History effects on induced and operant variability

2010 ◽  
Vol 38 (4) ◽  
pp. 426-437 ◽  
Author(s):  
A. da Silva Souza ◽  
J. Abreu-Rodrigues ◽  
A. A. Baumann
Keyword(s):  
Operant Variability ◽  
History Effects

Does What We See Shape History? Examining Workload History as a Function of Performance and Ambient/Focal Visual Attention

2021 ◽  
Vol 18 (2) ◽  
pp. 1-17
Author(s):  
Shannon P. Devlin ◽  
Jennifer K. Byham ◽  
Sara Lu Riggs
Keyword(s):  
Visual Attention ◽  
Eye Tracking ◽  
Performance Measure ◽  
Task Demands ◽  
Unexpected Finding ◽  
Impact Performance ◽  
History Effects ◽  
And Performance ◽  
Workload History ◽  
Over Time

Changes in task demands can have delayed adverse impacts on performance. This phenomenon, known as the workload history effect, is especially of concern in dynamic work domains where operators manage fluctuating task demands. The existing workload history literature does not depict a consistent picture regarding how these effects manifest, prompting research to consider measures that are informative on the operator's process. One promising measure is visual attention patterns, due to its informativeness on various cognitive processes. To explore its ability to explain workload history effects, participants completed a task in an unmanned aerial vehicle command and control testbed where workload transitioned gradually and suddenly. The participants’ performance and visual attention patterns were studied over time to identify workload history effects. The eye-tracking analysis consisted of using a recently developed eye-tracking metric called coefficient K , as it indicates whether visual attention is more focal or ambient. The performance results found workload history effects, but it depended on the workload level, time elapsed, and performance measure. The eye-tracking analysis suggested performance suffered when focal attention was deployed during low workload, which was an unexpected finding. When synthesizing these results, they suggest unexpected visual attention patterns can impact performance immediately over time. Further research is needed; however, this work shows the value of including a real-time visual attention measure, such as coefficient K , as a means to understand how the operator manages varying task demands in complex work environments.

In-Place FE Modeling of Unbonded Flexible Pipelines Capturing Pressure Stiffening and Decoupled Axial/Nonlinear Bending Stiffness

2010 ◽  
Author(s):  
Edvin Hanken ◽  
Evelyn R. Hollingsworth ◽  
Lars S. Fagerland
Keyword(s):  
Water Injection ◽  
Bending Stiffness ◽  
Axial Stiffness ◽  
Fe Model ◽  
Nonlinear Bending ◽  
Upheaval Buckling ◽  
History Effects ◽  
System Integrity ◽  
Non Linear ◽  
Bending Behaviour

For fast track pipeline projects the need for costly installation vessels and sophisticated materials for rigid pipeline water injection systems, have made flexible pipelines a competitive alternative. They can be installed with less costly construction vessels, provide a competitive lead time and a corrosion resistant compliant material. Flexible pipelines have relative high axial stiffness and low non-linear bending stiffness which is a challenge to model correctly with FE for in-place analyses of pipelines. Whilst some FE programs can model the non-linear bending behaviour of a flexible pipeline at a given pressure, current FE tools do not include the effect of increased bending resistance as the system is pressurized. Therefore, a 3D FE model in ANSYS was developed to simulate the decoupled axial and nonlinear bending behaviour of a flexible, including the bend stiffening effect for increasing pressure. A description of the model is given in this paper. It will be demonstrated how the FE model can be used to simulate the 3D nonlinear catenary behaviour of an high pressure flexible pipeline tied into a manifold during pressurization. Due to high manifold hub loads during pressurization it is essential that such a model is capable of capturing all effects during pressurization to achieve an acceptable confidence level of the system integrity. It is also described how the FE model is used for upheaval buckling design, capturing non-linearities and load history effects that can reduce the conservatism in the design.

scholarly journals History effects in low-field magnetoresistance of BPSSCO polycrystals

1994 ◽  
Vol 17 (6) ◽  
pp. 607-613
Author(s):  
A Das ◽  
A Banerjee ◽  
R Srinivasan
Keyword(s):  
History Effects ◽  
Low Field

A Physically Based Constitutive Description for Nonproportional Cyclic Plasticity

1991 ◽  
Vol 113 (2) ◽  
pp. 254-262 ◽  
Author(s):  
Fan Jinghong ◽  
Peng Xianghe
Keyword(s):  
Stress Responses ◽  
Sudden Change ◽  
Dislocation Cell ◽  
Cyclic Plasticity ◽  
Cyclic Process ◽  
Planar Slip ◽  
History Effects ◽  
Physically Based ◽  
Physical Foundation ◽  
Two Parameters

The hardening behavior of materials in nonproportional cyclic process is related to the internal changes of materials, such as dislocation cell for wary slip material and ladder or vein substructures for planar slip material. The multiplicatively separated form of hardening function f, in terms of nonhardening region proposed by Ohno [1], and the measure of nonproportionality A proposed by Banallal and Marquis in 1987 [2], is then explained on this physical foundation. The new contributions of this hardening function are: (a) two parameters (f2 and f3) dependent on A are used to differentiate between the influence of latent hardening realized by a sudden change of loading direction, and hereditary hardening associated with nonproportional loading, (b) a general differential form fi (i = 1,2,3) is proposed, and memorial parameters a1 and a3 are introduced to describe different deformation history effects for wary and planar slip materials, (c) different hardening mechanisms through fi are embedded into thermomechanically constitutive relation. The stress responses of 304 and 316 stainless steels subjected to biaxial nonproportional loadings at room temperature are analyzed and compared with the experimental results obtained by Chaboche [3], Tanaka [4, 5] and Ohno [1].

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