Finite Difference Time Domain Analysis of Diffusion Equations with Nonuniform Grids for Time-Resolved Reflectance of an Optical Pulse in Three-Dimensional Scattering Medium

An integral form of diffusion equations and their finite difference time domain (FDTD) analysis have been formulated. The analysis is extended to FDTD analysis with nonuniform grids in three-dimensional (3-D) scattering medium. It has been confirmed that 600 time steps in calculation sequences of the time-resolved reflectance for 3-D medium 80 × 80 × 30 mm³ in volume is completed within 4 seconds by utilizing 2³ and 4³ mm³ nonuniform cubic grids, when a conventional personal computer with 3 GHz CPU clock is used. The conditions for keeping numerical accuracies comparable to those in 2³ mm³ uniform grids are made clear. The proposed analysis greatly reduces time to run and memory space in 3-D scattering medium numerical analysis.     

Analyses of Cross Sections and Analyzing Powers in Low-Energy 2H(\vec d, n) 3He Reactions Based on the Invariant-Amplitude and Faddeev-Yakubovsky Methods

Cross sections as well as vector and tensor analyzing powers for the ²H() ³He reactions at energies around 30 keV are analyzed by the invariant-amplitude method. In addition, microscopic four-body calculations along the Faddeev-Yakubovsky method are reported, with limitations only on the interactions and intermediate states of the three-nucleon subsystem. The suppression of the cross section due to simultaneous polarizations of the projectile and the target is discussed comparing the results from both of these methods as well as from earlier works. Received July 1, 1996; revised January 27, 1997; accepted for publication January 28, 1997     

Electrochemical cyclization/cycloreversion reactions of diarylethenes

[reaction: see text]. Electrochemical oxidation of diarylethene derivatives induced cyclization or cycloreversion reactions. The reaction mechanism was studied with CV, absorption spectra, and theoretical calculation.     

Structure and Reactivity of an Asymmetric Synthetic Mimic of Nitrogenase Cofactor

The Mo nitrogenase catalyzes the ambient reduction of N₂ to NH₃ at its M‐cluster site. A complex metallocofactor with a core composition of [MoFe₇S₉C], the M‐cluster, can be extracted from the protein scaffold and used to facilitate the catalytic reduction of CN^?, CO, and CO₂ into hydrocarbons in the isolated state. Herein, we report the synthesis, structure, and reactivity of an asymmetric M‐cluster analogue with a core composition of [MoFe₅S₉]. This analogue, referred to as the Mo‐cluster, is the first synthetic example of an M‐cluster mimic with Fe and Mo positioned at opposite ends of the cluster. Moreover, the ability of the Mo‐cluster to reduce C₁ substrates to hydrocarbons suggests the feasibility of developing nitrogenase‐based biomimetic approaches to recycle C₁ waste into fuel products.     

Polymerization reactivity of unsaturated end group generated during the disproportionation in termination reaction of methyl methacrylate polymerization: A study using model compounds

Polymerizations of some vinyl monomers were carried out with 2,2′-azobisisobutyronitrile at 60°C in the presence of a methyl methacrylate (MMA) dimer ( I ) or a MMA polymer ( II ) with a double bond at their ends to confirm the polymerization reactivity of unsaturated end group generated during the disproportionation in termination reaction of MMA polymerization. It was found that the polymerizations of α-monosubstituted monomers have been much retarded than those of α,α-disubstituted monomers by the addition of I . Kinetic study on MMA and methyl acrylate polymerizations showed that the rate constant for the reaction of a propagating radical with I was 5.4 and 29.2 L/mol s in their polymerizations, respectively. ESR study using I and II suggested that an addition reaction was a predominant mechanism for the reaction of an unsaturated end group with a radical rather than a hydrogen abstraction.