Showing papers by "University of St Andrews published in 1990"

Three-dimensional finite-amplitude solutions in plane couette flow: bifurcation from infinity

Abstract: Finite-amplitude solutions of plane Couette flow are discovered. They take a steady three-dimensional form. The solutions are obtained numerically by extending the bifurcation problem of a circular Couette system between co-rotating cylinders with a narrow gap to the case with zero average rotation rate.

Experimental violation of Bell's inequality based on phase and momentum.

Abstract: Two-color photon pairs are selected by two double apertures placed to satisfy the phase-matching conditions at a down-conversion crystal. The different wavelengths are superposed at spatially separated points on a beamsplitter and coincident two-photon detections are measured. On adjusting phase plates in the beams before the beamsplitter an apparent nonlocal fourth-order interference effect is seen which violates Bell's inequality by several standard deviations.

Event-related brain potentials dissociate repetition effects of high- and low-frequency words.

Abstract: Event-related brain potentials (ERPs) were recorded while subjects detected nonwords interspersed among sequences of words of high or low frequency of occurrence. In Phase 1, a proportion of the words were repeated after six intervening items. In Phase 2, which followed after a break of approximately 15 min, the words were either repeats of items presented in the previous phase or new. Unrepeated low-frequency words evoked larger N400 components than did high-frequency items. In Phase 1, this effect interacted with repetition, such that no frequency effects were observed on N400s evoked by repeated words. In addition, the post-500-msec latency region of the ERPs exhibited a substantial repetition effect for low-frequency words, but did not differentiate unrepeated and repeated high-frequency words. In Phase 2, ERPs evoked by "old" and "new" high-frequency words did not differ in any latency region, while those evoked by old and new low-frequency words differed only after 500 msec. The interactive effects of frequency and repetition suggest that these variables act jointly at multiple loci during the processing of a word. The specificity of the post-500-msec repetition effect for low-frequency words may reflect a process responsive to a discrepancy between words' intra and extraexperimental familiarity.

Continuum fields in quantum optics.

Abstract: We formulate the quantum theory of optical wave propagation without recourse to cavity quantization. This approach avoids the introduction of a box-related mode spacing and enables us to use a continuum frequency space description. We introduce a complete orthonormal set of operators that can describe states of finite energy. The set is countable and the operators have all the usual properties of the single-mode frequency operators. With use of these operators a generalization of the single-mode normal-ordering theorem is proved. We discuss the inclusion of material dispersion and pulse propagation in an optical fiber. Finally, we consider the process of photodetection in free space, concluding with a discussion of homodyne detection with both local oscillator and signal fields pulsed.

Diel vertical migrations of marine fishes: an obligate or facultative process?

Abstract: Publisher Summary Diel vertical migrations are cyclic changes in the position of aquatic organisms in the water column that occur with 24-h periodicity. Such movements occur at various stages of the development of teleosts, although they are often more evident during the first year of life. Despite frequent study, fundamental questions concerning the nature of diel vertical migrations remain. For example, most life-history traits exhibit phenotypic plasticity in response to environmental factors during the development. From the fisheries viewpoint, an understanding of diel vertical migration is critical for surveys of abundance at all life-history stages. Such surveys of exploited populations of adult fish have long been employed during the stock assessment process and are becoming increasingly significant, particularly, in light of the difficulties associated with obtaining reliable commercial fishery statistics. This chapter presents a review of the studies of diel vertical migration of marine fish species. The extent to which fish exhibit plasticity in their patterns of diel migrations is examined, both with respect to varying environmental conditions and ontogeny. Most importantly, the chapter also assesses whether the patterns of diel vertical migration fits the criteria for endogenous circadian rhythms. Finally, it attempts to address whether the observed diel periodicity in depth occupied is a result of the endogenous effects whereby the periodicity is derived from the fishes' biochemistry or biophysics, rather than more direct effects of environmental stimuli, such as changes in light and temperature providing a cue for certain behavior.

