Numerical investigation of squeeze film lubrication on bioinspired hexagonal patterned surface

Purpose This paper aims to investigate the squeeze film lubrication properties of hexagonal patterned surface inspired by the epidermis structure of tree frog’s toe pad and numerically explore the working mechanism of hexagonal micropillar during the acquisition process of high adhesive and friction for wet contacts. Design/methodology/approach A two-dimensional elastohydrodynamic numerical model is employed for the squeezing contacts. The pressure distribution, load carrying capacity and liquid flow rate of the squeeze film are obtained through a simultaneous solution of the two-dimensional Reynolds equation and elasticity deformation equations. Findings Higher pressure is found to be longitudinally distributed across individual hexagonal pillar, with pressure peak emerging at the center of hexagonal pillar. Expanding the area density and shrinking the channel depth or initial film thickness will improve the magnitude of squeezing pressure. Relatively lower pressure is generated inside interconnected channels, which reduces the load carrying capacity of the squeeze film. Meanwhile, the introduction of microchannel is revealed to downscale the total mass flow rate of squeezing contacts. Originality/value This paper provides a good proof for the working mechanism of surface microstructures during the acquisition process of high adhesive and friction for wet contacts.

Generalized Reliability Analysis of Mechanical Systems with Imperfect Maintenance

Generalized reliability models and failure rate models of mechanical systems are developed in this paper according to the system working mechanism, which take the design parameters as input. The models consider strength degradation and imperfect maintenance. Besides, the models take into account the failure correlation caused by homologous load effect and the maintenance correlation owing to group maintenance. Unlike traditional reliability models, the models do not rely on empirical assumptions when considering failure correlation and maintenance correlation and have clear physical meaning. Moreover, the correctness and effectiveness of the models are verified by Monte Carlo simulations. Finally, the influences of failure correlation and maintenance correlation on generalized reliability, the influences of failure correlation on maintenance correlation, and the influences of maintenance correlation on failure correlation are analyzed via numerical examples. The results show that failure correlation and maintenance correlation have great influences on generalized reliability, and the interaction between the two correlation shows obvious time-varying characteristics.

Molecular basis of transcriptional repression of anti-CRISPR by anti-CRISPR-associated 2

CRISPR–Cas systems are well known host defense mechanisms that are conserved in bacteria and archaea. To counteract CRISPR–Cas systems, phages and viruses have evolved to possess multiple anti-CRISPR (Acr) proteins that can inhibit the host CRISPR–Cas system via different strategies. The expression of acr genes is controlled by anti-CRISPR-associated (Aca) proteins that bind to an upstream promoter and regulate the expression of acr genes during transcription. Although the role of Aca as a transcriptional repressor has been demonstrated, the mechanism of action of Aca has not been determined. Here, the molecular mechanism underlying the Aca2-mediated transcriptional control of acr genes was elucidated by determining the crystal structure of Aca2 from Oceanimonas smirnovii at a high resolution of 1.92 Å. Aca2 forms a dimer in solution, and dimerization of Aca2 is critical for specific promoter binding. The promoter-binding strategy of dimeric Aca2 was also revealed by performing mutagenesis studies. The atomic structure of the Aca family shown in this study provides insights into the fine regulation of host defense and immune-escape mechanisms and also demonstrates the conserved working mechanism of the Aca family.

Analysis of Preload of Three-Stator Ultrasonic Motor

The pre-pressure device of the ultrasonic motor plays a vital role in the design of the entire motor structure, the contact state of the stator and rotor of the motor, dynamic properties of the stator, friction and wear characteristics of the rotor; even the mechanical behaviors of the entire electric machinery have a profound impact. Appropriate pre-pressure is conducive to the smooth operation of the ultrasonic motor, so that the output performance remains excellent, reducing wear and effectively extend the service life of the motor. Therefore, the research on pre-stress is of great significance, as it can better optimize the structure of the three-stator ultrasonic motor and lay the foundation for the stable operation of the motor. First, this paper introduces the construction of the motor as a whole and the pre-pressure device briefly described the working mechanism of the motor, and then introduces the influence of the pre-pressure on the stator and rotor contact models, the position of the constant velocity point, and the modal frequency. Finally, the motor output under different pre-pressures is discussed. The performance experiment has determined the optimal pre-pressure interval, which provides help for its subsequent optimization.

