A Polycation Antimicrobial Peptide Mimic without Resistance Buildup against Propionibacterium Acnes

A preliminary study is reported for a polycation antimicrobial peptide (AMP) mimic against Propionibacterium acnes , which is associated with acne vulgaris, a common skin condition. Antibiotics are commonly used against P. acnes but buildup of resistance is well‐known. Worse, antibiotic regimens build up resistance for more sensitive bacteria such as Staphylococcus epidermidis . The polycation AMP mimic C12‐50, 1 , is chosen for the present study as it has been previously shown to have high antimicrobial effectiveness. This study reports that C12‐50 is active against P. acnes (strain ATCC 6919) with a minimum inhibitory concentration (MIC) of 6.3 µg mL⁻¹. To monitor resistance build‐up ten passages are conducted with C12‐50 against P. acnes . The MIC remains constant with no resistance buildup. Parallel studies with erythromycin confirm previously reported resistance buildup. The results point to a promising pathway to applications for polycation AMP mimics against P. acnes .     

Soil vehicle relationship: The peripheral force

During the past decades the author has continually worked on and perfected his conception of the interaction between the soil and the wheel. First, this work is summarized in this paper. The author then describes his conception of the mechanical interaction between them and clarifies the connection between the kinematic and dynamic processes that take place when a tractor is exerting pull. He shows by means of his kinematic model how the peripheral force is developed. Finally, he derives the appropriate equations for the computation of the peripheral force and the drawbar pull for both two-wheel-drive and four-wheel-drive tractors. Practical experience has proven that the concept is correct and the method is practical.     

HYDRODYNAMIC RESISTANCE EFFECT OF FLUID LAYER BETWEEN TWO IMMERSED APPROACHING PARTICLES

1. Introduction The mechanisms of impact and rebound of solid parti- cles in particulate flow systems are of interest over a wide range of application areas such as fluidized beds, pneu- matic transport, filtration processes, erosion and pollution control of suspended particles. In many cases, the colli- sions of particles against themselves and against walls may affect the properties of the mixture. Efforts have been made to describe the fundamental mechanics of particle collisions. The conta…     

护坡格构与坡面相互作用的研究

边坡防护中的锚固格构梁多采用Winkler假设计算内力,设计者通常忽略了边坡岩土体和格构之间摩擦阻力的影响。摩擦阻力对于预应力而言较小,但确实存在,在未加预应力锚固格构梁中不应忽略。本文提出了一种简单有效的计算方法,并结合工程实例,使格构梁的设计得以优化。     

电弧喷涂不锈钢涂层耐磨性的研究

研究了电弧喷涂３Ｃｒ１３和１Ｃｒ１８Ｎｉ９Ｔｉ不锈钢涂层的耐磨性，分析了喷涂工艺参数对３Ｃｒ１３涂层耐磨性的影响及涂层中孔隙的作用，并且深入探讨了涂层的磨损机理。     

宾汉流体阻力近似解公式精度的优化提高

针对前苏联学求解宾汉流体布金汉方程的阻力近似解公式，其与精确解最大偏差为6．7％，首次通过数学分析和三维优化计算，改变公式中的参数，使偏差大幅度降低．偏差是参数和核心流相对半径r^-O的函数，用极限判定了在r^-O闭区间内的连续性和间断点，为降低偏差提供了依据．绘制了偏差三维变化图，应用切片平面解决了多峰曲面的极值问题．最终优化出的参数使公式的最大偏差为2．6％，比6．7％降低了4．1％，优化后的公式，在管道输送阻力计算中更有实用价值．     

Creeping flow past and within a permeable spheroid

Flow past and within an isolated permeable spheroid directed along its axis of symmetry is studied. The flow velocity field is solved using the Stokes creeping flow equations governing the fluid motion outside the spheroid, and the Darcy equation within the spheroid. Expressions for the hydrodynamic resistance experienced by oblate and prolate spheroids are derived and analyzed. The limiting cases of permeable circular disks and elongated rods are examined. It is shown that the spheroid’s resistance varies significantly with its aspect ratio and permeability, expressed via the Brinkman parameter.     

动载下韧性撕裂在三种管线钢材中传播阻力的研究

阐述了用实验确定在常温及静载和动载条件下韧性撕裂在三种管线钢材中传播时的断裂比能值。实验中采用了销钉加载双面开槽的双悬脊梁(DCB)试件。应用能量平衡法对实验结果进行了分析。考察了加载速率和试件厚度对撕裂韧性的影响。结果表明,管线钢材对韧性撕裂传播的阻力在动载条件下增大,对较薄的试件及应变率敏感性较高的材料其增大更为明显。对于纯剪切断裂的传播来说,撕裂韧性一般随试件厚度的增大而增加。     

Effect of inflation pressure on motion resistance ratio of a high-lug agricultural tyre

A single wheel tyre facility at University Putra Malaysia (UPM) was used to check the validity of Wismer–Luth and Brixius equations in predicting the motion resistance ratio of a high-lug agricultural tyre and to investigate the effect of inflation pressure. A Bridgestone 5-12, 4 ply, lug M was tested on sandy-clay-loam soil. The experiments were conducted by running the tyre in towing mode. Three inflation pressures (i.e., 166, 193 and 221 kPa) were investigated and wheel numerics ranging between 0 and 70. The analysis of covariance (ANCOVA) revealed that both inflation pressure and wheel numeric have significant effects on tyre motion resistance ratio. Regression analysis was also conducted to determine the closeness of fit for Wismer–Luth’s and Brixius’ equations in predicting the motion resistance ratio of the tested tyre. Finally, three new logarithmic models for tyre motion resistance were formulated. The advantage of reducing tyre inflation pressure from 221 (nominal pressure) to 193 kPa on the motion resistance ratio of the high-lug agricultural tyre was pronounced. However, the tyre’s motion resistance ratio deteriorated with further reduction in tyre inflation pressure from 221 (nominal pressure) to 166 kPa.     

轴线平行圆柱体滚动接触时的轴向移动阻力

应用摩擦学中的预位移原理，求解轴线平行的两粗糙圆柱体滚动接触时的轴向移动阻力，分析了轴移速比、法向接触载荷、圆柱体表面粗糙层参数对轴向移动阻力的影响，并给出了计算轴向移动阻力的简化公式．