Metastable face-centered cubic ruthenium-based binary alloy for efficient alkaline hydrogen oxidation electrocatalysis

Metastable nanostructured electrocatalyst with a completely different surface environment compared to conventional phase-based electrocatalyst often shows distinctive catalytic property.Although Ru-based electrocatalysts have been widely investigated toward hydrogen oxidation reaction(HOR)under alkaline electrolytes,these studies are mostly limited to conventional hexagonal-close-packed(hcp)phase,mainly arising from the lack of sufficient synthesis strategies.In this study,we report the precise synthesis of metastable binary RuW alloy with face-centered-cubic(fcc)phase.We find that the introduction of W can serve as fcc phase seeds and reduce the formation energy of metastable fcc-RuW alloy.Impressively,fcc-RuW exhibits remarkable alkaline HOR performance and stability with the activity of 0.67 mA cm_(Ru)^(-2)which is almost five and three times higher than that of hcp-Ru and commercial Pt/C,respectively,which is attributed to the optimized binding strength of adsorbed hydroxide intermediate derived from tailored electronic structure through W doping and phase engineering.Moreover,this strategy can also be applied to synthesize other metastable fcc-RuCr and fcc-RuMo alloys with enhanced HOR performances.

Discrete gap breathers in a two-dimensional diatomic face-centered square lattice

In this paper we study the existence and stability of two-dimensional discrete gap breathers in a two-dimensional diatomic face-centered square lattice consisting of alternating light and heavy atoms, with on-site potential and coupling potential. This study is focused on two-dimensional breathers with their frequency in the gap that separates the acoustic and optical bands of the phonon spectrum. We demonstrate the possibility of the existence of two-dimensional gap breathers by using a numerical method. Six types of two-dimensional gap breathers are obtained, i.e., symmetric, mirror-symmetric and asymmetric, whether the center of the breather is on a light or a heavy atom. The difference between one-dimensional discrete gap breathers and two-dimensional discrete gap breathers is also discussed. We use Aubry＇s theory to analyze the stability of discrete gap breathers in the two-dimensional diatomic face-centered square lattice.

The 3D solitons and vortices in 3D discrete monatomic lattices with cubic and quartic nonlinearity

By virtue of the method of multiple-scale and the quasi-discreteness approach, we have discussed the nonlinear vibration equation of a 3D discrete monatomic lattice with its nearest-neighbours interaction. The 3D simple cubic lattices have the same localized modes as a 1D discrete monatomic chain with cubic and quartic nonlinearity. The nonlinear vibration in the 3D simple cubic lattice has 3D distorted solitons and 3D envelop solitons in the direction of kx = ky = kz = k and k = ±π/6α0 in the Brillouin zone, as well as has 3D vortices in the direction of kx = ky = kz = k and k = ±π/α0 in the Brillouin zone.

Instantaneous Creep in Face-centered Cubic Metals at Ultra- low Strain Rates by a High-resolution Strain Measurement

Instantaneous creep in face-centered cubic metals, 5N Al（99.999%）, 2N Al （99%） and 4N Cu （99.99%） with different grain sizes, was firstly investigated by sudden stress-change experiments at ultra- low strain rates ε ≤10-10 s-1 and temperature T 〈 0.32 Tn. The experimental results indicate that the observed instantaneous creep is strongly dependent on grain size, the concentration of impurity, and stacking fault energy. Creep in high-purity aluminum, 5N Al, with a very large grain size, d 〉 1600μm, shows non-viscous behavior, and is controlled by the recovery of dislocations in the boundary of dislocation cells. On the other hand, for 5N A1 with a small grain size, d=30μm, and low-purity aluminum, 2N A1, with d8= 25μm, creep shows viscous behavior and may be related to ＇low temperature grain boundary sliding＇. For high-purity copper, 4N Cu, with d= 40 grn and lower stacking fault energy, creep shows a non-viscous behavior, and is controlled by the recovery process of dislocations. For all of the samples, creep shows anelastic behavior.

