Forestry—Yesterday, Today and Tomorrow

A request to write a review of forestry of today for the Ames Forester, brings vividly to mind the conditions of twenty years ago, when the writer was just beginning forestry work as a student assistant in the government service Since that time the changes have been many. Forestry is now one of the great recognized professions, and is being applied commercially in great industries

Formation and desorption of negative ions from metal surfaces

Investigations of negative ion and electron emission from gas-covered metal surfaces due to the impact of low energy (30-300 eV) positive ions and, separately, photons (2-5 eV) are presented. In both cases, the negative ion formation process is thought to occur via electron tunneling from the surface or its substrate to a sputtered or photodesorbed neutral atom or molecule.;In particular, absolute total negative ion and electron yields for collisions of positive alkali ions with a gas-covered Mo substrate have been measured. Mass analysis of the sputtered negative ions show that O{dollar}\sb2\sp-{dollar} is the dominant ion at low impact energies. This coupled with the fact that threshold energies for observing secondary negative ions and electrons are the same suggests that electron production is correlated to the O{dollar}\sb2\sp-{dollar} production, and specifically that electrons are the result of autodetachment of excited O{dollar}\sb2\sp-{dollar}. This hypothesis provides an explanation of the mechanism responsible for the emission of electrons at low impact energies.;Relative yields for photodesorbed H{dollar}\sp-{dollar} from a barium substrate have been measured as a function of photon wavelength for the range of 245 to 585 nm. A description of the formation of H{dollar}\sp-{dollar} due to photodesorption of BaH on a surface is consistent with the known energetics of the system. An estimate of the absolute yield of photodesorbed H{dollar}\sp-{dollar} per incident photon has been made

Some Forestry Problems of the Prairies of the Middle West

A residence of several years in one of the central prairie states and two seasons spent in studying natural conditions through a belt of prairie country from the Mississippi to the foothills of the Rockies makes me feel that the problems of prairie forestry are not only intensely interesting, but that their early solution will be of vast importance to the future agricultural and commercial development of the entire middle West

Tetraphosphine Linkers for Immobilizing Catalysts and Studies of Polymer Degradation Mechanisms

The overall goal of the first project of this thesis was to find ways to improve homogeneous catalysts and render them more recyclable and thus improve their lifetimes. One way to generate such superior catalysts is to whether them to solid, insoluble supports. The nature of the latter is crucial for the activities and lifetimes of the catalysts. Flexible linkers such as long alkyl chains allow contact of the catalysts with the surface and potentially their decomposition. Tetraphosphine linkers with rigid tetraphenylelement cores had been immobilized previously. The rigid nature of the scaffold ligands prevented interactions with the reactive surface and led to an immobilized Wilkinson's catalyst that could be recycled many times in a batchwise manner. In this new project, in order to test whether further increasing the distance between the immobilized catalyst and the surface would improve the lifetime of the catalysts, biphenyl spokes have been incorporated into the tetraphosphine linkers. The catalytic activity of these new catalysts compares favorably with that of previously used flexible linkers. In the second project of this thesis polyetheretherketone (PEEK) polymers, which are utilized in applications of extreme service environments in the oil and gas industry, are studied. PEEK material is rather tolerant of high temperatures and pressures and chemically comparatively resistant. However, PEEK degrades quite rapidly in the commonly used ZnBr₂ containing completion fluids, in combination with the high temperatures and pressures needed for hydraulic fracturing. The degradation of the polymer leads to machine parts breaking during the operation and results in costly delays in the drilling process. Therefore, the main goal of the second project of this thesis was to elucidate the molecular mechanisms that lead to the degradation of the polymer, and to define the factors that influence these decomposition pathways. Mechanistic studies after the identification of the small molecules produced, reveal the simultaneous occurrence of several decomposition pathways. The initial reaction in the PEEK polymer is the C-C bond cleavage at the ketone position. Subsequently, bromination by the ZnBr₂ in the completion fluids, other radical based decompositions, and hydrolysis under the acidic conditions take place

Synthesis Of Novel Ionic Liquid Tagged Porphryin Media Designed For The Oxidation Of Lignin

The ever growing need for a viable renewable fuel source has led to this thesis project; the biomimetic lignin degradation by means of a homogeneous oxidative catalyst in corresponding ionic liquids. Lignin comprises nearly a third of lignocellulosic biomass and is cross-linked to both cellulose and hemicellulose. Current utilization methods of lignin do not generate the full value of the polymer, because they do not yield many of the valuable feed stock chemicals it is comprised of. To improve the value of the biomass as a whole and create a viable economy for the US\u27s transition to biofuels, better utilization methods need to be developed. To this end, we have developed ionic liquid tagged metalloporphyrin catalysts and coupled them in ionic liquids that are known to dissolve lignin in an attempt to more efficiently isolate the feedstock chemicals contained within lignin. Synthesis of four ionic liquid tagged metalloporphyrin catalysts has been completed with moderate yields. The array of catalysts has been synthesized, as the functionalization of the metalloporphyrin is known to have a great effect on its catalytic abilities. Recently groups have shown a significant increase in the reusability of the ionic catalysts when coupled with ionic liquids, helping a major hurdle in the biomimetic process. We have performed initial catalytic studies with two of our novel ionic metalloporphyrins and compared their activity with a non-ionic metalloporphyrin. Under similar conditions in 1-allyl-3-methylimidazolium xylenesulphonate our novel catalysts outperformed the comparative non-ionic porphyrin catalyst significantly

