Chukun Gao

Last Name

Gao

First Name

Chukun

ORCID

0000-0002-8614-6304

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Publications 1 - 10 of 12

Two millimeter diameter spherical rotors spinning at 68 kHz for MAS NMR
Chen, Pin-Hui; Gao, Chukun; Price, Lauren E.; et al. (2021)
Journal of Magnetic Resonance Open
Spherical rotors are a new paradigm in magic angle spinning (MAS) solid-state nuclear magnetic resonance (NMR). The simple geometry makes smaller diameter spheres and their utilization within narrow-bore NMR probes feasible. Here we report a 68 kHz spinning frequency of 2 mm diameter spheres using helium spinning gas outside the magnet and demonstrate the use of KMnO₄ to adjust the magic angle at a spinning frequency of 59.3 kHz for MAS NMR. We observe third-order spinning sidebands in the ⁵⁵Mn spectrum clearly showing the MAS frequency of 59.3 kHz, with KBr showing nearly no first-order spinning sidebands at a similar frequency. The spinning stability was ±0.5% during data acquisition without spinning regulation. To address concerns about the low NMR filling factor of MAS spheres, we employ a modified stator and a smaller coil and achieve three times higher NMR sensitivity then our previous coil geometries for MAS spheres. Advanced coil and rotor fabrication technologies are expected to further increase the spinning frequency and NMR sensitivity of MAS spheres.
Fabrication Procedures and Mechanical Supports of No-Insulation All-GdBCO Double Pancake Magnets in Liquid Helium
Gao, Chukun; Chen, Pin-Hui; Alaniva, Nicholas; et al. (2024)
IEEE Transactions on Applied Superconductivity
The no-insulation (NI) high-temperature superconductor (HTS) winding technique enables the fabrication of highly compact magnets with self-quench protection. NI pancake coils are implemented to develop a 28-T HTS magnet for the operation of a 792-GHz gyrotron, which is a microwave source for dynamic nuclear polarization nuclear magnetic resonance. To this end, three NI all-GdBCO double pancake (DP) magnets were fabricated using different winding diameters and procedures. The objective was to explore different mechanical coil protection mechanisms at high magnetic fields, including clamping, overband, and solder impregnation. Experiments in liquid helium using magnets with winding diameters of 18, 25, and 66 mm yielded a center field of 14.4, 11.2, and 8.1 T, respectively. The maximum currents applied to the DP magnets ranged from 780 to 1000 A. Both the 18 and 66 mm DP coils contained 400 m (2 × 200 m) HTS tape, while the 25 mm seamless DP coil consisted of only one continuous 200 m HTS tape. The 25 mm magnet with solder impregnation showed the best repeatability, although the current density was reduced owing to the solder thickness between the coil windings. Critical to the implementation of such coils in liquid helium is to effectively transfer high currents to the magnet, while not compromising the helium boil-off. Furthermore, the design of hybrid copper-HTS current leads capable of carrying current larger than 1000 A from room temperature to the HTS magnet at 4.2 K is presented. The implementation of liquid nitrogen-cooled hybrid copper-HTS current leads reduced the helium boil-off and permitted independent temperature control of the current leads.
Improving the sensitivity of MAS spheres using a 9.5 mm spherical shell with 219 μL sample volume spinning in a spherical solenoid coil
Gao, Chukun; Chen, Pin-Hui; Däpp, Alexander; et al. (2022)
Journal of Magnetic Resonance
Spherical rotors in magic angle spinning (MAS) nuclear magnetic resonance (NMR) experiments have potential advantages relative to cylindrical rotors in terms of ease of fabrication, low risk of rotor crash, easy sample exchange, and better microwave access. However, one major disadvantage so far of spherical rotors is poor NMR filling factor due to the small sample volume and large cylindrical radiofrequency (RF) coil. Here we present a novel NMR coil geometry in the form of a spherical coil. The spherical coil best fits the spherical sample to maximize sensitivity, while also providing excellent RF homogeneity. We further improve NMR sensitivity by employing a spherical shell as the rotor, thereby