Showing papers by "Royal Holloway, University of London published in 1982"
TL;DR: In this article, the chemical potential of the L-J, sf3 fluid was evaluated by molecular-dynamics simulation for a Lennard-Jones (L-J) fluid and for a shifted-force fluid over a wide range of temperature and density by Widom's [6] particleinsertion energy method.
Abstract: We have evaluated the chemical potential by molecular-dynamics simulation for a Lennard-Jones (L-J) fluid and for a Lennard-Jones shifted-force (L-J, sf) fluid over a wide range of temperature and density by Widom's [6] particle-insertion-energy method. We have also investigated, in some detail, more recent methods [10, 11] using the energy of a real particle, and combinations of both methods using the energy-distribution functions. We find that these methods are accurate, convenient and economical but are no better than the straightforward Widom method. We confirm that the molecular-dynamics method is as good, if not better, than the corresponding Monte-Carlo techniques and the grand-canonical Monte-Carlo method. We present results for the properties of the L-J, sf3 fluid, in particular the liquid-vapour co-existence curve, including the critical point, and compare them with those for the L-J fluid and for liquid argon. The method is of general application and, in particular, may be directly used for mol...
133 citations
TL;DR: The activity of fructose 2,6-bisphosphatase was increased severalfold upon incubation in the presence of cyclic-AMP-dependent protein kinase and cyclic AMP and from a greater sensitivity to the stimulatory action of ATP and of glycerol phosphate at neutral pH.
Abstract: An enzyme that catalyzes the stoichiometric conversion of fructose 2,6-bisphosphate into fructose 6-phosphate and inorganic phosphate has been purified from rat liver. This fructose 2,6-bisphosphatase copurified with phosphofructokinase 2 (ATP: D-fructose 6-phosphate 2-phosphotransferase) in the several separation procedures used. The enzyme was active in the absence of Mg2+ and was stimulated by triphosphonucleotides in the presence of Mg2+ and also by glycerol 3-phosphate, glycerol 2-phosphate and dihqdroxyacetone phosphate. It was strongly inhibited by fructose 6-phosphate at physiological concentrations and this inhibition was partially relieved by glycerol phosphate and dihydroxyacetone phosphate. The activity of fructose 2,6-bisphosphatase was increased severalfold upon incubation in the presence of cyclic-AMP- dependent protein kinase and cyclic AMP. The activation resulted from an increase in V (rate at infinite concentration of substrate) and from a greater sensitivity to the stimulatory action of ATP and of glycerol phosphate at neutral pH. The activity of fructose 2,6-bisphosphatase could also be measured in crude liver preparations and in extracts of hepatocytes. It was then increased severalfold by treatment of the cells with glucagon, when measured in the presence of triphosphonucleotides.
125 citations
68 citations
TL;DR: It is shown that these species differ because of reciprocal translocations between some chromosomes, and that they would therefore be unable to produce fertile hybrids.
Abstract: . Methods are described for making chromosome preparations from developing embryos of Helophorus, for producing C- and G-banding, and for staining the nucleolus organizer with silver. These methods are used to compare the karyotypes of two species currently included in H.aquaticus (L.). It is shown that these species differ because of reciprocal translocations between some chromosomes, and that they would therefore be unable to produce fertile hybrids. Morphological differences in the male and female genitalia are described, and the range of aedeagal variation shown by each species is established by reference to chromosome preparations from testis. Reference to the relevant type specimens shows that the two species are H.aequalis Thomson and H.aquaticus (L.). The latter is not a British species. Differences in the egg cocoons and third instar larvae are described. The present distributions and Pleistocene histories of the two species are described.
60 citations
TL;DR: In this paper, the Raman and infrared spectra of dimethyl formamide-h7, DMF-d6, DMFs-d7, (CH 3)214H13CHO, and (CH3)215N12CHO were measured.
58 citations
TL;DR: It is suggested that C. hirundinella has both a resting cyst, forming part of the life cycle, and a temporary cyst stage, which is less resistant to decay and do not show the reorganization of cell contents for dormancy.
