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The purpose of this study is to solve the issues of time-consuming and complicated computation of traditional measures, as well as the underutilization of two-dimensional (2D) phase-trajectory projection matrix, so a new set of features were proposed based on the projection of attractors trajectory to characterize the friction-induced attractors and to reveal the tribological behavior during the running-in process.

The frictional running-in experiments were conducted by sliding a ball against a static disk, and the friction coefficient was collected to reconstruct the friction-induced attractors. The projection of the attractors in 2D subspace was then mapped and the distribution of phase points was adapted to conduct the feature extraction.

The evolution of the proposed moment measures could be described as “initial rapid decrease/increase- midterm gradual decrease/increase- finally stable,” which could effectively reveal the convergence degree of the friction-induced attractors. Moreover, the measures could also describe the relative position of the attractors in phase–space domain, which reveal the amplitude evolution of signals to some extent.

The proposed measures could reveal the evolution of tribological behaviors during the running-in process and meet the more precise real-time running-in status identification.

The purpose of this study is to investigate the applicability of volume average which is extensively used for analyzing the heat and fluid flow (both for single-phase and solid/liquid-phase change) in a closed cell porous medium numerically.

Heat conduction equations for the solid frame and fluid (or phase change material) are solved for pore scale and volume average approaches. The study mainly focuses on the effect of porosity and the number of porous media unit cell on the agreement between the results of the pore scale and volume average approaches.

It is observed for the lowest porosity values such as 0.3 and the number of porous media unit cell as 4 in heat transfer direction, the results between two approaches may be questionable for the single-phase fluid. By increasing the number of porous media unit cell in heat transfer direction, the agreement between two approaches becomes better. In general, for high porosity values (such as 0.9) the agreement between the results of two approaches is in the acceptable range both for single-phase and solid/liquid-phase change. Two charts on the applicability of volume average method for single-phase and solid/liquid-phase change are presented.

The authors’ literature survey shows that it is the first time the applicability of volume average which is extensively used for analyzing the heat and fluid flow in a closed cell porous medium is investigated numerically.

The purpose of this study is to analyze heat transfer for solid–liquid phase change in two inclined cavities assisted with open cell and closed cell porous structures for enhancement of heat transfer and compare them.

The heat transfer analysis is done numerically. The set of conservation equations for mass, momentum and energy for phase change material (PCM) and conduction heat transfer equation for metal frame are solved. Furthermore, temperature and solid–liquid fraction distributions for a cavity filled only with PCM are also obtained for comparison. The porosity is 0.9 for both porous structures. Rayleigh number and inclination angle change from 1 to 10⁸, and from −90° to 90°, respectively.

The present study reveals that the use of closed cell structures not only can make phase change faster than open cell structure (except for Ra = 10⁸ and = 90°) but also provide more stable process. The use of a closed cell porous structure in a cavity with PCM can reduce melting period up to 55% more than a cavity with an open cell porous structure. The rate of this additional enhancement depends on Rayleigh number and inclination angle.

To the best of the authors’ knowledge, this is the first time that the comparison between closed cell and open cell porous structures for heat transfer enhancement in a solid/liquid phase change process is reported. Authors believe that the present study will lead more attentions on the use of closed cell porous structures.

The purpose of this paper is to study the adaptability of the tracked robot in complex working environment. It proposes an angle-changeable tracked robot with human–robot interaction in unstructured environment. The study aims to present the mechanical structure and human–robot interaction control system of the tracked robot and analyze the static stability of the robot working in three terrains, i.e. rugged terrain, sloped terrain and stairs.

The paper presents the mechanical structure and human–robot interaction control system of the tracked robot. To prevent the detachment of the tracks during obstacle navigation, a new type of passively adaptive device based on the relationship between the track’s variable angle and the forces is presented. Then three types of rough terrain are chosen to analyze the static stability of the tracked robot, i.e. rugged terrain, sloped terrain and stairs.

This paper provides the design method of the tracked robot. Owing to its appropriate dimensions, good mass distribution and limited velocity, the tracked robot remains stable on the complex terrains. The experimental results verify the effectiveness of the design method.

The theoretical analysis of this paper provides basic reference for the structural design of tracked robots.

We compare environmental impacts associated with incoming foreign direct investment versus domestic capital in China. We use aggregate data on Chinese provinces’ economic and pollution indicators to explore the effects of the financial origin of fixed capital. Our simultaneous models consider three prime channels through which these effects work: economic scale, sectoral composition, and pollution intensity. Results show that emissions associated with foreign financed capital are lower than with domestically financed capital for some but not all of the considered types of pollution.

The purpose of this paper is to study the influence of the cage dynamic unbalance on the dynamic performances in cylindrical roller bearings.

