Iterative solution of inverse scattering for a two-dimensional dielectric object

Two-dimensional inverse scattering for a dielectric cylinder was investigated. The problem was to reconstruct the dielectric constant distribution of a scatterer from the scattered field measured outside under the illumination of an incident wave. Theoretically, the inversion algorithm is derived using integral equation formulations together with the iterative technique. Note that the inverse problem is solved in the angular spectral domain instead of in the space domain. Therefore, the ill-posedness can be reduced and no regularization is needed. Numerical results show that with only one incident wave generated by a line source, good reconstruction is obtained even when the dielectric constant is fairly large and the Born approximation is no longer valid. The effects of random noise and measurement distance on imaging reconstruction were also investigated. © 1996 John Wiley & Sons, Inc.     

Microwave imaging of multiple conducting cylinders

Inverse scattering for multiple conducting cylinders is investigated. It is assumed that a plane wave is incident upon separate perfectly conducting cylinders of unknown shapes and the scattered field is measured outside, then, using prior knowledge of the rough positions of the scatterers, the shapes of the conducting scatterers can be reconstructed. The Newton-Kanotrovitch method is employed to solve nonlinear integral equations and the pseudoinverse technique is used to overcome the ill-posedness. Numerical examples are given to demonstrate the capability of the inversion algorithm. Good reconstruction is obtained even when the multiple scattering between two conductors is serious. The effect of noise on the reconstruction result is also investigated     

Characteristics of striplines with inhomogeneous cylindrical substrate

A mode-matching technique combined with Galerkin's method is proposed in this paper to analyze the characteristics of striplines embedded in an inhomogeneous cylindrical medium. The potential in each layer is expressed in terms of eigenmodes obtained numerically. Coupling between two sets of eigenmodes in contiguous layers is described by defining potential ratio coefficient matrices. An integral equation is derived based on these eigenmodes with charge on the stripline as unknown. The method of moments is then applied to solve this integral equation. Various parameters are analyzed for their effects on transmission characteristics.     

Increased production of amyloid precursor protein provides a substrate for caspase-3 in dying motoneurons

Biochemical and molecular mechanisms of neuronal cell death are currently an area of intense research. It is well documented that the lumbar spinal motoneurons of the chick embryo undergo a period of naturally occurring programmed cell death (PCD) requiring new gene expression and activation of caspases. To identify genes that exhibit changed expression levels in dying motoneurons, we used a PCR-based subtractive hybridization protocol to identify messages uniquely expressed in motoneurons deprived of trophic support as compared with their healthy counterparts. We report that one upregulated message in developing motoneurons undergoing cell death is the mRNA for amyloid precursor protein (APP). Increased levels of APP and beta-amyloid protein are also detected within dying motoneurons. The predicted peptide sequence of APP indicates two potential cleavage sites for caspase-3 (CPP-32), a caspase activated in dying motoneurons. When peptide inhibitors of caspase-3 are administered to motoneurons destined to undergo PCD, decreased levels of APP protein and greatly reduced beta-amyloid production are observed. Furthermore, we show that APP is cleaved by caspase-3. Our results suggest that differential gene expression results in increased levels of APP, providing a potential substrate for one of the cell death-activated caspases that may ultimately cause the demise of the cell. These results, combined with information on the toxic role of APP and its proteolytic by-product beta-amyloid, in the neurodegenerative disease Alzheimer's, suggest that events of developmental PCD may be reactivated in early stages of pathological neurodegeneration.     

Tamoxifen (antiestrogen) therapy in advanced breast cancer

Fifty-nine postmenopausal women with advanced breast cancer were treated with tamoxifen (antiestrogen), 20 mg orally twice a day for at least 2 months. They had been previously treated with other types of hormonal therapy or intensive chemotherapies, or both. Nineteen of the 59 patients (32%) had either a complete response (seven patients) or partial response (12 patients). The median duration of response was 9+ months. Tumors containing estrogen receptors and those that responded to previous hormonal manipulation tended to respond to tamoxifen (60% and 69%, respectively). Patients with receptor-negative tumor or with a history of failure of previous hormonal treatments did not respond to tamoxifen therapy. Tamoxifen is effective against advanced breast cancer. Side effects of the treatment were mild.     

Selective flocculation of fines

1　ＩＮＴＲＯＤＵＣＴＩＯＮＡｓｔｈｅｅａｒｔｈ’ｓｒｅｓｏｕｒｃｅｓａｒｅｂｅｉｎｇｃｏｎｓｕｍｅｄｓｔｅａｄｉｌｙａｎｄａｓｄｅｍａｎｄｆｏｒｍｉｎｅｒａｌｐｒｏｄｕｃｔｓｃｏｎｔｉｎｕｅｓｔｏｉｎｃｒｅａｓｅ ,ｔｈｅｎｅｅｄｔｏｕｔｉｌｉｚｅｌｏｗ ｇｒａｄｅｏｒｅｓｍｏｒｅｅｆｆｉｃｉｅｎｔｌｙｈａｓｂｅｃｏｍｅｍｏｒｅｓｅｖｅｒｅ .Ｔｈｉｓｉｎｄｅｅｄｒｅ ｓｕｌｔｓｉｎｔｈｅｇｅｎｅｒａｔｉｏｎｏｆａｌａｒｇｅｑｕａｎｔｉｔｙｏｆｆｉｎｅｐａｒｔｉ ｃｌｅｓｄｕｒｉｎｇｍｉｎｉｎｇａｎｄ…     

Low‐Temperature Growth of SnO2 Nanorod Arrays and Tunable n–p–n Sensing Response of a ZnO/SnO2 Heterojunction for Exclusive Hydrogen Sensors

Uniform SnO₂ nanorod arrays have been deposited at low temperature by plasma‐enhanced chemical vapor deposition (PECVD). ZnO surface modification is used to improve the selectivity of the SnO₂ nanorod sensor to H₂ gas. The ZnO‐modified SnO₂ nanorod sensor shows a normal n‐type response to 100 ppm CO, NH₃, and CH₄ reducing gas whereas it exhibits concentration‐dependent n–p–n transitions for its sensing response to H₂ gas. This abnormal sensing behavior can be explained by the formation of n‐ZnO/p‐Zn‐O‐Sn/n‐SnO₂ heterojunction structures. The gas sensors can be used in highly selective H₂ sensing and this study also opens up a general approach for tailoring the selectivity of gas sensors by surface modification.     

Analysis of linear coaxial antennas

Two types of linear coaxial antennas, coaxial-colinear antennas, and slotted coaxial antennas are studied to check the possibility of using them as the base-station antenna in personal communication systems. The slot voltages and input impedance of linear coaxial antennas are obtained by using a transmission-line analysis where the radiation effect is accounted by a shunt and a serial admittance, respectively. The current distribution is obtained by solving an integral equation using the method of moments. The radiation pattern and directivity are then obtained from the current distribution and the reflection coefficient inside the coaxial cable. Factors analyzed include frequency, coaxial filling permittivity and segment number