Static and Dynamic Properties of Semi-Crystalline Polyethylene.

Properties of extruded polymers are strongly affected by molecular structure. For two different semi-crystalline polymers, low-density polyethylene (LDPE) and ultra-high molecular weight polyethylene (UHMWPE), this investigation measures the elastic modulus, plastic flow stress and strain-rate dependence of yield stress. Also, it examines the effect of molecular structure on post-necking tensile fracture. The static and dynamic material tests reveal that extruded UHMWPE has a somewhat larger yield stress and much larger strain to failure than LDPE. For both types of polyethylene, the strain at tensile failure decreases with increasing strain-rate. For strain-rates 0.001⁻3400 s-1, the yield stress variation is accurately represented by the Cowper⁻Symonds equation. These results indicate that, at high strain rates, UHMWPE is more energy absorbent than LDPE as a result of its long chain molecular structure with few branches.This work was partially sponsored by Foundation of State Key Laboratory of Explosion Science and Technology of China under Grant No.KFJJ13-1Z, No. YBKT15-02 and Natural Science Foundation of China under Grant No.11102023. The authors would like to thank Chunmei Liu of the First Research Institute of the China Ministry of Public Security for assistance with the static tensile tests.This is the final version of the article. It first appeared from the Multidisciplinary Digital Publishing Institute via http://dx.doi.org/10.3390/polym804007

Perforation resistance of aluminum/polyethylene sandwich structure

© 2016 Elsevier Ltd. Ballistic tests were performed on two types of polyethylene core sandwich structures (AA6082/LDPE/AA6082 and AA6082/UHMWPE/AA6082) to investigate their perforation resistance. Bulging and dishing deformation of layered plates were compared under low-velocity impact by hemispherical-nosed projectiles. Different impact failure mechanisms leading to perforation were revealed for laminates composed of a pair of aluminum alloy face sheets separated by a polyethylene interlayer. Using the finite element code Abaqus/Explicit, the perforation behavior and distribution of energy dissipation of each layer during penetration were simulated and analysed. The deformation resistance and anti-penetration properties of polyethylene core sandwich structures were compared with those of monolithic AA6082-T6 plates that had the same areal density. Although the polyethylene interlayer enlarged the plastic deformation zone of the back face, the polyethylene core sandwich structure was a little less effective than the monolithic Al alloy target at resisting hemispherical-nosed projectile impact.The authors gratefully acknowledge the Foundation of State Key Laboratory of Explosion Science and Technology of China under Grant No. KFJJ13-1Z, and Natural Science Foundation of China under Grant No. 11102023, 11172071

Intraindividual association between shift work and risk of drinking problems: Data from the Finnish Public Sector Cohort

OBJECTIVES: Studies concerning the association between shift work and drinking problems showed inconsistent results. We used data from a large occupational cohort to examine the association between shift work and different types of drinking behaviour. METHODS: A total of 93 121 non-abstinent workers from the Finnish Public Sector Study were enrolled in the study. Six waves of survey data were collected between 2000 and 2017. Work schedules were categorised as regular day, non-night shift and night shift work, and shift intensities were calculated from registered working hour data. Two indicators of adverse drinking behaviour were measured: at-risk drinking (>7 and >14 drinks per week in women and men, respectively) and high-intensity drinking (measured as pass-out experience). Intraindividual analysis was conducted using fixed-effects regression to examine the association between shift work and drinking behaviours. RESULTS: Compared with regular day work, night shift work was associated with an increased risk of high-intensity drinking (OR 1.28, 95% CI 1.07 to 1.52) but a lower risk of at-risk drinking (OR 0.85, 95% CI 0.74 to 0.99). Shift workers who worked long shifts had a lower risk of at-risk drinking compared with those who rarely worked long shifts (OR 0.58, 95% CI 0.37 to 0.93). CONCLUSIONS: Associations between shift work and alcohol use vary according to drinking patterns. Workers engaged in high-intensity drinking more often during night shift schedules compared with day work, but did not drink averagely higher volume

Enantioseparation of flurbiprofen enantiomers using chiral ionic liquids by liquid‐liquid extraction

