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11.
Muhammad Taher Abuelma'atti 《International Journal of Infrared and Millimeter Waves》1991,12(8):911-918
An empirical model is presented for the current-voltage characteristics of resonanttunneling (RT) devices. By using this model an analytical study of millimeter-band electronic circuits employing RT devices can be performed. 相似文献
12.
Muhammad Faisal Nobuaki Sato Armando T. Quitain Hiroyuki Daimon Koichi Fujie 《国际化学动力学杂志》2007,39(3):175-180
The kinetics and pathway of hydrothermal decomposition of aspartic acid were studied using a continuous‐flow tubular reactor. The reaction was carried out in the temperature range of 200–260°C and at a pressure of 20 MPa. Deamination was the primary reaction, indicated by the presence of significant amount of ammonia, fumaric acid, or maleic acid in the products. Other reaction products were pyruvic acid, malic acid, and traces of succinic and lactic acid. Traces of alanine were also detected, showing the possibility of decomposing high‐molecular weight amino acids to obtain simple amino acids such as glycine or alanine. Results on the effect of reaction parameters demonstrated that decomposition of aspartic acid is highly temperature dependent under hydrothermal conditions. For a slight temperature difference of 60°C (from 200 to 260°C), the first‐order reaction rate constants of 0.003 significantly increased to 0.231 s?1. The activation energy was 144 kJ/mol, as calculated by the Arrhenius equation. No significant effect was exhibited by other reaction parameters such as pH and pressure. The results are useful in controlling the hydrolysis of proteinaceous materials toward high yield of aspartic acid under hydrothermal conditions. © 2007 Wiley Periodicals, Inc. 39: 175–180, 2007 相似文献
13.
Muhammad Ilyas Sarwar Sonia Zulfiqar Zahoor Ahmad 《Colloid and polymer science》2007,285(15):1733-1739
Fluoro-aramid-based sol/gel-derived nanocomposites were synthesized by condensing a mixture of 4,4′-(hexafluoro-isopropylidene)dianiline
and 1,3-phenylenediamine with terephthaloylchloride (TPC) in dimethylacetamide. TPC was added in slight excess to produce
amide chains with carbonyl chloride end groups and then replaced with alkoxy groups using aminophenyltrimethoxysilane to develop
bonding with the silica network. Mechanical, dynamic mechanical thermal, water absorption and morphological measurements were
carried out on the thin hybrid films. Increase in the tensile strength and modulus was observed as compared to pristine polyamide.
The thermal decomposition temperature was found in the range of 400–500 °C. The water absorption was found to be reduced with
higher silica content. The glass transition temperature and the storage moduli increased with increasing silica concentration.
The maximum increase in the T
g value (345 °C) was observed with 20 wt% silica. Scanning electron microscopy revealed the uniform distribution of silica
in the matrix with an average particle size ranging from 8 to 50 nm. 相似文献
14.
Muhammad Mufazzal Saeed 《Journal of Radioanalytical and Nuclear Chemistry》2006,267(2):427-433
Summary The sorption of microquantities of Tm(III) ions on washed polyurethane foam (PUF) from a mixture of aqueous solution and ethanol
containing PAN was examined. The maximum sorption of 3.18. 10-6M solution of Tm(III) ions was observed at pH 8 with 30-minute equilibration time. The optimum ratio of aqueous-ethanol phase
for the sorption of Tm(III) ions was found to be 3:1 v/v, respectively. The sorption rate of metal ions on PUF is followed a first order kinetics and obeyed the equation for an intra
particle diffusion process. The equilibrium concentration data of Tm(III) ions could be described satisfactorily by several
adsorption isotherms. The Freundlich adsorption isotherm constants 1/nand KFare 0.66±0.02 and (5.7±0.3). 10-3mol. g-1, respectively. The Langmuir isotherm constants for monolayer coverage (Q) and binding strength of sorption (b) are (2.5±0.7). 10-5mol. g-1and (1.6±0.1). 104l. mol-1, respectively. The sorption capacity derived from Dubinin-Radushkevich (D-R) isotherm is (1.7±0.2). 10-4mol. g-1and the sorption free energy (E) is 9.8±0.2 kJ. mol-1indicating chemisorption phenomena. The thermodynamic parameters indicate that the sorption of Tm(III) ions onto PUF is endothermic,
entropy driven and spontaneous in nature. 相似文献
15.
