Student Talks
Prospect of detecting scalar-field bubbles surrounding black-hole mergers
Mr. Samson Leong
11:40-11:55 in Astrophysics & Cosmology Session
In the past decade, gravitational-wave astronomy has provided us with a means to probe the strong-field regime of gravity and give us access to previously unobserved phenomena such as black-hole mergers. While being extremely successful to date, the true promise of gravitational-wave astronomy is its capability to identify signatures of physics beyond the Standard Model and General Relativity. In this study, we assess the detectability of one such case: a generic scalar field 'bubble' that surrounds binary black-hole mergers with a total mass of 100 Solar Mass. To this end, we perform Bayesian parameter estimation and model selection on numerically simulated signals from such systems injected in Advanced LIGO-Virgo noise. For a gravitational-wave signal at the typical loudness of current detections, we show that scalar fields with a magnitude of 0.01 can be conclusively disentangled from those that originated in a pure vacuum system.
Study of the Magnetic Horn for Neutrinos from Stored Muons (nuSTORM)
Mr. Hon Kin Chu
11:40-11:55 in Computational & Experimental Session
The performance of the proposed magnetic horn to be used in the Neutrinos from Stored Muons, nuSTORM, facility is investigated. The meson production process is monitored using simulations. The target and horn geometry were created using pyg4ometry. A magnetic field region inversely proportional to the radius is defined in the horn. Using a FLUKA simulation, a 100 GeV proton beam impinges on the target inside the horn which then focuses and delivers the produced pions into the pion transfer line. Different horn currents were applied for delivering 2.64, 5 and 7.2 GeV/c pions. The phases spaces of the pion beam were plotted using ROOT. Setting the emittance to 0.2 cm, the Twiss parameters are determined to be α = −0.42 ± 0.01, β = 410 ± 1 cm and γ = 0.00287 ± 0.00002 cm^−1 such that the best acceptance can be achieved.
Features Detection following the SuperNova Early Warning System
Mr. Ho Yeung Tse
11:55-12:10 in Astrophysics & Cosmology Session
The calculation is based on the SuperNova Early Warning System (SNEWS) which utilizes the early-arriving neutrino signals to predict the supernova. Calculations of the System aim to provide a fairly accurate probability sky-map of the location where the predicted supernova could be observed in the sky, and to anticipate some features of the supernova. Detected arrival time and the locations of different neutrinos will be used to perform a triangulation calculation to foresee the direction of incoming supernova, while analyzing the data gathered from neutrino burst can lead to the prognosis of features of the supernova. Algorithms detecting peaks, sudden drops and other features from Poisson distributed data are used. The feature detection component would be the main focus for the sharing.
SURE in SFU
Mr. Siu Chung Chan
11:55-12:10 in Computational & Experimental Session
1. Summary of my trip (4 mins) 2. Summary of my research (5 mins) 3. Conclusion (1 mins)
How fast is the Universe expanding?
Mr. Wangzheng ZHANG
12:10-12:25 in Astrophysics & Cosmology Session
The Hubble parameter is one of the most important cosmological parameters in the LCDM model, which describes the expanding rate of our universe. There is a famous deviation in the Hubble parameter measurements (Hubble tension), i.e., the Hubble parameter measured locally (by distance ladder, around 73.2+-1.2 km/s/Mpc) and globally (by Cosmic microwave background, 67.27+-0.6 km/s/Mpc). It is really necessary to develop more new independent measurements on the Hubble parameter. Then, in this talk, we will present a new way to measure the Hubble parameter nowadays using mean peculiar pairwise velocity, by combining observational data (Cosmicflows-3) and N-body simulations (Gadget-2).
Towards the Design of a Conformational Switchable Zinc Finger Analogue Regulating Cellular Behaviors
Mr. Ziqi WANG
12:10-12:25 in Computational & Experimental Session
Dynamic conformational changes in the secondary structures of proteins are essential to their functions and can regulate diverse cellular events. Herein, along with our experimental collaborators, we report the design of a synthetic polymer-based secondary structure analogue of Zinc finger (ZnF). Acting as a conformational switch between unfolded and folded states triggered by the addition of Zn2+ and EDTA, ZnF enables the manipulation of the accessibility of conjugated cell adhesive ligands to cell membrane receptors. On the basis of the self-avoiding walk (SAW) model, we computed the free energy barrier that the zinc coordination motif had to overcome and predicted the feasible length of the polymer chains. Our work provided guidance to experimental research on the synthesis of dynamic secondary structures to mediate desired cellular functions, such as the regulation of mechanosensing and differentiation of stem cells.
