Diffusion experiment

They then compared measured and predicted fluxes for diffusion experiments in the mixture He-N. The tests covered a range of pressures and a variety of compositions at the pellet faces but, like the model itself, they were confined to binary mixtures and isobaric conditions. Feng and Stewart [49] compared their models with isobaric flux measurements in binary mixtures and with some non-isobaric measurements in mixtures of helium and nitrogen, using data from a variety of sources. Unfortunately the information on experimental conditions provided in their paper is very sparse, so it is difficult to assess how broadly based are the conclusions they reached about the relative merits oi their different models. 

Protein molecules extracted from Escherichia coli ribosomes were examined by viscosity, sedimentation, and diffusion experiments for characterization with respect to molecular weight, hydration, and ellipticity. These dataf are examined in this and the following problem. Use Fig. 9.4a to estimate the axial ratio of the molecules, assuming a solvation of 0.26 g water (g protein)"V At 20°C, [r ] = 27.7 cm g" and P2 = 1.36 for aqueous solutions of this polymer. 

Heat Recovery and Seed Recovery System. Although much technology developed for conventional steam plants is appHcable to heat recovery and seed recovery (HRSR) design, the HRSRhas several differences arising from MHD-specific requirements (135,136). First, the MHD diffuser, which has no counterpart ia a conventional steam plant, is iacluded as part of the steam generation system. The diffuser experiences high 30 50 W/cm heat transfer rates. Thus, it is necessary to allow for thermal expansion of the order of 10 cm (137) ia both the horizontal and vertical directions at the connection between the diffuser and the radiant furnace section of the HRSR. 

Draxler, R. R., "A Summary of Recent Atmospheric Diffusion Experiments." National Oceanic and Atmospheric Administration Technical Memorandum ERL ARL-78. Silver Spring, MD, 1979. 

Most mutual diffusion experiments use Pick s second law, which permits the determination of D from measurements of the concentration distribution as a function of position and time ... 

It should be emphasized here that usual tracer diffusion experiments in LI2 ordered alloys due to diffusion of majority atoms mainly over their own sublattice do not give any of the strongly desired information about ordering kinetics. The study of order-order relaxations in contrast, yields a selective information Just about those atomic Jump processes which are related to ordering phenomena. 

The resolution of infra-red densitometry (IR-D) is on the other hand more in the region of some micrometers even with the use of IR-microscopes. The interface is also viewed from the side (Fig. 4d) and the density profile is obtained mostly between deuterated and protonated polymers. The strength of specific IR-bands is monitored during a scan across the interface to yield a concentration profile of species. While in the initial experiments on polyethylene diffusion the resolution was of the order of 60 pm [69] it has been improved e.g. in polystyrene diffusion experiments [70] to 10 pm by the application of a Fourier transform-IR-microscope. This technique is nicely suited to measure profiles on a micrometer scale as well as interdiffusion coefficients of polymers but it is far from reaching molecular resolution. 

Thus, for the investigation of buried polymer interfaces, several techniques with molecular resolution are also available. Recently NMR spin diffusion experiments [92] have also been applied to the analysis of a transition zone in polymer blends or crystals and even the diffusion and mobility of chains within this layer may be analyzed. There are still several other techniques used, such as radioactive tracer detection, forced Rayleigh scattering or fluorescence quenching, which also yield valuable information on specific aspects of buried interfaces. They all depend very critically on sample preparation and quality, and we will discuss this important aspect in the next section. 

However, it has been concluded from sorption and diffusion experiments that plutonium exists largely in the tetravalent state (53) and clearly not as Pu(V), in the intermediate pH-range under oxic conditions and at low carbonate concentration. This would be representative of many groundwaters and also in agreement with the calculated curves of Figure 2. 

In addition to giving conformational information, solid state NMR relaxation experiments can be used to probe the thermal motion of polymers in the hydrated cell wall (5). The motion of the polymers can give us clues as to the environment of the polymer. When there are both rigid and mobile polymers within a composite material, NMR spin-diffusion experiments can be used to find out how far apart they are. 

Huizenga, J. R., Grieger, P. F. Wall, F. T. (1950b). Electrolytic properties of aqueous solutions of polyacrylic add and sodium hydroxide. II. Diffusion experiments using radioactive sodium. Journal of the American Chemical Society, 72, 4228-32. 

Because of these factors, the fundamental experimental information about the interaction of metastable atoms with semiconductors and dielectrics is meant for the reflection coefficients that are determined with the aid of beam methods and for the coefficients of heterogeneous deactivation which are evaluated under diffusion conditions. However, the data in this event are fairly scarce and conflicting. The results obtained by the methods of electronic beams do not agree with diffusion experiments. Thus, Allison et al [ 137] report that the coefficients dealing with... 

The linearity, the pulse reproducibility and the stability of the complete system must be in the range of a few parts per million, otherwise image distortions or the wrong results in the diffusion experiments would be created. 

Figure 2. Spin-echo -NMR spectra from a diffusion experiment with a cubic phase of dDAVP (10%), MO (60%) and 2H20 (40%). Temperature 40 C, t=20 ms, A=24 ms, g=l 19 gauss/cm and 8=1.0,2.0..., 9.0 ms. The inset shows the aromatic region originating from dDAV P at a higher amplification. Also shown is the pulse sequence used in the NMR-diffusion method (see text for details).

