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581.
《高分子科学杂志,A辑:纯化学与应用化学》2013,50(8):965-976
The intrinsic viscosities [η] of polyacrylamide (PAM) having different average molecular weights are measured in various mixtures of water (good solvent) and N, N dimethyl formamide (DMF, nonsolvent) at different temperatures. The observed results show a significant variation of cosolvency as a function of solvent composition (?DMF). The nature of curves in [η] vs. ?DMF plot at different temperatures indicates the existence of two antagonistic effects. The unperturbed dimensions (Kθ) of the polymer are determined by a number of methods, which agree well with each other. The temperature coefficient of unperturbed dimension (K′), molecular extension factors (αn), characteristic ratio (Cα) and chain rigidity (σ) are evaluated and the effects of temperature, solvent composition are discussed. The volume related parameter VE and shape factor ν were also computed, which shows the shape of polymer molecules to be more or less spherical in solution. 相似文献
582.
We prove a topological two‐way characterization of the existence of fixed‐points, without using linear or convexity structures and provide applications in optimization‐related problems. Such a characterization is also demonstrated for a fixed‐component point, a slight generalization of a fixed point. 相似文献
583.
Relaxation parameter estimation and brain activation detection are two main areas of study in magnetic resonance imaging (MRI) and functional magnetic resonance imaging (fMRI). Relaxation parameters can be used to distinguish voxels containing different types of tissue whereas activation determines voxels that are associated with neuronal activity. In fMRI, the standard practice has been to discard the first scans to avoid magnetic saturation effects. However, these first images have important information on the MR relaxivities for the type of tissue contained in voxels, which could provide pathological tissue discrimination. It is also well-known that the voxels located in gray matter (GM) contain neurons that are to be active while the subject is performing a task. As such, GM MR relaxivities can be incorporated into a statistical model in order to better detect brain activation. Moreover, although the MR magnetization physically depends on tissue and imaging parameters in a nonlinear fashion, a linear model is what is conventionally used in fMRI activation studies. In this study, we develop a statistical fMRI model for Differential T2? ConTrast Incorporating T1 and T2? of GM, so-called DeTeCT-ING Model, that considers the physical magnetization equation to model MR magnetization; uses complex-valued time courses to estimate T1 and T2? for each voxel; then incorporates gray matter MR relaxivities into the statistical model in order to better detect brain activation, all from a single pulse sequence by utilizing the first scans. 相似文献
584.
Purpose
The purpose of this work is to characterize the noise in spinal cord functional MRI, assess current methods aimed at reducing noise, and optimize imaging parameters.Methods
Functional MRI data were acquired at multiple echo times and the contrast-to-noise ratio (CNR) was calculated. Independently, the repetition time was systematically varied with and without parallel imaging, to maximize BOLD sensitivity and minimize type I errors. Noise in the images was characterized by examining the frequency spectrum, and investigating whether autocorrelations exist. The efficacy of several physiological noise reduction methods in both null (no stimuli) and task (thermal pain paradigm) data was also assessed. Finally, our previous normalization methods were extended.Results
The echo time with the highest functional CNR at 3 Tesla is at roughly 75 msec. Parallel imaging reduced the variance and the presence of autocorrelations, however the BOLD response in task data was more robust in data acquired without parallel imaging. Model-free based approaches further increased the detection of active voxels in the task data. Finally, inter-subject registration was improved.Conclusions
Results from this study provide a rigorous characterization of the properties of the noise and assessment of data acquisition and analysis methods for spinal cord and brainstem fMRI. 相似文献585.
Identification,characterization, and high‐performance liquid chromatography quantification of process‐related impurities in vonoprazan fumarate 下载免费PDF全文
Lei Liu Na Cao Xingling Ma Kaihe Xiong Lili Sun Qiaogen Zou 《Journal of separation science》2016,39(7):1232-1241
High‐performance liquid chromatography analysis of vonoprazan fumarate, a novel proton pump inhibitor drug revealed six impurities. These were identified by liquid chromatography with mass spectrometry. Further, the structures of the impurities were confirmed by synthesis followed by characterization by mass spectrometry, NMR spectroscopy, and infrared spectroscopy. On the basis of these data and knowledge of the synthetic scheme of vonoprazan fumarate, the previously unknown impurity was identified as 1‐[5‐(2‐fluorophenyl)‐1‐(pyridin‐3‐ylsulfonyl)‐1H‐pyrrol‐3‐yl]‐N‐methyldimethylamine, which is a new compound. The possible mechanisms by which these impurities were formed were also discussed. A high‐performance liquid chromatography method was optimized in order to separate, selectively detect, and quantify all process‐related impurities of vonoprazan fumarate. The presented method has been validated in terms of linearity, limits of detection, and quantification, and response factors and, therefore, is highly suitable for routine analysis of vonoprazan fumarate related substances as well as stability studies. 相似文献
586.
