An Unmatched Radio Frequency Chain for Low-Field Magnetic Resonance Imaging

Magnetic Resonance Imaging (MRI) is a safe and versatile diagnostic tool for intracranial imaging, however it is also one of the most expensive and specialized making it scarce in low- to middle-income countries (LMIC). The affordability and portability of low-field MRI offers the potential for increased access to brain imaging for diseases like Hydrocephalus in LMIC. In this tutorial style work, we show the design of a low powered and low cost radio frequency chain of electronics to be paired with a previously reported prepolarized low-field MRI for childhood hydrocephalus imaging in sub-Saharan Africa where the incidence of this condition is high. Since the Larmor frequency for this system is as low as 180 kHz, we are able to minimize the impedance of the transmit coil to 5 ohms rather than match to 50 ohms as is traditionally the case. This reduces transmit power consumption by a factor of 10. We also show the use of inexpensive and commonly available animal enclosure fencing (“chicken wire”) as a shield material at this frequency and compare to more traditional shield designs. These preliminary results show that highly portable and affordable low-field MRI systems could provide image resolution and signal-to-noise sufficient for planning hydrocephalus treatment in areas of the world with substantial resource limitations. Employment of these technologies in sub-Saharan Africa offers a cost-effective, sustainable approach to neurological diagnosis and treatment planning in this disease burdened region.Fil: Harper, Joshua R.. Pennsylvania State University; Estados UnidosFil: Zárate Evers, Cristhian Manuel. Universidad Nacional de Asunción; Paraguay. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Krauch, Federico. Universidad Nacional de Asunción; ParaguayFil: Muhumuza, Ivan. Mbarara University Of Science And Technology; UgandaFil: Molina, Jorge. Universidad Nacional de Asunción; ParaguayFil: Obungoloch, Johnes. Mbarara University Of Science And Technology; UgandaFil: Schiff, Steven J.. Pennsylvania State University; Estados Unido

Light refraction effects in counterflow non-premixed flames

This paper presents the influence of light refraction on the broadening of CH∗ and C2 ∗ species experimental profiles in laminar counterflow non-premixed flames. In fact, by comparing CH∗ and C2 ∗ experimental and numerical profiles in a counterflow configuration, a broadening of these species experimental profiles is observed, and these species are frequently employed experimentally to determine important macroscopic combustion properties. Therefore in this work, in order to give an explanation of these phenomena, light refraction due to a high temperature gradient was considered. The Gladstone–Dale relation was used to estimate the medium refractive index along the burner axis, taking into account the gas density and composition. Then, a simple procedure for light refraction estimation of rays reaching the solid angle of the camera in counterflow non-premixed flames was proposed. Finally, the influence of refraction of light on CH∗ and C2 ∗ species thicknesses appears to be significant depending on the operating conditions of counterflow non-premixed flames. However, taking into account the difference between the experimental and numerical profiles thicknesses, this effect is not fully responsible for the experimental broadening. Nonetheless, the same procedure described here can be used in order to study the light refraction for other experimental configurations, such as those of transcritical flames, where the gas density variation is much higher, and consequently the light refraction would be greater.Fil: Alviso, Dario. Universidad Nacional de Asunción; Paraguay. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Mecánica. Laboratorio de Fluidodinámica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Zárate Evers, Cristhian Manuel. Universidad Nacional de Asunción; Paraguay. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Krauch, Federico. Universidad Nacional de Asunción; ParaguayFil: Artana, Guillermo Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Mecánica. Laboratorio de Fluidodinámica; ArgentinaFil: Rolón, Juan Carlos. Universidad Nacional de Asunción; Paragua

Development of a diesel-biodiesel-ethanol combined chemical scheme and analysis of reactions pathways

Diesel-biodiesel-ethanol blends have been the focus of intense research quite recently. Diesel is a complex fuel composed of hundreds of compounds indicating the difficulty of using diesel for experimental studies associated with numerical simulations. Biodiesel is also a complex mixture of methyl esters. When injected in a diesel engine in the pure form, it induces changes in combustion behavior which can impact pollutants emission. Consequently simplified synthetic fuels, called “surrogate fuels”, with shorter chain lengths and known physical chemical properties are chosen to carry combustion studies. Finally, ethanol is one of the liquid alternative fuels most widely studied. The present paper focuses on numerical studies of the combustion of diesel-biodiesel-ethanol blends using 0D auto-ignition delay and 1-D freely-propagating gaseous premixed flame configurations. The objective is to develop and validate a new chemical scheme by carefully combining two existing chemical schemes from the literature. The first one is the scheme due to Andrae (2011) for the combustion of diesel-ethanol blends and the second one is due to Luo et al. (2012) for a biodiesel surrogate. The approach consists of merging non common elementary reactions from both chemical schemes and analyzing the common reactions (having different reaction constants) in both chemical schemes in order to chose most relevant chemical pathways from each scheme so that the resulting merged scheme gives a good prediction of the auto-ignition delay and laminar flame speed19141142

Development of a diesel-biodiesel-ethanol combined chemical scheme and analysis of reactions pathways

International audienceDiesel-biodiesel-ethanol blends have been the focus of intense research quite recently. Diesel is a complex fuel composed of hundreds of compounds indicating the difficulty of using diesel for experimental studies associated with numerical simulations. Biodiesel is also a complex mixture of methyl esters. When injected in a diesel engine in the pure form, it induces changes in combustion behavior which can impact pollutants emission. Consequently simplified synthetic fuels, called “surrogate fuels”, with shorter chain lengths and known physical chemical properties are chosen to carry combustion studies. Finally, ethanol is one of the liquid alternative fuels most widely studied. The present paper focuses on numerical studies of the combustion of diesel-biodiesel-ethanol blends using 0D auto-ignition delay and 1-D freely-propagating gaseous premixed flame configurations. The objective is to develop and validate a new chemical scheme by carefully combining two existing chemical schemes from the literature. The first one is the scheme due to Andrae (2011) for the combustion of diesel-ethanol blends and the second one is due to Luo et al. (2012) for a biodiesel surrogate. The approach consists of merging non common elementary reactions from both chemical schemes and analyzing the common reactions (having different reaction constants) in both chemical schemes in order to chose most relevant chemical pathways from each scheme so that the resulting merged scheme gives a good prediction of the auto-ignition delay and laminar flame speed