Quasiparticle lifetime behaviour in a simplified self-consistent T-matrix treatment of the attractive Hubbard model in 2D

The attractive Hubbard model on a 2-D square lattice is studied at low electronic densities using the ladder approximation for the pair susceptibility. This model includes (i) the short coherence lengths known to exist experimentally in the cuprate superconductors, and (ii) two-particle bound states that correspond to electron pairs. We study the quasiparticle lifetimes in both non self-consistent and self-consistent theories, the latter including interactions between the pairs. We find that if we include the interactions between pairs the quasiparticle lifetimes vary approximately linearly with the inverse temperature, consistent with experiment.Comment: 2 pages, including 2 figures, to appear in the proceedings of the ICNS '9

Exploring the information behaviour of users of Welsh Newspapers Online through web log analysis

Purpose – Webometric techniques have been applied to many websites and online resources, especially since the launch of Google Analytics (GA). To date, though, there has been little consideration of information behaviour in relation to digitised newspaper collections. The purpose of this paper is to address a perceived gap in the literature by providing an account of user behaviour in the newly launched Welsh Newspapers Online (WNO). Design/methodology/approach – The author collected webometric data for WNO using GA and web server content logs. These were analysed to identify patterns of engagement and user behaviour, which were then considered in relation to existing information behaviour. Findings – Use of WNO, while reminiscent of archival information seeking, can be understood as centring on the web interface rather than the digitised material. In comparison to general web browsing, users are much more deeply engaged with the resource. This engagement incorporates reading online, but users’ information seeking utilises website search and browsing functionality rather than filtering in newspaper material. Information seeking in digitised newspapers resembles the model of the “user” more closely than that of the “reader”, a value-laden distinction which needs further unpacking. Research limitations/implications – While the behaviour discussed in this paper is likely to be more widely representative, a larger longitudinal data set would increase the study’s significance. Additionally, the methodology of this paper can only tell us what users are doing, and further research is needed to identify the drivers for this behaviour. Originality/value – This study provides important insights into the underinvestigated area of digitised newspaper collections, and shows the importance of webometric methods in analysing online user behaviour

The effects of an innovation involving choice : a thesis presented in partial fulfilment of the requirements for the degree of Master of Education at Massey University

A principal's observations are used to illuminate the effects of innovation on a school 'community'. Parents were given the opportunity to choose which of two optional programmes they wished to place their children in for one year. Over half the pupils (165) were placed in an alternative programme which broadly aimed to combine the advantages of the small rural with those of the larger urban school. Each teacher was responsible for a range of age groups and required to confer with individual pupils for at least fifteen minutes per week while senior pupils tutored others in the class. Planned provision for catering for different cognitive styles, interests and attitudes succumbed to the stresses associated with major changes, class size, inadequacies in training, and professional, bureaucratic and social constraints. The ramifications flowing from the exercise of choice greatly influenced all that transpired and became particularly significant as the roles, relationships, and functions of people were placed under increasing pressure. Whether to introduce new ideas gradually or quickly is a problem facing the innovator. It was found though that many factors aside from rapid change had unpredictable bearings on intended outcomes. The attempt to cater for the individual while seeking to capitalise on contextual social factors indicated that principals and teachers in novel situations need initial support and on-going training. It is suggested that a single organisation cannot fully serve competing interests or different sets of values and that the association of the word 'community' with a mandatory organisation like a state school erodes the capacity of many to understand that consensus largely typifies a true community in terms of fundamental values. Opportunity for considered choice in both value and other terms is advocated. It is asserted that, since major innovations have profound effects on personal equilibriums, interpersonal and intergroup relationships, and upon the ethos in which a geographically identifiable group of people function, an innovator should be able to rely on stability and suitability of personnel so that planned gradual change towards consensual goals is possible. The value of a monolithic state system of education offering relatively little choice is questioned. To mount viable alternatives permitting real choice is shown to be a rather daunting challenge

