Generalized modularity matrices

Various modularity matrices appeared in the recent literature on network analysis and algebraic graph theory. Their purpose is to allow writing as quadratic forms certain combinatorial functions appearing in the framework of graph clustering problems. In this paper we put in evidence certain common traits of various modularity matrices and shed light on their spectral properties that are at the basis of various theoretical results and practical spectral-type algorithms for community detection

Assessment of Bat Mortality and Activity at Buffalo Mountain Windfarm, Eastern Tennessee

Wind power has grown rapidly as an alternative energy source over the last decade. Although overall environmental impacts are relatively low, impacts to bats have yet to be fully assessed. Recent studies at other windfarms suggest regional variation in mortality rates and species affected. This study took place at Tennessee Valley Authority’s Buffalo Mountain Windfarm (BMW) in eastern Tennessee, currently the only commercial windfarm in the southeastern United States. Study objectives were to establish patterns of bat mortality and activity at BMW, and determine if and how they were related. Mortality monitoring consisted of regular carcass searches conducted since BMW began operation in fall of 2000 and continued through fall of 2003. The adjusted bat mortality rate of 20.82 bats/turbine/year for the three-year monitoring period was greater than the average adjusted bat mortality rate at eight other windfarms (1.7 bats/turbine/year) by over an order of magnitude, but less than halfthe preliminary mortality rate (47.5 bats/turbine/year) reported at the Mountaineer Wind Energy Center, WV for 2003. The BMW mortality rate included adjustments determined by search bias trials (n = 6), which measured searcher efficiency (37.1%) and length of time before carcasses were removed by scavengers (average 6.3 days). Average distance of fatalities from turbines was 19.9 ± 2.3 m and distances of bat fatalities decreased logistically from turbines (y = 0.1223 – 0.1345 ln (x), r2 = 0.84, P = 0.0002), with zero fatalities predicted at 40.6 m; therefore, plot size of 50 m radius was deemed sufficient. Bat mortality showed a strong seasonal peak during late summer / early fall, with 70% of all bat fatalities occurring between 1 August and 15 September 2001 - 2003. A total of 119 bat fatalities were comprised of six species. Red bat (Lasiurus borealis) was the most common (63.1%), followed by eastern pipistrelle (Pipistrellus subflavus, 24.4%) and hoary bat (L. cinereus, 10.1%). The remaining 4.2% of bat fatalities consisted of three species: big brown bat (Eptesicus fuscus, n = 2), silver-haired bat (Lasionycteris noctivagans, n = 2), and Seminole bat (L. seminolus, n = 1). Adults were more common then juveniles (63.5% and 36.5%), and males more common than females (71.9% and 28.1%). Bat activity was monitored with Anabat bat detectors and quantified as activity indices (AI), the proportion of one-minute increments in a night that contained one or more recorded bat calls. AI’s were compared across several time periods, locations, and altitudes, and compared with bat mortalities. Bat activity exhibited a seasonal peak in late summer / early fall during all three years, generally coinciding with the peak in mortality. Some of the variance associated with the likelihood of mortality was correlated with bat activity for 2002 and 2003 combined (r = 0.47, P \u3c 0.0001). Considering only fresh fatalities, bat activity levels were greater during nights containing fatalities than nights without fatalities (t = 2.54, P = 0.0067). However, bat activity was not related to fatalities when the time interval was expanded from individual nights to search intervals and all fatalities were used (t = -1.05, P = 0.15). This suggests great variation in bat activity between nights, making temporal resolution an important factor when correlating levels of bat mortality and activity. Bat activity levels were influenced by presence, size and habitat configuration surrounding water features, as well as by altitude. Six species were acoustically identified as present at the BMW site, five of which were found among the turbine fatalities. Three species were found proportionally less as turbine fatalities than were acoustically recorded (eastern pipistrelle, big brown bat, and silver-haired bat) and two species were found proportionally more (red bat and hoary bat), indicating a greater collision risk for the latter species. Overall numbers of bat fatalities at BMW, along with the lack of endangered species fatalities, indicate that population effects appear not to be significant. However, as the generation of electricity from wind increases in the eastern United States, it becomes critical to understand patterns in turbine-related mortality, and for future windfarm projects to determine population level effects of bat mortality

Global modelling of continental water storage changes ? sensitivity to different climate data sets

International audienceSince 2002, the GRACE satellite mission provides estimates of the Earth's dynamic gravity field with unprecedented accuracy. Differences between monthly gravity fields contain a clear hydrological signal due to continental water storage changes. In order to evaluate GRACE results, the state-of-the-art WaterGAP Global Hydrological Model (WGHM) is applied to calculate terrestrial water storage changes on a global scale. WGHM is driven by different climate data sets to analyse especially the influence of different precipitation data on calculated water storage. The data sets used are the CRU TS 2.1 climate data set, the GPCC Full Data Product for precipitation and data from the ECMWF integrated forecast system. A simple approach for precipitation correction is introduced. WGHM results are then compared with GRACE data. The use of different precipitation data sets leads to considerable differences in computed water storage change for a large number of river basins. Comparing model results with GRACE observations shows a good spatial correlation and also a good agreement in phase. However, seasonal variations of water storage as derived from GRACE tend to be significantly larger than those computed by WGHM, regardless of which climate data set is used

Moist turbulent Rayleigh-Benard convection with Neumann and Dirichlet boundary conditions

