Optimal escape from circular orbits around black holes

Using the theory of optimal rocket trajectories in general relativity, recently developed in arXiv:1105.5235, we show that the "obvious" manoeuvre of using a tangential instantaneous acceleration to escape a stable circular orbit in the Schwarzschild spacetime satisfies the optimality conditions if and only if the magnitude of the acceleration is smaller than a certain bound.Comment: 7 page

Evaluation of the potential of collagen from codfish skin as a biomaterial for biomedical applications

Collagen is one of the most widely used biomaterials, not only due its biocompatibility, biodegradability and weak antigenic potential, but also due to its role in the structure and function of tissues. Searching for alternative collagen sources, the aim of this study was to extract collagen from the skin of codfish, previously obtained as a by-product of fish industrial plants, and characterize it regarding its use as a biomaterial for biomedical application, according to American Society for Testing and Materials (ASTM) Guidelines. Collagen type I with a high degree of purity was obtained through acid-extraction, as confirmed by colorimetric assays, SDS-PAGE and amino acid composition. Thermal analysis revealed a denaturing temperature around 16 C. Moreover, collagen showed a concentration-dependent effect in metabolism and on cell adhesion of lung fibroblast MRC-5 cells. In conclusion, this study shows that collagen can be obtained from marine-origin sources, while preserving its bioactivity, supporting its use in biomedical applications.European Research Council grant agreement ERC-2012-ADG 20120216-321266 for the project ComplexiTEinfo:eu-repo/semantics/publishedVersio

Astaxanthin Restrains Nitrative-Oxidative Peroxidation in Mitochondrial-Mimetic Liposomes: A Pre-Apoptosis Model

Astaxanthin (ASTA) is a ketocarotenoid found in many marine organisms and that affords many benefits to human health. ASTA is particularly effective against radical-mediated lipid peroxidation, and recent findings hypothesize a "mitochondrial-targeted" action of ASTA in cells. Therefore, we examined the protective effects of ASTA against lipid peroxidation in zwitterionic phosphatidylcholine liposomes (PCLs) and anionic phosphatidylcholine: phosphatidylglycerol liposomes (PCPGLs), at different pHs (6.2 to 8.0), which were challenged by oxidizing/nitrating conditions that mimic the regular and preapoptotic redox environment of active mitochondria. Pre-apoptotic conditions were created by oxidized/nitr(osyl) ated cytochrome c and resulted in the highest levels of lipoperoxidation in both PCL and PCPGLs (pH 7.4). ASTA was less protective at acidic conditions, especially in anionic PCPGLs. Our data demonstrated the ability of ASTA to hamper oxidative and nitrative events that lead to cytochrome c-peroxidase apoptosis and lipid peroxidation, although its efficiency changes with pH and lipid composition of membranes.Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESPBPE fellowship)Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (Bolsa Produtividade em Pesquisa, Nivel 2, CNPq, Brazil)Programa Iberoamericano de Ciencia y Tecnologia para el Desarollo (CYTEDRed iberoamericana para el estudio de nuevos carotenoides bioactivos como ingredientes de alimentos, Spain)Univ Sao Paulo IQUSP, Inst Quim, Dept Bioquim, BR-05508000 Sao Paulo, SP, BrazilUniv Cruzeiro Sul, ICAFE, BR-01506000 Sao Paulo, SP, BrazilSuperintendencia Policia Tecn Cient, BR-05507060 Sao Paulo, SP, BrazilLychnoflora Pesquisa & Dev Prod Nat LTDA, BR-14030090 Ribeirao Preto, SP, BrazilGrp Fleury, BR-04344070 Sao Paulo, SP, BrazilUniv Fed Sao Paulo, Dept Ciencias Exatas & Terra, UNIFESP, BR-09972270 Diadema, SP, BrazilUniv Sao Paulo IQUSP, Inst Quim, Dept Quim Fundamental, BR-05508000 Sao Paulo, SP, BrazilCSIC, IATA, Dept Ciencia Alimentos, Calle Catedrat Agustin Escardino 7, Paterna 46980, SpainUniv Fed Sao Paulo, Dept Ciencias Exatas & Terra, UNIFESP, BR-09972270 Diadema, SP, BrazilFAPESP: 017/06032-2CNPq: 304663/2015-8RIENCBI: 112RT0445Web of Scienc

