关联挖掘中的时效度研究

传统的关联挖掘算法,以支持度和置信度作为评价标准来衡量规则是否有价值。然而,这种模式不能体现出数据的时效敏感特性,如Web数据和长期积累数据。文中将首次建立一个全新的时基模型来重新估计数据规则的价值,并给出时效度(time validity)作为新的规则价值衡量标准。最后,给出了基于这个新的时基模型的一种新并行算法。这种算法使得我们在挖掘过程中使用增量挖掘,而且使得用户可以通过互操作来优化挖掘过程。

评论时效度的影响因素分析

评论时效度是衡量评论质量的一个重要指标,同时评论质量的其他因子也影响着评论的时效度。因此,我们要想保障评论的时效度,就必须弄清楚什么是评论的时效度、时效度的影响因素,进而才能够在此基础上提出相关的策略来保障评论的时效度,以为评论时效度的保障提供实践依据和理论支持。

直播社会临场感研究:量表编制和效度检验

社会临场感(Social Presence,SP)在不同情境下的构成维度存在很大差异,目前现有的社会临场感研究和测量均不触及直播营销这样高实时立体互动的情况。本文构建并检验了直播社会临场感(Live Broadcast Social Presence,LBSP)的构成,开发了直播社会临场感测量量表。研究一采用项目分析法及探索性因素分析法等方法筛选确定正式量表,运用验证性因素分析(CFA)和平均变异抽取值(AVE)验证了直播社会临场感是一个三因素构念,包括共存临场感、交流临场感和情感临场感,且具有良好的构念效度。研究二通过构建法则网络并用结构方程模型的方法验证了LBSP量表具有良好的法则效度。研究三将已有的PSP量表和PP量表作为校标,检验了 LBSP量表的共时效度。本研究为今后展开直播模式下社会临场感相关商业和学术研究问题提供了有效的测量工具。

传统效度理论的缺陷与发展

在语言测试理论中，效度一直被认为是测试本身的一个质量指标，效度验证主要考察内容效度、参照某一标准的共时效度或是结构效度中的一项。90年代，Messic提出了统一的结构效度概念。它共有六个层面，不但包括了传统意义上的三种不同的效度，同时还包含了伦理价值、社会后果等游离于传统效度概念之外的内容。效度验证变成提出结构效度假设，然后收集六个层面的数据对假设进行论证的过程。通过对旧效度理论的批判和新效度理论的分析，我们发现传统的、只依靠某一种效度验证的做法是片面的，也是不科学的。

对大学英语四级模拟试题的效度分析

大学英语四级模拟考试的目的是为了帮助学生了解和熟悉四级全真题的难度和水平 ,因此它应该具有标准化考试的特征 ,并且应该和四级考试具有较好的共时效度。本文从内容效度和共时效度两方面对三套大学英语四级模拟题进行了分析 ,发现这些模拟考试试题在测试的语法和词汇的选样以及阅读速度等方面均存在不足 ,提出了模拟试题编写时试卷编写者需要具有现代教育测量学的知识 ,要熟悉测试的理论、方法和目标测试大纲 。

“三个突出”把握好政府舆论引导的“时、效、度”

在融媒体的新常态下,政府部门把握好舆论引导要做到突出"时"字确保"首发"定调、突出"度"字避免"过激"反应、突出"效"字重在"效果"明显,以符合传媒多元化发展趋势和适应媒体融合语境下的新闻应急工作,确保牢牢掌握舆论引导的话语权、主动权和主导权。

Ultrahigh strength and improved electrical conductivity in an aging strengthened copper alloy processed by combination of equal channel angular pressing and thermomechanical treatment

In this paper,equal channel angular pressing and thermomechanical treatment was employed to improve the strength and electrical conductivity of an aging strengthened Cu-Ti-Cr-Mg alloy,and the microstructure and properties of the alloy were investigated in detail.The results showed that the samples deformed by the combination of cryogenic equal channel angular pressing(ECAP)and rolling had good comprehensive properties after aging at 400℃.The tensile strength of the peak-aged and over-aged samples was 1120 MPa and 940 MPa,with their corresponding electrical conductivity of 14.7%IACS and 22.1%IACS,respectively.ECAP and cryogenic rolling introduced high density dislocations,leading to the inhibition of the softening effects and refinement of the grains.After a long time aging at 400℃,the alloy exhibited ultra-high strength with obvious increasing electrical conductivity.The high strength was attributed to the synergistic effect of work hardening,grain refinement strengthening and precipitation strengthening.The precipitation of a large amount of Ti atoms from the matrix led to the high electrical conductivity of the over-aged sample.