maximizing sample volume (219 μL in this case of 9.5 mm outer diameter spheres). The spinning gas is supplied by a 3D-printed ring stator external to the coil, thereby introducing a simplified form of MAS stators. In this apparatus, the RF field generated along the coil axis is perpendicular to the external magnetic field, regardless of rotor orientation. We observe a linear increase in sensitivity with increasing sample volume. We also simulate the RF performance of spherical and cylindrical solenoid coils with constant or variable pitch for spherical and cylindrical rotors, respectively. The simulation results show that spherical solenoid coils generate comparable B1 field intensities but have better homogeneity than cylindrical solenoid coils do.
Data-Driven Prediction of Molecular Biotransformations in Food Fermentation
Zhang, Dachuan; Jia, Cancan; Sun, Dandan; et al. (2023)
Journal of Agricultural and Food Chemistry
Fermentationproducts, together with food components, determinethe sense, nutrition, and safety of fermented foods. Traditional methodsof fermentation product identification are time-consuming and cumbersome,which cannot meet the increasing need for the identification of theextensive bioactive metabolites produced during food fermentation.Hence, we propose a data-driven integrated platform (FFExplorer, http://www.rxnfinder.org/ffexplorer/) based on machine learning and data on 2,192,862 microbial sequence-encodedenzymes for computational prediction of fermentation products. UsingFFExplorer, we explained the mechanism behind the disappearance ofspicy taste during pepper fermentation and evaluated the detoxificationeffects of microbial fermentation for common food contaminants. FFExplorerwill provide a valuable reference for inferring bioactive "darkmatter" in fermented foods and exploring the application potentialof microorganisms.
Watch-sized 12 Tesla all-high-temperature-superconducting magnet
Chen, Pin-Hui; Gao, Chukun; Alaniva, Nicholas; et al. (2023)
Journal of Magnetic Resonance
We demonstrate the construction of 7 Tesla and 12 Tesla all high-temperature-superconducting (HTS) magnets, small enough to fit on your wrist. The size of the magnet reduces the cost of fabrication, decreases the fringe field to permit facile siting of magnets, and decreases the stored energy of high field magnets. These small HTS-based magnets are being developed for gyrotron microwave sources for use in high-field nuclear magnetic resonance applications. The 7 Tesla and 12 Tesla magnets employ a no-insulation winding technique and are cooled to 4.2 Kelvin in a liquid helium cryostat. The 7 Tesla magnet is a single pancake coil, made of only 9.4 m of HTS tape, with an inner diameter of 8 mm and an outer diameter of 24 mm. This magnet was charged up to 1168 Amperes, generating a field of 7.3 Tesla. The 12 Tesla magnet is comprised of two pancake coils (inner diameter of 10 mm and outer diameter of 27 mm) connected in series. This magnet reached its maximum field at a current of 850 Amperes.
Highly stable magic angle spinning spherical rotors
Popp, Thomas M. Osborn; Däpp, Alexander; Gao, Chukun; et al. (2020)
Magnetic Resonance
Data-Driven Elucidation of Flavor Chemistry
Kou, Xingran; Shi, Peiqin; Gao, Chukun; et al. (2023)
Journal of Agricultural and Food Chemistry
Flavor molecules are commonly used in the food industry to enhance product quality and consumer experiences but are associated with potential human health risks, highlighting the need for safer alternatives. To address these health-associated challenges and promote reasonable application, several databases for flavor molecules have been constructed. However, no existing studies have comprehensively summarized these data resources according to quality, focused fields, and potential gaps. Here, we systematically summarized 25 flavor molecule databases published within the last 20 years and revealed that data inaccessibility, untimely updates, and nonstandard flavor descriptions are the main limitations of current studies. We examined the development of computational approaches (e.g., machine learning and molecular simulation) for the identification of novel flavor molecules and discussed their major challenges regarding throughput, model interpretability, and the lack of gold-standard data sets for equitable model evaluation. Additionally, we discussed future strategies for the mining and designing of novel flavor molecules based on multiomics and artificial intelligence to provide a new foundation for flavor science research.
