随着信息技术的发展,用户和组织对网络安全的关注度不断提高,数据加密传输逐渐成为主流,推动互联网中加密流量的比例不断攀升。然而,数据加密在保障隐私和安全的同时也成为非法内容逃避网络监管的手段。为实现加密流量的检测与分析,需...随着信息技术的发展,用户和组织对网络安全的关注度不断提高,数据加密传输逐渐成为主流,推动互联网中加密流量的比例不断攀升。然而,数据加密在保障隐私和安全的同时也成为非法内容逃避网络监管的手段。为实现加密流量的检测与分析,需要高效地识别出加密流量。但是,压缩流量的存在会严重干扰对加密流量的识别。针对上述问题,设计了基于滑动窗口和随机性特征的加密流量识别方案,以高效且准确地识别加密流量。具体来说,所提方案根据滑动窗口机制对会话中数据传输报文的有效载荷进行采样,获取能够反映原始流量信息模式的数据块序列,针对每个数据块使用随机性测度算法进行样本特征提取,为原始载荷构建随机性特征。此外,通过设计基于CART(classification and reqression tree)算法的决策树模型,在提高加密和压缩流量识别的准确率的同时,极大降低了针对加密流量识别的漏报率。基于对多个权威网站数据的随机抽样,构建均衡的数据集,并通过实验证明了所提方案的可行性和高效性。展开更多
The numerical simulation of extrudate swell is significant in extrusion processing.Precise prediction of extrudate swell is propitious to the control of melt flow and the quality of final products.A mathematical model...The numerical simulation of extrudate swell is significant in extrusion processing.Precise prediction of extrudate swell is propitious to the control of melt flow and the quality of final products.A mathematical model of three-dimensional（3D）viscoelastic flow through elliptical ring die for polymer extrusion was investigated.The penalty function formulation of viscoelastic incompressible fluid was introduced to the finite element model to analyze 3D extrusion problem.The discrete elastic viscous split stress（DEVSS）and streamline-upwind PetrovGalerkin（SUPG）technology were used to obtain stable simulation results.Free surface was updated by updating the streamlines which needs less memory space.According to numerical simulation results,the effect of zero-shear viscosity and elongation parameter on extrudate swell was slight,but with the increase of volumetric flow rate and relax time the extrudate swell ratio increased markedly.Finally,the numerical simulation of extrudate swell flow for low-density polyethylene（LDPE）melts was investigated and the results agreed well with others’work.These conclusions provided quantitative basis for the forecasting extrudate swell ratio and the controlling of extrusion productivity shape.展开更多
文摘随着信息技术的发展,用户和组织对网络安全的关注度不断提高,数据加密传输逐渐成为主流,推动互联网中加密流量的比例不断攀升。然而,数据加密在保障隐私和安全的同时也成为非法内容逃避网络监管的手段。为实现加密流量的检测与分析,需要高效地识别出加密流量。但是,压缩流量的存在会严重干扰对加密流量的识别。针对上述问题,设计了基于滑动窗口和随机性特征的加密流量识别方案,以高效且准确地识别加密流量。具体来说,所提方案根据滑动窗口机制对会话中数据传输报文的有效载荷进行采样,获取能够反映原始流量信息模式的数据块序列,针对每个数据块使用随机性测度算法进行样本特征提取,为原始载荷构建随机性特征。此外,通过设计基于CART(classification and reqression tree)算法的决策树模型,在提高加密和压缩流量识别的准确率的同时,极大降低了针对加密流量识别的漏报率。基于对多个权威网站数据的随机抽样,构建均衡的数据集,并通过实验证明了所提方案的可行性和高效性。
基金Supported by the National Science Foundation for Distinguished Young Scholars of China（50425517） the Shandong Province Natural Science Foundation（Y2007F59）
文摘The numerical simulation of extrudate swell is significant in extrusion processing.Precise prediction of extrudate swell is propitious to the control of melt flow and the quality of final products.A mathematical model of three-dimensional（3D）viscoelastic flow through elliptical ring die for polymer extrusion was investigated.The penalty function formulation of viscoelastic incompressible fluid was introduced to the finite element model to analyze 3D extrusion problem.The discrete elastic viscous split stress（DEVSS）and streamline-upwind PetrovGalerkin（SUPG）technology were used to obtain stable simulation results.Free surface was updated by updating the streamlines which needs less memory space.According to numerical simulation results,the effect of zero-shear viscosity and elongation parameter on extrudate swell was slight,but with the increase of volumetric flow rate and relax time the extrudate swell ratio increased markedly.Finally,the numerical simulation of extrudate swell flow for low-density polyethylene（LDPE）melts was investigated and the results agreed well with others’work.These conclusions provided quantitative basis for the forecasting extrudate swell ratio and the controlling of extrusion productivity shape.