Flurbiprofen is a kind of nonsteroidal anti‐inflammatory drug, which has been widely used in clinic for treatment of rheumatoid arthritis and osteoarthritis. It has been reported that S‐flurbiprofen shows good performance on clinic anti‐inflammatory treatment, while R‐enantiomer almost has no pharmacological activities. It has important practical values to obtain optically pure S‐flurbiprofen. In this work, chiral ionic liquids, which have good structural designability and chiral recognize ability, were selected as the extraction selector by the assistance of quantum chemistry calculations. The distribution behaviors of flurbiprofen enantiomers were investigated in the extraction system, which was composed of organic solvent and aqueous phase containing chiral ionic liquid. The results show that maximum enantioselectivity up to 1.20 was attained at pH 2.0, 25°C using 1,2‐dichloroethane as organic solvent, 1‐butyl‐3‐methylimidazole L‐tryptophan ([Bmim][L‐trp]) as chiral selector. The racemic flurbiprofen initial concentration was 0.2 mmol L−1, and [Bmim][L‐trp] concentration was 0.02 mol L−1. Furthermore, the recycle of chiral ionic liquids has been achieved by reverse extraction process of the aqueous phase with chiral selector, which is significant for industrial application of chiral ionic liquids and scale‐up of the extraction process

Expertise dissimilarity and creativity : the contingent roles of tacit and explicit knowledge sharing

Author name used in this manuscript: Wei He2014-2015 > Academic research: refereed > Publication in refereed journalAccepted ManuscriptPublishe

Structural basis for oligomerization and glycosaminoglycan binding of CCL5 and CCL3.

CC chemokine ligand 5 (CCL5) and CCL3 are critical for immune surveillance and inflammation. Consequently, they are linked to the pathogenesis of many inflammatory conditions and are therapeutic targets. Oligomerization and glycosaminoglycan (GAG) binding of CCL5 and CCL3 are vital for the functions of these chemokines. Our structural and biophysical analyses of human CCL5 reveal that CCL5 oligomerization is a polymerization process in which CCL5 forms rod-shaped, double-helical oligomers. This CCL5 structure explains mutational data and offers a unified mechanism for CCL3, CCL4, and CCL5 assembly into high-molecular-weight, polydisperse oligomers. A conserved, positively charged BBXB motif is key for the binding of CC chemokines to GAG. However, this motif is partially buried when CCL3, CCL4, and CCL5 are oligomerized; thus, the mechanism by which GAG binds these chemokine oligomers has been elusive. Our structures of GAG-bound CCL5 and CCL3 oligomers reveal that these chemokine oligomers have distinct GAG-binding mechanisms. The CCL5 oligomer uses another positively charged and fully exposed motif, KKWVR, in GAG binding. However, residues from two partially buried BBXB motifs along with other residues combine to form a GAG-binding groove in the CCL3 oligomer. The N termini of CC chemokines are shown to be involved in receptor binding and oligomerization. We also report an alternative CCL3 oligomer structure that reveals how conformational changes in CCL3 N termini profoundly alter its surface properties and dimer-dimer interactions to affect GAG binding and oligomerization. Such complexity in oligomerization and GAG binding enables intricate, physiologically relevant regulation of CC chemokine functions

W::Neo: A Novel Dual-Selection Marker for High Efficiency Gene Targeting in Drosophila

We have recently developed a so-called genomic engineering approach that allows for directed, efficient and versatile modifications of Drosophila genome by combining the homologous recombination (HR)-based gene targeting with site-specific DNA integration. In genomic engineering and several similar approaches, a “founder” knock-out line must be generated first through HR-based gene targeting, which can still be a potentially time and resource intensive process. To significantly improve the efficiency and success rate of HR-based gene targeting in Drosophila, we have generated a new dual-selection marker termed W::Neo, which is a direct fusion between proteins of eye color marker White (W) and neomycin resistance (Neo). In HR-based gene targeting experiments, mutants carrying W::Neo as the selection marker can be enriched as much as fifty times by taking advantage of the antibiotic selection in Drosophila larvae. We have successfully carried out three independent gene targeting experiments using the W::Neo to generate genomic engineering founder knock-out lines in Drosophila

Selection of tuning parameters in bridge regression models via Bayesian information criterion

We consider the bridge linear regression modeling, which can produce a sparse or non-sparse model. A crucial point in the model building process is the selection of adjusted parameters including a regularization parameter and a tuning parameter in bridge regression models. The choice of the adjusted parameters can be viewed as a model selection and evaluation problem. We propose a model selection criterion for evaluating bridge regression models in terms of Bayesian approach. This selection criterion enables us to select the adjusted parameters objectively. We investigate the effectiveness of our proposed modeling strategy through some numerical examples.Comment: 20 pages, 5 figure