Key to the outcome of the Queensland group’s research was the development of a different technique for detecting the light passing through the optical tweezers. This is important for making measurements in complex environments such as cells.” Better detection with structured light It also removes calibration requirements for other viscosity measurement techniques, since the kinetic energy is so closely connected to viscosity. “It is this key fact that allowed us to increase the speed of viscosity measurement by several orders of magnitude. “So, velocity measurement allows a direct measurement of viscosity, rather than the statistical inference that one is able to do with position measurement,” Bowen says. Raizen at the University of Texas at Austin, USA, showed that Einstein’s conjecture was inaccurate.īowen and his Queensland collaborators reasoned that if they could reach this regime where they could see the smooth trajectories of the microparticles in an optical trap, then they could measure the velocities of the particles, not just their positions, and calculate their kinetic energy and thus their viscosity. Bowen, a professor in the quantum optics laboratory at the University of Queensland, Australia.īack then, Einstein predicted that it would be impossible to take measurements fast enough to reach this “ballistic regime,” but in the past decade, experimenters led by OSA Fellow Mark G. “However, Einstein also realized that with fast enough measurements a different sort of behavior should emerge, where particles move in smooth trajectories, much like the ballistic trajectories of a ball when thrown,” says Warwick P. Beating Einstein’s predictionĮarly in the 20 th century, Albert Einstein provided a thermodynamic explanation of Brownian motion-the random motions of microparticles suspended in a fluid. A research team at an Australian university has measured small-scale fluid viscosity with temporal resolution on a few tens of microseconds by tracking a particle inside an optical trapping field with high precision (Nat. Previous methods of measuring viscosity on these short time and length scales required integration times of multiple seconds, so that they could not capture the rapidly changing dynamics of particle–liquid interactions. ![]() However, on the level of living cells and other biological materials, viscosity measurements can provide key information about phase transitions and dynamics on time scales of milliseconds or microseconds. Most examples of viscosity come from everyday macroscopic substances, from motor oil to honey. The performance of the proposed models is successfully tested for a turbulent channel flow.Researchers measured the viscosity, or stickiness, of liquids, which could have applications in biology. ![]() In this way, new models can be constructed by imposing appropriate restrictions in this space. In the present work, they are presented in a framework where all the models are represented as a combination of elements of a 5D phase space of invariants. Most of them are based on the combination of invariants of a symmetric second-order tensor that is derived from the gradient of the resolved velocity field. Eddy-viscosity models for Large-Eddy Simulation is probably the most popular example thereof: they rely on differential operators that should be able to capture well different flow configurations (laminar and 2D flows, near-wall behavior, transitional regime.). Since direct simulations of the incompressible Navier-Stokes equations are limited to relatively low-Reynolds numbers, dynamically less complex mathematical formulations are necessary for coarse-grain simulations. ![]() Building proper invariants for subgrid-scale eddy-viscosity models
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |