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61.
Optimising time-varying gradient orientation for microstructure sensitivity in diffusion-weighted MR
Drobnjak I Alexander DC 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,212(2):344-354
Here we investigate whether varying the diffusion-gradient orientation during a general waveform single pulsed-field gradient sequence improves sensitivity to the size of coherently oriented pores over having a fixed orientation. The experiment optimises the shape and the orientation of the gradient waveform in each of a set of measurements to minimise the expected variance of estimates of the parameters of a simple model. A key application motivating the work is measuring the size of axons in white matter. Thus, we use a two compartment white matter model with impermeable, single-radius cylinders, and search for waveforms that maximise the sensitivity to axon radius, intra-cellular volume fraction and diffusion constants. Output of the optimisation suggests the only benefit of allowing the gradient orientation to vary in the plane perpendicular to the cylinders is that we can gain perpendicular gradient strength by maximising two orthogonal gradients simultaneously. This suggests that varying orientation in itself does not increase the sensitivity to model parameters. On the other hand, the variation in a plane containing the parallel direction increases the sensitivity significantly because parallel sensitivity improves the diffusion constant estimates. However, we also find that similar improvement in the estimates can be achieved without optimising the orientation, but by having one measurement in the parallel and the rest in the perpendicular direction. The optimisation searches a very large space where it cannot hope to find the global minimum so we cannot make a categorical conclusion. However, given the consistency of the results in multiple reruns and variations of the experiments reported here, we can suggest that for probing coherently oriented systems, pulse sequences with variable orientation, such as double-wave vector sequences, do not offer more advantage than fixed orientation sequences with optimised shape. The advantage of varying orientation is however likely to emerge for more complex systems with dispersed pore orientation. 相似文献
62.
Martin Lamač Jiří Tauchman Sascha Dietrich Ivana Císařová Heinrich Lang Petr Štěpnička 《应用有机金属化学》2010,24(4):326-331
Amide coupling of (Sp)‐2‐(diphenylphosphanyl)ferrocene‐1‐carboxylic acid with appropriate terminal amines mediated by 1‐hydroxybenzotriazole and a carbodiimide affords multi‐donor amides terminally functionalized with planar‐chiral (Sp)‐2‐(diphenylphosphanyl)ferrocen‐1‐yl moieties in good to excellent yields. Palladium catalysts based on these ligands efficiently promote asymmetric allylic alkylation of 1,3‐diphenylallyl acetate with in situ generated dimethyl malonate anion to give the C‐alkylated product with ees up to 93% at room temperature. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
63.
Ivana M. Savic G. S. Nikolic Ivan M. Savic M. D. Cakic 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(13):2306-2313
Bioactive copper complexes with oligosaccharides, pullulan or dextran, are the objective of the present study, because of
their possible biomedical applications. The alkaline and acid hydrolysis of the Cu(II) complexes with reduced low-molar pullulan
or dextran were carried out by conductometric method. The influence of ligand constitutions on the stability of the complexes
was examined on the basis of ligand property. The complexes degradation during alkaline and acid hydrolysis were carried out
in sodium hydroxide and hydrochloric acid solutions of 0.1, 0.5, and 1.0 mol dm−3, at different temperature (25, 40, and 60°C, respectively). According to the obtained results by the conductivity investigation
during forced degradation studies, it could be concluded that the Cu(II) complexes show the small pharmaceutical stability
to both hydrolysis. 相似文献
64.
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66.
Ivana Bochicchio 《Ricerche di matematica》2011,60(2):179-192
The existence and physical uniqueness is proved for the restricted evolution problem in general relativity. Precisely, the
Einstein equations for the gravitational field are analyzed in harmonic and generic adapted coordinates in order to prove
the existence and uniqueness of solution in both systems of coordinates. 相似文献
67.
Felicita Bri?ki Nina Kop?i? Ivana ?osi? Dajana Ku?i? Marija Vukovi? 《Chemical Papers》2012,66(12):1103-1110
The tobacco industry produces large quantities of solid and liquid waste. This waste poses a significant environmental problem, as some major components are harmful and toxic. The aim of this work is to isolate and identify the nicotine-degrading microorganisms in the composting of tobacco waste. The bioremediation process for the detoxification of waste was carried out in a column reactor at an airflow-rate of 0.4 L min?1 kg?1. The concentrations of nicotine and number of CFU in the samples taken from reactor were monitored over nineteen days. After nineteen days, 89.8 % of nicotine conversion was obtained. A nicotine-degrading bacterium, strain FN, was isolated from the composting mass and identified as Pseudomonas aeruginosa on the basis of morphology, 16S rDNA sequence, and the phylogenetic characteristics. To confirm that the isolated Pseudomonas aeruginosa FN is the actual nicotine degrader, batch experiments were performed using tobacco leachate. It was confirmed that the strain FN possesses a considerable capacity to degrade nicotine with simultaneous COD removal. The Monod kinetic model for single substrate was applied to obtain the substrate degradation rate and half saturation constant. 相似文献
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Ale Ricka Libor Dostl Roman Jambor Vladimír Buchta Jirí Brus Ivana Císarov Michal Holcapek Jaroslav Holecek 《应用有机金属化学》2002,16(6):315-322
A set of seven [2,6‐bis(dimethylaminomethyl)phenyl]diphenyltin(IV) ({[(CH3)2NCH2]2(C6H3)}(C6H5)2Sn+X?) ionic organotin(IV) compounds (X = Br, NO3, CN, SCN, SeCN, BF4 and PF6) has been prepared and characterized by electrospray ionization mass spectrometry, 1H NMR spectroscopy in CDCl3,119Sn NMR in CDCl3 and DMSO‐d6 solution, as well as by 13C and 119Sn CP/MAS NMR spectroscopy and X‐ray diffraction techniques in the solid state. The in vitro antifungal activity of these water‐soluble ionic organotin(IV) compounds was compared with starting compounds and the antifungal drugs currently in clinical use. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
70.
The ultrasonic extraction (UE) of oil from the seeds of a semi-oriental tobacco (Nicotiana tabacum L.) plant strain by using n-hexane and petroleum ether was studied at different temperatures and seeds-to-solvent ratios. The oil yield depended on the seed comminution, the extraction temperature, the seeds-to-solvent ratio and the type of solvent. The oil yield was much higher if the seeds were ground before extraction. The oil yield increased with increasing the extraction temperature and with decreasing the seeds-to-solvent ratio. n-Hexane was somewhat more efficient in the oil extraction than petroleum ether. In recovering the tobacco seed oil (TSO), the UE was less efficient than the Soxhlet extraction. The advantage of the UE was a relatively high oil yield at 25 degrees C in a shorter time. The kinetics of UE of TSO was described using the model of unsteady diffusion through plant material. 相似文献