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排序方式: 共有61条查询结果,搜索用时 250 毫秒
31.
MP Blencowe 《Contemporary Physics》2013,54(4):249-264
Nanoelectromechanical systems (NEMS) are nano-to-micrometer scale mechanical resonators coupled to electronic devices of similar dimensions. NEMS show promise for fast, ultrasensitive force microscopy and for deepening our understanding of how classical dynamics arises by approximation to quantum dynamics. This article begins with a survey of NEMS and then describes certain aspects of their classical dynamics. In particular, we show that for weak coupling the action of the electronic device on the mechanical resonator can be effectively that of a thermal bath, this despite the device being a driven, far-from-equilibrium system. 相似文献
32.
Claire Besson Djamaladdin G. Musaev Vanina Lahootun Rui Cao Lise‐Marie Chamoreau Richard Villanneau Françoise Villain René Thouvenot Yurii V. Geletii Craig L. Hill Anna Proust 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(39):10233-10243
Reaction of the divacant polyoxometalate K8[γ‐XW10O36] (X=Si, Ge) with two equivalents of the metal‐nitrido precursor Cs2[RuVINCl5], at room temperature in water, produces K2(Me2NH2)2H2[γ‐XW10O38{RuN}2], X=Si ( DMA ‐ 1 a ) or Ge ( DMA ‐ 1 b ). The X‐ray crystal structures of both complexes show monomeric complexes with highly unusual vicinal terminal metal‐nitrido units. The Ru?N bond lengths are 1.594(10) and 1.612(11) Å in 1 a and 1 b , respectively. EXAFS studies confirmed the key structural assignments from X‐ray crystallography. The XANES spectrum of DMA‐1 a , diamagnetism, NMR (29Si and 183W) chemical shifts, voltammetric behavior, reductive titrations with [PW12O40]4?, and computational data are all consistent with d2 RuVI centers in these complexes. The FT‐IR and Raman spectra show the expected vibrational modes of the {γ‐XW10} unit and the Ru?N stretch at 1080 cm?1, respectively. Interestingly, reduction of DMA‐1 a by 4 equivalents of [PW12O40]4? produces NH3 in nearly quantitative yield. Cyclic voltammetry versus pH and calculations provide the energetics for the possible two‐electron reduction and two‐proton addition processes in this reaction. 相似文献
33.
A. A. Naberezhnov O. A. Alekseeva P. Yu. Vanina D. Yu. Chernyshov A. A. Sysoeva E. Rysiakiewicz-Pasek 《Bulletin of the Russian Academy of Sciences: Physics》2018,82(3):238-241
Temperature dependences of the order parameter in nanocomposites based on porous borosilicate glasses with mean pore diameters of 20 and 46 nm and filled with sodium nitrite are studied via the diffraction of synchrotron radiation. The mean diffraction sizes of NaNO2 nanoparticles in the pores of these matrices and the temperatures of the transition of sodium nitrite to the ferroelectric state are determined. It is shown that the phase transition for these nanoparticles remains a first-order phase transition. 相似文献
34.
Using a streak camera we have measured the three Stokes polarization parameters during a polarization switch of a vertical-cavity semiconductor laser. The switch occurs along a corkscrew path on the Poincare sphere and takes on average a few nanoseconds; this value agrees with a theoretical treatment based upon the Fokker-Planck equation. 相似文献
35.
Cannac M Pasqualini V Greff S Fernandez C Ferrat L 《Molecules (Basel, Switzerland)》2007,12(8):1614-1622
Fire is a dominant ecological factor in Mediterranean-type ecosystems. Management strategies include prescribed (controlled) burning, which has been used in the management of several species, such as Pinus nigra ssp laricio var. Corsicana, a pine endemic to Corsica of great ecological and economic importance. The effects of prescribed burning on Pinus laricio have been little studied. The first aim of this study was to characterize total and simple phenolic compounds in Pinus laricio. The second aim was to understand: i) the short term (one to three months) and medium term (three years) effects of prescribed burning, and ii) the effects of periodic prescribed burning on the production of phenolic compounds in Pinus laricio. The first result of this study is the presence of total and simple phenolic compounds in the needles of Pinus laricio. 3-Vanillyl propanol is the major compound. After a prescribed burning, the synthesis of total phenolic compounds increases in Pinus laricio for a period of three months. Total phenolic compounds could be used as bioindicators for the short-term response of Pinus laricio needles to prescribed burning. Simple phenolic compounds do not seem to be good indicators of the impact of prescribed burning because prescribed burnings are low in intensity. 相似文献
36.
