Yingzhong Ma

Yingzhong Ma

Staff Research Scientist

Bio

Yingzhong received his Ph.D. in physical chemistry from Umeå University, Sweden, under the supervision of Prof. Tomas Gillbro in 1999. The research during his stay in this Nordic country was focused on an ultrafast optical spectroscopic study of electronic excited-state energy and electron transfer processes in purple and green photosynthetic bacteria. He then joined the group of Prof. Alfred Holzwarth at the Max-Planck Institute for Radiation Chemistry (now the Max Planck Institute for Chemical Energy Conversion), Germany, where his work was centered on time-resolved spectroscopic characterization of artificial photosynthetic systems. Yingzhong moved to California in 2000 where he had an extended stay in the group of Prof. Graham Fleming, University of California, Berkeley. There he was given the opportunities of exploring several challenging questions, such as the physical mechanisms underlying the nonphotochemical quenching process that regulates photosynthetic light harvesting in plants as a protective response to changes in excessive incident light intensity, ultrafast electronic excited-state phenomena in semiconducting single- and doubled-walled carbon nanotubes, and laser-induced drug delivery, etc. These studies involved use of a suite of ultrafast laser spectroscopic tools, including two- and three-pulse photon echo, heterodyne-detected transient grating and transient absorption spectroscopies. In 2009, Yingzhong joined the Chemical Sciences Division as a staff member, where he initiated a systematic ultrafast spectroscopy research at ORNL, with specific focuses on understanding fundamental energy and charge transport phenomena with high spatial, spectral and temporal resolution. His research has since span from low-dimensional nanostructures, molecular systems to polymeric and semiconducting photovoltaic materials. In recent years, this research has seen major advances with the addition of several femtosecond laser systems, which are capable of producing pulse energies spanning over six orders of magnitude and very broad tunability ranging from UV to mid-infrared spectral regions, along with the development of a series of ultrafast optical spectroscopic and microscopic approaches for directly probing electronic, vibrational and thermal processes in both bulk systems and interfaces.

Projects

Ultrafast electronic spectroscopy of nanostructures and conjugated polymers

Multimodal optical imaging of spatially resolved electronic excited-state dynamics and trap states in highly heterogeneous materials based on femtosecond transient absorption microscopy and co-registered time-integrated imaging modalities (confocal reflectance, transmission, photoluminescence, and second-harmonic generation)

Femtosecond dynamics of strongly coupled exciton-plasmon heterostructures

Publications

Doughty, B.; Simpson, M. J.; Yang, B.; Xiao, K.; Ma, Y.-Z. Simplification of Femtosecond Transient Absorption Microscopy Data From CH3NH3PbI3 Perovskite Thin Films Into Decay Associated Amplitude Maps. Nanotechnology 2016, 27, 114002 (http://dx.doi.org/10.1088/0957-4484/27/11/114002).

Simpson, M. J.; Doughty, B.; Yang, B.; Xiao, K.; Ma, Y.-Z. Separation of Distinct Photoexcitation Species in Femtosecond Transient Absorption Microscopy. ACS Photon. 2016, 3, Article ASAP (http://dx.doi.org/10.1021/acsphotonics.5b00638).
*See the press release under the News section below.

Watson, B. R.; Yang, B.; Xiao, K.; Ma, Y.-Z.; Doughty, B.; Calhoun, T. R. Elucidation of Perovskite Film Micro-Orientations Using Two-Photon Total Internal Reflectance Fluorescence Microscopy. J. Phys. Chem. Lett. 2015, 6, 3283–3288 (http://dx.doi.org/10.1021/acs.jpclett.5b01474).

Simpson, M. J.; Doughty, B.; Yang, B.; Xiao, K.; Ma, Y.-Z. Spatial Localization of Excitons and Charge Carriers in Hybrid Perovskite Thin Films. J. Phys. Chem. Lett. 2015, 6, 3041-3047 (http://dx.doi.org/10.1021/acs.jpclett.5b01050).

Doughty, B.; Ma, Y.-Z.; Shaw, R. W. Probing Interfacial Electronic States in CdSe Quantum Dots using Second Harmonic Generation Spectroscopy. J. Phys. Chem. C 2015, 119, 2752−2760 (http://dx.doi.org/10.1021/jp510357p).

