Lower Coverage Ratio Research Articles

Urban types in rapidly urbanising cities - a typological approach in the analysis of urban types in Dar es Salaam

One of the challenges confronting rapidly urbanising cities is the fact that these cities are growing at unprecedented rates, sizes and densities. Besides, growth in these cities is largely unregulated. It has been observed by Habitat (1996) that cities have grown in at least four major ways namely; their size, spatial organisation, distribution of public services and employment base. While this situation can be related to global urbanization processes, the general poor knowledge on how these cities develop, densify, or acquire certain physical characteristics and how to characterize built environments has limited affective urban management and governance. Cities have sprawled to the extent that the negative externalities associated with horizontal growth undermines the functionality and efficiency in terms of service provision and land utilisation. Land underutilisation has been manifested even in some of the prime locations of the cities. The concept ‘urban types' has been employed to refer to sections of the built environment having a common set of physical characteristics in terms of house forms, density as depicted by number of storeys, land coverage and floor area ratios. An attempt to identify, classify and analyse urban types within the context of Dar es Salaam city is being made. It is notable from this characterisation that apart from urban types that constitute the core of the city, the immediate built environments reveal low density, low-rise house types and low land coverage and floor area ratios that have contributed to the sprawled city structure of Dar es Salaam. Journal of Building and Land Development Vol. 13 (2) 2006: pp. 1-21

The adsorption of zinc dialkyldithiophosphates on partially stabilized zirconia from hydrocarbon solution

Kinetics, isotherms and enthalpy of adsorption of zinc di-n-alkyl(di-n-alkylphenyl, di-n-dialkylphenyl)dithiophosphates (ZDTPs) lubricating oil additives on zirconia partially stabilized by yttria (PSZ) powder from hydrocarbon solution at temperatures 25 °C and 35 °C were done. The adsorption enthalpy has been determined using a Montcal calorimeter. ZDTP adsorption isotherms are Langmuir-like. The adsorption quantities and differential molar enthalpies $$\left(\Delta H_{\rm d}^{\rm a}\right)$$ of ZDTPs adsorption on PSZ are low for n-alkyl derivatives, the adsorption decreases with the increasing length of the hydrocarbon chain of the additive ZDTP, the unexpectedly for di-n-propyl ZDTP the differential molar enthalpies of adsorption at 25 °C are very low, near zero and for di-n-dialkylphenyl ZDTP only at lower coverage ratios are endothermic, at higher surface coverage for this and remaining additives are exothermic. At 35 °C all n-alkyl ZDTPs adsorb on PSZ endothermically endothermic, while both aryl ZDTPs exhibit exothermic effects. All ZDTPs are reversibly physisorbed at 25 °C and at 35 °C except for both mono- and dialkylphenyl ZDTPs, which are weakly chemisorbed.

The Impact of Debt-Equity Reporting Classifications on Firms' Decision to Issue Hybrid Securities

We test the influence of classification of securities into liabilities and equity on firms’ financing choices, using as our setting the change in reporting classification of hybrid securities following SFAS 150. We find that this change affected the decision of firms to issue mandatorily redeemable preferred shares (MRPS). Following the requirement that firms classify the debt-like hybrid security MRPS as a liability, the share of MRPS issuances in firms’ new financing declined. Characteristics of firms issuing MRPS also changed. While prior to SFAS 150 firms with higher levels of debt and lower coverage ratios chose to issue MRPS and not debt, after its adoption, the decision to issue MRPS is no longer related to firms’ pre-existing debt and coverage levels. Furthermore, our results indicate that before SFAS 150 managers were willing to bear the higher issuance fees of MRPS and chose to issue these debt-like hybrid securities over cheaper debt. The requirement to classify debt-like hybrids as a liability took away the reporting incentives for issuance and made these securities a less popular financing vehicle.

Free-energy of adsorption of a cationic surfactant onto Na-bentonite (Iran): inspection of adsorption layer by X-ray spectroscopy

The adsorption behaviour of hexadecylpyridinium bromide (CPB) onto bentonite was studied as a function of temperature under optimized condition of shaking time, and concentration of the adsorbate. Thermodynamic parameters such as Δ H°, and Δ S° were calculated from the slope and intercept of the linear plot of log K d against 1/ T. Based on the calculation of the thermodynamics of adsorption, it is evident that the principal contribution to the Δ G° of negative value (−10 to −14 kJ · mol −1) is the large positive value of Δ S° (58–60 J · K −1 · mol −1), whereas Δ H° is positive and in the range of 4–8 kJ · mol −1. Analysis of adsorption results obtained at temperatures (288, 297, 303, 307, 313) K showed that the adsorption pattern on bentonite followed the Langmuir isotherm. The Langmuir sorption maximum at different temperatures for CPB sorption are reported (1100 to 1534 mmol · kg −1). The adsorption of the cationic surfactant CPB on a hydrophilic smectite (bentonite) surface has also been investigated, especially in the range of low coverage ratios where surfactant ions are adsorbed through cation-exchange with the counterions of the clay. The intercalation of surfactant in the interlamellar space was followed by X-ray measurements. At low surfactant concentrations, there is a peak corresponding to d 001 of 1.32 nm, and after full coverage at about 1.5 CEC (cation-exchange capacity) value, two peaks are seen corresponding to interlamellar distances of both (2.0 and 3.8) nm. Fluorescence spectroscopy was used to obtain information about the adsorption layer of HDTMA at the interface.

