Revising threshold functions

A revision algorithm is a learning algorithm that identifies the target concept, starting from an initial concept. Such an algorithm is considered efficient if its complexity (in terms of the resource one is interested in) is polynomial in the syntactic distance between the initial and the target concept, but only polylogarithmic in the number of variables in the universe. We give an efficient revision algorithm in the model of learning with equivalence and membership queries for threshold functions, and some negative results showing, for instance, that threshold functions cannot be revised efficiently from either type of query alone. The algorithms work in a general revision model where both deletion and addition type revision operators are allowed.     

Threshold and growth mechanism of fatigue cracks under mode II and III loadings

ABSTRACT The fatigue crack growth behaviour of 0.47% carbon steel was studied under mode II and III loadings. Mode II fatigue crack growth tests were carried out using specially designed double cantilever (DC) type specimens in order to measure the mode II threshold stress intensity factor range, ΔK_IIth. The relationship ΔK_IIth > ΔK_Ith caused crack branching from mode II to I after a crack reached the mode II threshold. Torsion fatigue tests on circumferentially cracked specimens were carried out to study the mechanisms of both mode III crack growth and of the formation of the factory‐roof crack surface morphology. A change in microstructure occurred at a crack tip during crack growth in both mode II and mode III shear cracks. It is presumed that the crack growth mechanisms in mode II and in mode III are essentially the same. Detailed fractographic investigation showed that factory‐roofs were formed by crack branching into mode I. Crack branching started from small semi‐elliptical cracks nucleated by shear at the tip of the original circumferential crack.     

基于遗传算法的门限自回归模型在浅层地下水位预测中的应用

提出了建立门限自回归模型的一种简便通用的方法，用遗传算法可同时优化门限值和自回归系数．实例计算的结果说明了其可行性和有效性．该方法在各种工程时序预测中具有广泛的应用价值     

角调谐飞秒同步泵浦KTP红外光参量振荡器

用平均输出功率为１．１Ｗ，脉宽为９０ｆｓ的商用再生锁模Ｔｉ：Ｓａｐｐｈｉｒｅ激光器作为泵浦源，用ＫＴＰ作为非线性光学介质，制成一台同步泵浦飞秒光学参量振荡器。其输出调谐范围为１．０４μｍ至１．２６μｍ，平均输出功率在１００ｍｗ左右，脉宽仅约１００ｆｓ。     

13SiMnNiCrMoV钢切口疲劳裂纹萌生门槛值

本文研究在13SiMnNiCrMoV 结构钢中用尖裂纹的应力强度因子来反映三点弯曲缺口试样的疲劳裂纹萌生规律。当 R=0.1,f=100Hz,试样尺寸 B×W×L=12.5×25×117mm 时,缺口名义应力幅的门槛值为Δσ_(th)=3315ρ~(0.352) MPa,0.5mm≤ρ≤5mmΔK_(th)=250ρ~(0.352) MPam~(1/2)门槛值与ρ有关。同时得到缺口裂纹萌生的循环次数 N_i 与名义应力幅Δσ、缺口曲率半径ρ的定量关系是N_i=3.98×10~(22)ρ~(1.62)/Δσ~(4.85),N_i≤10~(5.5)并讨论了(ΔK_1/ρ~(1/2))_(th)与ρ无关的结论。     

稀疏气泡流动的粒子跟踪测速技术研究

采用动态阈值技术实现了对气泡图像的正确分割，利用灰度加权方法提高了气泡颗粒的定位精度。根据稀疏气泡流动图像的特点，提出了一种新的基于相关的粒子跟踪测速算法（2-HPTV）。通过进行两时刻中围绕待研究气泡所取的两个小的诊断窗口的相关运算，成功实现了气泡颗粒的轨迹追踪。实验表明本文算法较传统的PIV技术在测速精度上有很大程度的提高，与4帧粒子跟踪测速算法相比，降低了对摄像机帧频的要求，具有较强的实用性。     

A novel optical burst switching scheme—logical cascaded private subnet with start wavelength assignment policy

Many recent studies have convincingly demonstrated that network traffic exhibits a noticeable self-similar nature, which has a considerable impact on network performance, and most studies of optical burst switching (OBS) networks are under a fundamental assumption that full wavelength conversion is available throughout the network. In practice, however, economic and technical considerations are likely to dictate a more limited and sparse deployment of wavelength converters in the optical network. Therefore, we present a novel scheme for OBS networks, called logical cascaded private subnet (LCPN) with start wavelength assignment policy. We define the concept of canoe relative to cluster in self-similar traffic, and introduce a new device named payload segregator at the edge node as a gateway to the core node in OBS Networks. According to the changes in the edge node framework, we put forward the concept of cluster private subnet and canoe private subnet in the core node correspondingly. A new start wavelength assignment policy is proposed for the absence of (full) wavelength conversion capabilities in the core node of OBS Networks. The performance study indicates that, our new scheme is robust under self-similar traffic and wavelength continuity constraint.     

浮栅技术及其应用

介绍了浮栅技术的基本原理及应用情况。井对2种应用了浮栅技术的典型器件-浮栅MOS晶体管和神MOS晶体管做了详细介绍，分析了他们的基本结构和工作原理，以及建立浮栅MOS晶体管的等效模型，并说明了他们的应用情况及存在的不足。     

CZF90测井中子发生器使用寿命浅谈

Ｃ／Ｏ测井中采用同步测量技术来分析非弹性γ与俘获γ，但在一些ＭＳＩ Ｃ／Ｏ测井中发现非弹性γ的一小部分或一大部分超前于非弹性门而进入俘获门，我们把这一问题叫做“错位”。“错位”使得Ｃ／Ｏ的ＣＩ值不正常，测井曲线不合格。这样的仪器不能用来测井。吉林油田测井公司碳氧比维修班成功地解决了Ｃ／Ｏ仪器“错位”等技术难题，在该油田所使用的ＣＺＦ９０－９４－０９发生器已测井８８口，累计打靶时间２３０ｈ，并且至今