A simple method for preparation of polymer microcellular foams by in situ generation of supercritical carbon dioxide from dry ice

In this work, poly(methyl methacrylate) (PMMA) and PMMA/nanoclay nanocomposite microcellular foams were successfully prepared using a simple method based on in situ generation of supercritical carbon dioxide (CO₂) from dry ice. The method was compared with conventional methods exempted from high pressure pump and a separate CO₂ tank. Effect of various processing conditions such as saturation temperature and pressure and clay concentration on cellular morphology and hardness of the prepared microcellular foams was examined. State of the clay dispersion in the prepared PMMA/clay nanocomposites was characterized using X-ray diffraction and transmission electron microscopy techniques. Field emission scanning electron microscopy was used to study cellular morphology of the prepared foams. It was observed that elevation of saturation temperature from 85 to 105 °C at constant saturation pressure increased cell density and decreased average cell size of the prepared PMMA foams. Furthermore, an increase in saturation pressure from 120 to 180 bar resulted in a reduction in average cell diameter and an increase in cell density of the prepared PMMA foams. On the basis of the gathered results, optimum conditions for preparation of PMMA microcellular foams were determined and applied for preparation of PMMA/nanoclay microcellular foams. It was shown that incorporation of clay into the polymer matrix resulted in a finer and more uniform cellular morphology in the final microcellular foams. It was also observed that incorporation of nanoclay into the prepared foams, up to 3 wt%, led to a moderate increase in the foam hardness.     

The effect of carbon black and HALS hybrid systems on the UV stability of high-density polyethylene (HDPE)

In the present study, attempts were made to study the effect of a hybrid UV stabilizing system on high-density polyethylene (HDPE). For this purpose, high molecular weight PE was used to prepare samples containing different amounts of hindered amine light stabilizer (HALS), carbon black (CB) and HALS/CB systems as UV stabilizers. All samples were exposed to UV irradiation simulating 4 and 8 years of exposure to solar irradiation in central part of Iran (Yazd). FTIR results were used to estimate the carbonyl index (CI) of the samples. It showed that CI increased as UV exposure time increased. However, it was found out that in the samples having both stabilizers (HALS/CB), CI value was much less compared to other samples indicating that the presence of hybrid system would show a synergism effect on UV stabilization of HDPE. The gel content of all samples was measured and it confirmed the same results. The PECH sample (containing HALS and CB) showed the least gel content after equivalent time of 4 and 8 years of exposure (2 and 3.5 wt%, respectively) which was in accordance with CI result. Furthermore, the effect of different UV stabilizing systems on the mechanical properties of HDPE was studied. For this purpose, elastic modulus, elongation-at-break and yield stress of the samples were measured. It was found out that HALS/CB hybrid system preserved the mechanical properties of HDPE much better than the other systems, which was attributed to the synergistic effect of the simultaneous use of HALS and CB.     

Recording duration of ambient vibration monitoring for system identification of tall telecommunication towers

It is necessary to have reliable field measurement records for estimation of dynamic characteristics. Increasing duration of the record is one of the common methods for reduction of such errors in the results. Dynamic characteristics of telecommunication towers in higher modes are important for designers, but these parameters could be obtained from ambient vibration monitoring during typhoons in which duration of vibration is not long enough for reducing measurement errors. This paper suggests a procedure for obtaining the duration of recording time for more reliable determination of structural characteristics of telecommunication towers. It is suggested to record the vibration of towers in the form of a set of long‐term and short‐term duration recordings for lower and higher modes, respectively. This procedure was verified with field measurement of Milad telecommunication tower. The results show that natural frequencies determined by this procedure are in good agreement with finite element model analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

PSO-ANFIS modeling of viscosity for mixtures of Athabasca bitumen and a high-boiling n-alkane

The bitumen and heavy oil reservoirs are more in number than light crude oil reservoirs in the world. To increase the empty space between molecules and decrease viscosity, the bitumen was diluted with a liquid solvent such as tetradecane. Due to the sensitivity of enhanced oil recovery process, the accurate approximation for the viscosity of mentioned mixture is important. The purpose of this study was to develop an effective relation between the viscosity of Athabasca bitumen and heavy n-alkane mixtures based on pressure, temperature, and the weight percentage of n-tetradecane using the adaptive neuro-fuzzy inference system method. For this model, the value of MRE and R² was obtained as 0.34% and 1.00, respectively; so this model can be applied as an accurate approximation for any mixture of heavy oil with a liquid solvent.     

Characterization of uncertainty (probabilistic models) in verification of unreinforced masonry shear wall / Charakterisierung der Unschärfe (probabilistische Modelle) beim Nachweis von Wandscheiben aus unbewehrtem Mauerwerk

The model uncertainty has significant role in determination of safety factor. Eurocode has been considered partial factor covering uncertainties in the resistance model. Moreover, the model uncertainty has important role in full probabilistic verification. A stochastic analysis may yield to realistic results, only if the uncertainties have been involved in the calculation, properly. The uncertainty in predicted load‐carrying model may be identified by comparing the observed (experimental records) load‐carrying behaviour with the predicted value. Some general recommendations for considering uncertainty in probabilistic verifications are available in literature. In this study, the deviation of predicted values according to DIN EN 1996‐1‐1/NA model of masonry shear wall from test results has been derived. The best‐fitted distribution with associated statistical parameters (type of distribution, mean and coefficient of variation) has been proposed for uncertainty model. The uncertainty models have been compared with recommendations in the literature.     

