A complete VARMA modelling methodology based on scalar components

Abstract. This article proposes an extension to scalar component methodology for the identification and estimation of VARMA models. The complete methodology determines the exact positions of all free parameters in any VARMA model with a predetermined embedded scalar component structure. This leads to an exactly identified system of equations that is estimated using full information maximum likelihood.     

A new feature selection algorithm and composite neural network for electricity price forecasting

In a competitive electricity market, the forecasting of energy prices is an important activity for all the market participants either for developing bidding strategies or for making investment decisions. In this paper, a new forecast strategy is proposed for day ahead prediction of electricity price, which is a complex signal with nonlinear, volatile and time dependent behavior. Our forecast strategy includes a new two stage feature selection algorithm, a composite neural network (CNN) and a few auxiliary predictors. The feature selection algorithm has two filtering stages to remove irrelevant and redundant candidate inputs, respectively. This algorithm is based on mutual information (MI) criterion and selects the input variables of the CNN among a large set of candidate inputs. The CNN is composed of a few neural networks (NN) with a new data flow among its building blocks. The CNN is the forecast engine of the proposed strategy. A kind of cross-validation technique is also presented to fine-tune the adjustable parameters of the feature selection algorithm and CNN. Moreover, the proposed price forecast strategy is equipped with a few auxiliary predictors to enrich the candidate set of inputs of the forecast engine. The whole proposed strategy is examined on the PJM, Spanish and Californian electricity markets and compared with some of the most recent price forecast methods.     

Unsupervised texture segmentation using Gabor filters

This paper presents a texture segmentation algorithm inspired by the multi-channel filtering theory for visual information processing in the early stages of human visual system. The channels are characterized by a bank of Gabor filters that nearly uniformly covers the spatial-frequency domain, and a systematic filter selection scheme is proposed, which is based on reconstruction of the input image from the filtered images. Texture features are obtained by subjecting each (selected) filtered image to a nonlinear transformation and computing a measure of “energy” in a window around each pixel. A square-error clustering algorithm is then used to integrate the feature images and produce a segmentation. A simple procedure to incorporate spatial information in the clustering process is proposed. A relative index is used to estimate the “true” number of texture categories.     

Using 1H‐NMR spectroscopy for the kinetic study of the in situ solution free‐radical copolymerization of styrene and ethyl acrylate

The free‐radical copolymerization of styrene and ethyl acrylate in benzene‐d₆ as the solvent in the presence of benzoyl peroxide as an initiator at 70°C was studied by online ¹H‐NMR spectroscopy. The chemical composition of the copolymer at different reaction times was calculated from the conversion of the monomers to the copolymer, and then the reactivity ratios of styrene and ethyl acrylate were determined at both low and high conversions. Data for the overall monomer conversion versus the time were used to estimate the ratio k_pk_t^?0.5 for different compositions of the initial feed (k_p is the propagation rate constant, and k_t is the termination rate constant). k_pk increased with an increasing molar fraction of ethyl acrylate in the initial feed. The monomer mixture and copolymer compositions versus the overall monomer conversion were calculated with the data of ¹H‐NMR spectra. The incorporation of the styrene monomer into the copolymer structure was more favored than that of the ethyl acrylate monomer. Reducing the molar fraction of styrene in the initial feed intensified this. Drawing the molar fraction of styrene (or ethyl acrylate) in the copolymer chains versus that in the initial feed showed a tendency of the system toward random copolymerization. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Synthesis and characterization of novel biodegradable water dispersed poly(ether-urethane)s and their MWCNT-AS nanocomposites functionalized with aspartic acid as dispersing agent

New biodegradable poly(ether-urethane)s (PEU)s were synthesized via the reaction of L-leucine anhydride cyclo-peptide, polyethylene glycol-1000 and hexamethylene diisocyanate. Then, they were end-functionalized with aspartic acid (AS) as a dispersing agent and were dispersed in water. MWCNTs were also functionalized by AS under microwave irradiation. Polymer/MWCNT-AS composites and polymer/MWCNT-AS water dispersed composites were prepared through an ultrasound-assisted method. We have designed these PEUs with two different structural architectures (PA1and PA2) which can be readily dispersed in water (PA1-D and PA2-D). The structure and properties of the polymers, MWCNTs-AS and PEUs/MWCNTs-AS composites were investigated by FTIR and NMR spectroscopy methods and FE-SEM, TEM and TGA techniques. The particle sizes of the resulting PA1-D and PA2-D dispersions were in the range of 200–300 nm. The results showed that by increasing MWCNT-AS loading, the degradation rate and particle sizes of the dispersed composites decreased, while thermal stability and dispersion stability of the composite systems increased. The degradation tests of polymers and their composites in PBS at 37 °C after 10 days showed weight losses ranging from 23 to 44 and 17–37%, respectively. The cytotoxicity study of polymers using the direct-contact test on L929 mouse fibroblast cell line showed no toxicity. Other properties such as thermal stability, dispersion’s particle size, degradation rate and morphology of the composites were studied, and the effect of simultaneous dispersion of MWCNTs-AS and PEUs in water on the properties of the resulting mixtures was studied. We suggest that these polymers have tunable properties which may potentially be considered for drug carriers’ studies.     

