Levels and distribution of polybrominated diphenyl ethers in water, surface sediments, and bivalves from the San Francisco Estuary

Polybrominated diphenyl ethers (PBDEs) were found in water, surface sediments, and bivalve samples that were collected from the San Francisco Estuary in 2002. sigmaPBDE concentrations in water samples ranged from 3 to 513 pg/ L, with the highest concentrations found in the Lower South Bay (range 103-513 pg/L) region, which receives approximately 26% of the Estuary's wastewater treatment plant effluents. The sigmaPBDEs in sediments ranged from below detection limits to 212 ng/g dry wt, with the highest concentration found at a South Bay station (212 ng/g dry wt), which was up to 3 orders of magnitude higher than other stations. The sigmaPBDE concentrations ranged from 9 to 64 ng/g dry wt in oysters (Crassostrea gigas), from 13 to 47 ng/g dry wt in mussels (Mytilus californianus), and from 85 to 106 ng/g dry wt in clams (Corbicula fluminea). Only three PBDE congeners were detected in bivalves, BDE-47, BDE-99, and BOE-100; these are the most bioaccumulative congeners from the commercial Penta-BDE mixture.     

Ductile fracture characterization of polycarbonate by the R-curve method

The R-curve method was used to characterize the stable crack growth and the unstable ductile fracture of 3 mm thick polycarbonate sheets. In order to delimit the field of application of this method, several parameters describing the crack growth resistance were employed. The effect of specimen size and geometry was also studied. Besides limitations linked to test specimens size, the different parameters used are shown to aptly describe the tearing process of this material. When the plane stress region is dominant, the J-integral appears to be as a parameter well adapted to characterize ductile fracture.

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Résumé On a utilisé la méthode de la courbe R pour caractériser la croissance stable d'une fissure et la rupture ductile instable dans le cas de feillards de polycarbonate de 3 mm d'épaisseur. Afin de délimiter le champ d'application de cette méthode, on a utilisé divers paramètres décrivant la résistance à la propagation de la fissure. Les effets de la taille de l'éprouvette et de sa géométrie ont été également étudiés. On montre que les différents param`etres utilisés indiquent les limitations propres à la taille des éprouvettes et décrivent bien le processus d'arrachement qui caractérise le comportement de ce matériau. Lorsqu'il y a prédominance d'une région d'état plan de tension, l'intégrale J apparaît être un paramètre bien adapté à la caractérisation d'une rupture ductile.

     

Deformulation of commercial linear low‐density polyethylene resins by advanced fractionation and analysis

Linear low density polyethylene (LLDPE) exhibits a complex molecular structure that is characterized by molar mass and chemical composition distributions. Both molecular parameters complementarily influence the final application properties. Typically, the molecular structure of commercial polyolefins is characterized by a set of technical parameters including the melt flow index, the crystallization and melting temperatures and the comonomer content as obtained using Fourier transform infrared or NMR spectroscopy. LLDPEs with high comonomer contents are typically regarded as plastomers or elastomers. Due to their low crystallinities, characterization of these materials using crystallization‐based analytical techniques is of limited use since the majority of the material is rather amorphous. Such materials need specific alternative analytical methods that may be based on molar mass and/or chemical composition fractionation. Here it is shown that for a comprehensive analysis of LLDPEs with similar bulk properties, preparative molar mass fractionation (pMMF) and advanced analysis of the fractions are required. The pMMF fractions are comprehensively analyzed using size exclusion chromatography, differential scanning calorimetry and high‐temperature high‐performance liquid chromatography to provide detailed information on molar mass and copolymer composition. Correlated information of these molecular parameters is obtained by comprehensive two‐dimensional liquid chromatography. © 2019 Society of Chemical Industry     

The next evolution of MDE: a seamless integration of machine learning into domain modeling

Software and Systems Modeling - Machine learning algorithms are designed to resolve unknown behaviors by extracting commonalities over massive datasets. Unfortunately, learning such global...     

CONSTITUTIVE EQUATIONS FOR RIGID PLASTIC OR VISCOPLASTIC MATERIALS CONTAINING VOIDS

Abstract— A systematic numerical study is reported that uses a homogenization technique to consider the plastic and viscoplastic potential of a porous medium; the study also takes account of the interactions between cavities. Calculations are carried out in plane strain with cylindrical cavities for various stress states characterized by the ratio of the principal stresses and for various values of the porosity as well as of the strain hardening exponent of the matrix.
It is shown that the cavity growth rate is a strong function of the porosity, of the strain hardening exponent of the matrix and that it is a linear function of the stress triaxiality ratio. It is demonstrated that the growth models in an infinite body of Rice and Tracey or of Budiansky et al. can underestimate the cavity growth rate for intermediate stress triaxiality ratios, even for porosities as low as 1%.     

Stopping of crosslinking reaction in a PDMS polymer at the gel point

Summary A method has been developed to stop the crosslinking reaction of a polydimethylsiloxane system without disturbing the state of the sample. Oscillatory shear experiments on samples just before and just beyond the gelation point demonstrated the transition of the material from a viscoelastic liquid to a viscoelastic solid. At the gel point the loss modulus and the storage modulus were found to be identical over several decades of frequency and for temperatures ranging between -50°C and +180°C. Both moduli were proportional to the square root of the frequency.     

The complete sequence of a 6794 bp segment located on the right arm of chromosome II of Saccharomyces cerevisiae. Finding of a putative dUTPase in a yeast

The DNA sequence of a 6794 bp fragment located at about 100 kb from the right telomere of chromosome II from Saccharomyces cerevisiae has been determined. Sequence analysis reveals five open reading frames. One is the ARO4 gene encoding the 3-deoxy-D -arabinoheptulosonate 7-phosphate synthase. Another presents strong homology with the S5 ribosomal protein from bacteria. The open reading frame YBR1705 shows significant homology with dUTPase, suggesting for the first time the existence of such an enzyme in S. cerevisiae.     

Synthesis and characterization of novel natural rubber based cationic waterborne polyurethane—Effect of emulsifier and diol class chain extender

Novel cationic waterborne polyurethanes (cWPU) were synthesized by step‐growth polymerization of hydroxyl telechelic natural rubber, molecular weight of 2800 g mol^?1, toluene‐2,4‐diisocyanate, N‐methyl diethanolamine (NMDEA) as an emulsifier. The chemical structure of cWPU was confirmed by ¹H‐nuclear magnetic resonance and Fourier transform infrared spectroscopy. The amounts of NMDEA and ethylene glycol under isocyanate (NCO) index of 100 on the properties of cWPU were studied. It was found that cWPU was stable under the concentration of NMDEA more than 1.50 mol and the particle sizes decreased with increasing of NMDEA content. Also, contact angle shows more hydrophilic materials by increasing of NMDEA. Extended cWPU was found in two ranges of nano size. Chain extender has strongly affected cWPU film formation, increasing of mechanical properties, and thermal properties. In addition, stress–strain curve and scanning electron microscopy image shows the change of behavior from soft elastic to ductile plastic by adding ethylene glycol. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45715.     

Self-Supervised Monocular Depth and Motion Learning in Dynamic Scenes: Semantic Prior to Rescue

International Journal of Computer Vision - We introduce an end-to-end joint training framework that explicitly models 6-DoF motion of multiple dynamic objects, ego-motion, and depth in a monocular...