WesternUniversity
Department of Physics and Astronomy
PhD Public Lecture
Meghan McGill
Supervisors: Drs. Carol Jones & Aaron Sigut
“Gravitational Darkening of Classical Be Stars”
DATE: MONDAY, 22nd April 2013
TIME: 1:30 p.m.
PLACE: P&A Seminar Room PAB 100
All are welcome to attend.
Western University
DEPARTMENT OF PHYSICS AND ASTRONOMY
PHYSICS & ASTRONOMY COLLOQUIUM
Date: Thursday, 25th April 2013
Time: 1:30 p.m.
Location: Physics & Astronomy Seminar Room 100
Dr. Avery Broderick
Department of Physics & Astronomy
University of Waterloo & Perimeter Institute
“Imaging Supermassive Black holes on Horizon Scales”
ABSTRACT
Supermassive black holes, the million to billion solar mass cousins of the more commonly described remnants of massive stars, are now believed to exist at the centers of nearly all galaxies, and power some of the most energetic phenomena in the universe, with cosmological implications. Nevertheless, due to their compact nature, it remains unclear how supermassive black holes grow, how they launch the ultra-relativistic outflows observed, if gravity in the vicinity of their horizons is well described by general relativity, and even if event horizons exist. However, the Event Horizon Telescope, a developing Earth-sized millimeter-wave interferometer, has now probed two supermassive black holes on spatial scales smaller than their respective event horizons. I will describe how these observations are being performed, and how existing (and forthcoming) data from the Event Horizon Telescope is already providing novel insights into both their enigmatic behaviors and fundamental natures.
Refreshments will be available.
Poster: http://www.physics.uwo.ca/colloquia/Colloquia%20Notices/2012_2013/CHANG%20Colloquium.pdf
Western University
DEPARTMENT OF PHYSICS AND ASTRONOMY
PHYSICS & ASTRONOMY COLLOQUIUM
Date: Thursday, 18th April 2013
Time: 1:30 p.m.
Location: Physics & Astronomy Seminar Room 100
Dr. Gap Soo Chang
Department of Physics & Engineering Physics
University of Saskatchewan
“Carbon-based electronics: Achievements and Challenges”
ABSTRACT
The π-conjugated molecular semiconductors have recently emerged as important and promising materials for a wide field of advanced electronic applications due to their solution processability at low temperature, device fabrication on flexible substrates, and comparatively high speed of fabrication in a cost-efficient way. Organic field-effect transistors (OFETs), photovoltaic cells (OSCs), and light-emitting diodes (OLEDs) are good examples where organic semiconductors are being used, and some of them are tantalizingly close to being used in commercial applications. Moreover, organic semiconductors typically exhibit long spin-relaxation time and spin-coherence length when spin-polarized charge carriers are injected. These advantages enable us to utilize both spin and charge properties of electrons for information storage and processing, which are called Spintronics. However, development of practical electronic and spintronic devices based on organic semiconductors has hampered by several problems such as difficulty in obtaining high crystalline thin films, low carrier mobility, low light-energy conversion efficiency, and large conductivity mismatch between organic channel layer and metal electrodes. In this presentation, a variety of recent approaches to high performance organic electronics will be reviewed and technically challenging issues will be discussed.
Refreshments will be available.
Poster: http://www.physics.uwo.ca/colloquia/Colloquia%20Notices/2012_2013/SCOTT%20Colloquium.pdf
Western University
DEPARTMENT OF PHYSICS AND ASTRONOMY
PHYSICS & ASTRONOMY COLLOQUIUM
Date: Thursday, 15th November 2012
Time: 1:30 p.m.
Location: Physics & Astronomy Seminar Room 100
Dr. Douglas Scott
Department of Physics and Astronomy
University of British Columbia
“The Standard Cosmological Model”
ABSTRACT
All empirical evidence relating to our Universe is currently well explained by a basic model which contains only a few key ingredients: the background is described by homogeneous and isotropic solutions within General Relativity, in which there is domination by vacuum energy and cold dark matter in a roughly flat expanding geometry; the density fluctuations appear to be nearly scale-invariant, adiabatic and Gaussian; and all of today’s structure grew through gravitational instability. Within this picture the Universe is described by about 10 numbers, and they are now mostly known to about the first digit. So what is left to do? How many digits do we need? Where did these values come from? Are there more numbers that we haven’t thought of yet? Is this model anything like the Standard Model of Particle Physics?
Coffee & snacks will be available.
