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In the classical 'first approximation' theory of thin-shell structures, the constitutive relations for a generic shell element--i.e. the elastic relations between the bending moments and membrane stresses and the corresponding changes in curvature and strain, respectively--are written as if an element of the shell is flat, although in reality it is curved. In this theory it is believed that discrepancies on account of the use of 'flat' constitutive relations will be negligible provided the ratio shell-radius/thickness is of sufficiently large order. In the study of drawing of narrow, cylindrical 'tethers' from liposomes it has been known for many years that it is necessary to use instead a constitutive law which explicitly describes a curved element in order to make sense of the mechanics; and indeed such tethers are generally of 'thick-walled' proportions. In this paper we show that the proper constitutive relations for a curved element must also be used in the study, by means of shell equations, of the buckling of initially spherical thin-walled giant liposomes under exterior pressure: these involve the inclusion of what we call the 'M[kappa]' terms, which are not present in the standard 'first-approximation' theory. We obtain analytical expressions for both the bifurcation buckling pressure and the slope of the post-buckling path, in terms of the dimensions and elastic constants of the lipid bi-layer, and also the initial state of bending moment in the vesicle. We explain physically how the initial bending moment can affect the bifurcation pressure, whereas it cannot in 'first-approximation' theory. We use these results to map the conditions under which the vesicle buckles into an oblate, as distinct from a prolate ('rugby-ball') shape. Some of our results were obtained long ago by the use of energy methods; but our aim here has been to identify precisely what is lacking in 'first-approximation' theory in relation to liposomes, and so to put the 'shell equations' approach onto a firm footing in mechanics.

It is well-known that a 'tether' may be drawn out from a pressurized liposome by means of a suitably applied radial-outward force applied locally to the lipid bilayer. The tether is a narrow, uniform cylindrical tube, which joins the main vesicle in a short 'transition region. 'A first-order energy analysis establishes the broad relationship between the force F needed to draw the tether, the radius [R.sub.0] of the tether, the bending-stiffness constant B for the lipid bilayer and the membrane tension T in the pressurized liposome. The aim of the present paper is to study in detail the 'transition region' between the tether and the main vesicle, by means of a careful application of the engineering theory of axisymmetric shell structures. It turns out that the well-known textbook 'thin-shell' theory is inadequate for this purpose, because the tether is evidently an example of a thick-walled shell; and a novel ingredient of the present study is the introduction of elastic constitutive relations that are appropriate to the thick-shell situation. The governing equations are set up in dimensionless form, and are solved by means of a 'shooting' technique, starting with a single disposable parameter at a point on the meridian in the tether, which can be adjusted until the boundary conditions at the far 'equator' of the main vessel are satisfied. It turns out that the 'transition region' between the tether and the main vessel is well characterized by only a few parameters, while the tether and main vessel themselves are described by very simple equations. Introduction of the thick-shell constitutive relation makes little difference to the conformation of, and stress-resultants in, the main vessel; but it makes a great deal of difference in the tether itself. Indeed, a kind of phase-change appears to take place in the 'transition region' between these two zones of the liposome. [DOI: 10.1115/1.1500341]

Due to technological pressures the lubricant film thickness in EHD contacts has decreased over the years and will continue to do so for the foreseeable future. On the other hand, financial constraints cause the surface roughness in these contacts to decrease very slowly, or might even cause an increase. As a result, the ratio of film thickness to composite roughness will continue to decrease. The question that remains to be answered is to what extent this decrease will affect the contact performance. A third development makes this question even more acute, the request of increased reliability. As a consequence, the problem of the detailed understanding of the elastohydrodynamic lubrication with rough surfaces is as urgent as ever. Recent work has shown that the features inside the contact deform, and that the level of deformation is a function of the wavelength of the feature and the contact operating conditions, including slip. This last aspect of the problem, which has not been addressed previously, forms the central topic of the current paper. Instead of studying the deformation of a real roughness profile, the deformation of its sinusoidal Fourier components is investigated.

An analysis of plane stress and strain problems, in which a stress concentration factor of three results from the presence of a circular hole and the doubling of stress is the classical result of a uniform shaft undergoing torsion, confirms the validity of a more powerful result. This resembles another valid powerful result in which the hoop stress sigma(theta) round the hole is linked to stresses at the same points without a hole.

In studying the waiting times between failures of a series system whose components fail independently and are replaced upon failure, it is well known that for large systems in time cquilibrium, the distribution of waiting times is approximately exponential. Correction terms are available to account for the finite number of components. Here, correction terms are developed for the finite age of the system as well. Also numerical studiesare presented indicating the magnitude of the error in reliability predictions based on the assumption of time equilibrium when system age is really finite. [ABSTRACT FROM AUTHOR]

Focuses on the Industrial Relations Act of Great Britain, which simplified the procedures which need to be followed to abolish a Wages Council. Criterion for abolition; Commission on Industrial Relations' recommendation of abolition in the case of Industrial and Staff Canteens; How trade union attitudes have hardened against the Wages Council system.

Focuses on the use of the Westerguaard method of plane elastic analysis to obtain an exact solution to the problem of an elastic roller crossing a gap, intended to represent a scratch, on a rigid half-space.