Showing papers by "University College Dublin published in 1986"

Some Life-History Consequences of Modular Construction in Plants

Abstract: The nature and life-history consequences of modular construction in plants are discussed with particular reference to growth, reproduction and survival. Plants grow by the iteration of modular units and as a consequence growth can be described in terms of the population dynamics of these structural units. Changes in size, whether positive or negative, depend on the birth and death rates of modules; however, if the births continue to exceed the deaths, plants then have the capability of attaining enormous sizes, especially if they are clonal. The population nature of plant growth also means that plants of the same age may show large variation in individual size if individuals differ in their relative growth rates. Correlations between age and size are often, therefore, very weak. Constraints on the allocation of resources accumulated during growth have important implications for the reproductive schedules of plants, but the analysis of constraint functions has so far revealed little about the actual detail of these schedules. All the meristems of semelparous plants are involved in or die at reproduction and as a consequence death of the genet follows reproduction. For iteroparous plants, however, there are fundamental differences between the reproductive schedules of plants with a single shoot module and those with many shoot modules. The former demonstrate a relatively constant rate of reproduction from year to year following maturity whereas the latter show a continual increase in fecundity with size and age. The reproductive schedules of clonal plants are further discussed in relation to the allocation of meristems to either growth or reproduction. The pattern of mortality is examined at both the level of the module and the genet. Particular attention is focused on the survival and senescence of leaves and shoots; there is no equivalent regular shedding of organs in unitary organisms. Whereas genet senescence and death are coincident with shoot module death in semelparous plants, there is no evident relation between them in iteroparous plants. The life span of the genet reflects the birth and death rates of its modules and both aclonal and clonal plants that are iteroparous may achieve considerable longevity. The longevity of aclonal plants often seems to be restricted by the accumulation of dead material and the problems of being large. Clonal plants are, in contrast, potentially immortal. It is questionable whether the genets of iteroparous plants show senescence as defined for unitary organisms since there is no separation of germ plasm from soma and since apical meristems do not appear to senesce. Insofar as they retain the capacity for rejuvenescence from apical meristems, genets of modular organisms do not senesce; it is only the constituent organs that show senescence, death and decay.

The Second Dual of a JB* Triple System

Abstract: Summary Using ultrapowers and J * ideals we show that the second dual of a JB * triple system is a JB * triple system. This gives a short proof of a result originally proved in [1].

The influence of climatic factors on the distribution of C4 species in Europe

Abstract: A checklist of the currently-known C4 species which occur in Europe was compiled, and the number of these found in European territories was ascertained. Their contribution to the local floras range from 4.35% in the Azores to 0% in Svalbard. Subsequently, a stepwise multiple regression analysis was used to correlate the relative abundances of four subdivisions of C4 species with climatic variables derived for each territory from meteorological tables. The four subdivisions were: (a) total number of C4 species; (b) number of native C4 species; (c) C4 monocots and (d) C4 dicots. These values were expressed as percentages of either the total flora, (a), or the native flora ((b), (c) and (d)) for the regressions. The abundance of each C4 subdivision was found to be strongly correlated with temperature, and to a lesser extent, negatively with precipitation. Habitat information about the European C4 species was also analysed and it was concluded that their apparent preference for maritime and ruderal habitats indicates some form of competitive advantage of the pathway under saline or disturbed conditions. A small number of European C4 species was identified whose distribution appears to be anomalous with respect to temperature and/or soil moisture content.

