My affiliation is at the
Department of Mathematics and Statistics
of University of Helsinki (see also my
Departmental homepage).
Recent research projects supported by the Academy of Finland:

"Spectral analysis of boundary value problems in mathematical physics" (2012),

"Functional analysis and applications" (20102013),

"Mathematical models of pietzoelektric and elastic systems" (20132014)

"Spectrum of the piezoelectricity system" (20152016)

Also: "Spectral problems of Toeplitz and Laplace operators" (20152016), supported by the Väisälä Foundation
of the Finnish Academy of Sciences and Letters.
Responsible organizer of the following recent international conferences:

Mathematical Methods for Spectral Problems: Applications
to waveguides, periodic media and metamaterials,
Helsinki, March 5th7th, 2013.

Operator Theory and Analytic Function Spaces,
Helsinki, October 25th29th, 2010.

Functional Analysis Valencia 2010 (session organizer).
 Elliptic boundary problems, workshop, Helsinki, 12.6.2009
 Analytic function spaces, Joensuu, 29.5.2.6.2006
 Nonlinear parabolic problems, Espoo, 17.21.10.2005
 Functional analysis workshop (satellite conference of
ECM 2004 Stockholm) Joensuu, 20.24.6.2004
 Summer school "Function spaces and operator theory", Joensuu,
19.23.5.2003
 Functional analysis and related topics, Helsinki, 1999
Member of the Board of the
Finnish Mathematical Society during 19962011.
If you want to have a closer look at some of my papers,
please contact me by email!
Here is the complete list of publications.

My research topic is functional analysis, operator theory and applications.
The two main application areas are spectral elliptic boundary problems and operator theory / harmonic analysis in
analytic function spaces. There are also works on parabolic PDE's, deformation quantization,
and most recently, on coherent sheafs of vector valued analytic functions.

SOME MOST RECENT WORKS:

J.T, K.Vilonen, Cartan theorems for Stein manifolds over a discrete valuation base. Here is an
abstract.
S.A.Nazarov, J.T, Pathology of essential spectra of elliptic problems in periodic family of
beads threaded by a spoke thinning at infinity. Submitted.
Here is an abstract.
S.A.Nazarov, J.T, Singularities at the contact point of two kissing Neumann balls. Submitted.
Here is an abstract.
J.Bonet, J.T, Solid hulls of weighted Banach spaces of entire functions. To appear in Rev.Mat.Iberoamericana.
Here is an abstract.
J.T, J. Virtanen On generalized Toeplitz and little Hankel operators on Bergman spaces. Submitted.
Here is an abstract.
Other recent works concern quite classical problems on spectra and eigenfunctions of
the Dirichlet/Neumann Laplacian, spectra of open waveguides, an invisibility result for the linear waterwave
equation, and various aspects of Volterra and
Toeplitz operators on Bergmantype spaces.
TOPICS ON PARTIAL DIFFERENTIAL EQUATIONS:
 Boundary problems for elliptic PDE's.

1. Spectrum of the Neumann
problem for elliptic equations or systems in geometrically intriguing domains.

S.A.Nazarov, J.T,
Singularities at the contact point of two kissing Neumann balls.
Submitted.
S.A.Nazarov, J.T,
Pathology of essential spectra of elliptic problems in periodic family of beads threaded by a spoke thinning at infinity.
Submitted.
F.Bakharev, G.Cardone, S.A.Nazarov, J.T, Particular Rayleigh waves in composite plane.
Submitted.
G.Cardone, S.A.Nazarov, J.T, Spectra of open waveguides in periodic media.
Journal of Functional Analysis 269(2015), 23282364.
S.A.Nazarov, E.Peréz, J.T, Localization effect for Dirichlet eigenfunctions in thin nonsmooth domains.
Transactions A.M.S. 368 (2016), 47874829.
F.Ferraresso, J.T, Singular perturbation Dirichlet problem in a doubleperiodic perforated plane
Ann.Univ.Ferrara 61 (2015), 12161225
S.A.Nazarov, J.T, Structure of the Spectrum of a Periodic Family of Identical Cells Connected by Converging Apertures
J.Math.Sci.194, 1 (2013), 7282.
S.A.Nazarov, J.T, Spectral Anomalies of the Robin Laplacian in NonLipschitz Domains
J.Math.Sci.Univ.Tokyo 20, 1 (2013), 2790
S.A.Nazarov, K.Ruotsalainen, J.T, Spectral gaps in the Dirichlet and Neumann problems on the plane perforated
by a doubleperiodic family of cirular holes.
J.Math.Sci. 181,2 (2012), 164222.
 2. Spectral properties of the
linear elasticity
system.

