Año Académico 2012-2013

Universidad de Puerto Rico en Humacao Departamento de Física y Electrónica

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RESULTADOS DE INVESTIGACIONES SUBGRADUADA REALIZADA EN LOS CURSOS FISI 4161-65

Número 8

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RESULTADOS DE INVESTIGACIONES SUBGRADUADA REALIZADA EN LOS CURSOS FISI 4161-65

Tabla de Contenido

EXPLORING ELECTROSPINNING TO ASSEMBLE POLYMERIC STRUCTURES FOR ADSORPTION APPLICATIONS. Gerardo González-Rodríguez, Paola M. Vázquez-Dávila Advisor: Rogerio Furlan

4

ELECTROSPUN FIBERS OF [P(ND12OD-T2)]N ON P-DOPED SI: FABRICATION OF A SUB-MICRON SIZE P-N JUNCTION DIODE. Alexander O. Rosado Advisor: Nicholas J. Pinto

5

DEVICES AND SENSORS BASED ON PVDF-TRFE/SWNT’S COMPOSITES. Manuel Bonilla Advisors: Idalia Ramos and Nicholas Pinto

6

ELECTROSPUN FIBERS OF PLA/P3HT BLENDS FOR DEVICE AND SENSOR APPLICATIONS. William Serrano Advisor: Nicholas Pinto

7

THE KINEMATICS OF THE IONIZED HYDROGEN IN NGC 3372 (CARINA NEBULA). Clarissa Vázquez Colón, Milennys Velázquez Flores, Milzaida Merced Sanabria, Grace Fontánez Santana Advisors: Juan C. Cersosimo and Rafael J. Muller

8

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A COMPUTER SIMULATION OF RADIOTHERAPY TREATMENT OF PROSTATE CARCINOMA. Verónica De La Rosa-Rosario, Giovanni R. Deliz Advisor: Ernesto P. Esteban

9

OBSERVATION OF POSITION ANGLE AND SEPARATION OF BINARY STARS. Roberto Rodríguez, Marangely Diaz, Eframir Franco, Marialis Rosario, Yamil Nieves, Brian Torres, Nelson Vergara Advisors: Rafael J. Muller and Juan C. Cersosimo

10

ELECTROSPINNING OF NANOFIBERS SOLUTIONS WITH PVDF, DMF, ACETONE AND FE3O4 NANOPARTICLES. Paul A. Valle-Rivera, Raymond J. López-Hallman, Luis M. Martínez Advisors: Juan A. González, Rogerio Furlan

11-13

INFLUENCE OF A MAGNETIC FIELD IN THE ELECTROSPINNING OF NANOFIBERS CONTAINING FE3O4 NANOPARTICLES. Paul A. Valle-Rivera, Raymond J. López-Hallman, Luis M. Martínez Advisors: Juan A. González and Rogerio Furlan

14-15

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EXPLORING ELECTROSPINNING TO ASSEMBLE POLYMERIC STRUCTURES FOR ADSORPTION APPLICATIONS Gerardo González-Rodríguez, Paola M. Vázquez-Dávila Advisor: Rogerio Furlan Using a modified electrospinning process, polymeric structures with ramifications containing micro and nanofibers and round porous polymeric arrangements were easily assembled. This represents an innovative use of the electrospinning process to obtain polymeric structures that can find adsorption applications. The structures were formed using solutions with PVDF and DMF. PVDF is a polymer with excellent mechanical properties, chemical stability, ferroelectricity, high dielectric permittivity and unique pyroelectric and piezoelectric properties. DMF, is an excellent polar solvent for many compounds, and a multipurpose reagent. The electrospinning setup uses rectangular macro electrodes and the polymeric solution is injected close to the vertical wall of the positive electrode. The rectangular electrodes were made of aluminum with dimensions of 5.0 cm × 2.5 cm × 1.2 cm. The distance between electrodes varied from 14.5 cm to 30.5 cm and the voltages applied to the electrodes varied from 10 kV to 30kV. An insulin syringe (1 mL) was used for insertion of polymeric solution between electrodes. Polymer was injected close to the positive electrode keeping the syringe needle with angles between 22.5° and 67.5° with respect to the vertical wall of the electrode. The tip of the insulin syringe has to be in constant contact with the positive electrode and the polymer flow has to be constant. After polymer injection, streams are directed towards the grounded electrode. The polymeric streams liberate fragments that follow the intense electric field lines and aggregate on a corner of the grounded electrode. This aggregation starts to elongate following the intense electric field lines towards the positive electrode, rotating and creating new ramifications, assembling a structure as presented in Figure 1. A detail of of the ramifications is presented in Figure 2. Normally, three ramifications are observed and the typical diameter of the ramifications is in the range between 90 µm and 250 µm. This behavior shows that polymer from the streams is preferentially deposited on the extremes of the ramifications. During formation, the ramifications are kept extended, following electric field lines, due to presence of charges and/or connection with arriving polymer streams. The characteristics of the structures can be controlled by adjusting the viscosity of the solution, applied voltage and distance between electrodes. Example of formation of a polymeric structure

