bluuebunny/crossref_metadata_2025 huggingface dataset:
Enigmatic Microalgae from Aeroterrestrial and Extreme Habitats in Cosmetics: The Potential of the Untapped Natural Sources
Authors: Stoyneva-Gärtner Maya , Uzunov Blagoy , Gärtner Georg
Published: April 2020

With the increasing demand for natural and safe products in cosmetics, algae with their diverse and valuable bioactive compounds are gaining vital importance. Until now, cosmetics have focused mainly on the use of freshwater and marine algae. However, algae are not restricted to aquatic habitats. They are found in essentially every type of aeroterrestrial and extreme environment on the Earth. There, they have to cope with harsh ecological conditions and have developed special strategies to thrive in these inimical habitats. Although not thoroughly studied, their adaptations include protective biochemical compounds which can find their application or are already used in the field of cosmetics. With proper cultivation techniques, algae from these habitats can provide novel sources of high-value functional products for the cosmetics industry, which have the advantage of being obtained in eco-friendly and cost-effective processes. However, it has to be considered that a few aeroterrestrial and extremophilic algae can be toxin producers, and in order to ensure conformity to the safe quality standards, all new ingredients must be properly tested. The aim of the present review is to unveil the hidden and underestimated potential of the enigmatic algae of aeroterrestrial and extreme habitats for the rapidly developing modern cosmetic industries.
Hemocompatible Chitin-Chitosan Composite Fibers
Authors: Maevskaia Ekaterina N. , Kirichuk Oksana P. , Kuznetzov Sergei I. , Dresvyanina Elena N. , Yudin Vladimir V. , Morganti Pierfrancesco
Published: April 2020

Composite chitosan fibers filled with chitin nanofibrils (CNF) were obtained by the wet spinning method. The paper discusses the mechanical properties of such type fibers and their hemocompatibility, as well as the possibility of optimizing these properties by adding chitin nanofibrils. It was shown that low CNF concentration (about 0.5%) leads to an increase in fiber tensile strength due to the additional orientation of chitosan macromolecules. At the same time, with an increase in the content of CNF, the stability of the mechanical properties of composite fibers in a humid medium increases. All chitosan fibers, except 0.5% CNF, showed good hemocompatibility, even on prolonged contact with human blood. The addition of chitin nanofibers leads to decrease in hemoglobin molecules sorption due to the decline in optical density at wavelengths of 414 nm and 540 nm. Nevertheless, the hemolysis of fibers was comparable or even lesser that carbon hemosorbent, which is actively used in clinical practice.
Effect of Strains and V-Shaped Pit Structures on the Performance of GaN-Based Light-Emitting Diodes
Authors: Chen Shuo-Wei , Chang Chia-Jui , Lu Tien-Chang
Published: April 2020

Strains and V-shaped pits are essential factors for determining the efficiency of GaN-based light-emitting diodes (LEDs). In this study, we systematically analyzed GaN LED structures on patterned sapphire substrates (PSSs) with two types of growth temperature employed for prestrained layers and three different thickness of n-type GaN layers by using cathodoluminescence (CL), microphotoluminescence (PL), and depth-resolved confocal Raman spectroscopy. The results indicated that V-pits formation situation can be analyzed using CL. From the emission peak intensity ratio of prestrained layers and multiple quantum wells (MQWs) in the CL spectrum, information regarding strain relaxation between prestrained layers and MQWs was determined. Furthermore, micro-PL and depth-resolved confocal Raman spectroscopy were employed to validate the results obtained from CL measurements. The growth conditions of prestrained layers played a dominant role in the determination of LED performance. The benefit of the thick layer of n-GaN was the strain reduction, which was counteracted by an increase in light absorption in thick n-type doped layers. Consequently, the most satisfactory LED performance was observed in a structure with relatively lower growth temperature of prestrained layers that exhibited larger V-pits, leading to higher strain relaxation and thinner n-type GaN layers, which prevent light absorption caused by n-type GaN layers.
Capacitance Properties in Ba0.3Sr0.7Zr0.18Ti0.82O3 Thin Films on Silicon Substrate for Thin Film Capacitor Applications
Authors: Chen Xiaoyang , Mo Taolan , Huang Binbin , Liu Yun , Yu Ping
Published: April 2020

Crystalline Ba0.3Sr0.7Zr0.18Ti0.82O3 (BSZT) thin film was grown on Pt(111)/Ti/SiO2/Si substrate using radio frequency (RF) magnetron sputtering. Based on our best knowledge, there are few reports in the literature to prepare the perovskite BSZT thin films, especially using the RF magnetron sputtering method. The microstructure of the thin films was characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM), and capacitance properties, such as capacitance density, leakage behavior, and the temperature dependence of capacitance were investigated experimentally. The prepared perovskite BSZT film showed a low leakage current density of 7.65 × 10−7 A/cm2 at 60 V, and large breakdown strength of 4 MV/cm. In addition, the prepared BSZT thin film capacitor not only exhibits an almost linear and acceptable change (ΔC/C ~13.6%) of capacitance from room temperature to 180 °C but also a large capacitance density of 1.7 nF/mm2 at 100 kHz, which show great potential for coupling and decoupling applications.
Binary Liquid Crystal Mixtures Based on Schiff Base Derivatives with Oriented Lateral Substituents
Authors: Alnoman Rua B. , Hagar Mohamed , Ahmed Hoda A. , Naoum Magdi M. , Sobaih Hanefah A. , Almshaly Jawaher S. , Haddad Mawadh M. , Alhaisoni Rana A. , Alsobhi Tahani A.
Published: April 2020

