Floating Offshore Wind Turbines Oscillations Damping.

This article deals with the modelling and control of oscillations that appear on floating offshore wind turbines (FOWT). First, these offshore wind energy systems, located in deep waters, are described and the modeling approach is presented. Secondly, the traditional structural control strategies based on tuned mass-damper (TMD) systems for oscillations reduction are complemented with a passive mechanism called inerter in order to improve the performance of the structural controller. This work is based on a previous work by the authors in which the inerter was located in parallel to an existing TMD in the nacelle of the FOWT. In this work, the inerter is located between the tower and the barge and results are compared to those obtained previously showing better performance. The results here presented are promising in terms of oscillations damping, both in amplitude and frequency, and constitute preliminary results of the ongoing current research of the authors

Reflection matrices for the Uq[sl(r∣2m)(2)]U_{q}[sl(r|2m)^{(2)}] vertex model

The graded reflection equation is investigated for the $U_{q}[sl(r|2m)^{(2)}]$ vertex model. We have found four classes of diagonal solutions and twelve classes of non-diagonal ones. The number of free parameters for some solutions depends on the number of bosonic and fermionic degrees of freedom considered.Comment: 30 page

Radial distribution function of penetrable sphere fluids to second order in density

The simplest bounded potential is that of penetrable spheres, which takes a positive finite value $\epsilon$ if the two spheres are overlapped, being 0 otherwise. In this paper we derive the cavity function to second order in density and the fourth virial coefficient as functions of $T^*\equiv k_BT/\epsilon$ (where $k_B$ is the Boltzmann constant and $T$ is the temperature) for penetrable sphere fluids. The expressions are exact, except for the function represented by an elementary diagram inside the core, which is approximated by a polynomial form in excellent agreement with accurate results obtained by Monte Carlo integration. Comparison with the hypernetted-chain (HNC) and Percus-Yevick (PY) theories shows that the latter is better than the former for $T^*\lesssim 1$ only. However, even at zero temperature (hard sphere limit), the PY solution is not accurate inside the overlapping region, where no practical cancelation of the neglected diagrams takes place. The exact fourth virial coefficient is positive for $T^*\lesssim 0.73$, reaches a minimum negative value at $T^*\approx 1.1$, and then goes to zero from below as $1/{T^*}^4$ for high temperatures. These features are captured qualitatively, but not quantitatively, by the HNC and PY predictions. In addition, in both theories the compressibility route is the best one for $T^*\lesssim 0.7$, while the virial route is preferable if $T^*\gtrsim 0.7$.Comment: 10 pages, 2 figures; v2: minor changes; to be published in PR

The success factors for SMEs: Empirical evidence

This paper empirically analyzes the success factors for SMEs. Particularly, the paper intends to analyze if firm age, human resource costs, debt, venture capital funding, investment in innovation and productivity are success factors for SMEs. The effects were tested using static and dynamic panel data, on a data set of 200 Portuguese SMEs. The use of dynamic panel data is important in order to control for: endogeneity; time-invariant characteristics; possible collinearity between independent variables; effects from possible omission of independent variables; elimination of non-observable individual effects; and, the correct estimation of the relationship between the dependent variable in the previous and current periods. Our results reveal a positive impact on success of: human resource costs; investments in innovation; productivity; and, venture capital funding. We also confirm the negative impact of firm age and debt. Also, the results show evidence of persistence in success for the case of one of the success proxies used

The effects of violating detailed balance on critical dynamics

We present an overview of the effects of detailed-balance violating perturbations on the universal static and dynamic scaling behavior near a critical point. It is demonstrated that the standard critical dynamics universality classes are generally quite robust: In systems with non-conserved order parameter, detailed balance is effectively restored at criticality. This also holds for models with conserved order parameter, and isotropic non-equilibrium perturbations. Genuinely novel features are found only for models with conserved order parameter and spatially anisotropic noise correlations.Comment: 4 pages, revtex, no figure