The Physics of Pneumatic Tide Gauges

As a part of its programme to monitor sea level around the British Isles, the Institute of Coastal Oceanography and Tides has a requirement for a recording system which may be quickly and easily installed, and which gives results accurate to 0.01 metre. The traditional stilling-well installation, apart from being costly and difficult to install on a temporary basis, has a number of fundamental disadvantages which limit its ability to record true water levels accurately (Lennon , 1971). Furthermore, stilling-wells, may only be installed where a harbour wall, pier or other vertical structure exists, and such structures are seldom located in positions which are representative of open sea conditions. Pneumatic pressure tide gauges have a number of advantages : not only may they be easily installed on vertical structures, but they may also be used on open coast lines, along beaches, or wherever a light connecting tube can be run from an underwater gas outlet to a recorder ashore. By comparison with gauges which rely on submerged electrical transducers connected to a shore-based recorder by conducting cable, the vulnerable underwater parts of pneumatic gauges are both cheap and easily repaired. Before adopting the pneumatic tide gauge principle for routine measurements it was necessary to investigate the physics of such systems, so that sources of error could be eliminated or subject to correction. This report contains details of these investigations; their application to coastal sea level measurements is described in more detail elsewhere (Pugh, 1971). Details of the bubbler-type gauge which uses a continuous flow of air through a connecting tube to an underwater outlet are given in the first section. However, an extension of the bubbler-gauge theory shows that a flow of air is not strictly necessary, and details of a non-bubbling system are given in the second section. This latter type of gauge is similar to gauges which use a partially inflated bag, but it has the advantage that gauge datum is defined to the same accuracy as a bubbler-gauge datum. The third section of this paper shows how these results may be applied to the design of actual pneumatic tide gauge systems

Effect of the cation structure on the properties of homobaric imidazolium ionic liquids

In this work we investigate the structure–property relationships in a series of alkylimidazolium ionic liquids with almost identical molecular weight. Using a combination of theoretical calculations and experimental measurements, we have shown that re-arranging the alkyl side chain or adding functional groups results in quite distinct features in the resultant ILs. The synthesised ILs, although structurally very similar, cover a wide spectrum of properties ranging from highly fluid, glass forming liquids to high melting point crystalline salts. Theoretical ab initio calculations provide insight on minimum energy orientations for the cations, which then are compared to experimental X-ray crystallography measurements to extract information on hydrogen bonding and to verify our understanding of the studied structures. Molecular dynamics simulations of the simplest (core) ionic liquids are used in order to help us interpret our experimental results and understand better why methylation of C2 position of the imidazolium ring results in ILs with such different properties compared to their non-methylated analogues

Correction to "Long-term and recent changes in sea level in the Falkland Islands"

In the paper “Long-term and recent changes in sea level in the Falkland Islands” by P. L. Woodworth et al. (Journal of Geophysical Research, 115, C09025, doi:10.1029/2010JC006113, 2010), in paragraph 47 we adopted a value of −0.52 mm/yr for the estimated rate of present-day sea level change in the Falkland Islands due to glacial isostatic adjustment (GIA). This value was used to remove the contributions of GIA to our measurements of historical and recent rates of sea level change. However, it was based on a misreading of the data file of Peltier [2004] on the Permanent Service for Mean Sea Level Web site (http://www.psmsl.org/train_and_info/geo_signals/gia/peltier). More reasonable values to apply to the observed changes since the mid-nineteenth century and in recent years would be −0.69 and −0.61 mm/yr respectively. Consequently, the long-term rate of sea level change between 1842 and the early 1980s, after correction for air pressure effects and for GIA, reported as +0.75 ± 0.35 mm/yr in paragraphs 1, 47, 55, and 61 should be +0.92 ± 0.35 mm/yr, the corresponding rate between 1842 and the midpoint of recent data of 1.06 ± 0.22 mm/yr in paragraphs 48 and 55 should be 1.23 ± 0.22 mm/yr, and the corresponding rate since 1992 reported as 2.51 ± 0.58 mm/yr in paragraphs 1 and 52 becomes 2.60 ± 0.58 mm/yr. The middle of paragraph 63 becomes “The Stanley data suggest that the rate of change of sea level in East Falkland since 1992 has been approximately 2.6 mm/yr, a rate supported by information from satellite altimetry.” These small GIA model corrections have no bearing on the main findings of our paper on the difference in the rates of sea level change between the historical (1842 to present-day) and recent (last 2 decades) epoch

