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91.
Surman AJ Bonnet CS Lowe MP Kenny GD Bell JD Tóth E Vilar R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(1):223-230
This study shows that the relaxivity and optical properties of functionalised lanthanide‐DTPA‐bis‐amide complexes (lanthanide=Gd3+ and Eu3+, DTPA=diethylene triamine pentaacetic acid) can be successfully modulated by addition of specific anions, without direct Ln3+/anion coordination. Zinc(II)‐dipicolylamine moieties, which are known to bind strongly to phosphates, were introduced in the amide “arms” of these ligands, and the interaction of the resulting Gd–Zn2 complexes with a range of anions was screened by using indicator displacement assays (IDAs). Considerable selectivity for polyphosphorylated species (such as pyrophosphate and adenosine‐5′‐triphosphate (ATP)) over a range of other anions (including monophosphorylated anions) was apparent. In addition, we show that pyrophosphate modulates the relaxivity of the gadolinium(III) complex, this modulation being sufficiently large to be observed in imaging experiments. To establish the binding mode of the pyrophosphate and gain insight into the origin of the relaxometric modulation, a series of studies including UV/Vis and emission spectroscopy, luminescence lifetime measurements in H2O and D2O, 17O and 31P NMR spectroscopy and nuclear magnetic resonance dispersion (NMRD) studies were carried out. 相似文献
92.
We study the high‐contrast biharmonic plate equation with Hsieh–Clough–Tocher discretization. We construct a preconditioner that is robust with respect to contrast size and mesh size simultaneously based on the preconditioner proposed by Aksoylu et al. (Comput. Vis. Sci. 2008; 11 :319–331). By extending the devised singular perturbation analysis from linear finite element discretization to the above discretization, we prove and numerically demonstrate the robustness of the preconditioner. Therefore, we accomplish a desirable preconditioning design goal by using the same family of preconditioners to solve the elliptic family of PDEs with varying discretizations. We also present a strategy on how to generalize the proposed preconditioner to cover high‐contrast elliptic PDEs of order 2k, k>2. Moreover, we prove a fundamental qualitative property of the solution to the high‐contrast biharmonic plate equation. Namely, the solution over the highly bending island becomes a linear polynomial asymptotically. The effectiveness of our preconditioner is largely due to the integration of this qualitative understanding of the underlying PDE into its construction. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
93.
This paper deals with the field enhancement due to insertion of a bow-tie structure of perfectly conducting inclusions into the two-dimensional space with a given field. The field enhancement is represented by the gradient blow-up of a solution to the conductivity problem. The bow-tie structure consists of two disjoint bounded domains which have corners with possibly different aperture angles. The domains are parts of cones near the vertices which are nearly touching to each other. We construct functions explicitly which characterize the field enhancement. As consequences, we derive optimal estimates of the gradient in terms of the distance between two inclusions and aperture angles of the corners. The estimates show in quantitatively precise way that the field is enhanced beyond the corner singularities due to the interaction between two inclusions, and the blow-up rate is much higher than the one for the case of inclusions with smooth boundaries. 相似文献
94.
An efficient broadband out-coupler on silicon-on-insulator (SOI) with high-index contrast grating (HCG) is proposed. The presence of a silicon-air (high-index contrast) grating on the top silicon layer in SOI allows a strong interaction between the guided mode and the grating. The broadband design of the out-coupler is presented by optimising the various grating parameters. The design analysis and simulation of such an out-coupler is performed with finite difference method. Coupling efficiency of 54% is achieved over an ultra-wide wavelength range from 1500 nm to 1650 nm. 相似文献
95.
For the X-ray phase contrast imaging system, in addition to the hardware-related parameters, the object-image distance is an important parameter that affects the imaging results. Based on the Fresnel diffraction theory, the X-ray phase contrast formation mechanism is analyzed to find the theoretical relationship between the object-image distance parameter and the image contrast. Through the experimental simulation on a ball model, images with edge enhancement effect and image contrast data were obtained with regard to different object-image distance conditions. The analysis and experimental results show that, clear image information about the edges of the sample structures can be got if the object-image distance parameter is set suitably. 相似文献
96.
Quality-guided algorithm is a widely used method in phase unwrapping. This paper shows an accurate quality map based on fringe contrast for 3D shape measurement. Phase-shifted fringe patterns are projected onto an object surface by a programmable liquid crystal projector and recorded by a CCD camera. A wrapped phase map and a fringe contrast map are extracted from the deformed fringe patterns by the phase-shifting technique. Guided by the contrast map, the quality-guided unwrapping algorithm minimizes unwanted shadow and non-uniform surface reflectance effects and is able to retrieve a correct surface profile. Validity of the proposed method is tested on a fish model and a cutting tool specimen. 相似文献
97.
Emmanuelle Canet Didier Revel Rmy Forrat Claire Baldy-Porcher Michel de Lorgeril Laurent Sebbag Jean-Paul Vallee Dominique Didier Michel Amiel 《Magnetic resonance imaging》1993,11(8):1139-1145
Superparamagnetic iron oxide particles (SPIOs) are usually referred to as T2 MR contrast agents, reducing signal intensity (SI) on T2-weighted MR images (negative enhancement). This study reports the original use of SPIOs as T1-enhancing contrast agents, primarily assessed in vitro, and then applied to an in vivo investigation of a myocardial perfusion defect. Using a strongly T1-weighted subsecond MR sequence with SPIOs intravenous (IV) bolus injection, MR imaging of myocardial vascularization after reperfusion was performed, on a dog model of coronary occlusion followed by reperfusion. Immediately after the intravenous bolus injection of 20 μmol/kg of SPIOs, a positive signal intensity enhancement was observed respectively, in the right and left ventricular cavity and in the nonischemic left myocardium. Moreover, compared to normal myocardium, the remaining ischemic myocardial region (anterior wall of the left ventricle) appeared as a lower and delayed SI enhancing area (cold spot). Mean peak SIE in the nonischemic myocardium (posterior wall) was significantly higher than in the ischemic myocardium (anterior wall) (110 ± 23% vs. 74 ± 22%, Mann-Whitney test < 1%, n1 = 6, n2 − n1 = 0, U > 2). In conclusion, the T1 effect of SPIOs at low dose, during their first intravascular distribution, suggests their potential use as positive markers to investigate the regional myocardial blood flow and some perfusion defects such as the “no-reflow phenomenon”. 相似文献
98.
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100.
V. T. Volkov N. E. Grachev N. N. Nefedov A. N. Nikolaev 《Computational Mathematics and Mathematical Physics》2007,47(8):1301-1309
For a singularly perturbed parabolic equation in two dimensions, the formation of a solution with a sharp transition layer from a sufficiently general initial function is considered. An asymptotic analysis is used to estimate the time required for the formation of a contrast structure. Numerical results are presented. 相似文献