bluuebunny/crossref_metadata_2025 huggingface dataset:
The Turkish Cypriot Municipalities’ Productivity and Performance: An Application of Data Envelopment Analysis and the Tobit Model
Authors: Çağlar Onbaşıoğlu Dilber
Published: August 2021

Nowadays, countries are more concerned with the improvement of effectiveness and efficiency in public sector activities in the perspective of frugal innovation. The problem centers around how to obtain more and better public service with the limitations of the public incomes and indebtedness in preserving environmental conditions. This paper empirically investigates the efficiency, technical efficiency, productivity, and the determinants factor of implementing sustainable development policy of the five major municipalities in North Cyprus by conducting DEA and Tobit analyses during the period from 2004 to 2018 quarterly. The empirical results show that the size of the economically active population of a city, lower expenditures, and grants result in a higher efficiency, whereas the independent revenue sources (grants) and the per capita expenditures of North Cypriot municipalities have a negative effect on the efficiency. The employment rate in the municipalities has a considerable negative effect on the efficiency score. The results of Tobit analysis also show that population has a positive impact which may increase the technical efficiency. Finally, the findings of this study demonstrated that implementing proper environmental programs not only improve the efficiency of local government but also help the ecological sustainability and the geographical location of the regional changes and barriers for sustainable initiatives by using proper waste mechanism, clean water technology, and solar lighting.
Identifying the Determinants of Nongrain Farming in China and Its Implications for Agricultural Development
Authors: Guo Yuanzhi , Wang Jieyong
Published: August 2021

Promoted by rapid industrialization and urbanization, the structure and spatial pattern of farming in China has changed greatly, and nongrain farming (NGF) has become more common. However, excessive NGF in some areas is not conducive to sustainable agricultural development and threatens China’s food security. In this study, we briefly analyze the stage characteristics of NGF in China and investigate the spatial agglomeration of NGF and its influencing factors from the perspective of spatial econometrics. The results showed that the average annual growth rate of NGF in China from 1985 to 2019 was 0.64%, and there was a growing positive spatial correlation between NGF in each province. Spatial Durbin model (SDM) estimation showed that both the per capita disposable income of local rural residents and the local urbanization rate promoted the development of NGF, while local per capita farmland, road density, and the functional orientation of the main grain-producing areas had a negative impact on NGF. The per capita disposable income of rural households and urbanization rate in neighboring areas had a promoting effect on the development of NGF, while road density in neighboring areas was negatively correlated with NGF. Ultimately, some targeted measures are proposed to promote China’s agricultural development in the new era.
Land Use Transitions: Progress, Challenges and Prospects
Authors: Long Hualou , Zhang Yingnan , Ma Li , Tu Shuangshuang
Published: August 2021

The study of land use transition has generally become an important breakthrough point to deeply understand the human-land interaction and reveal major socio-economic development issues and related environmental effects. Attempting to provide scientific support for sustainable land use and environmental management, this review systematically analyzes the overall picture, development trends, key fields and hot topics of land use transition research in the past two decades from a comprehensive perspective, which incorporates two complementary parts including the systematic quantitative literature review (based on CiteSpace) and the traditional literature review. The results reveal that: a. current research presents three characteristics, i.e., focusing on complex social issues, driven by realistic demand, and research branches becoming clearer and more systematic; b. there are four key fields and hot topics in land use transition research, i.e., i. theories and hypothesis of land use transition; ii. measuring land use transition; iii. the impacts of land use transition on “social-economic-ecological” system; iv. drivers and regulation of land use transition. However, challenges remain, current land use transition research is still to some extent fragmented, and it should be enriched by integrating with land system science. The dominant morphology biased should be redressed by underlining the recessive morphology transition process. Meanwhile, new techniques and methods are necessary to observe, track, monitor and model the recessive attributes. Finally, distant drivers of land use transition should not be ignored in this rapidly globalizing world.
Evaluation of Tourism Development Potential on Provinces along the Belt and Road in China: Generation of a Comprehensive Index System
Authors: Chen Yuying , Li Yajie , Gu Xiangfeng , Chen Nan , Yuan Qing , Yan Ming
Published: August 2021

The evaluation of tourism development potential (TDP) is the crucial foundation and critical step for sustainable regional tourism development. Prior studies mainly evaluate TDP through the univariate potential model and the multi-indicator descriptive evaluation. However, these two methods have only limited effectiveness for the destination’s TDP in the context of the mesoscale level. Thus, this study aims to develop an effective multi-dimensional mesoscale to evaluate the destination’s TDP and construct a potential index model. Based on the literature review, this study develops four rule layers (tourism supply and consumption (X1), the demand and purchasing power of tourist source (X2), development value of destination resources (X3), and the contribution of the destination’s tourism industry (X4)) and 31 factor layers. All the factor layers are then assigned values based on the provincial statistics in China in 2019. Through SPSS 24.0, the current study uses the principal component analysis (PCA) to construct a provincial TDP index model for the research area: Y=0.2573X1+0.1305X2+0.3177X3+0.2945X4. The results show significant regional differences in the TDP index of the provinces along the Belt and Road (study area) in China. Among them, Guangdong has the most extensive TDP index, Qinghai has the smallest TDP index. The study also uses ArcGIS 10.2 for the function of kernel density analysis to visualize provincial TDP and finds significant spatial differences and a central-edge distribution pattern across provinces.
China’s Wildlife Management Policy Framework: Preferences, Coordination and Optimization
Authors: Feng Lu , Cai Qiyi , Bai Yang , Liao Wenjie
Published: August 2021