Shao, M.; Keum, J.; Chen, J.; He, Y.; Chen, W.; Browning, J. F.; Jakowski, J.; Sumpter, B. G.; Ivanov, I. N.; Ma, Y.-Z.; Rouleau, C. M.; Smith, S. C.; Geohegan, D. B.; Hong, K.; Xiao, K. The Isotopic Effects of Deuteration on Optoelectronic Properties of Conducting Polymers. Nat. Commun. 2014, 5, 4180 (http://dx.doi.org/10.1038/ncomms4180).

Pistner, A. J.; Pupillo, R. C.; Yap, G. P. A.; Lutterman, D. A.; Ma, Y.-Z.; Rosenthal, J. Electrochemical, Spectroscopic and 1O2 Sensitization Characteristics of 10,10-Dimethylbiladiene Complexes of Zinc and Copper. J. Phys. Chem. A 2014, 118, 10639−10648 (http://dx.doi.org/10.1021/jp506412r).

Teesdale, J.; Pistner, A. J.; Yap, G. P. A.; Ma, Y.-Z.; Lutterman, D. A.; Rosenthal, J. Reduction of CO2 Using a Rhenium Bipyridine Complex Containing Ancillary BODIPY Moieties. Catalysis Today 2014, 225, 149-157 (http://dx.doi.org/10.1016/j.cattod.2013.10.091).

Pistner, A. J.; Lutterman, D. A.; Ghidiu, M. J.; Ma, Y.-Z.; Rosenthal, J. Synthesis, Electrochemistry and Photophysics of a Family of Phlorin Macrocycles that Display Cooperative Fluoride Binding. J. Am. Chem. Soc. 2013, 135, 6601-6607 (http://dx.doi.org/10.1021/ja401391z).

Ma, Y.-Z.; Shaw, R. W.; Yu, X.; O’Neill, H. M.; Hong, K. Excited State Dynamics of Water-Soluable Polythiophene Derivatives: Temperature and Side-Chain Length Effects. J. Phys. Chem. B 2012, 116, 14451-14460 (http://dx.doi.org/10.1021/jp304526h).

Ma, Y.-Z.; Xiao, K.; Shaw, R. W. Exciton-Exciton Annihilation in Copper-Phthalocyanine Single-Crystal Nanowires. J. Phys. Chem. C 2012, 116, 21588-21593 (http://dx.doi.org/10.1021/jp3057543).

Graham, M. W.; Ma, Y.-Z.; Green, A. A.; Hersam, M. C.; Fleming, G. R. Pure optical dephasing dynamics in semiconducting single-walled carbon nanotubes. J. Chem. Phys. 2011, 134, 034504 (http://dx.doi.org/10.1063/1.3530582).

Graham, M. W.; Chmeliov, J.; Ma, Y.-Z.; Shinohara, H.; Green, A. A.; Hersam, M. C.; Valkunas, L.; Fleming, G. R. Exciton Dynamics in Semiconducting Carbon Nanotubes. J. Phys. Chem. B 2011, 115, 5201-5211 (http://dx.doi.org/10.1021/jp106250a).

Graham, M. W.; Ma, Y.-Z.; Green, A. A.; Hersam, M. C.; Fleming, G. R. Exciton Annihilation and Dephasing Dynamics in Semiconducting Single-Walled Carbon Nanotubes. Ultrafast Phenomena in Semiconductors and Nanostructure Materials Xiv Book Series: Proceedings of SPIE, Vol. 7600, 76001F, 2010 (http://dx.doi.org/10.1117/12.841194).

Wang, J.; Graham, M. W.; Ma, Y.-Z.; Fleming, G. R.; Kaindl, R. A. Ultrafast Spectroscopy of Midinfrared Internal Exciton Transitions in Separated Single-Walled Carbon Nanotubes. Phys. Rev. Lett. 2010, 104, 177401 (http://dx.doi.org/10.1103/PhysRevLett.104.177401).

Abramavicius, D.; Ma, Y.-Z.; Graham, M. W.; Valkunas, L.; Fleming, G. R. Exciton-exciton annihilation induces dephasing in semiconducting single-walled carbon nanotubes. Phys. Rev. B 2009, 79, 195445 (http://dx.doi.org/10.1103/PhysRevB.79.195445).
*Also selected for the June 15, 2009 issue of Virtual Journal of Nanoscale Science & Technology.

