			Home About us Contact

Far Field (far + field)

Distribution by Scientific Domains

Engineering	29%
Earth and Environmental Science	17%

Selected Abstracts

Virtual Electrode Polarization Leads to Reentry in the Far Field

JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 8 2001
ANNETTE E. LINDBLOM M.S.
Virtual Electrode Polarization. Introduction: Our previous article examined cardiac vulnerability to reentry in the near field within the framework of the virtual electrode polarization (VEP) concept. The present study extends this examination to the far field and compares its predictions to the critical point hypothesis. Methods and Results: We simulate the electrical behavior of a sheet of myocardium using a two-dimensional bidomain model. The fiber field is extrapolated from a set of rabbit heart fiber directions obtained experimentally. An S1 stimulus is applied along the top or left border. An extracellular line electrode on the top delivers a cathodal or anodal S2 stimulus. A VEP pattern matching that seen experimentally is observed and covers the entire sheet, thus constituting a far-field effect. Reentry arises from break excitation, make excitation, or a combination of both, and subsequent propagation through deexcited and recovered areas. Reentry occurs in cross-field, parallel-field, and uniform refractoriness protocols. For long coupling intervals (CIs) above CImakemin (defined as the shortest CI at which make excitation can take place), rotors move away from the cathodal electrode and the S1 site for increases in S2 strength and CI, respectively. For cathodal S2 stimuli, findings are consistent with the critical point hypothesis. For CIs below CImakemin, reentry is initiated by break excitation only, and the resulting reentrant patterns are no longer consistent with those predicted by the critical point hypothesis. Conclusion: Shock-induced VEP can explain vulnerability in the far field. The VEP theory of vulnerability encompasses the critical point hypothesis for cathodal S2 shocks at long CIs. [source]

Microsystems for Optical Cell Detection: Near versus Far Field

PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 1 2008
Stefan Kostner
Abstract Optical flow cytometry is a process where physical and (bio-) chemical parameters of single biological cells can be obtained in a flow-through setup by optical measurement techniques. Unlike conventional systems, where measurements are conducted in the optical far field, the proposed system senses the cell's optical projection in the near field by using integrated photodiodes. This allows for the attainment of additional parameters, e.g., size and shape, which are usually hidden in the far field. In addition, parameters such as refractive index and absorption of the cell influence the sensor signal. Additionally, with another setup, a different approach is followed to measure similar parameters with external detection using a DVD laser pickup head and a microchannel equipped with a mirror. This low-cost setup does not measure in the near field, and therefore, is dedicated to different parameters. In this contribution, results from measurements with polystyrene particles and biological cells (yeast and Chinese hamster ovary) are presented and the advantages and limitations of both systems are outlined. [source]

Experimental study of dynamic damage of an arch dam

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 3 2007
Haibo Wang
Abstract Seismic responses of a 292-m high arch dam were studied by experiment on a shaking table. The model system included the arch dam with contraction joints, a part of a reservoir, and a partial foundation with a topographic feature near the dam. Potential rock wedges on the abutments and the mechanical properties including uplift on the kinematic planes were carefully simulated. A damping boundary consisting of a viscous liquid was introduced to simulate the effect of dynamic energy emission to far field, which made the dynamic interaction between the dam and the foundation be adequately represented in the model test of an arch dam system. Dynamic responses of the arch dam system under a sequence of seismic loadings in increasing strength were examined. Eleven cracks or overstresses on the model dam due to the earthquake excitations were observed, and consequently, its natural frequency dropped by about 14%, but the model dam was stable under the hydrostatic load of the impounded water after the test. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Response of unbounded soil in scaled boundary finite-element method

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 1 2002
John P. Wolf
Abstract The scaled boundary finite-element method is a powerful semi-analytical computational procedure to calculate the dynamic stiffness of the unbounded soil at the structure,soil interface. This permits the analysis of dynamic soil,structure interaction using the substructure method. The response in the neighbouring soil can also be determined analytically. The method is extended to calculate numerically the response throughout the unbounded soil including the far field. The three-dimensional vector-wave equation of elasto-dynamics is addressed. The radiation condition at infinity is satisfied exactly. By solving an eigenvalue problem, the high-frequency limit of the dynamic stiffness is constructed to be positive definite. However, a direct determination using impedances is also possible. Solving two first-order ordinary differential equations numerically permits the radiation condition and the boundary condition of the structure,soil interface to be satisfied sequentially, leading to the displacements in the unbounded soil. A generalization to viscoelastic material using the correspondence principle is straightforward. Alternatively, the displacements can also be calculated analytically in the far field. Good agreement of displacements along the free surface and below a prism foundation embedded in a half-space with the results of the boundary-element method is observed. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Hydrologic responses to earthquakes and a general metric

