Events

Upcoming

Time and place: Dec. 10, 2021 12:15 PM1:15 PM, Niels Henrik Abels hus, 9th floor, seminar room 919

Abstract: The fungal kingdom is one of the most species-rich organismal groups, containing up to 6 million species worldwide with a large diversity of ecosystem functions. Multicellularity has evolved independently in fungi, and over time many different growth forms and structures have originated. I will present some basics on fungal growth and the formation of complex multicellular structures.

Online participation is possible too. Please contact "timokoch at uio.no" for the Zoom link. This talk is part of the Mechanics Lunch Seminar series. Bring-your-own-lunch and lots of questions.

Previous

Time and place: Dec. 3, 2021 12:15 PM1:15 PM, Niels Henrik Abels hus, 9th floor, seminar room 919

Abstract: Transport and mixing in multiphase flow through porous media plays a key role in a range of biological, geological, and engineered systems. Here, we use numerical simulations to investigate the effect of intermittent multiphase flow on fluid stretching and folding, a fundamental mechanism driving solute mixing and reaction in porous media. We show that, in contrast to steady single-phase flows, the concurrent flow of two immiscible phases induces chaotic mixing, characterized by exponential stretching in the pore space. The stretching rate is found to decay with increasing capillary number, implying that the increasing flow intermittency observed at lower capillary numbers enhances the mixing efficiency. We propose a mechanistic model to link the basic multiphase flow properties to the chaotic mixing rate, opening new perspectives to understand mixing and reaction in multiphase porous media flows. The results presented here form part of the background for the recently started RCN-funded project M4: Mixing in Multiphase flow through Microporous Media, which will also be introduced.

This talk is part of the Mechanics Lunch Seminar series. Bring-your-own-lunch and lots of questions.

Time and place: Nov. 26, 2021 12:15 PM1:15 PM, Niels Henrik Abels hus, 9th floor, seminar room 919

Abstract:  The cerebral circulation must ensure continuous blood perfusion of the brain which is the biggest oxygen consumer in the human body. It must also provide mechanisms for adaptability to changing oxygen demand as well as resilience to local blockages. We will look at such mechanisms at the level of the microcirculation where the mechanics of blood flow is dominated by red blood cells. We will find that red blood cells do not only play the role of oxygen carriers, but that they are an important element of blood flow regulation itself. To this end, we will compare results from in vitro studies in microfluidic chips to theoretical and computational models and to in vivo data from mice. We will derive local auto-regulation mechanisms for blood flow and will study how local modifications in the vascular network can modify the global hematocrit distribution. These results will emphasize the relevance of red blood cell mechanics and microvascular network geometry in cerebral blood perfusion.

This talk is part of the Mechanics Lunch Seminar series. Bring-your-own-lunch and lots of questions.

Time and place: Nov. 19, 2021 12:15 PM1:00 PM, Niels Henrik Abels hus, 9th floor, seminar room 919

Abstract:  Swimming bacteria, growing cell tissues, molecular motors, and microtubule systems confined to a substrate are examples of active matter films that exhibit long-range nematic (orientational) order. Intrinsic activity in these systems builds mechanical stresses that tend to destroy local nematic order through topological defects, which act as sources of persistent active flows.  The overall evolution and functionality of biological matter is greatly influenced by these orientational defects. Yet, their formation and dynamics are driven by a complex interplay between topological singularities in the nematic order and active flow instabilities, and this is not completely understood. 

Click title to continue reading abstract...

Time and place: Nov. 12, 2021 12:15 PMOct. 22, 2021 1:30 PM, Niels Henrik Abels hus, 9th floor, seminar room 919

Abstract:  Exchange processes across a porous-medium free-flow interface occur in a wide range of environmental, technical, and bio-mechanical systems.  In the course of these processes, flow dynamics in the porous domain and in the free-flow domain exhibit strong coupling, often controlled by mechanisms at the common interfaces.  Such processes need to be analyzed on small scales and new scale-bridging modeling concepts need to be developed for an accurate description also on larger scales (REV scale). Recent developments within the Collaborative Research Center "Interface-Driven Multi-Field Processes in Porous Media – Flow, Transport and Deformation" and the Cluster of Excellence SimTech at the University Stuttgart regarding such aspects for coupled free-flow and porous-medium flow systems will be presented in this talk.

