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61.
A. M. Andreev A. Sh. Azizov A. A. Bezborodov A. V. Papkov V. M. Pak 《Russian Electrical Engineering》2011,82(4):180-183
The results of comparative tests of the main electrophysical properties of a new type of high-efficiency heat-conducting insulation
for turbo generators with air and hydrogen cooling as compared to the traditional insulation are presented. It is shown that
the addition of modified varnish with a high thermal conductivity coefficient to the insulation material does not yield any
deterioration of its electrical properties. 相似文献
62.
63.
J. J. Pak M. L. Santella R. J. Fruehan 《Metallurgical and Materials Transactions B》1990,21(2):349-355
The thermodynamic activities of Ti at dilution in a series of Ag-Cu alloys and eutectic Ag-Cu alloys containing In or Sn were
measured using a galvanic cell technique employing a ThO2-8 pct Y2O3 electrolyte. The equilibrium oxide phase formed by the reaction of Ti (XTi > 0.004) in the Ag-Cu alloy melts with an A12O3 or ZrO2 crucible was Ti2O (s). The free energy of formation of Ti2O (s) was estimated from available thermodynamic data. Titanium activities were calculated from measured oxygen potentials
and the free energy of formation of Ti2O (s). Titanium in the eutectic Ag-Cu melt showed a positive deviation from ideal solution behavior at 1000°C, and its activity
coefficient at infinite dilution was about 6.5 relative to pure solid Ti. Indium and Sn did not increase the activity coefficient
of Ti in eutectic Ag-Cu melts. Silver increased the Ti activity coefficient in the Ag-Cu-Ti melts significantly. The Ti activity
coefficient value in liquid Ag was about 20 times higher than in eutectic Ag-Cu melt at 1000 °C. 相似文献
64.
The folic acid antagonists, methotrexate and aminopterin, are known to be teratogenic in humans. The critical period for their teratogenecity is suspected to be between 6 to 8 weeks post-conception. Fetal exposure from 10 to 32 weeks weeks post-conception to methotrexate alone or in combination with other anti-cancer drugs has not resulted in obvious teratogenic effects. Methotrexate is often used to treat cancers but is occasionally used as an abortifacient. The long-term outcome of the fetal aminopterin syndrome has been published in only four adults. We report on a 28-year-old man with fetal methotrexate syndrome and two children with mild manifestations of the syndrome. One child was inadvertently exposed to methotrexate from 7 1/2 through 30 weeks post-conception because his mother was receiving it for treatment of breast cancer. The other was exposed from 11 weeks and 5 days through 25 weeks in an attempt to induce abortion. The 28-year-old man has craniofacial and digital anomalies, growth retardation but normal intelligence as noted in the previously reported cases. These cases remind us of the teratogenicity of methotrexate and should serve as a warning that if methotrexate is used as an abortifaciant and an abortion does not ensue, there is a teratogenic risk. 相似文献
65.
Linear electro-elastic fracture mechanics of piezoelectric materials 总被引:20,自引:0,他引:20
Y. E. Pak 《International Journal of Fracture》1992,54(1):79-100
The concepts of linear elastic fracture mechanics, generalized to treat piezoelectric effects, are employed to study the influence of the electrical fields on the fracture behavior of piezoelectric materials. The method of distributed dislocations and electric dipoles, already existing in the literature, is used to calculate the electro-elastic fields and the energy-release rate for a finite crack embedded in an infinite piezoelectric medium which is subjected to both mechanical and electric loads. The energy-release rate expressions show that the electric fields generally tend to slow the crack growth. It is shown that the stress intensity factor criterion and the energy-release rate criterion differ when the energetics of the electric field is taken into account. The study of crack tip singular stress field yields a possible explanation for experimentally observed crack skewing in the presence of a strong electric field. 相似文献
66.
67.
Hee-Tak Kim Dae Jong You Hae-Kwon Yoon Sang Hoon Joo Chanho Pak Hyuk Chang In-Seob Song 《Journal of power sources》2008,180(2):724-732
The development of a cathode catalyst layer based on a supported Pt catalyst using an ordered mesoporous carbon (OMC) for direct methanol fuel cell is reported. An OMC with a mesopore structure between hexagonally arranged carbon nanorods is prepared using a template method. Platinum nanoparticles are supported on the OMC (Pt/OMC) with high metal loading of 60 wt.%. Compositional and morphological variations are made by varying the ionomer content and by compressing the catalyst layer to detect a parameter that determines the power performance. Increase in power density with decrease in the volume fraction of ionomer in the agglomerate comprising the Pt/OMC and the ionomer indicates that mass transport through the ionomer phase governs the kinetics of oxygen reduction. Impedance spectroscopic analysis suggests that a significant mass-transport limitation occurs at high ionomer content and in the compressed cathode. The power density of the optimum cathode layer, which employs a Pt/OMC catalyst with a Pt loading of 2 mg cm−2, is greater than that of a catalyst layer with 6 mg cm−2 Pt-black catalyst at a voltage higher than 0.4 V. This would lead to a significant reduction in the cost of the membrane electrode assembly. 相似文献
68.
A number of swimming microorganisms, such as ciliates (Opalina) and multicellular colonies of flagellates (Volvox), are approximately spherical in shape and swim using beating arrays of cilia or short flagella covering their surfaces. Their physical actuation on the fluid may be mathematically modeled as the generation of surface velocities on a continuous spherical surface—a model known in the literature as squirming, which has been used to address various aspects of the biological physics of locomotion. Previous analyses of squirming assumed axisymmetric fluid motion and hence required all swimming kinematics to take place along a line. In this paper we generalize squirming to three spatial dimensions. We derive analytically the flow field surrounding a spherical squirmer with arbitrary surface motion and use it to derive its three-dimensional translational and rotational swimming kinematics. We then use our results to physically interpret the flow field induced by the swimmer in terms of fundamental flow singularities up to terms decaying spatially as \({\sim } 1/r^3\) . Our results will make it possible to develop new models in biological physics, in particular in the area of hydrodynamic interactions and collective locomotion. 相似文献
69.
70.
An experimental study is carried out to determine the possibility of utilizing the recycled sinter ore dust for refinging flux for hot metal. The dust has good physical and chemical properties as an injection powder, however, it contains masses of about 0.24% S and a substantial amount of sulfur which can be picked up by the hot metal during the injection treatment. Therefore, sinter ore dust is mixed with burnt lime, fluorspar and sodium carbonate to increase the sulfide capacity of the flux. The fluxes are tested for hot metal dephosphorization and desulfurization in laboratory and plant scale experiments. The fluxes show an excellent dephosphorization efficiency without sulfur pick up. In case of the flux containing sodium carbonate masses of 10%, sulfur in hot metal is simultaneously removed. In addition, a higher manganese yield in hot metal is obtained in case of a sodium carbonate containing flux at the end of injection treatment. 相似文献