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991.
Masoud Bodaghi Hesam Zolfonoon Mohammadreza Tahriri Meysam Karimi 《Solid State Sciences》2009,11(2):496-500
In this present work, the synthesis of nanocrystalline α-Al2O3 using pure aluminum (Al) and Fe2O3 (hematite) as the precursors by mechanical alloying technique has been studied. The formation of α-Al2O3 nanocrystallites occurs during the solid-state reaction and through the reduction treatment. Also in this paper, effects of milling time on particle size and the lattice strain nanocrystalline α-Al2O3 have been investigated. Obtained powders were evaluated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential thermal analysis (DTA), thermal gravimetric analysis (TGA) and X-ray diffraction (XRD). The obtained results indicated that a reduction reaction was completed after 2 h milling in a planetary mill. The crystallite size of obtained α-alumina (α-Al2O3) was in general about 12 nm. Finally, the results showed appropriate homogeneity and dispersion of related nanocrystalline. 相似文献
992.
Adel Mostafa Hassan S. Bazzi 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,74(1):180-187
The interactions of the electron donors 2-aminopyridine (2APY) and 3-aminopyridine (3APY) with the π-acceptors tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), 2-chloro-1,3,5-trinitrobenzene (picryl chloride, PC), and 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil) were studied spectrophotometrically in chloroform at room temperature. The electronic and infrared spectra of the formed molecular charge transfer (CT) complexes were recorded. Photometric titration showed that the stoichiometries of the reactions were fixed and depended on the nature of both the donor and the acceptor. The molecular structures of the CT-complexes were, however, independent of the position of the amino group on the pyridine ring and were formulated as [(APY)(TCNE)], [(APY)(DDQ)], [(APY)(PC)], and [(APY) (chloranil)]. The formation constants (KCT), charge transfer energy (ECT) and molar extinction coefficients (CT) of the formed CT-complexes were obtained. 相似文献
993.
Abdollah Salimi Mohadeseh Izadi Rahman Hallaj Saied Soltanian Hassan Hadadzadeh 《Journal of Solid State Electrochemistry》2009,13(3):485-496
A simple procedure was developed to prepare a glassy carbon electrode modified with carbon nanotubes and Ruthenium (III) complexes.
First, 25 μl of dimethyl sulfoxide–carbon nanotubes solutions (0.4 mg/ml) was cast on the surface of the glassy carbon electrode
and dried in air to form a carbon nanotube film at the electrode surface. Then, the glassy carbon/carbon nanotube-modified
electrode was immersed into a Ruthenium (III) complex solution (direct deposition) for a short period of time (10–20 s for
multiwalled carbon nanotubes and 20–40 s for single-walled carbon nanotubes). The cyclic voltammograms of the modified electrode
in aqueous solution shows a pair of well-defined, stable, and nearly reversible redox couple, Ru(III)/Ru(II), with surface-confined
characteristics. The attractive mechanical and electrical characteristics of carbon nanostructures and unique properties and
reactivity of Ru complexes are combined. The transfer coefficient (α), heterogeneous electron transfer rate constants (k
s), and surface concentrations (Γ) for the glassy carbon/single-walled carbon nanotubes/Ru(III) complex-, glassy carbon/multiwalled carbon nanotubes/Ru(III)
complex-, and glassy carbon/Ru(III) complex-modified electrodes were calculated using the cyclic voltammetry technique. The
modified electrodes showed excellent catalytic activity, fast response time, and high sensitivity toward the reduction of
nicotinamide adenine dinucleotide in phosphate buffer solutions at a pH range of 4–8. The catalytic cathodic current depends
on the nicotinamide adenine dinucleotide concentration. In the presence of alcohol dehydrogenase, the modified electrode exhibited
a response to addition of acetaldehyde. Therefore, the main product of nicotinamide adenine dinucleotide electroreduction
at the Ru(III) complex/carbon nanotube-modified electrode was the enzymatically active NADH. The purposed sensor can be used
for acetaldehyde determination. 相似文献
994.
Richard M. Slevinsky Hassan Safouhi 《Journal of Computational and Applied Mathematics》2009,233(2):405-419
We present new formulae (the Slevinsky–Safouhi formulae I and II) for the analytical development of higher order derivatives. These formulae, which are analytic and exact, represent the kth derivative as a discrete sum of only k+1 terms. Involved in the expression for the kth derivative are coefficients of the terms in the summation. These coefficients can be computed recursively and they are not subject to any computational instability. As examples of applications, we develop higher order derivatives of Legendre functions, Chebyshev polynomials of the first kind, Hermite functions and Bessel functions. We also show the general classes of functions to which our new formula is applicable and show how our formula can be applied to certain classes of differential equations. We also presented an application of the formulae of higher order derivatives combined with extrapolation methods in the numerical integration of spherical Bessel integral functions. 相似文献
995.
Hassan Salarieh Aria Alasty 《Communications in Nonlinear Science & Numerical Simulation》2009,14(3):637-644
Active chaos control of a tapping mode atomic force microscope (AFM) model via delayed feedback method is presented. The feedback gain is obtained and adapted according to a minimum entropy (ME) algorithm. In this method, stabilizing an unstable fixed point of the system Poincare map is achieved by minimizing the entropy of points distribution on the Poincare section. Simulation results show the feasibility of the proposed method in applying the delayed feedback technique for chaos control of an AFM system. 相似文献
996.
