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111.
针对数控机床误差溯因方法复杂且适应性差的问题,提出了基于数控系统圆检测图形的特征角点分布规律,并与神经网络相结合实现对机床运动误差的快速溯因方法。首先,提取所生成圆图形的特征角点,构造反向间隙、周期误差等特征矩阵;然后结合神经网络将低维特征矩阵映射至高维特征空间,实现对数控机床误差的快速溯因。实验表明,该方法简单有效,误差识别准确率较高,且具有较强的通用性。 相似文献
112.
脉宽调制型变量喷雾系统雾量沉积分布 总被引:2,自引:4,他引:2
通过实验和理论分析建立了雾量分布模型,研究了雾量分布规律。研究表明:喷杆方向沉积变异系数在两喷头之间出现最低,而在两喷头正下方出现极高值;行驶方向的沉积变异系数沿着一定规律周期性变化,其周期与占空比相关;在相同压力的情况下,同一喷头的行驶方向及喷杆方向沉积变异系数的峰值均随着车速的提高而上升,随占空比的上升而下降;在研究范围内(40~60cm),变异系数的峰值随喷头高度的升高而降低;若车速和占空比均相同,110°扇形喷头的雾量分布较80°扇形喷头在时空方向上都更加均匀。 相似文献
113.
中国对虾育苗时间与温度的关系及其应用 总被引:2,自引:0,他引:2
根据多年的调研和试验资料,利用非线性积温模型,模拟了对虾幼体各发育阶段所需天数与水温的关系。在此基础上研究确定了亲虾产卵孵化期的气候决策模式;并应用模式计算出了我市亲虾产卵孵化的适宜时段。为亲虾适宜产卵孵化期的决策提供了科学方法。 相似文献
114.
改性木质素对砖红壤磷素有效性的影响 总被引:5,自引:0,他引:5
磷肥施入砖土壤后,土壤速效磷随着时间的推移,呈现下降的趋势。利用改性木质素缓释磷铵,可以有效地络合土壤活性钵,降低其活性,从而阻止土壤速效磷被固定,使土壤磷素维持在较高的水平。土壤中交换性钙和交换性镁对土壤速效磷的影响不大。 相似文献
115.
黄颡鱼(Pelteobagrus fulvidraco)是较为典型的淡水刺毒鱼类,本研究结合宏观毒棘骨骼标本制作和微观组织切片等方法,深入探究黄颡鱼的毒棘结构。研究结果表明,黄颡鱼的胸鳍和背鳍均具有尖锐的倒刺棘骨,棘骨外包围着皮膜,皮膜拥有能分泌毒液的毒腺细胞,它们共同组成了黄颡鱼毒棘装置。毒棘骨骼宏观结构表明,黄颡鱼的背鳍和胸鳍毒棘均具有贯穿全棘骨的中央管和包围棘骨的皮膜;背鳍棘骨细长、锥形,且轻微拱起,顶部骤尖,后缘为弱锯齿;胸鳍棘骨前后缘均有锯齿,但后缘为强锯齿。背鳍和胸鳍毒棘基部结构的髁突形状、大小、位置全然不同。微观结构显示,皮膜中的毒腺细胞聚集成层,位于鳞状上皮与色素层之间,未见导管与之相连,背鳍和胸鳍毒棘的分支性骨管中均未发现毒腺细胞。胸鳍和背鳍锁紧装置可让毒棘保持倒伏或者直立的锁定状态,降低猎物挣脱几率。本研究可深入了解黄颡鱼的毒棘结构和特征,增强人们对刺毒鱼类的认知,同时为淡水刺毒鱼类深入研究奠定基础。 相似文献
116.
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118.