F.Bakharev, J.T, Bands in the spectrum of a periodic elastic waveguide Submitted.
S.A.Nazarov, J.T, Elastic and piezoelectric waveguides may have
infinite number of gaps in their spectra, Comptes Rendus M\'ecanique. 344 (2016), 190194.
S.A.Nazarov, J.T, Spectral gaps for periodic piezoelectric waveguides. Zeitschrift Angew.Math.Phys. 66 (2015), 30173047
S.A.Nazarov, A.S.Slutskij, J.T,
Korn inequality for a thin rod with rounded ends.
Math.Methods Appl.Sci. 37, 16 (2014), 24632483
G.Cardone, S.A.Nazarov, J.T,
A criterion for the existence of the essential spectrum
for beakshaped elastic bodies.
J.Math. Pur. Appl. 92, 6 (2009), 628–650.
S.A.Nazarov, K.Ruotsalainen, J.T,
Essential spectrum of a periodic elastic waveguide may
contain arbitrarily many gaps.
Applicable Anal. 89,1 (2010), 109124.

3. Spectral problems with Steklov boundary condtions.

V.Chiado Piat, S.A.Nazarov, J.T, Embedded eigenvalues for waterwaves in a three
dimensional channel with a thin screen. Submitted.
S.A.Nazarov, J.T, Radiation conditions for the linear waterwave
problem in periodic channels. To appear in Math.Nachr.
A.S.BonnetBenDhia, S.A.Nazarov, J.T, Underwater topography invisible for surface waves at given
frequencies
Wave Motion 57 (2015), 129142.
F.Bakharev, K.Ruotsalainen, J.T, Spectral gaps for the linear surface wave model in periodic channels.
Quaterly J.Mech.Appl.Math. 67, 3 (2014), 343362
J.Martin, S.A.Nazarov, J.T, Spectrum of the linear water model for a twolayer liquid with cuspidal geometries at the interface
Z.Angew.Math.Mech. 118 (2014)
S.A.Nazarov, J.T, Properties of the Spectrum in the John Problem on a Freely Floating Submerged Body in a Finite Basin
Differential Eq. 49, 12 (2013), 15441559
S.A.Nazarov, J.T, Localization estimates for eigenfrequences of waves trapped by
freely floating body in channel.
SIAM J.Math.Anal. 45, 4 (2013), 25232545
S.A.Nazarov, J.T, J.Videman, Asymptotic behaviour of interfacial trapped modes in a twolayer fluid.
Wave Motion 50,2 (2013), 111126
S.A.Nazarov, J.T, Radiation conditions at the top of a rotational cusp in the theory
of waterwaves.
Math. Model. Numer. Anal. 45,4 (2011), 947979
 Parabolic PDE's
 1. Longtime asymptotics of
semilinear diffusion equations..

J.T, Long time asymptotics of subthreshold solutions of a semilinear
Cauchy problem.
Diff.Eq.Appl. 3,2 (2011), 279297
J.T, Asymptotical behaviour of a semilinear diffusion equation.
J.Evol.Equations 7,3 (2007), 429447
 2.
CahnHilliard equation.

T.Korvola, A.Kupiainen, J.T, Anomalous scaling for 3d CahnHilliard fronts.
Comm. Pure Appl. Math.
LVIII, (2005), 10771115.
J.Bricmont, A.Kupiainen, J.T, Stability of CahnHilliard fronts
Comm.Pure.Appl.Math. LII (1999), 839871.
 3.
Gradient blowup.

M.Fila, J.T, M.Winkler, Convergence to a singular steady state of
a parabolic equation with gradient.
Appl.Math.Letters 20 (2007), 578582.
TOPICS ON ANALYTIC FUNCTION SPACES:

Structure of analytic function spaces and sheaves
 1.
Coherent analytic sheaves:
extension of the Cartan theorems
A and B.

J.T, K.Vilonen, Cartan theorems for Stein manifolds over a discrete valuation base.
Manuscript, arXiv identifier 1609.03658

2.
Solid hulls of analytic function spaces.

J.Bonet, J.T, Solid hulls of weighted Banach spaces of entire functions.
To appear in Rev.Mat.Iberoamericana.

Toeplitz and Volterra operators
 1. Toeplitz operators on Bergman
spaces: boundedness, compactness and Fredholm
properties.

J.T, J.Virtanen,
On generalized Toeplitz and little Hankel operators on Bergman spaces.
Submitted.
A.Perälä, J.T, J.Virtanen, Toeplitz operators of DirichletBesov spaces.
To appear in Houston J.Math.
J.Bonet, J.T, A note about Volterra operators on weighted Banach spaces of entire functions
Math. Nachrichten 288 (2015), 12161225.
A.Perälä, J.T, J.Virtanen, New results and open problems on Toeplitz operators in Bergman spaces
New York J. Math. 17a (2011), 147164.
A.Perälä, J.T, J.Virtanen, Toeplitz operators with distributional symbols on Fock spaces.
Funct. et approx. 44,2 (2011), 203213.
W.Lusky, J.T, Toeplitz operators on Bergman spaces and Hardy multipliers.
Studia Math. 204 (2011), 137154.
J.T, J.Virtanen, Weighted BMO and Toeplitz operators on the
Bergman space A¹.
J. Operator Th. 68 (2012), 131140.
A.Perälä, J.T, J.Virtanen, Toeplitz operators with distributional symbols
on Bergman spaces.
Proc.Edinburgh Math.Soc. 54, 2 (2011), 505514.
J.T, J.Virtanen, Toeplitz operators on Bergman spaces with locally
integrable symbols.
Rev.Math.Iberoamericana 26,2 (2010), 693706.

