Effect of atomic ordering on environmental embrittlement of (Co, Fe)_3V alloy in gaseous hydrogen

The diffusible hydrogen contents in precharged (Co,Fe) 3V alloy were measured. It is found that atomic ordering can not promote hydrogen penetration in the (Co,Fe) 3V alloy. The ultimate tensile strength (UTS) and ductilities in various condition were also investigated. The results show that the UTS and elongation of disordered alloy are higher than that of ordered one with fixed diffusible hydrogen content and (Co,Fe) 3V alloy with ordered structure is highly susceptible to the embrittlement in hydrogen gas. The factor which may affect the susceptibility to the embrittlement of (Co,Fe) 3V alloy in hydrogen gas is mainly due to that the atomic ordering may accelerate the kinetics of the catalytic reaction for the dissociation of molecular hydrogen into atomic hydrogen. However, it can not be roled out that atomic ordering intensifies planar slip and restricts cross slip at the grain boundaries and enhances the susceptibility of the alloy to hydrogen embrittlement.

Relations between compositional modulation and atomic ordering degree in thin films of ternary Ⅲ-Ⅴ semiconductor alloys

This paper derives the expressions for the ordering degree and the modulation factor of A and B atoms in AXB1-xC epilayers of ternary III-V semiconductor alloys. Using these expressions, it identifies quantitatively the alternating atom-enhanced planes, compositional modulations, atomic ordering degree on the group-III sublattices and the fine structure of NMR spectra.

Using density functional calculations to elucidate atomic ordering of Pd-Rh nanoparticles at sizes relevant for catalytic applications

Pd-Rh nanoparticles are known to easily undergo surface restructuring in reactive environment. This study quantifies, with the help of density functional(DFT) calculations and a novel topological approach, atomic ordering and surface segregation effects in Pd-Rh particles with compositions 1:3, 1:1 and 3:1 containing up to 201 atoms(ca. 1.7 nm). The obtained data are used to reliably optimise energetically preferred atomic orderings in inaccessible by DFT Pd-Rh particles containing thousands of atoms and exhibiting sizes exceeding 5 nm, which are typical for catalytic metal particles. It is outlined, how segregation effects on the surface arrangement of Pd-Rh nanoalloy catalysts induced by adsorbates can be evaluated in a simple way within the present modelling setup.

Computer Simulation of Ordering and Atom Clustering in Aging Binary Al-Li Alloy

Ordering and atom clustering in aging binary Al-Li alloy has been investigated by computer simulation through calculating the long range order (Iro.) parameter and composition deviation order parameter from single-site occupation probabilities of Li atom. The results show that when the alloy lies in metastable region in the phase diagram ordering and atom clustering occur simultaneously. As the composition of the alloy increases ordering occurs earlier than atom clustering gradually. When the alloy lies in instable region atom clustering takes place after the congruent ordering completes. It has also been found that the incubation period of the phase transformation is shortened as the composition increases.

Higher-Order Squeezing for Atomic Dipole of a Three-Level Atom in the Kerr-Like Medium Cavity Fields

In this paper, evolution of the higher order squeezing for atomic dipole of three level atom in the Kerr like medium is investigated. The atom discussed has two configurations and is driven by the single mode coherent state field. Our results show that the squeezing effects are clearly influenced by nonlinear parameters, the initial atom state and the detuning.

High-order harmonic generation spectrum of an excited one-dimensional Coulomb atom in an intense laser field

Response of the wave packet of a one-dimensional Coulomb atom to an intense laser field is calculated using the symmetrized split operator fast Fourier method. The high-order harmonic generation （HHG） of the initial state separately being the ground and excited states is presented. When the hardness parameter a in the soft Coulomb potential V（x） =-1√x^2＋α is chosen to be small enough, the so-called hard Coulomb potential V（x）=1/｜x｜ can be obtained. It is well known that the hard one-dimensional Coulomb atom has an unstable ground state with an energy eigenvalue of - 0.5 and it has no states corresponding to physical states in the true atoms, and has the first and second excited states being degenerate. The parity effects on the HHG can be seen from the first and second excited states of the hard one-dimensional Coulomb atom. The HHG spectra of the excited states from both the soft and hard Coulomb atom models are shown to have more complex structures and to be much stronger than the corresponding HHG spectrum of the ground state of the soft Coulomb model with a = 2 in the same laser field. Laser-induced non-resonant one-photon emission is also observed.

