Comment on ``Validity of Feynman's prescription of disregarding the Pauli principle in intermediate states''

In a recent paper Coutinho, Nogami and Tomio [Phys. Rev. A 59, 2624 (1999); quant-ph/9812073] presented an example in which, they claim, Feynman's prescription of disregarding the Pauli principle in intermediate states of perturbation theory fails. We show that, contrary to their claim, Feynman's prescription is consistent with the exact solution of their example.Comment: 1 pag

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

Recent results in vine improvement regarding its resistance to downy and powdery mildews

Resistance to mildew remains very important under Portuguese conditions and induced mutations present a great interest to obtain it. γ -rays irradiation was applied to woody material and X-ray was used on in vitro cultures of stem apexes and leaf explants. After doses up to 2000 rad, two resistant mutants were selected: with γ -rays, the resistance being expressed as surrounding necrotic patches; with X-rays, the plant coming out from in vitro culture presented small necrotic patches. Concerning powdery mildew, we are developing new techniques for laboratorial inoculation, including a technique for sowing isolated spores. By using these, we can conduct studies on morphology and biology of the isolated colony, variability of the resistance within the rids varieties and genetic variability of the parasite. Some results concerning these areas are presented

Insights into the Limitations of Parameter Transferability in Heteronuclear SAFT-type Equations of State

The use of heteronuclear models are often viewed as ways to improve the predictive ability and parameter transferability of advanced association models, such as those derived from the Statistical Associating Fluid Theory (SAFT). Indeed, several results in the literature have suggested that this approach can be useful to accurately describe a given family/series of homologous compounds and their mixtures, with accuracies competitive (and in some cases better) than those obtained using the more traditional SAFT variants. However, the parameter transferability of the different groups, i.e. between different families of compounds, without the introduction of new groups or refitting existing ones, is seldom reported, and often overlooked, making an accurate evaluation of the heteronuclear models difficult. This work analyzes whether the increased complexity of a heteronuclear treatment of a SAFT-type EoS, namely the SAFT-{\gamma}-Mie EoS, results in a significant increase on both the predictive ability and parameter transferability of the model, across different families of compounds. This is done by using a case study involving some different (yet related) families of compounds, containing a small number of common functional groups. The results obtained show that the transferability of group parameters, across different families of compounds, in a heteronuclear SAFT-type EoS does not allow an adequate description of the phase equilibria of these systems. Therefore, to achieve a reasonable accuracy in the description of these systems, a specific refitting of group parameters is required for a given family, or even for a particular system, destroying the predictive capability of these models. Moreover, this increases the number of adjustable parameters to numbers similar to those used in homonuclear approaches, further reducing the advantages of using heteronuclear models

Entropy production and Kullback-Leibler divergence between stationary trajectories of discrete systems

The irreversibility of a stationary time series can be quantified using the Kullback-Leibler divergence (KLD) between the probability to observe the series and the probability to observe the time-reversed series. Moreover, this KLD is a tool to estimate entropy production from stationary trajectories since it gives a lower bound to the entropy production of the physical process generating the series. In this paper we introduce analytical and numerical techniques to estimate the KLD between time series generated by several stochastic dynamics with a finite number of states. We examine the accuracy of our estimators for a specific example, a discrete flashing ratchet, and investigate how close is the KLD to the entropy production depending on the number of degrees of freedom of the system that are sampled in the trajectories.Comment: 14 pages, 7 figure

Oxidative DNA damage protection and repair by polyphenolic compounds in PC12 cells

Biological systems are frequently exposed to excessive reactive oxygen species, causing a disturbance in the cells natural antioxidant defence systems and resulting in damage to all biomolecules, including nucleic acids. In fact, oxidative DNA damage is described as the type of damage most likely to occur in neuronal cells. In this study, three polyphenolic compounds, luteolin, quercetin and rosmarinic acid, were investigated for their protective effects against oxidative DNA damage induced in PC12 cells, a neuronal cell model. Although luteolin and quercetin prevented the formation of strand breaks to a greater extent than rosmarinic acid, this last one presented the highest capacity to repair strand breaks formation. In addition, rosmarinic acid was the only compound tested that increased the repair of oxidized nucleotidic bases induced with the photosensitizer compound [R]-1-[(10-chloro-4-oxo-3-phenyl-4H-benzo[a]quinolizin-1-yl) carbonyl]-2-pyrrolidine- methanol (Ro 19-8022). The activity of repair enzymes was indicated by the in vitro base excision repair assay, using a cell-free extract obtained from cells previously treated with the compounds to incise DNA. The protective effect of rosmarinic acid was further confirmed by the increased expression of OGG1 repair gene, observed through real time RT-PCR. The data obtained is indicative that rosmarinic acid seems to act on the intracellular mechanisms responsible for DNA repair, rather than by a direct effect on reactive oxygen species scavenging, as deducted from the effects observed for luteolin and quercetin. Therefore, these results suggest the importance of these polyphenols, and in particular rosmarinic acid, as protectors of oxidative stress-induced DNA damage that commonly occurs in several pathological conditions, such as neurodegenerative diseases.Fundação para a Ciência e a Tecnologia (FCT) - bolsa SFRH/BD/17174/2004

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

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