The influence of nanoparticle size on the magnetostrictive properties of cluster-assembled Tb-Fe nanofilms

The giant magnetostrictive Tb-Fe films assembled by nanoparticles have been prepared by the low energy cluster beam deposition. The dependence of the magnetostriction on the size of the nanoparticles is examined for the films. It is shown that the nanofilms have obtained higher saturation magnetostriction at the cluster size of 30 nm in average. The dependence of magnetostriction on particle size is ascribed to the degree of magnetic anisotropy which is related to the effective distance of exchange coupling between the adjacent Tb-Fe nanoparticles. This work demonstrates that the magnetostriction can be varied by tuning the particle size, which is important for control over the magnetostrictive properties of the films at nanoscale.     

Numerical study of cluster and particle rebound effects in a circulating fluidised bed

Gas-particle flows in a vertical two-dimensional configuration appropriate for circulating fluidised bed applications were investigated numerically. In the computational study presented herein the motion of particles was calculated based on a Lagrangian approach and particles were assumed to interact through binary, instantaneous, non-frontal, inelastic collisions including friction. The model for the interstitial gas phase is based on the Navier-Stokes equations for two-phase flows. The numerical study of cluster structures has been validated with experimental results from literature in a previous investigation. Numerical experiments were performed in order to study the effects of different cluster and particle rebound characteristics on the gas-particle flow behaviour.Firstly, we investigated the hard sphere collision model and its effect on gas-particle flow behaviour. The coefficient of restitution in an impact depends not only on the material properties of the colliding objects, but also on their relative impact velocity. We compared the effect of a variable restitution coefficient, dependent on the relative impact velocity, with the classical approach, which supposes the coefficient of restitution to be constant and independent of the relative impact velocity.Secondly, we studied the effects of different cluster properties on the gas-particle flow behaviour. Opposing clustering effects have been observed for different particle concentrations: within a range of low concentrations, groups of particles fall faster than individual particles due to cluster formation, and within a well-defined higher concentration range, return flow predominates and hindered settling characterises the suspension. We propose herein a drag law, which takes into account both opposing effects and have compared the resulting flow behaviour with that predicted by a classical drag law, which takes into account only the hindered settling effect.     

Role of Ti-based catalysts in the dehydrogenation mechanism of magnesium borohydride: A cluster approach

The role of Ti and Ti-based catalysts such as TiCl₃ and TiF₃ in the dehydrogenation of Mg(BH₄)₂ has been studied using a cluster approach and density functional theory. The optimized geometry of Mg(BH₄)₂ clusters mimics the structure it has in the crystalline form, but undergoes significant geometric distortion as well as changes in the natural bond orbital (NBO) charge after the addition of the catalysts. While all the catalysts lower the hydrogen desorption energy, elemental Ti appears to be the best catalyst followed by TiCl₃ and TiF₃. The lowering of the hydrogen desorption is shown to be due to the weakening of the BH bond which is caused by the interaction of Ti with H and Mg.     

Public Lifestyle in the Low-Density City

Much maligned, shopping centres have come to represent many of the negative aspects of low-density areas. They are all too often associated with high car dependency and a paucity of cultural and public amenities. Alex Wall questions this preconception. Could the well-conceived and designed shopping centre actually prove to be urban sprawl's redemption?. Copyright © 2008 John Wiley & Sons, Ltd.     

重庆组团式城市结构的演变和发展

重庆市历次城市规划证明,“多中心、组团式”的布局结构是符合重庆市情的理想的规划结构,也是重庆城市的惟一选择。在未来的城市发展和城市规划中,应主动地维护和发展这种城市布局模式。     

Work function changes in the Ag deposition on TiO2 (110)

In this study, changes in the TiO₂ (110) work function where followed during Ag deposition in the sub-monolayer regime. Changes in the surface are readily detected as changes in the work function. Significant differences where found in measurements at room temperature and at liquid nitrogen temperature, which can be attributed to differences in the growth mode at those temperatures.The observed work function lowering is evidence of dipole formation by Ag clusters on the TiO₂ surface. Since the size and shape of these clusters depend on the surface temperature the differences on the work function variation should be related with the polarization induced by the shape of such clusters.     