Turbulent Rayleigh-Benard convection with phase changes in an extended layer between two parallel impermeable planes is studied by means of three-dimensional direct numerical simulations for Rayleigh numbers between 10^4 and 1.5\times 10^7 and for Prandtl number Pr=0.7. Two different sets of boundary conditions of temperature and total water content are compared: imposed constant amplitudes which translate into Dirichlet boundary conditions for the scalar field fluctuations about the quiescent diffusive equilibrium and constant imposed flux boundary conditions that result in Neumann boundary conditions. Moist turbulent convection is in the conditionally unstable regime throughout this study for which unsaturated air parcels are stably and saturated air parcels unstably stratified. A direct comparison of both sets of boundary conditions with the same parameters requires to start the turbulence simulations out of differently saturated equilibrium states. Similar to dry Rayleigh-Benard convection the differences in the turbulent velocity fluctuations, the cloud cover and the convective buoyancy flux decrease across the layer with increasing Rayleigh number. At the highest Rayleigh numbers the system is found in a two-layer regime, a dry cloudless and stably stratified layer with low turbulence level below a fully saturated and cloudy turbulent one which equals classical Rayleigh-Benard convection layer. Both are separated by a strong inversion that gets increasingly narrower for growing Rayleigh number.Comment: 19 pages, 13 Postscript figures, Figures 10,11,12,13, in reduced qualit

Quantum information analysis of electronic states at different molecular structures

We have studied transition metal clusters from a quantum information theory perspective using the density-matrix renormalization group (DMRG) method. We demonstrate the competition between entanglement and interaction localization. We also discuss the application of the configuration interaction based dynamically extended active space procedure which significantly reduces the effective system size and accelerates the speed of convergence for complicated molecular electronic structures to a great extent. Our results indicate the importance of taking entanglement among molecular orbitals into account in order to devise an optimal orbital ordering and carry out efficient calculations on transition metal clusters. We propose a recipe to perform DMRG calculations in a black-box fashion and we point out the connections of our work to other tensor network state approaches

Bimetallic Cooperativity in Proton Reduction with an Amido‐Bridged Cobalt Catalyst

The bimetallic catalyst [CoII2(L1)(bpy)2]ClO4 (1), in which L1 is an [NN′2O2] fused ligand, efficiently reduced H+ to H2 in CH3CN in the presence of 100 equiv of HOAc with a turnover number of 18 and a Faradaic efficiency of 94 % after 3 h of bulk electrolysis at −1.6 V (vs. Ag/AgCl). This observation allowed the proposal that this bimetallic cooperativity is associated with distance, angle, and orbital alignment of the two Co centers, as promoted by the unique Co−Namido−Co environment offered by L1. Experimental results revealed that the parent [CoIICoII] complex undergoes two successive metal‐based 1 e− reductions to generate the catalytically active species [CoICoI], and DFT calculations suggested that addition of a proton to one CoI triggers a cooperative 1 e− transfer by each of these CoI centers. This 2 e− transfer is an alternative route to generate a more reactive [CoII(CoII−H−)] hydride, thus avoiding the CoIII−H− required in monometallic species. This [CoII(CoII−H−)] species then accepts another H+ to release H2

Food fortification - a feasible, cost-effective option in the fight against vitamin A deficiency in South Africa

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Annexin XIIIb: a novel epithelial specific annexin is implicated in vesicular traffic to the apical plasma membrane

The sorting of apical and basolateral proteins into vesicular carriers takes place in the trans-Golgi network (TGN) in MDCK cells. We have previously analyzed the protein composition of immunoisolated apical and basolateral transport vesicles and have now identified a component that is highly enriched in apical vesicles. Isolation of the encoding cDNA revealed that this protein, annexin XIIIb, is a new isoform of the epithelial specific annexin XIII sub-family which includes the previously described intestine-specific annexin (annexin XIIIa; Wice, B. M., and J. I, Gordon. 1992. J. Cell Biol. 116:405-422). Annexin XIIIb differs from annexin XIIIa in that it contains a unique insert of 41 amino acids in the NH2 terminus and is exclusively expressed in dog intestine and kidney, Immunofluorescence microscopy demonstrated that annexin XIIIb was localized to the apical plasma membrane and underlying punctate structures. Since annexins have been suggested to play a role in membrane-membrane interactions in exocytosis and endocytosis, we investigated whether annexin XIIIb, is involved in delivery to the apical cell surface. To this aim we used permeabilized MDCK cells and a cytosol-dependent in vitro transport assay. Antibodies specific for annexin XIIIb significantly inhibited the transport of influenza virus hemagglutinin from the TGN to the apical plasma membrane while the transport of vesicular stomatitis virus glycoprotein to the basolateral cell surface was unaffected. We propose that annexin XIIIb, plays a role in vesicular transport to the apical plasma membrane in MDCK cells

Analysis of weighted networks

The connections in many networks are not merely binary entities, either present or not, but have associated weights that record their strengths relative to one another. Recent studies of networks have, by and large, steered clear of such weighted networks, which are often perceived as being harder to analyze than their unweighted counterparts. Here we point out that weighted networks can in many cases be analyzed using a simple mapping from a weighted network to an unweighted multigraph, allowing us to apply standard techniques for unweighted graphs to weighted ones as well. We give a number of examples of the method, including an algorithm for detecting community structure in weighted networks and a new and simple proof of the max-flow/min-cut theorem.Comment: 9 pages, 3 figure

A measure of centrality based on the spectrum of the Laplacian

We introduce a family of new centralities, the k-spectral centralities. k-Spectral centrality is a measurement of importance with respect to the deformation of the graph Laplacian associated with the graph. Due to this connection, k-spectral centralities have various interpretations in terms of spectrally determined information. We explore this centrality in the context of several examples. While for sparse unweighted networks 1-spectral centrality behaves similarly to other standard centralities, for dense weighted networks they show different properties. In summary, the k-spectral centralities provide a novel and useful measurement of relevance (for single network elements as well as whole subnetworks) distinct from other known measures.Comment: 12 pages, 6 figures, 2 table