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Component positioning is an important part of aircraft assembly, aiming at the problem that it is difficult to accurately fall into the corresponding ball socket for the ball head connected with aircraft component. This study aims to propose a ball head adaptive positioning method based on impedance control.

First, a target impedance model for ball head positioning is constructed, and a reference positioning trajectory is generated online based on the contact force between the ball head and the ball socket. Second, the target impedance parameters were optimized based on the artificial fish swarm algorithm. Third, to improve the robustness of the impedance controller in unknown environments, a controller is designed based on model reference adaptive control (MRAC) theory and an adaptive impedance control model is built in the Simulink environment. Finally, a series of ball head positioning experiments are carried out.

During the positioning of the ball head, the contact force between the ball head and the ball socket is maintained at a low level. After the positioning, the horizontal contact force between the ball head and the socket is less than 2 N. When the position of the contact environment has the same change during ball head positioning, the contact force between the ball head and the ball socket under standard impedance control will increase to 44 N, while the contact force of the ball head and the ball socket under adaptive impedance control will only increase to 19 N.

In this paper, impedance control is used to decouple the force-position relationship of the ball head during positioning, which makes the entire process of ball head positioning complete under low stress conditions. At the same time, by constructing an adaptive impedance controller based on MRAC, the robustness of the positioning system under changes in the contact environment position is greatly improved.

This paper aims to study almost Ricci–Yamabe soliton in the context of certain contact metric manifolds.

The paper is designed as follows: In Section 3, a complete contact metric manifold with the Reeb vector field ξ as an eigenvector of the Ricci operator admitting almost Ricci–Yamabe soliton is considered. In Section 4, a complete K-contact manifold admits gradient Ricci–Yamabe soliton is studied. Then in Section 5, gradient almost Ricci–Yamabe soliton in non-Sasakian (k, μ)-contact metric manifold is assumed. Moreover, the obtained result is verified by constructing an example.

We prove that if the metric g admits an almost (α, β)-Ricci–Yamabe soliton with α ≠ 0 and potential vector field collinear with the Reeb vector field ξ on a complete contact metric manifold with the Reeb vector field ξ as an eigenvector of the Ricci operator, then the manifold is compact Einstein Sasakian and the potential vector field is a constant multiple of the Reeb vector field ξ. For the case of complete K-contact, we found that it is isometric to unit sphere S²ⁿ⁺¹ and in the case of (k, μ)-contact metric manifold, it is flat in three-dimension and locally isometric to Eⁿ⁺¹ × Sⁿ(4) in higher dimension.

All results are novel and generalizations of previously obtained results.

Fix-position preloading, centrifugal force and higher temperatures cause the bearing units in angular contact ball bearings to expand, changing the contact load and affecting bearing life. This study aims to examine the effect of thermal and centrifugal expansion on the fatigue life of fix-position preloaded angular contact ball bearings in high-speed operating conditions.

The contact loads on the inner and outer bearing rings were resolved according to the thermal and centrifugal expansion factors in the quasi-static position preloading model. The pressure and frictional stress distribution were used to calculate the subsurface stress in the contact area, while the Zaretsky model was used to determine the relative fatigue life of the inner and outer bearing rings.

Under fix-position bearing preloading, thermal and centrifugal expansion significantly affected the contact load and relative fatigue life. At the same axial preload, the inner ring contact load was higher than the outer ring contact load, with a maximum difference of 132.3%. The decrease in the inner ring relative life exceeded the outer ring contact load, with a maximum difference of 7.5%, compared to the absence of thermal and centrifugal expansion.

This study revealed the influence of thermal and centrifugal expansion on the fatigue life of angular contact ball bearings in high-speed service conditions.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2023-0065/

The purpose of this paper is to propose a fractal model of thermal contact conductance (TCC) of rough surfaces based on cone asperity.

A detailed numerical study is conducted to examine the effects of contact load, fractal dimensional, fractal roughness and material properties on the TCC of rough surfaces.

The results indicate that when the fractal dimension D is less than 2.5, the TCC of rough surfaces increases nonlinearly with the increase of the contact load. However, when the fractal dimension D is greater than or equal to 2.5, the TCC of rough surfaces increases linearly with the increase of the contact load; the TCC of the rough surfaces increases with the increase of the fractal dimension D and the decrease of the fractal roughness G; the material parameters also have an influence on the TCC of the rough surfaces, and the extent of the effect on the TCC is related to the fractal dimension D.

A fractal model of TCC of rough surfaces based on cone asperity is established in this paper. Some new results and conclusions are obtained from this work, which provides important theoretical guidance for further study of TCC of rough surfaces.

