Ablation behavior of elastomeric insulator based on nitrile rubber containing silica or silica-clay aerogels

Iranian Polymer Journal - Nitrile-based nanocomposite heat insulators are very attractive materials, due to their higher deformation bearing in special applications such as high temperature and...     

Thermo-responsive nanocarrier based on poly(N-isopropylacrylamide) serving as a smart doxorubicin delivery system

Iranian Polymer Journal - Smart temperature- and pH-responsive nanocarriers could be considered as potent vehicle in drug delivery systems. By this means, a thermo-responsive polymeric nanocarrier...     

Toward the design of robust multilayer graphene: mechanistic understanding of the role played by interlayer interactions

Journal of Materials Science - In the literature, while the mechanical responses of multilayer graphene have been investigated during uniaxial tensile stretch and nanoindentation tests, fundamental...     

A Novel Framework for Urban Flood damage Assessment

Water Resources Management - In the current study, a novel method is proposed to analyze the simultaneous impacts of non-stationarity in hydrological time series and land-use changes in urban areas...     

Modeling of the Fischer–Tropsch process using a Fe–Cu–K catalyst

In a bid to increase Fischer–Tropsch product selectivity, inorganics substances, such as copper, potassium, and others, were added to the catalyst. Although this approach in Fischer–Tropsch synthesis is very important, it has not been discussed widely. Isothermal product models in this type of synthesis and effective parameters are the same as pressure, while the H₂/CO feed ratio and space velocity have been studied over the spray-dried Fe–Cu–K catalyst by using statistical methods with experimental data. P = 1.0–2.5 MPa, H₂/CO feed ratio = 0.6–2.0, and space velocity = 0.07–0.1 1/h are the range of operating conditions in the spinning basket reactor. The experiment was carried out at a constant temperature of 523 K. The models can predict the reaction's product. Through these the optimal conditions in the reactor models can be determined, while the maximum and minimum amounts of products for oil, wax, and water are obtained under the optimized conditions. The models showed that the interaction between parameters played a key role. The main interactions for products are pressure and space velocity.     

Analysis of pressure fluctuations in fluidized beds. II. Reconstruction of the data by the Fokker–Planck and Langevin equations

In this part of the sequel we develop a continuum representation of the pressure fluctuation time series p(t) for a fluidized bed (FB), analyzed in part I, by using stochastic methods based on the Markov processes. It is shown that the data may be represented by Markov series with a Markov time scale t_M that is estimated based on the data. Using the relation between the Markov processes and the Kramers–Moyal (KM) expansion that is a continuum equation that involves, in principle, an infinite number of coefficients, we represent the pressure fluctuation time series by a KM expansion. However, since the third and higher-order coefficients of the expansion are very small, the KM expansion reduces to a Fokker–Planck (FP) equation that represents p(t) in terms of a drift and a diffusion coefficients that are computed based on the data. The FP equation is, in turn, equivalent to a Langevin equation, which is used to reconstruct the data, i.e. generate the time series that mimic, in a statistical sense, the original data. Thus, the Langevin equation may also be used to make probabilistic predictions for the future values of the pressure over time scales that are of the order of the Markov time scale t_M. The accuracy of the reconstructed series and, hence, their continuum representation, is demonstrated. We also compute the frequency of level-crossing at a given level α, i.e. the relative frequency (probability) of occurrence of the event defined, for two times t_i−1 and t_i, by, , where P(x) is the probability of the event. Thus, yields the frequency that a given pressure fluctuation level may be expected. The average time that one should wait in order to observe the pressure at a given level again is also computed. The two quantities may be particularly important for modeling of the FBs. A relation is presented between the drift and diffusion coefficients of the FP equation and the Hurst exponent that has previously been used to describe the pressure fluctuation time series in terms of self-affine stochastic distributions.     

Synthesis,characterization, and properties of co-poly(ether–urethane–urea)s containing lariat cryptand 22: Li<Superscript>+</Superscript> harvesting polymers

In this work, some segmented poly(ether–urethane–urea)s (PEUUs) containing aza crown ether (cryptand) were prepared and characterized. These polymers were synthesized via the reaction of kryptofix 22 with 2 mol excess of 4,4′-methylene-bis-(4-phenylisocyanate) (MDI), and different molecular weights of polyethylene glycols (PEGs). Morphology, thermal, and complexation properties of these polymers were studied by Fourier-transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), atomic absorption spectroscopy (AAS), and solid state NMR (S-NMR). The data confirmed complexation ability of these polymers for Li⁺ ion absorption and revealed the effect of Li⁺ ion complexation on the morphology and thermal behavior of the PEUUs.     

Stochastic game theoretical model for packet forwarding in relay networks

In this article, a new game theoretical method is proposed to model packet forwarding in relay networks. A simple case of relay network that consists of a source, a relay and a destination node communicating on a common channel is considered. A stationary Markovian game model is utilized to optimize the system performance in terms of throughput, delay and power consumption cost. Both cooperative and non-cooperative solutions are provided for this model. Best strategy set taken by players as well as system performance is studied for different system parameters. Also, the proposed method is extended to model a more general case of Ad-hoc networks considering different packet error rates in case of collision occurrence that improves the system performance further. Simulation results show that performance of the non-cooperative solution, in which players do not require to know each other’s selected strategy, asymptotically approaches the cooperative system performance. Hence, the proposed model with non-cooperative solution is an appropriate method to apply in practical Ad-hoc networks.     

An experimental investigation of pool boiling characteristics of alumina-water nanofluid over micro-/nanostructured surfaces

Abstract

Experiments were conducted to investigate the nucleate pool boiling heat transfer of pure water and alumina/water nanofluids on different micro- and nanostructured surfaces prepared via the thermal spray coating method. Results indicate that nanofluids boiling on all the test surfaces led to critical heat flux (CHF) values greater than that obtained for the base fluid (i.e., water). Higher roughness value, however, led to higher CHF values in boiling over the surfaces. Another finding of this study indicated that CHF values obtained with boiling on Cu-coated micro- and nanosurfaces were identical although the heat transfer coefficient (HTC) values obtained for boiling on the micro-structure surface were higher than those obtained for a nanostructured surface with almost the same roughness. A series of consecutive nanofluid boiling cycles were also performed on the aluminum-coated nanostructured surface. The CHF value obtained for water boiling on the surface undergoing repeated nanofluid boiling cycles was by 27% higher than that obtained for a clean surface although the relevant HTC values were nearly identical.