复合型碳气凝胶在应变传感器中的应用进展

碳气凝胶是一种具有三维多尺度结构的新型轻质多孔材料,其特点是高比表面积、高孔隙率、低密度、高耐热和导电性。当前,碳气凝胶在应变传感器、超级电容器、电磁屏蔽、吸波材料、隔热防火、高效吸附等领域有广泛的应用研究。文中介绍了碳气凝胶的制备方法,包括溶剂热还原法、冷冻干燥法以及模板法;综述了几种复合型碳气凝胶在应变传感器上的应用;对复合型碳气凝胶制备应变传感器的发展方向进行了展望。

Analysis of a Strong-Inhibition Polyamine Drilling Fluid

Drilling technologies based on oil-based drillingfluids and strong inhibitory saltwaterfluids are affected by draw-backs such as downhole accidents where sticking and wellbore instabilities occur.Existing polyamine drillingfluids also exhibit problems such as easy decomposition and poor inhibition performances.In order to mitigate these issues,additives can be used,such as polyamine inhibitors and the synthesis of nanometerfiltrate reducers.Tests conducted in the frame of this study with a polyamine drillingfluid and such additives show that thisfluid has the same inhibitory,plugging,lubricating,and wellbore-stability performances as oil-based drillingfluids.However,it has long-term anti-wear performances even better than those of oil-based drillingfluids.The out-comes of a series of comparisons with other sample cases(other wells)are reported and the advantages related to the proposedfluid discussed in detail.

甲基丙烯酸锌用量对天然橡胶高温蠕变性能的影响及数值模拟

研究甲基丙烯酸锌(ZDMA)用量对天然橡胶(NR)高温蠕变性能的影响,以及测试温度对NR/ZDMA硫化胶蠕变性能的影响,并采用广义Kelvin模型对该蠕变结果进行数值拟合。结果表明,随着ZDMA的用量从0 phr增加至4 phr,硫化胶的压缩应变逐渐下降,蠕变增量先减小后增大;随着测试温度从70℃升高至150℃,硫化胶的压缩应变和蠕变增量均逐渐增大。广义Kelvin模型可以高度拟合ZDMA/NR硫化胶的蠕变行为,拟合曲线的判定系数(R^2)大于0.99。

基于优化的MRF遥感影像分割算法

MRF图像分割算法由于其良好的抗噪性,在图像分割邻域应用广泛,但其存在过度分割现象,导致边缘分割模糊定位不准确。针对这一问题,文章首先在传统的MRF图像分割算法中引入可变权重的参数来连接标记场模型与特征场模型,使得两种模型之间形成一种平衡,获取可保持图像边缘、图像重要细节和具有区域一致性的分割结果。然后在边缘处自适应地引入边缘惩罚函数,调整势函数的能量对能量函数的贡献,减少分割时对边缘的模糊,提高对边缘的定位精度。通过实验结果分析表明,所提出的优化的MRF影像分割算法比传统的ICM迭代计算MRF分割算法和变权重的MRF分割算法具有更高分割精度。

未填充天然橡胶/反式丁戊橡胶共混胶的耐疲劳性能及疲劳破坏机理

研究了共混比对天然橡胶(NR)/反式-1,4-丁戊橡胶(TBIR)共混硫化胶的力学性能和耐疲劳性能的影响,以及共混胶的屈挠疲劳断裂机理。结果表明,随着共混胶中TBIR含量的增加,共混胶的拉伸强度先增加后降低,撕裂强度逐渐下降,而断裂伸长率和硬度变化不大。随着共混胶中TBIR含量的增加,共混胶的耐屈挠疲劳性能先升高后降低。当NR/TBIR共混比为50/50时,共混胶的耐屈挠疲劳性能最好。TBIR的结晶性是影响共混硫化胶耐疲劳性能的重要因素。当TBIR的含量低于50%时,硫化胶内部的微晶结构随着TBIR用量增大而增加,有利于增强橡胶的耐疲劳性能;但当TBIR的含量超过50%时,共混胶中微晶区的密度过大,无规分子链较少,对屈挠过程的能量耗散作用减弱,疲劳裂纹增长加快,因而硫化胶的耐疲劳性能反而下降。

The genomic landscapes of histone H3-Lys9 modifications of gene promoter regions and expression profiles in human bone marrow mesenchymal stem cells

Mesenchymal stem cells （MSCs） of nonembryonic origins possess the proliferation and multi-lineage differentiation potentials. It has been established that epigenetic mechanisms could be critical for determining the fate of stem cells, and MSCs derived from different origins exhibited different expression profiles individually to a certain extent. In this study, ChiP-on-chip was used to generate genome-wide histone H3-Lys9 acetylation and dimethylation profiles at gene promoters in human bone marrow MSCs. We showed that modifications of histone H3-Lys9 at gene promoters correlated well with mRNA expression in human bone marrow MSCs. Functional analysis revealed that many key cellular pathways in human bone marrow MSC self-renewal, such as the canonical signaling pathways, cell cycle pathways and cytokine related pathways may be regulated by H3-Lys9 modifications. These data suggest that gene activation and silencing affected by H3-Lys9 acetylation and dimethylation, respectively, may be essential to the maintenance of human bone marrow MSC self-renewal and multi-potency.

