Quantity and chemical composition of essential oil of peppermint (Mentha × piperita L.) leaves under different drying methods

This work was aimed at quantitative and qualitative analyses of the essential oil of peppermint leaves under different drying methods. Thin layer drying experiments of the leaves were performed in shade, hot air dryer (at temperatures of 50°C, 60°C, and 70°C), and microwave oven (at power levels of 200, 400, and 800 W). Essential oils of the fresh and dried samples were extracted by hydrodistillation and analyzed using gas chromatography-mass spectrometry (GC/MS). The highest (22.24 g/kg _{dry matter}) and the lowest (1.33 g/kg _{dry matter}) oil yields were obtained from the hot air-dried leaves at temperature of 50°C and microwave-dried leaves at power of 800 W, respectively. In general, increasing drying temperature decreased the essential oil content. The GC/MS analysis of essential oils showed that the chemical compounds belonged mostly to oxygenated monoterpenes class (72.34–86.41%). The chemical compounds group was significantly (p < 0.01) decreased by microwave drying at power levels of 200 and 400 W. The assessed drying methods caused significant (p < 0.05 and/or p < 0.01) variations in the main constituents of the peppermint leaves essential oil including menthol, menthone, menthofuran, 1,8-cineole, and menthyl acetate. The minimum (35.01%) and maximum (47.50%) concentrations of menthol, as the major compound of the oil, were found in hot air-dried leaves at temperature of 50°C and microwave-dried leaves at power of 400 W, respectively. The percentage of menthone, as the second constituent in the essential oil, was significantly lost (p < 0.01) under microwave drying.     

Phase transformation studies on the a-C coating under repetitive impacts

The phase transformation of hydrogen-free amorphous carbon (a-C) coating on tungsten high speed steel (SKH2) substrates under repetitive impact testing has been studied. The a-C coated disc was impacted by the chromium molybdenum steel (SCM420) pin at several different impact loads and impact cycles (up to 100,000) under lubricated conditions. The results show that the sp³ fractions of impacted a-C coating obtained from the surface of impact craters are significantly increased with impact cycles due to decreasing ID/IG ratio. This means that the amorphization of a-C coating also increased after several impact cycles. As for the full-width at half maximum (FWHM) of G peak characterization, it is shown that the hardness of impacted a-C coating is higher than the as-received. From the observation of surface roughness using atomic force microscopy (AFM), it is supposed that increasing sp³ fractions and the hardness of the impacted a-C coating during impact correlate to the reduction of surface roughness. In addition, the tribochemical reaction to the environment during impact occurred at the mating material, where the transfer layer adhered, as well as in the wear debris. This is due to the oxidation of ferrum (Fe) to magnetite (Fe₃O₄) and hematite (α-Fe₂O₃) phases with predominant peak at about 680 cm⁻¹ and 1317 cm⁻¹, respectively. The formation of Fe₃O₄ and α-Fe₂O₃ phases was revealed from Raman spectroscopy and the existence of oxide elements was verified by energy dispersive X-ray spectroscopic (EDS) analysis. Increasing the G peak position, together with a concomitant decrease of their width, it is believed that the structural transformation from sp³ to sp² is taking place within the wear debris and leads to the graphitization process at a higher contact pressure. It was suggested that the high contact pressure is not just only corresponding to the applied normal impact load, but it is also exerted by an oil lubricant during impact. A high contact pressure can significantly reduce the graphitization temperature and substantially accelerate the graphitization process. However, a significant phase transformation of the transfer layer on the SCM420 pin does not intensely occur because it is mainly coming from the surface layer of the impacted a-C coating, where the sp³ content increases and no wear debris is observed inside it.     

A closed-loop supply chain configuration considering environmental impacts: a self-adaptive NSGA-II algorithm

Applied Intelligence - Configuration of a supply chain network is a critical issue that contributes to choose the best combination for a set of facilities in order to attain an effective and...     

Developing a Model for Decision-Makers in Dynamic Modeling of Urban Water System Management

Water managers may modify many components of urban water systems to minimize water shortage. Since each modification activity has its own positive and negative effects, it is necessary to define an appropriate procedure to predict the consequences of each action. As the parameters of urban water supply and demand system have internal relationships in the time domain, a dynamic model is needed to forecast the result of changes and select the best modification activity. Here the Vensim® is applied as a modeling tool to choose the most effective water management activities in Tehran province. It has been found that the annual increase rate of water tariff by 16.4% and assigning 4.5% of revenue on reducing non-revenue water may be the most effective demand management activity to reduce water shortage in Tehran province. It has also been revealed that, even by implementing the most effective demand management activities in Tehran, the amount of required water in the next 10 years is more than the sustainable capacity of its resources and activities like seawater desalination are inevitable to prevent unsustainable use of water sources.

