140 research outputs found
Leading Effects in the Spectra of and Produced in , and Interactions
The spectra of leading and nonleading charmed baryons ( and
) as well as the asymmetries between these spectra measured in
, and pA collisions at in the E781
experiment are simultaneously described within the framework of Quark-Gluon
String Model (QGSM). It is shown that the charmed baryon spectra can be fitted
by QGSM curves calculated with the parameter of diquark fragmentation,
=0.006. It was obtained in this experiment that the asymmetry
between the spectra of and in collisions
is of nonzero value. It might be described in our model only assuming that the
string junction is transfered from target proton into the kinematical region of
pion projectile fragmentation.Comment: LaTeX, 12 pages, 2 epsfigures, replaced with the minor corrections in
language and in references, submitted to Phys.At.Nucl. 200
Individualisations citadines et développement d'une société civile : Abidjan et Dakar : rapport de recherche
Baryon charge transfer and production asymmetry between Lambda^0 and antiLambda^0 in hadron interactions
The predictions were done for asymmetry between production spectra of
Lambda^0 and antiLambda^0 at the energy of LHC experiments. The value of A(s)
should be situated in the band between two curves that are calculated in
Quark-Gluon String Model with two possible values of intercept
alpha_{SJ}(0)=0,5 and 0,9. Both curves describe the asymmetries measured at
lower energies up to RHIC experiments. The data of H1 experiment can be fitted
only with alpha_{SJ}(0)=0,9.Comment: LateX, 7 pages and 2 figures, poster presentation at PANIC'05, Santa
Fe, October 200
Analyse du polymorphisme de Plasmodium falciparum et de ses vecteurs Anopheles gambiae, An.arabiensis, An. funestus : rôle dans la pathogénicité du paludisme dans 2 stations du Sénégal
The broken cycle : universities, research and society in the Arab region : proposal for change
Neutrino Physics at the Turn of the Millenium
Recent solar & atmospheric nu-data strongly indicate need for physics beyond
the Standard Model. I review the ways of reconciling them in terms of 3-nu
oscillations. Though not implied by data, bi-maximal nu-mixing models emerge as
a possibility. SUSY with broken R-parity provides an attractive way to
incorporate it, opening the possibility of testing nu-anomalies at high- energy
colliders such as the LHC or at the upcoming long-baseline or nu- factory
experiments. Reconciling, in addition, the LSND hint requires a fourth, light
sterile neutrino, nus. The simplest are the most symmetric scenarios, in which
2 of the 4 neutrinos are maximally-mixed and lie at the LSND scale, while the
others are at the solar scale. The lightness of nus, the nearly maximal
atmospheric mixing, and the solar/atmospheric splittings all follow naturally
from the assumed lepton-number symmetry and its breaking. These basic schemes
can be distinguished at neutral-current-sensitive solar & atmospheric neutrino
experiments such as SNO. However underground experiments have not yet proven
neutrino masses, as there are many alternatives. For example flavour changing
interactions can play an important role in the explanation of solar and
contained atmospheric data and could be tested e.g through \mu \to e + \gamma,
\mu-e conversion in nuclei, unaccompanied by neutrino-less double beta decay.
Conversely, a short-lived numu might play a role in the explanation of the
atmospheric data. Finally, in the presence of a nus, a long-lived heavy nutau
could delay the time at which the matter and radiation contributions to the
energy density of the Universe become equal, reducing density fluctuations on
smaller scales, thus saving the standard CDM scenario, while the light nue,
numu and nus would explain the solar & atmospheric data.Comment: Invited talk at 2nd International Conference on Non-Accelerator New
Physics (NANP-99), Dubna, June 28 - July 3, 199
Catalogue des habitats forestiers de Guyane
Grâce à de nombreux efforts de prospections et d'inventaires naturalistes, la biodiversité guyanaise est de mieux en mieux connue et les listes d'espèces nouvelles ne cessent de s'allonger années après années. Cependant l'écosystème forestier ne se résume pas à une juxtaposition d'individus et d'espèces : de complexes relations interspécifiques régissent le fonctionnement des communautés qui sont elles-mêmes influencées par les conditions environnementales. dans lesquelles elles se développent. Gérer et conserver la biodiversité guyanaise implique de mieux cerner ces interactions entre faune, flore et environnement ; interactions qui façonnent toute une diversité d'habitats forestiers avec des dynamiques propres et des compositions originales. Plusieurs programmes de recherche se sont attelés à démêler cet écheveau écologique en se concentrant tout d'abord sur quelques plateformes scientifiques (Paracou, Nouragues, Piste de Saint-Elie) puis en élargissant la focale à l'ensemble de notre territoire sous l'impulsion des gestionnaires publics et des associations naturalistes guyanaises (programmes de recherche DIME, ECOTROP, HABITATS, etc.). Ce catalogue des habitats forestiers présente une synthèse de ces résultats sous la forme de fiches descriptives dressant un portrait précis des différents habitats naturels rencontrés en forêt guyanaise et des mécanismes qui les ont peu à peu façonnés. Un travail collectif important a été accompli pour fournir des éléments précis concernant les cortèges de grande faune, les peuplements d'arbres qui les abritent et la qualité des sols qui les supportent
Space-based research in fundamental physics and quantum technologies
Space-based experiments today can uniquely address important questions
related to the fundamental laws of Nature. In particular, high-accuracy physics
experiments in space can test relativistic gravity and probe the physics beyond
the Standard Model; they can perform direct detection of gravitational waves
and are naturally suited for precision investigations in cosmology and
astroparticle physics. In addition, atomic physics has recently shown
substantial progress in the development of optical clocks and atom
interferometers. If placed in space, these instruments could turn into powerful
high-resolution quantum sensors greatly benefiting fundamental physics.
We discuss the current status of space-based research in fundamental physics,
its discovery potential, and its importance for modern science. We offer a set
of recommendations to be considered by the upcoming National Academy of
Sciences' Decadal Survey in Astronomy and Astrophysics. In our opinion, the
Decadal Survey should include space-based research in fundamental physics as
one of its focus areas. We recommend establishing an Astronomy and Astrophysics
Advisory Committee's interagency ``Fundamental Physics Task Force'' to assess
the status of both ground- and space-based efforts in the field, to identify
the most important objectives, and to suggest the best ways to organize the
work of several federal agencies involved. We also recommend establishing a new
NASA-led interagency program in fundamental physics that will consolidate new
technologies, prepare key instruments for future space missions, and build a
strong scientific and engineering community. Our goal is to expand NASA's
science objectives in space by including ``laboratory research in fundamental
physics'' as an element in agency's ongoing space research efforts.Comment: a white paper, revtex, 27 pages, updated bibliograph
- …