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Records Added in April 2020
Records added in April 2020
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Showing records 62 to 86 of 86. [First] Page: 1 2 3 4 Last
Stabilization/Solidification of Strontium Using Magnesium Silicate Hydrate Cement
Tingting Zhang, Jing Zou, Yimiao Li, Yuan Jia, Christopher R. Cheeseman
April 14, 2020 (v1)
Subject: Materials
Keywords: leaching, magnesium silicate hydrate, radioactive waste, stabilization/solidification, strontium
Magnesium silicate hydrate (M−S−H) cement, formed by reacting MgO, SiO2, and H2O, was used to encapsulate strontium (Sr) radionuclide. Samples were prepared using light-burned magnesium oxide and silica fume, with sodium hexametaphosphate added to the mix water as a dispersant. The performance of the materials formed was evaluated by leach testing and the microstructure of the samples was also characterized. The stabilizing/solidifying effect on Sr radionuclide in the MgO−SiO2−H2O system with low alkalinity is demonstrated in the study. The leaching rate in a standard 42-day test was 2.53 × 10−4 cm/d, and the cumulative 42-day leaching fraction was 0.06 cm. This meets the relevant national standard performance for leaching requirements. Sr2+ was effectively incorporated into the M−S−H hydration products and new phase formation resulted in low Sr leaching being observed.
Research on Frequency Control of Islanded Microgrid with Multiple Distributed Power Sources
Yirong Liu, Xiaoli Wang, Shilin Wang
April 1, 2020 (v1)
Keywords: frequency control, islanded microgrid, microgrid, zone control
At present, some achievements have been made in the research on the energy management of microgrid operation. However, the research is mainly on the operation of grid-connected microgrid, while the research on the energy management of islanded microgrid is still relatively few. Frequency is one of the characteristics that affects the reliability and power quality of the microgrid. The essence of controlling frequency stability is to maintain source-load balance and redistribution of active power. Therefore, this paper proposes a frequency control strategy based on dynamically cutting machine to reduce load by analyzing the use priority of different distributed power supply and the division of load importance degree, and combining the influence degree of different frequency variation range on microgrid. To coordinate and control distributed power supply, energy storage device, and load in different frequency change areas, this paper proposes different control strategies. The seed strate... [more]
Numerical Analysis of Supersonic Impinging Jet Flows of Particle-Gas Two Phases
Guang Zhang, Guang Fei Ma, Heuy Dong Kim, Zhe Lin
April 1, 2020 (v1)
Keywords: impinging force, particle-gas flows, stokes number, supersonic impinging jet, wall shear stress
Supersonic impinging jet flows always occur when aircrafts start short takeoff and vertical landing from the ground. Supersonic flows with residues produced by chemical reaction of fuel mixture have the potential of reducing aircraft performance and landing ground. The adverse flow conditions such as impinging force, high noise spectrum, and high shear stress always take place. Due to rare data on particle-gas impinging jet flows to date, three-dimensional numerical simulations were carried out to investigate supersonic impinging jet flows of particle-gas two phases in the present studies. A convergent sonic nozzle and a convergent-divergent supersonic nozzle were used to induce supersonic impinging jet flows. Discrete phase model (DPM), where interaction with continuous phase and two-way turbulence coupling model were considered, was used to simulate particle-gas flows. Effects of different particle diameter and Stokes number were investigated. Particle mass loading of 10% were consid... [more]
Robust Model Selection: Flatness-Based Optimal Experimental Design for a Biocatalytic Reaction
Moritz Schulze, René Schenkendorf
April 1, 2020 (v1)
Keywords: differential flatness, model selection, model-based design of experiments, nonlinear programming, parameter uncertainty, point estimate method
Considering the competitive and strongly regulated pharmaceutical industry, mathematical modeling and process systems engineering might be useful tools for implementing quality by design (QbD) and quality by control (QbC) strategies for low-cost but high-quality drugs. However, a crucial task in modeling (bio)pharmaceutical manufacturing processes is the reliable identification of model candidates from a set of various model hypotheses. To identify the best experimental design suitable for a reliable model selection and system identification is challenging for nonlinear (bio)pharmaceutical process models in general. This paper is the first to exploit differential flatness for model selection problems under uncertainty, and thus translates the model selection problem to advanced concepts of systems theory and controllability aspects, respectively. Here, the optimal controls for improved model selection trajectories are expressed analytically with low computational costs. We further demo... [more]
