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K. DiGiacomo E. Norris F.R. Dunshea B.J. Hayes L.C. Marett W.J. Wales B.J. Leury 《Journal of dairy science》2018,101(7):6474-6485
Residual feed intake (RFI) is defined as the difference between the actual and expected feed intake required to support animal maintenance and growth. Thus, a cow with a low RFI can obtain nutrients for maintenance and growth from a reduced amount of feed compared with a cow with a high RFI. Variation in RFI is underpinned by a combination of factors, including genetics, metabolism, thermoregulation and body composition; hypothalamic-pituitary-adrenal (HPA) axis responsiveness is also a possible contributor. Responses to 3 metabolic challenges were measured in lactating and nonlactating dairy cattle. Sixteen Holstein Friesian cows with phenotypic RFI measurements that were obtained during the growth period (188–220 d old) were grouped as either low-calfhood RFI (n = 8) or high-calfhood RFI (n = 8). An ACTH (2 µg/kg of body weight), insulin (0.12 U/kg), and epinephrine (a low dose of 0.1 µg/kg and a high dose of 1.6 µg/kg of epinephrine) challenge were each conducted during both midlactation (122 ± 23.4 d in milk) and the nonlactating period (dry period; approximately 38 d after cessation of milking). Cows were housed in metabolism stalls for the challenges and were fed a diet of alfalfa cubes ad libitum for at least 10 d before the experiment (lactating cows also were offered a total of 6 kg of dry matter/d of crushed wheat grain plus minerals fed as 3 kg of dry matter at each milking) and were fasted for 12 h before the challenges. The efficiency of conversion of feed into milk (the ratio of feed consumed to milk produced over the 7 d before the experiment) during midlactation was better (lower) in low-calfhood RFI cows, although dry matter intake did not differ between RFI groups. Low-calfhood RFI cows exhibited a lower plasma cortisol response to the ACTH challenge than high-calfhood RFI cows, particularly in midlactation (?15%). The low-calfhood RFI cows had a greater plasma insulin-like growth factor-1 response to the insulin challenge and plasma fatty acid response to epinephrine compared with the high-calfhood RFI cows. These data suggest that high-calfhood RFI cows exhibit a more responsive HPA axis. As divergence in RFI measured during growth is retained (although reduced) during lactation, it is possible that energy is used to respond to HPA axis activation at the expense of production in high-calfhood RFI dairy cattle during lactation and contributes to a decrease in overall feed use efficiency. 相似文献
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叶片是风力机最重要的组成部分,在不同的风能资源情况下,翼型的选择对垂直轴风力机气动特性有着重要的影响。文章分别以NACA0018翼型(对称翼型)和NACA4418翼型(非对称翼型)建立3叶片H型垂直轴风力机二维仿真模型。应用数值模拟的研究方法,从功率系数、单个叶片切向力系数等方面比较两种风力机模型在不同叶尖速比下的气动特性,并采用风洞实验数据验证了流场计算的准确性。CFD计算结果表明:在低叶尖速比下,NACA4418翼型风力机气动特性优于NACA0018翼型风力机,适用于低风速区域;在高叶尖速比下,NACA0018翼型风力机气动特性较好,适用于高风速地区。而且在高叶尖速比时,NACA0018翼型在上风区时,切向力系数平均值要高于NACA4418翼型,在下风区时,NACA418翼型切向力系数平均值高。该研究可为小型垂直轴风力机翼型的选择提供参考。 相似文献
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In this study,the permeabilities of Berea and Otway sandstones were measured under different confining pressures,and porosity was investigated through mercury intrusion porosimetry(MIP).The total porosities of the Berea and Otway sandstones were approximately 17.4%and 25%,respectively.Pore size distributions of each sandstone were almost the same,but the pores in the Otway sandstone were slightly narrower.However,the permeability of the Otway sandstone was smaller than that of the Berea sandstone by one order of magnitude.Three-dimensional(3D)void geometry and geometrical properties of the void spaces relevant to flow were compared to obtain the relation between the permeability differences and porosities of the two sandstones.The 3D geometrical analysis using microfocus X-ray computed tomography(CT)was performed,and the pore geometries of both sandstones were compared using the 3D medial axis(3DMA)method.Pore and throat radii,pore coordination number,tortuosity,number of connecting paths,connecting path volume,and other factors were determined using 3DMA.The Otway sandstone was characterized by a small effective throat/pore radius ratio.Based on the fluid flow mechanism,the lower effective throat/pore radius ratio results in a lower permeability induced by the fluid energy loss,which means that the 3D geometrical shape of void spaces affects the permeability value. 相似文献
