16.3.16

16 במרץ 2016, 13:00 
011 kitot  
16.3.16

You are invited to attend a lecture

By

 

Or Danon

(M.Sc. student under the supervision of Prof. Moshe Tur)

School of Electrical Engineering, Tel-Aviv University, Tel-Aviv 69978, Israel

Fast and distributed optical fiber strain sensor using novel Brillouin sensing techniques

Fiber-optic based sensors are a promising technology for implementing Structural Health Monitoring (SHM), as well as many other security applications. Sensors based on the Brillouin effect are already used to monitor strain/temperature variations in long gas pipes, submarine cables, tunnels etc. In sensors based on the concept of Brillouin Optical Time Domain Analysis (BOTDA), the Brillouin Gain Spectrum (BGS) of the fiber is interrogated by launching a probe continuous wave (CW) and a pump pulse, with frequency difference around the Brillouin Frequency Shift (BFS). The probe wave gain time dependency is then translated into spatial dependency of the Brillouin gain along the fiber for the specific frequency difference between the probe and the pump waves. In conventional BOTDA, the BGS is interrogated at multiple points so it can be fully reconstructed. This approach, albeit robust, is time consuming as each reading is limited by twice the Time of Flight (TOF) of the pulse in the fiber. A novel technique suggested by our team called Slope Assisted BOTDA (SA-BOTDA) enables to overcome this limitation by interrogating the BGS at only one frequency, on its slope. The BFS is then calculated by knowing the local slope of the BGS.

The SA-BOTDA method however suffers from several drawbacks. First, in distributed sensing, the BFS may vary significantly along the fiber, causing the singular frequency chosen for interrogation to result in zero gain from some areas of the fiber. Second, changes in the pump power, due to various reasons such as polarization fading, coupling losses, depletion etc., cannot be separated from changes in the BFS, as only one parameter is measured.

In this talk we present recent advances which overcome these limitations. The variation of the BFS along the fiber is countered by varying the probe frequency during the travel of the pump pulse, a method called Tailored Probe BOTDA (TP-BOTDA). We demonstrate first experimental results for real time measuring of a vibrating bent cantilever beam, a realistic and challenging scenario applicable for SHM of UAVs, using state of the art measurement system developed within this thesis. We also present experimental demonstrations of techniques which use Double Slope Assisted BOTDA (DSA-BOTDA) to overcome the dependence of the slope on the pump power.

Wednesday, March 16, 2016, at 13:00

Room 011, Kitot Building

 

EE Seminar: Secure Computation of Social Prestige and Influence from Multiple Networks

~~(The talk will be given in English)

Speaker:   Prof. Tamir Tassa
                       The Department of Mathematics and Computer Science, Open University

Monday, May 30, 2016
15:00 - 16:00
Room 011, Kitot Bldg., Faculty of Engineering

Secure Computation of Social Prestige and Influence from Multiple Networks

Abstract

We study the problem of computing social prestige measures over multiple networks. We consider a setting in which there are several mutually non-trusting parties (called hosts), each one of them holding a proprietary social network on the same ground set of users (nodes). Those hosts wish to compute a prestige (or centrality) score for each of the users, without disclosing information about their private graphs.

We study three measures of prestige, one progressively extending the previous. The first measure counts the number of nodes reachable from a node within a given radius. The second measure, corresponding to the classic Katz score [L. Katz, A new status index derived from sociometric index, Psychometrika, 1953], extends the first one by counting the number of paths between any two nodes. The final one is an original extension of the Katz score to the multigraph case: not only the number of paths are counted, but also the multiplicity of these paths in the different networks is taken into consideration.

We then present a suite of multiparty protocols to compute the three measure of prestige. We show that our protocols are secure in the information-theoretic sense. We also study how to scale our protocols to very large graphs. Finally, we test our protocols on several real-world multigraphs: interestingly, the protocol to compute the most sensitive score (i.e., the multigraph prestige measure) is also the most scalable one and can be efficiently run on very large networks.

Joint work with Gilad Asharov, Francesco Bonchi, and David Garcia-Soriano

Bio:
Tamir Tassa is currently an associate professor in the Department of Mathematics and Computer Science at the Open University of Israel. Previously, he served as a lecturer and researcher in the School of Mathematical Sciences at Tel Aviv University, and in the Department of Computer Science at Ben Gurion University. During the years 1993-1996 he served as an assistant professor of Computational and Applied Mathematics at the University of California, Los Angeles. He earned his PhD in applied mathematics from the Tel Aviv University in 1993. His recent research interests include privacy-preserving data publishing and data mining, secure multi-party computation, secret sharing, and combinatorial optimization.

