4,868 research outputs found
Thermal hadron production in high energy collisions
It is shown that hadron abundances in high energy e+e-, pp and p{\bar p}
collisions, calculated by assuming that particles originate in hadron gas
fireballs at thermal and partial chemical equilibrium, are in very good
agreement with the data. The freeze-out temperature of the hadron gas fireballs
turns out to be nearly constant over a large center of mass energy range and
not dependent on the initial colliding system. The only deviation from chemical
equilibrium resides in the incomplete strangeness phase space saturation.
Preliminary results of an analysis of hadron abundances in S+S and S+Ag heavy
ion collisions are presented.Comment: 10 pages, 1 .eps figure, talk given at the Strangeness and Quark
Matter 97 conferenc
Relativistic positioning: four-dimensional numerical approach in Minkowski space-time
We simulate the satellite constellations of two Global Navigation Satellite
Systems: Galileo (EU) and GPS (USA). Satellite motions are described in the
Schwarzschild space-time produced by an idealized spherically symmetric non
rotating Earth. The trajectories are then circumferences centered at the same
point as Earth. Photon motions are described in Minkowski space-time, where
there is a well known relation, Coll, Ferrando & Morales-Lladosa (2010),
between the emission and inertial coordinates of any event. Here, this relation
is implemented in a numerical code, which is tested and applied. The first
application is a detailed numerical four-dimensional analysis of the so-called
emission coordinate region and co-region. In a second application, a GPS
(Galileo) satellite is considered as the receiver and its emission coordinates
are given by four Galileo (GPS) satellites. The bifurcation problem (double
localization) in the positioning of the receiver satellite is then pointed out
and discussed in detail.Comment: 16 pages, 9 figures, published (online) in Astrophys. Space Sc
Relativistic Positioning Systems: The Emission Coordinates
This paper introduces some general properties of the gravitational metric and
the natural basis of vectors and covectors in 4-dimensional emission
coordinates. Emission coordinates are a class of space-time coordinates defined
and generated by 4 emitters (satellites) broadcasting their proper time by
means of electromagnetic signals. They are a constitutive ingredient of the
simplest conceivable relativistic positioning systems. Their study is aimed to
develop a theory of these positioning systems, based on the framework and
concepts of general relativity, as opposed to introducing `relativistic
effects' in a classical framework. In particular, we characterize the causal
character of the coordinate vectors, covectors and 2-planes, which are of an
unusual type. We obtain the inequality conditions for the contravariant metric
to be Lorentzian, and the non-trivial and unexpected identities satisfied by
the angles formed by each pair of natural vectors. We also prove that the
metric can be naturally split in such a way that there appear 2 parameters
(scalar functions) dependent exclusively on the trajectory of the emitters,
hence independent of the time broadcast, and 4 parameters, one for each
emitter, scaling linearly with the time broadcast by the corresponding
satellite, hence independent of the others.Comment: 13 pages, 3 figures. Only format changed for a new submission.
Submitted to Class. Quantum Gra
Investigating scientific literacy: Scientistâs habits of mind as evidenced by their rationale of science and religious beliefs
Science and technology have been incredibly successÂŹful in purely technical terms. For instance, international air travel, space flight, and curing of hitherto untreatable medical illnesses all are now routine events. One feature of the incredible (and seemingly ever increasing) advance of science and technology is a sense of unease amongst the general population of scienceâs potential to change our lives, in sometimes unpredictable and alarming ways. Public understanding of science, or scientific literacy, is of increasing concern worldwide according to much recent literature
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Evaluation of an urban NMHC emission inventory by measurements and impact on CTM results
This paper presents an evaluation of the consistency of an urban state-of-the-art hydrocarbon (HC) emission inventory. The evaluation was conducted through the comparison of this inventory with hourly HC measurements during two summer months in the centre of Marseille, on the Mediterranean French coast. Factors of under or overestimation could be calculated for each compound on the basis of a systematic HC to HC ratio analysis. These results, associated with a deep analysis of the speciation profiles, show that most of the common and highly concentrated hydrocarbons (such as butanes) are too much predominant in the emission speciation, while the heavy and less common species (branched alkanes, substituted aromatics) are under-represented in the inventory. The urban diffuse sources appear here as one critical point of the inventories. The disagreements were shown to have a strong incidence on the representation of the air mass reactivity. In a last step, the identified uncertainties in emissions were implemented in an air-quality model for sensitivity studies. It was shown that the observed biases in the inventory could affect the regional ozone production, with a probable impact on ozone peaks of 2-10 ppbv over the area. © 2010 Elsevier Ltd
Local thermal equilibrium and ideal gas Stephani universes
The Stephani universes that can be interpreted as an ideal gas evolving in
local thermal equilibrium are determined. Five classes of thermodynamic schemes
are admissible, which give rise to five classes of regular models and three
classes of singular models. No Stephani universes exist representing an exact
solution to a classical ideal gas (one for which the internal energy is
proportional to the temperature). But some Stephani universes may approximate a
classical ideal gas at first order in the temperature: all of them are
obtained. Finally, some features about the physical behavior of the models are
pointed out.Comment: 20 page
Medium-modified average multiplicity and multiplicity fluctuations in jets
The energy evolution of average multiplicities and multiplicity fluctuations
in jets produced in heavy-ion collisions is investigated from a toy
QCD-inspired model. In this model, we use modified splitting functions
accounting for medium-enhanced radiation of gluons by a fast parton which
propagates through the quark gluon plasma. The leading contribution of the
standard production of soft hadrons is enhanced by a factor while
next-to-leading order (NLO) corrections are suppressed by , where
the parameter accounts for the induced-soft gluons in the medium. Our
results for such global observables are cross-checked and compared with their
limits in the vacuum.Comment: 8 pages and 4 figures. Version to be published in EPJ
El projecte Almirall a Cercles
El Projecte Almirall. Pensament i cultura del segle XIX neix per explicar la importĂ ncia del fons bibliogrĂ fic de la Biblioteca de lâAteneu BarcelonĂšs com a eina per entendre la recepciĂł dels corrents europeus del pensament, humanĂstic i cientĂfic en la societat catalana i espanyola de finals del Vuit-cents. AixĂČ Ă©s possible perquĂš lâAteneu BarcelonĂšs era el lloc on els intel·lectuals i els escriptors catalans podien llegir revistes i llibres europeus amb les Ășltimes novetats en els diferents camps del coneixement. Dâaquesta manera, en podien resumir les tesis en els diaris i en la premsa catalana, actuant aixĂ de vertaders intermediaris culturals dâaquestes idees. Avui en dia, i grĂ cies a la progressiva digitalitzaciĂł del fons bibliogrĂ fic, el Projecte Almirall ens permet de reconstruir la recepciĂł dâaquests corrents culturals dâuna manera matisadaThe Almirall Project: a portal of 19th-century culture and thinking was created to explain the importance of the collection of the Barcelona Athenaeum Library as a tool to understand the reception of European currents of thought, humanities and science in Catalan and Spanish society in the late nineteenth century. This is possible because the Barcelona Athenaeum was the place where Catalan intellectuals and writers could read European magazines and books about the latest developments in the various fields of knowledge. In this way, they were able to summarize the arguments in the Catalan newspapers and press, thereby acting as true cultural intermediaries of these ideas. Today, thanks to the progressive digitization of the bibliographic collection, Project Almirall allows us to reconstruct the reception of these cultural currents in a nuanced wa
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