Threshold values detection

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. 

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. 

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. 

The similarity between x, and the winning unit is compared with a threshold value, p, in the range from zero to one. When p, < P the input pattern, x, is not considered to fall into the existing class. It is decided that a so-called novelty is detected and the input vector is copied into one of the unused dummy units. Otherwise the input pattern, x, is considered to fall into the existing class (to resonate with it). A large p will result in many novelties, thus many small clusters. A small p results in few novelties and thus in a few large clusters. 

The distinction between detection and identification is important, since it may affect the overall response time and options. A detection occurs when a chosen parameter exceeds its threshold value. The detection may be nonspecific—that is, it registers the occurrence of an anomaly but does not necessarily indicate the presence of a particular threat substance. By contrast, identification establishes the identity of the threat substances in a given set. Nonspecific detection systems may have a relatively rapid response time compared with that of specific identification systems, but the former typically provide a lower confidence level that a threat substance is in fact present. In some cases, an alarm from a rapid but nonspecific detection system may be used... 

Here xik is an estimated value of a variable at a given point in time. Given that the estimate is calculated based on a model of variability, i.e., PCA, then Qi can reflect error relative to principal components for known data. A given pattern of data, x, can be classified based on a threshold value of Qi determined from analyzing the variability of the known data patterns. In this way, the -statistic will detect changes that violate the model used to estimate x. The 0-statistic threshold for methods based on linear projection such as PCA and PLS for Gaussian distributed data can be determined from the eigenvalues of the components not included in the model (Jack-son, 1992). 

The adsorption of HPAM on sand (Figure 4) is not detected below a threshold value of Ca2+ due to strong electrostatic repulsion between the polyelectrolyte and the highly charged negative surface. This threshold value, which was also observed in the case of monovalent ions (9), represents the point where the critical adsorption energy is overcome, and once this value is surpassed, adsorption increases sharply. This form of adsorption behavior is in line with predictions of theories on polyelectrolyte adsorption (20). 

Enantiomers of the same compound may have differing threshold values. This property was observed for a new, strong and high impact, flavor compound, 3-thio-2-methylpentan-l-ol, first detected in thermally processed materials but that is actually present in raw onions.54 First of all, there is a marked concentration effect at 1 ppm in 5% saltwater, the odor is described as sulfuric, burnt gum, sweaty, onion and at 0.5 ppb as meat broth, sweaty, onion, leek . Since there are two chiral centers (both dependent on carbon) there are four stereoisomers, all of which have been prepared 18a, 18b, 19a, 19b (Scheme 7). For this compound, enantiomers have the following marked differences in odor thresholds (but apparently all have the same general odor). 

The human taste threshold for PCP in drinking water is about 30 pg/L (USEPA 1980), a level far below the upper safe limit of 1.01 mg/L and near the no-observable-effect level of 21 pg/L (Table 23.7). Odor detection is not as sensitive as taste the odor threshold for PCP ranges from about 857 pg/L at 30°C, to 1600 pg/L at 20 to 22°C, to 12,000 pg/L at 60°C (USEPA 1980). It is not clear whether the determined organoleptic threshold values made the water undesirable or unfit for consumption (USEPA 1980). If fish and wildlife species of concern have PCP organoleptic thresholds that are similar to those of humans, or lower, will they too avoid contaminated habitats or diets ... 

The intensity of SHG is low but readily detectable for a photomultiplier. Note that although the sensitivity increases quadratically with laser intensity, the possibility of damage requires that the energy per unit area remains below a certain threshold value... 

The most common type of qualitative analysis is related to a binary response, with a presence-absence , yes-no or lower than-greater than answer to a main assumption, as for example is the concentration lower than a threshold value This method is interesting for the detection of unknown pollutants and can be easily carried out with screening procedures coupling real qualitative analysis with semi-quantitative responses. 

Another source of variation of threshold values is the treatment of panelists, that means comfort, motivation, interaction with panelleader, adaptation etc. These effects can be reduced using a proper detection method. Finally, different methods for threshold data treatment may produce different threshold values. 

Measurements of detection threshold values should use dynamic dilution techniques in odour free surroundings. 

Several extensive lists of threshold values, i.e. the minimum concentration in air, that is detected by 50% of the population, have been published (1, 2, 3, 4). However published threshold values for a particular compound can vary over a number of orders of magnitude, so they have to be treated with scepticism. 

The comparison of these two terms for faults of comparable intensity (he, a deviation of 10% from the true value) shows that for nominal values of Qgas the residual built from the estimation of [CO2] is much more sensitive to a fault of PCO2 than to a fault of Qgas- Two options are possible to manage this (i) select a low threshold to detect faults even for the less sensitive sensor with the risk to have a great number of false detections, (ii) select a threshold so that the most sensitive fault is correctly detected and include faults of the second sensor into this residual. 

Limit of detection (LOD) - a threshold value unlikely to be exceeded by the Instrument response when no analyte is present in the sample. 

Humans are more sensitive chan the test animals, so caution is required in extrapolating animal data to humans. The authors estimated a 6,650-fold safety factor between the EC50 for these threshold values and the CS concentration likely to cause the least detectable corneal damage in the human eye. 

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