Herding behaviour in a peripheral European stock market: the impact of the subprime and the European sovereign debt crises

The characteristics of the Portuguese stock market suggest that it is susceptible to herding behaviour. We investigate the existence of this behaviour in Portugal during periods of market stress, with emphasis on the subprime and European sovereign debt crises. We analyse the overall stock market, key industries, and portfolios divided by market capitalisation. The study is performed using both linear and nonlinear models, and the impact of conditional variance is taken into account. This paper shows evidence of herding behaviour when the nonlinear model is used and during periods of crisis. Investors imitate more assets of similar size than assets of the same industry. Finally, the evidence of herding behaviour is reduced when GARCH effects are taken into account

M\"obius and twisted graphene nanoribbons: stability, geometry and electronic properties

Results of classical force field geometry optimizations for twisted graphene nanoribbons with a number of twists $N_t$ varying from 0 to 7 (the case $N_t$=1 corresponds to a half-twist M\"obius nanoribbon) are presented in this work. Their structural stability was investigated using the Brenner reactive force field. The best classical molecular geometries were used as input for semiempirical calculations, from which the electronic properties (energy levels, HOMO, LUMO orbitals) were computed for each structure. CI wavefunctions were also calculated in the complete active space framework taking into account eigenstates from HOMO-4 to LUMO+4, as well as the oscillator strengths corresponding to the first optical transitions in the UV-VIS range. The lowest energy molecules were found less symmetric than initial configurations, and the HOMO-LUMO energy gaps are larger than the value found for the nanographene used to build them due to electronic localization effects created by the twisting. A high number of twists leads to a sharp increase of the HOMO $\to$ LUMO transition energy. We suggest that some twisted nanoribbons could form crystals stabilized by dipolar interactions

Evaluation of six nopal (Opuntia spp.) varieties for fodder production in the semi-arid Northeast, Brazil.

The main problems associated with production of fodder nopal in the Sertão region, Semi-arid Northeast, Brazil, are poor soils, high minimum temperature (above 20.5o C), and the armored scale insect (Diaspis echinocacti - Bouchè). A field trial was established in Petrolina, State of Pernambuco ( average rainfall 552.2 mm, 80% available from December to April) in April 2000. Six varieties were tested: three local varieties, ?Gigante?, the most cultivated, ?Redonda? (both Opuntia ficus-indica) and ?Doce? (Nopalea cochenillifera); the Clone IPA-20, furnished by IPA, a local research institution; two varieties provided by the Universidad. Autonoma de Chapingo, Mexico, COPENA F1 and COPENA V1. The experimental design was a CRB , with three replications. The plots had 16 m2 (four rows with eight plants/row) planting density was 20.000, plants/ha, for evaluation, only six plants of each central line were considered Manure was applied on biannual basis, at the rate of 2.86 kg/m. Weeding was performed manually. After four years (May 2004), the first harvest was done, collecting all fresh material except the basal cladode and the first layer of pads.. Annual fresh matter (FM) production was calculated dividing total yield by four. Mean production was 65.36 ± 22.99 ton FM/ha/year (CV = 35.17%). Varieties yields were: ?Gigante? nopal, 103.80 ton; ?Redonda? nopal, 78.04 ton; COPENA F1, 77.54 ton; Clone IPA-20, 74.15 ton; COPENA V1, 34.19 ton; ?Doce? nopal, 24.40 ton. ?Gigante? nopal was significantly superior (P<0.05) to the two last varieties, and ?Doce? nopal was inferior to all varieties. Height, longitudinal and transversal canopy diameters were, respectively: ?Gigante? nopal, 1.54, 1.09 and 1.08 m; ?Redonda? nopal, 1.07, 1.07 and 0.98 m; COPENA F1, 1.73, 1.08 and 0.90 m; Clone IPA-20, 1.38, 1.11 and 0.99 m; COPENA V1, 1.28, 0.91, 0.76 m; ?Doce? nopal, 1.06, 1.07, and 0.99 m. Other data that, such as, protein and fiber levels, might indicate that highest production does not assure the best variety for the region. COPENA F1 having shorter canopy diameter, in comparison to ?Gigante? nopal (0.90 vs. 1.08 m) would make it more