Direct photons in Pb+Pb at CERN-SPS from microscopic transport theory

Direct photon production in central Pb+Pb collisions at CERN-SPS energy is calculated within the relativistic microscopic transport model UrQMD, and within distinctly different versions of relativistic hydrodynamics. We find that in UrQMD the local momentum distributions of the secondaries are strongly elongated along the beam axis initially. Therefore, the pre-equilibrium contribution dominates the photon spectrum at transverse momenta above $\approx 1.5$ GeV. The hydrodynamics prediction of a strong correlation between the temperature and radial expansion velocities on the one hand and the slope of the transverse momentum distribution of direct photons on the other hand thus is not recovered in UrQMD. The rapidity distribution of direct photons in UrQMD reveals that the initial conditions for the longitudinal expansion of the photon source (the meson ``fluid'') resemble rather boostinvariance than Landau-like flow.Comment: 14 pages, RevTex, 5 Encapsulated-PostScript Figure

The Origin of Transverse Flow at the SPS

We study the transverse expansion in central Pb+Pb collisions at the CERN SPS. Strong collective motion of hadrons can be created. This flow is mainly due to meson baryon rescattering. It allows to study the angular distribution of intermediate mass meson baryon interactions.Comment: submitted to Phys. Lett.

LEY PIES SECOS, PIES MOJADO EN CONTEXTO DEL DERECHO INTERNACIONAL PÚBLICO

El trabajo contiene una riquísima información basada en documentos y testimonios de incalculable valor histórico, que nos presenta una vez más a nuestro invencible Fidel analizando y denunciando sobre las trágicas consecuencias de la Ley de Ajuste Cubano, la Ley de pies secos pies mojados y el Programa de Parole para los profesionales de la salud cubana lo cual constituye un elemento importante en el marco del proceso bilateral que ha permitido la firma de un nuevo acuerdo migratorio entre los dos países y que a la vez puntualiza para nuestros jóvenes profesores y estudiantes un recorrido por algunos aspectos medulares que se han venido tergiversando por los enemigos de la revolución, pero que siempre fueron puestos al descubierto mientras que el gobierno de Estados Unidos ocultaba las informaciones cada vez que morían personas en las operaciones de tráfico humano realizadas por los que se proponían alcanzar " el sueño americano" que a tantos engañó ,se muestra como supo captar como nadie la reducción moral en la que comenzaba a moverse una buena parte de los insurgentes cubanos que al final serían los beneficiados con todas las prebendas de la política migratoria que se estrenaba en 1966 que fue convertida en Ley y que hoy al firmarse un nuevo acuerdo migratorio entre los gobiernos de Estados Unidos y Cuba se le pone punto final a parte de esta política aunque permanece aún la Ley de Ajuste

Design and Experimental Validation of a Ducted Counter-rotating Axial-flow Fans System

An experimental study on the design of counter-rotating axial-flow fans was carried out. The fans were designed using an inverse method. In particular, the system is designed to have a pure axial discharge flow. The counter-rotating fans operate in a ducted-flow configuration and the overall performances are measured in a normalized test bench. The rotation rate of each fan is independently controlled. The relative axial spacing between fans can vary from 17% to 310%. The results show that the efficiency is strongly increased compared to a conventional rotor or to a rotor-stator stage. The effects of varying the rotation rates ratio on the overall performances are studied and show that the system has a very flexible use, with a large patch of high efficient operating points in the parameter space. The increase of axial spacing causes only a small decrease of the efficiencyComment: accepted in Journal of Fluid Engineerin

Microscopic Models for Ultrarelativistic Heavy Ion Collisions

In this paper, the concepts of microscopic transport theory are introduced and the features and shortcomings of the most commonly used ansatzes are discussed. In particular, the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) transport model is described in great detail. Based on the same principles as QMD and RQMD, it incorporates a vastly extended collision term with full baryon-antibaryon symmetry, 55 baryon and 32 meson species. Isospin is explicitly treated for all hadrons. The range of applicability stretches from $E_{lab} 200$ GeV/nucleon, allowing for a consistent calculation of excitation functions from the intermediate energy domain up to ultrarelativistic energies. The main physics topics under discussion are stopping, particle production and collective flow.Comment: 129 pages, pagestyle changed using US letter (8.5x11 in) format. The whole paper (13 Mb ps file) could also be obtained from ftp://ftp.th.physik.uni-frankfurt.de/pub/urqmd/ppnp2.ps.g

