A generalized quasi-boundary value method for the backward semi-linear time-fractional heat problem in a cylinder

We are concerned with a backward problem associated with a semi-linear time-fractional heat equation in an axis-symmetric cylinder, which arises from the modeling of the blast furnace steelmaking in metallurgy. Under some assumptions, the existence and uniqueness of the solution to the semi-linear problem is first established. The ill-posedness of the backward problem is then established, and we obtain the error estimates by a generalized quasi-boundary value regularization method. Finally, the numerical experiment is presented to demonstrate the effectiveness of the proposed method.     

一种基于级联半导体光放大器环镜的光串并转换器

为了实现高速光信号的降速处理,提出了一种基于级联半导体光放大器环镜(SLALOM)的光串并转换器,用于实现将高速串行光脉冲信号转换成低速并行光脉冲信号.该光串并转换器采用串联SLALOM组成,将前一级SLALOM的输出作为后一级SLALOM的输入;SLALOM之间的光传播时延为输入光信号比特周期;设置控制光与信号光脉冲时序,实现各级SLALOM光脉冲并行输出.通过采用1×10光串并转换器实现将80 Gb/s串行信号转换为10路8 Gb/s并行信号,并对控制、信号脉冲光功率和时间偏移量器件参量进行了优化.对于1×10光串并转换器,端口接收灵敏度差异小于10 dB.该光串并转换器光功率损耗小、易于扩展并行端口数目,可用于光通信领域中的高速解复用、光信号处理和光交换系统中.     

Copper(I) halides: A versatile family in coordination chemistry and crystal engineering

The copper(I) halide aggregates represent a versatile family in coordination chemistry and crystal engineering. First discovered a century ago these species have been intensively investigated in the last three decades because of their structural and luminescent uniqueness. This account reviews their research history and frontier (Section 1), synthetic routes (Section 2) and structural diversity (Section 3), and also offers personal perspectives (Section 4) on the growth, property and application of the copper(I) halide aggregates in coordination polymers.     

Aliphatic peptidyl hydroperoxides as a source of secondary oxidation in hydroxyl radical protein footprinting

Hydroxyl radical footprinting is a technique for studying protein structure and binding that entails oxidizing a protein system of interest with diffusing hydroxyl radicals, and then measuring the amount of oxidation of each amino acid. One important issue in hydroxyl radical footprinting is limiting amino acid oxidation by secondary oxidants to prevent uncontrolled oxidation, which can cause amino acids to appear more solvent accessible than they really are. Previous work suggested that hydrogen peroxide was the major secondary oxidant of concern in hydroxyl radical footprinting experiments; however, even after elimination of all hydrogen peroxide, some secondary oxidation was still detected. Evidence is presented for the formation of peptidyl hydroperoxides as the most abundant product upon oxidation of aliphatic amino acids. Both reverse phase liquid chromatography and catalase treatment were shown to be ineffective at eliminating peptidyl hydroperoxides. The ability of these peptidyl hydroperoxides to directly oxidize methionine is demonstrated, suggesting the value of methionine amide as an in situ protectant. Hydroxyl radical footprinting protocols require the use of an organic sulfide or similar peroxide scavenger in addition to removal of hydrogen peroxide to successfully eradicate all secondary oxidizing species and prevent uncontrolled oxidation of sulfur-containing residues.     

Empirical Gramian-based spatial basis functions for model reduction of nonlinear distributed parameter systems

Correct selection of spatial basis functions is crucial for model reduction for nonlinear distributed parameter systems in engineering applications. To construct appropriate reduced models, modelling accuracy and computational costs must be balanced. In this paper, empirical Gramian-based spatial basis functions were proposed for model reduction of nonlinear distributed parameter systems. Empirical Gramians can be computed by generalizing linear Gramians onto nonlinear systems, which results in calculations that only require standard matrix operations. Associated model reduction is described under the framework of Galerkin projection. In this study, two numerical examples were used to evaluate the efficacy of the proposed approach. Lower-order reduced models were achieved with the required modelling accuracy compared to linear Gramian-based combined spatial basis function- and spectral eigenfunction-based methods.     

The rôle of countercurrent chromatography in the fractionation of complex mixtures

The biologically active pricipals in nature are frequently present as only a few parts per million of complex mixtures of non-volatile components and often have limited stability. Their isolation often requires the application of all available techniques, such as adsorption chromatography, ion exchange procedures, size exclusion techniques, and solvent partition methods consistent with their physical properties and stability. The process of countercurret chromatography is essentially liquid-liquid chromatography in which the stationary liquid bed is retained in the column by a force field rather than by a solid supporting matrix. Adsorption effects are thereby eliminated. The technique is particularly advantageous in the preparative separation of milligram to gram quantities of polar and labile organic compounds and bio-particulate materials such as cells and cell fragments. Virtually any twophase solvent system, either aqueous or non-aqueous may be employed. Countercurrent chromatography (CCC) provides a convenlent alternative to adsorption chromatography for fractionation of natural products or other complex mixtures. In some cases, this high resolution method offers advantages with regard to the avoidance of contamination from solid adsorbents, versatility, and relatively inexpensive operation. The article covers some of the applications, selection of solvents, and advantages of CCC.     

