Individualization of Data-Segment-Related Parameters for Improvement of EEG Signal Classification in Brain-Computer Interface

In electroencephalogram (EEG) modeling techniques, data segment selection is the first and still an important step. The influence of a set of data-segment-related parameters on feature extraction and classification in an EEG-based brain-computer interface (BCI) was studied. An auto search algorithm was developed to study four datasegment-related parameters in each trial of 12 subjects’ EEG. The length of data segment (LDS), the start position of data (SPD) segment, AR order, and number of trials (NT) were used to build the model. The study showed that, compared with the classification ratio (CR) without parameter selection, the CR was increased by 20% to 30% with proper selection of these data-segment-related parameters, and the optimum parameter values were subject-dependent. This suggests that the data-segment-related parameters should be individualized when building models for BCI.

Effects of thermodynamics parameters on mass transfer of volatile pollutants at air-water interface

A transient three-dimensional coupling model based on the compressible volume of fluid （VOF） method was developed to simulate the transport of volatile pollutants at the air-water interface. VOF is a numerical technique for locating and tracking the free surface of water flow. The relationships between Henry＇s constant, thermodynamics parameters, and the enlarged topological index were proposed for nonstandard conditions. A series of experiments and numerical simulations were performed to study the transport of benzene and carbinol. The simulation results agreed with the experimental results. Temperature had no effect on mass transfer of pollutants with low transfer free energy and high Henry＇s constant. The temporal and spatial distribution of pollutants with high transfer free energy and low Henry＇s constant was affected by temperature. The total enthalpy and total transfer free energy increased significantly with temperature, with significant fluctuations at low temperatures. The total enthalpy and total transfer free energy increased steadily without fluctuation at high temperatures.

Design principle for parameters and interferences of tungsten carbide insert interface on roller bits

The lifetime of roll-bits with inserted tooth will be obviously decreased while drilling in strata and the tungsten carbide can be integrally separated from the roll-cone,which will need more trip out time to replace the roller bit.This study provides an entire analysis on stress as well as strength for teeth and tooth holes in loaded conditions.Qualities of tooth drop from matrix within roller bit.The optimized interferences of teeth inserted into the bit can be reasonably obtained by the critical interference derived from some relevant influence factors on the tooth-fixing quality of roller bits.

Effects of interface parameters on the transport properties of nanocomposites

This study introduces a continuum medium approximation(CMA)and an empirical effective medium approxi-mation(EMA)-type formulation to estimate the transport properties,including electrical conductivity,thermal conductivity,Seebeck coefficient,and Hall mobility,of nanostructured composites.The CMA incorporates the interface parameters mediated by newly introduced distribution functions to resolve predictions that deviate from the inclusion properties at its volume fraction of 1 in current EMAs and yields predictions agreed well with both the empirical EMA and experimental data.The empirical EMA-type formulation resolves the differ-ences in CMA predictions for the media A_(1-x)B_(x)and B_(1-x)A_(x)and provides a unique prediction that agrees very well with experimental data at a given volume fraction ranging from 0 to 1.The effects of the interface param-eters on the transport properties were investigated.The results indicated that the efficiency of nanostructured composites could be further improved by optimizing the interface parameters.

Experimental study on the shear behavior of grout-infilled specimens and micromechanical properties of grout-rock interface

The grout-rock interfacial property is one of the key factors associated with the strength of grouted rock masses.In this study,direct shear tests and nanoindentation tests were adopted to investigate the mechanical properties of the grout-rock interface at both the macroscale and microscale.The cohesion of the cement specimens was higher than that of the grout-infilled joint specimens,while their internal friction angle was lower than that of the grout-infilled joint specimens.A“separation method”for identifying the different phases according to the qualitative and quantitative estimations was introduced,and the irregular interfacial transition zone(ITZ)thickness and elastic modulus were estimated.The ITZ thickness of the grout-infilled sandstone specimen ranged from 0 to 30μm,whereas it was within the range of 10-40μm for the grout-infilled mudstone specimen.The average elastic modulus of the ITZ in grout-infilled sandstone and mudstone specimens was approximately 58.2%and 54.1%lower than that of the bulk grout,respectively.Regarding the incidence of the rock type,the interlacing between the grout and sandstone was better developed.The ITZ with a higher porosity and lower modulus had a significant effect on the mechanical properties of the grout-infilled specimens.