Detail of the ramifications assembled during electrospinning.

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ELECTROSPUN FIBERS OF [P(ND12OD-T2)]N ON P-DOPED SI: FABRICATION OF A SUB-MICRON SIZE P-N JUNCTION DIODE Alexander O. Rosado Advisor: Nicholas J. Pinto

The air stable n-doped polymer (poly[N,N-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis (dicarboximide)-2,6-diyll-alt-5,5-(2,2-bithiophene)]-[P(ND12OD-T2)]n was electrospun to obtain sub-micron diameter fibers. These fibers exhibited a charge mobility of ~10 -5 cm2/V-s when connected in a field effect transistor configuration. Individual fibers were used in the fabrication of a p-n diode and the characteristics analyzed using the standard diode equation. In additional to exhibiting rectification, the diode parameters could be reversibly tuned via UV illumination rendering it multifunctional. One advantage of our diode architecture is having the junction completely exposed to the environment thereby making it potentially useful a gas and light sensor.

Figure 1: Current-voltage characteristics at 300 K in vacuum of the p-n diode when the positive terminal of VB was connected to the doped Si substrate and when the positive terminal of VB was connected to the gold electrode. Inset above: SEM image of the actual fiber over the wafer edge. The scale bar is m. Inset below: Energy band diagram for the p-n diode in thermal equilibrium with no bias and assuming equal band gaps of ~1.6 eV for the two semiconductors.

Figure 2: Current-voltage characteristics for the p-n diode with the UV light OFF-green, ON-blue and OFF-red again. Inset: Resistance of an individual electrospun [P(ND12OD-T2)]n fiber to UV nm) illumination. The decrease in the resistance under illumination is consistent with the increase in the current in the main figure.

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RESULTADOS DE INVESTIGACIONES SUBGRADUADA REALIZADA EN LOS CURSOS FISI 4161-65

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DEVICES AND SENSORS BASED ON PVDF-TRFE/SWNT’S COMPOSITES Manuel Bonilla Advisors: Idalia Ramos and Nicholas Pinto Sensor devices were prepared using PVDF-TrFE/SWNT’s composite and compared with a pure SWNT’s sensor. Current as function of time measurement at room temperature shows an improved sensitivity a faster response time in the presence of acetone for the composite resistor device that was fabricated putting the composite solution between two gold electrodes in n doped Si substrate. The pure SWNT’s resistor produced a faster response time that the composite in the presence of NO2. Schottky diodes were prepared with the PVDF-TrFE/SWNT’s composite and the n doped Si. Successful rectification was obtained and changes in the turn on voltage and in the Ion/Ioff ratio were observed as the diode was in the environments of different gases. The composite improve the sensitivity of the devices that can be prepared fast and can be used to prepare a device with both diode and resistor functionalities. These sensor and the diodes can be reused after gas removal . 1.00

Figure 1 shows the normalized resistance of the pure SWNT and the composite PVDF-TrFE/SWNT sensors in the presence of acetone and NO2 gases. The response to acetone is rapid and true saturation can be observed, while for NO2 the sensor does not appear to saturate in the 300s time interval of the measurements. Nevertheless, in the four cycles presented in Figure 1, there is reproducibility. The response times of these sensors is presented in Table 1 and shows that composite sensors are much faster than pure SWNT sensor for acetone. This could be due the presence of the polymer that speeds gas entry into the fiber. From Figure 1 we see that acetone increases the resistance due to polymer swelling while NO2 decreases it and could be related to the doping effect that NO2 has on organic materials eg. graphene[2].

