Página 6 dos resultados de 6914 itens digitais encontrados em 0.016 segundos

‣ Layout and material gradation in topology optimization of functionally graded structures: a global-local approach

ALMEIDA, Sylvia R. M.; PAULINO, Glaucio H.; SILVA, Emilio C. N.
Fonte: SPRINGER Publicador: SPRINGER
Tipo: Artigo de Revista Científica
Português
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By means of continuous topology optimization, this paper discusses the influence of material gradation and layout in the overall stiffness behavior of functionally graded structures. The formulation is associated to symmetry and pattern repetition constraints, including material gradation effects at both global and local levels. For instance, constraints associated with pattern repetition are applied by considering material gradation either on the global structure or locally over the specific pattern. By means of pattern repetition, we recover previous results in the literature which were obtained using homogenization and optimization of cellular materials.; Brazilian agency CAPES[3516/06-7]; FAPESP[2008/51070-0]; Brazilian agencies FAPESP[06/57805-7]; CNPq[303689/2009-9]

‣ The Lipopolysaccharide Structures of Salmonella enterica Serovar Typhimurium and Neisseria gonorrhoeae Determine the Attachment of Human Mannose-Binding Lectin to Intact Organisms

Devyatyarova-Johnson, Marina; Rees, Ian H.; Robertson, Brian D.; Turner, Malcolm W.; Klein, Nigel J.; Jack, Dominic L.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /07/2000 Português
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Mannose-binding lectin (MBL) is an important component of the innate immune system. It binds to the arrays of sugars commonly presented by microorganisms and activates the complement system independently of antibody. Despite detailed knowledge of the stereochemical basis of MBL binding, relatively little is known about how bacterial surface structures influence binding of the lectin. Using flow cytometry, we have measured the binding of MBL to a range of mutants of Salmonella enterica serovar Typhimurium and Neisseria gonorrhoeae which differ in the structure of expressed lipopolysaccharide (LPS). For both organisms, the possession of core LPS structures led to avid binding of MBL, which was abrogated by the addition of O antigen (Salmonella serovar Typhimurium) or sialic acid (N. gonorrhoeae). Truncation of the LPS within the core led to lower levels of MBL binding. It was not possible to predict the magnitude of MBL binding from the identity of the LPS terminal sugar alone, indicating that the three-dimensional disposition of LPS molecules is probably also of importance in determining MBL attachment. These results further support the hypothesis that LPS structure is a major determinant of MBL binding.

‣ Polycystin-2 cation channel function in the human syncytiotrophoblast is regulated by microtubular structures

Montalbetti, Nicolás; Li, Qiang; Wu, Yuliang; Chen, Xing-Zhen; Cantiello, Horacio F
Fonte: Blackwell Science Inc Publicador: Blackwell Science Inc
Tipo: Artigo de Revista Científica
Português
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Polycystin-2 (PC2), encoded by PKD2, which is one of the genes whose mutations cause polycystic kidney disease, is abundantly produced in the apical domain of the syncytiotrophoblast (hST) of term human placenta. PC2, a TRP-type (TRPP2) non-selective cation channel, is present in primary cilia of renal epithelial cells, a microtubule-based ancillary structure with sensory function. The hST has abundant cytoskeletal structures, and actin filament dynamics regulate PC2 channel function in this epithelium. However, it is expected that the apical hST excludes microtubular structures. Here, we demonstrated by Western blot and immunocytochemical analyses that hST apical vesicles indeed contain microtubule structural components, including tubulin isoforms, acetylated α-tubulin, and the kinesin motor proteins KIF3A and KIF3B. PC2 and tubulin were substantially colocalized in hST vesicles. Treatment of hST vesicles with either the microtubular disrupter colchicine (15 μm) or the microtubular stabilizer paclitaxel (taxol, 15 μm) resulted in distinct patterns of microtubular re-organization and PC2 redistribution. We also observed that changes in microtubular dynamics regulate PC2 channel function. Addition of colchicine rapidly inhibited PC2 channel activity in lipid-bilayer reconstituted hST membranes. Addition of either tubulin and GTP...

