System size dependence of strangeness production at 158 AGeV

Strange particle production in A+A interactions at 158 AGeV is studied by the CERN experiment NA49 as a function of system size and collision geometry. Yields of charged kaons, phi and Lambda are measured and compared to those of pions in central C+C, Si+Si and centrality-selected Pb+Pb reactions. An overall increase of relative strangeness production with the size of the system is observed which does not scale with the number of participants. Arguing that rescattering of secondaries plays a minor role in small systems the observed strangeness enhancement can be related to the space-time density of the primary nucleon-nucleon collisions

System-size dependence of strangeness production in high-energy A+A collisions and percolation of strings

We argue that the shape of the system-size dependence of strangeness production in nucleus-nucleus collisions can be understood in a picture that is based on the formation of clusters of overlapping strings. A string percolation model combined with a statistical description of the hadronization yields a quantitative agreement with the data at sqrt s_NN = 17.3 GeV. The model is also applied to RHIC energies

Wie viel Struktur benötigt ein Wiki? Fallbeispiel wikibasiertes Intranet

Sowohl für Wissenswikis als auch Intranetwikis sind folgende Leitfragen zu klären: Wie und wer definiert die Inhaltsstruktur für das Enterprise Wiki? Wie kann der Nutzer selbst einen Überblick behalten und sicherstellen, dass die relevanten Informationen ankommen? Die Inhalte eines Wikis sind nicht unstrukturiert! Die Anwender bilden eine gewisse Struktur über Schlagworte und Seitenhierarchien. Zusätzlich bringt eine Gliederung in Wiki-Bereichen die notwendige Erststruktur und die erstellte Inhaltsübersichten die notwendige Transparenz

Auf der Suche nach dem Innersten der Welt : HIC for FAIR schafft Grundlagen für ein einmaliges Forschungszentrum

Die Eigenschaften der innersten Bausteine der Materie untersuchen in aufwendigen Experimenten Wissenschaftler am künftigen internationalen Forschungszentrum FAIR (Facility for Antiproton and Ion Research) in Darmstadt. Das von der Hessischen Landesregierung im Rahmen der Landes-Offensive zur Entwicklung Wissenschaftlich-ökonomischer Exzellenz (LOEWE) geförderte Exzellenzzentrum „HIC for FAIR“ (Helmholtz International Center for FAIR) macht die Physiker der Universität Gießen zu wichtigen Partnern in dem weltweit einmaligen Projekt auf der Suche nach der elementaren Struktur der Materie

Racial Profiling: Erfahrung, Wirkung, Widerstand

Racial Profiling ist eine diskriminierende und rechtswidrige polizeiliche Praxis, die nur wenig öffentliche Beachtung findet. Im Zentrum der Studie der Kollaborativen Forschungsgruppe Racial Profiling stehen Menschen in der Schweiz, für die rassistische Polizeikontrollen zum Alltag gehören. Hierzu führten wir Interviews mit Personen, die sich selbst als Schwarze*r, Person of Color, Jenische*r, Sinto*Sintezza, Rom*ni, Muslim*in, Asiat*in oder als Migrant*in bezeichnen sowie als Sexarbeiterin tätig sind. Sie alle sind von ähnlichen Formen der Kriminalisierung betroffen, unterliegen jedoch auch spezifischen polizeilichen Praktiken – je nach Geschlecht, Aufenthaltsstatus, Staatsangehörigkeit und sozioökonomischem Status. Neben den konkreten Erlebnissen kommen auch die Folgen und Wirkungen der Kontrollen für die Kontrollierten, betroffene Communitys sowie die Gesellschaft zur Sprache. Thematisiert werden zudem verschiedene Taktiken im Umgang mit der ständigen Gefahr, ins Visier der Polizei zu geraten sowie Strategien, um sich individuell, aber auch kollektiv gegen diese rassistische Praxis zur Wehr zu setzen

System size and centrality dependence of the balance function in A+A collisions at sqrt[sNN]=17.2 GeV

Electric charge correlations were studied for p+p, C+C, Si+Si, and centrality selected Pb+Pb collisions at sqrt[sNN]=17.2 GeV with the NA49 large acceptance detector at the CERN SPS. In particular, long-range pseudorapidity correlations of oppositely charged particles were measured using the balance function method. The width of the balance function decreases with increasing system size and centrality of the reactions. This decrease could be related to an increasing delay of hadronization in central Pb+Pb collisions

System size and centrality dependence of the balance function in A + A collisions at sqrt s NN = 17.2 GeV

Electric charge correlations were studied for p+p, C+C, Si+Si and centrality selected Pb+Pb collisions at sqrt s_NN = 17.2$ GeV with the NA49 large acceptance detector at the CERN-SPS. In particular, long range pseudo-rapidity correlations of oppositely charged particles were measured using the Balance Function method. The width of the Balance Function decreases with increasing system size and centrality of the reactions. This decrease could be related to an increasing delay of hadronization in central Pb+Pb collisions

Is the Hyporheic Zone Relevant beyond the Scientific Community?

