Wave-vector dependence of electron-optical phonon coupling in GaAs

Induced non equilibrium distribution of optical phonons allows direct measurement of electron-phonon coupling as a function of phonon wave-vector K. Results indicate that near K=0(K<20, 000 cm^?1 coupling between TO phonons and electrons is independent of K whereas LO phonons show a K^-2 dependence. Results also suggest that electron relaxation in the conduction band by multiple phonon production is quite significant.     

1H and 13C NMR spectra of 3,8-dimethoxyfuro[3,2-g]coumarin and maculine from Esenbeckia grandiflora Martius (Rutaceae)

One- and two-dimensional NMR experiments were used for the unambiguous assignment of the (1)H and (13)C NMR chemical shifts of the furoquinoline alkaloid maculine (1) and the new furanocoumarin 3,8-dimethoxyfuro[3,2-g]coumarin (2).     

Efficient heuristics for the workover rig routing problem with a heterogeneous fleet and a finite horizon

Onshore oil fields may contain hundreds of wells that use sophisticated and complex equipments. These equipments need regular maintenance to keep the wells at maximum productivity. When the productivity of a well decreases, a specially-equipped vehicle called a workover rig must visit this well to restore its full productivity. Given a heterogeneous fleet of workover rigs and a set of wells requiring maintenance, the workover rig routing problem (WRRP) consists of finding rig routes that minimize the total production loss of the wells over a finite horizon. The wells have different loss rates, need different services, and may not be serviced within the horizon. On the other hand, the number of available workover rigs is limited, they have different initial positions, and they do not have the same equipments. This paper presents and compares four heuristics for the WRRP: an existing variable neighborhood search heuristic, a branch-price-and-cut heuristic, an adaptive large neighborhood search heuristic, and a hybrid genetic algorithm. These heuristics are tested on practical-sized instances involving up to 300 wells, 10 rigs on a 350-period horizon. Our computational results indicate that the hybrid genetic algorithm outperforms the other heuristics on average and in most cases.     

Superelectrophilic bromination of deactivated aromatic rings with tribromoisocyanuric acid—an experimental and DFT study

The reaction of deactivated arenes with tribromoisocyanuric acid (TBCA) in 98% H₂SO₄ produced bromoarenes in good yields. The acidity of the medium controls the strength of the brominating agent and the amount of polybrominated products. DFT calculations at B3LYP/6-311++G^∗∗ level showed that the protonated TBCA (a superelectrophilic species) can easily transfer Br⁺ to deactivated arenes, in order to decrease internal charge-charge repulsion.     

Modelling creep tests in HMPE fibres used in ultra-deep-sea mooring ropes

Due to its low density and high strength, HMPE (high modulus polyethylene) fibres are being increasingly used in synthetic ropes for offshore mooring. Nevertheless, the occurrence of creep at sea temperature can be a shortcoming for its practical use. Creep tests performed at different load levels in a sub-system of the HMPE rope (yarn) are frequently used as a first step to obtain some information about the susceptibility to creep deformation at a given temperature. The present paper is concerned with the phenomenological modelling of creep tests in HMPE yarns. In this macroscopic approach, besides the classical variables (stress, total strain), an additional scalar variable related with the damage induced by creep process is introduced. An evolution law is proposed for this damage variable. The predicted lifetimes and elongations of HMPE specimens in creep tests at different load levels and room temperature are compared with experimental results showing a good agreement.     

ADDITION of THIO COMPOUNDS to (R)-LIMONENE CATALYZED by AMBERLYST-15

The addition of thioacids and thiophenol to (R)-limonene catalyzed by Amberlyst-15 produced the corresponding 9-thioester- or 9-thioether-p-menthene chemo- and regioselectively.     

A Convenient and Simplified Preparation of Both Enantiomers of α-Terpinyl Chloride

Several methodologies to produce α-terpinyl chloride from “hydrochlorination” of limonene were studied and the best results were obtained by reaction with 0.5 mol equiv. SOCl₂ in SiO₂ / CH₂Cl₂. Using this methodology (R)- and (S)-α-terpinyl chloride can easily be prepared in good yields from (R)- and (S)-limonene, respectively.     

A Clustering Search metaheuristic for the Point-Feature Cartographic Label Placement Problem

The Point-Feature Cartographic Label Placement (PFCLP) problem consists of placing text labels to point features on a map avoiding overlaps to improve map visualization. This paper presents a Clustering Search (CS) metaheuristic as a new alternative to solve the PFCLP problem. Computational experiments were performed over sets of instances with up to 13,206 points. These instances are the same used in several recent and important researches about the PFCLP problem. The results enhance the potential of CS by finding optimal solutions (proven in previous works) and improving the best-known solutions for instances whose optimal solutions are unknown so far.