Página 1 dos resultados de 1570 itens digitais encontrados em 0.014 segundos

## A generalized finite element method with global-local enrichment functions for confined plasticity problems

Kim, D. -J.; Duarte, C. A.; Proenca, Sergio Persival Baroncini
Fonte: SPRINGER; NEW YORK Publicador: SPRINGER; NEW YORK
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
35.93%
The main feature of partition of unity methods such as the generalized or extended finite element method is their ability of utilizing a priori knowledge about the solution of a problem in the form of enrichment functions. However, analytical derivation of enrichment functions with good approximation properties is mostly limited to two-dimensional linear problems. This paper presents a procedure to numerically generate proper enrichment functions for three-dimensional problems with confined plasticity where plastic evolution is gradual. This procedure involves the solution of boundary value problems around local regions exhibiting nonlinear behavior and the enrichment of the global solution space with the local solutions through the partition of unity method framework. This approach can produce accurate nonlinear solutions with a reduced computational cost compared to standard finite element methods since computationally intensive nonlinear iterations can be performed on coarse global meshes after the creation of enrichment functions properly describing localized nonlinear behavior. Several three-dimensional nonlinear problems based on the rate-independent J (2) plasticity theory with isotropic hardening are solved using the proposed procedure to demonstrate its robustness...

## Análise do trabalho em espaços confinados : o caso da manutenção de redes subterrâneas

Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
46.13%

## Segurança e saúde em espaços confinados à luz da NR33

Piattelli, Bianca Barreto
Tipo: Trabalho de Conclusão de Curso Formato: application/pdf
POR
Relevância na Pesquisa
36.02%

## Penetration by Gases to Sterilize Interior Surfaces of Confined Spaces

Opfell, John B.; Wang, Yui-Loong; Louderback, Allan L.; Miller, Curtis E.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
35.93%
The rate of penetration of gaseous sterilizing agents into confined spaces can be predicted from physical and chemical considerations. The exposure times required to obtain sterilizing concentrations of ethylene oxide in several configurations of confined space were predicted by computation and illustrated by experiment. The results of the computations are presented graphically.

## Structural Transitions of Confined Model Proteins: Molecular Dynamics Simulation and Experimental Validation

Lu, Diannan; Liu, Zheng; Wu, Jianzhong
Fonte: Biophysical Society Publicador: Biophysical Society
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
35.93%
Proteins fold in a confined space not only in vivo, i.e., folding assisted by molecular chaperons and chaperonins in a crowded cellular medium, but also in vitro as in production of recombinant proteins. Despite extensive work on protein folding in bulk, little is known about how and to what extent the thermodynamics and kinetics of protein folding are altered by confinement. In this work, we use a Gō-like off-lattice model to investigate the folding and stability of an all β-sheet protein in spherical cages of different sizes and surface hydrophobicity. We find whereas extreme confinement inhibits correct folding, a hydrophilic cage stabilizes the protein due to restriction of the unfolded configurations. In a hydrophobic cage, however, strong attraction from the cage surface destabilizes the confined protein because of competition between self-aggregation and adsorption of hydrophobic residues. We show that the kinetics of protein collapse and folding is strongly correlated with both the cage size and the surface hydrophobicity. It is demonstrated that a cage of moderate size and hydrophobicity optimizes both the folding yield and kinetics of structural transitions. To support the simulation results, we have also investigated the refolding of hen-egg lysozyme in the presence of cetyltrimethylammoniumbromide (CTAB) surfactants that provide an effective confinement of the proteins by micellization. The influence of the surfactant hydrophobicity on the structural and biological activity of the protein is determined with circular dichroism spectrum...

## Spatially confined folding of chromatin in the interphase nucleus

Mateos-Langerak, Julio; Bohn, Manfred; de Leeuw, Wim; Giromus, Osdilly; Manders, Erik M. M.; Verschure, Pernette J.; Indemans, Mireille H. G.; Gierman, Hinco J.; Heermann, Dieter W.; van Driel, Roel; Goetze, Sandra
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
36.03%
Genome function in higher eukaryotes involves major changes in the spatial organization of the chromatin fiber. Nevertheless, our understanding of chromatin folding is remarkably limited. Polymer models have been used to describe chromatin folding. However, none of the proposed models gives a satisfactory explanation of experimental data. In particularly, they ignore that each chromosome occupies a confined space, i.e., the chromosome territory. Here, we present a polymer model that is able to describe key properties of chromatin over length scales ranging from 0.5 to 75 Mb. This random loop (RL) model assumes a self-avoiding random walk folding of the polymer backbone and defines a probability P for 2 monomers to interact, creating loops of a broad size range. Model predictions are compared with systematic measurements of chromatin folding of the q-arms of chromosomes 1 and 11. The RL model can explain our observed data and suggests that on the tens-of-megabases length scale P is small, i.e., 10–30 loops per 100 Mb. This is sufficient to enforce folding inside the confined space of a chromosome territory. On the 0.5- to 3-Mb length scale chromatin compaction differs in different subchromosomal domains. This aspect of chromatin structure is incorporated in the RL model by introducing heterogeneity along the fiber contour length due to different local looping probabilities. The RL model creates a quantitative and predictive framework for the identification of nuclear components that are responsible for chromatin–chromatin interactions and determine the 3-dimensional organization of the chromatin fiber.