Improved efficiency and stability of perovskite solar cells with molecular ameliorating of ZnO nanorod/perovskite interface and Mg-doping ZnO

Despite the advanced efficiency of perovskite solar cells(PSCs),electron transportation is still a pending issue.Here the polymer polyvinylpyrrolidone(PVP)is used to enhance the electron injection,which is thanks to the passivation of the defects at the interface between the ZnO electron transporting layer(ETL)and the perovskite.The application of the PVP layer inhibits the device degradation,and 80%of the primary efficiency is kept after 30 d storage in air condition.Additionally,the efficiency of the device is further enhanced by improving the conductivity and crystallinity of the ZnO ETL via Magnesium(Mg)doping in the ZnO nanorods(ZnO NRs).Moreover,the preparation parameters of the ZnO NRs are optimized.By employing the high-crystallinity ZnO ETL and the PVP layer,the power conversion efficiency(PCE)of the champion device is increased from 16.29%to 19.63%.These results demonstrate the advantages of combining mesoscale manipulation with interface modification and doping together.

Elastic-viscoplastic field at mixed-mode interface crack-tip under compression and shear

For a compression-shear mixed mode interface crack, it is difficult to solve the stress and strain fields considering the material viscosity, the crack-tip singularity, the frictional effect, and the mixed loading level. In this paper, a mechanical model of the dynamic propagation interface crack for the compression-shear mixed mode is proposed using an elastic-viscoplastic constitutive model. The governing equations of propagation crack interface at the crack-tip are given. The numerical analysis is performed for the interface crack of the compression-shear mixed mode by introducing a displacement function and some boundary conditions. The distributed regularities of stress field of the interface crack-tip are discussed with several special parameters. The final results show that the viscosity effect and the frictional contact effect on the crack surface and the mixed-load parameter are important factors in studying the mixed mode interface crack- tip fields. These fields are controlled by the viscosity coefficient, the Mach number, and the singularity exponent.

Investigation of radiation influences on electrical parameters of 4H-SiC VDMOS

The radiation influences on electrical parameters of4H-SiC vertical double-implanted metal-oxide-semiconductor field effect transistor( VDMOS) are studied. By simulations on SRIM software and SILVACO software, the electrical parameters shifts of the device with defects in different regions are observed. The results indicate that the defects in different regions induced by radiations lead to different degradations of the electrical parameters. Non-ionization bulk defects in the JFET region make the drain-source on-state resistance Rdson increase,and those near the impact ionization center make the breakdown voltage Vbreakdownincrease. Moreover,the radiationinduced SiC/SiO2 interface defects,known as negative interface charges or positive interface charges,influence the electrical parameters significantly as well. The positive interface charges along the SiC/SiO2 interface above the channel region lead to a decrease in threshold voltage Vth,Rdsonand Vbreakdown,while positive interface charges along the Si C/Metal interface above the main junction of the terminal only leads to the decrease in Vbreakdown. The negative interface charges along the SiC/SiO2 interface above the channel region can make Vth,Rdsonand Vbreakdownincrease.

A simplified method for the determination of vertically loaded pile-soil interface parameters in layered soil based on FLAC3D

The numerical analysis of pile-soil interaction commonly requires a lot of trial works to determine the interface parameters and the accuracy cannot be ensured normally. Considering this, this paper first conducts a sensitivity analysis to figure out the influence of interface parameters on the bearing behavior of a single pile in sand. Then, a simplified method for the determination of pile-soil interface parameters in layered soil is proposed based on the parameter studies. Finally, a filed loading test is used for the validation of the simplified method, and the calculated results agree well with the monitoring data. In general, the simplified method proposed in this paper works with higher accuracy and consumes less time compared with the traditional trial works, especially on the determinations ofinterfacial cohesive and interracial friction angle.

