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在前文工作的基础上,结合MNDO/EHMO分子轨道方法和自然杂化轨道方法,具体计算了CC键和CP键的核自旋偶合常数.计算结果表明,1JCC和1JCP主要由成键原子的轨道杂化作用和键极性这两种结构因素所决定.为从简单价键理论角度解释和计算1JCC和1JCP值提供了简便直观的方法. 相似文献
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Finite-difference numerical simulation of ultrasound propagation in complex media such as cancellous bone represents a fertile alternative to analytical approaches because it can manage the complex 3D bone structure by coupling the numerical computation with 3D numerical models of bone microarchitecture obtained from high-resolution imaging modalities. The objective of this work was to assess in silico the sensitivity of ultrasound parameters to controlled changes of microarchitecture and variation of elastic constants. The simulation software uses a finite-difference approach based on the Virieux numerical scheme. An incident plane wave was propagated through a volume of bone of approximately 5 x 5 x 8 mm(3). The volumes were reconstructed from high-resolution micro-computed tomography data. An iterative numerical scenario of "virtual osteoporosis" was implemented using a dedicated image processing algorithm in order to modify the initial 3D microstructures. Numerical computations of wave propagation were performed at each step of the process. The sensitivity to bone material properties was also tested by changing the elastic constants of bone tissue. Our results suggest that ultrasonic variables (slope of the frequency-dependent attenuation coefficient and speed of sound) are mostly influenced by bone volume fraction. However, material properties and structure also appear to play a role. The impact of modifications of the stiffness coefficients remained lower than the variability caused by structural variations. This study emphasizes the potential of numerical computations tools coupled to realistic 3D structures to elucidate the physical mechanisms of interaction between ultrasound and bone structure and to assess the sensitivity of ultrasound variables to different bone properties. 相似文献
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赵乃良 《高校应用数学学报(A辑)》1996,(1):91-96
Nira Dyn等提出的四点插值法是一种典型的自由曲线离散造型方法,但该方法不能控制插值点的切向。本文利用薄板样很可能 量的极小化原理给出了具有切向控制的四点分插值条件。用户可以方便地交互控制任一插值点的切向,使得四点插值法更为有效和实用。 相似文献
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Yasuo Yamakoshi Takatoshi Nagano Jan CC Hu Fumiko Yamakoshi James P Simmer 《BMC biochemistry》2011,12(1):6
Background
Dentin sialophosphoprotein (Dspp) is a multidomain, secreted protein that is critical for the formation of tooth dentin. Mutations in DSPP cause inherited dentin defects categorized as dentin dysplasia type II and dentinogenesis imperfecta type II and type III. Dentin sialoprotein (Dsp), the N-terminal domain of dentin sialophosphoprotein (Dspp), is a highly glycosylated proteoglycan, but little is known about the number, character, and attachment sites of its carbohydrate moieties. 相似文献
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