Effect of order/disorder transformation on the sensitivity to environmental embrittlement of intermetallics

The mechanism involving the effect of disorder/order transformation on the environmental embrittlement in gaseous H2 is summarized. It is shown that there is no hydrogen embrittlement in disordered state of Kurnakov type intermetallics in gaseous H2. However, the H2-induced environmental embrittlement for the ordered alloy having identical chemical composition becomes severer as the degree of the order increases. The results of testing on the ion gage turned on and off during tensile testing show that the more sensitive to H2-induced hydrogen embrittlement for ordered alloy than disordered one is attributed to the fact that atomic ordering may accelerate the kinetics of the catalytic reaction to produce more atomic hydrogen. The results on simultaneous hydrogen charging show that disordered alloys embrittled as hydrogen atoms are forced into the material implying that the embrittlement of ordered alloy in gaseous H2 is also due to the acceleration of the kinetics of catalytic reaction. The above suggestion was further verified by the adsorption tests of Ni3Fe intermetallics powder. It is shown that the amount of chemically adsorbed hydrogen in ordered state is significantly larger than that adsorbed by the disordered alloy, indicating that the more sensitive to H2-induced embrittlement in the ordered state of alloy is essentially due to the accelerated catalytic reaction.

Single DNA molecular manipulation with atomic force microscopy

Nanomanipulation of DNA molecules or other biomolecules to form artificial patterns or structures at nanometer scale has potential applications in the construction of molecular devices in future industries. It may also lead to new insights into the interesting properties and behavior of this fantastic nature-selected molecule at the sin- gle-molecular level. Here we present a special method based on the combination of macroscopic “molecular comb- ing” and microscopic “molecular cutting” to manipulate DNA molecules and form complex patterns at nanometer scale on solid surfaces. A possible strategy for ordered DNA sequencing based on this nanomanipulation technique has also been proposed.

Volume sequences of characteristic atoms separated from experimental volumes of AuCu and AuCu_3 compounds

The systematic science of alloys(SSA)is a framework of the total energy and total volume able to be separated.The volume sequences of characteristic atoms at the central sites of the basic clusters in the fcc-based Au-Cu system are separated out from the experimental volumes of L10-AuCu and L12-AuCu3 compounds at room temperature only,by nine volume V-functions. From these volume sequences,the volumes,volumes of formation,ordering(excess)volumes and volume mismatch degrees of the L10-AuCu,L12-AuCu3 and L12-Au3Cu compounds,Au3Cu-,AuCu-and AuCu3-type ordered alloys with maximal ordering degree, and disordered Au1-xCux alloys are calculated.Among these functions,only ordering volumes of the compounds and ordered alloys obtained by the 6th V-function are negative,i.e.,the destruction of the superlattice is accompanied by an increase in volume,which is identical with the experimental results.Accompanying conclusions,the different descriptions of volumetric properties between traditional alloy theories and SSA framework are discussed.

Electromagnetically induced grating in a thermal N-type four-level atomic system

The electromagnetically induced grating effect in thermal and cold atoms has been studied theoretically. Studies have shown that, by adjusting the parameters, the first-order diffraction efficiency of the probe beam in the cold atomic system and the thermal atomic system is 34% and 31%, respectively, which is very close to the ideal diffraction efficiency of the sinusoidal grating. However, it is more difficult to prepare the cold atomic system than to prepare the thermal atomic system in the practical application, so the study of the electromagnetically induced grating effect in the thermal atomic system may be helpful for practical applications.

Ordered Sn distribution adjacent to the precipitate-matrix interface in a Mg-9.8wt.%Sn alloy

The major interface betweenβ-Mg_(3)Sn precipitate plate and theα-Mg matrix in a Mg-9.8wt.%alloy has been investigated using aberrationcorrected scanning transmission electron microscopy and first-principles calculations.It is found that Sn atoms orderly distribute in the single layer of theα-Mg matrix immediately adjacent to the broad surface ofβat the early stage of ageing.These Sn atoms substitute Mg atoms located at the centers of equilateral triangles constituted by three Mg columns in the outmost layer ofβ.First-principles calculations suggest that the ordered Sn distribution is energetically favored and it not only decreases the interfacial energy of theβ-matrix interface but also hinders the occurrence of 1/3<01■0>αshear that thickens theβplate.

Generation of Higher-Order Squeezing in Multiphoton Micromaser

The generation of study state hisher-Order squeezing in the sense of Hons andMandel [Phys. Rey. Lett. 54, 323 (1985) ; phys. Rev. A32,974 ( 1985 )] andalso of Hillery [Phys. Rev. A36 , 3796 (1987) ] in a multiphoton micromaser isstudied. The results show that the cotangent state which is generated by thecoherent trapping scheme in a niultiphoton microniaser can exhibit not onlysecond-order squeezing but alaso fourth-order and squared field aniplitudesqueezing. The influence of the cavity loss on the squeezings is investigated.

EAM Analysis of the Lattice Parameter Effect in Order-Disorder Transformation

The embedded atom method (EAM) was used to theoretically analyze the effect of the lattice parameter variation on the order-disorder transformation in binary alloys. Based on EAM, it is found that only one kind of order-disorder transition (second-order transition) exists for AB alloy. Three groups of order-disorder transformation can be observed for the A(3)B or AB(3) compounds. For group I, the order-disorder is a completely first-order transition. For group II, the order-disorder transformation is a classical first-order transition. For group III, the order-disorder transformation is found to be a second-order transition. The lattice parameter variations have a significant effect on E-2 coefficient, which is related to the ordering energy. These results are in good agreement with experiments.