Fertility trends, excess mortality, and the Great Irish Famine

Abstract: This paper has developed estimates of the age-specific mortality rates prevailing during the Great Irish Famine and has analyzed fertility trends during the 25 years before the Famine. Our calculations confirm that 1 million Irish people perished as a result of this disaster. This figure does not include the deaths among the 1.3 million emigrants who left Ireland during the Famine period. The Famine produced a significant drop in the fertility rate, and we estimate that more than 300,000 births did not take place as a result of the Famine. The effects were especially severe on the very young and the very old, a result echoed in the findings of demographic analyses of other famines. Our procedure permits a reconstruction of the Irish population by age and sex during the period 1821-1841. In addition, it yields year-by-year estimates of the birth rate over this period. We estimate that the rate fell by about 14 percent, a result robust to our assumptions regarding emigration. Economic historians have debated this issue, and we hope that our evidence, although preliminary, will be of assistance. Our analysis also permits year-by-year reconstruction of Irish population totals for the period 1821-1851. Two years are of particular interest. Virtually all recent writers, with the notable exception of Lee (1981), have suggested that the 1831 census returns overestimated the actual population resident in Ireland at that date. Our reconstruction supports the validity of the 1831 census figure. We obtain a total of 7,847,000, which is in good agreement with the disputed census figure of 7,767,000. But perhaps the most interesting figure is the population total for the end of 1845, the highest ever achieved in Ireland. We estimate that the population on the eve of the Great Famine was 8,525,000. Throughout the paper we have tried to highlight those areas in which the data are unreliable, unavailable, or distorted. We have tried to devise cross-checks for consistency and to test the sensitivity of the results to a range of assumptions. A case in point concerns the age-sex profile and volume of emigration to England, Scotland, and Wales. Additional work at the micro level would be helpful here. More solid evidence on Famine births would also be helpful. The parish registers we have sampled certainly provide a clue to trends, but we have only made a start in that respect. A much more comprehensive survey is needed to convey the national picture.(ABSTRACT TRUNCATED AT 400 WORDS)

Bianchi identities and the automatic conservation of energy-momentum and angular momentum in general-relativistic field theories

Abstract: Automatic conservation of energy-momentum and angular momentum is guaranteed in a gravitational theory if, via the field equations, the conservation laws for the material currents are reduced to the contracted Bianchi identities. We first execute an irreducible decomposition of the Bianchi identities in a Riemann-Cartan space-time. Then, starting from a Riemannian space-time with or without torsion, we determine those gravitational theories which have automatic conservation: general relativity and the Einstein-Cartan-Sciama-Kibble theory, both with cosmological constant, and the nonviable pseudoscalar model. The Poincare gauge theory of gravity, like gauge theories of internal groups, has no automatic conservation in the sense defined above. This does not lead to any difficulties in principle. Analogies to 3-dimensional continuum mechanics are stressed throughout the article.

A comparative study of the rod and coccoid forms of Campylobacter jejuni ATCC 29428

Abstract: Coccoid forms in cultures of a strain of the enteric pathogen Campylobacter jejuni were investigated. A culture containing 100% coccoid forms was non-viable. Coccoid forms had a lesser content of cytoplasmic components and nucleic acids than rods of C. jejuni. During the conversion to coccoid forms nucleotides leaked from the cells. The results of treatments with ionic and non-ionic detergents, and lysozyme and ethylenediaminetetraacetic acid indicated a changed cell wall in coccoid forms compared with rods. Using rate-zonal centrifugation coccoid forms were found to be less dense than rods. The results of this study indicate that the coccoid form of C. jejuni ATCC 29428 is a degenerate cell form which is undergoing cellular degradation.

Effect of nitrate-nitrogen limitation on photosynthesis of the diatom Phaeodactylum tricornutum Bohlin (Bacillariophyceae)

Abstract: Nitrate limited growth of the diatom Phaeodactylum tricornutum in chemostat cultures produced marked changes in biochemical composition and a six-fold reduction in the specific growth rate. This was associated with a reduction in the carbon and chlorophyll a specific light saturated rates, with little effect on light limited photosynthesis. Variations in specific growth rate were quantitatively related to carbon specific net photosynthesis and maximum chlorophyll a specific light saturated rates were positively correlated with cell nitrogen contents. The correlation between nitrogen content and photosynthesis for P. tricornutum and the differential effect of nitrogen supply on the light response curve of photosynthesis is qualitatively and quantitatively similar to published results for terrestrial vascular plants. There was little change in the photon (quantum) yield of photosynthesis which was not significantly different from 0.125mol O2 mol photon-1 the theoretical upper limit based on the Z scheme, even under severe nitrate deficiency. The capacity to maintain a high photon yield under nitrate limitation is discussed in relation to the nitrogen requirements of the stromal and membrane components of the photosynthetic apparatus.

