<?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>0121-750X</journal-id>
<journal-title><![CDATA[Ingeniería]]></journal-title>
<abbrev-journal-title><![CDATA[ing.]]></abbrev-journal-title>
<issn>0121-750X</issn>
<publisher>
<publisher-name><![CDATA[Universidad Distrital Francisco José de Caldas]]></publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id>S0121-750X2017000100083</article-id>
<article-id pub-id-type="doi">10.14483/udistrital.jour.reving.2017.1.a08</article-id>
<title-group>
<article-title xml:lang="es"><![CDATA[Monitoreo del Clima Espacial desde Colombia Mediante Radio Receptores Butterworth de Orden Superior]]></article-title>
<article-title xml:lang="en"><![CDATA[Space Weather Monitoring from Colombia Through Higher Order Butterworth Radio-Receivers]]></article-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Jaramillo Alvarado]]></surname>
<given-names><![CDATA[Andrés Felipe]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Galvis Rodríguez]]></surname>
<given-names><![CDATA[Hamilton David]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Quintero]]></surname>
<given-names><![CDATA[Edwin Andrés]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
</contrib-group>
<aff id="Af1">
<institution><![CDATA[,Universidad Tecnológica de Pereira Observatorio Astronómico Grupo de Investigación en astroingeniería alfa orión]]></institution>
<addr-line><![CDATA[ ]]></addr-line>
<country>Colombia</country>
</aff>
<pub-date pub-type="pub">
<day>00</day>
<month>04</month>
<year>2017</year>
</pub-date>
<pub-date pub-type="epub">
<day>00</day>
<month>04</month>
<year>2017</year>
</pub-date>
<volume>22</volume>
<numero>1</numero>
<fpage>83</fpage>
<lpage>97</lpage>
<copyright-statement/>
<copyright-year/>
<self-uri xlink:href="http://www.scielo.org.co/scielo.php?script=sci_arttext&amp;pid=S0121-750X2017000100083&amp;lng=en&amp;nrm=iso"></self-uri><self-uri xlink:href="http://www.scielo.org.co/scielo.php?script=sci_abstract&amp;pid=S0121-750X2017000100083&amp;lng=en&amp;nrm=iso"></self-uri><self-uri xlink:href="http://www.scielo.org.co/scielo.php?script=sci_pdf&amp;pid=S0121-750X2017000100083&amp;lng=en&amp;nrm=iso"></self-uri><abstract abstract-type="short" xml:lang="es"><p><![CDATA[Resumen  Contexto: Las fulguraciones solares y las eyecciones de masa coronal liberan al espacio grandes cantidades de radiación que, al alcanzar las capas exteriores de la atmósfera terrestre, alteran sus características eléctricas. El conjunto de fenómenos derivados de esta interacción se conoce como clima espacial y sus consecuencias incluyen fallas en los sistemas de geolocalización, las telecomunicaciones, las operaciones vía satélite, el seguimiento espacial, la radionavegación y la sobrecarga de redes eléctricas.  Método: En este trabajo se presenta el desarrollo de un radio receptor que permite adelantar el monitoreo del clima espacial desde Colombia. Además, se describe una metodología novedosa para el diseno de filtros analógicos de orden superior de característica Butterworth, a partir de la interconexión en paralelo de bancos de filtros de primero y segundo orden, obteniéndose la función de transferencia deseada.  Resultados:  El radio receptor desarrollado se instaló en la estación de monitoreo del clima espacial del Observatorio Astronómico de la Universidad Tecnológica de Pereira (OAUTP), Colombia, entrando en operación en diciembre de 2015. Desde esa fecha, el sistema ha registrado la actividad solar de forma ininterrumpida, detectando cuatro potentes explosiones solares clase C presentadas los días 15, 16 y 17 del mes de abril de 2016. Las señales recibidas por el radio receptor son enviadas a la base de datos global del Stanford Solar Center, de Stanford University, con el código UTP 0383.  