Threshold values

Figure 6.10 As is varied, some problems require only a cold utility below a threshold value.

Figure 6.11 In some threshold problems, only a hot utility is required below the threshold value of AT i .

In a situation as shown in Fig. 6.12a, with the optimal AT in at the threshold, then there is no pinch. On the other hand, in a situation as shown in Fig. 6.126, with the optimum above the threshold value, there is a demand for both utilities, and there is a pinch. 

The experimental conditions used to determine the CFPP do not exactly reflect those observed in vehicles the differences are due to the spaces in the filter mesh which are much larger in the laboratory filter, the back-pressure and the cooling rate. Also, research is continuing on procedures that are more representative of the actual behavior of diesel fuel in a vehicle and which correlate better with the temperature said to be operability , the threshold value for the Incident. In 1993, the CEN looked at two new methods, one called SFPP proposed by Exxon Chemicals (David et al., 1993), the other called AGELFI and recommended by Agip, Elf and Fina (Hamon et al., 1993). 

The aim of defect segmentation is to delimit the detected defect as precise as possible from the background which surrounds the defect (fig. 8). The extracted characteristics of a detected casting defect depend considerable on the threshold value which is used during the defect segmentation. 

Therefore an automatic method, which means an objective and reproducible process, is necessary to determine the threshold value. The results of this investigations show that the threshold value can be determined reproducible in the point of intersection of two normal distributed frequency approximations. 

The threshold value for screening out non significant AE sources is calculated on the basis of the mean (m) and of the standard deviation (a) TH = (m+Na), where N is an input floating variable. 

TEST FOR CONCENTRATED SOURCES THRESHOLD VALUE ON STANDARD DEVIATION (intNa). SCREEN ALL SOURCES WHOSE COUNTS ARB BELOW THRESHOLD... 

This function is described by Eq. (4), where Net, is the net signal, ff gives the threshold value where the neuron starts to react and I/a gives the width of the interval (see Figure 9-15). 

Low-pressure hysteresis is not confined to Type I isotherms, however, and is frequently superimposed on the conventional hysteresis loop of the Type IV isotherm. In the region below the shoulder of the hysteresis loop the desorption branch runs parallel to the adsorption curve, as in Fig. 4.26, and in Fig. 4.2S(fi) and (d). It is usually found that the low-pressure hysteresis does not appear unless the desorption run commences from a relative pressure which is above some threshold value. In the study of butane adsorbed on powdered graphite referred to in Fig. 3.23, for example, the isotherm was reversible so long as the relative pressure was confined to the branch below the shoulder F. 

Onc-Factor-at-a-Timc Optimization One approach to optimizing the quantitative method for vanadium described earlier is to select initial concentrations for ITiOz and 1T2S04 and measure the absorbance. We then increase or decrease the concentration of one reagent in steps, while the second reagent s concentration remains constant, until the absorbance decreases in value. The concentration of the second reagent is then adjusted until a decrease in absorbance is again observed. This process can be stopped after one cycle or repeated until the absorbance reaches a maximum value or exceeds an acceptable threshold value. 

W. H. Stahl, ed.. Compilation of Odor andTaste Threshold Values Data, American Society for Testing and Materials Data Series 48, Philadelphia, Pa., 1973. 

A persistent idea is that there is a very small number of flavor quaUties or characteristics, called primaries, each detected by a different kind of receptor site in the sensory organ. It is thought that each of these primary sites can be excited independently but that some chemicals can react with more than one site producing the perception of several flavor quaUties simultaneously (12). Sweet, sour, salty, bitter, and umami quaUties are generally accepted as five of the primaries for taste sucrose, hydrochloric acid, sodium chloride, quinine, and glutamate, respectively, are compounds that have these primary tastes. Sucrose is only sweet, quinine is only bitter, etc saccharin, however, is slightly bitter as well as sweet and its Stevens law exponent is 0.8, between that for purely sweet (1.5) and purely bitter (0.6) compounds (34). There is evidence that all compounds with the same primary taste characteristic have the same psychophysical exponent even though they may have different threshold values (24). The flavor of a complex food can be described as a combination of a smaller number of flavor primaries, each with an associated intensity. A flavor may be described as a vector in which the primaries make up the coordinates of the flavor space. 

