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Field Distribution (field + distribution)

Distribution by Scientific Domains

Engineering	26%
Life Sciences	20%
Physics and Astronomy	17%
Medical Sciences	14%
Polymers and Materials Science	8%
Earth and Environmental Science	5%

Selected Abstracts

Tectonic Framework and Deep Structure of South China and Their Constraint to Oil-Gas Field Distribution

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 1 2009
Qingchen WANG
Abstract: South China could be divided into one stable craton, the Yangtze Craton (YzC), and several orogenic belts in the surrounding region, that is the Triassic Qinling-Dabie Orogenic Belt (QDOB) in the north, the Songpan-Garzê Orogenic Belt (SGOB) in the northwest, the Mesozoic-Cenozoic Three-river Orogenic Belt (TOB) in the west, the Youjiang Orogenic Belt (YOB) in the southwest, the Middle Paleozoic Huanan Orogenic Belt (HOB) in the southeast, and the Mesozoic-Cenozoic Maritime Orogenic Belt (MOB) along the coast. Seismic tomographic images reveal that the Moho depth is deeper than 40 km and the lithosphere is about 210 km thick beneath the YzC. The SGOB is characterized by thick crust (>40 km) and thin lithosphere (<150 km). The HOB, YOB and MOB have a thin crust (<40 km) and thin lithosphere (<150 km). Terrestrial heat flow survey revealed a distribution pattern with a low heat flow region in the eastern YzC and western HOB and two high heat flow regions in the TOB and MOB respectively. Such a "high-low-high" heat flow distribution pattern could have resulted from Cenozoic asthenosphere upwelling. All oil-gas fields are concentrated in the central part of the YzC. Remnant oil pools have been discovered along the southern margin of the YzC and its adjacent orogenic belts. From a viewpoint of geological and geophysical structure, regions in South China with thick lithosphere and low heat flow value, as well as weak deformation, might be the ideal region for further petroleum exploration. [source]

Elementary Many-Particle Processes in Plasma Microfields

CONTRIBUTIONS TO PLASMA PHYSICS, Issue 3 2006
M. Yu.
Abstract The effect of electric and magnetic plasma microfields on elementary many-body processes in plasmas is considered. As detected first by Inglis and Teller in 1939, the electric microfield controls several elementary processes in plasmas as transitions, line shifts and line broadening. We concentrate here on the many-particle processes ionization, recombination, and fusion and study a wide area of plasma parameters. In the first part the state of art of investigations on microfield distributions is reviewed in brief. In the second part, various types of ionization processes are discussed with respect to the influence of electric microfields. It is demonstrated that the processes of tunnel and rescattering ionization by laser fields as well as the process of electron collisional ionization may be strongly influenced by the electric microfields in the plasma. The third part is devoted to processes of microfield action on fusion processes and the effects on three-body recombination are investigated. It is shown that there are regions of plasma densities and temperatures, where the rate of nuclear fusion is accelerated by the electric microfields. This effect may be relevant for nuclear processes in stars. Further, fusion processes in ion clusters are studied. Finally we study in this section three-body recombination effects and show that an electric microfield influences the three-body electron-ion recombination via the highly excited states. In the fourth part, the distribution of the magnetic microfield is investigated for equilibrium, nonequilibrium, and non-uniform magnetized plasmas. We show that the field distribution in a neutral point of a non-relativistic ideal equilibrium plasma is similar to the Holtsmark distribution for the electrical microfield. Relaxation processes in nonequilibrium plasmas may lead to additional microfields. We show that in turbulent plasmas the broadening of radiative electron transitions in atoms and ions, without change of the principle quantum number, may be due to the Zeeman effect and may exceed Doppler and Stark broadening as well. Further it is shown that for optical radiation the effect of depolarization of a linearly polarized laser beams propagating through a magnetized plasma may be rather strong. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Microstructural and Mechanical Investigations on Porcelain-Fused-to-Metal in Multilayer System

