Uracil as Nucleating Agent for Bacterial Poly[(3‐Hydroxybutyrate)‐co‐(3‐hydroxyhexanoate)] Copolymers

In this study, uracil has been introduced as the nucleating agent (NA) for bacterially synthesized poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyhexanoate)] (PHBHHx) copolymers with HHx content of 5, 10, 18 mol‐%, and poly(3‐hydroxybutyrate) (PHB) homopolymer for the first time. Its effect was compared with the conventional NA of PHB, that is, boron nitride (BN), and two other naturally occurring pyrimidine derivatives, i.e., thymine and cytosine. The effects of uracil on the crystallization kinetics, melting behavior, spherulite morphology, and crystalline structure of PHBHHx and PHB were investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and wide‐angle X‐ray diffraction (WAXD). Uracil and BN exhibit the comparable nucleation efficiency on the crystallization of PHB, whereas uracil shows much more effective nucleation ability than BN for PHBHHx copolymers. With incorporation of 1 wt.‐% uracil, PHBHHx with 0–10 mol‐% HHx units can finish crystallization upon cooling at 10 °C · min^?1. The crystallization half‐times (t_1/2) of all the PHB and PHBHHx samples decrease significantly with presence of uracil. The crystallization rate of polymers further enhances with increase in uracil concentration. With addition of 1 wt.‐% uracil, the t_1/2 value of PHBHHx with 10 mol‐% HHx units melt‐crystallizing at 80 °C decreases to ≈4.0% of the neat polymer, and the nucleation density increases by 3–4 orders of magnitude. The incorporation of uracil has no discernable effect on the crystalline structure of PHBHHx, as evidenced by WAXD results. It was proposed that the nucleation mechanism of the uracil/PHBHHx (or PHB) system might be the epitaxial nucleation.

     

Preparation of biodiesel with the help of ultrasonic and hydrodynamic cavitation

An alkali-catalyzed biodiesel production method with power ultrasonic (19.7 kHz) has been developed that allows a short reaction time and high yield because of emulsification and cavitation of the liquid-liquid immiscible system. Orthogonality experiments were employed to evaluate the effects of synthesis parameters. Furthermore, hydrodynamic cavitation was used for biodiesel production in comparison to ultrasonic method. Both methods were proved to be efficient, and time and energy saving for the preparation of biodiesel by transesterification of soybean oil.     

Homoclinic Cycle and Homoclinic Bifurcations of a Predator-prey Model with Impulsive State Feedback Control

In this paper, the homoclinic bifurcation of a predator-prey system with impulsive state feedback control is investigated. By using the geometry theory of semi-continuous dynamic systems, the existences of order-1 homoclinic cycle and order-1 periodic solution are obtained. Then the stability of order-1 periodic solution is studied. At last, an example is presented to illustrate the main results.     

Almost sure limit theorems of extremes of complete and incomplete samples of stationary sequences

Let \((X_{n}^{\ast})\) be an independent identically distributed random sequence. Let \(M_{n}^{\ast}\) and \(m_{n}^{\ast}\) denote, respectively, the maximum and minimum of \(\{X_{1}^{\ast},\cdots,X_{n}^{\ast}\}\). Suppose that some of the random variables \(X_1^{\ast},X_2^{\ast},\cdots\) can be observed and let \(\widetilde{M}_n^{\ast}\) and \(\widetilde{m}_n^{\ast}\) denote, respectively, the maximum and minimum of the observed random variables from the set \(\{X_1^{\ast},\cdots,X_n^{\ast}\}\). In this paper, we consider the asymptotic joint limiting distribution and the almost sure limit theorems related to the random vector \((\widetilde{M}_n^{\ast}, \widetilde{m}_n^{\ast}, M_n^{\ast}, m_n^{\ast})\). The results are extended to weakly dependent stationary Gaussian sequences.     

Separation of peptides by pressurized capillary electrochromatography

A pressurized electrochromatography (pCEC) instrument with gradient capability was used in this work for separation of peptides. Three separation modes, namely, pCEC, high-performance liquid chromatography and capillary electrophoresiscan be carried out with the instrument. In pCEC mode, the mobile phase is driven by both electroosmotic flow and pressurized flow, facilitating fine-tuning in selectivity of neutral and charged species. A continuous gradient elution can be carried out conveniently on this instrument, which demonstrates that it is more powerful than isocratic pCEC for separation of complicated samples. The effects of applied voltage, supplementary pressure and ion-pairing agents on separation of peptides in gradient pCEC were investigated. The effects of flow-rate of the pump and the volume of the mixer on resolution were also evaluated.     

