Robust optimization framework for cardinality constrained portfolio problem

One of the primary concerns on any asset allocation problem is to maintain a limited number of assets from the market. The problem becomes more complicated when the return of all risky assets are subject to uncertainty. In this paper, we propose a new portfolio modeling approach with uncertain data and it is also analyzed using different robust optimization techniques. The proposed formulations are solved using genetic algorithm. The implementation of the proposed method is examined on variety of well known benchmark data sets.     

The periodicity and robustness in a single-track train scheduling problem

The most important operating problem in any railway industry is to produce robust train timetables with minimum delays. The train scheduling problem is defined as an application of job shop scheduling which is considered to be one of the most interesting research topics. This paper deals with scheduling different types of trains in a single railway track. The authors have focused on the robust and periodic aspects of produced timetables. This paper is also concerned with some applicable constraints, such as the acceleration and deceleration times, station capacity and headway constraints. The periodic timetable for railways is modeled based on the periodic event scheduling problem (PESP). Furthermore, a fuzzy approach is used to reach a tradeoff among the total train delays, the robustness of schedules, and the time interval between departures of trains from the same origins. To solve large-scale problems, a meta-heuristic algorithm based on simulated annealing (SA) is utilized and validated using some numerical examples on a periodic robust train scheduling problem. Finally, a robustness measure is defined in order to assure the effectiveness of the proposed SA to find robust solutions.     

A blockchain-enabled security management framework for mobile edge computing

Mobile edge computing (MEC) integrates mobile and edge computing technologies to provide efficient computing services with low latency. It includes several Internet of Things (IoT) and edge devices that process the user data at the network's edge. The architectural characteristic of MEC supports many internet-based services, which attract more number of users, including attackers. The safety and privacy of the MEC environment, especially user information is a significant concern. A lightweight accessing and sharing protocol is required because edge devices are resource constraints. This paper addresses this issue by proposing a blockchain-enabled security management framework for MEC environments. This approach provides another level of security and includes blockchain security features like temper resistance, immutable, transparent, traceable, and distributed ledger in the MEC environment. The framework guarantees secure data storage in the MEC environment. The contributions of this paper are twofold: (1) We propose a blockchain-enabled security management framework for MEC environments that address the security and privacy concerns, and (2) we demonstrate through simulations that the framework has high performance and is suitable for resource-constrained MEC devices. In addition, a smart contract-based access and sharing mechanism is proposed. Our research uses a combination of theoretical analysis and simulation experiments to demonstrate that the proposed framework offers high security, low latency, legitimate access, high throughput, and low operations cost.     

A Volatile Solid Additive Enables Oligothiophene All-Small-Molecule Organic Solar Cells with Excellent Commercial Viability

The commercial viability of all-small-molecule (ASM) organic solar cells (OSCs) requires high efficiency, long-term stability, and low-cost production. However, satisfying all these factors at the same time remains highly challenging. Herein, a volatile solid additive, namely, 1,8-dichloronaphthalene (DCN) is demonstrated to simultaneously enhance the power conversion efficiency (PCE) and the storage, thermal as well as photo stabilities of oligothiophene ASM-OSCs with concise and low-cost syntheses. The improved PCEs are mainly due to the DCN-induced morphology control with improved exciton dissociation and reduced non-geminate recombination. Notably, the PCE of 16.0% stands as the best value for oligothiophene ASM-OSCs and is among the top values for all types of binary ASM-OSCs. In addition, devices incorporating DCN have shown remarkable long-term stability, retaining over 90% of their initial PCE after dark storage aging of 3000 h and thermal or light stressing of 500 h. The findings demonstrate that the volatile-solid-additive strategy can be a simple yet effective method of delivering highly efficient and stable oligothiophene ASM-OSCs with excellent commercial viability.     

