Conservation of Orbital Angular Momentum in Stimulated Down-Conversion

We report on an experiment demonstrating the conservation of orbital angular momentum in stimulated down-conversion. The orbital angular momentum is not transferred to the individual beams of the spontaneous down-conversion, but it is conserved when twin photons are taken individually. We observe the conservation law for an individual beam of the down-conversion through cavity-free stimulated emission.Comment: Submitted for publication in Phys. Rev. Let

Monoolein-based lipoplexes (DODAB/MO/DNA) as non-viral vector for transfection- from physicochemical characterization to biological application

Cationic liposomes/DNA (lipoplexes) have been widely used as non-viral vectors for transfection, the role of the neutral lipid in liposome formulation being determinant for the efficiency of this process [1,2]. In this work, we studied the potential of monoolein (MO) as helper lipid for cellular transfection. Lipoplexes composed of pDNA and dioctadecyldimethylammonium bromide (DODAB)/1-monooleoyl-rac-glycerol (MO) at different molar ratios (4:1, 2:1 and 1:1) were investigated, as well as different cationic lipid/DNA ratios. The physicochemical properties of the lipoplexes (size and charge), the formation of the lipoplexes, the effect of MO on pDNA condensation and the effect of heparin on percentage of pDNA release from the lipoplexes were also studied by Ethidium Bromide (EtBr) exclusion assays, Dynamic Light Scattering (DLS), Zeta Potential (æ) and electrophoresis. The cytotoxicity, transfection efficiency, as well as the intracellular localization of labeled DNA were evaluated on 293T cells. It was found that the presence of MO not only increases the efficiency of pDNA compactation, but also affects the physicochemical properties of lipoplexes, which could possibly interfere with lipoplex-cell interactions. The DODAB:MO (2:1) and (4:1) formulations were capable of efficiently mediate in vitro cell transfection. These results were consistent with fluorescence microscopy studies, which illustrated that lipoplexes were able to gain entry into the cytosol and deliver pDNA to the nucleus. Understanding the structure–activity relationship of MO based lipoplexes will give direction toward the development of safe and efficient gene delivery systems.Portuguese Foundation for Science and Technology (FCT) for financial support to Center of Physics and Center of Molecular & Environmental Biology and funding through projects PTDC/QUI/69795/2006 and SFRH/BD/46968/2009

Monoolein as helper lipid for non-viral transfection in mammals

Lipoplexes composed of pDNA and DODAB/MO at different molar ratios (4:1, 2:1 and 1:1) and different cationic lipid/DNA charge ratios were investigated. The physicochemical properties of the lipoplexes (size and charge), the pDNA complexation, and the effect of heparin on pDNA release, were studied by Dynamic Light Scattering, Zeta Potential, and Ethidium Bromide exclusion assays. The cytotoxicity, transfection efficiency and the intracellular localization of DNA were evaluated on 293T cells.The Portuguese Foundation for Science and Technology (FCT) for the financial support to the Center of Physics and Center of Molecular & Environmental Biology and funding through projects PTDC/QUI/69795/2006 and SFRH/BD/46968/2009 are acknowledged

Many-body system with a four-parameter family of point interactions in one dimension

We consider a four-parameter family of point interactions in one dimension. This family is a generalization of the usual $\delta$-function potential. We examine a system consisting of many particles of equal masses that are interacting pairwise through such a generalized point interaction. We follow McGuire who obtained exact solutions for the system when the interaction is the $\delta$-function potential. We find exact bound states with the four-parameter family. For the scattering problem, however, we have not been so successful. This is because, as we point out, the condition of no diffraction that is crucial in McGuire's method is not satisfied except when the four-parameter family is essentially reduced to the $\delta$-function potential.Comment: 8 pages, 4 figure

