Browsing by Author "Nguyen, A"
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- ItemAster-dependent nonvesicular transport facilitates dietary cholesterol uptake(American Association for the Advancement of Science (AAAS), 2023-11-10) Ferrari, A; Whang, E; Xiao, X; Kennelly, JP; Romartinez-Alonso, B; Mack, JJ; Weston, T; Chen, K; Kim, Y; Tol, MJ; Bideyan, L; Nguyen, A; Gao, YJ; Cui, LJ; Bedard, AH; Sandhu, J; Lee, SD; Fairall, L; Williams, KJ; Song, WX; Munguia, P; Russell, RA; Martin, MG; Jung, ME; Jiang, H; Schwabe, JWR; Young, SG; Tontonoz, PIntestinal absorption is an important contributor to systemic cholesterol homeostasis. Niemann-Pick C1 Like 1 (NPC1L1) assists in the initial step of dietary cholesterol uptake, but how cholesterol moves downstream of NPC1L1 is unknown. We show that Aster-B and Aster-C are critical for nonvesicular cholesterol movement in enterocytes. Loss of NPC1L1 diminishes accessible plasma membrane (PM) cholesterol and abolishes Aster recruitment to the intestinal brush border. Enterocytes lacking Asters accumulate PM cholesterol and show endoplasmic reticulum cholesterol depletion. Aster-deficient mice have impaired cholesterol absorption and are protected against diet-induced hypercholesterolemia. Finally, the Aster pathway can be targeted with a small-molecule inhibitor to manipulate cholesterol uptake. These findings identify the Aster pathway as a physiologically important and pharmacologically tractable node in dietary lipid absorption. © 2023 The Authors, exclusive licensee American Association for the Advancement of Science.
- ItemGeochemical tracers associated with methane in aquifers overlying a coal seam gas reservoir(Elsevier, 2024-07-15) Pearce, JK; Hofmann, H; Baublys, KA; Cendón, DI; Golding, SD; Herbert, SJ; Bhebhe, Z; Nguyen, A; Hayes, PJUnderstanding inter-aquifer connectivity or leakage of greenhouse gases and groundwater to aquifers overlying gas reservoirs is important for environmental protection and social licence to operate. Australia's Great Artesian Basin (GAB) is the largest artesian groundwater system in the world with groundwater extracted for agriculture, livestock, mines, energy, private or town water supply. Microbial coal seam gas (CSG) and production water are also extracted from the GAB. Here a range of groundwater tracers is used to investigate the potential for gas and groundwater connectivity between the CSG reservoir and aquifers. The GAB aquifer and alluvium contained a range of methane concentrations (0.001 to 2100 mg/L) that exhibit an increase with depth and δ13C-CH4. Aquifer and alluvium groundwater 87Sr/86Sr were in the range 0.7042 to 0.7082. CSG production waters however had non-radiogenic, distinctive 87Sr/86Sr signatures <0.7036, indicating a lack of significant groundwater leakage. One gassy aquifer bore with 160 mg/L methane conversely has 87Sr/86Sr, δ13C-CH4, δ2H-CH4 and δ13C-DIC values overlapping the CSG waters. In several aquifers δ34S-SO4 and δ18O-SO4 are sourced from windblown surface salts of inland Australian playa lakes in recharge waters. Bacterial sulphate reduction is additionally occurring in a regional aquifer. Cosmogenic isotopes and tritium show recent recharge and mixing with older groundwaters in several shallow aquifers. Groundwater and gas signatures indicate that leakage of groundwater and methane from the CSG reservoir was not occurring in the majority of areas investigated here. Methane was consistent with in situ generation in shallow GAB aquifers by primary microbial CO2 reduction or acetate fermentation. Connectivity of one alluvial bore and the underlying GAB aquifer could not be completely ruled out. Separately, one gassy Springbok GAB aquifer bore is either connected to the underlying CSG gas reservoir, or has in situ secondary microbial CO2 reduction producing methane from interbedded coal within the aquifer. This study is relevant to other basins in Australia and internationally where gas is observed in aquifers that overly conventional, unconventional or coal seam gas reservoirs. © 2024 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
- ItemIncreased phase coherence length in a porous topological insulator(American Physical Society (APS), 2023-06-15) Nguyen, A; Akhgar, G; Cortie, DL; Bake, A; Pastuovic, Z; Zhao, W; Liu, C; Chen, YH; Suzuki, K; Fuhrer, MS; Culcer, D; Hamilton, AR; Edmonds, MT; Karel, JThe surface area of Bi2Te3 thin films was increased by introducing nanoscale porosity. Temperature dependent resistivity and magnetotransport measurements were conducted both on as-grown and porous samples (23 and 70 nm). The longitudinal resistivity of the porous samples became more metallic, indicating the increased surface area resulted in transport that was more surfacelike. Weak antilocalization was present in all samples, and remarkably the phase coherence length doubled in the porous samples. This increase is likely due to the large Fermi velocity of the Dirac surface states. Our results show that the introduction of nanoporosity does not destroy the topological surface states but rather enhances them, making these nanostructured materials promising for low energy electronics, spintronics and thermoelectrics. ©2023 American Physical Society