ADVANCED ENGINEERING MATERIALS, Issue 4 2010
Adele Carradò
Results on porcelain-fused-to-metal (PFM) technique of ceramic films for biomedical applications on metal substrate are reported. The coating of metallic implants with bio-ceramic films (glassy and opaque ceramic) was proposed to be a solution for combining the mechanical properties of the metallic material with the bioactive character of the ceramic layer, leading to a better integration of the entire implant. The aim of this paper is to determine a stress field distribution by a non-destructive method as high-energy synchrotron X-ray diffraction in energy dispersive in the metal and glass ceramic bulk as well as at metal,opaque ceramic interface in PFM three layers sample. Tensile stresses were found in palladium substrate and compressive state in glass ceramic coating. Moreover thermal stresses induced by PFM coating at the interfaces were calculated by analytical mathematical model, confirming that the stresses induced, due to the selection of the materials, are low. Finally, the micro-structural and chemical characteristics of glassy and opaque bio-ceramic coatings on palladium alloy substrate were investigated and no inter-diffusion area between metal and ceramic could be detected as well as non-homogeneity in the interface ceramic. [source]

Leakage field distribution of a transformer for conventional and superconducting conditions

EUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 4 2002
P. Raitsios
The overall distribution of leakage field and current density in a transformer model with cylindrical windings in proximity to the core yokes is investigated from a different viewpoint than that of Kapp or Rogowski, i.e. by taking into consideration the conductivity of the conductive material. Using Maxwell's differential equations and the vector potential and by considering the conductivity of the conductive material, general equations are obtained for the components of the magnetic induction in a two dimensional space. From these components the leakage inductance is calculated and its application for conventional and superconducting conditions is examined. The distribution of current density in the windings is obtained from the vector potential. [source]

High Quality Factor Metallodielectric Hybrid Plasmonic,Photonic Crystals

ADVANCED FUNCTIONAL MATERIALS, Issue 12 2010
Xindi Yu
Abstract A 2D polystyrene colloidal crystal self-assembled on a flat gold surface supports multiple photonic and plasmonic propagating resonance modes. For both classes of modes, the quality factors can exceed 100, higher than the quality factor of surface plasmons (SP) at a polymer,gold interface. The spatial energy distribution of those resonance modes are carefully studied by measuring the optical response of the hybrid plasmonic,photonic crystal after coating with dielectric materials under different coating profiles. Computer simulations with results closely matching those of experiments provide a clear picture of the field distribution of each resonance mode. For the SP modes, there is strong confinement of electromagnetic energy near the metal surface, while for optical modes, the field is confined inside the spherical particles, far away from the metal. Coating of dielectric material on the crystal results in a large shift in optical features. A surface sensor based on the hybrid plasmonic,photonic crystal is proposed, and it is shown to have atomic layer sensitivity. An example of ethanol vapor sensing based on physisorption of ethanol onto the sensor surface is demonstrated. [source]

Network-magnetotelluric method and its first results in central and eastern Hokkaido, NE Japan

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2001
Makoto Uyeshima
Summary A new field observation technique based on the magnetotelluric (MT) method has been developed to determine deep and large-scale 3-D electrical conductivity distributions in the Earth. The method is named ,Network-MT', and employs a commercial telephone network, to measure voltage differences with long dipole lengths ranging from 10 to several tens of kilometres. This observation configuration enables us to obtain the telluric field distribution with nearly continuous coverage over a target region. Response functions are estimated between the respective voltage differences and the horizontal magnetic fields at a reference point. Owing to the long electrode spacing, the observed responses are relatively free from the effects of small-scale near-surface heterogeneity with a scalelength shorter than the typical electrode spacing. Therefore, physically meaningful direct comparison between the observations and model responses is feasible even if the fine-scale features of near-surface heterogeneity are ignored. This extensively reduces the difficulty, especially in 3-D MT interpretation. The first Network-MT experiment was performed in central and eastern Hokkaido, NE Japan, in 1989. It took about five months to complete all of the measurements, and used 209 dipoles to cover the target area of 200(EW) × 200(NS) km2. The long electrode spacing enabled us to obtain the voltage differences with a high signal-to-noise ratio. For 175 dipoles, the squared multiple coherency between the voltage difference and the horizontal magnetic field at Memambetsu Geomagnetic Observatory was determined to be more than 0.9 in the period from 102 to 104 s. 193 MT impedances were computed in tensor form by linear combination of the response functions. The estimated impedances generally possessed smooth period dependence throughout the period range. No drastic spatial change was observed in the characteristics of the tensors for neighbouring sites, and some regional trend could be detected in the spatial distribution. Thus, we confirmed the merit of the Network-MT method, that its responses are little affected by small-scale near-surface structures. The regional feature of the response implied a significant influence of the coast effect, and was well correlated with the regional geological setting in Hokkaido. Conventional Groom,Bailey tensor decomposition analysis revealed that the target region is not regionally one- or two-dimensional. Therefore, we developed a 3-D forward modelling scheme specially designed for the Network-MT experiment, and tried to reproduce the Network-MT responses directly. In the 3-D model, a realistic land,sea distribution was considered. The resistivity of sea water was fixed to be 0.25 , m and, as a first trial of 3-D modelling, the resistivity of the land was assumed to be uniform and its value was determined to be 200 , m by a simple one-parameter inversion. Overall agreements between the observations and the best-fit model responses indicated the importance of the 3-D coast effect in the target region. However, there remained significant discrepancies, especially in the phase of the responses, which provide a clue to determining a regional deep 3-D structure. [source]

