Impact and wear resistance of polymer nanocomposites at low filler content

It is well known that inorganic filler particles enhance the mechanical and tribological properties of polymers. The stiffness, toughness, and wear performance of the composites are extensively determined by the size, shape, volume content, and especially the dispersion homogeneity of the particles. In the present study, various amounts of micro‐ and nano‐scale particles (titanium dioxide TiO₂, 200–400 nm, calcium silicate CaSiO₃, 4–15 μm) were introduced into an epoxy polymer matrix for its reinforcement. The influence of these particles on the impact strength, dynamic mechanical thermal properties, and block‐on‐ring wear behavior was investigated. Using only the nano‐particles, the results demonstrate the best improvement in stiffness, impact strength, and wear resistance of the epoxy at a nano‐particle content of 4 vol% TiO₂. Therefore, this nanocomposite was used to act as a matrix for the CaSiO₃ micro‐particles, in the hope of finding synergistic effects between the micro‐ and the nano‐particles. Results show, in fact, a further improvement of wear resistance and stiffness, whereas the impact strength suffers. Geometrical properties of the particles, the homogeneous dispersion state, energy dissipating fracture mechanisms, and a transition of wear mechanisms mostly contribute to the increase in performance.     

Diversity in steroidogenesis of symbiotic microorganisms from planthoppers

Ergosta-5,7,24(28)-trien-3-ol (trienol)6 was isolated from the intracellular symbiotes (symbiotic microorganisms) of the planthoppers,Nilaparvata lugens andLaodelphax striatellus. The steroidogenic end product of the symbiotes was found to depend on the environmental conditions, i.e., although trienol6 was produced under symbiotic conditions, ergosterol4 was formed in aerobic culture. When the normal diet was replaced by a steroiddeficient artificial one, the ratio of 24-methylenecholesterol5 to total insect sterols was significantly increased. The above study offers further corroborating evidence for our assumption that the host insects require 24-methylenecholesterol5 as an alternate source for cholesterol1 under certain environmental conditions. In our previous biotransformation experiments, 24methylenecholesterol5 was shown to be an immediate precursor of cholesterol1. However, the complexity of the insects' vital functions hindered all subsequent attempted transformations into cholesterol1 of sitosterol2, trienol6, and ergosterol4, under injection conditions.     

Atomic force microscopy study on structure and properties of irradiation grafted silica particles in polypropylene‐based nanocomposites

Nanosilica particles treated by irradiation grafting polymerization can effectively improve the strength and toughness of a thermoplastic polymer at a rather low filler content. A detailed investigation on the modified nanoparticles in the absence and presence of a polypropylene matrix is carried out by using atomic force microscopy. The results indicate that the loosen agglomerates of the untreated SiO₂ became more compact due to the linkage between the nanoparticles offered by the grafting polymer. In addition, the molecules of the polypropylene matrix are able to diffuse into the modified nanoparticle agglomerates during the melt processing. Entanglement between the molecules of the grafting polymer and the matrix is thus available, which in turn facilitates a strong particle–matrix interfacial interaction. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2218–2227, 2001     

Stab and puncture characterization of thermoplastic-impregnated aramid fabrics

The cut and puncture resistance of thermoplastic (TP) impregnated, woven aramid fabric is characterized under quasi-static and dynamic stab testing conditions. Polyethylene, Surlyn^®, and co-extruded polyethylene–Surlyn films of various thicknesses are laminated into fabrics and compared with neat fabrics at equal weights and layer counts. The results show that TP-laminated fabrics improve the stab and puncture resistance of the fabrics, through a combination of increased cut resistance and reduced windowing. All films are shown to be effective, although thin Surlyn films appear to provide the best overall performance. The results also show that the TP films need to be integrally bonded to the fabrics in order to achieve synergistic property enhancement.     

Evaluation of metal/indium-tin-oxide for transparent low-resistance contacts to p-type GaN

In search of a better transparent contact to p-GaN, we analyze various metal/indium-tin-oxide (ITO) (Ag/ITO, AgCu/ITO, Ni/ITO, and NiZn/ITO) contact schemes and compare to Ni/Au, NiZn/Ag, and ITO. The metal layer boosts conductivity while the ITO thickness can be adjusted to constructive transmission interference on GaN that exceeds extraction from bare GaN. We find a best compromise for an Ag/ITO (3 nm/67 nm) ohmic contact with a relative transmittance of 97% of the bare GaN near 530?nm and a specific contact resistance of 0.03 Ω·cm². The contact proves suitable for green light-emitting diodes in epi-up geometry.     

基于生态保护的河流与近海水域的管理

德国是人口居住稠密的国家,大部分地区因经济和社会发展的需要而被开发利用,纯天然的自然环境已所剩无几.为了保护剩下的宝贵资源,与河流、近海水域管理有关的工程活动应以生态保护为导向,以尽量减少,甚至要努力防止对环境的不良影响.为了实现这个目标,德国联邦水文学会已经成功制定并实施了大量的以生态保护为导向的指导方针.     

Potential paracrine role of the pericardium in the regulation of cardiac function

OBJECTIVE: Both coronary and endocardial endothelium regulate cardiac contractile function via paracrine pathways. We investigated whether pericardial fluid (PF) and pericardial mesothelial cells (PMC) could exert a similar paracrine action. METHODS: Both PF and PMC were extracted from sheep pericardial space. Endothelin-1, prostaglandins and atrial natriuretic factor were measured in PF in vivo. In the other hand, PMC were grown on T-75 flasks and microcarrier beads to investigate endothelin-1, nitric oxide and prostaglandin pathways in vitro. In addition, effects of PF and PMC effluent were tested on adult rat cardiac myocyte contraction in vitro. RESULTS: In vitro, cultured PMC expressed endothelin-1 mRNA but not the endothelial nitric oxide synthase III, and released endothelin-1 and prostaglandins. Both PF and cultured PMC superfusate induced a potent, rapidly reversible decrease in the shortening of isolated rat cardiac myocytes. This effect was not associated with changes in intracellular calcium. In vivo, prostaglandins, atrial natriuretic factor and endothelin were present in PF. A greater concentration of atrial natriuretic factor was present in PF than in serum, suggesting molecular diffusion from the myocardium to PF. Preliminary results show that the instillation of vasoactive agents into the pericardial space of dogs rapidly alter coronary and systemic vascular tone, consistent with a molecular diffusion of these substances from PF into the myocardium and circulation. CONCLUSIONS: In addition to its mechanical role, the pericardium may contribute to the integration and the regulation of cardiovascular function via a paracrine mechanism.     

Psychopharmacotherapy in pregnancy and breast feeding

The primary purpose of this article is to review critically the literature on the use of psychotropic medications in pregnancy and during breast feeding in order to suggest strategies for the clinical management of these periods. Use of psychotropic medications during pregnancy may cause three complications: 1. teratogenicity, 2. perinatal syndromes (neonatal toxicity), and 3. postnatal behavioural sequelae (behavioural toxicity). The literature features few well-controlled studies concerning these points, so that the available information allows only few conclusions. Exposure to certain psychotropic drugs in utero may increase the risk for some specific congenital anomalies; there is mostly no strong evidence for behavioural toxicity in children exposed to psychotropic medications. Use of psychotropic drugs during pregnancy and breast feeding may be appropriate in many clinical situations and should include thoughtful weighing of risk of pre- and postnatal exposure versus risk of relapse following drug discontinuation. The authors try to present disorder-based guidelines for psychotropic drug use during pregnancy and breast feeding and for psychiatrically ill women who wish to conceive.