The Company You Keep: Qualitative Uncertainty in Providing Club Goods

Clubs are typically experience goods. Potential members cannot ascertain precisely beforehand their quality (dependent endogenously on the club's facility investment and number of users, itself dependent on its pricing policy). Members with unsatisfactory initial experiences discontinue visits. We show that a monopoly profit maximiser never offers a free trial period for such goods but, for a quality function homogeneous of any feasible degree, a welfare maximiser always does. When the quality function is homogeneous of degree zero, the monopolist provides a socially excessive level of quality to repeat buyers. In other possible regimes, the monopolist permits too little club usage.Clubs, qualitative uncertainty, monopoly, welfarist

Dark states in the magnetotransport through triple quantum dots

We consider the transport through a system of three coupled quantum dots in a perpendicular magnetic field. At zero field, destructive interference can trap an electron in a dark state -- a coherent superposition of dot states that completely blocks current flow. The magnetic field can disrupt this interference giving rise to oscillations in the current and its higher-order statistics as the field is increased. These oscillations have a period of either the flux-quantum or half the flux-quantum, depending on the dot geometry. We give results for the stationary current and for the shotnoise and skewness at zero and finite frequency.Comment: 7 pages, 7 figure

The Use of Computer Systems and Software Tools for Modelling Products

With a recent major enhancement of the facilities for computer aided engineering on the Loughborough campus all undergraduate students in the Department of Design and Technology have access to a powerful range of software tools running on sophisticated hardware. As designers, dealing with a variety of technological projects it is essential that students in Design and Technology are introduced to these facilities and are made aware of the advantages and limitations of this type of resource. Through learning about how to use these design tools during project work, students have the opportunity to assess the capabilities of the software and to exercise discrimination when it comes to selecting which resource to use for a particular application

Development and critical evaluation of a generic 2-D agro-hydrological model (SMCR_N) for the responses of crop yield and nitrogen composition to nitrogen fertilizer

Models play an important role in optimizing fertilizer use in agriculture to maintain sustainable crop production and to minimize the risk to the environment. In this study, we present a new Simulation Model for Crop Response to Nitrogen fertilizer (SMCR_N). The SMCR_N model, based on the recently developed model EU-Rotate_N for the N-economies of a wide range of crops and cropping systems, includes new modules for the estimation of N in the roots and an associated treatment of the recovery of soil mineral N by crops, for the reduction of growth rates by excessive fertilizer-N, and for the N mineralization from soil organic matter. The validity of the model was tested against the results from 32 multi-level fertilizer experiments on 16 different crop species. For this exercise none of the coefficients or parameters in the model was adjusted to improve the agreement between measurement and simulation. Over the practical range of fertilizer-N levels model predictions were, with few exceptions, in good agreement with measurements of crop dry weight (excluding fibrous roots) and its %N. The model considered that the entire reduction of soil inorganic N during growth was due to the sum of nitrate leaching, retention of N in fibrous roots and N uptake by the rest of the plant. The good agreement between the measured and simulated uptakes suggests that in this arable soil, losses of N from other soil processes were small. At high levels of fertilizer-N yields were dominated by the negative osmotic effect of fertilizer-N and model predictions for some crops were poor. However, the predictions were significantly improved by using a different value for the coefficient defining the osmotic effect for saline sensitive crops. The developed model SMCR_N uses generally readily available inputs, and is more mechanistic than most agronomic models and thus has the potential to be used as a tool for optimizing fertilizer practice

A MODEL FOR ESTIMATING INFORMATION SYSTEM REQUIREMENTS SIZE: PRELIMINARY FINDINGS

A model has been developed that estimates information system requirements size. The estimating model may be applied relatively early in the systems development life cycle. The model captures system statics with the entity-relationship data model and system dynamics by measuring events at the system boundary. Results on pilot data indicate the model may provide a reliable predictor of system size in terms of lines of code, holding personnel experience and technology constant in a 4GL development environment

Phase Transitions in Generalised Spin-Boson (Dicke) Models

We consider a class of generalised single mode Dicke Hamiltonians with arbitrary boson coupling in the pseudo-spin $x$-$z$ plane. We find exact solutions in the thermodynamic, large-spin limit as a function of the coupling angle, which allows us to continuously move between the simple dephasing and the original Dicke Hamiltonians. Only in the latter case (orthogonal static and fluctuating couplings), does the parity-symmetry induced quantum phase transition occur.Comment: 6 pages, 5 figue