Imaging the Electric-Field Distribution in Organic Devices by Confocal Electroreflectance Microscopy

ADVANCED FUNCTIONAL MATERIALS, Issue 8 2009
Michele Celebrano
Abstract Space resolved Stark spectroscopy is introduced as a non invasive optical technique for imaging electric field distribution in organic semiconductors. Stark spectroscopy relies on the electric field induced change in the absorption/reflection. It is shown that local monitoring of Stark shift with confocal spatial resolution provides quantitative information on the strength of the local field as well as charge distribution within the transport channel. [source]

Numerical solution of eddy current problems in ferromagnetic bodies travelling in a transverse magnetic field

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2003
W. Peterson
Abstract Eddy currents are investigated in a ferromagnetic bar travelling in a transverse magnetic field. Such an open boundary field problem is analysed by a hybrid approach based on Galerkin finite element formulation coupled with a separation of variables. A steady state is considered, introducing time-periodic boundary conditions. The resultant system of non-linear equations is solved by an iterative procedure based on Brouwer's fixed-point theorem. Numerical results are presented for a bar of circular cross-section made of cast steel or cast iron. Selected examples of the field distribution and characteristics of eddy-current power losses are enclosed in graphic form. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Modelling of photonic bandgap devices by the leaky mode propagation method

INTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 3 2003
Agostino Giorgio
Abstract Main modelling approaches used for investigating the Photonic bandgap (PBG) devices are reviewed. In particular, the model based on Leaky Mode Propagation (LMP) method is described. A complete analysis of the propagation characteristics, including the determination of modal propagation constants, electromagnetic field harmonics and total field distribution, transmission and reflection coefficients, total forward and backward power flow in the structure, guided and radiated power, and total losses, can be carried out by a computer program based on the LMP approach. The numerical results have been validated by comparisons with those obtained by using other more complex and expensive models. The new model shows some significant advantages in terms of very low computational time, absence of any a priori theoretical assumptions and approximations, capability of simulating the actual physical behaviour of the device and fast determination of the bandgap position.Copyright © 2003 John Wiley & Sons, Ltd. [source]

Numerical modelling of equilibrium charge separation in poled devices

INTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 6 2001
A. De Francesco
Abstract We describe an efficient numerical procedure for the equilibrium solution of the internal electric field distribution resulting from poling of photo-refractive materials. This technique has been developed to model the equilibrium state in poled bulk devices requiring bulk charge neutrality to facilitate the modelling of blocking boundaries for a high externally applied voltage (bias) in the kV range for a small number of points. This technique is an improvement on existing conventional numerical techniques employed for modelling semiconductor devices that are intended for low bias. This method can also accommodate the modelling of planar insulators and organic optical materials. We develop an algorithm incorporating the existing Newton,Raphson method for solving Kukhtarev's equations that enforces conservation of charge within the modelled system. We apply this technique to model one-dimensional charge separation in ultraviolet (UV) excited poling of glass and, report numerical equilibrium electric field distribution for a 2 kV bias. The convergence behaviour of the algorithm is investigated and compared against the Newton,Raphson method. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Climatic niche partitioning following successive invasions by fruit flies in La Réunion

