Natural frequency sensitivity and influence analysis of TBM cutterhead system

TBM cutterhead works in complex working conditions, which endures the reverse impact forces of rock breakage, resulting in parts abnormal failure. Hence, the study of the system inherent characteristics is the basis for cutterhead dynamic design. Based on the established vibration model of a TBM split-cutterhead system, the modal method is used in the dynamic model and the natural frequency sensitivity expressions to system parameters are deduced. Then a cutterhead system of a water conservancy project in China is taking as an example, the natural frequency sensitivity with respect to the cutterhead support stiffness and mass parameters is obtained, and the influence of the two parameters on natural characteristics is analyzed. The results show that, the 10th-20th order natural frequencies are mainly affected by the cutterhead support stiffness and mass parameters, and the 9th-11th order frequencies are mainly influenced by cutterhead moment of inertia. Besides, with the change of stiffness and mass parameters, the cutterhead system natural frequency curves cut across each other and there are also many inflection points in the sensitivity curves, then the modal jumping occurs near these points. The parameter sensitive points were obtained from the results, which can provide reference for TBM cutterhead system parameters matching

Using Three-Dimensional Lorenz Scatter Plots to Detect Patients with Atrioventricular Node Double Path Caused by Interpolated Ventricular Premature Systoles: A Case Study

A series of related electrophysiology phenomena can be caused by the occurrence of interpolated ventricular premature contraction. In our recent three-dimensional Lorenz R-R scatter plot research, we found that atrioventricular node double path caused by interpolated ventricular premature contraction imprints a specific pattern on three-dimensional Lorenz plots generated from 24-hour Holter recordings. We found two independent subclusters separated from the interpolated premature beat precluster, the interpolated premature beat cluster, and the interpolated premature beat postcluster, respectively. Combined with use of the trajectory tracking function and the leap phenomenon, our results reveal the presence of the atrioventricular node double conduction path. </p

Dynamic Characteristics Study with Multidegree-of-Freedom Coupling in TBM Cutterhead System Based on Complex Factors

A multidegree-of-freedom coupling dynamic model, which contains a joint cutterhead, an inner ring gear, a support shield body, and pinions, is established, considering the external stochastic excitations, time-varying meshing stiffness, transmission errors, clearance, and so forth. Based on the parameters of an actual project and the strong impact of external excitations, the modal properties and dynamic responses are analyzed, and the cutterhead joint surface loads are obtained and treated by rain flow count. Numerical results indicate that the low natural frequencies are 57 Hz and 61 Hz, and natural vibration modes are pinions-motors rotational mode and translational-overturning coupled mode of cutterhead with inner ring gear correspondingly. Besides, the axial and radial amplitude of dynamic responses are 0.55 mm and 0.25 mm, respectively. The frequencies of radial, torsional, and overturning vibrations are predominantly concentrated in 112 Hz and 120 Hz, which indicates that the vibration responses of cutterhead are mainly affected by the external excitations. Finally, as the rain-flow counting results have shown, the standard deviation of the cutterhead joint surface loads in each direction increases by 12–15 times, compared with that of the external excitations; therefore inertia effect should be considered in cutterhead design. The proposed research lays a foundation for dynamic performance optimization and fatigue crack growth life assessment of cutterhead structure

Principal Component Analysis and Cluster Analysis for Evaluating Free Amino Acids in Crayfish (Procambarus clarkii) from Different Co-culture Modes

To investigate the difference in the comprehensive quality of free amino acids (FAA) in crayfish meat from different co-culture modes, the FAA composition of crayfish tail meat from three representative co-culture modes in Xinghua city of Jiangsu province was determined, and the contribution of FAA to the taste of crayfish meat was evaluated by computing the taste active value (TAV). Comprehensive evaluation of FAA in crayfish meat was performed using principal component analysis (PCA) and cluster analysis. The results showed that 17 amino acids were found in crayfish meat from each co-culture mode, and the total amount of FAA was 21.80–27.11 mg/g. Arginine (Arg) was the most abundant FAA in all samples, accounting for 55.64%–67.76% of the total FAA, which was much more abundant than the other amino acids. Moreover, Arg contributed the most to the taste of crayfish meat. The TAV of the sweet amino acid alanine (Ala) and the bitter amino acid histidine (His) in crayfish were greater than 1 for all co-culture modes, indicating that both amino acids contributed to the taste of crayfish meat. The TAV of glutamic acid (Glu) as the amino acid with the strongest umami taste was greater than 1 only in crayfish meat from rice-crayfish mode with one-rice and two-crayfish in a field (RC2). Three principal components were extracted for the 17 amino acids, which cumulatively explained 89.937% of the total variance and could reflect the comprehensive information of amino acids in crayfish meat. The results of PCA showed that RC2 ranked first, and crayfish-crab mode (CC1) ranked last. The hierarchical cluster analysis divided crayfish meat from different co-culture modes into three categories. Similar results were obtained by PCA. This study demonstrated that the comprehensive quality of FAA in crayfish from rice-crayfish co-culture mode was better than that in crayfish from the other co-culture modes

Solar Intranetwork Magnetic Elements: bipolar flux appearance

The current study aims to quantify characteristic features of bipolar flux appearance of solar intranetwork (IN) magnetic elements. To attack such a problem, we use the Narrow-band Filter Imager (NFI) magnetograms from the Solar Optical Telescope (SOT) on board \emph{Hinode}; these data are from quiet and an enhanced network areas. Cluster emergence of mixed polarities and IN ephemeral regions (ERs) are the most conspicuous forms of bipolar flux appearance within the network. Each of the clusters is characterized by a few well-developed ERs that are partially or fully co-aligned in magnetic axis orientation. On average, the sampled IN ERs have total maximum unsigned flux of several 10^{17} Mx, separation of 3-4 arcsec, and a lifetime of 10-15 minutes. The smallest IN ERs have a maximum unsigned flux of several 10^{16} Mx, separations less than 1 arcsec, and lifetimes as short as 5 minutes. Most IN ERs exhibit a rotation of their magnetic axis of more than 10 degrees during flux emergence. Peculiar flux appearance, e.g., bipole shrinkage followed by growth or the reverse, is not unusual. A few examples show repeated shrinkage-growth or growth-shrinkage, like magnetic floats in the dynamic photosphere. The observed bipolar behavior seems to carry rich information on magneto-convection in the sub-photospheric layer.Comment: 26 pages, 14 figure

An environmentally friendly method for efficient atmospheric oxidation of pyrrhotite in arsenopyrite/pyrite calcine

Pyrite and arsenopyrite are the most common hosts for invisible gold, but pyrite and arsenic are refractory during conventional sulfide oxidation, which significantly challenges subsequent gold extraction. One option is high-temperature pretreatment of arsenical materials to sequester > 90% of the arsenic as a gas, then convert it to a stable form. This process produces a calcine similar in composition to pyrrhotite (Fe1-xS) but with higher porosity. In this study, the calcine product is oxidized with an efficient, cost-effective atmospheric process using acidic and near-neutral solutions. A sulfur mass balance analysis method based on iron sulfide thermal transformation in nitrogen atmosphere was developed to quantify the oxidation efficiency of pyrrhotite leaching. The optimization confirmed that > 90% of the calcine was oxidized by Fe3+ (5 and 10 g/L) and O2 (0.5 L/min) at pH 1 after 48 h and at 95 °C even without ultrafine grinding. Elemental sulfur was the main oxidation product when the oxidation pH was 1,2. This study provides the foundation for the development of a low-cost and environmentally friendly process option for pretreatment of arsenical sulfide refractory gold materials