Model-corrected microwave imaging through periodic wall structures

A model-based imaging framework is applied to correct the target distortion seen in microwave imaging through a periodic wall structure. In addition to propagation delays caused by the wall, it is shown that the structural periodicity induces high-order space harmonics leading to other ghost artifacts in the through-wall image. To overcome these distortions, the periodic layer Greens function is incorporated into the forward model. A linear back-projection solution and a nonlinear minimization solution are applied to solve the inverse problem. The model-based back-projection image corrects the distortion and has higher resolution compared with free space due to the inclusion of multipath propagation through the periodic wall, but considerable sidelobe clutter is present. The nonlinear solution not only corrects target distortion without clutter but also reduces the solution to a sparse form. © Copyright 2012 Paul C. Chang et al

A conformally invariant sphere theorem in four dimensions

In this paper we provide a sharp characterization of the smooth four-dimensional sphere. The assumptions of the theorem are conformally invariant, and can be reduced to an L^2 inequality of the Weyl tensor and positivity of the Yamabe invariant.Comment: 39 pages, 0 figure

Pickoff and spin-conversion quenchings of ortho-positronium in oxygen

The quenching processes of the thermalized ortho-positronium(o-Ps) on an oxygen molecule have been studied by the positron annihilation age-momentum correlation techinique(AMOC). The Doppler broadening spectrum of the 511 keV gamma-rays from the 2gamma annihilation of o-Ps in O_2 has been measured as a function of the o-Ps age. The rate of the quenching, consisting of the pickoff and the spin-conversion, is estimated from the positron lifetime spectrum. The ratio of the pickoff quenching rate to the spin-conversion rate is deduced from the Doppler broadening of the 511 keV gamma-rays from the annihilation of the o-Ps. The pickoff parameter ^1Z_eff, the effective number of the electrons per molecule which contribute to the pickoff quenching, for O_2 is determined to be 0.6 +- 0.4. The cross-section for the elastic spin-conversion quenching is determined to be (1.16 +- 0.01) * 10^{-19} cm^2.Comment: 4 pages with 5 eps figures, LaTeX2e(revtex4

Explaining lecture attendance behavior via structural equation modeling: Self-Determination Theory and the Theory of Planned Behavior

Some research suggests that university lecture attendance positively correlates with academic performance. Although there are several motivational pathways which may explain attendance, few studies have examined the psychosocial factors leading to student attendance intentions and behavior. Consequently, we evaluated via structural equation modeling (SEM) two prominent motivational theories to help explain lecture attendance: Self-Determination Theory (SDT) and The Theory of Planned Behavior (TPB). Undergraduates (N = 288) from two universities completed pre-semester motivation measurements and post-semester estimates of attendance. Student grades were also examined. SDT was not found to be an accurate model of attendance intentions or behavior. By contrast, TPB was found to be an adequate model to help explain attendance intentions and behavior. Lecture attendance did not significantly correlate with grades. If educators and students are committed to increasing lecture attendance rates, our findings suggest that the enhancement of perceived behavioral control, as well as optimistic intentions, may yield the greatest benefits with respect to students meeting their lecture attendance expectations

ROMA (Rank-Ordered Multifractal Analysis) for intermittent fluctuations with global crossover behavior

Rank-Ordered Multifractal Analysis (ROMA), a recently developed technique that combines the ideas of parametric rank ordering and one parameter scaling of monofractals, has the capabilities of deciphering the multifractal characteristics of intermittent fluctuations. The method allows one to understand the multifractal properties through rank-ordered scaling or non-scaling parametric variables. The idea of the ROMA technique is applied to analyze the multifractal characteristics of the auroral zone electric field fluctuations observed by SIERRA. The observed fluctuations span across contiguous multiple regimes of scales with different multifractal characteristics. We extend the ROMA technique such that it can take into account the crossover behavior -- with the possibility of collapsing probability distributions functions (PDFs) -- over these contiguous regimes.Comment: 24 pages, 18 figure