2,418 research outputs found
Radically different kinetics at low temperatures
No full text"""The use of the CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme, or Reaction Kinetics in Uniform Supersonic Flow) technique coupled with pulsed laser photochemical kinetics methods has shown that reactions involving radicals can be very rapid at temperatures down to 10 K or below. The results have had a major impact in astrochemistry and planetology, as well as proving an exacting test for theory.\footnote{H. Sabbah, L. Biennier, I. R. Sims, Y. Georgievskii, S. J. Klippenstein, I. W. M. Smith, Science \textbf{317}, 102 (2007).} The technique has also been applied to the formation of transient complexes of interest both in atmospheric chemistry\footnote{S. D. Le Picard, M. Tizniti, A. Canosa, I. R. Sims, I. W. M. Smith, Science \textbf{328}, 1258 (2010).} and combustion.\footnote{H. Sabbah, L. Biennier, S. J. Klippenstein, I. R. Sims, B. R. Rowe, J. Phys. Chem. Lett. \textbf{1}, 2962 (2010).}
Until now, all of the chemical reactions studied in this way have taken place on attractive potential energy surfaces with no overall barrier to reaction. The F + H HF + H reaction does possess a substantial energetic barrier ( 800 K), and might therefore be expected to slow to a negligible rate at very low temperatures. In fact, this H-atom abstraction reaction does take place efficiently at low temperatures due entirely to tunneling. I will report direct experimental measurements of the rate of this reaction down to a temperature of 11 K, in remarkable agreement with state-of-the-art quantum reactive scattering calculations by François Lique (Université du Havre) and Millard Alexander (University of Maryland). \footnote{ M. Tizniti, S. D. Le Picard, F. Lique, C. Berteloite, A. Canosa, M. H. Alexander, I. R. Sims, Nature Chemistry \textbf{6}, 141 (2014).}
It is thought that long chain cyanopolyyne molecules H(C)CN may play an important role in the formation of the orange haze layer in Titan’s atmosphere. The longest carbon chain molecule observed in interstellar space, HCN, is also a member of this series. I will present new results, obtained in collaboration with Jean-Claude Guillemin (Ecole de Chimie de Rennes) and Stephen Klippenstein (Argonne National Labs), on reactions of CH, CN\footnote{S. Cheikh Sid Ely, S. B. Morales, J. C. Guillemin, S. J. Klippenstein, I. R. Sims, J. Phys. Chem. A \textbf{117}, 12155 (2013).} and CN radicals (using a new LIF scheme by Hoshina and Endo\footnote{K. Hoshina, Y. Endo, J. Chem. Phys. \textbf{127}, 184304 (2007).}) which contribute to the low temperature formation of (cyano)polyynes."""Submitted by Mary Schlembach ([email protected]) on 2014-11-21T21:55:38Z
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James Bond: international man of gastronomy
No full textThis article is concerned with the representation of food and drink in Ian Fleming’s James Bond novels. In particular, it examines how the author uses Bond’s culinary knowledge and habits of consumption as an important constituent of his hero’s character. Similarly, the food choices of other characters, notably villains, are shown to be linked, by Fleming, to core aspects of their identity − principally their ethnicity. Bond’s impulse to observe and classify, very much in evidence in the novels’ food sequences, is examined in terms of the texts’ construction of Bond as a skilled identifier of signs
REIT capital structure : an examination of the use of unsecured debt over traditional equity and changes in dividend policy
No full textThesis (M.S.)--Massachusetts Institute of Technology, Dept. of Urban Studies and Planning, 1997 (first author), and Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Architecture, 1997 (second author).Includes bibliographical references (leaves 97-98).by Joshua T. Anderson and Ian R. Ponniah.M.S
Transforming Power Relationships: Leadership, Risk, and Hope. IHS Political Science Series No. 135, May 2013
No full textChronic communal conflicts resemble the prisoner’s dilemma. Both communities prefer peace to war. But neither trusts the other, viewing the other’s gain as its own loss, so
potentially shared interests often go unrealized.
