Stock Control with Random Opportunities for Replenishment

In most stock control systems, stock is replenished by re-ordering either at regular intervals or upon depletion below an agreed level. Situations sometimes arise, however, in which replenishment tends to be governed by the incidence of external opportunities which occur at irregular intervals, usually as a result of a complex schedule of production or distribution. Conventional stock control procedures can then become difficult to operate effectively; this article discusses an alternative procedure which can be used in such circumstances, and shows how optimum control levels may be calculated.     

Highly efficient infrared-to-visible energy upconversion in Er(3+):Y(2)O(3)

Very intense green and red emission was observed at room temperature from the (4)S(3/2) and (4)F(9/2) levels of Er(3+):Y(2)O(3). A cw diode laser at 975 nm was used as a pump for resonant sequential excitation of the (4)I(11/2) and (4)F(7/2) levels. The fluorescence was easily visible to the naked eye, even with 27 mW of excitation power. It was found that at 850 mW of cw excitation power the total luminance was 39,000 cd/m(2). This corresponds to ~100 muW of green emission and 270 muW of red emission.     

Role of intermolecular coupling in the photophysics of disordered organic semiconductors: aggregate emission in regioregular polythiophene

We address the role of excitonic coupling on the nature of photoexcitations in the conjugated polymer regioregular poly(3-hexylthiophene). By means of temperature-dependent absorption and photoluminescence spectroscopy, we show that optical emission is overwhelmingly dominated by weakly coupled H aggregates. The relative absorbance of the 0-0 and 0-1 vibronic peaks provides a powerfully simple means to extract the magnitude of the intermolecular coupling energy, of approximately 5 and 30 meV for films spun from isodurene and chloroform solutions, respectively.     

Novel synthesis of two-dimensional TiS2 nanocrystallites on Au111

We describe a novel approach to synthesize two-dimensional nanocrystalline TiS2 islands on Au111. Ti is deposited by physical vapor deposition at room temperature on AuS-covered Au111 surfaces. Subsequent annealing to temperatures between 670 K and 800 K leads to the formation of single-layer, triangular TiS2 islands. These TiS2 nanocrystallites reflect the structure of bulk TiS2, and are composed of S-Ti-S stacking units with hexagonally close-packed layers of sulfur atoms and titanium occupying the octahedral sites in between. The lattice constant of the hexagonal unit cell is 3.45 A. A superlattice with a repeat distance of 17.3 A results from the coincidence of five TiS2 units with six Au atoms and is observed in scanning tunneling microscopy and low energy electron diffraction. The triangular shape of the islands indicates a preference for one of the two possible edge terminations. The observation of two island orientations rotated by 60 degrees with respect to each other can be attributed to the formation of twin-related TiS2 domains. The population of the two different island orientations changes during annealing at 800 K indicating a thermodynamic preference for one of the possible stacking sequences.     

Low thresholds for a nonconventional polymer blend—Amplified spontaneous emission and lasing in F81−x:SYx system

A mixture of two polymer materials, poly (9,9‐dioctylfluorene) (F8), and one of the poly(para‐phenylenevinylene) derivatives, superyellow (SY) have been used to make F8_1?x:SY_x polymer blend system. Under a 3–5 ns pulsed‐laser excitation, this system showed excellent optical properties with low threshold values of ≈14 µJ/cm² and ≈8 µJ/cm² for amplified spontaneous emission and optically pumped lasing, respectively. The proposed system was also electroluminescent and an interesting candidate for future research on polymer injection lasers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 15–21     

The copolymer route to new luminescent materials for LEDs

The synthesis of the highly fluorescent mono‐ and bis‐silylated poly(1,4‐phenylene vinylene) derivatives 1 and 2 is reported. The Gilch dehydrohalogenation polycondensation and the Horner synthesis of strictly alternating copolymers have been used to prepare the copolymers 8‐11 and 14, 16‐18 , respectively, in which the tunability of various optoelectonic properties may be examined systematically.     

Properties of low-Dimensional metals at high pressure

Abstract

Low dimensional metals, in which the conduction electrons are confined to stacks or within layers, provide an important area of research into interactions in the electron gas and its coupling to the lattice. The metallic state is commonly unstable at low temperatures, and can be replaced by a wide variety of ground states, including the charge density wave (CDW) state, spin density wave (SDW) state, superconductivity etc. High pressure has always been an important experimental tool in this field, as many of the materials studied have high compressibilities, and it is often possible to switch from one ground state to another under pressure. We consider here the properties under pressure of a series of organo-metallic charge transfer salts in which the metallic behaviour is due to intermolecular delocalisation of the π electron systems of the ligand groups around the transition metal atom.     

Dual-function of alcohols in gold-mediated selective coupling of amines and alcohols

Oxidative coupling of alcohols (methanol and ethanol) and dimethylamine on atomic-oxygen-activated Au(111) occurs entirely on the surface to form the corresponding amides when the alkoxy of the alcohol and the amide derived from the amine are co-adsorbed. For effective oxygen-assisted coupling the formation of the amide requires excess methanol. Mechanistic studies reveal that molecularly adsorbed methanol removes excess adsorbed atomic oxygen efficiently, precluding either secondary oxidation or oxidative dehydrogenation of dimethylamide to the imine. The adsorbed amide then can react with the aldehyde produced by β-hydride elimination from the alkoxy to form the hemiaminal, the reactive intermediate leading to coupling. The selectivity for formamide production can be increased to nearly 100?% in excess methanol.