An extension of fuzzy TOPSIS for a group decision making with an application to tehran stock exchange

In financial markets, investors attempt to maximize their profits within a constructed portfolio with the aim of optimizing the tradeoffs between risk and return across the many stocks. This requires proper handling of conflicting factors, which can benefit from the domain of multiple criteria decision making (MCDM). However, the indexes and factors representing the stock performance are often imprecise or vague and this should be represented by linguistic terms characterized by fuzzy numbers. The aim of this research is to first develop three group MCDM methods, then use them for selecting undervalued stocks by dint of financial ratios and subjective judgments of experts. This study proposes three versions of fuzzy TOPSIS (Technique for Order Preference by Similarity to Ideal Solution): conventional TOPSIS (C-TOPSIS), adjusted TOPSIS (A-TOPSIS) and modified TOPSIS (M-TOPSIS) where a new fuzzy distance measure, derived from the confidence level of the experts and fuzzy performance ratings have been included in the proposed methods. The practical aspects of the proposed methods are demonstrated through a case study in the Tehran stock exchange (TSE), which is timely given the need for investors to select undervalued stocks in untapped markets in the anticipation of easing economic sanctions from a change in recent government leadership.     

Low temperature fabrication of hybrid solar cells using co-sensitizer of perovskite and lead sulfide nanoparticles

Our cost-effective approach for hybridizing methylammonium lead iodide and PbS nanoparticles at low temperature (≤100 °C) for photovoltaic devices is introduced. As employed into a perovskite based solar cell platform, effects of PbS on the device performance were investigated. Through experimental observations under simulated air-mass 1.5G illumination (irradiation intensity of 100 mWcm⁻²), the efficiency of a perovskite:PbS device is 11% higher than that of a pristine perovskite solar cell under the same fabrication conditions as a result of the broadened absorption range in the infrared region. The highest photovoltaic performance was observed at a PbS concentration of 2% with an open-circuit voltage, short-circuit current density, fill factor, and power-conversion efficiency of 0.557 V, 22.841 mA cm⁻², 0.55, and 6.99%, respectively. Furthermore, PbS NPs could induce hydrophobic modification of the perovskite surface, leading to an improvement of the device stability in the air. Finally, the low-temperature and cost-effective fabrication process of the hybrid solar cells is a good premise for developing flexible/stretchable cells as well as future optoelectronic devices.     

流线型回转体外形设计综述与线型拟合

综述了流线型回转体外形设计的主要方法：(1)具有精确数学表达式的几何组合外形曲线；(2)用源汇法设计回转体外形曲线；(3)用离散外形坐标型值表示的回转体线型。给出了流线型离散型值回转体线型的拟合解析表达式。这些外形设计方法与拟合解析表达式具有广泛的工程实用价值。     

土钉墙在粘性土基坑支护中的应用

土钉墙指以土钉支护为主,辅以其他各种措施提高土坡稳定性的复合支护形式。在闽东南基坑工程中该支护形式得到了广泛的应用。本文以福州某基坑为例详细介绍了土钉支护形式。文中首先根据基坑的工程地质条件,确定支护形式;其次结合支护设计方案和工程实际,采取相应的施工步骤和措施;最后介绍了施工过程中的监测。结果表明,该工程采用土钉墙的支护方案,既安全又经济合理,施工方便,可以为粘性土基坑边坡的设计与支护提供参考。对于土钉墙在粘性土基坑中的优化有待进一步研究。     

On the mechanical response of woven para-aramid protection fabrics

The initial condition of the structure of the fabric's knitting form, before applying a load, is closely correlated with the performance of the fabric under loading. The present study focuses on the mechanical response of para-aramid protection fabrics under tensile loading and suggests a knitting angle as a considerable factor for the behavior of the fabric. A global and a local method are applied to monitor the effect of this angle on the fabric's performance and deformation mechanism. The experimental results indicate that this angle affects both the fracture propagation mode and the fracture toughness. A failure onset detection mode, based on this angle, is also suggested, followed by a calculation of the further feasible deformation of a permanently deformed zone until the next failure.     

Influence of processing conditions on the ionic conductivity of holmium zirconate (Ho2Zr2O7)