Rivers are important ecosystems under continuous anthropogenic stresses. The hyporheic zone is a ubiquitous, reactive interface between the main channel and its surrounding sediments along the river network. We elaborate on the main physical, biological, and biogeochemical drivers and processes within the hyporheic zone that have been studied by multiple scientific disciplines for almost half a century. These previous efforts have shown that the hyporheic zone is a modulator for most metabolic stream processes and serves as a refuge and habitat for a diverse range of aquatic organisms. It also exerts a major control on river water quality by increasing the contact time with reactive environments, which in turn results in retention and transformation of nutrients, trace organic compounds, fine suspended particles, and microplastics, among others. The paper showcases the critical importance of hyporheic zones, both from a scientific and an applied perspective, and their role in ecosystem services to answer the question of the manuscript title. It identifies major research gaps in our understanding of hyporheic processes. In conclusion, we highlight the potential of hyporheic restoration to efficiently manage and reactivate ecosystem functions and services in river corridors

Insights into the high-energy γ-ray emission of Markarian 501 from extensive multifrequency observations in the Fermi era

We report on the γ-ray activity of the blazar Mrk 501 during the first 480 days of Fermi operation. We find that the average Large Area Telescope (LAT) γ-ray spectrum of Mrk 501 can be well described by a single power-law function with a photon index of 1.78 ± 0.03. While we observe relatively mild flux variations with the Fermi-LAT (within less than a factor of two), we detect remarkable spectral variability where the hardest observed spectral index within the LAT energy range is 1.52 ± 0.14, and the softest one is 2.51 ± 0.20. These unexpected spectral changes do not correlate with the measured flux variations above 0.3 GeV. In this paper, we also present the first results from the 4.5 month long multifrequency campaign (2009 March 15-August 1) on Mrk 501, which included the Very Long Baseline Array (VLBA), Swift, RXTE, MAGIC, and VERITAS, the F-GAMMA, GASP-WEBT, and other collaborations and instruments which provided excellent temporal and energy coverage of the source throughout the entire campaign. The extensive radio to TeV data set from this campaign provides us with the most detailed spectral energy distribution yet collected for this source during its relatively low activity. The average spectral energy distribution of Mrk 501 is well described by the standard one-zone synchrotron self-Compton (SSC) model. In the framework of this model, we find that the dominant emission region is characterized by a size ≲0.1 pc (comparable within a factor of few to the size of the partially resolved VLBA core at 15-43 GHz), and that the total jet power (≃1044 erg s-1) constitutes only a small fraction (∼10-3) of the Eddington luminosity. The energy distribution of the freshly accelerated radiating electrons required to fit the time-averaged data has a broken power-law form in the energy range 0.3 GeV-10 TeV, with spectral indices 2.2 and 2.7 below and above the break energy of 20 GeV. We argue that such a form is consistent with a scenario in which the bulk of the energy dissipation within the dominant emission zone of Mrk 501 is due to relativistic, proton-mediated shocks. We find that the ultrarelativistic electrons and mildly relativistic protons within the blazar zone, if comparable in number, are in approximate energy equipartition, with their energy dominating the jet magnetic field energy by about two orders of magnitude. © 2011. The American Astronomical Society

System-Size Dependence of Strangeness Production in Heavy-Ion Collisions at 158 AGeV

Strangeness enhancement in A+A collisions relative to p+p interactions as a signal for the transition to a deconfined state of strongly interacting matter was recently searched for mostly in high-energy collisions of heavy nuclei such as central Pb+Pb or Au+Au. The expectation is that in these large systems with about 360 participating nucleons such a transition is more likely because of a longer lifetime and higher energy density. However, earlier studies with lighter beams had demonstrated that already in S+S with 54 participants strangeness is significantly enhanced. In this work strange-particle production is studied as function of system size in symmetric central A+A collisions at 158 AGeV. Using the NA49 spectrometer at the CERN-SPS, yields and kinematic distributions of kaons, K*(892), the phi-meson and, for reference purposes, also of pions are measured in minimum-bias and inelasticity-selected p+p interactions, and in central C+C and Si+Si collisions. Together with earlier data for central S+S and Pb+Pb the results present a complete picture of the evolution of strangeness enhancement as function of system size. The data show a continuous increase of the strange-particle abundances in dependence on system size, with a fast rise in small systems and a saturation already for about 60 participating nucleons if comparing central A+A collisions only. On the basis of the present data and using microscopic models for A+A collisions an attempt is made to localize the origin of strangeness enhancement and to understand its evolution. For several reasons, rescattering is found to be an unlikely explanation, in particular for the lighter systems. The idea that the high string excitations - obtained in A+A collisions as a consequence of sequential N+N interactions - are responsible is dismissed on the basis of inelasticity-controlled p+p data. On the other hand, the geometry dependence indicated by a comparison of the central A+A data with those for peripheral Pb+Pb suggests that the density of the primary inelastic interactions in space-time plays a decisive role, because it is found to act as a scaling variable for the strangeness enhancement in all systems. The final conclusion of this work is that a high collision density leads to formation of coherent partonic (sub-)systems comprising several strings whose hadronization can be described statistically. Then, these systems and/or their hadronization must be subject to the phenomenon of canonical strangeness suppression respectively of grand-canonical strangeness enhancement. This would explain both the strangeness enhancement itself and its system-size dependence