Spectroscopic evidence for pi-pi interaction between poly(diallyl dimethylammonium) chloride and multiwalled carbon nanotubes

The interaction between multiwalled carbon nanotubes (MWCNTs) and aqueous poly(diallyl dimethylammonium) chloride (PDDA) was studied by X-ray photoelectron (XPS) and photoacoustic Fourier transform infrared (PA-FTIR) spectroscopies. We have found that the mild sonication of MWCNTs in aqueous PDDA results in a significant improvement of CNT dispersibility and greatly enhances their adhesion to Au and Si substrates. The MWCNT-PDDA interaction is due to the presence of an unsaturated contaminant in the PDDA chain, as confirmed by both XPS and PA-FTIR, which enters into a pi-pi interaction with the CNTs. Electrostatic group repulsions of the coated CNTs then provide the dispersibility and adhesion.     

Composition,Enthalpy, and Vaporization Temperature Calculation of Ag‐SiO<Subscript>2</Subscript> Plasmas with Air in the Temperature Range from 1000 to 6000 K and for Pressure Included between 1 and 50 bars

With the Gibbs free energy minimization method, the molar fraction of chemical species are determined in temperature range included between 1000 and 6000 K for several proportions of air, silver and silica and for pressures included between 1 and 50 bars. The enthalpy and the vaporization temperature of liquid silver and liquid silica are studied. The key role of pressure on composition, enthalpy and the vaporization temperature is shown. The electrical neutrality is study, and the importance of ionized gaseous silver at low temperature is shown even for low amount of silver. The increase of electronegative ions (Ag^– and O^–) with pressure is shown. The vapor pressures fitting coefficients of Ag and SiO₂ are given.     

57 Fe Mössbauer spectroscopy studies of chondritic meteorites from the Atacama Desert, Chile: Implications for weathering processes

Some terrestrial areas have climatic and geomorphologic features that favor the preservation, and therefore, accumulation of meteorites. The Atacama Desert in Chile is among the most important of such areas, known as dense collection areas. This desert is the driest on Earth, one of the most arid, uninhabitable locals with semi-arid, arid and hyper-arid conditions. The meteorites studied here were collected from within the dense collection area of San Juan at the Central Depression and Coastal Range of Atacama Desert. ⁵⁷Fe Mössbauer spectroscopy was used for quantitative analysis of the degree of weathering of the meteorites, through the determination of the proportions of the various Fe-bearing phases and in particular the amount of oxidized iron in the terrestrial alteration products. The abundance of ferric ions in weathered chondrites can be related to specific precursor compositions and to the level of terrestrial weathering. The aim of the study was the identification, quantification and differentiation of the weathering products in the ordinary chondrites found in the San Juan area of Atacama Desert.     

Transport Coefficients of Ag–SiO<Subscript>2</Subscript> Plasmas

Calculated values of viscosity, thermal and electrical conductivities of plasma formed in mixtures of silver (Ag) and silica (SiO₂) are presented. The calculations, which assume local thermodynamic equilibrium, are performed for three pressures (1, 10 and 30 atm) in the temperature range from 4,000 to 30,000 K. All the data for the potential interactions and the necessary formulations to obtain values of transport coefficients are given in details. For atmospheric pressure, five mixtures (100% Ag, 75% Ag and 25% SiO₂, 50% Ag and 50% SiO₂, 25% Ag and 75% SiO₂, 100% SiO₂) in weight percentage are studied. In order to analyse the pressure influence on the transport coefficients, three samples of Ag–SiO₂ mixtures (100% Ag, 50% Ag and 50% SiO₂, 100% SiO₂) in weight percentage are discussed for pressures of 1, 10 and 30 atm. In addition for the test case of oxygen plasma, we compare the computation code results with values obtained by other authors: discrepancies are found and explained.      

Riboflavin photodegradation and photosensitizing effects are highly dependent on oxygen and ascorbate concentrations

Riboflavin (RF) is a normal component of the eye lens which triggers a strong photosensitizing activity when exposed to light. Upon irradiation with short wavelength radiations below 400 nm, RF-photosensitized damage may occur. However, vitamin C is present at high concentrations in the normal lens and plays an important role in inhibiting these photosensitization processes. An in vitro simple model was used with the objective of understanding better the relationships between vitamin C and oxygen concentrations on the mechanisms of RF-mediated photodegradation of tryptophan (Trp), a target particularly sensitive to photo-oxidation. Under nitrogen, the RF decomposition reached its maximal value, and vitamin C and Trp photo-oxidation was negligible. When increasing oxygen pressure, RF photodegradation dropped and vitamin C photo-oxidation strongly increased and was maximal at 100% O2. RF-induced photodegradation of Trp first increased with oxygen concentration, up to 40 microM O2, and then decreased. RF and Trp degradation were significantly protected by vitamin C so that no more than 20% of the substrates concentration were oxidized in the presence of vitamin C higher than 0.8 mM. From our results we conclude that in the specific conditions of the normal lens, the high vitamin C concentration (2 mM) is compatible with the UVA radiation hazard, despite the presence of RF. However, if lenticular vitamin C decreases below 0.8 mM, photodegradation of RF may occur and Trp may therefore be photo-oxidized by a Type-I mechanism.     