JOURNAL OF ANIMAL ECOLOGY, Issue 2 2006
PIERRE-FRANÇOIS DUYCK
Summary 1Biological invasions have profound effects on community structure. The community composition following invasions can be influenced by the habitat diversity and the species' responses to abiotic factors. 2We evaluated the tolerance to climatic factors and analysed the field distribution of four polyphagous fruit flies (Diptera: Tephritidae) of La Réunion Island (three exotic species that successively invaded the island and the endemic species Ceratitis catoirii) in order to evaluate the opportunities of coexistence by niche differentiation. 3Atmospheric humidity and immersion in water in the laboratory greatly influence the survival of fruit fly pupae. While C. catoirii and C. rosa are very sensitive to desiccation, C. capitata and especially Bactrocera zonata are relatively tolerant. B. zonata also tolerated immersion in water much longer than did C. rosa and C. catoirii, that in turn were more resistant than C. capitata. Overall, field distributions agree with the predictions based on this study of humidity combined with previous data on the effects of temperature. 4Climatic niche partitioning promotes coexistence between some but not all pairs of invasive species. Thus, C. rosa can coexist with both C. capitata and B. zonata at the regional scale, while climatic niches are not different enough to promote coexistence of the latter two species. The endemic species has no private climatic niche either and this now very rare species could be in the process of extinction. 5By promoting coexistence or not, climatic diversity in invaded areas can directly affect the community composition following invasions. [source]

High-field MRSI of the prostate using a transmit/receive endorectal coil and gradient modulated adiabatic localization

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 2 2009
Jamie Near PhD
Abstract Purpose To demonstrate in vivo magnetic resonance spectroscopic imaging (MRSI) of the human prostate at 4.0T using a transmit/receive endorectal coil and a pulse sequence designed specifically for this application. Materials and Methods A solid, reusable endorectal probe was designed for both radiofrequency transmission and reception. Finite difference time domain (FDTD) simulations were performed to characterize the coil's electric field distribution, and temperature measurements were performed in a beef tissue phantom to determine the coil's safe operating limit. The localization by selective adiabatic refocusing (LASER) pulse sequence was implemented using six gradient modulated offset independent adiabatic (GOIA) pulses for very sharp, B1 -insensitive voxel localization. Results Based on the simulations and temperature measurements, the coil's safe operating limit was conservatively estimated to be 1.0W for 15 minutes. The transition width of the GOIA pulse selection profiles was only 6% of the bandwidth, compared with 22% for a specific absorption rate (SAR)-matched conventional adiabatic pulse. Using the coil and pulse sequence described here, MRSI data were successfully acquired from a patient with biopsy-proven prostate cancer, with a nominal voxel size of 0.34 cc in a scan time of 15 minutes. Conclusion This work demonstrates the safe and effective use of a transmit/receive endorectal coil for in vivo MRSI of the prostate. J. Magn. Reson. Imaging 2009;30:335,343. © 2009 Wiley-Liss, Inc. [source]

Manipulation of image intensity distribution at 7.0 T: Passive RF shimming and focusing with dielectric materials,

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2006
Qing X. Yang
Abstract Purpose To investigate the effects of high dielectric material padding on RF field distribution in the human head at 7.0 T, and demonstrate the feasibility and effectiveness of RF passive shimming and focusing with such an approach. Materials and Methods The intensity distribution changes of gradient-recalled-echo (GRE) and spin-echo (SE) images of a human head acquired with water pads (dielectric constant = 78) placed in specified configurations around the head at 7.0 T were evaluated and compared with computer simulation results using the finite difference time domain (FDTD) method. The contributions to the B1 field distribution change from the displacement current and conductive current of a given configuration of dielectric padding were determined with computer simulations. Results MR image intensity distribution in the human head with an RF coil at 7.0 T can be changed drastically by placing water pads around the head. Computer simulations reveal that the high permittivity of water pads results in a strong displacement current that enhances image intensity in the nearby region and alters the intensity distribution of the entire brain. Conclusion The image intensity distribution in the human head at ultra-high field strengths can be effectively manipulated with high permittivity padding. Utilizing this effect, the B1 field inside the human head of a given RF coil can be adjusted to reduce the B1 field inhomogeneity artifact associated with the wave behavior (RF passive shimming) or to locally enhance the signal-to-noise ratio (SNR) in targeted regions of interest (ROIs; RF field focusing). J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc. [source]