Metastable Face-Centered Cubic Structure and Structural Transition of Sn on 2H-NbSe2(0001)

Surface structures and properties of Sn islands grown on superconducting substrate 2H-NbSe2（0001）are studied using low temperature scanning tunneling microscopy or spectroscopy.The pure face-centered cubic（fee）structure of Sn surface is obtained.Superconductivity is also detected on the fcc-Sn（111）surface,and the size of superconducting gap on the Sn surface is nearly the same as that on the superconducting substrate.Furthermore,phase transition occurs from fcc-Sn（111）toβ-Sn（001）by keeping the sample at room temperature for a certain time.Due to the strain relaxation on theβ-Sn islands,both the in-plane unit cell and out-of-plane structures distort,and the height of surface atoms varies periodically to form a universal ripple structure.

Exact breathing soliton solutions in combined time-dependent harmonic-lattice potential

We investigate the explicit novel localized nonlinear matter waves of the cubic-quintic nonlinear Schr6dinger equation with spafiotemporal modulation of the nonlinearities and the harmonic-lattice potential using a modified similarity trans- formation. We also find that when the modulus of the Jacobian elliptic function in the limit closes to 1, the shapes of the breathing solitons may exhibit some interesting features, i.e., one breathing soliton dividing into two in the ground state. The stability of the exact solutions is investigated numerically such that some stable breathing soliton solutions are found.

关于能带宽度的一点修正

材料的能谱、能带宽度是材料能带结构的重要参数,是了解材料物理性质的基础.材料的几乎一切光学、力学、热学及电磁学等性质的测量结果,必须要有正确的能带结构才能得到合理的解释,凸显能带理论的重要性.针对目前国内大部分固体物理教材中,在利用紧束缚近似法讨论三维晶格能带宽度时未提及波矢方向,且能带宽度取值不合适的情况,讨论了沿不同波矢方向面心立方晶格的能带宽度,作为讨论晶格所对应晶体不同方向其它性质的基础.

稳定立方相结构的n型无铅AgBiSe_(2)基热电材料

n型AgBiSe_(2)基化合物的晶格热导率低,是一种很有潜力的高性能热电材料。然而,本征AgBiSe_(2)化合物在300~700 K之间存在两次相变,使其应用受限。因此,获得具有稳定结构的AgBiSe_(2)基化合物,并优化热电性能至关重要。本研究选择无铅的IV-VI族化合物SnTe与AgBiSe_(2)进行合金化,制备了(AgBiSe_(2))_(1-x)(SnTe)x(x=0.10~0.30)化合物。引入SnTe降低了AgBiSe_(2)立方相的相变温度,还有效抑制其发生可逆相变,得到了稳定的立方相(AgBiSe_(2))_(0.75)(SnTe)_(0.25)材料。SnTe引起晶格中原子高度无序分布,导致室温下晶格热导率从0.76 W·m^(–1)·K^(–1)(x=0.10)降低到0.51 W·m^(–1)·K^(–1)(x=0.30)。进一步Ag位掺杂Nb元素,可以提升载流子浓度,增加该体系((Ag1-yNbyBiSe_(2))0.75(SnTe)0.25化合物)的有效质量,大幅度提升电性能。室温下电导率由77.7 S·cm^(–1)(基体)增大到158.1 S·cm^(–1)(y=0.02)。同时,材料中的杂质点缺陷也逐步增加,高温下缺陷散射进一步降低晶格热导率。在700 K时,晶格热导率由0.56 W·m^(–1)·K^(–1)(未掺杂)降低至0.43 W·m^(–1)·K^(–1)(y=0.04),最终获得了立方相结构稳定的(Ag_(0.98)Nb_(0.02)BiSe_(2))_(0.75)(SnTe)_(0.25)材料,650 K的ZT达到0.32。上述研究结果表明,(AgBiSe_(2))_(0.75)(SnTe)_(0.25)化合物是一种具有低晶格热导率和稳定立方相结构的n型热电材料。本研究为高性能相变热电材料的晶体结构调控提出了新解决方案,有助于进一步推动其应用发展。

