Length and bursting of separation bubbles: A physical interpretation

A physical interpretation of the observed form of the pressure distribution beneath a two-dimensional separation bubble which modified the external inviscid pressure distribution only locally is given in terms of boundary layer concepts. A simple method for estimating along a mean streamline entrained into the underside of a growing shear layer through the transition region is discussed, and predictions of bubble bursting conditions and a lower bound on the bubble length are compared with experiment

Application of dimensional analysis and group theory to the solution of ordinary and partial differential equations Final report, 17 Jan. 1966 - 16 Jan. 1967

Dimensional analysis and group theory methods of solving ordinary and partial differential equation

Volatile hydrocarbons inhibit methanogenic crude oil degradation

Methanogenic degradation of crude oil in subsurface sediments occurs slowly, but without the need for exogenous electron acceptors, is sustained for long periods and has enormous economic and environmental consequences. Here we show that volatile hydrocarbons are inhibitory to methanogenic oil biodegradation by comparing degradation of an artificially weathered crude oil with volatile hydrocarbons removed, with the same oil that was not weathered. Volatile hydrocarbons (nC5-nC10, methylcyclohexane, benzene, toluene, and xylenes) were quantified in the headspace of microcosms. Aliphatic (n-alkanes nC12-nC34) and aromatic hydrocarbons (4-methylbiphenyl, 3-methylbiphenyl, 2-methylnaphthalene, 1-methylnaphthalene) were quantified in the total hydrocarbon fraction extracted from the microcosms. 16S rRNA genes from key microorganisms known to play an important role in methanogenic alkane degradation (Smithella and Methanomicrobiales) were quantified by quantitative PCR. Methane production from degradation of weathered oil in microcosms was rapid (1.1 ± 0.1 μmol CH4/g sediment/day) with stoichiometric yields consistent with degradation of heavier n-alkanes (nC12-nC34). For non-weathered oil, degradation rates in microcosms were significantly lower (0.4 ± 0.3 μmol CH4/g sediment/day). This indicated that volatile hydrocarbons present in the non-weathered oil inhibit, but do not completely halt, methanogenic alkane biodegradation. These findings are significant with respect to rates of biodegradation of crude oils with abundant volatile hydrocarbons in anoxic, sulphate-depleted subsurface environments, such as contaminated marine sediments which have been entrained below the sulfate-reduction zone, as well as crude oil biodegradation in petroleum reservoirs and contaminated aquifers

Semi-Classical Description of Antiproton Capture on Atomic Helium

A semi-classical, many-body atomic model incorporating a momentum-dependent Heisenberg core to stabilize atomic electrons is used to study antiproton capture on Helium. Details of the antiproton collisions leading to eventual capture are presented, including the energy and angular momentum states of incident antiprotons which result in capture via single or double electron ionization, i.e. into [He$^{++}\,\bar p$ or He$^{+}\,\bar p$], and the distribution of energy and angular momentum states following the Auger cascade. These final states are discussed in light of recently reported, anomalously long-lived antiproton states observed in liquid He.Comment: 15 pages, 9 figures may be obtained from authors, Revte

Experimental determination of stator endwall heat transfer

Local Stanton numbers were experimentally determined for the endwall surface of a turbine vane passage. A six vane linear cascade having vanes with an axial chord of 13.81 cm was used. Results were obtained for Reynolds numbers based on inlet velocity and axial chord between 73,000 and 495,000. The test section was connected to a low pressure exhaust system. Ambient air was drawn into the test section, inlet velocity was controlled up to a maximum of 59.4 m/sec. The effect of the inlet boundary layer thickness on the endwall heat transfer was determined for a range of test section flow rates. The liquid crystal measurement technique was used to measure heat transfer. Endwall heat transfer was determined by applying electrical power to a foil heater attached to the cascade endwall. The temperature at which the liquid crystal exhibited a specific color was known from a calibration test. Lines showing this specific color were isotherms, and because of uniform heat generation they were also lines of nearly constant heat transfer. Endwall static pressures were measured, along with surveys of total pressure and flow angles at the inlet and exit of the cascade

