Effect of Model Height and Model Position on Forming Table on Mouthguard Thickness in Thermoforming Using Circular Frame

Effectiveness and safety of mouthguards are greatly affected by its thickness. The aim of this study was to clarify the effect of model height and model position on the forming table on the mouthguard thickness in thermoforming using a circular frame. Mouthguards were thermoformed using 4.0-mm-thick ethylene-vinyl-acetate sheets and a vacuum forming machine. The sheet was sandwiched between circular frames and fixed to the clamp of the forming machine. Working models were two types of hard gypsum models trimmed so that the height of the anterior part was 25 mm (Model A) and 30 mm (Model B). The model was placed with its anterior rim positioned 40 mm (P40), 30 mm (P30), 20 mm (P20), or 10 mm (P10) from the front of the forming table. Differences in the reduction rate of the thickness due to the model height and model positions were analyzed by two-way ANOVA and Bonferroni’s multiple comparison test. Differences depending on the model height were observed at P40 at the incisal edge and P30, P20, and P10 on the labial surface, and the reduction rate of the thickness was significantly smaller in Model A (P < 0.01). As the distance from the model anterior rim to the front of the forming table was smaller, the rate of the thickness of the incisal edge and the labial surface decreases became larger. The rate of decrease in the thickness of the cusp and buccal surface was the smallest at P20. This study indicated that the difference in the thickness of the single-layer mouthguard depending on the model position on the forming table is affected by the model height. However, that is only the anterior part of the mouthguard, and the difference in thickness reduction rate is less than 5%. Additionally, in order to perform stable forming, it is useful to increase the distance from the model to the frame, and it is important to position the part whose thickness is desired to be maintained in the center of the forming table.

SNWPM:A Siamese Network Based Wireless Positioning Model Resilient to Partial Base Stations Unavailable

Artificial intelligence(AI)models are promising to improve the accuracy of wireless positioning systems,particularly in indoor environments where unpredictable radio propagation channel is a great challenge.Although great efforts have been made to explore the effectiveness of different AI models,it is still an open problem whether these models,trained with the data collected from all base stations(BSs),could work when some BSs are unavailable.In this paper,we make the first effort to enhance the generalization ability of AI wireless positioning model to adapt to the scenario where only partial BSs work.Particularly,a Siamese Network based Wireless Positioning Model(SNWPM)is proposed to predict the location of mobile user equipment from channel state information(CSI)collected from 5G BSs.Furthermore,a Feature Aware Attention Module(FAAM)is introduced to reinforce the capability of feature extraction from CSI data.Experiments are conducted on the 2022 Wireless Communication AI Competition(WAIC)dataset.The proposed SNWPM achieves decimeter-level positioning accuracy even if the data of partial BSs are unavailable.Compared with other AI models,the proposed SNWPM can reduce the positioning error by nearly 50%to more than 60%while using less parameters and lower computation resources.

MODELLING THE POLYALANINE BACKBONE STARTING FROM ALPHA-CARBON GUIDE POSITIONS

An automatic procedure for building a protein polyalanine backbone from guiding alpha-carbon positions is presented here,which is different from a previously developed'spare parts'approach(Jones and Thirup,1986;Claessens et al.,1989). In our procedure,the geometric restraint of angle N-CA-C is used to generate a list of polypeptide chains,and several filters are used later to select the best conformer.The most important filter is based upon the Ramachandran scatter plot of mainchain dihedral angles PHI and PSI.Results for all test cases are satisfactory,with more than 95%of peptide planes correctly reconstructed and the overall root-mean-square deviation less than 0.5 angstrom compared with the refined X-ray coordinates.

