Central to the biological function of microtubules is their ability to modify their length which occurs by addition and removal of subunits at the ends of the polymer, both in vivo and in vitro. This dynamic behavior is strongly influenced by temperature. Here, we show that the lateral interaction between tubulin subunits forming microtubule is strongly temperature dependent. Microtubules deposited on prefabricated substrates were deformed in an atomic force microscope during imaging, in two different experimental geometries. Microtubules were modeled as anisotropic, with the Young's modulus corresponding to the resistance of protofilaments to stretching and the shear modulus describing the weak interaction between the protofilaments. Measurements involving radial compression of microtubules deposited on flat mica confirm that microtubule elasticity depends on the temperature. Bending measurements performed on microtubules deposited on lithographically fabricated substrates show that this temperature dependence is due to changing shear modulus, implying that the lateral interaction between the protofilaments is strongly determined by the temperature. These measurements are in good agreement with previously reported measurements of the disassembly rate of microtubules, demonstrating that the mechanical and dynamic properties of microtubules are closely related. 相似文献
The method of active stabilization of the polarization and other parameters of the optical part of a two-pass fiber optic quantum cryptography has been proposed and implemented. The method allows the completely automated maintenance of the visibility of interference close to an ideal value (V ≥ 0.99) and the reduction of the instrumental contribution to the error in primary keys (QBER) to 0.5%. 相似文献
The security of keys in quantum cryptography systems, in contrast to mathematical cryptographic algorithms, is guaranteed by fundamental quantum-mechanical laws. However, the cryptographic resistance of such systems, which are distributed physical devices, fundamentally depends on the method of their implementation and particularly on the calibration and control of critical parameters. The most important parameter is the number of photons in quasi-single-photon information states in a communication channel. The sensitivity to a bright-pulse attack has been demonstrated in an explicit form for a number of systems. A method guaranteeing the resistance to such attacks has been proposed and implemented. Furthermore, the relation of physical observables used and obtained at the control of quantum states to the length of final secret keys has been obtained for the first time. 相似文献
(Di)chloro(di)nitrobenzofuroxans form substitution products involving carbon atoms with phenolates in isopropyl alcohol medium. In the case of 4,6-dinitro-5,7-dichlorobenzofuroxan, besides replacement of one chlorine atom and the formation of C-bonded product, we observed the hydrolysis of the second chlorine and replacement of it by hydroxyl group. Products of reaction of 4,6-dichloro-5-nitrobenzofuroxan with phenolates display excellent antimicrobial activity and have dual action, both against bacteria and fungi. 相似文献
The crystal and local structures of compounds formed in the Dy2O3–HfO2 system (at molar ratios from 1: 3 to 3: 1) in the course of isothermal annealing of X-ray amorphous mixed hydroxides at temperatures up to 1600°C have been studied. At the molar ratio Dy2O3: HfO2 from 1: 3 to 1: 1, crystallization leads to formation of single-phase defect fluorite solid solutions nDy2O3 ? mHfO2 with clearly pronounced nonequivalence of parameters of local environment of Dy3+ and Hf4+ cations. It has been found that Dy2H2O7 (Dy2O3: HfO2 = 1: 2) samples have a tendency to pyrochlore-type ordering in both the cationic and anionic sublattices. 相似文献
The results of investigation on the temperature dependences of strain of the regularly constructed fragments of the carbon
skeleton in linear polymers are reviewed. Stretching of the skeleton is induced under the action of twisting and bending vibrations
when both ends of an oscillating chain fragment are fixed. In this case, the anharmonic character of vibrations plays no key
role. At temperatures Tt and Tb, the statistics of atomic vibrations changes from quantum to classical, and the slope of the corresponding temperature dependences
changes as well. At T < Tt, vibrations are not excited, and the skeleton is extended owing to zero-point vibrations. At Tt, twisting vibrations are induced, and a skeleton of the molecules is extended with temperature linearly. At Tb, bending vibrations are activated, and the slope of the temperature dependences of the strain of the skeleton increases.
Additional stretching and an increased amplitude of vibrations of the skeleton carbon atoms are provided owing to the scattering
of stretching vibrations at the boundaries of crystals. 相似文献
Morphological, structural, adsorption, and catalytic properties of highly disperse titania prepared using sulfate and pyrogenic methods, and fumed titania-containing mixed oxides, were studied using XRD, TG/DTA, nitrogen adsorption, (1)H NMR, FTIR, microcalorimetry on immersion of oxides in water and decane, thermally stimulated depolarization current (TSDC) and catalytic photodecomposition of methylene blue (MB). Phase composition and aggregation characteristics of nanoparticles (pore size distribution) of sulfate and pyrogenically prepared titania are very different; temperature dependent structural properties are thus very different. Catalytic activity for the photodecomposition of MB is greatest (per gram of TiO(2) for the pure oxide materials) for non-treated ultrafine titania PC-500, which has the largest S(BET) value and smallest particle size of the materials studied. However, this activity calculated per m(2) is higher for PC-105, possessing a much smaller S(BET) value than PC-500. The activity per unit surface area of titania is greatest for the fumed silica-titania mixed oxide ST20. Calcination of PC-500 at 650 degrees C leads to enhancement of anatase content and catalytic activity, but heating at 800 and 900 degrees C lowers the anatase content (since rutile appears) and diminishes catalytic activity, as well as the specific surface area because of nanoparticle sintering. 相似文献
The spin polarization features of an electron system and the relaxation of nonequilibrium spin excitations near an even-denominator fractional state of 3/2 in a two-dimensional electron system based on the GaAs/AlGaAs heterostructure are experimentally investigated. It is shown that the 3/2 state is a singular point in the filling factor dependence of the spin ordering of the two-dimensional electron system, at which the spin subsystem is rearranged. A giant slowing down of the relaxation of spin excitations to the ground state is revealed in a certain range of filling factors near filling factor 3/2. 相似文献
A fundamentally new collective state, namely, the magnetofermionic condensate, is discovered during photoexcitation of a sufficiently dense gas of long-lived triplet cyclotron magnetoexcitons in a twodimensional Hall insulator with a high electron mobility, a filling factor of ν = 2, and temperatures of T < 1 K. The condensed phase coherently interacts with an external electromagnetic field, exhibits superradiant properties in the recombination of correlated condensate electrons with heavy holes in the valence band, and spreads nondissipatively in the layer of a two-dimensional electron gas to macroscopical large distances, transferring an integer spin. The observed effects are explained in terms of a coherent condensate in a nonequilibrium system of two-dimensional fermions with a fully quantized energy spectrum, in which a degenerate ensemble of long-lived triplet magnetoexcitons obeying the Bose statistics is present.