专题:中国非正规经济(下)

李明欢以非正规雇佣为主要内涵的非正规经济之所以能够在跨国领域大行其道,根源之一在于全球化正如同由跨国资本把握方向盘的巨型“压路机“,力图突破一切不利于其扩张之国境边界,朝着政治和

Survey of differential privacy in frequent pattern mining

频繁模式挖掘是数据挖掘的一个基本问题,其模式本身和相应计数都有可能泄露隐私信息.当前,差分隐私通过添加噪音使数据失真,有效实现了隐私保护的目的.首先介绍了差分隐私保护模型的理论基础;其次,详细综述了差分隐私下3种典型的频繁模式挖掘方法的最新研究进展,并进行对比性分析;最后对未来的研究方向进行了展望

高密度激光制造技术在超燃冲压发动机热防护中的应用

在高超声速飞行环境中，发动机的核心部件承受着高温高压高速气流烧蚀的极端恶劣工况，使得零部件的热防护成为关键问题之一。本文以发动机热防护为背景，阐述了与此相关的激光熔覆、激光打孔和激光焊接三大类典型高密度激光制造的应用。采用难熔金属的激光熔覆成形技术，形成与基体冶金结合的、具有梯度功能的熔覆层，提高了零件在高超声速气流烧蚀环境中的热防护能力。采用激光精微打孔技术可以在平面及曲面上实现各类异型孔和大深径比喷油群孔的加工。对发动机燃油冷却结构件进行激光搭接焊工艺试验，实现结构件上板焊透下板部分焊透的效果，变形小，结构强度高

Frequent Sequential Pattern Mining under Differential Privacy

频繁序列模式挖掘是数据挖掘领域的1个基本问题,然而模式本身及其支持度计数都有可能泄露用户隐私信息.差分隐私(differential privacy, DP)作为一种新出现的隐私保护技术,定义了一个相当严格的攻击模型,通过添加噪音使数据失真达到隐私保护的目的.由于序列数据内在序列性和高维度的特点 ,给差分隐私应用于频繁序列模式挖掘带来了挑战.对此提出了一种基于交互式差分隐私保护框架的频繁序列模式挖掘算法Diff-FSPM(differen tial-privacy frequent sequential pattern mining).该算法利用指数机制获取最优序列长度,并采用一种维规约策略获得原始序列数据集的规约表示,有效降低序列维度的影响;应用前缀树压缩频繁 序列模式,利用拉普拉斯机制产生的噪音扰动频繁模式的真实支持度计数,同时采用闭频繁序列模式和Markov假设,有效分配隐私预算,并利用一致性约束后 置处理,增强输出模式的可用性.理论角度证明算法满足epsilon-差分隐私,实验结果验证算法具有较好的可用性.Frequent sequential pattern mining is an exploratory problem in the field of data mining. However, directly releasing the discovered frequent patterns and the corresponding true supports may reveal the individuals' privacy. The state-of-the-art solution for this problem is differential privacy, which offers a strong degree of privacy protection by adding noise. Due to the inherent sequentiality and high-dimensionality in sequences, it is challenging to apply differential privacy to frequent sequential pattern mining. To address those problems, this paper presents a differentially private method called Diff-FSPM that uses an interactive way to find frequent patterns. To reduce the impact of dimensionality, Diff-FSPM first employs the exponential mechanism to obtain the optimal sequential length for truncating each sequence in the original dataset. After that, Diff-FSPM relies on a prefix-tree to compress all the frequent patterns, and then utilizes the Laplace mechanism to perturb the true support of the frequent patterns. To efficiently allocate the privacy budget, Diff-FSPM uses the closet frequent pattern and Markov assumption to guide the mining process. Finally, Diff-FSPM adopts a post-processing technique with consistency constraint to boost the accuracy of the returned noisy support counts. We theoretically prove that Diff-FSPM satisfies epsilon-differential privacy, and the experimental results show that it outperforms the existing methods in terms of utility

传感信号在接入网中传输的技术分析

文章提出了光纤通信网与传感网融合的设想,即利用已有光纤接入网的通信信道,让传感网络发出的传感信号在光纤接入网中传输。首先分析了这种设想的可行性,然后提出了按固定帧复用的方式对传感信号和通信信号进行耦合,并根据已有光纤接入网的结构建立了该系统的网络基本结构,重点分析了传感信号与通信信号复用时的时隙及带宽分配问题

Two-Dimensional Numerical Investigation for the Effects of Laser Process Parameters on Hole Type during Laser Drilling

针对孔型随激光工艺参数变化的特点,建立了具有光束传输和强度分布的激光打孔瞬态二维有限元模型,对孔型演化进行了数值模拟研究。模型考虑了激光束空间分布和材料相变潜热对孔的影响,给出了小孔的温度场瞬态分布和界面演化过程。结果表明,打孔速度随激光与材料作用时间增加而增大,钻孔速度大约在1 m/s量级,而孔径在打孔初期增大之后变化不大。比较了不同参数下各种孔型,包括直筒型、倒锥型和正锥型等,横截面的仿真结果与试验观测值吻合较好。仿真方法可以准确地模拟激光打通孔的过程,为实际工艺研究提供参考

GROWTH AND BIOENERGETICS OF THE SEA CUCUMBER APOSTICHOPUS JAPONICUS (ECHINODERMATA: HOLOTHUROIDEA) IN RESPONSE TO SEAWATER ACIDIFICATION AND WARMING

In recent years, threat to nearshore marine ecosystems and marine organisms caused by seawater acidification and seawater warming are becoming increasingly serious. In order to study the effects of CO_2-driven ocean acidification and warming on growth and energy budget of the sea cucumber Apostichopus japonicus, which is a key species in the coastal ecosystem of East Asia, four experimental treatments were set up, namely, control (seawater temperature of the Dalian coast, pCO_2 400 muatm), ocean warming (OW, seawater temperature of the Dalian coast plus 3℃, pCO_2 400 muatm), ocean acidification (OA, seawater temperature of the Dalian coast, pCO_2 1100 muatm) and Ocean acidification and warming (OAW, seawater temperature of the Dalian coast plus 3℃, pCO_2 1100 muatm). The result showed that A. japonicus in OW were not significantly affected in contrast to control. However, the specific growth rate (SGR) of A. japonicus in OA was the lowest, which decreased by 0.19%/d compared with the control treatment, and the body weight Coefficient variations of A. japonicus in OA was the largest. The final body weight and SGR of A. japonicus in OAW showed no significantly difference with those in control, bur ingestion rate and feces production rate were both significantly higher than those in the control. The bioenergetic pattern of A. japonicus in OW and OA did not change significantly compared with that in the control, but it changed significantly in OAW, with the percentage of the FCE being significantly higher than the other three treatments. Our study suggests that seawater acidification inhibited the growth of A. japonicus versus change its energy distribution pattern. The decrease of growth in OA mainly depended on the decrease of food ingestion. The combined effect of seawater acidification and rising temperature may compensate for the negative effect of seawater acidification on growth by changing the energy distribution pattern of A. japonicus