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排序方式: 共有994条查询结果,搜索用时 31 毫秒
51.
52.
Oleg A. Kazantsev Dmitry V. Orekhov Denis M. Kamorin Maria V. Savinova 《Designed Monomers and Polymers》2017,20(1):136-143
Concentration effects in the base-catalyzed hydrolysis of water-soluble methacrylates (3-(N,N-dimethylaminoethyl) methacrylate (DMAEMA), 2-hydroxyethyl methacrylate (HEMA) and oligo(ethylene glycol) methacrylates (OEGMAs)) have been studied. These monomers are rapidly hydrolyzed in the presence of bases at the room temperature in dilute aqueous solutions, but the reaction rate decreases sharply in highly concentrated solutions. A clear correlation was found between a form of the viscosity isotherm for DMAEMA solutions and the concentration dependence of the autocatalytic hydrolysis rate which indicates the connection of process kinetics with the structure of solutions. These data should be considered when carrying out homo- and copolymerization of the previously mentioned monomers in aqueous solutions. 相似文献
53.
将Al-5Mg-0.18Mn-0.2Sc-0.08Zr-0.01Fe-0.01Si(质量分数,%)合金铸锭进行多向等温锻造(应变12)或等径角挤压(应变10,325℃),再进行热轧(325℃)和冷轧(20℃),对比研究合金变形后的组织和力学行为.结果表明,对(亚)晶粒尺寸dUFG=2μm的超细晶组织合金进行多向等温锻造... 相似文献
54.
Zoltan Zyman Matthias Epple Anton Goncharenko Dmytro Rokhmistrov Oleg Prymak Kateryna Loza 《Journal of materials science. Materials in medicine》2017,28(3):52
Thermal evolution of amorphous calcium phosphate (ACP) powder from a fast nitrate synthesis with a Ca/P ratio of 1:1 were studied in the range of 20–980?°C. The powder consisted of amorphous dicalcium phosphate anhydrate (CaHPO4) after heating to 200?°C. CaHPO4 gradually condensed to amorphous calcium pyrophosphate Ca2P2O7 (CPP) between 200 to 620?°C. Amorphous CPP crystallized at 620–740?°C to a metastable polymorph α′-CPP of the high-temperature phase α-CPP and β-CPP. The α′-CPP/ β-CPP phase ratio reached a maximum at 800?°C (60?wt% α′-CPP/40?wt% β-CPP), and α′-CPP gradually transformed to β-CPP at a higher temperature. Some β-TCP occurred at 900?°C, so that a three-phasic mixture was obtained in the powder heated to 980?°C. The occurrence of metastable α′-CPP is attributed to Ostwald’s step rule, and a mechanism for β-TCP formation is proposed. The advantages of prospective biomaterials from these powders are discussed. 相似文献
55.
Carlo S. Iorio Olga Goncharova Oleg A. Kabov 《Microgravity science and technology》2009,21(Z1):313-319
When a layer of volatile liquid is exposed to a shear flow of inert gas, thermal patterns, in the form of interfacial ripples
and bulk plumes, are created by the combined action of evaporative, shear-driven and surface-tension-driven instabilities.
The topology of the interfacial thermal patterns is mainly influenced by the geometry of the evaporating surface, the thickness
of the evaporating layer, the intensity of the shear flow and by the physic-chemical properties of the working fluid. In this
paper, by means of numerical simulations, we focused our attention on the dynamics of the interfacial thermal patterns for
different working fluids and thicknesses of the volatile liquid layer. This study has been performed in the frame of the ESA
sponsored Space Program on heat and mass transfer CIMEX-1. The choice of the fluids—ethyl alcohol and FC72 (n-perfluorohexane)—the
reference values for the inert gas flow rate, the thickness of the liquid layer as well as the geometrical features of the
computational domain correspond exactly to the ones foreseen for the CIMEX-1 experiment. However, the main conclusions can
be considered of more general validity. 相似文献
56.
The results of activity made in the framework of preparation of the experiment SAFIR (Single fin condensAtion: FIlm local measuRements) of European Space Agency are presented. First prototype of the test cell has been developed and tested. Confocal technique has been adopted for condensate film thickness measurements. Experiments on condensation of the liquid FC-72 have been carried out. Average heat transfer coefficient has been measured in the range of 880–1440 W/m2 K and compared to the Nusselt theory. 相似文献
57.