4 × 10 Gbps WDM repeaterless transmission system using asymmetrical dispersion compensation for rural area applications

We demonstrate experimentally 4?×?10 Gbps wavelength division multiplexing repeaterless transmission system using non-return-to-zero differential phase-shift keying modulation format over 300-km standard single-mode fiber. The channels used were 1546.9, 1547.7, 1548.51 and 1549.2 nm with 100 GHz spacing. In this system design, a dispersion compensation module is used; multi-channel-chirped fiber Bragg grating was deployed with asymmetrical configuration with different compositions of dispersion values at the transmitting and the receiving sides. The transmission system was pumped bidirectionally with 1445 and 1455 nm wavelength in a forward direction, and three pump wavelengths of 1430, 1440 and 1450 nm are deployed for the backward direction. The total on–off Raman gain is 47 dB from total pump power of 1.862 W. The result for dispersion pre-compensation of ??2006.0 and ??2338.3 ps/nm has minimal effect on nonlinearity showing the best performance for 300-km repeaterless transmission system.     

Equivalence of the Lagrange interpolator for uniformly sampled signals and the scaled binomially windowed shifted sinc function

The maximally flat (MF) fractional delay (FD) filter which is in fact a Lagrange interpolator for uniformly sampled signals, has previously been shown to be equal to the scaled binomially windowed shifted version of the sinc function; the ideal interpolation kernel for band-limited signals. In this paper, another proof for this equivalence is presented. Unlike its counterparts available in the literature, the proof given here is neither strictly algebraic, nor deploys the explicit coefficient formulas of the MFFD filter. It follows a frequency domain approach based on the definition of this filter instead, and aims to provide more insight into the corresponding equivalence.     

Calculations of ~(86)Y production via various nuclear reactions

This study obtains a suitable reaction to produce ~(86)Y. The ~(86)Y excitation functions via ~(86)Sr(p,n)~(86)Y,~(86)Sr(d,2n)~(86)Y, ~(85)Rb(~3He,2n)~(86)Y and ~(85)Rb(α,3n)~(86)Y reactions were calculated by TALYS-1.0 code and compared with the reported measurement. Requisite thickness of targets was obtained by SRIM code for each reaction. The ~(86)Y production yield was evaluated with attention to excitation function and stopping power. The ~(86)Sr(p,n)~(86)Y reaction was determined as most interesting one due to its highest production yield and advantages to get high radionuclide and radiochemical purity.     

Synthesis of YVO<Subscript>4</Subscript>:Eu<Superscript>3+</Superscript> Nanophosphors Through the Use of Urea and Aniline Fuels and Study of Their Microstructures and Optical Properties

In this paper, YVO₄:Eu³⁺ nanophosphors were synthesized via the simple combustion method by urea and aniline, individually. The particle size of produced powders and the combustion flame temperature were explained in thermodynamic terms. These phosphors were characterized by X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, field emission scanning electron microscope and photoluminescence (PL) analyses. It was concluded that the amounts of released gas, adiabatic flame temperature, remaining compounds after combustion reaction, size of powders and optical properties depended strongly on the used combustion fuel. Also, the PL intensity of the phosphors synthesized by aniline was remarkably higher than that of phosphors synthesized by urea.     

A new general approach to determine more accurate comonomer reactivity ratios in controlled/living radical copolymerization systems

In controlled/living radical copolymerization (atom transfer radical copolymerization in this study) and in any other living chain‐growth copolymerization, the possible preferential addition of one of the comonomers onto the (macro)initiator‐derived (macro)radical can affect the copolymer composition, especially at low conversion; this results in inaccurate comonomer reactivity ratio estimation by the classic approach. A new general approach is introduced in this article, which allowed us to exclude the influence of the possible preferential addition of one of the comonomers onto the (macro)initiator‐derived (macro)radical on the copolymer composition at any conversion. According to this approach, copolymer chain grown during time t (t ≠ 0) is considered to be, in fact, the macroinitiator terminated with one of the comonomers under study, which will further grow during the time interval Δt′ = t′ ? t [where any reaction time t′ is considered to be grater than reaction time t, i.e. t′ > t] from a comonomer mixture with composition of f(t) [where f(t) is the molar ratio of comonomer i to comonomer j in the comonomer mixture] at time t. In such a situation, it is possible to obtain individual comonomer conversions [x_i(Δt′) and x_j(Δt′)], the overall comonomer conversion [x_ov(Δt′)], and the cumulative average copolymer composition for the copolymer formed during Δt′, from which more accurate comonomer reactivity ratios can be calculated by the various low‐ or high‐conversion methods, depending on the overall comonomer conversion. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011