Sharif Digital Repository

27Al NMR spectroscopy is a powerful tool for the study of coordination and solvation in both aqueous and nonaqueous solutions. In this study, the complexes coexisting upon dissolution of AlCl3 in acidic acetone + methanol solutions are shown to consist essentially of mixed hexacoordinated species of the general formula [Al(CH3OH) 6-n (CH3COCH3) n ]3+ (n=1,2 and 3), all exhibiting distinctly different 27Al shielding effects. The relative populations of the various mixed species are found to be highly dependent upon the acetone:methanol mole ratio that in the more acetone-rich mixtures with aluminum become appreciably coordinated by acetone. The results demonstrate that the key factor for the... 

In this work, phosphorus-31 and aluminum-27 nuclear magnetic resonance techniques were used to characterize the distribution of soluble aluminophosphate species in methanol + water and ethanol + water mixtures. The assignment of the peaks to alu-minate species was attempted, clarifying earlier work and producing information on the different aluminophosphate complexes. Nine peaks were observed at -0.41, -6.4, -7.5, -7.9, -13.1, -13.9, -16.6, -18.1 and -20.6 ppm. Four new peaks appeared in the 31P NMR spectra of the alcoholic aluminophosphate solutions and their intensities changed with changes of the alcohol:water volume ratio. These new peaks were observed in the presence of methanol or... 

Electrospinning is a simple and cheap process for forming one-dimensional (1D) nanofibers with controllable size, morphology, and chemistry. Besides these, the ultrahigh surface area with industrialization capability has attracted extensive interest in the research community. On the other hand, a photocatalytic process is a promising method for degrading organic pollutants that cannot be removed by conventional wastewater treatment. This review focuses on the recent progress of electrospun nanofibers for the photocatalytic degradation of water pollutants. The linkage between the electrospinning technique and the photocatalytic process is classified into two main categories: (1) polymeric... 

(ZnO)1-x(CdO)x nanofibers were fabricated via electrospinning of polymer precursor by subsequent annealing in air. Field emission scanning electron microscopy (FESEM) showed the smooth and beadless nanofibers and X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) showed the ZnO hexagonal and the CdO cubic structure. Diffuse reflectance spectroscopy (DRS) showed the band gap energy reduction by increasing the amount of CdO in (ZnO)1-x(CdO)x nanofibers that resulted in the photocatalytic activity under the visible light for dye degradation. Under the UV light CdO acted as both electron and hole sink in the (ZnO) 1-x(CdO)x nanofibers and a possible photocatalytic activity... 

In this paper we develop a formal semantics of security protocols. Its main virtue is that it is a generic model, in the sense that it is parameterized over e.g. the intruder model. Further characteristics of the model are a straightforward handling of parallel execution of multiple protocols, locality of security claims, the binding of local constants to role instances, and explicitly defined initial intruder knowledge. We validate our framework by analyzing the Needham-Schroeder-Lowe protocol  

Novel ZnO-carbon and ZnO nanofibers were fabricated by electrospinning of polymer precursor followed by subsequent annealing in nitrogen and air, respectively. Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) indicated the smooth and beadless nanofibers with wurtzite crystal structure. X-ray photoelectron spectroscopy (XPS) showed the presence of oxygen vacancies (VO) and chemisorbed O2 on the surface of the samples. Band gap narrowing of the ZnO-carbon nanofibers in comparison to ZnO were measured by diffuse reflectance spectroscopy (DRS). Photo-degradation of azo dye under the UV and visible light was evaluated and ZnO-carbon showed an enhancement in... 

Multi wall carbon nanotube (MWCNT) doped ZnO nanofibers were fabricated by electrospinning for the first time. We have successfully demonstrated the photocatalytic activity of doped nanofibers under visible light. Scanning electron microscopy showed that the diameter of MWCNT-doped ZnO nanofibers varied from 120 to 300 nm without agglomeration of MWCNT. Fourier transform infrared spectroscopy and X-ray diffraction studies proved the formation of ZnO bond and wurtzite structure with smaller crystal size in doped nanofibers. Raman spectra demonstrated slight shift in bond position after nanofiber doping, indicating the chemical bond between MWCNT and ZnO. X-ray photoelectron spectroscopy... 

In this paper, an artificial neural network (ANN) model has been developed to predict the yield and tensile strengths of hot pressed NiAl intermetallic compound based on the experimental data from Albiter et al. [A. Albiter, M. Salazar, E. Bedolla, R.A.L. Drew, R. Perez, Mater. Sci. Eng. A 347 (2003) 154]. The predicted results, with a correlation relation between 0.9791 and 0.9921, show a very good agreement with the experimental values. Furthermore, the sensitivity analysis was performed to investigate the importance of the effects of chemical composition and temperature on the mechanical behavior of hot pressed NiAl intermetallic compound. © 2008 Elsevier B.V. All rights reserved  

Worldwide energy and environmental issues are forcing researchers to develop a green approach to produce a clean energy. However, traditional methods in reforming of fossil fuels to produce hydrogen (H2) are causing CO2 emission. Hydrogen is therefore an indirect greenhouse gas with a global warming potential. Hydrogen with high specific energy density can be considered as an efficient energy carrier as compared to fossil fuels. But hydrogen production from water splitting reaction has low efficiency, which limits its generation by green approach. For addressing this issue, different chemical hole scavengers have been applied, which is causing further environmental and economic problems. By... 