Exogenous sources of inorganic carbon for photosynthesis by marine macroalgae1

Abstract: Thirty-five species of marine macroalgae were tested for their ability to remove inorganic carbon from seawater using the pH-drift technique. Six of these species, all Rhodophyta, were unable to use HCO3–. The remaining species exhibited a range in ability to use HCO3– and deplete inorganic carbon (Cτ); the three most effective species, all Chlorophyta, raised the pH to over 10.50, depleted the concentration of CO2 effectively to zero, and depleted the concentration of Cτ to less than 50% of that at air-equilibrium. In contrast, the six species restricted to CO2 did not raise the pH above 9.0 at a CO2 concentration of about 1.5 μmol · L-1 and depleted the concentration of Cτ to about 80% of that at air-equilibrium. Ability to raise pH and deplete Cτ was linked to the habitat in which the species grew. Five of the six species which lack the ability to use HCO3– grow subtidally in relatively low light beneath a canopy of larger Phaeophyta. None of these species grow in rockpools where carbon-depletion may occur. Species from rockpools were all effective at removing inorganic carbon. Competition for Cτ may be one of the factors that determines species composition in rockpools. There was a species-specific difference between the calculated concentration of Cτ at the end of a pH-drift experiment and that measured directly. Most, but not all, species with the ability to generate high pH-values showed a lower than calculated final concentration of Cτ consistent with precipitation of CaCO3. A number of Rhodophyta with no, or a limited, ability to use HCO3– showed the opposite response, with final concentrations of Cτ exceeding that calculated from the pH. Calculations based on the maximum gross rate of production of CO2 from HCO3– in the absence of external carbonic anhydrase confirmed the results of the pH-drift experiments by demonstrating HCO3– -use in Monostroma fuscum (Post et Rupr.) Wittr. And Ulva lactuca L. and the lack of this ability in Lomentaria articulate (Huds.) Lyngb. Rates of net photosynthesis at air-equilibrium were greater than 95% of those at 2.3 mmol Cτ· L-1 for many of the species which were able to use HCO3–, but on average only 72% for the six species restricted to CO2.

Modelling Muscle Power Output in a Swimming Fish

Abstract: Intact, electrically excitable fibre bundles were isolated from the fast and slow myotomal muscle of the bullrout ( Myoxocephalus scorpius L.). Power output was measured under conditions simulating their activity in a fish swimming at different speeds. Preparations were subjected to sinusoidal length changes of ±5% of resting length, and stimulated briefly during each cycle. The number and timing of stimuli were adjusted at each cycle frequency to maximise power output. Maximum power was produced at 5–7 Hz for fast fibres (25–35 W kg−1) and 2 Hz for slow fibres (5–8 Wkg−1). Under these conditions, pre-stretch of active muscle provides an important mechanism for storing potential energy for release during the shortening part of the cycle.

The Aspergillus nidulans npeA locus consists of three contiguous genes required for penicillin biosynthesis.

Abstract: Clones of Aspergillus nidulans genomic DNA spanning 20 kb have been isolated and shown by a combination of classical and molecular genetic means to represent the npeA locus, previously found to be one of four loci (npeA, npeB, npeC and npeD) involved in the synthesis of penicillin. As well as containing the gene encoding the second enzyme for penicillin biosynthesis, namely isopenicillin N synthetase (IPNS) (designated ipnA), our results show that these clones (pSTA200, pSTA201 and pSTA207) contain two more genes to form a cluster of three contiguous penicillin biosynthetic genes. Our evidence suggests that these genes encode delta (L-alpha-aminoadipyl)-L-cysteinyl-D-valine synthetase (ACVS) and acyl transferase (ACYT) (designated acvA and acyA respectively), the first and third enzymes required for penicillin biosynthesis, with the gene order being acvA-ipnA-acyA. Transcripts have been identified for the three genes and their approximate sizes determined--acvA 9.5 kb, ipnA 1.4 kb and acyA 1.6 kb. All three mRNA species are observed in cells grown in fermentation medium but not in cells grown in minimal medium, suggesting that the control of penicillin biosynthesis is, in part, at the level of mRNA accumulation. Finally our results show that acvA and ipnA genes are divergently transcribed, whilst acyA is transcribed in the same orientation as ipnA.

