.Ruggero Micheletto Laboratory-Yokohama City University- Micheletto Laboratory, Yokohama City University

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Ruggero Micheletto Laboratory-Yokohama City University-

2023

May 26

Giovanni Alfieri of Hitachi Energy: Lenzburg, CH, Yusuke Fujii and Ruggero Micheletto published "An ab initio study of the electronic properties of helium in wurtzite gallium nitride", published on Semiconductor Science and Technology number 38 reference page 074003618 (doi).

Using ab-initio calculations on the Cray XC50 supercomputer in Yokohama, they carried out a density functional theory study of substitutional He and related complexes (vacancies and dopants) in wurtzite GaN.They found for the first time that He is unstable at N-sites, moving to interstitial sites and forming a N vacancy (VN). This was observed for the case of substitutional He and for He complexed with n- or p-type dopants. The formation of VN, in such defects, gives rise to donor states close to the valence band edge (EV). On the other hand, they understood that the presence of a gallium vacancy leads to the formation of an energetically stable complex that gives rise to acceptor states close to the conduction band edge (EC).

May 19-24

APL

PhD candidate Kotaro Oikawa participated to the annual international conference of the Vision Sciences Society with a poster with the title "An experimental and theoretical study of the critical fusion frequency as a function of stimulus duty ratio". The abstract of his work has been published on Journal of Vision vol 23, issue 9 (doi). His study focused on the perception of flickering stimuli that stimulate the CFF phenomenon. Specifically, he measured CFF values as a function of the duty ratio of the light source in greater detail than in previous studies. He discovered for the first time that CFF decreases rapidly when the duty ratio is above 80% (lighting duration). He also created a theoretical model based on biologically known eye parameters, calculated the contrast from the signal perceived on the retina and simulated the CFF at a certain threshold value. The conference is located in a very beatiful place in Florida: pic !!

April 24

APL

Master M2 student Yoshida Shunra together with Yusuke Fujii, and Dr. Alfieri Giovanni published a study with the title "Time-correlated luminescence blinking in InGaN single quantum wells", by S. Yoshida, Y. Fujii, G. Alfieri and R. Micheletto. Published on Applied Physics Letters number 122, reference page 173506 (doi).

They studied how the blinking phenomenon in InGaN single quantum wells changes over time. They used two InGaN single quantum well samples, and confirmed that the luminescence intensity fluctuates in localized blinking regions. They found that these optical variations are not random but are instead correlated in pairs, with either positive or negative coefficient, to a distant reference blinking point. Mr. Yoshida realized a simple phenomenological model that shows how charge carriers are exchanged among pairs of adjacent opposite correlation regions. As a result, he suggested that the phenomenon is caused by fluctuations in the number of these exchanged carriers.

29 March

Ph.D. candidate Marcello Salustri together with Master student Yoshida Shunra, and R. Micheletto published a study with the title "Neural and axonal heterogeneity improves information transmission", by Marcello Salustri, Shunra Yoshida and Ruggero Micheletto. Published on Physica A: Statistical mechanics and its applications number 618, reference page 128627 (doi).

They simulated, at different scales, the spiking activity on a toroidal neural network realized in multiple dimensions with varying degrees of heterogeneity using the biological compatible Izhikevich neuron model. They found that increasing the heterogeneity and network dimension improved the robustness and propagation speed of the spiking activity. Their results demonstrate that the behavior of the spiking activity depends on both the cellular neural and axonal delay heterogeneity. They put down a simple theoretical framework compatible with the results of the simulations, a novel method to strategically analyze any similar networks.

8-9 March

Osaka Municipal University

Master student Shunra Yoshida was invited to give a talk at the Conference on applied (bio) geochemistry CAG2023 that was held in Fkih Ben Salah, Morocco.

His presentation was done remotely since the conference was hybrid, partially online, partially in presence. The title of his talk was Temporal correlation in InGaN quantum wells, a work based on studies made with Yusuke Fujii and prof. R. Micheletto.

