Structural features of AgCaCdMg2(PO4)3 and AgCd2Mg2(PO4)3, two new compounds with the alluaudite-type structure, and their catalytic activity in butan-2-ol conversion

AgCaCdMg₂(PO₄)₃ and AgCd₂Mg₂(PO₄)₃, two new compounds with the alluaudite-type structure, were synthesized by a solid state reaction in air at 750 °C. The X-ray powder diffraction pattern of AgCaCdMg₂(PO₄)₃ indicates the presence of small amounts of (Ca, Mg)₃(PO₄)₂ with the whitlockite structure, as impurity, whereas AgCd₂Mg₂(PO₄)₃ is constituted by pure alluaudite. The Rietveld refinements of the X-ray powder diffraction patterns indicate an ordered cationic distribution for AgCd₂Mg₂(PO₄)₃, with Ag on A(2)′, Cd on A(1) and M(1), and Mg on M(2), whereas a disordered distribution of Cd and Ca between the A(1) and M(1) sites is observed for AgCaCdMg₂(PO₄)₃. The catalytic properties of these compounds has been measured in reaction of butan-2-ol dehydrogenation. In the absence of oxygen, both samples exhibit poor dehydrogenation activity. All samples displayed no dehydration activity. Introduction of oxygen into the feed changed totally the catalytic behavior of the catalysts. The production of methyl ethyl ketone increases with time on stream and the reaction temperature. AgCaCdMg₂(PO₄)₃ is more efficient than AgCd₂Mg₂(PO₄)₃.     

Electrical properties of semimetallic and semiconducting alloys of Bi-Sb

Electrical resistivity studies have been carried out on three different Bi-Sb alloys in the temperature range 100–300 K. The observed behaviour of all the samples, in which one is semimetallic and other two are semiconductors, can be explained on the basis of the model presented for Bi-Sb energy bands at low temperature.     

Groundwater Rights and Legislation for Sustainable Development in Arid Regions: The Case of Saudi Arabia

The main objective of this article is to shed light on an important issue of water conservation-groundwater rights and legislation. Principles of groundwater rights are detailed and their applications to major aquifer systems, groundwater basins and wadis are discussed. Legislation and the clarification of water rights are vital for the sustainable development of groundwater. They are urgently needed in Saudi Arabia in particular and in all areas where demand exceeds supply. Legislation is one of the main pillars upon which any conservation policy is built. In this article a model is suggested for groundwater allocation in aquifers shared by more than one state.     

Prospects and challenges of using hydropower for electricity generation in Lebanon

In a region characterized by low water resources, Lebanon stands as an exceptional country in the Middle East. Several waterways present ample opportunity for utilization of hydropower. Before the civil war, several projects were undertaken to generate electricity through hydropower. A total installed capacity of 283 MW has aided Lebanon in supplementing its need of electricity from local renewable sources, thus reducing the overall bill of imported energy. The available hydropower generation constitutes currently 4–7% of the electricity generation depending on rainfall, with future plans expected to install another 205 MW of capacity. This use is in competition with water diversion for irrigation. Four different scenarios were analyzed to indicate the share of hydropower in the total production of electricity, with and without future irrigation and power projects, indicating that, by 2020, hydropower's share of electricity generation will vary between a maximum of 6.9% and a minimum of 1.2% depending on government plans regarding water use. Current value of potential energy available when water from the Litani river is used for hydropower is estimated to be around 20 cents per m³. Water uses planned should take this value into account.     

Effect of scale and corrosion inhibitors on well productivity in reservoirs containing asphaltenes

During oil production from several wells in Arabian Gulf area, significant productivity decline was noticed. One of the reasons behind the productivity decline might be asphaltene precipitation. Production data of the particular wells were collected and analyzed. It was found that many of these wells were injected with scale and corrosion inhibitors in downhole and surface equipment. Thus, it was desired to investigate the potential of formation damage due to asphaltene in the presence of scale and corrosion inhibitors as field chemicals. The effect of asphaltenes on the wettability, surface, and interfacial tensions were measured in the presence of scale and corrosion inhibitors. It was observed that the scale inhibitor did not indicate any alteration of the wettability, while the presence of corrosion inhibitor indicates high potential for wettability change into oil-wet conditions especially in the presence of asphaltenic oil. Similar results were obtained from the measurements of surface and interfacial tensions, in which corrosion inhibitors showed a significant decrease in surface and interfacial tensions. To assess the potential of asphaltene precipitation in the presence of both inhibitors and to study the effect of asphaltenes on the oil productivity, flooding experiments were carried out and oil/water relative permeability was determined.The results of flooding displacements showed that the presence of scale inhibitors indicates no effect on the oil/water relative permeability even in the presence of asphaltenes, while a significant decrease in oil relative permeability associated with an increase of residual oil saturation was observed in the presence of corrosion inhibitors.Mixture of scale and corrosion inhibitors showed no effect on relative permeability curves.     

Energy requirement of ultraviolet and AOPs for the post-treatment of treated combined industrial effluent

Post-treatment was carried out to eliminate the colour and COD of treated combined industrial effluent. Ozonation at a dose of 300 mg/h for 10 min resulted in 100% colour and 96% COD removal at pH 8 and temperature 25 °C. The application of UV/H₂O₂ resulted in 91% colour and 82% COD removal. 79% colour and 60% COD removal was obtained with the Fenton process after 60-min treatment in the presence of 170 mg/l H₂O₂, while the photo-Fenton process showed an almost complete elimination of both parameters. Electrical energy consumption showed that the photo-Fenton resulted in the highest removal efficiency with 95% removal in terms of colour and COD abatement rates. The electrical energy requirements of the tested processes followed the increasing order UV/Fe/H₂O₂ < O₃ < UV/H₂O₂ < UV.     

Taxonomy of interpolation constraints on recursive subdivision curves

Published online: 14 May 2002     

Comparison of Gelation Mechanism of Surimi between Heat and Pressure Treatment by Using Rheological and NMR Relaxation Measurements

ABSTRACT: The stress-relaxation and nuclear magnetic resonance (NMR) proton spin-spin relaxation time (¹H T₂) measurements were performed to elucidate the gelation mechanism of heated and pressurized surimi gels. Numerical inverse Laplace transformation of the stress-relaxation data showedlarge distributions of stress-relaxation times and the Kohlrauch-Williams-Watts (KWW) equation described well the stress-relaxation process for each gel. NMR measurement gave information about the content of the exposed protein surface. From these results it is considered that the heat treatment induces the denaturation and re-aggregation of protein, which contribute to the formation of strong network structure. On the other hand, the pressure treatment contributes to the formation of weak cross-links made by the aggregation of protein in native form.