我国大豆生产波动动因分析——基于省际面板模型的实证研究

在我国大豆生产波动频繁的情况下,找出影响大豆单产、种植面积的影响因素是实现“提单产、稳面积”的首要举措。研究采用1999~2020年21个省份面板数据,在分析大豆单产、种植面积的变化趋势基础上,根据大豆单产增减趋势,把大豆产区划分成增产区、减产区和波动区,采用改进的面板数据模型分别对三个产区的大豆单产和种植面积的影响因素进行实证分析。结果表明,机械化收割、产研结合、农药投入、小型拖拉机的投入是影响不同区域大豆单产的显著因素;机械化耕作是提升所有区域种植面积的显著因素,玉米种植面积、化肥投入、农药投入、灌溉条件、科研资金与人员投入、产研结合、机械化收割是影响不同区域大豆种植面积显著因素。根据分析,提出了相应政策建议。

曲面分型多方位斜向抽芯注塑模设计

针对滑块盖板曲面分型面,三维空间6方位斜向侧向抽芯的结构难点,提出了斜抽芯方向与主开模方向一致的减少斜抽芯数量的方法,成功将6方位斜向侧向抽芯简化为4方位斜向侧向抽芯。设计了T型块内侧斜向抽芯机构、斜导柱外侧斜向抽芯机构。为配合二次抽芯,模具采用动模一侧二次分型。为完成二次分型,设计了顺序定距分型机构和推出机构随行机构。经试模,该模具工作可靠,满足实际要求。

尾部倾斜的电池下壳注塑模设计

分析了尾部倾斜的电池下壳塑件的工艺特点,介绍了该塑件注塑模的结构设计和工作过程。根据塑件的外观质量要求,在塑件的非外观面设置点浇口进胶方式,从而避免了在塑件的外表面留下浇注痕迹;为使浇注系统凝料在开模后留在前模侧,采用非标的延伸式唧嘴和前模拉料销拉住凝料;为解决尾部末端细小结构采用镶件成型脱模困难的问题,采用在前模侧设置三组铲基滑块机构成型;塑件的内部扣位通过设置斜顶成型;脱模系统采用顶针、司筒、斜顶联合脱模机构,并用前模限位螺钉、限位拉杆、尼龙开闭器、压缩弹簧等零件控制开模运动顺序和分型定距。模具结构紧凑,运行可靠。

基于UG/NX的洗发水瓶盖注射模设计与模流分析

根据洗发水瓶盖的工艺要求,对塑件进行了结构分析,利用UG/NX4建立了三维数据图,进行了塑件体积与重量计算,并对塑件进行了注射模设计与模流分析。模具1模4腔、点浇口、三板模、模外定距分型,具有结构紧凑,工作可靠,操作方便,生产效率高等特点。对模具型腔与流道进行了模流分析,结果表明:模具浇注系统设置合理,塑料能完全充满型腔且流动平衡。型腔压力梯度均匀,不会出现滞流、溢料等质量缺陷,流体外表温度分布较均匀,表面质量能够得到保证。

An Intelligent Learning Algorithm for Improving BIM Object Classification and Recognition

Building information modeling(BIM)object classification takes a lot of time and energy.Misclassification or omission of any object may lead to the emergence of abnormal results,which have a great impact on the project workflow and results.Roundly understanding BIM object classification,by improving Swin Transformer classifier algorithm parameters,using the model primitives extracted from IFC format BIM model file,deep learning of 7 types of BIM object categories is taken.Through the performance and evaluation indicators obtained in training,the results improve the classification accuracy.

Numerical Analysis of Steady Smoldering of Biomass Rods

Understanding the steady mechanism of biomass smoldering plays a great role in the utilization of smoldering technology.In this study numerical analysis of steady smoldering of biomass rods was performed.A two-dimensional(2D)steady model taking into account both char oxidation and pyrolysis was developed on the basis of a calculated propagation velocity according to empirical correlation.The model was validated against the smoldering experiment of biomass rods under natural conditions,and the maximum error was smaller than 31%.Parameter sensitivity analysis found that propagation velocity decreases significantly while oxidation area and pyrolysis zone increase significantly with the increasing diameter of rod fuel.

Operation optimization of prefabricated light modular radiant heating system:Thermal resistance analysis and numerical study

The utilization of prefabricated light modular radiant heating system has demonstrated significant increases in heat transfer efficiency and energy conservation capabilities.Within prefabricated building construction,this new heating method presents an opportunity for the development of comprehensive facilities.The parameters for evaluating the effectiveness of such a system are the upper surface layer’s heat flux and temperature.In this paper,thermal resistance analysis calculation based on a simplified model for this unique radiant heating system analysis is presented with the heat transfer mechanism’s evaluation.The results obtained from thermal resistance analysis calculation and numerical simulation indicate that the thermal resistance analysis method is highly accurate with temperature discrepancies ranging from 0.44℃ to−0.44℃ and a heat flux discrepancy of less than 7.54%,which can meet the requirements of practical engineering applications,suggesting a foundation for the prefabricated radiant heating system.

