Intensity- versus-time plot

The "add-to-memory" signal averaging method currently available to us distorts fluorescence intensity versus time plots when the fluorescence intensity is a non-linear function of incident laser energy and the laser energy varies from shot to shot. For this reason we have not attempted detailed kinetic modelling of the observed fluorescence intensity decay curves recorded at high 532 nm laser fluence. 

The other possible mode is called the damped oscillatory mode and has a current versus time plot similar to Figure 3.9. This results in an irregular intensity versus time plot and the consequent loss of a considerable amount of light energy. A profile similar to Figure 3.8 results if R is high in comparison to L. Since R itself is only about 5 1 or less, the inductance must therefore be kept to a minimum. 

A second photomultiplier tube looking through a slit scans the oscilloscope trace and converts the time-density function into an intensity versus time plot. This second photomultiplier tube has an RC integration circuit in its anode to improve the statistical sampling by averaging the information. Zarowin states that, if the pulse rate is 100 per sec, and if the RC time is 1 sec, one obtains an effective increase in intensity of 100. This apparatus is shown in detail in Fig. 15. 

In Fig. 3.3-7 the intensity versus time plot is shown for an experiment at 180 MPa and 120°C. It can be seen that the intensity decreases exponentially within 100 s to 58% of its initial value. 

Calibration of the dosing (film-formation) rate was conducted via an XPS breakpoint analysi In this procedure, a plot of the XPS intensity is obtained as a function of dosing time (Fig. 2) from submonolayer to full-monolayer coverages, the intensity-versus-time plot has a fixed slope. The point at which the slope changes marks the time at which a second monolayer begins to form it is also taken as the total time (/ml) required to deposit one full monolayer. In the preparation of an n-ML film, the total dosing time was simply equated to ( x 7ml). At the end of each deposition, the alloy films were annealed at 900 K for 20 minutes to ensure that Pt and Co had become alloyed. Prior to and subsequent to the electrochemical experiments, interfacial composition was determined by LEISS, XPS or TPD, and surface structure by LEED. 

Invariably, measurements of decay of reactive molecules in solid glasses are found to be nonexponential, that is, first-order plots of ln[intensity] versus time are upwardly curved, as shown in Figure 10.3. 

Figure 10.3. First-order plots of ln[Intensity] versus time, showing idealized exponential decay (dotted line), and nonexponential decay from statistical distribution of matrix sites (solid line).

This approach uses a kinetic sequential principle to carry out multicomponent CL-based determinations. In fact, when the half-lives of the CL reactions involved in the determination of the analytes in mixture are appreciably different, the CL intensity-versus-time curve exhibits two peaks that are separate in time (in the case of a binary mixture) this allows both analytes to be directly determined from their corresponding calibration plots. In general, commercially available chemiluminometers have been used in these determinations, so the CL reaction was initially started by addition of one or two reaction ingredients. Thus, in the analysis of binary mixtures of cysteine and gluthatione, appropriate time-resolved response curves were obtained provided that equal volumes of peroxidase and luminol were mixed and saturated with oxygen and that copper(H) and aminothiol solutions were simultaneously injected [62, 63],... 

Figure 11.10. NW smart pixels, (a) Schematic of an integrated crossed NW FET and LED and the equivalent circuit, (b) Shows SEM image of a representative device, (c) Plots of current and emission intensity of the nanoLED as a function of voltage apphed to the NW gate at a fixed bias of -6V. (d) EL intensity versus time relation when a voltage applied to NW gate is switched between 0 and +4V for a fixed bias of -6V. [Reprinted with permission from Ref. 59. Copyright 2005 Wiley-VCH Verlag.]...

How do we extract the chemical shifts of all nuclei in the sample from the free-induction decay signal The answer is our old friend the Fourier transform. The FID is called a time-domain signal because it is a plot of the oscillating and decaying RF intensity versus time, as shown in Fig. 10.4 (the time axis is conventionally labeled t2, for reasons you will see shortly). Fourier transforming the FID produces afrequency-domain spectrum, a plot of RF intensity versus the frequencies present in the FID signal, with the frequency axis labeled v2 for frequency or F2 for chemical shift, as shown in Fig. 10.1. So the Fourier transform decomposes the FID into its component frequencies, revealing the chemical shifts of the nuclei in the sample. 

