Simulação de problemas de transferência de calor em regime permanente com uma relação entre condutividade térmica e temperatura constante por partes.

Este trabalho estuda a transferência de calor por condução considerando a condutividade térmica como uma função constante por partes da temperatura. Esta relação, embora fisicamente mais realista que supor a condutividade térmica constante, permite obter uma forma explícita bem simples para a inversa da Transformada de Kirchhoff (empregada para tratar a não linearidade do problema). Como exemplo, apresenta-se uma solução exata para um problema com simetria esférica. Em seguida, propôe-se uma formulação variacional (com unicidade demonstrada) que introduz um funcional cuja minimização é equivalente à solução do problema na forma forte. Finalmente compara-se uma solução exata obtida pela inversa da Transformada de Kirchhoff com a solução obtida via formulação variacional.

超重核合成机制—包含中子、质子跃迁的二维主方程

用双核模型研究超重核的合成机制，最主要的部分是由双核系统演化到复合核的熔合机制研究。双核模型认为超重复合核的形成是由弹核的核子全部转移到靶核所致。核子分中子和质子，在以前的研究中，描述熔合过程的主方程是一维的，以类弹核的质量数 为变量，与此对应的驱动势也是一维的。对确定的 ，其同位旋的确定是由较低的势能面确定的，这样确定的同位旋与反应系统的同位旋很接近。但是我们的研究发现，对入射道同位旋与复合系统同位旋相差较大的情况，入射道在双核系统势能面比较高的位置，有时甚至在最高位置，这时核子转移的同位旋路径比较复杂，以致一维主方程的描述给出错误的结果。为此，建立了以类弹碎片中子数 和质子数 为变量的二维主方程，并建立了二维主方程的分步差分的解法，完成了解二维主方程的程序编写。并对一些典型的弹核、靶核同位旋与复合系统同位旋相差较大的系统进行了研究。对这些反应道的研究表明，无论1D主方程对这些反应道的蒸发剩余截面的研究给出了过高、或过低的估计，2D主方程都能给出与实验值一致地结果。二维主方程适用于所有的弹靶组合入射道。对确定的超重核目标，可以较准确的对各种弹靶组合的合成几率给出预言，特别是研究合成超重核的同位素依赖性，因而极大增加了预言合成预期超重岛区域超重核的弹靶组合的选择性。本工作还检验了一维主方程的适用条件：入射点必须在比较接近二维驱动势谷底时才适用，这时一维主方程预言的蒸发剩余截面的结果与二维主方程的结果很接近

超重核合成机制—包含中子、质子跃迁的二维主方程

用双核模型研究超重核的合成机制，最主要的部分是由双核系统演化到复合核的熔合机制研究。双核模型认为超重复合核的形成是由弹核的核子全部转移到靶核所致。核子分中子和质子，在以前的研究中，描述熔合过程的主方程是一维的，以类弹核的质量数 为变量，与此对应的驱动势也是一维的。对确定的 ，其同位旋的确定是由较低的势能面确定的，这样确定的同位旋与反应系统的同位旋很接近。但是我们的研究发现，对入射道同位旋与复合系统同位旋相差较大的情况，入射道在双核系统势能面比较高的位置，有时甚至在最高位置，这时核子转移的同位旋路径比较复杂，以致一维主方程的描述给出错误的结果。为此，建立了以类弹碎片中子数 和质子数 为变量的二维主方程，并建立了二维主方程的分步差分的解法，完成了解二维主方程的程序编写。并对一些典型的弹核、靶核同位旋与复合系统同位旋相差较大的系统进行了研究。对这些反应道的研究表明，无论1D主方程对这些反应道的蒸发剩余截面的研究给出了过高、或过低的估计，2D主方程都能给出与实验值一致地结果。二维主方程适用于所有的弹靶组合入射道。对确定的超重核目标，可以较准确的对各种弹靶组合的合成几率给出预言，特别是研究合成超重核的同位素依赖性，因而极大增加了预言合成预期超重岛区域超重核的弹靶组合的选择性。本工作还检验了一维主方程的适用条件：入射点必须在比较接近二维驱动势谷底时才适用，这时一维主方程预言的蒸发剩余截面的结果与二维主方程的结果很接近

Multiphoton ionization of pyrrole-water mixed clusters

Multiphoton ionization of the hydrogen,bonded pyrrole-water clusters (C4H5N)(n)(H2O)(m) is studied with a reflectron-time of flight mass spectrometer at 355 mn. With increasing partial concentration of pyrrole in a gas mixture source, a series of poly-pyrrole-water binary-mixed cluster ions can be observed, including unprotonated cluster ions [(C4H5N)(x)(H2O)(y)](+), protonated cluster ions [(C4H5N)(x)(H2O)(y)](+) and dehydrogenated cluster ions [(C4H4N)(C4H5N)(x)(H2O)(y)](+). Ab initio calculations of their structures, bond strengths, charge distributions and reaction energies are carried out. Stable structures of these clusters are obtained from the calculations. A probable formation mechanism of the cluster ions [(C4H5N)(x)(H2O)(y)](+), [(C4H5N)(x)(H2O)(y)]H+ and [(C4H4N)(C4H5N)(x) (H2O)(y)](+) is supposed to be the ionization of clusters followed by dissociation.

