Terahertz-range chiral metamaterials based on helices made of metal-semiconductor nanofilms

Chiral metamaterials of the terahertz range are formed by means of rolling of strained nanofilms. Structural elements of these metamaterials are metal-semiconductor microhelices. Resonant optical activity of new metamaterials in the terahertz range is demonstrated. Arrays of model wire helices are formed and tested in the microwave range.     

Raman characterisation of single-walled carbon nanotubes produced by the catalytic pyrolysis of methane

Bundles of single-wall carbon nanotubes (SWCNT) were synthesised using a chemical vapour deposition technique. This basic process was optimised over a wide range of process parameters. For the optimal results, ethane was decomposed at 950 °C over a catalyst material consisting of 2% by wt Fe chemically deposited on an MgO support. The samples were characterised using scanning electron microscopy and transmission electron microscopy to show the presence of nanotubes and also to measure their diameters and the size of amorphous carbon deposits. Raman scattering was also used to probe the electronic properties and hence derive the distribution of diameters of the SWCNT. Samples were measured in both the radial breathing mode and tangential mode ranges using three different laser lines. For comparison purposes, similar data have been reported for a standard commercial SWCNT material (HiPCO). From the data, we can conclude that the tubes in our sample are significantly different to those in the HiPCO sample. In particular, we conclude that samples produced by our method contain a much narrower distribution of tube diameters than does the commercial sample.     

Experimental and numerical studies on buckling of cracked thin-plates under full and partial compression edge loading

Buckling failure is a common occurrence in thin plates under compression loading, in particular when there are some imperfections such as openings and cracks. This form of failure can often precede strength failure. In this paper, experimental and numerical studies on the critical buckling load of cracked plates subjected to axial compression is carried out. For this purpose, the rectangular plates made by 1200A aluminum alloy with central inclined crack are considered. The effects of crack length and orientation, thickness of plates and plate aspect ratio are investigated experimentally and numerically. Effects of boundary conditions and loadings are also studied by considering different types of supports and loading such as partial edge acting forces and supports. Finally, the results of experiments are compared with the results of numerical methods.     

Fatigue behavior of high-entropy alloys: A review

Fatigue failures cost approximately 4% of the United States’ gross domestic product (GDP). The design of highly fatigue-resistant materials is always in demand. Different from conventional strategies of alloy design, high-entropy alloys (HEAs) are defined as materials with five or more principal elements, which could be solid solutions. This locally-disordered structure is expected to lead to unique fatigue-resistant properties. In this review, the studies of the fatigue behavior of HEAs during the last five years are summarized. The four-point-bending high-cycle fatigue coupled with statistical modelling, and the fatigue-crack-growth behavior of HEAs, are reviewed. The effects of sample defects and nanotwins-deformation mechanisms on four-point-bending high-cycle fatigue of HEAs are discussed in detail. The influence of stress ratio and temperature on fatigue-crack-growth characteristics of HEAs is also discussed. HEAs could exhibit comparable or greater fatigue properties, relative to conventional materials. Finally, the possible future work regarding the fatigue behavior of HEAs is suggested.     

Crown ether complex cation ionic liquids: synthesis and catalytic applications for the synthesis of tetrahydro-4H-chromene and 1,4-dihydropyridine derivatives

A series of crown ether complex cation ionic liquids (CECILs) are synthesized by crown ethers chelated with sodium benzenesulfonates, and used as a green and environmental catalyst, for the synthesis of tetrahydro-4H-chromene and 1,4-dihydropyridine derivatives by three-component reactions of aromatic aldehydes and malononitrile with cyclic β-dicarbonyls or cyclic β-enaminoketones respectively, in H₂O/EtOH (1:1), at the reflux condition. CECILs, as a green and environmental catalyst, can be easily obtained and are stable. Furthermore, high conversions, short reaction times, and cleaner reaction profiles are some of the advantages of this method.     

K and J-Integral Variations Due to Residual Stresses in Welded Plates

Due to residual stress in a material, stress intensity factors (SIF) and also J-integral values are not constant and become path dependent parameters. Modified relations are used for calculations to take into account the effects of residual stresses. These relations give path independence values for the J-integrals in spite of existing the residual stresses. Effects of residual stresses due to welding on variations of SIF and J-integral are studied. Results have a good agreement with theoretical values obtained by weight function method. Through and surface cracks are considered on welded plate and distributions of J-integral on the crack front are obtained. Effects of lengths, depths and orientation angles of cracks are investigated due to applying only residual stress and also combination of residual and applied stresses. Redistributions of residual stress are determined for welded plates with through cracks and compared with experimental results in literature.     

Application of an Interior-Point Algorithm For Optimization of a Large-Scale Reservoir System

Optimization of a multi-reservoir system operation is challenging due to the non-linearity, stochasticity, and dimensionality involved in such a problem. In this research, a long-term planning model is presented for optimizing the operation of Iranian Karoon-Dez reservoir system using an interior-point algorithm. The system is the largest multi-purpose reservoir system in Iran with hydropower generation, water supply, and environmental objectives. The focus is on resolving the dimensionality of this problem while considering hydropower generation and water supply objectives. The weighting and constraints methods of multi-objective programming are used to assess the trade-off between water supply and hydropower objectives so as to find noninferior solutions. The computational efficiency of the proposed approach is demonstrated using historical data taken from Karoon-Dez reservoir system.     

Application of semi-definite programming to the design of multi-response experiments

The need to be able to design experiments with multiple responses is becoming apparent in many real-world applications. The generation of an optimal design to estimate the parameters of a multi-response model is a challenging problem. Currently available algorithms require the solution of many optimization problems in order to generate an optimal design. In this paper, the problem of multi-response D-optimal design is formulated as a semi-definite programming model and a relaxed form of it is solved using interior-point solvers. The main advantage of the proposed method lies in the amount of computation time taken to generate a D-optimal design for multi-response models. The proposed method is tested on several test problems and is shown to be very efficient with optimal designs being found very quickly in all cases. The robustness of the generated designs with respect to the variance-covariance matrix is also assessed for the test problems in order to show how a sensitivity analysis can be performed. The characteristics of the proposed method are also compared with those of other existing methods.     

Optimization of fusion behavior of the nanocomposites based on poly(vinyl chloride)/poly(epichlorohydrin‐co‐ethylene oxide)/organoclay

In this work, poly(vinyl chloride)/poly(epichlorohydrin‐co‐ethylene oxide) (PVC/ECO)/organoclay nanocomposites were prepared via melt processing and their fusion behaviors were comprehensively investigated. In this way, response surface methodology was employed to study the main and interactive effects of three parameters (Cloisite 30B content, ECO content, and rotor speed) on fusion of the PVC matrix. The results showed that ECO rubber has a negative influence on the fusion process, while optimal levels of other parameters are appropriate. Furthermore, the interactive plots revealed significant mutual effects of the parameters. Also, optimized levels of the parameters for achieving the best response were obtained by using contour plots. Since additives in PVC compounds have considerable effects on the fusion phenomenon, the results of the present study could be important from industrial point of view. J. VINYL ADDIT. TECHNOL., 25:98–105, 2019. © 2018 Society of Plastics Engineers     

Identification of Acid Mine Drainage Potential Using Sentinel 2a Imagery and Field Data

Mine Water and the Environment - Secondary iron minerals associated with acid mine drainage (AMD) such as copiapite, jarosite, schwertmannite, goethite, ferrihydrite, and hematite can be generated...