2,036 research outputs found

    Which mechanism underlies the water-like anomalies in core-softened potentials?

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    Using molecular dynamics simulations we investigate the thermodynamic of particles interacting with a continuous and a discrete versions of a core-softened (CS) intermolecular potential composed by a repulsive shoulder. Dynamic and structural properties are also analyzed by the simulations. We show that in the continuous version of the CS potential the density at constant pressure has a maximum for a certain temperature. Similarly the diffusion constant, DD, at a constant temperature has a maximum at a density ρmax\rho_{\mathrm{max}} and a minimum at a density ρmin<ρmax\rho_{\mathrm{min}}<\rho_{\mathrm{max}}, and structural properties are also anomalous. For the discrete CS potential none of these anomalies are observed. The absence of anomalies in the discrete case and its presence in the continuous CS potential are discussed in the framework of the excess entropy.Comment: 8 page

    The Heumann-Hotzel model for aging revisited

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    Since its proposition in 1995, the Heumann-Hotzel model has remained as an obscure model of biological aging. The main arguments used against it were its apparent inability to describe populations with many age intervals and its failure to prevent a population extinction when only deleterious mutations are present. We find that with a simple and minor change in the model these difficulties can be surmounted. Our numerical simulations show a plethora of interesting features: the catastrophic senescence, the Gompertz law and that postponing the reproduction increases the survival probability, as has already been experimentally confirmed for the Drosophila fly.Comment: 11 pages, 5 figures, to be published in Phys. Rev.

    Surface boundary layer characteristics over caatinga vegetation in tropical semiarid region of N-E Brazil

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    Some characteristic features of the atmospheric surface layer over a tropical semiarid station Petrolina (9.9◦S, 40.22◦W, 365.5 m) in N-E Brazil, are investigated, using data collected from a micrometeorological tower of 9 m height. This study utilizes the wind, temperature, humidity and carbon dioxide (CO2) data obtained for the month of July 2004. The diurnal variation of mean parameters such as temperature, relative humidity, wind speed and CO2 are studied. Turbulent statistics are computed using the eddy correlation technique, and are studied under the framework of Monin-Obukhov similarity theory with results compared with other experimental studies reported in the literature

    A case study on the eco-efficiency performance of a composite processing industry: evaluation and quantification of potential improvements

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    In this study, an attempt was made in order to measure and evaluate the eco-efficiency performance of a pultruded composite processing company. For this purpose the recommendations of World Business Council for Sustainable Development (WCSD) and the directives of ISO 14301 standard were followed and applied. The main general indicators of eco-efficiency, as well as the specific indicators, were defined and determined. With basis on indicators’ figures, the value profile, the environmental profile, and the pertinent eco-efficiency ratios were established and analyzed. In order to evaluate potential improvements on company eco-performance, new indicators values and eco-efficiency ratios were estimated taking into account the implementation of new proceedings and procedures, at both upstream and downstream of the production process, namely: i) Adoption of a new heating system for pultrusion die-tool in the manufacturing process, more effective and with minor heat losses; ii) Recycling approach, with partial waste reuse of scrap material derived from manufacturing, cutting and assembly processes of GFRP profiles. These features lead to significant improvements on the sequent assessed eco-efficiency ratios of the present case study, yielding to a more sustainable product and manufacturing process of pultruded GFRP profiles

    Adaptação ao cultivo e valorização de Lavandula luisieri

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    Foram estudadas diversas populações de Lavandula luisieri (Rozeira) Rivas-Martínez endémicas da Península Ibérica (Beira Interior, Castilla-la-Mancha e Andaluzia; acessos de Casal da Fraga, Mata, Penamacor e Vila Velha de Ródão – Portugal; Toledo e Sevilha – Espanha), comparando as populações relativamente ao óleo essencial (quantitativamente e qualitativamente), assim como, a sua actividade insecticida sobre pragas fitófagas (Spodoptera littoralis, Mysus persicae e Leptinotarsa decemlineata). Em função dos seus componentes escolheram-se as duas populações mais interessantes em termos da sua actividade biológica (Penamacor e Toledo) e instalaram-se dois campos produtivos em Castelo Branco e Saragoça, por forma a inferir sobre a influência do local de produção na qualidade do material vegetal obtido. Será fornecida informação técnica sobre a instalação destes campos

    Developmental Aspects of Glucose and Calcium Availability on the Persistence of Memory Function Over the Lifespan

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    An important aspect concerning the underlying nature of memory function is an understanding of how memories are acquired and lost. The stability, and ultimate demise, of memory over the lifespan of an organism remains a critical topic in determining the neurobiological mechanisms that mediate memory representations. This has important implications for the elucidation and treatment of neurodegenerative diseases such as Alzheimer’s disease (AD). One important question in the context of preserving functional plasticity over the lifespan is the determination of the neurobiological structural and functional changes that contribute to the formation of memory during the juvenile time frame that might provide protection against later memory dysfunction by promoting the establishment of redundant neural pathways. The main question being, if memory formation during the juvenile period does strengthen and preserve memory stability over the lifespan, what are the neurobiological structural or functional substrates that mediate this effect? One neural attribute whose function may be altered with early life experience and provide a mechanism to preserve memory through the lifespan is glucose transport-linked calcium (Ca2+) buffering. Because peak increases in glucose utilization overlap with a timeframe during which spatial training can enhance later memory processing, it might be the case that learning-associated changes in glucose utilization would provide an important neural functional change to preserve memory function throughout the lifespan. The glucose transporters are proteins that are reduced in AD pathology and there is evidence that glucose reductions can impair Ca2+ buffering. In the absence of an appropriate supply of ATP, provided via glucose transport and glycolysis, Ca2+ levels can rise leading

