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‣ Modelos de material para espumas poliméricas aplicadas a estruturas aeronáuticas em material compósito sanduíche; Material models for polymeric foams applied to aircraft structures in sandwich composite materials

Caliri Junior, Mauricio Francisco
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 08/07/2010 Português
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Estruturas aeronáuticas são em sua grande parte fabricadas em material compósito para que sejam atendidas as especificações de projeto. Entre essas estruturas destaca-se a estrutura sanduíche. A utilização desse tipo de estrutura requer estudos extensos em novos materiais, bem como na aplicação dos mesmos. Uma atenção especial para o núcleo dessas estruturas é necessária, pois este material é na verdade uma estrutura celular, como as espumas poliméricas. Esta dissertação busca concatenar a literatura com a prática ao estudar a calibração de modelos de material para descrever o comportamento mecânico de espumas poliméricas, bem como avaliar suas potencialidades e limitações. Estas espumas são estruturas celulares cujos mecanismos de falha consistem em respostas micro e macroscópicas. A identificação e quantificação desses comportamentos podem ser feitas através da investigação de modelos de material micro-mêcanicos ou fenomenológicos (macro-mecânicos) associados a ensaios e análises experimentais tanto do material celular quanto da estrutura na qual este material é utilizado. Cada abordagem, micro ou macro-mecânica, possui vantagens e desvantagens que no presente trabalho são discutidas para o material estudado (espuma polimérica rígida de PVC...

‣ Estruturas celulares, transição celular/dendritica e estruturas dendriticas na solidificação unidirecional transitoria; Cellular structures, cellular/dendritic transition and dendritic structures during transient unidirectional solidification

Daniel Monteiro Rosa
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 31/05/2007 Português
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As morfologias das estruturas de solidificação, caracterizadas principalmente por arranjos celulares e dendríticos, e suas grandezas representadas por espaçamentos celulares e dendríticos primários, secundários e terciários, controlam os perfis de segregação e a formação de segundas fases dentro das regiões intercelulares ou interdendríticas, que determinam as propriedades finais das estruturas fundidas. O presente trabalho pretende contribuir para o entendimento do desenvolvimento microestrutural de ligas binárias através da análise de dois sistemas binários que possuem elevada importância para a indústria na fabricação de peças fundidas automotivas e grades de baterias: Al-Si e Pb-Sb, respectivamente. Os experimentos realizados utilizaram dois diferentes dispositivos em que o calor é extraído somente pelo sistema de resfriamento a água, localizado no fundo (solidificação ascendente) e no topo (solidificação descendente) da lingoteira. As variáveis térmicas de solidificação foram determinadas pela leitura de temperaturas a partir de termopares posicionados dentro da lingoteira em diferentes posições em relação à superfície refrigerada. Estas variáveis térmicas foram confrontadas com as previsões teóricas de um modelo numérico de solidificação. Os aspectos macroestruturais e microestruturais foram caracterizados ao longo dos lingotes através de microscopia óptica. Para as ligas Al-Si foi realizada uma análise complementar do efeito da convecção térmica e constitucional nos espaçamentos dendríticos terciários na solidificação unidirecional transitória descendente. Ligas hipoeutéticas Pb-Sb foram utilizadas para analisar as influências das variáveis térmicas de solidificação e da concentração de soluto nas estruturas celulares...

‣ Process Development for Manufacturing of Cellular Structures with Controlled Geometry and Properties

Pinto,Paulo; Peixinho,Nuno; Soares,Delfim; Silva,Filipe
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2015 Português
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This study presents experimental results on the behaviour of aluminium alloy metal structures and foams manufactured by lost-wax casting and using 3D printed components for internal structure definition. Results for tensile tests, metallurgical properties, surface quality and geometry tolerances were obtained and discussed. The analysis focused on development geometries, used for adjusting manufacturing parameters and prototype geometries intended for geometrical and mechanical validation. The results are indicative of the viability of the method for producing foam structures suitable for mechanical loading.

