Poster Session 2015

Poster boards will be 3 feet high by 4 feet wide. Posters should be put up shortly before 6:00pm on Thursday July 30th in MP110 .

“Dielectric spectroscopy measurement of colloidal suspension in an intermediate-polarity solvent medium”
Zena Aljabal and Anand Yethiraj
Memorial University of Newfoundland
In this work, we plan to study the electrokinetic phenomena of colloids in a solvent with intermediate polarity by using the dielectric spectroscopy technique. Using the dielectric spectroscopy, we measure the complex impedance of polymethylmethacrylate (PMMA) spheres particles that are suspended in a mixture of the organic solvents cyclohexy bromide(C6 H11 Br,’CHB’) as a function of cis-decalin volume fraction φ and frequency, over the frequency range 0.1 Hz to 100 KHz. The real part of the impedance, Z′, gives us information about the conductivity, which is frequency dependent, while the imaginary part of the impedance, Z′′, reports on the dielectric constant. Unusual electrokinetic phenomena have been observed in real space, microscopy experiments, and the goal is to understand the underlying mechanism.

“Modeling X-ray line shapes of asphaltenes”
Haifa Alqahtani, John shirokoff and John Lewis
Memorial University of Newfoundland
Structural studies of asphalting in crude oil has been performed by X-ray diffraction (XRD). The XRD data is first probably fitted by mathematical function (Pearson VII, Pseudo-Voigt) and then modelled in Mathematica using a generalized Fermi function (GFF). The results are discussed in terms of their accuracy with respect to their profile fitting approach (background type, exponent, Lorentzian).

“Illuminating sunlight”
Aurelia Chenu, Agata Branczyk and John Sipe
Thermal light from the sun has an ultra-short coherence time of approximately 1.3 fs, a spectrum close to that of black-body radiation at approximately 5777 K, and is characterized by thermal photon-number statistics. It is well represented by direct products of statistical mixtures of single-frequency coherent states (typically plane waves). It seems reasonable to suspect that a decomposition in terms of multi-frequency coherent states (typically pulses) would as well be possible. However, we find that it cannot.
While the state of thermal light is represented by a density operator with unit trace, we demonstrate that no unit-trace density operator consisting of a mixture of single pulses can match the thermal state. Such a mixture cannot even give the correct result for the first-order correlation function. Nonetheless, it is possible to construct a trace-improper mixture that does yield a first-order correlation function at equal space points that matches that of thermal light.
Our results should help in the development of conceptual and calculational tools for understanding and designing nonlinear optical experiments to study excitation by thermal light, as well as provide the first building block towards refining our intuition and understanding of thermal state and incoherent excitation.

“Measurements of CFC-11 (CCl3F) and CFC-12 (CCl2F2) from space by MIPAS:
accuracy, precision and long-term stability”

Ellen Eckert, A. Laeng , S. Lossow, S. Kellmann,G. Stiller, T. von Clarmann, N. Glatthor,
M. Hopfner, M. Kiefer, H.Oelhaf, J. Orphal, B. Funke, U. Grabowski, F. Haenel,
A. Linden, G. Wetzel, W. Woiwode, P. F. Bernath, C. Boone, G. S. Dutton, J. W. Elkins,
A. Engel, J. C. Gille, F. Kolonjari, T. Sugita, G. C. Toon and K. A. Walker
Karlsruhe Institute of Technology
Data on chlorofluorocarbons (CFCs), which are long-lived atmospheric constituents, have been collected by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), a remote sounding instrument, aboard the European satellite Envisat. CFCs have been monitored for some decades by several other instruments, because of their ozone depleting potential. MIPAS contributed to this from July 2002 to April 2012. CFC-11 and CFC-12, among other species, are responsible for the formation of the Antarctic ozone hole since they can release active chlorine species which catalytically destroy ozone.
To ensure that the MIPAS data reflect the composition of the atmosphere sufficiently well and that there is no change in accuracy with time in the measurements, they were compared to measurements from instruments based on the ground and carried by balloons, airplanes and other satellites. The comparison reveals that the CFC-11 values below 15 km are slightly too high, but above that altitude the agreement is very good. The CFC-11 measurements are very stable throughout the measurement period. MIPAS CFC-12 measurements are generally in good agreement with other instruments. Up to 30 km they are temporally stable, while above that altitude percentage difference increases rapidly with time.

