共查询到20条相似文献,搜索用时 15 毫秒
1.
Density functional theory (DFT) studies on adsorption of several gaseous homo- and hetero-diatomic molecules (AB) including H2, O2, N2, NO and CO on external surface of H-capped pristine armchair (5, 5) single-walled carbon nanotube (SWCNT) were conducted. Structures of C70H10 and the corresponding C70H10–AB adducts were fully optimized at the B3LYP/6-311G* level of theory. Calculated HOMO/LUMO energy gaps (Eg), 13C NMR chemical shifts and IR/Raman parameters were analyzed and critically compared with available experimental data. Significant changes of carbon NMR atom chemical shifts (up to −100 ppm) and shielding anisotropies (up to −180 ppm) at sites of addition were observed. Functionalized SWCNTs produced IR and Raman spectra different from the pristine nanotube model. The selective changes in vibrational spectra will help in assigning the topology of functionalization at the nanotube wall. 相似文献
2.
Conformational problems are often subtle but very important in controlling many intricate features in chemistry and biochemistry. We have performed the conformational analysis of glycinamide using NMR experiments and computational studies. 1H NMR experiments suggest the prevalence of intramolecular hydrogen bonded conformation of glycinamide (2B) in acetonitrile, whereas, non-intramolecular hydrogen bonded conformation 2A is favoured in dimethylsulfoxide. The NOESY experiments carried out for glycinamide in DMSO-d6, showed stronger NOE interaction of the NHa-atom of amide group with CH2 than that of NHb-atom confirming the presence of conformer 2A. DFT calculations performed with explicit DMSO molecules also suggested a clear preference for the conformer 2A. The molecular dynamics simulations performed with the explicit DMSO molecules also showed that the intermolecular hydrogen bonding exists between the solvent and solute molecules to stabilize the conformer 2A. The present study sheds light on the debate of conformational preference of neutral glycinamide in the present literature. 相似文献
3.
分析了目前煤矿安全生产远程综合监控系统在数据传输过程中存在的问题,提出了一种基于Zigzag置换的数据传输方法。这种传输方法的实质是数据在传输过程中采用若干次置换,每次置换可以采用不同或相同的方式,通过对数据进行多次置换得到加密文件。文章分析了算法的时间复杂度,实验表明该方法具有时间复杂度低,算法简单等特点。该方法可以有效地解决煤矿安全生产远程综合监控系统中对生产数据传输的安全性和实时性要求。 相似文献
4.
Sets of points for which the Steiner minimal tree is known, are available only for some very special cases. This paper describes the Steiner minimal tree for a set of points forming the vertices of special zigzag lines. 相似文献
5.
基于Zigzag变换的数字图像置乱算法的研究 总被引:3,自引:0,他引:3
图像的隐藏与伪装技术是图像安全方面一个非常重要的研究领域.其中常用的图像置乱算法实现较为复杂,基于Zigzag变换的思想提出了一种新的数字图像置乱算法,并构造了两个具体的置乱变换方法.通过算法的仿真实验和结果分析表明该算法具有较好的置乱效果及较大的周期,并具有一定的抗攻击能力,从图像信息安全性及算法的时间复杂度方面分析,该算法优于Arnold等变换,将该类算法用于图像加密有一定的应用价值. 相似文献
6.
Silvia Abrahão Emilio Insfran José Angel Carsí Marcela Genero 《Information Sciences》2011,181(16):3356-3378
Numerous methods and techniques have been proposed for requirements modeling, although very few have had widespread use in practice. One drawback of requirements modeling methods is that they lack proper empirical evaluations. This means that there is a need for evaluation methods that consider both the theoretical and practical aspects of this type of methods and techniques. In this paper, we present a method for evaluating the quality of requirements modeling methods based on user perceptions. The evaluation method consists of a theoretical model that explains the relevant dimensions of quality for requirements modeling methods, along with a practical instrument with which to measure these quality dimensions. Basically, it allows us to predict the acceptance of a particular requirements modeling method in practice, based on the effort of applying the method, the quality of the requirements artifacts produced, and the user perceptions with regard to the quality of the method. The paper also presents an empirical test of the proposed method for evaluating a Rational Unified Process (RUP) extension for requirements modeling. That test was carried out through a family of experiments conducted with students and practitioners and provides evidence of the usefulness of the evaluation method proposed. 相似文献
7.
