Publications (2010-)
[H10a]	Hirosawa, F., Energy estimates for wave equations with time dependent propagation speeds in the Gevrey class. J. Differential Equations. 248 (2010), no. 12, 2972-2993.
[H10b]	Hirosawa, F., On second order weakly hyperbolic equations with oscillating coefficients and regularity loss of the solutions. Math. Nachr. 283 (2010), no. 12, 1771-1794.
[H10c]	Hirosawa, F., Energy estimates of wave equations with variable propagation speed in bounded domain. Algebraic structures in partial differential equations related to complex and Clifford analysis, 189–207, Ho Chi Ming City Univ. Educ. Press, Ho Chi Minh City, 2010.
[BuH11]	Bui, T. B. N. and Hirosawa, F., On energy estimates for second order hyperbolic equations with Levi conditions for higher order regularity. Ann. Univ. Ferrara Sez. VII Sci. Mat. 57 (2011), 317-339.
[BoH12]	Böhme, C. and Hirosawa, F., Generalized energy conservation for Klein-Gordon type equations. Osaka J. Math. 49 (2012), 297-323.
[HIP13]	Hirosawa, F., Inooka, T. and Pham, T. D., On the global solvability for semilinear wave equations with smooth time dependent propagation speeds. Progress in Partial Differential Equations: Asymptotic Profiles, Regularity and Well-Posedness, 153-181, Springer Proceedings in Mathematics & Statistics, 44, Springer, Heidelberg, 2013.
[HI13]	Hirosawa, F. and H. Ishida, On second order weakly hyperbolic equations and the ultradifferentiable classes. J. Differential Equations. 255 (2013), no. 7, 1437-1468.
[H15]	Hirosawa, F.  A class of non-analytic functions for the global solvability of Kirchhoff equation. Nonlinear Anal. 116 (2015), 37-63.
[EFH15]	Ebert, M. R., Fitriana, L. and Hirosawa, F., On the energy estimates of the wave equation with time dependent propagation speed asymptotically monotone functions, J. Math. Anal. Appl. 432 (2015), 654-677.
[EFH17]	Ebert, M. R., Fitriana, L. and Hirosawa, F., A remark on the energy estimates for wave equations with integrable in time speed of propagation. New trends in analysis and interdisciplinary applications, 481-488, Trends Math. Res. Perspect., Birkhauser/Springer, Cham, 2017.
[HN18]	Hirosawa, F. and Nascimento W. N., Energy estimates for the Cauchy problem of Klein-Gordon type equation with non-effective and very fast oscillating time-dependent potential. Ann. Mat. Pura Appl. 197 (2018), 817-841.

Preprints
[H]	On the energy estimate for Klein-Gordon type equations with time dependent singular mass.

Publications (-2009)
[HW09]	Hirosawa, F. and Wirth, J., Generalised energy conservation law for the wave equations with variable propagation speed. J. Math. Anal. Appl. 358 (2009), no. 1, 56-74.
[CHR08a]	Cicognani, M., Hirosawa, F. and Reissig, M., Loss of regularity for p-evolution type models. J. Math. Anal. Appl. 347 (2008), no. 1, 35-58.
[CHR08b]	Cicognani, M., Hirosawa, F. and Reissig, M., The Log-effect for p-evolution type models. J. Math. Soc. Japan. 60 (2008), no. 3, 819-863.
[CH08]	Cicognani, M. and Hirosawa, F., On the Gevrey well-posedness for second order strictly hyperbolic Cauchy problems under the influence of the regularity of the coefficients. Math. Scand. 102 (2008), no. 2, 283-304.
[HW08]	Hirosawa, F. and Wirth, J., C^m-theory of damped wave equations with stabilisation. J. Math. Anal. Appl. 343 (2008), no. 2, 1022-1035.
[H07]	Hirosawa, F., On the asymptotic behavior of the energy for the wave equations with time depending coefficients. Math. Ann. 339 (2007), no. 4, 819-839.
[H06]	Hirosawa, F., Global solvability for Kirchhoff equation in special classes of non-analytic functions. J. Differential Equations. 230 (2006), no. 1, 49-70.
[HR06]	Hirosawa, F. and Reissig, M., Levi condition for hyperbolic equations with oscillating coefficients. J. Differential Equations. 223 (2006), no. 2, 329-350.
[H05]	Hirosawa, F., Loss of regularity for second order hyperbolic equations with singular coefficients. Osaka J. Math. 42 (2005), no. 4, 767-790.
[HR04a]	Hirosawa, F. and Reissig, M., About the optimality of oscillations in non-Lipschitz coefficients for strictly hyperbolic equations. Ann. Scuola Norm. Sup. Pisa Cl. Sci. (5) 3 (2004), no. 3, 589-608.
[HR04b]	Hirosawa, F. and Reissig, M., Well-posedness in Sobolev spaces for second order strictly hyperbolic equations with non-differentiable oscillating coefficients. Ann. Global Anal. Geom. 25 (2004), no. 2, 99-119.
[HN03]	Hirosawa, F. and Nakazawa, H., Rapid decay of the total energy for dissipative wave equations. Tsukuba J. Math. 27 (2003), no. 2, 217-232.
[HR03]	Hirosawa, F. and Reissig, M., From wave to Klein-Gordon type decay rates. Nonlinear hyperbolic equations, spectral theory, and wavelet transformations, 95-155, Oper. Theory Adv. Appl., 145, Birkhäuser, Basel, 2003.
[H03a]	Hirosawa, F., Loss of regularity for the solutions to hyperbolic equations with non-regular coefficients - an application to Kirchhoff equation -. Math. Methods Appl. Sci. 26 (2003), no. 9, 783-799.
[H03b]	Hirosawa, F., On the Cauchy problem for second order strictly hyperbolic equations with non-regular coefficients. Math. Nachr. 256 (2003), 28-47.
[H02]	Hirosawa, F., Degenerate Kirchhoff equation in ultradifferential class. Nonlinear Anal. 48 (2002), no. 1, 77-94.
[H00]	Hirosawa, F., Energy decay for degenerate hyperbolic equations of Klein-Gordon type with dissipative term. Funkcial. Ekvac. 43 (2000), no. 1, 163-191.
[H99]	Hirosawa, F., Energy decay for a degenerate hyperbolic equation with a dissipative term. Publ. Res. Inst. Math. Sci., Kyoto Univ. 35 (1999), no. 3, 391-406.
[H98]	Hirosawa, F., Global solvability for the degenerate Kirchhoff equation. Ann. Scuola Norm. Sup. Pisa Cl. Sci. (4) 26 (1998), no. 1, 75-95.
[H97]	Hirosawa, F., Global solvability for the generalized degenerate Kirchhoff equation with real-analytic data in Rn. Tsukuba J. Math. 21 (1997), no. 2, 483-503.