Threshold sensitivity

Another method which should be cited apart from the others is to pyrolyze the sample in a hydrogen atmosphere. The sulfur is converted to H2S which darkens lead-acetate-impregnated paper. The speed of darkening, measured by an optical device, provides the concentration measurement. This method attains sensitivity thresholds of 0.02 ppm. 

Let us consider the calculation of sensitivity threshold in the case when the cracks are revealing by PT method. Constant distance H between crack s walls along the whole defect s depth is assumed for the simplicity. The calculation procedure depends on the dispersity of dry developer s powder [1]. Simple formula has to be used in the case when developer s effective radius of pores IC, which depends mainly on average particle s size, is smaller than crack s width H. One can use formula (1) when Re is small enough being less than the value corresponding maximum sensitivity (0,25 - 1 pm). For example. Re = 0,25 pm in the case when fine-dispersed magnesia oxide powder is used as the developer. In this case minimum crack s width H that can be detected at prescribed depth lo is calculated as... 

The solution of (2) gives the range of the values of crack s width, which can be revealed by prescribed product family and conditions of testing process. Minimum value H of this range corresponds to the sensitivity threshold for the case Re > H. 

One more obvious example illustrates strong influence of particle s sedimentation upon the sensitivity threshold. Assume that we have to ensure the detection of the cracks with the depth 10 > 2 mm in the case when the same product family indicated above is applied and h = 20 pm. The calculation using formula (1) shows that in the absence of sedimentation only the cracks with the width H > 2 pm could be detected. But when the effect of sedimentation results in the reduction of the value of developer layer thickness from h = 20 pm to h = 8 pm, then the cracks of substantially smaller width H > 0,17 pm can be revealed at the same length lo = 2 mm. Therefore we can state that due to the sedimentation of developer s particles the sensitivity threshold has changed being 12 times smaller. Similar results were obtained using formula (2) for larger particles of the developers such as kaolin powder. 

In comparison with traditional radiography testing ISONIC system allows to provide image analysis and printout with different sensitivity thresholds at the postprocessing stage... 

Such techniques imply analysis of chemical products of photolysis. Application of mass-spectrometers of various types is often hampered by a number of circumstances. These difficulties will be discussed later on. The EPR method, which is currently the most extensively employed technique, features low sensitivity and is usually used for analysis of primary fragments of photolysis. For this purpose, the radicals produced are frozen on the walls of a quartz pin and are thus accumulated inside the device. On one hand, this approach allows one to overcome the sensitivity threshold of the device. However, on the other hand, this excludes the possibility of direct kinetic measurements. The SS technique permits the use of weak light sources for detecting active particles under... 

Tse, F.L.S. and Jaffe, J.M. (1991). Preclinical Drug Disposition. Marcel Dekker, New York. Vinegar, A. and Jepson, G. (1996). Cardiac sensitization thresholds of halon replacement chemicals in humans by physiologically based pharmacokinetic modeling. Risk Analysis 16 571-579. 

The mechanism of sulfite-induced asthma is not well-understood. Reactions to sulfited foods probably depend on the sulfite residue level in the food, the sensitivity threshold of the individual, the type of food consumed, and whether sulfite exists in the free (more toxic) form or combined (less toxic) form. The toxicology of sulfites has been reviewed by Madhavi and Salunkhe (1995). Sulfite sensitivity is not a true allergic reaction (Taylor et al., 1988). The FDA initially estimated that more than 1 million Americans are sensitive to sulfites, but more recent estimates lowered the number of asthmatics who may be sulfite sensitive to 80,000-100,000 (Bush et al., 1986). 

Predictive identification of human skin sensitization thresholds. Contact Dermatitis, 53, 260-267. 

Performance is defined by the sensitivity threshold, or the minimum concentration of element in solution that will yield an analytical signal with amplitude equal to twice that of the average background signal. This classical definition leads to optimistic values that can vary from element to element. The limit of detection represents the concentration of an element that can be detected with a 95% confidence limit (cf. chapter 21). In general, measurements are made in a concentration domain that corresponds to 50 times the limit of detection. 

