Targeting the Force-Displacement Response of Thin-walled Structures Subjected to Crushing Load using Curve Decomposition and Topometry Optimization

This work introduces a new approach to targeting the dynamic response of thin-walled energy-absorbing structures through the decomposition of the force-displacement (FD) response and the use of topometry (thickness) optimization. The proposed method divides the nonlinear optimization problem into a series of analytical subproblems. In each iteration, an explicit dynamic analysis is carried out and the dynamic response of the structure is then used to define the subproblem. Numerical examples show that the algorithm can tailor the FD response of the structure to a target FD curve. Progressive collapse, which is a high-energy collapse mode and desired in design for crashworthy, is observed in the optimized thin-walled structures. The proposed algorithm is computationally efficient as it uses a fewer explicit simulations to reach the target response

Electrical control of metallic heavy-metal/ferromagnet interfacial states

Voltage control effects provide an energy-efficient means of tailoring material properties, especially in highly integrated nanoscale devices. However, only insulating and semiconducting systems can be controlled so far. In metallic systems, there is no electric field due to electron screening effects and thus no such control effect exists. Here we demonstrate that metallic systems can also be controlled electrically through ionic not electronic effects. In a Pt/Co structure, the control of the metallic Pt/Co interface can lead to unprecedented control effects on the magnetic properties of the entire structure. Consequently, the magnetization and perpendicular magnetic anisotropy of the Co layer can be independently manipulated to any desired state, the efficient spin toques can be enhanced about 3.5 times, and the switching current can be reduced about one order of magnitude. This ability to control a metallic system may be extended to control other physical phenomena.Comment: 20 pages, 7 figures, Accepted by Physical Review Applied (2017

Spin-orbit torque switching of synthetic antiferromagnets

We report that synthetic antiferromagnets (SAFs) can be efficiently switched by spin-orbit torques (SOTs) and the switching scheme does not obey the usual SOT switching rule. We show that both the positive and negative spin Hall angle (SHA)-like switching can be observed in Pt/SAF structures with only positive SHA, depending on the strength of applied in-plane fields. A new switching mechanism directly arising from the asymmetric domain expansion is proposed to explain the anomalous switching behaviors. Contrary to the macrospin-based switching model that the SOT switching direction is determined by the sign of SHA, the new switching mechanism suggests that the SOT switching direction is dominated by the field-modulated domain wall motion and can be reversed even with the same sign of SHA. The new switching mechanism is further confirmed by the domain wall motion measurements. The anomalous switching behaviors provide important insights for understanding SOT switching mechanisms and also offer novel features for applications.Comment: 40 pages, 14 figure

Influence of truss rod damage on prestressed concrete chord-stayed truss T-frame bridge

The prestressed concrete cable-stayed truss T- frame bridge is a novel type and complex structure. Truss damage is a common form of distress in this type of bridge. For studying the mechanical properties of truss members under the condition of the truss rod, a finite element model is established for analyzing the damage or failure of the truss rod. The effects on the deflection and frequency are compared and analyzed under the condition of damage or failure of the truss rod. The results show that the damage of the truss members has a significant effect on the deflection and frequency of the main beam. The damage of the upper chord affects the deflection of the entire T-beam, and the damage scope of the web member is limited to the abdominal area. The relationship between the damage of the truss members and the deflection of the main beam is nonlinear. Damage to truss members results in a reduction in fundamental frequency. Whole bridge truss damage has a more significant effect on frequency. Upper chord damage has a more significant effect on frequency than web members

Bleaching and dyeing of superfine wool powder/polypropylene blend film

Fibers based regenerated protein draw much attention for recycling discarded protein resources and can produce biodegradable and environmental friendly polymers. In this study, superfine wool powder is blended with polypropylene (PP) to produce wool powder/PP blend film through extrusion and hot-pressing. Hydrogen peroxide is used to bleach the black colored surface of the blend films. The effects of peroxide concentration, bleaching time and powder content on the final whiteness and mechanical properties of the blend films are investigated.The bleached films are dyed with acid red dyes and the dyed color is evaluated using a Computer Color Matching System. Color characters of dyed films, such as L*, a*, b*, &Delta;E*ab, C*ab and K/S values are measured and analyzed. The study not only reuses discarded wool resources into organic powder, widens the application of superfine wool powder on polymers, but also improves the dyeing properties of PP through the addition of protein content.<br /

