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991.
液压低频振动钻削系统的设计 总被引:1,自引:1,他引:0
介绍了振动钻削机械系统及扭矩检测系统的设计及构造,并利用该系统对若干典型材料进行振动钻削试验.结果表明:振动钻削具有钻削扭矩小、钻孔扭矩波动小等工艺效果. 相似文献
992.
M. Kundu 《Agricultural Water Management》2008,95(4):383-390
The hypothesis was tested, whether soil wetness and phosphorus status could regulate the evapotranspiration rate (ETR), which is of special interest in the lower Gangetic Plain. Rajmash was grown during November-February of 2003-2004 and 2004-2005 on a sandy loam soil, and was irrigated when cumulative pan evaporation (CPE) attained the value of 33 mm (CPE33); 44 mm (CPE44) and 66 mm (CPE66). Four levels of phosphate application were 0 kg P2O5 ha−1 (P0); 30 kg P2O5 ha−1 (P30); 60 kg P2O5 ha−1 (P60) and 90 kg P2O5 ha−1 (P90). Seed yield under CPE33 was 1.37 Mg ha−1 and reduced by 18% and 35%, respectively under CPE44 and CPE66. Continuous increasing trend in yield was recorded with an increase in phosphate level (PL). Irrespective of growth stages, similar trends were recorded for leaf area index (LAI). Maximum variation in LAI among the treatments was recorded at 60 days after sowing. On average, actual ETR was 1.37 mm day−1 under CPE33 and declined by 13% and 16% under CPE44 and CPE66, respectively. Variation in ETR under different PL was highest under CPE33 and lowest under CPE44. Except P90, irrespective of PL, highest value of water use efficiency (WUE) was obtained under CPE44. However, magnitude of net evapotranspiration efficiency (WUEET) and irrigation efficiency (WUEI) attained the highest level under CPE33 regime. All water use indices showed an increasing trend with the increase in phosphate level from 0 to 90 kg ha−1. Impact of phosphorus on various parameters was pronounced under CPE33. 相似文献
993.
994.
滑县地处豫北平原,位于河南省东北部,属黄河冲击平原地区一个典型的农业大县,也是国家级重点贫困县。滑县县委、县政府针对滑县的特殊地理位置以及当地的实际情况,重点从节水灌溉、实施水电等配套措施,彻底改善本地区旱涝不能保收、农机和水电等基础设施落后局面。农业综合开发极大地提高了粮食生产能力.同时.也提升了项目区周边群众对农业开发工作的信心和热情,在全县推进农业现代化进程中很好地发挥了示范、引领作用。 相似文献
995.
采用数理统计分析和数学建模方法,建立排种盘垂直速度和激振频率的数学模型,分析电磁振动排种盘的垂直速度和激振频率对排种均匀性的影响,并探讨它们对排种器的影响机理,为电磁振动排种器的研究提供重要依据。 相似文献
996.
采用CREM铸造工艺制备4045铝合金铸锭,借助光学显微镜研究了电磁场频率对φ100mm4045铝合金微观组织的影响.结果表明:电磁场频率对4045合金晶粒的细化有重要影响,当频率小于20Hz时,随着电流频率增大,晶粒发生细化,晶粒尺寸趋向均匀;当频率大于20Hz时,随着频率的增加,晶粒尺寸变大;当频率为20Hz时,微观组织为最佳. 相似文献
997.
