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An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
In vanadium dioxide, the interplay between coherent lattice transformation and electronic correlation drives an insulator-to-metal transition (IMT). This phase commutation can be triggered by temperature, pressure, doping or deposition of optical energy. Here we demonstrate that an atomically-strong terahertz electric field initiates a metastable ultrafast IMT in vanadium dioxide without a concomitant lattice transformation. The free-space terahertz field acts as off-resonant excitation with photon energy below the lattice phonons and the interband transitions. Differently from optical and infrared excitation, terahertz interaction leads to a full IMT by interband Zener tunneling with a negligible entropy deposition. In previous experiments the temporal dynamics of IMT in VO2 could be only indirectly inferred. We disentangle the electronic and lattice contributions to the IMT on a sub-picosecond timescale. Near the critical temperature the IMT becomes dissipative and the terahertz field concludes the lattice-assisted metallic nucleation initiated by heating. The method of strong-field induced phase transition presented here is applicable to a wide class of strongly correlated systems and will enable the discovery of novel metastable phases.
Abstract Passivity is perhaps the most basic concept in circuit theory. Unfortunately, the existing definitions of passivity are too restrictive and often contradict one another. In this paper, a new passivity definition is proposed which is applicable to all n ‐port and ( n + 1)‐terminal devices—including time‐varying, non‐linear , and distributed circuit elements. This definition generalizes and reconciles several recent conflicting definitions.
Stearoyl-acyl-carrier-protein (ACP) desaturase (EC 1.14.99.6) was purified to homogeneity from avocado mesocarp, and monospecific polyclonal antibodies directed against the protein were used to isolate full-length cDNA clones from Ricinus communis (castor) seed and Cucumis sativus (cucumber). The nucleotide sequence of the castor clone pRCD1 revealed an open reading frame of 1.2 kilobases encoding a 396-amino acid protein of 45 kDa. The cucumber clone pCSD1 encoded a homologous 396-amino acid protein with 88% amino acid identity to the castor clone. Expression of pRCD1 in Saccharomyces cerevisiae resulted in the accumulation of a functional stearoyl-ACP desaturase, demonstrating that the introduction of this single gene product was sufficient to confer soluble desaturase activity to yeast. There was no detectable identity between the deduced amino acid sequences of the castor delta 9-stearoyl-ACP desaturase and either the delta 9-stearoyl-CoA desaturase from rat or yeast or the delta 12 desaturase from Synechocystis, suggesting that these enzymes may have evolved independently. However, there was a 48-residue region of 29% amino acid sequence identity between residues 53 and 101 of the castor desaturase and the proximal border of the dehydratase region of the fatty acid synthase from yeast. Stearoyl-ACP mRNA was present at substantially higher levels in developing seeds than in leaf and root tissue, suggesting that expression of the delta 9 desaturase is developmentally regulated.
Abstract The effects of interaction with surrounding water on the dynamic response behaviour of cantilever tower structures are studied. Expressions for response to harmonic ground motion in individual modes of vibration, including hydrodynamic interaction, are presented, the accuracy of responses obtained by ignoring surface waves and compressibility of water in the hydrodynamic solutions is evaluated, the effects of hydrodynamic interaction on the fundamental period of vibration are studied and the commonly used ‘added mass’ approach to account for effects of surrounding water is examined. The conclusions deduced from the results of this investigation include the following. Interaction with surrounding water increases the fundamental period of vibration of the tower and decreases the modal damping ratio. Compressibility of water has essentially no influence in the hydrodynamic effects on slender towers. The traditional definition of added mass is conceptually deficient, but is simple to employ; the errors in this simple added mass representation are negligible for the first mode of vibration of towers.
