Influence of the axle load, tyre size and configuration on the compaction of a freshly tilled clayey soil

Enhancement of the potential root growth volume is the main objective of farmers when they establish a conventional tillage system. Therefore, the main function of primary tillage is to increase soil’s structural macroporosity. In spite of this, during secondary tillage operations on these freshly tilled soils, the traffic on seedbeds causes significant increases in soil compaction. The aim of this paper was to quantify soil compaction induced by tractor traffic on a recently tilled non consolidated soil, to match ballast and tyre size on the tractors used during secondary tillage. The work was performed in the South of the Rolling Pampa region, Argentina. Secondary tillage traffic was simulated by one pass of a conventional 2WD tractor, using four configurations of bias-ply rear tyres: 18.4×34, 23.1×30, 18.4×38 and 18.4×38 duals, two ballast conditions were used in each configuration. Soil bulk density and cone index in a 0 to 600 mm profile were measured before and after traffic. Topsoil compaction increased as did ground pressure. Subsoil compaction increased as total axle load increased and was independent from ground pressure. At heavy conditions, topsoil levels always showed higher cone index values. From 150 to 450 mm depth, the same tendency was found, but with smaller increases in the cone index parameter, 22 to 48%, averaging 35%. Finally, at the deepest layer considered, 600 mm, differential increases due to the axle load are great enough as to be considered similar to those found in the upper horizon, 36 to 64%, averaging 55%. On the other hand, bulk density tended to be less responsive than cone index to the traffic treatments. Topsoil compaction can be reduced by matching conventional bias-ply tyres with an optimized axle weight.     

Simulation on projectile with high rotating speed penetrating into the moving vehicular door

The numerical program LS-DYNA, is used to simulate the process of the projectile with high rotating speed penetrating into the moving vehicular door. Because of the moving of the vehicular door, the projectile will turn, and the ballistic trajectory will migrate. The paper provides a method to calculate the projectile’s angle of turning’s curve. In the process of the penetration, the projectile’s moving speed is 300 m/s, rotating speed is 0, 3600 n/s and 6370 n/s. The vehicular door’s moving speed is 0, 40 m/s and 80 m/s. The projectile is the semi-sphere nose projectile whose diameter is 7.62 mm; the vehicular door’s thickness is 2 mm. The material model is the JOHN-COOK material model that can characterize strain, strain rate hardening and thermal softening effects. Through comparing with the results by simulation to study the effects of the projectile’s final velocity, the angle of rotation and the ballistic trajectory’s migration with different projectile’s rotating speeds and the vehicular door’s moving speeds.     

Application of Vitamin E TPGS in ocular therapeutics – Attributes beyond excipient

Diseases affecting the anterior segment and the external surface of the eye are usually treated by drugs applied topically. The formulations designed for this purpose are developed to deliver active pharmaceutical agents to the eye optimally. These formulations are prepared by adding various agents (excipients) that help to maintain stability of the formulation, prevent microbial contamination, and allow easy administration with adequate drug bioavailability with the minimum ocular irritation and toxic effects at the administration site. The excipients do not have their own pharmacological actions, but Vitamin E TPGS (d-α-Tocopheryl polyethylene glycol 1000 succinate) seems to break this notion. Besides having drug formulation enhancement properties, it also possesses antioxidant properties, which have been found to have a beneficial effect on various ophthalmological diseases such as age-related macular degeneration, uveitis, glaucoma, and cataract. In this review, we primarily focus on the properties and applications of Vitamin E TPGS in ocular drug delivery and the benefits of Vitamin E (Vit E) in numerous sight-threatening ailments of the rear and front segment of the eye. Additionally, p-glycoprotein inhibition and the anti-cancer potential of vitamin E TPGS have also been summarized.     

穿破甲过程动力有限元近似理论及程序

本文一般性地介绍了穿破甲过程动力有限元的近似理论及笔者所编动力有限元程序;该程序已得到推广应用并可望在应用中加以完善。      

Propagation of Rayleigh waves on curved surfaces

The propagation and properties of Rayleigh waves on curved surfaces are investigated theoretically. The Rayleigh wave dispersion equation for propagation on a curved surface is derived as a parabolic equation, and its penetration depth is analyzed using the curved surface boundary. Reciprocity is introduced to model the diffracted Rayleigh wave beams. Simulations of Rayleigh waves on some canonical curved surfaces are carried out, and the results are used to quantify the influence of curvature. It is found that the velocity of the surface wave increases with greater concave surface curvature, and a Rayleigh wave no longer exists once the surface wave velocity exceeds the bulk shear wave velocity. Moreover, the predicted wave penetration depth indicates that the energy in the Rayleigh wave is transferred to other modes and cannot propagate on convex surfaces with large curvature. A strong directional dependence is observed for the propagation of Rayleigh waves in different directions on surfaces with complex curvatures. Thus, it is important to include dispersion effects when considering Rayleigh wave propagation on curved surfaces.     

