Post Doc: Low temp., superconductivity, magnetism: micro-SQUID-EPR at 30 mK on 3d/4f single molecule magnet spin qubits
EDUCATION
BSc (Physics): Jadavpur University, Kolkata
MSc (Physics): IIT Kanpur, India
PhD: IIT Kanpur, India
Post Doc: Karlsruhe Institute of Technology (KIT), Germany
RESEARCH, TEACHING, or OTHER INTERESTS
Condensed Matter Physics, Atomic and Molecular Physics, and Optics, Physical and Theoretical Chemistry
Unconventional Nuclear-Spin-Dependent Toroidal Ground States in Isotopologue ADy4 [2 × 2] Complexes Yaorong Chen, Eufemio Moreno-Pineda, Sagar Paul, Olaf Fuhr, Dieter Fenske, Wolfgang Wernsdorfer, Mario Ruben Journal of the American Chemical Society, 2026 Understanding how nuclear spin influences electronic spin relaxation in single-molecule magnets (SMMs) is essential for advancing quantum technologies. Isotopologue coordination chemistry offers a promising route to probe nuclear-spin effects, yet its role in relaxation dynamics into Single Molecule Toroic (SMT) systems remains unexplored. Here, we study two isotopically enriched ADy4 grid complexes, 164Dy4L4 (with I = 0) and 163Dy4L4 (with I = 5/2), combining μSQUID magnetometry down to 30 mK with ab initio calculations and spin-Hamiltonian modeling. Both isotopologues exhibit a pseudotoroidal ground state stabilized by noncollinear anisotropy axes and competing interactions, producing hexagonal angular maps and S-shaped hysteresis loops. The nuclear-spin-free 164Dy4L4 displays sharp quantum tunneling of magnetization (QTM) transitions, whereas hyperfine coupling in 163Dy4L4 generates a dense manifold of crossings, profoundly altering relaxation dynamics. Contrary to expectations, nuclear spins do not accelerate relaxation but promote hyperfine-mediated population transfer into the toroidal state, yielding slower dynamics and larger hysteresis openings. Temperature and sweep-rate dependences further reveal contrasting mechanisms: pure tunneling in 164Dy4L4 versus thermally assisted processes in 163Dy4L4. Overall, our findings demonstrate that nuclear spins exert a constructive and nonintuitive influence on toroidal SMMs, providing an additional lever for controlling low-temperature relaxation. Isotopically controlled lanthanide assemblies thus emerge as promising platforms for exploring quantum tunneling, spin–phonon coupling, and molecular-scale information storage/processing.
Ligand-field symmetry and magneto-optical correlations in a luminescent Dy(iii) single-molecule magnet Senthil Kumar Kuppusamy, Christian Pachl, Zhaoyang Jing, Sagar Paul, Benoît Heinrich, Olaf Fuhr, Svetlana Klyatskaya, Wolfgang Wernsdorfer, Annie K. Powell, Karin Fink, Mario Ruben Dalton Transactions, 2026 Magneto-optical correlations linking effective ligand-field (LF) symmetry and magnetization relaxation are presented for an emissive mononuclear Dy( iii) compound functioning as a single-molecule magnet (SMM).
Leveraging 3d-4f Coordination: Molecular Quantum Spring-Magnet Behavior in Axial Ni2Ln Complexes Zhaoyang Jing, Eufemio Moreno‐Pineda, Sagar Paul, Appu Sunil, Olaf Fuhr, Yaorong Chen, Wolfgang Wernsdorfer, Mario Ruben Angewandte Chemie International Edition, 2026 We report heterotrimetallic 3d–4f complexes, mimicking classical exchange spring magnets at the molecular scale. The complexes feature a linear Ni···Ln···Ni core, where the lanthanide ion is sandwiched between two Ni 2+ centers coordinated by N 3 O 3 ligand environments. The complexes are isostructural, while CASSCF calculations reveal collinear anisotropy axes and favorable electronic configurations for magnetic bistability in selected systems. Magnetic characterization via DC, AC, and µSQUID magnetometry down to 30 mK demonstrates slow magnetic relaxation and open hysteresis loops exclusively in Ni 2 Tb , Ni 2 Dy , and Ni 2 Ho . These systems exhibit ferromagnetic 3d‐4f coupling, while their isolated or antiferromagnetically coupled analogs ( Ni 2 Y , Zn 2 Tb / Dy ) and Ni 2 Er / Yb counterparts show fast relaxation and closed loops. Analysis suggests that the Ni 2+ ions alone, with modest anisotropy, deviate from the expected “hard” magnetic behavior due to a broad zero‐field QTM, while the Ln 3+ ions alone serve as the “soft” phase with large magnetic moments and sharp zero‐field QTM. Nevertheless, when brought together, their coupling and alignment of the anisotropy axis enhances the magnetic performance with exchange‐bias features mimicking the macroscopic exchange spring magnets. We highlight an optimal utilization of 3d‐4f coordination in designing molecular magnets with tunable relaxation and bistability, advancing prospects for quantum information and nanoscale magnetic devices.
