Mild and neutral deprotections catalyzed by cerium(IV) ammonium nitrate

The development of a novel, chemoselective, and catalytic deprotection methodology that proceeds under mild and neutral conditions is described, and its mechanism of action is analyzed in some detail. The scope, limitations, and advantages of this protocol are discussed. Selected applications in synthesis are also highlighted.     

Preheating Sensitization of a TATB Composition Part one: Chemical Evolution

We analyze the evolution of the sensitivity of a TATB composition after thermal cycles at elevated temperatures. Sensitization due to thermal cycles is of variable magnitude depending on the kind of the second stimulus (mechanical or thermal). In order to investigate the possible mechanisms which govern these phenomena, we perform an extensive study of the evolution of the chemistry and microstructure of our composition and we determine the sensitivity of our explosive to various stimuli after various temperature/duration cycles. This first paper is devoted to the study of TATB chemical evolutions. We present the results obtained for explosive decomposition, furazan generation, gas analyses and solid residue characterization.     

Osmotic cracking in unsaturated polyester matrices under humid environment

Glass fiber reinforced polyester composites are widely used in marine applications where they may undergo chemical and physical aging. For this kind of laminates, the durability is governed mainly by the matrix degradation. The mechanical property reduction is not induced only by hydrolytic aging but rather by the formation of cracks or blisters. That is the reason why it became of major interest to understand the microcrack nucleation mechanism in neat matrices, to study the crack propagation, and to evaluate the incidence of cracking on the tensile property loss. We first put forward a nucleation mechanism based on polyester‐organic molecule phase separation, and drew a simple kinetic model to take into account the existence of a crack induction time that is dependent on temperature and matrix structure. Crack propagation results from the build up of an osmotic pressure in microcavities, which is proportional to solute concentration. This second step has been studied in terms of crack density evolution and crack propagation rate. Finally, there is a good correlation between tensile mechanical properties variation and crack parameters. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2517–2526, 2001     

Combined GC/MS analytical procedure for the characterization of glycerolipid, waxy, resinous, and proteinaceous materials in a unique paint microsample

A novel GC/MS analytical procedure for the identification of lipids, waxes, proteins, and resinous materials in the same microsample from painted works of art has been optimized. It is based on a sample multistep chemical pretreatment (solvent extractions and microwave-assisted chemolysis) that is able to separate the various organic components into different fractions, which are suitably treated and derivatized before analysis. In particular, the procedure allows the complete saponification of wax esters and the completeness of the Cannizzaro type reaction of shellac acids in conditions that are suitable also for glycerides saponification. The method was tested on reference materials for the identification of proteinaceous binders (egg, collagen, casein) on the basis of the quantitative determination of the amino acid profile and the identification of glycerolipids (linseed oil, poppy seed oil, walnut oil, and egg), plant resins (Pinaceae resins, sandarac, mastic, and dammar), animal resins (shellac), tars or pitches, and natural waxes (beeswax, carnauba wax) on the basis of the determination of fatty acid, alcohol, and hydrocarbon profiles and of significant terpenic molecular markers. The procedure was applied to the characterization of three old paint microsamples. Animal glue, egg, linseed oil, beeswax, Pinaceae resin, dammar, and shellac were the identified materials found in mixtures and recognized as original and/or restoration substances.     

Theoretical analysis of the influence of defect parameters on photovoltaic performances of composition graded InGaN solar cells

In this paper, we have used simulations to evaluate the impact of the distribution of electrically active defects on the photovoltaic performances of InGaN-based solar cell. The simulations were carried out using Silvaco's ATLAS software. We have modeled a P-GaN/Grad-InGaN/i-In_0.53Ga_0.47N/Grad-InGaN/N-ZnO where Grad-InGaN corresponds to an InGaN layer with a graded composition. This layer is inserted to eliminate the band discontinuities at the interface between InGaN and the GaN and ZnO layers. The defects were modeled through the introduction of band tails and a Gaussian distribution of defects in i-InGaN material. We have evaluated the influence of band tail widths as well as the parameters of the Gaussian distribution (i.e. defect density, mean position and standard deviation) on the short-circuit current, the open-circuit voltage and the fill-factor (efficiency) of the solar cell. These results have allowed us to identify key structural parameters useful for the optimization of InGaN solar cells, as well as to give realistic estimates of the performances of such cells.     

Surface characterization of GSH-CdTe quantum dots

The surface characterization of CdTe QDs synthesized by a novel procedure using glutathione (GSH), low temperatures (60–90 °C) and K₂TeO₃ as the –Te precursor is reported. Fluorescence of the produced QDs is stable in the pH range 6–13 and QDs inside eukaryotic cells are highly fluorescent. The surface composition of GSH-CdTe QDs with different spectroscopic properties and particle size distributions was determined by XPS. The XPS analysis indicated that the QDs are essentially CdTe, although all nanoparticles contain 12–24% of CdO (and in one case also TeO₂). GSH decomposes with reaction time releasing small amounts of S⁻² ions that react with Cd(Te) to yield Cd(Te)S in a smaller amount than that of CdTe. Finally, the use of QDs in fluorescence mediated immunodetection of bacterial pathogens has been evaluated.     