“Optimizing molecular properties through in silicon molecular evolution”
Rene Fournier and Harneet Dhillon
York University
A method was developed to optimize molecular properties with respect to both chemical composition C and nuclear configuration X. We present test results where we minimize an objective function F(C,X) of H_pC_qN_rO_s (p=0-12, q=0-4,r=0-3, s=0-2, p+q+r+s =2-12) species, where F = R – G, R is an index of thermodynamic stability, and G is essentially the HOMO-LUMO gap. Both R and G are obtained from DFT calculations using the Gaussian software. Test runs produce familiar stable molecules such as H2O, CH4, and NH3. Future applications will deal with chemical compositions for which the physics and chemistry is not well known and where we could predict stable new species (e.g., super halogens and “magic clusters”). We can also replace G by any other property of interest, e.g., the electron affinity if we wish to discover new super halogens.

“Extending the observed length of the orphan star stream with the dark energy camera”
Lauren Hetherington, Carl Grillmair, Raymond Carlberg and Beth Willman
University of Toronto
The Orphan stream is a stellar stream more than 30 kpc in length and which crosses over 70 degrees of the sky. It’s the second strongest stream after the Sagittarius stream, while also being relatively dynamically cold. It’s orbital plane is nearly perpendicular to Sagittarius, so observations of both can better constrain the overall shape of the galactic halo. The Orphan increases in strength until extending beyond the footprint of the Sloan Digital Sky Survey (SDSS), implying that there is likely much more of it to discover. Finally, the Orphan’s progenitor is unknown. Using the wide field of view and high photometric precision of the Dark Energy Camera (DECam), we extend the Orphan stream beyond its currently known length, and potentially also discover its progenitor. This will allow us to better constrain the orbit of the Orphan stream and to more completely measure its linear density. In so doing, we can better measure both the overall smooth component of the Milky Way halo as well as the clumpy component, potentially including missing satellites. Lastly, discovering the progenitor would provide additional constraints on models of the stream, and allow us to learn more about the conditions necessary to form major streams similar to the Orphan.

“Testing the modified lognormal power-law probability distribution with young stellar clusters”
Deepakshi Madaan, Sophia Lianou and Shantanu Basu
University of Western Ontario
The initial mass function (IMF) is a distribution function describing the number of stars formed per mass interval at birth during a star forming event. Its importance lies in its application, as well as impact, in galaxy formation and evolution studies. We use young stellar clusters in the Local Group to test the Modified Lognormal Power-law Probability distribution recently proposed in Basu et al. 2015. We compare this distribution with the most commonly used functional forms describing the initial mass function in stellar populations analyses (Madaan et al.).

“Earth’s field MRI optimization and comparison”
Kaitlin McNeil, Paul Hungler and Sarah Creber
Royal Military College Canada
Magnetic resonance imaging (MRI) is used widely in the medical sciences to image human tissue for diagnostic and research purposes. Relatively little has been done, however, to investigate the applications of MRI for non-medicinal purposes, due in part to the prohibitive cost of equipment. The Earth’s field MRI (EFMRI) uses the Earth’s magnetic field as its primary field and thus provides a cost-effective means of imaging and making it more readily accessible to research and industry. In analyzing the capabilities of the EFMRI as a device for research and industry, multiple sample geometries were tested and data were compared with neutron imaging, a powerful non-destructive imaging technique.

“Custom engineered optical tweezers with a digital micro mirror device”
Emily E. Storey, Russell Pollari and Joshua N. Milstein
University of Toronto Mississauga
Optical tweezers use tightly focused laser beams to manipulate biological molecules and nanoparticles. We have designed a setup to control the intensity profile of optical tweezers with a digital micromirror device (DMD), enabling us to engineer the optical trapping potential. DMDs comprise an array of mirrors which are individually addressable and controlled via hinges to take one of two states. These states can be rapidly changed by uploading a binary image to the device, mapping each pixel to one mirror. With the DMD we can create arbitrary intensity distributions. Our setup alters the output using a custom built user interface. We have been able to generate several trap shapes including those with circular and square flat top profiles and are developing an iterative algorithm to refine the traps and reduce error. Our current optical tweezers use a liquid crystal spatial light modulator for trap generation that can adjust the beam phase only. Introducing the DMD to the setup adds amplitude control and faster modulation.

“Molecularly-linked gold nanoparticle films across the insulator-to-metal transition: from hopping to strong electron correlations”
Monique Tie and Al-Amin Dhirani
Materials which have strong electron-electron interactions are known to display a wide variety of exotic behaviours. We have found that molecularly-linked gold nanoparticle films represent a new class of materials that exhibit correlated electronic behaviours. Most notably, (a) they undergo a percolation insulator-to-metal transition as a function of film thickness, (b) as the system transitions from an insulator to a metal, a previously unobserved zero-bias conductance peak emerges, attributed to electron correlations, and (c) Coulomb effects play an important role in the conductance on both the insulating and metallic sides near the transition. On the insulating side near the transition, we observe hopping transport with significant Coulomb charging barriers (Efros-Shklovskii variable range hopping). On the metallic side, we have found that conductance behaves as a Fermi liquid with disorder mediated electron-electron interactions. Remarkably, in this barely-metallic phase, we have found elastic scattering lengths smaller than inter-atomic Au-Au separation, violating the Ioffe-Regel limit and signalling strong electron-electron interactions. These results show that gold nanoparticle films can serve as a new test bed for studying correlated electrons and illustrate the promise of a nano building-block strategy for fashioning novel correlated materials.