Multiband far-infrared observations of the NGC 6334 complex

Abstract: Multiband far-infrared (20-155 microns) observations of the large H II region/molecular cloud complex NGC 6334 are presented. The observations were performed simultaneously in four bands with effective wavelengths 21, 42, 71, and 134 microns. Eight far-infrared sources were detected which cover the range from sources with little of no continuum radio emission to well-developed H II regions. Maps of dust temperature and far-infrared optical depth of the complex are presented which reveal large-scale variations in the color temperature and optical depth. Star formation in the complex is discussed and it is concluded that a Rayleigh-Taylor instability generated by the gravitational attraction of the galactic plane can explain the regular separation of the far-IR sources.

Factor Content Functions and the Theory of International Trade

Abstract: This paper introduces the concepts of direct and indirect factor trade utility functions and uses them to derive Marshallian and Hicksian factor content functions, which express the quantities of factors of production embodied in net imports as functions of the exogenous variables facing the economy. The properties of these functions are discussed and they are used to derive a number of new results. In particular, it is shown that, in certain circumstances, the existence of gains from trade is sufficient for the Heckscher-Ohlin theorem to hold in its factor content form.

Stages of Climatic Change from Full Glacial to Holocene in Northwest Spain, Southern France and Italy: A Comparison of the Atlantic Coast and the Mediterranean Basin

Abstract: From 17,000 to 11,000 years before present polar water retreated northward and westward in the North Atlantic. A brief readvance took place between 11,000 and 10,000 yr. B.P. It might be anticipated that the retreat of polar water would be reflected most strongly in the vegetation record on the Atlantic Coast of northwest Spain and less strongly in the Mediterranean region which is more distant from the climatic influence of the Atlantic. At Sanabria Marsh and Lago de Ajo in northwest Spain herb-dominated vegetation was present before 13,000 years ago. Ice in the cirque of Lago de Ajo had melted some time before 13,000 yr. B.P. and was not reconstituted. Subsequent vegetation history suggests that invasion of tree birches followed by pine and oak took place between 13,000 and 10,000 yr. B.P. There is no clear evidence for a Younger Dryas event in northwest Spain, but a regression of oak and temporary reappearance of birch and pine at Sanabria Marsh is datable to the early Holocene. Ocean cores from the Atlantic west of the Iberian Peninsula and in the Bay of Biscay appear to record a Younger Dryas event which may also be weakly recorded in the Pyrenees. More detailed comparison of the land and ocean records is required to resolve a possible conflict of evidence. In southern Italy at Lake Monticchio a full glacial herb-dominated vegetation is recorded. The transition to the Holocene is marked first by a peak of birch pollen and then by the presence of deciduous trees. Pine is insignificant in the developing vegetation at deglaciation. In southern Italy there is no evidence for climatic fluctuations during deglaciation.

Does clinical clerkship alter students' attitudes to a career choice of psychiatry?

Abstract: Summary. A 50-item questionnaire, designed to link attitudes to psychiatry directly with how these might influence a career choice of psychiatry, was administered to medical students before and after their clinical clerkship in psychiatry. Many of these changed in a positive direction, e.g. ‘job satisfaction’, ‘life-style’, ‘training available’ and ‘multidisciplinary approach’. The influence of important people in their lives was predominantly negative; this may emphasize the impact of psychiatric ‘role models’. Male and female students differed in how they changed. Males appeared influenced by external factors, e.g. ‘work hours’ and ‘career structure’, and females by internal ones, e.g. ‘interest in knowing more about self. Females were also more likely to wish for a career in psychiatry. Psychiatry was ranked higher in career choice at the end of the clerkship.