Poster: http://www.physics.uwo.ca/colloquia/Colloquia%20Notices/2012_2013/NAIK%20Colloquium.pdf
Western University
DEPARTMENT OF PHYSICS AND ASTRONOMY
PHYSICS & ASTRONOMY COLLOQUIUM
Date: Thursday, 8th November 2012
Time: 1:30 p.m.
Location: Physics & Astronomy Seminar Room 100
Dr. Ratna Naik
Department of Physics and Astronomy
Wayne State University
“Raman Spectroscopy for Biomedical Diagnostics: Cancer detection in pediatric tumors and head and neck squamous cell carcinoma”
ABSTRACT
Recently, Raman spectroscopy has been used in the detection of a variety of cancers and other tissue abnormalities. Raman spectra can provide highly detailed chemical information about a tissue sample and its noninvasive nature makes it an attractive tool for in vivo applications in medicine. We have studied the archived tissues of head and neck squamous cell carcinoma and frozen pediatric tumors (neuroblastoma and ganglioneuroma) using Raman spectroscopy. The effects of tissue preservation and processing on the Raman spectral characteristics and their utility in diagnosing the disease state of the tissues is investigated. The study shows that Raman spectroscopy in conjunction with multivariate statistical methods, such as principal component analysis and discriminant function analysis, can identify the disease state of the tissues that is consistent with the histopathological diagnosis. An overview of principles of Raman spectroscopy and its applications to biomolecules, as well as the details of our findings, will be presented.
Refreshments will be available.
—CANCELLED— Please note that our speaker forTOMORROW’scolloquium has had to CANCELhis visit.
No colloquium tomorrow. Our apologies.
Western University
DEPARTMENT OF PHYSICS AND ASTRONOMY
PHYSICS & ASTRONOMY COLLOQUIUM
Date: Thursday, 25th October 2012
Time: 1:30 p.m.
Location: Physics & Astronomy Seminar Room 100
Dr. Carlos Silva
Département de Physique & Regroupement québécois sur les matériaux de pointe
Université de Montréal
“The dependence of charge recombination dynamics on the solid-state microstructure in neat, semicrystalline polymeric semiconductors”
ABSTRACT
We investigate the dynamics of geminate-polaron-pair recombination in the neat polymeric semiconductor regioregular poly(3-hexylthiophene) (P3HT) by means of time-resolved photoluminescence (PL) spectroscopy as a function of the solid-state microstructure, imposed by the molecular weight of the polymer and the thin-film processing route. At 10K, we observe delayed PL that originates from recombination of long-lived geminate-polaron pairs. The delayed PL decays over microsecond timescales, which is orders of magnitude longer than the exciton lifetime. We find that >36% of the total PL in solution-processed films of high-molecular-weight (331 kg/mol) material, which features a two-phase semicrystalline microstructure of alternating chain-entangled amorphous phases and crystalline lamella. In this microstructure, both the yield and the decay dynamics depend upon molecular weight. However, in films with dominant one-phase chain-extended microstructures, delayed PL is strongly suppressed. We thus find that a two-phase morphology leads to a higher yield of delayed PL with a higher distribution of decay rates than one-phase, chain-extended morphologies. By invoking a kinetic model including interconversion of excitons and geminate polarons, we conclude that geminate electron-hole pairs are on average further apart in two-phase morphologies, and that these microstructures result in a higher yield of geminate pairs that do not recombine within the timeframe of our experiment.
Refreshments will be available.
Department of Physics and Astronomy
MSc Public Lecture
Tahani Aldahri
Supervisor: Dr. John de Bruyn
“The behaviour of a falling particle in a funnel”
DATE: WEDNESDAY, 31st October 2012
TIME: 11:00 a.m.
PLACE: Physics & Astronomy Room 100
All are welcome to attend.
Poster: http://www.physics.uwo.ca/colloquia/Colloquia%20Notices/2012_2013/JOHN%20Colloquium.pdf
Western University
DEPARTMENT OF PHYSICS AND ASTRONOMY
PHYSICS & ASTRONOMY COLLOQUIUM
Date: Thursday, 1st November 2012
Time: 1:30 p.m.
Location: Physics & Astronomy Seminar Room 100
Dr. Sajeev John
Department of Physics
University of Toronto
“Light Trapping and Solar Energy Harvesting in Thin Film Photonic Crystals”
ABSTRACT
Photonic crystals are widely known for their light-trapping capabilities. This is often associated with the occurrence of a photonic band gap or other suppression in the electromagnetic density of states. This enables guiding of light on an optical micro-chip and unprecedented forms of strong-coupling between light and matter. In the past, practical applications of these effects have focused on information technology. More recently, an important opportunity has emerged in the area of energy technology. This arises from light-trapping in the higher bands of a photonic crystal, where the electromagnetic density of states is enhanced rather than suppressed. This enables unprecedented strong absorption of sunlight in a material with weak intrinsic absorption.