Conclusiones:  El radio telescopio desarrollado permite al Observatorio Astronómico OAUTP adelantar el monitoreo del clima espacial y de la actividad solar, enviando la información recibida a repositorios de acceso público a nivel mundial. No existen otros receptores de radio de este tipo operando en la actualidad en países ecuatoriales, una región de la Tierra donde los efectos de la actividad solar pueden conducir a nuevos conocimientos que aporten en la comprensión de este fenómeno. Además, los filtros de orden superior diseñados pueden tener aplicación en el campo de la instrumentación para la medición de señales eléctricas biomédicas.]]></p></abstract>
<abstract abstract-type="short" xml:lang="en"><p><![CDATA[Abstract  Context:  Solar flares and coronal mass ejections release great amounts of radiation to the outer space, altering the electrical properties of external layers in earth's atmosphere. The set of phenomena derived from this interaction is known as space weather, and its consequences include failures in the geolocation systems, telecommunications, satellite based operations, spatial tracking, radio navigation and overload of electrical network.  Method:  This paper presents the development of a radio receptor enabling monitoring of space weather from Colombia. A novel methodology to design analog high-order Butterworth filters is described, based on the parallel interconnection of filtering banks of first and second order, yielding the realization of the desired transfer function. These filters are then used to build a radio receptor to monitor the mentioned solar activity.  Results:  The radio receptor was installed in a space weather monitoring station in Colombia, specifi- cally in the Astronomical Observatory of the Universidad Tecnologica de Pereira (OAUTP), becoming operational on December 2015. From that date, the radio receptor has been registering solar activity uninterruptedly; and it has been able to detect four powerful solar explosions of class C, registered on the days 15, 16 and 17th in the month of April 2016. The received signals are sent to the Stanford Solar Center of Stanford University, with the code UTP 0383.  Conclusions:  The newly developed radio telescope is enabling the Astronomical Observatory OAUTP to monitor space weather and solar activity, sensing and registering such information in global publicly available repositories. No other radio receptors of this kind are currently operating from equatorial countries, a region on Earth were the effects of solar activity may lead to new insights in understanding this phenomena. Besides, we anticipate that the designed high order filters may have application as well in instruments for sensing biomedical electrical signals.]]></p></abstract>
<kwd-group>
<kwd lng="es"><![CDATA[Bancos de filtros]]></kwd>
<kwd lng="es"><![CDATA[clima espacial]]></kwd>
<kwd lng="es"><![CDATA[filtros Butterworth]]></kwd>
<kwd lng="es"><![CDATA[fulguraciones solares]]></kwd>
<kwd lng="es"><![CDATA[radiotelescopio]]></kwd>
<kwd lng="es"><![CDATA[Idioma: Español]]></kwd>
<kwd lng="en"><![CDATA[Butterworth filters]]></kwd>
<kwd lng="en"><![CDATA[filter banks]]></kwd>
<kwd lng="en"><![CDATA[radio telescope]]></kwd>
<kwd lng="en"><![CDATA[solar flares]]></kwd>
<kwd lng="en"><![CDATA[space climate.]]></kwd>
</kwd-group>