‣ Diverse Peptide Presentation of Rhesus Macaque Major Histocompatibility Complex Class I Mamu-A*02 Revealed by Two Peptide Complex Structures and Insights into Immune Escape of Simian Immunodeficiency Virus ▿

Liu, Jun; Dai, Lianpan; Qi, Jianxun; Gao, Feng; Feng, Youjun; Liu, Wenjun; Yan, Jinghua; Gao, George F.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /07/2011 Português
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Major histocompatibility complex class I (MHC I)-restricted CD8+ T-cell responses play a pivotal role in anti-human immunodeficiency virus (HIV) immunity and the control of viremia. The rhesus macaque is an important animal model for HIV-related research. Among the MHC I alleles of the rhesus macaque, Mamu-A*02 is prevalent, presenting in ≥20% of macaques. In this study, we determined the crystal structure of Mamu-A*02, the second structure-determined MHC I from the rhesus macaque after Mamu-A*01. The peptide presentation characteristics of Mamu-A*02 are exhibited in complex structures with two typical Mamu-A*02-restricted CD8+ T-cell epitopes, YY9 (Nef159 to -167; YTSGPGIRY) and GY9 (Gag71 to -79; GSENLKSLY), derived from simian immunodeficiency virus (SIV). These two peptides utilize similar primary anchor residues (Ser or Thr) at position 2 and Tyr at position 9. However, the central region of YY9 is different from that of GY9, a difference that may correlate with the immunogenic variance of these peptides. Further analysis indicated that the distinct conformations of these two peptides are modulated by four flexible residues in the Mamu-A*02 peptide-binding groove. The rare combination of these four residues in Mamu-A*02 leads to a variant presentation for peptides with different residues in their central regions. Additionally...

‣ TISSUE LEVEL SEGMENTATION AND TRACKING OF BIOLOGICAL STRUCTURES IN MICROSCOPIC IMAGES BASED ON DENSITY MAPS

Mosaliganti, K.; Gelas, A.; Gouaillard, A.; Megason, Sean G.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2009 Português
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During embryogenesis, cells coordinate to form geometric arrangements. These arrangements are initially noticed as stereotypical clumps of cells that further divide to form a rigorous structure with a high density of cells. In this work, we explore density-based segmentation and tracking of cellular structures as observed in microscopy images. Using a new modified form of the Mumford-Shah energy functional, we derived a variational level-set for density-based segmentation. The novelty of the work lies in evolving an initialized contour that represents a salient structure on density maps to automatically generate novel cell structures upon convergence. We validate our methods and show results on confocal ear images of the zebrafish embryo.

‣ A Simple Method for the Immunocytochemical Detection of Proteins Inside Nuclear Structures That Are Inaccessible to Specific Antibodies

Svistunova, Darya M.; Musinova, Yana R.; Polyakov, Vladimir Yu.; Sheval, Eugene V.
Fonte: SAGE Publications Publicador: SAGE Publications
Tipo: Artigo de Revista Científica
Publicado em /02/2012 Português
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It has been demonstrated elsewhere that a high concentration of an antigen within the nucleolus may prevent its proper recognition by specific antibodies. In this study, the authors found that a short proteinase treatment allowed for the detection of antigens in the nucleoli. The described approach is compatible with the simultaneous observation of proteins fused to fluorescent tags and with preembedding electron microscopy. It appears that the described method can be useful in situations when the proper recognition of antigens by specific antibodies is disturbed by a high density of cellular structures or a high concentration of antigens inside these structures.

‣ Campylobacter jejuni Translocation across Intestinal Epithelial Cells Is Facilitated by Ganglioside-Like Lipooligosaccharide Structures

