Showing papers by "Royal Holloway, University of London published in 1976"

Transport properties of molten alkali halides

Abstract: The transport properties of molten alkali halides have been calculated in molecular dynamics "experiments" based on rigid-ion pair potentials of the Huggins-Mayer form with parameters proposed by Tosi and Fumi. The coefficients of shear viscosity and electrical conductivity are obtained by computing the response of the system to a small applied field of the appropriate type, and the extension of the method to the calculation of current-current correlation functions of acoustic and optic character is also considered. Comparison with experimental data shows that the electrical conductivities are very well reproduced, but systematic discrepancies are found for diffusion coefficients and viscosities.

Heuristics for Scheduling Resource-Constrained Projects: An Experimental Investigation

Abstract: This paper considers the project scheduling problem with multiple constrained resources. Two classes of heuristic procedure, both making use of priority rules, are discussed: the parallel method, which generates just one schedule; and the sampling method, which generates a set of schedules using probabilistic techniques and selects the best schedule from this sample. An experimental investigation is described in which a set of projects with different characteristics is scheduled by each of these heuristics with a variety of priority rules. The effects of the heuristic method, the project characteristics and the priority rules are assessed. It is shown that the choice of priority rule is important with the parallel method, but with the sampling method, although it does affect the distribution of the sample, the choice of rule is not significant. The sampling method with sample size 100 is shown to produce samples at least 7% better than those generated by the corresponding parallel method, with 99% confidence. Further results are discussed and conclusions are presented.

Thermodynamic and dielectric properties of polar lattices

Abstract: Monte Carlo results are presented for the free energy and dielectric constant of systems of permanent dipoles disposed on the sites of simple cubic and face-centred cubic lattices as functions of the parameter ϑ = μ2ρ/kT. Alternative schemes are considered for taking account of the long-range character of the dipolar interaction, based on an Ewald-type sum or a reaction-field approximation; use of such a procedure is essential if the system is to have the correct dielectric properties. Different methods of calculating the dielectric constant are also compared. It is shown that the two methods of treating the long-range contribution to the energy lead to similar results for the dielectric constant, but use of the Ewald method apparently introduces a small but systematic error. The results on both free energy and dielectric constant are discussed in the light of predictions of a number of analytical approaches. In the case of the simple cubic lattice the general trend in the computed dielectric constant as ...

Effects of polarization on equilibrium and dynamic properties of ionic systems

Abstract: Molecular-dynamics calculations are reported for systems of ions in which the contribution to the interionic forces arising from polarization is taken explicitly into account. Two models of polarization are considered: a modification of that used for alkali-halide molecules by Tosi and Doyama and a simplified version of the shell model of lattice dynamics. In each case the effects of polarization are superimposed on an underlying rigid-ion pair potential of the type proposed by Tosi and Fumi. Calculations of the phonon spectra show that use of either model leads to agreement with experimental data on solid NaCl, which is considerably better than that achieved with the Tosi-Fumi potential alone; good results are also obtained for solid KI. Calculations for molten KI based on the shell model show that the effect of polarization in the liquid state is to increase significantly the diffusion coefficients, particularly that of the positive ion, and decrease the shear viscosity, but the effect on electrical conductivity is almost negligible. These results are broadly consistent with the known adequacy of the rigid-ion-model to account for the transport coefficients of molten alkali halides. Polarization is also shown to lead to a reduction in the characteristic frequencies and a considerably increased damping of collective longitudinal-optic-type modes in the liquid. The effect on other collective modes is less pronounced.