This talk is part of the Mechanics Lunch Seminar series. Bring-your-own-lunch and lots of questions.

Time and place: Nov. 12, 2021 12:15 PMOct. 22, 2021 1:30 PM, Niels Henrik Abels hus, 9th floor, seminar room 919

Abstract:  We present a second-order numerical scheme to compute capillary bridges between arbitrary solids by minimizing the total energy of all interfaces. From a theoretical point of view, this approach can be interpreted as the computation of generalized minimal surfaces using a Newton-scheme utilizing the shape Hessian. In particular, we give an explicit representation of the shape Hessian for functionals on shells involving the normal vector without reverting back to a volume formulation. From an algorithmic perspective, we combine a resolved interface via a triangulated surface for the liquid with a level-set description for the constraints stemming from the arbitrary geometry. The actual shape of the capillary bridge is then computed via finite elements provided by the FEniCS environment, minimizing the shape derivative of the total interface energy.

This talk is part of the Mechanics Lunch Seminar series. Bring-your-own-lunch and lots of questions.

Image may contain: Product, Rectangle, Purple, Automotive design, Grey.
Time and place: Nov. 5, 2021 12:15 PMOct. 22, 2021 1:00 PM, Niels Henrik Abels hus, 9th floor, seminar room 919

Abstract:  After a broad overview of the activities of MecaWet group at PMMH, the presentation will focus on the “dry side” of MecaWet.

Drawing a flat map of the Earth is fundamentally challenging as continents unavoidably end up distorted. Reciprocally, complex natural shapes such as the delicate shape of Orchidea petals emanate from differential growth. From an engineering point of view, similar shape changes can be obtained when flat patches embedded with a network of channels are inflated. We will discuss two opposite strategies involving stretchable elastomers or, conversely, stiff fabrics. Can we program the resulting 3D shapes? How robust are such inflated structures?

This talk is part of the Mechanics Lunch Seminar series. Bring-your-own-lunch and lots of questions.

Time and place: Oct. 22, 2021 12:15 PM1:00 PM, Niels Henrik Abels hus, 9th floor, seminar room 919

Abstract: Mixed-dimensional partial differential equations (PDEs) are equations coupling unknown fields defined over domains of differing topological dimensions. Such mixed-dimensional PDEs naturally arise in a wide range of fields including geology, biomedicine, and fracture mechanics. We introduce an automated framework dedicated to mixed-dimensional problems as part of the FEniCS library. This talk gives an overview of the abstractions and algorithms involved. The introduced tools will be illustrated by concrete examples of applications in biomedicine (see below for more detailed context).

This talk is part of the Mechanics Lunch Seminar series. Bring-your-own-lunch and lots of questions.

Time and place: Oct. 18, 2021 12:00 PM1:00 PM, Niels Henrik Abels hus, 12th floor, Abels utsikt

Abstract: The concept of symmetry breaking is well-known in physics, for instance in condensed matter, where it results from interactions in a many-body system — e.g., phase transition in a spin system. Yet, as physicists, we tend not to think of the patterned structures seen in living, many-body systems in terms of broken symmetries. Whether it is the spacing of knuckles on our hand, the collective alignment of hairs on an insect wing, or more globally the transformation of a homogeneous, isotropic embryo into a developed organism, symmetry breaking abounds in biology. What new insights can a physicist bring to understand the origin of these complex phenomena? (Click title to read full abstract below...)

