Transmitters definition

The term electrochromism was apparently coined to describe absorption line shifts induced in dyes by strong electric fields (1). This definition of electrocbromism does not, however, fit within the modem sense of the word. Electrochromism is a reversible and visible change in transmittance and/or reflectance that is associated with an electrochemicaHy induced oxidation—reduction reaction. This optical change is effected by a small electric current at low d-c potential. The potential is usually on the order of 1 V, and the electrochromic material sometimes exhibits good open-circuit memory. Unlike the well-known electrolytic coloration in alkaU haUde crystals, the electrochromic optical density change is often appreciable at ordinary temperatures. 

In the extraction procedure the yellow solution is allowed to stand for 10 minutes, and then extracted with 3 mL portions of a 3 1 mixture by volume of pentan-l-ol and ethyl acetate until the last extract is colourless. Make up the combined extracts to a definite volume (10 mL or 25 mL) with the organic solvent, and determine the transmittance (460 nm) at once. Construct the calibration curve by extracting known amounts of bismuth under the same conditions as the sample. 

We start with the definition of transmittance, as we pointed out previously, and we rewrite the equation here ... 

Now that we have completed our expository interlude, we continue our derivation along the same lines we did previously. The next step, as it was for the constant-noise case, is to derive the absorbance noise for Poisson-distributed detector noise as we previously did for constant detector noise. As we did above in the derivation of transmittance noise, we start by repeating the definition and the previously derived expressions for absorbance [3],... 

What is the mathematical definition of transmittance, T Define the parameters that are found in this mathematical definition. 

We have spoken frequently in this chapter about sensitivity and detection limit in reference to advantages and disadvantages of the various techniques. Sensitivity and detection limit have specific definitions in atomic absorption. Sensitivity is defined as the concentration of an element that will produce an absorption of 1% (absorptivity percent transmittance of 99%). It is the smallest concentration that can be determined with a reasonable degree of precision. Detection limit is the concentration that gives a readout level that is double the electrical noise level inherent in the baseline. It is a qualitative parameter in the sense that it is the minimum concentration that can be detected, but not precisely determined, like a blip that is barely seen compared to the electrical noise on the baseline. It would tell the analyst that the element is present, but not necessarily at a precisely determinable concentration level. A comparison of detection limits for several elements for the more popular techniques is given in Table 9.2. 

The transmittance is a dimensionless function of energy, just like the transmission. By definition, for a single-site model it equals unity, and is independent of energy. Using our simple model, we shall now calculate it for arbitrarily long chains. 

No divergences and dependence on the contact parameters Ti 2 remain in the form for r. It shows the transmittance function (at least in the weak-coupling limit) is indeed a well-defined molecular quantity. We can rewrite equation (38), taking into account the definition of 6 (see equation (35)) and the definition of the Chebyshev polynomials of the second kind U (cos 6) — sin[(n +l)0]/sin 6 as... 

For even indices, Unix) is an even function, therefore the transmittance is a symmetric function of energy. For u=l, r is constant and equals unity by definition, as we have mentioned. When n—2, we obtain ... 

The International Union of Pure and Applied Chemistry recommends that the definition should now be based on the ratio of the radiant power of incident radiation (Pq) to the radiant power of transmitted radiation (P). Thus, A = log(Po/P) = log T. In solution, Pq would refer to the radiant power of light transmitted through the reference sample. T is referred to as the transmittance. If natural logarithms are used, the quantity, symbolized by P, is referred to as the Napierian absorbance. Thus, B = ln(Po/P). The definition assumes that light reflection and light scattering are negligible. If not, the appropriate term for log(Po/P) is attenuance. See Beer-Lambert Law Absorption Coefficient Absorption Spectroscopy... 

One pharmacological theory of the mechanism underlying postural hypotension is the false-transmitter theory. Tyramine may be metabolized to an inactive metabolite (octopamine) that partially fills the NE storage vesicles with a false (inactive) transmitter, but definitive proof is lacking. 

Like presynaptic dopamine autoreceptors, presynaptic histamine autoreceptors are activated by the released endogenous transmitter to inhibit further histamine release, as shown by the increase in histamine release caused by antagonists at H3 receptors a definite piece of physiology. Evidence has been presented recently that cardiac postganglionic sympathetic neurons of the guinea pig synthesize and release histamine as a co-transmitter (Li et al. 2003 2006). These noradrenaline-histamine neurons possess H3 autoreceptors which, when activated, depress the release of both noradrenaline and histamine - unlike the D2-like autoreceptors of dopamine-neurotensin neurons which modulate the release of the two cotransmitters in opposite direction (see Section 2.2). It would be of interest to see whether, conversely, activation of ot2-autoreceptors inhibits the release of histamine in the guinea pig heart. 

Little research has focused on the differences in syrup composition by grade. While light transmittance is different (by grade definition), the trends in other aspects of syrup chemistry are not as simple. Two unpublished studies at the University of Vermont Proctor Maple Research Center show that there are no consistently predictable trends in bulk syrup chemistry related to grade (color class). 

The basic definition of reflectance, as used in colorimetry, is the ratio of the light flux reflected from a material to the light flux incident on the material. Reflectance involves accounting for all of the visible radiation in the system. This is in contrast to a reflectance factor, which is defined as the ratio of the light flux reflected from a material to light flux reflected from a standard material [23], Material standards of reflectance and transmittance are difficult to obtain. Reflectance, in particular, is difficult since the primary standard of reflectance is the perfect reflecting diffuser,... 

The purpose of a letter of transmittal is to refer to the original instructions or developments that have made the report necessary. The letter should be brief, but it can call the reader s attention to certain pertinent sections of the report or give definite results which are particularly important. The writer should express any personal opinions in the letter of transmittal rather than in the report itself. Personal pronouns and an informal business style of writing may be used. 

Here, A is the (decadic) absorbance e represents the molar (decadic) absorption coefficient, customarily expressed in dm /mol cm, equivalent to 1000 cm /mol c stands for the concentration in mol/dm and I for the thickness of the sample in cm. These definitions are not strictly in accordance with SI standards. Nevertheless, they are used in this book, because millions of data in these units are published. The transmittance or transmittance factor is given by r = /[Pg.17]

Figure 5.1-3a/b Definition of Iq and / for the determination of absorbance values from transmittance spectra. 

By carefully tuning and matching the probe and the various stages in the transmitter amplifier chain and by allowing for a wide rf bandwidth, it is possible to reduce phase transients (for a definition, see Haeberlen, 1976, Appendix D) to a level where their effect upon the m.p. spectrum becomes insignificant. We therefore confine ourselves here to study by simulations phase errors, nonuniform pulsewidths, and a power droop of the transmitter. 

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