A systematic approach to parameter optimization and its application to flight schedule simulation software

Journal of Heuristics - Industrial software often has many parameters that critically impact performance. Frequently, these are left in a sub-optimal configuration for a given application because...     

Ab initio calculations on octahedral (CH) x (NH)6−x

Octahedral 38-, 44- and 48-electron systems are closed-shells and could be stable. The latter two systems have a high energy and dissociate via a non-symmetric path. (NH)₆ in a chair conformation should be stable.     

Hydrogen adsorption in carbon nanostructures: comparison of nanotubes, fibers, and coals

Single-walled carbon nanotubes (SWNT) were reported to have record high hydrogen storage capacities at room temperature, indicating an interaction between hydrogen and carbon matrix that is stronger than known before. Here we present a study of the interaction of hydrogen with activated charcoal, carbon nanofibers, and SWNT that disproves these earlier reports. The hydrogen storage capacity of these materials correlates with the surface area of the material, the activated charcoal having the largest. The SWNT appear to have a relatively low accessible surface area due to bundling of the tubes; the hydrogen does not enter the voids between the tubes in the bundles. Pressure-temperature curves were used to estimate the interaction potential, which was found to be 580+/-60 K. Hydrogen gas was adsorbed in amounts up to 2 wt % only at low temperatures. Molecular rotations observed with neutron scattering indicate that molecular hydrogen is present, and no significant difference was found between the hydrogen molecules adsorbed in the different investigated materials. Results from density functional calculations show molecular hydrogen bonding to an aromatic C[bond]C that is present in the materials investigated. The claims of high storage capacities of SWNT related to their characteristic morphology are unjustified.     

Ab-initio calculations on the 1-imidazolyl radical

Ab-initio calculations on the 1-imidazolyl radical with a minimal basis set were performed. The ground state symmetry is calculated to be ²B₁(π); the first excited state is ²A₂(π) and lies at 0.359 eV. The σ-state shows a double minimum potential having its well 0.626 eV above the C_2v ground state minimum. The height of the inner hill, peaking at C_2v symmetry, is 0.612 eV; the state is of B₂ character. The reason for the distortion is discussed.     

Optosensing properties of fac-Re(CO)(3)(dpknph)Cl (dpknph=di-2-pyridyl ketone p-nitrophenyl hydrazone)

Optical and thermodynamic measurements on fac-Re(CO)(3)(dpknph)Cl in polar non aqueous solvents revealed the existence of two interlocked conformational forms for fac-Re(CO)(3)(dpknph)Cl. The equilibrium distribution of the low (alpha-) and high (beta-) energy conformations is solvent dependent, controlled by the dipole moment of the solvent molecules and their orientation around the total dipole of fac-Re(CO)(3)(dpknph)Cl. The interplay between the alpha- and beta-conformations of fac-Re(CO)(3)(dpknph)Cl, allowed calculations of their extinction coefficients, by forcing the equilibrium to shift to one conformation, using chemical stimuli. In DMSO and DMF extinction coefficients of 87 000+/-2000 and 35 000+/-2000 M(-1) cm(-1) were calculated for the beta- and alpha-conformations of fac-Re(CO)(3)(dpknph)Cl at lambda(max.), respectively. Thermo-optical measurements on fac-Re(CO)(3)(dpknph)Cl, allowed calculations of the activation parameters for the interconversion between the alpha- and beta-conformations of fac-Re(CO)(3)(dpknph)Cl. In DMSO and DMF changes in enthalpy (DeltaH(?)) of -11.2+/-1.3 and 10.9+/-0.5 kJmol(-1), entropy (DeltaS(?)) of -12.7+/-4.3 and 29.4+/-1.7 JK(-1) mol(-1), and free energy (DeltaG(?)) of -7.5+/-0.2 and+2.2+/-0.2 kJmol(-1) and hence equilibrium constants of 20.9+/-1.7 and 0.4+/-0.1 were calculated for fac-Re(CO)(3)(dpknph) at 295 K. The high values for the extinction coefficients and low values for the activation parameters for the interconversion between the alpha- and beta-conformations of fac-Re(CO)(3)(dpknph)Cl, in polar non aqueous solvents allowed the use of these systems as molecular sensors to probe their structural relaxation and interactions with their surroundings. These systems (fac-Re(CO)(3)(dpknph)Cl and surrounding solvent molecules) optically sense chemical and physical stimuli and their sensing power depends on the intensity and nature of these stimuli, i.e. the systems exhibit a high degree of sensitivity and selectivity.