High density dislocations enhance creep ageing response and mechanical properties in 2195 alloy sheet

The creep strain of conventionally treated 2195 alloy is very low,increasing the difficulty of manufacturing Al-Cu-Li alloy sheet parts by creep age forming.Therefore,finding a solution to improve the creep formability of Al-Cu-Li alloy is vital.A thorough comparison of the effects of cryo-deformation and ambient temperature large pre-deformation(LPD)on the creep ageing response in the 2195 alloy sheet at 160℃with different stresses has been made.The evolution of dislocations and precipitates during creep ageing of LPD alloys are revealed by X-ray diffraction and transmission electron microscopy.High-quality 2195 alloy sheet largely pre-deformed by 80%without edge-cracking is obtained by cryo-rolling at liquid nitrogen temperature,while severe edge-cracking occurs during room temperature rolling.The creep formability and strength of the 2195 alloy are both enhanced by introducing pre-existing dislocations with a density over 1.4×10^(15)m^(−2).At 160℃and 150 MPa,creep strain and creep-aged strength generally increases by 4−6 times and 30−50 MPa in the LPD sample,respectively,compared to conventional T3 alloy counterpart.The elongation of creep-aged LPD sample is low but remains relevant for application.The high-density dislocations,though existing in the form of dislocation tangles,promote the formation of refined T1 precipitates with a uniform dispersion.

商务英语阅读能力等级量表构建方法与原则

新经济的蓬勃发展催生了跨境电商,为满足国际化的商务环境,众多院校开设了商务英语专业,旨在培养复合型国际化外语人才。然而现有的教学存在目标模糊,课堂随意,评价缺失的情况。尽管中国英语能力等级量表已经颁布,但却是通用英语能力研发的,并不适合商务英语能力评价。构建指导性的商务英语量表迫在眉睫。商务英语阅读能力量表作为一个子表在内容上要以语言知识与能力为核心,同时涵盖专业商务知识与能力与通用知识与运用;要从就业市场、教学、考试大纲以及其他量表综合渠道收集阅读能力描述语;从教师学生专家三个方面调查数据进行等级分类,并验证确定等级;初步完成量表后试点使用收集即时效度证据,以此为基础对量表进行修订。

基于系统观的机遇特性与利用策略研究

以系统科学的方法,从企业内外环境入手,分析机遇产生背景的复杂性,进而提出机遇的四维特性,即机遇时效度、机遇广度、机遇深度和机遇概度,加以定义,并对机遇四维特性产生的原理和对企业战略的作用进行详细的分析;论述机遇、企业目标和企业资源能力的关系,得出机遇四维特性与企业所采取策略的对应关系。

Microstructure and mechanical properties of alloy 617B

The microstructure and mechanical properties of alloy 617 B in the process of 5000 h aging at 750 °C were systematically investigated by means of SEM, TEM and mechanical analysis. M23C6 particles were dispersed inside grains and distributed discontinuously along grain boundaries and γ′ phases were situated at intragranular sites in the process of aging. The size of precipitates increased with increasing aging time. Inter- and intra-granular carbide and γ′ phase particles inside grains resulted in the precipitation strengthening of this aged alloy, enhancing the strength and hardness. The aged alloy possessed good stabilities of hardness and strength during aging. An obvious decrease of the toughness of this aged alloy was due to γ′ phase particles limiting plastic deformation to the area nearby grain boundaries, resulting in the occurrence of crack along grain boundaries. Additionally, the intergranular cracks apparently led to a decrease in the toughness for this aged alloy due to carbide particles at grain boundaries. The toughness of this aged alloy was fairly stable possibly due to the unchanged distribution of the precipitates during aging.

