The work presents studies on the microstructure and mesostructure of nanostructured aluminum oxyhydroxide formed as a high porous monolithic material through the surface oxidation of aluminum liquidmetal solution in mercury in a temperature- and humidity-controlled air atmosphere. The methods of X-ray diffraction analysis, thermal analysis, the low temperature adsorption of nitrogen vapors, transmission electron microscopy, small-angle and very small-angle neutron scattering, and small-angle X-ray scattering are used for comprehensive investigation of the samples synthesized at 25°С as well as that annealed at temperatures up to 1150°C. It is found that the structure of the monolithic samples can be described within the framework of a three-level model involving primary heterogeneities (typical length scale of rc ≈ 9–19 Å), forming fibrils (cross-sectional radius R ≈ 36–43 Å and length L ≈ 3200–3300 Å) or lamellae (thickness T ≈ 110 Å and width W ≈ 3050 Å) which, in turn, are integrated into large-scale aggregates (typical size Rc ≈ 1.25–1.4 μm) with an insignificant surface roughness. It is shown that a high specific surface (~200 m2/g) typical for the initial sample is maintained upon its thermal annealing up to 900°С, and it decreases to 100 m2/g after heat treatment at 1150°С due to fibrillary agglomeration. 相似文献
The time characteristics of pulse generators based on sharp-recovery 4H : SiC drift diodes have been calculated. It has been found that the speed of n-base 4H-SiC diodes is superior to that of p-base diodes with the amplitude and initial pedestal in the output voltage (<5% of the amplitude) versus the time curve being the same. 相似文献
The expedience of using the ratio of inertial β and viscous α hydraulic coefficients of a fluid flow in porous structures as the characteristic linear scale, when generalizing the experimental data on internal heat transfer in porous media, is shown. It is demonstrated that the correlation Nu = A · Pe, with both criteria based on β/α ratio, most efficiently describes the experimental data for a wide set of ordered and disordered porous structures, including sintered spheres, network materials, sintered felt and cellular foams of high porosity. The coefficient A depends on porosity and is equal to 0.004 for spheres, networks and felts, and 0.0004 for foams. For any specific case the values of α and β coefficients can be readily obtained from testing materials under consideration, control samples, or full-scale articles. 相似文献
The lifetime of the neutron is one of the key physical quantities used to determine the weak interaction parameters and to test predictions of the theory of primary nucleosynthesis. The lifetime of the neutron has been measured in the reported experiment by the method of storing neutrons in a material trap with a gravitational valve. Fomblin grease UT-18 hydrogen-free fluorine polymer has been used as coating. The resistance of the coating to repeated cooling down to 80 K combined with heating up to 300 K has been studied. The probability of losses in the trap is as small as 1.5% of the neutron decay probability. The lifetime of the neutron τn = (881.5 ± 0.7stat ± 0.6syst)s obtained at the new step is in good agreement with a commonly accepted value of (880.2 ± 1.0) s presented by the Particle Data Group. 相似文献
The change in probability of spontaneous emission for emitter placed in one-dimensional photonic quasicrystal (optical Fibonacci lattice) was examined. When the dipole is placed in Fibonacci lattice two different scenarios can be expected: enhancing (if frequency and direction of the dipole emission correspond to optical eigenmode of structure, and position corresponds to maximum value of modes electric field profile) or suppression (in case of photonic band gap) of spontaneous emission rate. Fact that both effects are expressed in quasicrystals less than in the Bragg reflectors and in the microcavities was demonstrated. 相似文献
We consider elastoplastic systems which are piecewise homogeneous bodies composed of piezoelectric elements some of which have piezoelectrical properties. Electric series circuits consisting of resistors, capacitors, and inductance coils are applied to piezoelectric elements through the electrode coating on the body surface. The goal of the study is to develop efficient methods of mathematical modelling for determining the parameters of elements of the external electric circuit, which ensure, at prescribed resonance frequencies, the maximum damping properties of electroelastic bodies with external electric circuits. To choose effective circuits for solving the problem posed above, we suggest to pose the problem of natural vibrations of elastic bodies whose elements exhibit piezoeffect and have external electric circuits.As the most efficient approaches for calculating the electric circuit parameters necessary for the maximal damping, we propose some versions of equivalent circuits, which can be used to substitute elastic systems with piezoelectric elements. The most reliable equivalent substitution circuits are justified on the basis of the proposed problem of natural vibrations. Numerical results are obtained for a cantilever plate with a piezoelement connected through the electrode coated surface with a series electric circuit consisting of resistors, capacitors and inductance coils. 相似文献
Photophysical properties of aqueous solutions of the styryl dye 4-[(E)-2-(3,4-dimethoxyphenyl)-1-ethylpyridinium] perchlorate (1) in the presence of cucurbit[n]urils (CB[n]; n = 5, 6, 8) have been studied by fluorescent spectroscopy methods. The fluorescence intensity of a 10–6 mol L–1 solution of 1 increases by a factor of 12.6 upon the formation of 1 : 1 inclusion complexes with CB[6] or 1.3 in complexes with CB[8]. Upon the formation of inclusion complexes, the average lifetime of the electronically excited state of 1 increases to about 1 ns for both CB[6] and CB[8]. On the basis of fluorescence anisotropy measurements, the rotational relaxation times were estimated to be 408, 314, and 183 ps for the complexes with CB[6], CB[8], and for unbound 1, respectively. Using the fluorescence titration method developed for the case of poorly soluble cavitands, the binding constant of 1 with CB[6] was determined to be 1.1 × 105 L mol–1. The addition of CB[5] does not lead to changes in the photophysical properties of a solution of 1, indicating the absence of complexes between CB[5] and 1. It has been found on the basis of the experimental data that the fluorescence rate constant of 1 decreases about twice in the complex with CB[8], but doubles in the complex with CB[6]. 相似文献
A number of proteomic database search engines implement multi-stage strategies aiming at increasing the sensitivity of proteome analysis. These approaches often employ a subset of the original database for the secondary stage of analysis. However, if target-decoy approach (TDA) is used for false discovery rate (FDR) estimation, the multi-stage strategies may violate the underlying assumption of TDA that false matches are distributed uniformly across the target and decoy databases. This violation occurs if the numbers of target and decoy proteins selected for the second search are not equal. Here, we propose a method of decoy database generation based on the previously reported decoy fusion strategy. This method allows unbiased TDA-based FDR estimation in multi-stage searches and can be easily integrated into existing workflows utilizing popular search engines and post-search algorithms.
Compression isotherms and chemical compositions of stearic acid (HSt) monolayers applied onto an aqueous subphase containing cadmium ions have been studied in a wide pH range. The data obtained have been used to calculate the dependences of surface elasticity E2.5, change ΔA2.5 in the surface area per molecule at a constant two-dimensional pressure in the monolayer of 2.5 mN/m, and change Δ|ζ| in the absolute value of the ζ potential of particles formed from the material of a monolayer collapsed on the surfaces of aqueous solutions with the same compositions on the pH of the subphase. The obtained data are in good agreement with each other and unambiguously attest to the dependences of the surface (E2.5, ΔA2.5) and electrosurface (Δ|ζ|) characteristics of the monolayers on their chemical composition. This leads us to make the reasonable suggestion that two alternative reactions may occur between cadmium ions and the HSt monolayer with the formation of two salts, CdSt2 and Cd(OH)St. 相似文献