Design and Strategy of Series-Parallel Hybrid System Based on BSFC

In this paper,a drive control strategy is developed based on the characteristics of series-parallel plug-in hybrid system.Energy management strategies in various modes are established with the basis on the minimum brake specific fuel consumption(BSFC)curve of engine.The control strategy,which is based on rules and system efficiency,is adopted to determine the entry/exit mechanisms of various modes according to battery state of charge(SOC),required power and required speed.The vehicle test results verify that the proposed control strategy can improve vehicle economy efficiently and makes a good effect on engine control.

Temperature Compensation Algorithm for Hydraulic System Pressure Control

In this paper the control mechanism of solenoid valve is analyzed,which shows the solenoid valve control is actually the control of coil current.The response characteristic of coil current is related to coil inductance and resistance.The coil resistance is influenced greatly by the ambient temperature and the self-heating of coil,which affects the control precision of coil current.First,considering the heat dissipation mode of coil,the coil temperature model is established from the perspective of heat conduction,and a temperature compensation algorithm for hydraulic system pressure control is put forward.Then the hardware-in-the-loop testbed is set up by using the dSPACE platform,carrying out wheel cylinder pressurization tests with inlet valve fully opened at-40℃ and 20℃,and testing the actual pressure of wheel cylinder with the target pressures at-40℃ and 6 000 kPa/s(pressurization rate).The results show that the pressure control temperature compensation algorithm proposed in this paper accurately corrects the influence of resistance temperature drift on the response accuracy of wheel cylinder pressure.After the correction,the pressure difference is less than 500 kPa,which can meet the control accuracy requirements of solenoid valve,enriching the linear control characteristic of solenoid valve.

Dissolved Silica Adsorbed onto MnO_2 in Catalyzing the Decomposition of H_2O_2: Molecular Structural Rearrangement Revealed by FTIR,SEM-EDX and XRD

It has been generally unclear over the mechanism of inhibitory influence of silicate on structural rearrangement or solely physical adsorption onto manganese dioxide （MnO2） about the decomposition of hydrogen peroxide （H2O2）. Consequently, several experiments were carried out by using MnO2 as a catalyst for the decomposition of H2O2 in a concentration series under certain concentrations of silicates. The silicates were analyzed by using a molybdenum blue colorimetric method. The results showed that the determination of silicates was inhibited by H2O2, whose inhibitory effect was greatly increased by increasing its concentration, but not limited by pH. SEM-EDX （scanning electron microscopy-energy dispersive x-ray spectrometry） results showed that the adsorption of silicates onto the surface of MnO2 was not purely via a structural rearrangement, with increasing Mn atoms protruding on the outer surface by covering oxygen and silicon atoms. XRD （X-ray diffraction） and FTIR （Fourier transform infrared） spectra results further revealed no significant total crystal structural changes in MnO2 after the adsorption of silicates, but only a small shift of 0.21° at 2e from 56.36° to 56.15° , and a FTIR vibration showed at around 1 050 cm-1. The results, therefore, showed that silicate adsorption onto MnO2 took place via both surface adsorption and structural rearrangement by interfacial reaction.

治理环境与高薪养廉——来自中国上市公司的经验证据

本文利用我国上市公司2009-2015年的数据，在检验企业高管薪酬与高管腐败关系的基础上，重点研究了企业内外部治理环境对这种关系的影响，研究表明：企业高管薪酬与高管腐败正相关，即我国企业高管高薪不能起到养廉的作用，市场化进程和内部控制是有效的外部和内部治理机制，能够抑制高管薪酬与高管腐败之间的正向关系，内部控制的治理效果在国有企业更加明显;市场化进程的治理效果在非国有企业更加明显，党的十八大以来的反腐败斗争有效震慑了国有企业高管的腐败行为，本文为我国企业高管腐败的治理提供了经验证据，可以为企业反腐败工作的持续推进提供借鉴。

Finite element simulation of the micromachining of nanosized-silicon-carbide-particle reinforced composite materials based on the cohesive zone model

A finite element method based on the cohesive zone model was used to study the micromachining process of nanosized silicon-carbide-particle(SiCp) reinforced aluminum matrix composites. As a hierarchical multiscale simulation method, the parameters for the cohesive zone model were obtained from the stress-displacement curves of the molecular dynamics simulation. The model considers the random properties of the siliconcarbide-particle distribution and the interface of bonding between the silicon carbide particles and the matrix.The machining mechanics was analyzed according to the chip morphology, stress distribution, cutting temperature, and cutting force. The simulation results revealed that the random distribution of nanosized SiCp causes non-uniform interaction between the tool and the reinforcement particles. This deformation mechanics leads to inhomogeneous stress distribution and irregular cutting force variation.