Influence of poly(methyl methacrylate) impregnation ratio on the surface properties of fumed silica and on the glassy temperature of poly(methyl methacrylate) using inverse gas chromatographic analysis

The surface properties of poly(methyl methacrylate) (PMMA) impregnated fumed silicas, in a large range of impregnation ratios, were examined using inverse gas chromatography at infinite dilution. It was observed that the dispersive component γ s d does not decrease monotonously with the impregnation ratio. Two critical coverage ratios were evidenced corresponding at first to the shielding of the most energetic sites and then to the achievement of total coverage of the silica surface. The influence of the coverage ratio on the glassy temperature ( t g) of the adsorbed PMMA was also studied, which was evidenced down to a very low coverage ratio (1 monomer unit/nm 2).

Adsorption of a Cationic Surfactant on Na–Montmorillonite: Inspection of Adsorption Layer by X-Ray and Fluorescence Spectroscopies

The adsorption of the cationic surfactant BDDAC on a hydrophilic smectite (montmorillonite) surface has been investigated, especially in the range of low coverage ratios where surfactant ions are adsorbed through cation-exchange with the counterions of the clay. The surfactant coions (Cl−) were found to be adsorbed simultaneously with the cationic part after a complete alkyl ammonium ion-exchange of montmorillonite (CEC). We observe that organoclay particles remain flocculated in aqueous medium in almost all the range of adsorption isotherms up to 1.38 CEC and afterward redisperse incompletely. The intercalation of surfactant in the interlamellar space was followed by X-ray measurements. Fluorescence spectroscopy was used to obtain information about the adsorption layer at the interface. A calculation from geometrical considerations and from adsorption isotherms shows that below 1.38 CEC, there is a flat double layer in the interlamellar space and after this amount of adsorbed surfactant, an interstratified clay-surfactant mixed system is formed.

Adsorption of A Multifunctional Additive (ZnDTC) Onto Iron and Iron(III) Oxide from n-Decane

The adsorption of zinc diisooctylodithiocarbamate (ZnDTC) onto iron and iron(III) oxide from n-decane solution was studied. The adsorption isotherms were determined together with the variation of the apparent differential molar enthalpy of displacement for ZnDTC on both adsorbents at 298 K. The shapes of the iostherms for the adsorption of dithiocarbamate on iron and iron(III) oxide are quite different, especially in the low coverage ratio. The corresponding differential molar enthalpies of displacement for the two studied systems are exothermic. On iron, the very high exothermic values indicate a process of ZnDTC chemisorption, while on iron(III) oxide, the much lower enthalpic effects are characteristic of physisorption.

Bankruptcy Costs and the Financial Leasing Decision

The theory of financial leasing views financial leases as substitutes for secured debt. Empirical studies have reported a high positive correlation between lease ratios and debt ratios and that lessors earn higher rates of return than lenders. These results contradict traditional leasing theory. They are explained in this paper by recognizing the role bankruptcy costs play in the lease/borrow decision and the nature of the assets to be acquired by a firm. Leasing is shown to involve lower bankruptcy costs than borrowing. Our empirical analysis shows that lessee firms have lower retained earnings relative to total assets, higher growth rates, lower coverage ratios, higher debt ratios, and higher operating risk than non-lessee firms. Lessee firms also have significantly lower Altman Z-scores, a measure of bankruptcy potential. Overall, our results indicate that as bankruptcy potential increases, lease financing becomes an increasingly attractive financing option. We also find evidence to support an industry clientele effect in financial leasing.

The adsorption of polyoxyethylenated octyl and nonylphenol surfactants on carbon black and sulfur from aqueous solutions

The adsorption of nonionic surfactants from water solutions on the hydrophobic surfaces of sulfur and carbon black has been investigated. The isotherms and calorimetric experiments were also carried out after characterization of the solid particles. The isotherms of adsorption show the existence of a saturation plateau. The adsorption quantity depends on the length of polar and aliphatic chains. Calorimetric investigations of adsorption on the carbon black indicate the existence of considerable energetic heterogeneity. At low coverage ratios the enthalpy of adsorption is very high and exothermic. Subsequently it becomes progressively weaker and reaches the value of zero at θ = 0.

European Water-Cooled Lithium-Lead Blanket Designs for a Demo Reactor

Within the framework of the European DEMO blanket study programme, CEA and the JRC of ISPRA develop a water cooled lithium-lead blanket concept. Considering the low breeding coverage ratio of the DEMO-1 reactor configuration currently specified in the E-C programme, the use of beryllium was envisaged in order to reach the tritium self-sufficiency which corresponds to an equivalent tridimensional Tritium Breeding Ratio (TBR) above 1.05. This beryllium is either directly immersed in the liquid metal (Pb-17Li) or completely separated from it.