Abstract: Cyst formation in Ceratium hirundinella (O. F. Mull.) Bergh was studied by light and electron microscopy, using material from several lakes and reservoirs and also laboratory cultures. Cells preparing to encyst build up large quantities of starch and lipid and at the same time reduce their other cell components. The cyst is released from the theca as a naked cell bounded by a double membrane. The most commonly found cyst deposits a layer of electron-dense granules containing silicon on the outer membrane and lays down a cellulose-like material between the two membranes. Cysts without the electron-dense granules are commonly formed in cultures but rarely found in lakes. These cysts appear less resistant to decay and do not show the reorganization of cell contents for dormancy. It is suggested that C. hirundinella has both a resting cyst, forming part of the life cycle, and a temporary cyst stage.
52 citations
TL;DR: Chalcone isomerase (EC 5.6) from cell suspension cultures of Phaseolus vulgaris has been purified about 400-fold as discussed by the authors, which appears to require no cofactors, catalyses the isomerisation of both 6′-hydroxy and 6deoxy chalcones to the corresponding flavones.
51 citations
TL;DR: In this paper, the authors measured the colonization pattern of aquatic Hyphomycetes on five-gram leaf packs of oak and alder submerged in a stream and compared.
Abstract: The colonization-pattern of aquatic Hyphomycetes on five-gram leaf packs of oak and alder submerged in a stream was quantified and compared. There were three series of alder leaves, submerged two weeks apart, and one series of oak. Colonization of leaves by pectolytic bacteria was also measured. There were marked similarities in the colonization of all four series. Total spore counts/g dry wt of leaf rose to a peak followed by a decline. The time taken to peak colonization was slower in oak than in alder, and in alder depended on the level of inoculum in the stream, as did the extent of colonization. Pectolytic bacteria counts followed the pattern of total spore counts, suggesting the exploitation of the same substrates by bacteria and fungi. Temperature and micro-environmental factors influence the overall rate of leaf degradation. Alder I was skeletonized in 10 wks, Alders II and III in 12 wks and oak in 25 wks. The resource was shown to have an upper limit of microbial colonization, and within this ‘unit-community’ of microbes, there was an association of four dominant species of aquatic Hyphomycetes, together with about ten occasional species. The dominant species are subject to selection from the inoculum available in the stream and the formation and maintenance of the association appears to be the result of competitive interactions between species which results in a dynamic equilibrium. There is a low degree of resource specificity. The species equilibrium is 14 for all series, and species numbers are initially low, rise to a peak, then tend to decline. There is a taxonomic similarity of about 60% between successive stands of all series and between matched stands of alder.
48 citations
TL;DR: In this article, Semiclassical molecular dynamics of wave packets are studied. But they focus on wave packets and do not consider wave packets in the context of wave packet propagation.
Abstract: (1982). Semiclassical molecular dynamics of wave packets. Molecular Physics: Vol. 46, No. 3, pp. 671-677.
42 citations
TL;DR: The conformational energy map for the simplest possible dipeptide was obtained from the ab initio Gaussian-70 package using the STO-3G basis set as mentioned in this paper.
41 citations
TL;DR: There are several cell-free systems from eukaryotic organisms capable of in vitro carotenogenesis and an Amphidinium homogenate has been found to synthesize xanthophylls and P-carotene from MVA.
TL;DR: This paper examined European perceptions of non-Europeans (especially Malays) and the way ethnic attitudes affected colonial administration and concluded that the British influence upon the Malay's image of themselves was partly common to the empire as a whole and partly peculiar to Malaya.
TL;DR: Patterns of phytoalexin accumulation have been studied in response to varying concentrations of the crude and fractionated elicitor; 5-hydroxy isoflavonoid accumulation is highly dependent upon elicitor concentration, the dose-response curves for kievitone accumulation showing maxima at around 1 μg glucose equivalents per cotyledon, minima at 2–3 μg equivalents and increasing induction at higher concentrations.
