Oxygen density

FIG. 4 Normalized oxygen density profile perpendicular to the surface from simulations of pure water with adsorption energies of 12, 24, 36, and 48 kJ/mol (from bottom to top). The lower curves are shifted downwards by 0.5, 1.0, and 1.5 units. The inset shows the height of the first (diamonds) and second peak (crosses) as a function of adsorption energy. Water interacts with the surface through a Morse potential. (From Ref. 98.)... 

C05-0135. Liquid oxygen, used in some large rockets, is produced by cooling dry air to -183 °C. How many liters of dry air at 25 °C and 750 torr would have to be processed to produce 150 L of liquid oxygen (density =1.14 g/mL) ... 

The 630 nm band, on the other hand, shows no significant intensity variation when the foreign-gas density is varied an oxygen density squared behavior is observed regardless of the presence and concentration of the admixtures. This band arises from simultaneous transitions of both molecules of the O2-O2 complex. In this case, an O2 molecule cannot be replaced by a foreign gas particle without losing the band, or perhaps shifting it to a different part of the spectrum. 

Figure 17. Transverse and time average of the hydrogen and oxygen densities for (top) a < 0 and (bottom) a > 0, as a function of distance from the center of the slab. From Ref. 52, by permission.

Values of the parameters are given in Ref. 70.) The results of Ref. 35 showed that the wall induced a significant water-water repulsive force when two particles were simultaneously near the wall. To reproduce this effect in our classical simulation, we included an extra repulsion from the wall for oxygens that are close to one another. The parameters of this multibody force were adjusted so that the classical simulation reproduced the oscillations in the oxygen density which were obtained from the less phenomenological... 

Here r is the magnitude of the projection of the vector r — f2 between oxygens onto a plane parallel to the metal walls, and z and zz are the distances of oxygens 1 and 2 from the wall. Values of the parameters appear in Ref. 69, where the resulting oxygen densities from the classical and direct dynamics simulations are compared. While the densities are rather similar, the potential distributions are not, as emphasized above. 

Figure 20. Calculated oxygen density around the cuprous ion using the potential from first principles calculations as described in the text. From Ref. 69, by permission.

Ballard assembles and tests stacks, to confirm their characteristics and optimise such water management problems as electrolyte humidity control and cathode water removal, via wettable materials in the porous electrode, to the external air flow. Potential difficulties, exclusive to the water-producing PEFC, can be seen with 100% humidity in the tropics, and with freezing conditions in cool climates. High altitudes can be difficult for all fuel cell types, via low oxygen density. 

This system displays (Fig. 1.9) a traditional interfacial oxygen density profile that has been the object of measurement (Pratt and Pohorille, 2002), monotonic with a width 2-3 times the molecular diameter of a water molecule. This widthis somewhat larger than that of water-alkane liquid-liquid interfaces, though it is still not a broad interface. The enhanced widthis probably associated withroughness of the stationary alkyl layer the carbon density profile is shown in Fig. 1.9 as well. 

Figure 1.9 Carbon- and water-oxygen interfacial densities as a function of z. The dashed and solid lines indicate the observed carbon and oxygen densities, respectively, at 300 K determined from molecular simulation. The disks plot the water-oxygen densities reconstmcted from the proximal radial distribution function for carbon-oxygen (see Fig. 1.2), averaged over alkyl chain conformations sampled by the molecular simulation. The interfacial mid-point (z = 0) is set at the point where the alkyl carbon- and water-oxygen densities are equal. See Figs. 1.1 and 1.2, p. 7.

Consider now the mean oxygen density conditional on a specific alkyl configuration. Since that conditional mean oxygen density is less traditionally analyzed than the density profile shown in Fig. 1.9, we exploit another characterization tool, the proximal radial distribution (Ashbaugh and Paulaitis, 2001). Consider the volume that is the union of the volumes of spheres of radius r centered on each carbon atom see Fig. 1.10. The surface of that volume that is closer to atom i than to any other carbon atom has area fl, (r) with 0 < ff, (r) < 4tt. The proximal radial distribution function ( ) is defined as... 

Figure 1.10 Geometrical quantities in defining the proximal radial distribution function gp j(r) of Eq. (1.14). The surface proximal to the outermost carbon (carbon /), with area fi, (r) r, permits definition of the mean oxygen density in the surface volume element, conditional on the chain configuration p gprox ( )-...

The oxygen density distribution around H shows many interesting features. There are two oxygen atoms coordinating the H, and an observation volume... 

Figure 2 Spatial distribution functions displayed as three-dimensional maps showing the local oxygen density in liquid water. Above TIP4P water at ambient conditions Below PPC water along the co-existence line at 2U0 C. The iso-surfaces shown are for — 1.3 where the surfaces have been cf)k>ied according to their separation from the central molecule, as discu.sse

Figure 5 Oxygen-oxygen spatial distribution functions g r) for a 3 1 water-methanol solution at 25 °C. Above Water-water correlations for g f) = 2.0. Below Methanol-oxygen density around water for an iso-surface threshold of 1.75.

Figure 7 Abox>e Thr -dinw nsional map of the local oxygen density around luethylamine in an 18 1 mixture of water and metliylamine at 25 The surfaces show n correspond to 2.5 times the bulk value. Below Spatial distribution functions for water oxj gens (red), acetonitrile nitrogens (blue) and methyl groups (green) around a w ater molecule in an equimolar mixture of water and acetonitrile.

Figure 8 Three dimensional map of the local oxygen density around a benzene molecule in an aqueous benzene solutions. The density thresholds shown, black, gray and light-gray, are 5.0, 3.0 and 2.5 times the bulk density, respectively.

Figure 11. Free energy profile AA(z) for Na+ and Cl ions at the vacuum/ice basal plane interface at T = 225 K. In lower frame the oxygen density profile is shown.

The value of this ratio is close to one over most of the stratosphere during daytime, but increases rapidly above 40 km because of increasing atomic oxygen densities. At night, NO is quickly converted to NO2 up to altitudes of about 60 km. Figure 5.38 shows calculated one-dimensional model distributions of the various nitrogen species. The curves represent a steady state solution for average solar insolation. 

Fig. 7. Oxygen density profile from a 50 ps simulation of 385 water molecules that are confined on the left side by a simple (9-3) Lennard-Jones potential [137] and on the right side by 4 layers of mercury with a (111) surface structure.

Spohr investigated the dependence of the shape of the oxygen density profiles on the adsorption energy [56]. The model contains a simple scaling parameter. Do, that determines the adsorption energy (see Eq. (7) and Eq. (8)). 

Fig. 10. Oxygen density profiles from lOOps simulations of 700 water molecules between mercury surfaces with (111) surface structure in homogeneous external electric fields. The surface charge density (in units of pC cm ) is indicated.

Figure 16 shows the orientational distribution of the molecular dipole moment relative to the surface normal in various distance ranges from the Pt(lOO) (left) and the Hg(lll) surface (right). Additionally, the reduced oxygen density profile is plot-... 

Fig. 19. Top Number of neighbors kn and number of hydrogen bonded neighbors nns (for definition see text) as a function of the distance c from the surface for TIP4P water near Pt(lOO) (dashed) and near Hg( 111) (full). Bottom the oxygen density profiles near Pt( 100) (dashed) and Hz( 111) (full).

---