Interference management for spectral coexistence in a heterogeneous satellite network

With the advent of the fifth generation of mobile radio communication by 2020, there will be many challenges such as increasing service demand with low delay in providing billions of end users called the satellite mobile users. It is expected that terrestrial communication systems will be faced with a dense network having many small cells anywhere and anytime. Therefore, there are some remote regions in the world where terrestrial systems cannot provide any services to end users. Furthermore, because of lack of spectral resources, it is very important that the spectrum is shared between satellite systems and terrestrial equipment by a suitable solution to interference management. In this paper, a heterogeneous satellite network that includes low earth orbit (LEO) satellite constellation and terrestrial equipment is proposed to provide low delay services. In this type of structure, interference management based on transmission power control between LEO satellite systems and mobile users is very important for obtaining high throughput. Moreover, in order to mitigate interference, transmission power control is shown based on noncooperative Stackelberg game under many subgames through pricing‐based algorithm and convex optimization method. Finally, the simulation results show that the performance of this study's system model will be improved through the proposed algorithm.     

Key Aspects of Lithium Metal Anodes for Lithium Metal Batteries

Rechargeable batteries are considered promising replacements for environmentally hazardous fossil fuel‐based energy technologies. High‐energy lithium‐metal batteries have received tremendous attention for use in portable electronic devices and electric vehicles. However, the low Coulombic efficiency, short life cycle, huge volume expansion, uncontrolled dendrite growth, and endless interfacial reactions of the metallic lithium anode are major obstacles in their commercialization. Extensive research efforts have been devoted to address these issues and significant progress has been made by tuning electrolyte chemistry, designing electrode frameworks, discovering nanotechnology‐based solutions, etc. This Review aims to provide a conceptual understanding of the current issues involved in using a lithium metal anode and to unveil its electrochemistry. The most recent advancements in lithium metal battery technology are outlined and suggestions for future research to develop a safe and stable lithium anode are presented.     

Energy efficient teaching-learning-based optimization for the discrete routing problem in wireless sensor networks

Wireless sensor networks (WSNs) are composed of sensor nodes, having limited energy resources and low processing capability. Accordingly, major challenges are involved in WSNs Routing. Thus, in many use cases, routing is considered as an NP-hard optimization problem. Many routing protocols are based on metaheuristics, such as Ant Colony Optimization (ACO) and Particle Swarm Optimization (PSO). Despite the fact that metaheuristics have provided elegant solutions, they still suffer from complexity concerns and difficulty of parameter tuning. In this paper, we propose a new routing approach based on Teaching Learning Based Optimization (TLBO) which is a recent and robust method, consisting on two essential phases: Teacher and Learner. As TLBO was proposed for continuous optimization problems, this work presents the first use of TLBO for the discrete problem of WSN routing. The approach is well founded theoretically as well as detailed algorithmically. Experimental results show that our approach allows obtaining lower energy consumption which leads to a better WSN lifetime. Our method is also compared to some typical routing methods; PSO approach, advanced ACO approach, Improved Harmony based approach (IHSBEER) and Ad-hoc On-demand Distance Vector (AODV) routing protocol, to illustrate TLBO’s routing efficiency.     

Study of Alkali (Na,K)-Doped Cu2ZnSnS4 Thin Films Prepared by Sol–Gel Method

Semiconductors - The non-doped and alkali (Na,K)-doped Cu2ZnSnS4 (CZTS) thin films were prepared using the sol–gel spin-coating method on the glass substrate, and the changes in the...     

Measurement of Onset of Structural Relaxation in Melt-Quenched Phase Change Materials

Chalcogenide phase change materials enable non-volatile, low-latency storage-class memory. They are also being explored for new forms of computing such as neuromorphic and in-memory computing. A key challenge, however, is the temporal drift in the electrical resistance of the amorphous states that encode data. Drift, caused by the spontaneous structural relaxation of the newly recreated melt-quenched amorphous phase, has consistently been observed to have a logarithmic dependence in time. Here, it is shown that this observation is valid only in a certain observable timescale. Using threshold-switching voltage as the measured variable, based on temperature-dependent and short timescale electrical characterization, the onset of drift is experimentally measured. This additional feature of the structural relaxation dynamics serves as a new benchmark to appraise the different classical models to explain drift.     