Abstract: In wounded cotyledons ofPhaseolus vulgaris L. the accumulation of the 5-hydroxy isoflavonoids kievitone and 2′-hydroxygenistein precedes the major increases in the levels of the 5-deoxy compounds phaseollin and coumestrol. Increased phytoalexin levels are preceded by transient increases in the extractable activities of L-phenylalanine ammonia-lyase (EC 4.3.1.5.), chalcone synthase and chalcone isomerase (EC 5.5.1.6.). Accumulation of phytoalexins, above wounded control levels, is observed following treatment of excised cotyledons or hypocotyls with crude or fractionated elicitor preparations heat-released from the cell walls ofColletotrichum lindemuthianum. Chalcone synthase levels are also induced in cotyledons, although crude elicitor and all fractions suppress L-phenylalanine ammonia-lyase activity in both tissues. Kievitone is the major phytoalexin induced in cotyledons, whereas in hypocotyls phaseollin predominates. Patterns of phytoalexin accumulation have been studied in response to varying concentrations of the crude and fractionated elicitor; 5-hydroxy isoflavonoid accumulation is highly dependent upon elicitor concentration, the dose-response curves for kievitone accumulation showing maxima at around 1 μg glucose equivalents per cotyledon, minima at 2–3 μg equivalents and increasing induction at higher concentrations. Similar patterns are observed for L-phenylalanine ammonia-lyase and chalcone synthase levels, although the overall extent of these changes is masked by the high wound response. Accumulation of 5-deoxy isoflavonoids above control levels requires high elicitor concentrations; no experimental conditions were found under which phaseollin accumulated to higher levels than kievitone in cotyledons during the first 48 h after elicitation.
TL;DR: The results presented are unique in that the enzyme activity is specific for galactose and its lectin activity is Specific for glucose/mannose.
TL;DR: In this paper, a new molecular dynamics method is described which enables the simultaneous simulation of hard sphere collisions in the presence of "soft" forces, and it is shown that the Debye-Huckel theory, DHX, describes well the equation of state of charged hard spheres up to an equivalent electrolyte concentration of 1 M.
TL;DR: In this article, the results of 1H 400 MHz NMR studies on the MeSnCl3/D2O system at various concentrations have established the presence of a cationic monoalkyltin aquo-species.
TL;DR: In this paper, the free energy of a model of nitrogen is calculated over its liquid range by Monte Carlo methods and a comparison is made between the results of several Monte Carlo techniques.
Abstract: The free energy of a model of nitrogen is calculated over its liquid range by Monte Carlo methods. A comparison is made between the results of several techniques. The meaning of Metropolis Monte Ca...
TL;DR: In this paper, the feasibility conditions for distance-regular graphs are surveyed and a classification scheme is set up, and constructions and examples for the various cases are given, as well as a classification of different types of distance regular graphs.
Abstract: A distance-regular graph of diameter three is a natural generalization of a strongly regular graph, its structure being determined by five parameters. In this paper the feasibility conditions for such graphs are surveyed, and a classification scheme is set up. Constructions and examples for the various cases are given.
TL;DR: In this article, an iterative procedure for solving the likelihood equations is derived which includes the covariance determinant, which has many of the computational advantages of the direct representation of Godolphin (1977, 1978).
Abstract: SUMMARY Several authors have described methods for computing the exact maximum likelihood estimates for the parameters of a Gaussian moving average process. In this paper, an iterative procedure for solving the likelihood equations is derived which includes the covariance determinant. The procedure expresses the estimator of each parameter as a linear combination of a suitably large set of sample serial correlations which has many of the computational advantages of the direct representation of Godolphin (1977, 1978). It is also shown that the two procedures lead to virtually the same set of estimates for sample sizes likely to be encountered in practice. These results imply that the additional effort required to compute exact maximum likelihood estimates is hard to justify. Illustrations of all three procedures are given separately for the moving average model of order one: the iterative procedure for maximizing the exact likelihood function is less stable than the approximate procedures in certain cases.
TL;DR: In this paper, the first and second Legendre moments of the total pair distribution were calculated from the site-site distribution functions, g αγ(r αγ), which describe the fluids.
