anisotropy

各向异性
  • 文章类型: Journal Article
    天然产物二聚体具有有趣的结构特征,并且通常具有显着的药理活性。我们在这里报告了两个不常见的海洋gorgonian衍生的对称二聚体,WeizhouochronesA(1)和B(2),茚酮衍生的单体,它们是从南中国海收集的珊瑚Anthogorgiaochracea中分离出来的。这些二聚体是仅依赖于常规NMR数据如NOE和J-偶联的结构阐明的困难目标。这里,探索新兴方法在具有挑战性的分子结构阐明中的应用,我们探索了许多不同的各向异性和计算NMR方法。WeizhouochroneA的各向异性NMR参数的测量,包括残余偶极耦合(RDC)和残余化学位移各向异性(RCSA),使我们能够成功地确定平面结构及其相对配置。该结果通过基于DP4+概率和计算机辅助3D结构阐明(CASE-3D)的计算NMR分析得到证实。
    Natural product dimers have intriguing structural features and often have remarkable pharmacological activities. We report here two uncommon marine gorgonian-derived symmetric dimers, weizhouochrones A (1) and B (2), with indenone-derived monomers, that were isolated from the coral Anthogorgia ochracea collected from the South China Sea. These dimers are difficult targets for structure elucidation that solely relies upon conventional NMR data such as NOEs and J-couplings. Here, to explore the application of emerging methods on the structure elucidation of challenging molecules, we explored a number of different anisotropic and computational NMR approaches. The measurements of anisotropic NMR parameters of weizhouochrone A, including residual dipolar couplings (RDCs) and residual chemical shift anisotropy (RCSA), allowed us to successfully determine the planar structure and its relative configuration. This result was corroborated by a computational NMR analysis based on DP4+ probability and computer-assisted 3D structure elucidation (CASE-3D).
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  • 文章类型: Journal Article
    固态NMR方法的组合,用于提取合成后的23Na位移和四极参数,结构复杂的NaMnO2Na离子阴极材料,提出了在魔角旋转(MAS)下。我们证明,魔角转向实验与转子辅助种群转移(RAPT)的集成既可用于识别位移,也可用于提取其四极耦合的幅度范围。我们还演示了基于二维脉冲(TOP)的双剪切卫星过渡幻角旋转(TOP-STMAS)的适用性,显示了它如何产生具有分离位移和二阶四极各向异性的光谱,进而可用于分析无各向异性体磁化率(ABMS)引起的位移色散的四极线形,并确定各向同性位移和四极产物。结合所有这些实验,提取了所有观察到的Na环境的位移和四极参数,并与以前文献中报道的基于密度泛函理论(DFT)的模型产生了极好的一致性。我们期望这些方法为固态NMR探测顺磁性材料和其他表现出大位移色散的系统中的半整数四极核的新可能性打开大门。
    A combination of solid-state NMR methods for the extraction of 23Na shift and quadrupolar parameters in the as-synthesized, structurally complex NaMnO2 Na-ion cathode material, under magic-angle spinning (MAS) is presented. We show that the integration of the Magic-Angle Turning experiment with Rotor-Assisted Population transfer (RAPT) can be used both to identify shifts and to extract a range of magnitudes for their quadrupolar couplings. We also demonstrate the applicability of the two-dimensional one pulse (TOP) based double-sheared Satellite Transition Magic-Angle Spinning (TOP-STMAS) showing how it can yield a spectrum with separated shift and second-order quadrupolar anisotropies, which in turn can be used to analyze a quadrupolar lineshape free of anisotropic bulk magnetic susceptibility (ABMS) induced shift dispersion and determine both isotropic shift and quadrupolar products. Combining all these experiments, the shift and quadrupolar parameters for all observed Na environments were extracted and yielded excellent agreement with the density functional theory (DFT) based models that were reported in previous literature. We expect these methods to open the door for new possibilities for solid-state NMR to probe half-integer quadrupolar nuclei in paramagnetic materials and other systems exhibiting large shift dispersion.