A comparison of daphnid gut particles with the sestonic particles present in two Thames Valley reservoirs throughout 1970 and 1971

Abstract: Summary The numerically most abundant component of the seston in two of the Thames Valley storage reservoirs of the Metropolitan Water Board consisted of flocculent organic material which, together with the hyaline, transparent and blackened particles, formed the non-living sestonic fraction. The abundance of bacterio-plankton was estimated from plate counts which are known to provide an under-estimate of the bacteria present. The phytoplankton consisted of the larger flagellates present throughout the year together with a seasonal succession of algae in much greater numbers, namely the smaller flagellates, diatoms, colonial greens, Tribonema and Anabaena. A seasonal analysis of the gut contents of Daphnia magna, D. pulex and D. hyalina (occurring as important grazers in the reservoirs), revealed the presence of organic particles throughout the year plus cells or filaments of the prevailing alga at different seasons. During the summer, there were periods when the guts contained recognizable animal and plant debris. Flagellate and bacterial remains were never seen intact in the guts although these were abundant in the seston during early spring. The filamentous Tribonema was ingested when large crops of it were present. The most frequent size of ingested particle was between 1–2 μm and up to 60% of the animals examined contained particles which were neither longer nor wider than 20μm. Most of these animals ranged between 0·5–1·9 mm in length. A limiting factor for ingestion was thought to be width rather than length of particle and most very large particles found in the gut were long narrow and pliant filaments like Tribonema, or gelatinous colonial green algae, or flexible, foldable crustacean filtering limbs. There appeared to be no difference in the nature or size of particle ingested by the three different species of daphnids and any difference in maximal particle width observed was more likely to be related to body size than to species of consumer.

Carotenoids as additional taxonomic characters in fungi: A review

Abstract: The aim of this review is twofold: first to discuss some of the pitfalls of carotenoid identification in fungi and secondly to observe to what extent carotenoids may be useful as taxonomie characters. The results suggest that a number of carotenoids have been wrongly identified and that with newer techniques available, new carotenoids will almost certainly be identified which may help taxonomists. In a number of cases carotenoids are very good taxonomie markers.

Electron impact excitation of the n1P(n=2-5) and 23P states of helium at intermediate energies

Abstract: Calculations are reported on the electron impact excitation of the n1P (n=2,3,4,5) states of He from the ground state. The incident energy range covered is from threshold to 500 eV, and the calculations are carried out in the distorted-wave polarized-orbital model. Total cross sections for all n

Automorphic graphs and the Krein condition

Abstract: An automorphic graph is a distance-transitive graph, not a complete graph or a line graph, whose automorphism group acts primitively on the vertices. This paper shows that, for small values of the valency and diameter, such graphs are rare. The basic tool is the intersection array, for which there are several very restrictive feasibility conditions. In particular, a slight generalisation of the Krein condition of Scott and Higman is given, with a simplified proof.

Salmonellosis in wild mammals.

Abstract: One thousand two hundred and sixty-nine freeliving, wild mammals, representative of 16 species from estates in Berkshire, Oxfordshire and Surrey, were examined for the presence of salmonellas. Salmonella typhimurium was isolated from 1 and S. dublin from 7 house mice (Mus musculus). There were no isolations from the other species examined. It was concluded that the house-mice infected with S. dublin acquired the organism from experimentally infected cattle. The wild mammal population does not at present appear to constitute a reservior for infection of domestic animals.

The distribution of Nematospiroides dubius within the small intestine of laboratory mice.

Abstract: Analyses of primary infections of Nematospiroides dubius in male and female laboratory mice show that on days 4–6 post-infection worms occupy up to 50% of the small intestine but as the age of the infection increases worm populations are highly aggregated in relation to the anterior sections of the small intestine. Individual worms are also shown to be aggregated with respect to each other. Between days 42 and 60 postinfection, although the pattern of distribution of N. dubius along the small intestine does not significantly change, survival of worms is influenced by both age and sex of ASH/CSI S.P.F. mice, reasons for which are discussed in the light of previous work on primary infections of N. dubius in other strains of laboratory mice

On approximation with algebraic numbers of bounded degree

Abstract: In this paper we are interested in two related measures of the degree of approximation of a complex number ζ by algebraic numbers. For a given integer n ≥ 1, write wn(ζ) for the supremum of the exponents w for whichfor infinitely many polynomialsin Z[x] of height H(P) = max |av|. Clearly 0 ≤ w1 (ζ) ≤ w2 (ζ) ≤ …. On the other hand, write for the supremum of the exponents w for whichfor infinitely many algebraic numbers α of degree at most n.