‣ Whole cell 3D STORM reveals interactions between cellular structures with nanometer-scale resolution

Huang, Bo; Jones, Sara A.; Brandenburg, Boerries; Zhuang, Xiaowei
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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The ability to directly visualize nanoscopic cellular structures and their spatial relationship in all three dimensions will greatly enhance our understanding of molecular processes in cells. Here, we demonstrated multicolor three-dimensional (3D) stochastic optical reconstruction microscopy (STORM) as a tool to quantitatively probe cellular structures and their interactions. To facilitate STORM imaging, we generated photoswitchable probes in several distinct colors by covalently linking a photoswitchable cyanine reporter and an activator molecule to assist bioconjugation. 3D localization was performed in conjunction with focal plane scanning and correction for refractive index mismatch to obtain whole-cell images with a spatial resolution of 20–30 nm and 60–70 nm in the lateral and axial dimensions, respectively. Using this approach, we imaged the entire mitochondrial network in fixed monkey kidney BS-C-1 cells, and studied the spatial relationship between mitochondria and microtubules. The 3D STORM images revealed mitochondrial morphologies as well as mitochondria-microtubule contacts that were obscured in conventional fluorescence images.

‣ Formation of ordered cellular structures in suspension via label-free negative magnetophoresis

Krebs, Melissa D.; Erb, Randall M.; Yellen, Benjamin B.; Samanta, Bappaditya; Bajaj, Avinash; Rotello, Vincent M.; Alsberg, Eben
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 13/05/2009 Português
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The creation of ordered cellular structures is important for tissue engineering research. Here we present a novel strategy for the assembly of cells into linear arrangements by negative magnetophoresis using inert, cytocompatible magnetic nanoparticles. In this approach, magnetic nanoparticles dictate the cellular assembly without relying on cell binding or uptake. The linear cell structures are stable and can be further cultured without the magnetic field or nanoparticles, making this an attractive tool for tissue engineering.

‣ Nonlinear structured-illumination microscopy with a photoswitchable protein reveals cellular structures at 50-nm resolution

Rego, E. Hesper; Shao, Lin; Macklin, John J.; Winoto, Lukman; Johansson, Göran A.; Kamps-Hughes, Nicholas; Davidson, Michael W.; Gustafsson, Mats G. L.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
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Using ultralow light intensities that are well suited for investigating biological samples, we demonstrate whole-cell superresolution imaging by nonlinear structured-illumination microscopy. Structured-illumination microscopy can increase the spatial resolution of a wide-field light microscope by a factor of two, with greater resolution extension possible if the emission rate of the sample responds nonlinearly to the illumination intensity. Saturating the fluorophore excited state is one such nonlinear response, and a realization of this idea, saturated structured-illumination microscopy, has achieved approximately 50-nm resolution on dye-filled polystyrene beads. Unfortunately, because saturation requires extremely high light intensities that are likely to accelerate photobleaching and damage even fixed tissue, this implementation is of limited use for studying biological samples. Here, reversible photoswitching of a fluorescent protein provides the required nonlinearity at light intensities six orders of magnitude lower than those needed for saturation. We experimentally demonstrate approximately 40-nm resolution on purified microtubules labeled with the fluorescent photoswitchable protein Dronpa, and we visualize cellular structures by imaging the mammalian nuclear pore and actin cytoskeleton. As a result...

‣ Quantification of asymmetric microtubule nucleation at sub-cellular structures

Zhu, Xiaodong; Kaverina, Irina
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2011 Português
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Cell polarization is important for multiple physiological processes. In polarized cells, microtubules (MTs) are organized into a spatially polarized array. Generally, in non-differentiated cells, it is assumed that MTs are symmetrically nucleated exclusively from centrosome (microtubule organizing center, MTOC) and then reorganized into the asymmetric array. We have recently identified the Golgi complex as an additional MTOC that asymmetrically nucleates MTs toward one side of the cell. Methods used for alternative MTOC identification include microtubule re-growth after complete drug-induced depolymerization and tracking of growing microtubules using fluorescence labeled MT +TIP binding proteins in living cells. These approaches can be used for quantification of MT nucleation sites at diverse sub-cellular structures.

