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971.
Rizk Mostafa Shalaby Mustafa Kamal Esmail Abdo Mohammed Ali Mohammed S. Gumaan 《SILICON》2018,10(5):1861-1871
This article aims to reduce the melting temperature of lead-free solder alloy and promote its mechanical properties. Eutectic tin-silver lead-free solder has a high melting temperature 221 °C used for electronic component soldering. This melting temperature, higher than that of lead–tin conventional eutectic solder, is about 183 °C. The effect of the melt spinning process and copper additions into eutectic Sn-Ag solder enhances the crystallite size to about 47.92 nm which leads to a decrease in the melting point to about 214.70 °C, where the reflow process for low heat-resistant components on print circuit boards needs lower melting point solder. The results showed the presence of intermetallic compound Ag3Sn formed in nano-scale at the Sn-3.5Ag alloy due to short time solidification. The presence of new intermetallic compound, IMC from Ag0.8Sn0.2 and Ag phase improves the mechanical properties, and then enhances the micro-creep resistance especially at Sn-3.5Ag-0.7Cu. The higher Young’s modulus of Sn-3.5Ag-0.5Cu alloy 55.356 GPa could be attributed to uniform distribution of eutectic phases. Disappearance of tin whiskers in most of the lead-free melt-spun alloys indicates reduction of the internal stresses. The stress exponent (n) values for all prepared alloys were from 4.6 to 5.9, this indicates to climb deformation mechanism. We recommend that the Sn95.7-Ag3.5-Cu0.7 alloy has suitable mechanical properties, low internal friction 0.069, low pasty range 21.7 °C and low melting point 214.70 °C suitable for step soldering applications. 相似文献
972.
Abstract In this paper, a sliding mode speed observer for direct torque controlled (DTC) induction motor drives is developed. The speed observer accuracy is guaranteed through the current observer. The rotor speed is estimated by the observer based on the measured and estimated stator currents. The system is firstly simulated by MATLAB and then tested by hardware in the loop. Then, the application is implemented on a TMS320C6711, 32-bit fixed point digital signal processor (DSP). The experimental results show the robustness, feasibility, and performance of the proposed observer structure. 相似文献
973.
Mustafa Gazi Zainab Eniola Ojoro Hayrettin Ozan Gulcan 《Chemical Engineering Communications》2017,204(7):729-738
High-performance activated carbon-zinc oxide (Ac–ZnO) nanocatalyst was fabricated via the microwave-assisted technique. Ac–ZnO was characterized and the results indicated that Ac–ZnO is stable, had a band gap of 3.26?eV and a surface area of 603.5?m2g?1, and exhibited excellent adsorptive and degrading potentials. About 93% phenol was adsorbed within 550?min of reaction by Ac–ZnO. Impressively, a complete degradation was achieved in 90?min via a photo-Fenton/Ac–ZnO system under optimum conditions. An artificial neural network (ANN) model was developed and applied to study the relative significance of input variables affecting the degradation of phenol in a photo-Fenton process. The ANN results indicate that increases in both H2O2 and Ac–ZnO dosage enhanced the rate of phenol degradation. The highest rate constant at the optimum conditions was 0.093?min?1 and it was found to be consistent with the ANN-predicted rate constant (0.095?min?1). 相似文献
974.
Hadi Sofijan Tan Joo Shun Sahar Abbasiliasi Shuhaimi Mustafa Nyoman Tri Puspaningsih Saeid Kadkhodaei 《分离科学与技术》2017,52(5):834-842
A polymer–salt-based aqueous two-phase system (ATPS) was developed for the effective extraction and purification of extracellular β-xylosidase from the fermentation broth of recombinant Bacillus megaterium MS941. The effect of molecular weight (MW) of polyethylene glycol (PEG), tie-line length (TLL), volume ratio (VR), crude loading and pH on the recovery performance was evaluated. Under the optimal extraction conditions, β-xylosidase was successfully purified up to 23-fold with a recovery yield of 99% in the bottom salt-rich phase at PEG 4,000/potassium phosphate ATPS comprising TLL of 41.8, VR of 2.3, crude loading (CL) of 30% (w/w) at pH 6. 相似文献
975.
Thermoelectric and Magnetic Properties of Pt-Substituted $${BaFe_{4-{x}}Pt_{{x}}Sb_{12}}$$ Compounds
Murat Sertkol Sedat Ballıkaya Fatih Aydoğdu Adil Güler Mustafa Özdemir Yıldırhan Öner 《Journal of Electronic Materials》2017,46(1):73-78
\({BaFe_{4-{x}}Pt_{{x}}Sb_{12}}\) (x = 0, 0.1, 0.2) compounds were prepared by melting and annealing, followed by a spark plasma sintering method. Low-temperature thermoelectric and magnetic properties were investigated based on Seebeck coefficient, electrical and thermal conductivity and magnetization measurements. The structural properties of \({BaFe_{4-{x}}Pt_{{x}}Sb_{12}}\) (x = 0, 0.1, 0.2) compounds were ascertained by powder x-ray diffraction analysis, confirming that all samples have a main phase of a skutterudite structure with the space group Im\({\mathrm {\bar{3}}}\). The lattice parameters obtained, 9.202(5), 9.199(5) and 9.202(1) Å for x = 0, 0.1 and 0.2, respectively, were found consistent with literature. The Seebeck coefficient sign shows that holes are dominant carriers in all compounds. The local maximum Seebeck coefficient was observed around 50 K which may be a trace of paramagnon-drag effect of charge carriers. Thermal conductivity and electrical resistivity measurements were carried out between 4.2 and 300 K. Temperature dependence of electrical resistivity reflects that all samples show semi-metallic behavior in our temperature range of 4.2–300 K. Samples for x = 0.1 and x = 0.2 show Kondo-like behavior. In magnetization measurement, we observe that there are two successive magnetic transitions in Pt-substituted compounds; however, there is only one (transition from a paramagnetic state to long-range magnetic ordering) in Pt-free compounds. In Pt-substituted compounds, the first transition appears at \( T _{ {\rm c}}\) = 48 K. In addition, the second transition is observed at \( T _{ {\rm irr}}\) = 30 K where an intermediate state is observed before the magnetic ordering transforms to an irreversible ferromagnetic state. We concluded that Pt substitution on the Fe side effectual on the thermoelectric and magnetic properties of \({BaFe_{4-{x}}Pt_{{x}}Sb_{12}}\) (x = 0, 0.1, 0.2) compounds. 相似文献
976.
