DPD method

During all membrane exposures, concentrations of halogens and chlorine dioxide were periodically monitored by "wet chemical methods". Halogens were determined by the DPD colorimetric method described in references [13] and [14]. Chlorine dioxide at reasonably high concentrations (>10 ppm) can be determined by direct colorimetry [] ]. The intrinsic green color appears to obey Beer s law. At lower concentration levels, this chemical is determined by the DPD method. 

The residual portion of the total chlorine in a cooling system after the chlorine demand has been satisfied by the addition of chlorine in some form. Usually a combination of hypochlorite ions (OC1 ) and hypochlorous acid (HOC1) and measured by diethyl-p-phenylene diamine(DPD) method. Operators frequently add chlorine once per day for several hours to provide a free chlorine reserve of 0.1 to 0.3 ppm. 

Table 1.2 Results of application of a generalized DPD method to different penetrants in PDMS.

For the DPD method, as for the factorial design example above, we used three input variables and a High , Medium and Low value to represent each input distribution. The values used to represent these ranges are listed in Table A2.5. In the DPD case, the High and Low values were calculated as the median values of the upper and lower 33rd percentiles of the lognormal distributions used to represent the variance of the input parameters. The Medium value was set at the median value of each input distribution. 

Figure A2.4 compares the CDFs for intake obtained from factorial design and DPD methods with the exact analytical solution for the CDF of intake. The 27 data points from the DPD and factorial methods were used to plot the empirical CDF shown in Figure A2.4. Figure A2.5 compares the CDF for intake obtained from 2000 Monte Carlo simulations with the exact analytical solution for the CDF of intake. Figure A2.6 compares the CDF obtained from 200 Latin hypercube sampling Monte Carlo simulations with the exact analytical solution for the CDF of intake. The Monte Carlo and Latin hypercube sampling empirical CDFs were plotted using all simulation outcomes.

Figure A2.4 Comparison of the CDFs for intake obtained from factorial design and DPD methods with the exact analytical solution for the CDF of intake and with the worst-case scenario...

Fig. 7.5 (a) Active chlorine concentration vs. specific charge in discontinuous experiments with varying chloride concentration, (b) 15 min values of total chlorine concentration, (rotating MIO anode, 300 rpm, Ti cathode, 300 mA, 20-22°C, 0.150L, 240 ppm sulphate + 10 ppm nitrate + 50 ppm carbonate, as sodium salts, DPD method)... 

Figure 7.6 was obtained by carrying out electrolysis experiments at extremely low chloride concentrations. Both curves show a tendency of chlorine formation and destruction in terms of a spectrophotometrical DPD signal. Even if there are some uncertainties with respect to the DPD method (see Sect. 7.3.3.7) these results support the second theory (2). 

It was demonstrated that water electrolysis generates mixed oxidant systems. Oxidation-reduction potential (Hsu and Kao 2004) is not the best parameter for system characterisation. In general, the online analysis of generated species is an unsolved problem. Probably, not all electrolysis products are known. This can be seen in analysing the active and total chlorine concentration. The standard method uses DPD but the effect of other chemicals on the DPD method is one reason that active chlorine is sometimes incorrectly measured. Amperometric analysis and... 

Bergmann, M.E.H. (2006d) On DPD method application for drinking water disinfection analysis (in German). GWF Wasser Abwasser 147, 780-786. 

A serious drawback of DPD is the absence of a drag force between the central particle and the second one orbiting about the first particle. The dissipative force Fd representing the dot product of differential velocities between interacting particles and their relative position vector is then equal to zero. This relative motion may produce a net drag only when many particles are participating at the same time (Espanol 1998). This cumulative effect requires more particles to be involved and reduces the computational efficiency of the DPD method. 

The Diverse Property-Derived method (DPD method) is based on the partitioning of six noncorrelated molecular descriptors and physico-chemical properties [Ashton, Jaye et al, 1996]. These are a lipophilicity descriptor (CLOGP), an electrotopological index calculated as normalized sum of the squares of the atomic electrotopological state indices, the number of hydrogen-bond acceptors (HBA), the number of hydrogen-bond donors (HBD), a flexibility index defined as the ratio of the —> Kier shape descriptors over k, and the aromatic density defined as the number of aromatic rings over the molecular volume (Table Cl). 

DPD method = Diverse Property-Derived method —> cell-based methods... 

Chlorine may be analyzed photometrically by the quantitatively detectable product of CI2 with N,N-diethyl-p-phenylenediamine (DPD-Method DIN EN ISO 7393-2). A comparable procedure based on DPD is suitable for CIO2. Specific methods are requested for the analysis of air (colored product of airborne CI2 in a tube with a special reaction layer Moosbach et al. 1999). 

Chlorine in water may be analyzed by several wet chemical methods, which include iodometric, amperometric, and V,V-diethyl-p-phenylenediamine (DPD) methods based on titrations. It may also be analyzed by colorimetric methods using DPD, syringal-dazine, or 4,4, 4"- methylidynetris(fV,fV-dimethylaniline(leucocrystal violet)). 

Recently, Yamamoto and Hyodo have employed the DPD method for studying Nafion membranes [20]. The systems considered in this study were built using two distinct molecular species, denoted comb-shaped polymer ip) and water (w). The polymer was presented as a branched sequence of beads. It consisted of a main chain (backbone) of iV = 20 effective monomer units (-CF2CF2CF2CF2 ) linked with rig = 5 short side chains of = 2 units [-0CF2C(CF3)F0 and F2CF2S03H] the total number of interaction sites in the macromolecule was Np= N/, + n xn = 30. A water-like particle was modeled as the same size as the units of the Nafion fragment (<7 = 6.1 A) and represented four water molecules. The x parameters were found using an atomistic calculation. The DPD simulation was performed for water volume... 

Of all the conventional analyti DPD method is unique in providing a procedures, not only for the various chlorine but for their mixtures with residuals including chlorine dioxide and ozone. The Analytical Reference Environmental Protection Agency (EPA first report published in 1969, cone best overall accuracy and precision DPD titrametric method."... 

For the data compiled and discussed in this paper, the Orthotolidine and DPD Methods were primarily utilized. The modified procedures were used for the separate determination of free chlorine and the combined forms (monochloramine, dichloramine and nitrogen trichloride). U.V. spectroscopy was applied for the qualitative determination of the presence of both free and combined forms of chlorine. The spectra were compared with data presented by Zimmerman and Strong (1957) for absorption in the range of 200-400 mu. 

MILLS This is primarily the DPD method. It s an orthotolidine method. 

Momentum-Conserving Thermostats and the Dissipative Particle Dynamics (DPD) Method... 

Fig. 8.10 Comparisons of velocity autocorrelation ftmction (VAF) of various numerical methods by using very small stepsize h = 0.01. Standard DPD methods with three different values of friction coefficient were calculated by using DPD-Sl method to compare with other methods. 100 different runs were averaged to reduce the sampling errors after the system was well equilibrated...

Since the seminal work of Hoogerbrugge and Koelman [1,2], there have been several contributions to clarify and strengthen the theoretical underpinnings of DPD. Espanol and Warren [3] showed that the DPD method is associated with a Fokker-Planck equation, and when the fluctuation-dissipation theorem is applied to derive an expression relating terms in the dissipative and random force components, the... 

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