Diversity and antifungal susceptibility of yeasts from tropical freshwater environments in Southeastern Brazil

Yeast communities were isolated from water and sediment samples of two unpolluted natural lakes, located inside Rio Doce State Park, and two rivers located outside of this Park in Southeastern Brazil. A total of 134 yeast isolates were obtained and identified as belonging to 36 species. The numbers of fecal coliforms and yeast species were higher in rivers than in lakes. The genus Candida had the highest number of species with the presence of opportunistic pathogens such as Candida krusei, C. tropicalis, C. guilliermondii and C. parapsilosis. Yeasts able to grow at 37 degrees C were tested in relation to their susceptibility to common used antifungal drugs. Yeast isolates (13%) were susceptible to ketoconazole, 79% to fluconazole, 31% to terbinafine and 78% of the strains were susceptible to amphotericin B. Seven isolates from different Candida species were resistant to all antifungals tested. The high number of fecal coliforms found in these aquatic environments and the presence of resistant yeast strains to common used antifungal drugs suggest that these environments can pose potential health risks for people utilizing the contaminated waters.     

Analysis of a solar chimney power plant in the Arabian Gulf region

A simplified thermodynamics analytical model for steady airflow inside a solar chimney is performed. A simplified Bernoulli equation combined with fluid statics and ideal gas equation was implemented and solved using EES solver to predict the performance of the solar chimney power plant. The analytical model matched the experimental data and numerical study available in the literature. The developed analytical model was used to evaluate the effect of geometric parameters on the solar plant power generation. The analysis showed that chimney height and turbine pressure head are the most important physical variables for the solar chimney design. The study showed that second-law efficiency has non-monotonic relation with turbine pressure head. The model shows that second-law efficiency and power harvested increase with the increase of chimney height and/or diameter. The developed model is used to analyze the feasibility of solar chimney power plants for the UAE climate which possesses typical characteristics of the Gulf climate. The solar characteristics of the UAE are shown along with characteristic meteorological data. A solar chimney power plant with a chimney height of 500 m and a collector roof diameter of 1000 m would produce at least 8 MW of power. The amount of power produced during the summer would be higher where the demand in the Gulf area is the highest.     

THE ROLE OF HETEROATOMS IN JET FUEL INSTABILITY

ABSTRACT

The test fuel used in this investigation was a petroleum derived jet A fuel from Rastanura refinery, Saudi Arabia. The physical and chemical tests of fuel, and one month sunlight storage experiment exhibited the stability of fuel. Accelerated and ambient storage stability tests, conducted using model nitrogen compounds in jet-A fuel and n-decane, indicated that the rate of sediment formation was dependent on the structural features of nitrogen compounds and storage conditions. The pyrrole and indole derivatives did not produce any appreciable sediment except 2,6-dimethylpyrrole. Air, temperature, dissolved oxygen and light all strongly accelerate the process of sediment formation. On the other hand removal of dissolved oxygen significantly reduces it. Acids and phenols act respectively as accelerator and inhibitor towards sedimentation. The reaction has a low apparent activation energy and appears to involve a free radical oxidative self condensation of nitrogen compounds. The tower O/C ratios of sediment also supported the view point that oxidation is a key aspect of jet fuel thermal instability. Approximately 25 different types of possible structures were identified from average properties of sediments as analysed by elemental analysis, infrared and mass spectrometric methods.     

Semi-automatic detection and counting of oil palm trees from high spatial resolution airborne imagery

Plantation inventory and management require a range of fine-scale remote-sensing data. Remote-sensing images with high spatial and spectral resolution are an efficient source of such information. This article presents an approach to the extraction and counting of oil palm trees from high spatial resolution airborne imagery data. Counting oil palm trees is a crucial problem in specific agricultural areas, especially in Malaysia. The proposed scheme comprises six major parts: (1) discrimination of oil palms from non-oil palms using spectral analysis, (2) texture analysis, (3) edge enhancement, (4) segmentation process, (5) morphological analysis and (6) blob analysis. The average accuracy obtained was 95%, which indicates that high spatial resolution airborne imagery data with an appropriate assessment technique have the potential to provide us with vital information for oil palm plantation management. Information on the number of oil palm trees is crucial to the ability of plantation management to assess the value of the plantation and to monitor its production.     

AC Susceptibility and Superconducting Properties of Graphene Added YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−<Emphasis Type="Italic">d</Emphasis></Subscript>

The effect of graphene (G) addition on YBa₂Cu₃O_7?δ(G)_x (x =?0 ? 0.03 wt%) has been studied using the X-ray diffraction method, scanning electron microscopy, electrical resistance versus temperature, transport critical current density J_c, and AC susceptibility measurements. XRD patterns showed single-phase YBa₂Cu₃O_7?δ (YBCO) for all samples. SEM micrographs showed filling of the voids between YBa₂Cu₃O_7?δ grains as graphene was added. The temperature-dependent electrical resistance curves showed metallic normal state behavior and onset transition temperature T_conset between 90 and 92 K for all samples. AC susceptibility measurement showed transition temperature \(T_{\mathrm {c} \chi ^{\prime }}\) between 90 and 93 K. \(T_{\mathrm {c} \chi ^{\prime }}\) was maintained or improved slightly as graphene was added. The x =?0.001 wt% showed the highest J_c, i.e., 2750 A cm^?2 at 77 K and 5570 mA cm^?2 at 30 K which was 13 and 40 times higher than that of the non-added YBCO, respectively. The peak temperature T_p of the imaginary part of the susceptibility χ^″ was around 78–82 K for all samples indicating grain coupling was not weakened as graphene was added.     

Effect of gamma irradiation and silver doping on YBCO superconductor

The effect of -irradiation and silver doping on the properties of YBCO superconductors has been studied by electrical resistance measurements and x-ray diffraction techniques. The zero-resistance superconducting transition temperature of (YBCO)_1–xAg _x systematically increase by about 2 K with an increase of Ag content up tox=0.04. Further increase in Ag content decreases the transition temperature. The normal-state resistance decreases up to a factor of 3.4 with an increase of Ag content. No significant change in the transition width has been observed due to silver addition up tox=0.30. Undoped YBCO and the Ag-doped specimens of (YBCO)_1.96Ag_0.04 were irradiated with-rays up to an integrated-dose of 77 MR. The normal-state resistance of the specimens gradually increases and the transition temperature slightly decreases with increase of-dose. The intensities of the x-ray diffraction peaks of the monolayers of the sample powders decrease with -irradiation without noticeable change of diffraction angles or peak widths. These observations indicate that the high-T _c supconductor YBCO is quite sensitive to-irradiation but drastic lattice expansion does not occur up to a-dose of 77 MR.