Structural Analysis of the Layered Compounds Cu x TiS2

Abstract

A structural analysis of single crystals of the layered compounds Cu _x TiS₂ (x=0. 0.21 and 0.38), which were prepared by the iodine transport and the electrochemical methods, has been performed by X-ray diffraction. The displacement parameters of Ti and S atoms along the c axis are larger than those along the a axis. It is understood that the intra-layer bonding between Ti-Ti and S-S atoms is stronger than the inter-layer bonding between Ti-and S-layers. Both distances between Ti-and S-layers and between Cu-and S-layers are enlarged without changing the structure of the mother phase after intercalating Cu atoms.     

Bifurcations of steady states for the Eguchi–Oki–Matsumura model of phase separation

This article is concerned with bifurcations of steady states for a model system of phase separation, which is introduced by Eguchi–Oki–Matsumura (EOM). The system consists of coupled two evolution equations and admits steady state solutions with different energies. The bifurcation phenomena of these steady states with respect to the principal parameter, which is related to the temperature, are analyzed.     

Parity-odd asymmetries in W-jet events at the fermilab tevatron

Parity-odd asymmetries in the decay angular distribution of a W boson produced with a hard jet in pp[over ] collisions arise only from QCD rescattering effects. If observed, these asymmetries will provide a first demonstration that perturbative QCD calculation is valid for the absorptive part of scattering amplitudes. We propose a simple observable to measure these asymmetries and perform realistic Monte Carlo simulations at energies reached at the Fermilab Tevatron. It is shown that the Tevatron run II should provide sufficient statistics to test the prediction.     

The effect of morphology on sorption and transport of carbon dioxide in a polyimide from 3,3′,4,4′-biphenyltetracarboxylic dianhydride and 4,4′-oxydianiline

Sorption and transport of CO₂ have been investigated for polyimide films prepared from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 4,4′-oxydianilline (ODA) as well as for a chemically identical commercial polyimide film, Upilex-R. The BPDA-ODA polyimide films annealed above the glass transition temperature (270°C) are found to have some degree of ordering owing to molecular aggregation of polymer chains, whereas the films as-cast are amorphous. The solubility, permeability, and diffusion coefficients decrease significantly with increasing density or increasing average degree of molecular aggregation. The influence of morphology on the parameters in the dual-mode sorption and transport model has also been investigated. With an increase in density, the Langmuir capacity constant and the diffusion coefficients for Henry's law and Langmuir populations decrease by a larger factor than the Henry's law solubility constant. These results can be tentatively interpreted by assuming either a one-phase or two-phase structure for these polyimide films.     

High-temperature phases of poly(p-xylylene)

The crystal structure of poly(p-xylylene), as polymerized, is the α form. This transforms irreversibly to the β from by annealing or drawing. To clarify the mechanism of this transition, structural changes of the α and β crystals were examined with a high-temperature stage in the electron microscope. Two high-temperature phases, β₁ and β₂, were found and their structures were analyzed. In these structures lattice distortions due to rotational and translational motions of chains are in troduced, especially in the β₂ form. The α → β transition is induced through such a disordered phase. The statistical arrangement of a molecule in the β-form unit cell results from freezing the disorder in the high-temperature phases.     

Rational principles for modulating fluorescence properties of fluorescein

Rational design strategies based on practical fluorescence modulation mechanisms would enable us to rapidly develop novel fluorescence probes for target molecules. Here, we present a practical and general principle for modulating the fluorescence properties of fluorescein. We hypothesized that (a) the fluorescein molecule can be divided into two moieties, i.e., the xanthene moiety as a fluorophore and the benzene moiety as a fluorescence-controlling moiety, even though there is no obvious linker structure between them, and (b) the fluorescence properties can be modulated via a photoinduced electron transfer (PeT) process from the excited fluorophore to a reducible benzene moiety (donor-excited PeT; d-PeT). To evaluate the relationship between the reduction potential of the benzene moiety and the fluorescence properties, we designed and synthesized various derivatives in which the reduction potential of the benzene moiety was fine tuned by introducing electron-withdrawing groups onto the benzene moiety. Our results clearly show that the fluorescence properties of fluorescein derivatives were indeed finely modulated depending upon the reduction potential of the benzene moiety. This information provides a basis for a practical strategy for rational design of novel functional fluorescence probes.     

Thiol-catalyzed acyl radical cyclization of alkenals

Thiol-catalyzed direct generation of acyl radicals and their intramolecular addition to olefins of alkenals gave 2-substituted five- and six-membered cyclic ketones in reasonably good yields. The combination of odorless tert-dodecanthiol and AIBN or V-40 was the initiator of choice among surveyed radical generators for the cyclization of alkenals. Aldehydes having electron-deficient olefins cyclized more easily than those having unactivated olefins.     

The promoter effect of lanthana on MgO supported ruthenium catalysts for ammonia synthesis

When activated at high temperature (873 K) doped lanthana such as La₂O₃, Ce₂O₃, Sm₂O₃ derived from nitrate showed remarkable effect on the MgO-supported ruthenium activity for ammonia synthesis. The activity treated with hydrogen at 873 K became 5 times as active as that treated at 623 K. The activity levels were almost the same as those of the Ru-lanthana (support) system under the same activation condition. It was thought that the lanthana was partly reduced and a strong metal support interaction occurred. The partially reduced lanthana was thought to donate electrons to the contacting Ru atoms forming the active centers. The other characters such as the stability were also discussed by comparing with alkali promoters.     

Portable system for near-real time measurement of gaseous formaldehyde by means of parallel scrubber stopped-flow absorptiometry

Formaldehyde, HCHO, is one of the important causal agents of sick-building syndrome. It is also an important product of ambient air photochemistry. We report here a portable instrument capable of a 0.08 ppbv limit of detection (LOD) and a time resolution of 5 min that is useful for both indoor and ambient air applications. The detection is based on efficient gas collection and chromogenic reaction with 3-methyl-2-benzothiazolone hydrazone (MBTH) through a pair of alternately sampling small-bore porous-membrane tube diffusion scrubbers (DS). The chemistry is well established, requires no special reagent preparation or elevated reaction temperatures and permits the use of inexpensive light emitting diode (LED)-based detectors without need for long path cells. Stopped flow alternate sampling allows an HCHO collection performance, an order of magnitude better than any previous system with high throughput and high sensitivity. Results for indoor and ambient air analyses are presented.