A note on the second problem of Stokes for Maxwell fluids

New exact solutions corresponding to the second problem of Stokes for Maxwell fluids have been established by means of Laplace transforms. For large times, these solutions reduce to the well-known steady-state solutions which are periodic in time and independent of the initial conditions. Furthermore, the transient solutions are in accordance with the previous solutions obtained using the Fourier sine transform. The required time to get the steady-state is determined by graphical illustrations. This time decreases if the frequency of the velocity increases. The effects of the material parameters on the decay of the transients in time are also investigated by graphs.     

新型氧化锌纳米材料在电化学检测对硝基苯酚中的应用

通过溶剂热法控制合成了花生形氧化锌纳米材料,并利用扫描电子显微镜(SEM)、X射线粉末衍射仪(XRD)和傅里叶变换红外光谱(FTIR)对材料进行了表征和分析.循环伏安和Nyquist测试结果表明,该材料具有良好的电化学导电性,且对对硝基苯酚(p-NP)具有良好的选择性.侧分脉冲伏安法(DPV)测试结果表明,在p-NP浓度为0.8~24μmol/L和32~80μmol/L这2个浓度范围内,电流强度与浓度呈线性关系,通过3倍信噪比计算得出检测限分别为0.25和0.61μmol/L.该材料修饰的电极具有良好的稳定性和重现性,用于实际样品中p-NP含量的测定显示出优良的效果.     

A new method for the synthesis of organic–polyoxometallate hybrid compounds

The reaction of the Na₂MoO₄ or Na₂WO₄ salt with organic amine and PCl₅, SiCl₄ or TiCl₄ in hydrochloric acid medium under hydrothermal conditions yields organic–polyoxometallate hybrid compounds, with the following reaction formula: Na₂MO₄ + Lewis-base + XCl_n + HCl → (Lewis-baseH)_m(XM₁₂O₄₀) + NaCl + H₂O (M = Mo or W; X = P, Si, Ti,; n = 3–5). By using this method, four new complexes, [(CH₃)₂NH]₃[H₃PW₁₂O₄₀] (1), (C₂H₅OH)₃(H₃PMo₁₂O₄₀) (2), [DMDA]₂[H₄SiW₁₂O₄₀]·H₂O (3) (DMDA = 1 N,3 N-dimethyl-1,3-diazolidine) and [(DAN)₆][H₄TiW₁₂O₄₀]·4H₂O (DAN = 4,4′-dianiline) (4), were obtained, and their crystal structures are reported. Thermal analysis of 1, 2 and 4 has been carried out. The thermal analysis indicates that the Keggin anion skeleton begins to decompose at about 300 °C. The possibility of constructing hydrogen-bond interactions by association between the polyoxometallate and the organic compound is explored. The roles of solvents and organic groups in the formation of specific crystalline architectures are discussed. The crystal structure of [H₄TiW₁₂O₄₀], a hetero-transition-metal Keggin polyoxometallate with a square-plane TiO₄, has been reported. Four architectures developed by hydrogen-bond associations of different Keggin polyoxometallates and organic bearing N–H or O–H donor functions are described. The selected organic modules (4,4′-dianiline, 1,3-dimethylimidazolidine, dimethylamine and ethanol) possess hydrogen-donor functions to allow them to act as bridges between polyoxometallate groups. Depending on the nature of the donor group, the number of hydrogens available for bonding, the geometric features and the sizes of the organic modules, diverse assembling patterns have been observed ranging from one-dimensional to three-dimensional networks. For all the networks, H₃O⁺ and H⁺ act as actual linkers between the molecular units.     

Density functional theory for reactions of astrophysical interest

For astrophysical processes nuclear reactions close to the particle emission threshold are of particular importance. As representative examples we investigate pairing resonances and new low-energy multipole modes in light and heavy exotic nuclei with a large charge asymmetry. As a common theoretical background, density functional theory and Fermi Liquid Theory are used. In particular, we consider the spectroscopy particle unstable systems, carrying the properties of open quantum systems. Results for the continuum spectroscopy of ¹⁰Li, the neutron-rich carbon isotopes, and the electromagnetic response of Sn-isotopes ¹³⁸Ba are presented.     

