Extrinsic variability

The detection of chemical analytes can be based on changes in one or more of the physical characteristics of a thin film or layer in contact with the device surface. Some of the intrinsic film properties that can be utilized for detection include mass/area, elastic stiffness (modulus), viscoelasticity, viscosity, electrical conductivity, and permittivity. In addition, changes in extrinsic variables such as... 

Recently, an entropy-based approach has been introduced to compare the intrinsic and extrinsic variability of different descriptors, independent of their units and value ranges. The method was originally introduced in communication theory and is based on Shannon entropy, which calculates descriptor-entropy values using histogram representations. Shannon entropy is defined as ... 

The following arc the most important extrinsic variables affecting rp... 

This operation can induce extrinsic variability in agrochemical concentrations and fluxes in soils due to variability in application itself (random if broadcast nonrandom if banded) and the tillage operation. Weed scientists have examined such variability, in particular as related to herbicide efficacy ( 15 - 21 ). Such extrinsic variability in pesticide concentrations can also pose serious problems in obtaining representative soil samples for pesticide concentration determinations. 

At the Florida field site, we evaluated the significance of tillage-induced extrinsic variability in bromide (Br) and aldicarbfs total toxic residues (TTR) variability. 

FIGURE 1. Schematic diagram showing the sampling design used to evaluate the extrinsic variability in bromide and aldicarb TTR concentrations at the Florida site. 

The detection of chemical analytes can be based on changes in one or more of physical characteristics of thin film or layer in contact with the device surface. Some of the intrinsic film properties that can be utilized for detection include mass/area, elastic stiffness (modulus) viscoelasticity, viscosity electrical conductivity, and permittivity. In addition, changes in extrinsic variables such as temperature and pressure also produce a sensor response [31, 32]. SAW sensor works as a mass sensor, when analytes of interest comes in contact of polymer film, which is coated, on SAW device. Desired toxic gas is exposed to the device through the carrier gas such as Na and then gas molecules are desorbed [5, 33, 34]. Device has been tested for determining the characteristics such as (i) frequency shift with different concentration of vapor (ii) transient response for response and recovery times (iii) transient response for reproducibility of the sensor. Since arrangement has been made to compensate the... 

For example, with regard to the hot-spot theory outlined above, it would clearly be useful to understand the effects of changing the solvent, or the ambient temperature and at which the reaction was carried out. Furthermore, the design of ultrasonic probe systems allows for ready variation of the power input and occasionally variation of the frequency of the output. Hence, there are a number of factors that must be bom in mind when setting up a viable system. For this reason, the following section is devoted to a discussion of the effects of extrinsic variables on the sonochemical process. 

The credibility of the hot spot theory is reinforced by its ability to account for the effects of extrinsic variables on the sonochemical process. Nevertheless, the frequency of ultrasound applied is surprisingly irrelevant to the course of the reaction. Cleaning baths produce a range of frequencies which often vary from day to day, or even during the course of a reaction, and yet this has no discemable effect on the sonochemistry observed. 

Due to these characteristics, the possibility to build databases of NMR-based metabolic profiles of foodstuffs, in order to assess their quality, is becoming more and more actual [9]. However, when we apply multivariate analysis to our data fields or wish to compare databases obtained by NMR spectroscopy by other researchers, it is very important to consider the source of extrinsic variability originated by the employed experimental conditions, in terms of sample preparation, NMR acquisition parameters, signal-to-noise ratio, NMR spectral pre-treatment, NMR data pre-processing, as well as the strategy for NMR-based metabolomics (for an exhaustive introduction to the reported critical cmicepts see the manual by Axelson [10]). 

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