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Université de Fribourg

Determinants of local ant (Hymenoptera: Formicidae) species richness and activity density across Europe

Kumschick, Sabrina ; Schmidt-Entling, Martin H. ; Bacher, Sven ; Hickler, Thomas ; Espadaler, Xavier ; Nentwig, Wolfgang

In: Ecological Entomology, 2009, vol. 34, no. 6, p. 748 - 754

1. Species richness is influenced by local habitat features and large-scale climatic gradients. Usually, both influences are studied in isolation because of the divergent spatial scales at which they occur. Here, we compared the influence of large-scale climate and local habitat type on European ants using a continent-wide, standardised sampling programme.2. We investigated species richness and...

Université de Fribourg

Body size–climate relationships of European spiders

Entling, Wiebke ; Schmidt-Entling, Martin H. ; Bacher, Sven ; Brandl, Roland ; Nentwig, Wolfgang

In: Journal of Biogeography, 2009///doi: 10.1111/j.1365-2699.2009.02216.x

Aim: Geographic body size patterns of mammals and birds can be partly understood under the framework of Bergmann's rule. Climatic influences on body size of invertebrates, however, appear highly variable and lack a comparable, generally applicable theoretical framework. We derived predictions for body size–climate relationships for spiders from the literature and tested them using three...

Université de Fribourg

Alien species in a warmer world: risks and opportunities

Walther, Gian-Reto ; Roques, Alain ; Hulme, Philip E. ; Sykes, Martin T. ; Pyšek, Petr ; Kühn, Ingolf ; Zobel, Martin ; Bacher, Sven ; Botta-Dukát, Zoltán ; Bugmann, Harald ; Czúcz, Bálint ; Dauber, Jens ; Hickler, Thomas ; Jarošík, Vojtěch ; Kenis, Marc ; Klotz, Stefan ; Minchin, Dan ; Moora, Mari ; Nentwig, Wolfgang ; Ott, Jürgen ; Panov, Vadim E. ; Reineking, Björn ; Robinet, Christelle ; Semenchenko, Vitaliy ; Solarz, Wojciech ; Thuiller, Wilfried ; Vilà, Montserrat ; Vohland, Katrin ; Settele, Josef

In: Trends in Ecology & Evolution, 2009, vol. 24, no. 12, p. 686-693

Climate change and biological invasions are key processes affecting global biodiversity, yet their effects have usually been considered separately. Here, we emphasise that global warming has enabled alien species to expand into regions in which they previously could not survive and reproduce. Based on a review of climate-mediated biological invasions of plants, invertebrates, fishes and birds, we...

Université de Fribourg

Status of the endangered ivory gull, Pagophila eburnea, in Greenland

Gilg, Olivier ; Boertmann, David ; Merkel, Flemming ; Aebischer, Adrian ; Sabard, Brigitte

In: Polar Biology, 2009, vol. 32, no. 9, p. 1275-1286

The ivory gull, a rare high-Arctic species whose main habitat throughout the year is sea ice, is currently listed in Greenland as ‘Vulnerable’, and as ‘Endangered’ in Canada, where the population declined by 80% in 20 years. Despite this great concern, the status of the species in Greenland has been largely unknown as it breeds in remote areas and in colonies for which population data has...

Université de Fribourg

Information filtering based on transferring similarity

Sun, Duo ; Zhou, Tao ; Liu, Jian-Guo ; Liu, Run-Ran ; Jia, Chun-Xiao ; Wang, Bing-Hong

In: Physical Review E, 2009, vol. 80, no. 1, p. 017101

n this Brief Report, we propose an index of user similarity, namely, the transferring similarity, which involves all high-order similarities between users. Accordingly, we design a modified collaborative filtering algorithm, which provides remarkably higher accurate predictions than the standard collaborative filtering. More interestingly, we find that the algorithmic performance will approach...