Abstract: Various forms of the site superposition approximation (SSA) have been tested for fluids of homonuclear diatomic molecules. These approximations allow the first and second Legendre moments of the total pair distribution, function [Gtilde](r αγω1 αω2 γ to be calculated from the site-site distribution functions, g αγ(r αγ), which describe the fluids. These two Legendre moments, g 100(r αγ) and g 200(r αγ), together with the site-site distribution function (≡g 000(r αγ)) can be used to calculate many of the structural and thermodynamic properties of a simple ISM fluid. The most accurate SSA for calculating the g l00(r αγ) includes correlations along only two of the intermolecular distance which define the geometry of a molecular pair. This leads us to suggest a new family of simpler approximations, one of which is exact at low density and which accurately reproduces the pressure and mean squared torque of the fluids.
TL;DR: Three highly purified α-galactosidases, I, II 1 and II 2 have been isolated from resting Vicia faba seeds and form I is a tetrame.
TL;DR: In this paper, power studies for three tests of fit, namely the classical test given by Whittle, the widely-known measure given by Ljung and Box, and the recent test derived by Godolphin, are derived for the invertible time series models considered previously in an empirical study.
Abstract: Power studies for three tests of fit, namely the classical test given by Whittle, the widely-known test given by Ljung and Box, and the recent test given by Godolphin, are derived for the invertible time series models considered previously in an empirical study. The results demonstrate that it is possible to improve on the Ljung-Box test by employing more empirically-based alternatives. In particular, the test derived by Godolphin appears to be more powerful than the other tests. The results also suggest that the Whittle and Ljung-Box tests are complementary, so that the combination of both may yield a sensitive test procedure.
TL;DR: This paper shows how random access to data and recursive properties of the numerical procedure are both obstacles in the way of vectorizing current lattices gauge theory calculations on the CDC CYBER 205 to provide impressive reductions in the processing time required.
TL;DR: In this paper, the preferred conformation of the α-amino-isobutyric acid residue (α-AIB) is obtained without explicit computation of its wave function.
Abstract: Information about the preferred conformation of the α-amino-isobutyric acid residue (α-AIB) is obtained without explicit computation of its wave function. The conformation of lowest energy of this residue is close to the usual helical conformation and so the residue may occur at the 2 position of a type I or I' bend or in either position of a type Ill or Ill' bend. The available experimental information refers to a β bend formed from α-AIB-PRO and then the theory and experiment agree that the only possibility is a type III bend. It is predicted that a β sheet structure may be formed at rather higher energy and in the planar and not the pleated form. There is no apparent reason why this residue should not form an α helix. The simplified method used here is closely related to the partitioned potential energy methods which are widely used in this subject.
TL;DR: In this paper, the authors established certain topological conditions that ensure the free rolling and sliding of a convex body inside a polygonal body in the Euclidean plane.
Abstract: If C and C o are two convex bodies in E d we say that C slides (rolls) freely inside C o if the following condition is satisfied: for each x ∈ ∂ C 0 (and each rotation R ) there is a translation t such that, if gC = C + t (= RC + t ), then gC ⊂ C o and x ∈ ∂ gC . This work establishes certain topological conditions which ensure the free rolling and sliding of C inside C o . One consequence of these conditions is that, if ∂ K ∩ int gK is a topological ball for all rigid motions g , then K is a ball in the geometrical sense.
TL;DR: Using Monte Carlo techniques on a four-dimensional space-time lattice, this paper studied SU(N)/ZN gauge theories for N = 3, 4, 5 and 6, finding first-order phase transitions at critical inverse temperatures of βc = 6.40, 12.0, 19.5 and 32.0.
TL;DR: In this paper, the relative contributions from spin-rotation and dipole-dipole mechanisms vary: larger molecules have lower spin rotation and higher dipolar relaxation rates, while small molecules have higher spin rotation.
Abstract: Dipole-dipole relaxation via non-bonded protons is an important relaxation mechanism for119Sn in tri-n-propyltin and tri-n -butyltin compounds. This causes a negative nuclear Overhauser effect, arising from the negative magnetogyric ratio, which in some cases nulls the signal. The relative contributions from the spin-rotation and dipole-dipole mechanisms vary: larger molecules have lower spin-rotation and higher dipolar relaxation rates. The practical significance of large nuclear Overhauser enhancement factors in recording 119Sn spectra and the relation of the dipole-dipole contribution to the molecular motion and of the spin-rotation contribution to the absolute shift scale for 119Sn are discussed.