Tetraphosphine Linkers for Immobilizing Catalysts and Studies of Polymer Degradation Mechanisms

The overall goal of the first project of this thesis was to find ways to improve homogeneous catalysts and render them more recyclable and thus improve their lifetimes. One way to generate such superior catalysts is to whether them to solid, insoluble supports. The nature of the latter is crucial for the activities and lifetimes of the catalysts. Flexible linkers such as long alkyl chains allow contact of the catalysts with the surface and potentially their decomposition. Tetraphosphine linkers with rigid tetraphenylelement cores had been immobilized previously. The rigid nature of the scaffold ligands prevented interactions with the reactive surface and led to an immobilized Wilkinson's catalyst that could be recycled many times in a batchwise manner. In this new project, in order to test whether further increasing the distance between the immobilized catalyst and the surface would improve the lifetime of the catalysts, biphenyl spokes have been incorporated into the tetraphosphine linkers. The catalytic activity of these new catalysts compares favorably with that of previously used flexible linkers. In the second project of this thesis polyetheretherketone (PEEK) polymers, which are utilized in applications of extreme service environments in the oil and gas industry, are studied. PEEK material is rather tolerant of high temperatures and pressures and chemically comparatively resistant. However, PEEK degrades quite rapidly in the commonly used ZnBr₂ containing completion fluids, in combination with the high temperatures and pressures needed for hydraulic fracturing. The degradation of the polymer leads to machine parts breaking during the operation and results in costly delays in the drilling process. Therefore, the main goal of the second project of this thesis was to elucidate the molecular mechanisms that lead to the degradation of the polymer, and to define the factors that influence these decomposition pathways. Mechanistic studies after the identification of the small molecules produced, reveal the simultaneous occurrence of several decomposition pathways. The initial reaction in the PEEK polymer is the C-C bond cleavage at the ketone position. Subsequently, bromination by the ZnBr₂ in the completion fluids, other radical based decompositions, and hydrolysis under the acidic conditions take place

The Administration of Rent Rationing and Price Control Legislation

Symposium: The Administration of Rent Rationing and Price Control Legislatio

Scale-down model qualification study identifies parameters to improve full-scale robustness

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Field assessment of sediment trap efficiency under varying flow conditions

Knowledge of the collection efficiency of sediment traps, particularly under conditions of varying current speed, is presently more a matter of hope than confidence. We report here on a field experiment designed to determine, for a particular trap geometry, the effect of current speed and particle fall velocity on the collection efficiency of a moored trap relative to the presumably unbiased efficiency of an identical drifting trap. The experiment was performed in a deep estuarine tidal passage where a smoothly varying unidirectional flow and a spatially homogenous particle population mimicked laboratory flume conditions. A multiple-sample sediment trap integrated to a current meter partitioned the mass flux collected by the moored trap into one of four chambers according to the following speed intervals: \u3c12, 12–\u3c30, 30–\u3c50, and ≥50cm/s. The magnitude and particle characteristics of the flux collected at \u3c12 cm/s were indistinguishable from those simultaneously collected by drifting traps. At higher speeds, the relative efficiency of the moored trap ranged between 1% and 24% and the mean size and density of the trapped particles increased. These results support predictions based on laboratory studies that collection efficiency decreases with an increase in the trap Reynolds number or a decrease in particle fall velocity. The study demonstrates that consideration must be given to scaling both trap diameter and aspect ratio according to the expected flow conditions, and that knowledge of flow conditions at the trap mouth is necessary to properly interpret the flux data

Operational research in the evaluation of social security benefit policies

This thesis makes it possible for future reforms of the social security system to be based on the best available information. An approach to benefit policy analysis is defined and a technique for processing available data as required is identified. Progress on evaluating policies more faithfully in accord with expected performance rather than assuming perfect implementation is made. Having reviewed the development of the social security system and previous contributions to benefit policy analysis the requirements of an information system are defined. Available data sources are evaluated. This analysis highlights the complementary nature of the qualities of the Family Expenditure Survey and specialised sources. The use of iterative proportional fitting procedures to combine these sources in such a way as to exploit their strengths and minimise the impact of their weaknesses is advocated. Validation tests show the approach results in good estimates. Furthermore the approach is easy to understand and lies well in an analytic process geared towards increasing involvement of non-technical personnel. The same approach can be used to analyse the alternative benefit regimes for the distributional implications of hypothesised trends in aggregate variables. The need to consider operational issues when analysing policies is recognised. Two aspects of this problem are considered. An analysis of appeals data led to rankings of aspects of the benefit entitlement assessment procedure in terms of difficulty caused and persistence with which problems arose. The second analysis is a pilot study of inter-regional differences in population characteristics and aspects of benefit implementation to identify ways of improving the operational system generally. An important aspect of this analysis is the presentation of data on computer drawn maps - a further attempt to increase participation in the analytic process. Further development of this work should enable the evaluation of policy alternatives in terms of expected performance rather than on the assumption of perfect implementation