Sol‐to‐Gel Transition in Fast Evaporating Systems Observed by in Situ Time‐Resolved Infrared Spectroscopy

The in situ observation of a sol‐to‐gel transition in fast evaporating systems is a challenging task and the lack of a suitable experimental design, which includes the chemistry and the analytical method, has limited the observations. We synthesise an acidic sol, employing only tetraethylorthosilicate, SiCl₄ as catalyst and deuterated water; the absence of water added to the sol allows us to follow the absorption from the external environment and the evaporation of deuterated water. The time‐resolved data, obtained by attenuated total reflection infrared spectroscopy on an evaporating droplet, enables us to identify four different stages during evaporation. They are linked to specific hydrolysis and condensation rates that affect the uptake of water from external environment. The second stage is characterized by a decrease in hydroxyl content, a fast rise of condensation rate and an almost stationary absorption of water. This stage has been associated with the sol‐to‐gel transition.     

Effect of Acid Treatment of Montmorillonite on “Support‐Activator” Performance to Support Metallocene for Propylene Polymerization Catalyst

This work is focused on montmorillonite (MMT)‐based “support‐activators” (S‐As) for the metallocene‐catalyzed propylene polymerization. This catalyst was previously industrialized; however, for further technological advances, the activation mechanism is investigated. The chemical and morphological requirements of the S‐A are surveyed using both commercially available raw clay minerals (non‐acid‐treated) and acid‐treated clay minerals. The S‐A possessing strong‐acid sites (pK a < ?8.2) gives a highly active catalyst. Acid treatment of MMT induces morphological changes as well as the formation of strong acid sites. Based on pore size distribution analysis and atomic force microscopy observations, it is concluded that the strong acid sites are located in the small pores around the edge of the clay mineral (not in the interlayer), where the structure is disordered by the acid treatment.

     

Rapid one-step synthesis, characterization and functionalization of silica coated gold nanoparticles

This paper describes a rapid, simple and one-step method for preparing silica coated gold (Au@SiO₂) nanoparticles with fine tunable silica shell thickness and surface functionalization of the prepared particles with different groups. Monodispersed Au nanoparticles with a mean particle size of 16 nm were prepared by citrate reduction method. Silica coating was carried out by mixing the as prepared Au solution, tetraethoxysilane (TEOS) and ammonia followed by microwave (MW) irradiation. Although there are several ways of coating Au nanoparticles with silica in the literature, each of these needs pre-coating step as well as long reaction duration. The present method is especially useful for giving the opportunity to cover the colloidal Au particles with uniform silica shell within very short time and forgoes the use of a silane coupling agent or pre-coating step before silica coating. Au@SiO₂ nanoparticles with wide range of silica shell thickness (5-105 nm) were prepared within 5 min of MW irradiation by changing the concentration of TEOS only. The size uniformity and monodispersity were found to be better compared to the particles prepared by conventional methods, which were confirmed by dynamic light scattering and transmission electron microscopic techniques. The prepared Au@SiO₂ nanoparticles were further functionalized with amino, carboxylate, alkyl groups to facilitate the rapid translation of the nanoparticles to a wide range of end applications. The functional groups were identified by XPS, and zeta potential measurements.     

A novel small molecule fluorescent sensor for Zn2+ based on pyridine-pyridone scaffold

The development of a water-soluble and small molecular weight fluorescent probe, 3-(4-methoxyphenyl)-4-(methylsulfanyl)-6-(pyridin-2-yl)pyridin-2(1H)-one (3), for detecting Zn²⁺ based on pyridine-pyridone skeleton is reported. We observed a clear chelation enhanced fluorescence effect of 3 in the presence of Zn²⁺. Other fluorescent properties of 3 are discussed.     

Light-induced conformational change and product release in DNA repair by (6-4) photolyase

Proteins of the cryptochrome/photolyase family share high sequence similarities, common folds, and the flavin adenine dinucleotide (FAD) cofactor, but exhibit diverse physiological functions. Mammalian cryptochromes are essential regulatory components of the 24 h circadian clock, whereas (6-4) photolyases recognize and repair UV-induced DNA damage by using light energy absorbed by FAD. Despite increasing knowledge about physiological functions from genetic analyses, the molecular mechanisms and conformational dynamics involved in clock signaling and DNA repair remain poorly understood. The (6-4) photolyase, which has strikingly high similarity to human clock cryptochromes, is a prototypic biological system to study conformational dynamics of cryptochrome/photolyase family proteins. The entire light-dependent DNA repair process for (6-4) photolyase can be reproduced in a simple in vitro system. To decipher pivotal reactions of the common FAD cofactor, we accomplished time-resolved measurements of radical formation, diffusion, and protein conformational changes during light-dependent repair by full-length (6-4) photolyase on DNA carrying a single UV-induced damage. The (6-4) photolyase by itself showed significant volume changes after blue-light activation, indicating protein conformational changes distant from the flavin cofactor. A drastic diffusion change was observed only in the presence of both (6-4) photolyase and damaged DNA, and not for (6-4) photolyase alone or with undamaged DNA. Thus, we propose that this diffusion change reflects the rapid (50 μs time constant) dissociation of the protein from the repaired DNA product. Conformational changes with such fast turnover would likely enable DNA repair photolyases to access the entire genome in cells.     