The evolution of resonant water-wave oscillations

Abstract: This paper is concerned with the evolution of small-amplitude, long-wavelength, resonantly forced oscillations of a liquid in a tank of finite length. It is shown that the surface motion is governed by a forced Korteweg—de Vries equation. Numerical integration indicates that the motion does not evolve to a periodic steady state unless there is dissipation in the system. When there is no dissipation there are cycles of growth and decay reminiscent of Fermi–Pasta–Ulam recurrence. The experiments of Chester & Bones (1968) show that for certain frequencies more than one periodic solution is possible. We illustrate the evolution of two such solutions for the fundamental resonance frequency.

Incorporating syntactic information into a document retrieval strategy: an investigation

Abstract: This paper deals with mechanisms for performing text retrieval which incorporate a degree of linguistic processing into the overall strategy. We have performed some experiments using parsing of text an a test collection of documents and queries to try and find out exactly if and how parsing could contribute to an overall improvement in retrieval effectiveness. Investigating this topic has led us to the definition of a retrieval strategy which incorporates parsing of query text and a more “shallow” parsing of document texts, whose retrieval effectiveness is investigated and described. Our results indicate that significant improvements in retrieval effectiveness can be obtained by incorporating such linguistic processing into an overall retrieval strategy.

The AMIGO Project: advanced group communication model for computer-based communications environment

Abstract: In this paper we discuss and elaborate on the conceptual requirements as well as the tools of the General AMIGO Model for group communication. The special features of the model are examined with particular reference to the social and ethical implications in the communication process. The applicability of the AMIGO Model is demonstrated by examples, and we give indications of further work to refine and advance the model.

The countenance of curriculum action research

Abstract: (1986) The countenance of curriculum action research Irish Educational Studies: Vol 6, No 1, pp 17-47

Regulation of intracellular sodium and pH by the electrogenic H+ pump in frog skin.

Abstract: We have investigated the role of the electrogenic hydrogen ion pump in the regulation of intracellular sodium ion activity (a Na i ) and intracellular pH (pHi) in frog skin epithelial cells using double-barreled ion sensitive microelectrodes. WhenRana esculenta skin is mounted in an Ussing chamber and bathed in 1 mM Na2SO4 buffered to pH 7.34 with imidazole on the apical side and in normal Ringer on the serosal side, the apical addition of the carbonic anhydrase inhibitor, ethoxzolamide (10−4M) blocks net H+ ion excretion and Na absorption, producing a depolarization of 25–30 mV of the apical membrane, potential (Ψmc). We demonstrate the these changes are accompanied by a fall ina Na i from 6.2±0.5 mmol/l to 3.4±0.6 mmol/l and an increase in pHi from 7.20±0.03 to 7.38±0.08 (n=12 skins). Voltage clamping Ψmc to its control value in the presence of ethoxzolamide restoreda Na i but the pHi remained alkaline. Furthermore, the fall ina Na i produced by ethoxzolamide could be mimicked by voltage clamping Ψmc towards the value of the Nernst potential for Na at the apical membrane. These results indicate that the maintenance of the cellular Na+ transport pool is dependent on a favourable electrical driving force and counter-current generated by an electrogenic H+ pump at the apical membrane. Addition of amiloride (10−5 mol/l) or substitution of external Na+ by Mg2+ or K+ caused a hyperpolarization of Ψmc and a fall ina Na i . These effects were accompanied by an inhibition of H+ excretion and a fall in pHi of 0.14 ±0.08 units (n=6 skins). However, when the effect, of Na+ transport inhibition on Ψmc was prevented by imposing a voltage clamp no effects of amiloride on H+ excretion or pHi were observed. Moreover, the effect of amiloride on pHi could be reproduced in control skins by voltage clamping Ψmc to −100 mV. The metabolic inhibitors vanadate (1 mmol/l) and di-cyclo hexyl carbodiimide (5×10−5 mol/l) inhibited H+ excretion and decreased pHi from 7.28±0.08 to 7.02±0.06 and from 7.30±0.06 to 7.12±0.05 (n=6 skins), respectively. These results indicate that an apical membrane H+ ATPase plays a role in regulating pHi and the mechanism is sensitive to membrane potential.