Time and place: Oct. 15, 2021 12:15 PM1:00 PM, Niels Henrik Abels hus, 9th floor, seminar room 919

Abstract: Elimination of substances from the brain is believed to occur by a combination of convection and diffusion. In previous work, transport along perivascular spaces around blood vessels have been explicitly meshed and modeled, and also 1D-3D models have been used to model the interaction between blood and brain tissue. A problem with both these approaches is that it requires spatial information of all blood vessels within the brain and in addition may result in a computationally expensive system to solve. In this talk, I will introduce a homogenized model of transport in the brain, also taking into account transfer between different compartments (like blood and brain tissue) within the brain. Fluid flow in and between compartments are modeled with the mulitple-porosity elasticity theory (MPET), while transport within and between compartments are modeled with convection-diffusion equations. I will further show preliminary results from our model and compare with experimental data obtained in a glioma (brain tumor) patient, where transport between blood and brain is typically altered.

This talk is part of the Mechanics Lunch Seminar series. Bring-your-own-lunch and lots of questions.

Time and place: Oct. 8, 2021 12:15 PM1:00 PM, Niels Henrik Abels hus, 9th floor, seminar room 919

Abstract: My soft matter research group investigates the autonomous transformation of phospholipid agglomerates into membrane compartments through a sequence of topological changes on solid interfaces. This process is initiated by contact and wetting of artificially created as well as natural surfaces by the lipids, and proceeds via a network of interconnected lipid nanotubes to produce nearly uniform lipid bilayer compartments. Under minimal assumptions it is conceivable that such process could have occurred on the early Earth, where the autonomous formation of simple membrane compartments is presumed to have enabled encapsulation of nucleotides and prebiotic chemistry precursors. According to the currently accepted “bulk hypothesis”, such compartments have spontaneously formed under moderate environmental conditions from lipids suspended in bulk aqueous medium. Only very recently, surfaces have emerged as potential supporting structures for the self-assembly of prebiotic compartments. In my talk, I will report on new evidence for the involvement of surfaces in protocell nucleation and development. The talk will highlight the implications of the new findings for our understanding of possible origin of life processes, and argue that materials properties-driven autonomous processes on solid interfaces might have greater role in the development of life than currently considered.

Time and place: Aug. 27, 2021 12:15 PM1:00 PM, Niels Henrik Abels hus, 9th floor, seminar room 919

Abstract: It is known that a sessile drop subject to a forced vibration will vibrate in different shapes depending on the frequency of the forcing, the drop’s liquid properties and the liquid/solid/gas system. So the question then becomes, what can these vibrating drops help us understand? Here we find that we can use the motion of these drops to understand the constitutive law relating the drop’s apparent dynamic contact angle to its contact line velocity. We find we are able to extract mobility parameters like those described by the Davis-Hocking model, and that mobility parameters extracted in this fashion can be used in simulations of drop-drop coalescence to accurately predict post-coalescence dynamics.

This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting and bring-your-own-lunch.

Time and place: June 25, 2021 12:15 PM1:00 PM, Zoom

Abstract: Efficient and parameter robust solvers for multiscale/multiphysics systems, where the coupling is enforced by the Lagrange multipliers, rely on operators in fractional Sobolev spaces defined over the interface. Arguably, this feature is not unexpected as there is explicit coupling/an interfacial variable in the system. However, in this talk we show that even for coupled problems free of Lagrange multipliers the fractional operators are a crucial component for constructing robust preconditioners. Stokes-Darcy/Biot systems will be discussed.

This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting.

Zoom: To obtain the Zoom meeting details please contact Timo Koch (timokoch at math.uio.no).

Time and place: June 18, 2021 12:15 PM1:00 PM, Zoom

Abstract: New estimates of heat loss from Earth's interior (the mantle) suggest that the Pacific side of the planet has been losing heat at a much higher rate compared to the African side. The difference in heat loss amounts to almost 50 degrees more cooling of the Pacific side over the past 400 million years.

This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting.

Zoom: To obtain the Zoom meeting details please contact Timo Koch (timokoch at math.uio.no).

