Electroosmotic flow mixing in zigzag microchannels

In this study we performed numerical and experimental investigations into the mixing of EOFs in zigzag microchannels with two different corner geometries, namely sharp corners and flat corners. In the zigzag microchannel with sharp corners, the flow travels more rapidly near the inner wall of the corner than near the outer wall as a result of the higher electric potential drop. The resulting velocity gradient induces a racetrack effect, which enhances diffusion within the fluid and hence improves the mixing performance. The simulation results reveal that the mixing index is approximately 88.83%. However, the sharp-corner geometry causes residual liquid or bubbles to become trapped in the channel at the point where the flow is almost stationary, when the channel is in the process of cleaning. Accordingly, a zigzag microchannel with flat-corner geometry is developed. The flat-corner geometry forms a convergent-divergent type nozzle which not only enhances the mixing performance in the channel, but also prevents the accumulation of residual liquid or bubbles. Scaling analysis reveals that this corner geometry leads to an effective increase in the mixing length. The experimental results reveal that the mixing index is increased to 94.30% in the flat-corner zigzag channel. Hence, the results demonstrate that the mixing index of the flat-corner zigzag channel is better than that of the conventional sharp-corner microchannel. Finally, the results of Taguchi analysis indicate that the attainable mixing index is determined primarily by the number of corners in the microchannel and by the flow passing height at each corner.     

Hyper-Chaotic Color Image Encryption Based on Transformed Zigzag Diffusion and RNA Operation

With increasing utilization of digital multimedia and the Internet, protection on this digital information from cracks has become a hot topic in the communication field. As a path for protecting digital visual information, image encryption plays a crucial role in modern society. In this paper, a novel six-dimensional (6D) hyper-chaotic encryption scheme with three-dimensional (3D) transformed Zigzag diffusion and RNA operation (HCZRNA) is proposed for color images. For this HCZRNA scheme, four phases are included. First, three pseudo-random matrices are generated from the 6D hyper-chaotic system. Second, plaintext color image would be permuted by using the first pseudo-random matrix to convert to an initial cipher image. Third, the initial cipher image is placed on cube for 3D transformed Zigzag diffusion using the second pseudo-random matrix. Finally, the diffused image is converted to RNA codons array and updated through RNA codons tables, which are generated by codons and the third pseudo-random matrix. After four phases, a cipher image is obtained, and the experimental results show that HCZRNA has high resistance against well-known attacks and it is superior to other schemes.     

Non-linear convection due to compositional and thermal buoyancy in Earth's outer core

The linear stability of convection due to compositional and thermal buoyancy in Earth's outer core has been investigated. We have obtained the values of Takens-Bogdanov bifurcation points by plotting graphs of neutral curves corresponding to stationary and oscillatory convection for different values of physical parameters. We have derived a non-linear two-dimensional Landau-Ginzburg equation with real coefficients near the onset of stationary convection at a supercritical pitchfork bifurcation and two non-linear one-dimensional coupled Landau-Ginzburg type equations with complex coefficients near the onset of oscillatory convection at a supercritical Hopf bifurcation. We have studied Nusselt number contribution from a Landau-Ginzburg equation at the onset of stationary convection. We have discussed the stability regions of standing and travelling waves. We have also discussed the occurrence of secondary instabilities such as Eckhaus, zigzag and Benjamin-Feir instabilities. We have also derived the non-linear amplitude equation near the Takens-Bogdanov bifurcation point.     

自适应斜Z字形采样Hadamard单像素成像

单像素成像技术在成像速度和质量上已经取得一定的进展,然而,如何在保证成像质量的前提下提升成像速度仍然是一个待解决的问题。对Hadamard系数矩阵中每条斜列上的系数绝对值求取平均值后,发现其具有迅速减小的特征,基于此发现提出了一种自适应斜Z字形采样方法,以实现预期的成像质量和速度提升。实验结果表明,该方法可以有效减少采样次数与数据采集量,兼顾成像质量的同时提升了成像速度。在相同的采样率下,其成像质量优于顺序采样的单像素成像。     

Adsorption of epoxy and hydroxyl groups on zigzag graphene nanoribbons: Insights from density functional calculations

Density functional theory calculations have been used to investigate the adsorption of epoxy and hydroxyl groups on zigzag graphene nanoribbons. Our calculations show that the adsorbed epoxy groups and both the epoxy and hydroxyl groups on a ribbon surface can be transformed to a carbonyl pair and a carbonyl-hydroxyl pair. The energy barriers of these processes are 1.13 and 0.37 eV, respectively. In contrast to the reduced GO sheets, the stabilities of the carbonyl-hydroxyl pair and the carbonyl pair, with respect to the corresponding initial configuration, strongly depend on the adsorbed sites of groups. The vacancy defect improves the adsorptions of oxygen-containing groups on the surface. Because of the adsorption of new hydroxyl groups, the O-H bond belonging to the carbonyl-hydroxyl pair was highly dissociative and led to the formation of a highly stable carbonyl group with the release of water. The magnetic and electronic properties of the zigzag graphene nanoribbons were well tuned by different oxidized groups.     