Milling is one of the common machining methods that cannot be abandoned especially for machining of metallic materials. The
cutters with appropriate cutting parameters remove material from the workpiece. Surface roughness has the major influence
on both obtaining dimensional accuracy and quality of the product. A number of cutter path strategies are employed to obtain
the required surface quality. Zigzag machining is one of the mostly appealing cutting processes. Modeling of surface roughness
with traditional methods often results in inadequate solutions and can be very costly in terms of the efforts and the time
spent. In this research Genetic Programming (GP) has employed to predict a surface roughness model based on the experimental
data. The model has produced an accuracy of 86.43%. In order to compare GP performance, Artificial Neural Network (ANN) and
Adaptive Neuro Fuzzy Inference System (ANFIS) techniques were utilized. It was seen that the surface roughness model produced
by GP not only outperforms but also enables to produce more explicit models than of the other techniques. The effective parameters
can easily be investigated based on the appearances in the model and they can be used in prediction of surface roughness in
zigzag machining process. 相似文献
8.
Density functional theory (DFT) prediction of cis and trans perhydro- and perfluoro-2-methylene-4,5-dimethyl-1,3-dioxolanes structure, supported by vibrational analysis and calculation of multinuclear isotropic nuclear magnetic resonance (NMR) shieldings and indirect spin–spin couplings (SSCCs) was performed. The performance of the used methodology was verified on 1,3-dioxolane selected as model compound. The structures of hydrogenated and fluorinated monomers of POF materials were calculated using B3LYP and BLYP density functionals combined with 6-311++G(3df,2pd) basis set. The BLYP/6-311++G(3df,2pd) level of theory was suggested for vibrational analysis. Gauge independent atomic orbitals (GIAO) calculations were applied to distinguish between cis and trans isomers of the title 1,3-dioxolanes. For obtaining both accurate nuclear shieldings and individual spin–spin coupling constants the BHandH/aug-pcJ-2 level of theory was chosen. The protocol used for the calculations nicely showed remarkable differences in vibrational spectra and NMR parameters of cis and trans isomers of the studied 1,3-dioxolane derivatives before and after fluorination. 相似文献
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基于DCT与双随机矩阵的图像数字水印方案 总被引:2,自引:0,他引:2
在水印的嵌入与检测过程中用到了3个密钥,双随机矩阵和嵌入尺度作为秘密钥保证了水印嵌入的安全性,DCT系数矩阵之和则作为公开钥用于水印信息的部分认证.文中算法实现了将图像作为水印信息隐藏到载体图像中;把水印信息的每一点都通过某种方式嵌入到载体图像的多个点上;使得攻击者在不知道秘密钥的情况下无法删除或改变水印信息.通过实验对嵌入和检测结果进行了比较和分析,表明该算法具有很好的稳健性. 相似文献
12.
《Calphad》2018
Thermodynamic stability of the MoNi2 and MoNi8 compounds has been discussed in detail, and decision about their inclusion in thermodynamic assessment of the Mo–Ni system has been made. Enthalpies of formation of all Mo–Ni intermetallic compounds have been determined with the help of DFT calculations whereas enthalpies of mixing in the solid solutions are estimated using special quasi-random structures. Experimental phase equilibria information gathered in our recent partial investigation of the Mo–Ni system has been incorporated and thermodynamic reassessment of the Mo–Ni system has been performed with the help of the CALPHAD method. The calculated Mo–Ni phase diagram showed good agreement with selected experimental information. 相似文献
13.
