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Near Resonance Charge Exchange in Ion-Atom Collisions of Lithium Isotopes
No full textCollisions of ions and atoms of (6)Li and (7)Li are explored theoretically over a wide range of energy from 10(-14) to 1 eV. Accurate ab initio calculations are carried Out of the Born-Oppenheimer potentials and the nonadiabatic couplings that are responsible for the near resonance charge exchange. Scattering studies show that the calculated charge exchange cross section follows Wigner's law for inelastic processes for energies below 10(-10) eV and that the zero temperature rate constant for it is 2.1 x 10(-9) cm(3) s(-1). At collision energies much larger than the isotope shift of the ionization potentials of the atoms, we show that the near resonance charge exchange process is equivalent to the resonance charge exchange with cross sections having a logarithmic dependence on energy. A comparison with the Langevin model at intermediate energies is also presented
Dalgarno in Paris
No full textabstract : The paper reports on a recent discovery that in Paris two manuscripts are conserved, which are concerned with two distinct but closely connected inventions by George Dalgarno : a universal character and an artificial language. The manuscripts were written in 1657 by a visitor to Oxford who probably came from Paris. The paper recapitulates the early history of Dalgarno' s scheme, paying special attention to a broadsheet he published in 1657. The Paris manuscripts contain a faithful Latin translation of parts of the content of this broadsheet, and some additional material. The manuscripts enable us to fill in some of the details of the development of Dalgarno' s early scheme. Moreover, their very existence sheds further light on the network of scholarly contacts regarding universal language. Finally, the manuscripts illustrate the importance of the relationship between spoken and written language for 17th century ideas on universal language.RÉSUMÉ : Cet article rend compte de la découverte récente de deux manuscrits conservés à Paris, qui traitent de deux inventions par George Dalgarno (1616?- 1687) distinctes mais étroitement liées : un « caractère universel » et une langue artificielle. Les manuscrits ont été écrits en 1657 par un visiteur à Oxford qui probablement venait de Paris. L'article récapitule la première période du plan de Dalgarno, prêtant attention spécialement à une « grande feuille » publiée par Dalgarno en 1657. Les manuscrits parisiens contiennent une traduction fidèle de l'Anglais au Latin de certaines parties du contenu de cette grande feuille, et du matériel additionnel. Les manuscrits nous permettent de remplir quelques détails du développement du plan de Dalgarno. En outre, le fait même qu'ils existent éclaircit l'entrelacement des contactes entre savants relativement au thème de la langue universelle. Finalement, les manuscrits illustrent l'importance du rapport entre langue écrite et langue parlée pour les idées sur la langue universelle au xvne siècle.Maat Jaap, Cram David. Dalgarno in Paris. In: Histoire Épistémologie Langage, tome 20, fascicule 2, 1998. Théories des cas. pp. 167-179
Re-annotation of 12,495 prokaryotic 16S rRNA 3’ ends and analysis of Shine-Dalgarno and anti-Shine-Dalgarno sequences
No full textWe examined 20,648 prokaryotic unique taxids with respect to the annotation of the 3’ end of the 16S rRNA, which contains the anti-Shine-Dalgarno sequence. We used the sequence of highly conserved helix 45 of the 16S rRNA as a guide. By this criterion, 8,153 annotated 3’ ends correctly included the anti-Shine-Dalgarno sequence, but 12,495 were foreshortened or otherwise mis-annotated, missing part or all of the anti-Shine-Dalgarno sequence, which immediately follows helix 45. We re-annotated, giving a total of 20,648 16S rRNA 3’ ends. The vast majority indeed contained a consensus anti-Shine-Dalgarno sequence, embedded in a highly conserved 13 base “tail”. However, 128 exceptional organisms had either a variant anti-Shine-Dalgarno, or no recognizable anti-Shine-Dalgarno, in their 16S rRNA(s). For organisms both with and without an anti-Shine-Dalgarno, we identified the Shine-Dalgarno motifs actually enriched in front of each organism’s open reading frames. This showed to what extent the Shine-Dalgarno motifs correlated with anti-Shine Dalgarno motifs. In general, organisms whose rRNAs lacked a perfect anti-Shine-Dalgarno motif also lacked a recognizable Shine-Dalgarno. For organisms whose 16S rRNAs contained a perfect anti-Shine-Dalgarno motif, a variety of results were obtained. We found one genus, Alteromonas, where several taxids apparently maintain two different types of 16S rRNA genes, with different, but conserved, antiSDs. The fact that some organisms do not seem to have or use Shine-Dalgarno motifs supports the idea that prokaryotes have other robust mechanisms for recognizing start codons for translation.</div