多层尺寸梯度面心立方点阵结构力学性能研究

针对均匀点阵结构能量吸收性能低和截面梯度点阵结构刚度性能较差的问题,设计了多层尺寸梯度面心立方点阵结构,通过理论、仿真和试验方法研究了其力学性能。首先,采用SS316L不锈钢材料和选择性激光熔融(SLM)技术,制备了胞元尺寸梯度面心立方(SG-FCC)和均匀面心立方(U-FCC)两种点阵结构的试验件,并进行了准静态压缩试验;然后,在试验和有限元分析的基础上,获得了两种点阵结构在压缩过程的力学行为,基于杆梁变形理论和多层梯度点阵结构刚度组集方法,提出了两种点阵结构的等效弹性模量理论模型;最后,研究了不同梯度因子对SG-FCC点阵结构压缩性能的影响规律。试验结果表明:相比于U-FCC点阵结构,SG-FCC点阵结构的力学性能更加优异,其刚度和比刚度分别增长了17.8%和16.2%,吸能量和比吸能量分别提高了10.8%和10.36%。所提出的SG-FCC点阵结构弹性模量理论模型与试验和有限元分析结果相比吻合较好,误差小于10%,可用于SG-FCC点阵结构的刚度预测;当梯度因子为1.5时,SG-FCC点阵结构的刚度性能较好;当梯度因子为3时,SG-FCC点阵结构的吸能性能较好。该研究可为集高刚度和大吸能性能的轻质化结构设计和工程应用提供参考。

Face-centered cubic structured RuCu hollow urchin-like nanospheres enable remarkable hydrogen evolution catalysis

Ruthenium(Ru)is one of the most promising metals for its versatility in driving a wide range of catalytic reactions.However,owing to the intrinsic preference of hexagonal close-packed(hcp)phase for bulk Ru,currently,it is still challenging to construct Ru-based nanomaterials with face-centered-cubic(fcc)phase for optimizing their performance towards potential applications.Herein,we report a facile wet-chemical method to directly create unconventional fcc-structured Ru-copper hollow urchin-like nanospheres(fcc-RuCu HUNSs)as a class of efficient pH-universal hydrogen evolution reaction(HER)electrocatalyst.Interestingly,this synthetic strategy can be expanded to prepare other fcc-Ru-based alloy nanomaterials.Significantly,the novel fcc-RuCu HUNSs exhibit superior HER performance with the overpotential of only 25,34,40,and 26 m V to reach the current density of 10 mA cm^(-2)in 0.5 M H_(2)SO_(4),0.05 M H_(2)SO_(4),0.1 M KOH,and 1 M KOH,respectively,much lower than those of hcpRuCu HUNSs and commercial Pt/C.Density functional theory(DFT)calculations further indicate that their excellent pH-universal HER performance results from the optimized adsorption free energy of H and work functions.Our work highlights the importance of phase control to design high-efficiency nanocatalysts for relevant catalytic reactions in energy conversion.

Mechanism transition of cross slip with stress and temperature in face-centered cubic metals

A<110>/2 screw dislocation is commonly dissociated into two <112>/6 Shockley partial dislocations on{111} planes in face-centered cubic metals.As the two partials are not purely screw,different mechanisms of cross-slip could take place,depending on the stacking fault energy,applied stress and tempe rature.It is crucial to classify the mechanisms of cross-slip because each mechanism possesses its own reaction path with a special activation process.In this work,molecular dynamics simulations have been performed systematically to explore the cross-slip mechanism under different stresses and temperatures in three different metals Ag,Cu and Ni that have different stacking fault energies of 17.8,44.4 and 126.8 mJ/m^2,re spectively.In Ag and Cu with low stacking fault energy,it is observed that the cross-slip mechanism of screw dislocations changes from the Fleischer obtuse angle(FLOA),to the Friedel-Escaig(FE),and then to the FL acute angle(FLAA) at low temperatures,with increasing the applied stress.However,when the temperature increases,the FE mechanism gradually becomes dominant,while the FLAA only occurs at the high stress region.In particular,the FLOA has not been observed in Ni because of its high stacking fault energy.