The coronavirus disease 2019 pandemic led to global concerns about the delicate relationship between humans and wildlife. However, quantitative research on the elements of a wildlife management policy framework in a certain country is lacking. In this study, we try to close this research gap by analyzing the formulation preferences of key elements in the wildlife management policy framework, as well as the coordination between them, in China, which is generally regarded as a main wildlife consumption country. Based on the content analysis of China’s wildlife management policy documents, with a three-dimensional analytical framework, we find that: China’s wildlife management policy framework prefers the use of compulsory tools, while voluntary and mixed tools are not fully used; adequate attention is paid to the biodiversity conservation objectives and attention is paid to the objectives of public health protection and wildlife welfare, while the utilization objective is restricted to some extent; government sectors, industry, citizens, and non-governmental organizations are involved in wildlife management policies and the degrees of participation of citizens and non-governmental organizations are relatively low. In conclusion, we draw wider implications for China’s wildlife management policy formulation, arguing for a more coordinated and participatory policy framework.
The Hollowing Process of Rural Communities in China: Considering the Regional Characteristic
Authors: Liu Ying , Shu Liqiong , Peng Li
Published: August 2021

This study examined the hollowing process of rural communities, which is caused by migration, and explored its influence factors based on Hierarchical Linear Model (HLM) analysis in an attempt to explore effect of regional characteristic. To capture the essence of rural hollowing, a logical framework was constructed. The rural hollowing was then evaluated based on an index system. Based on the assessment, HLM analysis was conducted to explore the influence factors at the household and community levels. The results demonstrated significant differences of rural hollowing among villages. In addition, the hollowing was not only affected by household-level variables but also by community-level variables. Further, for rural hollowing, the household-level variable was endogenous drive, while the community-level variables were exogenous drive. Among all the endogenous influence factors, population quality was the most important, and thus the loss of highly educated talents will aggravate the trend of rural hollowing and hinder the sustainable development of the countryside. Furthermore, in addition to promoting economic development and its diversification to alleviate rural hollowing, improving the quality of the population is more important to the sustainable development of the countryside in China.
The Small Property Rights Housing Institution in Mainland China: The Perspective of Substitutability of Institutional Functions
Authors: Zhou Ziqi , Yau Yung
Published: August 2021

Despite its informal nature, small property rights housing (SPRH) proliferates in many Chinese cities. Given the institutional functions of the SPRH institution, it may not be desirable for the state to intervene in the SPRH sector. However, the institutional credibility and the institutional functions of SPRH are not completely endogenous, which contradicts the assumption of the credibility thesis. Based on the framework of the credibility thesis, this paper proposes the concept of the substitutability of institutional functions and develops a framework integrating the concepts of substitutability and credibility to examine the influence of functional substitutability on institutional credibility. Research hypotheses were tested with the data collected through a questionnaire survey on SPRH residents in Shenzhen and Chenzhou (n = 458). The analysis results of the combined model suggest that the supportive perceptions of actors for SPRH and the credibility of SPRH are significantly related to the substitutability of SPRH’s functions. The effect of the substitutability of social housing on credibility is found insignificant, while the impact of the substitutability of commercial housing on credibility is significant. However, the analysis results are city-specific. A significant negative correlation is found between the substitutability of formal housing institutions and the credibility of SPRH in Chenzhou but not in Shenzhen. This study attempted to refine the credibility thesis by clarifying the relationship between institutional functions and institutional credibility and examining the endogeneity of credibility.
Geological-Geomorphological and Paleontological Heritage in the Algarve (Portugal) Applied to Geotourism and Geoeducation
Authors: Martínez-Graña Antonio , Legoinha Paulo , Goy José Luis , González-Delgado José Angel , Armenteros Ildefonso , Dabrio Cristino , Zazo Caridad
Published: August 2021

A 3D virtual geological route on Digital Earth of the geological-geomorphological and paleontological heritage in the Algarve (Portugal) is presented, assessing the geological heritage of nine representative geosites. Eighteen quantitative parameters are used, weighing the scientific, didactic and cultural tourist interest of each site. A virtual route has been created in Google Earth, with overlaid georeferenced cartographies, as a field guide for students to participate and improve their learning. This free application allows loading thematic georeferenced information that has previously been evaluated by means of a series of parameters for identifying the importance and interest of a geosite (scientific, educational and/or tourist). The virtual route allows travelling from one geosite to another, interacting in real time from portable devices (e.g., smartphone and tablets), and thus making possible the ability to observe the relief and spatial geological distribution with representative images, as well as to access files with the description and analysis of each geosite. By using a field guide, each geosite is complemented with activities for carrying out and evaluating what has been learned; these resources allow a teaching–learning process where the student is an active part of the development and creation of content using new technologies that provide more entertaining and educational learning, teamwork and interaction with social networks. This itinerary allows the creation of attitudes and skills that involve geoconservation as an element for sustainable development.
Frailty in Stroke—A Narrated Review
Authors: Hassan Ebrahim Bani , Phu Steven , Warburton Elyce , Humaith Nihara , Wijeratne Tissa
Published: August 2021

