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排序方式: 共有164条查询结果,搜索用时 187 毫秒
41.
Martin Walter Dr. Walter D. C. Schenkeveld Assoc. Prof. Michael Reissner Assoc. Prof. Lars Gille Prof. Stephan M. Kraemer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(13):3286-3300
Chrysotile asbestos is a soil pollutant in many countries. It is a carcinogenic mineral, partly due to its surface chemistry. In chrysotile, FeII and FeIII substitute Mg octahedra (Fe[6]), and FeIII substitutes Si tetrahedra (Fe[4]). Fe on fiber surfaces can generate hydroxyl radicals (HO.) in Fenton reactions, which damage biomolecules. To better understand chrysotile weathering in soils, net Mg and Si dissolution rates over the pH range 3.0–11.5 were determined in the presence and absence of biogenic ligands. Also, HO. generation and Fe bulk speciation of pristine and weathered fibers were examined by EPR and Mössbauer spectroscopy. Dissolution rates were increased by ligands and inversely related to pH with complete inhibition at cement pH (11.5). Surface-exposed Mg layers readily dissolved at low pH, but only after days at neutral pH. On longer timescales, the slow dissolution of Si layers became rate-determining. In the absence of ligands, Fe[6] precipitated as Fenton-inactive Fe phases, whereas Fe[4] (7 % of bulk Fe) remained redox-active throughout two-week experiments and at pH 7.5 generated 50±10 % of the HO. yield of Fe[6] at pristine fiber surfaces. Ligand-promoted dissolution of Fe[4] (and potentially Al[4]) labilized exposed Si layers. This increased Si and Mg dissolution rates and lowered HO. generation to near-background level. It is concluded that Fe[4] surface species control long-term HO. generation and dissolution rates of chrysotile at natural soil pH. 相似文献
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The thermoelectric materials CoSb3 and LaFe3CoSb12 with skutterudite structure were subjected to high pressures using a diamond anvil high-pressure cell up to 20 GPa. Energy-dispersive X-ray diffraction was used to determine the dependence of the lattice parameter on pressure. No major change in the X-ray diffraction spectra was observed for both compounds, constituting evidence that both compounds are stable within this pressure range, despite their relatively open structures. Three distinct isothermal equations of state for solids under high pressure were fitted to the experimental data to determine the bulk modulus for both compounds. The filled skutterudite showed a greater compressibility than the unfilled one, this difference can be understood in terms of the larger lattice parameter of the former. 相似文献
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B. Niczyporuk Z. Jakubowski G. Nowak G. Folger B. Lurz U. Volland H. Wegener J. K. Bienlein R. Graumann H. -J. Trost M. Schmitz F. H. Heimlich R. Nernst A. Schwarz U. Strohbusch P. Zschorsch K. W. Chen A. C. König D. J. Schotanus M. Coles A. Engler R. W. Kraemer D. Marlow F. Messing C. Rippich S. Youssef A. Fridman G. Alexander A. Av-Shalom G. Bella J. Grunhaus M. Scheer LENA Collaboration 《Zeitschrift fur Physik C Particles and Fields》1982,15(4):299-309
The rationR=σ(e + e ?→hadrons)/σ(e + e ?→ µ+ µ?) was measured with the LENA detector at DORIS in a scan between 7.40 and 7.48 GeV and between 8.67 and 9.43 GeV center of mass energies. Corrected for QED radiative effects,R is found to be constant with an average value ofR=3.37 ±0.06stat±0.23syst. No narrow resonances withΓ ee (Γ had/Γ tot)?0.30 keV (95% C.L.) and no steps have been observed. Based on this value ofR, revised values for υ(1S) resonance parameters are presented. 相似文献
47.
Claude Roca Raymond Kraemer Jean-Pierre Majoral Jacques Navech Jean Franois Brault Philippe Savignac 《Magnetic resonance in chemistry : MRC》1976,8(8):407-412
The 1H n.m.r. spectra of some new 1,3,2-oxazaphosphorinanes are analysed. The stereochemistry and the ring conformation is discussed. The free energy and the torsional angle of the C-4? C-5 and C-5? C-6 fragments are calculated for some of these 1,3,2-oxazaphosphorinanes. 相似文献
48.
Ohne ZusammenfassungBericht der Aerodynamischen Versuchsanstalt Göttingen. 相似文献
49.
J. Anderson A. Engler R. Kraemer S. Toaff F. Weisser J. Díaz F. Dibianca W. Fickinger D. Robinson C. Sullivan C-Y. Chien B. Cox D. Feiock V. Sreedhar R. Zdanis C. Bromberg T. Ferbel P. Slattery 《Physics letters. [Part B]》1973,45(5):521-524
Data are presented concerning the energy dependence of the inclusive π- production cross section in π+d interactions. A growth of the cross section at large momentum transfers is parametrized and compared to observations at the ISR. 相似文献
50.
A copper(II)-quenched molecular beacon was prepared by attaching fluorescein to the 3'-end and a copper(II) complex to the 5'-end of DNA. In the presence of complementary DNA, copper(II) and dye are spatially separated in the duplex and fluorescence increases up to 15-fold, with excellent discrimination of single base mismatches. 相似文献