Simulation of Hydraulic Fracturing Using Different Mesh Types Based on Zero Thickness Cohesive Element
Minwei Chen, Min Li, Yanzeng Wu, Boqi Kang
April 1, 2020 (v1)
Keywords: finite element method, fracture intersection, hydraulic fractures, PPCZ element
Hydraulic fracturing is a significant technique in petroleum engineering to enhance the production of shale gas or shale oil reservoir. The process of hydraulic fracturing is extremely complicated, referring to the deformation of solid formation, fluid flowing in the crack channel, and coupling the solid with fluid. Simulation of hydraulic fracturing and understanding the course of the mechanism is still a challenging task. In this study, two hydraulic fracturing models, including the Khristianovic−Geertsma−de Klerk (KGD) problem and the hydraulic fracture (HF) intersection with the natural fracture (NF), based on the zero thickness pore pressure cohesive zone (PPCZ) element with contact friction is established. The element can be embedded into the edges of other elements to simulate the fracture initiation and propagation. However, the mesh type of the elements near the PPCZ element has influences on the accuracy and propagation profile. Three common types of mesh, triangle mesh, quad... [more]
Kinetic Modelling of the Coproduction Process of Fumaric and Malic Acids by Rhizopus arrhizus NRRL 1526
Victor Martin-Dominguez, Laura Bouzas-Santiso, Nieves Martinez-Peinado, Victoria E. Santos, Miguel Ladero
April 1, 2020 (v1)
Keywords: biorefinery, Fermentation, filamentous fungi, fumaric acid, kinetic modelling, malic acid
The production of organic acids by biotechnological processes has experienced a notable impulse with the advent of first and second generation biorefineries and the need of searching for renewable and sustainable feedstock, such as biomass. Fumaric acid is a promising biomonomer for polyamide production and a well-known acidulant and preservative in food and feed industries. Malic acid is a well-known food acidulant with a high market share. The biotechnological Fumaric and Malic acid production via fungi of the Rhizopus genus is being explored nowadays as a process for the valorization of food and food-related waste to obtain food ingredients and key platform chemicals of the so-called biochemical biorefinery. In this work, a preliminary study is performed to find reproducible conditions for the production of the acids by Rhizopus arrhizus NRRL 1526 by controlling fungi morphology and inoculum conditions. Afterwards, several production runs are performed to obtain biomass, glucose, an... [more]
Thermodynamic Performance Analysis of Hydrofluoroolefins (HFO) Refrigerants in Commercial Air-Conditioning Systems for Sustainable Environment
Muhammad Farooq, Ahsan Hamayoun, Muhammad Naqvi, Saad Nawaz, Muhammad Usman, Salman Raza Naqvi, Muhammad Imran, Rida Nadeem, Allah Razi, Ahmet Turan, Alberto Pettinau, John M. Andresen
April 1, 2020 (v1)
Keywords: alternative refrigerants, global warming potential, HFOs, modeling and simulation of energy systems, R1234ze(Z), R134a, vapor compression refrigeration cycle
Global warming is one of most severe environmental concerns that our planet is facing today. One of its causes is the previous generation of refrigerants that, upon release, remain in the atmosphere for longer periods and contribute towards global warming. This issue could potentially be solved by replacing the previous generation’s high global warming potential (GWP) refrigerants with environmentally friendly refrigerants. This scenario requires an analysis of new refrigerants for a comparison of the thermodynamic properties of the previously used refrigerants. In the present research, a numerical study was conducted to analyze the thermodynamic performance of specifically low GWP hydrofluoroolefens (HFO) refrigerants for an actual vapor compression refrigeration cycle (VCRC) with a constant degree of 3 K superheat. The output parameters included the refrigeration effect, compressor work input, the coefficient of performance (COP), and the volumetric refrigeration capacity (VRC), all... [more]
Energy-Economizing Optimization of Magnesium Alloy Hot Stamping Process
Mengdi Gao, Qingyang Wang, Lei Li, Zhilin Ma
April 1, 2020 (v1)
Keywords: energy-economizing, hot stamping, lightweight material, magnesium alloy, process parameters
