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A thermodynamic study on aqueous solutions of trans-Resveratrol (3,5,4′-trihydroxy-trans-stilbene) at 25.00 ± 0.02 °C, in 0.5 mol·dm?3 NaCl, has been conducted. The protolysis equilibria and the complex formation between trans-Resveratrol and a metal(II), namely Mn2+ and Cu2+, have been investigated. The experimental method consists of potentiometric, spectrophotometric (absorption and emission) acid–base titrations. The pH range investigated is 2.5 ≤ pH ≤ 13 for the binary system, while for the ternary system it is 2.5 ≤ pH ≤ 6. The results of the graphical and numerical methods adopted indicate, for all the systems investigated, the formation of a predominant Me(II)–trans-Resveratrol mononuclear complex. UV–Vis absorption spectra and desorption/ionization time of flight mass spectra show the occurrence of hydrolytic species exhibiting a higher molecular weight than the Resveratrol molecule, becoming more evident as the pH and the time increased. Moreover, high performance liquid chromatography analysis and infrared spectroscopy of aqueous cis/trans-Resveratrol solutions upon excitation at 300 nm have highlighted a highly fluorescent compound, with absorption maximum at 250 nm, and a blue shift in the fluorescence emission that have not previously been reported.  相似文献   
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Squarefree lexsegment ideals   总被引:6,自引:0,他引:6  
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The purpose of this study is to investigate the differential impact that inter-organizational network connections have on organizational level change. Drawing from the strategic leaning perspective on adaptation, this study investigates how the nature of inter-organizational ties among top management impact the cost and the effectiveness of an organizational level change process. To build on the existing empirical work in this area, this study employs a virtual experiment to create a controlled laboratory investigation of the hypothesized relationships among the strength, formalization, and functional equivalence of network ties; and the cost and effectiveness of an organizational change process. The findings of this study provide support for the strength of weak ties argument and structural hole theory, in addition to suggesting a caveat to Galbraith's information processing model. Furthermore, the results reveal that the tradeoff between increasing effectiveness and decreasing costs is not universally applicable across all decisions regarding network structure.  相似文献   
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In this paper we study some problems concerning bigraded ideals. By introducing the concept of bigeneric initial ideal, we answer an open question about diagonal subalgebras and we give a necessary condition for a function to be the bigraded Hilbert function of a bigraded algebra. Moreover, we give an upper bound for the regularity of a bistable ideal in terms of the degrees of its generators.  相似文献   
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Shifting Operations and Graded Betti Numbers   总被引:2,自引:0,他引:2  
The behaviour of graded Betti numbers under exterior and symmetric algebraic shifting is studied. It is shown that the extremal Betti numbers are stable under these operations. Moreover, the possible sequences of super extremal Betti numbers for a graded ideal with given Hilbert function are characterized. Finally it is shown that over a field of characteristic 0, the graded Betti numbers of a squarefree monomial ideal are bounded by those of the corresponding squarefree lexsegment ideal.  相似文献   
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This paper is a report of the impact of an externally funded, multiyear systemic reform project on students' science achievement on a modified version of the Third International Mathematics and Science Study (TIMSS) test in 33 small, rural school districts in two Midwest states. The systemic reform effort utilized a cascading leadership strategy of professional development delivered at summer workshops and through distance technologies and local leadership groups that focused on helping teachers work in communities of practice to adapt science inquiry lessons to teach and reinforce strategies and skills in language arts in the lessons. Science achievement scores of Grade 3 and Grade 6 student cohorts on the two forms of the TIMSS administered at the beginning, middle, and end of the professional development effort revealed a V‐shaped pattern of scores, suggesting that teachers struggled with the newly adapted science inquiries at first but then became more effective in their use. The impact of the adaptation strategy on the students' achievement, questions about the time needed for new instructional strategies to be embraced by teachers, and the wisdom of using “low stakes” achievement tests in studies are discussed.  相似文献   
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