89 B.C. Ng, S.T. Chan, J. Lin, and S.H. Tolbert "Using Polymer Conformation to Control Architecture in Semiconducting Polymer/Viral Capsid Assemblies." ACS Nano, 5, 7730-7738 (2011).


88 J. Yang, V. A. Kickhoefer, B. C. Ng, A. Gopal, L. A. Bentolila, S. John, S. H. Tolbert, and L. H. Rome "Vaults Are Dynamically Unconstrained Cytoplasmic Nanoparticles Capable of Half Vault Exchange." ACS Nano, 4, 7229-7240 (2010).

87 T. E. Quickel, V. H. Le, T. Brezensinski, S. H. Tolbert "On the Correlation between Nanoscale Structure and Magnetic Properties in Ordered Mesoporous Cobalt Ferrite (CoFe2O4) Thin Films." Nano Lett., 10, 2982-2988 (2010).

86. T. Brezesinski, J. Wang, S.H. Tolbert, and B. Dunn "Ordered mesoporous alpha-MoO3 with iso-oriented nanocrystalline walls for thin-film pseudocapacitors." Nature Mater., 9, 146-151 (2010).

85. T. Brezesinski, J. Wang, R. Senter, K. Brezesinski, B. Dunn, and S.H. Tolbert "On the Correlation between Mechanical Flexibility, Nanoscale Structure, and Charge Storage in Periodic Mesoporous CeO2 Thin Films." ACS Nano, 4, 967-977 (2010).


84. J.B. Levine, S.H. Tolbert, and R.B. Kaner "Advances in the Search for Superhard Ultra-Incompressible Metal Borides." Adv. Func. Mater., 19, 3519-3533 (2009).

83. A. L. Ayzner, C. J. Tassone, S. H. Tolbert, and B. J. Schwartz "Reappraising the Need for Bulk Heterojunctions in Polymer-Fullerene Photovoltaics: The Role of Carrier Transport in All-Solution-Processed P3HT/PCBM Bilayer Solar Cells." J. Phys. Chem. C, 113, 20050 (2009).

82. B. Tremolet de Villers, C. J. Tassone, S. H. Tolbert, and B. J. Schwartz "Improving the Reproducibility of P3HT:PCBM Solar Cells by Controlling the PCBM:Cathode Interface." J. Phys. Chem. C, 113, 18978 (2009).

81. X. Chen, B.L. Kirsch, R. Senter, S.H. Tolbert, and V. Gupta "Tensile Testing of Thin Films Supported on Compliant Substrates." Mechanics Mater., 41, 839-848 (2009).

80. Coquil, E.K. Richman, N.J. Hutchinson, S.H. Tolbert, and L. Pilon "Thermal Conductivity of Cubic and Hexagonal Mesoporous Silica Thin Films." J. Appl. Phys., 106, 034910 (2009).

79. S.D. Korlann, A.E. Riley, B.S. Mun, and S.H. Tolbert "Chemical Tuning of the Electronic Properties of Nanostructured Semiconductor Films formed through Surfactant Templating of Zintl Cluster." J. Phys. Chem. C, 113, 7697-7705 (2009).

78. M.B. Weinberger, J.B. Levine, H.-Y. Chung, R.W. Cumberland, H.I. Rasool, J.-M. Yang, R.B. Kaner, and S.H. Tolbert "Incompressibility and Hardness of Solid Solution Transition Metal Diborides: Ru1-xOsxB2." Chem. Mater., 21, 1915-1921 (2009).

77. T. Brezesinski, J. Wang, J. Polleux, B. Dunn, and S.H. Tolbert "Templated Nanocrystal Based Porous TiO2 Films for Next Generation Electrochemical Capacitors." J. Am. Chem. Soc., 131, 1802-1809, (2009).


76. R.D. Kennedy, A.L. Ayzner, D.D. Wanger, C.T Day, M. Halim, S.I. Khan, S.H. Tolbert, B.J. Schwartz, and Y. Rubin "Self-Assembling Fullerenes for Improved Bulk-Heterojunction Photovoltaic Devices." J. Am. Chem. Soc., 130, 17290-17292 (2008).

