Stable D8-branes and Tachyon Condensation in Type 0 Open String Theory

We consider non-BPS D8 (and D7) branes in type 0 open string theory and describe under which circumstances these branes are stable. We find stable non-BPS D7 and D8 in type 0 with and without D9-branes in the background. By extending the descent relations between D-branes to type 0 theories, the non-BPS D8-brane is considered as the result of a tachyon condensation of a D9 anti-D9 pair in type 0. We study the condensation of the open string tachyons in type 0 with generic gauge groups giving rise to different configurations involving non-BPS D8-branes and discuss the stability in each case. The results agree with the topological analysis of the vacuum manifold of the tachyon potential for each case.Comment: 16 pages, LaTeX, 1 figure, minor changes, references adde

Exotic Branes and Nonperturbative Seven Branes

We construct the effective action of certain exotic branes in the Type II theories which are not predicted by their spacetime supersymmetry algebras. We analyze in detail the case of the NS-7B brane, S-dual to the D7-brane, and connected by T-duality to other exotic branes in Type IIA: the KK-6A brane and the KK-8A brane (obtained by reduction of the M-theory Kaluza-Klein monopole and M9-brane, respectively). The NS-7B brane carries charge with respect to the S-dual of the RR 8-form, which we identify as a non-local combination of the electric-magnetic duals of the axion and the dilaton. The study of its effective action agrees with previous results in the literature showing that it transforms as an SL(2,Z) triplet together with the D7-brane. We discuss why this brane is not predicted by the Type IIB spacetime supersymmetry algebra. In particular we show that the modular transformation relating the D7 and NS-7B brane solutions can be undone by a simple coordinate transformation in the two dimensional transverse space, equivalent to choosing a different region to parametrize the SL(2,Z) moduli space. We discuss a similar relation between the D6 and KK-6A branes and the D8 and KK-8A branes.Comment: 42 pages, Latex, 1 figur

Brane Actions and String Dualities

An effective action for the M9-brane is proposed. We study its relation with other branes via dualities. Among these, we find actions for branes which are not suggested by the central charges of the Type II superalgebras.Comment: 11 pages, LaTeX, 1 figure; To be published in the proceedings of the TMR-meeting "Quantum Aspects of Gauge Theories, Supersymmetry and Unification", Corfu, Greece, September 199

The Heterotic Dyonic Instanton

The static Yang-Mills-Higgs dyonic instanton is shown to have a non-vanishing, but anti-self-dual, angular momentum 2-form with skew eigenvalues equal to the electric charge; for large charge the angular momentum causes the instanton to expand into a hyper-spherical shell. A class of exact multi dyonic instantons is then found and then generalized to a new class of 1/4 supersymmetric, non-singular, stationary, exact solutions of the ten-dimensional supergravity/Yang-Mills theory. These self-gravitating dyonic instantons yield new heterotic string solitons, to leading order in the inverse string tension.Comment: 18 pages, LaTeX, no figures. Previous revision was to include exact multi-solitons. Third version corrects typos and ADM energy formul

The Kaluza-Klein Monopole in a Massive IIA Background

We construct the effective action of the KK-monopole in a massive Type IIA background. We follow two approaches. First we construct a massive M-theory KK-monopole from which the IIA monopole is obtained by double dimensional reduction. This eleven dimensional monopole contains two isometries: one under translations of the Taub-NUT coordinate and the other under massive transformations of the embedding coordinates. Secondly, we construct the massive T-duality rules that map the Type IIB NS-5-brane onto the massive Type IIA KK-monopole. This provides a check of the action constructed from eleven dimensions.Comment: 29 pages, Latex file, 2 figures, typo and reference corrected, version to appear in Nucl. Phys.

Differentiated evolutionary rates in alternative exons and the implications for splicing regulation

BACKGROUND: Alternatively spliced exons play an important role in the diversification of gene function in most metazoans and are highly regulated by conserved motifs in exons and introns. Two contradicting properties have been associated to evolutionary conserved alternative exons: higher sequence conservation and higher rate of non-synonymous substitutions, relative to constitutive exons. In order to clarify this issue, we have performed an analysis of the evolution of alternative and constitutive exons, using a large set of protein coding exons conserved between human and mouse and taking into account the conservation of the transcript exonic structure. Further, we have also defined a measure of the variation of the arrangement of exonic splicing enhancers (ESE-conservation score) to study the evolution of splicing regulatory sequences. We have used this measure to correlate the changes in the arrangement of ESEs with the divergence of exon and intron sequences. RESULTS: We find evidence for a relation between the lack of conservation of the exonic structure and the weakening of the sequence evolutionary constraints in alternative and constitutive exons. Exons in transcripts with non-conserved exonic structures have higher synonymous (dS) and non-synonymous (dN) substitution rates than exons in conserved structures. Moreover, alternative exons in transcripts with non-conserved exonic structure are the least constrained in sequence evolution, and at high EST-inclusion levels they are found to be very similar to constitutive exons, whereas alternative exons in transcripts with conserved exonic structure have a dS significantly lower than average at all EST-inclusion levels. We also find higher conservation in the arrangement of ESEs in constitutive exons compared to alternative ones. Additionally, the sequence conservation at flanking introns remains constant for constitutive exons at all ESE-conservation values, but increases for alternative exons at high ESE-conservation values. CONCLUSION: We conclude that most of the differences in dN observed between alternative and constitutive exons can be explained by the conservation of the transcript exonic structure. Low dS values are more characteristic of alternative exons with conserved exonic structure, but not of those with non-conserved exonic structure. Additionally, constitutive exons are characterized by a higher conservation in the arrangement of ESEs, and alternative exons with an ESE-conservation similar to that of constitutive exons are characterized by a conservation of the flanking intron sequences higher than average, indicating the presence of more intronic regulatory signals

Brane dynamics in diverse backgrounds

iv+175hlm.;24c

The Massive Kaluza-Klein Monopole

We construct the (bosonic) effective worldvolume action of an M-theory Kaluza-Klein monopole in a background given by the bosonic sector of eleven-dimensional massive supergravity, i.e. a "massive Kaluza-Klein monopole". As a consistency check we show that the direct dimensional reduction along the isometry direction of the Taub-NUT space leads to the massive D-6-brane. We furthermore perform a double dimensional reduction in the massless case and obtain the effective worldvolume action of a type IIA Kaluza-Klein monopole.Comment: 16 pages, Latex, no figures, typos corrected, one reference adde

Exon creation and establishment in human genes

A comparative genomics study of alternatively spliced exons showing that the relative local abundance of splicing regulatory motifs influences splicing decisions in humans

Arribazones estivales en Puerto Madryn, Argentina, como materiales para la obtención de compost

Fil: Eyras, María Cecilia. Universidad Nacional de la Patagonia San Juan Bosco, Puerto Madryn, ChubutFil: Sar, Eugenia Alicia. Departamento Científico Ficología, Facultad de Ciencias Naturales y Museo, UNL