This is the abstract of the presentation link and a certificate of his presentation link.

2022

7-9 December

Osaka Municipal University

Prof. R. Micheletto was invited to the Osaka Municipal University to give a series of classes in an intensive course with the title Cognitive Informatics based on his text book "Cognitive informatics in English and Japanese" (link). The course was given at the Graduate School of Engineering Division of Physics and Electronics under the invitation of prof. Okamoto Koichi. Here are some picures of prof. Micheletto with his long time friend Koichi pic1, pic2, pic3. Here at dinner with professors Kenji Wada and Tetsuya Matsuyama pic4.

5-9 September

Master student Yoshida Shunra and R. Micheletto participated to the annual conference of the Vision Society of Japan with a research titled "Toward Video Communication under Low Bandwidth A Study on Compression and Restoration by Sampling Based on Visual Characteristics" realized in collaboration with Sun Zhe and the group of Hideo Yokota. The poster summarizing the research is here (in Japanese).

The home page of the conference is here.

Mister Yoshida realized a novel method to combine visual characteristics of an image, with its saliency map. He used error diffusion dithering process based compression and a framework for restoration from prior information only.
The method he proposed and the random cases are compared in terms of PSNR and SSIM. He found that his method outperforms the random case in both metrics.

Here is a picture of Mr. Yoshida in front of his poster explaining the details of his research pic. Here a picture of a dinner with Mr. Yoshida Shunra, profs Hideo Yokota, Sun Zhe and R. Micheletto pic. Here R. Micheletto with prof. Sun Zhe in front of the conference logo pic.

1 September

Master student Yoshida Shunra published a study with the title The influence of water and ethanol adsorption on the optical blinking in InGaN quantum wells with the collaboration of Fujii Yusuke, Alfieri Giovanni and Ruggero Micheletto (link).

He found that the blinking of InGaN material is strongly influenced by the presence of water. Especially he found that ethanol and water enhance the blinking a lot. He also found a way to show the differences in blinking intensity using in an original way cumulative histograms and seigmoid functions.

With the help of Dr. Alfieri, he also developed a qualitative explanation of the physical mechanisms related to liquid enhanced blinking.

15 June

Ph.D. candidate Marcello Salustri and R. Micheletto published the study titled "Heterogeneous Axonal Delay Improves the Spiking Activity Propagation on a Toroidal Network" (link), Cognitive Computation, Springer Nature, https://doi.org/10.1007/s12559-022-10034-2.

The work shows how, in a neural network, spatial heterogeneity favours faster propagation of spike signals. The heterogeinity studied is not relative to the type of neuron or to the stimulations, but to the axonal transmission delays between neurons. That is, in the artificial neuronal grid studied, the position of the neurons have a certain degree of randomnes. In the 400 neurons grid, only one is stimulated (called initiator) with constant current. All the others become active because they are connected to a von Neumann neighborhood, that ultimately reach the initiator. This study is in line with many studies that suggest that noise and chaos in neural networks improves information flow, and for the first time it extends this concept to inter-neuron axonal delay (a paradigm for inter-neuron distance).

8 Apr

Kahoko Takahashi (now at the Network Innovation Laboratories, NTT Japan), together with a team of scientists from Japan, China, Spain, United Kindom and Russia, realized a novel methodology to augment the efficiency and usability of EEG data.

With the help of prof. R. Micheletto they published a paper with the title "Data augmentation for Convolutional LSTM based brain computer interface system", by Kahoko Takahashi, Sun Zhe, Jordi Solé-Casals, Andrzej Cichocki, Anh Huy Phan, Hui-Hai Zhao, Shangkun Deng and Ruggero Micheletto. Published on Applied Soft Computing number 122, reference page 108811 (doi).

