Recrystallization Kinetics of 3C Silicon Carbide Implanted with 400 keV Cesium Ions

Polycrystalline 3C silicon carbide (SiC) was implanted at room temperature with 400 keV cesium ions to a dose of 10¹⁶ ions/cm². The samples were annealed at 600°C–1000°C for times up to 48 h to observe changes in the implantation zone crystallinity and density. The implanted regions were characterized by transmission electron microscopy (TEM) and secondary ion mass spectroscopy (SIMS) before and after annealing. It is shown that the implantation resulted in a 217 ± 2 nm amorphous region with microstructural damage extending to ~250 nm below the surface. Recrystallization of the amorphous region was observed to begin at 725°C. Densification was determined indirectly through changes in the measured implantation zone thickness. Measurable thickness, or densification, of the implanted region was not observed until temperatures greater than ~800°C. The SiC recrystallization began at the interface between the amorphous, damaged region, and the underlying polycrystalline material. Image analysis was used to quantify the fraction of crystalline phase as a function of time and temperature. The recrystallization kinetics exhibited Arrhenius dependency with an apparent activation energy of 480 kJ/mol. SIMS demonstrated that 60%–70% of the cesium was retained within the recrystallized microstructure after thermal annealing.     

A Group Theoretical Analysis of Conformational Flexibility

The chemical identity group of a conformationally flexible molecule has very special properties. An analysis of its group structure leads to a detailed interpretation of the properties of the conformationally flexible molecules and their permutation isomers. In contrast to conventional conformational analysis our treatment of conformationally flexible molecules on the basis of chemical identity groups emphasizes ensembles of interconverting conformers. This leads to an interpretation of the observed increase in “symmetry” through conformational flexibility.     

Spatial and symbolic factors in performance on the Trail Making Test.

Analyzed the relative contribution of spatial arrangement and symbolic complexity to performance of 24 young normal Ss (aged 20–51 yrs), 24 elderly normal Ss (aged 60–73 yrs), and 24 head-injured Ss (aged 18–47 yrs) on a trail making test (TMT). Test versions that permitted separation of spatial and symbolic factors were created. There were strong main effects of both spatial arrangement, symbolic complexity, and group. There was a significant interaction effect between spatial arrangement and symbolic complexity and between group and symbolic complexity. The relative difficulty of Forms A and B on the TMT may be due to differences in symbolic complexity and spatial arrangement and to interactions between these factors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Carbon dioxide reforming of methane over lanthanum-modified catalysts in a fluidized-bed reactor

Nickel on lanthanum-modified aluminas were prepared and tested as catalysts for the CO₂ + CH₄ 2CO + 2H₂ reaction in a fluidized-bed reactor. Attrition tests show that lanthanum increases the strength of the carrier significantly. TPR and XRD results indicate that nickel enters into positions in the Al-O spinel blocks of the subsurface LaAl₁₂O₁₉ phase. This results in lower reducibility and thus lower activity for the reforming reaction as compared to nickel on unmodified alumina. While the unmodified catalyst deactivated rapidly under the chosen test conditions, the modified catalysts seem to be stable over several hours. However, the stability is sensitive to the pretreatment conditions of the catalysts.     

Preparedness: Unpacking and clarifying the concept

Crisis studies increasingly focus on developing proactive strategies to minimize the effects of unwanted occurrences and contingencies. Preparedness constitutes a key component of this approach, as many crises are difficult to prevent. However, at the conceptual and practical levels, it remains difficult to distinguish preparedness from other crisis‐related concepts. This study draws on an extensive survey of the preparedness literature with the goal of elucidating its defining attributes. The results show that preparedness can be minimally characterized as measures that are of an active, continuous and anticipatory nature. Contextually definitions, however, may also include social, planned, non‐structural or enabling conceptual attributes.     

以实践为本，集百家之长

我从事软件工程研究多年,曾遇到过大大小小的很多问题,这里,我想谈谈软件外包中的需求问题。软件外包,最基本的意思,是指在软件开发生命周期的某一时间点,将软件开发工作移交给另一个团队。而绝大多数人在此过程中最容易犯的错误,是没有标明确切的时间点。很多人随随便便抛出一份需求说明,就希望别人据此开发出整个软件。这样做最大的问题是,你根本无法准确地描述出自己的需求,进而可能得不到符合需求的软件。     

Role of Oxygen in Microstructure Development at Solid-State Diffusion-Bonded Cu/α-Al2O3 Interfaces

Microstructure development at solid-state diffusion-bonded Cu/α-Al₂O₃ interfaces has been studied using optical and electron microscopy. High-purity Cu foil was bonded between basal-oriented α-Al₂O₃ single-crystal plates at 1040°C for 24 h in a vacuum of ∼1.3 × 10⁻⁴ Pa (1 × 10⁻⁶ torr). Optical microscopy of as-bonded specimens revealed a large Cu grain size, fine pores, and long needles of Cu₂O at the interface. Bulk specimens were annealed at 1000°C for various times under controlled oxygen partial pressures in CO/CO₂ mixtures. Consistent with a thermochemical analysis, CuAlO₂ could be formed at the interfaces. The CuAlO₂ was acicular and discontinuous, but occurred in a uniform distribution over the bulk specimen interfaces.     

Disperse Amphiphilic Submicron Particles as Non‐Covalent Supports for Cationic Homogeneous Catalysts

A simple method for the effective immobilization of homogeneous catalysts on polystyrene colloids via non‐covalent binding is demonstrated. Stable latices with sufficiently high loading of accessible borate anions are prepared via emulsion polymerization. Incorporation of cationic rhodium complexes, supported via their borate counter‐anion is efficient, and these supported homogeneous catalysts maintain constant catalytic activity for CC hydrogenation during several recycles, with very low metal leaching.