Weathering of stony meteorites in Antarctica

Weathering produces undesirable physical, chemical, and isotopic changes that might disturb the records of cosmochemical evolution that are sought in meteorites. Meteorites are physically disintegrated by crack propagation phenomena, including ice riving and secondary mineral riving, and are probably abraded by wind that is laden with ice crystals or dust particles. Chemical weathering proceeds by oxidation, hydration, carbonation, and solution and produces a variety of secondary minerals and mineraloids. Differential weathering under freezing conditions is discussed, as well as, the mineralogy of weathering products. Furthermore, the use of Antarctic alteration of meteorites could be used as an excellent analog for weathering on Mars or on cometary bodies

Non-equilibrium freezing of water-ice in sandy basaltic regoliths and implications for fluidized debris flows on Mars

Many geomorphic features on Mars were attributed to Earth-analogous, cold-climate processes involving movement of water or ice lubricated debris. Clearly, knowledge of the behavior of water in regolith materials under Martian conditions is essential to understanding the postulated geomorphic processes. Experiments were performed with sand-sized samples of natural basaltic regoliths in order to further elucidate how water/regolith interactions depend upon grain size and mineralogy. The data reveal important contrasts with data for clay-mineral substrates and suggest that the microphysics of water/mineral interactions might affect Martian geomorphic processes in ways that are not fully appreciated. Sand and silt sized fractions of two soils from the summit of Mauna Kea were used as Mars-analogous regolith materials. Temperatures were measured for water/ice phase transitions as wet slurries of individual soil fractions which were cooled or heated at controlled rates under a carbon dioxide atmosphere. Freezing and melting of ice was studied as a function of water/soil mass ratio, soil particle size, and thermal-cycle rate. Comparison tests were done under the same conditions with U.S. Geological Survey standard rock powders

Chemistry and mineralogy of Martian dust: An explorer's primer

A summary of chemical and mineralogical properties of Martian surface dust is offered for the benefit of engineers or mission planners who are designing hardware or strategies for Mars surface exploration. For technical details and specialized explanations, references should be made to literature cited. Four sources used for information about Martian dust composition: (1) Experiments performed on the Mars surface by the Viking Landers 1 and 2 and Earth-based lab experiments attempting to duplicate these results; (2) Infrared spectrophotometry remotely performed from Mars orbit, mostly by Mariner 9; (3) Visible and infrared spectrophotometry remotely performed from Earth; and (4) Lab studies of the shergottite nakhlite chassignite (SNC) clan of meteorites, for which compelling evidence suggests origin on Mars. Source 1 is limited to fine grained sediments at the surface whereas 2 and 3 contain mixed information about surface dust (and associated rock) and atmospheric dust. Source 4 has provided surprisingly detailed information but investigations are still incomplete

Antarctic Meteorite Newsletter, volume 9, no. 2

Preliminary description and classifications of meteorites that were completed since publication of the February issue are contained. Most large (greater than 150 g) specimens (regardless of petrologic type) and all pebble sized (less than 150 g) specimens of special petrologic type are represented by separate descriptions. However, specimens of nonspecial petrologic type are listed only as single line entries. For convenience, new specimens are also recast by petrologic type. Each macroscopic description summarizes features that were visible to the eye at the time the meteorite was first examined. Classification is based on microscopic petrography and resonnaissance-level electron-probe microanalysis. The pairing list was updated

Possible significance of cubic water-ice, H2O-Ic, in the atmospheric water cycle of Mars

The possible formation and potential significance of the cubic ice polymorph on Mars is discussed. When water-ice crystallizes on Earth, the ambient conditions of temperature and pressure result in the formation of the hexagonal ice polymorph; however, on Mars, the much lower termperature and pressures may permit the crystallization of the cubic polymorph. Cubic ice has two properties of possible importance on Mars: it is an excellant nucleator of other volatiles (such as CO2), and it undergoes an exothermic transition to hexagonal ice at temperatures above 170 K. These properties may have significant implications for both martian cloud formation and the development of the seasonal polar caps