Showing papers by "Newcastle University published in 1973"

On the development of a solitary wave moving over an uneven bottom

Abstract: The numerical and experimental results given in Madsen and Mei(16) are predicted using asymptotic methods and some knowledge of the Korteweg-de Vries (K-dV) equation. This is accomplished by first deriving, using formal asymptotic expansions, the K-dV equation valid over a variable depth. The depth is chosen, in the first instance, to slowly vary on the same scale as the initial (small) amplitude of the motion. The appropriate form of the Kd-V equation is thenwhere H(X,ξ) describes the surface profile and d(σX) is the changing depth. The rest of the paper is devoted to a study of this equation.

The function of teichoic acids in cation control in bacterial membranes

Abstract: 1. The effects of teichoic acids on the Mg(2+)-requirement of some membrane-bound enzymes in cell preparations from Bacillus licheniformis A.T.C.C. 9945 were examined. 2. The biosynthesis of the wall polymers poly(glycerol phosphate glucose) and poly(glycerol phosphate) by membrane-bound enzymes is strongly dependent on Mg(2+), showing maximum activity at 10-15mm-Mg(2+). 3. When the membrane is in close contact with the cell wall and membrane teichoic acid, the enzyme systems are insensitive to added Mg(2+). The membrane appears to interact preferentially with the constant concentration of Mg(2+) that is bound to the phosphate groups of teichoic acid in the wall and on the membrane. When the wall is removed by the action of lysozyme the enzymes again become dependent on an external supply of Mg(2+). 4. A membrane preparation that retained its membrane teichoic acid was still dependent on Mg(2+) in solution, but the dependence was damped so that the enzymes exhibited near-maximal activity over a much greater range of concentrations of added Mg(2+); this preparation contained Mg(2+) bound to the membrane teichoic acid. The behaviour of this preparation could be reproduced by binding membrane teichoic acid to membranes in the presence of Mg(2+). Addition of membrane teichoic acid to reaction mixtures also had a damping effect on the Mg(2+) requirement of the enzymes, since the added polymer interacted rapidly with the membrane. 5. Other phosphate polymers behaved in a qualitatively similar way to membrane teichoic acid on addition to reaction mixtures. 6. It is concluded that in whole cells the ordered array of anionic wall and membrane teichoic acids provides a constant reservoir of bound bivalent cations with which the membrane preferentially interacts. The membrane teichoic acid is the component of the system which mediates the interaction of bound cations with the membrane. The anionic polymers in the wall scavenge cations from the medium and maintain a constant environment for the membrane teichoic acid. Thus a function of wall and membrane teichoic acids is to maintain the correct ionic environment for cation-dependent membrane systems.

