The role of diffusion on the interface thickness in a ventilated filling box

We examine the role of diffusivity, whether molecular or turbulent, on the steady-state stratification in a ventilated filling box. The buoyancy-driven displacement ventilation model of Linden et al. (J. Fluid Mech., vol. 212, 1990, p. 309) predicts the formation of a two-layer stratification when a single plume is introduced into an enclosure with vents at the top and bottom. The model assumes that diffusion plays no role in the development of the ambient buoyancy stratification: diffusion is a slow process and the entrainment of ambient fluid into the plume from the diffuse interface will act to thin the interface resulting in a near discontinuity of density between the upper and lower layers. This prediction has been corroborated by small-scale salt bath experiments; however, full-scale measurements in ventilated rooms and complementary numerical simulations suggest an interface that is not sharp but rather smeared out over a finite thickness. For a given plume buoyancy flux, as the cross-sectional area of the enclosure increases the volume of fluid that must be entrained by the plume to maintain a sharp interface also increases. Therefore the balance between the diffusive thickening of the interface and plume-driven thinning favours a thicker interface. Conversely, the interface thickness decreases with increasing source buoyancy flux, although the dependence is relatively weak. Our analysis presents two models for predicting the interface thickness as a function of the enclosure height, base area, composite vent area, plume buoyancy flux and buoyancy diffusivity. Model results are compared with interface thickness measurements based on previously reported data. Positive qualitative and quantitative agreement is observed

Estimated Contribution of Four Biotechnologies to New Zealand Agriculture

The impact of biotechnology is an important consideration for New Zealand. The country depends significantly on agricultural production and exports (Ministry of Agriculture and Forestry, 2004), and has relied in part on modern biotechnology for productivity increases over the last 20 years (Evenson & Gollin, 2003; Jacobsen & Scobie, 1999; Ovenden, Anderson, Armstrong, & Mitchel, 1985). A recent survey of individuals in agriculture and biotechnology generated a comprehensive list of products and processes that are derived from four specific biotechnologies and are commercially significant in agriculture (Kaye-Blake, Saunders, Emanuelsson, Dalziel, & Wreford, 2005). This innovative research generated primary data on the actual impacts that biotechnology is currently having on agricultural production and produced a unique dataset of biotechnology products and processes and their value to New Zealand agriculture. Analysis found that these four biotechnologies are contributing approximately 206 million per year to agriculture. This analysis, however, assumed perfectly elastic international prices, and thus that New Zealand agricultural producers would capture the benefits of increased productivity. Literature on the impacts of productivity increases suggests that the distribution of benefits from increased productivity depends on how widely a technology is adopted. For example, genetic improvements in the crops of one country can allow domestic producers to increase producer surplus at the expense of producers in the rest of the world (Frisvold, Sullivan, & Raneses, 2003). By contrast, domestic farmers may be worse off if innovations are adopted in both the home country and the rest of the world (Moschini, Lapan, & Sobolevsky, 2000). The literature also suggests that specific impact of a novel technology is important to its impacts on agricultural producers. For example, technology that increases yields may be less beneficial for farmers than technology that reduces costs (Moschini et al., 2000). In addition, innovations that increase productivity of commodity products with low price elasticities of demand may not benefit farmers as much as innovations that increase consumer demand for agricultural products (Saunders & Cagatay, 2003). These findings are relevant because some features of New Zealand's primary sector suggest that international price impacts may be important. New Zealand is an open economy (Ministry of Agriculture and Forestry (MAF), 2004) and a significant exporter on world markets, particularly in pastoral products (Ministry of Agriculture and Forestry (MAF), 2004; Saunders & Cagatay, 2003). Modelling the movement of international prices may be done in several ways. The general equilibrium GTAP model (Hertel, 1997), for example, has been used to examine the potential impacts of biotechnology on producer and consumer welfare assuming different levels of adoption and consumer acceptance (e.g., Anderson & Jackson, 2005; Stone, Matysek, & Dolling, 2002). These impacts have also been analysed with partial equilibrium models, in particular models derived originally from the Uruguay Round of trade negotiations (Roningen, 1997), such as SWOPSIM (Frisvold et al., 2003; Roningen, Dixit, Sullivan, & Hart, 1991) and LTEM (Saunders & Cagatay, 2003). Partial equilibrium models are particularly appropriate for analysing impacts on a single sector of the economy: they allow substantial disaggregation by commodity and examination of the linkages that lead to model results (Gaisford & Kerr, 2001). In order to investigate the possible impact of biotechnological innovations on commodity prices and agricultural producers, the results of the original findings based on elastic prices were incorporated into a partial equilibrium model of world agricultural commodity trade (Cagatay & Saunders, 2003; Saunders & Cagatay, 2003). The model contained 19 commodities, including the major trade commodities for New Zealand (dairy products and meat). World trade was divided into 17 countries and the rest of the world, including New Zealand as a separate entity as well as the US, EU, Australia, Japan and others. As a partial equilibrium model, it examined the agricultural sector in isolation from other sectors of the economy. The base year was 2000, and impacts were modelled to 2005. The base solution modelled current production, which included biotechnological innovations. Alternative scenarios modelled the impact of the absence or loss of biotechnological innovations. The first scenario modelled the absence of innovations in all countries, while the second scenario examined the impact of innovations specific to New Zealand. The contribution of biotechnology to productivity was assessed separately for each commodity, using the original dataset (Kaye-Blake et al., 2005). For each commodity in the model, the analysis calculated the change in producer prices and total producer returns (price x quantity). The modelling results conformed to expectations. In the first scenario, a worldwide reduction in productivity in the primary sector led market prices to adjust upward in response to the lower production. For the second scenario, the price impacts were smaller for sectors with innovations specific to New Zealand. These changes were then combined with the original, constant-price estimate to calculate price-adjusted figures. The constant price analysis found that the contribution of the biotechnologies was 206 million. The first modelling scenario found that the economic benefit of the biotechnologies was only $19 million because increased productivity reduced commodity prices. The second scenario yielded an economic benefit of$191 million, suggesting that adopting New Zealandspecific innovations might not have a large impact on aggregate trade and might have allowed domestic producers to capture much of the increased welfare from innovations. Economic impacts, however, were spread unevenly across the commodities. In both trade scenarios, dairy producers increased producer returns through biotechnology, regardless of how widely the innovations were adopted. Meat producers, on the other hand, improved their returns when the innovations were specific to New Zealand, but were somewhat worse off when the innovations were available worldwide. This research contributes to understanding of the impacts of biotechnology in several ways. First, the productivity impacts were based on empirical findings regarding estimated impacts of actual commercially released biotechnologies; these were estimates of impacts that have actually occurred. Secondly, the productivity effects varied by commodity in the model, so that the impacts on different commodities could be estimated. Finally, by using a disaggregated, multi-commodity model, the cross-effects from resources shifting into other agricultural uses could be captured.Research and Development/Tech Change/Emerging Technologies,

