Constant background

Direct analysis with the fluoride lon-selective electrode requires addition of total ionic strength adjustor buffer solution (TISAB) to the standard and to unknown samples Some advantages of this addition are that it provides a constant background ion strength, ties up interfenng cations such as aluminum or iron, which form a complex with fluoride ions, and maintains the pH between 5 0 and 5 5 According to the manufacturer s claim, reproducibility of direct electrode measurement IS 2 0%, and the accuracy for fluonde ion measurement is 0 2% [27]... 

To establish the well drainage boundaries and fluid flow patterns within the TFSA-waterflood pilot, an interwell chemical tracer study was conducted. Sodium thiocyanate was selected as the tracer on the basis of its low adsorption characteristics on reservoir rocks (36-38), its low and constant background concentration (0.9 mg/kg) in produced fluids and its ease and accuracy of analysis(39). On July 8, 1986, 500 lb (227 kg) of sodium thiocyanate dissolved in 500 gal (1.89 m3> of injection brine (76700 mg/kg of thiocyanate ion) were injected into Well TU-120. For the next five months, samples of produced fluids were obtained three times per week from each production well. The thiocyanate concentration in the produced brine samples were analyzed in duplicate by the standard ferric nitrate method(39) and in all cases, the precision of the thiocyanate determinations were within 0.3 mg/kg. The concentration of the ion in the produced brine returned to background levels when the sampling and analysis was concluded. 

The basic features of this model have already been stated. The positive charge on the ion cores is smeared out into a constant background charge, which drops abruptly to zero at the metal surface. Using the... 

In this method, an entire calibration curve is measured for the primary ion in a constant background of interfering ion. aj(BG) is the activity of the constant interfering ion in the background. afiDL) is the low detection limit (LDL) of the Nernstian response curve of the electrode as a function of the primary-ion activity. In the mixed interference method the selectivity is calculated from the following equation ... 

Quantum Free-Electron Theory Constant-Potential Model, The simple quantum free-electron theory (1) is based on the electron-in-a-box model, where the box is the size of the crystal. This model assumes that (1) the positively charged ions and all other electrons (nonvalence electrons) are smeared out to give a constant background potential (a potential box having a constant interior potential), and (2) the electron cannot escape from the box boundary conditions are such that the wavefunction if/ is... 

Figure 3.6. Plot of energy E versus wavenumber k (a) for a free electron moving in a constant background potential and (b) for an electron moving in a periodic field in an one-dimensional crystal, (c) The energy bands for (b).

Note that this identity clearly shows that (dz/dx)y (dz/dx)e, i.e., that the variable held constant matters in these derivatives (Strictly speaking, a lazy notation such as dz/dx has no meaning whatsoever ) Although the inconvenient notation of partial derivatives makes it somewhat tedious to keep the inactive (constant) background variables in mind, it is important from a physical and pedagogical standpoint that this be done as carefully as possible. (The tedium of this notation is avoided in the geometrical thermodynamics to be presented in Part III.)... 

Since the power at zero frequency, X[0] 2, merely adds a constant background without much information content, the requirement for maximum excitation power P+ at positive frequencies is... 

Figure 4.2 Visual explanation of the effect of the constant background phase shift 8b on the resonance profile as a function of the phase shift 8(E) when it increases from 8b to 8b + jt. The partial-wave cross section 07(E) proportional to sin2 8(E) shows a symmetric peak for 8b = 0 and a symmetric dip for 8b = rr/2 since d<5(E)/d is symmetric with respect to Er, and an asymmetric profile with a peak and a dip for 8b = 7t/4. See text.

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