One-pot synthesis and characterization of hyperbranched poly(ester-amide)s from commercially available dicarboxylic acids and multihydroxyl secondary Amines

A convenient and cost-effective strategy for synthesis of hyperbranched poly(ester-amide)s from commercially available dicarboxylic acids (A(2)) and multihydroxyl secondary amine (CB2) has been developed. By optimizing the conditions of model reactions, the AB(2)-type intermediates were formed dominantly during the initial reaction stage. Without any purification, the AB(2) intermediate was subjected to thermal polycondensation in the absence of any catalyst to prepare the aliphatic and semiaromatic hyperbranched poly(ester-amide)s bearing multi-hydroxyl end-groups.

Electrochemistry of Microperoxidase-11 (MP-11) on Glassy Carbon Electrode Modified with Chitosan

In this paper, microperoxidase-11 (MP-11) was immobilized on glassy carbon electrode surface modified with chitosan by physical adsorption. The direct electrochemistry and the electrocatalytic behaviours to O-2 and the H2O2 of MP-11 on glassy carbon electrode modified with chitosan were characterized by cyclic voltammetry. The results indicate that MP-11 on modified electrode displays a quasi-reversible electrochemical process coupled with proton transfer in the phosphate buffer solutions(pH = 7.12). Direct electrochemical reaction of MP-11 on modified electrode has been realized. MP-11 on modified electrode can catalyze reduction for O-2 and H2O2. Both of the catalytic reductions are surface-controlled electrochemical process.

Synthesis and Characterization of Hyperbranched Poly(ether amide)s with Thermoresponsive Property and Unexpected Strong Blue Photoluminescence

A facile and efficient strategy for the syntheses of novel hyperbranched poly(ether amide)s (HPEA) from multihydroxyl primary amines and (meth)acryloyl chloride has been developed. The chemical structures of the HPEAs were confirmed by IR and NMR spectra. Analyses of SEC (size exclusion chromatography) and viscosity characterizations revealed the highly branched structures of the polymers obtained. The resultant hyperbranched polymers contain abundant hydroxyl groups. The thermoresponsive property was obtained from in situ surface modification of abundant OH end groups with N-isopropylacrylamide (NIPAAm). The study oil temperature-dependent characteristics has revealed that NIPAAm-g-HPEA exhibits an adjustable lower critical solution temperature (LCST) of about 34-42 degrees C depending on the grafting degree. More interestingly, the work provided an interesting phenomenon where the HPEA backbones exhibited strong blue photoluminescence.

Direct electrochemistry and bioelectrocatalysis of horseradish peroxidase immobilized on active carbon

For the first time horseradish peroxidase (HRP) immobilized on the surface of active carbon powder modified at the surface of a glassy carbon electrode has been shown to undergo a direct quasi-reversible electrochemical reaction. Its formal potential, E-o/, is -0.363 V in phosphate buffer solution (pH 6.8) at a scan rate of 100 mV/s and is almost independent of the scan rate in the range of 50-700 mV/s. The dependence of E-o/ on the pH of the buffer solution indicated that the conversion of HRP-Fe(III)/HRP-Fe(II) is a one-electron-transfer reaction process coupled with one-proton-transfer. The experimental results also demonstrated that the immobilized HRP retained its bioelectrocatalytic activity to the reduction of H2O2. Furthermore, the HRP adsorbed oil the surface of the active carbon powder can be stored at 4 degreesC for several months without any loss of the enzyme activity. The method presented for immobilizing HRP can be easily extended to immobilize and obtain the direct electrochemistry of other enzymes.

Synthesis and characterization of hyperbranched poly(ester-amide)s from commercially available dicarboxylic acids and multihydroxyl primary amines

A new method for syntheses of hyperbranched poly(ester-amide)s from commercially available A(2) and CBx type monomers has been developed on the basis of a series of model reactions. The aliphatic and semiaromatic hyperbranched poly(ester-amide)s with multihydroxyl end groups are prepared by in situ thermal polycondensation of intermediates obtained from dicarboxylic acids (A(2)) and multihydroxyl primary amines (CBx) in N,N-dimethylformamide. Analyses of FTIR, H-1 NMR, and C-13 NMR spectra revealed the structures of the polymers obtained. The MALDI-TOF MS of the polymers indicated that cyclization side reactions occurred during polymerization. The hyperbranched poly(ester-amide) s contain configurational isomers observed by C-13 and DEPT C-13 NMR spectroscopy. The DBs of the polymers were determined to be 0.38-0.62 by H-1 NMR or quantitive C-13 NMR and DEPT 135 spectra. These polymers exhibit moderate molecular weights, with broad distributions determined by size exclusion chromatography ( SEC), and possess excellent solubility in a variety of solvents such as N, N- dimethylacetamide, dimethyl sulfoxide, tetrahydrofuran, and ethanol, and display glass-transition temperatures (T(g)s) between -2.3 and 53.2 degrees C, determined by DSC measurements.

