Showing papers by "University of Bath published in 1977"

Bounds and self-consistent estimates for the overall properties of anisotropic composites

Abstract: B ounds of Hashin-Shtrikman type and self-consistent estimates for the overall properties of composites, which may be anisotropic, are developed. Bodies containing aligned ellipsoidal inclusions are considered particularly, generalizing previously known results. The overall thermal conductivity of a body containing aligned spheroidal inclusions is discussed as an example including, as limiting cases, bodies containing highly-conducting aligned needles and bodies containing aligned pennyshaped cracks.

Determinants of avian eggshell porosity

Abstract: The manner in which the porosity of avian eggshells varies with egg weight is discussed in relation to the number of pores, their cross-sectional area and length. Shell porosity and ways in which this can change to satisfy different environmental demands are discussed on the basis of a simple model which envisages the shell as being composed of columns of calcite.

The freshwater biology of adult anadromous Sea lampreys Petromyzon marinus

Abstract: The lengths, weights and condition factors of young adult lampreys caught feeding on Gaspereau, Alosa pseudoharengus. Shad, Alosa sapidissima, and White suckers, Catostomus commersoni, in the lake-like extensions of the St. John River system during May, suggest that many lampreys do not feed in the nine to ten months following the initiation of metamorphosis in mid-July. The mean lengths (d-95% confidence limits) of individuals taken in four samples between May 13 and 29 did not differ significantly and ranged from 132-7± 2-81 to 135-7 ±3-71 mm. A significant increase in mean condition factor from II15 to 1-353 during this time indicates that the short period spent feeding in May enables the animal to replenish its food reserves prior to its downstream migration. Since several of the 81 feeding adults caught between the latter part of June and mid-July, at a point 140 km from the estuary of the St. John, were still attached to spawning-run Atlantic salmon, Salmo salar, this teleost host had probably been responsible for their transport upstream. The wide range in their length (156-403 mm), together with the presence in the lakes in May of a few young adults larger than those which have only just started feeding, suggest that the time of onset of the parasitic phase is variable but may generally commence in either the late autumn or in the spring. Scarring on salmon due to lamprey attack was predominantly (84%) on the ventral surface between the operculum and caudal peduncle. Over 35 % of the salmon examined in June 1975 had been attacked, more of these attacks being on the right side of the body of both males (59-6%) and females (49-8%) than on either the left (20-2 and 23-7 %) or both sides (20-2 and 26-5 %). While lamprey attacks may cause some mortality among the smaller teleosts, any effect on salmon is probably indirect through causing increased susceptibility to infection and stress. The ability of adult anadromous Sea lampreys to feed and grow in fresh water demonstrates the relative ease with which landlocked forms could have been evolved in response to extreme environmental changes. This evolutionary step has involved a decline in the ability to osmoregulate in high salinities and a reduction in body size and fecundity, the adaptive significances of which are discussed. Data on upstream migrants indicate that males and females undergo length reductions of at least 11 and 15 % respectively between the time of their entry into fresh water and the completion of spawning.

Matched asymptotic expansions in nonlinear fracture mechanics—III. In-plane loading of an elastic perfectly-plastic symmetric specimen

Abstract: T he matched expansion method, introduced by the authors in two earlier papers (1976) devoted to mode III loading, is applied to the practically important case of mode I loading of a symmetric specimen. The method allows the linear elastic far-field to be considered separately from the elasto-plastic near-tip field, except for coupling through a set of parameters that are determined explicitly in the matching. The effects of the plasticity are thus found, once and for all, from the solution of a set of standard elasto-plastic problems for a semi-infinite crack in an infinite body, whose properties may be tabulated. The solution for any particular specimen geometry and loading then follows from a small set of linear elastic solutions for the specimen, which define, through coefficients γij appearing in their near-tip expansions, all the parameters in the “inner” and “outer” solutions. The effects of plasticity appear in these parameters only through a set of constants Cti that define the far-field expansions of the “inner” (near-tip) solutions: they are material constants, depending upon the constitutive relation for the material, but not upon specimen geometry and loading. The J-integral, being obtainable from the far-field, is expressed as an explicit asymptotic series in the loading parameter e, whose coefficients are given as functions of the “elastic” parameters γij and the material constants Ci. It is demonstrated that a plastic-zone correction term, ry, can be chosen to yield a two-term asymptotic expansion for J; the value of ry depends upon the yielding model only through the constant C1. The Dugdale (1960) model of yielding is treated, as a simple example for which all calculations can be performed analytically, and for which exact solutions are available for comparison. Finally, the near-tip solutions are constructed for a material obeying the Mises yield criterion and associated flow-rule, using a specially developed finite element program. The first eight of the constants Ci are tabulated, which suffice to define the J-integral up to terms of order e6 (where e is a loading parameter) and some representative near-tip features are displayed graphically. The computed value of C1 shows that the conventionally adopted value for the plastic-zone correction ry is too large by a factor of roughly 2.8, if it is to yield a genuine asymptotic estimate for J. As an example, the “elastic” parameters γij are found, from a boundary collocation program, for a centre-cracked square plate subjected to tensile loading; and a plot of J versus load, and the plastic-zone shape at a particular load level, are displayed.

