Intermolecular interactions and spectral shifts in energy transfer dye lasers

Short-range dye-dye intermolecular interactions in energy transfer dye lasers can produced pronounced blue shifts in the superradiant wavelength of the sensitized dye. The magnitude of the shift, which in some cases can exceed 20 nm, depends on the nature and concentration of the lasing dye and the donor:acceptor ratio.     

Systematics of nuclear matter and finite nuclei properties in a non-linear relativistic mean field approach

A phenomenological non-linear relativistic mean field approach is used to investigate primarily the properties of nuclear matter. The dimensionless parameters are adjusted using different empirical quantities which are discussed in detail: saturation conditions, the incompressibility parameter, symmetry energy and surface energy. Particular attention is paid to the cubic and quartic terms in the self-interaction part of the scalar field. The effective parameters are then used to study doubly magic finite nuclei in the Dirac-Hartree approximation. Different ground-state properties, binding energies, rms radii, density distributions, are then systematically analyzed and discussed. A remarkable agreement with experimental quantities is found and further possibilities are suggested.     

Efficient boron removal by using mesoporous matrices grafted with saccharides

Highly efficient boron removal from water was achieved by using mesoporous silica materials functionalised with saccharides.     

Sorption of propane and propylene in polyethylene

Measurements are reported of the solubility and concentration of propane and propylene in polyethylene, at temperatures from ?30°C to +30°C and pressures from 1.68 to 3.52 atm. Solubility of both gases in polymer depends on penetrant activity. Henry's law is not obeyed at high values of the penetrant activity, i.e., in the vicinity of the condensation point of the gas. The interaction between the solvent and the polymer is independent of pressure and a function of temperature. The propylene-polyethylene interaction seems to reach a maximum at 10°C within the range investigated. A physical mechanism, based on opposite effects of temperature upon polymer and penetrant, is suggested to explain the results.     

Accidental degeneracies and symmetry groups

It is usually assumed that the appearance of accidental degeneracy in the energy levels of a given Hamiltonian is due to a symmetry group. By considering the elementary problem of a rotator with spin-orbit coupling, when the strength of the latter is equal to the inverse of the moment of inertia, we find that this assumption does not explain the degeneracy of all the levels of the Hamiltonian. Thus the relation between accidental degeneracies and symmetry group merits further probing.     

Gas-phase thermolysis of sulfur compounds. Part IV. n-propyl allyl sulfide

The pyrolysis of n-propyl allyl sulfide has been studied in static and stirred-flow systems at temperatures between 270 and 400°C. Propene and 2,4,6-triethyl-1,3,5-trithiane were the only reaction products. The order of the reaction was 0.99 ± 0.05 at 377°C. The first-order rate coefficients followed the Arrhenius equation The rate coefficients and the product distribution remained unchanged when cyclohexene was used as carrier gas. A molecular mechanism involving a six-centered cyclic transition state is proposed to explain the present results. This mechanism is further supported by the pyrolysis of 4-thia-5-dideutero-1-heptene at 377°C, where only 3-deuteropropene is formed. The kinetic deuterium isotope effect had a value of 2.6 ± 0.3 at this temperature. The results are compared with those obtained in the pyrolysis of n-butyl allyl sulfide previously reported.     

A Shared Prebiotic Formation of Neopterins and Guanine Nucleosides from Pyrimidine Bases

The prebiotic origins of biopolymers and metabolic co-factors are key questions in Origins of Life studies. In a simple warm-little-pond model, using a drying phase to produce a urea-enriched solution, we present a prebiotic synthetic path for the simultaneous formation of neopterins and tetrahydroneopterins, along with purine nucleosides. We show that, in the presence of ribose and in a formylating environment consisting of urea, ammonium formate, and water (UAFW), the formation of neopterins from pyrimidine precursors is robust, while the simultaneous formation of guanosine requires a significantly higher ribose concentration. Furthermore, these reactions provide a tetrahydropterin–pterin redox pair. This model suggests a prebiotic link in the origin of purine nucleosides and pterin cofactors that provides a possible deep prebiotic temporal connection for the emergence of nucleic acids and metabolic cofactors.