INDEX sensitivity control

The condition number analysis is used after the RGA analysis to check the ease of the control structure. The condition number is commonly used as an index of controllability which is a ratio of the largest singular value to the smallest nonzero singular value of a matrix, i.e. the HEN gain matrix. Mathematically, condition number can be defined as a positive number that provides useful information on the sensitivity of matrix properties to variations in the elements of the matrix. In terms of process control, a large condition number indicates that it will be impractical, if not impossible, to satisfy the entire set of control objectives and vice versa for small values. Therefore, it is used to measure the performance of the structured control system by RGA of the designed HEN. This condition number analysis is used mainly... 

Refractive index 5x 10- lO" Almost universal, but only moderate sensitivity. Very temperature sensitive (control to 0.001 °C). Cannot be used with gradient elution. 

Refractive index detectors. These bulk property detectors are based on the change of refractive index of the eluant from the column with respect to pure mobile phase. Although they are widely used, the refractive index detectors suffer from several disadvantages — lack of high sensitivity, lack of suitability for gradient elution, and the need for strict temperature control ( + 0.001 °C) to operate at their highest sensitivity. A pulseless pump, or a reciprocating pump equipped with a pulse dampener, must also be employed. The effect of these limitations may to some extent be overcome by the use of differential systems in which the column eluant is compared with a reference flow of pure mobile phase. The two chief types of RI detector are as follows. 

The international normalized ratio (INR) is a method to standardize repotting of the prothrombin time, using the formula, INR = (PTpatie t/PTcontroi)ISI, where PT indicates the prothrombin times (for the patient and the laboratory control), and ISI indicates the international sensitivity index, a value that varies, depending upon the thromboplastin reagent and laboratory instrument used to initiate and detect clot formation, respectively. 

Refractive index detectors are not as sensitive as uv absorbance detectors. The best noise levels obtainable are about 1CT7 riu (refractive index units), which corresponds to a noise equivalent concentration of about 10-6 g cmT3 for most solutes. The linear range of most ri detectors is about 104. If you want to operate them at their highest sensitivity you have to have very good control of the temperature of the instrument and of the composition of the mobile phase. Because of their sensitivity to mobile phase composition it is very difficult to do gradient elution work, and they are generally held to be unsuitable for this purpose. 

For each concentration of chemical tested in the LLNA, a stimulation index (SI) is derived using the value obtained with the concurrent vehicle control as the denominator. Chemicals that induce an SI of three or more are defined as skin sensitizers. This threshold for positivity was based initially on empirical observations in investigations of both contact allergens and non-sensitizing chemicals [5], Subsequently, a retrospective statistical analysis of results obtained in the LLNA with a wider range of chemicals (130) confirmed that an SI value of 3 does indeed provide the most appropriate basis... 

Refractive index is a measure of the velocity of light in air divided by the velocity of light in the compound of interest. Accurate measurement of refractive indices requires careful temperature control. The refractive index is sensitive to the purity of the substance. 

Refractive Index 10 ng ml-1 1.6 x 10 7 RIU 5-14 All purpose temperature control for high sensitive detection, usually used for preparative LC or size exclusion LC, eluent must be isocratic... 

The test method is based on the fact that sensitizers induce a proliferation of lymphocytes in the lymph node draining the site of substance administration. The increased proliferation is proportional to the applied dose of the chemical and the potency of the allergen. Hence, the murine LLNA assesses proliferation in a dose-response manner, comparing it to the proliferation in a control group. The ratio of the proliferation after sensitizer application to the control group defines the Stimulation Index (SI). 

The refractive index detector, considered to be almost universal, is often used in series with a UV detector in the isocratic mode to provide a supplementary chromatogram. This detector, which is not highly sensitive, has to be temperature controlled, as does the column (0.1 °C). The baseline of the chromatogram has to be set to an intermediate position because it can lead to either positive or negative signals (Fig. 3.18). The detector can only be used in the isocratic mode because in gradient elution the composition of the mobile phase changes with time, as does the refractive index. Compensation, which is easily obtained in the case of a mobile phase of constant composition, is difficult to carry out when the composition at the end of the column differs from that at the inlet. 

The risk of post-transplant diabetes mellitus is greater with tacrolimus than with ciclosporin, but this was mostly true in black patients and during the initial months after transplantation (1084). In one study, insulin sensitivity, alpha and beta cell function, and beta cell reserve were studied in 14 hepatitis C-positive patients with liver transplants, who took tacrolimus or ciclosporin maintenance for 1 year (1085). The patients were matched for low prednisolone dosage (1.1 mg/day versus 1.3 mg/day), body mass index, lean body mass, and sex, and compared with eight controls. Insulin sensitivity and insulin secretory reserve were significantly different from controls, but there was no significant difference between ciclosporin and tacrolimus. 

Figure 19.5 Assessing chemicals for potential contact sensitivity. In the local lymph node assay the chemical in question is applied to both ears on three consecutive days. Control mice are treated with vehicle. Radioisotope is injected intravenously on day 6. The draining lymph nodes are removed 5 hours later and the proliferative response is measured by the incorporation of radio isotope. Results are frequently presented as a stimulation index (counts per min (cpm) for the test chemical/cpm for control). (Picture adapted from D. Sailstad, Lab Animal 31 36, 2002.)...

Charge transport is one of the important processes that control the speed of the PR index grating formation and the PR sensitivity. According to the standard theory of photorefraction [21], the response time for the formation and erasure of the space-charge field [xr in Eq. (21)] is proportional to the dielectric relaxation... 

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