关于纺织机械噪声评价标准的探讨

机器噪声的污染问题,日益受到世界各国的重视和关注,现在国际上对机器噪声的测量,主要采用声功率级。但用这种声功率级的评价指标尚有某些不足之处,本文拟在声功率级基础上,提出“机器噪声相对声功率系数”的概念,作为评价、比较、改进机器噪声及综合质量的补充指标,以弥补声功率级的不足。     

Carbocyclic and nitrogen-containing fused CH-acids with an annelated indenyl fragment. Thermogravimetric and X-ray structural analysis of 6H-indeno[1,2-b]quinoline

Based on thermogravimetric characteristics first obtained for the model 6H-indeno [1,2-b]quinoline, the scheme of thermal conversions of this compound in the temperature range 20–700 °C has been proposed, and the limit of its thermal stability (300 °C) has been determined. This temperature is recommended as the optimum for synthesizing fused benzoaza(diaza)fluorenes. Based on the results of X-ray structural analysis, the molecules of the studied indenoquinoline form centrosymmetric pairs, which are arranged in (110) layers. The molecules are orientationally disordered. The observed self-association of these molecules is similar to the - association of fused heterocyclic systems with-excessive and ****- deficient fragments. It has been suggested that interferon-inducing and antitumor compounds with an annelated indenyl fragment have a common mechanism of action according to the intercalation model of stacking structures.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 703–709, April, 1995.     

Real-time onboard wind and windshear determination,part 2: Detection

This paper is concerned with windshear detection in connection with real-time wind identification (Ref. 1). It presents a comparative evaluation of two techniques, one based on the shear/downdraft factor and one based on the wind difference index. The comparison is done with reference to a particular microburst, that which caused the 1985 crash of Flight Delta 191 at Dallas-Fort Worth International Airport.The shear/downdraft factor has the merit of combining the effects of the shear and the downdraft into a single entity. However, its effectiveness is hampered by the fact that, in a real situation, the windshear is accompanied by free-stream turbulence, which tends to blur the resulting signal. In turn, this results in undesirable nuisance warnings if the magnitude of the shear factor due to free-stream turbulence is temporarily larger than that due to true windshear. Therefore, proper filtering is necessary prior to using the shear/downdraft factor in detection and guidance. One effective way for achieving this goal is to average the shear/downdraft factor over a specified time interval . The effect of on the average shear/downdraft factor is studied.     

Covering with blocks in the non-symmetric case

Considering an infinite string of i.i.d. random letters drawn from a finite alphabet we define the cover timeW _n as the number of random letters needed until each pattern of lenghtn appears at least once as a substring. Sharp weak and a.s. limit results onW _n are known in the symmetric case, i.e., when the random letters are uniformly distributed over the alphabet. In this paper we determine the limit distribution ofW _n in the nonsymmetric case asn. Generalizations in terms of point processes are also proved.Dedicated to Endre Csáki on his 60th birthday.     

Dynamic structure factor in a random diffusion model

Let {X _t:0} denote random walk in the random waiting time model, i.e., simple random walk with jump ratew ^–1(X _t), where {w(x):x^d} is an i.i.d. random field. We show that (under some mild conditions) theintermediate scattering function F(q,t)=E ₀ (q^d) is completely monotonic int (E ₀ denotes double expectation w.r.t. walk and field). We also show that thedynamic structure factor S(q, w)=2 ₀ cos(t)F(q, t) exists for 0 and is strictly positive. Ind=1, 2 it diverges as 1/||^1/2, resp. –ln(||), in the limit 0; ind3 its limit value is strictly larger than expected from hydrodynamics. This and further results support the conclusion that the hydrodynamic region is limited to smallq and small such that ||D |q|², whereD is the diffusion constant.     

不同降水驱动的SWAT模型参数不确定性研究

以抚河流域与黑河流域为研究区,应用4种降水产品(CMORPH CMA、CMFD、CMADS、MSWEP)驱动SWAT模型模拟日流量,评估4种降水产品在湿润区与干旱区的适用性;使用自适应降维评估法选出流域的敏感参数,并进行一致性检验。结果表明:抚河流域4种降水产品的纳什效率系数(NSE)均在0.70以上,其中CMORPH CMA和CMADS的NSE均能达到0.82;黑河流域CMORPH CMA和CMADS的NSE大于等于0.76,而CMFD和MSWEP的NSE分别为0.72和0.74。抚河流域4种降水产品具有相同的敏感参数;黑河流域CMORPH CMA和CMADS有相同的6个敏感参数,而CMFD和MSWEP则分别有5个和8个敏感参数。4种降水产品在湿润流域和干旱流域都能得到较好的应用效果,但是CMORPH CMA和CMADS的模拟效果要优于CMFD和MSWEP。不同的降水输入也会对模型参数敏感性分析的结果产生影响,当降水表现越接近时,所筛选的敏感性参数也越相似。     

试验与服役数据融合的飞机结构安全寿命分析

针对飞机结构安全寿命分析中样本容量偏少的问题,综合考虑结构分散性和载荷分散性的飞机结构疲劳寿命是否服从对数正态分布或威布尔分布的情况,根据等损伤原理,将服役飞机实际飞行小时数等效转化为在同一试验载荷谱下的当量飞行小时数,以实现飞机结构试验疲劳寿命与服役使用数据的融合,采用随机右截尾情形下的极大似然估计方法估算疲劳寿命分布函数的参数,进行飞机结构安全寿命分析;最后以飞机结构疲劳寿命服从对数正态分布为例进行了算例分析,分析结果表明:在相同的可靠度和置信水平下,利用试验数据与服役使用数据融合方法可以显著增大样本容量,从而充分挖掘飞机结构可靠性的储备。     

方幂和中因子5的指数问题

设ｎ,ｘ,ｒ是正整数且ｒ＞１,ｎ＝５αｃ,５ｃ,给出方幂和中因子５的指数计算公式：Ｄ＝∑ｎ－１ｋ＝０（ｘ＋ｄｋ）ｒ,ｄ＝５ｓ＋１,ｓ≥０．     

透射焦散线法研究甲板开口边缘Ⅰ型裂纹的应力强度因子

为研究船舶甲板开口边缘受拉的Ⅰ型裂纹的应力强度因子,并探索焦散线方法在船舶结构中的应用,采用透射焦散线方法进行了实验研究．实验中模拟一般散货船带舱口的上甲板,制作了带孔有机玻璃透明试件,并采用加热法开出孔边裂纹．在数字焦散线实验系统中进行实验,获得了清晰的全场焦散线数字图象．应用焦散线图象自动处理程序精确地测出焦散线的最大直径以计算应力强度因子,并对裂纹尖端初始焦散线引起的实验误差作了处理．实验结果与理论值十分接近,表明船舶甲板开口边缘受拉的Ⅰ型裂纹的应力强度因子与甲板中的总纵拉力成正比．     

半平面多圆孔多裂纹反平面问题

运用复变函数及积分方程方法,求解了半平面域多圆孔多裂纹反平面问题．建立了两种类型的基本解．利用叠加原理和所得的基本解并沿圆孔和裂纹表面取待定的基本解密度函数,可得一组基本解密度函数为未知函数的Ｆｒｅｄｈｏｌｍ积分方程．通过该积分方程组的数值求解可以得到密度函数的离散值,进而得到裂纹尖端的应力强度因子．