75. A.L. Ayzner, D.D. Wanger, C.J. Tassone, S.H. Tolbert and B.J. Schwartz "Room to Improve Conjugated Polymer-Based Solar Cells: Understanding how Thermal Annealing Affects the Fullerene Component of a Bulk Heterojunction Photovoltaic Device." J. Phys. Chem. C, 112, 18711-18716 (2008).

74. X. Chen, E.K. Richman, B.L. Kirsch, R. Senter, S.H. Tolbert, and V. Gupta "Measurement of anisotropic fracture energies in periodic templated silica/polymer composite coatings." J. Appl Phys., 104, 083515 (2008).

73. E.K. Richman, T. Brezesinski, and S.H. Tolbert "Vertically Oriented Hexagonal Mesoporous Films Formed through Nanometer Scale Epitaxy." Nature Mat., 7, 712-717 (2008).

72. E.K. Richman, C.B. Kang, T. Brezesinski, and S.H. Tolbert "Ordered Mesoporous Silicon through Magnesium Reduction of Polymer Templated Silica Thin Films." Nano Lett., 8, 3075-3079 (2008).

71. B.C. Ng, M. Yu, L.H. Rome, H.G. Monbouquette, S.H. Tolbert "Encapsulation of Semiconducting Polymers in Vault Protein Cages."Nano Lett., 8, 3503-3509 (2008).

70. M. Yu, B.C. Ng, L.H. Rome, S.H. Tolbert, and H.G. Monbouquette "Reversible pH Lability of Crosslinked Vault Nanocapsules.” Nano Lett., 8, 3510-3515 (2008).

69. H.Y.Chung, M.B. Weinberger, J.M. Yang, S.H. Tolbert, and R. B. Kaner "Correlation Between Hardness And Elastic Moduli Of The Ultraincompressible Transition Metal Diborides RuB2, OsB2, and ReB2." Appl. Phys. Lett., 92, 261904 (2008).

68. S. Virji, B.H. Weiller, J. Huang, H. Shepherd, T. Faltens, P.C. Haussmann, R. Blair, R.B. Kaner, and S.H. Tolbert "Construction of a Polyaniline Nanofiber Gas Sensor.” J. Chem. Ed., 85, 1102-1104 (2008).

67. M.B. Weinberger, S.H. Tolbert, and A. Kavner "Osmium Metal Studied Under High Pressure and Nonhydrostatic Stress." Phys. Rev. Lett., 100, 045506 (2008).

66. H.-Y. Chung, J.-M. Yang, S.H. Tolbert and R.B. Kaner "Anisotropic Mechanical Properties Of Ultra-Incompressible, Hard Osmium Diboride." J. Mater. Res., 23, 1797-1801 (2008).


65. H.-Y. Chung, M.B. Weinberger, J.B. Levine, R. W. Cumberland, A. Kavner, J.-M. Yang, S.H. Tolbert and R.B. Kaner "Response to Comment on "Synthesis of Ultra-Incompressible Superhard Rhenium Diboride at Ambient Pressure." Science, 318, 1550 (2007).

64. I.B. Martini, I.M. Craig, W.C. Molenkamp, H. Miyata, S.H. Tolbert, and B.J. Schwartz "Controlling Optical Gain in Semiconducting Polymers by Nanoscale Chain Positioning and Alignment." Nature Nanotech., 2, 647-652 (2007).

63. H.-Y. Chung, M.B. Weinberger, J.B. Levine, A. Kavner, J.-M. Yang, and S.H. Tolbert "Synthesis of Ultra-Incompressible Superhard Rhenium Diboride at Ambient Pressure.” Science, 316, 436-439 (2007).

62. A.E. Riley and S.H. Tolbert "Synthesis and Characterization of Tin Telluride Inorganic/Organic Composite Materials with Nanoscale Periodicity Through Solution-phase Self-assembly: A New Class of Composite Materials Based on Zintl Cluster Self-oligomerization." Res. Chem. Intermed., 33, 111-124 (2007).


61. L.C. Huang, E.K. Richman, B.L. Kirsch, and S.H. Tolbert "Controlling Thickness in Hexagonal Polymer Templated Mesoporous Silica Films." Microporous and Mesoporous Mater., 96, 341-349 (2006).

60. A. P.-Z. Clark, A.J. Cadby, C. K-F Shen, Y.F. Rubin, and S.H. Tolbert "Synthesis and Self-Assembly of an Amphiphilic Poly(phenylene ethynylene) Ionomer." J. Phys. Chem. B, 110, 22088-22096 (2006).