14 Jan

Prof. R. Micheletto contribuited to the research "Hiding the Rabbit: Using a genetic algorithm to investigate shape guidance in visual search", by Avi M. Aizenman, Krista A. Ehinger, Farahnaz A. Wick, Ruggero Micheletto, Jungyeon Park, Lucas Jurgensen and Jeremy M. Wolfe. The paper is published on the Journal of Vision (link, PDF).

This work was initially developed in Harvard Medical School under the supervision of prof. Jeremy M. Wolfe. A novel genetic algorithm method was used to explore shape space and to stimulate hypotheses about shape guidance. Initially, observers searched for targets among 12 random distractors defined by the amplitude and phase of 10 radial frequencies. Reaction time (RT) was the measure of "fitness". The genetic algorithm was used to evolve toward an easier search task, distractors with faster RTs survived to the next generation, "mated" and produced offspring (new distractors for the next generation of search). To evolve a harder search, surviving distractors were those yielding longer RTs. Within eight generations of evolution, the method succeeds in producing visual searches either harder or easier than the starting search. This is a novel agnostic (doesn't require specific theory) methodology to find hard/easy shapes processed by the human visual system.

2021

7-9 July

Osaka Prefecture University

Prof. R. Micheletto was invited to the Osaka Prefecture University to give a series of classes in an intensive course with the title Cognitive Informatics based on his text book "Cognitive informatics in English and Japanese" (link). The course was given at the Department of Electronics, Mathematics and Physics under the invitation of prof. Okamoto Koichi. Here is a picure of prof. Micheletto with his long time friend Koichi pic.

23 January

Prof. R. Micheletto contribuited to the research "Deep levels in ion implanted n-type homoepitaxial GaN: Ion mass, tilt angle and dose dependence", by G. Alfieri, V.K. Sundaramoorthy and R. Micheletto. The paper is published on the Nuclear Instruments and Methods in Physics Research (link).

This work was realized by Dr. G. Alfieri (Hitachi Power Grids, Lenzburg, Switzerland) carrying out an electrical characterization study of defects in ion implanted n-type GaN. Several new defects were found below the conduction band edge and the nature of these defects is discussed in the manuscript with the aid of Monte Carlo collision simulations.

22 January

Yusuke Fjii

Master student Yusuke Fujii did a presentation at the conference "nano-optics research group" (link) with the participation of top level international researchers in Japan. His presentation title was "Research on optical blinking in InGaN/GaN single quantum wells" by Fujii Y. G. Alfieri and R. Micheletto. The slides of his presentation are here (Japanese, PDF, 1.7 Mb).

20-22 January

Akira Hirai

Master student Akira Hirai partecipated to the winter edition of the Japanese Vision Society meeting 2021. He also gave an oral presentation with the title "Visual search using VR environment and mathematical analysis of eye-gaze tracking data", by Akira Hirai and Ruggero Micheletto (PDF in English, 5.5 Mb).

2020

15 September

Master student Yusuke Fujii contribuited to the research "The Electronic Properties of Chlorine in GaN: An Ab Initio Study", by Y. Fujii, R. Micheletto and G. Alfieri. The paper appears on the journal Physica Status Solidi (b), published by Wiley " (link).

He contributed collaborating with Dr. G. Alfieri (Hitachi Power Grids, Lenzburg, Switzerland) with the ab-initio calculations and the density functional theory. It was found that Cl and its complexes explain the reported effects of Cl-RIE treated GaN on hole density and ohmic contact resistivity.

This result is very important because Chlorine-based reactive ion etching (RIE) is a fundamental processing step for the manufacturing of next generation GaN semiconductor devices.

28 May

Prof. R. Micheletto, prof. Aki Tosaka and Kotaro Oikawa published "Cognitive Informatics in English and Japanese", edited by Kyoritsu Publishing, Tokyo, Japan. This is the textbook of prof. Micheletto autumn course "Cognitive Informatics" at YCU undergraduate school. This books gives the big picture vision of the principles by wich the brain works from the physicist point of view.

