Blumlein传输线的解析分析

 在传输线应用中,负载终端匹配设计是一个重要问题。用拉普拉斯变换方法严格求解Blumlein传输线的电报方程,研究在纯电阻负载和带分布参数负载情况下,波在传输线中的瞬态传输过程,得到了清晰的物理图像,结果与通常的行波传播分析法完全一致。     

Kinetic and ESR studies on radical polymerization behavior of N‐(2‐phenylethoxycarbonyl)methacrylamide

Polymerization of N‐(2‐phenylethoxycarbonyl)methacrylamide (PECMA) with dimethyl 2,2′‐azobisisobutyrate (MAIB) was investigated in tetrahydrofuran (THF) kinetically and by means of electron spin resonance (ESR). The overall activation energy of the polymerization was calculated to be 58 kJ/mol. The initial polymerization rate (R_p) is expressed by R_p = k[MAIB]^0.3[PECMA]^2.3 at 60 °C. Such unusual kinetics may be ascribable to primary radical termination and to acceleration of propagation due to monomer association. Propagating poly(PECMA) radical was observed as a 13‐line spectrum by ESR under practical polymerization conditions. ESR‐determined rate constants of propagation (k_p, 4.7–10.5 L/mol s) and termination (k_t, 4.6 × 10⁴ L/ml s) at 60 °C are much lower than those of methacrylamide and methacrylate esters. The Arrhenius plots of k_p and k_t gave activation energies of propagation (24 kJ/mol) and termination (25 kJ/mol). The copolymerizations of PECMA with styrene (St) and acrylonitrile were examined at 60 °C in THF. Copolymerization parameters obtained for the PECMA (M₁) − St(M₂) system are as follows: r₁ = 0.58, r₂ = 0.60, Q₁ = 0.73, and e₁ = +0.22. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4264–4271, 2000     

四甲基对联苯二胺光敏化聚苯乙烯砜及其模型化合物二苄基砜分解机理的研究

N、N、 N’、N’-四平基对联苯二胺(NTMB)和 3、3’、5、5’-四甲基对联苯二胺(TMB)可以有效地光敏化二苄基砜(DBS)分解和聚苯乙烯砜(PSS)降解。敏化作用是按电子转移机理进行的,电子转移过程可以由NTMB的单重激发态,也可以由三重激发态发生。由三重态电子转移产生的三重态离子自由基对进一步反应生成产物的效率比单重态离子自由基对的效率高10倍。     

Study of a dynamical system with a strange attractor and invariant tori

A simple three-dimensional time-reversible system of ODEs with quadratic nonlinearities is considered in a recent paper by Sprott (2014). The author finds in this system, that has no equilibria, the coexistence of a strange attractor and invariant tori. The goal of this letter is to justify theoretically the existence of infinite invariant tori and chaotic attractors. For this purpose we embed the original system in a one-parameter family of reversible systems. This allows to demonstrate the presence of a Hopf-zero bifurcation that implies the birth of an elliptic periodic orbit. Thus, the application of the KAM theory guarantees the existence of an extremely complex dynamics with periodic, quasiperiodic and chaotic motions. Our theoretical study is complemented with some numerical results. Several bifurcation diagrams make clear the rich dynamics organized around a so-called noose bifurcation where, among other scenarios, cascades of period-doubling bifurcations also originate chaotic attractors. Moreover, a cross section and other numerical simulations are also presented to illustrate the KAM dynamics exhibited by this system.     

Termination of algorithm for computing relative Gr?bner bases and difference differential dimension polynomials

We introduce the concept of difference-differential degree compatibility on generalized term orders. Then we prove that in the process of the algorithm the polynomials with higher and higher degree would not be produced, if the term orders ‘?’ and ‘?′’ are difference-differential degree compatibility. So we present a condition on the generalized orders and prove that under the condition the algorithm for computing relative Gr?bner bases will terminate. Also the relative Gr?bner bases exist under the condition. Finally, we prove the algorithm for computation of the bivariate dimension polynomials in difference-differential modules terminates.     