Effects of Management on Soil Decomposers and Decomposition Processes in Grassland

Abstract: Decomposition processes in the worlds grasslands and croplands are considerably influenced by management. Factors such as fertilizer use, stocking and cutting intensity, choice of crops, cultivation practices and use of pesticides directly influence the nutrient supply for the decomposer community by affecting net primary production and how the resultant fixed chemical energy is utilized. Net primary production in grassland sites studied during the International Biological Programme ranged from 239 g/m2 dry mass in semiarid areas to 4557 g/m2 in subhunid tropics with temperate grasslands falling in the range 702 to 3470 g/m2 (Coupland 1979). The ranges reflect inherent differences in soil fertility and climate, but are also very much influenced by management. As much as 75% of plant production may be returned t the soil in extensively grazed, semiarid, natural grassland and as little as 3-5o may be assimilated by cattle (Coleman et al. 1976). At the other extreme, under conditions of intensive sheep grazing in temperate grasslands up to 60% of annual shoot production may be assimilated by the sheep (Hutchinson and King 1980a) while in intensively fertilized, mown grassland over 90% of shoot production may be harvested (Andrzejewska and Gyllenberg 1980).

Light absorption, photosynthesis and growth of Nannochloris atomus in nutrient-saturated cultures

Abstract: Nannochloris atomus was maintained in exponential growth at photon flux densities (PFD) from 400 to 700 nm, ranging from 10 to 200 μmol m-2 s-1. Growth was lightsaturated at PFDs in excess of 100 μmol m-2 s-1, with a mean light-saturated growth rate at 23 °C of 1.5×10-5s-1 (1.2 d-1). The light-limited growth rates extrapolated to a compensation PFD for growth that was not significantly different from zero, although no changes in cell numbers were observed in a single culture incubated at a PFD of 1.0 μmol m-2s-1. Dark-respiration rates were independent of PFD, averaging 1.7×10-6 mol O2 mol-1 C s-1 (0.14 mol O2 mol-1 C d-1). The maximum photon (quantum) efficiency of photosynthesis was also independent of PFD, with a mean value of 0.12 mol O2 mol-1 photon. The chlorophyll a-specific light absorption cross-section ranged from 3 to 6×10-3 m2 mg-1 chl a and was lowest at low PFDs due to intracellular self-shading of pigments associated with high cell-chlorophyll a contents. The C:chl a ratio increased from 10 to 40 mg C mg-1 chl a between PFDs of 14 and 200 μmol m-2 s-1. These new observations for N. atomus are compared with our previous observations for the diatom Phaeodactylum tricornutum in terms of an energy budget for microalgal growth.

Chemical composition and electron microscopy of the rodlet layer ofAspergillus nidulans conidia

Abstract: The rodlet layers of wild-type and white mutantAspergillus nidulans conidia were purified by a simple centrifugation procedure after conidial suspensions were subjected to sonication. Chemical analysis showed that the major components of wild-type rodlets were protein and melanin in almost equal amounts, followed by carbohydrate. White mutant rodlets differed from those of the wild-type strain in that the melanin content was very low. Histidine, aspartic acid, glutamic acid, glycine, and alanine were the most prominent amino acids in the rodlet layer of the white mutant, whereas cystine and methionine were not found. Electron microscopy studies showed that the rodlets of both white mutant and wild-type strains were grouped into fascicles, which varied from 80 to 160 nm in width. Individual rodlets measured 125–360 nm in length and 7 nm in diameter.