Nizakat Bib Misal Khan Amal Badshah Muhammad Ashraf Chaudry 《Radiation Physics and Chemistry》2005,73(6):362-364
Minimally processed cauliflower samples were irradiated, stored at 5 °C for 2 weeks and analyzed for sensory, physicochemical and microbiological qualities at 0th, 7th and 14th days. The data showed highest mean values of 7.93 and 7.57 for appearance and flavor, respectively, for 1.0 kGy treated samples. The D10 values of contaminating microorganisms on cauliflower were 0.20 (Escherischia coli) and 0.24 kGy (Salmonella paratyphae A.) and the resulting 5D10 value was 1.2 kGy. The study revealed that a dose of 1.5 kGy is enough for retention of quality and reduction of microbial load to 5D10 values in cauliflower during 2 weeks storage at refrigerated temperature. 相似文献
16.
Ahmad VU Khan A Farooq U Kousar F Khan SS Nawaz SA Abbasi MA Choudhary MI 《Chemical & pharmaceutical bulletin》2005,53(4):378-381
Three new tricyclic cis-clerodane type diterpenoids trivially named as limbatolide A (1), limbatolide B (2) and limbatolide C (3) have been isolated from the roots of Otostegia limbata along with two known compounds; oleanic acid and beta-sitosterol. The structure elucidation of the new compounds was based primarily on two-dimensional (2D) NMR techniques. Compounds 1-3 displayed inhibitory potential in a concentration-dependent manner against acetylcholinesterase (AChE; EC 3.1.1.7) and butyrylcholinesterase (BChE; EC 3.1.1.8) enzymes, respectively. 相似文献
17.
Tahir AA Molloy KC Mazhar M Kociok-Köhn G Hamid M Dastgir S 《Inorganic chemistry》2005,44(25):9207-9212
Ba(dmae)2 (dmaeH=N,N-dimethylaminoethanol, C4H11NO) reacts with Co(acac)2 (acac=2,4-pentanedionate) to produce the trinuclear coordination complex [Ba2Co(acac)4(dmae)3(dmaeH)] in an 85% yield. Spectroscopic and single-crystal X-ray diffraction experiments indicate that the complex possesses a structure in which two barium atoms and a cobalt atom are bridged by acac and dmae groups. The barium centers are eight and nine coordinate with BaO7N and BaO7N2 coordination spheres while the cobalt is a more regular CoO5N octahedron. This 2:1 heterobimetallic molecular complex was investigated as precursor for the deposition of thin film by AACVD. The film was characterized by SEM and XRD. TGA shows that the complex starts thermal decomposition upon heating in nitrogen atmosphere at 105 degrees C to produce barium cobalt oxide material of a Ba2CoO3 composition with an orthorhombic structure. The synthetic approach detailed here represents a unique route to the formation of a heterobimetallic barium cobalt coordination complex. 相似文献
18.
M. Aneesuddin P. N. Char M. Raza Hussain E. R. Saxena 《Journal of Thermal Analysis and Calorimetry》1983,26(2):205-215
When chalcopyrite is heated in air, up to 350? there is no marked change. Between 350 and 440?, surface material is oxidised to iron sulphate, CuSO4 and Fe2O3, while in regions not accessible to oxygen the formation of Cu5FeS4, FeS and S takes place. From 440 to 500? oxidation and sulphation phenomena occur. Stable compounds between 500 and 650? are iron sulphate, CuSO4 and Fe4O3, with a minor amount of 6CuO.Cu2O indicated at 650?. After the decomposition of iron sulphate, CuSO4 decomposes, first to CuO.CuSO4 and then to CuO. By 750? the sulphur has been totally lost from all compounds, while the oxides of copper and iron partly react to form CuFe2O4. Final products of oxidation between 800 and 850? are CuO, CuFe2O4 and Fe3O4. 相似文献
19.
Marine brown alga Dictyota dichotoma (Dictyotaceae) collected from Karachi coast of Arabian Sea yielded two new (1 and 2) enones (dolastane-diterpenoids) named: dichotenone-A and -B along with an olide (loliolide, 3) as a new source. Their structures have been characterized with the aid of 2D-NMR spectroscopic techniques. 相似文献
20.
Khan KM Shujaat S Rahat S Hayat S Atta-ur-Rahman Choudhary MI 《Chemical & pharmaceutical bulletin》2002,50(11):1443-1446
Eight new beta-N-substituted acyl hydrazides along with their corresponding acyl derivatives were synthesized and screened for in vitro beta-glucuronidase inhibition and found to be active against the enzyme. All of these compounds were found to be noncompetitive inhibitors except for N'-(2-cyanoethyl)-4-hydroxy benzohydrazide (10), which was found to be an uncompetitive inhibitor. Structure-activity relationship studies indicated that the benzyloxy group present in compounds 12 and 13 is responsible for the beta-glucuronidase inhibition activity. 相似文献