(a) 0.95 0.90

R/RN2

0.85 0.80 0.75 0.70 0.65 0.60 0.8 (b) 0.7

R/RN2

0.6

0.5

0.4

0.3

FE/SWNT were fabricated and tested in acetone and NO2. The composite sensors had a faster response time in acetone compared to NO2. A Schottky diode was also prepared using these same materials and the device retained its rectifying behavior in the presence of the sensing gas and there is recovery upon gas removal.

0.2 0

500

1000

1500

2000

2500

3000

T(s)

Fig. 1.Normalized resistance of individual sensors switching the gas ambience between (a) N2 and acetone (b) N2 and N02. PVDF-TrFE/ SWNT’s is in black and SWNT’s. in red. The arrows indicate the moment when the specified gas was introduced.

Table 1 Composite and pure SWNT’s sensors response time and recovery time Sample Sensing gas

PVDF-TrFE/SWNT’s Acetone

NO2

SWNT’s

Response time(s)

5

200

Acetone 15

Recovery time (s)

100

235

120

NO 2

180 200

This work was funded by NSF under grants PREM 0934195 and RUI 0965023. References [1]C. Staii, A.T. Johnson, Jr., M. Chen, A. Gelperin Nano Lett. Vol. 5, No. 9, pp. 1774-1778 , 2005. [2] F. Schedin , A. K. Geim , S. V. Morozov, E. W. Hill , P. Blake, M. I. Katsnelson & K. S. Novoselov Vol.6, pp. 652 –

RESULTADOS DE INVESTIGACIONES SUBGRADUADA REALIZADA EN LOS CURSOS FISI 4161-65

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ELECTROSPUN FIBERS OF PLA/P3HT BLENDS FOR DEVICE AND SENSOR APPLICATIONS William Serrano Advisor: Nicholas J. Pinto We have the performance of PLA, a biocompatible polymer, with P3HT that is a semiconductor. Here we see that that the addition of P3HT to PLA solution doesn’t change in the morphology of the fibers. The polymers were blended without change the properties of each of them. So, P3HT still being be a semiconductor (pdoped) and PLA thermoplastic aliphatic polyester.

SEM 1 5wt% PLA/CHCl3 SEM 2

A Basic Component: Diode For a solution of 3wt% PLA/CHCl3/P3HT, were the superficial tension is low and the behavior don’t permit the formation of fibers, we proceed to an electrical characterization.

5wt% PLA/

SEM 3 9wt% PLA/CHCl3 SEM 4 9wt% PLA/CHCl3/P3HT

Conclusion

SEM 5 13wt% PLA/CHCl3 SEM 6 13wt% PLA/ CHCl3/P3HT

Like empirically we know, we can see the changes in the fibers while the increase of the polymer. Also the blend of PLA and P3HT, with respect to only PLA, don’t change the electrospun morphology.

We successfully incorporated P3HT into PLA solution and prepared fibers via electrospinning without changing the electrical properties of P3HT. UV-vis characterization shows no polymer segregation in the blend. The electrical characterization shows that the diode has a higher rectification ratio in vacuum vs. air (1atm). Is good to remember that PLA is a biocompatible polymer and P3HT a semiconductor that can’t form fibers alone. This blend can be used for biocompatible electronics in a near future.

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THE KINEMATICS OF THE IONIZED HYDROGEN IN NGC 3372 (CARINA NEBULA) Vázquez Colón, Clarissa, Velázquez Flores, Milennys, Merced Sanabria Milzaida, Fontánez Santana, Grace Advisors: J.C. Cersosimo and R. J. Muller Radio recombination lines (RRLs) provide relevant information about the physical conditions of an HII region: the gas distribution, the kinematic, and the physical conditions where the line is detected. In the southern sky the NGC 3372 has been observed at various radio recombination lines, and the main discussion about its distribution is if the ionized gas arises from two separated structures or if there exists, an expansion showing profiles with concentrations t two radial velocities. (It is not clear what that sentence is trying to say.) As was shown in early observations the typical characteristic of the Carina Nebula is its complex kinematical structure. In Figure 1 are shown the location of the NGC3372 and the stellar clusters catalogued in the area1. The open clusters Tr 14 and 16 are located at the distance of the Carina Nebula. The large-scale dynamics measured across the nebula are extremely complex. Some interpretations involve merging spiral arms2, rotating neutral clouds3 and the low density extended HII regions4. Systematic HII studies in Carina Nebula were also undertaken5. In this paper we report on a detailed study of ionized hydrogen in the region of the open clusters Tr 14 and 16, located in Carina nebula’s region. It is suggested that only the clusters Tr 14 and 16 are associated with the ionized gas, at a distance of about 2400 pc6,7.