On the electrostatic equilibrium of granular flow in pneumatic conveying systems

AICHE JOURNAL, Issue 11 2006
Jun Yao
Abstract An analytical methodology involving the concept of "electrostatic equilibrium" is developed for granular flow in pneumatic conveying systems. The methodology can be used for estimation of the electrostatic field distribution at various sections of the system and explanation of the mechanisms involved for various electrostatic phenomena observed. For all cases conducted in the conveying system, there was a "charging time" required for the system to reach the state of "electrostatic equilibrium." Experiments conducted at different sections of the system showed that the time required increased in the order: horizontal pipe, vertical pipe, and pipe bend. Through a physical analysis, it is deduced that electrostatic equilibrium is related to the granules' behavior and local flow characteristics. In general, a longer time duration taken to reach equilibrium corresponds to a process with more complicated granular flow patterns. In the electrostatic equilibrium state, the field distribution shows the highest electrostatic field strength near the pipe wall, and this field strength degrades from the pipe wall to the pipe center. At various pipe sections, the highest strength occurs at the bend, in accord with observations that electric sparking first occurs at that location within the entire pneumatic conveying system. In the vertical pipe, granular distribution was measured using electrical capacitance tomography (ECT), and granular velocities were cross-referenced with those using particle image velocimetry (PIV). The electrostatic force at low air flow rates is found to be the primary cause for granules sticking to the pipe wall and results in the formation of the half-ring or ring structure. The state of electrostatic equilibrium is physically influenced by several elements in conveying systems. In a cyclic conveying system, a new pipe (or low humidity or no antistatic agent) tends to expedite the process to reach electrostatic equilibrium and attain high magnitude of electrostatic current at the state. In a non-cyclic horizontal conveying system, a thin film (pipe) is found to prolong the process duration to reach equilibrium, while the case with charged film (pipe) takes shorter duration to do so. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source]

Microwaves in soil remediation from VOCs.

AICHE JOURNAL, Issue 3 2004

Abstract This work presents the design of a microwave opened applicator useful to perform the Microwave Induced Steam Distillation (MISD) process for soil remediation treatments. The prototype has been also realized and used to irradiate a 40 x 30 cm area with a given electromagnetic field distribution. Experiments carried out by in situ operations on a soil contaminated with VOC's are reported. Finally, the experimental data collected are described by a mathematical model previously proposed. © 2004 American Institute of Chemical Engineers AIChE J, 50:722,732, 2004 [source]

Natural linewidth chemical shift imaging (NL-CSI)

MAGNETIC RESONANCE IN MEDICINE, Issue 1 2006
Adil Bashir
Abstract The discrete Fourier transform (FT) is a conventional method for spatial reconstruction of chemical shifting imaging (CSI) data. Due to point spread function (PSF) effects, FT reconstruction leads to intervoxel signal leakage (Gibbs ringing). Spectral localization by imaging (SLIM) reconstruction was previously proposed to overcome this intervoxel signal contamination. However, the existence of magnetic field inhomogeneities creates an additional source of intervoxel signal leakage. It is demonstrated herein that even small field inhomogeneities substantially amplify intervoxel signal leakage in both FT and SLIM reconstruction approaches. A new CSI data acquisition strategy and reconstruction algorithm (natural linewidth (NL) CSI) is presented that eliminates effects of magnetic field inhomogeneity-induced intervoxel signal leakage and intravoxel phase dispersion on acquired data. The approach is based on acquired CSI data, high-resolution images, and magnetic field maps. The data are reconstructed based on the imaged object structure (as in the SLIM approach) and a reconstruction matrix that takes into account the inhomogeneous field distribution inside anatomically homogeneous compartments. Phantom and in vivo results show that the new method allows field inhomogeneity effects from the acquired MR signal to be removed so that the signal decay is determined only by the "natural" R2 relaxation rate constant (hence the term "natural linewidth" CSI). Magn Reson Med, 2006. © 2006 Wiley-Liss, Inc. [source]

