二维条码和数字签名技术及其在毕业证书中的应用

由于二维条码技术的突出优点,在各领域应用越来越广泛.二维条码技术和数字签名技术相结合可以有效解决各类证书数字化带来的一些问题,可以避免签名伪造和内容篡改.文章介绍了这些技术在毕业证书数字化中的应用,提出了解决方案并进行了实现.类似地他们也可以推广应用到其他各类证卡系统中.

大城市内部商业环境满意度评价与消费区位决策研究-以北京市西城区和海淀区为例

Since 1990s, commercial conditions in China including commercial environment, retail types, scale of retail enterprises, spatial structure of retail and shopping decision making factors have changed. In order to keep up with these changes, commercial geography should set up new perspectives, theories and methods to analyze its internal mechanism and changing rules, and thus provide reasonable and practical scientific basis to commercial planning, location decision of retail enterprises and commercial environment construction. Taking Xicheng and Haidian District of Beijing as research case, which is a sector region from city center to rural region, this paper selects 12 commercial centers as most important study objects of this sector. This paper mainly makes use of the methods of Modeling, Pearson Bivaiiate Correlations Analysis, Factor Analysis and Logit model. Based on 1300 questionnaires and fieldwork, this paper focuses on modeling of Consumer Satisfaction of Commercial Environment (CSCE), evaluation of commercial environment and driving factors of consumers' shopping location decision. Firstly, this paper discusses the development of commercial geography and commercial environment evaluation, the new characteristics and trends of commercial development in Beijing and physical commercial environment of Xicheng and Haidian District of Beijing from chapter 1 to chapter 4. Secondly, this paper summarizes characteristics of residents' shopping behavior in chapter 5. Thirdly, this paper sets up an evaluative model of CSCE, and analyzes consumer satisfaction indexes of commercial environment and their spatial features in chapter 6. Fourthly, this paper infers how residents' attributes and shopping behaviors affect their preferences of shopping location and what are residents' shopping location decisions and their influencing factors in chapter 7. Fifthly, this paper constructs a significant index model and a pyramidal framework of CSCE, and further analyzes the diversity and competitive advantage of commercial environment in chapter 8. Finally, some conclusions are drawn as follows: 1. Characteristics of residents' shopping behavior mostly embody residents' time distance preference, commodity consumption preference, shopping time distribution and shopping activity characteristics. The important factors that influence shopping location choice of residents are distance, transportation, commodity price, commodity types and commodity quality. However, the important factors, which influence shopping location re-choice of residents, are commodity price, commodity quality, commodity types and transportation. 2. CSCE indexes of 12 commercial centers show us significant spatial characteristics, such as spatial differences of "Center-fringe region", spatial characteristics of axes, spatial diversity of ring roads and so on. 3. Influencing factors including factor endowments, relative establishment factor and location and transportation factor of commercial environment are of importance for CSCE. 4. Logit model 1 indicates that shopping behavior of residents is significantly and positively related to working in high-tech companies, high income and by car and positively related to high school diploma, by bus and subway. 5. Logit model 2 indicates that residents' shopping location decision is significantly and positively related to leisure establishment and relative restaurant and entertainment establishment and negatively related to commercial location, commodity price, service quality, parking site. 6. The significant index model and the pyramidal framework of CSCE indicate competitive advantages are crucial to attractive capability of commercial center, and competitive weakness limits development of commercial centers, in particular the weakness of service quality and parking site now is the chief factors restricting development of commercial centers