Surface morphology evolution of a thin polymeric supramolecular film by tuning interactions

A polymeric supramolecule consisting of symmetric polystyrene-block-poly(4-vinylpytidine) (PS-b-P4VP), dodecylbenzenesulfonic acid (DBSA), and 3-pentadecylphenol (PDP) was formed by proton transfer and hydrogen bonding. The surface morphology,of a thin film of the polymeric supramolecule has been investigated. The spherical PS microdomains embedded in a P4VP(DBSA)(1.0)(PDP)(1.0) matrix are observed for the as-cast film because the weight fraction, f(comb), of the P4VP(DBSA) (1.0)(PDP)(1.0) blocks is much higher than that of PS as a result of the non-covalent interactions of P4VP and DBSA and DBSA and PDR Upon annealing the PS-b-P4VP(1:1)(DBSA)(1.0)(PDP)(1.0) film at high temperatures, the hydrogen bonding between the DBSA and PDP diminishes, which leads to a change of overall morphology from an ordered sphere to a pitted structure.

Advances in gas-phase electrophilic aromatic substitution reaction

Recent advances in the gas - phase reaction of aromatics with cationic electrophiles are reviewed. The overall substitution reaction is analyzed in terms of its elementary steps. Mechanistic studies have been focused on the structure and reactivity of covalent and non - covalent ionic intermediates, which display a rich chemistry and provide benchmark reactivity models. Particular attention has been devoted to proton transfer reactions, which may occur intra or intermolecularly in arenium intermediates.

Gas-phase ion-molecule reactions of C-60 with the plasma of methyl acrylate

The gas-phase ion-molecule reactions of C-60 with the plasma generated from methyl acrylate under self-chemical ionization conditions were studied by use of a triple-quadrupole mass spectrometer. The adduct cation [C60C3H3O](+) and protonated molecular ion [C60H](+) were observed as the major product ions. The former adduct ion is formed by electrophilic reaction of C-60 with the ion [CH2=CHCO](+), a main fragment ion resulting from the methyl acrylate molecular ion [CH2=CHCOOCH3](+) through alpha cleavage. The latter ion is generated by proton transfer from protonated methyl acrylate to C-60. Semi-empirical quantum chemical calculations have been performed for the eight possible isomers of [C60C3H3O](+) at the Hartree-Fock level by use of the AMI method. The results show three types of cycloadducts as the most stable structures among the possible isomers.

Electrochemical preparation and characterization of silicotungstic heteropolyanion monolayer electrostatically linked aminophenyl on carbon electrode surface

In this paper, an organic-inorganic composite film of heteropolyanion was Formed by attaching a Keggin-type heteropolyanion, SiW12O404-, on carbon electrode surface derivatized by 4-aminophenyl monolayer. The composite film thus grafted on carbon electrode surface has good stability because of the ionic bonding character between SiW12O404- and surface aminophenyl groups. X-ray photoelectron spectroscopy, scanning tunneling microscopy, and cyclic voltammetry were used to characterize the composite film. Compared with SiW12O404- electrodeposited on a bare glassy carbon electrode (GCE), the composite film gives three more sharp and well-defined redox couples attributed to two one- and two-electron processes, and the analyses of the voltammograms of SiW12O404- anion in the composite film modified on GCE shows that its surface coverage is close to a closest packing monolayer. STM characterization shows that a two-dimensional order heteropolyanion monolayer was formed on HOPG substrate. The composite film provides a favorable environment for electron and proton transfer between SiW12O404- ion and electrode surface, which may make it suitable for various applications in sensors and microelectronics devices.

A study of dimethylferrocene diffusion and electrode kinetics using microelectrode voltammetry in poly(ethylene glycol) solvent

The heterogeneous electron transfer rate constant (k(s)) of dimethylferrocene (DMFc) was estimated using cyclic voltammetric peak potential separations taken typically in a mixed diffusion geometry regime in a polyelectrolyte, and the diffusion coefficient (D) of DMFc was obtained using a steady-state voltammogram. The heterogeneous electron transfer rate constant and diffusion coefficient are both smaller by about 100-fold in the polymeric solvent than in the monomeric solvent. The results are in agreement with the difference of longitudinal dielectric relaxation time (tau(L)) in the two kinds of solvents, poly(ethylene glycol) (PEG) and CH3CN, indicating that k(s) varies inversely with tau(L); k(s), is proportional to D of DMFc. Both D and k(s) of DMFc in PEG containing different supporting electrolytes and at different temperatures have been estimated. These results show that D and k(s) of DMFc increase with increasing temperature in the polyelectrolyte, whereas they vary only slightly with changing the supporting electrolyte.

NMR titration and molecular model MOPAC calculation of protonation processes of two MRI ligands

The protonation process of two DTPA bis(amide) derivatives, DTPA-BDMA and DTPA-BDEA, was studied by using H-1 NMR titration and MOPAC calculation. Their protonation process was proposed in the order of the central amine, the terminal amines, the central carboxyl, the terminal carboxyl, the other terminal carboxyl and central amine. During the protonation of the terminal amine, there existed a large fraction of proton transfer from the central amine to the other terminal amine.