bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial Distribution Characteristics and Influencing Factors of the Success or Failure of China’s Overseas Arable Land Investment Projects—Based on the Countries along the “Belt and Road”
Authors: Ma Linyan , Pan Zichun , Wang Yameng , Wei Feng
Published: November 2022

As globalization continues, overseas arable land investment is becoming a viable option for China to alleviate its agricultural growth constraints, and the “Belt and Road” initiative offers plenty of opportunities for China to invest in overseas arable land. This study used data from the Land Matrix, KOF, World Bank, CEPII, UNCTAD and other databases to analyze the spatial distribution characteristics and factors influencing the success or failure of China’s overseas farmland investment projects in countries along the “Belt and Road” project through spatial analysis and the Logit model. The results show that North America has the largest share of production versus contracted acreage in current acreage investment cases, and Asian projects have the highest success rate. Both successful and failed projects in China regarding arable land investment are highly correlated spatially and characterized by a strong concentration and low uniformity of distribution, with differences in the degree of concentration in Asia, Africa and other regions. The contracted area, host country participation and host country resource endowment, business environment and institutional quality have significant, inverted “U-shaped”, negative and positive effects on project success, respectively. In addition, the involvement of the host country has a significant negative impact on the success of investment projects in Africa, and the length of investment and the type of investment purpose have a significant positive and negative impact on the success of investment projects in Asian countries. Therefore, China’s overseas arable land investment should be based on a full examination of existing investment projects in each country, the selection of host countries with abundant resource endowments and a good business environment and institutional environment and the adoption of a model suitable for each location to carry out investments according to local conditions.
Forest and Land Rights at a Time of Deforestation and Climate Change: Land and Resource Use Crisis in Uganda
Authors: Bamwesigye Dastan , Chipfakacha Raymond , Yeboah Evans
Published: November 2022

Globally, nations are targeting to achieve the “Green Deal 2030” and “Biodiversity Strategy 2030” to protect and conserve forest ecosystems. Forest land rights that define the nature of forest use have been rendered useless in many developing countries. Uganda is an African country endowed with tropical rainforests. Forests and other protected areas continue to decline due to deforestation and forest degradation in Uganda. Moreover, Uganda is an example of a country with a high allocation of virgin forest land to investors for development projects including agriculture. This paper examined perceptions of Ugandans on property rights and associated factors that impact the implementation of these rights in Uganda. The study conducted a questionnaire survey and obtained a sample size of 199. Key informant interviews (KIIs) on land and forest land rights in Uganda were conducted to get to the bottom of the problem. The results confirm high corruption (82%) and crime in Uganda’s land and forest rights management. Respondents highlighted limited transparency in implementing land and forest property rights. The study concluded that corruption and a lack of transparency frustrate property rights implementation in Uganda. The study recommends the government to prioritize fighting corruption and promoting transparency in the management of land and forest property, among others resources. Properly implementing land rights is vital in protecting and conserving forest ecosystems and other resources.
The Influence of Environment on the Distribution Characteristics of Historical Buildings in the Songshan Region
Authors: Xu Zhenghui , Tian Guohang , Wei Kailu , Ma Yuhong , Zhang Shumei , Huang Yumei , Yao Xiaojun
Published: November 2022

The Songshan region is the core area of Huaxia culture. As an important part of urban characteristics, the Songshan region’s historical architectural heritage is of great significance in sustainable development aspects such as the natural environment, social culture, and so on. The purpose of this study is to clarify the influencing factors of the spatial and temporal distribution of historical buildings in the Songshan region, explore more reasonable conservation and renewal strategies of historical building spaces, and consequently form an effective design method to protect and inherit the historical cultural landscape. Based on the ArcGIS10.6 spatial analysis method, this study simulated the spatial and temporal distribution characteristics of historical buildings in the Songshan region, and analyzed the spatial and temporal distribution characteristics by geographic information system and mathematical statistics. On this basis, the integration of natural elements and social elements has been realized to explore the key factors affecting the distribution of historical buildings in this region. The main results are as follows: (1) the distribution of historical buildings in the Songshan region is not balanced as a whole and has the characteristics of cluster distribution, forming two extremely high-density areas in Luoyang City and Dengfeng City; (2) the overall distribution direction of historical buildings is northwest to southeast, and the distribution center is near Mount Song; (3) natural environmental factors such as topography, landforms, and water systems to which historical buildings belong, as well as the historical layers of the ancient city and the concept of “the Center of Heaven and Earth”, are the main factors affecting the spatial and temporal distribution of historical buildings in the Songshan region.
Who and Where Are the Observers behind Biodiversity Citizen Science Data? Effect of Landscape Naturalness on the Spatial Distribution of French Birdwatching Records
Authors: Guetté Adrien , Caillault Sébastien , Pithon Joséphine , Pain Guillaume , Daniel Hervé , Marchadour Benoit , Beaujouan Véronique
Published: November 2022

The study of spatial bias in opportunistic data produced by citizen science programs is mainly approached either from a geographical angle (site proximity, accessibility, habitat quality) or from the angle of human behavior and volunteer engagement. In this study we linked both by analyzing the effect of observer profile on spatial distribution of recordings. We hypothesized that observer profile biases spatial distribution of records and that this bias can be explained by landscape naturalness. First, we established observer profiles from analysis of the temporal and spatial distributions of their records as well as record contents. Second, we mapped a naturalness gradient at regional and local scales. Using a dataset of more than 7 million bird records covering a time span of 15 years from the west of France, we defined four types of observer: garden-watchers, beginners, naturalists, and experts. We found that recording intensity could be related to naturalness at regional level; most visited areas were those where naturalness was on average lower i.e., close to population basins and highly accessible due to well-developed road infrastructure. At local level (neighborhood of recording sites), we found that experts and naturalists recorded in areas of higher naturalness index than those of garden-watchers and beginners. These results highlight how records contributed by different types of observer may lead to complementary coverage of different areas of the landscape. Future studies should therefore fully consider observer heterogeneity and how different observer profiles are influenced by local landscape naturalness.
Aging Industries in the Regional Economy: How to Support an Aging China?
Authors: Xu Fan , Huang Yongming , Wang Qiang
Published: November 2022

This study investigates the law, distribution characteristics, and changing trend of the coordinated development of China’s aging industry and regional economy, as well as the factors which influence the degree of coordination between the aging industry and economic development on the provincial level. In doing so, we construct a comprehensive evaluation index system of the aging industry and regional economy development, introduce an entropy weight coupling model, and measure the coupling and coordinated development level of the two systems using data of 31 selected Chinese provinces (municipalities) from 2009 to 2019. The spatial Dubin model is then used to empirically analyze the influencing factors and spatial effect decomposition of the coordinated development of the aging industry and regional economy. We reach the following main results: (1) China’s aging industry is developing unevenly, with substantial regional differences, but these differences have narrowed in recent years. (2) China’s regional economic disparities have widened. The eastern regions have the highest level of development, while the northeast region’s growth rate of GDP has declined since 2014. (3) The coordinated development of the aging industry and regional economy in one region of China has a positive impact on its neighboring regions, and all Chinese regions exhibits high–high, low–low agglomeration characteristics in terms of their degree of coordination. (4) A variety of socioeconomic and demographic factors affect the coordinated development of the aging industry and regional economy. An important implication of these findings is that, China should improve population structure, population quality, and economic development quality in order to achieve a high-level coordinated development of the aging industry and regional economy.
Revisiting the Modal Verb huì with an Interactional Linguistic Approach
Authors: Zhou Yan
Published: November 2022

This study takes an interactional linguistics and conversation analysis-based approach to analyze the modal verb huì ‘will’ in the recurrent formular of commissive actions, [wǒ huì X (de)] ‘I will X.’ Data analyses show that this format has two variations differentiated by the prosodic stress on huì. The format with the unstressed huì is often observed in turn-initiating position where the speaker offers to perform a future action or informs the recipient of their arrangement of an established activity. The format with the stressed huì appears in both initiating and responding positions although it is less frequently observed. Stressed huì is often used to reassure the recipient of an existing commitment to performing a future action. This study highlights the significance of prosody in the study of modal verbs and the benefits of studying individual words in a linguistic formula situated in specific interactional contexts.
Role of Stress in the Origin of Life
Authors: Kompanichenko Vladimir , Kotsyurbenko Oleg
Published: November 2022

The article shows the compatibility of the concept of thermodynamic inversion (TI) of the origin of life with the theory of stress in (micro)biology. According to the proposed TI concept, the first microorganisms on Earth were formed through an effective (intensified and purposeful) response of organic microsystems to incessant oscillations of physicochemical parameters (i.e., to periodic stress) in a hydrothermal environment. This approach allows us to explain the ability of contemporary microorganisms to respond to stress at the individual and population levels. The ability of microorganisms to effectively react to environmental stress factors is corroborated by a number of molecular and other mechanisms that are described in the article.
Aptamer-Based Probes for Cancer Diagnostics and Treatment
Authors: Hu Xueqi , Zhang Dongdong , Zeng Zheng , Huang Linjie , Lin Xiahui , Hong Shanni
Published: November 2022

