Constraining the age of Lateglacial and early Holocene pollen zones and tephra horizons in southern Sweden with Bayesian probability methods

The sediment sequence from Hasseldala port in southeastern Sweden provides a unique Lateglacial/early Holocene record that contains five different tephra layers. Three of these have been geochemically identified as the Borrobol Tephra, the Hasseldalen Tephra and the 10-ka Askja Tephra. Twenty-eight high-resolution C-14 measurements have been obtained and three different age models based on Bayesian statistics are employed to provide age estimates for the five different tephra layers. The chrono- and pollen stratigraphic framework supports the stratigraphic position of the Borrobol Tephra as found in Sweden at the very end of the Older Dryas pollen zone and provides the first age estimates for the Askja and Hasseldalen tephras. Our results, however, highlight the limitations that arise in attempting to establish a robust, chronologically independent lacustrine sequence that can be correlated in great detail to ice core or marine records. Radiocarbon samples are prone to error and sedimentation rates in lake basins may vary considerably due to a number of factors. Any type of valid and 'realistic' age model, therefore, has to take these limitations into account and needs to include this information in its prior assumptions. As a result, the age ranges for the specific horizons at Hasseldala port are large and calendar year estimates differ according to the assumptions of the age-model. Not only do these results provide a cautionary note for overdependence on one age-model for the derivation of age estimates for specific horizons, but they also demonstrate that precise correlations to other palaeoarchives to detect leads or lags is problematic. Given the uncertainties associated with establishing age-depth models for sedimentary sequences spanning the Lateglacial period, however, this exercise employing Bayesian probability methods represents the best possible approach and provides the most statistically significant age estimates for the pollen zone boundaries and tephra horizons. Copyright (C) 2006 John Wiley & Sons, Ltd.

An elasto-plastic critical state framework for unsaturated soil.

Data from a series of controlled suction triaxial tests on samples of compacted speswhite kaolin were used in the development of an elasto–plastic critical state framework for unsaturated soil. The framework is defined in terms of four state variables: mean net stress, deviator stress, suction and specific volume. Included within the proposed framework are an isotropic normal compression hyperline, a critical state hyperline and a state boundary hypersurface. For states that lie inside the state boundary hypersurface the soil behaviour is assumed to be elastic, with movement over the state boundary hypersurface corresponding to expansion of a yield surface in stress space. The pattern of swelling and collapse observed during wetting, the elastic–plastic compression behaviour during isotropic loading and the increase of shear strength with suction were all related to the shape of the yield surface and the hardening law defined by the form of the state boundary. By assuming that constant–suction cross–sections of the yield surface were elliptical it was possible to predict test paths for different types of triaxial shear test that showed good agreement with observed behaviour. The development of shear strain was also predicted with reasonable success, by assuming an associated flow rule.

Influence of compaction procedure on the mechanical behaviour of an unsaturated compacted clay, Part 1: Wetting and Isotropic Compression

The influence of compaction pressure, compaction water content and type of compaction (static or dynamic) on subsequent soil behaviour during wetting and isotropic loading has been investigated by conducting controlled-suction tests on samples of unsaturated compacted speswhite kaolin. The results are interpreted within the context of an elastoplastic framework for unsaturated soils, to examine which compaction-induced effects can be explained simply by variation in the initial state of the soil and which require that soils produced by different compaction procedures are modelled as fundamentally different materials. The compaction pressure influences initial state, by affecting the initial position of the yield surface, but it also influences, to a limited degree, the positions of the normal compression lines for different values of suction. The compaction water content influences the initial suction, but also has a significant influence (greater than does compaction pressure) on the positions of the normal compression lines. A change from static to dynamic compaction has no significant effect on subsequent behaviour

Influence of compaction procedure on the mechanical behaviour of an unsaturated compacted clay. Part 2: shearing and constitutive modelling