An introduction to Bragg diffraction-based cold atom interferometry gravimeter

This paper presents a new type of cold atom interferometry gravimeter based on Bragg diffraction,w hich is able to increase the gravity m easurem ent sensitivity and stability of com m on Ram an atom gravim eters significantly. By com paring w ith Ram an transition,the principles and advantages of Bragg diffraction-based atom gravim eters have been introduced. The theoretical m odel for a tim e-dom ain Bragg atom gravim eter has been constructed. Som e key technical requirem ents for an n-order Bragg diffraction-based atom gravim eter have been deduced,including the tem perature of atom cloud,the diam eter,curvature radius,frequency,intensity,and tim ing sequence of Bragg lasers,etc. The analysis results are verified by the existing experim ental data in discussion. The present study provides a good reference for the understanding and construction of a Bragg atom gravim eter.

Synthesis of End Functional Polymers via Atom Transfer Radical Polymerization in Immobilized Catalytic System

Cross-linked polystyrene with azo-crown ether functional side chain (PSt-1, 10-dicarbonyl-3,6,9-trizaoeylcode-cane) was prepared under microwave irradiation and the structure was characterized through FT-IR and element analysis. The functionalized cross-linked polystyrene (cross-link degree, 3.5%) combining with immobilized catalyst system (CuBr and ethylα-bromo-isobutyrate) can catalyze atom transfer radical polymerization of Styrene. Neat polymer products can be obtained then. Complex of La and the polymer end group (EBiB) was synthesized. The third order nonlinear optical property of the polymer-La complex was investigated and the structure was also characterized by FT-IR and XPS.

金属有机骨架(MOFs)衍生材料及其在催化领域的研究进展

金属有机骨架(MOFs)材料是一类具有大比表面积和可调孔结构的新型多孔材料,近年来在催化制备精细化学品领域受到广泛关注。在实际催化过程中,MOFs较差的稳定性制约了其在许多反应中的应用。以MOFs为前驱体制备的MOFs衍生材料能够保留MOFs材料结构上的优势,同时解决其稳定性差的问题,极大拓展MOFs材料在催化反应中的应用。综述MOFs衍生材料在催化领域特别是在加氢和氧化制备精细化学品中的研究进展,并对MOF衍生材料面临的问题及其在催化领域的应用前景进行了展望。

耦合系数与腔衰减率对单原子腔场的二阶相关度及原子布居概率的影响

采用单原子J-C模型研究单个二能级原子与单模量子光场的相互作用.主要研究强耦合与弱耦合情况下,二阶相关度及原子布居概率随标度时间的变化.同时,分别探讨了弱耦合下原子与腔场的耦合系数及强耦合下腔场衰减率对二阶相关度及原子布居概率的影响.发现弱耦合下腔场与原子的耦合系数对光场反聚束效应有削弱作用,强耦合下腔场衰减率值对光场反聚束效应有增强作用.另外弱耦合下耦合系数与强耦合下腔衰减率对原子处于上能级概率均有抑制作用.

磁性原子链中的拓扑超导相竞争

穿过磁性原子环的磁通能够诱导拓扑超导,这种方法既不需要自旋轨道耦合也不需要螺旋磁序,为实现低维拓扑超导提供新的思路.本文介绍了在二维s波超导表面环状沉积铁磁序磁性原子链模型,阐述了在此模型中磁通诱导拓扑超导的原理.同时考虑实际实验,磁性原子链打破了二维衬底表面的空间反演对称性,带来了Rashba自旋轨道耦合,进而导致原子链螺旋磁序的出现.研究了Rashba自旋轨道耦合和螺旋磁序对拓扑超导态的影响.结果发现,自旋轨道耦合对原有拓扑态具有破坏性的影响,而螺旋磁序只是推动了相变点在参数空间的转移,不破坏原有拓扑态.

并发缺陷暴露、检测与规避研究综述

当今普遍流行的多核架构使得硬并发成为现实.为了从硬件的并发能力获益,并发程序设计正越来越流行.然而由于内在的并发性和不确定性,并发程序易于遭遇并发缺陷,并且它们难以检测、调试和修复.文中指出软件开发正从顺序模式转向并发模式的趋势,揭示并发程序和并发缺陷各自的三大特点,剖析并发缺陷面临的三大挑战,然后将并发缺陷分为死锁、数据竞争、原子性违背和顺序违背4类,并讨论4类并发缺陷的相互关系,接着就如何尽快暴露、及时检测和高效规避各类并发缺陷对已有研究作出分析、比较和归纳,最后从智能快速的缺陷暴露、通用准确的缺陷检测、确定性重放支持、软硬件协同设计和新的并发编程模型等5个方面展望了未来的研究重点.