A Spin Frustrated Hourglass {Gd 9 } Molecular Nanomagnet with Unusual Magnetocaloric Properties Sai P. K. Panguluri, Eufemio Moreno-Pineda, Concepción Molina-Jirón, Sagar Paul, Marc Ubach I Cervera, Emmanouil K. Charkiolakis, David Gracia, Marco Affronte, Wolfgang Wernsdorfer, Marco Evangelisti, Jürgen Schnack, Mario Ruben Journal of the American Chemical Society, 2025 High Resolution Image Download MS PowerPoint Slide We report a highly symmetric {Gd 9 } molecular nanocage with the formula [Gd 9 (BA) 16 (OH) 10 ]Cl·3(C 2 H 5 OH)·4(H 2 O), which crystallizes in the cubic space group Pn 3̅ n . The structure features two crystallographically distinct Gd 3+ ions, forming highly regular triangular Gd 3+ arrangements leading to a geometrically frustrated magnetic network. Magnetization measurements at 2 K reveal a broad plateau between 1.5 and 4 T, while zero-field heat capacity shows a Schottky anomaly centered at 0.6 K─indicative of low-lying excited states and competing magnetic interactions. The magnetocaloric effect, evaluated through both direct and indirect methods, exhibits a re-entrant profile in the isentropic curves, pointing to a nontrivial evolution of magnetic entropy under applied fields. To probe the origin of this behavior, we employed the finite-temperature Lanczos method on a model spin Hamiltonian. The results reveal that the antiferromagnetic exchange between Gd 3+ ions, combined with the frustration inherent to the {Gd 9 } geometry, leads to a degenerate ground state. An external field lifts this degeneracy, producing a regime with a sharply reduced density of states between 1.5 and 4 K, which underlies the unconventional magnetocaloric response. The {Gd 9 } cage thus represents a rare example of a spin-frustrated arrangement arising from competing antiferromagnetic interactions between the Gd 3+ . These findings demonstrate how frustrated topologies and tunable low-energy excitations can be exploited to modulate the magnetothermal properties, with potential implications for cryogenic magnetic cooling technologies.
Chiral Dysprosium-[7]Helicene Macrocycles Showing Record Single-Molecule Magnet Properties in the Lanthanide–Helicene Family Zhenhua Zhu, Tingting Wang, Lorenzo A. Mariano, Sagar Paul, Wolfgang Wernsdorfer, Alessandro Lunghi, Jinkui Tang Journal of the American Chemical Society, 2025 -diaxial manner and the two nearest nitrogen atoms dominantly contribute to the Orbach relaxation, driving the relaxation of the magnetization via the third Kramers doublet. Raman relaxation, responsible for the hysteresis closure at 12 K, is instead driven by delocalized phonons involving rigid movements of the ligands, counterions, and solvent. These findings pave a new way toward preparing and modulating magnetodynamics of lanthanide-helicene compounds.