Dynamic interaction of a pile with a transversely isotropic elastic half-space under transverse excitations

This investigation is concerned with a mathematical analysis of an elastic circular cylindrical pile embedded in a transversely isotropic half-space under lateral dynamic excitations. A combination of time-harmonic horizontal shear force and moment are applied at the top end of the pile. The boundary value problem is formulated by decomposing the pile-medium system into a fictitious pile and an extended transversely isotropic half-space. A Fredholm integral equation of the second kind governs the interaction problem, whose solution is then computed numerically. Selected results for dynamic compliance bending moment, displacement and slope profiles are presented for different transversely isotropic half-spaces to portray the influence of degree of anisotropy of the medium on various aspects of the solution.     

考虑桩土共同作用的钻孔灌注桩承载性状分析

以盖州北海渔民回迁楼工程为依托,选取其中的C14 号楼为研究对象,对其中两根试桩进行现场静载试验,并获得了Q-S 曲线、侧摩阻力随深度变化曲线、桩身轴力随深度变化曲线及桩土接触面相对位移随深度变化曲线. 然后根据现场勘查资料及有限元参数选取的经验值建立单桩模型,利用大型有限元分析软件ADINA 对单桩进行分析,并根据模拟数据及实测数据利用MATLAB 绘制了各项主要承载特性的对比曲线,一方面验证模型及参数的合理性,另一方面研究桩长对单桩各项主要承载特性的影响. 最后利用单桩验证过的模型及参数建立群桩模型,分析群桩的各项主要承载特性与桩长及桩间距的关系.     

不均匀土中有限长桩的横向瞬态波动

将Timoshenko梁模型引入到弹性地基粱中,土体对桩的作用用连续分布的弹簧来模拟,基于回传射线矩阵法,研究了桩顶受到横向冲击荷载作用下有限长桩的横向瞬态波动．经参数分析表明：土体刚度比对上软下硬、上硬下软两层地基中的有限长桩剪力波和弯矩波影响很大;从挠曲波曲线中难以辨别有无软硬夹层．     

合肥滨湖新区静压管桩单桩极限承载力与终压力关系的载荷试验研究

以合肥滨湖某安置房项目PHC管桩加固工程为依托,利用PHC静压管桩的载荷试验,对静压管桩的单桩极限承载力Qu、静压管桩施工中的终压力Pu进行了研究。得到以碎石层为持力层时,单桩极限承载力与终压力之间的关系,单桩竖向极限承载力小于终压力,且为终压力的60%~90%;通过对长径比(L/d)与压力比(Qu/Pu)进行回归分析,发现两者大致呈双曲线关系。建立了静压管桩单桩极限承载力与终压力之间关系的地区经验公式,便于在静压管桩施工中更加可靠地控制终压力。     

Negative differential resistance and rectification effects in zigzag graphene nanoribbon heterojunctions: Induced by edge oxidation and symmetry concept

By applying non-equilibrium Green's functions (NEGF) in combination with tight-binding (TB) model, we investigate and compare the electronic transport properties of H-terminated zigzag graphene nanoribbon (H/ZGNR) and O-terminated ZGNR/H-terminated ZGNR (O/ZGNR–H/ZGNR) heterostructure under finite bias. Moreover, the effect of width and symmetry on the electronic transport properties of both models is also considered. The results reveal that asymmetric H/ZGNRs have linear I–V characteristics in whole bias range, but symmetric H-ZGNRs show negative differential resistance (NDR) behavior which is inversely proportional to the width of the H/ZGNR. It is also shown that the I–V characteristic of O/ZGNR–H/ZGNR heterostructure shows a rectification effect, whether the geometrical structure is symmetric or asymmetric. The fewer the number of zigzag chains, the bigger the rectification ratio. It should be mentioned that, the rectification ratios of symmetric heterostructures are much bigger than asymmetric one. Transmission spectrum, density of states (DOS), molecular projected self-consistent Hamiltonian (MPSH) and molecular eigenstates are analyzed subsequently to understand the electronic transport properties of these ZGNR devices. Our findings could be used in developing nanoscale rectifiers and NDR devices.