Thermal decomposition and pore structure of pure and doped stannic oxide gel

The surface properties of a stannic oxide gel and its thermal dehydration products obtained both in vacuo and in the presence of air in the temperature range 100–600°C have been examined by N₂ adsorption. Phase and structural changes have been followed by differential thermal analysis and X-ray diffractometry. Complete pore structure analysis showed that samples dehydrated at or below 250°C were microporous. Above 250°C the pores were found to widen with increase of temperature, the widening occurring concurrently with the crystallisation process. Doping with cations of lower valency (Li⁺ and Al³⁺) than the host cation (Sn⁴⁺) had little effect on the pore structure and specific surface area for the low temperature samples (≤250°), whereas at higher temperatures, e.g. 600°C, it increased the specific area remarkably. The dope ions produce oxygen vacancies and hinder or retard sintering in SnO₂.     

The role of advertisements in the marketing of gated communities as a new Western suburban lifestyle: a case study of the Greater Cairo Region, Egypt

This paper examines the advertising themes and rhetoric that have been assembled in the marketing of the Greater Cairo Region’s (GCR) newly built gated communities. We demonstrate how place-marketing strategies, in this case, selling the Egyptian dream home, draws upon specific landscape offerings and values. It shows how aspects of globalization interact with processes of urbanization in the GCR to create new landscapes of housing consumption. The globalization of mass media has influenced consumption preferences and brought new consumption choices to the GCR’s residents. This study concludes that the demand for gated communities in the GCR, in large part, has been created by developers who foster an image of these areas as symbols of ‘modernism’ and Western lifestyles. Underlying these sales efforts is the common assumption held by developers, potential buyers and segments of the larger society that the lifestyles of Western urbanization should naturally emerge as the result of economic development.     

Performance evaluation of open-cycle solar regenerator using artificial neural network technique

Theoretical investigation on the performance of lithium chloride (LiCl) absorption cooling system using an artificial neural network (ANN) model is presented. Tabulated data from the literature are used to construct the ANN model. Solar collector desiccant/regenerator is applied to re-concentrate the working solution. Using the proposed model, the effect of system design parameters; namely regenerator length, and air flow rate on the performance of the system is demonstrated. The variation of the thermo-physical parameters along the regenerator length is highlighted.     

Environmental Messages in Multiple-family Housing: territory and personalization

The home and its private outdoor space may be characterized as primary territory. As such, it allows the occupants the opportunity to exert control over the activities and behaviours taking place. This paper examines how certain mechanisms are used to enhance or reflect residential territory and, thereby, promote one's sense of privacy, in the design of the adjoining outdoor spaces of homes in multiple-family housing in Abu-Nuseir, Jordan. Two surveys were conducted in Abu-Nuseir, comprising (1) a questionnaire and (2) a field inspection of the territorial marking and personalization of the immediate outdoor environment adjoining residential buildings. Occupants' use of actual and symbolic barriers as a means of manipulation and personalization is reviewed. Results suggest that the presence of actual and symbolic barriers is interpreted as a deterrent to intrusion and an indication of stronger occupant territorial attitudes. Territorial personalization in the environmental setting of multiple-family housing provides an ecological mechanism indicative of one's membership in a group and domain. Territorial features depend upon their inherent physical qualities, general symbolic meanings and the cultural milieu in which they exist.     

Radionuclide contamination of foods imported into Iraq following the Chernobyl nuclear reactor accident

Since early 1986, a monitoring program for radionuclides in imported foods has been carried out by the Iraqi Atomic Energy Commission. After the Chernobyl nuclear reactor accident in the Soviet Union, the program was expanded; our laboratory was officially designated by the Iraqi Government to measure radionuclide activity concentrations in foodstuff imported from countries known to be severely contaminated by Chernobyl radioactive fallout. Gamma-spectrometric analysis was used. Food items such as powdered milk, lamb meat, poultry, cereals and grains imported into Iraq before the Chernobyl accident did not contain any detectable fission products. However, all lamb meat, 81% of the lentil, 44% of the powdered milk and chick-pea, and 17% of the roast beef samples were contaminated with 137Cs or 134Cs and 137Cs. The highest 137Cs contamination levels found were 82, 147, 420, 6 and 4 Bq kg-1, respectively. Contamination by 134Cs was approximately 50% of the values given above.     

