Prediction of a surface state and a related surface insulator-metal transition for the (100) surface of stochiometric EuO

We calculate the temperature and layer-dependent electronic structure of a 20-layer EuO(100)-film using a combination of first-principles and model calculation based on the ferromagnetic Kondo-lattice model. The results suggest the existence of a EuO(100) surface state which can lead to a surface insulator-metal transition.Comment: 9 pages, 5 figures, Phys. Rev. Lett. (in press

On the origin of surface states in a correlated local-moment film

The electronic quasiparticle structure of a ferromagnetic local moment film is investigated within the framework of the s-f model. For the special case of a single electron in an otherwise empty energy band being exchange coupled to a fully ordered localised spin system the problem can be solved exactly and, for the spin-down electron, some marked correlation effects can be found. We extend our model to incorporate the influence of the surface on the electronic structure. Therefore we modify the hopping integrals in the vicinity of the surface. This leads to the existence of surface states, both for the spin-up and the spin-down spectral density of states. The interplay between the modification of the hopping integrals and the existence of surface states and correlation effects is discussed in detail.Comment: 9 pages, 9 figures, accepted for publication in European Physical Journal

A new possibility to monitor collisions of relativistic heavy ions at LHC and RHIC

We consider the radiation of particles of one bunch in the collective field of the oncoming bunch, called coherent bremsstrahlung (CBS). The main characteristics of CBS for LHC (in the Pb-Pb mode) and for RHIC are calculated. At LHC about $3.9 10^8 dE_\gamma/E_\gamma$ photons per second are expected for photon energies $E_\gamma \stackrel{<} {\sim} E_c= 93$ eV. It seems that CBS can be a potential tool for optimizing collisions and for measuring beam parameters. The bunch length can be found from the critical energy of the CBS spectrum; the transverse bunch size is related to the photon rate. A specific dependence of photon rate on the impact parameter between the beams allows for a fast control over the beam displacement.Comment: 9 pages + 4 figures, latex with poscript figures uuencode

Recasting Economics as if the Climate and Global Ecology Really Mattered

Peer reviewedPublisher PD

Real-time dynamics in Quantum Impurity Systems: A Time-dependent Numerical Renormalization Group Approach

We develop a general approach to the nonequilibrium dynamics of quantum impurity systems for arbitrary coupling strength. The numerical renormalization group is used to generate a complete basis set necessary for the correct description of the time evolution. We benchmark our method with the exact analytical solution for the resonant-level model. As a first application, we investigate the equilibration of a quantum dot subject to a sudden change of the gate voltage and external magnetic field. Two distinct relaxation times are identified for the spin and charge dynamics.Comment: 5 pages, 5 figure

Structural and Functional Organization of Macroarthropod Communities in a Mined Versus a Pristine Stream in the Cumberland Mountains of Eastern Tennessee

The effects of surface mining coal on the structural and functional organization of macroarthropod communities as a result of changes in the physical structure of small streams was investigated. Two first order streams in the Cumberland Mountains of eastern Tennessee, a pristine reference stream and a stream mined approximately 15 years earlier, were compared for particulate organic matter (POM) dynamics, structural and functional group composition, and productivity of their mecroarthropod communities. POM dynamics of the two streams were compared by measuring their input, standing stock, and processing in each stream. Macroinvertebrates were sampled with standard Surber samplers. The community structure of the two streams was compared in terms of taxonomic composition, abundance, species richness, and Shannon diversity. Functional group composition of the macroarthropod communities were compared using the functional group classification of Merritt and Cummins (1984). Productivity of the dominant taxa was calculated by the size-frequency method. The total productivity and productivity within functional feeding groups were then compared. Input and standing stock of POM in the two streams was similar. Faster rates of POM processing in the mined stream resulted from greater macroarthropod shredder densities. Differences in POM processing, macroarthropod functional group composition, and productivity within functional groups between the two streams suggest that their macroarthropod communities are functionally different. The lower abundance, species richness, and diversity were typical of the structural differences reported for other macroarthropod communities in mined streams of this region. Overall productivity of the surface mined stream was similar to the reference stream, although it was disturbed differently between functional groups. The results indicated that analysis of the functional group organization of mined streams reveals important differences in their ecology which could be underestimated or overlooked by conventional indices of community structure. Taxonomic surveys and diversity indices provide useful tools for monitoring and detection of environmental degradation. However, additional understanding of the causal relationships between environmental disturbance and biological change can be obtained from a functional approach which can identify its effects on specific biological processes in the stream community

Perturbative renormalisation of quark bilinear operators for overlap fermions with and without stout links and improved gauge action

We calculate lattice renormalisation constants of local and one-link quark operators for overlap fermions and improved gauge actions in one-loop perturbation theory. For the local operators we stout smear the SU(3) links in the fermionic action. Using the popular tadpole improved L\"uscher-Weisz actions at $\beta=8.45$ and $\beta=8.0$ we present numerical values for the Z factors in the $\bar{MS}$ scheme (partly as function of the stout smearing strength). We compare various levels of mean field (tadpole) improvement which have been applied to our results.Comment: 7 page