Abdelaziz Kacha My Hassan Hbid Rafael Bravo de la Parra 《Nonlinear Analysis: Real World Applications》2009,10(3):1662-1678
In this paper, we propose a mathematical model to study a bacteria–fish system, based upon the interactions between Clostridium botulinum and tilapia, Oerochromis mossambicus. The fish population is divided into susceptible and infected, and the infected fish population is considered structured by the level of infection. The model is thus a system with the infected fish equation being an evolution equation, while those corresponding to the susceptible fish and bacteria in water are ordinary differential equations. The model is firstly transformed into a system with distributed delay for susceptible fish and bacteria and, further, under some assumptions, into a system with discrete delay. The study of this system gives us some results concerning the existence, uniqueness, positivity and boundedness of solutions; we also discuss the existence and stability of its equilibrium points, including conditions for the appearance of Hopf bifurcation. The theoretical results are illustrated by some numerical simulations. 相似文献
997.
Carn F Saadaoui H Massé P Ravaine S Julian-Lopez B Sanchez C Deleuze H Talham DR Backov R 《Langmuir : the ACS journal of surfaces and colloids》2006,22(12):5469-5475
The synthesis of novel meso-/macroporous SiO2 monoliths by combining a nano-building-blocks-based approach with the confined geometry of a tailored air-liquid foam structure is described. The resulting macrostructure in which ordered close-packed colloidal silica nanoparticles constitute the monolith's scaffolds very closely resembles the tailored periodic air-liquid foam template. The void spaces between adjacent particles create textural mesoporosity; therefore, the as-prepared silica networks are characterized by hierarchical porosity at the macroscopic and mesoscopic length scales. The fine-tuning of both the liquid foam's fraction and the bubble size allows a rational design over the macroscopic cell morphologies (shape, Plateau border's length, and width). Striking results of this approach are the weak shrinkage of the as-synthesized opal-like scaffolds during the thermally induced sintering process and, in contrast with previous studies, the formation of closed-cell structures. Particle organization and the foam film surface roughness are investigated by atomic force microscopy (AFM), showing the influence of the liquid flow, within the foams' Plateau borders and films, on the final assemblies. 相似文献
998.
We describe the conformation and stereospecific 1H and 13C chemical shift assignments of longifolene 1 and its penultimate precursor 2 through the combined use of ab initio calculations and experimental NMR techniques. The predicted stable conformation for both compounds was similar and adopts a twisted chair conformation at the seven-membered ring where C4 lies on top of the exocyclic double bond. The calculated chemical shifts for the stable conformation agree well with the experimental values. 相似文献
999.
Gull N Kumar S Ahmad B Khan RH Kabir-ud-Din 《Colloids and surfaces. B, Biointerfaces》2006,51(1):10-15
The present study highlights the fact that the effect of additives (urea, monomethylurea, thiourea) on the supramolecular assemblies and proteins is strikingly similar. To investigate the effect, a viscometeric study on sphere-to-rod transition (s-->r) was undertaken in a system (3.5% tetradecyltrimethylammonium bromide+0.05 M NaBr + 1-pentanol [P.M. Lindemuth, G.L. Bertand, J. Phys. Chem. 97 (1993) 7769]) in the presence and absence of the said additives. [1-pentanol] needed for s-->r (i.e. [1-pentanol]s-->r) was determined from the relative viscosity versus [1-pentanol] profiles. It was observed that the additives preponed as well as postponed s-->r depending upon their nature and concentrations. These effects are explained in terms of increased polarity of the medium and the adsorption ability of urea/monomethylurea on the charged surfactant monomers of the micelle. In case of thiourea, postponement of s-->r was observed throughout which is attributed to its structure. To derive an analogy between micelles and proteins the additive-induced conformational changes of the protein, bovine serum albumin (BSA) was taken to monitor secondary structural changes and tryptophanyl fluorescence. A marked increase in secondary structure (far-UVCD) and increased tryptophanyl fluorescence with a marked blue shift in lambdamax was observed in presence of low concentrations of urea or alkylurea. This indicates that a more compact environment is created in presence of these additives, if added judiciously. Addition of thiourea to BSA caused a marked quenching without any significant change in lambdamax. The large decrease in tryptophanyl emission in presence of low thiourea concentrations seems to be specific and related to thiourea structure as no corresponding changes were observed in urea/alkylurea. All these effects pertaining to protein behavior fall in line with that of morphological observations on the present as well as surfactant systems studied earlier [S. Kumar, N. Parveen, Kabir-ud-Din, J. Phys. Chem. B 108 (2004) 9588]. 相似文献
1000.
Schneider BB Javaheri H Covey TR 《Rapid communications in mass spectrometry : RCM》2006,20(10):1538-1544
The motivation of this work was to study some of the properties of nanoelectrospray operation under conditions where the entire sprayed liquid is vaporized and inhaled into the vacuum system. Under these conditions the desolvation requirements, sampling efficiency, concentration versus mass sensitivity, and molar response characteristics of various compounds were studied. The combined efficiency of ion production from solution and transfer into the vacuum system, referred to as sampling efficiency, is presented under various inlet conditions including different flow rates, solution compositions, and compound types. Under ideal solvent conditions the results for favorable compounds show sampling efficiencies of 70-85% at flows in the range of 50-500 nL/min. Efficiencies were lower for aqueous samples and compounds of different structures gave different molar response factors under these high sampling efficiency conditions. The relative molar response factors are presented in terms of those observed with higher flow rate sources which operate at significantly lower sampling efficiencies. In all cases, operating in this flow regime, the ion count rate was directly proportional to the absolute mass of analyte molecules entering the source. The experimental source used to carry out these studies included gas nebulization to stabilize the electrospray process, a heated laminar flow chamber to enhance desolvation and ion production, and various atmosphere-to-vacuum aperture diameters to maximize ion transfer. 相似文献