The permeability of the asteroid podial wall to water and potassium ions

Abstract: Direct measurement of water loss from isolated podia of Luidia ciliaris under the influence of known levels of hydrostatic pressure has yielded a revised value for the permeability of this structure to water, namely 37.4 x 10-8 cm3/cm2.s.cm H2O pressure. The total fluid loss from a 50 g starfish will therefore be of the order of 0.75 ml/h. The mechanism for the replenishment of this fluid is discussed in the light of the traditional role of the madreporite. It would seem that adequate influx of fluid through this structure has not been observed, neither could it be responsible for ‘topping up’ in the case of arms severed from the parent body which still continue to move for considerable periods.

The historiography of Malaysia: Recent writings in English on the history of the area since 1874

Abstract: (1976). The historiography of Malaysia: Recent writings in English on the history of the area since 1874. The Journal of Imperial and Commonwealth History: Vol. 5, No. 1, pp. 82-110.

Characterization of a β-1,4-glucan hydrolase from the snail, Helix pomatia

Abstract: 1. 1. A β-1,4-glucan hydrolase (β-1,4-glucan 4-glucanohydrolase E.C. 3.2.1.4), purified to homogeneity from snail intestinal juice, has been characterized in terms of substrate specificity, kinetics of action and other properties. 2. 2. The purified glucanase degrades polysaccharides and oligosaccharides containing β-1,4-glucosidic linkages, the smallest substrate being cellotetraose. Glucans of the lichenin type, which contain both β-1,3- and β-1,4-glucosidic linkages, are also hydrolyzed. 3. 3. The Michaelis constants of the enzyme for carboxymethylcellulose and lichenin are identical (1·5 mg/ml), but the maximum velocity is higher towards the former substrate. 4. 4. The enzyme is without action on native cellulose and a number of other β-1,4-glycans, but acts slowly on salep mannan. 5. 5. Helix pomatia β-1,4-glucanase has maximum activity at pH 5·5–6·0, optimum temperature 45°C, and is stable at temperatures up to 45°C. 6. 6. The molecular weight as determined by polyacrylamide gel electrophoresis is 51,000. 7. 7. The enzyme is inhibited by EDTA and stabilized and activated by calcium ions suggesting that, like β-glucan hydrolases from plant and microbial sources, it is calcium-dependent.

Studies on the biology and distribution of Leptinus testaceus Müller within a community of mixed small mammal species

Abstract: 1 In a mixed small mammal community L.testaceus was found to infest A.sylvaticus more frequently than either C.glareolus or M.agrestis. 2 Male and female rodents carried similar numbers of the beetle. 3 Peak infestation on A.sylvaticus occurred during spring and summer suggesting a single major emergence period. 4 There was good correlation between the beetle index and the numbers of individuals of A.sylvaticus infested; this relationship resembled that found within certain host/ectoparasite relationships.

On the Cramér-Wold factorization

Abstract: SUMMARY Several authors have considered the problem of deriving the q moving average parameters of an autoregressive-moving average process of order (p, q), given estimates of the p autoregressive parameters and the first q members of the parent autocorrelation function; the problem was first raised by H. Cramer and H. Wold. The problem is discussed in connexion with the parameter estimation procedures of Walker (1961, 1962) and of Box & Jenkins (1970). An approach to the problem is described which is most suitable in the common cases where q is small; otherwise a factorization routine due to Wold (1954) is found to be preferable for most practical purposes when q is moderately large, whilst an iterative algorithm due to Tunnicliffe Wilson (1969) has more desirable properties in all other cases.