Experimental analysis of behavior

The experimental analysis of behavior is a science that studies the behavior of individuals across a variety of species. A key early scientist was B. F. Skinner who discovered operant behavior, reinforcers, secondary reinforcers, contingencies of reinforcement, stimulus control, shaping, intermittent schedules, discrimination, and generalization. A central method was the examination of functional relations between environment and behavior, as opposed to hypothetico-deductive learning theory that had grown up in the comparative psychology of the 1920–1950 period. Skinner's approach was characterized by observation of measurable behavior which could be predicted and controlled. It owed its early success to the effectiveness of Skinner's procedures of operant conditioning, both in the laboratory and in behavior therapy. Basic learning processes in behavior analysis Classical (or respondent) conditioning Classical conditioning In classical or respondent conditioning, a

Micromechanically inspired investigation of cemented granular materials: part I-from X-ray micro tomography to measurable model variables

Edward Ando, Gioacchino Viggiani

Cemented granular materials are abundant in nature and are often artificially produced. Their macroscopic behaviour is driven by small-scale material processes, which are generally classified as: grain breakage, cement damage and fragment rearrangement. This paper presents an experimental analysis of the latter two processes as observed through in-situ X-ray tomography and quantified by a suite of novel image processing approaches. This allows for example all particles and the bonds between them to be identified and their evolution to be individually quantified on a statistically representative volume, in 3D, throughout a loading test. We reveal the high spatial correlation between cement damage and strain rate and their effect on the isotropy of the bonds. Being the second of a two-part contribution, the overarching aim of this paper is to propose a general framework for the micro-inspired study of cemented granular materials. This is developed here, in Part I, in terms of multi-scale experimental quantification at sample and grain-level, while in Part II in terms of a two-way interaction with micro-inspired constitutive modelling.

SPRINGER HEIDELBERG2022

Analysis and Modeling of the Dynamics of Traction Forces during Cell Polarization and their Role in the Organization of Edge Activity

Zeno Messi

The capacity to break symmetry and organize activity to move directionally is a fundamental property of eukaryotic cells. To explain the organization of cell-edge activity, models commonly rely on front-to-back gradients of functional components or regulatory factors, but they do not explain how the front-back axis is defined in the first place. Recently, a novel and successful principle for self-organization of cell-edge activity was proposed, in which local cell-edge dynamics depends on the distance from the cell center, but not on the orientation with respect to the front-back axis. In this thesis, we test the hypothesis that edge motion is controlled by distance sensing via traction forces.\par We show that traction forces exerted on the substrate by polarizing cells are highly dynamical and follow motion of the cell-edge, that stress increases with the distance from the cell center and that maximal forces are located at a fixed distance from the edge near the sites of protrusion-retraction switches. We observe that traction forces correlate with edge extension in cell populations under different experimental conditions. We demonstrate with a fully mechanical model that distance dependence of the force is an emergent property of elastic fiber networks. We next show that dynamics of traction forces and cell-edge motion are correlated during protrusion-retraction cycles, indicating that traction forces trigger the switch from protrusion to retraction. Actin retrograde flow correlates with stress during retraction but not during protrusion suggesting that increase of stress during protrusion is independent of the motion of the actin network. Finally, incorporating a mechanism of cytoskeletal turnover in our model of fiber network we produce systems that display oscillatory fluctuations of their edge and other experimental behaviors.\par Our results provide strong evidence that traction forces play a major role in the organization of cell-edge activity and polarization.

EPFL2021

Analysis and Modeling of the Dynamics of Traction Forces during Cell Polarization and their Role in the Organization of Edge Activity

Zeno Messi

EPFL2021

Experimental analysis of behavior

Micromechanically inspired investigation of cemented granular materials: part I-from X-ray micro tomography to measurable model variables

Numerical modelling and experimental analysis of steel beam-to-column connections allowing for the influence of reinforced-concrete slabs

Analysis and Modeling of the Dynamics of Traction Forces during Cell Polarization and their Role in the Organization of Edge Activity

Micromechanically inspired investigation of cemented granular materials: part I-from X-ray micro tomography to measurable model variables

Numerical modelling and experimental analysis of steel beam-to-column connections allowing for the influence of reinforced-concrete slabs

Analysis and Modeling of the Dynamics of Traction Forces during Cell Polarization and their Role in the Organization of Edge Activity