Particle velocity is an important parameter in the so-called impedance-mismatch method of determining whether the shock from one material enters as a shock or rarefaction into another material in contact with the first material (see Vol 7, HI79-83 and Vol 9, S60). Two of the three commonly used Hugoniot curves (see Vol 7, H179—83) are in the form of P vs u or U vs u plots, and the third form, P vs v, depends on v, usually obtained via Eq 2 (see Vol 7, HI 80) The writer has suggested that input shock particle velocity is a better criterion for the shock sensitivity threshold of expls than input shock pressure (see Vol 9, S76)... 

The measurement system sensitivity threshold does not exceed 1 ppb. The time constant is determined by the electrochemical cell inertia and ranges 30 s, which corresponds to a 4-5-km and less than 300-m spatial resolution over the horizontal and vertical, respectively, for measurements during the ascent and descent of the aircraft. Atmospheric ozone concentration can be measured in-situ within the range of 0 - 4E+12 cm 3, with an accuracy not worse than 5 %. 

The shock sensitivity threshold for coarse particle size expls is generally lower than for finer particles of these expls, provided the comparison is made between coarse and fine particles at the same density. This somewhat unexpected result was first reported for Tetryl by Seely (Ref 6a). Subsequently it was observed by the writer for RDX (Ref 32), by Scott for PETN, RDX Tetryl (Ref 35), and for PETN by Dinegar et al (Ref 40)... 

Of course, this fact outlines ways to improve the physicochemical parameters of biomimetic sensor design and, consequently, the technological modernization of biomimetic electrode preparation. As concluded from the data in Figure 8.14, the sensitivity threshold of the designed sensor is very high (10 xwt. % aqueous ethyl alcohol) [14],... 

After these questions have been answered, the next step is to undertake a systematic analysis of the mixture itself, with the goal of identifying the toxicologically relevant components. For example, the concentration of compounds in the mixture could be compared to ecotoxicity data for those compounds to identify compounds most likely to contribute to mixture effects (exposure > sensitivity threshold), or grouping of compounds in the mixture according to modes of action. In the following steps, these issues are elaborated, starting with exposure assessment. 

The sensitization threshold is at half-wave potential -0.50 V of a sensitizer with displacement E1/2 to more positive region the sensitizing properties of nitroazoles are nonlinearly growing (see Table 3.43) [919], The best sensitizing properties are marked on nitroazoles, reduced in the potentials E1/2 range from -0.2 to -0.35 V. A linear dependence has been found out between one-electron redox potentials of nitroimidazoles and - log 1/R37 values (r=0.96, n=6). Parameter R37 characterizes an activity of a drug (37% of DNA X174 population survival) [919],... 

Modern HPLC systems equipped with analog-to-digital converters (ADCs) and initial data acquisition and signal analysis are performed by either built-in microprocessor or attached computer [38,39]. Depending on the data acquisition rate and initial analysis criterion (peak height, peak area, or sensitivity thresholds, etc.), the integration limits or area calculation could be erroneous, and in some cases the whole peaks could be missed. 

If some of the errors given above can be dominated for the real zirconia-based sensors, then the other constituents can be ignored. If only the additive constituent part takes place, then the zirconia gas sensor function assumes y = k x Aq), where the current value of the absolute sensor error, equal to A = Aq, is independent of the value of the measuring parameter. The value of the relative error y= Yq = Aq /jc is inversely proportional to the value of the measuring parameter, the sensor error growths up to 100% at X = Ag, that is, it is impossible to make a measurement in this case. The value of the measuring parameter x, equal to the value of the relative error of zero, is acceptedly called the sensitivity threshold of the sensor. 

Monkey (M. fascicularis) Birth to 7 yr old NoNOAEL 0.05 Increased vibration-sensitivity thresholds at 18 yr old Rice and Gilbert 1995... 

The threshold of sensitivity varies according to the instrument and the element being considered. Numerous comparative tables on detection limit values exist which are continually being updated as a result of the progress made in instrumentation. The sensitivity threshold corresponds to the minimum concentration of element in solution that will yield an analytical signal for which the amplitude is equal to three times the standard deviation calculated for an analytical blank. This classic definition leads to rather optimistic values and very variable with respect to the element. The detection limit of the instrument represents the concentration of an element, which allows detection with a confidence of 95 per cent (cf. Chapter 22). 

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