Effects of Mass Media and Cultural Drift in a Model for Social Influence

In the context of an extension of Axelrod's model for social influence, we study the interplay and competition between the cultural drift, represented as random perturbations, and mass media, introduced by means of an external homogeneous field. Unlike previous studies [J. C. Gonz\'alez-Avella {\it et al}, Phys. Rev. E {\bf 72}, 065102(R) (2005)], the mass media coupling proposed here is capable of affecting the cultural traits of any individual in the society, including those who do not share any features with the external message. A noise-driven transition is found: for large noise rates, both the ordered (culturally polarized) phase and the disordered (culturally fragmented) phase are observed, while, for lower noise rates, the ordered phase prevails. In the former case, the external field is found to induce cultural ordering, a behavior opposite to that reported in previous studies using a different prescription for the mass media interaction. We compare the predictions of this model to statistical data measuring the impact of a mass media vasectomy promotion campaign in Brazil.Comment: 10 pages, 3 figures; minor changes; added references. To appear in IJMP

Irreversible Opinion Spreading on Scale-Free Networks

We study the dynamical and critical behavior of a model for irreversible opinion spreading on Barab\'asi-Albert (BA) scale-free networks by performing extensive Monte Carlo simulations. The opinion spreading within an inhomogeneous society is investigated by means of the magnetic Eden model, a nonequilibrium kinetic model for the growth of binary mixtures in contact with a thermal bath. The deposition dynamics, which is studied as a function of the degree of the occupied sites, shows evidence for the leading role played by hubs in the growth process. Systems of finite size grow either ordered or disordered, depending on the temperature. By means of standard finite-size scaling procedures, the effective order-disorder phase transitions are found to persist in the thermodynamic limit. This critical behavior, however, is absent in related equilibrium spin systems such as the Ising model on BA scale-free networks, which in the thermodynamic limit only displays a ferromagnetic phase. The dependence of these results on the degree exponent is also discussed for the case of uncorrelated scale-free networks.Comment: 9 pages, 10 figures; added results and discussion on uncorrelated scale-free networks; added references. To appear in PR

External interaction management of VRML scenes for e-learning applications

This is an electronic version of the paper presenten at the International conference on International Workshop on Web3D Technologies in Learning, Education and Training (LET-Web3D 2004) held in Udine (Italy) on 2004This paper describes an innovative approach to solve some of the problems that arise when integrating virtual reality capabilities into e-learning environments. The VRML representation of a scene includes, along with its geometric description, a full specification of the student-scene interaction logic. This representation is rendered by a browser, which also orchestrates the interaction according to the logic. Such a mechanism implies reprogramming and/or replicating partly the logic when modifying the interaction scheme of a single scene for different students. It also prevents any external access to student’s actions or scene reactions, which is necessary for on-line evaluation or instruction. We propose to expand the standard interaction mechanism of VRML so that both the specification of the scene logic and the interaction flow are managed by an external and centralized entity following a clientserver approach, hence solving the identified problems, while additionally increasing design efficiency and content protection.This work has been partly supported by the Plan Nacional de Ciencia y Tecnología of the Spanish Government under project TIC2001-306

Magnetic properties of Ni nanoparticles dispersed in silica prepared by high-energy ball milling

We analyze the magnetic properties of mechanically ground nanosized Ni particles dispersed in a SiO_2 matrix. Our magnetic characterization of the as-milled samples show the occurrence of two blocking processes and that of non-monotonic milling time evolutions of the magnetic-order temperature, the high-field magnetization and the saturation coercivity. The measured coercivities exhibit giant values and a uniaxial- type temperature dependence. Thermal treatment carried out in the as-prepared samples result in a remarkable coercivity reduction and in an increase of the high-field magnetization. We conclude, on the basis of the consideration of a core (pure Ni) and shell (Ni-Si inhomogeneous alloy) particle structure, that the magnetoelastic anisotropy plays the dominant role in determining the magnetic properties of our particles

Razlike u razinama anti-Müllerovog hormona u krvnoj plazmi i reproduktivnih parametara između dvije vrste goveda Bos indicus i Bubalus bubalis