Binary mixtures of the laterally substituted Schiff base/ester derivatives, namely 4-((2- or 3-) substituted phenyl imino methyl) phenyl-4”-alkoxy benzoates, Ia–d, were prepared and mesomorphically studied by differential scanning calorimetry (DSC) and their mesophases identified by polarized optical microscopy (POM). The lateral group (1-naphthyl, 2-F, 2-Br, 3-F in Ia–d, respectively) is attached to different positions of the phenyl Schiff moiety. The mixtures investigated were made from two differently shaped compounds that differ from each other in the polarity, size, orientation, and relative positions of the lateral group. The results revealed that the binary mixture Ia/Ib (bearing the naphthyl and 2-flouro substituents) exhibited the SmA phase, which covered the whole composition range. For the mixtures Ib/Id (2-F and 2-Br), the isomeric lateral F-group in compound Ib distributed the SmA arrangement of Id. In the Ic/Id mixture bearing two positionally and structurally different substituents, the addition of Ic to Id resulted in solid binary mixtures where its behavior may be attributed to the negligible steric effect of the small electronegative fluorine atom compared to the Br atom. Density functional theory (DFT) theoretical calculations were carried out to estimate the geometrical parameters of individual components and to show the effect of these parameters in the mesophase behavior of the binary system, where the higher dipole moment of Id (6 Debye) may be the reason for its high π–π molecular stacking, which influences its mesophase range and stability.
Structural, Optical and Dynamic Properties of Thin Smectic Films
Authors: Śliwa Izabela , Zakharov A. V.
Published: April 2020

The problem of predicting structural and dynamic behavior associated with thin smectic films, both deposited on a solid surface or stretched over an opening, when the temperature is slowly increased above the bulk transition temperature towards either the nematic or isotropic phases, remains an interesting one in the physics of condensed matter. A useful route in studies of structural and optical properties of thin smectic films is provided by a combination of statistical–mechanical theories, hydrodynamics of liquid crystal phases, and optical and calorimetric techniques. We believe that this review shows some useful routes not only for the further examining of the validity of a theoretical description of thin smectic films, both deposited on a solid surface or stretched over an opening, but also for analyzing their structural, optical, and dynamic properties.
A Common Approach to the Conservation of Threatened Island Vascular Plants: First Results in the Mediterranean Basin
Authors: Fenu Giuseppe , Bacchetta Gianluigi , Christodoulou Charalambos S. , Cogoni Donatella , Fournaraki Christini , Gian Pietro Giusso del Galdo , Gotsiou Panagiota , Kyratzis Angelos , Piazza Carole , Vicens Magdalena , de Montmollin Bertrand
Published: April 2020

The Mediterranean islands represent a center of vascular plant diversity featuring a high rate of endemic richness. Such richness is highly threatened, however, with many plants facing the risk of extinction and in need of urgent protection measures. The CARE-MEDIFLORA project promoted the use of ex situ collections to experiment with in situ active actions for threatened plants. Based on common criteria, a priority list of target plant species was elaborated, and germplasm conservation, curation and storage in seed banks was carried out. Accessions were duplicated in the seed banks of the partners or other institutions. Germination experiments were carried out on a selected group of threatened species. A total of 740 accessions from 429 vascular plants were stored in seed banks, and 410 seed germination experiments for 283 plants species were completed; a total of 63 in situ conservation actions were implemented, adopting different methodological protocols. For each conservation program, a specific monitoring protocol was implemented in collaboration with local and regional authorities. This project represents the first attempt to develop common strategies and an opportunity to join methods and methodologies focused on the conservation of threatened plants in unique natural laboratories such as the Mediterranean islands.
Genetic Diversity and Population Structure of Acanthochiton rubrolineatus (Polyplacophora) Based on Mitochondrial and Nuclear Gene Markers
Authors: Xu Haowen , Chu Zhailin , Zhang Jing , Jing Meidong , Huang Ling
Published: April 2020

Acanthochiton rubrolineatus (Cryptoplacidae, Neoloricata, Polyplacophora) has a narrow distribution range along the seacoasts of China, the Korean Peninsula and Japan. We collected 238 samples from eight localities along the Chinese coast, and analyzed the genetic diversity and population structure with COI, 16S-rRNA and 28S-rRNA gene sequences. All analyses based on combined sequences of COI and 16S-rRNA suggested that there was evident genetic differentiation between the northern populations (YT, WH, DL, QD, LYG) and southern populations (ZS, YH, XM) of A. rubrolineatus. The haplotype distribution pattern and genetic diversity based on 28S-rRNA sequences also supported the genetic divergence between the two groups. Both groups had experienced population expansion after the ice age of Pleistocene, and an additional population bottleneck had happened in the southern group in recent history, which led to low genetic diversity of mitochondrial DNA and abnormally high diversity of nuclear DNA in this group. Our results suggested that the protection on A. rubrolineatus is necessary, and the northern and southern group should be protected separately.
An On-Demand Service for Managing and Analyzing Arctic Sea Ice High Spatial Resolution Imagery
Authors: Sha Dexuan , Miao Xin , Xu Mengchao , Yang Chaowei , Xie Hongjie , Mestas-Nuñez Alberto M. , Li Yun , Liu Qian , Yang Jingchao
Published: April 2020