Ultraslow Relaxation of Toroidal State in Ferrotoroidal Dysprosium Complex Deepanshu Chauhan, Sagar Paul, Dipanti Borah, Appu Sunil, Wolfgang Wernsdorfer, Maheswaran Shanmugam, Gopalan Rajaraman Journal of the American Chemical Society, 2025 Molecular systems are emerging candidates for quantum information science (QIS) due to their unique quantum behaviors and structural tunability, opening avenues for next-generation quantum technologies. While molecular nanomagnets (MNMs) have emerged as promising spin-based qubit candidates, achieving long coherence times and feasible readouts remains challenging. Among molecular nanomagnets, single-molecule toroics (SMTs) stand out as a particularly promising class, offering magnetically silent ground states, along with the unique ability to modulate their intrinsic chirality. Realizing toroidal states in molecular systems remains a significant hurdle, with the design and stabilization of ferrotoroidal (FT) moments posing an even greater level of complexity. Moreover, the anticipated slow relaxation of toroidal states has not been explicitly demonstrated, limiting their viability in molecular quantum devices. In this work, we report a tridecanuclear [Ga7Dy6(N-mdea)6(ClCH2COO)6(NO3)6(OH)12(H2O)6]·3Cl (1) complex, which exhibits an FT ground state. Remarkably, this complex shows slow relaxation of the toroidal states, experimentally observed for the first time, with a quantum tunneling of magnetization (QTM) relaxation time of ∼3.5 × 108 s (∼11 years), far surpassing the relaxation times reported for state-of-the-art Dy(III) based single-molecule magnets. The robust FT ground state in complex 1 is unequivocally established by μSQUID and corroborated by ab initio calculations, marking a major advance in the field of SMTs. This ultraslow relaxation, arising from quenched many-body tunneling processes, lays the foundation for integrating toroidal states into quantum technologies and offers a new design paradigm for molecular complexes in QIS.
Deciphering the Magnetostructural Criteria in DyIII and HoIII Macrocycle-Based Single-Molecule Magnets with Pseudo-D5h Symmetry: A Combined Single-Crystal Hysteresis and Theoretical Study Alexandros S. Armenis, Georgia P. Bakali, Sagar Paul, Konstantinos N. Pantelis, Luís Cunha-Silva, Jinkui Tang, Dimitris I. Alexandropoulos, Wolfgang Wernsdorfer, Eufemio Moreno-Pineda, Theocharis C. Stamatatos Inorganic Chemistry, 2025 The employment of the metal-ion-assisted [1+1] Schiff-base condensation has led to complexes [Ln(LN5)(Ph3SiO)2](PF6), where LnIII = DyIII (1-Dy) and HoIII (1-Ho), with close-to-ideal D5h local symmetry. For the Kramers DyIII system, slow magnetization relaxation was observed up to 64 K yielding a sizable Ueff value of 963 K, whereas the non-Kramers HoIII compound exhibited no out-of-phase signals at T > 2 K. Single-crystal magnetic hysteresis measurements uncovered the magnetization blockage of 1-Dy at T < 4 K with typical butterfly shaped loops, while open rectangular-shaped hysteresis loops were observed for 1-Ho below 0.2 K. Doping of the 1-Ho compound into a diamagnetic YIII matrix unveiled the hyperfine-driven QTM steps reflected by staircase-like hysteresis loops for 1-Ho@Y. Detailed analysis through ab initio calculations has shed light on the low-lying energy levels of both compounds leading to well-isolated and pure ground states of mJ = ±15/2 and mJ = ±8 for 1-Dy and 1-Ho, respectively. The magnetization relaxation for 1-Dy advances through the third excited state, whereas the significant tunnel splitting (Δtun) of ∼0.15 cm–1 in the ground state of 1-Ho has fostered the onset of fast tunneling relaxation.
Isolation of a planar π-aromatic Bi5− ring in a cobalt-based inverse-sandwich-type complex Julia Rienmüller, Benjamin Peerless, Sagar Paul, Florian Bruder, Wolfgang Wernsdorfer, Florian Weigend, Stefanie Dehnen Nature Chemistry, 2025 Monocyclic π-aromatic compounds are ubiquitous throughout almost all fields of natural sciences—as synthons in industrial processes, as ligands of metal complexes for catalysis or sensing and as bioactive molecules. Planar organocycles stand out through their specific way of overcoming electron deficiency by a non-localizable set of (4n + 2)π electrons. By contrast, all-metal aromatic monocycles are still rare, as metal atoms prefer to form clusters with multiply bonded atoms instead. This limits the knowledge and potential of corresponding compounds in chemical syntheses or for innovative materials. Here we report the successful generation of Bi5 −, the heaviest analogue of (C5H5)−. Its use as a ligand in [{IMesCo}2(µ,η5:η5-Bi5)] (1) was realized by reacting (TlBi3)2− with [(IMes)2CoCl] (where IMes is bis(1,3-(2,4,6-trimethylphenyl))imidazol-2-ylidene) in ortho-difluorobenzene. Compound 1 is mixed-valence Co0/CoI as verified by µ-SQUID measurements and density functional theory, and embeds the planar Bi5 − cycle in an inverse-sandwich-type manner. Capturing Bi5 − represents a landmark in the chemistry of all-metal aromatic molecules and defines a new era for aromatic compounds.
