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81.
In this article, two new highly linear tunable transconductor circuits are proposed. The transconductors employ only six MOS transistors operated in saturation region. The second transconductor is derived from the first one with a slight modification. Transconductance of both transconductors can be tuned by a control voltage. Both of the transconductors do not need any additional bias voltages and currents. Another important feature of the transconductors is their high input and output impedances for cascadability with other circuits. Besides, total harmonic distortions are less than 1.5% for both transconductors. A positive lossless grounded inductor simulator with a grounded capacitor is given as an application example of the transconductors. Simulation and experimental test results are included to show effectiveness of the proposed circuits. 相似文献
82.
Ultrasonic velocity and attenuation measurements (2.25 MHz center frequency) were used to follow bulk crystallization of lactose (43% and 46%) from gelatin (1.5% and 3%) gels at 25 °C, and compared to turbidity (500 nm) and isothermal calorimetric measurements. Ultrasonic velocity decreased slightly (approximately 0.5%) during crystallization while ultrasonic attenuation was low in the absence of lactose crystals and increased progressively during crystallization. The lag time before the onset of crystallization decreased and the maximum rate of increase in attenuation during crystallization increased with increasing lactose supersaturation but was not affected by gelatin concentration (P < 0.05). Similar results were seen in turbidity and isothermal calorimetric measurements. Ultrasonic attenuation measurements have the potential to measure crystallization kinetics in complex food matrices and to be applied on-line. Practical Application: Many foods contain crystals that affect their taste and texture (for example, lactose crystals can give a grainy defect in ice cream). The formation of crystals is often hard to predict so methods to measure the development of crystals inside real foods are useful. In this study, we show that as lactose crystallizes in a gelatin gel the ultrasonic attenuation--capacity to absorb sound--increases and can be related to the amount of crystals present. Ultrasound is easier to apply in real food processing than the existing methodologies. 相似文献
83.
This paper concentrates on the transport sector of six developing countries with similar common denominators, namely Turkey, Thailand, Pakistan, Morocco, Tunisia and Malaysia. By using standard econometric techniques, we analyse the evolution of oil demand for road transport in these countries in relation to independent variables such as income, population, price of gasoline and diesel etc. Unlike the treatment in the present literature on the subject, gasoline and diesel consumption are estimated separately due to the high share of diesel in the total transport sector consumption. On the basis of the estimation over the period 1970–1990, on a country by country basis, we forecast the demand for these six countries until 2010. The results of this study indicate that the transport sector will be the driving force for energy and oil demand as part of economic growth in these developing countries. Its share in the future energy market structure is expected to grow. Consequently, the (pricing) policies of oil products in this sector have a crucial role for shaping rational economic and energy strategies within the framework of rising environmental concern. 相似文献
84.
Yucel Birol Duygu İsler Mustafa Urgen 《Metallurgical and Materials Transactions A》2011,42(11):3316-3322
Thin hard coatings provide the much needed protection for steel thixoforming tools that must resist wear at high temperatures.
The wear resistance of AlTiN- and AlTiON-coated hot work tool steel was investigated at 1023 K (750 °C), measured to be the
cavity surface temperature shortly after the steel slurry was forced into the thixoforming die. The wear tests were repeated
in exactly the same fashion with uncoated tool steel samples to identify the impact of AlTiN and AlTiON coatings on the high-temperature
wear performance of X32CrMoV33 tool steel. The nature, the thickness, and the adherence of the oxide scales impact the tribological
behavior. The poor adherence and limited ductility of ferrous oxides promote the failure of the oxide scale impairing the
resistance to wear of the hot work tool steel at elevated temperatures. The substantial softening in the X32CrMoV33 hot work
tool steel is also critical in the wear volume loss it suffers. AlTiN and AlTiON coatings, on the other hand, form a stable
and protective oxide surface layer at high temperatures and therefore provide an enhanced resistance to oxidation. The latter
is relatively more resistant to oxidation and is thus the better of the two coatings tested in the present work. 相似文献
85.