F+D-2 reaction at ultracold temperatures
No full textWe present a quantum mechanical study of the reaction F+D-2 at ultracold temperatures based on the potential energy surface of Stark and Werner. Th
e reaction cross section at low energies is controlled by the tunneling through the activation barrier, a mechanism that is favored by the long duration of
the collision at those energies. Differences are found in the behavior of the reactive cross section compared to that for F+H-2, due to the changed mass a
nd zero point energy. A new feature is detected in the reaction probabilities and is attributed to a Feshbach resonance corresponding to a metastable state
in the exit channel
The reaction of F+D2 at ultralow temperatures: the effect of rotational excitation
No full textWe report an ab initio study of the dynamics of the reaction F + D-2 --> DF + D, where D-2 is initially in a rotationally excited state (j = 2). Th
e possibility of obtaining ultra-cold molecules and of investigating reaction dynamics at ultra-low temperature relies on the production of molecules in a
well defined quantum state and it is important to know the relative efficiency of the rotational quenching and of the chemical reaction. We examine here a
reaction with an activation barrier, the reaction of F with D-2, and we find that quenching dominates the reaction when the initial rotational level lies e
nergetically below the barrier, so severe trap loss may occur before the reaction can take place
Quenching of vibrationally excited CO(ν=2) molecules by ultra-cold collisions with 4He atoms
No full textThe quenching of vibrational excited CO(nu = 2) molecules by He atoms at ultra-low temperature is examined to determine the relative efficiency of the processes that involve the exchange of a double or a single quantum of vibrational energy. We find that at low temperature the double quantum exchange cross-section is orders of magnitude smaller than for the single quantum process. This result is valid for different initial rotational states of the CO mo lecule
H2 excitation in turbulent interstellar clouds
No full textWe discuss the observational differences between lines of sight that intercept a group of turbulent dissipative structures and lines of sight that cross less-active regions. Using time-dependent calculations we show that the energy level distribution of the hydrogen molecule evolves in time in response to the local thermal phase. We find that relatively simple models can explain the observed properties of molecular hydrogen in diffuse interstellar clouds in terms of time evolution induced by collisional excitation in a low-density, high-temperature gas
Nadine Dalgarno interviewed by Lyn Finch, 1 Feb 1986
No full textThe Queensland Homefront Collection consists of taped interviews conducted by Dr. Kay Saunders and others, correspondence with informants, printout of database. The Queensland Homefront 1939-1945 Oral History Project was funded by The University of Queensland Foundation and led by Dr Kay Saunders, Reader in the Department of History at the University of Queensland. A book entitled "Australia's frontline ; remembering the 1939-1945 war" was published as a result of the project
Dalgarno and Leibniz on the particles
No full textThis article discusses the treatment of linguistic particles in various contexts by seventeenth-century philosophers, linguists and logicians. Starting out with a discussion of the logical tradition which formed the background to many of these treatments, the article then focuses on the approach to the subject taken by George Dalgarno, author of the first artificial language published in the seventeenth century, and on Leibniz's study of particles in the context of his grand rational grammar project. The article argues that in spite of a shared background, Dalgarno's and Leibniz's work in this area was informed by widely different aims
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