ON THE CALCULATION OF FLOW OVER AND THROUGH A ROCK-FILL DAM

1.INTRODUCTIONInthedesignofanovertoppedrock--filldam,oneofthemajortasksistodecidethesizeofthedownstreamprotection.Theovertoppedrock--filldamismadeofporousmedia,thereforethewaterwillpenetrateintothedamfromtheupperfaceandemergeoutofitfromthelowerpart,whileitflowsoverthedam.Hence,theprotectionissubjectedtotheactionofboththeoverflowandtheseepageflow,andneitherofthemcanbenegligible.Inthiscase,theflowfieldconsistsoftwoparts:theopenflowandtheseepageflow,whichhavedifferentproperties.Infact,forthe…     

氯化氢浸渍活性炭净化汞蒸气的研究

用氯化氢对吸附汞热气用的活性炭进行浸渍处理是一种新的偿试。用氯化氢浸渍后的活性炭，对汞的吸附效率和吸附容量与没有浸渍的活性炭相比，均有很大的提高，同时，与其它吸附汞用的浸渍剂相比，具有价格低，来源广的优点，对汞的吸附效率平均在９５％以上。     

Isolation of acidophilic methane-oxidizing bacteria from northern peat wetlands

Acidic northern wetlands are an important source of methane, one of the gases that contributes to global warming. Methane oxidation in the surface of these acidic wetlands can reduce the methane flux to the atmosphere up to 90 percent. Here the isolation of three methanotrophic microorganisms from three boreal forest sites is reported. They are moderately acidophilic organisms and have a soluble methane monooxygenase. In contrast to the known groups of methanotrophs, 16S ribosomal DNA sequence analysis shows that they are affiliated with the acidophilic heterotrophic bacterium Beijerinckia indica subsp. indica.     

衰减曲线分析的诺模图

基于Arps递减方程,建立了衰减曲线分析的诺模图。应用该诺模图,可以方便地确定油气田的可采储量。     

增力式夹具的设计与应用

增力式夹具结构紧凑，夹紧迅速可靠。它可以用较少的原动力获得较大的夹紧力，其增力倍数据实际须要同设计者调整。而且，若按机构自锁条件设计，该夹具夹紧之后，实现自锁。本文对该夹具结构做了介绍，并通过理论分析，指出增力系数和夹具自锁的设计条件。     

一个低电阻率油气藏的测井评价

根据J油田大量岩芯分析资料,应用油藏流体分布理论和毛管压力计算方法,研究该油田低电阻率油气层的形成原因认为:地层水矿化度高(多数>20万ppm);微细孔隙发育,束缚水含量高;粘土矿物含量高且分布在碎屑颗粒表面等是形成低电阻率油气层的主要原因.一般常规测井评价时,对这种低电阻率油气层容易误释而丢弃.依据油气藏流体分布原理,应用毛管压力方法计算原始含油饱和度,可准确地识别出这种低电阻油气层,并可预测其产能.     

Hybrid strain based three node flat triangular shell elements—II. Numerical investigation of nonlinear problems

In a companion paper [M. L. Liu and C. W. S. To, Comput. Struct. 54, 1031–1056 (1995)] theories and incremental formulation of nonlinear shell structures discretized by the finite element method are discussed. The updated Lagrangian formulation and the incremental Hellinger-Reissner variational principle are adopted. The independently assumed fields employed are the incremental displacements and incremental strains. Based on the theory and incremental formulation explicit element stiffness and mass matrices of three node flat triangular shell finite elements are derived. In the present paper the derived element matrices are applied to nine examples. The latter include static and dynamic response analysis of shell structures with geometrical, material, and geometrical and material nonlinearities. The formulation adopted and element matrices derived are found to be accurate, flexible and applicable to various types of shell structures with geometrical and material nonlinearities.     

圆盘式高速金属冷锯机锯切功率的实验研究

对１６００圆盘式高速金属冷锯机进行了锯切功率的实验研究。对某厂四种有代表性的产品，用不同的进锯速度，实测每种条件下的锯切功率变化，和最大瞬时锯切功率与平均锯切功率之比。并以实测数据为基础，得出每种产品以进锯速度为自变量的平均锯切功率回归公式。这些工作，不仅可以为这种冷锯机锯切功率的理论研究提供依据，还可直接为使用和设计这种冷锯机给出具体参考数据。     

Effect of verification bias on positive and negative predictive values

The pairing of sensitivity and specificity expresses the efficacy of a test, and positive and negative predictive values measure the accuracy of a diagnostic test when applied to a particular patient. To calculate these measures, one has to know the true disease status of each patient. In practice, however, some patients may not be selected for verification of disease status. It has been shown that the estimated sensitivity and specificity may be biased if one includes in the study sample only the patients with verified disease statuses. This paper concerns the properties of the estimators of positive and negative predictive values using only patients with verified disease statuses. First, I show that these estimators are unbiased and provide consistent estimators for the variances of these estimators under the assumption that the probability of selecting a patient for a disease verification procedure does not depend directly on the true disease status of the patient. Then, I use the ML method to study the sensitivity of the naive estimators to the departure from the conditional independence assumption.     

可调谐的双波长钛宝石激光器

一台可调谐钛宝石激光器两个波长同时运转,在数ns以内同步,相对波长差最大可达55nm。观测到明显的两种波长激光的竞争和关联。由BBO实现了两波的和频与倍频。