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Banks PA, Kleist EM, Ruggiero MT. Investigating the function and design of molecular materials through terahertz vibrational spectroscopy. Nat Rev Chem 2023; 7:480-495. [PMID: 37414981 DOI: 10.1038/s41570-023-00487-w] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/13/2023] [Indexed: 07/08/2023]
Abstract
Terahertz spectroscopy has proved to be an essential tool for the study of condensed phase materials. Terahertz spectroscopy probes the low-frequency vibrational dynamics of atoms and molecules, usually in the condensed phase. These nuclear dynamics, which typically involve displacements of entire molecules, have been linked to bulk phenomena ranging from phase transformations to semiconducting efficiency. The terahertz region of the electromagnetic spectrum has historically been referred to as the 'terahertz gap', but this is a misnomer, as there exist a multitude of methods for accessing terahertz frequencies, and now there are cost-effective instruments that have made terahertz studies much more user-friendly. This Review highlights some of the most exciting applications of terahertz vibrational spectroscopy so far, and provides an in-depth overview of the methods of this technique and its utility to the study of the chemical sciences.
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Affiliation(s)
- Peter A Banks
- Department of Chemistry, University of Vermont, Burlington, VT, USA
| | - Elyse M Kleist
- Department of Chemistry, University of Vermont, Burlington, VT, USA
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Molecular Forcefield Methods for Describing Energetic Molecular Crystals: A Review. MOLECULES (BASEL, SWITZERLAND) 2022; 27:molecules27051611. [PMID: 35268712 PMCID: PMC8912029 DOI: 10.3390/molecules27051611] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/21/2022] [Revised: 02/25/2022] [Accepted: 02/26/2022] [Indexed: 11/16/2022]
Abstract
Energetic molecular crystals are widely applied for military and civilian purposes, and molecular forcefields (FF) are indispensable for treating the microscopic issues therein. This article reviews the three types of molecular FFs that are applied widely for describing energetic crystals—classic FFs, consistent FFs, and reactive FFs (ReaxFF). The basic principle of each type of FF is briefed and compared, with the application introduced, predicting polymorph, morphology, thermodynamics, vibration spectra, thermal property, mechanics, and reactivity. Finally, the advantages and disadvantages of these FFs are summarized, and some directions of future development are suggested.
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Dai X, Fan S, Qian Z, Wang R, Wallace VP, Sun Y. Prediction of the terahertz absorption features with a straightforward molecular dynamics method. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2020; 236:118330. [PMID: 32330823 DOI: 10.1016/j.saa.2020.118330] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2019] [Revised: 03/24/2020] [Accepted: 03/30/2020] [Indexed: 06/11/2023]
Abstract
In this paper, we provide a straightforward method to predict the terahertz absorption spectrum based on a fixed charge model with classic molecular dynamics calculations. The absorption features in the frequency range between 1 and 3.4 THz of stearic acid B-form and between 1 and 2.7 THz of C-form were successfully calculated. Most of the absorption peaks from the simulation correspond well with those from the measurements. By calculating the spatial and time-dependent energy accumulation in the molecular system, the core idea of our calculation method is further validated. Compared with the ab initio calculations, our method provides a computationally inexpensive way to accurately predict the locations of absorption features. With regard to the traditional molecular dynamic simulations, our method is able to extract the spatial distribution of the energy accumulation as well as the local motions in the molecular system.
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Affiliation(s)
- Xiangyu Dai
- College of Physics and Optoelectronic Engineering, Shenzhen University, 3688 Nanhai Road, Shenzhen 518060, Guangdong, China
| | - Shuting Fan
- College of Physics and Optoelectronic Engineering, Shenzhen University, 3688 Nanhai Road, Shenzhen 518060, Guangdong, China
| | - Zhengfang Qian
- College of Physics and Optoelectronic Engineering, Shenzhen University, 3688 Nanhai Road, Shenzhen 518060, Guangdong, China.
| | - Renheng Wang
- College of Physics and Optoelectronic Engineering, Shenzhen University, 3688 Nanhai Road, Shenzhen 518060, Guangdong, China.
| | - Vincent P Wallace
- Dept of Physics, The University of Western Australia, 35 Stirling Highway, Perth, WA 6009, Australia
| | - Yiwen Sun
- National-Regional Key Technology Engineering Laboratory for Medical Ultrasound, Guangdong Provincial Key Laboratory of Biomedical Measurements and Ultrasound Imaging, Department of Biomedical Engineering, School of Medicine, Shenzhen University, Shenzhen 518060, China.
