Structural layer coefficients

The structural layer coefficients (a,) are necessary to convert actual layer i thickness (D,-) into layer i structural number (SN,) using the following empirical relationship  

For the determination of the asphalt concrete structural coefficient, the methodology recommends the elastic (resilient) modulus ( ac) 20°C to be less than 450,000 psi 

As it can be seen, the structural layer coefficients for the granular base or sub-base layers may be derived from different laboratory tests including resilient modulus (Egg or sb)-Similarly, the structural layer coefficients for the cement-treated bases or bituminous-treated bases may be derived from unconfined compressive strength or Marshall stability, respectively, including elastic modulus. 

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The structural layer coefficients (afj depend on the type and function of layer material. These are asphalt concrete, granular base, granular sub-base, cement-treated and bituminous base. In order to estimate the structural layer coefficients, different charts have been developed. A sample of charts for asphalt concrete and granular base is shown in Figures 13.8 and 13.9. For other materials such as lime, lime fly ash and cement fly ash, the methodology suggests each agency to develop relevant charts. 

Figure 13.8 Chart for estimating structural layer coefficient of dense-graded asphalt concrete (o,) based on the elastic (resilient) modulus. (From AASHTO, AASHTO Guide for Design of Pavement Structures, Washington, DC American Association of State Highway and Transportation Officials, 1993. With permission.)...

It should be pointed out that the NBF equivalent thickness hw is 7.6 nm while after Cei,cr, hw = 8.1 nm. The small difference in NBF thickness cannot be treated quantitatively but is an indications that there is no free aqueous core in the NBF. Assuming the three-layer film structure, refraction coefficient of tetradecane ri = 1.43, and, refraction coefficient of water, m = 1.33, on the basis of X-ray diffraction, neutron scattering and NMR data [289], we obtain hi = 1.6 nm. Hence, h2 = 3.8 nm and the total film thickness h2 + 2h equals 7.0 nm. This value is close to the results obtained by a completely different method for the thickness of two hydrated dipalmitoyl phosphatidylcholine monolayers - 6.8 nm, reported by Marra [290]. 

There has been some work on the electrical characterisation of transparent p-type conductors, particularly Cul and CuSCN (Tennakone et al, 1998a, b). However, the characterisation focused on continuous thin films rather than on structured layers. For CuSCN, HaU mobilities of the order of 20 cm V s have been reported and similar values were found in Cul films (Rost, 1999), indicating that both materials are well-suited for device applications. So far, however, solar cells involving these materials with efficiencies beyond have not been reported. Both materials, CuSCN and Cul, have rather high diffusion coefficients for Cu diffusion. These findings raise the question if stable devices can be fabricated, or if Cu migration and diffusion effects may render thin-film devices inherently instable. 

RETORT CALCULATION During the retort process we assume that no oxygen is present so that only water transport is considered. At retort temperatures the diffusion coefficient of water in materials of interest is sufficiently high so that a pseudo-steady-state model, in which linear profiles are assumed across all structural layers, can be used. The EvOH layer is assumed to be at a uniform water activity at a given time which is good assumption based on water permeability measurements in EvOH at humidities found in package applications (13 ). 

Properties of the materials and layers, expressed in resilient modulus or subgrade, Mr or moduli for sub-base, sb> base, d asphalt layers constructed from asphalt concrete, Ef cy belong to the third category. The structural performance of each layer is expressed in layer coefficients (a, a2, etc.). 

A number of substances such as graphite, talc, and molybdenum disulfide have sheetlike crystal structures, and it might be supposed that the shear strength along such layers would be small and hence the coefficient of friction. It is true... 

Individual Coefficient of Heat Transfer Because of the comphcated structure of a turbulent flowing stream and the impracti-cabifity of measuring thicknesses of the several layers and their temperatures, the local rate of beat transfer between fluid and solid is defined by the equations... 

Cathodoluminescence microscopy and spectroscopy techniques are powerful tools for analyzing the spatial uniformity of stresses in mismatched heterostructures, such as GaAs/Si and GaAs/InP. The stresses in such systems are due to the difference in thermal expansion coefficients between the epitaxial layer and the substrate. The presence of stress in the epitaxial layer leads to the modification of the band structure, and thus affects its electronic properties it also can cause the migration of dislocations, which may lead to the degradation of optoelectronic devices based on such mismatched heterostructures. This application employs low-temperature (preferably liquid-helium) CL microscopy and spectroscopy in conjunction with the known behavior of the optical transitions in the presence of stress to analyze the spatial uniformity of stress in GaAs epitaxial layers. This analysis can reveal,... 

Lateral density fluctuations are mostly confined to the adsorbed water layer. The lateral density distributions are conveniently characterized by scatter plots of oxygen coordinates in the surface plane. Fig. 6 shows such scatter plots of water molecules in the first (left) and second layer (right) near the Hg(l 11) surface. Here, a dot is plotted at the oxygen atom position at intervals of 0.1 ps. In the first layer, the oxygen distribution clearly shows the structure of the substrate lattice. In the second layer, the distribution is almost isotropic. In the first layer, the oxygen motion is predominantly oscillatory rather than diffusive. The self-diffusion coefficient in the adsorbate layer is strongly reduced compared to the second or third layer [127]. The data in Fig. 6 are qualitatively similar to those obtained in the group of Berkowitz and coworkers [62,128-130]. These authors compared the structure near Pt(lOO) and Pt(lll) in detail and also noted that the motion of water in the first layer is oscillatory about equilibrium positions and thus characteristic of a solid phase, while the motion in the second layer has more... 

As expected from their structures, the elements are poor conductors of electricity solid F2 and CI2 have negligible conductivity and Br2 has a value of 5 X 10 ohm cm just below the mp. Iodine single crystals at room temperature have a conductivity of 5 x 10 ohm cm perpendicular to the be layer plane but this increases to 1.7 x 10 ohm cm" within this plane indeed, the element is a two-dimensional semiconductor with a band gap g 1.3eV (125kJmol" ). Even more remarkably, when crystals of iodine are compressed they become metallic, and at 350kbar have a conductivity of 10" ohm" cm", The metallic nature of the conductivity is confirmed by its negative temperature coefficient. 

The crystal quality of the InGaN QWs becomes poor mainly due to the lattice-constant mismatch and the difference of the thermal expansion coefficient between InN and GaN with increasing the In composition [4,5]. Therefore, in order to improve the external quantum efficiency (i/ext) of the InGaN-based LEDs and LDs, it is important to elucidate and optimize the effects of the various growth conditions for the InGaN active layer on the structural and optical properties. Recently, we reported a fabrication of efficient blue LEDs with InGaN/GaN triangular shaped QWs and obtained a substantial improvement of electrical and optical properties of the devices [6,7]. 

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