The odor detection-threshold values of organic compounds, water, and mineral oil have been determined by different investigators (Table 2 and 3) and may vary by as much as 1000, depending on the test methods, because human senses are not invariable in their sensitivity. Human senses are subject to adaption, ie, reduced sensitivity after prolonged response to a stimulus, and habituation, ie, reduced attention to monotonous stimulation. The values give approximate magnitudes and are significant when the same techiriques for evaluation are used. Since 1952, the chemistry of odorous materials has been the subject of intense research (43). Many new compounds have been identified in natural products (37—40,42,44—50) and find use in flavors. 

The flavor portion of a flavor compound gives it its name, acceptabiUty, and palatabiUty, and provides character fixation of the flavor, ie, relatively high boiling point soflds, usually in combination, are used at concentrations above thek threshold values at use level so that upon dilution the levels remain above threshold value and the perception of the flavor does not change. 

L. J. van Gemert and A. H. Nettenbreiger, Compilation of Odor Threshold Values in Air and Water, National Institute for Water Supply, Voolburg, the... 

Odors are measured by their intensity. The threshold value of one odor to another, however, can vary greatly. Detection threshold is the minimum physical intensity necessary for detection by a subject where the person is not required to identify the stimulus, but just detect the existence of the stimulus. Accordingly, threshold deterrninations are used to evaluate the effectiveness of different treatments and to estabflsh the level of odor control necessary to make a product acceptable (8). Concentration can also produce different odors for the same matenal. For example, indole (qv) in low concentrations has the smell of jasmine and a low threshold of perception. In high concentrations, it has a strong odor of feces and CX-naphthyl amine as well as a considerably higher threshold of perception. 

L-Amino acid Threshold value, mg/dL Sweet Sour Bitter Salty Umami... 

Odor data for the various amyl alcohols is limited. The lowest perceptible limit for 1-pentanol and / fZ-amyl alcohol are 10 and 0.04 ppm, respectively (135). tert-Axa[. alcohol has a threshold value of 2.3 ppm (and a 100% recognition level of 0.23 ppm) 3-methyl-1-butanol has an odor threshold of 7.0 ppm. The odor of 1-pentanol has been described as sweet and pleasant whereas that of 3-methyl-2-butanol is sour (135). 

Water Quality Standards. Water quaUty standards are usually based on one of two primary criteria, stream standards or effluent standards. Stream standards are based on dilution requirements for the receiving water quaUty based on a threshold value of specific pollutants or a beneficial use of the water. Effluent standards are based on the concentration of pollutants that can be discharged or on the degree of treatment required. 

The characteristic note of green beans is attributed to methoxypyrazines which have very low threshold values (10). The characteristic musty earthy note of robustas was recently identified as 2-methyhsobomeol [2371-42-8] (11). 

Stress Relaxation. Copper alloys are used extensively in appHcations where they are subjected to moderately elevated temperatures while under load. An important example is the spring member for contacts in electrical and electronic coimectors. Critical to rehable performance is the maintenance of adequate contact force, or stabiUty, while in service. Excessive decrease in this force to below a minimum threshold value because of losses in spring property can lead to premature open-circuit failure (see Electrical connectors). 

The industries which produce and handle various stone products emit considerable amounts of particulate matter at every stage of the operation. These particulates may include fine mineral dusts of a size to cause damage to the lungs. The threshold values for such dusts have been set quite low to prevent disabling diseases for the worker. 

PBDs were not observed for layers less than 23 /rm thick and the PBD film potential threshold varied from 4-5 kV at 23/rm to 11 kVatl75/rm [228]. A later study, possibly using a less valid method for measuring film potential, reported smaller threshold values [ 29 ]. The later study concluded that if film breakdown voltage is less than about 4 kV at 20/rm and about 8 kV at 200/rm, PBDs cannot be produced. This is shown schematically in Figure 2-6.5. 

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