Inrteractions [sic] between farm effluent application methods, tillage practices and soil nutrients : a thesis presented in partial fulfilment of the requirements for the degree of Master of Applied Science in Agricultural Engineering at Massey University, Palmerston North, New Zealand

Land disposal of liquid effluent has benefits for the environment and is economically viable. Firstly, it can reduce nutrient levels from wastes polluting waterways. Secondly, the land application of effluent has been the most common treatment method because it can provide some necessary nutrients for plant growth. In New Zealand, land application of farm liquid effluent is a common method for disposing agricultural wastes. However, there is little comparative information about nutrient recycling in soils treated with effluent using surface application or subsurface injection. A field trial was conducted to examine the effect of tillage on the transformation of nutrient added through dairyshed effluent. Liquid effluent was either injected at 10 cm depth or broadcast on the surface at the Massey University long-term tillage experiments which include permanent pasture, and crops sown with no-till and conventional tillage as main treatments. In the first experiment, raw dairyshed liquid effluent was applied in August 1997 at the rate of 120 m 3 ha -1 (30 kg N ha -1 equivalent). This was considered as a low rate of application. In the second experiment starting in December 1997, the application was at the rate of 600 m 3 ha -1 (150 kg N ha -1 ). At this rate, although the hydraulic loading was considered as a high rate, the nutrient loading was considered optimum. Soil samples were collected before application, after one week, one month, and two months of application, at two depths: 0-10 cm and 10-20 cm and the samples were analysed for total N, total P, NO 3 - , NH 4 + , exchangeable K, available Olsen-P. Throughout the experiments, interactions between nutrient status, methods of application and different tillage practices were analysed. In the case of injection method, soil samples were taken both in the centre of the injected row and 10cm horizontally away from the centre of row. At the low rate of application (first experiment), soil nitrogen and phosphorus status did not change significantly for up to two months after application. Soil ammonium concentration reduced immediately after one week then reduced slowly. Nitrate concentration reduced slowly during the first month and significantly reduced during the second month after application. Exchangeable K and Olsen-P were not significantly different among treatments. At the high rate of application (second experiment), levels of soil nitrogen and phosphorus reduced slightly after two months of application. Nitrate concentration in the soil increased in the first month, but steadily reduced during the second month. On the other hand, ammonium concentration reduced gradually over a period of two months. Ammonium in injected plots was higher than that in the broadcast plots. Pasture retained more ammonium concentration compared with no-till and conventional tillage plots. Moreover, nitrate content in the injection plots was similar to that in the broadcast. This may be related to low rainfall during the experiment period that may have restricted the denitrification and reduced nitrate losses through leaching. Generally, there was higher content of exchangeable K and available P in soil which resulted from effluent application. Method of effluent application had no effects on K and P concentrations. Overall, there was an increase in nutrients in soil after application of liquid effluent, especially at the topsoil. There was a greater retention of nutrients in no-till soil than the conventionally tilled soil. Subsoil injection of effluent allowed higher level of nutrient retention than the surface broadcast method. This may be due to reduced nitrogen losses caused by volatilization of ammonium

Polynomial Time Algorithm for Min-Ranks of Graphs with Simple Tree Structures

The min-rank of a graph was introduced by Haemers (1978) to bound the Shannon capacity of a graph. This parameter of a graph has recently gained much more attention from the research community after the work of Bar-Yossef et al. (2006). In their paper, it was shown that the min-rank of a graph G characterizes the optimal scalar linear solution of an instance of the Index Coding with Side Information (ICSI) problem described by the graph G. It was shown by Peeters (1996) that computing the min-rank of a general graph is an NP-hard problem. There are very few known families of graphs whose min-ranks can be found in polynomial time. In this work, we introduce a new family of graphs with efficiently computed min-ranks. Specifically, we establish a polynomial time dynamic programming algorithm to compute the min-ranks of graphs having simple tree structures. Intuitively, such graphs are obtained by gluing together, in a tree-like structure, any set of graphs for which the min-ranks can be determined in polynomial time. A polynomial time algorithm to recognize such graphs is also proposed.Comment: Accepted by Algorithmica, 30 page

An investigation into teaching description and retrieval for constructed languages : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Computer Science at Massey University

The research presented in this thesis focuses on an investigation on teaching concepts for constructed languages, and the development of a teaching tool, called VISL, for teaching a specific constructed language. Constructed languages have been developed for integration with computer systems to overcome ambiguities and complexities existing in natural language in information description and retrieval. Understanding and using properly these languages is one of the keys for successful use of these computer systems Unfortunately, current teaching approaches are not suitable for users to learn features of those languages easily. There are different types of constructed languages. Each has specific features adapted for specific uses but they have in common explicitly constructed grammar. In addition, a constructed language commonly embeds a powerful query engine that makes it easy for computer systems to search for correct information from descriptions following the conditions of the queries. This suggests new teaching principles that should be easily adaptable to teach any specific structured language's structures and its specific query engine. In this research, teaching concepts were developed that offer a multi-modal approach to teach constructed languages and their specific query engines. These concepts are developed based on the efficiencies of language structure diagrams over the cumbersome and non-transparent nature of textual explanations, and advantages of active learning strategies in enhancing language understanding. These teaching concepts then were applied successfully for a constructed language, FSCL, as an example The research also explains howr the concepts developed can be adapted for other constructed languages. Based on the developed concepts, a Computer Aided Language Learning (CALL) application called VISL is built to teach FSCL. The application is integrated as an extension module in PAC, the computer system using FSCL for description and retrieval of information in qualitative analysis. In this application, users will learn FSCL through an interconnection of four modes: FSCL structures through the first two modes and its specific query engine through the sccond two modes After going through four modes, users will have developed full understanding for the language. This will help users to construct a consistent vocabulary database, produce descriptive sentences conducive to retrieval, and create appropriate query sentences for obtaining relevant search results

Weakly Secure MDS Codes for Simple Multiple Access Networks

We consider a simple multiple access network (SMAN), where $k$ sources of unit rates transmit their data to a common sink via $n$ relays. Each relay is connected to the sink and to certain sources. A coding scheme (for the relays) is weakly secure if a passive adversary who eavesdrops on less than $k$ relay-sink links cannot reconstruct the data from each source. We show that there exists a weakly secure maximum distance separable (MDS) coding scheme for the relays if and only if every subset of $\ell$ relays must be collectively connected to at least $\ell+1$ sources, for all $0 < \ell < k$. Moreover, we prove that this condition can be verified in polynomial time in $n$ and $k$. Finally, given a SMAN satisfying the aforementioned condition, we provide another polynomial time algorithm to trim the network until it has a sparsest set of source-relay links that still supports a weakly secure MDS coding scheme.Comment: Accepted at ISIT'1