The simplest stochastic lattice model of an excitable medium is considered. Each lattice cell can be in one of three states: excited, refractory, or quiescent. Transitions between different cell ...states occur with the prescribed probabilities. The model is designed for studying the transfer of excitation in the cardiac muscle and nerve fiber at the cellular and subcellular levels, and also for modeling the spreading of epidemics. Elementary events on the lattice are simulated by the kinetic Monte Carlo method, which consists in constructing a Markov chain of the lattice states corresponding to the solution of the master equation. An effective algorithm for implementing the Kinetic Monte Carlo simulations is suggested. The number of the arithmetic operations at each time step of the proposed algorithm is practically independent of the lattice size, which enables making calculations on two- and three-dimensional lattices of a very large size (more than 10
9
cells). It is shown that the model reproduces the basic spatiotemporal structures (solitary traveling pulses, pulse trains, concentric and spiral waves, and spiral turbulence) characteristic of an excitable medium. The basic properties of traveling pulses and spiral waves for the considered stochastic lattice model are studied and compared with the known properties of deterministic equations of the reaction-diffusion type, which are usually employed for modeling excitable media.
The laser gyro frequency response is studied by means of numerical simulation using a phase equation. The calculation results are compared to the results of experimental measurements on a precision ...dynamic test-bench. Quantitative relationship between the threshold value of static lock-in zone and frequency response distortions is established. Numerical methods helped to obtain and experimentally confirm the quantitative dependence of frequency response distortion on the amplitude and frequency of meander-shaped dither. It is shown that the dither shape significantly affects the frequency response form. Furthermore, it is demonstrated that frequency-response distortions depend on conditions of its measurement, in particular, on the time. The conducted research allows dither parameters to be optimized with a view to increase the accuracy of measurements using laser gyroscopes.
The paper provides calculations of the Romelt furnace performance when using iron ores and coals of different composition. It was shown that at a given value of heat flux from the post-combustion ...zone into slag bath, furnace performance depends not only on the iron content of ore, but also on the fixed carbon content of coal. A regression equation was developed to reflect the dependence of the specific performance on these parameters. It was shown that the coal quality has a greater impact on furnace performance when the iron content of ore is low. It was found that if the iron content of ore increases, a relative decrease in specific consumption of coal and oxygen is the same for all coals. It was shown that the degree of post-combustion of gases weakly depends on the iron content of ore, and is mainly determined by the composition of utilized coal.
Thermal behavior of the orthorhombic (α) and triclinic (β) polymorphs of BiNbO4 was studied by the methods of high-temperature powder X-ray diffraction (HTPXRD) and differential scanning calorimetry ...(DCS) in the temperature range 25–1200 °C. The study revealed the sequence of thermal phase transformations and the new high-temperature modification, γ-BiNbO4, which was formed above 1001 °C and existed up to the melting temperature of BiNbO4. The incongruent melting of BiNbO4 was characterized by the formation of the cubic phase with the approximate composition Bi3NbO7. The HTPXRD method was used in this study to evaluate thermal deformations and to calculate thermal-expansion coefficients (TEC) of the three modifications of BiNbO4 (α, β, and γ). The average volumetric TECs of these three modifications were in the range 19–36 × 10–6 °C–1. The triclinic phase β-BiNbO4 demonstrated the highest anisotropy of thermal expansion. α-BiNbO4 was characterized by the minimal TEC and anisotropy, which indicated its greatest stability. The crystal structure of γ-BiNbO4 was determined at 1100 °C using powder data and was refined using the Rietveld method (the α-LaTaO4 structural type, the space group Cmc21, a = 3.95440(3) Å, b = 15.0899(1) Å, c = 5.65524(5) Å, V = 337.458(5) Å3, R wp = 4.82, R Bragg = 3.61%). The methods of thermal analysis and high-temperature powder X-ray diffraction revealed that, during the heating, bismuth orthoniobate underwent the following sequence of phase transitions: α-BiNbO4 → γ-BiNbO4 → β-BiNbO4 and β-BiNbO4 → γ-BiNbO4 → β-BiNbO4 or, at slow heating, β-BiNbO4 → (α-BiNbO4) → γ-BiNbO4 → β-BiNbO4, where γ-BiNbO4 is the high-temperature phase of bismuth orthoniobate.
The pyrochlore-type solid-solution formation in a Bi1.6Mg0.8–x Cu x Ta1.6O7.2−Δ system, synthesized for the first time, is observed at x ≤ 0.56. High-temperature X-ray diffraction showed that the ...pyrochlore phase exists in air up to 1080 °C, where its thermal decomposition leads to the segregation of (Mg,Cu)Ta2O6. The thermal expansion coefficients of the end member, Bi1.6Mg0.24Cu0.56Ta1.6O7.2−Δ, increase from 3.3 × 10–6 °C–1 at room temperature up to 8.7 × 10–6 °C–1 at 930 °C. Rietveld refinement confirmed that the pyrochlore crystal structure is disordered with space group Fd3̅m:2 (Z = 8, no. 227). Doping with copper results in a modest expansion of the cubic unit cell, promotes sintering of the ceramic materials, and induces their red-brown color. X-ray photoelectron spectroscopy demonstrated that the states of Bi(III) and Mg(II) are not affected by doping, and the effective charge of tantalum cations is lower than +5, while the Cu(II) states coexist with Cu(I). The electron spin resonance spectra display a single line with g = 2.2, ascribed to the dipole-broadened Cu2+ signal. The dielectric permittivity of Bi1.6Mg0.8–x Cu x Ta1.6O7.2−Δ ceramics may achieve up to ∼105, with the dielectric loss tangent varying in the range from 0.2 up to 12. Multiple dielectric relaxations are found at room temperature and above for all samples.
