Absolute calibration

By using an optically flat plate of a pure element such as Ni, TXRF systems can be calibrated in the sense of absolute calibration [4.32] ... 

Some electronic equipment has self-calibration routines built in to the start-up sequence. This should be taken as an indication of serviceability and not of absolute calibration. The device should still be subject to independent calibration at a defined frequency. 

On-line changing of solvent from DMSO to H2O for a starch glucan establishing an absolute calibration function characteristics of mass and molar degree of polymerization distribution for a broad distributed starch sample... 

O Kane, D. J., and Lee, J. (2000). Absolute calibration of luminometers with low-level light standards. Method. Enzymol. 305 87-96. 

Absolute calibration is of critical importance for the determination of molecular weights by the light-scattering method. The scattered intensity is so low compared with the incident beam at a distance of a few cm. being of the order of 10 lo) that a reliable direct comparison of the two beams using the same photocell is impractical. Several methods have been used, with results which are not always comparable, however. 

Other methods of calibration are discussed by Zimm and by Brice and co-workers.23 Owing to difiSculties of absolute calibration, a reference standard invariably is used. This may consist of a polymer solution of constant properties (i.e., not subject to degradation) or a bulk polymer, such as that used by Debye and Bueche. ... 

Fig. 3.5 Principle of a laser interferometer for absolute calibration of the transducer velocity. Li and L2 denote the lengths of the two light paths of the split laser beam, giving a path difference A5 = 2(Li - L2)...

The SH signal directly scales as the square of the surface concentration of the optically active compounds, as deduced from Eqs. (3), (4), and (9). Hence, the SHG technique can be used as a determination of the surface coverage. Unfortunately, it is very difficult to obtain an absolute calibration of the SH intensity and therefore to determine the absolute number for the surface density of molecules at the interface. This determination also entails the separate measurement of the hyperpolarizability tensor jS,-, another difficult task because of local fields effects as the coverage increases [53]. However, with a proper normalization of the SH intensity with the one obtained at full monolayer coverage, the adsorption isotherm can still be extracted through the square root of the SH intensity. Such a procedure has been followed at the polarized water-DCE interface, for example, see Fig. 3 in the case of 2-( -octadecylamino)-naphthalene-6-sulfonate (ONS) [54]. The surface coverage 6 takes the form ... 

In conclusion one can say that SEC is a very powerful method for polymer characterization, especially in combination with other composition sensitive or absolute calibration methods. A big advantage is also that the sample amount is fairly small, typically 10 mg. For more complex polymers, such as polyelectrolytes, enthalpic effects often become dominant and also for rather high molecular weight polymers chromatographic methods such as field-flow fraction (FFF) techniques might be more suitable. For fast routine measurements linear columns are often used. 

The rooms without aerosol sources and low ventilation rate (v<0.3 hf1 ) had low aerosol concentrations (2 103 - 104 cm-3) due to the small influence of the higher aerosol concentrations outdoors (aerosols by traffic and combustions) (Table la). In this case the aerosol in the room air was aged by coagulation and plateout and had less condensation nuclei of smaller sizes (d<100 nm). Rooms with a moderate ventilation show higher particle concentrations ((1-5) 10 cm 3) (Table Ila). With aerosol sources in a room (Table III) the aerosol concentrations can increase to 5 105 particles/cm3. The relative error of the measured particle concentration is in the order of 15% primary determined by the uncertainties of the absolute calibrations of the condensation nuclei counter. 

Fig. 4. Comparison of hydrogen content measurements. The curves show IR absorption measurements, using absorption cross sections of Brodsky el al., and Fang el al., whose absolute calibration was done by NRA, and total hydrogen measurements using 15N nuclear reaction. Note the discrepancy that arises at high hydrogen pressures, because of the presence of hydrogen that is not infrared active. (Reprinted with permission from the American Institute of Physics, Ross, R., Tsong, I.S.T., Messier, R., Lanford., W., Burman, C (1982). J. Vac. Sci. Tech. 20, 406.)...