Process Structuring

Abstract: ion is a means of avoiding unwanted complexity. Previously we indicated how very complex processes could be obtained from simple ones by combination, and noted that their separate correctness was insufficient to guarantee correctness of the combination. Abstraction plays a crucial role in mastering the complexity of such combinations. It allows, for example, a correctness proof for an entire system to be constructed from separate proofs for each process (under certain assumptions about its environment), plus a proof of cooperation (i.e., that all environmental assumptions are satisfied). The use of abstraction to establish properties of combinations of processes is not new [13]. It is tempting to assume that an abstraction of a combination of processes is the same as the combination of their separate abstractions [20]. Unfortunately this is not generally true. EXAMPLE: Consider a combined group of processes that are synchronized by means of P and V operations on semaphores, and an interpretation that \"loses\" the values of the semaphores. Now the abstraction (under this interpretation) of the combination will still reflect this synchronization, while the combination of the abstractions cannot be synchronized by the \"lost\" semaphores.ion of a combination of processes is the same as the combination of their separate abstractions [20]. Unfortunately this is not generally true. EXAMPLE: Consider a combined group of processes that are synchronized by means of P and V operations on semaphores, and an interpretation that \"loses\" the values of the semaphores. Now the abstraction (under this interpretation) of the combination will still reflect this synchronization, while the combination of the abstractions cannot be synchronized by the \"lost\" semaphores. Cornputmg Surveys, Vol 5, No I, March 1973 Recently, some attention has been devoted to the problem of finding restrictions which ensure that a combination of abstractions accurately models the abstraction of the, combination, or, equivalently, that combinations of refinements actually are a refinement of the intended combination [24). Suppose that we wish to establish the correctness and cooperation of a group of combined processes. First, we may use abstractions which select only the state variable sets of single processes; each image process now represents a single component of the combination, which may be studied separately. (The image will, of course, reflect nondeterministic changes in the input variables caused by other processes.) Next, we may study the abstraction ~hich reduces each sequence of actions within a single process that do not involve Input-output to a single action. Finally, if we ensure the mutual exclusion of the sequences of actions which constitute the input-output operations of separate processes, we can safely use the abstraction in which each such operation becomes a single action. There are two basic ways of achieving mutual exclusion of operations in a system involving asynchronous combination. Recalling the techniques discussed m Section 3.4, the availability of even fairly simple operations which are mutually exclusive may be used to ensure the mutual exclusion of operations consisting of arbitrarily many actions. Thus, this aspect of the correctness of a system can be treated as a recursive problem, with the mutual exclusion of operations on each level dependent on the achievement of mutual exclusion on a lower level. Of course, this recursion must terminate. It seems that the only technique for achiewng mutual exclusions ~hich is not based on a lower-level mutual exclusion mvolves an active clocking process which \"polls\" the processes it is clocking, and allows the critical operations to proceed one at a time. To date, practical applications of abstraction and combination in structuring complex systems have relied on informal conditions to assure that arguments about abstractions could be carried over to their refinements. Process Structuring • 25 This has, for example, been the case in the work of Dijkstra [13] and of Zurcher and Randell [37]. Both papers concern design methodologies in which the concept of levels of abstraction plays a central role. The former paper describes the design and structure of the \"THE\" multiprogramming system. The outstanding feature of this design methodology is the careful use of structure (in particular, levels) to enable the designers to satisfy themselves, a priori, as to the logical \"correctness\" of the system. The aim is to show that whenever a process is presented with a task, it will, under all circumstances, complete the task within a finite time and return to its \"homing position,\" ready to accept a new task. The proof proceeds in three stages: no process, while performing a single task, can lead to the generation of an infinite number of further tasks; when all processes have returned to their homing positions, no uncompleted tasks remain; there is no possibility of deadlock, so all processes must ultimately return to their homing positions. The feasibility of proofs of conjectures about systems as complex as the \"THE\" system depends strongly on the degree to which reliance on enumerative reasoning can be minimized [14]. The concept of multilevel processes is very useful in this regard. One can represent a group of sequential processes by a single image process, and prove that if this can progress, so can each of the set of processes of which it is an image. In further arguments it is then sufficient to satisfy oneself that the image process will always be able to progress. This technique can substantially reduce the number of situations which must be considered at each stage of the proof. Dijkstra also notes that this approach has significant advantages in testing a system as it is implemented. \" I t seems to be the designer's responsibility to construct his mechanism in such a way--i.e. so effectively structured--that at each stage of the testing procedure the number of relevant test cases will be so small that he can try them all and that ~hat is being tested will be so perspicuous that he will not have overlooked any situation.\" [13] The use of multilevel processes described Computing Surveys, Vol. 5, No. 1, M a r c h 1973 26 • J . J . Homing and B. Randell by Zurcher and Randell [37], on the other hand, grew out of the desire to simulate the design of a complex system as the design took shape. Thus, the simulation .would gradually evolve and grow, and possibly become the actual system. This naturally placed very severe demands on the understandability and modifiability of the simulation program, which were met, at least in part, by constructing it as a set of distinct levels. Each level represented, at an appropriate degree of abstraction, the state of the system and those actions of the system best described in terms of that particular abstraction. The number of sequential processes on a given level would be chosen independently of the number on any other level. (For example, one level might represent each of the dynamically varying number of jobs in the system as a sequential process; another level, each of the hardware processors as a sequential process.) There was a distinct methodological difference between these two efforts. Dijkstra's approach consisted of successively forming simpler images of lower-level operations, whereas Zurcher and Randell's approach consisted of successively forming refinements of higher-level actions. There is probably no single \"correct\" order in which to take a series of design, decisions, though it can usually be agreed that some orderings are better than others. Almost invariably, some early decisions (thought to have been clearly correct when they were made) will turn out to have been premature. A more extensive discussion of this topic is contained in [27]. 6. APPLICATIONS OF STRUCTURE \"The fact, then, that many complex systems have a nearly decomposable, hierarchic structure is a major facilitating factor enabling us to understand, to describe, and even to see such systems and their parts. Or perhaps the proposition should be put the other way round. If there are important systems in the world which are complex without being hierarchic, they may to a considerable extent escape our observation and our understanding. Analysis of their behavior would involve such detailed knowledge and calculation of the interactions of the elementary parts that it would be beyond our capacities of memory or computation.\" [30] Structuring techniques, and formalisms for their description, are of value only as they are applied. Our formalism has been developed because it, facilitates the careful consideration of both combination and abstraction ~4thin a uniform conceptual framework; we have concentrated on these two techniques because they are of profound importance in structuring the design and implementation of complex systems. Previous sections have discussed applications of particular techniques; in this concluding section we turn to more general uses. The importance of structuring is a result of its usefulness in mastering complexity. This applies whether one is trying to understand an existing system, or to design a proposed new system. The goal is to profit from this \"mastery\" by finding better ways of producing better systems, and, as an almost automatic by-product, better methods of documenting systems. However, it is important to recognize that structuring in itself is not necessarily beneficial; bad or excessive structuring may be valueless or even harmful. EXAMPLE: A program which has been divided into too many subroutines may not only be unreadable, but may also execute very inefficiently. The appropriate use of structure is still a creative task, and is, in our opinion, a central factor of any system designer's responsibility. \"When we cannot grasp a system as a whole, we try to find divisions such that we can understand each part separately, and also under

