Application of Sulfonic Acid Functionalized SBA‐15 as a New Nanoporous Acid Catalyst in the Green One‐Pot Synthesis of Spirooxindole‐4H‐pyrans

Sulfonic acid functionalized SBA‐15 (SBA‐Pr‐SO₃H) as a new nanoporous solid acid catalyst was applied in the green one‐pot synthesis of spirooxindole‐4H‐pyrans via condensation of isatins, malononitrile or methyl cyanoacetate or ethyl cyanoacetate, and 4‐hydroxycoumarin in water solvent. SBA‐Pr‐SO₃H was proved to be an efficient heterogeneous nanoporous solid acid catalyst with a pore size of 6 nm that could be easily handled and removed from the reaction mixture by simple filtration and can be recovered and reused for several times without any loss of activity. The significant merits of present methodology are its simplicity, short reaction time, good yields, and environmentally benign mild reaction condition as water was used as a green solvent.     

On the fractional derivatives of radial basis functions: Theories and applications

The paper provides the fractional integrals and derivatives of the Riemann‐Liouville and Caputo type for the five kinds of radial basis functions, including the Powers, Gaussian, Multiquadric, Matérn, and Thin‐plate splines, in one dimension. It allows to use high‐order numerical methods for solving fractional differential equations. The results are tested by solving two test problems. The first test case focuses on the discretization of the fractional differential operator while the second considers the solution of a fractional order differential equation.     

Gas phase pyrolysis of some cyclic dithioketals

A detailed analysis of the gas phase pyrolysis of 1,4-dithiaspiro[4,4]nonane(I), 1,5-dithiaspiro(5.4)decane(II), 1,4-dithiaspiro(4.5)decane(III), and 1,5-(5,5)undecane(IV) is presented. Pyrolysis resulted primarily in cleavage of the molecules to thiocyclopentanone and thiocyclohexanone. The products observed are discussed in relation to the effect of ring size in cyclic dithioketals. A definite correlation was noted between the thermal and their electron-impact-induced fragmentations of these materials.     

Effect of frit size on sintering, crystallization and electrical properties of wollastonite glass-ceramics

Wollastonite glass-ceramics were prepared through pressureless sintering. The sinterability of the prepared samples of the glassy powder in the system (SiO₂-CaO-Na₂O-Fe₂O₃-WO₃) was investigated in the temperature range 720-900 °C and soaking time of 180 min. The influence of the increase in the glass powder particle size on the sinterability and dielectric properties of the glass-ceramic samples was studied.The sintered specimens were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods. XRD analysis revealed that wollastonite was the main crystalline phase in the sintered glass-ceramics. Dielectric properties such as dielectric constant and dielectric loss were measured via a network analyzer at 10 GHz.It was observed that the increase of the glassy powder particle size improved the sinterability and dielectric properties of the glass-ceramic specimens. Wollastonite glass-ceramics with 16 μm particle size had maximum constant and minimum loss (ε_r = 10.10 and tan δ = 0.005) compared with the other glass-ceramics.     

Runaway electron generation decrease during a major disruption by limiter biasing in tokamaks

The high-energy current of runaway electrons during a major disruption in tokamak reactors can cause serious damage to the first wall of the reactors and reduce their life time. Therefore, finding a method to minimize runaway electron generation during a major disruption is much needed. Tokamak limiter biasing is one of the methods that can be used for controlling the radial electric field and can induce a transition to an improved confinement state. This paper attempts to examine the effect of limiter biasing on the generation of runaway electrons during a major disruption. To do so, a horizontal biased limiter placed on the tokamak was used. Main parameters such as plasma current, loop voltage, emitted hard X-ray intensity, magnetohydrodynamic (MHD) oscillation and H_α radiation and spectrum of hard X-rays, in the presence and absence of negative and positive limiter biasing, were measured. The results show that the application of limiter biasing during a major disruption can reduce runaway electron generation.     

Powers of the Vertex Cover Ideal of a Chordal Graph

In this article, Cohen–Macaulay chordal graphs and generalized star graphs are studied to show that all powers of the vertex cover ideal of such graphs have linear quotients. Moreover, it is shown that the Alexander dual of the clique complex of any chordal graph is vertex decomposable.     

Temperature dependent electrophysical characteristics of GaAs-polymer composite varistors

A composition of GaAs-polymer tiny particles was pressed at a temperature of 130 °C and a pressure of 60 MPa and its current–voltage characteristic was studied. The result shows that the prepared disk has varistor behavior and can therefore be used to protect circuits from low overvoltage transients higher than 62 V. Temperature dependence of current-voltage characteristic and the electrical conductivity of the sample were investigated in the temperature range of 25–100 °C. It has been found that increase in temperature results in lower breakdown voltage and nonlinearity coefficient. At high temperatures, nonlinearity in the I–V characteristic of sample disappears and the conductivity becomes Ohmic in nature. The sample has hysteresis which decreases through increase in temperature. Annealing effect on leakage current and breakdown voltage was both investigated and analyzed using SEM micrographs. Finally, the electrical bandgap of the sample was measured.     

Numerical study of the effect of turbulence on rate of reactions in the MILD combustion regime

In this paper, the importance of fluctuations in flow field parameters is studied under MILD combustion conditions. In this way, a turbulent non-premixed CH₄+H₂ jet flame issuing into a hot and deficient co-flow air is modeled using the RANS Axisymmetric equations. The modeling is carried out using the EDC model to describe the turbulence-chemistry interaction. The DRM-22 reduced mechanism and the GRI2.11 full mechanism are used to represent the chemical reactions of H₂/methane jet flame. Results illustrate that although the fluctuations in temperature field are small and the reaction zone volume are large in the MILD regime, the fluctuations in temperature and species concentrations are still effective on the flow field. Also, inappropriate dealing with the turbulence effect on chemistry leads to errors in prediction of temperature up to 15% in the present flame. By decreasing of O₂ concentration of hot co-flow air, the effect of fluctuations in flow field parameters on flame characteristics are still significant and its effect on species reaction rates does not decrease. On the other hand, although decreasing of jet inlet Reynolds number at constant inlet turbulence intensity addresses to smaller fluctuations in flow filed, it does not lead to lower the effect of turbulence on species distribution and temperature field under MILD combustion conditions.