Analytical solution for optical trapping force on a spherical dielectric particle for an arbitrary positioned focused beam is presented in a generalized Lorenz-Mie and vectorial diffraction theory. In this case the exact electromagnetic field is considered in the focal region. A double tweezers setup was employed to perform ultra sensitive force spectroscopy and observe the forces, demonstrating the selectively couple of the transverse electric (TE), transverse magnetic (TM) modes by means of the beam polarization and positioning, and to observe correspondent morphology-dependent resonances (MDR) as a change in the optical force. The theoretical prediction of the theory agrees well with the experimental results. The algorithm presented here can be easily extended to other beam geometries and scattering particles. G. Gouesbet, B. Maheu, G. Grehan, "Light scattering from a sphere arbitrarily located in a Gaussian beam using Bromwich formulation," J Opt Soc Am A, 5, 1427-1443 (1988

O setor elétrico brasileiro vem sofrendo sucessivas revisões e reformas nos últimos 30 anos. Ainda que, no discurso, essas reformas sempre visem ao melhor e mais universal atendimento às necessidades da sociedade, na prática, esse resultado nem sempre esteve em primeiro plano. E mesmo sendo um critério prioritário de planejamento, a garantia da segurança do abastecimento foi alterada ao longo dessa sucessão de mudanças no modelo setorial de gestão. Atualmente, em um cenário de planejamento da expansão e da operação de alta complexidade, esse critério ostenta o caráter de particularidade brasileira frente ao cenário internacional, pairando sobre a sociedade uma persistente ameaça de “crise” do serviço de energia elétrica. Nesse contexto, este artigo elabora uma reconstituição histórica do processo de planejamento do setor elétrico em termos da importância da segurança do abastecimento.

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The fluid lipid bilayer viscoelastic membrane of red blood cells (RBC) contains antigen glycolproteins and proteins which can interact with antibodies to cause cell agglutination. This is the basis of most of the immunohematologic tests in blood banks and the identification of the antibodies against the erythrocyte antigens is of fundamental importance for transfusional routines. The negative charges of the RBCs creates a repulsive electric (zeta) potential between the cells and prevents their aggregation in the blood stream. The first counterions cloud strongly binded moving together with the RBC is called the compact layer. This report proposes the use of a double optical tweezers for a new procedure for measuring: (1) the apparent membrane viscosity, (2) the cell adhesion, (3) the zeta potential and (4) the compact layer's size of the charges formed around the cell in the electrolytic solution. To measure the membrane viscosity we trapped silica beads strongly attached to agglutinated RBCs and measured the force to slide one RBC over the other as a function of the relative velocity. The RBC adhesion was measured by slowly displacing two RBCs apart until the disagglutination happens. The compact layer's size was measured using the force on the silica bead attached to a single RBC in response to an applied voltage and the zeta potential was obtained by measuring the terminal velocity after releasing the RBC from the optical trap at the last applied voltage. We believe that the methodology here proposed can improve the methods of diagnosis in blood banks.

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