Achieving positive-sum outcomes from apparently zero-sum struggles requires a kind of riskembracing leadership. To succeed leaders must: a) see power relations as potentially
positive-sum; b) strengthen negotiating adversaries instead of weakening them; and c) demonstrate hope for a positive future and take great personal risks to achieve it.
Such leadership is exemplified by Nelson Mandela and F.W. de Klerk in the South African democratic transition. To illuminate the strategic dilemmas Mandela and de Klerk faced, we examine the work of Robert Axelrod, Thomas Schelling, and Josep Colomer, who highlight important dimensions of the problem but underplay the role of risk-embracing leadership. Finally we discuss leadership successes and failures in the Northern Ireland settlement and the Israeli-Palestinian conflict
Losses of NG2 and NeuN immunoreactivity but not astrocytic markers during early reperfusion following severe focal cerebral ischemia
No full textDiane R. Lee, Stephen C. Helps, Ian L. Gibbins, Michael Nilsson, Neil R. Sim
URI Disambiguation in the Context of Linked Data
No full textThe Linked Data initiative has given rise to an increasing number of RDF datasets, many of which are freely accessible online. These resources often arise as a result of database exports; however sufficient consideration may not be given to the unseen implications caused when they are used in the wider context of the Semantic Web. This paper investigates two popular resources, DBLP and DBpedia, and discusses whether the issues regarding identity management and co-reference resolution have been suitably addressed. We find that a large percentage of authors in DBLP have been conflated, and that disambiguation pages have been incorrectly linked using owl:sameAs within DBpedia. Systems for dealing with these issues are presented, and directions are given for future research
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Ian McHarg on City Planning
No full textProfessor lan McHarg was a visiting scholar during the 1986-87 academic year in the Department of Landscape Architecture at the University of California at Berkeley. The Berkeley Planning Journal took this opportunity to interview Prof. McHarg on the subject of city and regional planning. Prof. McHarg is a Profesos r of Landscape Archi tecture and Regional Planning at the University of Pennsyl vania, also engaged in private practice, and the author of Design With Nature. The interview was conducted on April 20, 1987, by Cliff Ellis, a doctoral student in city and regional planning at Berkeley and editor of the Berkeley Planning Journal
Forward to the Past: la sfida della Storia in Machines Like Me di Ian McEwan
No full textIn his novel, Machines Like Me (2019), Ian McEwan offers an interesting example of “alternate history” while dealing with crucial ethical issues connected with the development of Artificial Intelligence. Instead of setting his story in the future, the author chooses to set it in the past, but he radically changes the contours of the latter. Hence, the England of the early 1980s is turned into a technologically advanced society, well ahead of the scientific progress of the early 21st century. Thus, the future casts its light on the past in what appears as a typically postmodernist mélange: besides mingling genres (from speculative fiction to uchronia), McEwan also performs an intriguing hybridization of fact and fiction. The paper intends to explore the rich historical dimension of the novel, which betrays the author’s interest in the reflection on history and on its narrativization – as well as its manipulation and/or contamination – within the literary text
Amélioration de la sensibilité de détection de la spectroscopie rotationnelle millimétrique dans les écoulements supersoniques uniformes pour des applications d’astrophysique de laboratoire
No full textDans cette thèse, nous présentons la conception et le développement de deux nouveaux instruments afin d’optimiser les conditions expérimentales pour des applications d'astrophysique de laboratoire. L’objectif est d’étudier les processus collisionnels en phase gazeuse d'intérêt astrochimique à basse température en utilisant la technique CPUF (chirped pulse in uniform flow). Ce travail s'inscrit dans le cadre du projet CRESUCHIRP, un programme pluriannuel visant à construire un nouvel appareil CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) couplé à deux spectromètres CP-FTmmW (Chirped-Pulse Fourier Transform mm-Wave) dans le but de déterminer les rapports de branchement