(The talk will be given in English)

Speaker:     Prof. Yoram Burak
                     Racah Institute of Physics, and Edmond and Lily Safra Center for Brain Sciences, Hebrew University
 

Monday, November 11^th, 2019
15:00 - 16:00

Room 011, Kitot Bldg., Faculty of Engineering

Spatial coding and computation by grid cell neurons in the mammalian brain
 

Abstract

he neural representation of an animal’s location within its environment has been studied since the discovery in 1971 of ‘place cells’ in the mammalian hippocampus, which are selectively active when an animal visits a particular location. The main source of input to the hippocampus within the brain, the entorhinal cortex, has been found in 2005 to contain neurons that are active in multiple locations within the animal’s environment. Remarkably, these locations are arranged on the vertices of a two-dimensional hexagonal lattice that tiles the plane. Both discoveries, of place cells and grid cells, were recognized by the 2014 Nobel Prize in Physiology or Medicine, awarded to John O’Keefe (UCL, London), May-Britt Moser, and Edvard Moser (NTNU, Trondheim). The periodic response of grid cells, as a function of the animal’s position, raises many questions – both about the mechanisms responsible for this periodicity, and about the properties of grid cell activity as a neural coding scheme for position. I will survey these questions, and will discuss how principles borrowed from statistical physics, nonlinear dynamics, and information theory have been applied to address them.

Short Bio
Yoram Burak is an Assistant Professor at the Edmond and Lily Safra Center for Brain Sciences, and the Racah Institute of Physics at the Hebrew University of Jerusalem. He received his B.Sc. (summa cum laude) from Tel-Aviv University in physics and computer science, and continued his graduate studies at Tel-Aviv University in theoretical physics. His Ph.D., supervised by Prof. David Andelman,  was awarded (with distinction) in 2005. He was a postdoctoral associate at the Kavli Institute for Theoretical Physics at the University of California at Santa Barbara and later a Swartz Postdoctoral Fellow at the Center for Brain Science at Harvard University. In 2012 he joined the Hebrew University. His research spans diverse topics in computational and theoretical neuroscience, including principles of neural coding, mechanisms of short-term memory, origins and consequence of stochasticity in neural networks, sensory perception, and spatial coding and computation in the brain.‏

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SCHOOL OF MECHANICAL ENGINEERING SEMINAR
Wednesday, January 1, 2020 at 14:00
Wolfson Building of Mechanical Engineering, Room 206

Development, Characterization and Implementation of Oscillatory Suction Actuator for Boundary Layer Control
Bar Mizrahi
M.Sc. student of Prof. Avraham ‘Avi’ Seifert

An experimental study of a new innovative fluidic device aimed at creating oscillatory suction and oscillatory blowing (OSOB) with no moving parts was conducted, to be used as an actuator for active flow control applications.
Following the previous generation highly successful SaOB (Steady Suction and Oscillatory Blowing) actuator, a new device was developed, with the aim to create both oscillatory suction (compared to steady suction in the SaOB) and oscillatory blowing. The use of unsteady suction has been shown both experimentally (by Morgulis) and theoretically (by Seifert) to be more efficient than its steady counterpart. The new actuator concept is based on the principle of pulsing a pair of ejectors by a single fluidic oscillator.
The study was conducted in three steps. The first step included benchtop characterization of the new actuator in still-air, with the focus on the oscillatory quality of the suction (also termed ‘switching quality’), and a wide range of suction velocities and frequencies. The second step included an investigation of the actuation – transitional boundary layer interaction over a flat-plate with zero-pressure-gradient, in a small-scale, low–speed wind tunnel. In this stage, four configurations were tested, including base flow (unexcited), steady suction, oscillatory suction, and oscillatory suction combined with oscillatory blowing. Two types of hot-wire surveys were conducted– surface mapping at a constant height above the plate and vertical velocity scan for boundary layer characterization. The third step included a comparison between steady to unsteady suction, both combined with oscillatory-blowing (SaOB and OSOB actuators), on a special-designed airfoil performance, which was tested in the Knapp-Meadow wind tunnel, with both a load-cell and pressure-taps.
The benchtop results show the actuator is capable of creating mean suction velocities of more than 30m/s, with fluctuations to mean ratio of up to 0.7, and wide-range, controllable frequency response. The actuation – boundary layer interaction results show a clear impact of the oscillatory suction on the flow field, expressed in dominant frequency maps and phase-lag maps. Integral parameters of the boundary layer present a shape-factor in the range 2≤H≤1.6 for the base flow, which points on a transitional boundary layer. Both the displacement and the momentum thickness decreased by applying steady and unsteady suction, with certain advantages to unsteady suction, especially at low suction magnitudes. The results of the comparison between the two actuators on the airfoil performance show an increase in the actuation efficiency of the oscillatory suction in comparison to steady suction, resulting from a lower energy consumption that leads to the same desired airfoil performance.

