Measurements of strongly-anisotropic g-factors for spins in single quantum states

We have measured the full angular dependence, as a function of the direction of magnetic field, for the Zeeman splitting of individual energy states in copper nanoparticles. The g-factors for spin splitting are highly anisotropic, with angular variations as large as a factor of five. The angular dependence fits well to ellipsoids. Both the principal-axis directions and g-factor magnitudes vary between different energy levels within one nanoparticle. The variations agree quantitatively with random-matrix theory predictions which incorporate spin-orbit coupling.Comment: 4 pages, 3 figures, 2 in colo

Incorporating episodicity into estimates of Critical Loads for juvenile salmonids in Scottish streams

International audienceCritical Load (CL) methodology is currently used throughout Europe to assess the risks of ecological damage due to sulphur and nitrogen emissions. Critical acid neutralising capacity (ANCCRIT) is used in CL estimates for freshwater systems as a surrogate for biological damage. Although UK CL maps presently use an ANC value of 0 ?eq l-1, this value has been based largely on Norwegian lake studies, in which brown trout is chosen as a representative indicator organism. In this study, an ANC value specific for brown trout in Scottish streams was determined and issues were addressed such as salmon and trout sensitivity in streams, episodicity, afforestation and complicating factors such as dissolved organic carbon (DOC) and labile aluminium (Al-L). Catchments with significant forest cover were selected to provide fishless sites and to provide catchment comparisons in unpolluted areas. Chemical factors were the primary determinant with land use a secondary determinant of the distribution of salmonid populations at the twenty-six study sites. ANC explained more variance in brown trout density than pH. The most significant index of episodicity was percent of time spent below an ANC of 0 ?eq l-1. An ANCCRIT value of 39 ?eq l-1 was obtained based on a 50% probability of brown trout occurrence. The use of this revised ANCCRIT value in the CL equation improved the relationship between trout status and exceedance of CLs. Uncertainties associated with variations in Al-L at any fixed ANCCRIT, particularly within forested catchments, and the role of DOC in modifying the toxicity of Al-L are discussed. Keywords: Critical Load, Critical acid neutralising capacity, brown trout, episodes, stream

Full Configuration Interaction wave function as a formal solution to the Optimized Effective Potential and Kohn-Sham models in finite basis sets

Using finite basis sets, it is shown how to construct a local Hamiltonian, such that one of its infinitely many degenerate eigenfunctions is the ground state full configuration interaction (FCI) wave function in that basis set. Formally, the local potential of this Hamiltonian is the optimized effective potential and the exact Kohn-Sham potential at the same time, because the FCI wave function yields the exact ground-state density and energy. It is not the aim of this paper to provide a new algorithm for obtaining FCI wave functions. A new potential is the goal

Electronic Energy Transfer to the S2 Level of the Acceptor in Functionalised Boron Dipyrromethene Dyes

Taking the high road: Highly efficient electronic energy transfer takes place from a set of appended aryl polycyclic hydrocarbons to an expanded boron dipyrromethene (Bodipy)-based dye (see figure) despite negligible spectral overlap with the lowest-energy excited state localised on the acceptor.A multi-component array has been constructed around an expanded boron dipyrromethene (Bodipy) dye that absorbs and emits in the far-red region. One of the appendages is a perylene-based moiety that is connected to the boron atom of the terminal Bodipy by a 1,4-diethynylphenylene connector. Despite the fact that there is almost negligible spectral overlap between fluorescence from the perylene unit and absorption by the Bodipy residue, electronic energy transfer is rapid and essentially quantitative. It is concluded that at least half of the photons absorbed by perylene are transferred to the upper-lying singlet excited state (S2) associated with the Bodipy-based acceptor. The second appendage is a pyrene unit that is covalently linked to fluorene, through an ethynylene spacer, and to the boron atom of the Bodipy terminus, through a 1,4-diethynylphenylene connector. Pyrene absorbs and emits at higher energy than perylene and there is strong spectral overlap with the Bodipy-based S2 state, and none with the corresponding S1 state. Electronic energy transfer is now very fast and exclusively to the S2 state of the acceptor. It is difficult to compute reasonable estimates for the rates of Coulombic energy transfer, because of uncertainties in the orientation factor, but the principle mechanism is believed to arise from electron exchange. Comparison with an earlier array built around a conventional Bodipy dye indicates that there are comparable electronic coupling matrix elements for the two systems. It is notable that pyrene is more strongly coupled to the Bodipy unit than perylene in both arrays. These new arrays function as highly effective solar concentrators