Dust-filled axially symmetric universes with a cosmological constant

Following the recent recognition of a positive value for the vacuum energy density and the realization that a simple Kantowski-Sachs model might fit the classical tests of cosmology, we study the qualitative behavior of three anisotropic and homogeneous models: Kantowski-Sachs, Bianchi type-I and Bianchi type-III universes, with dust and a cosmological constant, in order to find out which are physically permitted. We find that these models undergo isotropization up to the point that the observations will not be able to distinguish between them and the standard model, except for the Kantowski-Sachs model $(\Omega_{k_{0}}0)$ with $\Omega_{\Lambda_{0}}$ smaller than some critical value $\Omega_{\Lambda_{M}}$. Even if one imposes that the Universe should be nearly isotropic since the last scattering epoch ($z\approx 1000$), meaning that the Universe should have approximately the same Hubble parameter in all directions (considering the COBE 4-Year data), there is still a large range for the matter density parameter compatible with Kantowsky-Sachs and Bianchi type-III if $|\Omega_0+\Omega_{\Lambda_0}-1|\leq \delta$, for a very small $\delta$ . The Bianchi type-I model becomes exactly isotropic owing to our restrictions and we have $\Omega_0+\Omega_{\Lambda_0}=1$ in this case. Of course, all these models approach locally an exponential expanding state provided the cosmological constant $\Omega_\Lambda>\Omega_{\Lambda_{M}}$.Comment: 12 pages, 9 figures, 1 table. Published in Physical Review D 1

Presence of extracellular DNA in candida albicans biofilm matrix and its role in biofilm structure and antifungal susceptibility

Biofilms are structurally complex microconsortia of surface adhering cells embedded within an extracellular matrix (ECM) composed of substances produced and secreted by cells or derived from cell lysis. One of the recently discovered bacterial biofilms ECM components is the extracellular DNA (eDNA). Although the investigation on eDNA in fungal biofilms is scarce, preliminary studies suggest that eDNA may play a role in biofilms formed by the opportunistic fungal pathogen Candida albicans. Thus, the present study aimed at determining the eDNA content of C. albicans SC5314 biofilm ECM and the effect of DNase I treatment on biofilm formation and biofilm cells susceptibility to antifungals, as indicators of the role of eDNA in C. albicans biofilms. Results from our experiments showed that the ECM of C. albicans biofilms formed under conditions of flow for 48 h contained 3045.4 ± 227.3 ng eDNA/mg of protein. Additionally, using a microtiter plate model, we observed that different DNase treatments (0.02 - 2 mg/ml) did not affect further biofilm development by C. albicans adherent cells. However, DNase (> 0.03 mg/ml) promoted a general biomass reduction on C. albicans preformed biofilms. Finally, DNase (0.13 mg/ml) did not change C. albicans biofilm cells susceptibility to fluconazole, but increased their susceptibility to amphotericin B and caspofungin, as indicated by the lower SMIC compared to biofilms grown without DNase. This work presents evidence for the role of eDNA in C. albicans biofilm integrity and antifungal resistance consistent with eDNA being a key element of the ECM