Mirror Position Determination for the Alignment of Cherenkov Telescopes

Imaging Atmospheric Cherenkov Telescopes (IACTs) need imaging optics with large apertures to map the faint Cherenkov light emitted in extensive air showers onto their image sensors. Segmented reflectors fulfill these needs using mass produced and light weight mirror facets. However, as the overall image is the sum of the individual mirror facet images, alignment is important. Here we present a method to determine the mirror facet positions on a segmented reflector in a very direct way. Our method reconstructs the mirror facet positions from photographs and a laser distance meter measurement which goes from the center of the image sensor plane to the center of each mirror facet. We use our method to both align the mirror facet positions and to feed the measured positions into our IACT simulation. We demonstrate our implementation on the 4 m First Geiger-mode Avalanche Cherenkov Telescope (FACT).Comment: 11 figures, small ray tracing performance simulation, and implementation demonstratio

Consequences of kinetic non-equilibrium for the nuclear equation-of-state in heavy ion collision

Highly compressed nuclear matter created in relativistic heavy collisions is to large extent governed by local non-equilibrium. As an idealized scenario colliding nuclear matter configurations are studied within both, relativistic mean field theory and using more realistic in-medium interactions based on the Dirac-Brueckner T-matrix. The equation of state in anisotropic matter is thereby governed by two competing effects: The enlarged phase space volume in colliding matter tends to soften the internal potential energy of the subsystems whereas the relative motion of the two currents leads to a strong additional repulsion in the system. An effective EOS constructed for anisotropic momentum configurations shows a significant net softening compared to ground state nuclear matter. This effect is found to be to large extend independent on the particular choice of the nuclear interaction. A critical discussion of standard transport approaches with respect to the considered non-equilibrium effects is given.Comment: 41 pages, 13 figures, to appear in Nucl. Phys.

Data compression for the First G-APD Cherenkov Telescope

The First Geiger-mode Avalanche photodiode (G-APD) Cherenkov Telescope (FACT) has been operating on the Canary island of La Palma since October 2011. Operations were automated so that the system can be operated remotely. Manual interaction is required only when the observation schedule is modified due to weather conditions or in case of unexpected events such as a mechanical failure. Automatic operations enabled high data taking efficiency, which resulted in up to two terabytes of FITS files being recorded nightly and transferred from La Palma to the FACT archive at ISDC in Switzerland. Since long term storage of hundreds of terabytes of observations data is costly, data compression is mandatory. This paper discusses the design choices that were made to increase the compression ratio and speed of writing of the data with respect to existing compression algorithms. Following a more detailed motivation, the FACT compression algorithm along with the associated I/O layer is discussed. Eventually, the performances of the algorithm is compared to other approaches.Comment: 17 pages, accepted to Astronomy and Computing special issue on astronomical file format

FACT - Monitoring Blazars at Very High Energies

The First G-APD Cherenkov Telescope (FACT) was built on the Canary Island of La Palma in October 2011 as a proof of principle for silicon based photosensors in Cherenkov Astronomy. The scientific goal of the project is to study the variability of active galatic nuclei (AGN) at TeV energies. Observing a small sample of TeV blazars whenever possible, an unbiased data sample is collected. This allows to study the variability of the selected objects on timescales from hours to years. Results from the first three years of monitoring will be presented. To provide quick flare alerts to the community and trigger multi-wavelength observations, a quick look analysis has been installed on-site providing results publicly online within the same night. In summer 2014, several flare alerts were issued. Results of the quick look analysis are summarized.Comment: 2014 Fermi Symposium proceedings - eConf C14102.

Calibration and performance of the photon sensor response of FACT -- The First G-APD Cherenkov telescope

The First G-APD Cherenkov Telescope (FACT) is the first in-operation test of the performance of silicon photo detectors in Cherenkov Astronomy. For more than two years it is operated on La Palma, Canary Islands (Spain), for the purpose of long-term monitoring of astrophysical sources. For this, the performance of the photo detectors is crucial and therefore has been studied in great detail. Special care has been taken for their temperature and voltage dependence implementing a correction method to keep their properties stable. Several measurements have been carried out to monitor the performance. The measurements and their results are shown, demonstrating the stability of the gain below the percent level. The resulting stability of the whole system is discussed, nicely demonstrating that silicon photo detectors are perfectly suited for the usage in Cherenkov telescopes, especially for long-term monitoring purpose