Precipitation behavior and properties of a new high strength Al-Zn-Mg-Cu alloy

The microstructure and the associated hardness, strength and electrical conductivity of a new Al-Zn-Mg-Cu alloy during one-step ageing treatment were systematically studied. The results show that the electrical conductivity of the alloy increased continuously with increasing ageing temperature and ageing time. At the early stage of ageing, the hardness and strength of the alloy increased rapidly and then reached the peak value. When aged at 120 °C, the hardness and strength maintained at high level for a long time after the peak value. The main precipitations are GPI zones, GPII zones and metastable η′ phase. GPI and GPII zones are found in the alloy after ageing for 24 h at 120 °C, which indicates that some stable GP zones can exist through the ageing process. When aged at 160 °C, the hardness and strength decreased rapidly after the peak value. The precipitation process is significantly promoted compared with that aged at 120 °C. Both GPI zones and GPII zones disappeared after ageing for 1 h at 160 °C. The main precipitates are η′ phase when aged at 160 °C for 1 h. The main precipitates are η phase when the ageing time prolongs to 24 h.

Electrical and mechanical properties of Cu-Cr-Zr alloy aged under imposed direct continuous current

The Cu-Cr-Zr alloys were aged at different temperatures for different time with different current densities. The results show that both the electrical conductivity and hardness are greatly improved after being aged with current at a proper temperature. The electrical conductivity increases approximately linearly with increasing current density while the hardness remains constant. The microstructure observation reveals that a much higher density of dislocations and nanosized Cr precipitates appear after the imposition of current, which contributes to the higher electrical conductivity and hardness. The mechanism is related with three factors： 1） Joule heating due to the current, 2） migration of mass electrons, 3） solute atoms, vacancies, and dislocations promoted by electron wind force.

Effect of stress on microstructures of creep-aged 2524 alloy

Microstructures of creep-aged 2524 （A1-4.3Cu-1.5Mg） aged at 170 ℃ with various stresses （0, 173 and 250 MPa） were studied on a creep machine. Ageing hardness curves under various stresses were plotted and the corresponding microstructures were characterized by transmission electron microscopy （TEM）. The results show that the value of peak hardness is increased, while the time to reach the peak hardness is reduced under an external stress. Meanwhile, the length of S（Al2CuMg） phase is shorter and the number density of S phases is larger in the creep-aged alloy. The predominant contribution to the peak hardness can be ascribed to the GPB zones with an elastic stress.

Scale effects on non-cavitation hydrodynamics and noise of highly-skewed propeller in wake flow

Regarding the scale effects on propeller＇s noncavitation hydrodynamics and hydroacoustics, three similar 7bladed highly-skewed propellers in the wake flow are addressed with diameters of 250, 500 and 1 000 mm, respectively. The discrete line-spectrum noise and its standardized spectrum level scaling law, together with the total sound pressure level are analyzed. The non-cavitation noise predictions are completed by both the frequency domain method and the time domain method. As a fluctuated noise source, the time-dependent fluctuated pressure and normal velocity distribution on propeller blades are obtained by the unsteady Reynolds-averaged Navier-Stokes （ URANS ） simulation. Results show that the pressure coefficient distribution of three propellers on the 0.7R section is nearly superposed under the same advance ratio. The periodic thrust fluctuation of three propellers can exactly reflect the tonal components of the axial passing frequency （APF） and the blade passing frequency （BPF）, and the fluctuation enhancement from the small to the middle propeller at the BPF is greater than that from the middle to the big one. By the two noise prediction methods, the increment of the total sound pressure level from the small to the big propeller differs by 2.49 dB. Following the standardized scaling law, the spectrum curves of the middle and big propellers are nearly the same while significantly differing from the small one. The increment of both the line-spectrum level and the total sound pressure increases with the increase in diameter. It is suggested that the model scale of the propeller should be as large as possible in engineering to reduce the prediction error of the empirical scalin~ law and weaken the scale effects.

Springback and tensile strength of 2A97 aluminum alloy during age forming

The analysis of variance(ANOVA), multiple quadratic regression and radial basis function artificial neural network(RBFANN) methods were used to study the springback and tensile strength in age forming of 2A97 aluminum alloy based on orthogonal array. The ANOVA analysis indicates that the springback reaches the minimum value when age forming is performed at 210 °C for 20 h using a single-curvature die with a radius of 400 mm, and the tensile strength reaches the maximum value when age forming is performed at 180 °C for 15 h using a single-curvature die with a radius of 1000 mm. The orders of the importance for the three factors of pre-deformation radius, aging temperature and aging time on the springback and tensile strength were determined. By analyzing the predicted results of the multiple quadratic regression and RBFANN methods, the prediction accuracy of the RBFANN model is higher than that of the regression model.