A new system of equations for modeling the dynamics of long-wave perturbations on the surface of a viscous liquid film flowing down a vertical plane was investigated. It is shown that the system obtained agrees with a known system derived by the variable changing method but unlikely has a conservative form that is perfect for designing of numerical efficient conservative difference schemes. The system is reduced to a single conservative equation for the function analogous to the hydrodynamic stream function with the appropriate boundary conditions. For the case of moderate Reynolds number it is noted that the equation with boundary conditions coincide with the well known Shkadov’s model under the assumption of self-similar profile of longitudinal velocity. At small Reynolds numbers typical to the condition of microgravity it was proved that the system is reduces to one evolution equation for the film thickness. 相似文献
58.
Experimental Study of Laminar Convective Condensation of Pure Vapor Inside an Inclined Circular Tube
Yuriy Lyulin Igor Marchuk Sergey Chikov Oleg Kabov 《Microgravity science and technology》2011,23(4):439-445
Convective condensation of pure ethanol vapor inside a smooth tube of inner diameter 4.8 mm and of length 200 mm is studied.
The experiments have been carried out at temperature 58°C corresponding to the pressure of 440 mbar, the vapor mass velocity
varying from 0.24 to 2.04 kg/(m2 s). The dependency of the Heat Transfer Coefficient (HTC) is investigated experimentally both subject to the temperature
difference between the saturated vapor and the wall and subject to the condenser inclination. The results show that the HTC
reduces with growth of the temperature difference. The dependency of the HTC on inclination has a maximum in the range 15°–35°
due to the complex gravity drainage mechanism of the condensed liquid. The results could be useful for development of compact
effective cooling systems for space and ground application. 相似文献
59.
Yury Kapelyushin Yasushi Sasaki Jianqiang Zhang Sunkwang Jeong Oleg Ostrovski 《Metallurgical and Materials Transactions B》2017,48(2):889-899
Reduction of un-doped magnetite is developed topochemically with the formation of a dense iron shell. However, the reduction of alumina-doped magnetite to wüstite proceeds with the formation of a network-like structure which consists of criss-crossed horizontal and vertical plates of wüstite. Reduction of magnetite includes the conversion of Fe3+ to Fe2+ and the movement of iron cations from the tetrahedral sites on the {400} and {220} planes of magnetite to the octahedral sites on the {200} planes of wüstite. Alumina has a negligibly small solubility in wüstite. In the reduction of magnetite doped with Al2O3, rejected Al3+ cations from wüstite diffuse to the magnetite–hercynite solid solution. Enrichment of the Fe3O4–FeAl2O4 solution with alumina in the vicinity of the reduction interface restricts the growth of {220} planes of wüstite and nucleation of {220} planes adjusted to the existing planes, preventing the merging of wüstite plates during the reduction process. Reduction of magnetite from the magnetite–hercynite solid solution practically stops when the Al3+ content at the interface approaches the solubility limit. Wüstite in the separated plates is reduced further to iron. 相似文献
60.
The problem of reconstructing the reflectivity of a biological tissue is examined by means of blind deconvolution of the echo ultrasound signals. It is shown that the quality of the reconstruction procedure can be significantly improved when initially the ultrasonic pulse is accurately estimated. A new approach to the estimation of the ultrasound pulse echo sequences is proposed, using local polynomial approximation, which is closely related to the wavelet transform theory. This approach can be viewed as a modification of homomorphic deconvolution, by using bases different from the Fourier basis of the space of square-integrable functions L2. The bases used here are the orthogonal compactly supported wavelet bases. It is shown that the locality of the estimate can be extremely useful in number of cases of practical interest, resulting in estimates with smaller root-mean squared (rms) errors, as compared with estimates employing the Fourier basis. This approach is applied to ultrasound signals, for estimation of the ultrasound pulse log-spectrum from the log-spectrum of radio-frequency (RF) sequences. It is shown, conceptually and experimentally, that the proposed approach can provide robust and rapidly computed estimates of the ultrasound pulses from the RF-sequences, as obtained in the process of tissue scanning. The pulse phase was recovered using the minimum-phase assumption, which was found to hold for the transducers in use. The obtained pulse estimates are used for the deconvolution of the RF-sequences, which result in stable estimates of the tissue reflectivity function, fairly independent of the properties of the imaging system. Simulated data, data obtained from several phantoms and from in vitro experiments have been processed and the results seem to be quite promising. 相似文献