‣ Advances in high-resolution imaging – techniques for three-dimensional imaging of cellular structures

Lidke, Diane S.; Lidke, Keith A.
Fonte: Company of Biologists Publicador: Company of Biologists
Tipo: Artigo de Revista Científica
Publicado em 01/06/2012 Português
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A fundamental goal in biology is to determine how cellular organization is coupled to function. To achieve this goal, a better understanding of organelle composition and structure is needed. Although visualization of cellular organelles using fluorescence or electron microscopy (EM) has become a common tool for the cell biologist, recent advances are providing a clearer picture of the cell than ever before. In particular, advanced light-microscopy techniques are achieving resolutions below the diffraction limit and EM tomography provides high-resolution three-dimensional (3D) images of cellular structures. The ability to perform both fluorescence and electron microscopy on the same sample (correlative light and electron microscopy, CLEM) makes it possible to identify where a fluorescently labeled protein is located with respect to organelle structures visualized by EM. Here, we review the current state of the art in 3D biological imaging techniques with a focus on recent advances in electron microscopy and fluorescence super-resolution techniques.

‣ Complex Ordered Patterns in Mechanical Instability Induced Geometrically Frustrated Triangular Cellular Structures

Kang, Sung Hoon; Shan, Sicong; Kosmrlj, Andrej; Noorduin, Wim L.; Shian, Samuel; Weaver, James C.; Clarke, David R.; Bertoldi, Katia
Fonte: American Physical Society Publicador: American Physical Society
Tipo: Artigo de Revista Científica
Português
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Geometrical frustration arises when a local order cannot propagate throughout the space because of geometrical constraints. This phenomenon plays a major role in many systems leading to disordered ground-state configurations. Here, we report a theoretical and experimental study on the behavior of buckling-induced geometrically frustrated triangular cellular structures. To our surprise, we find that buckling induces complex ordered patterns which can be tuned by controlling the porosity of the structures. Our analysis reveals that the connected geometry of the cellular structure plays a crucial role in the generation of ordered states in this frustrated system.; Engineering and Applied Sciences; Physics

‣ Compaction through Buckling in 2D Periodic, Soft and Porous Structures: Effect of Pore Shape

Overvelde, Johannes Tesse Bastiaan; Shan, Sicong; Bertoldi, Katia
Fonte: Wiley Blackwell Publicador: Wiley Blackwell
Tipo: Artigo de Revista Científica
Português
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Soft cellular structures that comprise a solid matrix with a square array of holes open avenues for the design of novel soft and foldable structures. Our results demonstrate that by simply changing the shape of the holes the response of porous structure can be easily tuned and soft structures with optimal compaction can be designed.; Engineering and Applied Sciences

‣ Scaling and Selection in Cellular Structures and Living Polymers

Mukamel, David
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 28/02/1995 Português
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The dynamical behavior of two types of non-equilibrium systems is discussed: $(a)$ two-dimensional cellular structures, and $(b)$ living polymers. Simple models governing their evolution are introduced and steady state distributions (cell side in the case of cellular structures and length in the case of living polymers) are calculated. In both cases the models possess a one parameter family of steady state distributions. Selection mechanism by which a particular distribution is dynamically selected is discussed.; Comment: 12 pages, 2 figures, two seminars presented at the 1994 Les Houches Summer School ``Fluctuating Geometries in Statistical Mechanics and Field Theory.'' (also available at http://xxx.lanl.gov/lh94/)

‣ Numerical calculations of effective elastic properties of two cellular structures

