种蛋表面积和体积的新型公式及测算

采用修正椭球的方法,逼真地描绘出了种蛋的几何外形,并推导出了表面积和体积的解析公式。简单测量种蛋的几何尺寸,便能求得表面积和体积的数值。通过模拟图形与照片的比对,发现在几何特征上拟合效果良好。测算得到的体积,与溢水法测得的体积相比,误差小于千分之五。     

Differences in swimbladder volume between Baltic and Norwegian spring-spawning herring: Consequences for mean target strength

Fish swimbladders, where present, contribute most to the scattering of sound by fish, as measured by the target strength (TS). The volumes of the swimbladders of two different European stocks of Atlantic herring were compared to consider the effect on estimates of TS. Swimbladder volumes of Baltic and Norwegian spring-spawning herring (Clupea harengus) were measured, together with individual herring fat content. Swimbladder volumes were found to differ significantly between the two herring stocks. Baltic herring have a larger swimbladder volume, which is suggested to be associated with the fish's low fat content, which in turn may be linked to its specific energy budget and the low salinity of the Baltic Sea. A buoyancy model that considered the different salinity conditions and fat proportions was used to evaluate the observed differences in swimbladder volume. The swimbladder volume data were subsequently used to model the mean target strength as a function of depth and growth pattern. Backscattering of the swimbladder was modelled using the modal-series-based deformed-cylinder model (MSB-DCM), describing the swimbladder as a gas-filled, elongated prolate spheroid. The fish body component was modelled as a fluid-filled ellipsoid using the distorted wave Born approximation (DWBA). Modelling results support a different TS-to-size relationship for Baltic herring, with a stronger echo, due to the larger swimbladder. Depth- and length-dependent TS relationships based on the model results are suggested.     

Caudal vena cava point-of-care ultrasound in dogs with degenerative mitral valve disease without clinically important right heart disease

ObjectivesCaudal vena cava (CVC) diameter and collapsibility index (CVC_D and CVC_CI) have been used to assess intravascular volume status (IVS). Maladaptations with progressive degenerative mitral valve disease (DMVD) lead to hypervolemia. We hypothesised that stages of DMVD will affect ultrasonographic CVC variables in dogs without clinically important right heart disease.Animals, materials and methodsThis retrospective study included 79 dogs with DMVD presented to the cardiology department between January 2017 and 2019. Subxiphoid views were used to obtain CVC cineloops. By visual inspection, CVC was subjectively scored as flat, normal or fat. Maximal and minimal CVC_D were measured and indexed to aortic diameter (CVC_D-max/Ao and CVC_D-min/Ao); CVC_CI was calculated as (CVC_D-max-CVC_D-min)/CVC_D-max. Fisher's exact and Kruskal–Wallis tests were used to compare CVC variables.ResultsSubjective assessment was associated with American College of Veterinary Internal Medicine (ACVIM) stages (P < 0.001). The proportion of fat CVC was greater in stages C and D. In stage D, CVC_D-max/Ao was larger compared with stages B1, B2 and C (P = 0.002, P = 0.002 and P = 0.035, respectively). In stages C and D, CVC_D-min/Ao was larger compared with B1 (P = 0.016 and P = 0.001) and B2 (P = 0.002 and P < 0.001. In stages C and D, CVC_CI was less than stage B1 (P = 0.016 and P = 0.044) and B2 (P = 0.001 and P = 0.010).ConclusionsIn dogs with DMVD without clinically important right heart disease, CVC variables differ across ACVIM stage. Subjective and objective CVC variables may be used to predict hypervolemia.     

竹炭导电率及高导电率竹炭制备工艺研究

通过对竹炭炭化过程的研究，得出炭化温度，炭化时间是影响石墨化和导电性能的重要因素。实验测定了不同炭化时间与炭化温度下的体积电阻率，含水率和产率，提出了以干馏的方法获取普通的竹炭原料，并通过二次加工制备高导电率竹炭的方法及工艺。     

杨树氮肥适宜用量试验研究

采用田间小区试验,在施用一定量磷钾的基础上,研究不同氮用量对江汉平原杨树的生长及材积量的影响。研究表明:杨树每株施用纯氮100g,材积量每hm~2比对照多增2.84m~3,增产率66.98％,差异达极显著水平;每株杨树施用氮素100g比施用氮素50g,材积量每hm~2多增1.16m~3,多增产19.59％;株施氮素100g比不施用氪素每hm~2净增收入624元,投产比1.00:2.74。综合分析,江汉平原杨树每株施用氮素100g为宜。     

盗伐、滥伐林木材积测定(之一)

盗伐、滥伐林木材积涉及案件的性质和处罚。用1株伐倒木资料，分别立木状态、伐倒木状态计算其材积。为保证材积测定准确，当盗伐、滥伐林木呈伐倒木状态，且数量少时，宜采用中央断面区分求积式、牛顿区分求积式或二元材积表测定材积。     

白桦胸径和材积生长率相关关系的研究

根据地位指数的大小将白桦林分划分为好、中、差３个类型，通过没类型样地上的解析木资料分析，证明白桦的胸径和材积生长率存在关良好的相关关系。经过优选，建立了不同类型白桦林分的胸径与材积生长率相关模型，并依此编制出白桦一元材积生长率表，为准确预测白桦积生长率提供了理论上的依据。     

人工降雨条件下不同坡度红壤坡面迳流泥沙变化特征研究

在人工模拟降雨强度为1.44 mm/min的条件下,研究了不同坡度(β)红壤近似裸地坡面迳流、泥沙的变化特征,研究结果表明:①地表迳流量随坡度的增大而迅速增加。②当β≤23°时,土壤侵蚀量随坡度的增大而迅速增加;当25°≤β≤40°时,土壤侵蚀量随坡度变化较小。③坡面土壤侵蚀的临界坡度则介于23°~25°之间。④坡度与侵蚀量关系可用函数表示为:S=199.1×L1.65×tan1.4β(0°≤β≤23°)。     

浙江天童国家森林公园常绿阔叶林主要组成树种材积与生物量相关关系探讨

以天童国家森林公园常绿阔叶林主要组成树种为研究对象,通过测定其各组分生物量,建立了实测生物量与材积之间的回归模型,结果表明:主要组成树种各组分生物量与其材积之间存在着密切的相关关系,各主要树种材积与生物量的回归模型存在差异;回归方程精度较高,用于根据地区常绿阔叶林主要树种材积推算其生物量是可行的。     

单株立木材积测定方法的研究

单株立木材积的测定对林业生产和科学研究工作有着重要的作用,主要的测定方法是通过胸径、树高、上部直径或上部直径的高度来计算干形指数,然后计算单株立木材积。而不同的方法所用上部直径不同。本文用5个树种的解析木,分别对较常见的5种测定方法的测定精度进行了研究。得出的结论为:3/4形点法、0 5形点法、胸高形率法精度较高,绝对形率法、望高法精度较低。建议对干形饱满的树种采用3/4形点法、0 5形点法;对干形尖削的树种采用0 5形点法、胸高形率法。