Superconducting nitridized-aluminum thin films Alba Torras-Coloma, Leyre Martínez de Olcoz, Eva Céspedes, Elia Bertoldo, David López-Núñez, Sagar Paul, Wolfgang Wernsdorfer, Gemma Rius, P Forn-Díaz Superconductor Science and Technology, 2024
Unconventional Nuclear-Spin-Dependent Toroidal Ground States in Isotopologue A Dy 4 [2 × 2] Complexes Y Chen, E Moreno-Pineda, S Paul, O Fuhr, D Fenske, W Wernsdorfer, ... Journal of the American Chemical Society , 2026 2026
Angle Resolved Magnetic Chirality Control in a Dy3 Single Molecule Toroic E Moreno-Pineda, S Paul, Z Zhu, S Liu, A Sunil, J Tang, W Wernsdorfer 2026
Homochiral toroidal spin state in Dy (III)-based single-molecule toroics Z Zhu, X Ying, LC Adi, C Zhao, EJM Chew, L Ungur, S Paul, ... Nature Chemistry, 1-10 , 2026 2026 Citations: 4
Nutzen der 3d‐4f Koordination: Molekulares Quanten‐Feder‐Magnet‐Verhalten in axialen Ni 2 Ln Komplexen Z Jing, E Moreno‐Pineda, S Paul, A Sunil, O Fuhr, Y Chen, ... Angewandte Chemie 138 (5), e22076 , 2026 2026
Leveraging 3d‐4f Coordination: Molecular Quantum Spring‐Magnet Behavior in Axial Ni 2 Ln Complexes Z Jing, E Moreno‐Pineda, S Paul, A Sunil, O Fuhr, Y Chen, ... Angewandte Chemie International Edition 65 (5), e22076 , 2026 2026 Citations: 1
Ligand-field symmetry and magneto-optical correlations in a luminescent Dy (III) singlemolecule magnet S Kumar Kuppusamy, C Pachl, Z Jing, S Paul, B Heinrich, O Fuhr, ... 2026
µSQUID-EPR Reveals Topologically Quenched Tunnelling in a Lanthanide Molecule W Wernsdorfer, S Paul, E Moreno-Pineda, CCMJ de Moreno, A Sunil, ... 2026
Ligand-field symmetry and magneto-optical correlations in a luminescent Dy (iii) single-molecule magnet SK Kuppusamy, C Pachl, Z Jing, S Paul, B Heinrich, O Fuhr, S Klyatskaya, ... Dalton Transactions 55 (14), 5448-5465 , 2026 2026
A Spin Frustrated Hourglass {Gd 9 } Molecular Nanomagnet with Unusual Magnetocaloric Properties SPK Panguluri, E Moreno-Pineda, C Molina-Jirón, S Paul, MUI Cervera, ... Journal of the American Chemical Society 147 (47), 43578-43583 , 2025 2025
Chiral Dysprosium-[7] Helicene Macrocycles Showing Record Single-Molecule Magnet Properties in the Lanthanide–Helicene Family Z Zhu, T Wang, LA Mariano, S Paul, W Wernsdorfer, A Lunghi, J Tang Journal of the American Chemical Society 147 (46), 42815-42824 , 2025 2025 Citations: 4
Ultraslow Relaxation of Toroidal State in Ferrotoroidal Dysprosium Complex D Chauhan, S Paul, D Borah, A Sunil, W Wernsdorfer, M Shanmugam, ... Journal of the American Chemical Society 147 (43), 39572-39581 , 2025 2025 Citations: 7
From Strong to Weak Interaction: Reconciling SQUID and µSQUID-EPR Data in Anomalous Co (II) Dimers S Paul, M Dolai, JN Goswami, B Bhattacharya, F Emmerling, MGB Drew, ... Inorganic Chemistry Frontiers , 2025 2025 Citations: 3
Deciphering the Magnetostructural Criteria in Dy III and Ho III Macrocycle-Based Single-Molecule Magnets with Pseudo- D 5h Symmetry: A Combined Single … AS Armenis, GP Bakali, S Paul, KN Pantelis, L Cunha-Silva, J Tang, ... Inorganic Chemistry 64 (23), 11476-11489 , 2025 2025 Citations: 6
