Exciton-polariton transmission in quantum dot waveguides and a new transmission path due to thermal relaxation

Exciton-polariton transmission in quantum dot waveguides is investigated with quantum time-evolution equations in Liouville space for exciton wave packet dynamics. The transmission efficiency of the exciton-polariton wave with the longitudinal and transverse mode transformations strongly depends on the geometric parameters (bending angle and interdot distance) of the waveguides and on configuration of an additional branch attached to the waveguide. We have numerically demonstrated that the transmission efficiency significantly improves by controlling these geometric parameters and the configuration of the branched waveguide. The optimal bending angle for efficient transmission with the longitudinal and transverse mode transformations deviates from the right angle owing to more than nearest-neighbor-site interactions through a shortcut. We have also found that existence of thermal relaxation enables to open a new transmission channel along which the exciton-polariton transmission through the Coulomb interaction is suppressed.     

An exact zooming method

This paper presents an efficient and exact formulation for finding stress concentration factors using a zooming analysis. A favorable characteristics of this method is its ability to perform a zooming analysis with computations taking place only in the zooming area under consideration with no need to treat the region outside the zooming area. At the final zooming step, the flexibility of a limited zooming area is determined for all nodes, including the new nodes created in the zooming processes as well as those of the original system before zooming.     

Crystallization and melting of polyethylene under high pressure. II. Effect of pressure on melting behavior of various types of crystals

The effect of pressure on the melting point and volume of fusion of polyethylene was studied by high-pressure dilatometry. Starting materials were crystallized slowly from the melt under pressures of 1500, 3500, 5130 kg/cm², and 1 atm. It has been shown that the unusual behavior observed at pressures above 4000 kg/cm² is due to crystallization and melting of two kinds of extended-chain crystals differing in thermal stability. These are designated as ordinary extended-chain and highly extended-chain crystals, respectively. The relation between pressure P and melting temperature T_m of folded-chain, ordinary extended-chain, and highly extended-chain polyethylene was determined precisely. At pressures up to about 3000 kg/cm², plots of P against T_m for the crystal forms have almost the same curvature and then become parallel. But at pressures above 4000 kg/cm², ordinary extended-chain crystals show a linear increase of T_m with a constant slope of about 70 atm/deg. Curve for the highly extended-chain crystals changes in slope from 70 to 50 atm/deg at pressures between 3500 and 4300 kg/cm², and then show a sharp increase of T_m with increasing pressure. Experiments show that the meltingpoint curve of the highly extended-chain crystals overlaps that of the ordinary extended-chain crystals at pressures below 4000 kg/cm². Annealing experiments with folded-chain and ordinary extended-chain crystals have been made under high pressure. It is suggested that the formation of highly extended-chain crystals occurs stepwise through the formation and reorganization of ordinary extended-chain crystals from the original folded-chain crystals by a mechanism of partial melting and recrystallization at pressures above 4000 kg/cm².     

Metallic Ni nanoparticles confined in hexagonally ordered mesoporous silica material

Single nanometer-sized metallic Ni particles have been successfully deposited inside a hexagonally ordered mesoporous silica material by using a liquid-phase reductive deposition method.     

Practical and convenient synthesis of N-heterocycles: stereoselective cyclization of N-alkenylamides with t-BuOI under neutral conditions

[Structure: see text] tert-Butyl hypoiodite (t-BuOI) was found to be a powerful reagent for the cyclization of N-alkenylamides leading to a variety of N-heterocycles under extremely mild conditions. When N-alkenylsulfonamides were employed in the reaction, three- to six-membered saturated N-heterocycles were obtained in good to excellent yields with complete stereoselectivity. The method was applicable to the cyclization of alkenylbenzamide derivatives to afford N-, O- or N-, S-heterocycles.     

Ionic conduction in As2S3---Ag2S, GeS2---GeS---Ag2S and P2S5---Ag2S glasses

The glass-forming region in the system P---S---Ag was determined and density, thermal expansion, dc conductivity and the transport number of Ag ions were measured for P₂S₅---Ag₂S glasses found in the P---S---Ag system. The results for the transport number measurement show that P₂S₅---Ag₂S glasses are purely ionic conductors owing to the Ag ion migration, like most of the As₂S₃---Ag₂S and GeS₂---GeS---Ag₂S glasses reported previously. Glass structure and ionic conduction processes in As₂S₃---Ag₂S, GeS₂---GeS---Ag₂S and P₂S₅---Ag₂S glasses are discussed, based on their ionic conductivity and density data. The structural concept of -Ag₂S was applied to these glasses, which suggests that the Ag ions in the glasses are distributed in the available Ag ion sites in the non-conducting framework composed of both S anions and As, Ge or P cations. In each system the ionic conductivity increases linearly with increasing Ag⁺/total cation (%) in glass composition, the determining factor being the activation energy for ionic conduction alone. Thus, the activation energy in these glasses depends predominantly upon the molar ratio of Ag ions to total cation in the glass, irrespective of the kind of system. Small differences in the activation energy among the three systems can be interpreted as arising from differences in the field strength of As, Ge and P cations.     

Experimental demonstration of spin geometric phase: radius dependence of time-reversal Aharonov-Casher oscillations

A geometric phase of electron spin is studied in arrays of InAlAs/InGaAs two-dimensional electron gas rings. By increasing the radius of the rings, the time-reversal symmetric Aharonov-Casher oscillations of the electrical resistance are shifted towards weaker spin-orbit interaction regions with their shortened period. We conclude that the shift is due to a modulation of the spin geometric phase, the maximum modulation of which is approximately 1.5 rad. We further show that the Aharonov-Casher oscillations in various radius arrays collapse onto a universal curve if the radius and the strength of Rashba spin-orbit interaction are taken into account. The result is interpreted as the observation of the effective spin-dependent flux through a ring.     

Visible-light-triggered release of nitric oxide from N-pyramidal nitrosamines

Although many organic/inorganic compounds that release nitric oxide (NO) upon photoirradiation (phototriggered caged-NOs) have been reported, their photoabsorption wavelengths mostly lie in the UV region, because X-NO bonds (X=heteroatom and metal) generally have rather strong π-bond character. Thus, it is intrinsically difficult to generate organic compounds that release NO under visible light irradiation. Herein, the structures and properties of N-pyramidal nitrosamine derivatives of 7-azabicyclo[2.2.1]heptanes that release NO under visible light irradiation are described. Bathochromic shifts of the absorptions of these nitrosamines, attributed to HOMO (n)-LUMO (π*) transitions associated with the nonplanar structure of the N-NO moiety, enable the molecules to absorb visible light, which results in N-NO bond cleavage. Thus, these compounds are innate organic caged-NOs that are uncaged by visible light.