Net depth response of a depth-controllable (towed) gillnet for fish sampling

SUMMARY: Flume-tank experiments were performed to examine the depth response of a new type of depth-controlled gillnet. Variations of net depth were investigated as the warp was paid out and wound up for different changes of warp length, main sinker weights, and winch speeds. In most experiments, when the warp finished paying out, the net continued to descend and then ascended slightly to an equilibrium depth (overshoot phenomenon). The overshoot distance was nearly constant when the warp was wound up and increased linearly with increasing winch speed when the warp was paid out. An increase in winch speed reduced net settling time, which converged on a constant value for both paying out and winding up.     

长安区城市森林建设思路探讨

本文探讨了如何在西安市近郊长安区发展城市森林,以适应西安现代国际化大都市建设发展的需要。     

香菇简易开放式栽培高产菌株的早期鉴定

试验对５个香菇菌株进行简易开放式栽培并观察其特性，发现菌丝生长速度、锁状联合数与生物学效率相关性不密切，香菇的酶活性，子实体形成所需时间、子实体单重、菌盖重与生物学效率密切相关。     

沙尘暴应急监测方法研究

在沙尘暴应急监测方法研究中,通过对总悬浮颗粒物采样仪器及各种采样参数的研究确定和降尘采样器的研制,制定出沙尘暴应急监测方法。     

百合组培中鳞片处理及其颜色变化与鳞茎形成的关系

 研究了百合鳞片发育程度、切割段数、形态及生理变化、培养基的P 和K含量与鳞茎形成的关系。结果表明: 取中层鳞片、每片横切6 段的繁殖系数最高, 基部鳞片结鳞茎数最多, 且鳞茎发生最早。鳞片由基部向顶部繁殖系数递减。培养过程中鳞片颜色和形态变化依次为乳白色、浅黄、浅紫色、绿紫、鳞片干枯、鳞茎增大, 鳞片由浅黄变为绿紫色过程中叶绿素含量增加, 淀粉和可溶性糖含量下降。适当增加培养基中P、K的含量可提高鳞茎形成的数量和质量。     

沙尘物质的来源与防治途径

本文分析了沙尘暴形成的自然过程和危害特征,并探讨了内蒙古沙源区土壤颗粒物质的含量,指出沙尘暴的沙尘来源主要是退化草原、活化的沙地和裸露坡耕地等。同时根据风沙流运移规律及其和土壤颗粒的关系,提出了防治沙尘暴的关键技术原理,并探讨了有效控制沙尘暴的技术途径。     

Evaluation of sampling methods and assessment of the sample size to estimate the weed seedbank in soil, taking into account spatial variability

As field sampling is time consuming, it is necessary to develop efficient sampling techniques to obtain accurate estimates of the weed seedbank in soil. The relative efficiency between sampling schemes depends on the spatial variability in weed seed density across agricultural fields. Spatial variability of the weed seed density was characterized by theoretical correlograms. A systematic sampling (square grill) scheme was considered and it was found that, taking into account spatial variability, this sampling scheme was more efficient than simple random sampling. As a result, the sample size can be reduced in comparison with that given in previous studies, where spatial correlation was ignored. The reduction depends on the correlation structure defined as a function of the ratio, τ, between the nugget effect and the sill of the variogram. The maximum reduction of the sample size, without loss of either precision or confidence level corresponds to the case where there is no nugget effect, τ = 0. The opposite extreme case, where the reduction is nil, corresponds to the case of a pure nugget effect τ = 1. The abaci based on given expressions are provided to determine the sample size in species whose spatial pattern can be fitted either to a Poisson or to a negative binomial distribution.     

Heritability and genetic correlations between rumination time and production traits in Holstein dairy cows during different lactation phases

So far, rumination has been used as a proxy for monitoring dairy cow health at farm level. However, investigating its genetic aspects as well as its correlation with other important productive traits may turn this management tool into a new informative selection criterion. However, scientific evidences on genetic correlation among rumination time (RT) and milk production and milk composition are still scarce. Therefore, the objective of this study was to estimate the heritability of RT across three lactation phases and its genetic correlation with milk production, milk composition and somatic cell count (SCC). Results of our study showed that heritability for RT was 0.34 and was constant across lactation. The mean genetic correlations between RT and milk production and composition traits were 0.07 (milk production), ?0.07 (protein yield), ?0.31 (fat yield), and ?0.32 (fat/protein ratio). The mean genetic correlation between RT and the SCC was 0.05.     

多目标资源调查站位优化设计——以渤海为例

本研究以渤海为研究区域,通过数值模拟,分析了种类出现率(将基于渤海调查的17个主要渔业种类分为3类:Ⅰ类出现率≥70%,Ⅱ类出现率50%～70%,Ⅲ类出现率50%)和栖息水层对单种类资源量相对误差(Relative error, REE)的影响,不同调查站位数量(48和60)对定点采样与分层随机采样分析结果的影响,并优化了渤海多目标渔业资源调查的设计方案。结果显示,Ⅰ类中5种资源量REE在20%以内,Ⅱ类中3种资源量REE在30%以内,Ⅲ类中6种资源量REE在35%以内,即单种资源量评估值随种类出现率下降,相对误差变大;种类的栖息水层对种类资源量REE无明显影响。定点采样评估值随站位数量减少,精度下降(鱼类、虾类、蟹类、头足类的资源量指数和Margalef丰富度指数的REE分别增加了1.1%、2.5%、8.4%、4.4%和3.3%);分层随机采样可弥补站位数减少带来的精度下降,如站位数为48的分层随机采样获得的鱼类资源量指数评估精度(REE为4.6%)高于站位数为60的定点采样的精度(REE为7.7%),有助于减少调查成本和保护资源量低的种类。然而,每种采样方法并不能完全满足多目标最优,不同站位分配方案影响分层随机采样的精度,按照抽样费用最优准则设置站位,可获得精确度较高的鱼类、虾类、蟹类、头足类及黄鲫(Setipinnataty)、口虾蛄(Oratosquillaoratoria)、日本枪乌贼(Loligojaponica)、鳀鱼(Engraulis japonicus)、叫姑鱼(Johniusgrypotus)、泥脚隆背蟹(Carcinoplaxvestita)、中国对虾(Fenneropenaeus chinensis)等主要种类资源量评估结果,可作为渤海多目标种类资源调查的站位设计方案。     

谷物胚乳性状QTL区间作图的贝叶斯方法

将贝叶斯统计原理和胚乳性状的数量遗传模型相结合,以分离群体中各植株的分子标记基因型以及植株上若干粒种子胚乳性状的单粒观测值为数据模式,提出胚乳性状QTL区间作图的贝叶斯方法.该方法通过Gibbs以及Metropolis-Hastings抽样实现的马尔科夫链蒙特卡罗(MCMC)算法获得QTL效应和位置的估计.方法的有效性用染色体水平和基因组水平2套模拟方案进行验证,结果表明:贝叶斯方法能够准确地估计胚乳性状QTL的位置和效应,并同时区分2种显性效应.