Ma, Y.-Z.; Graham, M. W.; Green, A. A.; Stupp, S. I.; Hersam, M. C.; Fleming, G. R. Exciton Dephasing in Semiconducting Single-Walled Carbon Nanotubes. In Ultrafast Phenomena XVI, Springer, 2009; pp 277-279.

Ma, Y.-Z.; Graham, M. W.; Fleming, G. R.; Green, A. A.; Hersam, M. C. Ultrafast Exciton Dephasing in Semiconducting Single-Walled Carbon Nanotubes. Phys. Rev. Lett. 2008, 101, 217402 (http://dx.doi.org/10.1103/PhysRevLett.101.217402).
*Also selected for the December 1, 2008 issue of Virtual Journal of Nanoscale Science & Technology, and the December 2008 issue of Virtual Journal of Ultrafast Science.

Graham, M. W.; Ma, Y.-Z.; Fleming, G. R. Femtosecond Photon Echo Spectroscopy of Semiconducting Single-Walled Carbon Nanotubes. Nano Lett. 2008, 8, 3936-3941 (http://dx.doi.org/10.1021/nl802423w).

Ma, Y.-Z.; Graham, M. W.; Prantil, M. A.; Van Tassle, A. J.; Fleming, G. R. Vibrational Spectra and Dynamics of Electronically Excited Semiconducting Single-Walled Carbon Nanotubes. J. Phys. Chem. B 2008, 112, 16030-16034 (http://dx.doi.org/10.1021/jp805745k).

Ma, Y.-Z.; Miller, R. A.; Fleming, G. R.; Francis, M. B. Energy Transfer Dynamics in Light-Harvesting Assemblies Templated by the Tobacco Mosaic Virus Coat Protein. J. Phys. Chem. B 2008, 112, 6887-6892 (http://dx.doi.org/10.1021/jp8006393).

Zigmantas, D.; Ma, Y.-Z.; Read, E.; Fleming, G. R. Nonlinear Femtosecond Optical Spectroscopy Techniques in Photosynthesis. In Biophysical Techniques in Photosynthesis, V. II (Aartsma, T. J.; Matysik, J. eds.), Kluwer Academic Publishers, Dordrecht, 201-222, 2008 (http://dx.doi.org/10.1007/978-1-4020-8250-4_11).

Ma, Y.-Z.; Hertel, T.; Vardeny, Z. V.; Fleming, G. R.; Valkunas, L. Ultrafast spectroscopy of carbon nanotubes, In Carbon Nanotubes: Advanced Topics in the Synthesis, Structure, Properties and Applications; Jorio, A., Dresselhaus, G., Dresselhaus, M. S., Eds.; Springer, 2008; 111, pp 321-352 (http://dx.doi.org/10.1007/978-3-540-72865-8_10).

Mynar, J. L.; Goodwin, A. P.; Cohen, J. A.; Ma, Y.-Z.; Fleming, G. R.; Frechet, J. M. J. Two-Photon Degradable Supramolecular Assemblies of Linear-Dendritic Copolymers. Chem. Comm.2007, 20, 2081-2082 (http://dx.doi.org/10.1039/B701681F).

Ma, Y.-Z.; Graham, M. W.; Valkunas, L.; Bachilo, S.M.; Fleming, G. R. Probing Exciton Dynamics of Semiconducting Single-Walled Carbon Nanotubes Using Photon Echo Spectroscopy. In Ultrafast Phenomena XV, Springer, 2007; pp 686-688.

Ma, Y.-Z.; Valkunas, L.; Bachilo, S. M.; Fleming, G. R. Temperature Effects on Femtosecond Transient Absorption Kinetics of Semiconducting Single-Walled Carbon Nanotubes. Phys. Chem. Chem. Phys. 2006, 8, 5689-5693 (http://dx.doi.org/10.1039/B612207H).

Ma, Y.-Z.; Spataru, C. D.; Valkunas, L.; Bachilo, S. M.; Dexheimer, S. L.; Louie, S. G.; Fleming, G. R. Spectroscopy of Zigzag Single-Walled Carbon Nanotubes: Comparing Femtosecond Transient Absorption Spectra with Ab Initio Calculations. Phys. Rev. B 2006, 74, 085402 (http://dx.doi.org/10.1103/PhysRevB.74.085402).
*Also selected for the September 2006 issue of Virtual Journal of Ultrafast Science.

