Neutron skin of 208Pb, nuclear symmetry energy, and the parity radius experiment

A precise determination of the neutron skin thickness of a heavy nucleus sets a basic constraint on the nuclear symmetry energy (the neutron skin thickness is the difference of the neutron and proton rms radii of the nucleus). The parity radius experiment (PREX) may achieve it by electroweak parity-violating electron scattering (PVES) on 208Pb. We investigate PVES in nuclear mean field approach to allow the accurate extraction of the neutron skin thickness of 208Pb from the parity-violating asymmetry probed in the experiment. We demonstrate a high linear correlation between the parity-violating asymmetry and the neutron skin thickness in successful mean field forces as the best means to constrain the neutron skin of 208Pb from PREX, without assumptions on the neutron density shape. Continuation of the experiment with higher precision in the parity-violating asymmetry is motivated since the present method can support it to constrain the density slope of the nuclear symmetry energy to new accuracy.

Do Schools Discriminate Against Homosexual Parents? Evidence from an Internet Field Experiment

The recognition of homosexual rights is a controversial issue in many countries. Spain was the third country in the world (after Netherlands and Belgium) to introduce a law recognizing homosexual marriage and adoption of children. In this paper, we examine for the first time whether schools are more hesitant to give feedback to homosexual parents during children's pre-registration period in Spain. In order to do that, we designed an internet field experiment to be conducted in schools. We created three types of fictitious couples; one heterosexual, one male homosexual and one female homosexual, and send emails to schools making sexual orientation explicit. Our results show that men homosexual couples had a significant lower probability to receive and answer than heterosexual couples (22.5 percentage points less). No statistically significant differences in the response rate were found between female homosexual and heterosexual couples. This result suggests that male homosexual couples might be penalized because of the lack of a maternal figure. Keywords: Discrimination, field experiment, schools, homosexual rights. JEL codes: H41, I20, K36

Social Presence Approach Within the Question and Answering eLearning Model: An Experiment with a Multi-Agent System

The model of Questions Answering (Q&A) for eLearning is based on collaborative learning through questions that are posed by students and their answers to that questions which are given by peers, in contrast with the classical model in which students ask questions to the teacher only. In this proposal we extend the Q&A model including the social presence concept and a quantitative measure of it is proposed; besides it is considered the evolution of the resulting Q&A social network after the inclusion of the social presence and taking into account the feedback on questions posed by students and answered by peers. The social network behaviorwas simulated using a Multi-Agent System to compare the proposed social presence model with the classical and the Q&A models