Time-dependent Gain Measurements

A reconstruction of the measured time-dependent absorption spectra of the hydrogen-bonding complexes of HPTA with DMSO in DCM is shown in Fig. 3 as the superposition of the absorption and the gain bands of the photoacid. 

If multiple procedures are performed, a qualitative measure of time dependence can be gained. This is achieved by linking two ramps in an up-and-down sequence and examining the area of hysteresis. A second option is to connect three segments as an up ramp, a peak hold step, and a down ramp sequence this option has the effect of altering the area of hysteresis because the sample is broken down more effectively before the down step. 

Because the duration for one measurement is very short (e.g., with a 1-Hz input, a cycle is completed in 1 sec), a dynamic test is suitable for gaining information in a short time frame or for monitoring time-dependent changes in gel network properties. When monitoring the gelation process at a fixed frequency, it usually takes a few hours for G to become approximately constant. The constancy can be judged by a constant value of G at a fixed frequency during a subsequent frequency or strain sweep test, which usually takes several minutes. 

A practical consequence of architecture is to permit acoustical performances to large numbers of listeners by enclosing the sound source within walls. This dramatically increases the sound energy to listeners, particularly those far from the source, relative to free field conditions. A measure of the resulting frequency dependent gain of the room can be obtained from the EDR evaluated at time 0. This frequency response can be considered to be an equalization applied by the room, and is often easily perceived. 

MD simulation is advantageous for obtaining dynamic properties directly, since the MD technique provides not only particle positions but also particle velocities that enable us to utilize the response theory (e.g., the Kubo formula [175,176]) to calculate the transport coefficients from time-dependent correlation functions. For example, we will examine the self-diffusion process of a tagged PFPE molecular center of mass (Fig. 1.49) from the simulation to gain insight into the excitation of translational motion, specifically, spreading and replenishment. The squared displacement of the center mass of a molecule or a bead is used as a measure of translational movement. The self-diffusion coefficient D can be represented as a velocity autocorrelation function... 

One of the methods used in the production of liquid fuels from coal is to heat coal in the presence of solvents in order to dissolve and stabilize low molecular weight fragments. Many studies (1-6) have been devoted to elucidating the chemical mechanism of product formation in hydrogen donor and non-donor solvents. In most of these studies, the time dependence of the product yield was used as a measure of the rates of reaction, or the product yield was correlated with the solvent, the rank of the coal or other properties of the coal. In order to gain a better understanding of the nature of the coal-solvent interactions, we... 

Equation 6-6 tells us that the mean of 4 measurements is more precise by /4 = 2 than individual measurements in the data set. For this reason, averaging results is often used to improve precision. However, the improvement to be gained by averaging is somewhat limited because of the square root dependence seen in Equation 6-6. For example, to increase the precision by a factor of 10 requires 100 times as many measurements. It is better, if possible, to decrease x than to keep averaging more results, since s, is directly proportional to s, but only inversely proportional to the square root of N. The standard deviation can sometimes be decreased by being more precise in individual operations, by changing the procedure, and by using more precise measurement tools. 

Surface tension vs. temperature for PS and PTHF are shown in Figure 15. The data of Gains and Bender (17) on PS surface tensions (yGps) agree well with ours. However, our value for the surface tension of PTHF (yoPthf) is about 4.5 dynes/cm higher than Roe s value (18). The reason for this discrepancy is not clear. The y0i thf is always smaller than the yoPS by Ay = 3 dynes/cm, which is much smaller than the surface tension difference between the blocks of PS and polydimethylsiloxane. The time-dependent surface tensions of four blends (ST-PS, ST-PTHF, PS-PTHF, and PTHF-PS) were measured. To prepare the blends, the block or homopolymers were added in small amounts (0.3-1 wt %) to the homo-PS or PTHF. The mixture was completely dissolved in benzene, the solutions were quickly frozen by a dry ice-acetone mixture, and the samples were freeze dried. 

The growth rate (r) has been measured as a function of temperature ( from 1173 to 1400K) and residence time (from 0.2 to 5s). The measurements were performed in situ with a microbalance. The purified graphite substrates were hung in the isothermal section by a molybdenum wire, 100pm in diameter, to the microbalance beam. No radial temperature dependence has been detected. The growth rate here is the mass gain measured by means of the microbalance per unit time and substrate area in the steady state. 

Experimentation with step-scan interferometry in electrochemistry began in the early 1990s (cf Ref. [23]), and interest has grown steadily ]24, 29-31, 51-54]. Step-scan FTIR spectroscopy provides a means to investigate time- and frequency-dependent processes. Measurements are hmited to reversible systems. However, a great deal of insight can be gained into the molecular transformations that accompany the external perturbation [181-183]. 

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