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L. Elsner 《Linear algebra and its applications》2011,434(4):1058-1066
The well known bialternate product of two square matrices is re-examined together with another matrix product defined by means of the permanent function and having similar properties. Old and new results concerning both products are presented in a unified manner. A simple and elegant relation with the Kronecker product of matrices is also given. 相似文献
3.
Kathrin Schreglmann Martina Hoeche Sibylle Steinbeiss Sandra Reinnicke Martin Elsner 《Analytical and bioanalytical chemistry》2013,405(9):2857-2867
Environmental degradation of organic micropollutants is difficult to monitor due to their diffuse and ubiquitous input. Current approaches—concentration measurements over time, or daughter-to-parent compound ratios—may fall short, because they do not consider dilution, compound-specific sorption characteristics or alternative degradation pathways. Compound-specific isotope analysis (CSIA) offers an alternative approach based on evidence from isotope values. Until now, however, the relatively high limits for precise isotope analysis by gas chromatography—isotope ratio mass spectrometry (GC-IRMS) have impeded CSIA of sub-microgram-per-liter scale micropollutant concentrations in field samples. This study presents the first measurements of C and N isotope ratios of the herbicide atrazine and its metabolite desethylatrazine at concentrations of 100 to 1,000 ng/L in natural groundwater samples. Solid-phase extraction and preparative HPLC were tested and validated for preconcentration and cleanup of groundwater samples of up to 10 L without bias by isotope effects. Matrix interferences after solid-phase extraction could be greatly reduced by a preparative HPLC cleanup step prior to GC-IRMS analysis. Sensitivity was increased by a factor of 6 to 8 by changing the injection method from large-volume to cold-on-column injection on the GC-IRMS system. Carbon and nitrogen isotope values of field samples showed no obvious correlation with concentrations or desethylatrazine-to-atrazine ratios. Contrary to expectations, however, δ 13 C values of desethylatrazine were consistently less negative than those of atrazine from the same sites. Potentially, this line of evidence may contain information about further desethylatrazine degradation. In such a case, the common practice of using desethylatrazine-to-atrazine ratios would underestimate natural atrazine degradation. 相似文献
4.
Władysław Piotrowski Koen Lodefier Slawomir Kubacki Witold Elsner Erik Dick 《Flow, Turbulence and Combustion》2008,81(3):369-394
The present paper evaluates two unsteady transition modelling approaches: the prescribed unsteady intermittency method PUIM,
developed at Cambridge University and the dynamic unsteady intermittency method developed at Ghent University. The methods
are validated against experimental data for the N3-60 steam turbine stator profile for steady and for unsteady inlet flow
conditions. The characteristic features of the test case are moderately high Reynolds number and high inlet turbulence intensity,
which causes bypass transition. The tested models rely both on the intermittency parameter and are unsteady approaches. In
the prescribed method, the time-dependent intermittency distribution is obtained from integral relations. In the dynamic method,
the intermittency distribution follows from time-dependent differential equations. For unsteady computations, self-similar
wake profiles are prescribed at the inlet of the computational domain. Joint validation of the prescribed and the dynamic
unsteady intermittency models against experimental data shows that both methods are able to reproduce the global features
of the periodical evolution of the boundary layer under the influence of a periodically impinging wake. The overall quality
of the dynamic method is better than that of the prescribed method. 相似文献
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K. Lochmann A. Anikeenko A. Elsner N. Medvedev D. Stoyan 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(1):67-76
The performance of various structure characteristics in
the task of indicating structural peculiarities in packings of
hard spheres is investigated. Various characteristics based on
Voronoi polyhedra, spherical harmonics, and Delaunay simplices are
considered together with the pair correlation function and the
mean number of r-close triples. They are applied to a set of
hard sphere packings of density φ from 0.62 to 0.72. It turns
out that all used structure characteristics are able to indicate
changes of order from non-crystalline to crystalline packings.
However, not all of them are sensitive enough to indicate
different stages of structure transformation under densification.
The characteristics based on Delaunay simplices turn out to be the
most sensitive for this purpose.
For the models considered three principal structure classes are
found: packings of densities lower than the known critical value
0.64 showing a non-crystalline behavior; packings with
considerable crystalline regions for φ up to 0.66–0.67;
rather complete crystals although with numerous defects for φ
above 0.67. 相似文献