2016

Stereolithography - A Powerful Tool to Create almost Everything

Stereolithography or "SLA" printing is a powerful and widely used 3D printing technology for creating prototypes, models, and fully functional parts for production. This additive manufacturing process works by focusing an ultraviolet (UV) laser onto a vat of liquid resin. Layer by layer formation of a polymeric network allows printing parts that are almost impossible to create with other processes.At Formlabs, a startup that originated out of the MIT Media lab in 2011, we work on all aspects of SLA printing; we develop and manufacture 3D printers, resins, and software. In this talk, I will give a detailed overview of the printer technology, the chemistry of the materials, and how to use SLA for lots of exciting applications.

Microfluidics of sugar transport in plants

Plants can rightly be called masters of microengineering. Their survival and successful reproduction depends on their ability to overcome a series of physical challenges during growth and when transporting matter over great distances. In this talk, we focus on the microfluidic network responsible for energy distribution (the phloem). We combine experiments on living plants and biomimetic microfluidic devices to elucidate the basic physical principles that govern sugar transport in plants. We derive a scaling relation between the characteristic sizes of the plant organs, which optimizes the rate of sugar transport. Comparison with experimental data suggests that the pipe network is operating at or near the theoretical optimum. We further consider the coupling between photosynthesis and long-distance transport. While sap with high sugar concentration has the greatest transport potential, viscosity impedes flow, a phenomena analogous to congestion in traffic flows. The optimal sugar concentration for transport in plants is 25%, sweeter than Coke (10%) but much less viscous than maple syrup (65%). Although plants have generally evolved towards the theoretical optimum, a number of unusually sweet plants exist. This group consists primarily of crop plants such as corn (40%) and potato (50%), sugar junkies of the natural world.

Digital signalbehandling og bildeanalyse, UiO and PGS

The effects of moving rough sea surfaces on seismic data.

Enrico Fermi and the birth of modern nonlinear physics

In the early fifties in Los Alamos E. Fermi in collaboration with J. Pasta and S. Ulam investigated a one dimensional chain of equal masses connected by a weakly nonlinear spring. The key question was related to the understanding of the phenomenon of conduction in solids; in particular they wanted to estimate the time needed to reach a statistical equilibrium state characterized by the equipartition of energy among the Fourier modes. They approached the problem numerically using the MANIAC I computer; however, the system did not thermailize and  they observed a recurrence to the initial state (this is known as the FPU-recurrence). This unexpected result has led to the development of the modern nonlinear physics (discovery of solitons and integrability). In this seminar, I will give an historical overview of the subject and present the different approaches that have been proposed in the last 60 years for explaining this paradox. Very recent results on the estimation of the time scale and on  the explanation of the mechanism of equipartition will also be discussed.

Experimental investigation of linear stability mechanisms in stratified gas-liquid pipe flow

The evolution of interfacial waves on a stratified air water pipe flow is investigated experimentally. An oscillating plate introduced controlled perturbations at the inlet of the pipe. High speed cameras captured the evolution of these perturbations along the pipe by means of a phase-locked shadowgraphy technique. Thereby, it was possible to measure the temporal and the spatial evolution of the disturbances introduced in the flow. Particle image velocimetry was performed further downstream in order to evaluate changes in the base flow. 

A relatively large data bank has been gathered with varying air and water flow rates as well as varying amplitudes and frequencies of the inlet perturbations. Some preliminary results contain a qualitative assessment of linear vs. non-linear regimes and momentum transfer into the water layer.

Zebrafish embryos: a useful tool for the study of nanoparticle behavior in real time in a vertebrate