Aptamers are single-stranded DNA or RNA oligomers that have the ability to generate unique and diverse tertiary structures that bind to cognate molecules with high specificity. In recent years, aptamer researches have witnessed a huge surge, owing to its unique properties, such as high specificity and binding affinity, low immunogenicity and toxicity, and simplicity of synthesis with negligible batch-to-batch variation. Aptamers may bind to targets, such as various cancer biomarkers, making them applicable for a wide range of cancer diagnosis and treatment. In cancer diagnostic applications, aptamers are used as molecular probes instead of antibodies. They have the potential to detect various cancer-associated biomarkers. For cancer therapeutic purposes, aptamers can serve as therapeutic or delivery agents. The chemical stabilization and modification strategies for aptamers may expand their serum half-life and shelf life. However, aptamer-based probes for cancer diagnosis and therapy still face several challenges for successful clinical translation. A deeper understanding of nucleic acid chemistry, tissue distribution, and pharmacokinetics is required in the development of aptamer-based probes. This review summarizes their application in cancer diagnostics and treatments based on different localization of target biomarkers, as well as current challenges and future prospects.
Collagenase-Induced Mouse Model of Osteoarthritis—A Thorough Flow Cytometry Analysis
Authors: Boneva Blagovesta , Ralchev Nikola , Ganova Petya , Tchorbanov Andrey , Mihaylova Nikolina
Published: November 2022

Objectives: Osteoarthritis (OA) is a chronic degenerative disorder of the joint characterized by cartilage breakdown and synovial inflammation. A number of different cells of innate and adaptive immunity contribute to joint pathology during OA inflammation. The interaction between the local synovial and systemic inflammatory cellular response and the structural changes in the joint is still unknown. The objective of this study was to investigate the role of the different types of immune cells in the development of OA. Methods: Collagenase-induced osteoarthritis was induced in Balb/c mice; flow cytometry analysis; and histopathological damages were assessed in histological sections stained with H&E, Toluidine blue, and Safranin O. Results: Flow cytometry analysis showed B lymphocyte infiltration in the active phase of inflammation and an increase in the effector T cell population into the synovium. An increased activation state of cytotoxic T cells and of NK cell populations in the spleen and synovium was also found. The differentiation of NK cells from a cytotoxic phenotype in early OA to cells with an effector phenotype in the chronic phase of the disease followed. Conclusions: A number of different cells contribute to inflammatory processes in OA. The correlation between their phenotype and the inflammatory pathophysiology could result in the development of novel approaches to suppress destructive changes in the joint.
Analysis of Tool Wear and Counter Surface Roughness in the Flexible Abrasive Tool Finishing
Authors: Kumar Mayank , Sidpara Ajay , Racherla Vikranth
Published: November 2022

This work uses the solvent casting method to fabricate an elastomeric tool with polyurethane as the base material and silicon carbide (SiC) as embedded abrasive particles. The distribution of abrasive particles and the pore structure in the fabricated tools are analyzed. The fabricated tools are porous in nature and have self-replenishing as well as self-lubrication properties. Aluminum 6061 alloy and electroless nickel-phosphorus plating having different initial roughness are selected as workpieces to study the wear mechanisms and loading of the flexible abrasive tool. The rotational speed of the tool, tool compression, and feed rate are fixed input process parameters. Total finishing time, sliding distance, and roughness are varied to obtain output responses. The workpiece material is also taken into account as a variable parameter in this study. These materials are classified as different counter surfaces as their surface roughness and mechanical properties vary. The finishing time and sliding distance for these counter surfaces differ in order to relate their effects on tool wear and loading. The nickel-plated surface shows a higher percentage reduction in surface roughness of 92% as compared to the aluminum surface, with a 62% reduction in surface roughness. The coefficient of friction, wear, and tool condition are analyzed to understand the mechanism of tool wear and tool loading. In this process, both two-body and three-body abrasions occur simultaneously and continuously.
Antibacterial TaC-(Fe,Cr,Mo,Ni)-(Ag/Cu) Composite Coatings with High Wear and Corrosion Resistance in Artificial Seawater
Authors: Antonyuk Mariya N. , Kuptsov Konstantin A. , Sheveyko Alexander N. , Shtansky Dmitry V.
Published: November 2022

The synergistic effect of simultaneous mechanical wear, chemical/electrochemical corrosion (tribocorrosion) and microbial attack poses a serious threat to marine and coastal infrastructure. To address this important problem, we have developed composite coatings consisting of TaC (25–35 at.%) and a corrosion-resistant α-Fe(Cr,Ni,Mo)-based metal matrix, as well as bactericidal elements (Cu, Ag). Coatings 50–75 μm thick were obtained by electrospark deposition in vacuum. The coatings possess high hardness (up to 10 GPa) and resistance to cyclic dynamic loads compared with the stainless steel (SS) substrate. Tribocorrosion experiments showed that the decrease in the corrosion potential associated with the removal of a passivating film from the surface during friction was 2–2.5 times smaller for the Ag-containing coating than for the other tested materials. The material passivation rates were also different: almost instantaneous passivation of the Ag- and Cu-doped coatings, and slow passivation for several minutes of the Ag/Cu-free coating and SS. The Ag-containing coating shows the lowest friction coefficient (0.2–0.25) and a minimal wear rate (1.6 × 10−6 mm3/Nm) in artificial seawater. The Ag-doped coating also exhibits the most positive value of corrosion potential and the lowest current density. After exposure in seawater for 20 days, only the Ag-doped coating showed no signs of pitting corrosion. All the studied materials have a pronounced bactericidal effect against Bacillus cereus Arc30 bacteria. The resulting coatings can be used to protect steel products from tribocorrosion and fouling in seawater.
Investigating the Effect of Operating Parameters on the Wear of Abrasive Tools in the Polishing Stage of Granitic Building Stones
Authors: Farhadian Ali , Ghasemi Ebrahim , Hoseinie Seyed Hadi , Bagherpour Raheb
Published: November 2022

