Active Matter Alters the Growth Dynamics of Coffee Rings Agnese Callegari, Tugba Andaç, Pascal Weigmann, Sabareesh K. Velu, Erçag Pince, Giorgio Volpe & Giovanni Volpe
LAOP – Latin America Optics & Photonics Congress, Lima, Peru
12-15 November 2018
Abstract: We show that bacterial mobility starts playing a major role in determining the growth dynamics of the edge of drying droplets, as the droplet evaporation rate slows down.
Microscopic Engine Powered by Critical Demixing
Falko Schmidt, Alessandro Magazzù, Agnese Callegari, Luca Biancofiore, Frank Cichos & Giovanni Volpe LAOP – Latin America Optics & Photonics Congress, Lima, Peru
12-15 November 2018
Abstract: An optically trapped absorbing microsphere in a sub-critical mixture rotates around the optical trap thanks to diffusiophoretic propulsion, which can be controlled by adjusting the optical power, the temperature, and the criticality of the mixture.
Optical Trapping and Optical Manipulation
Giovanni Volpe & Agnese Callegari
Tutorial at LAOP – Latin America Optics & Photonics Congress, Lima, Peru
12-15 November 2018
Description: This course will review the theoretical underpinnings of optical trapping and optical manipulation; a review of recent applications; and provide a hands-on tutorial on the use of computational methods to simulate optical trapping and the motion of optically trapped particles.
Time: 09:00 – 13:00 Location: INICTEL-UNI, Lima, Peru
Information Controlled Structure Formation in Artificial Microswimmer Systems General Physics Colloquium by Frank Cichos, University of Leipzig, Germany
Abstract: Self-organization is the generation of order out of local interactions in non-equilibrium. It is deeply connected to all fields of science from physics, chemistry to biology where functional living structures self-assemble and constantly evolve all based on physical interactions. The emergence of collective animal behavior, of society or language are the result of self-organization processes as well though they involve abstract interactions arising from sensory inputs, information processing, storage and feedback resulting in collective behaviors as found, for example, in crowds of people, flocks of birds, schools of fish or swarms of bacteria.
We introduce such information based interactions to the behavior of self-thermophoretic microswimmers. A real-time feedback of swimmer positions is used as the information to control the swimming direction and speed of other swimmers. The emerging structures reveal frustrated geometries due to confinement to two dimensions. They diffuse like passive clusters of colloids, but posses internal dynamical degrees of freedom that are determined by the feedback delay and the noise in the system. As the information processing in the feedback loops can be designed almost arbitrarily complex systems with mixed feedback delays and noise will give rise to new emergent dynamics of the self-organized structures. The presented control schemes further allow the integration of machine learning algorithms to introduce an adaptive behavior of swimmers.
Clustering of Janus Particles in Optical Potential Driven by Hydrodynamic Fluxes
S. Masoumeh Mousavi, Sabareesh K. P. Velu, Agnese Callegari, Luca Biancofiore & Giovanni Volpe
Self-organisation is driven by the interactions between the individual components of a system mediated by the environment, and is one of the most important strategies used by many biological systems to develop complex and functional structures. Furthermore, biologically-inspired self-organisation offers opportunities to develop the next generation of materials and devices for electronics, photonics and nanotechnology. In this work, we demonstrate experimentally that a system of Janus particles (silica microspheres half-coated with gold) aggregates into clusters in the presence of a Gaussian optical potential and disaggregates when the optical potential is switched off. We show that the underlying mechanism is the existence of a hydrodynamic flow induced by a temperature gradient generated by the light absorption at the metallic patches on the Janus particles. We also perform simulations, which agree well with the experiments and whose results permit us to clarify the underlying mechanism. The possibility of hydrodynamic-flux-induced reversible clustering may have applications in the fields of drug delivery, cargo transport, bioremediation and biopatterning.
Aykut Argun will present a popular science talk on the principles and applications of optical tweezers at a PhD-student event called Gothenburg Ph.D. Pub.
Title: Optical tweezers and applications
Abstract: Can objects be moved contact-free only by the power of light?
The answer which deserved a Nobel Prize in Physics last week is yes.
Aykut Argun from GU Physics will present how in the next Ph.D. Pub.
Place: Haket – Bar å sånt, Första långgatan 32, 413 27 Gothenburg
Time: Wednesday, October 17, 2018 at 7 PM – 10 PM
Ripples in Thin Films
Seminar by Mazi Jalaal
from the Physics of Fluids laboratory
at the University of Twente, the Netherlands, EU
We present experimental observations of capillary ripples at the contact line of a droplet, spreading on a pre-wetted surface.
