3,017 research outputs found

    Morphological transition between diffusion-limited and ballistic aggregation growth patterns

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    In this work, the transition between diffusion-limited and ballistic aggregation models was revisited using a model in which biased random walks simulate the particle trajectories. The bias is controlled by a parameter λ\lambda, which assumes the value λ=0\lambda=0 (1) for ballistic (diffusion-limited) aggregation model. Patterns growing from a single seed were considered. In order to simulate large clusters, a new efficient algorithm was developed. For λ0\lambda \ne 0, the patterns are fractal on the small length scales, but homogeneous on the large ones. We evaluated the mean density of particles ρˉ\bar{\rho} in the region defined by a circle of radius rr centered at the initial seed. As a function of rr, ρˉ\bar{\rho} reaches the asymptotic value ρ0(λ)\rho_0(\lambda) following a power law ρˉ=ρ0+Arγ\bar{\rho}=\rho_0+Ar^{-\gamma} with a universal exponent γ=0.46(2)\gamma=0.46(2), independent of λ\lambda. The asymptotic value has the behavior ρ01λβ\rho_0\sim|1-\lambda|^\beta, where β=0.26(1)\beta= 0.26(1). The characteristic crossover length that determines the transition from DLA- to BA-like scaling regimes is given by ξ1λν\xi\sim|1-\lambda|^{-\nu}, where ν=0.61(1)\nu=0.61(1), while the cluster mass at the crossover follows a power law Mξ1λαM_\xi\sim|1 -\lambda|^{-\alpha}, where α=0.97(2)\alpha=0.97(2). We deduce the scaling relations \beta=\n u\gamma and β=2να\beta=2\nu-\alpha between these exponents.Comment: 7 pages, 8 figure

    Using lean thinking principles to reduce wastes in reconfiguration of car radio final assembly lines

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    Assembly lines are production systems designed to be oriented to the product and well known to be highly productive. Nevertheless, during this time-frame the product volumes could decrease and the assembly lines, previously very productive and efficient, becomes unproductive and inefficient. This happens in the car electronics components company where this study took place that due to customer's demand decrease, produced volumes also decreased and provoked the appearance of wastes related with too much occupied space, unbalanced workstations, more capacity than needed, outdated standard work sheets, bottlenecks, to conclude, too many non-added value activities. This paper presents a reconfiguration proposal for two final assembly lines with the goal of adapt physically the lines to the actual production volumes and eliminate the existing wastes. The proposed reconfiguration translates into very positive gains for the company, namely, the release of 22% of the space occupied by the production lines, a reduction in the number of operators, a 50% increase in productivity for each of the lines and an increase in the utilization rate (23% for line 1 and 13% for line 2). In total, the monetary gains associated with these improvements were, approximately, of 125,600 m.u. per year.Special thanks to engineer Hugo Moreira for all the advice given for the development of this project. Also, thanks to the company for all the cooperation and opportunity to apply knowledge acquired during the academic years. This work has been supported by FCT – Fundação para a Ciência e Tecnologia within the Project Scope: UID/CEC/00319/2019

    Danos e alternativas de controle do percevejo-de-renda na cultura da mandioca no estado do Rio Grande do Norte.

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    Indicadores de digestibilidade de dietas para ovinos contendo feno de ponta de cana-de-açúcar hidrolisado.

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    Made available in DSpace on 2017-12-18T23:24:49Z (GMT). No. of bitstreams: 1 RBSPA2017V18N1FENODEPONTADECANA.pdf: 190963 bytes, checksum: 9b647ac7ed3ea86ec0ade23af14eb5e5 (MD5) Previous issue date: 2017-12-18bitstream/item/169216/1/RBSPA-2017-V18-N1-FENO-DE-PONTA-DE-CANA.pd

    Desenvolvimento de livro interativo digital sobre sistema de integração lavoura-pecuária-floresta no polo agrícola de Paragominas no estado do Pará.

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    O desenvolvimento da informática e a popularização da internet expandiu o alcance de novas mídias. O conhecimento científico pode estar acessível e ao alcance das pessoas, que possuam mínimos conhecimentos de computação. O sistema de integração lavoura-pecuária-floresta (iLPF) está em fase inicial de adoção comercial e foi descrito na forma de livro interativo digital. O desenvolvimento regional foi relatado para divulgação de experiências exitosas com pecuária sustentável na Amazônia. A tecnologia é composta de uma série de princípios aplicados em torno da interação dos componentes florestais, agrícolas e pecuários do sistema. A mudança na paisagem rural é de longo prazo e pode ser descrita visualmente por meio de modelo de simulação digital, fotografia e vídeo. A síntese do conhecimento pode ser elaborada por vários tipos de modernas mídias amplamente disponíveis. O livro interativo digital foi desenvolvido tendo como base um banco de dados de fotografias e informações técnicas a respeito do polo agrícola de Paragominas. O trabalho foi inovador, sendo o primeiro livro interativo digital desenvolvido na Embrapa no Brasil

    Molecular mechanisms beyond glucose transport in diabetes-related male infertility

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    Diabetes mellitus (DM) is one of the greatest public health threats in modern societies. Although during a few years it was suggested that DM had no significant effect in male reproductive function, this view has been challenged in recent years. The increasing incidence of DM worldwide will inevitably result in a higher prevalence of this pathology in men of reproductive age and subfertility or infertility associated with DM is expected to dramatically rise in upcoming years. From a clinical perspective, the evaluation of semen parameters, as well as spermatozoa deoxyribonucleic acid (DNA) integrity, are often studied due to their direct implications in natural and assisted conception. Nevertheless, recent studies based on the molecular mechanisms beyond glucose transport in testicular cells provide new insights in DM-induced alterations in male reproductive health. Testicular cells have their own glucose sensing machinery that react to hormonal fluctuations and have several mechanisms to counteract hyper- and hypoglycemic events. Moreover, the metabolic cooperation between testicular cells is crucial for normal spermatogenesis. Sertoli cells (SCs), which are the main components of blood–testis barrier, are not only responsible for the physical support of germ cells but also for lactate production that is then metabolized by the developing germ cells. Any alteration in this tied metabolic cooperation may have a dramatic consequence in male fertility potential. Therefore, we present an overview of the clinical significance of DM in the male reproductive health with emphasis on the molecular mechanisms beyond glucose fluctuation and transport in testicular cells
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