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41.
Yongjun lv Jian Xu Yong Guo Shijun Shao 《Journal of inclusion phenomena and macrocyclic chemistry》2012,72(1-2):95-101
A novel fluorescent anion sensor 1 based on boradiazaindacenes (BODIPY) derivative was synthesized and its absorption and fluorescence properties were investigated in various solvents. 1 exhibited a red shift of absorption spectrum and fluorescence quenching in varying degree in the presence of F?, AcO?, H2PO4 ? and Cl? due to multiple hydrogen bonding interactions between these anions and calix[4]pyrrole receptor. As an anion sensor in the visible region, 1 displayed the similar selectivity and sensitivity toward anions compared to the parent calix[4]pyrrole. However, 1 can be used as an effective dual responsive optical sensor for F? via chromogenical and fluorogenical signals. 相似文献
42.
Jun-Sheng Zheng Xi-Zhao Wang Jin-Li Qiao Dai-Jun Yang Bing Li Ping Li Hong lv Jian-Xin Ma 《Electrochemistry communications》2010,12(1):27-31
Ir–V nanoparticles supported on microstructure controlled carbon nanofibers (CNFs) or on carbon black, Vulcan XC-72 (XC-72), have been synthesized via chemical reduction, and the oxygen reduction reaction (ORR) properties of catalysts are investigated in this paper. The physico-chemical properties are characterized by high resolution transmission electron microscope (HRTEM), N2 physisorption and electrochemical analysis. HRTEM results show that the metal nanoparticles are separated on carbon support with well-controlled particle size, dispersity, and composition uniformity. Moreover, the metal nanoparticles on CNFs have a smaller size than those on XC-72. Cyclic voltammetric analysis reveals that Ir–V/CNFs exhibits a higher ORR activity than Ir–V/XC-72, and this may be associated with the smaller metal nanoparticles and the stronger metal-support interaction of Ir–V/CNFs. Linear sweep voltammetric analysis at different rotation rates proves that ORR on the Ir–V/CNFs electrode is a 4e? process. 相似文献
43.
Friedrich Eisenbrand Nicolai Hähnle Dömötör Pálvölgyi Gennady Shmonin 《Mathematical Programming》2013,141(1-2):257-271
We consider the problem of testing whether the maximum additive integrality gap of a family of integer programs in standard form is bounded by a given constant. This can be viewed as a generalization of the integer rounding property, which can be tested in polynomial time if the number of constraints is fixed. It turns out that this generalization is NP-hard even if the number of constraints is fixed. However, if, in addition, the objective is the all-one vector, then one can test in polynomial time whether the additive gap is bounded by a constant. 相似文献
44.
M.?Vorona G.?VeinbergEmail author S.?Vikainis E.?Kuznetsov A.?Lebedev Yu.?Ponomarev A.?Chernobrovijs L.?Zvejniece M.?Dambrova 《Chemistry of Heterocyclic Compounds》2012,48(5):720-723
Two novel methods have been developed for the preparation of 2-[(4R)-2-oxo-4-phenylpyrrolidin-1-yl]acetamide ((R)-Phenotropil). In the first, n-butyl (3R)-4-amino-3-phenylbutyrate is alkylated with haloacetamide in DMF in the presence of potassium phosphate monohydrate, and the intermediate 4-carbamoylmethylamino-3-phenylbutyrate is subsequently cyclized by refluxing in toluene in the presence of potassium phosphate monohydrate and tetrabutylammonium bromide. In the second, chloroacetonitrile is used under similar conditions in place of the haloacetamide. Both methods lead to (R)-Phenotropil in 40-60% yields calculated on the starting n-butyl (3R)-4-amino-3-phenylbutyrate. 相似文献
45.