Valkunas, L.; Ma, Y.-Z.; Fleming, G. R. Exciton-Exciton Annihilation in Single-Walled Carbon Nanotubes. Phys. Rev. B 2006, 73, 115432 (http://10.1103/PhysRevB.73.115432).
*Also selected for the April 10, 2006 issue of Virtual Journal of Nanoscale Science & Technology and the April 2006 issue of Virtual Journal of Ultrafast Science.

Ma, Y.-Z.; Valkunas, L.; Dexheimer, S. L.; Fleming, G. R. Ultrafast Exciton Dynamics in Semiconducting Single-Walled Carbon Nanotubes. Mol. Phys. 2006, 104, 1179-1189 (http://dx.doi.org/10.1080/00268970500525564).

Goodwin, A. P.; Mynar, J. L.; Ma, Y.-Z.; Fleming, G. R.; Frechet, J. M. J. Synthetic Micelle Sensitive to IR Light via a Two-Photon Process. J. Am. Chem. Soc. 2005, 127, 9952-9953 (http://dx.doi.org/10.1021/ja0523035).

Ma, Y.-Z.; Valkunas, L.; Bachilo, S. M.; Fleming, G. R. Exciton Binding Energy in Semiconducting Single-Walled Carbon Nanotubes. J. Phys. Chem. B 2005, 109, 15671-15674 (http://dx.doi.org/10.1021/jp053011t).

Jung, G.; Ma, Y.-Z.; Prall, B. S.; Fleming, G. R. Ultrafast Fluorescence Depolarization in Yellow Fluorescent Protein (YFP) due to Its Dimerization. ChemPhysChem 2005, 6, 1628-1632 (http://dx.doi.org/10.1002/cphc.200400653).

Ma, Y.-Z.; Valkunas, L.; Dexheimer, S. L.; Bachilo, S. M.; Fleming, G. R. Femtosecond Spectroscopy of Optical Excitations in Single-Walled Carbon Nanotubes: Evidence for Exciton-Exciton Annihilation. Phys. Rev. Lett. 2005, 94, 157402 (http://dx.doi.org/10.1103/PhysRevLett.94.157402).
*Also selected for the May 2, 2005 issue of Virtual Journal of Nanoscale Science & Technology.

Ma, Y.-Z.; Stenger, J.; Dexheimer, S. L.; Bachilo, S. M.; Smalley, R. E.; Weisman, R. B.; Fleming, G. R. Correlation of the Electronic Transitions in Semiconducting Single-Walled Carbon Nanotubes. In Ultrafast Phenomena XIV, Springer, 2005; pp 331-333.

Pines, D.; Pines, E.; Ma, Y.-Z.; Fleming, G. R. Femtosecond Pump-Probe Measurements of Solvation Dynamics of Hydrogen-Bonding Complexes in Non-Associating Solvents. In Ultrafast Phenomena XIV, Springer, 2005; pp 425-427.

Pines, E.; Pines, D.; Ma, Y.-Z.; Fleming, G. R. Femtosecond Solvation Dynamics of Hydrogen-Bonding Complexes. In Femtochemistry and Femtobiology: Ultrafast Events in Molecular Science, Elsevier, 2004; pp 185-188.

Pines, E.; Pines, D.; Ma, Y.-Z.; Fleming, G. R. Femtosecond Pump-Probe Measurements of Solvation by Hydrogen-Bonding Interactions. ChemPhysChem 2004, 5, 1315-1327 (http://dx.doi.org/10.1002/cphc.200301004).

Ma, Y.-Z.; Stenger, J.; Zimmermann, J.; Bachilo, S. M.; Smalley, R. E.; Weisman, R. B.; Fleming, G. R. Ultrafast Carrier Dynamics in Single-Walled Carbon Nanotubes Probed by Femtosecond Spectroscopy. J. Chem. Phys. 2004, 120, 3368-3373 (http://dx.doi.org/10.1063/1.1640339).
*Also selected for the February 23, 2004 issue of Virtual Journal of Nanoscale Science & Technology and the March 2004 issue of Virtual Journal of Ultrafast Science.