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  • 文章类型: Journal Article
    可行性分析的初步结果对于在行为干预的神经生物标志物的新兴领域规划未来的随机对照试验(RCT)至关重要。当前的可行性研究使用MRI衍生的扩散成像数据来研究是否有可能在被诊断为自闭症谱系障碍(ASD)的人群中识别行为干预的神经生物标志物。call体与认知过程有关,并且先前在被诊断为ASD的人中发现了call体异常。我们使用病例对照设计来评估先前被诊断为ASD的干预者的类型与他们当前的call体白质完整性之间的关联。26名患有ASD的儿童和青少年,有或没有父母管理的行为干预史,用扩散数据采集序列进行MRI扫描.我们进行了基于道的空间统计和感兴趣区域分析。在病例(暴露于父母管理的行为干预)和对照(未暴露于父母管理的行为干预)之间,call体后部的各向异性值(被认为表明白质完整性)显着不同。根据剂量反应关系,通过行为干预的强度来调节效果。当前的可行性案例对照研究为估算该领域未来RCT所需的统计能力提供了基础。此外,该研究证明了有目的地制定的运动控制方案的有效性,并有助于确定感兴趣的候选区域.讨论了扩散张量成像在评估ASD治疗结果中的潜在临床应用。
    Tentative results from feasibility analyses are critical for planning future randomized control trials (RCTs) in the emerging field of neural biomarkers of behavioral interventions. The current feasibility study used MRI-derived diffusion imaging data to investigate whether it would be possible to identify neural biomarkers of a behavioral intervention among people diagnosed with autism spectrum disorder (ASD). The corpus callosum has been linked to cognitive processing and callosal abnormalities have been previously found in people diagnosed with ASD. We used a case-control design to evaluate the association between the type of intervention people diagnosed with ASD had previously received and their current white matter integrity in the corpus callosum. Twenty-six children and adolescents with ASD, with and without a history of parent-managed behavioral intervention, underwent an MRI scan with a diffusion data acquisition sequence. We conducted tract-based spatial statistics and a region of interest analysis. The fractional anisotropy values (believed to indicate white matter integrity) in the posterior corpus callosum was significantly different across cases (exposed to parent-managed behavioral intervention) and controls (not exposed to parent-managed behavioral intervention). The effect was modulated by the intensity of the behavioral intervention according to a dose-response relationship. The current feasibility case-control study provides the basis for estimating the statistical power required for future RCTs in this field. In addition, the study demonstrated the effectiveness of purposely-developed motion control protocols and helped to identify regions of interest candidates. Potential clinical applications of diffusion tensor imaging in the evaluation of treatment outcomes in ASD are discussed.
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    文章类型: Journal Article
    背景:只有一小部分精神分裂症患者出现紧张性症状。影像学研究表明,大脑运动回路与紧张症的潜在病理有关。然而,有关紧张型精神分裂症中这些回路的扩散性失调的数据很少。
    目的:评估精神分裂症伴紧张症患者的脑运动回路受累情况。
    方法:使用扩散张量成像(DTI)测量与运动电路链接的选定大脑区域中的白质信号。将7例紧张型精神分裂症患者的相关DTI数据与7例非紧张型精神分裂症患者的DTI数据进行了比较,匹配性别,年龄,和教育水平。
    结果:在call体的脾中发现了显着升高的分数各向异性值,小脑的右花梗,与没有卡通症的精神分裂症患者相比,右内囊。这一发现表明,在选定的运动相关的大脑区域中,扩散率发生了改变。
    结论:紧张型精神分裂症与特定运动脑区和相应回路的连接失调有关。需要进行未来的DTI研究,以解决精神分裂症相关紧张症在急性和缓解状态下的运动异常的神经相关性,以确定该疾病的特定病理生理学。
    BACKGROUND: Only a small proportion of schizophrenia patients present with catatonic symptoms. Imaging studies suggest that brain motor circuits are involved in the underlying pathology of catatonia. However, data about diffusivity dysregulation of these circuits in catatonic schizophrenia are scarce.