</article-meta>
</front><back>
<ref-list>
<ref id="B1">
<label>[1]</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Manoj]]></surname>
<given-names><![CDATA[S.]]></given-names>
</name>
<name>
<surname><![CDATA[Sundaram]]></surname>
<given-names><![CDATA[S.]]></given-names>
</name>
</person-group>
<article-title xml:lang=""><![CDATA[Dynamic Spectrum of Long Wave Terrestrial Radio Signals During Episodes of Ionospheric Disturbances Caused By Solar Activity]]></article-title>
<source><![CDATA[Journal of Chemical and Pharmaceutical Sciences]]></source>
<year>2016</year>
<volume>9</volume>
<numero>1</numero>
<issue>1</issue>
<page-range>548-53</page-range></nlm-citation>
</ref>
<ref id="B2">
<label>[2]</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Kulkarni]]></surname>
<given-names><![CDATA[P.]]></given-names>
</name>
<name>
<surname><![CDATA[Inan]]></surname>
<given-names><![CDATA[U. S.]]></given-names>
</name>
<name>
<surname><![CDATA[Bell]]></surname>
<given-names><![CDATA[T. F.]]></given-names>
</name>
<name>
<surname><![CDATA[Bortnik]]></surname>
<given-names><![CDATA[J.]]></given-names>
</name>
</person-group>
<article-title xml:lang=""><![CDATA[Precipitation Signatures of Ground-Based VLF Transmitters]]></article-title>
<source><![CDATA[Journal of Geophysical Research: Space Physics]]></source>
<year>2008</year>
<volume>113</volume>
<numero>A7</numero>
<issue>A7</issue>
<page-range>1-11</page-range></nlm-citation>
</ref>
<ref id="B3">
<label>[3]</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Petry]]></surname>
<given-names><![CDATA[A.]]></given-names>
</name>
<name>
<surname><![CDATA[de Souza]]></surname>
<given-names><![CDATA[J. R.]]></given-names>
</name>
<name>
<surname><![CDATA[de Campos Velho]]></surname>
<given-names><![CDATA[H. F.]]></given-names>
</name>
<name>
<surname><![CDATA[Pereira]]></surname>
<given-names><![CDATA[A. G.]]></given-names>
</name>
<name>
<surname><![CDATA[Bailey]]></surname>
<given-names><![CDATA[G. J.]]></given-names>
</name>
</person-group>
<article-title xml:lang=""><![CDATA[First Results of Operational Ionospheric Dynamics Prediction for the Brazilian Space Weather Program]]></article-title>
<source><![CDATA[Advances in Space Research]]></source>
<year>2014</year>
<volume>54</volume>
<page-range>22-36</page-range></nlm-citation>
</ref>
<ref id="B4">
<label>[4]</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Puerta]]></surname>
<given-names><![CDATA[L. M.]]></given-names>
</name>
<name>
<surname><![CDATA[Acuna]]></surname>
<given-names><![CDATA[A. C.]]></given-names>
</name>
<name>
<surname><![CDATA[Pulgarín]]></surname>
<given-names><![CDATA[O. E.]]></given-names>
</name>
<name>
<surname><![CDATA[Quitero]]></surname>
<given-names><![CDATA[E. A.]]></given-names>
</name>
</person-group>
<article-title xml:lang=""><![CDATA[Sistema para el Registro de Llamaradas Solares en la Banda Muy Baja de frecuencias]]></article-title>
<source><![CDATA[Revista de Investigaciones Universidad del Quindío]]></source>
<year>2014</year>
<volume>1</volume>
<numero>26</numero>
<issue>26</issue>
<page-range>103-11</page-range></nlm-citation>
</ref>
<ref id="B5">
<label>[5]</label><nlm-citation citation-type="">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Scherrer]]></surname>
<given-names><![CDATA[D.]]></given-names>
</name>
<name>
<surname><![CDATA[Mitchell]]></surname>
<given-names><![CDATA[R.]]></given-names>
</name>
<name>
<surname><![CDATA[Huynh]]></surname>
<given-names><![CDATA[T.]]></given-names>
</name>
<name>
<surname><![CDATA[Lord]]></surname>