Microstructure and microhardness of directionally solidified and heat-treated Nb-Ti-Si based ultrahigh temperature alloy

Directionally solidified （DS） specimens of Nb-Ti-Si based ultrahigh temperature alloy were heat-treated at （1 500 ℃, 50 h） and （1 500 ℃, 50 h） ＋ （1 100 ℃, 50 h）, respectively. The results show that the microstructures become uniform, the long and big primary （Nb,X）sSi3 （X represents Ti and Hf elements） plates in the DS specimens are broken into small ones, and the eutectic cells lose their lamellar morphology and their interfaces become blurry after heat-treatment. Meanwhile, the （Nb,X）sSi3 slices in the eutectic cells of the DS specimens coarsen obviously after heat-treatment. Homogenizing and aging treatments could effectively eliminate elemental microsegregation, and the segregation ratios of all elements in niobium solid solution （Nbss） in different regions tend to 1. After heat-treatment, the microhardness of retained eutectic cells increases evidently, and the maximum value reaches HV1 404.57 for the specimen directionally solidified with a withdrawing rate of 100 μm/s and then heat-treated at （1 500 ℃, 50 h） ＋ （1 100 ℃, 50 h）, which is 72.8 % higher than that under DS condition.

Stress/strain aging mechanisms in Al alloys from first principles

First-principles based calculations were carried out to explore the possible mechanisms of stress/strain aging in Al alloys. Potential effects of temperature and external stress/strain were evaluated on the solvus boundary of Al3Se in Al-Sc alloy, and the interface energy of Al/θ＂ in Al-Cu alloys. Results show that applying tensile strain/stress during conventional aging can significantly decrease the solubility entropy, by red-shifting the phonon DOS at high states. The resulted solvus boundary would shift up on the phase diagram, suggesting a reduced solubility limit and an increased maximum possible precipitation volume of AlaSc in Al-Sc alloy. Moreover, the applied strain/stress has different impacts on the formation energies of different orientated Al/θ＂ interfaces in Al-Cu alloys, which can be further exaggerated by the Poisson effect, and eventually affect the preferential precipitation orientation in Al-Cu alloy. Both mechanisms are expected to play important roles during stress/strain aging.

模压时效炉锻件温度软测量方法

针对模压时效炉锻件温度难以直接测量的问题,建立了基于混合核偏最小二乘(KPLS)算法的模压时效炉锻件温度软测量模型,通过采集较易获得的模压时效炉工作室炉壁温度估计锻件的实际温度.并采用局部加权算法确定训练样本权值,以提高软测量模型的精确度.实验结果表明,所建局部加权混合核偏最小二乘的软测量(LWKPLS)模型具有较好的数据适应性且能够满足实际温度预测的精度要求,解决了模压时效炉锻件温度难以直接测量导致铝合金产品欠温或过烧而带来的质量问题.

Distribution and evolution of aging precipitates in Al-Cu-Li alloy with high Li concentration

The evolution and distribution of the aging precipitates in 1460 Al-Li alloy with high Li concentration (2.14%, mass fraction) during T6 aging and two-step T8 (4% predeformation) aging were investigated through TEM. The aging precipitates include δ'(Al3Li) and T1 (Al2CuLi) phases, of which the δ' phases are formed first in grain interiors. A lot of δ'/GPI/δ' composite precipitates in which GPI zones are flanked with a pair of δ' phases, are formed at 145℃ of T6 aging, which are thermally stable. At 160℃ and 175℃ of T6 aging, many T1 phases nucleate first at subgrain boundaries and grain boundaries, and then form and grow within grains. As to the T8 aging, the δ'/GPI/δ' composite precipitates are formed during the first-step aging at 130℃ for 20 h, which are thermally stable during the second-step aging at 160℃. The plastic predeformation accelerates T1 nucleation within grains during the second-step aging at 160℃.