We investigate the effect of O impurities on the thermoelectric properties of ZnSe from a combination of first-principles and analytic calculations. It is demonstrated that dilute amounts of O impurities introduce peaks in the density of states (DOS) above the conduction band minimum, and that the charge density near the DOS peaks is substantially attracted toward O atoms due to their high electronegativity. The impurity-induced peaks in the DOS result in a sharp increase of the room-temperature Seebeck coefficient and power factor from those of O-free ZnSe by a factor of 30 and 180, respectively. Furthermore, this effect is found to be absent when the impurity electronegativity well matches the host that it substitutes. The results suggest that highly electronegativity-mismatched alloys can be designed for high performance thermoelectric applications.
FLUXNET is a global network of micrometeorological flux measurement sites that measure the exchanges of carbon dioxide, water vapor, and energy between the biosphere and atmosphere. At present over 140 sites are operating on a long-term and continuous basis. Vegetation under study includes temperate conifer and broadleaved (deciduous and evergreen) forests, tropical and boreal forests, crops, grasslands, chaparral, wetlands, and tundra. Sites exist on five continents and their latitudinal distribution ranges from 70°N to 30°S.\nFLUXNET has several primary functions. First, it provides infrastructure for compiling, archiving, and distributing carbon, water, and energy flux measurement, and meteorological, plant, and soil data to the science community. (Data and site information are available online at the FLUXNET Web site, http://www-eosdis.ornl.gov/FLUXNET/.) Second, the project supports calibration and flux intercomparison activities. This activity ensures that data from the regional networks are intercomparable. And third, FLUXNET supports the synthesis, discussion, and communication of ideas and data by supporting project scientists, workshops, and visiting scientists. The overarching goal is to provide information for validating computations of net primary productivity, evaporation, and energy absorption that are being generated by sensors mounted on the NASA Terra satellite.\nData being compiled by FLUXNET are being used to quantify and compare magnitudes and dynamics of annual ecosystem carbon and water balances, to quantify the response of stand-scale carbon dioxide and water vapor flux densities to controlling biotic and abiotic factors, and to validate a hierarchy of soil-plant-atmosphere trace gas exchange models. Findings so far include 1) net C02 exchange of temperate broadleaved forests increases by about 5.7 g C m~2 day-1 for each additional day that the growing season is extended; 2) the sensitivity of net ecosystem C02 exchange to sunlight doubles if the sky is cloudy rather than clear; 3) the spectrum of C02 flux density exhibits peaks at timescales of days, weeks, and years, and a spectral gap exists at the month timescale; 4) the optimal temperature of net C02 exchange varies with mean summer temperature; and 5) stand age affects carbon dioxide and water vapor flux densities.
ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTCatecholborane Bound to Titanocene. Unusual Coordination of Ligand σ-BondsJohn F. Hartwig, Clare N. Muhoro, Xiaoming He, Odile Eisenstein, Ramon Bosque, and Feliu MaserasView Author Information Department of Chemistry, Yale University P.O. Box 208107, New Haven, Connecticut 06520-8107 Laboratoire de Structure et Dynamique des Systemes̀ Moléculaires et Solides, UMR 5636 Université de Montpellier II, Montpellier, France Cite this: J. Am. Chem. Soc. 1996, 118, 44, 10936–10937Publication Date (Web):November 6, 1996Publication History Received21 June 1996Published online6 November 1996Published inissue 1 January 1996https://pubs.acs.org/doi/10.1021/ja962086vhttps://doi.org/10.1021/ja962086vrapid-communicationACS PublicationsCopyright © 1996 American Chemical SocietyRequest reuse permissionsArticle Views1637Altmetric-Citations146LEARN 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,Anions,Group 13 compounds,Inorganic compounds,Nuclear magnetic resonance spectroscopy Get e-Alerts
We report a new system for the silylation of aryl C-H bonds. The combination of [Ir(cod)(OMe)] 2 and 2,9-Me 2 -phenanthroline (2,9-Me 2 phen) catalyzes the silylation of arenes at lower temperatures and with faster rates than those reported previously, when the hydrogen byproduct is removed, and with high functional group tolerance and regioselectivity. Inhibition of reactions by the H 2 byproduct is shown to limit the silylation of aryl C-H bonds in the presence of the most active catalysts, thereby masking their high activity. Analysis of initial rates uncovered the high reactivity of the catalyst containing the sterically hindered 2,9-Me 2 phen ligand but accompanying rapid inhibition by hydrogen. With this catalyst, under a flow of nitrogen to remove hydrogen, electron-rich arenes, including those containing sensitive functional groups, undergo silylation in high yield for the first time, and arenes that underwent silylation with prior catalysts react over much shorter times with lower catalyst loadings. The synthetic value of this methodology is demonstrated by the preparation of key intermediates in the synthesis of medicinally important compounds in concise sequences comprising silylation and functionalization. Mechanistic studies demonstrate that the cleavage of the aryl C-H bond is reversible and that the higher rates observed with the 2,9-Me 2 phen ligand is due to a more thermodynamically favorable oxidative addition of aryl C-H bonds.
