spanning helices with an extensive hydrophilic region between helices six and seven. No striking homology was observed between the crnA protein and other reported membrane proteins of either prokaryotic or eukaryotic organisms, indicating that the crnA transporter may represent another class of membrane protein. Northern blotting results with wild-type cells show that (i) control of crnA expression is subject to nitrate (and nitrite) induction as well as nitrogen metabolite repression and (ii) regulation of the crnA gene is exerted at the level of mRNA accumulation, most likely at transcription, in response to the nitrogen source in the growth medium. Furthermore, similar studies with mutants of nirA and areA control genes and the niaD nitrate reductase structural gene show that crnA expression is mediated by the products of nirA (nitrate induction control gene), areA (nitrogen metabolite repression control gene), and niaD (involved in autoregulation of nitrate reductase).

Identification of an epitope on the P and V proteins of simian virus 5 that distinguishes between two isolates with different biological characteristics

Abstract: Two canine isolates of simian virus 5 (SV5), termed CPI+ and CPI-, were examined for their ability to react with a bank of monoclonal antibodies (MAbs) that had been previously raised against a human isolate of SV5. CPI- virus was originally isolated from the brain of a gnotobiotic dog infected with CPI+ virus and establishes persistent infections more readily than CPI+ in vitro. Of more than 50 MAbs tested, only one (P-k) reacted with CPI+ but not CPI-, enabling distinction between the two canine isolates. It had been shown previously that MAb P-k reacts with an epitope common to both the P and V proteins. In order to characterize further the epitope binding site of this MAb the P/V genes of CPI+ and CPI- were sequenced. There were four nucleotide differences between CPI+ and CPI-, three of which resulted in predicted amino acid substitutions. Synthetic peptides corresponding to regions encompassing these changes were made and radioimmune competition assays were used to identify the epitope binding site of MAb P-k. Sequence comparison of the P/V gene of CPI+ with the published sequence of a monkey isolate of SV5 (W3) revealed 14 nucleotide differences with five amino acid substitutions. The only amino acid substitution observed between CPI+, CPI- and W3 which altered the predicted secondary structures of the P and V proteins was a leucine to proline change that induced a predicted β-turn and resulted in the loss of binding of MAb P-k.

Dietary and Foraging Strategies of Baboons

Abstract: As large-bodied savannah primates, baboons have long been of special interest to students of human evolution: many different populations have been studied and dietary comparisons among them are becoming possible. Baboons' foraging strategies can be shown to combine high degrees of flexibility and breadth with selectivity. In this paper we develop and test multivariate models of the basis of diet selection for populations of montane and savannah baboons. Food selection is positively related to protein and lipid content and negatively to fibre, phenolics and alkaloids. Seasonal changes in dietary criteria predicted by these rules are tested and confirmed. Although nutritional bottlenecks occur at intervals, a comparison between long-term nutrient intakes in four different populations indicates convergence on lower degrees of variation than exist in superficial foodstuff profiles.

Visual processing of faces in temporal cortex: Physiological evidence for a modular organization and possible anatomical correlates

Abstract: Physiological recordings along the length of the upper bank of the superior temporal sulcus (STS) revealed cells each of which was selectively responsive to a particular view of the head and body. Such cells were grouped in large patches 3-4 mm across. The patches were separated by regions of cortex containing cells responsive to other stimuli. The distribution of cells projecting from temporal cortex to the posterior regions of the inferior parietal lobe was studied with retrogradely transported fluorescent dyes. A strong temporoparietal projection was found originating from the upper bank of the STS. Cells projecting to the parietal cortex occurred in large patches or bands. The size and periodicity of modules defined through anatomical connections matched the functional subdivisions of the STS cortex involved in face processing evident in physiological recordings. It is speculated that the temporoparietal projections could provide a route through which temporal lobe analysis of facial signals about the direction of others' attention can be passed to parietal systems concerned with spatial awareness.

