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201.
Peljo P Murtomäki L Kallio T Xu HJ Meyer M Gros CP Barbe JM Girault HH Laasonen K Kontturi K 《Journal of the American Chemical Society》2012,134(13):5974-5984
Oxygen reduction catalyzed by cofacial metalloporphyrins at the 1,2-dichlorobenzene-water interface was studied with two lipophilic electron donors of similar driving force, 1,1'-dimethylferrocene (DMFc) and tetrathiafulvalene (TTF). The reaction produces mainly water and some hydrogen peroxide, but the mediator has a significant effect on the selectivity, as DMFc and the porphyrins themselves catalyze the decomposition and the further reduction of hydrogen peroxide. Density functional theory calculations indicate that the biscobaltporphyrin, 4,5-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]-9,9-dimethylxanthene, Co(2)(DPX), actually catalyzes oxygen reduction to hydrogen peroxide when oxygen is bound on the "exo" side ("dock-on") of the catalyst, while four-electron reduction takes place with oxygen bound on the "endo" side ("dock-in") of the molecule. These results can be explained by a "dock-on/dock-in" mechanism. The next step for improving bioinspired oxygen reduction catalysts would be blocking the "dock-on" path to achieve selective four-electron reduction of molecular oxygen. 相似文献
202.
In this paper, we study the nonhomogeneous n-harmonic equation $$-{\rm div}\,(|{\nabla} u|^{n-2}{\nabla} u)=f$$ in domains ${\Omega\subset {\mathbb {R}^n}}$ (n?≥?2), where ${f\in W^{-1,\frac{n}{n-1}}(\Omega)}$ . We derive a sharp condition to guarantee the continuity of solutions u. In particular, we show that when n?≥ 3, the condition that, for some ${\epsilon >0 ,}$ f belongs to $${\mathfrak{L}}({\rm log}\,{\mathfrak{L}})^{n-1}({\rm log}\,{\rm log}\,{\mathfrak{L}})^{n-2}\cdots({\rm log}\cdots{\rm log}\,{\mathfrak{L}})^{n-2}({\rm log}\cdots{\rm log}\,{\mathfrak{L}})^{n-2+\epsilon}(\Omega)$$ is sufficient for continuity of u, but not for ${\epsilon=0}$ . 相似文献
203.
204.
Pekka Malo 《Physica A》2009,388(22):4763-4779
Electricity prices are known to exhibit multifractal properties. We accommodate this finding by investigating multifractal models for electricity prices. In this paper we propose a flexible Copula-MSM (Markov Switching Multifractal) approach for modeling spot and weekly futures price dynamics. By using a conditional copula function, the framework allows us to separately model the dependence structure, while enabling use of multifractal stochastic volatility models to characterize fluctuations in marginal returns. An empirical experiment is carried out using data from Nord Pool. A study of volatility forecasting performance for electricity spot prices reveals that multifractal techniques are a competitive alternative to GARCH models. We also demonstrate how the Copula-MSM model can be employed for finding optimal portfolios, which minimizes the Conditional Value-at-Risk. 相似文献
205.
Pekka Pyykkö Prof. Michiko Atsumi Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(46):12770-12779
The previous systems of triple‐bond and single‐bond self‐consistent, additive covalent radii, R(AB)=r(A)+ r(B), are completed with a fit for σ2π2 double‐bonds.The primary bond lengths, R, are taken from experimental or theoretical data corresponding to chosen group valencies. All r(E) values are obtained from the same, self‐consistent fit. Many of the calculated primary data came from E?CH2 and H? E?CH2 models. Homonuclear LE?EL, formaldehyde‐type Group 14–Group 16 and open‐shell, X 3 Σ Group‐16 dimer data are included. The standard deviation for the 316 included data points is 3 pm. 相似文献
206.
Molecular assays such as immunoassays are often performed using solid carriers and fluorescent labels. In such an assay format
a question can be raised on how much the fluorescence of the label is influenced by the bio-affinity binding events and the
solid carrier surface. Since changes in fluorescence intensity as labels bind to surfaces are notoriously difficult to quantify
other approaches are preferred. A good indicator, independent of the fluorescence intensity of the label, is the fluorescence
lifetime of the marker fluorophore. Changes in fluorescence lifetime reliably indicate the presence of dynamic quenching,
energy transfer or other de-excitation processes. A microsphere based assay system is studied under two-photon excitation.
Changes in fluorescence lifetime are studied as labeled protein conjugates bind on microsphere surfaces – both direct on the
surface and with a few nanometer distance from the surface. Fluorescence signal is measured from individual polystyrene microspheres
and the fluorescence lifetime histogram is simultaneously recorded. The results indicate that self-quenching and quenching
by the polystyrene surface are both present in such a system. However, the effect of the surface can be avoided by increasing
the distance between the surface and the label. Typical distances achieved by a standard sandwich type of assay, are already
sufficient to overcome the surface induced quenching in fluorescence detection. 相似文献
207.
Tallavaara P Jokisaari J 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2006,181(2):229-232
A novel technique to prepare pressurized glass insert samples for MAS rotors is described. In this technique, a small drop of epoxy is added to the tip of a piston and the gas is squeezed into the insert by pressing the piston. The amount of gas, i.e., pressure, in the sample can be controlled by the overall length of an insert test tube. As examples, (129)Xe NMR spectra taken from samples containing xenon gas, xenon gas and liquid crystal, and xenon gas, liquid crystal and porous solid, are shown. In principle, the method is feasible for making any kind of samples into glass inserts. 相似文献
208.
Kenneth V Christensen Henrik Leffers William P Watson Connie Sánchez Pekka Kallunki Jan Egebjerg 《BMC neuroscience》2010,11(1):9
Background
The amygdala-kindled rat is a model for human temporal lobe epilepsy and activity-dependent synaptic plasticity. Hippocampal RNA isolated from amygdala-kindled rats at different kindling stages was analyzed to identify kindling-induced genes. Furthermore, effects of the anti-epileptic drug levetiracetam on kindling-induced gene expression were examined. 相似文献209.
Nikolay Banichuk Alexander Barsuk Svetlana Ivanova Evgeni Makeev Pekka Neittaanmäki 《基于设计的结构力学与机械力学》2018,46(5):615-633
We consider an infinite continuous elastic beam that interacts with linearly elastic foundation and is under compression. The problem of the beam buckling is formulated and analyzed. Then the optimization of beam against buckling is investigated. As a design variable (control function) we take the parameters of cross-section distribution of the beam from the set of periodic functions and transform the original problem of optimization of infinite beam to the corresponding problem defined at the finite interval. All investigations are on the whole founded on the analytical variational approaches and the optimal solutions are studied as a function of problems parameters. 相似文献
210.
Pekka Pyykkö 《Molecular physics》2018,116(10):1328-1338
A ‘year-2017’ set of nuclear quadrupole moments, Q, is presented. Compared to the previous, ‘year-2008’ set, a major revision of the value, or an improvement of the accuracy is reported for 21H, 37, 3918Ar, 39, 40, 4119K, 6730Zn, 48Cd, 49In, 50Sn (Mössbauer state), 51Sb, 87Fr and 90Th. Slight improvements or valuable reconfirmations exist for 4Be, 6C, 16S, 17Cl, 33As, 35Br, 53I, 54Xe, 56Ba, 57La and 72Hf. 相似文献