Coupled Dynamics and Integrated Control for Position and Attitude Motions of Spacecraft:A Survey

Inspired by the integrated guidance and control design for endo-atmospheric aircraft,the integrated position and attitude control of spacecraft has attracted increasing attention and gradually induced a wide variety of study results in last over two decades,fully incorporating control requirements and actuator characteristics of space missions.This paper presents a novel and comprehensive survey to the coupled position and attitude motions of spacecraft from the perspective of dynamics and control.To this end,a systematic analysis is firstly conducted in details to show the position and attitude mutual couplings of spacecraft.Particularly,in terms of the time discrepancy between spacecraft position and attitude motions,space missions can be categorized into two types:space proximity operation and space orbital maneuver.Based on this classification,the studies on the coupled dynamic modeling and the integrated control design for position and attitude motions of spacecraft are sequentially summarized and analyzed.On the one hand,various coupled position and dynamic formulations of spacecraft based on various mathematical tools are reviewed and compared from five aspects,including mission applicability,modeling simplicity,physical clearance,information matching and expansibility.On the other hand,the development of the integrated position and attitude control of spacecraft is analyzed for two space missions,and especially,five distinctive development trends are captured for space operation missions.Finally,insightful prospects on future development of the integrated position and attitude control technology of spacecraft are proposed,pointing out current primary technical issues and possible feasible solutions.

Multi-model assessment of glacio-hydrological changes in central Karakoram, Pakistan

The multi-model assessment of glacio-hydrological regimes can enhance our understanding of glacier response to climate change.This improved knowledge can uplift our computing abilities to estimate the contributing components of the river discharge.This study examined and compared the hydrological responses in the glacier-dominated Shigar River basin(SRB)under various climatic scenarios using a semi-distributed Modified Positive Degree Day Model(MPDDM)and a distributed Glacio-hydrological Degree-day Model(GDM).Both glacio-hydrological models were calibrated and validated against the observed hydro-meteorological data from 1988–1992 and 1993–1997.Temperature and precipitation data from Shigar and Skardu meteorological stations were used along with field estimated degree-day factor,temperature,and precipitation gradients.The results from both models indicate that the snow and ice melt are vital contributors to sustain river flow in the catchment.However,MPDDM estimated 68%of rain and baseflow contribution to annual river runoff despite low precipitation during the summer monsoon,while GDM estimated 14%rain and baseflow contribution.Likewise,MPDDM calculated 32%,and GDM generated 86%of the annual river runoff from snow and ice melt.MPDDM simulated river discharge with 0.86 and 0.78 NSE for calibration and validation,respectively.Similarly,GDM simulated river discharge with improved accuracy of 0.87 for calibration and 0.84 NSE for the validation period.The snow and ice melt is significant in sustaining river flow in the SRB,and substantial changes in melt characteristics of snow and ice are expected to have severe consequences on seasonal water availability.Based on the sensitivity analysis,both models’outputs are highly sensitive to the variation in temperature.Furthermore,compared to MPDDM,GDM simulated considerable variation in the river discharge in climate scenarios,RCP4.5 and 8.5,mainly due to the higher sensitivity of GDM model outputs to temperature change.The integration of an updated melt module and two reservoir baseflow module in GDM is anticipated to advance the representation of hydrological components,unlike one reservoir baseflow module used separately in MPDDM.The restructured melt and baseflow modules in GDM have fundamentally enriched our perception of glacio-hydrological dynamics in the catchment.

基于导轨相关性的定位器误差模型分析与改进

飞机数字化装配中三坐标定位器的定位精度直接影响部件间的装配精度,提出一种改进的误差补偿模型以提高其定位精度。通过分析定位器堆栈式结构和导轨间相关性,改进各轴运动方向上的角误差模型;基于导轨相关性的误差、滚珠丝杠导程精度误差和轴向进给误差,建立改进后的定位器综合误差模型;进行传统误差补偿模型与改进误差补偿模型的对比实验。实验结果表明,基于导轨相关性改进的误差补偿模型与传统误差补偿相比,空间误差补偿效果的最大值可提高28.07%,均值可提高14.09%,有效提高了误差补偿效果以及飞机数字化装配的精度。