Photosynthesis is a light-driven process that sustains virtually all life on earth. However, light energy in excess of what is required for the saturation of photosynthesis causes photo-oxidative damage to the D1/32 kD (psbA gene product) reaction center protein of photosystem II. If not corrected, such photodamage could cause inhibition of photosynthesis and plant growth. Through evolution, organisms of oxygenic photosynthesis devised a unique repair mechanism by which to recover from this frequently occurring photo-oxidative damage. The repair process entails selective degradation and replacement of the photodamaged D1 reaction center protein in the thylakoid membrane of photosynthesis. In this chapter, up-to-date information about the photosystem II (PSII) damage and repair cycle in the model unicellular green alga Dunaliella salina Teod. [Eukaryota; Viridiplantae; Chlorophyta; Chlorophyceae; Chlamydomonadales; Dunaliellaceae; Dunaliella] is presented. The chapter first examines the physiology of cellular and chloroplast acclimation to irradiance. Examples of environmental and biotic factors that modulate the PSII photodamage are also provided. Lastly, the temporal sequence of events and current knowledge on the molecular mechanism of the PSII repair process are summarized in detail. Emphasis is placed on the role of the ELIP/Cbr protein and of the carotenoid zeaxanthin during D1 turnover and PSII repair. This chapter also examines the role of the chloroplast-localized heat-shock protein 70B (HSP70B) in facilitating the disassembly of photodamaged PSII and insertion of a de novo synthesized D1 protein in the PSII reaction center complex.
Rutile GeO<sub>2</sub> and related materials are attracting interest due to their ultrawide band gaps and potential for ambipolar doping in high-power electronic applications. This study examines the growth of rutile Sn<sub>1-<i>x</i></sub>Ge<sub><i>x</i></sub>O<sub>2</sub> films through oxygen-plasma-assisted hybrid molecular beam epitaxy (hMBE). The film composition and thickness are evaluated across a range of growth conditions, with the outcomes rationalized by using density functional theory calculations. We find that up to 34% Ge can be successfully incorporated into Sn<sub>1-<i>x</i></sub>Ge<sub><i>x</i></sub>O<sub>2</sub>/r-Al<sub>2</sub>O<sub>3</sub> (<i>x</i> ≤ 0.34) at 600 °C. Our phase diagram calculations suggest that spinodal decomposition occurs at Ge concentrations exceeding 34%. However, the formation of a Ge-rich rutile phase is inhibited by amorphization of the Ge-rich film and volatility of GeO. We therefore speculate that maximizing the Ge content requires higher Ge flux and more oxidizing environments, providing insights into the growth mechanism of Sn<sub>1-<i>x</i></sub>Ge<sub><i>x</i></sub>O<sub>2</sub> and paving the way toward the synthesis of pure rutile GeO<sub>2</sub> films.
A reversible physiological process provides for the temporal separation of oxygen evolution and hydrogen production in a microorganism, which includes the steps of growing a culture of the microorganism in medium under illuminated conditions to accumulate an endogenous substrate, depleting from the medium a nutrient selected from the group consisting of sulfur, iron, and/or manganese, sealing the culture from atmospheric oxygen, incubating the culture in light whereby a rate of light-induced oxygen production is equal to or less than a rate of respiration, and collecting an evolved gas. The process is particularly useful to accomplish a sustained photobiological hydrogen gas production in cultures of microorganisms, such as Chlamydomonas reinhardtii.
With no agreement yet reached between Greece and its creditors, there are doubts over whether the country will be able to make a scheduled debt repayment to the International Monetary Fund in early June. In an interview with EUROPP’s editor Stuart Brown, Barry Eichengreen discusses whether a compromise is still possible, what a default would mean for the country, and how well Europe is prepared for a potential Greek exit from the euro.
The configurational theory of organizations was used to analyze the relationships among organization environment, structure, and performance in proprietary nursing homes. This theory extends previous contingency theory research and conceptualization by including performance as the main focus behind organization design activities. Thirty proprietary nursing homes in the state of Washington responded to comprehensive interviews and survey questionnaires designed to measure variables specified in the configurational theory. The results of this study suggest partial support for the configurational theory; most notably in explaining differences in efficiency among nursing homes operating in low intensity environments.
In this paper, we proposed a discrete-time cellular neural network (DTCNN) structure for the labelling of digital images. First, we present the concept and the structure of reversible DTCNN, which can be used to generate 2D binary random image sequences. Then both the original image and the copyright label, which is often another binary image, are used to generate a binary random key image. The key image is then used to scramble the original image. Due to the reversibility of a reversible DTCNN, the same reversible DTCNN is used to recover the copyright label from a labelled image. Due to the high speed of a DTCNN chip, our method can be used to label image sequences, e.g., video sequences, in real time. Computer simulation results are presented.
We have confirmed that the precursor star of the unusual Supernova 1954J (also known as Variable 12) in NGC 2403 survived what appears to have been a super-outburst, similar to the 1843 Great Eruption of eta Carinae in the Galaxy. The apparent survivor has changed little in brightness and color over the last eight years, and a Keck spectrum reveals characteristics broadly similar to those of eta Car. This is further suggested by our identification of the actual outburst-surviving star in high-resolution images obtained with the Advanced Camera for Surveys on the Hubble Space Telescope. We reveal this ``supernova impostor'' as a highly luminous (M_V^0 ~ -8.0 mag), very massive (M_initial >~ 25 Msun) eruptive star, now surrounded by a dusty (A_V ~ 4 mag) nebula, similar to eta Car's famous Homunculus.
First-time demonstration of constitutive isoprene hydrocarbons production in a fermentative eukaryote operated through the mevalonic acid pathway. The work provides concept validation for the utilization of S. cerevisiae, as a platform for the production of volatile hydrocarbon biofuels and chemicals.
