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He Zhao,1,&ast; Yan-jun Wang,1,&ast; Rui-guo Wang,2 Da Liu,3 Ya-qing Duan,4 Yang-jin Liu,1 Yu-hong Zeng,5 Qin-peng Zhao,2 Zheng-ping Zhang2 1Department of Emergency Medicine, Honghui Hospital, Xi’an Jiaotong University, Xi’an, Shaanxi, 710054, People’s Republic of China; 2Department of Spine Surgery, Honghui Hospital, Xi’an Jiaotong University, Xi’an, Shaanxi, 710054, People’s Republic of China; 3Department of Orthopaedics, General Hospital of Western Theatre Command of PLA, Chengdu, Sichuan, 610083, People’s Republic of China; 4Department of Imaging, Honghui Hospital, Xi’an Jiaotong University, Xi’an, Shaanxi, 710054, People’s Republic of China; 5Department of Osteoporosis, Honghui Hospital, Xi’an Jiaotong University, Xi’an, Shaanxi, 710054, People’s Republic of China&ast;These authors contributed equally to this workCorrespondence: Zheng-ping Zhang, Department of Spine Surgery, Honghui Hospital, Xi’an Jiaotong University, No. 76 Nanguo Road, Xi’an, Shaanxi, 710054, People’s Republic of China, Tel +86 17791674069, Email hh_othem@163.comPurpose: Dual-energy X-ray absorptiometry (DXA) is commonly used for evaluation of bone mineral density before spinal surgery, but frequently leads to overestimation in degenerative spinal diseases due to osteoproliferation factors. We introduce a novel method to compare the predictive ability of Hounsfield Units (HU) and DXA methods to predict screw loosening after lumbar interbody fusion surgery in degenerative spinal diseases by measuring HU of pedicle screw trajectory on computed tomography (CT) images preoperatively.Patients and Methods: This retrospective study was conducted on patients who underwent posterior lumbar fusion surgery for degenerative diseases. CT HUs measurement was performed using medical imaging software, including the cancellous region on cross-sections of the vertebral body and three-dimensional pedicle screw trajectory. Receiver operating characteristic (ROC) curve analyses were performed for the risk of pedicle screw loosening in association with the Hounsfield scale and preoperative BMD, and the area under the curve (AUC) and the cutoff values were calculated.Results: A total of 90 patients were enrolled and were divided into loosening (n = 33, 36.7%) and non-loosening groups (n = 57, 63.3%). No significant differences in age, gender, length of fixation and preoperative BMD were found between both groups. The loosening group showed lower CT HU values in the vertebral body and screw trajectory than the non-loosening group. Screw trajectory HU (ST-HU) exhibited a higher AUC value than vertebral body HU (B-HU). The cutoff values of B-HU and ST-HU were 160 and 110 HUs, respectively.Conclusion: Three-dimensional pedicle screw trajectory HU values yields a stronger predictive value than vertebral body HU values and BMD and may provide more guidance for surgery. The risk of screw loosening is significantly increased at ST-HU < 110 or B-HU < 160 at L5 segment.Keywords: osteoporosis, degenerative spinal disease, fixation failure, imaging observation more...

The friction factor of an open channel flow is generally affected by the Reynolds number and the roughness conditions, and can be decided by laboratory or field measurements. During practical applications, researchers often find that a correct choice of the friction factor can be crucial to make a sound prediction of hydraulic problems. In this paper, a three-layer artificial neural network (ANN) was set up to predict the friction factors of an open channel flow, with the Reynolds number and the relative roughness as two input parameters. The Levenberg–Marquardt (LM) learning algorithm was employed to train the model by using laboratory experimental data, and the trained network was tested by a single set separated from the rest of the data and a good correlation between the experimental and predicted results has been obtained. Finally, the ANN simulated results were compared with the calculated results obtained by the empirical formula and both comparisons showed that the ANN model can be used to predict the non-linear relationship between the friction factor and its influencing factors correctly once enough samples are provided. The successful application proved that ANN model can be used in engineering practice as a convenient and effective method, and those traditional hydraulic problems which are mostly based on laboratory tests can be analyzed by ANN modelling. more...

The k-epsilon model was applied to establish the mathematical model of vertical round buoyant jet discharging into confined depth, and it was solved using the Hybrid Finite Analytic Method (HFAM). The numerical predictions demonstrate two generic flow patterns for different jet discharge and environmental parameters: (i) a stable buoyant flow discharge with the mixed fluid leaving the near-field warm in a surface warm water layer; (ii) an unstable buoyant flow discharge with recirculation and re-entrainment of warm water in the near field. Furthermore, the mixing characters of vertical round buoyant jet were numerically predicted. Both the stability criterion and numerical predictions of bulk dilutions are in excellent agreement with Lee and Jirka's experiments and theory. more...