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Spurious Absorption Frequency Appearance Due to Frequency Conversion Processes in Pulsed THz TDS Problems. SENSORS 2020; 20:s20071859. [PMID: 32230860 PMCID: PMC7181264 DOI: 10.3390/s20071859] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Revised: 03/05/2020] [Accepted: 03/24/2020] [Indexed: 01/19/2023]
Abstract
The appearance of the spurious absorption frequencies caused by the frequency conversion process at the broadband THz pulse propagation in a medium is theoretically and experimentally discussed. The spurious absorption frequencies appear due to both the frequency doubling and generation of waves with sum or difference frequency. Such generation might occur because of the nonlinear response of a medium or its non-instantaneous response. This phenomenon is confirmed by the results of a few physical experiments provided with the THz CW signals and broadband THz pulses that are transmitted through the ordinary or dangerous substances. A high correlation between the time-dependent spectral intensities for the basic frequency and generated frequencies is demonstrated while using the computer simulation results. This feature of the frequency conversion might be used for the detection and identification of a substance.
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Shi L, Duan XH, Zhu LG, Pei CH. Low-temperature dependence on the THz spectrum of CL-20/TNT energetic cocrystal by molecular dynamics simulations. J Mol Model 2020; 26:25. [PMID: 31927630 DOI: 10.1007/s00894-019-4270-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2019] [Accepted: 11/25/2019] [Indexed: 10/25/2022]
Abstract
Based on the unique advantages of terahertz (THz) spectrum on the detection of energetic cocrystals, the low-temperature dependent THz spectra of CL-20/TNT cocrystal were investigated by using molecular dynamics (MD) simulations from 5 to 296 K, as well as three different crystal faces, (001), (120), and (010). When the temperature decreases below 95 K, we have observed two new peaks for CL-20/TNT cocrystal, at 4.58 and 5.99 THz, respectively. Also, the THz peaks below 1.5 THz gradually disappear under cooling from 296 to 5 K, and they should originate from the lattice thermal vibrations. THz absorption peaks of CL-20/TNT cocrystal reveal frequency shifting, linearly dependent on temperature. Four of them are red shift and other two are blue shift of THz vibrational peaks of CL-20/TNT cocrystal with the temperature increase. The frequency shifts can be attributed to the effects of lattice thermal expansion on inter-/intramolecular vibrational modes as well as their coupling. From the temperature-dependent THz spectra of different crystal faces, we further confirm the response of different kinds of intermolecular interactions on the THz spectrum of CL-20/TNT cocrystal. Graphical abstractThe intermolecular interactions and peak positions of THz spectra of CL-20/TNT cocrystal in the range of 0-6 THz versus temperature.
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Affiliation(s)
- Lu Shi
- State Key Laboratory of Environment-friendly Energy Materials, Southwest University of Science and Technology, Mianyang, 621010, People's Republic of China
- Beijing National Laboratory for Molecular Sciences; Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, People's Republic of China
- University of Chinese Academy of Sciences, Beijing, 100049, People's Republic of China
| | - Xiao-Hui Duan
- State Key Laboratory of Environment-friendly Energy Materials, Southwest University of Science and Technology, Mianyang, 621010, People's Republic of China.
