A study of phase transitions for convergence analysis of spin glasses: application to portfolio selection problems

To date, the spin glass paradigm has been gainfully used in solving a number of optimization problems by devising a mapping between our understanding of spin interactions within a natural spin glass and the given optimization problems. Among the determining factors in a natural spin glass, phase transition is a physical phenomenon that is controlled by temperature. Depending on the spin glass’s phase, spin glasses behave differently and may or may not reach the globally desired optimum. This study aims to determine this critical temperature below which convergence to a global optimum is more likely. Furthermore, we aim to determine the main parameters that characterize this critical temperature. Specifically, the critical temperature is studied as applied to the portfolio selection problem. It is shown that below the critical temperature, the glass consistently reaches the optimal states, whereas, convergence to optimum becomes increasingly unlikely if temperature exceeds this critical temperature. Application to five of the world’s major financial markets reveals that the critical temperature is directly proportional to covariance and the average return of assets and does not depend on the number of assets. In other words, all stock markets, that have the same asset covariance and average return, also have the same critical temperature. This is confirmed by several empirical tests such as correlation, entropy and hamming distance.     

Multi-objective optimization of cylindrical segmented tubes as energy absorbers under oblique crushes: D-optimal design and integration of MULTIMOORA with combinative weighting

Structural and Multidisciplinary Optimization - Vehicles experience off-axial loads as well as axial loads during collisions. Hence, it is essential to have oblique loads be involved in...     

Enhanced electrocatalytic activity of nickel particles electrodeposited onto poly (m-toluidine) film prepared in presence of CTAB surfactant on carbon paste electrode for formaldehyde oxidation in alkaline medium

In this work, carbon paste electrode is coated with poly (m-toluidine) film by potentiodynamic electropolymerization of m-toluidine monomer in the presence of cetyltrimethyl ammonium bromide (CTAB-PMT/MCPE). Then electrolysis at fixed potential (−1.0 V versus reference electrode for 15 min) is employed for electrodepositing of Ni from 1.5 M NiSO₄ acidic solution at the surface of polymer-modified electrode for preparation of Ni/CTAB-PMT/MCPE. The general electrochemical behaviors of these modified electrodes are characterized by cyclic voltammetry in alkaline media. In alkaline medium (i.e. NaOH 0.1 M) a good redox behavior of Ni(III)/Ni(II) couple at the surface of these electrodes can be observed. The nickel particles electrodeposited at the surface of Ni/CTAB-PMT/MCPE exhibits a significant electrocatalytic activity towards oxidation of formaldehyde. Moreover, the effects of various parameters such as concentration of CTAB, concentration of formaldehyde, film thickness and monomer concentration on the electrooxidation of formaldehyde as well as long-term stability of the Ni/CTAB-PMT/MCPE have also been investigated.     

Material selection based on ordinal data

Ranking and choosing the best material is one of most important stages in material selection process. Using linear assignment method, the multi-criteria decision making (MCDM) approach is proposed in decision-making process to rank the materials for a given engineering component with respect to several criteria. The proposed material selection procedure is relatively simple, and can be a useful approach when material selection problem includes qualitative properties or user-interaction aspects. The suggested approach also can be use for quantitative properties. Three examples are included to demonstrate the suggested method. Result of proposed approach showed good agreement with other methods.     

Characterization of molybdenum black coatings on zinc substrates

Molybdenum black solar selective coatings have been prepared by a simple chemical conversion method on chemically etched zinc substrates. These coatings have been characterized using X-ray diffraction, electron diffraction, XPS and VIS-IR reflectance spectroscopy. Maximum solar absorptance obtained from these coatings was about 0.87 with an emittance of 0.13–0.17. Selectivity of the coatings, mainly attributed to the coating surface morphology, was studied by SEM. Structural studies show that the coating consists of a non-stoichiometric oxide of Mo, namely Mo₄O₁₁. XPS depth profiling studies show that the oxidation state of Mo reduces from +5 to +4 after argon ion bombardment. This revised version was published online in November 2006 with corrections to the Cover Date.     

A review of diseases associated with household air pollution due to the use of biomass fuels

Nearly one third of the world's population use biomass fuels such as coal, wood, animal dung, and crop residues as their primary source of domestic energy. Due to their incomplete combustion, a multitude of pollutants associated with high levels of indoor air pollution (IAP) are released which include suspended particulate matter (SPM), carbon monoxide, formaldehyde, nitrogen dioxide, polycyclic aromatic hydrocarbons (PAH), etc. There is a line of evidence that exposure to those pollutants can lead to increased risk of diseases including respiratory infections (e.g., pneumonia, tuberculosis and chronic obstructive pulmonary disease (COPD), lung cancer, and asthma), low birth weight, cataracts, and cardiovascular events. It is one of the major global public health threats that require greater efforts for prevention through research and policy-making. This review summarizes the available information on potential health risks associated with biomass fuel use.     

Morphology,mechanical, and physical properties of wet-spun cellulose acetate fiber in different solvent-coagulant systems and in-situ crosslinked environment

Wet spinning is a popular fiber manufacturing process where the effects of solvent and coagulant on the wet-spun fiber are significant. In this study, we have explored the effect of solvent-coagulant interaction and in-situ crosslinking on the wet-spun cellulose acetate (CA) fiber. Investigation on 12 different solvent-coagulant systems revealed that variation in the systems resulted in significant variance in morphology and mechanical property of the fiber. Remarkable increase in mechanical property was observed after in-situ crosslinking with citric acid and polyethylene glycol (PEG). Inclusion of sodium hypophosphite (NaH₂PO₂) as catalyst further increased tensile modulus (~407%) and crystallinity index (~46%) compared to CA fiber crosslinked with only citric acid. It was established that fiber from CA-DMSO solution crosslinked with 10% citric acid and 10% PEG extruded in ethanol showed the highest tensile modulus (~30 MPa). This in-depth study found an appropriate combination of solvent-coagulant for forming stable CA fiber, with the addition of crosslinkers and catalyst further increasing the strength and usability of the fiber.     

3D printing for soft robotics – a review

Soft robots have received an increasing attention due to their advantages of high flexibility and safety for human operators but the fabrication is a challenge. Recently, 3D printing has been used as a key technology to fabricate soft robots because of high quality and printing multiple materials at the same time. Functional soft materials are particularly well suited for soft robotics due to a wide range of stimulants and sensitive demonstration of large deformations, high motion complexities and varied multi-functionalities. This review comprises a detailed survey of 3D printing in soft robotics. The development of key 3D printing technologies and new materials along with composites for soft robotic applications is investigated. A brief summary of 3D-printed soft devices suitable for medical to industrial applications is also included. The growing research on both 3D printing and soft robotics needs a summary of the major reported studies and the authors believe that this review article serves the purpose.     

Extraction of Unconventional Bast Fibers from Kydia calycina Plant and their Characterisation

The Kydia calycina fibers were screened out from various plant sources through the water retting method and then the time duration for extraction of fibers was optimized. After optimization, the extracted Kydia calycina fibers were compared with cotton, flax, and jute fibers on the basis of physical and mechanical properties. The morphology of extracted fibers was also studied through SEM. The results showed that the Kydia calycina plant produces better quality bast fibers with respect to plants like jute and flax.