Lectures Graph theory concepts and Hands-on practice (Graph theory) by Giovanni Volpe within the graduate course Imaging in Neuroscience: With a focus on structural MRI methods organised by Karolinska Institute.
Venue: Alfred Nobels allé 23, room 317, campus Huddinge (Flemingsberg), Stockholm
Tuning phototactic robots with sensorial delays (Editors’ suggestion)
Maximilian Leyman, Freddie Ogemark, Jan Wehr & Giovanni Volpe
Physical Review E 98(26), 052606 (2018)
DOI: 10.1103/PhysRevE.98.052606
arXiv: 1807.11765
The presence of a delay between sensing and reacting to a signal can determine the long-term behavior of autonomous agents whose motion is intrinsically noisy.
In a previous work [M. Mijalkov, A. McDaniel, J. Wehr, and G. Volpe, Phys. Rev. X 6, 011008 (2016)], we have shown that sensorial delay can alter the drift and the position probability distribution of an autonomous agent whose speed depends on the illumination intensity it measures. Here, using theory, simulations, and experiments with a phototactic robot, we generalize this effect to an agent for which both speed and rotational diffusion depend on the illumination intensity and are subject to two independent sensorial delays. We show that both the drift and the probability distribution are influenced by the presence of these sensorial delays. In particular, the radial drift may have positive as well as negative sign, and the position probability distribution peaks in different regions depending on the delay.
Furthermore, the presence of multiple sensorial delays permits us to explore the role of the interaction between them.
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.
From the article New Docent in Physics (English) and Ny docent i fysik (Swedish)
Three questions for Giovanni Volpe, appointed Docent in Physics at the Faculty of Science, University of Gothenburg.
Interview by: Linnéa Magnusson
Photo by: Malin Arnesson
What is your research about?
“I am conducting research in several different areas. Part of my work concerns artificial micro swimmers. In simple terms, this is about biological and artificial objects of microscopic size that can get around by themselves and counteract microorganisms. Research on micro swimmers involves many possibilities within basic science, nanoscience and nanotechnology.
“I am collaborating with Karolinska Institutet on a project that deals with neurodegenerative diseases such as Alzheimer’s, Parkinson’s and ALS (amyotrophic lateral sclerosis). We have developed software that serves as a toolkit, helping us to detect these diseases at an early stage.
“Another project deals with optical trapping and optical manipulation. Using optical tweezers, I can measure microscopic forces, for example.
“Finally, I am also working on a project that involves managing the challenges of condensed matter physics – in other words, matter and processes at the atomic level. With the help of machine learning, we can handle complex algorithms.”
What can society learn from your research?
“I hope that our work with micro swimmers can become a foundation on which we can build, so that in the future we can use them in real life. For example, this could involve cleaning contaminated soil or developing what are known as chiral drugs – medications that are more selective and more controllable and that have fewer side effects. It is to be hoped that our work in neuroscience will lead us to quickly detect and treat neurodegenerative diseases.”
What do you think is most exciting about the future?
“What is most exciting is the possibility of using artificial intelligence to solve physical and medical problems. In the future we will go from people developing and testing ideas to have data and systems under investigation speak for themselves.
Tre frågor till Giovanni Volpe som antagits som oavlönad docent i fysik vid Naturvetenskapliga fakulteten, Göteborgs universitet.
Vad handlar din forskning om?
– Jag forskar inom flera olika områden. En del i mitt arbete handlar om konstgjorda ”micro swimmers”. Förenklat så handlar det om biologiska och artificiella föremål i mikroskopisk storlek som kan ta sig fram själva och motverka mikroorganismer. Forskning om ”Micro Swimmers” innebär en mängd möjligheter inom grundvetenskap, nanovetenskap och nanoteknik.
