Completeness and unbiased estimation of mean vector in the multivariate group sequential case

We consider estimation after a group sequential test about a multivariate normal mean, such as a χ² test or a sequential version of the Bonferroni procedure. We derive the density function of the sufficient statistics and show that the sample mean remains to be the maximum likelihood estimator but is no longer unbiased. We propose an alternative Rao-Blackwell type unbiased estimator. We show that the family of distributions of the sufficient statistic is not complete, and there exist infinitely many unbiased estimators of the mean vector and none has uniformly minimum variance. However, when restricted to truncation-adaptable statistics, completeness holds and the Rao-Blackwell estimator has uniformly minimum variance.     

泡沫铝防护钢筋混凝土板的抗爆性能

为研究多孔吸能材料泡沫铝板对工程结构的抗爆防护作用,开展室外爆炸破坏实验,分别对设置不同泡沫铝防护层的钢筋混凝土(reinforced concrete,RC)板在爆炸荷载下的动态响应及破坏模式进行了研究,并运用LS-DYNA软件建立了有限元模型。通过与实验对照,验证了模型的可行性,对比分析了有、无泡沫铝防护层钢筋混凝土板的损伤破坏规律,并讨论了泡沫铝密度梯度分布和纵筋配筋率的影响。结果表明:有限元模型能够有效分析含泡沫铝防护层RC板的动态响应及其破坏形态;泡沫铝防护层能够有效减小钢筋混凝土板的挠度变形,降低试件的破坏程度;泡沫铝密度由下到上递增情况对RC板的减爆效果最好;增大配筋率可以提升泡沫铝防护RC板整体抗爆性能。     

A Concise Total Synthesis of (−)‐Himalensine A

The daphniphyllum alkaloids are a structurally fascinating and remarkably diverse family of natural products. General strategies for the chemical synthesis of their challenging architectures are highly desirable for efficiently accessing these intriguing alkaloids and addressing their pharmaceutical potential. Herein, a concise strategy designed to provide general and diversifiable access to various daphniphyllum alkaloids is described and utilized in the asymmetric synthesis of (?)‐himalensine A, which was accomplished in 14 steps. Key features of this strategy include a Cu‐catalyzed nitrile hydration, a Heck reaction to construct the challenging 2‐azabicyclo[3.3.1]nonane motif, a Meinwald rearrangement reaction, six, pot‐economic reactions, and the minimal use of protecting groups, which significantly improved the overall synthetic efficiency.     

Protecting‐Group‐Free Total Synthesis and Biological Investigation of Cabucine Oxindole A†

Owing to their challenging structures and promising biological profiles, spirooxindole alkaloids have long attracted much attention from the synthetic community. Herein, we wish to describe a concise, protecting‐group‐free total synthesis of cabucine oxindole A, a putative natural spirooxindole alkaloid and a possible biosynthetic congener of cabucine and palmirine. Key transformations of our approach include a one‐step, organocatalytic and enantioselective construction of the spiro[pyrrolidine‐3,3’‐oxindole] moiety and a Korte rearrangement to furnish the final dihydropyran motif. Biological investigation of 1 and its synthetic intermediates revealed lactone 2 as a mild MOLT‐4 and MCF7 cell line inhibitor.     

Collapse and swelling of poly(N‐isopropylacrylamide‐co‐sodium acrylate) copolymer brushes grafted on a flat SiO2 surface

Poly(N‐isopropylacrylamide‐co‐sodium acrylate) copolymer brushes grafted on SiO₂‐coated quartz crystal surface were prepared with a surface‐immobilized initiator. The collapse and swelling of the thermally sensitive copolymer brushes in water were studied with quartz crystal microbalance in situ. The frequency and dissipation changes with the temperature increasing in the range 20–38 °C indicate that the brushes undergo a continuous collapse transition. Our results show that the copolymer brushes collapse to a state where the brushes were prepared. A hysteresis was observed in the cooling process. Fourier transform infrared (FTIR) results revealed that the formation of some additional hydrogen bonds within the copolymer chains at their collapsed state is responsible for the hysteresis. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 770–778, 2006     