基于分层误差补偿的飞机柔性工装定位精度提高方法

飞机柔性工装中三坐标定位器的定位精度直接影响飞机大部件间的装配精度。提出了一种分层误差补偿模型以提高其定位精度,首先对定位器堆栈式结构和导轨间相关性进行分析,改进各轴运动方向上的角误差,提高整体线性误差补偿精度;然后采用遗传算法优化的神经网络对线性补偿后误差较大的位置点进行非线性误差补偿;最后将线性模型和非线性模型结合,提出了分层误差补偿模型,并进行了传统误差补偿模型和分层误差补偿模型的对比实验。实验结果表明,分层误差补偿模型与传统误差补偿模型相比,空间误差补偿效果最大可提高58.09%、均值可提高46.92%,有效地改善了误差补偿效果,提高了飞机数字化装配的精度。

基于dSPACE的压电定位器迟滞非线性实验平台设计

为加强学生对非线性问题的认识与理解,设计了一套基于dSPACE的压电陶瓷纳米定位器迟滞非线性半实物仿真实验平台。首先,详细介绍了实验平台的组成;其次,基于实验平台采集压电定位器的迟滞非线性数据,并应用一般最小二乘法辨识得到Prandtl-Ishlinskii模型,进而应用解析法得到PI逆模型;最后,在前馈通路上串联压电定位器的PI逆模型以补偿其迟滞非线性特性,从而将非线性系统转为伪线性系统。学生在实验过程中不仅可以加深对非线性特性以及逆系统法的理解,还可以通过参数辨识法以及逆补偿法切实解决一类智能材料的迟滞非线性问题,提高学生将理论知识与工程实践相结合的能力,培养自动化专业学生解决复杂工程问题的能力。

变位焊接机器人系统的运动建模及分析

研究变位焊接机器人系统的同步协调运动的实现。在SolidWorks2010软件中建立了该机器人系统模型,同时给出了其同步协调运动的算法和实现步骤;以半球面空间螺旋曲线为焊接路径,对机器人与变位机的同步协调运动进行仿真分析,发现焊枪末端能够以较高精度和较好位姿跟踪该焊缝曲线,为变位焊接机器人系统的同步协调运动的实现提供了理论依据。

教育与主观社会地位——基于地位寻求理论的实证分析

教育不仅能提升个人社会地位,而且对家庭的社会地位亦有不可小觑的作用。因此,近些年中国家庭子女教育支出的攀比趋势越发明显。采用中国家庭追踪调查数据2010、2012、2014年数据,对面板有序Probit模型进行估计,结果表明:个人受教育年限对个人主观社会地位具有正向显著影响;参照组平均教育年限对个人主观社会地位具有负向显著影响;个人教育年限的交互项对个人主观社会地位具有正向作用,表明教育水平越高,越不易受到社会比较的负面影响。研究证实了教育的位置性特征对主观社会地位具有显著影响。

基于模糊Smith控制的智能阀门定位器

针对工业调节阀中广泛存在的时滞现象,提出一种基于模糊原理的带有Smith预估器的智能阀门定位器控制方法。分析智能阀门定位器的结构和原理,通过设计Smith预估器补偿滞后时间,实现超前响应,克服时滞对系统性能的影响;通过模糊控制与PID控制结合,设计调整模糊规则,实现控制器参数的自整定。两者结合构成模糊Smith方法,提高了系统的动静态性能。模糊内模控制器对克服时滞、提高系统性能有良好的效果,将模糊Smith器与模糊内模控制器及PID控制器进行仿真研究对比。仿真结果表明,模糊Smith控制方法比模糊内模控制方法和传统PID方法更能有效地提高调节阀的快速性,克服时滞,改善系统性能。

阀体密封面变位焊接机器人系统运动学建模

为了获得与时间序列相对应的离散焊点位姿,以更易于求得焊枪—焊点间的相对位姿,提出基于弗莱那—雪列矢量理论的曲线焊缝中离散焊点的位姿求解及焊缝坐标系构建方法。基于变位机—机器人主、从运动链末端的耦合约束关系,提出以船型焊为最佳焊位时的协同焊接运动学模型及参数求解流程,据此求得协同焊接过程中机器人和变位机的关节转角、角速度和角加速度。变位机—机器人协同焊接阀体密封面的运动仿真和现场实验表明,该系统能够平稳、准确地完成预期的焊接任务,证实了所提协同焊接运动学模型及参数求解方法正确可行,为研发自动化焊接生产线奠定了必要的基础。

