The Redshift Periodicity of Galaxies as a Probe of the Correctness of General Relativity

Recent theoretical work determines the correct coupling constant of a scalar field to the Ricci curvature of spacetime in general relativity. The periodicity in the redshift distribution of galaxies observed by Broadhurst et al., if genuine, determines the coupling constant in the proposed scalar field models. As a result, these observations contain important information on the problem of whether general relativity is the correct theory of gravity in the region of the universe at redshifts z < 0.5.     

On the tail problem in cosmology

The tail problem for the propagation of a scalar field is considered in a cosmological background, taking a Robertson-Walker spacetime as a specific example. The explicit radial dependence of the general solution of the Klein-Gordon equation with non-minimal coupling is derived, and the inapplicability of the standard calculation of the reflection and transmission coefficients to the study of scattering of waves by the cosmological curvature is discussed.     

The influence of aluminum on the thermal decomposition of hexabromocyclododecane

The influence of aluminum on the thermal stability of hexabromocyclododecane (HBCD) was investigated. HBCD pyrolysis was carried out using thermogravimetric analyzers and a laboratory scale reactor. The identification of decomposition products was based on FTIR and gas-chromatographic/mass-spectrometric techniques. The results obtained confirmed that the presence of aluminum caused a lower thermal stability of HBCD. However, the presence of aluminum also resulted in a significant increase of the char yield and caused the shift towards an exothermic decomposition process. The analysis of the decomposition products showed that the presence of aluminum triggers polycondensation reactions during HBCD thermal degradation.     

Principal component analysis application in polycyclic aromatic hydrocarbons “mussel watch” analyses for source identification

This article aims to show how a careful pre-treatment of data can be used to demonstrate various features embedded in a given data set obtained from a “mussel watch” survey, namely site- and source-specific characteristics and weather-related changes, and to provide indications so as to allow comparison with analyses performed on another substrate matrix. Polycyclic aromatic hydrocarbons (PAHs) biomonitored in the aquatic environment by means of caged mussels are compared by site and by season. Moreover, their fingerprints were compared to marine sediments and atmospheric airborne PAHs. The characterization of the sampling stations by means of the multivariate technique called principal component analysis (PCA) allows distinguishing the prevalence of pyrogenic or petrogenic types of pollution and between two kinds of combustibles. This was confirmed by jointly analyzing the percent composition of sea (mussel) and air (filter) samples.     

Photochemical degradation of polycyclic aromatic hydrocarbons (PAH) in real and laboratory conditions

Studies were carried out on the effects induced by the main components of airborne particulate matter (APM) as soot, inorganic and cyclohexane soluble substances and by glass fiber filters on photodegradation of pyrene, benz(a)anthracene and benzo(a)pyrene exposed to UV and solar radiation. In both experimental models tested hydrocarbons showed a higher photochemical stability when absorbed on APM. Inorganic components of APM slightly enhance UV photodegradation. In real condition (outdoor exposure to solar radiation) PAH half lives generally showed a good linear correlation with mean solar radiation intensity; only degradation rate of benzo(a)pyrene on APM, exposed to sunlight was practically constant. Pyrene, in particular, showed a higher degradation rate when high ozone concentrations (0.2 ppm) occurred.     

On-line preconcentration and ICP determination for trace metal analysis

The use of a closed-loop on-line enrichment procedure in combination with an ICP plasma emission spectrometer has been developed for the analysis of trace metal ions, such as Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn. The procedure utilizes a preconcentration column filled with an anion exchange resin and 8-hydroxy-7-iodoquinoline-5-sulphonic acid is added to the sample prior to preconcentration. Details on the optimization of pretreatment and instrumental conditions are described. Results obtained for the analysis of river water and antarctic seawater are reported.Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, Austria     

Three-component Biginelli cyclocondensation reaction using C-glycosylated substrates. Preparation of a collection of dihydropyrimidinone glycoconjugates and the synthesis of C-glycosylated monastrol analogues

The aldehyde-ketoester-urea cyclocondensation reaction has been revisited using C-glycosylated reagents with the aim of exploring a potential entry to a library of dihydropyrimidinone glycoconjugates. A collection of 13 mono- and bis-C-glycosylated dihydropyrimidinones has been prepared by a parallel synthesis approach using the three-component promoter CuCl/AcOH/BF(3) x Et(2)O. The sugar residues have been installed at either N1, C4, or C6 in the monoglycosylated derivatives and at both the C4 and C6 in the bisglycosylated products. The mono- and bisglycosylated products at C4 and C6 were obtained as mixtures of diastereoisomers with good to excellent selectivities due to the asymmetric induction by the sugar residue in the formation of the C4 stereocenter of the dihydropyrimidinone ring. Individual stereoisomers were isolated as pure compounds and their structures assigned with the aid of X-ray crystallography and chiroptical properties. As a demonstration of this new concept in the Biginelli reaction, the synthesis of two C4 epimer monastrol analogues bearing the ribofuranosyl moiety at C6 has been described.     

Advanced pulse calibration techniques for the quantitative analysis of TG–FTIR data

Two different pulse calibration techniques to estimate the total quantities of evolved gaseous substances formed in thermogravimetric (TG)–FTIR runs were compared and assessed. A gas-pulse calibration method was based on the use of a specific device able of sending a known quantity of a gaseous compound of interest to the FTIR analyzer. A second calibration method was based on the vaporization in the TG analyzer of liquid solutions of the compound of interest. Data obtained by these techniques were compared to those from conventional concentration-based calibration. The results confirmed the reliability of pulse calibration techniques to obtain quantitative data on evolved gaseous products in TG–FTIR applications. Moreover, both the gas-pulse and the vaporization-based calibration techniques proved to have several advantages with respect to conventional techniques. Among these are the need of a more limited number of standards and no need for online gas dilution systems.     

Covalent versus electrostatic nature of the strong hydrogen bond: discrimination among single, double, and asymmetric single-well hydrogen bonds by variable-temperature X-ray crystallographic methods in beta-diketone enol RAHB systems

Beta-diketone enols are known to form intramolecular...O=C-C=C-OH... resonance-assisted hydrogen bonds (RAHBs) with O...O distances as short as 2.39-2.44 A. However, even the most accurate diffraction studies have not been able to assess with certainty whether these very strong hydrogen bonds (H-bonds) are to be described as proton-centered O...H...O bonds in a single-well (SW) potential or as the dynamic or static mixing of two O-H...O <= => O...H-O tautomers in a double-well (DW) one. This contribution reexamines the problem and shows that diffraction methods are fairly able to assess the SW or DW nature of the H-bond formed and, in the second case, its dynamic or static nature, provided a Bayesian approach is used which associates a number of experimental techniques (X-ray crystallography at variable temperature, difference Fourier maps, least-squares refinement of proton populations, Hirshfeld's rigid-bond test) with a reasonable prior, that is the full set of possible proton-transfer (PT) pathways for the O-H...O system derived from theoretical calculations. The method is first applied to three beta-diketone enols, whose crystal structures were determined in the interval of temperatures 100-295 K and then generalized to the interpretation of a much wider set of beta-diketone enol structures derived from the literature, making it possible to establish a general relationship between chemical structure (symmetric or dissymmetric substitution, steric compression or stretching, increased pi-bond delocalizability), H-bond strength, and the shape of the PT-barrier. Final results are interpreted in terms of simplified VB theory and state-correlation (or avoided-crossing) diagrams.