Nanosized metal deposits on titanium dioxide for augmenting gas-phase toluene photooxidation

The build-up of intermediate species on the surface of TiO₂ during gas-phase toluene (C₇H₈) photodegradation has been observed to deactivate the photocatalyst. Nanosized metallic deposits on the TiO₂ surface may enhance the photocatalytic process and improve photocatalyst performance. In this study, noble (Ag, Au) and platinum group (Pt, Pd, Rh) metals, at a nominal loading of 0.5 at.%, were deposited onto Degussa P25 TiO₂ to enhance photocatalyst performance and inhibit deactivation. Pd, Rh and Au deposits delayed photocatalyst deactivation by a factor of 2, while Pt deposits delayed photocatalyst deactivation by a factor of 20, when compared with neat TiO₂. Ag deposits did not improve photocatalyst activity. Metal deposit performance was related to the work function of each metal, however, the Pt finding suggested that these effects are not governed solely by this aspect, but factors such as deposit characteristics and/or thermal catalytic properties of the metals may be influential.     

Preconditioned Krylov subspace method for the solution of least-squares problems

We consider preconditioned Krylov subspace iteration methods, e.g., CG, LSQR and GMRES, for the solution of large sparse least-squares problems min ∥Ax – b ∥₂, with A ∈ R ^m×n, based on the Krylov subspaces K_k (BA, Br) and K_k (AB, r), respectively, where B ∈ R ^n×m is the preconditioning matrix. More concretely, we propose and implement a class of incomplete QR factorization preconditioners based on the Givens rotations and analyze in detail the efficiency and robustness of the correspondingly preconditioned Krylov subspace iteration methods. A number of numerical experiments are used to further examine their numerical behaviour. It is shown that for both overdetermined and underdetermined least-squares problems, the preconditioned GMRES methods are the best for large, sparse and ill-conditioned matrices in terms of both CPU time and iteration step. Also, comparisons with the diagonal scaling and the RIF preconditioners are given to show the superiority of the newly-proposed GMRES-type methods. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

通过表面机械加工调控Zr52.5Cu17.9Ni14.6Al10Ti5非晶合金的结构和韧性

作为一种新型结构材料,非晶态合金的韧性需要进一步提高.提高非晶态合金韧性的方法有引入枝晶相、调整其成分改变其泊松比影响其剪切带衍生、裂纹扩展等.本文通过表面机械加工的方法来调控非晶态合金的微观结构及韧性.我们采用真空电弧熔炼、亚稳态薄板离心浇铸系统制备了Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅(原子百分比)(Vit105)非晶合金板,并用表面机械研磨处理方法 (surface mechanical attrition treatment, SMAT),在Vit105板上形成纳米尺度局域类晶体序结构.基于差示扫描量热分析、纳米压痕实验,我们发现SMAT处理后的Vit105合金板表面附近弛豫焓更低,微观结构更加均匀、稳定.通过显微维氏硬度计测试,发现SMAT处理后样品的表面附近硬度增大,硬度值分布也更均匀.通过三点弯断裂实验,可得到SMAT处理后合金板缺口韧度值从70.7±4.7 MPa·m^1/2提高到112.8±3.7 MPa·m^1/2<...     

Synthesis and properties of cross-linkable DNA duplex using 4-amino-2-oxo-6-vinyl-1,3,5-triazine

We synthesized the DNA oligonucleotide containing a new cross-linkable 4-amino-2-oxo-6-vinyltriazine (AOVT) nucleobase analogue (Et-AOVT) and evaluated these properties. Our results of the cross-link assay and thermal denaturing assay of duplexes containing AOVT demonstrated that the additional aza of AOVT has an impact on the duplex stability and crosslink properties. Our data suggests that the additional 5-aza of AOVT is involved in the hydrogen bonding with the complementary guanine, and this hydrogen bonding system successfully flipped the reactive vinyl group out to the major groove of the duplex demonstrating a new paradigm of a “cross-linkable duplex”.     

Efficient Synthesis of Polycyclic γ-Lactams by Catalytic Carbonylation of Ene-Imines via Nickelacycle Intermediates

The nickel(0)-catalyzed carbonylative cycloaddition of 1,5- and 1,6-ene-imines with carbon monoxide (CO) is reported. Key to this reaction is the efficient regeneration of the catalytically active nickel(0) species from nickel carbonyl complexes such as [Ni(CO)₃L]. A variety of tri- and tetracyclic γ-lactams were thus prepared in excellent yields with 100 % atom efficiency. Preliminary results on asymmetric derivatives promise potential in the synthesis of enantioenriched polycyclic γ-lactams.