115,313 research outputs found
Influence of gas hydrate morphology on the seismic velocities of sands
No full textThis paper reports the results of a series of resonant column tests on specimens where gas hydrate has been formed in sands using an “excess water” technique. In these specimens the amount of hydrate formed is restricted by the amount of gas in the specimen and with an excess of water being present in the pore space. Results of resonant column tests carried out to determine compressional and shear wave velocities suggest that gas hydrate formed in this way are frame supporting. In contrast, the behavior observed in sands where the hydrate is formed from finite water where the remaining pore space is saturated with methane gas, termed in this paper the “excess gas” method, exhibits a cementing behavior, while tetrahydrofuran-hydrate sands or where the hydrate is formed from dissolved methane within the pore water, exhibit a pore-filling behavior for hydrate saturations less than 40%. For sands where the hydrate is formed using the excess water method, much larger volumes of hydrate are required before a significant increase in shear wave velocity occurs, although increases in compressional wave velocity are seen at lower hydrate contents. These results suggest that hydrate interaction with the sediment is strongly dependent on morphology, and that natural hydrate may exhibit contrasting seismic signatures depending upon the geological environment in which it forms.<br/
Decision procedures for multiple auctions
No full textThis paper presents a decision theoretic framework that an autonomous agent can use to bid effectively across multiple, simultaneous auctions. Specifically our framework enables an agent to make rational decisions about purchasing multiple goods from a series of auctions that operate different protocols (we deal with the English, Dutch, First-Price Sealed Bid and Vickrey cases). The framework is then used to characterise the optimal decision that an agent should take. Finally, we develop a practical algorithm that provides a heuristic approximation to this ideal
Trial Selection Theory: A Unified Model
Full text linkThis paper provides a formal model of the trial selection process that incorporates the Priest-Klein hypothesis and alternative theories of selection. We derive the conditions under which the hypothesis is valid, and examine implications for the relationship between trial outcome uncertainty and litigation. The model suggests a generalization of the hypothesis.
Gas hydrate growth morphologies and their effect on the stiffness and damping of a hydrate bearing sand
No full textUsing a specially constructed Gas Hydrate Resonant Column (GHRC), the University of Southampton explored different methods of hydrate synthesis and measured the properties of the resulting sediments, such as shear wave velocity (Vs), compressional wave velocity (Vp) and their respective attenuation measurements (Qs -1 and Qp -1). Two approaches were considered. The first utilises an excess gas technique, where known water volume in the pore space dictates the quantity of hydrate. The second approach uses a known quantity of methane gas within the water saturated
pore space to constrain the volume of hydrate. Results from the two techniques show that hydrates formed in excess gas environments cause stiffening of the sediment structure at low concentrations (3%), whereas, even at high concentrations of hydrate (40%) in excess water environments, only moderate increase in stiffness was observed. Additionally, attenuation results show a peak in damping at approximately 5% hydrate in excess gas tests, whereas in excess water tests, damping continues to increase with increasing hydrate content in the pore space. By considering the results from the two approaches, it becomes apparent that formation method has an influence on the properties of the hydrate bearing sand, and must therefore influence the morphology of the hydrate in the pore space
A Software Framework for Automated Negotiation
No full textIf agents are to negotiate automatically with one another they must share a negotiation mechanism, specifying what possible actions each party can take at any given time, when negotiation terminates, and what is the structure of the resulting agreements. Current standardization activities such as FIPA [2] and WS-Agreement [3] represent this as a negotiation protocol specifying the flow of messages. However, they omit other aspects of the rules of negotiation (such as obliging a participant to improve on a previous offer), requiring these to be represented implicitly in an agent's design, potentially resulting incompatibility, maintenance and re-usability problems. In this chapter, we propose an alternative approach, allowing all of a mechanism to be formal and explicit. We present (i) a taxonomy of declarative rules which can be used to capture a wide variety of negotiation mechanisms in a principled and well-structured way; (ii) a simple interaction protocol, which is able to support any mechanism which can be captured using the declarative rules; (iii) a software framework for negotiation that allows agents to effectively participate in negotiations defined using our rule taxonomy and protocol and (iv) a language for expressing aspects of the negotiation based on OWL-Lite [4]. We provide examples of some of the mechanisms that the framework can support