<given-names><![CDATA[W.]]></given-names>
</name>
<name>
<surname><![CDATA[Lord]]></surname>
<given-names><![CDATA[M.]]></given-names>
</name>
</person-group>
<source><![CDATA[SuperSID Manual - Space Weather Monitors]]></source>
<year>2009</year>
</nlm-citation>
</ref>
<ref id="B6">
<label>[6]</label><nlm-citation citation-type="confpro">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Baki]]></surname>
<given-names><![CDATA[R. A.]]></given-names>
</name>
<name>
<surname><![CDATA[El-Gamal]]></surname>
<given-names><![CDATA[M. N.]]></given-names>
</name>
</person-group>
<source><![CDATA[A Low-Power, 5-70MHz, 7fh-Order Filter with Programmable Boost, Group Delay, and Gain Using Instantaneous Companding]]></source>
<year></year>
<conf-name><![CDATA[ Low Power Electronics and Design International Symposium]]></conf-name>
<conf-date>2001</conf-date>
<conf-loc> </conf-loc>
<page-range>299-304</page-range></nlm-citation>
</ref>
<ref id="B7">
<label>[7]</label><nlm-citation citation-type="confpro">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Henrici]]></surname>
<given-names><![CDATA[F.]]></given-names>
</name>
<name>
<surname><![CDATA[Becker]]></surname>
<given-names><![CDATA[J.]]></given-names>
</name>
<name>
<surname><![CDATA[Buhmann]]></surname>
<given-names><![CDATA[A.]]></given-names>
</name>
<name>
<surname><![CDATA[Ortmanns]]></surname>
<given-names><![CDATA[M.]]></given-names>
</name>
<name>
<surname><![CDATA[Manoli]]></surname>
<given-names><![CDATA[Y.]]></given-names>
</name>
</person-group>
<source><![CDATA[A Continuous-Time Field Programmable Analog Array Using Parasitic Capaci- tance Gm-C Filters]]></source>
<year></year>
<conf-name><![CDATA[ Chair of Microelectronics, Circuits and System ISCAS IEEE International Symposium]]></conf-name>
<conf-date>2007</conf-date>
<conf-loc> </conf-loc>
<page-range>2236-9</page-range></nlm-citation>
</ref>
<ref id="B8">
<label>[8]</label><nlm-citation citation-type="confpro">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Li]]></surname>
<given-names><![CDATA[Y.]]></given-names>
</name>
<name>
<surname><![CDATA[Zhang]]></surname>
<given-names><![CDATA[X.]]></given-names>
</name>
<name>
<surname><![CDATA[Zhu]]></surname>
<given-names><![CDATA[L.]]></given-names>
</name>
<name>
<surname><![CDATA[Song]]></surname>
<given-names><![CDATA[W.]]></given-names>
</name>
</person-group>
<source><![CDATA[The Study of Analog Evolvable Chebyshev Transconductance Filters]]></source>
<year></year>
<conf-name><![CDATA[ World Congress on Intelligent Control and Automation]]></conf-name>
<conf-date>2008</conf-date>
<conf-loc> </conf-loc>
<page-range>4531-6</page-range></nlm-citation>
</ref>
<ref id="B9">
<label>[9]</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Geiger]]></surname>
<given-names><![CDATA[R. L.]]></given-names>
</name>
<name>
<surname><![CDATA[Sanchez]]></surname>
<given-names><![CDATA[E.]]></given-names>
</name>
</person-group>
<article-title xml:lang=""><![CDATA[Active Filter Design Using Operational Transconductance Amplifiers: A Tutorial]]></article-title>
<source><![CDATA[IEEE Circuits and Devices Magazine]]></source>
<year>1985</year>
<page-range>20-32</page-range></nlm-citation>
</ref>
<ref id="B10">
<label>[10]</label><nlm-citation citation-type="confpro">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Garradhi]]></surname>
<given-names><![CDATA[K.]]></given-names>
</name>
<name>
<surname><![CDATA[Hassen]]></surname>
<given-names><![CDATA[N.]]></given-names>
</name>
<name>
<surname><![CDATA[Besbes]]></surname>