Game and player: C. albicans biofilm lifestyle and extracellular DNA

DNA is as a structural component of bacterial biofilms extracellular matrix (ECM). Although evidences have shown that DNA may play a role in C. albicans biofilms, further studies are required to understand the contribution of extracellular DNA (eDNA) in C. albicans biofilm lifestyle. Herein we aimed to determine the eDNA content of C. albicans SC5314 biofilm ECM and the effect of DNase I and exogenous DNA treatments on biofilm formation and biofilm cells susceptibility to antifungals. First, for eDNA estimation in C. albicans biofilm ECM, biofilms were formed under flow conditions for 48 h. ECM was isolated and its DNA and protein contents were determined. Second, DNase (0.02 - 2 mg/ml) and exogenous DNA (10 - 2560 ng/ml) were added at different stages of biofilm development (microtiter plate model under static conditions). The effect of 24 h treatments was evaluated in terms of biofilm biomass by crystal violet assay (A550). Third, for antifungal testing, biofilms (in 96-well plates) were challenged with amphotericin B (0.06 - 16 mg/l), caspofungin (0.008 to 2 mg/l), and fluconazole (4 - 1024 mg/l) alone or in combination with DNase (0.125 mg/ml) or exogenous DNA (320 ng/ml). Sessile minimum inhibitory concentrations (SMIC) were determined at 80 % inhibition compared to drug-free controls using the XTT reduction assay. RPMI medium was used in all the assays. On one hand, C. albicans biofilms ECM contained 3045.4 ± 227.3 ng eDNA/mg of protein. On the other hand, DNase or exogenous DNA treatments did not affect further biofilm development by C. albicans adherent cells. In contrast, DNase (> 0.03 mg/ml) promoted a general biomass reduction on C. albicans preformed biofilms, as indicated by the reduction of A550 compared with the control. Furthermore addition of exogenous DNA (> 160 ng/ml) to preformed biofilms led to an increase in biofilm biomass, similarly assessed by the higher A550 readings compared with control biofilms. Finally, DNase I (0.125 mg/ml) did not change C. albicans biofilm cells susceptibility to fluconazole, but increased their susceptibility to amphotericin B and caspofungin, as indicated by the lower SMIC compared to biofilms grown without DNase. In contrast, exogenous DNA (320 ng/ml) did not affect C. albicans biofilm cells susceptibility against these antifungals

Uma ferramenta de e-portfólios para o LearningOnWeb

We describe a new approach for the management of e-Portfolios that is being designed for LearningOnWeb, a platform we are currently developing at the University of Coimbra. Our aim is an e- portfolio module that not only lets students maintain their portfolios of assignments, but also facilitates formative assessment by teachers, cross-assessment by colleagues, and reflexive improvement by the owners of the portfolios. We believe that this approach may inspire further insight on the provision of portfolio management tools in e-learning platforms.Neste artigo descrevemos uma plataforma de e-learning actualmente em desenvolvimento na Universidade de Coimbra, o LearningOnWeb, com especial ênfase numa nova abordagem para a gestão de e-Portfolios. O nosso objectivo é desenvolver um módulo de e-portfolios que não só permita aos estudantes gerir o seu portfólio de trabalhos, mas também facilitar a avaliação formativa por parte dos docentes, avaliação cruzada pelos colegas e aperfeiçoamento reflexivo por parte dos possuidores dos portfólios. Acreditamos que esta abordagem pode servir de inspiração para dotar plataformas de e-learning com gestão de portfólios