For contemporary American young adults (aged 18–29), coresidence with parents is now the most common living arrangement. Recent research on residential transitions out of and back into the parental home shows that residential independence is still common, meaning that many young adults coreside with parents after first leaving the nest. The timing of residential independence and subsequent coresidence is often tied to other life-course outcomes, such as relationships and employment, as well as characteristics of the family context, such as family structure and financial resources. A small body of research also demonstrates that residential transitions are common following criminal justice contact experiences such as arrests and periods of incarceration. While this association does not appear to be explained by the family context, the current study argues there are several reasons to anticipate heterogeneity in coresidence patterns based on the childhood family context. Drawing on data from the 1997 cohort of the National Longitudinal Survey of Youth, I find that criminal justice contact is associated with coresidence with parents during young adulthood in a fairly consistent manner across different dimensions of family context (although parental education may play a role). These findings demonstrate the power of the criminal justice system in directing or redirecting residential trajectories and have implications for both individuals with contact and their families.

Contact problems are central to solid mechanics as contact is the principal method of applying loads to a deformable body and the point with resulting stress concentration is often the most critical point within the body. This paper presents a finite element model for the elastic contact between two cylinders at several positions. The effects of friction and surface roughness have been considered. The contact between two skew cylinders is also investigated. Results from finite element model show a good agreement with those of analytical solutions available in the literature. It was seen that the geometry of contacting bodies and orientation of applied load effect highly on contact stresses. Although the effect of surface roughness was seen to be more than that of friction, both of them can be assumed negligible in elastic contact problems.

The purpose of this paper is to reveal the dynamic contact characteristics of the slip ring. Dynamic contact resistance models considering wear and self-excited were established based on fractal theory.

The effects of tangential velocity, stiffness and damping coefficient on dynamic contact resistance are studied. The relationships between fractal parameters, wear time and contact parameters are revealed.

The results show that the total contact area decreases with the friction coefficient and fractal roughness under the same load. Self-excited vibration occurs at a low speed (less than 0.6 m/s). It transforms from stick-slip motion at 0.4 m/s to pure sliding at 0.5 m/s. A high stiffness makes contact resistance fluctuate violently, while increasing the damping coefficient can suppress the self-excited vibration and reduce the dynamic contact resistance. The fractal contact resistance model considering wear is established based on the fractal parameters models. The validity of the model is verified by the wear tests.

The results have a great significance to study the electrical contact behavior of conductive slip ring.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-09-2023-0300/

Tribeca is a predominantly wealthy, white neighborhood in New York City and is a microcosm of the service-and-information-based economy that characterizes many communities in global cities today. Tribeca residents are mostly affluent and work in high-end, service-oriented professions, consuming low-end personal services produced locally. Many of the people who provide these personal services in Tribeca are foreign-born. This chapter explores the nature of intergroup contact between native residents and immigrant service workers to understand how they navigate social boundaries of race/ethnicity, nation-of-origin, occupation, and social class.

This chapter is based on six years of ethnographic data collection and participant observation, in addition to interviews with 66 informants, including both immigrant service workers and Tribeca residents.

This research highlights the importance of local contextual factors in shaping how people perceive one another and interact. Although in Tribeca this intergroup contact fails to alter boundaries of race, class, and nation-of-origin, residents and immigrants still have meaningful interpersonal contact, which is the result of bridging, or overlooking, existing social boundaries.

The results of this research challenge the assumption that relations between natives and immigrants in stratified settings are characterized by resentment or hostility. Instead, contextual factors in Tribeca shape intergroup perceptions and contact in a way that allows for positive interpersonal, albeit largely superficial, relationships to take root.

Formal and informal interactions in the political elite and between the political elite and other actors have attracted a great deal of research (Petersson, 1996; Munk Christiansen, Möller, & Togeby, 2001; Moore, Sobieraj, Whitt, Mayorova, & Beaulieu, 2002). However, such research has mainly been concerned with the contacts of leading politicians once they have already become part of the elite, not the role that contacts might have played in their recruitment.

Extant research suggests that salespeople can significantly impact consumers’ outcome perceptions. Examines the importance of initial contact with salespeople on consumers’ perceptions of value and the impact of salesperson service failure on perceptions of value among non‐purchasers. An exit survey of shoppers was conducted to realistically study these issues. Results show that outcome perceptions were significantly lower when either there was no contact with salespeople, or the consumer had to initiate the contact. The retailer that had the highest percentage of salesperson initiated contact, earned the highest perception ratings and also had the highest ratio of buyers to browsers. Furthermore, non‐purchasers that experienced service failures (slow service or offended by a salesperson) discounted not just the perception of that retail visit, but also overall value compared to other retailers. These results suggest that retailers must encourage their sales staff to initiate consumer contact.