A5042697710- Physics of Superconductivity and Magnetism
- Quantum, superfluid, helium dynamics
- Superconducting Materials and Applications
- High-pressure geophysics and materials
- Atomic and Subatomic Physics Research
- Science Education and Pedagogy
- Advanced Condensed Matter Physics
- Rare-earth and actinide compounds
- Superconductivity in MgB2 and Alloys
- Magnetic and transport properties of perovskites and related materials
- Magnetic properties of thin films
- Iron-based superconductors research
- Children's Physical and Motor Development
- Aerogels and thermal insulation
- Surface Modification and Superhydrophobicity
- Methane Hydrates and Related Phenomena
- Magnetic Properties of Alloys
- Innovative Teaching Methods
- Inorganic Fluorides and Related Compounds
- Sports Performance and Training
- Problem and Project Based Learning
- Gyrotron and Vacuum Electronics Research
- Body Composition Measurement Techniques
- Advanced Thermodynamic Systems and Engines
- Quantum and electron transport phenomena
University of British Columbia
2012-2024
University of British Columbia Hospital
2022
Vancouver Foundation
2020
Schools of Visual Arts, The Royal Danish Academy of Fine Arts
2017-2018
University of Alberta
2005-2011
Georgia Institute of Technology
2004
University of Lethbridge
1997
Westinghouse Electric (Japan)
1972
Simon Fraser University
1967
In the quest for superconductors with high transition temperatures (T$_\mathrm{c}$s), one emerging motif is that unconventional superconductivity enhanced by fluctuations of a broken-symmetry phase near quantum-critical point. While recent experiments have suggested existence requisite broken symmetry in high-T$_\mathrm{c}$ cuprates, signature electronic structure has thus far remained elusive, leaving their importance question. We use magnetic fields exceeding 90 tesla to access underlying...
Mesopontine cholinergic neurons have long been thought to play a key role in behavioral state control. In particular, they implicated the process of EEG desynchrony and generation rapid eye movement (REM) sleep. However, profile identified mesopontine has not unequivocally demonstrated. an attempt address this issue, vivo microdialysis was used monitor acetylcholine (ACh) release across rat thalamus, major projection site neurons. Because REM periods rats are short duration, method developed...
The recent torsional oscillator results of Kim and Chan suggest a supersolid phase transition in solid 4He. We have used piezoelectrically driven diaphragm to study the flow helium through an array capillaries. Our measurements showed no indication low temperature flow, placing stringent restrictions on response pressure difference. average speed at temperatures was less than 1.2x10-14 m/s, corresponding velocity least 7 orders magnitude smaller critical velocities inferred from measurements.
Nematicity has emerged as a key feature of cuprate superconductors, but its link to other fundamental properties such superconductivity, charge order, and the pseudogap remains unclear. Here we use measurements transport anisotropy in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{y}$ distinguish two types nematicity. The first is associated with short-range charge-density-wave modulations doping region near $p=0.12$. It detected Nernst coefficient, not resistivity. second type prevails...
[This paper is part of the Focused Collection on Gender in Physics.] It established that male students outperform female almost all commonly used physics concept inventories. However, there significant variation factors contribute to gap, as well direction which they influence it. presently unknown if such a gender gap exists relatively new Concise Data Processing Assessment (CDPA) and, therefore, whether gendered actions teaching lab might influence—or be influenced by—the gap. To begin get...
The recent torsional oscillator results of Kim and Chan suggest a supersolid phase transition in solid 4He confined Vycor. We have used capacitive technique to directly monitor density changes for helium Vycor at low temperature piezoelectrically driven diaphragm study the pressure-induced flow into pores. Our measurements showed no indication mass redistribution that could mimic decoupling put an upper limit about 0.003 microm/s on any pores
Torsional oscillator experiments on solid 4He show frequency changes which suggest mass decoupling, but the onset is broad and accompanied by a dissipation peak. We have measured elastic shear modulus over range, from 0.5 Hz to 8 kHz, observe similar behavior-stiffening These features are associated with dynamical crossover in thermally activated relaxation process disordered system rather than true phase transition. If there transition dc response, e.g., supersolid state, it must occur below 55 mK.
Recent experiments showed that the shear modulus of solid 4He stiffens in same temperature range (below 200 mK) where mass decoupling and supersolidity have been inferred from torsional oscillator measurements. The two phenomena are clearly related crystal defects, particularly dislocations, appear to be involved both. We studied effects annealing applying large stresses on elastic properties 4He, using both acoustic resonances direct low-frequency low-amplitude measurements modulus. Both...