59. D. Sun, A.E. Riley, A.J. Cadby, E.K. Richman, S.D. Korlann, and S.H. Tolbert "Hexagonal Nanoporous Germanium Through Surfactant-driven Self-Assembly of Zintl clusters." Nature, 441, 1126-1130 (2006).

58. A.E. Riley, S.D. Korlann, E.K. Richman, and S.H. Tolbert "Synthesis of Semiconducting Thin Films with Nanometer-Scale Periodicity by Solution-Phase Coassembly of Zintl Clusters with Surfactants." Angew. Chem. Int. Ed., 45, 235-241 (2006).


57. S.D. Korlann, A.E. Riley, B.L. Kirsch, B.S. Mun, and S.H. Tolbert "Chemical Tuning of the Electronic Properties in a Periodic Surfactant-Templated Nanostructured Semiconductor." J. Am. Chem. Soc., 127, 12516-12527 (2005).

56. A.J. Cadby and S.H. Tolbert “Controlling Optical Properties and Interchain Interactions in Semiconducting Polymers by Encapsulation in Periodic Nanoporous Silicas with Different Pore Sizes." J. Phys. Chem. B, 109, 17879-17886 (2005).

55. A. P.-Z. Clark, K-F Shen, Y.F. Rubin, and S.H. Tolbert "An Amphiphilic Poly(phenylene ethynylene) as the Structure-Directing Agent for Periodic Nanoscale silica Composite Materials." Nano Lett., 5, 1647-1652 (2005).

54. B.L. Kirsch, X. Chen, E.K. Richman, V. Gupta, and S.H. Tolbert "Probing the Effects of Nanoscale Architecture on the Mechanical Properties of Hexagonal Silica/Polymer Composite Thin Films." Adv. Funct. Mater. 15, 1319-1327 (2005).

53. O. Trofymulk, A.A. Levchenko, S.H. Tolbert, and A. Navrotsky "Energetics of Mesoporous Silica: Investigation into Pore Size and Symmetry." Chem. Mater., 17, 3772-3783 (2005).

52. R.B. Kaner, J.J. Gilman, and S.H. Tolbert "Materials science – Designing Superhard Materials." Science, 308, 1268-1269 (2005).

51.R.W. Cumberland, M.B. Weinberger, J.J. Gilman, S. M. Clark, S.H. Tolbert, and R. B. Kaner "Osmium Diboride, An Ultra-Incompressible, Hard Material." J. Am. Chem. Soc., 127, 7264-7265 (2005).

50. A. Rugge, J.S. Park, R.G. Gordon, and S.H. Tolbert "Tantalum(V) Nitride Inverse Opals as Photonic Structures for Visible Wavelengths." J. Phys. Chem. B, 109, 3764-3771 (2005).

49. A.M. Lapeña, A.F. Gross, and S.H. Tolbert "Examining the Role of Surfactant Packing in Phase Transformation of Periodic Templated Silica/Surfactant Composites." Langmuir, 21, 470-480 (2005).


48. A. Cadby and S.H. Tolbert "Control Of Optical Polaron Production In Semiconducting Polymers Using Host-Guest Chemistry In Hexagonal Nanoporous Silica."Polym. Preprints, 45, 208-209 (2004).

47. D. Sun, C.W. Kwon, G. Baure, E.K. Richman, J. MacLean, B. Dunn, and S.H. Tolbert "The Relationship Between Nanoscale Structure and Electrochemical Properties of Vanadium Oxide Nanorolls." Adv. Funct. Mater. 14, 1197-1204 (2004).

46. B.L. Kirsch, A.E. Riley, A.F. Gross, and S.H. Tolbert "Probing the Effects of Interfacial Chemistry on the Kinetics of Phase Transitions in Amorphous and Tetragonal Zirconia Nanocrystals." Langmuir, 20, 11247-11254 (2004).

45. B.L. Kirsch, E.K. Richman, A.E. Riley, and S.H. Tolbert "In-Situ X-ray Diffraction Study of the Crystallization Kinetics of Mesoporous Titania Films."J. Phys. Chem. B, 108, 12698-12706 (2004).