Investigation of the Massive Infrared Dark Cloud in Star Formation
Ms. Yanhanle ZHAO
12:25-12:40 in Astrophysics & Cosmology Session
The Massive infrared dark clouds have been investigated to analyse the early evolution of protostellar clusters. Research on these dense clouds may reveal the gas dynamics and the formation of the protostars of different scales. We study the sensitive 1.3 mm continuum and spectral line emission data from CO, 13CS, and N2D+ of the G14.225-0.506 cloud using the Atacama Large Millimeter/Submillimeter Array (ALMA). By the interferometry techniques and Common Astronomy Software Applications (CASA), images of different pointings of the G14.225-0.506 cloud are generated from the calibrated observational data, from which the physical and chemical properties of clumps fragmentation, outflow dynamics, etc. could be explored in further analysis to better understand the formation of stars.
Control over Light Soaking Effect in All-Inorganic Perovskite Solar Cells
Ms. XIAO WU
12:25-12:40 in Computational & Experimental Session
Perovskite solar cells (PSCs) have drawn attractive attention in photovoltaic community, among which the single-junction organic-inorganic hybrid PSCs have realized a remarkable efficiency of 25.7%. However, the incorporation of organic A-site cations, such as methylammonium (MA+) and formamidinium (FA+), imposes intrinsic drawbacks in thermal and light stability, being inevitable obstacles on the road of the commercialization of PSCs. Consequently, extensive research efforts have been devoted to developing all-inorganic PSCs, most of which employ Cesium ions to replace the organic cations. My recent studies on the all-inorganic PSCs found that constant light illumination on the device would cause increases of efficiency outputs, which is known as light soaking (LS) effect. In this talk, I will discuss on how the light would influence the device performance of CsPb(I1-xBrx)3 based PSCs, followed by the mechanism behind, and the strategy to minimize the LS effect for more stable output.
Emulating Cosmological Growth Function with Machine Learning
Mr. Ngai Pok Kwan
14:25-14:40 in Astrophysics & Cosmology Session
Growth function is an important parameter in cosmological simulations. It governs the movements and clustering of matter. Analytically, calculating the growth function requires solving an ordinary differential equation. However, solving an ODE in each step of the simulation is time-consuming. Therefore, an emulator is used to speed up the calculation. The emulator consists of two parts, the artificial neural network part and interpolation part. The neural network predicts the position and value of knots for interpolation. The third-order B-Spline interpolation is used to ensure the growth function is smooth and differentiable.
Sensor control and DAQ software development for use with underground cryogenic experiments operating transition edge sensor light detectors
Ms. Ying Chan
14:25-14:40 in Computational & Experimental Session
The Cryogenic Underground Observatory of Rare Events (CUORE) experiment searches for the neutrinoless double beta decay (0νββ) in 130Te at the Gran Sasso National Laboratory (LNGS) in Italy. In order to catch the rare decay event, highly pure crystals of tellurium dioxide (TeO2) are used as bolometers under ultra-cold cryogenic temperatures. To maintain the sensitivity of the crystal detectors, temperature must be in the millikelvin range and is carefully monitored and maintained by a cryostat. In order to monitor the cryostat, the Triton software communicates with the pressure sensors to provide continuous feedback. Switching from Leybold CENTER THREE to GRAPHIX THREE pressure controller, the communication between Triton software and GRAPHIX THREE becomes different from that with CENTER THREE. I developed a translator program to facilitate serial communication between the devices. This translator program is written on a Raspberry Pi in Python which can be generalized and extended to other monitoring applications. Also, in order to monitor the data detection with the transition edge sensor light detectors (TES) outside the Faraday room, we have developed a software that allows instant display with the data taken. This aims to be a high-performance DAQ that may be of use to a variety of experiments. Here I will explain the design of the translator program, and I will also discuss the implementation of the data acquisition software in LabVIEW which allows remote monitoring of data taking and can generate real-time noise power spectra with configurable averaging, allowing for quick evaluation of noise conditions.
