Major
Publications of Ru-Shan Wu
Monographs:
"Scattering and Attenuation of Seismic Waves ", edited by Wu
and Aki, volume I, 1988; volume II, 1989; volume III, 1990. Birkhäuser
Verlag, Boston.
"Advances
in Wave Propagation in Heterogeneous Earth ", edited by Wu and
Maupin, 2006, v.48 of "Advances in Geophysics", Series editor
R. Dmowska, Academic Press, Elsevier.
Special Issue
edited:
"Waves in Complex Media", special issue for Phys. Earth
& Planet Int., v. 120, No. 3,
edited by R.S. Wu, 2000, Elsevier, New York.
Recently Submitted
Papers:
·
He, Y. and Wu, R.S., 2009, One-Way/One-Return Boundary Element Method
and Salt Internal Multiples, Geophysics,
submitted.
·
Zhu, X. and Wu, R.S., 2009, Imaging Diffraction
Points Using the Local Image Matrices Generated in Prestack Migration, Geophysics, submitted.
·
Cao, J. and Wu, R.S., 2009, Image amplitude compensations: Comparison of propagator
amplitude recovery and acquisition aperture correction, Geophysics, submitted.
·
Cao, J. and Wu, R.S., 2009, Lateral velocity
variation related correction in asymptotic true-amplitude one-way propagators, Geophysical Prospecting, submitted.
·
Gao, J.H., Yang, S.L., Wang, D.X. and Wu, R.S.,
2009, Estimation of quality factor Q from instantaneous frequency at the
envelope peak of seismic signal in wavelet domain, Geophysics, accepted.
Published Papers:
- Wu, R.S. and Xie, X.B., 2009, Modeling primaries of acoustic/elastic waves by
one-return approximation, The
Leading Edge, in May’s issue.
- Jia, X. and Wu, R.S., 2009, Superwide-angle one-way wave propagator and
its applications in imaging steep salt flanks, Geophysics, in press.
- Cao,
J. and Wu, R.S., 2009,
Full-wave directional illumination analysis in frequency domain, Geophysics, in press.
- Cao,
J. and Wu, R.S., 2009, Fast
acquisition aperture correction in prestack depth migration using beamlet
decomposition, Geophysics, in
press.
- Wu, R.S., Wang, Y. and Luo, M.,
2008, Beamlet migration using local cosine basis, Geophysics, 73,
S207-217.
- Cao,
J. and Wu, R.S., 2008, Amplitude compensation of one-way wave
propagators in inhomogeneous media and its application to seismic imaging:
Special issue "Computational geophysics", Communications in
computational physics, 3, No
1, 203-221.
- Zheng, Y.
and Wu, R.S., 2008, Theory of
transmission fluctuations in random media with a depth-dependent
background velocity structure, in: Earth Heterogeneity and Scattering
Effects on Seismic Waves (eds H. Sato and M.Fehler), Advances of
Geophysics Series Vol. 50,
21-41.
- Wu, X.Y. and Wu, R.S.,
2008, Seismic Wave propagation, in "Handbook of signal processing in acoustics",
Springer-Verlag, v. 2,
1535-1544.
- Gao, J.H., Zhou, Y., Mao, J.,
Chen, W., Wu, R.S., and Li, Y, 2007, A wave propagation method in
local angle domain, Chinese J. of Geophys. , 50, 249-2
- Feng,
W., Wu, R.S., and Ma, Z.T.,
2006, Beamlet decomposition of one-way wave propagator and the application
to illumination analysis and target-oriented imaging, Chinese J. of Geophys..
- Zheng, Y.C., Wu, R.S. and
Lay, T., 2006, Inverting the power spectrum for a heterogeneous medium, Geophys.
J. Intern., doi: 10.1111/j.1365-246X.2006.03241
- Wu, R.S., Xie, X.B.
and Wu, X.Y., 2006, One-way and one-return approximations for fast elastic
wave modeling in complex media, Chapter 5 of " Advances in Wave
Propagation in Heterogeneous Earth", edited by R.S. Wu and V.