We describe designs of 3D photonic crystal silicon-based solar cells that enhance the overall absorption of sunlight using architectures consisting of just 1 micron (equivalent bulk thickness) of silicon. These crystals trap light through a parallel-to-interface negative refraction (PIR) effect and other optical resonances that occur over a broad angular and frequency range. These 3D photonic crystals exhibit an enhanced electromagnetic density of states, consisting of slow group velocity modes, in which the flow of energy is transverse to the depth of a thin film of material. In the case of a modulated nanowire photonic crystal solar cell, it is possible to absorb roughly 75% of all available sunlight in the wavelength range of 400–1100 nm, using one micron of silicon. In the case of conical nano-pore silicon photonic crystal, roughly 85% of all available sunlight is absorbed. The power conversion efficiencies of these one-micron photonic crystals rival those of present-day solar cells using up to 300 microns of silicon. These photonic crystals offer additional opportunities for solar spectral reshaping to rival and possibly surpass the famous Shockley-Queisser power conversion efficiency limit of 33%.
Coffee & snacks will be available.
Poster: http://www.physics.uwo.ca/colloquia/Colloquia%20Notices/2012_2013/SILVA%20Colloquium.pdf
Western University
DEPARTMENT OF PHYSICS AND ASTRONOMY
PHYSICS & ASTRONOMY COLLOQUIUM
Date: Thursday, 25th October 2012
Time: 1:30 p.m.
Location: Physics & Astronomy Seminar Room 100
Dr. Carlos Silva
Département de Physique & Regroupement québécois sur les matériaux de pointe
Université de Montréal
“The dependence of charge recombination dynamics on the solid-state microstructure in neat, semicrystalline polymeric semiconductors”
ABSTRACT
We investigate the dynamics of geminate-polaron-pair recombination in the neat polymeric semiconductor regioregular poly(3-hexylthiophene) (P3HT) by means of time-resolved photoluminescence (PL) spectroscopy as a function of the solid-state microstructure, imposed by the molecular weight of the polymer and the thin-film processing route. At 10K, we observe delayed PL that originates from recombination of long-lived geminate-polaron pairs. The delayed PL decays over microsecond timescales, which is orders of magnitude longer than the exciton lifetime. We find that >36% of the total PL in solution-processed films of high-molecular-weight (331 kg/mol) material, which features a two-phase semicrystalline microstructure of alternating chain-entangled amorphous phases and crystalline lamella. In this microstructure, both the yield and the decay dynamics depend upon molecular weight. However, in films with dominant one-phase chain-extended microstructures, delayed PL is strongly suppressed. We thus find that a two-phase morphology leads to a higher yield of delayed PL with a higher distribution of decay rates than one-phase, chain-extended morphologies. By invoking a kinetic model including interconversion of excitons and geminate polarons, we conclude that geminate electron-hole pairs are on average further apart in two-phase morphologies, and that these microstructures result in a higher yield of geminate pairs that do not recombine within the timeframe of our experiment.
Refreshments will be available.
Poster: http://www.physics.uwo.ca/colloquia/Colloquia%20Notices/2012_2013/LEE%20Colloquium.pdf
Western University
DEPARTMENT OF PHYSICS AND ASTRONOMY
PHYSICS & ASTRONOMY COLLOQUIUM
Date: Thursday, 18th October 2012
Time: 1:30 p.m.
Location: Physics & Astronomy Seminar Room 100
Dr. M. Howard Lee
Department of Physics and Astronomy
University of Georgia
“Defining chaos the physics way”
ABSTRACT
Much of what has been shown in numerical studies on chaos may be termed “symptoms” of chaos. There must be a cause or causes of chaos. A definition for chaos could emerge if these causes could be unearthed. Doing so—that is, finding definitions that follow from proofs—is the physics approach. It differs from the math approach of giving definitions that precede proofs. The field of chaos is a meeting place of two cultures.
In this talk I will discuss how one can arrive at a definition of chaos through a fixed-point spectrum of the logistic map—the Ising model of chaos. This spectrum is obtained by a process similar to taking the thermodynamic limit in statistical mechanics. Put simply, the spectrum looks like an unbroken string of irrational points. It can explain the symptoms of chaos that have been observed.
Cookies will be available.