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排序方式: 共有275条查询结果,搜索用时 15 毫秒
81.
The operation of ice-going vessels depends on the condition of the hull surface. Corrosion increases the roughness of ship hull, which increases drag and fuel consumption. The hull surface smoothness is maintained by using coatings and cathodic protection. The cold brackish water is different from ocean water as it has lower salt content, lower conductivity, and higher concentration of dissolved oxygen. These factors mean that the design of the cathodic protection system for ship hulls requires different design values, such as protection current density and protected length, than those given in cathodic protection standards. In this paper, we have estimated the protection current density with polarization curves and the protected length by using Wagner number and dimension and conductivity scaling. In brackish water the protection current density was two times that in ocean water. The protected length in brackish water varied between 10 and 15% of that in ocean water. In poorly conducting brackish water, the current capacity of a cathodic protection system is used mostly for overcoming the solution resistance, not for delivering protection current. 相似文献
82.
V.P.S. Awana Anurag Gupta E. Takayama-Muromachi M. Karppinen S.K. Malik V. Ganesan 《Solid State Communications》2004,129(2):117-121
A Tb-123 phase with the composition, TbSr2Cu2.7Mo0.3O7+δ, has been synthesized in single-phase form by the solid-state reaction route. Its phase purity has been confirmed from neutron powder diffraction studies. The as-synthesized Tb-123 sample does not show superconductivity down to 5 K. On the other hand, an unusually high antiferromagnetic ordering temperature (TN) of around 7 K is seen for the Tb moments. After 120-atm-O2 post-annealing, bulk superconductivity is achieved in this compound with a superconducting transition temperature (Tc) of about 30 K, without any significant effect on TN. To achieve higher oxygen content and higher Tc, the as-synthesized sample was subjected to high-pressure oxygenation, carried out in a closed cell, at 5 GPa and 400 °C in the presence of AgO as an excess-oxygen source. This sample exhibited superconductivity onset at around 80 K with a Meissner fraction larger than 10% at 5 K. Our observation of superconductivity at 80 K is the highest Tc to-date for the Tb-123 type compounds. 相似文献
83.
J. Lindén T. Karlemo M. Karppinen T. Katila M. Lippmaa A. Nara L. Niinistö I. Tittonen K. Ullakko H. Yamauchi 《Hyperfine Interactions》1994,93(1):1635-1639
The rare-earth site of samples having the compositions (Fe,Cu)Sr2(Eu,Ce)
n
Cu2O4+2n+z (n=2 and 3) were studied by151Eu Mössbauer spectroscopy. The results obtained are compared with measurements of EuBa2Cu3O7– (123) and Bi2Sr2(Ca1–yEuy)Cu2O8+E
(2212) samples. The full quadrupole Hamiltonian of the 21.5-keV -transition was applied in analyzing the measured spectra. Simultaneous fitting of spectra recorded from crystallites oriented in various directions was used to determine the hyperfine parameters of then= 2 and 3 samples. Two different electric field gradients, not discernible in simple random crystallite measurements, were obtained for then=3 series. 相似文献
84.
Reaction of pernosylated diethylenetriamine and 2-substituted propane-1,3-diols in dry THF in the presence of triphenylphosphine and diisopropyl azodicarboxylate gives the corresponding protected 9-substituted 1,4,7-triazacyclodecanes. The Mitsunobu reaction was also used in the preparation of 3-substituted 1,5,9-triazacyclododecanes and macrocyclic pyridine derivatives. 相似文献
85.
M. Karppinen H. Yamauchi H. Suematsu K. Isawa M. Nagano R. Itti O. Fukunaga 《Journal of solid state chemistry》1997,130(2):213-222
The LaCuO3−yperovskite is considered as the first member of the 01(n−1)nseries of “layered cuprates.” Highly oxidized, stoichiometric LaCuO3is stabilized under very high oxygen pressures, and was synthesized in a cubic-anvil-type high-pressure apparatus at 5 GPa and 1400°C using excess amounts of KClO4as an external oxidizing agent. Upon heating under ambient pressure the rhombohedral high-pressure phase loses oxygen yielding tetragonal, monoclinic, and orthorhombic forms of LaCuO3−yas intermediate products before the final decomposition into La2CuO4and CuO or Cu2O around 800°C. All three oxygen-deficient LaCuO3−yphases could be isolated and their stability limits and corresponding oxygen contents conveniently investigated by annealing stoichiometric LaCuO3in a thermobalance of high sensitivity in order toin situdetect the exact amount of oxygen loss. The nominal copper valence values calculated from the oxygen contents are compared and discussed with XPS data as well as with the results evaluated from magnetic susceptibility measurements. 相似文献
86.
87.
Jari Taskinen 《Mathematische Nachrichten》1995,171(1):303-314
88.
Assuming the existence of genuine unsheared triads, we examine the possibility of having unsheared tetrads, particularly unsheared
genuine tetrads. 相似文献
89.
Kuwata-Gonokami M Saito N Ino Y Kauranen M Jefimovs K Vallius T Turunen J Svirko Y 《Physical review letters》2005,95(22):227401
We examine the spectral dependence in the visible frequency range of the polarization rotation of two-dimensional gratings consisting of chiral gold nanostructures with subwavelength features. The gratings, which do not diffract, are shown to exhibit giant specific rotation (approximately 10(4) degrees/mm) of polarization in direct transmission at normal incidence. The rotation is the same for light incident on the front and back sides of the sample. Such reciprocity indicates three dimensionality of the structure arising from the asymmetry of light-plasmon coupling at the air-metal and substrate-metal interfaces. The structures thus enable polarization control with quasi-two-dimensional planar objects. However, in contradiction with recently suggested interpretation of experiments on larger scale but otherwise similar structures, the observed polarization phenomena violate neither reciprocity nor time-reversal symmetry. 相似文献
90.
Janne Raula Matti Lehtim?ki Maarit Karppinen Maxim Antopolsky Hua Jiang Antti Rahikkala Esko I. Kauppinen 《Journal of nanoparticle research》2012,14(7):1-14
In this article, we describe the synthesis of new and ion-selective nanofiltration (NF) membranes using polyvinylidene fluoride (PVDF) nanofibers and hyperbranched polyethylenimine (PEI) as building blocks. These new nanofibrous composite (NFC) membranes consist of crosslinked hyperbranched PEI networks supported by PVDF nanofibrous scaffolds that are electrospun onto commercial PVDF microfiltration (MF) membranes. A major objective of our study was to fabricate positively charged NF membranes that can be operated at low pressure with high water flux and improved rejection for monovalent cations. To achieve this, we investigated the effects of crosslinker chemistry on membrane properties (morphology, composition, hydrophobicity, and zeta potential) and membrane performance (salt rejection and permeate flux) in aqueous solutions (2,000?mg/L) of four salts (NaCl, MgCl2, Na2SO4, and MgSO4) at pH 4, 6, and 8. We found that an NFC?CPVDF membrane with a network of PEI macromolecules crosslinked with trimesoyl chloride has a high water flux (~30?L?m?2?h?1) and high rejections for MgCl2 (~88 %) and NaCl (~65 %) at pH 6 using a pressure of 7?bar. The overall results of our study suggest that PVDF nanofibers and hyperbranched PEI are promising building blocks for the fabrication of high performance NF membranes for water purification. 相似文献