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841.
用真空电弧熔炼法制备了Ce2 Co17-xMx(M =Ga ,Al和Si)化合物。通过X射线衍射和磁性测量手段 ,研究了非磁性替代原子Ga,Al和Si的加入对Ce2 Co17化合物的居里温度和饱和磁化强度的影响 ,其中Si在Ce2 Co17化合物中的固溶度最小 ,并使居里温度和饱和磁化强度下降幅度最大。 相似文献
842.
A.C.oscillopolarographyintroducedbyHeyrovskyinl94lhasbeendevelopedintoanewfieldofelectroanalyticalchemistry-osciIIographicanaIysis'.Astothedevelopmentofelectrode,thechangefromthedroppingmercuryeIectrode(DME)tothesolidelectrode(thehangingmercurydropelectrodeormercuryfilmelectrode)makesoscillographicanalysisarealpracticalvaIue2.Hencedevelopinganewtypeofelectrodeisimportantfortheprogressofoscillographicanalysis.Thepresentpaperdescribestheinvestigationofoscillographicchrono-potentiometryatsilv… 相似文献
843.
844.
Xiaotie Deng Toshihide Ibaraki Hiroshi Nagamochi Wenan Zang 《Mathematical Programming》2000,87(3):441-452
Combinatorial optimization games deal with cooperative games for which the value of every subset of players is obtained by
solving a combinatorial optimization problem on the resources collectively owned by this subset. A solution of the game is
in the core if no subset of players is able to gain advantage by breaking away from this collective decision of all players.
The game is totally balanced if and only if the core is non-empty for every induced subgame of it.?We study the total balancedness
of several combinatorial optimization games in this paper. For a class of the partition game [5], we have a complete characterization
for the total balancedness. For the packing and covering games [3], we completely clarify the relationship between the related
primal/dual linear programs for the corresponding games to be totally balanced. Our work opens up the question of fully characterizing
the combinatorial structures of totally balanced packing and covering games, for which we present some interesting examples:
the totally balanced matching, vertex cover, and minimum coloring games.
Received: November 5, 1998 / Accepted: September 8, 1999?Published online February 23, 2000 相似文献
845.
Li‐Ping Li Guang‐She Li Wen‐Hui Su Xu‐Dong Zhao Xiaoyang Liu 《Hyperfine Interactions》2000,128(4):409-415
A series of hexaborides La1?xEuxB6 (x=0.0–1.0) were synthesized under a pressure of 3.5 GPa and at a temperature of 1600○C using La2O3, Eu2O3 and amorphous boron as the starting materials. The products were characterized by X‐ray Diffraction (XRD) and Mössbauer spectroscopy. XRD data analysis shows that all samples crystallize in a cubic CsCl‐type structure, and the cell volume increases with x. Room temperature 151Eu Mössbauer measurements reveal that Eu ions in all samples are in the divalent state, except for the x=1.0 sample where a small amount of Eu3+ ions was detected. The quadrupole splitting of the Eu2+ ions is positive. Eu ions were reduced from trivalent to divalent during the high‐pressure and ‐temperature processes. The isomer shifts of the Eu2+ ions are all smaller than ?12.5 mm/s, suggesting that there is no valence fluctuation in the samples. The hexaborides doped by divalent Eu are not metallic. 相似文献
846.
From Maxwell’ s equations for electromagnetic fields, time-averaged energy flow density vector of stable monochromatic linearly
polarized light in an isotropic insulative nonmagnetic medium is deduced. By the introduction of time-averaged energy flow
density rays and the definition of new generalized refractive indexn
G1, Fermat’s principle of geometric optics is further generalized and its application conditions are discussed. The generalized
Fermat' s principle can be used to describe stable transmission of light in a medium with variable refractive index. The necessary
and sufficient conditions of a nondivergent and nonfocusing light beam are derived from this Fermat’s principle.
Project supported by the National Natural Science Foundation of China (Grant No. 69789801) and Guangdong Provincial Natural
Science Foundation of China. 相似文献
847.
Yang Gao Simin Yang Minwei She Jianhong Nie Yanping Huo Qian Chen Xianwei Li Xiao-Qiang Hu 《Chemical science》2022,13(7):2105
We report a practical route for the synthesis of valuable 3-aryl anthranils from readily available anthranils and simple arenes by using the classical electrophilic aromatic substitution (EAS) strategy. This transformation goes through an electrophilic substitution and rearomatisation sequence by employing Tf2O as an effective activator. A wide range of arenes were compatible in this transformation, delivering various structurally diversified 3-aryl anthranils in good yields and high regioselectivity. In addition, a variety of readily available feedstocks such as olefins, alkenyl triflates, silyl enolethers, carbonyl compounds, thiophenols and thiols could also participate in the reaction to achieve the C3 alkenylation, alkylation and thioetherification of anthranils. Of note, the synthesized 3-aryl anthranils proved to be a highly robust platform to access a series of biologically active compounds, drug derivatives and organic optoelectronic materials.A practical route for the synthesis of valuable 3-aryl anthranils from readily available anthranils and simple arenes has been achieved through an electrophilic substitution and rearomatization sequence by employing Tf2O as an effective activator. 相似文献
848.
849.
离子色谱法(安培检测器)测定血清、尿及头发中微量碘 总被引:7,自引:0,他引:7
This paper intreduces a reasonable pretreatment method for IC-amperometric method employed to measuretrace amount of iodine in serum, urine and hair. The resultant graph is simple and clear,and withoutinterference in a general way. The limits of detection for iodine in serum,urine and hair are 0.007,0.003μg/mL and 0. 046μg/g, respectively.The recovery of iodine added into the sample is 82~93%. The coefficient ofvariation is less than 9%. Trace amount of bromine in the sample can also be measured simultan 相似文献
850.
We wish to explore all edges of an unknown directed, strongly connected graph. At each point, we have a map of all nodes and edges we have visited, we can recognize these nodes and edges if we see them again, and we know how many unexplored edges emanate from each node we have visited, but we cannot tell where each leads until we traverse it. We wish to minimize the ratio of the total number of edges traversed divided by the optimum number of traversals, had we known the graph. For Eulerian graphs, this ratio cannot be better than two, and two is achievable by a simple algorithm. In contrast, the ratio is unbounded when the deficiency of the graph (the number of edges that have to be added to make it Eulerian) is unbounded. Our main result is an algorithm that achieves a bounded ratio when the deficiency is bounded. © 1999 John Wiley & Sons, Inc. J Graph Theory 32: 265–297, 1999 相似文献