Ni对RPV模拟钢中富Cu原子团簇析出的影响

用原子探针层析技术和时效模拟方法,研究了不同N i含量并且提高了Cu含量的反应堆压力容器(RPV)用模拟钢中富Cu、富N i和富Mn原子团簇的形成。结果表明,提高钢中的N i含量会促使富Cu原子团簇的析出,富Cu原子团簇中含有N i和Mn。实验检测到富N i的原子团簇,团簇中含有Cu和Mn,富N i原子团簇可以作为富Cu原子团簇析出时的形核区。实验还检测到富Mn原子团簇,当Mn原子团簇中含有较高的N i时,它也可以成为富Cu原子团簇析出时成核的地方。由于钢中的合金元素N i在形成富N i原子团簇后会成为富Cu原子团簇析出时成核区,因而提高N i的含量将促进富Cu原子团簇的析出,这是合金元素N i会增加压力容器钢中子辐照脆化敏感性的本质原因。     

Catalysis by very small Au clusters

We review recent theoretical and experimental work on the catalytic properties of Au clusters that contain a few atoms and are supported on an oxide surface. The clusters are mass-selected and landed slowly on the oxide surface in ultra-high vacuum. STM measurements show that the clusters do not fragment and do not damage the surface when they are deposited nor do they coarsen after deposition. Their catalytic activity changes non-monotonically with the number of atoms and is sensitive to the nature of the support and to additives (hydroxyls, water, Na, Cl) present on the surface. Binary clusters (e.g. Au_nSr) can be more active than unary ones. Very recent work has managed to study catalysis by such clusters under realistic pressure conditions; their performance is very different from (and sometimes better than) that of large clusters.     

Nonlinear electronic dynamics in free and deposited sodium clusters: Quantal and semi-classical approaches

The optical response of sodium clusters is studied using fully three-dimensional electronic dynamics, in real time, with an explicit ionic background. The obtained spectra are shown to come close to experimental results for free clusters. We use the approach also to compute the response of sodium clusters deposited on a NaCl(1 0 0) surface. The flattening of the clusters induced by the surface results in a shift and a large fragmentation of the plasmon resonance.     

Non-collinear structure of Cr trimer on the surface of non-magnetic metals

Magnetic structure of Cr trimer clusters on non-magnetic metal substrate has been calculated by recursion method within Anderson model. The values of the moments are enhanced relatively to bulk bcc Cr due to the reduction of coordination number. Angles between the moments depend on the relations between hopping parameters V_ij, determined by the interatomic distance in the cluster. We performed systematic calculations of the ground state for different values of parameters V₁₂=V₁₃ and V₂₃. For V₁₂V₂₃ ground state corresponds to moments on the atoms 2 and 3 with opposite direction, whereas the moment on atom 1 is perpendicular to them. For V₁₂=V₂₃ the angle between each pair of moments equals 2π/3 and the total moment of the trimer is zero. A decrease of V₂₃ versus V₁₂ leads to collinear state with moment on the atom 1 antiparallel to the moments on second and third. Calculation in external magnetic field reveals the co-existence of two self-consistent states with essentially different total magnetic moments. In weak field these solutions are very close in energy whereas with the increase of the field the state with larger moment is stabilized.     

Electron emission from surfaces bombarded by MeV atom clusters

Pronounced suppression of electron emission from surfaces bombarded by fast clusters is one of the well-known vicinage effects. However, the main mechanism of the suppression still remains unsolved. In this paper, recent electron spectroscopy studies of the vicinage effect at Tsukuba are reviewed with emphasis on the suppression mechanism of the electron emission in the transport stage. We discuss that the interference of wake potentials generated by the cluster atoms is effective to disturb the electron transport. This mechanism reasonably accounts for the observed suppression of electron emission.     

Computer simulation studies of Ar clusters

Results of the solid-liquid transition of Ar₁₃ cluster in a spherically symmetric external potential have been presented. The transition temperature is observed to show an elevation with pressure. The broadening of the heat capacity peaks indicate the transition becoming more diffused with pressure. The icosahedral structure of the cluster remains unaltered under pressure. Ar₅₅ cluster has also been studied by similar approach. A possible connection between glass transition phenomenon and melting of clusters under pressure has been examined. Communication no. 1413 from Solid State and Structural Chemistry Unit.     

An Algorithm for Mining Gradual Moving Object Clusters Pattern From Trajectory Streams

The discovery of gradual moving object clusters pattern from trajectory streams allows characterizing movement behavior in real time environment, which leverages new applications and services. Since the trajectory streams is rapidly evolving, continuously created and cannot be stored indefinitely in memory, the existing approaches designed on static trajectory datasets are not suitable for discovering gradual moving object clusters pattern from trajectory streams. This paper proposes a novel algorithm of gradual moving object clusters pattern discovery from trajectory streams using sliding window models. By processing the trajectory data in current window, the mining algorithm can capture the trend and evolution of moving object clusters pattern. Firstly, the density peaks clustering algorithm is exploited to identify clusters of different snapshots. The stable relationship between relatively few moving objects is used to improve the clustering efficiency. Then, by intersecting clusters from different snapshots, the gradual moving object clusters pattern is updated. The relationship of clusters between adjacent snapshots and the gradual property are utilized to accelerate updating process. Finally, experiment results on two real datasets demonstrate that our algorithm is effective and efficient.     

