An algebraic extension of Dirac quantization: Examples

An extension of the Dirac procedure for the quantization of constrained systems is necessary to address certain issues that are left open in Dirac's original proposal. These issues play an important role especially in the context of non-linear, diffeomorphism invariant theories such as general relativity. Recently, an extension of the required type was proposed by one of us using algebraic quantization methods. In this paper, the key conceptual and technical aspects of the algebraic program are illustrated through a number of finite dimensional examples. The choice of examples and some of the analysis is motivated by certain peculiar problems endemic to quantum gravity. However, prior knowledge of general relativity is not assumed in the main discussion. Indeed, the methods introduced and conclusions arrived at are applicable to any system with first class constraints. In particular, they resolve certain technical issues which are present also in the reduced phase space approach to quantization of these systems.Comment: 43 pages, Latex, CGPG-94/6-1. (References added; particularly to earlier work by C.J.Isham using group theoretic ideas, in the introduction.

Contingent plan structures for spacecraft

Most current AI planners build partially ordered plan structures which delay decisions on action ordering. Such structures cannot easily represent contingent actions. A representation which can is presented. The representation has some other useful features: it provides a good account of the causal structure of a plan, can be used to describe disjunctive actions, and it offers a planner the opportunity of even less commitment than the classical partial order on actions. The use of this representation is demonstrated in an on-board spacecraft activity sequencing problem. Contingent plan execution in a spacecraft context highlights the requirements for a fully disjunctive representation, since communication delays often prohibit extensive ground-based accounting for remotely sensed information and replanning on execution failure

Defect physics of BaCuChF (Ch=S, Se, Te) p-type transparent conductors

Native point defects, defect complexes, and oxygen impurities in BaCuChF were studied using density functional theory calculations, self-consistent thermodynamic simulations, and various experimental techniques. Unintentional p-type conductivity in BaCuChF is explained by the presence of copper vacancies with transition levels in the valence band. These acceptor-like defects are partially compensated by donor-like chalcogen vacancies with transition levels deep in the gap. Chalcogen vacancies also cause the experimentally observed sub-gap photoluminescence, optical absorption, and persistent photoconductivity in BaCuSF and BaCuSeF. In thermodynamic equilibrium, both copper and chalcogen vacancies have low formation enthalpies and are likely to form defect complexes among themselves and with fluorine interstitials. The calculated Fermi level pinning range in BaCuChF is narrow and located close to the valence band maximum. It makes BaCuChF a suitable transparent p-type contact layer for optoelectronic applications, but hinders attempts to fabricate transparent thin film transistors using this material. Oxygen-related defects do not affect bulk BaCuChF properties, but surface oxidation decreases the mean free path of free holes by almost an order of magnitude.Comment: 28 pages, 5 figure

What does validation of cases in electronic record databases mean? The potential contribution of free text

Electronic health records are increasingly used for research. The definition of cases or endpoints often relies on the use of coded diagnostic data, using a pre-selected group of codes. Validation of these cases, as ‘true’ cases of the disease, is crucial. There are, however, ambiguities in what is meant by validation in the context of electronic records. Validation usually implies comparison of a definition against a gold standard of diagnosis and the ability to identify false negatives (‘true’ cases which were not detected) as well as false positives (detected cases which did not have the condition). We argue that two separate concepts of validation are often conflated in existing studies. Firstly, whether the GP thought the patient was suffering from a particular condition (which we term confirmation or internal validation) and secondly, whether the patient really had the condition (external validation). Few studies have the ability to detect false negatives who have not received a diagnostic code. Natural language processing is likely to open up the use of free text within the electronic record which will facilitate both the validation of the coded diagnosis and searching for false negatives

EmergencyGrid:Planning in Convergence Environments

Government agencies are often responsible for event handling, planning, coordination, and status reporting during emergency response in natural disaster events such as floods, tsunamis and earthquakes. Across such a range of emergency response scenarios, there is a common set of requirements that distributed intelligent computer systems generally address. To support the implementation of these requirements, some researchers are proposing the creation of grids, where final interface and processing nodes perform joint work supported by a network infrastructure. The aim of this project is to extend the concepts of emergency response grids, using a convergence scenario between web and other computational platforms. Our initial work focuses on the Interactive Digital TV platform, where we intend to transform individual TV devices into active final nodes, using a hierarchical planning structure. We describe the architecture of this approach and an initial prototype specification that is being developed to validate some concepts and illustrate the advantages of this convergence planning environment

In Service CO2 and NOX Emissions of Euro 6/VI Cars, Light- and Heavy- dutygoods Vehicles in Real London driving: Taking the Road into the Laboratory

Driving on-the-road has more frequent and prompt acceleration/decelerations than in the type-approval light-duty test conditions (NEDC), with Real Driving Emissions (RDE) of CO2 and NOX known to be considerably higher. Despite permissible limits of NOX emissions at type approval reducing significantly, in-service emissions from diesel vehicles have, in reality, not reduced at all through the Euro 1–5 / I–V emission standards. TfL commissioned a programme of laboratory testing to better understand the in-service emission performance of Euro 6/VI vehicles over the TfL London Drive Cycle (LDC). This cycle was constructed from instrumented car data making repeated circuits of a set route at different times of day. Twelve Euro 6 passenger cars were tested over the entire 140 kms of the LDC from a warm-start. Three HGVs were tested over the suburban sub-cycle (40kms) in laden and un-laden condition. NOX emissions from the petrol cars were at a low level and below, or at, their type approval limit of 0.06 g.km-1. Only one SCR equipped diesel car achieved NOX emissions close to their 0.08 g.km-1 type approval limit. NOX emissions from diesel cars with only LNT NOX controls were between 3 and 13 times higher than their type approval limit (conformity factors). A diesel supermini was emitting NOX at the same level as the fully laden 40T artic HGV tested

Financial Expertise of Directors

The composition and functioning of corporate boards is at the core of the academic and policy debate on optimal corporate governance. But does board composition matter for corporate decisions? In this paper, we analyze the role of financial experts on boards. In a novel panel data set on board composition, we find that financial experts significantly affect corporate decisions, though not necessarily in the interest of shareholders. First, when commercial bankers join boards, external funding increases and investment-cash flow sensitivity diminishes. But, the increased financing affects mostly firms with good credit and poor investment opportunities. Second, investment bankers on the board are associated with larger bond issues, but also worse acquisitions. Third, we find little evidence that financial expertise matters for compensation policy or for experts without affiliation to a financial institution. The results suggest a tradeoff between outside incentives (e.g. bank profits) and the incentive to maximize firm value. Requiring financial expertise on boards, as mandated by regulatory proposals, may not benefit shareholders if conflicting interests are neglected.

Data quality in European primary care research databases. Report of a workshop held in London September 2013

Primary care research databases provide a significant resource for health services and epidemiological research. However since data are recorded primarily for clinical care their suitability for research may vary widely according to the research application or recording practices of individual general practitioners. A methodological approach for characterising data quality is required. We describe a one-day workshop entitled “Towards a common protocol for measuring and monitoring data quality in European primary care research databases”. Researchers, database experts and clinicians were invited to give their perspectives on data quality and to exchange ideas on what data quality metrics should be made available to researchers. We report the main outcomes of this workshop, including a summary of the presentations and discussions and suggested way forward