385 research outputs found
Extracting particle freeze-out phase-space densities and entropies from sources imaged in heavy-ion reactions
The space-averaged phase-space density and entropy per particle are both
fundamental observables which can be extracted from the two-particle
correlation functions measured in heavy-ion collisions. Two techniques have
been proposed to extract the densities from correlation data: either by using
the radius parameters from Gaussian fits to meson correlations or by using
source imaging, which may be applied to any like pair correlation. We show that
the imaging and Gaussian fits give the same result in the case of meson
interferometry. We discuss the concept of an equivalent instantaneous source on
which both techniques rely. We also discuss the phase-space occupancy and
entropy per particle. Finally, we propose an improved formula for the
phase-space occupancy that has a more controlled dependence on the uncertainty
of the experimentally measured source functions.Comment: 14 pages, final version, to appear PRC. Fixed typos, added refs. for
last section, added discussions of imaging and d/p ratio
Dissolved organic matter characteristics of deciduous and coniferous forests with variable management: different at the source, aligned in the soil
This dataset contains the data to the article: "Dissolved organic matter characteristics of deciduous and coniferous forests with variable management: different at the source, aligned in the soil" published in BiogeosciencesDFG/108154260/ElementkreislĂ€ufe in GrĂŒnland- und Waldökosystemen der BiodiversitĂ€tsexploratorien in AbhĂ€ngigkeit von LandnutzungsintensitĂ€t und damit verknĂŒpfter BiodiversitĂ€t/BECycle
Strange particle production at RHIC in a single-freeze-out model
Strange particle ratios and pT-spectra are calculated in a thermal model with
single freeze-out, previously used successfully to describe non-strange
particle production at RHIC. The model and the recently released data for phi,
Lambda, anti-Lambda, and K*(892) are in very satisfactory agreement, showing
that the thermal approach can be used to describe the strangeness production at
RHIC.Comment: We have added the comparison of the model predictions to the newly
released Lambda and K*(892) pT-spectra from STA
A phenomenological equation of state for isospin asymmetric nuclear matter
A phenomenological momentum-independent (MID) model is constructed to
describe the equation of state (EOS) for isospin asymmetric nuclear matter,
especially the density dependence of the nuclear symmetry energy
. This model can reasonably describe the general
properties of the EOS for symmetric nuclear matter and the symmetry energy
predicted by both the sophisticated isospin and momentum dependent MDI model
and the Skyrme-Hartree-Fock approach. We find that there exists a nicely linear
correlation between and as well as between and , where and represent, respectively, the
slope and curvature parameters of the symmetry energy at the normal nuclear
density while and are, respectively, the
incompressibility and the third-order derivative parameter of symmetric nuclear
matter at . These correlations together with the empirical
constraints on , and lead to an
estimation of -477 MeV MeV for the
second-order isospin asymmetry expansion coefficient for the incompressibility
of asymmetric nuclear matter at the saturation point.Comment: 9 pages, 4 figures, contribution to Special Topic on Large-Scale
Scientific Facilities (LSSF) in Science in China Series G: Physics, Mechanics
& Astronom
Neutral Pions and Eta Mesons as Probes of the Hadronic Fireball in Nucleus-Nucleus Collisions around 1A GeV
Chemical and thermal freeze-out of the hadronic fireball formed in symmetric
collisions of light, intermediate-mass, and heavy nuclei at beam energies
between 0.8A GeV and 2.0A GeV are discussed in terms of an equilibrated,
isospin-symmetric ideal hadron gas with grand-canonical baryon-number
conservation. For each collision system the baryochemical potential mu_B and
the chemical freeze-out temperature T_c are deduced from the inclusive neutral
pion and eta yields which are augmented by interpolated data on deuteron
production. With increasing beam energy mu_B drops from 800 MeV to 650 MeV,
while T_c rises from 55 MeV to 90 MeV. For given beam energy mu_B grows with
system size, whereas T_c remains constant. The centrality dependence of the
freeze-out parameters is weak as exemplified by the system Au+Au at 0.8A GeV.
