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911.
Semi-crystalline polymers can be deformed up to a very high strain. The deformation process involves frequently a complete molecular rearrangement of the chain-folded lamellar morphology into a more or less chain-unfolded fibrillar microstructure. This transformation is likely to occur through an intermediate state of high molecular disorder at a local scale. It led to the formulation of a concept of strain-induced melting-recrystallization process as a main mechanism of the structure transformation. In contrast, several structural features occurring at moderate plastic strains are relevant to strictly crystallographic processes. The plastic deformation process of semicrystalline polymers and the micromechanisms involved are discussed. A critical discussion of experimental findings is made to point out the strength or the deficiency of the various argumentations. It is demonstrated that the crystallographic slip mechanisms, including slips: transverse and along the chains are the basic deformation mechanisms in the deformation sequence, active at all strain levels. Direct microscopic evidence of chain slip activity even at well advanced stages of the deformation process is presented. In contrary, the melting-recrystallization seems to be restricted to the high-strain stage accompanied by chain unfolding and perhaps limited to only a small fraction of the crystalline phase. In addition the experimental results demonstrates clearly that the cavitation, necessary in the Peterlin's model, is really unessential in producing high deformation and appearance of the final highly oriented structure. This can be effectively accomplished with only crystallographic mechanisms employed. A very important role in the deformation sequence is played by the partially reversible shear deformation of amorphous interlamellar layers, producing not only high orientation of amorphous component but also influencing deeply the deformation of crystalline phase, since both phases are strongly connected and must deform simultaneously and consistently. 相似文献
912.
在水溶液中,以PAMAM树形分子为模板,乙醇为还原剂,制备了树形分子包裹的金纳米颗粒,其水溶性好,可以稳定放置1年以上;通过控制Au3+与PAMAM树形分子的摩尔比,可以得到粒径可控的金纳米颗粒,其粒径范围为1~4nm,分别在385和402nm处出现强的共振瑞利光散射峰和荧光峰.室温下,荧光量子产率达到10%以上,比其它文献报道的金纳米颗粒的荧光量子产率高2个数量级以上,这一特性使其在潜指纹识别、光催化等方面具有很大的应用潜力. 相似文献
913.
Julie M. Stanley Christopher K. ChanXiaoping Yang Richard A. Jones Bradley J. Holliday 《Polyhedron》2010
Herein we report for the first time the complete characterization and photophysical properties of tris(dibenzoylmethanido)(1,10-phenanthroline)samarium(III) (Sm(DBM)3phen) in the absence of a polymer matrix. The solid state structure of Sm(DBM)3phen has been determined by single-crystal X-ray crystallography and shows the geometry of the local coordination environment around the samarium(III) ion to be a slightly distorted square antiprism. The absolute quantum yield and luminescence lifetime were measured as 0.86 ± 0.40% and 41 ± 2 μs, respectively. 相似文献
914.
An hydroxyl substituted hexa(phenoxy)cyclotriphosphazene (3) is reacted with silicon phthalocyanine (4), SiPc(Cl)2, to give an axially-disubstituted phenoxycyclotriphosphazenyl silicon phthalocyanine (5). In this study, an axially phosphazene substituted phthalocyanine complex synthesized at the first time. Newly synthesized silicon phthalocyanine complex has been fully characterized by elemental analysis, ESI mass spectrometry, FT-IR, 1H, 13C and 31P NMR spectroscopy. Photophysical (fluorescence quantum yield and lifetime) and photochemical (singlet oxygen generation and photodegradation quantum yield) properties of complex 5 are reported in DMSO. The fluorescence quenching behaviour of this complex by 1,4-benzoquinone (BQ) is also reported in DMSO. 相似文献
915.
采用联合脱铝法制备了一系列高硅铝比Y型沸石FSY,并对其加La老化的LaFSY催化裂化性能进行了研究. 结果表明, (NH4)2SiF6处理和水热处理两个步骤联合可有效调节FSY沸石的酸密度,所得LaFSY沸石具有适量强酸位和较少弱酸位,在保持高微反活性的同时有效地降低了重油结焦率. 以大庆常压渣油为裂化原料,与另一种广泛使用的工业催化剂相比,该LaFSY沸石为活性组分的微球催化剂可使轻质产品收率由85.4%提高到88.9%, 而结焦率由9.0%下降到7.5%. 相似文献
916.
In this article, a new route for conversion of camptothecin to 7‐ethylcamptothecin and 7‐propylcamptothecin is described. Compared with previous reports, the reaction time of the new synthetic route was greatly shortened to 30 min, and the products were obtained in high yield. 相似文献
917.
Sergey Kotrechko 《哲学杂志》2013,93(33):3049-3058
It is shown that the temperature effect on the variance of local shear stresses is the main factor pre-determining the temperature law of the yield stress of nano-sized crystals. The results of molecular dynamics simulations of uniaxial tension of Mo, α-Fe and W nanowires in three crystallographic directions ([100], [110] and [111]) over the temperature range 100–1000 K are presented. It is found that within this temperature range, the yield stress of nano-sized crystals varies not exponentially, as for bulk single crystals, but is a parabolic function of temperature. 相似文献
918.
We grew Na and K co-doped Eu:SrI2 [Na,Eu:SrI2 and K,Eu:SrI2] crystals by a modified micro-pulling-down method to reveal the co-doping effects on the crystal growth and scintillation properties. The non-codoped, Na0.5%, Na1.0%, K0.5% and K1.0%,Eu:SrI2 crystals indicated high transparency while the milky parts were generated in the Na5.0% and K5.0%,Eu:SrI2 crystals. The light yields of Na,Eu:SrI2 and K,Eu:SrI2 crystals under γ-ray irradiation were decreased by the Na and K co-doping. On the other hand, there was a small change within 940–1020 ns in the decay times by the Na and K co-doping. In the light yield proportionality under γ-ray irradiation, the non-proportionality in the low energy region was improved by Na and K co-doping. 相似文献
919.
Guocan Li Ke Hu Kiyoshi C. D. Robson Prof. Serge I. Gorelsky Prof. Gerald J. Meyer Prof. Curtis P. Berlinguette Prof. Michael Shatruk 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(5):2173-2181
Two novel tris‐heteroleptic Ru–dipyrrinates were prepared and tested as sensitizers in the dye‐sensitized solar cell (DSSC). Under AM 1.5 sunlight, DSSCs employing these dyes achieved power conversion efficiencies (PCEs) of 3.4 and 2.2 %, substantially exceeding the value achieved previously with a bis‐heteroleptic dye (0.75 %). As shown by electrochemical measurements and DFT calculations, the improved PCEs stem from the synthetically tuned electronic structure, which affords more negative excited state redox potentials and favorable electron injection into the TiO2 conduction band. Electron injection was quantified by nanosecond transient absorption spectroscopy, which revealed that the highest injection yield is achieved with the dye that acts as the strongest photoreductant. 相似文献
920.
We consider a manufacturer’s stochastic production/inventory problem under periodic review and present methods for safety stock determination to cope with uncertainties that are caused by stochastic demand and different types of yield randomness. Following well-proven inventory control concepts for this problem type, we focus on a critical stock policy with a linear order release rule. A central parameter of this type of policy is given by the safety stock value. When non-zero manufacturing lead times are taken into account in the random yield context, it turns out that safety stocks have to be determined that vary from period to period. We present a simple approach for calculating these dynamic safety stocks for different yield models. Additionally, we suggest approaches for determining appropriate static safety stocks that are easier to apply in practice. In a simulation study we investigate the performance of the proposed safety stock variants. 相似文献