Browsing by Author "Chuaqui, Hernan"

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    Germicidal effect of UV light on epiphytic fungi isolated from blueberry
    (PONTIFICIA UNIV CATOLICA CHILE, FAC AGRONOMIA INGENIERIA FORESTAL, 2012) Latorre, Bernardo A.; Rojas, Susana; Diaz, Gonzalo A.; Chuaqui, Hernan
    B.A. Latorre, S. Rojas, G.A. Diaz, and H. Chuaqui. 2012. Germicidal effect of UV light on epiphytic fungi isolated from blueberry. Cien. Inv. Agr. 39(3): 473-480. The present study examined the inactivation effect of ultraviolet (UV) light on the conidia of Botrytis cinerea Cladosporium cladosporioides, C. herbarum and Pestalotiopsis clavispora, common pathogens of blueberry (Vaccinium corymbosum), often found as epiphytes. The fungi were grown at 20 degrees C in acidified potato dextrose agar (APDA) in the dark; conidial suspensions (10(6) conidia mL(-1)) were placed the bottom of 5 cm glass Petri plates with a maximum height of 0.5 mm. Uncovered plates were immediately exposed to either UVA (lambda = 361 nm), UVB (lambda = 302 nm) or UVC (lambda = 254 nm) at doses between 40 and 110 mJ.cm(2). The results were expressed as survival ratios Nt/N0 (the number of colonies obtained after conidia were exposed to UV irradiance/the total number of fungal colonies in the non-irradiated controls). The fungal-dependent rate constants (k), a measure of the mortality rate, were estimated from an exponential model. The species in order of greatest to least resistance to UV light were Cladosporium cladosporioides, C. herbarum, R clavispora and B. cinerea. The type of fungal species and the dose of UV irradiance had a significant (P <= 0.001) influence on Nt/N0. The interaction between the fungal species and the UV irradiance dose was significant (P <= 0.004) only when the conidia were exposed to UVB or UVC. The resistance of Cladosporium spp. to UV radiation may explain the ubiquity of Cladosporium spp. in nature and could allow for the abundant populations of Cladosporium spp. often found on the foliage, flowers and fruits of blueberries.
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    Refractive optical measurements on the Llampudken generator
    (AMER INST PHYSICS, 2006) Suzuki, Francisco; Veloso, Felipe; Molina, Francisco; Mitchell, Ian; Chuaqui, Hernan; Aliaga Rossel, Raul; Favre, Mario; Wyndham, Edmund; HerreraVelazquez, JJE
    Experiments with two different configurations of dense z-pinches have been carried out on the Llampudken generator with the objective of investigating the time evolution of the discharges. These configurations were studied with refractive optical measurements using the second harmonic of a Nd:YAG laser (10 ns FVVM lambda=532 run). The Llampudken generator delivered a pulse current of 450 kA with a 260 ns rise time. Refractive optical measurements with schlieren diagnostics were made using an optical system which provided two frames per discharge. The original beam was split into two separate beams with perpendicular polarizations using a polarizer beam splitter and an extra path length was introduced into one of the beams delaying it with respect to the other. The path through the discharge chamber was equal for both beams therefore providing identical views of the plasma at two different times. The images were recorded on 35mm cameras using suitably orientated polarizers to select the corresponding beam. As a complementary diagnostic technique, MCP cameras with exposure time of 2 ns were used to obtain VUV images of the loads. Preliminary results of these experiments will be presented and discussed.
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    The formation of ring shaped laser plasmas on a metal surface
    (AMER INST PHYSICS, 2006) Veloso, Felipe; Chuaqui, Hernan; Aliaga Rossel, Raul; Favre, Mario; Mitchell, Ian; Wyndham, Edmund; HerreraVelazquez, JJE
    A method to produce ring plasmas on a metal surface is presented. The ring plasma is produced by focusing a laser pulse into an annular shape. This is achieved by using a combination of a converging lens and an axicon. The axicon is a rotationally symmetric prism. The radius of the focused ring is determined by the base angle of the axicon, and the focal length of the converging lens. The experiments are performed on a titanium surface, using a 0.18 J, 10 ns, 1064 nm pulsed, from a Nd:YAG laser. The background gas is hydrogen, at pressures in the atmospheric range. The ring structure was measured using schlieren imaging and Mach Zehnder interferometry. The expansion velocities of the laser-produced plasma in the background gas were measured in two directions; parallel and perpendicular to the metallic surface. Characteristic values are 5-9(.)10(3) m/s, for the ring radius expansion, parallel to the surface, and 1.0-1.7(.)10(4) m/s, perpendicular to the surface. Characteristic electron densities of the order of 10(18) cm(-3) were measured, with hollow radial profiles. The temperature of the plasma was estimated to be between 0.1 and 0.4 eV. This ring plasma is used as precursor plasma to achieve a hollow gas embedded z-pinch.