Operating parameters affect the wear of abrasive tools during the polishing stage in building stone processing plants. This study investigates the effects of essential operating parameters including polishing head pressure, head rotation speed and water flow rate on the wear of the abrasive tools. For this purpose, a building stone abrasivity test was used to determine the weight loss of the abrasive tools during laboratory polishing of fifteen different types of Iranian granitic building stones. The standard operating parameters of the test were a polishing head pressure of 5 bar, a head rotation speed of 300 revolutions per minute (rpm), and a water flow rate of 4 L/min. The values of the operating parameters were changed to values within the range from ±25% and ±50% of the standard conditions in order to investigate the effect of variations in these parameters on the wear of the abrasive tools during the polishing stage. The results of different tests showed that the wear of the abrasive tools was directly proportional to the pressure up until a critical value of around 6.25 bar, after which it gradually decreased. This nonlinear wear behavior does not conform to Archard’s well-known classical wear law. The FESEM images of the worn surfaces showed that due to excessive load, debonded abrasive particles could not be pulled out from the pin surface and led to an interlocking phenomenon between the pin and stone surface. It was also found that the wear of the abrasive tools increased with increasing head rotation speed, while it decreased with the water flow rate. Moreover, the main wear mechanism of tests was abrasive wear and in some cases with a mixture mode of adhesion and delamination.
Lubrication Performance and Mechanism of Electrostatically Charged Alcohol Aqueous Solvents with Aluminum–Steel Contact
Authors: Hu Xiaodong , Wang Ying , Tang Hongmei , Xia Yu , Huang Shuiquan , Xu Xuefeng , Zhang Ruochong
Published: November 2022

Alcohol aqueous solvents were prepared by individually adding n-propanol, isopropanol, 1,2-propanediol, and glycerol to deionized water for use as lubricants for the electrostatic minimum quantity lubrication (EMQL) machining of aluminum alloys. The tribological characteristics of those formulated alcohol solvents under EMQL were assessed using a four-ball configuration with an aluminum–steel contact, and their static chemisorption on the aluminum surfaces was investigated. It was found that the negatively charged alcohol lubricants (with charging voltages of −5 kV) resulted in 31% and 15% reductions in the coefficient of friction (COF) and wear scar diameter (WSD), respectively, in comparison with those generated using neutral alcohol lubricants. During the EMQL, static charges could help dissociate the alcohol molecules, generating more negative ions, which accelerated the chemisorption of those alcohol molecules on the aluminum surfaces and thereby yielded a relatively homogeneous-reacted film consisting of more carbon and oxygen. This lubricating film improved the interfacial lubrication, thus producing a better tribological performance for the aluminum alloys. The results achieved from this study will offer a new way to develop high-performance lubrication technologies for machining aluminum alloys.
Dynamic Response and Numerical Simulation of Closed-Cell Al Foams
Authors: Xia Yinzheng , Shi Jianchao , Mu Yongliang
Published: November 2022

The drop hammer impact test was carried out to investigate the dynamic response of closed-cell Al foams. A relatively reasonable method was also developed to evaluate the velocity sensitivity of cellular material. The typical impact load–displacement curve exhibited two stages containing the initial compression stage and the progressive crushing stage. Three compressive damage behaviors and four failure modes of closed-cell Al foams were revealed, while the effect of velocity on the impact properties and the energy absorption capacity of different specimens were investigated. The results showed that the specific energy absorption of the specimens increased with the increasing density of the specimen and the impact velocity. However, the specimens with higher specific energy absorption seemed not to indicate better cushioning performance due to the shorter crushing displacement. In addition, the uniaxial impact simulation of two-dimensional (2D) Voronoi-based foam specimens was conducted at higher impact velocities. The simulation results of impact properties and deformation behavior agreed reasonably well with the experimental results, exhibiting similar velocity insensitivity of peak loads and deformation morphologies during uniaxial impact.
Evaluation of the Interfacial Interaction Ability between Basalt Fibers and the Asphalt Mastic
Authors: Wu Bangwei , Pei Zhaohui , Xiao Peng , Lou Keke
Published: November 2022