Quantitative lung perfusion mapping at 0.2 T using FAIR True-FISP MRI

MAGNETIC RESONANCE IN MEDICINE, Issue 5 2006
Petros Martirosian
Abstract Perfusion measurements in lung tissue using arterial spin labeling (ASL) techniques are hampered by strong microscopic field gradients induced by susceptibility differences between the alveolar air and the lung parenchyma. A true fast imaging with steady precession (True-FISP) sequence was adapted for applications in flow-sensitive alternating inversion recovery (FAIR) lung perfusion imaging at 0.2 Tesla and 1.5 Tesla. Conditions of microscopic static field distribution were assessed in four healthy volunteers at both field strengths using multiecho gradient-echo sequences. The full width at half maximum (FWHM) values of the frequency distribution for 180,277 Hz at 1.5 Tesla were more than threefold higher compared to 39,109 Hz at 0.2 Tesla. The influence of microscopic field inhomogeneities on the True-FISP signal yield was simulated numerically. Conditions allowed for the development of a FAIR True-FISP sequence for lung perfusion measurement at 0.2 Tesla, whereas at 1.5 Tesla microscopic field inhomogeneities appeared too distinct. Perfusion measurements of lung tissue were performed on eight healthy volunteers and two patients at 0.2 Tesla using the optimized FAIR True-FISP sequence. The average perfusion rates in peripheral lung regions in transverse, sagittal, and coronal slices of the left/right lung were 418/400, 398/416, and 370/368 ml/100 g/min, respectively. This work suggests that FAIR True-FISP sequences can be considered appropriate for noninvasive lung perfusion examinations at low field strength. Magn Reson Med, 2006. © 2006 Wiley-Liss, Inc. [source]

Evanescent fields,Direct measurement, modeling, and application

MICROSCOPY RESEARCH AND TECHNIQUE, Issue 3 2007
S.T. Huntington
Abstract The evanescent field surrounding an exposed planar waveguide in silica is accurately measured using scanning near field optical microscopy (SNOM) and compared to models of the field distribution. Distortions in the field due to edge effects and the proximity of the mode to the surface are all detected. The characterized field is use to quantitatively explore the difference in collection efficiency between contact mode SNOM and intermittent contact mode SNOM. A strong correlation between tip oscillation amplitude and detection efficiency is determined. Microsc. Res. Tech., 2007. © 2007 Wiley-Liss, Inc. [source]

Wideband cross-coupled filter using defected stepped impedance resonator

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2010
Bian Wu
Abstract A novel wideband cross-coupled band-pass filter based on defected stepped impedance resonator (DSIR) is presented in this article. Although the DSIR has opposite impedance characteristic and field distribution to the microstrip SIR, its resonant property is similar to the latter. The internal coupling coefficients of DSIRs are found to be large enough for the wideband filter design. A four-pole, cross-coupled band-pass filter with f0 = 1.6 GHz and FBW = 12% is designed and fabricated using the folded DSIR. Experimental result has good agreement with the simulation. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 558,561, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24972 [source]

Design of WiFi/WiMAX dual-band E-shaped patch antennas through cavity model approach

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2010
Heng-Tung Hsu
Abstract The design of dual-band, single patch microstrip antenna covering 2.4 and 3.5 GHz for WiFi and WiMAX applications based on E-shaped patch is presented. Although cavity model analysis is included in the design procedure, the slotted configuration is treated as the perturbed cavity to characterize the resonant frequencies of corresponding modes. Additionally, the feed point position is determined through the field distribution resulted from the modal analysis. A new equivalent circuit model based on the coupled resonators theory is proposed for analysis purposes. The relationship between cavity model analysis and antenna resonances is further evidenced by the surface current distributions on the conductors. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 471,474, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24954 [source]

Aperture field reconstruction by calculated cylindrical near field

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 11 2008
Alcino Castelo Boso
Abstract A method for determining the aperture field distribution of an array antenna from near-field measurement over the surface of a right circular cylinder enclosing the antenna is applied here. The approach relies on the concept of information content of the field. The truncation problem is solved by picking up the information that is lost due to the finite size of scanning area, in points of the space reachable by the measurement system. In this article, we rebuild the field at the aperture from near-field cylindrical calculated on the surface of measure, with dependence on the variable phi, and without dependence on the variable phi. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2849,2851, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23825 [source]

Analysis of circular waveguides with soft and hard surfaces realized by strip-loaded walls using asymptotic boundary conditions

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 6 2001
Ahmed A. Kishk
Abstract Soft and hard walls are realized for a circular waveguide with walls coated by a uniform dielectric layer of appropriate thickness and loaded with conducting strips. The strips are oriented along the waveguide axis (z -axis) for hard surfaces or ,-directed for soft surfaces in a periodic form. The simple approximate asymptotic strip boundary condition (ASBC) is used to analyze the structure. For the dominant mode, when the waveguide walls are hard or soft, a linear field distribution across the waveguide cross section can be obtained. Then the waveguide can be used as an antenna with good linear polarization. The characteristics of such waveguides are presented with sample radiation patterns as compared with hollow waveguide radiation patterns. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 29: 433,436, 2001. [source]