本文利用乌鲁木齐河年最大洪水流量的时间序列.从吸引子的关联维数分析了32年来乌鲁木齐河年最大洪水流量变化的混沌性质及其特征.对认识该系统的特征提供了更多有意义的信息. 相似文献
587.
Ricci GB De Carli D Colonnese C Di Gennaro G Quarato PP Cantore G Esposito V Garreffa G Maraviglia B 《Magnetic resonance imaging》2004,22(10):1487-1492
We studied a new procedure of BOLD/fMRI acquisition in epilepsy. They use the benzodiazepine effect to achieve a more reliable baseline for statistical analysis. The method works only in the MR domain without EEG correlation. It compares the EPI images during interictal epileptic discharges and the images “inactivated” by benzodiazepine.
The results in five out of eight patients show that this procedure in comparison with the EEG/fMRI method gives a net improvement of spatial definition of BOLD areas. These preliminary results seem to confirm the hypothesis that the better BOLD/fMRI procedure in epilepsy is to make use of physical features of MR that, unlike EEG, is not influenced by the distance of intercerebral sources and consequently allows a more complete and undistorted display of BOLD areas. 相似文献
588.
采用电感耦合等离子体原子发射光谱法对REACH法规涉及产品中铅、铬、钴、砷、锡、铝、锆、钼和硼的含量进行测定。0.2g样品经微波消解处理,聚合物材质试样以8mL硝酸和2mL过氧化氢为消解试剂;无机非金属材质试样以6mL硝酸、2mL过氧化氢和2mL氢氟酸为消解试剂。各元素的方法检出限均低于15mg·kg-1。方法的加标回收率在82.4%~108%之间,测定值的相对标准偏差(n=7)在3%~6%之间。 相似文献
589.
Shin-ichiro Gozu Kouichi Akahane Naokatsu Yamamoto Akio Ueta Naoki Ohtani 《Physica E: Low-dimensional Systems and Nanostructures》2006,32(1-2):230
InGaAs/AlAsSb systems lattice matched to InP have two distinguishable features: a high conduction band offset and type-II band configuration. Although, the former results in a large intersubband transition (ISBT) at conduction band, the latter makes it difficult to use the effective interband transition (IBT). To overcome this latter problem, the effect of the Sb was investigated because Sb would act as a band modulator from type-II to type-I. In0.57Ga0.43As1-xSbx/AlAs0.48Sb0.52 single quantum well (SQW) samples with various Sb compositions x, were grown on GaAs substrates via AlAs0.48Sb0.52 buffer layer. Their photoluminescence (PL) properties were examined to identify their band configurations. When the excitation laser power was increased, the PL property of In0.57Ga0.43As SQW sample, showed a larger blue shift than that of ones. This indicates that the band configuration modulates from type-II to type-I when the antimonide composition is larger than 0.13. These findings indicate that new functional devices can be fabricated using a combination of IBT and ISBT. 相似文献
590.
V. Hannstein G. C. Hegerfeldt 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,38(2):415-422
A simplified scheme for the investigation of cooperative effects in
the quantum jump statistics of small numbers of fluorescing atoms
and ions in a trap is
presented. It allows the analytic treatment of three
dipole-dipole interacting four-level systems which model the
relevant level scheme of Ba+ ions. For the latter, a huge rate of
double and triple jumps was reported in a former experiment and the
huge rate was attributed to the dipole-dipole interaction. Our theoretical
results show that the effect of the dipole-dipole interaction on these rates
is at most 5% and that for
the parameter values of the experiment there is practically no
effect. Consequently it seems that the
dipole-dipole interaction can be ruled out as a possible explanation for
the huge rates reported in the experiment. 相似文献