Chipped Stone Assemblage of the Layer B of the Kamyana Mohyla 1 Site (South-Eastern Ukraine) and the Issue of Kukrek in the North Meotic Steppe Region

The layer B is one of the lower layers of the long stratigraphic sequence of the Kamyana Mohyla 1 site. The layer B received eight new AMS radiocarbon dates that clarified its chronology: 7950–7300 calibrated years BC. They are in a reasonable correspondence with the dates for lower and upper layers. The lithic assemblage belongs to Kukrek cultural aspect. It is characterized by pencil-like conical cores, Kukrek inserts, Kukrek burins and Dęby burins, nongeometric microliths (oblique points). The assemblage finds close parallels in the sites of Kukrek, Ihren VIII, Melnychna Krucha SU4 and Domchi-Kaia. They can be united into Kukrek sensu stricto cultural unit. The overlying layer C yielded somewhat different complex that finds parallels in the materials of the so-called “Kukrek cultural tradition.” Due to clear stratigraphic position of these units in the Kamyana Mohyla 1 sequence, we are able to differentiate Kukrek sensu stricto and “Kukrek cultural tradition” and suggest their respective chronological positions

Guidelines for DNA recombination and repair studies: Cellular assays of DNA repair pathways

Understanding the plasticity of genomes has been greatly aided by assays for recombination, repair and mutagenesis. These assays have been developed in microbial systems that provide the advantages of genetic and molecular reporters that can readily be manipulated. Cellular assays comprise genetic, molecular, and cytological reporters. The assays are powerful tools but each comes with its particular advantages and limitations. Here the most commonly used assays are reviewed, discussed, and presented as the guidelines for future studies

Asymmetric Error Correction Models for the Oil-Gasoline Price Relationship

The existing literature on price asymmetries does not systematically investigate the sensitivity of the empirical results to the choice of a particular econometric specification. This paper fills this gap by providing a detailed comparison of the three most popular models designed to describe asymmetric price behaviour, namely asymmetric ECM, autoregressive threshold ECM and ECM with threshold cointegration. Each model is estimated on a common monthly dataset for the gasoline markets of France, Germany, Italy, Spain and UK over the period 1985-2003. All models are able to capture the temporal delay in the reaction of retail prices to changes in spot gasoline and crude oil prices, as well as some evidence of asymmetric behaviour. However, the type of market and the number of countries which are characterized by asymmetric oil-gasoline price relations vary across models. The asymmetric ECM yields some evidence of asymmetry for all countries, mainly at the distribution stage. The threshold ECM strongly rejects the null hypothesis of symmetric price behaviour, particularly in the case of France and Germany. Finally, the ECM with threshold cointegration finds long-run asymmetry for each country in the reaction of retail prices to oil price changes

Controlled cationic polymerization of cyclopentadiene with B(C6F5)3 as a coinitiator in the presence of water

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Cationic polymerization of isobutyl vinyl ether in aqueous media: physical chemistry tricks to fight against thermal runaway

International audienceCationic polymerization of isobutyl vinyl ether (IBVE) in aqueous media (suspension, dispersion or emulsion), using mainly BF3OEt2 as a co-initiator is reported. A high exotherm was observed while carrying out the polymerization in aqueous suspension, whereas in dispersion (mixture of water and n-hexane as reaction medium) or in emulsion particularly, efficient heat transfer decreased thermal runaway. Poly(isobutyl vinyl ether)s with M-n up to 8600 g mol(-1) and relatively broad molecular weight distribution (M-w/M-n = 2.5-3.5) in high yield (>85%) were synthesized in aqueous dispersion. In direct emulsion, using BRIJ(R)98 (7 wt% to monomer) as a surfactant, polymers of low molecular weight (M-n = 80%), while aldehyde (12-16%) and alkenal (0.5-3.5%) end groups were found in minor proportions

Controlled/Living Cationic Polymerization of p-Methoxystyrene in Solution and Aqueous Dispersion Using Tris(pentafluorophenyl)borane as a Lewis Acid: Acetonitrile Does the Job

International audienceThe living cationic polymerization of p-methoxystyrene using the 1-(4-methoxyphenyl)ethanol/B(C6F5)3 initiating system in solution and in aqueous dispersion is reported. Solution experiments first showed that the molar mass of the obtained polymers increases in direct proportion to the monomer conversion and the molar mass distribution stays narrow in the course of the polymerization (Mw/Mn ~ 1.2). The living nature of the growing chains was confirmed by sequential monomer addition experiments, although matrix-assisted laser desorption ionization time-of-flight mass spectroscopy (MALDI-TOF-MS) revealed some hydroxyl elimination under monomer-starved conditions. Aqueous suspension polymerization of p-methoxystyrene using the same initiating system did not show a good control of molar masses, since after polymerization has proceeded at the interface up to critical DP, oligomers terminated by water penetrate inside the particles where they stop propagating. This limitation was leveled off for the first time by polymerizing p-methoxystyrene in an aqueous dispersion, i.e., in a mixture of H2O:CH3CN 3:2 (v/v). Under these conditions, the hydroxyl-terminated poly(p-methoxystyrene)s can be reactivated by B(C6F5)3 located inside the particles to reinitiate the polymerization; molar masses thus increase with conversion, up to 3000 g mol-1, and exhibit a narrow molar mass distribution (Mw/Mn ~ 1.3) and an almost pure hydroxylated functionality

Cationic Polymerization of Styrene Derivatives and Cyclopentadiene Catalyzed by B(C6F5)3 in Aqueous Media: Comparison of Suspension, Emulsion and Dispersion Processes

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