Reducing the mass of vehicles is an effective way to improve energy efficiency and mileage. Therefore, hot stamping is developed to manufacture lightweight materials used for vehicle production, such as magnesium and aluminum alloys. However, in comparison with traditional cold stamping, hot stamping is a high-energy-consumption process, because it requires heating sheet materials to a certain temperature before forming. Moreover, the process parameters of hot stamping considerably influence the product forming quality and energy consumption. In this work, the energy-economizing indices of hot stamping are established with multiobjective consideration of energy consumption and product forming quality to find a pathway by which to obtain optimal hot stamping process parameters. An energy consumption index is quantified by the developed models, and forming quality indices are calculated using a finite element model. Response surface models between the process parameters and energy-econom... [more]
Coupling Layout Optimization of Key Plant and Industrial Area
Yan Wu, Siyu Xu, Huan Zhao, Yufei Wang, Xiao Feng
April 1, 2020 (v1)
Keywords: coupled layout, hybrid algorithm, key plant, multi-floor structure
Layout problems are an engineering task that heavily relies on project experience. During the design of a plant, various factors need to be considered. Most previous efforts on industrial layout design have focused on the arrangement of facilities in a plant. However, the area-wide layout was not thoroughly studied and the relationship between plant layout and area-wide layout was rarely mentioned. In this work, the key plant that has the greatest impact on the industrial area is figured out first, and then the coupling relationships between the key plant and the industrial area are studied by changing the occupied area and length-width ratio of the key plant. Both of them are achieved by changing the floor number. A hybrid algorithm involving the genetic algorithm (GA) and surplus rectangle fill algorithm (SRFA) is applied. Various constraints are considered to make the layout more reasonable and practical. In the case study, a refinery with 20 plants is studied and the catalytic crac... [more]
DEM Investigation of the Influence of Particulate Properties and Operating Conditions on the Mixing Process in Rotary Drums: Part 2—Process Validation and Experimental Study
Jakub Hlosta, Lucie Jezerská, Jiří Rozbroj, David Žurovec, Jan Nečas, Jiří Zegzulka
April 1, 2020 (v1)
Keywords: DEM, homogenization, Mixing, particulates, rotating drum, validation
The process of homogenization of particulates is an indispensable part of many industrial processes, and, therefore, it is necessary to pay a special attention to this area and develop it. This paper deals with a complex study of homogenization of particulate matters in a rotary drum in terms of shape, size, and density of particles. In addition, the influence of operating parameters, such as drum filling capacity, rotational speed, and drum filling pattern are also investigated. Studies of reproducibility of discrete element method simulations, effects of rotary drum sizes or effects of drum volumetric filling to the mixture homogeneity index were also carried out. In general, the least satisfactory values of the homogeneity index resulted from the mixing of particles with different densities. The dominating factor of homogenization was the drum filling-up degree. The course of the homogeneity index in 140, 280, and 420 mm drums was very similar and after five revolutions of the drum,... [more]
Current Advances in Biofouling Mitigation in Membranes for Water Treatment: An Overview
Daniela Pichardo-Romero, Zahirid Patricia Garcia-Arce, Alejandra Zavala-Ramírez, Roberto Castro-Muñoz
April 1, 2020 (v1)
Subject: Materials
Keywords: biofouling, composite membranes, membrane technologies, polymer blending
Membranes, as the primary tool in membrane separation techniques, tend to suffer external deposition of pollutants and microorganisms depending on the nature of the treating solutions. Such issues are well recognized as biofouling and is identified as the major drawback of pressure-driven membrane processes due to the influence of the separation performance of such membrane-based technologies. Herein, the aim of this review paper is to elucidate and discuss new insights on the ongoing development works at facing the biofouling phenomenon in membranes. This paper also provides an overview of the main strategies proposed by “membranologists” to improve the fouling resistance in membranes. Special attention has been paid to the fundamentals on membrane fouling as well as the relevant results in the framework of mitigating the issue. By analyzing the literature data and state-of-the-art, the concluding remarks and future trends in the field are given as well.
