Liquid-crystal patterns of rectangular particles in a square nanocavity

Using density-functional theory in the restricted-orientation approximation, we analyse the liquid-crystal patterns and phase behaviour of a fluid of hard rectangular particles confined in a two-dimensional square nanocavity of side length $H$ composed of hard inner walls. Patterning in the cavity is governed by surface-induced order, capillary and frustration effects, and depends on the relative values of particle aspect ratio $\kappa\equiv L/\sigma$, with $L$ the length and $\sigma$ the width of the rectangles ($L\ge\sigma$), and cavity size $H$. Ordering may be very different from bulk ($H\to\infty$) behaviour when $H$ is a few times the particle length $L$ (nanocavity). Bulk and confinement properties are obtained for the cases $\kappa=1$, 3 and 6. In the confined fluid surface-induced frustration leads to four-fold symmetry breaking in all phases (which become two-fold symmetric). Since no director distorsion can arise in our model by construction, frustration in the director orientation is relaxed by the creation of domain walls (where the director changes by $90^{\circ}$); this configuration is necessary to stabilise periodic phases. For $\kappa=1$ the crystal becomes stable with commensuration transitions taking place as $H$ is varied. In the case $\kappa=3$ the commensuration transitions involve columnar phases with different number of columns. Finally, in the case $\kappa=6$, the high-density region of the phase diagram is dominated by commensuration transitions between smectic structures; at lower densities there is a symmetry-breaking isotropic $\to$ nematic transition exhibiting non-monotonic behaviour with cavity size.Comment: 31 pages, 15 figure

Frequency and damping evolution during experimental seismic response of civil engineering structures

The results of the seismic tests on several reinforced-concrete shear walls and a four-storey frame are analysed in this paper. Each specimen was submitted to the action of a horizontal accelerogram, with successive growing amplitudes, using the pseudodynamic method. An analysis of the results allows knowing the evolution of the eigen frequency and damping ratio during the earthquakes thanks to an identification method working in the time domain. The method is formulated as a spatial model in which the stiffness and damping matrices are directly identified from the experimental displacements, velocities and restoring forces. The obtained matrices are then combined with the theoretical mass in order to obtain the eigen frequencies, damping ratios and modes. Those parameters have a great relevance for the design of this type of structures

A local landscape in transition between production and consumption goals: new management arrangements and new challenges for governance.

Around all towns in the Alentejo region, the landscape is dominated by an agricultural mosaic, where small scale farming dominates, composed of olive groves combined with pastures, fruit orchards, and vegetable gardens, in the most fertile and water abundant soils. This is a totally different pattern then the large scale landscape of the extensive silvo-pastoral systems in the latifundia that normally is associated with the region. It is not the most know, but it is the landscape where people live or see in their everyday life. These small scale farm units have increasingly lost their importance as production units over the last decades, even if farming has been maintained by aging local population. In the last two decades, these parcels became extremely attractive for new comers, who settle in the rural context as lifestyle farmers, or simply as new residents (permanent or week-end houses). These new comers have higher economic possibilities, often rebuilding the houses and investing in the land. They search for a new life quality. Farming and the production of food have been loosing their importance – but it is increasing again, due to the raising demand for local and quality food products and the difficult economic situation of many families. As farming is concerned, new arrangements emerge: the new owners may be able to keep farming, often with new or reshaped production objectives, markets and models; they may search for associated older farmers in the area who support them with their knowledge and with this maintain the traditional farm systems; or they may let others, new comers or locals, use their land. The mixture of the different trends calls for new management arrangements, where the traditional cooperation and neighbour relations are reshaped. These new arrangements are emerging but still need to be strengthened and acknowledged by authorities and policies, so they can unfold

A local landscape in transition between production and consumption: can new management arrangements preserve the local landscape character?

Around towns in the Alentejo region, the landscape is dominated by a characteristic agricultural small scale mosaic. These areas are central in the region landscape character, – even if the large scale latifundia landscape of the extensive silvo-pastoral systems is most commonly associated with the region. In the last two decades, these parcels became extremely attractive for new comers, who settle in the rural context as residents, week-end visitors, being often also lifestyle farmers. The paper presents a case-study landscape, in Montemor-o-Novo, a small town 100 km from Lisbon, highly subject to the pressure for consumption uses, by urban users. The study shows that the new owners, even if they have settled in the area due to the tranquility and social bindings of the rural, end up doing farming, with new or reshaped production objectives, markets and models, but at the same time maintaining the traditional farm systems. Thus, the landscape character is maintained, so far. Nevertheless, the role of these neo-rurals and lifestyle farmers is still an unseen role, both by the agriculture and the planning sectors. And thus the question is, whether the combination of actors and land management drivers will continue maintaining the landscape in the futur

The Mass of the Convective Zone in FGK Main Sequence Stars and the Effect of Accreted Planetary Material on Apparent Metallicity Determinations

The mass of the outer convective zone in FGK main sequence stars decreases dramatically with stellar mass. Therefore, any contamination of a star's atmosphere by accreted planetary material should affect hotter stars much more than cool stars. If recent suggestions that high metal abundances in stars with planets are caused by planetesimal accretion are correct, then metallicity enhancements in earlier-type stars with planets should be very pronounced. No such trend is seen, however.Comment: Submitted ApJ Letters March 26th; accepted April 30th. 12 pages, 2 figure