A generic tool for cost estimating in aircraft design

A methodology to estimate the cost implications of design decisions by integrating cost as a design parameter at an early design stage is presented. The model is developed on a hierarchical basis, the manufacturing cost of aircraft fuselage panels being analysed in this paper. The manufacturing cost modelling is original and relies on a genetic-causal method where the drivers of each element of cost are identified relative to the process capability. The cost model is then extended to life cycle costing by computing the Direct Operating Cost as a function of acquisition cost and fuel burn, and coupled with a semi-empirical numerical analysis using Engineering Sciences Data Unit reference data to model the structural integrity of the fuselage shell with regard to material failure and various modes of buckling. The main finding of the paper is that the traditional minimum weight condition is a dated and sub-optimal approach to airframe structural design.

Economic cost of age-related macular degeneration: a review of recent research

As the population of most developed countries ages so the prevalence of diseases such as age-related macular degeneration (AMD) are likely to increase. To facilitate planning and informed debate regarding making provisions for this disease it is important that we have a clear understanding of the economic impact of visual impairment associated with AMD. In this paper we assess the state of current knowledge based on a review of published evidence in scientific journals. Based on our assessment of the evidence we argue that the paucity of research studies on the subject and wide variation in estimates produced from the few studies available make it difficult to assess with confidence the likely average direct cost-of-illness associated with AMD. We further argue that significant gaps in our understanding of the costs of AMD (particularly in respect of indirect costs) also exist. Current research should be augmented by more comprehensive studies.

Query cost estimation through remote system contention states analysis over the Internet

Query processing over the Internet involving autonomous data sources is a major task in data integration. It requires the estimated costs of possible queries in order to select the best one that has the minimum cost. In this context, the cost of a query is affected by three factors: network congestion, server contention state, and complexity of the query. In this paper, we study the effects of both the network congestion and server contention state on the cost of a query. We refer to these two factors together as system contention states. We present a new approach to determining the system contention states by clustering the costs of a sample query. For each system contention state, we construct two cost formulas for unary and join queries respectively using the multiple regression process. When a new query is submitted, its system contention state is estimated first using either the time slides method or the statistical method. The cost of the query is then calculated using the corresponding cost formulas. The estimated cost of the query is further adjusted to improve its accuracy. Our experiments show that our methods can produce quite accurate cost estimates of the submitted queries to remote data sources over the Internet.

Turbulent diffusion and mixing in interstellar dark clouds with adsorption onto grains

This paper reports the results of models of dark cloud chemistry incorporating a depth dependent density distribution with diffusive mixing and adsorption onto grains. The model is based on the approach taken by Xie et al. (1995), with the addition of grain accretion effects. Without diffusion, the central regions of the cloud freeze out in less than 10(7) years. Freeze-out time is dependent on density, so the diffuse outer region of the cloud remains abundant in gas for about an order of magnitude longer. We find that fairly small amounts of diffusive mixing can delay freeze-out at the centre of the model cloud for a time up to an order of magnitude greater than without diffusion, due to material diffusing inward from the edges of the cloud. The gas-phase lifetime of the cloud core can thus be increased by up to an order of magnitude or more by this process. We have run three different grain models with various diffusion coefficients to investigate the effects of changing the sticking parameters.

Temperature-Driven Mixing-Demixing Behavior of Binary Mixtures of the Ionic Liquid Choline Bis(trifluoromethylsulfonyl)imide and Water

The ionic liquid (2-hydroxyethylammonium)trimethylammonium) bis(trifluoromethylsulfonyl)imide (choline bistriflimide) was obtained as a supercooled liquid at room temperature (melting point = 30 degrees C). Crystals of choline bistriflimide suitable for structure determination were grown from the melt in situ on the X-ray diffractometer. The choline cation adopts a folded conformation, whereas the bistriflimide anion exhibits a transoid conformation. The choline cation and the bistriflimide anion are held together by hydrogen bonds between the hydroxyl proton and a sulfonyl oxygen atom. This hydrogen bonding is of importance for the temperature-dependent solubility proper-ties of the ionic liquid. Choline bistriflimide is not miscible with water at room temperature, but forms one phase with water at temperatures above 72 degrees C (equals upper critical solution temperature). H-1 NMR studies show that the hydrogen bonds between the choline cation and the bistriflimide anion are substantially weakened above this temperature. The thermophysical properties of water-choline bistriflimide binary mixtures were furthermore studied by a photopyroelectric technique and by adiabatic scanning calorimetry (ASC). By photothermal analysis, besides highly accurate values for the thermal conductivity and effusivity of choline bistriflimide at 30 degrees C, the detailed temperature dependence of both the thermal conductivity and effusivity of the upper and lower part of a critical water-choline bistriflimide mixture in the neighborhood of the mixing-demixing phase transition could be determined with high resolution and accuracy. Together with high resolution ASC data for the heat capacity, experimental values were obtained for the critical exponents alpha and beta, and for the critical amplitude ratio G(+)/G(-). These three values were found to be consistent with theoretical expectations for a three dimensional Ising-type of critical behavior of binary liquid mixtures.

Development of operator independent bone cement vacuum mixing system for joint replacement surgery,

(2006) Vol. 35 No. 8 317

Effect of temperature and mixing conditions on quality and consistency of poly(methyl methacrylate) bone cement

The mixing of poly(methyl methacrylate) (PMMA) bone cement has been studied to develop methods for preparing a consistently high quality cement. A novel droplet test experimental procedure was developed that characterised the wetting characteristics involved in bone cement mixing. Using this technique it was established that increased wetting occurred by mixing bone cement at a lower temperature (-28 degreesC) than normal mixing at room temperature.