Intrinsic reaction rate and the effects of operating conditions in dimethyl ether synthesis from methanol dehydration

The kinetic behavior of a commercial γ-Al₂O₃ catalyst for the methanol to dimethyl ether (DME) dehydration reaction has been investigated using a differential fixed bed reactor at the pressure range 1–16 barg within a temperature range of 260–380 °C. The experimental runs were performed in a wide range of feed to water ratios. The experiments were designed by general full factorial design (GEFD) and a novel rate equation has been developed which exhibited the best fitting with our experimental data. Based on the analysis of variance (ANOVA), the following order of importance for operating conditions was obtained when the objective function is the yield of DME: Temperature >Water % in feed >Pressure. In addition, the optimum operating conditions for the maximum yield of DME, were found at T= 380°C, P=16 barg and zero wt% of water in the feed.     

Effectiveness of Zataria multiflora Boiss essential oil and grape seed extract impregnated chitosan film on ready-to-eat mortadella-type sausages during refrigerated storage

BACKGROUND: The effectiveness of chitosan films containing Zataria multiflora Boiss essential oil (ZEO) (5 and 10 g kg^?1) and grape seed extract (GSE) (10 g kg^?1) on lipid oxidation and microbial (lactic acid bacteria, aerobic mesophiles and inoculated Listeria monocytogenes) characteristics of mortadella sausage at 4 °C for 21 days was evaluated. The release of total phenolics (TPs) into sausage was also assessed. RESULTS: All films exhibited antibacterial activity against L. monocytogenes on agar culture media. Chitosan films containing ZEO were the most effective on the growth of bacteria. The growth of L. monocytogenes was significantly inhibited by ZEO‐GSE containing films especially during storage of the sausages for 6 days. Aerobic mesophiles and lactic acid bacteria were the most sensitive and resistant groups to films by 0.1–1.1 and 0.1–0.7 log cycles reduction, respectively. Sausages wrapped by 10 g kg^?1 GSE + 10 g kg^?1 ZEO films had the lowest degrees of lipid oxidation, which was 23% lower than the control. The TPs of ZEO films decreased to zero after 6 days, whereas TPs of GSE films followed a slight decrease during the storage. CONCLUSION: Antimicrobial/antioxidant chitosan film could be developed by incorporating GSE and ZEO for extending the shelf life of mortadella sausage. Copyright © 2011 Society of Chemical Industry     

A new mathematical approach to improve residual stress measurement in ring-core method

Journal of Mechanical Science and Technology - III-conditioning at the inverse equation of integral method in ring-core residual stress measurement leads to high stress sensitivity to strain...     

Comparison of essential oils compositions of Nepeta persica obtained by supercritical carbon dioxide extraction and steam distillation methods

Essential oil of Nepeta persica cultivated in Iran was obtained by steam distillation and supercritical (carbon dioxide) extraction methods. The oils were analysed by capillary gas chromatography using flame ionization and mass spectrometric detections. The compounds were identified according to their retention indices and mass spectra (EI, 70 eV). The effects of different parameters such as pressure, temperature, modifier volume and extraction times (dynamic and static) on the supercritical fluid extraction (SFE) of N. persica oil were investigated. The results showed that under the pressure of 20.3 MPa, temperature of 45 °C, methanol of 1.5% v/v), dynamic extraction time of 50 min and static extraction time of 25 min extraction was more selective for the 4αβ,7α,7aα-nepetalactone. Twelve compounds were identified in the steam-distilled oil. The major components of N. persica were 4αβ,7α,7aα-nepetalactone (26.5%), cis-β-farnesene (4.4%) and 3,4α-dihydro-4aα,7α,7aα-nepetalactone (3.5%). However, by using supercritical carbon dioxide under optimum conditions, only two components have more than 90.0% of the oil. The extraction yield based on steam distillation was 0.08% (v/w). On the other hand, using SFE extraction yield in the range of 0.22–8.90% (w/w) were obtained at different conditions. The results show that, in Iranian N. persica oil, 4αβ,7α,7aα-nepetalactone is a major component.     

