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Temperature changes, transients induced

The flow sensitivity indicates that while a detector may be accurately balanced in terms of resistance and voltage, the reference flow only reduces the flow sensitivity of the analytical column flow by a factor of three to four. Much of the drift due to flow changes comes from the flow controllers. One type commonly used today has been found to have a mass flowrate proportional to absolute temperature. Flow induced noise, however, can come from column temperature fluctuations. Even if the front of the column is fed from a perfect flow source, a temperature change in the column will lead to a viscosity change in the carrier gas. Since the gas is compressible, a transient flow change occurs in the detector. Needless to say, a fluctuation in column temperature also leads to a fluctuation in the bleed level, which affects the recorder baseline by a much more direct process. [Pg.240]

Thermal shock testing of an alumina/20 vol.% SiC whisker composite showed no decrease in flexural strength with temperature transients up to 900°C.33 Monolithic alumina, on the other hand, shows significant decreases in flexural strength with temperature changes of >400°C. The improvement is a result of interaction between the SiC whiskers and thermal-shock induced cracks in the matrix, which prevents coalescence of the cracks into critical flaws. [Pg.63]

Fig. 3. (A) Difference spectrum constructed from absorbance change transients in PS-1 particles poised at —625 mV [in the presence of dithionite] in a pH 10 buffer. Each transient was induced by a 3-s iliumination (B) AA obtained directiy with a P700-enriched, PS-i particie in a conventionai, commerciai spectrophotometer in the light-minus-dark mode (C) AA between 350 and 750 nm measured at 200 K with a Triton-fractionated, PS-1 particle from pea chloroplasts the spectrum shown was obtained by first illuminating at 200 K for 45 m and then at 215 K for three 30-m incremental periods. Figure source (A) Swarthoff, Gast, Amesz and Buisman (1982) Photoaccumulation of reduced primary electron acceptors of photosystem I of photosynthesis. FEBS Lett 146 131 (B) Ikegami and Ke (1984) A 160-kilodalton photosystem-l reaction-center complex. Low temperature absorption and EPR spectroscopy of the early electron acceptors. Biochim Biophys Acta 764 75 (C) Mansfield and Evans (1985) Optical difference spectrum of the electron acceptor Ao in photosystem I. FEBS Lett 190 239. Fig. 3. (A) Difference spectrum constructed from absorbance change transients in PS-1 particles poised at —625 mV [in the presence of dithionite] in a pH 10 buffer. Each transient was induced by a 3-s iliumination (B) AA obtained directiy with a P700-enriched, PS-i particie in a conventionai, commerciai spectrophotometer in the light-minus-dark mode (C) AA between 350 and 750 nm measured at 200 K with a Triton-fractionated, PS-1 particle from pea chloroplasts the spectrum shown was obtained by first illuminating at 200 K for 45 m and then at 215 K for three 30-m incremental periods. Figure source (A) Swarthoff, Gast, Amesz and Buisman (1982) Photoaccumulation of reduced primary electron acceptors of photosystem I of photosynthesis. FEBS Lett 146 131 (B) Ikegami and Ke (1984) A 160-kilodalton photosystem-l reaction-center complex. Low temperature absorption and EPR spectroscopy of the early electron acceptors. Biochim Biophys Acta 764 75 (C) Mansfield and Evans (1985) Optical difference spectrum of the electron acceptor Ao in photosystem I. FEBS Lett 190 239.
We have presented here the first observation of transient molecular reorientation induced in a liquid crystal by a -switched laser pulse. The response time of molecular reorientation in the nematic phase is of the order of 10—100 psec. Although this is 10 —10 times longer than the duration of the laser pulse, transient molecular reorientation is still strong enough to yield an easily detectable phase shift in the probe beam. Residual al> sorption and subsequent very rapid radiationless conversion into heat can result in a temperature rise in the medium which decays via heat diffusion with relaxation times in the 10—200 msec range. The temperature rise also induces a refractive-index change in the medium and hence a phase shift in the probe beam. This thermal effect and the molecular reorientation are initiated simultaneously by the pulsed laser excitation. They are in general coupled... [Pg.195]

The general experimental approach used in 2D correlation spectroscopy is based on the detection of dynamic variations of spectroscopic signals induced by an external perturbation (Figure 7.43). Various molecular-level excitations may be induced by electrical, thermal, magnetic, chemical, acoustic, or mechanical stimulations. The effect of perturbation-induced changes in the local molecular environment may be manifested by time-dependent fluctuations of various spectra representing the system. Such transient fluctuations of spectra are referred to as dynamic spectra of the system. Apart from time, other physical variables in a generalised 2D correlation analysis may be temperature, pressure, age, composition, or even concentration. [Pg.560]

We used short broadband pump pulses (spectral width 200 cm 1, pulse duration 130 fs FWHM) to excite impulsively the section of the NH absorption spectrum which includes the ffec-exciton peak and the first three satellite peaks [4], The transient absorbance change signal shows pronounced oscillations that persist up to about 15ps and contain two distinct frequency components whose temperature dependence and frequencies match perfectly with two phonon bands in the non-resonant electronic Raman spectrum of ACN [3] (Fig. 2a, b). Therefore the oscillations are assigned to the excitation of phonon wavepackets in the ground state. The corresponding excitation process is only possible if the phonon modes are coupled to the NH mode. Self trapping theory says that these are the phonon modes, which induce the self localization. [Pg.563]


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See also in sourсe #XX -- [ Pg.34 , Pg.35 , Pg.36 , Pg.37 , Pg.38 , Pg.39 , Pg.40 ]




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