The term 2D NMR, which stands for two-dimensional NMR, is something of a misnomer. All the NMR spectra we have discussed so far in this book are two dimensional in the sense that they are plots of signal intensity versus frequency (or its Fourier equivalent, signal intensity versus time). By contrast, 2D NMR refers to spectroscopic data that are collected as a function of two time scales, tx (evolution and mixing) and t2 (detection). The resulting data set is then subjected to separate Fourier transformations of each time domain to give a frequency-domain 2D NMR spectrum of signal intensity versus two frequencies, Fx (the Fourier transform of the t time domain) and F2 (the Fourier transform of the t2 time domain). Thus, a 2D NMR spectrum is actually a three-dimensional data set ... 

The intensity of a Raman peak at a given excitation wavenumber cU is related to the area under the curve in the overlap versus time plot. However, only the overlap in the short time region of the plot will be important in determining the Raman spectra of large molecules in condensed media because the damping factor is always nonzero. For example, when the damping factor is 300 cm , most of the recurrences die and the first peak will... 

If emission from multiple excited states were the cause of the observed spectrum, it is expected that the lifetimes of the states would be different. Lifetime measurements were made by monitoring the decay at a number of wavelengths. In all of the measurements, the slope of the plot of the log of the intensity versus time was the same. These results do not provide conclusive proof that only one state is emitting. If more than one excited state is involved, the differences in the emission lifetimes could be less than the uncertainty in the measurements ( 2/xs). There is no way of predicting how large the differences in lifetimes should be. However, it is unlikely that two different spin-orbit states would have such similar lifetimes. 

Figure 3.10 Three-dimensional plots of photoluminescence intensity versus time and photon energy for (a) bulk GaAs and (b) 250 A GaAs/250 A Alo.38Gao,62As MQW. Source Rosenwaks et al. (1993).

Figure 1 shows the plots of the fluorescence Intensity versus time for several different concentrations of formaldehyde. About 75% of the fluorescence can be obtained within the first minute and... 

Figure 1 Plots of fluorescence intensity versus time in enzymatic method ...

Values of the rate constants of inhibition of the first order reaction were determined as a tangent of the angle of declination on the plot of log of intensity versus time. The rate constant of inhibition of the second order reaction calculated in this way,... 

The reciprocal of the square root of the chemiluminescence intensity versus time gives a linear relationship as published by Kihara and Hosoda [26]. In the region where the plot gives a straight line, the slope is the value of fkhfj. This parameter is named CL-decay rate and may be used to evaluate the thermal history of different polymers. 

FIGURE 3.2 Plot of the reciprocal of the square root of chemiluminescence intensity versus time obtained at 170°C under nitrogen for free and stabilized low-density polyethylene films with the different phenolic antioxidants (0.1% w/w). 

Therefore, the interferograin is the sum of all the frequencies (plotted as intensity versus time). By performing a Fast Fourier Transform algorithm using a computer, the infrared spectrum is obtained in which intensity is now plotted versus frequency (usually given in cra ). Therefore, by means of the interferometer, an FTIR instrument can analyze all frequencies simultaneously. unlike a dispersive instrument that examines the frequencies one at a time. 

Fig. 2.18 A Confocal fluorescence microscope images of the QDs on (Aa) a flat gold film, (Ab) the conical Au array, and (Ac) the dimpled Au array. (Ad) 3D visualization of the fluorescence intensity in (Ac) [60]. The QD has an emission wavelength of 597 nm. The excitation laser source was a 543 nm HeNe laser. (B) Field snapshot image from FDTD simulation results of Au coated dimpled structure. (C) Plots for the near-zone field intensity versus time in the dimpled Au structure [60]. Reproduced with permission [60]. Copyright 2013, Royal Society of Chemistry...

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