Steganalysis of neural networks based on parameter statistical bias

Many pretrained deep learning models have been released to help engineers and researchers develop deep learning-based systems or conduct research with minimall effort. Previous work has shown that at secret message can be embedded in neural network parameters without compromising the accuracy of the model. Malicious developers can, therefore, hide malware or other baneful information in pretrained models, causing harm to society. Hence, reliable detection of these vicious pretrained models is urgently needed. We analyze existing approaches for hiding messages and find that they will ineluctably cause biases in the parameter statistics. Therefore, we propose steganalysis methods for steganography on neural network parameters that extract statistics from benign and malicious models and build classifiers based on the extracted statistics. To the best of our knowledge, this is the first study on neural network steganalysis. The experimental results reveal that our proposed algorithm can effectively detect a model with an embedded message. Notably, our detection methods are still valid in cases where the payload of the stego model is low.     

基于动态博弈的补贴模式对机场群航线网络结构的影响研究

为探讨不同补贴模式对机场群航线网络结构的影响，本文构建了关于机场、航空公司和乘客之间的动态博弈模型，通过逆向归纳法得到了纳什均衡条件. 研究结果发现：（1）不同的补贴模式对多机场航线网络结构产生重要影响，低补贴模式促使机场群倾向于形成点对点航线网络结构，反之，在高补贴模式下机场群易于形成枢纽辐射航线网络； （2）在较低的空铁联运总运营成本环境下，补贴竞争使得航空公司倾向于选择系统内的大型机场作为枢纽机场；反之，如果空铁联运总运营成本相对较高，补贴竞争使得航空公司倾向于选择小机场作为枢纽节点； （3）随航班固定成本和空铁联运总运营成本的增大，大型机场作为枢纽节点的概率逐渐减少，而小机场被选为枢纽节点的概率将逐渐增大. 随着机场群内大型机场腹地服务人口比例的增大，航空公司选择点对点航线网络的概率在减小. 研究结论能够为民航管理部门科学制定和应用航线补贴政策提供决策依据.     

Moving beyond Volatility Index (VIX): HARnessing the term structure of implied volatility

This paper considers how information from the implied volatility (IV) term structure can be harnessed to improve stock return volatility forecasting within the state-of-the-art HAR model. Factors are extracted from the IV term structure and included as exogenous variables in the HAR framework. We found that including slope and curvature factors leads to significant forecast improvements over the HAR benchmark at a range of forecast horizons, compared with the standard HAR model and HAR model with VIX as IV information set.     

基于40Cr高温动态力学性能的磨削表面动态再结晶行为

通过分离式霍普金森压杆(SHPB)实验得到了40Cr合金钢在高温高应变率下真应力-真应变曲线，据此确定了材料发生动态再结晶的临界条件.采用解析法和实验法分别求解了磨削强化层的温度场和塑性应变场分布.结果表明，磨削强化层在磨削深度方向具有较大的温度和塑性应变梯度;150μm强化层内会发生奥氏体转变;磨削表面最高温度可达1060℃.在磨削亚表面60μm内会产生剧烈的塑性变形，达到了再结晶的临界条件.较大的磨削深度使磨削强化层塑性应变增大，再结晶现象越充分，微观组织细化程度越高.     

可控变胞码垛机器人控制系统设计及实验

为了提高变胞式工业机器人在实际工业生产中的效率以及稳定性,基于可控变胞码垛机器人设计了一种新型的码垛路径运行方式,对其进行运动学仿真并设计了相应的控制系统.其中控制系统采用"运动控制卡+工控机"的上下位机控制模式,使用闭环步进电机及驱动器组成机器人的运动系统,使用光电开关、气动插销及电磁离合器等硬件组成变胞动作执行系统,引入电机脉冲补偿值以减少变胞前后的运动误差.提出新型码垛路径的实现方法,并搭建机器人控制系统,以6 kg负载进行实验,测试结果显示理论位移与实测位移之间的误差不超过0.6 mm.研究表明该控制系统运行安全可靠,能够满足可控变胞码垛机器人的控制要求,同时也为变胞式工业机器人的控制系统设计提供了参考.     

