Shiqian Ni, Yanqin Zhang and Zhen Quan
When the clearance oil film of hydrostatic bearing friction pair is in critical lubrication state, the phenomenon of zero flow of local lubricating oil will aggravate the oil film…
Abstract
Purpose
When the clearance oil film of hydrostatic bearing friction pair is in critical lubrication state, the phenomenon of zero flow of local lubricating oil will aggravate the oil film temperature rise, which needs to be solved.
Design/methodology/approach
In this paper, the critical lubrication parameter equation and the oil film temperature rise mathematical model are derived for the new type q1-205 double rectangular cavity hydrostatic bearing. Based on a combination of theoretical analysis, simulation and experimental verification, this paper analyzes the flow characteristics and temperature rise characteristics of the lubricating oil when the hydrostatic bearing is in a critical lubrication state under different operating conditions and finally obtains the critical lubrication state of the oil film.
Findings
This study found that the numerical simulations and the derived formulas agree with the results. When the oil film is in critical lubrication, the cross-section side flow of the oil side is almost zero. The heat cannot be taken away in time, resulting in the local temperature rise of the oil film, which causes serious heat accumulation.
Originality/value
It is concluded that the operating condition parameters corresponding to the critical lubrication state provide a theoretical basis for the selection of actual hydrostatic bearing operating conditions, which is of great scientific significance.
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Juliette M. Iacovino and Sherman A. James
Over the past several decades, scholars and universities have made efforts to increase the retention of students in higher education, but graduation rates remain low. Whereas…
Abstract
Over the past several decades, scholars and universities have made efforts to increase the retention of students in higher education, but graduation rates remain low. Whereas two-thirds of high school graduates attend college, fewer than half graduate. The likelihood of graduation decreases even more for Black, Latino, American Indian, and low-income students, who have a 12–15% lower chance of earning their degree. The importance of psychosocial adjustment to student persistence has received relatively less attention than academic and social integration. Racial/ethnic minority students face unique challenges to psychosocial adjustment in college, including prejudice and discrimination, unwelcoming campus environments, underrepresentation, and a lack of culturally appropriate counseling resources. The current chapter will discuss the impact of these challenges on the persistence, academic success, and health of racial/ethnic minority students, and strategies that universities can employ to create inclusive policies, resources and campus environments that empower students of color and maximize their success.
Ada T. Cenkci, Megan S. Downing, Tuba Bircan and Karen Perham-Lippman
Elena R. Agadullina, Andrey Lovakov and Natalia V. Kiselnikova
The first year of college is a stressful life period connected with the experience of loneliness, isolation and depression since the majority of freshmen can no longer maintain an…
Abstract
Purpose
The first year of college is a stressful life period connected with the experience of loneliness, isolation and depression since the majority of freshmen can no longer maintain an equally close relationship with school friends and family. Social networks have become a significant part of students' daily lives and might be an effective tool for maintaining relationship and reducing loneliness. There are contradictory results concerning the relationship between social networks sites (SNS) use and feelings of loneliness.
Design/methodology/approach
A four-week experiment was conducted to study the effect of SNS on feelings of social and emotional loneliness across freshmen. The treatment group (n = 40) took a break from SNS, while the control group (n = 37) used SNS as usual.
Findings
Comparison of the treatment and control groups showed that quitting SNS does not change either feeling of social/emotional loneliness. This paper also found that feelings of social and emotional loneliness did not depend on freshmen's positive/negative attitudes toward being alone.
Originality/value
This study is one of the few that uses experimental design to study the effects of using social networks on the psychological state of students in the context of higher education. The results showed that refusing SNS use can have a positive potential for psychological well-being of freshmen since solitude can be used by them as time for self-discovery and self-development. According to the results, social networks neither increase nor decrease the feeling of loneliness, and offline learning and communication environment plays a more significant role in the adaptation of freshmen. These results allow to take a new look at the studies related to the relationship between SNS use and loneliness and the role of social networks in the adaptation of freshmen.
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Meng Jiang, Yang Liu, Ke Li, Zhen Pan, Quan Sun, Yongzhe Xu and Yuan Tao
The purpose of this paper is to study the reliability of sintered nano-silver joints on bare copper substrates during high-temperature storage (HTS).