A Retrofit Hierarchical Architecture for Real-Time Optimization and Control Integration
Xiaochen Li, Lei Xie, Xiang Li, Hongye Su
April 1, 2020 (v1)
Keywords: extremum-seeking control, hierarchical architecture, least-squares regression, necessary conditions of optimality, optimal operation, self-optimizing control
To achieve the optimal operation of chemical processes in the presence of disturbances and uncertainty, a retrofit hierarchical architecture (HA) integrating real-time optimization (RTO) and control was proposed. The proposed architecture features two main components. The first is a fast extremum-seeking control (ESC) approach using transient measurements that is employed in the upper RTO layer. The fast ESC approach can effectively suppress the impact of plant-model mismatch and steady-state wait time. The second is a global self-optimizing control (SOC) scheme that is introduced to integrate the RTO and control layers. The proposed SOC scheme minimizes the global average loss based on the approximation of necessary conditions of optimality (NCO) over the entire operating region. A least-squares regression technique was adopted to select the controlled variables (CVs) as linear combinations of measurements. The proposed method does not require the second order derivative information,... [more]
Novel Concept of Cogeneration-Integrated Heat Pump-Assisted Fractionation of Alkylation Reactor Effluent for Increased Power Production and Overall CO2 Emissions Decrease
Miroslav Variny, Patrik Furda, Ladislav Švistun, Miroslav Rimár, Ján Kizek, Norbert Kováč, Peter Illés, Ján Janošovský, Jakub Váhovský, Otto Mierka
April 1, 2020 (v1)
Keywords: alkylate production, CO2 emissions, cogeneration, combustion engine, emission factor, marginal electric efficiency, rectification, steam turbine
Alkylate produced by catalyzed reaction of isobutane and olefin-rich streams is a desired component for gasoline blending. Fractionation of the alkylation reactor effluent is energy demanding due to the presence of close boiling point components and solutions cutting its energy intensity; expenses associated with this process are investigated intensely nowadays. This paper presents a novel conceptual design and techno-economic analysis of alkylation reaction effluent fractionation revamp to reach a cut in energy costs of the fractionation process without the need to revamp the rectification columns themselves, providing thus an alternative approach to a more sustainable alkylation process. Two cases are considered—A. additional steam turbine installation or B. combustion engine-driven heat pump-assisted rectification. Mathematical modeling of the considered system and its revamp is applied using the “frozen technology” approach. Real system operation features and seasonal variations ar... [more]
Feasibility Assessment of Two Biogas-Linked Rural Campus Systems: A Techno-Economic Case Study
Liqin Zhu, Congguang Zhang
April 1, 2020 (v1)
Keywords: biomass conversion, eco-campus, sustainable development, Technoeconomic Analysis
The principle of sustainable development is becoming more and more prominent in various schools, and the eco-campus in rural areas often has more room for display. The identification and assessment of cost-effective biomass resources appropriate for recycling represent an opportunity that may significantly improve the comprehensive efficiency of an eco-campus system, resulting in remarkable investment savings, pollution reduction, as well as reducing energy consumption and resources waste. The economic feasibility of two biogas-linked rural campus systems (Fanjiazhai Middle School, FJZ and Xidazhai Middle School, XDZ, Yangling, China), as well as their key technologies, is investigated, the two systems respectively represent two biobased agricultural production modes. It is found that the initial investment, operating investment, and total revenue of FJZ system is 1.37 times, 2.39 times, and 1.71 times of XDZ system respectively, thus indicating that FJZ campus is proved to be a “large... [more]
An Online Contaminant Classification Method Based on MF-DCCA Using Conventional Water Quality Indicators
Yanni Zhu, Kexin Wang, Youxin Lin, Hang Yin, Dibo Hou, Jie Yu, Pingjie Huang, Guangxin Zhang
April 1, 2020 (v1)
Keywords: abnormal fluctuation analysis, cosine distance classification, D–S evidential theory, MF-DCCA, online contaminant classification
Emergent contamination warning systems are critical to ensure drinking water supply security. After detecting the existence of contaminants, identifying the types of contaminants is conducive to taking remediation measures. An online classification method for contaminants, which explored abnormal fluctuation information and the correlation between 12 water quality indicators adequately, is proposed to realize comprehensive and accurate discrimination of contaminants. Firstly, the paper utilized multi-fractal detrended fluctuation analysis (MF-DFA) to select indicators with abnormal fluctuation, used multi-fractal detrended cross-correlation analysis (MF-DCCA) to measure the cross-correlation between indicators. Subsequently, the algorithm fused the abnormal probability of each indicator and constructed the abnormal probability matrix to further judge the abnormal fluctuation of indicators using D−S evidence theory. Finally, the singularity index of the cross-correlation function and th... [more]
Review of the Numerical Modeling of Compression Molding of Sheet Molding Compound
Gustaf Alnersson, M. Waseem Tahir, Anna-Lena Ljung, T. Staffan Lundström
April 1, 2020 (v1)
Keywords: compression molding, numerical modeling, sheet molding compound
A review of the numerical modeling of the compression molding of the sheet molding compound (SMC) is presented. The focus of this review is the practical difficulties of modeling cases with high fiber content, an area in which there is relatively little documented work. In these cases, the prediction of the flows become intricate due to several reasons, mainly the complex rheology of the compound and large temperature gradients, but also the orientation of fibers and the micromechanics of the interactions between the fluid and the fibers play major roles. The details of this during moldings are discussed. Special attention is given to the impact on viscosity from the high fiber volume fraction, and the various models for this. One additional area of interest is the modeling of the fiber orientation.
