京津冀一次区域性暴雨特征分析

利用FNL再分析资料、卫星资料和自动站资料对2019年7月22~23日京津冀一次区域性暴雨过程进行了环流形势、卫星云图、动热力结构的分析。结果表明:此次暴雨发生在500hPa两槽一脊、副热带高压北抬、低空急流的大尺度环流背景下。西南方向的水汽输送和黄渤海的补充水汽为暴雨提供了良好的水汽条件,在河北中部的水汽辐合抬升则为暴雨提供了抬升条件。此次暴雨的产生受中尺度对流云团的连续生成合并影响,降水效率高。在暴雨中心整层表现为低层辐合、高层辐散,上升速度中心明显,使得高层的抽吸作用更强,更有利于上升运动的维持与发展,为降水强度增大提供了有力的动力条件,高空弱冷空气的入侵对能量锋区不稳定能量的释放起到了触发作用。     

The effects of density and artificial substrate on intensive shrimp Litopenaeus vannamei nursery production

Recirculating aquaculture systems (RAS) can be installed indoors, allowing year-round production of tropical animals in nearly any climate. A nursery phase is commonly used in Litopenaeus vannamei production since it allows for enhanced biosecurity and better quantification of animals while reducing space requirements. However, it is unclear whether animal density and inclusion of artificial substrate may improve shrimp performance during the nursery phase. In this experiment, we compared shrimp production parameters in two stocking densities with or without the use of an artificial substrate by creating four treatments: low-density LD; 1500 PL/m⁻³, low-density with substrate LDS, high-density HD; 3000 PL/m⁻³), and high-density with substrate (HDS). The LDS and HDS treatments included 0.46-m² of high-density polyethylene 2.5-cm mesh as a substrate, which increased the tank surface area by 21 %. Each treatment was randomly assigned to four 160-l culture tanks, each with a biofilter. The shrimp had an initial weight of 4 mg and were grown for 50 days. The low-density treatments had significantly higher dissolved oxygen (DO) and pH than the high-density treatments (P ≤ 0.001). Specifically, LDS had the highest DO and pH followed by the LD, HD, and HDS treatments, respectively. High-density treatments had significantly higher NO₂-N levels than low-density treatments during week 2 of the experiment when an unusually high concentration of nitrite was observed. FCR was significantly lower in both low-density treatments than in high-density treatments. At harvest, the total biomass (kg m⁻³) was significantly higher in high-density treatments than in low-density treatments (P ≤ 0.001), and the HDS treatment had a significantly greater biomass output than HD. Producers should consider artificial substrate and higher densities during nursery production to maximize shrimp production; however, the effects on water quality should also be taken into account.     

藏北地区草地资源及其合理利用

本文论述了藏北地区草地资源的类型、数量、分布和载畜潜力，分析了存在的主要问题的继续发展的基本因素，提出了挖掘资源潜力、实行季节性畜徼业、增加草地投入等具体措施。     

华北山区草地资源及其生产力的研究

华北山区位于温带——暖温带，东经１０７°～１２３°，北纬３５°～４３°。包括山东丘陵区，太行山区，冀北辽西山地区，阴山山地区四部分。该区属于农牧业交错区，农业、牧业（农区牧业和草地牧业）、林业十分发达，并且在迅速发展。华北山区是我国小麦、玉米和杂粮的主要产区。草地类型多样，饲草料丰富，又是养牛业、养羊业、养猪业相当发达的地区。经统计，华北山区总人口为５６２９万，总土地面积３５４５万ｈａ，天然草地总面积为１５８８．９１万ｈａ，占土地总面积的４４．８２％，人均草地０．２８２３ｈａ。各个区的草地类型不同，生产力差异显著（ｐ＜０．０１）。     

浙北地区早熟松花菜品种比较试验

在浙北松花菜秋季栽培区选择试点,对6个早熟松花菜新品种进行了比较试验。试验结果表明,浙农松花50天是浙北地区秋季抢早栽培的较为理想的品种,而农美50天产量潜力最大,但成熟期略迟,生产上可根据实际情况加以应用。     

Use of Porcine Meal in Plant‐based Practical Diets for Pacific White Shrimp,Litopenaeus vannamei