Louwen, Rogier; Nieuwenhuis, Edward E. S.; van Marrewijk, Leonie; Horst-Kreft, Deborah; de Ruiter, Lilian; Heikema, Astrid P.; van Wamel, Willem J. B.; Wagenaar, Jaap A.; Endtz, Hubert P.; Samsom, Janneke; van Baarlen, Peter; Akhmanova, Anna; van Belkum,
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /09/2012 Português
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Translocation across intestinal epithelial cells is an established pathogenic feature of the zoonotic bacterial species Campylobacter jejuni. The number of C. jejuni virulence factors known to be involved in translocation is limited. In the present study, we investigated whether sialylation of C. jejuni lipooligosaccharide (LOS) structures, generating human nerve ganglioside mimics, is important for intestinal epithelial translocation. We here show that C. jejuni isolates expressing ganglioside-like LOS bound in larger numbers to the Caco-2 intestinal epithelial cells than C. jejuni isolates lacking such structures. Next, we found that ganglioside-like LOS facilitated endocytosis of bacteria into Caco-2 cells, as visualized by quantitative microscopy using the early and late endosomal markers early endosome-associated protein 1 (EEA1), Rab5, and lysosome-associated membrane protein 1 (LAMP-1). This increased endocytosis was associated with larger numbers of surviving and translocating bacteria. Next, we found that two different intestinal epithelial cell lines (Caco-2 and T84) responded with an elevated secretion of the T-cell attractant CXCL10 to infection by ganglioside-like LOS-expressing C. jejuni isolates. We conclude that C. jejuni translocation across Caco-2 cells is facilitated by ganglioside-like LOS...

‣ In vitro reconstruction of branched tubular structures from lung epithelial cells in high cell concentration gradient environment

Hagiwara, Masaya; Peng, Fei; Ho, Chih-Ming
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 27/01/2015 Português
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We have succeeded in developing hollow branching structure in vitro commonly observed in lung airway using primary lung airway epithelial cells. Cell concentration gradient is the key factor that determines production of the branching cellular structures, as optimization of this component removes the need for heterotypic culture. The higher cell concentration leads to the more production of morphogens and increases the growth rate of cells. However, homogeneous high cell concentration does not make a branching structure. Branching requires sufficient space in which cells can grow from a high concentration toward a low concentration. Simulation performed using a reaction-diffusion model revealed that long-range inhibition prevents cells from branching when they are homogeneously spread in culture environments, while short-range activation from neighboring cells leads to positive feedback. Thus, a high cell concentration gradient is required to make branching structures. Spatial distributions of morphogens, such as BMP-4, play important roles in the pattern formation. This simple yet robust system provides an optimal platform for the further study and understanding of branching mechanisms in the lung airway, and will facilitate chemical and genetic studies of lung morphogenesis programs.

‣ Extragalactic Large-Scale Structures behind the Southern Milky Way. -- II. Redshifts Obtained at the SAAO in the Crux Region

Fairall, A. P.; Woudt, P. A.; Kraan-Korteweg, R. C.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 20/05/1997 Português
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In our systematic optical galaxy search behind the southern Milky Way, 3760 (mostly unknown) galaxies with diameters D > 0.2 arcminutes were identified in the Crux region (287 < l < 318 degrees, |b| < 10 degrees, Woudt & Kraan-Korteweg 1997). Prior to this investigation, only 65 of these galaxies had known redshifts. In order to map the galaxy distribution in redshift space we obtained spectra for 226 bright (B_J < 18.0 mag) objects with the 1.9m telescope of the South African Astronomical Observatory (SAAO). Two main structures crossing the Galactic Plane in the Crux region have now become clear. A narrow, nearby filament from (l,b) = (340 deg, -25 deg) to the Centaurus cluster can be traced. This filament runs almost parallel to the extension of the Hydra-Antlia clusters found earlier and is part of what we have earlier termed the ``Centaurus Wall'' extending in redshift-space between 0 < v < 6000 km/s (Fairall & Paverd 1995). The main outcome of this survey however, is the recognition of another massive extended structure between 4000 < v < 8000 km/s. This broad structure, dubbed the Norma Supercluster (Woudt et al. 1997), runs nearly parallel to the Galactic Plane from Vela to ACO 3627 (its centre) from where it continues to the Pavo cluster. This massive structure is believed to be associated with the Great Attractor. The survey has furthermore revealed a set of cellular structures...

