Search for direct photons from S-Au collisions at 200 GeV/nucleon

The CERES experiment has measured inclusive photon production in S-Au collisions of 200 GeV/nucleon at the CERN SPS. No evidence for direct emission of photons was found. For the kinematic region 2.1<y<2.65 and 0.4 GeV/c<p??<2.0 GeV/c the yield andp??-dependence of the observed photons are well reproduced by hadron decays. Furthermore, their production rate is found to be proportional to the charged particle density. The systematic errors comparing the measured and expected photon yield result in an upper limit of 14% for the emission of direct photons in central S-Au collisions. For a photon source with a yield depending quadratically on the charged particle density the limit can be reduced to 7%.     

Bi-directional terahertz emission from gold-coated nanogratings by excitation via femtosecond laser pulses

We report on the investigation of terahertz (THz) emission from gold-coated nanogratings (500 nm grating constant) upon femtosecond laser irradiation (785?nm, 150?fs, 1?kHz, ??1?mJ/pulse). Unlike common assumptions, THz emission is not only observed in case of rear side irradiation (through substrate (Welsh et al. in Phys. Rev. Lett. 98:026803, 2007; Welsh and Wynne in Opt. Express 17:2470?C2480, 2009)) of the nanograting, but also in case of front side excitation (through air). Furthermore in both cases, THz emission propagates in the direction of laser beam propagation and reverse. Based on these findings, we suggest a new approach to describe the newly observed phenomena. Using a highly sensitive and fast superconducting transition edge sensor (TES) as calorimeter, it was possible to directly measure the absolute energy of the emitted THz pulses in a defined spectral and spatial range, enabling for the first time a quantitative analysis of the THz emission process.     

Highly dynamic and versatile pulsed fiber amplifier seeded?by?a?superluminescence diode

We propose and investigate a high power superluminescence diode (SLD) as a pulsed seed source for a highly dynamic and versatile pulse fiber amplifier system. The SLD provides, contrary to conventional Fabry?CPérot laser diodes, a smooth and broad output spectrum which is independent of the input pulse parameters. The output pulses from the SLD are as short as 10?ns with up to 150?mW peak power. Moreover, the pulses can be directly shaped by modulating the injection current of the SLD. Pulse shaping in an amplifier configuration is demonstrated without the observation of stimulated Brillouin scattering (SBS) due to the provided spectral bandwidth of 10?nm FWHM. Further spectral shaping was realized with a band pass filter in the amplifier chain.     

Electrolyte based on fluorinated cyclic quaternary ammonium ionic liquids

Ionic liquids, ILs, based on fluorinated pyrrolidinium and piperidinium ammonium cations and imide anion were prepared and characterized. The physicochemical and electrochemical properties of these ILs including melting point, glass transition and degradation temperatures, viscosity, ionic conductivity, and electrochemical stability were determined and compared to alkyl pyrrolidinium and piperidinium ILs. The incorporation of a CF₃ group instead of a CH₃ induces an increase of the IL viscosity, thus a conductivity decrease. However, good ionic conductivity is obtained with fluorinated pyrrolidinium IL. Cyclic amine ILs with propyl alkyl chain or fluorinated ammonium exhibit very high electrochemical stability toward oxidation. The effect of the addition of LiTFSI on the IL properties was studied with the same methodology.     

Mini Review of Poincar�� Invariant Quantum Theory

We review the construction and applications of exactly Poincaré invariant quantum mechanical models of few-degree of freedom systems. We discuss the construction of dynamical representations of the Poincaré group on few-particle Hilbert spaces, the relation to quantum field theory, the formulation of cluster properties, and practical considerations related to the construction of realistic interactions and the solution of the dynamical equations. Selected applications illustrate the utility of this approach.     

Synthesis and characterization of hollow ��-Fe2O3 sub-micron spheres prepared by sol�Cgel

In this work we report the preparation of magnetic hematite hollow sub-micron spheres (??-Fe₂O₃) by colloidal suspensions of ferric nitrate nine-hydrate (Fe(NO₃)₃·9H₂O) particles in citric acid solution by following the sol?Cgel method. After the gel formation, the samples were annealed at different temperatures in an oxidizing atmosphere. Annealing at 180°C resulted in an amorphous phase, without iron oxide formation. Annealing at 250°C resulted in coexisting phases of hematite, maghemite and magnetite, whereas at 400°C, only hematite and maghemite were found. Pure hematite hollow sub-micron spheres with porous shells were formed after annealing at 600°C. The characterization was performed by X-ray diffraction (XRD), Mössbauer spectroscopy (MS) and scanning electron microscopy (SEM).     

Aggregates of iron in ytterbium films

Films of ytterbium doped with iron (0.3?C1.6 at.% Fe) have been prepared by co-deposition of atomic beams of the elements onto Kapton substrates under high vacuum. Iron is immiscible in ytterbium and various iron species are expected to occur. XRD reveals a mixture of fcc and hcp ytterbium. The Mössbauer spectra are interpreted with contributions from monomeric iron on interstitial sites, two types of neighboring substitutional iron aggregates and two types of clusters formed upon diffusion. The present data supplement earlier data obtained for 0.5 and 5 at.% Fe. There is no systematic correlation of cluster formation with increasing iron concentration. There are indications that clusters are formed more easily for thin films. We conclude that cluster formation occurs mainly on the film surface and is limited by the slow diffusion from inside films.