Effect of ammonia on survival and osmoregulation in different life stages of the lobster Homarus americanus

Abstract: Acute toxicity of ammonia was determined for cultured larval, postlarval, and wild adult lobsters (Homarus americanus) in 1988. Ammonia tolerance was found to increase with ontogenetic development. Based on 96-h LC50 values of 58 mg l−1 NH4 + + NH3 l−1 seawater (0.72 mg NH3 l−1) for Stage I larvae, 87 mg NH4 + + NH3 l−1 (1.7 mg NH3 l−1) for Stage II larvae, 125 mg NH4 + + NH3 l−1 (2.13 mg NH3) for Stage III larvae, 144 mg NH4 + + NH3 l−1 (2.36 mg NH3 l−1) for Stage IV postlarvae, 377 mg NH4 + + NH3 l−1 (5.12 mg NH3 l−1) for adult lobsters at 5°C and 219 mg NH4 + + NH3 l−1 (3.25 mg NH3 l−1) for adult lobsters at 20°C, recommendations for “safe” levels of total ammonia and un-ionized ammonia were calculated using an application factor of 0.1. Effects of ammonia on osmoregulatory capacity were studied on postlarvae and adults. Ability of postlarvae and adults to hyper-regulate in low-salinity media decreased after exposure to ammonia. In postlarval lobsters, osmoregulatory capacity was significantly affected in ammonia concentrations exceeding 32 mg l−1. Osmoregulatory capacity in adult lobsters (5 and 20°C) was affected at 150 mg l−1. In postlarval lobsters, a minimum exposure time of 12 h was required to impair osmoregulatory capacity. The decrease in hemolymph osmotic pressure was caused by lower hemolymph sodium concentrations. The presence of ammonia in the external medium could markedly affect the Na+/NH4 + transport mechanism by permanently, temporarily, or partially impairing the transport sites for sodium.

Regeneratively initiated self-mode-locked Ti:sapphire laser.

Abstract: It is demonstrated that the incorporation of an acousto-optic modulator within the cavity of a self-mode-locked Ti:sapphire laser can lead to self-starting and stable generation of pulses that have durations of 60 fs when the acousto-optic device is driven regeneratively from the laser output. Data are also presented that show that the application of cavity-frequency locking techniques dramatically improves the phase noise characteristics of the mode-locked laser.

Event-related potentials related to recognition memory. Effects of unilateral temporal lobectomy and temporal lobe epilepsy.

Abstract: SUMMARY Event-related potentials (ERPs) were recorded during a continuous recognition memory task for visually presented words, with a 6 item lag between the first and second presentation of each word. The subjects consisted of: (i) a control group of patients with primary generalized epilepsy: (ii) patients who had undergone either a left or a right anterior temporal lobectomy; (iii) unoperated patients with either left or right unilaternal temporal lobe epilepsy. In the controls, ERPs to detected ‘old’ words were reliably more positive-going in the interval 300to600 ms post-stimulus than were ERPs to ‘new’ items. In both left and right lobectormy patients, ‘old/new’ ERP differences in the same latency range were significantly smaller than in the controls, and did not differ significantly from zero. At midline electrodes, old/new effects in the temporal lobe epilepsy patients were of similar magnitude to those of the controls. In contrast to the control data, the old/new effects in the temporal lobe epilepsy patients were asymmetric, in that they were smaller over the hemisphere ipsilateral to the seizure focus than over the contralateral hemisphere. No relationship was found across subjects between the magnitude of old/new ERP effects and verbal memory performance. In a second task, occasional non-words had to be discriminated against a background of sequentially presented words, some of which were repetitions of the immediately proceeding item. ERPs evoked by repeated words were more positive-going than were those to first presentations; this effect was reliable, and of equivalent size, in all patient groups. It is concluded that in the recognition task, old/new ERP effects are dependent on temporal lobe functioning, but that the anterior temporal lobe is not the principal locus of the generators of these effects. The cognitive processes reflected by these effects do not appear to be strongly lateralized to one hemisphere, and neither do they seem to be necessary for normal verbal memory.

Efficient KEX2-Like Processing of a Glucoamylase-Interleukin-6 Fusion Protein by Aspergillus Nidulans and Secretion of Mature Interleukin-6

Abstract: We have designed an expression vector for the secretion of human interleukin-6 (hIL-6) in which the mature protein is fused through a spacer peptide, containing a KEX-2 like protein processing signal, to the entire Aspergillus niger glucoamylase (glaA) gene. Transformation of Aspergillus nidulans with this vector results in fungal strains secreting equimolar amounts of the glucoamylase and IL-6 proteins. The KEX2-type processing signal, Lys-Arg, is recognized and cleaved efficiently by an enzyme present in A. nidulans resulting in the secretion of an authentic mature hIL-6 protein at levels of up to 5 mg/l.

