走进DXCC——远距离通信(DXing)和DXCC奖状

中国的业余无线电正处在一个飞速发展的状态,使用短波进行通联的爱好者也日益增多。2007年黄岩岛远征时,大约有400多个中国大陆的业余电台和BS7H做过联络,而2008年奥运特设台期间,与奥运特设台通联过的中国大陆的业余电台大约有1100多个。在大家不仅限于U/V通联,试验用短波进行更远距离的通联,参加竞赛和远征时,他们已经不再满足于国内通联以及和附近的日本,韩国,俄罗斯等国家的业余电台进行通联。DXCC(DX Century Club)——这个作为一个真正的短波业余无线电爱好者追求的一个近期目标,就自然地成为很多短波初级爱好者的关注焦点。DXCC简而言之就是和100个及以上的DXCC实体进行通联并成功交换QSL卡片。本连载旨在引导业余无线电短波初学爱好者如何获得DXCC。内容来自一本美国ARRL图书——《DXCCHandbook》,笔者根据自身经验对于原书内容有部分注解,删节或补充,希望对业余无线电短波初学爱好者有所帮助。     

知识表示应用模型研究

作为当今社会的关键性资源，知识管理成为研究和应用人员普遍关注的问题为了研究知识表示的数学理论基础，定义了一种知识表示模型，以库所、变迁和弧等组成的有色多元组集合表示知识库系统，单个知识对象由元组表示，运用替代变迁对知识进行层次化和结构化的系统表示，以城市给水管网设备系统为例说明该模型的应用     

抹茶牛奶护色方法研究

因抹茶牛奶在货架期中容易褪色,本文研究了葡萄糖酸锌、维生素E、D-异抗坏血酸钠和遮光条件下对抹茶牛奶颜色稳定性的影响,重点考察D-异抗坏血酸钠不同添加量的影响效果.实验通过采用分光色差计测定色差值,进行贮藏实验等方法,探讨抹茶牛奶的颜色稳定性.结果表明,葡萄糖酸锌可以延缓抹茶绿色和风味的变化;维生素E可以保护抹茶的绿色...     

U形预应力混凝土板桩在河道护岸工程中的应用

U形板桩自上世纪90年代在荷兰、日本等国家出现,并广泛应用于水利、航道护岸、基坑维护等工程中,取得了良好的工程效果。随着国内研发及技术水平的提高,某板桩生产厂家在近年已研发出U形预应力混凝土板桩,并成功应用于工程实践当中,本文结合工程设计实例阐述该类型桩在河道护岸中的应用,为同类工程提供借鉴。     

Prevalence and antimicrobial susceptibility of Salmonella isolated from a variety of raw meat sausages in Gaborone (Botswana) retail stores

The objective of the study was to provide baseline data on the prevalence and antimicrobial susceptibility of Salmonella in different types of raw meat sausages directly accessible to the consumers in Gaborone, Botswana. A total of 300 raw sausages comprising 79 beef, 78 pork, 72 chicken, and 71 mutton samples were concurrently analyzed for the presence of Salmonella using a conventional culture method and a validated PCR method. The PCR assay results were in full concordance with those of the conventional culture method for the detection of Salmonella. Sixty-five (21.7%) of 300 samples were positive for Salmonella by both the conventional culture method and PCR assay. Even though more chicken samples contained Salmonella than did any other sausage type, the difference in the presence of Salmonella among the four sausages types was not significant. Eleven serotypes were identified, and Salmonella enterica subsp. salamae II was most prevalent in all the sausage types. Beef sausages generally had higher mesophilic bacterial counts than did the other three sausage types. However, higher microbial counts were not reflective of the presence of salmonellae. Susceptibility of the Salmonella enterica serotypes to 20 antimicrobial agents was determined, and Salmonella Muenchen was resistant to the widest array of agents and was mostly isolated from chicken sausages. Regardless of the meat of origin, all 65 Salmonella isolates were resistant to at least four antimicrobial agents: amikacin, gentamicin, cefuroxime, and tombramycin. This resistance profile group was the most common in all four sausage types, comprising 90% of all Salmonella isolates from beef, 71% from pork, 63% from mutton, and 35% from chicken. These results suggest that raw sausages pose a risk of transmitting multidrug-resistant Salmonella isolates to consumers.     

Enhancement of hematite bioreduction by natural organic matter

The effects of natural organic matter (NOM), ferrozine, and AQDS (anthraquinone-2,6-disulfonate) on the reduction of hematite (alpha-Fe2O3) by Shewanella putrefaciens CN32 were studied. It has been proposed that NOM enhances the reduction of Fe(III) by means of electron shuttling or by Fe(II) complexation. Previously both mechanisms were studied separately using "functional analogues" (AQDS for electron shuttling and ferrozine for complexation) and are presently compared with seven different NOMs. AQDS enhanced hematite reduction within the first 24 h of incubation, and this had been ascribed to electron shuttling. Most of the NOMs enhanced hematite reduction after 1 day of incubation indicating that these materials could also serve as electron shuttles. The effect of ferrozine was linear with concentration, and all of the NOMs exhibited this behavior. Fe(II) complexation only enhanced hematite reduction after sufficient Fe(II) had accumulated in the system. Fe(II) complexation appeared to alleviate a suppression of the hematite reduction rate caused by accumulation of Fe(II) in the system. Addition of Fe(II) to the hematite suspension, prior to inoculation with CN32, significantly inhibited hematite reduction and greatly diminished the effects of all of the organic materials, although some enhancement was observed due to addition of anthroquinone-2,6-disulfonate. These results demonstrate that NOM can enhance iron reduction by electron shuttling and by complexation mechanisms.     

