Doppler-shift attenuation measurements on Mg by (α, α') and (p,p') reactions

The (α, α') and (p, p') reactions have been used to populate states in ²⁴Mg in order to measure lifetimes of ten states by the Doppler-shift attenuation method. The shifted γ-rays were observed by a planar 5.6 cm³ Ge(Li) detector at 90° to the beam at the target in coincidence with the scattered particles observed in either of two particle detectors located symmetrically with respect to the beam. A computer coupled dual two-parameter arrangement permitted concurrent measurements for all states appreciably populated. The present measured transition probabilities are compared with predictions from a truncated j-j coupling shell-model calculation.     

A carbon-13 NMR study of some metal carbonyl compounds containing one-electron ligands

Carbon-13 NMR spectral data for complexes having the general formula CpM(CO)_nX (Cp = η⁵-C₅H₅; M = Mo or W, n = 3; M = Fe, n = 2; X = halogen, methyl or acetyl) and their phosphine and isocyanide substitution products are reported. For CpM(CO)₃X complexes two carbonyl resonances (1 : 2 ratio) are observed in all cases, consistent with the retention of the “piano-stool” geometries observed in the solid state. Substituted complexes CpM(CO)₂(L)X (M = Mo or W; L = PR₃ or cyclohexyl isocyanide) are unequivocally assigned cis or trans geometries on the basis of the number of observed carbonyl resonances and values of ²J(PC) for the phosphine substituted derivatives. Spectral data for [M(CO)₅X]^? (M = Cr, Mo or W; X = Cl, Br or I) and η⁷-C₇H₇Mo(CO)₂X and the halide derivatives above generally show an increase in the shielding for carbonyls adjacent to the halide ligand in the order Cl < Br < I. Carbonyl resonances are more shielded in isostructural complexes in the order Cr < Mo < W (triad effect).     

Bioaccumulation and biotransformation of 1-hydroxypyrene by the marine whelk Neptunea lyrata

In the marine environment, organisms can be exposed to oxidised forms of polycyclic aromatic hydrocarbons. Bioaccumulation and biotransformation of these derivatives has rarely been investigated and would lead to a better understanding of the overall fate of polycyclic aromatic hydrocarbons and that of other phenolic contaminants. The marine whelk Neptunea lyrata was exposed to 1-hydroxypyrene through its diet over 35 days. Extracts from the muscle and visceral mass of each animal were analysed by liquid chromatography with fluorescence detection. The quantified compounds included 1-hydroxpyrene and the phase II metabolites pyrene sulphate, pyrene glucuronide and one isomer of pyrenediol disulphate. The hydroxylated hydrocarbon was highly retained with 78% of the exposure amount recovered primarily from the visceral mass of the whelks, while the muscle accounted for 4% of the body burden. Whelks efficiently biotransformed 1-hydroxypyrene with a mean of 81% of the compound detected as phase II metabolites. The novel biotransformation product, pyrenediol disulphate, accounted for the largest proportion of the 1-hydroxypyrene derivatives detected at body burdens below 200?ng. At higher body burdens, bioaccumulation increased. Control animals showed trace levels of pyrene derivatives with 76% represented by metabolites. This study highlights the importance of investigating the multiple fates of reactive chemicals in order to interpret exposure.     

ON THE IMPULSIVE BEVERTON–HOLT EQUATION AND EXTINCTION CONDITIONS IN POPULATION DYNAMICS

Abstract This paper is devoted to investigate extinction and nonextinction conditions of the extended Beverton–Holt equation (BHE) for dynamics of populations in Ecology when potential discontinuities at sampling points are included in the model. The proposed model is described by means of four sequences of parameters. Two of them are the intrinsic growth rate and the carrying capacity sequences which are included in the basic BHE model. The other two ones, namely, the harvesting (i.e., the hunting or fishing quota) and the internal consumption (which can include positive and negative migrations in the considered population habitat) sequences are included to parameterize the model discontinuities. Such discontinuities are related to impulses in the corresponding continuous‐time logistic equation. The obtained results establish how the harvesting quota and/or the internal consumption has to be fixed to guarantee the population nonextinction or, eventually, its extinction. Finally, some controllability results related to the search of a carrying capacity sequence such that the solution of the proposed impulsive BHE tracks a reference one are obtained.     

Precise atomic mass determinations at mass 124

The Manitoba II high-resolution mass spectrometer has been used to determine eight precise atomic mass differences amongst ¹²⁴Sn, ¹²⁴Te, ¹²⁴Xe, ¹³C³⁷Cl₃ and ⁵⁴Fe³⁵Cl₂. Precise values have been derived for the double β- decay energies of ¹²⁴Xe and ¹²⁴Sn and for the masses of ¹²⁴Sn, ¹²⁴Te, ¹²⁴Xe and ⁵⁴Fe. The precision of the mass of ¹²⁴Xe has been improved by a factor of ≈150.     

Optical determination of Cr(VI) using regenerable, functionalized sol-gel monoliths

Transparent, pyridine-functionalized sol-gel monoliths have been formed and their use in Cr(VI) sensing applications is demonstrated. The monoliths were immersed in acidic Cr(VI)-containing solutions, and the Cr(VI) uptake was monitored using UV-vis and atomic absorption spectroscopies. At concentrations at the ppm level, the monoliths exhibit a yellow color change characteristic of Cr(VI) uptake, and this can be measured by monitoring the absorption change at about 350 nm using UV-vis spectroscopy. Concentrations at the ppb level are below the limit of detection using this wavelength of 350 nm for measurement. However, by adding a diphenylcarbazide solution to monoliths that have been previously immersed in ppb-level Cr(VI) solutions, a distinct color change takes place within the gels that can be measured at about 540 nm using UV-vis spectroscopy. Concentrations as low as 10 ppb Cr(VI) can be measured using this method. The monoliths can then be regenerated for subsequent sensing cycles by thorough washing with 6.0 M HCl. The factors affecting monolith uptake of Cr(VI) have been explored. In addition, the gels have been characterized using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) measurements.     

磺基水杨酸修饰电极联吡啶钌电化学发光体系测定可待因的研究

基于磷酸可待因对联吡啶钌在该电极上的电化学及其发光行为的增敏作用,建立了一种直接测定磷酸可待因的电化学发光新方法。在最佳实验条件下,磷酸可待因在1.0×10-4～4.0×10-6mol/L和4.0×10-6～2.0×10-7mol/L与相对发光强度呈线性关系,检出限为1.0×10-7mol/L(S/N=3)。连续测定4.0×10-7mol/l磷酸可待因5次,发光强度的RSD为2.7%。方法用于模拟尿样中磷酸可待因的测定,结果满意。     

Derivation and synthesis of renewable surfactants

This critical review focuses on the origins and preparation of bio-based surfactants, defined here as non-soap, amphiphilic molecules in which the carbon atoms are derived from annually renewable feedstocks. Environmental concerns and market pressures have led to greater relevance of these chemicals in commercial applications in recent years and extensive research has gone into exploring new classes of surfactants. Highlighted here are examples of bio-based surfactants that are produced on an industrial scale and/or are based on abundant starting materials. The trend of increasing use of renewable resources as starting materials for surfactants is introduced, followed by extensive discussion of the major classes of bio-derived hydrophobes and hydrophiles. Also discussed is the status of research and development with regard to biosynthetically produced surfactants. Finally, concluding remarks address the potential for new surfactant molecular structures as a result of ongoing development in the chemistry of biorefineries, i.e., that the transformation of lignocellulose into fuels is likely to support the manufacturing of new bio-based coproducts (238 references).