Compensation time scale

Fig. 2.9.7 Hahn spin-echo rf pulse sequence combined with bipolar magnetic field gradient pulses for hydrodynamic-dispersion mapping experiments. The lower left box indicates field-gradient pulses for the attenuation of spin coherences by incoherent displacements while phase shifts due to coherent displacements on the time scale of the experiment are compensated. The box on the right-hand side represents the usual gradient pulses for ordinary two-dimensional imaging. The latter is equivalent to the sequence shown in Figure 2.9.2(a).

The marine carbonate system is thought to participate in another set of interlinked processes that acts to regulate atmospheric CO2 levels over time scales of 5 to lOky. This shorter cycle is commonly referred to as carbonate compensation and appears... 

As described in Chapter 21.7, a system of biogeochemical feedbacks act to stabilize the major ion composition of seawater. Some operate on short time-scale cycles, such as calcite compensation, and others operate over longer periods, such as the basalt-carbonate buffer. The linkages in the crustal-ocean-atmosphere fectory that act on the major ions also influence atmospheric CO2 levels and seawater s pH and alkalinity. 

The time-scale of molecular vibrations is of the order of 10 13 s, just outside the ps range. Internal conversions and in particular vibrational cascades therefore fall into the femtosecond (10-15s) time-scale. However, the spin-forbidden processes of intersystem crossing take place in times of a few ps to several ns. The case of benzophenone is a good example of the compensation between spin and orbital angular momentum. The rise of the triplet state absorption shows that intersystem crossing is completed within some 20 ps. 

Minimization of time scale measurements Ultrafast undistorted cyclic voltammetry may be performed at ultramicroelectrodes using an ultrafast potentiostat allowing on-line ohmic drop compensation. 

Sylvestre and Kabal, 1992] Sylvestre, B. and Kabal, P. (1992). Time-scale modification of speech using an incremental time-frequency approach with waveform structure compensation. Proc. IEEEICASSP-92, pages 81-84. 

Experimentally, these effects are tested by fluorescence and absorption measurements. These directly probe solvent polarization dynamics on molecular time-scales [100, 101]. For instance, the time resolved fluorescence spectrum of a chromophore, whose excited state dipole moment is subject to interactions with the surrounding solvent molecules, will exhibit fluorescence spectra that are strongly solvent dependent. The solvent molecules attempt to compensate the changes of charge density in the chromophore and, in sum, the fluorescence... 

Christofides, P. D. and Daoutidis, P. (1996b). Compensation of measurable disturbances in two-time-scale nonlinear systems. Automatica, 32, 1553-1573. 

As for most enzyme mediated reactions, increases in temperature often increase activity in a characteristic fashion. The response of an enzyme to temperature increases, often evaluated as the Qjq parameter (i.e., the increase in activity over a 10°C range), varies among and within enzyme systems and can show compensation. Staal et al. (2003) have evaluated Qjo responses for N2 fixation on short time scales in a range of cyanobacteria including Trkhodesmium, which exhibited a Qio of 1.12 for dark N2 fixation over the temperature range of 20—35°C, and a much... 

In the case of triads S and 6 the same considerations apply, but the initial electron transfer step 2 is now much slower, and the quantum yields of C-p +. Q - are reduced to 0.57 and 0.34 respectively. Evidently, any additional decrease in k /k for these molecules cannot compensate for the decreased quantum yield in step 2, and the yield of C -P-Q " drops somewhat. Elucidation of the details of this effect must await transient absorption studies on the picosecond time scale which will allow the determination of the lifetimes of intermediate states. 

Depending on tlie time. scale of deactivation, the catalytic activity can be restored in different ways. For example, in fluid catalytic cracking, where the deactivation is very fast, a recirculating leacTor is used for continuous catalyst regeneration. However, if the deactivation is slow and constant conversion is desired 10 meet certain environmental regulations as in VOCoxidation, the temperature level can be used to compensate fur the loss of intrinsic catalytic activity. Under such additions, the deactivation effects are measured by the temperature increase required to maintain constant conversion. 

Laser ionization mass spectrometry of explosives and chemical warfare simulants has been studied using nanosecond laser pulses. Primary ions observed in many of these studies were NO and PO, which are not unique signatures of the parent molecules. It is now widely accepted that after absorption of the first photon, the parent molecule dissociates on a time scale of about 100 femtoseconds (fs). We can attempt to compensate for this rapid dissociation by using ultrafast laser pulses of a corresponding time duration." Here we compare the nanosecond, ultrafast, and SPI approaches. 

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