碳纳米管吸附铜原子的密度泛函理论研究

采用密度泛函方法对铜原子在有限长（5,5）椅型单壁碳纳米管的吸附行为进行了研究.计算结果表明,铜原子吸附在管外壁要比吸附在管内壁能量上更为有利,在管外壁碳原子顶位吸附最佳,属于明显的化学吸附.且用前线轨道理论对其成键特性进行了分析,表明在顶位吸附时主要由铜原子的4s轨道电子与碳纳米管中耦合的σ-π键形成新的σ键.此外还对比计算了两种典型位置电子密度,发现顶位吸附的成键中有更大的电子云重叠.进一步表明在某些情况下铜碳原子可以成键. 关键词： 碳纳米管 铜原子 成键特性     

荧光光谱成像在生物芯片蛋白量化分析中的应用研究

采用荧光光谱成像并结合椭圆偏振技术研究了３-氨基３-乙氧基硅烷(APTES)修饰及其与戊二醛(APTES-Glu)共同修饰的两种不同表面上固定的羊抗人抗体活性和数量及其荧光免疫结合。研究结果表明：应用荧光光谱成像在APTES-Glu表面上检测到的FITC标记人血清蛋白分子的数量为APTES表面结合的2.8倍,而应用椭圆偏振技术在前者表面上检测到的FITC标记人血清蛋白分子的数量为后者表面上的2.2倍。这个结果说明：在荧光免疫检测中,荧光光谱成像完全可用于分析不同表面固定蛋白的免疫活性和半定量的检测。     

氧掺杂对钠在石墨烯上吸附性能的影响

采用基于密度泛函理论的第一性原理方法,研究了本征石墨烯(P-graphene)和氧掺杂的石墨烯(O-graphene)吸附钠原子的吸附能、电荷密度、态密度以及储存量.结果表明,两种石墨烯中,钠原子的最佳吸附位置都是H位. O-graphene对钠原子的吸附能是-4.347 eV,比P-graphene对钠原子的吸附能(-0.71 eV)低很多. O-graphene中钠原子与氧原子和碳原子发生轨道杂化,P-graphene中没有杂化现象. O-graphene能够吸附10个钠原子,较P-graphene多.因此,O-graphene更适合储钠.     

Surface effects in plastic deformation of metals

It is now accepted that the appearance of slip bands on the surface of a plastically deformed metal is evidence that the deformation is not homogeneous but is concentrated on relatively few atomic planes. Recent microscopical experiments have suggested that this conclusion is only valid in the later stages of deformation and that the first fractional per cent of strain is much more nearly homogeneous. Theories to account for both these stages of deformation are examined in the light of microscopical evidence.

The validity of conclusions about internal processes based on experiments on the surface is discussed; it is shown that the surface finish affects not only the appearance of internal processes but also the processes themselves.

In cases where the deformation is not homogeneous the balance of evidence is that it is also not continuous in time: instead, slip on an active slip plane tends to a limit which is reached either gradually or suddenly depending on the nature of the metal and the conditions of stress. The same processes which stop slip on the active planes produce general hardening of the metal. However, slip can restart on or near to former slip planes as a result of mechanisms activated by temperature and stress, and can, in favourable cases, continue until fracture. Therefore slip bands, the sources of hardening, are also places of weakness.     

Evaluation of activity through dynamic laser speckle using the absolute value of the differences

When a material is illuminated with a laser beam, it is possible to verify a phenomenon known as dynamic speckle or biospeckle. It exhibits an interference image that contains lots of information about the process being analyzed, and one of its most important applications is determining the activity quantity from the materials under study. The numerical analysis of the dynamic speckle images can be carried out by means of a co-occurrence matrix (COM) that assembles the intensity distributions of a speckle pattern with regard to time. An operational method that is widely used on the biospeckle COMs is the inertia moment (IM). Some studies demonstrate that IM is more sensitive on analyzing processes that involve high activities or high frequencies if considering the spectral analysis of the phenomena. However, when this variation is not so intense, this method is less efficient. For low variations on the activity or low frequencies, qualitative methods such as wavelet based entropy and cross-spectrum analysis have presented better results; however, processes that are in the intermediate range of activity are not well covered for any of these techniques mentioned earlier. The contribution of this research is to present an alternative approach, based on the absolute value of the differences (AVD) when handling the biospeckle COM. By using AVD on the seed-drying process, was found that it is efficient on verifying the behavior of the intermediate frequencies. Accumulated sum test (Coates and Diggle) showed that AVD and IM are generated from the same stochastic process. Thus, AVD is useful as an alternative method in some cases or even as a complementary tool for analyzing the dynamic speckle, mainly when the information of the activity is not present on high frequencies.     