It introduces human perception, neural networks and the basics of artificial intelligence with hands-on programming examples in python and Octave language.

This book is written in English with parallel translation in Japanese on adjacent pages.

2019

24 December

Yusuke Fjii

Prof. R. Micheletto and Master Student Yusuke Fujii visited Kyoto University department of Electronic Engineering. Y. Fujii made an informal colloquium with prof. Yoichi Kawakami about his research on the blinking phenomena in InGaN materials.

12-14 June

Osaka Prefecture University

Prof. R. Micheletto was invited to the Osaka Prefecture University to give a series of classes in an intensive course with the title Cognitive Informatics based on his text book "Cognitive informatics in English and Japanese" (in print). The course was given at the Department of Electronics, Mathematics and Physics under the invitation of prof. Okamoto Koichi. Here is a picure of prof. Micheletto at a dinner with prof. Okamoto and other Department leaders pic.

16-22 May

Master student K Konno and R. Micheletto participated to the Vision Science Society annual meeting VSS 2019. Kazuki Konno presented a poster with the title "What are the features of shapes easy to remember in the visual search?" by K. Konno and R. Micheletto. The poster is available here: 1. This is a pictures of him at the poster presentation: pic and here a picture at work at the "demo night" event of the conference pic.

2018

30 November

Master student Kahoko Takahashi contribuited to the book "Intelligent Computing", edited by K. Arai, K. Kohei, B. Supriya and R. Bhatia, published by Springer.

She contributed to the research article "Using a Hierarchical Temporal Memory Cortical Algorithm to Detect Seismic Signals in Noise" by R. Micheletto, Kahoko Takahashi and A. Kim. This work is part of the Proceedings of the 2018 Computing Conference held in London, GB (10-12 July 2018).

A quasi final version of the paper is here (link), while the final book version is online at Springer's link.

12 November

B4 student Yusuke Fujii contribuited to a research presented at the International Workshop on Nitride Semiconductors (IWN 2018) held in Kanazawa, Japan. The presentation title was "Ab Initio Study of Substitutional Chlorine and Related Complexes in GaN" by Giovanni Alfieri, Yusuke Fujii and R. Micheletto. It was summarized in a poster (pdf) and abstract (pdf).

24-27 October

Takahashi Kahoko

Prof. R. Micheletto and master student Kahoko Takahashi participated to The 28th Annual Conference of the Japanese Neural Network Society (JNNS2018). She delivered a poster talk with the title Empirical mode decomposition for improved EEG signal classification with Convolutional Neural Network in Brain-Computer interface experiments by Kahoko Takahashi, Sun Zhe, Jordi Sol-Casals, Andrzej Cichocki, Anh Huy Phan and R. Micheletto. She also published a research abstract with the same title pdf.
Kahoko Takahashi together with Dr. Sun Zhe (former Micheletto laboratory member, now at RIKEN) and other coauthors worked in the field of Brain-Computer interfaces. They studied the detection of EEG brain signals and developed an elaboration using an original Convolutional Neural network. In particular, she demonstrated that with the use of advanced mathematical techniquels like Empirical Mode Decomposition, it is possible to improve detection and reduce the number of actual experiments needed for the training of the network.

5 October

Prof. Cristiano Giordani published: Simulation of the song motor pathway in birds: A single neuron initiates a chain of events that produces birdsong with realistic spectra properties by C. Giordani, H. Rivera-Gutierrez, Sun Zhe and R. Micheletto, link.
The neural pathway simulates the complete neural structure with few neurons, but it is able to reproduce recognizable bird sounds, here is an example in wave format audio. In this video the spontaneously emerging live dynamics of the network is noticeable (blocks hight represents membrane potential, the two rings the HVCs and RAs clusters and the horizontal block extension is the syrinx pressure). This study confirms experiments on animals and on humans, where results have shown that single neurons are responsible for the activation of complex behavior or are associated with high-level perception events.

