气动工具的噪声防治

气动工具在我国机械制造等各行业广泛应用的同时,工作时的排气噪声对周围环境也造成了一定的污染。介绍了治理噪声所采用的消声装置及设计方法,通过消声后的试验数据及噪声频譜对比分析,用正交试验法解决功率与噪声的矛盾,通过这种方法使噪音降低最大,功率损耗最小,这种消声装置原理治理噪声效果显著。     

On-line acoustic viscometry in oil condition monitoring

The paper describes the theoretical standpoints of developing magnetoelastic viscometers and a concept of viscosity measurement. The magnetoelastic viscometer has shown the readings close to the capillary viscometer. Testing of the oils with PMMA viscosity-index improvers by viscometers has indicated changes in rheological properties observed in the non-Newtonian behavior of the oils. With increase in content or molecular weight of the improver, the non-Newtonian behavior of the oil appeared at lower frequencies of viscosity measurements.     

Construction application of Fibre/Mesh method for protecting concrete columns in fire

In this paper, a construction application of a technique to improve the fire resistance of high strength concrete is presented. Before the construction application, fire tests of three hours duration were carried out in accordance with ISO-834. Three types of mitigating methods, namely, a specimen with no protection (control), with fireproof panel protection and with the combination of polypropylene fibre reinforcement and metal mesh confinement (Fibre/Mesh), were applied to full sized columns for comparison purposes. The fire resistance performance of all columns was tested under loads. After the fire tests, the severity of spalling of specimens was assessed, and the best performing technique, Fibre/Mesh, for spalling protection was selected for an application in practice. The process of the construction application is described in detail, including pumping, pouring and compacting of the concrete. The concrete quality was examined and the behaviour of the concrete was observed. Consequently, it was verified that this new spalling resistance technique is feasible in practice.     

Strengths and flexural strain of CRC specimens at low temperature

Crumb rubber concrete (CRC) is made by adding rubber crumbs into conventional concrete. This study undertakes an experimental study on the cubic compressive strength, axial compressive strength, flexural strength and splitting tensile strength of CRC specimens at both ambient temperature 20 °C and low temperature ?25 °C. The flexural stress–strain responses were also recorded. The averaged size of rubber crumbs used in the study is about 1.5 mm. Four levels of rubber contents are investigated, which are 0%, 5%, 10% and 15% by volume, respectively. The mix design aimed at 40 MPa of compressive strength and 100 mm of slump for all the CRC specimens. The results show that CRC increases its magnitude in strengths when temperature decreases, which is similar to the case of conventional concrete, but still exhibits ductility in low temperature. The conclusion from this study is that CRC may be more beneficial in its application in low temperature environments than in ambient temperature environments.     

生石灰桩加固既有建筑物湿陷性黄土地基试验研究及工程应用

采用生石灰桩加固湿陷性黄土地基是工程中常用的手段,但对于生石灰桩的体积膨胀系数和吸水率工程中常利用经验取值.为了进行更深入的研究,本文结合实际工程,通过固结仪分析了生石灰桩在不同土压力下的膨胀和吸水特性,得出了特定条件下生石灰桩体积膨胀系数及吸水率与深度的关系,进而得出了生石灰桩的平均体积膨胀系数和平均吸水率,从而为不...     

孕早期脐血流与出生不良结局的关系

目的:探讨孕早期多普勒超声静脉导管血流异常与围产儿预后的相关性.方法:应用彩色多普勒超声检测同期妊娠11-13+6周于我院产前保健的单胎孕妇胎儿的静脉导管血流频谱.其中静脉导管血流频谱异常者69例为研究组,静脉导管血流频谱正常者143例作为对照组,比较两者的妊娠结局情况.结果:孕11-13+6周胎儿脐血流异常组有3例因严重心脏畸形而中期引产,有1例早产后因严重心脏畸形而夭折;胎儿脐血流正常组无严重异常情况,两组间有显著统计学差异.结论:孕早期静脉导管血流异常与新生儿不良预后有关,包括新生儿死亡、新生儿畸形.孕早期静脉导管血流异常对胎儿心脏畸形诊断的阳性预测价值:4/69＝5.8%,阴性预测价值为100%;早孕期存在静脉导管异常血流应加强围产保健.     

浅述乙肝两对半

近几年来,人们的生活水平在逐渐提高,但乙肝患者却并未减少,何况中国是乙肝高发大国,所以有些人谈肝色变,但事实上,有些情况并不会引起什么不好的结果,只要大家对乙肝两对半有一个正确的认识.     

减氮、加菌、改善土壤物理性状提高大豆固氮能力

氮是大豆生长必须的营养元素之一.大豆是豆科作物,具有共生固氮能力,据估算东北黑土区大豆共生固氮潜力在150～200 kg/hm2之间,同时大豆的共生固氮能力受多种因素的影响.土壤中的根瘤菌对氮的响应表现为使用过多的氮肥会抑制根瘤菌的繁殖生长,但少量地使用化肥有利于提高大豆的共生固氮能力.改善土壤物理性状能够增加土壤中的根瘤数量,进而提高大豆的共生固氮能力.基于上述事实我们提出了减氮、加菌、改善土壤物理性状的模式,该模式将大豆产量提高了15.3%,氮肥节约了33.3%.