    OBJECTIVE: To assess the involvement of brain motor circuits in schizophrenia patients with catatonia.
    METHODS: Diffusion tensor imaging (DTI) was used to measure white matter signals in selected brain regions linked to motor circuits. Relevant DTI data of seven catatonic schizophrenia patients were compared to those of seven non-catatonic schizophrenia patients, matched for sex, age, and education level.
    RESULTS: Significantly elevated fractional anisotropy values were found in the splenium of the corpus callosum, the right peduncle of the cerebellum, and the right internal capsule of the schizophrenia patients with catatonia compared to those without catatonia. This finding showed altered diffusivity in selected motor-related brain areas.
    CONCLUSIONS: Catatonic schizophrenia is associated with dysregulation of the connectivity in specific motoric brain regions and corresponding circuits. Future DTI studies are needed to address the neural correlates of motor abnormalities in schizophrenia-related catatonia during the acute and remitted state of the illness to identify the specific pathophysiology of this disorder.
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  • 文章类型: Journal Article
    为了研究各向异性对BCC材料形成极限的影响,将速率相关的自洽晶体可塑性模型与Marciniak-Kuczyñski模型相结合。当并行运行多个应变路径的模拟时,模型的计算速度提高了24倍。这种加速使各种BCC纹理的形成极限的全面调查,如γ,σ,α,η和ε纤维和均匀(随机)纹理。这些模拟表明,晶体学织构对所得的成形极限图具有显着影响(正面和负面影响)。例如,γ纤维织构,由于高r值,通常通过热机械加工来寻求,在考虑的纹理中,在平衡的双轴应变路径中具有最高的成形极限,但在平面应变路径下具有最低的成形极限。根据当前模型产生的结果进行系统的调查,称为\'VPSC-FLD\',表明r值不能作为形成极限应变的良好度量。然而,模型预测表明r值与成形极限应力之间存在一定程度的相关性。
    A rate-dependent self-consistent crystal plasticity model was incorporated with the Marciniak-Kuczyński model in order to study the effects of anisotropy on the forming limits of BCC materials. The computational speed of the model was improved by a factor of 24 when running the simulations for several strain paths in parallel. This speed-up enabled a comprehensive investigation of the forming limits of various BCC textures, such as γ, σ, α, η and ϵ fibers and a uniform (random) texture. These simulations demonstrate that the crystallographic texture has significant (both positive and negative) effects on the resulting forming limit diagrams. For example, the γ fiber texture, which is often sought through thermo-mechanical processing due to a high r-value, had the highest forming limit in the balanced biaxial strain path but the lowest forming limit under the plane strain path among the textures under consideration. A systematic investigation based on the results produced by the current model, referred to as \'VPSC-FLD\', suggests that the r-value does not serve as a good measure of forming limit strain. However, model predictions show a degree of correlation between the r-value and the forming limit stress.
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  • 文章类型: Journal Article
    The emerging class of topological materials provides a platform to engineer exotic electronic structures for a variety of applications. As complex band structures and Fermi surfaces can directly benefit thermoelectric performance it is important to identify the role of featured topological bands in thermoelectrics particularly when there are coexisting classic regular bands. In this work, the contribution of Dirac bands to thermoelectric performance and their ability to concurrently achieve large thermopower and low resistivity in novel semimetals is investigated. By examining the YbMnSb2 nodal line semimetal as an example, the Dirac bands appear to provide a low resistivity along the direction in which they are highly dispersive. Moreover, because of the regular-band-provided density of states, a large Seebeck coefficient over 160 µV K-1 at 300 K is achieved in both directions, which is very high for a semimetal with high carrier concentration. The combined highly dispersive Dirac and regular bands lead to ten times increase in power factor, reaching a value of 2.1 mW m-1 K-2 at 300 K. The present work highlights the potential of such novel semimetals for unusual electronic transport properties and guides strategies towards high thermoelectric performance.
