Correlating the TL response of γ-irradiated natural quartz to aluminum and hydroxyl point defects

This paper investigates the relationship between Al- and OH-related point defects with the thermoluminescent (TL) response of natural quartz sensitized with high doses of γ radiation and heat-treatments. For this, specimens from a single crystal were progressively irradiated with doses of ⁶⁰Co from 2 to 50 kGy. After each step of sensitization, the absorption bands related to [AlO₄]⁰, [AlO₄/H]⁰, [H₄O₄]⁰ and Li-dependent OH point defects were measured by optical absorption and infrared (IR) spectroscopy. The sensitization of the 280 °C TL peak increased up to 15 kGy and then its intensity remained constant. The absorption intensity at 470 nm increased with γ doses suggesting a progressive creation of [AlO₄]⁰ acting as recombination centers for the sensitized peak. At the same time, the TL intensity of the 90 °C peak decreased with the accumulated dose. This effect was not related to the saturation in the number of recombination centers because both [H₄O₄]⁰ and [AlO₄]⁰ bands were increasing after 50 kGy. Compared to the as-received condition, it was found that IR bands associated with [AlO₄/H]⁰ and Li-dependent OH decreased with the effect of heat-treatments. The precursor for [AlO₄]⁰ is [AlO₄/Li]⁰ and the Li species dislodged from [AlO₄/Li]⁰ and Li-dependent OH centers play an important role in the sensitization process.     

Picosecond resonant two-photon ionization of cold sodium clusters

Large sodium clusters, up ton=21, generated by a low-temperature modification of the laser ablation gas jet source were ionized with two photons of visible radiation from an amplified picosecond dye-laser system.     

Protein fluorescence measurements within electrospray droplets

The conformation of cytochrome c molecules within electrospray droplets is investigated by monitoring the laser induced fluorescence of its single tryptophan residue (Trp-59). By increasing the alcohol concentration of the electrosprayed solutions, protein denaturation is induced, giving rise to significant changes in the intensity of the detected fluorescence. Comparison with analogous denaturation experiments in solution provides information about the relative protein conformations and differences between the bulk-solution and droplet environments. Both electrospray-plume and bulk-solution fluorescence measurements using low methanol concentration solutions indicate the presence of folded protein structures. At high methanol content, fluorescence measurements are consistent with the presence of partly denatured or unfolded conformations. At intermediate methanol content, differences are observed between the extent of denaturation in solution and that within the droplets, suggesting electrosprayed proteins have more compact structures than those detected in bulk measurements using solutions of similar composition. This infers that some fraction of the proteins within the droplets have refolded relative to their bulk-solution conformation. Protein denaturation experiments using the low vapor pressure solvent 1-propanol indicate that differences between the droplet and solution measurements are not due to solvent evaporation effects. It is suggested that different droplet conformations are more likely the result of protein diffusion to the droplet surface and effects of the droplet/air interface. To our knowledge, these are the first reported measurements of protein fluorescence within electrospray droplets.     

Control of the orbital delocalization and implications for molecular rectification in the radical anions of porphyrins with coplanar 90 degrees and 180 degrees beta,beta'-fused extensions

Through-porphyrin electronic communication is investigated using "linear-type" and "corner-type" bis(quinoxalino)porphyrins in free-base form and their ZnII, CuII, NiII, and PdII derivatives. These compounds are porphyrins with quinoxalines fused on opposite or adjacent beta,beta'-pyrrolic positions; they were synthesized from 5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)-porphyrin-2,3,12,13- and -2,3,7,8-tetraone, respectively, by reaction with 1,2-phenylenediamine. The degree of electron spin delocalization into the fused rings in the pi-radical anions of the free-base and metal(II) bisquinoxalinoporphyrins was elucidated by electrochemistry, UV-vis absorption, and electron spin resonance (ESR) spectra of the singly reduced species and density functional theory calculations. Hyperfine splitting patterns in the ESR spectra of the pi-radical anions show that symmetric molecules have delocalized electron spin, indicating that significant inter-quinoxaline interactions are mediated through the central porphyrin unit, these interactions being sufficient to guarantee through-molecule conduction. However, when molecular symmetry is broken by tautomeric exchange of the inner nitrogen hydrogens in the free-base porphyrin with a corner-type quinoxaline substitution pattern, the pi-radical anion becomes confined so that one quinoxaline group is omitted from spin delocalization. This indicates the appearance of a unidirectional barrier to through-molecule conduction, suggesting a new motif for chemically controlled rectification.     