Dynamical theory of a bidimensional system with an infinite number of degrees of freedom

The dynamical theory of a bidimensional model of hard squares with elastic collisions is presented. The time evolution is shown to exist on a large class of infinite configurations. Moreover, it is proved that any equilibrium state, that is any solution of the equilibrium equations, is concentrated on this set of allowed initial configurations and is invariant under the time evolution.     

变形及电场作用对石墨烯电学特性影响的第一性原理计算

利用基于密度泛函理论的第一性原理方法,系统研究了变形、电场及共同作用对石墨烯电学特性影响的电子机理.研究表明,本征石墨烯的能隙及态密度值在费米能级处均为0,呈现出半金属特性;在一定的变形量下对石墨烯施加剪切、拉伸、扭转及弯曲变形作用,发现剪切和扭转变形对打开石墨烯能隙的作用明显;对本征石墨烯施加不同方向的电场,可知010电场方向对打开石墨烯能隙的作用效果最强.这是因为该电场方向下石墨烯C-C原子间的布居数正值较大,成键键能较高,而负值数值较小,反键键能较低;线性增加电场强度,石墨烯的能隙呈线性增长势;变形及电场共同作用下,外加电场提高了变形对打开石墨烯能隙的作用效果,但不及两种外场叠加的作用效果.     

Method for the determination of dopant concentrations of luminescent ions

We report on a new method for determining dopant ion concentrations in laser materials. This method is based on optical absorption spectroscopy. In contrast to other methods used to measure the dopant concentration that are based on absorption measurements, this method does not require the knowledge of the absorption cross sections. An advantage of this method compared to the micro probe analysis is that only concentrations of dopant ions of a certain valency, which are luminescent, are detected. The method is sensitive especially for small doping concentrations of ions with high absorption cross sections. Another application of this method is the determination of the ratio between luminescent dopant ions to the total number of dopant ions in the case that not all dopant ions are on crystal sites that allow for optical transitions.     

富勒烯C32分子器件结构和传导特性的理论研究

利用基于第一性原理的密度泛函理论(DFT)和非平衡格林函数(NEGF)方法对富勒烯C32分子及在C32的距离最远的两个碳原子处外接Li电极的C32分子器件进行了电子结构、电子传输性质的研究。设计了C32笼内嵌入Mg原子,外接Li电极的分子器件。通过计算,得出了两个分子器件的电子传输谱,分析了他们的电子结构和电子输运特性。说明了C32分子器件的电子传输主要集中于C32分子的壳表上,并且分子球的内侧和外侧的电子传输相近似。在C32分子内部嵌入Mg原子后,分子器件的电子传输仍主要集中在分子表面上,但在系统Mg@C32中,表面内侧的电子传输要比表面外侧的电子传输强。通过比较,结果表明两种富勒烯分子的电子传输性能顺序为Mg@C32>C32。     

Optimal quantum estimation of the coupling constant of Jaynes-Cummings interaction

We address the estimation of the coupling constant of the Jaynes-Cummings Hamiltonian for a coupled qubit-oscillator system. We evaluate the quantum Fisher Information (QFI) for the system undergone the Jaynes-Cummings evolution, considering that the probe initial state is prepared in a Fock state for the oscillator and in a generic pure state for the qubit; we obtain that the QFI is exactly equal to the number of excitations present in the probe state. We then focus on the two subsystems, namely the qubit and the oscillator alone, deriving the two QFIs of the two reduced states, and comparing them with the previous result. Next we focus on possible measurements on the system, and we find out that if population measurement on the qubit and Fock number measurement on the oscillator are performed together, the Cramer-Rao bound is saturated, that is the corresponding Fisher Information (FI) is always equal to the QFI. We compare also the performances of these energy measurements performed alone, that is when one of the two subsystem is ignored. We show that, when the qubit is prepared in either the ground or the excited state, the local measurements are still optimal. Finally we investigate the case when the harmonic oscillator is prepared in a thermal state and observe how, particularly for small values of the coupling constant, the QFI increases with the average number of thermal photons of the initial state.     