Sea ice acts as both an indicator and an amplifier of climate change. High spatial resolution (HSR) imagery is an important data source in Arctic sea ice research for extracting sea ice physical parameters, and calibrating/validating climate models. HSR images are difficult to process and manage due to their large data volume, heterogeneous data sources, and complex spatiotemporal distributions. In this paper, an Arctic Cyberinfrastructure (ArcCI) module is developed that allows a reliable and efficient on-demand image batch processing on the web. For this module, available associated datasets are collected and presented through an open data portal. The ArcCI module offers an architecture based on cloud computing and big data components for HSR sea ice images, including functionalities of (1) data acquisition through File Transfer Protocol (FTP) transfer, front-end uploading, and physical transfer; (2) data storage based on Hadoop distributed file system and matured operational relational database; (3) distributed image processing including object-based image classification and parameter extraction of sea ice features; (4) 3D visualization of dynamic spatiotemporal distribution of extracted parameters with flexible statistical charts. Arctic researchers can search and find arctic sea ice HSR image and relevant metadata in the open data portal, obtain extracted ice parameters, and conduct visual analytics interactively. Users with large number of images can leverage the service to process their image in high performance manner on cloud, and manage, analyze results in one place. The ArcCI module will assist domain scientists on investigating polar sea ice, and can be easily transferred to other HSR image processing research projects.
Weyl Prior and Bayesian Statistics
Authors: Jiang Ruichao , Tavakoli Javad , Zhao Yiqiang
Published: April 2020

When using Bayesian inference, one needs to choose a prior distribution for parameters. The well-known Jeffreys prior is based on the Riemann metric tensor on a statistical manifold. Takeuchi and Amari defined the α -parallel prior, which generalized the Jeffreys prior by exploiting a higher-order geometric object, known as a Chentsov–Amari tensor. In this paper, we propose a new prior based on the Weyl structure on a statistical manifold. It turns out that our prior is a special case of the α -parallel prior with the parameter α equaling − n , where n is the dimension of the underlying statistical manifold and the minus sign is a result of conventions used in the definition of α -connections. This makes the choice for the parameter α more canonical. We calculated the Weyl prior for univariate Gaussian and multivariate Gaussian distribution. The Weyl prior of the univariate Gaussian turns out to be the uniform prior.
Time-Dependent Pseudo-Hermitian Hamiltonians and a Hidden Geometric Aspect of Quantum Mechanics
Authors: Mostafazadeh Ali
Published: April 2020

A non-Hermitian operator H defined in a Hilbert space with inner product ⟨ · | · ⟩ may serve as the Hamiltonian for a unitary quantum system if it is η -pseudo-Hermitian for a metric operator (positive-definite automorphism) η . The latter defines the inner product ⟨ · | η · ⟩ of the physical Hilbert space H η of the system. For situations where some of the eigenstates of H depend on time, η becomes time-dependent. Therefore, the system has a non-stationary Hilbert space. Such quantum systems, which are also encountered in the study of quantum mechanics in cosmological backgrounds, suffer from a conflict between the unitarity of time evolution and the unobservability of the Hamiltonian. Their proper treatment requires a geometric framework which clarifies the notion of the energy observable and leads to a geometric extension of quantum mechanics (GEQM). We provide a general introduction to the subject, review some of the recent developments, offer a straightforward description of the Heisenberg-picture formulation of the dynamics for quantum systems having a time-dependent Hilbert space, and outline the Heisenberg-picture formulation of dynamics in GEQM.
Bayesian Model Averaging and Prior Sensitivity in Stochastic Frontier Analysis
Authors: Makieła Kamil , Mazur Błażej
Published: April 2020

This paper discusses Bayesian model averaging (BMA) in Stochastic Frontier Analysis and investigates inference sensitivity to prior assumptions made about the scale parameter of (in)efficiency. We turn our attention to the “standard” prior specifications for the popular normal-half-normal and normal-exponential models. To facilitate formal model comparison, we propose a model that nests both sampling models and generalizes the symmetric term of the compound error. Within this setup it is possible to develop coherent priors for model parameters in an explicit way. We analyze sensitivity of different prior specifications on the aforementioned scale parameter with respect to posterior characteristics of technology, stochastic parameters, latent variables and—especially—the models’ posterior probabilities, which are crucial for adequate inference pooling. We find that using incoherent priors on the scale parameter of inefficiency has (i) virtually no impact on the technology parameters; (ii) some impact on inference about the stochastic parameters and latent variables and (iii) substantial impact on marginal data densities, which are crucial in BMA.
Can Local Policies Reduce the Gap between ‘Centers’ and ‘Inner Areas’? The Case of Italian Municipalities’ Expenditure
Authors: Romagnoli Luca , Mastronardi Luigi
Published: April 2020

