Protection against oxidation, by CVD or SPS coatings of hafnium carbide and silicon carbide, on carbon/carbon composites

protection of carbon/carbon composites against oxidation at high temperatures. However HfC and most of metallic carbides present a non stoechiometric composition with carbon vacancies. As a consequence, the oxidation resistance is poor at low temperatures (500-1000°C). In order to overcome this main drawback the HfC can be associated with silicon carbide (SiC) presenting a better oxidation resistance at lower temperatures. Two coating routes have been studied; the first one is the Chemical Vapour Deposition which enables to obtain very thin coatings and the second one is the Spark Plasma Sintering technique which permits to get new microstructures of coatings. On first hand, this study describes the CVD conditions for the deposition of HfC from the metallic hafnium pellets to get hafnium chlorides followed by the reduction of the chlorides by H2 and the deposition of HfC with the methane as carbon precursor. This enables to get an alternated multilayer microstructure made of a first layer of SiC on top of which the first layer of HfC is deposited and so on to a ten alternated layer deposit [1]. Please click Additional Files below to see the full abstract

Possible Superconductivity at 37 K in Graphite-Sulfur Composite

Sulfur intercalated graphite composites with diamagnetic transitions at 6.7 K and 37 K are prepared. The magnetization hysteresis loops (MHL), Xray diffraction patterns, and resistance were measured. From the MHL, a slight superconducting like penetration process is observed at 15 K in low field region. The XRD shows no big difference from the mixture of graphite and sulfur indicating that the volume of the superconducting phase (if any) is very small. The temperature dependence of resistance shows a typical semiconducting behavior with a saturation in low temperature region. This saturation is either induced by the de-localization of conducting electrons or by possible superconductivity in this system.Comment: CHIN. PHYS.LETT v18 1648 (2001

Towards improved socio-economic assessments of ocean acidification’s impacts

Ocean acidification is increasingly recognized as a component of global change that could have a wide range of impacts on marine organisms, the ecosystems they live in, and the goods and services they provide humankind. Assessment of these potential socio-economic impacts requires integrated efforts between biologists, chemists, oceanographers, economists and social scientists. But because ocean acidification is a new research area, significant knowledge gaps are preventing economists from estimating its welfare impacts. For instance, economic data on the impact of ocean acidification on significant markets such as fisheries, aquaculture and tourism are very limited (if not non-existent), and non-market valuation studies on this topic are not yet available. Our paper summarizes the current understanding of future OA impacts and sets out what further information is required for economists to assess socio-economic impacts of ocean acidification. Our aim is to provide clear directions for multidisciplinary collaborative research

A DMRG Study of Low-Energy Excitations and Low-Temperature Properties of Alternating Spin Systems

We use the density matrix renormalization group (DMRG) method to study the ground and low-lying excited states of three kinds of uniform and dimerized alternating spin chains. The DMRG procedure is also employed to obtain low-temperature thermodynamic properties of these systems. We consider a 2N site system with spins $s_1$ and $s_2$ alternating from site to site and interacting via a Heisenberg antiferromagnetic exchange. The three systems studied correspond to $(s_1 ,s_2 )$ being equal to $(1,1/2),(3/2,1/2)$ and $(3/2,1)$; all of them have very similar properties. The ground state is found to be ferrimagnetic with total spin $s_G =N(s_1 - s_2)$. We find that there is a gapless excitation to a state with spin $s_G -1$, and a gapped excitation to a state with spin $s_G +1$. Surprisingly, the correlation length in the ground state is found to be very small for this gapless system. The DMRG analysis shows that the chain is susceptible to a conditional spin-Peierls instability. Furthermore, our studies of the magnetization, magnetic susceptibility $\chi$ and specific heat show strong magnetic-field dependences. The product $\chi T$ shows a minimum as a function of temperature T at low magnetic fields; the minimum vanishes at high magnetic fields. This low-field behavior is in agreement with earlier experimental observations. The specific heat shows a maximum as a function of temperature, and the height of the maximum increases sharply at high magnetic fields. Although all the three systems show qualitatively similar behavior, there are some notable quantitative differences between the systems in which the site spin difference, $|s_1 - s_2|$, is large and small respectively.Comment: 16 LaTeX pages, 13 postscript figure