Direct observation of metastable face-centered cubic Sb2Te3 crystal

Although phase change memory technology has developed drastically in the past two decades, the cognition of the key switching materials still ignores an important member, the face-centered cubic Sb2Te3. Apart from the well-known equilibrium hexagonal Sb2Te3 crystal, we prove the metastable face-centered cubic Sb2Te3 phase does exist. Such a metastable crystal contains a large concentration of vacancies randomly occupying the cationic lattice sites. The face-centered cubic to hexagonal phase transformation of Sb2Te3, accompanied by vacancy aggregation, occurs at a quite lower temperature compared to that of Ge2Sb2Te5 alloy. We prove that the covalent-like bonds prevail in the metastable Sb2Te3 crystal, deviating from the ideal resonant features. If a proper doping technique is adopted, the metastable Sb2Te3 phase could be promising for realizing reversibly swift and low-energy phase change memory applications. Our study may offer a new insight into commercialized Ge-Sb-Te systems and help in the design of novel phase change materials to boost the performances of the phase change memorv device.

Effective Stacking Fault Energy in Face-Centered Cubic Metals

As a typical configuration in plastic deformations, dislocation arrays possess a large variation of the separation of the partial dislocation pairs in face-centered cubic（fcc） metals. This can be manifested conveniently by an effective stacking fault energy（SFE）. The effective SFE of dislocation arrays is described within the elastic theory of dislocations and verified by atomistic simulations. The atomistic modeling results reveal that the general formulae of the effective SFE can give a reasonably satisfactory prediction for all dislocation types, especially for edge dislocation arrays. Furthermore, the predicted variation of the effective SFE is consistent with several previous experiments, in which the measured SFE is not definite, changing with dislocation density. Our approach could provide better understandings of cross-slip and the competition between slip and twinning during plastic deformations in fcc metals.

基于格子Boltzmann法岩体裂隙粗糙特征对渗流的影响

裂隙在岩体中的形貌结构复杂,岩体裂隙的粗糙特征对裂隙的渗透性存在较大影响。目前传统的数值模拟软件主要是以等效连续介质为基础的宏观评价,无法模拟裂隙微小结构内的介观渗流特征;虽然存在考虑裂隙粗糙特征的粗糙裂隙渗透评估模型,但是将粗糙裂隙的剖面高度标准偏差值作为粗糙特征的定量表征缺乏物理意义并且存在局限性。首先运用W-M(Weierstrass-Mandelbrot)函数构建具有不同分形维数的二维粗糙单裂隙数字模型。其次基于格子Boltzmann法理论通过编程实现介观尺度的渗流模拟,并结合以裂隙剖面高度标准偏差值作为粗糙特征定量表征的立方定律公式进行分析。结果表明:以裂隙剖面高度标准偏差值作为粗糙特征定量表征的立方定律公式存在不足;以分形维数作为粗糙特征定量表征的局部修正立方定律公式相对可行。研究对于地下水污染防治以及地下水资源评估有着重要的工程实际意义。

Equilibrium Energy and Entropy of Vortex Filaments in the Context of Tornadogenesis and Tornadic Flows

In this work, we study approximations of supercritical or suction vortices in tornadic flows and their contribution to tornadogenesis and tornado maintenance using self-avoiding walks on a cubic lattice. We extend the previous work on turbulence by A. Chorin and collaborators to approximate the statistical equilibrium quantities of vortex filaments on a cubic lattice when both an energy and a statistical temperature are involved. Our results confirm that supercritical (smooth, “straight”) vortices have the highest average energy and correspond to negative temperatures in this model. The lowest-energy configurations are folded up and “balled up” to a great extent. The results support A. Chorin’s findings that, in the context of supercritical vortices in a tornadic flow, when such high-energy vortices stretch, they need to fold and transfer energy to the surrounding flow, contributing to tornado maintenance or leading to its genesis. The computations are performed using a Markov Chain Monte Carlo approach with a simple sampling algorithm using local transformations that allow the results to be reliable over a wide range of statistical temperatures, unlike the originally used pivot algorithm that only performs well near infinite temperatures. Efficient ways to compute entropy are discussed and show that a system with supercritical vortices will increase entropy by having these vortices fold and transfer their energy to the surrounding flow.