This narrative review provides a summary introduction to the relationship between stroke and physical and cognitive frailty syndromes and the neuro-inflammatory similarities (including inflammaging) between the two. The review argues the potential effects of Post COVID-19 Neurological Syndrome (PCNS, also known as Long COVID) with similar pathophysiology. Many patients who have suffered from acute stroke experience long-lasting symptoms affecting several organs including fatigue, brain fog, reduced physical activity, loss of energy, and loss of cognitive reserve, culminating in the loss of independence and poor quality of life. This is very similar to the emerging reports of PCNS from different parts of the world. Stroke, particularly in older adults with comorbidities appears to impact the health and welfare of patients by reducing central neuronal input and neuromuscular function, with muscular atrophy and neuropsychiatric complications. The cumulative effects can potentially lead to a range of physical and cognitive frailty syndromes, which, in many cases may be attributed to persistent, maladapted, low grade, chronic inflammation. Meanwhile, post-COVID-19 Neurological Syndrome (also known as Long COVID Syndrome) appears to share a similar trajectory, adding further urgency for investigations into the mechanisms underlying this constellation of symptoms.
Metabolic Constellations, Clusters, and Renal Function: Findings from the 2013–2018 National Health and Nutrition Examination Surveys
Authors: Adair Kathleen E. , Ylitalo Kelly R. , Forsse Jeffrey S. , Funderburk LesLee K. , Bowden Rodney G.
Published: August 2021

Metabolic syndrome (MetS) is associated with decreased renal function and chronic kidney disease (CKD). To date, no research regarding the sixteen possible constellations resulting in the diagnosis of MetS has been elucidated. The purpose of this study is to report renal function in sixteen metabolic constellations grouped into four metabolic clusters. Individuals (n = 2767; representing 86,652,073 individuals) from the 2013–2018 National Health and Nutrition Examination Surveys who met the criteria for MetS were included. Sixteen possible constellations of three or more risk factors were analyzed for renal function. Four metabolic clusters representing MetS with hyperglycemia (Cluster I), MetS with hypertension (Cluster II), MetS with hyperglycemia and hypertension (Cluster III), or MetS with normoglycemia and normotension (Cluster IV) were assessed for renal function and CKD status. Cluster III had the highest odds of CKD (OR = 2.57, 95% CL = 1.79, 3.68). Clusters II and III had the lowest renal function and were not different from one another (87.82 and 87.28 mL/min/1.73 m2, p = 0.71). The constellation with the lowest renal function consisted of hypertension, high triglycerides, and a large waist circumference (82.86 mL/min/1.73 m2), whereas the constellation with the highest renal function consisted of hyperglycemia, low HDL, and a large waist circumference (107.46 mL/min/1.73 m2). The sixteen constellations of MetS do not have the same effects on renal function. More research is needed to understand the relationship between the various iterations of MetS and renal function.
Recent Advances in Preparation and Testing Methods of Engine-Based Nanolubricants: A State-of-the-Art Review
Authors: Akl Sayed , Elsoudy Sherif , Abdel-Rehim Ahmed A. , Salem Serag , Ellis Mark
Published: August 2021

Reducing power losses in engines is considered a key parameter of their efficiency improvement. Nanotechnology, as an interface technology, is considered one of the most promising strategies for this purpose. As a consumable liquid, researchers have studied nanolubricants through the last decade as potential engine oil. Nanolubricants were shown to cause a considerable reduction in the engine frictional and thermal losses, and fuel consumption as well. Despite that, numerous drawbacks regarding the quality of the processed nanolubricants were discerned. This includes the dispersion stability of these fluids and the lack of actual engine experiments. It has been shown that the selection criteria of nanoparticles to be used as lubricant additives for internal combustion engines is considered a complex process. Many factors have to be considered to investigate and follow up with their characteristics. The selection methodology includes tribological and rheological behaviours, thermal stability, dispersion stability, as well as engine performance. Through the last decade, studies on nanolubricants related to internal combustion engines focused only on one to three of these factors, with little concern towards the other factors that would have a considerable effect on their final behaviour. In this review study, recent works concerning nanolubricants are discussed and summarized. A complete image of the designing parameters for this approach is presented, to afford an effective product as engine lubricant.
Preparation and Mechanical Properties of Microcapsule-Based Self-Healing Cementitious Composites
Authors: Jiang Shiping , Lin Zhiyang , Tang Can , Hao Wenfeng
Published: August 2021

