Exposure rate constant

R-m7(h Ci)). Exposure rate X(R/h) at a distance d (m) from a gamma-ray source of radioactivity A (Ci) can be approximated by using this exposure rate constant T as follows ... 

The radiation exposure varies inversely with the square of the distance from the source. Each radionuclide has an exposure rate constant, r, which is given in units of R-cm2/mCi-h at 1 cm or in SI units, pGy-m2/GBq-h at 1 m, and these values for UC, 13N, 150, 18F, and 82Rb are given in Table 9.3. The exposure X per hour at distance d(cm) from an n mCi source is given by... 

Table 9.3. Exposure rate constants of common positron-emitting radionuclides...

When it was observed that the DNQ/novolac resists in use at the time became more transparent on exposure (i.e., they bleached). Dill used this change in optical absorbance as a way of monitoring the kinetics of exposure. He developed a first-order model of exposure consisting of three parameters A, B, and C, now called the Dill model, which accurately fit the experimental measurement results of the transmittance of a resist coating on an optically matched glass wafer as a function of exposure dose. The Dill parameters A, B, and C, describe bleachable absorbance, nonbleachable absorbance, and exposure rate constant, respectively." ... 

The length and amount of cracks is assessed according to the Bayer method [72,73]. The ISO standard ozone test conditions involve a test temperature of 40°C zE 1°C and an ozone level of 50 5 pphm, with a test duration of 72 h. Testing is done under static [72] and/or dynamic strain [73]. These are accelerated tests and should be used for the relative comparison of compounds, rather than for the prediction of long-term service life. The method is rather complicated and demands a long duration of ozone exposure. Therefore, in some cases the rate constants of the antiozonants reaction with ozone in solution are used instead to evaluate the efficiency of different antiozonants [74]. 

Lim CB et al Reduction in the rates of protein and amino acid catabolism to slow down the accumulation of endogenous ammonia a strategy potentially adopted by mudskippers during aerial exposure in constant darkness. J Exp Biol 2001 ... 

This new analytical method determines the rate constant and activation energy of Kevlar s photooxidative processes. The 0.2 atm of oxygen-18-labelled environment in a solar chamber simulates the air-exposure under sunlight conditions. The technique also allows the radial 0-distribution measurement from the fiber surface toward the fiber center. The data from the accelerated experimental conditions in the solar chamber in an 02-atmosphere are differentiated from the usual daylight exposure effects. 

While these models simulate the transfer of lead between many of the same physiological compartments, they use different methodologies to quantify lead exposure as well as the kinetics of lead transfer among the compartments. As described earlier, in contrast to PBPK models, classical pharmacokinetic models are calibrated to experimental data using transfer coefficients that may not have any physiological correlates. Examples of lead models that use PBPK and classical pharmacokinetic approaches are discussed in the following section, with a focus on the basis for model parameters, including age-specific blood flow rates and volumes for multiple body compartments, kinetic rate constants, tissue dosimetry,... 

Some introductory comments on the conceptual basis of SPMD uptake (ku) and release (ke) rate constants and the associated sampling rates (i.e., Rs) are in order. The can be conceptualized as the volume of air or water cleared of chemical per unit sampler mass or volume per unit time (e.g., mL g d or mL mL d ) and Rs is the volume of air or water cleared per unit time (e.g., L d ). Thus, the only difference between ku and Rs is that Rs is not normalized to a unit mass or unit volume of sampler. In the context of organism exposure (see Section l.L), the SPMD is equivalent to the encounter volume times the fractional bioavailability of the chemical (which excludes dietary uptake). The release rate constant (d ) is equal to kuK J. 

Meadows et al. (1998) conducted a 28 d exposure of brown trout (Salmo trutta), standard SPMDs and hexane fllled dialysis bags (Sodergren, 1987) to spring water (total organic carbon < 1 mg L ) contaminated with PCBs. Trout were not fed during the exposure, and temperature and flow conditions remained constant throughout the exposure. A good correlation (r = 0.89) was found between the uptake rate constants ( u,fs) for whole body trout and the uptake rate constants... 

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