科创中国

k-median问题的近似算法研究一直是计算机科学工作者关注的焦点.基于均衡限制条件,利用反向贪心策略,给出求解该问题的随机近似算法.证明该算法以较大的概率满足其近似性能比的期望值为(3 +O(ln(ln(k)/a)).该算法的时间复杂度为O([k/aln(k)]2(n+m)),其中n和m分别代表设施集合以及客户点集的大小.最后,通过计算机实验验证了k-median问题的反向贪心算法的实际计算效果.

There is less research on vertical sculptured grinding technology.Especially in high vertical surface grinding process with the cup abrasive wheel,the thermal damage is prone to happen and undermine the grinding surface integrity.This problem limits to improve the grinding efficiency and the grinding ratio greatly.Through the analysis of vertical surface grinding process and features in depth,this paper revealed the inherent mechanism of higher grinding temperature in the process of vertical sculptured grinding using the cup wheel.Based on the previous research achievements,the grinding experiments on TC4(Ti-6Al-4V)and GH4169 are carried out utilizing the self-inhaling internal cooling wheel.The experimental results show that the self-inhaling internal cooling wheel can efficiently reduce the grinding surface temperature.Moreover,the inherent mechanism of reducing the grinding temperature using the internal cooling method is revealed.Meanwhile,under the same grinding conditions,the grinding ratio during the experiments on GH4169 using self-inhaling internal cooling method is about 3 times as high as using conventional external cooling method.And the grinding forces can be reduced by about 20%.This research revealed the inherent mechanism of higher grinding temperature in the process of vertical sculptured grinding using the cup wheel,which provides theoretical basis for the design and application of self-inhaling internal cooling wheel.At the same time,an efficient and non-invasive surface grinding method of TC4 and GH4169 is presented.

The identification of maximum road friction coefficient and optimal slip ratio is crucial to vehicle dynamics and control.However,it is always not easy to identify the maximum road friction coefficient with high robustness and good adaptability to various vehicle operating conditions.The existing investigations on robust identification of maximum road friction coefficient are unsatisfactory.In this paper,an identification approach based on road type recognition is proposed for the robust identification of maximum road friction coefficient and optimal slip ratio.The instantaneous road friction coefficient is estimated through the recursive least square with a forgetting factor method based on the single wheel model,and the estimated road friction coefficient and slip ratio are grouped in a set of samples in a small time interval before the current time,which are updated with time progressing.The current road type is recognized by comparing the samples of the estimated road friction coefficient with the standard road friction coefficient of each typical road,and the minimum statistical error is used as the recognition principle to improve identification robustness.Once the road type is recognized,the maximum road friction coefficient and optimal slip ratio are determined.The numerical simulation tests are conducted on two typical road friction conditions(single-friction and joint-friction)by using CarSim software.The test results show that there is little identification error between the identified maximum road friction coefficient and the pre-set value in CarSim.The proposed identification method has good robustness performance to external disturbances and good adaptability to various vehicle operating conditions and road variations,and the identification results can be used for the adjustment of vehicle active safety control strategies.

目的 探讨常规超声按照乳腺影像报告及数据系统(BI-RADS)标准与超声弹性应变率比值法对触诊阴性乳腺肿块的诊断价值.方法 常规超声检查按照BI-RADS-US标准将85例患者91个触诊阴性乳腺病灶进行分级,并于穿刺活检或手术切除前进行超声弹性应变率比值法测定.以病理诊断为金标准,构建受试者应用工作特征曲线( ROC),比较2种不同方法的诊断价值.结果 触诊阴性乳腺恶性病灶弹性应变率比值远大于良性病灶(分别为6.92±5.91和2.49±3.26),两者比较差异显著(P<0.01);弹性应变率比值法与BI RADS-US标准的曲线下面积(AUC)分别为0.891和0.818.两者比较差异无统计学意义(P>0.05);2种方法联合应用构建ROC曲线AUC为0.976,与BI-RADS-US标准比较差异有统计学意义(P<0.01),与弹性应变率比值法比较差异有统计学意义(P<0.05).结论 弹性应变率比值法对触诊阴性乳腺病灶的良恶性评估价值明显;常规超声与超声弹性成像联合应用有助于判断触诊阴性乳腺病灶的良恶性,具有重要的临床应用价值.