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In this work, the 2D-diffusion equation is used to model the diffusion process of a pollutant in calm and shallow waters. The diffusion coefficient was considered spatially constant and only dependent on the nature of the substance. The idea and the numerical schemes (forward difference, backward difference and center difference) were applied to a domain in the XY plane of sideways 1, where the distribution of the contaminant can be seen. Neumann boundary conditions equal to zero or zero flow at the boundary have been used, in order to make a cut at said boundary for the modeling. The computational program carried out allows moving the contaminant source to any point of the domain and seeing its distribution in real time, it is also possible to add other contaminant sources and observe their diffusion. As the value of the contaminant concentration decreases over time, a slowdown in the speed of the wave is observed; the modeling allows monitoring the distribution of the contaminant for all time. Therefore, the developed numerical model can be used to predict the distribution of contaminants in liquids.

The effect of magnetic field of 0.3 T on the concentration, distribution of sizes in suspension and zeta potential of colloidal gold and colloidal silver nanoparticles, obtained by considering the pulsed laser ablation in double distilled water was studied. The magnetic field was transverse to the direction of incidence of the laser radiation and parallel to the surface of a submerged target. An Nd: YAG laser was used (1064 nm in wavelength, 10 ns in duration, repetition rate of 10 Hz and 37 mJ of energy) to ablate targets. The colloids were characterized by inductively coupled plasma optical emission spectroscopy, ultraviolet-visible spectroscopy, dynamic light scattering and zeta potential. Concentration analysis suggested that applying magnetic field of 0.3 T during nanoparticle synthesis leads to higher concentration. Applying magnetic field led to an eleven percent increase in the concentration of the colloid with gold nanoparticles and a five percent increase in the concentration of the colloidal silver nanoparticles. The absorption spectra suggested the presence of spherical nanoparticles. When analyzing the effect of the magnetic field on the hydrodynamic size distribution of the nanoparticles and the zeta potential of the colloids, no significant changes were evidenced. The magnetic confinement of the plasma induced by laser ablation caused changes in the characteristics of the colloids.

In this work, we studied the microfibers of a textile (T-shirt) of the Chimú culture. This culture developed on the northern coast of Peru. To determine the raw material and structural quality of the microfibers, the results of the Chimú textile were compared with the corresponding results for the microfibers of cotton from the northern coast of Peru (native cotton). Scanning electron microscopy images revealed that the Chimú textile yarns are composed of a set of interwoven microfibers. Energy-dispersive X-ray spectroscopy and pulsed laser-induced plasma spectroscopy techniques allowed the identification of characteristic cellulose atoms in the microfibers of Chimú textile and native cotton. Only for the Chimú textile, these spectroscopic techniques allowed the identification of atoms corresponding to natural dyes and powder residues. Attenuated total reflection Fourier transform infrared spectroscopy identified the same molecular bonds for the microfibers of Chimú textile and native cotton. For the microfibers of Chimú textile and native cotton, the X-ray diffractograms showed peaks characteristic of the cellulose Ig polymorphism of monoclinic P21 structure. The raw material of the Chimú textile is cotton and the microfibers of this material show significant structural stability. Resumen En este trabajo se estudiaron las microfibras de un textil (camiseta) de la cultura Chimú. Esta cultura se desarrolló en la costa norte del Perú. Para determinar la materia prima y calidad estructural de las microfibras, los resultados del textil Chimú fueron comparados con los correspondientes para las microfibras del algodón de la costa norte del Perú (algodón nativo). Las imágenes de microscopia electrónica de barrido revelaron que los hilos del textil Chimú están compuestos por un conjunto de microfibras entrelazadas. Las técnicas de espectroscopia de rayos X por energía dispersiva y de plasmas inducidos por laser permitieron identificar átomos característicos de la celulosa en las microfibras del textil Chimú y del algodón nativo. Únicamente para el textil Chimú, estas técnicas espectroscópicas permitieron identificar átomos que corresponderían a tintes naturales y a residuos de polvo. La espectroscopia de infrarrojo con transformada de Fourier por reflexión total permitió identificar los mismos enlaces moleculares para las microfibras del textil Chimú y del algodón nativo. Para las microfibras del textil Chimú y del algodón nativo, los difractogramas de rayos X mostraron picos característicos del polimorfismo de la celulosa Iß de estructura monoclínica P21. La materia prima del textil Chimú es el algodón y las microfibras del mismo presentan una significativa estabilidad estructural.

Se determinaron los umbrales de ablación láser de los metales cobre, oro y plata para la radiación láser de 1064 nm de un láser Nd:YAG de nanosegundos utilizándose la técnica fotoacústica pulsada para registrar las señales fotoacústicas producidas debido a la interacción del metal con los pulsos láser. Dichas señales se analizaron mediante correlación estándar y los cambios en la amplitud fotoacústica conforme aumento la fluencia láser. Los resultados indican que las señales fotoacústicas son muy sensibles a cambios físicos que experimenta una muestra solida debido a la interacción con pulsos láser, pudiendo diferenciarse claramente el cambio del régimen termoelástico al de ablación y por consiguiente el umbral de ablación. Los valores obtenidos para la fluencia umbral fueron: (1.71±0.08) J/cm2 para el cobre, (1.65±0.09) J/cm2 para el oro y (1.15±0.05) J/cm2 para la plata.

Se reporta la respuesta fotoacústica de un sensor piezoeléctrico que fue irradiado con pulsos láser de longitudde onda de 1064 nm y distinta energía emitidos por un láser Nd:YAG. La medida de la energía de los pulsoslaser se hizo con un medidor, marca Newport modelo 1936-R con sensor piroeléctrico y las señales fotoacústicascon un osciloscopio Tektronix, modelo DPO3054 de 500 MHz. Experimentalmente se encontró una dependencialineal entre la intensidad de la señal fotoacústica del sensor piezoeléctrico y la energía del pulso laser. La sensibilidadde la respuesta fotoacústica del sensor fue dependiente de la placa protectora. Para placas de aluminio y aluminiopintado de negro fueron (6.52 ± 0.06)mV/mJ y (51.2 ± 1.5)mV/mJ respectivamente. Se concluyó que este tipo de sensor piezoeléctrico es muy sensible a los cambios de energía de láseres pulsados de 1064 nm, su respuesta es directamente proporcional a la energía incidente, es apropiado para mediciones de energía de láseres pulsados en tiempo real y, no se ve afectado por ruidos acústicos ni condiciones de iluminación del laboratorio. We report the photoacoustic response of a piezoelectric sensor that was irradiated with laser pulses of wavelength of 1064 nm and different energy emitted by an Nd:YAG laser. The measurement of laser pulse energy was done with a meter, Newport model 1936-R with pyroelectric sensor and the photoacoustic signals with a Tektronix oscilloscope, model DPO3054 of 500 MHz. Experimentally, we found a linear dependence between the intensity of the photoacoustic signal of the piezoelectric sensor and the energy of the laser pulse. The sensitivity of the photoacoustic response of the sensor was dependent on the protective plate. For aluminum and aluminum plates painted black were (6.52 ± 0.06)mV/mJ and (51.2 ± 1.5)mV/mJ respectively. It was concluded that this type of piezoelectric sensor is very sensitive to the energy changes of 1064 nm pulsed lasers, its response is directly proportional to the incident energy, it is suitable for energy measurements of lasers pulsed in real time and it is not seen affected by acoustic noises or lighting conditions of the laboratory.