对苯二甲酸二甲酯(DMT)与乙二醇(EG)的酯交换反应模拟动力学

本文在ε-NTU法的基础上,用模拟函数理论方法,拟合DMT与EG在醋酸盐催化下的酯交换反应的动力学模型,得出了相应的反应速度表达式。结果表明:在实验条件下的酯交换反应既不是一级或二级反应,也不是三级反应,是一个二次线型反应,这也恰好证明了Yamanis对以往动力学处理怀疑的正确性。此外对模型中引入参数的物理意义进行了探讨。     

Graft copolymerization onto jute fiber: Ceric ion-initiated graft copolymerization of methyl methacrylate

Graft copolymerization of methyl methacrylate (MMA) was carried out on both defatted and bleached jute fibers using ceric ammonium sulfate (CAS) as the initiator. In order to obtain the optimum condition for grafting, the effects of initiator concentrations, temperature, time of reaction, lignin content of jute, and the monomer concentration were studied. The maximum percent grafting and grafting efficiency were found to be 132% and 0.71, respectively. Kinetic studies showed that at 0.03M CAS, the reaction appeared to obey the second-order process. The activation energies were found to be 7.74 and 5.12 kcal/mole for defatted (lignin content, 15.7%) and chlorite-bleached jute (lignin content 10%), respectively. The activation energies of graft copolymerization of MMA onto jute fiber are compared with the energies of activation of graft copolymerization of acrylonitrile (AN).     

Vinyl monomers bearing chromophore moieties and their polymers. VIII. synthesis and fluorescence behavior of a vinyloxy monomer having an electron‐accepting chromophore moiety,p‐((vinyloxy)methyl)benzonitrile,and its polymers

A vinyloxy monomer having an electron‐accepting chromophore moiety, p‐((vinyloxy)methyl)benzonitrile (VOMBN), was synthesized by reaction of p‐(hydroxymethyl)benzonitrile with ethyl vinyl ether (EVE) in the presence of mercuric acetate. VOMBN can easily be cationically homopolymerized and copolymerized with EVE by using Lewis acids such as boron trifluoride etherate (BF₃ · OEt₂) as a catalyst and radically copolymerized with maleic anhydride (MAn) using AIBN as an initiator. The fluorescence behaviors of VOMBN, its copolymer P(VOMBN‐co‐MAn), and its saturated model compound p‐(ethoxymethyl)benzonitrile (EOMBN) were investigated in acetonitrile. It has been found that the fluorescence intensity of VOMBN is much lower than its copolymer and EOMBN at the same chromophore concentration. A fluorescence “structural self‐quenching effect” (SSQE) is also observed for VOMBN as we have reported previously [Li, F. M.; Chen, S. J.; Li, Z. C.; Qiu, J. J Polym Sci Polym Chem 1996, 34, 1881]. This phenomenon has been attributed to the inter‐ and intramolecular charge transfer interaction between the electron‐accepting cyanophenyl chromophore and the electron‐donating vinyloxy group in the same molecule. The dependence of the fluorescence intensity of VOMBN on solvents of different viscosities is evidence that the SSQE of VOMBN mainly occurs intramolecularly. The fluorescence of EOMBN and P(VOMBN‐co‐MAn) was quenched by a series of electron‐rich vinyloxy compounds which do not have chromophore moieties, such as dihydrofuran (2H‐furan), dihydropyran (2H‐pyran), furan, and EVE. It is observed that the higher the electron‐donating ability of the quenchers, the greater the quenching efficiency. P(VOMBN) and the random copolymers of VOMBN with EVE show broader fluorescence spectra as compared to the alternating copolymer P(VOMBN‐co‐MAn). This indicates that there is a mutual interaction between the adjacent cyanophenyl groups in P(VOMBN) and P(VOMBN‐co‐EVE), whereas such an interaction does not exist for P(VOMBN‐co‐MAn) in which the cyanophenyl groups are isolated by the rigid succinic anhydride rings. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 179–187, 1999     

Second-order effect of an elastic circular shaft during torsion

In this paper we deal with the second-order effect of an elastic circular shaft duringtorsion.The analysis is based on the method of co-moving coordinates and the strain-rotation decomposition theorem in continuum mechanics.By using asymptotic expansionmethods,we comfirm that the effect of axial elongation and distortion of plane cross-section exists in an elastic circular shaft during large torsion and give the expressions ofthe axial force and the torque.