A novel interfacial thermodynamic model for predicting solubility of nanoparticles coated by stabilizers

To improve the stability of nanoparticles in aqueous solution,polymer or surfactant,etc.are often added in solutions during the preparation process of nanoparticles,which can induce new interfaces that influence the solubility of nanoparticles.In this work,a novel interfacial thermodynamic model for describing the Gibbs energy of the nanoparticles coated by stabilizers was proposed to predict the solubility of nanoparticles.Within the developed model,the activity coefficient of nano metal system was determined by Davies model and that of nano drug system by Perturbed-Chain Statistical Associating Fluid Theory(PC-SAFT).The Gibbs energy of the interface was established as a function of molecular parameters via the application for nano metal system.Furthermore,the model was further used to predict the solubility of nano drugs itraconazole,fenofibrate,and griseofulvin.It was found that the Gibbs energy of the interface plays an important role especially when the radius of nano metal is less than 40 nm,and the developed model can predict the solubility of nano drug with high accuracy in comparison with the experimental data as well as predict the changing trend of solubility of nano drugs that increases as the particle size decreases.Meanwhile,the stabilization mechanism of stabilizers on nano drugs was studied which provided theoretical guidance for the selection of polymer or surfactant stabilizer.These findings showed that the developed model can provide a reliable prediction of the solubility of nanoparticles and help to comprehend the stabilization mechanism of the stabilizers on nano drugs with different particle sizes,which is expected to provide important information for the design of nano drugs formulations.

Effect of parameters on interface of the brazed ZrO_2 ceramic and Ti-6Al-4V joint using Ti-based amorphous filler

A commercially available Ti47Zr2sCu14Nin （at. pct） amorphous filler foil was used to join ZrO2 ceramic and Ti-6A1-4V alloy. According to experimental observations, the interface microstructure accounts for the mechanical properties of the joints. The effects of brazing conditions and parameters on the joint properties were investigated. The joint shear strength showed the highest value of about 108 MPa and did not monotonously increase with the brazing time increasing. It was shown that decreasing of brazing cooling rate and appropriate filler foil thickness gave higher joint strength.

液滴碰撞超疏水表面上附着不相溶液滴机理研究

以数值模拟为主要手段对液滴碰撞超疏水表面上附着不相溶液滴演变过程及内在机理进行了系统性的研究工作。首先,发掘出附着模式、弹开Ⅰ模式以及弹开Ⅱ模式等三种液滴碰撞的典型演变模式;其次,从能量角度揭示了Weber数(We)、Bond数(Bo)以及Ohnesorg数(Oh)等无量纲参数对于液滴碰撞动力学行为的影响规律;最后,建立了液滴碰撞典型演变模式与We、Bo、Oh等无量纲参数的依赖关系图谱。结果表明:碰撞液滴之间的能量传递、转换以及黏性耗散直接影响液滴碰撞的动力学行为;随着Oh的减小、Bo的减小以及We的增大,液滴碰撞典型演变模式出现从附着模式到弹开模式的转捩;We-Oh对液滴碰撞典型演变模式的影响规律与We-Bo近乎一致。

装配工艺参数对止口螺栓连接结构力学特性的影响分析

以航空发动机转子系统中止口螺栓连接结构为研究对象,基于单螺栓连接结构分析弯曲刚度的非线性特征,利用ANSYS实体单元建模方法分析连接结构的弯曲刚度,重点讨论了有无止口连接、预紧力、螺栓直径、止口过盈量等装配工艺参数对连接结构弯曲刚度的影响规律,并分析了止口连接结构对转子系统固有特性的影响.研究结果表明:止口连接结构的弯曲刚度呈现分段特性;增大预紧力、螺栓直径以及止口过盈量能提高连接结构弯曲刚度;有无止口连接结构的转子系统前三阶固有频率的相对误差小于2%,止口连接结构能够降低转子系统的最大振动幅值.

