Facile synthesis of layered sodium disilicates as efficient and recoverable nanocatalysts for biodiesel production from rapeseed oil

In this study, α, β and δ phases of layered sodium disilicates were synthesized and used as heterogeneous catalysts for transesterification of rapeseed oil with methanol to methyl esters (biodiesel). The catalysts were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) technique, Fourier transform infrared spectroscopy (FT-IR), N₂ adsorption-desorption, and thermogravimetric analysis (TGA-DTA). δ-Na₂Si₂O₅ showed better catalytic efficiency than the other two phases of sodium disilicate, and showed excellent activity at the optimized conditions. The transesterification conditions, such as the catalyst dosage, molar ratio of methanol to oil, reaction temperature and reaction time were investigated. The results revealed that with a catalyst loading of 4?wt%, methanol to oil ratio of 30:1, reaction temperature of 65?°C and reaction time of 3?h, conversion of biodiesel reached 97.8%.     

Sensitivity enhancement of a MEMS sensor in nonlinear regime

The aim of this study is to enhance the sensitivity of a micro electro mechanical Gyroscope in nonlinear regime. Sensitivity enhancement is achieved by applying appropriate Hoping voltages which pushes the micro-beam to the basin of attraction of a desired periodic attractor. The studied model is a silicon clamped–clamped micro beam actuated by an electrostatic voltage which is a combination of a constant DC and a harmonic AC voltage in the drive mode direction and a pure DC voltage in the direction of sense mode. The external angular velocity about the horizontal axis is used to create the Coriolis force along the sense mode. The governing differential equation of the motion is derived using Hamiltonian principle and discretized to two nonlinear Duffing type ODE’s using Galerkin method. Shooting method is utilized to obtain the frequency response curve, and to capture the periodic solutions of the motion. The stabilities of the periodic orbits are investigated by the Floquet theory. The results depict that the response of the system is highly affected by the applied DC and AC voltage; corresponding to a constant DC voltage, the more is the AC voltage, the more is the sensitivity. Based on the DC voltage the system exhibits both hardening and softening effects. The capacity of the capacitors is determined and the effects of the various applying Hoping voltages on capacity of them are investigated. The frequency response curve of the micro-beam for various quality factors are obtained and compared with the literature.     

Weighted Sum Rate Maximization Under the Given PAPR Constraints for a Multi-user OFDM System

Wireless Personal Communications - Orthogonal frequency division multiplexing (OFDM) is proved to be the best candidate to support the colossal increase in mobile users and their required high rate...     

Designing a MapReduce performance model in distributed heterogeneous platforms based on benchmarking approach

MapReduce framework is an effective method for big data parallel processing. Enhancing the performance of MapReduce clusters, along with reducing their job execution time, is a fundamental challenge to this approach. In fact, one is faced with two challenges here: how to maximize the execution overlap between jobs and how to create an optimum job scheduling. Accordingly, one of the most critical challenges to achieving these goals is developing a precise model to estimate the job execution time due to the large number and high volume of the submitted jobs, limited consumable resources, and the need for proper Hadoop configuration. This paper presents a model based on MapReduce phases for predicting the execution time of jobs in a heterogeneous cluster. Moreover, a novel heuristic method is designed, which significantly reduces the makespan of the jobs. In this method, first by providing the job profiling tool, we obtain the execution details of the MapReduce phases through log analysis. Then, using machine learning methods and statistical analysis, we propose a relevant model to predict runtime. Finally, another tool called job submission and monitoring tool is used for calculating makespan. Different experiments were conducted on the benchmarks under identical conditions for all jobs. The results show that the average makespan speedup for the proposed method was higher than an unoptimized case.

     

A stochastic process-based server consolidation approach for dynamic workloads in cloud data centers

The Journal of Supercomputing - With the development of information technology, there is a need for computational works everywhere and every time. Thus, people should be able to carry out their...     

A reliable energy-aware approach for dynamic virtual machine consolidation in cloud data centers

The Journal of Supercomputing - To achieve energy efficiency in data centers, dynamic virtual machine (VM) consolidation as a key technique has become increasingly important nowadays due to the...     

Nano-magnetic-iron Oxides@choline Acetate as a Heterogeneous Catalyst for the Synthesis of 1,2,3-Triazoles

In this research, four cholines supported on core–shell iron oxides, Fe₂O₃@MgO@Ch.OAc (choline acetate), Fe₂O₃@MgO@Ch.OH (choline hydroxide), Fe₃O₄@Ch.OAc, Fe₃O₄@Ch.OH, were synthesized. The synthesized catalysts were tested in 1,2,3-triazoles synthesis by the reaction of nitromethane, aldehyde, and benzyl azide in EtOH as a green solvent. Among four synthesized heterogeneous catalysts, the Fe₂O₃@MgO@ch.OAc showed superior catalytic activity for the reaction and afforded the desired triazoles in good isolated yields under mild reaction conditions.

Graphic Abstract

     

An Energy Efficient Autonomous Method for Coverage Optimization in Wireless Multimedia Sensor Networks

In this paper, a distributed method for coverage optimization of random deployed WMSNs utilizing motility and mobility capabilities of nodes, is proposed. The aims followed by the method are first, maximizing the coverage ratio by minimizing both the covered overlapping areas, and the coverage holes after random deployment, and second, enhancing energy efficiency of the coverage optimization procedure, by minimizing the needed rotations and specially movements, comparing with the previous schemes. To these aims, the most appropriate location and orientation of the nodes are calculated round by round considering all the possible nested compositions of rotation and movement. But, rotating and moving the nodes are performed after terminating the algorithm rounds and achieving the decisive results. So, the proposed method does not impose the overhead of trial and error of rotation or relocation on the network nodes. The performance of the proposed approach has been compared with the previous works for different network configurations; simulation results show that the proposed approach outperforms the previous schemes in terms of both coverage ratio and energy efficiency.