Showing papers by "Newcastle University published in 1970"

Teichoic Acids and Membrane Function in Bacteria

Abstract: Selective destruction of teichoic acid reduces the ability of bacterial cell walls to bind Mg2+ ions.

A revision of the Jurassic reptile Hallopus victor (Marsh), with remarks on the classification of crocodiles

Abstract: The unique holotype of Hallopus victor (Marsh), from the Upper Jurassic of Garden Park, Colorado, is redescribed. The bones previously identified as pubes (Marsh 1890) or ischia (von Huene 1914) are regarded here as the left radius and ulna, and the ‘ ulna5 and ‘radius5 of previous workers are considered to be the left radiale and ulnare. Marsh’s identification (1890) of the ischium and his orientation of the scapula and femur (1896) are upheld. The presence of a humerus on the larger slab is confirmed. Hallopus is interpreted as a highly specialized, cursorial crocodilian, with slender, hollow bones, a greatly elongated radiale and ulnare, and a roller-like joint between these and the metacarpals. The manus is pentadactyl with a symmetrical distribution of lengths about the central axis and some proximal wedging-out of the metacarpals. The iliac blade is elongated and resembles that of Orthosuchus , the ischium is reminiscent of that of Protosuchus . The femur has a lesser trochanter, a fourth trochanter and a ‘pseudointernal9 trochanter, but no greater trochanter. The tibia is longer than the femur. The tarsus is basically crocodilian in pattern, but greatly compressed and specialized. The first metatarsal is reduced to an elongated splint, permanently recessed into metatarsal II. Metatarsals II to IV are symmetrical in length with III longest, metatarsal V is reduced, pointed, and lacks phalanges. The interpretation put forward provides a consistent explanation of the peculiarities of the skeleton of Hallopus as a variant on the basic crocodilian plan. The details of the articulation of the carpal and tarsal joints are described as far as preservation permits, and possible movements are considered. The carpometacarpal and tarsal joints are simple hinges, but the proximal carpal joint appears to have been relatively immobile and the elongation of the radiale and ulnare is viewed as a device to compensate for the increase in length of the tibia. The femur has an off-set, ball-like head and evidently moved essentially in a parasagittal plane. The pes is functionally tridactyl, with the metatarsals locked together proximally. It is concluded that both fore- and hind-feet were digitigrade during movement, although in a stationary pose the metatarsus may have been in contact with the ground. Some aspects of the pelvic and hind-limb musculature are briefly discussed. Functional analogies from the locomotory point of view are limited by the lack of cursorial quadrupedal archosaurs for comparison. It is concluded that a hare-like bounding gallop was the most probable type of fast locomotion in Hallopus . Although no skull bones have been identified, evidence from the postcranial skeleton is adduced to show that Hallopus is of pedeticosaurid descent. The relationships of early crocodilomorphs are discussed, and it is deduced that two basic stocks diverged from a common ancestry during the middle part of the Trias. These two groups are included in an expanded Order Crocodylomorpha. The Suborder Crocodylia has the Triassic Stegomosuchidae as its radicle and contains ‘ normal ’ crocodiles (including the Sebecosuchia but not the Baurusuchidae). The suborder Paracrocodylia is proposed for mainly cursorial forms, to include the infraorders Pedeticosauria, Baurusuchia and Hallopoda. Diagnoses for these groupings are presented. An origin for both stocks from a form close to Cerritosaurus is postulated. Erpetosuchus and Dyoplax are not now regarded as crocodilomorphs. The possibility of an early cursorial phase in crocodilian evolution is briefly discussed, and it is tentatively suggested that the gallop occasionally observed in young crocodiles (Cott 1961) may be a relic of a primitive type of locomotion in the group. The significance of this to the emergence of the crocodilian type of shoulder-girdle is considered.

Coral Skeletons: An Explanation of Their Growth and Structure

Abstract: Coral skeletons are constructed of aragonitic crystals organized into fan systems. A theoretical model for the growth of such fan systems, which depends upon competition between crystals for space in which to grow, is corroborated by vital staining with sodium alizarinesulfonate. Fan systems of crystals compete with each other to form larger fan systems until large, relatively stable fans are produced. It is these relatively stable fan systems that have been observed in optical thin sections of coral skeletons.

Spatially periodic dynamos

Abstract: It is established analytically that, in a precisely defined sense, almost all steady spatially periodic motions of a homogeneous conducting fluid will give dynamo action at almost all values of the conductivity. The same result is obtained for motions periodic in space-time. The asymptotic form of the growing field, for an arbitrary initial field of finite energy, is also presented. Dynamo action is first shown to require that for some real vector there is a magnetic field solution of the form B= H exp (pt+ij. x), where H is a complex function of position (or of position and time) with the same periodicity as the motion, and p has positive real part, indicating growth. This number p is an eigenvalue of a linear differential operator on the space of admissible functions H. The first term of a power series in j for the eigenvalues/) which vanish to zero order is studied. It is thus proved sufficient for dynamo action that the determinant of the symmetric part of a certain 3 x 3 tensor, a function of the motion and conductivity, is non-zero. Finally, it is shown that this determinant is an analytic function of the conductivity, and is non-zero in a small conductivity limit for nearly all motions. This proves the stated result.