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《Ceramics International》2019,45(11):13726-13731
Rod-like ZrB2 crystals were synthesized at 1600 °C in Ar atmosphere by boro/carbothermal reduction using ZrOCl2⋅8H2O, B4C and carbon powders as raw materials. The optimum molar ratio of raw materials required to form pure ZrB2 grains was found to be 2: 1.2: 3. With increase in temperature and subsequent heat preservation stage, ZrB2 powders grew into a rod-like morphology along the c axis. The rod-like ZrB2 grains obtained at 1600 °C have diameters of 0.5–3 μm and high aspect ratios of >8. Effects of molar ratio of raw materials, heating temperature and holding time on the phase composition and final morphology were investigated. Growth mechanism of rod-like ZrB2 grains was also analyzed. 相似文献
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Benedetto Rocchio Claudio Chicchiero Maria Vittoria Salvetti Stefania Zanforlin 《风能》2020,23(4):915-938
The present study is focused on modeling of dynamic stall behavior of a pitching airfoil. The deep stall regime is in particular considered. A model is proposed, which has a low implementation and computational complexity but yet is able to deal with different types of dynamic stall conditions, including those characterized by multiple vortex shedding at the airfoil leading edge. The proposed model is appraised against an extensive data set of experimental (α,CL) curves for NACA0012. The results of an existing widely used model, having comparable complexity, are also shown for comparison. The proposed model is able to well reproduce not only the classic curves of deep dynamic stall but also the curves characterized by lift oscillations at high angles of attack due to the shedding of multiple vortices. Furthermore, the model appears to be robust to variations of its parameters from the optimal values and of the airfoil geometry. Finally, the model is successfully implemented in a commercial CFD software and applied to the simulation of a vertical axis wind turbine within the actuator cylinder approach. The accuracy of the prediction of the turbine power coefficient in the whole rotation cycle is very good for the optimal working condition of the turbine, for which the model parameters were calibrated. Fairly good accuracy is also obtained in significantly different working conditions without any further calibration. 相似文献
8.
基于闭环磁通门技术的传感器广泛应用在测量大电流中的小剩余电流以及噪声共模电流。这类传感器的精度以及对大电流的隔离能力使之成为漏电流检测的最优方案,但通常缺点是成本昂贵且体积庞大。本文介绍了一种新型小尺寸且利用霍尔闭环技术对太阳能系统中的漏电流进行测量的传感器:新一代的LDSR产品。 相似文献
9.
Mengyu Hong Chi-Tang Ho Xin Zhang Ruilin Zhang Yanan Liu 《International Journal of Food Science & Technology》2021,56(7):3311-3321
The human body hosts enormous diversity of microbiota. Recently, the importance of microbial communities to host physiology has been recognised. Evidence is now emerging that the bidirectional communication between the central nervous system and gastrointestinal tract may affect human nerves, cognition and behaviour through the gut-brain axis (GBA). Although the connection between enteropathy and neurological diseases has been found, it now seems intestinal microorganisms represent the direct mediator of psychopathology. The interactions between host neurological function and intestinal microbiota suggested dietary is a possible way to alleviate psychopathological and neurodegenerative diseases. This review discusses the possible effect of intestinal microbiota on the changes of nerves and emotions in human brain. Maintaining healthy diet strategies should be an important part of preventing neurological diseases and psychopathologies caused by systemic metabolic changes. We hope to provide a novel insight for the design of dietary therapies from the perspective of GBA. 相似文献
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