ISO 9000 Quality Standards in Construction

There is risk involved in any construction project. A contractor's quality assurance system is essential in preventing problems and the reoccurrence of problems. This system ensures consistent quality for the contractor's clients. An evaluation of the quality systems of 15 construction contractors in Saudi Arabia is discussed here. The evaluation was performed against the ISO 9000 standard. The contractors' quality systems vary in complexity, ranging from an informal inspection and test system to a comprehensive system. The ISO 9000 clauses most often complied with are those dealing with (1) inspection and test status; (2) inspection and testing; (3) control of nonconformance product; and (4) handling, storage, and preservation. The clauses least complied with concern (1) design control; (2) internal auditing; (3) training; and (4) statistical techniques. Documentation of a quality system is scarce for the majority of the contractors.     

Modeling and simulation of solar-powered liquid desiccant regenerator for open absorption cooling cycle

This paper presents the modeling and simulation of solar-powered desiccant regenerator used for open absorption cooling cycles. The input heat, which is the total radiation incident on an inclined surface, is evaluated via a solar radiation model in terms of the location, day of the year, and time of the day. Calcium Chloride (CaCl₂) is applied as the working desiccant in this investigation. The solar radiation model is integrated with the desiccant regenerator model to produce a more realistic simulation. A finite difference method is used to simulate the combined heat and mass transfer processes that occur in the liquid desiccant regenerator. The system of equations is solved using the Matlab-Simulink platform. The effect of the important parameters, namely the regenerator length, desiccant solution flow rate and concentration, and air flow rate, on the performance of the system is investigated. It has been found that the vapor pressure difference has a maximum value for a given regenerator length. It is also shown that for specified operating conditions, a maximum value of the coefficient of performance occurs at a given range of air and solution flow rates. Therefore, it is essential to select the design parameters for each ambient condition to maximize the coefficient of performance of the system.     

Terahertz Photon Mixing Effect in Gapped Graphene

We theoretically calculate the terahertz waves mixing effect in doped graphene with a finite bandgap. The temperature dependence of the nonlinear intraband optical response at bandgap opening of few tens of meV are investigated. When the external electric field is weak, a moderate level of bandgap opening is found to slightly enhance the nonlinear optical response. The optical response is however significantly altered under strong-field condition. The strong-field nonlinear optical conductivity exhibits two distinct response ‘hot spot’: (i) low temperature with large bandgap and (ii) high temperature with small bandgap. The electric field required for the nonlinear response to dominate over the linear response is typically in the order of 10⁴ V/cm. This value increases rapidly by a factor of 10 in large bandgap and high temperature regimes. Our results suggest that photon mixing effect in gapped graphene is strongly gapped dependent and hence the bandgap opening has to be carefully engineered in order to optimize the photon mixing effect in gapped graphene.     

A quantitative analysis of hydrogen production efficiency of the extreme thermophile Caldicellulosiruptor owensensis OL

Caldicellulosiruptor owensensis strain OL^T (DSM 13100) is an obligately anaerobic, extreme thermophilic bacterium that is capable of utilizing a broad range of carbohydrates and producing H₂ as a metabolic by-product. The performance of C. owensensis on glucose and xylose was analyzed in lab-scale bioreactors to assess its potential use in biohydrogen production. Acetate, H₂, and CO₂ were the main end products during exponential growth of the organism on either sugar. Lactate production was triggered during the transition into the stationary phase and was associated with an increase in the levels of specific l-lactate dehydrogenase activity. In addition, minor amounts of ethanol and propionate could be detected. H₂ and acetate yields were lower on xylose than on glucose, marking an opposite trend to biomass and lactate yields. The influence of elevated H₂ partial pressure on product distribution was more dramatic in xylose-fermenting cultures. Replacement of yeast extract in the medium with a standard vitamins solution improved H₂ yield on both sugars, where it reached 100% of the theoretical maximum, i.e. 4 mol per mol hexose, on glucose. By using the defined medium, both the maximum specific growth rate and the maximum volumetric H₂ production rate of C. owensensis increased significantly on glucose and almost doubled on xylose. Screening other sugars besides glucose and xylose revealed a clear sugar-dependent product-distribution pattern and a direct correlation between biomass and lactate yields, which might be explained considering energy metabolism of the cells. The organism is proposed as a new candidate for biohydrogen production at high yields.     

MODIFICATION OF ASPHALT BY CHEMICAL TREATMENT WITH SULPHUR

Abstract

The Theological properties of asphalt of different chemical compositions were assessed after treating them with sulphur at various reaction conditions. To correlate the observed alterations in the physical properties of the products with changes in the chemical composition, a study on model compounds was conducted to throw some light on this issue.