The Demulsification Properties of Cationic Hyperbranched Polyamidoamines for Polymer Flooding Emulsions and Microemulsions
Yangang Bi, Zhi Tan, Liang Wang, Wusong Li, Congcong Liu, Zhantao Wang, Xiangchen Liu, Xinru Jia
April 1, 2020 (v1)
Subject: Other
Keywords: cationic hyperbranched polymers, demulsifiers, interfacial tension, microemulsion, polymer-flooding emulsion, turbidity
Polymer flooding emulsions and microemulsions caused by tertiary oil recovery technologies are harmful to the environment due to their excellent stability. Two cationic hyperbranched polyamidoamines (H-PAMAM), named as H-PAMAM-HA and H-PAMAM-ETA, were obtained by changing the terminal denotation agents to H-PAMAM, which was characterized by 1H NMR, FT-IR, and amine possession, thereby confirmed the modification. Samples (300 mg/L) were added to the polymer flooding emulsion (1500 mg/L oil concentration) at 30 °C for 30 min and the H-PAMAM-HA and H-PAMAM-ETA were shown to perform at 88% and 91% deoil efficiency. Additionally, the increased settling time and the raised temperature enhanced performance. For example, an oil removal ratio of 97.7% was observed after dealing with the emulsion for 30 min at 60 °C, while 98.5% deoil efficiency was obtained after 90 min at 45 °C for the 300 mg/L H-PAMAM-ETA. To determine the differences when dealing with the emulsion, the interfacial tension, ζ... [more]
Systematic Experimental Investigation of Segregation Direction and Layer Inversion in Binary Liquid-Fluidized Bed
Alberto Di Renzo, Giacomo Rito, Francesco P. Di Maio
April 1, 2020 (v1)
Keywords: expansion, layer inversion, liquid-fluidization, Mixing, multi-component beds, segregation
Multi-component liquid-fluidized beds are encountered in a variety of industrial processes. Often, segregation severely affects the performance of the process unit. Unfortunately, size-driven and density-driven separation processes may occur with a complex interplay, showing prevailing mechanisms that change with the operating conditions. For example, when the solids exhibit contrasting differences in size and density, even the direction of segregation can turn out hard to predict, giving rise for some systems to the so-called “layer inversion phenomenon”. A systematic experimental investigation is presented on 14 different binary beds composed of glass beads and ABS spheres with different size and density ratios and different bed composition. The analysis allows assessing the reliability of a model for predicting the segregation direction of fluidized binary beds (the Particle Segregation Model, PSM). By measurements of the solids’ concentration at the surface, expansion/segregation p... [more]
The Dependence of Effective Distribution Coefficient on Growth Rate and Mass Transfer Coefficient for P-Xylene in Solid-Layer Melt Crystallization
Lie-Ding Shiau
April 1, 2020 (v1)
Subject: Materials
Keywords: crystallization, growth rate, impurity, melt, para-xylene
The solid-layer growth kinetics and resulting crystal purity for a well-mixed p-xylene (PX) melt with impurity of o-xylene (OX) or ethylbenzene (EB) were studied in this work at various cooling temperatures. A correlation based on the energy balance was adopted to describe the dependence of growth rate on the temperature gradient between melt and cooling medium. An empirical equation based on the mass balance was proposed to relate the effective distribution coefficient with growth rate, mass transfer coefficient, and impurity mole fraction. By fitting the proposed empirical equation with the experimental effective distribution coefficients, the mass transfer coefficients for the PX/OX and PX/EB mixtures were retrieved respectively.