| | - Li-Guo Zhu
- Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang, 621900, Sichuan, People's Republic of China
| | - Chong-Hua Pei
- State Key Laboratory of Environment-friendly Energy Materials, Southwest University of Science and Technology, Mianyang, 621010, People's Republic of China
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Trofimov VA, Varentsova SA, Zakharova IG, Zagursky DY. Conservative finite-difference scheme for the problem of THz pulse interaction with multilevel layer covered by disordered structure based on the density matrix formalism and 1D Maxwell's equation. PLoS One 2018; 13:e0201572. [PMID: 30070996 PMCID: PMC6072102 DOI: 10.1371/journal.pone.0201572] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2018] [Accepted: 07/17/2018] [Indexed: 11/18/2022] Open
Abstract
On the basis of the Crank-Nicolson method, we develop a conservative finite-difference scheme for investigation of the THz pulse interaction with a multilevel medium, covered by a disordered layered structure, in the framework of the Maxwell-Bloch equations, describing the substance evolution and the electromagnetic field evolution. For this set of the partial differential equations, the conservation laws are derived and proved. We generalize the Bloch invariant with respect to the multilevel medium. The approximation order of the developed finite-difference scheme is investigated and its conservatism property is also proved. To solve the difference equations, which are nonlinear with respect to the electric field strength, we propose an iteration method and its convergence is proved. To increase the computer simulation efficiency, we use the well-known solution of Maxwell’s equations in 1D case as artificial boundary condition. It is approximated using Cabaret scheme with the second order of an accuracy. On the basis of developed finite-difference scheme, we investigate the broadband THz pulse interaction with a medium covered by a disordered structure. This problem is of interest for the substance detection and identification. We show that the disordered structure dramatically induces an appearance of the substance false absorption frequencies. We demonstrate also that the spectrum for the transmitted and reflected pulses becomes broader due to the cascade mechanism of the high energy levels excitation of molecules. It leads to the substance emission at the frequencies, which are far from the frequency range for the incident pulse spectrum. Time-dependent spectral intensities at these frequencies are weakly disturbed by the disordered cover and, hence, they can be used for the substance identification.
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Affiliation(s)
- Vyacheslav A. Trofimov
- Faculty of Computational Mathematics and Cybernetics, Lomonosov Moscow State University, Moscow, Russia
- * E-mail:
| | - Svetlana A. Varentsova
- Faculty of Computational Mathematics and Cybernetics, Lomonosov Moscow State University, Moscow, Russia
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Azuri I, Hirsch A, Reilly AM, Tkatchenko A, Kendler S, Hod O, Kronik L. Terahertz spectroscopy of 2,4,6-trinitrotoluene molecular solids from first principles. Beilstein J Org Chem 2018; 14:381-388. [PMID: 29507643 PMCID: PMC5815306 DOI: 10.3762/bjoc.14.26] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2017] [Accepted: 01/22/2018] [Indexed: 11/25/2022] Open
Abstract
We present a computational analysis of the terahertz spectra of the monoclinic and the orthorhombic polymorphs of 2,4,6-trinitrotoluene. Very good agreement with experimental data is found when using density functional theory that includes Tkatchenko–Scheffler pair-wise dispersion interactions. Furthermore, we show that for these polymorphs the theoretical results are only weakly affected by many-body dispersion contributions. The absence of dispersion interactions, however, causes sizable shifts in vibrational frequencies and directly affects the spatial character of the vibrational modes. Mode assignment allows for a distinction between the contributions of the monoclinic and orthorhombic polymorphs and shows that modes in the range from 0 to ca. 3.3 THz comprise both inter- and intramolecular vibrations, with the former dominating below ca. 1.5 THz. We also find that intramolecular contributions primarily involve the nitro and methyl groups. Finally, we present a prediction for the terahertz spectrum of 1,3,5-trinitrobenzene, showing that a modest chemical change leads to a markedly different terahertz spectrum.