## Conformational Transition of Giant DNA in a Confined Space Surrounded by a Phospholipid Membrane

Kato, Ayako; Shindo, Eri; Sakaue, Takahiro; Tsuji, Akihiko; Yoshikawa, Kenichi
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.94%
It has been established that a long DNA molecule exhibits a large discrete conformational change from a coiled state to a highly folded state in aqueous solution, depending on the presence of various condensing agents such as polyamines. In this study, T4 DNA labeled with fluorescent dyes was encapsulated in a cell-sized microdroplet covered with a phospholipid membrane to investigate the conformational behavior of a DNA molecule in such a confined space. Fluorescence microscopy showed that the presence of Mg2+ induced the adsorption of DNA onto the membrane inner-surface of a droplet composed of phosphatidylethanolamine, while no adsorption was observed onto a phosphatidylcholine membrane. Under the presence of spermine (tetravalent amine), DNA had a folded conformation in the bulk solution. However, when these molecules were encapsulated in the microdroplet, DNA adsorbed onto the membrane surface accompanied by unfolding of its structure into an extended coil conformation under high concentrations of Mg2+. In addition, DNA molecules trapped in large droplets tended not to be adsorbed on the membrane, i.e., no conformational transition occurred. A thermodynamic analysis suggests that the translational entropy loss of a DNA molecule that is accompanied by adsorption is a key factor in these phenomena under micrometer-scale confinement.

## Chiral Photochemistry in a Confined Space: Torquoselective Photoelectrocyclization of Pyridones within an Achiral Hydrophobic Capsule#

Sundaresan, Arun Kumar; Gibb, Corinne L. D.; Gibb, Bruce C.; Ramamurthy, V.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.03%
Chiral induction during the photoelectrocyclization of pyridones included within octa acid (OA) capsule has been established. Chiral induction is brought about by a chiral auxiliary appended to the reactive pyridone moiety. Importantly, the same chiral auxiliary while ineffective in acetonitrile solution is found to be effective within the confined space of OA capsule. The diastereomeric excess of 92% obtained here is comparable only to that in solid state. OA capsule, we believe, provides restriction to the rotational motions of the reactant pyridone and chiral auxiliary and thus places the chiral auxiliary in a selective conformation with respect to the reactive pyridone part. A correlation between the position of the methyl group on the pyridone ring and diastereoselectivity was noted. Structures of the host-guest complexes were examined by 1H NMR and the data was used to obtain preliminary information concerning the mechanism of chiral induction within the confined spaces of OA capsule.

## Evolution of Space Dependent Growth in the Teleost Astyanax mexicanus

Gallo, Natalya D.; Jeffery, William R.
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.23%
The relationship between growth rate and environmental space is an unresolved issue in teleosts. While it is known from aquaculture studies that stocking density has a negative relationship to growth, the underlying mechanisms have not been elucidated, primarily because the growth rate of populations rather than individual fish were the subject of all previous studies. Here we investigate this problem in the teleost Astyanax mexicanus, which consists of a sighted surface-dwelling form (surface fish) and several blind cave-dwelling (cavefish) forms. Surface fish and cavefish are distinguished by living in spatially contrasting environments and therefore are excellent models to study the effects of environmental size on growth. Multiple controlled growth experiments with individual fish raised in confined or unconfined spaces showed that environmental size has a major impact on growth rate in surface fish, a trait we have termed space dependent growth (SDG). In contrast, SDG has regressed to different degrees in the Pachón and Tinaja populations of cavefish. Mating experiments between surface and Pachón cavefish show that SDG is inherited as a dominant trait and is controlled by multiple genetic factors. Despite its regression in blind cavefish...

