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21.
Franti?ek Slanina 《Journal of statistical physics》2009,135(5-6):935-950
The “reversible ratchet” model of interacting Brownian motors, introduced by us earlier, is investigated using a one-site approximation of a mean-field type. We confirm the effect of enhanced efficiency due to repulsive interaction and we provide arguments suggesting that the enhancement is of energetic, rather than entropic, origin. We also check the validity of the fluctuation theorem for stationary particle current. 相似文献
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Vivekananda S Sadílek M Chen X Adams LE Turecek F 《Journal of the American Society for Mass Spectrometry》2004,15(7):1068-1079
The title radical (1) is generated in the gas-phase by collisional neutralization of carbonyl-protonated oxolan-3-one. A 1.5% fraction of 1 does not dissociate and is detected following reionization as survivor ions. The major dissociation of 1 (approximately 56%) occurs as loss of the hydroxyl H atom forming oxolan-3-one (2). The competing ring cleavages by O[bond]C-2 and C-4[bond]C-5 bond dissociations combined account for approximately 42% of dissociation and result in the formation of formaldehyde and 2-hydroxyallyl radical. Additional ring-cleavage dissociations of 1 resulting in the formation of C(2)H(3)O and C(2)H(4)O cannot be explained as occurring competitively on the doublet ground (X) electronic state of 1, but are energetically accessible from the A and higher electronic states accessed by vertical electron transfer. Exothermic protonation of 2 also produces 3-oxo-(1H)-oxolanium cation (3(+)) which upon collisional neutralization gives hypervalent 3-oxo-(1H)-oxolanium radical (3). The latter dissociates spontaneously by ring opening and expulsion of hydroxy radical. Experiment and calculations suggest that carbohydrate radicals incorporating the 3-hydroxyoxolan-3-yl motif will prefer ring-cleavage dissociations at low internal energies or upon photoexcitation by absorbing light at approximately 590 and approximately 400 nm. 相似文献
24.
Dynamic properties of simple mechanical 1 DOF system containing soft stop is described and analyzed. The proposed general dynamical impact model respects the nonlinearity of the restoring contact force between solid bodies as function of deformation and velocity. It describes the real behavior of impacting system more exact than the piecewise linear model or the Kelvin–Voigt model and even model based on application of constant coefficient of restitution. Free and forced vibrations of system with Hertz's contact are investigated and domains of various types of impact motion, response curves and phase-plane trajectories are presented. 相似文献
25.
The inhibition of the oxygen evolution rate (OER) in Chlorella vulgaris by 2-alkylsulphanyl-4-pyridinecarbothioamides (APCTs; alkyl = methyl up to hexadecyl) was studied. APCTs were found to inhibit
photosynthetic electron transport (PET) which resulted in the inhibition of OER in algae. The inhibitory activity of APCTs
was highly dependent on the alkyl chain length of the 2-alkylsulphanyl substituent and the corresponding dependence showed
a bilinear course with the decyl derivative as being the most active inhibitor. Using EPR spectroscopy, the site of APCT action
in the algal photosynthetic apparatus was determined. It was confirmed that APCT interacted mainly with the D. intermediate,
i.e. with tyrosine radical (TyrD) occurring at the 161st position in D2 protein which is situated on the donor side of photosystem 2. 相似文献
26.
Tomáš Opravil Petr Ptáček František Šoukal Jaromír Havlica Jiří Brandštetr Lenka Opravilová 《Journal of Thermal Analysis and Calorimetry》2013,112(3):1401-1406
The expansion effect of laboratory-prepared expansive additives for M-type expansive cement was investigated at the early stage of hydration by the multicell isoperibolic calorimeter and volumetric technique based on Archimedes’ principle. The relative volume changes and heat released during hydration are strongly affected by the content of lime in the expansive additive due to the influence of CaO on the kinetics and mechanism of formation of ettringite. The increasing content of lime favours the formation of monosulphate and its later transformation to ettringite generating expansion stress. The effect of expansive additive on the behaviour of mortar samples was measured as linear elongation of test blocks using Graf-Kaufman dilatometer. Lower or higher content of lime in expansion additive slightly decreases the 7th-day compressive and flexural strength of samples while this effect is negligible for expansive additive with nominal composition of ettringite. 相似文献
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28.
Long Chen František Hartl Howard M. Colquhoun Barnaby W. Greenland 《Tetrahedron letters》2017,58(19):1859-1862
A library of 18 conjugated, rod-like compounds with either one or two viologen residues were synthesized and characterized electrochemically. Containing up to 8 aromatic/heterocyclic rings in conjugation, the members of the library differ in the substitution pattern of electron-withdrawing or -donating groups on the aromatic substituents of the viologen units. The first and second half-wave potentials of each member were found to be linearly correlated with the calculated pKb values of the aromatic end-groups. This relationship will enable the half-wave potentials of related, novel, substituted viologen species to be predicted using a simple, empirical formula. 相似文献
29.
Glogarová M Hampl F Lejček L Novotná V Svoboda J Cigl M 《The Journal of chemical physics》2010,133(22):221102
For the first time, domains with twisted structures have been established in planar samples of achiral compounds in tilted smectic C phase. This evidences separation of molecular conformers differing in the sense of axial chirality and confirms polar C(2) symmetry of these domains. A simple model considering polar surface anchoring energy and bulk energy of the twist can account for this finding. Conditions for coexistence of twisted and homogeneous domains are discussed. 相似文献
30.
Elucidating the Structure of Chiral Molecules by using Amplified Vibrational Circular Dichroism: From Theory to Experimental Realization
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Dr. Sérgio R. Domingos Prof. Dr. František Hartl Prof. Dr. Wybren Jan Buma Prof. Dr. Sander Woutersen 《Chemphyschem》2015,16(16):3363-3373
Recent experimental observations of enhanced vibrational circular dichroism (VCD) in molecular systems with low‐lying electronically excited states suggest interesting new applications of VCD spectroscopy. The theory describing VCD enhancement through vibronic coupling schemes was derived by Nafie in 1983, but only recently experimental evidence of VCD amplification has demonstrated the extent to which this effect can be exploited as a structure elucidation tool to probe local structure. In this Concept paper, we give an overview of the physics behind vibrational circular dichroism, in particular the equations governing the VCD amplification effect, and review the latest experimental developments with a prospective view on the application of amplified VCD to locally probe biomolecular structure. 相似文献