Search results

This paper aims to clarify the size and morphology of transition metal dichalcogenides has an impact on lubrication performance of Cu-based composites. This study is intended to show that Cu-based electrical contact materials containing Nb_0.91Ti0.09Se₂ have better electrical and tribological properties than those containing NbSe₂. The tribological properties of Cu-based with different Ti-dopped NbSe₂ content were also discussed.

The NbSe₂ and Nb_0.91Ti_0.09Se₂ particles were fabricated by thermal solid state reaction method. The powder metallurgy technique was used to fabricate composites with varying Nb_0.91Ti_0.09Se₂ mass fraction. The phase composition of Cu-based composites was identified by X-ray diffraction, and the morphology of NbSe₂/Nb_0.91Ti_0.09Se₂ and the worn surface of composites were characterized by scanning electron microscopy and transmission electron microscopy. In addition, the tribological properties of composites were appraised using a ball-on-disk multi-functional tribometer. The data of friction coefficient and resistivity were analyzed and the corresponding conclusion was drawn.

In comparison with the pure copper, Cu-based composites containing Nb_0.91Ti_0.09Se₂/NbSe₂ had a lower friction coefficient, illustrating the Nb_0.91Ti_0.09Se₂ with nano-size particles prepared in this work is a perfect choice for the fabrication of excellent electrical contact composites. Compared to composites with NbSe₂, composites containing Nb_0.91Ti_0.09Se₂ have better tribological and electrical properties.

Because of the use of thermal solid state reaction method, the size of NbSe₂ and Nb_0.91Ti_0.09Se₂ is relatively large. Therefore, the fabrication of finer particles of Nb_0.91Ti_0.09Se₂ is encouraged.

In this paper, the authors discuss the tribological and electrical properties of Cu-based composites, and the value of optimum obtained as Nb_0.91Ti_0.09Se₂ content is 15 Wt.%.

As a frequently observed business phenomenon, the use of product scarcity to improve a product’s market performance has received increasing attention from both academics and practitioners. The resulting literature has covered a wide variety of issues based on various theories, using different research methods, in a diverse range of settings. However, this diversity also makes it difficult to grasp the core themes and findings, and to see the outstanding knowledge gaps. This paper aims to review previous studies on the use of product scarcity in marketing and identifies new directions for future research.

A systematic review was conducted to identify and analyse 66 research papers published in business and management journals between 1970 and 2017.

The authors examined the underlying theories of scarcity-based marketing, and developed a conceptual framework that describes the key factors of product scarcity and how they influence both consumers and the market. They also highlighted some key achievements in modelling the processes involved in using product scarcity in marketing.

This analysis of the identified papers suggests that there are substantial gaps in our knowledge of this field, which opens up new paths for future research. For future research, the authors identified three directions aimed at: addressing the practical needs of firms in understanding product scarcity; guiding the implementation of scarcity-based strategies; and measuring, monitoring and predicting the level of product scarcity and its impacts during implementation.

Financial analysts act as crucial conduits of information between firms and stakeholders. However, comparatively little is known about how these information intermediaries evaluate the believability and importance of corporate disclosures. We argue that a firm’s level of managerial discretion, or latitude of executive action, acts as a cue for financial analysts, which helps them interpret and respond to voluntary management earnings forecasts. Our study provides strong, robust evidence that financial analysts find management forecasts significantly less believable in low-discretion than in high-discretion environments, and therefore tend to be much less responsive to these forecasts. We also show that managerial discretion is especially impactful on analysts’ responses in those circumstances where analysts are typically most uncertain about how to interpret management forecasts.

The purpose of this paper is to investigate the definitions, dimensions, and classifications of online communities together with their potential to produce value for business. Those value options are then discussed in the context of empirical vignettes showing examples of business models focussed on one of the two potential benefits coming from online communities – clear financial gains and intangible long-run returns.

This paper uses systematic literature review method. In total, 67 academic paper in the area of business and management were chosen for the analysis.

