Melting curve of sodium at high pressure

A semiempirical model equation of state is developed in terms of bulk modulus and the Grüneisen parameter to compute the melting temperature of sodium in the gigapascal range of pressure. The model successfully explains the increase and decrease of T _m as the pressure increases. Computed values of the critical pressure and temperature are in very good agreement with the experimental observations.     

Performance optimization for terahertz quantum cascade laser at higher temperature using genetic algorithm

The aim of this work is to establish an approach for obtaining improved design parameters for high temperature operation of terahertz quantum cascade lasers using a multi-objective evolutionary algorithm. For studying the lasing conditions of a quantum cascade laser, a self-consistent model is adopted. This model uses standard wave function approximation and effective mass approximation with relevant scattering mechanisms to solve Schrodinger’s equation for the cascaded quantum wells. Fermi’s Golden Rule is then used to calculate the corresponding lifetime of each eigen states. To describe the coherent evolution of wave functions and phase breaking, density matrix formalism is employed. Subsequently, laser rate equations are used for calculating the parameters related to electronic transport in the device. These parameters are then utilized for investigating the temperature dependence of existing terahertz quantum cascade lasers. Finally, using an optimization technique based on Genetic algorithm, design parameters for resonant-phonon quantum cascade laser are obtained within the terahertz frequency range. The results illustrate that this optimization process can offer improvement in the performance of quantum cascade lasers in terahertz region at an elevated temperature. Moreover, the results also reveal that significant increase in operating temperature of a resonant phonon terahertz QCL is unlikely and hence novel design approaches should be considered for operating THz QCLs at room temperature.     

Influence of the double bond position in combustion chemistry of methyl butene isomers: A shock tube and laser absorption study

Shock tube experiments have been carried out on 2-methyl-1-butene (2M1B), 2-methyl-2-butene (2M2B), and 3-methyl-1-butene (3M1B)—the three isomers of methyl butene compound. Carbon monoxide (CO) time-histories and ignition delay times are obtained behind reflected shockwaves over the temperature range of 1350-1630 K and pressures of 8.3-10.5 atm with stoichiometric mixtures of 0.075% fuel in O₂/Ar. Comparative ignition study reveals that 3M1B ignites significantly faster than the other two isomers, while 2M1B dissociates earlier but ignites later than 2M2B. Possible mechanisms for this behavior are discussed with ignition delay time sensitivity and reaction path analysis. In addition, time-resolved CO measurements are compared with three different reaction mechanisms from the literature. Sensitivity analyses have been carried out to identify important reactions that need attention to accurately predict the chemistry of these isomers. Further investigation into the rates of unimolecular fuel decomposition reactions and C₃H₃ + O₂ = CH₂CO + HCO reaction are suggested based on the current investigation.     

Thermoelastic and thermodynamic properties of harzburgite—An upper mantle rock

A number of thermoelastic and thermodynamic properties such as compressibilities, specific heat ratio, specific heat capacities, Grüneisen parameters, Debye temperature, the melting temperature, and their dependence on temperature and pressure have been obtained for the harzburgite rock of Oman ophiolite suite. Debye temperature Θ_D and the ratio of the specific heats are the basic inputs which are determined here by making use of the seismic velocities and the density data. The specific heat capacities C_P and C_V are evaluated from the thermodynamic equations as well as from the Debye theory. These data along with the computed values of compressibilities have been used to evaluate the Grüneisen parameter and its dependence on temperature through thermodynamic and acoustic relations. The computed values of the Debye temperature has also been found very helpful to estimate the melting temperature of the rock whose pressure dependence is analyzed following the Clausius-Clapeyron equation.