Maupin (V.48 of " Advances in Geophysics", Series editor
R. Dmowska), Elsevier, 266-323. PDF
file
- Wu, R.S., Wu, X.Y. and
Xie, X.B., 2006, Simulation of high-frequency wave propagation in complex
crustal waveguides using generalized screen propagators, Chapter 6 of
" Advances in Wave Propagation in Heterogeneous Earth",
edited by R.S. Wu and V. Maupin (V.48 of " Advances in Geophysics",
Series editor R. Dmowska), Elsevier, 324-364. PDF
file
- Xie, X.B., Jin, S. and Wu,
R.S., 2006, Wave-equation based seismic illumination analysis, Geophysics,
71, No 5, S169-177. PDF
file
- Wu, R.S. and Chen, L.,
2006, Mapping directional illumination and acquisition dip-response using
beamlet propagators, Geophysics, 71, No 4, S147-159. PDF
file
- Chen, L., Wu, R.S. and
Chen, Y., 2006, Beamlet migration based on Gabor-Daubechies frame
decomposition, Geophysics, 71, No 2, S37-52. PDF
file
- Wu, X.Y. and Wu, R.S.,
2006, AVO modeling using elastic thin-slab method, Geophysics, 71,
No 5, C57-67. PDF
file
- Hong, T.K. and Wu, R.S.,
2005, Scattering of elastic waves in geometrically anisotropic random
media and its implication to sounding of heterogeneity in the earth's deep
interior, Geophys. J. Int., 163(1), 324-338.
- Zheng, Y.C., and Wu, R.S.,
2005, Measurement of phase fluctuations for transmitted waves in random
media, Geophys. Res. Lett., 32, 2005GL023179. PDF
file
- Ge, Z., Fu, L.Y., and Wu,
R.S., 2005, P-SV wavefield connection technique for regional wave
propagation simulation, Bull. Seis. Soc. Am., 95, No. 4, 1375-1386.
- Han, Q.Y. and Wu, R.S.,
2005, One-way dual-domain propagators for scalar qP-wave in VTI media, Geophysics,
70, No. 2, D9-17.
- Xie, X.B. and Wu, R.S.,
2005, Multicomponent elastic wave prestack depth migration using elastic
screen method, Geophysics, 70,
s30-37.
- Yang, D.H., Lu, M., Wu,
R.S. and Peng, J., 2004, An optimal nearly analytic discrete method
for 2D acoustic and elastic wave equations, BSSA, 94, N.5, 1982-1991.
- Hong, T.K., Wu, R.S.
and B.L.N. Kennett, 2004, Stochastic feature in scattering, Phys, Earth
Planet. Inter., in press.
- Hong, T.K., B.L.N. Kennett,
and R.S. Wu, 2004, Effects of the density perturbation in
scattering, Geophys. Res. Lett., 31 (13), L13602, doi:10.1029/2004GL019933.
- Chen, L., R.S. Wu, and
Wang, W.J., 2004, Common angle image gathers obtained from
Gabor-Daubechies beamlet prestack depth migration, Chinese J. of
Geophys., 47(5), 876-885.
- Chen, L., R.S. Wu, and
Chen, Y., 2004, Construction and application of local scattering matrix
based on wavefield extrapolation in the Gabor-Daubechies beamlet domain, Chinese
J. of Geophys., 47(2),
289-298.
- Feng, W., Wang, H.Z., Wu,
R.S. and Ma, Z.T., 2004, The migration of synthetic waves for
target-oriented controlled illumination: Geophysical Prospecting for
Petroleum, 43(3), 223-228.
- Pride, S.R., Harris, J.M.,
Johnson, D.L., Mateeva, A., Nihei, K.T., Nowack, R.L., Rector, J.W.,
Spetzler, H., Wu, R.S., Yamomoto, T., Berryman, J.G. and Fehler,
M., 2003, Permeability dependence of seismic amplitudes, The Leading
Edge, 22, No 6, 518-525.
- Wu, R.S., 2003, Wave
propagation, scattering and imaging using dual-domain one-way and
one-return propagators, Pure and Appl. Geophys., 160(3/4), 509-539.
- Wu, R.S., 2002,
Spatial coherences of seismic data and the application to characterization
of small-scale heterogeneities, In: "Characterization in the Crust
and Upper Mantle: Nature, Scaling and Seismic Properties", J. A.
Goff and K. Holliger, eds., Kluwer Academic, New York, 321-344.
- Wu, R.S. and Chen, L.,
2002, Wave propagation and imaging using Gabor-Daubechies beamlets, "Theoretical
and Computational Acoustics, World Scientific, New Jersey, 661-670.
