Dependence of thermal conductivity on electrical resistivity in Bismuth-Tellurides

The p-type (Bi_0.25Sb_0.75)₂Te₃ doped with 3-12 wt% excess Te alone and n-type Bi₂(Te_0.94Se_0.06)₃ codoped with 0.017-0.026 wt% Te and 0.068-0.102 wt% I were prepared by the Bridgman method, to produce intentionally polycrystalline. Some of the as-grown specimens were annealed, in order to prepare specimens with much different ρ. These polycrystalline specimens have almost the same degree of alignment of the c plane parallel to the freezing direction. The electrical rersistivity ρ and thermal conductivity κ were measured at 298 K along the freezing direction and κ was plotted as a function of ρ. As a result, the lattice components κ_ph obtained by subtracting the electronic component κ_el from the observed κ were found to decrease almost linearly with a decrease of ρ in both p- and n-type specimens, where κ_el was calculated using Wiedemann-Franz law. This tendency is consistent with the conventional result that κ_ph becomes negligible small in metals. The significant decrease in κ_ph with decrease in ρ is considered to be caused predominantly by the phonon scattering due to dopants. The relationship between κ_ph and ρ was first clarified in the intermediate region between the metal and insulator.     

Numerical Verification Methods for Solutions of the Free Boundary Problem

We propose two methods to enclose the solution of an ordinary free boundary problem. The problem is reformulated as a nonlinear boundary value problem on a fixed interval including an unknown parameter. By appropriately setting a functional space that depends on the finite element approximation, the solution is represented as a fixed point of a compact map. Then, by using the finite element projection with constructive error estimates, a Newton-type verification procedure is derived. In addition, numerical examples confirming the effectiveness of current methods are given.     

Fine-tuning of boron complexes with cage-shaped ligand geometry: rational design of triphenolic ligand as a template for structure control

Boron complexes surrounded with organic cages were controlled precisely by a remote atom placed at the bottom of the cage. A replacement of the bottom tether atom (carbon or silicon) changed the characteristics (kinetic and thermodynamic factors) of boron complexes by geometric effects. A theoretical study shows that the bottom atoms also control eigenvalues of MO. This cage complex will provide a systematic template for fine-tuning of metal complexes to create various properties.     

New concept of solute distribution around a diffusive crystal-solution interface of a binary Lennard-Jones mixture from the viewpoint of molecular dynamics

Directional crystallization from a binary mixture was performed by pseudo-NpT ensemble molecular dynamics. The initial crystal phase having a face-centered-cubic (fcc) structure grew toward the whole cell according to the temperature gradient in the universal cell. The growing crystal phase was not planar even though the solute molecules grew in two-dimensional coordinates because the solvent molecules disturbed the crystallization of the solute molecules at the diffusive crystal-solution interface. This represented the essential phenomenon of solute distribution during crystallization. Consequently, the growing crystal phase still contained solvent molecules having a liquid structure. The time change of the solute composition in the early phase of crystal growth showed an increase in solute composition as the time step proceeded. The resulting solute composition in this early phase was considered at different temperature gradients in the universal cell and it increased as the temperature of the initial crystal-solution interface increased. A new distribution coefficient model was proposed as a function of the difference between the local solute composition and bulk solute composition in the solution around the crystal-solution interface. The impurity-solvent distribution coefficient could be represented by the new model for faster growth of the lower temperature's initial interface. As regards a better distribution coefficient, there was found to be a very dilute solution phase over the crystal phase. The new variable "distribution rate" instead of the ambiguous variable "growth rate" was considered as a function of temperature gradient in the universal cell.     

A Bioinspired Synthesis of (±)‐Rubrobramide, (±)‐Flavipucine,and (±)‐Isoflavipucine

A biomimetic synthesis of naturally occurring lactams rubrobramide, flavipucine, and isoflavipucine is described. The key step is a regioselective Darzens reaction between isobutyl glyoxal and an α‐bromo‐β‐ketoamide. The construction of the core tricyclic ring system of rubrobramide was achieved by a cascade reaction in a single step from an α,β‐epoxy‐γ‐lactam. Furthermore, the absolute configuration of naturally occurring (+)‐rubrobramide was determined by vibrational circular dichroism. (±)‐Flavipucine and (±)‐isoflavipucine were synthesized from an epoxyimide, which was prepared by reaction of isobutyl glyoxal with a protected α‐bromo‐β‐ketoamide. Deprotection of the epoxyimide and formation of the pyridone ring gave (±)‐flavipucine, which was converted into (±)‐isoflavipucine by thermal isomerization.     

Synthesis of phenyl furyl sulfides and phenyl furyl ethers by nucleophilic substitution of nitrofurans

Phenyl furyl sulfides ( 3a‐j ) and phenyl furyl ethers ( 3k‐n ), which are useful in synthesizing furocondensed 3‐ring compounds, can be synthesized by nucleophilic substitution of nitrofurans having electron withdrawal groups. In our experiments using 5‐nitrofurans having electron withdrawal groups ( 2a‐i ), nucleophilic substitution readily occurred with the benzenethiolate anion of thiosalicylic acid ( 1a ), the benzenethiolate anion of thiosalicylate ester ( 1b ), and the phenylate anions of salicylate esters ( 1c‐d ) to yield phenyl furyl sulfides ( 3a‐j ) and phenyl furyl ethers ( 3k‐n ).     

Analysis of voice source characteristics using a constrained polynomial representation of voice source signals

To analyze the characteristics of voice source signals from speech, a model is presented in the form of polynomial function by expanding the definition of the Rosenberg model. In combination with the all-pole assumption of the vocal-tract filter, methods are described for the pitch-synchronous speech analysis and temporal search of the glottal opening and closing instants. Because the source and filter models are both linear, the parameter estimation problem can be conveniently solved. In addition, the temporal search method can refine the locations of the glottal events and improve the accuracy of the parameter estimation. Analyses of non-nasalized voiced speech are conducted using an electroglottographic device from which the initial estimate of the temporal information is given.     

Preparation of alpha-elastin nanoparticles by gamma irradiation

Nanoparticles were prepared by utilizing the thermosensitive aggregation of alpha-elastin and gamma ray crosslinking. Three different heating process, “Slow heating”, “Fast heating”, and “Heat shock”, were applied for the aggregation of the alpha-elastin and examined to yield nanoparticles by gamma rays crosslinking. As a result, only “Slow heating” process yielded nanoparticles with diameters of about ca. 300 nm above cloud point (CP) and about ca. 100 nm below CP, and a narrow size distribution above 1.0 mg/ml concentration (exclude 1.0 mg/ml).