Time and place: June 11, 2021 12:15 PM1:00 PM, Zoom

Abstract: Magmatic intrusions into the earth's crust lead to geological formations such as sills, laccholites and volcanoes. The conventional approach is to threat the intrusive fluid as Newtonian and viscous, while the host-rock is assumed to behave purely elastic. However, Magma is known to have non-Newtonian properties. In addition, field studies indicate that visco-elastic deformation of the host rock is an important effect in the propagating fracturing. We thus want to investigate the effect of introducing a yield-stress fluid in the intrusion process. We perform an experiment based on the elasto-hydro-dynamical approach, but where we change the injected fluid from a viscous (glycerol) to a yield-stress fluid (carbopol). We are interested in seeing how this potentially can change the dynamics of the intrusion compared with the viscous case. 

This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting.

Zoom: To obtain the Zoom meeting details please contact Timo Koch (timokoch at math.uio.no).

Time and place: May 21, 2021 12:15 PM1:00 PM, Zoom

Abstract: In computational mechanics, high fidelity simulations of a parameterized partial differential equation (PDE) are often computational expensive, which make them impractical for real-time predictions. Non-intrusive reduced order modelling aims to address this problem with a fast low rank approximation. This is usually done in two phases: the model is built in the offline phase and the prediction is done in the online phase. In the offline phase, data points, or so-called snapshots, are collected from simulations or measurements. The reduced basis space can then be obtained from the dataset using Proper Orthogonal Decomposition. In the online phase, the solution for a new set of parameters is obtained by first recovering the expansion coefficients for the reduced basis and then projecting them back into the uncompressed real-life space. The non-intrusive approach relies on a statistical mapping between the coefficients and the parameters. Various methods have been proposed to do so, this seminar will discuss radial basis function interpolations and dynamic mode decompositions.

This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting.

Zoom: To obtain the Zoom meeting details please contact Timo Koch (timokoch at math.uio.no).

Time and place: May 7, 2021 12:15 PM1:00 PM, Zoom

Abstract: Graphics processing units, or GPUs, offer significantly increased performance for some scientific computing workloads. But in the case of finite element simulations on unstructured meshes, the benefits of using GPUs are still the subject of an ongoing discussion for which there is no clear conclusion. We describe our work on improving the GPU acceleration of a finite element solver framework called FEniCS, where code is automatically generated for the user from a high-level description of their finite element problem. We use automated code generation to offload the assembly of linear systems to a GPU, while taking care that data transfers between CPU and GPU do not become a performance bottleneck. We provide examples to show that GPUs and automated code generation can be used to accelerate finite element solvers. Even though more work is needed to find efficient GPU-based linear solvers, our improvements to FEniCS can be used as a starting point for exploring the potential of GPU acceleration for finite element simulations.

This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting.

Zoom: To obtain the Zoom meeting details please contact Timo Koch (timokoch at math.uio.no).

Time and place: Apr. 9, 2021 12:15 PM1:00 PM, Zoom

Abstract:Due to their large mass and small aspect ratio, icebergs pose a threat to boats and offshore structures. Small icebergs and bergy bits can cause harm to platform hulls and are more difficult to discover remotely. When there is a risk of collision between icebergs and platforms, it is necessary to deflect its drifting course to ensure safe human operations in polar offshore regions. In this talk, I will present iceberg towing experiments carried out on Svalbard in September 2020...

This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting.

Zoom: To obtain the Zoom meeting details please contact Timo Koch (timokoch at math.uio.no).

Time and place: Mar. 26, 2021 12:15 PM1:00 PM, Zoom

Abstract: We report on the observation of gravity-capillary wave turbulence on the surface of a fluid in a high-gravity environment. By using a large-diameter centrifuge, the effective gravity acceleration is tuned up to 20 times Earth’s gravity. The transition frequency between the gravity and capillary regimes is thus increased up to one decade as predicted theoretically. A frequency power-law wave spectrum is observed in each regime and is found to be independent of the gravity level and of the wave steepness. While the timescale separation required by weak turbulence is well verified experimentally regardless of the gravity level, the nonlinear and dissipation timescales are found to be independent of the scale, as a result of the finite size effects of the system (large-scale container modes) that are not taken currently into account theoretically.

This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting.

Zoom: To obtain the Zoom meeting details please contact Timo Koch (timokoch at math.uio.no).