苏北临港化工产业园区人才紧缺现状探究——以连云港临港化工产业园区为例

随着社会经济体制改革的不断深入,我国地方区域经济不断出现新的态势和特点。苏北临港化工产业园区化工产业发展势头强劲,带动了一批相关产业的发展,对化工各种人才需求日益增加。高校人才的培养不能满足人才的需求。本文对苏北临港化工产业园区人才需求变化及流失做了进一步探究。     

Age-dependent changes in eumelanin composition in hairs of various ethnic origins

Hair pigmentation is one of the most conspicuous phenotypes of humans. From a chemical point of view, however, data remain scarce regarding human hair pigmentation characteristics. To determine melanin content and composition in human eumelanic hair from individuals of different ethnic origins and at different ages, we collected hair from 56 subjects with eumelanic hair from each group of African-American, East Asian, and Caucasian origin. The 56 subjects consist of 14, seven each of males and females, each from four age classes of younger than 11, between 12 and 19, between 20 and 45, and older than 46. We analysed hair colour scale, total melanin value, and contents of pyrrole-2,3,5-tricarboxylic acid (PTCA) and pyrrole-2,3-dicarboxylic acid (PDCA). We measured age-dependent increases in the relative quantity of eumelanin in pigmented human hairs in the three ethnic groups. Regarding melanin composition, we observed an increase in the PDCA/PTCA ratio with age in African-American and Caucasian hairs until approaching the quite constant level of the ratio in East Asian hairs in the elderly individuals. Our results evidence differences in the content and composition of eumelanin in human hair among African-American, Caucasian and East Asian individuals. Furthermore, we show evidence of age-dependent changes in the quantity and quality of eumelanin in pigmented human hairs. In particular, the age-dependent modification of the PDCA/PTCA ratio, a marker for 5,6-dihydroxyindole units in eumelanin, suggests a chronological evolution of hair follicle melanocyte phenotype (e.g. decrease in dopachrome tautomerase expression).     

Rapid magnetic biomonitoring and differentiation of atmospheric particulate pollutants at the roadside and around two major industrial sites in the U.K

Emissions of particulate matter (PM) from vehicle and industrial sources constitute a hazard to human health. Here, we apply biomagnetic monitoring to (a) discriminate between potential PM(10) sources around a steelworks and (b) examine magnetic source differentiation for a combined, U.K.-based, magnetic data set (steelworks, roadside, power-generating site). Tree leaves (sampled September 2009, as passive PM receptors) and putative sources were subjected to rapid magnetic characterization (magnetic remanence measurements). Fuzzy cluster analysis of the combined data set identified three clusters, showing that particulates emitted from vehicle fleets (e.g., diesel/petrol), and from different industrial processes can be magnetically differentiated. Cluster analysis of the steelworks leaf receptors and potential sources identified seven magnetic groupings. Leaves from one PM "hotspot" showed no affinity with any available source sample, suggesting an as yet untested PM source. These data indicate the value of fast, inexpensive magnetic techniques for particulate source discrimination and indication of "missing" sources.     

Formation of toxic 2-nonyl-p-benzoquinones from α-tertiary 4-nonylphenol isomers during microbial metabolism of technical nonylphenol

In many environmental compartments, microbial degradation of α-quaternary nonylphenols proceeds along an ipso-substitution pathway. It has been reported that technical nonylphenol contains, besides α-quaternary nonylphenols, minor amounts of various α-H, α-methyl substituted tertiary isomers. Here, we show that potentially toxic metabolites of such minor components are formed during ipso-degradation of technical nonylphenol by Sphingobium xenophagum Bayram, a strain isolated from activated sewage sludge. Small but significant amounts of nonylphenols were converted to the corresponding nonylhydroquinones, which in the presence of air oxygen oxidized to the corresponding nonyl-p-benzoquinones-yielding a complex mixture of potentially toxic metabolites. Through reduction with ascorbic acid and subsequent analysis by gas chromatography-mass spectrometry, we were able to characterize this unique metabolic fingerprint and to show that its components originated for the most part from α-tertiary nonylphenol isomers. Furthermore, our results indicate that the metabolites mixture also contained several α, β-dehydrogenated derivatives of nonyl-p-benzoquinones that originated by hydroxylation induced rearrangement, and subsequent ring and side chain oxidation from α-tertiary nonylphenol isomers. We predict that in nonylphenol polluted natural systems, in which microbial ipso-degradation is prominent, 2-alkylquinone metabolites will be produced and will contribute to the overall toxicity of the remaining material.