Transmittance calculations

EN ISO 6946 Building components and building elements—thermal resistance and thermal transmittance—calculation method. 1998. Brussels European Committee for Standardization... 

The 13C chemical shifts, offsets relative to the transmitter, calculated and observed DQ frequencies for the correlations to C14 are summarized in Table 1. 

The Lambert and Beer theory is reserved for transmittance calculations for very transparent samples. Dating back to the eighteenth and nineteenth centuries, the Lambert and Beer laws state that the absorbence [log(l/T)] for a transparent sample is proportional to the thickness and the concentration of the colorant [4]. 

Figure 16.27 illustrates the dependence of the relative error on the transmittance, calculated for a constant error of 0.01 T in reading the scale. It is evident from the figure that, while the minimum occurs at 36.8% T, a nearly constant minimum error occurs over the range of 20 to 65% T (0.7 to 0.2 A). The percent transmittance should fall within 10 to 80% T (A = 1 to 0.1) in order to prevent large errors in spectrophotometric readings. Hence, samples should be diluted (or concentrated), and standard solutions prepared, so that the absorbance falls within the optimal range. 

Table I. Absorbance and Transmittance Calculations For Each Wavelength of a Fusion H Bulb Medium Pressure Mercury Arc Lamp...

F. 7.26 a Transmittance spectra of the Y2O3 ceramics sintered at 1473-1773 K after annealing at 1323 K. b Transmittanee at 2 = 550 and 2000 nm as a function of sintering temperature. The dashed line indieates transmittance calculated from the refractive index of Y2O3 single crystal. Reproduced with permission from [119]. Copyright 2012, Elsevier... 

The transmittance calculated for the director distribution in the B effect (Fig. 4.35) strongly depends on the applied voltage. For a purely homeotropic monodomain sample and U effect threshold, Fig. 4.1(b)) the curve T(i) markedly oscillates with the incident angle i when i i. The amplitude of the oscillations reaches the maximum possible value T => 1 (R => 0) for the angles i close to ig. The oscillations appear due to the interference effect between the waves reflected from the upper z = 0 and lower z = d boundaries of the cell (Fig. 4.34). This effect becomes more pronounced for i => ig where the reflectance and transmit-... 

Equation [19] allows direct comparison between high resolution measurements of transmittance (/( )/ Jo(A)) and transmittance calculated from spectral parameters, pressure of the absorbing gas, and the temperature. It should be noted that knowledge of the spectral line HWHH (7) is required, as well as an instrument capable of measuring the transmittance at high resolution. In practice, values of (usually converted to line strengths) for different... 

Vitreous siUca transmission curves are shown in Figure 7. The hydroxyl concentration for each siUca type is Hsted in Table 9. These curves represent only the general characteristics of the different siUca types and should not be used for calculations of transmittance. 

A guarded hot-plate method, ASTM D1518, is used to measure the rate of heat transfer over time from a warm metal plate. The fabric is placed on the constant temperature plate and covered by a second metal plate. After the temperature of the second plate has been allowed to equiUbrate, the thermal transmittance is calculated based on the temperature difference between the two plates and the energy required to maintain the temperature of the bottom plate. The units for thermal transmittance are W/m -K. Thermal resistance is the reciprocal of thermal conductivity (or transmittance). Thermal resistance is often reported as a do value, defined as the insulation required to keep a resting person comfortable at 21°C with air movement of 0.1 m/s. Thermal resistance in m -K/W can be converted to do by multiplying by 0.1548 (121). 

Thermal resistance is the reciprocal of thermal conductance. It is expressed as m KTW. Since the purpose of thermal insulation is to resist heat flow, it is convenient to measure a material s performance in terms of its thermal resistance, which is calculated by dividing the thickness expressed in meters by the thermal conductivity. Being additive, thermal resistances facilitate the computation of overall thermal transmittance values (t/-values). 

Thermal transmittance (t/-value) defines the ability to an element of structure to transmit heat under steady-state conditions. It is a measure of the quantity of heat that will flow through unit area in unit time per unit difference in temperature of the individual environments between which the structure intervenes. It is calculated as the reciprocal of the sum of the resistance of each component part of the structure, including the resistance of any air space or cavity and of the inner and outer surfaces. It is expressed as W/m K. 

The overall thermal transmittance, t/, is used to calculate the total heat flow. For a plane surface of area A and a steady temperature difference AT, it is... 

When a spectrophotometer is used it is unnecessary to make comparison with solutions of known concentration. With such an instrument the intensity of the transmitted light or, better, the ratio I,/I0 (the transmittance) is found directly at a known thickness /. By varying / and c the validity of the Beer-Lambert Law, equation (9), can be tested and the value of may be evaluated. When the latter is known, the concentration cx of an unknown solution can be calculated from the formula ... 

They may be classified by their structure, as coin, cylindrical and pin types. Table 5, 6, 7 respectively show their specifications. Applications of Li -(CF)n batteries as power sources are spreading from professional and business uses, such as in wireless transmitters and integrated circuit (IC) memory preservation, to consumer uses in electronic watches, cameras, calculators, and the like. Pin-type batteries are used for illumination-type fishing floats with a light-emitting diode. Coin-type batteries, which have a stable packing insulation, separator, and electrolyte for high... 