Self-healing concrete designs can protect against deterioration and improve durability. However, there is no unified conclusion regarding the effective preparation and mechanical properties of self-healing concrete. In this paper, microcapsules are used in cement-based materials, the reasonable dosage of microcapsules is determined, and the self-healing performance of the microcapsule self-healing system under different curing agents is explored. The microcapsules and curing agent are shown to enhance the flexural and compressive strength of mortar specimens at relatively low contents. The optimal microcapsule content in terms of compressive strength is 1–3%. When the content of the microcapsule reaches 7%, the strength of the specimen decreases by approximately 30%. Sodium fluorosilicate is better-suited to the microcapsule self-healing cement-based system than the other two fluorosilicates, potassium fluorosilicate and magnesium, which have similarly poor healing performance as curing agents. Healing time also appears to significantly influence the microcapsule self-healing system; mortar specimens that healed for 28 days are significantly higher than those that healed for 7 days. This work may provide a valuable reference for the design and preparation of self-healing cementitious composite structures.
Deformation Behavior and Microstructural Evolution of T-Shape Upsetting Test in Ultrafine-Grained Pure Copper
Authors: Jiang Hongpeng , Yan Guangqiang , Li Jianwei , Xu Jie , Shan Debin , Guo Bin
Published: August 2021

Ultrafine-grained (UFG) materials can effectively solve the problem of size effects and improve the mechanical properties due to its ultra-high strength. This paper is dedicated to analyzing the deformation behavior and microstructural evolution of UFG pure copper based on T-shape upsetting test. Experimental results demonstrate that: the edge radius and V-groove angle have significant effects on the rib height and aspect ratio λ during T-shape upsetting; while the surface roughness has little effect on the forming load in the first stage, but in the second stage the influence becomes significant. The dynamic recrystallization temperature of UFG pure copper is between 200 °C and 250 °C.
Loss Factor Behavior of Thermally Aged Magnetorheological Elastomers
Authors: Aziz Siti Aishah Abdul , Mazlan Saiful Amri , Ubaidillah Ubaidillah , Mohamad Norzilawati , Sedlacik Michal , Nordin Nur Azmah , Nazmi Nurhazimah
Published: August 2021

Polymer composites have been widely used as damping materials in various applications due to the ability of reducing the vibrations. However, the environmental and surrounding thermal exposure towards polymer composites have affected their mechanical properties and lifecycle. Therefore, this paper presents the effect of material-temperature dependence on the loss factor and phase shift angle characteristics. Two types of unageing and aging silicone-rubber-based magnetorheological elastomer (SR-MRE) with different concentrations of carbonyl iron particles (CIPs), 30 and 60 wt%, are utilized in this study. The morphological, magnetic, and rheological properties related to the loss factor and phase shift angle are characterized using a low-vacuum scanning electron microscopy, and vibrating sample magnetometer and rheometer, respectively. The morphological analysis of SR-MRE consisting of 30 wt% CIPs revealed a smoother surface area when compared to 60 wt% CIPs after thermal aging due to the improvement of CIPs dispersion in the presence of heat. Nevertheless, the rheological analysis demonstrated inimitable rheological properties due to different in-rubber structures, shear deformation condition, as well as the influence of magnetic field. No significant changes of loss factor occurred at a low CIPs concentration, whilst the loss factor increased at a higher CIPs concentration. On that basis, it has been determined that the proposed changes of the polymer chain network due to the long-term temperature exposure of different concentrations of CIPs might explain the unique rheological properties of the unaged and aged SR-MRE.
Acenaphthoquinoxaline Derivatives as Dental Photoinitiators of Acrylates Polymerization
Authors: Pyszka Ilona , Jędrzejewska Beata
Published: August 2021

A series of dyes based on the acenaphthoquinoxaline skeleton was synthesized. Their structure was modified by introducing electron-withdrawing and electron-donating groups, increasing the number of conjugated double bonds and the number and position of nitrogen atoms, as well as the arrangement of aromatic rings (linear or angular). The dyes were investigated as a component in the photoinitiating systems of radical polymerization for a potential application in dentistry. They acted as the primary absorber of visible light and the acceptor of an electron, which was generated from a second component being an electron donor. Thus, the radicals were generated by the photoinduced intermolecular electron transfer (PET) process. Electron donors used differed in the type of heteroatom, i.e., O, S and N and the number and position of methoxy substituents. To test the ability to initiate the polymerization reaction by photoinduced hydrogen atom transfer, we used 2-mercaptobenzoxazole as a co-initiator. The effectiveness of the photoinitiating systems clearly depends on both the modified acenaphthoquinocaline structure and the type of co-initiator. The lower amount of heat released during the chain reaction and the polymerization rate comparable to this achieved for the photoinitiator traditionally used in dentistry (camphorquinone) indicates that the studied dyes may be valuable in this field.
Molecularly Imprinted Polymers as Solid-Phase Microextraction Fibers for the Isolation of Selected Antibiotics from Human Plasma
Authors: Szultka-Młyńska Małgorzata , Janiszewska Daria , Buszewski Bogusław
Published: August 2021