     

Calculating Price Elasticity of Water Demand Using Gene Expression Programming Based on Economic,Social and Meteorological Variables

Determining the changing rate of water consumption through altering parameters such as water tariffs can help water companies select appropriate water policies. This paper is intended to find the proper relation between the water price elasticity of demand and some social, economic and climatic variables that are released annually by international organizations like the United Nations Development Program and the World Bank. By using genetic algorithm, different combinations of water price elasticity of demand and variables like gross domestic product, per capita gross domestic product, gross national income, precipitation, human development index, average temperature and household size have been analyzed. It was found that the absolute price elasticity of water demand has positive relationships with precipitation and price of water. It has also been found that the gross national income, average percent of consumers who have secondary education and human development index have a negative relation with the absolute price elasticity of water demand.

     

Carbosilisiothermic Reduction of Rutile to Produce Nano-Sized Particles of TiC and Its Composite with SiO2

Ceramic nanoparticles of TiC were successfully synthesized in a matrix of SiO₂ by high-energy ball milling with subsequent heat treatment. The milling procedure includes milling of a mixture of TiO₂, Si, and graphite powders at ambient temperature in an inert gas (Ar) atmosphere. The structural evaluation of powder particles has been accomplished by XRD, TEM, SEM, EDX, and DSC. XRD results suggest that the TiC-SiO₂ nonocomposite was produced after 10 hours of mechanical activation with subsequent heat treatment at 1473 K (1200 °C) for 7 minutes. TEM images reveal that the TiC and SiO₂ crystallites are <14 and 12 nm in size, respectively. The fracture toughness, and Vickers hardness values of the TiC-SiO₂ nanocomposite are measured to be 3.82 MPa m^1/2 and 19.9 GPa, respectively. Dimethylsulfoxide is used to eliminate SiO₂ from the final products.     

The multiobjective stochastic CRITIC–TOPSIS approach for solving the shipboard crane selection problem

The duty of shipboard cranes is to lift and lower loads, as well as to handle floating facilities to lower or higher positions by means of fixed wire ropes, pulleys, and hook, and so forth. Hence, they play an important role in the productivity of servicing or manufacturing systems. Since each crane has distinguished properties than the others with respect to criteria and decision-makers (DMs) may express the different standpoints regarding them, the crane selection problem (CSP) can be considered as a group multicriteria decision-making (MCDM) problem. In this paper, interval type-2 fuzzy sets (IT2FSs) are first used to evaluate cranes with respect to criteria. The synthetic value method of IT2FSs is then handled to integrate the ratings expressed as IT2FSs of each crane with respect to criteria into the single fuzzy rating. Finally, the multiobjective criteria importance through inter-criteria correlation (CRITIC)–technique for order of preference by similarity to ideal solution (TOPSIS) approach is applied to solve the CSP in which CRITIC and TOPSIS are used to determine the objective weights and score of cranes, respectively. In addition, the limit distance mean (LDM) is introduced for ranking interval type-2 fuzzy ratings in the above two techniques. In contrast, to demonstrate the potential application, the proposed methodology is implemented in a real case study and the ranking results are compared with those published in the literature.     

Frequency–amplitude relations for cross‐coupled voltage‐controlled oscillator

Dependence of frequency on amplitude and control bias is considered for the cross‐coupled voltage‐controlled oscillator. Closed form expressions are derived for frequency of oscillation as a function of amplitude, for positive and negative control bias voltages. Theory of nonlinear ordinary differential equations is utilized to show that the capacitance–voltage relation is the main cause of frequency shift with amplitude. Furthermore, the case of small amplitudes relative to control voltage is analyzed, and a closed form expression is derived for dependence of frequency on amplitude. This relation is then verified using the concept of effective capacitance. The effective capacitance approach is also used to extend the analysis to large voltage swings. Dependence of frequency on tuner control voltage is calculated for both bias polarities. Implications of the aforementioned equations for voltage‐controlled oscillator performance are discussed. Numerical calculations and simulations are used to compare and verify the closed form equations, showing good agreement. Copyright © 2012 John Wiley & Sons, Ltd.     

A new successive approximation architecture for high-speed low-power ADCs

A new high-speed successive approximation analog-to-digital converter (ADC) architecture is presented. Two-bits extraction in each clock cycle is the key idea to double the conversion speed. Generating reference levels for three comparators with only two digital-to-analog converter (DACs), is another novelty of the new architecture. The proposed DAC structure allows a substantial reduction in overall control logic complexity. A 10-bit 40 Ms/S successive approximation ADC was designed based on the proposed architecture in CMOS technology. The simulation results show that the proposed architecture introduces 7% reduction in power consumption over conventional architecture. Furthermore, chip area for the new ADC is 40% less than what otherwise would be needed by an ADC using conventional architecture.