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21.
The willows Salix matsudana x alba and S. kinuyanagi, and the leguminous shrub Dorycnium rectum, are used for soil conservation in New Zealand and have potential value as browse plants. Two experiments were conducted in the lower North Island to ascertain the effect of selected establishment and cutting practices on their browse yield and nutritive value. A hill site experiment determined the effect of rooted and unrooted stem cuttings on establishment and initial production of the Salix species. A flat site experiment determined the effect of cutting height (0.10–0.30 m, 0.80 m, and 1.20 m above ground) and cutting frequency (once or twice per year) on yield of the Salix species and D. rectum. The establishment and dry matter (DM) yields of the Salix species were unaffected by the type of stem cutting. S. matsudana x alba (1.2 kg DM/tree) plants yielded more edible DM than S. kinuyanagi (0.9 kg DM/tree) and D. rectum (0.4 kg DM/tree). Cutting height had no effect on edible DM yield but affected total DM yield of the Salix species. Nitrogen concentration in edible DM, of all species, was 18–22 g/kg DM. In vitro organic matter digestibility of S. matsudana x alba (648–691 g/kg DM) and D. rectum (664–666 g/kg DM) was greater than S. kinuyanagi (611–615 g/kg DM). The condensed tannin concentration in edible DM of S. kinuyanagi was four-fold higher than in S. matsudana x alba (255 vs. 59 g/kg DM). It was concluded that S. matsudana x alba had the greatest potential as a browse species and D. rectum the least.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
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The fatigue behavior of plywood specimens under shear through thickness was examined on the basis of strain energy to obtain
common empirical equations for the fatigue process and failure criterion under various loading conditions. Specimens were
cut from commercial plywood panels of 9-mm thickness. Loading conditions were set as follows: a square waveform at a loading
frequency of 0.5 Hz, a triangular waveform at 0.5 Hz, and a triangular waveform at 5.0 Hz. Peak stress applied was determined
to be 0.5, 0.7, and 0.9 of static strength, that is, stress levels of 0.5, 0.7, and 0.9. The stress-strain relationships were
measured throughout the fatigue test, and the strain energy was obtained at each loading cycle. Loading conditions apparently
affected the relationship between stress level and fatigue life. On the other hand, the relationship between mean strain energy
per cycle and fatigue life was found to be independent of loading conditions. Mean strain energy per cycle obtained as the
fatigue limit was 5.85 kJ/m3 per cycle. Assuming that the accumulation of strain energy is a fatigue indicator, the fatigue process and failure criterion
for the plywood specimens under the three loading conditions were commonly expressed by the relationship between cumulative
strain energy and loading cycles. 相似文献
24.
Masaki?HaradaEmail author Kohei?Komatsu Tomoyuki?Hayashi Masahiko?Karube 《Journal of Wood Science》2004,50(5):450-454
A wooden lattice floor with high stiffness and damping capacity has been developed to solve noise problems in wooden apartment houses. The lattice floor consisted of Douglas fir glulam beams with inserted steel plate joints and drift pins. To examine the structural performance of the floor, dynamic excitation and static loading tests were conducted on the full size floor. The first and second order resonance frequencies of the floor were 13.5Hz and 27.0Hz, respectively. These frequencies are similar to the peak frequency of a conventional wooden floor and the combined floor fabricated from glued laminated timber and iron. The maximum static load of the floor was 127kN. The apparent flexural rigidity was less than half the value of several floors studied in the past. However, it is considered that the stiffness is improved by constructing panels and this floor has almost equivalent performance. Relative deflection was not affected by the loading history.Part of this study was presented at the International Wood Engineering Conference, New Orleans, October 1996. 相似文献
25.
This paper took the upper-lower wide belt sander B229 with four-feet wide belts, manufactured in China, as the study target.
By means of framework dynamic design, we study its vibration characteristics by commencing from the place having horizontal
defects and used experimental modal analysis (EMA) and power spectrum density (PSD) to observe the sanding parts and the whole
machine, respectively. In the modal test, we mainly adopted the cross spots testing method to get the frequency response function
of the fixed spots to every excitation vibration spot, then applied the SISO frequency response function and the frequency
response function fitting method to identify and complete parameter recognition, respectively. The typical frequency response
function chart of the whole machine and its sanding parts, as well as its second-order mode charts of contacting roller, were
obtained. Through PSD analysis, we can get the amplitude-frequency spectrum and drive frequency.
Translated from Scientia Silvae Sinicae, 2005, 41(6): 132–137 [译自: 林业科学] 相似文献
26.
本文对杠杆压铊张紧系统带锯产生振动的原因,进行了试验和理论研究。用2034型频谱分析仪试验表明,带锯条振动属于复杂周期信号的离散型频谱,是由多个简谐振动叠加而成;同时理论考察分析表明,带锯条杠杆压铊张紧系统不同于秤量重物的“平衡秤”,不可能达到“静平衡”,而是在锯轮参数激振作用下形成周期性受迫振动。锯轮参数激振和杠杆压铊张紧系统位移激振之间交互作用,是使带锯条产生周期振动并引起张紧力发生变化的重要原因。 相似文献
27.
国产人造板宽带砂光机功率谱密度和试验模态分析 总被引:3,自引:0,他引:3
以国产B229型四四砂架人造板双面宽带砂光机为研究对象,从易产生横纹缺陷入手,对其砂架部件、整机等分别采用试验模态分析(EMA)及功率谱密度法(PSD)来开展振动动态特性研究。在模态试验中,采取测量点固定、改变激振点的跑点测量方法,得到固定测量点对各激振点频响函数,并应用SISO频响函数识别法,通过频响函数曲线拟合来完成模态参数识别,获到典型的整机、砂架部件的频响函数图和接触辊的二阶振型图。通过PSD分析,获得砂光机的PSD图谱和激励频率等。 相似文献
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从中国知网检索到1988年至2013年间该领域文献451篇,统计文献的时间分布和期刊分布,基于词频的统计分析和对文献的研究,总结出教学研究中的热点,有助于任课教师厘清教学中的重点、难点,提升教学效果。 相似文献