Arbitrary Size (arbitrary + size)

Distribution by Scientific Domains


Selected Abstracts


A Polymorphic Dynamic Network Loading Model

COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 2 2008
Nie Yu (Marco)
The polymorphism, realized through a general node-link interface and proper discretization, offers several prominent advantages. First of all, PDNL allows road facilities in the same network to be represented by different traffic flow models based on the tradeoff of efficiency and realism and/or the characteristics of the targeted problem. Second, new macroscopic link/node models can be easily plugged into the framework and compared against existing ones. Third, PDNL decouples links and nodes in network loading, and thus opens the door to parallel computing. Finally, PDNL keeps track of individual vehicular quanta of arbitrary size, which makes it possible to replicate analytical loading results as closely as desired. PDNL, thus, offers an ideal platform for studying both analytical dynamic traffic assignment problems of different kinds and macroscopic traffic simulation. [source]


Using geostatistics to elucidate temporal change in the spatial variation of aeolian sediment transport

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 6 2003
Adrian Chappell
Abstract Little is known about the spatial and temporal scales of variation in aeolian processes. Studies that aim to investigate surface erodibility often sample aeolian sediment transport at the nodes of a regular grid of arbitrary size. Few aeolian transport investigations have the resources to obtain sufficient samples to produce reliable models for mapping the spatial variation of transport. This study reports the use of an innovative nested strategy for sampling multiple spatial scales simultaneously using 40 sediment samplers. Reliable models of the spatial variation in aeolian sediment transport were produced and used for ordinary punctual kriging and stochastic simulated annealing to produce maps for several wind erosion events over a 25 km2 playa in western Queensland, Australia. The results support the existence of a highly dynamic wind erosion system that was responding to possibly cyclic variation in the availability of material and fluctuations in wind energy. The spatial scale of transport was considerably larger than the small scale expected of the factors controlling surface erodibility. Thus, it appears that transport cannot be used as a surrogate of erodibility at the scale of this investigation. Simulation maps of transport provided considerably more information than those from kriging about the variability in aeolian sediment transport and its possible controlling factors. The proposed optimal sampling strategy involves a nested approach using ca 50 samplers. Copyright © 2003 John Wiley & Sons, Ltd. [source]


Oxidative Inorganic Multilayers for Polypyrrole Film Generation

ADVANCED FUNCTIONAL MATERIALS, Issue 13 2010
Mikko Salomäki
Abstract A controlled nanoscale fabrication of conducting polymer films sets severe requirements for the preparation method and substrate. A new and versatile approach for producing thin polypyrrole films on a variety of surfaces is presented. Purely inorganic thin films are first prepared from poly(metaphosphate) and tetravalent metal ions using a sequential layer-by-layer technique. Redox-active cerium(IV) polyphosphate multilayer and redox-inactive zirconium(IV) and hafnium(IV) polyphosphate multilayers are prepared. Cerium-based polyphosphate films grow exponentially with the number of layers but multilayers containing zirconium or hafnium exhibit a linear buildup process. All the studied systems produce relatively smooth films with initial bilayer thickness less than 2,nm. The cerium(IV) containing film is redox-active, which is shown by its capability to form a polypyrrole layer on its surface by oxidation of pyrrole monomers in the adjacent aqueous solution. This is a general method to produce thin oxidative films of arbitrary size and form on a wide variety of surfaces. [source]


A unified framework for transmission-disequilibrium test analysis of discrete and continuous traits

GENETIC EPIDEMIOLOGY, Issue 1 2002
Ying Liu
Abstract This paper presents a unified framework for transmission-disequilibrium tests for discrete and continuous traits. A conditional score test is derived that maximizes power to detect small effects for any exponential family distribution, which includes binary and normal distributions, and distributions that are skewed or have non-normal kurtosis. The specific distributional form need not be specified, and the method applies to sibships of arbitrary size. Formulas for the distribution of the test statistic are given for models including complex genetic effects (additive, dominant, and recessive gene action), covariates, multiple gene models including gene-gene interactions or heterogeneity, and gene-environment interactions. We develop refinements of our method for trait-based sampling designs and multiple siblings that can have dramatic effects on power. Genet. Epidemiol. 22:26,40, 2002. © 2002 Wiley-Liss, Inc. [source]


Improving Kirchhoff migration with repeated local plane-wave imaging?

