1,200 research outputs found
Solving AX-equations
No full textTitle: Solving AX-equations Author: Jan Butora Department: Department of algebra Supervisor: doc. RNDr. Jiří Tůma, DrSc., Department of algebra Abstract: In this work, we present concept of AX-equations and focus on two such equations. Using similiar techniques, we build a theory for both equations, which allows us to express number of their solutions based only on their parameters. Using this theory, we demonstrate on an example that differential steps, used in differential cryptanalysis of modular addition, are not independent. Moreover, based on this theory we introduce and implement fast algorithms for searching solutions. Keywords: differential cryptanalysis, AX-equations, modular addition, carry, sol- vability conditio
Theoretical investigation on radiation tolerance of Mn+1 AX(n) phases
No full textTernary M(n + 1)AX(n) phases with layered hexagonal structures, as candidate materials used for next-generation nuclear reactors, have shown great potential in tolerating radiation damage due to their unique combination of ceramic and metallic properties. However, Mn + 1AXn materials behave differently in amorphization when exposed to energetic neutron and ion irradiations in experiment. We first analyze the irradiation tolerances of different M(n + 1)AX(n) (MAX) phases in terms of electronic structure, including the density of states ( DOS) and charge density map. Then a new method based on the Bader analysis with the first-principle calculation is used to estimate the stabilities of MAX phases under irradiation. Our calculations show that the substitution of Cr/V/Ta/Nb by Ti and Si/Ge/Ga by Al can increase the ionicities of the bonds, thus strengthening the radiation tolerance. It is also shown that there is no obvious difference in radiation tolerance between Mn (+ 1)AC(n) and Mn (+ 1)AN(n) due to the similar charge transfer values of C and N atoms. In addition, the improved radiation tolerance from Ti3AlC2 to Ti2AlC ( Ti3AlC2 and Ti2AlC have the same chemical elements), can be understood in terms of the increased Al/TiC layer ratio. Criteria based on the quantified charge transfer can be further used to explore other M(n + 1)AX(n) phases with respect to their radiation tolerance, playing a critical role in choosing appropriate MAX phases before they are subjected to irradiation in experimental test for future nuclear reactors
Assessing the impact of xylanase activity on the water distribution in wheat dough: A 1H NMR study
No full textThe molecular mobility of water and biopolymers in wheat dough and the influence of xylanases thereon was investigated with time domain proton nuclear magnetic resonance relaxometry. To reduce the complexity, model systems containing starch, gluten and/or water-unextractable arabinoxylan (WU-AX) were used. In the starch-WU-AX-water model, starch binds water fast but less strong compared to WU-AX, resulting in water withdrawal from starch during resting. In contrary, WU-AX did not affect the water distribution in a gluten-WU-AX-water system, despite the higher water retention capacity (WRC) of WU-AX compared to gluten. In a starch-gluten-WU-AX-water model and in wheat flour, water was distributed over the different constituents including WU-AX. Addition of xylanase reduced the WRC of WU-AX, resulting in a release of water. Therefore, the beneficial effect of xylanase on dough and bread quality can, in part, be attributed to the redistribution of water, initially bound by WU-AX, between the other flour constituents.sponsorship: Sofie Leys acknowledges the Institute for the Promotion of Innovation through Science and Technology in Flanders (IWT Vlaanderen, Brussels, Belgium) for financial support. Yamina De Bondt acknowledges the Research Foundation - Flanders (FWO - Vlaanderen, Brussels, Belgium) for a position as PhD fellow (Grant number: 1199919N). The authors are grateful to Anneleen Pauly for the fruitful discussions. (Institute for the Promotion of Innovation through Science and Technology in Flanders (IWT Vlaanderen, Brussels, Belgium), Research Foundation - Flanders (FWO - Vlaanderen, Brussels, Belgium)|1199919N)status: Publishe
Ab initio study of irradiation tolerance for different M(n+1)AX(n) phases: Ti3SiC2 and Ti3AlC2
No full textLayered ternary M(n+1)AX(n) (MAX) materials are recently proposed to be promising candidates for future fission and fusion programmes because of their unique properties inherited from both ceramics and metals. However, different M(n+1)AX(n) materials demonstrate different behaviors when exposed to energetic neutron or ion irradiations. Based on first-principles calculations, we have investigated the irradiation tolerance of two typical M(n+1)AX(n) materials: Ti3SiC2 and Ti3AlC2 from two aspects. First, we make a detailed analysis on the interatomic bonding characters, which are believed to be responsible for the resistance to radiation-induced amorphization. Second, the formation energies of various intrinsic and antisite defects in these two compounds are calculated in order to elucidate their amorphization mechanism. Our results show that the absence of orbitals overlap of Al-C in Ti3AlC2 renders it more resistant to amorphization compared to Ti3SiC2. In addition, the antisite defects Al-Ti(1) and Al-Ti(2) in Ti3AlC2 have much lower formation energies compared to Si-Ti(1) and Si-Ti(2) in Ti3SiC2, which implies that the replacement of Ti with Al is easier than Si, thus providing an alternative way to accommodate the defects resulted from irradiation damage cascades. These results indicate that Ti3AlC2 is more irradiation tolerant than Ti3SiC2, in accordance with experimental observations. Our results have profound implications for the choice of appropriate MAX phase with best performance to be used in next reaction reactors. (C) 2014 AIP Publishing LLC
