2021 Fall term

30th of September
Asger Mortensen, Quantum Plasmonics (https://mortensen-lab.org/research.html) hosted by Anders Mikkelsen

21st of October
Otto Muskens, Nanophotonics (https://www.phys.soton.ac.uk/people/om1v08) hosted by Magnus Borgström

25th of November
Dvira Segal, Quantum Thermodynamics (https://sites.chem.utoronto.ca/chemistry/dsegal/) hosted by Andreas Wacker

2021 Spring term

June 10^th 15:15

Is in-memory computing the next frontier in deep learning acceleration?

Dr. Abu Sebastian, IBM Research, Zurich

Host: Mattias Borg

Talk abstract

The rise of artificial intelligence and in particular, deep learning, is a key driver for innovations in computing systems. There is a significant effort towards the design of custom ASICs based on reduced precision arithmetic and highly optimized dataflow. However, the need to shuttle millions of synaptic weight values between the memory and processing units, remains unaddressed. In-memory computing (IMC) is an emerging computing paradigm that addresses this challenge of processor-memory dichotomy. Attributes such as synaptic efficacy and plasticity can be implemented in place by exploiting the physical attributes of memory devices such as phase-change memory (PCM). It is shown that, using custom “additive noise training”, software equivalent accuracy deep learning inference is possible. Moreover, using a mixed-precision training approach, iso-accuracy training is also possible. The IMC approach can be easily extended to spiking neural networks and to also implement additional entities such as explicit associative memory in an efficient manner for memory augmented neural networks. I will also present some recent advances on IMC compute cores based on PCM and device-level innovations for improved compute precision. Finally, I will provide a brief overview of photonic in-memory computing that could facilitate unprecedented latency and compute density.

February 11^th 15:15

Nanofluidics for Single Particle Catalysis and Single Molecule Detection flavoured with a little bit of Entrepreneurship

Prof. Christoph Langhammer, Department of Physics, Chalmers University of Technology,
Göteborg

Host: Jonas Tegenfeldt

Talk abstract

Nanofluidics have been developed as a means to control the transport of fluids at the nanoscale and to investigate molecules, such as DNA, in nanoconfinement. In this talk, I will outline the key findings of our research that aims at combining the concept of nanofluidics with optical nanospectroscopy and imaging using visible light, in the context of plasmonics, heterogeneous catalysis and label-free single molecule detection. More specifically, I will tell the story of how realizing the seemingly simple idea of placing a single nanoparticle inside a nanofluidic channel, has enabled us to study catalytic reactions in an entirely new way and to for example visualize that, just like in real life, having good neighbors actually is important. Then I will demonstrate how a light scattering effect highly unwanted in these catalysis experiments, upon a second careful look, opened the door to a groundbreaking new microscopy method. This “Nanofluidic Scattering Microscopy”, which now is the core technology of our startup Envue Technologies AB, makes it possible to image individual biomolecules in free motion inside a nanofluidic structure, and to determine both their mass and hydrodynamic radius, without the need for any labels or surface attachment.

January 21^st 15:15

Virus diffusion at the cell surface: from cell-surface mimics to live cell microscopy

Dr. Marta Bally, Department of Clinical Microbiology & Wallenberg Centre for Molecular Medicine,
Umeå University, e-mail: Marta [dot] bally [at] umu [dot] se (Marta[dot]bally[at]umu[dot]se)

Host: Christelle Prinz

Abstract

Viruses are small pathogenic particle that rely on hijacking a cellular host to replicate and spread. The initial recruitment of a virus particle to the cell surface is a complex dynamic multistep process that requires diffusion of the virus particle through the glycocalyx, the sugar coat covering cells, to reach the cell membrane where it may further diffuse laterally in search of a suitable point of entry. Many viruses, including herpes simplex virus (HSV), initiate their recruitment on the host cell by binding to carbohydrates found on the cell surface and in the glycocalyx, in particular sulfated glycosaminoglycans (GAGs), heparan sulfate for example. This initial recognition is crucial in the viruses’ life cycle as it leads to infection. Equally important is however, the capability of the virus to overcome these interactions upon egress to ensure virus propagation. A tight regulation of such interactions is also essential in the context of virus transport at the cell surface since binding a high amount of receptors with high affinity might trap the virion at the cell surface before it meets entry receptors, while a too weak binding may not be enough for attachment of the particle or to ensure sufficient residence time for entry.

In our work, we study the molecular mechanisms modulating HSV binding, release and diffusion at the cell surface. To do so, our experimental approach is based on probing interactions between individual virus particles and the cell surface using a combination of minimal cell-surface mimics and live cell microscopy. A minimal model of the cell’s carbohydrate coat based on the end-on immobilization of GAG chains makes it possible to study the details of virus-GAG interactions. [1-3] These findings can be further correlated with the behavior of the virus on live cells, where single particle investigation provide fine details on the different steps leading to viral entry. [4]
Taken together, our research contributes to a better understanding of the mechanisms regulating the interaction between a virus and the surface of its host. Such insights will without doubt facilitate the design of more efficient antiviral drugs or vaccines.
 
[1] Altgarde, N., et al., Mucin-like Region of Herpes Simplex Virus Type 1 Attachment Protein Glycoprotein C (gC) Modulates the Virus-Glycosaminoglycan Interaction. Journal of Biological Chemistry, 2015. 290(35): p. 21473-21485.
 
[2]. Peerboom, N., et al., Binding Kinetics and Lateral Mobility of HSV-1 on End-Grafted Sulfated Glycosaminoglycans. Biophysical Journal, 2017. 113(6): p. 1223-1234.
 
[3] Delguste et al. Regulatory Mechanisms of the Mucin-Like Region on Herpes Simplex Virus during Cellular Attachment. ACS Chemical Biology, 2019, 14, 3, 534–542
 
[4] Abidine, Y., et al., Cellular glycosaminoglycans and viral carbohydrates regulate diffusion of herpesvirus simplex virus 1 in the glycocalyx. Submitted.