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1.
Mostafa A. G. Sanad A. M. Kashif I. El-Saghier A. A. 《Journal of Materials Science Letters》1985,4(5):571-574
Journal of Materials Science Letters - 相似文献
2.
The molecular weight of polyacrylic acid (PAA) was determined by a viscometric method using NaNO3 as solvent at 30°C. The specific electric conductivities (σ) of PAA as well as PAA doped with carbon black (CB), chromium oxide (Cr2O3), and cupferron with different concentrations (from 0.25 to 1 wt %) were measured at a temperature range 360–400 K. IR spectra of some polymers were determined and it was shown that when PAA was doped with 0.5 wt % CB, a C? O? C band appeared at 775–875 cm?1. The positron annihilation lifetime (PAL) spectra in PAA doped with the above‐mentioned dopants were measured as a function of their concentrations. It was observed that the short lifetime intensity I1 decreased, whereas the intermediate lifetime intensity I2, which is related to the conductivity of the material, increased with increasing the wt % of Cr2O3 and cupferron as well as at low concentrations of CB. These results are discussed in terms of the conducting island model. It was found that there were distinct positive relationships between σ and I2. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 877–883, 2002; DOI 10.1002/app.10381 相似文献
3.
Novel diols containing imide groups were prepared via condensation of aromatic dianhydrides with 5‐amino‐1‐naphthol. The diimide–dinaphthols prepared were characterized by conventional methods and used to synthesize new poly(urethane–imide)s (PUIs). All the polymers were characterized and their physical properties, such as solubility, solution viscosity, thermal stability, and thermal behaviour were studied. The polymers obtained showed more thermal stability than typical polyurethanes because of the presence of the imide groups. Copyright © 2003 Society of Chemical Industry 相似文献
4.
Mohammad Hossein Keshavarz 《含能材料》2006,14(6):449-452
A new method for prediction of Gurney velocity of explosives is introduced in which energy output is correlated with the heat of detonation, the number of moles of gaseous products of detonation per gram of explosive and the average molecular weight of gaseous products. It is assumed that the CHNO explosive reacts to form products composed of N2 , CO, H2O, CO2, H2,O2 and C(s) as determined by the oxygen balance of the unreacted compound. Good agreement is obtained between measured and calculated values of Gurney velocity as compared to previous correlations which assumed the reaction products to consist of N2 , H2O, CO2 and either C(s) or O2. 相似文献
5.
Behrooz?HassaniEmail author Mostafa?Khanzadi S.?Mehdi?Tavakkoli 《Structural and Multidisciplinary Optimization》2012,45(2):223-233
The Isogeometric Analysis (IA) method is applied for structural topology optimization instead of finite elements. For this
purpose, a control point based Solid Isotropic Material with Penalization (SIMP) method is employed and the material density
is considered as a continuous function throughout the design domain and approximated by the Non-Uniform Rational B-Spline
(NURBS) basis functions. To prevent the formation of layouts with porous media, a penalization technique similar to the SIMP
method is used. For optimization an optimality criteria is derived and implemented. A few examples are presented to demonstrate
the performance of the method. It is shown that, dissimilar to the element based SIMP topology optimization, the resulted
layouts by this method are independent of the number of the discretizing control points and checkerboard free. 相似文献
6.
Fatigue crack propagation (FCP) experiments were conducted on beta Ti-15-3 alloy under various loading conditions to examine the constancy of the specific enthalpy for fracture, advanced by the Crack Layer (CL) theory as a material parameter characteristic of its intrinsic toughness. The energy release rate and the irreversible work were determined from load-displacement curves during crack propagation. Microscopic and diffraction analyses were conducted to identify the damage mechanisms ahead of the crack tip. A damage zone whose geometry exhibited plane strain character at the initial stage of crack propagation was observed optically. The damage zone transformed into plane stress configuration when the crack reached half its critical length. Damage mechanisms involved slip lines and microcracking which is believed to ensue from intense accumulation of slip processes. The magnitude of microcracking became more weighty as the crack moved deeper into plane stress dominance. The damage preceding crack advance was quantitatively assessed as the crack resistance moment which is the volume of transformed material per unit crack extension. Application of the CL theory to the data generated under a wide range of applied stress levels gave rise to a constant value of the specific enthalpy of fracture, 20 MJ/m3. This value is in close agreement with the specific energy of slip lines computed from microstructural considerations. 相似文献
7.
We consider the use of quadratic approximate value functions for stochastic control problems with input‐affine dynamics and convex stage cost and constraints. Evaluating the approximate dynamic programming policy in such cases requires the solution of an explicit convex optimization problem, such as a quadratic program, which can be carried out efficiently. We describe a simple and general method for approximate value iteration that also relies on our ability to solve convex optimization problems, in this case, typically a semidefinite program. Although we have no theoretical guarantee on the performance attained using our method, we observe that very good performance can be obtained in practice.Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
8.
The stoichiometric association constants, K, the thermodynamic association constant, KA, and the other thermodynamic parameters such as ΔS°, ΔH° and ΔG° for the association between each of the Ca and Mg ions with benzoate, o-toloate, o-chlorobenzoate and salycylate have been determined at 25°C, 35°C and 45°C in aqueous media. Ion-selective electrode technique has been used in the measurements of Ca and Mg ion activitiesThe trend of association behavior of both Ca and Mg aromatic salts could not be explained on the basis of pKa of the mother organic acids but could be explained based on the trend of Hammet function σ of these salts themselves relative to the corresponding benzoate salt. 相似文献
9.
Kh. M. Mostafa 《应用聚合物科学杂志》1995,56(2):263-269
Graft polymerization of acrylic acid (AA) onto rice starch using postassium permanganate/acid redox system as initiator was investigated. When starch was reacted with KMnO4 solution, MnO2 was deposited onto starch. The dependence of MnO2 amount deposited was directly related to KMnO4 concentration. Subjecting the MnO2-containing starch to a solution consisting of monomer (AA) and acid (citric, tartaric, oxalic and hydrochloric acid) formed poly(AA)–starch graft copolymers. The graft yield, expressed as meq COOH/100 g starch, was measured by the amount of MnO2 deposited, AA concentration, material-to-liquor ratio, kind and concentration of acid, as well as temperature and duration. Finally, the newly prepared poly(AA)–starch graft copolymers were applied to cotton textiles to determine their suitability as sizing agents. The highest graft yield was obtained with citric acid and the least with hydrochloric acid, with tartaric and oxalic acid in between. The graft yield increased by increasing the concentration of acid to a certain concentration beyond which grafting leveled off. A similar trend was observed when the magnitude of grafting was related to the amount of MnO2 deposited. The graft yield increased by increasing the polymerization temperature from 30° to 50°C. Increasing the temperature to 60°C is accompanied by decreased grafting. On the other hand, fabric samples sized with poly(AA)–starch graft copolymers acquire higher tensile strength, elongation at break, and abrasion resistance than that sized with native rice starch, i.e., poly(AA)–starch graft copolymers serve as good sizing agents for cotton textiles. A tentative mechanism for grafting rice starch with AA using the KMnO4/acid redox system was elucidated. © 1995 John Wiley & Sons, Inc. 相似文献
10.
Atlam Mostafa Torkey Hanaa El-Fishawy Nawal Salem Hanaa 《Pattern Analysis & Applications》2021,24(3):993-1005
Pattern Analysis and Applications - Coronavirus (COVID-19) is one of the most serious problems that has caused stopping the wheel of life all over the world. It is widely spread to the extent that... 相似文献