Experimental and theoretical determination of 1-3 piezocomposite electroacoustic tensor

We report the development of two methods for determining the effective electroacoustic tensor of 1-3 piezocomposite material, one experimental and one theoretical based on homogenization techniques. The main aim was to compare and validate the results provided by these approaches. The slowness surfaces of bulk wave were computed in the large wavelength domain and were fitted to obtain the effective properties of the composite. Model predictions are discussed and compared with the Smith's model. The experimental method is an inversion technique comparing measurement of transmission coefficient through the piezocomposite plate with the simulated coefficient. The accuracy and stability of the minimization procedure is discussed. Experimental results obtained from two piezocomposite test plates are presented and compared with theory.     

Novel 1,4-homofragmentation via an alpha-lactone

Conversion of an alpha,alpha-dichloroester to the corresponding alpha-keto acid was unexpectedly complicated by a novel 1,4-homofragmentation. Investigation of the kinetics of this reaction revealed a mechanism involving an alpha-lactone intermediate, which can lead to both the desired alpha-keto acid and the 1,4-homofragmentation, with the product distribution being dependent upon reaction conditions. This information allowed development of a process that affords the alpha-keto acid exclusively and should be generally applicable to the preparation of alpha-keto acids from alpha,alpha-dichloroesters or acids.     

Singly Hydrogen Bonded Supramolecular Ligands for Highly Selective Rhodium‐Catalyzed Hydrogenation Reactions

H bonds make the catalysts! A single hydrogen bond between ligands coordinated to a rhodium center is critical for the formation of pure supramolecular catalysts for asymmetric hydrogenation reactions. The ester group of the amidite ligand (see scheme) also forms a hydrogen bond with the coordinated substrate. Use of the heterocomplex afforded the highest enantioselectivity reported to date for the hydrogenation of several ester substrates.

     

Assessing indoor air exposures using passive sampling with bioanalytical methods for estrogenicity and aryl hydrocarbon receptor activity

Passive air sampling was undertaken using polyurethane foam passive air samplers at three types of locations, including indoors (six offices) at buildings in the central business district (CBD) and at a private suburban home (indoor and outdoor) located 9 km from the CBD in Brisbane, Queensland, Australia. Estrogenic (E-SCREEN—MCF7-BOS) and aryl hydrocarbon receptor (AhR) (CAFLUX—H4G1.1c2) activity were assessed for samples collected from each of these locations. The samples were tested either as crude extracts (“untreated”) or were subjected to H₂SO₄ silica gel (“treated”) for each location in order to determine whether chemicals, which are not resistant to this treatment like polycyclic aromatic hydrocarbons, potentially account for the observed activity. In most cases, H₂SO₄ treatment resulted in a statistically significant reduction of potency for both endpoints, suggesting that chemicals less resistant to treatment may be responsible for much of the detected biological activity in these locations. Estrogenic potency measurements (<0.22–185 pg m⁻³) were highest in the indoor offices, followed by the indoor suburban home and finally the outdoor suburban home (which was not estrogenic). Total AhR activity for crude extracts (1.3–10 pg m⁻³) however was highest for the outdoor suburban home site. Levels of polycyclic aromatic hydrocarbons were monitored indoors and outdoors at the suburban home. At that location, polycyclic aromatic hydrocarbon air concentrations were on average approximately two times higher outdoor than indoor, while AhR potency was five times higher outdoor than indoor. No significant correlation was found between the estrogenic and AhR activity (P = 0.88) for the sites in this study. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Optimal intermittence in search strategies under speed-selective target detection

Random search theory has been previously explored for both continuous and intermittent scanning modes with full target detection capacity. Here we present a new class of random search problems in which a single searcher performs flights of random velocities, the detection probability when it passes over a target location being conditioned to the searcher speed. As a result, target detection involves an N-passage process for which the mean search time is here analytically obtained through a renewal approximation. We apply the idea of speed-selective detection to random animal foraging since a fast movement is known to significantly degrade perception abilities in many animals. We show that speed-selective detection naturally introduces an optimal level of behavioral intermittence in order to solve the compromise between fast relocations and target detection capability.     

Variable temperature STM study of Co deposition on a dodecanethiol self assembled monolayer

The present scanning tunneling microscopy study reports on the growth processes of Co vapor-deposited on a dodecanethiol (DDT) self-assembled monolayer (SAM)/Au(111). We observe strongly modified surface and depth diffusions of Co adatoms depending on the growth temperature. Co deposited at 300 K shows an extremely incomplete regime of condensation on the organic layer. Besides, Co penetrates the DDT monolayer and resides at the DDT/Au(111) interface as 2D clusters. This phenomenon takes place through defects in the SAM which are transient channels. In contrast, Co deposited at 50 K shows a complete condensation and nucleates on defects of the SAM layer as 3D islands sitting most likely on top of the DDTs. These results are of interest in the growing field of organic spintronics where the quality of the organic/ferromagnetic interface is a key issue.     

Copper and iron complexes as visible‐light‐sensitive photoinitiators of polymerization

The utilization of visible lights for the fabrication of polymeric materials is recognized as a promising and environmentally friendly approach. This process relies on the photochemical generation of reactive species (e.g., radicals, radical cations, or cations) from well‐designed photoinitiators (PIs) or photoinitiating systems (PISs) to initiate the polymerization reactions of different monomers (acrylates, methacrylates, epoxides, and vinyl ethers). In spite of the fact that metal complexes such as ruthenium‐ or iridium‐based complexes have found applications in organic and polymer synthesis, the search of other low‐cost metal‐based complexes as PISs is emerging and attracting increasing attentions. Particularly, the concept of the photoredox catalysis has appeared recently as a unique tool for polymer synthesis upon soft conditions (use of light emitting diodes and household lamp). This highlight focuses on recently designed copper and iron complexes as PI catalysts in the application of photoinduced polymerizations (radical, cationic, interpenetrated polymer networks, and thiol‐ene) or controlled radical polymerization under visible light irradiation. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2673–2684