The aim of the study was to prospectively assess the diagnostic accuracy of 1.5 T diffusion-weighted imaging (DWI) for 5 to 10 mm metastatic cervical lymph nodes of patients with nasopharyngeal carcinoma (NPC). All patients with histopathologically confirmed NPC underwent DWI with 2 b values of 0 and 800 s/mm2 were enrolled. The shortest axial diameter and mean apparent diffusion coefficient (ADC) value were recorded when lymph nodes with a shortest axial diameter from 5 to 10 mm were measured. The correlation between the pathological diagnoses and mean ADC values in the benign and metastatic lymph nodes were compared using the Z test. Receiver operating characteristic (ROC) curve analysis was performed to evaluate the diagnostic performance of DWI. Three hundred fourteen nodes of 52 patients with NPC consisted of 46.5% (146/314) metastatic lymph nodes and 53.5% (168/314) benign lymph nodes. The mean ADC value (×10–3 mm2/s) of benign lymph nodes was (1.110 ± 0.202), which was significantly higher than that of metastatic nodes (0.878 ± 0.159) (P < 0.05). The sensitivity, specificity, positive predictive value, and negative predictive value, accuracy for differentiating metastatic from benign lymph nodes using a cutoff ADC value of 0.924 × 10–3 mm2/s was 83.56%, 82.74%, 80.79%, 85.28%, and 82.80%, respectively. The area under the ROC curve was 0.851 (95% confidence intervals: 0.807–0.889). This study demonstrated that DWI is helpful in detecting 5 to 10 mm metastatic lymph nodes of patients with NPC.
An improved engineering model of silicon solar cell is proposed, which uses only four electrical parameters under standard test conditions provided by manufactures. Simulation and experimental results show that the model error was 6 percent below for various combinations of solar radiation and temperature and its accuracy is sufficient for most practical engineering cases.
Traditional square current driving method has deficiencies in muting and efficiency when controlling the brushless DC motor. This paper presents a method of space vector pulse width modulation for BLDCM, which is in five-segment type. A mathematical model of BLDCM, which is in d-q coordinate system, was established. Then, the experimental platform was constructed with the STM32F103 for BLDCM of electric vehicle. And the experiment results verify the properties of little torque ripple, smooth operation and low switching losses. Besides, the system dynamic and static performance is greatly improved, and has strong robustness. The method proposed overcomes the shortcomings of square current driving method in control efficiency and motor noise.
Aiming at the demerit of the traditional flux coupling driving circuit, an improved driving circuit is proposed which has some advantages, such as simple structure, low cost, the driving source isolated from the main circuit, etc. The proposed circuit can be used on the maximum power point tracking circuit of solar cell which has a wide range duty cycle. The circuit principle analysis is given. At last, experimental results are provided to verify its practicability.
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