Application of Mössbauer Spectroscopy to the Study of Corrosion

Corrosion research, and the need to fully understand the effects that environmental conditions have on the performance of structural steels, is one area in which Mössbauer spectroscopy has become a required analytical technique. This is in part due to the need to identify and quantify the nanophase iron oxides that form on and protect certain structural steels, and that are nearly transparent to most other spectroscopic techniques. A review is given of the most recent Mössbauer characterization of rusts that have formed on structural steels exposed to different environments. Mössbauer spectroscopy is playing an important role in a new corrosion program in the United States in which steel bridges, old and new, are being evaluated for corrosion problems that may reduce their serviceable lifetimes. Mössbauer spectroscopy has been used to characterize the corrosion products that form the protective patina on weathering steel, as well those that form in adverse environments in which the oxide coating is not adherent or protective to the steel. Mössbauer spectroscopy has also become an important analytical technique for investigating the corrosion products that have formed on archeological artifacts, and it is providing guidance to aid in the removal of the oxides necessary for their preservation.     

基底表面纳米织构对非晶四面体碳膜结构和摩擦特性的影响研究

本文利用离子束表面改性技术对基底表面进行不同时间的轰击, 形成不同规则的纳米织构, 对不同织构的变化规律进行了研究, 同时, 利用磁过滤真空阴极电弧技术, 在具有不同纳米织构的各基底上沉积相同时间的四面体非晶碳薄膜. 采用原子力显微镜对各基底的织构进行形貌分析, 结果表明, 高能粒子束的轰击对基底表面形貌有较大的影响, 根据离子束轰击时间的不同, 可以在基底表面形成各种不同规则的纳米织构, 轰击15 min后发现基底表面形成点阵纳米织构, 之后随着时间的增加, 基本维持点阵结构. 通过X射线光电子能谱仪和摩擦磨损试验仪对沉积在具有不同织构的基底上的ta-C薄膜进行测试, 研究表明, 基底表面纳米织构的非晶层结构引起薄膜内部sp³键的含量降低, 释放了薄膜的内应力, 同时发现基底表面纳米织构将ta-C薄膜磨损时间从不足10 min提高到约70 min, 有效提高了薄膜的耐磨性.     

Effect of compressibility on the stability of a perfectly conducting plasma jet of plane and cylindrical geometry

The effect of compressibility on the stability of plasma jets with boundaries (tangential discontinuity surfaces) of different configurations is studied. It is shown that, depending on the relationship between the MHD parameters of the jet and the surrounding medium, the compressibility may have a stabilizing or a destabilizing effect. It is also shown that, under certain conditions, the compressibility effect depends on the perturbation wavelength.     

钠在空位石墨烯上吸附性能的研究

采用基于密度泛函理论的第一性原理方法,研究了本征石墨烯和空位石墨烯吸附钠原子的电荷密度、吸附能、态密度和储存量.结果表明,在两种石墨烯中,钠原子的最佳吸附位置都为H位.空位石墨烯对钠原子的吸附能是-2. 46 eV,约为本征石墨烯对钠原子吸附能的3. 4倍;钠原子与空位石墨烯中的碳原子发生轨道杂化,而与本征石墨烯没发生轨道杂化现象.存在一个空位的石墨烯能够吸附5个钠原子,与本征石墨烯相比显著提高.因此,空位石墨烯有望成为一种潜在的储钠材料.     