The aim of this study was to examine the synthesis of novel molecularly imprinted polymer (MIP)-coated polythiophene and poly(3-methylthiophene) solid-phase microextraction fibers using the direct electropolymerization method. Synthesized SPME fibers were characterized with the use of various physicochemical instrumental techniques. MIP-SPME coatings were successfully applied to carry out the selective extraction of selected antibiotic drugs (amoxicillin, cefotaxime, metronidazole) and their metabolites (amoxycilloic acid, amoxicillin diketopiperazine, desacetyl cefotaxime, 3-desacetyl cefotaxime lactone, hydroxymetronidazole). Solid-phase microextraction parameters for the simultaneous determination and identification of target compounds were optimized using the central composite design (CCD), and they accounted for 5–15 min for desorption time, 3–10 for the pH of the desorption solvent, and 30–100 μL for the volume of the desorption solvent. High-performance liquid chromatography and mass spectrometry (MS) detectors such as quadrupole time-of-flight (Q-TOF MS) and triple quadrupole (QqQ MS) were applied to determine and to identify selected antibiotic drugs and their metabolites. The MIP-coated SPME are suitable for the selective extraction of target compounds in biological samples from patients in intensive care units.
A Modified Compact Tension Test for Characterization of the Intralaminar Fracture Toughness of Tri-Axial Braided Composites
Authors: May Michael , Kilchert Sebastian , Gerster Tobias
Published: August 2021

The application of braided composite materials in the automotive industry requires an in-depth understanding of the mechanical properties. To date, the intralaminar fracture toughness of braided composite materials, typically used for describing post-failure behavior, has not been well-characterized experimentally. In this paper, a modified compact tension test, utilizing a relatively large specimen and a metallic loading frame, is used to measure the transverse intralaminar fracture toughness of a tri-axial braided composite. During testing, a relatively long fracture process zone ahead of the crack tip was observed. Crack propagation could be correlated to the failure of individual unit cells, which required failure of bias-yarns. The transverse interlaminar fracture toughness was found to be two orders of magnitude higher than the reference interlaminar fracture toughness of the same material. This is due to the fact, that intralaminar crack propagation requires breaking of fibers, which is not the case for interlaminar testing.
Agar Acts as Cathode Microskin to Extend the Cycling Life of Zn//α-MnO2 Batteries
Authors: Zuo Linqing , Sun Haodong , Yuan Xinhai , Wen Juan , Chen Xi , Zhou Shiyu , Wu Yuping , van Ree Teunis
Published: August 2021

The Zn/MnO2 battery is a promising energy storage system, owing to its high energy density and low cost, but due to the dissolution of the cathode material, its cycle life is limited, which hinders its further development. Therefore, we introduced agar as a microskin for a MnO2 electrode to improve its cycle life and optimize other electrochemical properties. The results showed that the agar-coating layer improved the wettability of the electrode material, thereby promoting the diffusion rate of Zn2+ and reducing the interface impedance of the MnO2 electrode material. Therefore, the Zn/MnO2 battery exhibited outstanding rate performance. In addition, the agar-coating layer promoted the reversibility of the MnO2/Mn2+ reaction and acted as a colloidal physical barrier to prevent the dissolution of Mn2+, so that the Zn/MnO2 battery had a high specific capacity and exhibited excellent cycle stability.
A Multidisciplinary Journey towards Bone Tissue Engineering
Authors: Pedrero Sara G. , Llamas-Sillero Pilar , Serrano-López Juana
Published: August 2021

Millions of patients suffer yearly from bone fractures and disorders such as osteoporosis or cancer, which constitute the most common causes of severe long-term pain and physical disabilities. The intrinsic capacity of bone to repair the damaged bone allows normal healing of most small bone injuries. However, larger bone defects or more complex diseases require additional stimulation to fully heal. In this context, the traditional routes to address bone disorders present several associated drawbacks concerning their efficacy and cost-effectiveness. Thus, alternative therapies become necessary to overcome these limitations. In recent decades, bone tissue engineering has emerged as a promising interdisciplinary strategy to mimic environments specifically designed to facilitate bone tissue regeneration. Approaches developed to date aim at three essential factors: osteoconductive scaffolds, osteoinduction through growth factors, and cells with osteogenic capability. This review addresses the biological basis of bone and its remodeling process, providing an overview of the bone tissue engineering strategies developed to date and describing the mechanisms that underlie cell–biomaterial interactions.
Improving Marine Concrete Performance Based on Multiple Criteria Using Early Portland Cement and Chemical Superplasticizer Admixture
Authors: Lee Taegyu , Lee Jaehyun , Jeong Jaewook , Jeong Jaemin
Published: August 2021