Scaling Effects on Muscle Function: Power Output of Isolated Fish Muscle Fibres Performing Oscillatory Work

Abstract: Bundles of 3–10 live fast fibres were isolated from the abdominal myotomes of cod ( Gadus morhua L.) 13–67 cm in length. The preparations performed work under conditions simulating their activity during swimming: sinusoidal length changes were imposed about in situ fibre length, and the fibres were stimulated at a selected phase in each cycle. Strain amplitude, and the number and timing of stimuli were chosen to give maximum power output over a wide range of cycle/tailbeat frequencies. For each preparation power output was maximal at a particular frequency, although the peaks were rather broad. As the size of the fish increased the cycle frequency for maximum power output (f opt ) decreased, from 12.5 Hz (13 cm fish) to 5 Hz (67 cm fish) (f opt = 1.67 L −0.52 , where L is body length).

Idempotent rank in finite full transformation semigroups

Abstract: The subsemigroup Sing n of singular elements of the full transformation semigroup on a finite set is generated by n(n − l)/2 idempotents of defect one. In this paper we extend this result to the subsemigroup K(n, r) consisting of all elements of rank r or less. We prove that the idempotent rank, defined as the cardinality of a minimal generating set of idempotents, of K(n, r) is S(n, r) , the Stirling number of the second kind.

Change detection in SAR imagery

Abstract: The author describes two separate SAR (synthetic aperture radar) image change detection schemes: (1) model based image segmentation (2) image object identification using neural networks. The neural network approach performs slightly better than the model based scheme in terms of both time and detection rates. >

Expression of the genome of potato leafroll virus: readthrough of the coat protein termination codon in vivo.

Abstract: An antiserum was raised against a fusion protein containing part of the 56K polypeptide (P5) encoded by the open reading frame (ORF) at the 3' end of the genome of potato leafroll virus (PLRV). This antiserum reacted specifically with 80K and 90K polypeptides in PLRV-infected protoplasts, with a 90K polypeptide in infected potato tissue and with a 53K polypeptide in protein extracted from purified particles of PLRV. Monoclonal antibodies raised against purified PLRV particles also reacted with these polypeptides, as well as with the 23K coat protein. Virus particles partially purified from infected protoplasts contained some 90K polypeptide as well as the major 23K coat protein. The ORFs of the 23K coat protein and P5 are contiguous and in frame. The results suggest that the P5 polypeptide of PLRV occurs in infected cells as part of a readthrough protein comprising the 23K coat protein joined to the P5 amino acid sequence. Moreover the readthrough protein can be assembled into virus particles as a minor component together with the main 23K component. The P5 protein may thus contribute to properties of PLRV determined by its virus particle surface.

A comparison of air and water as environments for photosynthesis by the intertidal alga fucus spiralis (phaeophyta)1

Abstract: The response of photosynthesis and respiration of the intertidal brown alga Fucus spiralis L. to light and temperature at ambient and elevated concentrations of inorganic carbon was investigated. The light-saturated rate of photosynthesis was greater in air at 15° C and 20° C, but greater in water at 10° C. Light compensation point and Ik was about 50% lower under submerged relative to emerged conditions, whereas the initial slope of photosynthesis versus irradiance was higher, except at 20° C. Under both submerged and emerged conditions light-saturated photosynthesis was limited to a similar degree (78%, and 65%, respectively) by the availability of inorganic carbon at naturally occuring concentrations. In air, slight desiccation at tissue water contents of about 96% to 92% caused a stimulation in the rate of net photosynthesis to 110–148% of fully hydrated fronds. At lower water contents the rate of net photosynthesis declined linearly with decreasing water content and became zero at a water content of about 15%. Dark respiration declined linearly with tissue water content and remained positive to a water content of 8%. Upon reimmersion the fronds showed a complete recovery within 35 min following desiccation to a water content of 20–30%. Thus F. spiralis seems to be very tolerant to desiccation. Since F. spiralis photosynthesizes effectively in air, even at a higher rate than in water as long as it has not lost a large proportion of its water in desiccation, the alternating exposure to air may be beneficial by increasing the daily carbon gain compared to a fully submerged situation.

Stability in a Persistent Store Based on a Large Virtual Memory

Abstract: Persistent systems support mechanisms which allow programs to create and manipulate arbitrary data structures which outlive the execution of the program which created them. A persistent store supports mechanisms for the storage and retrieval of objects in a uniform manner regardless of their lifetime. Since all data of the system is in this repository it is important that it always be in a consistent state. This property is called integrity. The integrity of the persistent store depends in part on the store being resilient to failures. That is, when an error occurs the store can recover to a previously recorded consistent state. The mechanism for recording this state and performing recovery is called stability. This paper considers an implementation of a persistent store based on a large virtual memory and shows how stability is achieved.