IX.—The Postcranial Skeleton of Ensthenopteron foordi Whiteaves*

Abstract: Well preserved material of the crossopterygian fish Eusthenopteron enables fresh reconstructions and interpretations of its postcranial skeleton to be given. Comparisons throughout with other bony fishes show that it may be primitive in many features. Similarities with early amphibians such as the screw-shaped glenoid, the form of the humerus (on which an attempt to restore the pectoral musculature is based), the dorsal bicipital ribs and the possibility of a sacral attachment, throw much light on the origin of the tetrapod postcranial skeleton, particularly of the cheiropterygium. A functional analysis of the skeleton of Ensthenopteron is attempted, suggesting that it resembled the pike (Esox) in its mode of life and that it may have been capable of short journeys “walking” overland. The possible selective factors stimulating the evolution of such a fish, and further evolution to the tetrapod stage are discussed.

Aggregation of ferrihaems. Dimerization and protolytic equilibria of protoferrihaem and deuteroferrihaem in aqueous solution

Abstract: 1. The absorption spectra of deutero- and proto-ferrihaem in aqueous solution at 25 degrees C show marked changes with concentration and pH in the Soret band region. Quantitative studies of these phenomena imply that they are associated with ferrihaem dimerization and with protolytic equilibria involving monomeric (M) and dimeric (D) ferrihaem species according to the scheme: [Formula: see text] 2. For deuteroferrihaem we obtain K=1.9x10(-2), pK(a(M))=7.1, pK(a(D))=7.4. Protoferrihaem has a much higher dimerization constant, K=4.5 and pK(a(D))=7.5 (pK(a(M)) is not accessible). 3. Possible structural relationships between monomeric and dimeric ferrihaem species in solution are discussed in relation to recent work on the oxo-bridged nature of crystalline ferrihaem dimers.

The characterization of microporous carbons by means of the dubinin-radushkevich equation

Abstract: The Dubinin-Radushkevich (D-R) equation of adsorption predicts a Rayleigh distribution of adsorption free energy with adsorption (micropore) volume. Only when this distribution is present in microporous solids will a completely linear D-R plot result. Adsorption data of carbon dioxide at 195°K and nitrogen and argon at 77°K on various microporous polymer carbons are interpreted in terms of the D-R equation and distributions of free energy with pore volume. In no case is the complete Rayleigh distribution found to apply and corresponding deviations from linear D-R plots occur. Highly activated carbons show a bimodal distribution of free-energy values to nitrogen and argon at 77°K, but not to CO 2 at 195°K. Tentative suggestions for this behavior are presented.

Evidence from Gravity Anomalies for Thinning of the Lithosphere beneath the Rift Valley in Kenya

Abstract: Summary A detailed gravity survey of part of the Gregory Rift Valley in Kenya has shown a positive Bouguer anomaly over the rift floor between 0.25" N and 1.25" S. The anomaly is between 40 and 80 km wide and has an amplitude of 300-6OOg.u. (30-60mgal). Attempts to account for the anomaly with shallow mass-distributions lead to geologically unreasonable models. The geophysical and geological data are best satisfied if the anomaly is due to a dense intrusion. The required body must be about 20 km wide, and its upper surface must be less than 3 kin below the land surface. Other evidence in favour of this interpretation is presented, and it is shown that the models developed here are consistent with the crustal models of the area deduced from long-wavelength gravity anomalies by other workers. An intrusion of the magnitude inferred in this paper represents extreme thinning of the lithosphere below the rift valley.

XII.—The Postcranial Skeleton of Rhipidistian Fishes Excluding Eusthenopteron

Abstract: In a previous paper (Andrews and Westoll 1970) the postcranial skeleton of the best known rhipidistian, Eusthenopteron, was described, and its bearing on the origin of the tetrapod postcranial skeleton discussed. The postcranial remains of other Rhipidistia are now described as far as they are known, and comparisons are made with Eusthenopteron and other forms where relevant. Possible modes of function are considered in relation to the habitats in which these fishes may have lived. These studies have made it necessary to revise rhipidistian classification; the Family Rhizodontidae is re-defined and placed alone in a third Order of Rhipidistia (the Rhizodontida, alongside the better known Osteolepidida and Holoptychiida). Fresh insight has been gained into the following morphological problems: the composition of the osteolepid ring-like centrum, the origin of the tetrapod scapular blade and the diphyletic origin of the tetrapods.