The relativistic modeling of tidal disruption event rate as a function of supermassive black hole mass and spin
Mr. Hao Tse HUANG
14:40-14:55 in Astrophysics & Cosmology Session
The tidal disruption event (TDE) occurs when an unfortunate star in a galactic nucleus comes too close to the supermassive black hole (SMBH) and gets torn apart by the tidal force. Part of the debris of the destroyed star will subsequently be accreted onto the SMBH, and in the process leads to the luminous flare detectable by the telescope. The rate at which the TDE can happen is increasingly suppressed by the growth of the black hole mass and the event horizon. Since both the strength of the tidal force and the size of the event horizon are dependent on not only the mass but also the spin of the SMBH, measuring the TDE rate as a function of SMBH mass has the potential to reveal the spin distribution of the SMBH in the universe. In this talk, I will show how the analytical form of the relativistic tidal force can be combined with the numerical method to predict the TDE rate as a function of SMBH mass and spin, which can be compared with future observation surveys that promise to detect hundreds, if not thousands, TDEs. I will also highlight the importance of another often-ignored factor, stellar population age, in interpreting future observation data.
Crystal Channelling for Hadron Therapy Accelerators
Mr. Hoi Lun Ng
14:40-14:55 in Computational & Experimental Session
Crystal channelling is a process that bends charged particles using the cumulative electrostatic forces from the lattice structure of a crystal. It has a great prospect in accelerator-related applications, especially as a replacement for kicker magnets due to its compact size. While many studies on crystal channelling have been conducted, most of them are focusing on the application with high-energy beam as used in the Super Proton Synchrotron and Large Hadron Collider. In this study, crystal channelling in low energy (KE from 60 to 250MeV) for hadron therapy treatments in a medical accelerator is investigated. The behaviour of the crystal was explored both in isolation, to understand its physical properties, and within the context of a full accelerator, to replace an extraction septum magnet used in the Proton-Ion Medical Machine Study (PIMMS) synchrotron with the use of a Monte-Carlo simulation programme combining beam dynamic simulations with particle-matter interactions. We demonstrate that the channelling effect, with many real-life application potential, was difficult to obtain at low energies.
Constraining gravitational wave amplitude birefringence with GWTC-3
Mr. Chi Kit Ng
14:55-15:10 in Astrophysics & Cosmology Session
One of the major problems that physicists are facing nowadays is Einstein's theory of general relativity (GR) does not agree with quantum theories at some length scales. In recent decades, theorist has been working on many beyond-GR theories to unify both of them. Some of these theories such as Chern-Simons gravity suggest that there is gravitational wave (GW) amplitude birefringence. In our study, we perform parameter estimation (PE) to constrain the strength of GW amplitude birefringence. Compare to similar previous studies on the same topic, we perform PE on more events, including events in the third LIGO-Virgo catalog (GWTC-3); and we used a more accurate model of birefringence to describe the phenomenon. Our preliminary result shows that we can obtain a constraint tighter than all previous studies.
Self-supervised machine Learning methods for fission event classification with time projection chamber data
Mr. Ho Ting Wong
14:55-15:10 in Computational & Experimental Session
Fission properties, including the fission barrier and the charge distributions of fission fragments, are important in constraining our understanding of the symmetry energy and nuclear shell effects. An experiment investigating the fission properties of exotic nuclei in the lead region was performed with the Active-Target Time Projection Chamber (AT-TPC) at the National Superconducting Cyclotron Laboratory (NSCL). Since fission events occur with low probability, one of the challenges is to extract fission events from among the large number of background events. In this poster, we present machine learning methods to classify fission events. To minimize the need for labeling, pre-training is performed with a self-supervised task using the PointNet architecture. Fission events are then identified by examining the latent space of this model. We use both one-class support vector machines and k-means clustering on the PointNet latent space to identify fission events. Preliminary results show the capability of the model in extracting fission events. The results were compared with a non-machine learning method. The results and analysis will be presented.
Could Low-Mass-Small-Radius White Dwarfs be Fermionic Dark Matter-Admixed White Dwarfs?
