对于基于划分的聚类算法随机选取初始聚类中心导致初始中心敏感,聚类结果不稳定、集群效率低等问题,提出一种基于MapReduce框架和改进的密度峰值的划分聚类算法(based on MapReduce framework and improved density peak partition clus...对于基于划分的聚类算法随机选取初始聚类中心导致初始中心敏感,聚类结果不稳定、集群效率低等问题,提出一种基于MapReduce框架和改进的密度峰值的划分聚类算法(based on MapReduce framework and improved density peak partition clustering algorithm,MR-IDPACA)。首先,通过自然最近邻定义新的局部密度计算方式,将搜索样本密度峰值点作为划分聚类算法的初始聚类中心;其次针对算法在大规模数据下运行时间复杂,提出基于E2LSH(exact Euclidean locality sensitive hashing)的一种分区方法,即KLSH(K of locality sensitive hashing)。通过该方法对数据分区后结合MapReduce框架并行搜寻初始聚类中心,有效减少了算法在搜索初始聚类中心时的运行时间;对于MapReduce框架中的数据倾斜问题,提出ME(multistage equilibrium)策略对中间数据进行多段均衡分区,以提升算法运行效率;在MapReduce框架下并行聚类,得到最终聚类结果。实验得出MR-IDPACA算法在单机环境下有着较高的准确率和较强的稳定性,集群性能上也有着较好的加速比和运行时间,聚类效果有所提升。展开更多
The advancement of effective and stable non-precious metal-based catalysts for oxygen evolution reactions(OER)with a lowcost and simple technique is essential for the practical application of rechargeable zinc–air ba...The advancement of effective and stable non-precious metal-based catalysts for oxygen evolution reactions(OER)with a lowcost and simple technique is essential for the practical application of rechargeable zinc–air battery(ZAB).However,facilitating the deep reconstruction of electrocatalysts to form active species remains a significant challenge.Here,a simple two-step method composed of impregnation and carbonization process is proposed to synthesize N,S co-doped microcrystalline cellulose-derived carbon-supported nickel sulfide(Ni_(3)S_(2))nanoparticles.The in situ Raman reveals that Fe substitution promotes the reconstruction of Ni_(3)S_(2),accompanied by the cleavage of the Ni–S bond,leading to the deep reconstruction into(Ni,Fe)OOH(DR-(Ni,Fe)OOH)during the OER.Moreover,density functional theory calculations reveal that Fe substitution induces a downshift in the energy band structure,which lowers the energy barriers and thereby improves the kinetics of the OER.The generated DR-(Ni,Fe)OOH delivers a relatively low overpotential of 260 m V and superior durability for 50 h under OER condition.The ZAB incorporating DR-(Ni,Fe)OOH+Pt/C as the air cathode demonstrates superior efficiency and durability,achieving a peak power density of 188.3 m W cm^(-2),a specific capacity of 811.1 m Ah g^(-1),and long-term stability exceeding 200 h.展开更多
Binary digit representation of partial sums for random variables has been investigated, and a good upper bound of moments of maximum partial sums for random variables has been reduced by using this representation. As ...Binary digit representation of partial sums for random variables has been investigated, and a good upper bound of moments of maximum partial sums for random variables has been reduced by using this representation. As an applications, stability and strong law of large numbers have been discussed. Many known classical results have been refined.展开更多
文摘对于基于划分的聚类算法随机选取初始聚类中心导致初始中心敏感,聚类结果不稳定、集群效率低等问题,提出一种基于MapReduce框架和改进的密度峰值的划分聚类算法(based on MapReduce framework and improved density peak partition clustering algorithm,MR-IDPACA)。首先,通过自然最近邻定义新的局部密度计算方式,将搜索样本密度峰值点作为划分聚类算法的初始聚类中心;其次针对算法在大规模数据下运行时间复杂,提出基于E2LSH(exact Euclidean locality sensitive hashing)的一种分区方法,即KLSH(K of locality sensitive hashing)。通过该方法对数据分区后结合MapReduce框架并行搜寻初始聚类中心,有效减少了算法在搜索初始聚类中心时的运行时间;对于MapReduce框架中的数据倾斜问题,提出ME(multistage equilibrium)策略对中间数据进行多段均衡分区,以提升算法运行效率;在MapReduce框架下并行聚类,得到最终聚类结果。实验得出MR-IDPACA算法在单机环境下有着较高的准确率和较强的稳定性,集群性能上也有着较好的加速比和运行时间,聚类效果有所提升。
基金financially supported by the National Natural Science Foundation of China(32301514)the Young Elite Scientist Sponsorship Program by CAST(YESS20220240)。
文摘The advancement of effective and stable non-precious metal-based catalysts for oxygen evolution reactions(OER)with a lowcost and simple technique is essential for the practical application of rechargeable zinc–air battery(ZAB).However,facilitating the deep reconstruction of electrocatalysts to form active species remains a significant challenge.Here,a simple two-step method composed of impregnation and carbonization process is proposed to synthesize N,S co-doped microcrystalline cellulose-derived carbon-supported nickel sulfide(Ni_(3)S_(2))nanoparticles.The in situ Raman reveals that Fe substitution promotes the reconstruction of Ni_(3)S_(2),accompanied by the cleavage of the Ni–S bond,leading to the deep reconstruction into(Ni,Fe)OOH(DR-(Ni,Fe)OOH)during the OER.Moreover,density functional theory calculations reveal that Fe substitution induces a downshift in the energy band structure,which lowers the energy barriers and thereby improves the kinetics of the OER.The generated DR-(Ni,Fe)OOH delivers a relatively low overpotential of 260 m V and superior durability for 50 h under OER condition.The ZAB incorporating DR-(Ni,Fe)OOH+Pt/C as the air cathode demonstrates superior efficiency and durability,achieving a peak power density of 188.3 m W cm^(-2),a specific capacity of 811.1 m Ah g^(-1),and long-term stability exceeding 200 h.
文摘Binary digit representation of partial sums for random variables has been investigated, and a good upper bound of moments of maximum partial sums for random variables has been reduced by using this representation. As an applications, stability and strong law of large numbers have been discussed. Many known classical results have been refined.