Mouthguard Thermoforming Method to Decrease Palatal Thickness While Maintaining Labial and Buccal Thickness

Wearing a mouthguard reduces the risk of sports-related injuries, but a more comfortable design is required in order to increase the wearing rate. The aim of this study was to investigate a thermoforming method that decreases palatal thickness while maintaining labial and buccal thickness. Mouthguards were fabricated from an ethylene-vinyl acetate sheet (thickness: 4.0 mm) by using a vacuum forming machine. Four working models were prepared: 1) the anterior height was 25-mm and the posterior height was 20-mm (model A), 2) model A with the palate trimmed (model B), 3) heights 5 mm greater than model A (model C), and 4) model C with the palate trimmed (model D). The two forming conditions were as follows: 1) The sheet was formed when it sagged 15 mm below the level of the sheet frame at the top of the post under ordinary use (control);2) The sheet frame at the top of the post was lowered and the sheet covered the model when it sagged by 15 mm. The rear side of the model was pushed to move the model forward 20 mm, and then the sheet was formed (MP). Differences in mouthguard thickness due to forming conditions and model forms were analyzed by two-way analysis of variance and Bonferroni’s multiple comparison tests. Difference in forming conditions was similar for all model forms;for the MP, the thickness of the incisal edge, labial surface, cusp and buccal surface were greater, and the palatal surface was thinner than the control. On the labial and buccal surface, the thickness difference due to the model form was observed only for the MP, and models A and B were thicker than models C and D. The palatal thickness tended to be thin in the models with the trimmed palate. This study suggested that the labial and buccal thickness of the mouthguard can be maintained, and the palatal thickness can be decreased by using the model with the palate trimmed with the forming method in which the model position is moved forward immediately before the vacuum formation.

四轮定位仪主销倾角检定模型及可靠性分析

针对目前汽车四轮定位仪检定装置在检定过程中无法准确检定主销倾角的问题,基于空间几何分析,建立了四轮定位仪主销倾角检定数学模型。通过对模型空间几何关系的分析推导,验证了检定主销倾角的原理,并研制了基于多自由度空间正切机构的新型全自动四轮定位仪主销倾角检定装置。该装置采用了球铰底座和杆端关节轴承,能够独立完成主销后倾和主销内倾的调整,从原理上消除了主销合成运动所造成的运动误差。考虑运动副间隙,对检定装置进行了运动可靠性分析研究,建立了检定机构的非连续接触可靠性分析模型,分析并推算出了考虑倾角输出偏差的检定机构倾角输出偏差的方差公式。对装置进行了主销后倾角和主销内倾角检测,结果符合国标要求的精度。该设计为后续的四轮定位仪检定装置的设计提供了一定的借鉴。

Temperature-dependent bias-stress-induced electrical instability of amorphous indium-gallium-zinc-oxide thin-film transistors

The time and temperature dependence of threshold voltage shift under positive-bias stress（PBS） and the following recovery process are investigated in amorphous indium-gallium-zinc-oxide（a-IGZO） thin-film transistors. It is found that the time dependence of threshold voltage shift can be well described by a stretched exponential equation in which the time constant τ is found to be temperature dependent. Based on Arrhenius plots, an average effective energy barrier Eτ stress= 0.72 eV for the PBS process and an average effective energy barrier Eτ recovery= 0.58 eV for the recovery process are extracted respectively. A charge trapping/detrapping model is used to explain the threshold voltage shift in both the PBS and the recovery process. The influence of gate bias stress on transistor performance is one of the most critical issues for practical device development.