- Wu, R.S., Chen, L. and
Wang, Y., 2002, Prestack migration/imaging using synthetic beam-sources
and plane-sources, Special issue of "Studia Geoph. et Geod.",
46, 651-666.
- Fu, L.Y. and Wu, R.S.
and Campillo, M., 2002, Energy partition and attenuation of regional
phases by random free-surface, Bull. Seis. Soc. Am., 92, 1992-2007.
- Jin, S., Mosher, C.C. and Wu,
R.S., 2002, Offset-domain pseudo-screen prestack depth migration, Geophysic
, 67, 1895-1902.
- Jin, S., Xu, S.Y. and Wu,
R.S., 2002, Wave equation based pre-stack depth migration using
generalized screen propagator, Chinese J. of Geophysics , 45,
723-729.
- Sato, H., Fehler, M. and Wu,
R.S., 2002, Scattering and attenuation of seismic waves in the
Lithosphere, "Intern. Handbook of Earthquake & Engineering
Seismology, Part A", Ed. William H.K. Lee, Hiroo Kanamori, Paul
Jennings and Carl Kisslinger, Academic Press, 195-208.
- Chen, L., Wu, R.S.,
Chen, Y. and W. Wang, 2001, Acoustic wavelets applied to seismic signal
decomposition, Chinese Journal of Geophysics, 44(3), 369-378.
- Wu, R.S., Jin, S., and
Xie, X.B., 2001, Generalized screen propagators and the applications to
seismic imaging, Oil Geophysical Prospecting, 36(6), 655-664 (in Chinese with English abstract).
- Wu, X.Y. and Wu, R.S.,
2001, Lg wave simulation in heterogeneous crusts with surface topography
using screen propagators, J. Geophys. International, 146, 670-678.
- Xie, X.B. and Wu, R.S.,
2001, Modeling elastic wave forward propagation and reflection using the
complex screen method, J. Acoust. Soc. Am., 109, 2629-2535.
- Fu, L.Y. and Wu, R.S.,
2001, A hybrid BE-GS method for modeling regional wave propagation, Pure
and Appl. Geophys., 158,
1251-1277.
- Wu, R.S., Jin, S. and
Xie, X.B., 2000, Energy partition and attenuation of Lg waves by numerical
simulations using screen propagators, Phys, Earth Planet. Inter., 120, 227-244.
- Wu, R.S., Jin, S. and
Xie, X.B., 2000, Seismic wave propagation and scattering in heterogeneous
crustal waveguides using screen propagators: I SH waves, Bull. Seis.
Soc. Am., 90, 401-413.
- De Hoop, M., Rousseau, J. and
Wu, R.S., 2000, Generalization of the phase-screen approximation
for the scattering of acoustic waves, Wave Motion, 31, 43-70.
- Fu, L.Y. and Wu, R.S.,
2000, Infinite boundary element absorbing boundary for wave propagation
simulation, Geophysics, 65,
596-602.
- Liu, Y. B., Wu, R. S.
and Ying, C. F., 2000, Scattering of elastic waves by an elastic or
viscoelastic cylinder, J. Geophys. Int., 142, 439-460.
- Wang, Y.Z. and Wu, R.S.,
2000, Seismic data compression by adaptive local cosine/sine transform, Geophysical
Prospecting, 48, 1009-1031.
- Jin, S., Wu, R.S., and
Peng, C., 1999, Seismic depth migration with pseudo-screen propagators: Computational
Geosciences, 3, 321-335.
- Zhang, J., Walter, W.R., Lay,
T., and Wu, R.S., 1999, Polarization of surface waves in Central California from earthquakes along the
circum-Pacific rim, J .Geophys. Res., in press.
- Fan, G., Wallace, T., Zhao,
D., and Wu, R.S., 1999, A seismic tomography study of deep velocity
structure, Computerized Tomography, Theory and Appl., 8,
1-8.
- Huang, L.J., M. Fehler and R.S.
Wu, 1999, Extended local Born Fourier migration method, Geophysics,
64, 1524-1534.
- Jin, S., and Wu, R.S.,
1999, Depth migration with a windowed screen propagator, Journal of
Seismic Exploration, 8(1),
27-38.