Proper Particle Size Range for Resistance to Chemical Oxidation: A Perspective on the Recalcitrance of Beanpod Biochar for Soil Carbon Sequestration

The effect of particle size on the recalcitrance of biochar against oxidation has been regarded as one of the most important factors influencing its stability and transportation in soils. Little is known about the peculiar stability of different particle sizes under chemical oxidation conditions. In this study, several sizes of biochar particles derived from beanpod were produced,and their stabilities were tested by using acid dichromate and hydrogen peroxide. We discovered that the 60-100 mesh size of particles produced at 400 and 500 ℃ showed the least carbon loss under the oxidation of both dichromate and hydrogen peroxide. In addition, this particle size also shows great stability at 600 and 700 ℃, but this stability was not observed below 300 °C for all temperature-dependent biochars. Medium-sized particles composed of exclusively heterogeneous components produced a biochar at temperatures over 400 ℃ with comparatively stronger chemical anti-oxidation characteristics. The chemical recalcitrance of biochar should be reevaluated based on particle size before soil application.

Dynamic Evaluation of Rationality of Land Use Structure in the Changsha-Zhuzhou-Xiangtan Area

The rationality of land use structure was evaluated with dynamic TOPSIS method based on changing data of land use from 2008 to 2011 in the Changsha-Zhuzhou-Xiangtan area. The results showed that during 2008- 2011,the rationality of land use structure was totally high,the dynamic value hi of Changsha,Zhuzhou,Xiangtan and the Changsha-Zhuzhou-Xiangtan area was 0. 7954,0. 7821,0. 8245 and0. 8186,respectively; the value Ci( tk) reflecting the rationality of land use structure at different time points was rapidly increased,and the gap between regions was not big and shrinking. According to the grey relational analysis,the change of different land use types had different effects on the rationality of land use structure: transportation land,the land for cities,towns and villages and the land for mining and industry are most highly correlated with the rationality of land use structure,while arable land,woodland,water area and water conservancy facility land have also an important impact on the rationality of land use structure; controlling the excessive growth of transportation land,the land for cities,towns and villages and the land for mining and industry,protecting arable land,forest land,water area and water conservancy facility land,and moderately increasing the garden plot,plays a decisive role in optimizing the land use structure in the Changsha-Zhuzhou-Xiangtan area.

Challenges and Methods to Improve Well Cementing Quality for 177.8 mm Liner in Gaoshiti-Moxi Area

Gaoshiti-Moxi structure belt of An-Yue Sinian gas reservoir, which was China’s largest monomer Marine carbonate gas reservoir up to now, located in vying-dragon female temple structure group that belong to the ancient uplift slope of the middle of Sichuan. With the exploration and development of high temperature and high pressure carbonate reservoir, a large number of challenges and problems, such as long isolation section, active oil-gas show, large temperature difference, prone to super retarding cement slurry and gas channeling at flare position, have been encountered in the cementing of 177.8 mm hang-liner. In order to solve these problems, numerous measures and methods have been put into use for reducing the safety risk of cementing and improving cementing quality. The large temperature difference channeling cement slurry system, effective anti-pollution spacer and high-pressure packer type liner hanger were developed and applied for field tests in the early stage of development. In addition, equilibrium pressure cementing technology, optimizing of centralizer placement and plasma column structure, improvement of pump displacement and hold pressure while waiting on cement were used to ensure nice displacement efficiency and cementing quality. As Moxi X well for example, the cementing quality factor of merit was 40.29% and the qualification rate was up to 78.87% after adopting the cementing measures and methods above. The cementing quality was much higher than previous level and provided technical support for Gaoshiti-Moxi area.

Optimal Hedging Strategies of Stock Index Futures Based on the Perspective of Information Asymmetry

Based on two different risk measurement criteria, this article studied the optimal hedging strategies of stock index futures in the case of asymmetric information, and discussed the influence of insider information on the hedging effect. Through simulation analysis, it can be shown that hedging people with insider information can save hedging costs to a certain extent, which also explains the reason why investors try to obtain corporate information in actual investment activities.