Modified multiple-component scattering power decomposition for PolSAR data based on eigenspace of coherency matrix

A modified multiple-component scattering power decomposition for analyzing polarimetric synthetic aperture radar(PolSAR)data is proposed.The modified decomposition involves two distinct steps.Firstly,ei⁃genvectors of the coherency matrix are used to modify the scattering models.Secondly,the entropy and anisotro⁃py of targets are used to improve the volume scattering power.With the guarantee of high double-bounce scatter⁃ing power in the urban areas,the proposed algorithm effectively improves the volume scattering power of vegeta⁃tion areas.The efficacy of the modified multiple-component scattering power decomposition is validated using ac⁃tual AIRSAR PolSAR data.The scattering power obtained through decomposing the original coherency matrix and the coherency matrix after orientation angle compensation is compared with three algorithms.Results from the experiment demonstrate that the proposed decomposition yields more effective scattering power for different PolSAR data sets.

导滑板精密注射模的设计与制造

介绍了高精度塑料制品成型对注射成型工艺、成型模具和成型机的要求,并分析了此种带通孔的高精度平板类塑料制品注射模的结构特点以及易于产生变形、造成尺寸和位置精度超差,出现废品的原因和防止的有效方法。

Significant contributions of the petroleum industry to volatile organic compounds and ozone pollution:Insights from year-long observations in the Yellow River Delta

The petroleum industry is a significant source of anthropogenic volatile organic compounds(VOCs),but up to now,its exact impact on urban VOCs and ozone(O_(3))remains unclear.This study conducted year-long VOC ob-servations in Dongying,China,a petroleum industrial region.The VOCs from the petroleum industry(oil and gas volatilization and petrochemical production)were identified by employing the positive matrix factorization model,and their contribution to O_(3) formation was quantitatively evaluated using an observation-based chemical box model.The observed annual average concentration of VOCs was 68.6±63.5 ppbv,with a maximum daily av-erage of 335.3 ppbv.The petroleum industry accounted for 66.5%of total VOCs,contributing 54.9%from oil and gas evaporation and 11.6%from petrochemical production.Model results indicated that VOCs from the petroleum industry contributed to 31%of net O_(3) production,with 21.3%and 34.2%contributions to HO_(2)+NO and RO_(2)+NO pathways,respectively.The larger impact on the RO_(2) pathway is primarily due to the fact that OH+VOCs ac-count for 86.9%of the primary source of RO_(2).This study highlights the critical role of controlling VOCs from the petroleum industry in urban O_(3) pollution,especially those from previously overlooked low-reactivity alkanes.

洗发水瓶盖注射模设计

以常见的海飞丝洗发水瓶盖为例,进一步说明在模具设计的理念中,应具有大胆、灵活、广阔的思维能力的重要性。

螺纹卡爪结构件注射模设计

介绍了螺纹卡爪式结构件注射模设计、模具工作过程和卡爪脱模结构在注射模中的应用。模架类型选用简化型三板模,针对该塑件头部卡爪倒扣的结构特点,充分利用塑胶材料韧性良好的特性,采用多次分型的结构来对卡爪倒扣进行强脱,动模滑块对半的侧抽芯开模方式,最后由顶杆板推出塑件,机械手抓取塑件来实现自动生产。

Loose-stratification model in separation process for vanadium pre-concentration from stone coal

A technology of one-stage roughing and one-stage scavenging vanadium pre-concentration with shaking table was investigated for improving vanadium grade and decreasing acid consumption minerals content based on the quantitative evaluation of minerals by scanning electronic microscopy （QEMSCAN）. In order to visually illustrate how the vanadium-bearing minerals were separated from system, a loose-stratification model was established with Bagnold shear loose theory and Kelly stratification hypothesis. Through the model, it was inferred that fine fraction and coarse fraction of vanadium-bearing muscovite particles easily became the concentrate in roughing and scavenging stages, respectively. The type of the dominant effect on the loose-stratification was confirmed. In the roughing stage, gravity sedimentation played a leading role in the loose-stratification process. However, in the scavenging stage, shearing dispersion pressure caused by asymmetric motion of table deck took an important part in the loose-stratification process. Finally, the correction of the loose-stratification model was validated by the practical experiment.

股市风险VaR与ES的动态度量与分析

首先描述金融时间序列的一般特性,从收益率的波动性与分布两方面进行考虑,建立起计算时变风险值VaR和ES的模型,并在多种分布情形下动态测算上证综合指数的风险,结果表明基于GED分布的VaR模型能够较好地刻画高频时间序列的尖峰肥尾性及杠杆效应等特性,而ES模型则有效地弥补了VaR模型的不足之处。

Influence of land use characteristics and trip attributes on commuting mode choice: a case of Nanjing

The effects of socio-demographics, land use characteristics and trip attributes on the commute mode choice are studied with a nested logit （NL） model. Based on the random utility maximum theory, the NL model is formulated. The analysis is carried out in the main area of Nanjing. Direct and cross elasticities are calculated to analyze the effects of travel time and travel cost on the selection of travel mode choice. The results reveal that the non-motorized travel modes are more attractive in the areas with higher housing and employment accessibility and car owners are found to be more likely to commute to work by car. The bus and subway choice probabilities are more sensitive to changes in travel times than to changes in travel costs. In conclusion, a comprehensive public transit system and effective integration of land use and transportation policies help to relieve the traffic congestion levels caused by the increasing urban sprawl.