For the highest beam energies the fraction of nucleons excited to resonance
states reaches freeze-out values of nearly 15 %, suggesting resonance densities
close to normal nuclear density at maximum compression. In contrast to the
particle yields, which convey the status at chemical freeze-out, the shapes of
the related transverse-mass spectra do reflect thermal freeze-out. The observed
thermal freeze-out temperatures T_th are equal to or slightly lower than T_c,
indicative of nearly simultaneous chemical and thermal freeze-out.Comment: 42 pages, 12 figure
Head of State of Exception
During the escalation of the âGerman Autumnâ in 1977 the Federal German government resorted to a specific form of crisis management that had been described as an undeclared state of exception. It was Federal chancellor Helmut Schmidt in the first place who oversaw the anti-terrorist measures in the situation room where the executive branch ruled for six weeks beyond any parliamentary control. This article examines the role that Helmut Schmidt had played for the creation of a âsubjective state of exceptionâ (Julius Hatschek) and how this could be seen as stemming from Schmidtâs earlier experiences and handling of crisis situations dating back to the 1960s. In this regard it has to be asked with Giorgio Agamben, if in the West German case, the state of exception had become the rule
Aspects of thermal and chemical equilibration of hadronic matter
We study thermal and chemical equilibration in 'infinite' hadron matter as
well as in finite size relativistic nucleus-nucleus collisions using a BUU
cascade transport model that contains resonance and string degrees-of-freedom.
The 'infinite' hadron matter is simulated within a cubic box with periodic
boundary conditions. The various equilibration times depend on baryon density
and energy density and are much shorter for particles consisting of light
quarks then for particles including strangeness. For kaons and antikaons the
chemical equilibration time is found to be larger than 40 fm/c for all
baryon and energy densities considered. The inclusion of continuum excitations,
i.e. hadron 'strings', leads to a limiting temperature of 150 MeV.
We, furthermore, study the expansion of a hadronic fireball after
equilibration. The slope parameters of the particles after expansion increase
with their mass; the pions leave the fireball much faster then nucleons and
accelerate subsequently heavier hadrons by rescattering ('pion wind'). If the
system before expansion is close to the limiting temperature , the slope
parameters for all particles after expansion practically do not depend on
(initial) energy and baryon density. Finally, the equilibration in relativistic
nucleus-nucleus collision is considered. Since the reaction time here is much
shorter than the equilibration time for strangeness, a chemical equilibrium of
strange particles in heavy-ion collisions is not supported by our transport
calculations. However, the various particle spectra can approximately be
described within the blast model.Comment: 39 pages, LaTeX, including 18 postscript figures, Nucl. Phys. A, in
pres
Temperatures of Exploding Nuclei
Breakup temperatures in central collisions of 197Au + 197Au at bombarding
energies E/A = 50 to 200 MeV were determined with two methods. Isotope
temperatures, deduced from double ratios of hydrogen, helium, and lithium
isotopic yields, increase monotonically with bombarding energy from 5 MeV to 12
MeV, in qualitative agreement with a scenario of chemical freeze-out after
adiabatic expansion. Excited-state temperatures, derived from yield ratios of
states in 4He, 5Li, 6Li, and 8Be, are about 5 MeV, independent of the
projectile energy, and seem to reflect the internal temperature of fragments at
their final separation from the system.
PACS numbers: 25.70.Mn, 25.70.Pq, 25.75.-qComment: 10 pages, RevTeX with 4 included figures; Also available from
http://www-kp3.gsi.de/www/kp3/aladin_publications.htm
Key components of learning ecologies: a Delphi assessment
This is the accepted version of the following article: GonzĂĄlezâSanmamed, M. , MuñozâCarril, P. and SantosâCaamaño, F. (2019), Key components of learning ecologies: A Delphi assessment. Br J Educ Technol, 50: 1639-1655, which has been published in final form at https://doi.org/10.1111/bjet.12805. This article may be used for
non-commercial purposes in accordance with the Wiley Self-Archiving Policy (http://www.wileyauthors.com/self-archiving)The educational landscape has changed in recent years, requiring reflection about new pedagogical methods and theories. There are three important perspectives as drivers of pedagogical reflection: lifelong and lifeâwide learning, the idea of learning as a social construct in which internal elements and changing external factors converge, and the recognition of technology as a resource that can promote ubiquitous and expanded learning. Learning ecology has been proposed as a conceptual and empirical framework, but its still emergent nature along with its multidimensionality and complexity require further exploration. The Delphi study we present as part of a broader research project aims to identify the components of learning ecologies. Three panel rounds with international experts were carried out, after which two important dimensions emerged in the structure of learning ecologies. The first is related to intrinsic âlearning dispositions,â which is made up of three categories: the subject's ideas about learning, their motivations and expectations. The second dimension, called âlearning processes,â comprises four components: relationships, resources, actions and context. The identification of the components of learning ecologies and their influence on formal, nonâformal and informal training processes will provide guidance for educational policies and help to better organize training programmesWe thank the Spanish Ministry of Economy and Competitiveness for their support of our study under a research project entitled âHow the best University Teachers Learn: Impact on Learning Ecologies on Quality of Teachingâ (ECO4LEARNâHE) (Reference: EDU2015â67907âR)S
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