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  • Author or Editor: Li Cheng x
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Abstract  

Thermal behavior of nitroguanidine (NQ) has been investigated by TG/DSC-MS-FTIR simultaneous analysis performed under both isothermal and nonisothermal conditions. The isothermal test at 230 °C indicated that the release of gas products can be divided into several stages. The processing of the non-isothermal data, namely 5, 10, 15, and 20 K/min, was performed by using Netzsch Thermokinetics. The dependence of the activation energy evaluated by Friedman’s isoconversional method on the conversion degree shows that the investigated process is complex one, and can be divided into three parts. The mechanism of the process and the corresponding kinetic parameters were determined by Multivariate Non-linear Regression Program. The kinetic results was used to simulate the thermal decomposition of NQ under isothermal condition at 210 °C. The simulated curve is in agreement with the tested curve. The obtained results were also used for prediction of the thermal lifetime of NQ corresponding to a certain temperature.

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Abstract.

We prove some new direct and converse results on simultaneous approximation by the combinations of Bernstein–Kantorovich operators using the Ditzian–Totik modulus of smoothness.

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Summary The Institute of Higher Education, Shanghai Jiao Tong University published on the web the Academic Ranking of World Universities and attracted wide attentions worldwide. 60% of their criteria are based on the databases using scientometrics. They were aware of all possible technical problems, have gone through “clean up” processes and made necessary corrections. Highly cited researchers and articles published in Nature and Science were identified one by one and attributed to the correct institutions. They are confident that errors including human ones in their data are less than two percent. They will continue their ranking efforts, improve their ranking methodologies and provide more choices on the ranking lists.

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Abstract

The purpose of the study was to investigate the effects of three kinds of flame retardant (FR), boric acid, zinc borate, and borax on the thermal curing behavior of urea–formaldehyde (UF) resin. Both pH value and gel time were measured to study the curing characters of the UF resin with different loading levels of FR. In addition, differential thermal analysis was also used to obtain kinetic analyses parameter. The results showed that boric acid decreased pH value of UF resin, and reduced gel time of the UF resin. There are no significant changes of the UF resin curing characters with different loading levels of FR. The activation energies for curing reaction of UF resins in the presence of boric acid, zinc borate, and borax, were 84.37, 84.41, and 118.4 kJ/mol, respectively, higher than that of the control one (75.38 kJ/mol). All FRs showed adverse effect on the curing behavior of the UF resin.

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A simple, rapid, and effective high-performance thin-layer chromatographic (HPTLC) method has been established for differentiating among the polysaccharides present in six traditional Chinese medicines (TCM), Cordyceps sinensis, Ganoderma lucidum, Astragalus memberanaceus, Panax ginseng, Panax quinquefolii , and Panax notogiseng . Acid hydrolyzates of the polysaccharides were analyzed by HPTLC with two detection reagents, aniline-diphenylamine-phosphoric acid and ninhydrin, and scanning densitometry. The compounds were separated on silica gel plates with chloroform- n -butanol-methanol-acetic acid-water 4.5:12.5:5:1.5:1.5 ( v/v ) as mobile phase. Seven monosaccharides and two glucuronic acids were used as reference compounds. The results showed that hydrolysis of polysaccharides can release specific molecules present in the herbal species in addition to the monosaccharides present. This is useful for distinguishing the origins of the polysaccharides in Chinese medicines.

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Abstract  

The relative errors (e%) in the determination of the activation energy from the slope of the Kissinger straight line ln(β/βT p 2) vs. 1/T p (β is the heating rate) are in-depth discussion. Our work shows that the relative errors is a function containing the factors of x p and Δx p, not only x p (x p = E/RT p, E is the activation energy, T p is the temperature corresponding to maximum process rate, R is the gas constant). The relative error between E k and E p will be smaller with the increase of the value of x and/or with the decrease of the value of Δx. For a set of different heating rates in thermal analysis experiments, the low and close heating rates are proposed from the kinetic theory.

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Abstract  

The effect of itaconic acid (IA) content and heating rate on the stabilization reactions in poly(acrylonitrile-co-itaconic acid) (P(AN-co-IA)) was investigated by differential scanning calorimetry (DSC) with peak-resolving method. Increasing IA content was effective in decreasing the initial temperature and the heat evolved, and found to enhance oxidative reactions to some extent. While, promoting heating rate resulted in a shift of the exotherm to a higher temperature and a more rapid liberation of heat. The percentage of area of the first exothermic peak increased with increasing heating rate, which would be attributed to the enhancement of the free radical cyclization reactions.

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Abstract

The effect of MnC2O4 nanoparticles on the thermal decomposition of double-base propellant composed of nitrocellulose (NC) and triethylene glycol dinitrate (TEGDN) has been investigated by TG/DSC–MS–FTIR coupling technique. The results show that the decomposition of TEGDN/NC propellant has two stages, the first stage is the volatility and decomposition of TEGDN, the second is the decomposition of NC. The addition of MnC2O4 nanoparticles gets the onset temperature of first stage higher, and makes the activation energy of decomposition of TEGDN grow by about 20–30 kJ/mol. The catalytic also accelerates the total weight loss, and makes the peak temperatures of DSC curves higher. The activation energy of the second stage has a decrease of 20–40 kJ/mol. MS and FTIR analysis show that the catalyst gets the gas products of macromolecular significantly reduce, while small molecules increase significantly. It also results in the decrease of H2O, N2O, and NO2, and the increase of NO and HCN. Above all, the catalytic improves the thermal stability of TEGDN/NC propellant, make it more safety in storage, and make the decomposition easier and more thorough in main reaction zone.

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Abstract  

The energy-loss straggling for low-energetic 16O ion in Co, Ni and Lu was measured. The obtained results were compared with various theoretical predictions. The variance of foil thickness was measured by different methods and the target quality was discussed.

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Abstract  

The effects of temperature, heating-time, concentration of HNO3 and γ-ray irradiation on the valence states of iodine in a simulated fuel solution of a medical isotope production reactor (MIPR) were investigated. About 83% of I was oxidized to IO3 and 10% of I was oxidized to I2 in uranyl nitrate solution after heating at 70 °C for 6 hours. Heating and existence of oxidant, U and ionizing radiation accelerate the oxidation process of iodine, and results in most of the iodine being produced in high oxidation states such as in IO3 and IO4 . The results indicate that the production of 131I by MIPR can be carried out by extraction of iodine in high oxidation states from the fuel solution.

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