29,548 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
Positioning with stationary emitters in a two-dimensional space-time
The basic elements of the relativistic positioning systems in a
two-dimensional space-time have been introduced in a previous work [Phys. Rev.
D {\bf 73}, 084017 (2006)] where geodesic positioning systems, constituted by
two geodesic emitters, have been considered in a flat space-time. Here, we want
to show in what precise senses positioning systems allow to make {\em
relativistic gravimetry}. For this purpose, we consider stationary positioning
systems, constituted by two uniformly accelerated emitters separated by a
constant distance, in two different situations: absence of gravitational field
(Minkowski plane) and presence of a gravitational mass (Schwarzschild plane).
The physical coordinate system constituted by the electromagnetic signals
broadcasting the proper time of the emitters are the so called {\em emission
coordinates}, and we show that, in such emission coordinates, the trajectories
of the emitters in both situations, absence and presence of a gravitational
field, are identical. The interesting point is that, in spite of this fact,
particular additional information on the system or on the user allows not only
to distinguish both space-times, but also to complete the dynamical description
of emitters and user and even to measure the mass of the gravitational field.
The precise information under which these dynamical and gravimetric results may
be obtained is carefully pointed out.Comment: 14 pages; 5 figure
Two-dimensional approach to relativistic positioning systems
A relativistic positioning system is a physical realization of a coordinate
system consisting in four clocks in arbitrary motion broadcasting their proper
times. The basic elements of the relativistic positioning systems are presented
in the two-dimensional case. This simplified approach allows to explain and to
analyze the properties and interest of these new systems. The positioning
system defined by geodesic emitters in flat metric is developed in detail. The
information that the data generated by a relativistic positioning system give
on the space-time metric interval is analyzed, and the interest of these
results in gravimetry is pointed out.Comment: 11 pages, 5 figures. v2: a brief description of the principal
bibliography has been adde
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
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 theory of relativistic {\em location systems} is sketched. An interesting
class of these systems is that of relativistic {\em positioning systems,} which
consists in sets of four clocks broadcasting their proper time. Among them, the
more important ones are the {\em auto-located positioning systems,} in which
every clock broadcasts not only its proper time but the proper times that it
receives from the other three. At this level, no reference to any exterior
system (the Earth surface, for example) and no synchronization are needed. Some
properties are presented. In the SYPOR project, such a structure is proposed,
eventually anchored to a classical reference system on the Earth surface, as
the best relativistic structure for Global Navigation Satellite Systems.Comment: 8 pages; 1 figure; to appear in Proc. Spanish Relativity Meeting
ERE-2005, Oviedo (Spain); v2: minor formal change
Student teachers' perception of their role and responsibilities as Catholic educators
This article is concerned with 26 primary and secondary student teachers' early perception of themselves as Catholic educators in Scotland. It analyses their perspectives on what it means to be a Catholic teacher, what is expected of them by the Church and what motivated them to chose this particular career path. Discussion of these issues reveals an astute awareness of their role in the Catholic sector but a deep apprehension about their ability to succeed in fulfilling this. Their religious biographies and identities highlight much about the Scottish context of which they are a part, yet their responses to faith indicate differing levels of confidence in teaching, particularly with regard to the content of the Religious Education curriculum which they are expected to implement. The challenge these students present to the major stakeholders in Scottish education is to provide them with adequate support in developing their own faith - and knowledge and understanding of it - in order to enable them to carry out their role as Catholic teachers effectively within the state funded system
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