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941.
Field aligned starting (FAS) is a technique for starting three-phase cage induction motors on either three-phase or single-phase supply lines under varying load conditions with minimal inrush currents. The technique starts the motor independent of the mains supply with a high transient torque before connecting the spinning motor to the mains. It is imperative to the operation of FAS that the spinning motor be connected to the mains at the correct time. Incorrectly timed mains connection can result in negative transient torques with the severity to slow, or possibly stall the already started motor. As the implementation of FAS is not possible without a predictive mechanism by which the correct moment of mains connection can be found in advance, this paper proposes a simple, low cost, yet effective self-calibrating method which ensures that the timing of the mains connection is correct under all starting conditions. Critical issues vital to a successful self-calibration under transient and varying starting conditions are investigated and presented with both experimental and simulated results to show that self-calibration is an indispensable part of FAS technique. 相似文献
942.
Ndigui Billong U.C. Melo F. Louvet D. Njopwouo 《Construction and Building Materials》2009,23(6):2457-2460
In this study, a pozzolanic binder containing lime and a common thermally activated kaolinitic clay, at 750 °C, was formulated. The chemical, mineralogical and pozzolanic properties of raw materials were determined. The percentage of lime in the binder varies between 20% and 30%. The binder was used as a stabilizer in compressed lateritic soil in which water–solid (laterite and binder) and laterite–binder ratios vary, respectively, from 0.12 to 0.20 and 4 to 9. Sodium hydroxide (NaOH) was added as a chemical activator in the mixture. The NaOH–binder ratio varies from 0.02 to 0.04. The average effect of each component of the mixture on compressive strength, water absorption and apparent density of compressed laterite after 7 or 28 days of conservation at 40 ± 1 °C in an atmosphere saturated with water vapour was evaluated in a screening design of the “design in graeco – latin squares” type. It was observed that water–solid and laterite–binder ratios are the factors that influence more the properties of the products. Compressive strength increases up to a water–solid ratio of 0.16 then decreases for higher ratios. Compressive strength decreases with the increase of laterite–binder ratio. Water absorption decreases with the increase of water–solid ratio up to 0.16 then sharply increases for higher ratios. However, water absorption decreases slightly with the increase in the lime content of the binder and sodium hydroxide–binder ratio. The maximum apparent density is observed at water–solid ratio of 0.16. It increases when sodium hydroxide–binder and laterite–binder ratios increase. 相似文献
943.
T.U. NWABUEZE 《Journal of food quality》2009,32(5):669-683
Parboiling and dehulling are two closely associated primary operations preceding African breadfruit ( Treculia africana ) seed kernel extraction and subsequent utilization in any food form. Three process variable conditions for parboiling the seeds (quantity of parboiled seeds, parboiling temperature and parboiling time) for dehulling and kernel extraction were investigated using a central composite design. The objectives of the research were to maximize kernel and extraction yields and dehulling and machine efficiencies through process variable combinations. Maximum kernel mass (91.33%) was obtained at the center point process combination (12 kg, 80C and 13 min, respectively). Extraction yield and total recovered wastes were 94.08 and 7.31%, while dehulling and machine efficiencies were 72.62 and 96.97%, respectively. Models developed by response surface analysis for these responses ranged from 62 to 93%. Temperature effects on kernel mass, extraction yield and total wastes were both linear and quadratic.
Dehulling operation, to a great extent, is dependent on parboiling process conditions. This research located the optimum combination of process variables that would lead to maximum kernel yield and machine efficiency using second-order central composite design and response surface analysis. It also reported the ability of locally fabricated power-driven commercial attrition mill, designed for grinding cereals and grain-legumes, to thresh and dehull parboiled African breadfruit whole seeds. Because the seeds are extracted,parboiled and dehulled before their utilization in any food form, information obtained in this research would be needful not only to processors of African breadfruit seeds, but also to those processing grain-legumes and other seeds requiring dehulling process before conversion into any food form. 相似文献
PRACTICAL APPLICATIONS
Dehulling operation, to a great extent, is dependent on parboiling process conditions. This research located the optimum combination of process variables that would lead to maximum kernel yield and machine efficiency using second-order central composite design and response surface analysis. It also reported the ability of locally fabricated power-driven commercial attrition mill, designed for grinding cereals and grain-legumes, to thresh and dehull parboiled African breadfruit whole seeds. Because the seeds are extracted,parboiled and dehulled before their utilization in any food form, information obtained in this research would be needful not only to processors of African breadfruit seeds, but also to those processing grain-legumes and other seeds requiring dehulling process before conversion into any food form. 相似文献
944.
Sarun P.M. Vinu S. Shabna R. Biju A. Guruswamy P. Syamaprasad U. 《Applied Superconductivity, IEEE Transactions on》2009,19(1):35-38
The magnetic field (B ) dependence of electric field versus transport current density (E-J characteristics) of Bi1.6Pb0.5Sr2-xHoxCa1.1Cu2.1O8+delta superconductor was studied for x from 0.000 to 0.200. The behavior of supercurrent flow under magnetic fields in Ho-doped (Bi,Pb)-2212 is explained using thermally activated flux-creep. The n -value and characteristic pinning energy ( Uc) estimated from E-J characteristics show that at applied fields, the flux-lines in Ho-doped samples are in the glass-state. A correlation is observed between n -index and Jc of doped samples. The highly enhanced critical current density (Jc) and n-index in both self- and applied-fields due to Ho-doping is of great scientific and technological significance. 相似文献
945.
