In the last 30 days

• Open/close Soccer: Is scoring goals a predictable Poissonian process?

  A. Heuer et al  2010 EPL 89 38007 Tag this article

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  The non-scientific event of a soccer match is analysed on a strictly scientific level. The analysis is based on the recently introduced concept of a team fitness ( Eur. Phys. J. B, 67 (2009) 445) and requires the use of finite-size scaling. A uniquely defined function is derived which quantitatively predicts the expected average outcome of a soccer match in terms of the fitness of both teams. It is checked whether temporary fitness fluctuations of a team hamper the predictability of a soccer match. To a very good approximation scoring goals during a match can be characterized as independent Poissonian processes with pre-determined expectation values. Minor correlations give rise to an increase of the number of draws. The non-Poissonian overall goal distribution is just a consequence of the fitness distribution among different teams. The limits of predictability of soccer matches are quantified. Our model-free classification of the underlying ingredients determining the outcome of soccer matches can be generalized to different types of sports events.

• Open/close Superconductivity and phase diagram in iron-based arsenic-oxides ReFeAsO_1−δ (Re = rare-earth metal) without fluorine doping

  Zhi-An Ren et al  2008 EPL 83 17002 Tag this article

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  Here we report a new class of superconductors prepared by high-pressure synthesis in the quaternary family ReFeAsO _1−δ (Re=Sm, Nd, Pr, Ce, La) without fluorine doping. The onset superconducting critical temperature ( T _c ) in these compounds increases with the reduction of the Re atom size, and the highest T _c obtained so far is 55 K in SmFeAsO _1−δ. For the NdFeAsO _1−δ compound with different oxygen concentration a dome-shaped phase diagram was found.

• Open/close Superconductivity in the iron-based F-doped layered quaternary compound Nd[O_{1 − x} F_x]FeAs

  Zhi-An Ren et al  2008 EPL 82 57002 Tag this article

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  Here we report a new quaternary iron-arsenide superconductor Nd[O _{1− x} F _x ]FeAs , with the onset resistivity transition at 51.9 K and Meissner transition at 51 K. This compound has the same crystal structure as LaOFeAs, and becomes the second superconductor after Pr[O _{1− x} F _x ]FeAs that superconducts above 50 K.

• Open/close Competing orders and spin-density-wave instability in La(O_1−xF_x)FeAs

  J. Dong et al  2008 EPL 83 27006 Tag this article

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  The interplay between different ordered phases, such as superconducting, charge or spin ordered phases, is of central interest in condensed-matter physics. The very recent discovery of superconductivity with a remarkable T _c =26 K in Fe-based oxypnictide La(O _{1− x}F _x )FeAs (see Kamihara Y. et al., J. Am. Chem. Soc., 130 (2008) 3296) is a surprise to the scientific community and has generated tremendous interest. The pure LaOFeAs itself is not superconducting but shows an anomaly near 150 K in both resistivity and dc magnetic susceptibility. Here we provide combined experimental and theoretical evidences showing that a spin-density-wave (SDW) state develops at low temperature, in association with electron Nematic order. The electron-doping by F suppresses the SDW instability and induces the superconductivity. Therefore, the La(O _{1− x}F _x )FeAs offers an exciting new system showing competing orders in layered compounds.

• Open/close Experimental Evidence for a Photon Anticorrelation Effect on a Beam Splitter: A New Light on Single-Photon Interferences

  P. Grangier et al  1986 Europhys. Lett. 1 173 Tag this article

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  We report on two experiments using an atomic cascade as a light source, and a triggered detection scheme for the second photon of the cascade. The first experiment shows a strong anticorrelation between the triggered detections on both sides of a beam splitter. This result is in contradiction with any classical wave model of light, but in agreement with a quantum description involving single-photon states. The same source and detection scheme were used in a second experiment, where we have observed interferences with a visibility over 98%.

• Open/close Observation of Fermi-surface–dependent nodeless superconducting gaps in Ba_0.6K_0.4Fe₂As₂

  H. Ding et al  2008 EPL 83 47001 Tag this article

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  We have performed a high-resolution angle-resolved photoelectron spectroscopy study on the newly discovered superconductor Ba _0.6K _0.4Fe ₂As ₂ ( T _c=37 K). We have observed two superconducting gaps with different values: a large gap (Δ~12 meV) on the two small hole-like and electron-like Fermi surface (FS) sheets, and a small gap (~6 meV) on the large hole-like FS. Both gaps, closing simultaneously at the bulk transition temperature ( T _c), are nodeless and nearly isotropic around their respective FS sheets. The isotropic pairing interactions are strongly orbital dependent, as the ratio 2Δ/ k _B T _c switches from weak to strong coupling on different bands. The same and surprisingly large superconducting gap due to strong pairing on the two small FSs, which are connected by the (π, 0) spin-density-wave vector in the parent compound, strongly suggests that the pairing mechanism originates from the inter-band interactions between these two nested FS sheets.

• Open/close Hybrid description of complex molecules

  P. Español  2009 EPL 88 40008 Tag this article

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  We present a hybrid description of complex molecules in which one of the molecules is described in full atomistic detail, while the rest of molecules is represented at a coarse-grained level with their centers-of-mass variables. Based on Zwanzig's projection method, we derive the equations of motion for the coupled detailed/coarse-grained system, which turn out to be of the form of Dissipative Particle Dynamics.

• Open/close Tachyonic spectral fits of γ-ray bursts

  R. Tomaschitz  2010 EPL 89 39002 Tag this article

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  Evidence for superluminal radiation in γ-ray burst (GRB) spectra is pointed out. The spectral maps of GRB 941017, GRB 990123, and GRB 990104 are analyzed. The superluminal radiation modes are generated by the shock-heated ultra-relativistic source plasma. The tachyonic radiation field is a real Proca field with negative mass-square, coupled to the electron gas by a frequency-dependent fine-structure constant. At GeV energies, the coupling constant approaches a limit value, so that the radiation field is minimally coupled to the electron current. In the soft γ-ray band, the interaction with the GRB plasma becomes nonlocal, due to the varying coupling strength depending on the energy of the radiated modes. The spectral fitting with tachyonic flux densities generated by nonlocal plasma currents is explained. Estimates of the tachyonic luminosity, temperature, and internal energy of the electronic source plasma are obtained from the spectral fits.

• Open/close About the temperature of moving bodies

  T. S. Bíró and P. Ván  2010 EPL 89 30001 Tag this article

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  Relativistic thermodynamics is constructed from the point of view of special relativistic hydrodynamics. A relativistic four-current for heat and a general treatment of thermal equilibrium between moving bodies are presented. The different temperature transformation formulas of Planck and Einstein, Ott, Landsberg and Doppler appear upon particular assumptions about internal heat current.

• Open/close Superconductivity at 25 K in hole-doped (La_1-xSr_x)OFeAs

  Hai-Hu Wen et al  2008 EPL 82 17009 Tag this article

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  By partially substituting the tri-valence element La with di-valence element Sr in LaOFeAs, we introduced holes into the system. For the first time, we successfully synthesized the hole-doped new superconductors (La _{1- x}Sr _x )OFeAs. The maximum superconducting transition temperature at about 25 K was observed at a doping level of x=0.13. It is evidenced by Hall effect measurements that the conduction in this type of material is dominated by hole-like charge carriers, rather than electron-like ones. Together with the data of the electron-doped system La(O _{1- x}F _x )FeAs, a generic phase diagram is depicted and is revealed to be similar to that of the cuprate superconductors.