‣ A modular approach to adaptive structures

Pagitz, Markus; Pagitz, Manuel; Hühne, C.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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A remarkable property of nastic, shape changing plants is their complete fusion between actuators and structure. This is achieved by combining a large number of cells whose geometry, internal pressures and material properties are optimized for a given set of target shapes and stiffness requirements. An advantage of such a fusion is that cell walls are prestressed by cell pressures which increases, decreases the overall structural stiffness, weight. Inspired by the nastic movement of plants, Pagitz et al. 2012 Bioinspir. Biomim. 7 published a novel concept for pressure actuated cellular structures. This article extends previous work by introducing a modular approach to adaptive structures. An algorithm that breaks down any continuous target shapes into a small number of standardized modules is presented. Furthermore it is shown how cytoskeletons within each cell enhance the properties of adaptive modules. An adaptive passenger seat and an aircrafts leading, trailing edge is used to demonstrate the potential of a modular approach.; Comment: 15 pages, 9 figures

‣ A Simple Optimum-Time FSSP Algorithm for Multi-Dimensional Cellular Automata

Umeo, Hiroshi; Nishide, Kinuo; Kubo, Keisuke
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 13/08/2012 Português
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The firing squad synchronization problem (FSSP) on cellular automata has been studied extensively for more than forty years, and a rich variety of synchronization algorithms have been proposed for not only one-dimensional arrays but two-dimensional arrays. In the present paper, we propose a simple recursive-halving based optimum-time synchronization algorithm that can synchronize any rectangle arrays of size m*n with a general at one corner in m+n+max(m, n)-3 steps. The algorithm is a natural expansion of the well-known FSSP algorithm proposed by Balzer [1967], Gerken [1987], and Waksman [1966] and it can be easily expanded to three-dimensional arrays, even to multi-dimensional arrays with a general at any position of the array.; Comment: In Proceedings AUTOMATA&JAC 2012, arXiv:1208.2498

‣ AdCell: Ad Allocation in Cellular Networks

Alaei, Saeed; Hajiaghayi, Mohammad T.; Liaghat, Vahid; Pei, Dan; Saha, Barna
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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With more than four billion usage of cellular phones worldwide, mobile advertising has become an attractive alternative to online advertisements. In this paper, we propose a new targeted advertising policy for Wireless Service Providers (WSPs) via SMS or MMS- namely {\em AdCell}. In our model, a WSP charges the advertisers for showing their ads. Each advertiser has a valuation for specific types of customers in various times and locations and has a limit on the maximum available budget. Each query is in the form of time and location and is associated with one individual customer. In order to achieve a non-intrusive delivery, only a limited number of ads can be sent to each customer. Recently, new services have been introduced that offer location-based advertising over cellular network that fit in our model (e.g., ShopAlerts by AT&T) . We consider both online and offline version of the AdCell problem and develop approximation algorithms with constant competitive ratio. For the online version, we assume that the appearances of the queries follow a stochastic distribution and thus consider a Bayesian setting. Furthermore, queries may come from different distributions on different times. This model generalizes several previous advertising models such as online secretary problem \cite{HKP04}...

‣ Cellular Structures for Computation in the Quantum Regime

Benjamin, S. C.; Johnson, N. F.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 21/08/1998 Português
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We present a new cellular data processing scheme, a hybrid of existing cellular automata (CA) and gate array architectures, which is optimized for realization at the quantum scale. For conventional computing, the CA-like external clocking avoids the time-scale problems associated with ground-state relaxation schemes. For quantum computing, the architecture constitutes a novel paradigm whereby the algorithm is embedded in spatial, as opposed to temporal, structure. The architecture can be exploited to produce highly efficient algorithms: for example, a list of length N can be searched in time of order cube root N.; Comment: 11 pages (LaTeX), 3 figures

‣ A decision procedure for well-formed linear quantum cellular automata

Durr, Christoph; LeThanh, Huong; Santha, Miklos
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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In this paper we introduce a new quantum computation model, the linear quantum cellular automaton. Well-formedness is an essential property for any quantum computing device since it enables us to define the probability of a configuration in an observation as the squared magnitude of its amplitude. We give an efficient algorithm which decides if a linear quantum cellular automaton is well-formed. The complexity of the algorithm is $O(n^2)$ in the algebraic model of computation if the input automaton has continuous neighborhood.