The interfacial properties between the asphalt mastic and fibers plays an essential role in the fiber-enhanced asphalt mixture properties. However, there is a lack of comprehensive studies on the indicators to evaluate the interfacial interaction ability of fibers with the asphalt mastic. Therefore, this paper selected three types of basalt fibers (denoted as A-BF, B-BF and C-BF) coated with different impregnating agents to prepare the fiber asphalt mastic. The Dynamic Shear Rheometer (DSR) test-based indicators, pull-out strength, and adhesion work were used to access the fiber asphalt mastic interfacial interaction ability. The differences between different indicators were compared and analyzed. The results show that all the selected indicators in this paper can effectively reflect the different fiber asphalt mastic interfacial properties. The evaluation results with different indicators are consistent. The interfacial interaction between fibers and the asphalt mastic increases with increasing temperature. The evaluation result with adhesion work is the most accurate. However, the pull-out strength test is simple, and the test result correlates well with adhesion work, which can be adopted daily to evaluate the fiber asphalt mastic interfacial properties.
Effect of Al and Fe Doping on the Electrochemical Behavior of Li1.2Ni0.133Mn0.534Co0.133O2 Li-Rich Cathode Material
Authors: Medvedeva Anna , Makhonina Elena , Pechen Lidia , Politov Yury , Rumyantsev Aleksander , Koshtyal Yury , Goloveshkin Alexander , Maslakov Konstantin , Eremenko Igor
Published: November 2022

This article studies the doping of Li-rich cathode materials. Aluminum and iron were chosen as dopants. Li-rich cathode materials for lithium-ion batteries, which were composed of Li1.2Ni0.133Mn0.534Co0.133O2 with a partial replacement of cobalt (2 at %) by iron and aluminum, were synthesized. The dopants were introduced at the precursor synthesis stage by co-precipitation. The presence of Fe and Al in the composition of the synthesized samples was proved by inductively coupled plasma mass spectrometry, X-ray diffraction analysis and X-ray microanalysis. The cathode materials were tested electrochemically. The incorporation of Al and Fe into the structure of lithium-enriched materials improved the cyclability and reduced the voltage fade of the cathodes. An analysis of the electrochemical data showed that the structural changes that occur in the initial cycles are different for the doped and starting materials and affect their cycling stability. The partial cation substitution suppressed the unfavorable phase transition to lower-voltage structures and improved the electrochemical performance of the materials under study.
Stimuli-Responsive Star Polymer as an Admixture for Crystallization of Hollow Crystals
Authors: Lemanowicz Marcin , Chrzanowska Justyna , Kotek Milena , Mielańczyk Anna , Kupczak Maria , Niewolik Daria , Korytkowska-Wałach Anna , Klymenko Olesya , Kocur Alicja , Neugebauer Dorota
Published: November 2022

Polymers are becoming a very popular tool in the crystallization of different compounds. In this work, a new method of crystallization is proposed using stimuli-responsive star polymer in order to obtain hollow structure crystals. In these experiments, amphiphilic copolymer of acrylic acid (AA) and methyl acrylate (MA) were used for isohydric crystallization via they cooling of KCl in deionized water solution. The experiments were realized in quartz cuvette with a magnetic stirrer using a specialized spectrometer with precise temperature control. The crystallization course was monitored by the absorbance readings and analysis of the nucleation energetic effect. It was proved that the moment of the polymer’s phase transition occurrence had an important role in the crystal growth process. On the other hand, the occurrence of phase transition did not trigger the nucleation. The supercoolings achieved in the presence of the polymer were significantly higher compared to pure salt crystallization. On the basis of analysis of Particle Size Distribution (PSD) and Critical Aggregation Concentration (CAC) of the polymer, it was proposed that the hydrophobic particles of macromolecules created from polymeric aggregates served as templates for the formation of hollow crystals. Their purity was verified using thermogravimetric analysis (TGA), 1H NMR, and XRD. Only trace amounts of polymer were found in the crystalline product.
Characterization of a Magnesium Fluoride Conversion Coating on Mg-2Y-1Mn-1Zn Screws for Biomedical Applications
Authors: Gambaro Sofia , Nascimento M. Lucia , Shekargoftar Masoud , Ravanbakhsh Samira , Sales Vinicius , Paternoster Carlo , Bartosch Marco , Witte Frank , Mantovani Diego
Published: November 2022

