多路径下桃园射频信号传输特性

为解决无线传感器网络在桃园中的快速部署问题,该文研究了2.4 GHz无线射频信号在桃园中的传播特性。依据角度选取4条传输路径,在3种(0.5、1.5、2.5 m)典型的天线高度,同时测量丢包率和路径损耗情况,分析表明两者具有明显的相关性,天线高度和通信距离是路径损耗的主要影响因素。在天线高度为0.5和1.5 m时,可靠传输距离为6个行距(27 m);在天线高度为2.5 m时,可靠传输距离大于14个行距(63 m),因此冠层顶部为布设天线的最佳位置。对路径损耗数据进行回归分析,发现其在每种天线高度,每条传输路径下对数模型最适合作为路径损耗模型,模型的R2最大为0.945,最小为0.732。为研究节点部署于桃园任意位置时的路径损耗情况,便于节点快速灵活地部署,在3种天线高度下对路径损耗数据进行对数回归分析,R2最大为0.976,最小为0.939。最后对2组模型进行了验证,表明模型可以预测射频信号在桃园中的路径损耗情况,该文研究结果为无线传感器网络在桃园中的部署提供了参考。     

无线信道的研究

在无线通信当中,信道是重要组成的部分,信号在传输时会受到多径延迟和路径衰落以及多普勒频移带来的衰落影响。本文详细讨论了无线信道中传输时典型衰落：瑞利衰落、菜斯衰落。介绍了信道衰落的建模方法,并用计算机仿真,得到QPSK信号在不同信道下误码情况。     

锌试剂褪色分光光度法测定茶叶和茶水中的锰

研究了锌试剂褪色光度法测定茶叶和茶水中锰含量的方法.结果表明在一定条件下,锰含量在2.7～32.0 μg/L范围内遵守比耳定律,检测限为0.14 μg/L,方法的表观摩尔吸光系数为8.28×105 L/(mol·cm).经用于茶叶和茶水样品分析,相对标准偏差(RSD)为1.9%～3.4%,回收率为94.7%～103.1%.结果令人满意.     

纸坊沟流域生态经济系统演变规律研究 —兼论“退耕还林（草）”下生态经济系统演变规律

生态经济系统演变过程分为4个阶段,纸坊沟流域经过20余年的综合治理初步步入第Ⅲ阶段;以纸坊沟流域为例,在分析不同阶段系统演变驱动力的基础上,研究了生态经济系统演变规律:(1)生态系统对经济系统作用的滞后性,(2)系统结构决定系统功能,但人类根据自己的需要通过对系统功能的预期,调整系统结构,(3)生态经济系统循环中的投入主体在不同阶段具有不同表现形式。探讨了“退耕还林(草)工程”下生态经济系统“凸变”演替的具体表现,即“退耕还林(草)工程”是对资源需求量的强制规定,“退耕还林(草)工程”经济补偿政策使生产经营者对资源的需求量减少,退耕还林(草)”工程使实施区域直接过度到第Ⅱ阶段后期或第Ⅲ阶段。     

Distribution of Feline Blood Types Detected in the Copenhagen Area of Denmark

Jensen, A. L., A. B. Olesen and J. Arnbjerg: Distribution of feline blood types detected in the Copenhagen area of Denmark. Acta vet. scand., 1994, 35, 121-124.–The purpose of the present study was to make the first survey of the distribution of feline AB blood types in the Copenhagen area of Denmark. A total of 244 cats (139 purebred cats and 105 Domestic Shorthair cats) were tested. 93% of all tested cats had blood type A. Neither an AB nor an O type cat was detected and thus, the frequency of blood type B among all tested cats was 7%. Most type B cats were purebred cats (Birman, British Shorthair and Persian cats). No association between sex and blood type could be demonstrated among British Shorthair and Persian cats. Thus, the present study indicates that cats in Denmark predominantly have blood type A, and that blood type B cats are rare, except for certain breeds such as Birman and British Shorthair cats.     

设施葡萄叶萎蔫现象发生原因初探

为探明设施葡萄叶萎蔫现象的发生原因,调查了设施葡萄生长的环境条件,结果认为设施内气温与地温比例失调和结实过量是叶萎蔫现象发生的主要原因,土壤碱性化、土壤板结和CEC偏低也是叶萎蔫现象发生的重要原因,设施内葡萄的栽植位置加重叶萎蔫现象发生程度.     

