48,199 research outputs found
Memory effects in response functions of driven vortex matter
Vortex flow in driven type II superconductors shows strong memory and history
dependent effects. Here, we study a schematic microscopic model of driven
vortices to propose a scenario for a broad set of these kind of phenomena
ranging from ``rejuvenation'' and ``stiffening'' of the system response, to
``memory'' and ``irreversibility'' in I-V characteristics
Analysis of Stiffening Methods and Effects on Irregular Single-layer Lattice Shell Structures
Local stiffening is often a good solution to mechanical property problems of irregular single-layer lattice shell structures. The effects of three local stiffening methods, namely section enlargement stiffening, planar truss stiffening, and space truss stiffening, on their structural stiffness, strength, and overall stability were analyzed in this study. A practical engineering example showed that these three stiffening methods could effectively reduce the deformation of the lattice shell under vertical and lateral loads, reduce the comprehensive stress ratio, and increase the buckling eigenvalue and ultimate bearing capacity factor. The local space truss stiffening method had the best comprehensive effect. The same stiffening methods were applied to a regular lattice shell and the analysis showed that the stiffening effect on a regular shell is quite different from that on an irregular lattice shell. The three stiffening methods could not reduce its deformation under vertical loading but could reinforce the strength and overall stability of the structure effectively. Proper suggestions are proposed according to the preceding analysis in case a single-layer lattice shell structure cannot meet the demands of the design code
Analysis of Stiffening Methods and Effects on Irregular Single-layer Lattice Shell Structures
Local stiffening is often a good solution to mechanical property problems of irregular single-layer lattice shell structures. The effects of three local stiffening methods, namely section enlargement stiffening, planar truss stiffening, and space truss stiffening, on their structural stiffness, strength, and overall stability were analyzed in this study. A practical engineering example showed that these three stiffening methods could effectively reduce the deformation of the lattice shell under vertical and lateral loads, reduce the comprehensive stress ratio, and increase the buckling eigenvalue and ultimate bearing capacity factor. The local space truss stiffening method had the best comprehensive effect. The same stiffening methods were applied to a regular lattice shell and the analysis showed that the stiffening effect on a regular shell is quite different from that on an irregular lattice shell. The three stiffening methods could not reduce its deformation under vertical loading but could reinforce the strength and overall stability of the structure effectively. Proper suggestions are proposed according to the preceding analysis in case a single-layer lattice shell structure cannot meet the demands of the design code
Inelastic seismic behavior of stiffening systems : multi-span simply-supported (MSSS) bridges
Stiffening behavior can result from interaction between a structure (base system) and its surrounding environment as in the MSSS bridge soil-structure interaction. In this study, three MSSS bridge cases are parametrically analyzed and their dynamic characteristics and behavior are presented and discussed. Later, for investigating stiffening behavior, a simplified stiffening model is introduced and an extensive parametric study with more than 367,000 analyzed cases is performed. In the parametric study, different stiffening parameters (i.e., stiffness, strength, gap size, and mass), 41 strong motion records, and several damage criteria are considered and effects of the stiffening parameters variations on the dynamic response of simple stiffening systems are presented. It is shown that on the average the displacement response is lower for stiffening systems, consistent with pushover analysis based on the seismic codes. However, considering many other damage indices like dissipated hysteretic energy and low-cycle fatigue damage index, it is quite likely that a stiffening system would sustain more damage than an elastic-plastic system. At the end, suitable design response spectra for stiffening systems are developed and their practical implications for MSSS bridges are demonstrated
Age-related vascular stiffening: causes and consequences
Arterial stiffening occurs with age and is closely associated with the progression of cardiovascular disease. Stiffening is most often studied at the level of the whole vessel because increased stiffness of the large arteries can impose increased strain on the heart leading to heart failure. Interestingly, however, recent evidence suggests that the impact of increased vessel stiffening extends beyond the tissue scale and can also have deleterious microscale effects on cellular function. Altered extracellular matrix (ECM) architecture has been recognized as a key component of the pre-atherogenic state. Here, the underlying causes of age-related vessel stiffening are discussed, focusing on age-related crosslinking of the ECM proteins as well as through increased matrix deposition. Methods to measure vessel stiffening at both the macroscale and microscale are described, spanning from the pulse wave velocity measurements performed clinically to microscale measurements performed largely in research laboratories. Additionally, recent work investigating how arterial stiffness and the changes in the ECM associated with stiffening contributed to endothelial dysfunction will be reviewed. We will highlight how changes in ECM protein composition contribute to atherosclerosis in the vessel wall. Lastly, we will discuss very recent work that demonstrates endothelial cells are mechano-sensitive to arterial stiffening, where changes in stiffness can directly impact endothelial cell health. Overall, recent studies suggest that stiffening is an important clinical target not only because of potential deleterious effects on the heart but also because it promotes cellular level dysfunction in the vessel wall, contributing to a pathological atherosclerotic state
Influence of active stiffening on dynamic behaviour of piezo-hygro-thermo-elastic composite plates and shells
The active stiffening and active compensation analyses are carried out to present the influence of active stiffness on the dynamic behaviour of piezo-hygro-thermo-elastic laminates. A coupled piezoelectric finite element formulation involving a hygrothermal strain field is derived using the virtual work principle and is employed in a nine-noded field consistent Lagrangian element. The closed-loop system is modelled with elastic stiffness, active stiffness introduced by isotropic actuator lamina and geometric stiffness due to stresses developed by hygrothermal strain. Through a parametric study, the influence of active stiffening and active compensation effects on the dynamics of cross-ply and angle-ply laminated plates and shells are highlighted. The active stiffening on thin shells is significantly influenced by boundary effects and the actuator efficiency further decreases with increase in curvature. The reduction in natural frequencies of cross-ply laminates due to hygrothermal strain is actively compensated by active stiffening; however, it is observed that the actuator performance reduces significantly with increase in curvature particularly in angle-ply laminates, which demands the use of directional actuators. The active stiffening and active compensation effects are low in moderately thick piezo-hygro-thermo-elastic plates and shells, which are less influenced by boundary conditions
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