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Affiliation(s)
- Ido Azuri
- Department of Materials and Interfaces, Weizmann Institute of Science, Rehovoth 76100, Israel
| | - Anna Hirsch
- Department of Materials and Interfaces, Weizmann Institute of Science, Rehovoth 76100, Israel
| | - Anthony M Reilly
- School of Chemical Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland
| | - Alexandre Tkatchenko
- Physics and Materials Research Unit, University of Luxembourg, L-1511 Luxembourg
| | - Shai Kendler
- Israel Institute for Biological Research, Ness Ziona 74100, Israel
| | - Oded Hod
- Department of Physical Chemistry, School of Chemistry, The Raymond and Beverly Sackler Faculty of Exact Sciences and The Sackler Center for Computational Molecular and Materials Science, Tel Aviv University, Tel Aviv 6997801, Israel
| | - Leeor Kronik
- Department of Materials and Interfaces, Weizmann Institute of Science, Rehovoth 76100, Israel
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Trofimov VA, Varentsova SA. The Anomalous Influence of Spectral Resolution on Pulsed THz Time Domain Spectroscopy under Real Conditions. SENSORS 2017; 17:s17122883. [PMID: 29231895 PMCID: PMC5751648 DOI: 10.3390/s17122883] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/19/2017] [Revised: 12/03/2017] [Accepted: 12/05/2017] [Indexed: 11/16/2022]
Abstract
We have studied the spectral resolution influence on the accuracy of the substance detection and identification at using a broadband THz pulse measured under real conditions (at a distance of more than 3 m from a THz emitter in ambient air with a relative humidity of about 50%). We show that increasing spectral resolution leads to manifestation of small-scale perturbations (random fluctuations) in the signal spectrum caused by the influence of the environment or the sample structure. Decreasing the spectral resolution allows us to exclude from consideration this small-scale modulation of the signal as well as to detect the water vapor absorption frequencies. This fact is important in practice because it allows us to increase the signal processing rate. In order to increase the detection reliability, it is advisable to decrease the spectral resolution up to values of not more than 40% of the corresponding spectral line bandwidth. The method of spectral dynamics analysis together with the integral correlation criteria is used for the substance detection and identification. Neutral substances such as chocolate and cookies are used as the samples in the physical experiment.
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Affiliation(s)
- Vyacheslav A Trofimov
- Faculty of Computational Mathematics and Cybernetics, Lomonosov Moscow State University, Leninskiye Gory, Moscow 119992, Russia.
| | - Svetlana A Varentsova
- Faculty of Computational Mathematics and Cybernetics, Lomonosov Moscow State University, Leninskiye Gory, Moscow 119992, Russia.
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Trofimov VA, Varentsova SA. Essential Limitations of the Standard THz TDS Method for Substance Detection and Identification and a Way of Overcoming Them. SENSORS 2016; 16:s16040502. [PMID: 27070617 PMCID: PMC4851016 DOI: 10.3390/s16040502] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/31/2016] [Revised: 03/26/2016] [Accepted: 03/29/2016] [Indexed: 11/19/2022]
Abstract
Low efficiency of the standard THz TDS method of the detection and identification of substances based on a comparison of the spectrum for the signal under investigation with a standard signal spectrum is demonstrated using the physical experiments conducted under real conditions with a thick paper bag as well as with Si-based semiconductors under laboratory conditions. In fact, standard THz spectroscopy leads to false detection of hazardous substances in neutral samples, which do not contain them. This disadvantage of the THz TDS method can be overcome by using time-dependent THz pulse spectrum analysis. For a quality assessment of the standard substance spectral features presence in the signal under analysis, one may use time-dependent integral correlation criteria.
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Affiliation(s)
- Vyacheslav A Trofimov
- Faculty of Computational Mathematics and Cybernetics, Lomonosov Moscow State University, Leninskiye Gory, Moscow 119992, Russia.
| | - Svetlana A Varentsova
- Faculty of Computational Mathematics and Cybernetics, Lomonosov Moscow State University, Leninskiye Gory, Moscow 119992, Russia.
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Abstract
Interest in molecular crystals has grown thanks to their relevance to pharmaceuticals, organic semiconductor materials, foods, and many other applications. Electronic structure methods have become an increasingly important tool for modeling molecular crystals and polymorphism. This article reviews electronic structure techniques used to model molecular crystals, including periodic density functional theory, periodic second-order Møller-Plesset perturbation theory, fragment-based electronic structure methods, and diffusion Monte Carlo. It also discusses the use of these models for predicting a variety of crystal properties that are relevant to the study of polymorphism, including lattice energies, structures, crystal structure prediction, polymorphism, phase diagrams, vibrational spectroscopies, and nuclear magnetic resonance spectroscopy. Finally, tools for analyzing crystal structures and intermolecular interactions are briefly discussed.