Tuncer, Enis
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/04/2004 Português
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Young's moduli of regular two-dimensional truss-like and eye-shape-like structures are simulated by using the finite element method. The structures are the idealizations of soft polymeric materials used in the electret applications. In the simulations size of the representative smallest units are varied, which changes the dimensions of the cell-walls in the structures. A power-law expression with a quadratic as the exponential term is proposed for the effective Young's moduli of the systems as a function of the solid volume fraction. The data is divided into three regions with respect to the volume fraction; low, intermediate and high concentrations. The parameters of the proposed power-law expression in each region are later represented as a function of the structural parameters, unit-cell dimensions. The presented expression can be used to predict structure/property relationship in materials with similar cellular structures. It is observed that the structures with volume fractions of solid higher than 0.15 exhibit the importance of the cell-wall thickness contribution in the elastic properties. The cell-wall thickness is the most significant factor to predict the effective Young's modulus of regular cellular structures at high volume fractions of solid. At lower concentrations of solid...

‣ Analysis of Poisson Networks and Their Relation with Random Cellular Structures

Karimipour, V.; Saaidi, Kh.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 13/03/1996 Português
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We perform a detailed analysis of the statistical properties of Poisson networks and show that the metric and topological properties of random cellular structures, can not be derived from simple models of random networks based on a poisson point distribution [1]. In particular we show that Lewis and Aboav-Wieare laws are not obeyed in these network.; Comment: 17 pages , Latex , 3 Figures available upon request

‣ Compliant Pressure Actuated Cellular Structures

Pagitz, Markus
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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A novel concept for pressure actuated cellular structures that can change their shape between any two given one-dimensional functions was published by Pagitz et al 2012 Bioinspir. Biomim. 7. However, the underlying computational framework is limited to two cell rows and assumes frictionless cell corner hinges. This article extends previous work by taking into account an arbitrary number of cell rows, hinge eccentricities and rotational prings at hinges. Hence it is possible to design compliant pressure actuated cellular structures that can change their shape between any given set of one-dimensional functions. Furthermore, a potential based optimization approach is introduced that reduces the number of iterations by an order of magnitude.; Comment: 24 pages, 10 figures

‣ Hierarchical Cellular Structures in High-Capacity Cellular Communication Systems

Jain, R. K.; Katiyar, Sumit; Agrawal, N. K.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/10/2011 Português
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In the prevailing cellular environment, it is important to provide the resources for the fluctuating traffic demand exactly in the place and at the time where and when they are needed. In this paper, we explored the ability of hierarchical cellular structures with inter layer reuse to increase the capacity of mobile communication network by applying total frequency hopping (T-FH) and adaptive frequency allocation (AFA) as a strategy to reuse the macro and micro cell resources without frequency planning in indoor pico cells [11]. The practical aspects for designing macro- micro cellular overlays in the existing big urban areas are also explained [4]. Femto cells are inducted in macro / micro / pico cells hierarchical structure to achieve the required QoS cost effectively.; Comment: 7 pages, 8 figures, International Journal

‣ Sine-Gordon Solitons, Kinks and Breathers as Physical Models of Nonlinear Excitations in Living Cellular Structures

Ivancevic, Vladimir G.; Ivancevic, Tijana T.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 02/05/2013 Português
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Nonlinear space-time dynamics, defined in terms of celebrated 'solitonic' equations, brings indispensable tools for understanding, prediction and control of complex behaviors in both physical and life sciences. In this paper, we review sine-Gordon solitons, kinks and breathers as models of nonlinear excitations in complex systems in physics and in living cellular structures, both intra-cellular (DNA, protein folding and microtubules) and inter-cellular (neural impulses and muscular contractions). Key words: Sine-Gordon solitons, kinks and breathers, DNA, Protein folding, Microtubules, Neural conduction, Muscular contraction; Comment: 55 pages, 11 figures, Latex. arXiv admin note: text overlap with arXiv:quant-ph/9512021, arXiv:hep-ph/9505401, arXiv:nlin/0205044, arXiv:cond-mat/0209427, arXiv:cond-mat/9906020, arXiv:patt-sol/9809011 by other authors