Breaking a novel colour image encryption algorithm based on chaos

Recently, a colour image encryption algorithm based on chaos was proposed by cascading two position permutation operations and one substitution operation, which are all determined by some pseudo-random number sequences generated by iterating the logistic map. This paper evaluates the security level of this encryption algorithm and finds that the position permutation-only part and the substitution part can be separately broken with only ?(log₂(3MN))/8? and 2 chosen plain-images, respectively, where MN is the size of the plain-image. The effectiveness of the proposed chosen-plaintext attack is supported by concise theoretical analyses, and is verified by experimental results.     

Stainless steel coated by Cu NPs via dopamine coupling for antifouling application

Biofouling is very harmful in diverse industries. Copper nanoparticles (Cu NPs) possess excellent antifouling performances. In this study, in situ generation of Cu NPs on dopamine modified 304 stainless steel (SS) surface layer-by-layer in weak alkaline solution was reported. Field emission scanning electron microscope equipped with energy dispersive spectrometer, atomic force microscope, and X-ray photoelectron spectroscopy were utilized to analyze the surface morphology and chemical composition of the modified SS. The results demonstrated that the surface of SS was coated with polydopamine (PDA) and Cu NPs successfully. The robustness assay of the Cu NPs surface demonstrated that most Cu NPs had bound on the surface of the stainless steel firmly. Antimicrobial assays showed that modified surface possessed the ability of resistance of Escherichia coli and Staphylococcus aureus to an effectiveness of 92.1% and 80.4%, respectively. The presence of copper offers the coatings' excellent capability to inhibit effectively the adhesion of marine diatom Phaeodactylum tricornutum to an effectiveness of 98.15%. This strategy exhibited a realistic paradigm for further improving the antifouling performances of hull surfaces.     

圆形中空夹层钢管超高性能钢纤维混凝土柱抗爆性能野外实验与数值模拟

通过6根圆形中空夹层钢管超高性能钢纤维混凝土(UHPSFRCFDST)柱爆炸破坏实验,研究了轴压、折合距离、空心率和迎爆面形状对其动态响应及损伤破坏的影响,并运用LS-DYNA软件建立了爆炸荷载作用下UHPSFRCFDST柱动态响应的有限元模型。在验证了模型有效性的基础上,运用参数化分析方法,研究了轴压比、空心率、含钢率、内层和外层钢管径厚比及其强度等关键参数对圆形UHPSFRCFDST柱抗爆性能的影响。结果表明:有限元模型能够有效地分析UHPSFRCFDST柱在爆炸荷载作用下的动态响应及损伤破坏;在小于临界轴压时,提高轴压比能够提升UHPSFRCFDST柱抗爆性能,但超过临界轴压后继续提高反而会加重其损伤破坏;减小空心率或内、外层钢管径厚比均可有效提升UHPSFRCFDST柱的抗爆性能,提高含钢率或外层钢管强度也能达到相同效果,但提高内层钢管强度对其抗爆性能的提升作用并不显著。     

Growth of spinel crystals in vanadium slag and their characterization

Morphology of vanadium slags were investigated by scanning electron microscopy (SEM). The mineralogical phases were characterized by energy disperse X‐ray spectrometry (EDS) and powder X‐ray diffraction (XRD). The obtained results show that spinels and silicates are the major phases in the vanadium slag, and V is concentrated in Fe_xV_3‐xO₄ and Mg_x(V, Ti)_3‐xO₄. Both the spinel grain size and volume fraction in the slag with higher V₂O₃ content are much larger than that with lower V₂O₃ content. (Fe, Mn)₂SiO₄ and (Fe, Mn)SiO₃ have a higher proportion in the slag with lower V₂O₃ and higher SiO₂ content. The relation among cooling conditions and grain size and volume fraction of spinels is also discussed. It is found that low cooling rate and long holding time benefit spinel crystal growth, especially for the interval of 1200‐1250 °C. Both mean diameter and volume fraction of spinels could achieve or exceed the industry vanadium slag when holding more than 45 min. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)