A vortex tube is a simple mechanical device, which splits a compressed gas stream into a cold and hot stream without any chemical reactions or external energy supply. This paper presents the results of a series of experiments focusing on various geometries of the “cold end side” for different inlet pressures and cold fractions. Specifically, the tests were conducted using different cold end orifice diameters.Energy separation and energy flux separation efficiencies are defined and used to recover characteristic properties of the vortex tube. These are used to show an appropriate scale to non-dimensionalize the energy separation effect. The experimental results indicate that there is an optimum diameter of cold end orifice for achieving maximum energy separation. The results also show that the maximum value of energy separation was always reachable at a 60% cold fraction irrespective of the orifice diameter and the inlet pressure. The results are compared with the previous studies on internal flow structure, and optimal operating parameters are shown to be consistent with a matching of orifice size with the secondary circulation being observed. 相似文献
946.
In this study, current and voltage transfer function filters using single active component, namely, current backward transconductance amplifier (CBTA) are presented. The proposed structures are a single-input three outputs (SITO) current-transfer function filter, a single-input four-output (SIFO) voltage transfer function filter and three-input single-output (TISO) voltage transfer function filter. The proposed filters have low active and passive sensitivities and use canonical number of electronics components. The validity of the proposed circuits is demonstrated by PSPICE simulations and experimental results. Operation range of the CBTA and its parasitic effects are also discussed. 相似文献
947.
This article describes the results of an investigation concerning with the failure of a pipe which was carrying oil from the
control oil unit to the steam turbine control valves servomotor. The failure was in the form of a crack, propagating horizontally
along the pipe. The crack initiated on the outside of the pipe. The cause of the failure was investigated by conducting visual
examination, detailed macro and microstructural examinations and determining the composition of material from the failed pipe.
The composition of the pipe material was analyzed by atomic absorption spectrometer. The failure of the oil pipe was attributed
to stress corrosion cracking. The pipe material is A312 TP 304L. Recommendation to minimize such failures includes coating
the pipe to prevent contact with chloride from the surrounding marine environment. 相似文献
948.
Results are presented for binary intermolecular interactions and thermophysical properties in the temperature range between
70K and 1,000K of gaseous fluorine (F2), and between 200K and 1,000K of chlorine (Cl2), bromine (Br2), and iodine (I2). Our studies are carried out with an (n − 6) Lennard-Jones temperature-dependent potential (LJTDP). The underlying model takes into account the influence of vibrational
excitations on the equilibrium distance R
m(T) and potential well depth e(T){\varepsilon(T)} . The potential parameters at T = 0K have been obtained by minimization of the sum of squared deviations between experimentally determined and calculated
second pVT- and acoustic virial coefficients, B and β, and viscosities η, normalized to their relative experimental error a
exp. The majority of the available experimental data are well reproduced within their experimental errors. Tables and fitting
formulae for a fast and reliable prediction of the thermophysical properties and potential parameters are also presented. 相似文献
949.
U. Götze Th. Weber C. Linke A. Schmidt 《Materialwissenschaft und Werkstofftechnik》2009,40(7):566-572
Target Costing for Materials – Potentialities and Methodology Target Costing is a standard instrument of cost management in business administration, but hardly mentioned in the economic oriented literature on material sciences. Nevertheless there are high potentialities for developers, producers, or users of materials regarding the improvement of efficiency. Therefore, this article will present these potentialities of a material oriented Target Costing. Besides, the general methodology of Target Costing will be modified to meet the specifics of materials from the perspectives of users of materials on the one hand and developers respectively producers of materials on the other. 相似文献
950.
The relative activity of the potential slip systems in Sn is examined by comparing an experiment of a single shear lap deformation
with simulations using the viscoplastic self-consistent crystal plasticity model developed by Lebensohn and Tomé. In a single
shear lap specimen made using eutectic Sn-Ag solder on copper pull tabs, the initially polished side was characterized using
orientation mapping before and after 0.8 shear deformation at 25°C at a shear strain rate of 0.1/s. The critical resolved
shear stress of potential slip systems and the rate sensitivity was altered by trial and error until good agreement between
experimentally observed and computed texture was obtained. This result indicated that slip on {101) and {211) planes is much
more difficult to activate than on other slip systems for the grain orientations present in this sample. This particular sample
showed much activity on the {010)〈101] slip system, but the activation of this slip system may be related to the initial dominant
orientation in the specimen. This result is compared with literature and related experiments on ball grid arrays in a companion
paper in this volume that show similar trends. As lead-free solder joints are commonly single crystals or multicrystals, this
particular result is not indicative of lead-free solder joints as a whole, but must be interpreted in the context of a larger
data set. 相似文献