3种无损检测技术评估足尺规格材的静态弹性模量 总被引:2,自引:0,他引:2
首先利用横向振动、纵向基频振动和超声波3种无损检测法获得天然林樟子松Pinus sylvestris var.mongolica足尺规格材(38 mm×89 mm×4 000 mm)和人工林杉木Cunninghamia lanceolata足尺规格材(45 mm×90 mm×2 500 mm)动态弹性模量,同时根据D198-99(American Society for Testing and Materials)标准测试了其静态弹性模量;进而通过探讨动态与静态弹性模量之间的相互关系。研究结果表明,无论对哪种木材的规格材,利用上述3种无损检测方法获得动态弹性模量(Etv,Efr,Eusw)与静态弹性模量(Etru)平均值之间的关系为:Eusw〉Efr〉Etru〉Etv;动态弹性模量与静态弹性模量之间的线性相关极显著,表明这3种无损检测方法均可以用于评估规格材的静态弹性性质;从设备的方便、可靠和易操作等方面综合考虑,利用纵向基频振动法来评估规格材的静态弹性模量,其预测效果更为理想;天然林樟子松和人工林杉木比较而言,动静态弹性模量线性相关决定系数前者大于后者,即预测天然林樟子松规格材效果更好。 相似文献
998.
输油泵变频节能技术分析与运用 总被引:1,自引:1,他引:0
针对长输管道中输油泵的变频节能技术问题,对输油泵变频调速控制系统的节能原理、基本工作原理及在实际运用中影响变频调速范围的因素进行了分析,分析结果表明,输油泵变频节能技术在长输管道节能降耗应用中具有优越性和重要意义。 相似文献
999.
As herd sizes and labour costs increase, and the availability of skilled labour decreases, efficient use of available labour becomes more important in dairy cow systems. Two experiments were conducted to examine the effect of reducing the frequency of application of inorganic nitrogen (N) fertilizer on inputs of labour and performance of dairy cows. Experiments 1 (duration of 169 d) and 2 (duration of 179 d) involved fifty-eight and forty multiparous Holstein–Friesian dairy cows, respectively, in mid-lactation. In each experiment, in the 'infrequent' treatment fertilizer was applied to all paddocks on a single occasion at the start of each grazing cycle, while in treatment 'frequent', fertilizer was applied on three occasions each week, within 2 or 3 d of each paddock having been grazed. The experimental treatments were started from 30 March and 29 March in Experiments 1 and 2 respectively. Total N application rates were approximately 360 and 250 kg N ha−1 in Experiments 1 and 2 respectively. Concentrate feed (4·0 kg per cow) was offered daily in both experiments. With the 'infrequent' treatment, highest concentrations of crude protein and nitrate in herbage were observed in swards grazed approximately 10 d after N fertilizer was applied. Treatment had no significant effect on milk yield, milk fat and protein concentrations, and final live weight and body condition score of cows in either experiment. Milk urea and plasma urea concentrations were not significantly affected by treatment. Calculated application times of fertilizer for a herd of 100 dairy cows were 107 and 83 min week−1 for the 'frequent' and 'infrequent' treatments respectively. 相似文献
1000.
Eastern Gamagrass [ Tripsacum dactyloides (L.) L.] is a perennial C4 grass with potentially high productivity. Intensive management through the application of nitrogen (N) fertilizer and frequency of cutting, however, may be required to maximize its potential for forage production. This study determined the long-term and residual responses of Eastern Gamagrass in terms of dry matter (DM) yield and tiller density to three annual application rates (0, 50 or 100 kg ha−1 ) of a N-fertilizer solution applied by broadcasting or knife placement for 5 out of the 10 years of the study, and harvested using one-cut or two-cut regimes. Application of N-fertilizer increased total DM yield in the 5 years of N applications by 0·44 with the first increment of 50 kg N ha−1 , and by an additional 0·15 with the next increment of 50 kg N ha−1 . In the first year that directly followed N-fertilizer applications, DM yield was 0·175 higher than the no fertilizer treatment when 50 kg ha−1 had been previously applied and a further 0·16 higher when 100 kg ha−1 had been previously applied. Dry matter yields were greater from the one-cut than the two-cut regime only in years when no N-fertilizer was applied. Knife placement of N-fertilizer increased total DM yield only at 100 kg N ha−1 . Tiller densities were generally higher under the one-cut than the two-cut regime, particularly when N-fertilizer was broadcast. The application of N-fertilizer increased herbage production, especially when responses in the year subsequent to application are considered. 相似文献