Bone tissue engineering : state of the art and future trends

Although several major progresses have been introduced in the field of bone regenerative medicine during the years, current therapies, such as bone grafts, still have many limitations. Moreover, and in spite of the fact that material science technology has resulted in clear improvements in the field of bone substitution medicine, no adequate bone substitute has been developed and hence large bone defects/injuries still represent a major challenge for orthopaedic and reconstructive surgeons. It is in this context that TE has been emerging as a valid approach to the current therapies for bone regeneration/substitution. In contrast to classic biomaterial approach, TE is based on the understanding of tissue formation and regeneration, and aims to induce new functional tissues, rather than just to implant new spare parts. The present review pretends to give an exhaustive overview on all components needed for making bone tissue engineering a successful therapy. It begins by giving the reader a brief background on bone biology, followed by an exhaustive description of all the relevant components on bone TE, going from materials to scaffolds and from cells to tissue engineering strategies, that will lead to engineered bone.Portuguese Foundation for Science and Technology through funds from POCTI and/or FEDER programs

Novel starch-based scaffolds for bone tissue engineering : cytotoxicity, cell culture, and protein expression

Starch-based biomaterials and scaffolds have been proposed for several biomedical applications. In the present work new scaffolds based on a 50/50 (wt%) blend of corn starch/ethylene-vinyl alcohol (SEVA-C) were studied. These scaffolds were processed by a melt-based technology, which has been used before with other starch-based materials but never with SEVA-C. Scanning electron microscopy (SEM) observation showed that the developed porous structures were 60% porous with pore size between 200 and 900 μm and a reasonable degree of interconnectivity. Moreover, scaffolds presented a compressive modulus of 117.50 ± 3.7 MPa and a compressive strength of 20.8 ± 2.4 MPa. Cytotoxicity evaluation was performed according to ISO/EN 10993 part 5 guidelines, and revealed that the developed scaffolds were nontoxic and did not inhibit cell growth. Direct contact assays were also carried out by use of a cell line of human osteoblast-like cells (SaOS-2). Cells were seeded (3 × 105 per scaffold) and allowed to grow for 4 weeks at 37°C, in a humidified atmosphere containing 5% CO2. Total protein assay showed that the cells were able to grow for the 4 weeks of the experiment. These data were further confirmed by SEM. Moreover, a cell viability assay (MTS test) demonstrated that cells were perfectly viable after the 4 weeks of culture, showing the adequacy of the developed structure in supporting them. Finally, Western blot analysis revealed that osteopontin was being actively expressed by the cells, which, in association with collagen deposition observed by SEM, seems to indicate that bone extracellular matrix was being deposited. Consequently it is believed that starch-based scaffolds should be considered as an alternative for bone tissue-engineering applications in the near future.Fundação para a Ciência e Tecnologia (FCT

Platinum nanoparticles as pH sensor for intelligent packaging

Pt nanoparticles were produced by reverse micelle templating using DTAB. The resulting nanoparticles showes sizes between 250nm and 500nm and formed clusters. Thioglycolic acid (TGA) was covalently attached to the nanoparticle surface as a stabilizer and as. The Pt nanoparticles were dispersed in water and the dependence of its absorvance on the pH of the solution was studied. The spectra showed surface plamon absorption band at 280nm and also red shifted bands that were attributed to clusters of nanoparticles. It was found that the fraction of cluster population depends on the pH of the aqueous solution and that the response of the Pt nanoparticles to pH variations has a memory effect (hysteresis). The possibility of using these Pt nanoparticles in smart labels for food packaging is outlined.Fundação para a Ciência e a Tecnologia (FCT)FEDERCFUMProject NANO/NTec- SQA/0033/200

The motion of two masses coupled to a massive spring

We discuss the classical motion of a spring of arbitrary mass coupled to two arbitrary massive blocks attached at its ends. A general approach to the problem is presented and some general results are obtained. Examples for which a simple elastic function can be inferred are discussed and the normal modes and normal frequencies obtained. An approximation procedure to the evaluation of the normel frequencies in the case of uniform elastic function and mass density is also discussed.Comment: Standard Latex file plus three eps figure