Relationship between basicity and nucleophilicity

The empirical concepts of basicity and nucleophilicity are related but not strictly proportional. Hence, the aim of this study is to help in elucidating the range where both concepts are directly proportional. To do this, the relationship between a recently introduced nucleophilicity index and the proton affinity (PA) of several families of bases has been studied. A good correlation between the PA and the nucleophilicity index using HF and HCN as electrophilic partner has been found. Our studies show that the correlation exists only when the interaction is soft–soft in character and for strong bases with weak acids. However, the relationship is not only valid for exothermic reactions as it has been previously postulated but also for endothermic reactions. Copyright © 2007 John Wiley & Sons, Ltd.     

Relationship between the Structure and Photostability of Decahydroacridine Derivatives

The absorption and photoluminescence spectra of a number of derivatives of 3,3,6,6-tetramethyl-N-phenyl-decahydroacridine-1,8-dione with a regular change in the structure of molecules are investigated. Their electronic structure is calculated. The nature of some of the spectral bands is established. Significant differences in the efficiency of the processes of photochemical transformations of dyes exposed to UV irradiation have been revealed; these changes are attributable to the different donor-acceptor properties of the substituents introduced. A mechanism of phototransformations that agrees with both calculations of the electronic structure of molecules and the spectral-luminescent characteristics of the initial and irradiated compounds is suggested. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 4, pp. 454–459, July–August, 2005.     

Relationship between physical constants and the electron mass

We assume a specific relationship between the different characteristic radii of the electron and from this we obtain another relation between the physical constantse, G, =e ²/c and the mass of the electron.     

Relationship between the auger parameter and the energy gap

In this communication we show that for different semiconductors which do not contain transition metal ions, the shift in the extra-atomic relaxation energy for the metal ion with the core hole-as measured by the Wagner Auger parameter shift with respect to the metallic state-is roughly linearly correlated to the energy gap with a slope approximately equal to −1. The relationship, useful from a practical point of view, can be rationalized using the qualitative concepts of local and non-local screening developed by Veal and Paulikas and the direct relation between the band gap and anion electronegativity.

The core-hole screening for the semiconductors that follow the correlation can be described by the non-local screening mechanism. In this case, the polarized ligands transfer electronic charge to the unfilled s-p metal orbitals which are pulled down to the energy level of the local anion valence band by the core hole. Semiconductors containing transition metal ions, for which local screening mechanisms can occur by transferring the charge from the ligands to the localized d electronic levels, do not follow the correlation. This is due to the fact that the Auger parameter of the cation in the compound is similar to that of the atom in the metallic state. This result indicates that the relaxation energy in the transition metal compounds can be similar to the screening energy in the metallic state.     

Relationship between low-frequency noise and the stability of nonequilibrium structures

V. I. Lenin All-Union Electrical Engineering Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 7, pp. 885–890, July, 1989.     

Relationship between the Faceting of Crystals and Their Formation Mechanism

Doklady Physics - The observed occurrence of nano- and microcrystals without faceting in low-temperature processes of their formation may be due to the nonclassical mechanism of crystal growth by...     

Relationship between the noise-induced persistent current and the dephasing rate

ac noise in disordered conductors causes both dephasing of the electron wave functions and a dc current around a mesoscopic ring. We demonstrate that the dephasing rate tau(-1)(varphi) in long wires and the dc current , induced by the same noise and averaged over an ensemble of small rings, are connected in a remarkably simple way: tau(varphi) = C(beta)e. Here e is an electron charge, and the constant C(beta) approximately 1 depends on the Dyson symmetry class. The relationship seems to agree reasonably with experiments. This suggests that the two puzzles, anomalously large persistent current and the low-temperature saturation of the dephasing, may have a common solution.     

Relationship between Transport Phenomena and Characteristics of the Cluster Structure

Technical Physics - Using a statistical approach, we have estimated the size of water clusters and the number of free molecules participating in transport phenomena. The sizes of clusters and the...     

虹膜区域选取与识别率对应关系分析

在人眼自然张开状态下,虹膜遭受睫毛、眼睑和反射光斑不同程度地干扰而失去了部分信息,因此需要找出虹膜保留面积与虹膜识别率之间的对应关系,从而根据小同的识别率要求估计不同的人眼最小张开程度.利用相关系数识别方法作为评测手段分别在不同的虹膜图库中进行了实验.结果证明,选取靠近瞳孔的虹膜内环区域与整个虹膜区域的比率在大于37.5%时,或者暴露的虹膜两侧扇形的角度大于70.时,就可以获得区分个体的特征量,达到比较稳定的识别率.实验结果还给出了虹膜内环区域而积与识别率的对应关系曲线以及虹膜两侧扇形区域面积与识别率之间的对应关系曲线.     

针对WWW业务的光缓存优化设计

研究了异步光分组网中的输出光缓存问题，与以往不同的是在处理光分组到达时间间隔时采用Weibull分布，以便更有效地描述互联网中的WWW业务流量类型．通过建立基于Weibull分布的排队模型，得到了排队模型中的丢包率的解析式，并根据数值解得出了光缓存系统的丢包率、系统实际利用率、服务窗口利用率以及平均排队时间随光纤延时线单位缓存时间变化的关系曲线．研究结果表明：在不同的业务强度和缓存深度下选取恰当的单位缓存时间，可以优化光缓存系统的性能．     

三棱镜偏向角与入射角关系的研究

根据三棱镜偏向角与入射角的关系,讨论了最小偏向角和最小入射角,为实验中掌握出射光线的移动规律,准确判断最小偏向角的位置提供了理论依据.     

测量结果表达式与不确定度关系的研究与探讨

测量不确定度和结果表达是学习物理实验的重要概念,它是衡量测量结果可靠性和准确程度的标志.本文就这些概念以及它们之间关系一一进行阐述,以有利于学生学习与参考.     

坐标表象与任意力学量表象的关系

通过讨论坐标表象和任意力学量表象的关系,首先分析了具有连续本征值的算符本征函数δ函数归一化的由来,在此基础上研究得出一个结论,即任意力学量算符在坐标表象中的本征函数和坐标算符在任意力学量表象中的本征函数互为共轭复数,又根据这个结论对本征函数封闭性的物理意义做了一种新的解释.