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Objective: To solve the problem that the roller is inconvenient to operate and the concept of rolling friction coefficient and sliding friction coefficient is confused. Methods: EDEM software was used to simulate the white milling process. Taking MNAW18 rice mill as a reference and taking Feng Liangyou series brown rice as a sample, a set of method for measuring discrete element simulation parameters of rice mill was established by independently setting up an experimental bench and combining with simulation calibration. Results: Using the self-made collision coefficient experimental device and video motion processing software, the collision recovery coefficients between brown rice and brown rice, roller and screen were 0.34, 0.24 and 0.43 respectively. Based on the relationship between inclined angle and static friction coefficient, the static friction experiment is designed. The static friction coefficients between brown rice and brown rice, roller and screen were 0.467, 0.881 and 0.550 respectively. The rolling friction coefficient was calibrated through the combination of brown rice stacking angle experiment, brown rice inclined plane rolling experiment and discrete element simulation experiment. The rolling friction coefficients between brown rice and brown rice, roller and screen were 0.013, 0.101 and 0.159 respectively. Conclusion: Through the secondary simulation, the error between the simulation results and the measured results is within a reasonable range, which indicates that the parameter calibration data is reliable.

Objective： Explore the effects of vibration mill's vibration mass on superfine grinding performance of wheat bran. Methods： A series of vibration impact grinding experiments of wheat bran was carried out by adjusting the grinding medium mass and wheat bran mass, respectively. Results： When the wheat bran mass was unchanged, the yield of wheat bran superfine powder showed a non-linear characteristic of first increasing and then decreasing with the increase of the quality of the grinding medium, and the maximum difference rate reached 123.53%. The quality of wheat bran micro powder also increased firstly and then decreased with the increase of grinding medium mass. However, when the grinding medium mass was unchanged, the yield of wheat bran superfine powder showed characteristic of first decreasing and then increasing with the increase of the quality of the grinding medium, and the maximum difference rate reacheds 588.69%. With the increase of wheat bran mass, the quality of wheat bran micro powder decreased firstly and then increased. It was also found that the sensitivity of wheat bran superfine powder yield to wheat bran mass was higher than that of wheat bran superfine powder yield to grinding medium mass. Conclusion： The grinding medium mass and wheat bran mass of vibration mill have significant effects on the superfine grinding of wheat bran, but the effect levels are different.

Objective To compare the clinical effects of the two methods of intruding overerupted molars by micro⁃ screws. Methods 21 overerupted molars were selected and ramdomly divided into group A and group B. Group A was implanted with one microscrew anchorage at the side of the buccolingual tongue, and the force was produced by the ten⁃ sion spring. Group B was implanted with two microscrews combined with nickel ⁃ titanium fragments to lower the mo⁃ lars. The distances, velocities and microscrew anchorage failure rates were measured and compared between the two groups. Results Two methods can achieve significant depressing effect, however, the failure rate of micro⁃screws was different in the two methods. The failure rates of group A and group B were 27.3% and 5.0%, respectively. The average speed of group A was 0.37 mm / month, and group B was 0.33 mm / month. Conclusion Both microscrew anchorage methods can effectively intrude overerupted upper molars. The speed of intrusion with microscrews directly is faster than NiTi Segmental arch and microscrews, but the implant failure of microscrews is higher.

Objective To study the clinical features of children with recurrent medulloblastoma (MB) and treatment regimens. Methods A retrospective analysis was performed on 101 children with recurrent MB who were admitted to the hospital from August 1, 2011 to July 31, 2017. The children were followed up to July 31, 2020. The Kaplan-Meier method was used for survival analysis. The Cox regression model was used for multivariate regression analysis. Results Of the 101 children, 95 underwent remission induction therapy, among whom 51 had response, resulting in a response rate of 54%. The median overall survival (OS) time after recurrence was 13 months, and the 1-, 3-, and 5-year OS rates were 50.5%±5.0%, 19.8%±4.0%, and 10%±3.3% respectively. There was no significant difference in the 5-year OS rate between the children with different ages (<3 years or 3-18 years), sexes, pathological types, or Change stages, between the children with or without radiotherapy before recurrence or re-irradiation after recurrence, and between the children with different times to recurrence (<12 months or ≥12 months after surgery) (P>0.05). There were significant differences in the 5-year OS rate between the children with or without reoperation after recurrence and between the children with different recurrence sites (P<0.05). The children with reoperation after recurrence had a significantly longer survival time than those without reoperation (P=0.007), and the risk of death in children undergoing reoperation after recurrence was 0.389 times (95% confidence interval: 0.196-0.774) that in children who did not undergo such reoperation. Conclusions As for the recurrence of MB, although remission induction therapy again can achieve remission, such children still have a short survival time. Only reoperation can significantly prolong survival time, and therefore, early reoperation can be considered to improve the outcome of children with recurrent MB. [ABSTRACT FROM AUTHOR]

Objective To study the clinical effect of surgery combined with chemotherapy and radiotherapy in children with central primitive neuroectodermal tumor (cPNET), as well as the risks factors for poor prognosis. Methods A retrospective analysis was performed for the clinical data of 42 children who were diagnosed with cPNET from June 2012 to September 2018. Results The 42 children had a median overall survival (OS) time of 2.0 years and a median event-free survival (EFS) time of 1.3 years; the 1-, 3-, and 5-year OS rates were 76.2%±6.6%, 41.4%±8.7%, 37.3%±8.8% respectively, and the 1-, 3-, and 5-year EFS rates were 64.3%±7.4%, 32.7%±8.0%, 28.0%±8.1% respectively. The univariate analysis showed that there were significant differences in the OS and EFS rates among the children with different patterns of surgical resection, chemotherapy cycles, and risk grades (P<0.05), and there was also a significant difference in the OS rate between the children receiving radiotherapy and those not receiving radiotherapy (P<0.05). The multivariate Cox regression analysis showed that chemotherapy cycles and risk grade were independent influencing factors for EFS and OS rates (P<0.05). The EFS and OS rates increased with the increase in chemotherapy cycles and the reduction in risk grade. Conclusions Multimodality therapy with surgery, chemotherapy, and radiotherapy is an effective method for the treatment of cPNET in children. Early diagnosis and treatment and adherence to chemotherapy for as long as possible may improve EFS and OS rates. [ABSTRACT FROM AUTHOR]

Objective To investigate the effect of bevacizumab in the treatment of children with optic pathway glioma (OPG). Methods A retrospective analysis was performed for the clinical data of 30 children with OPG who underwent chemotherapy. According to whether bevacizumab was used, they were divided into conventional chemotherapy (carboplatin, vincristine and etoposide) group with 12 children and combined chemotherapy (bevacizumab, carboplatin, vincristine and etoposide) group with 18 children. The children were followed up to 6 months after chemotherapy, and the two groups were compared in terms of visual acuity and tumor size before and after chemotherapy and adverse reactions during chemotherapy. Results The combined chemotherapy group had a significantly higher proportion of children achieving tumor regression than the conventional chemotherapy group (P<0.05), while there were no significant differences between the two groups in the proportion of children with improved visual acuity or adverse reactions (P>0.05). No chemotherapy-related death was observed in either group. Conclusions Bevacizumab combined with conventional chemotherapy can effectively reduce tumor size. Compared with conventional chemotherapy, such combination does not increase adverse reactions and can thus become a new direction for the treatment of OPG in children. [ABSTRACT FROM AUTHOR]