RESUMO
Pre-stressed bolted joints are widely used in civil structures and industries. The tightening force of a bolt is crucial to the reliability of the joint connection. Loosening or over-tightening of a bolt may lead to connectors slipping or bolt strength failure, which are both harmful to the main structure. In most practical cases it is extremely difficult, even impossible, to install the bolts to ensure there is a precise tension force during the construction phase. Furthermore, it is inevitable that the bolts will loosen due to long-term usage under high stress. The identification of bolt tension is therefore of great significance for monitoring the health of existing structures. This paper reviews state-of-the-art research on bolt tightening force measurement and loosening detection, including fundamental theories, algorithms, experimental set-ups, and practical applications. In general, methods based on the acoustoelastic principle are capable of calculating the value of bolt axial stress if both the time of incident wave and reflected wave can be clearly recognized. The relevant commercial instrument has been developed and its algorithm will be briefly introduced. Methods based on contact dynamic phenomena such as wave energy attenuation, high-order harmonics, sidebands, and impedance, are able to correlate interface stiffness and the clamping force of bolted joints with respective dynamic indicators. Therefore, they are able to detect or quantify bolt tightness. The related technologies will be reviewed in detail. Potential challenges and research trends will also be discussed.
RESUMO
Long non-coding RNAs (lncRNAs), which represent a novel group of non-protein-coding RNAs and are commonly defined as RNA molecules larger than 200 nucleotides in length, have been shown to get involved in diverse biological processes, such as cell growth, apoptosis, migration and invasion. In addition, aberrant expression of lncRNAs has been discovered in human tumors, where they function as either oncogenes or tumor suppressor genes. Recently tumorigenic effects of one specific lncRNA, termed as 'HOXA transcript at the distal tip' (HOTTIP), on the initiation and progression of human cancer has been widely reported. An increasing amount of data has shown that dysregulation of HOTTIP is associated with various malignancies including hepatocellular carcinoma, pancreatic cancer, gastric cancer and colorectal cancer, and affects the survival and prognosis of cancer patients. Here, we focus on the current knowledge of HOTTIP in various cancers and illustrate the corresponding mechanism and biological function of HOTTIP during tumor development.