The influence of compaction pressure, compaction water content and type of compaction (static or dynamic) on subsequent soil behaviour was investigated by conducting controlled-suction triaxial tests on samples of unsaturated compacted speswhite kaolin. Compaction pressure influences initial state, by determining the initial position of the yield surface, thus affecting, among other things, the shape of stress–strain curves during shearing. Compaction pressure also influences, to a limited degree, the positions of the normal compression lines for different values of suction, but it has no effect on critical state relationships. The effect of compaction pressure can probably be modelled solely in terms of initial state if an anisotropic elastoplastic model incorporating rotational hardening is employed, whereas the parameters defining the slopes and intercepts of the normal compression lines for different values of suction require adjustment with variation of compaction pressure if a conventional isotropic hardening elastoplastic model is employed. Compaction water content influences the initial suction, but also has a substantial influence on normal compression lines and a noticeable effect on the volumetric behaviour at critical states. It is likely that soil samples compacted at different water contents will have to be modelled as different materials, irrespective of whether an isotropic or anisotropic hardening elastoplastic model is employed. A change from static to dynamic compaction has no significant effect on subsequent behaviour.

A Simple Triaxial System for Evaluating the Performance of Unsaturated Soils Under Repeated Loading

Unsaturated soils constitute a large proportion of the foundation materials supporting infrastructure throughout the world and they are subject to various loading conditions. This paper describes the development of a simple system for testing unsaturated soils under repeated loading. The equipment was comprised of a modified triaxial cell with hydraulic loading system, hall-effect transducers for on-sample strain measurements, and thermocouple psychrometer for suction measurements. A number of undrained monotonic and repeated loading triaxial tests were performed on compacted samples of kaolin clay in order to attest the newly developed system. The results yielded some useful information on the resilient modulus and permanent deformation of a soil when subjected to repeated loading. There is some difference between the failure deviator stress of samples subjected to repeated and monotonic loading, though repeated loading continued to result in a significant permanent deformation. This paper is aimed at demonstrating the key features of the equipment using preliminary data generated as part of the on-going research.

Reaction of tetracyanoethylene with alpha,beta-unsaturated ketones

Synthesis and Chemistry of simple tetracyanoalkanes is well studied. We performed tetracyanoethylation of unsaturated ketones with an active double bond in alpha-position. The reaction of tetracyanoethylene with alpha,beta-unsaturated ketones may result in four probable products depending on the character of substituents.

Performance of Unsaturated Compacted Clay Under Repeated Loading Effects of Confining Pressure, Initial Compaction Effort and Water Content

While a significant number of geotechnical structures are subjected to static loading, many, such as avement subgrade, also are subjected to cyclic or dynamic loading. While the performance of saturated soils under repeated, cyclic or dynamic loading conditions is still a topic of research, similar interests are growing when the soilcondition is unsaturated. This paper examines the performance of unsaturated soils under repeated loading. As part of the research, a triaxial system was developed which incorporates small strain measurements using Hall-effect transducers, in addition to suction measurements taken using a psychrometer. Tests were conducted on samples of kaolin under constant water mass conditions. The results address the effects of compaction effort and water content at the time of compaction on the overall performance of unsaturated soils, under different amplitudes of loading and different confining pressures. The results show that suction in the sample reduced with increasing number of loading cycles of the same magnitude. The resilient modulus initially increased with increasing water content up to approximately optimum water content, and substantially reduced with further increase in water content. Key Words: suction, resilient modulus, subgrade, repeated loading, small strain measurements, compaction.

Detection of Groundwater flow zones in low productivity boreholes (Submitted)

Conventional methods of detecting groundwater flow zones in open boreholes installed in fractured bedrock aquifers rely on either contrasts in water quality or on significant rates of vertical flow. In low productivity boreholes these methods have proced of limited value. Tracer tests completed in six low productivity bedrock boreholes installed into fresh Precambrian crystalline bedrock revealed measurable dilution, despite very low tranmissivities. Fluorescent tracer profiles generated during discharge pumping permitted identification of the principle zones contributing to flow. High resolution acoustic televiewer strike and dip measurements of fractures corresponding to these zones revealed a consistent pattern of regional lineament trends and suggested a strongly anisotropic flow pattern in bedrock.