GEOFLUIDS (ELECTRONIC), Issue 1-2 2010
CHI-YUEN WANG
Geofluids (2010) 10, 206,216 Abstract Hydrologic responses to earthquakes, including liquefaction, changes in stream and spring discharge, changes in the properties of groundwater such as geochemistry, temperature and turbidity, changes in the water level in wells, and the eruption of mud volcanoes, have been documented for thousands of years. Except for some water-level changes in the near field which can be explained by poroelastic responses to static stress changes, most hydrologic responses, both within and beyond the near field, can only be explained by the dynamic responses associated with seismic waves. For these responses, the seismic energy density e may be used as a general metric to relate and compare the various hydrologic responses. We show that liquefaction, eruption of mud volcanoes and increases in streamflow are bounded by e , 10,1 J m,3; temperature changes in hot springs are bounded by e , 10,2 J m,3; most sustained groundwater changes are bounded by e , 10,3 J m,3; geysers and triggered seismicity may respond to seismic energy density as small as 10,3 and 10,4 J m,3, respectively. Comparing the threshold energy densities with published laboratory measurements, we show that undrained consolidation induced by dynamic stresses can explain liquefaction only in the near field, but not beyond the near field. We propose that in the intermediate field and far field, most responses are triggered by changes in permeability that in turn are a response to the cyclic deformation and oscillatory fluid flow. Published laboratory measurements confirm that changes in flow and time-varying stresses can change permeability, inducing both increases and decreases. Field measurements in wells also indicate that permeability can be changed by earthquakes in the intermediate field and far field. Further work, in particular field monitoring and measurements, are needed to assess the generality of permeability changes in explaining far-field hydrologic responses to earthquakes. [source]

A semi-spectral modelling of landslide tsunamis

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2008
Nazmi Postacioglu
SUMMARY A new, semi-spectral technique based on integral equations is introduced for the landslide tsunami problem. The technique does not use the shallow water approximation and resolves the dispersive surface wavefield generated by sliding material over a bathymetric profile. The wave scattering due to the bathymetric profile on which the slide occurs is calculated solving an integral equation. On the free surface, the linearized kinematic and dynamic boundary conditions are imposed. Method of images is adopted to solve for a source-sink distribution on the bathymetry to simulate the motion of the landslide and to satisfy the kinematic condition on the sea bottom. An asymptotic relation for the far field is also derived. The application to a landslide tsunami generation scenario in the Sea of Marmara reveals that a thickness H submarine mass failure on the southern rim of the Ç,narc,k Basin would create a wave peak of around 0.5 H on the ,1000 m deep Ç,narc,k Basin. [source]

Role of lateral mantle flow in the evolution of subduction systems: insights from laboratory experiments

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2004
Francesca Funiciello
SUMMARY We present 3-D laboratory experiments constructed to investigate the pattern of mantle flow around a subducting slab under different boundary conditions. In particular we present a set of experiments, characterized by different conditions imposed at the trailing edge of the subducting plate (that is, plate fixed in the far field, plate detached in the far field, imposed plate motion). Experiments have been performed using a silicone slab floating inside a honey tank to simulate a thin viscous lithosphere subducting in a viscous mantle. For each set, we show differences between models that do or do not include the possibility of out-of-plane lateral flow in the mantle by varying the lateral boundary conditions. Our results illustrate how a subducting slab vertically confined over a 660-km equivalent depth can be influenced in its geometry and in its kinematics by the presence or absence of possible lateral pathways. On the basis of these results we show implications for natural subduction systems and we highlight the importance of suitable simulations of lateral viscosity variations to obtain a realistic simulation of the history of subduction. [source]

Virtual Electrode Polarization Leads to Reentry in the Far Field

Autonomous off-road navigation with end-to-end learning for the LAGR program

JOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 1 2009
Max Bajracharya
We describe a fully integrated real-time system for autonomous off-road navigation that uses end-to-end learning from onboard proprioceptive sensors, operator input, and stereo cameras to adapt to local terrain and extend terrain classification into the far field to avoid myopic behavior. The system consists of two learning algorithms: a short-range, geometry-based local terrain classifier that learns from very few proprioceptive examples and is robust in many off-road environments; and a long-range, image-based classifier that learns from geometry-based classification and continuously generalizes geometry to appearance, making it effective even in complex terrain and varying lighting conditions. In addition to presenting the learning algorithms, we describe the system architecture and results from the Learning Applied to Ground Robots (LAGR) program's field tests. © 2008 Wiley Periodicals, Inc. [source]

An accurate evaluation of the nonsymmetrical components of Green's functions for multilayered media in the near-field region

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 4 2009
Alaa K. AbdelmageedArticle first published online: 9 FEB 200
Abstract The discrete complex image method has proved to be one of the most efficient techniques to evaluate Green's functions for multilayered media, particularly in the near- and intermediate-field regions. Although the extraction of surface waves extends its validity to the far field, it suffers from erroneous results that contaminate the computation of the near field. To handle this problem for the nonsymmetrical components of Greens functions, we follow the same approach adopted by the author and others for the symmetrical components where a number of artificial poles are extracted for each physical surface-wave pole occurrence. This approach has proved its validity and yielded good results in all field regions. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 881,885, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24201 [source]

