Temperature sensitivity time constant

Uncoupled Rate Constants. An initial evaluation of polymerization kinetics is presented in Figure (2), constrained by viscosity invariant rate constants K. The slopes of these straight lines give initial estimates of Rgg/Kp according to Equation (14). Figure 3 presents graphically a power law relationship between K g/Kp and viscosity at 21°C and at 16.6 C. More scatter In Yu s data may be attributed to the use of an older GPC instrument of relatively low resolution. The ratio Kgq/Kp is temperature-sensitive a change of the order or five times is observed if the temperature is reduced by 4.4°C and viscosity is kept constant. 

During the last years, so-called microhotplates (pHP) have been developed in order to shrink the overall dimensions and to reduce the thermal mass of metal-oxide gas sensors [7,9,15]. Microhotplates consist of a thermally isolated stage with a heater structure, a temperature sensor and a set of contact electrodes for the sensitive layer. By using such microstructures, high operation temperatures can be reached at comparably low power consumption (< 100 mW). Moreover, small time constants on the order of 10 ms enable applying temperature modulation techniques with the aim to improve sensor selectivity and sensitivity. 

The third block in Fig. 2.1 shows the various possible sensing modes. The basic operation mode of a micromachined metal-oxide sensor is the measurement of the resistance or impedance [69] of the sensitive layer at constant temperature. A well-known problem of metal-oxide-based sensors is their lack of selectivity. Additional information on the interaction of analyte and sensitive layer may lead to better gas discrimination. Micromachined sensors exhibit a low thermal time constant, which can be used to advantage by applying temperature-modulation techniques. The gas/oxide interaction characteristics and dynamics are observable in the measured sensor resistance. Various temperature modulation methods have been explored. The first method relies on a train of rectangular temperature pulses at variable temperature step heights [70-72]. This method was further developed to find optimized modulation curves [73]. Sinusoidal temperature modulation also has been applied, and the data were evaluated by Fourier transformation [75]. Another idea included the simultaneous measurement of the resistive and calorimetric microhotplate response by additionally monitoring the change in the heater resistance upon gas exposure [74-76]. 

Temperature dependence proton relaxivity 188 relaxation rate 144-5 Temperature-sensitive contrast agents 218-19 Th -" 368 Ti "" 347 Tilt angle 242 Time constant 14 Time correlation functions 76 Time-dependent mechanism 14 Time-dependent perturbation methods 23 Time-dependent perturbation theory 45-8 Titanium(III) 115,134-5,161 TPEN 224 TPPS 219... 

Figure 2 shows the thermal correlation times rc, calculated from the longitudinal relaxation times in the usual way (1). The time constant rc is a direct measure of the molecular mobility, and one recognizes that at room temperature the molecular mobility of cyclohexane is about 200 times greater than that of benzene. As the corresponding heats of adsorption (5) differ only by a factor 1.5, proton relaxation is extremely sensitive to specific interaction (c/. (6)). 

The reaction system, the experiment procedure, and the analytical method used for the determination of micromixing in the TIJ mixer are the same as those described in the last section of this book but Mahajan et al. correlated their experimental data not with impinging velocity w() but with the jet Reynolds number Re. Also, the researchers employed the measure of increasing both the initial concentration CBo and the reaction temperature to raise the sensitivity of the procedure. The characteristic reaction time constant tK = 200 ms at 25 °C and CBo = 2.5 mM, while rR = 65 ms at 35 °C and CB0 = 4.7 mM, which can be used to bound the micromixing times, rM, no greater than them, respectively. 

In contrast, the interwell time t(ct) is very temperature-sensitive and might change virtually unboundedly in a sufficiently narrow temperature interval. [Note that under constant particle volume the parameter a according to its definition (4.75) may be treated as the inverse temperature.] Qualitatively, the behavior of t(ct) is as follows. At low potential barriers (a [Pg.555]

Thermistors have the desirable characteristics of small size, narrow spans, fast response (their time constant can be under 1 second), and a very high sensitivity. They do not need a cold-junction compensation, errors due to contact or lead-wire resistance are insignificant, and they are well suited for remote temperature sensing. They are inexpensive, their stability increases with age, and they are the most sensitive differential temperature detectors available. 

One of the characteristic features of the luminescence in a-Si H is the broad distribution of recombination times. Fig. 8.14 shows the luminescence decay extending from 10" s to 10 s (Tsang and Street 1979). The data are inverted in the lower part of the figure to give the distribution of lifetimes, which has its peak at 10" -10" s at low temperature and is 2-3 orders of magnitude wide. The shape of the distribution is sensitive to the excitation intensity for reasons discussed shortly and the time constants are even longer at very low intensity. 

Enzyme 0.228 mM in 0.1 M phosphate buffer (pH 7.0), temperature 105 K, 100 kHz modulation frequency, 1.0 mT modulation amplitude, 2 mW power (20 dB), 0.2 s time constant, 0.10 mTls scan rate, 9.39148 GHz microwave frequency. Key 1, oxidized enzyme P as 1, but 5 X instrument sensitivity 2, reduced enzyme, sensitivity as in V 3, oxidized enzyme, lyophilized at 0 C, redissolved. Asm Agio = 1.1 4, oxidized enzyme, after treatment with Chelex 100, AisolAno = 1.0, sensitivity in 3 and 4 as in V. (Reproduced, with permission, from Ref. 18. Copyright 1979,... 

Fig. 8. MIONP enhancement of nuclear spin polarization in a polycrystalline sample of pentacene doped naphthalene/ (a) Build-up curve for the enhanced spin polarization, with an MIONP repetition rate of 50 Hz (determined by the laser) the time constant for the build-up was 3730 s. TCP is an acronym for integrated cross-polarization - the authors term for their variant of the ISE. (b) 13.6 MHz single-shot H NMR spectra, taken with (top) and without bottom) MIONP enhancement (respectively, acquired at 100 K and room temperature). The top spectrum was obtained with a 10,000 s MIONP build-up time. The enormous sensitivity enhancement obtained with ONP is clear from comparing the two spectra. (Figures courtesy of K. Takeda and T. Terao, reprinted from Ref. [71], copyright 2001, with permission from Elsevier.)...

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