Modelling and experimental verification of a solar-powered liquid desiccant cooling system for greenhouse food production in hot climates

Experiments and theoretical modelling have been carried out to predict the performance of a solar-powered liquid desiccant cooling system for greenhouses. We have tested two components of the system in the laboratory using MgCl2 desiccant: (i) a regenerator which was tested under a solar simulator and (ii) a desiccator which was installed in a test duct. Theoretical models have been developed for both regenerator and desiccator and gave good agreement with the experiments. The verified computer model is used to predict the performance of the whole system during the hot summer months in Mumbai, Chittagong, Muscat, Messina and Havana. Taking examples of temperate, sub-tropical, tropical and heat-tolerant tropical crops (lettuce, soya bean, tomato and cucumber respectively) we estimate the extensions in growing seasons enabled by the system. Compared to conventional evaporative cooling, the desiccant system lowers average daily maximum temperatures in the hot season by 5.5-7.5 °C, sufficient to maintain viable growing conditions for lettuce throughout the year. In the case of tomato, cucumber and soya bean the system enables optimal cultivation through most summer months. It is concluded that the concept is technically viable and deserves testing by means of a pilot installation at an appropriate location

A solar powered liquid-desiccant cooling system for greenhouses

Liquid desiccant systems are of potential interest as a means of cooling greenhouses to temperatures below those achieved by conventional means. However, only very little work has been done on this technology with previous workers focussing on the cooling of human dwellings using expensive desiccants such as lithium salts. In this study we are designing a system for greenhouse cooling based on magnesium chloride desiccant which is an abundant and non-toxic substance. Magnesium chloride is found in seawater, for example, and is a by-product from solar salt works. We have carried out a detailed experimental study of the relevant properties of magnesium rich solutions. In addition we have constructed a test rig that includes the main components of the cooling system, namely a dehumidifier and solar regenerator. The dehumidifier is a cross-flow device that consists of a structured packing made of corrugated cellulose paper sheets with different flute angles and embedded cooling tubes. The regenerator is of the open type with insulated backing and fabric covering to spread the flow of desiccant solution. Alongside these experiments we are developing a mathematical model in gPROMS® that combines and simulates the heat and mass transfer processes in these components. The model can be applied to various geographical locations. Here we report predictions for Havana (Cuba) and Manila (Philippines), where we find that average wet-bulb temperatures can be lowered by 2.2 and 3°C, respectively, during the month of May

Determining benefits from B2B e-commerce : a strategic approach

A request from a powerful customer to exchange information electronically is an important external stimulus to the business strategy of a supplier. Prior research indicates that sub-optimal benefits, if any, are the typical result of such a stimulus. In this research, B2B ecommerce alignment between business strategy and IT strategy is proposed as a determinant of enhanced business benefits from electronic information exchange. A multiple case study approach in the Australian automotive industry is used to examine this proposition. As more electronic information is exchanged using a range of electronic modes, thus creating complex interorganizational systems, this research provides insights for suppliers about how to achieve greater benefits from B2B e-commerce.Una petición proveniente de un cliente poderoso para intercambiar información electrónicamente es un estímulo externo importante para la estrategia de negocios de un proveedor. Una investigación previa indica que los beneficios óptimos, si se producen, son el resultado de un estímulo así. En esta investigación, la alineación de comercio online B2B entre estrategias de negocios y estrategias de IT fueron propuestas como determinantes para obtener beneficios de intercambios de información electrónica. Un estudio de múltiples casos en la industria automotivacional australiana se usa para estudiar esta proposición. Conforme más información electrónica se intercambia usando un rango de métodos electrónicos, se crean complejos interorganismos, esta investigación proporciona pistas para cómo los proveedores pueden alcanzar mejores beneficios del comercio electrónico B2B

Virginia Technology and Engineering Education Association 1978-2018: Celebrating Six Decades of Progress