Utilization of Pyrolytic Carbon Black Waste for the Development of Sustainable Materials
Faizan Ali, Mishmal Ahmed Khan, Muhammad Ahmed Qurashi, Syyed Adnan Raheel Shah, Nasir Mahmood Khan, Zia Khursheed, Hafiz Shahzaib Rahim, Hunain Arshad, Muhammad Farhan, Muhammad Waseem
April 1, 2020 (v1)
Subject: Materials
Keywords: eco-friendly, materials, sustainable, waste management
The sustainable development of materials is one of the key targets in the modern era of engineering. These materials are developed by different waste products, following the concept of the circular economy. This study focuses on investigating the properties of concrete using carbon black as a partial replacement of natural fine aggregate at different percentages. Experiments were designed according to the British Standard (BS1881-Part-119) and American Standard (ASTM C-78) by including carbon black in concrete beams to perform as filler material to develop sustainable concrete. In this study, mechanical properties of concrete were targeted by developing beams using different percentages (0%, 25%, 50%, 75%, and 100%) as a replacement of fine aggregates. These beams were tested for flexural strength and, later on, the same beams were cut in the form of cubes, following the equivalent cube test mechanism for the compressive strength test. The waste carbon black lightweight concrete develo... [more]
Optimization of Microwave-Assisted Extraction Process of Callicarpa candicans (Burm. f.) Hochr Essential Oil and Its Inhibitory Properties against Some Bacteria and Cancer Cell Lines
Quoc Toan Tran, Thu Le Vu Thi, Tien Lam Do, Hong Minh Pham Thi, Bich Hoang Thi, Quang Truyen Chu, Phuong Thao Lai Phuong, Huu Nghi Do, Hoai Thu Hoang Than, Thu Thuy Ta Thi, Van Huyen Luu, Phuong Thi Mai Duong, Huong Thi Thu Phung
April 1, 2020 (v1)
Keywords: anti-proliferative activity, antimicrobial activities, Callicarpa candicans, essential oil, microwave-assisted extraction, Optimization, response surface methodology, the MAHD
Callicarpa candicans (Burm. f.) Hochr. (Callicarpa cana L.) is a medicinal plant that is distributed mainly in the tropics and subtropics of Asia and finds a wide range of uses in traditional medicine. In this study, we attempted and optimized the microwave-assisted hydro-distillation (MAHD) process to obtain essential oil from the leaves of C. candicans. In addition, the obtained oil was analyzed for volatile composition by gas chromatography−mass spectrometry (GC-MS) and assayed for bioactivity against several bacteria and cancer cell lines. To optimize the extraction process, response surface methodology (RSM) in combination with central composite design (CCD) was adopted. Experimental design and optimization were carried out with respect to three experimental factors including the ratio of water to raw material, extraction time, and microwave power. The optimal extraction conditions were obtained as follows: water to raw material ratio of 6/1 (v/w), extraction time 42 min, and micr... [more]
Evaluation of Thermal Effects on the Bioactivity of Curcumin Microencapsulated with Porous Starch-Based Wall Material Using Spray Drying
Chenwei Huang, Shengwen Wang, Huaiwen Yang
April 1, 2020 (v1)
Subject: Other
Keywords: color attribute, encapsulated curcumin, free radical scavenging activity, oven heating, spray drying
Curcumin was microencapsulated by porous starch using a spray dryer with a particle size between 1.5 and 2.0 µm and subjected to water bath (40−100 °C) and oven heating (150−200 °C) in comparison to non-encapsulated samples. The minimum possible encapsulation rate ranged from 26.75 to 52.23%. A reasonable thermal stability was observed after water bath heating with regard to 2,2-diphenyl-1-picrylhydrazyl free radical (DPPH) scavenging activity. On the other hand, the increase in oven heating temperature caused significant alterations compared with the control samples (p < 0.05). The encapsulated particles subjected to oven heating at 170 °C demonstrated serious collapse. The DPPH scavenging activity of non-encapsulated curcumin was significantly reduced (p < 0.05) from 48.94% ± 3.72% (control, 0 °C) to 40.42% ± 2.23% (oven heating, 160 °C); however, remained stable for the encapsulated samples (51.18% ± 4.86%−50.02% ± 1.79%) without significant difference (p < 0.05). The ABTS... [more]
