School of Mechanical Engineering Seminar
Monday, October 19, 2015 at 15:00
Wolfson Building of Mechanical Engineering, Room 206

Jamming by Shape

Eial Teomy

School of Mechanical Engineering, Tel Aviv University

PhD Student of Dr. Yair Shokef

In colloidal and granular systems, energy and temperature do not play a major role. The dynamics of such systems are dominated by the geometrical packing fraction of their constituents and may be described by various kinetically-constrained models. We focus on the Kob-Andersen model, which is defined as a lattice gas with only on-site exclusion, for which particles can move to neighboring sites only if they have less than a certain number of occupied neighbors. Most previous research considered infinite systems, while actual experimental systems are finite. We consider finite-size and semi-infinite system in any dimension, which are infinite in several directions, but finite in the other directions.

By increasing the density of particles in the system, it becomes jammed, i.e. almost all the particles can never move according to the kinetic constraints. It has been proven that a system which is infinite in all directions, gets jammed only at a density of 1, when all lattice sites are occupied by particles. We find, analytically and numerically, that non-infinite systems become jammed at some finite, size- and shape-dependent density which nears 1 as the size of the system is increased.

Because the jamming density depends on the shape of the system, it is possible to jam or unjam the system just by changing its shape, without altering its total volume or particle density. In the protocol we give here, the jamming transition does not occur by exerting forces on the system, but by performing ensemble averages over systems with fixed shape and density.

You are invited to attend a lecture

By:

Alina Karabchevsky

Optoelectronics Research Centre, University of Southampton, Southampton, SO17 1BJ, UK

Email: A.Karabchevsky@soton.ac.uk

Molecules, glass and light

In this seminar, I will introduce the fundamentals of guided optics. A brief overview will be given over design, fabrication and characterization of integrated optical components and microfluidic channels. I will focus on the conceptual importance of the integrated optics and surface modification for chemo- and bio-applications. The potential of disorder-enhanced photonics in vibrational spectroscopy on waveguides will be discussed and new directions will be proposed.

Vibrational spectroscopy relies on absorption of electromagnetic radiation by molecular vibrations.

It is a powerful tool for drawing information on molecular structure and dynamics.

In the first part of the talk I will present an intriguing physical effect of disorder-enhanced absorption of light by molecular overtones of amines in a: 1) silicate channel waveguide and 2) microtapered fiber with adsorbed gold nanoparticles. Due to the guides’ surface modification, aromatic rings tend to stack together, and N-H bonds in amines form hydrogen bonds with each other. This 8 nm thick multilayer structure of lamellar liquid crystal shape leads to the switch from ballistic to diffusive propagation of light which results in the enhanced absorption. I will also address a dynamics of absorption as a function of time of adsorption of the organic molecules on waveguide. These phenomena are expected to find application in organic solution based optical sensors for detection of explosive materials and diagnostics of psychoactive stimulants based on amines.

In the second part of the talk, I will present a theoretical study of composite plasmonic waveguide structures for design of integrated optical components and Purcell enhanced chemiluminescence in a microfluidic channel.

Thursday, July 16 2015, at 11:00

Room 011, Kitot building

You are invited to attend a lecture

By:

Mr. Shay Elmalem

M.Sc. student of Prof. Emanuel Marom

Electrical Engineering, Physical Electronics Department

Athermalized Infrared Imaging as well as Visible Light Imaging  with Extended Depth of Field using Composite Phase Masks

Infra-Red (IR) imaging became quite popular in recent years. Until the beginning of the 21st century, only expensive IR imaging systems were common, mainly for military applications. In the last decade, IR imaging systems became very wide spread for industrial and civilian applications. Due to such growing market, the need to develop techniques for producing inexpensive IR imaging systems became much more prominent.

One of the most popular materials for IR lenses is Germanium (Ge), due to many attributes. However, Ge has a very unique drawback, due to the sensitivity of its refractive index with the temperature (which is 100 times higher than that of glass). This change in refractive index due to temperature results in a temperature-dependent focal length. Many approaches have been developed to solve the thermal focal shift (TFS), known as 'IR Lens Athermalization', so that the use of Ge as an optical material would be viable. All of the known approaches solve the TFS by complex optical design or by using post-processing algorithms. We present a way to treat the TFS as a Depth of Field (DOF) problem, and as such to solve it by using an all-optical DOF phase mask. The DOF mask is made of composite structure, designed to provide improved imaging performance for broad wavelength band along with wide temperature range. Some of the solutions developed can fit also for imaging system working in the visible band of the spectrum which require extended depth of field (with regards to broad wavelengths band only, since thermal effects practically don’t exist in this band).  Simulation results will be presented and discussed.

Thursday, July 16 2015, at 15:00

Room 011, Kitot building