Dynamic control of split flow in packed column supercritical fluid chromatography using dual resistively heated restrictors

Remote control of the vent/detector split flow ratio in packed column supercritical fluid chromatography (pSFC) with flame ionization detector (FID) is demonstrated using a dual heated restrictor method. Restrictors stemming from a Tee at the separation column outlet were, respectively, fixed into an FID and a vent port, and their individual temperatures were controlled using resistively heated wires. Subsequently, both system pressure and split flow could be manipulated. For example, for applied restrictor temperatures examined up to 600°C, corresponding vent/FID split flow ratios between 2 and 7 were observed depending on the port heated. As well, column pressures around 16–23 MPa were also achievable over the same range. Conversely, isobaric altering of the split flow ratio was possible when opposing positive and negative temperature gradients were applied at the two restrictors. Under these conditions, the system pressure varied less than 1% RSD over a 10 min period. As an application, the method was used to establish stable detector operation in the analysis of n‐alkanes under pSFC‐FID conditions that initiated flame instability. Results indicate that this technique could be a relatively simple and inexpensive means of controlling system pressure and detector split flow ratios in pSFC‐FID.     

Analysis of Polymer Dynamics by NMR Modulated Gradient Spin Echo

NMR modulated gradient spin echo method, which allows the quantification of polymer segmental displacement via the measurement of the velocity autocorrelation, requires the formulation of theoretical predictions in the frequency domain in order to test their validity. We worked out the velocity autocorrelation spectrum of the segmental motion according to the Rouse and the tube/reptation model to compare it to the experimental results obtained by the new NMR technique. The analysis of polybutadiene shows the segmental velocity autocorrelation spectrum typical for the reptation-like motion of polymer in a “tube”. The measurement of bulk water indicates a kind of Rouse motion in a network of hydrogen bonds.     

Headspace sorptive extraction using silicone tubes for the determination of chlorobenzenes in water

A new approach for headspace sorptive extraction is presented and demonstrated for the determination of 12 chlorobenzenes in water samples. It consists of a silicone tube (15-mm length) arranged around a stainless steel rod. This device is fixed on a septum cap and exposed to the headspace of 50 mL of a salt-saturated water sample. After extraction (60-min optimized extraction time), thermodesorption is carried out by direct insertion of the silicone tube into the thermodesorption-gas chromatography-mass spectrometry system. Desorption of the analytes is performed at 250 °C for 5 min with a gas flow of 50 mL/min. Repeatability (relative standard deviation 5–10%), extraction yields (9–46%), enrichment factors (129–657), and detection limits (0.002–0.012 μg/L) were determined and four real water samples were analyzed with the headspace tube extraction. The results were verified by standard addition. A comparison of headspace tube extraction with other headspace enrichment techniques underlined the high extraction capacity of the proposed method. A big advantage of tube extraction is the low cost of the silicone material. The tubes can be discarded after single use, avoiding carryover problems and cross-contamination. Figure Scheme of the HS-tube extraction and thermodesorption system     

Delta shocks and vacuum states in vanishing pressure limits of solutions to the relativistic Euler equations for polytropic gases

The Riemann solutions for the Euler system of conservation laws of energy and momentum in special relativity for polytropic gases are considered. It is rigorously proved that, as pressure vanishes, they tend to the two kinds of Riemann solutions to the corresponding pressureless relativistic Euler equations: the one includes a delta shock, which is formed by a weighted δ-measure, and the other involves vacuum state.     

双屈服面法测量金属材料动高压屈服强度的若干改进

在J.R.Asay等提出的双屈服面法（简称AC方法）测量动态屈服强度的基础上,对实验设计和数据处理做了部分改进。在实验设计方面,在满足实验物理设计的前提下,将 AC方法的卸载实验装置(双层飞片和双台阶样品)简化为单飞片和单台阶样品,以简化波系作用,并减少了声速测量不确定度的引入因素。在数据处理方面,发现由Lagrange声速和工程应变关系曲线外推求预冲击态的体积声速容易引入较大的不确定度,而通过Lagrange声速和粒子速度关系曲线可以更清晰地得到塑性卸载起始点,使图解法和积分法得到的屈服强度值趋于一致。利用改进后的AC方法,得到了低温退火后LY12铝在20.0 GPa预冲击压力下的屈服强度为0.6 GPa。     

Health shock risk,critical illness insurance,and housing services

This paper studies a consumption–investment problem involving health shock risk, perishable consumption, and consumption of housing services. Additionally to a risk-free asset and a stock index, the agent can invest in real estate. I analyze the impact of health shocks on the optimal consumption and investment decisions in model specifications with and without the possibility to buy critical illness insurance. I discuss the influence of critical illness insurance on the optimal strategy and analyze the drivers of the optimal critical illness insurance demand. The results indicate that health shock risk has potentially devastating consequences, especially for young agents. It turns out that critical illness insurance is an excellent instrument for hedging health shock risk and for consumption smoothing across different health states. Optimal critical illness insurance demand is decreasing in financial wealth and increasing in human wealth. Real estate prices have a minor influence on optimal critical illness insurance demand.     

一类奇摄动非线性边值问题激波解的Sinc-Galerkin方法

讨论了一类非线性奇摄动方程的激波问题.利用Sinc-Galerkin方法,构造出边值问题的激波解,并由Newton法得到其近似解.     

强激光诱导冲击波参数的计算研究

首先简要介绍了强激光诱导冲击波研究的重要性,然后讨论了强激光诱导冲击波的形成机理,在此基础上得到了利用材料的特性参数、激光参数和环境参数计算该冲击波参数的数学模型,并实际计算了激光参数为I_0=0～10~9w/cm~2,τ=15ns,λ=1.06μm,材料为铝时的结果,通过实验验证,其计算结果与其它方法所得结果基本吻合.     

绝热流Chaplygin气体的Riemann问题

本文研究了绝热流Chaplygin气体动力学方程组,利用特征分析方法,在得到所有基本波的基础上,构造出Riemann问题的所有解.Riemann解由前向疏散波(激波)、后向疏散波(激波)、接触间断以及δ波构成.     

Silicone rod and silicone tube sorptive extraction

This review focuses on the applications of silicone in the form of tubes or rods for sorptive extraction of organic compounds as sample preparation method in combination with various chromatographic techniques. Silicone rods (SRs) and silicone tubes (STs) have the advantage of being inexpensive, flexible and robust. SRs and STs with different sizes and volumes of silicone (8–635 μL) have so far been applied for the extraction/preconcentration of a large variety of organic micropollutants from different matrices. The theoretical principle of SR and ST extraction in comparison with similar microextraction techniques is presented as well as a summary of the published applications of SR and ST extraction in combination with gas chromatography (GC) or liquid chromatography (LC). Furthermore, the use of SRs and STs for time-integrated (passive) sampling is reported.