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排序方式: 共有261条查询结果,搜索用时 15 毫秒
21.
Syed Mustafa Muhammad Waseem Abdul Naeem Khizar Hussain Shah Tauqeer Ahmad Muhammad Safdar 《中国化学》2010,28(11):2204-2208
The current study focuses on the synthesis and sorption properties of two mixed oxides of iron and silicon prepared by physical mixing (M1) and sequential precipitation methods (M2). Both the mixed oxides were synthesized from equimolar ratios of Fe(OH)3 and SiO2 and characterized for surface area, EDX, XRD and PZC. The surface area, micropore volume and average pore width of the oxide M1 were higher as compared to the oxide M2. However, potentiometric titrations revealed that mixed oxide synthesized by this method had a very high capacity towards Cd2+ ions as compared to the mixed oxide M1. Sorption of Cd2+ ions at pH 5 on mixed oxide, M2 was found to increase with temperature in the range 288 to 318 K. Langmuir equation was found applicable to the sorption data with R2>0.99. Entropy (ΔS?), enthalpy (ΔH?) and free energy changes (ΔG?) were calculated which revealed the process to be endothermic and spontaneous in nature. 相似文献
22.
Chromium(III) sorption on macroporous strong cation exchanger Amberlyst‐15 (H+) was studied as a function of time and temperature. The rate constant values for chromium(III) sorption were calculated both for film and particle diffusion processes. The temperature was found to have a positive effect on both the diffusional processes. From the rate constant values, the energy of activation was calculated using the well‐known Arrhenius equation. The high values of energy of activation confirmed the film diffusional nature of the process. Equilibrium data were explained with the help of Langmuir equation. Various thermodynamic parameters (ΔH?, ΔS? and ΔG?) from chromium(III) exchange on the resin were calculated. The ΔG? values were found to be negative while both the ΔH? and ΔS? were positive. 相似文献
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24.
A molecular thermodynamic model for polyelectrolyte systems—called pePC-SAFT—is proposed. The effect of charged monomers within the polyelectrolyte chain is explicitly taken into account in the reference term by replacing the hard-chain contribution of the PC-SAFT model by a charged-hard-chain contribution. Moreover, counterion condensation is accounted for to determine the effective number of charges along the polyion as well as of free counterions. The electrostatic contribution of the free counterions is described by a Debye–Hückel term. 相似文献
25.
Javed Ahmad Muhammad Ehsan MazharMuhammad Qadeer Awan Muhammad Naeem Ashiq 《Physica B: Condensed Matter》2011,406(18):3484-3488
Potassium substituted nanosized magnesium aluminates having a nominal composition Mg1−xKxAl2O4 where x=0.0, 0.25, 0.5, 0.75, 1.0 have been synthesized by the chemical co-precipitation method. The samples have been characterized by means of X-ray diffraction (XRD), scanning electron microscope (SEM), and dc electrical resistivity measurements. The XRD results reveal that the samples are spinel single phase cubic close packed crystalline materials. The calculated crystallite size ranges between 6 and 8 nm. The behaviour of the lattice constant seems to deviate from the Vegard's law. While X-ray density clearly increases, the bulk density and consequently, the percentage porosity do not exhibit a significant change on increasing the K+ content. The SEM micrographs suggest homogeneous distribution of the nanocrystallites in the samples. The dc electrical resistivity exhibits a typical semiconducting behaviour. Substitution of a Mg2+ ion by a K+ ion provides an extra hole to the system, which forms small polaron. Thermally activated hopping of these small polarons is believed to be the conduction mechanism in the Mg1−xKxAl2O4. The activation energy of hopping of small polarons has been calculated and found K+ ions content dependent. 相似文献
26.
27.
Naeem Jan 《Journal of statistical physics》1994,77(3-4):915-917
A Monte Carlo simulation of the Partridge-Barton model is presented which in a limiting case gives extreme senescence in the sense of immediate death after sexual maturity. 相似文献
28.
Mehwish Iqtedar Mohammad Nadeem Hira Naeem Roheena Abdullah Shagufta Naz Qurat ul Ain Syed 《Natural product research》2015,29(11):1012-1019
The industrialisation of lignocellulose conversion is impeded by expensive cellulase enzymes required for saccharification in bioethanol production. Current research undertakes cellulase production from pretreated Saccharum spontaneum through Trichoderma viride HN1 under submerged fermentation conditions. Pretreatment of substrate with 2% NaOH resulted in 88% delignification. Maximum cellulase production (2603 ± 16.39 U/mL/min carboxymethyl cellulase and 1393 ± 25.55 U/mL/min FPase) was achieved at 6% substrate at pH 5.0, with 5% inoculum, incubated at 35°C for 120 h of fermentation period. Addition of surfactant, Tween 80 and metal ion Mn+2, significantly enhanced cellulase yield. This study accounts proficient cellulase yield through process optimisation by exploiting cheaper substrate to escalate their commercial endeavour. 相似文献
29.
Shahid Hussain Arshad Muhammad Nawaz Naeem Nazra Sultana Zafar Iqbal Abdul Ghafar Shah 《Archive of Applied Mechanics (Ingenieur Archiv)》2011,81(8):999-1016
In the present work, vibration characteristics of thin functionally graded cylindrical shells are studied under the influence
of various boundary conditions. Fabrication of FGM cylindrical shell is carried out by using exponential volume fraction law.
Strain- and curvature-displacements relationships are taken from Love’s thin shell theory. The frequency equation in the form
of eigenvalue problem is obtained by adapting the Rayleigh-Ritz method. Characteristic beam functions are assumed to approximate
the axial modal dependence. Effects of exponential volume fraction law on the natural frequencies of the FGM cylindrical shells
for various boundary conditions are studied against circumferential wave number, length to radius ratio and thickness to radius
ratio for different values of power law exponents. Results evaluated show good agreement with those available in the literature. 相似文献
30.
I. Naeem 《Journal of Mathematical Analysis and Applications》2008,342(1):70-82
We obtain Noether and partial Noether operators corresponding to a Lagrangian and a partial Lagrangian for a system of two linear second-order ordinary differential equations (ODEs) with variable coefficients. The canonical form for a system of two second-order ordinary differential equations is invoked and a special case of this system is studied for both Noether and partial Noether operators. Then the first integrals with respect to Noether and partial Noether operators are obtained for the linear system under consideration. We show that the first integrals for both the Noether and partial Noether operators are the same. This can give rise to further studies on systems from a partial Lagrangian viewpoint as systems in general do not admit Lagrangians. 相似文献