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61.
The ionization of six compounds of bis-phenolic amides was studied spectrophotochemically in DMF-water mixture. The compounds showed two pKa values in the range of 5.97-7.32 for pKa1 and 7.61-8.44 for pKa2. The obtained values of Ka were normalized using the distribution diagrams of the different species and found to be in the range of 5.81-7.42 for pKa1 and 7.48-8.27 for pKa2. 相似文献
62.
A
modulated dsc study on the in situ polymerization of cyclic butylene terephthalate
oligomers 总被引:1,自引:0,他引:1
Z. A. Mohd Ishak P. P. Shang J. Karger-Kocsis 《Journal of Thermal Analysis and Calorimetry》2006,84(3):637-641
The polymerization of a cyclic butylene terephthalate
(CBT) oligomer was studied as a function of temperature (T=200
and 260°C, respectively) by modulated DSC (MDSC). The first heating was
followed by cooling after various holding times (5, 15 and 30 min) prior to
the second heating which ended always at T=260°C.
This allowed us to study the crystallization and melting behavior of the resulting
polybutylene terephthalate (PBT), as well. In contrary to the usual belief,
the CBT polymerization is exothermic and the related process is superimposed
to that of the CBT melting. The melting behavior of the PBT was affected by
the polymerization mode (performed below or above the melting temperature
of the PBT product) of the CBT. Annealing above the melting temperature of
PBT yielded a product featuring double melting. This was attributed to the
presence of crystallites with different degrees of perfection. The crystals
perfection which occurred via recrystallization/remelting was manifested by
a pronounced exothermic peak in the non-reversing trace. 相似文献
63.
Simple and sensitive spectrophotometric methods for the assay of retinol have been presented. The first method was based on the reaction of retinol with iodine to give a molecular charge-transfer complex, the retinol acting as n-donor and iodine as -electron acceptor. The second method depends on the formation of a highly coloured stable radical anion between retinol and 7,7,8,8-tetracyanoquinodimethane (TCNQ as a -electron acceptor. The molecular ratios of the reactants in the complexes have been established and the experimental conditions leading to maximum charge-transfer bands were also studied. Beer's law is obeyed over the retinol concentration range 2.5–26 µg/ml. The proposed procedures have been applied successfully to the analysis of drug formulation. The average recovery and average standard deviation was 99.99 ±1.13% with retinol-iodine and 100.001 ± 1.31% with retinol-TCNQ. A kinetic study was performed by heating retinol at 50°C for different periods of time, the result obtained by plotting log c against time indicates that thermal decomposition of retinol is of first order. The results obtained by both methods were in good agreement with those obtained by the official method. The developed procedures were found to be simple, accurate and precise and can be used for the determination of retinol in presence of its degradation products. 相似文献
64.
M. M. Ibrahim M. M. Wakkad E. Kh. Shokr H. A. Abd-El-Ghani 《Journal of Thermal Analysis and Calorimetry》1991,37(4):813-827
The thermal diffusivities, specific heats and thermal conductivities of the binary compositions Sb40Te60 and Sb40Se60 and the ternary composition Sb40Te30Se30 were measured in the range 320 to 500 K. It was found that the environmental temperature, the content of Se in the composition and the conditions of measurements are decisive factors greatly influencing both the values and the behaviour ot the thermal parameters, and the mechanisms of thermal transport. Although the tested compositions exhibit semiconducting behaviour, the free charge carrier component of the thermal conductivity was so small as to be negligible. Thus, it could be concluded that the observed thermal conductivity is attributable to both photon and phonon mechanisms.
Zusammenfassung Im Temperaturbereich 320–500 K wurde das Temperaturleitvermögen, die spezifische Wärme und die Wärmeleitfähigkeit der binären Kompositionen Sb40Te60 bzw. Sb40Se60 und der ternären Komposition Sb40Te30Se30 untersucht. Man fand, daß die Umgebungstemperatur, der Se-Gehalt der Kompositionen und die Meßbedingungen entscheidende Faktoren sind, welche sowohl Wert als auch Verhalten der thermischen Parameter, weiterhin den Mechanismus des Wärmetransportes beeinflussen. Obwohl die untersuchten Kompositionen Halbleiterverhalten zeigten, war die freie Ladungsträgerkomponente der Wärmeleitfähigkeit so gering, daß sie vernachlässigt werden konnte. Somit konnte darauf geschlossen werden, daß die beobachtete Wärmeleitfähigkeit sowohl Photonen- als auch Phononenmechanismen zugeschrieben werden kann.相似文献
65.
