Telomerisation par catalyse redox—III. Etude de la reactivite des telogenes du type r-cc13, selon la nature du substituant r vis-a-vis du styrene

Among the various chloromethanes and chloroethanes, only compounds of the type R-CCl₃ are reactive telogens for styrene in catalysed telomerizations of the type due to Vofsi. We have found evidence for a new type of breakdown of CCl₃Br to CCI₂Br and CI in addition to the known breakdown to CC1₃ and Br'. A Hammet equation has been established for the telomerization involving styrene and telogens of the type RCCl₃. Excellent correlation has been found between the logarithm of the reactivity of a telogen and the Taft constant of the group R.     

Ozone and UV radiation over southern South America: climatology and anomalies

Ozone and UV radiation were analyzed at eight stations from tropical to sub-Antarctic regions in South America. Ground UV irradiances were measured by multichannel radiometers as part of the Inter American Institute for Global Change Radiation network. The irradiance channels used for this study were centered at 305 nm (for UV-B measurements) and 340 nm (for UV-A measurements). Results were presented as daily maximum irradiances, as monthly averaged, daily integrated irradiances and as the ratio of 305 nm to 340 nm. These findings are the first to be based on a long time series of semispectral data from the southern region of South America. As expected, the UV-B channel and total column ozone varied with latitude. The pattern of the UV-A channel was more complex because of local atmospheric conditions. Total column ozone levels of < 220 Dobson Units were observed at all sites. Analysis of autocorrelations showed a larger persistence of total column ozone level than irradiance. A decreasing cross-correlation coefficient between 305 and 340 nm and an increasing cross-correlation coefficient between 305 nm and ozone were observed at higher latitudes, indicating that factors such as cloud cover tend to dominate at northern sites and that ozone levels tend to dominate at southern sites. These results highlight the value of long-term monitoring of radiation with multichannel radiometers to determine climatological data and evaluate the combination of factors affecting ground UV radiation.     

Mediated modeling of the impacts of enhanced UV-B radiation on ecosystem services

This article describes the use of group model building to facilitate interaction with stakeholders, synthesize research results and assist in the development of hypotheses about climate change at the global level in relation to UV-B radiation and ecosystem service valuation. The objective was to provide a platform for integration of the various research components within a multidisciplinary research project as a basis for interaction with stakeholders with backgrounds in areas other than science. An integrated summary of the scientific findings, along with stakeholder input, was intended to produce a bridge between science and policymaking. We used a mediated modeling approach that was implemented as a pilot project in Ushuaia, Argentina. The investigation was divided into two participatory workshops: data gathering and model evaluation. Scientists and the local stakeholders supported the valuation of ecosystem services as a useful common denominator for integrating the various scientific results. The concept of economic impacts in aquatic and marsh systems was represented by values for ecosystem services altered by UV-B radiation. In addition, direct local socioeconomic impacts of enhanced UV-B radiation were modeled, using data from Ushuaia. We worked with 5 global latitudinal regions, focusing on net primary production and biomass for the marine system and on 3 plant species for the marsh system. Ecosystem service values were calculated for both sectors. The synthesis model reflects the conclusions from the literature and from experimental research at the global level. UV-B is not a significant stress for the marshes, relative to the potential impact of increases in the sea level. Enhanced UV-B favors microbial dynamics in marine systems that could cause a significant shift from primary producers to bacteria at the community level. In addition, synergetic effects of UV-B and certain pollutants potentiate the shift to heterotrophs. This may impact the oceanic carbon cycle by increasing the ratio of respiratory to photosynthetic organisms in surface waters and, thus, the role of the ocean as a carbon sink for atmospheric CO2. In summary, although changes in the marine sector due to anthropogenic influences may affect global climate change, marshes are expected to primarily be affected by climate change.     

A study of connectivity on dynamic graphs: computing persistent connected components

4OR - This work focuses on connectivity in a dynamic graph. An undirected graph is defined on a finite and discrete time interval. Edges can appear and disappear over time. The first objective of...     

