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31.
A study of the effect of drug, kanamycin, on the growth metabolism of recombinant Escherichia coli B 1 was carded out by microcalorimeter monitoring of the metabolic activity of treated cells. Power-time curves of growing recombinant Escherichia coli cell suspensions, treated with different kanamycin doses, were recorded. The extent of the effect was evaluated by changes in the slopes of the microcalorimetric curves and the kinetics of the drug action was interpreted from the time at which these changes reached their maximum values and maintained their maximum values. Experimental dose-effect relationships conform to the median-effect principle of the mass-action law: fa/(1-fa)=(D/D50)^m. A plot of y=lg[(fa)^1-1]^-1 versus x=lg D gives the slope m, D50 and R∞. The experimental results revealed that high concentration of kanamycin had an inhibitory effect on the growth of recombinant Escherichia coli B 1 in the lg phase, and had a promoting effect in the stationary period. Moreover, it was demonstrated that microcalorimetry was a reliable method for the detection of modulatory effects in biology. 相似文献
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本文针对在工科高等数学的教学中 ,学生对极限这一重要概念难以把握和理解的现象 ,提出了分三个层次并从哲学的角度来理解这一思想 ,为学生最终解决这一难点提供了一种有效的方法 . 相似文献
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以乙二胺为手臂分子制备的DNA修饰电极及其伏安性能 总被引:5,自引:0,他引:5
Carboxyl was formed on the surface of glassy carbon electrode(GCE) by electrochemical oxidation. Ethylenediamine(En) was used as the arm molecule to link carboxyl with dsDNA using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC) and N- hydroxysuccinimide (NHS) as the activators to prepare dsDNA modified electrode(dsDNA/En/GCE). It was shown that dsDNA couM be covalently immobilized on the surface of GCE. ssDNA modified electrode(ssDNA/En/GCE) was obtained via the thermal denaturation of dsDNA/En/GCE. The dsDNA/En/GCE and ssDNA/En/GCE were characterized by voltammetry with methylene blue(MB) as the indicator. The results indicated that the currents of the redox peaks of MB at ssDNA/En/GCE were larger than those at dsDNA/En/GCE, and the currents of the redox peaks at En/GCE were the smallest. The peak-currents of MB at the DNA modified electrode had good reproducibility after multi-denaturation and hybridization cycles. 相似文献
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金属射流侵彻起爆炸药的研究 总被引:1,自引:0,他引:1
本文描述了聚能金属射流侵彻起爆炸药的试验装置和方法。聚能金属射流是用标准空心装药产生的,空心装药的尺寸为直径40mm,高度66mm,药型罩为紫铜,顶角60,底直径36mm,壁厚0.75mm,炸药为钝化黑索今,密度1.6800.005Mg/m~3。炸高为72mm时的最大穿深为1506mm45~#钢靶柱。用2MV脉冲闪光X射线摄影仪测量了金属射流穿透不同厚度的钢靶板后的头部运动速度及直径,作出了射流头部速度对钢靶板厚度的标定曲线及拟合曲线公式。炸药对射流侵彻起爆的感度,采用使炸药产生50%概率爆轰的钢靶板厚度(即临界厚度)表示,相对应的临界的流速度可用标定曲线或拟合公式求得。文中给出了TNT.Comp.B及TATB炸药的射流侵彻起爆感度.最后对结果进行了讨论。 相似文献
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Large eddy simulations of a circular orifice jet with and without a cross-sectional exit plate
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The effect of a cross-sectional exit plane on the downstream mixing characteristics of a circular turbulent jet is in- vestigated using large eddy simulation (LES). The turbulent jet is issued from an orifice-type nozzle at an exit Reynolds number of 5 ×104. Both instantaneous and statistical velocity fields of the jet are provided. Results show that the rates of the mean velocity decay and jet spread are both higher in the case with the exit plate than without it. The existence of the plate is found to increase the downstream entrainment rate by about 10% on average over the axial range of 8-30de (exit diameter). Also, the presence of the plate enables the formation of vortex rings to occur further downstream by 0.5-1 .Ode. A physical insight into the near-field jet is provided to explain the importance of the boundary conditions in the evolution of a turbulent jet. In addition, a method of using the decay of the centreline velocity and the half-width of the jet to calculate the entrainment rate is proposed. 相似文献
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This paper analyses the downstream developments of the mean and the turbulent velocity fields of a plane jet. Based on the conservation of mass and the conservation of momentum, the mean-velocity half width (reflecting the jet spread rate) and the relative mass flow rate (jet entrainment) are related to the decay rate of the centreline mean velocity. These relations are not subject to self-preservation. Both analytical and experimental results suggest that the jet spread rate (K1) and the entrainment rate (K3) (and thus the decay rate K2) can be well estimated from the centreline velocity, i.e., K1 ≈ 0.6K2 and K3 ∝K2. The effect of initial mean velocity and RMS velocity profiles on the downstream mean velocity field appears to be embodied in the constants K1 K2 and K3. The analytical relationship for the self-preserving Reynolds shear stress, obtained for the first time, works well. 相似文献
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为研究大学生群体租车意愿以及出行方式选择行为的影响.本研究采用自主设计调查问卷,以宁夏银川市大学生为研究对象,获取大学生旅游出行特征数据.首先对问卷中23项旅游动机项进行因子分析提取公因子;然后对因子得分进行聚类分析将大学生群体划分为4类;再者进行相关性分析,筛选与大学生出行选择行为密切相关的影响因素;最后基于MNL模型构建涵盖旅游动机的大学生旅游租车出行方式选择行为度量模型.研究结果表明,旅游动机对大学生旅游租车意愿有显著影响,且不同出行方式间影响程度存在差异.该模型预测精度较高,对大学生群体旅游产品的研发具有指导意义,为进一步研究游客出行决策行为提供了理论依据. 相似文献