This study sought to examine the performance design of concrete mix proportions to ensure chloride resistance and early strength with respect to C35 (35 MPa), which is the minimum compressive strength class of concrete used in a marine environment. For the proposed concrete mixture, C24 (24 MPa) was selected and binders for concrete were manufactured using a blend of OPC (ordinary Portland cement), EPC (early Portland cement), and GGBS (ground granulated blast-furnace slag). The results of the experiment confirmed that the combined use of EPC and GGBS greatly improve the early-strength development and chloride resistance of concrete. An analysis revealed that the time for removal of forms can be reduced by 5–9 h from the aspect of early concrete strength. Moreover, in terms of construction productivity, EPC and GGBS were reduced by up to 16.39 h/cycle compared to other concretes. Regarding economic and environmental impacts, EPC and GGBS were more effective than C35 concrete. This study is significant as its findings help make it possible to examine the most economical concrete mix design in relation to strength development according to the application of EPC, GGBS, and PC-based admixtures.
Response and Deterioration Mechanism of Bitumen under Acid Rain Erosion
Authors: Zhang Xuemei , Hoff Inge , Saba Rabbira Garba
Published: August 2021

Acid rain as an important environmental issue has a negative impact on bitumen performance, thereby shortening the service life of asphalt pavements. Thus, this research aims to investigate the response of bitumen to acid rain and its deterioration mechanism. For this purpose, the simulated acid rain was prepared to erode neat bitumen and short-term aged bitumen. The hydrogen ion concentration of the acid rain, and the morphological, physical, chemical, and rheological properties of the bitumen were evaluated by means of a pH meter, scanning electron microscopy, physical tests, Fourier transform infrared radiation with attenuated total reflectance, and dynamic shear rheometer. The results showed that bitumen properties were severely affected by acid rain, and the changes in bitumen properties were highly related to the erosion time, leading to a reduction in pH value by 0.2 of residual acid rain, rougher bitumen surface, and stiffer bitumen with more oxygen-containing functional groups and fewer carbonyl acid groups (around 10% decrement) after 90 days erosion. These changes contributed to two deterioration mechanisms: oxidation and dissolution of carbonyl acid. Oxidation and dissolution are, respectively, the dominant actions for neat bitumen and aged bitumen during the erosion process, which eventually leads to various responses to acid rain.
Terahertz Sensor via Ultralow-Loss Dispersion-Flattened Polymer Optical Fiber: Design and Analysis
Authors: Luo Wanli , Jiang Peng , Xu Qiang , Cao Lei , Jones Adam , Li Kang , Copner Nigel , Gong Yongkang
Published: August 2021

A novel cyclic olefin copolymer (COC)-based polymer optical fiber (POF) with a rectangular porous core is designed for terahertz (THz) sensing by the finite element method. The numerical simulations showed an ultrahigh relative sensitivity of 89.73% of the x-polarization mode at a frequency of 1.2 THz and under optimum design conditions. In addition to this, they showed an ultralow confinement loss of 2.18 × 10−12 cm−1, a high birefringence of 1.91 × 10−3, a numerical aperture of 0.33, and an effective mode area of 1.65 × 105 μm2 was obtained for optimum design conditions. Moreover, the range dispersion variation was within 0.7 ± 0.41 ps/THz/cm, with the frequency range of 1.0–1.4 THz. Compared with the traditional sensor, the late-model sensor will have application value in THz sensing and communication.
Special Issue: Thermal Analysis of Materials
Authors: Ushakov Sergey V. , Hayun Shmuel
Published: August 2021

The measurement of any physical property as a function of temperature brings the method used into the realm of thermal analysis [...]
Nanocarbon Type Xerogel Materials Designed for Water Desalination
Authors: Hristea Gabriela , Iordoc Mihai , Culcea Andreea
Published: August 2021

The relative performance of different porous solids in different applications is highly dependent on the internal pore structure of each material. Highly porous carbon materials can be prepared by evaporative drying and the pyrolysis of resorcinol-formaldehyde gels. By determining the correct synthesis parameters, the pore system of such materials can be reshaped. Depending on some important processing factors such as the dilution ratio or the initial pH of the precursor solution, various porous or non-porous carbon materials can be synthesized. This paper addresses carbon xerogels (CX) designed as a material electrode in capacitive deionization (CDI) systems for water desalination. In this work CX materials were synthesized via poly-condensation reactions of resorcinol with formaldehyde (RF) on a carbon felt sheet followed by pyrolysis. The resulting sheets were used as electrodes to develop a CDI experimental multi-cell laboratory system. The initial pH of the RF solution and the dilution ratio effect on the resulting carbon surface area and structure were analyzed. Surface area measurements using the BET method and an electrochemical capacitance evaluation of the obtained xerogels through electrochemical impedance spectroscopy were also performed. Finally, using our experimental CDI multi-cell laboratory system based on the obtained CX, we discuss the experimental data for the desalination rate as a function of the voltage and salt concentration. As a result, the developed model’s efficiency is demonstrated. The main goal of this work was to develop an efficient electrode-based novel carbon that could be commercially competitive, as well as to create guidelines for future desalination research using CX electrode materials.
Considerations on Temperature Dependent Effective Diffusion and Permeability of Natural Clays
Authors: Wesenauer Florian , Jordan Christian , Azam Mudassar , Harasek Michael , Winter Franz
Published: August 2021