    Entanglement study of the 1D Ising model with Added Dzyaloshinsky-Moriya interaction

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    We have studied occurrence of quantum phase transition in the one-dimensional spin-1/2 Ising model with added Dzyaloshinsky-Moriya (DM) interaction from bi- partite and multi-partite entanglement point of view. Using exact numerical solutions, we are able to study such systems up to 24 qubits. The minimum of the entanglement ratio R \equiv \tau 2/\tau 1 < 1, as a novel estimator of QPT, has been used to detect QPT and our calculations have shown that its minimum took place at the critical point. We have also shown both the global-entanglement (GE) and multipartite entanglement (ME) are maximal at the critical point for the Ising chain with added DM interaction. Using matrix product state approach, we have calculated the tangle and concurrence of the model and it is able to capture and confirm our numerical experiment result. Lack of inversion symmetry in the presence of DM interaction stimulated us to study entanglement of three qubits in symmetric and antisymmetric way which brings some surprising results.Comment: 18 pages, 9 figures, submitte

    Implante transcateter valve‐in‐valve para disfunção de biopróteses cirúrgicas aórticas

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    RESUMOIntroduçãoEstudos recentes têm demonstrado a eficácia do implante transcateter valve‐in‐valve para o tratamento de disfunção de biopróteses em pacientes de alto risco cirúrgico. Apresentamos nossa experiência inicial com o implante valve‐in‐valve.MétodosCaracterizamos o perfil clínico, ecocardiográfico e do procedimento, e reportamos os resultados de médio prazo de pacientes com disfunção de bioprótese submetidos a implante valve‐in‐valve em posição aórtica.ResultadosIncluímos sete pacientes do sexo masculino, com idade de 72,6 ± 10,0 anos. O escore STS foi 9,6 ± 10,5%, e o EuroSCORE logístico foi 22,7 ± 14,7%. Três pacientes apresentavam dupla disfunção; dois tinham insuficiência; e dois exibiam estenose isolada. A via transfemoral foi utilizada em seis casos, e a transapical, em um caso. Os dispositivos implantados incluíram as próteses Sapien XT (n = 5) e CoreValve (n = 2). O sucesso do procedimento foi obtido em seis (85,7%) casos. Após o procedimento, o gradiente médio reduziu‐se de 38,2 ± 9,6mmHg para 20,9 ± 5,9mmHg, e a área valvar elevou‐se de 1,2 ± 0,4cm2 para 1,5 ± 0,5cm2. Ao final de 1 ano, não ocorreram óbitos e nem outros desfechos adversos significativos; 80% dos pacientes encontravam‐se em classe funcional NYHA I/II. Os gradientes transvalvares e a área valvar permaneceram inalterados nesse período.ConclusõesO procedimento valve‐in‐valve foi eficaz na maioria dos pacientes de alto risco cirúrgico com disfunção de bioprótese. Quando realizado em pacientes bem selecionados, resulta em desfechos clínicos e hemodinâmicos satisfatórios.ABSTRACTBackgroundRecent studies have demonstrated the efficacy of the transcatheter valve‐in‐valve implantation for the treatment of bioprosthesis dysfunction in high‐risk surgical patients. This study presents the initial experience with valve‐in‐valve implantation.MethodsClinical, echocardiographic, and procedural profiles were characterized, and the mid‐term results of patients with surgical bioprosthesis dysfunction submitted to valve‐in‐valve implantation in the aortic position were reported.ResultsSeven male patients were included, aged 72.6 ± 10.0 years. The STS score was 9,6 ± 10,5%, and the logistic EuroSCORE was 22.7 ± 14.7%. Three patients had combined aortic bioprosthesis failure; two had isolated regurgitation; and two had isolated stenosis. The transfemoral access was used in six cases, and the transapical access in one case. Implanted devices included Sapien XT (n = 5) and CoreValve (n = 2) prostheses. Procedural success was achieved in six (85.7%) cases. After the procedure, the mean gradient decreased from 38.2 ± 9.6mmHg to 20.9 ± 5.9mmHg, and the valve area increased from 1.2 ± 0.4cm2 to 1.5 ± 0.5cm2. After 1 year, there were no deaths and no other significant adverse outcomes; 80% of patients were in NYHA functional class I/II. The transvalvular gradients and valve area remained unchanged in this period.ConclusionsThe valve‐in‐valve procedure was effective in most high‐risk surgical patients with bioprosthesis dysfunction. When performed in well‐selected patients, it results in satisfactory clinical and hemodynamic outcomes
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