短时冻融条件下残积土与冻融界面抗剪强度衰减规律对比分析

为了分析短时冻融对浅层边坡稳定性造成的影响,揭示短时冻融条件下残积土和冻融界面抗剪强度损伤规律,通过盐水降低冰点实现冻融界面,进行不同冻融条件下快剪试验。试验结果表明:冻融主要损伤发生在前3次冻融循环过程中,含水率为21.5%时损伤最大,残积土和冻融界面的黏聚力损伤分别为41%和22%,内摩擦角为14%和10%,约占趋于稳定时的85%。黏聚力的损伤程度大于内摩擦角,且随含水率的增大而增大。冻融循环对残积土和冻融界面的强度及强度指标的影响差异随含水率增大、循环次数增加、冷端温度增大而增大。冻融作用对残积土的强度指标损伤程度均较冻融界面大,且强度指标均随着冻融次数增多呈指数衰减趋势。

碾压混凝土分层碾压离散元模拟及施工成层细观机理研究

碾压混凝土(RCC)坝特有的大仓面分层碾压工艺带来的层间结合质量问题,是影响其安全运行的重要因素。从施工控制的角度分析RCC施工成层机理,进而合理调整碾压参数,可有效保证大坝的施工质量。首先,通过RCC分层碾压试验,分析了碾压过程中含层面RCC的沉降规律、压实度及抗剪强度,为后续离散元模拟提供了基础;然后,建立并验证了RCC双层碾压与抗剪试验离散元模型;最后,给出了表征层间结合质量的骨料嵌入值指标,进而从孔隙率、层间骨料嵌入、层面应力分布、层间抗剪强度等方面分析了RCC施工成层的细观机理。结果表明:碾压参数对RCC的嵌入值、压实特性、层面应力和层间结合质量均有一定影响;嵌入值是影响层间抗剪强度的重要因素,二者呈线性相关,嵌入值每增加1 mm,模拟抗剪强度约增加1.583 MPa;激振力的增加以及行进速度、碾压厚度的减小均有利于提高层间结合质量,且碾压厚度是影响层间结合质量的最敏感参数。研究结果可为施工中RCC层间结合质量控制标准的制定提供理论依据。

新旧混凝土结合面剪切强度参数分析和计算研究

新旧混凝土结合面的抗剪强度是装配式混凝土结构和混凝土结构加固等领域重点关注的问题.基于搜集、整理的新旧混凝土结合面(以下简称结合面)的剪切试验数据库(含439个试件),对GB 50010―2010、ACI 318―19、Eurocode 2、PCI7th四个规范所给结合面抗剪建议计算式进行对比分析.结果表明:在各参数的影响下,ACI结果的保证率表现最好,而Eurocode 2计算强度的拟合效果最好;在结合面宽度达到300~400 mm时,GB 50010―2010的表现最好,但安全富余均较低,相对误差最大达到9倍.对数据库进行参数分析,发现结合面剪切强度τ_(exp)存在尺寸效应,与结合面的沿剪切方向尺寸关联较大;且τ_(exp)与夹紧力ρfy有较好的相关性.基于分析结果,根据叠加计算理论,对计算式提出建议和修正:分析引入尺寸效应系数β;同时修正了摩擦系数μ;应用了数据库拟合的销栓力分段函数,极大值为6.6 MPa.经对比验算证明,修正计算式在有无插筋及各种粗糙度情况下的误差最小,拟合效果最好,可为工程应用提供参考.

