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液体核磁共振扩散序谱(DOSY)可以通过测定溶质分子的自扩散系数(Dt)来研究该分子在溶液中的表观分子量(M).Dt与测试体系和分子本身性质相关,蛋白质体系较为复杂,从而增加了蛋白质自扩散系数(Dt-protein)测定的难度.本文以3-(三甲基硅基)丙磺酸钠(DSS)为内标,以蛋白质分子与DSS自扩散系数的比值(Dr)来表征蛋白质分子在溶液中的表观分子量(Mprotein),该方法降低了缓冲体系对Mprotein的影响,使得Mprotein主要由分子本身的性质决定.在此基础上,测定了不同分子量蛋白质分子相对于DSS的Dr,拟合得到了Dr与Mprotein的相关关系:lgMprotein =-2.6488 lgDr-0.7863,相关系数(R2)为0.997.最后测定了通过大肠杆菌表达纯化得到的SARS冠状病毒主蛋白酶C端结构域(Mpro-C)分子相对于DSS的Dr,并计算出与文献结果一致的Mprotein,进一步验证了拟合公式的准确性和实用性. 相似文献
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基于微磁学模拟方法研究末端形状对NiFe纳米薄膜的磁反转和自旋波本征动力学特性的调制及磁反转与自旋波模式软化间的内在联系.纳米薄膜微磁结构的相变总是伴随着某种自旋波模式的软化,软化自旋波模式空间分布预示微磁结构相变的路径.存在一临界裁剪度(h0).当裁剪度h<h0时,磁振荡局域于末端边缘的EM自旋波软化诱导磁反转从磁体末端边缘磁矩失稳开始,边缘失稳区域向中央扩展形成反转畴,最后反转畴逐渐移出膜面外而实现反转.当h≥h0时,形状各向异性导致边缘局域化模式自旋波被抑制,反转场附近一致模式自旋波的软化诱导磁体一致反转. 相似文献
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面对日益复杂的勘探对象, D-T2二维核磁共振技术在实际应用中面临无法兼顾扩散系数测量范围和横向弛豫分辨率的困境. 脉冲序列作为D-T2二维核磁共振数据采集的核心技术, 其性能优劣直接影响应用效果, 在综合对比PFG, STE-PFG, BP-PFG、改良式CPMG, 扩散编程, 多回波间隔CPMG脉冲序列性能的基础上, 有效融合脉冲梯度场、恒定梯度场D-T2脉冲序列的优点, 本文提出一种基于脉冲梯度场的双变量、两窗口D-T2脉冲序列改进设计. 针对两个窗口的D-T2二维核磁共振数据反演, 为突破现有反演方法无法兼顾反演精度和解谱效率的瓶颈, 本着第二个窗口回波信号为主、第一个窗口回波信号为辅的原则, 本文提出一种同时使用两个窗口数据参与解谱的联合TSVD反演方法. 气水、油水、稠油、油气水模型不同信噪比条件下的数值模拟结果表明, 本文提供的D-T2改进脉冲序列达到了平衡扩散系数测量范围和横向弛豫分辨率的设计要求, 本文提供的联合TSVD反演方法也有效平衡了反演精度要求和解谱效率. 文中的D-T2改进脉冲序列及联合TSVD反演方法在复杂油气藏流体识别和产能预测中具有广泛的应用前景, 可为促进国内D-T2二维核磁共振岩心分析技术的发展提供有利条件. 相似文献
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通过分析基于脉冲压缩原理的反褶积方法,提出了具有广泛用途的广义Lp模准则,像脉冲反褶积、极小熵反褶积、L1模反褶积和D模反褶积等都为其特例。根据有限维欧氏空间的L。模性质和高维欧氏空间的几何性质,分析了广义Lp模方法中的参数影响。为了比较不同反褶积方法的脉冲压缩效果,给出了一类判别函数,从理论上证明了,为什么对非小相位信号L1模法的脉冲压缩效果优于脉冲反褶积;D模反褶积要比常规极小熵法更具有"简单性"。广义Lp模准则为构造、分析新的反褶积方法和进一步研究最优脉冲压缩准则提供了必要的理论基础。 相似文献
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核磁共振(NMR)的纵向弛豫时间(T1)、横向弛豫时间(T2)、自扩散系数(D0),以及T2-T1、T2-D0测量目前广泛应用于石油测井行业.在测量D0的SGSE序列中,通过逐渐增大90°和180°脉冲之间的时间间隔(Td),可以对液体扩散行为产生的影响进行调节.然而Td的"起点"、"步进数"和"终点"等参数必须设置得当才能准确测量T1和D0.目前参数的设置依赖多次的人工调整和测量人员的经验,耗时且使用门槛较高.本文用蒙特卡罗方法进行大量随机模拟,根据前面若干点的测量结果筛选出满足要求的随机值,预测下一个测量点的位置.该算法可以实时更新参数设置,实现自动化测量,达到降低测量门槛、缩短测量时间的目的.经验证,该算法可以适用于T1、D0的测量. 相似文献
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定量磁共振成像(MRI)可量化组织特性,是科学研究和临床研究的重要工具.旋转坐标系下的自旋-晶格弛豫时间(T1ρ)能反映水与大分子之间的低频交互作用,在3 T及以上的高场环境下,T1ρ受水和不稳定质子之间化学交换的影响较大,通过测量弛豫率随自旋锁定场强度的变化而得到其分布情况(T1ρ散布),可用于分析和量化质子的交换过程,因此T1ρ散布是一种重要的定量MRI技术.然而,获得不同自旋锁定场强下T1ρ加权图像的时间过长,限制了其应用范围.针对这一问题,本研究提出一种基于多弛豫信号补偿策略的快速T1ρ散布成像方法.该方法将不同锁定频率下的T1ρ加权图像补偿到同一信号强度水平,并结合低秩与稀疏建立重建模型.实验结果表明,该方法在加速倍数高达7倍时仍获得了较好的重建结果. 相似文献
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G. Hebbinghaus W. Gast A. Krämer-Flecken R. M. Lieder J. Skalski W. Urban 《Zeitschrift für Physik A Hadrons and Nuclei》1987,328(4):387-392
High-spin states in186Pt have been populated by the188Os (α, 6n) reaction and were investigated with the OSIRIS spectrometer. A shape coexistence at high spins was established in the nucleus186Pt, which lies on the border between light prolate and heavy oblate Pt nuclei. Two bands corresponding to predominantly prolate shapes and one band of predominantly oblate shape have been observed. For prolate shapes a (π h 9/2)2 alignment and for oblate shapesa (vi 13/2)2 alignment has been found. 相似文献