The aim of this study was to evaluate the possible relationships between reproductive parameters and Anti Mullerian Hormone (AMH) levels in two closely related bovine species. AMH levels and the reproductive parameters of 50 water buffaloes (Bubalus bubalis) and 50 Zebu cattle (Bos indicus) of the same age and raised in similar conditions were evaluated. Clinical data were obtained from the farm in specialized designed format, and AMH was measured by ELISA. The results show that Zebu cattle had higher AMH levels than water buffaloes (P<0.0001), while water buffaloes exhibited better reproductive parameters: days open to pregnancy (P<0.0001), parity (P<0.0005), age at first calving (P<0.0001), and intercalving period (P<0.0001). Although both species have different reproductive parameters, no correlations were found between AMH and the reproductive parameters evaluated in either species. Finally, pregnant Zebu cattle and water buffalo showed a tendency to have lower AMH levels than non-pregnant counterparts. The results are paradoxical as the species with lower AMH levels exhibited better reproductive parameters, suggesting that the reproductive parameters within the herd do not depend solely on the ovarian reserve of females.Cilj je ovog rada bio procijeniti je li moguće ustanoviti povezanost između reproduktivnih parametara i razina anti-Müllerovog hormona (AMH) u dvije blisko srodne vrste goveda. Analizirane su razine AMH i reproduktivni parametri 50 bivola (Bubalus bubalis) i 50 zebu goveda (Bos indicus) iste dobi uzgojenih u sličnim uvjetima. Klinički podatci dobiveni su s farme u posebno osmišljenom pokusu. AMH je određivan pomoću ELISA metode. Rezultati pokazuju da su razine AMH više u goveda nego u bivola (P<0,0001). Bivoli su pokazali bolje reproduktivne parametre: servisno razdoblje (P<0,0001), paritet (P<0,0005), dob kod prvog teljenja (P<0,0001) i međutelidbeno razdoblje (P<0,0001). Premda obje vrste imaju različite reproduktivne parametre, nije ustanovljena povezanost između AMH i analiziranih reproduktivnih parametara niti u jedne od istraživanih vrsta. Zaključno, steone ženke goveda i bivola pokazuju tendenciju manjih razina AMH u usporedbi s nesteonim. Rezultati dobiveni u ovoj studiji su paradoksalni, jer vrste s nižim AMH razinama pokazuju bolje reproduktivne parametre. Ovi rezultati ukazuju na to da reproduktivni parametri unutar krda ne ovise samo o rezervi jajnih stanica u ženki

Microestructure and mechanical properties of biomorphic SiC obtained from eucalyptus

El desarrollo de materiales cerámicos con una estructura de tipo celular, similar a la del hueso o la madera, ha sido una cuestión que ha suscitado un gran interés en los últimos años. Su atractivo se debe al hecho de poseer una estructura porosa altamente interconectada de baja densidad, perfeccionada por la evolución. En el caso del SiC biomórfico (bio-SiC) el proceso de fabricación es sencillo: se piroliza una pieza de madera y a continuación se inyecta con silicio líquido, el material así obtenido es un compuesto Si/SiC en el que el SiC mimetiza la estructura de la madera original. En este trabajo se estudian las propiedades mecánicas del SiC biomórfico fabricado a partir de eucalipto (madera dura con una distribución bimodal de poros). Se ha estudiado el comportamiento mecánico del mismo (resistencia a compresión, resistencia a flexión, tenacidad de fractura y módulo de elasticidad) entre 25 y 1350 o C. Asimismo, se discute la relación entre el comportamiento mecánico del material y su microestructura.The development of cellular ceramics with a biological structure, like bones and wood, has been a matter of interest in recent years. A low density highly interconnected structure, perfected by evolution, rises as the principal advantage of these materials. In the case of biomimetic SiC (biomorphic SiC, or bioSiC), the fabrication process technique is quite simple: a piece of wood is pyrolysed and is infiltrated with molten silicon after, the final product is a composite Si/SiC, which replicates the wood anisotropic microstructure This work focus on the mechanical properties of bioSiC fabricated using eucalyptus wood as precursor (hard wood with a bimodal channel distribution). It has been studied the mechanical behavior of this bioSiC (compression strength, flexure strength, fracture toughness and elastic modulus) between 25 and 1350 o C. It is also discussed the relationship between mechanical behavior of the material and its microstructure

A new measure of health motivation influencing food choices and its association with food intakes and nutritional biomarkers in European adolescents

Objective:To develop a scale to assess health motivation influencing food choices and to explore its performance in the associations with food intakes and nutritional biomarkers. Design:Psychometric study using cross-sectional self-report questionnaires and nutritional biomarkers. Setting:Multi-centre investigation conducted in ten European cities. Participants:2954 adolescents who were included in the HELENA study and completed the Food Choices and Preferences (FCP) questionnaire. Results:Nineteen out of 124 items of the FCP questionnaire were in the same dimension. Sixteen presented adequate parameters for the Scale of evaluatiOn of Food choIcEs (SOFIE). The scores were positively associated with the intakes of cereals, dairy products, meats and eggs, and fish, as well as with blood concentrations of vitamin C, ß-carotene, n-3 fatty acids, cobalamin, holo-transcobalamin and folate; scores were negatively associated with the intake of alcohol. Conclusions:SOFIE can improve the assessment of motivation influencing food choices based on items with the best performance and is proposed as a new measure to health-related studies