38 research outputs found
Solum depth spatial prediction comparing conventional with knowledge-based digital soil mapping approaches
Charge induced chemical dynamics in glycine probed with time resolved Auger electron spectroscopy
In the present contribution, we use x rays to monitor charge induced chemical dynamics in the photoionized amino acid glycine with femtosecond time resolution. The outgoing photoelectron leaves behind the cation in a coherent superposition of quantum mechanical eigenstates. Delayed x ray pulses track the induced coherence through resonant x ray absorption that induces Auger decay. Temporal modulation of the Auger electron signal correlated with specific ions is observed, which is governed by the initial electronic coherence and subsequent vibronic coupling to nuclear degrees of freedom. In the time resolved x ray absorption measurement, we monitor the time frequency spectra of the resulting many body quantum wave packets for a period of 175 fs along different reaction coordinates. Our experiment proves that by measuring specific fragments associated with the glycine dication as a function of the pump probe delay, one can selectively probe electronic coherences at early times associated with a few distinguishable components of the broad electronic wave packet created initially by the pump pulse in the cation. The corresponding coherent superpositions formed by subsets of electronic eigenstates and evolving along parallel dynamical pathways show different phases and time periods in the range of amp; 8722;0.3 0.1 amp; 120587; amp; 8804; amp; 120601; amp; 8804; 0.1 0.2 amp; 120587; and 18.2 1.7 amp; 8722;1.4 amp; 8804; amp; 119879; amp; 8804;23.9 1.2 amp; 8722;1.1 fs. Furthermore, for long delays, the data allow us to pinpoint the driving vibrational modes of chemical dynamics mediating charge induced bond cleavage along different reaction coordinate
Transition and Stability of Copolymer Adsorption Morphologies on the Surface of Carbon Nanotubes and Implications on Their Dispersion
In this study, the adsorption morphologies as well as stability and transitions of a commercial dispersant copolymer (BYK 9076) on the surface of multiwalled carbon nanotubes (MWCNTs) were studied using Fourier transform infrared and UV-vis spectroscopy, dynamic light scattering, and electron microscopy techniques. The results show that the dispersion of carbon nanotubes in ethanol does not increase continuously with increasing copolymer/CNT ratio, which is correlated with the adsorption morphologies of the copolymer on the CNT surface. At a ratio of copolymer/CNT below 0.5, the morphology is random, shifting to a hemimicelle structure at a ratio from 0.5 to 1.0 while at ratios above 1.0, a cylindrical pattern is seen. The hemimicelle morphology is able to prevent the agglomeration of CNTs when the CNT concentration increases to 8.7 mg/mL, while cylindrical morphology is more efficient and stable to provide dispersion of CNTs at higher concentrations of CNTs
Kooperative Chemieaufgaben: Eine neue Rolle fĂĽr Eltern beim auĂźerschulischen Lernen
Sumfleth E, Nicolai N, Wild E, Gerber J. Kooperative Chemieaufgaben: Eine neue Rolle fĂĽr Eltern beim auĂźerschulischen Lernen. In: Pitton A, ed. Gesellschaft fĂĽr Didaktik der Chemie und Physik: Chemie- und physikdidaktische Forschung und naturwissenschaftliche Bildung. MĂĽnster: LIT Verlag; 2003: 162-164
Glass-fibre-reinforced composites with enhanced mechanical and electrical properties - Benefits and limitations of a nanoparticle modified matrix
Nanoparticles and especially carbon nanotubes (CNTs) provide a high potential for the modification of polymers. They are very effective fillers regarding mechanical properties, especially toughness. Furthermore, they allow the implication of functional properties, which are connected to their electrical conductivity, into polymeric matrices. In the present paper, different nanoparticles, as fumed silica and carbon black, were used to optimise the epoxy matrix system of a glass-fibre-reinforced composite. Their nanometre-size enables their application as particle-reinforcement in FRI's produced by the resin-transfer-moulding method (RTM), without being filtered by the glass-fibre bundles. Additionally, an electrical field was applied during curing, in order to enhance orientation of the nanofillers in z-direction. The interlaminar shear strengths of the nanoparticle modified composites were significantly improved (+16%) by adding only 0.3 wt.% of CNTs. The interlaminar toughness G(Ic) and G(IIc) was not affected in a comparable manner. The laminates containing carbon nanotubes exhibited a relatively high electrical conductivity at very low filler contents, which allows the implication of functional properties, such as stress-strain monitoring and damage detection
Kooperative Problemlöseprozesse zum Thema Säure-Base
Sumfleth E, Rumann S, Buttler N, Wild E, Exeler J, Gerber J. Kooperative Problemlöseprozesse zum Thema Säure-Base. In: Brechel R, ed. Zur Didaktik der Chemie und Physik. Alsbach: Leuchtturmverlag; 2002: 215-217