Sistemas de recompensa: Uma analise empírica de antecedentes e consequências

O objectivo principal deste estudo consistiu em analisar os antecedentes e consequências da configuração do sistema de recompensas. O trabalho avaliou a influência da cultura dominante de uma organização nas características do sistema de recompensas, bem como os efeitos deste no desempenho dos sujeitos. A questão de partida era: qual o contributo da configuração do sistema de recompensas de uma organização para a explicação do nível do desempenho dos seus trabalhadores? Este problema de investigação pode por sua vez subdividir-se nas seguintes questões: que dimensões da cultura organizacional influenciam a configuração do sistema de remuneração? Quais os efeitos do sistema de recompensas de uma organização no desempenho dos seus trabalhadores? Os resultados sugerem que as características do sistema de recompensas de uma organização sofrem influências da cultura organizacional dominante, no que se refere nomeadamente ao nível da orientação competitiva ou orientação humanista. A cultura dominante e o nível de remuneração influem de forma significativa na percepção de equidade, ou seja, organizações com cultura orientada para a competição geram percepções de iniquidade enquanto que organizações de matiz cooperativo promovem percepções de equidade. Por último, as características do sistema de recompensas influenciam múltiplas dimensões do desempenho organizacional.ABSTRACT: This study analyzed some antecedents and consequences of an organization’s reward system. The study evaluated the influence of the dominant culture on the characteristics of the reward system, as well as the effects of this system on organizational behavior. The departing question was: what is the contribution of the reward system to the explanation of behavior in organizations? This research problem was subdivided in the following questions: what dimensions of the culture organizational do influence the compensation system? What are the effects of the reward system? Results suggest that the characteristics of rewards are influenced by the dominant cultural type, operationalized as competitive and humanist orientations. Culture and reward systems influence the perception of fairness, in the sense that organizations with competitive cultures tend to generate more perceptions of inequity, while cooperative organizations promote perceptions of equity.info:eu-repo/semantics/publishedVersio

A Pyranoxanthone as a potent antimitotic and sensitizer of cancer cells to low doses of Paclitaxel

Microtubule-targeting agents (MTAs) remain a gold standard for the treatment of several cancer types. By interfering with microtubules dynamic, MTAs induce a mitotic arrest followed by cell death. This antimitotic activity of MTAs is dependent on the spindle assembly checkpoint (SAC), which monitors the integrity of the mitotic spindle and proper chromosome attachments to microtubules in order to ensure accurate chromosome segregation and timely anaphase onset. However, the cytotoxic activity of MTAs is restrained by drug resistance and/or toxicities, and had motivated the search for new compounds and/or alternative therapeutic strategies. Here, we describe the synthesis and mechanism of action of the xanthone derivative pyranoxanthone 2 that exhibits a potent anti-growth activity against cancer cells. We found that cancer cells treated with the pyranoxanthone 2 exhibited persistent defects in chromosome congression during mitosis that were not corrected over time, which induced a prolonged SAC-dependent mitotic arrest followed by massive apoptosis. Importantly, pyranoxanthone 2 was able to potentiate apoptosis of cancer cells treated with nanomolar concentrations of paclitaxel. Our data identified the potential of the pyranoxanthone 2 as a new potent antimitotic with promising antitumor potential, either alone or in combination regimens.Portugal 2020: PTDC/SAU-PUB/28736/2017 (POCI-01-0145-FEDER-028736; FCT: SFRH/BD/116167/2016/ SFRH/BD/140844/2018/ PD/00016/2012info:eu-repo/semantics/publishedVersio

Terrestrial impact structures as geoheritage: an assessment method of their scientific value and its application to Brazil

Terrestrial impact structures are geological and geomorphological features with particular importance to understand the history and evolution of the planet. Impact structures are scattered around the world but in many countries these features are under threat, essentially due to anthropic factors. Impact structures with higher scienti c value should be considered as geological heritage and, consequently, be subjected to geoconservation strategies. In order to select the most important impact structures to be properly conserved and managed, this paper proposes a quantitative assessment method of the scienti c value of these structures. The eight Brazilian impact structures were used to test this method that has the potential to be applied to any geological context in any country. The structures known as Araguainha Dome-MT and Serra da Cangalha-TO reached a higher scienti c value, which justi es the need to develop geoconservation strategies and a proper management.The Conselho Nacional de Pesquisa e Desenvolvimento (CNPq / National Council for Research and Development) and the Programa Ciências sem Fronteiras / Science Without Borders Programme are acknowledged for the support of the postdoctoral grant No 233209/2013-1 of the 1st author. The work was co-funded by the European Union through the European Regional Development Fund, based on COMPETE 2020 (Programa Operacional da Competitividade e Internacionalização), project ICT (UID/ GEO/04683/2013) with reference POCI-01-0145- FEDER-007690 and Portuguese funds provided by Fundação para a Ciência e Tecnologia.info:eu-repo/semantics/publishedVersio