Ana Bravo - Academia.edu (original) (raw)

Papers by Ana Bravo

ChemInform, 2010

ABSTRACT N-Deprotection of Z- and Boc-aminomethylene pseudodipeptide methyl esters yielded not on... more ABSTRACT N-Deprotection of Z- and Boc-aminomethylene pseudodipeptide methyl esters yielded not only the expected linear deprotected compounds but also the 2-ketopiperazine cyclic analogues. The extent of lactamization was found to be dependent on the nature of the amino acid, the sequence order, and the deprotection conditions. Hydrogenation of Z-pseudodipeptides containing N-terminal basic amino acids in acidic media afforded linear compounds, while replacement of these basic residues by Leu gave mixtures of linear and cyclic pseudodipeptides. The reverse-sequence analogues, with Lys or Arg at the C-terminus, yielded the corresponding 2-ketopiperazines as the only reaction products. Opposite results were obtained for C-terminal Leu derivatives in which almost no cyclization occurred. Hydrogenation under neutral conditions gave mainly cyclic derivatives, while linear analogues were predominant after treatment of Boc-protected pseudodipeptides with trifluoroacetic acid or HCl.

Journal of the Chemical Society, Chemical Communications, 1995

Asian Journal of Mathematics, 2011

Over fields of characteristic zero, resolution of singularities is achieved by means of an induct... more Over fields of characteristic zero, resolution of singularities is achieved by means of an inductive argument, which is sustained on the existence of the so called hypersurfaces of maximal contact. We report here on an alternative approach which replaces hypersurfaces of maximal contact by generic projections. Projections can be defined in arbitrary characteristic, and this approach has led to new invariants when applied to the open problem of resolution of singularities over arbitrary fields. We show here how projections lead to a form of elimination of one variable using invariants that, to some extent, generalize the notion of discriminant. This exposition draws special attention on this form of elimination, on its motivation, and its use as an alternative approach to inductive arguments in resolution of singularities. Using techniques of projections and elimination one can also recover some well known results. We illustrate this by showing that the Hilbert-Samuel stratum of a d-dimensional non-smooth variety can be described with equations involving at most d variables. In addition this alternative approach, when applied over fields of characteristic zero, provides a conceptual simplification of the theorem of resolution of singularities as it trivializes the globalization of local invariants.

Proceedings of the London Mathematical Society, 2003

Let XXX be a closed subscheme embedded in a scheme WWW, smooth over a field bfk{\bf k}bfk of characte... more Let XXX be a closed subscheme embedded in a scheme WWW, smooth over a field bfk{\bf k}bfk of characteristic zero, and let mathcalI(X){\mathcal I} (X)mathcalI(X) be the sheaf of ideals defining XXX. Assume that the set of regular points of XXX is dense in XXX. We prove that there exists a proper, birational morphism, pi:WrlongrightarrowW\pi : W_r \longrightarrow Wpi:WrlongrightarrowW, obtained as a composition of monoidal transformations, so that if XrsubsetWrX_r \subset W_rXrsubsetWr denotes the strict transform of XsubsetWX \subset WXsubsetW then:(1) the morphism pi:WrlongrightarrowW\pi : W_r \longrightarrow Wpi:WrlongrightarrowW is an embedded desingularization of XXX (as in Hironaka's Theorem);(2) the total transform of mathcalI(X){\mathcal I} (X)mathcalI(X) in mathcalOWr{\mathcal O}_{W_r}mathcalOWr factors as a product of an invertible sheaf of ideals mathcalL{\mathcal L}mathcalL supported on the exceptional locus, and the sheaf of ideals defining the strict transform of XXX (that is, mathcalI(X)mathcalOWr=mathcalLcdotmathcalI(Xr){\mathcal I}(X){\mathcal O}_{W_r} = {\mathcal L} \cdot {\mathcal I}(X_r)mathcalI(X)mathcalOWr=mathcalLcdotmathcalI(Xr)).Thus (2) asserts that we can obtain, in a simple manner, the equations defining the desingulariza...

The Journal of Organic Chemistry, 1998

Evidence for a molecule-induced homolysis of dimethyldioxirane by several classes of organic comp... more Evidence for a molecule-induced homolysis of dimethyldioxirane by several classes of organic compounds (alkanes, alkenes, ethers, alcohols, aldehydes, iododerivatives) is reported. Carbon-centered radicals, arising from alkanes, ethers, and aldehydes, are trapped by ...

The Journal of Organic Chemistry, 2001

Zephyrus: Revista de prehistoria y …, 1994

RESUMEN: En este trabajo se expone el conjunto metodológico de prospección adoptado para conocer ... more RESUMEN: En este trabajo se expone el conjunto metodológico de prospección adoptado para conocer los asentamientos de la Edad del Hierro en la comarca de Alcántara (Cáceres). Los fuertes contrastes del medio geográfico y la poca visibilidad en las zonas cubiertas de jarales impedían llevar a cabo un proyecto de prospección intensiva tradicional debido a las dificultades que las zonas de riberos, las más propicias para localizar los castros, oponían a ello. Para solucionarlo se adoptaron diferentes técnicas de información que se completaron con la prospección selectiva guiada y el muestreo aleatorio.

Advances in Mathematics, 2010

We introduce an upper semi-continuous function that stratifies the highest multiplicity locus of ... more We introduce an upper semi-continuous function that stratifies the highest multiplicity locus of a hypersurface in arbitrary characteristic (over a perfect field). The blow-up along the maximum stratum defined by this function leads to a form of simplification of the singularities, known as the reduction to the monomial case. Contents Part 3. Elimination 7. Elimination via universal invariants 8. A smooth local projection and the elimination algebra 9. Elimination algebras and permissible monoidal transformations Part 4. Main Theorem and inductive invariants 10. Main Theorem 10.1 11. Proof of Theorem 10.1 12. The non-simple case 13. Stratification of the singular locus by smooth strata Part 5. Epilogue and example References Key words and phrases. Resolution of singularities. Rees algebras. 2000 Mathematics subject classification. 14E15.