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    New Mn II energy levels from STIS-HST spectrum of the HgMn star HD 175640

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    The NIST database lists several Mn II lines that were observed in the laboratory but not classified. They cannot be used in spectrum synthesis because their atomic line data are unknown. These lines are concentrated in the 2380-2700 A interval. We aimed to assign energy levels and log gf values to these lines. Semi-empirical line data for Mn II computed by Kurucz were used to synthesize the ultraviolet spectrum of the slow-rotating, HgMn star HD 175640. The spectrum was compared with the high-resolution spectrum observed with the HST-STIS equipment. A UVES spectrum covering the 3050-10000 A region was also examined. We determined a total of 73 new energy levels, 58 from the STIS spectrum of HD 175640 and another 15 from the UVES spectrum. The new energy levels give rise to numerous new computed lines. We have identified more than 50% of the unclassified lines listed in the NIST database and have changed the assignement of another 24 lines. An abundance analysis of the star HD 175640, based on the comparison of observed and computed ultraviolet spectra in the 1250-3040 A interval, is the by-product of this study on Mn II.Comment: Paper accepted by Astronomy & Astrophysic

    Stable Marriage with Ties and Bounded Length Preference Lists

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    We consider variants of the classical stable marriage problem in which preference lists may contain ties, and may be of bounded length. Such restrictions arise naturally in practical applications, such as centralised matching schemes that assign graduating medical students to their first hospital posts. In such a setting, weak stability is the most common solution concept, and it is known that weakly stable matchings can have different sizes. This motivates the problem of finding a maximum cardinality weakly stable matching, which is known to be NP-hard in general. We show that this problem is solvable in polynomial time if each man's list is of length at most 2 (even for women's lists that are of unbounded length). However if each man's list is of length at most 3, we show that the problem becomes NP-hard and not approximable within some d > 1, even if each woman's list is of length at most 4

    Ratification vote on taxonomic proposals to the International Committee on Taxonomy of Viruses (2016)

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    This article lists the changes to virus taxonomy approved and ratified by the International Committee on Taxonomy of Viruses (ICTV) in April 2016. Changes to virus taxonomy (the Universal Scheme of Virus Classification of the International Committee on Taxonomy of Viruses [ICTV]) now take place annually and are the result of a multi-stage process. In accordance with the ICTV Statutes (http://​www.​ictvonline.​org/​statutes.​asp), proposals submitted to the ICTV Executive Committee (EC) undergo a review process that involves input from the ICTV Study Groups (SGs) and Subcommittees (SCs), other interested virologists, and the EC. After final approval by the EC, proposals are then presented for ratification to the full ICTV membership by publication on an ICTV web site (http://​www.​ictvonline.​org/​) followed by an electronic vote. The latest set of proposals approved by the EC was made available on the ICTV website by January 2016 (https://​talk.​ictvonline.​org/​files/​proposals/​). A list of these proposals was then emailed on 28 March 2016 to the 148 members of ICTV, namely the EC Members, Life Members, ICTV Subcommittee Members (including the SG chairs) and ICTV National Representatives. Members were then requested to vote on whether to ratify the taxonomic proposals (voting closed on 29 April 2016)

    A Unified Model of Codon Reassignment in Alternative Genetic Codes

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    Many modified genetic codes are found in specific genomes in which one or more codons have been reassigned to a different amino acid from that in the canonical code. We present a model that unifies four possible mechanisms for reassignment, based on the observation that reassignment involves a gain and a loss. The loss could be the deletion or loss of function of a tRNA or release factor. The gain could be the gain of a new type of tRNA for the reassigned codon, or the gain of function of an existing tRNA due to a mutation or a base modification. In the codon disappearance mechanism, the codon disappears from the genome during the period of reassignment. In the other mechanisms, the codon does not disappear. In the ambiguous intermediate mechanism, the gain precedes the loss; in the unassigned codon mechanism, the loss precedes the gain; and in the compensatory change mechanism, the loss and gain spread through the population simultaneously. We present simulations of the gain-loss model and demonstrate that all four mechanisms are possible. The frequencies of the different mechanisms are influenced by selection strengths, number of codons undergoing reassignment, directional mutation pressure and the possibility of selection for reduced genome size.Comment: Latex file, 11 pages including 5 ps figures; revised version; to appear in 'Genetics
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