First-principles local density functional calculation of the electronic structure and work function of zigzag single-wall carbon nanotubes (SWCNTs) and graphene under strain are presented. We found that there is a small circumference strain even for unstrained zigzag SWCNTs that release the curvature energy of the tube. Therefore, we propose that there are two effects contributing to the opening of the band gap of unstrained (3q, 0) SWCNTs: the electron transfer enhancement effect and the circumference strain effect. We show that the band gap and work function of strained zigzag SWCNTs can be successfully estimated from the band structure and work function of strained graphene based on the zone folding method with circumference strain effect. The circumference strain effect is crucial to obtain a correct result. The rate of change of the band gap with respect to the strain for zigzag SWCNTs is almost independent of the value of the strain and the radius of the tube. 相似文献
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Developing an explanatory theoretical model of website usability is pivotal for understanding usable website design. Such a model would explain and help predict the effects of website usability on online purchases, but few studies have been devoted to such model development. As an exploratory effort, we adopted and extended Kaplan's landscape preference model by including factors of legibility, coherence, variety, and mystery, and examined their effect on cognitive and affective appraisals and their impact on purchase intention. A field survey with 495 online customers using two different categories of websites was conducted to validate the research model. A multi-group analysis with gender and age was performed to cross-validate it. Our findings demonstrated that the proposed model explained a large amount of the variance of purchase intention, invariant across different subgroups. Key implications for theory and practice are discussed. 相似文献
16.
M.C. HorrilloAuthor Vitae J. MartíAuthor VitaeD. MatataguiAuthor Vitae J.P. SantosAuthor VitaeI. SayagoAuthor Vitae J. GutiérrezAuthor VitaeI. Martin-FernandezAuthor Vitae P. IvanovAuthor VitaeI. GràciaAuthor Vitae C. CanéAuthor Vitae 《Sensors and actuators. B, Chemical》2011,157(1):253-259
In this work we report on the fabrication and characterization of single-walled carbon nanotubes (SWCNTs) as sensitive layers for the detection of simulants of Chemical Warfare Agents (CWAs). The microsensor fabrication has been achieved after the wafer scale integration of the selective synthesis of SWCNTs as sensitive layer. Their electrical characterization has been carried out by measuring the resistance changes of the SWCNT networks when interacting with very low concentrations of CWA simulants such as dimethyl methyl phosphonate (DMMP), dipropylene glycol methyl ether (DPGME) and dimethylacetamide (DMA) at low temperatures, which are simulants of Sarin, Nitrogen Mustard and Distilled Mustard, respectively. 相似文献
17.
In this paper, the two-dimensional Warped Discrete Fourier Transform (2-D WDFT) is developed based on the concept of the 1-D WDFT. An exact computation algorithm is developed for 2-D WDFT based on matrix factorizing with special structure. A fast algorithm is then proposed to reduce greatly the computational complexity of the inverse 2-D WDFT. Finally, numerical examples are given to show the efficiency of the proposed approach. 相似文献
18.
本文提出一种基于时空混沌系统的图像加密算法。首先对明文图像进行Zigzag方式扫描置乱,再对置乱后的图像分块;然后用Logistic混沌系统生成的伪随机序列对其进行置乱,置乱结束后对其进行整数小波变换,利用基于耦合映像格子CML的混沌系统生成三个伪随机序列对低频小波系数进行置乱操作,同时对低频小波系数进行扩散,然后进行整数小波逆变换;最后再由基于CML的混沌系统生成两个伪随机序列对图像像素值进行扩散操作,得到最终的加密图像。经测试,该算法具有良好的加密性能,可以有效抵挡差分、明文等攻击。 相似文献
19.
In this paper, the two-dimensional Warped Discrete Fourier Transform(2-D WDFT) is developed based on the concept of the 1-D WDFT. An exact computation algorithm is developed for 2-D WDFT based on matrix factorizing with special structure. A fast algorithm is then proposed to reduce greatly the computational complexity of the inverse 2-D WDFT. Finally, numerical examples are given to show the efficiency of the proposed approach. 相似文献