Hydroxyapatite is the most important bio ceramic, due to its structure and chemical composition which is similar to bone. Since feeble fracture toughness, brittleness and low tensile strength have restricted their use, for overcoming this problem, they were often used as a secondary component. HAp-Al2O3 nano-composite powder combined the benefits of biocompatibility of HAp and high strength of Al2O3. When HAp-Al2O3 nano-composite powders were sintered at a higher temperature than 1100- 1200°C, HAp was decomposed and converted to the second phase of TCP, due to the formation of calcium aluminate increasing decomposition speed of HAp to TCP at higher degree than 1100-1200°C temperatures;... 

Global environmental pollution and energy supply demand have been regarded as important concerns in recent years. Metal oxide semiconductor photocatalysts is a promising approach to apply environmental remediation as well as fuel generation from water splitting and carbon dioxide reduction. ZnO nanostructures have been shown promising photocatalytic activities due to their non-toxic, inexpensive, and highly efficient nature. However, its wide band gap hinders photo-excitation for practical photocatalytic applications under solar light as an abundant, clean and safe energy source. To overcome this barrier, many strategies have been developed in the last decade to apply ZnO nanostructured... 

Ceramic-matrix composites containing TiC-TiN have been used in a variety of application because of their superior properties such as high hardness, good wear resistance and high chemical stability. In this research, effect of coke and coke/calcium beds in synthesis of Al2O3-Ti(C, N) composites using alumino-carbothermic reduction ofTiO2 has been investigated. Al, TiO2 and active carbon with additives of extra carbon and NaCl and without additives, in separate procedures, have been mixed. Afterwards, mixtures were pressed and synthesized in 1200°C for 4hrs, in coke and coke/calcium beds, separately. Al2O3-Ti(C,N) composite was synthesized in ternary system of Al-TiO2-C with excess carbon and... 

Network-on-Chips (NoCs) usually use regular mesh-based topologies.Regular mesh topologies are not always efficient because of power and area constraints which should be considered in designing system-on-chips.To overcome this problem,irregular mesh NoCs are used for which the design of routing algorithms is an important issue.This paper presents a novel routing algorithm for irregular mesh-based NoCs called "i-route". In contrast to other routing algorithms,this algorithm can be implemented on any arbitrary irregular mesh NoC without any change in the place of IPs. In this algorithm, messages are routed using only 2 classes of virtual channels. Simulation results show that using only 2... 

An analytical approach which is popular in micromechanical studies has been extended to the solution for the interference fit problem of the femoral stem in cementless total hip arthroplasty (THA). The multiple inhomogeneity problem of THA in transverse plane, including an elliptical stem, a cortical wall, and a cancellous layer interface, was formulated using the equivalent inclusion method (EIM) to obtain the induced interference elastic fields. Results indicated a maximum interference fit of about 210 μm before bone fracture, predicted based on the Drucker-Prager criterion for a partially reamed section. The cancellous layer had a significant effect on reducing the hoop stresses in the... 

The combined effects of SiC and carbon additives on the densification, structure and characteristics of pressureless sintered ZrB2-SiC ceramic composites were studied. The ZrB2-SiC (1-10wt%) composite powders were mixed by 1-2wt% carbon. The prepared powder mixtures were then cold-consolidated and sintered in argon environment in the temperature range of 1800-2100°C for 2h. The constituted phases and microstructural evolutions were studied using x-ray diffraction and scanning electron microscope equipped with an energy dispersive x-ray detector. The obtained results concluded that the densification was increased by extending the sintering time and also by prior holding... 

Abstract: Photocatalysis using semiconductors has emerged as a promising wastewater treatment process to overcome the major challenges faced by conventional technologies. The advantages of ZnO nanomaterials over other semiconductors, and their structure-dependent properties, make them important building blocks in nanotechnology as multifunctional materials. Moreover, it has been confirmed that ZnO nanomaterials can exhibit high performance in photodegradation of organic dyes for treatment of industrial effluent. The wurtzite structure of ZnO contains polar and nonpolar planes; the low surface energy and thermodynamic stability of the nonpolar planes enable formation of one-dimensional (1D)... 

This work presents some new optimization approaches to implementation of Medium Access Control (MAC) layer of IEEE 802.11 wireless networking protocol using general purpose DSP and gate array systems. Optimization starts at design level. The hardware/software partitioning of the MACs architecture is optimized in the sense of minimal implementation burden, while maintaining the system's functionalities and performance. The proposed partitioning and implementation technique obviates the use of any Real Time Operating System (RTOS), which leads to a simple, high speed, and low memory structure of the MACs software. Also, solutions such as using hash tables and pipeline processing are given and... 

In this paper, the effects of Stone-Wales (SW) defect on transport properties of armchair graphene nanoribbons (AGNRs) are studied using tight binding calculations combined with nonequilibrium Green's function (NEGF). We evaluate transmission and density of states (DOS) in two cases, pristine and defective AGNR, and we compare the results. Our results indicate that in the latter case, a larger bandgap is made due to symmetry breaking in GNR layer  

Traditional electromyography-assisted optimization (TEMG) models are commonly employed to compute trunk muscle forces and spinal loads for the design of clinical/treatment and ergonomics/prevention programs. These models calculate muscle forces solely based on moment equilibrium requirements at spinal joints. Due to simplifications/assumptions in the measurement/processing of surface EMG activities and in the presumed muscle EMG-force relationship, these models fail to satisfy stability requirements. Hence, the present study aimed to develop a novel stability-based EMG-assisted optimization (SEMG) method applied to a musculoskeletal spine model in which trunk muscle forces were estimated by...