Artificial aging of acrylurethane and alkyd paints: a micro-ATR spectroscopic study

The degradation of two paints during different standard tests was studied using micro-ATR spectroscopy. Standard test conditions do not give the same relative degree of aggressiveness depending on the binder. The IR results obtained with an acrylurethane top coat reveal that the degradation mostly proceeds through a direct or radical-induced scission of the urethane linkage. The chemical heterogeneity of the aged specimens was clearly underlined from high dispersal of their IR response. The advance in chemical degradation was found to be directly related to the UV light dose received by the samples, hence showing negligible influence of other exposure parameters (moisture, industrial atmosphere…). In contrast to the acrylurethane top coat, the behaviour of a glycerophthalic alkyd system appears to be dependent on exposure conditions other than UV radiation exposure. In that case, it was shown that with standard test cycles alternating UV, heat, moisture and SO₂ atmosphere exposures, the chemical change of the alkyd system was controlled by acidic hydrolytic backbone degradation of the phthalate moieties, hence resulting in chalking. This result was confirmed by an estimate of degree of chalking from IR results: chalking of the paint was related to the increase in the mineral IR absorption response relative to the organic one of the aged samples.     

Prospects for strangeness measurement in ALICE

The study of strangeness production at LHC will bring significant information on the bulk chemical properties, its dynamics, and the hadronization mechanisms involved at these energies. The ALICE experiment will measure strange particles from topology (secondary vertices) and from resonance decays over a wide range in transverse momentum and shed light on this new QCD regime. These motivations will be presented as well as the identification performance of ALICE for strange hadrons. (for the ALICE Collaboration) The text was submitted by the author in English.     

Effects of methanol on photosynthetic processes and growth of Lemna gibba

Effects of methanol on growth and photosynthetic activity of Lemna gibba exposed under continuous illumination were examined. As a higher plant, L. gibba appeared to be much more sensitive to methanol inhibitory effect compared with some algae (Theodoridou et al. [2002] Biochim. Biophys. Acta, 1573, 189-198). We found that stimulatory or inhibitory effects were strongly dependent on the methanol concentration and the time of exposure. When the exposure was up to 0.2% methanol, the growth rate of biomass was improved by 50%. However, stimulatory effect of methanol appeared to be smaller when plants were exposed for 48 h compared with 24 h. Increase in biomass induced by methanol was not based on the increase in primary photosynthetic process but rather on accommodation of energy dissipation during photosynthesis. Inhibitory effect on the growth of L. gibba already observed for 0.5% methanol was strongly associated with the increase in the nonphotochemical energy dissipation. The ratio between biomass and methanol concentration appeared to determine the stimulatory or the inhibitory effect. Suggested explanations for the stimulatory and the inhibitory effects are presented.     

Dielectric investigation of interphase formation in composite materials. I. Ionic conductivity and permittivity exploration

The aim of this study was to demonstrate the application of dielectric spectroscopy to composite material characterization during processing. Therefore, the microdroplet pullout test was used to follow the mechanical interfacial properties during processing. The results showed that interfacial shear stress strongly depends on the pressure, temperature, and process time at resin deposition. These observations were understood with dielectric spectroscopy. Literature data were first applied to our system. Results based on the ionic conductivity signal showed the existence of a mutual diffusion mechanism at the interface The mechanism rate constant depends strongly on the temperature, pressure, and process time. In a second part, we developed a way to follow the penetration depth with the permittivity signal. This approach is based on electric field line exploitation. The results highlighted the same observations. In conclusion, it appears that the adhesion of matrix–fiber is increased by composite processing at the monomeric state of the resin. Moreover, this study shows that this improvement is a consequence of a mutual diffusion mechanism at the interface. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2154–2161, 2000     

Telomeres photoreticulables—1. Synthese de telomeres photoreticulables a partir du cinnamate et de l'acetate de vinyle

Photocrosslinkable telomers containing cinnamoyl groups can be prepared by two methods, viz, (i) direct telomerisation of vinyl cinnamate using either redox initiation (FeCl₃ benzoin-CuCl₂) or conventional radical initiation (benzoyl peroxide), and (ii) esterification of polyvinylalcohol telomers with cinnamoyl chloride. The former method gives products which are extensively cyclised, as indicated by i.r. and NMR spectra, whereas the latter method gives materials in which all the cinnamoyl groups are available for crosslinking.     

Telomeres photoreticulables—3. Synthèse de telomeres photoreticulables a partir du cinnamate d'allyle et de l'acetate d'allyle

Photocrosslinkable telomers cannot be prepared by the direct telomerisation of allyl cinnamate. However, such materials can be prepared by reaction of cinnamoyl chloride with hydrolysed telomers of allyl acetate. Transfer constants of the three telogens, (H-P(0)(OEt)₂, CCl₂HCO₂CH₃ and CCl₃CO₂CH₃) towards allyl acetate were determined also.