分类： 数学 >> 几何与拓扑 提交时间： 2023-02-22
摘要： In this paper, we give a complete classifification of harmonic and biharmon#2; ic Riemannian submersions : (R^3 , g_Sol) (N^2 , h) from Sol space into a surface by proving that there is neither harmonic nor biharmonic Riemann#2; ian submersion : (R^3 , g_Sol) (N^2 , h) from Sol space no matter what the base space (N2 , h) is. We also prove that a Riemannian submersion : (R^3 , g_Sol) (N^2 , h) from Sol space exists only when the base space is a hyperbolic space form.
分类： 数学 >> 几何与拓扑 提交时间： 2023-02-22
摘要： In this paper, we study biharmonic isometric immersions of a surface into and biharmonic Riemannian submersions from 3-dimensional Berger spheres. We obtain a classifification of proper biharmonic isometric immersions of a surface with constant mean curvature into Berger 3-spheres. We also give a complete classifification of proper biharmonic Hopf tori in Berger 3-sphere. For Riemannian submersions, we prove that a Riemannian submersion from Berger 3-spheres into a surface is biharmonic if and only if it is harmonic.
分类： 数学 >> 数学（综合） 分类： 信息科学与系统科学 >> 信息安全技术 提交时间： 2023-02-18
摘要： 构造线性码是编码密码理论中的重要研究课题.码的重量分布和重量谱的决定在编码理论中也有着基本的理论意义，而且在保密通信中有重要作用.本文构造了一类3-重和一类4-重二元线性码，并完全确定了它们的重量分布和重量谱.
分类： 数学 >> 计算数学 提交时间： 2023-02-15 合作期刊: 《桂林电子科技大学学报》
摘要： 估计寨卡和登革热(DEN)疫情从亚洲输入中国及引起本地暴发的风险。基于20152017年国外疫情和流动人口 数据,构建输入模型估计输入病例数,并计算基于不同温度和群体免疫水平下分支过程的本地疫情传播概率及基本再生 数。中国的寨卡输入病例主要来自新加坡、泰国和越南,预测的病例数分别为7.0(95% CI:6.5~7.5)、2.0(95% CI:1.8~ 2.2)和1.0(95% CI:0.9~1.1);登革热输入病例主要来自泰国、马来西亚、新加坡、越南、菲律宾、印度尼西亚、印度和韩 国,预测的病例数分别为700.0(95% CI:679.8~720.2)、654.1(95% CI:641.8~666.2)、376.3(95%CI:368.2~384.1)、 277.1(95% CI:268.55~285.33)、241.2(95% CI:233.6~248.8)、67.0(95% CI:59.6~74.5)、9.1(95% CI:6.7~11.3)和 3.0(95% CI:1.9~4.1)。温度在28.9 ℃左右是最适宜寨卡和登革热传播的条件,此时发生本地传播的风险概率分别为 24.4%和99.9%。将人类群体免疫水平从0增加到0.2和0.6,寨卡和登革热的基本再生数分别为8.1、6.7、3.2和3.2、 2.7、1.3。输入病例更多来自于南亚,中国中南和东南是暴发本地传播的高风险地区,特别是在6-8月。新加坡疫情更容易 导致寨卡在中国传播,而泰国、越南、马来西亚和新加坡疫情是中国发生登革热本地传播的最大导火索。
分类： 数学 >> 计算数学 提交时间： 2023-02-15 合作期刊: 《桂林电子科技大学学报》
摘要： 为了进一步提高求解Volterra型积分微分的数值精度,针对一种变系数Volterra型积分微分方程,提出了2种 Legendre 谱Galerkin 数值积分法。采用Galerkin Legendre 数值积分对 Volterra 型积分微分方程的积分项进行预处理,对 其构造Legendre tau 格式,同时用Chebyshev-Gauss-Lobatto 配置点对变系数和积分项部分进行计算,并通过对方程的定义 区间进行分解,提出了一种多区间 Legendre 谱Galerkin 数值积分法。该方法的格式对于奇数阶模型具有对称结构。此 外,通过引入Volterra 型积分微分方程的最小二乘函数,构造了Legendre谱Galerkin最小二乘数值积分法。该方法对应的 代数方程系数矩阵是对称正定的。数值算例验证了这2种Legendre 谱Galerkin 数值积分方法的高阶精度和有效性。
分类： 数学 >> 应用数学 提交时间： 2023-02-15
摘要： In recent years, mixed integer linear programming (MILP, in short) gradually becomes a popular tool of automated cryptanalyses in symmetric ciphers, which can be used to search differential characteristics and linear approximations with high probability/correlation. A key problem in the MILP method is how to build a proper model that can be solved efficiently in the MILP solvers like Gurobi or Cplex. It is known that a MILP problem is NP-hard, and the numbers of variables and inequalities are two important measures of its scale and time complexity. Whilst the solution space and the variables in many MILP models built for symmetric cryptanalyses are fixed without introducing dummy variables, the cardinality, i.e., the number of inequalities, is a main factor that might affect the runtime of MILP models. We notice that the norm of a MILP model, i.e., the maximal absolute value of all coefficients in its inequalities, is also an important factor affecting its runtime. In this work we will illustrate the effects of two parameters cardinality and norm of inequalities on the runtime of Gurobi by a large number of cryptanalysis experiments. Here we choose the popular MILP solver Gurobi and view it a black box, construct a large number of MILP models with different cardinalities or norms by means of differential analyses and impossible differential analyses for some classic block ciphers with SPN structure, and observe their runtimes in Gurobi. As a result, our experiments show that although minimizing the number of inequalities and the norm of coefficients might not always minimize the runtime, it is still a better choice in most situations.
分类： 数学 >> 控制和优化 提交时间： 2023-02-01
摘要： The aim of this paper is first to establish a general prediction framework for turning (period) term structures in COVID-19 epidemic related to the implementation of emergency risk man#2;agement in the practice, which allows us to conduct the reliable estimation for the peak period based on the new concept of Turning Period (instead of the traditional one with the focus on Turning Point) for infectious disease spreading such as the COVID-19 epidemic appeared early in year 2020. By a fact that emergency risk management is necessarily to implement emergency plans quickly, the identification of the Turning Period is a key element to emergency planning as it needs to provide a time line for effective actions and solutions to combat a pandemic by reducing as much unexpected risk as soon as possible. As applications, the paper also discusses how this Turning Term (Period) Structure is used to predict the peak phase for COVID-19 epidemic in Wuhan from January/2020 to early March/2020. Our study shows that the predication framework established in this paper is capa#2;ble to provide the trajectory of COVID-19 cases dynamics for a few weeks starting from Feb.10/2020 to early March/2020, from which we successfully predicted that the turning period of COVID-19 epi#2;demic in Wuhan would arrive within one week after Feb.14/2020, as verified by the true observation in the practice. The method established in this paper for the prediction of Turning Term (Period)Structures, and associated criteria for the Turning Term Structure of COVID-19 epidemic is expected to be a useful and powerful tool to implement the so-called dynamic zero-COVID-19 policy ongoing basis in the practice.
点击量
待评议
点击量
下载量
评论
通过