Time and place: Mar. 12, 2021 12:15 PM1:00 PM, Zoom

Abstract: I will present a Biot-Stokes formulation created by Ricardo Ruiz-Baier. The formulations consists of a fluid-structure interaction model for flow of a Newtonian fluid, coupled with Biot consolidation equations through an interface, and incorporates total pressure as an unknown in the poroelastic region. I will also present a preconditioner for this system which is robust in all parameters and apply the model to a third circulation process to show the velocity fields in the brains subarachnoid space.

This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting.

Zoom: To obtain the Zoom meeting details please contact Timo Koch (timokoch at math.uio.no).

Time and place: Feb. 26, 2021 12:15 PM1:00 PM, Zoom

Abstract: If a droplet smaller than the capillary length is placed on a substrate with a conical shape, it spreads by itself in the direction of growing fibre radius. We describe this capillary spreading dynamics by developing a lubrication flow approximation on a cone and by using the perturbation method of matched asymptotic expansions. The droplet velocity is found to increase with the cone angle but decrease with the cone radius. We show that a film is formed at the receding part of the droplet, much like the classical Landau–Levich–Derjaguin film. By using the approach of matching asymptotic profiles in the film region and the quasi-static droplet, we obtain the same film thickness as the results from the lubrication approach. Our results show that manipulating the droplet size, the cone angle and the slip length provides different schemes for guiding droplet motion and coating the substrate with a film.​

This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting.

Zoom: To obtain the Zoom meeting details please contact Timo Koch (timokoch at math.uio.no).

Time and place: Jan. 15, 2021 12:15 PM1:00 PM, Zoom

Abstract: Physics-informed neural networks (PINNs) are a new and promising methodology to combine deep learning with partial differential equations (PDE). PINNs extend deep neural networks by regularizing their output to fulfill any given PDE, allowing to solve both forward and inverse PDE problems utilizing high-performance machine learning libraries such as Tensorflow and PyTorch. This talk will give a short introduction to PINNs and provide a detailed, tutorial-style code demonstration on their implementation in PyTorch.

This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting.

Zoom: To obtain the Zoom meeting details please contact Timo Koch (timokoch at math.uio.no).

Time and place: Dec. 4, 2020 12:15 PM1:00 PM, Zoom

Abstract: Intraluminal vesicle (ILV) formation plays a crucial role in the attenuation of growth factor receptor signaling. The endosomal sorting complex required for transport (ESCRT-0 to -III/VPS4) mediates this process. The general dogma has been that upstream ESCRTs (0 to II) sequester receptors at the surface of endosomes and the downstream ESCRTs (III/VPS4) remodel the endosome membrane leading to the abscission and formation of receptor-containing ILVs. We now show that upstream ESCRTs not only sequester cargo, but in addition play a crucial role for the initiation of membrane shape remodeling in ILV budding. Through a combination of mathematical modeling and experimental measurements we show that upstream ESCRTs facilitate ILV budding by crowding with a high density in the membrane neck region.

This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting.

Zoom: To obtain the Zoom meeting details please contact Timo Koch (timokoch at math.uio.no).

Time and place: Nov. 20, 2020 12:15 PM1:00 PM, Zoom

Abstract: Due to the fluid nature of biological membranes, proteins are able to diffuse along the membrane surface. Additionally, several processes of vesicle formation require protein recruitment.  We discuss, on one hand, the implications of fixed membrane shapes in protein diffusion, and on the other hand, the effects of protein diffusion and recruitment in membrane shape transformation. 

This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting.

Zoom: To obtain the Zoom meeting details please contact Timo Koch (timokoch at math.uio.no).

Time and place: Nov. 13, 2020 12:15 PM1:00 PM, Zoom

Abstract: Magnetic Resonance Elastography (MRE) is an emerging technique to measure the bio-mechanical properties of tissue in vivo. We present measurements of the shear modulus in healthy subjects, and in patients with brain cancer.

This talk is part of the Mechanics Lunch Seminar series. That means 20min talks plus discussion in an informal setting.

Zoom: To obtain the Zoom meeting details please contact Timo Koch (timokoch at math.uio.no).