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F plasmid replication during the Escherichia coli division cycle was investigated by using the membrane-elution technique to produce cells labeled at different times during the division cycle and scintillation counting for quantitative analysis of radioactive plasmid DNA. The F plasmid replicated, like the minichromosome, during a restricted portion of the bacterial division cycle; i.e., F plasmid replication is cell-cycle specific. The F plasmid replicated at a different time during the division cycle than a minichromosome present in the same cell. F plasmid replication coincided with doubling in the rate of enzyme synthesis from a plasmid-encoded gene. When the cell cycle age of replication of the F plasmid was determined over a range of growth rates, the cell size at which the F plasmid replicated followed the same rules as did replication of the bacterial chromosome--initiation occurred when a constant mass per origin was achieved--except that the initiation mass per origin for the F plasmid was different from that for the chromosome origin. In contrast, the high-copy mini-R6K plasmid replicated throughout the division cycle.
An extraordinary downfield-shifted <sup>29</sup> Si{<sup>1</sup> H} NMR signal is seen at δ=338.5 for the platinum silylene complex [(dippe)(H)Pt=SiMes<sub>2</sub> ][MeB(C<sub>6</sub> F<sub>5</sub> )<sub>3</sub> ] (2). This remarkably stable metal silylene complex was obtained from 1 in the first intramolecular 1,2-hydride migration from silicon to a transition metal. dippe=iPr<sub>2</sub> PCH<sub>2</sub> CH<sub>2</sub> PiPr<sub>2</sub> , Mes=2,4,6-Me<sub>3</sub> C<sub>6</sub> H<sub>2</sub> .
ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTAn Alternative Synthetic Approach toward Dendritic Macromolecules: Novel Benzene-Core Dendrimers via Alkyne CyclotrimerizationStefan Hecht and Jean M. J. FréchetView Author Information Department of Chemistry, University of California Berkeley, California 94720-1460 Cite this: J. Am. Chem. Soc. 1999, 121, 16, 4084–4085Publication Date (Web):April 13, 1999Publication History Received7 December 1998Published online13 April 1999Published inissue 1 April 1999https://pubs.acs.org/doi/10.1021/ja9842215https://doi.org/10.1021/ja9842215rapid-communicationACS PublicationsCopyright © 1999 American Chemical SocietyRequest reuse permissionsArticle Views857Altmetric-Citations58LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Addition reactions,Cyclization,Dendrons,Hydrocarbons,Molecules Get e-Alerts
Age-related changes in cortical thickness have been observed during adolescence, including thinning in frontal and parietal cortices, and thickening in the lateral temporal lobes. Studies have shown sex differences in hormone-related brain maturation when boys and girls are age-matched, however, because girls mature 1-2 years earlier than boys, these sex differences could be confounded by pubertal maturation. To address puberty effects directly, this study assessed sex differences in testosterone-related cortical maturation by studying 85 boys and girls in a narrow age range and matched on sexual maturity. We expected that testosterone-by-sex interactions on cortical thickness would be observed in brain regions known from the animal literature to be high in androgen receptors. We found sex differences in associations between circulating testosterone and thickness in left inferior parietal lobule, middle temporal gyrus, calcarine sulcus, and right lingual gyrus, all regions known to be high in androgen receptors. Visual areas increased with testosterone in boys, but decreased in girls. All other regions were more impacted by testosterone levels in girls than boys. The regional pattern of sex-by-testosterone interactions may have implications for understanding sex differences in behavior and adolescent-onset neuropsychiatric disorders.
Abstract A sp 3 –sp 2 CC cross‐coupling reaction catalyzed by gold in the absence of a sacrificial oxidant is described. Vital to the success of this method is the implementation of a bimetallic catalyst bearing a bis(phosphino)amine ligand. A mechanistic hypothesis is presented, and observable transmetalation, CBr oxidative addition, and CC reductive elimination in a model gold complex are shown. We expect that this method will serve as a platform for the development of novel transformations involving redox‐active gold catalysts.
Although it flows through regions of northwestern California that are thought to be relatively well watered, the Eel River is increasingly stressed by drought and water withdrawals. We discuss how critical threshold changes in summer discharge can potentially tilt the Eel from a recovering salmon-supporting ecosystem toward a cyanobacterially degraded one. To maintain food webs and habitats that support salmonids and suppress harmful cyanobacteria, summer discharge must be sufficient to connect mainstem pools hydrologically with gently moving, cool base flow. Rearing salmon and steelhead can survive even in pools that become isolated during summer low flows if hyporheic exchange is sufficient. But if the ground water discharge that sustains river flow during summer drought drops below critical levels, warm stagnant conditions will kill salmonids, and cyanobacteria will thrive. Challenges and opportunities for restoring the Eel and increasing its resilience to climate extremes, water diversions, and excessive loading of fine sediments point toward exploring how land use and terrestrial vegetation affect delivery from uplands of water, heat, sediments, solutes, organic matter, and organisms—in ways that either heal or damage rivers.
In this paper we generalize the horseshoe twist theorem of Brown and Chua [1991] and derive a wide class of ODEs, with and without dissipation terms, for which the Poincare map can be expressed in closed form as FTFT where T is a generalized twist. We show how to approximate the Poincaré maps of nonlinear ODEs with continuous periodic forcing by Poincare maps which have a closed-form expression of the form FT 1 T 2 … T n where the T i are twists. We extend the twist-and-flip map to three dimensions with and without damping. Further, we demonstrate how to use the square-wave analysis to argue for the existence of a twist-and-flip paradigm for the Poincare map of the van der Pol equation with square-wave forcing. We apply this analysis to the cavitation bubble oscillator that appears in Parlitz et al. [1991] and prove a variation of the horseshoe twist theorem for the twist-and-shift map, which models the cavitation bubble oscillator. We present illustrations of the diversity of the dynamics that can be found in the generalized twist-and-flip map, and we use a pair of twist maps to provide a specific and very simple illustration of the Smale horseshoe. Finally, we use the twist-and-shift map of the cavitation bubble oscillators to demonstrate that the addition of sufficient linear damping to a dynamical system having PBS (Poincaré–Birkhoff–Smale) chaos may cause the chaos to become detectable in computer simulations.