Reappraisal of ethylene glycol mono‐ethyl ether (egme) method for surface area estimations of clays

Abstract: Summary Using an ethylene glycol mono-ethyl ether (EGME) retention method, full unimolecular layer coverage of Ca-montmorillonite surfaces was established in 2 hours in an evacuated system (0.5 mm Hg) containing a free liquid surface of EGME and dry CaCl2, as a separate phase. EGME retention in the presence of CaCl2-EGME solvate led to incomplete unimolecular layer coverage, the EGME retention being governed by exchangeable Ca-EGME interaction and not by the real extent of the clay surface. Unlike montmorillonite which has the two layers of EGME molecules between adjacent alumino-silicate sheets, a vermiculite intercalated only one layer of EGME in the interlamellar space. Relevant X-ray and differential thermal microanalysis data are provided.

The effect of high sugar concentrations on the heat resistance of vegetative micro-organisms.

Abstract: Summary. The effect of sucrose or mixtures of sucrose and glucose, in the heating menstruum, on the heat resistance of 4 organisms, Salmonella senftenberg, Salm. typhimurium, Saccharomyces rouxii and Torulopsis globosa, was investigated and the results have been expressed in terms of D and z values against water activity (aw). The effect on the cell of sucrose solutions, both with and without heat, was also investigated. Measurements of cell volume obtained from phase contrast micrographs and of O.D. showed that as the sucrose concentration increased, the volume of the cell decreased. The increased heat resistance exhibited by cells in sucrose solutions of low aw is thought to be the result of a dehydration of the cell together with a reduction in the pore size of the cell wall.