Université de Fribourg

Neutron to mirror-neutron oscillations in the presence of mirror magnetic fields

Altarev, I. ; Baker, C. A. ; Ban, G. ; Bodek, K. ; Daum, M. ; Fierlinger, P. ; Geltenbort, P. ; Green, K. ; Grinten, M. G. D. van der ; Gutsmiedl, E. ; Harris, P. G. ; Henneck, R. ; Horras, M. ; Iaydjiev, P. ; Ivanov, S. ; Khomutov, N. ; Kirch, K. ; Kistryn, S. ; Knecht, A. ; Knowles, Paul E. ; Kozela, A. ; Kuchler, F. ; Kuźniak, M. ; Lauer, T. ; Lauss, B. ; Lefort, T. ; Mtchedlishvili, A. ; Naviliat-Cuncic, O. ; Paul, S. ; Pazgalev, Anatoly ; Pendlebury, J. M. ; Petzoldt, G. ; Pierre, E. ; Plonka-Spehr, C. ; Quéméner, G. ; Rebreyend, D. ; Roccia, S. ; Rogel, G. ; Severijns, N. ; Shiers, D. ; Sobolev, Yu. ; Stoepler, R. ; Weis, Antoine ; Zejma, J. ; Zenner, J. ; Zsigmond, G.

In: Physical Review D, 2009, vol. 80, no. 3, p. 032003

We performed ultracold neutron storage measurements to search for additional losses due to neutron (n) to mirror-neutron (n') oscillations as a function of an applied magnetic field B. In the presence of a mirror magnetic field B', ultracold neutron losses would be maximal for B~B'. We did not observe any indication for...

Université de Fribourg

A large sample study of spin relaxation and magnetometric sensitivity of paraffin-coated Cs vapor cells

Castagna, Natascia ; Bison, Georg ; Di Domenico, Gianni ; Hofer, Adrian ; Knowles, Paul ; Macchione, Catherine ; Saudan, Hervé ; Weis, Antoine

In: Applied Physics B, 2009, vol. 96, no. 4, p. 763-772

We have manufactured more than 250 nominally identical paraffin-coated Cs vapor cells (28 mm inner diameter bulbs) for multi-channel atomic magnetometer applications. We describe our dedicated cell characterization apparatus. For each cell we have determined the intrinsic longitudinal, Γ ₀₁, and transverse, Γ ₀₂, relaxation rates. Our best cell shows Γ...

Université de Fribourg

Efficient technique for measuring laser frequency stability

Sargsyan, A. ; Papoyan, A.V. ; Sarkisyan, D. ; Weis, Antoine

In: European Physical Journal - Applied Physics, 2009, vol. 48, p. 20701

We propose a new technique for measuring the frequency stability of cw laser radiation. The technique relies on using the laser to be tested as a coupling laser in a scheme of electromagnetically-induced transparency (EIT), either on a Λ or a ladder system. A second, frequency tunable laser (stabilization of this laser is not needed) is used both to act as the EIT probe laser, and to form an...

Université de Fribourg

Scattering information obtained by optical microscopy: Differential dynamic microscopy and beyond

Giavazzi, Fabio ; Brogioli, Doriano ; Trappe, Véronique ; Bellini, Tommaso ; Cerbino, Roberto

In: Physical Review E, 2009, vol. 80, no. 3, p. 031403

We describe the use of a bright-field microscope for dynamic light scattering experiments on weakly scattering samples. The method is based on collecting a time sequence of microscope images and analyzing them in the Fourier space to extract the characteristic time constants as a function of the scattering wave vector. We derive a theoretical model for microscope imaging that accounts for (a) the...

Université de Fribourg

Microscopic modeling of energy relaxation and decoherence in quantum optoelectronic devices at the nanoscale

Taj, David ; Iotti, R. C. ; Rossi, F.

In: The European Physical Journal B, 2009///doi: 10.1140/epjb/e2009-00363-4

We shall review and discuss the key problem of providing a microscopic modeling of state-of-the-art electronic quantum devices. In particular we shall focus on the description of energy-relaxation and decoherence phenomena, explicitly showing the intrinsic limitations of some of the existing treatments (the conventional Markovian approach) via analytical results, and proposing an alternative...