Full potential calculation of structural, elastic properties and high-pressure phase of binary noble metal carbide: ruthenium carbide

We present in this paper the results of an ab initio theoretical study within the local density approximation (LDA) to determine in rock-salt (B1), cesium chloride (B2), zinc-blende (B3), and tungsten carbide (WC) type structures, the structural, elastic constants, hardness properties and high-pressure phase of the noble metal carbide of ruthenium carbide (RuC).The ground state properties such as the equilibrium lattice constant, elastic constant, the bulk modulus, its pressure derivative, and the hardness in the four phases are determined and compared with available theoretical data. Only for the three phases B1, B3, and WC, is the RuC mechanically stable, while in the B2 phase it is unstable, but in B3 RuC is the most energetically favourable phase with the bulk modulus 263 GPa, and at sufficiently high pressure (P_t=19.2 GPa) the tungsten carbide (WC) structure would be favoured, where ReC-WC is meta-stable.The highest bulk modulus values in the B3, B2, and WC structures and the hardnesses of H(B3)=36.94 GPa, H(B1)=25.21 GPa, and H(WC)=25.30 GPa indicate that the RuC compound is a superhard material in B3, and is not superhard in B1 and WC structures compared with the H(diamond)=96 GPa.     

Expedious synthesis for α, β-unsaturated coumarin derivatives using boran chelates: A novel class of potential antibacterial and antioxidant agents

A new family of coumarin derivatives (4a–i) containing a chalcone moiety was synthesized by condensation of 3-acetyl-4-difluoro boryloxycoumarin (2) with aryl and heteroaryl aldehydes with piperidine in chloroform. Resulting compounds were characterized by IR, ¹³C, ¹H NMR and UV visible spectroscopy. Compound 3-((2E)-3-(3,4,5-Trimethoxy-phenyl)prop-2-enoyl)-2(H)-chromen-2-one (4g) was characterized by single crystal X-ray diffraction. The antioxidant and antibacterial activities of the obtained compounds 4a-i was evaluated. The biological activity found for these compounds is discussed against their structural features, physical and chemical properties.     

Well posedness and stability result for a thermoelastic laminated Timoshenko beam with distributed delay term

In this work, we consider a linear thermoelastic laminated timoshenko beam with distributed delay, where the heat conduction is given by cattaneoâs law. we establish the well posedness of the system. For stability results, we prove exponential and polynomial stabilities of the system for the cases of equal and nonequal speeds of wave propagation.     

Study of femtosecond soliton dynamics in photonic crystal fiber using the moment method

We investigate the dynamics of femtosecond solitons in photonic crystal fibers (PCFs) by including high-order dispersion terms until to sixth-order in the generalized nonlinear Schrödinger equation, in addition to the nonlinear effects of the self phase modulation, self steepening and Raman scattering. We calculate theoretically the pulse parameters using the moment method. In the case of the fundamental soliton, our computed equations are coupled and difficult to solve analytically. However, we use the finite difference method to calculate numerically pulse parameters using an initially hyperbolic secant pulse at 1550-nm with different peak powers along 10m-PCF. Our numerical results show that the nonlinear regimes allow obtaining pulse compressions and initial pulse amplitudes. Furthermore, we remark a pulse broadening, and weak shifts of the peak power positions and frequencies in the critical and dispersive regimes. The use of an initial chirp provides a better pulse compressions and especially for low input powers. Also, the initial positive chirp reduces the optimal compression position lengths, while the negative one increases them. Therefore, we conclude that our theoretical calculations and numerical simulation results show that the moment method associated with the finite differences method is effective for the study of femtosecond pulse dynamics in PCFs.     

Electronic structure of (BP)n/(BAs)n (0 0 1) superlattices

An accurate ab initio full potential linear muffin-tin orbital method has been used to investigate the structural, electronic and optical properties of BP, BAs and their (BP)_n/(BAs)_n superlattices (SLs). The exchange-correlation potential is treated with the local density approximation of Perdew and Wang (LDA-PW). The calculated structural properties of BP and BAs compounds are in good agreement with available experimental and theoretical data. It is found that BP, BAs and their alloys exhibit an indirect fundamental band gap. The fundamental band gap decreases with increasing the number of monolayer n. The optical properties show that the static dielectric constant significantly decreases in superlattices compared to their binary compounds.     

Entropy generation in developing laminar fluid flow through a circular pipe with variable properties

Entropy generation in a circular pipe is analyzed numerically. A two-dimensional solution for the velocity ant temperature profiles is obtained considering temperature dependent thenmophysical properties. Uniform wall heat flux case is considered as the thermal boundary condition. The distribution of the entropy generation rate is investigated throughout the volume of the fluid as it flows through the pipe. Engine oil is selected as the working fluid. In addition, ethylene glycol and air are used in a parametric study. The total entropy generation rate is calculated by integration over the various cross-sections as well as over the entire volume. The results are compared with those obtained for the constant viscosity case. A considerable discrepancy is found between the two cases since the viscosity of these fluids is highly sensitive to the temperature variation.     

Host-guest inclusion complex between β-cyclodextrin and paeonol: A theoretical approach

Host-guest interactions of β-cyclodextrin (β-CD) with paeonol (PAE) were simulated using semi-empirical PM3 and both ONIOM2 [(B3LYP/6-31G*:PM3), (HF/6-31G*:PM3)] methods. The results obtained with PM3 method clearly indicate that the complexes formed are energetically favored with or without solvent, the model 1 (PAE entering into the cavity of β-CD from its wide side by OCH3 group) is found more favored than the model 2 (PAE entering into the cavity of β-CD from its wide side by COCH3 group). Finally, natural bonding orbital (NBO) analysis was performed based on ONIOM2 optimized complexes to quantify the donor–acceptor interactions between PAE and β-CD.     

Stability analysis of whirl flutter in rotor-nacelle systems with freeplay nonlinearity

Nonlinear Dynamics - Tiltrotor aircraft are growing in prevalence due to the usefulness of their unique flight envelope. However, aeroelastic stability—particularly whirl flutter...     

Performance comparison with different methods for ethanol/O2 biofuel cell based on NAD+ cofactor immobilized and activated by two types of carbon nanoparticles

Journal of Solid State Electrochemistry - Biofuel cells are an attractive alternative to conventional fuel cells, because they use biological catalysts. We report in this article the construction...