We sampled isolated trees and tree clusters from a blue oak, Quercus douglasii, savanna to determine the spatial heterogeneity of fine root biomass and soil carbon across the landscape as a function of tree size and configuration. We aimed to understand how fine root structure enables sustained ecosystem metabolism through a summer of limited moisture and high heat and facilitates resource acquisition during the short period of high resource supply. An additional goal was to provide a basis for upscaling root biomass and soil carbon to the landscape scale. We sampled trees of different size and tree clusters via a stratified sampling scheme that accounted for spatial heterogeneity in root biomass and soil carbon with lateral distance from the tree bole, or cluster centre, and soil depth. We upscaled these estimates using site-specific information from a lidar survey. We found that fine roots and soil carbon are spatially heterogeneous in their landscape distribution and greatly increase with tree size. We also found that Q.douglasii possesses a dimorphic fine root architecture, uniquely suited to the region's climatic constraints and exhibits morphological plasticity among trees of different size and physical setting.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSolvatochromism as a probe of the microenvironment in dendritic polyethers: transition from an extended to a globular structureCraig J. Hawker, Karen L. Wooley, and Jean M. J. FrechetCite this: J. Am. Chem. Soc. 1993, 115, 10, 4375–4376Publication Date (Print):May 1, 1993Publication History Published online1 May 2002Published inissue 1 May 1993https://pubs.acs.org/doi/10.1021/ja00063a071https://doi.org/10.1021/ja00063a071research-articleACS PublicationsRequest reuse permissionsArticle Views809Altmetric-Citations210LEARN 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-Alertsclose Get e-Alerts
While O is often seen in spectra of Type Ia supernovae (SNe Ia) as both\nunburned fuel and a product of C burning, C is only occasionally seen at the\nearliest times, and it represents the most direct way of investigating\nprimordial white dwarf material and its relation to SN Ia explosion scenarios\nand mechanisms. In this paper, we search for C absorption features in 188\noptical spectra of 144 low-redshift (z < 0.1) SNe Ia with ages <3.6 d after\nmaximum brightness. These data were obtained as part of the Berkeley SN Ia\nProgram (BSNIP; Silverman et al. 2012) and represent the largest set of SNe Ia\nin which C has ever been searched. We find that ~11 per cent of the SNe studied\nshow definite C absorption features while ~25 per cent show some evidence for C\nII in their spectra. Also, if one obtains a spectrum at t < -5 d, then there is\na better than 30 per cent chance of detecting a distinct absorption feature\nfrom C II. SNe Ia that show C are found to resemble those without C in many\nrespects, but objects with C tend to have bluer optical colours than those\nwithout C. The typical expansion velocity of the C II {\\lambda}6580 feature is\nmeasured to be 12,000-13,000 km/s, and the ratio of the C II {\\lambda}6580 to\nSi II {\\lambda}6355 velocities is remarkably constant with time and among\ndifferent objects with a median value of ~1.05. While the pseudo-equivalent\nwidths (pEWs) of the C II {\\lambda}6580 and C II {\\lambda}7234 features are\nfound mostly to decrease with time, we see evidence of a significant increase\nin pEW between ~12 and 11 d before maximum brightness, which is actually\npredicted by some theoretical models. The range of pEWs measured from the BSNIP\ndata implies a range of C mass in SN Ia ejecta of about (2-30) * 10^-3 M_Sun.\n
Pore ‐ size ‐ specific functionalization is a novel approach that allowspreviously undreamed of control of the location of groups undergoing reaction in the surface modigication of preformedporous polymers. That sozespecific functionalization makes possible the simultaneous accommodation of seemingly incompatible requirements is demonstrated by the preparation of porous polyner beads with bimodal surface chemistry. Applications of this technique are foreseen in thechromatographic separation of complex miztures, sensors, catalyses, and eczyme immobilization.
Reactive carbon capture (RCC) is a promising solution for carbon capture and utilization. RCC involves CO2 capture, typically with amine solutions to form carbamate, followed by immediate conversion into value-added chemicals and fuels, typically via electrochemical means. RCC may enhance CO2 reduction (CO2R) by overcoming the inherent limiting low solubility of CO2 in aqueous solutions. In this work, we present a systematic study of the influence of monoethanolamine (MEA) on CO2R performance over an Ag cathode in KHCO3 electrolytes. Contrary to prior work, the study finds no evidence for the direct reduction of carbamate anions. Instead, the presence of MEA suppresses the rate of CO formation while increasing that of H2. These results are supported by a boundary-layer continuum model of mass transport and reaction that correctly predicts experimental trends and demonstrates that MEA reduces the concentration of CO2 near the cathode. Thus, alternative strategies are necessary to achieve RCC in aqueous environments.