Implication of ultraviolet light in the etiology of uveal melanoma: A review

Uveal melanoma is the most frequent intraocular cancer and the second most common form of melanoma. It metastasizes in half of the patients and the prognostic is poor. Although ultraviolet (UV) radiation is a proven risk factor for skin melanoma, the role of UV light in the etiology of uveal melanoma is still contradictory. We have compared epidemiological and genetic evidences of the potential role of UV radiation in uveal melanoma with data on cutaneous melanoma. Even though frequently mutated genes in skin melanoma (e.g. BRAF) differ from those found in uveal melanoma (i.e. GNAQ, GNA11), their mutation pattern bears strong similarities. Furthermore, we provide new results showing that RAC1, a gene recently found harboring UV‐hallmark mutation in skin melanoma, is also mutated in uveal melanoma. This article aims to review the work done in the last decades to understand the etiology of uveal melanoma and discuss new avenues, which shed some light on the potential role of UV exposure in uveal melanoma.     

Numerical Simulation of Darcy and Forchheimer Force Distribution in a HBC Fuse

We present the breaking of a short-circuit current in a HBC fuse simulation based on an isentropic non-stationary model in a porous medium for a one dimensional geometry. The fluid flow is affected by the nature of the gas and by the morphology of the silica sand. To model the gas–silica sand interaction, we introduce two classical laws: the Darcy's law due to the viscous interaction and the Forchheimer's law due to the inertial force. Numerical simulations with realistic physical parameters have been performed using a finite volume scheme with a fractional step technique. We show the evolution of Darcy and Forchheimer forces during time and according to the position in the fuse. We place in prominent position the fact that either force is predominant in the fuse according to the time and the position which justifies a numerical treatment to cover all the situations.     

Pyrimidine (6-4) pyrimidone photoproduct mapping after sublethal UVC doses: nucleotide resolution using terminal transferase-dependent PCR

UVC irradiation of genomic DNA induces two main types of potentially mutagenic base modifications: cyclobutane pyrimidine dimers (CPDs) and the less frequent (15-30% of CPD levels) pyrimidine (6-4) pyrimidone photoproducts (6-4PP). Ligation-mediated PCR (LMPCR), a genomic sequencing technique, allows CPD mapping at nucleotide resolution following irradiation with sublethal doses of UVB or UVC for most cell types. In contrast, a dose of 80 J/m(2) of UVC that is lethal for the majority of cell types is necessary to map 6-4PP by the LMPCR technique. This compromises the use of LMPCR to study the repair of 6-4PP. To date, no other techniques have been developed to study 6-4PP repair at nucleotide resolution. We have therefore adapted a recently developed technique for the mapping of 6-4PP: terminal transferase-dependent PCR (TDPCR). TDPCR is in many ways similar to LMPCR. This technique is more sensitive and allows the mapping of 6-4PP at UVC doses as low as 10 J/m(2) in genomic DNA and in living cells.     

Toxic Interaction Between Solar Radiation and Cigarette Smoke on Primary Human Keratinocytes

Solar radiation and cigarette smoke are two environmental risk factors known to affect skin integrity. Although the toxic effects of these factors on skin have been widely studied separately, few studies have focused on their interaction. The objective of this study was to evaluate and understand the synergistic harmful effects of cigarette smoke and solar rays on human primary keratinocytes. The keratinocytes were exposed to cigarette smoke extract (CSE) and then irradiated with a solar simulator light (SSL). The viability, as determined by measuring metabolic activity of skin cells, and the levels of global reactive oxygen species (ROS) were evaluated after exposure to CSE and SSL. The combination of 3% CSE with 29 kJ m⁻² UVA caused a decrease of 81% in cell viability, while with 10% to 20% CSE, the cell viability was null. This phototoxicity was accompanied by an increase in singlet oxygen but a decrease in type I ROS when CSE and SSL were combined in vitro. Surprisingly, an increase in the CSE's total antioxidant capacity was also observed. These results suggest a synergy between the two environmental factors in their effect on skin cells, and more precisely a phototoxicity causing a drastic decrease in cell viability.