Comparison Theorems for Eigenvalues of Elliptic Operators and the Generalized Pólya Conjecture

We establish comparison theorems for eigenvalues between higher order elliptic equations on compact manifolds with boundary. As an application, it follows that if the Pólya conjecture is true then so is the generalized Pólya conjecture proposed by Ku et al. (J Differ Equ 97:127–139, 1992). We also obtain new lower bound for the eigenvalues of higher order elliptic equations on bounded domains in a Euclidean space.     

Synthesis of stable luminescent microspheres by a simple method

An easy procedure for preparing microspheres containing CdSe/CdS core-shell quantum dots (QDs) was demonstrated. The luminescent properties of this microsphere were characterized by fluorescence microscopy and fluorescence spectrophotometry. Scanning electron microscopy was also used in this study. Laser confocal microscopy was carried out to describe the distribution of QDs in the microsphere. Especially, the stability of microspheres was investigated. It was found that the getting microsphere was very stable in water and showed values for physiological conditions. The inherent stability of the spheres, as well as their photostability, allows them to be used in biological applications.     

TG-FTIR, Py-two-dimensional GC–MS with heart-cutting and LC–MS/MS to reveal hydrocyanic acid formation mechanisms during glycine pyrolysis

To elucidate the formation process of HCN from the pyrolysis of glycine, the small molecule gaseous pyrolysates, H₂O, NH₃, CO₂, CO, HNCO, and HCN, were analyzed in real-time by TG-FTIR. The appearance of the volatile pyrolysis products and the solid residue was determined in real-time at their corresponding formation temperatures by online Py-two-dimensional GC–MS with heart-cutting and LC–MS/MS. The pyrolysis of 2,5-diketopiperazine, a thermolytic by-product of glycine pyrolysis, was also studied. The results showed that: (1) the pyrolysis of glycine can be divided into three temperature ranges 200–300, 300–440, and 440–900 °C; HCN forms in each range with three peaks appearing at 273, 422, and 763 °C, respectively. (2) The mechanistic pathways of HCN formation from glycine in the low- and high-temperature heating stages are different. Below 273 °C, glycine undergoes a decarboxylation reaction to produce methylamine, which subsequently forms HCN by means of dehydrogenation. Above 300 °C, glycine gives relatively large amounts of HCN via 2,5-diketopiperazine and subsequent HNCO or methylenimine formation.     

Synthesis of size-controlled acid-resistant hybrid calcium carbonate microparticles as templates for fabricating "micelles-enhanced" polyelectrolyte capsules by the LBL technique

Size-controlled, low-dispersed calcium carbonate microparticles were synthesized in the presence of the amphiphilic block copolymer polystyrene-b-poly(acrylic acid) (PS-b-PAA) by modulating the concentration of block copolymer in the reactive system. This type of hybrid microparticles have acid-resistant properties. By investigating the aggregation behaviors of PS-b-PAA micelles by transmission electron microscopy (TEM), the mechanism of hybrid calcium carbonate formation illustrated that the block copolymer served not only as "pseudonuclei" for the growth of calcium carbonate nanocrystals, but also forms the supramicelle congeries, a spherical framework, as templates for calcium carbonate nanocrystal growth into hybrid CaCO(3) particles. Moreover, this pilot study shows that the hybrid microparticle is a novel candidate as a template for fabricating multilayer polyelectrolyte capsules, in which the block copolymer is retained within the capsule interior after core removal under soft conditions. This not only facilitates the encapsulation of special materials, but also provides "micelles-enhanced" polyelectrolyte capsules.     

以L-酒石酸正己酯-硼酸配合物作为反相液相色谱手性流动相添加剂拆分5种β-受体阻滞剂

本文以L-酒石酸正己酯-硼酸配合物为手性流动相添加剂,建立了普萘洛尔、艾司洛尔、美托洛尔、比索洛尔、索他洛尔和阿替洛尔六种β-受体阻滞剂的反相高效液相色谱手性分离方法。对影响对映体分离的主要因素：L-酒石酸正己酯、硼酸浓度,缓冲溶液种类、浓度、pH值和有机改性剂-甲醇含量等进行了详细考察。最佳色谱条件为：Venusil MP-C18色谱柱（4.6 mm × 250 mm,5 μm）,流动相为15 mmol/L乙酸铵-甲醇（体积比为20: 80或30: 70,含60 mmol/L硼酸,70 mmol/L L-酒石酸正己酯,醋酸调节pH值6.00）,检测波长214 nm。在最佳分离条件下,五对对映体（普萘洛尔、艾司洛尔、美托洛尔、比索洛尔、索他洛尔）可以分别获得基线分离。     

以两亲性共聚物为模板溶胶-凝胶法制备WO3多孔薄膜及其 氢致变色特性的研究

报道了以六氯化钨为原料, 以两亲性的无规共聚物聚苯乙烯-co-聚烯丙醇(PS-co-PAAL)和三嵌段共聚物聚氧乙烯-b-聚氧丙烯-b-聚氧乙烯(PEO-b-PPO-b-PEO)为模板, 采用溶胶-凝胶法制备了WO3多孔薄膜. 利用热重分析仪(TGA)、粉末X射线衍射仪(XRD)、扫描电子显微镜(SEM)、原子力显微镜(AFM)等表征手段, 研究了模板和热处理温度对薄膜孔结构的影响; 并通过H2敏测试以及利用紫外可见分光光度计(UV), 研究了薄膜的氢敏性能和着色前后的透射光谱. 结果表明, 以无规共聚物PS-co-PAAL为模板制得的WO3薄膜, 经400 ℃热处理后, 可得到呈交联网状的多孔结构, 并表现出最佳的氢致变色性能.     

核磁共振中多量子相干扩散行为的理论表述和计算机模拟

Self-diffusion is one of the most fundamental motions of particles in liquid. Nuclear magnetic resonance （NMR）provides a convenient and noninvasive means for accurately measuring the self-diffusion coefficient of molecules in solution. The theoretical expressions of apparent diffusion rates of MQCs are given and computer simulation based on the method to measure the self-diffusion coefficient by NMR was discussed and the random walk model of particles is used to simulate the apparent diffusion behaviors of intra-molecular and inter-molecular multiple-quantum coherences（MQCs）. The results of computer simulation agree well with theoretical predictions.     

In-site observation of the crystallization of nylon-6 mediated by the interfacial hydrogen bonds

Hydrogen bonds exist in many polymer systems and play a large role in the physical and chemical properties. In this study, nylon-6, which consists of repeated amide groups and contains large number of hydrogen bonds, is chosen as an example. Meanwhile, the oxidized unzipped MWCNTs (μCNTs) with oxygenated species such as carboxyl and hydroxyl groups are used as mediator to regulate the crystallization process of nylon-6 thin films. In-site experimental techniques, including Fourier transform infrared spectroscopy, X-ray diffraction spectroscopy, and polarized optical microscopy were utilized to get more direct insights on the crystallization mechanism of nylon-6 and μCNTs systems.