This study analyzes the links between Italian inner area municipalities’ expenditure and per capita incomes, considered as a proxy of well-being. Inner areas are territorial contexts characterized by a significant distance from the centers, the main supply poles of essential services. Following a top-down approach, the paper at first demonstrates the existence of a global convergence process in per capita incomes, with a faster rate of convergence in inner areas with respect to centers; then, attention is focused on local administrations’ policies and their impact on incomes in Italian inner areas. The paper gives a twofold contribution to the debate about the implementation of territorial cohesion policies: (a) on one side, public expenditure data are considered for the first time in an econometric model regarding Italian inner areas; (b) on the other side, the reference territorial subdivision is the lowest possible, giving the opportunity to investigate the changes in well-being at the finest scale.
Technical Efficiency of Smallholder Agriculture in Developing Countries: The Case of Ethiopia
Authors: Tenaye Anbes
Published: April 2020

The efficient use of inputs is indispensable in many developing countries, such as Ethiopia. This study assesses the level and determinants of technical efficiency of smallholder farmers using the true fixed effects (TFE) model. The TFE model separates inefficiency from unobserved heterogeneity. Empirical data come from four rounds of panel data (1994–2009) from the Ethiopian rural household survey (ERHS). A one-step maximum likelihood estimator was employed to estimate the Cobb-Douglas stochastic frontier production function and factors influencing technical efficiency. The results indicated that the major variables affecting technical efficiency are policy responsive, albeit to varying degrees: education of the household head, family size, farm size, land fragmentation, land quality, credit use, extension service, off-farm employment, and crop share. The analyses also identify variables amenable to policy changes in the production function: labor, traction power, farm size, seeds, and fertilizer. The mean household-level efficiency for the surveyed farmers is 0.59, indicating that farmers could improve technical efficiency. This implies that smallholder farms in Ethiopia can reduce the input requirement of producing the average output by 41% if their operations become technically efficient. This study recommends that the above policy variables be considered to make Ethiopian smallholder farmers more efficient.
A Meta-Analysis of the Cognitive, Affective, and Interpersonal Outcomes of Flipped Classrooms in Higher Education
Authors: Jang Hwan Young , Kim Hye Jeong
Published: April 2020

This paper aims to quantify the effects of flipped classrooms in higher education by reviewing 43 empirical studies of students’ cognitive, affective, and interpersonal outcomes. The innovative pedagogy of a flipped classroom in higher education fosters a sustainable, interactive, and student-centered learning environment (as opposed to the traditional lecture style, in which there is little room for interaction). This study’s results show the positive effects of flipped classrooms and highlight the improvement in students’ educational outcomes between 2012 and 2017. Overall, effect sizes were medium—effect size (ES) = 0.35, 95% confidence interval (CI) = 0.24 to 0.47—across three outcome domains using a random effects model. In the outcomes, affective (ES = 0.59), interpersonal (ES = 0.53), and cognitive (ES = 0.24) domains were of a higher order than the effect sizes. However, the results indicated that flipped classrooms benefitted students studying chemistry, engineering, mathematics, and physics less than they did students studying other subjects.
Interactive Trimap Generation for Digital Matting Based on Single-Sample Learning
Authors: Chen Zhenpeng , Zheng Yuanjie , Li Xiaojie , Luo Rong , Jia Weikuan , Lian Jian , Li Chengjiang
Published: April 2020

Image matting refers to the task of estimating the foreground of images, which is an important problem in image processing. Recently, trimap generation has attracted considerable attention because designing a trimap for every image is labor-intensive. In this paper, a two-step algorithm is proposed to generate trimaps. To use the proposed algorithm, users must only provide some clicks (foreground clicks and background clicks), which are employed as the input to generate a binary mask. One-shot learning technique achieves remarkable progress on semantic segmentation, we extend this technique to perform the binary mask prediction task. The mask is further used to predict the trimap using image dilation. Extensive experiments were performed to evaluate the proposed algorithm. Experimental results show that the trimaps generated using the proposed algorithm are visually similar to the user-annotated ones. Comparing with the interactive matting algorithms, the proposed algoritm is less labor-intensive than trimap-based matting algorithm and achieved more accuate results than scribble-based matting algorithm.
A Low Complexity Joint Encryption-Modulation Method for IoT Sensor Transceivers
Authors: Hoang Dai , Tran Thi , Nakashima Yasuhiko
Published: April 2020