Location detection and disambiguation from twitter messages

A remarkable amount of Twitter messages are generated every second. Detecting the location entities mentioned in these messages is useful in text mining applications. Therefore, techniques for extracting the location entities from the Twitter textual content are needed. In this work, we approach this task in a similar manner to the Named Entity Recognition (NER) task, but we focus only on locations, while NER systems detect names of persons, organizations, locations, and sometimes more (e.g., dates, times). But, unlike NER systems, we address a deeper task: classifying the detected locations into names of cities, provinces/states, and countries in order to map them into physical locations. We approach the task in a novel way, consisting in two stages. In the first stage, we train Conditional Random Fields (CRF) models that are able to detect the locations mentioned in the messages. We train three classifiers: one for cities, one for provinces/states, and one for countries, with various sets of features. Since a dataset annotated with this kind of information was not available, we collected and annotated our own dataset to use for training and testing. In the second stage, we resolve the remaining ambiguities, namely, cases when there exists more than one place with the same name. We proposed a set of heuristics able to choose the correct physical location in these cases. Our two-stage model will allow a social media monitoring system to visualize the places mentioned in Twitter messages on a map of the world or to compute statistics about locations. This kind of information can be of interest to business or marketing applications.     

Potential of different additives to improve performance of potassium carbonate for CO<Subscript>2</Subscript> absorption

The performance of potassium carbonate (K₂CO₃) solution promoted by three amines, potassium alaninate (K-Ala), potassium serinate (K-Ser) and aminoethylethanolamine (AEEA), in terms of heat of absorption, absorption capacity and rate was studied experimentally. The experiments were performed using a batch reactor, and the results were compared to pure monoethanolamine (MEA) and K₂CO₃ solutions. The heat of absorption of K₂CO₃+additive solution was calculated using the Gibbs-Helmholtz equation. In addition, a correlation for prediction of CO₂ loading was presented. The results indicated that absorption heat, absorption rate and loading capacity of CO₂ increase as the concentration of additive increases. The blend solutions have higher CO₂ loading capacity and absorption rate when compared to pure K₂CO₃. The heat of CO₂ absorption for K₂CO₃+additive solutions was found to be lower than that of the pure MEA. Among the additives, AEEA showed the highest CO₂ absorption capacity and absorption rate with K₂CO₃. In conclusion, the K₂CO₃+AEEA solution with high absorption performance can be a potential solvent to replace the existing amines for CO₂ absorption.     

Extraction of β-carotene from orange peels

Extraction of β-carotene from orange peels and its nutritional evaluation through feeding study were carried out to compare the bioavailability of the extractable β-carotene with that of synthetic β-carotene. The highest yield of extractable β-carotene was recovered using a mixture of acetone and hexane (1 : 1 v/v) as a solvent in a ratio of 15 : 1 (solvent/sample) and an extraction time of 15 minutes. Growth of rats fed a diet containing β-carotene extracted from orange peels was normal and their weight gain during feeding period was real. In addition, bioavailability of the extractable β-carotene was higher than that of synthetic β-carotene, as a result of the presence of extra oils in the diet that contained β-carotene extracted from orange peels. Finally, the economical advantage can be reached by extracting β-carotene from orange peels. The bioavailability of this extractable β-carotene was high enough to compete with that of commercial synthetic β-carotene. So, it can be strongly recommended to produce such product in a large scale.     

Stress calculation for plastic helical gears under a real transverse contact ratio

Calculation methods of plastic helical gears with a real transverse contact ratio have never been studied in depth. The methods used in some references assume a uniform load distribution along the line of contact or don’t take into consideration the effect of premature mesh between one or more pair of teeth during engagement, which is not in good agreement with numerical results. This paper is focused on analysis of plastic helical gears. The nonuniform load distribution obtained from the proposed mathematical model is based on the calculation of the real contact ratio representing the real number of pairs of teeth in contact. This model also leads to the distribution of the tooth bending stress and the contact stress along the area of contact.