Ground vibration from trains: experimental parameter characterization and validation of a numerical model
No full textTrains running on railway tracks on the surface of the ground or in tunnels induce vibrations in the ground which propagate away from the track. These may be experienced as feelable vibration or as audible rumbling noise in the buildings nearby, both of which are difficult to control. As the properties of the ground differ widely between locations they must be characterized for a particular site in order to make reliable predictions. This article describes field measurements of the vibration at two sites with soft clay soil in Southern England. The properties of the ground material, including its layered structure, have been identified from comparisons between results of a layered ground model and measurements obtained using impact excitation. Presentation in the wavenumber-frequency domain is particularly helpful for this purpose. Measurements of vibrations from passing trains are then compared with predictions using a semianalytical model for ground vibration from trains and good agreement is found.<br/
The effects of hydrate on the strength and stiffness of some sands
No full textGas hydrates can form more or less at the same time as seafloor sediment. They can have the effect of significantly stiffening and strengthening deep‐ocean sediments. Subsequent increases in situ temperature or decreases in pressure may trigger hydrate dissociation, leading to large reductions in the strength and stiffness of the sediment and possible seafloor instability. Gas hydrate dissociation not only removes cementing. It also releases freshwater and significant amounts of trapped gas that are dependent on multiple factors such as type of sediment, available pore space, hydrate morphology, and hydrate saturation. The presence of pock marks in areas of known seabed instability suggests that hydrate dissociation may have been a factor in triggering failure at these locations. Having reviewed the mechanisms by which the strength and stiffness of seabed sediment may be changed during dissociation, this paper reports the results of laboratory testing to evaluate the effects of loss of hydrate cement on strength and stiffness, for a range of sand‐sized materials with differing particle size, specific surface area, and particle shape, using a laboratory gas hydrate triaxial apparatus. The results suggest that both the strength and the stiffness of hydrate‐cemented granular materials are affected significantly by the specific surface available for hydrate cementation and, to a certain extent, by the particle shape. Uniform coarse granular sediments of lower specific surface area can suffer significant loss of stiffness and strength upon hydrate dissociation, changing the sediment from dilative to contractive. Finer‐grained sediments appear less affected by dissociation
A Multi-Language Comparison of Influences on Author Verification using Character N-Grams
No full textWe create a new multi-language corpus for author verification based on Wikipedia talkpages, and evaluate the influence that differences in topic and time have on character n-gram author profiles. Topic alignment between two texts is found to increase author verification precision, and an authors writing style is found to change over time, but not more significantly after 3 years than after 1 year.Information ArchitectureWISElectrical Engineering, Mathematics and Computer Scienc
The vanishing author in computer-generated works: a critical analysis of recent Australian case law
Full text linkAbstract
The use of software is ubiquitous in the creation of many copyright works, yet the requirement in copyright law that every work have a human author who engages in independent intellectual effort means that its use may prevent copyright subsistence. Several recent Australian cases have refocused attention on authorship as an essential criterion of copyright subsistence, and these cases suggest that much computer-produced output may be authorless and thus lack copyright protection. This article, the first in a two-part series, analyses how each case deals with the question of authorship of computer-produced works and why the use of software diminishes copyright protection for a significant number of computer-generated works. The article critiques the application of conventional notions of human authorship developed in the pre-computer age to modern productions and suggests alternative approaches to authorship that satisfy both the major objectives of copyright policy and the need to adapt to the computer age. The article argues that, without a broader judicial approach to authorship of computer-generated works, Parliament must remedy the lacuna in protection for these ‘authorless’ works. Possible solutions for reform are suggested. In a forthcoming article, the author comprehensively examines those reform proposals
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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