Some Recent Developments in Time-Series Analysis

Abstract: SUMMARY Recently published books on time series are briefly reviewed. Then a critical assessment is made of recent practical developments in time-series analysis, including the treatment of trend and seasonality, the Box-Jenkins forecasting procedure, adaptive filtering, Bayesian forecasting, spectral analysis, autoregressive spectrum estimation, the use of the Fast Fourier Transform and the identification of linear systems. The gas furnace data of Box and Jenkins are re-examined with somewhat surprising results. Finally, the relationship between time and spatial processes is briefly considered.

An arbitrary classification of the pore systems in avian eggshells

Abstract: An arbitrary classification of the pore systems in shells has been based on the observations made during a survey with a scanning electron microscope of the eggs of c. 60 avian species. The classification is intended primarily to aid comparative studies of shell function and field studies of the overall contribution of the shell to the embryo's well-being. The location and form of the external orifice of the pore was used to define four major types of pore systems: (1) outer orifice open—the pore canal terminates at the surface of the shell; (2) outer orifice occluded—the pore canal terminates at the surface of the shell but the orifice is occluded by amorphous, waxy material; (3) outer orifice capped—the pore canal terminates at the outer edge of the true shell and its orifice is capped and, in many species, plugged by a stratum of vesicles, either organic or inorganic, which clothes the entire surface of the shell, and (4) outer orifice reticulate—the pore canal terminates at the edge of the column layer and its orifice is covered by a calcareous stratum containing a plexus of tubules. Each group was further divided on the form of the pore canals; shells having unbranched pore canals were put into one category and those in which some pores branched into another.

Quantitative Studies on the Generation of Aerosols of Erwinia carotovora var. atroseptica by Simulated Raindrop Impaction on Blackleg‐infected Potato Stems

Abstract: Quantitative studies on the generation of bacterial aerosols by simulated raindrop impaction on potato stems infected with the blackleg organism Erwinia carotovora var. atrosep:ica have shown that, theoretically, airborne transmission might result in re-contamination of blackleg-free potato stocks.

What Does a Proof Do if it Does Not Prove

Abstract: One of the more interesting problems to arise from the Kuhnian (1) analysis of science is the problem of communication between scientists with differing cognitive commitments. By conceiving of scientists as being bound by monistic paradigms which change at times of scientific revolution Kuhn raised the problem of how scientists working within rival paradigms communicate. Kuhn refers to the adherents of the rival paradigms as talking ‘through each other’ (2) which implies that little communication between paradigms occurs.

Seasonal succession of algae in a eutrophic stream in Southern England

Abstract: The epipelic and epilithic algal communities in a small eutrophic stream situated in southern England expanded rapidly during March of both 1973 and 1974 primarily in response to changing light conditions. Although numbers varied greatly during the summer, these fluctuations were probably not due to nutrient, temperature or light conditions. High rates of disappearance of algae from the substrate were correlated with flooding, a deterioration of attachment characteristics and high metabolic rates. The episammic algal community consisted of only a few species, all of which showed maximum development during the summer. Although the well developed attachment mechanism and small size of the species undoubtedly aid in their ability to colonize sand grains, each species must be able to withstand frequent burial in the bottom deposits. Although temperature was probably an important factor controlling the number of epiphytes associated with Cladophora glomerata, light seemed to be of relatively less importance. Large numbers of isopods, amphipods and copepods occurred in the stream but their grazing seemed to have had little effect of the standing crop of the algae.

THE SENSITISING EFFECT OF A SUNSCREENING AGENT, p‐AMINOBENZOIC ACID, ON NEAR UV INDUCED DAMAGE IN A REPAIR DEFICIENT STRAIN OF ESCHERICHIA COLI*

Abstract: . The use of repair deficient strains of bacteria for detecting mutagenic properties of chemical species is now an established technique. In this paper we present inactivation results obtained with Escherichia coli K12 AB2480 (uvr A rec A) which indicate that p-aminobenzoic acid, a common component of sunscreening formulations, may increase the frequency of lethal damage induced in DNA when cell populations are exposed to near ultraviolet radiation. Preliminary experiments, utilising the selective action of photoenzymatic repair, indicated that the sensitisation to near ultraviolet radiation is partially but not wholly due to increased formation of pyrimidine dimers.