44. W. Molenkamp, H. Miyata, and S.H. Tolbert, "Highly Polarized Luminescence from Optical Quality Films of Semiconducting Polymers Aligned within Oriented Mesoporous Silica."J. Am. Chem. Soc., 126, 4476-4477 (2004).


43. A. Rugge, J.S. Becker, R.G. Gordon, and S.H. Tolbert, "Tungsten Nitride Inverse Opals by Atomic Layer Deposition.” Nano Lett., 3, 1293-1297 (2003).

42. A. Rugge, W.T. Ford, and S.H. Tolbert, "From a Colloidal Crystal to an Interconnected Colloidal Array: a Mechanism for a Spontaneous Rearrangement." Langmuir, 19, 7852-7861, (2003).

41. A.E. Riley, G.W. Mitchell, P.A. Koutentis, M. Bendikov, P. Kaszynki, F. Wudl, and S.H. Tolbert, "Liquid Crystalline Phase Behavior in a Zwitterionic Tetraazapentacene." Adv. Func. Mater., 13, 531-540 (2003).

40. A.F. Gross, M.R. Diehl, K.C. Beverly, E.K. Richman, and S.H. Tolbert, "Controlling Magnetic Coupling between Cobalt Nanoparticles through Nanoscale Confinement in Hexagonal Mesoporous Silica." J. Phys. Chem. B, 107, 5475-5482 (2003).

39. B.L. Kirsch and S.H. Tolbert "Stabilization of Isolated Hydrous Amorphous and Tetragonal Zirconia Nanoparticles Through the Formation of a Passivating Alumina Shell." Adv. Func. Mater., 13, 281-288 (2003).

38. A.E. Riley and S.H. Tolbert, "Synthesis of Periodic Hexagonal Surfactant Templated Platinum Tin Tellurides – Narrow Band Gap Inorganic/Organic Composites." J. Am. Chem. Soc., 125, 4551-4559 (2003).

37. A.F. Gross, S.Yang, A. Navrotsky, and S.H. Tolbert, "In-Situ Calorimetric Study of the Hexagonal-to-Lamellar Phase Transformation in a Silica/Surfactant Composite." J. Phys. Chem. B, 107, 2709-2718 (2003).


36. A.M. Lapeña, J.J. Wu, A.F. Gross, and S.H. Tolbert, "Using High Pressure Phase Stability to Determine the Internal Pressure of Silica/Surfactant Composites." J. Phys. Chem. B, 106, 11720-11724 (2002).

35. A. Rugge and S.H. Tolbert, "The Effect Of Electrostatic Interactions On Crystallization In Binary Colloidal Films." Langmuir, 18, 7057-7065 (2002).

34. J. Wu, L. Zhao, E.L. Chronister, and S.H. Tolbert, "Elasticity through Nanoscale Distortions in Periodic Surfactant Templated Porous Silica under High Pressure." J. Phys. Chem. B., 106, 5613-5621 (2002).

33. A.F. Gross, V.H. Le, B.L. Kirsch, and S.H. Tolbert, "Chemical Control of Phase Transformation Kinetics in Periodic Silica/Surfactant Composites." J. Am. Chem. Soc., 124, 3713-3724 (2002).


32. A.F. Gross, V.H. Le, B.L. Kirsch, A.E. Riley, and S.H. Tolbert, "Correlations Between Silica Chemistry and Structural Changes in Hydrothermally Treated Hexagonal Silica/Surfactant Composites Examined by In-Situ X-ray Diffraction."Chem. Mater., 13, 3571-3579 (2001).

31. A.F. Gross, V.H. Le, B.L. Kirsch, S.H. Tolbert, "Understanding Phase Stability in Silica/Surfactant Composites through the Study of a Curvature Driven Rectangular Intermediate." Langmuir, 17 3496-3504 (2001).

30. S.H. Tolbert, C.C. Landry, G.D. Stucky, B.F. Chmelka, P. Norby, J. Hanson, and A. Monnier, “Phase Transitions in Mesostructured Silica/Surfactant Composites – Surfactant Packing and the Role of Charge Density Matching." Chem. Mater, 13, 2247-2256 (2001).

29. S.H. Tolbert, J. Wu, A.F. Gross, T.-Q. Nguyen, and B.J. Schwartz, "Directional Energy Migration in an Oriented Nanometer-Scale Host/Guest Composite: Semiconducting Polymers Threaded into Mesoporous Silica."Microporous Mesoporous Mater., 44-45, 445-451 (2001).