The literature review shows multitude of online communities definitions and classifications, but hardly any comprehensive attempt to map the phenomena in full. This paper is looking into recognising potential revenue streams from online businesses and other non-financial benefits that can be combined to create strong and sustainable value proposition.

Drawing on the literature reviewed a novel categorisation of the commercial opportunities offered by the online communities is presented. These opportunities are discussed in a context of business model design.

This paper aims to focus on investigating the failure mode of fused deposition modeling (FDM) fabricated parts by using acoustic emission (AE) technique.

Considering the special prototyping way of FDM, the failure modes of FDM-fabricated parts were investigated experimentally. One test was carried out and the other two describe what has been observed on this basis. Acoustic emissions are obtained during the tensile process. AE features of peak frequency, energy and amplitude are extracted and preliminarily analyzed. Then, the unsupervised clustering method of k-means is applied to explore the relationship between the failure modes and the AE signals.

Failure modes of filament debonding and breakage can be successfully recognized by the pattern recognition technique of k-means.

The results obtained can help us understand the failure process of FDM printed parts. This will provide an available monitoring method in the application of FDM-fabricated parts.

This paper has investigated and characterized the failure modes of FDM fabricated parts for the first time.

The main cause of aseptic inflammation after an in vivo implantation is that Poly(L-lactide) (PLLA) and Poly(D-lactide) have a slower degradation and absorption rate, while Poly(D, L-lactide) (PDLLA) has a much faster degradation rate than PLLA because of its amorphous structure. Also, the hydrolyzate of Hydroxyapatite (HA) is alkaline, which can neutralize local tissue peracid caused by hydrolysis of Polylactic acid.

In this study, the selective laser sintering (SLS) technique was chosen to prepare bone scaffolds using nano-HA/PDLLA composite microspheres, which were prepared by the solid-in-oil-in-water (S/O/W) method. First, the SLS parameters range of bulk was determined by the result of a single-layer experiment and the optimized parameters were then obtained by the orthogonal experiment. The tensile property, hydrophobicity, biocompatibility, biological toxicity and in vitro degradation of the samples with optimized SLS parameters were characterized.

As a result, the samples showed a lower tensile strength because of the many holes in their interior, which was conducive to better cell adhesion and nutrient transport. In addition, the samples retained their inherent properties after SLS and the hydrophobicity was improved after adding nano-HA because of the OH group. Furthermore, the samples showed good biocompatibility with the large number of cells adhering to the material through pseudopods and there was no significant difference between the pure PDLLA and 10% HA/PDLLA in terms of biological toxicity. Finally, the degradation rate of the composites could be tailored by the amount of nano-HA.

This study combined the S/O/W and SLS technique and provides a theoretical future basis for the preparation of drug-loaded microsphere scaffolds through SLS using HA/PDLLA composites.

The purpose of this paper is to find homoclinic breather waves, rogue waves and soliton waves for a (3 + 1)-dimensional generalized Kadomtsev–Petviashvili (gKP) equation, which can be used to describe the propagation of weakly nonlinear dispersive long waves on the surface of a fluid.

The authors apply the extended Bell polynomial approach, Hirota’s bilinear method and the homoclinic test technique to find the rogue waves, homoclinic breather waves and soliton waves of the (3 + 1)-dimensional gKP equation.

The results imply that the gKP equation admits rogue waves, homoclinic breather waves and soliton waves. Moreover, the authors also find that rogue waves can come from the extreme behavior of the breather solitary wave. The authors analyze the propagation and interaction properties of these solutions to better understand the dynamic behavior of these solutions.

These results may help us to further study the local structure and the interaction of waves in KP-type equations. It is hoped that the results can help enrich the dynamic behavior of such equations.

The purpose of this paper is to assess the importance of group position and consciousness in predicting people’s perceptions of police fairness in China.

This study used survey data collected from 1,095 respondents in Shanghai. Multivariate regression was used to analyze the effects of group positions and group consciousness variables on perceived police fairness, controlling for personal, experiential and neighborhood factors.