The problem of computing the dimension of spaces of splines whose elements are piecewise polynomials of degreed withr continuous derivatives globally has attracted a great deal of attention recently. We contribute to this theory by obtaining dimension formulae for certain spaces of super splines, including the case where varying amounts of additional smoothness is enforced at each vertex. We also explicitly construct minimally supported bases for the spaces. The main tool is the Bernstein-Bézier method.Communicated by Klaus Höllig. 相似文献
66.
Mohd Salmi Md. Noorani William Parry 《Bulletin of the Brazilian Mathematical Society》1992,23(1-2):137-151
We derive a Chebotarev Theorem for finite homogeneous extensions of shifts of finite type. These extensions are of the form
:X×G/H→X×G/H where
(x,gH)=(σx, α(x)gH), for some finite groupG and subgroupH. Given a σ-closed orbit τ, the periods of the
-closed orbits covering τ define a partition of the integer |G/H|. The theorem then gives us an asymptotic formula for the number of closed orbits with respect to the various partitions
of the integer |G/H|. We apply our theorem to the case of a finite extension and of an automorphism extension of shifts of finite type. We also
give a further application to ‘automorphism extensions’ of hyperbolic toral automorphisms.
Financially supported by Universiti Kebangsaan Malaysia 相似文献
67.
Hesham Ibrahim Saleh 《中国化学会会志》2002,49(3):341-348
The reactions between strontium and iron nitrates have been studied in an open atmosphere system using three different molar ratios, 1:1 (I), 1:2 (II) and 2:1 (III) at different temperatures as pointed out from the DTA data. The reaction mechanism was discussed based on the chemical composition characterized by means of thermal analysis, X‐ray diffraction patterns, infrared spectra and magnetic susceptibility. It was found that the reaction products depend on both temperature of reaction and the ratio between reactants. The reaction products were found to be composed of a variety of iron compounds that possess different valences: SrFeO2.86, SrFeO2.97, SrFe2O4, SrFe12O19, Sr2Fe2O5 and Sr7Fe10O22 in addition to some accessory reaction products namely α‐Fe2O3 and FeO(OH). 相似文献
68.
Yousry M. Issa Hosny Ibrahim Adel F. Shoukry Sabry K. Mohamed 《Mikrochimica acta》1995,118(3-4):257-263
Ion-association complexes of antazoline HCl [I], hydralazine HCl [II], amiloride HCl [III] and quinine sulphate [IV] with [Co(SCN)4]2– and [Co(NO2)6]3– were precipitated and the excess unreacted cobalt complex was determined. A new method using atomic emission and atomic absorption spectrometry for the determination of the above drugs in pure solutions and pharmaceutical preparations is given. The drugs can be determined in the ranges 0.3–3.0, 0.19–1.96, 0.3–3.0, and 0.78–7.82 mg/25 ml solutions of I, II, III, and IV, respectively, with mean relative standard deviations of 0.65–2.03 % and recovery values of 95.76–101.2% indicating high precision and accuracy. 相似文献
69.
Glasses of the composition XNa2O · 4Al2O3 (96-X) B2O3 (mole%) where X = 10, 20, 30 to which 0.03 g V2O5 per 100 g glass was added, were prepared by normal melting. Their absorption characteristics together with the corresponding V-free base glasses were determined before and after gamma irradiation. The characteristic spectra of the unirradiated glasses show absorption bands at 315, 470, 560–580, 610–650, 700–870, and 860–1000 nm, indicating the presence of vanadium ions in more than one oxidation state, viz, V5+, V4+, and V3+. Gamma irradation of V-containing glasses causes the formation of color centers in the glass matrices, with absorption bands at 330, 500, and 610 nm, and photoreduced [V3+] and [V2+] ions with absorption bands at 350–355 and 530–570 and 520 nm, respectively. Photoreduced [V4+] may also be formed, giving rise to absorptions at 690–700 and 750–800 nm. The induced vanadium ions are found to absorb at shorter wavelengths than the intrinsic ones. An explanation based on the difference in the field energy of the two states is given. 相似文献
70.
I. M. Chung Mohd Ali A. Ahmad C. Y. Yu K. H. Ma J. G. Gwag Y. J. Park 《Chemistry of Natural Compounds》2005,41(6):650-653
One new compound 3,7,11,15,19-pentamethyl-9α,10α,11α,17α,18α-pentahydroxy-n-tetracosan-1-oxy-p-hydroxycaffeoate (oryzaterpenyl
caffeoate) (1), together with three known fatty acids linoleic acid, stearic acid and myristic acid were isolated and identified from the
rice grain of Oryza sativa. The structure of the new compound was elucidated by 1D and 2D NMR spectroscopic techniques (1H-1HCOSY, 1H-13C HETCOR) aided by EI-MS, and IR spectra.
__________
Published in Khimiya Prirodnykh Soedinenii, No. 6, pp. 535–537, November–December, 2005. 相似文献