MgF2-coated screws made of a Mg-2Y-1Mn-1Zn alloy, called NOVAMag® fixation screws (biotrics bioimplants AG), were tested in vitro for potential applications as biodegradable implants, and showed a controlled corrosion rate compared to non-coated screws. While previous studies regarding coated Mg-alloys have been carried out on flat sample surfaces, the present work focused on functional materials and final biomedical products. The substrates under study had a complex 3D geometry and a nearly cylindrical-shaped shaft. The corrosion rate of the samples was investigated using an electrochemical setup, especially adjusted to evaluate these types of samples, and thus, helped to improve an already patented coating process. A MgF2/MgO coating in the µm-range was characterized for the first time using complementary techniques. The coated screws revealed a smoother surface than the non-coated ones. Although the cross-section analysis revealed some fissures in the coating structure, the electrochemical studies using Hanks’ salt solution demonstrated the effective role of MgF2 in retarding the alloy degradation during the initial stages of corrosion up to 24 h. The values of polarization resistance (Rp) of the coated samples extrapolated from the Nyquist plots were significantly higher than those of the non-coated samples, and impedance increased significantly over time. After 1200 s exposure, the Rp values were 1323 ± 144 Ω.cm2 for the coated samples and 1036 ± 198 Ω.cm2 for the non-coated samples, thus confirming a significant decrease in the degradation rate due to the MgF2 layer. The corrosion rates varied from 0.49 mm/y, at the beginning of the experiment, to 0.26 mm/y after 1200 s, and decreased further to 0.01 mm/y after 24 h. These results demonstrated the effectiveness of the applied MgF2 film in slowing down the corrosion of the bulk material, allowing the magnesium-alloy screws to be competitive as dental and orthopedic solutions for the biodegradable implants market.
Hot Deformation Behavior and Simulation of Hot-Rolled Damage Process for Fine-Grained Pure Tungsten at Elevated Temperatures
Authors: Lv Yongqi , Zhao Siqi , Liu Tao , Cheng Huichao , Fan Jinglian , Huang Yuanchun
Published: November 2022

Fine-grained pure tungsten fabricated by a sol drying reduction low-temperature sintering method and hot isothermal compression tests were performed by using the Gleeble 3800 thermo mechanical simulator at deformation temperatures from 1273 K to 1473 K and strain rates from 0.001 s−1 to 1 s−1. In addition, the constitutive equation was established by least square method combined with the Zerilli–Armstrong model, and the hot deformation behavior was discussed. Moreover, based on constitutive equation, the influence of the rolling process and its parameters on temperature, strain, density and rolling force in the hot rolling process was investigated at elevated temperature by the finite element model (FEM). Furthermore, the form of rolling damage and its formation mechanism were analyzed. Results showed the grains of pure tungsten are dense, irregular polyhedral spherical and very fine, and the average grain size is about 5.22 μm. At a high strain rate, the flow stress increases rapidly with the increase in strain, while the stress–strain curve shows a flattening trend in the tested strain rate range with increasing temperature, and no flow stress peak exists, showing obvious dynamic recovery characteristics. Furthermore, the FEM simulation showed that compared with the rolling temperature, the reduction has a greater influence on the temperature, stress–strain field and its distribution. There are three kinds of damage in the hot rolling process: transverse cracks, longitudinal cracks and side cracks, which are attributed to the competition between additional stress caused by uneven deformation and material strength. Moreover, the control method of hot rolling defects had been preliminarily proposed. These results should be of relevance for the optimum design of the hot rolling process of pure tungsten.
Calibration Method for In-Process Identification of Tangential Specific Cutting Force in Milling
Authors: Janota Miroslav , Kolář Petr , Falta Jiří , Kozlok Tomáš
Published: November 2022

The cutting forces that occur during machining cause static and dynamic deformations of the machine–tool–workpiece system. In general, the cutting force is spatial. However, knowledge of the tangential component of the cutting force is crucial for the optimum use of the power installed on the spindle. An important parameter for cutting force modeling is the tangential cutting force coefficient. This paper focuses on the approach of the in-process identification of the cutting and edge components of the tangential cutting force coefficient, using the spindle power signal read directly from the machine tool control system. Such procedures have already been described in the available literature. The key point for the successful implementation of these methods is the identification and avoidance of the passive torque signal. This paper describes the operational calibration of the spindle drive system. The calibration procedure is based on the tap test using modal hammer excitation and the spindle power signal response. The proposed procedure was successfully validated using a machine–machine comparison approach and a machine–dynamometer validation approach. The results are consistent with those in the available literature. With this method, we were able to determine the cutting component of the tangential specific cutting force with a deviation of 1% from the reference system and an edge component of 10%. The modal hammer method only enables the avoidance of dynamometers in the machine calibration procedure.
Influence of Position of Intake Struts on Unsteady Load and Vibration of First-Stage Rotor
Authors: Peng Wei , Ren Xiaodong , Li Xuesong , Gu Chunwei , Wu Hong , Que Xiaobin
Published: November 2022

To investigate the influence law and mechanism of the relative circumferential position of intake struts on the unsteady load and vibration of the first stage rotor, the first 1.5-stage of a heavy-duty gas turbine compressor with intake struts was numerically simulated. The analysis of the flow field and vibration of the rotor blade reveals that the circumferential position of intake struts has little effect on aerodynamic performance but obviously changes the unsteady load and vibration level of the rotor blade. When strut and inlet guide vane wakes coincide, they are strengthened, resulting in the overall enhancement of the unsteady load and vibration on the rotor blade. The circumferential position of struts changes the combined effect of strut wakes and the first stage stator potential flow on the rotor blade, which has an obvious influence on the unsteady load and vibration in the middle chord length but has little influence on the unsteady load near the leading and trailing edges. Research results provide reference and guidance for the installation of struts.
Uniaxial Load Specification for Vehicle Knuckle Part Using Maximum Stress Similarity in Triaxial Load Case
Authors: Kim Chan-Jung
Published: November 2022