Nanoengineering Hybrid Supramolecular Multilayered Biomaterials Using Polysaccharides and Self‐Assembling Peptide Amphiphiles 下载免费PDF全文
Developing complex supramolecular biomaterials through highly dynamic and reversible noncovalent interactions has attracted great attention from the scientific community aiming key biomedical and biotechnological applications, including tissue engineering, regenerative medicine, or drug delivery. In this study, the authors report the fabrication of hybrid supramolecular multilayered biomaterials, comprising high‐molecular‐weight biopolymers and oppositely charged low‐molecular‐weight peptide amphiphiles (PAs), through combination of self‐assembly and electrostatically driven layer‐by‐layer (LbL) assembly approach. Alginate, an anionic polysaccharide, is used to trigger the self‐assembling capability of positively charged PA and formation of 1D nanofiber networks. The LbL technology is further used to fabricate supramolecular multilayered biomaterials by repeating the alternate deposition of both molecules. The fabrication process is monitored by quartz crystal microbalance, revealing that both materials can be successfully combined to conceive stable supramolecular systems. The morphological properties of the systems are studied by advanced microscopy techniques, revealing the nanostructured dimensions and 1D nanofibrous network of the assembly formed by the two molecules. Enhanced C2C12 cell adhesion, proliferation, and differentiation are observed on nanostructures having PA as outermost layer. Such supramolecular biomaterials demonstrate to be innovative matrices for cell culture and hold great potential to be used in the near future as promising biomimetic supramolecular nanoplatforms for practical applications. 相似文献
977.
Photoluminescence characterization and heat treatment effect on luminescence behavior of BaTa2O6:Dy3+ phosphor 下载免费PDF全文
Mustafa İlhan Mete Kaan Ekmekçi Ayhan Mergen Cemalettin Yaman 《International Journal of Applied Ceramic Technology》2017,14(6):1134-1143
Undoped and Dy3+‐doped barium tantalate phosphors were synthesized by the solid‐state reaction method at 1425°C. Also, 10 mol% Dy3+‐doped BaTa2O6 was sintered between 1150 and 1425°C in order to determine temperature effect on structural and luminescence properties. Afterwards, they were characterized by XRD, SEM‐EDS and photoluminescence (PL) analyses. PL spectra exhibited the excitation peaks between 300 and 440 nm. Two typical emissions were observed at 486.2 nm (blue) and 577.7 nm (yellow) due to the 4F9/2→6H15/2 and 4F9/2→6H13/2 transitions, respectively. Emission intensities increased with increasing doping concentration of Dy3+ up to 10 mol% and then decreased due to the concentration quenching effect. Moreover, depending on the increase in heat treatment temperature, the intensity of emission reached maximum at 1425°C. The calculated CIE chromaticity coordinates of phosphors located in the white light region. 相似文献
978.
Differently than in the past, today environmental problems have local, national and international concern. The environmental problems in the Black Sea region are a good example for this phenomenon. These problems have affected all six countries that have shores with the Black Sea. The current study analyses these problems in detail. It intends to detect potential reasons for problems and provide suggestions to solve these problems by considering the economic dimensions. In addition, the impact of problems on the city life is examined. Also, the roles and importance of voluntary organizations on solving environmental problems are emphasized. 相似文献
979.
The prediction of Los Angeles (LA) abrasion loss from some indirect tests is useful for practical applications. For this purpose,
LA abrasion, electrical resistivity, density and porosity tests were carried out on 27 different rock types. LA abrasion loss
values were correlated with electrical resistivity and a good correlation between the two parameters was found. To see the
effect of rock class on the correlation, regression analysis was repeated for igneous rocks, metamorphic rocks and sedimentary
rocks, respectively. It was seen that correlation coefficients were increased for the rock classes. In addition, the data
were divided into two groups according to porosity and density, respectively. After repeating regression analysis for these
porosity and density groups, stronger correlations were obtained compared to the equation derived for all rocks. The validity
of the derived equations was statistically tested and it was shown that all derived equations were significant. Finally, it
can be said that all derived equations can alternatively be used for the estimation of LA abrasion loss from electrical resistivity. 相似文献
980.
Evaluation of various digestion procedures for trace element contents of some food materials 总被引:2,自引:0,他引:2
The levels of trace elements in different types of food material consumed in Turkey were determined by flame and graphite furnace atomic absorption spectrometry. Food samples were digested with dry ashing, wet ashing and microwave digestion procedures in this study. The microwave digestion procedure was chosen for the digestion of all the food samples because it required shorter time and made higher recovery (specially for Se). Fe, Cu, Mn, Zn, Al and Se were determined by flame and graphite furnace atomic absorption spectrometry, respectively. Relative standard deviations (RSD) were found below 10%. The accuracy of the procedure was confirmed by certified reference materials. Moreover, this procedure was easier to use when compared with dry and wet digestions. 相似文献