A series of porous clay samples prepared at different pretreatment temperatures have been tested in a diffusion chamber. Diffusivity and permeability were examined in a temperature range from ambient to 900 °C. Gaseous mixtures of O2, CO2, and N2 have been applied, as these species are the relevant gases in the context of clay brick firing and similar thermochemical processes. Diffusive transport characteristics have been determined by means of the mean transport-pore model, and permeability has been evaluated by Darcy’s law. CO2 diffusivity increased strongly with temperature, whereas O2 diffusion was limited to a certain level. It is proposed that one should consider CO2 surface diffusion in order to explain this phenomenon. The diffusion model was expanded and surface diffusion was included in the model equation. The results of the model fit reflected the important role of incorporated carbonates of the clay foundation in gas-phase (molecular or Knudsen) diffusivity. CO2 surface diffusion was observed to exhibit similar coefficients for two different investigated clays, and is therefore indicated as a property of natural clays. Permeability showed a progressive rise with temperature, in line with related literature.
Plastic Forming of Sandwich Panels and Numerical Analyses of the Forming Processes Based on Elastoplastic Equivalent Model
Authors: Zhang Ya , Chen Qingmin , Wang Mingwei , Zhang Xi , Cai Zhongyi
Published: August 2021

This paper studies the plastic forming of sandwich panels and proposes a universal elastoplastic equivalent method suitable for sandwich panels. To verify the generality of the equivalent method, according to the different core structures, the cores of bi-directional trapezoidal sandwich (BTS) panels and aluminum foam sandwich (AFS) panels are equated to orthotropic and isotropic (special orthotropic) single-layer panels respectively. Through the finite element (FE) numerical simulation of the mesoscopic model of the sandwich panel, the elastoplastic constitutive relationship of the equivalent core model is established, and then the macroscopic equivalent model of the sandwich panel is established. The FE numerical simulation of plastic forming was carried out for the mesoscopic model and equivalent model of BTS panel and AFS panel, and plastic forming experiments were conducted for the sandwich panel through a multi-point forming (MPF) test machine. The results show that the relative errors of the section average stress at the same position of the equivalent model and the mesoscopic model of sandwich panels are all within 4%; compared with the experimental results, the equivalent model of the sandwich panel has high forming accuracy and small shape error, which verifies the high accuracy and generality of the equivalent method. Moreover, using the sandwich panel equivalent model effectively reduces the calculation time of the numerical simulation.
Green and Short Preparation of CeO2 Nanoparticles with Large Specific Surface Area by Spray Pyrolysis
Authors: Wu Yongfu , Li Hong , Bian Xue , Wu Wenyuan , Wang Zhenfeng , Liu Yubao
Published: August 2021

Green and short preparation of CeO2 nanoparticles with large specific surface area from rare earth extraction (CeCl3) was successfully achieved by spray pyrolysis (SP). In this method, a precursor solution is first prepared by mixing CeCl3, C6H8O, and H2O in the requisite quantities. Subsequently, the precursor consisting of a mixture of CeO2 and C was obtained by SP method by using the precursor solution. Finally, the calcination at 500 °C~800 °C in air for two hours to transform the precursor to CeO2 nanoparticles. Thermodynamic analysis and experimental studies were performed to determine the optimal SP temperature and citric acid amount. The results indicated that the maximum specific surface area (59.72 m2/g) of CeO2 nanoparticles were obtained when the SP temperature was 650 °C and the molar ratio of citric acid to CeCl3 was 1.5.
Compressive Strength of Conventional Glass Ionomer Cement Modified with TiO2 Nano-Powder and Marine-Derived HAp Micro-Powder
Authors: Ivanišević Ana , Rajić Valentina Brzović , Pilipović Ana , Par Matej , Ivanković Hrvoje , Baraba Anja
Published: August 2021

The aim of this research was to investigate the compressive strength (CS), breaking strength (BS), and compressive modulus (CM) of conventional glass ionomer cement (GIC) modified with TiO2 nano particles, marine-derived hydroxyapatite (md-HAp) microparticles (<45 µm), and a combination of TiO2 NP and md-HAp particles. The materials used in the study were conventional GIC Fuji IX GP Extra (GC Corporation, Tokyo, Japan), TiO2 powder P25 (Degussa, Essen, Germany), and HAp synthesized from cuttlefish bone and ground in a mortar to obtain md-HAp powder. md-HAp was characterized using FTIR and SEM analysis. There were four groups of GIC samples: (i) Fuji IX control group, (ii) powder modified with 3 wt% TiO2, (iii) powder modified with 3 wt% HAp, and (iv) powder modified with 1.5 wt% TiO2 + 1.5 wt% HAp. Measurements were performed in a universal testing machine, and CS, BS, and CM were calculated. Statistical analysis was performed using ANOVA and Tukey’s tests. CS, BS, and CM differed significantly between the Fuji IX control group and all experimental groups while differences between the experimental groups were not statistically significant. The addition of TiO2 NP, md-HAp micro-sized particles, and a combination of TiO2 and md-HAp reduced the CS, BS, and CM of conventional GICs when mixed at the powder/liquid (p/l) ratio recommended by the manufacturer.
Investigation of Cavitation Bubble Dynamics Considering Pressure Fluctuation Induced by Slap Forces
Authors: Wang Xiaoyu , Zhou Shenghao , Shan Zumeng , Yin Mingang
Published: August 2021

