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Increasing Field (increasing + field)

Distribution by Scientific Domains
Physics and Astronomy50%

Selected Abstracts

A microfluidic study of mechanisms in the electrophoresis of supercoiled DNA

ELECTROPHORESIS, Issue 12 2008
Dammika P. Manage
Abstract In this work, microfluidic chips were used to study the electrophoresis of supercoiled DNA (SC DNA) in agarose. This system allowed us to study the electrophoretic and trapping behaviours of SC DNA of various lengths, at various fields and separation distances. Near a critical electric field the DNA is trapped such that the concentration falls exponentially with distance. The trapping of such circular DNA has been explained in terms of the ,lobster trap' or ,impalement' model where shorter fibres become trapping sites at higher fields, leading to an ongoing (and gradual) increase in trapping with increasing field. By contrast, the present study suggests that under some circumstances the traps have a barrier such that only when the DNA has sufficient energy (at high enough fields) can it become trapped, leading to a sudden transition in behaviours at the critical field. We propose an ,activated impalement' mechanism of trapping in which only at sufficiently high fields is the SC DNA impaled and trapped for long times. The critical electric field appears to be inversely proportional to the length of the DNA molecule, suggesting that the force required to impale the SC DNA is constant. [source]

Transport in MgB2 near critical temperature

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2006
P. Va
Abstract Longitudinal and transverse voltages have been studied on samples of MgB2. The non-zero transverse voltage has been observed in close vicinity of critical temperature in zero external magnetic field while far enough from Tc this voltage has been zero. It merges into transverse even voltage in magnetic field which is suppressed with increasing field and increasing transport current as well. New scaling between transverse and longitudinal resistivities has been observed in the form ,xy , d,xx/dT. Several models trying to explain observed results are discussed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Effect of magnetic field on electrical properties of nanocrystalline poly(vinylidene fluoride) samples

POLYMER INTERNATIONAL, Issue 11 2009
Prashant Shukla
Abstract BACKGROUND: The electrical properties of nanocrystalline poly(vinylidene fluoride) (PVDF) samples of 20 µm in thickness were measured in terms of thermally stimulated current (TSC), conduction current and dielectric constant after application of a magnetic field. RESULTS: TSC shows the release of trapped charges inside the material that enhances the current with magnetic field. The reason for the polarity reversal of the current with reversal of the magnetic field polarity is due to the change in spin of electrons depending upon the direction of the magnetic field. CONCLUSION: The magnetic field causes trapping of charge carriers in different traps, as the reason for the increase of activation energy with increasing field. The flow of conduction current at constant temperature in magnetically polarized PVDF is governed by Poole,Frenkel and Schottky,Richardson mechanisms. The decrease in dielectric constant at a certain alternating current (AC) frequency and magnetic field with temperature is caused by magnetic polarization in addition to the AC field. Copyright © 2009 Society of Chemical Industry [source]

Magnetic field-dependence study of the magnetocaloric properties of a superparamagnetic nanoparticle system: a Monte Carlo simulation

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2008
D. Serantes
Abstract The influence of the applied magnetic field on the magnetocaloric properties of a fine magnetic particle system has been studied using a Monte Carlo technique. By simulating zero field cooling (ZFC) curves under different strengths of the applied magnetic field, we have analyzed the variation of the entropy for temperatures above the maximum of the ZFC curves, where the process is reversible. The entropy curves have been observed to behave in a different fashion at low values of the magnetic field, where the peak only slightly shifts to higher temperatures with increasing fields. For larger fields, the peak rapidly shifts to higher temperatures, while the overall shape of the curve broadens over a wide temperature range. It is also observed that the blocking temperature as a function of the magnetic field shows the feature of a change from a bell-like shape to a monotonically decreasing function, resembling what is found experimentally for intermediate values of the sample concentration. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]