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Field Profile (field + profile)

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Life Sciences	25%

Selected Abstracts

Characterization of voltage degradation in dynamic field gradient focusing

ELECTROPHORESIS, Issue 5 2008
Jeffrey M. Burke
Abstract Dynamic field gradient focusing (DFGF) is an equilibrium gradient method that utilizes an electric field gradient to simultaneously separate and concentrate charged analytes based on their individual electrophoretic mobilities. This work describes the use of a 2-D nonlinear, numerical simulation to examine the impact of voltage loss from the electrodes to the separation channel, termed voltage degradation, and distortions in the electric field on the performance of DFGF. One of the design parameters that has a large impact on the degree of voltage degradation is the placement of the electrodes in relation to the separation channel. The simulation shows that a distance of about 3,mm from the electrodes to the separation channel gives the electric field profile with least amount of voltage degradation. The simulation was also used to describe the elution of focused protein peaks. The simulation shows that elution under constant electric field gradient gives better performance than elution through shallowing of the electric field. Qualitative agreement between the numerical simulation and experimental results is shown. The simulation also illustrates that the presence of a defocusing region at the cathodic end of the separation channel causes peak dispersion during elution. The numerical model is then used to design a system that does not suffer from a defocusing region. Peaks eluted under this design experienced no band broadening in our simulations. Preliminary experimental results using the redesigned chamber are shown. [source]

Feature removal and isolation in potential field data

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2004
F. Boschetti
SUMMARY With the aim of designing signal processing tools that act locally in space upon specific features of a signal, we compare two algorithms to remove or isolate individual anomalies in potential field profiles. The first method, based on multiscale edge analysis, leaves other features in the signal relatively untouched. A second method, based on iterative lateral continuation and subtraction of anomalies, accounts for the influence of adjacent anomalies on one another. This allows a potential field profile to be transformed into a number of single anomaly signals. Each single anomaly can then be individually processed, which considerably simplifies applications such as inversion and signal processing. [source]

Magnetic field of high-phase order and compact transmission lines

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 1 2002
Hanafy M. IsmailArticle first published online: 14 DEC 200
Abstract Research has been conducted in high phase order (HPO) power transmission wherein 6 or 12 phases are used to transmit power in less physical space and with reduced environmental effects than conventional designs. In this paper, existing 3-phase double circuit transmission lines (TL) are reconfigured to 6-phase systems for the purpose of calculating and comparing the magnetic field of both systems. The magnetic field of several single-phase configurations; flat, vertical, delta and inverted-delta with the same degree of compaction is calculated and analysed at 1m height above the ground level. The magnetic field of the inverted-delta arrangement, which showed the lowest field profile, is compared with the magnetic field of 6- and 12-phase TLs having the same degree of line compaction and current loading conditions. The three systems are analysed when their lowest conductors had the same clearance to ground in one case and when their highest conductor positions were matched in another case. A comparison between 12-, 6- and 3-phase double circuit TLs having the same degree of compaction, the same phase voltage, the same clearance to ground and the same current per conductor is made to demonstrate if HPO lines reduce fields or not. The 6- and 12-phase lines are raised while keeping their conductors within the space, which would be taken by the conductors of the double circuit line. In this case, the highest conductor positions of the two systems are matched and the magnetic field is recomputed to conclude the results. The vector magnetic field potential concept, as extended to HPO transmission lines, together with a flexible developed computer program are used to calculate and present the magnetic flux density components profiles around the mentioned systems. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Chemical shift imaging (CSI) by precise object displacement,,

MAGNETIC RESONANCE IN CHEMISTRY, Issue 3 2006
Sebastien Leclerc
Abstract A mechanical device (NMR lift) has been built to displace vertically an object (typically an NMR sample tube) inside the NMR probe with an accuracy of 1 µm. A series of single pulse experiments are performed for incremented vertical positions of the sample. With a sufficiently spatially selective radio-frequency (r.f.) field, one obtains chemical shift information along the displacement direction (one-dimensional chemical shift imaging (CSI)). Knowing the vertical r.f. field profile (the amplitude of the r.f. field along the vertical direction), one can reconstruct the spectrum associated with all the slices corresponding to consecutive sample positions and improve the spatial resolution, which is simply related to the accuracy of the displacement device. Beside tests performed on phantoms, the method has been applied to solvent penetration in polymers and to benzene diffusion in a heterogeneous zeolite medium. Copyright © 2006 John Wiley & Sons, Ltd. [source]

1-D Self-consistent Fluid Modelling of the Pulsed Magnetron Discharge

PLASMA PROCESSES AND POLYMERS, Issue S1 2009
Philip Thomason
Abstract A 1-D fluid code simulation of the region above the racetrack in a magnetron discharge has been developed to yield predictions for the temporal evolution of the axial plasma parameters during pulsed DC operation. To take into account anomalous cross-field diffusion transport rates, an effective magnetic field profile has been calculated based on the real experimental values, to yield ratios in the effective electron gyro and collision frequencies comparable with Bohm diffusion. Pulse frequencies from 100 to 500,kHz are considered, with gas pressures ranging from 0.25 to 0.65,Pa. The model results for the plasma potential, electron and ion densities, during the pulse cycle agree well with experimental measurements made in the Liverpool magnetron using time-resolved Langmuir and emissive probes. In the bulk plasma, the predictions for electron temperature are close to the measured values; however, in the sheath region they are artificially high due to the model assumption that only Maxwellian distributed electrons exist in all regions of the discharge. This inadequacy in the model and the methods to improve has been discussed. Results for DC magnetrons are also shown. [source]

