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Pulse Experiments (pulse + experiment)
Selected AbstractsBehavior of Corophium volutator (Crustacea, Amphipoda) exposed to the water-accommodated fraction of oil in water and sedimentENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2008Cornelia Kienle Abstract We investigated the short-term effects of the water accommodated fraction (WAF) of weathered Forties crude oil on the behavior of Corophium volutator in the Multispecies Freshwater Biomonitor® (MFB). When exposing C. volutator to 25 and 50% WAF in aqueous exposures, hyperactivity with an additional increase in ventilation was detected, whereas exposure to 100% WAF led to hypoactivity (narcosis). In a sediment exposure with 100% WAF, there was an increased tendency toward hyperactivity. In a pulse experiment, hyperactivity appeared at and after a 130-min exposure to 50% WAF in a majority of cases. Our experiments suggest that the behavior of C. volutator as measured in the MFB may be an appropriate parameter for coastal monitoring. [source] Coherent Properties of Quantum Dot Two-Level SystemsISRAEL JOURNAL OF CHEMISTRY, Issue 4 2006Artur Zrenner In a single self-assembled InGaAs quantum dot, the one-exciton ground-state transition defines a two-level system, which appears as an extremely narrow resonance of only a few ,eV width. The resonant interaction of this two-level system with cw laser fields can be studied in detail by photocurrent spectroscopy, revealing the fine structure of the excitonic ground state as well as the effects of nonlinear absorption and power broadening. For the case of pulsed laser fields and in the absence of decoherence, the two-level system represents a qubit. Excitations with ps laser pulses result in qubit rotations, which appear as Rabi oscillations in photocurrent experiments. Double pulse experiments further allow us to infer the decoherence time and to perform coherent control on a two level system. [source] Parahydrogen induced polarization of barbituric acid derivatives: 1H hyperpolarization studiesMAGNETIC RESONANCE IN CHEMISTRY, Issue 8 2008Meike Roth Abstract Homogeneous hydrogenation of barbituric acid derivatives with parahydrogen yields a substantial increase of the 1H NMR signals of the reaction products. These physiologically relevant compounds were hydrogenated at both ambient and elevated temperatures and pressures using a standard cationic rhodium catalyst. The resulting nonthermal nuclear spin polarization (hyperpolarization) is limited by the spin,lattice relaxation time T1 of the corresponding nuclei in the products, being shorter than the time constant of the hydrogenation. The signal-to-noise ratio of the NMR spectra could be further increased upon signal averaging the antiphase PHIP signals of 25 successive scans following 30° pulse experiments and a delay of 10 s. Copyright © 2008 John Wiley & Sons, Ltd. [source] Chemical shift imaging (CSI) by precise object displacement,,MAGNETIC RESONANCE IN CHEMISTRY, Issue 3 2006Sebastien Leclerc Abstract A mechanical device (NMR lift) has been built to displace vertically an object (typically an NMR sample tube) inside the NMR probe with an accuracy of 1 µm. A series of single pulse experiments are performed for incremented vertical positions of the sample. With a sufficiently spatially selective radio-frequency (r.f.) field, one obtains chemical shift information along the displacement direction (one-dimensional chemical shift imaging (CSI)). Knowing the vertical r.f. field profile (the amplitude of the r.f. field along the vertical direction), one can reconstruct the spectrum associated with all the slices corresponding to consecutive sample positions and improve the spatial resolution, which is simply related to the accuracy of the displacement device. Beside tests performed on phantoms, the method has been applied to solvent penetration in polymers and to benzene diffusion in a heterogeneous zeolite medium. Copyright © 2006 John Wiley & Sons, Ltd. [source] Stimulation, Monitoring, and Analysis of Pathway Dynamics by Metabolic Profiling in the Aromatic Amino Acid PathwayBIOTECHNOLOGY PROGRESS, Issue 6 2004M. Oldiges Using a concerted approach of biochemical standard preparation, analytical access via LC-MS/MS, glucose pulse, metabolic profiling, and statistical data analysis, the metabolism dynamics in the aromatic amino acid pathway has been stimulated, monitored, and analyzed in different tyrosine-auxotrophic l -phenylalanine-producing Escherichiacoli strains. During the observation window from ,4 s (before) up to 27 s after the glucose pulse, the dynamics of the first five enzymatic reactions in the aromatic amino acid pathway was observed by measuring intracellular concentrations of 3-deoxy- d -arabino-heptulosonate 7-phosphate DAH(P), 3-dehydroquinate (3-DHQ), 3-dehydroshikimate (3-DHS), shikimate 3-phosphate (S3P), and shikimate (SHI), together with the pathway precursors phosphoenolpyruvate (PEP) and P5P, the lumped pentose phosphate pool as an alternative to the nondetectable erythrose 4-phosphate (E4P). Provided that a sufficient fortification of the carbon flux into the pathway of interest is ensured, respective metabolism dynamics can be observed. On the basis of the intracellular pool measurements, the standardized pool velocities were calculated, and a simple, data-driven criterion-called "pool efflux capacity" (PEC)-is derived. Despite its simplifying system description, the criterion managed to identify the well-known AroB limitation in the E. coli strain A (genotype ,( pheA tyrA aroF)/pJF119EH aroFfbrpheAfbramp) and it also succeeded to identify AroL and AroA (in strain B, genotype ,( pheA tyrA aroF)/pJF119EH aroFfbrpheAfbraroB amp) as promising metabolic engineering targets to alleviate respective flux control in subsequent l -Phe producing strains. Furthermore, using of a simple correlation analysis, the reconstruction of the metabolite sequence of the observed pathway was enabled. The results underline the necessity to extend the focus of glucose pulse experiments by studying not only the central metabolism but also anabolic pathways. [source] | |||||||||||||