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<article article-type="research-article" dtd-version="1.3" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xml:lang="en"><front><journal-meta><journal-id journal-id-type="publisher-id">najo</journal-id><journal-title-group><journal-title xml:lang="en">Nanosystems: Physics, Chemistry, Mathematics</journal-title><trans-title-group xml:lang="ru"><trans-title>Наносистемы: физика, химия, математика</trans-title></trans-title-group></journal-title-group><issn pub-type="ppub">2220-8054</issn><issn pub-type="epub">2305-7971</issn><publisher><publisher-name>Университет ИТМО</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="doi">10.17586/2220-8054-2018-9-2-179-186</article-id><article-id custom-type="elpub" pub-id-type="custom">najo-690</article-id><article-categories><subj-group subj-group-type="heading"><subject>Research Article</subject></subj-group><subj-group subj-group-type="section-heading" xml:lang="en"><subject>MATHEMATICS</subject></subj-group><subj-group subj-group-type="section-heading" xml:lang="ru"><subject>МАТЕМАТИКА</subject></subj-group></article-categories><title-group><article-title>Level crossings of eigenvalues of the Schrodinger Hamiltonian of the isotropic harmonic¨ oscillator perturbed by a central point interaction in different dimensions</article-title><trans-title-group xml:lang="ru"><trans-title></trans-title></trans-title-group></title-group><contrib-group><contrib contrib-type="author" corresp="yes"><name-alternatives><name name-style="western" xml:lang="en"><surname>Fassari</surname><given-names>S.</given-names></name></name-alternatives><bio xml:lang="en"><p>U. Valladolid, 47011 Valladolid</p><p>PO Box 1132, Via F. Rusca 1, CH-6601 Locarno, Switzerland</p><p>Via Plinio 44, I-00193 Rome, Italy</p></bio><email xlink:type="simple">silvestro.fassari@uva.es</email><xref ref-type="aff" rid="aff-1"/></contrib><contrib contrib-type="author" corresp="yes"><name-alternatives><name name-style="western" xml:lang="en"><surname>Gadella</surname><given-names>M.</given-names></name></name-alternatives><bio xml:lang="en"><p>U. Valladolid, 47011 Valladolid</p></bio><email xlink:type="simple">gadella@fta.uva.es</email><xref ref-type="aff" rid="aff-2"/></contrib><contrib contrib-type="author" corresp="yes"><name-alternatives><name name-style="western" xml:lang="en"><surname>Glasser</surname><given-names>M. L.</given-names></name></name-alternatives><bio xml:lang="en"><p>U. Valladolid, 47011 Valladolid</p><p>Potsdam, NY, 13699 USA</p></bio><email xlink:type="simple">laryg@tds.net</email><xref ref-type="aff" rid="aff-3"/></contrib><contrib contrib-type="author" corresp="yes"><name-alternatives><name name-style="western" xml:lang="en"><surname>Nieto</surname><given-names>L. M.</given-names></name></name-alternatives><bio xml:lang="en"><p>U. Valladolid, 47011 Valladolid</p><p> </p></bio><email xlink:type="simple">luismiguel.nieto.calzada@uva.es</email><xref ref-type="aff" rid="aff-2"/></contrib><contrib contrib-type="author" corresp="yes"><name-alternatives><name name-style="western" xml:lang="en"><surname>Matfa62@gmail.com</surname><given-names>F.</given-names></name></name-alternatives><bio xml:lang="en"><p>PO Box 1132, Via F. Rusca 1, CH-6601 Locarno</p><p>Via Plinio 44, I-00193 Rome, Italy</p></bio><xref ref-type="aff" rid="aff-4"/></contrib></contrib-group><aff xml:lang="en" id="aff-1"><institution>Departamento de F´ısica Teorica, At´omica y´	Optica; CERFIM; Dipartimento di Fisica Nucleare, Subnucleare e delle Radiazioni, Univ. degli Studi Guglielmo Marconi</institution><country>Spain</country></aff><aff xml:lang="en" id="aff-2"><institution>Departamento de F´ısica Teorica, At´omica y´	Optica</institution><country>Spain</country></aff><aff xml:lang="en" id="aff-3"><institution>Departamento de F´ısica Teorica, At´omica y´	Optica; Department of Physics, Clarkson University</institution><country>Spain</country></aff><aff xml:lang="en" id="aff-4"><institution>CERFIM; Dipartimento di Fisica Nucleare, Subnucleare e delle Radiazioni, Univ. degli Studi Guglielmo Marconi</institution><country>Switzerland</country></aff><pub-date pub-type="collection"><year>2018</year></pub-date><pub-date pub-type="epub"><day>12</day><month>08</month><year>2025</year></pub-date><volume>9</volume><issue>2</issue><elocation-id>179–186</elocation-id><permissions><copyright-statement>Copyright &amp;#x00A9; Fassari S., Gadella M., Glasser M.L., Nieto L.M., matfa62@gmail.com F., 2025</copyright-statement><copyright-year>2025</copyright-year><copyright-holder xml:lang="ru">Fassari S., Gadella M., Glasser M.L., Nieto L.M., matfa62@gmail.com F.</copyright-holder><copyright-holder xml:lang="en">Fassari S., Gadella M., Glasser M.L., Nieto L.M., matfa62@gmail.com F.</copyright-holder><license xml:lang="ru" license-type="creative-commons-attribution" xlink:href="https://creativecommons.org/licenses/by/4.0/" xlink:type="simple"><license-p>Данная работа распространяется под лицензией Creative Commons Attribution 4.0.</license-p></license><license xml:lang="en" license-type="creative-commons-attribution" xlink:href="https://creativecommons.org/licenses/by/4.0/" xlink:type="simple"><license-p>This work is licensed under a Creative Commons Attribution 4.0 License.</license-p></license></permissions><self-uri xlink:href="https://nanojournal.ifmo.ru/jour/article/view/690">https://nanojournal.ifmo.ru/jour/article/view/690</self-uri><abstract><p>In this brief presentation, some striking differences between level crossings of eigenvalues in one dimension (harmonic or conic oscillator with a central nonlocal δ0-interaction) or three dimensions (isotropic harmonic oscillator with a three-dimensional delta located at the origin) and those occurring in the two-dimensional analogue of these models will be highlighted.</p></abstract><kwd-group xml:lang="en"><kwd>harmonic oscillator</kwd><kwd>point interactions</kwd><kwd>renormalisation</kwd><kwd>eigenvalues</kwd><kwd>level crossing</kwd></kwd-group><funding-group><funding-statement xml:lang="en">S. Fassari wishes to acknowledge Prof. I. Popov’s kind invitation to present the main points of this article in one of the sessions of the conference “Mathematical Challenge of Quantum Transport in Nanosystems, Pierre Duclos Workshop”, held at ITMO University, Saint Petersburg, Russia (September 26-27, 2017). Stimulating discussions with Prof. M.J. Lopez and Prof. J. Negro are kindly acknowledged. Partial financial support is acknowledged to the Spanish Junta de Castilla y Leon and FEDER (Project VA057U16) and MINECO (Project´ MTM2014-57129-C2-1-P). S. Fassari and M.L. Glasser also wish to thank the entire staff at Departamento de F´ısica Teorica, At´	omica y´	Optica, Universidad de Valladolid, for their warm hospitality throughout their stays.´</funding-statement></funding-group></article-meta></front><back><ref-list><title>References</title><ref id="cit1"><label>1</label><citation-alternatives><mixed-citation xml:lang="ru">Albeverio S., Gesztesy F., Høegh-Krohn R., Holden H. 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