Cover Feature: The Interplay of Single Ion Anisotropy and Magnetic 3 d ‐4 f Interactions in V III 2 Ln III 2 Butterfly Complexes (ChemistryEurope 3/2025) J Arneth, XF Li, J Braun, S Paul, M Schulze, CE Anson, W Wernsdorfer, ... ChemistryEurope 3 (3), e202580302 , 2025 2025
The Interplay of Single Ion Anisotropy and Magnetic 3 d ‐4 f Interactions in V III 2 Ln III 2 Butterfly Complexes J Arneth, XF Li, J Braun, S Paul, M Schulze, CE Anson, W Wernsdorfer, ... ChemistryEurope 3 (3), e202500011 , 2025 2025 Citations: 2
Isolation of a planar π-aromatic Bi 5 − ring in a cobalt-based inverse-sandwich-type complex J Rienmüller, B Peerless, S Paul, F Bruder, W Wernsdorfer, F Weigend, ... Nature Chemistry 17 (4), 547-555 , 2025 2025 Citations: 13
Unveiling the Werner-Type Cluster Chemistry of Heterometallic 4f/Post-Transition Metals: A {Dy 3 Bi 8 } Complex Exhibiting Quantum Tunneling Steps in the … KH Baka, D Liu, S Paul, W Wernsdorfer, J Tang, LF Chibotaru, ... Inorganic Chemistry 64 (4), 1962-1974 , 2025 2025 Citations: 3
π-Aromatic Bi5––The Heaviest Analogue of Cyclopentadienide (C5H5)–Finally Captured in the Mixed-Valent Compound [{IMesCo} 2 (μ, η5: η5-Bi5)] S Dehnen, F Weigend, W Wernsdorfer, J Rienmueller, B Peerless, S Paul 2024
Record quantum tunneling time in an air-stable exchange-bias dysprosium macrocycle Z Zhu, S Paul, C Zhao, J Wu, X Ying, L Ungur, W Wernsdorfer, F Meyer, ... Journal of the American Chemical Society 146 (28), 18899-18904 , 2024 2024 Citations: 50
Superconducting nitridized-aluminum thin films A Torras-Coloma, L Martínez de Olcoz, E Céspedes, E Bertoldo, ... Superconductor Science and Technology 37 (3), 035017 , 2024 2024 Citations: 11
MOST CITED SCHOLAR PUBLICATIONS
Record quantum tunneling time in an air-stable exchange-bias dysprosium macrocycle Z Zhu, S Paul, C Zhao, J Wu, X Ying, L Ungur, W Wernsdorfer, F Meyer, ... Journal of the American Chemical Society 146 (28), 18899-18904 , 2024 2024 Citations: 50
Insight into ferromagnetic interactions in Cu II–Ln III dimers with a compartmental ligand A Panja, S Paul, E Moreno-Pineda, R Herchel, NC Jana, P Brandão, ... Dalton Transactions 53 (6), 2501-2511 , 2024 2024 Citations: 22
Isolation of a planar π-aromatic Bi 5 − ring in a cobalt-based inverse-sandwich-type complex J Rienmüller, B Peerless, S Paul, F Bruder, W Wernsdorfer, F Weigend, ... Nature Chemistry 17 (4), 547-555 , 2025 2025 Citations: 13
Superconducting nitridized-aluminum thin films A Torras-Coloma, L Martínez de Olcoz, E Céspedes, E Bertoldo, ... Superconductor Science and Technology 37 (3), 035017 , 2024 2024 Citations: 11
Stochastic resonance in thermally bistable Josephson weak links and micro-SQUIDs S Paul, G Kotagiri, R Ganguly, H Courtois, CB Winkelmann, AK Gupta Physical Review Applied 15 (2), 024009 , 2021 2021 Citations: 11
Micron size superconducting quantum interference devices of lead (Pb) S Paul, S Biswas, AK Gupta Superconductor Science and Technology 30 (2), 025017 , 2017 2017 Citations: 8
Ultraslow Relaxation of Toroidal State in Ferrotoroidal Dysprosium Complex D Chauhan, S Paul, D Borah, A Sunil, W Wernsdorfer, M Shanmugam, ... Journal of the American Chemical Society 147 (43), 39572-39581 , 2025 2025 Citations: 7