- Wu, R.S. and Wang,
Y.Z., 1999, New flexible segmentation technique in seismic data
compression using local cosine transform, "Wavelet Applications in
Signal and Image Processing", Proc. SPIE 3813, 784-794.
- Jin, S., Wu, R.S. and
Xie, X.B., 1998, Wave equation-based decomposition and imaging for
multicomponent seismic data, J. of Seis. Exploration, 7, 145-158
- Wu, R.S. and Wang,
Y.Z., 1998, Comparison of propagator decomposition in seismic imaging by
wavelets, wavelet-packets, and local harmonics, Mathematical Methods in
Geophysical Imaging V, Proc. SPIE, v. 3453, 163-179.
- Jin, S., Wu, R.S. and
Ma, Z., 1998, Decomposition and migration for multicomponent seismic data,
Mathematical Methods in Geophysical Imaging V, Proc. SPIE, v. 3453,
2-13.
- Wang, Y.Z. and Wu, R.S.,
1998, Decomposition and compression of Kirchhoff migration operator by
adapted wavelet packet best bases, Wavelet Applications in Signal and
Image Processing VI, Proc. SPIE , v. 3458, 246-258.
- Chen, Y., Chen, L., Liu, Z.
and Wu, R.S., 1997, A new fractal approach to the clustering of
earthquakes: physical fractal analysis, Bull. Seis. Soc. Am., 88,
89-94.
- Wu, R.S., 1997,
Spatio-temporal distribution of seismic power for a random absorptive slab
in a half space, The proceedings of waves in random and other complex
media, 273-288.
- Wu, R.S. and Yang, F.,
1997, Seismic imaging in wavelet domain: Decomposition and compression of
imaging operator, Wavelet Applications in Signal and Image Processing
V, Proc. SPIE, v. 3169, 148-162.
- Wu, R.S., 1996,
Synthetic seismograms in heterogeneous media by one-return approximation, Pure
and Applied Geophys., 148, 155-173.
- Wu, R.S. and M.V. de
Hoop, 1996, Accuracy analysis and numerical tests of screen propagators
for wave extrapolation, Mathematical methods in geophysical imaging IV,
(ed. Hassanzadeh, S.), Proc. SPIE, v. 2822, 196-209.
- Mosher, C.C, Foster, D.J. and
Wu, R.S., 1996, Phase shift migration with wave packet algorithms, Mathematical
methods in geophysical imaging IV, (ed. Hassanzadeh, S.), Proc. SPIE,
v. 2822, 2-16.
- Huang, L.J. and Wu, R.S.,
1996, 3D prestack depth migration with acoustic pseudo-screen propagators,
Mathematical methods in geophysical imaging IV, (ed. Hassanzadeh, S.),
Proc. SPIE, v. 2822, 40-51.
- Wu, R.S. and Huang,
L.J. , 1995, Reflected wave modeling in heterogeneous acoustic media using
the De Wolf approximation, "Mathematical methods in geophysical
imaging III", (ed. Hassanzadeh, S.), SPIE-The International
Society for Optical Engineering, 176-186.
- Liu, Y.B, Y.M. Li and Wu,
R.S. , 1994, Seismic wave propagation in layered transversely
isotropic porous media, Acta Geophysica Sinica, 37, 499-514.
- Liu, Y.B, Y.M. Li, Wu, R.S.
and S.M. Yu , 1994, Far-field radiation patterns and energies from
different seismic sources in a fluid-filed borehole, Acoustical
Imaging, 20 , 691-697.
- Huang, L.J. and Wu, R.S. ,
1994, Multifrequency Backscattering Tomography (MFBT) in vertically varying
background, Acta Geophysica Sinica, 37, 80-100.
- Wu, R.S. Z.Y. Xu and
X.P. Li, 1994, Heterogeneity spectrum and scale-anisotropy in the upper
crust revealed by the German continental deep-drilling (KTB) holes, Geophys.
Res. Lett., 21, 911-914.
- Liu, Y.B. and Wu, R.S. ,
1994, A comparison between phase-screen, finite difference and
eigenfunction expansion calculations for scalar waves in inhomogeneous
media, Bull. Seis. Soc. Am., 1154-1168.
- Wu, R.S. and X.B. Xie,
1994a, Multi-screen backpropagator for fast 3D elastic prestack migration,
Mathematical Methods in Geophysical Imaging II, SPIE vol. 2301,
181-193..