基于成像算子优化的微震逆时定位方法

针对目前微震逆时定位成像存在的问题,提出一种优化后的成像算子,对模型数据进行抗噪性、误差速度以及检波器分布和数量进行测试,并提出采用峰度值作为定位成像结果的评价标准。结果表明,优化后的成像条件在定位能量聚焦程度和成像分辨率上都得到了提升,对含速度误差和含噪微震数据都有较好的成像结果,并且对检波器的分布和数量有较好的适应性,取得了较为理想的定位效果。     

Mechanical behavior of a near α titanium alloy under dynamic compression: Characterization and modeling

Dynamic compression tests under strain rates from 870 s^?1 to 2100 s^?1 were conducted for a near α Ti–8Al–1Mo–1V titanium alloy with equiaxed microstructure. Compression behavior, adiabatic shearing and band microstructure were investigated via characterization and calculation. The results demonstrate that all dynamic constitutive curves exhibited obvious stress fluctuation phenomenon with double increase-decrease changing stages at the primary stage of compression. The dislocation multiplication theory can be used to explain this phenomenon. After the stress fluctuation period, work hardening coexisted with the thermal softening, resulting in the slow hardening tendency in constitutive curves. J-C model was utilized to quantify the dynamic constitutive curves. The deviations between the predicted and experimental curves under high strain rates may be attributed to the over-consideration of thermal softening effect in J-C model. Adiabatic shearing band (ASB) began to form under the strain rate of 2100 s^?1. A total shearing strain of 8.1 within ASB achieved in 8.9 μs, corresponding to a local strain rate of about 9.1 × 10⁵ s^?1 and is over 430 times of the macro strain rate. Post annealing was conducted on ASB before EBSD characterization. Due to the static recrystallization during annealing, the α phase within ASB generally presented as ultra-fine grains less than 1 μm in diameter.     

Theoretical and experimental design of Pt-Co(OH)_2 electrocatalyst for efficient HER performance in alkaline solution

Design efficient electrocatalysts become significant for the hydrogen evolution reaction (HER) in alkaline solution.Here,the HER performance on Pt-Co(OH)2 has been investigated by using DFT calculations.Compared with pure Pt,the Pt-Co(OH)2 shows excellent hydrogen binding energy (-0.29 eV) and hydrogen adsorption free energy (0.02 eV).More strikingly,the water dissociation process on Pt-Co(OH)2 is an exothermic reaction while that of Pt is an endothermic reaction,demonstrating that the Pt-Co(OH)_2 is an excellent catalyst for HER in alkaline medium.Then the two-step electrodepositions was used to fabricate Pt-Co(OH)2 on the carbon paper (CP).The Pt-Co(OH)_2/CP shows the lowest overpotential of only 37.6 mV at a current density of 10 mA cm~(-2) in 0.1M KOH,the smallest Tafel slope of58 mV dec~(-1) and the good stability for 20000s without obvious degradation.     

大物质分选机在餐厨垃圾预处理中的应用

餐厨垃圾预处理阶段物质分选对整体处理工艺影响较大，如果分选不到位，浆料中杂物多，会导致管道磨损严重、设备故障率高等问题。通过调节进料频率及大物质分选机的运行频率，探究大物质分选机较优的运行参数范围，使分选工作更加有效。试验结果表明：大物质分选机运行频率为70 Hz，进料频率小于17 Hz为较优运行参数，此时设备电流值较低且波动曲线较为平稳，分选料中有机质质量占比在33%~37%，与其他工况相比，有机质质量占比至少低了3%；运行工况的变化不会对浆料的组成成分造成影响，其中剩余物、果皮和骨头质量占比较大，三者占比总和在98%以上，其他杂物质量占比不超过2%。     

数学专业师范生教学技能的调查研究--以四川文理学院为例

教学技能是教师最重要的专业素质，是师范生在大学期间需要掌握的基础职业技能。通过调查研究表明，数学专业大学生教学基本功发展不平衡，不同年级学生的教学技能水平存在显著差异。教学实践、课改认知、教学交流、自主练习是影响教学技能的四个主因子。男女生在表达技能、教学设计技能、几何作图技能等方面差异显著，而在教材分析、多媒体使用方面不存在显著性差异。要通过完善教学技能培养机制，夯实师范基础技能培养，改革教学技能培养方式等途径，合力提高师范生的教学技能，增强就业竞争力。