A study of some novel cationic complexes of the group 4 metals and their applications in Ziegler-Natta catalysis

The reactions between antimony(v) chloride and the monocyclopentadienyl metal trichlorides of Group 4 (CpMCl3 for M = Ti, Sr and Hf) in acetonitrile solution have afforded new hexachloroantimonate salts. These cationic metal-containing products have been isolated and characterised using IR, 1H NMR, elemental analysis, and in two cases, X-ray crystallography. The analogous pentamethylcyclopentadienyl (Cp*) systems have also been investigated, with largely similar results. Depending on the stoichiometry employed in the reaction, the relevant mono-, di- and tri-cationic complexes can be formed via halide exchange. For the Cp/Cp*TiCl3 series, a 1:1 or 2:1 ratio of Sb:Ti affords [CpTiCl2(MeCN)3][SbCl6] and [CpTiCl(MeCN)4][SbCl6]2 respectively. A ratio of 1:6 is required to yield pure [CpTi(MeCN)5][SbCl6]3. The 16-electron, pseudo-octahedral geometry of the latter complex was confirmed by X-ray analysis. A similar situation is found in the analogous Zr and Hf cases. However, the formation of the triply-charged complexes is accompanied by an expansion in coordination number about the metal centre; X-ray crystallographic studies revealed the 18-electron [CpZr(MeCN)6][SbCl6]3 to exhibit a pseudo-pentagonal bipyramidal geometry. The reactivity of the CpTi3+ salt towards a variety of both neutral and anionic species has been investigated. In acetonitrile solution, the complex rects with amines to give insoluble mixtures of partially substituted products. Adduct formation with ethers and trimethylphosphine is slow and only occurs when non-coordinating solvents are employed. The complex reacts with inorganic salts to reform neutral CpTiX3 compounds by simple anion exchange. The Ziegler-Natta catalytic activity of the cationic series has been studied. In the presence of methylaluminoxane cocatalysts, the complexes polymerise ethene but their activity is inversely proportional to the charge on the metal

Non-user benefits emanating from enhanced water flow to the Yala Protected Area Complex

Water is a multiple use resource. Increasing scarcity and competition from various sectors is an important dimension to be considered in its management. Understanding the value of water to different water uses is, therefore, necessary to assist decision-making in water allocation among sectors. Although water used in agriculture can be valued using production function approaches, such direct valuation methods are not available for the environmental uses of water. This paper uses non-market valuation methods to estimate the economic value of a committed flow through a unique ecosystem, the Yala Protected Area Complex (YPC). The Yala Protected Area Complex is an important wildlife refuge situated in south-eastern Sri Lanka. Its large land extent, undisturbed nature, and abundance and diversity of fauna contribute to its uniqueness. The fact that the YPC is also the most visited national park in Sri Lanka is partially a result of this uniqueness. However, maintenance of the park’s ecosystem depends on the flow of the Menik Ganga. This flow is regulated by the Veheragala Reservoir Project, and there is now discussion of reducing flow into the park by about half of the current level. The proposed plan ensures dry season flow into the YPC and, therefore, has been deemed acceptable. However, there is a possibility that farmers will demand further water releases during the dry season which could in turn endanger the planned downstream water releases. So there is a potential trade-off between environmental and irrigation uses of water. A willingness to pay (WTP) survey was conducted in ten districts in Sri Lanka during the fourth quarter of 2008 to estimate the WTP of the general population of the country towards maintaining this important environmental resource. In the hypothetical market presented, participants were told of the need for financial contributions from the general public to ensure the release of a minimum downstream flow commitment of 50 MCM. Participants were also informed of how this flow would enhance the ecosystem of the YPC. A single bound dichotomous choice contingent valuation approach was used as the elicitation format. Nonobligatory voluntary contributions were solicited towards a trust fund that could be used to ensure release of the required quantity of water downstream during dry months. According to the results of a binary logistic regression, income, age, and religious attachments are important factors affecting the decision to contribute to environmental flow maintenance to the YPC. Sixty-five percent of respondents were willing to pay something to ensure the maintenance of an adequate environmental flow in the YPC. The estimated mean WTP for water releases to enhance the YPC is Sri Lankan Rupees (SLR) 435 per year. Over the requested payment horizon of 10 years, the present value of aggregate WTP from the Sri Lankan population to enhance the ecosystem of the YPC is SLR 12 billion. This quantity greatly surpasses the present value of net benefits from rice farming estimated at SLR 0.64 billion, which would be generated if the same quantity of water was used for irrigation for 10 years (assuming current prices and input intensities). Thus, there is a clear opportunity for national welfare gain by ensuring adequate flow in YPC.Length: pp.37-47Water useMultiple useWildlifeHabitatsEcosystemsIrrigation waterWater allocation