 

30 במאי 2016, 15:00 
חדר 011, בניין כיתות-חשמל  

EE Seminar: PAPR Reduction in Single-Carrier Modulation with Markovian Constraint

~~
Speaker: Yonathan Tate,
M.Sc. student under the supervision of Dr. Dan Raphaeli

Wednesday, March 23, 2016 at 15:00
Room 011, Kitot Bldg., Faculty of Engineering

PAPR Reduction in Single-Carrier Modulation with Markovian Constraint

Abstract

The peak to average power ratio (PAPR) characteristic of a communication signal is of importance when power amplifiers (PA) are in need. In such cases, the span of the signal’s power must reside inside the linear region of the PA in order to avoid signal saturation, which leads to both in-band and out-band interferences. When the PAPR is high, the average power must therefore be backed-off (BO) to avoid saturation, and in turn the transmission becomes more error-prone. Such difficulties exist for example in satellite communication, where single carrier transmission with high spectral efficiency is common.
In this work we propose a novel approach for shaping for PAPR reduction which on one hand achieves better PAPR reduction than known techniques, and on the other hand is practical in the sense of integrating well with modern iterative error correcting schemes, specifically turbo codes. The proposed approach is based on using carefully selective puncturing of ECC parity bits to achieve non-equiprobable symbol signaling, which is designed to reduce the PAPR. The proposed technique has been tested in simulations on a 16-QAM constellation with various data rates, and an overall gain of over 1.6 dB is demonstrated in some cases against non-shaped signaling.

 

23 במרץ 2016, 15:00 
חדר 011, בניין כיתות-חשמל  

Dr' Ori Shoshani סמינר מחלקתי

11 באפריל 2016, 15:00 
וולפסון 206  
0
Dr' Ori Shoshani סמינר מחלקתי

 

 

 

 

 

School of Mechanical Engineering Seminar
Monday, April 11, 2016 at 15:00
Wolfson Building of Mechanical Engineering, Room 206

 

 

Using Nonlinearity to Reduce Phase Noise in MEMS-based Oscillators

 

Dr. Ori Shoshani

 

 

Due to their inherent compatibility with semiconductor technology and their ability to fulfill device miniaturization requirements, micro-electro-mechanical-system (MEMS) resonating elements are an attractive replacement for quartz crystals in time-keeping applications. They offer fast-responding, low power consumption elements that are readily integrable with electronic circuits in fabrication.  However, as the dimensions of MEMS devices are reduced, resonator frequency becomes highly dependent upon fabrication variances and environmental disturbances that result in degradation of frequency stability.  Moreover, in order to satisfy signal-to-noise ratio specifications, these MEMS devices often need to operate at amplitudes where nonlinear effects come into play, which leads to further degradation in the frequency precision. This talk will provide an overview of frequency stability in MEMS-based oscillators and describe some recently developed approaches to enhancing frequency stability by addressing, and even exploiting, system nonlinearities. Specifically, the use of synchronization and zero-dispersion points in the resonator frequency response will be discussed, and theoretical conditions for optimal operating points will be introduced.  Experimental validation of the results, obtained from experimental collaborators in the Kenny group at Stanford University and in the López group at Argonne National Laboratory, will also be presented.

 

Bio: Oriel Shoshani received the B.S. degree in mechanical engineering from Ben-Gurion University of the Negev, Beer-Sheva, Israel, in 2008 and the Ph.D. degree (direct program) in mechanical engineering from Technion-Israel Institute of Technology, Haifa, Israel, in 2014, for which he worked on problems related to fluid-structure interactions. Currently, he is a postdoctoral fellow in the Department of Mechanical and Aerospace Engineering at Florida institute of Technology and a visiting scholar in the Department of Physics and Astronomy at Michigan State University. His current research interests include dynamics of fluctuating nonlinear vibrational systems and applications to micro/nano-electro-mechanical systems.

 

 

 

 

 

10/3/16

10 במרץ 2016, 15:30 
 
10/3/16

You are invited to attend a lecture

By

 

Oren Pe'eri

 

 

M.Sc student of Prof. Menachem Nathan and Prof. Michael Golub

Electrical Engineering, Physical Electronics Department

Tel Aviv University

 

 

Direct Reconstruction of Spectral Signatures in Optical-Digital Snapshot Spectral Imaging Systems

 

Abstract

This thesis is dedicated to a new approach in spectral imaging. We use an imaging system that includes a spectral disperser, a micro-lens array (MLA), imaging lenses and a monochromatic sensor that records a mix of spectral and spatial data ("spectral cube") in a multiplexed form. We develop a special demultiplexing algorithm for direct extraction of spatial maps corresponding to spectral signatures of interest from the sensor data. This "signature mapping" is based on prior knowledge of spectral signatures of specific materials and on the assumption that the original spectral cube consists of their linear superimposition. Direct extraction of the spatial map of signatures marks the areas where the original image is abundant in specific chemical materials. As such, it substantially reduces the data volume by a ratio of the number of wavelength bands to the number of spectral signatures. The developed method and algorithms are validated by computer simulation of the spectral imaging system with the aid of spectral cubes of real multi-spectral images of gas plumes.

 

Thursday, March 10, 2016, at 15:30

Room 011, Kitot building

 

 

 

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