An experiment was developed as a simple alternative to existing analytical methods for the simultaneous quantitation of glucose (substrate) and glucuronic acid (main product) in the bioprocesses Kombucha by using FTIR spectroscopy coupled to multivariate calibration (partial least-squares, PLS-1 and artificial neural networks, ANNs). Wavelength selection through a novel ranked regions genetic algorithm (RRGA) was used to enhance the predictive ability of the chemometric models. Acceptable results were obtained by using the ANNs models considering the complexity of the sample and the speediness and simplicity of the method. The accuracy on the glucuronic acid determination was calculated by analysing spiked real fermentation samples (recoveries ca. 115%). 相似文献
37.
Mikhail A. Matsko Marina P. Vanina Ludmila G. Echevskaya Vladimir A. Zakharov 《Journal of Thermal Analysis and Calorimetry》2013,113(2):923-932
The successive self-nucleation/annealing technique (SSA) by differential scanning calorimetry has been applied to study the heterogeneity of ethylene–hexene-1 copolymers produced with supported catalytic systems of different compositions: highly active supported Ziegler–Natta (Z–N) catalysts—a titanium–magnesium catalyst TiCl4/MgCl2 (TMC) and a vanadium–magnesium catalyst VCl4/MgCl2 (VMC), a supported zirconocene catalyst Me2Si(Ind)2ZrCl2/SiO2 (MAO), and a chromium-oxide catalyst CrO3/SiO2. Comparative data by SSA technique with the same temperature program were obtained for copolymers differed by MWD from narrow to very broad (Mw/Mn = 2.4–54) and short chain branching distribution from narrow (zirconocene catalyst) to very broad (TMC and chromium oxide catalysts). It is demonstrated that copolymers produced with the zirconocene catalyst have the narrowest melting range and do not contain thick lamellae. The widest lamella thickness distribution has been found for a copolymer produced with the chromium-oxide catalyst. Copolymers produced with the supported Z–N catalysts are ranked in the middle with a more narrow lamella thickness distribution for copolymer prepared with VMC as compared with the one produced with TMC. The SSA results are compared with the data on copolymer fractionation by TREF. It is shown that these methods give a good correlation for copolymers with narrow short-chain branching distribution produced with the supported zirconocene catalyst. In the case of copolymers produced with TMC, TREF yields a higher content of the high-branched fractions. 相似文献
38.
39.
Lahootun V Besson C Villanneau R Villain F Chamoreau LM Boubekeur K Blanchard S Thouvenot R Proust A 《Journal of the American Chemical Society》2007,129(22):7127-7135
The ruthenium-nitrido POM derivative [PW11O39{RuVIN}]4- has been synthesized by reaction between [PW11O39]7- and [RuVINCl5]2- or [RuVINCl4]-. Its molecular structure has been confirmed from multinuclear 31P and 183W NMR spectroscopy together with an EXAFS study, while the oxidation state of the ruthenium bearing the nitrido ligand has been inferred both from 183W NMR and XANES analysis at the Ru-K edge. The potential of [PW11O39{RuVIN}]4- in N-atom transfer reactions has been demonstrated through reaction with triphenylphosphine, which ultimately leads to the release of the bis(triphenylphosphane)iminium cation [PPh3=N=PPh3]+ through several intermediates, among which the phosphoraniminato derivative [PW11O39{RuVNPh3}]3- has been structurally characterized. Its unusual oxidation state is in accordance with its EPR spectrum. 相似文献
40.
N. A. Leonenko E. A. Vanina E. M. Veselova G. G. Kapustina 《Russian Journal of General Chemistry》2013,83(13):2759-2764
Nonlinear effects of pulsed and continuous laser radiation on mineral samples from technogenic placers in the Amur river region, containing submicron gold which cannot be extracted by modern gravity separation methods, were studied. The formation of self-organized gold structures on the surface of silicate matrix was detected, and general relations for the agglomeration and concentration of “nonrecoverable” gold species were found. The agglomeration process was simulated by a nonlinear heat conduction equation for onedimensional case including laser radiation parameters. 相似文献