- ItemTest-retest reliability and inter scanner variability of 11C-raclopride striatal binding potentials between two INVEON PET/CT imaging systems for naïve Sprague Dawley rats(Wiley, 2014-04-16) Callaghan, PD; Zahra, D; Wimberley, CA; Arthur, A; Rahardjo, GL; Hamze, H; Davis, E; Nguyen, A; Boisson, F; Perkins, G; Pascali, G; Reilhac, A; Grégoire, MCBackground: 11C-raclopride is a routine tracer for quantification of dopamine D2 receptors in neurological and psychiatric disease. D2 imaging in key longitudinal models has significant utility of understanding mechanisms and therapeutic interventions. Aims: Optimisation of preclinical imaging and data analysis protocols for 11C-raclopride in rat brain. Methods: a) Test-retest reliability: Naïve male Sprague Dawley rats (n = 6) underwent test-retest assessment of binding potential variability, with two scans, 1 week apart. Rats were anaesthetised (1–5% isoflurane) and received 11C-raclopride (>0.1 nmol, 20–40 MBq) during 1 hour image acquisition (Siemens Inveon PET/CT), followed by a 10 minute CT scan. b) Assessment of the intersystem variability of the INVEON scanners (n = 12). Test-retest experiments were performed on a second INVEON system. c) Assessment of inter system variability with arterial blood sampling (n = 5). Acquisitions were performed (as above) with prior femoral artery cannulation: 23 blood samples (∼30 ul) were collected during PET acquisition, and plasma metabolite corrected input functions generated. PET list mode data were histogrammed (23 frames) and reconstructed with 2D filtered backprojection algorithm. The impact of some post-reconstruction image processing techniques, such iterative deconvolution of the image and data denoising techniques, onto the accuracy and reliability of the computed parameter of interest were also investigated. Binding potential parametric maps were calculated from the dynamic PET data (using either a standard reference tissue modelling using the cerebellum TAC (test-retest), and or a 2 compartment kinetic modelling with input function). Preliminary results: Significant improvements were seen for tissue activity data after denoising /iterative deconvolution (see figure). Analysis of binding potential data are currently in progress. Conclusion: Assessment of within and intersystem variability will aid the appropriate statistical design of future longitudinal 11C-raclopride imaging studies. Improvements from post-reconstruction image processing techniques show significant benefits. © 1999-2022 John Wiley & Sons, Inc.
- ItemTop-down patterning of topological surface and edge states using a focused ion beam(Springer Nature, 2023-03-27) Bake, A; Zhang, Q; Ho, CS; Causer, GL; Zhao, WY; Yue, ZJ; Nguyen, A; Akhgar, G; Karel, J; Mitchell, DRG; Pastuovic, Z; Lewis, RA; Cole, JH; Nancarrow, M; Wang, XL; Cortie, DLThe conducting boundary states of topological insulators appear at an interface where the characteristic invariant ℤ2 switches from 1 to 0. These states offer prospects for quantum electronics; however, a method is needed to spatially-control ℤ2 to pattern conducting channels. It is shown that modifying Sb2Te3 single-crystal surfaces with an ion beam switches the topological insulator into an amorphous state exhibiting negligible bulk and surface conductivity. This is attributed to a transition from ℤ2 = 1 → ℤ2 = 0 at a threshold disorder strength. This observation is supported by density functional theory and model Hamiltonian calculations. Here we show that this ion-beam treatment allows for inverse lithography to pattern arrays of topological surfaces, edges and corners which are the building blocks of topological electronics. Open Access This article is licensed under a Creative Commons Attribution 4.0 © Crown Copyright 2023
- ItemTransport measurements in porous Bi2Te3 thin films(American Physical Society, 2022-03-16) Akhgar, G; Nguyen, A; Cortie, DL; Bake, A; Zhao, WY; Liu, C; Fuhrer, MS; Culcer, D; Hamilton, AR; Edmonds, MT; Karel, JRecent theoretical work has predicted the existence of disordered topological insulators , however, minimal experimental work has been conducted on disordered TIs. Here we used molecular-beam epitaxy (MBE) to grow Bi2Te3 thin films that were comprised of nanocrystals embedded in an amorphous matrix. Further disorder was introduced through Ne ion irradiation which produced porosity in the films. In this talk we will present magnetoresistance measurements on porous Bi2Te3, where weak anti-localisation (WAL) was observed. The magnetoresistance curves were fitted using a Dirac Fermion model specifically derived to model weak antilocalization in TIs. Our results also show that the temperature dependence of the phase coherence length in porous Bi2Te3, with an increased surface to volume ratio, exhibits 2D-like transport.