GEOPHYSICAL PROSPECTING, Issue 6 2005
A SAR-inspired signal-processing approach in prestack depth imaging
ABSTRACT A local plane-wave approach of generalized diffraction tomography in heterogeneous backgrounds, equivalent to Kirchhoff summation techniques when applied in seismic reflection, is re-programmed to act as repeated synthetic aperture radar (SAR) imaging for seismic prestack depth migration. Spotlight-mode SAR imaging quickly provides good images of the electromagnetic reflectivity of the ground via fast Fourier transform (FFT)-based signal processing. By calculating only the Green's functions connecting the aircraft to the centre of the illuminated patch, scattering structures around that centre are also recovered. SAR technology requires us to examine seismic imaging from the local point of view, where the quantity and quality of the available information at each image point are what are important, regardless of the survey geometry. When adapted to seismics, a local image of arbitrary size and sampling is obtained by FFT of seismic energy maps in the scattering wavenumber domain around each node of a pre-calculated grid of Green's functions. These local images can be used to generate a classic prestack depth-migrated section by collecting only their centres. However, the local images also provide valuable information around the centre, as in SAR. They can therefore help to pre-analyse prestack depth migration efficiently, and to perform velocity analysis at a very low cost. The FFT-based signal-processing approach allows local, efficient and automatic control of anti-aliasing, noise and resolution, including optimized Jacobian weights. Repeated local imaging could also be used to speed up migration, with interpolation between local images associated with a coarse grid of Green's functions, as an alternative to interpolation of Green's functions. The local images may, however, show distortions due to the local plane-wave approximation, and the velocity variations across their frame. Such effects, which are not necessarily a problem in SAR, should be controlled and corrected to further enhance seismic imaging. Applications to realistic models and to real data show that, despite the distortion effects, the local images can yield similar information to prestack depth migration, including common-image-point gathers for velocity analyses and AVO/AVA effects, at a much lower cost when a small target is considered. [source]


Thin Films: One Nanometer Thin Carbon Nanosheets with Tunable Conductivity and Stiffness (Adv. Mater.

ADVANCED MATERIALS, Issue 12 2009
12/2009)
Andrey Turchanin and co-workers report on page 1233 on the fabrication and characterization of atomically thin (,1 nm) carbon films and membranes with tunable conductivity and stiffness, arbitrary size and shape. These carbon nanosheets are produced using self-assembled monolayers of aromatic molecules, which are cross-linked by electrons, detached from the surfaces, and subsequently pyrolized. The technical applicability of these novel materials is demonstrated by incorporating them into a microscopic pressure sensor. The optical microscopy image shows a folded nanosheet transferred onto an oxidized silicon wafer. [source]


One Nanometer Thin Carbon Nanosheets with Tunable Conductivity and Stiffness

ADVANCED MATERIALS, Issue 12 2009
Andrey Turchanin
Atomically thin (,1,nm) carbon films and membranes whose electrical behavior can be tuned from insulating to conducting are fabricated by a novel route. These films present arbitrary size and shape based on molecular self-assembly, electron irradiation, and pyrolysis, and their technical applicability is demonstrated by their incorporation into a microscopic pressure sensor. [source]


On the use of Somigliana's formula and Fourier series for elasticity problems with circular boundaries

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2003
S. L. Crouch
Abstract This paper considers the problem of an infinite, isotropic elastic plane containing an arbitrary number of non-overlapping circular holes and isotropic elastic inclusions. The holes and inclusions are of arbitrary size and the elastic properties of all of the inclusions can, if desired, be different. The analysis is based on the two-dimensional version of Somigliana's formula, which gives the displacements at a point inside a region V in terms of integrals of the tractions and displacements over the boundary S of this region. We take V to be the infinite plane, and S to be an arbitrary number of circular holes within this plane. Any (or all) of the holes can contain an elastic inclusion, and we assume for simplicity that all inclusions are perfectly bonded to the material matrix. The displacements and tractions on each circular boundary are represented as truncated Fourier series, and all of the integrals involved in Somigliana's formula are evaluated analytically. An iterative solution algorithm is used to solve the resulting system of linear algebraic equations. Several examples are given to demonstrate the accuracy and efficiency of the numerical method. Copyright © 2003 John Wiley & Sons, Ltd. [source]


On the effectiveness of cone mosaic geometry in sampling patterns near the Nyquist frequency

ACTA OPHTHALMOLOGICA, Issue 2009
H GINIS
Purpose The cone mosaic is characterised by a quasi-periodic hexagonal organization. The purpose of this work was to develop a mathematical model of cone mosaic including irregularities and to employ this model to evaluate its effectiveness in sampling simple patterns including optotypes (letters) of different sizes and gratings. Methods Cone mosaic images were analyzed using purposely-developed computer programs and a stochastic model of the human cone mosaic was created. The computer-generated mosaics were used to sample sequences of patterns translated to positions randomly extracted from experimental data of fixational eye movements. The sampling efficiency was evaluated as the RMS difference between the initial and the sampled pattern. Similar simulations were performed using a periodic mosaic of equal average cone size. Results Sampling efficiency (as described by the minimum RMS difference) was better for the quasi-perioding sampling compared to the periodic sampling especially when the sampled pattern involved spatial frequencies higher than 20 cpd. The periodic sampling performed better only in the case where the spatial frequencies in the Fourier spectrum of the sampled pattern exactly matched the spatial frequency associated to the cone spacing (divided by an integer). However the quasi-periodic sampling was more effective in all other pattern sizes and orientations. Conclusion Although the trichromatic nature of the human cone mosaic as well as the neural organization in the retina after phototransduction were not taken into account, our simulations demonstrate that the geometric irregularities at the cone mosaic may result to more efficient sampling of simple patterns of arbitrary size and orientation. [source]