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1.
[reaction: see text] Ring-opening metathesis polymerization (ROMP) of a photochromic 1, 2-bis(3-thienyl)cyclopentene monomer generated a series of novel polymers. All polymers exhibit reversible light-activated interconversion between their colorless-open and their colored-closed forms. 相似文献
2.
The non-isothermal devitrification of Na2O · 2 CaO · 3 SiO2 glass has been studied by differential thermal analysis in order to evaluate, from DTA curves, the temperature of maximum nucleation rate, Tm, and the activation energy values, Ec, for crystal growth.The temperature, Tm=580°C, is very close to the glass transition temperature, Tg=570°C, and the value of Ec=78 Kcal mole?1 for the surface crystal growth is nearly the same as the value Ec=89 kcal mole?1 for the bulk crystal growth; both are consistent with the activation energy for viscous flow. It is also pointed out that the nucleation rate—temperature curve and the crystallization rate—temperature curve are partially overlapped. 相似文献
3.
The surface and bulk crystallization of Li2O · 2 SiO2 glass has been studied by differential thermal analysis and the influence of the specific surface area of the sample and the nucleation heat treatment on the crystallization kinetics is pointed out. The kinetic parameters were also evaluated from the DTA curves and related to the crystallization mechanism. The results agree well with the isothermal data reported in the literature. 相似文献
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A. Buri A. Costantini G. Laudisio R. Fresa M. Catauro F. Branda 《Journal of Thermal Analysis and Calorimetry》1997,49(2):863-868
Glasses of composition expressed by the following general formula xCaO·(1?x)SiO2 (0.30≤x≤0.50) can be prepared by means of the sol-gel route starting from tetramethylorthosilicate and calcium nitrate tetrahydrate They are all difficult to prepare by means of the traditional technique of quenching the melt, because of the high liquidus temperature,T 1 t that in the case ofx=0.3 glass isT 1 =1650°C. The DTA apparatus appears a valuable tool for defining the procedure necessary to obtain the glass through the sol-gel route. The glassx=0.3 is bioactive. The experimental results suggest that the gel structures, such as obtained at room temperature, are very similar; only at high temperature do the reactions of hydrolysis and polycondensation go to completion and the structural units characteristic of each glass are obtained. 相似文献
7.
Luciani G. Costantini A. Branda F. Scardi P. Lanotte L. 《Journal of Thermal Analysis and Calorimetry》2003,72(1):105-111
A traditional TG apparatus was modified by placing two permanent magnets producing a controlled magnetic field (TG(M): Magneto
Thermogravimetry). This technique proved to be useful to study both structural relaxation and crystallisation of ferromagnetic
metallic glasses. Results obtained for the amorphous alloys Fe40Ni40P14B6 and Fe62.5Co6Ni7.5Zr6Nb2Cu1B15, are reported in this paper. Structural relaxation can be evaluated by measuring changes in Curie temperature induced by
thermal treatments. Crystallisation in TG(M) is detected through a change in the measured apparent mass (difference between
the sample mass and magnetic force driving it upward). These results were confirmed by DSC analysis. Whether the obtained
crystalline phase is ferromagnetic, it can be identified through its Curie temperature, measured by TG(M). In fact the value
of 770°C measured as Curie temperature of crystallised Fe62.5Co6Ni7.5Zr6Nb2Cu1B15led to conclude that the only ferromagnetic crystalline phase is a-Fe. These hypothesis was confirmed by XRD analysis, showing
that the first crystallisation yields to a-Fe nanocrystals.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
An unprecedented combination of photochromism and electrochromism is observed for two 1,2-bis(dithienyl)cyclopentene derivatives; the ring-opening reactions are photochemically driven while the ring-closing reactions can be triggered by electrochemical oxidation. 相似文献
9.
A gel of composition 3CaO·2SiO2 was synthesised by means of sol–gel route involving hydrolysis of tetramethyl orthosilicate (TMOS) with calcium nitrate in alcoholic medium, and polycondensation reaction. The gel was submitted to DTA and TGA analysis and the resulted material was examined by FTIR spectroscopy and X-ray powder diffractometry. The thermal treatments required for the gel into glass conversion led to a partially devitrified product. The XRD analysis showed that the structure obtained is highly depolymerised. 相似文献
10.
Martin Branda 《Optimization Letters》2014,8(3):861-875
This paper deals with the theory of sample approximation techniques applied to stochastic programming problems with expected value constraints. We extend the results of Branda (Optimization 61(8):949–968, 2012c) and Wang and Ahmed (Oper Res Lett 36:515–519, 2008) on the rates of convergence to the problems with a mixed-integer bounded set of feasible solutions and several expected value constraints. Moreover, we enable non-iid sampling and consider Hölder-calmness of the constraints. We derive estimates on the sample size necessary to get a feasible solution or a lower bound on the optimal value of the original problem using the sample approximation. We present an application of the estimates to an investment problem with the Conditional Value at Risk constraints, integer allocations and transaction costs. 相似文献