Kinetic and morphological study of a magnesium ethoxide‐based Ziegler–Natta catalyst for propylene polymerization

BACKGROUND: Kinetic and morphological aspects of slurry propylene polymerization using a MgCl₂‐supported Ziegler–Natta catalyst synthesized from a Mg(OEt)₂ precursor are investigated in comparison with a ball‐milled Ziegler–Natta catalyst. RESULTS: The two types of catalyst show completely different polymerization profiles: mild activation and long‐standing activity with good replication of the catalyst particles for the Mg(OEt)₂‐based catalyst, and rapid activation and deactivation with severe fragmentation of the catalyst particles for the ball‐milled catalyst. The observed differences are discussed in relation to spatial distribution of TiCl₄ on the outermost part and inside of the catalyst particles. CONCLUSION: The Mg(OEt)₂‐based Ziegler–Natta catalyst is believed to show highly stable polymerization activity and good replication because of the uniform titanium distribution all over the catalyst particles. Copyright © 2008 Society of Chemical Industry     

北京妫水河湿地植物多样性调查与评价研究

为探究北方缺水地区湿地植物物种多样性变化,选取北京市延庆区妫水河为研究区,采用物种丰富度(R),Shannon-Wiener指数(H),Simpson指数(D)和Peilou均匀度指数(J)作为植物群落多样性指标,使用方差法和典型对应分析(CCA)对不同河段和区域间湿地植物物种分布与环境因子之间的响应关系进行研究。研究结果表明:研究区现有湿地植物93种,隶属于44科76属,优势科有菊科(Asteraceae)、禾本科(Poaceae)、豆科(Fabaceae)和莎草科(Cyperaceae); 93种植物的Shannon-Wiener指数(H)小于3,Simpson指数(D)和Peilou均匀度指数(J)介于0. 5～0. 75之间,物种数量总体不多,但分布较均匀,处于中等水平;对湿地植物群落形成及生长影响较大的水质因子依次为全氮(TN)、p H和化学需氧量(COD)。     

Root growth and phosphorus and potassium uptake by two corn genotypes in the field

In a field study P and K uptake by two corn (Zea mays L.) genotypes which differed in root growth was investigated. The effect of differences in root growth on P and K uptake was assessed using a mechanistic-mathematical model which describes nutrient uptake by growing plant roots in soil. Nitrogen was applied at 0 and 227 kg ha^–1 to Pioneer 3732 and B73xMo17 corn grown on Raub silt loam (fine-silty, mixed, mesic Aquic Argiudoll) and at 227 kg N ha^–1 to these two genotypes on Chalmers silt loam (finesilty, mixed, mesic, Typic Haplaquoll). Root growth and P and K uptake by the two corn genotypes was measured 31, 47, 75 and 91 d after planting on the Raub and 31, 47, 61 and 75 d after planting on the Chalmers soil.Root growth and P and K uptake by B73xMo17 was greater than that of Pioneer 3732 on N-fertilized Raub soil. On Chalmers soil the difference in root growth between the two genotypes resulted in an increase in K but not P uptake. The higher soil P level of the Chalmers appears to have offset possible differences in P uptake due to root size. There were no differences between the two genotypes in either the percentage of roots with root hairs, or the density or length of root hairs. Phosphorus and K uptake calculated with the simulation models for both corn genotypes on both soils over each of three growth periods agreed with observed P (Y = 0.68X + 1.71; r = 0.944^**) and K (Y = 0.88X + 15.52; r = 0.928^**) uptake. Differences in P and K uptake between B73xMo17 and Pioneer 3732 resulted primarily from the difference in root growth in the topsoil. A high correlation was found between root surface area and P (r = 0.893^**) and K (r = 0.928^**) uptake by both corn genotypes on both the soils.Journal paper No. 10,316 Purdue Univ. Agric. Exp. Stn., W. Lafayette, In 47906. Contribution from the Dep. of Agron. This paper was supported in part by a grant from the Tennessee Valley Authority.     

填埋场高密度聚乙烯膜缺陷渗漏试验及计算模型研究

因施工等原因造成土工膜渗漏十分常见,但渗漏量的计算是工程建设和运营面临的重大难题。本研究通过室内试验,测试了不同高密度聚乙烯(HDPE)膜厚度(w=0.5、1.0mm)、缺陷孔径(φ=3、5、10 mm)和膜上不同压力水头(h=0.3、0.5、0.65、0.8 m)时的缺陷渗漏量,并建立数学模型进行拟合。结果表明:相对于膜厚度而言,膜缺陷大小和压力水头高度对渗漏量的影响更大;渗漏量可表达为膜缺陷大小和水头高度的幂函数,但不同工况下的系数有别,因此实际工程应通过试验方式确定。     

Treatment of vulvovaginal candidiasis in pregnancy. A comparative study

A carefully controlled comparative study showed miconazole nitrate 2% vaginal cream (Monistat) to be a highly effective agent in the treatment of vaginal candidiasis in pregnant subjects. Miconazole nitrate was significantly more effective than nystatin (Mycostatin) in the treatment of vaginal candidiasis in all three trimesters of pregnancy, and also more effective regardless of whether the candidal infection was primary or recurrent. Observations relating to the safety of this therapy during pregnancy were made and discussed.     

Microflora of the nasal cavity and its sensitivity to antibiotics in patients with chronic rhinitis treated by cryotherapy

Cryotherapy is used in treatment of chronic rhinitis and pharyngitis. The effect of cryotherapy on the qualitative and quantitative composition of the microflora was studied. Staphylococci prevailed in the rhinitis patients, streptococci, Clebsiella and Neisseria being registered more rarely. The staphlococcal isolates were highly sensitive to monomycin, neomycin, erythromycin and levomycetin. The results of the dynamic study showed that the flora composition did not significantly change during cryotherapy and the sensitivity level of the staphylococcal isolates to the antibodies remained unchanged.     

Clinical precision of the Rinne test

The precision of the Rinne test at 128-2048 Hz was studied in 100 ears with confirmed conductive pathologies. The number of negative (diagnostic) Rinnes decreased significantly with fall in frequency. While there were significantly more negative than positive Rinnes at 128 and 256 Hz, there were significantly more positive results at higher frequencies; indicating that the Rinne is not reliably diagnostic above 256 Hz. However, the possibility of vibrotactile responses must be remembered with low frequency tuning forks. Also, conductive lesions manifested as high tone air-bone gaps will not be identified with low frequency Rinne tests. Air-bone gaps of 25 to 40 dB, depending on frequency, are necessary for the Rinne to identify the presence of conductive components in most cases. Gaps of 25-30 dB for 128 Hz; 35-40 dB for 256 Hz; 55-60 dB for 512 Hz; and 45-50 dB for 1024 Hz, are necessary for the Rinne to meet a 75% correct detection criterion. The 2o48 Hz Rinne does not attain even chance detection. The Rinne test cannot be validly employed as a criterion against which other measures can be evaluated.