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91.
Sakamoto Y Kaneda M Terasaki O Zhao DY Kim JM Stucky G Shin HJ Ryoo R 《Nature》2000,408(6811):449-453
Mesostructured composite materials, with features ranging from 20 to 500 A in size, are obtained by the kinetically controlled competitive assembly of organic and inorganic species into nanostructured domains. Short-range order is limited, and long-range order is determined by weak forces such as van der Waals or hydrogen-bonding. Three-dimensional mesoporous materials obtained by removing the organic phase are of particular interest for applications such as catalysis and chemical sensing or separation, for which structural features such as cavity shape, connectivity and ordered bimodal porosity are critical. But atomic-scale structural characterization by the usual diffraction techniques is challenging for these partially ordered materials because of the difficulty in obtaining large (> 10 microm) single crystals, and because large repeat spacings cause diffraction intensities to fall off rapidly with scattering angle so that only limited small-angle data are available. Here we present a general approach for the direct determination of three-dimensional mesoporous structures by electron microscopy. The structure solutions are obtained uniquely without pre-assumed models or parametrization. We report high-resolution details of cage and pore structures of periodically ordered mesoporous materials, which reveal a highly ordered dual micro- and mesoscale pore structure. 相似文献
92.
Montgomery KT Lee E Miller A Lau S Shim C Decker J Chiu D Emerling S Sekhon M Kim R Lenz J Han J Ioshikhes I Renault B Marondel I Yoon SJ Song K Murty VV Scherer S Yonescu R Kirsch IR Ried T McPherson J Gibbs R Kucherlapati R 《Nature》2001,409(6822):945-946
Our sequence-tagged site-content map of chromosome 12 is now integrated with the whole-genome fingerprinting effort. It provides accurate and nearly complete bacterial clone coverage of chromosome 12. We propose that this integrated mapping protocol serves as a model for constructing physical maps for entire genomes. 相似文献
93.
Methods for backcasting,nowcasting and forecasting using factor‐MIDAS: With an application to Korean GDP 下载免费PDF全文
We utilize mixed‐frequency factor‐MIDAS models for the purpose of carrying out backcasting, nowcasting, and forecasting experiments using real‐time data. We also introduce a new real‐time Korean GDP dataset, which is the focus of our experiments. The methodology that we utilize involves first estimating common latent factors (i.e., diffusion indices) from 190 monthly macroeconomic and financial series using various estimation strategies. These factors are then included, along with standard variables measured at multiple different frequencies, in various factor‐MIDAS prediction models. Our key empirical findings as follows. (i) When using real‐time data, factor‐MIDAS prediction models outperform various linear benchmark models. Interestingly, the “MSFE‐best” MIDAS models contain no autoregressive (AR) lag terms when backcasting and nowcasting. AR terms only begin to play a role in “true” forecasting contexts. (ii) Models that utilize only one or two factors are “MSFE‐best” at all forecasting horizons, but not at any backcasting and nowcasting horizons. In these latter contexts, much more heavily parametrized models with many factors are preferred. (iii) Real‐time data are crucial for forecasting Korean gross domestic product, and the use of “first available” versus “most recent” data “strongly” affects model selection and performance. (iv) Recursively estimated models are almost always “MSFE‐best,” and models estimated using autoregressive interpolation dominate those estimated using other interpolation methods. (v) Factors estimated using recursive principal component estimation methods have more predictive content than those estimated using a variety of other (more sophisticated) approaches. This result is particularly prevalent for our “MSFE‐best” factor‐MIDAS models, across virtually all forecast horizons, estimation schemes, and data vintages that are analyzed. 相似文献
94.