Dielectrophoresis-based microfluidic platform to sort micro-particles in continuous flow

Non-invasive separation of particles with different sizes and sensitivities has been a challenge and interest for point-of-care diagnostics and personalized treatment. Dielectrophoresis is widely known as a powerful technique to sort the particles and (most importantly to) distinguish cells and monitor their state without the need for biochemical tags. In this paper, a dielectrophoresis-based microchannel design is proposed which allows for continuous particle sorting and separation under the applied AC field. It is also practical to implement the platform for monitoring cell behavior irregularities caused by certain diseases toward diagnosis and treatment. In this regard, the device employs dielectrophoretic (DEP) force exerted on the particles by only two electrodes with oblique arrangement in the channel. The electrodes are arranged with a bevel angle to the fluid flow direction but they are not parallel and therefore a gradually decreasing electric field is achieved along the channel’s width. As a result, the dielectrophoretic force, acting on the particles of different sizes, would also gradually decrease along channels width which renders the necessary distinguishing lateral displacements of particles for separation. Therefore, the particles with different sizes can be sorted in a continuous-flow regime and be received at multiple outlet reservoirs with no need to turn the electric field on/off. The presented device is fabricated and evaluated in the experiment to prove its feasibility. Afterward, using numerical simulations, we investigate the optimum design parameters in the presented device to enhance device efficiency for separating particles with different size ranges.

     

An improved fuzzy preference programming to evaluate entrepreneurship orientation

This paper describes an approach to measuring the entrepreneurship orientation (EO) of firms. EO is a widely accepted way to measure the degree in which a firm is entrepreneurial. The scale has three dimensions – innovativeness, risk-taking and proactiveness – each of which is assessed using multiple items. Measuring EO is important for entrepreneurial firms and for organizations like venture capitalists, business angels, investment banks and governments investing in these firms. Both the traditional statistical and the simple approach of assessing the overall level of EO (adding item scores) have their disadvantages. The aim of this article is to discuss these disadvantages and describe how some of them can be removed by using fuzzy analytic hierarchy process (AHP), which is a multi-criteria decision-making (MCDM) method that is particularly suited to tackle multi-dimensional, fuzzy, and perception-based constructs such as EO. We first improve a fuzzy AHP and then apply it using the pairwise comparisons of three experts to evaluate the EO of 59 small to medium-sized enterprises (SMEs) and rank the firms based on their EO score. The results indicate that proactiveness is by far the most important dimension, followed by innovativeness. Furthermore, there are considerable differences when it comes to the weights of the items.     

Magnetic Nanoparticle-Supported Cu–NHC Complex as an Efficient and Recoverable Catalyst for Nitrile Hydration

Magnetic nanoparticles supported N-heterocyclic carbene–Cu complex was prepared and authenticated by FT-IR, SEM, EDX, VSM, powder-XRD. The catalytic activity of these magnetically retrievable NPs was investigated for hydration of nitriles as the simplest route for the synthesis of amides in an atom-economical manner. A wide range of nitriles containing various functional groups such as olefin, aldehyde, nitro, carboxylic acid was examined in this transformation to generate their corresponding amides in the aqueous medium. The immobilized catalyst was easily recovered using an external magnet and reused for six times without significant loss of its catalytic activity.

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One-Pot,Sequential Four-Component Synthesis of Benzo[a]chromeno[2,3-c]phenazine Derivatives Using SiO2–SO3H as an Efficient and Recoverable Catalyst Under Conventional Heating and Microwave Irradiation

Silica sulfuric acid (SiO₂–SO₃H) has been used as an effective and reusable solid catalyst for the one-pot, two-step, four-component microwave-assisted synthesis of benzo[a]chromeno[2,3-c]phenazine derivatives by the condensation reaction of 2-hydroxynaphthalene-1,4-dione, o-phenylenediamine, aldehydes, and cyclic 1,3-dicarbonyl compounds. This new procedure has a number of advantages such as: high yields, very short reaction time, operational simplicity, simple work-up procedures and avoidance of hazardous or toxic catalysts, and organic solvents and is devoid of inessential derivatization and generation of hazardous substances. Moreover, the catalyst shows high thermal stability and can be recovered and reused without loss of reactivity.     

A study on the role of polypropylene fibers and silica nanoparticles on the compression properties of silicone rubber composites as a material of finger joint implant

In this study, different contents of SiO₂ nanoparticles and polypropylene fibers were added to silicone rubber matrix as a material of finger joint implants and mechanical properties of these composites were investigated before and after being soaked in simulated body fluid. Results of compression test revealed that compression stress of silicone rubber by addition of the 2 wt% silica and 2 wt% PP fibers increased from 0.98 to 1.9 and 2.37 MPa, respectively. These stresses decreased after being soaked in SBF and water absorption results proved this. Increasing silica contents caused an increase in water absorption while increasing PP fibers showed contrary behavior.