Photo-switching and nonlinear optical behaviors of center linked bent-core azobenzene liquid crystalline polymers

A new class of two series (I and II) of center linked bent-core azobenzene liquid crystalline polymers were prepared. They were prepared from two different spacer lengths (2 and 10) between polymer backbone and bent-core mesogen. The bent-core mesogen possesses photoactive linking group with variable terminal chains (7, 8, and 9). The synthesized precursors, monomers, and polymers were characterized by FT-IR, ¹H NMR, and ¹³C NMR spectroscopy. Thermal stability of polymers was examined by thermogravimetric analysis. The mesophase transition of monomers and polymers were observed through polarized optical microscopy, and confirmed by differential scanning calorimetry. Among the two series of polymers, the second series of polymers possesses liquid crystalline properties. The photo-switching properties of bent-core azo polymers were investigated using UV–Vis spectroscopy, trans to cis isomerization occurs around 35 s in chloroform and 65 s in thin film, where as reverse processes take place almost 32 h in chloroform. The photo-switching processes of polymer IIa precedes faster and also longer time thermally stable when compared with recently reported similar polymers. Negative optical nonlinear refractive index and optical limiting properties of the polymers were measured using Nd-YAG laser.     

Adhesion and Debonding of Soft Elastic Films on Rough and Patterned Surfaces

With the help of simulations based on energy minimization, we have studied the effect of roughness of a rigid contactor with sinusoidal and step patterns on the adhesion-debonding cycle of a soft thin elastic film. The surface instability engendered by attractive forces between the contactor and the film produces a regularly spaced array of columns in the bonding phase. The inter-column spacing is governed largely by periodicity of the contactor pattern. Decreased periodicity of the pattern favors intermittent collapse of columns rather than a continuous peeling of contact zones. An increase in the amplitude of roughness decreases the maximum force required for debonding and increases the snap-off distance. The net effect results in a reduced work for debonding. Introduction of noise and increased step-size in simulations decreases the pull-off force and the snap-off distance, as in the case of a smooth contactor. Finally the study reveals that a patterned contactor can be used as a potential template in the patterning of soft interfaces.     

Thermo-mechanical model with adaptive boundary conditions for friction stir welding of Al 6061

Thermo-mechanical simulation of friction stir welding can predict the transient temperature field, active stresses developed, forces in all the three dimensions and may be extended to determine the residual stress. The thermal stresses constitute a major portion of the total stress developed during the process. Boundary conditions in the thermal modeling of process play a vital role in the final temperature profile. The heating and cooling rates with the peak temperature attained by the workpiece determine the thermal stress. Also, predicting realistic peak temperature becomes important as the operating temperature at the interface of tool-workpiece is very close to the solidus temperature of the aluminum workpiece.The convection heat-transfer coefficients of the surfaces exposed to air can be theoretically determined using Newton's law of cooling. Contact conductance depends on the pressure at the interface and has a non-uniform variation. The actual pressure distribution along the interface is dependent on the thermal stress from local temperature and non-linear stress–strain state. Therefore, applying an adaptive contact conductance can make the model more robust for process parameter variations.A finite element thermo-mechanical model with mechanical tool loading was developed considering a uniform value for contact conductance and used for predicting the stress at the workpiece and backplate interface. This pressure distribution contours are used for defining the non-uniform adaptive contact conductance used in the thermal model for predicting the thermal history in the workpiece. The thermo-mechanical model was then used in predict stress development in friction stir welding.     

Dilutional and modified ultrafiltration reduces pulmonary hypertension after operations for congenital heart disease: a prospective randomized study

OBJECTIVE: A prospective randomized study was performed to test whether removal of endothelin-1, by ultrafiltration techniques, will reduce pulmonary hypertension after operations for congenital heart disease. METHODS: Twenty-four patients with pulmonary hypertension (systolic pulmonary/systemic arterial pressure ratio > 60%) undergoing cardiac operations were randomized into a control group (n = 12) having conventional ultrafiltration and an experimental group (n = 12) undergoing dilutional ultrafiltration during and modified ultrafiltration after cardiopulmonary bypass. Plasma endothelin-1, nitric oxide metabolites, and cyclic guanosine monophosphate were assayed before bypass, 10 minutes into bypass, after bypass, and 0, 3, 6, and 12 hours after the operation in both groups, as well as in the ultrafiltrates and after modified ultrafiltration in the experimental group. Both groups received alpha-blockers (chlorpromazine and/or prazosin) postoperatively using the same guidelines. RESULTS: The ultrafiltrates contained significant amounts of endothelin-1 (1.81 +/- 0.86 pg/ml, dilutional, and 6.44 +/- 1.82 pg/ml, modified ultrafiltrate). Endothelin-1 and the pulmonary/systemic pressure ratio were significantly lower in experimental compared with control patients. Nitric oxide metabolites and cyclic guanosine monophosphate increased similarly in both groups for 12 hours after the operation (p = not significant). Three of 12 control patients (25%) but no experimental patients had pulmonary hypertensive crises (p = 0.07). The experimental patients required significantly less ventilatory support (67 +/- 47 hours vs 178 +/- 139 hours for control patients, p = 0.048). CONCLUSIONS: Dilutional and modified ultrafiltration reduce endothelin-1 and the pulmonary/systemic pressure ratio postoperatively and may become an important adjunct for preventing pulmonary hypertension after operations for congenital heart disease in high-risk patients.     

Adaptive gait control for a walking robot

Walking vehicles have the potential to emulate the superior off-road mobility of biological systems. However, it is important to make the walking machine terrain adaptive and versatile, and to minimize man's role as an operator in order to realize this potential. Terrain adaptive locomotion involves intelligent foothold selection and the control of gait to produce the desired motion. This requires a departure from the idealized, structured stepping patterns for statically stable gaits which have been the object of considerable research. A modified wave gait is used to demonstrate that it is possible for the vehicle velocity to be varied continuously in accordance with higher level commands even with irregular, asymmetric, and changing support patterns, A varying duty factor is employed to enable optimal leg cycling frequencies. Implementation of gait control algorithms and results from a computer simulation are also presented.     

MiniPCI、PCMCIA模块打头阵：WiMAX推进商品化速度

在硝烟弥漫的宽带战场,强大的网络接入能力、低成本、高收益等优点无疑是竞争力所在.WiMAX可作为无线DSL或无线Cable技术来弥补有线技术的不足,同时也被部分业界人士视作新一移动基础设施或第四代无线移动应用的互补技术.目前OEM、ODM相关发展厂商正通过采用具弹性系统架构的ASIC以降低成本,加速WiMAX技术推向市场的时间.