Ge掺杂β-Ga2O3晶体的发光性能研究

采用浮区法(FZ)生长Ge掺杂β-Ga2O3晶体,利用XRD和Raman光谱研究了掺杂对晶体结构的影响.透射光谱测试表明,随着Ge离子掺杂浓度增加,Ge∶ β-Ga2O3晶体光学带隙增大.在4.67 eV紫外光激发下,Ge∶ β-Ga2O3晶体的发光强度与β-Ga2O3晶体相当,发光衰减时间比β-Ga2O3晶体更快.     

Multi-Hop Question Generation Using Hierarchical Encoding-Decoding and Context Switch Mechanism

Neural auto-regressive sequence-to-sequence models have been dominant in text generation tasks, especially the question generation task. However, neural generation models suffer from the global and local semantic semantic drift problems. Hence, we propose the hierarchical encoding–decoding mechanism that aims at encoding rich structure information of the input passages and reducing the variance in the decoding phase. In the encoder, we hierarchically encode the input passages according to its structure at four granularity-levels: [word, chunk, sentence, document]-level. Second, we progressively select the context vector from the document-level representations to the word-level representations at each decoding time step. At each time-step in the decoding phase, we progressively select the context vector from the document-level representations to word-level. We also propose the context switch mechanism that enables the decoder to use the context vector from the last step when generating the current word at each time-step.It provides a means of improving the stability of the text generation process during the decoding phase when generating a set of consecutive words. Additionally, we inject syntactic parsing knowledge to enrich the word representations. Experimental results show that our proposed model substantially improves the performance and outperforms previous baselines according to both automatic and human evaluation. Besides, we implement a deep and comprehensive analysis of generated questions based on their types.     

对羟基二联苯诱导的表面金属-有机键断裂

金属-有机杂化结构是表面在位反应过程中常见的中间体. 金属-有机杂化结构中金属-有机键的断裂需要克服较高的活化能垒, 往往会引起一系列竞争副反应以及分子的脱附. 本文利用扫描隧道显微镜研究了 4,4′-二羟基联苯分子在金属表面与预先制备的金属-有机链的作用, 发现其氧端能有效地降低金属有机杂化体系断键的能垒, 使得金属-有机键的断键反应能在较低的温度下进行. 该结果提供了一种调控表面反应中间物的新手段.     

A two-photon ratiometric fluorescent probe for real-time imaging and quantification of NO in neural stem cells during activation regulation

Developing a novel tool capable of real-time monitoring and accurate quantification of NO is critical to understanding its role in physiological and pathological processes. Herein, a two-photon ratiometric fluorescent probe (NOP) was developed for real-time imaging and quantification of NO based on fluorescence resonance energy transfer-photoinduced electron transfer (FRET-PET). In this developed probe, coumarin (CM) and naphthalimide with o-phenylenediamine (NPM) were rationally designed as a fluorescent donor and acceptor, respectively, to enable a ratiometric fluorescence response to NO. The developed NO probe demonstrated good detection linearity with the concentration of NO in the range of 0.100–200 μM, with a detection limit of 19.5 ± 1.00 nM. Considering the advantages of high selectivity, good accuracy and rapid dynamic response (<15 s), the developed NO probe was successfully applied for real-time imaging and accurate quantification of NO in neural stem cells (NSCs) and different regions of mouse brain tissue with a penetration depth of 350 μm. Using this powerful tool, it was found that NO regulated the activation and differentiation of quiescent NSCs (qNSCs). In addition, NO-induced differentiation of qNSCs into neurons was found to be dose-dependent: 50.0 μM NO caused about 50.0% of qNSCs to differentiate into neurons. Moreover, different regions of the mouse brain were observed to be closely related to the concentration of NO, and the concentration of NO in the DG region was found to be lower than that in the S1BF, CA1, LD and CPu of the Alzheimer''s disease (AD) mouse brain. The symptoms of AD mice were significantly improved through the treatment with NO-activated NSCs in the DG region.

Developing a novel tool capable of real-time monitoring and accurate quantification of NO is critical to understanding its role in physiological and pathological processes.