Globalization has forced impressive growth rates in international trade within the last decades and although food trade hasn't been able to keep pace with this general development it is one of the most economic-political sensitive areas in international negotiations. Furthermore transportation of food is characterized mainly by perishability and challenges transport logistics especially when crossing boarders or even regions. Therefore the main aim of this paper is to provide a detailed overview of present boardercrossing food transportation by analysing food trade in value and quantities as well as to identify development tendencies between 1990 and 2005. Furthermore to explain the observed developments determinants of changes will be analysed and a final discussion of the key issues in transporting food at a global dimension will round the paper. (author's abstract) / Series: Schriftenreihe des Instituts für Transportwirtschaft und Logistik - Verkehr

In the current wave of economic instability, the world is witnessing significanteconomic progress in the sub-Saharan Africa. In this particular part of the worldamong the best performing developing economies, Ethiopia’s progress is con-sidered as an example for achievements in the region in last decade. The gov-ernment of Ethiopia believes in building huge infrastructures in the whole coun-try and especially in the economically vital geographies like the capital AddisAbaba. The project I have proposed aims to contribute to the smooth function-ing of the Addis Light Rail Transit after its launch. This bachelor’s thesis in-tends to design and develop an application based on the technology of web ser-vices for Internet and smart phone users. So the App updates data on the arrivalof a train on a particular station, in the case of unlikely delay the app informsthe users on new schedules. The application provides a functionality to searchfor available upcoming journeys and allows the customers to pay for the jour-ney from the device they are having on their hand. Finally, the project providesinsights on the usability of the implemented applications based on summativeevaluation technique.

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The traditional colloid filtration model has been recognized to not fully describe transport of microorganisms in porous media under many conditions. Potential reasons for the discrepancies between colloid filtration theories and observed data are summarized into three aspects in the dissertation, including physicochemical heterogeneity, a blocking effect in the attachment process, and irreversible straining. A new transport model is developed to incorporate these non-ideal phenomena. First, both the collision-efficiency coefficient and the detachment-rate coefficient are formulated as probability density functions with log-normal distributions to represent physicochemical heterogeneity of both microbial and porous-medium grain surfaces. Second, the blocking effect is represented by appending a modified random sequential adsorption (RSA) function to the kinetic rate equation. Third, a semi-empirical equation is developed to describe the straining effect.The new model is then evaluated with a series of sensitivity analyses and illustrative applications to measured data. Sensitivity analysis on the role of probability density function (PDF) in collision efficiency and detachment rate coefficient shows that heterogeneity causes longer tailing in breakthrough curves, This effect is controlled by the implementation of the PDF in the detachment rate coefficient because the lower values among a series of detachment rate coefficients delay detachment. Straining phenonmena have received more and more attentions for protozoa transport. The new semi-empirical straining equation derived in the dissertation provides reasonable matches to the colloid data and cryptosporidium data. The Blocking effect is another process of concern for microbial transport, as shown in the analysis of microsporidium column experiments herein. The new model also proved to be successful for simulating MS-2 virus transport. The work presented will help enhance our understanding of biocolloid transport in porous media.

No description available.

For years, TCP has been the first choice for data transportation for the Internet. It provides reliable data delivery with the help of its flow control and congestion control mechanism. In order to improve TCP performance many modifications were proposed to the TCP congestion control mechanisms. However, some of the features of cognitive radio networks make TCP perform poorly in terms of throughput. Some of these features of cognitive radio networks are frequent bandwidth variation, licensed user interruption, and disconnections due to spectrum sensing. These features cause packet losses and time-outs which are mistakenly categorized as congestion losses by TCP. In this thesis, the TCP framework was modified to work efficiently in cognitive radio networks. Markov model that captures the behaviour of TCP is developed and used to evaluate the performance of the proposed protocol.

For years, TCP has been the first choice for data transportation for the Internet. It provides reliable data delivery with the help of its flow control and congestion control mechanism. In order to improve TCP performance many modifications were proposed to the TCP congestion control mechanisms. However, some of the features of cognitive radio networks make TCP perform poorly in terms of throughput. Some of these features of cognitive radio networks are frequent bandwidth variation, licensed user interruption, and disconnections due to spectrum sensing. These features cause packet losses and time-outs which are mistakenly categorized as congestion losses by TCP. In this thesis, the TCP framework was modified to work efficiently in cognitive radio networks. Markov model that captures the behaviour of TCP is developed and used to evaluate the performance of the proposed protocol.

No description available.

Field observations are made of the formation of backwash ripples on the beachface, formed by undular hydraulic jumps generated by backwash down the beach face colliding with wave bores. Measured ripple wavelengths range from set averages of 48 to 70 cm. Within a particular set of ripples there is a tendency for the spacing to decrease in the offshore direction. These field observations are compared with laboratory experiments where undular jumps are generated in a flume, and with a computer simulation model which models both the flow within an undular hydraulic jump and the resulting sediment transport which gives rise to the backwash ripples. The computer model involves a numerical solution of the Boussinesq equations which govern the fluid flow, and sediment transport equations which relate the sand transport rate to the local mean flow velocity. The computer model permits a study of the detailed time-history of the undular jump development and the formation of the backwash ripples. This model shows good agreement with the field observations of backwash ripples, predicting an offshore decrease in their spacing as observed. The laboratory experiments showed a similar result so long as the Froude number of the supercritical flow before the jump occurs is small, on the order of 1.4. Differences between the computer model and experiments were small and arose principally from the neglect of internal friction and surface tension in the model. The study demonstrates the usefulness of the simultaneous application of computer simulation models and laboratory experiments to understand complex flow and sediment transport conditions such as occur on beaches. / Graduation date: 1979 / Best scan available for figures 1 & 2. Original is a black and white photocopy.

Thesis (M.S.)--Joint Program in Oceanography/ Applied Ocean Science and Engineering, Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution, 2003. / Title from Web page (viewed on Mar. 24, 2008). Includes bibliographical references (p. 37-40).