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41.
From the reaction of C60F18 with benzene in the presence of SbCl5 we have isolated a compound of 1252 amu indicated to be C60F14OFPh3, a fluoroxyfullerene. Temperature-variable 1H NMR shows that one phenyl group suffers restricted rotation on cooling to 218 K, attributed to the presence of the OF group which, as in the case of the recently characterised C60F17OF, fails to give a signal for this group in the 19F NMR. We have isolated also, C60F14O2FPh3 (1268 amu) a mixture of oxahomo derivatives of C60F14OFPh3 arising from oxygen insertion into FCCF bonds. Theoretical calculations for C60F14OFPh3 indicate that the phenyl group nearest to the OF group is twisted out of the plane containing the other two. 相似文献
42.
Photo-degradation and photo-stabilisation of the two-phase system poly(vinyl chloride)-polybutadiene
The photo-oxidative degradation of poly(vinyl chloride) (PVC)/polybutadiene (PB) blends has been studied. After uv irradiation, photo-grafting of the PVC and PB phases was observed. Photolysis of PVC accelerates cis-trans isomerisation of PB. Both phases, PVC and PB, are photo-degraded according to free radical oxidation mechanisms. The rates of these processes can be decreased by the addition of metal chelates, such as commercially produced Cyasorb uv light absorber 1084 (2,2′-thiobis(4-t-octylphenolato)-n-butylamine nickel(II)) and Cyasorb uv light absorber 2548 (cobalt dicyclohexyldithiophosphinate). 相似文献
43.
Ahmed Galal Soher A. Darwish Rasha A. Ahmed 《Journal of Solid State Electrochemistry》2007,11(4):521-530
Conducting polymers were deposited on the surface of platinum and glassy carbon electrodes. The monomers used were N-methyl pyrrole and 3-methyl thiophene. The electrochemical synthesis of the polymer was achieved using constant applied potential
or cyclic polarization techniques in acetonitrile as a solvent and tetra-alkyl ammonium salts as supporting electrolyte. The
resulting conducting polymeric film was modified with an inorganic metal complex, namely, Cu–phthalocyanine or Co–phthalocyanine.
Two different approaches were adopted for the modification: (1) the first was to directly apply the metal–phthalocyanine layer
on the surface of the polymer, and (2) the second was by the inclusion of the metal–phthalocyanine in a sol–gel matrix that
was in turn applied to the conducting polymer film. In the first part of this work, we studied the effect of changing the
type of polymer matrix and the central metal of the inorganic complex on the electrochemical behavior of the resulting film.
We also found that changing the method of metal–phthalocyanine application to the polymer film affected the electrochemical
response and kinetics at the electrode surface. The new electrode was tested for the reduction of hydrogen peroxide and showed
better conversion efficiency compared to conventional surfaces, which suggests its use in fuel cell applications. 相似文献
44.
M. A. Darwish 《Journal of Applied Mathematics and Computing》1999,6(3):633-637
In this paper we study the stability theorems for nonlinear Fredholm-Volterra integral equations system. 相似文献
45.
We introduce Erdélyi‐Kober fractional quadratic integral equation with supremum, namely . This equation contains as special cases numerous integral equations studied by other authors. We show that there exists at least one monotonic solution belonging to C[0, 1] of our equation. The main tools in our analysis are Darbo fixed point theorem and the measure of noncompactness related to monotonicity which was introduced by Bana? and Olszowy. Finally, we present an example for illustrating the natural realizations of our abstract results. 相似文献
46.
A simple, accurate, and sensitive spectrophotometric method for analysis of selective serotonin reuptake inhibitors (SSRIs) has been developed and validated. The analysis was based on the formation of colored charge-transfer complexes between the intact molecule of SSRI drug as an n-electron donor and each of tetracyanoquinodimethane (TCNQ) or p-chloranilic acid (pCA) as electron acceptors. The formed complexes were measured spectrophotometrically at 842 and 520 nm for TCNQ and pCA, respectively. Different variables and parameters affecting the reactions were studied and optimized. Under the optimum reaction conditions, linear relationships with good correlation coefficients (0.9975-0.9996) were found between the absorbances and the concentrations of the investigated drugs in the concentration ranges of 4-50 and 20-400 microg/mL with TCNQ and pCA, respectively. With all the investigated drugs, TCNQ gave more sensitive assays than pCA; the limits of assay detection were 2.5-4.8 and 20-40 microg/mL with TCNQ and pCA, respectively. The intra- and interassay precisions were satisfactory; the relative standard deviations did not exceed 2%. The proposed procedures were successfully applied to the analysis of the studied drugs in pure form and pharmaceutical formulations with good accuracy; the recovery values were 98.4-102.8 +/- 1.24-1.81%. The results obtained from the proposed method were statistically comparable with those obtained from the previously reported methods. 相似文献
47.
