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With a simple graph G on [n], we associate a binomial ideal PG generated by diagonal minors of an n × n matrix X = (xij) of variables. We show that for any graph G, PG is a prime complete intersection ideal and determine the divisor class group of K[X]/PG. By using these ideals, one may find a normal domain with free divisor class group of any given rank. 相似文献
73.
Cristian Paz Robles Viviana Burgos Sebastin Suarez Ricardo Baggio 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(11):1007-1010
The natural compound dendocarbin A, C15H22O3, is a sesquiterpene lactone isolated for the first time from Drimys winteri for var chilensis. The compound crystallizes in the orthorhombic space group P212121 and its X‐ray crystal structure confirmed the S/R character of the chiral centres at C‐5/C‐10 and C‐9/C‐11, respectively. The α‐OH group at C‐11 was found to be involved in intermolecular hydrogen bonding, defining chains along the <100> 21 screw axis. 相似文献
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Copula-based measures of dependence structure in assets returns 总被引:1,自引:0,他引:1
Viviana Fernandez 《Physica A》2008,387(14):3615-3628
Copula modeling has become an increasingly popular tool in finance to model assets returns dependency. In essence, copulas enable us to extract the dependence structure from the joint distribution function of a set of random variables and, at the same time, to isolate such dependence structure from the univariate marginal behavior. In this study, based on US stock data, we illustrate how tail-dependency tests may be misleading as a tool to select a copula that closely mimics the dependency structure of the data. This problem becomes more severe when the data is scaled by conditional volatility and/or filtered out for serial correlation. The discussion is complemented, under more general settings, with Monte Carlo simulations and portfolio management implications. 相似文献
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Viviana Fernandez 《Physica A》2007,386(1):267-282
In this article, we study the behavior of the stock prices of a subset of eight U.S. industries from the late 1800's to the Great Depression. In particular, we focus on the potential presence of volatility shifts, the persistence of volatility, and on the degree of co-movement of stock returns prior to and during the Great Depression. Our findings show that stock markets became particularly volatile toward the mid 1930's, but that the persistence of volatility tended to decrease around the same time period. In that regard, we find little evidence that such behavior is driven by trading volume. In addition, we conclude that the overall correlation across the different industries was relatively more significant in statistical terms from 1921 to part of the Great Depression (1929-1931; 1933-1934 and 1936). 相似文献
79.
The coupling of 2-(tributylstannyl)cyclopent-2-enone with several (π-allyl)palladium complexes derived from allylic electrophiles was investigated as the key step in the synthesis of jasmonoids. These compounds have an important role in plant development, triggering direct and indirect responses when harmed to induce pest resistance. Palladium-catalyzed coupling conditions to obtain a jasmonoid library are described. The retention of geometry of the olefin in the allyl group is not always observed due to syn-anti isomerization of the (π-allyl)palladium complex. The methodology was employed for the synthesis of a simplified jasmonic acid analog. 相似文献
80.
Luigi Giovanni Bernardo Sichi Fernanda Zapater Pierre Laura Viviana Calvache Arcila Guilherme Schmitt de Andrade Joo Paulo Mendes Tribst Pietro Ausiello Alessandro Espedito di Lauro Alexandre Luiz Souto Borges 《Molecules (Basel, Switzerland)》2021,26(20)
The aim of this study was to evaluate the effect of biologically oriented preparation technique on the stress concentration of endodontically treated upper central incisors restored with zirconia crown (yttria-stabilized zirconia polycrystalline ceramic) through finite element analysis (FEA). Four models of maxillary central incisors containing enamel, dentin, periodontal ligament, cortical and medullary bone were created in CAD. Each model received a polymeric core-build up with nanofilled dental resin composite. The evaluated models were SM—preparation in shoulder 90°; CM—chamfer preparation; BOPT—biologically oriented preparation technique and BOPTB—BOPT preparation 1 mm below the cement-enamel junction. All models received zirconia crowns (5Y-TZP), fiberglass post and 1 mm ferrule. The models were imported into the analysis software with parameters for mechanical structural testing using the maximum principal stress and the tensile strength as the analysis criteria. Then, load of 150 N was applied at the cingulum with 45° slope to the long axis of the tooth, with the fixed base for each model. The type of marginal preparation affected the stresses concentration in endodontically treated teeth and in the zirconia crown margin. Considering the stress magnitude only, BOPT is a viable option for anterior monolithic zirconia crowns; however, with the highest stress magnitude at the restoration margin. 相似文献