Application of Principle of Work and Energy in Its Differential Form to MDOF Systems

This paper is intended to reveal some new aspects of the principle of work and energy in its differential form. A theorem is given to state the principle of work and energy in differential form that can be applied alone to build up all the dynamical equations of a special class of MDOF mechanical systems. Some illustrations and discussions are presented to demonstrate the refined applicability of the principle of work and energy in its differential form through the comparison  with the Lagrange equation method

Fatigue test setups and analysis methods for asphalt mixture: A state-of-the-art review

Summary: Fatigue performance evaluation on asphalt mixture provides an essential reference for asphalt mixture design and pavement structure design. Laboratory fatigue test has been widely used by researchers and engineers to assess the fatigue performance of asphalt mixture, due to its low cost, high efficiency, and strong operability. To ensure performance assessment reliability, fatigue test operated in the laboratory needs to simulate the loading and environmental conditions occurring in the field asphalt layer. As a result, loading setups in laboratory fatigue tests, including loading mode, loading frequency, loading waveform, temperature, and the controlled mode, have been carefully devised by researchers. This paper reviews the above common setups in fatigue tests, which aims to illustrate the classical and latest considerations as well as ideas proposed by researchers for improving fatigue test procedures. As fatigue response data of asphalt mixture is measured from fatigue test, an analysis method is required to process the data and identify fatigue behaviors of the material. Presently, the frequently-used fatigue data analysis methods include the fatigue life model, stiffness-modulus-based method, energy-based method, and viscoelastic continuum damage (VECD) method. This paper also provides a review survey on the main concepts, indicators, and models included in those methods to facilitate their applications. Meanwhile, the latest research progress and outputs related to the four methods are also introduced and discussed to reveal the state-of-the-art developments in this research area

Simultaneous Determination of Six Active Components in Oviductus Ranae via Quantitative Analysis of Multicomponents by Single Marker

A method, quantitative analysis of multicomponents by single marker (QAMS), was established in this article to investigate the quality control of a traditional Chinese medicine, Oviductus Ranae. 7-Hydroxycholesterol, 7-ketocholesterol, 4-cholesten-3-one, stigmasterol, 7-dehydrocholesterol, and cholesterol were selected as the indexes of quality evaluation of Oviductus Rana. The determination was achieved on an Agilent HC-C18 column (4.6 mm × 250 mm, 5 μm) using methanol with water (87 : 13 v/v) as mobile phase at the flow rate of 2.0 mL/min. Cholesterol was used as an internal standard to determine the relative correction factors between cholesterol and other steroidal constituents in Oviductus Ranae. The contents of those steroidal constituents were calculated at the same time. To evaluate the QAMS method, an external standard method was used to determine the contents of six steroidal constituents. No significant difference was observed when comparing the quantitative results of QAMS with the results of external standard method. The proposed QAMS method was proved to be accurate and feasible based on methodological experiments. QAMS provided a simple, efficient, economical, and accurate way to control the quality of Oviductus Ranae

Fracture Propagation Modes of Lower Cambrian Shale Filled with Different Quartz Contents under Seepage-Stress Coupling

The content and spatial distribution of brittle minerals, such as quartz, are important factors in determining the fracture initiation mechanism induced by hydraulic fracturing in shale reservoirs. To further research the impact of quartz content in shales of the Lower Cambrian Niutitang Formation in northern Guizhou on the fracture expansion of its reservoir, 7 groups of randomly filling shale models with different quartz contents were established using rock failure process analysis (RFPA2D-flow) code for numerical test studies under seepage-stress coupling, and 5 samples were also subjected to uniaxial compression tests using the INSTRON 1346 electrohydraulic servo-controlled material testing machine (200T). The results show that the average growth rate of the compressive strength and the fracture proportion for a quartz content of 50% to 65% are 4.22 and 1.15 times higher than those for 35% to 50%, respectively. Fractures sprout, expand, and breakdown in the shale matrix or at the junctions of the shale matrix and quartz grains. The mechanical properties and pattern of the fracture extension of the shale in the physical tests are similar to those in the numerical tests, indicating the reliability of the numerical simulations. The fractal dimension curves at different stress levels are divided into three stages: flattening, increasing, and surging, and the fractal dimension value for a quartz content of 50%~65% at a 100% stress level is 1.02 times higher than that for 35%~50%. The high degree of natural fracture development in high quartz content formations in shale gas reservoirs is of some reference value for logging data. The research results provide a reference value for the content and spatial distribution of brittle minerals for the initiation mechanism and fracture propagation of hydraulic fracturing in shale reservoirs

Numerical study of hydraulic fracturing on single-hole shale under fluid–solid coupling

Abstract To investigate the hydraulic fracture extension pattern of single-hole shale during hydraulic fracturing under fluid–solid coupling, this paper utilizes seepage–stress–damage coupling software to establish a mechanical model of hydraulic fracture initiation in single-hole shale under different pore pressure increments in seven groups. The results reveal that under the action of a single-hole pressure gradient, shale is destabilized and destroyed by shale instability after two damage degradations under the coupled action of hydraulic and peripheral pressures, the fracture network is fully developed, and the stress decreases sharply. The final damage pattern of the hydraulic fracture distribution is categorized into two types: “X” and “Y”. The hydraulic gradient under hydraulic fracturing is distributed as a closed-loop strip, the hydraulic gradient decreases layer by layer from the inside to the outside, the seepage field and stress field interact with each other, and the pore water pressure and stress are coupled with each other, resulting in increasingly complete fracture development

Unraveling the roles of CD44/CD24 and ALDH1 as cancer stem cell markers in tumorigenesis and metastasis

Abstract CD44/CD24 and ALDH1 are widely used cancer stem cell (CSC) markers in breast cancer. However, their expression is not always consistent even in the same subtype of breast cancer. Systematic comparison of their functions is still lacking. We investigated the expression of CD44, CD24 and ALDH1 in different subtypes of breast cancer cells, and explored their relationship with cancer progression. We defined a parameter CD44/CD24 ratio to present the expression level of CD44 and CD24 and found that high CD44/CD24 ratio and ALDH1+ are both indicators for cancer malignancy, but play different functions during tumor progression. High CD44/CD24 ratio is more related to cell proliferation and tumorigenesis, which is confirmed by mammosphere formation and tumorigenesis in xenotransplanted mice. ALDH1+ is a stronger indicator for cell migration and tumor metastasis. Suppression of CD44 and ALDH1 by siRNA led to decreased tumorigenicity and cell migration capacity. The combination of high CD44/CD24 ratio and ALDH1+ would be a more reliable way to characterize CSCs. Moreover, both high CD44/CD24 ratio and ALDH1+ were conserved during metastasis, from the primary tumors to the circulating tumor cells (CTCs) and the distant metastases, suggesting the significant value of these CSC markers in assisting cancer detection, prognostic evaluation, and even cancer therapeutics