Silver Atomic Quantum Clusters of Three Atoms for Cancer Therapy: Targeting Chromatin Compaction to Increase the Therapeutic Index of Chemotherapy

Nanomaterials with very low atomicity deserve consideration as potential pharmacological agents owing to their very small size and to their properties that can be precisely tuned with minor modifications to their size. Here, it is shown that silver clusters of three atoms (Ag₃‐AQCs)—developed by an ad hoc method—augment chromatin accessibility. This effect only occurs during DNA replication. Coadministration of Ag₃‐AQCs increases the cytotoxic effect of DNA‐acting drugs on human lung carcinoma cells. In mice with orthotopic lung tumors, the coadministration of Ag₃‐AQCs increases the amount of cisplatin (CDDP) bound to the tumor DNA by fivefold without modifying CDDP levels in normal tissues. As a result, CDDP coadministered with Ag₃‐AQCs more strongly reduces the tumor burden. Evidence of the significance of targeting chromatin compaction to increase the therapeutic index of chemotherapy is now provided.     

Dynamics of clusters of charged particulates in electromagnetic fields

The dynamics of rigid clusters of charged particulates is the subject of this work. The work ascertains what properties of the cluster control its dynamic response to an external electromagnetic field. A primary focus is on the role of the distribution of the charges within the cluster and the effects of the Lorentz force on the overall body's linear and angular momentum. The presentation contains a derivation of the equations governing a charged cluster's dynamics and development of corresponding numerical methods for the simulation. Numerical examples are presented, along with comparisons to qualitative analytical results, where possible. Copyright © 2010 John Wiley & Sons, Ltd.     

Organization of copper nanoclusters in Langmuir-Blodgett films

Stable nanoclusters of Cu were synthesized using Langmuir-Blodgett films of octadecylsuccinic acid (ODSA) as template. The Langmuir-Blodgett films of ODSA formed from subphase containing copper ions were first subjected to sulphidation (S) using sodium sulphide and then hydrogenated (H) using hydrogen gas. Diffuse reflectance UV-visible spectroscopy (DIR-UV-vis), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) used to characterize these films indicated the formation of Cu(0) metallic clusters ranging in size from 3 ∼ 10 nm.     

Superatomic Gallium Clusters in Dendrimers: Unique Rigidity and Reactivity Depending on their Atomicity

Superatoms have been investigated due to their possible substitution for other elements. The solution-phase synthesis of superatoms has attracted attention to realize the availability of superatoms. However, the previous approach is basically limited to the formation of a single cluster. Here, superatoms are investigated and the number of valence electrons in these superatoms is changed by designing the number of gallium atoms present. Based on the dendrimer template method, clusters consisting of 3, 12, 13, and other numbers of atoms have been synthesized. The halogen-like superatomic nature of Ga₁₃ is structurally and electrochemically observed as completely different to the other clusters. The gallium clusters of 13 and 3 atoms, which can fill the 2P and 1P superatomic orbitals, respectively, exhibit different reactivities. The 3-atom gallium cluster is suggested as being reduced to Ga₃H₂⁻ due to the lower shift of energy levels in the unoccupied orbitals. The results for these gallium clusters provide candidates for superatoms.     

Sources of Inter-Firm Heterogeneity in Accessing Knowledge-Creation Benefits Within Technology Clusters

We build on recent literature to highlight the distinction between knowledge-diffusion and knowledge-creation benefits of technology clustering and argue that firms located in technology clusters will have differential access to the latter. To explain the antecedents of such differential access, we first argue that clustering gives rise to three knowledge-creation benefits: easier identification of potential knowledge partners with complementary knowledge, easier initiation of knowledge partnerships and increased effectiveness of knowledge partnerships. Subsequently, we develop a conceptual model and propositions that focus on a cluster firm's awareness of knowledge assets inside the cluster, attractiveness as a knowledge partner and ability to benefit from knowledge partnerships to explain differential access by firms to these three knowledge-creation benefits that clustering provides. This study highlights the theoretical significance of distinguishing externality-type benefits of technology clustering from benefits that firms need to actively pursue, and discusses implications for firms' location decisions.     

超微细颗粒体系微观结构的研究进展

简述了近年来国内外超微细颗粒结构特征及其聚团机理的研究进展,这些特征包括:径向分布函数、分形维数、配位数等系统静态结构性质和在流体媒介中外力场作用下超微细颗粒的聚团机理等动态性质,探讨了超微细颗粒的微观结构研究的发展方向。     

Epistemic Communities and Cluster Dynamics: On the Role of Knowledge in Industrial Districts

This paper questions the prevailing notions that firms within industrial clusters have privileged access to “tacit knowledge” that is unavailable—or available only at high cost—to firms located elsewhere, and that such access provides competitive advantages that cause the growth and development of both firms and regions. It outlines a model of cluster dynamics emphasizing two mutually interdependent processes: the concentration of specialized and complementary epistemic communities, on the one hand, and entrepreneurship and a high rate of new firm formation on the other.     

团簇产生原理及方法

结合在团簇源方面的工作系统评述了目前各种团簇源装置产生团簇的原理和方法 ,给出了它们的结构示意图和一些典型应用 ;对团簇源今后的发展方向进行了展望