Collection of multiple data sets for each time span, with frequent alternation of the polarization, is an essential feature of our protocol. This provides some protection against the effects of drifts in laser power, photomultiplier quantum yield, and absolute calibration of the TAC, photochemical decomposition of the dye, and any other long-term processes that may alter the measured fluorescence response curves. Separate analysis of each data set is necessary to provide an indication of the uncertainty in run-to-run reproducibility and to detect and delete the rare spurious data set. 

These investigations showed that the T04 olfactometer can deliver repeatable dilutions, but that an absolute calibration was needed before use. The main problems arise from the flow rates measured in the lower ranges of the rotameter scales, which are less accurate than the upper ranges. If the upper ranges only are used, then consistent results should be obtainable. The olfactometer should be used in the same orientation as when calibrated. 

Paur, R. Comparison of uv photometry and gas phase titration as candidate methods for absolute calibration of ozone gennator output in the subpart-per-million range. Paper Presented at the American Society for Testing and Materiab Conference on Calibration in Air Monitoring, Boulder, University of Colorado, Aug. 5-7, 1975. 

TTie unique capabilities of the system, including the method of absolute calibration, have been described by Corns et al. [17, 18]. 

Calibration methods I modified luminol standard II absolute calibration HI Hastings-Weber light standard IV luminol standard V mean value obtained by different determination methods, including chemical titrations VI triplet yield of 0.3 E mol for TMD, obtained with DBA. 

The disadvantages are the need to correct for regeneration of OH in the instrument from H02 and ROz reactions at high ambient NO concentrations and, as with LIF, the uncertainty in the absolute calibration. 

Light scattering photometer, with absolute calibration carried out in advance plus appropriate neutral filters, and data collection system... 

Note The absolute temperature changes within 45 days at a given depth are small. Thus, it would be convenient to have an instrument which allows us to measure T with an accuracy of at least 0.01 K. Furthermore, an absolute calibration stability of 0.01 K is a prerequisite to calculate Ez from T. 

The calculated cross-section curves are compared with experimental data in Fig. 18. The fact that the total cross-section curves pass through the experimental point for an average collision energy of 45 meV was required in the fit calculations. As seen in Fig. 9, the value obtained by Howard et al.54 for an average collision energy of 370 meV also lies on the calculated curve. However, for a given absolute calibration of T(/i), as the energy... 

Although spectroradiometers appear to have many advantages, their use in comparison to simpler broadband detectors in dense monitoring UV networks is not necessarily the best choice. First, because in general are unable to produce continuous measurements, since even the faster instruments would need a few minutes to complete a typical UV scan, while broadband detectors can be sampled easily once every a few seconds. The second reason is their purchase and operational cost, which can be 5-10 times higher than for a typical broadband detector. Finally, due to their extreme sensitivity their operation and maintenance requires special experimental support and experienced, well-trained personnel. Despite these disadvantages, their superior quality imposes the existence of at least on spectroradiometer to support each network and provide proper absolute calibration of the broadband detectors. 

The characteristics of radiation instruments may change significantly in time, either due to aging of their optical components or due to environmental impacts on their optical characteristics. Therefore arises the necessity of applying strict absolute calibration, maintenance, and quality control protocols to assure the quality of the produced measurements. Only then, the measurements produced by instruments deployed at various locations can give comparable results, which can be safely used for scientific research. 

As for the second condition, usually the spectral response, which is provided by the instrument manufacturers, is used. For the erythemal broadband detectors, it has been demonstrated that regular testing of their spectral sensitivity is needed, in addition and prior to their absolute calibration. This is because their spectral sensitivity is determined fiom a series of optical filters and other components (e.g. the phosphor layer) that may degrade with time or with environmental conditions (e.g. humidity), changing therefore its characteristics. 

At the end, the absolute (calibrated) signal from an eiythemal broadband detector is given by ... 

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