Implementing logical connectives in constraint programming

Combining constraints using logical connectives such as disjunction is ubiquitous in constraint programming, because it adds considerable expressive power to a constraint language. We explore the solver architecture needed to propagate such combinations of constraints efficiently. In particular we describe two new features named satisfying sets and constraint trees. We also make use of movable triggers (Gent et al., 2006) [1], and with these three complementary features we are able to make considerable efficiency gains.A key reason for the success of Boolean Satisfiability (SAT) solvers is their ability to propagate Or constraints efficiently, making use of movable triggers. We successfully generalise this approach to an Or of an arbitrary set of constraints, maintaining the crucial property that at most two constraints are active at any time, and no computation at all is done on the others. We also give an And propagator within our framework, which may be embedded within the Or. Using this approach, we demonstrate speedups of over 10,000 times in some cases, compared to traditional constraint programming approaches. We also prove that the Or algorithm enforces generalised arc consistency (GAC) when all its child constraints have a GAC propagator, and no variables are shared between children. By extending the Or propagator, we present a propagator for AtLeastK, which expresses that at least k of its child constraints are satisfied in any solution.Some logical expressions (e.g. exclusive-or) cannot be compactly expressed using And, Or and AtLeastK. Therefore we investigate reification of constraints. We present a fast generic algorithm for reification using satisfying sets and movable triggers.     

Trust Me, I'm an Analyst

Requirements projects are all about people. This column discusses trust as one important but overlooked element of requirements project, and explores different ways to increase trust.     

Free Time Activities and Quality of Urban Life

The citizen participation movement of the 1960's, as embodied in the anti-poverty program, opened new opportunities for the development of working relationships between professional planners and low-income neighborhood residents. A Pittsburgh study on resident assessments of conditions in anti-poverty program neighborhoods suggests that these relationships can offer false assurances of democracy to planners who prefer to operate with popular sanction. On the basis of much supportive evidence, planners and citizen participants in Pittsburgh's anti-poverty program were highly critical of existing neighborhood conditions. However, the results of a survey of over 6,000 residents indicate that these views were not shared by the vast majority of the people living in the neighborhoods. This discrepancy between the high level of dissatisfaction expressed by a relatively small number of citizen participants and the apparent contentment of their neighbors highlights the role of activist minorities in the citizen participation movement—a phenomenon that deserves careful evaluation by planners seeking to legitimate their low-income neighborhood activities through resident involvement.     

Energy policies avoiding a tipping point in the climate system

Paleoclimate evidence and climate models indicate that certain elements of the climate system may exhibit thresholds, with small changes in greenhouse gas emissions resulting in non-linear and potentially irreversible regime shifts with serious consequences for socio-economic systems. Such thresholds or tipping points in the climate system are likely to depend on both the magnitude and rate of change of surface warming. The collapse of the Atlantic thermohaline circulation (THC) is one example of such a threshold. To evaluate mitigation policies that curb greenhouse gas emissions to levels that prevent such a climate threshold being reached, we use the MERGE model of Manne, Mendelsohn and Richels. Depending on assumptions on climate sensitivity and technological progress, our analysis shows that preserving the THC may require a fast and strong greenhouse gas emission reduction from today's level, with transition to nuclear and/or renewable energy, possibly combined with the use of carbon capture and sequestration systems.     

The effect of substituted alkynes on nickel catalyst morphology and carbon fiber growth

The growth of shaped carbon nanomaterials from a range of substituted alkynes over a NiO catalyst was investigated. It was found that the structure of the substituted alkyne affected both catalyst morphology and carbon fiber growth. For linear alkynes (1-pentyne to 1-octyne) the fiber morphology and yield varied with the type of alkyne used. It was also found that hetero-atoms (Cl, Br, OH and NH₂) greatly impacted carbon fiber growth and structure. An analysis of the catalyst particles associated with the carbon fibers grown from various alkynes showed that different alkynes gave differently shaped Ni catalyst particles. It was found that pre-treatment of the catalyst with an alkyne such as trimethylsilyl acetylene or ethynyl aniline (that did not give fiber growth), followed by treatment with acetylene initiated fiber growth morphologies (Y-junction, helical or straight fibers) different from that observed after direct treatment with acetylene. Further, sequential fiber growth from two alkynes that were both capable of producing fibers (e.g. methyl prop-2-ynoate followed by prop-2-yn-1-amine) resulted in ‘co-block’ fiber growth. These results highlight the dynamic relationships that exists between carbon source, catalyst morphology and carbon nanomaterial growth.     

Polyethylene glycol-water and polypropylene glycol-water solutionsas benign reaction solvents

Aqueous solutions of low molecular weight polypropylene and polyethylene glycol are proposed for use as novel, safe, environmentally friendly solvents. Not only are these solvents relatively nontoxic, but they are also nonvolatile, which eliminates the possibility of fugitive gaseous emissions. Many organic compounds have been found to be soluble in these polyglycol solutions; thus, they could be used as replacement solvents in various chemical processes. One use of the solvents could be as the medium for conducting chemical reactions, and this has been investigated. In particular, three classes of organic reactions, S N 1, S N 2, and Diels-Alder, have been conducted in the polyglycol solutions. Rate constants were obtained and compared to those for the traditional organic solvents. For the S N 1 reaction and the Diels-Alder reactions, the rate constants in the polyglycol solvents were greater than those found for the frequently used organic solvents.     

Anisotropic core–shell nanocomposites by direct covalent attachment of a side-functionalized poly(3-hexylthiophene) onto ZnO nanowires

Inorganic-organic hybrid solar cells have demonstrated great potential for the development of next generation flexible electronics to deliver efficient energy conversion. The interfacial morphology and structure between donor and acceptor are determinative to the device performance. Here, we report on novel core–shell hybrid heterojunction nanostructures by covalently grafting side-functionalized poly(3-hexylthiophene) onto ZnO nanowires without ligand linkers. Solvatochromism of polythiophene is utilized to control the polymer morphology at interface. Study into the photophysics of nanohybrids demonstrates an elongated conjugation length of the polymer backbone at the interface and fast interfacial charge transfer. These results provide critical insight into the utilization of molecular composites to control donor–acceptor interfaces and further enable the use of anisotropic nanohybrids as photovoltaic elements for the massive fabrication of high efficiency devices.     

Special issue on emergence in human-like intelligence toward cyber-physical systems

Neural Computing and Applications -     

Development of a Methodology for Understanding the Potency of Risk Connectivity

The Strategic Risk Register System (SRRS) is proposed by the writers as a practical methodology to enable the connectivity of risks to be elicited and evaluated so that the most potent risks in a system can be identified. The SRRS methodology builds on the impact × likelihood paradigm by introducing a connectivity matrix to modify traditional risk registers and uses graph theories to depict the relations between risks. Several techniques are employed to visualize and interpret the significance of the results. A case study is used to demonstrate how the SRRS works in practice. This paper builds on the 3-year research program called STRATrisk, commissioned by the Department for Trade and Industry (DTI) in the UK, which reported that the assessment of the interconnectivity of risks is necessary to understand key risks in complex systems.