File structures using hashing functions

Abstract: A general method of file structuring is proposed which uses a hashing function to define tree structure Two types of such trees are examined, and their relation to trees studied in the past is explained Results for the probability distributions of path lengths are derived and illustrated

Some relationships between implicit Runge-Kutta, collocation and Lanczosτ methods, and their stability properties

Abstract: In this paper relationships between various one-step methods for the initial value problem in ordinary differential equations are discussed and a unified treatment of the stability properties of the methods is given. The analysis provides some new results on stability as well as alternative derivations for some known results. The term stability is used in the sense ofA-Stability as introduced by Dahlquist. Conditions for any polynomial collocation method or its equivalent to beA-Stable are derived. These conditions may be easily checked in any particular case.

The Rikitake two-disc dynamo system

Abstract: It is shown that the solution of the Rikitake two-discdynamo system may be described by an orbiting point which, for sufficiently large time, lies arbitrarily close to a limit surface of bounded area. Reversal of the field currents of the dynamo coils are shown to occur in the juxtaposed regions of the two sheets of the limit surface. The two singular points of the system are shown, by Liapounov's direct method, to be unstable foci. An asymptotic theory is developed for the case of small difference in dynamo velocities; the theory is applied to cases of small dissipation in which orbits tend to become nearly periodic with a single oscillation between reversals.

Shallow water waves on shear flows

Abstract: An equation for waves on the surface of a flow with shear is deduced and shown to reduce by suitable scaling to the classical equation of Korteweg & de Vries, which describes such motions on a stationary flow. For steady flows the corresponding theory of cnoidal waves is obtained and the results of Benjamin (1962) for a solitary wave recovered.

The Mechanics of Stridulation in Bush Crickets (Tettigonioidea, Orthoptera): I. The Tegminal Generator

Abstract: 1. A method has been devised by which the isolated tegmina of bush crickets can be actuated in such a manner as to simulate the insect9s natural song. 2. The actuator was used to make a detailed analysis of the mechanics of sound production, with particular reference to the emission of the more or less pure tone at 15 kHz., characteristic of Homorocoryphus nitidulus . 3. Results involving damping and cautery indicated that the area of the right tegmen responsible for the radiation of this sound was the mirror frame, the vein enclosing the classical mirror membrane. 4. Further experiments involving transduced sound and a probe microphone led to the construction of sound radiation maps of the right tegmen which supported the above view. 5. The cantilever hypothesis, involving the mirror frame with the axis of the vestigial file as the cantilever9s rotational axis, was considered in the light of the Homorocoryphus type. 6. The Homorocoryphus type differed from the Conocephalus type (on which the cantilever hypothesis was based) in that a simpler cantilever is formed in a line direct from the plectrum to the tip of the frame arm.

Electron detachment from H- ions by electron impact

Abstract: A crossed beam method has been used to measure cross sections for H-+e to H+2e for interaction energies between 12 and 1000 eV For energies greater than 40 eV there is excellent agreement with measurements of Dance, Harrison and Rundel and when the energy exceeds 200 eV, the measurements confirm calculations by Inokuti and Kim based on Bethe's approximation No evidence of structure was found in the detachment function

Analysis of the code relating sequence to secondary structure in proteins.

Abstract: PROTEIN conformation depends for its specificity and stability on the interactions of side-chain groups. A complete analysis of the stability of such frequently occurring features as helical regions in terms of the energy of interaction of atoms and groups of atoms is very complex, and there has therefore been considerable interest in empirical rules for the formation of helical regions1,2. Attempts have been made to correlate helicity with amino-acids taken singly3–6 and in pairs7,9. The importance of amino-acid sequence as well as content has been established8,9.

A review of Red Sea heat flow

Abstract: There are now twelve heat flow measurements in the Red Sea made with heat flow probes from survey ships and several sets of temperature measurements made in deep exploration boreholes. The oceanic measurements are in water depths ranging from 0.94 to 2.70 km and all but one of these measurements give values significantly higher than the world mode of 46 mW m -2 (1.1 ). They include the world record high oceanic measurement of more than 3307 mW m -2 (79.0) in the neighbourhood of the hot brine pools. These measurements show that the deep axial trough of the Red Sea is associated with high heat flow, the values being similar to those found in the mid-Indian Ocean rift, the mid-Atlantic rift and over the crest of the East Pacific rise. It is of considerable interest to see if there is also high heat flow over the Red Sea margins and the main purpose of this paper is to examine temperature data from deep exploration boreholes. The boreholes are drilled mainly in rock salt, sandstones and shales. A discussion is given of the thermal conductivities assumed for these rocks. The boreholes have depths of up to 4 km and in some cases the temperature measurements enable an estimate to be made of the heat flow. These are also found to be high. The significance of the high heat flow to ideas concerning the structure and evolution of the Red Sea is discussed.