Physical layer encryption (PLE) is a new research trend for securing data in communication systems. However, conventional procedures in works on PLE are of high complexity and degrade the packet error rate (PER) performance of the system. They are therefore not yet suitable for IoT sensors’ transceiver, which has limited power and computational resource. In this paper, we propose a low complexity PLE method named as joint encryption-modulation (JEM) for small transceivers such as IoT sensors. In our JEM method, data is encrypted after modulation to preserve high security. Our JEM method does not make change the constellation of the modulation after encryption; therefore, the encryption does not degrade PER performance of the system as the conventional works do. Furthermore, the encryption is performed by XOR gates and multiplexers only. It is, therefore, low complexity. Our experiment results show that the JEM method improves about 3 dB of PER performance as compared with that of conventional works. JEM method can support multiple modulation types such as BPSK, QPSK, 16-256 QAM within a small hardware cost. Compared with conventional works, JEM’s hardware resource is reduced by 87.5% in terms of FPGA synthesis and 86.5% in terms of the ASIC circuit. ASIC static power consumption of JEM is reduced by 80.6%.
Performance Analysis of Interference-Aware Multi-Packet Reception Networks
Authors: Furtado Antonio , Oliveira Rodolfo , Bernardo Luis , Dinis Rui
Published: April 2020

Decentralized wireless networks are gaining increasing popularity as they do not need a fixed infrastructure. Simultaneously, multiple research initiatives have led to different findings at the PHY layer of the wireless communication systems, which include Multi-Packet Reception (MPR) techniques that enable a receiver to decode multiple packets that are transmitted simultaneously. However, the distributed nature of decentralized wireless networks demands different network control policies that should take into account the MPR capabilities to increase the network performance. This work studies the performance of a wireless network composed of multiple transmitters that are willing to transmit to a single receiver. This receiver has MPR capability and adopts an Energy-based Sensing (EBS) technique to enable uplink users’ transmissions without interfering with the ongoing transmissions from other transmitters. The first remark to be made is that the MPR technique performance depends on the channel propagation conditions and on the amount of time the receiver needs to detect the spectrum’s occupancy state. However, it is shown that by increasing the number of samples needed to increase the sensing accuracy, the receiver may degrade its throughput, namely if the receiver is equipped with a single radio, that is sequentially used for sensing and transmitting (split-phase operation). The results presented in the paper show the impact of the channel propagation condition and EBS parameterization on wireless network throughput and the cases where the receiver MPR capture performance is greatly improved by the use of a spectrum sensing technique.
Application of Terahertz Spectroscopy to Rubber Products: Evaluation of Vulcanization and Silica Macro Dispersion
Authors: Hirakawa Yasuyuki , Yasumoto Yuki , Gondo Toyohiko , Sone Ryota , Morichika Toshiaki , Minato Takakazu , Hojo Masahiro
Published: April 2020

Industrial applications of terahertz (THz) technology are becoming more widespread. In particular, novel evaluation methods for essential rubber products are being developed. THz absorbance spectra of various rubber polymers and reagents enable visualization of filler dispersions and vulcanization reactions. Here, improved visualization of the vulcanization reaction in thick rubber samples is discussed. Silica macro-dispersion is also analyzed because it is a general filler in automobile tires and has been difficult to evaluate with conventional techniques.
An Integrated Toolbox for the Engagement of Citizens in the Monitoring of Water Ecosystems
Authors: Krommyda Maria , Rigos Anastasios , Bolierakis Spyridon-Nektarios , Theodoropoulos Theodoros , Tamascelli Stefano , Simeone Luca , Sdongos Evangelos , Amditis Angelos
Published: April 2020

The monitoring of water ecosystems requires consistent and accurate sensor measurements, usually provided from traditional in-situ environmental monitoring systems. Such infrastructure, however, is expensive, hard to maintain and available only in limited areas that had been affected by extreme phenomena and require continuous monitoring. Due to climate change, the monitoring of larger areas and extended water ecosystems is imperative, raising the question of whether this monitoring can be disengaged from the in-situ monitoring systems. Due to climate change and extreme weather phenomena, more citizens are affected by environmental issues and become aware of the need to contribute to their monitoring. As a result, they are willing to offer their time to support the collection of scientific data. Collecting such data from volunteers, with no technical knowledge and while using low-cost equipment such as smart phones and portable sensors, raises the question of data quality and consistency. We present here a novel integrated toolbox that can support the organization of crowd-sourcing activities, ensure the engagement of the participants, the data collection in a consistent way, enforce extensive data quality controls and provide to local authorities and scientists access to the collected information in a uniform way, through widely accepted standards.
Tan-Sun Transformation-Based Phase-Locked Loop in Detection of the Grid Synchronous Signals under Distorted Grid Conditions
Authors: Tan Guangjun , Zong Chunan , Sun Xiaofeng
Published: April 2020

When three-phase voltages are polluted with unbalance, DC offsets, or higher harmonics, it is a challenge to quickly detect their parameters such as phases, frequency, and amplitudes. This paper proposes a phase-locked loop (PLL) for the three-phase non-ideal voltages based on the decoupling network composed of two submodules. One submodule is used to detect the parameters of the fundamental and direct-current voltages based on Tan-Sun transformation, and the other is used to detect the parameters of the higher-harmonic voltages based on Clarke transformation. By selecting the proper decoupling vector by mapping Hilbert space to Euclidean space, the decoupling control for each estimated parameter can be realized. The settling time of the control law can be set the same for each estimated parameter to further improve the response speed of the whole PLL system. The system order equals the number of the estimated parameters in each submodule except that a low-pass filter is required to estimate the average amplitude of the fundamental voltages, so the whole PLL structure is very simple. The simulation and experimental results are provided in the end to validate the effectiveness of the proposed PLL technique in terms of the steady and transient performance.
Validation and Numerical Sensitivity Study of Air Baffle Photovoltaic-Thermal Module
Authors: Kim Yu-Jin , Lee Kwang-Seob , Yang Libing , Entchev Evgueniy , Kang Eun-Chul , Lee Euy-Joon
Published: April 2020

