Silver chloride supported on Vitamin B1 -Organometallic magnetic catalyst: synthesis,density functional theory study and application in A3-coupling reactions

A highly efficient Fe₃O₄@VitB₁–Ag(I) magnetic catalyst has been obtained using surface modification of Fe₃O₄. To this end, silver chloride was immobilized on Fe₃O₄ nanoparticles via vitamin B₁ biomolecules. The synthesized biocompatible magnetic catalyst was applied in an A³-coupling reaction in the presence of aldehyde, amine and phenyl acetylene under solvent-free conditions and afforded the desired products in excellent yields. Also, interactions between metal and ligand in the Fe₃O₄@VitB₁–Ag(I) were studied using theoretical calculations.     

Nonlinear optical and structural properties of M@C N endohedrals (M = Li,Ca and Sc,N = 60 and 70)

We have investigated the static (ω = 0) and frequency-dependent nonlinear optical (NLO) properties of the M@C _N endohedrals (M = Li, Ca, Sc, N = 60 and 70) using the SSH (Su–Schrieffer–Heeger) approximation and sum-over-state (SOS) approach. Also, we study the effects of displacement and alkali, alkaline earth and lanthanide metal atoms and type of cage on the hyperpolarisabilities of the M@C _N endohedrals. The hyperpolarisability magnitudes and spectra are in agreement with experiment and the work of others using the SSH approximation. Our results indicate that the cage-type effect on the NLO spectra of M@C _N endohedrals is dramatic. Also, atom type has little effect on the highest peak value. These relationships between the atom and cage type and hyperpolarisability values may be beneficial to experimentalists when designing new NLO materials with large NLO responses.     

Oxidative coupling of methane in a fixed bed reactor over perovskite catalyst： A simulation study using experimental kinetic model

The oxidative coupling of methane （OCM） to ethylene over a perovskite titanate catalyst in a fixed bed reactor was studied experimentally and numerically. The two-dimensional steady state model accounted for separate energy equations for the gas and solid phases coupled with an experimental kinetic model. A lumped kinetic model containing four main species CH4, O2, COx （CO2, CO）, and C2 （C2H4 and C2H6） was used with a plug flow reactor model as well. The results from the model agreed with the experimental data. The model was used to analyze the influence of temperature and feed gas composition on the conversion and selectivity of the reactor performance. The analytical results indicate that the conversion decreases, whereas, C2 selectivity increases by increasing gas hourly space velocity （GHSV） and the methane conversion also decreases by increasing the methane to oxygen ratio.     

Inelastic Electron Transport Through a Carbon Fullerene Junction

Effects of inelastic electron–phonon interactions and different contact geometries on the electron transport and thermoelectric properties of the C₆₀ molecule are studied by Green’s function theory within the framework of polaron transformation. It is seen that the current (I _e ) and energy flux (I _Q ) values with respect to the contact types are ordered as I _e/q (C ₁)?I _e/q (C ₆)?I _e/q (C ₅). The results reveal that the thermopower–energy curves have strictly monotonic character which show the staircase structures. Their stair numbers depend on contact types and presence of electron–phonon interactions. It is shown that the oscillatory behavior of thermal conductance is dramatically dependent on contact types and e–p interactions. Also, the values of the dimensionless figures of merit (ZT ₀) lie in the interval [0.322 ×?10^??7, 0.194 ×?10^??3], and effect of contact types is small on the values of ZT ₀s.     

N24B24分子结的电子传输

利用GW近似和非平衡格林函数结合的方法 研究了耦合到两个金属触点的N₂₄B₂₄分子的电子传输性. 计算结果表明,在单个和多个原子触点的态密度曲线上分别出现四个和三个谐振隧峰. 在I-V特性曲线上出现断路状态和微分负阻效应. 对于一、四、六、八原子的触点在电压分别在 ∓4.5、∓4、∓4.6、∓4.3 V表现出微分负阻效应行为. I-V特性在以低电压断开状态,呈独立的触点类型. I-V曲线取决于触点类型,并且表明N₂₄B₂₄分子呈现半导体的特性.     

