Neural Network Training with Highly Incomplete Datasets published in Machine Learning: Science and Technology

Working principles for training neural networks with highly incomplete dataset: vanilla (upper panel) vs GapNet (lower panel) (Image by Yu-Wei Chang.)
Neural Network Training with Highly Incomplete Datasets
Yu-Wei Chang, Laura Natali, Oveis Jamialahmadi, Stefano Romeo, Joana B. Pereira, Giovanni Volpe
Machine Learning: Science and Technology 3, 035001 (2022)
arXiV: 2107.00429
doi: 10.1088/2632-2153/ac7b69

Neural network training and validation rely on the availability of large high-quality datasets. However, in many cases only incomplete datasets are available, particularly in health care applications, where each patient typically undergoes different clinical procedures or can drop out of a study. Since the data to train the neural networks need to be complete, most studies discard the incomplete datapoints, which reduces the size of the training data, or impute the missing features, which can lead to artefacts. Alas, both approaches are inadequate when a large portion of the data is missing. Here, we introduce GapNet, an alternative deep-learning training approach that can use highly incomplete datasets. First, the dataset is split into subsets of samples containing all values for a certain cluster of features. Then, these subsets are used to train individual neural networks. Finally, this ensemble of neural networks is combined into a single neural network whose training is fine-tuned using all complete datapoints. Using two highly incomplete real-world medical datasets, we show that GapNet improves the identification of patients with underlying Alzheimer’s disease pathology and of patients at risk of hospitalization due to Covid-19. By distilling the information available in incomplete datasets without having to reduce their size or to impute missing values, GapNet will permit to extract valuable information from a wide range of datasets, benefiting diverse fields from medicine to engineering.

Invited Talk by G. Volpe at Active and Intelligent Living Matter Conference, Erice, 30 June 2022

Artificial intelligence in microscopy, photonics, and active matter
Giovanni Volpe
30 June 2022, 16:20 (CEST)
Active and Intelligent Living Matter Conference
Erice, Italy, 26 June-1 July 2022

After a brief overview of artificial intelligence, machine learning and deep learning, I will present a series of recent works in which we have employed deep learning for applications in microscopy, optical tweezers, and active matter. In particular, I will explain how we employed deep learning to enhance digital video microscopy, to perform virtual staining of tissues, to estimate the properties of anomalous diffusion, to characterize microscopic force fields, to improve the calculation of optical forces, and to characterize nanoparticles. Finally, I will provide an outlook on the future for the application of deep learning in these fields.

Deep learning in light–matter interactions published in Nanophotonics

Artificial neurons can be combined in a dense neural network (DNN), where the input layer is connected to the output layer via a set of hidden layers. (Image by the Authors.)
Deep learning in light–matter interactions
Daniel Midtvedt, Vasilii Mylnikov, Alexander Stilgoe, Mikael Käll, Halina Rubinsztein-Dunlop and Giovanni Volpe
Nanophotonics, 11(14), 3189-3214 (2022)
doi: 10.1515/nanoph-2022-0197

The deep-learning revolution is providing enticing new opportunities to manipulate and harness light at all scales. By building models of light–matter interactions from large experimental or simulated datasets, deep learning has already improved the design of nanophotonic devices and the acquisition and analysis of experimental data, even in situations where the underlying theory is not sufficiently established or too complex to be of practical use. Beyond these early success stories, deep learning also poses several challenges. Most importantly, deep learning works as a black box, making it difficult to understand and interpret its results and reliability, especially when training on incomplete datasets or dealing with data generated by adversarial approaches. Here, after an overview of how deep learning is currently employed in photonics, we discuss the emerging opportunities and challenges, shining light on how deep learning advances photonics.

Invited Talk by G. Volpe at International Workshop On Active Systems, IIT Madras, India, 9 June 2022.

Emergent Complex Behaviors in Active Matter
Giovanni Volpe
9 June 2022, 14:30 (IST)
Online for MNBF Workshop: International Workshop On Active Systems
IIT Madras, India, 8-9 June 2022

Label-free nanofluidic scattering microscopy of size and mass of single diffusing molecules and nanoparticles published in Nature Methods

Kymographs of DNA inside Channel II. (Image by the Authors.)
Label-free nanofluidic scattering microscopy of size and mass of single diffusing molecules and nanoparticles
Barbora Špačková, Henrik Klein Moberg, Joachim Fritzsche, Johan Tenghamn, Gustaf Sjösten, Hana Šípová-Jungová, David Albinsson, Quentin Lubart, Daniel van Leeuwen, Fredrik Westerlund, Daniel Midtvedt, Elin K. Esbjörner, Mikael Käll, Giovanni Volpe & Christoph Langhammer
Nature Methods 19, 751–758 (2022)
doi: 10.1038/s41592-022-01491-6