We use Digital Holographic Microscopy to measure the micro-scale undulation of the thin film. By raising the capillary number, the amplitude of the undulations increases at first and subsequently decreases.
At critical values of the capillary number, the ripples disappear. Using linear stability analysis, we further provide theoretical counterparts for the experimental observations, explaining the non-monotonic dependency on the capillary number
Place: PJ Lecture Hall Time: 9 October, 2018, 11:00
Cell differentiation and pattern formation in the transition to multicellularity: lessons from the microbial world Seminar by Mariana Benitez Keinrad
from the Laboratorio Nacional de Ciencias de la Sostenibilidad,
Universidad Nacional Autónoma de México (UNAM), Mexico.
Multicellular development occurs in plants, animals and other lineages, and involves the complex interaction among biochemical, physical and ecological factors. Our group has focused on the study of microbial multicellular organisms, which have been considered useful models to study the evolutionary transition to multicelullarity. I present some of our theoretical and experimental work, and discuss the physical and chemical processes that, in coordination with molecular regulatory networks, appear to be relevant for cell differentiation, patterning and morphogenesis in microbial aggregates.
Jalpa Soni reports on her outreach experience on 28 September 2018 to a local high school within the “European Researchers’ Night”.
On Spetember 28, 2018 under the realm of “European Researchers’ Night”, organised by Marie-Skolodwska-Curie Actions (MSCA, H2020), Brussels became the hub of science and research communication with the general public. Researchers from across Europe, mainly funded by various H2020 programs, gathered in Brussels to celebrate scientific temperament and spread its importance in everyday life.
Other than Brussels, universities and research institutions in over 340 cities all over Europe and neighbouring countries also participated in similar events where science and research was celebrated.
The University of Gothenburg (UGOT) also participated in this event by organising school visits for researchers to talk about science and life as a researcher to young students. Thanks to UGOT, I also got a chance to get involved in the “Researchers’ Friday” to go to a school and interact with students about my work and about researchers in general.
I visited the school named KLARA Teoretiska Gymnasium to talk to final year high school students who are about to enter university in a couple of months. Therefore, this was the ideal age group who might be interested in choosing science for higher education and would be curious about how is it to be a scientist.
I intended to tell them about my research project as well as to connect its implications in everyday scenarios of life. Beyond that, I was hoping for an engaging question-answer session where they could ask me anything related to science as a career.
I prepared a small speech where I could tell them about what I work on, and why, and to mention several related phenomena of nature. I also intended to tell them about the kind of applications of my experiments.
It was a wonderful experience. It really exceeded my expectations.
I have been involved in outreach activities before as well, but this was my first such experience in Sweden and I loved it. The students were very interested in what I had to say and what I was working in.
The following Q&A session was quite interesting as they asked many questions ranging from why I decided to study physics to how is it to live in different countries! Some wanted to know how scientists find the problems they work on and some were more interested in how do researchers keep motivated if an experiment fails!
At the end, they also had fun with the hands-on experiment I had brought with me to demonstrate some of the things I had talked about.
It was quite amazing to see that young students, on the verge of entering university, were so aware of the need of scientific mindset in general. I hope that some of them will choose research as their future interests and will contribute to the quest of knowledge.
Here is my speech:
My name is Jalpa and I am a researcher at the university of Gothenburg. I work at the department of Physics, which means I am a physicist. But what is it that I actually do? and more importantly why? Well, physics is behind almost everything we do in our everyday life! All of the technologies, radio, TV, computers, phones or the way we travel around with bikes, cars or planes came into existence because of physics. The very nature of universe can be understood with the laws of Physics. You might have heard the saying that “mathematics is the language of science”, and it’s true, isn’t it? But physics is the heart of science! From looking at stars in the universe to how we “see” things can be understood with Physics. However, today our knowledge has expanded so much that science is branched out in so many fields and subfields. And all these subfields are also being updated everyday, bringing more data. More data means more understanding. More data also means more challenges… and that means more technological developments. One of the recent example is the new iPhones that Apple announced this month. If you have followed, you might already know that their newer models are running on a nanometer size chip – that is one-billionth of a meter – claimed to be the smallest chip for a smartphone ever! That has been possible because physicists have been studying what happens at those scales with matter.