Materials by Design:

Three-Dimensional (3D) Nano-Architected Meta-Materials. Part I

Julia R. Greer

Departments of Materials Science, Mechanics, and Medical Engineering

California Institute of Technology, Pasadena, CA

http://www.jrgreer.caltech.edu

Creation of extremely strong and simultaneously ultra lightweight materials can be achieved by incorporating architecture into material design. In our research, we design and fabricate three-dimensional (3D) nano-architected materials that can exhibit superior and often tunable thermal, photonic, electrochemical, and ­mechanical pro­­­per­­ties at ex­tre­me­ly low mass densities (lighter than aerogels), which renders them useful, and often enabling, in many scientific pursuits and tech­no­lo­gi­cal applications. Dominant properties of such meta-materials are driven by their multi-scale nature: from characteristic material microstructure (atoms) to individual constituents (nanometers) to structural components (microns) to overall architectures (millimeters and above). 

To harness the beneficial properties of 3D nano-architected meta-materials, it is critical to assess their properties at each relevant scale while capturing over­all structural complexity. Our research is focused on fabrication and synthesis of such architected materials using 3D lithography, nanofabrication, and additive manufacturing (AM) techniques, as well as on investigating their mechanical, biochemical, electrochemical, electromechanical, and thermal properties as a function of architecture, constituent materials, and microstructural detail. We strive to uncover the synergy between the internal atomic-level microstructure and the nano-sized external dimensionality, where competing material- and structure-induced size effects drive overall response and govern these properties.

In Part I of the Seidman Lectures, I will focus on the mechanics of 3D nano-architected materials, which include compression, tension, and fracture experiments and simulations, as well as quasi-static vs. dynamic loading for a broad range of materials. I will describe an example where unusual mechanical properties of these nano-architected materials enable creating stimulus-responsive reconfigurable materials through electrochemistry.

Some relevant publications:

1. D. Yee, M. Lifson, J.R. Greer, Additive manufacturing of 3D architected multifunctional metal oxides, Adv. Mater. (2019) in press, DOI: 10.1002/adma.201901345.
2. X. Zhang et al, Lightweight, flaw-tolerant, and ultrastrong nanoarchitected carbon. PNAS, 116(14) (2019) 6665-72.
3. X. Xia et al., Electrochemically reconfigurable architected materials, Nature, 573 (2019) 205-13.
4. A.J. Mateos et al., Discrete‐continuum duality of architected materials: Failure, flaws, and fracture, Adv. Funct Mater., 29 (2019) article 1806772.
5. L.A. Shaw et al., Computationally efficient design of directionally compliant metamaterials, Nature Commun., 10 (2019) article 291.
6. A. Vyatskikh et al., Additive manufacturing of 3D nano-architected metals, Nature Commun., 9 (2018) article 593.
7. V. Chernow et al., Polymer nanolattices as mechanically tunable 3-dimensional photonic crystals, Appl. Phys. Lett., 107 (2015) article 101905.
8. L.R. Meza, S. Das, J.R. Greer, Strong, lightweight and recoverable three-dimensional ceramic nanolattices, Science,  345 (2014) 1322-6.