28. A.F. Gross, E.J. Ruiz, V. Le, and S.H. Tolbert, "The Role of Silica Chemistry in Controlling Phase Transitions in Silica/Surfactant Composite Materials."Microporous Mesoporous Mater., 44-45, 785-791 (2001).

27. T.-Q. Nguyen, J. Wu, S. H. Tolbert, B. J. Schwartz "Control of Energy Transport in Conjugated Polymers using an Ordered Mesoporous Silica Matrix." Adv. Mater., 13, 609-611, 542 (2001).

26. C.C. Landry, S.H. Tolbert, K.W. Gallis, A. Monnier, G.D. Stucky, P. Norby, and J.C. Hanson, "Phase Transitions in Mesostructured Silica/Surfactant Composites. Mechanisms for Change and Applications to Materials Synthesis." Chem. Mater, 13, 1600-1608 (2001).

25. J. Wu, M. Abu-Omar, S.H. Tolbert, "Fluorescent Probes of the Molecular Environment within Mesostructured Silica/Surfactant Composites under High Pressure." Nano Lett., 1, 27-31 (2001).

24. B.J. Schwartz, T.-Q. Nguyen, J. Wu, and S.H. Tolbert, "Interchain and Intrachain Exciton Transport in Conjugated Polymers: Ultrafast Studies of Energy Migration in Aligned MEH-PPV/Mesoporous Silica Composites." Synthetic Metals, 116, 35-40 (2001).


23. J. Wu, X. Liu, and S.H. Tolbert, "High Pressure Stability in Ordered Mesoporous Silicas – Rigidity and Elasticity through Nanometer Scale Arches." J. Phys. Chem. B., 104, 11837-11841 (2000).

22. A.F. Gross, E.J. Ruiz, and S.H. Tolbert, "Effect of Framework Polymerization on the Phase Stability of Periodic Silica/Surfactant Nanostructured Composites." J. Phys. Chem. B, 104, 5448-5461 (2000).

21. T.-Q. Nguyen, J. Wu, V. Doan, B.J. Schwartz, and S.H. Tolbert, "Control of Energy Transfer in Oriented Conjugated Polymer-Mesoporous Silica Composites." Science, 288, 652-656 (2000).


20. J. Wu, A.F. Gross, and S.H. Tolbert, "Host Guest Chemistry Using an Oriented Mesoporous Host: Alignment and Isolation of a Semiconducting Polymer in the Nano-Pores of an Ordered Silica Matrix." J. Phys. Chem. B., 103, 2374-2384 (1999).

19. A.B. Herhold, C.C. Chen, C.S. Johnson, S.H. Tolbert, and A.P. Alivisatos, "Structural Transformations and Metastability in Semiconductor Nanocrystals." Phase Transitions, 68, 1-25 (1999).


18. S.H. Tolbert, A. Firouzi, G.D. Stucky, and B.F. Chmelka, "Magnetic Field Alignment of Ordered Silicate-Surfactant Composites and Mesoporous Silica." Science, 278, 264-268 (1997).

17. Firouzi, D.J. Schaefer, S.H. Tolbert, G.D. Stucky, and B.F. Chmelka, "Magnetic-Field-Induced Orientational Ordering of Alkaline Lyotropic Silicate-Surfactant Liquid Crystals." J. Am. Chem. Soc., 119, 9466-9477 (1997).

16. S.H. Tolbert, P. Sieger, G.D. Stucky, S.M.J. Aubin, C.-C. Wu, and D.N. Hendrickson, "Control of Inorganic Layer Thickness in Self-Assembled Iron Oxide/Surfactant Composites." J. Am. Chem. Soc., 119, 8652-8661 (1997).

15. S.H. Tolbert, T.E. Schäffer, J. Feng, P.K. Hansma, and G.D. Stucky, "A New Phase of Oriented Mesoporous Silicate Thin Films." Chem. Mater., 9, 1962-1967 (1997).

14. P.F. Feng, X. Bu, S.H. Tolbert, and G.D. Stucky, "Synthesis and Characterizations of Chiral Tetrahedral Cobalt Phosphates with Zeolite ABW and Related Frameworks." J. Am. Chem. Soc., 119, 2497-2504 (1997).

