How to Control Robots Interacting with Dynamic Environment

The goal of this paper is to shed light on the control problem of constrained robot motion from the aspect of the dynamical nature of the environment with which the robot is in contact. Therefore, the criticism of traditional hybrid control which allows position/force feedback loops to split into independent control with respect to position and force, is not the main point we want to make. Reference to the papers written by the founders of hybrid control and their numerous followers served only to better understand the reason and motivation for suggesting a different approach to control of robots interacting with environment.The paper has a predominantly review character, based on recently published work. It also contains some new, unpublished results in the framework of the unified approach to the position/force control of robots, proposed by the present author and his co-workers. By pointing to the possibility of introducing an environment dynamics in the contact tasks of the machining type, the author emphasizes that the proposed dynamically interactive control can be applied to a completely different class of tasks, in which a contact is made between the system (constructions or structure) and very specific kinds of dynamic environments.     

Variability in the proliferative responsiveness of cultured human vascular smooth muscle cells to alpha-thrombin

alpha-Thrombin, a key enzyme of the coagulation cascade, is also a potent mitogen for many cell types. In the present study, the responsiveness to alpha-thrombin of cultured human vascular smooth muscle cells (HVSMC) derived from either vein or normal and atherosclerotic arteries was investigated. All HVSMC populations examined responded mitogenically to alpha-thrombin. However, the extent of this response varied between different cell populations. No significant differences were observed between HVSMC derived from vein versus artery or atherosclerotic versus normal tissues. The responsiveness of a specific HVSMC culture to alpha-thrombin was not affected by cell density and remained constant over several passages. Unlike platelet-derived growth factor BB (PDGF-BB), alpha-thrombin did not exhibit any significant chemotactic effects on HVSMC or induce their anchorage independent growth in semi-solid medium. The hypothesis that the observed variability in HVSMC responsiveness to alpha-thrombin is due to the heterogeneity of cultured HVSMC is raised and discussed.     

Quantum phase transitions in 2D antiferromagnets

Quantum Monte Carlo results for the T = 0 order-disorder transition of two-dimensional dimerized quantum Heisenberg antiferromagnets are presented. For a two-layer model, with the dimers having one member on each plane, the finite-size scaling of the staggered structure factor and the staggered susceptibility is consistent with the 3D classical Heisenberg universality class, as required if the transition is described by the 2+1-dimensional non-linear sigma-model. However, for models with the dimers in a single plane, the behavior does not appear to be consistent with this universality class.