– Jag samarbetar med Karolinska Institutet inom ett projekt som handlar om neurodegenerativa sjukdomar, som Alzheimers sjukdom, Parkinsons sjukdom och ALS. Vi har utvecklat en programvara som fungerar som en verktygslåda, som hjälper oss att tidigt upptäckta dessa sjukdomar.
– Ett annat projekt handlar om optisk fångst och optisk manipulation. Med hjälp av optiska pincetten kan jag exempelvis mäta mikroskopiska krafter.
– Till sist arbetar jag även med ett projekt som handlar om att hantera utmaningar med den kondenserade materiens fysik, alltså materia och processer på atomär nivå. Till hjälp har vi inlärningsmaskiner som kan hantera komplexa algoritmer.
Vad kan samhället lära av din forskning?
– Jag hoppas att arbetet med ”Micro swimmers ” kan bli en grund att bygga vidare på. Så att vi i framtiden kan använda ”Micro swimmers ” i verkliga livet. Det kan exempelvis handla om att kunna rengöra förorenad jord eller utveckla så kallade kirala läkemedel, det vill säga mediciner som är både mer selektiva, mer styrbara och har mindre biverkningar. Arbetet inom neurovetenskap kommer förhoppningsvis leda till att vi snabbt kan upptäcka och behandla neurodegenerativa sjukdomar.
Vad tycker du är mest spännande i framtiden?
– Det som är mest spännande är möjligheten att använda artificiell intelligens för att lösa fysiska och medicinska problem. I framtiden kommer vi att gå från att det är människor som utvecklar och testar idéer till att det är datorer och system som kommer att undersöka och analysera varandra.
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
Microscopic Engine Powered by Critical Demixing
Falko Schmidt, Alessandro Magazzù, Agnese Callegari, Luca Biancofiore, Frank Cichos & Giovanni Volpe
SPIE Nanoscience + Engineering, Optical trapping and Optical Manipulation XV, San Diego (CA), USA
19-23 August 2018
During the last few decades much effort has gone into the miniaturization of machines down to the microscopic scale with robotic solutions indispensable in modern industrial processes and play a central role in many biological systems. There has been a quest in understanding the mechanism behind molecular motors and several approaches have been proposed to realize artificial engines capable of converting energy into mechanical work. These current micronsized engines depend on the transfer of angular momentum of light, are driven by external magnetic fields, due to chemical reactions or by the energy flow between two thermal reservoirs. Here we propose a new type of engine that is powered by the local, reversible demixing of a critical binary liquid. In particular, we show that an absorbing, optically trapped particle performs revolutions around the optical beam because of the emergence of diffusiophoresis and thereby produces work. This engines is adjustable by the optical power supplied, the temperature of the environment and the criticality of the system.
Reference: Schmidt et al., Phys. Rev. Lett. 120(6), 068004 (2018) DOI: 10.1103/PhysRevLett.120.068004
Stability of graph theoretical measures in structural brain networks in Alzheimer’s disease
Gustav Mårtensson, Joana B. Pereira, Patrizia Mecocci, Bruno Vellas, Magda Tsolaki, Iwona Kłoszewska, Hilkka Soininen, Simon Lovestone, Andrew Simmons, Giovanni Volpe & Eric Westman
Scientific Reports 8, 11592 (2018)
DOI: 10.1038/s41598-018-29927-0
Graph analysis has become a popular approach to study structural brain networks in neurodegenerative disorders such as Alzheimer’s disease (AD). However, reported results across similar studies are often not consistent. In this paper we investigated the stability of the graph analysis measures clustering, path length, global efficiency and transitivity in a cohort of AD (N = 293) and control subjects (N = 293). More specifically, we studied the effect that group size and composition, choice of neuroanatomical atlas, and choice of cortical measure (thickness or volume) have on binary and weighted network properties and relate them to the magnitude of the differences between groups of AD and control subjects. Our results showed that specific group composition heavily influenced the network properties, particularly for groups with less than 150 subjects. Weighted measures generally required fewer subjects to stabilize and all assessed measures showed robust significant differences, consistent across atlases and cortical measures. However, all these measures were driven by the average correlation strength, which implies a limitation of capturing more complex features in weighted networks. In binary graphs, significant differences were only found in the global efficiency and transitivity measures when using cortical thickness measures to define edges. The findings were consistent across the two atlases, but no differences were found when using cortical volumes. Our findings merits future investigations of weighted brain networks and suggest that cortical thickness measures should be preferred in future AD studies if using binary networks. Further, studying cortical networks in small cohorts should be complemented by analyzing smaller, subsampled groups to reduce the risk that findings are spurious.
