Free variables and first-class environments

A simple set of extensions to theSCHEME language removes the need for a distinguished top level interaction environment by providing first-class environments. These extensions also provide a powerful mechanism for code packaging and may be used to implement simple object-oriented systems. In addition, a mechanism is presented that implements compiled references to free variables as efficiently as in languages likeC, provided the code does not directly manipulate first-class environments. The mechanism requires a simple static analysis performed by the compiler and meshes with a slower mechanism used by both interpreted code and compiled code that manipulates first-class environments.Author's new affiliation is Digital Equipment Corporation, Cambridge Research FacilityThe authors want to express their gratitude to Christopher Hanson of the MIT Scheme Team for his help with an early version of this paper and his invaluable comments on several subsequent drafts. Prof. Harold Abelson of MIT provided encouragement and also contributed a number of helpful comments.     

Interpretation of electrochemical measurements made during micro-scale abrasion-corrosion

This paper brings together and analyzes recent work based on the interpretation of the electrochemical measurements made on a modified micro-abrasion-corrosion tester used in several research programmes. These programmes investigated the role of abradant size, test solution pH in abrasion-corrosion of biomaterials, the abrasion-corrosion performance of sintered and thermally sprayed tungsten carbide surfaces under downhole drilling environments and the abrasion-corrosion of UNS S32205 duplex stainless steel. Various abrasion tests were conducted under two-body grooving, three-body rolling and mixed grooving-rolling abrasion conditions, with and without abrasives, on cast F75 cobalt-chromium-molybdenum (CoCrMo) alloy in simulated body fluids, 2205 in chloride containing solutions as well as sprayed and sintered tungsten carbide surfaces in simulated downhole fluids. Pre- and post-test inspections based on optical and scanning electron microscopy analysis are used to help interpret the electrochemical response and current noise measurements made in situ during micro-abrasion-corrosion tests. The complex wear and corrosion mechanisms and their dependence on the microstructure and surface composition as a function of the pH, abrasive concentration, size and type are detailed and linked to the electrochemical signals. The electrochemical versus mechanical processes are plotted for different test parameters and this new approach is used to interpret tribo-corrosion test data to give greater insights into different tribo-corrosion systems. Thus new approaches to interpreting in-situ electrochemical responses to surfaces under different abrasive wear rates, different abrasives and liquid environments (pH and NaCl levels) are made. This representation is directly related to the mechano-electrochemical processes on the surface and avoids quantification of numerous synergistic, antagonistic and additive terms associated with repeat experiments.     

Extracting pumps for breastfeeding

Nursing mothers can use a variety of devices to aid them while they are breastfeeding their children. Among these are pumps which extract milk from their breasts. In this article, the general features of different types of extracting pumps available to nursing mothers are described. Nurses will be able to acquire knowledge not only about how these devices work but nurses can learn when their use is indicated, what their exact operating procedures are, as well as their advantages and disadvantages. Nurses shall then be better prepared to advise nursing mothers as to which device is most appropriate for them in any given circumstance. Therefore, nurses can provide proper health care leading to the continuation and success of breastfeeding.     

Goal‐oriented adaptivity using unconventional error representations for the multidimensional Helmholtz equation

In goal‐oriented adaptivity, the error in the quantity of interest is represented using the error functions of the direct and adjoint problems. This error representation is subsequently bounded above by element‐wise error indicators that are used to drive optimal refinements. In this work, we propose to replace, in the error representation, the adjoint problem by an alternative operator. The main advantage of the proposed approach is that, when judiciously selecting such alternative operator, the corresponding upper bound of the error representation becomes sharper, leading to a more efficient goal‐oriented adaptivity. While the method can be applied to a variety of problems, we focus here on two‐ and three‐dimensional (2‐D and 3‐D) Helmholtz problems. We show via extensive numerical experimentation that the upper bounds provided by the alternative error representations are sharper than the classical ones and lead to a more robust p‐adaptive process. We also provide guidelines for finding operators delivering sharp error representation upper bounds. We further extend the results to a convection‐dominated diffusion problem as well as to problems with discontinuous material coefficients. Finally, we consider a sonic logging‐while‐drilling problem to illustrate the applicability of the proposed method.     

Using split capabilities for access control

The fundamental problem of access control is to limit what a process can do to an object and when that process can do if. For example, any access control mechanism must know whether to honor a request to read or write a particular file. Unfortunately, the access control mechanisms we use when sharing resources over the Internet were designed in the days when networking computers was a rarity. Many security breakdowns currently occurring come from the resulting mismatch between today's realities and the assumptions made in designing those mechanisms. We developed split capabilities to make the system scalable. If we used conventional capabilities, we would need a capability for every combination of access rights. That's not a problem in some systems where a capability is a single word. However, our design required over 100 bytes per resource. This fact presented us with a problem because of two of our design principles, "every thing is a resource" and "no special cases." Split capabilities allow us to define a single resource that can represent an arbitrary set of access rights to a large set of resources.     

Accessories for breastfeeding; supplementary nutritional system for breastfeeding

Maternal breastfeeding is a physiological process which almost all women are capable of performing. Some special circumstances, such as the adoption of a baby, the problems a baby has sucking, or the temporary interruption of milk secretion, can cause difficulties and this is when the use of the so-called breastfeeding supplements is warranted. We describe the SNS supplementary nutritional system so that health professionals may understand its characteristics, use, and applications and therefore be able to offer women the necessary advise and assistance during breastfeeding.     

Morphology and mechanical properties of polymer nanocomposites with a poly(hydroxy ether of bisphenol A) matrix

The poly(hydroxy ether of bisphenol A) (phenoxy (Ph)) has been revealed as a polymeric matrix able to intercalate in, and partially exfoliate a commercial organically modified montmorillonite. Dispersion was attributed to chemical interactions between the Ph and the inorganic clay. A significant increase in the modulus of elasticity (33% with 3.8% montmorillonite (MMT) addition) was observed, together with an unusual increase in ductility attributed to surfactant migration, that should allow tailoring of the processing conditions to widen exfoliation. Ph‐based nanocomposites could be used as a nanostructured masterbatch for producing new polymer nanocomposites by mixing the masterbatch with the polymeric matrices that either miscibilize or are compatible with Ph. Copyright © 2006 Society of Chemical Industry