A theoretical investigation on the two pulses copropagation and the red-shifted radiation generation in a photonic crystal fiber with two zero-dispersion wavelengths are presented. It is found the intensity of the red-shifted radiation components can be enhanced when the fiber is pumped with two pulses and the pulse trapping occurs. As the input peak power of the pump pulse is increased under the phenomenon of pulse trapping, the intensity of the red-shift radiation can be further enhanced. The above effects can be explained by the energy transfer from the Raman soliton to the red-shifted radiation components due to the effect of pulse trapping and the effect of higher-order dispersion. 相似文献
46.
Dömötör Pálvölgyi 《Discrete and Computational Geometry》2010,44(3):577-588
We show that for any concave polygon that has no parallel sides and for any k, there is a k-fold covering of some point set by the translates of this polygon that cannot be decomposed into two coverings. Moreover,
we give a complete classification of open polygons with this property. We also construct for any polytope (having dimension
at least three) and for any k, a k-fold covering of the space by its translates that cannot be decomposed into two coverings. 相似文献
47.
Peijun Wang Xiaoli Chao Yilong Wu Yusha lv 《Annals of Global Analysis and Geometry》2018,54(4):473-487
In the present note, the geometric structures and topological properties of harmonic p-forms on a complete noncompact submanifold \(M^{n}(n\ge 4)\) immersed in Hadamard manifold \(N^{n+m}\) are discussed, where \(M^{n}\) and \(N^{n+m}\) are assumed to have flat normal bundle and pure curvature tensor, respectively. Firstly, under the assumption that \(M^{n}\) satisfies the \((\mathcal {P}_\rho )\) property (i.e., the weighted Poincaré inequality holds on \(M^{n}\)) and the \((p,n-p)\)-curvature of \(N^{n+m}\) is not less than a given negative constant, using Moser iteration, the space of all \(L^{2}\) harmonic p-forms on \(M^{n}\) is proven to have finite dimensions if \(M^{n}\) has finite total curvature. Furthermore, if the total curvature is small enough or \(M^{n}\) has at most Euclidean volume growth, two vanishing theorems are, respectively, established for harmonic p-forms. Note that the two vanishing theorems extend several previous results obtained by H. Z. Lin. 相似文献
48.
49.
J.?Kaupu?sEmail author 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,45(4):459-463
The recently published experimental data for specific heat Cp
of liquid helium in zero gravity conditions very close to the
λ–transition have been discussed. We have shown
that these data allow different interpretations.
They can be well interpreted within the perturbative
RG approach and within our recently developed theory, as well.
Allowing the logarithmic correction, the corresponding fits lie
almost on top of each other over the whole range of the reduced
temperatures t (for bin averaged data)
6.3 ×10-10 < t < 8.8 ×10-3.
However, the plot of the effective exponent α eff(t)
suggests that the behaviour of Cp, probably, changes very close to Tλ.
To clarify this question, we need more accurate data for t<10-7.
In addition, we show that the experimental data
for superfluid fraction of liquid helium close to Tλ
within t ∈[3 ×10-7;10-4] can be better fit
by our exponents ν=9/13 ≃0.6923, Δ=5/13 ≃0.3846
than by the RG exponents ν≃0.6705 and Δ≃0.5.
The latter ones are preferable to fit the whole measured range
t ∈[3 ×10-7;10-2] where, however, remarkable
systematic deviations appear.
Our estimated value 0.694 ±0.017 of the asymptotic exponent ν
well agrees with the theoretical prediction ν=9/13. 相似文献
50.
We introduce a novel and general approach for digitalization of line segments in the plane that satisfies a set of axioms naturally arising from Euclidean axioms. In particular, we show how to derive such a system of digital segments from any total order on the integers. As a consequence, using a well-chosen total order, we manage to define a system of digital segments such that all digital segments are, in Hausdorff metric, optimally close to their corresponding Euclidean segments, thus giving an explicit construction that resolves the main question of [J. Chun, M. Korman, M. Nöllenburg, and T. Tokuyama. Consistent digital rays. Discrete Comput. Geom., 42(3):359–378, 2009]. 相似文献