Knuckle parts have a complex relationship with adjacent vehicle parts, making it difficult to determine the proper fatigue evaluation specification when considering vehicle operation. An accelerated triaxial load case for the knuckle part was derived using a combination of four event modules from the test code developed by the Korea Automotive Technology Institute. The fatigue damage analysis of the front and rear knuckle models was conducted with respect to the accelerated triaxial load case, and the maximum stress was measured at hotspots for the magnitude and orientation of the critical plane. The sensitivity analysis of the knuckle models was conducted for six directions of the unit force, and the proper uniaxial force orientations of the two knuckle models were determined for the maximum stress similarity in the triaxial load case in terms of the magnitude and orientation of the critical plane. The final uniaxial load specification was derived by adjusting the magnitude of the candidate uniaxial load and the error analysis showed reliable results through inverse safety factors with 0.02, 0.04 error, and critical plane angles with 10.8, 0.8 degrees error for front and rear knuckles, respectively, verified by comparing the maximum stress similarity between the triaxial and uniaxial load cases.
Research on Dynamic Characteristics of Flap Actuation System Considering Joint Clearance and Flexibility
Authors: Wan Qi , Liu Geng , Liu Qi , Tong Ruiting , Ma Shangjun
Published: November 2022

The flight control effects and flight quality of the aircraft are influenced by the flap actuation system directly. The main motivation of this research is to develop a rigid-flexible model of the flap actuation system with clearance and to explore the coupling effects of clearance joints and flexible bodies on the system’s dynamic characteristics. A modified contact force model is used to a joint with small clearance, heavy load, and large contact area. Then, the effectiveness of an embedded modeling method of this modified model is verified. Based on this method, a rigid-flexible coupling model of the flap actuation system with multi clearance joints is established. Moreover, the influence of system parameters, such as clearance size and clearance joint position, and coupling effects of the flexibility and joint clearance on dynamic responses, are analyzed. The results show that: (1) flexible bodies act as a suspension to reduce negative effects of joint clearance on dynamic responses of a clearance-contained system; (2) one flexible body can reduce the oscillation phenomenon of joint clearances, yet the suspension effect will be gradually weaken with the increase of the clearance joint number; (3) coupling effects of the elastic deformation owing to multi flexible bodies and the collision interaction between multi clearance joints make the system tend to chaos, and the system stability is reduced. This study can contribute to predicting the collision characteristics of the aircraft transmission system and improving the transmission accuracy, response speed, and stability of the aircraft.
Design and Performance Analysis of a Double-Outlet-Rod Magnetorheological Damper for Impact Load
Authors: Wang Chenglong , Zhang Jiwei , Liu Guoming , Shang Huan , Wei Xueqian
Published: November 2022

In order to improve the performance of magnetorheological dampers under impact load, a double-rod magnetorheological damper is designed in this paper, and its multi-physical field coupling model is established. The performance of a double-rod magnetorheological damper under impact conditions is characterized from the aspects of viscosity, velocity, peak pressure, impact energy consumption and viscous damping force ratio. The research contents include: a comparison of dynamic characteristics such as the viscosity, velocity and pressure of the magnetorheological damper under impact conditions and low-speed vibration; the influence of temperature on the mechanical performance parameters of the magnetorheological damper, such as peak pressure, impact energy dissipation and viscous damping force ratio, under impact load; and the establishment of a peak sensitivity function to study the influence of three key structural parameters on the magnetic flux density and impact energy dissipation at the damper damping channel. On the basis of the above theoretical research, an impact test of the processed double-rod magnetorheological damper prototype under different excitation currents is carried out. The results show that the viscosity distribution of the damping channel activation region (i.e., the region where the magnetorheological effect occurs after energization) of the magnetorheological damper under impact is disordered, the region of the structural flow in the semi-solid state is small and the influence of the Coulomb damping force is greatly weakened. When the current is 0.5 A, the viscous damping force accounts for 91.2%, and the viscous damping force plays a major role in buffering energy absorption. With an increase in working temperature, the effect of the Coulomb damping force decreases, and the peak pressure and impact energy consumption of the MR damper decrease greatly. With increasing excitation current, this reduction is further increased. The influence of gap height, piston diameter and effective length on magnetic flux density and impact energy dissipation is determined via the peak sensitivity function. When the change in the structural parameters ∆α is 30%, the change in the piston diameter has the greatest influence on the peak sensitivity of the magnetic flux density, and the peak sensitivity index of the magnetic flux density reaches 25%. The change in clearance height has the greatest influence on the impact energy consumption, and the peak sensitivity index of the impact energy consumption reaches 115%. This shows that the magnetic flux density is most affected by the piston diameter, and the impact energy consumption is most affected by the clearance height. The test results show that the test pressure peak-change curve is consistent with the simulation pressure peak-change curve, and the pressure peak error between the two is within 10%.
Estimating Value-at-Risk and Expected Shortfall: Do Polynomial Expansions Outperform Parametric Densities?
Authors: Castillo-Brais Brenda , León Ángel , Mora Juan
Published: November 2022

