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411.
A new effect is described by which primordial gravity waves leave a permanent signature in the large scale structure of the Universe. The effect occurs at second order in perturbation theory and is sensitive to the order in which perturbations on different scales are generated. We derive general forecasts for the detectability of the effect with future experiments and consider observations of the prereionization gas through the 21 cm line. It is found that the Square Kilometer Array will not be competitive with current cosmic microwave background constraints on primordial gravity waves from inflation. However, a more futuristic experiment could, through this effect, provide the highest ultimate sensitivity to tensor modes and possibly even measure the tensor spectral index. It is thus a potentially quantitative probe of the inflationary paradigm. 相似文献
412.
Multicomponent Double Diels–Alder/Nazarov Tandem Cyclization of Symmetric Cross‐Conjugated Diynones to Generate [6‐5‐6] Tricyclic Products
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Rachael A. Carmichael Prof. Wesley A. Chalifoux 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(26):8781-8785
The construction of complex polycyclic terpenoid products in an efficient and step‐economical manner using multicomponent and tandem processes is highly valuable. Herein, we report a tandem cyclization sequence that initiates with a multicomponent double Diels–Alder reaction of cross‐conjugated diynones, followed by a Nazarov cyclization to efficiently produce [6‐5‐6] tricyclic products with excellent regio‐ and diastereoselectivity. This methodology generates five new carbon–carbon bonds, three rings, quaternary or vicinal quaternary carbons, and stereogenic centers in a one‐pot reaction. 相似文献
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Back Cover: The Critical Role Played by the Catalytic Moiety in the Early‐Time Photodynamics of Hydrogen‐Generating Bimetallic Photocatalysts (ChemPhysChem 17/2016)
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Brouwer’s views on the foundations of mathematics have inspired the study of intuitionistic logic, including the study of the intuitionistic propositional calculus and its extensions. The theory of these systems has become an independent branch of logic with connections to lattice theory, topology, modal logic, and other areas. This paper aims to present a modern account of semantics for intuitionistic propositional systems. The guiding idea is that of a hierarchy of semantics, organized by increasing generality: from the least general Kripke semantics on through Beth semantics, topological semantics, Dragalin semantics, and finally to the most general algebraic semantics. While the Kripke, topological, and algebraic semantics have been extensively studied, the Beth and Dragalin semantics have received less attention. We bring Beth and Dragalin semantics to the fore, relating them to the concept of a nucleus from pointfree topology, which provides a unifying perspective on the semantic hierarchy. 相似文献
418.
Paolo Lecchi Jinghua Zhao Wesley S. Wiggins Tzong‐Hao Chen Greg P. Bertenshaw Ping F. Yip Brian C. Mansfield John M. Peltier 《Rapid communications in mass spectrometry : RCM》2009,23(12):1817-1824
Direct injection mass spectrometric analysis of biological samples is potentially an attractive approach to the discovery of diagnostic patterns for specific pathophysiological conditions because of its speed and simplicity. Despite the possible benefits offered by such a method, its extensive application has been limited so far by several factors, including the inadequate reproducibility of the analytical results. We describe a method for monitoring and optimizing the performance of mass spectrometers used for biomarker discovery studies, based on the analysis of patterns of standardized spectral features. The method was successfully applied to maintaining spectral reproducibility during a multi‐day analysis of hundreds of serum samples despite an ion source failure, which necessitated minor maintenance. The monitoring method allowed the early detection of that failure and the restoration of the spectral profiles after the system was restarted. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
419.
Claire Deville Sandeep K. Padamati Jonas Sundberg Vickie McKee Wesley R. Browne Christine J. McKenzie 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2016,128(2):555-559
A MnII complex, [Mn(dpeo)2]2+ (dpeo=1,2‐di(pyridin‐2‐yl)ethanone oxime), activates O2, with ensuing stepwise oxidation of the methylene group in the ligands providing an alkoxide and ultimately a ketone group. X‐ray crystal‐structure analysis of an intermediate homoleptic alkoxide MnIII complex shows tridentate binding of the ligand via the two pyridyl groups and the newly installed alkoxide moiety, with the oxime group no longer coordinated. The structure of a MnII complex of the final ketone ligand, cis‐[MnBr2(hidpe)2] (hidpe=2‐(hydroxyimino)‐1,2‐di(pyridine‐2‐yl)ethanone) shows that bidentate oxime/pyridine coordination has been resumed. H218O and 18O2 labeling experiments suggest that the inserted O atoms originate from two different O2 molecules. The progress of the oxygenation was monitored through changes in the resonance‐enhanced Raman bands of the oxime unit. 相似文献
420.
Wesley B. Swords Sarah J. C. Simon Fraser G. L. Parlane Dr. Rebecca K. Dean Cameron W. Kellett Dr. Ke Hu Prof. Gerald J. Meyer Prof. Curtis P. Berlinguette 《Angewandte Chemie (International ed. in English)》2016,55(20):5956-5960
A homologous series of donor–π–acceptor dyes was synthesized, differing only in the identity of the halogen substituents about the triphenylamine (TPA; donor) portion of each molecule. Each Dye‐X (X=F, Cl, Br, and I) was immobilized on a TiO2 surface to investigate how the halogen substituents affect the reaction between the light‐induced charge‐separated state, TiO2(e?)/ Dye‐X+ , with iodide in solution. Transient absorption spectroscopy showed progressively faster reactivity towards nucleophilic iodide with more polarizable halogen substituents: Dye‐F < Dye‐Cl < Dye‐Br < Dye‐I . Given that all other structural and electronic properties for the series are held at parity, with the exception of an increasingly larger electropositive σ‐hole on the heavier halogens, the differences in dye regeneration kinetics for Dye‐Cl , Dye‐Br , and Dye‐I are ascribed to the extent of halogen bonding with the nucleophilic solution species. 相似文献