Figure 1: Map1 of the region studied. It shows the relative spatial distribution of the optical emission (bright areas) and infrared (dark areas). The boxes indicate the stellar clusters. Tr 14 and 16 are located in the area of NGC 3372. The remaining clusters are at different distances.

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A COMPUTER SIMULATION OF RADIOTHERAPY TREATMENT OF PROSTATE CARCINOMA Verónica De La Rosa-Rosario, Giovanni R. Deliz Advisor: Ernesto P. Esteban

Prostate cancer detected in any country including Puerto Rico have been increasing among men fifty years and older. If the prostate cancer is confined, prostatectomy surgery and radiotherapy are the standard treatments. However, if metastasis occurs, chemotherapy followed by a radiotherapy treatment may provide relieve but cancer may have spread to other body organs and could be lethal. In this research, two topics are studied. First, it is PSA dynamics. In particular, a comparison between PSA secreted by malign and benign prostate cells. Secondly, we use a developed biomathematical model (PRHSJ, vol 29, 3, 2010) to simulate external beam radiation to the prostate. Because prostatic cancers are significantly sensitive to changes in dose fractionation, the goal is to obtain the optimal fractionation for the treatment of prostatic cancer using either low or high dose rates. Also, using the developed computer program is possible to estimate when a recurrence could take place. Finally, the obtained results are compared with the standard linear-quadratic model. This research was supported by the University of Puerto Rico-Humacao and the RISE program at UPRH.

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OBSERVATION OF POSITION ANGLE AND SEPARATION OF BINARY STARS Roberto Rodríguez, Marangely Diaz, Eframir Franco, Marialis Rosario, Yamil Nieves, Brian Torres, Nelson Vergara Advisors: R. J. Muller and J.C. Cersosimo

We continue to observe 125 binary star systems and report on our observations. We use the 31 inch NURO telescope at Flagstaff, Arizona and analyze our images at the Humacao University Observatory. We obtained the data using the 31 inch NURO Telescope at the Anderson Mesa location of Lowell Observatory near Flagstaff, Arizona, in May and September. We gathered the data using the 2K x 2K CCD camera - NASACAM - at the prime focus of the telescope. The data is sent in the form of a paper at the Journal for double star observing (JDSO). The Journal transfers the data to the Washington Double Star Catalog of the U.S. Naval Observatory where it is included in the catalog and acknowledged.

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ELECTROSPINNING OF NANOFIBERS SOLUTIONS WITH PVDF, DMF, ACETONE AND FE3O4 NANOPARTICLES Paul A. Valle-Rivera, Raymond J. López-Hallman, Luis M. Martínez, Advisors: Juan A. González and Rogerio Furlan This study aims at evaluating the effects of several concentrations of poly (vinylidene fluoride) (PVDF), N,N-dimethylformamide (DMF) and acetone solutions combined with iron oxide nanopowder (Fe3O4 particle diameter of 20 nm to 30 nm) on the behavior of formation of nanofibers using electrospinning. In order to get oriented nanofibers, a DC Motor with a speed controller was set up to rotate the sample during the synthesis. The morphology of the nanofibers and solutions was analyzed by Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Best results were found with the polymeric solutions containing PVDF, DMF and acetone at a concentration of 18 wt % and DMF to acetone ratio of 3 to 1. Nanopowder to PVDF ratios of 1:5, 1:10, and 1:15 were analyzed. Lower concentrations of PVDF resulted in the deposition of drops, characteristic of the electrospray process. The concentration of PVDF ratio at 1:15 resulted in nanofibers with a diameter of 150 nm to 250 nm, as verified by SEM. However, the diameters of the fibers were non-uniform due to the formation of iron oxide agglomerates. Electrospinning A high voltage power supply (ES30, 0-30KV) was used to create an electrical field, and was previously determined to use an applied voltage of 15KV. The Becton Dickinson syringe used was 0.5cc in size, and the needle was 0.40mm in diameter and 13mm in length. With the intention to acquire oriented nanofibers deposited on a silicon wafer, a DC step motor with a speed controller was setup to rotate the sample and was placed at the midpoint position of the electric current. The DC motor was connected to a 2 cm plastic cylinder with the silicon attached and the speed of rotation during the collection remained at 1 revolution per second. The distance between the needle and the metal collector was set at 10 cm. A diagram depicting this setup just described is shown in Figure 1.