Soil Thin-Layer Vapor Diffusion. An example of an autoradiogram obtained from a diffusion experiment is shown in Figure 2. The extent of diffusion of metolachlor, alachlor, and butylate is given in TABLE II. Butylate diffusion increased during the 24... 

NMRrelaxation and diffusion experiments provide important insights into both the internal molecular dynamics and the overall hydrodynamic behavior of unfolded and partly folded states. Local variations in backbone dynamics are correlated with propensities for local compaction of the polypeptide chain that results in constriction of backbone motions (Eliezer et al., 1998, 2000). This can occur through formation of... 

Following immersion of the glass slides in a 1.0 (w/v) BSA-BSA solution to a depth of 2.1 cm for 30 min at 21°C, the slides were thoroughly rinsed in PBS by dilution/displacement. The slides were then completely immersed in PBS, where they were kept for different lengths of time, i.e., for 1, 2, 4, and 16 hrs. Thereafter, the slides were removed and air-dried and placed on X-ray film between Lanex Intensifying Screens as described above. The supernatants from these diffusion experiments were then concentrated 10 times by evaporation in order to establish their radioactive content. 

In this chapter we will focus on molecular ordering and confinement effects in pores. Diffusion experiments with the pulse-field gradient method ([162-165] and references therein) and characterization of the surface properties using NMR of noble gases such as 129Xe ([166-171] and references therein), or 83Kr [172], will be omitted due to excellent reviews that have appeared quite recently in these areas. 

It is of considerable practical importance to have some idea of how far an atom or ion will diffuse into a solid during a diffusion experiment. An approximate estimate of the depth to which diffusion is significant is given by the penetration depth, xp, which is the depth where an appreciable change in the concentration of the tracer can be said to have occurred after a diffusion time t. A reasonable estimate can be given with respect to the root mean square displacement of the diffusing... 

Diffusion coefficients in amorphous solids such as oxide glasses and glasslike amorphous metals can be measured using any of the methods applicable to crystals. In this way it is possible to obtain the diffusion coefficients of, say, alkah and alkaline earth metals in silicate glasses or the diffusion of metal impurities in amorphous alloys. Unlike diffusion in crystals, diffusion coefficients in amorphous solids tend to alter over time, due to relaxation of the amorphous state at the temperature of the diffusion experiment. 

The fraction of vacancies in a crystal of NaCl, riy/N due to a population of Schottky defects, is 5 x 10-5 at 1000 K. In a diffusion experiment at this temperature, the activation energy for self-diffusion of Na was found to be 173.2 kJ mol-1. Determine the potential barrier that the diffusing ions have to surmount. 

The normal state of affairs during a diffusion experiment is one in which the concentration at any point in the solid changes over time. This situation is called non-steady-state diffusion, and diffusion coefficients are found by solving the diffusion equation [Eq. (S5.2)] ... 

Figure S5.1 Straight-line graph of In c versus x2 from a diffusion experiment The slope of the graph allows a value for the diffusion coefficient, D, to be determined.

Solutions for some diffusion experiment geometries (Fig. S5.2) are summarized in Table S5.1. In Figure S5.2a-S5.2c the initial concentration of the tracer is fixed, and the amount remaining as the diffusion progresses will diminish over the course of the experiment. In the other cases (Fig. S5.2d and S5.2e) the initial concentration at the surface is maintained as a constant throughout the experiment. 

For convenience, only one-dimensional random movement will be considered. In this case, an atom is constrained to jump from one stable site to the next in the x direction, the choice of +x or -x being selected in a random way.6 For example, imagine a diffusion experiment starting with a thin layer of N atoms on the surface of a crystal. 

Surprisingly, in a random-walk diffusion experiment, although the concentration of atoms in the initial layer always remains greater than in the bulk, it does not mean that these atoms have not diffused. They have taken just as many steps as those furthest from the starting layer ]... 

Table 5.5. Profile of concentrations CK (%) in the glass during a rhyolite-basalt diffusion experiment (Alibert and Carron, 1980).

Figure 5.11 Iqdari and Velde s (unpub. data) Ce diffusion experiment on apatite. Adjustment of the distance to the mineral surface as a function of Ce concentrations.

The test, theoretical relationship between the non-dimensional relative concentration (cRC), and the root time factor (r) may be seen in Fig. 5. Mohamed and Yong [142] analyzed the results obtained from the diffusion experiment shown in Fig. 5 a, b, using the information from solution of the equation above. The theoretical correlation in Fig. 5 c shows a linear relationship up to a relative concentration of 0.2 (80% equilibrium). At a relative concentration of 0.1 (90% equilibrium), the abscissa is used to determine the point on the experimental curve corresponding to a relative concentration of 0.1 (i.e., 90% of the steady state equilibrium time). 

However, we must keep in mind the limitations of this approach, especially the transfer of consistent sets of dispersion parameters to the propagation of air pollution in the vicinity of a source. The Gaussian plume formula should be used only for those downwind distances for which the empirical diffusion coefficients have been determined by standard diffusion experiments. Because we are interested in emissions near ground level and immissions nearby the source, we use those diffusion parameters which are based on the classification of Klug /12/ and Turner /13/. The parameters are expressible as power functions,... 

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