Valency-bond studies of some conjugated hydrocarbons—II Pentalene, and some preliminary results on heptalene

Valency-bond studies of the still unknown molecule pentalene C8H6 in which the molecular symmetry may be either D2h or C2h show that a more stable molecule (lower ground state energy) is found for the lower symmetry, and that marked alternation of bond lengths occurs. The corresponding Penney-Dirac bond orders have been determined. Preliminary results for heptalene forecast a similar conclusion

Mode mixing and losses in misaligned microcavities

We present a study on the optical losses of Fabry-Pérot cavities subject to realistic transverse mirror misalignment. We consider mirrors of the two most prevalent surface forms: idealised spherical depressions, and Gaussian profiles generated by laser ablation. We first describe the mode mixing phenomena seen in the spherical mirror case and compare to the frequently-used clipping model, observing close agreement in the predicted diffraction loss, but with the addition of protective mode mixing at transverse degeneracies. We then discuss the Gaussian mirror case, detailing how the varying surface curvature across the mirror leads to complex variations in round trip loss and mode profile. In light of the severe mode distortion and strongly elevated loss predicted for many cavity lengths and transverse alignments when using Gaussian mirrors, we suggest that the consequences of mirror surface profile are carefully considered when designing cavity experiments

Efficient operator method for modelling mode mixing in misaligned optical cavities

The transverse field structure and diffraction loss of the resonant modes of Fabry-P'erot optical cavities are acutely sensitive to the alignment and shape of the mirror substrates. We develop extensions to the `mode mixing’ method applicable to arbitrary mirror shapes, which both facilitate fast calculation of the modes of cavities with transversely misaligned mirrors and enable the determination and transformation of the geometric properties of these modes. We show how these methods extend previous capabilities by including the practically-motivated case of transverse mirror misalignment, presenting the ability to study the rich and complex structure of the resonant modes

Rapid Assessment of Physical Habitat Sensitivity to Abstraction (RAPHSA)

Physical habitat is one measure of river ecosystem health that is sensitive to changes in flow or channel geometry. It can be used to assess the impacts on the river ecosystem of changes to the flow regime caused by abstractions, or impoundment or alterations to channel geometry that result from river engineering, such as flood management works. An appropriate flow regime is recognised as an essential supporting element to achieving Good Ecological Status in water bodies, as required under the European Water Framework Directive. In England and Wales, the Environment Agency achieves appropriate flow regimes through the management of abstractions and ensuring sufficient water is released from dams. In addition, the Environment Agency is required to undertake environmental impact assessments of flood defence schemes and other river engineering works. Physical habitat comprises the physical conditions in a river that determine its suitability for different species and communities, including water depth and velocity. The relationship between physical habitat variables and discharge define the degree to which the physical environment changes as flow varies. How these relationships change with channel geometry provides a measure of the sensitivity of the river to flow change. Physical habitat–flow relationships can be defined for any river reach, but require repeat measurements of hydraulic properties at a range of flows, followed by hydraulic modelling and habitat use data by target species (if the curves are to be related to particular organisms). The Environment Agency thus requires a set of operational tools that assess physical habitat in a consistent manner regardless of the amount of data available. This paper reports on a study to define a risk-based toolkit for physical habitat assessment. The risk-based approach is a trade-off between avoiding unnecessary work, and the costs of achieving an acceptable level of certainty such that decisions can be made with reasonable confidence. This approach involves starting with simple tools and adopting more complex techniques if necessary; that is, use the simplest approach that gives an acceptable level of confidence, moving to a higher level if the degree of uncertainty is too high. The toolkit was developed through analysis of 66 physical habitat modelling studies across the UK. Each tool requires different input data, thus entailing various levels of investment in field data collection. It is recognised that the results from all tools are uncertain. However, in broad terms, the more data available and the more complex a tool used, the better the understanding, although employing a complex tool does not guarantee less uncertainty

Using the physical properties of artefacts to manage through‐life knowledge flows in the built environment: an initial exploration

Effective through‐life management of built facilities requires effective through‐life knowledge management to support it. The KIM (Immortal Information and Through‐Life Knowledge Management) project attempted to develop such an approach, based on a dichotomy of knowledge and information. Knowledge is conceived in terms of communities of practice. An initial philosophical analysis demonstrates deficiencies in this conception. Drawing inspiration from production theory, a tripartite analysis is offered, suggesting that knowledge flows consist of: social practices, information and physical properties. Literature on physical properties from design studies, production management and ethnomethodology is briefly reviewed to demonstrate the information bearing functions of physical properties. Fieldwork conforming to the unique adequacy requirement of methods was carried out on construction sites, in hotel and hospital facilities during the use stage of their life cycles. Safety barriers on construction sites were found to have informational properties beyond their function as a physical barrier. The quality of information delivered by wayfinding signs was found to depend upon both the physical placement of the signs in relation to the surrounding environment and the physical layout of the sign itself. It was found that social practices are institutionalized to repair the knowledge flow when the physically instantiated wayfinding system breaks down. Finally, through the investigation of practices surrounding emergency resuscitation equipment, it was found that if the physical properties of information are not designed to mesh with the work practices of the setting, this will lead to a breakdown in the knowledge flow. It is suggested that elements of knowledge management, ethnomethodology, production management and design studies might be integrated to form the basis of a hybrid discipline