Eight spectrophotometric methods for determination of ribavirin have been developed and validated. These methods were based on the oxidation of the drug by different inorganic oxidants: ceric ammonium sulfate, potassium permanganate, ammonium molybdate, ammonium metavanidate, chromium trioxide, potassium dichromate, potassium iodate, and potassium periodate. The oxidation reactions were performed in perchloric acid medium for ceric ammonium sulfate and in sulfuric acid medium for the other reagents. With ceric ammonium sulfate and potassium permanganate, the concentration of ribavirin in its samples was determined by measuring the decrease in the absorption intensity of the colored reagents at 315 and 525 nm, respectively. With the other reagents, the concentration of ribavirin was determined by measuring the intensity of the developed colored reaction products at the wavelengths of maximum absorbance: 675, 780, 595, 595, 475, and 475 nm for reactions with ammonium molybdate, ammonium metavanidate, chromium trioxide, potassium dichromate, potassium iodate, and potassium periodate, respectively. Different variables affecting the reaction conditions were carefully studied and optimized. Under the optimum conditions, linear relationships with good correlation coefficients (0.9984-0.9998) were found between the absorbance readings and the concentrations of ribavirin in the range of 4-1400 microg/mL. The molar absorptivities were correlated with the oxidation potential of the oxidants used. The precision of the methods were satisfactory; the values of relative standard deviation did not exceed 1.64%. The proposed methods were successfully applied to the analysis of ribavirin in pure drug material and capsules with good accuracy and precision; the recovery values were 99.2-101.2 +/- 0.48-1.30%. The results obtained using the proposed spectrophotometric methods were comparable with those obtained with the official method stated in the United States Pharmacopeia. 相似文献
48.
Mohamed Abdalla Darwish Bessem Samet 《Numerical Functional Analysis & Optimization》2018,39(3):276-294
Using the technique of a suitable measure of noncompactness in Banach algebra, we prove an existence theorem for some functional-integral equations in Banach algebra, namely Erdélyi–Kober quadratic functional-integral equation. This equation contains as particular cases a lot of integral equations that appear in many branches of nonlinear analysis and its applications. The obtained result is illustrated by an example. 相似文献
49.
M. A. Darwish 《Journal of Applied Mathematics and Computing》1999,6(2):305-313
In this paper we give some sufficient conditions for the existence and uniqueness of a continuous solution of the system of
Urysohn-Volterra equation with hysteresis. 相似文献
50.
F. Hilbert und N. A. Darwish 《Fresenius' Journal of Analytical Chemistry》1971,255(5):357-361
Zusammenfassung Es wird eine Analysenmethode für Cyanid, komplexe Cyanide, Ammoniak und Cyanat in oxydierende Chlorverbindungen enthaltenden Lösungen beschrieben. Nach unseren Ergebnissen kann auch in solchen Lösungen freies Cyanid enthalten sein. Die Bestimmungen sind nebeneinander nicht durchzuführen, daher werden nach Reduktion mit Arsenitlösung folgende Trennungen durch Wasserdampfdestillation (Wd.) durchgeführt: 1. Wd. bei pH 12; erfaßt wird NH3 bzw. NH4
+ und ein kleiner Teil des Cyanates (Hydrolyse zu NH3). Dieser Teil ist bei kontrollierten Bedingungen proportional der Cyanatkonzentration. 2. Wd. bei pH 7 (Phosphatpuffer). Erfaßt wird freies Cyanid. 3. Wd. bei pH 0 zur Abtrennung des Gesamtcyanids. 4. Verseifung des Cyanats (pH 1, Cyanatkonzentration unter 1,2 g/l) und Wd. bei pH 12. Erfaßt wird die Summe an Ammoniak und Cyanat.
Determination of free and complex cyanide, cyanate and ammonia in presence of each other
A procedure is described for the analysis of solutions containing cyanide, complex cyanides, ammonia and oxidizing chlorine compounds. Our results show the possible existence of free cyanide ions in such solutions. Simultaneous determination is impossible; therefore, after reduction with arsenite solution, the following separations are made by steam distillation (s. d.): (1) S.d. at pH 12 gives the sample ammonia and some ammonia produced by hydrolysis of cyanate (this is under controlled conditions proportional to the cyanate concentration). (2) S.d. at pH 7 (phosphate buffer) gives the free cyanide. (3) S.d. at pH 0 separates complex and free cyanide. (4) Hydrolysation of cyanate at pH 1 (cyanate conc. below 1.2 g/l) and following s.d. at pH 12 gives the sum of sample ammonia and the ammonia equivalent to the cyanate content.相似文献