(First Paragraph) Technology and engineering education in Virginia and the nation is coming to a crossroads. Recent growth in state directives, new courses, and ever-changing funding for science, technology, engineering, and mathematics (STEM) education influences the supply of Technology Education teachers, leading to what some say is a dire future for our profession and association. This history is gathered to emphasize the importance and value of what we teach in Virginia public schools. It also captures who was involved with the association leadership over the years

Geographic Market Definition in an International Context

Market definition is generally regarded as a key step in antitrust analysis. Market definition has two components. Product market definition seeks to include all products that are meaningful substitutes. Geographic market definition seeks to incorporate all relevant sources of the product in question. This paper is concerned with geographic market definition and, in particular, how geographic markets are defined in situations where competition may, at least to some extent, transcend national boundaries. The subject of the paper may be of some current interest for two reasons. First, the perception is widespread that, over the past twenty or so years, competition in many products and services has become increasingly international in scope and that this trend will continue. Second, the way in which foreign competition is taken into account in performing the antitrust analysis can have a dramatic impact on the legal or policy conclusions that are reached in a particular instance. The legality of a proposed merger, for example, may turn entirely on how competition from foreign sellers is treated. For antitrust purposes, when we say that competition has become more international in scope, we mean primarily that the range of possible suppliers for many goods and services to U.S. consumers increasingly includes sellers who do not produce or are not primarily headquartered in the United States or that an increasing portion of sales by American-based firms are to customers abroad. Many aspects of antitrust are potentially affected by these changes. Some of the more complex issues involve jurisdictional considerations and these will not be discussed here. As we will see, however, the subject of market definition exposes almost all of the substantive (as opposed to jurisdictional) considerations that come into play when we take account of the international aspect of certain markets. The paper has three main parts. The first focuses on the role market definition plays in antitrust analysis and, in particular, the link between market definition and market power. The second explores the particular issues that are raised with respect to market definition when there is an international aspect to competition. The final section addresses some of the empirical questions raised by the largely theoretical analysis of the first two parts of the paper

Chaotic and integrable magnetic fields in one-dimensional hybrid Vlasov-Maxwell equilibria

In this paper, we develop a one-dimensional, quasineutral, hybrid Vlasov-Maxwell equilibrium model with kinetic ions and massless fluid electrons and derive associated solutions. The model allows for an electrostatic potential that is expressed in terms of the vector potential components through the quasineutrality condition. The equilibrium states are calculated upon solving an inhomogeneous Beltrami equation that determines the magnetic field, where the inhomogeneous term is the current density of the kinetic ions and the homogeneous term represents the electron current density. We show that the corresponding one-dimensional system is Hamiltonian, with position playing the role of time, and its trajectories have a regular, periodic behavior for ion distribution functions that are symmetric in the two conserved particle canonical momenta. For asymmetric distribution functions, the system is nonintegrable, resulting in irregular and chaotic behavior of the fields. The electron current density can modify the magnetic field phase space structure, inducing orbit trapping and the organization of orbits into large islands of stability. Thus the electron contribution can be responsible for the emergence of localized electric field structures that induce ion trapping. We also provide a paradigm for the analytical construction of hybrid equilibria using a rotating two-dimensional harmonic oscillator Hamiltonian, enabling the calculation of analytic magnetic fields and the construction of the corresponding distribution functions in terms of Hermite polynomials

Studies on the Effects of Maintenance of Hamster Adrenals in Vitro

Whole adrenals of the young adult hamster were maintained in culture. In most of the experiments the organ was supported on lens paper, but, latterly, cellulose and gelatin sponge were used. The culture media employed were (1) Ringer\u27s Solution (no nutrient), and (2) a nutrient mixture consisting of modified Krebs-Ringer\u27s Solution, lactalbumen hydrolysate, yeast extract and horse serum. The maintenance period was up to seven days, and the culture medium was freshened regularly in certain cases. Organs were weighed at the beginning and end, and sometimes during maintenance. Histological appearance at termination was compared with that of a freshly extirpated adrenal. In absence of nutrient, weight remained constant for the first day of culture, decreased over the following two to three days, and then leveled off at about 60 percent of its initial value. By contrast, organs cultured in the nutrient medium showed quite random variations in weight. There appeared to be no correlation between maintenance of weight and histological preservation; in point of fact, all organs which were well preserved after more than one to two days in vitro had lost weight considerably. Histological criteria are discussed

