Time-domain measurement system

Bond et al. [791 ] studied strategies for trace metal determination in seawater by ASV using a computerised multi-time domain measurement method. A microcomputer-based system allowed the reliability of the determination of trace amounts of metals to be estimated. Peak height, width, and potential were measured as a function of time and concentration to construct the database. Measurements were made with a potentiostat polarographic analyser connected to the microcomputer and a hanging drop mercury electrode. The presence of surfactants, which presented a matrix problem, was detected via time domain dependent results and nonlinearity of the calibration. A decision to pretreat the samples could then be made. In the presence of surfactants, neither a direct calibration mode nor a linear standard addition method yielded precise data. Alternative ways to eliminate the interferences based either on theoretical considerations or destruction of the matrix needed to be considered. 

In time domain measurements, the electrochemical system is subjected to a potential variation that is the resultant of many frequencies, like a pulse or white noise signal, and the time-dependent current from the cell is recorded. The stimulus and the response can be converted via Fourier transform methods to spectral representations of amplitude and phase angle frequency, from which the desired impedance can be computed as a function of frequency. 

We should note that, given the difference in quantum yield between the free and bound probe, the fractional intensities utilized in Fig. 7 actually represent small percentages of bound probe on a molar basis. In fact, considering the accuracy of the differential phase measurement (better than O.r) one can detect, in this system, on the order of 0.1% bound probe. This phenomenon also occurs in time-domain measurements. Specifically, if one monitors the anisotropy decay of a system which displays multiple lifetimes associated with multiple rotational diffusion rates then one may observe a decline at short times of the anisotropy followed by a rise at latter times and subsequent decrease. This dip and rise effect has been observed by Millar and co-workers in studies on protein-DNA interactions, specifically in the case of the interaction of a fluorescent DNA duplex with the Klenow fragment of DNA polymerase. 

The new generation of digital sampling oscilloscopes (36,45) and specially designed time-domain measuring setups (TDMS) (38) offer comprehensive, high precision, and automatic measuring systems for TDS hardware support. They usually have a small jitter faetor (< 1.5 ps), important for rise time, a small flatness of ineident pulse (< 0.5% for all amplitudes), and in some systems a unique option for... 

However, NMR has the potential of being very useful in process analysis due to it being a noncontact and nondestructive technique. Another problem that was faced when NMR was initially tried as an online application was that laboratory instruments were simply moved into the plant. Process operators found problems in the calibration and maintenance of these instruments. Recently, small, dedicated NMR systems have been developed, which in turn has led to more reports of online NMR. Time domain measurements (low field, low resolution) are far more... 

A difficulty with time-domain measurements is brought about by overlap of fission chains, and this precludes, in practice, measurements of systems with latge Inherent sources and thermal systems. To avoid tMs difficulty, an expression equivalent to Eq. (3) was obtained in the frequency domain ... 

Electric breakdown is a process in which the conductivity of an electrically stressed electrode gap changes from values characteristic of insulators to those of semiconductors or metals. The process is very fast and proceeds usually in the nanosecond time domain. Measurement methods which are to monitor electronic breakdown require careful consideration of the various components and of the observable quantity. Advanced systems have been employed for the optical observation of streamers in liquids (Devins et al., 1976 Hebner, 1988). Very few experiments have been reported in the literature in which electronic initiation or propagation of the breakdown process in liquids has been monitored by electrical measurement circuits. 

Fig. 8 Dotted lines are the shear stress in the time domain measured at an excitation frequency of 1 Hz for different strain amplitudes ranging from 0.03 to 1. The temperature was set to T = 15.1 °Cto measure a glassy system. With increasing strain amplitude an increasing dissipative energy is measured, associated with an increasing area of the closed Lissajous curves. After exceeding the yield stress oy, that is indicated by the grey lines, the shear stress shows a distorted shape, which reflects the onset of nonlinearity. The MCT based predictions are depicted with full lines and show an overall good agreement with the experimental data, reprinted from Brader et al. [3], copyright 2010, American Physical Society...

