Thermodynamic measurements in a high pressure hydrogen-oxygen flame using Raman scattering from a broadband excimer laser

Raman scattering is an inelastic molecular scattering process in which incident radiation is reemitted at a fixed change in frequency. Raman spectroscopy can be used to measure the number density and temperature of the irradiated species. The strength of the Raman signal is inversely proportional to the wavelength raised to the fourth power. Consequently, high signal to noise ratios are obtained by using ultraviolet (UV) excitation sources. Using UV sources for Raman Spectroscopy in flames is complicated by the fact that some of the primary constituents in hydrogen-oxygen combustion absorb and reemit light in the UV and these fluorescence processes interfere with the Raman signals. This problem has been handled in atmospheric pressure flames in some instances by using a narrowband tunable excimer laser as a source. This allows for detuning from absorption transitions and the elimination of interfering fluorescence signals at the Raman wavelengths. This approach works well in the atmospheric pressure flame; however, it has two important disadvantages. First, injection-locked narrowband tunable excimer lasers are very expensive. More importantly, however, is the fact that at the high pressures characteristic of rocket engine combustion chambers, the absorption transitions are broadened making it difficult to tune to a spectral location at which substantial absorption would not occur. The approach taken in this work is to separate the Raman signal from the fluorescence background by taking advantage of the fact that Raman signal has nonisotropic polarization characteristics while the fluorescence signals are unpolarized. Specifically, for scattering at right angles to the excitation beam path, the Raman signal is completely polarized. The Raman signal is separated from the fluorescence background by collecting both horizontally and vertically polarized signals separately. One of the polarizations has both the Raman signal and the fluorescence background while the other has only the fluorescence signal. The Raman scatter is the difference between the signals. By choosing an appropriate optical setup, both signals can be obtained simultaneously with the same monochromator; hence, time resolved measurements are possible using this approach

Experimental investigation of a simulated LOX injector flow field and other nonintrusive measurement efforts

Efforts to improve the characteristics of fuel-oxidizer mixing in liquid rocket combustors have lead to a swirl element design for a liquid oxygen injector which is being considered for use on the STME. For the design which is the subject of this investigation, the oxygen enters the injector element perpendicular to the injector axis and nearly tangent to the circular injector wall. This swirl element is at one end of a tube and the injector exit is at the other. This geometric configuration creates a plume in the shape of a conical sheet. This sheet is either primarily contiguous liquid or droplets depending on the pressure drop in the injector and the distance from the injector exit. Probe-based devices such as two-dimensional grid patternators have been used to investigate simulated LOX injector flow fields (Hulka). The primary work described herein is an effort to use optical techniques to investigate the plume of a swirl injector element. For this investigation, a high pressure (500 psig) cold flow test facility was constructed. Water was used as the LOX simulate and air pressure was used to drive the injector flow field. Laser-induced fluorescence (LIF) from dye seeded into the water was used to obtain quantitative measurements of the time-averaged water concentration distribution in the plume. Scattered laser light and LIF were used for time averaged plume visualization and scattered light from a strobe with a 1 microsecond pulse was used for time-resolved plume visualization. During the Summer Faculty Fellowship for which this report was developed, an additional effort, unrelated to the swirl injector investigation, was made to resolve fluctuations in the combustion product composition in the exhaust of a hybrid rocket motor. A brief description of this effort is included herein

Novel Josephson effects between multi-gap and single-gap superconductors

Multi-gap superconductors can exhibit qualitatively new phenomena due to existence of multiple order parameters. Repulsive electronic interactions may give rise to a phase difference of $\pi$ between the phases of the order parameters. Collective modes due to the oscillation of the relative phases of these order parameters are also possible. Here we show that both these phenomena are observable in Josephson junctions between a single-gap and a multi-gap superconductor. In particular, a non-monotonic temperature dependence of the Josephson current through the junction reveals the existence of the $\pi$ phase differences in the multi-gap superconductor. This mechanism may be relevant for understanding several experiments on the Josephson junctions with unconventional superconductors. We also discuss how the presence of the collective mode resonantly enhances the DC Josephson current when the voltage across the junction matches the mode frequency. We suggest that our results may apply to MgB$_2$, 2H-NbSe$_2$, spin ladder and bilayer cuprates.Comment: 4 pages, 2 figure

Blended learning as an effective pedagogical paradigm for biomedical science

Blended learning combines face-to-face class based and online teaching and learning delivery in order to increase flexibility in how, when, and where students study and learn. The development, integration, and promotion of blended learning in frameworks of curriculum design can optimize the opportunities afforded by information and communication technologies and, concomitantly, accommodate a broad range of student learning styles. This study critically reviews the potential benefits of blended learning as a progressive educative paradigm for the teaching of biomedical science and evaluates the opportunities that blended learning offers for the delivery of accessible, flexible and sustainable teaching and learning experiences. A central tenet of biomedical science education at the tertiary level is the development of comprehensive hands-on practical competencies and technical skills (many of which require laboratory-based learning environments), and it is advanced that a blended learning model, which combines face-to-face synchronous teaching and learning activities with asynchronous online teaching and learning activities, effectively creates an authentic, enriching, and student-centred learning environment for biomedical science. Lastly, a blending learning design for introductory biochemistry will be described as an effective example of integrating face-to-face and online teaching, learning and assessment activities within the teaching domain of biomedical science. DOI: 10.18870/hlrc.v3i4.16

Mathematics Achievement of Regular Education Students by Placement in Inclusion and Non-Inclusion Classrooms and Their Principals\u27 Perceptions of Inclusion

This study examined mathematics achievement of fourth and fifth grade students in Mississippi and principals\u27 perceptions of inclusion. A sample of 462 students from eight separate elementary schools was selected for this study. Fifteen principals completed the Principal and Inclusion Survey regarding inclusion education. Eight of the 15 principals were interviewed with 10 open-ended questions regarding their perceptions of inclusion. Data were analyzed using an independent two-tailed t test and Pearson product moment correlation. The independent two-tailed / test was used to determine differences in mathematics achievement for fourth and fifth grade students in inclusion classrooms compared to non-inclusion classrooms and by gender. Qualitative data were gathered for the eight principal interviews. Data were coded to analyze recurring themes throughout the interviews. Pearson product moment correlation was used to investigate a correlation between mathematics achievement and principal perceptions of inclusion. Results of the data analysis showed no significant differences at the .05 level in mathematics achievements between regular education students in inclusion classrooms compared to non-inclusion classrooms. Descriptives concerning the Principal and Inclusion Survey indicated that principal perceptions regarding inclusion were very similar. An independent two tailed t test showed a significant difference by gender of principals regarding appropriate placement for students with disabilities. Qualitative data resulted in four emerging themes regarding the eight principal interviews regarding their perceptions of inclusion. The themes that emerged from the data included: 1. roles and relationships of teachers in inclusionary practices, 2. parental involvement, knowledge, and respect for inclusion education, 3. principals\u27 responsibilities in the conflicting nature of inclusionary practices, 4. the physical environment inclusive to learning for inclusion education