The dynamics of water vapor sorption on a composite sorbent in the presence of unsorbable components

Preliminary mathematical processing of the experimental data on the dynamics of water vapor adsorption on a composite adsorbent was performed. The approximate time dependence of water vapor pressure was constructed. An analytic equation describing changes in the mean temperature of adsorbent grains as a function of the duration of measurements depending on water vapor pressure was obtained, and an asymptotic approximation equation was suggested. The system under consideration was shown to pass two “diffusion” stages in the dynamics of pressure changes and changes in the mean temperature of grains. The characteristic times of the diffusion stages monotonically increased as the fraction of an unadsorbable component in the gas phase of the system grew.     

On some classes of Lindelöf Σ-spaces

We consider special subclasses of the class of Lindelöf Σ-spaces obtained by imposing restrictions on the weight of the elements of compact covers that admit countable networks: A space X is in the class LΣ(?κ) if it admits a cover by compact subspaces of weight κ and a countable network for the cover. We restrict our attention to κ?ω. In the case κ=ω, the class includes the class of metrizably fibered spaces considered by Tkachuk, and the P-approximable spaces considered by Tka?enko. The case κ=1 corresponds to the spaces of countable network weight, but even the case κ=2 gives rise to a nontrivial class of spaces. The relation of known classes of compact spaces to these classes is considered. It is shown that not every Corson compact of weight ℵ₁ is in the class LΣ(?ω), answering a question of Tkachuk. As well, we study whether certain compact spaces in LΣ(?ω) have dense metrizable subspaces, partially answering a question of Tka?enko. Other interesting results and examples are obtained, and we conclude the paper with a number of open questions.     

Degradation of Pt/C catalysts in start-stop cycling tests

The stability of highly disperse 50 wt % Pt catalysts deposited on carbon supports with various porosity and morphology is tested in accelerated oxidative experiments in the potential range of 1–1.5 V (RHE) in 0.1 M HClO₄ solution. The electrochemically active surface area of platinum (S _Pt) is determined based on the charge of adsorbed hydrogen by the cyclic voltammetry (CVA) method. The specific activity per mass unit (the mass catalytic activity (MCA)) and the electrochemically active surface area of the active component (surface catalytic activity (SCA)) are determined in the oxygen electroreduction reaction (OERR) by the method of rotating disk electrode (RDE). It is shown that the catalyst degradation is mainly due to the growth of Pt particles and the corrosion of the carbon support. It is found that under these cycling conditions, the rate of the S _Pt decline depends inversely on the cycle number throughout the cycling interval (up to 60000 cycles) for all catalysts, which points to the quadratic dependence of the degradation rate on S _Pt. Two regions are revealed in the MCA and SCA dependences on the cycle number, In the first region (from 0 to 8–10 thousand cycles), a sharp decrease in MCA and SCA is observed for all catalysts, which can be associated with the restructuring or passivation of the Pt particle surface due to the oxide formation on oxidative cycling. In the second region, the relative stabilization of MCA and the linear increase in SCA are observed for all catalysts without exception. The linear increase in SCA is due to the growth of Pt particles and the size effect. It is shown that carbonization of the carbon support leads to enhancement of its cycling stability.     

Preparation of pure monodisperse calcium carbonate particles

The non-template synthesis of monodisperse spherical particles of calcium carbonate is reported. Particles of a 3.5–4.5 μm size were produced by precipitation of calcium carbonate from alcohol solution at subzero temperatures.     

The Lindel?f number of Cp(X)×Cp(X) for strongly zero-dimensional X

We prove that if X is a strongly zero-dimensional space, then for every locally compact second-countable space M, C _p (X, M) is a continuous image of a closed subspace of C _p (X). It follows in particular, that for strongly zero-dimensional spaces X, the Lindel?f number of C _p (X)×C _p (X) coincides with the Lindel?f number of C _p (X). We also prove that l(C _p (X ⁿ )^κ) ≤ l(C _p (X)^κ) whenever κ is an infinite cardinal and X is a strongly zero-dimensional union of at most κcompact subspaces.     

Two-Stage Growth of La0.7Sr0.3MnO3 Clusters in Magnetron Plasma under Modulation of Particle Flow by Ion-Acoustic Wave and Its Deposition on Glass

Physics of the Solid State - Films with amorphous structure are grown by magnetron sputtering of La0.7Sr0.3MnO3 targets. The clusterization kinetics of magnetron plasma in the flow of interacting...     

Influence of nonadsorbable component on the dynamics of water sorption on composite adsorbent

Experimental data are analyzed on water adsorption in the presence of a nonadsorbable component on the composite adsorbent silica gel impregnated with calcium chloride for different partial pressures of water and air. It is established that the mass-transfer mechanism inside the grain is Knudsen diffusion. It is shown that a dynamic structure is formed in the system, with increased concentration of the nonadsorbable component close to the external surface of the grain, causing externally diffusive resistance. The coefficients of heat exchange between the grain and the gas phase are defined.     

“Negative” gap in the spectrum of localized states of (In<Subscript>2</Subscript>O<Subscript>3</Subscript>)<Subscript>0.9</Subscript>(SrO)<Subscript>0.1</Subscript>

The reflection R(?ω), transmission t(?ω), absorption α(?ω), and refraction n(?ω) spectra of polycrystalline In₂O₃–SrO samples with low optical transparency, which contain In₂O₃ and In₂SrO₄ crystallites with In₄SrO_{6 + δ} interlayers, are examined. In the region of small ?ω values, the reflection coefficient decreases as the resistance of samples saturated with oxygen increases. Spectral dependences n(?ω) and α(?ω) are calculated using the classical electrodynamics relations. The results are compared to the data based on the t(?ω) spectra. The calculated absorption spectra are interpreted within the model with an overlap of tails of the density of states in the valence band and in the conduction band. A “negative” gap E _gn in the density of states with a width from–0.12 to–0.47 eV is formed in highly disordered samples in this model. It is demonstrated that the high density of defects and the band of deep acceptor states of strontium in the major matrix In₂O₃ phase are crucial to tailing of the absorption edge and its shift toward lower energies. The direct gap E _gd = 1.3 eV corresponding to the In₂SrO₄ phase is determined. The energy band diagram and the contribution of tunneling, which reduces the threshold energy for interband optical transitions, are discussed.     

On integrability in elementary functions of certain classes of complex nonautonomous equations

This work is devoted to the search for integrability cases of a certain class of complex, linear second-order, nonautonomous ordinary differential equations.