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• The equivalent method from bolted connections to spectral problem is presented. • The integrable system equivalent to a bolted connection is established. • A novel mathematical model is proposed for evaluating bolt preload. • The proposed model considers the geometric and physical parameters. • The preload is especially sensitive to the geometric parameters of connected parts. Accurate evaluation of preload in system with double-bolted connections is critical for the service performance of engineering structures or equipment. However, the theoretical framework for assessing preload is imperfect. An equivalent approach from the tightening process of double-bolted joints to second-order spectral problem of the energy-dependent potential is firstly established. This paper proposes a novel nonlinear model of bolt preload considering physical and geometric parameters by proving the completely integrability of systems used bolted connections. The experimental device for hmeasuring displacement and bolt preload was developed to verify the accuracy of proposed model. Results show that the maximum relative error is not more than 3%. Finally, the influences of elastic modulus, density, holes spacing, and height on preload are analyzed. [ABSTRACT FROM AUTHOR]

The clamping force relaxation of bolted joints caused by contact creep at ambient temperature has a significant impact on the service performance of offshore structures, which may increase their vulnerability to additional non-typical loads. Maxwell and Kelvin architectures are introduced to analyze the creep displacement of rough surfaces in contact. Subsequently, a theoretical model is established to characterize the functional relationship between contact creep and clamping force relaxation. The model parameters are obtained from a compression creep experiment. An experimental device is developed to validate the proposed model. The experimental results show a good agreement with theoretical calculations. In addition, the influences of bolt preload and surface topography on the clamping force relaxation are investigated quantitatively, and find that the clamping force relaxation is proportional to the surface roughness. Thus, controlling surface topography and bolt preload could be an effective way to improve performance of bolted joints for steel structures. • Contact creep displacement at ambient-temperature creep is analyzed. • The functional relationship between creep and relaxation is characterized. • A novel experimental method is proposed to obtain the model parameters. • The clamping force relaxation decreases with the increase of surface roughness. [ABSTRACT FROM AUTHOR]

Preload relaxation, caused by elastic interaction between tightened bolts, is one of the major reasons for non-uniformity of pretension force. But how to accurately assess the residual tension of a bolt is still extremely difficult. This paper considers two types of multiple bolted joint and six kinds of tightening sequence. Based on the deformation compatibility equation and elastic interaction stiffness, the generalized mathematical model for evaluating residual preload of bolts is established. Certain model parameters are obtained through numerical simulation. To analyze the influence of initial tightening torque, spacing between bolt holes, bolt material and gasket material on the elastic interaction stiffness, experimental devices and test procedures are developed. Furtherly, preload relaxation models are validated by tests conducted on six types of multi-bolted joint with the same surface roughness. Results of the proposed mathematical model of pretension force show a good consistency with those of corresponding experiment. • A mathematical model for estimating preload relaxation of bolted joint subjected to elastic interaction was established. • The elastic interaction stiffness between bolts was analyzed based on developed Experimental devices and test procedures. • The proposed mathematical model of pretension force shows a good consistency with the corresponding experiment. [ABSTRACT FROM AUTHOR]

MiR-34a has been reported as a non-coding RNA universally expressed in normal old cells and a probable suppressor of diverse cancer cells; however, this miRNA's expression and anti-tumor mechanism in esophageal squamous cancer cells (ESCC) remains unclear. We explored these questions in three human ESCC lines, KYSE-450, KYSE-410, and ECa-109, with wild-type p53 and mutant p53 backgrounds. Through a specific stem-loop RT primer for miR-34a, we examined the relevant expression level of miR-34a in these three cell lines using real-time reverse transcription PCR (qRT-PCR). We found that the expression level of miR-34a induced by the DNA damage agent adrmycin (ADR) was both p53- and time-dependent. Following incubation with miR-34a, cellular growth inhibition was exhibited differently in the three cell lines harbored with different p53 backgrounds. Furthermore, the MTT assay demonstrated an miR-34a-related cytotoxic effect in cell growth. Senescence-associated β-galactosidase (SA-β-Gal) staining was used to examine senescence-like phenotypes induced by miR-34a. Mechanistic investigation suggested that the down-regulation of Sirtuin1 (SIRT1) and up-regulation of p53/p21 contributed to the anti-tumor mechanism of miR-34a in wild-type p53 ECa-109 cells, while neither of the apoptosis-related proteins PARP and caspase-3 caused significant changes. In summary, our findings indicated that the intrinsic expression of miR-34a was relatively low and was expressed differently among different p53 backgrounds and ADR treatment times. The anti-tumor effect of miR-34a was primarily dependent on the regulation of SIRT1 and p53/p21 protein, not apoptosis-associated proteins. [ABSTRACT FROM AUTHOR]

• Based on simulation, a new method for analyzing self-loosening of bolts is proposed. • The simulation with helix angle thread is adopted to improve the analysis accuracy. • The self-loosening behavior of bolt can be caused by elastic slip. • Elastic-plastic deformation is the main factor of bolt self-loosening behavior. • Tightening torque and friction coefficient also affect the self-loosening behavior. The self-loosening of high strength bolt caused by vibration has been widely studied. However, the short-term self-loosening behavior of the high strength bolt when it is not subject to an external load has not received attention. This behavior will also lead the bolt preload to attenuate. Since the theoretical analysis of self-loosening behavior is difficult, this paper uses the finite element method to construct an accurate three-dimensions model with thread lift angle for numerical analysis. A new method is proposed to analyze the self-loosening behavior. The self-loosening behavior caused by the elasticity and plasticity of the bolted joint at different deformation periods is compared and analyzed. Besides, the evolution of the self-loosening behavior under different conditions is explored. The analysis results show that the torsional deformation of the thread leads to the relative slip of the internal and external threads. This results in the self-loosening of the thread in the elastic condition. In the elastic–plastic deformation condition, the self-loosening behavior is caused by the relative slip of the internal and external threads and plastic deformation. The weight of plastic deformation is greater. In addition, this behavior has the characteristics of increasing with increased tightening torque and decreasing with increased friction coefficient. [ABSTRACT FROM AUTHOR]