We assess Value-at-Risk (VaR) and Expected Shortfall (ES) estimates assuming different models for the standardized returns: distributions based on polynomial expansions such as Cornish-Fisher and Gram-Charlier, and well-known parametric densities such as normal, skewed-t and Johnson. This paper aims to analyze whether models based on polynomial expansions outperform the parametric ones. We carry out the model performance comparison in two stages: first, with a backtesting analysis of VaR and ES; and second, using loss functions. Our backtesting results show that all distributions, except for normal ones, perform quite well in VaR and ES estimations. Regarding the loss function analysis, we conclude that polynomial expansions (specifically, the Cornish-Fisher one) usually outperform parametric densities in VaR estimation, but the latter (specifically, the Johnson density) slightly outperform the former in ES estimation; however, the gains of using one approach or the other are modest.
Numerical Investigation of Heat Transfer Enhancement in a Microchannel with Conical-Shaped Reentrant Cavity
Authors: Muzhaimey Syarif Syahrul Syazwan , Ghazali Nik Nazri Nik , Zainon Mohd Zamri , Badruddin Irfan Anjum , Hussien Mohamed , Kamangar Sarfaraz , Ahammad N. Ameer
Published: November 2022

The current study is focused on improving the thermal performance of the microchannel heat sink (MCHS) using the passive reentrant cavity approach. The MCHS physical model’s single channel was used in a three-dimensional numerical simulation. The basic geometrical layout of the MCHS’s computational domain was drawn from previously published research and verified using numerical and analytical correlations that were already in existence. The innovative conical-shaped microchannel heat sink’s (CMCHS) properties for heat transmission and fluid flow were examined numerically under steady-state conditions with laminar flow and a constant heat flux. At various flow velocities and configurations, the impacts of the geometrical parameters on pressure drops and heat transfer were examined. The outcome demonstrates a tremendously positive thermal performance with a significantly greater pressure drop than the traditional straight channel. In the microchannels with the conical-shaped reentrant cavities and minimal pressure loss, convection heat transfer is significantly improved. The findings of the present investigation demonstrate that the conical-shaped MCHS is practical and has a good chance of being used in real-world settings.
Evaluation of Educational Interventions Based on Average Treatment Effect: A Case Study
Authors: Liang Jingyu , Liu Jie
Published: November 2022

Relative to randomized controlled trials (RCTs) with privacy and ethical concerns, observational studies are becoming dominant in education research. In an observational study, it is necessary and important to correctly evaluate the effects of different interventions (i.e., covariates) on student performance with observational data. However, these effects’ evaluation results are probably derived from biased estimations because the distributions of “control” and “treatment” student groups can hardly be equivalent to those in RCTs. Moreover, the collected covariates on possible educational interventions (i.e., treatments) may be confounded with student characteristics that are not included in the data. In this work, an estimation method based on the Rubin causal model (RCM) is proposed to calculate the average treatment effect (ATE) of different educational interventions. Specifically, with the selected covariates, the propensity score (i.e., the probability of treatment exposure conditional on covariates) is considered as a criterion to stratify the observational data into sub-classes with balanced covariate distributions between the control and treatment groups. Combined with Neyman’s estimation, the ATE of each sample is then obtained. We verify the effectiveness of this method with real observational data on student performance and its covariates.
Math Learning in a Science Museum—Proposal for a Workshop Design Based on STEAM Strategy to Learn Mathematics. The Case of the Cryptography Workshop
Authors: Roldán-Zafra Juan , Perea Carmen
Published: November 2022

In mathematics teaching, great efforts are made, and diverse teaching strategies are employed in order to facilitate students’ learning process. Informal environments have proven to be conducive and motivating spaces for science learning. In particular, science museums can be used as a complement and collaborate in order to leverage each of their strengths to motivate mathematics learning. Educational models give a global explanation to the learning process. Taking into account all these aspects and considering van Hiele’s model as didactic reference, we propose the design of a general workshop that has among its objectives the learning of mathematics. To do this, we start from the three main elements and processes set forth in van Hiele’s model: insight, reasoning levels and learning phases. The insight or student’s competence are formulated through Hoffer’s abilities, and for the development of the activities of the learning phases, the STEAM (science, technology, engineering, art and maths) strategy. Once the general proposal has been made, we use it to design a scientific workshop for learning mathematics about cryptography. Our greatest challenge was in generating activities adapted to the established requirements. It would be interesting, for future works, to design research to evaluate the effectiveness of the proposal presented. Moreover, it would be interesting to develop a proposal for assessing student learning.