The influence of phosphorus, zinc and manganese on absorption and translocation of iron in watercress

Abstract: Absorption and translocation of iron by intact watercress plants (Rorippa nasturtium-aquaticum (L) Hayek) was studied in short period uptake experiments utilising 59Fe labelled ferric chloride. Total translocation of iron was inhibited by increasing levels of phosphorus, zinc and manganese in the nutrient medium; the elevated phosphorus and zinc concentrations enhanced iron absorption into roots, but increased retention of absorbed iron in translocating portions of the plant. High levels of manganese in the medium reduced the initial absorption of iron into the root system.

Changes in haemopoietic sites during the metamorphosis of the lampreys Lampetra fluviatilis and Lampetra planeri

Abstract: An investigation has been made in both the parasitic lamprey Lampetra fluviatilis and in its non-parasitic derivative Lampetra planeri of the rate at which the fat column replaces the typhlosole and nephric fold as the principal site of haemopoiesis. In the typhlosole, blood cell formation started to decline prior to the onset of external metamorphosis and had ceased within four weeks of the commencement of transformation. In the nephric fold haemopoiesis continued for several weeks in the region where the larval opisthonephros persisted but was never observed in the newly developing adult kidney. Soon after the onset of external metamorphosis the fat column started to become haemopoietic and later became the main site of blood cell formation. The rate at which the haemopoietic function was transferred from the nephric fold and typhlosole to the fat column was greater in L. fluviatilis than in L. planeri. Since a similar more rapid change in L. fluviatilis has also been found in the switch from larval to adult haemoglobin, the former type of haemoglobins may be produced only in erythrocytes originating in the nephric fold and typhlosole, whereas the latter type may be restricted to cells developed in the fat column. It is also suggested that the functional significance of the alteration in haemopoietic sites is related to changes at metamorphosis in the three regions where blood cell formation occurs.

Commutativity of time-varying systems

Abstract: Results are given concerning the commutativity of time-varying systems. It is shown that a constant-parameter dynamic system does not commute with a time-varying dynamic system. Conditions are derived for low-order time-varying systems to commute. A general condition for a set of time-varying systems to commute is the existence of a variable time scaling which reduces the time-varying systems to a set of constant-parameter systems.

Detection of symmetries in combinatorial functions by spectral means

Abstract: The detection of symmetries in switching functions is proposed using Rademacher-Walsh spectral techniques rather than Boolean-based methods. It is shown that the spectral domain can provide an immediate guidance to which symmetries may be present in any given function by a single necessary but not sufficient numerical test. Sufficiency may be proved by further simple checks. The power of the method enables a comprehensive range of symmetries to be defined, of which complete symmetry in all input variables is merely a special case. The possible use of symmetries in the efficient synthesis of given functions is briefly indicated.

The effects of disruptive behaviour on teachers

Abstract: (1977). THE EFFECTS OF DISRUPTIVE BEHAVIOUR ON TEACHERS. Educational Review: Vol. 29, No. 3, pp. 181-187.

The design of easily tested circuits using mapping and spectral techniques

Abstract: The results of a theoretical study of the application of mapping and spectral techniques to the design of digital circuits, with special emphasis on combinational circuits, are given. The method has the great advantage that the derivation of circuit tests is an integral part of the circuit synthesis procedure. Other advantages of the method are that very elegant designs are produced which are compatible with all modern fabrication technologies and permit low-cost implementation. This technique is fundamentally different to conventional methods of deriving easily tested circuits.

An ultrasonic study of the elastic phase transition in In-Cd Alloys

Abstract: Indium rich, In-Cd alloys undergo a f.c.c. to f.c.t. structural phase transition which the presence of a cubic invariant in the Hamiltonian renders first order. Ultrasonic wave velocity measurements have been made in single crystals of both the f.c.c. and f.c.t. phases, emphasis being placed on behaviour near the phase transition. The shear modulus ½(C 11-C 12) tends to very small values in both phases as the transition temperature T c is approached: the onset of instability is manifested as softening of the acoustic phonon branch with wave vector (110), particle displacement (110) near the Brillouin zone centre. However, in contrast to its behaviour in the In-Tl alloys, ½(C 11-C 12) does not go to zero in the In-Cd alloys. This finding corresponds to the more recognizable first-order character of the transition in the In-Cd compared to that in In-Tl alloys. The effect of the enhanced acoustic mode softening at T c on the wave velocity and Young's modulus surfaces is discussed. In addition to the...

Isolation of a glutaminergic receptor fraction from locust muscle.