Figure 1. Setup of electrospinning experiment

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Concerning the electrospinning process, the use of a motor with a controlled speed helped to obtain a more organized fiber deposition on the silicon substrate. Figure 2 shows SEM images of typical nanofibers obtained from samples with different concentrations of nanopowder.  As clearly depicted, the nanofibers did not result uniform, and present with agglomerates of nanoparticles.  It is speculated that the agglomeration most probably occurred during the electrospinning process, since the fibers are uniformly dispersed in the solution.

Figure 2. Micrographs of the samples processed from polymeric solutions containing PVDF at 18 wt %, dissolved in DMF and acetone (3 to 1), and nanopowder to PVDF at ratios of: (a) 1:5, (b) 1:10, and (c) 1:15. Figure 3 presents the average diameter distribution for different nanopowder concentrations. These results demonstrate the influence of the concentration of nanopowder over the obtained diameter of the fiber. Fibers with an intermediate ratio of nanopowder to PVDF ratio (i.e. 1:10) presented a higher average diameter then samples with ratios of 1:5 and 1:15.  It is speculated that this effect can be related to the agglomeration of the nanoparticles, which in turn depends of the amount of PVDF in the solution. As seen in Figure 3, the increase of the fiber diameter at nanopowder to PVDF ratio of 1:10 makes the imperfections caused by the agglomerates on the surface less visible; suggesting that the nanoparticles have inserted inside the nanofiber.

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Figure 3. Average diameter of nanofibers from polymeric solutions containing PVDF at 18 wt %, dissolved in DMF and acetone (3 to 1) with nanopowder to PVDF at ratios of: (a) 1:5, (b) 1:10, and (c) 1:15. Conclusions This work demonstrated that it was possible to obtain fibers at the nanometer scale using the electrospinning process with all the different ratios of nanopowder to PVDF studied. In addition, using a motor with controlled speed helped to obtain a more organized fiber deposition on the silicon substrate. Furthermore, the results demonstrate the influence of the concentration of nanopowder over the obtained diameter and the uniformity of the fiber.

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INFLUENCE OF A MAGNETIC FIELD IN THE ELECTROSPINNING OF NANOFIBERS CONTAINING FE3O4 NANOPARTICLES Paul A. Valle-Rivera, Raymond J. López-Hallman Luis M. Martínez, Advisors: Juan A. González and Rogerio Furlan

In this work we investigate the effect of a magnetic field on the electrospinning of polymeric nanofibers containing magnetic nanoparticles (Iron Oxide nanopowder, Fe 3O4, particle diameter of 20 nm to 30 nm). Polymeric solutions containing PVDF, DMF and acetone with a concentration of 18 wt % and DMF to acetone ratio of 3 to 1 were used. Nanopowder to PVDF ratios of 1:5, 1:10, and 1:15 were analyzed. During electrospinning, two Helmholtz coils were mounted on the system in order to create a uniform magnetic field. Different separations, angles and magnetic fields were applied to the nanofibers. The morphology of the nanofibers and solutions was analyzed by Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The addition of a magnetic field controlled the directionality of the polymer flow but the fibers were not well-oriented. We have yet to determine the best DC voltage for improved results. Magnetic Electrospinning Magnetic Field was applied during the electrospinning in situ. A pair of Helmholtz Coils, each having 200 turns, and carrying a current which varied between 0.5 to 3 Amperes, separated with a distance equivalent to the radius of the circular loops which are 10.5 cm. They produce a homogeneous magnetic field B in the mid-plane between the two circular coils, given by: B

o

N o I 2R

Where B is the Magnetic Field, is the permeability constant, I the current in Amperes and R is the radius of the circular coils. ES30 High Voltage Power Supply (0-30KV) was used at 15KV to create an electric field.

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Número 8

Figure 1. Experimental Setup for the Magnetic Electrospinning

Finally the following figure, we can observe a response of the nanofibers with higher magnetic fields in this case, an axial cylindrical neodymium magnet of 6500 gauss. Figure 2a shown a 100x magnified nanofiber without magnetic field. In figure 4b, the same nanofibe , but this time after applying the magnetic field.

