Abstract This paper addresses the impact of natural gas composition on both the operability and emissions of lean premixed gas turbine combustion system. This is an issue of growing interest due to the challenge for gas turbine manufacturers in developing fuel-flexible combustors capable of operating with variable fuel gases while producing very low emissions at the same time. Natural gas contains primarily methane (CH4) but also notable quantities of higher order hydrocarbons such as ethane (C2H6) can also be present. A deep understanding of natural gas combustion is important to obtain the highest combustion efficiency with minimal environmental impact. For this purpose, Large Eddy Simulations of an annular combustor sector equipped with a partially-premixed burner are carried out for two different natural gas compositions with and without including the effect of flame strain rate and heat loss resulting in a more adequate description of flame shape, thermal field and extinction phenomena. Promising results, in terms of NOx, compared against available experimental data, are obtained including these effects on the flame brush modelling, enhancing the fuel-dependency under non adiabatic condition.
This research work deals with the plane wave diffraction by a coated perfect electrically conducting wedge with arbitrary apex angle.The uniform layer covering the impenetrable wedge is made of a standard double positive material or an unfamiliar double negative metamaterial with negative permittivity and permeability at the operating frequencies.The propagation mechanism is studied when the incidence direction is perpendicular to the edge of the composite structure, and uniform asymptotic solutions are proposed to evaluate the diffraction contribution for both the polarizations.Such approximate solutions are obtained by using the Uniform Asymptotic Physical Optics approach based on electric and magnetic equivalent surface currents radiating in the neighboring free space.The related expressions are user-friendly and provide reliable field values as verified by numerical tests involving a full-wave electromagnetic solver.
Abstract Background Visceral Leishmaniasis (VL) is endemic in 88 countries, in areas of relatively low incidence with a relevant proportion of immune suppressed patients clinical presentation, diagnosis and management may present difficulties and pitfalls. Methods Demographic data, clinical, laboratory features and therapeutic findings were recorded in patients identified by a regional VL disease registry from January 2007 to December 2010. Results A total of 55 patients (36 adults mean age 48.7 years, 19 children median age 37.5 months) were observed presenting with 65 episodes. All childen were immunocompetent, whereas adults affected by VL included both immunocompetent (n°17) and immunesuppressed (n°19) patients. The clinical presentation was homogeneous in children with predominance of fever and hepato-splenomegaly. A wider spectrum of clinical presentations was observed in immunocompromised adults. Bone marrow detection of intracellular parasites (Giemsa staining) and serology (IFAT) were the most frequently used diagnostic tools. In addition, detection of urinary antigen was used in adult patients with good specificity (90%). Liposomal amphotericin B was the most frequently prescribed first line drug (98.2% of cases) with 100% clinical cure. VL relapses (n°10) represented a crucial finding: they occurred only in adult patients, mainly in immunocompromised patients (40% of HIV, 22% of non-HIV immunocompromised patients, 5,9% of immunocompetent patients). Furthermore, three deaths with VL were reported, all occurring in relapsing immunocompromised patients accounting for a still high overall mortality in this group (15.8%). Conclusions The wide spectrum of clinical presentation in immunesuppresed patients and high recurrence rates still represent a clinical challenge accounting for high mortality. Early clinical identification and satisfactory treatment performance with liposomal amphotericin B are confirmed in areas with low-level endemicity and good clinical standards. VL needs continuing attention in endemic areas where increasing numbers of immunocompromised patients at risk are dwelling.
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