Structures of the magnetoionic media around the Fanaroff,Riley Class I radio galaxies 3C 31 and Hydra A

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2008
R. A. Laing
ABSTRACT We use high-quality Very Large Array (VLA) images of the Fanaroff,Riley Class I radio galaxy 3C 31 at six frequencies in the range 1365,8440 MHz to explore the spatial scale and origin of the rotation measure (RM) fluctuations on the line of sight to the radio source. We analyse the distribution of the degree of polarization to show that the large depolarization asymmetry between the north and south sides of the source seen in earlier work largely disappears as the resolution is increased. We show that the depolarization seen at low resolution results primarily from unresolved gradients in a Faraday screen in front of the synchrotron-emitting plasma. We establish that the residual degree of polarization in the short-wavelength limit should follow a Burn law and we fit such a law to our data to estimate the residual depolarization at high resolution. We discuss how to interpret the structure function of RM fluctuations in the presence of a finite observing beam and how to address the effects of incomplete sampling of RM distribution using a Monte Carlo approach. We infer that the observed RM variations over selected areas of 3C 31, and the small residual depolarization found at high resolution, are consistent with a power spectrum of magnetic fluctuations in front of 3C 31 whose power-law slope changes significantly on the scales sampled by our data. The power spectrum P(f) can only have the form expected for Kolmogorov turbulence [P(f) ,f,11/3] on scales ,5 kpc. On larger scales, we find . We briefly discuss the physical interpretation of these results. We also compare the global variations of RM across 3C 31 with the results of three-dimensional simulations of the magnetic-field fluctuations in the surrounding magnetoionic medium. We infer that the RM variation across 3C 31 is qualitatively as expected from relativistic-jet models of the brightness asymmetry wherein the apparently brighter jet is on the near side of the nucleus and is seen through less magnetoionic material than the fainter jet. We show that our data are inconsistent with observing 3C 31 through a spherically symmetric magnetoionic medium, but that they are consistent with a field distribution that favours the plane perpendicular to the jet axis , probably because the radio source has evacuated a large cavity in the surrounding medium. We also apply our analysis techniques to the case of Hydra A, where the shape and the size of the cavities produced by the source in the surrounding medium are known from X-ray data. We emphasize that it is essential to account for the potential exclusion of magnetoionic material from a large volume containing the radio source when using the RM variations to derive statistical properties of the fluctuations in the foreground magnetic field. [source]

Electromagnetic fields in jets

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2007
B. D. Sherwin
ABSTRACT The magnetic fields and energy flows in an astronomical jet described by our earlier model are calculated in detail. Though the field distribution varies with the external pressure function p(z), it depends only weakly on the other boundary conditions. Individual field lines were plotted; the lines become nearly vertical at the bottom and are twisted at the top. An animation of a field line's motion was made, which shows the line being wound up by the accretion disc's differential rotation and rising as a result of this. The distribution of Poynting flux within the jet indicates that much of the energy flows up the jet from the inside of the accretion disc but a substantial fraction flows back down to the outside. [source]

Electroluminescence uniformity in green LEDs and dual color blue/green stacking LEDs

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007
Grigory Onushkin
Abstract The uniformity of Electroluminescence (EL) of green and blue/green stacking InGaN Light Emitting Diodes (LED) has been studied and analyzed by various techniques. Comparative measurements of Photo-Luminescence (PL), Cathode-Luminescence (CL) and EL allow us to conclude that non-uniform distribution of EL in studied LEDs is caused by non-uniformity of acceptors distribution over the p-GaN area. It was found that there are some defective areas in p-GaN having locally low level of acceptor concentration. These areas correspond to the surface hexagonal shaped pyramids on p-GaN surface. The locally low doping level changes the field distribution, injection properties and the EL emission properties for these defective points. Optimization of p-GaN growth conditions will improve the EL uniformity and increase the efficiency of green and blue/green LEDs. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Orientation of specialist and generalist fungivorous ciid beetles to host and non-host odours