‣ Quasi-Linear Cellular Automata

Moore, Cristopher
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 20/01/1997 Português
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Simulating a cellular automaton (CA) for t time-steps into the future requires t^2 serial computation steps or t parallel ones. However, certain CAs based on an Abelian group, such as addition mod 2, are termed ``linear'' because they obey a principle of superposition. This allows them to be predicted efficiently, in serial time O(t) or O(log t) in parallel. In this paper, we generalize this by looking at CAs with a variety of algebraic structures, including quasigroups, non-Abelian groups, Steiner systems, and others. We show that in many cases, an efficient algorithm exists even though these CAs are not linear in the previous sense; we term them ``quasilinear.'' We find examples which can be predicted in serial time proportional to t, t log t, t log^2 t, and t^a for a < 2, and parallel time log t, log t log log t and log^2 t. We also discuss what algebraic properties are required or implied by the existence of scaling relations and principles of superposition, and exhibit several novel ``vector-valued'' CAs.; Comment: 41 pages with figures, To appear in Physica D

‣ Determining a regular language by glider-based structures called phases fi_1 in Rule 110

Martinez, Genaro Juarez; McIntosh, Harold V.; Mora, Juan C. Seck Tuoh; Vergara, Sergio V. Chapa
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 22/06/2007 Português
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Rule 110 is a complex elementary cellular automaton able of supporting universal computation and complicated collision-based reactions between gliders. We propose a representation for coding initial conditions by means of a finite subset of regular expressions. The sequences are extracted both from de Bruijn diagrams and tiles specifying a set of phases fi_1 for each glider in Rule 110. The subset of regular expressions is explained in detail.; Comment: by publish in Journal of Cellular Automata

‣ Self-synchronization of Cellular Automata: an attempt to control patterns

Sanchez, J. R.; Lopez-Ruiz, R.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 28/11/2005 Português
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The searching for the stable patterns in the evolution of cellular automata is implemented using stochastic synchronization between the present structures of the system and its precedent configurations. For most of the known evolution rules with complex behavior a dynamic competition among all the possible stable patterns is established and no stationary regime is reached. For the particular rule coded by the decimal number 18, a self-synchronization phenomenon can be obtained, even when strong modifications to the synchronization method are applied.; Comment: 10 pages, 5 figures

‣ Cellular Automata in Stream Ciphers

Fúster-Sabater, Amparo
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/05/2010 Português
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A wide family of nonlinear sequence generators, the so-called clock-controlled shrinking generators, has been analyzed and identified with a subset of linear cellular automata. The algorithm that converts the given generator into a linear model based on automata is very simple and can be applied in a range of practical interest. Due to the linearity of these automata as well as the characteristics of this class of generators, a cryptanalytic approach can be proposed. Linear cellular structures easily model keystream generators with application in stream cipher cryptography.; Comment: 26 pages, 1 figure

‣ Cellular objects and Shelah's singular compactness theorem

Beke, Tibor; Rosicky, Jiri
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/06/2014 Português
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The best-known version of Shelah's celebrated singular cardinal compactness theorem states that if the cardinality of an abelian group is singular, and all its subgroups of lesser cardinality are free, then the group itself is free. The proof can be adapted to cover a number of analogous situations in the setting of non-abelian groups, modules, graph colorings, set transversals etc. We give a single, structural statement of singular compactness that covers all examples in the literature that we are aware of. A case of this formulation, singular compactness for cellular structures, is of special interest; it expresses a relative notion of freeness. The proof of our functorial formulation is motivated by a paper of Hodges, based on a talk of Shelah. The cellular formulation is new, and related to recent work in abstract homotopy theory.

‣ On Soliton Collisions between Localizations in Complex Elementary Cellular Automata: Rules 54 and 110 and Beyond

Martinez, Genaro J.; Adamatzky, Andrew; Chen, Fangyue; Chua, Leon
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 26/01/2013 Português
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In this paper we present a single-soliton two-component cellular automata (CA) model of waves as mobile self-localizations, also known as: particles, waves, or gliders; and its version with memory. The model is based on coding sets of strings where each chain represents a unique mobile self-localization. We will discuss briefly the original soliton models in CA proposed with {\it filter automata}, followed by solutions in elementary CA (ECA) domain with the famous universal ECA {\it Rule 110}, and reporting a number of new solitonic collisions in ECA {\it Rule 54}. A mobile self-localization in this study is equivalent a single soliton because the collisions of these mobile self-localizations studied in this paper satisfies the property of solitonic collisions. We also present a specific ECA with memory (ECAM), the ECAM Rule $\phi_{R9maj:4}$, that displays single-soliton solutions from any initial codification (including random initial conditions) for a kind of mobile self-localization because such automaton is able to adjust any initial condition to soliton structures.