排序方式: 共有70条查询结果,搜索用时 15 毫秒
21.
Dirk H.J. Poot Wouter Pintjens Marleen Verhoye Annemie Van Der Linden Jan Sijbers 《Magnetic resonance imaging》2010
Echo planar imaging (EPI) is an ultrafast magnetic resonance imaging (MRI) technique that allows one to acquire a 2D image in about 100 ms. Unfortunately, the standard EPI images suffer from substantial geometric distortions, mainly originating from susceptibility differences in adjacent tissues. To reduce EPI distortions, correction methods based on a field map, which is a map of the off-resonance frequencies, have been developed. In this work, a nonlinear least squares estimator is used to optimize the estimation of the field map of the B0 field. The model of the EPI and reference data includes parameters for the phase evolution, the complex magnitude, the relaxation of the MRI signal and the EPI-specific phase difference between odd and even echoes, and from these parameters, additional corrections might be computed. The reference data required to estimate the field map can be acquired with a modified EPI-sequence. The proposed method is tested on simulated as well as experimental data and proves to be significantly more robust against noise, compared to the previously suggested method. 相似文献
22.
Valentini M Vaccaro A Rehor A Napoli A Hubbell JA Tirelli N 《Journal of the American Chemical Society》2004,126(7):2142-2147
We report the application of the pulse gradient spin-echo (PGSE) NMR technique (PGSE NMR) to the analysis of large colloidal materials, specifically vesicles formed from macromolecular amphiphiles and nanoparticles. Measurements of size and size distribution were demonstrated to be comparable to those obtained through dynamic light scattering or hydrodynamic chromatography. In comparison to these more common analytical methods, the use of PGSE NMR is particularly advantageous in that, as a spectroscopic technique, it adds chemical selectivity to the study of physical dimensions. In this way, chemically different species contemporarily present in a sample may be individually studied. In addition, we demonstrate the use of PGSE NMR to probe the existence of equilibria between macroamphiphiles present in solution and those present in vesicles or on the surface of nanoparticles. This feature in particular opens exciting possibilities for the characterization of the phase behavior and of the surface adsorption phenomena of colloids. 相似文献
23.
Induction of tumor necrosis factor-alpha by UVB: a role for reactive oxygen intermediates and eicosanoids 总被引:3,自引:0,他引:3
UVB irradiation induces nuclear factor-kappaB (NF-kappaB) activation, tumor necrosis factor-alpha (TNF-alpha) expression and reactive oxygen intermediates (ROI) in keratinocytes. We investigated whether ROI play a role in UVB-induced TNF-alpha mRNA expression. The antioxidants N-acetyl cysteine, NAC, epigallocathin gallate, EGCG, butylated hydroxyanisole (BHA) and vitamin C could reduce UVB-induced TNF-alpha mRNA levels to various degrees; vitamin E (alpha-tocopherol) had no effect. BHA was the most potent inhibitor. The oxidant tertiary butylated hydroperoxide could effectively induce TNF-alpha mRNA expression. Nordihydroguaiaretic acid (NDGA) and MK-886, inhibitors of lipoxygenase (LOX), and indometacin and quinacrine, inhibitors of cyclooxygenase (COX) and phospholipase A2, respectively, could also reduce UVB-induced TNF-alpha mRNA expression. Inhibition by NDGA was in concordance with the results for BHA. NDGA, indometacin, quinacrine and BHA could also effectively inhibit the inhibitor of NF-kappaB degradation, thereby maintaining NF-kappaB inactivity. In conclusion, we show that ROI are implicated in the induction of TNF-alpha mRNA by UVB and that not all antioxidants are equally effective inhibitors. COX products and more importantly LOX products, which themselves are products of an oxidative metabolism, are the main ROI implicated in this induction of TNF-alpha expression by UVB probably via activation of NF-kappaB. 相似文献
24.
Karl Peeters Karolien De Wael Annemie Adriaens Gerald Falkenberg Laszlo Vincze 《Spectrochimica Acta Part B: Atomic Spectroscopy》2008
The influence of X-ray resonant Raman scattering on the detection capabilities of copper(II) tetrasulphonated phthalocyanine (CuTSPc) thin-films on gold electrodes has been investigated by means of synchrotron radiation X-ray fluorescence. In particular the paper focuses on the influence of the excitation energy in the relative narrow energy region of 9.2 to 11.7 keV on the detection limits and the peak-to-background ratios of copper. 相似文献
25.