The Other Side of the Fence:Reconceptualizing the “Camp” and Migration Zones at the Borders of Spain

This article explores the dynamics of the space of exception at the borders of Europe in the Spanish enclave of Melilla, and the neighboring Moroccan city of Oujda. Building upon field research conducted in the spring of 2008, I ask how we can understand the political space of migration not simply as exceptional, but as shaped by the mobility of the irregular migrants moving outside of the frameworks, policies, and practices of the state. By privileging the migrant narrative and making use of Rancière's conception of politics as shaped by the demands of those who “have no part,” I suggest an alternative way of understanding the politics of exception and agency of non-citizens—that is, one of disruption and demands to open up powerful potentials for change in an otherwise rigid regime.

Selective Hydrogenation of alpha,beta-Unsaturated Aldehydes and Ketones using Novel Manganese Oxide and Platinum Supported on Manganese Oxide Octahedral Molecular Sieves as Catalysts

The selective hydrogenation of ,-unsaturated aldehydes and ketones has been studied using ketoisophorone and cinnamaldehyde as model substrates using manganese oxide octahedral molecular sieve (OMS-2) based catalysts. For the first time, OMS-2 has been shown to be an efficient and selective hydrogenation catalyst. High selectivities for either the CC or CO double bond at approximate to 100% conversion were achieved by using OMS-2 and platinum supported on OMS-2 catalysts. Density functional theory (DFT) calculations showed that the dissociation of H2 on OMS-2 was water assisted and occurred on the surface Mn of OMS-2(001) that had been modified by an adsorbed H2O molecule. The theoretically calculated activation barrier was in good agreement with the experimentally determined value for the hydrogenation reactions, indicating that H2 dissociation on OMS-2 is likely to be the rate-determining step. A significant increase in the rate of reaction was observed in the presence of Pt as a result of the enhancement of H2 dissociative adsorption and subsequent reaction on the Pt or spillover of the hydrogen to the OMS-2 support. The relative adsorption strengths of ketoisophorone and cinnamaldehyde on the OMS-2 support compared with the Pt were found to determine the product selectivity.

Effects of confining pressure and water content on performance of unsaturated compacted clay under repeated loading

This paper examines the performance of unsaturated soils under repeated loading. As part of the research, a triaxial system was developed that incorporates small-strain measurements using Hall effect transducers, in addition to suction measurements taken using a psychrometer. Tests were conducted on samples of kaolin under constant water mass conditions. The results address the effects of compaction effort and water content at the time of compaction on the overall performance of unsaturated soils, under different amplitudes of loading and different confining pressures. The results show that suction in the sample reduced with increasing number of loading cycles of the same magnitude. The resilient modulus initially increased with increasing water content up to approximately optimum water content, and then reduced substantially with further increase in water content.

In search of common grounds: Stitching the divided landscape of urban parks in Belfast's interface zones

Political and spatial contestation in divided cities contributes to strategies of self-defense that utilize physical and spatial settings to enable the constitution of social boundaries, borders and territories.
Urban parks that are designed to ease division through an open transitional landscape can instead facilitate further segregation through their spatial order and facility layout. This paper investigates the role of the spatial design and material landscape of integrated parks in Belfast interface areas as instruments of engagement or division. It does so by analyzing the spatial organization of the parks’ facilities and the resultant ‘social voids.’ Space, time and distance were found to be effective tools for the negotiation of privacy, the manifestation of power, and the interplay of dominance and self-confidence. In the context of a divided city, strong community-culture tends to reproduce new boundaries and territories within the shared landscape. Through user interviews and spatial analysis, this paper outlines the design principles that influence spatial behavior in the urban parks of contested urban landscapes. It argues that despite granting equal access to shared public facilities, social voids and physical gaps can instill practices of division that deepen territorial barriers, both psychologically and spatially.