Effect of Petroleum Hydrocarbons on Microbial Populations in an Arctic Lake

A sea-curtain enclosed section of a lake 240 km south of Prudhoe Bay, Alaska was exposed to Prudhoe crude oil in July 1976. One year following exposure to the oil, no significant differences were detected between the waters or sediments of the oiled versus control area in rates of turnover of glucose. Total numbers of bacteria were slightly higher in oiled than in control waters. There were no differences in numbers of sediment bacteria. Rates of uptake of hexadecane and napthalene by sediment microbes were not linear with time. Hexadecane was taken up sooner and faster than was napthalene. In 0 some incubations, significantly (88 - 95% probability level) greater rates of hydrocarbon uptake were measured for oiled than for control sediments. Only incorporated, not mineralized, hydrocarbons were measured due to methodological problems. Several methods of using 14C-labelled hydrocarbons in a field situation are presented

Thermodynamic properties and thermal correlation lengths of a Hubbard model with bond-charge interaction

We investigate the thermodynamics of a one-dimensional Hubbard model with bond-charge interaction X using the transfer matrix renormalization group method (TMRG). Numerical results for various quantities like spin and charge susceptibilities, particle densities, specific heat and thermal correlation lengths are presented and discussed. We compare our data also to results for the exactly solvable case X/t=1 as well as to bosonisation results for weak coupling X/t << 1, which shows excellent agreement. We confirm the existence of a Tomonaga-Luttinger and a Luther-Emery liquid phase, in agreement with previous studies at zero temperature. Thermal singlet-pair correlation lengths are shown to dominate density and spin correlations for finite temperatures in certain parameter regimes.Comment: 13 pages, revte

Electromagnetic transitions of the helium atom in superstrong magnetic fields

We investigate the electromagnetic transition probabilities for the helium atom embedded in a superstrong magnetic field taking into account the finite nuclear mass. We address the regime \gamma=100-10000 a.u. studying several excited states for each symmetry, i.e. for the magnetic quantum numbers 0,-1,-2,-3, positive and negative z parity and singlet and triplet symmetry. The oscillator strengths as a function of the magnetic field, and in particular the influence of the finite nuclear mass on the oscillator strengths are shown and analyzed.Comment: 10 pages, 8 figure

Covariant description of inelastic electron--deuteron scattering:predictions of the relativistic impulse approximation

Using the covariant spectator theory and the transversity formalism, the unpolarized, coincidence cross section for deuteron electrodisintegration, $d(e,e'p)n$, is studied. The relativistic kinematics are reviewed, and simple theoretical formulae for the relativistic impulse approximation (RIA) are derived and discussed. Numerical predictions for the scattering in the high $Q^2$ region obtained from the RIA and five other approximations are presented and compared. We conclude that measurements of the unpolarized coincidence cross section and the asymmetry $A_\phi$, to an accuracy that will distinguish between different theoretical models, is feasible over most of the wide kinematic range accessible at Jefferson Lab.Comment: 54 pages and 24 figure

Helium in superstrong magnetic fields

We investigate the helium atom embedded in a superstrong magnetic field gamma=100-10000 au. All effects due to the finite nuclear mass for vanishing pseudomomentum are taken into account. The influence and the magnitude of the different finite mass effects are analyzed and discussed. Within our full configuration interaction approach calculations are performed for the magnetic quantum numbers M=0,-1,-2,-3, singlet and triplet states, as well as positive and negative z parities. Up to six excited states for each symmetry are studied. With increasing field strength the number of bound states decreases rapidly and we remain with a comparatively small number of bound states for gamma=10^4 au within the symmetries investigated here.Comment: 16 pages, including 14 eps figures, submitted to Phys. Rev.

What are communities of practice? A comparative review of four seminal works

This paper is a comparative review of four seminal works on communities of practice. It is argued that the ambiguities of the terms community and practice are a source of the concept's reusability allowing it to be reappropriated for different purposes, academic and practical. However, it is potentially confusing that the works differ so markedly in their conceptualizations of community, learning, power and change, diversity and informality. The three earlier works are underpinned by a common epistemological view, but Lave and Wenger's 1991 short monograph is often read as primarily about the socialization of newcomers into knowledge by a form of apprenticeship, while the focus in Brown and Duguid's article of the same year is, in contrast, on improvising new knowledge in an interstitial group that forms in resistance to management. Wenger's 1998 book treats communities of practice as the informal relations and understandings that develop in mutual engagement on an appropriated joint enterprise, but his focus is the impact on individual identity. The applicability of the concept to the heavily individualized and tightly managed work of the twenty-first century is questionable. The most recent work by Wenger – this time with McDermott and Snyder as coauthors – marks a distinct shift towards a managerialist stance. The proposition that managers should foster informal horizontal groups across organizational boundaries is in fact a fundamental redefinition of the concept. However it does identify a plausible, if limited, knowledge management (KM) tool. This paper discusses different interpretations of the idea of 'co-ordinating' communities of practice as a management ideology of empowerment

Leukocytes are primed in peripheral blood for activation during term and preterm labour†

We hypothesized that the priming and activation of maternal leukocytes in peripheral blood is a key component of parturition, and that inappropriate preterm priming of leukocytes might initiate preterm labour and delivery. The purpose of this study was to characterize peripheral blood leukocyte activation during human term and preterm labour. We obtained blood samples from pregnant women at term and preterm, both in labour and not in labour. Leukocytes were characterized according to cell subtype and cell surface marker expression. Additionally, we quantified leukocyte cytokine mRNA production, migratory ability and reactive oxygen species production of neutrophils and macrophages. We found that both term and preterm labour were associated with an increase in monocyte and neutrophil proportion or number—neutrophil migratory ability and cell surface marker expression indicating activation. Messenger RNA expression of IL-1β and IL-8, MCP-1 and TLR-2 was also increased. We conclude that leukocytes in peripheral blood are primed in preparation for activation during term and preterm labour, and that this may contribute to the pathophysiological events of parturition. These data may lead to novel therapies and diagnostic tools for the prevention and/or diagnosis of preterm birth

Quantum Correlation in One-dimensional Extend Quantum Compass Model

We study the correlations in the one-dimensional extended quantum compass model in a transverse magnetic field. By exactly solving the Hamiltonian, we find that the quantum correlation of the ground state of one-dimensional quantum compass model is vanishing. We show that quantum discord can not only locate the quantum critical points, but also discern the orders of phase transitions. Furthermore, entanglement quantified by concurrence is also compared.Comment: 8 pages, 14 figures, to appear in Eur. Phys. J.