A sensitive, rapid ferricyanide-mediated toxicity bioassay developed using Escherichia coli

A need for rapid toxicity techniques has seen recent research into developing new microbiological assays and characterising their toxicity responses using a range of substances. A microbiological bioassay that determines changes in ferricyanide-mediated respiration for toxicity measurement (FM-TOX) shows particular promise. The development and optimisation of an improved FM-TOX method, incorporating novel features, is described using Escherichia coli as the biocatalyst. Omission of an exogenous carbon source, used in previously described FM-TOX assays, substantially improves the assay sensitivity. In addition, the development of a two-step procedure (toxicant exposure followed by determination of microbial respiratory activity) was found to enhance the inhibition of E. coli by 3,5-dichlorophenol and four other toxicants, compared to single-step procedures. Other assay parameters, such as the ferricyanide concentration, exposure times and optical density of the biocatalyst were also optimised, sometimes based on practical aspects. Toxicity tests were carried out using the adopted technique on both organic and inorganic toxicants, with classic sigmoid-shaped dose-response curves observed, as well as some non-standard responses. IC₅₀ data is presented for a number of common toxicants. The optimised assay provides a good foundation for further toxicity testing using E. coli, as well as the potential for expanding the technique to utilise other bacteria with complementary toxicity responses, thereby allowing use of the assay in a range of applications.     

共轭二烯烃定向加成研究进展

以1,3-丁二烯为代表的共轭二烯烃是重要的有机合成原料,在有机合成领域有重要的应用价值.综述了以1,3-丁二烯等为代表的共轭二烯烃定向加成的研究进展,并展望了其发展和应用前景.     

Simultaneous determination of methylene blue and new methylene blue by slab optical waveguide spectroscopy and artificial neural networks

A slab optical waveguide (SOWG) has been used for study of adsorption of both methylene blue (MB) and new methylene blue (NMB) in liquid-solid interface. Adsorption characteristics of MB and NMB on both bare SOWG and silanized SOWG by octadecyltrichlorosilane (ODS) were compared. The simultaneous determinations of both MB and NMB were explored by flow injection SOWG spectrophotometric analysis and artificial neural networks (ANNs) for the first time. Concentrations of MB and NMB were estimated simultaneously with the ANNs. Results obtained with SOWG were compared with those got by conventional UV-visible spectrophotometry.     

ON NUMEROV SCHEME FOR NONLINEAR TWO-POINTS BOUNDARY VALUE PROBLEM

1.IntroductionInstudyingsomeproblemsarisinginelectromagnetism,biology)astronomy,bound-arylayerandothertopics,weoftenmeetnonlineartwo--pointsboundaryproblem,i.e.,findingyECo[0,11nC2(0,1)suchthatwhereor,garecertainconstants,andf(x,z)EC'(0,1)xC'(--co,co).Undersomeconditionsonf(x,z),wecanusetheframeworkof[1]toinvestigatetheexistenceanduniquenessofitssolutions.Alsotherearealotofliteratureconcerningitsnumericalsolutio.s[2--'].Inparticular,N..ero.15]proposedafamousfinitedifferenceschemewiththeaccu…     

Optimal Distributed Dynamic Advertising

We propose a novel approach to modeling advertising dynamics for a firm operating over a distributed market domain based on controlled partial differential equations of the diffusion type. Using our model, we consider a general type of finite-horizon profit maximization problem in a monopoly setting. By reformulating this profit maximization problem as an optimal control problem in infinite dimensions, we derive sufficient conditions for the existence of its optimal solutions under general profit functions, as well as state and control constraints, and provide a general characterization of the optimal solutions. Sharper, feedback-form characterizations of the optimal solutions are obtained for two variants of the general problem. The first author gratefully acknowledges financial support by the NSF, the DAAD, the SFB 611 (Bonn), and the Max-Planck-Institut für Mathematik (Leipzig) through an IPDE fellowship.     

Fritz Reiche and the Emergency Committee in Aid of Displaced Foreign Scholars

I discuss the family background and early life of the German theoretical physicist Fritz Reiche (1883–1969) in Berlin; his higher education at the University of Berlin under Max Planck (1858–1947); his subsequent work at the University of Breslau with Otto Lummer (1860–1925); his return to Berlin in 1911, where he completed his Habilitation thesis in 1913, married Bertha Ochs the following year, became a friend of Albert Einstein (1879–1955), and worked during and immediately after the Great War. In 1921 he was appointed as ordentlicher Professor of Theoretical Physics at the University of Breslau and worked there until he was dismissed in 1933. He spent the academic year 1934–1935 as a visiting professor at the German University in Prague and then returned to Berlin, where he remained until, with the crucial help of his friend Rudolf Ladenburg (1882–1952) and vital assistance of the Emergency Committee in Aid of Displaced Foreign Scholars, he, his wife Bertha, and their daughter Eve were able to emigrate to the United States in 1941 (their son Hans had already emigrated to England in 1939).From 1941–1946 he held appointments at the New School for Social Research in New York, the City College of New York, and Union College in Schenectady, New York, and then was appointed as an Adjunct Professor of Physics at New York University, where his contract was renewed year-by-year until his retirement in 1958.