Intramolecular rhodium carbenoid insertion reactions

Imperial Users onl

Analysis of meteorological data from RRS Charles Darwin cruises CD46 and CD47 (BOFS experiment)

The IOSDL MultiMet meteorological instrumentation system was used during the BOFS experiment on RRS Charles Darwin cruises 46 and 47. This report describes and evaluates the quality of the meteorological data obtained. Recommendations for using the data include a 0.45°C correction to the forward dry bulb temperature and the use of wind directions from the main mast wind vane rather than the foremast propellor -vane. The temperature difference between the foremast and wheelhousetop psychrometer measurements was found to be a function of solar radiation and wind speed. A model of this effect was developed. From anemometer comparisons acceleration of the air flow over the ship was estimated to be 4%. The solar radiation sensors agreed to within a few W/m2 except for anomalous values on two days

"Reversed" alamethicin conductance in lipid bilayers

Alamethicin at a concentration of 2 micrograms/ml on one side of a lipid bilayer, formed at the tip of a patch clamp pipette from diphytanoyl phosphatidylcholine and cholesterol (2:1 mol ratio) in aqueous 0.5 M KCl, 5 mM Hepes, pH 7.0, exhibits an asymmetric current-voltage curve, only yielding alamethicin currents when the side to which the peptide has been added is made positive. Below room temperature, however, single alamethicin channels created in such membranes sometimes survive a sudden reversal of the polarity. These "reversed" channels are distinct from transiently observed states displayed as the channel closes after a polarity reversal. Such "reversed" channels can be monitored for periods up to several minutes, during which time we have observed them to fluctuate through more than 20 discrete conductance states. They are convenient for the study of isolated ion-conducting alamethicin aggregates because, after voltage reversal, no subsequent incorporation of additional ion-conducting aggregates takes place

Pile and Pile Group Capacity: Some Findings from Centrifuge Tests

The London Geotechnical Centrifuge Centre at City University London is a major experimental research facility for the Geotechnical Engineering Research Group. Some findings from two recent doctoral research projects are presented. The projects were aimed at improving our understanding of piled foundations. Pile group behaviour was studied with particular emphasis in determining the efficiency and load capacity of non standard group arrangements. The project was related directly to a development in London UK in which high capacity foundations were constructed using a Perimeter group arrangement of minipiles since that was all that could be constructed given onerous site constraints. The centrifuge research gave new insights into how pile groups carry large loads and demonstrated that Perimeter group arrangements make much more efficient use of piles than Grid groups. The second project was again industry driven and demonstrated that modifying the profile of a pile shaft can give significant increase in capacity with relatively little additional pile material

Ground movements generated by sequential Twin-tunnelling in over-consolidated clay

The expansion of urban populations comes with an associated demand for increased public transport. An often utilised solution is to construct a rapid transit system within tunnels. Generally, a pair of tunnels are constructed within relative close proximity. The construction of these tunnels will generate ground movements which have the potential to cause damage to existing surface and subsurface structures. Modern tunnelling practice aims to reduce these movements to a minimum; however there is still a requirement for accurate assessment of settlements. For tunnels driven in clay, superposition of settlement predictions made by considering a single tunnel is an accepted method used to estimate movements around pairs of tunnels. This presumes that the movements generated from the construction of the second tunnel are not influenced in any way by the presence of the first tunnel. A series of plane strain centrifuge model tests have been conducted to explore the validity of superposition as a prediction method. The tests consisted of a sequential twin-tunnel construction with varied centre-to-centre spacing in over-consolidated clay. Relatively complex apparatus facilitated a predefined volume loss whilst monitoring surface settlement, tunnel support pressures and pore-water pressures. The measured data were assessed against superposition for surface vertical settlements in the plane perpendicular to an advancing tunnel face. The results highlight some inconsistencies with the superposition method

Explanation for twin tunnelling-induced surface settlements by changes in soil stiffness on account of stress history

In this article, a group of representative centrifuge tests were selected for numerical modelling to explain the surface settlements induced by sequential twin tunnelling. Both Modified Cam Clay model (MCC) and Three-Surface Kinematic Hardening model (3-SKH) were adopted in the simulation, which indicated the use of 3-SKH model conduced to mimicking more closely centrifuge model response. Via performing more contrastive numerical analyses with 3-SKH model, the influence of the first tunnel event on the stiffness of the soil around the second tunnel was quantitatively investigated, whereby the mechanism behind the observed surface settlements was finally made clear

Apparatus for centrifuge modelling of top down basement construction with heave reducing piles

The construction of deep basements in urban areas is associated with many risks and problems among which is the possible damage to existing structures and services resulting from settlements near the excavation. A number of methods are routinely employed to attempt to control these movements (e.g. top-down construction, use of stiff diaphragm walls). This paper discusses the methodology and practicalities of a series of centrifuge model tests designed to investigate the effect of deep basement construction. Two sets of experimental apparatus are described in detail and their effectiveness in terms of robustness and generation of repeatable data are assessed. It is shown that using relatively simple techniques and equipment it is possible to model many of the features associated with top-down construction

A dynamic simulation model for possum and gorse control on a farm woodlot

Managers of farm woodlots in New Zealand are confronted by two major problems: possums and gorse. If these remain uncontrolled then they have a severe impact on the returns from farm woodlots. This paper presents a system dynamics model which has been developed to assist in the analysis of control measures for managing gorse and possums on a farm woodlot in the Makara Valley, Wellington. The model has four main sectors: a tree growth module for radiata pine; a growth module for gorse; a module for the stock of possums present in the habitat; and a module of financial indicators. A number of control experiments are presented which indicate the long term financial and physical consequences of different gorse and possum control measures. The model clearly demonstrates the complex nature of the dynamic behaviour of a system involving biological and environmental factors (ie possums, gorse and trees) and human intervention (in terms of silviculture, and possum and gorse control)