Evaluation of the Applicability of Different Dielectric Models for Soil Moisture Retrieval based on the Ground-based Radiometer Measurements

Based on soil moisture and freeze/thaw comprehensive experiments conducted at the north-eastern part of the Tibetan Plateau, the L-band brightness temperature, the in-situ soil moisture and temperature, vegetation leaf area index are measured simultaneously for the purpose of evaluating performances on forward brightness temperature simulation and soil moisture retrieval using four dielectric constant models, including Wang-Schmugge, Mironov, Dobson, and Four-Phase model. The forward brightness temperature simulations indicate that the difference of simulated brightness temperature between Wang schmugge model and the other three dielectric constant models is most significant at lower soil moisture content condition (soil moisture is less than 0.23 m3·m^-3) , nevertheless, the difference of Mironov model simulation is most significant in contrast with the ones of other three models at higher soil moisture condition (soil moisture is greater than 0.23 m3·m^-3). The practical retrieval of soil moisture from the ground-based radiometer measurements indicate that Wang-Schmugge model can effectively reduce the underestimation of soil moisture at the horizontal polarization, this resulted an improvement to the accuracy of retrieved soil moisture. Mironov model can reduce the underestimation of retrieved soil moisture at the vertical polarization. In accordance with a state-of-the-art parameterization scheme, the evaluation of performances of four dielectric constant models at the typical alpine meadow is potential for selecting optimum soil moisture retrieval by using soil dielectric model from space-borne L-band radiometer observation over the Tibetan Plateau     

The final bleaching of eucalypt kraft pulps with hydrogen peroxide: relationship with industrial ECF bleaching history and cellulose degradation

BACKGROUND: The process of chemical pulp bleaching is based for the most part in chlorine dioxide within elemental chlorine free (ECF) technologies. The use of greener alternatives such as bleaching with hydrogen peroxide (P stage) is not widely used owing to selectivity concerns related to transition metal‐catalyzed decomposition reactions. Even at the final stage where peroxide is recognized to boost brightness and improve the brightness stability of the bleached pulp, cellulose degradation often overcomes these advantages. This paper presents the results of studies intended to optimize final peroxide bleaching performance considering two standard ECF industrial bleaching sequences: the conventional DED and the ECF‐light OQ(PO)D (stages name: D—chlorine dioxide; E—alkaline extraction; O—oxygen; Q—chelation, (PO)—hydrogen peroxide pressurized with oxygen). RESULTS: The addition of sodium diethylenetriaminepentaacetate (DTPA) was the most effective option in terms of DED pulp bleachability and selectivity with hydrogen peroxide, as well as in terms of brightness reversion. As regards the OQ(PO)D pulp, a blend of DTPA and magnesium was the most beneficial in those properties. CONCLUSIONS: The choice of the best hydrogen peroxide stabilizer, among the different tested combinations of magnesium and chelants (EDTA and DTPA) studied, in terms of pulp bleachability, bleaching selectivity and brightness reversion is dependent on the impact of the previous bleaching stages on metallic nature and content. The pulp Mg/(Fe + Cu) ratio was highlighted as a process parameter controlling cellulose degradation in peroxide bleaching. Copyright © 2010 Society of Chemical Industry     

自动适应环境光变化的显示终端研制

为了满足特殊场合的显示需要而研制的特种显示设备,建立了显示终端亮度和环境光照度之间的数学关系。为了满足不同用户的需求,文章提出了一种根据用户的调节结果来修正该数学关系的方法,并在此基础上完成了原理样机的研制。采用国产硅光电池和滤光片能够较为准确地测量环境光照度和显示亮度,并使系统能按对应关系以最佳的亮度来工作,用户在不满意的情况下,可以通过按键来人工调节亮度,单片机以人工调节的结果来改变该数学关系,并能记忆该数学关系。此显示终端能满足户外和高、低温环境下的特殊要求。     

大功率白光LED封装技术对器件寿命的影响

通过功率LED器件封装工艺技术的改进来降低芯片结温,从而减缓器件光衰速率,延长其预期的工作寿命时间。对用于封装的关键原材料的选取进行了对比实验,指出了采用纳米级材料改进导热可降低热阻,论述了正确选用混胶材料和工艺,可以减缓器件光衰速率,达到在较高的环境温度条件下,器件使用寿命大于50 000 h。论述了器件芯片的结温对光、电、色性能的影响和不同结温其预期工作寿命时间也不同的关联性。     

印制板半水清洗技术研究

免清洗焊膏在回流焊接过程中,产生大量透明的固体残留物,分布在焊盘四周.对于军用电子等高可靠性设备,残留物不仅影响印制板表面涂覆质量,而且影响产品的可靠性.研究了助焊剂残留物的半水清洗工艺,通过光学检查和离子浓度检测检查清洗质量.在工艺试验的基础上,掌握了关键要素和控制方法,确定了合适的工艺参数,用于生产作业指导.     

阳离子施胶增效剂的合成及应用

以丙烯酸甲酯、苯乙烯、丙烯酰胺、阳离子单体等为主要原料,采用无皂乳液聚合法合成了系列阳离子乳液,详细研究了聚合反应条件对其性能的影响,并与阴离子分散石油树脂胶分别对麦草浆和木浆进行协同施胶实验.结果表明,在乳液用量为0.2%(对绝干浆料)时,麦草浆纸页施胶度增幅可达33%,白度增加5.2%ISO;木浆纸页施胶度增幅可达37%,白度增加4.2%ISO.     

机电产品色彩设计同工作环境的关系

从自然环境、工业环境、人文环境三个方面入手，论述了机电产品的色彩设计同工作环境的关系，并提供了机电产品主体色彩配置方案与对策。     

视亮度及其应用

介绍了视亮度概念，并着重讨论了视亮度在照明工程科学和实际照明工程中应用。     

浅谈现代化展厅影响光环境的因素

本文以上海科技馆为实例,通过调查不同年龄人群对展厅光环境的评价以及在不同光环境下的心理感受,从心理学的角度探讨了影响现代化展厅光环境的若干因素,并提出了合理创造光环境的一些建议.     

Innovative advances in LED technology

An overview of the rapid progress in the developments of the inorganic light emitting diode (LED) technology is presented. Innovative structures and designs of the device have led to dramatic improvements of the performance in LED technology, groundbreaking performance records are being reported constantly. This article summaries the recent progress of the high brightness LEDs, and describes the LED structures from the basic pn homojunction, to heterojunction, and eventually the use of nano-scale low-dimensional structures in the device fabrication. Some of the novel structures and designs of the most recent developed high brightness LEDs, as well as the conventional and innovative ways of producing white LEDs are briefly discussed.