des réactions d’intérêt astrochimique. Bien que la spectroscopie CP-FTmmW soit très bien adaptée aux applications à basse température, son efficacité est affectée par de nombreuses difficultés techniques, la plus notable étant l'élargissement collisionnel, un phénomène induit par les collisions qui atténuent le signal moléculaire des espèces étudiées. Une série de mesures spectroscopiques avec un spectromètre en bande Ka a été réalisée à température ambiante pour évaluer son impact en utilisant deux molécules d'intérêt astrochimique, l’acrylonitrile et le benzonitrile sont mis en collisions avec l’hélium. Les résultats illustrent la nécessité d'optimiser l'environnement du CRESU pour permettre une détection quantitative des produits de réaction. Dans ce travail, nous présentons le développement de l'appareil SKISURF (SKImmed uniform SUpeRsonic Flow), où le flux CRESU est échantillonné via un skimmer dans un processus d'expansion secondaire, ayant lieu dans un environnement à température et pression beaucoup plus basses en créant des conditions favorables pour la détection du signal moléculaire. Un spectromètre en bande E est utilisé pour la caractérisation et la réalisation des premières mesures du rapport de branchement de la réaction CN+ éthylène à 35 K, le sondage a été effectué à une température de ~ 5 K. Un système d’une tuyère de Laval pulsée a été conçu, construit et caractérisé comme deuxième technique pour augmenter la sensibilité du CPUF. Il repose sur la pulsation des jets du CRESU à une fréquence synchronisée à l’aide d'un hacheur aérodynamique placé en amont de la tuyère de Laval ce qui permet d'augmenter l'efficacité du pompage et de réduire l'effet de pression. Il permet également de générer des flux à des températures beaucoup plus basses que celles de l'appareil CRESU classique, jusqu'à ~ 6 K. Le système présente aussi un avantage économique car il réduit la quantité de gaz et d'espèces consommés. Les aspects de la conception et la caractérisation à l'aide de méthodes numériques et expérimentales des instruments nouvellement développés sont évoqués.In this thesis we present the design and the development of two novel instruments to optimize the experimental conditions for laboratory astrophysics applications to study gas phase collisional processes of astrochemical interest at low temperatures using the CPUF (chirped pulse in uniform flow) technique. CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) apparatus coupled with two Chirped-Pulse Fourier Transform mm-Wave (CP-FTmmW) spectrometers with the aim of the determination of branching ratios of multi-channel reactions relevant to astrochemistry. Although CP-FTmmW spectroscopy is very well suited for low temperature applications, its sensitivity is challenged by many technical difficulties, the most notorious is pressure broadening, a phenomenon induced by collisions that attenuates the molecular signal of the species studied. A series of spectroscopic measurements with a Ka band spectrometer were carried out at room temperature to assess its impact using two molecules of astrochemical interest, vinyl cyanide and benzonitrile colliding with a helium buffer. The results illustrate the need to optimize the CRESU environment to allow sensitive detection of reaction products. In this work we present the development of the SKISURF (SKImmed uniform SUpeRsonic Flow) apparatus, where the CRESU flow is sampled via a skimmer in a secondary expansion process, into a much lower temperature and pressure environment creating favorable conditions for the detection of the molecular signal. An E band spectrometer is used for the characterization and conducting the first measurements of the branching ratio of the CN+ ethylene reaction at 35 K, the probing has been carried out at a temperature of 5 K. A pulsed Laval nozzle system has been designed, built and characterized as a second technique to increase the sensitivity of CPUF. It relies on pulsing the CRESU flows at a synchronized frequency with the use of an aerodynamic chopper upstream of the Laval nozzle which helps to increase the pumping efficiency and reduce the pressure effect. It also allows to generate a much lower temperature flows than the classic CRESU apparatus down to ~ 6 K. In addition, the system presents an economical advantage as it reduces the amount of gas and species consumed. The design aspects and the characterization using both numerical and experimental methods of the newly developed instruments are discussed
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