<?xml version="1.0" encoding="ISO-8859-1"?><article 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">
<front>
<journal-meta>
<journal-id>1409-2433</journal-id>
<journal-title><![CDATA[Revista de Matemática Teoría y Aplicaciones]]></journal-title>
<abbrev-journal-title><![CDATA[Rev. Mat]]></abbrev-journal-title>
<issn>1409-2433</issn>
<publisher>
<publisher-name><![CDATA[Centro de Investigaciones en Matemática Pura y Aplicada (CIMPA) y Escuela de Matemática, San José, Costa Rica.]]></publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id>S1409-24332022000200225</article-id>
<article-id pub-id-type="doi">10.15517/rmta.v29i2.46390</article-id>
<title-group>
<article-title xml:lang="en"><![CDATA[Cosmological exact solutions of Petrov type D. a mixture of two fluids: dark energy and radiation]]></article-title>
<article-title xml:lang="es"><![CDATA[Soluciones cosmológicas exactas del tipo Petrov D. una mezcla de dos fluidos: energía oscura y radiación]]></article-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Alvarado Marín]]></surname>
<given-names><![CDATA[Rodrigo]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Angulo Sibaja]]></surname>
<given-names><![CDATA[Andrés A.]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Vargas Obando]]></surname>
<given-names><![CDATA[Mauricio]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
</contrib-group>
<aff id="Af1">
<institution><![CDATA[,Universidad de Costa Rica Centro de Investigaciones Espaciales (CINESPA) y Escuela de Física ]]></institution>
<addr-line><![CDATA[ ]]></addr-line>
<country>Costa Rica</country>
</aff>
<aff id="Af2">
<institution><![CDATA[,Universidad de Costa Rica Escuela de Física ]]></institution>
<addr-line><![CDATA[ ]]></addr-line>
<country>Costa Rica</country>
</aff>
<aff id="Af3">
<institution><![CDATA[,Universidad de Costa Rica Escuela de Física ]]></institution>
<addr-line><![CDATA[ ]]></addr-line>
<country>Costa Rica</country>
</aff>
<pub-date pub-type="pub">
<day>00</day>
<month>12</month>
<year>2022</year>
</pub-date>
<pub-date pub-type="epub">
<day>00</day>
<month>12</month>
<year>2022</year>
</pub-date>
<volume>29</volume>
<numero>2</numero>
<fpage>225</fpage>
<lpage>238</lpage>
<copyright-statement/>
<copyright-year/>
<self-uri xlink:href="http://www.scielo.sa.cr/scielo.php?script=sci_arttext&amp;pid=S1409-24332022000200225&amp;lng=en&amp;nrm=iso"></self-uri><self-uri xlink:href="http://www.scielo.sa.cr/scielo.php?script=sci_abstract&amp;pid=S1409-24332022000200225&amp;lng=en&amp;nrm=iso"></self-uri><self-uri xlink:href="http://www.scielo.sa.cr/scielo.php?script=sci_pdf&amp;pid=S1409-24332022000200225&amp;lng=en&amp;nrm=iso"></self-uri><abstract abstract-type="short" xml:lang="en"><p><![CDATA[Abstract In this paper, two exact solutions of the Einstein's equations are obtained for an anisotropic and homogeneous symmetry of Petrov Type D, the difference between both solutions lies in how relevant is the expansión that is presented initially, either on an axis or on a perpendicular plane. Both solutions represent a mixture of two fluids with minimum interaction: dark energy (P = -µ) and radiation (P = µ/3). The singularities and the influence that these fluids have on this metric are studied; the Hubble parameters, the deceleration parameter and the role that these fluids representon them are determined and analyzed. Additionally, their temperatura and the role that both play on this magnitude are determined.]]></p></abstract>
<abstract abstract-type="short" xml:lang="es"><p><![CDATA[Resumen En este trabajo se obtienen dos soluciones exactas de las ecuaciones de Einstein para una simetría anisotrópica y homogénea del Tipo Petrov D, la diferencia entre ambas soluciones radica en que tan relevante es la expansión que se presenta inicialmente, ya sea en un eje o en un plano perpendicular. Dichas soluciones representan una mezcla de dos fluidos con mínima interacción: energía oscura (P = -µ) y radiación (P = µ/3). Se estudia las singularidades y la influencia que estos fluidos tienen en esta métrica; así como el parámetro de Hubble, el parámetro de desaceleración y la influencia que estos fluidos tienen en ellos. Además, se determina su temperatura y el papel que ambos juegan en esta magnitud.]]></p></abstract>
<kwd-group>
<kwd lng="en"><![CDATA[cosmology]]></kwd>
<kwd lng="en"><![CDATA[exact solution]]></kwd>
<kwd lng="en"><![CDATA[Einstein]]></kwd>
<kwd lng="en"><![CDATA[temperature]]></kwd>
<kwd lng="en"><![CDATA[Hubble]]></kwd>
<kwd lng="en"><![CDATA[deceleration parameter]]></kwd>
<kwd lng="en"><![CDATA[Kretschmann]]></kwd>
<kwd lng="en"><![CDATA[singularity.]]></kwd>
<kwd lng="es"><![CDATA[cosmología]]></kwd>
<kwd lng="es"><![CDATA[solución exacta]]></kwd>
<kwd lng="es"><![CDATA[Einstein]]></kwd>
<kwd lng="es"><![CDATA[temperatura]]></kwd>
<kwd lng="es"><![CDATA[Hubble]]></kwd>
<kwd lng="es"><![CDATA[parámetro de deceleración]]></kwd>
<kwd lng="es"><![CDATA[Kretschmann]]></kwd>
<kwd lng="es"><![CDATA[singularidad.]]></kwd>
</kwd-group>
</article-meta>
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