Using Linux server as a gateway between the local area network and the Internet may lead to slow pace in network transmission and even data loss. In this study,the above problem and its solution were discussed.
隧道已经在互联网中大量部署。隧道通信中两次端到端通信及途中封装及解封装的特点,会导致隧道出口出现重组现象。分析了隧道中重组的具体代价,表明重组极大地影响着隧道转发性能。对现有隧道MTU问题解决方案进行了研究,提出了在隧道入...隧道已经在互联网中大量部署。隧道通信中两次端到端通信及途中封装及解封装的特点,会导致隧道出口出现重组现象。分析了隧道中重组的具体代价,表明重组极大地影响着隧道转发性能。对现有隧道MTU问题解决方案进行了研究,提出了在隧道入口实施的SFCT(SRC Fragment Completely for Tunnel)模型和FATE(Fragment in Advance on Tunnel Entry)模型来规避隧道中的重组,并给出了主要类型隧道中MTU问题的方案选择策略。模拟实验验证了其可用性及较好的性能。展开更多
A novel phytoplasma was detected in a cherry plum（Prunus cerasifera Ehrh） tree that mainly showed yellow leaf symptom. The tree was growing in an orchard located in Yangling District, Shaanxi Province, China. The le...A novel phytoplasma was detected in a cherry plum（Prunus cerasifera Ehrh） tree that mainly showed yellow leaf symptom. The tree was growing in an orchard located in Yangling District, Shaanxi Province, China. The leaves started as chlorotic and yellowing along leaf minor veins and leaf tips. Chlorosis rapidly developed to inter-veinal areas with the whole leaf becoming pale yellow in about 1-4 wk. Large numbers of phytoplasma-like bodies（PLBs） were seen under transmission electron microscopy. The majority of the PLBs was spherical or elliptical vesicles, with diameters in range of 0.1-0.6 μm, and distributed in the phloem cells of the infected tissues. A 1 246-bp 16 S ribosomal RNA（rRNA） gene fragment was amplified from DNA samples extracted from the yellow leaf tissues using two phytoplasma universal primer pairs R16mF2/R16mR1 and R16F2n/R16R2. Phylogenetic analysis using the 16 S rRNA gene sequence suggested that the phytoplasma associated with the yellow leaf symptoms belongs to a novel subclade in the aster yellows（AY） group（16SrI group）. Virtual and actual restriction fragment length polymorphism（RFLP） analysis of the 16 S rRNA gene fragment revealed that the phytoplasma was distinguishable from all existing 19 subgroups in the AY group（16SrI） by four restriction sites, Hinf I, Mse I, Sau3 A I and Taq I. The similarity coefficients of comparing the RFLP pattern of the 16 S rRNA gene fragment of this phytoplasma to each of the 19 reported subgroups ranged from 0.73 to 0.87, which indicates the phytoplasma associated with the cherry plum yellow leaf（CPYL） symptoms is probably a distinct and novel subgroup lineage in the AY group（16SrI）. In addition, the novel phytoplasma was experimentally transmitted to periwinkle（Catharanthus roseus） plants from the tree with CPYL symptoms and then back to a healthy 1-yr-old cherry plum tree via dodder（Cuscuta odorata） connections.展开更多
文摘Using Linux server as a gateway between the local area network and the Internet may lead to slow pace in network transmission and even data loss. In this study,the above problem and its solution were discussed.
文摘隧道已经在互联网中大量部署。隧道通信中两次端到端通信及途中封装及解封装的特点,会导致隧道出口出现重组现象。分析了隧道中重组的具体代价,表明重组极大地影响着隧道转发性能。对现有隧道MTU问题解决方案进行了研究,提出了在隧道入口实施的SFCT(SRC Fragment Completely for Tunnel)模型和FATE(Fragment in Advance on Tunnel Entry)模型来规避隧道中的重组,并给出了主要类型隧道中MTU问题的方案选择策略。模拟实验验证了其可用性及较好的性能。
基金supported by the 111 Project from the Ministry of Education of China (B07049)the PhD Program Foundation from the Ministry of Education of China (20100204110004)the National Natural Science Foundation of China (31371913)
文摘A novel phytoplasma was detected in a cherry plum（Prunus cerasifera Ehrh） tree that mainly showed yellow leaf symptom. The tree was growing in an orchard located in Yangling District, Shaanxi Province, China. The leaves started as chlorotic and yellowing along leaf minor veins and leaf tips. Chlorosis rapidly developed to inter-veinal areas with the whole leaf becoming pale yellow in about 1-4 wk. Large numbers of phytoplasma-like bodies（PLBs） were seen under transmission electron microscopy. The majority of the PLBs was spherical or elliptical vesicles, with diameters in range of 0.1-0.6 μm, and distributed in the phloem cells of the infected tissues. A 1 246-bp 16 S ribosomal RNA（rRNA） gene fragment was amplified from DNA samples extracted from the yellow leaf tissues using two phytoplasma universal primer pairs R16mF2/R16mR1 and R16F2n/R16R2. Phylogenetic analysis using the 16 S rRNA gene sequence suggested that the phytoplasma associated with the yellow leaf symptoms belongs to a novel subclade in the aster yellows（AY） group（16SrI group）. Virtual and actual restriction fragment length polymorphism（RFLP） analysis of the 16 S rRNA gene fragment revealed that the phytoplasma was distinguishable from all existing 19 subgroups in the AY group（16SrI） by four restriction sites, Hinf I, Mse I, Sau3 A I and Taq I. The similarity coefficients of comparing the RFLP pattern of the 16 S rRNA gene fragment of this phytoplasma to each of the 19 reported subgroups ranged from 0.73 to 0.87, which indicates the phytoplasma associated with the cherry plum yellow leaf（CPYL） symptoms is probably a distinct and novel subgroup lineage in the AY group（16SrI）. In addition, the novel phytoplasma was experimentally transmitted to periwinkle（Catharanthus roseus） plants from the tree with CPYL symptoms and then back to a healthy 1-yr-old cherry plum tree via dodder（Cuscuta odorata） connections.
文摘目的利用AFLP分型和分子标记了解我院鲍曼不动杆菌(Acinetobacter baumannii.AB)菌株亲缘性和传播途径。方法应用PCR方法,对17种内酰胺酶基因、6种氨基糖苷类修饰酶基因、耐消毒剂和磺胺基因、整合子遗传标记(整合酶基因)、Tn21/Tn501转座子遗传标记(汞离子还原酶基因)进行检测;采用扩增片段长度多态性(Amplified Fragment Length Polymorphism,AFLP)进行AB菌分型;对检测结果作样本聚合分析讨论菌株亲缘性并根据临床资料研究AB的传播途径。结果27株AB不仅TEM、OXA-23群、ADC等内酰胺酶基因携带率高,而且包括aac(3)-Ⅰ、aa(c6′)-Ⅰ、an(t3″)-Ⅰ氨基糖苷类修饰酶编码基因,qacE△1-sul1耐消毒剂和磺胺基因,Ⅰ类整合酶基因携带率高。多基因聚合分析发现存在至少3个克隆。AFLP分型发现耐药菌是由同一个克隆进化而来。结论医院的ICU病房已经成为耐药AB菌发生、进化、传播的核心环节。加强ICU的管理工作是防止院内耐药AB菌流行的重要手段。而控制抗生素的使用,可以使AB菌的耐药性逐步减弱。
