Strategic Directions in Object-Oriented Programming

This paper has provided an overview of the field of object-oriented programming. After presenting a historical perspective and some major achievements in the field, four research directions were introduced: technologies integration, software components, distributed programming, and new paradigms. In general there is a need to continue research in traditional areas:\ud (1) as computer systems become more and more complex, there is a need to further develop the work on architecture and design; \ud (2) to support the development of complex systems, there is a need for better languages, environments, and tools; \ud (3) foundations in the form of the conceptual framework and other theories must be extended to enhance the means for modeling and formal analysis, as well as for understanding future computer systems

On Object-Orientation

Although object-orientation has been around for several decades, its key concept abstraction has not been exploited for proper application of object-orientation in other phases of software development than the implementation phase. We mention some issues that lead to a lot of confusion and obscurity with object-orientation and its application in software development. We describe object-orientation as abstract as possible such that it can be applied to all phases of software development

Coarse-Grained Model for Phospholipid/Cholesterol Bilayer

We construct a coarse-grained (CG) model for dipalmitoylphosphatidylcholine (DPPC)/cholesterol bilayers and apply it to large-scale simulation studies of lipid membranes. Our CG model is a two-dimensional representation of the membrane, where the individual lipid and sterol molecules are described by point-like particles. The effective intermolecular interactions used in the model are systematically derived from detailed atomic-scale molecular dynamics simulations using the Inverse Monte Carlo technique, which guarantees that the radial distribution properties of the CG model are consistent with those given by the corresponding atomistic system. We find that the coarse-grained model for the DPPC/cholesterol bilayer is substantially more efficient than atomistic models, providing a speed-up of approximately eight orders of magnitude. The results are in favor of formation of cholesterol-rich and cholesterol-poor domains at intermediate cholesterol concentrations, in agreement with the experimental phase diagram of the system. We also explore the limits of the novel coarse-grained model, and discuss the general validity and applicability of the present approach

Confinement Effects on Phase Behavior of Soft Matter Systems

When systems that can undergo phase separation between two coexisting phases in the bulk are confined in thin film geometry between parallel walls, the phase behavior can be profoundly modified. These phenomena shall be described and exemplified by computer simulations of the Asakura-Oosawa model for colloid-polymer mixtures, but applications to other soft matter systems (e.g. confined polymer blends) will also be mentioned. Typically a wall will prefer one of the phases, and hence the composition of the system in the direction perpendicular to the walls will not be homogeneous. If both walls are of the same kind, this effect leads to a distortion of the phase diagram of the system in thin film geometry, in comparison with the bulk, analogous to the phenomenon of "capillary condensation" of simple fluids in thin capillaries. In the case of "competing walls", where both walls prefer different phases of the two phases coexisting in the bulk, a state with an interface parallel to the walls gets stabilized. The transition from the disordered phase to this "soft mode phase" is rounded by the finite thickness of the film and not a sharp phase transition. However, a sharp transition can occur where this interface gets localized at (one of) the walls. The relation of this interface localization transition to wetting phenomena is discussed. Finally, an outlook to related phenomena is given, such as the effects of confinement in cylindrical pores on the phase behavior, and more complicated ordering phenomena (lamellar mesophases of block copolymers or nematic phases of liquid crystals under confinement).Comment: 25 pages, 17 figures, to be published in Soft Matte

Manipulation of expressions in a relational algebra

This paper describes a syntax for expressions based on the relational algebra. A tree representation is generated when an expression is analyzed. Transformations on the tree representations of expressions are applied in order to obtain improvements with respect to the speed of evaluation in a data base environment

Effects of vertical confinement on gelation and sedimentation of colloids

We consider the sedimentation of a colloidal gel under confinement in the direction of gravity. The confinement allows us to compare directly experiments and computer simulations, for the same system size in the vertical direction. The confinement also leads to qualitatively different behaviour compared to bulk systems: in large systems gelation suppresses sedimentation, but for small systems sedimentation is enhanced relative to non-gelling suspensions, although the rate of sedimentation is reduced when the strength of the attraction between the colloids is strong. We map interaction parameters between a model experimental system (observed in real space) and computer simulations. Remarkably, we find that when simulating the system using Brownian dynamics in which hydrodynamic interactions between the particles are neglected, we find that sedimentation occurs on the same timescale as the experiments, however the thickness of the "arms" of the gel is rather larger in the experiments, compared with the simulations. An analysis of local structure in the simulations showed similar behaviour to gelation in the absence of gravity