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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 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
Editorial:volume 31 issue 4
No full textIn this editorial we report on a workshop of editors of educational technology and open and distance education journals held in Barcelona, Spain in June of this year, attended by Barney Dalgarno on behalf of the AJET editorial team. Some of the key issues discussed during the workshop included editorial processes, author services, sustainability of business models, and emerging impact metrics. Overall the workshop was a valuable opportunity to compare the processes used by AJET with those used by other journals. An online network of participating editors has now been established and a commitment has been made to come together for similar events in the future
Nanometric depth resolution from multi-focal images in microscopy
No full textWe describe a method for tracking the position of small features in three dimensions from images recorded on a standard microscope with an inexpensive attachment between the microscope and the camera. The depth-measurement accuracy of this method is tested experimentally on a wide-field, inverted microscope and is shown to give approximately 8 nm depth resolution, over a specimen depth of approximately 6 mm, when using a 12-bit charge-coupled device (CCD) camera and very bright but unresolved particles. To assess low-flux limitations a theoretical model is used to derive an analytical expression for the minimum variance bound. The approximations used in the analytical treatment are tested using numerical simulations. It is concluded that approximately 14 nm depth resolution is achievable with flux levels available when tracking fluorescent sources in three dimensions in live-cell biology and that the method is suitable for three-dimensional photo-activated localization microscopy resolution. Sub-nanometre resolution could be achieved with photon-counting techniques at high flux levels
Rf-field-induced feshbach resonances
No full textA rigorous quantum theory of atomic collisions in the presence of radio frequency (rf) magnetic fields is developed and applied to elucidate the effects of combined dc and rf magnetic fields on ultracold collisions of Rb atoms. We show that rf fields can be used to induce Feshbach resonances, which can be tuned by varying the amplitude and frequency of the rf field. The rf-induced Feshbach resonances occur also in collisions of atoms in low-field-seeking states at moderate rf field strengths easily available in atom chip experiments, which opens up the world of tunable interactions to magnetically trappable atomic quantum gases. © 2010 The American Physical Society
Experimental characterization of Cis-acting elements important for translation and transcription in Halophilic Archaea
No full textSummary The basal transcription apparatus of archaea is well characterized. However, much less is known about the mechanisms of transcription termination and translation initation. Recently, experimental determination of the 5´-ends of ten transcripts from Pyrobaculum aerophilum revealed that these are devoid of a 5´-UTR. Bioinformatic analysis indicated that many transcripts of other archaeal species might also be leaderless. The´-ends and 3´-ends of 40 transcripts of two haloarchaeal species, Halobacterium salinarum and Haloferax volcanii, have been determined. They were used to characterize the lengths of 5´-UTRs and 3´-UTRs and to deduce consensus sequence-elements for transcription and translation. The experimental approach was complemented with a bioinformatics analysis of the H. salinarum genome sequence. Furthermore, the influence of selected 5´-UTRs and 3´-UTRs on transcript stability and translational efficiency in vivo was characterized using a newly established reporter gene system, gene fusions, and real-time PCR. Consensus sequences for basal promoter elements could be refined and a novel element was discovered. A consensus motif probably important for transcriptional termination was established. All 40 haloarchaeal transcripts analyzed had a 3´-UTR (average size 57 nt), and their 3´-ends were not posttranscriptionally modified. Experimental data and genome analyses revealed that the majority of haloarchaeal transcripts are leaderless, indicating that this is the predominant mode for translation initiation in haloarchaea. Surprisingly, the 5´-UTRs of most leadered transcripts did not contain a Shine-Dalgarno (SD) sequence. A genome analysis indicated that less than 10% of all genes are preceded by a SD sequence and even most proximal genes in operons lack a SD sequence. Seven different leadered transcripts devoid of a SD sequence were efficiently translated in vivo, including artificial 5´-UTRs of random sequences. Thus, an interaction of the 5´-UTRs of these leadered transcripts with the 16S rRNA could be excluded. Taken together, either a scanning mechanism similar to the mechanism of translation initiation operating in eukaryotes or a novel mechanism must operate on most leadered haloarchaeal transcripts. Author Summary Expression of the information encoded in the genome of an organism into its phenotype involves transcription of the DNA into messenger RNAs and translation of mRNAs into proteins. The textbook view is that an mRNA consists of an untranslated region (5´-UTR), an open reading frame encoding the protein, and another untranslated region (3´-UTR). We have determined the 5´-ends and the 3´-ends of 40 mRNAs of two haloarchaeal species and used this dataset to gain information about nucleotide elements important for transcription and translation. Two thirds of the mRNAs were devoid of a 5´-UTR, and therefore the major pathway for translation initiation in haloarchaea involves so-called leaderless transcripts. Very unexpectedly, most leadered mRNAs were found to be devoid of a sequence motif believed to be essential for translation initiation in bacteria and archaea (Shine-Dalgarno sequence). A bioinformatic genome analysis revealed that less than 10% of the genes contain a Shine-Dalgarno sequence. mRNAs lacking this motif were efficiently translated in vivo, including mRNAs with artificial 5´-UTRs of total random sequence. Thus, translation initiation on these mRNAs either involves a scanning mechanism similar to the mechanism operating in eukaryotes or a totally novel mechanism operating at least in haloarchaea
Didascalocophus, or, The deaf and dumb mans tutor to which is added a discourse of the nature and number of double consonants, both which tracts being the first (for what the author knows) that have been published upon either of the subjects / by Geo. Dalgarno.
No full textDidascalocophus : or the deaf and dumb mans tutor, to which is added a discourse of the nature and number of double consonants: both which tracts being the first (for what the author knows) that have been published upon either of the subjects
No full texthttps://ida.gallaudet.edu/deaf_rare_books/1048/thumbnail.jp
Deep sequencing reveals global patterns of mRNA recruitment during translation initiation
No full textIn this work, we developed a method to systematically study the sequence preference of mRNAs during translation initiation. Traditionally, the dynamic process of translation initiation has been studied at the single molecule level with limited sequencing possibility. Using deep sequencing techniques, we identified the sequence preference at different stages of the initiation complexes. Our results provide a comprehensive and dynamic view of the initiation elements in the translation initiation region (TIR), including the S1 binding sequence, the Shine-Dalgarno (SD)/anti-SD interaction and the second codon, at the equilibrium of different initiation complexes. Moreover, our experiments reveal the conformational changes and regional dynamics throughout the dynamic process of mRNA recruitment
THE PHOTODISSOCIATION OF THE LITHIUM MOLECULE
No full textAuthor Institution: Harvard-Smithsonian Center for AstrophysicsThe photo dissociation of the lithium molecule is studied theoretically. Detailed calculations are presented of the oscillator strengths for the and transitions which show chat direct photo-dissociation into the vibrational continuum of the excited state is negligible as is spontaneous radiative dissociation following discrete absorption. We argue that photodissociation occurs mostly by discrete absorption into the state followed by nonradiative transitions into the and states. A theoretical description of the dissociation mechanism is given
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