Optical tweezers and their applications
Paolo Polimeno, Alessandro Magazzù, Maria Antonia Iata, Francesco Patti, Rosalba Saija, Cristian Degli Esposti Boschi, Maria Grazia Donato, Pietro G. Gucciardi, Philip H. Jones, Giovanni Volpe & Onofrio M. Maragò
Journal of Quantitative Spectroscopy and Radiative Transfer 218(October 2018), 131—150 (2018)
DOI: 10.1016/j.jqsrt.2018.07.013
Optical tweezers, tools based on strongly focused light, enable optical trapping, manipulation, and characterisation of a wide range of microscopic and nanoscopic materials. In the limiting cases of spherical particles either much smaller or much larger than the trapping wavelength, the force in optical tweezers separates into a conservative gradient force, which is proportional to the light intensity gradient and responsible for trapping, and a non-conservative scattering force, which is proportional to the light intensity and is generally detrimental for trapping, but fundamental for optical manipulation and laser cooling. For non-spherical particles or at intermediate (meso)scales, the situation is more complex and this traditional identification of gradient and scattering force is more elusive. Moreover, shape and composition can have dramatic consequences for optically trapped particle dynamics. Here, after an introduction to the theory and practice of optical forces with a focus on the role of shape and composition, we give an overview of some recent applications to biology, nanotechnology, spectroscopy, stochastic thermodynamics, critical Casimir forces, and active matter.
Active Atoms and Interstitials in Two-dimensional Colloidal Crystals
Kilian Dietrich, Giovanni Volpe, Muhammad Nasruddin Sulaiman, Damian Renggli, Ivo Buttinoni & Lucio Isa
Physical Review Letters 120(26), 268004 (2018)
DOI: 10.1103/PhysRevLett.120.268004
arXiv: 1710.08680
We study experimentally and numerically the motion of a self-phoretic active particle in two-dimensional loosely packed colloidal crystals at fluid interfaces. Two scenarios emerge depending on the interactions between the active particle and the lattice: the active particle either navigates throughout the crystal as an interstitial or is part of the lattice and behaves as an active atom. Active interstitials undergo a run-and-tumble-like motion, with the passive colloids of the crystal acting as tumbling sites. Instead, active atoms exhibit an intermittent motion, stemming from the interplay between the periodic potential landscape of the passive crystal and the particle’s self-propulsion. Our results constitute the first step towards the realization of non-close-packed crystalline phases with internal activity.
Emergent Complex Behaviors in Active Matter
Giovanni Volpe
TU Dresden, Dresden, Germany
3 May 2018
After a brief introduction of active particles, I’ll present some recent advances on the study of active particles in complex and crowded environments.
First, I’ll show that active particles can work as microswimmers and microengines powered by critical fluctuations and controlled by light.
Then, I’ll discuss some examples of behavior of active particles in crowded environments: a few active particles alter the overall dynamics of a system; active particles create metastable clusters and channels; active matter leads to non-Boltzmann distributions and alternative non-equilibrium relations; and active colloidal molecules can be created and controlled by light.
Finally, I’ll present some examples of the behavior of active particles in complex environments: active particles often perform 2D active Brownian motion; active particles at liquid-liquid interfaces behave as active interstitials or as active atoms; and the environment alters the optimal search strategy for active particles in complex topologies.
