Effects of fade distribution on a mobile satellite down-link and up-link performance in a frequency reuse cellular configuration

In a mobile satellite system with a frequency reuse cellular configuration, significant co-channel interference can be experienced due to the antenna side-lobe level. The signal will be subjected not only to its own fading, but also to the effect of the varying degree of fading on the co-channel interferer, and this interference will behave differently in the up and in the down-link. This paper presents a quantitative evaluation of the combined effects of fades and co-channel interference on a mobile satellite link.     

Estimation of dynamically evolving ellipsoids with applications to medical imaging

The estimation of dynamically evolving ellipsoids from noisy lower-dimensional projections is examined. In particular, this work describes a model-based approach using geometric reconstruction and recursive estimation techniques to obtain a dynamic estimate of left-ventricular ejection fraction from a gated set of planar myocardial perfusion images. The proposed approach differs from current ejection fraction estimation techniques both in the imaging modality used and in the subsequent processing which yields a dynamic ejection fraction estimate. For this work, the left ventricle is modeled as a dynamically evolving three-dimensional (3-D) ellipsoid. The left-ventricular outline observed in the myocardial perfusion images is then modeled as a dynamic, two-dimensional (2-D) ellipsoid, obtained as the projection of the former 3-D ellipsoid. This data is processed in two ways: first, as a 3-D dynamic ellipsoid reconstruction problem; second, each view is considered as a 2-D dynamic ellipse estimation problem and then the 3-D ejection fraction is obtained by combining the effective 2-D ejection fractions of each view. The approximating ellipsoids are reconstructed using a Rauch-Tung-Striebel smoothing filter, which produces an ejection fraction estimate that is more robust to noise since it is based on the entire data set; in contrast, traditional ejection fraction estimates are based only on true frames of data. Further, numerical studies of the sensitivity of this approach to unknown dynamics and projection geometry are presented, providing a rational basis for specifying system parameters. This investigation includes estimation of ejection fraction from both simulated and real data.     

Expected interference in wireless networks with geometric path loss: a closed-form approximation

In this letter, we derive 2λπP/((α - 2)g^{(α - 2)} as a closed-form approximation of the expected interference around a receiver in wireless networks. We use a geometric path loss model, assume that nodes are randomly distributed, and that only nodes outside a guard zone around the receiver simultaneously transmit. The derived solution depends on the path loss exponent α, node density λ, transmission power per node P, and the radius g of the guard zone. The simplicity of this solution makes it widely applicable in wireless network analysis.     

Video mediated social interaction between groups: System requirements and technology challenges

This paper discusses results from research related to the use of television as a device that supports social interaction between close-knit groups in settings that include more than two locations, each location being potentially equipped with more than one camera. The paper introduces the notion of a framing experience, as a specific scenario or situation within which social communication takes place. It reports on the evaluation of some of the key attributes of social communication through semi-structured interviews, with 16 families across four European countries. The inferences drawn from this study are reduced to four system capabilities including the ability to support: excitement, engagement and entertainment; high quality, reliable audiovisual communications; flexibility and adaptability sufficient to support the unpredictable and reactive nature of human interaction and discourse. These system requirements are, in turn, reduced to a number of technology challenges which if solved will help enable effective social communications between groups, mediated by the television. These technology challenges include: high quality reliable audio visual communication; interaction orchestration, multimedia interpretation and multimedia composition. Finally the paper reflects on the impact the use of framing experiences, such as those described here, could have on strategy and policy for service providers and regulators.     

Terahertz Heterodyne Array Receivers for Astronomy

Journal of Infrared, Millimeter, and Terahertz Waves - We review the development of multi-pixel heterodyne receivers for astronomical research in the submillimeter and terahertz spectral domains....     

Influence of Temperature on Shockley Stacking Fault Expansion and Contraction in SiC PiN Diodes

While Shockley stacking fault (SSF) creation and expansion within 4H-SiC bipolar devices is well known, only recently was it observed that this expansion and the associated increase in the forward voltage drop (V _f) could be completely reversed via low-temperature annealing. Here we report the temperature dependence of the recovery rate of the V _f drift via annealing, reporting an activation energy of 1.3 ± 0.3 eV. The V _f drift was observed to saturate following extended electrical stressing, and it was observed that the value of V _f at this saturation was inversely proportional to the stressing temperature. We also observed that SSF and V _f drift recovery could occur in highly stressed diodes at elevated temperatures even under high current injection conditions (14 A/cm²).     

Image superresolution using support vector regression.

A thorough investigation of the application of support vector regression (SVR) to the superresolution problem is conducted through various frameworks. Prior to the study, the SVR problem is enhanced by finding the optimal kernel. This is done by formulating the kernel learning problem in SVR form as a convex optimization problem, specifically a semi-definite programming (SDP) problem. An additional constraint is added to reduce the SDP to a quadratically constrained quadratic programming (QCQP) problem. After this optimization, investigation of the relevancy of SVR to superresolution proceeds with the possibility of using a single and general support vector regression for all image content, and the results are impressive for small training sets. This idea is improved upon by observing structural properties in the discrete cosine transform (DCT) domain to aid in learning the regression. Further improvement involves a combination of classification and SVR-based techniques, extending works in resolution synthesis. This method, termed kernel resolution synthesis, uses specific regressors for isolated image content to describe the domain through a partitioned look of the vector space, thereby yielding good results.