激光焊接熔透特征信号同轴增效提取方法研究

熔透检测是实现高功率激光焊接质量在线控制的重要环节,但由于介观尺度下的低辐值熔透特征信号产生于激光匙孔底部被匙孔喷射物质和周围干扰信号完全掩盖,熔透状态难以被直接获取,常规检测多以间接测量为主。将光谱透视技术、红外显微成像技术、光电传感技术及空间定位提取技术相结合,提出一种激光焊接熔透特征信号同轴增效提取方法。以高功率激光在匙孔内壁激发的荧光辐射源作为直接检测信号,利用不同发光体的谱段特性在红外谱段有效分离并抑制激光焊接匙孔上方的等离子体、金属蒸汽焰、粒子团簇等强干扰信号,使红外荧光信号得到有效增强,实现光谱透视显像效果。同时采用自行研制的激光焊接同轴显微光路系统,利用红外显微成像原理提取到匙孔内壁受激辐射荧光的红外显微实像。并以此为基础对高功率激光焊接熔透状态与匙孔内部影像特征进行关联研究,发现与熔透状态直接相关的低辐射值特征现象及特征区域的存在。通过视觉辅助定位调节和熔透特征位置试验矫正等寻位方式,依次提高定位精度,直至将传感器光电感应芯片高精度定位至荧光辐射实像中的熔透特征区域。由此通过光谱透视-显微成像-介观寻位萃取的逐层光学分离方式,实现了对匙孔熔透特征数据的精准提取和最大化增强。试验结果表明,基于多种光谱及光学处理技术复合应用的大功率固体激光焊熔透特征同轴增效提取方法对激光熔透特征信号增强效果显著,可作为一种新型的高功率激光焊接熔透在线检测手段。     

Molecular modelling of amphipathic basic model peptides: Interactions in aqueous solutions and in the presence of lipids

Molecular modelling calculations based on experimental data obtained in solution and in small unilamellar vesicles are used to study interactions between amphiphilic basic peptides and membranes. The behaviour of such peptides during the initial and final stages of the adsorption process is our primary interest. Primary sequences of 20 amino acid residues were designed with equal numbers of basic lysines and hydrophobic leucines in order to get an amphipathic α helix. First, in solution, aggregates with an increasing number (up to nine) of helical monomers were built up and the hydrophobic solvent accessible surface per monomer was analysed on energy minimised structures. This showed that aggregates with 5–8 of monomers should be equally probable, in reasonable accordance with experimental data. In addition, models of membranes with 21 dimyristoyl-phosphatidylcholine lipids were constructed; amphiphilic peptides were merged into these assemblies with their axes parallel to the monolayer surface and the whole lipid/peptide complex was submitted to a few steps of simulated annealing and further energy minimisation techniques in order to equilibrate alkyl chains in the vicinity of the peptide. These simulations yield an estimation of the penetration depth for the peptide in the monolayer of ∼3.2 ?, whereas experimental approaches to this question were not productive. The modification in the peptide net electrical charge by interchanging Leu in Lys residues in such systems is also examined: for low-charged peptides the penetration depth increases. Received: 20 May 1998 / Accepted : 3 September 1998 / Published online: 7 December 1998     

Effect of magnetic field on plasma control during CO2 laser welding

During high power CO₂ laser beam welding, the plasma above the keyhole has a shielding effect that it not only absorbs part of the laser energy but also defocuses the laser beam. As a result, the welding efficiency and the aspect ratio of the welds are influenced. In order to reduce the effect of plasma, helium as a plasma control gas has been used successfully and effectively. However, the cost of helium in Southeast Asia is extremely high and therefore the production cost is significantly increased when helium is used as a continuous bleeding plasma control gas. To search for an alternative plasma control technique, feasibility in using magnetic effect as a control tool is explored in this paper. The influences of the magnetic field strength, laser power, welding speed, field direction and shielding gas (e.g. helium and argon) on the penetration depth and the width of bead were also investigated. Experimental results indicated that the magnetic field can influence the shielding effect of the plasma without using plasma control gas. It was found that at a suitable magnetic field strength the penetration depth was increased by about 7%, but no significant difference on the width of bead was found. Moreover, it was shown that the plasma control effect can be achieved at low magnetic field strength and the penetration depth can be increased significantly under argon atmosphere.     

关于最弱受约束电子势模型理论中势函数物理意义的讨论

从屏蔽、贯穿和极化作用考虑,对最弱受约束电子势模型理论(简称WBEPM理论)的势函数进行了讨论.通过一系列推导、论证,得出WBEPM理论的有效势的物理意义为:势函数中的第一项表示最弱受约束电子在有效核电荷+Z＇e中心场中的势能;第二项代表最弱受约束电子对非最弱受约束电子和核组成的"实”的极化作用所引起的偶极子场中的势能.     

纳米MgO掺杂聚乙烯微观特性的分子动力学模拟研究

电力系统高压电缆的主要绝缘材料为聚乙烯,为了提升聚乙烯的热稳定性以及减弱水分对其的渗透能力,采用纳米MgO掺杂聚乙烯,利用分子动力学模拟方法建立包含低密度聚乙烯(LDPE)、不同颗粒半径的MgO纳米团簇以及相同质量分数水分的复合模拟模型.研究结果表明,水分会降低复合体系的玻璃化温度,MgO的掺杂则会提高复合体系的玻璃化温度,减弱聚乙烯分子链的运动并减小复合体系的自由体积,使得复合体系结构更加稳定,从而增强了聚乙烯材料的热稳定性能.此外发现水分子的扩散随着温度的上升而增大,纳米MgO的添加会与水分子形成氢键抑制水分子的扩散,同时自由体积的缩减使水分子的溶解度系数与扩散系数都减小,导致水分子的渗透能力减弱,更难以渗透进聚乙烯材料破坏其结构.研究结果可为聚乙烯的水树枝生长以及老化过程的抑制提供有益的参考.