Some general effects of phosphorus deficiency on growth and development

Abstract: Summary A number of general effects of phosphorus deficiency on plant growth are described. The experiments employed a wide range of species from different ecological habitats. Most species followed a similar pattern regardless of ecological origin. Seed size seemed to be the principal factor determining the severity of deficiency in short-term experiments. Deficiency affected root/shoot ratio, hydration and leuco-anthocyanin content. Even when plants were severely affected by deficiency they were sensitive to the physical environment.

Dielectric constant of non-polar fluids

Abstract: The theory of the static dielectric constant of non-polar fluids is re-examined using graph-theoretical techniques. A sample of arbitrary shape in an applied static electric field E 0 is considered...

Developmental Verbal Dyspraxia

Abstract: SummaryFeatures of developmental dyspraxia are described and comparisons are made with acquired conditions. The interrelationship of aphasia and dyspraxia is discussed. Consideration of the underlying mechanisms includes a description of the role of proprioception in acquisition and maintenance of speech and this is reviewed with reference to other perceptual processes. Some features which characterise the speech of the dyspraxic child are described and this, is followed by reference to current evaluative measures with indications for therapeutic programmes.

On an asymptotic solution of the Korteweg–de Vries equation with slowly varying coefficients

Abstract: The variable-coefficient Korteweg–de Vries equation \[ H_X + {\textstyle\frac{3}{2}}d^{-\frac{7}{4}}HH_{\xi} + {\textstyle\frac{1}{6}}\kappa d^{\frac{1}{2}}H_{\xi\xi\xi} = 0 \] with d = d (e X ) is discussed for solitary-wave initial profiles. A straightforward asymptotic solution for e → 0 is constructed and is shown to be non-uniform both ahead of and behind the solitary wave. The behaviour ahead is rectified by matching to the appropriate exponential form and, together with the use of conservation laws for the equation, the nature of the solution behind the solitary wave is discussed. This leads to the formulation of the solution in the oscillatory ‘tail’, which is again matched directly. The results are applied to the development of the solitary wave into variable-depth water, and the predictions are compared with those obtained, for example, by Grimshaw (1970, 1971). Finally, the asymptotic behaviour of both the solitary wave and the oscillatory tail are assessed in the light of some numerical integrations of the equation.

The gravitational field of three- dimensional galaxies

Abstract: The simplest method of calculating gravitational fields is to use a set of biorthogonal pairs of mass-potential functions. A suitable set of functions for three dimensional mass distributions is derived which uses ultraspherical polynomials. Algorithms for computing the gravitational field are discussed which attempt to maximise computational efficiency.

Palaeolimnology and Palaeomagnetism

Abstract: MAGNETIC studies of freshwater sediments from northwest England and Northern Ireland have revealed a wide range of applications of magnetic measurements to palaeolimnological studies. They have also shown that lacustrine sediments give a unique record of past changes in the geomagnetic field. This letter is chiefly concerned with the uses of magnetic measurements in helping to interpret lacustrine successions; Creer et al.1 have already discussed the implications of the secular changes of the Earth's magnetic field as recorded in the sediments of Lake Windermere.

Morphogenetic and proliferative changes in the regenerating lung of the rat.

Abstract: Unilateral extirpation of the lung in rats is followed by increased mitotic activity in alveolar cells of the contralateral lung, reaching a maximum six to seven days after operation. The response is delayed if the cavity created by the operation is packed with plastic sponge. Unilateral collapse of the lung without removal of tissue also leads to a contralateral mitotic response. Changes in the rate of cell proliferation evidently are not directly dependent on changes in tissue mass and it is suggested that compensatory growth in the lung may be controlled by chemical factors whose local concentration depends on variations in the rate of blood flow. Other changes which follow partial extirpation, observed particularly in the residual tissue of resected lungs, include high rates of proliferation in pleural cells, sub-pleural tissue and bronchial epithelium. It appears that in the regenerating lung new tissue may be formed partly by the proliferation of cells in the main mass of residual tissue and partly by more localized changes in specific tissues.