Geographic Market Definition in an International Context

Market definition is generally regarded as a key step in antitrust analysis. Market definition has two components. Product market definition seeks to include all products that are meaningful substitutes. Geographic market definition seeks to incorporate all relevant sources of the product in question. This paper is concerned with geographic market definition and, in particular, how geographic markets are defined in situations where competition may, at least to some extent, transcend national boundaries. The subject of the paper may be of some current interest for two reasons. First, the perception is widespread that, over the past twenty or so years, competition in many products and services has become increasingly international in scope and that this trend will continue. Second, the way in which foreign competition is taken into account in performing the antitrust analysis can have a dramatic impact on the legal or policy conclusions that are reached in a particular instance. The legality of a proposed merger, for example, may turn entirely on how competition from foreign sellers is treated. For antitrust purposes, when we say that competition has become more international in scope, we mean primarily that the range of possible suppliers for many goods and services to U.S. consumers increasingly includes sellers who do not produce or are not primarily headquartered in the United States or that an increasing portion of sales by American-based firms are to customers abroad. Many aspects of antitrust are potentially affected by these changes. Some of the more complex issues involve jurisdictional considerations and these will not be discussed here. As we will see, however, the subject of market definition exposes almost all of the substantive (as opposed to jurisdictional) considerations that come into play when we take account of the international aspect of certain markets. The paper has three main parts. The first focuses on the role market definition plays in antitrust analysis and, in particular, the link between market definition and market power. The second explores the particular issues that are raised with respect to market definition when there is an international aspect to competition. The final section addresses some of the empirical questions raised by the largely theoretical analysis of the first two parts of the paper

Energy saving and solar electricity in fan-ventilated greenhouses

Greenhouse cultivation is an energy intensive process therefore it is worthwhile to introduce energy saving measures and alternative energy sources. Here we show that there is scope for energy saving in fan ventilated greenhouses. Measurements of electricity usage as a function of fan speed have been performed for two models of 1.25 m diameter greenhouse fans and compared to theoretical values. Reducing the speed can cut the energy usage per volume of air moved by more than 70%. To minimize the capital cost of low-speed operation, a cooled greenhouse has been built in which the fan speed responds to sunlight such that full speed is reached only around noon. The energy saving is about 40% compared to constant speed operation. Direct operation of fans from solar-photovoltaic modules is also viable as shown from experiments with a fan driven by a brushless DC motor. On comparing the Net Present Value costs of the different systems over a 10 year amortization period (with and without a carbon tax to represent environmental costs) we find that sunlight-controlled system saves money under all assumptions about taxation and discount rates. The solar-powered system, however, is only profitable for very low discount rates, due to the high initial capital costs. Nonetheless this system could be of interest for its reliability in developing countries where mains electricity is intermittent. We recommend that greenhouse fan manufacturers improve the availability of energy-saving designs such as those described here

Wiki or Word? Evaluating Tools for Collaborative Writing and Editing

Businesses and other organizations are relying increasingly on virtual teams to perform a range of business activities. A key challenge in utilizing virtual teams is to support collaboration among team members who are separated by distance and/or time. In this paper we use a research model based on a combination of the Technology Acceptance Model (TAM) and the Task Technology Fit (TTF) model to examine two approaches to supporting students in collaboratively creating and editing a report for an introductory course in information systems. In our study, one group of students used MS Word with Track Changes turned on combined with emailing the document among students. A second group was provided access to a wiki where they created the report. Results show that students found the Word and email combination more useful and easier to use than the wiki environment in completing the project. Further, there was no perceived difference in the effort of collaboration between the two methods. This study raises questions about the widely held belief that web-based collaboration platforms are superior to emailing documents among collaborators