政企关系、境外直接投资与雇员规模:基于民营上市公司的实证研究

民营企业已经成为我国境外直接投资的主力军。政企关系在民营企业经济管理过程中扮演着重要角色,对民营企业境外直接投资也有重要影响。与此同时,政企关系和境外直接投资都会影响民营企业的雇员行为。基于此,本文以2012-2017年沪深A股上市民营企业为样本,实证检验政企关系对民营企业境外直接投资和雇员规模的影响、境外直接投资对企业雇员规模的影响以及政府对民营企业不同干预目标之间的替代效应。研究结果表明,政企关系会促进民营企业境外直接投资,也会增加雇员规模;境外直接投资行为会扩大民营企业雇员规模;政府对民营企业境外直接投资的干预和对民营企业雇员行为的干预之间存在替代效应。本研究丰富了境外直接投资影响因素方面的文献,回应了社会对境外直接投资就业效应的关切,也拓展了对政府如何影响民营企业行为的理论认识。

下弯管直弯比对新型密排式液-固循环流化床换热器稳定流态化性能的影响

在液-固循环流化床换热器中,两相流流态化流动的稳定性和均匀性不仅反映了换热器防垢除垢效果,还直接影响换热器的换热效率。为了提高流化床换热器的换热效率,探求床层内颗粒流动规律,在传统液-固循环流化床换热器中应用了新型密排式下流化箱结构并完成了稳定运行实验。基于实验结果,对采用计算颗粒流体力学方法(CPFD)模拟的流场分布结果进行有效性对比,实验结果与模拟结果的误差在10%以内,验证了模拟方法的可靠性。采用CPFD方法对下弯管直管段长度与弯曲半径之比进行了优选,下弯管直管段与弯曲半径之比为5:1时,液-固循环流化床换热器的除垢效果最佳,换热效率最高。

Emerging contaminants:A One Health perspective

Environmental pollution is escalating due to rapid global development that often prioritizes human needs over planetary health.Despite global efforts to mitigate legacy pollutants,the continuous introduction of new substances remains a major threat to both people and the planet.In response,global initiatives are focusing on risk assessment and regulation of emerging contaminants,as demonstrated by the ongoing efforts to establish the UN’s Intergovernmental Science-Policy Panel on Chemicals,Waste,and Pollution Prevention.This review identifies the sources and impacts of emerging contaminants on planetary health,emphasizing the importance of adopting a One Health approach.Strategies for monitoring and addressing these pollutants are discussed,underscoring the need for robust and socially equitable environmental policies at both regional and international levels.Urgent actions are needed to transition toward sustainable pollution management practices to safeguard our planet for future generations.

The behaviors of gas-liquid two-phase flow under gas kick during horizontal drilling with oil-based muds

Natural gas is easily soluble in oil-based muds(OBM),leading to complex flow behavior in wellbores,especially in horizontal wells.In this study,a new transient flow model considering wellbore-formation coupling and gas solubility on flow behavior is developed to simulate gas kicks during horizontal drilling with OBM.Furthermore,the effect of gas solubility on parameters such as bottom-hole pressure(BHP),gas void fraction and mixture velocity in the flow behavior is analyzed.Finally,several critical factors affecting flow behavior are investigated and compared to gas kicks in water-based muds(WBM)where the effect of solubility is neglected.The results show that the invading gas exists as dissolved gas in the OBM and as free gas in the WBM.Before the gas escapes from the OBM,the pit gain is zero and there is barely any change in the BHP,annulus return flow rate and mixture velocity,which means that detecting gas kicks through these warning signs can be challenging until they get very close to the surface and develop rapidly.However,in WBM drilling,these parameters change quickly with the increasing gas kick time.Additionally,for both cases,the longer the horizontal length and the greater reservoir permeability,the greater the decrease in BHP,and the shorter the time for gas to migrate from the bottom-hole to the wellhead.A larger flow rate contributes to a greater initial BHP and a lesser BHP reduction.This research is of value in characterizing gas kick behavior and identifying novel ways for early gas kick detection during horizontal drilling with OBM.

Decomposition of Covariate-Dependent Graphical Models with Categorical Data

Graphical models are wildly used to describe conditional dependence relationships among interacting random variables.Among statistical inference problems of a graphical model,one particular interest is utilizing its interaction structure to reduce model complexity.As an important approach to utilizing structural information,decomposition allows a statistical inference problem to be divided into some sub-problems with lower complexities.In this paper,to investigate decomposition of covariate-dependent graphical models,we propose some useful definitions of decomposition of covariate-dependent graphical models with categorical data in the form of contingency tables.Based on such a decomposition,a covariate-dependent graphical model can be split into some sub-models,and the maximum likelihood estimation of this model can be factorized into the maximum likelihood estimations of the sub-models.Moreover,some sufficient and necessary conditions of the proposed definitions of decomposition are studied.