Mr. Cheuk Yin LUK
15:10-15:25 in Astrophysics & Cosmology Session
Many peculiar white dwarfs with low mass and small radius have been observed. This study investigated fermionic dark matter admixed white dwarf model, which is a possible explanation of these compact white dwarfs. It was found that, due to the strong gravitational attraction of the dark matter core, an admixed white dwarf, with dark matter particle mass ranging from 0.5GeV to 100GeV, is typically smaller in size with the same total mass. Besides, the Chandrasekhar mass limit is also decreased. We developed a simple parametrisation of our result to obtain the dark matter mass fraction with known total mass and normal matter radius more easily. Our result indicates the possibility that low mass small radius peculiar white dwarf can be a fermionic dark matter white dwarf.
WS2-Flake-Sandwiched, Au-Nanodisk-Enabled High-Quality Fabry–Pérot Nanoresonators for Photoluminescence Modulation
Ms. He HUANG
15:10-15:25 in Computational & Experimental Session
The increasing demand for compact and high-performance photonic devices drives the development of optical resonators with nanoscale sizes and ultrahigh quality factors. Fabry–Pérot (FP) resonators, the most widely employed optical resonators, can support ultrahigh quality factors in the simple structure, which is particularly attractive for applications in lasers, filters, and ultrasensitive sensors. However, the construction of FP resonators with both nanoscale sizes and high quality factors has still faced challenges. Herein we demonstrate the construction of FP nanoresonators out of single Au nanodisks (NDs) and a Au film, with a WS2 flake sandwiched in between. The atomically flat surfaces of the WS2 flake and Au NDs benefit mirror alignment and boost the quality factor up to 76. The nanoresonators can support FP resonances with different mode orders in the visible region. The optical properties and formation mechanisms of the high-quality FP modes are systematically studied. The FP modes are further hybridized with excitons in the WS2 flake spacer, enabling the modulation of the WS2 indirect bandgap emissions. Our study combines the advantages of plasmonic nanoparticles and FP resonators, providing a promising platform for the development of compact nanophotonic devices such as tunable nanolasers, smart sensors, and photonic-circuit elements.
Investigation of Differentiable Gravitational Wave Phenomenological Model
Mr. Ka Ho Lam
15:35-15:50 in Astrophysics & Cosmology Session
Gravitational wave phenomenological waveform models are models for generating waveform approximants using simple analytic functions as its ansatz. Using these models, we can generate robust waveforms quickly with adequate accuracy. Hence, it is well suited to be used in gravitational wave analysis including matched filtering, parameter estimation, etc. Currently, phenomenological waveform models are constructed using similar procedures, i.e. design amplitude and phase ansatzes in segments and tunable parameters in the model’s ansatz are optimized separately. With the recent implementation of the differentiable model, namely IMRPhenomD, and the automatic differentiation algorithm, we try to optimize the entire waveform using the gradient descent method. In this short presentation, we begin with a brief introduction to gravitational wave phenomenological models. Then, we discuss how this optimization scheme can improve the model’s accuracy. Furthermore, this enables us to have a more in-depth analysis of the model’s ansatz and shed light on how we can design a better phenomenological model.
Exploring the Structure and Membrane Insertion Mechanism of VacA via Molecular Dynamics (MD)
Mr. YITAO GOU
15:35-15:50 in Computational & Experimental Session
Helicobacter pylori (H. pylori) infects over half of the human population in the world and is a main cause of stomach ulcers. As one of the major virulence factors secreted by H. pylori, Vacuolating toxin (VacA) molecules can insert into lipid bilayers and oligomerize to form a hexameric membrane channel. It has been proposed that cell vacuolation results primarily from the formation of such channels. Here, we propose a structural model of the VacA channel via molecular dynamics (MD) simulations. Our model is stabler than a previously proposed model and allows pore water to flow continuously, thereby, providing the structural support for vacuolating the cell and inducing cell apoptosis. In addition, MD captures the spontaneous insertion of the VacA N-terminal hydrophobic region into a lipid bilayer, providing a molecular picture of VacA membrane insertion mechanism.
