Approximation of integrable functions based on \phi -transform

Let \(E\) be a bounded subset of real line which contains its infimum and supremum. In this paper, we have defined the \(\phi -\) transform and its inverse, where \(\phi \) is a function from \(E\) into \((0,1]\) . We will have shown that real-valued integrable functions on \([a, b]\) and real-valued continuous functions on \(E\) can be approximated by this transformation with an arbitrary precision.     

New fluorene‐based thermally stable five‐ and six‐membered rings polyimides with enhanced solubility

A novel ester diamine, 9‐(3,5‐diaminobenzoyloxy) fluorene, as a new monomer for preparation of polyimides was synthesized via two successive reactions. In the first step, reaction of 3,5‐dinitrobenzoylchloride with 9‐hydroxy fluorene in the presence of sodium hydroxide led to preparation of 9‐(3,5‐dinitrobenzoyloxy) fluorene. Second reaction was reduction of the nitro groups by tin (II) chloride and fuming hydrochloric acid to produce 9‐(3,5‐diaminobenzoyloxy) fluorene. The new diamine containing bulky fluorene group was characterized and polycondensed with different dianhydrides via two methods to produce polyimides. The new five‐membered and six‐membered ring polyimides were characterized and their properties including solubility behavior, inherent viscosity, thermal behavior and stability, and crystallinity were studied. They exhibited favorable balance of physical and thermal properties and their solubility were improved without sacrificing their thermal stability. Six‐membered rings polyimides showed higher thermal stability and lower solubility in comparison to related five‐membered ring polyimides. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and properties of novel thermally stable pyridine‐based poly(amide imide amide)s

The 2,6‐bis(4‐nitrobenzamido)pyridine was prepared via reaction of 2,6‐diaminopyridine with two moles of 4‐nitrobenzoyl chloride in the presence of propylene oxide. Catalytic reduction of nitro groups of 2,6‐bis(4‐nitrobenzamido)pyridine with hydrazine yielded 2,6‐bis(4‐aminobenzamido)pyridine. Reaction of this diamine with two moles of trimellitic anhydride afforded a diacid with preformed amide and imide structures. Poly(amide imide amide)s were prepared by direct polycondensation reactions of the diacid with different diamines in the presence of triphenyl phosphite. All the precursors and polymers were fully characterized using common spectroscopic methods and elemental analysis and physical properties of the polymers including solution viscosity, thermal stability, thermal behavior, and solubility were studied. According to the obtained results the polymers showed high thermal stability and enhanced solubility. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Plasma effects in semiconducting nanowire growth

Three case studies are presented to show low-temperature plasma-specific effects in the solution of (i) effective control of nucleation and growth; (ii) environmental friendliness; and (iii) energy efficiency critical issues in semiconducting nanowire growth. The first case (related to (i) and (iii)) shows that in catalytic growth of Si nanowires, plasma-specific effects lead to a substantial increase in growth rates, decrease of the minimum nanowire thickness, and much faster nanowire nucleation at the same growth temperatures. For nucleation and growth of nanowires of the same thickness, much lower temperatures are required. In the second example (related to (ii)), we produce Si nanowire networks with controllable nanowire thickness, length, and area density without any catalyst or external supply of Si building material. This case is an environmentally-friendly alternative to the commonly used Si microfabrication based on a highly-toxic silane precursor gas. The third example is related to (iii) and demonstrates that ZnO nanowires can be synthesized in plasma-enhanced CVD at significantly lower process temperatures than in similar neutral gas-based processes and without compromising structural quality and performance of the nanowires. Our results are relevant to the development of next-generation nanoelectronic, optoelectronic, energy conversion and sensing devices based on semiconducting nanowires.     