Regardless of their own hukou status, individuals who live in high migrant areas expressed less favorable attitudes toward police fairness. Meanwhile, people who displayed greater degrees of sensitivity to bias in law rated police fairness less favorably, whereas people who expressed higher levels of moral alignment with the law and belief in no choice but to obey the police rated police fairness more favorably. Lower levels of neighborhood disorder and higher degrees of cohesion were also associated with more positive evaluations of police fairness.

The authors’ measure of migrant concentration was constructed based on respondents’ own assessments of this neighborhood feature. Future studies should consider using objective measures to supplement the construction of migrant concentration variables. The authors’ group consciousness variables are limited as they are general, non-residential status specific and only capture part of the traditionally conceptualized variable of group consciousness. Future study should employ better-worded items that can tap precisely into people’s various dimensions of social consciousness based on their group status.

Training officers has to give a high priority to the principles of both procedural and distributive justice, and implement performance and evaluation policies that support fair and responsive police behavior, particularly during situations where citizens report crime to and seek help from the police.

Despite their high relevance, variables reflecting group position have received marginal attention in previous research on public evaluations of the police in China. This study represents a first attempt to examine how the interactions between residence status and the level of neighborhood migrant concentration influence Chinese attitudes toward police fairness.

Aero-engine components endure combined high and low cycle fatigue (CCF) loading during service, which has attracted more research attention in recent years. This study aims to construct a new framework for the prediction of probabilistic fatigue life and reliability evaluation of an aero-engine turbine shaft under CCF loading if considering the material uncertainty.

To study the CCF failure of the aero-engine turbine shaft, a CCF test is carried out. An improved damage accumulation model is first introduced to predict the CCF life and present high prediction accuracy in the CCF loading situation based on the test. Then, the probabilistic fatigue life of the turbine shaft is predicted based on the finite element analysis and Monte Carlo analysis, where the material uncertainty is taken into account. At last, the reliability evaluation of the turbine shaft is conducted by stress-strength interference models based on an improved damage accumulation model.

The results indicate that predictions agree well with the tested data. The improved damage accumulation model can accurately predict the CCF life because of interaction damage between low cycle fatigue loading and high cycle fatigue loading. As a result, a framework is available for accurate probabilistic fatigue life prediction and reliability evaluation.

The proposed framework and the presented testing in this study show high efficiency on probabilistic CCF fatigue life prediction and can provide technical support for fatigue optimization of the turbine shaft.

The novelty of this work is that CCF loading and material uncertainty are considered in probabilistic fatigue life prediction.

The purpose of this paper is to systematically investigate the dynamic strain aging (DSA) effect in solid solution treated IN718 at different temperatures through experiments and simulations to gain an understanding of the inelastic deformation mechanisms.

In the present work, uniaxial tensile tests have been carried out in conjunction with finite element (FE) simulations to investigate the behaviour of the solid solution treated Inconel 718 superalloy at different temperatures and strain rates. Dynamic strain aging (DSA) effects, which manifested during the tests in the form of a negative strain rate sensitivity and stress serrations, are investigated. The most significant DSA effect occurs at 500°C and at a strain rate of 10–4 s-1. In a newly proposed rate-dependent constitutive formulation, the DSA model, proposed by McCormick, Kubin and Estrin, was introduced into slip-assisted solute hardening, and an activation energy-dependent exponential flow rule was adopted.

The observed negative strain rate sensitivity and stress serrations are well predicted by a 3 D FE. The FE results indicate that the equivalent plastic strain rate distribution in the specimen gauge length is as highly inhomogeneous as in the other materials exhibiting DSA effects such as aluminium and titanium alloy. During inelastic deformation, propagating high strain rate bands can be closely correlated to the stress serrations.

For the DSA effect in solid solution treated IN718, the existing researching mainly focuses on the mechanical properties experiment and microstructure observation. In this study, a constitutive formulation, combined with the DSA model, has been proposed, and the mechanical behaviors, including the DSA effect, have been well predicted by a finite element model.