The role of intermediate layers in the c-axis conductivity of layered superconductors

A simplified model of c axis transport in the high T_c superconductors is presented. Expressions are found for the c axis optical conductivity, the d.c. resistivity, and the c axis penetration depth. Within the framework of this model, the pseudogap in the optical conductivity arises naturally as a result of the layered band structure of the high T_c materials. We discuss the occurence of the pseudogap in terms of three parameters: a band gap Delta_{ps}, a temperature dependent scattering rate Gamma(T), and the strength of the interlayer coupling t_{perp}. We are also able to find analytic expressions for the d.c. conductivity and the low temperature penetration depth in terms of these three parameters. This work is an attempt to present a simple, unified picture of c axis properties in the high T_c cuprates.Comment: 3 pages, 2 figures, Proceedings of Spectroscopies of Novel Superconductors '97, To be published in J. Phys. Chem. Solid

Working around the crisis in Libya

This is the first in a series of chair’s notes in Libyan Studies. We hope that future notes will address easier topics and more straightforward success, but for now we think it is important to communicate what we are doing given the difficult circumstances of Libya today. We trust that this report is useful, and we welcome any feedback

Phylogenetics, divergence and morphology of New Zealand Eleotridae (Gobiomorphus Gill) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Ecology at Massey University, Palmerston North, New Zealand

The genus Gobiomorphus Gill (1863) is the only representative freshwater Eleotridae in New Zealand and is comprised of seven species, of which four are diadromous. The species are endemic to New Zealand and are widespread around lowland streams and coasts (with non-diadromous species penetrating further inland). The only other Gobiomorphus species are G. coxii and G. australis, which are endemic to Australia. Eleotridae are stocky fishes of small size (up to 150 mm in length) (McDowall, 1990) and are characterised by two dorsal fins, large pectoral fins, separate thoracic pelvic fins (fused in gobies) and the absence of a lateral line (McDowall. 1990; Allen et al., 2002). Gobiomorphus has had a particularly turbulent taxonomic history in the literature, spanning approximately 150 years from Gill (1863) to the present, where many species have been synonymised with one another (particularly, most Gobiomorphus species were synonymised with G. gobioides) due the plasticity of many morphological characters. Additionally, similar morphologies have led to identification difficulties. Phenotypic plasticity can also make cladistic approaches difficult (e.g. Vrijenhoek, 1998; Orti et al., 1994), for example there has been a lot of controversy surrounding G. alpinus and its species status. Furthermore, studies of evolution using morphological characters often lack an accurate perspective on relationships and origins of fish species, in particular, little information exists on the evolutionary origins of the Gobiomorphus genus. Genetic studies have contributed to resolving problems with taxonomically difficult groups by detecting diversity between morphologically similar species (where DNA variation is often not expressed phenotypically), and examining geographical divergence within species (e.g. Vrijenhoek, 1998; Kocher et al., 1989). Thus, this thesis employed two regions of mitochondrial DNA (cytochrome b and control region) to resolve issues surrounding species identification, morphological variation, phylogenetic relationships (including divergence), origins and the evolution of diadromy within the Gobiomorphus group. Mitochondrial DNA sequences were obtained from all seven Gobiomorphus species in New Zealand, as well as from both Australian Gobiomorphus. The morphology of both G. basalis and G. breviceps in the lower North Island was also examined. The results suggested that the Australasian Gobiomorphus are a polyphyletic group, although with the exclusion of G. australis the rest of the species formed a monophyletic group. The Australian group formed a polyphyletic group basal to the New Zealand monophyletic group. Gobiomorphus hubbsi, a diadromous species was found to be a sister group to the New Zealand Gobiomorphus. Clock calibrations indicated that the New Zealand and Australian groups have been isolated for about 6-37 Myr, suggesting that the New Zealand species dispersed here (in a single event) from Australia post-Gondwana break-up. These results are discussed in terms of New Zealand's geological history. Once in New Zealand there was a series of radiations; the most recent radiation produced the non-diadromous species (G. breviceps, and a G. basalis, G. cotidianus (although not all populations are diadromous) and G. alpinus species complex). Furthermore, G. huttoni and G. gobioides (both diadromous) formed a monophyletic group that is part of the first radiation, indicating that diadromy is a primitive feature of Gobiomorphus. Mitochondrial DNA accurately distinguished between G. breviceps and G. basalis (suggesting a genetic basis to morphological variation), and coupled with morphological data, identified pectoral fin ray counts as the best quantitative character for differentiating the species. However, within species high morphological variation was observed that did not fit expected patterns of geographical divergence. Limited time periods may have obscured subtle morphological divergence between catchments. Mitochondrial DNA revealed some unique haplotypes within both catchments, whereas some catchments shared identical haplotypes. The lack of divergence between catchments may have been due in part to connections during the Pleistocene, whereas populations with unique haplotypes may have been isolated for a greater length of time. Collectively, these studies highlighted the usefulness of mitochondrial DNA for exploring; phylogenetic relationships (including divergence) and solving problems with taxonomically difficult groups, and origins of fish species. Furthermore, the use of molecular data coupled with morphological data can be used to aid in the improvement of identification of morphologically similar species

What can research deliver for organic farming?

The research needs of any applied subject are always influenced by three major groups of criteria. These are the economic/political, the societal/ethical and the technical/scientific. This is especially the case for Organic Farming which explicitly sets out to present a positively value based approach to agriculture, an activity, which has commonly become dominated by the commercial economics of an industrial society. To maintain this ethical stance Organic Farming must challenge some of the tenets of conventional economics and politics and must work within the particular societal context. Its scientific needs are then driven either by the need to increase its role in terms of market share or the need to achieve its aims more effectively in respect of product quality and/or delivery of environmental goods. In this paper I examine the current opportunities for Organic Farming in relation to the present state of farming economics and the current expectations of society, considering both food production and the delivery of environmental services which are paid from the public purse, e.g. via the Common Agricultural Policy (CAP). I use these criteria to analyse what are the current primary research needs in relation to the science and ethical base of Organic Agriculture

Using Kelgin to Increase Heat Resistance and Strength of the Sheet of Paper Against Prolonged Heating

The purpose of this paper has been to examine what properties of sheet strength may be stabilized by the use of kelgin in a size press application and after a subsequent heating period. A softwood kraft pulp was used because of the strength properties which it possesses. Alkaline sizing with Aquapel and Kymene was felt to be the best because of the alkaline p.H. range which was desired. The sheets were sized with solutions of Kelgin (M .V.) of varying concentrations and treated at 150 and 175 °C. The effects were studied using the M.I .T. Fold Test, the Instron Tensile (kg to rupture), and the Instron Elongation. The results showed that as the concentrations of the kelgin size solutions increased, some protection was afforded the fiber against prolonged heating. The strength loss was appreciable in the samples which were treated at the different temperatures. The room temperature samples showed higher strength properties than either of the samples heated at 150 or 175°C. which was as expected. It was shown that the high viscosity of the kelgin solutions at the concentrations of 1.00 and 1.25 percent tended to . give a tapering off of the protection which was expected. A viscosity reducer (Azite 900 Liquifier) was used in conjunction with the kelgin solutions to study the effects of a reduced viscosity on strength maintenance. It was shown that the liquefier did indeed increase the penetration of the kelgin into the sheet and provide a better protection. The experimental findings demonstrate that the use of kelgin in the form of a sizing solution can give beneficial results against loss of strength upon prolonged heating. It was also shown that the magnitude of this effect was not as great as had been expected from previous findings