The dynamic analysis model which considering cage dynamic unbalance is presented, and the relationship between the cage dynamic unbalance and the cage stability, the cage slip ratio and the cage skew angle is investigated.

Cage dynamic unbalance has a great effect on the cage stability. The cage dynamic unbalance which in an axial excursion affects the cage characteristics is greater than that only in the radial direction. The cage slip ratio and the cage skew increases with the cage dynamic unbalance, especially with the axial excursion. The non-metal cage is more sensitive to the cage dynamic unbalance than that of the metal cage.

The analytical method and model can be applied by the bearing engineering designers.

This paper aims to provide a theoretical principle for the stability control of robot climbing stairs, autonomously based on human–robot interaction. Through this research, tracked mobile robots with human-robot interaction will be extensively used in rescue in disaster, exploration on planetary, fighting in battle, and searching for survivors in collapsed buildings.

This paper introduces the tracked mobile robot, based on human–robot interaction, and its six moving postures. The dynamic process of climbing stairs is analyzed, and the dynamic model of the robot is proposed. The dynamic stability criterion is derived when the tracked mobile robot contacts the stairs steps in one, two and more points. A further conduction of simulation on the relationship of the traction force and bearing force vs the velocity and acceleration in the three cases was carried out.

This paper explains that the tracked mobile robot, based on human–robot interaction, can stably climb stairs so long as the velocity and acceleration satisfy the dynamic stability criterion as noted above. In addition, the experiment tests the correctness of dynamic stability analysis when the tracked mobile robot contacts the stair steps in one, two or more points.

This paper provides the mechanical structure and working principle of the tracked mobile robot based on human–robot interaction and proposes an identification method of dynamic stability criterion when the robot contacts the stairs steps in one, two and more points.

According to the crusade of the United Nations sustainable development goals (SDGs-6, 7,8,12 and 13) that addressed pertinent issues around, clean access to water, access to energy, responsible consumption and climate change mitigation alongside, respectively, Paris Kyoto Protocol agreement of mitigation of climate changes issues of vision 2030.

This purpose of this study aimed to assess the Environmental Kuznets Curve hypothesis following the ecological footprint perspective with a data set covering the period 1995–2018. It is well-established that anthropogenic human activities are the root cause of environmental deterioration. To this end, the current study is fitted in a multivariate framework to ameliorate for omitted variable bias for the data set from 1995–2018 on a quarterly frequency using autoregressive distributive lag methodology. Subsequently, the stationarity status of the study underlines series were examined with a conventional unit root test and the Pesaran’s bounds test for cointegration analysis.

Empirical evidence from the bounds test to cointegration traces the co-integration relationship between ecological footprint, conventional energy use, foreign direct investment, international tourism arrival and water resources over the sampled period. The study, in the long run, affirms the N-shaped relationship between ecological footprint and foreign direct investment in Vietnam. Additionally, the present study validates the hypothesis of energy consumption-induced pollution emissions. The relationship between international tourism arrival and quality of the environment is statistically positive in both the short-run and long-run, as 1% in international tourism arrival worsens the quality of the environment by 0.45% and 0.4% in the short-run and long-run, respectively. Interestingly, water resource's major environmental issues that have plagued the Vietnam economy are inversely related to ecological footprint. Based on findings, Vietnamese policymakers may need to consider drafting appropriate environmental policies to tackle global warming while concurrently boosting economic development.

The present study focuses on Vietnam on the determinant of environmental quality measured by a broader indicator (ecological footprint). It is well-established that anthropogenic human activities are the root cause of environmental deterioration. The present study claims to distinct from previous literature in two-folds, namely, in terms of scope. Vietnam holds a very interesting energy mix and environmental dynamics, which has been ignored in the literature. Second, we argue to be the first based on our survey to explore the theme by incorporation of water resources and foreign direct investment intensification in the conventional pollution determinant model. This is in a bid to highlights the policy blueprint for the country (Vietnam), which is currently plagued with high pollution issues and the region at large.

The purpose of this paper is to bring into the public domain converging ways of thinking about reality and human systems, exploring parallels between the theory of Physical Vacuum and the concept of Qi in Medical Qigong science.

The approach adopted in this paper includes: review of the relevant literature; dialogues between the first two authors over an eight-month period; review of the findings and discussion of interpretations by all.

There is evidence for the existence of an ideal information field. This field is a real space-time torsion structure. Qi is a torsion field. It spreads with superluminal velocity and connects the whole Universe. Any entity is in a constant dynamic connection with everything else in the Universe.

This paper offers limited discussion of the wider area of scientific discoveries.

The findings may impact future interdisciplinary research, health/well-being practices and public policy.

There is no known to us publication interpreting the parallels between the theory of the Physical Vacuum and the concept of Qi.