Modelling Climate Change Impacts on Agriculture and Forestry with the Extended LTEM (Lincoln Trade and Environment Model)

In the land-based sectors, agricultural production generally is a source of carbon, while forestry may be thought to act as a sink. This paper focuses on new research examining the interaction of the two. The core of the research is the Lincoln Trade and Environment model (LTEM), a partial equilibrium model which links trade in NZ with the main trading countries overseas, through to production and associated environmental consequences . This paper reports on research expanding the model to include forestry from incorporating the capabilities of the Global Forest Products Model (GFPM) into the LTEM and hence producing an integrated model of agricultural and forestry land-uses for NZ and overseas. The paper extends the environmental modelling capabilities of the LTEM to include the impacts of climate change. The paper thereby reports on the development of a model of international trade that encompasses major agricultural commodities and forestry, complete with linkages and feedback with the environment and differentiated international markets. The paper then presents results of scenarios around changes in consumer behaviour and production using the new model.Environmental Economics and Policy,

The development of a multi-criteria decision analysis aid to help with contraceptive choices: My Contraception Tool.

My Contraception Tool (MCT) applies the principles of multi-criteria decision analysis to the choice of contraceptive method. Its purpose is to make the decision-making process transparent to the user and to suggest a method to them based on their own preferences. The contraceptive option that emerges as optimal from the analysis takes account of the probability of a range of outcomes and the relative weight ascribed to them by the user. The development of MCT was a collaborative project between London School of Hygiene & Tropical Medicine, Brook, FPA and Maldaba Ltd. MCT is available online via the Brook and FPA websites. In this article we describe MCT's development and how it works. Further work is needed to assess the impact it has on decision quality and contraceptive behaviour

Capital Based Sustainability Indicators as a Possible Way for Measuring Agricultural Sustainability

This paper takes the capital based approach to sustainability and applies this to examine the sustainability of different farming methods. The capital based approach argues that for future generations to be as well off as the present than the capital base should at least be maintained. The paper explores some of the issues around this approach such as the definition of capitals, their measurement and weakness in the approach which do not account for the resilience of system and/ or the substitutability of capitals. The paper outlines how this could be applied to agriculture and show sustainability across different farming methods. The data used is from the ARGOS (Agricultural Research Group on Sustainability) project which has collected data on social, economic and environmental factors from kiwifruit orchards green, green organic and gold, for five years. The results show little significant differences across orchard types. This may be due to the homogeneity of kiwifruit orchards and it is intended to expand this to the sheep sector to examine this further.Agricultural and Food Policy,

Process versus product: which determines consumer demand for genetically modified apples?

One debate in the literature regarding consumers’ reactions to genetically modified food (GMF) centres on whether consumers react to the process of gene technology or to the specific GMF products. Results from a choice experiment survey in New Zealand indicate that consumers are heterogeneous with regard to GMF and that some modifications are viewed more positively than others. These findings suggest that for some consumers the process of gene technology is the decisive factor in evaluatingGMF, while for others the different potential GMF products are valued according to their enhanced attributes.choice modelling, consumer surveys, food, genetic modification, preferences, Consumer/Household Economics, Demand and Price Analysis,

Tetris is Hard, Even to Approximate

In the popular computer game of Tetris, the player is given a sequence of tetromino pieces and must pack them into a rectangular gameboard initially occupied by a given configuration of filled squares; any completely filled row of the gameboard is cleared and all pieces above it drop by one row. We prove that in the offline version of Tetris, it is NP-complete to maximize the number of cleared rows, maximize the number of tetrises (quadruples of rows simultaneously filled and cleared), minimize the maximum height of an occupied square, or maximize the number of pieces placed before the game ends. We furthermore show the extreme inapproximability of the first and last of these objectives to within a factor of p^(1-epsilon), when given a sequence of p pieces, and the inapproximability of the third objective to within a factor of (2 - epsilon), for any epsilon>0. Our results hold under several variations on the rules of Tetris, including different models of rotation, limitations on player agility, and restricted piece sets.Comment: 56 pages, 11 figure