Investigation on localized states in GaN nanowires.

GaN nanowires with diameters ranging between 50 and 500 nm were investigated by electrical and photoinduced current techniques to determine the influence of their size on the opto-electronic behavior of nanodevices. The conductivity, photoconductivity, and persistent photoconductivity behavior of GaN nanowires are observed to strongly depend on the wire diameter. In particular, by spectral photoconductivity measurements, three main sub-band-gap optoelectronic transitions were detected, ascribed to the localized states giving rise to the characteristic blue, green, and yellow bands of GaN. Photoconductivity with below-band-gap excitation varies orders of magnitude with the wire diameter, similarly to that observed for near-band-edge excitation. Moreover, yellow-band-related signal shows a superlinear behavior with respect to the band-edge signal, offering new information for the modeling of the carrier recombination mechanism along the nanowires. The photoconductivity results agree well with a model which takes into account a uniform distribution of the localized states inside the wire and their direct recombination with the electrons in the conduction band.

An evaluation of certain Salmonella detection methods in surface water.

Two different procedures were employed for detecting Salmonella spp. in environmental water samples: a rapid method (enrichment in Salmosyst Broth and plating in Rambach Agar-Merck) and a longer assay (pre-enrichment in Buffered Peptone Water, enrichment in Selenite-Cistyne Broth and plating in Brilliant Green Agar-Difco). The efficiency of microbiological tests was measured by the following criteria: recovery, sensitivity and specificity. The results analysed by the Kendall concordance coefficients demonstrated that the rapid method appeared more effective even if poorly specific.

Comparison of different selective methods for detection of Listeria species in surface water.

Tests were carried out to evaluate the efficiency of various combinations of selective enrichment and plating techniques using pure cultures of Listeria monocytogenes, Listeria seeligeri and Listeria innocua in suspension and samples of surface water. The best yields for the various Listeria spp. were obtained after a single passage in LEB (Oxoid) or LEB Buffered (Oxoid) and after using Palcam and Oxford agar (Oxoid). Palcam agar was, however, shown to be the most efficient means of detecting the Listeria spp. in the natural water samples.