Slab sizes

Figure 4.6 Geometric effects at the electrochemical Ni(lll)/H20 interface for adsorbed H2O. Open symbols are for a five-layer slab and filled symbols for a three-layer slab hence, slab size is shown to not influence greatly the outcome of these calculations [Taylor et al., 2006a],...

Slab size 250t X 1950W X 9600L, maximum weight 30t... 

The above methods have been applied to the analysis of several water reflected critical slab assemblies (Table Q which varied widely in size, metal to water volume ratio, and fuel density. Each asseinbly consisted Of a uniform array of 1.1-in. square zirconium bundle boxes containing 0.9-in. wide fuel bearing Zircaliqr elements separated by water channels. Fuel bearing extensions were polled into a slab as the control rods were withdrawn. The slab size was such that the rod-free value Of keff (determined from extrapolated rod worths) exceeded unity by less than The fueled height of each assembly was 36 in. Activation shapes were measured with U-235-Zircaloy wires located in Zircaloy wands Inserted horizontally into the assembly through slots in the bundle box walls.. ... 

We discuss below the Nb(OOl) and Mo(001) surfaces as examples of bcc transition metal surfaces and the Pd(lll) surface as an example of an fee transition metal surface. As an illustration for chemisorption, we consider the case of hydrogen on the Pd(lll) surface. Except for the case of the Nb(OOl) surface which was done with a plane wave basis, the calculations were performed using the mixed basis method in a repeated slab geometry with slab size usually 7 to 11 atomic layers thick. 

Complete CO adsorption calculations were carried out using a slab with six layers of copper at the bulk geometry, oriented to expose the Cu(001) surface perpendicular to the z-axis, and periodic within the slab. Co-ordinates of the molecule were allowed to vary around a distance of 6 a.u. from the C and O atoms to the surface (i.e., little overlap). This slab size has been shown to be the smallest that adequately converges the physical properties under investigation in DFT-PBE studies. CO coverage was one molecule per face. 

Thus for equal-size spheres the force between them is just xn f/siab-siab(J ) d is directly related to the potential energy between two slabs [13]. This point is examined further in the problems at the end of the chapter. 

The siipercell plane wave DFT approach is periodic in tliree dimensions, which has some disadvantages (i) thick vacuum layers are required so the slab does not interact with its images, (ii) for a tractably sized unit cell, only high adsorbate coverages are modelled readily and (iii) one is limited in accuracy by the fonn of the... 

For flat samples such as press cured slabs the resistivity may be computed from the foUowiag formula where p = resistivity, R = resistance, A = area of the sample (the effective area of the smaller electrode if two electrodes of different sizes ate used), and t = thickness of the sample. 

Usually, particle size has relatively little effect on Raman line shapes unless the particles are extremely small, less than 100 nm. For this reason, high-quality Raman spectra can be obtained from powders and from polycrystalline bulk specimens like ceramics and rocks by simply reflecting the laser beam from the specimen surface. Solid samples can be measured in the 90° scattering geometry by mounting a slab of the solid sample, or a pressed pellet of a powder sample so that the beam reflects from the surface but not into the entrance slit (Figure 3). 

Slabs of narrow width beveled on edges (and sometimes radiused on faces). They are fitted longitudinally on large-sized pipes with face conforming closely to the circumference. 

Manufacturers of laboratory equipment feature special sinks and drains with high chemical resistance. Sinks made from slabs of Alberene stone, which were popular for many years, often had traps made of lead. The softness of lead made the traps hard to clean out, and the job required tender loving care with a wrench of just the right size. 

The installer engaged by the furniture supplier did a truly professional job. It was finished sooner than expected. There was some fear that the monolithic countertop slabs, which were pre-fabri-cated at the factory, might have size discrepancies. They did not, due to very careful measurements taken when the order was placed. The plumbing contractor chosen by the engineering firm did excellent work. The electrical contractor was pleased with the way circuits had been planned, and the planner in turn was highly satisfied with his installation. At the laboratory operator s request, all information regarding installation and maintenance was saved and later filed. The contractors admitted that this was not their common practice, but they were all in favor of it. 

The similarity of the results obtained for finite elusters and the infinite slab allows to eonclude in favour of the validity of the eluster model of adequate size (6 or 8 molybdenum atoms). In addition to the chemisorption of organic molecules on solid surfaces which is generally considered as a localized phenomenon, the interaction between molybdenum oxide and an adsorbate can also be represented by a loeal eomplex formed by a finite eluster and the adsorbed molecule. Indeed, the study of the evolution of the electronic properties as a funetion of the cluster size shows that, for a eluster eontaining 6 or 8 molybdenum atoms, most of the electronic properties converge towards limit values. This eonvergence is sensitive to the direction of the cluster growth. On the other hand, the electronic properties of the (001), (010) and (100) faces are not identieal, the type of surface atoms being different these results allow to predict that the characteristics of the chemisorption step will depend on the particular face on which it takes place. 

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