- Wu, R.S., 1994,
Wide-angle elastic wave one-way propagation in heterogeneous media and an
elastic wave complex-screen method, J. Geophys. Res., 99,
751-766.
- Wu, R.S., F.V. Araujo
and L.J. Huang, 1994, Multi-frequency backscattering tomography for
constant and vertically varying backgrounds, Int. J. of Imaging Syst.
& Tech., 5, 7-21.
- Huang, L.J., Wu, R.S. ,Y,M.
Li, 1993, Generalized holography and multidimensional inverse scattering, in
"Applied Seismic Tomography", W.C. Yang and Y.M. Li (Eds.),
Geological Press, Peking (in Chinese), 1 42-163.
- Liu, Y.B, Y.M. Li, Wu,
R.S. and S.M. Yu, 1993b, Radiative energies from downhole source and
array source, Petroleum Geophysical Prospecting, 28,
389-395.
- Liu, Y.B, Y.M. Li, Wu,
R.S. ,S.M. Yu, 1993a, Far-field radiation pattern of downhole source
and array source, Petroleum Geophysical Prospecting, 28,
- Huang, L.J., Y.M. Li and Wu,
R.S. ,1992, Wave-front ray tracing met hod for image reconstruction, Chinese
J. of Geophys., 35, 281-293.
- Flatté, S.M., Wu,
R.S. and Z.K. Shen, 1991, Nonlinear inversion of phase and amplitude
coherence functions at NORSAR for a model of nonuniform heterogeneities, Geophys.
Res. Lett., 18, 1269-1272.
- Wu, R.S., and X.B.
Xie, 1991, Numerical test on stochastic tomography, Phys, Earth Planet.
Inter., 67, 180-193.
- Bataille, K., Wu, R.S.,
and S.M. Flatt<^'e>é, 1990, Inhomogeneities near the core-mantle
boundary evidenced from seismic wave scattering. - a review, in
"Seismic Wave Scattering and Attenuation" ed. by Wu and Aki, Pure
and Applied Geophys., 132, 151-173.
- Wu, R.S. and S.M.
Flatté, 1990, Transmission fluctuations of seismic waves across
seismic arrays, in "Seismic Wave Scattering and Attenuation" ed.
by Wu and Aki, Pure and Applied Geophys., 132, 175-196.
- Wu, R.S.,1989d,
Imaging principle of randomly heterogeneous medium by transmitted waves, Geophysics
in China in the Eighties, -in commemoration of the 80th birthday of professor
Fu Cheng-yi, Academic Book and Periodicals Press, Beijing, (in Chinese
with English abstract), 360-378.
- Wu, R.S., 1989c, The
perturbation method for elastic wave scattering, in "Seismic Wave
Scattering and Attenuation" ed. by Wu and Aki, Pure and Applied
Geophys., 131, 605-637.
- Wu, R.S. ,1989b,
Seismic wave scattering, invited article for the "Encyclopedia of
Geophysics", ed. by D. James, Van Nostrand Reinhold and Comp.,
1166-1187.
- Wu, R.S.,1989a,
Representation integrals for elastic wave propagation containing either
the displacement term or the stress term alone, Phys. Rev. lett., 62,
497-500.
- Wu, R.S., 1988, On
"Stratigraphic filter theory: Combined effects of parallel bedding
and random inhomogeneities" (I. Lerche), Geophysics, 53,
995-997.
- Wu, R.S. and K. Aki,
1988b, Seismic wave scattering in the three-dimensionally heterogeneous
earth, in the special issue "Seismic Wave Scattering and
Attenuation" ed. by Wu and Aki, Pure and Applied Geophys., 128,
1-6.
- Toksöz, M.N., A.M.
Dainty, E.R. Reiter and Wu, R.S. ,1988, A model for attenuation and
scattering in the earth's crust, in the special issue "Seismic Wave
Scattering and Attenuation" ed. by Wu and Aki, Pure and Applied
Geophys., 128, 81-100.
- Wu, R.S. and K. Aki,
1988a, Multiple scattering and energy transfer of seismic waves,
-separation of scattering effect from intrinsic attenuation. II.
Application of the theory to Hindu Kush
region, in the special issue "Seismic Wave Scattering and
Attenuation" ed. by Wu and Aki, Pure and Applied Geophys., 128,
49-80.