Rell L. Parker John Du Richard L. Shinn Adam G. Drury FangChi Hsu John L. Roberston Thomas E. Cecere Avril U. Arendse John H. Rossmeisl 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2022,36(2):694
BackgroundSeizures in the early postoperative period after intracranial surgery may affect outcome in dogs.ObjectivesTo determine the incidence of early postoperative seizures (EPS) in dogs with brain tumors, identify specific risk factors for EPS, and determine if EPS affects outcome.AnimalsEighty‐eight dogs that underwent 125 intracranial surgeries for diagnosis and treatment of rostrotentorial brain tumors.MethodsRetrospective cohort study. All patients with a diagnosis of rostrotentorial brain tumor from 2006 to 2020 were included. Early postoperative seizures were diagnosed by observation of seizure activity within 14 days of neurosurgery. Previously diagnosed structural epilepsy, perioperative anticonvulsant drug (ACD) use, magnetic resonance imaging (MRI), and tumor characteristics were evaluated. Outcome measures included neurologic and nonneurologic complications, duration of hospitalization, and survival to discharge.ResultsDogs with rostrotentorial brain tumors had EPS after 16/125 (12.8%) neurosurgical procedures (95% confidence interval [CI], 7%‐19%). Presence of previous structural epilepsy was not associated with EPS risk (P = 1). Perioperative ACD use also was not associated with EPS (P = .06). Dogs with EPS had longer hospitalization (P < .001), were more likely to have neurologic complications postsurgery (P = .01), and were less likely to survive to discharge (P = .01).Conclusions and Clinical ImportanceIt is difficult to predict which dogs are at risk of EPS because the presence of previous structural epilepsy and the use of perioperative ACDs was not associated with EPS. However, seizures in the early postoperative period are clinically important because affected dogs had prolonged hospitalization, more neurologic complications, and decreased short‐term survival. 相似文献
119.
[目的]探究黄土丘陵区土地利用方式变化前后土壤养分及生态化学计量比的变化特征,为该区农业生产以及生态恢复工作提供科学依据。[方法]选取山西省永和县岔口小流域因生态工程的实施而改变土地利用方式的坡改梯地(梯田)、退耕还林地(林地)、地埂核桃园地(园地)3种样地为研究对象,以现有坡耕地为对照,利用时空互代法,比较不同土地利用方式变化前后0—20 cm,20—40 cm土壤C,N,P,K含量以及生态化学计量比的差异。[结果]①流域各种生态恢复措施实施后,土壤C,N元素含量明显增加,梯田、林地、园地0—40 cm土壤有机C含量分别是坡耕地的1.38,2.44和1.09倍,全N含量分别是坡耕地的1.76,2.66,1.68倍。P,K元素增加量不明显,林地相比其他2种土地利用方式对C,N元素的固持更加明显;②通过分析土壤养分化学计量比的关系,发现流域土壤的限制性元素为C,N元素;③流域土壤养分及计量比之间存在着稳定的耦合关系,C-N之间的耦合关系最为显著且在各元素和生态化学计量比稳定方面发挥着重要作用。[结论]流域3种土地利用方式有效地改变了土壤全量养分含量和元素的生态化学计量比,有利于流域的生态保护和植被修复。 相似文献
120.
The availability of nitrogen (N) contained in crop residues for a following crop may vary with cultivar, depending on root traits and the interaction between roots and soil. We used a pot experiment to investigate the effects of six spring wheat (Triticum aestivum L.) cultivars (three old varieties introduced before mid last century and three modern varieties) and N fertilization on the ability of wheat to acquire N from maize (Zea mays L.) straw added to soil. Wheat was grown in a soil where 15N‐labeled maize straw had been incorporated with or without N fertilization. Higher grain yield in three modern and one old cultivar was ascribed to preferred allocation of photosynthate to aboveground plant parts and from vegetative organs to grains. Root biomass, root length density and root surface area were all smaller in modern than in old cultivars at both anthesis and maturity. Root mean diameter was generally similar between modern and old cultivars at anthesis but was greater in modern than in old cultivars at maturity. There were cultivar differences in N uptake from incorporated maize straw and the other N sources (soil and fertilizer). However, these differences were not related to variation in the measured root parameters among the six cultivars. At anthesis, total N uptake efficiencies by roots (total N uptake per root weight or root length) were greater in modern than in old cultivars within each fertilization level. At maturity, averaged over fertilization levels, the total N uptake efficiencies by roots were 292?336 mg N g?1 roots or 3.2?4.0 mg N m?1 roots for three modern cultivars, in contrast to 132?213 mg N g?1 roots or 0.93?1.6 mg N m?1 roots for three old cultivars. Fertilization enhanced the utilization of N from maize straw by all cultivars, but root N uptake efficiencies were less affected. We concluded that modern spring wheat cultivars had higher root N uptake efficiency than old cultivars. 相似文献