Visual and somatosensory processing in the macaque temporal cortex: the role of 'expectation'.

Abstract: The somatosensory and visual properties of cells in a polymodal region of temporal cortex were studied in 4 awake behaving macaque monkeys. When stimulated passively and out of sight, cells with tactile responses were found to have very large receptive fields covering most of the body surface and an apparent lack of selectivity for size, shape or texture of the tactile stimulus. These properties are equivalent to those described for the anaesthetized preparation (Bruce et al. 1981). Our study revealed that tactile responses were influenced by the degree to which stimuli could be ‘expected’. Tactile stimulation arising from active exploration of novel surfaces produced vigourous neuronal responses but equivalent stimulation of the skin arising when the monkey contacted ‘expected’ surfaces such as itself or items with which it had become familiar produced no responses. The responses of cells to active or passive tactile stimulation were attenuated when the monkey could see the objects causing the stimulation. For cells responsive to more than one sensory modality, visual and somatosensory responses were associated in a compatible manner. Cells responsive to the onset of touch were selective for the sight of objects moving towards the monkey, whereas cells selective for the offset of touch were responsive to the sight of movements away from the monkey.

Thermal acclimation and muscle contractile properties in cyprinid fish.

Abstract: After several weeks of cold acclimation, the swimming performance of some fish is increased at low temperatures and decreased at high temperatures. The temperature compensation of locomotory activity involves changes in central patterns of muscle fiber recruitment and in the properties of the peripheral nervous system and muscle tissues. In some freshwater fish belonging to the family Cyprinidae, including the goldfish (Carassius auratus), the common carp (Cyprinus carpio), and the roach (Rutilus rutilus), the intrinsic contractile properties of muscles are modified by thermal acclimation. Parameters that can be altered by temperature acclimation in both fast and slow muscle fibers include isometric twitch contraction time, maximum force production, and unloaded shortening speed. The molecular mechanisms responsible for these changes in contractility are discussed.

Presenting words without interior letters: Superiority over single letters and influence of postmask boundaries.

Abstract: Five experiments examined the perceptibility of exterior letter combinations of words in brief pattern-postmasked displays.

Temperature acclimation and the expression of contractile protein isoforms in the skeletal muscles of the common carp (Cyprinus carpio L.)

Abstract: Common carp (Cyprinus carpio L.) were acclimated to either 2, 5, 8, 11, 15, 20, or 23°C for 12 weeks (12 h light: 12 h dark). Fish did not feed after 6 weeks at temperatures below 8°C. Skinned fibres were prepared from fast myotomal muscle by freeze-drying. Measured at 0°C unloaded contraction velocity (Vmax) and maximum isometric tension generation (Po) were 2–3 times higher in the 11°C-than 23°C-acclimated groups, and had intermediate values in 15 °C-acclimated fish. Po and Vmax at 0°C were not significantly different for carp maintained at 2, 5, 8, or 11°C. Measured at the acclimation temperature of each group Vmax and Po were 51% and 71% lower for fibres from 2°C- than 23°C-acclimated fish. The results indicate a partial capacity adaptation of muscle power output in fish acclimated between 11°C and 23°C. At 8°C the ATPase activity of myofibrils was 2 times higher in fish acclimated to 8°C than to 20°C. The effects of temperature acclimation on the protein composition of myofibrils was investigated using one- and two-dimensional electrophoresis. Peptide maps of purified myosin heavy chains and actin prepared by proteolytic digestion with either Staphylococcus aureus V8 protease or chymotrypsin were similar for both acclimation groups. The molecular weights and isoelectric points of the major isoforms of tropomyosin, troponin C, troponin I, troponin T, and myosin light chains (MLC1, MLC2 and MLC3) were also similar in 8°C- and 20°C-acclimated carp. A 20 kDa molecular weight protein with a pI intermediate between that for MLC2 and MLC3 was found in myofibrils and single fibres from carp acclimated to 8°C but was not present in carp acclimated to 20°C. It is suggested that this band corresponds to a myosin light chain isoform unique to cold-acclimated fish. Evidence was also obtained that myofibrils from warm-acclimated fish contained a second minor isoform of troponin I.