连续排水边界下考虑指数渗流的软土一维非线性固结分析

为研究考虑边界排水的时效特性、变荷载、非达西渗流以及土体非线性特性的饱和软土固结问题,通过引入连续排水边界,建立考虑指数渗流和土体非线性的固结方程。利用有限差分法得到变荷载及瞬时荷载下基于连续排水边界考虑指数渗流的软土一维非线性固结解答,通过渗流形式退化和边界退化的方法,将所得解答与达西渗流下的解答及传统排水边界下的解答对比验证了该文差分法解答的可靠性。基于所得解答,详细分析了界面参数、指数渗流及土体非线性等因素对固结特性的影响。结果表明:界面参数取值越大则边界排水能力越大,边界排水性能较差时提高界面参数取值能有效提高边界排水能力;边界排水性能主要影响土体固结前期,而指数渗流主要影响固结后期;实际工程中如果关注固结的整个过程,则需要考虑边界排水性能的影响,但如果只关注固结后期的沉降值,则可忽略边界排水性能的影响。

应用微波网络分析的界面刚度超声检测研究

界面刚度是表征装配结构性能的重要参数,作为常见的无损检测方式,超声检测被广泛应用于界面刚度检测,但现有界面刚度超声检测仍存在一定不足。对现有实验方法进行改良,在传统超声检测理论基础上,将微波网络分析从电磁波领域迁移到超声波领域,将“场”理论与“路”理论相结合,通过检测微波网络分析仪S参数表征界面刚度,并与软件有限元仿真和传统超声检测实验结果进行对比,对界面刚度进行检测与评价。研究显示,相比于传统超声检测,使用微波网络S参数表征接触界面刚度时,检测方法简化实验流程,且检测结果更符合实际接触情况。微波网络分析与超声检测相结合的检测方法在重大装备关键装配界面接触情况测试中具有重要应用前景。

固体推进剂黏弹性参数的确定及细观损伤演化

固体推进剂力学模型参数的准确性对其宏观力学响应预测具有重要的意义,为解耦标定固体推进剂非线性黏弹性模型参数,提出一种基于台阶应力松弛试验的模型参数确定方法。通过台阶应力松弛平衡响应确定固体推进剂弹性部分参数,通过小变形下的应力松弛确定无量纲松弛模量,分析一种固体推进剂力学响应。研究结果表明:固体推进剂在台阶应力松弛及单轴拉伸条件下的力学性能预测结果与试验结果吻合,验证了所提方法的有效性;由于平衡响应包含损伤,采用该方法标定的参数可用于预测含损伤固体推进剂力学响应。在此基础上,提出一种基于推进剂模型参数标定等效黏合剂力学参数的方法,并通过引入基于黏弹性脱湿准则的相界面模型建立代表性体积单元计算模型,实现在宽应变(~100%)范围内推进剂脱湿损伤分析,为推进剂宏观力学性能预测及细观损伤演化分析提供了支撑。

50 Gbit/s前传光模块关键技术研究与应用展望

随着全球5G网络的规模化商用及移动互联网流量的迅猛增长,更为丰富的无线频谱资源得以释放,高速率光模块在无线前传网络中的需求日益凸显。聚焦于50 Gbit/s前传光模块的关键技术,深入剖析了前传网络的两种主要组网方式,分析了前传链路的典型传输距离及链路损耗情况,探讨了10 km场景下粗波分复用(coarse wavelength division multiplex,CWDM)中各波长的最大色散值和最小色散值,并研究了相应的色散补偿策略,通过实验验证了不同多径干扰(multi-path interference,MPI)强度下系统光功率代价的变化,详细分析了多径干扰噪声对系统误码性能的潜在影响,为前传光模块参数的优化提供了重要的理论依据。此外,深入研究了50 Gbit/s前传光模块的光电芯片技术方案,对多种不同类型光模块的参数性能进行了严格的测试,提出了针对50 Gbit/s前传光模块光电接口参数的标准化建议,详细介绍了当前50 Gbit/s前传光模块在国内外的标准现状,并展望了未来应用的发展趋势。