PHYSIOLOGICAL ENTOMOLOGY, Issue 3 2000
Roger Guevara
Abstract Most ciids (Ciidae) are strict fungivores specialized on fruit bodies of wood-rotting fungi. The Ciidae includes both specialist and generalist species. Recent evidence suggests that ciids locate and discriminate their potential hosts based mainly on fungal odours. In this study, we investigated the field distribution of ciids in a local woodland near Bath, U.K. We also evaluated experimentally the behavioural responses of ciids to host and non-host fungi in an olfactometer, and explored potential differences in putative aroma compounds in host fungi. Our field data showed that Octotemnus glabriculus, Cis boleti and Cis nitidus have preference for one host species, whereas C. bilamellatus has no preference. The experimental evidence was in accordance with the field observations. The specialists O. glabriculus, C. boleti and C. nitidus were specifically attracted to odour compounds of their preferred host fungi: Coriolus versicolor for the first two beetles and Ganoderma adspersum for the latter one. By contrast, the generalist C. bilamellatus was attracted to odours from C. versicolor, G. adspersum and Piptoporus betulinus. The evidence from this and other published studies suggest that ciids depend mainly on fruit body odours for location and discrimination of their host fungi. In accordance with this, we observed diffierential behavioural responses of ciids to aroma compounds of host and non-host species. [source]

Multichannel mapping of fetal magnetocardiogram in an unshielded hospital setting

PRENATAL DIAGNOSIS, Issue 5 2005
Donatella Brisinda
Abstract Objectives To evaluate the feasibility of unshielded in-hospital multichannel mapping of fetal magnetocardiogram (FMCG), with a 36-channel system for standard adult magnetocardiographic (MCG) recordings, and its reliability according to the recommended standards for FMCG. Methods FMCG was ambulatory mapped with a 36-channel MCG system, in six normal pregnancies at different gestational ages. MCG analysis included adaptive digital filtering of 50 Hz, signal averaging, reconstruction of magnetic field distribution (MFD) and source localization. Fixed Point Independent Component Analysis algorithm (FastICA) was used to reconstruct the FMCG, separating them from maternal contamination and noise. Results The quality of FMCG recorded after the 32nd gestational week and reconstructed with FastICA was close to FMCG obtained in shielded rooms, and good enough to measure cardiac intervals and heart rate variability parameters. In two cases, reconstruction of the MFD during the QRS allowed three-dimensional localization of ventricular sources. Conclusions A first demonstration has been given that multichannel mapping of FMCG can be performed in unshielded clinical environments, with resolution good enough for contactless assessment of fetal cardiac electrophysiology. FastICA processing on unshielded FMCG, recorded after the 32nd week, provided beat-to-beat analysis and heart rate variability assessment. Further work is needed to improve signal reconstruction in early pregnancy. Copyright © 2005 John Wiley & Sons, Ltd. [source]

A single magnetic field exposure system for sequential investigation of real time and downstream cellular responses

BIOELECTROMAGNETICS, Issue 1 2004
Raj R. Rao
Abstract To be able to correlate real time membrane potential or ion flux changes with further downstream gene transcription responses due to extremely low frequency (ELF) electromagnetic field (EMF) exposure, we devised an experimental system consisting of a pair of symmetric circular coils. This system can be used on an inverted microscope stage (real time signaling) as well as inside controlled environment incubators (gene transcription end points). The system includes a unique, custom made switch box for blinding the experimental staff and a power amplifier. We report herein the design and characterization of the system with respect to parameters considered important in in vitro ELF,EMF exposure studies, including linear magnetic field distribution, compensation for microscope objective lens interference, heating effects of the coils, and harmonic content of the signals. Bioelectromagnetics 25:27,32, 2004. © 2003 Wiley-Liss, Inc. [source]

Creation of arrays of cell aggregates in defined patterns for developmental biology studies using dielectrophoresis

BIOTECHNOLOGY & BIOENGINEERING, Issue 5 2010
Rama Yusvana
Abstract It is shown that dielectrophoresis,the movement of particles in non-uniform electric fields,can be used to create engineered skin with artificial placodes of different sizes and shapes, in different spatial patterns. Modeling of the electric field distribution and image analysis of the cell aggregates produced showed that the aggregation is highly predictable. The cells in the aggregates remain viable, and reorganization and compaction of the cells in the aggregates occurs when the artificial skin is subsequently cultured. The system developed could be of considerable use for the in vitro study of developmental processes where local variations in cell density and direct cell,cell contacts are important. Biotechnol. Bioeng. 2010;105: 945,954. © 2009 Wiley Periodicals, Inc. [source]