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41.
R. P. Spielmann Jin Zhen H. J. Triebel V. Nicolas M. Heller E. Bü cheler 《Magnetic resonance imaging》1992,10(6):893-901
To correlate the appearance of poststenotic jets on gradient echo images with features of localized Doppler spectra of the jets, we studied an in vitro model of steady flow-through stenoses of 86, 96, and 99% area reduction. As fluids, water and a 40% glycerol solution in water were used. MRI was performed with a 1.5 T whole body imager and gradient echo images were obtained in planes parallel to the direction of flow. Doppler spectra were acquired separately from the MR measurements at 1 cm intervals for a distance of 10 cm downstream from the stenosis. Poststenotic signal void was observed for water and for the 40% glycerol solution only if the mean velocity within the stenosis exceeded a limit of 50–60 cm/sec. On the MR images, the jets could be divided into two segments: A proximal jet segment of uniform width equal to the diameter of the stenosis, followed by a distal jet segment which was characterized by broadening and then dissipating signal void. Except for the 99% stenosis, a high signal intensity core was present within the proximal jet segment. In the proximal jet segment, the Doppler measurements showed a low temporal fluctuation of the maximal flow velocity and only little flow opposite to the main flow direction. In the distal jet segment, the velocity fluctuation and the intensity of reverse flow increased sharply. The high signal intensity core of the jet was associated with a poststenotic zone of constant maximal flow velocity. The results demonstrate a close relationship between characteristic features of poststenotic jets in MRI and pulsed Doppler sonography. 相似文献
42.
43.
本文在相干理论的基础上,推导了光栅成像中的光强分布和物像位置关系,并给出一组具有不同参数的实验照片及一组借助计算机绘制的强度分布图。 相似文献
44.
停流—荧光动力学分析法测定痕量钛的研究 总被引:3,自引:1,他引:2
利用自行组装的停流-荧光动力学分析仪,采用停流法汇合流体动力注入技术,研究了钛与3.5-二溴水杨基荧光酮的荧光增强动力学反应性质,讨论了流速、进样时间对方法灵敏度和精密度的影响,提出了一个快速、简便、精确测定钛的分析方法,并用于稀土样品及合成样品中痕量钛的测定.方法检测限为8×10~(-3)ppm,大多数元素的干扰均可用动力学方法消除. 相似文献
45.
美国自适应光学联合公司(AOA)在哈佛大学 PAPA 探测器的基础上研制成功的光子数字化编址摄象机是一种具有极高探测灵敏度的光子计数式二维微光摄象机。采用多通道光学编码方法,可对光电倍增管探测到的每一个光电于事件产生相应的(x,y,T)时-空坐标数据,微机采集来自光子摄象机的数据流供实时图象显示和处理。 相似文献
46.
建立了脱镁叶绿素a和脱镁叶绿素b的联合同步荧光分析法。方法简便快速。脱镁叶绿素a和脱镁叶绿素b的线性范围分别为0~400ng/ml和0~200ng/ml,检出限分别为1ng/ml和0.5ng/ml。 相似文献
47.
Emrys A. Jones Nicholas P. Lockyer John C. Vickerman 《International journal of mass spectrometry》2007,260(2-3):146
Recent developments in desorption/ionisation mass spectrometry techniques have made their application to biological analysis a realistic and successful proposition. Developments in primary ion source technology, mainly through the advent of polyatomic ion beams, have meant that the technique of secondary ion mass spectrometry (SIMS) can now access the depths of information required to allow biological imaging to be a viable option.Here the role of the primary ion C60+ is assessed with regard to molecular imaging of lipids and pharmaceuticals within tissue sections. High secondary ion yields and low surface damage accumulation are demonstrated on both model and real biological samples, indicating the high secondary ion efficiency afforded to the analyst by this primary ion when compared to other cluster ion beams used in imaging. The newly developed 40 keV C60+ ion source allows the beam to be focused such that high resolution imaging is demonstrated on a tissue sample, and the greater yields allow the molecular signal from the drug raclopride to be imaged within tissue section following in vivo dosing.The localisation shown for this drug alludes to issues regarding the chemical environment affecting the ionisation probability of the molecule; the importance of this effect is demonstrated with model systems and the possibility of using laser post-ionisation as a method for reducing this consequence of bio-sample complexity is demonstrated and discussed. 相似文献
48.
S. S. Banerjee S. Goldberg Y. Myasoedov M. Rappaport E. Zeldov A. Soibel F. de la Cruz J. van der Beek M. Konczykowski T. Tamegai V. Vinokur 《Pramana》2006,66(1):43-54
Disorder and porosity are parameters that strongly influence the physical behavior of materials, including their mechanical,
electrical, magnetic and optical properties. Vortices in superconductors can provide important insight into the effects of
disorder because their size is comparable to characteristic sizes of nanofabricated structures. Here we present experimental
evidence for a novel form of vortex matter that consists of inter-connected nanodroplets of vortex liquid caged in the pores
of a solid vortex structure, like a liquid permeated into a nanoporous solid skeleton. Our nanoporous skeleton is formed by
vortices pinned by correlated disorder created by high-energy heavy ion irradiation. By sweeping the applied magnetic field,
the number of vortices in the nanodroplets is varied continuously from a few to several hundred. Upon cooling, the caged nanodroplets
freeze into ordered nanocrystals through either a first-order or a continuous transition, whereas at high temperatures a uniform
liquid phase is formed upon delocalization-induced melting of the solid skeleton. This new vortex nanoliquid displays unique
properties and symmetries that are distinct from both solid and liquid phases. 相似文献
49.
Rb(5PJ)+Rb(5PJ)→Rb(5JS)+Rb(nl=5D,7S)碰撞能量合并 总被引:1,自引:1,他引:0
研究了Rb(5PJ)+Rb(5PJ)→Rb(nlJ')+Rb(5S)碰撞能量合并过程,利用单模半导体激光器分别共振激发Rb原子的5P1/2或5P3/2态,利用另一与泵浦激光束反向平行的单模激光束作为吸收线探测激发态原子密度及其空间分布,吸收线分别调至5P1/2→5D3/2和5P3/2→7S1/2跃迁.由激发态原子密度和谱线荧光比得到碰撞能量合并过程的截面,对5P3/2激发,碰撞转移得到5D5/2,5D3/2和7S1/2的截面分别是(1.32士0.59)×10-14,(1.18士0.53)×10-14和(3.21士1.44)×10-15cm2;对5P1/2激发,碰撞转移到5D5/2和5D3/2的截面分别是(6.57士2.96)×10-15和(5.90士2.66)×10-15cm2.与其他的实验结果进行了比较. 相似文献
50.
Arabinda Mallick 《Journal of luminescence》2006,118(2):165-172
Solvatochromic effects on the fluorescence behavior of 7-hydroxy-4-methyl-8-(4′-methyl-piperazine-1′ yl)methylcoumarin (HMMC) was studied in different solvents. The fluorescence of HMMC was found to be highly sensitive to both the polarity and the protic character of the solvent. Exploiting the polarity-sensitive fluorescence property of HMMC, its excited-state dipole moment has been determined. Fluorescence (Förster) resonance energy transfer (FRET) process from HMMC to a potent bioactive molecule 3-acetyl-4-oxo-6,7-dihydro-12 H indolo-[2,3-a] quinolizine (AODIQ) was studied. From the determined KSV and R0 values, it is argued that a long-range dipole-dipole interaction is operating for the energy transfer mechanism. The energy transfer efficiency (E) and the distance between the acceptor and the donor (r0) have been determined. 相似文献