Mechanical response of plectonemic DNA: an analytical solution

We consider an elastic rod model for twisted DNA in the plectonemic regime. The molecule is treated as an impenetrable tube with an effective, adjustable radius. The model is solved analytically and we derive formulas for the contact pressure, twisting moment and geometrical parameters of the supercoiled region. We apply our model to magnetic tweezer experiments of a DNA molecule subjected to a tensile force and a torque, and extract mechanical and geometrical quantities from the linear part of the experimental response curve. These reconstructed values are derived in a self-contained manner, and are found to be consistent with those available in the literature.Comment: 14 pages, 4 figure

Descobrindo “para-formalidades”: atividades que gritam por espaço

A pesquisa trabalha no sentido de mapear e dar visibilidade às cenas “para-formais” encontradas no espaço público dos centros de cidades latinoamericanas. Entendemos “para-formal” como todas as atividades encontradas no espaço público da cidade que não fazem parte de seu desenho urbano (original), mas que “agora” fazem parte de seu cotidiano. A investigação se dá a partir de cartografias urbanas, fazendo uso de recursos infográficos e sendo divulgado em tempo real por meio de website. Destacamos as principais “paraformalidades” encontradas na maioria das cidades que estudamos: trailers, para-ciclos inventados, para-formal no formal, vendedores isolados móveis e o grandes conjuntos para-formais. Podemos adiantar que é possível compreender que esses equipamentos são parte da cidade e devem ser levados em consideração pelos arquitetos e urbanistas, tanto em novos projetos como em revitalizações arquitetônicas e urbanísticas.The research works towards mapping and profiling the scenes “para-formal” found in the public space of the centers of Latin American cities. We understand “para-formal” as all activities found in the public space of the city that are not part of their urban design (the original), but that “now” part of their daily lives. The research starts from urban cartography, making use of infographics and resources being released in real time via the website. Highlight the main “to-tape” found in most cities we studied: trailers, for-cycles invented, paraformal in the formal, isolated mobile sallers and large ensembles para-formals. We anticipate that it is possible to understand that the equipment is part of the city and should be considered by architects and planners, both in new projects such as in architectural and urban revitalization.Eje 3: Derecho a la ciudad: mutaciones, recomposiciones, adaptaciones, reformulaciones.Facultad de Arquitectura y Urbanism

Descobrindo “para-formalidades”: atividades que gritam por espaço

A pesquisa trabalha no sentido de mapear e dar visibilidade às cenas “para-formais” encontradas no espaço público dos centros de cidades latinoamericanas. Entendemos “para-formal” como todas as atividades encontradas no espaço público da cidade que não fazem parte de seu desenho urbano (original), mas que “agora” fazem parte de seu cotidiano. A investigação se dá a partir de cartografias urbanas, fazendo uso de recursos infográficos e sendo divulgado em tempo real por meio de website. Destacamos as principais “paraformalidades” encontradas na maioria das cidades que estudamos: trailers, para-ciclos inventados, para-formal no formal, vendedores isolados móveis e o grandes conjuntos para-formais. Podemos adiantar que é possível compreender que esses equipamentos são parte da cidade e devem ser levados em consideração pelos arquitetos e urbanistas, tanto em novos projetos como em revitalizações arquitetônicas e urbanísticas.The research works towards mapping and profiling the scenes “para-formal” found in the public space of the centers of Latin American cities. We understand “para-formal” as all activities found in the public space of the city that are not part of their urban design (the original), but that “now” part of their daily lives. The research starts from urban cartography, making use of infographics and resources being released in real time via the website. Highlight the main “to-tape” found in most cities we studied: trailers, for-cycles invented, paraformal in the formal, isolated mobile sallers and large ensembles para-formals. We anticipate that it is possible to understand that the equipment is part of the city and should be considered by architects and planners, both in new projects such as in architectural and urban revitalization.Eje 3: Derecho a la ciudad: mutaciones, recomposiciones, adaptaciones, reformulaciones.Facultad de Arquitectura y Urbanism