Global consequences of afforestation and bioenergy cultivation on ecosystem service indicators

Land management for carbon storage is discussed as being indispensable for climate change mitigation because of its large potential to remove carbon dioxide from the atmosphere, and to avoid further emissions from deforestation. However, the acceptance and feasibility of land-based mitigation projects depends on potential side effects on other important ecosystem functions and their services. Here, we use projections of future land use and land cover for different land-based mitigation options from two land-use models (IMAGE and MAgPIE) and evaluate their effects with a global dynamic vegetation model (LPJ-GUESS). In the land-use models, carbon removal was achieved either via growth of bioenergy crops combined with carbon capture and storage, via avoided deforestation and afforestation, or via a combination of both. We compare these scenarios to a reference scenario without land-based mitigation and analyse the LPJ-GUESS simulations with the aim of assessing synergies and trade-offs across a range of ecosystem service indicators: carbon storage, surface albedo, evapotranspiration, water runoff, crop production, nitrogen loss, and emissions of biogenic volatile organic compounds. In our mitigation simulations cumulative carbon storage by year 2099 ranged between 55 and 89 GtC. Other ecosystem service indicators were influenced heterogeneously both positively and negatively, with large variability across regions and land-use scenarios. Avoided deforestation and afforestation led to an increase in evapotranspiration and enhanced emissions of biogenic volatile organic compounds, and to a decrease in albedo, runoff, and nitrogen loss. Crop production could also decrease in the afforestation scenarios as a result of reduced crop area, especially for MAgPIE land-use patterns, if assumed increases in crop yields cannot be realized. Bioenergy-based climate change mitigation was projected to affect less area globally than in the forest expansion scenarios, and resulted in less pronounced changes in most ecosystem service indicators than forest-based mitigation, but included a possible decrease in nitrogen loss, crop production, and biogenic volatile organic compounds emissions

Retrofitting Crude Oil Refinery Heat Exchanger Networks to Minimise Fouling While Maximising Heat Recovery

The use of fouling factors in heat exchanger design and the lack of appreciation of fouling in traditional pinch approach has often resulted badly designed crude preheat networks that are expensive to maintain. The development of thermal and pressure drop models for crude oil fouling has allowed its effects to be quantified, so that techno-economic analyses can be performed and various design options compared. Application of these fouling models is carried out on two levels: on the assessment of adding extra area to individual exchangers, and the design of a complete network using the Modified Temperature Field Plot. Application to a refinery case study showed that both at the exchanger and network levels, designing for maximum heat recovery using traditional pinch approach results in the least efficient heat recovery over a time period when fouling occurs

Transnational social capital: the socio‐spatialities of civil society

Civil society remains a contested concept, but one that is widely embedded in global development processes. Transnationalism within civil society scholarship is often described dichotomously, either through hierarchical dependency relations or as a more amorphous networked global civil society. These two contrasting spatial imaginaries produce very particular ideas about how transnational relations contribute to civil society. Drawing on empirical material from research with civil society organizations in Barbados and Grenada, in this article I contend that civil society groups use forms of transnational social capital in their work. This does not, however, resonate with the horizontal relations associated with grassroots globalization or vertical chains of dependence. These social relations are imbued with power and agency and are entangled in situated historical, geographical and personal contexts. I conclude that the diverse transnational social relations that are part of civil society activity offer hope and possibilities for continued civil society action in these unexpected spatial arrangements