## Fiber Optic Projection-Imaging System for Shape Measurement in Confined Space

Chen, Lujie; Bavigadda, Viswanath; Kofidis, Theodoros; Howe, Robert D.
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.03%
A fiber-based projection-imaging system is proposed for shape measurement in confined space. Owing to the flexibility of imaging fibers, the system can be used in special scenarios that are difficult for conventional experimental setups. Three experiments: open space, closed space, and underwater are designed to demonstrate the strength and weakness of the system. It is shown that when proper alignment is possible, relatively high accuracy can be achieved; the error is less than 2% of the overall height of a specimen. In situations where alignment is difficult, significantly increased error is observed. The error is in the form of gross-scale geometrical distortion; for example, flat surface is reconstructed with curvature. In addition, the imaging fibers may introduce fine-scale noise into phase measurement, which has to be suppressed by smoothing filters. Based on results and analysis, it is found that although a fiber-based system has its unique strength, existing calibration and processing methods for fringe patterns have to be modified to overcome its drawbacks so as to accommodate wider applications.

## Fiber Optic Projection-Imaging System for Shape Measurement in Confined Space

Chen, Lujie; Bavigadda, Viswanath; Kofidis, Theodoros; Howe, Robert D.
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
46.03%
A fiber-based projection-imaging system is proposed for shape measurement in confined space. Owing to the flexibility of imaging fibers, the system can be used in special scenarios that are difficult for conventional experimental setups. Three experiments: open space, closed space, and underwater are designed to demonstrate the strength and weakness of the system. It is shown that when proper alignment is possible, relatively high accuracy can be achieved; the error is less than 2% of the overall height of a specimen. In situations where alignment is difficult, significantly increased error is observed. The error is in the form of gross-scale geometrical distortion; for example, flat surface is reconstructed with curvature. In addition, the imaging fibers may introduce fine-scale noise into phase measurement, which has to be suppressed by smoothing filters. Based on results and analysis, it is found that although a fiber-based system has its unique strength, existing calibration and processing methods for fringe patterns have to be modified to overcome its drawbacks so as to accommodate wider applications.

## Beyond the “Right Stuff”: The role of group processes in isolated confined extreme environments

Krins, Phillip William
Tipo: Thesis (PhD); Doctor of Philosophy (PhD)
EN
Relevância na Pesquisa
36.03%
The purpose of this thesis was to apply mainstream theoretical social psychology to group dynamics in isolated confined extreme (ICE) environments, with a particular focus on the context of long duration spaceflight. This was done by providing a thorough review of both the ICE environment psychology literature and the social psychological literature. From this it emerged that significant gaps existed within the ICE literature around the understanding of group processes. A review of relevant social psychology literature suggested that the social identity perspective may have much to offer in advancing the understanding of group processes in these environments. It was argued that processes related to social identification plays a key role in the team functionality. Of particular note was how social ‘norms’ could influence social identification processes and group functioning. Crew heterogeneity had been cited as a potential concern in much ICE literature, so group norms that related to diversity were investigated. Three theoretical chapters provided a review of space and ICE environment psychology literature, social psychology literature and diversity literature. Five experiments are reported in this thesis. The first, an exploratory field study which study took place during an expedition into the Australian Outback...

## CFD benchmark on hydrogen release and dispersion in confined, naturally ventilated space with one vent

GIANNISSI Stella; SHENTSOV Volodymir; MELIDEO DANIELE; CARITEAU Benjamin; BARALDI Daniele; VENETSANOS Alexander; MOLKOV Vladimir
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Articles in Journals Formato: Printed
ENG
Relevância na Pesquisa
35.94%
A CFD benchmark was performed within the HyIndoor project, to study hydrogen release and dispersion in a confined space with natural ventilation and one vent. Three experiments, performed earlier by CEA at their GAMELAN 1 m3 facility, were considered for this benchmark. In all three tests helium (instead of hydrogen for safety reasons) was released vertically upwards at 60 NL/min from a 20 mm orifice near the centre of the enclosure. A different vent size was used for each test. Three HyIndoor partners (JRC, NCSRD and UU) participated in the benchmark, with three different CFD codes, (ANSYS Fluent, ADREA-HF and ANSYS CFX) and three different turbulence models respectively (transitional SST, standard k-ε, dynamic Smagorinski LES). In general, good agreement was found between predicted and measured helium concentrations. However, in the case of the vent with the smallest vertical extension (vent c) all predictions overestimate the concentration at the lower part of the enclosure at steady state.; JRC.F.2-Energy Conversion and Storage Technologies

## Confined-space synthesis of single crystal TiO2 nanowires in atmospheric vessel at low temperature: a generalized approach