Photovoltaic-Thermal (PVT) is a type of technology that generates electricity and heat simultaneously at the point of use. The generated electricity could be used on site or exported to the grid while the thermal output could be utilized for space and water heating. There is a lot of research for solar air heating with experiment or CFD (Computational Fluid Dynamics), but CFD has the disadvantage that it would indicate impractical results. In this paper, a numerical PVT baseline model was developed and validated with Separate Effect Test (SET) data to increase reliability. The numerical study was conducted by considering the effect of baffle lengths and baffle slopes on outlet temperature, total heat transfer and pressure drop inside PVT air module. An optimum PVT baffle length and slope design were suggested. The baseline numerical PVT model agreed well with the test data set as indicated by 1.25% error for inlet–outlet temperatures difference. The sensitivity study was conducted by changing the PVT baffle length and slope. The optimum baffle design was concerned with both heat transfer and pressure drop at the same time with ratio. The baffle length should be kept under 150 mm and baffle slope should be greater than 30° to achieve better air mixing in PVT air channel and unit heat transfer compared to baffle slope less than 30°.
Conceptual Design and Simulation of a Self-Adjustable Heaving Point Absorber Based Wave Energy Converter
Authors: Aderinto Tunde , Li Hua
Published: April 2020

Different concepts and methods have been proposed and developed by many researchers to harvest ocean wave energy. In this paper, a new self-adjustable wave energy converter concept is presented, which changes its inertia through ballasting and de-ballasting using sea water. The trigger of ballasting and de-ballasting is controlled by the critical wave period. Therefore, the self-adjustable wave energy converter is able to interact at resonance with the ocean waves at two different resonant bandwidths. Ten years real wave data with hourly resolution from a selected location in Gulf of Mexico was used in this paper to decide the critical wave period and other parameters of the wave energy converter. The annual energy performance of the self-adjustable wave energy converter was also estimated and compared with non-adjustable wave energy converter with similar dimensions. Structural analysis including both static and fatigue analysis was performed on the self-adjustable wave energy converter to determine its survivability with the real ocean wave data. The results show that the self-adjustable wave energy converter is able to capture more energy than non-adjustable wave energy converter, and is able to survive during the hash ocean wave conditions.
Conceptual Design Development of a Fuel-Reforming System for Fuel Cells in Underwater Vehicles
Authors: Jung Seung-Kyo , Cha Won-Sim , Park Yeong-In , Kim Shin-Hyung , Choi Jungho
Published: April 2020

An air-independent propulsion system containing fuel cells is applied to improve the operational performance of underwater vehicles in an underwater environment. Fuel-reforming efficiently stores and supplies hydrogen required to operate fuel cells. In this study, the applicability of a fuel-reforming system using various fuels for underwater vehicles was analyzed by calculating the fuel and water consumptions, the amount of CO2 generated as a byproduct, and the amount of water required to dissolve the CO2 using aspen HYSYS (Aspen Technology, Inc., Bedford, MA, USA). In addition, the performance of the fuel-reforming system for methanol, which occupies the smallest volume in the system, was researched by analyzing performance indicators such as methanol conversion rate, hydrogen, yield and selectivity, and reforming efficiency under conditions at which pressure, temperature, steam-to-carbon ratio (SCR), and hydrogen separation efficiency vary. The highest reforming efficiency was 77.7–77.8% at 260 °C and 270 °C. At SCR 1.5, the reforming efficiency was the highest, which is 77.8%, and the CO2 generation amount was the lowest at 1.46 kmol/h. At high separation efficiency, the reforming efficiency increased due to the reduction of reactants, and a rate at which energy is consumed for endothermic reactions also decreased, resulting in a lower CO2 generation amount.
Air Conditioning Energy Saving from Cloud-Based Artificial Intelligence: Case Study of a Split-Type Air Conditioner
Authors: Lee Dasheng , Tsai Fu-Po
Published: April 2020

