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| 1 | 太阳紫外辐射增加对材料的作用显示文摘合成高分子,天然生物高分子以及其它一些商品材料都要受到太阳紫外辐射(UV)的有害作用。这些材料,特别是塑料在需要经常曝露于日光的环境下的应用,只有利用光稳定剂和(或)表面处理对它们进行保护才有可能。因此,由于部分臭氧减少引起的日光UV含量的任何增高都将增加这些材料的光降解速率,减少它们在户外的应用寿命。这种由日光中UV辐射增加引起的破坏的性质和程度可用作用光谱(action spectra)进行定量表征。虽然在文献上报道了几个高分子的作用光谱,现有资料常不足以对增加的破坏进行可靠的估计。高分子材料的配方,所使用的破坏判据乃至解释数据的方式都常常能影响结果。然而,从已有的资料可清楚看出,短波UV-B过程是引起曝露于日光下的高分子的光破坏的主要原因,这些破坏包括从变色直到整体机械性能的丧失。在许多情况下这些变化仍未有清楚的分子水平的解释。可以用在高分子配方中加入更多量常用光稳定剂的方法来减轻日光中增加的UV含量的作用。但是,这个方法包含了以下假设:a)在日光光谱改变了的情况下这些光稳定剂仍继续有效;b)这些稳定剂曝露于富UV的日光下自身是光稳定的;c)在足够低的深度下它们仍足够有效以达到经济的目的。尚缺乏有关这方面的实验资料。正在进行的研究,特别是有关高分子在极端环境条件下曝露的研究,可能会使这些问题变得更加清晰。用光稳定性更好的塑料和其它材料来代替原来的材料也是一个引人注意的解决方法。上述两种解决方法都将增加应用的塑料产品的价格。随着塑料大量取代传统的材料在许多方面的应用,这是需要考虑的重要问题,尤其在发展中国家更是如此。 | Anthony L.Andrady Mohamed B.Amin S.Haleem Hamid 胡兴洲 Ayako Torikai | 1995 | 人类环境杂志1995，24，3： | 4 |
| 2 | Optoelectronic Response of GeZn_(2)O_(4) through the Modified Becke-Johnson Potential显示文摘A first-principles technique capable of describing the nearly excited states of semiconductors and insulators,namely the modified Becke–Johnson(mBJ)potential approximation,is used to investigate the electronic band structure and optical properties of spinel oxides:GeZn_(2)O_(4).The predicted band gaps using the mBJ approximation are significantly more accurate than the proposed previous theoretical work using the common LDA and GGA.Band gap dependent optical parameters,like the dielectric constant,index of refraction,reflectivity and optical conductivity are calculated and analyzed.The results from the dielectric constant shows that the numerical value of the static dielectric,after dropping constantly,becomes less than zero and the material exhibits metallic behavior.The refractive index also drops below unity for photons higher than 18 eV,which indicates that the velocities of incident photons are greater than the velocity of light.However,these phenomena can be explained by the fact that a signal must be transmitted as a wave packet rather than a monochromatic wave.This comprehensive theoretical study of the optoelectronic properties predicts that these materials can effectively be used in optical devices. | Iftikhar Ahmad B.Amin M.Maqbool S.Muhammad G.Murtaza S.Ali N.A.Noor | 2012 | Chinese Physics Letters2012，29，9： | 0 |
| 3 | Robust Half-Metallicity in a Chromium-Substituted AlN显示文摘We investigate half metallicity in a chromium(Cr)-substituted AlN dilute magnetic semiconductor using the full-potential linearized augmented plane-wave method.Our results show that Al_(0.75)Cr_(0.25)N is half metal and holds a net integer magnetic moment of 3μβwith lattice compression.The half−metallic nature is maintained from the relaxed lattice constant 4.36Åto 4.09Å.An abrupt change of the physical properties is observed at a robust transition lattice constant of 4.09Å,and the material transforms from half metal to metal.We find that up to 6%compression,the material maintains its half-metallic nature.Furthermore,we also confirm that the origin of ferromagnetism in Al_(0.75)Cr_(0.25)N is double exchange. | S.Arif Iftikhar Ahmad B.Amin H.A.Rahnamaye Aliabad | 2011 | Chinese Physics Letters2011，28，10： | 0 |
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