2. Toeplitz operators and
locally convex spaces.

J.Bonet, J.T, Toeplitzoperators on the space of analytic functions with logarithmic
growth.
J.Math.Anal.Appl. 353 (2009), 428435.
M.Engliš, J.T, Deformation quantization and Borel's theorem in locally convex
spaces.
Studia Math. 180,1 (2007), 7793.

Bergmantype projections
 1. Weighted supnorm estimates.

P.Erkkilä, J.T, Supnorm estimates for Bergman projections on
regulated domains.
Math.Scand. 102, 1 (2008), 111130.
J.Bonet, M.Engliš, J.T, Weighted L∞estimates for Bergman projections.
Studia Math.171,1 (2005), 6792.
M.Engliš, T.Hänninen, J.T,
Minimal L∞type spaces on strictly pseudoconvex domains
on which the Bergman projection is continuous.
Houston J. Math. 32,1 (2006)
J.T, On the continuity of the Bergman and Szegö
projections.
Houston J.Math. 30,1 (2004), 171190.
 2. General projections for
rapidly decreasing weights.

W.Lusky, J.T, On weighted spaces of holomorphic functions of
several variables.
Israel J.Math. 176,1 (2010), 381399.
W.Lusky, J.T, Bounded holomorphic projections for exponentially
decreasing weights.
J. Function Spaces Appl. 6, 1 (2008), 5970.
 Composition operators
 Composition operators on
Blochtype spaces and hyperbolic function classes.

F.PerezGonzales, J.Rättyä, J.T, Lipschitz continuous and compact composition operators on hyperbolic classes.
Mediterranean J.Math. 8,1 (2011), 123135.
O.Blasco, M.Lindström, J.T, BlochtoBMOA compositions in several complex
variables.
Complex Var. Theory Appl. 50, 14 (2005), 10611080.
SELECTION OF PAPERS ON VARIOUS TOPICS IN
FUNCTIONAL ANALYSIS:
Weighted inductive limits of entire functions
(K.D.Bierstedt, J.Bonet,J.Taskinen).
Monatshefte Math.
154, 2 (2008), 103120.
Regularly decreasing weights and the topological
subspace problem. Math. Nachr.278, 10 (2005), 18.
The essential norm of BlochtoQp composition
operators (M.Lindström, S.Makhmutov, J.Taskinen). Can.Math.Bull. 47,2
(2004), 4959.
Subspace problem for
weighted inductive limits
revisited. (J.Bonet, J.Taskinen) Rocky Mountain Math.J. 30, 1 (2000), 8599.
Composition operators between weighted Banach spaces
of analytic functions (J.Bonet, P.Domanski, M.Lindström, J.Taskinen).
J.Austr. Math. Soc. (Ser. A) 64 (1998), 101118.
Associated weights and spaces of holomorphic functions
(K.D.Bierstedt, J.Bonet, J.Taskinen).
Studia Math. 127, 2 (1998), 137168.
Compact composition operators on general weighted
spaces. Houston J.Math. 27 (2001), 203218.
Linearization of holomorphic mappings on C(K)spaces.
Isr.J.Math. 92 (1995), 207219.
An application of averaging operators to multilinearity.
Math. Annalen 297.3 (1993), 567572.
A continuous surjection from the unit interval onto
the unit square. Rev. Mat. Univ.
Complutense Madrid 6.1 (1993), 101120.
A Fr\'echetSchwartz space with basis having a complemented
subspace without basis. Proc. Amer. Math. Soc. 113,1
(1991), 151155.
Nondistinguished Fréchet function spaces
(J.Bonet, J.Taskinen).
Bull. Soc. Roy. Sci. Liége 58, 483490 (1989)
On the injective tensor product of (DF)spaces
(A.Defant, K.Floret, J.Taskinen).
Arch. Math. 57, 149154
(1991).
On a problem of topologies in infinite dimensional holomorpy
(J.M. Ansemil, J.Taskinen). Arch. Math. 54, 6164
(1990)
(FBa) and (FBB)spaces. Mathematische Zeitschrift 198,
339365 (1988)
The Projective Tensor Product of FréchetMontel Spaces.
Studia Mathematica 91, 1730 (1988).
Counterexamples to "Probléme des topologies" of Grothendieck.
Ann. Acad. Sci. Fenn. Ser. A I. Diss. 63 (1986).
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