Recording soccer players' heart rates during matches.

Abstract: The aim of this study was to examine the possibility of obtaining information about the heart rate and physiological load imposed on soccer players during a game. The study was conducted on 27 soccer players, 9 each from semi‐professional, university and recreational soccer teams. Players from all positions (attack, midfield and defence) were selected for the study. Each subject's heart rate was monitored during a match using a short‐range radio telemetry (Sport TesterTM PE3000), and was sampled at 5‐s intervals. The results indicate that it is possible to monitor successfully the heart rate of players with such equipment. The mean heart rate and standard deviation for each player during match play were: semi‐professional players (172 ± 12, 176 ± 9 and 166 ± 15 for forwards, midfielders and defenders, respectively); university players (171 ± 13, 173 ± 10 and 156 ± 13 for forwards, midfielders and defenders, respectively); and recreational players (173 ± 13, 170 ± 12 and 162 ± 13 for forwards, mid...

Temperature and metabolic rate in sedentary fish from the Antarctic, North Sea and Indo-West Pacific Ocean

Abstract: Resting metabolic rate $$(\dot V_{O_{2[rest]} } )$$ was measured in demersal stages of the teleostNotothenia neglecta Nybelin from the South Orkney Islands, Antarctica, from 1985 to 1987. The relationship between $$\dot V_{O_{2[rest]} } $$ and body mass (Mb) conformed to the general relationship $$\dot V_{O_{2[rest]} } = aMb^b $$ , wherea is a proportionality constant andb is the scaling exponent. $$\dot V_{O_{2[rest]} } $$ (mg O2 h−1) was found to scale toMb (0.82±0.011) in the summer (November to April, 1.6 to 1 850 g,n=56) and toMb (0.76±0.013) in the winter (May to October, 0.9 to 1 850 g,n=57) (values ofb are means ± SD). Although the scaling exponents were significantly different (P<0.01), $$\dot V_{O_{2[rest]} } $$ was similar in the juvenile stages of summer- and winter-caught fish matched for body mass. The effects of activity on oxygen consumption was studied using a Brett respirometer. Adult stages had a factorial aerobic scope for activity $$(\dot V_{O_{2[max]} } :\dot V_{O_{2[rest]} } )$$ of 5.7, which is similar to that reported for demersal fish from temperate latitudes. The effects of temperature on resting metabolism was investigated in fish with similar sedentary lifestyles from the North Sea (Agonus cataphractus andMyoxocephalus scorpius) and the Indo-West Pacific (Paracirrhites forsteri, P. arcatus, Neocirrhites armatus andExallias brevis). Extrapolated values of $$\dot V_{O_{2[rest]} } $$ for the tropical species approached zero at 5 to 10°C. For a standard 50 g fish, $$\dot V_{O_{2[rest]} } $$ for the tropical species at 25°C was in the range 3.4 to 4.4 mg O2 h−1, compared with 1.3 mg O2 h−1 forNotothenia neglecta at its acclimation temperature. Thus, the maximum metabolic rate of sedentary tropical species at 24°C is likely to be 2 to 4 times higher than inN. neglecta at 0°C. This suggests that the energy available for sustained activity $$(\dot V_{O_{2[max]} } - \dot V_{O_{2[rest]} } )$$ is significantly lower in cold- than in warm-water fish.

Mesogenic Behaviour of some 1,4,8,11,15,18,22,25-Octa-alkylphthalocyanines

Abstract: Discotic columnar mesophase behaviour exhibited by ten metal-free and copper 1,4,8,11,15,18,22,25- octa-alkylphthalocyanines has been characterised by optical microscopy, differential scanning calorimetry, x-ray diffraction and electronic absorption spectroscopy. Compounds with side-chains as short as hexyl exhibit one or more mesophases, and a total of three different mesophases are apparent for the series as a whole. The highest temperature mesophase is assigned as Dhd. At lower temperatures, some compounds develop a second mesophase of hexagonal symmetry, whereas others form a mesophase of rectangular symmetry. One example shows all three mesophases.

