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排序方式: 共有809条查询结果,搜索用时 15 毫秒
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阶次带宽与频率间隔对声学测试结果具有重大影响。为研究这一影响,对某农用汽车四缸四冲程发动机的排气尾管噪声信号进行采集,使用LMS Test.lab软件,基于卡尔曼滤波器原理得到该发动机尾管噪声频谱。采用阶次分析法对分别取不同阶次带宽和频率间隔下测试得到的阶次噪声进行研究。研究表明:阶次的带宽越大,其阶次噪声的声压级就越大,阶次带宽取0.5是噪声测试分析中可选取的最大合理值。频率间隔越大,频率分辨率就越差,噪声信号就难以辨别,噪声测试中合理的频率间隔为1 Hz或1.25 Hz。为噪声测试中,合理选取阶次带宽和频率间隔提供试验和理论依据。 相似文献
754.
Jean-Noel Gardeur Nicolas Mathis Jean Brun-Bellut 《Aquaculture (Amsterdam, Netherlands)》2007,273(1):50-63
Fractional factorial design is a practical approach for studying multiple factors, with a minimum of experimental units. The objective of this work was to study the simultaneous effects of nutritional and environmental factors on both growth and flesh quality of common perch (Perca fluviatilis), a new inland aquaculture species. This study sought answering the two following questions: (i) which combinations of factors allow improving growth, food efficiency, and technological, sensorial and nutritional qualities? (ii) is it possible to simultaneously improve growth performances and flesh quality? In a first experiment, twelve factors (7 nutritional and 5 environmental factors) were each tested at 2 levels in a fractional factorial design in 24 independent recirculating 500 L tanks. The best 4 combinations identified in this first experiment were then validated in a second experiment. The first phase of the multifactorial approach used here allowed revealing emergent information: i) there is a combination of factors that allows reducing both the heterogeneity of the production and the losses of nitrates and phosphates, while preserving good characteristics of growth and quality of fillets; ii) it is possible to improve the quality of the aquatic production system, without decreasing significantly growth efficiency; iii) the effect of a given factor, even such an important one like diet, temperature or target biomass, depends on the levels of the other rearing factor levels, thus the usual reference optimum used for a given factor has no meaning theoretically and can be questioned according to the levels of the other factors which act altogether on the functioning of the rearing system.The input factor combinations resulting in a significant enhancement of single output variables or several output variables were identified (e.g. improvement of feed efficiency, and/or fillet docosahexanoic acid content). Our results clearly demonstrate a strong interdependence of input factors into the animal rearing system, particularly between nutritional and environmental ones. 相似文献
755.
Guillaume Mairesse Marielle Thomas Jean-Noël Gardeur Jean Brun-Bellut 《Aquaculture (Amsterdam, Netherlands)》2007,262(1):86-94
The ante mortem determinism of the quality components in fish is multivariate. Among the various influencing factors, the effects of (i) rearing biomass, (ii) dietary features and (iii) domestication process on the technological and nutritional variables in perch Perca fluviatilis here were studied using two-levels fractional factorial design 24-1 (resolution IV). This work allowed identifying two main factors, i.e. domestication and diet composition, which influence both technological and nutritional variables. Domestication was the parameter showing the greatest effect on both filleting yield (FY) and total saturated fatty acids (SFA) content, whereas diet composition chiefly influenced viscerosomatic index (VSI) and total poly- and mono-unsaturated fatty acids (PUFA and MUFA) contents. Domesticated fish exhibited higher FY (42.8%) and total SFA (25.1% of total fatty acids or FA) content than wild fish (FY = 40.1%, total SFA = 22.9%). Concerning the effect of food composition, diet including only fish oil as lipid source (FO) induced higher VSI than diet including vegetable oil (FV) VSI = 8.8% vs 7.4%, respectively). Moreover, FV diet induced higher n-6 PUFA but lower n-3 PUFA contents in fillets than did the FO diet (total n-6 PUFA = 6.3% vs 5.4% and total n-3 PUFA = 52.6% vs 55.2% of total FA respectively). FV fish fillets had significantly higher total MUFA (17.7% of total FA) contents in muscle than FO fish (14.8%). Concerning this last variable, domestication played only a role in interaction with diet composition. With FO diet, no difference in total MUFA content between wild and domesticated perch was noticed. However, total MUFA content increased with FV diet and was significantly higher in fillets of wild fish (18.7% vs 16.6% of total FA for domesticated). No effect of either feeding rate or initial biomass on the body composition was noticed. In addition, perivisceral fat content was not influenced by any treatment. 相似文献
756.
对水稻微分光谱和植被指数的探讨 总被引:3,自引:0,他引:3
通过不同供氮水平的田间试验,分析了微分光谱对消除水稻冠层光谱的背景影响和植被指数在农学参数测定中的作用。结果表明:由微分光谱所得的红边位置、红边斜率与盖度、叶面积指数及供氮水平之间有一定的相关性;水稻多光谱植被指数RVI、NDVI与叶面积指数LAI及其地上部生物量之间有极显著相关性;高光谱植被指数及其变量与植被盖度、供氮水平之间存在相关性。这些表明,用微分光谱技术与植被指数方法监测水稻的田间供氮水平和长势似乎是可行的。 相似文献
757.
基于马尔科夫二次规划模型的黑龙江省林业产业结构的有序度测算与优化 总被引:2,自引:0,他引:2
通过运用二次规划数学模型求得林业产业结构的马尔科夫转移矩阵,对2012-2020年黑龙江省林业产业目标结构进行预测,选择2012,2015和2020年计算结果为参照标准,测算1998-2011年黑龙江省林业产业结构的发展有序度,定量考察黑龙江省林业产业结构优化调整程度。结果表明:黑龙江省林业产业结构正处于动态的优化中,尤其是2006-2011年,依据选取的3个参照标准,有序度值依次为0.97~0.98,0.92~0.93和0.89~0.90,说明近些年黑龙江省林业产业结构调整程度较好,但仍需进一步深化调整。根据研究结果及黑龙江省林业产业现状,提出优化林业产业结构的思路与策略。 相似文献
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NVH性能是影响车辆舒适性的重要因素之一。对某SUV车型加速过程中当发动机转速为1 300 r/min和1 600 r/min时的轰鸣声问题进行排查研究,通过阶次分析、模态分析、工作变形分析,发现两个转速下的轰鸣声均是由车架局部模态引起。为此,通过采取在对应位置加装动力吸振器的措施,有效抑制车架局部模态,道路试验结果表明车内轰鸣声得到明显改善,主观评价可接受,车内噪声整体降低7 dB(A)左右。 相似文献
760.