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101.
Chenze Qi Shuihe Zhang Yanjie Wu Yurong Zhong Dakang Song Tianmin Wang 《Journal of Polymer Science.Polymer Physics》1999,37(5):465-472
The o‐Ps lifetime τ3 and the intensity I3 of ST‐AN copolymers and ST‐MMA copolymers have been determined by using the positron annihilation technique. The average free volume hole radius R is estimated according to Tao's and Eldrup's model. The result shows that the average free volume hole size mainly attributes to lateral group volume and polarity of macromolecular chain as well as polymerizing temperature, and the o‐Ps intensity I3 to the effect of the lateral group volume and the polarity. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 465–472, 1999 相似文献
102.
Rena Haruki Hironori Kouno Masanori Hosoyamada Taku Ogawa Nobuhiro Yanai Nobuo Kimizuka 《化学:亚洲杂志》2019,14(10):1723-1728
Molecular self‐assembly is a powerful means to construct nanoscale materials with advanced photophysical properties. Although the protection of the photo‐excited states from oxygen quenching is a critical issue, it still has been in an early phase of development. In this work, we demonstrate that a simple and typical molecular design for aqueous supramolecular assembly, modification of the chromophoric unit with hydrophilic oligo(ethylene glycol) chains and hydrophobic alkyl chains, is effective to avoid oxygen quenching of triplet–triplet annihilation‐based photon upconversion (TTA‐UC). While a TTA‐UC emission is completely quenched when the donor and acceptor are molecularly dispersed in chloroform, their aqueous co‐assemblies exhibit a clear upconverted emission in air‐saturated water even under extremely low chromophore concentrations down to 40 μm . The generalization of this nano‐encapsulation approach offers new functions and applications using oxygen‐sensitive species for supramolecular chemistry. 相似文献
103.
Chang-Zheng Yuan 《Frontiers of Physics》2015,10(6):101401
With its unique data samples at energies of 3.8–4.6 GeV, the BESIII experiment made a significant contribution to the study of charmonium and charmonium-like states, i.e., the XYZ states.We review the results for observations of the Zc(3900) and Zc(4020) states, the X(3872) in e+e− annihilation, and charmonium ψ(13D2) state, as well as measurements of the cross-sections of ωχcJ and ηJ/ψ, and the search for e+e−→ γχcJ and γY (4140). We also present data from BESIII that may further strengthen the study of the XYZ and conventional charmonium states, and discuss perspectives on future experiments. 相似文献
104.
105.
采用慢正电子湮没光谱研究低能质子辐照下ZnO白漆的光学退化。研究结果表明,随质子辐照注量的增加, 多普勒展宽谱的S参数逐渐减小,W参数逐渐增大。质子辐照下S-W参数拟合曲线的斜率发生改变。S参数的减小可以归结为锌空位含量的减少以及准正电子素的形成。准正电子素{单电离氧空位(捕获一个电子)+正电子}的形成,能够降低正电子湮没的速率,导致S参数减小。S参数的减小证实了质子辐照导致ZnO白漆中单电离氧空位数量的增加。S-W参数拟合曲线斜率的变化可以归结于质子辐照下双电离氧空位向单电离氧空位的转变。 相似文献
106.
107.