A billionth of a meter! Being able to study something that small is fascinating, right? A few decades ago, that would have been unimaginable, except for science fiction maybe. But today we talk about nanorobots that can go in our bodies and perform medical tasks for us! Technological advances have once again reduced the boundaries inside science and once again interdisciplinary science is becoming more exciting, to use it to improve life in general.
I also work in both biology and physics, occasionally using some chemistry as well as a bit of maths to explain the theory of my experiments. Among my various projects, the main theme is to study small things – of micron size – that is one-millionth of a meter. Specifically, I study the pattern of microorganisms (like bacteria), how they move around in various conditions.
But the effects I study with them are observed even in human scales. (showing some slides with images at this point)
For example, look at these penguins! These are emperor penguins, they live in Antarctica. These penguins huddle, gather around and move in large groups. And since it’s very cold environment where they live, they need to keep themselves warm! Look at these nice patterns they create while they move. They lean on the one in front of them and then rotate around in small steps, shifting positions from the outer side to the centre of the circle. This way, they are warm once inside the centre, the newcomers come and join the outside, but eventually everyone gets a chance to move inside for a while at least. The shifting pattern allows that to happen and everybody is happy.
Now look at these birds! They make beautiful patterns when they fly around together. As you might already guess, generally migrating birds make such large groups because it’s easier to keep the predators away. Also, it’s easier to hunt this way. In Denmark, they cause the effect of the “black sun” or the “sort sol” as the Danes call it. Every year in spring and autumn, the European starlings migrate from southern Europe to Scandinavia – near baltic sea – to breed. In Denmark, groups can get as big as a million birds and they cover the sun right around sunset to choose their nesting place, causing the “sort sol”.
In the ocean, large groups of fish also move in beautiful patterns!
Okay, all these patterns are nice to look at! but why are they important? right?
Well, look at this. Any of you find it familiar? It’s a scene of a crowd from one of the games, right? Did you know this particular game became a really big deal because of this particular scene? any guesses why? I will give you a hint – it’s the people! The number of people they simulated for this scene is what made the history. Wonder why is a crowd scene in a video game such a big deal? It’s because simulating a crowd of people is a lot more difficult than one would think! Look at this crowd simulation, you can see how it describes the people in a real crowd! There will be much more collisions and much more mingling in a real crowd! And it’s important to make crowd simulations more realistic to improve disaster management, isn’t it? For example, to design proper evacuation protocols in a fire-alarm situations, or for earthquake evacuation protocols. It would be good to be able to design public places accommodating good emergency protocols! Understanding these patterns of nature can help us achieve that on a more efficient manner.
And now let’s get back to the small world! At micron scales, look at these bacteria – they behave in nice and familiar looking patterns as well! And it’s important to understand how they move in various environment, like how they spread on a bad slice of bread, or in a rotten fruit, or in our body! Such studies could tell us how to stop the unwanted ones to enter our system and to select the good ones for benefits. Because not all bacteria are bad, some are good for our body, help us digest our food for example.
So, one of my project is related to this. We study bacteria in a complex environment and see how they find their way around it. We put some bacteria and some small particles (around the same size as bacteria but made of silica) together and monitored what happens to the bacteria. As it turns out they make highways, which are reused by the following bacteria, and this way they actually move in longer distances compared to when there are no obstacles. Bacteria alone move in more circular patterns, while in an obstacle environment their circles get bigger! We are trying to understand the mechanism behind this kind of motion and we want to see if that can be used to design artificial robots based on bacterial motion.
Now, I also want to study these things in three dimensions, more realistic! The read world is 3D! So I am building a microscope to do 3D imaging at high speeds to monitor live motions of these microorganisms. It’s called a light-sheet microscope and it looks like this! Not at all like a typical microscope! And this is one of the 3D video I took earlier this week. It’s short, but I think you can see the 3D volume and the motion of particles in 3D.
So, this is what I do! I also work with some other projects and I will talk about them if you are interested. Thank you for listening and feel free to ask any questions!
Alessandro Magazzù has been awarded a best oral contribution “Soft Matter poster price” during the conference Italian Soft Matter Days 2018, held in Padua, Italy on September 13-14, 2018. The prize has been given by Emanuela Zaccarelli, editorial board members of the Soft Matter journal. This prize mainly consists in an invitation to submit a manuscript without the pre-screening by the Editors. It also includes a “poster prize” and a personal yearly subscription to the journal.