Measuring acetic acid dimer modes by ultrafast time-domain Raman spectroscopy

Acetic acid is capable of forming strong multiple hydrogen bonds and therefore different dimeric H-bonded structures in neat liquid phase and in solutions. The low frequency Raman spectra of acetic acid (neat, in aqueous solution and as a function of temperature) were obtained by ultrafast time and polarization resolved optical Kerr effect (OKE) measurements. Isotropic OKE measurements clearly reveal a specific totally symmetric mode related to the dimeric structure H-bond stretching mode. The effects of isotope substitution, water dilution and temperature on this mode were investigated. These results together with anisotropic OKE measurements and density functional theory calculations for a number of possible dimers provide strong evidence for the cyclic dimer structure being the main structure in liquid phase persisting down to acetic acid concentrations of 10 M. Some information about the dimer structure and concentration dependence was inferred.     

A new wall-damping function for large eddy simulation employing Kolmogorov velocity scale

A new wall-damping function, based on the Kolmogorov velocity scale, for large eddy simulation (LES) is proposed, which accounts for the near-wall effect. To calculate the Kolmogorov velocity scale, u_ε, the dissipation rate of turbulent energy, ε, is needed. In LES, however, the dissipation rate is generally not solved, unlike in the Reynolds averaged Navier-Stokes (RANS) simulations, e.g., k-ε models. Although, in some previous studies, the dissipation rate of the subgrid-scale (SGS) turbulent energy, ε_SGS, is used instead of ε in calculating the Kolmogorov velocity scale, the scale obtained using such a method overly depends on the grid resolution employed and is generally inappropriate. Accordingly, the wall-damping function using the incorrect velocity scale also depends on the grid resolution and gives an inadequate wall effect. This is because ε_SGS contains only the components in the scale smaller than the grid-filter width, which obviously varies with the grid resolution employed. In this study, to overcome this problem, we propose a method for estimating the Kolmogorov velocity scale with a technique of conversion in LES, and the estimated one is utilized in the wall-damping function. The revised wall-damping function for LES is tested in channel flows and a backward-facing step flow. The results show that it yields a proper near-wall effect in all test cases which cover a wide range of grid resolution and Reynolds numbers. It is also shown that all three kinds of SGS models incorporating the present wall-damping function provide good predictions, and it is effective both in one-equation and 0-equation SGS models. These results suggest that the use of the proposed wall-damping function is a refined and versatile near-wall treatment in LES with various kinds of SGS models.     

Real Time and Full-range Complex Fourier Domain Optical Coherence Tomography

High speed complex full-range Fourier domain optical coherence tomography (FD-OCT) is demonstrated. This FD-OCT requires only a single A-scan for each single transversal position for full-range Fourier domain optical coherence tomography. The Fourier transform method is applied along the direction of the B-scan to reconstruct complex spectra, and the complex spectra compose a full-range OCT image.     

Computer-Generated Holograms Based on the Three-Dimensional Fourier Spectrum

A method to synthesize a computer-generated hologram (CGH) of real-existing objects from projection images is proposed. Different from other similar methods, our method enables the synthesis of a CGH with only one-dimensional (1-D) mechanical scanning of the objects. Our method is connected with the three-dimensional (3-D) Fourier spectrum of the objects by the 3-D central slice theorem (CST). Two efficient recording techniques for projection images and numerical experiments to verify our principle is discussed. A comparison between the two techniques is also presented from the viewpoint of diffraction efficiency. © 2005 The Optical Society of Japan     

Effect of the final-state interaction on the initial core–hole lifetime: the case of the 4s-hole lifetime of Sn metal

The first theoretical study of the effect of the final-state interaction on the initial core–hole lifetime is presented. The 4s-hole lifetime width of Sn metal is calculated by an ab-initio atomic many-body theory (Green’s function method). When the final-state interaction in the 4p4d two-hole state, created by the 4s⁻¹−4p⁻¹4d⁻¹ f super Coster–Kronig (CK) transition of the initial 4s hole, is explicitly taken into account, the ab-initio atomic many-body calculation of the 4s-hole X-ray photoelectron spectroscopy (XPS) spectrum of Sn atom can provide excellent agreement with experiment in both the 4s-hole energy and the 4s-hole lifetime width. Otherwise, the many-body calculation underestimates considerably the 4s-hole lifetime width. The 4p4d two-hole state interacts strongly with the 4d triple-hole state by the 4p⁻¹4d⁻¹−4d⁻³ f super CK transition. The interaction affects greatly the initial 4s-hole lifetime width.