Concept and Development of an Accelerated Repeated Rolling Wheel Load Simulator (ARROWS) for Fatigue Performance Characterization of Asphalt Mixture

Fatigue performance is one of the most important properties that affect the service life of asphalt mixture. Many fatigue test methods have been developed to evaluate the fatigue performance in the lab. Although these methods have contributed a lot to the fatigue performance evaluation and the development of fatigue related theory and model, their limitations should not be ignored. This paper starts by characterizing the stress state in asphalt pavement under a rolling wheel load. After that, a literature survey focusing on the experimental methods for fatigue performance evaluation is conducted. The working mechanism, applications, benefits, and limitations of each method are summarized. The literature survey results reveal that most of the lab test methods primarily focus on the fatigue performance of asphalt mixture on a material level without considering the effects of pavement structure. In addition, the stress state in the lab samples and the loading speed differ from those of asphalt mixture under rolling wheel tire load. To address these limitations, this paper proposes the concept of an innovative lab fatigue test device named Accelerated Repeated Rolling Wheel Load Simulator (ARROWS). The motivation, concept, and working mechanism of the ARROWS are introduced later in this paper. The ARROWS, which is under construction, is expected to be a feasible and effective method to simulate the repeated roll wheel load in the laboratory.

The analysis of modern tools of positioning of the working mechanism road construction ma-chines on building

The task of positioning the working mechanisms CRM at this time is not enough. As a result of the analysis the purpose of research is set, namely: to increase of functioning efficiency mechanisms CRM with working environment using mathematical models and adaptation algorithm in a limited time decision. Such methods of analysis include fractal analysis, neural network method, fuzzy set method, geostatistical data analysis. The element base of positioning systems and benefits of implementation are substantiated. The use of a GPS intensifier makes it possible to predict the work of actuators CRM in real time. The result of the research is algorithm of positioning the working mechanisms CRM: determination of the location of the base CRM in a 3-dimensional coordinate system; filtering measurements; predicting the position of the working mechanism (the algorithm for choosing a solution for the state of the monitored object is based on both the probability of obtaining certain results and their usefulness). The originality lies in the fact that the using modern information and software tools allows to describe the trajectory in the coordinate system of the base machine in accordance with the point measurement, and describe the relationship between changed coordinates, which makes it possible to model and predict the workflow. Proposals for the use of software in positioning systems, which provides adaptive optimization and advantages of introduction of the newest technologies of intellectualization of work processes.

Design of heat exchanger for the production of synthesis silica

This study aims to analyze and develop a heat exchanger (HE) application for the manufacture of silica nanoparticles synthesis from agricultural waste. This shell and tube-type HE is designed simply, but it still refers to the existing design rules. The design of a shell and tube type HE with one pass shell and tube with turbulence flow. The specifications of the HE apparatus are 1.93 m in shell length, 0.203 m in shell diameter, 0.020 m in inner tube diameter, 0.022 m in outer tube diameter, and 0.016 m in thickness. The results showed an effectiveness value of 66.38% with an impurity factor of 0.01314. This informed that although the shell and tube-typed HE does not meet the requirements and standards for being set in industrial applications, it can be useful as a learning method regarding the design process, working mechanism, and analyzing the performance of the HE.

Design of heat exchanger for the production of zinc imidazole framework-8 (ZIF-8) particles

The design of a heat exchanger is very effective to reduce total production costs, compared to buying a ready-made exchanger. This study aims to design a heat exchanger with a manual calculation analysis method to get dimension calculations of the heat exchanger. Dimension calculation of heat exchanger aims to determine the quality of the heat exchanger based on the overall heat transfer coefficient and the dirt factor that occurs in the heat exchanger. The designed heat exchanger is a shell and tube type with 1 (one) pass shell and 2 (two) pass tubes using water as hot fluid and cold fluid. The fluid flow is assumed to be the opposite. The results show the effectiveness of the heat exchanger reaches more than 50%. The performance of the designed heat exchanger is relatively good but it still does not meet the minimum requirements of the established dirt factor. This research can be useful as a learning method regarding the design process, working mechanism, and heat exchanger performance.