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Affiliation(s)
- Gregory J O Beran
- Department of Chemistry, University of California , Riverside, California 92521, United States
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Joshi K, Losada M, Chaudhuri S. Intermolecular Energy Transfer Dynamics at a Hot-Spot Interface in RDX Crystals. J Phys Chem A 2016; 120:477-89. [PMID: 26741283 DOI: 10.1021/acs.jpca.5b06359] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The phonon mediated vibrational up-pumping mechanisms assume an intact lattice and climbing of a vibrational ladder using strongly correlated multiphonon dynamics under equilibrium or near-equilibrium conditions. Important dynamic processes far from-equilibrium in regions of large temperature gradient after the onset of decomposition reactions in energetic solids are relatively unknown. In this work, we present a classical molecular dynamics (MD) simulation-based study of such processes using a nonreactive and a reactive potential to study a fully reacted and unreacted zone in RDX (1,3,5-trinitro-1,3,5-triazocyclohexane) crystal under nonequilibrium conditions. The energy transfer rate is evaluated as a function of temperature difference between the reacted and unreacted regions, and for different widths and cross-sectional area of unreacted RDX layers. Vibrational up-pumping processes probed using velocity autocorrelation functions indicate that the mechanisms at high-temperature interfaces are quite different from the standard phonon-based models proposed in current literature. In particular, the up-pumping of high-frequency vibrations are seen in the presence of small molecule collisions at the hot-spot interface with strong contributions from bending modes. It also explains some major difference in the order of decomposition of C-N and N-N bonds as seen in recent literature on initiation chemistry.
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Affiliation(s)
- Kaushik Joshi
- Applied Research Institute, University of Illinois at Urbana-Champaign , Champaign, Illinois 61820, United States
| | - Martin Losada
- Applied Sciences Laboratory, Washington State University , Spokane, Washington 99210-1495, United States
| | - Santanu Chaudhuri
- Applied Research Institute, University of Illinois at Urbana-Champaign , Champaign, Illinois 61820, United States
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Pharmaceutical Terahertz Spectroscopy and Imaging. ADVANCES IN DELIVERY SCIENCE AND TECHNOLOGY 2016. [DOI: 10.1007/978-1-4939-4029-5_5] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
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Fileti EE, Chaban VV, Prezhdo OV. Exploding Nitromethane in Silico, in Real Time. J Phys Chem Lett 2014; 5:3415-3420. [PMID: 26278455 DOI: 10.1021/jz501848e] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Nitromethane (NM) is widely applied in chemical technology as a solvent for extraction, cleaning, and chemical synthesis. NM was considered safe for a long time, until a railroad tanker car exploded in 1958. We investigate the detonation kinetics and explosion reaction mechanisms in a variety of systems consisting of NM, molecular oxygen, and water vapor. Reactive molecular dynamics allows us to simulate reactions in time-domain, as they occur in real life. High polarity of the NM molecule is shown to play a key role, driving the first exothermic step of the reaction. Rapid temperature and pressure growth stimulate the subsequent reaction steps. Oxygen is important for faster oxidation, whereas its optimal concentration is in agreement with the proposed reaction mechanism. Addition of water (50 mol %) inhibits detonation; however, water does not prevent detonation entirely. The reported results provide important insights for improving applications of NM and preserving the safety of industrial processes.
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Affiliation(s)
- Eudes Eterno Fileti
- †Instituto de Ciência e Tecnologia, Universidade Federal de São Paulo, 12231-280, São José dos Campos, São Paulo, Brazil
| | - Vitaly V Chaban
- ‡MEMPHYS - Center for Biomembrane Physics, Odense M, 5230, Kingdom of Denmark
| | - Oleg V Prezhdo
- §Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States
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