The analysis of trace metals in surface waters from Scotland and Wales

188 water samples taken from Scottish and Welsh lakes in 1995/6 have been analysed for a range of trace metals, Hg, As, Se, Be, V, Cr, Co, Ni, Cu, Zn, Mo, Ag, Cd, Sb, Ba, Tl, Pb, & Bi. At all sites Hg, As, Se, Be, Bi, Pb and Ag were below limits of detection by the ICP-MS. The other elements showed various geographical distributions. In Wales, the south-central region and Anglesey appeared consistently higher and it is suggested that these are due to former mining and contemporary smelting activities respectively. In Scotland, distributions were move diverse although southern and south-west Scotland often appeared to show elevated levels as did sites on Orkney and Shetland. In general, lake sites in the north-west and Hebrides showed lower concentrations. Pnncipal Components Analysis (PCA) was used to try and determine any patterns in the data, but the results were inconclusive. The PC axes explained little of the variability within the data and clusters of sites on the bi-plots show little in common. However, only geographical location was available to be used m the PCA interpretation and it may be that other factors (lake and catchment characteristics, other water chemistry) would help explain the data more fully. The data included in this report are from smgle water samples taken over a short period of time. Therefore, althougl1 the data may show a useful 'snap-shot' of the situation, more information would be available from analyses of the sediment record (to put the data into temporal context) and other substrates where metal accumulation takes place. This would have the advantage of producing a time averaged metal value, but more importantly would mean more values above analytical detection and hence a better idea of metal distribution

Critical loads of sulphur and nitrogen for surface waters in Northern Ireland

A survey of 140 surface waters (lakes, streams and reservoirs) across Northern Ireland was carried out in March 2000. One site was selected to represent each 10km OS NI grid square in Northern Ireland using a map of freshwater sensitivity to identify the most acid sensitive water body in each grid squar

Heavy Top Quark Searches in the Di-Lepton Mode at the Tevatron

We present the results of a detailed study of the effects of $b$-tagging on the heavy top-quark signal and backgrounds for the modes of the di-lepton plus two high transverse energy jets at the Fermilab Tevatron. The general characteristics of the heavy top-quark signal events are also discussed so that a comparison can be made between $b$-tagging and imposing stringent kinematical cuts to eliminate backgrounds.Comment: uses PHYZZX and TABLES macros, 10 pages, four figures not included (available by request), FERMILAB-Pub-93/105-

Momentum Correlations of Charmed Pairs Produced in π−−Cu\pi^{-}-Cu Interactions at 230 GeV/c

We study the production characteristics of 557 pairs of charmed hadrons produced in $\pi^{-}-Cu$\ interactions at 230~GeV/c using a momentum estimator for charmed hadrons with missing decay products. We find, the mean value of the transverse momentum squared of the charmed pairs is $=(1.98\pm 0.11\pm 0.09)\;$ GeV$^2$/c$^2$, the mean rapidity difference is $=0.54\pm 0.02\pm 0.24$, and the mean effective mass is $=(4.45\pm 0.03\pm 0.13)\;$ GeV/c$^2$. Comparing these results with the next-to-leading order QCD predictions we find an agreement for the \yd\ and \mef, whilst the measured mean value of \pts\ is significantly larger than the predicted value.Comment: 10 pages, LaTeX, 4 (pages) postscript figure