Cavitation erosion is induced by the penetrating pressure from implosion of cavitation bubbles nearby solid boundary. The bubble evolution and the subsequent collapse pressure are especially important to evaluate the erosion degradation of solid boundary materials. The bubble dynamics equation taking into account the influence of distance between bubble and solid boundary is formulated to investigate the effect of boundary wall on bubble evolution process. The pressure fluctuation induced by slapping forces is adopted to evaluate the bubble dynamic characteristics. Negative pressure period which reflects the effect of vibration velocity and gap clearance also has large influence on bubble dynamics. The effects of standoff distance, initial radius and negative pressure period on bubble evolution and collapsing shock pressure are discussed. Maximum bubble radius increases with standoff distance and initial radius, while shock pressure increases with distance and decreases with bubble initial radius, and both of them increase with negative pressure period.
Green STEM to Improve Mathematics Proficiency: ESA Mission Space Lab
Authors: Garcia-Piqueras Manuel , Ruiz-Gallardo José-Reyes
Published: August 2021

The main goal of this study was to improve students’ outcomes and perception in Mathematics. For this, 12 out of 34 voluntary students were involved in an international contest: European Space Agency (ESA) Mission Space Lab. The experience was organized as STEM, under a guided PjBL. Students identified an environmental problem, executed a way to monitor it from the International Space Station (ISS) and interpreted the data received. Students’ final report was awarded by ESA. Additionally, participants increased their performance in their math final exams compared to the control group. Furthermore, the perception of students and their families about the usefulness of mathematics was very positive. The only drawback detected was the increase of workload. Thus, Green STEM, using direct instruction and guide in PjBL, may be a good tool to improve students’ grades and opinion about the importance of mathematics.
Machine Learning Approach for Modeling and Control of a Commercial Heliocentris FC50 PEM Fuel Cell System
Authors: Derbeli Mohamed , Napole Cristian , Barambones Oscar
Published: August 2021

In recent years, machine learning (ML) has received growing attention and it has been used in a wide range of applications. However, the ML application in renewable energies systems such as fuel cells is still limited. In this paper, a prognostic framework based on artificial neural network (ANN) is designed to predict the performance of proton exchange membrane (PEM) fuel cell system, aiming to investigate the effect of temperature and humidity on the stack characteristics and on tracking control improvements. A large part of the experimental database for various operating conditions has been used in the training operation to achieve an accurate model. Extensive tests with various ANN parameters such as number of neurons, number of hidden layers, selection of training dataset, etc., are performed to obtain the best fit in terms of prediction accuracy. The effect of temperature and humidity based on the predicted model are investigated and compared to the ones obtained from real-time experiments. The control design based on the predicted model is performed to keep the stack operating point at an adequate power stage with high-performance tracking. Experimental results have demonstrated the effectiveness of the proposed model for performance improvements of PEM fuel cell system.
Dynamical Continuous Discrete Assessment of Competencies Achievement: An Approach to Continuous Assessment
Authors: Sánchez-Ruiz Luis-M. , Moll-López Santiago , Moraño-Fernández Jose-Antonio , Roselló María-Dolores
Published: August 2021

Learning is a non-deterministic complex dynamical system where students transform inputs (classes, assignments, personal work, gamification activities, etc.) into outcomes (acquired knowledge, skills, and competencies). In the process, students generate outputs in a variety of ways (exams, tests, portfolios, etc.). The result of these outputs is a grade aimed at measuring the (level of) competencies achieved by each student. We revisit the relevance of continuous assessment to obtain this grading. We simultaneously investigate the generated outputs in different moments as modifiers of the system itself, since they may reveal a variation of the level of competencies achievement previously assessed. This is a novelty in the literature, and a cornerstone of our methodology. This process is called a Dynamical Continuous Discrete assessment, which is a form of blended assessment that may be used under traditional or blended learning environments. This article provides an 11-year perspective of applying this Dynamical Continuous Discrete assessment in a Mathematics class for aerospace engineering students, as well as the students’ perception of continuous assessments.
An Improved Estimation Algorithm of Space Targets Pose Based on Multi-Modal Feature Fusion
Authors: Hua Jiang , Hao Tonglin , Zeng Liangcai , Yu Gui
Published: August 2021

The traditional estimation methods of space targets pose are based on artificial features to match the transformation relationship between the image and the object model. With the explosion of deep learning technology, the approach based on deep neural networks (DNN) has significantly improved the performance of pose estimation. However, the current methods still have problems such as complex calculation, low accuracy, and poor real-time performance. Therefore, a new pose estimation algorithm is proposed in this paper. Firstly, the mask image of the target is obtained by the instance segmentation algorithm, and its point cloud image is obtained based on a depth map combined with camera parameters. Finally, the correlation among points is established to realize the prediction of pose based on multi-modal feature fusion. Experimental results in the YCB-Video dataset show that the proposed algorithm can recognize complex images at a speed of about 24 images per second with an accuracy of more than 80%. In conclusion, the proposed algorithm can realize fast pose estimation for complex stacked objects and has strong stability for different objects.