内螺纹变截面铜管拉伸工艺的研究

此文提出了内螺纹变截面铜管分段拉仲一次成形新工艺,并就工艺因素对该管拉伸成形的影响进行了试验研究,从而为合理制订成形工艺提供了依据。     

金属加工过程中应力状态的分析方法

分析简单地拉伸、压缩和扭转的情况时,应力状态能容易地被确定.但是,实际上在金属加工过程中材料是承受复杂的应力状态,在模具——工件接触面上增加有摩擦力.而且,这些应力和摩擦力一般地沿着接触面变化.准确的计算或预测载荷、力、应力和温度,不但对设计适宜的设备是重要的,而且对研究工艺期间材料的变化过程也是重要的.本文将讨论材料变形过程中所运用的主要分析方法及其优缺点.     

Postfledging Dispersal of White-crowned Pigeons: Implications for Conservation of Deciduous Seasonal Forests in the Florida Keys

From 1988 to 1991, we studied the postfledging dispersal of 31 radio-tagged White-crowned Pigeons ( Columba leucocephala ) from three natal keys in Florida Bay. Immature birds dispersed from the natal keys at 26–45 days after batching, and most young dispersed more than 20 km during the first 10 days postdispersal. Dispersing birds flew either north to the Florida mainland or east to northeast to the mainline Florida Keys. On the mainland, immature birds fed nearly exclusively within Everglades National Park or an adjacent state wildlife management area. On the mainline keys, White-crowned Pigeons selectively used 5.01–20 ha forest fragments (p < 0.10) during the first 72 hours postdispersal. After this period, dispersing birds showed no preference among fragment size classes but used deciduous seasonal forests more frequently than suburban habitat(p < 0.10). The spatial pattern of dispersal on the mainline keys suggests that, during the first 72 hours postdispersal. White-crowned Pigeons are not able to reach northern Key Largo, where 69% of the deciduous seasonal forests are protected in state or federal ownership. Protection of large forest fragments, especially on southern Key Largo, should be a priority for maintaining populations of White-crowned Pigeons. These forests provide a series of "stepping stones" that enable dispersing immature White-crowned Pigeons to fly to more distant areas where habitat availability is less restricted. This species is threatened in Florida and may play an important role in maintaining plant species diversity in the seasonal deciduous forests of south Florida by dispersing seeds of at least 37 species of trees and shrubs. Protection of sufficient habitat to allow successful postfledging dispersal of this important seed disperser will also protect the ecosystem's biodiversity.     

圆形烟道烟尘采样点位置确定之正误

采样点位置的确定是烟尘测试中的一项基础工作。在全国沿用10多年的确定圆形圆形烟道烟尘采样点位置的计算表中的数据,经验算有60％有误;原来以烟道中心为基准的计算公式虽然正确,但实用性差。为了进一步完善烟气测试理论,提高监测质量,提出以烟道内壁为基准的新计算公式。运用新、旧2种计算公式得到一致的计算结果—新计算表,进一步证实了原计算表中的错误。