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R. B. KING 《Molecular physics》2013,111(10):1567-1577
Topological representations (top-reps), which originally were developed to model molecular polyhedral isomerization processes, can be extended to depict the relationships between the polygons and polyhedra involved in Jahn-Teller (JT) distortions. Using this approach, the top-rep of the E ? (b 1g + b 2g) distortion of square planar molecules to rectangle and rhombus isomers becomes a rhombus in which the vertices alternately represent distortions to the rectangle and rhombus isomers. Similarly the top-rep of the E ? e distortion of regular Oh octahedra to elongated D4h tetragonal bipyramids becomes a triangle in which the vertices represent the three distinct tetragonal bipyramids from a given octahedron and the edge midpoints represent lower symmetry rhombic D2h intermediates. A regular octahedron can be used as a top-rep for the T ? (e + t 2) distortions of regular octahedra if the 6 vertices represent distortions to D4h tetragonal bipyramid isomers, the 8 face midpoints represent distortions to D3d trigonal antiprism isomers, and the 12 edge midpoints represent lower symmetry rhombic D2h intermediates. In the case of Jahn-Teller T ? h distortions of regular Ih icosahedra, the corresponding top-rep becomes a regular icosahedron in which the 12 vertices represent distortions to pentagonal D5d isomers, the 20 face midpoints represent distortions to trigonal D3d isomers, and the 30 edge midpoints represent D2h intermediates. A 4-dimensional analogue of the tetrahedron (i.e. the 4-simplex) can be used as a top-rep for the G ? g problem and the H ? g component of the H ? (g + 2h) problem for JT distortions of regular icosahedra. In this case the 5 vertices and the 10 edge midpoints correspond to Th isomers and D3d intermediates, respectively. 相似文献
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X. H. Zhou L. Ma Y. B. Xing Y. H. Zhang Y. X. Guo X. G. Lei C. Y. Xie M. Oshima Y. Toh M. Koizumi A. Osa Y. Hatsukawa M. Sugawara M. M. Ndontchueng 《The European Physical Journal A - Hadrons and Nuclei》2006,28(3):271-275
Excited states in 188Tl have been studied experimentally using the 157Gd (35Cl, 4n) reaction at a beam energy of 170MeV. A rotational band built on the πh
9/2 ⊗ νi
13/2 configuration with oblate deformation has been established for 188Tl. Based on the structure systematics of the oblate πh
9/2 ⊗ νi
13/2 bands in the heavier odd-odd Tl nuclei, we have tentatively proposed spin values for the new band in 188Tl. The πh
9/2 ⊗ νi
13/2 oblate band in 188Tl shows low-spin signature inversion, and it can be interpreted qualitatively by the two-quasiparticle plus rotor model including
a J-dependent p-n residual interaction. 相似文献
15.