Two growth trials were conducted to evaluate and confirm the efficacy of a porcine meal (PM) with high protein content (>90%) as an alternative feed ingredient in commercial‐type feed formulation for Pacific white shrimp, Litopenaeus vannamei. Six experimental diets were formulated for the two growth trials. The first five diets contained increasing levels (0, 1, 2, 4, and 6%) of PM as a replacement for soybean meal in a plant‐based diet with low inclusion level (6%) of fish meal (FM). The last experimental diet was produced utilizing 4.2% PM to completely replace FM. In Trial 1, shrimp (1.5 g initial mean weight, 20 shrimp/tank, n = 4) were offered test diets for 6 wk in a semirecirculation system. At the end of Trial 1, shrimp fed with the diet containing 6% PM exhibited significantly enhanced weight gain (WG), feed conversion ratio (FCR), and survival compared to those fed with the diet devoid of FM. As survival was poor across all treatments and different densities could mask growth results the trial was repeated. In Trial 2, shrimp (0.85 g, 15 shrimp/tank, n = 4) were offered diets for 6 wk. Dietary supplementation of PM at 6% significantly improved WG, FCR, and apparent net protein retention in contrast with the treatment devoid of FM, confirming the same trends in Trial 1. No significant difference was detected in protein, lipid, moisture, and mineral profiles of whole‐body shrimp as well as survival across all the treatments. Results of this study indicate that PM is a good high protein source in shrimp feeds, which can be included up to 6% in the low FM‐based diet without compromising the growth of shrimp.     

月相对北太平洋海域柔鱼钓获率的影响

月相是影响光诱鱿钓作业效率的重要因素之一。通过对1995~2000年北太平洋8~10月150°E~165°E柔鱼盛渔期的生产统计分析,各月月相在朔期间的产量分别为望期间产量的1.16、1.53和1.20倍,平均日产量分别增加0.38 t/d、0.9 t/d和0.21 t/d。经过GAM模型分析,月相对日产量的影响是显著的,其PC f值均在0.14以下,模型分析结果满意。     

森林抚育对华北落叶松生长影响的调查与分析

为研究森林抚育措施对华北落叶松生长的影响,在宝鸡市马头滩林业局选择华北落叶松人工纯林作为研究对象,对经过抚育措施后影响华北落叶松生长进行了调查与分析,结果表明:1、华北落叶松林分进行抚育后平均胸径和生长率都是增加。 2、华北落叶松林分进行抚育后平均胸径和生长率增长的年数不同,在抚育后2-3年达到了最大值,林分进行抚育后生长率变化规律是先增加后下降,呈正态曲线的变化趋势,说明其生长速度由于生长空间增大而加快。     

北美的分级测试项目简介

本文介绍了北美的分级测试项目的背景,简要介绍了锯材应力赋值的历史以及促使锯材工业进行此项研究的原动力.     

Assessing the efficacy and impact of management of an invasive species in a protected area: Poa annua on sub‐Antarctic Macquarie Island

Plant eradication is difficult, particularly in remote, protected areas. The Southern Ocean Islands are very isolated and highly protected, but the flora contains many alien plants. Small restricted populations have been eradicated, but eradication of established species has proven difficult. A better understanding of the efficacy of control methods at sub‐Antarctic temperatures and their off‐target impacts may increase eradication success. With interest in controlling non‐native Poa annua in the region, we aimed to determine if physical and chemical methods can control P. annua (the sub‐Antarctic biotype) in sub‐Antarctic conditions and examined their impact on native plants. We quantified the effectiveness of physical control methods on P. annua in situ on sub‐Antarctic Macquarie Island through field‐based experiments and assessed their selectivity on P. annua compared with native grasses. We also quantified the effectiveness of several herbicides on P. annua at sub‐Antarctic temperatures and assessed their selectivity on native grasses. Of the four physical disturbance methods tested, none effectively reduced P. annua cover as one‐off treatments. Of the herbicide treatments, glyphosate and trifloxysulfuron sodium were effective and were less damaging to native grass species, indicating potential selectivity. Physical control was of limited effectiveness, but did not affect native species richness. An integrated weed management programme utilising the strategic use of selective herbicides with follow‐up chemical and physical intervention may balance control and biodiversity outcomes. This research highlights the importance of site‐specific testing of control methods and understanding off‐target impacts of control when managing alien plant species in protected areas.