Films of Bacterial Cellulose Prepared from Solutions in N-Methylmorpholine-N-Oxide: Structure and Properties
Igor S. Makarov, Gulbarshin K. Shambilova, Markel I. Vinogradov, Pavel V. Zatonskih, Tatyana I. Gromovykh, Sergey V. Lutsenko, Nаtalia A. Arkharova, Valery G. Kulichikhin
April 1, 2020 (v1)
Subject: Materials
Keywords: bacterial cellulose, cellulose solution, film formation, mechano-chemical activation, N-methylmorpholine-N-oxide, rheology, structure
In the present study, one of the possible methods of the bacterial cellulose processing is proposed via its dissolution in N-methylmorpholine-N-oxide using the stage of mechano-chemical activation of the solid polymer−solvent system. Preliminary solid-phase activation is apparently a decisive factor affecting the dissolution rate of bacterial cellulose in N-methylmorpholine-N-oxide. The effects of bacterial cellulose concentration, solvent nature, degree of polymerization and temperature on dissolution time were studied. The rheological behavior of the solutions does not change at 120 °C for at least half an hour that allowed us to process such solutions for films preparation. The films from these solutions by means of dry-wet jet spinning in aqueous coagulant were formed. The structure of the nascent cellulose and formed films was tested by the X-ray diffraction method and SEM. The thermal behavior of the films revealed an increase in the carbon yield for the formed films compared to... [more]
A Semi-Continuous PWA Model Based Optimal Control Method for Nonlinear Systems
Xinjian Zhu, Chunyue Song, Jun Zhao, Zuhua Xu
April 1, 2020 (v1)
Keywords: MPC, nonlinear system, optimal control, PWA model, semi-continuous
To alleviate the mode mismatch of multiple model methods for nonlinear systems when completely discrete dynamical equations are adopted, a semi-continuous piecewise affine (SCPWA) model based optimal control method is proposed. Firstly, a SCPWA model is constructed where modes evolve in continuous time and continuous states evolve in discrete time. Thanks to this model, a piecewise affine (PWA) system can switch at any time instant whereas mode switching only occurs at sample instants when a completely discrete PWA model is adopted, which improves the prediction accuracy of multi-models. Secondly, the switching condition is relaxed such that operating subspaces have overlaps and switching condition parameters are introduced. As a consequence, an optimal control problem with fixed mode switching sequence is established. Finally, a SCPWA model based model predictive control (MPC) policy is designed for nonlinear systems. The convergence of the MPC algorithm is proved. Compared with widel... [more]
Effect of Drying on Lettuce Leaves Using Indirect Solar Dryer Assisted with Photovoltaic Cells and Thermal Energy Storage
Pedro Cerezal Mezquita, Aldo Álvarez López, Waldo Bugueño Muñoz
April 1, 2020 (v1)
Keywords: lettuce leaves, mathematical modeling, solar drying, thin layer drying
The thin layer drying behavior of lettuce leaves was investigated using an indirect pilot solar dryer with thermal energy storage in water, equipped with solar collectors and photovoltaic cells. The drying procedure consisted of shredded lettuce leaves, temperature ≤ 52 °C, airspeed, 1.0 m∙s−1, and process time ~10.0 h. Fifteen drying models were adjusted to the experimental data obtained; three models with maximum values of coefficient of determination (R2)—Page, Midilli, and Kucuk, and Weibull Distribution, whose values of R2 ≥ 0.998, and other statistical parameters, χ2, SSE, and RMSE values closer to zero were chosen. The initial browning index BI = 120.5 ± 0.7 decreased compared to the dry sample BI = 78.99 ± 0.5, with chromatic coordinate degradations a* and b*; but not the luminosity L*; where ΔE = 8.26; whose meaning is that the dry sample is a “more opaque brownish color” due to the difference in the chroma ΔC = 6.65, and with a change from the yellow-green to yellow-red zone,... [more]
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