502 research outputs found
Soot formation in a turbulent swirling flow
The qualitative understanding of soot formation in simple models of gas turbine primary-zone combustors is summarized. Soot formation in flame radiation and air pollution was investigated. Results are presented, namely: (1) if the fuel is premixed with air in approximately stoichiometric proportions, the sequence of states that a fluid element undergoes as it burns is quite different from the sequence when liquid or vapor fuel is injected into an air-flow; (2) swirling flows, as are typical or swirl-can combustors, when burning, can amplify small aerodynamic disturbances upstream of the swirl vanes; and (3) different fuels form significantly different amounts of soot. Each of these effects makes major changes in the amount of soot formed in a given combustor
Laboratory measurements in a turbulent, swirling flow
Measurements of soot inside a flame-tube burner using a special water-flushed probe are discussed. The soot is measured at a series of points at each burner, and upon occasion gaseous constitutents NO, CO, hydrocarbons, etc., were also measured. Four geometries of flame-tube burners were studied, as well as a variety of different fuels. The role of upstream geometry on the downstream pollutant formation was studied. It was found that the amount of soot formed in particularly sensitive to how aerodynamically clean the configuration of the burner is upstream of the injector swirl vanes. The effect of pressure on soot formation was also studied. It was found that beyond a certain Reynolds number, the peak amount of soot formed in the burner is constant
Euler-Lagrange relationship for random dispersive waves Scientific report
Euler-Lagrange relationship for random dispersive wave
Euler-Lagrange relationship for random dispersive waves
Euler-Lagrange relationship for random dispersive wave
Fast optimal transition between two equilibrium states
We demonstrate a technique based on invariants of motion for a time-dependent
Hamiltonian, allowing a fast transition to a final state identical in theory to
that obtained through a perfectly adiabatic transformation. This method is
experimentally applied to the fast decompression of an ultracold cloud of
Rubidium 87 atoms held in a harmonic magnetic trap, in the presence of gravity.
We are able to decompress the trap by a factor of 15 within 35 ms with a strong
suppression of the sloshing and breathing modes induced by the large vertical
displacement and curvature reduction of the trap. When compared to a standard
linear decompression, we achieve a gain of a factor of 37 on the transition
time.Comment: 5 pages, 4 figures, an error in Eq. (2) has been correcte
A subsonic D-region probe-theory and instrumentation Scientific report no. 247
D-layer, subsonic, ion and electron probe operational mobility theory and instrumentation descriptio
Two-Dimensional Magnetic Resonance Tomographic Microscopy using Ferromagnetic Probes
We introduce the concept of computerized tomographic microscopy in magnetic
resonance imaging using the magnetic fields and field gradients from a
ferromagnetic probe. We investigate a configuration where a two-dimensional
sample is under the influence of a large static polarizing field, a small
perpendicular radio-frequency field, and a magnetic field from a ferromagnetic
sphere. We demonstrate that, despite the non-uniform and non-linear nature of
the fields from a microscopic magnetic sphere, the concepts of computerized
tomography can be applied to obtain proper image reconstruction from the
original spectral data by sequentially varying the relative sample-sphere
angular orientation. The analysis shows that the recent proposal for atomic
resolution magnetic resonance imaging of discrete periodic crystal lattice
planes using ferromagnetic probes can also be extended to two-dimensional
imaging of non-crystalline samples with resolution ranging from micrometer to
Angstrom scales.Comment: 9 pages, 11 figure
The contribution of teacher education to universities: a case study for international teacher educators
This paper reports on the initial stage of a research project which aims to develop deeper understanding of the contribution teacher education, as a sub-discipline within Education, makes to Higher Education in England. The study is located in the intersection between the domains of teacher education and higher education scholarship, which in England represents a contested and ambiguous professional space. Tensions between competing accountability measures, pulling away from university-based to exclusively school-based teacher education, are exacerbated by proposed policy changes arising from the government's recent market review. Findings drawn from analysis of qualitative data from a national survey are discussed in the context of Elizabeth Povinelli's critique of late liberalism and previous scholarship on the nature of teacher educators’ work. Evidence from the study demonstrates numerous benefits to higher education of hosting teacher education departments, including contributions to standard metrics, regional development and knowledge exchange within a strategic social justice agenda. However, teacher educators themselves may find articulating these benefits difficult, because of marginalisation from the dominant ways of achieving and accounting for excellence in the modern university. These findings offer a cautionary tale to international colleagues whose governments may be embarking on equivalent paths of teacher education reform
An Easily Constructed, Tuning Free, Ultra-broadband Probe for NMR
We have developed an easy to construct, non-resonant wideband NMR probe. The
probe is of the saddle coil geometry and is designed such that the coil itself
forms a transmission line. The probe thus requires no tuning or matching
elements. We use the probe with a spectrometer whose duplexer circuitry employs
a simple RF switch instead of the more common lambda/4 lines, so the entire
probe and spectrometer perform in an essentially frequency-independent manner.
Despite being designed with electro- and magnetostatic formulas, the probe
performs well at frequencies up to 150 MHz and beyond. We expect that with
additional design effort, the probe could be modified for use at significantly
higher frequencies. Because our construction method relies on commercial
circuit fabrication techniques, identical probes can be easily and accurately
produced
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