Shoshan MS Shalev DE Adriaens W Merkx M Hackeng TM Tshuva EY 《Chemical communications (Cambridge, England)》2011,47(22):6407-6409
The first NMR structure of a Cu(I)-bound metallochaperone model with the conserved sequence MT/HCXXC revealed that at pH ~3.0 and ~6.8 Cu(I) binds through one Cys and the Met rather than the two Cys residues, differently than at pH ~8.5. This suggests a possible role of Met in metal transport. 相似文献
26.
Insights in the plasma-assisted growth of carbon nanotubes through atomic scale simulations: effect of electric field 总被引:1,自引:0,他引:1
Carbon nanotubes (CNTs) are nowadays routinely grown in a thermal CVD setup. State-of-the-art plasma-enhanced CVD (PECVD) growth, however, offers advantages over thermal CVD. A lower growth temperature and the growth of aligned freestanding single-walled CNTs (SWNTs) makes the technique very attractive. The atomic scale growth mechanisms of PECVD CNT growth, however, remain currently entirely unexplored. In this contribution, we employed molecular dynamics simulations to focus on the effect of applying an electric field on the SWNT growth process, as one of the effects coming into play in PECVD. Using sufficiently strong fields results in (a) alignment of the growing SWNTs, (b) a better ordering of the carbon network, and (c) a higher growth rate relative to thermal growth rate. We suggest that these effects are due to the small charge transfer occurring in the Ni/C system. These simulations constitute the first study of PECVD growth of SWNTs on the atomic level. 相似文献
27.
Mark Dowsett Annemie Adriaens Bart Schotte Gareth Jones Laurence Bouchenoire 《Surface and interface analysis : SIA》2009,41(7):565-572
We have monitored the growth of lead decanoate coatings in real time using electrochemical impedance spectroscopy (EIS) and synchrotron X‐ray diffraction in a unique environmental cell. The measurements involved the immersion of lead substrates in a 0.05 M sodium decanoate solution and the simultaneous collection of spectroscopic and electrochemical data as the coating deposits. In separate experiments, the surface morphology was investigated with SEM. The stratigraphy and thickness of layers after 6 h of treatment (?1.5 µm) was determined using RBS and ultra low energy SIMS combined with surface profilometry. Weight‐gain measurements were also carried out. Overall, the results are consistent with an initially parabolic process, due simply to diffusionally limited two‐dimensional growth across the surface from nucleation sites. This becomes linear over time as one‐dimensional vertical growth sets in at full coverage (layer closure). The X‐ray data and the microscopy show that the coating consists of fine, interlocking, randomly oriented flake‐shaped crystals, with no obvious epitaxial relationship to the lead substrate. The growth rate of the coating and its corrosion resistance are extremely sensitive to preparation method of the NaC10 solution in ways which are still under investigation. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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29.
Annemie Adriaens 《Mikrochimica acta》1996,124(1-2):89-98
The elemental composition and the internal structure of two slag samples have been analyzed and compared using scanning electron microscopy-wavelength dispersive spectrometry and secondary ion mass spectrometry. The first sample studied is a vitreous accretion found on a ceramic crucible sherd, which originates from an Early Bronze Age site in the Kestel/Göltepe area of Anatolia. The intention for examining this glassy-looking material was to verify whether it corresponds in composition to a tin slag. The results of these measurements form part of a research project involving the search for ancient tin production in Turkey and have a direct relevance on the study of tin sources in the near East. Kestel/Göltepe is presumably the first local tin source found in the Anatolian area and in view of this, the vitreous accretion is compared with a medieval tin slag from a more distant source: the Crift Farm in Cornwall, UK. Results of the present study show that both samples are composed of silicates, each with different admixtures of oxides and metals and confirm that the Anatolian crucible accretion corresponds in composition to a typical metallic tin slag. 相似文献
30.
Van den Driessche B Esmans EL Van der Linden A Van Dongen W Schaerlaken E Lemière F Witters E Berneman Z 《Rapid communications in mass spectrometry : RCM》2005,19(14):1999-2004
Rats were intravenously injected with a single high dose (10 mg/kg) of the alkylating agent melphalan in order to study DNA-adduct formation. Quantitation of a dGuo-melphalan adduct was done by isotope dilution mass spectrometry using capillary liquid chromatography/mass spectrometry (LC/MS) and [15N5]-labeled dGuo-melphalan as internal standard. DNA-adduct levels were studied in bone marrow, liver and kidney. The instrumental detection limit of the method was determined to be 900 fg (S/N 3, pure standard). These first results clearly show a 10 times higher adduct level in bone marrow compared to kidney and a 6 times higher level compared to liver. More experiments will be necessary to gather more information on the pharmacokinetics of melphalan-DNA adducts under in vivo conditions. 相似文献