<given-names><![CDATA[K.]]></given-names>
</name>
</person-group>
<source><![CDATA[Low Voltage Low Power Analog Circuit Design OTA Using Signal Attenuation Technique in Universal Filter Application]]></source>
<year></year>
<conf-name><![CDATA[ 12th International Multi-Conference on Systems, Signals &amp; Devices]]></conf-name>
<conf-date>2015</conf-date>
<conf-loc> </conf-loc>
<page-range>1-7</page-range></nlm-citation>
</ref>
<ref id="B11">
<label>[11]</label><nlm-citation citation-type="confpro">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Neshatvar]]></surname>
<given-names><![CDATA[N.]]></given-names>
</name>
</person-group>
<source><![CDATA[Design of Low Frequency Analog Low Pass Filter Using Tunable Pseudo Resistors]]></source>
<year></year>
<conf-name><![CDATA[ Middle East Conference on Biomedical Engineering (MECBME)]]></conf-name>
<conf-date>2014</conf-date>
<conf-loc> </conf-loc>
<page-range>39-42</page-range></nlm-citation>
</ref>
<ref id="B12">
<label>[12]</label><nlm-citation citation-type="confpro">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Damera]]></surname>
<given-names><![CDATA[S.]]></given-names>
</name>
<name>
<surname><![CDATA[Karsilayan]]></surname>
<given-names><![CDATA[A.]]></given-names>
</name>
<name>
<surname><![CDATA[Silva]]></surname>
<given-names><![CDATA[J.]]></given-names>
</name>
</person-group>
<source><![CDATA[Design of Minimally-Invasive All-Pole Analog Lowpass Filters]]></source>
<year>2014</year>
<conf-name><![CDATA[ IEEE 57th International Midwest Symposium on Circuits and Systems (MWSCAS)]]></conf-name>
<conf-loc> </conf-loc>
<page-range>1025-8</page-range></nlm-citation>
</ref>
<ref id="B13">
<label>[13]</label><nlm-citation citation-type="confpro">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Rezazadeh Reyhani]]></surname>
<given-names><![CDATA[A.]]></given-names>
</name>
<name>
<surname><![CDATA[Jayanthmurthy]]></surname>
<given-names><![CDATA[C.]]></given-names>
</name>
<name>
<surname><![CDATA[Gillman]]></surname>
<given-names><![CDATA[B.]]></given-names>
</name>
<name>
<surname><![CDATA[Walling]]></surname>
<given-names><![CDATA[J.]]></given-names>
</name>
<name>
<surname><![CDATA[Belz]]></surname>
<given-names><![CDATA[J.]]></given-names>
</name>
<name>
<surname><![CDATA[Farhang]]></surname>
<given-names><![CDATA[B.]]></given-names>
</name>
</person-group>
<source><![CDATA[An Analog Adaptive Notch Filter Based on the Noise Cancellation Principle]]></source>
<year></year>
<conf-name><![CDATA[ IEEE International Symposium on Circuits and Systems (ISCAS)]]></conf-name>
<conf-date>2015</conf-date>
<conf-loc> </conf-loc>
<page-range>2660-3</page-range></nlm-citation>
</ref>
<ref id="B14">
<label>[14]</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Drost]]></surname>
<given-names><![CDATA[B.]]></given-names>
</name>
<name>
<surname><![CDATA[Talegaonkar]]></surname>
<given-names><![CDATA[M.]]></given-names>
</name>
<name>
<surname><![CDATA[Hanumolu]]></surname>
<given-names><![CDATA[P. K.]]></given-names>
</name>
</person-group>
<article-title xml:lang=""><![CDATA[Analog Filter Design Using Ring Oscillator Integrators]]></article-title>
<source><![CDATA[IEEE Journal of Solid-State Circuits]]></source>
<year>2012</year>
<volume>47</volume>
<numero>12</numero>
<issue>12</issue>
<page-range>3120-9</page-range></nlm-citation>
</ref>
<ref id="B15">
<label>[15]</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Chi-Hsiang]]></surname>
<given-names><![CDATA[Lo]]></given-names>
</name>
</person-group>
