The Jahn-Teller instability with accidental degeneracy

The Jahn-Teller theorem predicts that orbitally degenerate complexes in solids can lower their energy by a distortion which lowers their symmetry. Exact degeneracy is not necessary for this instability; usually it suffices if the actual separation of the energy levels involved is less than the energy reduction which would result if they were exactly degenerate. We discuss various cases of accidental degeneracy in cubic and tetrahedral systems. With accidental degeneracy it is possible to get mixed distortions which involve both trigonal and tetragonal distortions. These have probably been observed for the negative vacancy in silicon, and possibly for the neutral vacancy in diamond. The theory is applied to both these cases, and it is compared with the earlier qualitative arguments of Watkins

Design of Parametrically Forced Patterns and Quasipatterns

The Faraday wave experiment is a classic example of a system driven by parametric forcing, and it produces a wide range of complex patterns, including superlattice patterns and quasipatterns. Nonlinear three-wave interactions between driven and weakly damped modes play a key role in determining which patterns are favored. We use this idea to design single and multifrequency forcing functions that produce examples of superlattice patterns and quasipatterns in a new model PDE with parametric forcing. We make quantitative comparisons between the predicted patterns and the solutions of the PDE. Unexpectedly, the agreement is good only for parameter values very close to onset. The reason that the range of validity is limited is that the theory requires strong damping of all modes apart from the driven pattern-forming modes. This is in conflict with the requirement for weak damping if three-wave coupling is to influence pattern selection effectively. We distinguish the two different ways that three-wave interactions can be used to stabilize quasipatterns, and we present examples of 12-, 14-, and 20-fold approximate quasipatterns. We identify which computational domains provide the most accurate approximations to 12-fold quasipatterns and systematically investigate the Fourier spectra of the most accurate approximations

The optical absorption of the neutral vacancy in diamond

Optical absorption by the neutral vacancy in diamond has been predicted to occur between the ground 1E state and the 1T2 excited state. Both these states are orbitally degenerate and should show Jahn Teller distortions. We have calculated the Huang-Rhys Factor for the transition (the fraction of the intensity in the zero phonon line) and the first and second moments of the absorption band. Also we discuss the response of the zero phonon line to externally applied stresses. Our model assumes that the vacancy interacts with just six modes, corresponding to the normal modes of the neighbours of the vacancy. The coupling of the electronic and nuclear motion is estimated from an LCAO model. The results are compared with observations of the GR1 band, which has been attributed to the vacancy. The predicted Huang-Rhys factor S ~ 3.7 and the first and second moments of the band support this identification. Further our model predicts that luminescence from this band should be unpolarised, as observed. However the predicted stress splitting of the zero phonon line differs from that observed. Possible explanations of this are discussed

Peer effects in risk taking: Envy or conformity?

We examine two explanations for peer effects in risk taking: relative payoff concerns and preferences that depend on peer choices. We vary experimentally whether individuals can condition a simple lottery choice on the lottery choice or the lottery allocation of a peer. We find that peer effects increase significantly, almost double, when peers make choices, relative to when they are allocated a lottery. In both situations, imitation is the most frequent form of peer effect. Hence, peer effects in our environment are explained by a combination of relative payoff concerns and preferences that depend on peer choices. Comparative statics analyses and structural estimation results suggest that a norm to conform to the peer may explain why peer choices matter. Our results suggest that peer choices are important in generating peer effects and hence have important implications for modeling as well as for policy

ELECTRONIC STRUCTURE OF GE IN SIO2

It is argued that one-electron theory is insufficient to account for the origin of the observed spectra of Ge in SiO2 ( alpha -quartz) crystals. A simple model is employed to show that impurity states responsible for ESR spectra of SiO2:Ge are stabilised by many-electron polarisation effects associated with the Ge atom itself and its immediate oxygen neighbour