Bleaching and dyeing of superfine wool powder/polypropylene blend film

Fibers based regenerated protein draw much attention for recycling discarded protein resources and can produce biodegradable and environmental friendly polymers. In this study, superfine wool powder is blended with polypropylene (PP) to produce wool powder/PP blend film through extrusion and hot-pressing. Hydrogen peroxide is used to bleach the black colored surface of the blend films. The effects of peroxide concentration, bleaching time and powder content on the final whiteness and mechanical properties of the blend films are investigated. The bleached films are dyed with acid red dyes and the dyed color is evaluated using a Computer Color Matching System. Color characters of dyed films, such as L*, a*, b*, ΔE*ab, C*ab and K/S values are measured and analyzed. The study not only reuses discarded wool resources into organic powder, widens the application of superfine wool powder on polymers, but also improves the dyeing properties of PP through the addition of protein content

Aerodynamic shape optimization of co-flow jet airfoil using a multi-island genetic algorithm

The co-flow jet is a Zero-Net-Mass-Flux (ZNMF) active flow control strategy and presents great potential to improve the aerodynamic efficiency of future fuel-efficient aircraft. The present work is to integrate the co-flow jet technology into aerodynamic shape optimization to further realize the potential of co-flow-jet technology and improve co-flow jet airfoil performance. The optimization results show that the maximum energy efficiency ratio of lift-augmentation and drag-reduction increased by 203.53% (α=0◦) and 10.25% (α=10◦) at the Power-1 condition (power coefficient of 0.3), respectively. A larger curvature is observed near the leading edge of the optimized aerodynamic shape, which leads to the early onset of flow separation and improves energy transfer efficiency from the jet to the free stream. In addition, the higher mid-span of the optimized airfoil is characterized by accelerating the flow in the middle of the airfoil, increasing the strength of the negative pressure zone, thus improving the stall margin and enhancing the co-flow jet circulation

Endothelial nitric oxide synthase expression is progressively increased in primary cerebral microvascular endothelial cells during hyperbaric oxygen exposure

Exposure to hyperbaric oxygen (HBO) can lead to seizures. Many studies have demonstrated that there exist a very close relationship between the alteration of cerebral blood flow (CBF) and the onset of seizures. Nitric oxide (NO) may play a key role in the change of CBF during exposure, and modulation of endothelial nitric oxide synthase (eNOS)-derived NO by HBO is responsible for early vasoconstriction, whereas late HBO-induced vasodilation depends upon a large amount of NO from both eNOS and neuronal nitric oxide synthase (nNOS). To investigate the effect of HBO on the activity and expression of eNOS in cerebral microvascular endothelial cells (CMEC) in vitro, primarily cultured CMEC from neonatal rats were exposed to oxygen at 500 kPa [5 atmosphere absolute (ATA)] for 10, 20, 30, 60 and 120 minutes (min), then eNOS activity, protein and mRNA contents in cells were detected. Our results showed that immediately after exposure, 30, 60 and 120 min HBO exposures did not alter NOS activity. When detected no matter immediately or six hours (h) after exposure, these exposures also did not alter eNOS protein and mRNA levels. However, when detected 24 h after exposure, 30, 60 and 120 min exposures upregulated eNOS protein content by 39%, 60% and 40% respectively. 10 and 20 min exposures upregulated eNOS mRNA content by about 15%, while 30, 60 and 120 min exposures upregulated it by about 20–30%. The increased eNOS protein and mRNA contents at 24 h after exposure may reflect new protein synthesis for eNOS. Our studies showed that with the exposing protocols we used, HBO did induce eNOS expression increase in CMEC. However, compared with the decrease of CBF in vivo, which occurred in a relative short time after rat was exposed to HBO above 4 ATA, the responses of eNOS in CMEC in vitro were a little slow. Thus we considered that for the vasodilation in the late period of HBO exposure before seizure, the effect of NO produced by eNOS was limited