Consistent Analytic Embedded Atom Potential for Face-Centered Cubic Metals and Alloys

A consistent empirical embedded-atom potential that includes a long range force was developed for fcc （face-centered cubic） metals and alloys. The proposed potential for pure metals does not require modification of the initial function form when being applied to alloy systems. The potential parameters of this model were determined by fitting lattice constant, three elastic constants, cohesive energy, and vacancy formation energies of the pure metals and the heats of solution of the binary alloys via an optimization technique. Parameters for Ag, AI, Au, Cu, Ni, Pd and Pt were obtained. The obtained parameters were used to calculate the bulk modulus, divacancy formation energy, crystal stability, stacking fault energy, vacancy migration energy, and melting point for each pure metal and the heats of formation and lattice constants for binary alloys. The predicted values were in good agreement with experimental results.

基于立方体格网法的树冠体积计算与预估模型建立

以北京地区10种常见乔木为研究对象,通过三维激光扫描仪获取其点云数据,利用树冠表面三角网配合立方体格网法计算其树冠体积,与点云中提取所得的林木因子分析建立树冠体积和胸径、树高、平均冠幅、冠高的预估方程,并检验其精度。以银杏为研究目标进行了实验,结果表明:银杏的树冠体积与胸径、树高、平均冠幅、冠高均显著相关,通过分析选取了银杏树冠体积的三因子(胸径、平均冠幅、冠高)最优模型,并对模型进行了检验,检验结果表明,模型拟合效果较好,预估精度达到90.5%,可以使用该模型进行银杏的体积估算;同时对所选其他树种进行三因子模型拟合,模型检验结果表明,三因子模型均能够较好地对该树种的树冠体积进行估测。

Experimental and numerical simulation of bird-strike performance of lattice-material-infilled curved plate

The anti-bird-strike performance of a lattice-material-infilled curved plate is investigated herein.Since automatically filling the curved structure by classical lattice material filling methods will cause a large number of manufacturing defects,a space-dependent lattice material filling method for the curved plate is firstly proposed in this paper Next,using a face-centered cubic lattice,a lattice-material-infilled test piece with a hollow ratio of 40.8%is built.The test pieces are manufactured via additive manufacturing using titanium alloy.In bird-strike experimental tests,the test pieces are crashed against gelatin birds at an impact velocity of 200 m/s.Dynamic strain gauges are used to record the crash history and the results are discussed.Furthermore,a numerical analysis to simulate the bird-strike experiment is performed.The results from the experimental tests and numerical simulation agree well.This work shows that the lattice-material-infilled curved plate yields promising bird-strike resistance.Therefore,lattice-infilled materials are feasible for protecting aerospace components against bird-strike as well as for reducing the component weight.

Z曲线的理论研究(英文)

DNA序列与正四面体(RT)中的映象点(D格点)具有对应关系.一系列D格点形成晶格(D 晶格).D晶格证明是面心立方晶格,并揭示了D格点的空间分布规律.在此基础上得到Z曲线的一些特性, 如Z曲线束具有S4群的对称性,Z曲线均在最大正四面体的内切球内等等.

基于位置和能量的水下无线传感网路由协议

为了保证水下三维无线传感器网络对监测区域的高覆盖率,并减少网络中节点数量以降低组网成本,选用体心立方格结构进行传感器节点的部署。为了将节点收集到的信息高效地传递给网络使用者,提出了一种体心立方格部署下的网络路由协议。该协议基于节点位置与能量信息计算对数据包的转发概率,在保证数据包高投递率的同时减少冲突的发生;利用后续转发节点的反馈信息检测网络空洞的出现,并通过控制发送功率来改变节点的通信范围以穿越空洞。仿真结果表明,在保证网络连通性及数据包投递率的同时,该协议能够提高网络能量利用效率、平衡节点的能量消耗。