In vitro three-stage continuous fermentation of wheat arabinoxylan fractions and induction of hydrolase activity by the gut microflora
No full textIn vitro fermentations were carried out by using a model of the human colon to stimulate microbial activities of gut bacteria. The model consisted of a three-stage culture system. Bacterial populations were evaluated under the effect of three types of arabinoxylan, a nonstarch polysaccharide derived from wheat, the water-unextractable arabinoxylan fraction (WU-AX), WU-AX pretreated with exogenous xylanase and the soluble water-extractable arabinoxylan fraction (WE-AX). The xylanase pretreated (WU-AX) had a stimulatory effect upon colonic bifidobacteria throughout all three vessels. Counts of Bacteroides spp. and Clostridium spp. were also both significantly reduced. Addition of the WU-AX substrates to the first vessel resulted in induction of bacterial synthesis of extracellular hydrolytic enzymes xylanase and ferulic acid esterase which are both required for bacterial metabolism of WU-AX; this induction was significantly greater with the xylanase treated WU-AX.</p
The re-positive definite solutions to the matrix inverse problem AX= B
No full textAbstractAn n × n complex matrix A is termed Re-positive definite (Re-pd) if the real part of x∗Ax is positive for every nonzero complex n-vector x. This paper is concerned with constructing complex Re-pd matrices and solving the following matrix inverse problem: Given complex matrices X and B, find the set of all complex Re-pd matrices A such that AX = B
The Re-nonnegative definite solutions to the matrix inverse problem AX = B
No full textAbstractAn n × n complex matrix A is termed Re-nonnegative definite (Re-nnd) if the real part of x∗Ax is nonnegative for every complex n-vectorx. This paper is mainly concerned with solving the following matrix inverse problem: Given complex matrices X and B, find the set of all complex Re-nnd matrices A such that AX = B
Mode of endosperm and wholemeal arabinoxylans solubilisation during rye breadmaking: Genotypic diversity in the level, substitution degree and macromolecular characteristics
No full textAbstractInsight into solubilisation mechanisms of rye arabinoxylans during breadmaking is important for understanding the biochemical processes that affect bread attributes. Purified ethanol precipitated water-extractable arabinoxylans (WE-AX) and residual unextractable counterparts (WU-AX) were isolated from rye flours and resulting breads. While the endosperm flours had lower endoxylanase activities and higher arabinose-to-xylose ratios of WU-AX than those of corresponding wholemeals, there were not any significant differences between them in the mean amounts of WU-AX hydrolysed during breadmaking. Nevertheless, they were highly affected by rye cultivar used for breadmaking. On average, 42% and 36% of WU-AX were recovered in bread WE-AX fraction, causing its 11% and 8% increase, respectively for endosperm and wholemeal breads. Bread WE-AX, however, had lower molecular weights than those of starting flours, implying chains depolymerisation. Degree of AX solubilisation depends mainly on rye genotype used, determining combined effect of enzymatic and acid hydrolyses, associations and fine structure of AX
Alteration of Bacillus subtilis XynA endoxylanase substrate selectivity by site-directed mutagenesis
No full textBacillus subtilis endoxylanase XynA was engineered by site-directed mutagenesis to alter its substrate selectivity, i.e. the ratio of its capacity to solubilise water-unextractable arabinoxylans (WU-AX) to its capacity to hydrolyse water-extractable AX (AE-AX). Four surface exposed aromatic residues were targeted for mutation to alanine, either individually (Y113 and W185) orjointly (F48, Y94, Y113 and W185), based on the general role of aromatic residues in the binding of endoxylanases to insoluble substrates and the hypothesis that they affect the activity of endoxylanases towards WU-AX. Determination of the substrate selectivity factors and WU-AX degradation profile of the wild type and mutant enzymes using an elaborate procedure requiring incubation of native wheat flour WU-AX and WE-AX with different enzyme levels showed that mutants W185A and 4mutA, the mutant containing all four mutations, displayed lower selectivity towards WU-AX than the wild type recombinant endoxylanase. Each of the endoxylanases had similar binding activity to wheat flour WU-AX and insoluble oat spelt xylan. (c) 2007 Elsevier Inc. All rights reserved.status: Publishe
Relative activity of endoxylanases towards water-extractable and water-unextractable arabinoxylans in wheat bran
No full textDifferences in endo-beta -1,4-xylanase functionality result from the different ability of the enzymes to convert water-unextractable arabinoxylan (WU-AX) into solubilised AX (S-AX) and to degrade water-extractable arabinoxylan (WE-AX) and S-AX to lower molecular weight. These respective endoxylanse activities and their relative proportions were deternubed for two endoxylanses from Bacillus subtilis and Aspergillus aculeatus, according to a generally applicable procedure. Isolated wheat WE-AX and WU-AX containing wheat squeege starch prepared and incubated with different levels of endoxylanases. The supernatants were analysed for reducing xylose (RX) formed and WU-AX solublised. Molecular weights of the products formed were assessed. Relstive activities differed widely for the two endoxylanses. Based on the results and additional enzyme-substrate binding experiments, mechanisms possibly accounting for these differences are discussed. (C) 2001 Academic Press.status: Publishe
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