Contrasting microcystin production and cyanobacterial population dynamics in two Planktothrix -dominated freshwater lakes

ENVIRONMENTAL MICROBIOLOGY, Issue 10 2005
Ingmar Janse
Summary Microcystin concentrations in two Dutch lakes with an important Planktothrix component were related to the dynamics of cyanobacterial genotypes and biovolumes. Genotype composition was analysed by using denaturing gradient gel electrophoresis (DGGE) profiling of the intergenic transcribed spacer region of the rrn operon (rRNA-ITS), and biovolumes were measured by using microscopy. In Lake Tjeukemeer, microcystins were present throughout summer (maximum concentration 30 µg l,1) while cyanobacterial diversity was low and very constant. The dominant phototroph was Planktothrix agardhii. In contrast, Lake Klinckenberg showed a high microcystin peak (up to 140 µg l,1) of short duration. In this lake, cyanobacterial diversity was higher and very dynamic with apparent genotype successions. Several genotypes derived from DGGE field profiles matched with genotypes from cultures isolated from field samples. The microcystin peak measured in Lake Klinckenberg could be confidently linked to a bloom of Planktothrix rubescens, as microscopic and genotypic analysis showed identity of bloom samples and a toxin-producing P. rubescens culture. Toxin-producing genotypes were detected in the microbial community before they reached densities at which they were detected by using microscopy. Cyanobacterial biovolumes provided additional insights in bloom dynamics. In both lakes, the microcystin content per cell was highest at the onset of the blooms. Our results suggest that while genotypic characterization of a lake can be valuable for detection of toxic organisms, for some lakes a monitoring of algal biomass has sufficient predictive value for an assessment of toxin production. [source]

Propagation Dynamics of Epileptiform Activity Acutely Induced by Bicuculline in the Hippocampal,Parahippocampal Region of the Isolated Guinea Pig Brain

EPILEPSIA, Issue 12 2005
Laura Uva
Summary:,Purpose: Aim of the study is to investigate the involvement of parahippocampal subregions in the generation and in the propagation of focal epileptiform discharges in an acute model of seizure generation in the temporal lobe induced by arterial application of bicuculline in the in vitro isolated guinea pig brain preparation. Methods: Electrophysiological recordings were simultaneously performed with single electrodes and multichannel silicon probes in the entorhinal, perirhinal, and piriform cortices and in the area CA1 of the hippocampus of the in vitro isolated guinea pig brain. Interictal and ictal epileptiform discharges restricted to the temporal region were induced by a brief (3,5 min) arterial perfusion of the GABAA receptor antagonist, bicuculline methiodide (50 ,M). Current source density analysis of laminar field profiles performed with the silicon probes was carried out at different sites to establish network interactions responsible for the generation of epileptiform potentials. Nonlinear regression analysis was conducted on extracellular recordings during ictal onset in order to quantify the degree of interaction between fast activities generated at different sites, as well as time delays. Results: Experiments were performed in 31 isolated guinea pig brains. Bicuculline-induced interictal and ictal epileptiform activities that showed variability of spatial propagation and time course in the olfactory,temporal region. The most commonly observed pattern (n = 23) was characterized by the initial appearance of interictal spikes (ISs) in the piriform cortex (PC), which propagated to the lateral entorhinal region. Independent and asynchronous preictal spikes originated in the entorhinal cortex (EC)/hippocampus and progressed into ictal fast discharges (around 25 Hz) restricted to the entorhinal/hippocampal region. The local generation of fast activity was verified and confirmed both by CSD and phase shift analysis performed on laminar profiles. Fast activity was followed by synchronous afterdischarges that propagated to the perirhinal cortex (PRC) (but not to the PC). Within 1,9 min, the ictal discharge ceased and a postictal period of depression occurred, after which periodic ISs in the PC resumed. Unlike preictal ISs, postictal ISs propagated to the PRC. Conclusions: Several studies proposed that reciprocal connections between the entorhinal and the PRC are under a very efficient inhibitory control (1). We report that ISs determined by acute bicuculline treatment in the isolated guinea pig brain progress from the PC to the hippocampus/EC just before ictal onset. Ictal discharges are characterized by a peculiar pattern of fast activity that originates from the entorhinal/hippocampal region and only secondarily propagates to the PRC. Postictal propagation of ISs to the PRC occured exclusively when an ictal discharge was generated in the hippocampal/entorhinal region. The results suggest that reiteration of ictal events may promote changes in propagation pattern of epileptiform discharges that could act as trigger elements in the development of temporal lobe epilepsy. [source]