Quantitative characterization of carrier injection across metal–organic interfaces using Bardeen theory

We have investigated the contact between a metal and an organic/polymeric (o/p) material and we have introduced a relation for carrier injection using Bardeen theory. A series of narrow barriers is considered in the semiconductor side to account for the localized nature of the carriers in the o/p material. As an application of the model, we have calculated the hopping rate of carriers in terms of the contact parameters. Also, we have discussed the hopping of carriers deep into the organic dielectric. Finally, we have explored the hopping rate in practical contacts between polyfluorene-based polymers and different electrodes.     

Thermosensitive folic acid-targeted poly (ethylene-<Emphasis Type="Italic">co</Emphasis>-vinyl alcohol) hemisuccinate polymeric nanoparticles for delivery of epirubicin to breast cancer cells

A novel thermosensitive folic acid (FA)-targeted succinylated poly (ethylene-co-vinyl alcohol) (EVOH) (EVOHS-FA) nanocarrier was synthesized for the specific delivery of epirubicin (EPI) to MCF-7 breast cancer cell line. Three different ratios of synthesized EVOH-Suc were reacted with FA. The structure of the desired products (EVOHS₄₀-FA, EVOHS₆₀-FA and EVOHS₈₀-FA) was confirmed by ¹H NMR and FTIR techniques. Nanoparticles were obtained by nano-precipitation procedure using DMSO/H₂O as solvent/anti-solvent. The particle size, zeta potential, entrapment efficacy and in vitro release profile of the final formulations in different temperatures were measured. The optimized nanoparticles had the particle size of 214 ± 8.5 nm, zeta potential of ?29.6 mV, PDI of 0.198 ± 0.04, and a high encapsulation efficiency that released the drug efficiently within 450 h at the temperature of 40 °C compared to 37 °C. The morphology of nanoparticles was studied by scanning electron microscopy. The in vitro cytotoxicity was evaluated using the MTT assay on MCF-7 cell lines in response to temperatures of 37 and 40 °C. The MTT assay indicated that the targeted nanoparticles carrying EPI were significantly more cytotoxic than the non-targeted nanoparticles and the free drug at 40 °C.     

Effects of cooling channel blockage on fuel plate temperature in Tehran Research Reactor

In this study, the variation of the temperature distribution of the fuel plate in Tehran Research Reactor core was studied in case of coolant channels blockage. While the experimental method is not possible, both the analytical and simulation methods were used to obtain the more reliable data. The results show that one channel blockage will increase the fuel temperature to about 100%, but it does not lead to clad melt down still. With further calculation and simulation it is understood that if the coolant velocity drops to 90% of its nominal value, it may causes the clad melt-ing down. At least two channels with complete blockage even at the positions far from the core center can also melt down the clad.     

The synthesis of nano-sized ZSM-5 zeolite by dry gel conversion method and investigating the effects of experimental parameters by Taguchi experimental design

In this study ZSM-5 Nano particles with high crystallinity were synthesized using a dry gel conversion technique. An L9 orthogonal array of the Taguchi method was applied to investigate the effect of synthesis parameters, such as crystallization time, gel drying temperature, molar composition of template (TPAOH) and water content in the crystallization stage on crystallinity and particle size of the ZSM-5 catalyst. The products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Beside short crystallization time, the particle sizes were considerably smaller in comparison with those prepared using the hydrothermal method. The results showed that the particle size and crystallinity increased with increasing water content and crystallization time. The effects of gel drying temperature and molar composition of template were found to be more complex, however. Comparing to hydrothermal method, ZSM-5 samples synthesized with the dry gel conversion exhibited higher selectivity to gasoline than other hydrocarbons.     

Fullerene: biomedical engineers get to revisit an old friend

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