缺陷对钠在石墨烯上吸附性能的影响

采用基于密度泛函理论的第一性原理方法,研究了本征石墨烯和缺陷石墨烯吸附钠原子的电荷密度、吸附能、态密度和储存量.结果表明,本征石墨烯中,钠原子的最佳吸附位置为H位,缺陷石墨烯中,钠原子的最佳吸附位置为T_D位.缺陷石墨烯对钠原子的吸附能是-4.423 eV,约为本征石墨烯对钠原子吸附能的2.5倍;钠原子与缺陷石墨烯中的碳原子发生轨道杂化,而与本征石墨烯没有发生轨道杂化现象.缺陷石墨烯能够吸附10个钠原子,与本征石墨烯相比显著提高.因此,缺陷石墨烯有望成为一种潜在的储钠材料.     

卷曲效应对单壁碳纳米管电子结构的影响

利用计入卷曲效应的单壁碳纳米管(SWCNT)的能量色散关系,计算最低导带的电子速度及有效质量,并与不计入卷曲效应的结果进行了比较.计算结果表明:卷曲效应对电子速度及有效质量的影响与SWCNT的类型密切相关,金属锯齿型SWCNT对卷曲效应最为敏感,其次是扶手椅型SWCNT,最不敏感的是半导体锯齿型SWCNT.由此可以推断,卷曲效应对金属锯齿型SWCNT电子结构及低偏压输运特性影响最大,其次是扶手椅型SWCNT,影响最不明显的是半导体锯齿型SWCNT.这些结果与实验测量及密度泛函理论计算结果完全一致. 关键词： 单壁碳纳米管 卷曲效应 电子速度 电子有效质量     

The effect of anisotropy of a rough sea surface on the generation of acoustic radiation

A model that relates the frequency-angular characteristics of wind waves on the sea surface to the frequency spectrum of acoustic radiation generated by them is constructed. Based on empirical wave energy distribution functions, it is shown that, in the vicinity of the peak of the wind wave spectrum, the intensity of acoustic radiation strongly depends on the model chosen for the angular distribution function ?(α) and on its parameters. At high frequencies, four to five times higher than the dominant wave frequency, it is possible to assume that, to a first approximation, ?(α) = const. In the intermediate frequency range, between the dominant frequency and the high frequencies, the predominant contribution to the sound radiation is made by the waves that travel in the direction close to orthogonal with respect to the wind.     

Theoretical study of the effect of spin-selective adsorption of water molecules on MgO surface

The effect of spin-selective adsorption of water molecules on the surface of MgO crystal is theoretically studied. The study is performed using two different approaches, i.e., quantum-chemical simulation and an analytical calculation in a quasiclassical approximation. The adsorption energy is calculated using the B3LYP density functional and the 6–311G* basis set. The calculated value of the adsorption energy 0.70 eV agrees well with an experimental value of 0.65 eV. It is established that the energy difference of adsorbed ortho- and para-water molecules is negligible and, thus, the difference of the adsorption energies is completely determined by the energy difference of free molecules in ortho- and para-states. It follows from the analytical calculation that this result is essentially general and is related not only to an MgO surface, but to any other surface on which the energy barrier for rotation of the adsorbed molecule is much larger than the corresponding rotational constant. Based on this, the conclusion is reached that the effect of spin-selective adsorption on these surfaces should not be observed under normal conditions.     

Effect of coherence property of incident light on prism waveguide coupling

The accurate reflection coefficient of prism waveguide coupler that takes coherence property of incident light into account is obtained at first. Based on the reflection coefficient, the effect of coherence property of incident light on prism coupling is discussed in this work. It is shown that extra damping in waveguide caused by the coherence property is larger for high-order resonant mode than that for low-order mode. For 100 fs Gaussian pulses incidence, the reflected spectra at different resonant modes are obtained theoretically and experimentally, which show that coherence property has a strong effect on prism coupling at high-order modes.     

Effect of bending anisotropy on the 3D conformation of short DNA loops

The equilibrium three dimensional shape of relatively short loops of DNA is studied using an elastic model that takes into account anisotropy in bending rigidities. Using a reasonable estimate for the anisotropy, it is found that cyclized DNA with lengths that are not integer multiples of the pitch take on nontrivial shapes that involve bending out of planes and formation of kinks. The effect of sequence inhomogeneity on the shape of DNA is addressed, and shown to enhance the geometrical features. These findings could shed some light on the role of DNA conformation in protein-DNA interactions.