Using ERP as a basis for Enterprise application integration

Architecting and implementing e-Business supply chain solutions across and within the modern day enterprise, is now becoming a necessity in order to maintain competitive and be adaptable to market needs. As such, the integration of information and processes is a vital step, using technologies such as using Enterprise Resource Planning (ERP), Supply Chain Management (SCM) and enterprise portal platforms. The effective sharing of resource planning and other enterprise related data across and within the enterprise is typically seen as a facet of a business to business (B2B) platform. However, such infrastructures typically involve a tight integration across intra and inter-organisational systems. This paper examines an Enterprise Application Integration (EAI) initiative taken by a global manufacturer of industrial automation products, which attempted to utilise ERP as an integration tool across its internal B2B infrastructure, to achieve such an aim. This paper discusses those integration considerations and complexities, experienced by the case company upon embarking on an EAI integration programme through the adoption of a core ERP as a catalyst for organizational change. In doing so the authors present an analysis of the inherent risks and limitations of this approach in terms of previously published literature in the field, relating to technology-driven organizational change and EAI impact and adoption frameworks

Model of the Belousov-Zhabotinsky reaction

The article describes results of the modified model of the Belousov-Zhabotinsky reaction, which resembles rather well the limit set observed upon experimental performance of the reaction in the Petri dish. We discuss the concept of the ignition of circular waves and show that only the asymmetrical ignition leads to the formation of spiral structures. From the qualitative assumptions on the behavior of dynamic systems, we conclude that the Belousov-Zhabotinsky reaction likely forms a regular grid.Comment: 17 pages, 12 figure

KIAI and ISLAMIC BANK (the Typology of Kiai Based on Their Perception and Behaviour Toward Islamic Bank)

This article aims to explain the perceptions and behavior of Moslem scholars (ulama/kiai) on the coast of Central Java toward Islamic banks. It is unassailable that finding out the kiai's perception and behavior toward Islamic banks becomes unavoidable because the kiai occupies a very important position in the social structure as an agent of social change. In order to have an approriate understanding toward the perception and behavior, this study used qualitative-phenomenological approach. The main source of primary data were obtained from the kiai in Pekalongan region by using purposive sampling technique. Indepth-interview as the prominent method in gaining data was reinforced by observation method. To get validity of data, internal and external validity were performed. The former was taken through four stages, namely triangulation, emic process, member checking and prolonged time; and the latter through transferability. Data were analyzed inductively through three cronological steps, e.i. data reduction, display and conclusion drawing. Based on the perceptions and behavior of scholars toward Islamic banks, this study concludes that there are three categories of kiai. The first is an idealist compromise (kompromis-idealis) which argues that Islamic banks do not fully comply with sharia compliance yet, the use of Islamic banks is compulsory and conventional banks are not substitutes for Islamic banks. The second is a realistic compromise (kompromis realistis) which infers that Islamic banks are not fully accordance with sharia commpliance, the use of Islamic banks is not mandatory, but conventional banks are not substitutes for Islamic banks. The third is resistance (resisten) which argues that Islamic banks are not much different from conventional banks, so making use of Islamic bank is not obligation, and conventional banks substitute Islamic banks

Constructed wetlands: Prediction of performance with case-based reasoning (part B)

The aim of this research was to assess the treatment efficiencies for gully pot liquor of experimental vertical- flow constructed wetland filters containing Phragmites australis (Cav.) Trin. ex Steud. (common reed) and filter media of different adsorption capacities. Six out of 12 filters received inflow water spiked with metals. For 2 years, hydrated nickel and copper nitrate were added to sieved gully pot liquor to simulate contaminated primary treated storm runoff. The findings were analyzed and discussed in a previous paper (Part A). Case-based reasoning (CBR) methods were applied to predict 5 days at 20°C N-Allylthiourea biochemical oxygen demand (BOD) and suspended solids (SS), and to demonstrate an alternative method of analyzing water quality performance indicators. The CBR method was successful in predicting if outflow concentrations were either above or below the thresholds set for water-quality variables. Relatively small case bases of approximately 60 entries are sufficient to yield relatively high predictions of compliance of at least 90% for BOD. Biochemical oxygen demand and SS are expensive to estimate, and can be cost-effectively controlled by applying CBR with the input variables turbidity and conductivity