<article-title xml:lang=""><![CDATA[A 6 mW 750 MHz anti-aliasing filter for receiver analog front-end]]></article-title>
<source><![CDATA[Analog Integrated Circuits and Signal Processing]]></source>
<year>2014</year>
<volume>79</volume>
<numero>3</numero>
<issue>3</issue>
<page-range>599-604</page-range></nlm-citation>
</ref>
<ref id="B16">
<label>[16]</label><nlm-citation citation-type="">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Avendano]]></surname>
<given-names><![CDATA[L. E.]]></given-names>
</name>
</person-group>
<source><![CDATA[Sistemas Electrónicos Analógicos: Un Enfoque Matricial]]></source>
<year>2007</year>
<page-range>420-3</page-range><publisher-loc><![CDATA[Editorial Universidad Tecnológica de Pereira ]]></publisher-loc>
</nlm-citation>
</ref>
<ref id="B17">
<label>[17]</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Rojas]]></surname>
<given-names><![CDATA[H. E.]]></given-names>
</name>
<name>
<surname><![CDATA[Rivas]]></surname>
<given-names><![CDATA[E.]]></given-names>
</name>
<name>
<surname><![CDATA[Jaramillo]]></surname>
<given-names><![CDATA[A. A.]]></given-names>
</name>
</person-group>
<article-title xml:lang=""><![CDATA[Aspectos técnicos y normativos para el monitoreo y medición de armónicos]]></article-title>
<source><![CDATA[Ingeniería]]></source>
<year>2014</year>
<volume>19</volume>
<numero>2</numero>
<issue>2</issue>
<page-range>129-46</page-range></nlm-citation>
</ref>
<ref id="B18">
<label>[18]</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Galvis]]></surname>
<given-names><![CDATA[H. D.]]></given-names>
</name>
<name>
<surname><![CDATA[Quintero]]></surname>
<given-names><![CDATA[E. A.]]></given-names>
</name>
<name>
<surname><![CDATA[Cardona]]></surname>
<given-names><![CDATA[L. F.]]></given-names>
</name>
</person-group>
<article-title xml:lang=""><![CDATA[Development of a Magnetic Loop Antenna for the Detection of Jovian Radiowaves at 20.1 MHz]]></article-title>
<source><![CDATA[Tecciencia]]></source>
<year>2016</year>
<volume>11</volume>
<numero>20</numero>
<issue>20</issue>
<page-range>21-46</page-range></nlm-citation>
</ref>
<ref id="B19">
<label>[19]</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Artola]]></surname>
<given-names><![CDATA[A.]]></given-names>
</name>
<name>
<surname><![CDATA[Mills]]></surname>
<given-names><![CDATA[E.]]></given-names>
</name>
<name>
<surname><![CDATA[Estrada]]></surname>
<given-names><![CDATA[P.]]></given-names>
</name>
</person-group>
<article-title xml:lang=""><![CDATA[Correlación entre la variabilidad en la banda VLF en Francisco Morazán y la actividad solar]]></article-title>
<source><![CDATA[Ciencias Espaciales]]></source>
<year>2016</year>
<volume>6</volume>
<numero>1</numero>
<issue>1</issue>
<page-range>1-24</page-range></nlm-citation>
</ref>
<ref id="B20">
<label>[20]</label><nlm-citation citation-type="">
<collab>Space Weather Monitors</collab>
<source><![CDATA[Stanford Solar Center. S.f.]]></source>
<year></year>
</nlm-citation>
</ref>
<ref id="B21">
<label>[21]</label><nlm-citation citation-type="">
<collab>Space Weather Monitors, Stanford Solar Center</collab>
<source><![CDATA[UTP 0383,]]></source>
<year></year>
</nlm-citation>
</ref>
<ref id="B22">
<label>[22]</label><nlm-citation citation-type="">
<collab>Monitor CEC</collab>
<source><![CDATA[]]></source>
<year></year>
</nlm-citation>
</ref>
<ref id="B23">
<label>[23]</label><nlm-citation citation-type="">
<collab>Stanford Solar Center de Stanford University</collab>
<source><![CDATA[]]></source>
<year></year>
</nlm-citation>
</ref>
</ref-list>
</back>
</article>