Vortices in a type-II superconductor form lattice structure that melts when the thermal displacement of vortices is an appreciable fraction distance between vortices. In anisotropic high-Tc superconductor, such as YBa2Cu3Oy, magnetic field value where this melting occurs can be much lower than mean-field critical Hc2. We examine transition YBa2Cu3Oy with oxygen content y from 6.45 to 6.92, and fit data theory vortex-lattice melting. The quality fits indicates resistive state indeed vortex...
The Concise Data Processing Assessment (CDPA) was developed to probe student abilities related the nature of measurement and uncertainty handling data. diagnostic is a ten question, multiple-choice test that can be used as both pre-test post-test. A key component development process interviews with students, which were uncover common modes thinking validate item wording. To evaluate reliability discriminatory power this diagnostic, we performed statistical tests focusing on analysis (item...
Aerogels are very compliant materials---even small stresses can lead to large deformations. In this paper we present measurements of the linear deformation high porosity aerogels during adsorption low surface tension fluids, performed using a variable differential transformer. We show that significant occur under conditions common in studies helium aerogel, and degree aerogel capillary condensation scales with tension. This scaling may then be used suggest limits on safe temperatures for...
Torsional oscillator experiments show evidence of mass decoupling in solid 4He. This is amplitude dependent, suggesting a critical velocity for supersolidity. We observe similar behavior the elastic shear modulus. By measuring modulus over wide frequency range, we can distinguish between an dependence which depends on and one some other parameter such as displacement. In contrast with torsional behavior, magnitude stress, not velocity. interpret our results terms motion dislocations are...
The motion of electrons in the vast majority conductors is diffusive, obeying Ohm’s law. However, recent discovery and growth high-purity materials with extremely long electronic mean free paths has sparked interest non-Ohmic alternatives, including viscous ballistic flow. Although transport regimes have been discovered across a range materials—including two-dimensional electron gases, graphene, topological semimetals, delafossite metals—determining their nature proved to be challenging....
Abstract Metabolic fate of xenobiotics in plant tissues has an important role the ultimate these compounds natural and engineered systems. Chlorophenols are class used a variety biocides have been shown to be resistant microbial degradation. Three chlorophenyl glycosides were extracted from Lemna minor exposed 2,4-dichlorophenol (DCP). The products identified as 2,4-dichlorophenyl-β-D-glucopyranoside (DCPG), 2,4-dichlorophenyl-β-D-(6-O-malonyl)-glucopyranoside (DCPMG)...
Reconstruction of the Fermi surface in cuprate YBa${}_{2}$Cu${}_{3}$O${}_{y}$ is thought to be caused by one two types charge-density waves. Identifying which responsible could help researchers understand high-temperature superconductivity that cuprates exhibit. New experiments show short-range two-dimensional waves lead reconstruction.
We have studied the microwave electrodynamics of single crystal iron-based superconductors Ba$_{0.72}$K$_{0.28}$Fe$_2$As$_2$ (hole-doped, $T_\mathrm{c}$ $\approx $30 K) and Ba(Fe$_{0.95}$Co$_{0.05}$)$_2$As$_2$ (electron-doped, $\approx$20 K), by cavity perturbation broadband spectroscopy. SQUID magnetometry was used to confirm quality homogeneity samples under study. Through techniques, temperature dependence in-plane London penetration depth $\Delta\lambda(T)$, therefore superfluid phase...
Data are presented for the first use of novel DNA-barcoded aerosol test particles that have been developed to track fate airborne contaminants in populated environments. Until DNATrax (DNA Tagged Reagents Aerosol eXperiments) were developed, there was no way rapidly validate air transport models with realistic respirable range 1–10 μm diameter. The particles, at Lawrence Livermore National Laboratory (LLNL) and tested assistance Pentagon Force Protection Agency, safe effective materials...
The electrical resistivity rho_c of the underdoped cuprate superconductor YBCO was measured perpendicular to CuO_2 planes on ultra-high quality single crystals in magnetic fields large enough suppress superconductivity. incoherent insulating-like behavior at high temperature, characteristic all cuprates, is found cross over a coherent regime metallic low temperature. This crossover coincides with emergence small electron pocket detected Fermi surface via quantum oscillations, Hall and...
We have investigated the adsorption and desorption of helium near its liquid-vapor critical point in silica aerogels with porosities between 95% 98%. used a capacitive measurement technique which allowed us to probe density inside aerogel directly, even though samples were surrounded by bulk helium. The aerogel's very low thermal conductivity resulted long equilibration times so we monitored pressure density, both surrounding bulk, waited at each until all had stabilized. Our measurements...
Following recent torsional oscillator measurements which appear to show the 'non-classical rotational inertia' characterizes a supersolid, number of experiments have searched for evidence unusual behavior in other properties. We developed new technique measuring shear modulus solid helium at low frequencies and small strains. In hexagonal close packed (4)He, increases dramatically below 200 mK, temperature range where decoupling is seen oscillators. The anomaly frequency independent, depends...