Thermo‐hydrodynamic‐mechanical multiphase flow model for CO2 sequestration in fracturing porous media

In this paper, we introduce a fully coupled thermo‐hydrodynamic‐mechanical computational model for multiphase flow in a deformable porous solid, exhibiting crack propagation due to fluid dynamics, with focus on CO₂ geosequestration. The geometry is described by a matrix domain, a fracture domain, and a matrix‐fracture domain. The fluid flow in the matrix domain is governed by Darcy's law and that in the crack is governed by the Navier–Stokes equations. At the matrix‐fracture domain, the fluid flow is governed by a leakage term derived from Darcy's law. Upon crack propagation, the conservation of mass and energy of the crack fluid is constrained by the isentropic process. We utilize the representative elementary volume‐averaging theory to formulate the mathematical model of the porous matrix, and the drift flux model to formulate the fluid dynamics in the fracture. The numerical solution is conducted using a mixed finite element discretization scheme. The standard Galerkin finite element method is utilized to discretize the diffusive dominant field equations, and the extended finite element method is utilized to discretize the crack propagation, and the fluid leakage at the boundaries between layers of different physical properties. A numerical example is given to demonstrate the computational capability of the model. It shows that the model, despite the relatively large number of degrees of freedom of different physical nature per node, is computationally efficient, and geometry and effectively mesh independent. Copyright © 2017 John Wiley & Sons, Ltd.     

Synthesis of new vinyl ether functionalized silica for UV-patterning

We report a new ORganically MOdified SILicates (ORMOSILs) stable sol based on vinyl ether function which can be deposited as a layer and structured by mean of UV radiation through a mask or by direct laser writing. Silica matrix is synthesized by sol–gel process and organic network is formed by photopolymerization. One of the potential applications is the fabrication of integrated optical circuits. [2-(3,4 epoxycyclohexyl ethyltrimethoxysilane)] has already used for the fabrication of such devices and to develop microstructures on an organic substrate by cationic polymerization. Obtained results show some weakness such as an important contribution of OH and aliphatic CH groups to the attenuation at 1550 nm wavelength and low conversion rate of organic polymerization involving poor mechanical properties. This work treats on the design of a new generation of hybrid materials with a very high reactivity and low amount of groups involved in the attenuation. We have chosen vinyl ether function as reactive organic part for her highest polymerization rate via cationic way. The new synthesized molecule is 4-vinylether phenyltriethoxysilane. Sol–gel kinetic reactions were monitored by liquid ²⁹Si-NMR spectroscopy. In order to obtain the highest reactive multifunctional oligomers and the lowest OH groups, hydrolysis and polycondensation reactions were followed as a function of time, temperature and pH of the water involved in the hydrolysis conditions. Finally, we show the feasibility to microstructure films deposited with this sol.     

Prototropic rearrangements of unsaturated hydrocarbons promoted by iron carbonyls

Results from the thermal and photochemical reactions of $\text{cis}$-1,3-pentadiene and 4-methyl-1,3-pentadiene with iron pentacarbonyl are described together with those obtained from the thermolysis and photolysis of their η²-iron tetracarbonyl and η⁴-iron tricarbonyl complexes. Consideration of these results, and some recent related work of others, allows a new reaction path to be formulated for alkene and diene isomerizations promoted by iron carbonyls.