Abstract: Electrophoresis of the purified receptor was performed in a 5 % gel containing 40: 1 (w/w) acrylamide/ bisacrylamide and 0.1 % Triton X-100, at pH 8.9 (Tris/glycine), with a 2.5 % stacking gel. A single protein band was obtained. Isoelectric focusing in the pH range 4-6 of the [3H]toxin-receptor complex shows PI to be about pH5. Acetylcholinesterase activity is absent. Electrophoresis in sodium dodecyl sulphate/polyacrylamide gels was used to reveal the subunits of the receptor (Table 1). Cat and rabbit muscle receptors showed the same subunit pattern. From the variation in the values quoted for all sources (Table l), a characteristic subunit pattern of the acetylcholine-receptor protein has not as yet been established. The purified receptor binds nicotinic cholinergic ligands strongly and selectively. The respective affinities for these are very close to those reported (Dolly & Barnard, 1974) for this receptor in an initial extract of denervated cat muscle.

The Modification of Nuclear Proteins by ADP-ribosylation

Abstract: When incubated in vitro purified mouse nuclei incorporate NAD into poly(ADP-Rib). Analysis of the product on CsDl/urea gradients showed that a large proportion of the poly(ADP-Rib) was not attached to protein. The free poly(ADP-Rib) did not appear to arise through degradation and its chain length was significantly longer than the poly(ADP-Rib) attached to proteins. Fractionation of the proteins on hydroxyapatite revealed that tissue-specific modification of both the histones and non-histone proteins, had occurred. In the case of one protein species there was evidence for the existence of several forms with different numbers of ADP-Rib residues.

Cosmic spherules as rounded bodies in space

Abstract: COSMIC spherules obtained from deep-sea sediments have generally been accepted as extraterrestrial; but their mode of formation has been uncertain. On chemico-mineralogical evidence and the study of polished sections, it is difficult to refute the assumption that the spherules are merely the droplets shed from the fusion crust of a meteorite as it ablates in the atmosphere. We are now re-examining a new spherule collection (diameter > 50 µm) from surface red clay samples used previously1; that is, Atlantic A2 (24°30′N, 64°47′W, 5949-m depth) and Pacific (22°07′S, 115°10′W, 3,060–3,200-m depth). Scanning electron microscopy of 40 ‘stony’ spherules and 25 ‘irons’ has led us to consider a new hypothesis—that the cosmic spherule is a round body in space and those that we find suffer only slight alteration during their grazing flight through the atmosphere. Interesting surface features exist on many of the spherules, both stones and irons, which make it difficult to believe that they have been sprayed from a meteorite. If our hypothesis can be substantiated, then cosmic spherules become important objects in their own right, a cometary origin beingas distinct possibility. We now show some of these surface feature and mention other supporting evidence. From the surface appearance we can classify the spherules into different types and forms, and all forms occur with similar relative frequency in Atlantic and Pacific oceans.

Some factors effecting algal densities in a eutrophic farmland stream

Abstract: Population dynamics of attached algae in a eutrophic farmland stream (Wellow Brook, England) were correlated through multiple regression analyses with changes in 7 physico-chemical parameters (temperature, light, water velocity, pH, NO3−N, P2O5−P, SiO2−Si). Samples were taken every 2 weeks for 25 consecutive months between June 1973 and June 1975. The relative significance of the 7 parameters in controlling densities varied widely depending on species. Overall light was most important, accounting for 28 and 17% of density changes in the epipelon and epilithon respectively. While winter flooding caused a sharp reduction in the density of these 2 communities, the concentration of P2O5−P and NO3−N and pH usually had little effect on numbers. The 7 parameters did not exert major control over the epiphyton, normally accounting for <30% of densities variation. Grazing by the protozoan Frontonia acuminata may have significantly reduced the density of the epipelon for 2 months during the spring but otherwise was of no importance to any community.

The function of root systems in mineral nutrition of watercress (Rorippa nasturtium-aquaticum (L) Hayek)

Abstract: The ability of ‘adventitious’ and ‘basal’ root systems of watercress (Rorippa nasturtium-aquaticum (L) Hayek) to absorb mineral nutrients from surrounding media has been demonstrated using radioisotopes 32P, 86Rb and 59Fe. Controlled experiments on single whole plants cultured in a dualmedium-apparatus, indicate that both root systems have a capacity for nutrient absorption. Analysis of axillary shoots formed during a seven day experimental period show that a greater proportion of phosphate and potassium, gained from the ambient media, was absorbed by the adventitious root system, although there was a greater mass of basal root tissue. Extensive translocation of nutrients to actively growing plant organs occurs from absorption sites on both root systems. re]19760504