国产300MW机组摆动燃烧器控制系统的改进

张家口发电厂5号锅炉改造摆动燃烧器,通过实验建模的方法得出了摆动燃烧器调节再热汽温的对象特性,同时还介绍了该系统的控制策略和现场控制系统,并运用MATLAB软件对控制参数进行了优化。

Analysis of thermal-mechanical coupled characteristics of vehicle twin-tube shock absorber

A comprehensive model that included mechanical dynamics of the shock absorber coupled with its thermal properties was proposed innovatively.Moreover a thermal-mechanical coupled model which reflected the closed-loop positive feedback system was established by using MATLAB/SIMULINK,and some curves of shock absorber temperature rising characteristic were obtained by simulation ＆computation under several operating modes and different parameters conditions.Research results show that：shock absorber design parameters,external excitations,and thermo-physical properties parameter,such as oil density have effect on the shock absorber temperature rising characteristic.However other thermo-physical properties parameters,such as oil specific heat,cylinder density,cylinder specific heat,and cylinder thermal conductivity,have no effect on it.The results may be used for studying reliability design of the shock absorber.

智能电气阀门系统先进PID控制器

作为调节阀核心部件的智能阀门定位控制器,在工业控制领域得到广泛的应用。文章通过研究电动调节阀门定位器的结构组成与控制原理,并结合工业控制过程中对阀门定位器的要求,分别在软件与硬件上对阀门定位器进行优化,从而实现低功耗与精准定位的目的,同时提出了一种基于模糊PID控制方法,使得系统的调节时间更短、超调量更小、抗干扰性更强。仿真实验表明模糊PID控制比常规的PID控制更为优越。

Source apportionment and suitability evaluation of seasonal VOCs contaminants in the soil around a typical refining-chemical integration park in China

Accurate source apportionment of volatile organic compounds(VOCs)in soil nearby petrochemical industries prevailing globally,is critical for preventing pollution.However,in the process,seasonal effect on contamination pathways and accumulation of soil VOCs is often neglected.Herein,Yanshan Refining-Chemical Integration Park,including a carpet,refining,synthetic rubber,and two synthetic resin zones,was selected for traceability.Season variations resulted in a gradual decrease of 31 VOCs in soil from winter to summer.A method of dry deposition resistance model coupling partitioning coefficient model was created,revealing that dry deposition by gas phase was the primary pathway for VOCs to enter soil in winter and spring,with 100 times higher fux than by particle phase.Source profiles for five zones were built by gas sampling with distinct substance indicators screened,which were used for positive matrix factorization factors determination.Contributions of the five zones were 14.9%,20.8%,13.6%,22.1%,and 28.6%in winter and 33.4%,12.5%,10.7%,24.9%,and 18.5%in spring,respectively.The variation in the soil sorption capacity of VOCs causes inter-seasonal differences in contribution.The better correlation between dry deposition capacity and soil storage of VOCs made root mean square and mean absolute errors decrease averagely by 8.8%and 5.5%in winter compared to spring.This study provides new perspectives and methods for the source apportionment of soil VOCs contamination in industrial sites.

Numerical Study on Comparison of Negative and Positive Surface Discharge in c-C_(4)F_(8)/CF_(3)I/CO_(2) Gas Mixture

The dynamics of negative surface discharges in c-C_(4)F_(8)/CF_(3)I/CO_(2) gas mixture is investigated here with a 2D fuid model.The distributions of ion concentration,electric field strength and photon flux during the propagation of the streamer are obtained by solving the drift-diffusion equations of particles and Poisson's equation,and the photon flux variation function during the propagation is also fitted.It is found that the streamer branches occur when the streamer transitions from the upper surface of the insulator to the side surface,and then when the streamer approaches the plane electrode,the photon flux will increase significantly.On this basis,the positive and negative surface discharge models are compared in terms of streamer characteristics,particle characteristics and streamer branches.It is found that the streamer has a higher electron concentration and electric field in the positive model.The streamer develops“floating”in the positive surface discharge,while it is close to the surface of the insulator in the negative model.In addition,the negative streamer branch has a wider width and develops further.