Exposure of mediterranean countries to ocean acidification

This study examines the potential effects of ocean acidification on countries and fisheries of the Mediterranean Sea. The implications for seafood security and supply are evaluated by examining the sensitivity of the Mediterranean to ocean acidification at chemical, biological, and macro-economic levels. The limited information available on impacts of ocean acidification on harvested (industrial, recreational, and artisanal fishing) and cultured species (aquaculture) prevents any biological impact assessment. However, it appears that non-developed nations around the Mediterranean, particularly those for which fisheries are increasing, yet rely heavily on artisanal fleets, are most greatly exposed to socioeconomic consequences from ocean acidification. © 2014 by the authors; licensee MDPI, Basel, Switzerland

Descobrindo “para-formalidades”: atividades que gritam por espaço

A pesquisa trabalha no sentido de mapear e dar visibilidade às cenas “para-formais” encontradas no espaço público dos centros de cidades latinoamericanas. Entendemos “para-formal” como todas as atividades encontradas no espaço público da cidade que não fazem parte de seu desenho urbano (original), mas que “agora” fazem parte de seu cotidiano. A investigação se dá a partir de cartografias urbanas, fazendo uso de recursos infográficos e sendo divulgado em tempo real por meio de website. Destacamos as principais “paraformalidades” encontradas na maioria das cidades que estudamos: trailers, para-ciclos inventados, para-formal no formal, vendedores isolados móveis e o grandes conjuntos para-formais. Podemos adiantar que é possível compreender que esses equipamentos são parte da cidade e devem ser levados em consideração pelos arquitetos e urbanistas, tanto em novos projetos como em revitalizações arquitetônicas e urbanísticas.The research works towards mapping and profiling the scenes “para-formal” found in the public space of the centers of Latin American cities. We understand “para-formal” as all activities found in the public space of the city that are not part of their urban design (the original), but that “now” part of their daily lives. The research starts from urban cartography, making use of infographics and resources being released in real time via the website. Highlight the main “to-tape” found in most cities we studied: trailers, for-cycles invented, paraformal in the formal, isolated mobile sallers and large ensembles para-formals. We anticipate that it is possible to understand that the equipment is part of the city and should be considered by architects and planners, both in new projects such as in architectural and urban revitalization.Eje 3: Derecho a la ciudad: mutaciones, recomposiciones, adaptaciones, reformulaciones.Facultad de Arquitectura y Urbanism

Probing complex RNA structures by mechanical force

RNA secondary structures of increasing complexity are probed combining single molecule stretching experiments and stochastic unfolding/refolding simulations. We find that force-induced unfolding pathways cannot usually be interpretated by solely invoking successive openings of native helices. Indeed, typical force-extension responses of complex RNA molecules are largely shaped by stretching-induced, long-lived intermediates including non-native helices. This is first shown for a set of generic structural motifs found in larger RNA structures, and then for Escherichia coli's 1540-base long 16S ribosomal RNA, which exhibits a surprisingly well-structured and reproducible unfolding pathway under mechanical stretching. Using out-of-equilibrium stochastic simulations, we demonstrate that these experimental results reflect the slow relaxation of RNA structural rearrangements. Hence, micromanipulations of single RNA molecules probe both their native structures and long-lived intermediates, so-called "kinetic traps", thereby capturing -at the single molecular level- the hallmark of RNA folding/unfolding dynamics.Comment: 9 pages, 9 figure