‣ Cellular structures using $\textbf{U}_q$-tilting modules

Andersen, Henning Haahr; Stroppel, Catharina; Tubbenhauer, Daniel
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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We use the theory of $\textbf{U}_q$-tilting modules to construct cellular bases for centralizer algebras. Our methods are quite general and work for any quantum group $\textbf{U}_q$ attached to a Cartan matrix and include the non semi-simple cases for $q$ being a root of unity and ground fields of positive characteristic. Our approach also generalize to certain categories containing infinite-dimensional modules. As an application, we recover several known cellular structures (which all fit into our general set-up) as we illustrate in a list of examples.; Comment: 51 pages, lots of figures, comments welcome, some typos corrected

‣ Design of Pressure Actuated Cellular Structures

Pagitz, Markus
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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A novel concept for pressure actuated cellular structures was published in Pagitz et al 2012 Bioinspir. Biomim. 7. The corresponding mathematical foundation for the simulation and optimization of compliant cellular structures with eccentric cell corner hinges was published in Pagitz 2015 arXiv:1403.2197. The aim of this article is threefold: First, analytical expressions for optimal materials of compliant cellular structures with identical properties are derived as a function of cell sizes. It is shown that cellular structures can be made from either a large, small number of highly, lowly pressurized cells that consist of a stiff, soft material. Second, extensions to the previously published numerical model are presented and their application ranges are determined. Third, end cap designs for prismatic cells are developed that can withstand substantial differential pressures while being flexible enough to allow large cross sectional shape changes. Furthermore, a manufacturing approach that is based on cytoskeletons is presented.; Comment: 18 pages, 15 figures

‣ Identification of large-scale cellular structures on the Sun based on the SDO and PSPT data

Efremov, V. I.; Parfinenko, L. D.; Solovev, A. A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 04/12/2014 Português
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Three independent sets of data: i). series of filtergrams obtained in line CaII K (393.416 nm) with the ground-based telescope Precision Solar Photometric Telescope (PSPT) of Mauna Loa Solar Observatory; ii). series of filtergrams of Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO) in {\lambda}160 nm and iii). series of magnetograms of Helioseismic and Magnetic Imager (HMI) of SDO have been processed to reveal reliably the existence of spatial cellular structures on the solar photosphere at scale about of 300 arcsec. This scale is intermediate between supergranules and giant cells (~30,000 and ~300,000 kilometers across, respectively). To identify the different spatial structures the tens of two-dimensional power spectra (2DFFT) have been averaged. For one-dimensional photometric cross sections of frames, the Fourier power spectra (FFT) and wavelet transforms (Morlet 5-th order) have been calculated.; Comment: 10 pages, 6 figures. Accepted in Astrophys Space Sci

‣ Impulse Transfer during Sand Impact with a Cellular Structure

Holloman, Ryan L.; Deshpande, Vikram; Wadley, Haydn N. G.
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; accepted version
Português
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This is the accepted manuscript. The final version is available from Elsevier at http://www.sciencedirect.com/science/article/pii/S0734743X15000123.; Compressible cellular metal sandwich structures made from a 3D assembly of square cross section 6061 T6 aluminum alloy tubes, and face sheets of the same alloy have been attached to a vertical pendulum and impacted by synthetic wet sand with an incident velocity of ~300 ms-1. The transmitted impulse of samples with thick (relatively rigid) and thin face sheets are compared to that transferred by an incompressible solid aluminum test block of the same dimensions. A discrete particle-based simulation method was used to simulate the experiments and to investigate the soil particle ? structure interaction with the cellular structures. The simulated results agreed very well with experimental data; both showed that the impulse transferred to cellular structures with a 22 MPa core strength was 10-15% less than that transferred to a solid block of similar dimensions. However, the simulations reveal that the some of this apparent mitigation resulted from a subtle sand interaction between the bottom of the test structure and the sand box used for the tests. When this sand box effect was eliminated in the simulations...