Role of Al atom on structural and magnetic properties of β-SiC:Cr

The electronic structure, magnetic properties and also the bonding mechanism of the pure SiC and compounds SiC:Cr and SiC:Cr:Al have been studied using the Quantum SPRESSO Software within the density-functional theory (DFT). β-SiC, which is a nonmagnetic semiconductor, has more applications in industry. For the magnetic property, it is alloyed with transition metal. One of the transition metal is chromium. The calculations showed that its alloy at both Si site and C site (SiC:Cr) changes the physical properties of the host material and contributes in the molecular bond. It is seen that if the Al atom was doped in the compounds, SiC:Cr will produce hole carriers and the magnetic properties will thus increase to the considerable values due to the mediation effect. The magnetic property will create the up and down spin band gap to filter carriers. The charge density distribution illustrates that the Al atom has the atomic behavior in the compounds Sic:Cr:Al and does not contribute in the molecular bond. For comparison, the calculations were performed for the pure β-SiC.     

Using 3-cell chaotic map for image encryption based on biological operations

Recently, image encryption has emerged as an extremely urgent need to provide high protection for secure images against being used without any authorization. In the present paper, the 3-cell chaotic map known as cycling chaos was employed for image encryption based on biological operations. In order to increase security of the proposed method, the 120-bits secret key is used. DNA Sequences and cycling chaos were used to scramble the positions of the image pixels, and then the pixels grey values were modified using a mask DNA generated by cycling chaos. The obtained results demonstrated high security of the proposed method, and it was found acceptably resistant against different well-known attacks.     

Modeling the oxidative coupling of methane： Heterogeneous chemistry coupled with 3D flow field simulation

The oxidative coupling of methane (OCM) over titanate perovskite catalyst has been developed by three-dimensional numerical simulations of flow field coupled with heat transfer as well as heterogeneous kinetic model. The reaction was assumed to take place both in the gas phase and on the catalytic surface. Kinetic rate constants were experimentally obtained using a ten step kinetic model. The simulation results agree quite well with the data of OCM experiments, which were used to investigate the effect of temperature on the selectivity and conversion obtained in the methane oxidative coupling process. The conversion of methane linearly increased with temperature and the selectivity of C2 was practically constant in the temperature range of 973–1073 K. The study shows that CFD tools make it possible to implement the heterogeneous kinetic model even for high exothermic reaction such as OCM.     

Structural,magneto and optical properties of BX − 1NXC and BXNX − 1C cages (X = 12, 24 and 36)

The effect of carbon doping on the structural, optical and magneto properties of the B_XN_X cages has been studied using the B3LYP/6-31G^* level of density functional theory. With replacing one B or N atom with one C atom on the B_XN_X cages, the structural and symmetric properties, the optical absorption spectra and the band gaps of the B_XN_X cages change and the B_XN_X cages become magnetic. Our calculations conclude that the B_{X ? 1}N_XC and B_XN_{X ? 1}C cages can be interesting candidates for application in optoelectronics and spintronics.     

Electronic Transport Through N24B24 Molecular Junction

We have investigated the electron transport properties of a N₂₄B₂₄ molecule coupled to two metallic contacts with a combination of GW approximation and the non-equilibrium Green's-function technique. The calculations indicate that the four and three resonant tunneling peaks are seen for the density of states (DOS) curves in the cases of single and multiple atomic contacts, respectively. The off state and negative di erential resistance (NDR) effect are observed in the I-V characteristics of the N₂₄B₂₄ molecule. The NDR behavior is also observed in voltages of about ∓4.5, ∓4, ∓4.6, and ∓4.3 V for one, four, six, and eight atomic contacts. Also, the I-V characteristics of N₂₄B₂₄ are in off state at low voltages that is independent of the contact types. The current curves against the gate voltage depend on contact types and indicate that N₂₄B₂₄ molecule behaves as a semiconductor.