First-principles Study on the Electronic and Bonding Properties of PbTiO3 (110) Polar Terminations

The electronic structures and bonding properties of the (110) polar terminations of cubic PbTiO₃ were examined by the first-principles calculations at the generalized gradient approximation level. Two stoichiometric (PbTiO and O₂) and three nonstoichiometric(TiO, Pb, and O) terminations were considered in this study. With the aid of the calculated electron density differences, atomic charges, band structures, and densities of states, the charge redistributions and electronic properties were evaluated in detail. Furthermore, based on the calculated results of the cleavage energies, relaxation energies, and surface energies of the investigated terminations, the charge compensation by the modification of the surface stoichiometry and the fillings of surface states were thermodynamically evaluated.     

Controlled radical polymerization of cholesteryl acrylate and its block copolymer with styrene via the RAFT process

Reversible addition fragmentation chain transfer (RAFT) polymerization of cholesteryl acrylate (ChA) was conducted using S-1-dodecyl-S′-(α,α′-dimethyl-α′′-acetic acid)trithiocarbonate as CTA and AIBN as initiator in toluene at 80 °C. The polymerization was investigated at two different CTA concentrations (0.025 and 0.040 M). Polymerization of ChA with CTA concentration of 0.040 M proceeds in a controlled/living manner as evidenced by linear increase of the molecular weight with conversion and narrow polymer polydispersity (PDI < 1.2). With lower initial CTA concentration, namely 0.025 M, although poly(cholesteryl acrylate) (PChA) exhibiting narrow molecular weight distributions could be synthesized, the polymerization showed relatively low control with many termination products. Chain extension polymerizations were performed starting from either the PChA or the polystyrene (PS) block, and well-defined copolymers based on ChA and styrene were prepared. Thermal properties of PChA and PS-b-PChA copolymer were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), and the results showed that both PChA and PS-b-PChA are amorphous polymers. PChA begins to decompose at ca. 218 °C with maximum weight loss rate at 351 °C, while PS-b-PChA shows double weight loss rate peaks located at 345 and 415 °C, respectively.     

A Road Less Traveled to Functional Polymers: Epoxide Termination in Living Carbanionic Polymer Synthesis

Functional polymers possess tremendous potential both in academia and in industry. In particular, oxiranes offer manifold possibilities for the introduction of single hydroxyl or multiple orthogonal functionalities in carbanionic polymerization. Here, we present a brief overview of the fascinating possibilities arising from the employment of common as well as individually designed epoxide derivatives for the synthesis of end‐functional polymers. Continuous flow techniques can be utilized for the rapid generation and screening of precisely defined hydroxyl‐modified polymers. The utilization of functionalized polymers as precursors for the formation of complex macromolecular architectures (e.g., miktoarm star polymers) is summarized and potential applications as well as future perspectives are discussed.

     

Efficient Purification of Camptothecin via Aqueous Two-phase System Composed of 1,1,3,3-Tetramethylguanidinium Benzoate Ionic Liquid and K2CO3

After being hydrolyzed into corresponding hydrosoluble carboxylate by 1,1,3,3,-tetramethylguanidine (TMG), camptothecin was extracted via the aqueous two-phase systems composed of ionic liquid 1,1,3,3- tetramethylguanidinium(TMGM) carboxylate and K₂CO₃, and was regenerated at the final by dilute aqueous hydrochloric acid. Among the ionic liquids, TMGM benzoate showed the best effect, TMGM formate the worst, this results were consistent with the liposolubilities of different carboxylic acid components in the ionic liquids. Through two-step extraction of TMGM benzoate ionic liquid/K₂CO₃ aqueous two-phase under a favorable condition, camptothecin was obtained in a purity of 98.3% and a total yield of 85.1%, from the crude camptothecin extract with a purity of 14.2%.     

氧化还原可逆荧光探针的研究及其在细胞成像中的应用进展

细胞氧化还原可逆状态的动态变化可以提供丰富的生理、病理信息,因此可以瞬时、动态检测细胞氧化还原状态变化的分析方法越来越受到人们的关注.基于荧光探针的荧光分析法因其直观、简便、可原位操作、信息丰富等特点,近年来在氧化还原分析等研究方面得到了较为广泛的应用.本文对近年来氧化还原可逆荧光探针研究及其在细胞成像中的应用进展进行了评述,并对其发展前景进行了展望.引用文献54篇.