THE EFFECT OF PHOTO-CROSSLINKING ON THE ORIENTATION STABILITY OF POLYVINYL ALCOHOL CONTAINING 4-NITRO-4′-ALKOXYSTILBENE AND CINNAMYL PENDENT GROUPS

Crosslinking is one of the effective routes for improving the orientation stability of poled polymer films. The derivative of polyvinyl alcohol containing 4-nitro-4'-alkoxystilbene and photo-crosslinkable cinnamyl groups as side chains has been synthesized. The in-situ simultaneous photo-crosslinking poling of synthesized polymer films has teen performed, The second order nonlinear optical coefficient d(33) of poled film is 11 pm/V. The SHG measurements show that the break-over temperature of SHG signal is raised obviously after irradiation, its orientation stability is doubled as compared with that of non-crosslinking samples.

Head Orientation Stability of Underwater Snake-Like Robot Swimming

In prior research,the orientation of head of the snake-like robot is changed according to the sinusoidal wave. To solve this problem,we propose Central Pattern Generator( CPG)-based control scheme with head-controller to stabilize the head of the underwater snake-like robot. The advantage of the CPG-based control scheme with head-controller is that the head of the underwater snake-like robot is direct to the target orientation during swimming. The relation between CPG parameters and orientation stability of head is discussed.The adaptation of the proposed method to environment changes is tested. The influences of CPG parameters and hydrodynamic forces on the orientation offset of head are investigated. The target orientation( the input of headcontroller) with an experimental optimization is calculated through a convenient method. To prove the feasibility of the proposed methodology,the different swimming modes have been implemented in our simulation platform.The results show that the oscillation of head's orientation is inhibited effectively,and the proposed method has strong adaptation to environment and CPG parameters changes.

A Rate-Dependent Crystal Plasticity Analysis of Orientation Stability in Biaxial Tension of Magnesium

The development of texture during plastic deformation plays an important role in determining the stretch formability of magnesium alloy sheets.In this study,the orientation stability during equibiaxial tension of magnesium was analyzed based on three dimensional lattice rotations calculated by using a rate-dependent crystal plasticity model and assuming five different combinations of slip modes.The results show that no orientations can satisfy the stability criteria with both zero rotation velocity and convergent orientation flow in all dimensions.However,relatively stable orientations with zero rotation velocity and an overall convergence are found.They are featured by characteristic alignments of specific crystallographic directions in the macroscopic axis of contraction,depending on the slip modes involved in the deformation.It is also shown that the orientation stability varies significantly with the deviation of deformation mode from equibiaxial tension.The simulation results are briefly discussed in comparison with pre-existing experiments.

Effects of thinning on stand structure and tree stability in an afforested oriental beech(Fagus orientalis Lipsky) stand in northeast Turkey

We studied relationships between stand structure and stand stability according to thinning intensity in an afforested oriental beech stand. Various thinning intensities were applied in sample stands. We sampled eight plots in stands that were lightly thinned, eight plots in heavily thinned stands and eight plots in unthinned stands as a control. Height and diameter distributions of the stands were measured to assess stand structure. We quantified individual tree stability and collective stability. Heavy thinning during the first thinning operation damaged the storied structure of the stand in thicket stage and affected collective structuring ability. While most control plots had multi-storied stands, after light and heavy thinning two-storied structure became more common.Large gaps occurred in the canopy after heavy thinning. On average, nine tree collectives were formed per sampling plot in the untreated stand, seven collectives after thinning in 2008 and four collectives after thinning in 2009. Stable trees accounted for 17 % of trees in control plots, 24 % in lightly thinned plots, and 15 % in heavily thinned plots. Collective stability values were 83 % in control plots, 82 % in lightly thinned plots and 36 % in heavily thinned plots. We conclude that it is necessary to retain collective structuring capacity during thinning operations for sustaining stand stability.

Orientation density and workspace analysis of a parallel stabilized platform testing system

An optimized workspace calculation method is proposed for parallel stabilized platform testing systems.This method refines the searched space progressively in order to approach the boundary of the workspace from both the inside and the outside of it.The orientation density is defined and used as an evaluation index to calculate the orientation workspace.The algorithm of the orientation density is embedded into the computer program of the workspace calculation.Then the workspaces of the testing system are solved.In the solution,the orientation density is regarded as a discrete function of the reachable workspace.As a result,the reachable workspace and the orientation workspace are represented in the same multidimensional graphs.Finally the useful workspace of the testing system is determined based on these results.This case study indicates that the calculation efficiency is enhanced by adopting the optimized method and the practicability of workspace study is improved by proposing the orientation density.