A wave diffraction problem with higher order impedance boundary conditions

In this paper, we consider an impedance boundary transmission problem for the Helmholtz equation originated by a problem of wave diffraction by an infinite strip with higher order imperfect boundary conditions. Operator theoretical methods and relations between operators are built to deal with the problem and, as consequence, a transparent interpretation of the problem in an operator theory framework are associated to the problem. In particular, different types of operator relations are exhibited for different types of operators acting between Lebesgue and Sobolev spaces on a finite interval and the positive half-line. All this has consequences in the understanding of the structure of this type of problems. At the end, we describe when the operators associated with the problem enjoy the Fredholm property in terms of the initial space order parameters.publishe

Dirac and Majorana heavy neutrinos at LEP II

The possibility of detecting single heavy Dirac and Majorana neutrinos at LEP II is investigated for heavy neutrino masses in the range $M_N=(\sqrt s/2, \sqrt s)$. We study the process $e^+e^- \longrightarrow \nu_{\ell} \ell q_i \bar q_j$ as a clear signature for heavy neutrinos. Numerical estimates for cross sections and distributions for the signal and the background are calculated and a Monte Carlo reconstruction of final state particles after hadronization is presented.Comment: 4 pages, 8 figure

Behind the boardroom's door: the role and contribution of corporate boards

So far, academicians have not been able to empirically confirm that boardroom reforms will lead to more effective boards and ultimately positively affect corporate performance. As social actors we all have biased views, as do boardroom members, thus it is necessary to analyse directors’ perceptions about their role in order to understand if they are aligned and acting accordingly. The research goal is then to understand what is, in fact, directors’ role and contribution. Through a survey-based method board members from Portuguese listed firms were requested to rate the Chairman, the Board, the Senior Independent Director and the CEO performance, through their own perceptions. The survey draws three key conclusions: first, there are, generally, many inconsistencies around the board role boundaries between the chairman and the CEO and, particularly, around their strategic involvement. Second, tensions arise from the way this relationship evolves affecting both teams (the executive and non-executive directors) and third, there is an absence of a clear picture of the board’s role regarding its strategic involvement. This study, whilst exploring and understanding directors and their interactions inside the boardroom in a non-Anglo-American context, contributes to opening the ‘black-box’ of board dynamics, thus ‘dismantling the fortress’ in boards studies

Hyers-Ulam stability of a certain Fredholm integral equation

In this paper, by using Fixed point Theorem we establish the Hyers-Ulam stability and Hyers-Ulam-Rassias stability of certain homogeneous Fredholm Integral equation of the second kind and non-homogeneous equation.info:eu-repo/semantics/publishedVersio

Sodium dodecyl sulfate allows the persistence and recovery of biofilms of Pseudomonas fluorescens formed under different hydrodynamic conditions

The effect of the anionic surfactant sodium dodecyl sulfate (SDS) on Pseudomonas fluorescens biofilms was investigated using flow cell reactors with stainless steel substrata, under turbulent (Re=5200) and laminar (Re=2000) flow. Steady-state biofilms were exposed to SDS in single doses (0.5, 1, 3 and 7 mM) and biofilm respiratory activity and mass measured at 0, 3, 7 and 12 h after the SDS application. The effect of SDS on biofilm mechanical stability was assessed using a rotating bioreactor. Whilst high concentrations (7 mM) of SDS promoted significant biofilm inactivation, it did not significantly reduce biofouling. Turbulent and laminar flow-generated biofilms had comparable susceptibility to SDS application. Following SDS exposure, biofilms rapidly recovered over the following 12 h, achieving higher respiratory activity values than before treatment. This phenomenon of posttreatment recovery was more pronounced for turbulent flow-generated biofilms, with an increase in SDS concentration. The mechanical stability of the biofilms increased with surfactant application, except for SDS concentrations near the critical micellar concentration, as measured by biofilm removal due to an increase in external shear stress forces. The data suggest that although SDS exerts antimicrobial action against P. fluorescens biofilms, even if only partial and reversible, it had only limited antifouling efficacy, increasing biofilm mechanical stability at low concentrations and allowing significant and rapid recovery of turbulent flow-generated biofilms.Fundação para a Ciência e a Tecnologia (FCT