Pulsed field extraction

A successful modification to the technique involves delayed pulsed-field extraction which allows discrimination between zero and near-zero kinetic energy electrons. About 1 ps after the laser pulse has produced photoelectrons, a small voltage pulse is applied. This has the effect of amplifying the differences in fhe velocities of fhe phofoelecfrons and allows easy discrimination befween fhem as a resulf of fhe differenf times of arrival af fhe defector. In fhis way only fhe elections which originally had zero kinetic energy following ionization can be counted to give fhe ZEKE-PE specfmm. 

Fig. 2.18. (a) The even (upper panel) and odd (lower panel) SH responses of a 20 nm Gd(0001) film at 90 K using 815nm/35fs laser pulses. Transient reflectivity change is also displayed in the upper panel (solid black curve). The inset shows the experimental scheme with the magnetization oriented perpendicular to the plane of incidence, (b) The oscillatory part of the even and odd SH fields extracted from (a). The inset shows the corresponding FT spectra. From [59]... 

When the pulsed-field ionization signal of a single excited Rydberg peak is measured as a function of the delay time between the extraction field pulse... 

Diffusional behavior of sorbed species is studied by NMR using one of three approaches the van Vleck method of moments, relaxation measurements, and the pulsed-field-gradient method. An example of the use of the method of moments is the work of Stevenson (194) on H resonances in zeolite H-Y (see Section III,K). Another is the study by Lechert and Wittem (284) of C6H6 and C6H3D3 adsorbed on zeolite Na-X. Analysis of second moments of H resonances allowed the intra- and intermolecular contributions to the spectra to be extracted. Similarly, second moments of H and 19F spectra of cyclohexane, benzene, fluorobenzene, and dioxane on Na-X provided information about orientation of molecules within zeolitic cavities (284-287). 

Lee, W., Revington, M. J., Arrowsmith, C. and Kay, L. E. (1994). A pulsed field gradient isotope-filtered 3D 13C HMQC-NOESY experiment for extracting intermolecular NOE contacts... 

Extraction can be enhanced by the application of a dc or pulsed electric field, typically on the order of 1 kV/cm. This requires that the aqueous phase be dispersed and the organic phase be of low conductivity. The improvement in mass transfer rate is due to the breakup of large drops by the action of the field and to the increase of drop velocity resulting in increased mass transfer coefficients. It has also been found that low-frequency pulsed fields are effective in breaking up emulsions in the settler stage of mixer-settler units. 

To reduce the kinetic energy spread among ions with the same m/z ratio leaving the source, a time lag or delay between ion formation and extraction can be introduced. The ions are first allowed to expand into a field-free region in the source and after a certain delay (hundreds of nanoseconds to several microseconds) a voltage pulse is applied to extract the ions outside the source. This mode of operation is referred to as delayed pulsed extraction to differentiate it from continuous extraction used in conventional instruments. Delayed pulsed extraction, also known as pulsed ion extraction, pulsed extraction or dynamic extraction, is a revival of time-lag focusing, which was initially developed by Wiley and McLaren in the 1950s, shortly after the appearance of the first commercial TOF instrument. 

The NMRI technique uses an induction coil surrounding the sample to image nuclear spin density that results from the nuclear spin system rearrangement. An initial magnetic pulsed field orients the nuclear spin system and then it relaxes back toward a random state. Because of the relaxation time and that tomographic reconstruction is needed to extract the 3-D details, there are time limitations (Altobelli et al., 1992) (currently of the order of 10-ms, at best). Consequently, the technique has been used mostly for steady or quasi-steady laminar flows because of the rather low data acquisition rate. However, modifications to allow turbulent and unsteady flows to be investigated have been reported and new... 

DSB repair have been conducted at relatively high doses, sufficient to induce substantial cell killing. Conventional methods of detecting DSB repair in vivo, which are based on extraction of DNA and measurement of mobility in pulsed-field electrophoresis, require doses diat induce 100 or more breaks per cell. For the human genome, these correspond to acute doses of approximately 3 Gray (Gy) or more of low-linear energy transfer (LET) radiation (5). 

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