冰蓄冷低温送风空调系统风管管路分析研究

研究得出冰蓄冷低温送风空调系统较常规空调系统在风管管路阻力及风管截面积的优越性。依据管路阻力计算公式利用VB语言编写风管比摩阻的计算程序,并利用该计算程序对相同工况下的典型的低温送风温度与常规送风温度的比摩阻进行计算,进而得到风管管路阻力,同时计算得出各送风温度下的风管截面积,并进行对比分析。相同计算条件下,冰蓄冷低温送风空调系统的风管沿程阻力是常规送风系统的40%—70%;采用8℃低温送风方式时,其风管截面积较常规空调可减少20%—30%。与常规空调系统相比,采用冰蓄冷低温送风空调系统可明显减小风管的沿程阻力和截面积,大大降低了风机耗能和建筑层高,节省了运行及建材费用。     

真空冷冻干燥结合微乳液法制备纳米ZnO

真空冷冻干燥技术结合反相微乳液法制备了纳米ZnO粉体。利用XRD、TEM及表面积分析仪对制备过程、粉体的结构、形貌、比表面积、孔容进行了表征。探讨了煅烧温度、干燥方式及真空冷冻干燥的主要参数对纳米ZnO的影响。结果表明:该方法较常规方法制备的纳米ZnO粒径小(平均19nm)、分散性好、比表面积大(567.9m2.g-1),对亚甲基蓝溶液的降解(降解率98.6%)具有较高的光催化活性。     

Throaty Voice Quality: Subglottal Pressure, Voice Source, and Formant Characteristics

"Throaty" voice quality has been regarded by voice pedagogues as undesired and even harmful. This study attempts to identify acoustic and physiological correlates of this quality. One male and one female subject read a text habitually and with a throaty voice quality. Oral pressure during p-occlusion was measured as an estimate of subglottal pressure. Long-term average spectrum analysis described the average spectrum characteristics. Sixteen syllables, perceptually evaluated with regard to throaty quality by five experts, were selected for analysis. Formant frequencies and voice source characteristics were measured by means of inverse filtering, and the vocal tract shape of the throaty and normal versions of the vowels [a,u,i,ae] of the male subject were recorded by magnetic resonance imaging. From this material, area functions were derived and their resonance frequencies were determined. The throaty versions of these four vowels all showed a pharynx that was narrower than in the habitually produced versions. To test the relevance of formant frequencies to perceived throaty quality, experts rated degree of throatiness in synthetic vowel samples, in which the measured formant frequency values of the subject were used. The main acoustic correlates of throatiness seemed to be an increase of F1, a decrease of F4, and in front vowels a decrease of F2, which presumably results from a narrowing of the pharynx. In the male subject, voice source parameters suggested a more hyperfunctional voice in throaty samples.     

基于熵效率模型的环渤海地区海洋经济系统韧性研究

可持续发展理论难以深入解释区域经济为何能在扰动因素下保持增长, 而“韧性”是解析区域经济演化的重要概念. 本文基于演化韧性视角, 提出海洋经济系统韧性概念, 建立以信息熵为基础的评价体系, 并构建熵投入和熵产出的熵效率模型, 应用SBM模型测算环渤海地区17个沿海城市在16年间的海洋经济系统熵效率, 最后分析了海洋经济系统熵变过程及韧性的演化规律与机制. 研究表明2000~2015年环渤海地区: (1)海洋经济系统的发展与韧性水平的提升由系统熵流与熵产生所形成的负熵所驱动; (2)海洋经济系统韧性经历由慢到快、由差到优的发展过程, 目前韧性整体相对较好, 城市间的差异依然显著; (3)海洋经济系统的完善与韧性的提升主要依赖于海洋经济系统压力输出的持续减小, 以及适应与更新能力的提升, 而受生产力水平与扰动因素的影响较小; (4)为保持海洋经济持续健康增长, 应在强调可持续发展的同时, 注重提升海洋经济系统的韧性水平.     

