Featured in EPL

Featured articles from recent issues of EPL.

Direct measurement of the speed of sound in a complex plasma under microgravity conditions¹
by M. Schwabe, K. Jiang, S. Zhdanov, T. Hagl, P. Huber, A. V. Ivlev, A. M. Lipaev, V. I. Molotkov, V. N. Naumkin, K. R. Sütterlin, H. M. Thomas, V. E. Fortov, G. E. Morfill, A. Skvortsov and S. Volkov

‘We present a direct measurement of the speed of sound in a three-dimensional complex plasma —a room-temperature plasma that contains micrometer-sized particles as fourth component. In order to obtain an undisturbed system, the setup was placed under microgravity conditions on board the International Space Station. The speed of sound was measured with the help of Mach cones excited by a supersonic probe particle moving through the extended particle cloud at Mach numbers M3. We use the Mach cone relation to infer the particle charge and compare with that predicted by standard theories. In addition, we compare our results with a numerical simulation. In both experiment and simulation, we observe a double Mach cone structure…’

Evolution of strategies for the collective-risk social dilemma relating to climate change²
by G. Greenwood

‘This paper describes an N-person social dilemma game created to study how climate change agreement strategies develop. The players in this game are trying to collect a target amount for a climate aid fund. Players (countries) fall into three categories: cooperators who contribute their fair share, altruists who contribute more than their fair share and defectors who contribute nothing. In all cases we would evolve a set of player strategies that collected the target sum (− 0%/+0.5%). Our results indicate defection is a preferred strategy, but trigger strategies can markedly improve contributions. Our game is designed to see what motivates countries to live up to their agreements to contribute to climate change aid funds…’

See also: ‘Trigger’ strategy to prevent climate policy freeriding on Environmental Research Web.

First measurement of the total proton-proton cross-section at the LHC energy of √s=7 TeV³
by the TOTEM Collaboration, G. Antchev, P. Aspell, I. Atanassov, V. Avati, J. Baechler, V. Berardi, M. Berretti, E. Bossini, M. Bozzo, P. Brogi, E. Brücken, A. Buzzo, F. S. Cafagna, M. Calicchio, M. G. Catanesi, C. Covault, T. Csörgő, M. Deile, K. Eggert, V. Eremin, R. Ferretti, F. Ferro, A. Fiergolski , F. Garcia, S. Giani, V. Greco, L. Grzanka, J. Heino, T. Hilden, M. R. Intonti, J. Kašpar, J. Kopal, V. Kundrát, K. Kurvinen, S. Lami, G. Latino, R. Lauhakangas, T. Leszko, E. Lippmaa, M. Lokajíček, M. Lo Vetere, F. Lucas Rodríguez, M. Macrí, L. Magaletti, A. Mercadante, S. Minutoli, F. Neme, H. Niewiadomski, E. Oliveri, F. Oljemark, R. Orava, M. Oriunno, K. Österberg, P. Palazzi, J. Procházka, M. Quinto, E. Radermacher, E. Radicioni, F. Ravotti, E. Robutti, L. Ropelewski, G. Ruggiero, H. Saarikko, G. Sanguinetti, A. Santroni, A. Scribano, W. Snoeys, J. Sziklai, C. Taylor, N. Turini, V. Vacek, M. Vitek, J. Welti & J. Whitmore

‘TOTEM has measured the differential cross-section for elastic proton-proton scattering at the LHC energy of √s = 7 TeV analysing data from a short run with dedicated large-β* optics. A single exponential fit with a slope B=(20.1±0.2^stat±0.3^syst) GeV⁻² describes the range of the four-momentum transfer squared |t| from 0.02 to 0.33 GeV². After the extrapolation to |t|=0, a total elastic scattering cross-section of (24.8±0.2^stat±1.2^syst) mb was obtained. Applying the optical theorem and using the luminosity measurement from CMS, a total proton-proton cross-section of (98.3±0.2^stat±2.8^syst) mb was deduced which is in good agreement with the expectation from the overall fit of previously measured data over a large range of center-of-mass energies. From the total and elastic pp cross-section measurements, an inelastic pp cross-section of (73.5±0.62^statsyst) mb was inferred…’

Observing different quantum trajectories in cavity QED⁴
by M. F. Santos & A. R. R. Carvalho

‘The experimental observation of quantum jumps is an example of single open quantum systems that, when monitored, evolve in terms of stochastic trajectories conditioned on measurements results. Here we present a proposal that allows the experimental observation of a much larger class of quantum trajectories in cavity QED systems. In the microwave regime, three-level atoms probe the cavity field while in the optical case the field probes atomic states. In the first situation the cavity field evolves stochastically between highly non-classical states while the second case allows for the monitoring of engineered thermal baths that are crucial for recent proposals for probing entanglement decay and also for entanglement protection…’

1. doi:10.1209/0295-5075/96/55001 [↩]
2. doi:10.1209/0295-5075/95/40006 [↩]
3. doi:10.1209/0295-5075/96/21002 [↩]
4. doi:10.1209/0295-5075/94/64003 [↩]

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