Ipek AkinElif Yilmaz Filiz SahinOnuralp Yucel Gultekin Goller 《Ceramics International》2011,37(8):3273-3280
Alumina (Al2O3) and alumina-yttria stabilized zirconia (YSZ) composites containing 3 and 5 mass% ceria (CeO2) were prepared by spark plasma sintering (SPS) at temperatures of 1350-1400 °C for 300 s under a pressure of 40 MPa. Densification, microstructure and mechanical properties of the Al2O3 based composites were investigated. Fully dense composites with a relative density of approximately 99% were obtained. The grain growth of alumina was inhibited significantly by the addition of 10 vol% zirconia, and formation of elongated CeAl11O18 grains was observed in the ceria containing composites sintered at 1400 °C. Al2O3-YSZ composites without CeO2 had higher hardness than monolithic Al2O3 sintered body and the hardness of Al2O3-YSZ composites decreased from 20.3 GPa to 18.5 GPa when the content of ZrO2 increased from 10 to 30 vol%. The fracture toughness of Al2O3 increased from 2.8 MPa m1/2 to 5.6 MPa m1/2 with the addition of 10 vol% YSZ, and further addition resulted in higher fracture toughness values. The highest value of fracture toughness, 6.2 MPa m1/2, was achieved with the addition of 30 vol% YSZ. 相似文献
86.
87.
Some of the basic concerns in the analysis of spouted-bed hydrodynamics are the flow pattern and the pressure field of the fluid and the spout shape. These are closely related with other design concerns such as spoutability, minimum spouting velocity and maximum spoutable bed depth. A computer program was developed in order to determine the flow pattern, pressure distribution in the fluid phase and the spout shape for a given operational condition. The computer program relies upon a two region model with a spout and annulus element for an axisymmetric bed. The paper presents some results for grain drying beds and compares them with the existing experimental data qualitatively. 相似文献
88.
The effect of inorganic salts such as sodium chloride and sodium sulfate on the performance of the activated sludge process was examined. When proper acclimation procedures were followed, the adverse effects of salts on the process were minimized. One of the parameters monitored, effluent suspended solids, had very low values (less than 10 mg l−1) up to an inflow sodium chloride concentration of about less than 35 gl−1. The chemical oxygen demand of the effluent increased steadily with increasing sodium chloride concentrations, but biochemical oxygen demand values remained very low (less than 5 mg l−1) which indicated that the increase in chemical oxygen demand was due to the portion that cannot be degrated biologically. The effect of sodium sulfate on the system was even less profound. In addition to the effluent being very clear and low in suspended solids, the chemical oxygen demand removal efficiency remained high. 相似文献
89.
F. Birol 《腐蚀工程科学与技术》2014,49(3):228-235
Corrosion of twin belt and twin roll cast AlMg3Mn sheet samples was investigated. The AlMg3Mn sheet samples submitted to immersion tests undergo alkaline pitting around Al–Fe and αc-Al(Fe,Mn)Si intermetallic particles in the twin roll and twin belt cast samples respectively. The weight loss is higher in the latter and increases with increasing homogenisation temperature for both groups. The twin roll cast AlMg3Mn samples reveal very few and small alkaline corrosion pits and hence much less weight loss in the immersion tests. The pitting activity is governed in the immersion tests by the microgalvanic corrosion activities between the intermetallic particles and the matrix while the anodic particles were inactive. 相似文献
90.
Tolga Tavsanoglu Ceren Begum Murat Alkan Onuralp Yucel 《JOM Journal of the Minerals, Metals and Materials Society》2013,65(4):562-566
In this study, WC (tungsten carbide) thin films were deposited on high-speed steel (AISI M2) and Si (100) substrates by direct current magnetron sputtering of a tungsten carbide target having 7% cobalt as binding material. The properties of the coatings have been modified by the change in the bias voltages from grounded to 200 V. All the coatings were deposited at 250°C constant temperature. The microstructure and the thickness of the films were determined from cross-sectional field-emission gun scanning electron microscope micrographs. The chemical composition of the film was determined by electron probe micro analyzer. The x-ray diffractometer has been used for the phase analyses. Nanoindentation and wear tests were used to determine the mechanical and tribological properties of the films, respectively. It is found that the increase in the bias voltages increased drastically the hardness and elastic modulus, decreased the friction coefficient values and increased the wear resistance of tungsten carbide thin films by a phase transformation from metallic W (tungsten) to a nonstoichiometric WC1?x (tungsten carbide) phase. 相似文献