Roper resonances in chiral quark models

We derive a method to calculate the multi-channel K matrix applicable to a broad class of models in which mesons linearly couple to the quark core. The method is used to calculate pion scattering amplitudes in the energy region of low-lying P11 and P33 resonances. A good agreement with experimental data is achieved if in addition to the elastic channel we include the $\pi\Delta$ and $\sigma N$ ($\sigma\Delta$) channels where the $\sigma$-meson models the correlated two-pion decay. We solve the integral equation for the K matrix in the approximation of separable kernels; it yields a sizable increase of the widths of the $\Delta(1232)$ and the N(1440) resonances compared to the bare quark values.Comment: 17 pages, 7 figure

A chiral quark model for meson electro-production in the region of D-wave resonances

The meson scattering and electroproduction amplitudes in the D13, D33 and D15 partial waves are calculated in a coupled-channel formalism incorporating quasi-bound quark-model states, extending our previous studies of the P11, P33 and S11 partial waves. The vertices of the baryon-meson interaction including the s- and d-wave pions and $\rho$-mesons, the s-wave $\eta$-meson, and the $s$- and p-wave $\sigma$-mesons are determined in the Cloudy Bag Model, with some changes of the parameters to reproduce the widths of the resonances. The helicity amplitudes and the electroproduction amplitudes exhibit consistent behavior in all channels but tend to be too weak compared to the experiment. We discuss possible origins of this discrepancy which arises also in the constituent quark model calculations.Comment: 11 pages, 11 figures, accepted for publication in EPJ

Ensuring Professionalism of the External Evaluation Commission: The Slovenian Case Study

In 2006–2007, the Slovenian higher education (HE) system took the first steps toward building a national model of institutional external evaluation (IEE), which would be comparable with other European models. In the first part of the article, the authors discuss the main tendencies within the European he area. This is followed by an outline of the developments in the field of quality assurance within Slovenian he, stressing the years 2006 and 2007. The scientific contribution of the article lies in the evaluation outcomes of the national pilot IEES, with focus on the professional competences of the External evaluation commission (EEC) members. Observation results stress the importance of the proper training of EEC members. The authors propose that a systematic follow-up on the EEC work needs to be established and a code of ethics drawn up, highlighting the preferred values and principles of EEC members.quality assurance, higher education, external evaluation, institutional evaluation, external evaluation commission

Stimolazione da etanolo del sistema dopaminergico mesolimbico: ruolo dell'acetaldeide

Evidence shows that acetaldehyde (ACD), the main metabolite of alcohol previously considered only a toxic substance, may actually mediates the reinforcing effects of ethanol (EtOH) (1). Accordingly, in rodents ACD is self-administred and stimulates the firing of Ventral Tegmental Area (VTA) mesolimbic dopaminergic neurones (2,3). Moreover, recent data show that ACD blockade by sequestration with D-penicillamine or by alcohol dehydrogenase competitive inhibition with 4-methylpyrazolean prevent various electrophysiological and behavioral effects of EtOH (3,4). In this study, we used in vivo microdialysis to measure dopamine (DA) output in the Nucleus Accumbens shell (Nacbs) of male albino Wistar rats in response to a challenge with ACD and EtOH. Both EtOH (0.5, 1.0, 2.0 g/kg) and ACD (10,20 40 mg/kg) were administered by gavage (i.g.) in order to mimic the route of administration used by humans. To further research the effect of ACD on the mesolimbic DAergic system, ACD (50, 75, 100 µM) was administered via reverse dialysis within the VTA while measuring DA output in the NAcbs. Intragastric EtOH and ACD administration dose-dependently increased DA extracellular levels in (i.g. administration) was more potent than EtOH, eliciting similar effects on DA outflow in the NAcbs at doses 50-fold lower. These findings support the hypothesis that ACD has central nervous system effects in its own right and show that ACD stimulates mesolimbic DAergic neurons by an NAcbs. Our results, togheter with the data in the literature, allows to conclude that ACD plays a key role in the EtOH-induced stimulation of mesolimbic pathway and possibly in its rewarding and motivational properties. 1) Quartemont et Al., TIPS 25(3): 130-4, 2004 2) Rodd-Henricks et Al., PBB 72:55-64, 2002 3) Foddai et Al., Neuropsych. 29(3): 530-6, 2004 4) Font et Al., Neuropsych. 184(1): 56-64, 200

Axial amplitudes for Delta excitation in chiral quark models

We study the axial amplitudes for the N-Delta transition in models with quarks and chiral mesons. A set of constraints on the pion field is imposed which enforces PCAC and the off-diagonal Goldberger-Treiman relation. The quark contribution to the amplitudes in general strongly underestimates the C^A_5 amplitude as well as the piNDelta strong coupling constant. We show that the results are considerably improved in models that, in addition to the pion cloud, incorporate a fluctuating sigma field inside the baryon.Comment: 13 pages LaTeX2e, 4 EPS figures within the text; Requires elsart.cls (Submitted for publication in Phys. Lett. B). Section 4 revise