Graduate Program in Physics at UFSC, Florianópolis

 THE PHYSICS GRADUATE PROGRAM invites everyone to the seminar: 

  Memristors: a primer and perspectives 

Prof. Dr. Gilberto Medeiros

UFMG

 Abstract:

Memristors are one class of devices that cannot be described or emulated by association of resistors, capacitors and inductors. A pinched hysteresis is usually the fingerprint of memristive behaviour [1,2]. Beyond simple modelling presented in the early 70s [1,2], significant experimental progress has been achieved, to the point where now there are several companies and research teams working with these devices in a number of applications ranging from neuromorphic computing [3,4] to non-volatile memories [5]. Here I will discuss the anatomy of conductive channels in memristors, by means of structural and chemical characterization afterproper identification through pressure modulated conductance experiments [6]. Subsequently, the upper limits of switching speeds of these devices will be discussed [7], as well as our modelling results [8]. Finally, complementing the modelling picture I will conclude showing our latest results on noise characteristics of these intriguing devices [9].

References

[1] L. O. Chua, “Memristor – missing circuit element”. IEEE Trans. Circuit Theory CT-18, 507-519 (1971).

[2] L. O. Chua, & S. M. Kang, “Memristive devices and systems”. Proceedings of the IEEE 64,209-223 (1976).

[3] M. Prezioso, et al. “Training and operation of an integrated neuromorphic network basedon metal-oxide memristors”, Nature 521, 61-64 (2015).

[4] J.J. Yang, D.B. Strukov & D.R. Stewart, “Memristive devices for computing”, Nature Nanotech. 8, 13-24 (2013).

[5] for example, http://www.crossbar-inc.com/

[6] F. Miao et al., “Anatomy of a Nanoscale Conduction Channel Reveals the Mechanism of a High-Performance Memristor”, Adv. Mater. 23, 5633-5640 (2011).

[7] A. C. Torrezan, J. P. Strachan, G. Medeiros-Ribeiro, & R.S. Williams, “Sub-nanosecondswitching of a tantalum oxide memristor”, Nanotechnology 22, 485203 (2011).

[8] J.P. Strachan, et al. “State Dynamics and Modeling of Tantalum Oxide Memristors”, IEEETransactions on Electron Devices 60, 2194-2202 (2013).

[9] W. Yi, et al., “Quantized Conductance coincides with State Instability and Excess Noise inTantalum Oxide Memristors”, Nature Communications, in press.

Date: 17/March/2017 – (friday) – Place: Sala 212 – Auditório do Departamento de Física- Time: 10h15min

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O Programa de Pós-Graduação em Física e o Parque Viva Ciência convidam a todos para:

Planetas extrassolares e vida no universo

Professor Roberto Saito

A vida como conhecemos é um fenômeno planetário até o momento limitado ao nosso lar no Universo, a Terra. Entretanto, nas últimas duas décadas a astronomia vem passando por um momento único, com a descoberta de um número cada vez maior de planetas orbitando outras estrelas, os chamados planetas extrassolares. Alguns desses novos mundos são especialmente importantes por suas similaridades com a Terra, o que permitiria abrigar vida. Nesse seminário falaremos sobre a busca e o estudo de planetas extrassolares, nosso conhecimento atual sobre exoplanetas potencialmente habitáveis e as perspectivas que a busca por vida fora da Terra nos reservam nas próximas décadas.

Data e horário: 15 de março de 2017, às 18:30h
Local: Auditório do Depto. de Química

THE PHYSICS GRADUATE PROGRAM invites everyone to the seminar: 

Phase transitions and self-organized criticality in networks of stochastic spiking neurons. 

Prof. Dr. Osame Kinouchi

Departamento de Física – FFCLRP – USP

 Abstract:

Phase transitions and critical behavior are crucial issues both in theoretical and experimental neuroscience. We report analytic and computational results about phase transitions and self-organized criticality (SOC) in networks with general stochastic neurons. The stochastic neuron has a firing probability given by a smooth monotonic function Phi(V) of the membrane potential V, rather than a sharp firing threshold. We find that such networks can operate in several dynamic regimes (phases) depending on the average synaptic weight and the shape of the firing function Phi. In particular, we encounter both continuous and discontinuous phase transitions to absorbing states. At the continuous transition critical boundary, neuronal avalanches occur whose distributions of size and duration are given by power laws, as observed in biological neural networks. We also propose and test a new mechanism to produce SOC: the use of dynamic neuronal gains — a form of short-term plasticity probably in the axon initial segment (AIS) — instead of depressing synapses at the dendrites (as previously studied in the literature). The new self-organization mechanism produces a slightly supercritical state, that we called SOSC, in accord to some intuitions of Alan Turing.

Date: 19/December/2016 – (monday) – Place: Sala 212 – Auditório do Departamento de Física- Time: 10h30min