Urban structures for lower-cost housing projects

The use of computers in the analysis and design of individual structures is known and widely used in practice. There are many operational computer programs such as ICES-STRUDL, ELAS, NASTRAN, WANG, and others which are readily available at the computation centers around the world. These programs are able to perform the analysis, either by direct stiffness method or by finite element technique of various structures and some of these programs will carry the study into complete design. The profession of structural engineering is fortunate to have an access to such a wealthy software library.The theme of this paper is not to deal with any individual computer program applicable to a particular structural unit, but to integrate the analysis and design computer programs with the total analysis and design of a housing project in an urban area. This concept defines an INTEGRATED SYSTEMS APPROACH to total analysis and design. The value of this approach stems from the fact that a structural engineer can not develop an efficient design for a structure in an urban project unless he is fully aware of all pertinent factors which are related to his structural unit. The Integrated Systems Approach will secure an optimum design for the project.Since one of the major concerns of our civilization is the provision of decent lower-cost housing for every citizen, structural engineers need to participate in this great endeavor by extending the application of their technical knowledge to its solution. Due to the size and complexity of the problem, the use of the computers is imperative. The Integrated Systems Approach is defined by a set of individual computer programs linked together. The structural analysis and design programs incorporated in this system use the data generated by the other general project study programs. It is obvious that the structural programs form the major part of the programming system. The Integrated Systems Approach to analysis and design stresses the point that the structural engineer should not consider only the factors for an optimum solution from the points of view of strength, durability and materials used. He has to be aware of other very pertinent socio-economic factors to develop a design to be happily accepted by the public.     

Investigation of coal-fired power plants in Turkey and a case study: Can plant

About 61% of the total installed capacity for electrical power generation in Turkey is provided by thermal resources, while 80% of the total electricity is generated from thermal power plants. Of the total thermal generation, natural gas accounts for 49.2%, followed by coal for 40.65%, and 9.9% for liquid fuel. This study deals with investigation of the Turkish coal-fired power plants, examination of an example plant and rehabilitation of the current plants. Studied plant has a total installed capacity of 2 × 160 MW and has been recently put into operation. It is the first and only circulating fluidized bed power plant in the country. Exergy efficiencies, irreversibilities, and improvement factors of turbine, steam generator and pumps are calculated for plant selected. Comparison between conventional and fluidized bed power plant is made and proposed improving techniques are also given for conventional plants.     

Full flexible performance characterization of a feedback applied transistor with LNA applications

In this paper, the full flexible performance characterization of a transistor with series inductive/parallel capacitive feedback is carried out in terms of LNA applications. For this purpose, the input VSWR V_in–maximum available gain G_Tmax variations are constructed for a high technology low-noise transistor that is subject to the required noise figure F_req(f) ≥ F_min(f) along the device's operation band depending on the feedback. These V_in–G_Tmax variations result in the application of a design chart that indicates which value of feedback can be applied within which region of the operation band with the improvable trade-off between the V_in and output VSWR V_out for the Freq(f) ≥ Fmin(f). Following this, the optimum trade-off between V_in and V_out is made for the necessary operation frequency regions using the load impedance Z_L as an instrument with the predetermined source impedance Z_S. Finally, the LNA applications of a series inductive/parallel capacitive feedback applied transistor with the optimum V_in, V_out, and G_T subject to Freq(f) ≥ Fmin(f) ≥ are also presented as distributed across the entire bandwidth in the different operation bands. It can be concluded that this rigorous work will enable a designer to utilize the entire operation frequency band of transistor through using only a single series inductive/parallel capacitive feedback for the LNA designs of Freq(f) ≥ Fmin(f) with the optimum trade-offs among its performance measures.     

Polydimethylsiloxane (PDMS)-based antibacterial organic–inorganic hybrid coatings

UV-curable antibacterial organic–inorganic hybrid coatings were prepared by sol–gel method. Triethoxysilane-terminated poly(dimethylsiloxane) (TESi-PDMS) as a new coupling agent to improve the compatibility between organic and inorganic phases was synthesized. PDMS-based urethane methacrylate oligomer was obtained by reacting isophorone diisocyanate with hydroxyethyl methacrylate and hydroxyl-terminated PDMS. The formulations were applied onto polycarbonate panels and then cured by UV radiation. Physical properties of UV-cured free films such as gel content, stress–strain, and conversion of acrylate double bond were examined. In addition, the antibacterial effects of the coatings were investigated. Nanosilver-containing formulations exhibited high antibacterial effect against Escherichia coli and Staphylococcus aureus. Thermogravimetric analysis indicated that thermal stability of the hybrids was significantly higher than the organic polymer. Contact angle measurement showed that addition of silane precursor increased the contact angle from 95° to 110°.     

