My MR Author ID in MathSciNet is 832714, researcherID in Web of Sciences is G-4339-2016, Orcid ID in Scopus is 0000-0002-0982-8360 and here is my Google Scholar profile.

List of publications

  1. R. Klén, G. Martin: Distortion and topology, to appear in J. Anal. Math. (arXiv)
  2. R. Klén, J. Talponen, A. Rasila: On Smoothness of Quasihyperbolic Balls, to appear in Ann. Acad. Sci. Fenn. Math. (arXiv)
  3. X. Zhang, R. Klén, V. Suomala, M. Vuorinen: Volume growth of quasihyperbolic balls. Mat. Sb. 208 (2017), no. 6, 902-914. (arXiv)
  4. R. Klén, V. Todorcevic, M. Vuorinen: Teichmüller's problem in space. J. Math. Anal. Appl. 455 (2017), 1297-1316. (arXiv)
  5. B.A. Bhayo, R. Klén, J. Sándor: New trigonometric and hyperbolic inequalities. Math. Notes (Miskolc) 18 (2017), 125-137. (arXiv)
  6. P. Hariri, R. Klén, M. Vuorinen, X. Zhang: Some remarks on the Cassinian metric. Publ. Math. Debrecen 90/3-4 (2017), 269-285. (arXiv)
  7. R. Klén: Hyperbolic type distances in starlike domains. Results Math. 72 (2017), 47-69. (arXiv)
  8. P. Hästö, R. Klén, S. Sahoo, M. Vuorinen: Geometric properties of phi-uniform domains. J. Analysis 24 (2016), 57-66. (arXiv)
  9. R. Klén, M.R. Mohanpatra, S.K. Sahoo: Geometric properties of the Cassinian metric. Math. Nachr. published online on 5th December 2016. (arXiv)
  10. P. Harjulehto, P. Hästö, R. Klén: Generalized Orlicz spaces and related PDE, Nonlinear Anal. 143 (2016), Pages 155-173.
  11. R. Klén, T. Noponen, J. Koikkalainen, J. Lötjönen, K. Thielemans, E. Hoppela, H. Sipilä, M. Teräs, J. Knuuti: Evaluation of motion-correction methods for dual-gated cardiac positron emission tomography/computed tomography imaging, Nucl. Med. Commun. 37(9), 2016, 956-68.
  12. R. Klén, M. Vuorinen, X. Zhang: On isometries of Conformally Invariant Metric, J. Geom. Anal. 26 (2016), 914-923. (arXiv)
  13. S. Hokuni, R. Klén Y. Li, M. Vuorinen: Balls in the triangular ratio metric, Complex Analysis and Dynamical Systems VI. Part 2, 105-123, Contemp. Math. 667, Amer. Math. Soc., Providence, RI, 2016. (arXiv)
  14. P. Hästö, R. Klén: Solution of two conjectures of Klén, Lindén, Vuorinen and Wang. Comput. Methods Funct. Theory 16 (2016), 283-286.
  15. T. Kokki, R. Klén, T. Noponen, J. Pärkkä, V. Saunavaara, E. Hoppela, M. Teräs, J. Knuuti: Linear relation between spirometric volume and the motion of cardiac structures - MRI and clinical PET study. J. Nucl. Cardiol. 23 (2016), 475-485.
  16. T. Noponen, R. Klén, T. Kokki, J. Teuho, K. Thielemans, J. Koikkalainen, E. Hoppela, H. Sipilä, J. Lötjönen, M. Teräs, J. Knuuti: Development of Motion Correction Methods for Cardiac PET Imaging. European Journal of Nuclear Medicine and Molecular Imaging 42 (2015), S72-S72.
  17. P. Harjulehto, R. Klén: Examples of fractals satisfying the quasihyperbolic boundary condition. Aust. J. Math. Anal. Appl. 12 (2015), no. 1, Art. 9. (arXiv)
  18. J. Chen, P. Hariri, R. Klén, M. Vuorinen: Lipschitz conditions, triangular ratio metric, and quasiconformal maps. Ann. Acad. Sci. Fenn. Math. 40, 2015, 683-709. (arXiv)
  19. A. Baricz, B.A. Bhayo, R. Klén: Convexity properties of generalized trigonometric and hyperbolic functions. Aequationes Math. Volume 89, Issue 3 (2015), 473-484. (arXiv)
  20. P. Harjulehto, R. Klén, M. Koskenoja: Analyysiä reaaliluvuilla, Unigrafia, Helsinki, 2014, 356 pages, ISBN 978-952-93-4162-7. (A calculus textbook for the first year students.)
  21. R. Klén, H. Lindén, M. Vuorinen, G. Wang: The visual angle metric and Möbius transformations - Comput. Methods Funct. Theory October 2014, Volume 14, Issue 2-3, pp 577-608. (arXiv)