Design and Implementation of a Mechanical Semipersistent Switch for HTS Magnets
Käser, Timon; Björgvinsdóttir, Snædís; Gao, Chukun; et al. (2025)
IEEE Transactions on Applied Superconductivity
Persistent-mode operation of superconducting magnets requires a persistent switch, usually a heater, to close their superconducting circuits. Here, we describe a mechanical copper switch that utilizes pressure to vary resistance. This switch is designed to provide a low-resistance short between two high-temperature superconducting (HTS) charging electrodes in an all-HTS pancake-coil magnet. The switch is able to achieve a contact resistance as low as 460 n ohm by pressing gold-coated copper surfaces together at 3.0 kN. At 77 K, with an HTS pancake coil charged to 0.45 T, the magnetic field decayed slowly with the switch closed. The decay fits to a 3.6-mu ohm resistance, most of which arises from unrelated insufficient connections within the HTS magnet itself. The design shows the potential of building a persistent-mode superconducting magnet with a mechanical switch, where, as an example, a 30-T magnet with an inductance of 5.9 H has a field drift of -6 ppm/h.
In Situ Detection of Endogenous HIV Activation by Dynamic Nuclear Polarization NMR and Flow Cytometry
Overall, Sarah A.; Price, Lauren E.; Albert, Brice J.; et al. (2020)
International Journal of Molecular Sciences
We demonstrate for the first time in-cell dynamic nuclear polarization (DNP) in conjunction with flow cytometry sorting to address the cellular heterogeneity of in-cell samples. Utilizing a green fluorescent protein (GFP) reporter of HIV reactivation, we correlate increased 15N resonance intensity with cytokine-driven HIV reactivation in a human cell line model of HIV latency. As few as 10% GFP+ cells could be detected by DNP nuclear magnetic resonance (NMR). The inclusion of flow cytometric sorting of GFP+ cells prior to analysis by DNP-NMR further boosted signal detection through increased cellular homogeneity with respect to GFP expression. As few as 3.6 million 15N-labeled GFP+ cells could be readily detected with DNP-NMR. Importantly, cell sorting allowed for the comparison of cytokine-treated GFP+ and GFP− cells in a batch-consistent way. This provides an avenue for normalizing NMR spectral contributions from background cellular processes following treatment with cellular modulators. We also demonstrate the remarkable stability of AMUPol (a nitroxide biradical) in Jurkat T cells and achieved in-cell enhancements of 46 with 10 mM AMUPol, providing an excellent model system for further in-cell DNP-NMR studies. This represents an important contribution to improving in-cell methods for the study of endogenously expressed proteins by DNP-NMR.
23 Tesla high temperature superconducting pocket magnet
Gao, Chukun; Chen, Pin-Hui; Alaniva, Nicholas; et al. (2024)
Superconductor Science and Technology
We present a compact 23 T no-insulation (NI) magnet that was wound with 60 m of 10 mm wide high temperature superconducting (HTS) tape. The magnet consists of only one pocket-sized double pancake (DP) coil with an inner diameter of ∼6 mm, a height of 20 mm, and an outer diameter of 41.6 mm. Another NI coil of similar size but with a larger inner diameter of 8 mm reached a slightly lower magnetic field of 21 T. We also present a smaller coil which was wound with only 20 m of HTS tape and still achieved a magnetic field of 16 T. During the experiments in liquid helium, each coil was charged to a current between 690 A and 850 A, corresponding to a high current density of 1500–1900 A mm−2. The small bore size and high current density contributed to the high fields generated by these coils. We present the fabrication details, helium tests and repeatability analysis of these 'pocket' magnets.

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Chukun Gao

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