Generalized Processing for Pulsed Synthetic Aperture Radar

The Range-Doppler Algorithm (RDA) and the Chirp-Scaling Algorithm (CSA) process Synthetic Aperture Radar (SAR) data with approximations to ideal SAR processing. These approximations are invalid for data from systems with wide bandwidths, large bandwidths, and/or low center frequencies. While simple and efficient, these frequency-domain methods are thus limited by the SAR parameters. This paper explores these limits and proposes a generalized chirp-scaling approach for extending the utility of frequency-domain processing. We demonstrate how different order approximations of the SAR signal in the two-dimensional frequency domain affect image focusing for varying SAR parameters. From these results, a guideline is set forth which suggests the required order of approximation terms for proper focusing. A proposed generalized frequency-domain processing approach is derived. This method is an efficient arbitrary-order chirp-scaling algorithm that processes the data using the appropriate number of approximation terms. The new method is demonstrated using simulated data

The BYU Micro-SAR: Theory and Application of a Small LFM-CW Synthetic Aperture Radar

The BYU microSAR is a new, low-cost Synthetic Aperture Radar (SAR) system developed by students at Brigham Young University. The simple design is based on a linear frequency modulated continuous wave signal (LFM-CW) which reduces the size and power compared to a conventional pulsed SAR system. The BYU microSAR is small enough to y on a small UAV, further reducing the cost of operation and extending the use of SAR into new areas. Due to the LFM-CW design, modi ed SAR processing algorithms are needed which account for the movement of the platform during data collection. SAR processing assumes that the sensor is moving in a straight line at a constant speed, but in actuality a UAV or airplane will deviate, often signi cantly, from this ideal. This non-ideal motion can seriously degrate the SAR image quality. This paper presents the design of the BYU microSAR, the theory of operation, and the modi ed processing algorithms which account for the continuous motion

RNA interference-mediated c-MYC inhibition prevents cell growth and decreases sensitivity to radio- and chemotherapy in childhood medulloblastoma cells

BACKGROUND: With current treatment strategies, nearly half of all medulloblastoma (MB) patients die from progressive tumors. Accordingly, the identification of novel therapeutic strategies remains a major goal. Deregulation of c-MYC is evident in numerous human cancers. In MB, over-expression of c-MYC has been shown to cause anaplasia and correlate with unfavorable prognosis. METHODS: To study the role of c-MYC in MB biology, we down-regulated c-MYC expression by using small interfering RNA (siRNA) and investigated changes in cellular proliferation, cell cycle analysis, apoptosis, telomere maintenance, and response to ionizing radiation (IR) and chemotherapeutics in a representative panel of human MB cell lines expressing different levels of c-MYC (DAOY wild-type, DAOY transfected with the empty vector, DAOY transfected with c-MYC, D341, and D425). RESULTS: siRNA-mediated c-MYC down-regulation resulted in an inhibition of cellular proliferation and clonogenic growth, inhibition of G1-S phase cell cycle progression, and a decrease in human telomerase reverse transcriptase (hTERT) expression and telomerase activity. On the other hand, down-regulation of c-MYC reduced apoptosis and decreased the sensitivity of human MB cells to IR, cisplatin, and etoposide. This effect was more pronounced in DAOY cells expressing high levels of c-MYC when compared with DAOY wild-type or DAOY cells transfected with the empty vector. CONCLUSION: In human MB cells, in addition to its roles in growth and proliferation, c-MYC is also a potent inducer of apoptosis. Therefore, targeting c-MYC might be of therapeutic benefit when used sequentially with chemo- and radiotherapy rather than concomitantly