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排序方式: 共有241条查询结果,搜索用时 31 毫秒
21.
This study deals with O2− generation in corona discharge (CD) in point to plane geometry for single flow ion mobility spectrometry (IMS) with gas outlet located behind the ionization source. We have designed CD of special geometry in order to achieve the high O2− yield. Using this ion source we have achieved in zero air conditions that up to 74% all negative ions were O2− or O2−(H2O). It has been demonstrated that the non-electronegative nitrogen positively influences the efficiency of O2− generation in O2/N2 mixtures. The reduced ion mobility of 2.27 cm2 V−1 s−1 has been measured for O2−/O2−(H2O) ions in zero air. Additional ions detected in zero air (less than 200 ppb CO2) using the mass spectrometric and IMS technique were, NO2−, N2O2− (2.37 cm2 V−1 s−1), NO3−, N2O3− and N2O3−(H2O). The CO3− and CO4− ions have been detected after the introduction of 5 ppm CO2 into zero air. 相似文献
22.
Karamov O. G. Rybalkin V. P. Makarova N. I. Metelitsa A. V. Kozyrev V. S. Borodkin G. S. Popova L. L. Breń V. A. Minkin V. I. 《Russian Chemical Bulletin》2011,60(1):168-174
New dihetarylethenes containing the six-membered bridging moiety, viz., N
2-alkyl-5-furyl-4-thienylpyridazinones, were synthesized. These compounds have photochromic properties in solution. The hindered
rotation of the thiophene and furan rings around the single bonds that link these rings to the double bond of the pyridazinone
moiety results in the formation of mixtures of chiral diastereomers in solution, the lifetimes of the diastereomers being
no longer than 0.2 s. The photochromic rearrangement of pyridazinones is characterized by the highly efficient photocoloration
and the photobleaching, which is an order of magnitude less efficient, in the absence of thermal relaxation processes. 相似文献
23.
In Bani?, ?repnjak, Merhar and Milutinovi? (2010) [2] the authors proved that if a sequence of graphs of surjective upper semi-continuous set-valued functions fn:X→X2 converges to the graph of a continuous single-valued function f:X→X, then the sequence of corresponding inverse limits obtained from fn converges to the inverse limit obtained from f. In this paper a more general result is presented in which surjectivity of fn is not required. The result is also generalized to the case of inverse sequences with non-constant sequences of bonding maps. Finally, these new theorems are applied to inverse limits with tent maps. Among other applications, it is shown that the inverse limits appearing in the Ingram conjecture (with a point added) form an arc. 相似文献
24.
Jirkovský JS Panas I Ahlberg E Halasa M Romani S Schiffrin DJ 《Journal of the American Chemical Society》2011,133(48):19432-19441
A novel strategy to direct the oxygen reduction reaction to preferentially produce H(2)O(2) is formulated and evaluated. The approach combines the inertness of Au nanoparticles toward oxidation, with the improved O(2) sticking probability of isolated transition metal "guest" atoms embedded in the Au "host". DFT modeling was employed to screen for the best alloy candidates. Modeling indicates that isolated alloying atoms of Pd, Pt, or Rh placed within the Au surface should enhance the H(2)O(2) production relative to pure Au. Consequently, Au(1-x)Pd(x) nanoalloys with variable Pd content supported on Vulcan XC-72 were prepared to investigate the predicted selectivity toward H(2)O(2) production for Au alloyed with Pd. It is demonstrated that increasing the Pd concentration to 8% leads to an increase of the electrocatalytic H(2)O(2) production selectivity up to nearly 95%, when the nanoparticles are placed in an environment compatible with that of a proton exchange membrane. Further increase of Pd content leads to a drop in H(2)O(2) selectivity, to below 10% for x = 0.5. It is proposed that the enhancement in H(2)O(2) selectivity is caused by the presence of individual surface Pd atoms surrounded by gold, whereas surface ensembles of contiguous Pd atoms support H(2)O formation. The results are discussed in the context of exergonic electrocatalytic H(2)O(2) synthesis in Polymer Electrolyte Fuel Cells for the simultaneous cogeneration of chemicals and electricity, the latter a credit to production costs. 相似文献
25.
An alternative approach to the study of Jordan ideals in associative algebras is considered. The same method can be used when analogous questions in graded algebras are treated. 相似文献
26.
This work presents a systematic theoretical study on Cu(I) and Cu(II) cations in variable hydrogen sulfide-aqua-ammine ligand fields. These ligands model the biologically most common environment for Cu ions. Molecular structures of the complexes were optimized at the density functional theory (DFT) level. Subsequent thorough energy analyses revealed the following trends: (i) The ammine complexes are the most stable, followed by those containing the aqua and hydrogen sulfide ligands, which are characterized by similar stabilization energies. (ii) The most preferred Cu(I) coordination number is 2 in ammine or aqua ligand fields. A qualitatively different binding picture was obtained for complexes with H(2)S ligands where the 4-coordination is favored. (iii) The 4- and 5-coordinated structures belong to the most stable complexes for Cu(II), regardless of the ligand types. Vertical and adiabatic ionization potentials of Cu(I) complexes were calculated. Charge distribution (using the natural population analysis (NPA) method) and molecular orbital analyses were performed to elucidate the nature of bonding in the examined systems. The results provide in-depth insight into the Cu-binding properties and can be, among others, used for the calibration of bioinorganic force fields. 相似文献
27.
Tadej Dolenec Sbreveivana Lambasbrevea Matej Dolenec 《Isotopes in environmental and health studies》2013,49(1):77-85
Analyses of nitrogen stable isotopes in the marine sea grass Posidonia oceanica were used to investigate the influence of fish farming on the coastal ecosystem of Vrgada Island in the Murter Sea, Central Adriatic. The results show a statistically significant 15N enrichment (up to 4.7‰ at p?<?0.005) in P. oceanica leaf and shoot tissues from fish cage sites with respect to the unaffected offshore reference site of Lumbarda Reef Flat (Kornati Islands). Heavy nitrogen enrichment was also detected in other benthic organisms analysed during this study and is attributed to the absorption and assimilation of 15N-enriched fish farm derived nitrogen waste. 相似文献
28.
29.
Let c(x 1,?…?,?x d ) be a multihomogeneous central polynomial for the n?×?n matrix algebra M n (K) over an infinite field K of positive characteristic p. We show that there exists a multihomogeneous polynomial c 0(x 1,?…?,?x d ) of the same degree and with coefficients in the prime field 𝔽 p which is central for the algebra M n (F) for any (possibly finite) field F of characteristic p. The proof is elementary and uses standard combinatorial techniques only. 相似文献
30.
Let R be a ring and let A be a subset of R. A map f : A→ R is commuting on A if [f(x),x]= 0 for all xεA where [x,y] = xy — yx. Suppose that R is a prime ring of characteristic ≠2 with extended centroid C. If L is a noncommutative Lie ideal of R and f:L→R an additive commuting map, then there is λε C and an additive map ∈: L→ C such that f(v) = λ(v)=λv+∈((v) for all vεL. 相似文献