“Temperature mapping superconducting cavities”
Dominique Trischuk, Robert Orr, Eli Bourassa, Syed Haider Abidi and Shu Qing Wang
University of Toronto
We are studying the performance of 9-cell superconducting RF cavities. Our tests are designed to map the surface temperature of the cavities at cryogenic temperatures (2-4K). The thermometers are constructed at the University of Toronto using 100Ω resistors. We are currently testing a new temperature map design, that involves 36 semi-circular boards and over 600 thermometers. We hope this new design can be used in the future to investigate the surface treatments of superconducting cavities.

“Monolayer FeSe/SrTiO3”
Tatiana A. Webb, Dennis Huang, Can-Li Song, Harris Pirie, Shiang Fang, Cui-Zu Chang, Jagadeesh S. Moodera, Efthimios Kaxiras and Jennifer E. Hoffman
University of British Columbia
Monolayer FeSe grown on SrTiO3 has a superconducting transition temperature an order of magnitude higher than bulk FeSe. The large energy scales which have been observed in the high Tc (65 K; He Nature Materials 2013), superconducting gap (15 meV; Wang Chinese Physics Letters 2012), and high energy phonons (near 100 meV; Lee Nature 2014) point to a pairing mechanism involving states at comparable energies from the Fermi level, including empty bands. We use in-situ scanning tunneling microscopy to study both the filled and empty electronic states of monolayer FeSe/SrTiO3 grown via molecular beam epitaxy. Quasiparticle interference imaging reveals a new electron band above the Fermi level, such that both empty and filled states exist near the center of the Brillouin zone within 100meV of the Fermi surface (Huang arXiv 2015).

“Limitations of T2-contrast 3D-fast spin echo sequences in the differentiation of radiation fibrosis versus tutor recurrence”
Andrea Vargas, Laurent Milot, Simon Graham and Philip Beatty
University of Toronto
The development of extended radiofrequency (RF) refocusing pulse trains with variable flip angles (VFA) instead of conventional 180 degree refocusing pulses, enabled the acquisition of 3D Fast Spin Echo (3D-FSE) for T2-weighted contrast [1]. The use of VFAs does, however, store magnetization in the longitudinal direction and consequently alters signal intensities relative to 2D-FSE. Signal alterations are problematic in treatment monitoring, because the differentiation of radiation fibrosis from recurrent tumors can be obscured. The classification of fibrosis versus tumor recurrence has previously been based on estimated ratios of the tissue-to-muscle signal, radiation fibrosis is expected to have a relatively low signal (similar to muscle, with a tissue-to-muscle ratio close to 1.0) while recurrent or untreated tumors are expected to have a ratio close to 3.0 in T2 weighted images [2]. In a 3D-FSE experiment, the equivalent T2 contrast (to the 2D-FSE scan) is targeted by calculating the effective echo time for a given VFA train using an Echo Phase Graph (EPG) [3] algorithm and representative relaxation values (T1rep/T2rep). Current methods choose brain tissues for these representative values, with the correction scheme validated by comparing 2D and 3D-FSE brain images [4]. To date, detailed assessments have not been performed for body applications. It is of particular interest to investigate signal and contrast changes with tissues that exhibit T2 relaxation values that are different from those in the brain using different T1rep/T2rep values.
We evaluate the performance of methods to correct the T2-contrast in 3D-FSE sequences in the treatment monitoring of a body application (cervix) which encompasses a relatively wide range of clinically important T2 values (35 ms <T2 < 84 ms) at 1.5T. 2) Furthermore, we explore the effects of using two different representative tissues to produce equivalent 2D T2 contrast in 3D-FSE.

“Photometric monitoring and period changes in BE Lyn”
Mehrnoush Zomederis, Paul A. Delaney and George J. Conidis
York University
High Amplitude Delta Scuti (HADS) stars show both radial and non-radial luminosity pulsations. The variations are due to the expansion and contraction of the star. These evolving stars are near the end of their life cycle, slowly entering the instability strip, off the main sequence on the Hertzprung-Russell (H-R) diagram. We examined BE Lyn, also known as HD 79889 using 77 new times of maximum light observed at the York University Observatory from 2005 to 2015, combined with data taken from literature. An updated linear ephemeris and O-C plot was used to calculate a more accurate period and to investigate any rate of change of its pulsation period.