中国煤中氟的环境地球化学研究

氟是煤中含量较高的微量元素，大多在20-500mg／kg，平均值为150mg／kg左右。煤在燃烧时，其中的氟化物将发生分解，大部分以日F、SiF_4等气态污染物形式排入大气，不仅严重腐蚀锅炉和烟气净化设备，而且造成大气氟污染和生态环境的破坏。氟是人体所必需的微量元素，但摄入过量则会催患氟斑牙和氟骨症。燃煤污染型氟中毒为我国所独有，导致了近1500万患者，这是人类有史以来最严重的环境污染导致的健康危害事件。因此，根据目前国内外对煤咔l氟的研究进展，研究中国煤中氟的含量、分布及其影响因素；燃煤型氟中毒的环境地球化学特征；选煤脱氟的机理；粮食中氟的分析方法既有理论意义又有现实价值。通过本文的研究，得出以下几点认识：1、通过在全国有计划的系统取样。统一采用当前最有效的分析方法-高温热水解-离子选择性电极法来获得中国煤炭的平均氟含量。与世界煤相比，中国煤含氟量正常，绝大部分（90％）煤的含氟范围为47～347mg／kg，全国煤 氟平均含量为136mg／kg。澄清了长期以来关于中国煤炭高氟的错误认识，为正确计算燃煤的氟排放通量并评价其环境影响提供了较准确的基础资料。2、中国煤中氟含量与灰分显著正相关，表明煤中氟主要以无机矿物形式赋存。3、在本批样品中按变质程度的不同，煤含氟量由低到高依次为贫煤、长焰煤、无烟煤、气煤、焦煤、肥煤、瘦煤和褐煤。煤中的氟主要赋存于无机矿物中，以无机形态赋存的氟不受煤变质程度的影响。从褐煤到无烟煤，煤中的氟含量和煤变质程度之间没有必然的关系，在讨论煤氟含量与变质程度的关系时要考虑氟的赋存形态的影响，以统计分析的方法来研究其间的相互关系时要慎下结论，某些变化趋势不一定就是必然的规律。4、在本批样品中按地质时代的不同，煤中氟含量由低到高依次为早石炭世、中侏罗世、早侏罗世、早二叠世、晚石炭世、中石炭一世、晚侏罗世、第三纪和晚三叠世。煤中的氟含量受物质来源、成煤环境、后期地质地球化学作用等多种因素的影响，而我国幅员辽阔、成煤期多、煤田分布广，而且同地质时代的不同煤矿区（或者地质单元）可以具有相同条件，也可具有不同条件，致使影响含氟量的各种因素大多只具有局部性，造成成煤时代等单一因素的作用可能为其它各种因素的作用所掩盖，对此有必要进行更深入具体的研究。5、拌煤的粘土取自土壤的淀积层，其氟含量非常高。中国煤氟的含量不高，远低于淀积层粘土的氟含量。在燃煤型氟中毒病区通常用粉煤与粘土加水搅拌制成湿的煤泥在无烟囱的炉灶内燃烧。使用烟煤和无烟煤的燃煤型氟病区的氟主要来自于拌煤的粘土。我们突破了长期以来关于氟源是高氟煤的错误认识，这为正确、有效地防治燃煤型地氟病提供了新的思路。6、在石煤污染型氟病区石煤的风化淋溶对水环境、粮食作物的含氟量影响不大，但其燃烧后释放出的的气态、气溶胶态和尘态氟会污染室内空气、粮食、蔬菜和饮水从而导致人体摄氟过量而中毒。改良炉灶，改变在厨房烘烤、存放辣椒的陋习，经常清扫室内，尤其是室内上部灰尘，防止灰尘坠落污染食物、饮水等，对．预防氟中毒有重要意义。7、选煤可降低灰分、硫分，同时还能有效脱除煤中的氟及其他有害微量元素，从而可减少运输成本，降低粉煤灰的收集、处理和处置与有害微量元素的排放控制费用，提高燃烧热效率，符合以预防为主的国家环保政策，要大力倡导。8、我们采集的病区玉米第二次酸浸时浸出液含氟量低于检测限；而辣椒由于含油较多，辣椒油阻碍了氟的浸出，这导致浸泡两、三次后在浸出液中还能检测出氟。在地氟病区采用酸浸一离子选择性电极法测定氟含量时，玉米浸泡一次即可满足研究需要，而对于辣椒则宜进行多次浸泡。一次或多次未浸出的氟含量基本为一个定值，在研究地氟病时不用对此作太多考虑，但在制订粮食的含氟量及人体的摄氟量标准时要将这一部分氟考虑进去。