Ab initio study of cubyl chains and networks

The spatial arrangements and physical properties of one- and two-dimensional structures, based on the amazing cubane (C(8)H(8)) molecule, are investigated in detail. In particular, we compute the electronic structure, both by first principle calculations and by semiempirical methods. The elastic and vibrational properties are evaluated as well. All these results are compared with those of the single cubane molecule, in order to elucidate the influence of dimensionality.     

Styrene and methyl methacrylate polymerization using diphenylzinc-cocatalyst systems. part II.

Various diphenylzinc–additive systems were used to initiate homopolymerization of styrene and of methyl methacrylate. The polymers obtained were characterized by size exclusion chromatography, by ¹H– and ¹³C–NMR and measurements of intrinsic viscosities [η]. These data indicated that polymerization is much influenced by: The nature of the additive employed, the proportion of the additive relative to diphenylzinc and the condition of polymerization.     

A linear programming problem in harmonic analysis

For a given subset E of the natural numbers it is desired to maximize Σ_n?Ea_n subject to a_n?0, 1+Σ_n?Ea_n cosnθ?0 for θ?[0,π]. A dual program is defined, and a duality principle is established. Extensions to other series of functions are given, and these include the motivating example of P. Delsarte [Philips Res. Repts.27 (1972), 272–289].     

Elastic scattering of deuterons by 14C from Ed = 4 to 10 MeV

Angular distributions for the elastic scattering of deuterons by ¹⁴C were measured at nine energies between E_d = 4.2 and 10 MeV. Excitation functions were taken in 50 keV steps from E_d = 4 to 10 MeV. A resonance was observed at E_d = 4.5 MeV, which corresponds to an excitation energy of 14.41 MeV in ¹⁶N. An analysis using an optical model plus a single-level formula derived from the R-matrix formalism yields an l-value assignment of l = 4 for this resonance. Of the three J^π values allowed for l = 4 (J^π = 3⁺, 4⁺, 5⁺), the value of J_π = 3⁺ is found to be slightly preferred. Possible identification of this resonance with an analog in ¹⁶O is discussed. The angular distributions measured at off-resonance energies were analyzed with an optical-model potential which has a surface-peaked imaginary well. The energy dependence of the real and imaginary well depths are explicitly determined in the present work for E_d = 4 to 10 MeV. The best-fit optical-model parameters obtained from the present study are compared to those from the ¹⁴N(d, d)¹⁴N work.     

Effects of nuclear deformation on neutron total cross sections

Neutron total cross section differences have been determined for ^150,152,154Sm from 0.8 to 15 MeV by measuring transmission ratios. Significant differences were observed for ^152,150Sm and for ^154,150Sm. Evidence is presented that these results can be attributed to nuclear deformation.     

Vibrational modes of free nanoparticles: from atomic to continuum scales

Vibration analysis of free standing silicon nanoparticles, with sizes ranging from 0.732 to 4.223 nm, are calculated using two different methods: molecular mechanics and classical continuum elasticity. Three different geometries are studied: cubes, spheres, and tetrahedrons. Continuum mechanics methods provide good estimates of the lowest natural frequency of particles having at least 836 (R>1.5 nm) and 800 (R>1.28 nm) atoms for cube- and tetrahedron-shaped nanostructures, respectively. Equations for vibrational frequencies of smaller particles as a function of size are proposed. The vibrational modes obtained from both methods were practically the same for the sphere- and tetrahedron-shaped particles with a large number of atoms. However, for the cube geometry only the shape of the modes corresponding to the lowest couple of frequencies occur in the same order. In general, vibrational modes shapes obtained using both methods are the same although the order in which they appear may be shifted.     

Engineering heterogenous catalysts for chemical CO2 utilization: Lessons from thermal catalysis and advantages of yolk@shell structured nanoreactors

The development of catalytic materials for the recycling CO2 through a myriad of available processes is an attractive field,especially given the current climate...