30 August

The work of Tsutsumi Toshiaki, R. Micheletto, G. Alfieri and Y. Kawakami "The relation between optical instabilities and absorbed materialg in photoluminescence with [0001] InGaN single quantum well" has received an in-text citation in AIP Advances! In-text citation are like uber-citations, it means that the study has not only being read, but that it is deeply influential on other researcher, to the level that they felt the need to mention it directly in their report.

This is a link to the in-text citation pdf.

3 August

Master student K. Konno participated to the summer meeting of the Vision Society of Japan VSJ. He presented a posters with the title: "Influence on the Speed and Space Perception using Optical Illusions" by K. Konno and R. Micheletto.

The poster is available here: poster (Japanese).

10 July

Prof. R. Micheletto contributed to the book Future courses of Human Societies with a chapter "Nanotechnology and future technological evolutions". This books is about the long-term future evolution of human society from multiple points of view. Different chapters approach the influcence of different technologies on societies of the far future. Chapters are written by prominent scientists and researchers all over the world that are experts in the field. For example Dr. Claudio Capiglia, prof. Junichiro Fukai, prof. Vesselin Popovski and many others.

The volume is edited by prof. Kleber Ghimire who teaches topics related to Social Economy in YCU and contributed to the first chapter of the book "Future as an object of enquiry".

The book is published by the Taylor and Francis group and here is a link to the page describing the book.

24 May

Dr. Giovanni Alfieri (Ph.D. at ABB Corporate Research, Switzerland) published "Electrically active point defects in Mg implanted n-type GaN grown by metal-organic chemical vapor deposition" by G. Alfieri, V. K. Sundaramoorthy, and R. Micheletto.

The paper demonstrates for the first time the presence of at least nine electrically active levels in Mg implanted GaN. These defects are located below the conduction band edge, and their possible microscopic structure was discussed in the light of previous DFT simulations and other results in literature (link).

18-23 May

Prof. R. Micheletto participated to the Vision Science Society annual meeting VSS 2018. In collaboration with his Master student Kazuki Konno and graduated Tomoharu Nagahama he presented two posters. The first with the title "Psychophysical influence of visual perception on person's behavior using optical illusions in a background" by K. Konno and R. Micheletto, the secondo one with title "Virtual Reality study of the influence of environment color and luminosity in depth perception " by T. Nagahama and R. Micheletto.

The poster are available here: 1 and 2. This is a pictures of prof. Micheletto at the poster presentation: pic.

17 May

Master Student Kahoko Takahashi participated to the "SSA 2018", the Seismological Society of the Americas annual meeting. She presented a work with the title "Detection of seismic signals under low SNR condition using an artificial neural network: toward the development of a dense low cost citizen seismic network in Japan" by K. Takahashi, H. Uematsu, Sun Zhe, R. Micheletto and A. Kim (poster). In the same meeting prof. Micheletto presented a poster with the title "Detection of Background Seismic Waves Anomalies With a Hierarchical Temporal Memory (HTM) Cortical Algorithm" by R. Micheletto and K. Takahashi (poster). In this work prof. Micheletto addresses the possibility to use innovative Hyerarchical Temporal Memory algorithms to detect anomalies deeply embebbed in seismic signals noise (some introductory material about this research is here).

For her work Miss Takahashi got a Travel Grant prize (pic) !

26 March

Prof R. Micheletto was interviewed by the Italian National TV !! Here is a link to the video (in Italian, but you can watch it!).

Prof. Micheletto briefly describes his research topics in YCU.

Two students of prof. Micheletto's laboratory Nagahama Tomoharu and Ishizuka Ayaka collaborated to the realization of the film. There is a brief appearance of the cat Chaby too!

The interview was realized by Director Michele Cinque.

for OLDER NEWS (~2017) click here