Genome shuffling leads to rapid phenotypic improvement in bacteria 总被引:51,自引:0,他引:51
For millennia, selective breeding, on the basis of biparental mating, has led to the successful improvement of plants and animals to meet societal needs. At a molecular level, DNA shuffling mimics, yet accelerates, evolutionary processes, and allows the breeding and improvement of individual genes and subgenomic DNA fragments. We describe here whole-genome shuffling; a process that combines the advantage of multi-parental crossing allowed by DNA shuffling with the recombination of entire genomes normally associated with conventional breeding. We show that recursive genomic recombination within a population of bacteria can efficiently generate combinatorial libraries of new strains. When applied to a population of phenotypically selected bacteria, many of these new strains show marked improvements in the selected phenotype. We demonstrate the use of this approach through the rapid improvement of tylosin production from Streptomyces fradiae. This approach has the potential to facilitate cell and metabolic engineering and provide a non-recombinant alternative to the rapid production of improved organisms. 相似文献
95.
金熙哲 《齐齐哈尔大学学报(自然科学版)》2006,22(1):1-6
研究了软件可信成长模型的bayesian推论和模型选择方法。如果用内在错误和错误之间的时间间隔来模化成长模型,在软件开发阶段,可以非常有效的利用其成长模型。本文在解决多重积分问题时利用Gibbs抽样方法来计算出算后分布。一般顺序统计量模型依赖具有扩散算前分布特性的软件。对一般顺序统计量模型依实行了bayesian总体参数的推断,还实行了有效的模型选择方法。模型的设定和判断标准可用于利用方差相乘和的适合度鉴定和趋势鉴定。为了取得相应的值例,本文在分析错误资料时利用了AllenP.NikoraandMichaelR.Lyu[13]提出的SYS2软件错误资料。 相似文献
96.
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98.
Mi Gyung Kim 《Annals of science》2013,70(3):291-318
The balloon mania between 1783 and 1785 put an extraordinary strain on the Paris Academy of Sciences, threatening its status as the highest tribunal of European science. Faced with repeated royal directives and public frenzy, the Academy manoeuvred carefully to steer the research toward the hydrogen balloon and thereby to maintain its scientific superiority. Antoine-Laurent Lavoisier seized this moment when the promise of ‘the empire of airs’ brought science to the centre of public attention to push his theoretical reform for chemistry. He utilized the established protocol of the Academy and the resources of the Republic of Letters to broadly publicize his first decomposition of water in April 1784. Once he attained the publicity and the balloon fever began to cool, he staged a much more elaborate experiment for the experts in February 1785. Although this second, large-scale experiment cost much expense and effort, Lavoisier never published a full account. The differential care given to the two experiments can only be understood in their divergent rhetorical contexts. The written accounts in 1784 addressed the court of public opinion, while the exclusive performance in 1785 aimed at the court of experts to inaugurate the collaborative phase of the Chemical Revolution. 相似文献
99.
Chaehyun Yook Shaul Druckmann Jinhyun Kim 《Cellular and molecular life sciences : CMLS》2013,70(24):4747-4757
Mapping mammalian synaptic connectivity has long been an important goal of neuroscientists since it is considered crucial for explaining human perception and behavior. Yet, despite enormous efforts, the overwhelming complexity of the neural circuitry and the lack of appropriate techniques to unravel it have limited the success of efforts to map connectivity. However, recent technological advances designed to overcome the limitations of conventional methods for connectivity mapping may bring about a turning point. Here, we address the promises and pitfalls of these new mapping technologies. 相似文献
100.
Interleukin (IL)-17 is a pro-inflammatory cytokine that plays critical roles in host defense against extracellular bacteria and fungi and also in the pathogenesis of autoimmune diseases. While CD4+ TCRαβ+ T helper (Th) 17 cells are the best-described cellular source of IL-17, many innate-like T cells are in fact potent producers of IL-17. Given the increasing interest in therapeutic modulation of the IL-17 axis, it is crucial to better understand the cellular origins of IL-17 in various infection and diseases settings. While the diverse population of IL-17-producing T cells share many common characteristics, notable differences also exist. In this review, we discuss the heterogeneity of IL-17-producing T cell types focusing on their development, regulation, and function. 相似文献