Chengying Xie Xiaohong Zhou Yuhu Zhang Yingxiang Guo Xiangguo Lei Yong Zheng Minliang Liu Litao Song Hualei Wang Haiping Yu Wentao Guo Peng Luo Zhijun Wu Lihua Zhu Xiaoguang Wu 《中国科学G辑(英文版)》2005,48(4):442-449
High-spin states in 190Tl have been studied via the 160Gd(35Cl, 5nγ) reaction. The level scheme, consisting of the πh
9/2⊗vi
13/2 oblate band and a cascade with character of single particle excitations, has been established. Spin values have been firmly
assigned to the oblate band in 190Tl, resulting in low-spin signature inversion in the πh
9/2⊗vi
13/2 oblate band for the first time. Based on the similarity of the level structure in doubly odd Tl nuclei, spin values for the
oblate bands in 192–200Tl should be re-assigned, and a consistent low-spin signature inversion has occurred in these oblate deformed nuclei. The
low-spin signature inversion phenomena can be interpreted qualitatively by using the 2-quasiparticle plus rotor model including
p-n residual interactions. 相似文献
16.
Liu QH Haijun Z Liu JX Zhong-Can OY 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》1999,60(3):3227-3233
An analytic solution for the Helfrich spontaneous curvature membrane model [H. Naito, M.Okuda, and Ou-Yang Zhong-Can, Phys. Rev. E 48, 2304 (1993); 54, 2816 (1996)], which has the conspicuous feature of representing a circular biconcave shape, is studied. Results show that the solution in fact describes a family of shapes, which can be classified as (i) a flat plane (trivial case), (ii) a sphere, (iii) a prolate ellipsoid, (iv) a capped cylinder, (v) an oblate ellipsoid, (vi) a circular biconcave shape, (vii) a self-intersecting inverted circular biconcave shape, and (viii) a self-intersecting nodoidlike cylinder. Among the closed shapes (ii)-(vii), a circular biconcave shape is the one with a minimum of local curvature energy. 相似文献
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Elastic, strength, electronic properties and vibrational spectra of Ne@C60 (I h) in its ground electronic state (X 1Ag) were investigated with density functional theory at B3PW91/6-31G level via structure distortions. The elastic properties were obtained from the potential energy curves (PECs) in all of the five independent distortional directions of the molecule with symmetries of 1. D 5d, 2. D 3d, 3. D 2h, 4. C 2h(1) and 5. C 2h(2). PECs were examined where the structure of Ne@C60 was destroyed. The necessary energies to destroy the structure were thus obtained, which illuminated the stability of Ne@C60. PECs were found to be anisotropic and were accurately fitted to polynomials. Elongations in the direction of D 5d and compression in D 2h encountered potential energy surface cross-linkages, which might be considered as a single electron pump for further application in the design of single electron devices. Time-dependent B3PW91/6-31G analysis predicted significant electronic spectra changes associated with structure distortions. Similarities and differences of the properties were compared with those in C60 and He@C60. 相似文献
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Abstract The crystal structure of Rb2CdCl4 has been studied by X-ray diffraction at 295 and 160 K in the initial phase D 17 4h as well as at 105 K in the ferroelastic phase. It was found that the phase transition D 17 4h ? D 10 2h takes place instead of D 17 4h ? D 18 2h as proposed earlier. The first of the transitions corresponds to unequal and the second to equal Φ-tilts of CdCl6-octahedra around the a and b axes of the tetragonal unit cell. 相似文献
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The Hartree-Fock (HF) minima for the nucleus28Si were obtained for the prolate, oblate and spherical shapes using the interaction obtained by Preedom and Wildenthal. The
interaction gives rise to large energy separation between the prolate and the oblate shapes. The spherical solution is just
2 MeV above the lowest HF (oblate) minimum. The spectrum projected from the oblate HF state is in good agreement with the
experimental spectrum. The transition probabilities for the different energy levels also agree reasonably well. The configuration
mixing calculations performed on the basis of states projected from the three shapes indicate that there is no significant
mixing of different projected states. The second 0
2
+
state, thus obtained, corresponds to the third 0
3
+
state in the experimental spectrum and stems dominantly from the spherical HF state. It is seen that the structure of the
energy levels of28Si, especially the second 0
2
+
level is very sensitive to the two body interaction. The results are compared with those obtained using the renormalised
interaction of Kuo. 相似文献