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  • 文章类型: Journal Article
    An approach engaging Vertical Electrical Sounding (VES) and remote sensing data was carried out with a view to developing groundwater potential and aquifer vulnerability maps of the study area. One hundred and one (101) depth sounding data were acquired using Schlumberger array, with half maximum current electrode separation (AB/2) of 100 m. The VES were quantitatively interpreted using partial curve matching and computer aided iteration to determine the geoelectrical parameters of each station. The remote sensing data were processed using the application of Geographic Information System-based multi-criteria technique ArcGIS software. Eight (8) parameters namely lineament density, drainage density, slope, transmissivity, hydraulic conductivity, coefficient of anisotropy, aquifer thickness and resistivity were used to produce the groundwater potential model while five (5) parameters namely, lineament density, slope, longitudinal conductance, hydraulic conductivity and thickness of layer overlying the delineated aquifer were also used to produce the vulnerability model. The final output of overlay parameters for estimating the groundwater potential gave an index that ranged from 1-5. The zone categorised as low groundwater potential covered about 80% of the area. The majority of the area falls within low (about 80%) vulnerability and low groundwater potential rating while being relatively protected from potential contaminants infiltrating from the surface. The prediction accuracy of the groundwater potential model was established via existing hand-dug well correlation analysis.
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  • 文章类型: Journal Article
    皱纹是许多生物组织中普遍存在的表面现象,被认为在动脉健康中起重要作用。由于动脉高度非线性,各向异性,多层复合体系,有必要研究结合这些材料特性的起皱。一些研究已经检查了具有非线性各向同性材料关系的表面起皱机制。然而,与各向异性本构模型相关的起皱,如Ogden-Gasser-Holzapfel(OGH),适用于软生物组织,特别是动脉,仍然需要调查。这里,OGH参数的影响,如纤维的取向,刚度,和皱纹开始时的分散,通过分析由薄层组成的双层系统来阐明皱纹的波长和振幅,坚硬的neo-Hookean膜和经受压缩的柔软OGH底物。使用有限元分析和分析线性扰动方法来预测出现皱纹的临界收缩应变。结果表明,除了刚度不匹配,与纤维刚度和分布相关的各向异性特征可用于自然分层系统以调节起皱和随后的折叠行为。对(x-y)平面中的纤维在x方向上受到压缩的双层系统的进一步分析显示,起皱应变和波长对纤维角度的复杂依赖性,刚度,和分散。通过利用从OGH模型导出的线性化各向异性特性的近似来捕获这种行为。这种对这种动脉壁样系统中起皱的理解将有助于确定起皱机制在生物动脉中的作用,以及其合成对应物的设计。
    Wrinkling is a ubiquitous surface phenomenon in many biological tissues and is believed to play an important role in arterial health. As arteries are highly nonlinear, anisotropic, multilayered composite systems, it is necessary to investigate wrinkling incorporating these material characteristics. Several studies have examined surface wrinkling mechanisms with nonlinear isotropic material relationships. Nevertheless, wrinkling associated with anisotropic constitutive models such as Ogden-Gasser-Holzapfel (OGH), which is suitable for soft biological tissues, and in particular arteries, still requires investigation. Here, the effects of OGH parameters such as fibers\' orientation, stiffness, and dispersion on the onset of wrinkling, wrinkle wavelength and amplitude are elucidated through analysis of a bilayer system composed of a thin, stiff neo-Hookean membrane and a soft OGH substrate subjected to compression. Critical contractile strain at which wrinkles occur is predicted using both finite element analysis and analytical linear perturbation approach. Results suggest that besides stiffness mismatch, anisotropic features associated with fiber stiffness and distribution might be used in natural layered systems to adjust wrinkling and subsequent folding behaviors. Further analysis of a bilayer system with fibers in the (x-y) plane subjected to compression in the x direction shows a complex dependence of wrinkling strain and wavelength on fiber angle, stiffness, and dispersion. This behavior is captured by an approximation utilizing the linearized anisotropic properties derived from OGH model. Such understanding of wrinkling in this artery wall-like system will help identify the role of wrinkling mechanisms in biological artery in addition to the design of its synthetic counterparts.
