Movatterモバイル変換

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Relativistic mean field theory with mesons σ, ω, π and ρ mediating interactions and nucleons as basic fermions has been very successful in describing nuclear matter and finite nuclei. However, in heavy-ion collisions, where the c. m. energy of two colliding nucleons will be in the hundreds of GeV region, nucleons are not expected to behave as point-like particles. Analyses of elastic pp and ¯pp scattering data in the relevant c. m. energy range show that the nucleon is a composite (...) object—a topological soliton or Skyrmion embedded in a condensed quark-antiquark ground state. Against this backdrop, we formulate an effective field theory model of nuclear matter based on the gauged linear σ-model where quarks are the basic fermions, but the mesons still mediate the interactions. The model describes the nucleon as a Skyrmion and produces a q¯q ground state analogous to a superconducting ground state. Quarks are quasi-particles in this ground state. When the temperature exceeds a critical value, the scalar field in the ground state vanishes, quarks become massless, and a chiral phase transition occurs leading to chiral symmetry restoration. We explore the possibility of a first order phase transition in this model by introducing suitable self-interactions of the scalar field. Internal structures of the Skyrmions are ignored, and they are treated as point-like fermions. (shrink)

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The nonlinear σ-model with vector mesons introduced as gauge bosons and an interacting chiral quark sector depicts the nucleon as a topological soliton embedded in a chiral condensate. High-energy elastic pp and ¯pp scattering data from CERN ISR and SPS Collider appear to provide strong evidence in favor of this nucleon structure.

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Concerns that cash payments to people who inject drugs (PWID) to reimburse research participation will facilitate illicit drug purchases have led some ethical authorities to mandate department store/supermarket vouchers as research reimbursement. To examine the relative efficacy of the two forms of reimbursement in engaging PWID in research, clients of two public opioid substitution therapy clinics were invited to participate in a 20–30 min, anonymous and confidential interview about alcohol consumption on two separate occasions, 4 months apart. Under the crossover (...) design, at Time 1, clients of Clinic 1 were offered $A20 cash as reimbursement, while clients of Clinic 2 were offered an $A20 voucher; at Time 2, the form of reimbursement was reversed. Using clinic records to determine the denominator (number of clients dosed), we found that compared with clients offered a voucher, a significantly higher proportion of clients who were offered cash participated in the survey (58% (139/241) vs 74% (186/252); χ2=14.27; p=0.0002). At first participation, respondents most commonly reported planning to purchase food/drinks/groceries (68%), cigarettes (21%) and transport/fuel (11%) with their payments, with those reimbursed in cash more likely to report planning to fund transport/fuel (19% vs 1%; p<.01) and less likely to report planning to purchase food/drinks/groceries (62% vs 76%; p=0.02). Just three out of 155 cash participants reported planning to purchase illicit drugs with their payment. Results demonstrate that modest cash payments enhanced recruitment of this group, an important consideration given the challenges of delineating the parameters of a population defined by illegal activity, seemingly without promoting excessive additional drug use. (shrink)

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