Measurement of diffusion coefficients using a quick echo split NMR imaging technique

A new method for the ultrafast generation of diffusion-weighted images is reported. The technique combines a quick echo split NMR imaging sequence with the principle of Stejskal and Tanner. It allows to determine the diffusion constant with nearly the same accuracy as the conventional spin-echo technique, requiring only a fraction of the time. The determined values for water doped with 1 g Cu(NO₃)₂ per liter of H₂O and pure acetone were D_water = (1.95 ± 0.02) × 10⁻⁹ m²/s and D_acetone = (4.05 ± 0.02) × 10⁻⁹ m²/s at 18.5°C. They are in good agreement both with literature and our own reference measurements using a diffusion-weighted spin-echo sequence. In addition, the temperature dependence of D_water was measured in the range of 18.5–45.9°C and a good correspondence with reported data was found.     

用快波加热燃烧等离子体

在把离子伯恩斯坦波处理成对快阿尔芬波的响应下，导出了点火托卡马克等离子体的离子回旋共振加热的二阶模转换方程。这个二阶方程的数值积分表明，结果与由高阶方程的计算很好地一致。只有在弱阻尼的情况下，α粒子吸收的功率才是重要的。     

椭圆截面等离子体柱离子回旋频率附近的本征振荡

本文用椭圆柱座标系导出了波导管中和自由边界情况下波的色散关系,计算了椭圆截面波导管中快磁流体波和慢波的本征模。通过计算得出,在时,快波可以在等离子体的高密度区域传播,而慢波只能在低密度区域传播。     

Regularity in Sobolev spaces for the fast diffusion and the porous medium equation

The degenerate parabolic equation

     

Universal scaling between structural relaxation and caged dynamics in glass-forming systems: Free volume and time scales

It is shown that the Debye-Waller factor (DW), a measure of the cage dynamics, is contributed by free-volume in o-terphenyl (OTP) and glycerol. An elementary ansatz provides an alternative way to get the reduced DW from Positron Annihilation Lifetime Spectroscopy (PALS). The ansatz supports the scaling of the slow relaxation with the fast caged dynamics over about ten decades in relaxation times in OTP and glycerol. Both PALS and neutron scattering experiments show that, in order to evidence the scaling, the observation times must be shorter than the time scales of the relaxation processes.     

一种菲涅尔全息图的快速算法

通过分析菲涅尔全息图计算模型,发现大量的平方运算和三角函数运算是计算速度的瓶颈,提出了一种菲涅尔全息图的快速计算方法.根据菲涅尔全息图的数学模型,利用三角函数的和差化积公式,将全息图的数学模型变换为由仅与水平或垂直方向有关的独立分量,通过四则运算来表示.在菲涅尔全息图的计算中,用少量的三角函数、平方运算和大量的四则运算代替原来大量的三角函数和平方运算,减少了全息图的运算量.实验表明,采用该算法后全息图的计算速度提高了9倍以上.     

Studies on thermionic ionisation detection in comprehensive two-dimensional gas chromatography

This study explores the application of specific thermionic ionisation detection in comprehensive 2-D GC (GC x GC) and represents the first report of GC x GC with nitrogen phosphorus detection (GC x GC-NPD). Of particular interest is the performance of the NPD with respect to peak parameters of asymmetry and sensitivity. Since GC x GC produces much narrower peaks than obtained with fast GC (e.g. 100 ms vs. <1 s) the effect of detector response time and any lack of symmetry arising from the detection step is important if peak separation (resolution) is to be maintained. It was observed that detector gas flows had a significant impact on peak asymmetry and peak magnitude, and that optimisation of the detector was critical, particularly for complex sample analysis by GC x GC-NPD. Peak asymmetries ranging from As = 1.8 to 8.0 were observed under different conditions of detector gas flows. Comparison of GC x GC-NPD with GC x GC-flame ionisation detection (FID) showed the former to be approximately 20 times more sensitive for the detection of nitrogen-containing methoxypyrazines analytes, and GC x GC-NPD had a larger linear detection range compared to GC x GC-FID. Furthermore, comparison of GC x GC-NPD and GC x GC-TOFMS chromatograms for the analysis of coffee head-space demonstrated the benefits of selective detection, ultimately realised in a comparatively simplified contour plot.     

Fast HPLC method for the determination of glimepiride, glibenclamide, and related substances using monolithic column and flow program

This work presents a fast method for the simultaneous separation and determination of glimepiride, glibenclamide, and two related substances by RP LC. The separation was performed on a Chromolith Performance (RP-18e, 100 mm x 4.6 mm) column. As mobile phase, a mixture of phosphate buffer pH 3, 7.4 mM, and ACN (55:45 v/v) was used. Column oven temperature was set to 30 degrees C. The total chromatographic run time was 80 s. This was achieved using a flow program from 5 to 9.9 mL/min. Precisions of the interday and the intraday assay for both retention times and peak areas for the four analyzed compounds were less than 1.2%. The method showed good linearity and recovery. The short analysis time makes the method very valuable for quality control and stability testing of drugs and their pharmaceutical preparations.     

A new approach for fast, simultaneous NO/NO2 analysis: application of basic features of multiphoton-induced ionization and dissociation of NOx

A new method of simultaneously recording NO and NO2 concentrations in complex gas mixtures is described. This method is based on resonance enhanced multiphoton ionization (REMPI), on time-of-flight mass analysis, and on monitoring the kinetic energy released upon dissociation of NO2. Its benefits are high speed and high flexibility. NO/NO2 analysis can therefore be combined with the simultaneous monitoring of other components. For instance, NH3 is a compound of interest when studying the chemical reactions of NO(x) in catalytic converters of combustion engines. The spectroscopic excitation schemes used for this new method are discussed in detail. Its reliability has been demonstrated by performing measurements at an industrial motor test facility. This novel technique performs well in comparison with conventional NO(x) analysis using chemiluminescence detection.