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  • 文章类型: Journal Article
    实验确定了具有球形外壳的圆柱形X1252Cf源的中子各向异性发射。金属材料和外壳形状对各向异性因素的影响,FI(θ),通过蒙特卡洛计算进行评估,在进行测量之前。计算结果表明,光形和球形外壳减少了来自圆柱源的中子各向异性发射,并且材料的性质不会在很大程度上影响各向异性发射。当采用球形铝保护外壳时获得的实验结果还表明,在宽的天顶角范围内,各向异性因子接近1.0。考虑到源的处理和对源的机械冲击措施。我们设计了一个SUS304球形保护箱,用于翻新的源输送设备。使用SUS304制成的球形保护外壳,测得的各向异性因子FI(90)确定为1.002±0.002(k=1)。实验结果还表明,测得的各向异性因子在天顶角为55至125°之间呈平坦分布。
    The anisotropic emission of neutrons from a cylindrical X1 252Cf source with the spherical external casing was experimentally determined. The influence of metal materials and shapes of the external casing to the anisotropy factor, FI(θ), was assessed by the Monte Carlo calculation, before performing the measurement. The results of the calculation implied that light- and spherical-shaped external casing decreases the anisotropic emission of neutrons from a cylindrical source and the nature of the material does not affect the anisotropic emission to a large extent. The experimental results obtained when a spherical-shaped aluminum protection case was employed also revealed that the anisotropy factor was close to 1.0 with a wide zenith angle range. Considering the source handling and measures against mechanical impact to the source, we designed an SUS304-made spherical protection case for a renovated source delivering apparatus. With the SUS304-made spherical protection case, the measured anisotropy factor FI(90) was determined to be 1.002 ± 0.002 (k = 1). Results from the experiments also indicated that the measured anisotropy factor has a flat distribution from 55 to 125° with zenith angle.
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  • 文章类型: Case Reports
    BACKGROUND: Pusher syndrome is a disorder of postural control. It is associated with unilateral lesions on central vestibular system. In the current study, we attempted to identify and investigate neural connectivity of the parieto-insular vestibular cortex in a patient with pusher syndrome, using diffusion tensor imaging.
    METHODS: A 60-year-old male patient had left hemiplegia due to an infarction on right premotor cortex, primary motor cortex, corona radiata and temporal and occipital lobe. The patient had severe motor weakness in left upper and lower limb, left side neglect and significant pusher syndrome.
    METHODS: Patient was diagnosed with left hemiplegia due to an infarction in the right middle cerebral artery territory at the neurology department of a university hospital.
    METHODS: One patient and 5 control subjects of similar age participated. Diffusion tensor imaging data were acquired at 4-month and 12-month after the initial injury.
    RESULTS: Fractional anisotropy, mean diffusivity, and tract volume (TV) were measured. TV values in both affected and unaffected hemispheres of the patient were significantly decreased at 4-month compared to those of control subjects. In the unaffected hemisphere of the patient, TV value showed significant increase at 12-month compared to that at 4-month. Although the TV value at 12-month of the affected hemisphere was out of reference range, TV was considerably increased compared to that at 4-month. Mean values for fractional anisotropy or mean diffusivity in 2 hemispheres did not show significant difference compared to those of control subjects regardless of month.
    CONCLUSIONS: Restoration of an injured projection pathway between the vestibular nuclei and parieto-insular vestibular cortex with recovery of pusher syndrome was found in a patient with stroke.
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