Heat pulse-probe

Recently, Lubbert and Larson (1990) analyzed the local mixing behavior in bubble columns and in air-lift fermentors utilizing a heat pulse-probe experiment. They considered the spreading of an originally narrowly distributed clump along the principle flow direction. Based on theory, the width of the spreading cloud (i.e. standard deviation) can be described by ... 

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. 

Due to the short length of a probe temperature rise (about 1 ps) the measurement stage is shifted to the cooling tail followed by the shock heating pulse.The cooling process is recorded due to relatively low, so-called monitoring current across the probe. The shock pulse may be superimposed on... 

For the limiting case of an infinitesimally small probe with an infinitesimally short heating pulse, the solution for Eq. (2.15) for the interval of temperature decay takes the form ... 

Figure 1 (A) Spatial dependence of a single-frequency (harmonically driven) thermal wave. Frequency 20.0 Hz, diffusivity 1 X lO m s L (B) Spatial dependence of the thermal wave observed at various times after application of a heat pulse. Diffusivity 1 xIO m s L The instantaneous phase (j> — cot. (Reprinted from Power JF (1993) Scanning probes III Photoacoustic and photothermal imaging. In Morris MD (ed.) Microscopic and Spectroscopic Imaging of the Chemicai State, pp. 255-302. New York Dekker, courtesy of Marcel Dekker, Inc.)...

In general, the physical structure of the tissue must be broken down mechanically followed by an extraction procedure, before the sample can be analyzed. Homogenization using blenders, probe homogenizers, cell disrupters, sonicators, or pestle grinders is particularly useful for muscle, liver, and kidney samples. Regardless of the method used for tissue disruption, the pulse, volume of extraction solvent added, and temperature should be validated and standardized in order to ensure reproducible analytical results. During cell disruption, care should be taken to avoid heat build-up in the sample, because the analyte may be heat labile. 

In the cross modulation experiments (Mentzoni and Row, 1963 Mentzoni and Rao, 1965), an electron plasma is briefly heated by a microwave pulse while a weak microwave signal probes the mean electron energy. Assuming no electron loss and insignificant ambient gas heating, these authors derived the following equation for the relaxation of electron Maxwellian temperature T.toward the ambient temperature T ... 

Differential heats of NH adsorption were measured for the samples outgassed at different temperatures ranging from 400 to 800°C. Ammonia was chosen as a basic probe because its size is small, which may limitate diffusion effects in small pore zeolite materials. The variations of the differential heats of adsorption are plotted in fig. 3 as a function of the successive pulses of... 

Fig. 2.5 An ion kinetic energy distribution of field desorbed He ions taken with a pulsed-laser time-of-flight atom-probe. In pulsed-laser stimulated field desorption of field adsorbed atoms, atoms are thermally desorbed from the surface by pulsed-laser heating. When they pass through the field ionization zone, they are field ionized. Therefore the ion energy distribution is in every respect the same as those in ordinary field ionization. Beside the sharp onset, there are also secondary peaks due to a resonance tunneling effect as discussed in the text. The onset flight time is indicated by to, and resonance peak positions are indicated by arrows. Resonance peaks are pronounced only if ions are collected from a flat area of the...

Fig. 3.4 (c) Penn State design tip exchange setup ffor an FIM or a pulsed-laser atom-probe with a vacuum lock. The tip can be heated by passing a current through the wire loop. The tip is mounted on an internal gimbal and is cooled through a copper braid by a refrigerator. 

The laser system consisted of a home-built Ti sapphire fs laser oscillator and regenerative amplifier (RGA). The pulse duration was 50 fs at 800 nm and 1 kHz repetition rate. The output of the RGA was split into two parts. One part was used as pump pulse. The other part served as a source for the generation of probe pulses with the help of a non-collinear optical parametric amplifier (NOPA, Clark). The sample preparation was explained elsewhere [7]. Briefly, sodium (Alfa Aesar) was used as received and sodium bromide (Alfa Aesar) was dried and re-crystallized under vacuum. The preparation of the samples was carried out in a glovebox under argon atmosphere. Localized electrons were generated by heating the metal-salt mixture to 800 °C, i.e. well above the melting point of the salt. 

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