Ma, Y.-Z.; Holt, N. E.; Li, X.-P.; Niyogy, K. K.; Fleming, G. R. Evidence for Direct Carotenoid Involvement in the Regulation of Photosynthetic Light Harvesting. Proc. Natl. Acad. Sci. USA 2003, 100, 4377-4382 (http://dx.doi.org/10.1073/pnas.0736959100).

Xu, Q.-H.; Ma, Y.-Z.; Fleming, G. R. Optical Heterodyne Detected Transient Grating (OHD-TG) Studies on the Reactive and Non-Reactive Resonant Systems. In Ultrafast Phenomena XIII, Springer, 2003; pp 420-422.

Psencík, J.; Ma, Y.-Z.; Arellano, J. B.; Hála, J.; Gillbro, T. Excitation Energy Transfer Dynamics and Excited State Structure in Chlorosomes of Chlorobium Phaeobacteroides. Biophys. J. 2003, 84, 1161-1179 (http://dx.doi.org/10.1016/S0006-3495(03)74931-5).

Yang, N. C.; Yang, D. H.; Steele, I. M.; Li, H.; Ma, Y.-Z.; Fleming, G. R. Photochemistry of Dianthrylsilanes: A Study of ,* Interaction. J. Am. Chem. Soc. 2003, 125, 5107-5110 (http://dx.doi.org/10.1021/ja020403u).

Xu, Q.-H.; Ma, Y.-Z.; Fleming, G. R. Different Real and Imaginary Components of the Resonant Third-Order Polarization Revealed by Optical Heterodyne Detected Transient Grating Spectroscopic Studies of Crystal Violet: Model and Experiment. J. Phys. Chem. A 2002, 106, 10755-10763 (http://dx.doi.org/10.1021/jp014714n).

Psencík, J.; Ma, Y.-Z.; Arellano, J. B.; Garcia-Gil, J.; Holzwarth, A. R.; Gillbro, T. Excitation Energy Transfer in Chlorosomes of Chlorobium Phaeobacteroides Strain CL1401: The Role of Carotenoids. Photosynth. Res. 2002, 71, 5-18 (http://dx.doi.org/10.1023/A:1014943312031).

Xu, Q.-H.; Ma, Y.-Z.; Stiopkin, I. V.; Fleming, G. R. Wavelength Dependent Resonant Homodyne and Heterodyne Transient Grating Spectroscopy with a Diffractive Optics Method: Solvent Effect on the Third-Order Signal. J. Chem. Phys. 2002, 116, 9333-9340 (http://dx.doi.org/10.1063/1.1473653).

Xu, Q.-H.; Ma, Y.-Z.; Fleming, G. R. Heterodyne Detected Transient Grating Spectroscopy in Resonant and Non-Resonant Systems using a Simplified Diffractive Optics Method. Chem. Phys. Lett. 2001, 338, 254-262 (http://dx.doi.org/10.1016/S0009-2614(01)00281-0).

Holzwarth, A. R.; Katterle, M.; Müller, M. G.; Ma, Y.-Z.; Prokhorenko. V. Electron-Transfer Dyads Suitable for Novel Self-Assembled Light-Harvesting Antenna/Electron-Transfer Devices. Pure and Applied Chem. 2001, 73, 469-474 (http://dx.doi.org/10.1351/pac200173030469).

Neerken, S.; Ma, Y.-Z.; Aschenbrücker, J.; Schmidt, K. A.; Nowak, F. R.; Permentier, H. P.; Aartsma, T. J.; Gillbro, T.; Amesz, J. Kinetics of Absorbance and Anisotropy upon Excited State Relaxation in the Reaction Center Core Complex of a Green Sulfur Bacterium. Photosynth. Res. 2000, 65, 261-268 (http://dx.doi.org/10.1023/A:1010647205220).

Arellano, J. B.; Psencík, J.; Borrego, C. M.; Ma, Y.-Z.; Guyoneaud, R.; Garcia-Gil, J.; Gillbro, T. Effect of Carotenoid Biosynthesis Inhibition on the Chlorosome Organization in Chlorobium Phaeobacteroides Strain CL1401. Photochem. Photobiol. 2000, 71, 715-723 (http://dx.doi.org/10.1562/0031-8655(2000)0710715EOCBIO2.0.CO2).

