Peak concentrations

Various types of diffusion models are available which can use as input emission patterns, climatological data, and population data to rank sampling locations by concentration threshold, resolution of peak concentrations, and frequency of exposure (4) or to rank sampling locations for maximum sensitivity to source emission changes, to provide coverage of as many sources or to cover as large a geographic area as possible (5). 

In this case a-y is 419 m. The peak concentration can be found from the measurements, or from the Gaussian distribution fitted to the data and the peak concentration obtained from the fitted distribution. Provided that the emission rate Q, the height of release H, and the mean wind speed u are known, the standard deviation of the vertical distribution of the pollutant can be approximated from either the peak concentration (actual or fitted) or the cross wind integrated (CWI) concentration from one of the following equations ... 

Using the data from Fig. 19-11, the calculated cr from the CWI concentration is 239 m from the observed peak concentration it is 232 m and from the fitted peak concentration it is 235 m. Note that errors in any ofthe parameters H, Q, or u, will cause errors in the estimated [Pg.314]

Air jets are used to create enough air movement inside the room to circulate and mix the whole room air. This strategy is often called dilution ventilation as the contaminants created inside the room are mixed into the whole room volume thus reducing the local peak concentrations. 

In the steady state, the peak concentration and the trough concentration can be distinguished. 

The calculated peak concentration is not always the measured concentration. For bi-exponential kinetics the calculated peak concentration is less, but after oral dosing, the calculated peak concentration is higher than the highest measurable plasma concentration. The peak concentration provides a target for the loading dose to start with (Dload). 

The effect area should remain constant (AUEC = const.). Thus the target concentration (Ctarget) might be derived from the normal peak concentration (Cpeak). 

Ozone is a relatively unstable species which is easily destroyed by various chemical processes. Its peak concentration is several parts of ozone per million parts of air, and it is found primarily in the stratosphere, the region between about 10 and 50 km above the Earth s surface. 

Methadone is a p receptor agonist with special properties that make it particularly useful as a maintenance agent. Rehably absorbed orally, it does not reach peak concentration until about 4 hours after administration and maintains a large extravascular reservoir (Kreek 1979). These properties minimize acute euphoric effects. The reservoir results in a plasma half-life of 1—2 days, so there are usually no rapid blood level drops that could lead to withdrawal syndromes between daily doses. Effective blood levels are in the range of 200-500 ng/mL. Trough levels of 400 ng/mL are considered optimal (Payte and Khouri 1993). There is wide variability among individuals in blood levels with identical doses (Kreek 1979), and some have inadequate levels even with doses as high as 200 mg/day (Tennant 1987 Tenore 2003). 

The distribution of endosulfan and endosulfan sulfate was evaluated in the brains of cats given a single intravenous injection of 3 mg/kg endosulfan (Khanna et al. 1979). Peak concentrations of endosulfan in the brain were found at the earliest time point examined (15 minutes after administration) and then decreased. When tissue levels were expressed per gram of tissue, little differential was observed in distribution among the brain areas studied. However, if endosulfan levels were expressed per gram of tissue lipid, higher initial levels were observed in the cerebral cortex and cerebellum than in the spinal cord and brainstem. Loss of endosulfan was most rapid from those areas low in Upid. Endosulfan sulfate levels peaked in the brain at 1 hour postadministration. In contrast, endosulfan sulfate levels in liver peaked within 15 minutes postadministration. The time course of neurotoxic effects observed in the animals in this study corresponded most closely with endosulfan levels in the central nervous system tissues examined. 

Samples must be representative of the environment in relation to study objectives and to permit comparison of data with appropriate standards, i.e. average concentrations, time-weighted exposures, peak concentrations, etc. Replicate samples may be advisable. 

It should be noted that, in two of these studies, " the perfusion parameter used to define the mismatch was not CBF or MTT, but instead the time it took for contrast concentration to reach peak concentration in each image voxel after contrast injection ( time to peak or TTP). TTP measurements are often used as rough approximations of MTT measurements because calculation of CBF and MTT are somewhat complex, requiring a mathematical process called deconvolution. The details of deconvolution are beyond the scope of this chapter, and the reader is referred to other sources for further explanation. In many clinical settings, maps of parameters like TTP that do not require deconvolution may be available much more quickly than those that do require deconvolution. TTP is less specific than MTT in detecting underperfused tissue because it does not distinguish between delayed contrast arrival time (such as that related to perfusion via collateral vessels) and truly prolonged intravascular transit time. 

Experiments demonstrate that oral absorption of trichloroethylene in animals is extensive and metabolism is rapid. A study of F344 rats which were fasted for 8 hours prior to oral dosing by gavage found a rapid appearance of trichloroethylene in the blood which peaked after 0.75 hours, while the peak concentrations of the metabolites trichloroethanol and TCA occurred at 2.5 and 12 hours, respectively (Templin et al. 1995). The same investigators also dosed beagle dogs and found that blood concentrations of trichloroethylene, trichloroethanol, and TCA peaked after 1, 2.5, and 24 hours, respectively. In both species, TCA concentration did not peak until well after the trichloroethylene concentration in blood was below detectable levels (Templin et al. 1995). 

It is readily observed that the expression within brackets for the peak concentration C forms a geometric progression in which the first term equals one and with a common ratio of e . (The common ratio is the factor which results from dividing a term of the progression by its preceding one.) For the sum of the finite progression in eq. (39.41) we obtain after n cycles ... 

In this special case when the time between dosings is equal to the half-life time of the drug, we can deduce that the minimum (steady-state) plasma concentration with repeated dosing is equal to the peak concentration, obtained from a single dose. Under this condition, the corresponding maximum (steady-state) concentration is twice as much as the minimum one. 

Other non-compartmental parameters that are easily obtainable from a plasma concentration curve are the time of appearance of the maximum and the peak concentration value Cp(r ,). 

FIG. 77. Room-temperature photoluminescence spectra of Er-implanted PECVDa-Si H, annealed at 400°C. The implantation energy and dose were 125 keV and 4 x 10 Er/cm". respectively, which resulted in peak concentration of 0.2 at.%. "Low-0" and "high-O" denote a peak oxygen concentration in a-Si H of 0.3 and 1.3 at.9c. respectively. The inset shows the 1.54-/im peak intensity as a function of annealing temperature, for both oxygen concentrations. (From J. H. Shin. R. Serna, G. N. van den Hoven, A. Polman, W. G. J. H. M. van Sark, and A. M. Vredenberg. Appl. Phys. Lett. 68. 697 (1996). 1996, American Institute of Physics, with permission.]... 

Figure 7A shows the timeeourse of [ H]MDA accumulation and clearance from rat brain after a subcutaneous injection. Peak concentration, which was reached at 45 minutes, was equivalent to 165 (36 trg/g). To... 

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