Electric field pulse

Linear Dichroism. In this technique, the DNA molecules are aligned either by an applied electric field pulse or in a flow gradient. The orientation of the aromatic residues of the metabolite model compounds bound to the DNA (either covalently or non-covalently) relative to the orientation of the DNA bases is probed utilizing linearly polarized light. The linear dichroism A A can be either negative or positive, and is defined as... 

Ade-Omowaye BIO, Rastogi NK, Angersbach A and Knorr D. 2002. Osmotic dehydration of bell peppers influence of high intensity electric field pulses and elevated temperature treatment. J Food Eng 54 35—43. Ajlouni S, Kremer S and Masih L. 2001. Lycopene contents in two different tomato cultivars. Food Aust... 

Rastogi, N.K., Eshtiagi, M.N., and Knorr, D. 1999. Accelerated mass transfer during osmotic dehydration of high intensity electrical field pulse pretreated carrots. J. Food Sci. 64, 1020-1023. 

Apart from the temperature-jump technique, other relaxation methods that have been used are those of ultrasonic absorption" " and electric-field pulse. Another technique that has been used for some of the more slowly included guest molecules is that of stopped-flow. ... 

Fig. 3.(a) Response of the purple membrane as well as apomembrane following an electrical field pulse of 20 kV/cm, measuring light 300 nm with polarization angle 55°. (6) See above, fluorescence difference was recorded as indicator of umbilliferon. 

Essentially, this method is based on subjecting cell membranes to a short external electric field pulse of an intensity comparable to the electric field strength of the membrane 77). Under these conditions the membrane breaks down locally and becomes permeable. This process is reversible, i.e. the membrane reconstitutes its original properties in time intervals which can be experimentally controlled. 

The use of a smectic A LC instead of a nematic LC allows for memory-type H-PDLCs, as shown by Date et al. [25], At an appropriate temperature for the LC used, the grating could be switched off with a 10 ms electric field pulse of 30 V/p,m. In contrast, nematic H-PDLCs require a continuous application of the field to maintain the off state. The smectic H-PDLCs were turned back on by warming them above a critical temperature. 

To study rapid reactions, traditional batch and flow techniques are inadequate. However, the development of stopped flow, electric field pulse, and particularly pressure-jump relaxation techniques have made the study of rapid reactions possible (Chapter 4). German and Japanese workers have very successfully studied exchange and sorption-desorption reactions on oxides and zeolites using these techniques. In addition to being able to study rapid reaction rates, one can obtain chemical kinetics parameters. The use of these methods by soil and environmental scientists would provide much needed mechanistic information about sorption processes. 

Methods such as nuclear magnetic resonance (NMR), electron spectroscopy for chemical analysis (ESCA), electron spin resonance (ESR), infrared (IR), and laser raman spectroscopy could be used in conjunction with rate studies to define mechanisms. Another alternative would be to use fast kinetic techniques such as pressure-jump relaxation, electric field pulse, or stopped flow (Chapter 4), where chemical kinetics are measured and mechanisms can be definitively established. 

Another consideration in choosing a kinetic method is the objective of one s experiments. For example, if chemical kinetics rate constants are to be measured, most batch and flow techniques would be unsatisfactory since they primarily measure transport- and diffusion-controlled processes, and apparent rate laws and rate coefficients are determined. Instead, one should employ a fast kinetic method such as pressure-jump relaxation, electric field pulse, or stopped flow (Chapter 4). 

Application of Electric Field Pulse Techniques 96 Supplementary Reading 97... 

Relaxation methods can be classified as either transient or stationary (Bernasconi, 1986). The former include pressure and temperature jump (p-jump and t-jump, respectively), and electric field pulse. With these methods, the equilibrium is perturbed and the relaxation time is monitored using some physical measurement such as conductivity. Examples of stationary relaxation methods are ultrasonic and certain electric field methods. Here, the reaction system is perturbed using a sound wave, which creates temperature and pressure changes or an oscillating electric field. Chemical relaxation can then be determined by analyzing absorbed energy (acous-... 

Electric field pulse methods have only recently been used to study adsorption-desorption phenomena on heterogeneous systems such as soils and soil constituents. This ingenious application is discussed in a later section. 

Another chemical relaxation method that can be used to determine the kinetics of fast reactions on soil constituents is the electric field pulse technique. This technique was developed by Hachiya et al. (1980) to study the kinetics of I03 adsorption and desorption on Ti02 and by Sasaki et al. (1983) to investigate ion-pair formation on the surface of a-FeOOH. Excellent review articles on electric field methods are found in DeMaeyer (1969), Hemmes (1979), and Eyring and Hemmes (1986). 

Hachiya et al. (1980) and Sasaki et al. (1983) appear to be the only researchers who have applied electric field pulse techniques to the study of kinetics of soil constituent reactions. In the latter study, ion-pair formation... 

Sasaki, M., Morlya, M. Yasunaga, T., and Astumian, R. D. (1983). A kinetic study of ion-pair formation on the surface of a-FeOOH in aqueous suspensions using the electric field pulse technique. J. Phys. Chem. 87, 1449-1453. 

In all the above processes, only the first one ( + ) is a photochemical change while the rest (— ) are nonradiative chemical changes. It should be mentioned that the first step does not have to be photochemically induced for the methods discussed here to be applicable. Heat pulses or electric field pulses could provide the initial perturbation that changes A into the other intermediates that are to be identified by using a probe Raman laser. 

ZEKE-PES was pioneered by Miiller-Dethlefs, Sander and Schlag18,25. They and others26 recorded the zero kinetic energy photoelectrons produced by absorption of one or more photons to a resonant ion state as a function of pulsed laser excitation wavelength. ZEKE electrons were extracted by an electric field pulse which permitted a delay between the creation and collection of electrons. During this delay, non-ZEKE electrons departed the focal volume, leaving only ZEKE electrons for collection by the extraction pulse. 

Fig. 7.8 Acoustic excitation by an electric field pulse acting on a charge distribution.

In a realistic experiment we cannot work with zero-width kicks . Any realistic electric field pulse has a finite width. Therefore, we replace the periodic S function drive in (5.3.2) by an array of finite-width pulses according to... 

Fig. 5.14. A beam of Csl molecules passed between an array of sharp charged edges a method for generating electric field pulses in the molecule s rest-firame.

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