Change detection in SAR imagery

Abstract: The two major difficulties associated with SAR image change detection are addressed. These are the removal of speckle noise and the registration of information between images. The problem of image registration is severe in airborne SAR imagery due to the unpredictable nature of the aircraft track. Although inertial navigation systems may be employed to measure this motion, the accuracy obtained is insufficient to allow the creation of large rectilinear images. However, autofocus techniques are used here to measure residual aircraft motions thus allowing the production of large geometrically accurate images. The second problem of speckle reduction has been approached in two ways. The first technique applies an intensity segmentation algorithm to each image and the regions generated by this segmentation are then compared using the change detection algorithm. An alternative approach to the problem of speckle removal is to use neural network methods to learn the speckle removal and region generation ...

Top executive pay and performance

Abstract: Using data on 241 of Britain's largest industrial companies, the pay received by top executives in 1985 is studied as a function of corporate performance. An attempt is made to estimate the extent to which executive pay and shareholder wealth are linked. Rival explanations, relating pay to the assets, employment level and turnover of the company, are also examined. No support is found for the managerialist view that remuneration tends to be correlated with size attributes. The results do, however, suggest that, while much of the variation in executive pay remains unexplained, there is evidence of executive remuneration policy serving to effect incentive alignment between the executive's and shareholders' interests.

The development of swimming rhythmicity in post-embryonic Xenopus laevis.

Abstract: The post-embryonic development of ‘Active’ swimming in immobilized Xenopus laevis tadpoles has been examined during the first day of larval life. In Xenopus embryos (stage 37—38; Nieuwkoop & Faber 1956), the rhythmic ventral root activity underlying swimming occurs as single brief 7 ms) compound impulses on each cycle. However, by stage 42 (about 24 h after hatching), ventral root discharge consists of bursts lasting around 20 ms per cycle. In addition to increased burst duration in each cycle of larval swimming, the range of cycle periods within an episode increases, although mean period values ( ca . 70-80 ms) remain similar to those of the younger animal. Consequently, motoneurons at developmental stage 42 are active during swimming for a greater percentage {ca. 25 %) of cycle time than at stage 37—38 ( ca . 10% ). Developmental stage 40 ( ca . 12 h post-hatching) is an intermediate stage in rhythm development. V entral root discharge varies from bursts of 10-20 ms at the start of an episode to embryonic {ca. 1 ms) spikes at the end of an episode. Furtherm ore, discharge varies from bursts of activity in rostral segments of stage 40 larvae to 7 ms spikes more caudally, as in embryos. The data thus suggest that Xenopus swimming rhythmicity develops relatively rapidly, along a rostrocaudal gradient, and may involve acquisition of multiple spiking in spinal neurons.

Metamorphosis in the lobster homarus (decapoda): a review

Abstract: A homarid lobster hatches as a prelarva and then molts successively through three larval instars (stages I, II, and III), one postlarval stage (IV), and numerous juvenile stages. Between the larval and the postlarval stages their anatomy undergoes major changes as the anatomical features characteristic of larval forms are replaced by those found on juveniles and adults. Physiology, ecology, and ethology also change progressively through stages IV and V, during which the lobster shifts from the planktonic behavior of the larva to the benthic existence of the juvenile and adult. This transition from larva to postlarva, specifically the molt from stage III to stage IV, is a true metamorphosis in which the eyestalk neuroendocrine tissue seems to be involved.

A computer-video aided time motion analysis technique for match analysis

Abstract: The purpose of this study was to find out suitable methods for obtaining objective data on the time spent by players of different positions during walking, jogging, cruising, sprinting and standing still during match play activities. Computer programs and filming analyses with a simple notation system based upon symbolic representations of movements have been devised for analysis of individual players' behaviour. A technique was devised and employed with a small group of university players, aged 19-21 years of age. The subjects were filmed in several matches, and the video recordings were analysed using a microcomputer. The ratio of the time spent for the players were 56% walking, 30% jogging, 4% cruising, 3% sprinting and 7% standing still. ANOVA revealed that there are significant differences among the players for different positions on the field, for example the time spent on walking, jogging and standing still differed (P less than 0.05) among attackers, defenders and midfielders. A new method has been developed to obtain reliable information about the players' movement and performance in the game. The Authors believe that there should be further studies carried out involving more teams at different levels of performance to substantiate these preliminary findings.