- Lo T.W., M.N. Toksöz,
S.H. Xu and Wu, R.S., 1988, Ultrasonic laboratory tests of
geophysical tomographic reconstruction, Geophysics, 53,
947-956.
- Flatté S.M. and Wu,
R.S., 1988, Small-scale structure in the lithosphere and asthenosphere
deduced from arrival-time and amplitude fluctuations at NORSAR, J. of
Geophys. Res., 93 6601-6614.
- Wu, R.S. and Aki, K.,
1988, Introduction: Seismic scattering in three-dimensionally
heterogeneous earth, Pure and Appl. Geophys., 128, 1-6.
- Toksöz, M.N., Wu,
R.S. , and K.P. Schmitt, 1987, Physical mechanisms contributing to
seismic attenuation in the crust, Strong ground motion seismology,
ed. by Erdik, M.O. and M.M. Toksoz, D. Reidel Publishing Comp. 225-247.
- Wu, R.S. and M.N.
Toksoz, 1987, Diffraction tomography and multi-source holography applied
to seismic imaging, Geophysics, 52, 11-25.
- Wu, R.S., 1986b,
Heterogeneity spectrum, wave scattering response of a fractal random
medium and the rupture processes in the medium, J. of Wave-Material
Interaction, 1, 79-96.
- Wu, R.S., 1986a,
Fractal dimensions of fault surfaces and the inhomogeneity spectrum of the
lithosphere revealed from seismic wave scattering, proceedings of the
international symposium on multiple scattering of waves in random media
and random rough surfaces, July 29 - Aug.2, 1985, Pennsylvania, 929-940.
- Wu, R.S. and K. Aki,
1985c, The fractal nature of the inhomogeneities in the lithosphere
evidenced from seismic wave scattering, Pure and Appl. Geophys., 123,
805-818.
- Wu, R.S., 1985b,
Gaussian beams, complex rays, and the analytic ex tension of Green's
function in smoothly inhomogeneous media, Geophys. J. R. astr. Soc., 83,
93-110.
- Wu, R.S. ,1985a,
Multiple scattering and energy transfer of seismic waves, -separation of
scattering effect from intrinsic attenuation I. Theoretical modelling, Geophys.
J. R. astr. Soc., 82, 57-80.
- Wu, R.S. and A.
Ben-Menahem, 1985, The elastodynamic near field, Geophys. J. R. astr.
Soc., 81, 609-621.
- Aki, K., Wu, R.S., and
R. Nowack, 1985, Seismic wave scattering and lithospheric heterogeneity,
in A.U. Kerr (ed.) The VELA program: A twenty-five year review of basic
research, Defense Advanced Research Projects Agency, 419-423.
- Wu, R.S., and K. Aki,
1985b, Elastic wave scattering by a random medium and the small scale
inhomogeneities in the lithosphere, J. Geophys. Res., 90
10261-10273.
- Wu, R.S., and K. Aki,
1985a, Scattering characteristics of waves by an elastic heterogeneity, Geophysics,
50, 582-595.
- Wu, R.S., 1982b, Mean
field attenuation and amplitude attenuation due to wave scattering, Wave
motion, 4 305-316.
- Wu, R.S., 1982a,
Attenuation of short period seismic waves due to scattering, Geophys.
Res. Lett., 9, 9-12.
- Wu, R.S. and S.H. Xu,
1980, Determination of underground profile of electromagnetic absorption--
a method of geometrical digital imaging, Geophysical and geochemical
prospecting, 6.
- Wu, R.S. and S.H. Xu,
1979, Digital holography applied to borehole electromagnetic wave
exploration, Acta Seismologica Sinica, 1, no.2, 197-213.
- Wu, R.S., and S.H. Xu,
1978, A fast algorithm for near region in holographic reconstruction, Acta
Geophysica Sinica, 21, no.3, 262-267.
- Wu, R.S. ,Wu, Y.L.,
Liu, C.R., Peng, C.Y., and M.J. Wang, 1977, Multi-frequency synthetic
detecting holography, Acta Geophysica Sinica, 20, 33-38.
- The Research Group of
Holography, Chinese Academy of Geological Sciences, 1976, "A
multi-frequency synthetic detecting holography with high depth
resolution", Peking,
China.