This study developed cloud-based artificial intelligence (AI) that could run AI programs in the cloud and control air conditioners remotely from home. AI programs in the cloud can be altered any time to provide good control performances without altering the control hardware. The air conditioner costs and prices can thus be reduced by the increasing energy efficiency. Cloud control increased energy efficiency through AI control based on two conditions: (1) a constant indoor cooling rate and (2) a fixed stable range of indoor temperature control. However, if the two conditions cannot be guaranteed or the cloud signals are lost, the original proportional-integral-differential (PID) control equipped in the air conditioner can be used to ensure that the air conditioner works stably. The split-type air conditioner tested in this study is ranked eighth among 1177 air conditioners sold in Taiwan according to public data. It has extremely high energy efficiency, and using AI to increase its energy efficiency was challenging. Thus, this study analyzed the literature of AI-assisted controls since 1995 and applied it to heating, ventilation, and air conditioning equipment. Two technologies with the highest energy saving efficiency, a fuzzy + PID and model-based predictive control (MPC), were chosen to be developed into two control methodologies of cloud-based AI. They were tested for whether they could improve air conditioning energy efficiency. Energy efficiency measurement involved an enthalpy differential test chamber. The two indices, namely the energy efficiency ratio (EER) and cooling season power factor (CSPF), were tested. The EER measurement is the total efficiency value obtained when testing the required electric power at the maximum cooling capacity under constantly controlled temperature and humidity. CSPF is the tested efficiency value under dynamic conditions from changing indoor and outdoor temperatures and humidity according to the climate conditions in Taiwan. By using the static energy efficiency index EER for evaluation, the fuzzy + PID control could not save energy, but MPC increased the EER value by 9.12%. By using the dynamic energy efficiency index CSPF for evaluation, the fuzzy + PID control could increase CSPF by 3.46%, and MPC could increase energy efficiency by 7.37%.
Battery Energy Storage Systems in Microgrids: Modeling and Design Criteria
Authors: Moncecchi Matteo , Brivio Claudio , Mandelli Stefano , Merlo Marco
Published: April 2020

Off-grid power systems based on photovoltaic and battery energy storage systems are becoming a solution of great interest for rural electrification. The storage system is one of the most crucial components since inappropriate design can affect reliability and final costs. Therefore, it is necessary to adopt reliable models able to realistically reproduce the working condition of the application. In this paper, different models of lithium-ion battery are considered in the design process of a microgrid. Two modeling approaches (analytical and electrical) are developed based on experimental measurements. The derived models have been integrated in a methodology for the robust design of off-grid electric power systems which has been implemented in a MATLAB-based computational tool named Poli.NRG (POLItecnico di Milano—Network Robust desiGn). The procedure has been applied to a real-life case study to compare the different battery energy storage system models and to show how they impact on the microgrid design.
Numerical Optimization of a Four-Cylinder Double-Acting Stirling Engine Based on Non-Ideal Adiabatic Thermodynamic Model and SCGM Method
Authors: Cheng Chin-Hsiang , Tan Yi-Han
Published: April 2020

The aim of this study is to optimize a four-cylinder, double-acting α-type Stirling engine with wobble-yoke mechanism using an optimization scheme incorporated with an efficient thermodynamic model. In this study, the non-ideal adiabatic thermodynamic model is improved by taking into account factors including pressure drops due to the sudden expansion or contraction of flow cross-sectional areas in the engine, multiple nodes in the regenerator adopted to accurately capture the temperature gradient in the regenerator, and the dependence of the transport properties (thermal conductivity and dynamic viscosity) of the working fluid on temperature and pressure. A parametric analysis is firstly performed to identify the designed parameters that need to be optimized. In this study, engine optimization is carried out by using the simplified conjugate-gradient method (SCGM). The effects of the weighting coefficients of the objective function are studied. For a particular case considered, the optimization successfully elevates the power output from 1062.56 to 1659.72 W, and thermal efficiency from 27.41% to 37.22%. Furthermore, the robustness of the optimization method is tested by giving different sets of initial guesses. It is found that the present approach can stably lead to the same optimal design and is independent of the initial guess.
Transactive Energy Market for Energy Management in Microgrids: The Monash Microgrid Case Study
Authors: Khorasany Mohsen , Azuatalam Donald , Glasgow Robert , Liebman Ariel , Razzaghi Reza
Published: April 2020

Transactive energy is a novel approach for energy management and trading, which can be used in microgrids to facilitate the integration of distributed energy resources (DERs) in existing networks. The key feature in transactive energy is using market-based solutions for energy management. Hence, an appropriate transactive energy market (TEM) framework should be designed to enable and incentivize DER owners to participate in different markets. The efficient implementation of TEM for microgrid energy management encompasses the application of a variety of design principles. In this rapidly developing area, this paper presents a complete proposal of the TEM as a framework for the design, implementation, and deployment of transactive energy solutions for energy management in microgrids. In particular, we outline the requirements to design an effective market mechanism for the TEM. The applicability of this perspective is demonstrated through the introduction of the Monash Microgrid as a real-world implementation of a TEM solution, where a complete hardware and software foundation is presented as a platform to deploy a market-based solution for microgrid energy management. This is further illustrated through an example scenario, where the application of TEM is discussed to demonstrate the impact of considered design choices on achieving desired objectives.
Comparison of Bimetallic Fe-Cu and Fe-Ca Oxygen Carriers for Biomass Gasification
Authors: Muriungi Beatrice , Wang Lijun , Shahbazi Abolghasem
Published: April 2020