Production and aging of highly porous 17-4 PH stainless steel

This study describes production of highly porous 17-4 PH stainless steel for biomedical implant applications by space holder-sintering technique. 17-4 PH stainless steel powders were mixed with space holder and then compacted. For designing pore properties, both spherical and irregular shaped carbamide with different particle size ranges were used as space holder and removed by water leaching. Porous 17-4 PH steel specimens were sintered at 1,260?°C for 40?min. Boron was used as a liquid phase sintering additive. In addition, sintered specimens were aged in order to increase mechanical properties. Specimens were austenitized at 1,050?°C and then quenched. Quenched specimens were aged at times of 1?C6?h at temperatures between 450 and 570?°C. The pore size and shape of the 17-4 PH stainless steel foams replicated the initial size and shape of the carbamide particles. This suggests that pore properties can be designed by using proper size, shape and content of space holder.     

Statistical investigation of the cotton dyeing kinetics of CI Reactive Black 5 dye

In this study, the dyeing kinetics of CI Reactive Black 5 dye was statistically investigated. Cotton fabrics were dyed with this dye under different conditions by the exhaustion technique. Dye samples were taken from the dyebath from the start to the end of the process at 10 min intervals in order to determine the percentage dye exhaustion. The transmittance of the coloured dyebath samples was measured using a UV‐vis spectrophotometer. The results were investigated by statistical methods using analysis of variance and regression curves. The dye exhaustion of the cotton fabrics was found to change as a function of the dyeing parameters. Times of half‐dyeing were determined from the regression curves.     

Effects of carbamide shape and content on processing and properties of steel foams

Spherical and irregular carbamide particles covered with Fe–1.5% Mo steel powder have been employed to produce foams using space holder-water leaching technique in powder metallurgy. Foams having porosities between 49.2% and 71.0% were produced after sintering at 1200 °C for 60 min. The effect of carbamide shape and content on the foams’ processing, microstructure and mechanical properties has been evaluated. Using irregular carbamide particles and increasing its content decreased leaching time. The extents of specimens’ volumetric expansion after carbamide leaching and volumetric shrinkage after sintering also depended on volume fraction and carbamide shape. Final porosity was directly related to the added fraction of carbamide. Pore shape was similar to initial carbamide particle shape. Foams having irregular pore shape were observed to have compressive yield strengths between 20 MPa and 92 MPa and Young's moduli between 0.45 GPa and 2.69 GPa. The corresponding values for foams having spherical pore shape varied between 25 MPa and 112 MPa and between 0.71 GPa and 2.91 GPa, respectively. The foams’ strength increased with increasing relative density. Microstructure having spherical pores resulted in better compressive behavior.     

Alkaline sulfide pretreatment of an antimonial refractory Au-Ag ore for improved cyanidation

This paper presents the alkaline sulfide pretreatment of an antimonial refractory gold and silver ore. In the ore, gold occurs mainly as gold-silver alloys and as associated with quartz and framboidal pyrite grains, and, to a small extent, as the inclusions within antimonial sulfides. Silver is present extensively as antimonial sulfides such as andorite. Alkaline sulfide pretreatment was shown to allow the decomposition of the antimonial sulfide minerals (up to 98% Sb removal) and to remarkably improve the amenability of gold (e.g., from <49% up to 83%) and silver (e.g., from <18% up to 90%) to subsequent cyanide leaching. An increase in reagent concentration (1–4 mol/L Na₂S or NaOH) and temperature (20–80°C), and a decrease in particle size seem to produce an enhancing effect on metal extraction. These findings suggest that alkaline sulfide leaching can be suitably used as a chemical pretreatment method prior to the conventional cyanidation for antimonial refractory gold and silver ores.     

Microstructural evolution and mechanical properties of severely deformed Al-12Si casting alloy by equal-channel angular extrusion

Microstructural evolution and mechanical properties of Al-12Si alloy subjected to equal-channel angular extrusion (ECAE) were investigated. The high stresses imposed in ECAE led to the fragmentation of the needle-shaped eutectic silicon plates into smaller particles. The length and width of the Si particles decreased from 35.5±31.8 μm and 13.7±8.9 μm without ECAE to 2.7±1.1 μm and 1.3±0.4 μm after six ECAE passes, respectively. The average aspect ratio of 3.2±1.8 for the Si particles in the as-cast condition decreased to 1.18±0.8 after six ECAE passes with a corresponding increase in the average roundness of 0.26±0.19 to 0.61±0.19. ECAE increased the strength, ductility, and impact toughness of the alloy. The increase in the tensile and yield strengths after six passes was about 68 % and 100 %, respectively. The alloy after six ECAE passes exhibited 12 % elongation to failure, which was almost eight times higher than that of the as-cast alloy. The absorbed energy increased with an increase in the number of passes, finally reaching 11. 5 J/cm² after six passes, which is about four times higher than that of the as-cast alloy.