FLIGHT CLASSIFICATION MODEL BASED ON TRANSITIVE CLOSURE ALGORITHM AND APPLICATION TO FLIGHT SEQUENCING PROBLEM

A new arrival and departure flight classification method based on the transitive closure algorithm （TCA） is proposed. Firstly, the fuzzy set theory and the transitive closure algorithm are introduced. Then four different factors are selected to establish the flight classification model and a method is given to calculate the delay cost for each class. Finally, the proposed method is implemented in the sequencing problems of flights in a terminal area, and results are compared with that of the traditional classification method（TCM）. Results show that the new classification model is effective in reducing the expenses of flight delays, thus optimizing the sequences of arrival and departure flights, and improving the efficiency of air traffic control.

Water quality changing trends of the Miyun Reservoir

In order to simulate changes in the water quality of the Miyun Reservoir dueto continuous descent of surface water level, a 3-D ecological hydrodynamic model was developedthrough coupling the water quality analysis simulation program (WASP) with the environmental fluiddynamics code (EFDC). The model was then calibrated and verified. Four scenarios (S1, S21, S22 andS23) were simulated using the model. Results show that the water quality of the Miyun Reservoirunder conditions of low surface water level is apparently affected by different amounts of inflowand different total phosphorus (TP) loadings. The chlorophyll-a concentration might exceed 10 μg/Lin many areas of the Miyun Reservoir (This limitative value is seen as a critical value ofeutrophication) when large loadings of TP enter due to the amount of inflow increasing. Results ofscenario S23 indicate that control of TP loadings can decrease chlorophyll-a concentrationeffectively, and the water quality of the Miyun Reservoir will improve or retain its status quo.

多向抽芯的三次分型注塑模具设计

结合塑件具有多方位结构特征,设计了一副多向抽芯的三次分型注塑模具。针对塑件曲面分型面设计,通过减少与主开模方向不一致的抽芯数量,确定塑件存在3个不同方位抽芯的结构难点。针对结构难点,通过设计弯销+滑块的定模斜抽芯机构实现斜向通孔成型,设计弯销+滑块的动模内抽芯机构实现卡扣成型,设计斜抽镶件的动模斜抽芯机构实现凸起孔成型。为确保3种抽芯机构顺利脱模,模具结构采用三次分型设计,通过合理控制开模顺序实现塑件推出。为配合动模斜抽芯机构运动,模具结构采用动定模分型后,动模一侧再分型,并提出一种新的顶杆机械式动模分型机构。模具结构形式新颖,动作可靠,可为同类设计提供参考。

Gaussian mixture model clustering with completed likelihood minimum message length criterion

An improved Gaussian mixture model （GMM）- based clustering method is proposed for the difficult case where the true distribution of data is against the assumed GMM. First, an improved model selection criterion, the completed likelihood minimum message length criterion, is derived. It can measure both the goodness-of-fit of the candidate GMM to the data and the goodness-of-partition of the data. Secondly, by utilizing the proposed criterion as the clustering objective function, an improved expectation- maximization （EM） algorithm is developed, which can avoid poor local optimal solutions compared to the standard EM algorithm for estimating the model parameters. The experimental results demonstrate that the proposed method can rectify the over-fitting tendency of representative GMM-based clustering approaches and can robustly provide more accurate clustering results.

Numerical simulation of flow regions in red mud separation thickener's feedwell by analysis of residence-time distribution

The residence-time distribution （RTD） and the compartment model were applied to characterizing the flow regions in red mud separation thickener’s feedwells. Combined with the experimental work, validated mathematical model as well as three-dimensional computational fluid dynamics （CFD） model was established to analyze the flow regions of feedwells on an industrial scale. The concept of RTD, although a well-known method for the characterization of mixing behavior in conventional mixers and reactors, is still a novel measure for the characterization of mixing in feedwells. Numerical simulation results show that the inlet feed rate and the aspect ratio of feedwells are the most critical parameters which affect the RTD of feedwell. Further simulation experiments were then carried out. Under the optimal operation conditions, the volume fraction of dead zone can reduce by10.8% and an increasement of mixing flow volume fraction by 6.5% is also observed. There is an optimum feed inlet rate depending on the feedwell design. The CFD model in conjunction with the RTD analysis then can be used as an effective tool in the design, evaluation and optimization of thickener feedwell in the red mud separation.