Vector space model for the generalized parts grouping problem

The vector perturbation approach is introduced for addressing the generalized parts grouping problem, identifying part families for a general set of suppliers, not just a single supplier. This method is driven by the need for flexible and lean supply chain systems. A vector space model is used to represent a set of operation sequences as opposed to the traditional matrix and integer programming models in group technology. Using this approach, we find that we are able to generate part groups from 90% of the available parts, in which all the operation sequences are preserved. This contrasts the traditional methods using which only 66% of the available parts can be grouped. Furthermore, a vector representation of operation sequences provides an intuitive means for discovering the natural structure of the part data. From these results, we conclude that this technique can dramatically improve the effectiveness of the entire supply chain.     

Surface nanostructures created by cluster-surface impact

This paper presents a review of the production of surface nanostructures from the controlled deposition of size-selected clusters on graphite. At high enough impact energies, the clusters can be implanted into the graphite surface to create open ‘well’ structures. Scanning tunnelling microscopy (STM) measurements, coupled with molecular dynamics (MD) simulations, for Au₇⁺, Ag₇⁺ and Si₇⁺ clusters exhibit scaling relations which reveal that the implantation depth scales linearly with the momentum of the clusters in all cases. At lower impact energies, the clusters can be pinned on the graphite surface when the impact energy exceeds a critical (threshold) value, thus allowing the fabrication of monodispersed cluster arrays which are stable at room temperature (and above). One application of such cluster arrays is to bind protein molecules; atomic force microscopy (AFM) measurements in buffer solution demonstrate dispersed arrays of both chaperonin and horseradish peroxidase molecules on graphite substrates decorated with size-selected Au_N⁺ clusters.     

基于预测机制的自适应负载均衡算法

工作负载特征对Web服务器集群中负载均衡调度算法的性能有重要影响。针对负载特征在调度算法所起作用的分析和讨论,提出基于预测机制的自适应负载均衡算法（RR_MMMCS-A-P）。通过监测工作负载,预测后续请求到达率和请求大小,快速调整相应参数,实现集群中各服务器之间的负载均衡。实验表明,无论是对计算密集型任务还是数据密集型任务,RR_MMMCS-A-P同基于CPU和CPU-MEM的调度算法相比在缩短平均响应时间方面具有较好的性能。     

DSMC prediction of granular temperatures of clusters and dispersed particles in a riser

Flow behavior of gas and particles in a CFB riser is simulated by a Euler-Lagrangian approach. Collisional interaction of particles is modeled by a direct simulation Monte Carlo (DSMC) method. The coefficient of restitution depends on the relative velocity between two particles by taking into account both the viscoelastic and plastic deformations of particles. The Newtonian equations of motion are solved for each simulated particle in the system. The interaction between gas phase and simulated particles is determined by means of Newtonian third law. A criterion proposed by Soong et al. [C.H. Soong, K. Tuzla, J.C. Chen, Experimental determination of clusters size and velocity in circulating fluidized beds, in: J.F. Large, C. Laguerie Eds., Fluidization VIII Engineering Foundation, New York, 1995, pp. 219-227.] is used to obtain information of clusters. A model for the determination of the number of particles inside a cluster is proposed from kinetic theory of granular flow. The flow behavior of clusters and dispersed particles in the riser is numerically predicted. Distributions of granular temperature of clusters and dispersed particles are computed from velocity distributions. The upward moving clusters give a high granular temperature in comparison to the downward moving clusters. The granular temperature of the dispersed particles is an order of magnitude larger than that of the clusters. The computed collision frequencies of dispersed particles and clusters from DSMC are lower than those from kinetic theory of granular flow.