  22. R. Klén, Y. Li, S.K. Sahoo, M. Vuorinen: On the stability of phi-uniform domains. Monatsh. Math. 174 (2014), Issue 2, pp 231--258. (arXiv)
  23. R. Klén, V. Manojlovic, S. Simic, M. Vuorinen: Bernoulli inequality and hypergeometric functions. Proc. Amer. Math. Soc. 142 (2014), 559-573 , (arXiv)
  24. R. Klén, M. Vuorinen, X. Zhang: Quasihyperbolic metric and Möbius transformations. Proc. Amer. Math. Soc. 142 (2014), no. 1, 311–-322, (arXiv)
  25. R. Klén, M. Vuorinen, X. Zhang: Inequalities for the generalized trigonometric and hyperbolic functions. J. Math. Anal. Appl 409 (2014), no. 1, 521–-529. (arXiv)
  26. R. Klén: Local convexity properties of Apollonian and Seittenranta's metric balls. Conform. Geom. Dyn. 17 (2013), 133-144, (arXiv)
  27. R. Klén, Y. Li, M. Vuorinen: Subdomain geometry of hyperbolic type metrics. - Transactions of the Institute of Mathematics of the National Academy of Sciences of Ukraine, Vol. 10, N 4-5 (2013), 190-206. (arXiv)
  28. R. Klén, M. Vuorinen: Inclusion relations of hyperbolic type metric balls II - Publ. Math. Debrecen 83/1-2 (2013), 21-42. (arXiv)
  29. R. Klén, V. Suomala: Dimension of the boundary in different metrics - Math. Scand. 112 (2013), 275-301. (arXiv)
  30. R. Klén, M. Vuorinen: Inclusion relations of hyperbolic type metric balls - Publ. Math. Debrecen 81/3-4 (2012), 289-311. (arXiv)
  31. R. Klén, M. Vuorinen: Apollonian circles and hyperbolic geometry - J. Analysis 19 (2011), 41-60. (arXiv)
  32. E. Lankinen, A. Saraste, T. Noponen, R. Klén, M. Teräs, T. Kokki, S. Kajander, M. Pietilä, H. Ukkonen, J. Knuuti: Coronary plaque imaging in patients with unstable angina pectoris using dual gated [18F]-FDG PET/CT - Eur. Heart J. Suppl. 13 (2011), A2.
  33. R. Klén, A. Rasila, J. Talponen: Quasihyperbolic Geometry in Euclidean and Banach Spaces - J. Analysis 18 (2010), 261-278. (arXiv)
  34. R. Klén: Close-to-convexity of Quasihyperbolic and j-metric Balls - Ann. Acad. Sci. Fenn. Math. 35 (2010), 493-501. (arXiv)
  35. R. Klén, M. Visuri, M. Vuorinen: On Jordan type inequalities for hyperbolic functions - J. Inequal. Appl. Vol. 2010, Article ID 362548, 14pp. (arXiv)
  36. R. Klén, T. Noponen, J. Koikkalainen, J. Lötjönen, K. Thielemans, E. Hoppela, H. Sipilä, M. Teräs, J. Knuuti: CT based motion correction of dual gated cardiac PET images - J. Nucl. Med. 51 (2010), no. supplement 2 1367
  37. T. Kokki, H.T. Sipilä M. Teräs, T. Noponen, N. Durand-Schaefer, R. Klén, J. Knuuti: Dual gated PET/CT imaging of small targets of the heart: Method description and testing with a dynamic heart phantom - J. Nucl. Cardiol. 17 (2009), 71-84.
  38. R. Klén: On hyperbolic type metrics - Ann. Acad. Sci. Fenn. Math. Diss. 152, 2009, 49pp.
  39. R. Klén: Local Convexity Properties of Quasihyperbolic Balls in Punctured Space - J. Math. Anal. Appl. 342 (2008), 192-201. (arXiv)
  40. R. Klén: Local Convexity Properties of j-metric Balls - Ann. Acad. Sci. Fenn. Math. 33 (2008), 281-293. (arXiv)


  41. The Fourier Condition Based Comparison of Parameters for Spherical Symmetric Volume Elements Using Computer Simulated Data (joint work with J. Lindén, J. Johansson and M. Teräs)
  42. Local convexity properties of the triangular ratio metric balls (joint work with P. Hariri and M. Vuorinen) (arXiv)
  43. Optimal number of gates in dual gated cardiac PET (joint work with multiple authors)
  44. Hyperbolic distance between hyperbolic lines
  45. Ptolemy constant and uniformity (joint work with E. Harmaala) (arXiv)