Bioeconomic meta-modelling of Indonesian agroforests as carbon sinks

In many areas of developing countries, economic and institutional factors often combine to give farmers incentives to clear forests and repeatedly plant food crops without sufficiently replenishing the soils. These activities lead to large-scale land degradation and contribute to global warming through the release of greenhouse gases into the atmosphere. We investigate whether agroforestry systems might alleviate these trends when carbon-credit payments are available under the Clean Development Mechanism of the Kyoto Protocol. A meta-modelling framework is adopted, comprising an econometric-production model of a smallholding in Sumatra. The model is used within a dynamic-programming algorithm to determine optimal combinations of tree/crop area, tree-rotation length, and firewood harvest. Results show the influence of soil-carbon stocks and discount rates on optimal strategies and reveal interesting implications for joint management of agriculture and carbon.bio-economic meta-modelling, Indonesia, agroforestry, carbon credits, dynamic programming, Environmental Economics and Policy, Resource /Energy Economics and Policy,

Breathers and kinks in a simulated crystal experiment

We develop a simple 1D model for the scattering of an incoming particle hitting the surface of mica crystal, the transmission of energy through the crystal by a localized mode, and the ejection of atom(s) at the incident or distant face. This is the first attempt to model the experiment described in Russell and Eilbeck in 2007 (EPL, v. 78, 10004). Although very basic, the model shows many interesting features, for example a complicated energy dependent transition between breather modes and a kink mode, and multiple ejections at both incoming and distant surfaces. In addition, the effect of a heavier surface layer is modelled, which can lead to internal reflections of breathers or kinks at the crystal surface.Comment: 15 pages, 12 figures, based on a talk given at the conference "Localized Excitations in Nonlinear Complex Systems (LENCOS)", Sevilla (Spain) July 14-17, 200

Optimal Land-Use Decisions in the Presence of Carbon Payments and Fertilizer Subsidies: An Indonesian Case Study

The Clean Development Mechanism of the Kyoto Protocol provides the opportunity for smallholders to receive financial rewards for adopting tree-based systems that are sustainable. In this paper a meta-model is developed to simulate interactions between trees, crops and soils under a range of management regimes for a smallholding in Sumatra. The model is used within a dynamic-programming algorithm to determine optimal tree/crop areas, tree-rotation lengths, firewood-harvest and fertilizer application rates for a landholder faced with deteriorating land quality and opportunities to receive carbon credits and fertiliser subsidies. It is found th at profit maximising management strategies depend on initial soil quality. For example, incentives to participate in carbon projects only exist when the soil is degraded because the opportunity cost of the forgone crop production is low. Also, when soil-carbon stocks are low only trees should be grown and residues added to the soil to increase carbon stocks until a threshold level is reached, when it becomes optimal to switch to a steady-state system of crops with fertiliser. In this case, tree rotation lengths depend on carbon and fertiliser prices; where increases in these prices decrease the opportunity cost of growing trees and allow for longer rotations. If, however, the initial soil-carbon stock is high, the profit-maximising strategy is to grow only crops and use fertiliser, which initially depletes the soil of carbon until a steady state is reached and maintained.Land Economics/Use,

Tree-crop interactions and their environmental and economic implications in the presence of carbon-sequestration payments

Growing trees with crops has environmental and economic implications. Trees can help prevent land degradation and increase biodiversity while at the same time allow for the continued use of the land to produce agricultural crops. In fact, growing trees alongside crops is known to improve both the productivity and sustainability of the land. However, due to high labour-input requirements, high costs of establishment, and delayed revenue returns, trees are often not economically attractive to landholders. Because of the Kyoto Protocol, and the growing emphasis on market-based solutions to environmental problems, the ability of trees to sequester and store CO2 has altered the economic landscape of agroforestry systems. The economic and management implications of carbon-sequestration payments on agroforestry systems are addressed in this study using a bioeconomic modelling approach. An agroforestry system in Indonesia is simulated using a biophysical process model. A general economic analysis of this system, from the standpoint of individual landholders, is then developed and the implications for management and policy are discussed.agroforestry, bioeconomics, tree/crop interactions, carbon credits, baselines, Environmental Economics and Policy, Land Economics/Use,