Synthesis, characterization and magnetic properties of halogenated tetranuclear cubane-like nickel (ii) complexes M Aryaeifar, HA Rudbari, E Moreno-Pineda, JV Cuevas-Vicario, S Paul, ... New Journal of Chemistry 48 (8), 3603-3613 , 2024 2024 Citations: 7
Magnetization reversal across multiple serial barriers in a single nanoparticle S Paul, G Kotagiri, R Ganguly, A Subramanian, H Courtois, ... Physical Review B 105 (18), L180410 , 2022 2022 Citations: 7
Deciphering the Magnetostructural Criteria in Dy III and Ho III Macrocycle-Based Single-Molecule Magnets with Pseudo- D 5h Symmetry: A Combined Single … AS Armenis, GP Bakali, S Paul, KN Pantelis, L Cunha-Silva, J Tang, ... Inorganic Chemistry 64 (23), 11476-11489 , 2025 2025 Citations: 6
Magnetic behaviour of a spin-canted asymmetric lanthanide quinolate trimer L Batista, S Paul, C Molina-Jirón, JA Jaén, D Fensker, O Fuhr, M Ruben, ... Dalton Transactions 53 (31), 12927-12935 , 2024 2024 Citations: 5
Probing magnetism of individual nano-structures using Nb μ-SQUIDs in hysteresis free mode S Paul, G Kotagiri, R Ganguly, H Parashari, H Courtois, CB Winkelmann, ... Journal of Magnetism and Magnetic Materials 503, 166625 , 2020 2020 Citations: 5
Homochiral toroidal spin state in Dy (III)-based single-molecule toroics Z Zhu, X Ying, LC Adi, C Zhao, EJM Chew, L Ungur, S Paul, ... Nature Chemistry, 1-10 , 2026 2026 Citations: 4
Chiral Dysprosium-[7] Helicene Macrocycles Showing Record Single-Molecule Magnet Properties in the Lanthanide–Helicene Family Z Zhu, T Wang, LA Mariano, S Paul, W Wernsdorfer, A Lunghi, J Tang Journal of the American Chemical Society 147 (46), 42815-42824 , 2025 2025 Citations: 4
Modulating quantum tunnelling of magnetization in Dy isotopologue dimers TT Ruan, E Moreno-Pineda, S Paul, M Schulze, S Schlittenhardt, ... Dalton Transactions 53 (42), 17281-17290 , 2024 2024 Citations: 4
From Strong to Weak Interaction: Reconciling SQUID and µSQUID-EPR Data in Anomalous Co (II) Dimers S Paul, M Dolai, JN Goswami, B Bhattacharya, F Emmerling, MGB Drew, ... Inorganic Chemistry Frontiers , 2025 2025 Citations: 3
Unveiling the Werner-Type Cluster Chemistry of Heterometallic 4f/Post-Transition Metals: A {Dy 3 Bi 8 } Complex Exhibiting Quantum Tunneling Steps in the … KH Baka, D Liu, S Paul, W Wernsdorfer, J Tang, LF Chibotaru, ... Inorganic Chemistry 64 (4), 1962-1974 , 2025 2025 Citations: 3
The Interplay of Single Ion Anisotropy and Magnetic 3 d ‐4 f Interactions in V III 2 Ln III 2 Butterfly Complexes J Arneth, XF Li, J Braun, S Paul, M Schulze, CE Anson, W Wernsdorfer, ... ChemistryEurope 3 (3), e202500011 , 2025 2025 Citations: 2
Leveraging 3d‐4f Coordination: Molecular Quantum Spring‐Magnet Behavior in Axial Ni 2 Ln Complexes Z Jing, E Moreno‐Pineda, S Paul, A Sunil, O Fuhr, Y Chen, ... Angewandte Chemie International Edition 65 (5), e22076 , 2026 2026 Citations: 1
Design of a 3D vector magnet for micro-SQUID magnetometry S Paul, H Parashari, AK Gupta, G Sinha Proc. Indian Particle Accelerator Conf. , 2018 2018 Citations: 1