P. E. Keivanidis Dr. S. Baluschev Dr. G. Lieser Dr. G. Wegner Prof. 《Chemphyschem》2009,10(13):2316-2326
We present results of steady‐state and transient photoluminescence studies of molecularly doped poly(fluorene) films. We study blends with increasing content of the triplet emitter (2,3,7,8,12,13,17,18‐octaethyl‐porphyrinato)PtII (PtOEP) when dispersed in the polymeric poly(fluorene) matrix of the poly[9,9‐di‐(2‐ethylhexyl)‐fluorenyl‐2,7‐diyl] (PF26) derivative. We carry out a unified study of the photophysical reactions that are involved in the energy transfer processes in this system by probing the three luminescence processes of a) PF26 fluorescence, b) triplet–triplet annihilation (TTA) induced up‐converted PF26 delayed fluorescence and c) PtOEP phosphorescence. With increasing PtOEP content, the process of photon energy recycling in the PF26:PtOEP system is manifested from the quenching of the TTA‐induced up‐converted PF26 delayed fluorescence and it is rationalized with the use of Forster theory of resonant energy transfer. Based on the combined results of the photophysical and the transmission electron microscopy characterization of the as‐spun PF26:PtOEP films, we determine the onset of PtOEP aggregation at 2–3 wt % PtOEP content. The analysis of the photophysical data is based on the use of modified Stern–Volmer photokinetic models that are appropriate for the solid state. A static component in the PL quenching of PF26 is revealed for PtOEP contents below 2 wt %. The modified Stern–Volmer kinetic scheme further suggests that co‐aggregation effects between PF26 and PtOEP are operative with an association constant of ground state complex formation kbind ~15–17 M ?1. The involvement of the ground state heterospecies in the TTA‐mediated PF26 up‐converted luminescence is discussed. The participation of an electron‐exchange step, in the excited state energy transfer pathway between PtOEP and PF26, is proposed for the activation mechanism of the PF26 up‐converted fluorescence. 相似文献
108.
目前,正负电子湮灭过程的核子激发态N*产生的实验数据主要来自于粲偶素能区。粲偶素衰变到核子激发态过程类似于其类时电磁形状因子测量过程,正反粲夸克短程湮灭提供了近乎于点源的胶子强子化过程。与γN,eN,πN反应互补,这一新的N*产生源具有同位旋和低自旋筛选的优势。综述了正负电子湮灭过程的核子激发态N*产生的实验情况和相关的唯象进展,同时讨论未来发展的一些新方向,如正负电子湮灭过程的核子激发态N*产物的一些新来源等。Up to now, the N* production from e+e- annihilations has been studied only around charmonium region. Charmonium decays to N*s are analogous to (time-like) EM form factors in that the charm quark annihilation provides a nearly pointlike (ggg) current. Complementary to other sources, such as πN, eN and γN reactions, this new source for N* spectroscopy has a few advantages, such as an isospin filter and a low spin filter. The experimental results on N* from e+e- annihilations and their phenomenological implications are reviewed. Possible new sources on N* production from e+e- annihilations are discussed. 相似文献
109.
Well-annealed 316L stainless steel was first cold rolled to 10% and 20% reductions in thickness and then irradiated by 50 keV He+ to a dose of 1 × 1020 He+/m2 at room temperature. Thermal desorption spectroscopy was used to investigate the helium desorption behaviour at different helium trapping states. The results showed that high-density dislocations had stronger inhibitory effect for helium desorption at temperatures from 800 to 1200 K. Positron annihilation Doppler broadening spectroscopy measurements were used to investigate the distribution of helium irradiation-induced defects. The S–E and ΔS–E plots clearly demonstrated that the helium irradiation-induced defects were trapped and restricted in motion by dislocations. The interaction between dislocations and helium irradiation-induced defects in deformed 316L stainless steel was investigated. 相似文献
110.
Bangyun Xiong Xiuqin Tang Chunqing He Hui Cao Jingpei Huo Jie Luo Haiying He 《Chinese Journal of Physics (Taipei)》2018,56(1):355-361
Tunable mesoporous titania (TiO2) thin films were synthesized via a sol-gel method using an amphiphilic triblock copolymer F38 as the structural template. The dependence of crystalization, pore morphology and interconnectivity of TiO2 films on the weight ratio of F38 was studied by wide-angle X-ray diffraction, field emission scanning electron microscopy and Doppler broadening of positron annihilation radiation spectroscopy based on a slow positron beam. By loading more F38, the crystallization of TiO2 films is enhanced, accompanied by a decrement in oxygen vacancies/grain boundaries. Smaller and isolated mesopores are formed in the films prepared with F38 less than 15?wt%. The pore percolation occurs when the weight ratio of F38 is up to 20?wt% and larger and interconnected worm-like pores are formed. 相似文献