174 research outputs found

    Explicit Model Realizing Parton-Hadron Duality

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    We present a model that realizes both resonance-Regge (Veneziano) and parton-hadron (Bloom-Gilman) duality. We first review the features of the Veneziano model and we discuss how parton-hadron duality appears in the Bloom-Gilman model. Then we review limitations of the Veneziano model, namely that the zero-width resonances in the Veneziano model violate unitarity and Mandelstam analyticity. We discuss how such problems are alleviated in models that construct dual amplitudes with Mandelstam analyticity (so-called DAMA models). We then introduce a modified DAMA model, and we discuss its properties. We present a pedagogical model for dual amplitudes and we construct the nucleon structure function F2(x,Q2). We explicitly show that the resulting structure function realizes both Veneziano and Bloom-Gilman duality.Comment: 11 pages, 8 figure

    Color separate singlets in e+ee^+e^- annihilation

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    We use the method of color effective Hamiltonian to study the properties of states in which a gluonic subsystem forms a color singlet, and we will study the possibility that such a subsystem hadronizes as a separate unit. A parton system can normally be subdivided into singlet subsystems in many different ways, and one problem arises from the fact that the corresponding states are not orthogonal. We show that if only contributions of order 1/Nc21/N_c^2 are included, the problem is greatly simplified. Only a very limited number of states are possible, and we present an orthogonalization procedure for these states. The result is simple and intuitive and could give an estimate of the possibility to produce color separated gluonic subsystems, if no dynamical effects are important. We also study with a simple MC the possibility that configurations which correspond to "short strings" are dynamically favored. The advantage of our approach over more elaborate models is its simplicity, which makes it easier to estimate color reconnection effects in reactions which are more complicated than the relatively simple e+ee^+e^- annihilation.Comment: Revtex, 24 pages, 7 figures; Compared to the previous version, 1 new figure is added and Monte-Carlo results are re-analyzed, as suggested by the referee; To appear in Phys. Rev.

    Inequalities of quality of life in unemployed young adults: A population-based questionnaire study

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    BACKGROUND: It is well known that unemployment is a great problem both to the exposed individual and to the whole society. Unemployment is reported as more common among young people compared to the general level of unemployment. Inequity in health status and life-satisfaction is related to unemployment. The purpose of this population-based study was to describe QOL among unemployed young people compared to those who are not unemployed, and to analyse variables related to QOL for the respective groups. METHODS: The sample consisted of 264 young unemployed individuals and 528 working or studying individuals as a reference group. They all received a questionnaire about civil status, educational level, immigration, employment status, self-reported health, self-esteem, social support, social network, spare time, dwelling, economy and personal characteristics. The response rate was 72%. The significance of differences between proportions was tested by Fisher's exact test or by χ(2 )test. Multivariate analysis was carried out by means of a logistic regression model. RESULTS: Our results balance the predominant picture of youth unemployment as a principally negative experience. Although the unemployed reported lower levels of QOL than the reference group, a majority of unemployed young adults reported good QOL, and 24% even experienced higher QOL after being unemployed. Positive QOL related not only to good health, but also to high self-esteem, satisfaction with spare time and broad latitude for decision-making. CONCLUSION: Even if QOL is good among a majority of unemployed young adults, inequalities in QOL were demonstrated. To create more equity in health, individuals who report reduced subjective health, especially anxiety need extra attention and support. Efforts should aim at empowering unemployed young adults by identifying their concerns and resources, and by creating individual programmes in relation not only to education and work, but also to personal development

    PYTHIA 6.4 Physics and Manual

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    The PYTHIA program can be used to generate high-energy-physics `events', i.e. sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide as accurate as possible a representation of event properties in a wide range of reactions, within and beyond the Standard Model, with emphasis on those where strong interactions play a role, directly or indirectly, and therefore multihadronic final states are produced. The physics is then not understood well enough to give an exact description; instead the program has to be based on a combination of analytical results and various QCD-based models. This physics input is summarized here, for areas such as hard subprocesses, initial- and final-state parton showers, underlying events and beam remnants, fragmentation and decays, and much more. Furthermore, extensive information is provided on all program elements: subroutines and functions, switches and parameters, and particle and process data. This should allow the user to tailor the generation task to the topics of interest.Comment: 576 pages, no figures, uses JHEP3.cls. The code and further information may be found on the PYTHIA web page: http://www.thep.lu.se/~torbjorn/Pythia.html Changes in version 2: Mistakenly deleted section heading for "Physics Processes" reinserted, affecting section numbering. Minor updates to take into account referee comments and new colour reconnection option

    A model for net-baryon rapidity distribution

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    In nuclear collisions, a sizable fraction of the available energy is carried away by baryons. As the baryon number is conserved, the net-baryon BBˉB-\bar{B} retains information on the energy-momentum carried by the incoming nuclei. A simple and consistent model for net-baryon production in high energy proton-proton and nucleus-nucleus collisions is presented. The basic ingredients of the model are valence string formation based on standard PDFs with QCD evolution and string fragmentation via the Schwinger mechanism. The results of the model are presented and compared with data at different centre-of-mass energies and centralities, as well as with existing models. These results show that a good description of the main features of net-baryon data is possible in the framework of a simplistic model, with the advantage of making the fundamental production mechanisms manifest.Comment: 9 pages, 12 figures; in fig. 11 a) the vertical scale was correcte

    Pulsatile blood flow, shear force, energy dissipation and Murray's Law

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    BACKGROUND: Murray's Law states that, when a parent blood vessel branches into daughter vessels, the cube of the radius of the parent vessel is equal to the sum of the cubes of the radii of daughter blood vessels. Murray derived this law by defining a cost function that is the sum of the energy cost of the blood in a vessel and the energy cost of pumping blood through the vessel. The cost is minimized when vessel radii are consistent with Murray's Law. This law has also been derived from the hypothesis that the shear force of moving blood on the inner walls of vessels is constant throughout the vascular system. However, this derivation, like Murray's earlier derivation, is based on the assumption of constant blood flow. METHODS: To determine the implications of the constant shear force hypothesis and to extend Murray's energy cost minimization to the pulsatile arterial system, a model of pulsatile flow in an elastic tube is analyzed. A new and exact solution for flow velocity, blood flow rate and shear force is derived. RESULTS: For medium and small arteries with pulsatile flow, Murray's energy minimization leads to Murray's Law. Furthermore, the hypothesis that the maximum shear force during the cycle of pulsatile flow is constant throughout the arterial system implies that Murray's Law is approximately true. The approximation is good for all but the largest vessels (aorta and its major branches) of the arterial system. CONCLUSION: A cellular mechanism that senses shear force at the inner wall of a blood vessel and triggers remodeling that increases the circumference of the wall when a shear force threshold is exceeded would result in the observed scaling of vessel radii described by Murray's Law
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