制动器热衰退机理的研究与分析

影响制动器稳定性的关键因素是热衰退,我们通过摩托车制动器综合性能试验台对两种不同的摩擦材料做了热衰退相关试验,并利用扫描电子显微镜(SEM)对制动器摩擦表面摩擦前后的表面形貌进行观察分析和对比,发现热衰退产生的强弱程度与材料的成分和配方有密切关系。粉末冶金摩擦材料中不含有机组分,热衰退表现并不明显;而树脂摩擦材料中含大量有机粘结剂,热衰退较为明显。从而提出了摩擦材料的相关改进方案以提高制动器的抗热衰退性能。     

Abomasal parasite syndrome in North American elk (Cervus elaphus canadensis)

CASE HISTORY An 18-month clinical course of chronic ill-thrift, weight loss and emaciation, and eventual death occurred in a group of 520 translocated elk of mixed age and sex. Trans-location was carried out without regard to animal welfare or health risks associated with the translocation. Mortality was approximately 84% (436/520) despite supportive nutritional and medical treatment.

PATHOLOGICAL FINDINGS: General clinical and post-mortem examinations indicated only Se and Cu imbalances and nutritional inadequacy. Additional purposeful post-mortem examination and histological evaluation of tissue sections from four of the affected adult elk demonstrated elevated abomasal pH and proliferative abomasal lesions as the most significant findings, consistent with Type-II ostertagiosis; intra-lesional nematodes were seen in the abomasum of two animals.

DIAGNOSIS: Fading elk syndrome, or abomasal parasite syndrome in elk.

CLINICAL RELEVANCE: Abomasal parasite syndrome initiated by Type-II ostertagiosis should be considered as a differential diagnosis in cases of ill-thrift and wasting in elk or elk-red deer hybrids. Changes to the architecture and secretory function of the abomasal wall lead to apparently irreversible digestive pathophysiology and nutritional disease.     

光照强度对两种土壤类型烟叶褪色的影响

【目的】探究烟叶存放过程中光照强度对不同土壤类型烤烟褪色程度的影响。【方法】以"粤烟97"烤后烟叶C3F为试验材料,研究了3种光照强度对2种土壤类型产出的烤后烟叶色素含量、色度和色差值的影响,并对烟叶褪色程度进行划分。【结果】在不同光照条件下,烤烟的各色素含量、色差值和色度值均有所下降,随着光照强度的提高,烤烟的各指标下降越明显。而在同一光照强度处理下,沙泥田烤烟各指标下降量大于紫色土田烤烟,其烟叶在强光处理30d时,类胡萝卜素下降91.14μg/g,色差b值下降13.9,色度Y值下降15.1。通过聚类分析的结果建立了MLP神经网络模型,将烟叶褪色程度分为轻度、中度和重度。【结论】光照强度会导致烤烟色素分解,且光照强度越大,褪色越严重;紫色土田烤烟较沙泥田烤烟不易褪色。     

The intrinsic cause of color fading in sliced cooked cured beef during chilled storage

The relationship between color change and other physical and chemical characteristics of sliced cooked cured beef (SCCB ) during chilled storage were investigated using principal components analysis (PCA ) to determine the color fading causes. Samples were prepared and stored at 8°C for up to 35 days in a vacuum package to simulate a supermarket storage environment; related indicators were measured periodically every week. The results showed that the first PC explained 59.82% of the total variation, and the second explained 22.28%. PC 1 was a concentrated reflection of color changes of SCCB during storage and PC 2 was an environment factor causing the change of color. The change in apparent redness is mainly caused by redox reaction of the nitroso hemochromogen (NH ) (eigenvectors of a* , C and NH in PC 1 were all the maximum value of 0.28); a* was correlated with NH (0.96), free sulfhydryls (0.98), carbonyl derivatives (?0.95) formed during protein oxidation, and malondialdehyde (?0.98) and dienes (?0.92) formed by lipid oxidation. Color fading was significantly correlated with oxidizing and reducing power, existing forms of nitrogen and with the pH of the meat matrix. Changes in the internal environment of the sample initially influenced L* and b* values, and subsequently a* .