Nonlinear vibration and rippling instability for embedded carbon nanotubes

Based on the rippling deformations, a nonlinear continuum elastic model is developed to analyze the transverse vibration of single-walled carbon nanotubes (SWCNTs) embedded on a Winkler elastic foundation. The nonlinear natural frequency has been derived analytically for typical boundary conditions using the perturbation method of multi-scales. The results indicate that the nonlinear resonant frequency due to the rippling is related to the stiffness of the foundation, the boundary conditions, the excitation load-to-damping ratio, and the diameter-to-length ratio. Moreover, the rippling instability of carbon nanotubes, as a structural instability, is introduced and the influences of several effective parameters on this kind of instability are widely discussed.     

Miniaturised coplanar waveguide-fed antenna and band-notched design for ultra-wideband applications

A miniaturised coplanar waveguide-fed ultra-wideband (UWB) antenna is presented here. The wideband operation is obtained through an optimised curvature of the radiating element. The input impedance of the antenna is matched using an elliptically tapered coplanar waveguide line. A high-band rejection characteristic at wireless local area network frequencies is achieved by inserting an v-shaped slot on the antenna surface. The frequency domain dispersion characteristic is studied by means of the antenna transfer function both numerically and experimentally. Time domain characteristic of the antenna is investigated in detail for both UWB single-band and multiband schemes. In order to efficiently characterise the antenna system for an arbitrary pulse source excitation, the pole/residue model of the antenna system transfer function is presented using the matrix-pencil method.     

Equation of State for Molten Alkali Metals from Surface Tension. Part II

This work presents a new method for predicting the equation of state for molten alkali metals, based on statistical–mechanical perturbation theory from two scaling constants that are available from measurements at ordinary pressures and temperatures. The scaling constants are the surface tension and the liquid density at the boiling temperature (_b, _b). Also, a reference temperature, T _Ref, is presented at which the product (T _Ref T _b ^1/2 ) is an advantageous corresponding temperature for the second virial coefficient, B ₂(T). The virial coefficient of alkali metals cannot be expected to obey a law of corresponding states for normal fluids, because two singlet and triplet potentials are involved. The free parameter of the Ihm–Song–Mason equation of state compensates for the uncertainties in B ₂(T). The vapor pressure of molten alkali metals at low temperatures is very low and the experimental data for B ₂(T) of these metals are scarce. Therefore, an equation of state for alkali metals from the surface tension and liquid density at boiling temperature (_b, _b) is a suitable choice. The results, the density of Li through Cs from the melting point up to several hundred degrees above the boiling temperature, are within 5%.     

Optimization using simulation and response surface methodology with an application on subway train scheduling

This paper presents a technique based on discrete‐event simulation and response surface methodology to model and then optimize the schedule of subway train travels. The aim of this study is to find appropriate headways—time intervals between the travels of two consecutive trains—at different hours in order to optimize average passenger travel time and rate of carriage fullness. For physical reasons and the observance of safety standards, an increase in the train speed in order to decrease average passenger travel time may not exceed some specified limits. One of the ways to decrease this average is to appropriately adjust headways of trains in the schedule. For this purpose, a metamodel of multinomial type is fitted to the data obtained from simulation tests to describe the relation between input variables (headways) and output variables (average passenger travel time in system and carriage fullness rate), and then optimal combinations of input variables are obtained using a weighed metric method and sequential quadratic programming.     

Comparison of Direct and Indirect Measurements of the Saturation Magnetization of Barium Hexaferrite Synthesized by Coprecipitation

This paper compares the magnetic properties of barium hexaferrite (BaM) powder synthesized by the coprecipitation method as determined by two- magnon scattering theory (microwave spectroscopy) and a direct method (vibrating-sample magnetometry). The microstructural, structural, loss, and magnetic properties were measured by x-ray diffractometry, field-emission scanning electron spectroscopy, network analysis, and vibrating-sample magnetometry, respectively. By using the two-magnon scattering theory and the reflection loss data, the saturation magnetization was calculated. The results revealed that the saturation magnetization determined by the use of the two-magnon scattering theory is about 54.75 emu/g, which closely conforms to the experimental value of 55.00 emu/g obtained using vibrating-sample magnetometry.