Effect Of Field Amplification Research Articles

Combination of flow injection with capillary electrophoresis. Part 3. On-line sorption column preconcentration capillary electrophoresis system

A combined flow injection (FI)–capillary electrophoresis (CE) system with a split-flow interface reported previously was used for on-line preconcentration of pseudoephedrine by solid phase extraction on a micro-column packed with C 18. Aqueous samples were loaded on the column at 1.0 ml min −1 for 90 s and eluted by a mixed eluent of 40% 62.5 mM acetate buffer (pH 4.0) and 60% acetonitrile at 0.2 ml min −1. A zone-sampling approach was employed to sample 45 μl of the most concentrated zone of the eluate, which was injected into the FI–CE split-flow interface using a phosphate buffer carrier, with a 25 μl water zone preceding the sampled eluate zone to achieve enhanced field amplification effects. Sensitivity enhancements of 60 fold (180 fold with 4 min sample loading) were thus achieved with a sample throughput of 9 h −1 and 4.7% relative standard deviations ( n = 10, 2 μg ml −1 pseudoephedrine) for peak area evaluation, without significant degradation of column efficiency.

New Insights into The Transport and Field-Enhancement Effects in Sol-Gel Derived Colossal Magnetoresistive Thin Films

ABSTRACTThe transport mechanism underlying the colossal magnetoresistance (CMR) of doped manganites is not yet understood and their technological applications are limited by the high fields (∼IT) required to obtain any significant MR. Following the development of a polymeric chemical synthesis route, we have investigated the O2p unoccupied density of states in sol-gel derived Lal-xSrxMnO3 (0 < x < 0.7) thin films grown epitaxially on LaA1O3, by electron energy-loss spectroscopy at sub-eV resolution. The spectra show a distinct prepeak in the OK edge at the Fermi level, the intensity of which correlates directly with the conductivity of the film. Similar correlation was also obtained for La0.7Sr0.3MnO3-z annealed in vacuum to obtain well defined oxygen content (z) in the film. This confirms that the charge carriers in these manganese perovskites have significant oxygen 2p hole character and suggests that the “double exchange” mechanism has to be modified. In another set of experiments we have studied room-temperature field amplification effects to enhance the low-field sensitivity of La0.7Sr0.3MnO3-z films sandwiched between two thin rectangular slices of either α-Fe or Mn-Zn ferrite. This field amplification leads to an enhanced low-field MR value as high as 6% at an external field of 500 Oe which is 6 times the value observed without the amplification.

Microcapillary waves on liquid electrodes in high electric fields

The initiation and sustaining of field emission processes from a liquid surface are based mainly on the effect of field amplification at the surface microtips. Such microtips form under different types of hydrodynamic instabilities. However, the threshold field of such instabilities has a very high value. At the same time, there are some situations when one needs to excite the emission using an arbitrary low amplitude of the external voltage. In this paper, in order to solve this problem, the process of preliminary excitation of the surface by an ultrasonic field on the liquid emitter surface has been studied. The theory developed has shown that, as a result of parametric instability, the formation of surface microstructures is possible. Such structures can be produced at very low levels of ultrasonic power. This fact is of particular importance for large surface area cathodes. The dependence of the geometric parameters of the surface structures both on frequency and power of the ultrasonic field is determined theoretically. Experiments with field pulses in the nanosecond range confirm the decrease of the explosive emission mechanism when preliminary ultrasonic excitation is used.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>