Formation and Characterization of Titanium Modif Aluminide Coatings on IN738LC

HISTORICALLY superalloys have been used in gasturbine applications with a protective coating to combatoxidation problems in aero engines and hot corrosionproblems in industrial and marine engines.Theprotective coatings used are predominantly of thediffusion type produced by variety of techniques suchas pack cementation,chemical vapor deposition,slurryfusion and hot dipping[1,2].The purpose of this typeof coatings is to increase the amount of Al at thesurface of a component,so that a protec…     

Memory for emotional trait adjectives in clinically depressed youth

An experiment was conducted to examine memory for emotional trait adjectives in depressed children and adolescents. Two groups of children and adolescents, clinically depressed participants and non-clinical controls, were compared on computerized versions of recall and recognition memory tasks. Three groups of words (positive trait adjectives, negative trait adjectives, and categorized neutral words) were used in the experiment. Results showed that the depressed group recalled significantly more negative adjectives than positive adjectives, whereas the control group recalled the same number of positive and negative adjectives. This effect was predicted by the association between age and level of depression, with the depression-related bias becoming stronger with age. Signal detection analysis revealed that the depressed group did not show any bias in the recognition task. The findings are discussed with respect to cognitive theories of depression with consideration of the developmental implications.     

Hybrid Fractal-Wavelet Method for Multi-Channel EEG Signal Compression

In this paper, a hybrid method is proposed for multi-channel electroencephalograms (EEG) signal compression. This new method takes advantage of two different compression techniques: fractal and wavelet-based coding. First, an effective decorrelation is performed through the principal component analysis of different channels to efficiently compress the multi-channel EEG data. Then, the decorrelated EEG signal is decomposed using wavelet packet transform (WPT). Finally, fractal encoding is applied to the low frequency coefficients of WPT, and a modified wavelet-based coding is used for coding the remaining high frequency coefficients. This new method provides improved compression results as compared to the wavelet and fractal compression methods.     

A nondominated ranked genetic algorithm for bi-objective single machine preemptive scheduling in just-in-time environment

Motivated by just-in-time (JIT) manufacturing, we study the bi-objective scheduling problem of minimizing the total weighted earliness and the number of tardy jobs on a single machine, in which machine idle time and preemption are allowed. The problem is known to be NP-hard. In this paper, we propose a new mathematical model, with nonlinear terms and integer variables which cannot be solved efficiently for medium- and large-sized problems. A method combining the new ranked-based roulette wheel selection algorithm with Pareto-based population ranking algorithm, named nondominated ranking genetic algorithm (NRGA), has been presented to find nondominated solutions in a reasonable time. Various operators and parameters of the proposed algorithm are reviewed to calibrate the algorithm by means of the Taguchi method. A number of numerical examples are solved to demonstrate the effectiveness of the proposed approach. The solutions obtained via NRGA are compared against solutions obtained via ε-constraint method in small-sized problems. Experimental results show that the proposed NRGA is competitive in terms of the quality and diversity of solutions in medium- and large-sized problems.     

Wear assessment of plasma nitrided AISI H11 steel

Plasma nitriding is one of the effective methods for improvement of the hardness, wear and corrosion resistance of steels. In this research AISI H11 hot working tool steel was plasma nitrided in various gas mixtures for different times and temperatures. The morphology, size and composition of nitride nanoparticles formed on the surface of the specimens were investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD). The wear behavior of plasma nitrided samples was studied by means of unlubricated pin-on-disc method under constant load of 80 N, sliding speed of 1 m/s, sliding distance of 2000 m at room temperature. The results showed plasma nitriding process improved the wear behavior of H11 steel. The increase in time and temperature of plasma nitriding decreased the hardness and increased the wear weigh loss of the specimens.     

Measurement of Urbach edge and midgap states in amorphous silicon p-i-n devices

Urbach energy of valence band tails and mid-gap defect densities are important parameters for determining the performance of amorphous silicon (a-Si:H) devices. In this paper, we examine a technique which allows one to determine these parameters in device structures, as opposed to in films. The technique consists of measuring sub-gap quantum efficiency as a function of reverse bias and photon wavelength. We show that there is a distinction between the response of tail states and mid-gap states to the application of reverse bias, and that by analyzing these differences, one can locate the energies of the mid-gap states in the device. The technique gives an accurate measurement of Urbach edge of tail states, even on textured substrates, but only estimates mid-gap states within a factor of 2.