Nanopowders of holmium zirconate (Ho₂Zr₂O₇) synthesised through carbon neutral sol-gel method were pressed into pellets and individually sintered for 2 h in a single step sintering (SSS) process from 1100 °C to 1500 °C at 100 °C interval and in a two step sintering (TSS) process at (I) −1500 °C for 5 min followed by (II) - 1300 °C for 96 h. Relative density of each of the sintered pellet was determined using the Archimedes’ technique and the theoretical density was calculated from crystal structure data. Grain size was obtained from SEM micrographs using ImageJ. Pellets processed by TSS have been found to be denser (98 %) with less grain growth (1.29 μm) as compared to the pellets processed using SSS process. Ionic conductivity of Ho₂Zr₂O₇ pellets sintered by two different processes was measured using ac impedance spectroscopy technique over the temperature range of 350 °C–750 °C in the frequency range of 100 mHz–100 MHz for both heating and cooling cycles. The temperature dependence of bulk (2.67⨯10⁻³ Scm⁻¹) and grain boundary (2.50⨯10⁻³ Scm⁻¹) conductivities of Ho₂Zr₂O₇ prepared by TSS process are greater than those processed by SSS process suggesting the strong influence of processing conditions and grain size. Results of this study, indicates that the TSS is the preferable route for processing the holmium zirconate as it can be sintered to exceptionally high densities at lower temperature, exhibits less grain growth and enhanced ionic conductivity compared with the samples processed by SSS process. Hence, holmium zirconate can be considered as a promising new oxide ion conducting solid electrolyte for intermediate temperature SOFC applications between 350 °C and 750 °C temperature range.     

Aid of a metallic functional layer on Ni/YSZ anode for Direct Methane Fuel Cell

Aid of a metallic overlayer to nickel/yttrium-stabilized-zirconia (Ni/YSZ) anode is investigated in Direct Methane Fuel Cell. Copper modified nickel metallic overlayer shows high activity for fuel cell performance and good stability to coking in methane atmosphere. The copper-nickel overlayer provides advantages of material compatibility with the substrate and catalytic function on copper-modified nickel sites. The results suggest that the overlayer is effective for decomposition of methane and tolerant to coking by removal of deposited carbon via oxidation and gasification reaction.     

The effect of hyperbranched polyester and zirconium slag nanoparticles on the impact resistance of epoxy resin thermosets

A hyperbranched polyester (HBP) was synthesized through a polymerization of AB₂ approach with succinic anhydride and diethanolamine. The effect of HBP and Zirconium slag nanoparticle (ZSN, a kind of solid waste in Zirconium industry) content on the toughness enhancement and morphology of diglycidyl ether of bisphenol A epoxy resin (DGEBA) thermosets was studied. The results indicated that HBP can greatly improve the impact strength (IS) of epoxy thermosets, but the flexural strength (FS) was decreased with increasing the HBP content. The IS of epoxy thermosets modified with ZSN was also improved, and the FS decreases as increase of ZSN. The thermosets modified with both HBP and ZSN showed excellent IS and FS. The toughening enhancement mechanism was also discussed.     

Remaining useful life prediction of PEMFC based on cycle reservoir with jump model

Accurate prognosis of limited durability is one of the key factors for the commercialization of proton exchange membrane fuel cell (PEMFC) on a large scale. Thanks to ignoring the structure of the PEMFC and simplifying the prognostic process, the data-driven prognostic approaches was the commonly used for predicting remaining useful life (RUL) at present. In this paper, the proposed cycle reservoir with jump (CRJ) model improves the ESN model, changes the connection mode of neurons in the reservoir and speeds up the linear fitting process. The experiment will verify the performance of CRJ model to predict stacks voltage under static current and quasi-dynamic current conditions. In addition, the reliability of the CRJ model is verified with different amount of data as the training and test sets. The experimental results demonstrate that the CRJ model can achieve better effect in the remaining useful life prognosis of fuel cells.     

Subsolidus solution and electrical properties of Sr-substituted bismuth magnesium niobate pyrochlores

Here we investigated the structural and dielectric properties of (Bi_3.36Mg_0.64-xSr_x)(Mg_1.28Nb_2.72)O_13.76 (0≤ x≤0.5) subsolidus solution. Sr-substituted bismuth magnesium niobate (BMSN) pyrochlores were prepared by solid-state reaction at 1025 °C over 1–2 days. X-ray diffraction (XRD) analysis confirmed that the BMSN pyrochlores crystallise in cubic symmetry, space group Fd3m with lattice parameters in the range 10.5968 (4)-10.5671 (17) Å. The surface morphologies of these samples, as confirmed by Scanning Electron Microscopy (SEM), were composed of irregular shaped grains. Both Scherrer and Williamson-Hall methods revealed that the crystallite sizes were in the range 46–75 nm. No thermal event was discernible over the temperature range 30–1000 °C, thus confirming the thermal stability of these materials. On the other hand, Arrhenius conductivity plots showed the BMSN pyrochlores to be highly insulating with activation energies of ~1.20–1.49 eV. At ~30 °C and 1 MHz, BMSN pyrochlores exhibited moderate high bulk dielectric constants, ɛ’, 90–186 and low dielectric losses, tan δ in the order of 10⁻²–10⁻¹, respectively. Both the ɛ’ and tan δ values of the BMSN pyrochlores showed a nearly two-fold decrease with increasing Sr concentration. Negative temperature coefficient of capacitances, TCC, −408 to −713 ppm/°C were recorded over ~30–300 °C at 1 MHz.