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921.
ZHOU Shu-Hua 《中国物理C(英文版)》2011,35(5)
The possible change of nuclear decay rates in different environments has long been an interesting topic due to its importance not only in nuclear physics but also in astrophysics, geological dating, condensed matter physics, etc. The progress in the investigation of variations in nuclear decay rates are reviewed. 相似文献
922.
In this paper, temperature-dependent birefringence theory of liquid crystal is used to investigate the temperature effect on the threshold voltage. An expression for describing the non-linear relationship between the threshold voltage and temperature is deduced. In addition, we theoretically discuss the temperature effect on the transmitted ratio of the namatic twisted liquid crystal without the applied voltage and with the applied voltage. It is found that the transmitted ratio is decreased linearly as temperature is increased when the liquid crystal is not applied with voltage, but the transmitted ratio is increased linearly as temperature is increased when the liquid crystal is applied with voltage. The threshold voltages and the transmitted ratio are measured at different temperatures. The experimental data are consistent with the theoretical calculated results. 相似文献
923.
分析了有机化学教学中存在的突出问题,提出了提高有机化学教学效果的建议。 相似文献
924.
复合土工膜作为一种新型的防渗结构体应用于堆石坝工程,效果突出,但是在土工膜的锚固处容易产生应力集中,出现“端部固定效应”.本文结合国外某工程实例,应用商业软件FLAC3D,采用三维显式有限差分法分别对不同锚固方式情况下复合土工膜的应力、变形进行计算分析.结果表明,采用不同的土工膜锚固方式对其受力有一定的影响,在实际工程中,应采用合适的复合土工膜锚固方式改善土工膜的受力状态,减小“端部固定效应”的影响 相似文献
925.
本文从转载点喷雾、掘进机内外喷雾、水炮弹、除尘器四个方面阐述了在机掘工作面所采用的综合防尘技术,在实际生产中应用后,煤尘得到了有效的控制,达到了理想的防尘效果。 相似文献
926.
Spontaneous excitation of a circularly accelerated atom coupled with vacuum Dirac field fluctuations
We study the spontaneous excitation of a circularly accelerated atom coupled with vacuum Dirac field fluctuations by separately calculating the contribution to the excitation rate of vacuum fluctuations and a cross term which involves both vacuum fluctuations and radiation reaction, and demonstrate that although the spontaneous excitation for the atom in its ground state would occur in vacuum, such atoms in circular motion do not perceive a pure thermal radiation as their counterparts in linear acceleration do since the transition rates of the atom do not contain the Planckian factor characterizing a thermal bath. We also find that the contribution of the cross term that plays the same role as that of radiation reaction in the scalar and electromagnetic fields cases differs for atoms in circular motion from those in linear acceleration. This suggests that the conclusion drawn for atoms coupled with the scalar and electromagnetic fields that the contribution of radiation reaction to the mean rate of change of atomic energy does not vary as the trajectory of the atom changes from linear acceleration to circular motion is not a general trait that applies to the Dirac field where the role of radiation reaction is played by the cross term. 相似文献
927.
928.
Günter Paulus Schiemenz 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):185-202
Abstract Contrary to claims in the literature, the 31P NMR signal positions of ortho-dimethylaminomethyl-substituted triarylphosphines do not provide evidence for hypercoordination at phosphorus; the observed highfield shifts relative to triphenylphosphine are rather due to the ortho-effect. In (8-dimethylamino-naphth-1-yl)phosphines, the signal positions similar to that of triphenylphosphine are the result of the highfield ortho-effect and a lowfield peri-substituent effect of about the same magnitude whose nature remains to be explored. 相似文献
929.
《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):2447-2456
We showed that imidoyl- and phosphaethenyl(alkali metals) would thermodynamically prefer the Z-configuration. The bond model analysis of the electronic structures showed that the Z-preference should originate from 1,2-metallobridging by the delocalization of lone pairs on N or P to vacant p-orbitals of the alkali metals and from the antiperiplanar effect of the delocalization from σ C—M to σ? N(P)—R 2 and from n N(P) to the C—R1. The Z-preference increases by more electron-withdrawing groups at the carbon atom of the double bond. However, substitution at the nitrogen/phosphorus results in E-preference because of 1,4-chelation of the lone pair of the substituents to alkali metals. Most of halogen derivatives were not stable and eliminate metal halides. 相似文献
930.
Zaira Domínguez Javier Hernández Lorena Silva-Gutiérrez Magali Salas-Reyes Mario Sánchez Gabriel Merino 《Phosphorus, sulfur, and silicon and the related elements》2013,188(4):772-784
The effect of electron-withdrawing (EW) and electron-releasing (ER) substituents on the 31P NMR chemical shifts and the structural parameters of a series of tris-(p-X-aryl)selenophosphates is reported in this article. Similarly to O-aryl phosphates and O-aryl thiophosphates, EW groups attached to aromatic rings induce a shielding effect on the 31P NMR signal. After a detailed experimental and theoretical analysis, we confirmed that the selenium atom is the main part responsible for the charge density transfer toward phosphorus through a back-bonding effect. The obtained 1JP-Se values for the complete series agree with this observation. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. 相似文献