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151.
为阐明喷泉产生的细菌气溶胶空间分布特性,利用大肠杆菌NK5449作为试验菌株,通过喷泉喷洒试验,使用安德森六级空气采样器采集喷泉周围空间的细菌气溶胶,研究各级细菌气溶胶的浓度和粒径分布特征和变化规律,并分析其与液滴直径的相关性.结果表明,在高度0.75~1.75 m,距离喷头0.5~3 m的范围内,细菌气溶胶总浓度在(38±15)~(676±92)CFU·m-3之间,并随着高度的增加和与喷头之间水平距离的增大而逐渐降低,且与液滴直径呈显著负相关(P0.05);随着与喷头水平距离的增大,粒径大于4.7μm的细菌气溶胶粒子所占比例出现先降后升的变化趋势;而粒径在2.1~4.7μm之间的粒子所占比例则是先升后降.与喷头水平距离0.5 m以外的各点,细菌气溶胶粒子的粒径大都集中在1.1~4.7μm范围内.距离喷泉较远处的人吸入小粒径细菌气溶胶的风险不容忽视. 相似文献
152.
We retrospectively studied 26 fetuses with isolated mild cerebral ventriculomegaly diagnosed between 1992 and 1998 and defined by a lateral ventricular atrial diameter of 10–15 mm without any other cerebral anomaly. Our objectives were to determine maternal risk factors, to evaluate complementary investigations, to assess developmental prognosis and to propose possible management. During pregnancy 10/26 patients had regressive ventriculomegalies, ten remained borderline at birth and six were confirmed postnatally. No maternal risk factors were identified. Prenatal investigations were carried out in 69% of cases but in only a few cases supplied any information. Postnatal examinations revealed one case of Down syndrome and one of porencephaly. Four children were lost to follow-up. In the 22 other cases, four had developmental delay. Early and unexplained mild ventriculomegaly appears to have a good prognosis. If ventriculomegaly is persistent, prenatal management should be carried out to investigate chromosomal abnormalities, viral infection, and fetal cerebral parenchymal damage. A long postnatal clinical follow-up is required. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
153.
基于新型反应器的好氧颗粒污泥的稳定性控制 总被引:1,自引:0,他引:1
为避免好氧颗粒污泥随着粒径和密度的变化屡次出现其稳定性失去控制,导致好氧颗粒污泥系统运行失败的状况发生,开发了一种新型反应器能够很好地控制好氧颗粒污泥的粒径和密度.新反应器结合旋流器的使用提供了2种排泥方式,其一是短的沉淀时间,将大粒径和高密度的颗粒污泥存留在反应器中;其二是一种专有的污泥排除工艺,选择出反应器内潜在的可能存在进一步粒径增长和密度扩大从而破坏反应器运行稳定的大粒径和高密度的颗粒,并将其排除.以上2种方式保证了反应器内颗粒污泥的粒径长期维持在300~1 000μm,进而维持整个系统的稳定性.对新型反应器生成的颗粒污泥进行动力学参数的测定,该工艺所形成颗粒的能量维持系数为0.08~0.10,就新陈代谢活动的代谢途径而言,相比传统颗粒污泥系统发生较大改变,维持新陈代谢活动所消耗COD较传统工艺偏高.另外,出水水质COD的降解率平均达到92%,氨氮降解率平均达到60%. 相似文献
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158.
西安市路面积尘不同粒径矿物组成研究 总被引:5,自引:1,他引:5
对西安市路面积尘粒径分布和不同粒径中矿物质量组成的研究表明,路面积尘质量主要集中在30~50目(0.59~0.297mm),其次在140~160目(0.105~0.088mm),<200目(<0.074mm)的粒径中。同时给出不同粒径中矿物的分布特点,较细粒径中矿物含量稍高于较粗粒径中的含量。细颗粒表面积大,更易吸附较多的有毒有害物质,对环境的影响较明显。 相似文献
159.
O.E. Petel D. Mack A.J. Higgins R. Turcotte S.K. Chan 《Journal of Loss Prevention in the Process Industries》2007,20(4-6):578-583
The critical diameter and critical thickness of two heterogeneous explosives were measured experimentally. By comparing these experimentally determined values of critical diameter and critical thickness, the role of front curvature in the failure of the detonation can be investigated. Current theories of detonation based on front curvature would predict the critical diameter should be twice the critical thickness. Experimentally, the expected two-to-one ratio was only validated for the case of a heterogeneous explosive with very fine scale heterogeneities. The ratios of critical diameter to critical thickness (for the two selected explosives) are also compared to previously measured values for homogeneous (liquid) explosives in order to contrast the dominant failure mechanism in these different explosives. 相似文献
160.
Summary Biological effects of extremely low-frequency electromagnetic fields (ELF-EMF) on microcirculation were investigated in vivo by monitoring arteriole diameters in conscious mice. Measurements of blood vessel diameter were monitored 33 min non-stop
before during and after exposure with ELF-EMF and every 389 ms blood vessel diameter were calculated.
Using a dorsal skinfold chamber (DSC), and following caudal vein injection of FITC-dextran 250 kDa, the microvasculature (initial
arteriole diameter of 45–80 μm), was examined by intravital microscopy and video images were recorded for a total time of
33 min. Arteriole diameter was continuously measured by on-line analysis using a High-speed Digital Machine Vision System
CV-2100, using an edge-gap detection algorithm. Since vessel diameters exhibit rhythmic variation expressed by vasomotion,
for estimation of microcirculatory activity we used both raw data for frequency analysis of vasomotion (measured frequencies
of vasomotion were in the range 0.008÷0.1 Hz) and evaluate mean blood vessel diameter for each 1 min period of time, and make
a comparison between Pre, Exposure/Sham exposure and Post exposure periods, with the aim to evaluate possible changes in mean
blood vessel diameter as a result of ELF-EMF action.
During EMF exposure and post-exposure periods, arteriole diameters increased significantly compared with the pre-exposure
period, and the changes were larger during post-exposure. In contrast to sham exposure, vasodilatation of the microvasculature
was significantly greater during exposure and post-exposure to 16 Hz EMF. These findings suggest that ELF-EMF may have potential
therapeutic use benefit for treating vascular disorders. 相似文献