With the rapid development of space science projects,large deployable mechanisms have been widely used.However,due to the effects of mechanical friction and gravitational acceleration,on-orbit mechanisms cannot be alw...With the rapid development of space science projects,large deployable mechanisms have been widely used.However,due to the effects of mechanical friction and gravitational acceleration,on-orbit mechanisms cannot be always deployed to the expected pose.For some precision optical mechanisms,even a minor deviation can result in significant error,so it needs to be measured and corrected.In this paper,the deployment process was modeled and simplified as rotation under single-rotation-axis constraint and translation under single-direction constraint.To solve the problem,a method based on cross-ratio invariability was proposed.The proposed method does not rely on camera calibration techniques,as well as artificial marking points,both of which are necessary in PnP.Instead,only three calibration images before launch and a measurement image on orbit were required.Simulations and experiments demonstrated that the proposed method is more accurate than PnP.In addition,experiments also proved that the feasibility of the proposed method under dark conditions with the aid of a light source and some reflective marking points.展开更多
通过压缩信道状态信息(Channel Status Information,CSI)传输码字降低大规模多输入多输出(Multiple-Input Multiple-Output,MIMO)系统的CSI反馈开销,可以有效减少计算资源的使用和信息传输时间的消耗。针对如何使用轻量化模型准确估计...通过压缩信道状态信息(Channel Status Information,CSI)传输码字降低大规模多输入多输出(Multiple-Input Multiple-Output,MIMO)系统的CSI反馈开销,可以有效减少计算资源的使用和信息传输时间的消耗。针对如何使用轻量化模型准确估计低压缩比条件下CSI反馈的问题,通过设计的轻量化迭代交叉网络(Iterative Cross Network,ICNet)模型,在用户端使用设计的迭代压缩模块压缩CSI反馈,基站端使用设计的迭代重建模块估计CSI反馈,以较高的准确率和较低的时间消耗估计了低压缩比条件下的CSI反馈。在COST2100模型生成的数据样本下评估了ICNet在低压缩比条件下的鲁棒性,实验表明,在较小的1/64压缩比条件下,ICNet的归一化均方误差比次优值降低了8.48%,ICNet的参数量降低了35%左右。展开更多
A natural compactification of the virtual configuration space of N points on the Riemann sphere C is constructed by using cross-ratios. We show that this compactification is homeomorphic to the Bers＇ compactification...A natural compactification of the virtual configuration space of N points on the Riemann sphere C is constructed by using cross-ratios. We show that this compactification is homeomorphic to the Bers＇ compactification of the virtual moduli space of a punctured Riemann sphere of type N. In particular, the system of global and explicit coordinates of this standard compactification is given by cross-ratios.展开更多
Let QS* (S 1) be the space of quasisymmetric homeomorphisms of the unit circle such that the corresponding subspace of the universal Teichmu¨ller space has Weil-Petersson metric.In this paper we give a necessary ...Let QS* (S 1) be the space of quasisymmetric homeomorphisms of the unit circle such that the corresponding subspace of the universal Teichmu¨ller space has Weil-Petersson metric.In this paper we give a necessary condition for a quasisymmetric homeomorphism to belong to QS *(S 1) from the aspect of cross-ratio distortion.展开更多
目的探讨成年人群中单核细胞与高密度脂蛋白胆固醇比值(monocyte-to-high-density lipoprotein cholesterol ratio,MHR)与肌肉减少症之间的关联。方法从2011~2018年4个周期的国家健康与营养调查(National Health and Nutrition Examinat...目的探讨成年人群中单核细胞与高密度脂蛋白胆固醇比值(monocyte-to-high-density lipoprotein cholesterol ratio,MHR)与肌肉减少症之间的关联。方法从2011~2018年4个周期的国家健康与营养调查(National Health and Nutrition Examination Survey,NHANES)中选取了8085例20岁及以上的参与者进行横断面研究。采用多元Logistic回归模型来评估MHR与肌肉减少症之间的关联。方差膨胀因子(variance inflation factors,VIF)检查变量间的多重共线性。通过限制性立方样条探究非线性关系,同时进行了交互作用检验和亚组分析。结果在完全调整的模型中发现,MHR与肌肉减少症呈正相关(OR=2.56,95%CI:1.73~3.79,P<0.001)。这种关联在吸烟和心血管疾病参与者中更加突出。此外,限制性立方样条分析显示,MHR与肌肉减少症之间的关系是线性的。结论MHR与肌肉减少症发病风险呈正相关,可能是早期识别肌肉减少症的潜在指标。展开更多
基金Supported in part by the National Natural Science Foundation of China(No.62271148).
文摘With the rapid development of space science projects,large deployable mechanisms have been widely used.However,due to the effects of mechanical friction and gravitational acceleration,on-orbit mechanisms cannot be always deployed to the expected pose.For some precision optical mechanisms,even a minor deviation can result in significant error,so it needs to be measured and corrected.In this paper,the deployment process was modeled and simplified as rotation under single-rotation-axis constraint and translation under single-direction constraint.To solve the problem,a method based on cross-ratio invariability was proposed.The proposed method does not rely on camera calibration techniques,as well as artificial marking points,both of which are necessary in PnP.Instead,only three calibration images before launch and a measurement image on orbit were required.Simulations and experiments demonstrated that the proposed method is more accurate than PnP.In addition,experiments also proved that the feasibility of the proposed method under dark conditions with the aid of a light source and some reflective marking points.
基金supported by Grants-in-Aid for Scientific Research (C) (Grant No. 23540202)Grant-in-Aids for Scientific Research (B) (Grant No. 20340030)
文摘A natural compactification of the virtual configuration space of N points on the Riemann sphere C is constructed by using cross-ratios. We show that this compactification is homeomorphic to the Bers＇ compactification of the virtual moduli space of a punctured Riemann sphere of type N. In particular, the system of global and explicit coordinates of this standard compactification is given by cross-ratios.
文摘Let QS* (S 1) be the space of quasisymmetric homeomorphisms of the unit circle such that the corresponding subspace of the universal Teichmu¨ller space has Weil-Petersson metric.In this paper we give a necessary condition for a quasisymmetric homeomorphism to belong to QS *(S 1) from the aspect of cross-ratio distortion.