Non-user benefits emanating from enhanced water flow to Yala Protected Area Complex. Abstract only

EcosystemsWater resource managementMultiple useDecision makingWater allocationEnvironmental flows

Data-driven methods for tracking improvement

The tracking precision required by modern industrial applications is continuously increasing. Feedback control alone is often no longer capable of giving the necessary tracking accuracy and so the use of two-degree-of-freedom controllers, which include a feedforward term, has become commonplace. Traditionally the feedforward term is a filter based on the inverse of an identified model of the system. It is, however, not possible to obtain very high precision tracking with this approach because the identified model will always suffer from model uncertainty. In this thesis, data-driven methods are investigated. These methods derive the feedforward control directly from measured data and thus avoid the system identification step, which is where the model uncertainty is introduced. They are, therefore, capable of producing higher precision tracking than the traditional methods. For the general tracking problem, a precompensator controller is considered as the feedforward term. This controller filters the desired output signal before it is applied as an input to the system. The precompensator's parameters are tuned directly using measured data. These data are affected by stochastic disturbances, such as measurement noise. The effect of these disturbances on the calculated parameters is studied and the correlation approach is used to reduce it. For the specific problem where the tracking task is repetitive, a situation frequently encountered in industrial applications, Iterative Learning Control is proposed. Iterative Learning Control uses measurements from previous repetitions to adjust the system's input for the current repetition in a manner that improves the tracking. As measurements are used, the calculated input is sensitive to the stochastic disturbances. The effect of these disturbances on the learning procedure is examined and algorithms, which are less sensitive to their presence, are developed. Extensions of the methods are also made for linear parameter varying systems in which the system's dynamics change as a function of a scheduling parameter. The developed methods are successfully applied to an industrial linear motor positioning system

Data-driven tuning of linear parameter varying precompensators

Methods for direct data-driven tuning of the parameters of precompensators for LPV systems are developed. Since the commutativity property is not always satisfied for LPV systems, previously proposed methods for LTI systems that use this property cannot be directly adapted. When the ideal precompensator giving perfect mean tracking exists in the proposed precompensator parameterisation, the LPV transfer operators do commute and an algorithm using only two experiments on the real system is proposed. It is shown that this algorithm gives consistent estimates of the ideal parameters despite the presence of stochastic disturbances. For the more general case, when the ideal precompensator does not belong to the set of parameterised precompensators, another technique is developed. This technique requires a number of experiments equal to twice the number of precompensator parameters and it is shown that the calculated parameters minimise the mean squared tracking error. The theoretical results are demonstrated in simulation

Polymicrobial oral biofilm models: simplifying the complex

Over the past century, numerous studies have used oral biofilm models to investigate growth kinetics, biofilm formation, structure and composition, antimicrobial susceptibility and host–pathogen interactions. In vivo animal models provide useful models of some oral diseases; however, these are expensive and carry vast ethical implications. Oral biofilms grown or maintained in vitro offer a useful platform for certain studies and have the advantages of being inexpensive to establish and easy to reproduce and manipulate. In addition, a wide range of variables can be monitored and adjusted to mimic the dynamic environmental changes at different sites in the oral cavity, such as pH, temperature, salivary and gingival crevicular fluid flow rates, or microbial composition. This review provides a detailed insight for early-career oral science researchers into how the biofilm models used in oral research have progressed and improved over the years, their advantages and disadvantages, and how such systems have contributed to our current understanding of oral disease pathogenesis and aetiology

Vol. 2 Ch. 5 Scale and Community in Hopewell Networks (SCHoN): Summary of Preliminary Results

https://ideaexchange.uakron.edu/encountering_hopewell/1015/thumbnail.jp

Vol. 2 Ch. 4 Material Choice and Interaction on Brown\u27s Bottom

https://ideaexchange.uakron.edu/encountering_hopewell/1014/thumbnail.jp