The determination of effective wavelength is of interest here. For each sample of aluminum (of thickness d cm emergent beam current u), an aluminum foil of thickness Ad was placed in the photometer between sample and detector, so that a reduced emergent beam current could be read. The per cent transmittance of the foil, 100f2/fi, was then calculated, and the effective wavelength was read from a plot (e.g., Figure 3-4) calculated from known values of at different wavelengths.12 This calculation is based upon the relationship... 

The turnover rate of a transmitter can be calculated from measurement of either the rate at which it is synthesised or the rate at which it is lost from the endogenous store. Transmitter synthesis can be monitored by administering [ H]- or [ " C]-labelled precursors in vivo these are eventually taken up by neurons and converted into radiolabelled product (the transmitter). The rate of accumulation of the radiolabelled transmitter can be used to estimate its synthesis rate. Obviously, the choice of precursor is determined by the rate-limiting step in the synthetic pathway for instance, when measuring catecholamine turnover, tyrosine must be used instead of /-DOPA which bypasses the rate-limiting enzyme, tyrosine hydroxylase. 

One approach, and the first to be adopted, is to study transmitter release from slices which have been preloaded with radiolabelled transmitter. In these experiments, drug-induced changes in the release of transmitter is usually monitored using the doublepulse technique. This involves comparing the effects of a test drug on the amount of transmitter released in response to a reference pulse and a second identical test pulse. If all the radiolabelled transmitter that overflows in the effluent is collected, and the amount which remains in the slice at the end of the experiment is also measured, it is possible to calculate not only how much radiolabelled transmitter was originally contained in the slice but also the effects of drugs on fractional release , i.e. the proportion of the store of radiolabelled transmitter which is released by nerve stimulation. As with... 

A stock solution of the triazole in hexane was made up and diluted to various strengths, and 1.0-ml. aliquots of the diluted solutions were carried through the procedure described below. The transmittance of the colored solutions obtained from 10 to 50 micrograms of the 118-phenyldihydrotriazole was plotted against concentration to make a standard curve. In subsequent analyses, the amount of Compound 118 is readily calculated from the amount of dihydrotriazole formed. 

To consider pH as a controlled variable, we use a pH electrode to measure its value and, with a transmitter, send the signal to a controller, which can be a little black box or a computer. The controller takes in the pH value and compares it with the desired pH, what we call the set point or reference. If the values are not the same, there is an error, and the controller makes proper adjustments by manipulating the acid or the base pump—the actuator.2 The adjustment is based on calculations using a control algorithm, also called the control law. The error is calculated at the summing point where we take the desired pH minus the measured pH. Because of how we calculate the error, this is a negative feedback mechanism. 

A more sophisticated implementation is full metering control (Fig. 10.6). In this case, we send the signals from the fuel gas controller (FC in the fuel gas loop) and the air flow transmitter (FT) to the ratio controller (RC), which takes the desired flow ratio (R) as the set point. This controller calculates the proper air flow rate, which in turn becomes the set point to the air flow controller (FC in the air flow loop). If we take away the secondary flow control loops on both the fuel gas and air flow rates, what we have is called parallel positioning control. In this simpler case, of course, the performance of the furnace is subject to fluctuations in fuel and air supply lines. 

For ratioed spectra, it is of interest to ascertain the effect of the various noise sources on the ratioed spectrum (i.e., the transmittance or reflectance spectrum as the case may be), on the absorbance spectrum, and also to determine, as was done previously [1, 2, 5], the optimum value for the sample to have that will give the minimum error of the calculated value. 

There are still a variety of ways we can approach the calculations. We could assume that Es or Er were constant and examine how the noise varies as the other was changed. We could also hold the transmittance constant and examine how the transmittance noise varies as both Es and Er are changed proportionately. 

Er has dropped to five standard deviations, the optimum transmittance has dropped to 3.2, and then drops off quickly below that value. Surprisingly, the optimum value of transmittance appears to reach a minimum value, and then increase again as Er continues to decrease. It is not entirely clear whether this is simply appearance or actually reflects the correct description of the behavior of the noise in this regime, given the unstable nature of the variance values upon which it is based. In fact, originally these curves were computed only for values of Er equal to or greater than three due to the expectation that no reasonable results could be obtained at lower values of Er. However, when the unexpectedly smooth decrease in the optimum value of %T was observed down to that level, it seemed prudent to extend the calculations to still lower values, whereupon the results in Figure 45-11 were obtained. 

In the case we investigated there, we had previously derived that the calculated transmittance for an individual reading was... 

We keep learning more about the history of noise calculations. It seems that the topic of the noise of a spectrum in the constant-detector-noise case was addressed more than 50 years ago [1], Not only that, but it was done while taking into account the noise of the reference readings. The calculation of the optimum absorbance value was performed using several different criteria for optimum . One of these criteria, which Cole called the Probable Error Method, gives the same results that we obtained for the optimum transmittance value of 32.99%T [2], Cole s approach, however, had several limitations. The main one, from our point of view, is the fact that he directed his equations to represent the absorbance noise as soon as possible in his derivation. Thus his derivation, as well as virtually all the ones since then, bypassed consideration of the behavior of noise of transmittance spectra. This, coupled with the fact that the only place we have found that presented an expression for transmittance noise had a typographical error as we reported in our previous column [3], means that as far as we know, the correct expression for the behavior of transmittance noise has still never been previously reported in the literature. On the other hand, we do have to draw back a bit and admit that the correct expression for the optimum transmittance has been reported. 

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