More sophisticated methods that actually measure volumetric water content can also be used, such as time domain reflectometry (TDR). In Figure 14, an example of TDR results is presented. Both the calculated and measured (i.e., TDR) volumetric water contents provide a similar picture of the profile water status by depth with time. Proper soil characterization data, such as those shown in Table 6, are necessary for these calculations and improve understanding of the test system. The determination of water-holding capacity (WHC) at 0.03 MPa field capacity (FC) and 1.5 MPa... 

Performance data Two moisture monitoring systems were installed, one at Disposal Area A and one at Disposal Area AB plus in May and November 1999, respectively. Each monitoring system has two stacks of time domain reflectometry probes that measure soil moisture at 24-in. intervals to a maximum depth of 78 in., and a station for collecting weather data. Based on nearly 3 years of data, there is generally <5% change in the relative volumetric... 

In frequency-domain FLIM, the optics and detection system (MCP image intensifier and slow scan CCD camera) are similar to that of time-domain FLIM, except for the light source, which consists of a CW laser and an acousto-optical modulator instead of a pulsed laser. The principle of lifetime measurement is the same as that described in Chapter 6 (Section 6.2.3.1). The phase shift and modulation depth are measured relative to a known fluorescence standard or to scattering of the excitation light. There are two possible modes of detection heterodyne and homodyne detection. 

In order to implement frequency domain based sensing systems capable of monitoring the temporal luminescence of sensors, in few seconds, data must be collected at multiple frequencies simultaneously. Single-frequency techniques have been used to make frequency domain measurements of luminescent decays. 14, 23 28) This approach is unsuitable for real-time applications since data must be acquired at several frequencies in order to precisely and accurately determine the temporal variables of luminescent systems. 1 Each frequency requires a separate measurement, which makes the single frequency approach too slow to monitor the evolution... 

Carl Zeiss, Inc. also describes a spectrofluorometer system for process monitoring," but it does not currently appear as a standard marketed product on their web site. HORIBA Jobin Yvon also markets a fluorescent process analyzer, but it is a laser-induced time-domain based measurement system tailored for uranium or equivalent analysis." Finally, while numerous miniature spectrofluorometers are also available (Carl Zeiss, StellarNet Inc., Ocean Optics and Avantes), they are not packaged and configured for process applications. Although there is an established need and continued growing interest in realtime process spectrofluorometry, relative to conventional process spectroscopic instruments such as NIR, UV-vis and Raman, commercial process spectrofluorometers are currently available on a very limited basis. 

The relaxation rate R t) described by Eqs. (4.49)-(4.51) embodies our universal recipe for dynamically controlled relaxation [10, 21], which has the following merits (i) it holds for any bath and any type of interventions, that is, coherent modulations and incoherent interruptions/measurements alike (ii) it shows that in order to suppress relaxation, we need to minimize the spectral overlap of G( ), given to us by nature, and Ffo)), which we may design to some extent (iii) most importantly, it shows that in the short-time domain, only broad (coarse-grained) spectral features of G( ) and Ffa>) are important. The latter implies that, in contrast to the claim that correlations of the system with each individual bath mode must be accounted for, if we are to preserve coherence in the system, we actually only need to characterize and suppress (by means of Ffco)) the broad spectral features of G( ), the bath response function. The universality of Eqs. (4.49)-(4.51) will be elucidated in what follows, by focusing on several limits. 

Ultrafast vibrational spectroscopy offers a variety of techniques for unraveling the microsopic dynamics of hydrogen bonds occurring in the femto- to picosecond time domain. In particular, different vibrational couplings can be separated in nonlinear experiments by measuring vibrational dynamics in real-time. Both coherent vibrational polarizations and processes of population and energy relaxation have been studied for a number of hydrogen bonded systems in liquids [1],... 

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