Ma, Y.-Z.; Aschenbrücker, J.; Miller, M.; Gillbro, T. Ground-State Vibrational Coherence in Chlorosomes of Chlorobium Phaeobacteroides. Chem. Phys. Lett. 1999, 300, 465-472 (http://dx.doi.org/10.1016/S0009-2614(98)01368-2).

Ma, Y.-Z.; Miller, M.; Gillbro, T. Excitation Energy Transfer and Trapping Dynamics in the FMO-Containing Reaction Centre Complex of Chlorobium Tepidum. In Photosynthesis: Mechanisms and Effects (Garab, G., Ed.), Kluwer Academic Publishers, Dordrecht, 1998; Vol. 1, pp 535-538 (http://dx.doi.org/10.1007/978-94-011-3953-3_125).

Aschenbrücker, J.; Ma, Y.-Z.; Miller, M.; Gillbro, T. Redox- and Pump Intensity Dependence of Energy Transfer in Chlorosomes of Cb. Phaeobacteroides. In Photosynthesis: Mechanisms and Effects (Garab, G., Ed.), Kluwer Academic Publishers, Dordrecht, 1998; Vol. 1, pp 153-156 (http://dx.doi.org/10.1007/978-94-011-3953-3_37).

Neerken, S.; Permentier, H. P.; Aschenbrücker, J.; Ma, Y.-Z.; Francke, C.; Schmidt, K. A.; Gillbro, T.; Aartsma, T. J.; Amesz, J. Relaxation and Trapping in Reaction Centers of the Green Sulfur Bacterium Prosthecochloris Aestuarii. In Photosynthesis: Mechanisms and Effects (Garab, G., Ed.), Kluwer Academic Publishers, Dordrecht, 1998; Vol. 1, pp 539-542 (http://dx.doi.org/10.1007/978-94-011-3953-3_126).

Cox, R. P.; Miller, M.; Aschenbrücker, J.; Ma, Y.-Z.; Gillbro, T. The Role of Bacteriochlorophyll E and Carotenoids in Light Harvesting in Brown-Colored Green Sulfur Bacteria. In Photosynthesis: Mechanisms and Effects (Garab, G., Ed.), Kluwer Academic Publishers, Dordrecht, 1998; Vol. 1, pp 149-152 (http://dx.doi.org/10.1007/978-94-011-3953-3_36).

Ma, Y.-Z.; Cogdell, R. J.; Gillbro, T. Femtosecond Energy Transfer Dynamics between Bacteriochlorophylls in the B800820 Antenna Complex of the Photosynthetic Purple Bacterium Rhodopseudomonas Acidophila (Strain 7750). J. Phys. Chem. B 1998, 102, 881-887 (http://dx.doi.org/10.1021/jp9721762).

Ma, Y.-Z.; Cogdell, R. J.; Gillbro, T. Energy Transfer and Exciton Annihilation in the B800850 Antenna Complex of the Photosynthetic Purple Bacterium Rhodopseudomonas Acidophila (Strain 10050): A Femtosecond Transient Absorption Study. J. Phys. Chem. B 1997, 101, 1087-1095 (http://dx.doi.org/10.1021/jp962470e).

Ma, Y.-Z.; Cox, R. P.; Gillbro, T.; Miller, M. Bacteriochlorophyll Organization and Energy Transfer Kinetics in Chlorosome from Chloroflexus Aurantiacus Depend on the Light Regime during Growth. Photosynth. Res. 1996, 47, 157-165 (http://dx.doi.org/10.1007/BF00016178).

Specialized Equipment

1 kHz and 250 kHz femtosecond Ti:Sapphire regenerative amplifiers in combination with their associated visible and infrared optical parametric amplifiers as well as frequency mixers, which enable to routinely generate 50 fs laser pulses with high pulse energies and broad tenability

High repetition and low pulse energy femtosecond Ti:Sapphire unamplified oscillators

Multimodal optical imaging microscope based on femtosecond transient absorption and other co-registered time-integrated imaging modalities

Widefield nonlinear optical imaging microscope for one- and two-photon fluorescence, second-harmonic generation, and other multiple wave mixing imaging with sub-diffraction limited spatial resolution

Surface-specific broadband vibrational sum-frequency generation spectroscopic apparatus

Broadband femtosecond transient absorption spectroscopic apparatus

Time-resolved fluorescence spectrometer

Time-domain thermoreflectance (TDTR) spectroscopic apparatus