Time resolving power

The information amount of process analyses (under which term all time-dependent studies from chemical process control up to dynamic and kinetic studies are summarized) increases by the factor of time resolving power... 

Time resolution efficiency coefficient (R, time resolving power, see Eq. (9.33), it time resolution needed)... 

Fig. 8a-c, Time-resolved power spectrum for (a) fluctuations in scattered radiation (b)for fluctuations in fluorescence of Rhodatnine B, (c) Rose Bengal all normalised to the 130 MHz beat. 

FIGURE 8.3 Time-resolved power spectra (TRPS) estimated by Fourier transforms (FTs) of the time-segmental velocity autocorrelation functions (TSVAFs) of the active center. The spectra indicate the intensities of the vibrational modes of the active center in the globin. The intensities over 3500 cm" are zero (not shown). The photodissociation is achieved at t = Ops, after the previous equilibrium MD stimulation is denoted by negative time duration. The intensities of power spectra are depicted as functions of the vibrational frequency. The ordinate axes indicate the absolute FT intensity in arbitrary units. The spectrum (-5 < t < Ops) is that of MbCO, while the other spectra are those of Mb -i- CO. (From Okazaki, I. et al., Chem. Phys. Lett., 337,151, 2001. With permission.)... 

An interesting notion is the time-resolving power of SARIS, currently experimentally limited to a time resolution of approximately 1 s. This is, however, in a range where at least slow growth processes, adsorption, and desorption, or surface reactions can be followed in situ and in realtime. 

Many photochemical and photophysical phenomena occur on a time scale shorter than a nanosecond. In order to follow such fast phenomena by infrared spectroscopy, picosecond to femtosecond time-resolved infrared measurements are required. Since time resolving in this time range cannot be performed by utilizing the fast-response capability of a detector and the time-resolving power of an electronic circuit (gate circuit, etc.), the following optical methods are mainly used (i) a method based on the upconversion (optical gating) process, and (ii) a method which detects pulsed infrared radiation itself. At present, the latter method is commonly used for picosecond to femtosecond time-resolved measurements. 

Probably the simplest mass spectrometer is the time-of-fiight (TOP) instrument [36]. Aside from magnetic deflection instruments, these were among the first mass spectrometers developed. The mass range is theoretically infinite, though in practice there are upper limits that are governed by electronics and ion source considerations. In chemical physics and physical chemistry, TOP instniments often are operated at lower resolving power than analytical instniments. Because of their simplicity, they have been used in many spectroscopic apparatus as detectors for electrons and ions. Many of these teclmiques are included as chapters unto themselves in this book, and they will only be briefly described here. 

Generally, the attainable resolving power of a TOE instrument is limited, particularly at higher mass, for two major reasons one inherent in the technique, the other a practical problem. First, the flight times are proportional to the square root of m/z. The difference in the flight times (t and t ,+i) for two ions separated by unit mass is given by Equation 26.5. 

Typical mass resolution values measured on the LIMA 2A range from 250 to 750 at a mass-to-charge ratio M/ Z= 100. The parameter that appears to have the most influence on the measured mass resolving power is the duration of the ionization event, which may be longer than the duration of the laser pulse (5—10 ns), along with probable time broadening effects associated with the l6-ns time resolution of the transient recorder. ... 

The development of devices that provide a direct measure of stress or particle velocity led to observations of new rate-dependent mechanical responses and showed the power of such time-resolved measurements. The quartz gauge was the first of these devices with nanosecond time resolution, but its upper operating limit of 4 GPa limited its application. The development of the VISAR has had the most substantial impact on capabilities. VISAR systems, with time-resolution approaching 1 ns and the ability to work to pressures of 100 GPa, provide capabilities that have substantially altered the scientific descriptions of shock-compressed matter. 

In 1993, Jorgenson s group improved upon then earlier reverse phase HPLC-CZE system. Instead of the six-port valve, they used an eight-port electrically actuated valve that utilized two 10-p.L loops. While the effluent from the HPLC column filled one loop, the contents of the other loop were injected onto the CZE capillary. The entii e effluent from the HPLC column was collected and sampled by CZE, making this too a comprehensive technique, this time with enhanced resolving power. Having the two-loop valve made it possible to overlap the CZE runs. The total CZE run time was 15 s, with peaks occurring between 7.5 and 14.8 s. In order to save separation space, an injection was made into the CZE capillary every 7.5s,... 

The diazo systems have the advantage of being cheap and easy to develop into the final image. The resolving power is about ten times better that that of silver images. However, the light sensitivity of diazo systems is lower than that of silver photography by a factor of 106 to 108. 

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