Two bimetallic Fe-Cu and Fe-Ca oxygen carriers were studied for chemical looping gasification (CLG) of biomass. The SEM results indicated that there was no obvious agglomeration on the bimetallic Fe-Cu oxygen carrier supported on Al2O3 and Fe-Ca oxygen carrier after five redox cycles while agglomeration occurred on CuO supported on Al2O3 due to the low melting point of CuO. The XRD results indicated the presence of copper-ferrite and calcium-ferrite phases in the bimetallic materials. The two bimetallic oxygen carriers can be re-oxidized with air to form a crystalline that is similar to the fresh materials. The Fe-Ca oxide became active at 360 °C which was lower than 380 °C for the Fe-Cu oxygen carrier. The high thermal stability and redox reactivity of bimetallic Fe-Cu and Fe-Ca oxygen carriers make the bimetallic oxygen carriers more suitable for recycling during CLG. The method for preparing Fe-Cu oxygen carriers had no significant impact on biomass conversion efficiency but had significant effect on the quality of syngas. Proper control of the biomass/oxygen carrier mass ratio is critical to achieve high selectivity towards gasification instead of combustion. The Fe-Ca oxygen carrier could achieve higher selectivity towards gasification than the Fe-Cu oxygen carrier.
Relative Free Energy Function and Structural Theory of Thermoeconomics
Authors: Valero Antonio , Torres César
Published: April 2020

This paper explores the advantages of using relative free energy instead of exergy to build a mathematical theory of thermodynamic costs to diagnose malfunctions in thermal systems. This theory is based on the definition of a linearized characteristic equation that represents the physical behavior of each component. The physical structure of the system described by its energy interrelationships is called “primal”, and its derivatives are the costs and consumptions. The obtained costing structure is the mathematical “dual” of its primal. The theory explains why the F and P cost assessment rules and any other suggestion may (or may not be) rational under a given disaggregation scheme. A result of the theory is a new thermodynamic function, called the relative free energy, and a new parameter called deterioration temperature due to a component’s deterioration cause, characterized by a h-s thermodynamic trajectory describing the effects on the exiting stream. The relative free energy function allows for an exact relationship between the amount of used resources and the increase in entropy generation caused by the deterioration path of the component. This function allows the obtaining of, for the first time, an appropriate characteristic equation for a turbine and a new definition of efficiency that does not depend on the environment temperature but on its deterioration temperature. Also, costing with relative free energy instead of exergy may open a new path for more precise and straightforward assessments of component deteriorations.
Numerical Studies on Teeter Bed Separator for Particle Separation
Authors: Zhu Xueshuai , Liu Junli , Cao Chao , Dong Yalin , Wei Tao
Published: April 2020

Teeter Bed Separators (TBS) are liquid–solid fluidized beds that are widely used in separation of coarse particles in coal mining industry. The coal particles settle in the self-generating medium bed resulting in separation according to density. Due to the existence of self-generating medium beds, it is difficult to study the sedimentation of particles in TBS through experiments and detection methods. In the present research, a model was built to investigate the bed expansion characteristics with water velocity based on the Euler–Euler approach, and to investigate the settling of foreign particles through bed based on the Euler–Lagrange approach in TBS. Results show that the separation of in TBS should be carried out at low water velocity under the condition of stable fluidized bed. Large particles have a high slip velocity, and they are easily flowing through the bed into the light product leading to a mismatch. The importance of self-generating bed on separation of particle with narrow size ranges are clarified. The model provides a way for investigating the separation of particles in a liquid–solid fluidized bed and provides suggestions for the selection of operation conditions in TBS application.
Consensus Control for Reactive Power Sharing Using an Adaptive Virtual Impedance Approach
Authors: Alsafran Ahmed S. , Daniels Malcolm W.
Published: April 2020

Reactive power sharing among distributed generators (DGs) in islanded microgrids (MGs) presents control challenges, particularly in the mismatched feeder line condition. Improved droop control methods independently struggle to resolve this issue and centralized secondary control methods exhibit a high risk of collapse for the entire MG system under any failure in the central control. Distributed secondary control methods have been recently proposed to mitigate the reactive power error evident in the presence of mismatched feeder lines. This paper details a mathematical model of an adaptive virtual impedance control that is based on both leaderless and leader-followers consensus controls with a novel triangle mesh communication topology to ensure accurate active and reactive power sharing. The approach balances an enhanced rate of convergence with the anticipated implementation cost. A MATLAB/Simulink model with six DG units validates the proposed control performance under three different communication structures: namely, ring, complete, and triangle mesh topologies. The results suggest that leaderless consensus control is a reliable option with large DG systems, while the leader-followers consensus control is suitable for the small systems. The triangle mesh communication topology provides a compromise approach balancing the rate of convergence and the expected cost. The extensibility and scalability are advantages of this topology over the alternate ring and complete topologies.
Improved PSO: A Comparative Study in MPPT Algorithm for PV System Control under Partial Shading Conditions
Authors: Hayder Wafa , Ogliari Emanuele , Dolara Alberto , Abid Aycha , Ben Hamed Mouna , Sbita Lasaad
Published: April 2020

This paper deals with the implementation and analysis of a new maximum power point tracking (MPPT) control method, which is tested under variable climatic conditions. This new MPPT strategy has been created for photovoltaic systems based on Particle Swarm Optimization (PSO). The novel Improved Particle Swarm Optimization (IPSO) algorithm is tested in several simulations which have been implemented in view of the various system responses such as: voltage, current, and power. The performances of the proposed IPSO algorithm have been completed and compared with results of well-established methods adopted in the literature showing a higher accuracy.