Thermal behavior of the orthorhombic (α) and triclinic (β) polymorphs of BiNbO
was studied by the methods of high-temperature powder X-ray diffraction (HTPXRD) and differential scanning calorimetry ...(DCS) in the temperature range 25-1200 °C. The study revealed the sequence of thermal phase transformations and the new high-temperature modification, γ-BiNbO
, which was formed above 1001 °C and existed up to the melting temperature of BiNbO
. The incongruent melting of BiNbO
was characterized by the formation of the cubic phase with the approximate composition Bi
NbO
. The HTPXRD method was used in this study to evaluate thermal deformations and to calculate thermal-expansion coefficients (TEC) of the three modifications of BiNbO
(α, β, and γ). The average volumetric TECs of these three modifications were in the range 19-36 × 10
°C
. The triclinic phase β-BiNbO
demonstrated the highest anisotropy of thermal expansion. α-BiNbO
was characterized by the minimal TEC and anisotropy, which indicated its greatest stability. The crystal structure of γ-BiNbO
was determined at 1100 °C using powder data and was refined using the Rietveld method (the α-LaTaO
structural type
the space group Cmc2
, a = 3.95440(3) Å, b = 15.0899(1) Å, c = 5.65524(5) Å, V = 337.458(5) Å
, R
= 4.82, R
= 3.61%). The methods of thermal analysis and high-temperature powder X-ray diffraction revealed that, during the heating, bismuth orthoniobate underwent the following sequence of phase transitions: α-BiNbO
→ γ-BiNbO
→ β-BiNbO
and β-BiNbO
→ γ-BiNbO
→ β-BiNbO
or, at slow heating, β-BiNbO
→ (α-BiNbO
) → γ-BiNbO
→ β-BiNbO
, where γ-BiNbO
is the high-temperature phase of bismuth orthoniobate.
In this work, we report an efficient synthesis approach of disodium terephthalate and its application as a potential battery anode material. Disodium terephthalate is upcycled from waste polyethylene ...terephthalate flakes with the aid of an ultrafast microwave irradiation process within 2 minutes. The phase and chemical purity of the as-synthesized disodium terephthalate is confirmed by X-ray diffraction, Fourier-transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy. The electrochemical behavior of this low-cost, environmentally benign organic molecular compound is studied in Li- and Na-ion cells. The density functional theory-based calculations are performed to get insights into specifics of electronic properties of Li- and Na-ion cells and rationalize the differences in behavior for the two systems. The delithiation potential of a disodium terephthalate anode is found to be approximately 0.65 V higher than the desodiation potential. The disodium terephthalate-carbon black (Super P) composite electrode delivers discharge capacities of 182 and 224 mAh g–1 at a current density of 25 mA g–1 after 50 cycles in Li-ion and Na-ion cells, respectively. The better C-rate performance of the composite anode for a Li-ion cell, as compared to a Na-ion cell, is due to inferior mobility of Na-ions in the electrode material, which is largely defined by ion size.
ABSTRACT
We present an analysis of the outer Galaxy giant molecular filament (GMF) G214.5-1.8 (G214.5) using IRAM 30m data of 12CO, 13CO, and C18O. We find that the 12CO (1-0) and (2-1) derived ...excitation temperatures are near identical and are very low, with a median of 8.2 K, showing that the gas is extremely cold across the whole cloud. Investigating the abundance of 13CO across G214.5, we find that there is a significantly lower abundance along the entire 13 pc spine of the filament, extending out to a radius of ∼0.8 pc, corresponding to Av ≳ 2 mag and Tdust ≲ 13.5 K. Due to this, we attribute the decrease in abundance to CO freeze-out, making G214.5 the largest scale example of freeze-out yet. We construct an axisymmetric model of G214.5’s 13CO volume density considering freeze-out and find that to reproduce the observed profile significant depletion is required beginning at low volume densities, n ≳ 2000 cm−3. Freeze-out at this low number density is possible only if the cosmic-ray ionization rate is ∼1.9 × 10−18 s−1, an order of magnitude below the typical value. Using time scale arguments, we posit that such a low ionization rate may lead to ambipolar diffusion being an important physical process along G214.5’s entire spine. We suggest that if low cosmic-ray ionization rates are more common in the outer Galaxy, and other quiescent regions, cloud-scale CO freeze-out occurring at low column and number densities may also be more prevalent, having consequences for CO observations and their interpretation.
Results of investigations of the stability of a structural Nb–Cr alloy subjected to cyclic mechanical loading have been presented. It has been established that, upon deformation, the alloy shows a ...structural instability that manifests in the form of a local cyclic microinhomogeneous redistribution of elements depending on the applied external loads and, as a process for the refinement and growth of crystallites. Based on these phenomena, the oscillating character of significant internal structural stresses has been explained, which are changed in the region that is limited by the strengthening–softening curves and characterizes the cyclic strength of the alloy.
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