1,723 research outputs found
Semihard Interactions in Nuclear Collisions Based on a Unified Approach to High Energy Scattering
Our ultimate goal is the construction of a model for interactions of two
nuclei in the energy range between several tens of GeV up to several TeV per
nucleon in the centre-of-mass system. Such nuclear collisions are very complex,
being composed of many components, and therefore some strategy is needed to
construct a reliable model. The central point of our approach is the
hypothesis, that the behavior of high energy interactions is universal
(universality hypothesis). So, for example, the hadronization of partons in
nuclear interactions follows the same rules as the one in electron-positron
annihilation; the radiation of off-shell partons in nuclear collisions is based
on the same principles as the one in deep inelastic scattering. We construct a
model for nuclear interactions in a modular fashion. The individual modules,
based on the universality hypothesis, are identified as building blocks for
more elementary interactions (like e^+ e^-, lepton-proton), and can therefore
be studied in a much simpler context. With these building blocks under control,
we can provide a quite reliable model for nucleus-nucleus scattering, providing
in particular very useful tests for the complicated numerical procedures using
Monte Carlo techniques.Comment: 10 pages, no figures; Proc. of the ``Workshop on Nuclear Matter in
Different Phases and Transitions'', Les Houches, France, March 31 - April 10,
199
Self-Consistency Requirement in High-Energy Nuclear Scattering
Practically all serious calculations of exclusive particle production in
ultra-relativistic nuclear or hadronic interactions are performed in the
framework of Gribov-Regge theory or the eikonalized parton model scheme.
It is the purpose of this paper to point out serious inconsistencies in the
above-mentioned approaches.
We will demonstrate that requiring theoretical self-consistency reduces the
freedom in modeling high energy nuclear scattering enormously.
We will introduce a fully self-consistent formulation of the
multiple-scattering scheme in the framework of a Gribov-Regge type effective
theory.
In addition, we develop new computational techniques which allow for the
first time a satisfactory solution of the problem in the sense that calculation
s of observable quantities can be done strictly within a self-consistent
formalism.Comment: 7 pages, 6 figure
Relationships between threshold-based PROP sensitivity and food preferences of Tunisians
International audienceThe extent to which taste responses - and notably the genetically determined sensitivity to 6-npropylthiouracil (PROP) - influences food preferences and food use is still a matter of debate. We addressed the issue on the basis of a behavioural and anthropological study performed in Tunis in 1999. The working sample consists of 123 adults of both sexes (38 men, 85 women), aged 19 to 59, in various social categories. Taste recognition thresholds for sucrose, fructose, sodium chloride, quinine hydrochloride, citric acid, tannic acid, oak tannin and PROP were determined by presenting, in a semi-randomised order (blind-test), series of graded aqueous solutions of each product. Subjects also tasted and rated the pleasantness/unpleasantness of 4 supra-threshold solutions of NaCl and sucrose. All subjects completed a checklist of 43 food items representative of Tunisian diet, rated in terms of flavour, cost, effect on health and prestige on a Labelled Affective Magnitude (LAM) scale. According to the underlying distribution of PROP thresholds, the subjects were separated into three categories: "non-tasters", "medium-threshold tasters", and "low-threshold tasters". Results bring out the specificity of low-threshold tasters, as exhibiting a greater taste sensitivity for most tested substances. Low-threshold taster status is also linked to higher mean food preferences ratings irrespective of sex, age and socio-cultural influences. Tasters as a group (medium-threshold tasters + low-threshold tasters) do not exhibit a higher percentage of food dislikes; however PROP sensitivity is negatively correlated with hedonic responses to NaCl solutions. These results together with the evidence of a limited set of food actually used by low-threshold tasters suggest that these subjects might have difficulties at overcoming an inherent neophobia
Parton-Based Gribov-Regge Theory
We present a new parton model approach for hadron-hadron interactions and, in particular, for the initial stage of nuclear collisions at very high energies (RHIC, LHC and beyond). The most important aspect of our approach is a self-consistent treatment, using the same formalism for calculating cross sections and particle production, based on an effective, QCD-inspired field theory, where many of the inconsistencies of presently used models will be avoided. In addition, we provide a unified treatment of soft and hard scattering, such that there is no fundamental cutoff parameter any more defining an artificial border between soft and hard scattering. Our approach cures some of the main deficiencies of two of the standard procedures currently used: the Gribov-Regge theory and the eikonalized parton model. There, cross section calculations and particle production cannot be treated in a consistent way using a common formalism. In particular, energy conservation is taken care of in case of particle production, but not concerning cross section calculations. In addition, hard contributions depend crucially on some cutoff, being divergent for the cutoff being zero. Finally, in case of several elementary scatterings, they are not treated on the same level: the first collision is always treated differently than the subsequent ones. All these problems are solved in our new approach
A Polynomial Translation from the Two-Variable Guarded Fragment with Number Restrictions to the Guarded Fragment
We consider a two-variable guarded fragment with number restrictions for binary relations and give a satisfiability preserving transformation of formulas in this fragment to the three-variable guarded fragment. The translation can be computed in polynomial time and produces a formula that is linear in the size of the initial formula even for the binary coding of number restrictions. This allows one to reduce reasoning problems for many description logics to the satisfiability problem for the guarded fragment
Environmental risks and challenges associated with neonicotinoid insecticides
Neonicotinoid use has increased rapidly in recent years, with a global shift toward insecticide applications as seed coatings rather than aerial spraying. While the use of seed coatings can lessen the amount of overspray and drift, the near universal and prophylactic use of neonicotinoid seed coatings on major agricultural crops has led to widespread detections in the environment (pollen, soil, water, honey). Pollinators and aquatic insects appear to be especially susceptible to the effects of neonicotinoids with current research suggesting that chronic sublethal effects are more prevalent than acute toxicity. Meanwhile, evidence of clear and consistent yield benefits from the use of neonicotinoids remains elusive for most crops. Future decisions on neonicotinoid use will benefit from weighing crop yield benefits versus environmental impacts to nontarget organisms and considering whether there are more environmentally benign alternatives
Conservation et introduction de lémuriens sur l'ßlot Mbouzy (Mayotte)
Ă Mayotte, l'Ăźlot Mbouzi est un lieu remarquable par son milieu naturel en grande partie prĂ©servĂ©, alors qu'il se situe Ă proximitĂ© de la ville principale, Mamoudzou. Il fait l'objet d'une demande de classement en rĂ©serve naturelle. Nous pensons utile d'apporter quelques Ă©lĂ©ments pouvant servir Ă la rĂ©flexion sur l'avenir de cet Ăźlot, et d'Ă©tablir une sorte d'Ă©tat des lieux concernant son intĂ©rĂȘt biologique. Quelles sont les possibilitĂ©s d'Ă©quilibre Ă long terme entre les populations animales et vĂ©gĂ©tales, sachant qu'une association (loi de 1901) consacr
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