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1.
Gabriela Jeronimo Teresa Krick Juan Sabia Martín Sombra 《Foundations of Computational Mathematics》2004,4(1):41-117
We present a bounded probability algorithm for the computation of the
Chowforms of the equidimensional components of an algebraic variety. In particular,
this gives an alternative procedure for the effective equidimensional decomposition
of the variety, since each equidimensional component is characterized by its Chow
form.
The expected complexity of the algorithm is polynomial in the size and the geometric
degree of the input equation system defining the variety. Hence it improves (or
meets in some special cases) the complexity of all previous algorithms for computing Chow forms. In addition to this, we clarify the probability and uniformity aspects,
which constitutes a further contribution of the paper.
The algorithm is based on elimination theory techniques, in line with the geometric
resolution algorithm due to M. Giusti, J. Heintz, L. M. Pardo, and their collaborators.
In fact, ours can be considered as an extension of their algorithm for zero-dimensional
systems to the case of positive-dimensional varieties. The key element for dealing
with positive-dimensional varieties is a new Poisson-type product formula. This
formula allows us to compute the Chow form of an equidimensional variety from a
suitable zero-dimensional fiber.
As an application, we obtain an algorithm to compute a subclass of sparse resultants,
whose complexity is polynomial in the dimension and the volume of the input
set of exponents. As another application, we derive an algorithm for the computation
of the (unique) solution of a generic overdetermined polynomial equation system. 相似文献
2.
Natural irones from the essential oil of Iris rhizomes develop by oxidative degradation of C31-triterpenoids produced by the plant. Two enantiomeric forms of irones are found in Iris, oils of different origin. The optical properties and CD spectra of irones, dihydroirones and their C31-precursors are reported and their absolute stereochemistry is determined. 相似文献
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Chemical investigation of the marine-derived fungus Ascochyta salicorniae led to the isolation of two novel natural products, ascospiroketals A (1) and B (2). From a biosynthetic standpoint, the compounds possess new ring systems. [structure: see text]. 相似文献
6.
Guo T Geis S Hedman C Arndt M Krick W Sonzogni W 《Journal of the American Society for Mass Spectrometry》2007,18(5):817-825
Beta-methylamino-L-alanine (BMAA) is a neurotoxic amino acid that can be produced by cyanobacteria in aqueous environments. To analyze this compound by gas chromatography/mass spectrometry (GC/MS), BMAA must be derivatized to a nonpolar, volatile compound. This can be accomplished by reacting BMAA with ethyl chloroformate. While carrying out electron ionization (EI) mass spectrometric analysis on the (13)C-labeled derivative, it was discovered that the formation of an ion with a peak at m/z 245.12 is the result of [CH(3)CH(2)O.] loss from the amino groups resulting from alpha-cleavage. This differs from previous reports that attributed this peak to alpha-cleavage of the carboxylic ester portion of the BMAA derivative. This finding is important for understanding BMAA derivative mass spectrometric fragmentation patterns and ultimately to properly identifying and quantifying BMAA. Fragmentation pathways for the formation of other major peaks observed in the EI mass spectra are also proposed. 相似文献
7.
Martin Avendano Teresa Krick Ariel Pacetti 《Foundations of Computational Mathematics》2006,6(1):82-120
The main result of this paper is a new version of Newton-Hensel lifting
that relates to interpolation questions. It allows one to lift polynomials in ℤ[x] from information modulo a prime number
p ≠ 2 to a power pk for any k, and its originality is that it is a mixed version that not only lifts the coefficients of the polynomial but
also its exponents. We show that this result corresponds exactly to a Newton--Hensel lifting of a system of 2t generalized
equations in 2t unknowns in the ring of p-adic integers ℤp. Finally, we apply our results to sparse polynomial interpolation in ℤ[x]. 相似文献
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Seibert SF Eguereva E Krick A Kehraus S Voloshina E Raabe G Fleischhauer J Leistner E Wiese M Prinz H Alexandrov K Janning P Waldmann H König GM 《Organic & biomolecular chemistry》2006,4(11):2233-2240
Chemical investigation of the marine fungus Ascochyta salicorniae led to the isolation of two new epimeric compounds, ascolactones A (1) and B (2), in addition to the structurally-related polyketides hyalopyrone (3), ascochitine (4), ascochital (5) and ascosalipyrone (6). The absolute configurations of the epimeric compounds 1 and 2 were assigned as (1R,9R) and (1S,9R), respectively, through simulation of the chiroptical properties using quantum-chemical CD calculations, and chiral GC-MS subsequent to oxidative cleavage (Baeyer-Villiger oxidation) of the side chain. In silico screening using the PASS software identified some of the A. salicorniae compounds (1-6) as potential inhibitors of protein phosphatases. Compound was found to inhibit the enzymatic activity of MPtpB with an IC(50) value of 11.5 microM. 相似文献
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María Gallego Joaquín Calbo Dr. Juan Aragó Rafael M. Krick Calderon Fernando H. Liquido Takahiro Iwamoto Allison K. Greene Edward A. Jackson Dr. Emilio M. Pérez Prof. Dr. Enrique Ortí Prof. Dr. Dirk M. Guldi Prof. Dr. Lawrence T. Scott Prof. Dr. Nazario Martín 《Angewandte Chemie (International ed. in English)》2014,53(8):2170-2175
Herein, we investigate the association of a fullerene fragment, hemifullerene C30H12, with an electron‐donating bowl‐shaped tetrathiafulvalene derivative (truxTTF). UV/Vis titrations and DFT calculations support formation of the supramolecular complex, for which an association constant of log Ka=3.6±0.3 in CHCl3 at room temperature is calculated. Remarkably, electron transfer from truxTTF to C30H12 to form the fully charge‐separated species takes place upon irradiation of the associate with light, constituting the first example in which a fullerene fragment mimics the electron‐accepting behavior of fullerenes within a supramolecular complex. 相似文献