13. A.V. Kadavanich, A. Mews, S.H. Tolbert, X. Peng, M.C. Schlamp, J.C. Lee, and A.P. Alivisatos, "Structural Investigations Of Colloidal Semiconductor Nanocrystal Heterostructures: Faceting And Epitaxy" Advances in Microcrystalline and Nanocrystalline Semiconductors. R.W. Collins, P.M. Fauchet, I. Shimizu, and J.-C. Vial, eds. Mater. Res. Soc. Symp. Proc., 452, 353-358 (1997).


12. A.M. Belcher, C. Zaremba, Q. Huo, C.C. Landry, S.H. Tolbert, A. Firouzi, M. Janicke, P.K. Hansma, D. E. Morse, B.F. Chmelka, S. Schacht, I.G. Voigt-Martin, F. Schüth, and G.D. Stucky, "The Organic/Inorganic Interface and Materials Synthesis in the Nano- to Macroscale Continuum" Chemistry on the Nanometer Scale, the Robert A. Welch Foundation 40th Conference on Chemical Research , (Robert A. Welch Foundation, Houston TX, 1996) pp. 101-112.

11. S.H. Tolbert, A.B. Herhold, L.E. Brus, and A.P. Alivisatos, "Pressure Induced Structural Transformations in Silicon Nanocrystals: Surface and Shape Effects." Phys. Rev. Lett., 76, 4384-4387 (1996).

10. A.B. Herhold, S.H. Tolbert, A.A. Guzelian, and A.P. Alivisatos, "A Comparison of Pressure-Induced Structural Transformations in CdSe, InP, and Si Nanocrystals." Fine Particles Science and Technology From Micro to Nanoparticles, E. Pilizzetti, Ed., NATO ASI Proceedings (Kluwer Academic Publishers, Dordrecht, 1996) pp. 331-342.


9. S.H. Tolbert and A.P. Alivisatos, "High Pressure Phase Transitions in Semiconductor Nanocrystals." Ann. Rev. Phys. Chem., 46, 595-625 (1995).

8. S.H. Tolbert, A.P. Alivisatos, "The Wurtzite to Rock Salt Structural Transformation in CdSe Nanocrystals under High Pressure." J. Chem. Phys., 102, 4642-4656 (1995).


7. S.H. Tolbert, A.B. Herhold, C.S. Johnson, and A.P Alivisatos, "A Comparison of Quantum Confinement Effects on the Electronic Absorption Spectra of Direct and Indirect Gap Semiconductor Nanocrystals." Phys. Rev. Lett., 73, 3266-3269 (1994).

6. S.H. Tolbert and A.P Alivisatos, "Size Dependence of a First Order Solid-Solid Phase Transition: The Wurtzite to Rock Salt Transformation in CdSe Nanocrystals." Science, 265, 373-376 (1994).


5. S.H. Tolbert and A.P Alivisatos, "Se EXAFS Study of the Elevated Wurtzite to Rock Salt Structural Phase Transition in CdSe Nanocrystals" Nanophase Materials: Synthesis Properties-Applications, G.C. Hadipanayis and R.W. Siegel, eds., NATO ASI Proceedings (Kluwer Academic Publishers, Dordrecht, 1993) pp. 471-482.

4. S.H. Tolbert and A.P Alivisatos, "Size Dependence of the Solid-Solid Phase Transition in CdSe Nanocrystals." Zeit. Phys. D - Atoms, Molecules and Clusters, 26, 56-58 (1993)


3. S.H. Tolbert, A.P. Alivisatos, H.E. Lorenzana, M.B. Kruger, and R. Jeanloz, "Raman Studies on C60 at High Pressures and Low Temperatures." Chem. Phys. Lett., 188, 163-167 (1992).


2. J.R Heath, J.M. Hawkins, A.P. Alivisatos, R.J. Saykally, T.A. Lewis, S.D. Loren, A. Meyer, Y. Shibato, S.H. Tolbert, and J.J. Shiang, "C60 Research at the University of California at Berkeley." Proc. of the 1990 Materials Research Conference, Boston, MA, Nov. 25-29 (1990).

1. R.B. Markowitz, S. Tolbert, and W.S. Dynan, "Promoter Evolution in BK Virus: Functional Elements Are Created at Sequence Junctions." J. Virology, 64, 2411-2415 (1990).