Student teachers’ concept definitions of area and their understanding about two-dimensionality of area

We examine what kind of concept definitions of area a group of Finnish primary and lower secondary student teachers (N = 82) use, and how the quality of the definitions is associated with the participants’ success in seven exercises involving area. We are especially interested in how the understanding of the two-dimensionality of area appears in the participants’ responses. Only six student teachers were able to give a mathematically precise and correct definition of area. Altogether 26 participants defined it as ‘the size of a figure’ and 20 respondents required that a figure must be bounded. Further, 22 of them associated area with a formula or an example and eight respondents gave an incorrect or nonsensical definition. On average, student teachers master rather well the area formulae of a circle and a rectangle but already the relationship between the surface area of a cube and its volume is less commonly perceived. Most student teachers associate the area of an irregular domain with the method of exhaustion but clearly fewer of them acknowledge the difference between the area and an approximation of it. Surprisingly, there is only a weak Spearman correlation between the participants’ scores in the test exercises and the qualitatively ordered categories of concept definitions.     

Adsorption of Some Tailor-Made Styrylpyridinium Dyes on Sodium Dodecylsulphate-Treated Eggshell Particles (SDS-ESP): Impact of Dye Chain-Length and Substituent

Eggshell particles (ESP), a solid bio-waste, treated with sodium dodecylsulfate (SDS) have been examined for the adsorption of some tailor-made cationic styrylpyridinium dyes. The adsorbent is characterized through Fourier transform infrared spectroscopy and scanning electron microscopy. The anionic headgroups of the surfactant bilayer on the SDS-treated ESP (SDS-ESP) provide avenue for binding with the dye molecules. Dependence of equilibrium adsorption capacity on various adsorption parameters and effects of substituent and hydrophobic tail of the adsorbate on adsorption are enumerated. Physical adsorption obeying pseudo-second order kinetics has been proposed. (Supplemental materials are available for this article. Go to the publisher's online edition of Journal of Dispersion Science and Technology to view the free supplemental file.)     

Spatial visualization and measurement of area: A case study in spatialized mathematics instruction

The purpose of this study was to explore the influence of spatial visualization skills when students solve area tasks. Spatial visualization is closely related to mathematics achievement, but little is known about how these skills link to task success. We examined middle school students’ representations and solutions to area problems (both non-metric and metric) through qualitative and quantitative task analysis. Task solutions were analyzed as a function of spatial visualization skills and links were made between student solutions on tasks with different goals (i.e., non-metric and metric). Findings suggest that strong spatial visualizers solved the tasks with relative ease, with evidence for conceptual and procedural understanding. By contrast, Low and Average Spatial students more frequently produced errors due to failure to correctly determine linear measurements or apply appropriate formula, despite adequate procedural knowledge. A novel finding was the facilitating role of spatial skills in the link between metric task representation and success in determining a solution. From a teaching and learning perspective, these results highlight the need to connect emergent spatial skills with mathematical content and support students to develop conceptual understanding in parallel with procedural competence.     

Application of the quadrilateral area coordinate method： a new element for laminated composite plate bending problems

Recently, some new quadrilateral finite elements were successfully developed by the Quadrilateral Area Coordinate (QAC) method. Compared with those traditional models using isoparametric coordinates, these new models are less sensitive to mesh distortion. In this paper, a new displacement-based, 4-node 20-DOF (5-DOF per node) quadrilateral bending element based on the first-order shear deformation theory for analysis of arbitrary laminated composite plates is presented. Its bending part is based on the element AC-MQ4, a recent-developed high-performance Mindlin-Reissner plate element formulated by QAC method and the generalized conforming condition method; and its in-plane displacement fields are interpolated by bilinear shape functions in isoparametric coordinates. Furthermore, the hybrid post-processing procedure, which was firstly proposed by the authors, is employed again to improve the stress solutions, especially for the transverse shear stresses. The resulting element, denoted as AC-MQ4-LC, exhibits excellent performance in all linear static and dynamic numerical examples. It demonstrates again that the QAC method, the generalized conforming condition method, and the hybrid post-processing procedure are efficient tools for developing simple, effective and reliable finite element models. The project is supported by the National Natural Science Foundation of China (10502028), the Special Foundation for the Authors of the Nationwide (China) Excellent Doctoral Dissertation (200242), and the Science Research Foundation of China Agricultural University (2004016).     

The difficulty of “length × width”: Is a square the unit of measurement?

In individual interviews, 220 students in grades 4, 6, 8, and 9 were given one task, and 72 eighth graders were given three tasks to answer two questions: (a) Is a square the unit of measurement for an area for students in grades 4-8? and (b) Does a square have a space-covering characteristic for students in grade 8? The answers to both questions were No (except for eighth (and ninth) graders in advanced sections of mathematics). The difficulty of “length × width” is explained in light of Piaget's theory, and educational implications are discussed.