Label-free characterization of single biomolecules aims to complement fluorescence microscopy in situations where labeling compromises data interpretation, is technically challenging or even impossible. However, existing methods require the investigated species to bind to a surface to be visible, thereby leaving a large fraction of analytes undetected. Here, we present nanofluidic scattering microscopy (NSM), which overcomes these limitations by enabling label-free, real-time imaging of single biomolecules diffusing inside a nanofluidic channel. NSM facilitates accurate determination of molecular weight from the measured optical contrast and of the hydrodynamic radius from the measured diffusivity, from which information about the conformational state can be inferred. Furthermore, we demonstrate its applicability to the analysis of a complex biofluid, using conditioned cell culture medium containing extracellular vesicles as an example. We foresee the application of NSM to monitor conformational changes, aggregation and interactions of single biomolecules, and to analyze single-cell secretomes.

Harshith Bachimanchi presented his half-time seminar on 10 May 2022

Harshith Bachimanchi’s half-time seminar. (Photo by Y.-W. Chang.)
Harshith Bachimanchi completed the first half of his doctoral studies and defended his half-time on 10th May 2022.

The presentation was held in hybrid format, with part of the audience present in the Nexus room and the rest connected through zoom. The half-time consisted of a presentation of his past and planned projects followed by discussion and questions proposed by his opponent Bernhard Mehlig.

The presentation started with a description of his project about combining holographic microscopy with deep learning to measure the dry mass and three-dimensional swimming patterns of marine microorganisms (Microplankton life histories revealed by holographic microscopy and deep learning). Thereafter, he discussed about some of the new experiments in marine microbial ecology where the technique is currently being used. In the last section, he outlined the proposed continuation of his PhD on studying active matter systems in marine microscopic environments using holographic microscopy and artificial neural networks.

DeepTrack won the pitching competition at the Startup Camp 2022. Congrats!

DeepTrack team members (left to right) Henrik, Giovanni and Jesus. (Picture by Jonas Sandwall, Chalmers Ventures.)
The DeepTrack team, composed by Henrik Klein Moberg, Jesus Pineda, Benjamin Midtvedt and Giovanni Volpe, won the pitching competition at the Startup Camp 2022 organised by Chalmers Ventures.

In the event, held on Tuesday, 15 March 2022, 16:00-19:00, the ten teams that had gone through the training at the Startup Camp and developed their company ideas, pitched their companies on stage to a panel of entrepreneur experts, the other nine teams, and all business coaches at Chalmers Ventures. DeepTrack obtained the first place among the ten participants. Congrats!

Here a few pictures from the final pitching event of the Startup Camp.

Henrik. (Picture by Jonas Sandwall, Chalmers Ventures.)
DeepTrack team members (left to right) Henrik, Giovanni and Jesus. (Picture by Jonas Sandwall, Chalmers Ventures.)
Panelists. (Picture by Jonas Sandwall, Chalmers Ventures.)

Featured in:
University of Gothenburg – News and Events: AI tool that analyses microscope images won startup competition and AI-verktyg som analyserar mikroskopbilder vann startup-tävling
(Swedish)

Invited Talk by G. Volpe at Complex Lagrangian Problems of Particles in Flows, 15 March 2022

An illustration of anomalous diffusion. (Image by Gorka Muñoz-Gil.)
The Anomalous Diffusion Challenge: Objective comparison of methods to decode anomalous diffusion
Giovanni Volpe
Complex Lagrangian Problems of Particles in Flows
Online, 15 March 2022, 10:15 CET

Deviations from Brownian motion leading to anomalous diffusion are found in transport dynamics from quantum physics to life sciences. The characterization of anomalous diffusion from the measurement of an individual trajectory is a challenging task, which traditionally relies on calculating the trajectory mean squared displacement. However, this approach breaks down for cases of practical interest, e.g., short or noisy trajectories, heterogeneous behaviour, or non-ergodic processes. Recently, several new approaches have been proposed, mostly building on the ongoing machine-learning revolution. To perform an objective comparison of methods, we gathered the community and organized an open competition, the Anomalous Diffusion challenge (AnDi). Participating teams applied their algorithms to a commonly-defined dataset including diverse conditions. Although no single method performed best across all scenarios, machine-learning-based approaches achieved superior performance for all tasks. The discussion of the challenge results provides practical advice for users and a benchmark for developers.

Links:
Complex Lagrangian Problems of Particles in Flows program