Microsystems for Optical Cell Detection: Near versus Far Field

Laser diodes with highly strained InGaAs MQWs and very narrow vertical far fields

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2006
F. Bugge
Abstract The effect of variation of the number of highly strained InGaAs quantum wells embedded in GaAs layers on the crystal quality of the epitaxial layers and AlGaAs/GaAs laser diodes was investigated. With four quantum wells and very thick waveguide layers, reasonable efficient laser diodes emitting above 1100 nm with a narrow vertical far field (FWHM = 15°) were obtained. Broad area laser diodes with 200 µm stripe width and an optimised doping profile emit nearly 20 W cw output power. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Absence of corneal endothelium injury in non-human primates treated with and without ophthalmologic drugs and exposed to 2.8,GHz pulsed microwaves,,

BIOELECTROMAGNETICS, Issue 4 2010
Shin-Tsu Lu
Abstract Microwave-induced corneal endothelial damage was reported to have a low threshold (2.6,W/kg), and vasoactive ophthalmologic medications lowered the threshold by a factor of 10,0.26,W/kg. In an attempt to confirm these observations, four adult male Rhesus monkeys (Macaca mulatta) under propofol anesthesia were exposed to pulsed microwaves in the far field of a 2.8,GHz signal (1.43,±,0.06,µs pulse width, 34,Hz pulse repetition frequency, 13.0,mW/cm2 spatial and temporal average, and 464,W/cm2 spatial and temporal peak (291,W/cm2 square wave equivalent) power densities). Corneal-specific absorption rate was 5.07,W/kg (0.39,W/kg/mW/cm2). The exposure resulted in a 1.0,1.2,°C increase in eyelid temperature. In Experiment I, exposures were 4,h/day, 3 days/week for 3 weeks (nine exposures and 36,h total). In Experiment II, these subjects were pretreated with 0.5% Timolol maleate and 0.005% Xalatan® followed by 3 or 7 4-h pulsed microwave exposures. Under ketamine,xylazine anesthesia, a non-contact specular microscope was used to obtain corneal endothelium images, corneal endothelial cell density, and pachymetry at the center and four peripheral areas of the cornea. Ophthalmologic measurements were done before and 7, 30, 90, and 180 days after exposures. Pulsed microwave exposure did not cause alterations in corneal endothelial cell density and corneal thickness with or without ophthalmologic drugs. Therefore, previously reported changes in the cornea exposed to pulsed microwaves were not confirmed at exposure levels that are more than an order of magnitude higher. Bioelectromagnetics 31:324,333, 2010. Published 2010 Wiley-Liss, Inc. [source]

Magnifying Superlenses and other Applications of Plasmonic Metamaterials in Microscopy and Sensing

CHEMPHYSCHEM, Issue 4 2009
Igor I. Smolyaninov Dr.
Abstract Every last detail: New advances in the construction of metamaterials enable the creation of artificial optical media, whose use in microscopy can provide resolution that is not determined by the conventional diffraction limit. The picture shows a superposition of an AFM image of a plasmonic metamaterial onto the corresponding optical image obtained using a conventional optical microscope. Over the past century, the resolution of conventional optical microscopes, which rely on optical waves that propagate into the far field, has been limited because of diffraction to a value of the order of a half-wavelength (,0/2) of the light used. Although immersion microscopes have slightly improved resolution, of the order of ,0/2n, the increased resolution is limited by the small range of refractive indices n of available transparent materials. However, now we are experiencing a quick demolition of the diffraction limit in optical microscopy. In the last few years, numerous nonlinear optical microscopy techniques based on photoswitching and saturation of fluorescence have demonstrated far-field resolution of 20 to 30 nm. In a parallel development, recent progress in metamaterials has demonstrated that artificial optical media can be created, whose use in microscopy can provide resolution that is not determined by the conventional diffraction limit. The resolution of linear immersion microscopes based on such metamaterials is only limited by losses, which can be minimized by appropriate selection of the constituents of the metamaterials used and by the wavelength(s) used for imaging. It is also feasible to compensate for losses by adding gain to the structure. Thus, optical microscopy is quickly moving towards resolution of around 10 nm, which should bring about numerous revolutionary advances in lithography and imaging. [source]

Comparison of image reconstruction by using near-field and far-field data for an imperfect conductor

INTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 2 2001
Chien-Ching Chiu
Abstract Image reconstruction by using near-field and far-field data for an imperfectly conducting cylinder is investigated. A conducting cylinder of unknown shape and conductivity scatters the incident wave in free space and the scattered near and far fields are measured. By using measured fields, the imaging problem is reformulated into an optimization problem and solved by the genetic algorithm. Numerical results show that the convergence speed and final reconstructed results by using near-field data are better than those obtained by using far-field data. This work provides both comparative and quantitative information. © 2001 John Wiley & Sons, Inc. Int J RF and Microwave CAE 11: 69,73, 2001. [source]