(a)

(b)

Figure 2. Optical images of samples processed from polymeric solutions containing PVDF with a concentration of 18 wt % dissolved in DMF to Acetone ratio of 3 to 1. Nanopowder to PVDF ratio of 1:5: (a) without electromagnetic field, and (b) after magnetic field of 6500 Gauss was applied.

Conclusions In summary, electrospinning with in situ magnetic field using magnetic nanopowder like Fe3O4 is an important setup to study the magnetic properties of PVDF and Fe 3O4 nanofibers. The application of the electromagnetic field during fiber deposition resulted with better polymer deposition towards the silicon substrate and for future work will be easier collecting in nanofibers right on target. The presence of the uniform electromagnetic field leads to smoother fibers that exhibit magnetism at room temperature in the range of 100 to 700 nm. Fe 3O4 agglomerates with a diameter of 120 nm were distributed in all the samples of this study.

Nota de los editores La inclusión de la investigación y la labor creativa son fundamentales para el desarrollo integral de los estudios subgraduados. Los miembros del Departamento de Física y Electrónica reconocen la importancia de estos elementos como parte fundamental de la labor académica. La aplicación del conoci-

Proyectos Auspiciadores: 1. 2.

Puerto Rico Space Grant Consortium (NASA) Puerto Rico Alliance for Minority Participation (LSAMP)

3.

NSF

5. 6.

- Penn-UPR Partnership for Research and Education in Materials (DMR-0353730) - Research in Undergraduate Institutions ( RUI) RISE Program at UPRH PRIDCO

miento en la búsqueda de nuevas verdades y la interpretación del mundo que nos rodea, permite el desarrollo del pensamiento crítico; es una herramienta académica innovadora para motivar y satisfacer la curiosidad intelectual del los/las estudiantes. Además contribuye al desarrollo social y cultural agilizando la inserción en el ciclo económico de Puerto Rico y del mundo. La inmersión de estudiantes en investigación subgraduada se hace desde los inicios del programa de Bachillerato de Física Aplicada a la Electrónica, en 1987, mediante el ofrecimiento del curso Investigación Subgraduada (FISI 4161). La usual contratación de Profesores con peritaje en investigación capturó el interés de los estudiantes de Bachillerato para involucrarse en tan digna tarea. El esmero y dedicación de los profesores ayudó a ellos mismos a trasformar las técnicas de enseñanza debido al desafío que implica investigar y formar a estudiantes en la disciplina. La consecuencia de estos esfuerzos condujo a aumentar el ofrecimiento debido al interés de los estudiantes en hacer investigación. En consecuencia se atendió la demanda de los estudiantes, incluyendo los curso de Investigación Subgraduada (FISI 4162 FISI 4163 y FISI 4164). Los cuatro cursos mencionados se ofrecen regularmente desde agosto de 1993. El compromiso permitió a la academia refinar las estrategias de enseñanza-aprendizaje, que en esencia son el modelo tomado por el constructivismo, el método de prueba y error. Después de veinticuatro años de esfuerzo, el Departamento cuenta con una decena de profesores que escriben propuestas, consiguen fondos externos y hacen presentaciones en reuniones internacionales de ciencia, y publican periódicamente en revistas de circulación internacional. En el Departamento hay tres laboratorios dedicados a la investigación y un laboratorio de instrucción equipado con instrumentos de primera línea en el que se ofrecen dos cursos de concentración. También otras facilidades de investigación son los recursos del Observatorio Astronómico de Humacao, en el cual la preparación obtenida por los estudiantes les facilita tener opción de seguir estudios . Vale destacar el compromiso de la Institución (UPRH) que hace posible la investigación subgraduada, es por ello que me complace reconocer a las diferentes administraciones que están y han colaborando en este esfuerzo. El reconocimiento es también extendido a los profesores por la labor de adiestramiento a los estudiantes. La revista de investigación subgraduada fue concebida para que sea un instrumento administrativo que permita la visibilidad de esta actividad, pero además es un documento dirigido a los estudiantes, profesores y la comunidad científica de Puerto Rico, con el propósito de divulgar las actividades académicas que han sido pioneras en el Sistemas UPR junto con otros Recintos. Este instrumento estará además disponible en la Internet para permitir el acceso a todas las comunidades.

Universidad de Puerto Rico en Humacao Departamento de Física y Electrónica Call Box 860 Humacao PR 00792 www.uprh.edu/fisica Tel. 787-850-9344-9381 Fax: 787-850-9308