Wang, Xiaoyue; Wang, Hai; Zhou, Yu; Liu, Yong; Li, Baojun; Zhou, Xiang; Shen, Hui
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.94%
Extensive efforts have been devoted to develop innovative synthesis strategies for nanomaterials in order to exploit the true potential of nanotechnology. However, most approaches require high temperature or high pressure to favor crystallization. Here we highlight an unconventional approach for the confined-space synthesis of the single crystal TiO2 nanowires in the atmospheric vessel at low temperature by cleverly manipulating the unique physical properties of straight-chain saturated fatty acids. Our method also applys to icosane due to its straight-chain saturated hydrocarbon structure and similar physical properties to the saturated fatty acids. Interestingly, we also found that the unsaturated fatty acids can facilitate the crystal growth, but their bent chains lead to the formation of TiO2 particle aggregates. In addition, we demonstrate the growth of TiO2 nanowires on arbitrary substrates, which are of great importance for their wider applications. We thus anticipate our presented method to be a possible starting point for non-classical crystallization strategies and be easily adapted for the fabrication of all other inorganic materials.

## The confined space inside carbon nanotubes can dictate the stereo- and regioselectivity of Diels-Alder reactions

Smith, N M; Swaminathan Iyer, K.; Corry, Ben
Fonte: Royal Society of Chemistry Publicador: Royal Society of Chemistry
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.94%
Chemical reactions inside carbon nanotubes can yield unusual outcomes. Molecular dynamics simulations show that within the confined space of carbon nanotubes, the 1,4-exo adduct of a Diels-Alder cycloaddition may be produced instead of the 9,10-adduct, wh

## Quantum statistics of ideal gases in confined space

Dai, Wu-Sheng; Xie, Mi
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.94%
In this paper, the effects of boundary and connectivity on ideal gases in two-dimensional confined space and three-dimensional tubes are discussed in detail based on the analytical result. The implication of such effects on the mesoscopic system is also revealed.; Comment: 7 pages, Latex

## Frequency Quantized Nondiffracting X Waves in a Confined Space

Lu, Jian-yu
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.94%
This paper presents theoretical results indicating that newly discovered nondiffracting beams we call X waves, can propagate in a confined space (wave guide) with specific quantized temporal frequencies. These results could have applications in nondispersive transmission of acoustic, electromagnetic (microwaves) and optical energy through wave guides as well as provide new localized wave functions of de Broglie waves in quantum mechanics.; Comment: A side-band "arXiv:physics/0607059 v1 7 Jul 2006" on the first page is added for referencing (needed due to PDF only submission). Otherwise this version is exactly the same as the previous one

## Geometry effects in confined space

Dai, Wu-Sheng; Xie, Mi
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.13%
In this paper we calculate some exact solutions of the grand partition functions for quantum gases in confined space, such as ideal gases in two- and three-dimensional boxes, in tubes, in annular containers, on the lateral surface of cylinders, and photon gases in three-dimensional boxes. Based on these exact solutions, which, of course, contain the complete information about the system, we discuss the geometry effect which is neglected in the calculation with the thermodynamic limit $V\to \infty$, and analyze the validity of the quantum statistical method which can be used to calculate the geometry effect on ideal quantum gases confined in two-dimensional irregular containers. We also calculate the grand partition function for phonon gases in confined space. Finally, we discuss the geometry effects in realistic systems.; Comment: Revtex,15 pages, no figure

## The linking number and the writhe of uniform random walks and polygons in confined spaces

Panagiotou, E.; Millett, K. C.; Lambropoulou, S.
Tipo: Artigo de Revista Científica
Random walks and polygons are used to model polymers. In this paper we consider the extension of writhe, self-linking number and linking number to open chains. We then study the average writhe, self-linking and linking number of random walks and polygons over the space of configurations as a function of their length. We show that the mean squared linking number, the mean squared writhe and the mean squared self-linking number of oriented uniform random walks or polygons of length $n$, in a convex confined space, are of the form $O(n^2)$. Moreover, for a fixed simple closed curve in a convex confined space, we prove that the mean absolute value of the linking number between this curve and a uniform random walk or polygon of $n$ edges is of the form $O(\sqrt{n})$. Our numerical studies confirm those results. They also indicate that the mean absolute linking number between any two oriented uniform random walks or polygons, of $n$ edges each, is of the form O(n). Equilateral random walks and polygons are used to model polymers in $\theta$-conditions. We use numerical simulations to investigate how the self-linking and linking number of equilateral random walks scale with their length.; Comment: 29 pages, 12 figures