Abstract
Purpose
The purpose of this paper is to study the reliability of sintered nano-silver joints on bare copper substrates during high-temperature storage (HTS).
Design/methodology/approach
In this study, HTS at 250 °C was carried out to investigate the reliability of nano-silver sintered joints. Combining the evolution of the microstructure and shear strength of the joints, the degradation mechanisms of joints performance were characterized.
Findings
The results indicated that the degradation of the shear properties of sintered nano-silver joints on copper substrates was attributed to copper oxidation at the silver/copper interface and interdiffusion of interfacial elements. The joints decreased by approximately 57.4% compared to the original joints after aging for 500 h. In addition, severe coarsening of the silver structure was also an important cause for joints failure during HTS.
Originality/value
This paper provides a comparison of quantitative and mechanistic evaluation of sintered silver joints on bare copper substrates during HTS, which is of great importance in promoting the development of sintered silver technology.
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Zhen Yan, Dong Jiang, Xiaoming Gao, Can Zhang, Ming Hu, Dapeng Feng, Jiayi Sun, Lijun Weng and Chao Wang
This paper aims to study the tribological behavior of the WS2/oil-impregnated porous polyimide (PPI) solid/liquid composite system, in which both PFPE (perfluoropolyether) and…
Abstract
Purpose
This paper aims to study the tribological behavior of the WS2/oil-impregnated porous polyimide (PPI) solid/liquid composite system, in which both PFPE (perfluoropolyether) and SiCH (silahydrocarbons) oils with different hydrocarbon chains were used, respectively. Lubricating mechanism of the composite system was also explored.
Design/methodology/approach
The tribological behaviors of the WS2 films against the PPI cylindrical pins before and after immersing oil were evaluated under different loads by a reciprocating-type ball-on-disc tribometer.
Findings
The composite system exhibited the low and stable friction coefficient after the running-in stage, and the lubricant oil played a positive effect. It was found that the WS2/PFPE composite system exhibited more excellent lubricating property, although sole SiCH far exceeds PFPE in lubrication. The abnormal phenomenon mainly resulted from the influence of the oil amount. XRD results on the wear track surfaces indicated that PFPE and SiCH oils with different hydrocarbon chains were likely to preferentially adsorb to the edge plane and basal plane of the WS2 crystals, respectively.
Originality/value
In previous studies, liquid lubricants were directly dripped or spin-coated on the solid lubricant surface. Based on its potential advantage in application, the tribological behavior and mechanism of the solid lubricating film/oil-impregnated PPI composite system were investigated in this study.
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Bangcheng Liu, Ningyu Tang and Xiaomei Zhu
The purpose of this research is to investigate how generalisable the public service motivation (PSM) observed in Western society is to China and to examine the effects of public…
Abstract
Purpose
The purpose of this research is to investigate how generalisable the public service motivation (PSM) observed in Western society is to China and to examine the effects of public service motivation on job satisfaction.
Design/methodology/approach
Exploratory factor analysis and confirmatory factor analysis techniques are applied to survey data of 191 public servants in China to investigate the generalisability of Western PSM. Using hierarchical regression analysis, the paper examines the effects of the dimensions of PSM on job satisfaction.
Findings
The results show that the public service motivation observed in the West exists in China, but the generalisability of the construct is limited. Three of the four dimensions of public service motivation (attraction to public policy making, commitment to the public interest, and self‐sacrifice) exist in China, but the fourth dimension (compassion) is unconfirmed.
Originality/value
The paper is the first to examine the generalisability and instrumentality of PSM as observed in Western society to China. The results indicate that the public service motivation observed in the West also exists in China, but that the generalisability is limited. Public service motivation emerges from the results as a positively significant predictor of job satisfaction in the public sector of China. It enhances the applicability and meaningfulness of the concept of public service motivation across political and cultural environments.
