Boxcar technique

A single photon gives rise to an electric pulse, which in good photomultipliers has a length of only a few nanoseconds. A Time-to-Amplitude pulse height Converter (TAC) is a critical component when using this technique. A clock is started when the excitation pulse is fired. The clock runs 

In Fig.9.24 examples of decay curves recorded using delayed-concide-nce techniques with an acousto-optic modulator are shown for excited Ba states. Two-step excitation is used and only the second laser is pulse-modulated. Lifetime results are also given for the 6sns Sq and 6snd Do sequences of Ba in the figure. An overall trend of r - n f is found, but strong localized perturbations are also evident. These are due to admixtures into 

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James D. R., Siemiarczuk A. and Ware W. R. (1992) Stroboscopic Optical Boxcar Technique for the Determination of Fluorescence Lifetimes, Rev. Sci. Instrum. 63, 1710-1716. 

James, D.R., Siemiarczuk, A. and Ware, W.R. (1992). Stroboscopic optical boxcar technique for the determination of fluorescence lifetimes. Review of Scientific Instruments, 63,1710-1716. 

The CARS signal is generated within the common overlap-volume of the three incident beams. This boxcar technique increases the spatial resolution considerably, which may reach values below 1 mm. 

Useful with shallow boxcar and rolling scars. CO2 and/or Er YAG lasers are utilized for this technique. After the treatment, silicone sheeting, gauze and tube netting are placed over the treated area and maintained for 24 h (the silicone sheeting remains for another 48 h). The patient is instructed to soak the treated area every 2-4 h with cold water for 20 min and then apply an occlusive ointment. Re-epithelialization is completed in 10 days. A new treatment can be performed after 6-8 weeks. 

In order to compress the measured data through a wavelet-based technique, it is necessary to perform a series of convolutions on the data Becau.se of the finite size of the convolution filters, the data may be decomposed only after enough data has been collected so as to allow convolution and decomposition on a wavelet basis. Therefore, point-bypoint data compression as done by the boxcar or backward slope methods is not possible using wavelets. Usually, a window of data of length 2" m e Z, is collected before decomposition and selection of the appropriate... 

Fig. 20. Performance of data compression techniques (a) orthonormal wavelet (b) backward slope (c) boxcar.

Before closing our discussion of transient phenomena it should be remarked that the emission transients are sometimes nonexponential, due to electric field effects (Makram-Ebeid, 1980), nonuniform doping, and other causes. When this problem exists, the standard boxcar or lock-in techniques (Fig. 9c) will give spurious results (White et al., 1979). Thus, the transients themselves should always be examined before any data are taken. Methods of dealing with nonexponential behavior are discussed elsewhere (Kirchner et al., 1981). 

In some instances, the design of the data acquisition system may be driven by the requirements of a specific application. In ICP-MS, for example, the masses of the elemental isotopes are well known, so only those masses need to be investigated. In such a situation, an attractive technique is the use of a number of single-channel devices, such as boxcar integrators [38], each of which is responsible for continually monitoring a specific mass of interest. At the expense of complete mass spectral coverage, a simple, inexpensive system that generates relatively small amounts of data with real-time temporal resolution can be utilized. 

The technique of boxcar injections (not to be confused with boxcar chromatography) can be extremely productive for iso-cratic elution in any mode of chromatography and should always be considered when scaling up a separation. The preparative HPLC of an enantiomeric mixture utilising a chiral stationary phase is described here to demonstrate the approach for separation of a binary mixture. 

It is important to note that the technique of boxcar injections is by no means restricted to chiral separations and should always be considered for any separation performed under isocratic elution. 

LEI as an analytical technique thus requires a tunable laser, an atom reservoir, a galvanic detection system and read-out electronics including a boxcar integrator. It was first realized experimentally with a flame as the atom reservoir using pneumatic nebulization for sample uptake [670]. 

Luminescence decay curves of both complexes excited with the 337 nm fundamental of the N2 laser at 77 K fit sufficiently well to a single exponential analysis. However, time resolution of the emission of Ir(ppy)2(bpy)+ via boxcar averaging techniques reveals a structured emission at long delay times... 

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