The effect of preferential flow on the short and long-term spatial distribution of surface applied solutes in a structured soil

We measured the lateral distribution of Br in a well-structured soil (clayey, kaolinitic, thermic Typic Kanhapludults) over a period of 40 days following a leaching event with Br-tagged water (Event-1) and the subsequent vertical transport of solute that occurred following a second leaching event (Event-2). The objectives were to determine the time required for solutes to become uniformly distributed laterally after Event-1, and the effect that degree of spatial distribution had on the subsequent vertical movement induced by Event-2. Six field plots, 1.2 by 1.2 m, were exposed to Event-1. Three of the plots were sampled 1, 5, or 40 days later. The three remaining plots were exposed to Event-2 either 1, 5, or 40 days following Event-1 and they were sampled the day following Event-2. A total of 319 samples were taken from a 38.5 by 38.5 cm area in the center of each plot at each of five depths ranging from 5 to 60 cm. Bromide was practically uniformly distributed in the surface layer immediately following Event-1, as indicated by a coefficient of variation (CV) of 25% among the 319 samples, but became progressively more non-uniformly distributed as depth increased. At 60 cm, the CV had increased to 240%. The longer we delayed sampling following Event-1, the more uniform was the lateral distribution of Br. During the 40 days following Event-1, Br became practically uniformly distributed across all layers, and the center of mass moved from 8 to 16 cm below the surface. Event-2 caused Br to move deeper within the soil profile when it occurred the day following Event-1 than when it occurred later, but because drainage occurred during the 40-day delay, the center of Br mass was located 26–27 cm below the surface after Event-2 regardless of the delay time.     

陕京输气管道采用浮桶漂管穿越河流

在陕京输气管道穿越北拒马河工程中,采用了浮桶漂管法,成功地完成了此次穿越施工。指出在适宜的水文地质条件下可选用浮桶漂管法,并对其施工方法、施工程序及各程序的具体做法均作了较详细的介绍。该施工方法可缩短工期、降低造价、对于地下水位高、渗水速度快的砂卵石层河床优先推荐选用。     

Analysis of the Medium Pressure Range in Urban Gas Transmission and Distribution System

According to the analysis of technology and economy about the gas supply with the medium pressure in gas pipeline network of urban gas transmission and distribution system,a more economical and feasible pressure value is obtained.     

一类时变一阶线性微分方程组参数辨识的一种方法

本文给出一类时变一阶线性微分方程组：ｄｘ（ｔ）ｄｔ＝ａｘ（ｔ）＋ｂｒ－ｔｙ（ｔ）,ｄｙ（ｔ）ｄｔ＝ｃｒｔｘ（ｔ）＋ｄｙ（ｔ）的参数ａ,ｂ,ｃ,ｄ,ｒ的一种辨识方法     

对应分析方法的注记

本文说明了对应分析中变量的协方差阵是一个退化矩阵。阐述了要进行对应分析时,原始数据应满足的条件。通过讨论得出进行对应分析若需要对原始数据作标准化处理时,模标准化、最大值标准化和总和标准化总是可行的,应用极差标准化是有条件的;而中心化、离差标准化和标准差标准化则不可使用     

Vagococcus salmoninarum II—qPCR,tropism and egg-associated transmission

Vagococcus salmoninarum was identified as the causative agent of a chronic epizootic in broodstock “coaster” brook trout (Salvelinus fontinalis) at the Iron River National Fish Hatchery. The epizootic spanned more than a year, was unresponsive to multiple florfenicol treatments, and resulted in >50% mortality of the affected fish. The decision was made to cull the remaining fish during spawning, which presented an opportunity to more thoroughly examine V. salmoninarum sampling methods, organ tropism and vertical transmission. A newly developed qPCR targeting the pheS gene was used in concert with bacterial culture to show that V. salmoninarum indeed disproportionately affects females and has a tropism for female reproductive tissues. The study demonstrates that some female reproductive tissues (e.g. ovarian fluid, unfertilized eggs) are also an effective option for non-lethal detection. Despite the widespread presence of V. salmoninarum in ovarian fluid and on egg surfaces, we found no evidence of intra-ova transmission.     

Quantifying the impact of temperature variation on birnavirus transmission dynamics in hard clams Meretrix lusoria

Susceptibility of hard clams Meretrix lusoria to birnavirus (BV) infections caused by temperature variations, from a mechanistic perspective, has rarely been explored. We used a deterministic susceptible–infectious–mortality (SIM) model to derive temperature-dependent key epidemiologic parameters based on data sets of viral infections in hard clams subjected to acute temperature changes. To parameterize seasonal pattern dependence, we estimated monthly based cumulative mortality and basic reproduction numbers (R₀) between 1997 and 2017 by way of statistical analysis. Two alternative disease control models were also proposed to assess status of controlled temperature-mediated BV infection by using, respectively, control reproduction number (R_C)-control line criterion and removal strategy-based control measure. We showed that based on R_C-control strategy, when temperatures ranged from 15 to 26.8°C, proportion of susceptible hard clams removed should be at least 0.22%. Based on removal-control strategy, we found that by limiting pond water temperature to 25–30°C, together with increased removal rates and periods to remove hard clams, it is better to remove hard clams from June and August to reduce both mortality rate and spread of BV. Our results can be used to monitor BV transmission potential in hard clams that will contribute to government control strategy to eradicate future BV epidemics.     

A comparative epizootiologic study of the two fish‐pathogenic serovars of Vibrio vulnificus biotype 2

Vibrio vulnificus biotype 2 is subdivided into two main serovars, serovar E, able to infect fish and humans, and serovar A, only virulent for fish. Serovar E emerged in 1976 as the causative agent of a haemorrhagic septicaemia (warm‐water vibriosis) affecting eels cultured in brackish water. Serovar A emerged in 2000 in freshwater‐cultured eels vaccinated against serovar E, causing warm‐water vibriosis with fish showing a haemorrhagic intestine as the main differential sign. The aim of the present work was to compare the disease caused by both serovars in terms of transmission routes, portals of entry and host range. Results of bath, patch‐contact and oral‐anal challenges demonstrated that both serovars spread through water and infect healthy eels, serovar A entering mainly by the anus and serovar E by the gills. The course of the disease under laboratory conditions was similar for both serovars in terms of transmission and dependence of degree of virulence on water parameters (temperature and salinity). However, the decrease in degree of virulence in fresh water was significantly greater in serovar E than in serovar A. Finally, both serovars proved pathogenic for tilapia, sea bass and rainbow trout, but not for sea bream, with significant differences in degree of virulence only in rainbow trout. In conclusion, serovar A seems to represent a new antigenic form of V. vulnificus biotype 2 with an unusual portal of entry and is better adapted to fresh water than serovar E.     

对称矩阵的一些性质和定理

讨论了有关对称矩阵的一些性质和定理,为以后研究对称矩阵的相关理论,提供了方便的途径.     

用初等变换求矩阵的特征值问题

依据矩阵初等变换的定理及其性质,证明了任意1个n级复矩阵A,都存在1个n级可逆矩阵p,使得p-1 AP=Λ为1个上三角矩阵.从而把求任意1个n级矩阵的特征值的问题通过初等变换转化为求上三角形矩阵的特征值的问题,并给出了求解的具体步骤.