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Zhen Zhao, Zhiyong Fan, Yigang Sun and Zhexu Liu
In modern integrated modular avionics (IMA), it plays an important role to guarantee safety and reliability of the system. The safety and reliability of communication scheduling…
Abstract
Purpose
In modern integrated modular avionics (IMA), it plays an important role to guarantee safety and reliability of the system. The safety and reliability of communication scheduling plays a crucial role in this IMA platforms-based network system. To verify the safety and reliability of the communication scheduling in this network, sufficient and typical test data must be generated to input into the network, obtain and evaluate the corresponding output.
Design/methodology/approach
To generate communication scheduling data, this paper presents an iterative communication scheduling data generation algorithm for a configured network of IMA platforms. First, the algorithm generates all possible communication schedules for the first timestamp. Then, constraint is introduced to decrease the quantity of communication schedules to improve the efficiency. The communication schedules are gradually extended to the second timestamp until the final timestamp, i.e. length of communication scheduling sequence.
Findings
To verify the efficiency and feasibility of the algorithm, a model is built based on the architecture analysis and design language (AADL) by mapping the correlation time of generated communication scheduling data into task properties. Schedulability is analyzed by loading this model into AADL Inspector. The simulation result illustrates that the proposed algorithm is efficient and feasible.
Practical implications
The proposed method can provide data support for communication scheduling test for the network of IMA platforms.
Originality/value
A constraint-based iterative communication scheduling data generation algorithm is proposed for the network of IMA platforms automatically.
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Yujie Quan, Philipp Drescher, Faming Zhang, Eberhard Burkel and Hermann Seitz
The purpose of this paper is to fabricate cellular Ti6Al4V with carbon nanotube (CNT)-like structures by selective electron beam melting and study the resultant mechanical…
Abstract
Purpose
The purpose of this paper is to fabricate cellular Ti6Al4V with carbon nanotube (CNT)-like structures by selective electron beam melting and study the resultant mechanical properties based on each respective geometry to provide fundamental information for optimizing molecular architectures and predicting the mechanical properties of cellular solids.
Design/methodology/approach
Cellular Ti6Al4V with CNT-like zigzag and armchair structures are fabricated by selected electron beam melting. The microstructures and mechanical properties of these samples are evaluated utilizing scanning electron microscopy, synchrotron radiation X-ray and compressive tests.
Findings
The mechanical properties of the cellular solids depend on the geometry of strut architectures. The armchair-structured Ti6Al4V samples exhibit Young’s modulus from 501.10 to 707.60 MPa and compressive strength from 8.73 to 13.45 MPa. The zigzag structured samples demonstrate Young’s modulus from 548.19 to 829.58 MPa and compressive strength from 9.32 to 16.21 MPa. The results suggest that the zigzag structure of the Ti6Al4V cellular solids can achieve improved mechanical properties and the mechanism for the enhanced mechanical properties in the zigzag structures was revealed.
Originality/value
The results provide an innovative example for modulating the mechanical properties of cellular titanium by adjusting the unit cell geometry. The Ti6Al4V cellular solids with single-walled CNT-like structures could be used as light-weight construction components or filters in industries. The Ti6Al4V with multiwalled CNT-like structures could be used as new scaffolds for biomedical applications.
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Radwan Alkebsee, Ahsan Habib and Junyan Li
This paper aims to examine the association between green innovation and the cost of equity in China. This study relies on the investors’ base perspective and shareholders’…
Abstract
Purpose
This paper aims to examine the association between green innovation and the cost of equity in China. This study relies on the investors’ base perspective and shareholders’ perceived risk perspective to investigate the relation between green innovation and the cost of equity in China.
Design/methodology/approach
The paper uses firm-fixed effect regression for a sample of Chinese public companies for the period 2008–2018.
Findings
The authors find a negative relationship between green innovation and the cost of equity capital. This negative association is found to be more pronounced for less financially constrained firms, during periods of high economic policy uncertainty, and for firms with a strong internal control environment. Finally, the paper shows that the negative association became more pronounced after the passage of the Environmental Protection Law of China in 2012. The results remain robust to possible endogeneity concerns.
Originality/value
This study contributes to the green innovation literature by documenting that shareholders favorably view firms implementing green innovation policies. The study also has policy implications for Chinese regulators in improving the green credit policy.