Electric Current Effects on the Corrosion Behaviour of High Chromium Ferritic Steels

The high-temperature corrosion behaviour of the Cr containing ferritic alloys Crofer 22 APU and Crofer 22 H were investigated for their potential application as interconnects in planar-type solid oxide electrolysis cells (SOECs) operating at 800 °C for syngas production in steam/CO₂ co-electrolysis mode. To simulate the operating conditions for this application, oxidation tests in relevant atmospheres with and without electric current were conducted. The corrosion behaviour was influenced by the electric current resulting in accelerated oxidation on the negative side and suppressed oxidation on the positive side. The scale structure was influenced by a combination of atmosphere and electric current effects. The modified oxidation of the interconnect steels due to the electric current effect could have detrimental impact for the O₂ side and beneficial effect for the CO₂/H₂O side in an SOEC stack operating in co-electrolysis mode.     

Influence of the surrounding ambient on the reliability of the electrical characterization of thin oxide layers using an atomic force microscope

Physical and electrical properties of thin oxide films have been studied using the atomic force microscope (AFM). Experiments have been done in three different surroundings: in air and in secondary vacuum (∼10⁻⁶ mbar) without and with a heating stage in order to study the influence of the surrounding ambient on the reliability of the electrical characterization of thin oxide films. It is shown that by applying a positive voltage at the AFM tip and in the presence of a water layer at the oxide’s surface in air ambient, the behavior of the oxide film is very different compared to the same experiment conducted in secondary vacuum. It is thought that in air, H⁺ ions are injected through the oxide, forming attached hydrogen defects in it. These electrically active defects form a path in the oxide between the tip and the substrate facilitating the passage of charges through the oxide, which can be described by a Trap Assisted Tunneling (TAT) mechanism. The results show that working in vacuum with a heating stage is an important condition for the reliability of the characterization of oxides since the breakdown phenomenon is largely reduced due to the absence of the water layer. Moreover, the creation of hillocks (protrusions appearing on the surface after the electrical stress) on the oxide’s surface is decreased under vacuum.     

Fruit load or fruit position alters response to temperature and subsequently cherry tomato quality

Changes in fruit–source ratio during the growth and maturation of cherry tomato fruits were studied in combination with increased fruit temperature. Six treatments were compared: the presence or absence of local heating combined with different fruit origins (7P, fruit from trusses pruned to seven flowers; 14P, proximal fruits; 14D, distal fruits from trusses pruned to 14 flowers). 7P were less sensitive to heating whereas 14P and 14D showed greater reduction in water and dry matter (DM) content. Distal fruits had the lowest structural DM (sDM), which could be due to a lower fruit cell number. Heating further decreased the sDM, so that fruit sink size was the lowest for distal fruits subjected to heating. Under low competition (7P), heating had a beneficial effect on sugar and lycopene content, whereas acids, β‐carotene and vitamin C content were reduced. Under high competition (14P, 14D), heating increased the ratio sDM–DM. This was mainly due to the reduced content of sugars and acids, but also to the reduced accumulation of secondary metabolites such as vitamin C, β‐carotene and lycopene. This study underlines the interactions between fruit temperature and the fruit–source ratio and the consequences for fruit composition and nutritional quality. Copyright © 2005 Society of Chemical Industry     

Smoking too few cigarettes to be at risk? Smokers' perceptions of risk and risk denial,a French survey

Background

Past studies on smokers'' risk perception have produced mixed results. We endorsed a new approach to assess smokers'' perceptions of risk by asking them to estimate threshold values for the cancer risk associated with daily consumption of tobacco and number of smoking years. We expected that many smokers would endorse a “risk denial” attitude, with threshold estimates higher than their own smoking consumption and duration.

Methodology

A French national telephone survey (n = 3820; 979 current smokers) included several questions about smoking behaviours and related beliefs.

Results

Among current smokers, 44% considered that smoking can cause cancer only for a daily consumption higher than their own consumption, and an additional 20% considered that the cancer risk becomes high only for a smoking duration higher than their own. Most smokers also agreed with other “risk denial” statements (“smoking is not more dangerous than air pollution,” “some people smoke their whole life but never get sick”). Those who considered they smoked too few cigarettes to be at risk were less likely to report personal fear of smoking related cancer.

Conclusion

Risk denial is quite widespread among smokers and does not simply reflect a lack of information about health risks related to tobacco. Fully informing smokers about their risks may necessitate changing the way they process information to produce beliefs and limiting their capacity to generate self exempting beliefs.