Improved Targeted sub-threshold Search for Strongly Lensed Gravitational Waves with Sky Location Constraint
Mr. Hang Yan Chong
15:50-16:05 in Astrophysics & Cosmology Session
Gravitational lensing is an important field in both astrophysics and cosmology as it could provide a large amount of crucial information about our universe unmatched by other phenomena such as the determination of the expansion rate of the universe and the distribution of dark matter. Until recently, gravitational lensing had only been applied to observing the electromagnetic spectrum. Since the first successful observation of gravitational waves back in 2015, discussions had started to try to find lensed gravitational wave signals. However, in most cases, the lensed image should be much dimmer than the original signal, which might be buried in the noise as it could not pass the normal detection threshold. Our work would be to improve the existing TESLA searching pipeline to suit our need for lensing searches. We hope to recover the originally buried sub-threshold lensed signal from the collected data. Our work would be implemented in the TESLA pipeline for future uses.
A Look into Ultracold Molecular Physics
Mr. Chak Tim Wong
15:50-16:05 in Computational & Experimental Session
The molecular structure is studied and the common ways of cooling atoms are analyzed with the focus on the reasons for their failures in cooling molecules. The theoretical background of the formation of ultracold molecules through photo-association is demonstrated with the discussion of its applications and importance in the field and the rest.
Massive Scalar Polarization of Gravitational Wave
Mr. Cheuk Nam Chong
16:05-16:20 in Astrophysics & Cosmology Session
The famous theory of General Relativity (GR) devised by Albert Einstein prognosticates on the existence of gravitational waves[1], which is confirmed by LIGO (Laser Interferometer Gravitational-Wave Observatory) back in 2016. As travelling oscillations of gravitational field (and thus the name gravitational waves)[2], gravitational waves can be decomposed into six independent polarizations, classified into three groups of two [3]. They are the tensor polarizations, vector polarizations and scalar polarizations[3]. Tensor polarizations of gravitational waves, in GR, are massless and travel in the speed of light [1], while the other polarizations are forbidden [3]. If polarizations are massive, they would travel in a speed slower than the speed of light, determined by their frequencies and mass [1]. This project examines the possibility of the co-existence of massless tensor polarizations and massive scalar polarizations in current detections by studying the time delay between the massless tensor and massive scalar signal from the same source (twin signal), in the hope of comparing the GR and non-GR hypotheses. [1]: arXiv:1812.04350v2 [2]: arXiv:0903.0338v1 [3]: LIGO-P1700276
Heterogenous phase transition mediated by MoTe2 edge reconstruction
Mr. Haolin Liu
16:05-16:20 in Computational & Experimental Session
Molybdenum ditelluride (MoTe2) as a typical quasi-2D transition metal dichalcogenide (TMD) adopts distinct electronic behaviors for its two stable forms: hexagonal (2H) and distorted octahedral (1T′) phase. While currently various approaches are available for the preparation for one certain phase or triggering a transition between the two phases, the actual atomic reconstruction process behind the phase transition remains largely unclear. In this work, we discussed the influence of different edges in monolayer MoTe2 of 2H and 1T' phases based on the ab-initio density functional theory (DFT) method. It is found that Te vacancies introduced on the Mo edge of 2H-MoTe2 provide opportunities for a local 2H-1T′ phase change, and structure optimizations on some 1T'-MoTe2 ribbon models with proper edge Te reconstructions resulted in lowered total energy. Therefore, these specific edge components can possibly play essential roles in a spontaneous phase transition in MoTe2.
16:20-16:35 in Astrophysics & Cosmology Session
813nm Magic Wavelength Trapping for Strontium Atom
Mr. Hin Fung Tang
16:20-16:35 in Computational & Experimental Session
By cooling and trapping Boson atoms, Bose Einstein Condensation could be achieved and wave nature of atoms could be observed. If atoms could be continuously loaded into the trap, continuous Bose Einstein Condensation could be achieved and hence forming atom laser. However, there would be loss of the number of atoms during cooling. In order to reduce the loss of atom number and sustain the condensation, a high laser power with magic wavelength is needed. Through calculation, a magic wavelength of 813nm added to the current experimental setup would induce a same trapping potential between two cooling states which maximize the number of atoms, while a high laser power could increase the trap depth so atoms won't be easily escape from the trap. Therefore, a tapered amplifier is needed for amplifying a 813nm laser source, and the design and alignment of tapered amplifier is needed. With the tapered amplifier installed to the experiment, the number of atoms in the trap should be able to increase, sustaining a longer continuous Bose Einstein Condensation.